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Original Research By Young Twinkle Students (ORBYTS): Ephemeris Refinement of Transiting Exoplanets

May 2020
Monthly Notices of the Royal Astronomical Society 504(4)

DOI:10.1093/mnras/staa1245

Authors:

Billy Edwards

University College London

Quentin Changeat

University of Groningen

Kai Hou Yip

University College London

Angelos Tsiaras

University College London

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We report follow-up observations of transiting exoplanets that have either large uncertainties (>10 minutes) in their transit times or have not been observed for over three years. A fully robotic ground-based telescope network, observations from citizen astronomers and data from TESS have been used to study eight planets, refining their ephemeris and orbital data. Such follow-up observations are key for ensuring accurate transit times for upcoming ground and space-based telescopes which may seek to characterise the atmospheres of these planets. We find deviations from the expected transit time for all planets, with transits occurring outside the 1 sigma uncertainties for seven planets. Using the newly acquired observations, we subsequently refine their periods and reduce the current predicted ephemeris uncertainties to 0.28 - 4.01 minutes. A significant portion of this work has been completed by students at two high schools in London as part of the Original Research By Young Twinkle Students (ORBYTS) programme.

Projected uncertainties in the transit time of the planets studied here.

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Observed minus calculated mid-transit times for all planet studied here. Transit midtime measurements from this work are shown in black, while literature T 0 values included in our calculation are in red. The green data point shows the updated T 0 reported. The black line denotes the new ephemeris of this work with the dashed lines showing the associated 1 uncertainties. For comparison, the previous literature ephemeris are given in red. Downloaded from https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/staa1245/5831727 by University College London user on 13 May 2020

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All the observations of WASP-122 b used in this work.

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All the observations of WASP-45 b used in this work.

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All the observations of WASP-119 b used in this work. Downloaded from https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/staa1245/5831727 by University College London user on 13 May 2020

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ORBYTS: Ephemeris Reﬁnement of Transiting Exoplanets 1

Original Research By Young Twinkle Students (ORBYTS):

Ephemeris Reﬁnement of Transiting Exoplanets

Billy Edwards1★, Quentin Changeat1, Kai Hou Yip1, Angelos Tsiaras1, Jake Taylor2,

Bilal Akhtar3, Josef AlDaghir3, Pranup Bhattarai3, Tushar Bhudia4, Aashish

Chapagai3, Michael Huang3, Danyaal Kabir4, Vieran Khag4, Summyyah Khaliq4,

Kush Khatri3, Jaidev Kneth4, Manisha Kothari4, Ibrahim Najmudin3, Lobanaa

Panchalingam4, Manthan Patel3, Luxshan Premachandran4, Adam Qayyum4, Prasen

Rana3, Zain Shaikh3, Sheryar Syed4, Harnam Theti4, Mahmoud Zaidani3, Manasvee

Saraf1, Damien de Mĳolla1, Hamish Caines1, Anatasia Kokori5,6, Marco Rocchetto7,1,

Matthias Mallonn8, Matthieu Bachschmidt9, Josep M. Bosch10, Marc Bretton11,

Philippe Chatelain12, Marc Deldem13, Romina Di Sisto14,15, Phil Evans16,17, Eduardo

Fernández-Lajús14,15, Pere Guerra18, Ferran Grau Horta19, Wonseok Kang20, Taewoo

Kim20, Arnaud Leroy21, František Lomoz22, Juan Lozano de Haro23, Veli-Pekka

Hentunen24, Yves Jongen25, David Molina26, Romain Montaigut21, Ramon Naves27,

Manfred Raetz28, Thomas Sauer29, Americo Watkins30, Anaël Wünsche11, Martin

Zibar31, William Dunn1, Marcell Tessenyi32,1, Giorgio Savini1,33,32, Giovanna

Tinetti1,32 & Jonathan Tennyson1,32

ABSTRACT

We report follow-up observations of transiting exoplanets that have either large uncertainties (>10

minutes) in their transit times or have not been observed for over three years. A fully robotic ground-based

telescope network, observations from citizen astronomers and data from TESS have been used to study

eight planets, reﬁning their ephemeris and orbital data. Such follow-up observations are key for ensuring

accurate transit times for upcoming ground and space-based telescopes which may seek to characterise the

atmospheres of these planets. We ﬁnd deviations from the expected transit time for all planets, with transits

occurring outside the 1 sigma uncertainties for seven planets. Using the newly acquired observations, we

subsequently reﬁne their periods and reduce the current predicted ephemeris uncertainties to 0.28 - 4.01

minutes. A signiﬁcant portion of this work has been completed by students at two high schools in London as

part of the Original Research By Young Twinkle Students (ORBYTS) programme.

1 INTRODUCTION

Over the past decade, thousands of exoplanets have been detected

via the transit method. Current and future observatories such as the

Transiting Exoplanet Survey Satellite (TESS, Ricker et al. (2014))

and the PLAnetary Transits and Oscillations of stars (PLATO, Rauer

et al. (2016)) satellite are expected to discover tens of thousands

more. Upcoming ground and space-based telescopes such as the

European Extremely Large Telescope (E-ELT, Brandl et al. (2018)),

the Thirty Meter Telescope (TMT, Skidmore et al. (2018)), the Giant

Magellan Telescope (GMT, Fanson et al. (2018)), the James Webb

Space Telescope (JWST, Greene et al. (2016)), Twinkle (Edwards

et al. 2019c) and Ariel (Tinetti et al. 2018) will characterise the at-

mospheres of a large population of exoplanets via transit and eclipse

spectroscopy at visible and infrared wavelengths. These missions

will move the exoplanet ﬁeld from an era of detection into one

of characterisation, allowing for the identiﬁcation of the molecular

species present and their chemical proﬁle, insights into the atmo-

spheric temperature proﬁle and the detection and characterisation

of clouds (e.g. Rocchetto et al. (2016); Rodler (2018); Kawashima

et al. (2019); Changeat et al. (2019)). However, observing time on

these exceptional facilities will be precious. Therefore observations

of transiting exoplanets will need to have a limited time window

while ensuring that enough margin is included to avoid a transit

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2B. Edwards et al.

event being partially, or completely, missed. Large errors in the

ephemeris of a planet increase the observation time required to en-

sure the full transit is captured and thus reduce the eﬃciency, and

science yield, of these missions. Accurate ephemeris data, collected

over a long baseline, can also be used to search for, and characterise,

other planets in the system via transit time variations.

Just after discovery, the time of the next transit for a planet is

well known. Unfortunately the accuracy of predicted future transits

degrades over time due to the increased number of epochs since

the last observation and the stacking of the period error. In extreme

cases this can mean the transit time is practically lost, with errors of

several hours (e.g. Corot-24 b & c, Alonso et al. (2014)). In addi-

tion to this, extrapolating transit times from only a few data points

over a limited baseline can easily introduce bias (e.g. Benneke et al.

(2017)). Finally, we could expect transit times to shift due to dy-

namical phenomena such as tidal orbital decay, apsidal precession

or from gravitational interactions with other bodies in the system

(see e.g. Agol et al. (2005); Maciejewski et al. (2016); Bouma et al.

(2019)). These can only be understood, and mitigated for, by reg-

ularly observing targets over a long baseline. In the era of TESS,

which is expected to ﬁnd several thousand transiting planets (Sulli-

van et al. 2015;Barclay et al. 2018), this will become increasingly

diﬃcult due to the sheer number of targets and require a coordinated

eﬀort by many groups and telescope networks to prepare for charac-

terisation by the next generation facilities. This campaign will need

data from both ground-based facilities and space-based telescopes

such as TESS, CHEOPS and Twinkle.

Ground-based follow-up will require not only a large number

of telescopes but many person-hours to plan observations and pro-

cess the data. Citizen astronomers, citizen science and educational

outreach oﬀer an excellent opportunity to support future space mis-

sions. Given the brightness of the host stars of planets found by

TESS, even modestly sized telescopes can be used to re-observe

these systems, reducing the errors on their ephemeris. The ability

of small ground-based telescopes to contribute to exoplanet science

is well known (e.g. Kabath et al. (2019)). The Next Generation

Transit Survey (NGTS, Wheatley et al. (2018)) has shown that sub-

millimag precision is achievable by simultaneously observing the

same transit with many identical small telescopes and combining

data. Using such methods could expand the number of exoplanets

that are observable from the ground.

Here we present a project to reﬁne the ephemerides of eight

exoplanets using a fully robotic telescope network, observations

from citizen astronomers and data from TESS; a signiﬁcant portion

of the work has been completed by high school students via the

ORBYTS programme.

2 OUTREACH AND CITIZEN SCIENCE PROJECTS

The observations and analysis presented here have been achieved

via engagement with several citizen science and outreach initiatives

and a brief description of each of these is given below.

2.1 ORBYTS

Original Research By Young Twinkle Students (ORBYTS) is an

educational programme in which secondary school pupils work on

original research linked to the Twinkle Space Mission under the

tuition of PhD students and other young scientists (McKemmish

et al. 2017a;Sousa-Silva et al. 2018). The ORBYTS programme has

been run since 2012 and is jointly managed by Blue Skies Space Ltd.

(BSSL) and University College London (UCL). The Twinkle Space

Mission1is a new, fast-track satellite designed for launch by 2024

and has been conceived for providing faster access to space-based

spectroscopic data. While the satellite will also survey Solar System

objects (Edwards et al. 2019a,b), a key science case for Twinkle is

the characterisation of a population of extrasolar planets via transit

and eclipse spectroscopy (Edwards et al. 2019c). ORBYTS oﬀers

school pupils the chance to enrich our understanding of these new

worlds by improving our knowledge of the molecules they’re made

of, their orbits and their physical properties. This provides a unique

opportunity for pupils to undertake cutting-edge science that has a

meaningful impact on a future space mission.

To achieve this, ORBYTS partners dynamic, passionate sci-

ence researchers with secondary schools, where, through fortnightly

school visits over an academic year, the researcher teaches the stu-

dents undergraduate-level physics. The goal of every partnership is

that school students will have the opportunity to use this new knowl-

edge to contribute towards publishable research. Pupils get hands

on experience of scientiﬁc research and work closely with young

scientists. By partnering schools with relatable researchers, the pro-

gramme aims to not only improve student aspirations and scientiﬁc

literacy, but also help to address diversity challenges by dispelling

harmful stereotypes, challenging any preconceptions about who can

become a scientist. The organisers and tutors strongly believe that all

school students should have the opportunity to become involved in

active scientiﬁc research and to be culturally connected to space mis-

sions. Previous projects have included providing accurate molecular

transition frequencies with the ExoMol group (Chubb et al. 2018a,b;

McKemmish et al. 2017b;McKemmish et al. 2018;Darby-Lewis

et al. 2019) as these line lists are crucial for atmospheric retrievals.

During the current project the students selected suitable follow-

up targets, scheduled observations and analysed the observational

data.

2.2 Exoplanet Transit Database

The Exoplanet Transit Database (ETD, Poddaný et al. (2010)) was

established in 2008 and is a web-based application which is open to

any exoplanet observer. The ETD is a project of the Variable Star

and Exoplanet Section of the Czech Astronomical Society and the

site consists of three parts, the ﬁrst of which provides predictions

of the upcoming transits. The second section allows for users to

upload new data and the ﬁnal function is the display of the observed

- calculated diagrams (O-C). The ETD has hundreds of contributors

and the database contains thousands of observations. While all ob-

servations are analysed by the ETD system to produce these graphs,

the data can also be downloaded. The ETD does not facilitate a

ranking of planets based on their current uncertainties.

2.3 ExoWorlds Spies

ExoWorlds Spies2is a project that started in early 2018, aiming

to monitor transiting exoplanets through long-term regular obser-

vations using small and medium scale telescopes. This eﬀort, is

supported by citizen astronomers, the Holomon Astronomical Sta-

tion and the Telescope Live network. The project promotes the idea

that research is an eﬀort that everyone can contribute and, thus, it is

1http://www.twinkle-spacemission.co.uk

2https://exoworldsspies.com

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ORBYTS: Ephemeris Reﬁnement of Transiting Exoplanets 3

open to collaborations with the public, including school and univer-

sity students. To facilitate this, user-friendly data analysis tools and

a dedicated website have been developed as part of the project, in

order to disseminate the material to as many people as possible. The

website includes audiovisual material, information on the project,

data analysis tools, instructions, observational data and graphics.

All sources are online, free, and available for everyone both in En-

glish and Greek. So far, the ExoWorlds Spies database includes

approximately 60 transit observations of more than 25 diﬀerent ex-

oplanets, from both the North and the South hemisphere, including

recently discovered planets with limited data available. A number

of these transits are already available on the website for members

of the general public, students, and citizens to analyse.

2.4 ExoClock

ExoClock has been established as part of the ground-based char-

acterisation campaign for the Ariel space mission. Ariel aims to

observe 1000 exoplanets during its primary mission, characterising

their atmospheres and seeking to understand the chemical diversity

of planets in our galaxy (Tinetti et al. 2018). The Ariel Mission Ref-

erence Sample (MRS), the planets observed by the mission, will be

selected from a large list of potential targets. The selection criterion

will aim to produce a multifarious population of planets for study.

However, the lack of basic knowledge such as stellar variability

and the expected transit time of the system, may mean a planet is

not selected for observation, potentially reducing the impact of the

mission. ExoClock aims to facilitate a coordinated programme of

ground-based observations to maximise the eﬃciency of the Ariel

mission. The programme also aims to stimulate engagement with

citizen astronomers, allowing them to contribute to an upcoming

ESA mission. The site ranks the potential Ariel targets from Ed-

wards et al. (2019d), prioritising those that have a large uncertainty

in their next transit time. These can then be ﬁltered by the location

of the observer and the telescope size, providing a list of exoplanet

transits which would be observable in the near future. The ExoClock

initiative has the explicit rule that all those who upload data for a

planetary system will be included on any subsequent publications.

3 TARGET SELECTION

There are several major exoplanet catalogues from which one can

compile a list of potential planets. The most widely used and com-

prehensive is the NASA Exoplanet Archive3(Akeson et al. 2013).

The NASA catalogue was accessed in February 2019 and the transit

error by mid 2019 (the end time of this project) was calculated for

each planet. The next transit of a planet, 𝑇𝑐, can be calculated from

𝑇𝑐=𝑇0+𝑛·𝑃(1)

where 𝑃is the period of the planet, 𝑇0is the last measured transit

time and n is the number of epochs since this last observation. Both

𝑇0and 𝑃have errors associated with their measurement and thus

the error on the predicted transit time, Δ𝑇𝑐is given by

Δ𝑇𝑐=qΔ𝑇2

0+ (𝑛·Δ𝑃)2(2)

assuming no co-variance between the two parameters. There is,

of course, a correlation between the ﬁtted period and mid time

but this co-variance is generally negligible. Suitable targets were

3https://exoplanetarchive.ipac.caltech.edu

found by ﬁltering this list to include only those with a large transit

uncertainty (>10 minutes) or those that had not been observed for

3 or more years. We note that the ephemeris of many of the large,

gaseous planets with signiﬁcant transit uncertainties were reﬁned

by Mallonn et al. (2019) and these were excluded from the study.

The choice of targets was restricted by the size of the telescopes

(0.35 – 0.6 m, see Section 4) due to the star magnitude and transit

depth but still many planets with substantial ephemeris errors were

found to be observable.

4 DATA ACQUISITION

Table 1contains the planets for which data was obtained and the ex-

pected transit error on 1𝑠𝑡 July 2019. Although some of the planets

observed here are around relatively fainter stars, they are all poten-

tially suitable for spectroscopic follow-up and could be observed

by Ariel (Edwards et al. 2019d). They may also be potential targets

for characterisation by Twinkle, JWST or ground-based facilities.

Observations of these targets were scheduled between February and

April 2019.

4.1 Robotic Ground-based Telescope Network

For the new observations presented here we use the Telescope Live

global network of robotic telescopes4. Telescope Live is a web appli-

cation oﬀering end-users the possibility to purchase images obtained

on-demand from a network of robotic telescopes. Telescope Live

kindly provided access to their telescopes for a total of 150 hours.

At the time of writing the network consists of eight telescopes dis-

tributed across three observatories: a 1m ASA RC-1000AZ, a 0.6m

Planewave CDK24 and two 0.5m ASA 500N located at El Sauce

Observatory in Chile; a 0.7m ProRC 700 and two 0.1m Takahashi

FSQ-106ED located at IC Astronomy in Spain; a 0.1m Takahashi

FSQ-106ED located at Heaven’s Mirror Observatory in Australia.

The majority of observations were performed using a V ﬁlter (Lu-

minance). Additionally we obtained a light curve of WASP-122 b

using a 1.0 m Sinistro from the Las Cumbres Observatory (LCO)

network5thanks to the Educational Proposal FTPEPO2014A-004

led by Paul Roche.

4.2 ETD and ExoWorldSpies

For the selected planets, the ETD was searched for additional ob-

servations. The ETD provides a ranking of data quality from 1 to 5.

Having removed observations with a data quality of less than 3, as

well as excluding other unsuitable light curves via visual inspection,

we found a total of 31 light curves from citizen astronomers: 5 of

CoRoT-6 b, 21 of KPS-1 b, 3 of WASP-45 b and 2 of WASP-122 b.

All these observations were undertaken as part of the TRansiting Ex-

oplanetS and CAndidates (TRESCA) project6and are summarised

in Table 3. From ExoWorldSpies, we included an observation of

WASP-83 b in our analysis. Additionally, the new observations

taken as part of this work have been added to the ExoWorldsSpies

and ExoClock databases.

4https://telescope.live

5https://lco.global

6http://var2.astro.cz/EN/tresca

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4B. Edwards et al.

Table 1. Exoplanets for which observations were acquired and the calculated uncertainty in their transit mid time on 1𝑠𝑡 July 2019 based on data from the

NASA Exoplanet Archive.

Planet Planet Radius [R𝐽] Star V Mag Uncertainty [minutes] Last Observed Reference

CoRoT-6 b 1.17 13.9 2.7 2010 Fridlund et al. (2010)

KELT-15 b 1.44 11.2 15.7 2015 Rodriguez et al. (2016)

KPS-1 b 1.03 13.0 57.6 2018 Burdanov et al. (2018)

K2-237 b 1.65 11.6 13.0★2018 Soto et al. (2018)

WASP-45 b 1.16 12.0 5.3 2013 Anderson et al. (2012)

WASP-83 b 1.04 12.9 11.9 2015 Hellier et al. (2015)

WASP-119 b 1.40 12.2 15.7 2016 Maxted et al. (2016)

WASP-122 b 1.74 11.0 4.9†2016 Turner et al. (2016)

★The independent discovery paper (Smith et al. 2018) suggests an uncertainty 3.8 minutes

†The independent discovery paper (Rodriguez et al. 2016) suggests an uncertainty 3.4 minutes

4.3 TESS

Having observed the southern hemisphere, TESS is now survey-

ing the northern hemisphere and thus has observed several of the

planets studied here. We searched the Mikulski Archive for Space

Telescopes (MAST7) and found that TESS has observed K2-237 b,

KELT-15 b, WASP-45 b, WASP-83 b, WASP-119 b and WASP-122

b. A pipeline was built to ﬁnd, acquire, reduce, and analyse the

data. For a given target, the code searches MAST and returns all

the data collected on the host star from various observatories. The

list is ﬁltered to see if TESS has observed the star and, if so, the

Presearch Data Conditioning (PDC) light curve, which has had non-

astrophysical variability removed and ‘bad data’ eliminated through

the methods outlined in the TESS guide8, is downloaded. The data

product is a time-series for each sector (∼27 days) with a cadence of

two minutes. After excluding the poor data, we recovered 7 K2-237

b transits, 12 for KELT-15 b, 8 for WASP-45 b, 4 of WASP-83 b

along with 37 for WASP-119 b and 13 of WASP-122 b.

5 DATA REDUCTION AND ANALYSIS

The Telescope Live network automatically gathers calibration

frames and provides the data in a reduced format (though the raw

and calibration frames can also be downloaded). These frames were

analysed using the HOlomon Photometric Software (HOPS) which

aligns the frames and normalises the ﬂux of the target star by us-

ing selected comparison stars. This software is open-source and

available on Github9.

The photometric light curves from all sources were ﬁtted using

PyLightcurve (Tsiaras et al. 2016), another code which is publicly

available10. Initially ﬁt parameters were the orbital semi-major axis

scaled by the stellar radius (𝑎/𝑅∗), the orbital inclination (𝑖), the

planet-star radius ratio (𝑅𝑝/𝑅∗), the midpoint of the transit (𝑇) and

the orbital period (𝑃). In each case the Markov chain Monte Carlo

(MCMC) was run with 100,000 iterations, a burn of 30,000 and 200

walkers. The limb darkening coeﬃcients were ﬁxed to theoretical

7http://archive.stsci.edu

8https://spacetelescope.github.io/notebooks/notebooks/

MAST/TESS/beginner_tour_lc_tp/beginner_tour_lc_tp.html

9https://github.com/HolomonAstronomicalStation/hops

10 https://github.com/ucl-exoplanets/pylightcurve

values from Claret et al. (2012,2013) according to the stellar param-

eters obtained from the planet discovery papers. Previous analyses

show that the trends in ground-based light curves can be approxi-

mated with simple functions of only very few free parameters, for

example low order polynomials over time (e.g. Southworth (2011);

Maciejewski et al. (2016); Mackebrandt et al. (2017); Mallonn et al.

(2019)). Hence we detrended all ground-based light curves using a

simple second-order polynomial. We then removed all data points

with residuals greater than 3 sigma from the best-ﬁt model. For

TESS data, we used the ﬂatten function from Wotan (Hippke et al.

2019), an open-source python suite developed for comprehensive

time-series detrending of exoplanet transit survey data11 .

Next we ﬁtted each light curve individually with 𝑎/𝑅∗,𝑖and

𝑅𝑝/𝑅∗allowed to vary within 1 𝜎of the values from the literature

(or the new values computed here) while 𝑇was ﬁtted with bounds

of 3𝜎. For targets which had been observed by TESS, we reﬁned the

planet transit parameters (𝑅𝑝/𝑅∗,𝑖,𝑎/𝑅∗) and these are provided in

Tables 4-6. The uncertainties on each ﬁtted mid-time are obtained

from the posterior distributions of the MCMC chains. We convert

all our mid-times into BJD𝑇 𝐷𝐵 using the tool from Eastman et al.

(2010). Having ﬁt the mid transit time for all the data, we use

a weighted least squares ﬁt to obtain a linear period for the data

analysed in this work and any previous mid-times from the literature

(also converted to BJD𝑇 𝐷𝐵). We varied the reference transit time,

𝑇0, and report the value which minimised the co-variance between

𝑇0and 𝑃.

Finally, we used the literature ephemerides from Table 2to

compute ‘observed minus calculated’ residuals for all transit times

and used our reﬁned ephemeris to predict the uncertainty on the

transit times when Ariel is launched in 2028 as shown in Figure 1.

6 RESULTS

Our analysis shows signiﬁcant drifts in the transit times of all plan-

ets studied here, with only one planet (KPS-1 b) having observed

transits within the 1 sigma errors on the expected time as shown

in Figure 2. Even in this case, the observed transit was consider-

ably oﬀset from that predicted. K2-237 b, KELT-15 b, WASP-45 b,

WASP-83 b, WASP-119 b and WASP-122 b were observed by TESS

11 https://github.com/hippke/wotan

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ORBYTS: Ephemeris Reﬁnement of Transiting Exoplanets 5

Table 2. Summary of literature ephemeris data used here.

Planet Mid Time [𝐵 𝐽 𝐷𝑇 𝐷𝐵 ] Period [days] Reference

CoRoT-6 b 2454595.6144 ±0.0002 8.886593±0.000004 Fridlund et al. (2010)

K2-237 b 2457684.8101 ±0.0001 2.18056±0.00002 Soto et al. (2018)

KELT-15 b 2457029.1663+0.0078

−0.0073 3.329441±0.000016 Rodriguez et al. (2016)

KPS-1 b 2457508.37019+0.0079

−0.0078 1.706291±0.000059 Burdanov et al. (2018)

WASP-45 b 2455441.269995±0.00058 3.1260876±0.0000035 Anderson et al. (2012)

WASP-83 b 2455928.886085±0.0004 4.971252±0.000015 Hellier et al. (2015)

WASP-119 b 2456537.547779±0.002 2.49979±0.00001 Maxted et al. (2016)

WASP-122 b 2456665.224782±0.00021 1.7100566+0.0000032

−0.0000026 Turner et al. (2016)

in the ﬁrst year of operations and we demonstrate the great poten-

tial the mission has for reﬁning orbital parameters. The capability

of TESS to provide accurate updated ephemeris for bright, short

period planets has previously been shown in Bouma et al. (2019).

As the primary two year mission covers almost the entire sky,

the ephemerides of many of the known planets could be updated

once the data is released. For short period planets, TESS data gives

multiple, high-precision, complete transits allowing the uncertainty

on both the period and 𝑇0of these planets to be reduced. A summary

of the ﬁndings for each planet is given below.

CoRoT-6 b: Raetz et al. (2019) found that CoRoT plan-

ets seemed to have slightly underestimated uncertainties in their

ephemerides and our analysis of CoRoT-6 b agrees with their ﬁnd-

ings. The last transit of CoRoT-6 b was found to be 23 minutes after

the calculated transit time despite the predicted uncertainty being

less than 3 minutes. The new observations help reduce the uncer-

tainty on the transit time but we note there is not currently enough

data to accurately constrain the period.

K2-237 b: There are two independent discovery papers for

K2-237 b. Using the ephemeris data from Soto et al. (2018) one

could expect an uncertainty of 13 minutes in the transit mid time

while Smith et al. (2018) claims a greater precision on the period

and thus predicts an uncertainty of 3 minutes. In reality we discover

a shift of nearly 15 minutes and ﬁnd our data to have a closer ﬁt to

the ephemeris of Soto et al. (2018). However, given the short period

of the planet (∼2.18 days), over 400 orbits have occurred since the

discovery. The diﬀerence is therefore equivalent to an error in the

period of ∼1.5 s, compared to a claimed uncertainty in the period

of 0.5 s), and shows how slight errors in the accuracy of exoplanet

ephemerides can lead to signiﬁcant deviations from the expected

transit time, highlighting the beneﬁt of following-up targets on a

regular basis.

KELT-15 b: This hot-Jupiter had not been re-observed with

transit photometry since its discovery meaning the uncertainty in

its transit time had risen to nearly 16 minutes. In the 4 years since,

several hundred orbits had occurred and a 20 minute deviation from

the expected transit time was found.

KPS-1 b: The newly observed transits for this planet were the

only ones to fall within the 1 sigma errors in our sample. However,

a deviation from the expected transit time of over 30 minutes was

found, which is still a substantial residual. The uncertainty on the

transit time of KPS-1 b is predicted to be less than 10 minutes until

after the launch of Ariel in 2028.

WASP-45 b: The predicted uncertainty on WASP-45 b was

around 5 minutes but had not been re-observed for several years. The

O-C plot from ETD showed a slight divergence from that expected

but it was not until the TESS data was analysed the full extent

became clear with the transit arriving 15 minutes early.

WASP-83 b: For WASP-83 b, the newly observed transits

occurred ∼30 minutes after the expected time, well outside the 1

sigma error of ∼12 minutes. Having not been observed since 2015,

300 orbits had passed. The literature orbital period diﬀers by only

6 seconds from the updated value reported here, again highlighting

the need for consistent follow-up.

WASP-119 b: With a reported discovery ephemeris in 2013

and an uncertainty of over 10 minutes, WASP-119 b was an obvious

choice for follow-up. The combination of TESS data and a ground-

based observations uncovered a drift of nearly 20 minutes over the

700 orbits since discovery.

WASP-122 b: Also known as KELT-14 b, this planet has two

independent discovery papers (Turner et al. 2016;Rodriguez et al.

2016). These papers gave uncertainties of 3.4 and 4.9 minutes on

the current transit mid time and the planet had not been re-observed

since its discovery. Our observations found the transits of WASP-

122 b to be occurring around 5 minutes early, just outside the 1

sigma errors. We ﬁnd our data has a better ﬁt to the period from

Turner et al. (2016).

Hence we detect signiﬁcant variations in the observed transit

time from the expected for most of the planets studied here. An over-

conﬁdence in the predicted transit time is a known issue and analy-

sis of measured-to-predicted timing deviations of 21 exoplanets by

Mallonn et al. (2019) indicated a trend of slightly underestimated

uncertainties in the ephemerides while Raetz et al. (2019) made a

similar ﬁnding for CoRoT planets. Mallonn et al. (2019) found an

average deviation of 1.4𝜎while here we ﬁnd a 2.2𝜎divergence. We

note that this is largely driven by CoRoT-6 b, which was observed

to transit 7.7𝜎from the expected time, and removing this planet

reduces the average deviation to 1.5𝜎.

Here our analysis claims sub-second uncertainties on the pe-

riods of K2-237 b, WASP-45 b, WASP-83 b, WASP-119 b and

WASP-122 b which should keep the uncertainty on the transit times

of these planets to below 15 minutes until well after the launch of

Ariel in 2028 (see Figure 1). Nevertheless, we would advocate fur-

ther follow up of these planets, the others studied here and further

planets with seemingly accurate ephemeris data to ensure errors

are not underestimated. A cause of this can be the short baseline

over which the period of the planet is determined when it is ﬁrst

discovered. When extrapolated over long times periods, even slight

inaccuracies in the ﬁtted period can cause signiﬁcant deviations.

Other sources of larger than expected uncertainties can be due to

underestimated systematics in the data, stellar activity, tidal eﬀects

or transit timing variations (TTVs) due to other bodies in the sys-

tem. Additionally, while the co-variance between T0and the period

is minimised during ﬁtting, it is non-zero. These eﬀects can only

be mitigated for by regularly observing transits over a long time

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6B. Edwards et al.

period and to achieve this a well-organised ground and space-based

campaign is required.

In any case, we emphasise that even in the event of the

ephemerides being aﬀected by astrophysical disturbances, our new

ephemerides present the best available basis for future follow-up

studies.

7 DISCUSSION

The next generation of telescopes (JWST, Ariel, ELTs etc.) will

require rigorous scheduling to minimise overheads and maximise

science outputs. This means interesting science targets could see

their observing priority degraded if their ephemerides are not accu-

rate enough, even if they are excellent targets for atmospheric char-

acterisation. Many currently known planets have large ephemeris

uncertainties and analysis by Dragomir et al. (2019) suggests many

TESS targets will have errors of >30 minutes less than a year af-

ter discovery due to the short baseline of TESS observations. To

maintain, and verify, the ephemeris of these planets will require

follow-up observations over the coming years from the ground and

from space.

Given the brightness of the host stars and the large transit

depths of many of these planets, modestly sized telescopes can play

a crucial role in this activity. To achieve regular observations of all

known exoplanets, telescope time must be eﬃciently utilised. As it

is not always clear when the most recent observations of a target oc-

curred, follow-up observations need to be coordinated to maximise

the eﬀectiveness of the data. Community-wide citizen science ef-

forts, such as the Exoplanet Transit Database and Exoplanet Timing

Survey (Zellem et al. 2019) and ExoClock, need to be established

to create a network of individuals and groups to monitor new dis-

coveries. This need not be limited to citizen astronomers but should

include all research groups with access to telescopes of all sizes.

This organised and structured approach should build upon the work

of existing schemes.

Researcher engagement with citizen astronomers, citizen sci-

ence and in educational outreach oﬀers an excellent opportunity to

support future space missions. Stimulating this engagement and de-

vising a coordinated approach to maintaining exoplanet ephemeris

will be imperative in the coming years. Projects such as the ETS,

ExoClock and ORBYTS need to become more widespread and

methodical in their approach to transit follow-up (the selection of

targets here was somewhat ad-hoc and this is what needs to be

avoided). Finally, it is critical that data from these observations is

publicly available, especially for planets which display deviations

in transit mid-time.

Here we homogeneously analyse the data but the reduction

method has diﬀered between observers which can lead to inconsis-

tencies. The ETD provides a rating of the quality of the uploaded,

from 1-5, but its vetting is perhaps not as extensive as other databases

such as the Minor Planet Center. A systematic approach is required,

with guidelines that ensure all data is processed in the correct man-

ner. For exoplanet observations, the choice of comparison stars, the

provision of correct timing and overall consistency are paramount.

Performing such quality checks on the data can be complex, re-

quiring signiﬁcant data storage and processing capabilities, but are

critical if high precision ephemerides are to be obtained. Thus future

projects should allow the submission of raw images, along with the

necessary calibration ﬁles, to allow for the data to homogeneously

reduced and analysed and, if an observer wishes to download data,

the output format needs to be consistent to ensure eﬃcacy. Being

Figure 1. Projected uncertainties in the transit time of the planets studied

here.

able to accept, and return, various data products from the raw frames

to the light curve will increase the functionality of such a project.

Alternatively, easy to use codes which automatically process the

data without the need for human input (e.g. in the choice of compar-

ison stars) could be used. ExoClock is expected to be expanded to

provide such a platform for planets that could potentially be studied

by Ariel.

8 CONCLUSIONS

We present follow-up observations of eight exoplanets with large

uncertainties in their predicted transit time via a network of

robotic ground-based telescopes and data from TESS. We reﬁne

the ephemeris data for these planets and for seven of them, ﬁnd that

the observed transit time was outside the predicted uncertainties.

This can only be mitigated for by regularly following up targets

and, given the number of planets that are expected to be detected

in the coming years, such an eﬀort will require a large amount of

telescope time. Therefore a coordinated approach is required and

citizen astronomers and educational outreach provide an excellent

opportunity to contribute towards this eﬀort. Schemes which stim-

ulate this engagement will be crucial in maintaining transit times

for the next generation of telescopes.

9 ACKNOWLEDGEMENTS

The authors wish to thank Dr Ehsan Pedram from Preston Manor

School and Martin Yates from Beal High School for their dedication

in organising the outreach sessions, devoting their spare time for the

beneﬁt of their students. We also thank Telescope Live for kindly

proving access to their telescope network, without which this project

would not have been possible. Access to the LCO network was

provided to the ORBYTS programme by the Faulkes Telescope

Project which is coordinated by Cardiﬀ University and Swansea

University. Additionally, we thank Paul Edwards for supplying data

storage solutions. This paper includes data collected by the TESS

mission which is funded by the NASA Explorer Program. TESS data

is publicly available via the Mikulski Archive for Space Telescopes

(MAST). This research has also used the NASA Exoplanet Archive,

which is operated by the California Institute of Technology, under

contract with the National Aeronautics and Space Administration

through the Exoplanet Exploration Program. This work has been

funded through the European Union’s Horizon 2020 research and

innovation programme (grant agreement No 758892, ExoAI), and

with the STFC grants ST/P000282/1, ST/P002153/1, ST/S002634/1

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ORBYTS: Ephemeris Reﬁnement of Transiting Exoplanets 7

Figure 2. Observed minus calculated mid-transit times for all planet studied here. Transit midtime measurements from this work are shown in black, while

literature T0values included in our calculation are in red. The green data point shows the updated T0reported. The black line denotes the new ephemeris of

this work with the dashed lines showing the associated 1𝜎uncertainties. For comparison, the previous literature ephemeris are given in red.

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8B. Edwards et al.

and ST/T001836/1. Finally, we thank the MAPS Faculty at UCL for

their partial funding of the ORBYTS programme.

10 AFFILIATIONS

1Department of Physics and Astronomy, University College

London, Gower Street, London, WC1E 6BT, UK

2Department of Physics (Atmospheric, Oceanic and Planetary

Physics), University of Oxford, Parks Rd, Oxford, OX1 3PU, UK

3Preston Manor High School, Carlton Avenue East, Wembley, HA9

8NA, UK

4Beal High School, Woodford Bridge Road, Ilford, Essex, IG4 5LP,

5Royal Observatory Greenwich, London, UK

6Birkbeck, University of London, Malet Street, London, WC1E

7HX, UK

7Spaceﬂux Ltd., 71-75 Shelton Street, Covent Garden, London,

WC2H 9JQ, UK

8Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16,

D-14482 Potsdam, Germany

9Club d’Astronomie de Wittelsheim, Wittelsheim, France

10Santa Maria de Montmagastrell Remote Observatory

11Observatory of Baronnies Provençales, 05150 Moydans, France

12Observatoire Sadr Chili

13Les Barres Observatory, Lamanon, France

14Facultad de Ciencias Astronómicas y Geofísicas, Universidad

Nacional de La Plata, Paseo del Bosque S/N-1900 La Plata,

Argentina

15Instituto de Astrofísica de La Plata (CCT La Plata - CON-

ICET/UNLP), Argentina

16Rarotonga Observatory, Cook Islands

17El Sauce Observatory, Coquimbo Province, Chile

18Observatori Astronómic Albanyá, Camí de Bassegoda, Albanyá

17733 , Girona, Spain

19Observatory Ca l’Ou, San Martí Sesgueioles

20National Youth Space Center, Goheung, Jeollanam-do, 59567,

Republic of Korea,

21OPERA Observatory, 33820 Saint Palais, France,

22Observatory of Josef Sadil, Havlíčkova 514, Sedlčany CZ-264

01, Czech Republic

23Observatorio de Elche, Elche, Spain

24Taurus Hill Observatory, 79480 Kangaslampi, Finland

25Observatoire de Vaison la Romaine, Au Palis, 84110 Vaison la

Romaine, France

26Anunaki Observatory, Manzanares El Real, Spain

27Montcabrer Observatory

28Raetz Observatory, Stiller Berg 6, 98587 Herges-Hallenberg,

Germany

29International Citizen Observatory, Germany

30British Astronomical Association, Burlington House, Piccadilly,

London W1J 0DU, UK

31Variable Star and Exoplanet Section of Czech Astronomical

Society, Vsetínská 941/78, 757 01 Valašské Meziříčí, Czech

Republic

32Blue Skies Space Ltd., 69 Wilson Street, London, EC2A 2BB,

33University College London Observatory, Mill Hill, London,

NW7 2QS, UK

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ORBYTS: Ephemeris Reﬁnement of Transiting Exoplanets 9

Table 3: General information about the observationsconducted and analysed in this work. The label corresponds to that given in Figures 3-4.

Planet Date Telescope Filter Exposure Time [s] Mid Time [BJD] Mid TimeEr ror Epoch Label

09 July 2010 ETD, Sauer Clear 90 2455386.52167 0.00085 63 G1

17 July 2010 ETD, Sauer Clear 90 2455395.40632 0.00074 64 G2

CoRoT-6 b 17 June 2015 ETD, Molina Clear 300 2457190.50697 0.00698 266 G3

19 July 2018 ETD, Kang R 300 2458319.10958 0.00102 393 G4

22 June 2019 ETD, Evans Clear 300 2458656.80291 0.00242 431 G5

K2-237 b 16 April ElSauce V 30 2458589.73380 0.00061 370 G1

TESS S12 I 120

2458631.16350 0.00095 389 T1

2458633.34306 0.00077 390 T2

26 May 2019 2458635.52308 0.00078 391 T3

till 2458637.70413 0.00095 392 T4

18 June 2019 2458646.42401 0.00089 396 T5

2458648.60616 0.00097 397 T6

2458650.78837 0.00090 398 T7

TESS S7,9 I 120

2458494.13536 0.00068 -10 T1

2458497.46521 0.00061 -9 T2

2458500.79344 0.00062 -8 T3

2458507.45364 0.00067 -6 T4

08 January 2019 2458510.78149 0.00068 -5 T5

KELT-15b till 2458514.11222 0.00066 -4 T6

27 March 2019 2458547.40593 0.00073 6 T7

2458550.73620 0.00077 7 T8

2458554.06598 0.00072 8 T9

2458560.72358 0.00078 10 T10

2458564.05458 0.00074 11 T11

2458567.38262 0.00075 12 T12

19 February 2019 Warrumbungle V 120 2458534.08713 0.0024 2 G1

21 March 2019 Warrumbungle V 120 2458564.05478 0.00358 11 G2

12 March 2019 ETD, Jongen Clear 120 2458554.34979 0.00064 -10 G1

22 March 2019 ETD, Wunsche V 120 2458564.58226 0.00096 -4 G2

22 March 2019 ETD, Wunsche Clear 120 2458564.58759 0.00164 -4 G3

22 March 2019 ETD, Raetz Clear 60 2458564.58547 0.00090 -4 G4

22 March 2019 ETD, Jongen Clear 120 2458564.58697 0.00093 -4 G5

22 March 2019 ETD, Guerra CBB 120 2458564.58415 0.00060 -4 G6

29 March 2019 ETD, Wunsche Clear 120 2458571.40954 0.00182 0 G7

29 March 2019 ETD, Jongen Clear 120 2458571.41164 0.00047 0 G8

29 March 2019 ETD, Friedli/Kropf V 60 2458571.40894 0.00025 0 G9

29 March 2019 ETD, Watkins R 30 2458571.41121 0.00065 0 G10

KPS-1 b 29 March 2019 ETD, Guer ra I 180 2458571.41002 0.00098 0 G11

20 April 2019 ETD, Wunsche Clear 120 2458593.59136 0.00147 13 G12

20 April 2019 ETD, Jongen Clear 120 2458593.59541 0.00113 13 G13

02 May 2019 ETD, Raetz Clear 120 2458605.53684 0.00099 20 G14

14 May 2019 ETD, Bretton I 120 2458617.47815 0.00085 27 G15

14 May 2019 ETD, Guerra V 180 2458617.48126 0.00066 27 G16

14 May 2019 ETD, Raetz Clear 120 2458617.48309 0.00079 27 G17

14 May 2019 ETD,Bosch V 200 2458617.48291 0.00035 27 G18

14 May 2019 ETD, Watkins V 30 2458617.48255 0.00162 27 G19

31 May 2019 ETD, Bretton Clear 120 2458634.54617 0.00026 37 G20

31 May 2019 ETD, Jongen Clear 120 2458634.54662 0.00050 37 G21

15 August 2011 ETD, Evans Clear 60 2455782.01348 0.00097 -550 G1

16 July 2012 ETD, Sauer R 60 2456119.62831 0.00097 -442 G2

27 December 2016 ETD, Lajus R 10 2457660.78567 0.00056 51 G3

TESS S2 I 120

2458354.77330 0.00093 273 T1

WASP-45 b 2458357.89881 0.00085 274 T2

2458361.02613 0.00079 275 T3

23 August 2018 2458364.15241 0.00110 276 T4

till 2458370.40257 0.00089 278 T5

20 September 2019 2458373.52974 0.00096 279 T6

2458376.65588 0.00077 280 T7

2458379.78198 0.00088 281 T8

02 April 2019 El Sauce R 120 2458205.73765 0.00083 213 G1

28 March 2019

TESS S10 I 120

2458573.61364 0.00090 287 T1

WASP-83 b till 2458578.58484 0.00095 288 T2

22 April 2019 2458588.52739 0.00114 290 T3

2458593.49776 0.00094 291 T4

TESS S1-4,7,11 I 120

2458327.40896 0.00064 -33 T1

2458329.90921 0.00063 -32 T2

2458332.40913 0.00069 -31 T3

2458334.90914 0.00059 -30 T4

2458337.40888 0.00071 -29 T5

2458342.40948 0.00063 -27 T6

2458344.90830 0.00062 -26 T7

2458347.40851 0.00147 -25 T8

2458349.90839 0.00063 -24 T9

2458352.40769 0.00061 -23 T10

2458354.90856 0.00080 -22 T11

2458357.40699 0.00074 -21 T12

2458359.90699 0.00071 -20 T13

2458362.40801 0.00070 -19 T14

2458364.90547 0.00082 -18 T15

2458369.90681 0.00067 -16 T16

2458372.40655 0.00079 -15 T17

2458374.90585 0.00074 -14 T18

2458377.40605 0.00064 -13 T19

2458379.90440 0.00071 -12 T20

2458387.40490 0.00071 -9 T21

2458389.90515 0.00068 -8 T22

2458392.40410 0.00066 -7 T23

2458394.90473 0.00087 -6 T24

2458397.40311 0.00064 -5 T25

27 July 2018 2458399.90351 0.00064 -4 T26

WASP-119 b till 2458402.40275 0.00058 -3 T27

18 May 2019 2458404.90377 0.00059 -2 T28

2458412.40318 0.00071 1 T29

2458414.90327 0.00070 2 T30

2458417.40304 0.00064 3 T31

2458422.40234 0.00068 4 T32

2458424.90216 0.00060 6 T33

2458427.40244 0.00066 7 T34

2458429.90269 0.00063 8 T35

2458432.40216 0.00062 9 T36

2458434.90223 0.00069 10 T37

2458492.39645 0.00117 33 T38

2458494.89668 0.00129 34 T39

2458497.39677 0.00123 35 T40

2458499.89584 0.00128 36 T41

2458502.39712 0.00112 37 T42

2458504.89546 0.00127 38 T43

2458507.39514 0.00130 39 T44

2458509.89502 0.00123 40 T45

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10 B. Edwards et al.

2458512.39476 0.00122 41 T46

2458514.89459 0.00130 42 T47

2458602.38802 0.00085 77 T48

2458604.88824 0.00088 78 T49

2458607.38852 0.00076 79 T50

2458614.88619 0.00089 82 T51

2458617.38771 0.00084 83 T52

2458619.88570 0.00083 84 T53

2458622.38559 0.00076 85 T54

07 March 2019 Warrumbungle V 60 2458549.89284 0.00596 56 G1

18 January 2017 ETD, Evans R 75 2457771.62839 0.00035 -59 G1

30 January 2017 ETD, Evans R 80 2457783.59845 0.00044 -52 G2

02 March 2019 LCO V 5 2458544.57156 0.00061 393 G3

TESS S7 I 120

2458493.27195 0.00052 363 T1

2458494.98245 0.00056 364 T2

2458496.69209 0.00056 365 T3

2458498.40213 0.00055 366 T4

08 January 2019 2458500.11221 0.00056 367 T5

WASP-122 b till 2458501.82282 0.00054 368 T6

01 February 2019 2458505.24207 0.00055 370 T7

2458506.95200 0.00055 371 T8

2458508.66246 0.00054 372 T9

2458510.37276 0.00053 373 T10

2458512.08277 0.00058 374 T11

2458513.79187 0.00060 375 T12

2458515.50265 0.00056 376 T13

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ORBYTS: Ephemeris Reﬁnement of Transiting Exoplanets 11

Parameter Units CoRoT-6 b K2-237 b KELT-15 b

R∗Star Radius [R] 1.025±0.026†1.43+0.06

−0.07

‡1.481+0.091

−0.041

★

M∗Star Mass [M] 1.05±0.05 1.28+0.03

−0.04

‡1.181+0.051

−0.050

★

T𝑒 𝑓 𝑓 Star Eﬀective Temperature [K] 6090±70†6257±100‡6003+56

−52

★

Fe/H Star Metallicity -0.2±0.1†0.14 ±0.05‡0.047±0.032★

log(g∗) Star Surface Gravity [cgs] 4.43±0.1†4.24±0.1‡4.168+0.019

−0.044

★

𝜌∗Star Density [𝜌] 1.31±0.09†0.144+0.017

−0.014

‡0.514+0.034

−0.076

★

R𝑃Planet Radius [R𝐽] 1.166±0.035 †1.6944+0.0118

−0.0103 1.4745+0.0033

−0.0415

R𝑃Planet Radius [R⊕] 13.068±0.392†18.5935+0.1298

−0.1136 16.18020+0.00364

−0.45555

R𝑃/R∗Planet Radius in Stellar Radii 0.1198±0.0036 †0.12342+0.00086

−0.00075 0.1000 +0.00022

−0.00281

𝛿Transit Depth 0.17±0.0008†0.01523+0.00021

−0.00019 0.0100+0.00005

−0.00056

M𝑃Planet Mass [M𝐽] 2.96±0.34†1.6±0.11‡0.910 +0.210

−0.220

★

M𝑃Planet Mass [M⊕] 940.74±108.06†509±35‡289+67

−70

★

P Period [days] 8.886621±0.0000063 2.1805358±0.0000010 3.329468±0.000012

T0Transit Mid Time [BJD𝑇 𝐷𝐵 ] 2454826.66625±0.00054 2457782.93422±0.00014 2458527.42971±0.00017

a Semi-major axis [AU] 0.0855±0.0015 †0.03602+0.00023

−0.00042 0.04778+0.00022

−0.0082

a/R∗Semi-major axis in stellar radii 17.94±0.33†5.6138+0.0364

−0.0655 6.940+0.032

−0.118

i Inclination [degrees] 89.07±0.3†84.888+0.024

−0.264 88.339 +0.169

−0.052

b Impact Parameter 0.291±0.091†0.500±0.00583 0.1946±0.0048

e Eccentricity Fixed to zero Fixed to zero Fixed to zero

†Fridlund et al. (2010), ‡Soto et al. (2018), ★Rodriguez et al. (2016)

Table 4. Summary of updated system parameters for CoRoT-6 b, K2-237 b and KELT-15 b.

Parameter Units KPS-1 b WASP-45 b WASP-83 b

R∗Star Radius [R] 0.907 +0.086

−0.082

†0.945 ±0.087 †1.05+0.06

−0.04

∗

M∗Star Mass [M] 0.892 +0.090

−0.100

‡0.909±0.060 ‡1.11±0.09 ∗

T𝑒 𝑓 𝑓 Star Eﬀective Temperature [K] 5165 ±90 †5140±200 ‡5510±110 ∗

Fe/H Star Metallicity 0.22 ±0.13 †0.43 ±0.06 ★0.29±0.12 ∗

log(g∗) Star Surface Gravity [cgs] 4.47 ±0.06 †4.43±0.18 ★4.44 +0.02

−0.04

∗

𝜌∗Star Density [𝜌] 1.68 +0.41

−0.32

†1.08±0.25 ★1.40 +0.10

−0.18

∗

R𝑃Planet Radius [R𝐽] 1.03 +0.13

−0.12

†1.079 +0.047

−0.016 1.039 +0.012

−0.008

R𝑃Planet Radius [R𝐸] 11.5 +1.5

−1.3

†11.849+0.519

−0.173 11.402 +0.129

−0.086

R𝑃/R∗Planet Radius in Stellar Radii 0.1143 +0.0037

−0.0034

†0.1149+0.0050

−0.0017 0.09947+0.00113

−0.00075

𝛿Transit Depth 0.01306 +0.00165

−0.00170

†0.01319 +0.00116

−0.00039 0.009895 +0.00224

−0.00015

M𝑃Planet Mass [M𝐽] 1.090 +0.086

−0.087

†1.007±0.053 ‡0.30±0.03 ∗

M𝑃Planet Mass [M⊕] 346.4 +27.3

−27.7

†320.0421±16.844 ‡95±10 ∗

P Period [days] 1.7063270±0.0000036 3.12607637±0.00000060 4.97129175±0.00000051

T0Transit Mid Time [BJD𝑇 𝐷𝐵 ] 2458571.41092±0.00035 2457501.35468±0.00022 2457146.85256±0.00013

a Semi-major axis [AU] 0.0269 ±0.001 †0.04295 +0.00048

−0.00161 0.0592 +0.0019

−0.0009

a/R∗Semi-major axis in stellar radii 6.38+0.77

−0.72

†9.78+0.11

−0.36 12.1 3+0.39

−0.19

i Inclination [degrees] 83.20+0.88

−0.90

†84.98+0.03

−0.31 88.91+0.50

−0.43

b Impact Parameter 0.754 ±0.049 †0.855±0.032 0.28 ±0.007

e Eccentricity Fixed to zero Fixed to zero Fixed to zero

†Burdanov et al. (2018), ‡Anderson et al. (2012), ★Mortier et al. (2013), ∗Hellier et al. (2015)

Table 5. Summary of updated system parameters for KPS-1 b, WASP-45 b and WASP-83 b.

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12 B. Edwards et al.

Parameter Units WASP-119 b WASP-122 b

R∗Star Radius [R] 1.2±0.1 †1.52±0.03 ‡

M∗Star Mass [M] 1.02±0.06 †1.239±0.039 ‡

T𝑒 𝑓 𝑓 Star Eﬀective Temperature [K] 5650±100 †5720±130 ‡

Fe/H Star Metallicity 0.14±0.10 †0.32±‡

log(g∗) Star Surface Gravity [cgs] 4.26±0.08 †4.166±0.016 ‡

𝜌∗Star Density [𝜌] 0.76 ±0.25 †0.495±0.025 ‡

R𝑃Planet Radius [R𝐽] 1.3542 +0.0039

−0.0023 1.712 +0.009

−0.006

R𝑃Planet Radius [R𝐸] 14.860 +0.043

−0.0255 18.785 +0.102

−0.068

R𝑃/R∗Planet Radius in Stellar Radii 0.11344 +0.00032

−0.00019 0.1132 +0.0006

−0.0004

𝛿Transit Depth 0.012868 +0.000074

−0.000044 0.012815 +0.000139

−0.000093

M𝑃Planet Mass [M𝐽] 1.23±0.08 †1.284±0.032 ‡

M𝑃Planet Mass [M⊕] 391±25 †408.1±10.2 ‡

P Period [days] 2.4998052 ±0.0000017 1.71005344±0.00000032

T0Transit Mid Time [BJD𝑇 𝐷𝐵 ] 2458409.903247±0.000086 2457872.52231±0.00015

a Semi-major axis [AU] 0.03851 +0.00008

−0.00021 0.03024 +0.00007

−0.00019

a/R∗Semi-major axis in stellar radii 6.902 +0.014

−0.037 4.279+0.01

−0.027

i Inclination [degrees] 86.99 +0.01

−0.11 78.595 +0.009

−0.010

b Impact Parameter 0.362 ±0.002 0.846 ±0.005

e Eccentricity Fixed to zero Fixed to zero

†Maxted et al. (2016), ‡Turner et al. (2016)

Table 6. Summary of updated system parameters for WASP-119 b and WASP-122 b.

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ORBYTS: Ephemeris Reﬁnement of Transiting Exoplanets 13

Figure 3. All the observations of WASP-122 b used in this work.

Figure 4. All the observations of WASP-45 b used in this work.

Figure 5. All the observations of WASP-119 b used in this work.

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14 B. Edwards et al.

Figure 6. All the observations of KPS-1 b used in this work.

Figure 7. The observation of K2-237 b used in this work.

Figure 8. All the observations of KELT-15 b used in this work.

Figure 9. All the observations of WASP-83 b used in this work.

Figure 10. The observation of CoRoT-6 b used in this work.

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ORBYTS: Ephemeris Reﬁnement of Transiting Exoplanets 15

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Transit Timing Variation of K2-237b: Hints Toward Planet Disk Migration

Preprint

Full-text available

Sep 2024

Hot Jupiters should initially form at considerable distances from host stars and subsequently migrate towards inner regions, supported directly by transit timing variation (TTV). We report the TTV of K2-237b, using reproduced timings fitted from \textit{Kepler} K2 and \textit{TESS} data. The timings span from 2016 to 2021, leading to an observational baseline of 5 years. The timing evolution presents a significant bias to a constant period scenario. The model evidence is evaluated utilizing the Bayesian Information Criterion (BIC), which favours the scenario of period decay with a

\Delta

BIC of 14.1. The detected TTV induces a period decay rate (

\dot{P}

) of -1.14

\pm

0.28

\times

^{-8}

days per day (

-

0.36 s/year). Fitting the spectral energy distribution, we find infrared excess at the significance level of 1.5

\sigma

for WISE W1 and W2 bands, and 2

\sigma

level for W3 and W4 bands. This potentially reveals the existence of a stellar disk, consisting of hot dust at 800

\pm

300 K, showing a

L_{dust}/L_{\ast}

of 5

\pm

\times

^{-3}

. We obtain a stellar age of 1.0

^{+1.4}_{-0.7}

\times

^{9}

yr from isochrone fitting. The properties of K2-237b potentially serve as a direct observational support to the planet disk migration though more observation are needed.

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Article

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Mar 2024

We report the discovery and confirmation of the Transiting Exoplanet Survey Satellite (TESS) single-transit, warm and dense sub-Saturn, TIC 139270665 b. This planet is unusually dense for its size: with a bulk density of 2.13 g cm ⁻³ (0.645 R J , 0.463 M J ), it is the densest warm sub-Saturn of the TESS family. It orbits a metal-rich G2 star. We also found evidence of a second planet, TIC 139270665 c, with a longer period of 1010 − 220 + 780 days and minimum mass M P sin i of 4.89 − 0.37 + 0.66 M J . First clues of TIC 139270665 b’s existence were found by citizen scientists inspecting TESS photometric data from sector 47 in 2022 January. Radial velocity measurements from the Automated Planet Finder combined with TESS photometry and spectral energy distributions via EXOFASTv2 system modeling suggested a 23.624 − 0.031 + 0.030 day orbital period for TIC 139270665 b and also showed evidence for the second planet. Based on this estimated period, we mobilized the Unistellar citizen science network for photometric follow-up, capitalizing on their global distribution to capture a second transit of TIC 139270665 b. This citizen science effort also served as a test bed for an education initiative that integrates young students into modern astrophysics data collection. The Unistellar photometry did not definitively detect a second transit, but did enable us to further constrain the planet’s period. As a transiting, warm, and dense sub-Saturn, TIC 139270665 b represents an interesting laboratory for further study to enhance our models of planetary formation and evolution.

ExoClock Project. III. 450 New Exoplanet Ephemerides from Ground and Space Observations

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Mar 2023

The ExoClock project has been created to increase the efficiency of the Ariel mission. It will achieve this by continuously monitoring and updating the ephemerides of Ariel candidates, in order to produce a consistent catalog of reliable and precise ephemerides. This work presents a homogenous catalog of updated ephemerides for 450 planets, generated by the integration of ∼18,000 data points from multiple sources. These sources include observations from ground-based telescopes (the ExoClock network and the Exoplanet Transit Database), midtime values from the literature, and light curves from space telescopes (Kepler, K2, and TESS). With all the above, we manage to collect observations for half of the postdiscovery years (median), with data that have a median uncertainty less than 1 minute. In comparison with the literature, the ephemerides generated by the project are more precise and less biased. More than 40% of the initial literature ephemerides had to be updated to reach the goals of the project, as they were either of low precision or drifting. Moreover, the integrated approach of the project enables both the monitoring of the majority of the Ariel candidates (95%), and also the identification of missing data. These results highlight the need for continuous monitoring to increase the observing coverage of the candidate planets. Finally, the extended observing coverage of planets allows us to detect trends (transit-timing variations) for a sample of 19 planets. All the products, data, and codes used in this work are open and accessible to the wider scientific community.

The Unistellar Exoplanet Campaign: Citizen Science Results and Inherent Education Opportunities

Article

Full-text available

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This paper presents early results from and prospects for exoplanet science using a citizen science private/public partnership observer network managed by the SETI Institute in collaboration with Unistellar. The network launched in 2020 January and includes 163 citizen scientist observers across 21 countries. These observers can access a citizen science mentoring service developed by the SETI Institute and are also equipped with Unistellar Enhanced Vision Telescopes. Unistellar technology and the campaign’s associated photometric reduction pipeline enable each telescope to readily obtain and communicate light curves to observers with signal-to-noise ratio suitable for publication in research journals. Citizen astronomers of the Unistellar Exoplanet (UE) Campaign routinely measure transit depths of ≳1% and contribute their results to the exoplanet research community. The match of the detection system, targets, and scientific and educational goals is robust. Results to date include 281 transit detections out of 651 processed observations. In addition to this campaign’s capability to contribute to the professional field of exoplanet research, UE endeavors to drive improved science, technology, engineering, and mathematics education outcomes by engaging students and teachers as participants in science investigations, that is, learning science by doing science.

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Full-text available

Jan 2023

A precise transit ephemeris serves as the premise for follow-up exoplanet observations. We compare TESS Object of Interest (TOI) transit timings of 262 hot Jupiters with the archival ephemeris and find 31 of them having TOI timing offsets, among which WASP-161b shows the most significant offset of −203.7 ± 4.1 minutes. The median value of these offsets is 17.8 minutes, equivalent to 3.6 σ . We generate TESS timings in each sector for these 31 hot Jupiters, using a self-generated pipeline. The pipeline performs photometric measurements to TESS images and produces transit timings by fitting the light curves. We refine and update the previous ephemeris, based on these TESS timings (uncertainty ∼1 minute) and a long timing baseline (∼10 yr). Our refined ephemeris gives the transit timing at a median precision of 0.82 minutes until 2025 and 1.21 minutes until 2030. We regard the timing offsets to mainly originate from the underestimated ephemeris uncertainty. All the targets with timing offset larger than 10 σ present earlier timings than the prediction, which cannot be due to underestimated ephemeris uncertainty, apsidal precision, or Rømer effect as those effects should be unsigned. For some particular targets, timing offsets are likely due to tidal dissipation. Our sample leads to the detection of period-decaying candidates of WASP-161b and XO-3b reported previously.

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Thanks to their short orbital periods and hot extended atmospheres, hot Jupiters are ideal candidates for atmosphere studies with high-resolution spectroscopy. New stable spectrographs help improve our understanding of the evolution and composition of those types of planets. By analyzing two nights of observations using the ESPRESSO high-resolution spectrograph, we studied the architecture and atmosphere of hot Jupiter WASP-122b (KELT-14b). By analyzing the Rossiter-McLaughlin (RM) effect, we measured the spin-orbit angle of the system to be deg. This result is in line with literature obliquity measurements of planetary systems around stars with effective temperatures cooler than 6500 K. Using the transmission spectroscopy, we studied the atmosphere of the planet. Applying both the single-line analysis and the cross-correlation method, we looked for Ca i Cr i FeH Fe i Fe ii H

_2

O Li i Mg i Na i Ti i TiO V i VO, and Y i . Our results show no evidence of any of these species in WASP-122b's atmosphere. The lack of significant detections can be explained by either the RM effect covering the regions where the atmospheric signal is expected and masking it, along with the low signal-to-noise ratio (S/N) of the observations or the absence of the relevant species in its atmosphere.

Transit timing variation of K2-237b: hints toward planet disc migration

Article

Sep 2024

Hot Jupiters should initially form at considerable distances from host stars and subsequently migrate towards inner regions, supported directly by transit timing variation (TTV). We report the TTV of K2-237b, using reproduced timings fitted from Kepler K2 and TESS data. The timings span from 2016 to 2021, leading to an observational baseline of 5 yr. The timing evolution presents a significant bias to a constant period scenario. The model evidence is evaluated utilizing the Bayesian Information Criterion (BIC), which favours the scenario of period decay with a

\Delta

BIC of 14.1. The detected TTV induces a period decay rate (

\dot{P}

) of −1.14

\pm 0.28\times 10^{-8}

d per day (

-

0.36 s/yr). Fitting the spectral energy distribution, we find infrared excess at the significance level of 1.5

\sigma

for WISE W1 and W2 bands, and 2

\sigma

level for W3 and W4 bands. This potentially reveals the existence of a stellar disc, consisting of hot dust at 800

\pm

300 K, showing a

L_{\mathrm{ dust}}/L_{\ast }

of 5

\pm\ 3\times 10^{-3}

. We obtain a stellar age of 1.0

^{+1.4}_{-0.7}\, \times 10^{9}

yr from isochrone fitting. The properties of K2-237b potentially serve as a direct observational support to the planet disc migration though more observation are needed.

Simultaneous multicolour transit photometry of hot Jupiters HAT-P-19b, HAT-P-51b, HAT-P-55b, and HAT-P-65b

Article

Full-text available

Jan 2024
MON NOT R ASTRON SOC

Accurate physical parameters of exoplanet systems are essential for further exploration of planetary internal structure, atmospheres, and formation history. We aim to use simultaneous multicolour transit photometry to improve the estimation of transit parameters, to search for transit timing variations (TTVs), and to establish which of our targets should be prioritised for follow-up transmission spectroscopy. We performed time series photometric observations of 12 transits for the hot Jupiters HAT-P-19b, HAT-P-51b, HAT-P-55b, and HAT-P-65b using the simultaneous four-colour camera MuSCAT2 on the Telescopio Carlos Sánchez. We collected 56 additional transit light curves from TESS photometry. To derive transit parameters, we modelled the MuSCAT2 light curves with Gaussian processes to account for correlated noise. To derive physical parameters, we performed EXOFASTv2 global fits to the available transit and radial velocity data sets, together with the Gaia DR3 parallax, isochrones, and spectral energy distributions. To assess the potential for atmospheric characterisation, we compared the multicolour transit depths with a flat line and a clear atmosphere model. We consistently refined the transit and physical parameters. We improved the orbital period and ephemeris estimates, and found no evidence for TTVs or orbital decay. The MuSCAT2 broadband transmission spectra of HAT-P-19b and HAT-P-65b are consistent with previously published low-resolution transmission spectra. We also found that, except for HAT-P-65b, the assumption of a planetary atmosphere can improve the fit to the MuSCAT2 data. In particular, we identified HAT-P-55b as a priority target among these four planets for further atmospheric studies using transmission spectroscopy.

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Article

Full-text available

Nov 2023

We present analysis of the atmospheres of 70 gaseous extrasolar planets via transit spectroscopy with Hubble’s Wide Field Camera 3 (WFC3). For over half of these, we statistically detect spectral modulation that our retrievals attribute to molecular species. Among these, we use Bayesian hierarchical modeling to search for chemical trends with bulk parameters. We use the extracted water abundance to infer the atmospheric metallicity and compare it to the planet’s mass. We also run chemical equilibrium retrievals, fitting for the atmospheric metallicity directly. However, although previous studies have found evidence of a mass–metallicity trend, we find no such relation within our data. For the hotter planets within our sample, we find evidence for thermal dissociation of dihydrogen and water via the H ⁻ opacity. We suggest that the general lack of trends seen across this population study could be due to (i) the insufficient spectral coverage offered by the Hubble Space Telescope’s WFC3 G141 band, (ii) the lack of a simple trend across the whole population, (iii) the essentially random nature of the target selection for this study, or (iv) a combination of all the above. We set out how we can learn from this vast data set going forward in an attempt to ensure comparative planetology can be undertaken in the future with facilities such as the JWST, Twinkle, and Ariel. We conclude that a wider simultaneous spectral coverage is required as well as a more structured approach to target selection.

Quantifying the dust in SN 2012aw and iPTF14hls with ORBYTS

Article

Dec 2022
MON NOT R ASTRON SOC

Core-collapse supernovae (CCSNe) are capable of producing large quantities of dust, with strong evidence that ejecta dust masses can grow significantly over extended periods of time. Red-blue asymmetries in the broad emission lines of CCSNe can be modelled using the Monte Carlo radiative transfer code damocles, to determine ejecta dust masses. To facilitate easier use of damocles, we present a Tkinter graphical user interface (GUI) running damocles. The GUI was tested by high school students through the Original Research By Young Twinkle Students (ORBYTS) programme, who used it to measure the dust masses formed at two epochs in Type IIP CCSNe SN 2012aw and iPTF14hls, demonstrating that a wide range of people can contribute to scientific advancement. Bayesian methods quantified uncertainties on our model parameters. From the red scattering wing in the day 1863 Hα profile of SN 2012aw, we constrained the dust composition to large (radius >0.1 μm) silicate grains, with a dust mass of

6.0^{+21.9}_{-3.6}\times 10^{-4}~M_\odot

. From the day 1158 Hα profile of SN 2012aw, we found a dust mass of

3.0^{+14}_{-2.5}\times 10^{-4}

M⊙. For iPTF14hls, we found a day 1170 dust mass of 8.1

^{+81}_{-7.6}\times 10^{-5}

M⊙ for a dust composition consisting of 50 per cent amorphous carbon and 50 per cent astronomical silicate. At 1000 days post explosion, SN 2012aw and iPTF14hls have formed less dust than the peculiar Type II SN 1987A, suggesting that SN 1987A may have formed a larger dust mass than typical Type IIP’s.

Toward a More Complex Description of Chemical Profiles in Exoplanet Retrievals: A Two-layer Parameterization

Article

Full-text available

Nov 2019
ASTROPHYS J

State of the art spectral retrieval models of exoplanet atmospheres assume constant chemical profiles with altitude. This assumption is justified by the information content of current data sets which do not allow, in most cases, for the molecular abundances as a function of pressure to be constrained. In the context of the next generation of telescopes, a more accurate description of chemical profiles may become crucial to interpret observations and gain new insights into atmospheric physics. We explore here the possibility of retrieving pressure-dependent chemical profiles from transit spectra, without injecting any priors from theoretical chemical models in our retrievals. The "two-layer" parameterization presented here allows for the independent extraction of molecular abundances above and below a certain atmospheric pressure. By simulating various cases, we demonstrate that this evolution from constant chemical abundances is justified by the information content of spectra provided by future space instruments. Comparisons with traditional retrieval models show that assumptions made on chemical profiles may significantly impact retrieved parameters, such as the atmospheric temperature, and justify the attention we give here to this issue. We find that the two-layer retrieval accurately captures discontinuities in the vertical chemical profiles, which could be caused by disequilibrium processes—such as photochemistry—or the presence of clouds/hazes. The two-layer retrieval could also help to constrain the composition of clouds and hazes by exploring the correlation between the chemical changes in the gaseous phase and the pressure at which the condensed phase occurs. The two-layer retrieval presented here therefore represents an important step forward in our ability to constrain theoretical chemical models and cloud/haze composition from the analysis of future observations.

Small bodies science with the Twinkle space telescope

Article

Full-text available

Sep 2019

2019 Society of PhotoOptical Instrumentation Engineers (SPIE). Twinkle is an upcoming 0.45-m space-based telescope equipped with a visible and two near-infrared spectrometers covering the spectral range 0.4 to 4.5 μm with a resolving power R 250 (λ < 2.42 μm) and R 60 (λ > 2.42 μm). We explore Twinkle's capabilities for small bodies science and find that, given Twinkle's sensitivity, pointing stability, and spectral range, the mission can observe a large number of small bodies. The sensitivity of Twinkle is calculated and compared to the flux from an object of a given visible magnitude. The number, and brightness, of asteroids and comets that enter Twinkle's field of regard is studied over three time periods of up to a decade. We find that, over a decade, several thousand asteroids enter Twinkle's field of regard with a brightness and nonsidereal rate that will allow Twinkle to characterize them at the instrumentation's native resolution with SNR > 100. Hundreds of comets can also be observed. Therefore, Twinkle offers researchers the opportunity to contribute significantly to the field of Solar System small bodies research.

Wōtan : Comprehensive Time-series Detrending in Python

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ASTRON J

MARVEL analysis of the measured high-resolution spectra of 14 NH

Article

Full-text available

Jun 2019

Rovibronic energy levels are determined for four low-lying electronic states (X 3Σ-, A ³Π, a 1Δ, and c 1Π) of the imidogen free radical (14NH) using the Marvel (Measured Active Rotational-Vibrational Energy Levels) technique. Compilation of transitions from both laboratory measurements and solar spectra, found in 18 publications, yields a dataset of 3002 rovibronic transitions forming elements of a measured spectroscopic network (SN). At the end of the MARVEL procedure, the majority of the transitions form a single, self-consistent SN component of 2954 rovibronic transitions and 1058 energy levels, 542, 403, and 58 for the X 3Σ-, A ³Π, and c 1Π electronic states, respectively. The a 1Δ electronic state is characterized by 55 Λ-doublet levels, counting each level only once. Electronic structure computations show that unusually the CCSD(T) method does not accurately predict the a 1Δ excitation energy even at the complete basis set limit.

An Updated Study of Potential Targets for Ariel

Article

Full-text available

May 2019
ASTRON J

Ariel has been selected as ESA's M4 mission for launch in 2028 and is designed for the characterization of a large and diverse population of exoplanetary atmospheres to provide insights into planetary formation and evolution within our Galaxy. Here we present a study of Ariel's capability to observe currently known exoplanets and predicted Transiting Exoplanet Survey Satellite (TESS) discoveries. We use the Ariel radiometric model (ArielRad) to simulate the instrument performance and find that ~2000 of these planets have atmospheric signals which could be characterized by Ariel. This list of potential planets contains a diverse range of planetary and stellar parameters. From these we select an example mission reference sample (MRS), comprised of 1000 diverse planets to be completed within the primary mission life, which is consistent with previous studies. We also explore the mission capability to perform an in-depth survey into the atmospheres of smaller planets, which may be enriched or secondary. Earth-sized planets and super-Earths with atmospheres heavier than H/He will be more challenging to observe spectroscopically. However, by studying the time required to observe ~110 Earth-sized/super-Earths, we find that Ariel could have substantial capability for providing in-depth observations of smaller planets. Trade-offs between the number and type of planets observed will form a key part of the selection process and this list of planets will continually evolve with new exoplanet discoveries replacing predicted detections. The Ariel target list will be constantly updated and the MRS re-selected to ensure maximum diversity in the population of planets studied during the primary mission life.

Remote-sensing Characterisation of Major Solar System Bodies with the Twinkle Space Telescope

Article

Full-text available

Mar 2019

Remote-sensing observations of Solar System objects with a space telescope offer a key method of understanding celestial bodies and contributing to planetary formation and evolution theories. The capabilities of Twinkle, a space telescope in a low Earth orbit with a 0.45m mirror, to acquire spectroscopic data of Solar System targets in the visible and infrared are assessed. Twinkle is a general observatory that provides on demand observations of a wide variety of targets within wavelength ranges that are currently not accessible using other space telescopes or that are accessible only to oversubscribed observatories in the short-term future. We determine the periods for which numerous Solar System objects could be observed and find that Solar System objects are regularly observable. The photon flux of major bodies is determined for comparison to the sensitivity and saturation limits of Twinkle's instrumentation and we find that the satellite's capability varies across the three spectral bands (0.4-1, 1.3-2.42, and 2.42-4.5{\mu}m). We find that for a number of targets, including the outer planets, their large moons, and bright asteroids, the model created predicts that with short exposure times, high-resolution spectra (R~250, {\lambda} < 2.42{\mu}m; R~60, {\lambda} > 2.42{\mu}m) could be obtained with signal-to-noise ratio (SNR) of >100 with exposure times of <300s.

Ephemeris refinement of 21 hot Jupiter exoplanets with high timing uncertainties

Article

Full-text available

Jan 2019

Transit events of extrasolar planets offer a wealth of information for planetary characterization. However, for many known targets, the uncertainty of their predicted transit windows prohibits an accurate scheduling of follow-up observations. In this work, we refine the ephemerides of 21 hot Jupiter exoplanets with the largest timing uncertainties. We collected 120 professional and amateur transit light curves of the targets of interest, observed with a range of telescopes of 0.3 m-2.2 m, and analyzed them along with the timing information of the planets discovery papers. In the case of WASP-117b, we measured a timing deviation compared to the known ephemeris of about 3.5 h, and for HAT-P-29b and HAT-P-31b the deviation amounted to about 2 h and more. For all targets, the new ephemeris predicts transit timings with uncertainties of less than 6 min in the year 2018 and less than 13 min until 2025. Thus, our results allow for an accurate scheduling of follow-up observations in the next decade.

Transit analysis of the CoRoT-5, CoRoT-8, CoRoT-12, CoRoT-18, CoRoT-20, and CoRoT-27 systems with combined ground- and space-based photometry

Article

Feb 2019
MON NOT R ASTRON SOC

We have initiated a dedicated project to follow-up with ground-based photometry the transiting planets discovered by CoRoT in order to refine the orbital elements, constrain their physical parameters, and search for additional bodies in the system. From 2012 September to 2016 December we carried out 16 transit observations of six CoRoT planets (CoRoT-5 b, CoRoT-8 b, CoRoT-12 b, CoRoT-18 b, CoRoT-20 b, and CoRoT-27 b) at three observatories located in Germany and Spain. These observations took place between 5 and 9 yr after the planet’s discovery, which has allowed us to place stringent constraints on the planetary ephemeris. In five cases we obtained light curves with a deviation of the mid-transit time of up to ∼115 min from the predictions. We refined the ephemeris in all these cases and reduced the uncertainties of the orbital periods by factors between 1.2 and 33. In most cases our determined physical properties for individual systems are in agreement with values reported in previous studies. In one case, CoRoT-27 b, we could not detect any transit event in the predicted transit window.

WASP-4b Arrived Early for the TESS Mission

Article

May 2019
ASTRON J

The Transiting Exoplanet Survey Satellite ( TESS ) recently observed 18 transits of the hot Jupiter WASP-4b. The sequence of transits occurred 81.6 ± 11.7 s earlier than had been predicted, based on data stretching back to 2007. This is unlikely to be the result of a clock error, because TESS observations of other hot Jupiters (WASP-6b, 18b, and 46b) are compatible with a constant period, ruling out an 81.6 s offset at the 6.4 σ level. The 1.3 day orbital period of WASP-4b appears to be decreasing at a rate of ms per year. The apparent period change might be caused by tidal orbital decay or apsidal precession, although both interpretations have shortcomings. The gravitational influence of a third body is another possibility, though at present there is minimal evidence for such a body. Further observations are needed to confirm and understand the timing variation.

Detectable Molecular Features above Hydrocarbon Haze via Transmission Spectroscopy with JWST : Case Studies of GJ 1214b-, GJ 436b-, HD 97658b-, and Kepler-51b-like Planets

Article

Apr 2019

Some of the exoplanets observed thus far show featureless or flat transmission spectra, possibly indicating the existence of clouds and/or haze in their atmospheres. Thanks to its large aperture size and broad wavelength coverage, the James Webb Space Telescope (JWST) is expected to enable a detailed investigation of exoplanet atmospheres, which could provide important constraints on the atmospheric composition obscured by clouds/haze. Here, we use four warm (≾1000 K) planets suitable for atmospheric characterization via transmission spectroscopy, GJ 1214b, GJ 436b, HD 97658b, and Kepler-51b, as examples to explore molecular absorption features detectable by JWST even in the existence of hydrocarbon haze in the atmospheres. We simulate photochemistry, the growth of hydrocarbon haze particles, and transmission spectra for the atmospheres of these four planets. We find that among the planetary parameters considered, super-Earths with hazy, relatively hydrogen-rich atmospheres are mostly expected to produce detectable molecular absorption features such as a quite prominent CH_4 feature at 3.3 μm, even for the extreme case of the most efficient production of photochemical haze. For a planet that has extremely low gravity, such as Kepler-51b, haze particles grow significantly large in the upper atmosphere due to the small sedimentation velocity, resulting in the featureless or flat transmission spectrum in a wide wavelength range. This investigation shows that, in most cases, the transmission spectra with muted features measured by Hubble Space Telescope do not preclude strong features at the longer wavelengths accessible by JWST.

Original Research By Young Twinkle Students (ORBYTS): Ephemeris Refinement of Transiting Exoplanets

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