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Photometry of the Didymos System across the DART Impact Apparition

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Abstract

On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes. Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite’s orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from 2022 July to 2023 February. We focus here on decomposable lightcurves, i.e., those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the postimpact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ∼1 day after impact and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days postimpact. This bulk photometric behavior was not well represented by an HG photometric model. An HG 1 G 2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least 2023 March. Its persistence implied ongoing escape of ejecta from the system many months after DART impact.
Photometry of the Didymos System across the DART Impact Apparition
Nicholas Moskovitz
1
, Cristina Thomas
2
, Petr Pravec
3
, Tim Lister
4
, Tom Polakis
1
, David Osip
5
, Theodore Kareta
1
,
Agata Rożek
6
, Steven R. Chesley
7
, Shantanu P. Naidu
7
, Peter Scheirich
3
, William Ryan
8
, Eileen Ryan
8
, Brian Skiff
1
,
Colin Snodgrass
6
, Matthew M. Knight
9
, Andrew S. Rivkin
10
, Nancy L. Chabot
10
, Vova Ayvazian
11
,
Irina Belskaya
12,13
, Zouhair Benkhaldoun
14
, Daniel N. Berteşteanu
15
, Mariangela Bonavita
6
, Terrence H. Bressi
16
,
Melissa J. Brucker
16
, Martin J. Burgdorf
17
, Otabek Burkhonov
18
, Brian Burt
1
, Carlos Contreras
5
, Joseph Chatelain
4
,
Young-Jun Choi
19,20
, Matthew Daily
4
, Julia de León
21
, Kamoliddin Ergashev
18
, Tony Farnham
22
, Petr Fatka
3
,
Marin Ferrais
23
, Stefan Geier
24,25
, Edward Gomez
4,26
, Sarah Greenstreet
27
, Hannes Gröller
16
, Carl Hergenrother
28
,
Carrie Holt
22
, Kamil Hornoch
3
, Marek Husárik
29
, Raguli Inasaridze
11,30
, Emmanuel Jehin
31
, Elahe Khalouei
32
,
Jean-Baptiste Kikwaya Eluo
33
, Myung-Jin Kim
19
, Yurij Krugly
13,34
, Hana Kučáková
3
, Peter Kušnirák
3
,
Jeffrey A. Larsen
35
, Hee-Jae Lee
19
, Cassandra Lejoly
16
, Javier Licandro
21
, Penélope Longa-Peña
36
,
Ronald A. Mastaler
16
, Curtis McCully
4
, Hong-Kyu Moon
19
, Nidia Morrell
5
, Arushi Nath
37
, Dagmara Oszkiewicz
34
,
Daniel Parrott
38
, Liz Phillips
4,39
, Marcel M. Popescu
40
, Donald Pray
41
, George Pantelimon Prodan
40
, Markus Rabus
42
,
Michael T. Read
16
, Inna Reva
43
, Vernon Roark
44
, Toni Santana-Ros
45,46
, James V. Scotti
16
, Taiyo Tatara
35
, Audrey Thirouin
1
,
David Tholen
44
, Volodymyr Troianskyi
34,47,48
, Andrew F. Tubbiolo
16
, and Katelyn Villa
9
1
Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86004, USA; nmosko@lowell.edu
2
Northern Arizona University, USA
3
Astronomical Institute of the Academy of Sciences of the Czech Republic, Fričova 298, Ondr
ejov, CZ-25165, Czech Republic
4
Las Cumbres Observatory, Goleta, CA, USA
5
Las Campanas Observatory, Chile
6
Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, EH9 3HJ, UK
7
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
8
New Mexico Institute of Mining and Technology/Magdalena Ridge Observatory, 801 Leroy Place, Socorro, NM 87801, USA
9
Physics Department, United States Naval Academy, 572C Holloway Road, Annapolis, MD 21402, USA
10
Johns Hopkins University Applied Physics Laboratory, USA
11
E. Kharadze Georgian National Astrophysical Observatory, Abastumani, Georgia
12
LESIA, Observatoire de Paris, Université PSL, CNRS, Université Paris Cité, Sorbonne Université, Meudon, France
13
Institute of Astronomy, V.N. Karazin Kharkiv National University, Kharkiv, Ukraine
14
Oukaïmeden Observatory, High Energy Physics and Astrophysics Laboratory, Cadi Ayyad University, BP 2390, Marrakech, Morocco
15
Astronomical Institute of the Romanian Academy, Romania
16
LPL/UA, USA
17
Universität Hamburg, Faculty of Mathematics, Informatics and Natural Sciences, Department of Earth Sciences, Meteorological Institute, Bundesstraße 55,
D-20146 Hamburg, Germany
18
Ulugh Beg Astronomical Institute, Tashkent, Uzbekistan
19
Korea Astronomy and Space Science Institute, 776, Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Republic of Korea
20
University of Science and Technology, 217, Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
21
Instituto de Astrofísica de Canarias, Spain
22
University of Maryland, USA
23
Florida Space Institute, University of Central Florida, 12354 Research Parkway, Orlando, FL 32826, USA
24
Gran Telescopio Canarias (GRANTECAN), Cuesta de San José s/n, E-38712, Breña Baja, La Palma, Spain
25
Instituto de Astrofísica de Canarias, Vía Láctea s/n, E-38200, La Laguna, Tenerife, Spain
26
School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
27
DiRAC Institute and the Department of Astronomy, University of Washington, USA
28
Ascending Node Technologies, LLC, Tucson, AZ, USA
29
Astronomical Institute of the Slovak Academy of Sciences, 059 60 Tatranská Lomnica, The Slovak Republic
30
Samtskhe-Javakheti State University, Akhaltsikhe, Georgia
31
Space sciences, Technologies & Astrophysics Research (STAR)Institute, University of Liège, Belgium
32
Astronomy Research Center, Research Institute of Basic Sciences, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
33
Vatican Observatory, V-00120 Vatican City State, Italy
34
Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
35
USNA, USA
36
Centro de Astronomía, Universidad de Antofagasta, Av. Angamos 601, Antofagasta, Chile
37
MonitorMyPlanet, Toronto, Canada
38
Tycho Tracker, USA
39
Department of Physics, University of California, Santa Barbara, USA
40
Astronomical Institute of the Romanian Academy, 5 Cuţitul de Argint, 040557 Bucharest, Romania
41
Sugarloaf Mountain Observatory, South Deereld, MA, USA
42
Departamento de Matemática y Física Aplicadas, Facultad de Ingeniería, Universidad Católica de la Santísima Concepción, Alonso de Rivera 2850, Concepción,
Chile
43
Fesenkov Astrophysical Institute, Almaty, Kazakhstan
44
University of Hawaii, USA
45
Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Carr. de San Vicente del Raspeig, s/n, E-03690 San Vicente del
Raspeig, Alicante, Spain
46
Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Carrer de Martí i Franquès, 1, E-08028, Barcelona, Spain
47
Department of Physics and Astronomy FMPIT of Odesa I.I. Mechnykov National University, Pastera Street 42, 65082 Odesa, Ukraine
The Planetary Science Journal, 5:35 (28pp), 2024 February https://doi.org/10.3847/PSJ/ad0e74
© 2024. The Author(s). Published by the American Astronomical Society.
1
48
Department of Physics and Methods of Teaching, Faculty of Physics and Technology, Vasyl Stefanyk Precarpathian National University, Shevchenko Street 57,
76000 Ivano-Frankivsk, Ukraine
Received 2023 September 21; revised 2023 October 27; accepted 2023 October 30; published 2024 February 7
Abstract
On 2022 September 26, the Double Asteroid Redirection Test (DART)spacecraft impacted Dimorphos, the
satellite of binary near-Earth asteroid (65803)Didymos. This demonstrated the efcacy of a kinetic impactor for
planetary defense by changing the orbital period of Dimorphos by 33 minutes. Measuring the period change relied
heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and
eclipses)as a direct probe of the satellites orbital period. A total of 28 telescopes contributed 224 individual
lightcurves during the impact apparition from 2022 July to 2023 February. We focus here on decomposable
lightcurves, i.e., those from which mutual events could be extracted. We describe our process of lightcurve
decomposition and use that to release the full data set for future analysis. We leverage these data to place
constraints on the postimpact evolution of ejecta. The measured depths of mutual events relative to models showed
that the ejecta became optically thin within the rst 1 day after impact and then faded with a decay time of about
25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness
enhancement after about 20 days postimpact. This bulk photometric behavior was not well represented by an HG
photometric model. An HG
1
G
2
model did t the data well across a wide range of phase angles. Lastly, we note the
presence of an ejecta tail through at least 2023 March. Its persistence implied ongoing escape of ejecta from the
system many months after DART impact.
Unied Astronomy Thesaurus concepts: Near-Earth objects (1092);Asteroids (72);Small Solar System
bodies (1469)
Supporting material: machine-readable table
1. Introduction
Binary systems are estimated to represent about 15% of the
near-Earth asteroid population (Pravec et al. 2006). Discovered
as a binary in 2003 November (Pravec et al. 2003), the near-
Earth asteroid (65803)Didymos is an 760 m oblate spheroid
with a 150 m satellite known as Dimorphos (Naidu et al.
2020; Daly et al. 2023). Based on extensive lightcurve (Pravec
et al. 2022)and radar (Naidu et al. 2020)observations, the
binary dynamics of this system have been well established
(Naidu et al. 2022; Scheirich & Pravec 2022). Didymos has a
rotation period =2.260 0 ±0.0001 hr, and Dimorphos had an
orbit period =11.921 481 ±0.000016 hr (Naidu et al. 2022).
This orbit period uncertainty of <60 ms makes Didymos one of
the best-characterized binary asteroids in the solar system. Such
precision was achievable because Didymos is an eclipsing
binary. Mutual eventsoccultations and eclipsescan be
detected in time series photometry of Didymos and thus can
serve as a chronometer for the orbital period of Dimorphos.
Given the state of knowledge of the Didymos system and
favorable observing apparitions in the 2020s, this system was
selected as the target for NASAs Double Asteroid Redirection
Test (DART)mission (Cheng et al. 2016; Rivkin et al. 2021).
Following its launch from Vandenberg Space Force Base on
2021 November 24 and a relatively short 10 month cruise
phase, the DART spacecraft intentionally impacted Dimorphos
on 2022 September 26 (at JD 2459849.46834). This was the
worldʼsrst full-scale planetary defense experiment and was
designed to change the orbital period of Dimorphos as a test of
asteroid deection via kinetic impactor. In terms of level 1
mission requirements (Rivkin et al. 2021), the impact by
DART was to change the orbit period by at least 73 s, which
would then be measured via ground-based observations to a
precision of 10% or 7.3 s (0.002 hr). DART impacted
Dimorphos head-on (Daly et al. 2023)so that its orbital period
decreased.
The DART spacecraft had a relatively simple payload that
included a high-resolution imager called the Didymos Recon-
naissance and Asteroid Camera for Optical navigation
(DRACO; Fletcher et al. 2018)and a 6U CubeSat called the
Light Italian CubeSat for Imaging of Asteroids (LICIACube;
Dotto et al. 2021), built by the Italian Space Agency (ASI).
LICIACube separated from the DART spacecraft 2 weeks
before impact and provided yby imagery of the impact ejecta
plume from about 30 to 320 s after impact (Dotto &
Zinzi 2023). Following these in situ operations, continued
characterization of the system relied on remote telescopic
observations.
An extensive campaign of ground- and space-based
observations was coordinated to study the aftermath of the
DART impact and meet the level 1 requirements of the
mission. The primary component of this campaign involved
lightcurve photometry and the measurement of mutual events
(Section 2). Based on the analysis of lightcurves from prior
apparitions (Pravec et al. 2022), the methodology for this
campaign was well established. In short, high-quality photo-
metry (rms residuals of generally <0.01 mag)was needed to
enable the decomposition of lightcurves (Section 4)into their
constituent parts: the 2.26 hr rotation of Didymos, a possible
rotational signature from Dimorphos, drops in ux due to
mutual events, and, in the postimpact environment, the
evolution of ejecta. These stringent data requirements had to
be sustained across many facilities, many hours for each
lightcurve, and the duration of the apparition. Observing
circumstances such as apparent magnitude and declination.
inuenced campaign planning. For example, large-aperture
facilities were primarily used at the beginning and end of the
apparition when Didymos was faintest. Overall, this coordi-
nated approach proved highly successful, yielding from just the
rst month of postimpact data a new orbital period for
Original content from this work may be used under the terms
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The Planetary Science Journal, 5:35 (28pp), 2024 February Moskovitz et al.
Dimorphos of 11.372 ±0.017 hr, corresponding to a change of
33 minutes relative to the preimpact value (Thomas et al.
2023). In this work, we expand the scope of the lightcurve data
set from that presented in Thomas et al. (2023)to now include
a full 8 months of data across the 20222023 apparition.
For denitional purposes, we hereafter refer to a lightcurve
as a time series of photometry collected by a single facility on a
single night. A lightcurve session or observing run refers to the
window in which a single lightcurve was obtained. We refer to
the primary lightcurve as the rotational signature of Didymos.
The term secondary refers to Dimorphos. Mutual events come
in four avors: secondary eclipses (Dimorphos passes into
shadow),secondary occultations (Dimorphos moves behind
Didymos),primary eclipses (the shadow of Dimorphos passes
over Didymos), and primary occultations (Didymos is covered
by Dimorphos).
In total, 28 observatories contributed data that were accepted
as part of the DART lightcurve campaign (Section 3). This
produced a massive data set of 224 lightcurves with hundreds
of mutual events detected from 2022 July to 2023 February.
The associated decompositions (Section 5)provided a basis for
detailed modeling of the orbital and rotational dynamics in the
Didymos system (Naidu et al. 2023; Scheirich et al. 2024).We
note that these two modeling efforts represent independent
assessments of the lightcurve data set. The lightcurves
presented here are a superset of the data analyzed in Scheirich
et al. (2024)because their data quality requirements were more
stringent, resulting in 193 lightcurves accepted for their
analysis. These two analyses were meant to be completely
independent, so it is expected that different acceptance criteria
were applied. However, the Naidu et al. (2023)and Scheirich
et al. (2024)orbit solutions agree within formal uncertainties, a
good indication that the less stringent approach here did not
bias the results.
Our primary objective here is to provide an overview of the
lightcurve campaign, associated data sets, and analysis;
however, we also leverage these data to address the evolution
of postimpact ejecta. The measured depths of mutual events
served as a proxy for the optical depth and fading of ejecta
(Section 6). The photometry of Didymos, averaged over
lightcurve variations, allowed for characterizing the photo-
metric phase curve and determining when ejecta no longer
contributed signicant ux to the system (Section 7). Lastly,
ejecta in the form of an extended tail persisted through to the
end of the apparition; we quantify the tails contribution to the
total ux as a function of time (Section 8). Modeling of the
dynamics of the Didymos system and renements to the orbital
period change of Dimorphos are presented elsewhere (e.g.,
Naidu et al. 2023; Scheirich et al. 2024). Discussion of our
results and prospects for future work serve as a conclusion to
this paper (Section 9).
2. DART Lightcurve Campaign
The Didymos system underwent a highly favorable appari-
tion in 20222023 (Figure 1). This apparition was unusually
long, with Didymos positioned at solar elongations greater than
100°for nearly 11 months, from 2022 May to 2023 April.
During this time, the system was predicted to reach a peak
brightness of V=14.5 mag at the end of 2022 September,
coincident with the DART impact. Didymos only gets this
bright every few decades. The last time it was brighter than
15th magnitude was in 2003, when Dimorphos was discovered
(Pravec et al. 2003). It will not get this bright again until 2062
October. At these magnitudes, obtaining high-quality photo-
metry is possible across a wide range of telescope apertures.
We show in the following sections that telescope apertures
down to 0.5 m in diameter were able to achieve strict data
quality requirements and thus made signicant contributions to
the lightcurve campaign. Achieving the missions level 1
requirement of measuring the orbital period change of
Dimorphos from ground-based facilities (Rivkin et al. 2021)
was largely possible because of the system brightness in this
apparition.
The viewing geometry of Didymos in the impact apparition
was in some ways advantageous. For example, a wide range of
solar phase angles, from a maximum of 76°to a minimum of
6°, enabled photometric (e.g., Section 7)and polarimetric (e.g.,
Bagnulo et al. 2023)phase curve analyses. However, the
ranges of declination and Galactic latitude (Figure 1)posed
interesting challenges. Given moderate negative declinations
(around 35°)in the days after impact followed by a transition
into northern declinations in late October, the observing
campaign necessitated a global approach that leveraged
telescopes in both the Northern and Southern Hemispheres.
A Galactic plane crossing 24 days after impact (on 2022
October 20)was expected to degrade the quality of the
photometry due to contamination by background sources for at
least a week or two in late October. This turned out not to be a
signicant issue, as viable lightcurves were obtained through-
out the Galactic plane crossing (Section 4). More problematic
was the high background and low elongation from a full Moon
on 2022 October 9. This led to a gap in viable lightcurves for
about a week in the middle of the month. Fortunately, the
postimpact brightening of Didymos by about 1.5 mag (Gray-
kowski et al. 2023)allowed for short exposure times and thus
helped to mitigate these issues of crowded elds and high
background.
Taking these observational factors into account, the mission
developed a 20222023 observing plan that spanned nine
individual lunations, with the impact lunation split into pre- and
post-DART impact windows (Table 1). The lunations repre-
sented windows outside of full Moon conditions when the
highest-quality data were likely to be obtained. These covered
the full apparition starting in 2022 July with preimpact
lunations L1L4 and then postimpact lunations that increased
from L0 to L5, ending in 2023 February. Data were obtained
after the L5 lunation in 2023 March, but insufcient temporal
coverage and low signal-to-noise ratios (S/N)rendered these
data unusable for our analysis here. Unsurprisingly, the number
of viable lightcurves and associated decompositions (Table 1)
tracked inversely with the apparent magnitude of Didymos. At
the beginning (Pre-L1)and end (L5)of the apparition, when
Didymos was faintest, telescopes with apertures >2m in
diameter were required to collect data of sufcient quality. The
primary goal of observations in the preimpact lunations was to
conrm the dynamics of the system as determined by Naidu
et al. (2022)and Scheirich & Pravec (2022). There was also
interest in measuring the rotation period of Dimorphos in the
preimpact data, but that signature was never clearly detected,
perhaps due to its oblate shape (Daly et al. 2023).
For all lunations, the mission established strict data quality
requirements to ensure successful lightcurve decompositions
(Section 4). These requirements were largely based on
experience gained from previous apparitions in 2003, 2015,
3
The Planetary Science Journal, 5:35 (28pp), 2024 February Moskovitz et al.
2017, 2019, 2020, and 2021 (e.g., Naidu et al. 2022; Pravec
et al. 2022; Scheirich & Pravec 2022). Requirements provided
to observers leading up to the apparition included photometric
precision of at least 0.01 mag exposure
1
and a temporal
cadence of no more than 180 s between exposures to ensure
adequate sampling of mutual events. The choice of photometric
lter was not prescribed because our primary photometric
analysis was based on differential magnitudes, and we assumed
that Didymos had no rotational color variability that would
affect combining data from different lters. Observers were
encouraged to employ whatever lter would yield the highest
S/N with their instrument. Typically, lightcurves were
accepted for analysis only if they spanned at least one full
rotation of Didymos (2.26 hr), though exceptions were made
for some short lightcurve segments when data from other
facilities were taken close enough in time to enable a clean
decomposition. These short segments were often useful in
lling out specic rotational phases of Didymos that were not
covered by adjacent lightcurves. Decompositions were per-
formed on batches of data in which the morphology of the
Didymos lightcurve was roughly constant. We discuss this
process in greater detail in Section 4.
Though observations were planned in the days immediately
after impact to monitor the evolution of the ejecta plume, the
clearing of ejecta and its contribution to the measured
photometry of the system was expected to confuse the
detection of mutual events for many days or even weeks after
impact (Fahnestock et al. 2022). Given the full Moon on
October 9 and the Galactic plane crossing a little over a week
later (Figure 1), it was unclear whether mutual event detections
and thus a period change determination would be possible in
the rst month after impact. Thus, the lightcurve campaign had
to be both comprehensive (e.g., facilities spanning a range of
apertures and locations on Earth)and exible (e.g., in telescope
scheduling)to effectively respond to whatever was the outcome
of the impact experiment.
To help observers prepare for postimpact observational
challenges, such as low Galactic latitude and a bright Moon, a
list of practice targets was provided. This list was intended to
help test and rene the capabilities of instruments under
challenging conditions and to help establish data analysis
procedures that would enable rapid turnaround of reduced
lightcurves. Test targets were selected from the catalog of
known asteroids in the astorb database (Moskovitz et al. 2022)
that had analogous observing conditions to Didymos in 2022
October. Specically, we selected near-Earth objects with
14.5 <V<16.5, solar elongation >90°, and nonsidereal rates
of motion between 1 25 and 7 5 minute
1
. This list of test
targets was posted online and dynamically updated on a daily
basis to incorporate newly discovered objects and handle
changes in observability. This list was additionally subdivided
based on conditions related to lunar phase, lunar elongation,
and Galactic latitude. Three windows of observing conditions
were dened: (1)lunar phase >75%, lunar elongation >60°,
and Galactic latitude >20°;(2)25% <lunar phase <75%,
30°<lunar elongation <50°, and Galactic latitude <10°; and
(3)lunar phase <25%, lunar elongation >45°, and Galactic
latitude <20°. These three windows represented the conditions
for Didymos from October 1 to 11, October 15 to 19, and
October 20 to 27, respectively. For the year leading up to
impact, any given night was likely to have one to three test
targets available that met these conditions.
The full extent of the 20222023 campaign involved
contributions from many observers and facilities across the
globe. Details of the 224 individual lightcurves presented in the
remainder of this work are given in Appendix Table A1. For
completeness, we include here data collected by the invest-
igation team from 2022 July to 2023 February. Some of these
observations (UT 2022 July 27, 2022 September 28October
10)were previously reported in Thomas et al. (2023).We
present only those data that met the quality requirements
described above. Many dozens of additional data sets (about
25% of those submitted by the investigation team)were
Figure 1. Observing circumstances for Didymos in the 20222023 apparition. The start dates of individual lightcurves (Table A1)are indicated across the top as green
vertical bars. Labels for pre- and postimpact lunations are shown along with full Moon dates. The apparent magnitude, Galactic latitude, and declination of Didymos
were calculated from Lowell Observatorys astorb system (Moskovitz et al. 2022). Didymos reached a minimum magnitude of V=14.5 coincident with the DART
impact on 2022 September 26 (vertical gray line). Gaps in lightcurve coverage were generally due to the full Moon; however, a Galactic plane crossing in mid-October
also affected the number of viable lightcurves.
4
The Planetary Science Journal, 5:35 (28pp), 2024 February Moskovitz et al.
unfortunately not accepted as viable for lightcurve analysis.
However, some of these data sets have provided and will
continue to provide valuable insights into other aspects of the
postimpact Didymos environment (e.g., Kareta et al. 2023).
3. Telescope Facilities
A total of 28 telescopes contributed viable data to the
lightcurve campaign (Figure 2, Table 2). These telescopes
ranged in diameter from 0.5 up to 6.5 m and employed a wide
variety of instruments. In addition, the photometric lters and
tracking modes (sidereal versus nonsidereal)varied from one
facility to the next. This approach to building the lightcurve
data set was a natural consequence of the diversity and scope of
the DART investigation team and may have helped to
minimize systematic biases that could have affected outcomes
if fewer facilities were involved. Careful control of systematics
and data quality were essential to the success of the campaign
and were the primary challenge to building the full data set.
Though the general methodology of collecting images with
CCD cameras and measuring lightcurves is hardly novel, the
DART campaign required that this be done at high precision
(subpercent photometry)across a large number of facilities and
be sustained for multiple hours within a night and across many
months throughout the apparition.
To achieve these high standards, individual observers were
encouraged to adopt whatever reduction methods worked best
for their data. However, some aspects of the reductions were
common to most data sets. In the postimpact window, aperture
sizes signicantly larger than the local seeing (57radius for
many of the data sets in October)were typically used to
account for the extended brightness of the ejecta cloud. This
was important to compensate for centroiding errors related to
the complicated point-spread function of the postimpact
system. It was found that the larger apertures generally caused
higher noise levels in individual data points but much better
point-to-point consistency across each lightcurve. In nearly all
cases, circular aperture photometry was employed. Reductions
involved testing a range of photometric aperture sizes to
optimize both the S/N of individual measurements and the
Figure 2. Global distribution of telescopes that contributed lightcurves to the 20222023 campaign. See text for details of facilities and instruments. Earth at night
image credit: NASA/NOAA.
Table 1
DART Campaign Lunations
Lunation Data Range (JD)Data Range (UTC)Lightcurves Decompositions
Pre-L1 2459762.6669 2459767.9728 2022-07-02T04:00 2022-07-07T11:20 5 1
Pre-L2 2459791.6504 2459791.9057 2022-07-31T03:36 2022-07-31T09:44 1 1
Pre-L3 2459809.5313 2459828.6771 2022-08-18T00:45 2022-09-06T04:15 16 4
Pre-L4 2459834.5636 2459848.8959 2022-09-12T01:31 2022-09-26T09:30 22 3
L0 2459850.6063 2459862.7933 2022-09-28T02:33 2022-10-10T07:02 54 13
L1 2459869.6181 2459886.0129 2022-10-17T02:50 2022-11-02T12:18 27 4
L2 2459900.7059 2459915.9442 2022-11-17T04:56 2022-12-02T10:39 48 7
L3 2459927.9180 2459944.8952 2022-12-14T10:01 2022-12-31T09:29 30 6
L4 2459955.5764 2459974.7416 2023-01-11T01:50 2023-01-30T05:47 16 2
L5 2459986.5711 2460000.8285 2023-02-11T01:42 2023-02-25T07:53 5 2
Note. The range of dates in which data were obtained are given for preimpact lunations L1L4 and postimpact lunations L0L5. The number of individual lightcurves
and decompositions are given for each lunation.
5
The Planetary Science Journal, 5:35 (28pp), 2024 February Moskovitz et al.
consistency of intranight measurements. In general, the
magnitudes reported by each facility were converted to
differential values by subtracting off the mean of each
lightcurve outside of mutual events. Though error bars were
reported for most lightcurves, these were not measured in a
consistent way across all data sets and thus were largely
ignored in our analysis.
Some telescopes elected to track at half of the nonsidereal
rates of the asteroid. This was particularly true around the time
of minimum geocentric distance, when the nonsidereal rates
reached a maximum of 8minute
1
. Fortunately, the asteroid
was also brightest at this time, and thus long exposures were
not required. Generally, exposures times were kept below the
level where signicant elongation of the point-spread function
occurred, eliminating the need for noncircular apertures. Noise
characteristics for these data were dominated by the signal from
the asteroid (and its morphologically complex ejecta cloud),as
opposed to being background-limited. Thus, the use of circular
apertures for these data, when the asteroid and stars may have
been slightly trailed, did not introduce signicant background
noise into the measurements.
As a way to ensure that the period change measurement was
adequately supported, the DART project contracted several
facilities to carry out lightcurve observations. These included
the 6.5 m Magellan Baade and 1 m Swope telescopes at Las
Campanas Observatory in Chile, the 2.4 m Magdalena Ridge
Observatory (MRO)in New Mexico, the 4.3 m Lowell
Discovery Telescope (LDT)in Arizona, and the Las Cumbres
Observatory Global Telescope (LCOGT)network of 1 m
facilities. All other facilities that contributed to the lightcurve
campaign were not directly contracted by the project. These
unsupported observatories contributed a majority of the
lightcurves to the overall data set and serve as a testament to
the global interest in the DART experiment.
In the following subsections, we summarize in order of
aperture size the telescope, instrument, and reduction methods
used by each facility. Details on individual lightcurves are in
Appendix Table A1. In addition, a large le is included with
this manuscript as supporting data that contains all of the
individual lightcurve measurements (38,532 in total)and the
associated decomposed residuals that were used for mutual
event analysis (Section 4). All original ts les from the
contracted facilities will be made publicly available through
NASAs Planetary Data System Small Body Node.
3.1. 6.5 m Magellan-Baade
The Baade 6.5 m telescope is located at Las Campanas
Observatory, in the Atacama Desert in the north of Chile, at an
elevation of 2400 m. We employed the Inamori-Magellan Areal
Camera and Spectrograph (IMACS)instrument (Dressler et al.
2011), which is equipped with two arrays of eight 2k ×4k e2v
detectors, where each array provides a different pixel scale.
Only the IMACS-F2 array with detector number 2 was used for
this project, which has 15 μm pixels that each image 0 2 when
unbinned. The asteroid was observed with a Sloan rlter and
xed pointings on the sky, letting the asteroid cross the
detectorseld while changing to a new pointing when
necessary.
The IMACS-F2 raw images were processed in the standard
way, i.e., bias subtraction and at-elding. Astrometry was
Table 2
Details of Facilities that Contributed to the 20222023 Lightcurve Campaign
Telescope Instrument Location IAU Code(s)No. of Lightcurves
6.5 m Magellan Baade IMACS Las Campanas, Chile 269 1
4.3 m LDT LMI Happy Jack, Arizona, USA G37 8
4.1 m SOAR Goodman Cerro Pachón, Chile I33 2
2.4 m MRO MRO2k CCD Magdalena Ridge, New Mexico, USA H01 11
2.0 m FTN MuSCAT3 Haleakala, Hawaii, USA F65 1
1.8 m VATT STA 4k CCD Mount Graham, Arizona, USA 290 2
1.8 m BOAO e2v 4k CCD Bohyunsan, South Korea 344 2
1.5 m Danish Telescope DFOSC La Silla, Chile W74 42
1.5 m AZT-22 Telescope SNUCAM Maidanak Observatory, Uzbekistan 188 2
1.5 m TCS MuSCAT2 Tenerife, Spain 954 4
1.1 m Hall Telescope NASA42 Anderson Mesa, Arizona, USA 688 27
1 m LCOGT Sinistro McDonald Observatory, Texas, USA V37, V39 5
1 m LCOGT Sinistro Siding Spring, Australia Q63, G64 2
1 m LCOGT Sinistro Sutherland, South Africa K91, K92, K93 9
1 m LCOGT Sinistro Cerro Tololo, Chile W85, W86, W87 11
1 m LCOGT Sinistro Tenerife, Spain Z31, Z24 10
1 m JKT Andor 2k CCD La Palma, Spain 950 2
1 m Swope Telescope e2v 4k CCD Las Campanas, Chile 304 19
1 m Tien-Shan Telescope Apogee 3k CCD Tien-Shan, Kazakhstan N42 1
0.9 m Spacewatch 4-CCD mosaic Kitt Peak, Arizona, USA 691 14
0.8 m IAC80 CAMELOT2 Observatorio del Teide, Spain 954 1
0.7 m AC-32 Telescope FLI 2k CCD Abastumani, Georgia 119 5
0.6 m Ondr
ejov Telescope Moravian 2k CCD Ondr
ejov, Czech Republic 557 4
0.6 m Sugarloaf Telescope SBIG 2k CCD Deereld, Massachusetts, USA L4
0.6 m G2 Telescope FLI 2k CCD Stará Lesná Observatory, Slovakia L1
0.6 m TN Andor iKon-L BEX2 Oukaïmeden Observatory, Morocco Z53 8
0.6 m TN FLI ProLine 3041-BB La Silla, Chile I40 25
0.5 m T72 iTelescope FLI 4k CCD Deep Sky Chile Observatory, Chile X07 1
Note. IAU assigned observatory codes are given when available. The number of individual lightcurves contributed by each facility is listed in the nal column.
6
The Planetary Science Journal, 5:35 (28pp), 2024 February Moskovitz et al.
performed with our own Python scripts built using the astropy
package. Aperture photometry was measured on the asteroid
and a selection of the brightest stars in every pointing to
estimate the individual image zero-points and the differential
photometry of the asteroid. The photometry was measured
using our own Python scripts and the SEP Python library
(Barbary 2018)source extraction tools. For the zero-points, the
stars were matched against the Gaia DR3 catalog (Gaia
Collaboration et al. 2021)when possible and against the
PanSTARRS catalog when not.
3.2. 4.3 m Lowell Discovery Telescope (LDT)
The LDT is located in Happy Jack, Arizona, at an elevation
of 2360 m. All LDT images were obtained with the Large
Monolithic Imager (LMI),a6k×6k e2v CCD with 15 μm
pixels. LMI images a 12eld of view at an unbinned pixel
scale of 0 12 pixel
1
. All images were obtained in 3 ×3
binning mode with a broad VR lter that provided high
throughput from about 500 to 700 nm. For all LDT observa-
tions, the telescope was tracked at sidereal rates, allowing the
asteroid to pass through xed star elds. Multiple pointings
were used in a single night when the motion of the asteroid
exceeded the instrument eld of view. Individual exposure
times ranged from 15 to 160 s across the apparition.
The reduction of LMI images followed standard at-eld
and bias correction techniques. The photometry of Didymos
was measured and calibrated using the Python-based Photo-
metry Pipeline (PP; Mommert 2017)as described in Pravec
et al. (2022). In summary, PP employed SExtractor (Bertin &
Arnouts 1996)to extract sources from the elds, Scamp
(Bertin 2006)to register the astrometry of those sources relative
to the Gaia DR2 reference catalog (Gaia Collaboration et al.
2018), and then calibrated the photometry relative to the
PanSTARRS Data Release 1 catalog (PS DR1; Flewelling et al.
2020). Only eld stars with solar-like colors (i.e., grand
ricolors within 0.2 mag of the Sun)were used for
photometric calibration. Typically, more than 10 eld stars
were used to calibrate each image. A curve-of-growth analysis
was performed each night to optimize the photometry aperture.
This analysis aimed to optimize both the S/N of individual
measurements and the consistency of intranight measurements
to minimize point-to-point scatter. Aperture radii ranged from
3.5 to 7 pixels (1262 52)across the apparition.
3.3. 4.1 m Southern Astrophysical Research (SOAR)Telescope
The SOAR telescope is located on Cerro Pachón in central
Chile at an elevation of 2713 m. Images were obtained with the
Goodman spectrograph and imager (Clemens et al. 2004),
which employs an e2v 231-84 CCD with 4k ×4k pixels. In
imaging mode, the CCD receives a 7 2 circular eld of view on
a3k×3k portion of the chip. The unbinned pixel scale is
015 pixel
1
. We operated the camera in 2 ×2 binning mode
with a VR lter that provided high throughput from
approximately 500 to 700 nm. Individual image exposure
times were 90 s.
The reduction and measuring of photometry from the SOAR
data followed an identical procedure to that used for LDT. The
PP referenced the Gaia DR2 (Gaia Collaboration et al. 2018)
and PanSTARRS (Flewelling et al. 2020)catalogs for
astrometric and photometric calibration. Aperture radii of 7
pixels (21)and 6 pixels (1 8)were used on the nights of UT
2022 July 4 and 2022 July 5, respectively.
3.4. 2.4 m Magdalena Ridge Observatory (MRO)
The MRO fast-tracking 2.4 m telescope is located at an
elevation of 3250 m in the Magdalena Mountains near Socorro,
New Mexico. All MRO images were acquired with MRO2K,
which is an Andor iKon-L 936 camera operating at 188K,
utilizing a 2048 ×2048 back-illuminated e2v CCD with
13.5 μm pixels. The unbinned pixel scale is 0 13 pixel
1
yielding a 4 5 eld of view. All lightcurve data were acquired
in 4 ×4 binning mode using either the Bessell Ror broadband
VR lter while tracking on Didymos to maximize its signal.
Observations early in the apparition required separate images of
comparison star elds due to Didymoss rapid nonsidereal
motion. For this reason, this time period also necessitated
having photometric sky conditions. Exposure times ranged
from 15 to 150 s throughout the apparition.
MRO images were reduced according to standard dark, bias,
and at-eld correction techniques. The photometry of
Didymos was measured using the IRAF Aperture Photometry
(APPHOT)package (Tody 1986). The instrumental magnitude
of Didymos was measured in each eld using apertures that
ranged from 4 to 10 pixels (215 2)depending on seeing
conditions. In addition, an ensemble of typically ve to eight
stars in each comparison eld was also measured in either the
same image or a separate comparison star image. An initial
analysis was performed on the comparison stars to assess their
robustness. A temporally interpolated average magnitude of the
comparison stars was then subtracted from each Didymos
instrumental magnitude, resulting in a differential magnitude.
The resulting lightcurve magnitudes were then reported as
relativewith an arbitrary zero-point.
3.5. 2.0 m Faulkes North
Faulkes Telescope North (FTN)is located on Haleakala,
Maui, in Hawaii. FTN images were collected with MuSCAT3
(Narita et al. 2020), a four-channel simultaneous imager with g,
r,i, and zchannels. The four independent channels employ
2k ×2k Princeton Instruments CCDs from the Pixis and
Sophia model lines. Each CCD images a 9 1eld of view at a
scale of 0 27 pixel
1
. Individual exposure times were 30 s for
all channels.
Reduction of the MuSCAT3 images employed the Astro-
ImageJ (AIJ; Collins et al. 2017)package. Within AIJ, the
multiple-aperture differential photometry tool was used to settle
on an optimal aperture radius of 12 pixels and a background
annulus with an inner radius of 15 and an outer radius of 20
pixels. The measured uxes from each of the four simultaneous
griz exposures were combined into a single arbitrary magnitude
and then calibrated against the Gaia DR3 catalog (Gaia
Collaboration et al. 2021). Four eld stars per frame with
roughly solar-like colors were used for this calibration.
3.6. 1.8 m Vatican Advanced Technology Telescope (VATT)
The VATT is located at Mount Graham, Arizona, and is an
aplanatic Gregorian 1.8 m f/9 telescope with a 0.38 m f/0.9
secondary mirror. The VATT4K CCD camera was used for all
VATT observations and consists of a STA0500A 4096 ×4096
pixel back-illuminated detector with 15 ×15 μm pixels.
VATT4K images have a 12 5eld of view and were obtained
7
The Planetary Science Journal, 5:35 (28pp), 2024 February Moskovitz et al.
in a 2 ×2 binning mode yielding a binned pixel scale of
038 pixel
1
.
For VATT data, the telescope was tracked at sidereal rates
with multiple pointings in a single night to keep the asteroid
within the eld of view. Individual exposures of 30 and 60 s in
duration were taken through a Harris V-band lter. The
reduction of VATT4K images followed standard at-eld
and bias correction techniques. The observations were
measured using the Tycho Tracker software (Parrott 2020)
with photometry calibrated relative to the ATLAS stellar
catalog (Tonry et al. 2018). Photometric calibration was
derived from eld stars with solar-like colors. A circular
photometric aperture with a radius of 11 pixels (41)was used
in conjunction with a sky background annulus with an inner
radius of 23 pixels (85)and an outer radius of 33
pixels (12 2).
3.7. 1.8 m Bohyunsan Optical Astronomy Observatory (BOAO)
BOAO is located in Yeongcheon, Korea, at an altitude of
1143 m. Observations were conducted using the 1.8 m
telescope at BOAO with an e2v 4k CCD and a Cousins R
lter. All images were taken in 2 ×2 binning mode with an
effective pixel scale of 0 43 pixel
1
, resulting in a eld of view
of 14 7×14 7. Individual exposure times were set to 100 s.
The images from BOAO were reduced using the IRAF
software package. We performed calibration procedures,
including bias, dark, and at-eld corrections, following
standard protocols. To calculate the World Coordinate System
(WCS)solution, we utilized the SCAMP package (Bertin 2006)
and matched elds to the Gaia DR2 catalog (Gaia Collabora-
tion et al. 2018). Aperture photometry was conducted on these
images using the IRAF/APPHOT package. The aperture radius
was set to 10 pixels (45)to minimize point-to-point scatter.
The photometric calibrations were performed following the
method of Gilliland & Brown (1988), namely, using ensemble
normalization employing standard magnitudes obtained from
the PS DR1 (Flewelling et al. 2020). For consistency, we
converted the PS DR1 magnitudes to the Johnson
Cousins system using empirical transformation equations
(Tonry et al. 2012).
3.8. 1.54 m Danish Telescope
The 1.54 m Danish Telescope is located at La Silla
Observatory, Chile, at an elevation of 2366 m. It is operated
jointly by the Niels Bohr Institute, University of Copenhagen,
Denmark, and the Astronomical Institute of the Academy of
Sciences of the Czech Republic. All images in the DART
campaign were obtained by the Danish Faint Object
Spectrograph and Camera (DFOSC)with an e2v CCD 231-
41 sensor and standard JohnsonCousins Vand Rphotometric
lters (Bessell 1990). The CCD sensor has 2048 ×2048 square
pixels (13.5 μm size), and we used it in 1 ×1 binning mode to
produce a scale of 0 396 pixel
1
and a 13.5 ×13.5 arcmin
2
eld of view. For the observations taken in September and the
rst half of 2022 October, the telescope was tracked at sidereal
rates, allowing the asteroid to pass through xed star elds. For
the observations taken from 2022 October 29 to 2023 January
29, the telescope was tracked at half the apparent rate of the
asteroid, providing star and asteroid images of the same prole
in one frame that facilitated obtaining robust photometric
reduction. Multiple pointings were used in a single night for the
observations taken in September and the rst half of October,
when the motion of the asteroid in a night exceeded the
instrumental eld of view. We used a single set of local
reference stars for each night of observations from late 2022
October through late 2023 January. Individual exposure times
ranged from 6 to 150 s across the apparition.
The reduction of the images followed standard at-eld and
bias-frame correction techniques. The photometry of Didymos
was measured and calibrated using Aphot, a synthetic aperture
photometry software developed by M. Velen and P. Pravec at
Ondr
ejov Observatory. It reduces asteroid images with respect
to a set of eld stars, and the reference stars are then calibrated
in the JohnsonCousins photometric system using Landolt
(1992)standard stars on a night with photometric sky
conditions. This resulted in R-magnitude errors of about
0.01 mag. Typically, eight local reference eld stars, which
were checked for stability (nonvariable, not of extreme colors),
were used on each night or for each pointing on nights before
mid-October. Aperture radii from 6 to 10 pixels (244 0)
were found optimal on the individual nights.
3.9. 1.5 m AZT-22 telescope at Maidanak Observatory
The 1.5 m AZT-22 telescope is located n the western part of
Maidanak Mountain in the south of Uzbekistan at an elevation
of 2593 m. The Didymos observations were carried out with
the Seoul National University 4k ×4k CCD Camera (SNU-
CAM), which has 4096 ×4096 square 15 μm pixels with a
CCD chip manufactured by Fairchild Instruments (Im et al.
2010). All images were obtained with an unbinned pixel scale
of 0 27 pixel
1
and a eld of view 18 1 ×18 1 through the R
lter. The telescope was tracked at sidereal rates, and the
exposure times were set to 60 s.
The primary reduction of images was performed in a
standard way with master bias and master ats, the latter was
constructed from twilight ats obtained on nearby nights under
photometric conditions. Aperture photometry was performed
using MPO Canopus.
49
The ATLAS catalog (Tonry et al.
2018)was used to obtain calibrated Rmagnitudes for the
asteroid based on comparison stars with colors close to the Sun.
Five solar-type stars were used to calibrate the frames. The
diameter of the aperture used for the comparison stars was 11
pixels, or about 3. The images of the asteroid were slightly
trailed over the 60 s exposures, so asteroid measurements were
made with an elliptical aperture of 11 ×13 pixels. These
aperture dimensions were chosen to roughly approximate
isophotes for the stars and asteroid.
3.10. 1.5 m Telescopio Carlos Sánchez (TCS)
The TCS belongs to the Instituto de Astrofísica de Canarias
and is located at Teide Observatory (latitude 28°1801 8N;
longitude +16°3039 2 W; altitude 2387 m). Typical seeing
for this location is in the range of 1.015. The observations
were performed with the MuSCAT2 instrument (Narita et al.
2019), which is mounted on the Cassegrain focus of the
telescope. A system of lenses reduces the focal length of the
system to a ratio of f/4.4.
This instrument allows simultaneous photometric observa-
tions in four visible broadband lters, namely, g(400550),r
(550700),i(700820), and z
s
(820920)nm. At the end of
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The Planetary Science Journal, 5:35 (28pp), 2024 February Moskovitz et al.
each of the four channels, there are independently controllable
CCD cameras (1024 ×1024 pixels). They have a pixel size of
0.44 arcsec pixel
1
and a eld of view of 7.4 ×7.4 arcmin
2
.
The telescope was tracked at sidereal rates with the asteroid
crossing the entire eld of view. Because of the small eld of
view, multiple pointings were needed during the same
observing session. The single image exposure times were 15
s for the rst three sessions (UT 2022 September 30, 2022
October 7, and 2022 October 16)and 30 s for the last (UT 2022
November 16).
The preprocessing of the images included bias and at-eld
corrections. The remaining background patterns were removed
using the GNU Astro package (Akhlaghi & Ichikawa 2015;
Akhlaghi 2019). The lightcurves were rst measured with PP
(Mommert 2017). For astrometric registration, we used the
Gaia catalog (Gaia Collaboration et al. 2018). We discarded all
images for which the astrometric registration failed (due to bad
tracking or variable sky conditions). The PanSTARRS catalog
(Flewelling et al. 2020)was used for photometric calibration.
PP was run with a xed aperture of 4 4(10 pixels).
A second data reduction was performed using IRAF
(Tody 1986). In order to improve the S/N, we combined the
images taken simultaneously by the four channels into a single
one. Then, we performed differential photometry using the
APPHOT package from IRAF. The magnitudes were computed
using an aperture of 4 4, and nine comparison stars from the
same eld of view were used to compute the differential
photometry. To further improve the S/N, we binned every four
exposures into a single point. We then spliced lightcurve
segments from different pointings into a single lightcurve. The
offsets between the lightcurve segments were computed using
the calibrated photometry derived with PP on the observations
made with the glter.
3.11. 1.1 m Hall
The 1.1 m Hall Telescope is located on Anderson Mesa, 9 air
miles southeast of Flagstaff, Arizona, at an elevation of
2203 m. All images were taken with the NASA42 camera, a
custom-built CCD camera with a 4K ×4K array of 15 μm
pixels. The image scale after applying 3 ×3 binning was
1.09 arcsec pixel
1
, with a eld of view of 24. Images were
taken through a broadband VR lter. In the rst month after the
DART impact, the Didymos system was moving at a rate of
over 6minute
1
. Therefore, tracking was done at half of the
ephemeris rate of the asteroid, and three pointings were
typically made during the night. Exposure times ranged from
90 to 180 s.
Data reduction began with image calibration with MaxIm
DL,
50
using sets of 15 bias and at frames that were typically
collected at the beginning of each night. Groups of images at
each pointing were astrometrically solved, registered, and
aligned in MaxIm DL. Photometry was performed with MPO
Canopus. Typically, ve comparison stars with solar color
(BVcolor between 0.5 and 0.9)were used. Comparison star
magnitudes were obtained from the ATLAS catalog (Tonry
et al. 2018), which is incorporated directly into MPO Canopus.
Star subtraction and outright rejection of frames were necessary
in cases where the asteroid passed through dense star elds.
The photometric aperture ranged from 7 pixels (76)to 13
pixels (14 2).
3.12. 1 m Las Cumbres Observatory Global Telescope Network
(LCOGT)
LCOGT is a global network of 25 telescopes in three size
classes at seven sites around the world (Brown et al. 2013). For
the DART lightcurve observations, the 1.0 m telescope
network was used, and observations were requested using the
NEOexchange Target and Observation Manager (Lister et al.
2021)system. Data were obtained from LCOGT sites located at
1. Cerro Tololo Observatory, District IV, Chile (three 1.0 m
telescopes; MPC site codes W85, W86, W87);
2. South African Astronomical Observatory, Sutherland,
South Africa (three 1.0 m telescopes; MPC site codes
K91, K92, K93);
3. McDonald Observatory, Fort Davis, Texas (two 1.0 m
telescopes; MPC site codes V37, V39); and
4. Teide Observatory, Canary Islands, Spain (two 1.0 m
telescopes; MPC site codes Z31, Z24).
All of the LCOGT 1.0 m images were obtained with the
Sinistro instruments, each containing a 4k ×4k Fairchild CCD
with 15 μm pixels. The Sinistro imagers provide a
¢´ ¢
2
6. 5 26. 5 eld of view with an unbinned pixel scale of
0389 pixel
1
. All images were obtained in 1 ×1 binning
mode with a PanSTARRS-w lter (equivalent to SDSS
¢+ ¢+
¢
gri
), which provided high throughput between 400
and 850 nm. The telescopes were tracking at half Didymoss
on-sky ephemeris rate throughout the observations. Individual
exposures times ranged from 27.5 to 150 s.
The reduction of the Sinistro images followed a two-step
process. Initial reduction to basic calibrated data products
involving bias and dark subtraction, at-elding, and astro-
metric tting were performed automatically within minutes of
readout of the frame by the LCOGT BANZAI pipeline
(McCully et al. 2018). The basic calibrated data were then
automatically retrieved from the LCOGT Science Archive and
pipeline processed through the PP (Mommert 2017)and
NEOexchange (NEOx; Lister et al. 2021)pipelines.
Both pipelines used SExtractor (Bertin & Arnouts 1996)to
extract sources from the image and SCAMP (Bertin 2006)to
perform the astrometric registration to the Gaia DR2 catalog
(Gaia Collaboration et al. 2018)and then calibrated against PS
DR1 (Flewelling et al. 2020)or the Gaia DR2 catalog,
depending on the decl. of Didymos at the time of the
observations. This zero-point calibration within the NEOx
pipeline was performed using the calviacat (Kelley &
Lister 2022)package. A preliminary reduction was generally
done with the PP to perform a curve-of-growth analysis and an
optimal aperture radius for the main NEOx reductions and to
act as a cross-check on the reductions. Due to the low Galactic
latitude of Didymos in the early 2022 OctoberNovember data
and the variable and differential reddening of the eld stars, we
did not use the features of either PP or calviacat to restrict
the eld stars to having solar-like colors. Given the crowded
elds, persistence of ejecta, fading of the target, and analysis
focused on differential magnitudes, the choice of nonsolar-type
stars for eld calibration had no discernible inuence on the
quality of the photometry calibration.
3.13. 1 m Jacobus Kapteyn Telescope (JKT)
The JKT is equipped with an Andor 2k CCD camera and
situated at the Roque de los Muchachos Observatory on La
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Palma. The telescopeseld of view is 11 6 ×11 6, and the
image scale is 0 34 pixel
1
. The observations were obtained
using the Johnson Rlter, and we utilized sidereal tracking.
Exposure times of 100 s were used.
Data from the JKT were processed using standard reduction
procedures and aperture photometry, with the commercial
software MPO Canopus following established procedures (e.g.,
Oszkiewicz et al. 2020,2021,2023). We selected ve
comparison stars in each eld with signicantly higher S/Ns
than the target, ensuring they had roughly solar colors
(approximately 0.5 <BV<0.95 or 0.35 <gr<0.85).
An aperture 21 pixels in diameter was employed. For
calibration, we used PS DR1 (Flewelling et al. 2020).
3.14. 1 m Swope
The Swope 1.0 m telescope is located at Las Campanas
Observatory, in the Atacama Desert in the north of Chile, at an
elevation of 2400 m. The Swope telescope is equipped with a
4k ×4k e2v detector with 15 μm pixels covering a 30×30
area with 0 435 pixels. The Swope data set encompassed a
total of 8733 Sloan rimages taken across 19 nights. In 5 of 15
nights, a single pointing was used to follow Didymos, while for
the other nights, two pointings were necessary. For each
pointing, the brightest 50 stars in the eld were selected as
standards to achieve photometric calibration of the individual
images and estimate the differential photometry of the asteroid.
Swope images are read out by four ampliers, producing four
quadrant les for each exposure. Each of these quadrants was
processed separately with standard techniques, namely, bias
subtraction, linearity correction, and at-elding. After normal-
ization by the individual gains, the full image was rebuilt as a
single ts le. The astrometric solution was achieved with an
iterative process, starting with a preliminary solution created using
the WCS routine within the astropy package, and then improved
by matching star positions against their Gaia coordinates.
Instrumental aperture photometry was performed using the Python
package SEP (Barbary 2018)on every image for the asteroids
and the brightest stars positions across a set of apertures from 3 to
20 pixels in radius. To estimate the photometric zero-points on
individual images, we used several Python packages. astroquery
was used to query the VizieR and Horizon databases to identify
Gaia sources within 2of our set of bright eld stars and obtain
the coordinates of the asteroid for the given time stamp in each
image. The gaiaxpy
51
Python package was used to request and
download synthetic photometry of Gaia stars (Gaia Collabora-
tion et al. 2021)in the Sloan rband when available. We found
more than 30 Gaia stars with available synthetic photometry in
most pointings, and in only two cases did we retrieve fewer
than 10 stars. This allowed us to determine robust statistics for
the zero-points. For each image, we estimated a median,
rejected outliers, and measured the standard deviation to
provide an error on the zero-point, which was typically around
0.010.02 mag frame
1
. Final photometry of the Didymos
Dimorphos system was estimated by adding the zero-points to
its instrumental magnitude for each image.
3.15. 1 m Zeiss Telescope at Tien-Shan Observatory
The 1 m Zeiss telescope at Tien-Shan Observatory is located
at 2800 m altitude in the Almaty region of Kazakhstan. The
observations were carried out with the front-illuminated CCD
camera PL09000 (made by Finger Lakes Instruments)with a
sensor of 3056 ×3056 pixels and a pixel size of 12 μm. The
images covered a 19 1×19 1 eld of view. The asteroid was
observed with a JohnsonCousins Rlter. The observations
were carried out with the telescope tracking at sidereal rates and
the camera in 2 ×2 binning mode (producing an image scale =
075 pixel
1
). At the end of December, the asteroid was
moving across the sky at an angular rate of 1 2 minute
1
and
thus was trailed by about 2.4 pixels during the 90 s exposures.
Reduction of the images included removal of an average dark
frame and normalization with a median dome at eld.
Didymoss brightness was measured with the AstPhot software
(Mottola et al. 1995). The size of the aperture was chosen to
maximize the S/N based on measurements of several bright stars.
An aperture radius of 6 pixels (45)was determined to be
optimal. An elliptical aperture of 6 ×7 pixels was used for the
slightly elongated asteroid. As with the AZT-22 data, these
apertures were chosen to roughly approximate isophotes for the
stars and asteroid. The Rmagnitudes of comparison stars were
taken from the ATLAS catalog (Tonry et al. 2018)and used to
calibrate the asteroid using the MPO Canopus software package.
3.16. 0.9 m Spacewatch
SPACEWATCH
®
operates Steward Observatoryʼs0.9m
telescope on Kitt Peak, in Arizona, at an elevation of 2080 m.
Images were obtained with the Spacewatch mosaic camera, a
mosaic of four e2v 4k ×2k CCDs with 13.5 μmpixels.Ithasan
effective eldofviewof2.9deg
2
at an unbinned pixel scale of
1pixel
1
. The images were obtained unbinned with a broadband
Schott OG-515 lter, which has a long-pass transmission prole
with a cut-on wavelength at 515 nm. Individual exposures ranged
from 16 to 104 s across the apparition.
The reduction followed standard bias, at-eld, and fringe
correction techniques. The photometry of the Didymos system
was measured and calibrated using the PP (Mommert 2017)
and MPO Canopus following the same procedures as applied to
the LDT and Hall telescopes, respectively.
3.17. 0.8 m at the Instituto de Astrofísica de Canarias (IAC80)
The 0.8 m at the Instituto de Astrofísica de Canarias (IAC80)
telescope, equipped with the CAMELOT2 instrument, is located
at the Observatorio del Teide on Tenerife. CAMELOT2 features a
4k ×4k back-illuminated CCD. The on-sky pixel scale is
0322 pixel
1
, providing a theoretical eld of view of 22 ×22
arcminutes
2
. However, due to vignetting caused by the lters, the
useful squared eld of view is 11.8 ×11.8 arcmin
2
.Thedatawere
obtained using the Johnson Rlter, and sidereal tracking was
employed. An exposure time of 135 s and aperture diameter of 19
pixels were used.
Data reduction and measurement of photometry for the
IAC80 data followed the same procedures as used for data from
the JKT (Section 3.13).
3.18. 0.7 m AC-32 Telescope of the Abastumani Astrophysical
Observatory
The 0.7 m AC-32 telescope is a Maksutov meniscus telescope
at the