ABSTRACT: The Exoplanet Characterisation Observatory (EChO) is a space mission dedicated to undertaking spectroscopy of transiting exoplanets over the widest wavelength range possible. It is based around a highly stable space platform with a 1.2 m class telescope. The mission is currently being studied by ESA in the context of a medium class mission within the Cosmic Vision programme for launch post 2020. The payload suite is required to provide simultaneous coverage from the visible to the mid-infrared and must be highly stable and effectively operate as a single instrument. In this paper we describe the integrated spectrometer payload design for EChO which will cover the 0.4 to 16 micron wavelength band. The instrumentation is subdivided into 5 channels (Visible/Near Infrared, Short Wave InfraRed, 2 x Mid Wave InfraRed; Long Wave InfraRed) with a common set of optics spectrally dividing the input beam via dichroics. We discuss the significant design issues for the payload and the detailed technical trade-offs that we are undertaking to produce a payload for EChO that can be built within the mission and programme constraints and yet which will meet the exacting scientific performance required to undertake transit spectroscopy.
SPIE Proceedings of Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave, Amsterdam; 07/2012
ABSTRACT: Quantum beat spectroscopy is combined with triple-resonance vibrational overtone excitation to measure the Stark coefficients (SCs) of the water molecule for 28 rovibrational levels lying from 27,600 to 41,000 cm(-1). These data provide a stringent test for assessing the accuracy of the available potential energy surfaces (PESs) and dipole moment surfaces (DMSs) of this benchmark molecule in this energy region, which is inaccessible by direct absorption. SCs, calculated using the combination of a high accuracy, spectroscopically determined PES and a recent ab initio DMS, are within the 1% accuracy of available experimental data for levels below 25,000 cm(-1), and within 4.5% for coefficients associated with levels up to 35,000 cm(-1). However, the error in the computed coefficients is over 60% for the very high rovibrational states lying just below the lowest dissociation threshold, due, it seems, to lack of a high accuracy PES in this region. The comparative analysis suggests further steps, which may bring the theoretical predictions closer to the experimental accuracy.
The Journal of chemical physics 06/2012; 136(24):244308. · 3.09 Impact Factor
ABSTRACT: The shift coefficients for the lines of the ν1 + ν2 + ν3 and ν2 + 2ν3 bands of H2O in the region from 9403 to 9413 cm−1 are measured and calculated. The measurements are performed using an intracavity laser spectrometer based on a neodymium
laser with a determination error of the line center of 0.003–0.004 cm−1. The Ar, Kr, and Xe noble gases, as well as nitrogen, oxygen, and hydrogen were used as buffer gases. The coefficients of
shifts in eight H2O absorption lines induced by oxygen, nitrogen, and atmospheric air pressures fall into the region from −0.004 to −0.069 cm−1/bar. The calculations are performed by a semiempirical method using variational wave functions, which, in contrast to other
studies, correctly takes into account intramolecular interactions. The calculated values agree satisfactorily with experimental
Optics and Spectroscopy 04/2012; 105(1):25-31. · 0.61 Impact Factor
The European Physical Journal D 01/2012; 66(1):31. · 1.48 Impact Factor
ABSTRACT: Exoplanetary science is one of the fastest evolving fields of today's astronomical research, continuously yielding unexpected and surprising results. Ground-based planet-hunting surveys, together with dedicated space missions such as Kepler and CoRoT, are delivering an ever-increasing number of exoplanets, over 690, and ESA's Gaia mission will escalate the exoplanetary census into the several thousands. The next logical step is the characterization of these new worlds. What is their nature? Why are they as they are? Use of the Hubble Space Telescope and Spitzer Space Telescope to probe the atmospheres of transiting hot, gaseous exoplanets has opened perspectives unimaginable even just 10 years ago, demonstrating that it is indeed possible with current technology to address the ambitious goal of characterizing the atmospheres of these alien worlds. However, these successful measurements have also shown the difficulty of understanding the physics and chemistry of these exotic environments when having to rely on a limited number of observations performed on a handful of objects. To progress substantially in this field, a dedicated facility for exoplanet characterization, able to observe a statistically significant number of planets over time and a broad spectral range will be essential. Additionally, the instrument design (e.g., detector performances, photometric stability) will be tailored to optimize the extraction of the astrophysical signal. In this paper, we analyze the performance and tradeoffs of a 1.2/1.4 m space telescope for exoplanet transit spectroscopy from the visible to the mid-IR. We present the signal-to-noise ratio as a function of integration time and stellar magnitude/spectral type for the acquisition of spectra of planetary atmospheres for a variety of scenarios: hot, warm, and temperate planets orbiting stars ranging in spectral type from hot F- to cooler M-dwarfs. Our results include key examples of known planets (e.g., HD 189733b, GJ 436b, GJ 1214b, and Cancri 55 e) and simulations of plausible terrestrial and gaseous planets, with a variety of thermodynamical conditions. We conclude that even most challenging targets, such as super-Earths in the habitable zone of late-type stars, are within reach of an M-class, space-based spectroscopy mission.
The Astrophysical Journal 01/2012; 746(1):45. · 6.02 Impact Factor
ABSTRACT: We present the line broadening and self�broadening coefficients of the water isotopologue HD16O
and study their dependence on quantum numbers up to J = 50 for P�, Q�, and R�branches. Three calculation
techniques have been used: the analytical model in the case of known quantum transition identification in
normal modes; the JJ' dependence in the case when only J and level symmetry are known, and the semi�
empirical calculation technique for 50 ≥ J > 15.The derived regularities for the broadening coefficients of
water vapor lines allow accurate calculation of HD16O spectra including millions of weak lines from the VTT line list (Voronin, Tennyson, and Tolchenov).
Atmospheric and Oceanic Optics 01/2012; 25(1-ISSN 1024�8560):27-34.
ABSTRACT: A dedicated mission to investigate exoplanetary atmospheres represents a
major milestone in our quest to understand our place in the universe by placing
our Solar System in context and by addressing the suitability of planets for
the presence of life. EChO -the Exoplanet Characterisation Observatory- is a
mission concept specifically geared for this purpose. EChO will provide
simultaneous, multi-wavelength spectroscopic observations on a stable platform
that will allow very long exposures. EChO will build on observations by Hubble,
Spitzer and groundbased telescopes, which discovered the first molecules and
atoms in exoplanetary atmospheres. EChO will simultaneously observe a broad
enough spectral region -from the visible to the mid-IR- to constrain from one
single spectrum the temperature structure of the atmosphere and the abundances
of the major molecular species. The spectral range and resolution are tailored
to separate bands belonging to up to 30 molecules to retrieve the composition
and temperature structure of planetary atmospheres. The target list for EChO
includes planets ranging from Jupiter-sized with equilibrium temperatures Teq
up to 2000 K, to those of a few Earth masses, with Teq ~300 K. We have
baselined a dispersive spectrograph design covering continuously the 0.4-16
micron spectral range in 6 channels (1 in the VIS, 5 in the IR), which allows
the spectral resolution to be adapted from several tens to several hundreds,
depending on the target brightness. The instrument will be mounted behind a 1.5
m class telescope, passively cooled to 50 K, with the instrument structure and
optics passively cooled to ~45 K. EChO will be placed in a grand halo orbit
around L2. We have also undertaken a first-order cost and development plan
analysis and find that EChO is easily compatible with the ESA M-class mission
ABSTRACT: Exoplanetary science is among the fastest evolving fields of today's
astronomical research. Ground-based planet-hunting surveys alongside dedicated
space missions (Kepler, CoRoT) are delivering an ever-increasing number of
exoplanets, now numbering at ~690, with ESA's GAIA mission planned to bring
this number into the thousands. The next logical step is the characterisation
of these worlds: what is their nature? Why are they as they are? The use of the
HST and Spitzer Space Telescope to probe the atmospheres of transiting hot,
gaseous exoplanets has demonstrated that it is possible with current technology
to address this ambitious goal. The measurements have also shown the difficulty
of understanding the physics and chemistry of these environments when having to
rely on a limited number of observations performed on a handful of objects. To
progress substantially in this field, a dedicated facility for exoplanet
characterization with an optimised instrument design (detector performance,
photometric stability, etc.), able to observe through time and over a broad
spectral range a statistically significant number of planets, will be
essential. We analyse the performances of a 1.2/1.4m space telescope for
exoplanet transit spectroscopy from the visible to the mid IR, and present the
SNR ratio as function of integration time and stellar magnitude/spectral type
for the acquisition of spectra of planetary atmospheres in a variety of
scenarios: hot, warm, and temperate planets, orbiting stars ranging in spectral
type from hot F to cool M dwarfs. We include key examples of known planets
(e.g. HD 189733b, Cancri 55 e) and simulations of plausible terrestrial and
gaseous planets, with a variety of thermodynamical conditions. We conclude that
even most challenging targets, such as super-Earths in the habitable-zone of
late-type stars, are within reach of a M-class, space-based spectroscopy
AAS/Division for Extreme Solar Systems Abstracts; 09/2011
ABSTRACT: Rotational cooling of HD+ by superelastic collisions (SEC) with electrons was observed at the Heidelberg test storage ring by merging a beam of rotationally hot HD+ ions with an electron beam at zero relative energy. Neutral fragments resulting from DR events were recorded at different electron densities using a high resolution imaging detector and a large-area, energy sensitive detector. The data allowed to deduce the time dependence of the population of three groups of rotational angular momentum states J built on the vibrational ground state of the ion together with the corresponding DR rate coefficients. The latter are found to be (statistical uncertainties only) α0,1,2 = 3.8(1), α3,4 = 4.0(2), and α5,6,7 = 9.0(1.3) in units of 10−8 cm3/s, in reasonable agreement with the average values derived within the MQDT approach. The time evolution of the population curves clearly reveals that rotational cooling by SEC takes place, which can be well described by using theoretical SEC rate coefficients obtained by combining the molecular R-matrix approach with the adiabatic nuclear rotation approximation. We verify the ΔJ = −2 coefficients, which are predicted to be dominant as opposed to the ΔJ = −1 coefficients and to amount to (1 − 2) 10−6 cm3/s, to within 30%.
Journal of Physics Conference Series 07/2011; 300(1):012006.
ABSTRACT: We present an analysis of seven primary transit observations of the hot Neptune GJ436b at 3.6, 4.5, and 8 μm obtained with the Infrared Array Camera on the Spitzer Space Telescope. After correcting for systematic effects, we fitted the light curves using the Markov Chain Monte Carlo technique. Combining these new data with the EPOXI, Hubble Space Telescope, and ground-based V, I, H, and Ks published observations, the range 0.5-10 μm can be covered. Due to the low level of activity of GJ436, the effect of starspots on the combination of transits at different epochs is negligible at the accuracy of the data set. Representative climate models were calculated by using a three-dimensional, pseudospectral general circulation model with idealized thermal forcing. Simulated transit spectra of GJ436b were generated using line-by-line radiative transfer models including the opacities of the molecular species expected to be present in such a planetary atmosphere. A new, ab-initio-calculated, line list for hot ammonia has been used for the first time. The photometric data observed at multiple wavelengths can be interpreted with methane being the dominant absorption after molecular hydrogen, possibly with minor contributions from ammonia, water, and other molecules. No clear evidence of carbon monoxide and carbon dioxide is found from transit photometry. We discuss this result in the light of a recent paper where photochemical disequilibrium is hypothesized to interpret secondary transit photometric data. We show that the emission photometric data are not incompatible with the presence of abundant methane, but further spectroscopic data are desirable to confirm this scenario.
The Astrophysical Journal 03/2011; 731(1):16. · 6.02 Impact Factor
Journal of Molecular Spectroscopy 01/2011; 268:123. · 1.51 Impact Factor
Journal of Physics Conference Series 01/2011; 300:012018.
Journal of Physics B: Atomic Molecular and Optical Physics. 01/2011; 44:055203.
ABSTRACT: We present 'BYTe', a comprehensive 'hot' line list for the ro-vibrational
transitions of ammonia, 14NH3, in its ground electronic state. This line list
has been computed variationally using the program suite TROVE, a new
spectroscopically-determined potential energy surface and an ab initio dipole
moment surface. BYTe, is designed to be used at all temperatures up to 1500K.
It comprises 1137650964 transitions in the frequency range from 0 to 12000
cm-1, constructed from 1366519 energy levels below 18000 cm-1 having J values
below 36. Comparisons with laboratory data confirm the accuracy of the line
list which is suitable for modelling a variety of astrophysical problems
including the atmospheres of extrasolar planets and brown dwarfs.
ABSTRACT: We demonstrate that cold molecules (H2 and benzene) can be created at temperatures below 1 mK by sympathetic cooling with laser-cooled rare gas atoms on timescales of seconds. The thermalization process is studied using the direct simulation Monte Carlo (DSMC) method, which allows a detailed analysis of the atomic and molecular spatial and energy distributions as a function of time. As part of this study, ultracold elastic cross sections for Ar–Ar and Ar–C6H6 are also calculated.
New Journal of Physics 11/2010; 12(11):113002. · 4.18 Impact Factor
ABSTRACT: More than 460 exoplanets, i.e. planets orbiting a star different from
our Sun, are now known thanks to indirect detection techniques. In
recent years, attention has switched from finding planets to
characterising them. Among the variety of exoplanets discovered so far,
special attention is devoted to those planets which transit their parent
star. Most recent observations with Hubble and Spitzer Space Telescopes,
in fact, have proved being possible to use the wavelength/time
dependence of the combined light star-planet to identify key chemical
components and the thermal structure of the planet's atmosphere.
We present here new spectroscopic observations obtained with different
ground-based telescopes of select targets, including hot-Jupiters and a
ABSTRACT: This is the second of a series of articles reporting critically evaluated rotational–vibrational line positions, transition intensities, pressure dependences, and energy levels, with associated critically reviewed assignments and uncertainties, for all the main isotopologues of water. This article presents energy levels and line positions of the following singly deuterated isotopologues of water: HD16O, HD17O, and HD18O. The MARVEL (measured active rotational–vibrational energy levels) procedure is used to determine the levels, the lines, and their self-consistent uncertainties for the spectral regions 0–22 708, 0–1674, and 0–12 105 cm−1 for HD16O, HD17O, and HD18O, respectively. For HD16O, 54 740 transitions were analyzed from 76 sources, the lines come from spectra recorded both at room temperature and from hot samples. These lines correspond to 36 690 distinct assignments and 8818 energy levels. For HD17O, only 485 transitions could be analyzed from three sources; the lines correspond to 162 MARVEL energy levels. For HD18O, 8729 transitions were analyzed from 11 sources and these lines correspond to 1864 energy levels. The energy levels are checked against ones determined from accurate variational nuclear motion computations employing exact kinetic energy operators. This comparison shows that the measured transitions account for about 86% of the anticipated absorbance of HD16O at 296 K and that the transitions predicted by the MARVEL energy levels account for essentially all the remaining absorbance. The extensive list of MARVEL lines and levels obtained are given in the Supplementary Material of this article, as well as in a distributed information system applied to water, W@DIS, where they can easily be retrieved. In addition, the transition and energy level information for H217O and H218O, given in the first paper of this series [Tennyson, et al. J Quant Spectr Rad Transfer 2009;110:573–96], has been updated.
Journal of Quantitative Spectroscopy and Radiative Transfer 01/2010; 111(15):2160-2184. · 3.19 Impact Factor
ABSTRACT: High-resolution spectra of comet 8P/Tuttle were obtained in the frequency range 3449.0–3462.2 cm−1 on 2008 January 3 ut using CGS4 with echelle grating on United Kingdom Infrared Telescope. In addition to observing solar pumped fluorescent lines of H2O, the long integration time (152 min on target) enabled eight weaker H2O features to be assigned, most of which had not previously been identified in cometary spectra. These transitions, which are from higher energy upper states, are similar in character to the so-called SH lines recorded in the post Deep Impact spectrum of comet Tempel 1. We have identified certain characteristics that these lines have in common, and which in addition to helping to define this new class of cometary line give some clues to the physical processes involved in their production. Finally, we derive an H2O rotational temperature of and a water production rate of (1.4 ± 0.3) × 1028 molecules s−1.
Monthly Notices of the Royal Astronomical Society 09/2009; 398(3):1593 - 1600. · 4.90 Impact Factor