369 research outputs found
The Status of Spectroscopic Data for the Exoplanet Characterisation Missions
The status of laboratory spectroscopic data for exoplanet characterisation
missions such as EChO is reviewed. For many molecules (eg H2O, CO, CO2, H3+,
O2, O3) the data are already available. For the other species work is actively
in progress constructing this data. Much of the is work is being undertaken by
ExoMol project (www.exomol.com). This information will be used to construct and
EChO-specific spectroscopic database.Comment: Experimental Astronomy, accepte
ExoMol line lists IV: The rotation-vibration spectrum of methane up to 1500 K
A new hot line list is calculated for CH in its ground electronic
state. This line list, called 10to10, contains 9.8 billion transitions and
should be complete for temperatures up to 1500 K. It covers the wavelengths
longer than 1 m and includes all transitions to upper states with energies
below cm and rotational excitation up to . The
line list is computed using the eigenvalues and eigenfunctions of CH
obtained by variational solution of the Schr\"{o}dinger equation for the
rotation-vibration motion of nuclei employing program TROVE. An ab initio
dipole moment surface and a new 'spectroscopic' potential energy surface are
used. Detailed comparisons with other available sources of methane transitions
including HITRAN, experimental compilations and other theoretical line lists
show that these sources lack transitions both higher temperatures and near
infrared wavelengths. This line list is suitable for modelling atmospheres of
cool stars and exoplanets. It is available from the CDS database as well as at
www.exomol.com.Comment: Submitted to MNRA
Detecting chirality in molecules by linearly polarized laser fields
A new scheme for enantiomer differentiation of chiral molecules using a pair
of linearly polarized intense ultrashort laser pulses with skewed mutual
polarization is presented. The technique relies on the fact that the
off-diagonal anisotropic contributions to the electric polarizability tensor
for two enantiomers have different signs. Exploiting this property, we are able
to excite a coherent unidirectional rotation of two enantiomers with a {\pi}
phase difference in the molecular electric dipole moment. The approach is
robust and suitable for relatively high temperatures of molecular samples,
making it applicable for selective chiral analysis of mixtures, and to chiral
molecules with low barriers between enantiomers. As an illustration, we present
nanosecond laser-driven dynamics of a tetratomic non-rigid chiral molecule with
short-lived chirality. The ultrafast time scale of the proposed technique is
well suited to study parity violation in molecular systems in short-lived
chiral states
Laboratory spectra of hot molecules: data needs for hot super-Earth exoplanets
The majority of stars are now thought to support exoplanets. Many of those
exoplanets discovered thus far are categorized as rocky objects with an
atmosphere. Most of these objects are however hot due to their short orbital
period. Models suggest that water is the dominant species in their atmospheres.
The hot temperatures are expected to turn these atmospheres into a (high
pressure) steam bath containing remains of melted rock. The spectroscopy of
these hot rocky objects will be very different from that of cooler objects or
hot gas giants. Molecules suggested to be important for the spectroscopy of
these objects are reviewed together with the current status of the
corresponding spectroscopic data. Perspectives of building a comprehensive
database of linelist/cross sections applicable for atmospheric models of rocky
super-Earths as part of the ExoMol project are discussed. The
quantum-mechanical approaches used in linelist productions and their challenges
are summarized.Comment: Molecular Astrophysics (in press) Review article 96 pages, 17
Figures, 2 Tables, 267 reference
ExoMol: molecular line lists for exoplanet and other atmospheres
The discovery of extrasolar planets is one of the major scientific advances
of the last two decades. Hundreds of planets have now been detected and
astronomers are beginning to characterise their composition and physical
characteristics. To do this requires a huge quantity of spectroscopic data most
of which is not available from laboratory studies. The ExoMol project will
offer a comprehensive solution to this problem by providing spectroscopic data
on all the molecular transitions of importance in the atmospheres of
exoplanets. These data will be widely applicable to other problems and will be
used for studies on cool stars, brown dwarfs and circumstellar environments.
This paper lays out the scientific foundations of this project and reviews
previous work in this area.
A mixture of first principles and empirically-tuned quantum mechanical
methods will be used to compute comprehensive and very large rotation-vibration
and rotation-vibration-electronic (rovibronic) line lists. Methodologies will
be developed for treating larger molecules such as methane and nitric acid.
ExoMol will rely on these developments and the use of state-of-the-art
computing.Comment: MNRAS (in press
The ExoMol Atlas of Molecular Opacities
The ExoMol project is dedicated to providing molecular line lists for
exoplanet and other hot atmospheres. The ExoMol procedure uses a mixture of ab
initio calculations and available laboratory data. The actual line lists are
generated using variational nuclear motion calculations. These line lists form
the input for opacity models for cool stars and brown dwarfs as well as for
radiative transport models involving exoplanets. This paper is a collection of
molecular opacities for 52 molecules (130 isotopologues) at two reference
temperatures, 300 K and 2000 K, using line lists from the ExoMol database. So
far, ExoMol line lists have been generated for about 30 key molecular species.
Other line lists are taken from external sources or from our work predating the
ExoMol project. An overview of the line lists generated by ExoMol thus far is
presented and used to evaluate further molecular data needs. Other line lists
are also considered. The requirement for completeness within a line list is
emphasized and needs for further line lists discussed
Temperature-dependent molecular absorption cross sections for exoplanets and other atmospheres
Exoplanets, and in particular hot ones such as hot Jupiters, require a very
significant quantities of molecular spectroscopic data to model radiative
transport in their atmospheres or to interpret their spectra. This data is
commonly provided in the form of very extensive transition line lists. The size
of these line lists is such that constructing a single model may require the
consideration of several billion lines. We present a procedure to simplify this
process based on the use of cross sections. Line lists for water, H, HCN
/HNC and ammonia have been turned into cross sections on a fine enough grid to
preserve their spectroscopic features. Cross sections are provided at a fixed
range of temperatures and an interpolation procedure which can be used to
generate cross sections at arbitrary temperatures is described. A web-based
interface (www.exomol.com/xsec) has been developed to allow astronomers to
download cross sections at specified temperatures and spectral resolution.
Specific examples are presented for the key water molecule.Comment: Icarus (submitted
ExoCross: a general program for generating spectra from molecular line lists
ExoCross is a Fortran code for generating spectra (emission, absorption) and
thermodynamic properties (partition function, specific heat etc.) from
molecular line lists. Input is taken in several formats, including ExoMol and
HITRAN formats. ExoCross is efficiently parallelized showing also a high degree
of vectorization. It can work with several line profiles such as Doppler,
Lorentzian and Voigt and support several broadening schemes. Voigt profiles are
handled by several methods allowing fast and accurate simulations. Two of these
methods are new. ExoCross is also capable of working with the recently proposed
method of super-lines. It supports calculations of lifetimes, cooling
functions, specific heats and other properties. ExoCross can be used to convert
between different formats, such as HITRAN, ExoMol and Phoenix. It is capable of
simulating non-LTE spectra using a simple two-temperature approach. Different
electronic, vibronic or vibrational bands can be simulated separately using an
efficient filtering scheme based on the quantum numbers
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