Empirical line lists and absorption cross sections for methane at high temperature

Hot methane is found in many "cool" sub-stellar astronomical sources including brown dwarfs and exoplanets, as well as in combustion environments on Earth. We report on the first high-resolution laboratory absorption spectra of hot methane at temperatures up to 1200 K. Our observations are compared to the latest theoretical spectral predictions and recent brown dwarf spectra. The expectation that millions of weak absorption lines combine to form a continuum, not seen at room temperature, is confirmed. Our high-resolution transmittance spectra account for both the emission and absorption of methane at elevated temperatures. From these spectra, we obtain an empirical line list and continuum that is able to account for the absorption of methane in high temperature environments at both high and low resolution. Great advances have recently been made in the theoretical prediction of hot methane, and our experimental measurements highlight the progress made and the problems that still remain.Comment: 9 pages, 5 figures and 3 tables. For associated online data see http://dx.doi.org/10.1088/0004-637X/813/1/1

Referencing Sources of Molecular Spectroscopic Data in the Era of Data Science: Application to the HITRAN and AMBDAS Databases

The application described has been designed to create bibliographic entries in large databases with diverse sources automatically, which reduces both the frequency of mistakes and the workload for the administrators. This new system uniquely identifies each reference from its digital object identifier (DOI) and retrieves the corresponding bibliographic information from any of several online services, including the SAO/NASA Astrophysics Data Systems (ADS) and CrossRef APIs. Once parsed into a relational database, the software is able to produce bibliographies in any of several formats, including HTML and BibTeX, for use on websites or printed articles. The application is provided free-of-charge for general use by any scientific database. The power of this application is demonstrated when used to populate reference data for the HITRAN and AMBDAS databases as test cases. HITRAN contains data that is provided by researchers and collaborators throughout the spectroscopic community. These contributors are accredited for their contributions through the bibliography produced alongside the data returned by an online search in HITRAN. Prior to the work presented here, HITRAN and AMBDAS created these bibliographies manually, which is a tedious, time-consuming and error-prone process. The complete code for the new referencing system can be found at \url{https://github.com/hitranonline/refs}.Comment: 11 pages, 5 figures, already published online at https://doi.org/10.3390/atoms802001

A HITRAN-formatted UV line list of S2_2 containing transitions involving X\,^{3}\Sigma^{-}_{g}, B\,^{3}\Sigma^{-}_{u}, and B''\,^{3}\Pi_{u} electronic states

The sulfur dimer (S$_2$) is an important molecular constituent in cometary atmospheres and volcanic plumes on Jupiter's moon Io. It is also expected to play an important role in the photochemistry of exoplanets. The UV spectrum of S$_2$ contains transitions between vibronic levels above and below the dissociation limit, giving rise to a distinctive spectral signature. By using spectroscopic information from the literature, and the spectral simulation program PGOPHER, a UV line list of S$_2$ is provided. This line list includes the primary B\,^{3}\Sigma^{-}_{u}-X\,^{3}\Sigma^{-}_{g} ($v'$=0-27, $v''$=0-10) electronic transition, where vibrational bands with $v'$$\geq$10 are predissociated. Intensities have been calculated from existing experimental and theoretical oscillator strengths, and semi-empirical strengths for the predissociated bands of S$_2$ have been derived from comparisons with experimental cross-sections. The S$_2$ line list also includes the B''\,^{3}\Pi_{u}-X\,^{3}\Sigma^{-}_{g} ($v'$=0-19, $v''$=0-10) vibronic bands due to the strong interaction with the $B$ state. In summary, we present the new HITRAN-formatted S$_2$ line list and its validation against existing laboratory spectra. The extensive line list covers the spectral range 21700$-$41300~cm$^{-1}$ ($\sim$242$-$461~nm) and can be used for modeling both absorption and emission.Comment: Accepted to the Monthly Notices of the Royal Astronomical Societ

EXPERIMENTAL LINE LISTS OF HOT METHANE

Line lists of CH$_{4}$ at high temperatures (up to 900$^{circ}$C) have been produced between 2500 and 5000 cm$^{-1}$. This spectral range contains the pentad and octad regions, and includes numerous fundamental, overtone and hot bands. Our method makes use of a quartz sample cell that is heated by a tube furnace. Four spectra are then recorded at each temperature using a Fourier transform infrared spectrometer at high resolution (0.02 cm$^{-1}$). By combining these four spectra at each temperature, the emission and absorption from the cell and molecules are accounted for, and we obtain the true transmission spectrum of hot CH$_{4}$. Analysis of this series of spectra enables the production of line lists that include positions, intensities and empirical lower state energies. We also compare our line lists to the best available theoretical line lists at high temperatures. Whilst our experimental line lists contain fewer lines than theoretical line lists, we are able to demonstrate the quality of our observed spectra by considering our observations as absorption cross sections. This is important at elevated temperatures, when numerous blended lines appear as a continuum

HYDROGEN AND NITROGEN BROADENED ETHANE AND PROPANE ABSORPTION CROSS SECTIONS

High-resolution infrared absorption cross sections are presented for the $nu_{9}$ band of ethane (C$_{2}$H$_{6}$) at 823 cm$^{-1}$. These cross sections make use of spectra recorded at the Australian Synchrotron using a Fourier transform infrared spectrometer with maximum resolution of 0.00096 cm$^{-1}$. The spectra have been recorded at 150, 120 and 90 K for hydrogen and nitrogen broadened C$_{2}$H$_{6}$. They cover appropriate temperatures, pressures and broadening gases associated with the atmospheres of the Outer Planets and Titan, and will improve atmospheric retrievals. The THz/Far-IR beamline at the Australian Synchrotron is unique in combining a high-resolution Fourier transform spectrometer with an �enclosive flow cooling� (EFC) cell designed to study molecules at low temperatures. The EFC cell is advantageous at temperatures for which the vapor pressure is very low, such as C$_{2}$H$_{6}$ at 90 K. Hydrogen broadened absorption cross sections of propane between 700 and 1200 cm$^{-1}$ will also be presented based on spectra obtained at the Canadian Light Source

Exploring Halo Substructure with Giant Stars IV: The Extended Structure of the Ursa Minor Dwarf Spheroidal

We present a large area photometric survey of the Ursa Minor dSph. We identify UMi giant star candidates extending to ~3 deg from the center of the dSph. Comparison to previous catalogues of stars within the tidal radius of UMi suggests that our photometric luminosity classification is 100% accurate. Over a large fraction of the survey area, blue horizontal branch stars associated with UMi can also be identified. The spatial distribution of both the UMi giant stars and the BHB stars are remarkably similar, and a large fraction of both samples of stars are found outside the tidal radius of UMi. An isodensity contour map of the stars within the tidal radius of UMi reveals two morphological peculiarities: (1) The highest density of dSph stars is offset from the center of symmetry of the outer isodensity contours. (2) The overall shape of the outer contours appear S-shaped. We find that previously determined King profiles with ~50' tidal radii do not fit well the distribution of our UMi stars. A King profile with a larger tidal radius produces a reasonable fit, however a power law with index -3 provides a better fit for radii > 20'. The existence of UMi stars at large distances from the core of the galaxy, the peculiar morphology of the dSph within its tidal radius, and the shape of its surface density profile all suggest that UMi is evolving significantly due to the tidal influence of the Milky Way. However, the photometric data on UMi stars alone does not allow us to determine if the candidate extratidal stars are now unbound or if they remain bound to the dSph within an extended dark matter halo. (Abridged)Comment: accepted by AJ, 32 pages, 15 figures, emulateapj5 styl

Origin and extent of the opacity challenge for atmospheric retrievals of WASP-39 b

As the James Webb Space Telescope (JWST) came online last summer, we entered a new era of astronomy. This new era is supported by data products of unprecedented information content that require novel reduction and analysis techniques. Recently, Niraula et al. 2022 (N22) highlighted the need for upgraded opacity models to prevent facing a model-driven accuracy wall when interpreting exoplanet transmission spectra. Here, we follow the same approach as N22 to explore the sensitivity of inferences on the atmospheric properties of WASP-39 b to the opacity models used. We find that the retrieval of the main atmospheric properties from this first JWST exoplanet spectrum is mostly unaffected by the current state of the community's opacity models. Abundances of strong opacity sources like water and carbon dioxide are reliably constrained within $\sim$0.30 dex, beyond the 0.50 dex accuracy wall reported in N22. Assuming the completeness and accuracy of line lists, N22's accuracy wall is primarily driven by model uncertainties on broadening coefficients and far-wing behaviors, which we find to have marginal consequences for interpreting the transmission spectra of large, hot, high-metallicity atmospheres such as WASP-39 b, in opposition to emission spectra and climate modeling which depend on deeper parts of a planetary atmosphere. The origin of the opacity challenge in the retrieval of metal-rich hot Jupiters via transmission spectroscopy will thus mostly stem from the incompleteness and inaccuracy of line lists.Comment: 10 Pages, 6 Figure

Polarization correlations for electron-impact excitation of the resonant transitions of Ne and Ar at low incident energies

The electron-polarized-photon coincidence method is used to determine linear and circular polarization correlations in vacuum ultraviolet (VUV) for the differential electron-impact excitation of neon and argon resonance transitions at impact energies of 25 and 30 eV at small scattering angles up to 40. The circular polarization correlation is found to be positive in the case of Ne at 25 eV and supports the prediction of the present B-spline R-matrix theory concerning the violation of a long-established propensity rule regarding angular momentum transfer in electron-impact excitation of S→P transitions. Comparisons with the results from the present relativistic distorted-wave approximation and an earlier semirelativistic distorted-wave Born model are also made. For the case of Ar, at 25 and 30 eV, the circular polarization measurements remain in agreement with theory, but provide limited evidence as to whether or not the circular polarization at small scattering angles is also positive. For the linear polarizations, much better agreement with theory is obtained than in earlier measurements carried out by S. H. Zheng and K. Becker