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ABSTRACT Observations of planetary material polluting the atmospheres of white dwarfs are an important probe of the bulk composition of exoplanetary material. Medium- and high-resolution optical and ultraviolet spectroscopy of seven white dwarfs with known circumstellar dust and gas emission are presented. Detections or meaningful upper limits for photospheric absorption lines are measured for: C, O, Na, S, P, Mg, Al, Si, Ca, Ti, Cr, Fe, and Ni. For 16 white dwarfs with known observable gaseous emission discs (and measured photospheric abundances), there is no evidence that their accretion rates differ, on average, from those without detectable gaseous emission. This suggests that, typically, accretion is not enhanced by gas drag. At the effective temperature range of the white dwarfs in this sample (16 000–25 000 K) the abundance ratios of elements are more consistent than absolute abundances when comparing abundances derived from spectroscopic white dwarf parameters versus photometric white dwarf parameters. Crucially, this highlights that the uncertainties on white dwarf parameters do not prevent white dwarfs from being utilized to study planetary composition. The abundances of oxygen and silicon for the three hydrogen-dominated white dwarfs in the sample with both optical and ultraviolet spectra differ by 0.62 dex depending on if they are derived from the optical or ultraviolet spectra. This optical/ultraviolet discrepancy may be related to differences in the atmospheric depth of line formation; further investigations into the white dwarf atmospheric modelling are needed to understand this discrepancy.
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A 1.46–2.48 μm spectroscopic atlas of a T6 dwarf (1060 K) atmosphere with IGRINS: first detections of H2S and H2, and verification of H2O, CH4, and NH3 line lists
ABSTRACT We present Gemini South/IGRINS observations of the 1060 K T6 dwarf 2MASS J08173001−6155158 with unprecedented resolution ($$R\equiv \lambda /\Delta \lambda =45\, 000$$) and signal-to-noise ratio (S/N > 200) for a late-type T dwarf. We use this benchmark observation to test the reliability of molecular line lists used up-to-date atmospheric models. We determine which spectroscopic regions should be used to estimate the parameters of cold brown dwarfs and, by extension, exoplanets. We present a detailed spectroscopic atlas with molecular identifications across the H and K bands of the near-infrared. We find that water (H2O) line lists are overall reliable. We find the most discrepancies amongst older methane (CH4) line lists, and that the most up-to-date CH4 line lists correct many of these issues. We identify individual ammonia (NH3) lines, a hydrogen sulfide (H2S) feature at 1.5900 $$\mu$$m, and a molecular hydrogen (H2) feature at 2.1218 $$\mu$$m. These are the first unambiguous detections of H2S and H2 absorption features in an extra-solar atmosphere. With the H2 detection, we place an upper limit on the atmospheric dust concentration of this T6 dwarf: at least 500 times less than the interstellar value, implying that the atmosphere is effectively dust-free. We additionally identify several features that do not appear in the model spectra. Our assessment of the line lists is valuable for atmospheric model applications to high-dispersion, low-S/N, high-background spectra, such as an exoplanet around a star. We demonstrate a significant enhancement in the detection of the CH4 absorption signal in this T6 dwarf with the most up-to-date line lists.
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- Award ID(s):
- 1910969
- PAR ID:
- 10368398
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 514
- Issue:
- 3
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 3160-3178
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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