Toward Robust Atmospheric Retrieval on Cloudy L Dwarfs: the Impact of Thermal and Abundance Profile Assumptions
Constraining L dwarf properties from their spectra is challenging. Near-infrared (NIR) spectra probe a limited range of pressures, while many species condense within their photospheres. Condensation creates two complexities: gas-phase species “rain out” (decreasing in abundances by many orders of ma...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2023-01-01
|
| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/acbb07 |
| _version_ | 1797695855543713792 |
|---|---|
| author | Melanie J. Rowland Caroline V. Morley Michael R. Line |
| author_facet | Melanie J. Rowland Caroline V. Morley Michael R. Line |
| author_sort | Melanie J. Rowland |
| collection | DOAJ |
| description | Constraining L dwarf properties from their spectra is challenging. Near-infrared (NIR) spectra probe a limited range of pressures, while many species condense within their photospheres. Condensation creates two complexities: gas-phase species “rain out” (decreasing in abundances by many orders of magnitude) and clouds form. We designed tests using synthetic data to determine the best approach for retrieving L dwarf spectra, isolating the challenges in the absence of cloud opacity. We conducted atmospheric retrievals on synthetic cloud-free L dwarf spectra derived from the Sonora Bobcat models at SpeX resolution using a variety of thermal and chemical abundance profile parameterizations. For objects hotter than L5 ( T _eff ∼ 1700 K), the limited pressure layers probed in the NIR are mostly convective; parameterized pressure–temperature ( PT ) profiles bias results and free, unsmoothed profiles should be used. Only when many layers both above and below the radiative-convective boundary are probed can parameterized profiles provide accurate results. Furthermore, a nonuniform abundance profile for FeH is needed to accurately retrieve bulk properties of early-to-mid L dwarfs. Nonuniform prescriptions for other gases in NIR retrievals may also be warranted near the L/T transition (CH _4 ) and early Y dwarfs (Na and K). We demonstrate the utility of using realistic, self-consistent models to benchmark retrievals and suggest how they can be used in the future. |
| first_indexed | 2024-03-12T03:17:16Z |
| format | Article |
| id | doaj.art-ab1c4f3b845c438ea3022984d4e5e128 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-12T03:17:16Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-ab1c4f3b845c438ea3022984d4e5e1282023-09-03T14:08:23ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-019471610.3847/1538-4357/acbb07Toward Robust Atmospheric Retrieval on Cloudy L Dwarfs: the Impact of Thermal and Abundance Profile AssumptionsMelanie J. Rowland0https://orcid.org/0000-0003-4225-6314Caroline V. Morley1https://orcid.org/0000-0002-4404-0456Michael R. Line2https://orcid.org/0000-0002-2338-476XDepartment of Astronomy, University of Texas at Austin , 2515 Speedway C1400, Austin, TX 78712, USA ; mrowland@utexas.eduDepartment of Astronomy, University of Texas at Austin , 2515 Speedway C1400, Austin, TX 78712, USA ; mrowland@utexas.eduSchool of Earth & Space Exploration, Arizona State University , Tempe, AZ 85287, USAConstraining L dwarf properties from their spectra is challenging. Near-infrared (NIR) spectra probe a limited range of pressures, while many species condense within their photospheres. Condensation creates two complexities: gas-phase species “rain out” (decreasing in abundances by many orders of magnitude) and clouds form. We designed tests using synthetic data to determine the best approach for retrieving L dwarf spectra, isolating the challenges in the absence of cloud opacity. We conducted atmospheric retrievals on synthetic cloud-free L dwarf spectra derived from the Sonora Bobcat models at SpeX resolution using a variety of thermal and chemical abundance profile parameterizations. For objects hotter than L5 ( T _eff ∼ 1700 K), the limited pressure layers probed in the NIR are mostly convective; parameterized pressure–temperature ( PT ) profiles bias results and free, unsmoothed profiles should be used. Only when many layers both above and below the radiative-convective boundary are probed can parameterized profiles provide accurate results. Furthermore, a nonuniform abundance profile for FeH is needed to accurately retrieve bulk properties of early-to-mid L dwarfs. Nonuniform prescriptions for other gases in NIR retrievals may also be warranted near the L/T transition (CH _4 ) and early Y dwarfs (Na and K). We demonstrate the utility of using realistic, self-consistent models to benchmark retrievals and suggest how they can be used in the future.https://doi.org/10.3847/1538-4357/acbb07Brown dwarfsL dwarfsAtmospheric structureAtmospheric compositionStellar atmospheresPlanetary atmospheres |
| spellingShingle | Melanie J. Rowland Caroline V. Morley Michael R. Line Toward Robust Atmospheric Retrieval on Cloudy L Dwarfs: the Impact of Thermal and Abundance Profile Assumptions The Astrophysical Journal Brown dwarfs L dwarfs Atmospheric structure Atmospheric composition Stellar atmospheres Planetary atmospheres |
| title | Toward Robust Atmospheric Retrieval on Cloudy L Dwarfs: the Impact of Thermal and Abundance Profile Assumptions |
| title_full | Toward Robust Atmospheric Retrieval on Cloudy L Dwarfs: the Impact of Thermal and Abundance Profile Assumptions |
| title_fullStr | Toward Robust Atmospheric Retrieval on Cloudy L Dwarfs: the Impact of Thermal and Abundance Profile Assumptions |
| title_full_unstemmed | Toward Robust Atmospheric Retrieval on Cloudy L Dwarfs: the Impact of Thermal and Abundance Profile Assumptions |
| title_short | Toward Robust Atmospheric Retrieval on Cloudy L Dwarfs: the Impact of Thermal and Abundance Profile Assumptions |
| title_sort | toward robust atmospheric retrieval on cloudy l dwarfs the impact of thermal and abundance profile assumptions |
| topic | Brown dwarfs L dwarfs Atmospheric structure Atmospheric composition Stellar atmospheres Planetary atmospheres |
| url | https://doi.org/10.3847/1538-4357/acbb07 |
| work_keys_str_mv | AT melaniejrowland towardrobustatmosphericretrievaloncloudyldwarfstheimpactofthermalandabundanceprofileassumptions AT carolinevmorley towardrobustatmosphericretrievaloncloudyldwarfstheimpactofthermalandabundanceprofileassumptions AT michaelrline towardrobustatmosphericretrievaloncloudyldwarfstheimpactofthermalandabundanceprofileassumptions |