Title: Understanding Atmospheres Across the Stellar-Substellar Boundary
Abstract:
Ultracool Subdwarfs, objects that have metallicities significantly lower than that of the Sun and ages greater than 5Gyr, provide insight into understanding how metallicity affects observable features of low-mass stars and brown dwarfs. Currently, substellar subdwarfs are thought to have cloudless atmospheres due to reduced condensate opacities from their low-metallicities. In this talk, I aim to explore the nature of clouds in subdwarfs using both observational and theoretical approaches I ask: (1) Are subdwarfs cloudless? and (2) How does their thermal profile compare to objects of similar effective temperature (Teff) or spectral type? By creating distance-calibrated spectral energy distributions (SEDs), I will compare one of the bluest known subdwarfs, SDSS J1256, to various aged sources of similar Teff and/or bolometric luminosity to examine the overall SED shape and features in the NIR bands, as well as compare fundamental parameters and place SDSS J1256 in context with the larger subdwarf population. To explore the nature of clouds in subdwarfs, I use the Brewster retrieval framework to examine a sample of subdwarfs and comparative sources to explore what may be causing the differences seen in the SEDs of these sources. In this talk, I will discuss the results for the widely separated co-moving low-mass d/sdL7+T7.5p pair SDSS J1416+1348AB to determine if the pair formed and evolved together and their cloud properties. Additionally, I will discuss preliminary results from a comparative sample of field sources of similar temperature or spectral type to SDSS J1416A to determine how the PT profile of these objects compares and what may drive the differences we see in their spectra.
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