Abstract
Abstract We present the distance-calibrated spectral energy distribution (SED) of the sdL3.5 subdwarf SDSS J125637.13−022452.4 (J1256−0224) using its Gaia DR2 parallax. We report the bolometric luminosity and semi-empirical fundamental parameters, as well as updated UVW velocities. The SED of J1256−0224 is compared to field-age and low-gravity dwarfs of the same effective temperature (T eff) and bolometric luminosity. In the former comparison, we find that the SED of J1256−0224 is brighter than the field source in the optical, but dims in comparison beyond the J band, where it becomes fainter than the field from the H through W2 bands. Compared to the young source, it is fainter at all wavelengths. We conclude that J1256−0224 is depleted of condensates compared to both objects. A near-infrared band-by-band analysis of the spectral features of J1256−0224 is done and is compared to the equivalent T eff sample. From this analysis, we find a peculiar behavior of the J-band K i doublets whereby the 1.17 μm doublet is stronger than the field or young source, as expected, while the 1.25 μm doublet shows indications of low gravity. In examining a sample of four other subdwarfs with comparable data, we confirm this trend across different subtypes indicating that the 1.25 μm doublet is a poor indicator of gravity for low-metallicity objects. In the K-band analysis of J1256−0224, we detect the 2.29 μm CO line of J1256−0224, previously unseen in the low-resolution SpeX data. We also present fundamental parameters using Gaia parallaxes for nine additional subdwarfs with spectral types M7–L7 for comparison. The 10 subdwarfs are placed in a temperature sequence, and we find a poor linear correlation with spectral type. We present polynomial relations for absolute magnitude in JHKW1W2, effective temperature, and bolometric luminosity versus spectral type for subdwarfs.
Highlights
Brown dwarfs are low-mass, low-temperature objects that are unable to sustain stable hydrogen burning in their cores and cool throughout their lifetime
In this work we present the distance-calibrated spectral energy distribution (SED) of J1256−0224 and compared it to objects of the same effective temperature and bolometric luminosity
We show that the best comparison objects are not of the same spectral type (L3.5), but instead are field- and low-gravity objects 3 to 4 subtypes earlier (M9L0)
Summary
Brown dwarfs are low-mass, low-temperature objects that are unable to sustain stable hydrogen burning in their cores and cool throughout their lifetime. 75 MJup, brown dwarfs lie between the boundary of low mass stars and planets (Saumon et al 1996; Chabrier & Baraffe 1997) Classified based on their red optical or nearinfrared (NIR) spectra, the observed population of brown dwarfs have effective temperatures of 250 − 3000 K corresponding to late-type M, L, T and Y spectral types (Kirkpatrick 2005; Burgasser et al 2002; Cushing et al 2011). Low-gravity dwarfs are identified by red near-infrared colors, weak alkali lines, and enhanced metal oxide absorption in the optical (Kirkpatrick et al 2006, 2010; Cruz et al 2009; Allers et al 2010). The best values for previously published data on J1256−0224, as well as values we present in this paper are listed Table 1
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