Understanding Fundamental Properties and Atmospheric Features of Subdwarfs via a Case Study of SDSS J125637.13–022452.4^∗

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 parallax and its resultant 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, its 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 4 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 9 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.

WISEA J041451.67–585456.7 and WISEA J181006.18–101000.5: The First Extreme T-type Subdwarfs?

“…The T0 spectral standard (SDSS J120747.17+024424.8; Looper et al 2007) is the best match to both WISEA 0414−5854 and WISEA 1810−1010 in the J band; however, the H and K fluxes are depressed relative to peak in J, as compared with the standard (Figure 2, top panels). This behavior is similar to what is seen in the latest L-type subdwarfs, where the spectra are relatively featureless and the infrared flux peaks blueward of the peak location typically seen for field L dwarfs at the H band (Gonzales et al 2018). This shift is most likely due to collision-induced absorption (CIA) from H 2 , which broadly absorbs across the near-infrared with a peak in absorption at the fundamental vibration frequency at 4161 cm −1 (2.4 μm; Linsky 1969;Borysow et al 1997;Burgasser et al 2003).…”

“…T eff estimates of 1200-1400 K correspond to spectral types of L7 to T1.5 for field type brown dwarfs (Filippazzo et al 2015), in agreement with the best matching spectral standard. Note, however, that the effective temperatures of late-type sdMs and sdLs are generally warmer than their field counterparts for a given spectral subtype (e.g., Zhang et al 2017b;Gonzales et al 2018), although it is unclear if this trend extends into the T dwarf regime. We therefore tentatively assign a spectral type of esdT0 ±1 for both of these objects.…”

“…Second, photometric distances are typically constructed for the field population of brown dwarfs and therefore may not be appropriate for subdwarfs. Those relations that do pertain to subdwarfs either do not yet extend to the T dwarf regime (Schilbach et al 2009;Zhang et al 2017b;Gonzales et al 2018) or are only appropriate for sdT type brown . Near-infrared spectra of WISEA 0414−5854 (black, left panels) and WISEA 1810−1010 (black, right panels) compared to two low-temperature PHOENIX models.…”

A Reanalysis of the Fundamental Parameters and Age of TRAPPIST-1*

“…Objects in each comparative sample were chosen from (1) Filippazzo et al (2015), which examined a large sample of field and low-gravity objects, (2) Faherty et al (2016), which examined a large sample of low-gravity sources, or (3) Gonzales et al (2018), which examined subdwarfs later than sdM6 with parallax measurements. The bolometric luminosities in each sample were empirically derived, while their effective temperatures were semi-empirically derived using radii from evolutionary models depending on the age.…”

New Candidate Extreme T Subdwarfs from the Backyard Worlds: Planet 9 Citizen Science Project

“…22 The luminosity sequence of T subdwarfs is presently not well-mapped. L subdwarfs do exhibit different luminosity versus type trends than field L dwarfs in certain photometric bands (e.g.,Gonzales et al 2018).…”