SDSS J125637-022452: a high proper motion L subdwarf

TL;DR

This paper reports the discovery of a high proper motion, metal-poor L subdwarf with mixed spectral features, indicating a very low-mass star likely belonging to the Galactic halo, characterized by its unique spectral and kinematic properties.

Contribution

The discovery of a new high proper motion L subdwarf with mixed spectral features and halo kinematics, highlighting its low metallicity and distinct infrared colors.

Findings

High proper motion of 0.617 arcsec/yr detected

Spectral features show a mix of late-M and mid-L characteristics

Object exhibits bluer near-infrared colors due to H2 collision-induced absorption

Abstract

We report the discovery of a high proper motion L subdwarf ($\mu$ =0.617arcsec/yr) in the Sloan Digital Sky Survey spectral database. The optical spectrum from the star SDSS J125637-022452 has mixed spectral features of both late-M spectral subtype (strong TiO and CaH at 7000A) and mid-L spectral subtype (strong wings of KI at 7700A, CrH and FeH), which is interpreted as the signature of a very low-mass, metal-poor star (ultra-cool subdwarf) of spectral type sdL. The near infrared (NIR) (J-Ks) colors from 2MASS shows the object to be significantly bluer compared to normal L dwarfs, which is probably due a strong collision induced absorption (CIA) due to H2 molecule. This is consistent with the idea that CIA from H2 is more pronounced at low metallicities. Proper motion and radial velocity measurements also indicate that the star is kinematically "hot" and probably associated with the Galactic halo population.