Colors and Kinematics of L Dwarfs From the Sloan Digital Sky Survey

TL;DR

This study presents a large sample of L dwarfs from SDSS, analyzing their colors, distances, and kinematics to understand their population characteristics and age distribution.

Contribution

It provides a new, larger sample of L dwarfs with detailed color, distance, and velocity data, revealing correlations between color and age, and identifying different dynamical populations.

Findings

L dwarfs are bluer than previously known at certain spectral types.

Color correlates with velocity dispersion, indicating age differences.

Evidence for both young and old disk populations among L dwarfs.

Abstract

We present a sample of 484 L dwarfs, 210 of which are newly discovered from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic database. We combine this sample with known L dwarfs to investigate their $izJHK_S$ colors. Our spectroscopically selected sample has $\sim$0.1 magnitude bluer median $J-K_S$ colors at a given spectral type (for L0 to L4) than previously known L dwarfs, which reflects a bias towards redder L dwarfs in past selection criteria. We present photometric distance relations based on $i-z$ and $i-J$ colors and derive distances to our L dwarf sample. We combine the distances with SDSS/2MASS proper motions in order to examine the tangential velocities. For the majority of our spectroscopic sample, we measured radial velocities and present three dimensional kinematics. We also provide H$\alpha$ detections for the fraction of our sample with sufficient quality spectra. Comparison of the velocities of our L dwarf sample to a kinematic model shows evidence for both cold and hot dynamical populations, consistent with young and old disk components. The dispersions of these components are similar to those found for M dwarfs. We also show that $J-K_S$ color is correlated with velocity dispersion, confirming a relationship between $J-K_S$ color and age.