# Exploring the age dependent properties of M and L dwarfs using Gaia and SDSS

## TL;DR

This study analyzes a large sample of M and L dwarfs using Gaia and SDSS data to explore their age-dependent properties, magnetic activity, and kinematic characteristics, revealing correlations with age, metallicity, and activity levels.

## Contribution

It provides new relations between Gaia colors and spectral types for late-M and L dwarfs and investigates how magnetic activity and kinematics relate to stellar age and population.

## Key findings

- Halpha active stars are redder and brighter, indicating magnetic inflation or binarity.
- Vertical velocity and action dispersion correlate with Halpha emission, serving as age indicators.
- Stars below the main sequence exhibit high tangential velocities, suggesting an old, low-metallicity population.

## Abstract

We present a sample of 74,216 M and L dwarfs constructed from two existing catalogs of cool dwarfs spectroscopically identified in the Sloan Digital Sky Survey (SDSS). We cross-matched the SDSS catalog with Gaia DR2 to obtain parallaxes and proper motions and modified the quality cuts suggested by the Gaia Collaboration to make them suitable for late-M and L dwarfs. We also provide relations between Gaia colors and absolute magnitudes with spectral type and conclude that (G-RP) has the tightest relation to spectral type for M and L dwarfs. In addition, we study magnetic activity as a function of position on the color-magnitude diagram, finding that Halpha magnetically active stars have, on average, redder colors and/or brighter magnitudes than inactive stars. This effect cannot be explained by youth alone and might indicate that active stars are magnetically inflated, binaries and/or high metallicity. Moreover, we find that vertical velocity and vertical action dispersion are correlated with Halpha emission, confirming that these two parameters are age indicators. We also find that stars below the main sequence have high tangential velocity which is consistent with a low metallicity and old population of stars that belong to the halo or thick disk.