LSST Survey Strategies and Brown Dwarf Parallaxes

TL;DR

The paper evaluates LSST survey strategies to optimize the measurement of parallaxes for thousands of brown dwarfs, significantly expanding current samples and informing community input.

Contribution

It develops a model to estimate brown dwarf parallaxes in LSST, assesses observing strategies, and provides recommendations to maximize scientific return.

Findings

Nearly tenfold increase in brown dwarf parallax samples.

Sample size remains stable across various survey strategies.

Identifies potential conflicts with twilight time allocations.

Abstract

The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) has the potential to measure parallaxes for thousands of nearby ultracool dwarfs, enabling improved measurements of the brown dwarf luminosity function. We develop a simple model to estimate the number of L dwarfs and T dwarfs with parallaxes with signal-to-noise ratio greater than ten in the baseline LSST survey. High quality astrometry imposes scheduling constraints. We assess different possible observing strategies using quantitative metrics and make recommendations as part of the LSST community input process. We find that the new substellar parallax sample will represent a nearly order-of-magnitude increase on existing samples, with ~50-100 objects per spectral type bin for late-L to mid-T dwarfs. The sample size is robust (+/- 5%) against most survey strategy changes under consideration, although we do identify areas of tension with other uses of twilight time that could have larger impact.