Target Selection for the SDSS-III MARVELS Survey

TL;DR

This paper details the target selection process for the MARVELS survey, highlighting the challenges of accurately filtering dwarf stars from giants and proposing improved methods using proper motion and infrared data.

Contribution

It introduces a new target selection method utilizing reduced proper motion and infrared flux measurements, improving dwarf star identification for large spectroscopic surveys.

Findings

Initial low-res spectra failed to filter out giants effectively.

Proper motion cuts reduced giant contamination to below 30%.

Infrared Flux Method improved temperature estimates for target stars.

Abstract

We present the target selection process for the Multi-object APO Radial Velocity Exoplanets Large-area Survey (MARVELS), which is part of the Sloan Digital Sky Survey (SDSS) III. MARVELS is a medium-resolution ($R \sim 11000$) multi-fiber spectrograph capable of obtaining radial velocities for 60 objects at a time in order to find brown dwarfs and giant planets. The survey was configured to target dwarf stars with effective temperatures approximately between $4500$ and $6250 \, \mbox{K}$. For the first 2 years MARVELS relied on low-resolution spectroscopic pre-observations to estimate the effective temperature and $\log(g)$ for candidate stars and then selected suitable dwarf stars from this pool. Ultimately, the pre-observation spectra proved ineffective at filtering out giant stars; many giants were incorrectly classified as dwarfs, resulting in a giant contamination rate of $\sim$30\% for the first phase of the MARVELS survey. Thereafter, the survey instead applied a reduced proper motion cut to eliminate giants and used the Infrared Flux Method to estimate effective temperatures, using only extant photometric and proper-motion catalog information. The target selection method introduced here may be useful for other surveys that need to rely on extant catalog data for selection of specific stellar populations.