The Gaia spectrophotometric standard stars survey. I. Preliminary results

TL;DR

This paper details the initial results of ground-based campaigns to establish a grid of about 200 spectrophotometric standard stars with high internal and absolute flux calibration precision for Gaia data calibration.

Contribution

It introduces the selection criteria, survey strategy, and data analysis methods for building a spectrophotometric standard star catalog for Gaia calibration.

Findings

Identification of a delta Scuti variable among standard candidates.

Development of a candidate selection and monitoring process.

Preliminary list of suitable and rejected standard stars.

Abstract

We describe two ground based observing campaigns aimed at building a grid of approximately 200 spectrophotometric standard stars (SPSS), with an internal ~1% precision and tied to Vega within ~3%, for the absolute flux calibration of data gathered by Gaia, the ESA astrometric mission. The criteria for the selection and a list of candidates are presented, together with a description of the survey strategy and the adopted data analysis methods. We also discuss a short list of notable rejected SPSS candidates and difficult cases, based on identification problems, literature discordant data, visual companions, and variability. In fact, all candidates are also monitored for constancy (within \pm5 mmag, approximately). In particular, we report on a CALSPEC standard, 1740346, that we found to be a delta Scuti variable during our short-term monitoring (1-2 h) campaign.