Enabling Gaia observations of naked-eye stars

Abstract

The ESA Gaia space astrometry mission will perform an all-sky survey of stellar objects complete in the nominal magnitude range G = [6.0 -20.0]. The stars with G < 6.0, i.e. those visible to the unaided human eye, would thus not be observed by Gaia. We present an algorithm configuration for the Gaia on-board autonomous object observation system that makes it possible to observe very bright stars with G = [2.0-6.0). Its performance has been tested during the in-orbit commissioning phase achieving an observation completeness of ∼ 94% at G = 3 -5.7 and ∼ 75% at G = 2 -3. Furthermore, two targeted observation techniques for data acquisition of stars brighter than G=2.0 were tested. The capabilities of these two techniques and the results of the in-flight tests are presented. Although the astrometric performance for stars with G < 6.0 has yet to be established, it is clear that several science cases will benefit from the results of the work presented here.

TheGaiamission

“…The 230 brightest stars in the sky (G < 3 mag, loosely referred to as very bright stars) receive a special treatment to ensure complete sky coverage at the bright end (Martín-Fleitas et al 2014;Sahlmann et al 2016). Using the Gaia observing schedule tool (GOST 2 ), their transit times and across-scan transit positions are predicted, based on propagated Hipparcos astrometry and the operational scanning law, and SIF data are acquired for these stars in the sky mapper (SM) and subsequently downloaded.…”

GaiaFGK benchmark stars: Effective temperatures and surface gravities

“…The V magnitudes range from 0 to 8. About two thirds of the stars are fainter than 3 mag and will be included in the magnitude range observed by Gaia (see Martín-Fleitas et al 2014 for a discussion of the detection of bright stars with Gaia). The stars are evenly distributed along the celestial equator, and all but ten stars have declinations within ±30 deg.…”

Gaia Astrometric Science Performance – Post-Launch Predictions

“…Their standard errors will hence be (much) larger than predicted through this model. Stars brighter than G = 3 mag will be observed with a special mode with associated non-trivial calibration challenges (Martín-Fleitas et al, 2014); the end-of-life astrometric standard errors for these stars will amount to at least several dozens of µas. For stars between 3 and 12 mag, reduced CCD integration times (through the use of Time-DelayedIntegration -TDI -gates) will be used to limit saturation.…”