Enabling science with Gaia observations of naked-eye stars

Abstract

ESA's Gaia space astrometry mission is performing an all-sky survey of stellar objects. At the beginning of the nominal mission in July 2014, an operation scheme was adopted that enabled Gaia to routinely acquire observations of all stars brighter than the original limit of G∼6, i.e. the naked-eye stars. Here, we describe the current status and extent of those observations and their on-ground processing. We present an overview of the data products generated for G<6 stars and the potential scientific applications. Finally, we discuss how the Gaia survey could be enhanced by further exploiting the techniques we developed.

Spotting stellar activity cycles in Gaia astrometry

“…TGAS sample) are: AX Mic, σ Dra, and GX And. Upcoming efforts to measure astrometry of the brightest stars with Gaia may expand the sample of stars with detectable activity cycles (Martin-Fleitas et al 2014;Sahlmann et al 2016).…”

“…The TGAS sample does not include the brightest stars in the sky (Michalik et al 2015). Ongoing efforts throughout the beginning of the Gaia mission have made progress towards measuring astrometry of naked-eye stars, and it is possible that ultimately there will be no bright limit for Gaia astrometry (Martin-Fleitas et al 2014;Sahlmann et al 2016). Since the final mission bright limit is not yet established, we choose to consider only the stars with Gaia astrometry already published in TGAS, and ignore the brighter stars which may be accessible to Gaia astrometry in the future.…”

The Gaia mission

“…The onboard detection is effective at the bright end down to magnitude G ∼ 3 mag: the detection efficiency is ∼94% at G = 3 mag and drops rapidly for brighter stars to below 10% for G = 2 mag. 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; https://gaia.esac.esa.int/gost/ index.jsp), 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.…”

“…Bright stars: As already mentioned in Sect. 6.5, the onboard detection efficiency at the bright end drops from ∼94% at G = 3 mag to below 10% for G = 2 mag and brighter (Sahlmann et al 2016). Whereas special sky-mapper SIF images are acquired for the 230 very bright stars with G < 3 mag (Sect.…”

A detector interferometric calibration experiment for high precision astrometry

“…However, because of this 10 µas threshold, Gaia will only discover gas giants. There is an ongoing study to see whether a special electronic readout mode could be used to measure stars brighter than V mag = 6, but the accuracy would still be around the 10 µas mark, as opposed to degraded accuracy (Sahlmann et al 2016).…”