Radial velocities for the HIPPARCOS-<i>Gaia</i>Hundred-Thousand-Proper-Motion project

Abstract

(abridged) The Hundred-Thousand-Proper-Motion (HTPM) project will determine\nthe proper motions of ~113500 stars using a 23-year baseline. The proper\nmotions will use the Hipparcos data, with epoch 1991.25, as first epoch and the\nfirst intermediate-release Gaia astrometry, with epoch ~2014.5, as second\nepoch. The expected HTPM proper-motion standard errors are 30-190 muas/yr,\ndepending on stellar magnitude. Depending on the characteristics of an object,\nin particular its distance and velocity, its radial velocity can have a\nsignificant impact on the determination of its proper motion. The impact of\nthis perspective acceleration is largest for fast-moving, nearby stars. Our\ngoal is to determine, for each star in the Hipparcos catalogue, the\nradial-velocity standard error that is required to guarantee a negligible\ncontribution of perspective acceleration to the HTPM proper-motion precision.\nWe employ two evaluation criteria, both based on Monte-Carlo simulations, with\nwhich we determine which stars need to be spectroscopically (re-)measured. Both\ncriteria take the Hipparcos measurement errors into account. For each star in\nthe Hipparcos catalogue, we determine the confidence level with which the\navailable radial velocity and its standard error, taken from the XHIP\ncompilation catalogue, are acceptable. We find that for 97 stars, the radial\nvelocities available in the literature are insufficiently precise for a 68.27%\nconfidence level. We also identify 109 stars for which radial velocities are\ncurrently unknown yet need to be acquired to meet the 68.27% confidence level.\nTo satisfy the radial-velocity requirements coming from our study will be a\ndaunting task consuming a significant amount of spectroscopic telescope time.\nFortunately, the follow-up spectroscopy is not time-critical since the HTPM\nproper motions can be corrected a posteriori once (improved) radial velocities\nbecome available.\n

Keywords

Affiliated Institutions

• European Space Research and Technology Centre NL

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