Moreover, the science goal of the Gaia mission is to produce parallaxes with an error of 0.0067 mas for the brighter stars. The scans will be completed and the naked eye and high proper motion stars will be added to a future release. So am I disappointed with all this? Not really. TGAS completeness/incompleteness #GaiaSprint #MindTheGaps /tKCzRjYm1f Gaia scientist Ronald Drimmel tweated the incompleteness maps: As the Gaia data that went into TGAS was gathered only over the first few months of the mission, some of the sky was not completely scanned. I have ignored the possible systematic error in producing Tycho Galaxy but it does place a question mark over much of the map.Īnother limitation is caused by Gaia's incomplete sky scans during the DR1 period. This is not even as far as the Orion nebula and not that much further than the Hipparcos results from the 1990s. If we add this to the 0.32 mas measurement error, Bailer-Jones's formula gives us a usable distance of 323 parsecs. In addition to the 0.32 mas parallax measurement error for most of the TGAS stars, the Gaia DR1 release notes warn that the Gaia data may have a systematic error and that this error might be as high as 0.3 mas. This might explain the odd dearth of bright stars near the Sun in the Tycho Galaxy map of the solar neighbourhood. The net effect is that no naked eye stars and few stars close to the Sun are included in TGAS (and therefore appear on Tycho Galaxy).
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