Querying GAIA DR2 for Polaris (for example using https://gea.esac.esa.int/archive/) yields empty parallax columns. Anyone knows why it was not measured/published?
2
-
$\begingroup$ For source id 576402619921505664 I also see phot_g_mean_mag at about 10.45 -- perhaps this isn't actually Polaris (what search did you do?) $\endgroup$– user21Jun 8, 2018 at 18:22
-
$\begingroup$ Yes, I filled Polaris in Name box and submitted, got that source id. Thanks for explanation. $\endgroup$– JurajJun 9, 2018 at 19:07
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
1
My query for stars north of +75° and brighter than magnitude 4 returns only 6 stars, brightest of which is γ Cephei. Polaris may be too bright for Gaia. Even if it doesn't saturate the detector, a bright star will probably have larger astrometric errors than a star between magnitudes 6 and 12. DR2 coverage of magnitude 5 and brighter stars is better than DR1 but still rather sparse. Section 3.1 of this paper plots parallax coverage vs. magnitude and explains why some stars have positions but not parallaxes.
-
7$\begingroup$ Polaris has magnitude close to 2, and and GAIA DR2 states that its bright limit is at about mag 3, so Polaris is too bright to be in the catalogue $\endgroup$– Dr ChuckJun 9, 2018 at 8:58