Planet Hunters Talk

Gaia mission: first data release

  • ajamyajax by ajamyajax

    "One billion stars in 3-D: Gaia's billion-star map hints at treasures to come"

    http://phys.org/news/2016-09-billion-stars-d-gaia-billion-star.html

    A few useful links:

    http://gea.esac.esa.int/archive/

    http://gaia.esac.esa.int/documentation/GDR1/Catalogue_consolidation/sec_cu1cva/sec_cu9gat.html#SS1

    Posted

  • Shellface by Shellface

    Welcome to the Gaia era!

    There are hundreds and hundreds of places where the overall significance of Gaia is discussed, so there is no need to repeat them here. However, it is worth discussing what we can do with the first-release data.

    Previously parallaxes were difficult to come by for K2 (and Kepler) stars. Hipparcos, the previous all-sky astrometric mission, is only complete down to V~9, which is comparable to the brightest stars targeted by Kepler. The Gaia first release gives parallaxes for stars in common with Tycho, which is complete down to V~11.5 - giving parallxes to a small-but-significant number of Kepler targets for the first time. This means that a good number of Kepler/K2 targets now have parallaxes.

    Parallaxes are usually given in units of milliarcseconds (mas). To convert such a parallax into distance, simply divide it by 1000 and then calculate 1/ans. This will give the distance in parsecs, so multiply the value by 3.26… to have it in light-years. Errors on parallaxes are given in the Gaia archive, but for the first release it is recommended to add a 0.3 mas systematic error.

    The most basic application for parallaxes we can use is to place a star on the Hertzsprung-Russell diagram. This allows for some simple estimates for the stellar parameters, and also helps identify false positives (e.g a dwarf with 1% transits may have a planet, but a giant with 1% transits cannot). For this we need a parallax and a V-band magnitude to get absolute magnitude (here is a simple calculator), and then either Teff or a colour proxy plus the absolute magnitude to place the star on the H-R diagram (e.g here).

    A more derived use for parallaxes is to use isochrones to directly evaluate the stellar parameters. This requires information that is not readily available for K2 targets without follow-up (in particular metallicity), so I won't discuss the process in detail. However, expect to see Gaia parallaxes used for this purpose in K2 papers.

    For example, look at K2-93 (HIP 41378, EPIC 211311380). At V = 8.9 this star has a Hipparcos parallax of 8.56 ± 1.24 mas (116.8 ± 17.3 parsecs). The Gaia release 1 parallax is 9.83 ± 0.30 mas, so adding the recommended systematic error gives a parallax of 9.83 ± 0.60 mas (101.7 ± 6.2 pc). Despite being based on a small subset of the total Gaia data the parallax is twice as precise as the Hipparcos one, which is strong indication of Gaia's precision.

    By the end of the Gaia mission the astrometric data is expected to lead to the detection of hundreds-to-thousands of planets, which compares with the ~zero current planet discoveries by astrometry. Gaia will be most sensitive to planets with periods of a few years, which is rather complementary to Kepler.

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  • Artman40 by Artman40

    Note that there are currently several dozen Kepler host stars with a known planet that are close enough for Gaia (in its final data release) to detect additional Jupiter-like planets. TESS will increase this number by a lot. This means that it's very likely that many close exoplanet host stars will have exoplanets detected by both Kepler/TESS and Gaia. This will provide much better understanding of the structure of planetary systems than Kepler alone, TESS alone or Gaia alone.

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  • ajamyajax by ajamyajax

    "Gaia spies two temporarily magnified stars"

    http://phys.org/news/2016-10-gaia-spies-temporarily-magnified-stars.html

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