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Thread: AAS: rethinking the Kepler data using Gaia data

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    Default AAS: rethinking the Kepler data using Gaia data



    https://aasnova.org/2018/07/17/a-ste...dii-with-gaia/

    Kepler data alone significantly mis estimates stellar radii.
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    Default Re: AAS: rethinking the Kepler data using Gaia data

    Eeek! Brought back memories of the catastrophic fail with my project on what my limited data told me were main sequence K stars. Turns out most of them were giants. Further implication - K giants almost seem to be more numerous than K dwarfs. Might have to revisit that thought someday.

    More to the point: so, you find, say, a Neptune mass planet orbiting around what the Kepler data says is a dwarf. Then, the Gaia parallax comes in, and based on that, the star has to be a giant. So...would the Neptune mass world get upgraded to, say Jupiter mass?

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    Default Re: AAS: rethinking the Kepler data using Gaia data

    Quote Originally Posted by ThinkerX View Post
    Eeek! Brought back memories of the catastrophic fail with my project on what my limited data told me were main sequence K stars. Turns out most of them were giants. Further implication - K giants almost seem to be more numerous than K dwarfs. Might have to revisit that thought someday.
    Seem should be in quotes. The spatial density of K giants is much much lower than K dwarfs. They are simply visible further away.

    More to the point: so, you find, say, a Neptune mass planet orbiting around what the Kepler data says is a dwarf. Then, the Gaia parallax comes in, and based on that, the star has to be a giant. So...would the Neptune mass world get upgraded to, say Jupiter mass?
    A parallax that puts the star further away makes the star a giant makes the orbit much larger. So an upgrade in the size of the planet is required also.
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    Default Re: AAS: rethinking the Kepler data using Gaia data

    Seem should be in quotes. The spatial density of K giants is much much lower than K dwarfs. They are simply visible further away.
    Agreed - and yet...

    way back in the 70's there was an astronomer named Stephenson. From what I can tell, he seems to have had a fairly good reputation. Anyhow, for whatever reason, he took it upon himself to do a count of relatively nearby main sequence K stars. He appears to have had the requisite photometric equipment, and knew how to employ it. Yet, for all this, trigonometric parallaxes revealed the majority of his 'dwarfs' to be giants.

    I also looked over the 'Kepler Index Catalogue' - the original target list, complete with rough distances - back in the early stages of that mission. There wasn't a great deal of info available on most of those stars - often the 'B' and 'V' values were...dubious (missing, or with error bars in excess of 0.5 magnitudes). Most had 2MASS data, but that was of limited value. Ever afterward, I had...reservations...about the accuracy of the distances given for those stars. I admit, though, I thought they had a better grip on the giant/sub-giant situation.

 

 

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