Gaia search question.

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Janus
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Gaia search question.

Post #1by Janus » 31.03.2021, 17:17

Does anyone here know how to do a search of the Gaia data for a specific subset?

In particular what I am seeking is extra solar objects with a parallax > 0.01
Or parallax > 10, depending on which way it is written out.
I need position, proper motion, relative velocity, and whether it is approaching or receding.

I know they have very good and valid reasons for the way they have everything setup.
However, it is mostly gibberish to me.
The limitation is mine.
Simply hoping for an easier solution than downloading it all, then filtering it myself.


Janus.

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SevenSpheres
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Post #2by SevenSpheres » 01.04.2021, 12:49

If you're using the Gaia Archive, you can (in the Search -> Basic tab) click "Extra conditions", then "Add condition" (circled). You can then enter the condition you want (in this case, parallax >= 10), as shown in the screenshot.
gaiaarchive2.png
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Topic author
Janus
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Joined: 13.08.2016
With us: 4 years 8 months

Post #3by Janus » 01.04.2021, 15:46

@SevenSpheres

Thank you very much.
All of that information, and they fail to provide illustrations.
Stuck in their own world where everyone who belongs already knows everything, so no explanation needed.
Not their fault really, translating is hard.

Could I impose further and ask how to determine doppler from from all that.
I am sure the answer is there, however, they have cryptographically hashed it behind astronomy terms whose words mean what they want them to mean.
Whether it is simple or complicated doesn't matter, once I can make a formula out of it, I can automate it.
Worst case is some if/then/else or case/switch fun, been there, done that, broke the compiler.

Same problem I have with a lot of fields.
Common words used in custom ways, while providing no clue how to translate.
It seems like every time I learn a new thing/area/field, I find I already knew most of it, but using different words for exactly the same things.


Janus.

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SevenSpheres
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Post #4by SevenSpheres » 01.04.2021, 17:28

Janus wrote:I need position, proper motion, relative velocity, and whether it is approaching or receding.
Janus wrote:Could I impose further and ask how to determine doppler from from all that.

Position is in the ra and dec columns. These are right ascension and declination, in degrees.
Proper motion is in the pmra and pmdec columns (not selected by default, can be selected under "Display columns"). These are in milliarcseconds per year.
Radial velocity (related to Doppler shift) is in the dr2_radial_velocity column (I guess there's no radial velocity data in EDR3?). It's in kilometers per second; apparently a negative value means the object is moving toward us, and a positive value that it's moving away from us. Only some entries have radial velocity data, many (most?) do not.
All determined from a look at the Gaia Archive page and Wikipedia just now.
My Addons: viewtopic.php?f=23&t=19978 • (formerly) Contributing to development as much as I can • Discord server admin
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