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I'm attempting to create a map of all objects within 50LY, including main-sequence stars, binaries, planemos, etc. As such, I'm trying to do it all from first principles, building a micro-ETL to scrape SIMBAD data and build a model. However - I'm experiencing some issues with getting distance measurements from ADGL queries. Watch the following:

Using TAP (http://simbad.u-strasbg.fr/simbad/sim-tap)

SELECT * FROM BASIC WHERE main_id like '%alf%Cen%'

Returns 4 rows:

enter image description here

However - when I check out the mesDistance table with this query:

SELECT * FROM mesDistance WHERE oidref IN (3396297, 3396059, 3396054, 7880120)

Returns empty.... So maybe there's a missing parent. Let's check h_link

SELECT * FROM h_link WHERE parent IN (3396297, 3396059, 3396054, 7880120) OR child in (3396297, 3396059, 3396054, 7880120)

Which yields no new objects. 3396059 is the top level object and it has no distance measurement.

However, many other objects show up just fine, such as Proxima Centauri (OID = 3379714 )

It's VERY hit or miss where distance measurements exist and where they don't, but it makes it impossible to query objects based on relative distance. I'm guessing that maybe this has something to do with the age of the catalogs or studies which create a new distance measurement. If a catalog is old enough, it probably wasn't digitized or forced into the SIMBAD ADQL model...

Does anybody have some good suggestions on how to get distance data for nearby stars? Preferably something modern, or with the ability to join it to SIMBAD references. I'd like not to have to do a fuzzy join based on RA/DEC or scraping through alternate IDs. That can get messy or break table grain.

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  • $\begingroup$ Is this parallax data ultimately coming from Gaia? If so, the problem may be that Gaia data skips a few hundred of the brightest stars because of instrument limits. $\endgroup$
    – Steve Linton
    Jan 11, 2021 at 14:19

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Well - not sure why distance and parallax tables are empty, but I missed something super simple, the PLX_VALUE column on the BASIC table.

SELECT * FROM BASIC WHERE plx_value IS NOT NULL ORDER BY plx_value DESC

OR convert to distance with D = 1000/PLX_VALUE for dist in parsecs

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  • $\begingroup$ Note that taking the reciprocal of the parallax is a biased estimator of the distance. It should only be used where the uncertainty in the parallax is smaller than about 10%. If not, then there is no simple correspondence between parallax and distance. $\endgroup$
    – ProfRob
    Jan 11, 2021 at 13:51
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Not strictly on-topic, but just in case anyone is interested not so much in the methodology (i. e. querying via SIMBAD) but rather in the result: Using CDS's VizieR-service one can access two relevant catalogues concerning the solar neighbourhood:

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  • $\begingroup$ It's highly relevant because SIMBAD isn't a catalogue that is easy to interpret and using it as a "source" is fraught with difficulties (like this one). $\endgroup$
    – ProfRob
    Feb 26, 2022 at 17:54

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