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I made an extract of GAIA DR2 data for parallaxes greater than 500mas. Surprisingly I see a very significant number of sources with parallax greater that 1000, making them much closer than Proxima. This should lead to excited newspaper headlines, but i haven't seen those yet... Am I missing something?

You can see my extract of data here:

https://gist.github.com/agnes1/1492e94b5e9c0ef71f6ae7944964b666

Some GAIA source_id rows to look at include:

4039503676370417664

4042946384760661504

4042338732771057920

4046453826887613696

But there are many more. The closest source I find is 4062964299525805952 with parallax of 1851mas. It has a phot_g_mean_mag of 19.63355... Would I be right in assuming this is a brown dwarf?

Another thing I note is that there is a surge of vmag 19/20 sources within 10 parsecs. These are obviously so faint GAIA doe not detect similar sources beyond 10 parsecs. To give some numbers I count 1722 sources (most mag 19/20) within 10 parsecs and only 606 sources in a shell of equal volume beyond that. Again, would these all be (a very large number of) brown dwarfs?

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    $\begingroup$ Have you compared your data with any other sources of information about nearby stellar or sub-stellar objects? Surely this info is abundant on the internet. $\endgroup$
    – user10106
    May 2, 2018 at 7:27
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    $\begingroup$ GAIA DR2 has only been out for a few days. Other parallax surveys (e.g. Hipparchos) have not had the sensitivity to detect such faint sources. Certainly Wikipedia does not mention these nearby objects: en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs $\endgroup$
    – Ags1
    May 2, 2018 at 7:36
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    $\begingroup$ Also note the GAIA DR1 data excluded these faint magnitudes and also excluded nearby objects with high proper motion, so these sources were not in DR1 either. $\endgroup$
    – Ags1
    May 2, 2018 at 10:01

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These are spurious data points. They are likely genuine objects, but the parallax value is incorrect. There are a small number of these in the Gaia data set.

There are 59 object with a parallax greater than Proxima Centuri. These don't represent genuine objects, instead they are when two sources are closely aligned (within about 0.2 arcsec). Most of these are found in the milky way, where there are lots of stars close together.

See https://www.cosmos.esa.int/web/gaia/forum#!/thread/1688565/1688576

And section 9 of https://arxiv.org/pdf/1804.09365.pdf

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    $\begingroup$ Yes, it is explained in this paper: arxiv.org/pdf/1804.09366.pdf. The advice is basically to ignore all faint high-parallax sources. $\endgroup$
    – Ags1
    May 2, 2018 at 18:57
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    $\begingroup$ Can you summarise the content in the link. $\endgroup$
    – James K
    May 3, 2018 at 16:40

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