Updated stars.dat including Gaia DR2 data (update 2020-11-30)

[ajtribick]

Quick guide on how to check these kind of issues:

Go to the SIMBAD Query by identifier page, query for "alf Cas"
This brings up the entry for the star.
Near the bottom of the page there is a section called "External archives". This lists the star's entry in various catalogues.
Click the link titled Gaia DR2 418551920279473536.
Take a look at the parallax listed there (and its error). This might give you some idea of what's going on.

Note that the distances in stars.dat are not simple 1/parallax. For Gaia stars, the relevant catalogue is the Gaia Geometric Distance Catalogue, which can be queried on the Gaia Archive website.
Click Search, then select "Advanced (ADQL)".
Enter the following query

Code: Select all

SELECT *
FROM external.gaiadr2_geometric_distance
WHERE source_id = 418551920279473536

You will see a result with 1 row. There is a small icon which looks like a table, which shows a tooltip "Display top 2000 results". Click it.
Take a look at the value in the r_est column, which contains the estimated distance in parsecs.

Spoiler

The Gaia DR2 parallax for this star is really bad, probably because it's a bit too bright for Gaia to measure reliably, at least using the Gaia DR2 pipeline.

[DrJMOS]

Hi Ajtribick

You will see a result with 1 row. There is a small icon which looks like a table, which shows a tooltip "Display top 2000 results". Click it.
Take a look at the value in the r_est column, which contains the estimated distance in parsecs.

...is done

mean 1.3737 kpc is true?

Ajtribick, do you know a script to mark all O-B type stars of your addon too?

Added after 4 hours 50 minutes:
I found Kaus Media star distance to 4346 parsec and Garnet Star at 3070 parsec in Gaia DR2 but i can not find in Gaia DR2 to the next stars:

Aludra
Aspidiske
HD 105435
30 CMa

[ajtribick]

mean 1.3737 kpc is true?

I see you didn't check what was inside the spoiler tag...
Gaia cannot measure the brightest stars, and of the ones it can measure the bright ones tend to have fairly unreliable parallaxes. Since at the moment I only take the XHIP distances if there is no Gaia parallax, stars like Alpha Cassiopeiae and Delta Sagittarii end up being placed at distances computed from the unreliable Gaia parallax.

Ajtribick, do you know a script to mark all O-B type stars of your addon too?

No, but this should be fairly straightforward to implement. I leave it as an exercise for the reader

[DrJMOS]

No, but this should be fairly straightforward to implement. I leave it as an exercise for the reader

Yep! very helpful to fix arms of the Milky Way viewtopic.php?f=5&t=20576

[ajtribick]

I've released a new version v1.0.4 which uses relative parallax error to choose between Gaia DR2 and XHIP parallaxes (this affects the cases of Alpha Cas and Delta Sgr mentioned by DrJMOS, they should be back at more reasonable distances). This affects 1787 stars out of a total 2499574. There's also some refactoring of the code involved but that's not particularly relevant for actually using the data files.

See the top of the thread for the link.

(This is still compatible with pre-1.6.2 Celestia)

[DrJMOS]

I've released a new version v1.0.4 which uses relative parallax error to choose between Gaia DR2 and XHIP parallaxes (this affects the cases of Alpha Cas and Delta Sgr mentioned by DrJMOS, they should be back at more reasonable distances). This affects 1787 stars out of a total 2499574. There's also some refactoring of the code involved but that's not particularly relevant for actually using the data files..

Hi Ajtribick,

Thank you, great fix, works better!!!

[Art Blos]

DrJMOS < What are these red marks in the screenshot?

[DrJMOS]

DrJMOS < What are these red marks in the screenshot?

Hi Art Blos, red marks is a custom adaptation of the original addon Graticules of Selden Ball to see distances inside the Milky way in light years in galactic plane (graticule of 1 ly to 200000 ly). Beyond the galaxy continue the distances with council of giants ring (yellow circle) and Redshift distances z=0.01 to z=1000 (in red circles onto edge of Planck background)

https://www.classe.cornell.edu/~seb/celestia/graticules.html#4

[Art Blos]

Hi Art Blos, red marks is a custom adaptation of the original addon Graticules of Selden Ball to see distances inside the Milky way in light years in galactic plane (graticule of 1 ly to 200000 ly). Beyond the galaxy continue the distances with council of giants ring (yellow circle) and Redshift distances z=0.01 to z=1000 (in red circles onto edge of Planck background)

Can you share your version?

[DrJMOS]

Can you share your version?

of course, I'll create a new post: viewtopic.php?f=23&t=20629

[ajtribick]

A quick update with regards to the now-released Gaia EDR3.

The process I'm using to generate stars.dat relies on several sources external to the Gaia release itself, including:

• The geometric distance catalogue, that estimates the distances with an exponentially-decaying distance prior based on a galactic model rather than a simple 1/parallax calculation.
• More complete cross-matches to HIP2/TYC2 than the cross-match tables included in the Gaia releases. A quick check of the number of entries in the gaiaedr3.hipparcos2_best_neighbour table shows it is more complete than DR2, but it still falls short of the source I'm actually using for the cross-match.

Equivalent sources for Gaia EDR3 do not exist yet, so I'm not going to be creating an EDR3-based stars.dat in the immediate future.