Celestia Forums

I know there is a possibility that this question has been covered before so, if it has, could someone please direct me to the relevant posting(s), thank you.

I am interested in how Celestia calculates approximate values for the following items when no direct data exists in the star catalogue used (i.e. the Tycho-2 catalogue):

Distance to star
Stellar Type
Size (rSun)
Surface Temperature
Stellar Mass
Rotational Period

I have tried looking at the source code and have a very limited idea, but I have no programming experience and have found it extremely difficult to decipher.

My question is: Can some-one explain to me, in simple, linear terms, the process by which Celestia accomplishes these calculations?

I ask, as I am interested in developing my own personal, searchable star database based on a number of publicly available catalogues (such as the Tycho-2 catalogue).

Many thanks,

Todd P.

Distance to star: as specified in its catalog entry (using trig to convert from parallax to position in space)

Stellar Type: as specified in its catalog entry

Size (rSun): either calculated using Stephan-Boltzmann law and the star's bolometric magnitude (a table lookup based on the star's spectral type and luminosity class), or as specified in its catalog entry, which has priority.

Surface Temperature: table lookup from Stellar Type, using data from Lang's _Astrophysical Data: Planets and Stars_

Stellar Mass: as specified in its catalog entry (but not used for anything)

Rotational Period: table lookup from Stellar Type, using data from Lang's _Astrophysical Data: Planets and Stars_


Celestia's binary star catalog "stars.dat" was created directly from the Hipparcos catalog, not from the extended Tycho catalog. Corrections to mistakes in the Hipparcos catalog are provided in Celestia's textual star catalog "revised.stc".

Thanks Selden,

That's definitely helped put me more in the clear, and onto the right track.

However, my bind is that some catalogues omit parallax and/or spectral type.

I was going to visit Pascal Hartmann's webpage to see if he could help me, as he was the one who compiled the 2 million star database for Celestia from the Tycho-2 catalogue, but his webpage has suffered a case of 'web-rot'.

Once again, thanks for your help.

Todd P

The only substantial professional catalog that I'm aware of that contains both individual distance values and spectral types is the Hipparcos catalog.

A catalog of almost 50 million stars has been generated using SDSS "photometric distances" but their distances are only correct on the average. Individual stars will not necessarily be at the distances attributed to them.

See http://www.arxiv.org/abs/astro-ph/0510520

Todd,
you may also find this site useful:

http://www.astronexus.com/general/data/hyg.php

It contains a number of diffrenet datasets synthesised from Hyparcos (sic), Yale and Gliese 3 catalogues.

Once converted into a useful database format, I've found it rather good (I use it for star-mapping in CHView).

Hope its useful,

Cormoran

Thanks for your help.

I'll be sure to check out these two links you've both provided.

I've been following up on some leads and have found this:

All-sky Compiled Catalogue of 2.5 million stars (Kharchenko, 2001)
VizieR On-line Data Catalog I/280A

This catalogue lists parallax and spectral types, where known.

For those that are interested go to:
http://cdsweb.u-strasbg.fr/viz-bin/Cat?I/280A