Re: [Celestia-developers] Fixes to the star database

[Andrew T. <ajt...@go...>]

On further research, a large number of those stars are in open
clusters, so I've used WEBDA distances to the appropriate clusters for
them. Two others I resorted to Tycho parallaxes - the errors are large
enough to be useless, but the luminosity seems to work out fairly
reasonable for the spectral types.

Andrew

2009/2/1 Andrew Tribick <ajt...@go...>:
> Ok I changed the RA/Dec limit to 25 mas because it felt slightly wrong
> to exclude Alpha Centauri B. The question is what to do about the
> various bright (Vmag<6) stars that get rejected. Not implementing them
> at all seems unsatisfactory (as an example of where not including them
> causes problems, the rejected star Beta Phoenicis is part of the
> constellation drawing for Phoenix).
>
> What I have done is to take the parallax with the lowest fractional
> uncertainty from the HIP1 and HIP2 catalogues and used that to create
> an entry in revised.stc, provided that the parallax is greater than
> 0.2 mas. For the most part this seems to result in reasonably
> appropriate luminosities for the spectral types. There are however a
> few cases where this fix is not possible: these are:
>
> HIP 21148 - (1 Cam) - Vmag=5.78 - both parallaxes negative
> HIP 41074 - Vmag=5.88 - both parallaxes negative
> HIP 51192 - Vmag=4.65 - HIP1 negative; HIP2 = 0.06 +/- 0.28
> HIP 62931 (Kap Cru) - Vmag=5.89 - both parallaxes negative
> HIP 67861 - Vmag=5.83 - both parallaxes negative
> HIP 81702 - Vmag=5.57 - both parallaxes negative
> HIP 88298 - Vmag=5.72 - both parallaxes negative
> HIP 89341 (Mu Sgr) - Vmag=3.84 - HIP1 = 0.11 +/- 0.98; HIP2 = 0.09 +/- 0.28
> HIP 89439 (15 Sgr) - Vmag=5.29 - HIP1 negative; HIP2 = 0.1 +/- 0.45
> HIP 89440 (16 Sgr) - Vmag=5.96 - both parallaxes negative
>
> Not sure what to do about these.
>
> Andrew
>
> 2009/1/31 Andrew Tribick <ajt...@go...>:
>> Following discussion with Fridger on the forums, I have revised the
>> rejection criteria used in building the star database. Instead of
>> trying to use a graded system to reject the stars, I am now using hard
>> cutoffs: stars are now rejected if they fail any of the following:
>>
>> 1. Magnitude information must be present.
>> 2. The parallax must be greater than 0.2 mas.
>> 3. The error in the parallax must be less than the parallax itself.
>> 4. The error in the position, given by Sqrt((e_RA*cos(Dec))^2 +
>> e_Dec^2) must be less than 20 mas.
>>
>> The values of 0.2 mas and 20 mas were chosen because those values were
>> used as grade boundaries in the original database generating code
>> (buildstardb.cpp).
>>
>> If anyone wants to suggest revisions to the criteria, it would be
>> better to have this sooner rather than later.
>>
>> Andrew
>>
>