An error in extrasolar.stc

Cham · Post #1by **Cham** » 12.03.2007, 01:36

I've found something weird, in the extrasolar.stc file. There's a white dwarf with a radius of ... 4236 Sol ! The exoplanet orbiting it is VERY close to the star :

I think the absMag is wrong.

Cham · Post #2by **Cham** » 12.03.2007, 01:46

Hmmm, I'm not sure anymore it's an error in the stc file. May be a conflict with something else. I'll have to investigate. Sorry.

Cham · Post #3by **Cham** » 12.03.2007, 02:22

There's definitely something terribly wrong.

I desactivated ALL my extras (placing the entire folder somewhere else on the HD), and the problem is still there.

If I change the SpectralType "D" to SpectralType "WD", in the extrasolar.stc, I get a tiny white dwarf of about 600 km radius !!

Please, is someone else can confirm this with the latest CVS Celestia ?

I recall it's about the WD J1623-266/PSR 1620-26 B/PSR B1620-26 B/PSR J1623-2631 B. It's a white dwarf orbiting a pulsar, and there's an exoplanet orbiting around them.

Post #4by **ElChristou** » 12.03.2007, 02:36

I confirm the issue...

Cham · Post #5by **Cham** » 12.03.2007, 02:37

ElChristou wrote:I confirm the issue...

!! OMG !!

Johaen · Post #6by **Johaen** » 12.03.2007, 03:27

I can confirm that it's not an issue with (atleast my install of) Celestia 1.5.0pre2.

A quick check of extrasolar.ssc shows:

Code: Select all

"WD J1623-266:PSR 1620-26 B:PSR B1620-26 B:PSR J1623-2631 B"
{
   ...
   SpectralType "D"  # white dwarf
   ...
}

revent · Post #7by **revent** » 12.03.2007, 04:08

This 1996 article http://www.journals.uchicago.edu/ApJ/journal/issues/ApJL/v473n2/5453/sc0.html gives a V of 21.3 for the white dwarf.

Post #8by **chris** » 12.03.2007, 06:24

It's a bug that I introduced when I added bolometric corrections for white dwarf magnitudes. The temperature of a white dwarf with an unspecified temperature code was getting set to a nonsense value. I've committed the one-line fix to CVS, and the calculated radius of PSR 1620-26 B is now a much more reasonable value. Cham, thank you for reporting this bug.

--Chris

Cham · Post #9by **Cham** » 12.03.2007, 06:29

Thanks Chris,

Post #10by **granthutchison** » 12.03.2007, 21:39

Cham PMed me about this while he thought there was a problem with the stc itself.
The AbsMag for this object was just tweaked in order to come up with a reasonable radius under Celestia's previous code (which we know tends to produce excessively small white dwarfs because of the absent bolometric correction).
It'll probably need retweaked under the new code.

Grant

Post #11by **granthutchison** » 12.03.2007, 22:01

Cham wrote:If I change the SpectralType "D" to SpectralType "WD", in the extrasolar.stc, I get a tiny white dwarf of about 600 km radius !!

IIRC, adding the initial W makes Celestia parse the object as a Wolf-Rayet star, which is why you get the sudden change in radius ...

Grant

Post #12by **chris** » 12.03.2007, 22:34

granthutchison wrote:
Cham wrote:If I change the SpectralType "D" to SpectralType "WD", in the extrasolar.stc, I get a tiny white dwarf of about 600 km radius !!
IIRC, adding the initial W makes Celestia parse the object as a Wolf-Rayet star, which is why you get the sudden change in radius ...

I'm guessing that the star is too far away (12400 ly) to be detected optically, forcing us to invent a plausible magnitude. I could modify Celestia to automatically compute the brightness from the radius and temperature when a magnitude isn't specified, but PSR 1620-26B seems like a pretty rare case.

--Chris

revent · Post #13by **revent** » 14.03.2007, 07:58

chris wrote:I'm guessing that the star is too far away (12400 ly) to be detected optically, forcing us to invent a plausible magnitude. I could modify Celestia to automatically compute the brightness from the radius and temperature when a magnitude isn't specified, but PSR 1620-26B seems like a pretty rare case.

The article link I posted earlier is from an optical separation of the system. It was done with a 3.5m active optics telescope, though. Wish I had one of those in my backyard.

Hungry4info · Post #14by **Hungry4info** » 14.03.2007, 22:34

(off topic) The image you provided shows the PSR B1620-26 system inside the M4 Cluster, or at least within a dense star area. In my version of Celestia, the cluster is not given. Are the stars based on real data? If so, where can I obtain an STC for them?

Cham · Post #15by **Cham** » 14.03.2007, 23:50

Hungry4info wrote:(off topic) The image you provided shows the PSR B1620-26 system inside the M4 Cluster, or at least within a dense star area. In my version of Celestia, the cluster is not given. Are the stars based on real data? If so, where can I obtain an STC for them?

The stars in M4 are all fakes. They comes from Rassilon M4 addon, who made it using one of his generators.