Deriving Stellar Tempreture

[bigbluestar]

I have run into another selfteaching astronomy problem. Please correct were I am wrong because its not a matter of if. Now one method used to inicate stellar tempreture is by its coulour index. I'v been using the B-V index. Now weather I am using charts or using
B-V = -3.684 log(T) + 14.551
for log(T) < 3.961
B-V = 0.344 [log(T)]^2 -3.402 log(T) +8.037
for log(T) >3.961
Now these equation work great except sometimes I come across stars that don't quite make sense. I'm sure there is a reason I just have not come across one. Here is an example

Enter WR142 at 20:21:44.22 +37:22:30.7
Note the designation WR. Yes ladies and gents its a Wolfe Rayet star.
Well here is the problem Sinbad records its B-V as 1.43. That effectivly puts the stars tempreture at 3,644 kelvins. Well last time I check these things burn in excess of 40,000 kelvins.

Well I know what your saying well you should use more sources like a good astronomer. Well I did here are some other sources
Lick NPM2 Catalog reads the same star as B-V = 1.47 mag
7th Catalog of Galactic Wolf-Rayet stars reads B-V = 1.39 and a follow up observation of 1.38 all within reasonalbe range but none close enough to reach a tempreture of over 40,000k so were am i going wrong

Thank you in advance Please help me out self teaching bites....

[ngc3314]

I have run into another selfteaching astronomy problem. Please correct were I am wrong because its not a matter of if. Now one method used to inicate stellar tempreture is by its coulour index. I'v been using the B-V index. Now weather I am using charts or using
B-V = -3.684 log(T) + 14.551
for log(T) < 3.961
B-V = 0.344 [log(T)]^2 -3.402 log(T) +8.037
for log(T) >3.961
Now these equation work great except sometimes I come across stars that don't quite make sense. I'm sure there is a reason I just have not come across one. Here is an example

Enter WR142 at 20:21:44.22 +37:22:30.7
Note the designation WR. Yes ladies and gents its a Wolfe Rayet star.
Well here is the problem Sinbad records its B-V as 1.43. That effectivly puts the stars tempreture at 3,644 kelvins. Well last time I check these things burn in excess of 40,000 kelvins.

Well I know what your saying well you should use more sources like a good astronomer. Well I did here are some other sources
Lick NPM2 Catalog reads the same star as B-V = 1.47 mag
7th Catalog of Galactic Wolf-Rayet stars reads B-V = 1.39 and a follow up observation of 1.38 all within reasonalbe range but none close enough to reach a tempreture of over 40,000k so were am i going wrong

Thank you in advance Please help me out self teaching bites....

Two things to watch out for:

The (B-V) value can be increased (reddened) by intervening dust. Photometry over a wide wavelength range or spectroscopy are needed to tell when this is an issue.

Also, WR stars have as their defining characteristic strong emission lines from the stellar winds, and these can be strong enough to affect their brightnesses in some filters. The emission lines are formed elsewhere than in dense media in thermodynamic equilibrium (to which the photosphere itself is a rough approximation), so their radiation does not follow the blackbody-like usual relation between color and temperature.

[Tim Thompson]

Check the source for your color index formulas. Maybe they only work for main sequence stars?

[bigbluestar]

Two things to watch out for:

The (B-V) value can be increased (reddened) by intervening dust. Photometry over a wide wavelength range or spectroscopy are needed to tell when this is an issue.

Also, WR stars have as their defining characteristic strong emission lines from the stellar winds, and these can be strong enough to affect their brightnesses in some filters. The emission lines are formed elsewhere than in dense media in thermodynamic equilibrium (to which the photosphere itself is a rough approximation), so their radiation does not follow the blackbody-like usual relation between color and temperature.


I see..... that explains it. I was doing similar work on a cluster of stars and when I compared them to there known stellar tempreture they were all off by the same amount. While the same formulas would work perfectly for many other stars. Thank you now another question for you. I have difficulty finding full spectra for stars excpecially non famous stars. Photometric data is no problem though so my question is if I were to use say anyother bandpass U B V R I J H K L that might have a similar formula to compensate for the reddning.
BTW hay is getting spectrums so difficult. I mean everything else is so available freely on the public domain. Even data retrieved from the most modern and most expensive projects are available free but not spectra? I know they exist because the phometric data was was gained from it and so much more spectrum related information you can find. But they keep the actuall Image or the graph interpretation of it sshhhh

Anyways if anyone knows how to either sovle my reddening problem by using other means of examining the spectra of the star, or if you know of a data base that has spectra many stars I would reeeaaaaaalllllllyyyyyy apreciate it

-----Tim Thompson---- I thought that might have been a problem too so I had checked charts that made predictions on the coulor index to tempreture and referenced it with the formula and they were dead on. I also checked several references of these said charts. NGC3314 I think sumed it quite up with this reddening effect.

[Ken G]

Anyways if anyone knows how to either sovle my reddening problem by using other means of examining the spectra of the star, or if you know of a data base that has spectra many stars I would reeeaaaaaalllllllyyyyyy apreciate it.
I don't know how you can de-redden your B-V, but I can tell you that the winds described by ngc3314 make it very difficult to interpret temperatures of Wolf-Rayet stars. In fact, if you can determine the photospheric temperature of that object, I would say that you have a publishable research result!