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Characterizing Star Temp with Color Camera

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#1 garyhawkins

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Posted 04 March 2021 - 03:07 PM

Typically, star temp is characterized by taking measurement using photometric filters and then calculating GBp-GRp or similar and relating that back to star temperature either with a lookup table or formula.

 

Being new to photometry, I don't have a standard set of filters, or a mono camera for that matter.  I have a ZWO ASI533MC.  This camera has the following spectral response.

 

IMX533 Spectral Response.jpg

 

This spectral response is not so different from Johnson-Cousins B, V, R filters, particularly if you have a UV/IR cut filter to limit out-of-band response.

 

Thus, I wonder if I could use the image data from my 533 to determine star temp, but separating images into R, G and B channels and, after appropriate normalization, determine if there was a relationship between Blue ADU (norm) - Red ADU (norm) and star temp.  Early results look promising:

 

Color_Temp.PNG

 

Clearly, I need a lot more data to be sure.

 

Has anyone else looked at this or is aware of work looking at this?

 

CS Gary



#2 AstroBrett

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Posted 04 March 2021 - 03:22 PM

The passbands on the photometric filters are much narrower with significantly less overlap than the filters in the Bayer array. In practice, you would be able to determine a general correlation as you have already seen, and that would give you a general idea for most situations. What you will find is there will be the occasional data point which will give results wildly divergent from the accepted values, so as long as you keep the caveats in mind, you should be OK.

 

Looking at your data, you already have one example of the potential problems, where the star shown at a temperature of 4000 degrees is well off your regression line, to an extent in excess of half of the range. These sorts of anomalies will occur since the Bayer passbands are both wider and overlap to a larger extent than do the J-C photometric filters. 

 

Brett


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#3 robin_astro

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Posted 05 March 2021 - 10:51 AM

spectroscopic measurements are the definitive way of measuring Teff but in the absence of interstellar extinction which can significantly affect the result you should be able to generate a correlation. (B-V is normally used). Here for example is the relationship between spectral class and photometric colours for various filters for main sequence stars

https://www.stsci.ed...nr/intrins.html

and the relationship between spectral class and effective temperature

https://sites.uni.ed...ctraltemps.html

 

Cheers

Robin


Edited by robin_astro, 05 March 2021 - 10:59 AM.

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#4 garyhawkins

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Posted 05 March 2021 - 02:00 PM

Many thanks for this information.  The reason I chose GBp-GRp was because it corresponded to by V17 Mag/Color database within ASTAP.  That being said, all of these combinations work, so I'll try some others.

 

spectroscopic measurements are the definitive way of measuring Teff but in the absence of interstellar extinction which can significantly affect the result you should be able to generate a correlation. (B-V is normally used). Here for example is the relationship between spectral class and photometric colours for various filters for main sequence stars

https://www.stsci.ed...nr/intrins.html

and the relationship between spectral class and effective temperature

https://sites.uni.ed...ctraltemps.html

 

Cheers

Robin



#5 robin_astro

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Posted 05 March 2021 - 03:42 PM

This reference pulls it all together (for main sequence stars at least) and is very current having been updated only a couple of days ago

http://www.pas.roche...colors_Teff.txt

 

 

Cheers

Robin


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