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Looking for spectra of SAO 138885 & 138886

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#1 ssmith

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Posted 06 June 2020 - 01:05 PM

I have been looking at Color Contrasting double stars and comparing their color differences to their differences in their spectral types.  When I plot these differences there is a reasonable correlation as seen below.  One of my data points is the optical pair S639 in Virgo which is a clear outlier looking at my plot and I suspect the spectral class of the magnitude 10 secondary which is listed as K0 in Simbad is in error.  Looking at my photos and its color index I suspect it is at least a late F or early G star. Sky Safari lists the spectra of the primary as M0 III which also makes the spectral difference a bit greater but this measurement was from 1926.  Is there a chance that someone here with a spectrograph could take a look at the spectral class of these two stars?  

 

S 639 Vir data.jpeg

 

120mm 5-11-17 237 small.jpg

 

Spec vs Color.jpeg


Edited by ssmith, 06 June 2020 - 01:47 PM.

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#2 NJScope

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Posted 08 June 2020 - 07:18 AM

Steve:

I couldn't find any spectra for either star at the LAMOST DR5 site, however photometric data from the APASS (B-V=0.559) and 2MASS (B-V=0.564) catalogs would suggest that SAO 138886 is a late F or early G class star.   In addition,  these results are supported by Gaia DR2 where Teff for SAO 138886 is estimated to be 5756 K, a value consistent with an early G class star.



#3 robin_astro

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Posted 08 June 2020 - 10:12 AM

Also total galactic extinction is low in this direction with E(B-V) ~0.03 so B-V should be a reasonable indicator of temperature

 

Robin



#4 NJScope

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Posted 08 June 2020 - 02:08 PM

Robin:

 

Yes, I should have added that information.   Considering it's Bailer-Jones derived distance is very close (~134 pc), the Amores and Lepine  model (ALextin), which factors in distance, estimates that E(B-V) is even smaller (~0.007).   


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#5 ssmith

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Posted 08 June 2020 - 06:28 PM

Kevin & Robin  -

 

Thanks for your input.  I revised the spectral types for S639 based on your inputs and here is the revised plot.  S639 falls into place.  I may redo the entire plot and use the difference in Teff instead of Spectral Type and see what that reveals.

 

Spec vs B-V rev1.jpg




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