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 Post subject: Star colours
PostPosted: Wed, 17-07-19, 18:52 GMT 
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Joined: Mon, 07-01-08, 13:30 GMT
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Location: Switzerland
Playing around with Burnashev et al. (1985)

Chromaticity plots - horizontal and vertical axes are chromaticity x, y repsepctively. Major ticks = 0.1.
The outer curve represents monochromatic spectra, the ends joined by the line of purples (dotted line). The triangle represents the range of sRGB. The curve going through the middle represents the Planckian locus. D65 is represented by a cross.

By spectral type: Red = M, Blue = O
Attachment:
spectralTypes.png
spectralTypes.png [ 90.41 KiB | Viewed 1032 times ]


By luminosity class Blue = subdwarf, Magenta = supergiant. (Prefixes mapped: sd = VI, d = V, g = III, c = I)
Attachment:
luminosityClass.png
luminosityClass.png [ 88.22 KiB | Viewed 1032 times ]


Still to come: carbon stars (need to update the spectral type parser a bit).


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 Post subject: Re: Star colours
PostPosted: Wed, 17-07-19, 19:57 GMT 
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Interesting!

I'll get to it tomorrow.

Actually, in the past, I have done a lot of work with star colors for globulars and halo stars around galaxies (faintstars.cpp)


There were months of pure astrophysical research before I was ready for coding ;-). In order to get the subtle star colors and the luminosity distributions right for the 157 globulars, a lot of high-tech analysis with Maple was required:

First of all, here is the long list of clickable scientific papers about globular cluster data and theoretical issues that entered my underlying analysis:

http://www.celestialmatters.org/users/t ... apers.html
Click on titles NOT on filenames!

Furthermore, here are just two extensive, well-commented Maple worksheets that should provide a good impression about the kind of underlying research work...

http://www.celestialmatters.org/users/t ... s_King.pdf

Here one task was to work out via least-square fits an analytical form for the luminosity function of globular clusters, with data taken from various Hubble telescope measurements. A subsequent task was to find a universal scaling prescription for the individually measured V-I Color-Magnitude-Relations(CMR), after reddening corrections were subtracted. The final aim was to obtain a simple and fast color description of ALL globulars in terms of relatively few parameters...This effort was actually successful.

In the second worksheet,

http://www.celestialmatters.org/users/t ... itting.pdf

I performed a new least-square fit of the simple yet accurate and fast King profile to the brightness measurements for about 85 globulars, with the resulting best-fit parameters being directly written into the 'globulars.dsc' data file. For each globular cluster you see two plots in the worksheet: one from before the fit and one displaying the improved matching after the fit! The improvement in realism was quite dramatic altogether.

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 Post subject: Re: Star colours
PostPosted: Fri, 19-07-19, 19:50 GMT 
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The carbon star spectral types correspond to the same temperatures as G4-M giants.

Carbon stars (red)
S-type stars (orange)
G4-M giants, bright giants, supergiants (blue)

Attachment:
carbonStars.png
carbonStars.png [ 82.22 KiB | Viewed 994 times ]


The carbon stars appear to be notably redder than the equivalent oxygen stars, which suggests that we should not necessarily use the blackbody colour corresponding to the same effective temperature.

There are two Wolf-Rayet stars included, one each from the WN and the WC categories. In the following, the WN is blue, WC is red:

Attachment:
wolfRayet.png
wolfRayet.png [ 75.67 KiB | Viewed 994 times ]


The WN star appears to be a fairly reasonable blackbody, the WC star is not. It would be useful to know whether or not this is just a problem with the data in the source, more optical spectra of Wolf-Rayet stars would be useful, also including the WO class.


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