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Star Magnitude Discrepancy

I'm compiling a carbon star list in SS. Can you explain why the visual magnitude for the stars is different to the magnitude range listed in the variability data section. For example TT Tauri has a visual magnitude of 8.02, but a listed magnitude range of 10.2 to 12.2. Carbon stars are variable and hence that's why they have a magnitude range, but why is the visual magnitude and the magnitude range so different. Is the magnitude range measured in the photographic/blue part of the spectrum, and that's why it is fainter than the visual magnitude.  

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    Bill Tschumy

    Allan,

    I asked Tim about this.  He is the one that actually compiles the database we from various catalogs.  His response:

    "The numbers probably come from different catalogs.  The range comes from the GCVS.  The magnitude itself comes from hipparcos/tycho (if the star is bright enough) or GSC.  You'd probably have to look at each one on a case-by-case basis.  The tycho/hipparcos visual magnitudes are all from the visual (V) part of the spectrum and are probably very reliable.  The GCVS magnitude ranges are probably more suspect.  Yeah, this one does seem like a bigger discrepancy than most."

    In the process of creating SkySafari, we have found the professional catalogs are filled with all sorts of errors.  This could just be one of them.  We generally use the catalog "as is" and don't try to make small corrections to them as that would be a never ending task.

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    Allan Wade

    Thanks Bill. I did some more digging today, and I found some research papers on some of these carbon stars. I found the variable magnitude range as listed for the star in Sky Safari is exactly the same as the photographic magnitude listed in the research paper. I think its safe to conclude that the reason for the different magnitude listed for the same star is that one figure is for the visual magnitude and the other is for the photographic magnitude.    

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    Bill Tschumy

    So, I guess the GCVS catalog must have use the photographic range in this case.  I don't think that is normally the case.  Thanks for digging into it.

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