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From John Greaves: === Taichi Kato commented / asided : > # From John Greaves. It seems to me quite a few people has taken his words > # too seriously. I must comment before forwarding that this kind of analysis > # can easily be too speculative, and should better regarded as a simple > # number trick before more substantial evidence becomes available. > # Please don't attempt to write a flash news entitled: > # "Astronomers discovered an unreasonably luminous object potentially > # associated with transient X-ray emission of unknown origin" ;-) Right then... I can readily agree with the sentiments expressed above, but I've got to have a semantic quibble about the use of the word 'trick'. A trick is a deception, a slight of hand, an attempt to misdirect away from reality. Granted, I was loosely juggling numbers with no great precision, but using U-B as balmer line intensity index and any index between V and J, possibly even H, as a temperature index, both being behaving independently to reddening, is an acceptable means of astrophysically assessing the spectral type of a star. An excess of J-Ks is an astrophysical means of noting that there is a greater flux in this bandpass than can be attributed to the black body curve of the star alone, and is often (though probably not universally) attributed to being actually from the black body curve of matter circumstellar to that star. Distance modulus is standard stuff, interstellar absorption and typical absolute magnitudes for spectral types and classes of stars are well reviewed and pretty much at the consensus level. The hard evidence from the Henden U-B and B-V data, and, the J-Ks excess evidence and the above noted accepted consensus on some things state this star is a B type star with near infrared excess. Whether it is anything more exotic than that is, as noted in the opening quoted comments, a matter for further study, primarily via fresh observation. I completely agree on that. Not a big point (this email probably reads more pedantic than it's meant), and as I say, a semantic quibble more than anything, but the word 'trick' suggests false, which is just as bad as people interpreting the case as proven. Certainly, more work is needed now, if only to be able to remove the object from candidacy, because now it can't be readily dismissed. Incidentally, I didn't mention that I 'control experiment' assessed the candidate object's result by looking at a relatively nearby equally red star. There 'Q' and J-Ks agreed on that object being a late K type star. When looking at an object, I always like to get the feel of the quality of data for the local field. The assessment I made was a quick look one, based on valid principles. However, in detail it is sensitive to the quality of the measurements, the biggest one of which (and the one I failed to mention) being the complete lack of decent astrometric constraints. Integral error boxes may be relatively small nowadays compared to past instances for such discoveries, but when you are staring directly down to the Galactic Centre the sheer increase in coincidental line of sight objects can more than make up for that. More on this separately. Cheers John
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