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>>>>>>Over the last several years I have made scattered observations of the SR variable T CMa. This star is plotted on VSS RASNZ charts 987/988 for VY CMa and has a catalogue range of 9.5 to 11 and period 309 days but no spectrum indicated. My observations have shown little variation, ranging between 11.2 and 12.0. Intrigued by a lack of variation in my observations, I recently checked both the vsnet and AAVSO light curves for T CMa and was surprised to find it being recorded by other observers mostly between magnitudes 9 and 9.5. A check of the AAVSO chart for VY CMa shows T CMa plotted but this chart does not plot a magnitude 9.2 field star 2 arcmin SW of the variable. This chart is probably not intended for observing T CMa and I suspect the observations in both the vsnet and the AAVSO refer to the field star and not T CMa. If my suspicians are correct, this still leaves a question over the true variations of T CMa.<<<<< Peter: You are absolutely correct: the star we've been observing is GSC 6541 1249, and the low level of variation reported is explained with it non being a variable star ;-(( I also made scatter observations of this field and estimated what I thought it was T CMa every time I observed VY CMa. Since the AAVSO chart identified the 9th mag. star with T CMa, I never suspected anything unusual, but T CMa being a very low amplitude variable star. I must confess I never took a proper look at its color (I wasn't too involved with this isuue when I started observing it). From Tycho-2 (Bessell-reduced) data its B-V is 0.65. Brian wrote: > My suggestion would be that the nominal variability that led to > the designation is completely spurious and comes from the vagaries of > the mixing of visual and photographic data when the whole business was > very poorly understood. Tellingly, the 'GuL' has only one other set > of just six observations (by Hoffmeister) in later volumes, suggesting > the star was of no interest to any one, probably because it isn't > variable---or not variable in the way stated. > The modern photometric data (specifically Tycho-2 and 2MASS) > indicate a little-reddened star near A0. Such a star might have > variations of very small (~0.01 mag.) amplitude, but not likely with > the couple-magnitudes and 300-day period suggested a hundred years ago. > I presume this star is in the comfortable range of brightness for > ASAS3, which (I fearlessly predict) will show the star to be constant. I support this conclussion since there is no red star in the area, which arises the question of how some published data come to be published. I am compiling a catalogue of corrected data and I can tell you I get a new surprise every day. I can see some kind of rush in publishing conclussions when -evidently- the amount of data are not enough to establish them. ASAS-3 data for the two stars involved: GSC 6541 1249 V= 9.20 (+/-0.02) constant. GSC 6541 1273 V= 10.90 (+/-0.07) constant? ( the proximity of GSC 6541 82 makes the data unreliable due to ASAS-3 pixel resolution) I think a misidentification caused the maximum magnitude was established with GSC 6541 1249, and the minimum with GSC 6541 1273. The feeling when this cases turn up is that there may be lots of cases when we still observe the wrong star or a constant star wrongly identified as a variable. Good for Peter for this finding! Regards, Sebastian.
Return to the Powerful Daisaku Nogami
vsnet-adm@kusastro.kyoto-u.ac.jp
