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R. Wasatonic, E. Guinan, S. Engle (Villanova University)
TV Gem (HD 42475) is a semi-regular M1 Iab supergiant accompanied by a less luminous B3.5 IV companion. The star is a bright (V = 6.2 to 6.8) member of the Gem OB1 Association at a distance of ~1.2 kpc. Recent lunar occultation interferometric K-band observations by Mondal and Chandrasekhar yield an angular diameter of 4.46 ± 0.07 mas and show the presence of two dust shells located at ~13 and ~500 stellar radii from the star. Since 1997 we have been carrying out intensive V-band and narrow-to-intermediate band Wing near-IR (712 nm, 754 nm, and 1040 nm) photometry. This photometry indicates, for the first time, the presence of a long-term period of ~6.16 years and the more familiar lower amplitude semi-regular (350-450 d) brightness changes. Variations in the molecular TiO \gamma (0,0) 719 nm band strength are determined from the near-IR observations, and yield spectral type changes from M1 (Teff ~ 3750K) at maximum light to M3 (Teff ~ 3450K) at minimum light. A near-IR color index and the TiO strengths are also used to estimate effective temperature, luminosity, and radius variations throughout the pulsational cycles. These variations indicate that TV Gem pulsates in the fundamental mode globally with the observed 6.16 year period. However, the year-by-year light variations are more complex, implying that on smaller local atmospheric scales TV Gem does not follow simplified models of a spherically symmetrical pulsating star. The overall photometrically determined mean values of Teff, Luminosity, and Radius are -- Teff ~ 3600K, L ~ 80000 Lsun, and R ~ 700 Rsun. The observed long-term variation patterns and calculated ranges of these parameters may provide deeper insights into pulsational theories of TV Gem in particular and luminous M-types supergiants in general.
This research is supported in part by NSF/RUI Grants AST-0507542 and AST-0507536 which we gratefully acknowledge.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.