Rick Wasatonic

Wing Near-Infrared, TiO-Band, and V-Band Photometry of Chromospherically Active Star λ Andromedae

As a pilot program, Wing near-IR, TiO-band, and V-band photometry is being conducted of the RS Canum Venaticorum type, chromospherically active, G8 IV–III star λ Andromedae. The objective is to investigate a possible relationship between variation of the ~54 day rotationally starspot modulated visual light curve and TiO absorption strength. The TiO (γ, 0, 0) absorption band strength at λ = 719 nm is very sensitive to temperature for cool stars and manifests itself in cooler starspot regions (T ≤ 4000 K). TiO photometry has an advantage over conventional photometry in that it provides unambiguous measures of the fractional cool starspot coverage. In addition, as the stars rotate, the variation in the TiO index yields information about the longitudinal distribution of the starspots. Importantly, combining the TiO photometry with the V-band and near-IR light curves allows the discrimination of white-light faculae (=hot spot) and cool starspot contributions. Initial results of this study indicate that the observed V-band and near-IR continua light variations found for λ And primarily arise from bright spot (plage) features rather than dark starspots as is usually assumed. This is in contrast to current theories that the visual light variation is solely due to dark spots. Models using both bright and dark spot features have been developed and are being used to fit the light and TiO-index curves. The models account for cool/hot spot characteristics such as projected filling factor and temperature. The long-term variation of V light and TiO index have been investigated to search for any activity cycles.

THE AGE AND MASS OF THE α HERCULIS TRIPLE-STAR SYSTEM FROM A MESA GRID OF ROTATING STARS WITH 1.3 ⩽ M/M ☉ ⩽ 8.0*

?1 Her is the second closest asymptotic giant branch (AGB) star to the Sun, and the variable luminous M5 Ib-II member of a triple-stellar system containing G8 III and A9 IV-V components. However, the mass of this important star was previously uncertain, with published values ranging from ~2-15?M ?. As shown by this study, its fortuitous membership in a nearby resolved triple-star system makes it possible to determine its fundamental properties including its mass and age. We present over 20?years of VRI photometry of ?1 Her as well as Wing intermediate-band near-IR TiO and NIR continuum photometry. We introduce a new photometry-based calibration technique and extract the effective temperature and luminosity of ?1 Her, in agreement with recent interferometric measures. We find average values of T eff = 3280 ? 87 K and log (L/L ?) = 3.92 ? 0.14. With the MESA code, we calculate a dense grid of evolutionary tracks for Galactic low- to intermediate-mass (1.3 to 8 M ?) rotating stars from the pre-main sequence phase to the advanced AGB phase. We include atomic diffusion and rotation mechanisms to treat the effects of extra elemental mixing. Based on the observed properties of the ? Herculis stars, we constrain the age of the system to lie in the range 0.41 to 1.25?Gyr. Thus, the mass of ?1 Her lies in the range 2.175 ? M/M ? ? 3.250. We compare our model-based age inference with recent tracks of the Geneva and STAREVOL codes, and show their agreement. In the prescribed mass range for ?1 Her, the observed 12C/13C and 16O/17O ratios are consistent (within 2?) with the ratios predicted by the MESA, Geneva, and STAREVOL codes.

Times-Series Photometry & Spectroscopy of the Bright Blue Supergiant Rigel: Probing the Atmosphere and Interior of a SN II Progenitor

As the 7 th brightest star and the most luminous star in the solar neighborhood, Rigel (β Orionis) is a very intriguing object. This blue supergiant (B8 Iab; V-mag = +0.05–0.18-mag; B–V = -0.03), at a distance (from Hipparcos) of ~240±35 pc has a 〈M V 〉 = -6.7 mag. The following physical properties were determined via spectroscopic, photometric, and interferometric studies: L/L ⊙ ≈ 66,000 K; T eff ≈ 12,000 K; M/M ⊙ ≈ 17±3; R/R ⊙ ≈ 70; τ ≈ 3–10 Myr. Interestingly Rigel has similar physical properties with the 12 th mag blue supergiant progenitor of SN 1987A: Sanduleak -69° 202a. Thus Rigel (along with its co-asterism Betelgeuse) are likely to be the nearest progenitors of a Type II supernova. Such a nearby explosion would be V ≈ -11 th mag (similar to a quarter moon).