Pulsation of the K 2.5 giant star GSC 09137-03505?

Abstract

In July, 1999, the Hubble Space Telescope (HST) pointed for more than 8 days continuously at the globular cluster 47 Tucanae. Two guide stars were used during this campaign by the Fine Guidance Sensors (FGS). Using more than 19 million photometric FGS data for the guide star GSC 09137-03505 we found brightness variability corresponding to three approximately equidistant frequencies. The detected frequencies range from 21 to 71 [micro Hertz] with amplitudes between 341 and 291 ppm. Multicolor CCD photometry was obtained at the Cerro Tololo Inter–American Observatory to derive color information for the guide stars. In addition, flux calibrated spectra were observed at the South African Astronomical Observatory. Temperature and surface gravity were determined from a comparison of observed and synthetic spectral fluxes using the NEMO (Vienna New Model Grid of Stellar Atmospheres) model atmosphere grid developed by Heiter et al. (2002, A&A, 392, 619) and Nendwich et al. (2004, CoAst, 144, 43). We also performed linear nonadiabatic analyses of various stellar models in an attempt to interprete [sic] the frequencies.