Wing Near-Infrared, TiO-Band, andV-Band Photometry of Chromospherically Active Star Andromedae

Abstract

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 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 ( , 0, 0) absorption band strength at = 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 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.

Active cool stars and He I 10 830 Å: the coronal connection

“…Since giant stars have extended chromospheres, these velocities become comparable to the stellar escape velocity, and can be said to mark the presence of a stellar wind. At the time when we observed the He i 10 830 Å line in λ And, Mirtorabi et al (2003) monitored the star searching for periodicity in visible light and in photospheric spot coverage. During the period of our NOT observations of λ And, no important changes occurred in the observations of Mirtorabi et al (2003), and the He i λ10 830 did not show substantial changes in strength either.…”

Photometric evidence for two-temperature photospheric inhomogeneities on magnetically active K dwarf stars

“…In fact, some authors have found that for the less active stars the variability at the optical wavelengths is significantly influenced by faculae, if not quite dominated, e.g. Mirtorabi et al (2003), Radick et al (1990Radick et al ( , 1998, while for the most active stars the effect of starspots dominates and faculae are not required to obtain quite satisfactory light curves models (e.g. Henry et al 1995;Lanza et al 1998).…”

Spot activity in the RS CVn binary DM Ursae Majoris

“…The TiO‐band strengths obtained by O'Neal et al (2004) in 1998 seem to be showing the expected anticorrelation with the visual brightness of DM UMa. Mirtorabi, Wasatonic & Guinan (2003) have reported that in the long‐period RS CVn binary λ And the TiO‐band strengths measured using narrow‐band filters show the expected anticorrelation only at certain observing seasons and that the same is probably true for the active RS CVn binary II Peg. In connection with the lack of anticorrelation at all times, O'Neal et al (2004) have pointed out the possible inadequacy of the two‐component model of RS CVn stars consisting of only the unspotted and spotted photospheric regions.…”