Photometry



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Photometry

R. Wasatonic (LVAAS, VU research consultant) carried out photoelectric photometry on the SRc supergiant Her A as part of a continuing program with the National Solar Observatory to collaborate radial velocity studies with photometrically generated light curves. This photometry was combined with APT photoelectric photometry obtained by Guinan and McCook to construct a more complete coverage of Her A's light variations. The resultant light curves proved to be more complex than anticipated, and subsequent studies and period analyses by Guinan and Wasatonic indicate the presence of 93-day and 126-day periods. These two periods give rise to a beat period of 355 days. This period ties in well with a 350-day RV period obtained by M. Smith(CSC) using the NSO's McMath telescope.

Wasatonic also conducted photoelectric photometry of the bright red supergiants and giants Ori, Tau and the Mira-type variables Ceti and RT Cygni photometrically in the visual (5500 Å) and in the near IR (7190 Å, 7450 Å, and 10400 Å). The IR filters are a subset of an 8-color system developed by Dr. Robert Wing at OSU. Their central wavelengths were picked so that a TiO index can be calculated from the standardized magnitudes obtained through each filter; this TiO index can then be used as a M-star spectral-subtype indicator. Additionally, IR light curves can be generated and compared against the visual light curve to characterize photometric differences that arise from the different wavelength regions.

No significant light variations have yet been found in Tau from about two months of monitoring. However, both Ceti and RT Cygni have decreased in brightness from August to October 1996 by 2 magnitudes in the visual, about one magnitude in the 7190 Å and 7450 Å regions, and only a few tenths of a magnitude in the 10400 Å\ region; these are indications of atmospheric expansion and cooling that can result in TiO formation, causing a drop in visual light that is greater than any IR loss. It should be emphasized that these observations spanned only 2-3 months, and that a longer time interval is needed before complete visual and IR light curves can be generated to characterize all photometric features.

As a pilot study, Wasatonic, in collaboration with Guinan, is carrying out photometry of the bright RS CVn star And (V = 3.86; G8 IV-III; P = 54.5d). The observations are being made with a subset of the Wing TiO filters to attempt to measure the manifestation of large cool starspots that may cause changes in the TiO indices as they rotate. Observations are planned through March 1997.



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Next: Chromospherically Active Stars: Up: CURRENT RESEARCH Previous: Chromospherically Active Stars



Astronomy
Fri Nov 8 13:37:39 EST 1996