Photometry and hydrogen alpha observations of the binary system FF Aquarii

Details Photometry and hydrogen alpha observations of the binary system FF Aquarii Photometry and hydrogen alpha observations of the binary system FF Aquarii

Mar 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...295..393m&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 295, no. 2, p. 393-402

Astronomy and Astrophysics

Astrophysics

9

Companion Stars, Eclipsing Binary Stars, Emission Spectra, H Alpha Line, Stellar Activity, Stellar Orbits, Subdwarf Stars, Ubv Spectra, Astronomical Photometry, Doppler Effect, Light Curve, Stellar Spectrophotometry

Scientific paper

We report on UBV photometry and moderate resolution hydrogen alpha spectrophotometry of the evolved binary system FF Aqr (sdOB + G8 III), performed at the Catania Astrophysical Observatory. The spectrophotometric data were collected in 1990 and 1991, while the photometric light curve is based essentially on observations obtained in 1990. The hydrogen alpha emission line which is associated with the cool star of the system shows a clear modulation with the orbital phase, a definite maximum occurring near the secondary eclipse. The net emission profile of all 1990 spectra, obtained by subtracting the absorption profile of a standard star, displays a very broad emission component (approximately equal to 10 A) and a narrow one (approximately equal to 3 A). The intensity of the latter is modulated with the orbital phase and seems to disappear near the primary eclipse. In the 1991 spectra the broad component is not always visible, while the narrow one is clearly present with the same behavior as the 1990 curve. The Doppler shifts of the narrow hydrogen alpha emission, measured with respect to the photospheric lines of the cool secondary star are consistent with an emission region placed on the G8 III star hemisphere facing the hotter subdwarf. The photometric light variations outside the eclipses show some difference with respect to that observed by Dworetsky et al. (1977a) and by Dorren et al. (1983). Our V light curve is more symmetric, the maximum light occurring at phase approximately equal to 0.5, and the variation amplitude is significantly smaller. A simple model in which the radiation from the subdwarf reaching the cool companion is completely thermalized in the atmosphere of the latter accounts for both the narrow hydrogen alpha emission component and UBV out-of eclipse light variation.

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