Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984a%26a...132..219v&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 132, no. 1, March 1984, p. 219-228. Sponsorship: Statens Naturvidenskabelige F
Astronomy and Astrophysics
Astrophysics
26
A Stars, Eclipsing Binary Stars, Light Curve, Stellar Spectra, Stellar Structure, Abundance, Astrometry, Radial Velocity, Stellar Evolution, Stellar Motions, Stellar Spectrophotometry, Stellar Temperature
Scientific paper
New coude spectrograms and uvby light curves are analyzed to determine absolute dimensions of the components of PV Puppis (HR 3009, 2 Pup B), a bright double-lined late A-type eclipsing binary of fairly short period (P = 1 d.67) and small orbital eccentricity (e =0.05). Based on 26 plates, the spectroscopic orbits are very well-determined and yield almost identical masses of 1.5 Msun for both components, with a mean error better than 1%. A study of the line profiles shows the stars to be in synchronous rotation and of nearly equal luminosity,LB/LA =0.95±0.02. In spite of some intrinsic variability, the uvby light curves (1023 points in each colour) yield well-defined photometric elements, according to which the stars have the same effective temperatures (6920 K) and almost identical radii of 1.5 Rsun, which are also determined to within about 1 %. Spectroscopic and photometric results for e and ω in the eccentric orbit and for the luminosity ratio are in very good agreement. The observed values of log g (4.27) are near the upper limit found in other well-observed systems and show that PV Pup is essentially unevolved. This is confirmed by its location just above the ZAMS for Hejlesen's (1980) theoretical stellar evolution models, but compositions of either rather low He abundance (X, Z) = (0.80, 0.02) or, perhaps less likely because the δm-1 index is normal, high metal abundance (X, Z) = (0.70, 0.04) are required to match the observed temperatures; the age found for PV Pup when adopting the former set of models is 1 109 yr. Analysis of the intrinsic light variations yields the surprising result that these seem to be periodic with a period of 1d.92 stable over several years. A period of 0d.48 (1/4 of the best period) is also possible, but then the maxima do not quite repeat from cycle to cycle. The b - y and β indices, which show little if any variation with binary phase, vary systematically with phase in the 1d.92 period. Both b - y and β vary consistently in a manner corresponding to a temperature variation of the stars, Te being higher by about 140 K at light maximum than at light minimum. The corresponding brightness difference is about 0m.06 in b. The period and other characteristics of these light variations correspond neither to stellar pulsations nor to plausible models of surface inhomogeneities, and we have been unable to identify them with any known class of variability in A stars. We finally conclude, mainly because of the observed radial velocity difference, that the double star ADS 6348 (Sep. 17") of which PV Pup is the fainter member, does not form a physically bound system, but is merely an optical pair.
Andersen Jeppe J.
Vaz Luiz Paulo Ribeiro
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