SV Centauri Research Articles

Analysis of photometric light curves solution for massive contact OB binary stars. LY Aurigae, BH Centauri, SV Centauri

We searched for signs of the presence of circumstellar gaseous matter in photometric data for massive contact early-type binaries by analyzing residual curves (the dependence of the difference between the observed and theoretical brightness variations on the orbital-period phase) for three such stars. The residual curves make it possible to estimate the influence of gas in the common envelope on the observed light curves for different phase intervals and to qualitatively describe the character of the distortion of the light from the system’s components. Changes of the residual curves from filter to filter indicate varying conditions in the circumstellar matter. Changes of the residual curves from one observation epoch to another indicate varying conditions in the circumstellar matter. We compared the residual curves obtained for different photometric bands and epochs via a correlation analysis. The distortion of light from the components of LY Aurigae in the ultraviolet differs from that in the visual. The distortion of light from the components of SV Centauri is appreciable, but not selective, and does not vary in time, while the distortion of light from BH Centauri possesses a strong selective component. A comparison of the radii computed for the components of BH Centauri and SV Centauri shows that the gas distribution near these binaries varies in time.

Photometry and spectroscopy of the very close early type binary SV Centauri

view Abstract Citations (15) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometry and Spectroscopy of the Very Close Early Type Binary SV Centauri Rucinski, S. M. ; Baade, D. ; Lu, W. X. ; Udalski, A. Abstract New high-quality observations of this unusual early type contact binary are presented. BVRI photometry of SV Cen provides a precise moment of minimum in March 1990. From high-resolution profiles of the He I line at 492.1 nm a new, improved set of orbital parameters was derived. Intrinsic line profile variability was not detected in either component and both photometry and spectroscopy. Low-noise spectra of the region around He II 468.6 nm showed no feature at any orbital phase, thus not giving a clue on the location of the source of a far-UV flux excess previously inferred from IUE observations. Since, for technical reasons, simultaneous EUV spectrophotometry with the Voyager spacecraft was lost, the temperature of this possible ultrahot spot could not be further constrained. Publication: The Astronomical Journal Pub Date: February 1992 DOI: 10.1086/116084 Bibcode: 1992AJ....103..573R Keywords: B Stars; Binary Stars; Stellar Spectrophotometry; Ultraviolet Astronomy; Centaurus Constellation; Extreme Ultraviolet Radiation; Helium; Light Curve; Stellar Evolution; Stellar Orbits; Astrophysics; BINARIES: CLOSE; BINARIES: SPECTROSCOPIC full text sources ADS | data products SIMBAD (3)

Irregular Period Variations of Eclipsing Binaries

Considering a small number of representative systems among them U Cephei, SV Centauri, V471 Tauri, EM Cygni, the case is made for irregular period variations playing a substantial role in the observed changes of close binary periods.

The Masive Binary SV Centauri

Current light synthesis models of SV Centauri require a highly overcontact system with an 8000K temperature discontinuity between components. Current evolutionary models support the overcontact status, and describe the system as in the final stage of rapid mass transfer prior to mass reversal, calculated to occur within 2500 years. Light synthesis simulation provides a poor fit to the observations, and requires an ad hoc assumption to fit the substantial O'Connell effect.IUE spectra have been reported to indicate the presence of a 200 000K source of small dimensions in the system. New spectrum synthesis results demonstrate there is no hot spot, but there is extra radiation longwards of 200nm that is unaccounted for by the overcontact model.Postulated presence of an accretion disk around the mass gainer prospectively overcomes the observational anomalies. Formation of the accretion disk apparently violates the Lubow-Shu criterion. A reasonable scenario nonetheless supports accretion disk formation. Conflict with the theoretical models can be resolved on the postulate that the spherical accretion assumed in those models render them inapplicable to this system.

Evolutionary computations of the early-type contact binary SV Centauri

Evolutionary models of the early-type contact binary SV Centauri are recalculated with contact condition taken into account. Two types of the contact condition are employed in the contact phase. With the initial masses of 13.4 and 7.0M ⊙ for the component stars, the observed features such as the rate of mass transfer, the degree of contact, and the positions of both components in the H-R diagram can be reproduced. In agreement with the conclusion given in the previous paper (Nakamuraet al., 1978), this indicates that the binary system SV Cen is actually in the rapid phase of mass transfer preceding the reversal of the mass ratio. In contrast to the steadily increasing character of the rate of mass transfer shown in the previous paper, however, the rate of mass transfer suddenly turns to decrease as soon as the system evolves into the contact phase. This decreasing character continues until the rate drops to a minimum. In such contact phase the radius of the primary component remains almost unchanged, the secondary component increases its radius slowly, and the degree of contact increases in a definite way. Except a slight difference in the degree of contact evaluated, the use of different expressions for the contact condition does not produce practically any appreciable difference in the results.

Structure and Evolution of SV Centauri

AbstractOptical photometric and spectroscopic observations of the eclipsing binary SV Cen were used to derive orbital elements and absolute dimensions of the peculiar early-type contact system. UV spectroscopic observations obtained with the IUE satellite yielded the detection of mass loss from the system forming an expanding circumbinary envelope. SV Cen exhibits a non-uniform rate of period decrease, with major variations on a time scale of a few years. The period changes are explained in terms of loss of angular momentum carried away by the ejected matter. Short-term fluctuations of the stellar wind on a time scale of a few hours were found from an analysis of the envelope line profiles of UV resonance lines. A model of the system is derived, and the evolutionary stage and interaction processes are discussed.

Evolution of Early-Type Contact Binaries

SV Centauri is an early-type contact binary for which detailed physical data have been obtained from observations (Wilson and Starr 1976). The orbital period is p = 1.659 days and the separation is a = 16.1 R⊙. The radii of component Stars A and B are, respectively, R = 7.2 and 6.9 R⊙ so that they are in overcontact. The masses and the luminosities are M = 11.1 and 9.3 M⊙, and L = 2830 and 10900 L⊙ for Stars A and B, respectively. The more massive Star A is called the primary star but its luminosity is fainter than Star B. This implies that it is in the phase of rapid mass transfer and mass is outflowing from Star A. Indeed one of the most interesting and important points of this system is that the rate of period change is measured to be dP/dt = −9.4 × 10−8 (Irwin and Landolt 1972) which corresponds to the mass transfer rate of dMA/dt = −4 × 10−4 M⊙ yr−1.

A Remarkable Change in Period of SV Centauri

SV Centauri (= HD 102552; 11h43m05s, -60°00.6 (1900)) is a contact binary showing the largest known variation of period. The system, which shows double lines at quadratures, consists of Bl and B2 components of 9.4 and 11.1 solar masses respectively (Irwin, J.B. and Landolt, A.U.,P.A.S.P. 84, 686. 1972). Recent observations (Eggen, O.J.,A.J. 83, 288, 1978) indicate that the eclipses are considerably shallower than found in 1970.

SV Centauri: An Unusual Example of Mass Transfer

We have analysed the recent Irwin–Landolt observations of the eclipsing binary SV Centauri for photometric parameters, by differential corrections. We find that the photometric secondary component (lower temperature star) is the more massive but less luminous star, that the system is an ‘ early-type ’ contact binary, and that the amount of overcontact is large (≃ 0·7). However, the main point of this paper is to argue that the large rate of period change in SV Cen (one of the largest known, in terms of dP/P) is almost certainly due to mass transfer, with the flow from the more to the less massive star. SV Cen thus becomes the second such case known. Mass transfer was given only scant attention in earlier discussions of the period change. We calculate a mass transfer rate of about |$4 \times 10^{-4} M_{\odot}/\text{yr}.,$| which is approximately 30 times that of β Lyrae. The secondary component is underluminous for its mass, and the primary component overluminous, as expected for stars which are rapidly losing and gaining mass, respectively.

SV CENTAURI - A TRULY CONTACT BINARY.

ABSTRACT A light-curve-synthesis program which implements interpolation in a grid of nongray model atmospheres has been used to determine the geometrical elements of SV Cen by simultaneous differentialcorrection fitting of the three-color light curves obtained in UBV by Irwin and Landolt (1972). Solutions with the mass ratio fixed at its spectroscopic value of 0.84 reveal an extraordinarily high degree of contact between the components (fill-out parameter f = 0.10 ::::: 0.02) and a rather high temperature of the less massive component relative to the more massive component. The large local temperature excess of the secondary star, X = A TIT = 0.78 :::: 0.03 (which results in temperatures 28,000 and 17,0000 K, for the less massive and more massive compounds, respectively) is difficult to understand in the framework of the contact model but might be related to the thermal-time-scale mass-transfer stage of the evolution of SV Cen. Key words: light-curve synthesis - mass transfer

A PHOTOMETRIC AND SPECTROSCOPIC INVESTIGATION OF SV CENTAURI

ABSTRACT The fi Lyrae-type eclipsing binary SV Cen has been observed photoelectrically and spectroscopically at the Cerro Tololo Inter-American Observatory and is also a double-lined spectroscopic binary. The primary component has the UBV colors of a reddened B1 star, a mass of 9.4, and a mean radius of 6.5 in solar units; the same data for the secondary component are B2, 11.1, and 6.6. There is evidence from the light curves that 22% of the light comes from a third component not seen spectroscopically at primary minimum. The period has decreased 0.14% in the last 75 years and is still decreasing. The variation of period could be caused by orbital motion about a mass of approximately 250,000 solar masses but this hypothesis is also ruled out by radial velocity considerations. The 33.6-year periodicity of the secondary fluctuation in period as studied by O'Connell is not confirmed by the recent times of minima. There is no spectroscopic evidence of gas streams or shells. A prediction ephemeris for 1972 is tmin = JD0244139.120 + E. Key words: eclipsing binaries - spectroscopic binaries - stellar masses - variation of period

THE CHANGING PERIOD OF SV CENTAURI

THE CHANGING PERIOD OF SV CENTAURI

The Eclipsing Binary SV Centauri

About 1500 estimates on Riverview plates, together with 500 estimates made by Schmidt at Leiden and earlier observations by Miss Leavitt, Dawson, Dugan and Wright, were used to investigate the period of SV Centauri. Seventy epochs of primary, and twenty-seven of secondary, minimum were obtained between 1893 and 1949. It was found that the observed times of minimum could be represented by a periodic fluctuation superimposed on a parabola, which itself represents a secular decrease of period. The secondary fluctuation has a period of 33.6 years and a semi-amplitude of 0.21 days. It can be explained as due to the motion of the binary about a third star, the variation of period being caused by the varying light-time across this orbit. The elements of the orbit were computed by Woltjer's method. The following results were obtained :—e=0.32, ω=l59°, a sin i= 38 astronomical units, Periastron 1922.5, Mass-function=49. The secular change of period is very large, from 1d.66151 in 1893 to 1d.65929 in 1949. If this change is periodic, the period is very long. If it were due to the motion of the triple star about a fourth star the mass-function would have to be at least 10,000. The decrease of period may be due to the interchange of matter between the components of the binary system (which are almost in contact), as suggested by Kuiper for β Lyrae. The secondary fluctuation may possibly be due to a similar cause. The orbital elements of the binary were determined from the mean light curve derived from the Riverview plates. The orbit was found to be slightly eccentric. The stars are almost in contact. The spectrum of the companion has not yet been observed. It is estimated that at primary minimum most of the light comes from the companion and it ought to be possible to determine its spectrum at that time.