Apsidal motion in massive close binary systems. I. HD 165052 an extreme case?

We present a new set of radial-velocity measurements of the spectroscopic binary HD 165052 obtained by disentangling of high-resolution optical spectra. The longitude of the periastron (60 +- 2 degrees) shows a variation with respect to previous studies. We have determined the apsidal motion rate of the system (12.1 +- 0.3 degree/yr), which was used to calculate the absolute masses of the binary components: M_1 = 22.5 +- 1.0 and M_2 = 20.5 +- 0.9 solar masses. Analysing the separated spectra we have re-classified the components as O7Vz and O7.5Vz stars

Close-In Substellar Companions and the Formation of sdB-Type Close Binary Stars

The sdB-type close binaries are believed to have experienced a common-envelope phase and may evolve into cataclysmic binaries (CVs). About 10% of all known sdB binaries are eclipsing binaries consisting of very hot subdwarf primaries and low-mass companions with short orbital periods. The eclipse profiles of these systems are very narrow and deep, which benefits the determination of high precise eclipsing times and makes the detection of small and close-in tertiary bodies possible. Since 2006 we have monitored some sdB-type eclipsing binaries to search for the close-in substellar companions by analyzing the light travel time effect. Here some progresses of the program are reviewed and the formation of sdB-type binary is discussed

Evolution and Outbursts of Cataclysmic Variables

Mass transfer and accretion are very important to understand the evolution and observational properties of cataclysmic variables (CVs). Due to the lack of an accretion disk, eclipsing profiles of polars are the best source to study the character of mass transfer in CVs. By analyzing long-term photometric variations in the eclipsing polar HU Aqr, the property of mass transfer and accretion are investigated. The correlation between the brightness state change and the variation of the ingress profile suggests that both the accretion hot spot and the accretion stream are produced instantaneously. The observations clearly show that it is the variation of mass transfer causing the brightness state changes that is a direct evidence of variable mass transfer in a CV. It is shown that it is the local dark-spot activity near the L1 point to cause the change of the mass transfer rather than the activity cycles of the cool secondary star. Our results suggest that the evolution of CVs is more complex than that predicted by the standard model and we should consider the effect of variable mass accretion in nova and dwarf nova outbursts

Long-Term Optical Monitoring of Eta Carinae. Multiband light curves for a complete orbital period

The periodicity of 5.5 years for some observational events occurring in Eta Carinae manifests itself across a large wavelength range and has been associated with its binary nature. These events are supposed to occur when the binary components are close to periastron. To detect the previous periastron passage of Eta Car in 2003, we started an intensive, ground-based, optical, photometric observing campaign. We continued observing the object to monitor its photometric behavior and variability across the entire orbital cycle. Our observation program consisted of daily differential photometry from CCD images, which were acquired using a 0.8 m telescope and a standard BVRI filter set at La Plata Observatory. The photometry includes the central object and the surrounding Homunculus nebula. We present up-to-date results of our observing program, including homogeneous photometric data collected between 2003 and 2008. Our observations demonstrated that Eta Car has continued increasing in brightness at a constant rate since 1998. In 2006, it reached its brightest magnitude (V ~ 4.7) since about 1860s. The object then suddenly reverted its brightening trend, fading to V = 5.0 at the beginning of 2007, and has maintained a quite steady state since then. We continue the photometric monitoring of Eta Car in anticipation of the next "periastron passage", predicted to occur at the beginning of 2009.Comment: Accepted by A&A. The paper contains 3 figures and 2 table

Long-term decrease and cyclic variation in the orbital period of the eclipsing dwarf nova V2051 OPH

V2051 Oph is a deeply eclipsing dwarf nova with an orbital period below the period gap of cataclysmic variables (CVs). It has been photometrically monitored since 2008 June and 24 mid-eclipse times of the white dwarf have been obtained. The changes in the orbital period are investigated using all of the available mid-eclipse times. A continuous period decrease with a rate of Ṗ =-5.93 10-10 days yr-1 was discovered to be superimposed on a periodic variation with a small amplitude of 0.d000329 and a period of 21.64 years. The standard theory predicted that the evolution of CVs below the period gap is driven by gravitational radiation. However, angular momentum loss (AML) via gravitational radiation is insufficient to explain this decrease, and additional AML via magnetic braking that is about five times the gravitational radiation rate is required. This is consistent with the theoretical requirement indicating that magnetic braking of the fully convective star is not completely stopped. The cyclic oscillation was interpreted as the variation of the arriving eclipse time via the presence of a third body because the required energy for the Applegate mechanism is much larger than that radiated from the secondary in 10 years. Its mass is derived as M3sin i' = 7.3 (±0.7) Jupiter mass. For orbital inclinations i' ≥ 30°.3, it would be a planetary object. The giant circumbinary planet is orbiting around V2051 Oph at an orbital separation of about 9.0 astronomical units (AU) in an eccentric orbit (e' = 0.37). These conclusions support the ideas that some planets could survive stellar late evolution and that dwarf novae are also planetary hosting stars.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Long-term decrease and cyclic variation in the orbital period of the eclipsing dwarf nova V2051 OPH

V2051 Oph is a deeply eclipsing dwarf nova with an orbital period below the period gap of cataclysmic variables (CVs). It has been photometrically monitored since 2008 June and 24 mid-eclipse times of the white dwarf have been obtained. The changes in the orbital period are investigated using all of the available mid-eclipse times. A continuous period decrease with a rate of Ṗ =-5.93 10-10 days yr-1 was discovered to be superimposed on a periodic variation with a small amplitude of 0.d000329 and a period of 21.64 years. The standard theory predicted that the evolution of CVs below the period gap is driven by gravitational radiation. However, angular momentum loss (AML) via gravitational radiation is insufficient to explain this decrease, and additional AML via magnetic braking that is about five times the gravitational radiation rate is required. This is consistent with the theoretical requirement indicating that magnetic braking of the fully convective star is not completely stopped. The cyclic oscillation was interpreted as the variation of the arriving eclipse time via the presence of a third body because the required energy for the Applegate mechanism is much larger than that radiated from the secondary in 10 years. Its mass is derived as M3sin i' = 7.3 (±0.7) Jupiter mass. For orbital inclinations i' ≥ 30°.3, it would be a planetary object. The giant circumbinary planet is orbiting around V2051 Oph at an orbital separation of about 9.0 astronomical units (AU) in an eccentric orbit (e' = 0.37). These conclusions support the ideas that some planets could survive stellar late evolution and that dwarf novae are also planetary hosting stars.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Is WX CEN a possible type Ia supernova progenitor with wind-driven mass transfer?

WX Cen is one of a few compact binary supersoft X-ray sources (CBSS) in the Galaxy that is a possible Type Ia supernova (SN Ia) progenitor. The supersoft X-ray radiation is explained as hydrostatic nuclear burning on the surface of the white dwarf component that is accreting hydrogen from a stellar companion at a high rate. If the mass donor in this system has a low mass, as has been suggested in the literature, one would expect a high wind-driven mass transfer rate. In that case, the orbital period of the system should increase. To test this theoretical prediction, we have monitored the system photometrically since 2010. By using four newly determined eclipse timings together with those collected from the literature, we discovered that the orbital period is decreasing at a rate of dP/dt = -5.15 × 10-7 days yr -1. The long-term decrease in the orbital period is contrary to the prediction that the system is powered by wind-driven accretion. It therefore seems plausible that the mass donor could be more massive than the white dwarf, and that the mass transfer is driven by the thermal instability of the donor star. This finding suggests that WX Cen is a key object to check the physical mechanisms of mass accretion in CBSS. The corresponding timescale of the period change is about yr, indicating that WX Cen may evolve into an SNe Ia within one million years in the Galaxy.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

The massive Wolf-Rayet Binary LSS1964 (=WR29), II: the V light curve

Context. WR 29 is a known WN7h+O double-lined binary system with a rather short period (3.164 days). Aims. We search for light variations to determine the inclination of the system and thus the absolute masses of both components. Methods. We observed photometrically the field of WR 29 between December, 2002, and February, 2006. Results. We find that the V light of WR 29 varies in phase with the spectroscopic period of 3.16412 days, presenting two minima corresponding to the conjunctions of the binary components. Numerical models fitted to the light curve indicate an orbital inclination of about 44◦, and masses of 53 M and 42 M for the O- and WN-type components, respectively.Fil: Gamen, Roberto Claudio. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Fernandez Lajus, Eduardo Eusebio. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Niemela, Virpi Sinikka. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Barba, Rodolfo Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; Argentin

A Circumbinary Planet in Orbit Around the Short-Period White-Dwarf Eclipsing Binary RR Cae

By using six new determined mid-eclipse times together with those collected from the literature, we found that the Observed-Calculated (O-C) curve of RR Cae shows a cyclic change with a period of 11.9 years and an amplitude of 14.3s, while it undergoes an upward parabolic variation (revealing a long-term period increase at a rate of dP/dt =+4.18(+-0.20)x10^(-12). The cyclic change was analyzed for the light-travel time effect that arises from the gravitational influence of a third companion. The mass of the third body was determined to be M_3*sin i' = 4.2(+-0.4) M_{Jup} suggesting that it is a circumbinary giant planet when its orbital inclination is larger than 17.6 degree. The orbital separation of the circumbinary planet from the central eclipsing binary is about 5.3(+-0.6)AU. The period increase is opposite to the changes caused by angular momentum loss via magnetic braking or/and gravitational radiation, nor can it be explained by the mass transfer between both components because of its detached configuration. These indicate that the observed upward parabolic change is only a part of a long-period (longer than 26.3 years) cyclic variation, which may reveal the presence of another giant circumbinary planet in a wide orbit.Comment: It will be published in the MNRA