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Register a new userUBVRI photopolarimetry of the long period eclipsing AM Herculis binary V1309
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Authors
S. Katajainen
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We report simultaneous UBVRI photo-polarimetric observations of the long period (7.98 h) AM Her binary V1309 Ori. The length and shape of the eclipse ingress and egress varies from night to night. We suggest this is due to the variation in the brightness of the accretion stream. By comparing the phases of circular polarization zero-crossovers with previous observations, we confirm that V1309 Ori is well synchronized, and find an upper limit of 0.002 percent for the difference between the spin and orbital periods. We model the polarimetry data using a model consisting of two cyclotron emission regions at almost diametrically opposite locations, and centered at colatitude 35 (deg) and 145 (deg) on the surface of the white dwarf. We also present archive X-ray observations which show that the negatively polarised accretion region is X-ray bright.
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V383Sco was discovered to be an eclipsing binary at the beginning of the XX century. This system has one of the longest orbital periods known (13.5yr) and was initially classified as a zet_Aur-type variable. It was then forgotten for decades. This study provides a detailed look at the V383Sco, using new data obtained around the last eclipse in 2007/8. There was a suspicion that this system could be similar to eclipsing systems with extensive dusty disks like EECep and eps_Aur. This and other, alternative hypotheses are considered. The ASAS-3 VI light curves have been used to examine photometric changes. Low-(LRS) and high-res.(HRS) spectra have been used for spectral classification, to analyse line profiles, as well as to determine the reddening, radial velocities (RVs) and distance. The SED was analysed. Using original numerical code, we performed a simplified model of the eclipse, taking into account the pulsations of one of the components. The LRS shows traces of molecular bands, characteristic of an M-type supergiant. The presence of this star in the system is confirmed by SED, by a strong dependence of the eclipse depth on the photometric bands, and by pulsational changes. The presence of a low excitation nebula around the system has been inferred from [OI] 6300A emission. Analysis of the RVs, reddening, and P-L relation for Mira-type stars imply a distance to the V383Sco of 8.4+-0.6 kpc. The distance to the nearby V381Sco is 6.4+-0.8 kpc. The very different and oppositely directed RVs of these systems (89.8 vs -178.8 km/s) seem to be in agreement with a bulge/bar kinematic model of the Galactic centre and inconsistent with purely circular motion. We have found evidence for the presence of a pulsating M-type supergiant in the V383Sco which periodically obscures the much more luminous F0I-type star, causing the deep (possibly total) eclipses which vary in duration and shape.
We report extensive spectroscopic and differential V-band photometric observations of the 18.4-day detached double-lined eclipsing binary LV Her (F9V), which has the highest eccentricity (e = 0.613) among the systems with well-measured properties. We determine the absolute masses and radii of the components to be M1 = 1.193 +/- 0.010 M(Sun), M2 = 1.1698 +/- 0.0081 M(Sun), R1 = 1.358 +/- 0.012 R(Sun), and R2 = 1.313 +/- 0.011 R(Sun), with fractional errors of 0.9% or better. The effective temperatures are 6060 +/- 150 K and 6030 +/- 150 K, respectively, and the overall metallicity is estimated to be [m/H] = +0.08 +/- 0.21. A comparison with current stellar evolution models for this composition indicates an excellent fit for an age between 3.8 and 4.2 Gyr, with both stars being near the middle of their main-sequence lifetimes. Full integration of the equations for tidal evolution is consistent with the high eccentricity, and suggests the stars spin axes are aligned with the orbital axis, and that their rotations should be pseudo-synchronized. The latter prediction is not quite in agreement with the measured projected rotational velocities.
Eclipsing binary DI Herculis (DI Her) is known to exhibit anomalously slow apsidal precession, below the rate predicted by the general relativity. Recent measurements of the Rossiter-McLauglin effect indicate that stellar spins in DI Her are almost orthogonal to the orbital angular momentum, which explains the anomalous precession in agreement with the earlier theoretical suggestion by Shakura. However, these measurements yield only the projections of the spin-orbit angles onto the sky plane, leaving the spin projection onto our line of sight unconstrained. Here we describe a method of determining the full three-dimensional spin orientation of the binary components relying on the use of the gravity darkening effect, which is significant for the rapidly rotating stars in DI Her. Gravity darkening gives rise to nonuniform brightness distribution over the stellar surface, the pattern of which depends on the stellar spin orientation. Using archival photometric data obtained during multiple eclipses spread over several decades we are able to constrain the unknown spin angles in DI Her with this method, finding that spin axes of both stars lie close to the plane of the sky. Our procedure fully accounts for the precession of stellar spins over the long time span of observations.
Twenty-one new optical light curves, including five curves obtained in 2009 and sixteen curves detected from the AAVSO International Database spanning from 1977 to 2011, demonstrate 16 new primary minimum light times in the high state. Furthermore, seven newly found low-state transient events from 2006 to 2009 were discovered, consisting of five Gaussian-shaped events and two events with an exponential form with decay timescales of $<$0.005 days; these timescales are one order of magnitude shorter than those of previous X-ray flare events. In the state transition, two special events were detected: a disrupted event with an amplitude of $sim$ 2 mag and a duration of $sim$ 72 minutes and continuing R-band twin events larger than all known R-band flares detected in M-type red dwarfs. All 45 available high-state data points spanning over 35 yr were used to construct an updated O-C diagram of objectname{AM Herculis}, which clearly shows a significant sine-like variation with a period of 12-15 yr and an amplitude of 6-9 minutes. Using the inspected physical parameters of the donor star, the secular variation in the O-C diagram cannot be interpreted by any decided angular momentum loss mechanism, but can satisfy the condition $tau_{dot{rm M}_{2}}simeqtau_{rm KH}>>tau_{dot{rm R}_{rm 2}}$, which is required by numerical calculations of the secular evolution of cataclysmic variables. In order to explain the prominent periodic modulation, three plausible mechanisms - spot motion, the light travel-time effect, and magnetic active cycles - are discussed in detail.
The Sloan Digital Sky Survey has been instrumental in obtaining a homogeneous sample of the rare AM CVn stars: mass-transferring binary white dwarfs. As part of a campaign of spectroscopic follow-up on candidate AM CVn stars from the Sloan Digital Sky Survey, we have obtained time-resolved spectra of the g=20.2 candidate SDSS J155252.48+320150.9 on the Very Large Telescope of the European Southern Observatory. We report an orbital period of 3376.3+/-0.3 s, or 56.272+/-0.005 min, based on an observed `S-wave in the helium emission lines of the spectra. This confirms the ultracompact nature of the binary. Despite its relative closeness to the orbital period minimum for hydrogen-rich donors, there is no evidence for hydrogen in the spectra. We thus classify SDSS J1552 as a new bona fide AM CVn star, with the second-longest orbital period after V396 Hya (P=65.5 min). The continuum of SDSS J1552 is compatible with either a blackbody or helium atmosphere of 12,000-15,000 K. If this represents the photosphere of the accreting white dwarf, as is expected, it puts the accretor at the upper end of the temperature range predicted by thermal evolution models. This suggests that SDSS J1552 consists of (or formerly consisted of) relatively high-mass components.
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