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Register a new userV1135 Herculis: a double-lined eclipsing binary with an Anomalous Cepheid
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\\\"Om\\\"ur \\c{C}akirli Or
Publication date
2013
fields
Physics
and research's language is
English
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BVR light curves and radial velocities for the double-lined eclipsing binary V1135,Her were obtained. The brighter component of V1135,Her is a Cepheid variable with a pulsation period of 4.22433$pm$0.00026 days. The orbital period of the system is about 39.99782$pm$0.00233 days, which is the shortest value among the known Type,II Cepheid binaries. The observed B, V, and R magnitudes were cleaned for the intrinsic variations of the primary star. The remaining light curves, consisting of eclipses and proximity effects, are obtained. Our analyses of the multi-colour light curves and radial velocities led to the determination of fundamental stellar properties of both components of the interesting system V1135,Her. The system consists of two evolved stars, G1+K3 between giants and supergiants, with masses of M$_1$=1.461$pm$0.054 Msun ~and M$_2$=0.504$pm$0.040 {Msun} and radii of R$_1$=27.1$pm$0.4 {Rsun} and R$_2$=10.4$pm$0.2 {Rsun}. The pulsating star is almost filling its corresponding Roche lobe which indicates the possibility of mass loss or transfer having taken place. We find an average distance of d=7500$pm$450 pc using the BVR magnitudes and also the V-band extinction. Location in the Galaxy and the distance to the galactic plane with an amount of 1300 pc indicate that it probably belongs to the thick-disk population. Most of the observed and calculated parameters of the V1135,Her and its location on the color-magnitude and period-luminosity diagrams lead to a classification of an Anomalous Cepheid.
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Multi-color light curves and radial velocities for TYC,1031,1262,1 have been obtained and analyzed. TYC,1031,1262,1 includes a Cepheid with a period of 4.15270$pm$0.00061 days. The orbital period of the system is about 51.2857$pm$0.0174 days. The pulsation period indicates a secular period increase with an amount of 2.46$pm$0.54 min/yr. The observed B, V, and R magnitudes were cleaned for the intrinsic variations of the primary star. The remaining light curves, consisting of eclipses and proximity effects, are obtained and analyzed for orbital parameters. The system consists of two evolved stars, F8II+G6II, with masses of M$_1$=1.640$pm$0.151 {Msun} and M$_2$=0.934$pm$0.109 {Msun} and radii of R$_1$=26.9$pm$0.9 {Rsun} and R$_2$=15.0$pm$0.7 {Rsun}. The pulsating star is almost filling its corresponding Roche lobe which indicates the possibility of mass loss or transfer having taken place. We find an average distance of d=5070$pm$250,pc using the BVR and JHK magnitudes and also the V-band extinction. Kinematic properties and the distance to the galactic plane with an amount of 970 pc indicate that it belongs to the thick-disk population. Most of the observed and calculated parameters of the TYC,1031,1262,1 lead to a classification of an Anomalous Cepheid.
We report the discovery and characterisation of a new M-dwarf binary, with component masses and radii of M1 = 0.244 -0.003/+0.003 Msun, R1 = 0.261 -0.009/+0.006 Rsun, M2 = 0.179 -0.001/+0.002 Msun, R2 = 0.218 -0.011/+0.007 Rsun, and orbital period of ~4.1 days. The M-dwarf binary HATS551-027 (LP 837-20) was identified as an eclipsing binary by the HATSouth survey, and characterised by a series of high precision photometric observations of the eclipse events, and spectroscopic determinations of the atmospheric parameters and radial velocity orbits. HATS551-027 is one of few systems with both stellar components lying in the fully-convective regime of very low mass stars, and can serve as a test for stellar interior models. The radius of HATS551-027A is consistent with models to 1 sigma, whilst HATS551-027B is inflated by 9% at 2 sigma significance. We measure the effective temperatures for the two stellar components to be Teff,1 = 3190 +/- 100 K and Teff,2 = 2990+/-110 K, both are slightly cooler than theoretical models predict, but consistent with other M-dwarfs of similar masses that have previously been studied. We also measure significant Halpha emission from both components of the binary system, and discuss this in the context of the correlation between stellar activity and the discrepancies between the observed and model temperatures.
Based on new observations and improved modeling techniques, we have reanalyzed seven Cepheids in the Large Magellanic Cloud. Improved physical parameters have been determined for the exotic system OGLE LMC-CEP-1718 composed of two first-overtone Cepheids and a completely new model was obtained for the OGLE LMC-CEP-1812 classical Cepheid. This is now the shortest period Cepheid for which the projection factor is measured. The typical accuracy of our dynamical masses and radii determinations is 1%. The radii of the six classical Cepheids follow period--radius relations in the literature. Our very accurate physical parameter measurements allow us to calculate a purely empirical, tight period--mass--radius relation that agrees well with theoretical relations derived from non-canonical models. This empirical relation is a powerful tool to calculate accurate masses for single Cepheids for which precise radii can be obtained from Baade--Wesselink-type analyses. The mass of the type-II Cepheid $kappa$ Pav, $0.56 pm 0.08 M_odot$, determined using this relation is in a very good agreement with theoretical predictions. We find large differences between the p-factor values derived for the Cepheids in our sample. Evidence is presented that a simple period--p-factor relation shows an intrinsic dispersion, hinting at the relevance of other parameters, such as the masses, radii, and radial velocity variation amplitudes. We also find evidence that the systematic blueshift exhibited by Cepheids, is primarily correlated with their gravity. The companion star of the Cepheid in the OGLE LMC-CEP-4506 system has a very similar temperature and luminosity, and is clearly located inside the Cepheid instability strip, yet it is not pulsating.
R144 is a WN6h star in the 30 Doradus region. It is suspected to be a binary because of its high luminosity and its strong X-ray flux, but no periodicity could be established so far. Here, we present new Xshooter multi-epoch spectroscopy of R144 obtained at the ESO Very Large Telescope (VLT). We detect variability in position and/or shape of all the spectral lines. We measure radial velocity variations with an amplitude larger than 250 km/s in NIV and NV lines. Furthermore, the NIII and NV line Doppler shifts are anti-correlated and the NIV lines show a double-peaked profile on six of our seven epochs. We thus conclude that R144 is a double-lined spectroscopic binary. Possible orbital periods range from 2 to 6 months, although a period up to one year is allowed if the orbit is highly eccentric. We estimate the spectral types of the components to be WN5-6h and WN6-7h, respectively. The high luminosity of the system (log Lbol/Lsun ~ 6.8) suggests a present-day total mass content in the range of about 200 to 300 Msun, depending on the evolutionary stage of the components. This makes R144 the most massive binary identified so far, with a total mass content at birth possibly as large as 400 Msun. We briefly discuss the presence of such a massive object 60 pc away from the R136 cluster core in the context of star formation and stellar dynamics.
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.
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