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Register a new userEvolutionary process of the interacting binary V495 Centauri
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Added by
Jaime Andr\\'es Rosales Guzm\\'an
Publication date
2018
fields
Physics
and research's language is
English
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We present a simple model for the Double Periodic Variable (DPV) V495 Cen, which evolves as a binary system of intermediate mass, where the gainer cannot accrete at high rate, limited by the Eddington accretion rate, leading to the formation of an accretion disc. The theoretical model begins at the zero age main sequence considering the rotation for both stars. For this purpose we used the stellar evolution code MESA, developed to calculate the evolution of stars in a wide range of parameters. We started the model adjusting fundamental parameters published for this system through a chi-square optimization algorithm, and adopting an initial orbital period of 3.9 days and initial masses for the primary component $M_{i,d} = 3.40$ $M_{odot}$ and $M_{i,g}= 3.18$ $M_{odot}$ for the gainer, with a metallicity associated to this type of DPV of $Z = 0.02$. The method converged successfully for eight free degrees and 5% of confidence with a chi-square of $Delta chi^{2}_{0.95,8}= 0.212$. We describe each evolutionary stage of both components until that the donor reaches 20% core helium depletion as stop criterion. We offer a complementary analysis for understanding the mechanism of the magnetic dynamos inside the donor star using the Tayler-Spruit formalism. Currently, the theoretical model is consistent with the fundamental parameters published for V495 Cen and we discuss how our predictions can help to develop efficients theoretical models for DPV stars.
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Double Periodic Variables (DPV) are among the new enigmas of semi-detached eclipsing binaries. These are intermediate-mass binaries characterized by a long photometric period lasting on average 33 times the orbital period. We present a spectroscopic and photometric study of the DPV V495 Cen based on new high-resolution spectra and the ASAS V-band light curve. We have determined an improved orbital period of $33.492 pm 0.002$ d and a long period of 1283 d. We find a cool evolved star of $M_{2}=0.91pm 0.2 M_{odot}$, $T_{2}= 6000pm 250 K$ and $R_{2}=19.3 pm 0.5 R_{odot}$ and a hot companion of $M_{1}= 5.76pm 0.3 M_{odot}$, $T_{1}=16960pm 400 K$ and $R=4.5pm0.2 R_{odot}$. The mid-type B dwarf is surrounded by a concave and geometrically thick disc, of radial extension $R_{d}= 40.2pm 1.3 R_{odot}$ contributing $sim$ 11 percent to the total luminosity of the system at the V band. The system is seen under inclination $84.!!^{circ}8$ $pm$ $0.!!^{circ}6$ and it is at a distance $d= 2092 pm 104.6$ pc. The light curve analysis suggests that the mass transfer stream impacts the external edge of the disc forming a hot region 11 % hotter than the surrounding disc material. The persistent $V<R$ asymmetry of the H$alpha$ emission suggests the presence of a wind and the detection of a secondary absorption component in He I lines indicates a possible wind origin in the hotspot region.
DY Cen has shown a steady fading of its visual light by about 1 magnitude in the last 40 years suggesting a secular increase in its effective temperature. We have conducted non-LTE and LTE abundance analyses to determine the stars effective temperature, surface gravity, and chemical composition using high-resolution spectra obtained over two decades. The derived stellar parameters for three epochs suggest that DY Cen has evolved at a constant luminosity and has become hotter by about 5000 K in 23 years. We show that the derived abundances remain unchanged for the three epochs. The derived abundances of the key elements, including F and Ne, are as observed for the extreme helium stars resulting from a merger of an He white dwarf with a C-O white dwarf. Thus, DY Cen by chemical composition appears to be also a product of a merger of two white dwarfs. This appearance seems to be at odds with the recent suggestion that DY Cen is a single-lined spectroscopic binary.
We analyze the evolution of the potentially habitable planet Proxima Centauri b to identify environmental factors that affect its long-term habitability. We consider physical processes acting on size scales ranging from the galactic to the stellar system to the planets core. We find that there is a significant probability that Proxima Centauri has had encounters with its companion stars, Alpha Centauri A and B, that are close enough to destabilize an extended planetary system. If the system has an additional planet, as suggested by the discovery data, then it may perturb planet bs eccentricity and inclination, possibly driving those parameters to non-zero values, even in the presence of strong tidal damping. We also model the internal evolution of the planet, evaluating the roles of different radiogenic abundances and tidal heating and find that magnetic field generation is likely for billions of years. We find that if planet b formed in situ, then it experienced 169 +/- 13 million years in a runaway greenhouse as the star contracted during its formation. This early phase could remove up to 5 times as much water as in the modern Earths oceans, possibly producing a large abiotic oxygen atmosphere. On the other hand, if Proxima Centauri b formed with a substantial hydrogen atmosphere (0.01 - 1% of the planets mass), then this envelope could have shielded the water long enough for it to be retained before being blown off itself. After modeling this wide range of processes we conclude that water retention during the host stars pre-main sequence phase is the biggest obstacle for Proxima bs habitability. These results are all obtained with a new software package called VPLANET.
The types of instability in the interacting binary stars are reviewed. The project Inter-Longitude Astronomy is a series of smaller projects on concrete stars or groups of stars. It has no special funds, and is supported from resources and grants of participating organizations, when informal working groups are created. Totally we studied 1900+ variable stars of different types. The characteristic timescale is from seconds to decades and (extrapolating) even more. The monitoring of the first star of our sample AM Her was initiated by Prof. V.P. Tsesevich (1907-1983). Since more than 358 ADS papers were published. Some highlights of our photometric and photo-polarimetric monitoring and mathematical modelling of interacting binary stars of different types are presented: classical, asynchronous, intermediate polars and magnetic dwarf novae (DO Dra) with 25 timescales corresponding to different physical mechanisms and their combinations (part Polar); negative and positive superhumpers in nova-like and many dwarf novae stars (Superhumper); eclipsing non-magnetic cataclysmic variables; symbiotic systems (Symbiosis); super-soft sources (SSS, QR And); spotted (and not spotted) eclipsing variables with (and without) evidence for a current mass transfer (Eclipser) with a special emphasis on systems with a direct impact of the stream into the gainer stars atmosphere, or V361 Lyr-type stars. Other parts of the ILA project are Stellar Bell (interesting pulsating variables of different types and periods - M, SR, RV Tau, RR Lyr, Delta Sct) and Novice(=New Variable) discoveries and classification with a subsequent monitoring for searching and studying possible multiple components of variability. Special mathematical methods have been developed to create a set of complementary software for statistically optimal modelling of variable stars of different types.
New spectroscopic observations of the double-lined eclipsing binary AQ,Cas are presented. All available spectroscopic and photometric observations have been analysed for the fundamental properties of the components. Analyses show that the system consists of a massive primary with a mass of 17.63$pm$0.91 M$_{odot}$ and radius of 13.48$pm$0.64R$_{odot}$ and a secondary with 12.56$pm$0.81 M$_{odot}$ and radius of 23.55$pm$0.73 R$_{odot}$, corresponding spectral types of B0.5($pm$2) II-III + B3($pm$1) II. The secondary star fills its corresponding Roche lobe and mass transfer to the primary star is going on. This stream considerably does affect the photometric observations both starting from the second quarter up to the first contact of primary eclipse and just at the second maximum. Thus, the light curve is distorted and tightly depended on the wavelength of the observations. The available multi passband light curves have been analysed by taking the stream effects, as either hot or cool spots, into account. The comparison of the models and observations in the $log(L/L_{odot})$ - $log T_{eff}$ and $log g - log T_{eff}$ diagrams clearly shows that the more massive star is consistent with models and is predicted to be close to the phase of hydrogen shell ignition. Average distance to the system is estimated as 4150$pm$240 pc using the BVJHK magnitudes and V-passband extinction.
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