64 research outputs found

    Accretion disks in Algols: progenitors and evolution

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    There are only a few Algols with measured accretion disk parameters. These measurements provide additional constraints for tracing the origin of individual systems, narrowing down the initial parameter space. We investigate the origin and evolution of 6 Algol systems with accretion disks to find the initial parameters and evolutionary constraints for them. With a modified binary evolution code, series of close binary evolution are calculated to obtain the best match for observed individual systems. Initial parameters for 6 Algol systems with accretion disks were determined matching both the present system parameters and the observed disk characteristics. When RLOF starts during core hydrogen burning of the donor, the disk lifetime was found to be short. The disk luminosity is comparable to the luminosity of the gainer during a large fraction of the disk lifetime.Comment: 8 pages, 6 figures , accepted by A&

    Mass and angular momentum loss during RLOF in Algols

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    We present a set of evolutionary computations for binaries with a B-type primary at birth. Some liberal computations including loss of mass and angular momentum during binary evolution are added to an extensive grid of conservative calculations. Our computations are compared statistically to the observed distributions of orbital periods and mass ratios of Algols. Conservative Roche Lobe Over Flow (RLOF) reproduces the observed distribution of orbital periods decently but fails to explain the observed mass ratios in the range 0.4-1. In order to obtain a better fit the binaries have to lose a significant amount of matter, without transferring too much angular momentum.Comment: 6 pages, 5 figures. to appear in the proceedings of the meeting Massive Stars in Interacting Binaries, eds. N. St.-Louis and T. Moffa

    Mass loss out of close binaries

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    In a liberal evolutionary scenario, mass can escape from a binary during eras of fast mass transfer. We calculate the mass lost by binaries with a B-type primary at birth where mass transfer starts during hydrogen core burning of the donor. We simulate the distribution of mass-ratios and orbital periods for those interacting binaries. The amount of time the binary shows Algol characteristics within different values of mass-ratio and orbital period has been fixed from conservative and liberal evolutionary calculations. We use these data to simulate the distribution of mass-ratios and orbital periods of Algols with the conservative as well as the liberal model. We compare mass-ratios and orbital periods of Algols obtained by conservative evolution with those obtained by our liberal model. Since binaries with a late B-type primary evolve almost conservatively, the overall distribution of mass-ratios will only yield a few Algols more with high mass-ratios than conservative calculations do. Whereas the simulated distribution of orbital periods of Algols fits the observations well, the simulated distribution of mass-ratios produces always too few systems with large values.Comment: 6 pages, 6 figures, accepted for publication in A&A; accepted versio

    Blue supergiant progenitor models of Type II supernovae

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    In the present paper we show that within all the uncertainties that govern the process of Roche lobe overflow in Case Br type massive binaries, it can not be excluded that a significant fraction of them merge and become single stars. We demonstrate that at least some of them will spend most of their core helium burning phase as hydrogen rich blue stars, populating the massive blue supergiant region and/or the massive Be type star population. The evolutionary simulations let us suspect that these mergers will explode as luminous hydrogen rich stars and it is tempting to link them to at least some super luminous supernovae.Comment: Accepted for publication in A&A; accepted versio

    Spin-up and hot spots can drive mass out of a binary

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    The observed distribution of periods and mass ratios of Algols with a B type primary at birth was updated. Conservative evolution fails to produce the large fraction with a high mass ratio: i.e. q in [0.4-0.6]. Interacting binaries thus have to lose mass before or during Algolism. During RLOF mass is transferred continuously from donor to gainer. The gainer spins up; sometimes up to critical velocity. Equatorial material on the gainer is therefore less bound to the system. The material coming from the donor through the first Langrangian point impinges violently on the surface of the gainer or the edge of the accretion disc, creating a hot spot in the area of impact. The sum of rotational energy (fast rotation) and radiative energy (hot spot) depends on the mass-loss rate. The sum of both energies on a test mass located in the impact area equals exactly its binding energy at some critical value. As long as the mass transfer rate is smaller than this value the gainer accepts all the mass coming from the donor: RLOF happens conservatively. But as soon as the critical rate is exceeded the gainer will acquire no more than the critical value and RLOF runs into its liberal era. Low mass binaries never achieve mass-loss rates larger than the critical value. Intermediate mass binaries evolve mainly conservatively but mass will be blown away from the system during the short era of rapid mass transfer soon after RLOF-ignition. Binaries with 9+5.4 solar masses (P in [2-4] d) evolve almost always conservatively. Only during some 20,000 years the gainer is not capable of grasping all the material that comes from the donor. During this short lapse of time a significant fraction of the mass of the system is blown into interstellar space. The mass ratio bin [0.4-0.6] is now much better represented.Comment: 12 pages, 7 figures, accepted for publication in A&A; accepted versio

    Mass loss out of close binaries. II

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    Liberal evolution of interacting binaries has been proposed previously by several authors in order to meet various observed binary characteristics better than conservative evolution does. Since Algols are eclipsing binaries the distribution of their orbital periods is precisely known. The distribution of their mass ratios contains however more uncertainties. We try to reproduce these two distributions theoretically using a liberal scenario in which the gainer star can lose mass into interstellar space as a consequence of its rapid rotation and the energy of a hot spot. In a recent paper (Van Rensbergen et al. 2010, A&A) we calculated the liberal evolution of binaries with a B-type primary at birth where mass transfer starts during core hydrogen burning of the donor. In this paper we include the cases where mass transfer starts during hydrogen shell burning and it is our aim to reproduce the observed distributions of the system parameters of Algol-type semi-detached systems. Our calculations reveal the amount of time that an Algol binary lives with a well defined value of mass ratio and orbital period. We use these data to simulate the distribution of mass ratios and orbital periods of Algols. Binaries with a late B-type initial primary hardly lose any mass whereas those with an early B primary evolve in a non-conservative way. Conservative binary evolution predicts only ~ 12 % of Algols with a mass ratio q above 0.4. This value is raised up to ~ 17 % using our scenario of liberal evolution, which is still far below the ~ 45 % that is observed. Observed orbital periods of Algol binaries larger than one day are faithfully reproduced by our liberal scenario. Mass ratios are reproduced better than with conservative evolution, but the resemblance is still poor.Comment: 11 pages, 6 figures, accepted for publication in A&A; accepted versio

    Pulsar Parallaxes at 5 GHz with the Very Long Baseline Array

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    We present the first pulsar parallaxes measured with phase-referenced pulsar VLBI observations at 5 GHz. Due to the steep spectra of pulsars, previous astrometric measurements have been at lower frequencies. However, the strongest pulsars can be observed at 5 GHz, offering the benefit of lower combined ionospheric and tropospheric phase errors, which usually limit VLBI astrometric accuracy. The pulsars B0329+54, B0355+54 and B1929+10 were observed for 7 epochs spread evenly over 2 years. For B0329+54, large systematic errors lead to only an upper limit on the parallax (pi < 1.5 mas). A new proper motion and parallax were measured for B0355+54 (pi = 0.91 +- 0.16 mas), implying a distance of 1.04+0.21-0.16 kpc and a transverse velocity of 61+12-9 km/s. The parallax and proper motion for B1929+10 were significantly improved (pi = 2.77 +- 0.07 mas), yielding a distance of 361+10-8 pc and a transverse velocity of 177+4-5 km/s. We demonstrate that the astrometric errors are correlated with the angular separation between the phase reference calibrator and the target source, with significantly lower errors at 5 GHz compared to 1.6 GHz. Finally, based on our new distance determinations for B1929+10 and B0355+54, we derive or constrain the luminosities of each pulsar at high energies. We show that, for thermal emission models, the emitting area for X-rays from PSR B1929+10 is roughly consistent with the canonical size for a heated polar cap, and that the conversion of spin-down power to gamma-ray luminosity in B0355+54 must be low. The new proper motion for B1929+10 also implies that its progenitor is unlikely to have been the binary companion of the runaway O-star zeta-Ophiuchi.Comment: 8 pages, including 3 figures and 3 tables; emulateapj; ApJ submitte

    On the origin and evolutionary state of RZ Cas, KO Aql and S Equ

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    Aims. Determination of the present evolutionary state and the restrictions on the initial mass ratios of RZ Cas, KO Aql and S Equ. Methods. Comparison of mass gaining stars with evolutionary models of single stars with the same mass and subsequent comparison with accretion tracks from simultaneous conservative binary evolution. Results. The gainers are in an early main sequence stage (Xc greater than 0.5), with KO Aql being almost unevolved (assuming quasi-thermal equilibrium). The initial donor/gainer mass ratios Mdi/Mgi must be larger than three to obtain the present mass and luminosity of the gainers.Comment: 4 pages, 2 figures, accepted for publication in A&A; accepted versio

    The origin of runaway stars

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    Milli-arcsecond astrometry provided by Hipparcos and by radio observations makes it possible to retrace the orbits of some of the nearest runaway stars and pulsars to determine their site of origin. The orbits of the runaways AE Aurigae and mu Columbae and of the eccentric binary iota Orionis intersect each other about 2.5 Myr ago in the nascent Trapezium cluster, confirming that these runaways were formed in a binary-binary encounter. The path of the runaway star zeta Ophiuchi intersects that of the nearby pulsar PSR J1932+1059, about 1 Myr ago, in the young stellar group Upper Scorpius. We propose that this neutron star is the remnant of a supernova that occurred in a binary system which also contained zeta Oph, and deduce that the pulsar received a kick velocity of about 350 km/s in the explosion. These two cases provide the first specific kinematic evidence that both mechanisms proposed for the production of runaway stars, the dynamical ejection scenario and the binary-supernova scenario, operate in nature.Comment: 5 pages, including 2 eps-figures and 1 table, submitted to the ApJ Letters. The manuscript was typeset using aaste
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