Extent of pollution in planet-bearing stars

(abridged) Search for planets around main-sequence (MS) stars more massive than the Sun is hindered by their hot and rapidly spinning atmospheres. This obstacle has been sidestepped by radial-velocity surveys of those stars on their post-MS evolutionary track (G sub-giant and giant stars). Preliminary observational findings suggest a deficiency of short-period hot Jupiters around the observed post MS stars, although the total fraction of them with known planets appears to increase with their mass. Here we consider the possibility that some very close- in gas giants or a population of rocky planets may have either undergone orbital decay or been engulfed by the expanding envelope of their intermediate-mass host stars. If such events occur during or shortly after those stars' main sequence evolution when their convection zone remains relatively shallow, their surface metallicity can be significantly enhanced by the consumption of one or more gas giants. We show that stars with enriched veneer and lower-metallicity interior follow slightly modified evolution tracks as those with the same high surface and interior metallicity. As an example, we consider HD149026, a marginal post MS 1.3 Msun star. We suggest that its observed high (nearly twice solar) metallicity may be confined to the surface layer as a consequence of pollution by the accretion of either a planet similar to its known 2.7-day-period Saturn-mass planet, which has a 70 Mearth compact core, or a population of smaller mass planets with a comparable total amount of heavy elements. It is shown that an enhancement in surface metallicity leads to a reduction in effective temperature, in increase in radius and a net decrease in luminosity. The effects of such an enhancement are not negligible in the determinations of the planet's radius based on the transit light curves.Comment: 25 pages, 8 figures, submitted to Ap

The Evolutionary Status of SS433

We consider possible evolutionary models for SS 433. We assume that common-envelope evolution is avoided if radiation pressure is able to expel most of a super-Eddington accretion flow from a region smaller than the accretor's Roche lobe. This condition is satisfied, at least initially, for largely radiative donors with masses in the range 4-12 solar masses. For donors more massive than about 5 solar masses, moderate mass ratios q = M_2/M_1 > 1 are indicated, thus tending to favor black-hole accretors. For lower mass donors, evolutionary considerations do not distinguish between a neutron star or black hole accretor. In all cases the mass transfer (and mass loss) rates are much larger than the likely mass-loss rate in the precessing jets. Almost all of the transferred mass is expelled at radii considerably larger than the jet acceleration region, producing the "stationary" H-alpha line, the infrared luminosity, and accounting for the low X-ray luminosity.Comment: 13 pages, Astrophysical Journal Letters, accepte

WD + MS systems as the progenitor of SNe Ia

We show the initial and final parameter space for SNe Ia in a ($\log P^{\rm i}, M_{\rm 2}^{\rm i}$) plane and find that the positions of some famous recurrent novae, as well as a supersoft X-ray source (SSS), RX J0513.9-6951, are well explained by our model. The model can also explain the space velocity and mass of Tycho G, which is now suggested to be the companion star of Tycho's supernova. Our study indicates that the SSS, V Sge, might be the potential progenitor of supernovae like SN 2002ic if the delayed dynamical-instability model due to Han & Podsiadlowski (2006) is appropriate. Following the work of Meng, Chen & Han (2009), we found that the SD model (WD + MS) with an optically thick wind can explain the birth rate of supernovae like SN 2006X and reproduce the distribution of the color excess of SNe Ia. The model also predicts that at least 75% of all SNe Ia may show a polarization signal in their spectra.Comment: 6 pages, 2 figures, accepted for publication in Astrophysics & Space Science (Proceeding of the 4th Meeting on Hot Subdwarf Stars and Related Objects, edited by Zhanwen Han, Simon Jeffery & Philipp Podsiadlowski

Donor Stars in Black-Hole X-Ray Binaries

We study theoretically the formation of black-hole (BH) X-ray binaries. Consistency of the models with the observed relative numbers of systems with low-mass (<2 M_sun) and intermediate-mass (~2 M_sun - M_{BH}) donors leads to severe constraints on the evolutionary parameters of the progenitors. In particular, we find that (i) BH progenitor masses cannot exceed about 2 M_{BH}; (ii) high values of the common-envelope efficiency parameter (alpha_{CE} > 1) are required, implying that energy sources other than orbital contraction must be invoked to eject the envelope; (iii) the mass-loss fraction in helium-star winds is limited to be <50%. Outside of this limited parameter space for progenitors we find that either BH X-ray binary formation cannot occur at all or donors do not have the full range of observed masses. We discuss the implications of these results for the structure of massive hydrogen-rich stars, the evolution of helium-stars, and BH formation. We also consider the possible importance of asymmetric kicks.Comment: 29 pages, 6 figures, accepted for publication in The Astrophysical Journa

Optoacoustic solitons in Bragg gratings

Optical gap solitons, which exist due to a balance of nonlinearity and dispersion due to a Bragg grating, can couple to acoustic waves through electrostriction. This gives rise to a new species of ``gap-acoustic'' solitons (GASs), for which we find exact analytic solutions. The GAS consists of an optical pulse similar to the optical gap soliton, dressed by an accompanying phonon pulse. Close to the speed of sound, the phonon component is large. In subsonic (supersonic) solitons, the phonon pulse is a positive (negative) density variation. Coupling to the acoustic field damps the solitons' oscillatory instability, and gives rise to a distinct instability for supersonic solitons, which may make the GAS decelerate and change direction, ultimately making the soliton subsonic.Comment: 5 pages, 3 figure

Birthrates and delay times of Type Ia supernovae

Type Ia supernovae (SNe Ia) play an important role in diverse areas of astrophysics, from the chemical evolution of galaxies to observational cosmology. However, the nature of the progenitors of SNe Ia is still unclear. In this paper, according to a detailed binary population synthesis study, we obtained SN Ia birthrates and delay times from different progenitor models, and compared them with observations. We find that the Galactic SN Ia birthrate from the double-degenerate (DD) model is close to those inferred from observations, while the birthrate from the single-degenerate (SD) model accounts for only about 1/2-2/3 of the observations. If a single starburst is assumed, the distribution of the delay times of SNe Ia from the SD model is a weak bimodality, where the WD + He channel contributes to the SNe Ia with delay times shorter than 100Myr, and the WD + MS and WD + RG channels to those with age longer than 1Gyr.Comment: 11 pages, 2 figures, accepted by Science in China Series G (Dec.30, 2009

Field Blue Stragglers and Related Mass Transfer Issues

This chapter contains my impressions and perspectives about the current state of knowledge about field blue stragglers (FBS) stars, drawn from an extensive literature that I searched. I conclude my review of issues that attend FBS and mass transfer, by a brief enumeration of a few mildly disquieting observational facts.Comment: Chapter 4, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G. Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe

On the Recognition of Fan-Planar and Maximal Outer-Fan-Planar Graphs

Fan-planar graphs were recently introduced as a generalization of 1-planar graphs. A graph is fan-planar if it can be embedded in the plane, such that each edge that is crossed more than once, is crossed by a bundle of two or more edges incident to a common vertex. A graph is outer-fan-planar if it has a fan-planar embedding in which every vertex is on the outer face. If, in addition, the insertion of an edge destroys its outer-fan-planarity, then it is maximal outer-fan-planar. In this paper, we present a polynomial-time algorithm to test whether a given graph is maximal outer-fan-planar. The algorithm can also be employed to produce an outer-fan-planar embedding, if one exists. On the negative side, we show that testing fan-planarity of a graph is NP-hard, for the case where the rotation system (i.e., the cyclic order of the edges around each vertex) is given

Spectroscopic abundance analysis of dwarfs in young open cluster IC 4665

We report a detailed spectroscopic abundance analysis for a sample of 18 F-K dwarfs of the young open cluster IC 4665. Stellar parameters and element abundances of Li, O, Mg, Si, Ca, Ti, Cr, Fe and Ni have been derived using the spectroscopic synthesis tool SME (Spectroscopy Made Easy). Within the measurement uncertainties the iron abundance is uniform with a standard deviation of 0.04 dex. No correlation is found between the iron abundance and the mass of the stellar convective zone, and between the Li abundance and the Fe abundance. In other words, our results do not reveal any signature of accretion and therefore do not support the scenario that stars with planets (SWPs) acquire their on the average higher metallicity compared to field stars via accretion of metal-rich planetary material. Instead the higher metallicity of SWPs may simply reflect the fact that planet formation is more efficient in high metallicity environs. However, since that many details of the planet system formation processes remain poorly understood, further studies are needed for a final settlement of the problem of the high metallicity of SWPs. The standard deviation of [Fe/H] deduced from our observations, taken as an upper limit on the metallicity dispersion amongst the IC 4665 member stars, has been used to constrain proto-planetary disk evolution, terrestrial and giant planets formation and evolution processes. Our results do not support the possibility that the migration of gas giants and the circularization of terrestrial planets' orbits are regulated by their interaction with a residual population of planetesimals and dust particles.Comment: 18 pages, 6 figures, accepted for publication in Ap

Nearby low-mass triple system GJ795

We report the results of our optical speckle-interferometric observations of the nearby triple system GJ795 performed with the 6-m BTA telescope with diffraction-limited angular resolution. The three components of the system were optically resolved for the first time. Position measurements allowed us to determine the elements of the inner orbit of the triple system. We use the measured magnitude differences to estimate the absolute magnitudes and spectral types of the components of the triple: $M_{V}^{Aa}$=7.31$\pm$0.08, $M_{V}^{Ab}$=8.66$\pm$0.10, $M_{V}^{B}$=8.42$\pm$0.10, $Sp_{Aa}$ $\approx$K5, $Sp_{Ab}$ $\approx$K9, $Sp_{B}$ $\approx$K8. The total mass of the system is equal to $\Sigma\mathcal{M}_{AB}$=1.69$\pm0.27\mathcal{M}_{\odot}$. We show GJ795 to be a hierarchical triple system which satisfies the empirical stability criteria.Comment: 6 pages, 2 figures, published in Astrophysical Bulleti