Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
V380 Cygni - Request for new observations
The problem of apsidal motion for V380 Cygni is reviewed. From theexisting observations it is difficult to determine an accurate apsidalperiod. We argue that further observations are needed.
| Aus den IBVS 5680, 5682, 5684, 5690, 5694, 5681, 5685, 5686, 5687, 5688, 5689, 5692, 5695, 5696, 5697, 5698.
Not Available
| New grids of stellar models including tidal-evolution constants up to carbon burning. III. From 0.8 to 125 Mȯ: the Large Magellanic Cloud (Z = 0.007-0.01)
In this paper, we present new specific stellar models for the LargeMagellanic Cloud. In order to take the observational uncertainties inthe chemical composition into account, we have computed two grids: (X,Z) = (0.730, 0.010) and (0.739, 0.007). The covered mass range was 0.80up to 125 Mȯ. The effects of rotation can beinvestigated by using the gravity-darkening exponents that are availablefor each track. The tidal constant E_2, depth of the convective outerzone, and the radius of gyration are computed and presented in asuitable format for studying the tidal evolution of a given closebinary. The isochrones (and also those corresponding to the previousgrids) will be presented in a future paper.
| A high-resolution spectroscopy survey of β Cephei pulsations in bright stars
We present a study of absorption line-profile variations in early-B typenear-main-sequence stars without emission lines. We have surveyed atotal of 171 bright stars using the Nordic Optical Telescope (NOTSA),William Herschel Telescope (ING) and Coudé Auxiliary Telescope(ESO). Our sample contains 75% of all O9.5-B2.5 III-V non-emission-linestars brighter than 5.5 mag. We obtained high signal-to-noise,high-resolution spectra of the SiIII λ4560 triplet - for 125stars of our sample we obtained more than one spectrum - and examinedthese for pulsational-like line-profile variations and/or structure. Weconclude that about half of our sample stars show evidence forline-profile variations (LPV). We find evidence for LPV in about 65% ofour sample stars brighter than V=5.5. For stars with rotationalbroadening V sin i 100 km s-1, we find evidence for LPVin about 75% of the cases. We argue that it is likely that these LPV areof pulsational origin, and that hence more than half of thesolar-neighbourhood O9.5-B2.5 III-V stars is pulsating in modes that canbe detected with high-resolution spectroscopy. We detected LPV in 64stars previously unknown to be pulsators, and label these stars as newβ Cep candidates. We conclude that there is no obvious differencein incidence of (pulsational) LPV for early-B type near-main-sequencestars in binaries or in OB associations, with respect to single fieldstars.
| Core Overshoot: An Improved Treatment and Constraints from Seismic Data
We present a comprehensive set of stellar evolution models for Procyon Ain an effort to guide future measurements of both traditional stellarparameters and seismic frequencies toward constraining the amount ofcore overshoot in Procyon A and possibly other stars. Currentobservational measurements of Procyon A when combined with traditionalstellar modeling only place a large upper limit on overshoot ofαOV<1.1. By carrying out a detailed pulsationanalysis, we further demonstrate how p- and g-mode averaged spacings canbe used to gain better estimates of the core size. For both p- andg-modes, the frequency spacings for models without overshoot are clearlyseparated from the models with overshoot. In addition, measurements ofthe l=0 averaged small p-mode spacings could be used to establishProcyon A's evolutionary stage. For a fixed implementation of overshootand under favorable circumstances, the g-mode spacings can be used todetermine the overshoot extent to an accuracy of +/-0.05HP.However, we stress that considerable confusion is added due to theunknown treatment of the overshoot region. This ambiguity might beremoved by analyzing many different stars. A simple nonlocal convectiontheory developed by Kuhfuss is implemented in our stellar evolution codeand contrasted with the traditional approaches. We show that this theorysupports a moderate increase of the amount of convective overshoot withstellar mass of ΔαOV~=+0.10 between 1.5 and 15Msolar. This theory places an upper limit on Procyon A's coreovershoot extent of ~0.4HP, which matches the limit imposedby Roxburgh's integral criterion.
| Observed Orbital Eccentricities
For 391 spectroscopic and visual binaries with known orbital elementsand having B0-F0 IV or V primaries, we collected the derivedeccentricities. As has been found by others, those binaries with periodsof a few days have been circularized. However, those with periods up toabout 1000 or more days show reduced eccentricities that asymptoticallyapproach a mean value of 0.5 for the longest periods. For those binarieswith periods greater than 1000 days their distribution of eccentricitiesis flat from 0 to nearly 1, indicating that in the formation of binariesthere is no preferential eccentricity. The binaries with intermediateperiods (10-100 days) lack highly eccentric orbits.
| Asteroseismology of the β Cephei star ν Eridani: massive exploration of standard and non-standard stellar models to fit the oscillation data
We present the results of a detailed seismic modelling of the βCephei star ν Eridani with the Liège evolution and pulsationcodes. We selected four clearly detected, well-identified andindependent pulsation modes from the frequency spectrum obtained from arecent five-month multisite, multitechnique campaign, while previousmodelling work only took into account three frequencies. We show bymeans of a massive exploration of the parameter space that no standardstellar model both matches and excites these four observed modes, incontrast to the conclusion reached when considering only threefrequencies. Therefore, we have considered stellar models with differentmetal mixtures and different initial hydrogen abundance values. We showthat an increase in the relative number fraction of iron throughout thewhole star or a large decrease in the initial hydrogen abundance makethe stellar models matching the four selected modes satisfy allobservational constraints and we provide the general properties of thebest such physical models.
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| Apsidal Motion in Binaries: Rotation of the Components
A sample of 51 separated binary systems with measured apsidal periodsand rotational velocities of the components is examined. The ranges ofthe angles of inclination of the equatorial planes of the components tothe orbital plane are estimated for these systems. The observed apsidalvelocities can be explained by assuming that the axes of rotation of thestars are nonorthogonal to the orbital plane in roughly 47% of thesystems (24 of the 51) and the rotation of the components is notsynchronized with the orbital motion in roughly 59% of the systems (30of 51). Nonorthogonality and nonsynchrony are defined as deviations from90° and a synchronized angular velocity, respectively, at levels of1 or more.
| The massive and evolved EBS V380 Cygni: A case of critical evolution
The evolution and the internal structure of the double-lined eclipsingbinary V380 Cyg showing apsidal motion is investigated. The systemconsists of an evolved massive primary with a mass of 11.1 +/- 0.5Msun and a secondary which is still close to the ZAMS and hasa mass of 6.95 +/- 0.25 Msun. The core overshooting parameteralphaov was recently determined for this star as 0.6 +/- 0.1.However, such a value was derived using error bars in the effectivetemperature which seem to be unrealistically small. In addition, thereis no independent support for this value of alphaov eitherfrom Colour-Magnitude Diagrams of clusters or from double-linedeclipsing binaries. Therefore, we decided to compute stellar models withseveral values of core-overshooting parameter in order to try todisentangle this apparent disagreement. In order to compare theobservations with the theoretical predictions, we decided to use theratio of the effective temperatures,TR=Teff2/Teff1, rather than the effectivetemperatures themselves to avoid problems with calibrations and/or modelatmosphere dependencies. Contrary to what has been previouslyestablished, we have found acceptable common ages foralphaov= 0.2, 0.4, and 0.6 which fit the TR, the masses, theradii and the apsidal-motion rate simultaneously. Such indeterminationin alphaov should not be interpretated as a negative result.Instead, it indicates that errors in alphaov cannot bedetermined with a precision of 0.1 if realistic observational error barsare used; we are dealing with an EBS in a very critical phase ofevolution. Moreover, these new inferred values of alphaovimply that the dependency of convective core overshooting on the stellarmass, if it exists, is more uncertain and less pronounced than previousinvestigations suggested.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| Apsidal Motion in Detached Binary Stars: Comparison of Theory and Observations
A list of 62 detached binaries having reliable data on the rotation ofthe line of apsides is considered. Theoretical estimates of the rate ofapsidal motion are obtained. These estimates are compared withobservational data. It is shown that cases in which the theoreticalestimate exceeds the observed value are several times more frequent thancases in which the theoretical value is lower than the observed one.This discrepancy increases when systems with more reliable observationaldata are considered.
| Detached double-lined eclipsing binaries as critical tests of stellar evolution. Age and metallicity determinations from the HR diagram
Detached, double-lined spectroscopic binaries that are also eclipsingprovide the most accurate determinations of stellar mass, radius,temperature and distance-independent luminosity for each of theirindividual components, and hence constitute a stringent test ofsingle-star stellar evolution theory. We compile a large sample of 60non-interacting, well-detached systems mostly with typical errorssmaller than 2% for mass and radius and smaller than 5% for effectivetemperature, and compare them with the properties predicted by stellarevolutionary tracks from a minimization method. To assess the systematicerrors introduced by a given set of tracks, we compare the resultsobtained using three widely-used independent sets of tracks, computedwith different physical ingredients (the Geneva, Padova and Granadamodels). We also test the hypothesis that the components of thesesystems are coeval and have the same metallicity, and compare thederived ages and metallicities with the ones obtained by fitting asingle isochrone to the system. Overall, there is a good agreement amongthe different determinations, and we provide a comprehensive discussionon the sub-sample of systems which either present problems or haveestimated metallicities. Although within the errors the published trackscan fit most of the systems, a large degeneracy between age andmetallicity remains. The power of the test is thus limited because themetallicities of most of the systems are unknown. The full version ofTable 6 is only available in the electronic form athttp://www.edpsciences.org
| New results on the apsidal-motion test to stellar structure and evolution including the effects of dynamic tides
We revised the current status of the apsidal-motion test to stellarstructure and evolution. The observational sample was increased by about50% in comparison to previous studies. Classical and relativisticsystems were analyzed simultaneously and only systems with accurateabsolute dimensions were considered. New interior models incorporatingrecent opacity tables, stellar rotation, mass loss, and moderate coreovershooting were used as theoretical tools to compare the predictedwith the observed shifts of the position of the periastron. The stellarmodels were computed for the precise observed masses and the adoptedchemical compositions are consistent with the corresponding tables ofopacities to avoid the inherent problems of interpolation in mass and in(X, Z). The derived chemical composition for each individual system wasused to infer the primordial helium content as well as a law ofenrichment. The values found are in good agreement with those obtainedfrom various independent sources. For the first time, the effects ofdynamic tides are taken into account systematically to determine thecontribution of the tidal distortion to the predicted apsidal-motionrate. The deviations between the apsidal-motion rates resulting from theclassical formula and those determined by taking into account theeffects of dynamic tides are presented as a function of the level ofsynchronism. For systems close to synchronisation, dynamic tides causedeviations with respect to the classical apsidal-motion formula due tothe effects of the compressibility of the stellar fluid. For systemswith higher rotational angular velocities, additional deviations due toresonances arise when the forcing frequencies of the dynamic tides comeinto the range of the free oscillation modes of the component stars. Theresulting comparison shows a good agreement between the observed andtheoretical apsidal-motion rates. No systematic effects in the sensethat models are less mass concentrated than real stars and nocorrelations with the evolutionary status of the systems were detected.
| Observational Tests and Predictive Stellar Evolution
We compare 18 binary systems with precisely determined radii and massesfrom 23 to 1.1 Msolar and stellar evolution models producedwith our newly revised code TYCHO. ``Overshooting'' and rotationalmixing were suppressed in order to establish a baseline for isolatingthese and other hydrodynamic effects. Acceptable coeval fits are foundfor 16 pairs without optimizing for heavy-element or helium abundance.The precision of these tests is limited by the accuracies of theobserved effective temperatures. High-dispersion spectra and detailedatmospheric modeling should give more accurate effective temperaturesand heavy-element abundances. PV Cas, a peculiar early A system, EK CepB, a known post-T Tauri star, and RS Cha, a member of a young OBassociation, are matched by pre-main-sequence models. Predicted massloss agrees with upper limits from IUE for CW Cep A and B. Relativelypoor fits are obtained for binaries having at least one component in themass range 1.7
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Classification and properties of UV extinction curves
The catalog of Savage et al. (\cite{ref27}) reporting colour excesses of1415 stars from ANS photometry offers the opportunity to deeplyinvestigate the characteristics of UV extinction curves which differfrom the standard extinction of the diffuse interstellar medium. To thisaim we have selected a sample of 252 curves, which have been comparedwith the relations derived by Cardelli et al. (\cite{ref4}; CCM in thefollowing) for a variety of R_V values in the range 2.4-5 and have beenclassified as normal if they fit at least one of the CCM curves oranomalous otherwise. We find that normal curves with small R_V are justas numerous as those with large R_V. The anomalous objects are arrangedinto two groups according to the strength of the bump at 0.217 mu . Fora given value of c_2 this increases along the sequence: type Aanomalous, normals and type B anomalous, suggesting that this sequenceshould correspond to an increase of the amount of small grains along thesightline. Considerations concerning the environmental characteristicsindicate that the anomalous behaviour is not necessarily tied to theexistence of dense gas clouds along the line of sight.
| The mass dependence of the overshooting parameter determined from eclipsing binary data
High-precision data on absolute dimensions of evolved eclipsing binarieshave been used for a quantitative evaluation of the significance ofconvective overshoot in the stellar core. Eight detached double-linedeclipsing binaries with components close to or beyond the terminal agemain sequence (TAMS) and masses between 2 and 12Msolar havebeen compared with evolutionary models using different overshootingparameters. The results are robust and indicate a systematic increase ofthe amount of convective overshoot with the stellar mass. Suchdetermination constitutes a fundamental point for stellar structure andevolution theory.
| Chemical composition of eclipsing binaries: a new approach to the helium-to-metal enrichment ratio
The chemical enrichment law Y(Z) is studied by using detacheddouble-lined eclipsing binaries with accurate absolute dimensions andeffective temperatures. A sample of 50 suitable systems was collectedfrom the literature, and their effective temperatures were carefullyre-determined. The chemical composition of each of the systems wasobtained by comparison with stellar evolutionary models, under theassumption that they should fit an isochrone to the observed propertiesof the components. Evolutionary models covering a wide grid in Z and Ywere adopted for our study. An algorithm was developed for searching thebest-fitting chemical composition (and the age) for the systems, basedon the minimization of a χ2 function. The errors (andbiases) of these parameters were estimated by means of Monte Carlosimulations, with special care put on the correlations existing betweenthe errors of both components. In order to check the physicalconsistency of the results, we compared our metallicity values withempirical determinations, obtaining excellent coherence. Theindependently derived Z and Y values yielded a determination of thechemical enrichment law via weighted linear least-squares fit. Our valueof the slope, ΔY/ΔZ=2.2+/-0.8, is in good agreement withrecent results, but it has a smaller formal error and it is free ofsystematic effects. Linear extrapolation of the enrichment law to zerometals leads to an estimation of the primordial helium abundance ofYp=0.225+/-0.013, possibly affected by systematics in theeffective temperature determination.
| CQ Cep - a close Wolf-Rayet binary system + a third body ?
Not Available
| Eclipsing Binaries as Astrophysical Laboratories: Internal Structure, Core Convection, and Evolution of the B-Star Components of V380 Cygni
New photometric solutions have been carried out on the importanteccentric eclipsing system V380 Cygni (B1.5 II-III+B2 V) from UBVdifferential photoelectric photometry obtained by us. The photometricelements obtained from the analysis of the light curves have beencombined with the spectroscopic solution recently published by Popper& Guinan and have led to the physical properties of the systemcomponents. The effective temperature of the stars has been determinedby fitting IUE UV spectrophotometry to Kurucz model atmospheres andcompared with other determinations from broadband and intermediate-bandstandard photometry. The values of mass, absolute radius, and effectivetemperature for the primary and secondary stars are 11.1+/-0.5Msolar, 14.7+/-0.2 Rsolar, 21,350+/-400 K, and6.95+/-0.25 Msolar, 3.74+/-0.07 Rsolar,20,500+/-500 K, respectively. In addition, a redetermination of thesystem's apsidal motion rate has been done from the analysis of 12eclipse timings obtained from 1923 to 1995. The apsidal motion studyyields the internal mass distribution of the more luminous component.Using stellar structure and evolutionary models with modern inputphysics, tests on the extent of convection in the core of the moremassive B1.5 II-III star of the system have been carried out. Both theanalysis of the logg-logTeff diagram and the apsidal motionstudy indicate a star with a larger convective core, and thus morecentrally condensed, than currently assumed. This has been quantified inform of an overshooting parameter with a value ofαov~0.6+/-0.1. Finally, the tidal evolution of thesystem (synchronization and circularization times) has also beenstudied.
| The Large Magellanic Cloud Eclipsing Binary HV 2274: Fundamental Properties and Comparison with Evolutionary Models
We are carrying out an international, multiwavelength program todetermine the fundamental properties and independent distance estimatesof selected 14th to 15th magnitude eclipsing binaries in the Large andSmall Magellanic Clouds (LMC and SMC). Eclipsing binaries withwell-defined double-line radial velocity curves and light curves providevaluable information on orbital and physical properties of theircomponent stars. These properties include, among other characteristics,stellar mass and radius. These can be measured with an accuracy anddirectness unachievable by any other means. The study of stars in theLMC and SMC, where the metal abundances are significantly lower thansolar (by one-third to one-tenth) provides an important opportunity totest opacities and stellar atmosphere, interior, and evolution models.For the first time, we can also measure direct mass-luminosity relationsfor stars outside our Galaxy. In a previous paper we demonstrated how aprecise distance to the LMC-corresponding to(V0-Mv)LMC=18.30+/-0.07 mag-could bedetermined using the 14th magnitude LMC eclipsing binary HV 2274. Inthis paper we concentrate on the determination of the orbital andphysical properties of HV 2274 and its component stars from analyses oflight curves and new radial velocity curves formed from Hubble SpaceTelescope (HST)/Goddard High-Resolution Spectrograph observations. HV2274 (B1-2 IV-III+B1-2 IV-III Vmax~+14.2 P=5.73 days) is aparticularly appealing star because it is a detached binary that has aneccentric orbit (e=0.136) and shows rapid apsidal motion. The results ofthese analyses yield reliable masses and absolute radii, as well asother physical and orbital properties of the stars and the system. FromUV/optical spectrophotometry (1150-4820 Å) of HV 2274 obtainedwith the HST Faint Object Spectrograph, the temperatures and themetallicity ([Fe/H]=-0.45+/-0.06) of the stars were found, as well asthe interstellar extinction of the system. The values of the mass,absolute radius, and effective temperature for the primary and secondarystars are 12.2+/-0.7 Msolar, 9.9+/-0.2 Rsolar,23000+/-180 K and 11.4+/-0.7 Msolar, 9.0+/-0.2Rsolar, 23110+/-180 K, respectively. The age of the system(τ=17+/-2 Myr), helium abundance (Y=0.26+/-0.03), and a lower limitof the convective core overshooting parameter ofαov~0.2 were obtained by fitting the stellar data withevolution models of Claret & Giménez. HV 2274 has a relativelywell determined (and fast) apsidal motion period of U=123+/-3 yr. Froman analysis of apsidal motion, additional information and constraints onthe structure of the stars can be obtained. The apsidal motion analysiscorroborates that some amount of convective core overshooting(αov between 0.2 and 0.5) is needed.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Apsidal Motion in Double Stars. I. Catalog
A catalog of 128 double stars with measured periods of apsidal motion iscompiled. Besides the apsidal periods, the orbital elements of binariesand physical parameters of components (masses, radii, effectivetemperatures, surface gravities) are given. The agreement of the apsidalperiods found by various authors is discussed.
| V380 Cygni Once More: A Close Detached Binary with an Evolved B-Type Component. I. Spectroscopic Orbits
New spectroscopic and photometric observations of V380 Cygni, a brightearly B-type binary with an eccentric orbit and an evolved primary, B1.5II-III, make possible a thorough study of this important, if not unique,system. In this first of two papers, the spectroscopic material isdiscussed. Values of the masses and provisional values of the radii aregiven, as is a spectroscopic estimate of the light ratio. The secondpaper will analyze the photometric material, including apsidal motion.The determination, with some degree of reliability, of the fundamentalproperties of an evolved early B-type star in the 10 solar mass rangewill enable its structure and evolutionary status to be compared withthe predictions of models, including a sensitive test of convective-coreovershooting.
| Determination of empirical mass-luminosity and mass-radius relations for main-sequence stars that are the components of eclipsing binary systems
Based on a new catalog of photometric, geometrical, and absoluteelements for 112 eclipsing binary systems with both components on themain sequence and with known photometric and spectroscopic orbitalelements, we redetermined the mass-luminosity and mass-radius relations:M_bol = 4.46 - 9.52 lg M (lg M > -0.4), M_bol = 6.58 - 5.00 lg M (lgM <= -0.4), lg R = 0.096 + 0.652 lg M (lg M > 0.14), lg R = 0.049+ 0.993 lg M (lg M <= 0.14). For most systems, the masses and radiiof the components are determined with an accuracy of 2-3% and 2-4%,respectively. We estimated the parameters of these relations by theleast-squares method using the procedure for correcting the estimatesthus obtained for noise in the argument.
| The binary system V373 Cas: orbital elements, parameters of the components, and helium abundance
CCD spectra with high resolution and large signal-to-noise ratio areused to study the binary system V373 Cas, which includes two early Bstars, and is apparently undergoing a very early phase of mass exchangebetween the components. The new radial velocity measurements made itpossible to improve the system's orbital elements and to refine the massestimates for the components: M_orb = 18.6 +/- 2.4 M for the primary(star A) and 14.2 +/- 1.9M_solar for the secondary (star B). Aself-consistent method for estimation of the effective temperature andgravitational acceleration yields T_eff = 23,200 +/- 600 K and lg g= 3.0+/- 0.2 for component A and T_eff = 26,800 +/- 1500 K and lg g = 3.5 +/-0.2 for component B. These parameters correspond to the spectral typesB0.5-B1 (II-Ib) for A and B0.5 III for B. The helium abundance isenhanced in the atmospheres of both components: He/H = 0.23 +/- 0.03 and0.18 +/- 0.02 for A and B, respectively. This helium abundance excessconfirms that He/H depends on age, and is consistent with the fact thatboth the components of V373 Cas are near the end of the main sequencestage. The magnesium abundance for the primary is close to the solarvalue, suggesting that its metallicity may be normal. The rotationvelocities sin i = 130 +/- 10 km/s (A) and 60 +/- 5 km/s (B) are derivedfrom the He I lines. These confirm the conclusion of Hill and Fisherthat the rotation of the components in their orbital motion isasynchronous. The masses M_ev estimated using evolutionary tracks areoverestimated by 34% for the both components, compared to the moreaccurate values M_orb determined from the orbit analysis. This is thelargest known discrepancy between M_ev and M_orb for a binary system ofthis type. The age of the system is 7-8 million years.
| Helium Enrichment of the Atmospheres of B and O Stars: New Aspects of the 20-Year-Old Problem
An analysis of the latest data for close binary systems consisting of Oand early B stars shows that during the first half of the lifetime onthe main sequence, the components of such systems retain the initialhelium abundance He/H = 0.08-0.09 in their atmospheres. Subsequently,He/H abruptly increases approximately twofold in a short interval ofrelative ages t/t_MS between 0.5 and 0.7, and this enhanced He/H remainsconstant until the main-sequence stage is complete. Single O starsexhibit a similar nonmonotonic dependence of He/H on t/t_MS with adiscontinuity at t/t_MS ~ 0.6. A preliminary analysis performed forsingle early B stars leads us to conclude that in this case He/H mayalso increase steeply at t/tMS 0.6. The data available for early B starsreveal no correlation of He/H with the observed projected rotationalvelocity vsini and with the equatorial rotational velocity v. Nor isthere any correlation when changing to the values of v_0sini and v_0corresponding to the initial time t = 0. It is noted that the currenttheoretical models of mixing on the main sequence can explain neitherthe abrupt increase in He/H at t/t_MS ~ 0.6 nor the lack of correlationwith rotation. New high-quality spectroscopic observations of early Bstars and new helium-abundance determinations are needed to increase theaccuracy of the initial data. In particular, of interest is to obtainaccurate values of He/H for pulsating Beta Cep stars, because most ofthem have relative ages t/t_MS > 0.5.
| Photometric Separation of Stellar Properties Using SDSS Filters
Using synthetic photometry of Kurucz model spectra, we explore thecolors of stars as a function of temperature, metallicity, and surfacegravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. Thesynthetic colors show qualitative agreement with the few publishedobservations in these filters. We find that the locus of synthetic starsis basically two-dimensional for 4500 < T < 8000 K, whichprecludes simultaneous color separation of the three basic stellarcharacteristics we consider. Colors including u' contain the mostinformation about normal stellar properties; measurements in this filterare also important for selecting white dwarfs. We identify two differentsubsets of the locus in which the loci separate by either metallicity orsurface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly toG stars), the locus separates by metallicity; for photometric error of afew percent, we estimate metallicity to within ~0.5 dex in this range.In the range -0.15 < g' - r' < 0.00 (corresponding roughly to Astars), the locus shows separation by surface gravity. In both cases, weshow that it is advantageous to use more than two colors whendetermining stellar properties by color. Strategic observations in SDSSfilters are required to resolve the source of a ~5% discrepancy betweensynthetic colors of Gunn-Stryker stars, Kurucz models, and externaldeterminations of the metallicities and surface gravities. The syntheticstar colors can be used to investigate the properties of any normal starand to construct analytic expressions for the photometric prediction ofstellar properties in special cases.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Hattyú |
| Rektaszcenzió: | 19h50m37.30s |
| Deklináció: | +40°35'59.0" |
| Vizuális fényesség: | 5.69 |
| Távolság: | 787.402 parszek |
| RA sajátmozgás: | -2.7 |
| Dec sajátmozgás: | -6.4 |
| B-T magnitude: | 5.599 |
| V-T magnitude: | 5.669 |
Katalógusok és elnevezések:
|
INHABITED SKY
