目录
图像
上传图像
DSS Images Other Images
相关文章
Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
| The Evolution of Cataclysmic Variables as Revealed by Their Donor Stars
We present an attempt to reconstruct the complete evolutionary pathfollowed by cataclysmic variables (CVs), based on the observedmass-radius relationship of their donor stars. Along the way, we updatethe semi-empirical CV donor sequence presented previously by one of us,present a comprehensive review of the connection between CV evolutionand the secondary stars in these systems, and reexamine most of thecommonly used magnetic braking (MB) recipes, finding that evenconceptually similar ones can differ greatly in both magnitude andfunctional form. The great advantage of using donor radii to infermass-transfer and angular-momentum-loss (AML) rates is that they samplethe longest accessible timescales and are most likely to represent thetrue secular (evolutionary average) rates. We show explicitly that ifCVs exhibit long-term mass-transfer-rate fluctuations, as is oftenassumed, the expected variability timescales are so long that othertracers of the mass-transfer rate—including white dwarf (WD)temperatures—become unreliable. We carefully explore how much ofthe radius difference between CV donors and models of isolatedmain-sequence stars may be due to mechanisms other than mass loss. Thetidal and rotational deformation of Roche-lobe-filling stars produces ~=4.5% radius inflation below the period gap and ~= 7.9% above. Acomparison of stellar models to mass-radius data for non-interactingstars suggests a real offset of ~= 1.5% for fully convective stars(i.e., donors below the gap) and ~= 4.9% for partially radiative ones(donors above the gap). We also show that donor bloating due toirradiation is probably smaller than, and at most comparable to, theseeffects. After calibrating our models to account for these issues, wefit self-consistent evolution sequences to our compilation of donormasses and radii. In the standard model of CV evolution, AMLs below theperiod gap are assumed to be driven solely by gravitational radiation(GR), while AMLs above the gap are usually described by an MB law firstsuggested by Rappaport et al. We adopt simple scaled versions of theseAML recipes and find that these are able to match the data quite well.The optimal scaling factors turn out to be f GR = 2.47± 0.22 below the gap and f MB = 0.66 ± 0.05above (the errors here are purely statistical, and the standard modelcorresponds to f GR = f MB = 1). This revisedmodel describes the mass-radius data significantly better than thestandard model. Some of the most important implications and applicationsof our results are as follows. (1) The revised evolution sequence yieldscorrect locations for the minimum period and the upper edge of theperiod gap; the standard sequence does not. (2) The observed spectraltypes of CV donors are compatible with both standard and revised models.(3) A direct comparison of predicted and observed WD temperaturessuggests an even higher value for f GR, but this comparisonis sensitive to the assumed mean WD mass and the possible existence ofmass-transfer-rate fluctuations. (4) The predicted absolute magnitudesof donor stars in the near-infrared form a lower envelope around theobserved absolute magnitudes for systems with parallax distances. Thisis true for all of our sequences, so any of them can be used to set firmlower limits on (or obtain rough estimates of) the distances toward CVsbased only on P orb and single epoch near-IR measurements.(5) Both standard and revised sequences predict that short-period CVsshould be susceptible to dwarf nova (DN) eruptions, consistent withobservations. However, both sequences also predict that the fraction ofDNe among long-period CVs should decline with P orb above theperiod gap. Observations suggest the opposite behavior, and we discussthe possible explanations for this discrepancy. (6) Approximate orbitalperiod distributions constructed from our evolution sequences suggestthat the ratio of long-period CVs to short-period, pre-bounce CVs isabout 3 × higher for the revised sequence than the standard one.This may resolve a long-standing problem in CV evolution. Tablesdescribing our donor and evolution sequences are provided inelectronically readable form.
| Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue. II. Two spotted M < 1 M_? systems at different evolutionary stages
Aims: We present the results of our detailed spectroscopic andphotometric analysis of two previously unknown <1 M_? detachedeclipsing binaries: ASAS J045304-0700.4 and ASAS J082552-1622.8. Methods: With the HIgh Resolution Echelle Spectrometer (HIRES) on theKeck-I telescope, we obtained spectra of both objects covering largefractions of orbits of the systems. We also obtained V and I bandphotometry with the 1.0-m Elizabeth telescope of the South AfricanAstronomical Observatory (SAAO). The orbital and physical parameters ofthe systems were derived with the PHOEBE and JKTEBOP codes. Weinvestigated the evolutionary status of both binaries with several setsof widely-used isochrones. Results: Our modelling indicates that(1) ASAS J045304-0700.4 is an old, metal-poor, active system withcomponent masses of M1 = 0.8338 ± 0.0036M?, M2 = 0.8280 ± 0.0040M? and radii of R1 = 0.848 ± 0.005R? and R2 = 0.833 ± 0.005R?, which places it at the end of the Main Sequenceevolution - a stage rarely observed for this type of stars. (2) ASASJ082552-1622.8 is a metal-rich, active binary with component masses ofM1 = 0.7029 ± 0.0045 M?, M2= 0.6872 ± 0.0049 M? and radii of R1 =0.694+0.007-0.011 R? andR2 = 0.699+0.011-0.014R?. Both systems show significant out-of-eclipsevariations, probably owing to large, cold spots. We also investigatedthe influence of a third light in the second system.Light curves are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/526/A29
| The most plausible explanation of the cyclic period changes in close binaries: the case of the RS CVn-type binary WW Dra
Cyclic period changes are a fairly common phenomenon in close binarysystems and are usually explained as being caused either by the magneticactivity of one or both components or by the light travel time effect(LTTE) of a third body. We searched the orbital period changes in 182EA-type (including the 101 Algol systems used by Hall), 43 EB-type and53 EW-type binaries with known mass ratio and spectral type of thesecondary component. We reproduced and improved the diagram in Hallaccording to the new collected data. Our plots do not support theconclusion derived by Hall that cyclic period changes are restricted tobinaries having a secondary component with spectral type later than F5.The presence of period changes among systems with a secondary componentof early type indicates that magnetic activity is one, but not the only,cause of the period variation. It is discovered that cyclic periodchanges, probably resulting from the presence of a third body, are morefrequent in EW-type binaries among close systems. Therefore, the mostplausible explanation of the cyclic period changes is the LTTE throughthe presence of a third body. Using the century-long historical recordof the times of light minimum, we analysed the cyclic period change inthe Algol binary WW Dra. It is found that the orbital period of thebinary shows a ~112.2-yr cyclic variation with an amplitude of ~0.1977d.The cyclic oscillation can be attributed to the LTTE by means of a thirdbody with a mass no less than 6.43Msolar. However, nospectral lines of the third body were discovered, indicating that it maybe a candidate black hole. The third body is orbiting the binary at adistance closer than 14.4 au and may play an important role in theevolution of this system.
| The V-band Empirical Mass-luminosity Relation for Main Sequence Stars
Stellar mass is an indispensable parameter in the studies of stellarphysics and stellar dynamics. On the one hand, the most reliable way todetermine the stellar dynamical mass is via orbital determinations ofbinaries. On the other hand, however, most stellar masses have to beestimated by using the mass luminosity relation (MLR). Therefore, it isimportant to obtain the empirical MLR through fitting the data ofstellar dynamical mass and luminosity. The effect of metallicity canmake this relation disperse in the V-band, but studies show that this ismainly limited to the case when the stellar mass is less than0.6M? Recently, many relevant data have been accumulatedfor main sequence stars with larger masses, which make it possible tosignificantly improve the corresponding MLR. Using a fitting methodwhich can reasonably assign weights to the observational data includingtwo quantities with different dimensions, we obtain a V-band MLR basedon the dynamical masses and luminosities of 203 main sequence stars. Incomparison with the previous work, the improved MLR is statisticallysignificant, and the relative error of mass estimation reaches about 5%.Therefore, our MLR is useful not only in the studies of statisticalnature, but also in the studies of concrete stellar systems, such as thelong-term dynamical study and the short-term positioning study of aspecific multiple star system.
| Accurate masses and radii of normal stars: modern results and applications
This article presents and discusses a critical compilation of accurate,fundamental determinations of stellar masses and radii. We haveidentified 95 detached binary systems containing 190 stars (94 eclipsingsystems, and ? Centauri) that satisfy our criterion that the massand radius of both stars be known within errors of ±3% accuracyor better. All of them are non-interacting systems, and so the starsshould have evolved as if they were single. This sample more thandoubles that of the earlier similar review by Andersen (Astron AstrophysRev 3:91-126, 1991), extends the mass range at both ends and, forthe first time, includes an extragalactic binary. In every case, we haveexamined the original data and recomputed the stellar parameters with aconsistent set of assumptions and physical constants. To these we addinterstellar reddening, effective temperature, metal abundance,rotational velocity and apsidal motion determinations when available,and we compute a number of other physical parameters, notably luminosityand distance. These accurate physical parameters reveal the effects ofstellar evolution with unprecedented clarity, and we discuss the use ofthe data in observational tests of stellar evolution models in somedetail. Earlier findings of significant structural differences betweenmoderately fast-rotating, mildly active stars and single stars, ascribedto the presence of strong magnetic and spot activity, are confirmedbeyond doubt. We also show how the best data can be used to testprescriptions for the subtle interplay between convection, diffusion,and other non-classical effects in stellar models. The amount andquality of the data also allow us to analyse the tidal evolution of thesystems in considerable depth, testing prescriptions of rotationalsynchronisation and orbital circularisation in greater detail thanpossible before. We show that the formulae for pseudo-synchronisation ofstars in eccentric orbits predict the observed rotations quite well,except for very young and/or widely separated stars. Deviations dooccur, however, especially for stars with convective envelopes. Thesuperior data set finally demonstrates that apsidal motion rates aspredicted from General Relativity plus tidal theory are in goodagreement with the best observational data. No reliable binary dataexist, which challenge General Relativity to any significant extent. Thenew data also enable us to derive empirical calibrations of M and R forsingle (post-) main-sequence stars above {0.6 M_{odot}}. Simple,polynomial functions of T eff, log g and [Fe/H] yield M and Rwithin errors of 6 and 3%, respectively. Excellent agreement is foundwith independent determinations for host stars of transiting extrasolarplanets, and good agreement with determinations of M and R from stellarmodels as constrained by trigonometric parallaxes and spectroscopicvalues of T eff and [Fe/H]. Finally, we list a set of 23interferometric binaries with masses known to be better than 3%, butwithout fundamental radius determinations (except ? Aur). Wediscuss the prospects for improving these and other stellar parametersin the near future.
| Distances to Four Solar Neighborhood Eclipsing Binaries from Absolute Fluxes
Eclipsing binary (EB)-based distances are estimated for four solarneighborhood EBs by means of the Direct Distance Estimation (DDE)algorithm. Results are part of a project to map the solar neighborhoodEBs in three dimensions, independently of parallaxes, and providestatistical comparisons between EB and parallax distances. Apart fromjudgments on adopted temperature and interstellar extinction, DDE'ssimultaneous light-velocity solutions are essentially objective and workas well for semidetached (SD) and overcontact binaries as for detachedsystems. Here, we analyze two detached and two SD binaries, all doublelined. RS Chamaeleontis is a pre-main-sequence (MS), detached EB withweak ? Scuti variations. WW Aurigae is detached and uncomplicated,except for having high metallicity. RZ Cassiopeiae is SD and has veryclear ? Scuti variations and several peculiarities. R CanisMajoris (R CMa) is an apparently simple but historically problematic SDsystem, also with weak ? Scuti variations. Discussions includesolution rules and strategies, weighting, convergence, and third lightproblems. So far there is no indication of systematic band dependenceamong the derived distances, so the adopted band-calibration ratios seemconsistent. Agreement of EB-based and parallax distances is typicallywithin the overlapped uncertainties, with minor exceptions. We alsosuggest an explanation for the long-standing undermassiveness problem ofR CMa's hotter component, in terms of a fortuitous combination of lowmetallicity and evolution slightly beyond the MS.
| Absolute dimensions of solar-type eclipsing binaries. II. V636 Centauri: A 1.05 {M}ȯ primary with an active, cool, oversize 0.85 {M}ȯ secondary
Context: The influence of stellar activity on the fundamental propertiesof stars around and below 1 Mȯ is not well understood.Accurate mass, radius, and abundance determinations from solar-typebinaries exhibiting various levels of activity are needed for a betterinsight into the structure and evolution of these stars. Aims: Weaim to determine absolute dimensions and abundances for the solar-typedetached eclipsing binary V636 Cen, and to perform a detailed comparisonwith results from recent stellar evolutionary models. Methods:uvby light curves and uvbyβ standard photometry were obtained withthe Strömgren Automatic Telescope, radial velocity observationswith the CORAVEL spectrometer, and high-resolution spectra with theFEROS spectrograph, all at ESO, La Silla. State-of-the-art methods wereapplied for the photometric and spectroscopic analyses. Results:Masses and radii that are precise to 0.5% have been established for thecomponents of V636 Cen. The 0.85 Mȯ secondary componentis moderately active with starspots and Ca ii H and K emission, and the1.05 Mȯ primary shows signs of activity as well, but ata much lower level. We derive a [Fe/H] abundance of -0.20 ± 0.08and similar abundances for Si, Ca, Ti, V, Cr, Co, and Ni. Correspondingsolar-scaled stellar models are unable to reproduce V636 Cen, especiallyits secondary component, which is ~10% larger and ~400 K cooler thanpredicted. Models adopting significantly lower mixing-length parametersl/Hp remove these discrepancies, seen also for othersolar-type binary components. For the observed [Fe/H], Claret models forl/Hp = 1.4 (primary) and 1.0 (secondary) reproduce thecomponents of V636 Cen at a common age of 1.35 Gyr. The orbit iseccentric (e = 0.135 ± 0.001), and apsidal motion with a 40%relativistic contribution has been detected. The period is U = 5 270± 335 yr, and the inferred mean central density concentrationcoefficient, log(k_2) = -1.61 ± 0.05, agrees marginally withmodel predictions. The measured rotational velocities, 13.0 ± 0.2(primary) and 11.2 ± 0.5 (secondary) km s-1, are inremarkable agreement with the theoretically predicted pseudo-synchronousvelocities, but are about 15% lower than the periastron values. Conclusions: V636 Cen and 10 other well-studied inactive and activesolar-type binaries suggest that chromospheric activity, and its effecton envelope convection, is likely to cause radius and temperaturediscrepancies, which can be removed by adjusting the model mixing lengthparameters downwards. Noting this, the sample may also lend support totheoretical 2D radiation hydrodynamics studies, which predict a slightdecrease of the mixing length parameter with increasing temperature/massfor inactive main sequence stars. More binaries are, however, needed fora description/calibration in terms of physical parameters and level ofactivity.Based on observations carried out at the Strömgren AutomaticTelescope (SAT), the Danish 1.54 m telescope, and the 1.5 m telescope(62.L-0284) at ESO, La Silla, Chile. Table A.1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/502/253
| Artificial Intelligence Approach to the Determination of Physical Properties of Eclipsing Binaries. I. The EBAI Project
Achieving maximum scientific results from the overwhelming volume ofastronomical data to be acquired over the next few decades demandsnovel, fully automatic methods of data analysis. Here we concentrate oneclipsing binary (EB) stars, a prime source of astrophysicalinformation, of which only some hundreds have been rigorously analyzed,but whose numbers will reach millions in a decade. We describe theartificial neural network (ANN) approach which is able to surmount thehuman bottleneck and permit EB-based scientific yield to keep pace withfuture data rates. The ANN, following training on a sample of 33,235model light curves, outputs a set of approximate model parameters[T2/T1, (R1+R2)/a,esinω, ecosω, and sini] for each input light curve data set.The obtained parameters can then be readily passed to sophisticatedmodeling engines. We also describe a novel method polyfit forpreprocessing observational light curves before inputting their data tothe ANN and present the results and analysis of testing the approach onsynthetic data and on real data including 50 binaries from the Catalogand Atlas of Eclipsing Binaries (CALEB) database and 2580 light curvesfrom OGLE survey data. The success rate, defined by less than a 10%error in the network output parameter values, is approximately 90% forthe OGLE sample and close to 100% for the CALEB sample-sufficient for areliable statistical analysis. The code is made available to the public.Our approach is applicable to EB light curves of all classes; this firstpaper in the eclipsing binaries via artificial intelligence (EBAI)series focuses on detached EBs, which is the class most challenging forthis approach.
| Mass-luminosity relation of intermediate-mass stars
The mass-luminosity relation (MLR) for intermediate-mass stars is basedon data on detached double-lined eclipsing binaries. However, there is anotable difference between the parameters of B0V-G0V components ofeclipsing binaries and those of single stars. Single early-type starsare rapid rotators, whereas tidal forces produce synchronous rotation inclose binaries and all such pairs are synchronized, so components ofclose binaries rotate more slowly. As is well known, stellar rotationchanges stellar evolution and the global parameters of a star.In this work we collect data on fundamental parameters of stars withmasses m > 1.5msolar. They are components of binaries withP > 15 d and consequently are not synchronized with the orbitalperiods and presumably are rapid rotators. These stars are believed toevolve similarly with single stars. Modern data on masses, absolute andbolometric luminosities, radii and temperatures of detachedmain-sequence double-lined eclipsing binary components (i.e. presumablyslow rotators) are also collected.Mass-luminosity, mass-temperature and mass-radius relations of close andwide binaries are presented, as well as their Hertzsprung-Russelldiagram. For the mass range 4.5 < m/msolar < 5.5 (lateB stars) it was found that rapid rotators exhibit slightly higherluminosities and larger radii than predicted by the standard relations,and their main sequence is shifted to the right-hand side with respectto that of the close binary components. The resulting relations forrapidly and slowly rotating A-F and early B stars are not statisticallydifferent.As our estimations show, for the given mass range the effect on theinitial mass function (IMF) is marginal, but there is no way to estimatethe degree to which the effect may be important for higher masses.Available observational data for m > 12msolar are too poorto make definite conclusions. Knowledge of the MLR should come fromdynamical mass determinations of visual binaries combined with spatiallyresolved precise photometry. Then the IMF should be revised for thatmass range.
| On the Correlation between the Magnetic Activity Levels, Metallicities, and Radii of Low-Mass Stars
The recent increase in the number of radius measurements of very lowmass stars from eclipsing binaries and interferometry of single starshas raised more questions about what could be causing the discrepancybetween the observed radii and those predicted by models. The two mainexplanations being proposed are a correlation between the radii of thestars and either their activity levels or their metallicities. Thispaper presents a study of such correlations using all the data publishedto date. The study also investigates correlations between the radiusdeviations from the models and the masses of the stars. There is noclear correlation between activity level and radius for the single starsin the sample. These single stars are slow rotators, with typicalvelocities vrotsini<3.0 km s-1. A clearcorrelation however exists in the case of the faster rotating members ofbinaries. This result is based on the X-ray emission levels of thestars. There also appears to be an increase in the deviation of theradii of single stars from the models as a function of metallicity, aspreviously indicated by Berger et al. The stars in binaries do not seemto follow the same trend. Finally, the Baraffe et al. models reproducewell the radius observations below 0.30-0.35 Msolar, wherethe stars become fully convective, although this result is preliminarysince almost all the sample stars in that mass range are slow rotatorsand metallicities have not been measured for most of them. The resultsindicate that stellar activity and metallicity play an important role indetermining the radius of very low mass stars, at least above 0.35Msolar.
| Effect of tidal evolution in determining the ages of eclipsing-variable early main sequence close binary systems
New Claret evolutionary model-tracks, constructed for the first time forstudying close binary systems (CBS) including tidal evolution constants,are used to determine the age of 112 eclipsing-variable stars in theSvechnikov-Perevozkina catalog by the method of isochrones. There issome interest in comparing the calculated ages with previous estimatesobtained for these same close binary systems using evolutionarymodeltracks for individual stars taking their mass loss into account. Acorrelation of the ages of the principal and secondary components isnoted, which is most marked for massive close binaries with principalcomponents having masses M1 ? 3 M?. Arejuvenating effect is found to occur for the systems studied here ascalculated on the new tracks; it is most distinct for low-mass closebinaries with a total mass M1 + M2 ? 3.5M? and is predicted theoretically in terms of magneticbraking. The calculated broadband grid of isochrones, from zero-agemain-sequence (ZAMS) to the age of the galaxy, can be used forestimating the ages of close binaries from other catalogs. Ages aregiven for the 112 eclipsing-variable close binaries with detachedcomponents lying within the main sequence.
| Accurate masses of low mass stars GJ 765.2AB (0.83 Mȯ + 0.76 Mȯ)
Context: Because of the lack of precise masses, the coverage of themain-sequence empirical mass-luminosity relation for stars in the massrange from 0.6 Mȯ to 0.9 Mȯ isincomplete. The nearby K-type visual and spectroscopic binary GJ 765.2 =MLR 224 is a good candidate for new reliable points in this significantpart of the relation. Aims: We have found a combined orbital solutionfor the pair and derived physical properties of the components usinginterferometric and spectroscopic data. Methods: Thediffraction-limited speckle observations were mostly collected at the 6m BTA telescope, and the velocities of the components were obtainedusing the CORAVEL radial velocity scanner on the Swiss 1 m telescope. Results: In a combined solution, the orbital period is found to be11.919 yr. The masses of the GJ 765.2 components areMA=0.831± 0.020 Mȯ andMB=0.763± 0.019 Mȯ. The obtainedorbital parallax of the system, π_orb=31.0±0.5 mas, is 7percent lower than the Hipparcos value. The absolute V magnitudes of thestars, derived from the measured speckle magnitude differences, are:MVA=5.99±0.04 andMVB=6.64±0.05. The effective temperaturesof the components, T_effA=5060±130 K andT_effB=4690±160 K, follow from the V-K and J-K colorindices. The star metallicity value, estimated from the 6 m telescopespectrum, is [M/H]=-0.35±0.15 dex. Conclusions: .The presentedindividual masses have 2.4% and 2.5% relative accuracies. Therefore, thecomponents of GJ 765.2 rank among a dozen stars with masses accurate towithin a few percent in the mass range 0.6-0.9 Mȯ. Theexisting data on the kinematics of GJ 765.2 and its chromosphericactivity indicate that the binary belongs to the middle age (3-4×109 yr) thin disk population of the galaxy.Based on observations made with the 6 m BTA telescope, which is operatedby the Special Astrophysical Observatory, Russia, and the Observatoirede Haute-Provence, operated by the Centre National de la RechercheScientifique de France. Tables 1 and 2 are only available in electronicform at http://www.aanda.org
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Tertiary companions to close spectroscopic binaries
We have surveyed a sample of 165 solar-type spectroscopic binaries (SB)with periods from 1 to 30 days for higher-order multiplicity. Asubsample of 62 targets were observed with the NACO adaptive opticssystem and 13 new physical tertiary companions were detected. Anadditional 12 new wide companions (5 still tentative) were found usingthe 2MASS all-sky survey. The binaries belong to 161 stellar systems; ofthese 64 are triple, 11 quadruple and 7 quintuple. After correction forincompleteness, the fraction of SBs with additional companions is foundto be 63% ± 5%. We find that this fraction is a strong functionof the SB period P, reaching 96% for P<3d and dropping to34% for P>12^d. Period distributions of SBs with and withouttertiaries are significantly different, but their mass ratiodistributions are identical. The statistical data on the multiplicity ofclose SBs presented in this paper indicates that the periods and massratios of SBs were established very early, but the periods of SB systemswith triples were further shortened by angular momentum exchange withcompanions.
| The Eclipsing Binary V1061 Cygni: Confronting Stellar Evolution Models for Active and Inactive Solar-Type Stars
We present spectroscopic and photometric observations of the eclipsingsystem V1061 Cyg (P=2.35 days). A third star is visible in the spectrum,and the system is a hierarchical triple. We combine the radialvelocities for the three stars, times of eclipse, and intermediateastrometric data from the Hipparcos mission (abscissa residuals) toestablish the elements of the outer orbit, which is eccentric and has aperiod of 15.8 yr. We determine accurate values for the masses, radii,and effective temperatures of the binary components:MAa=1.282+/-0.015 Msolar,RAa=1.615+/-0.017 Rsolar, andTAaeff=6180+/-100 K for the primary (star Aa), andMAb=0.9315+/-0.0068 Msolar,RAb=0.974+/-0.020 Rsolar, andTAbeff=5300+/-150 K for the secondary (Ab). Themass of the tertiary is determined to be MB=0.925+/-0.036Msolar and its effective temperature isTBeff=5670+/-150 K. Current stellar evolutionmodels agree well with the properties of the primary but show a verylarge discrepancy in the radius of the secondary, in the sense that thepredicted values are ~10% smaller than observed (a ~5 ? effect).In addition, the temperature is cooler than predicted, by some 200 K.These discrepancies are quite remarkable given that the star is only 7%less massive than the Sun, the calibration point of all stellar models.We identify the chromospheric activity as the likely cause of theeffect. Inactive stars agree very well with the models, while activeones such as V1061 Cyg Ab appear systematically too large and too cool.
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| Precise CCD Times of Minima of Selected Eclipsing Binaries
We present 135 precise CCD minima timings for 93 eclipsing binariesobtained at Ondrejov observatory during 2003-2004.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| Up-to-Date Linear Elements of Eclipsing Binaries
About 1800 O-C diagrams of eclipsing binaries were analyzed and up-todate linear elements were computed. The regularly updated ephemerides(as a continuation of SAC) are available only in electronic form at theInternet address: http://www.as.ap.krakow.pl/ephem/.
| An Assessment of Dynamical Mass Constraints on Pre-Main-Sequence Evolutionary Tracks
We have assembled a database of stars having both masses determined frommeasured orbital dynamics and sufficient spectral and photometricinformation for their placement on a theoretical H-R diagram. Our sampleconsists of 115 low-mass (M<2.0 Msolar) stars, 27pre-main-sequence and 88 main-sequence. We use a variety of availablepre-main-sequence evolutionary calculations to test the consistency ofpredicted stellar masses with dynamically determined masses. Despitesubstantial improvements in model physics over the past decade, largesystematic discrepancies still exist between empirical and theoreticallyderived masses. For main-sequence stars, all models considered predictmasses consistent with dynamical values above 1.2 Msolar andsome models predict consistent masses at solar or slightly lower masses,but no models predict consistent masses below 0.5 Msolar,with all models systematically underpredicting such low masses by5%-20%. The failure at low masses stems from the poor match of mostmodels to the empirical main sequence below temperatures of 3800 K, atwhich molecules become the dominant source of opacity and convection isthe dominant mode of energy transport. For the pre-main-sequence samplewe find similar trends. There is generally good agreement betweenpredicted and dynamical masses above 1.2 Msolar for allmodels. Below 1.2 Msolar and down to 0.3 Msolar(the lowest mass testable), most evolutionary models systematicallyunderpredict the dynamically determined masses by 10%-30%, on average,with the Lyon group models predicting marginally consistent masses inthe mean, although with large scatter. Over all mass ranges, theusefulness of dynamical mass constraints for pre-main-sequence stars isin many cases limited by the random errors caused by poorly determinedluminosities and especially temperatures of young stars. Adopting awarmer-than-dwarf temperature scale would help reconcile the systematicpre-main-sequence offset at the lowest masses, but the case for this isnot compelling, given the similar warm offset at older ages between mostsets of tracks and the empirical main sequence. Over all age ranges, thesystematic discrepancies between track-predicted and dynamicallydetermined masses appear to be dominated by inaccuracies in thetreatment of convection and in the adopted opacities.
| CCD Minima for Selected Eclipsing Binaries in 2003
Not Available
| A Census of the Young Cluster IC 348
We present a new census of the stellar and substellar members of theyoung cluster IC 348. We have obtained images at I and Z for a42'×28' field encompassing the cluster andhave combined these measurements with previous optical and near-infraredphotometry. From spectroscopy of candidate cluster members appearing inthese data, we have identified 122 new members, 15 of which havespectral types of M6.5-M9, corresponding to masses of ~0.08-0.015Msolar by recent evolutionary models. The latest census forIC 348 now contains a total of 288 members, 23 of which are later thanM6 and thus are likely to be brown dwarfs. From an extinction-limitedsample of members (AV<=4) for a16'×14' field centered on the cluster, weconstruct an initial mass function (IMF) that is unbiased in mass andnearly complete for M/Msolar>=0.03 (<~M8). Inlogarithmic units where the Salpeter slope is 1.35, the mass functionfor IC 348 rises from high masses down to a solar mass, rises moreslowly down to a maximum at 0.1-0.2 Msolar, and then declinesinto the substellar regime. In comparison, the similarly derived IMF forTaurus from Briceño et al. and Luhman et al. rises quickly to apeak near 0.8 Msolar and steadily declines to lower masses.The distinctive shapes of the IMFs in IC 348 and Taurus are reflected inthe distributions of spectral types, which peak at M5 and K7,respectively. These data provide compelling, model-independent evidencefor a significant variation of the IMF with star-forming conditions.Based on observations obtained at Keck Observatory, Steward Observatory,the MMT Observatory, and the Canada-France-Hawaii Telescope. Thispublication makes use of data products from the Two Micron All SkySurvey, which is a joint project of the University of Massachusetts andthe Infrared Processing and Analysis Center/California Institute ofTechnology, funded by the National Aeronautics and Space Administrationand the National Science Foundation.
| Age and metallicity of a globular cluster in the dwarf spheroidal galaxy DDO 78
We present the results of moderate resolution spectroscopy for aglobular cluster in the M81 group dwarf spheroidal galaxy DDO 78. TheDDO 78 globular cluster, 4 Milky Way globular clusters, spectroscopicand radial velocity standards were observed with the Long-slitspectrograph of the 6-m telescope (SAO RAS, Russia). Lickspectrophotometric indices were determined in the bandpasses adopted byBurstein et al. (\cite{Bur84}). We have derived the mean metallicity ofthe globular cluster in DDO78 to be [Fe/H] =-1.6 +/- 0.1 dex by takingthe weighted mean of metallicities obtained from the strength of severalabsorption features. We have estimated an age for the globular clusterof 9-12 Gyr similar to that found for the Galactic globular cluster NGC362, which resembles the DDO 78 cluster in its chemical abundance andintegrated spectrophotometric properties.
| 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
| Testing Models of Stellar Evolution for Metal-poor Stars: An Interferometric-spectroscopic Orbit for the Binary HD 195987
We report spectroscopic and interferometric observations of themoderately metal-poor double-lined binary system HD 195987, with anorbital period of 57.3 days. By combining our radial-velocity andvisibility measurements, we determine the orbital elements and deriveabsolute masses for the components of MA=0.844+/-0.018Msolar and MB=0.6650+/-0.0079 Msolar,with relative errors of 2% and 1%, respectively. We also determine theorbital parallax, πorb=46.08+/-0.27 mas, corresponding toa distance of 21.70+/-0.13 pc. The parallax and the measured brightnessdifference between the stars in V, H, and K yield the component absolutemagnitudes in those bands. We also estimate the effective temperaturesof the stars as TAeff=5200+/-100 K andTBeff=4200+/-200 K. Together with detailedchemical abundance analyses from the literature giving [Fe/H]~-0.5(corrected for binarity) and [α/Fe]=+0.36, we use these physicalproperties to test current models of stellar evolution for metal-poorstars. Among the four that we considered, we find that no single modelfits all observed properties at the measured composition, although weidentify the assumptions in each one that account for the discrepancy,and we conclude that a model with the proper combination of assumptionsshould be able to reproduce all the radiative properties. Theindications from the isochrone fits and the pattern of enhancement ofthe metals in HD 195987 are consistent with this being a thick diskobject, with an age of 10-12 Gyr.
| uvbyβ Photometry of Selected Eclipsing Binary Stars
New uvbyβ observations of 51 eclipsing binary stars are presented,and outside-eclipse averages for 45 of them are given. Many of thesebinaries are detached main-sequence pairs that have been discovered tobe double-lined spectroscopic binaries and appear suitable fordeterminations of accurate absolute dimensions and masses. Photometricproperties are recomputed for 14 of the binaries, for which absoluteproperties have been published previously. Intercomparisons are madewith previous photometry, when available, and notes are given for someindividual systems.
| Determination of the Ages of Close Binary Stars on the Main Sequence from Evolutionary Model Stars of Claret and Gimenez
A grid of isochrones, covering a wide range of stellar ages from thezero-age main sequence to 10 billion years, is calculated in the presentwork on the basis of the model stars of Claret and Gimenez withallowance for convective overshoot and mass loss by the components. Theages of 88 eclipsing variables on the main sequence from Andersen'scatalog and 100 chromospherically active stars from Strassmeier'scatalog are calculated with a description of the method of optimuminterpolation. Comparisons with age determinations by other authors aregiven and good agreement is established.
| Studies of Intermediate-Mass Stellar Models Using Eclipsing Binaries
Evolutionary computations for intermediate-mass stars are analyzed usingobserved parameters for eclipsing SB2 binaries and theoreticalparameters based on evolutionary tracks. Modern observations cannot beused to distinguish between models with and without convectiveovershooting for stars in the vicinity of the main sequence.Statistically significant discrepancies between the observed andcomputed stellar parameters are associated with systematic errors inphotometric effective temperatures. After taking into account systematiceffects, the theoretical computations fit the observational datauniformly well throughout the entire mass interval studied. Empiricaland semiempirical (i.e., reduced to the ZAMS and with solar elementalabundances) formulas for the mass-luminosity, mass-effectivetemperature, and mass-radius relations are proposed.
| Age and Metallicity Estimates for Moderate-Mass Stars in Eclipsing Binaries
We estimate the ages and metallicities for the components of 43 binarysystems using a compilation of accurate observational data on eclipsingbinaries for which lines of both components are visible in theirspectra, together with two independent modern sets of stellar evolutionmodels computed for a wide range of masses and chemical abundances. Theuncertainties of the resulting values are computed, and their stabilityis demonstrated. The ages and metallicity are compared with thosederived in other studies using different methods, as well as withindependent estimates from photometric observations and observations ofclusters. These comparisons con firm the reliability of our ageestimates. The resulting metallicities depend significantly on thechoice of theoretical model. Comparison with independent estimatesfavors the estimates based on the evolutionary tracks of the Genevagroup.
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
