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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.
| Radii of Rapidly Rotating Stars, with Application to Transiting-Planet Hosts
The currently favored method for estimating radii and other parametersof transiting-planet host stars is to match theoretical models toobservations of the stellar mean density ?*, theeffective temperature T eff, and the composition parameter[Z]. This explicitly model-dependent approach is based on readilyavailable observations, and results in small formal errors. Itsperformance will be central to the reliability of results fromground-based transit surveys such as TrES, HAT, and SuperWASP, as wellas to the space-borne missions MOST, CoRoT, and Kepler. Here, I use twocalibration samples of stars (eclipsing binaries (EBs) and stars forwhich asteroseismic analyses are available) having well-determinedmasses and radii to estimate the accuracy and systematic errors inherentin the ?* method. When matching to the Yonsei-Yalestellar evolution models, I find the most important systematic errorresults from selection bias favoring rapidly rotating (hence probablymagnetically active) stars among the EB sample. If unaccounted for, thisbias leads to a mass-dependent underestimate of stellar radii by as muchas 4% for stars of 0.4 M sun, decreasing to zero for massesabove about 1.4 M sun. Relative errors in estimated stellarmasses are three times larger than those in radii. The asteroseismicsample suggests (albeit with significant uncertainty) that systematicerrors are small for slowly rotating, inactive stars. Systematic errorsarising from failings of the Yonsei-Yale models of inactive starsprobably exist, but are difficult to assess because of the small numberof well-characterized comparison stars having low mass and slowrotation. Poor information about [Z] is an important source of randomerror, and may be a minor source of systematic error as well. Withsuitable corrections for rotation, it is likely that systematic errorsin the ?* method can be comparable to or smaller than therandom errors, yielding radii that are accurate to about 2% for moststars.
| Searching for transiting circumbinary planets in CoRoT and ground-based data using CB-BLS
Aims: Already from the initial discoveries of extrasolar planets it wasapparent that their population and environments are far more diversethan initially postulated. Discovering circumbinary (CB) planets willhave many implications, and in this context it will again substantiallydiversify the environments that produce and sustain planets. We searchfor transiting CB planets around eclipsing binaries (EBs). Methods: CB-BLS is a recently-introduced algorithm for the detectionof transiting CB planets around EBs. We describe progress in searchsensitivity, generality and capability of CB-BLS, and detection tests ofCB-BLS on simulated data. We also describe an analytical approach forthe determination of CB-BLS detection limits, and a method for thecorrect detrending of intrinsically-variable stars. Results: Wepresent some blind-tests with simulated planets injected to real CoRoTdata. The presented upgrades to CB-BLS allowed it to detect all theblind tests successfully, and these detections were in line with thedetection limits analysis. We also correctly detrend bright eclipsingbinaries from observations by the TrES planet search, and present someof the first results of applying CB-BLS to multiple real light curvesfrom a wide-field survey. Conclusions: CB-BLS is now matureenough for its application to real data, and the presented processingscheme will serve as the template for our future applications of CB-BLSto data from wide-field surveys such as CoRoT. Being able to putconstraints even on non-detection will help to determine the correctfrequency of CB planets, contributing to the understanding of planetformation in general. Still, searching for transiting CB planets isstill a learning experience, similarly to the state of transitingplanets around single stars only a few years ago. The recent rapidprogress in this front, coupled with the exquisite quality ofspace-based photometry, allows to realistically expect that iftransiting CB planets exist - then they will soon be found.Based on observations obtained with CoRoT, a space project operated bythe French Space Agency, CNES, with participation of the ScienceProgramme of ESA, ESTEC/RSSD, Austria, Belgium, Brazil, Germany andSpain.
| 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
| Absolute Dimensions of the F-Type Eclipsing Binary Star VZ Cephei
We present new V-band differential photometry and radial velocitymeasurements of the unevolved, 1.18 day period, F+G-type, double-linedeclipsing binary VZ Cep. We determine accurate values for the absolutemasses, radii, and effective temperatures as follows: M A =1.402 ± 0.015 M sun, R A = 1.534 ±0.012 R sun, and T eff = 6690 ± 160 K forthe primary, and M B = 1.1077 ± 0.0083 Msun, R B = 1.042 ± 0.039 R sun,and T eff = 5720 ± 120 K for the secondary. Acomparison with current stellar evolution models suggests an age of 1.4Gyr for a metallicity that is near solar. The temperature differencebetween the stars, which is much better determined than the absolutevalues, is found to be ~ 250 K larger than predicted by theory. If allof this discrepancy is attributed to the secondary (which would then betoo cool compared to models), the effect would be consistent withsimilar differences found for other low-mass stars, generally believedto be associated with chromospheric activity. However, the radius of VZCep B (which unlike the primary, still has a thin convective envelope)appears normal, whereas in other stars affected by activity the radiusis systematically larger than predicted. Thus, VZ Cep poses a challengenot only to standard theory but also to our understanding of thediscrepancies in other low-mass systems.
| Absolute Properties of the Spotted Eclipsing Binary Star CV Boötis
We present new V-band differential brightness measurements as well asnew radial-velocity measurements of the detached, circular, 0.84 dayperiod, double-lined eclipsing binary system, CV Boo. These data, alongwith other observations from the literature, are combined to deriveimproved absolute dimensions of the stars for the purpose of testingvarious aspects of theoretical modeling. Despite complications fromintrinsic variability that we detect in the system, and despite therapid rotation of the components, we are able to determine the absolutemasses and radii to better than 1.3% and 2%, respectively. We obtain MA = 1.032 ± 0.013 M sun and R A= 1.262 ± 0.023 R sun for the hotter, larger, andmore-massive primary (star A), and M B = 0.968 ± 0.012M sun and R B = 1.173 ± 0.023 Rsun for the secondary. The estimated effective temperaturesare 5760 ± 150 K and 5670 ± 150 K, respectively. Theintrinsic variability with a period ~1% shorter than the orbital periodis interpreted as being due to modulation by spots on one or bothcomponents. This implies that the spotted star(s) must be rotatingfaster than the synchronous rate, which disagrees with predictions fromcurrent tidal evolution models according to which both stars should besynchronized. We also find that the radius of the secondary is largerthan expected from stellar evolution calculations by ~10%, a discrepancyalso seen in other (mostly lower-mass and active) eclipsing binaries. Weestimate the age of the system to be approximately 9 Gyr. Bothcomponents are near the end of their main-sequence phase, and theprimary may have started the shell hydrogen-burning stage.
| Four-colour photometry of eclipsing binaries. XLI.. uvby light curves for AD Bootis, HW Canis Majoris, SW Canis Majoris, VZ Hydrae, and WZ Ophiuchi
Context: Accurate mass, radius, and abundance determinations frombinaries provide important information on stellar evolution, fundamentalto central fields in modern astrophysics and cosmology. Aims:Within the long-term Copenhagen Binary Project, we aim to obtainhigh-quality light curves and standard photometry for double-lineddetached eclipsing binaries with late A, F, and G type main-sequencecomponents, needed for the determination of accurate absolute dimensionsand abundances, and for detailed comparisons with results from recentstellar evolutionary models. Methods: Between March 1985 and July2007, we carried out photometric observations of AD Boo, HW CMa, SW CMa,V636 Cen, VZ Hya, and WZ Oph at the Strömgren Automatic Telescopeat ESO, La Silla. Results: We obtained complete {uvby} lightcurves, ephemerides, and standard {uvby}? indices for all sixsystems. For V636 Cen and HW CMa, we present the first modern lightcurves, whereas for AD Boo, SW CMa, VZ Hya, and WZ Oph, they are bothmore accurate and more complete than earlier data. Due to a high orbitaleccentricity (e = 0.50), combined with a low orbital inclination (i =84.7°), only one eclipse, close to periastron, occurs for HW CMa.For the two other eccentric systems, V636 Cen (e = 0.134) and SW CMa (e= 0.316), apsidal motion has been detected with periods of 5270 ±335 and 14 900 ± 3600 years, respectively.Based on observations carried out with the Strömgren AutomaticTelescope (SAT) at ESO, La Silla, Chile. Appendix A is only available inelectronic form at http://www.aanda.org Tables 6-13 are only availablein electronic 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/487/1081
| New absolute magnitude calibrations for detached binaries
Lutz-Kelker bias corrected absolute magnitude calibrations for thedetached binary systems with main-sequence components are presented. Theabsolute magnitudes of the calibrator stars were derived at intrinsiccolours of Johnson-Cousins and 2MASS (Two Micron All Sky Survey)photometric systems. As for the calibrator stars, 44 detached binarieswere selected from the Hipparcos catalogue, which have relative observedparallax errors smaller than 15% (σπ/π≤0.15).The calibration equations which provide the corrected absolute magnitudefor optical and near-infrared pass bands are valid for wide ranges ofcolours and absolute magnitudes: -0.18<(B-V)0<0.91,-1.6
| The helium abundance and ΔY/ΔZ in lower main-sequence stars
We use nearby K dwarf stars to measure the helium-to-metal enrichmentratio ΔY/ΔZ, a diagnostic of the chemical history of thesolar neighbourhood. Our sample of K dwarfs has homogeneously determinedeffective temperatures, bolometric luminosities and metallicities,allowing us to fit each star to the appropriate stellar isochrone anddetermine its helium content indirectly. We use a newly computed set ofPadova isochrones which cover a wide range of helium and metal content.Our theoretical isochrones have been checked against a congruous set ofmain-sequence binaries with accurately measured masses, to discuss andvalidate their range of applicability. We find that the stellar massesdeduced from the isochrones are usually in excellent agreement withempirical measurements. Good agreement is also found with empiricalmass-luminosity relations.Despite fitting the masses of the stars very well, we find thatanomalously low helium content (lower than primordial helium) isrequired to fit the luminosities and temperatures of the metal-poor Kdwarfs, while more conventional values of the helium content are derivedfor the stars around solar metallicity.We have investigated the effect of diffusion in stellar models and theassumption of local thermodynamic equilibrium (LTE) in derivingmetallicities. Neither of these is able to resolve the low-heliumproblem alone and only marginally if the cumulated effects are included,unless we assume a mixing-length which is strongly decreasing withmetallicity. Further work in stellar models is urgently needed.The helium-to-metal enrichment ratio is found to be ΔY/ΔZ =2.1 +/- 0.9 around and above solar metallicity, consistent with previousstudies, whereas open problems still remain at the lowest metallicities.Finally, we determine the helium content for a set of planetary hoststars.
| 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.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| New light on the old problem of lithium pre-main sequence depletion: models with 2D radiative-hydrodynamical convection
The Teff location of pre-main sequence (PMS) evolutionarytracks depends on the treatment of overadiabaticity. We present here thePMS evolutionary tracks computed by using the mixing length theory (MLT)of convection in which the ?MLT = l/Hpparameter calibration is based on 2D hydrodynamical models by Ludwig etal. These MLT-?2D stellar models and tracks are verysimilar to those computed with non-grey ATLAS9 atmospheric boundaryconditions and full spectrum of turbulence (FST) convection model bothin the atmosphere and in the interior. The comparison of the new trackswith the location on the Hertzsprung-Russell (HR) diagram of PMSbinaries is not completely satisfactory, as some binary components arelocated at too low Teff. Besides, the PMS lithium depletionin the MLT-?2D tracks is still much larger than thatexpected from the observations of lithium in young open clusters. Thisresult is similar to that of FST models. Thus, in spite of the fact that2D radiative-hydrodynamical models should provide a better convectiondescription than any local model, their introduction is not sufficientto reconcile theory and observations. Lithium depletion in youngclusters points towards a convection efficiency which, in PMS, should besmaller than in the MS. The PMS lithium depletion decreasessignificantly in FST models if we reduce the solar metallicity down tothe value suggested by Asplund et al., but the corresponding solar modeldoes not reproduce the depth of the convective zone as determined byhelioseismology.
| 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.
| New Times of Minima of Some Eclipsing Binary Stars
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| Optical Photometry and Spectroscopy of the Suspected ``Cool Algol'' AV Delphini: Determination of the Physical Properties
We present new spectroscopic and BVRI photometric observations of thedouble-lined eclipsing binary AV Del (period=3.85 days) conducted oversix observing seasons. A detailed radial velocity and light-curveanalysis of the optical data shows the system to be most likelysemidetached, with the less massive and cooler star filling its Rochelobe. The system is probably a member of the rare class of ``coolAlgol'' systems, which are distinguished from the ``classical'' Algolsystems in that the mass-gaining component is also a late-type starrather than a B- or A-type star. By combining the spectroscopic andphotometric analyses, we derive accurate absolute masses for thecomponents of M1=1.453+/-0.028Msolar andM2=0.705+/-0.014Msolar and radii ofR1=2.632+/-0.030Rsolar andR2=4.233+/-0.060Rsolar, as well as effectivetemperatures of 6000+/-200 and 4275+/-150 K for the primary andsecondary, respectively. There are no obvious signs of activity(spottedness) in the optical light curve of the binary.
| New Times of Minima of Some Eclipsing Variables
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| 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/.
| Times of Minima of Eclipsing Binary Stars
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| Optical Photometry and X-Ray Monitoring of the ``Cool Algol'' BD +05°706: Determination of the Physical Properties
We present new photometric observations in the BVRI bands of thedouble-lined eclipsing binary BD +05°706 conducted over threeobserving seasons, as well as new X-ray observations obtained with ROSATcovering a full orbital cycle (P=18.9 days). A detailed light-curveanalysis of the optical data shows the system to be semidetached,confirming indications from an earlier analysis by Torres et al.(published in 1998), with the less massive and cooler star filling itsRoche lobe. The system is a member of the rare class of cool Algolsystems, which are different from the ``classical'' Algol systems inthat the mass-gaining component is also a late-type star rather than aB- or A-type star. By combining the new photometry with a reanalysis ofthe spectroscopic observations reported by Torres et al., we deriveaccurate absolute masses for the components ofM1=2.633+/-0.028 Msolar andM2=0.5412+/-0.0093 Msolar, radii ofR1=7.55+/-0.20 Rsolar andR2=11.02+/-0.21 Rsolar, as well as effectivetemperatures of 5000+/-100 and 4640+/-150 K, for the primary andsecondary, respectively. There are obvious signs of activity(spottedness) in the optical light curve of the binary. Our X-ray lightcurve clearly shows the primary eclipse but not the secondary eclipse,suggesting that the primary star is the dominant source of the activityin the system. The depth and duration of the eclipse allow us to infersome of the properties of the X-ray-emitting region around that star.
| Times of Minima of Eclipsing Binaries
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| Times of Minima of Eclipsing Binaries
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| 149 Bedeckungssterne der BAV-Programme. Eine Analyse der Beobachtungstatigkeit seit den Angangen.
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| Times of Minima of Eclipsing Binaries
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| Photoelectric Minima of Eclipsing Binaries
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| BD +05 706: A New Member of the Class of ``Cool Algols''
We report the serendipitous discovery of an Algol-type binary with anorbital period of 18.9 days, in which both components are cool giants(G8 III and K1-K2 III). Few systems with these characteristics are knownand are referred to as ``cool Algols,'' as opposed to the ``classicalAlgols'' in which the mass-gaining component resembles an early-typemain-sequence star. The nature of this object, which is a strong X-raysource, was discovered in the course of a spectroscopic search for TTauri stars among ROSAT All-Sky Survey sources. We derive a double-linedspectroscopic orbit leading to minimum masses of M_A = 2.481 +/- 0.023M_ȯ and M_B = 0.515 +/- 0.011 M_ȯ and a corresponding mass ratioof q ~ 0.21. We measure also projected rotational velocities of 22 and31 km s^-1, respectively, and a luminosity ratio of l_B/l_A = 1.06 +/-0.04 at ~5200 Å. The system is probably semidetached, with theaxial spin of the components synchronized with the orbital motion, andthe probability of eclipses is high. The general properties of BD +05deg706, most likely a result of case B mass exchange, are very similarto those of the other known members of this class. We discuss thecorrelation between the mass of the hotter, detached components andtheir effective temperature for all cool Algols, noted previously by D.M. Popper, as well as a trend with the orbital period. Chromosphericactivity indicators in BD +05 deg706 are compared with those of othermembers of its class, as well as with those of the classical Algols andthe RS CVn binaries. Some of the observations reported here wereobtained with the Multiple Mirror Telescope, a joint facility of theSmithsonian Institution and the University of Arizona. Based onobservations obtained during program 57.E-0646 with the 1.5 m telescopeof the European Southern Observatory on La Silla, Chile. Based onobservations obtained with the 1.23 m and 2.2 m telescopes of theGerman-Spanish Calar Alto Observatory, Spain.
| Four colour photometry of late-type binary systems. I. First UVBY beta light curves of ZZ Ursae Majoris
This paper presents first complete uvby light curves of the late-typedetached eclipsing binary ZZ UMa (G0V + G8V, P=2.2993 deg). This binarysystem has been observed during eight campaigns at the Calar AltoObservatory (Almeria, Spain)and at the Sierra Nevada Observatory(Granada, Spain). 294 points distributed over the binary period andcovering both eclipses are given. The comparison stars used to calculatethe differential light curves (SAO 15242 and SAO 15251) were confirmedas being good reference stars with constant flux. These observations arepart of a 6 year uvby and Hβ monitoring program of low masseclipsing binaries whose main objective is to provide accurate absoluteastrophysical parameters for late-type main sequence stars. Detailsabout the standardisation process and accuracy of the photometry arealso given. The internal accuracy of the standard photometry measured asthe mean RMS of the differences between standard and observed values forthe standard stars observed along the program is only a fewmillimagnitudes. Detailed analysis of ZZ UMa, based on these lightcurves, will be published separately. Based on observations collectedwith the Spanish 1.5m telescope at Calar Alto, Almeria, Spain, and theSpanish 1m telescope at Sierra Nevada, Granada, Spain. Tables 2 and 3will be accessible only in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr//Abstract.html
| The ROSAT Galactic Plane Survey: Analysis of a low latitude sample area in Cygnus
The analysis of the part of the ROSAT all-sky survey covering thegalactic plane is the scope of a dedicated project called the ROSATGalactic Plane Survey. In order to statistically understand the natureof the ~14,000 sources discovered by ROSAT at |b| <= 20 degrees, anumber of sample areas have been chosen for follow-up opticalidentification. In this paper we present the X-ray and optical materialgathered in a region located in the Cygnus constellation, centered at l= 90 degrees, b = 0 degrees and covering an area of 64.5deg2. A total of 95 and 128 sources are detected with amaximum likelihood larger than 10 and 8 respectively. With a typicalsurvey exposure time of the order of 700 to 900 s the flux completenesslevel is ~0.02 cnts s^{-1} corresponding to ~2 10^{-13} erg cm^{-2}s^{-1}. The position of the sample area allows to investigate the softX-ray content of a rather typical region of the galactic plane. In thispaper we describe the details of the observational procedures and datareduction. For each ROSAT source we list the main X-ray characteristicstogether with those of the proposed optical identification. Whenappropriate, we also show optical spectra and finding charts. The fullanalysis and discussion of these data are presented in a companion paper(\cite[Motch et al. 1997]{ref13}). Tables 2 to 6 are also available inelectronic form at the CDS via anonymous ftp cdsarc.u-strasbg.fr.Figures are only published electronically and are made available athttp://www.ed-phys.fr/Abstract.html.
| The ROSAT galactic plane survey: analysis of a low latitude sample area in Cygnus.
We present the analysis of the point source content of a low galacticlatitude region selected from the ROSAT all-sky survey. The test fieldis centered at l=90deg, b=0deg and has an area of 64.5deg^2^. A total of128 soft X-ray sources are detected above a maximum likelihood of 8.Catalogue searches and optical follow-up observations show that in thisdirection of the galactic plane, 85% of the sources brighter than 0.03PSPC cts/s are identified with active coronae. F-K type stars represent67%(+/-13%) of the stellar identifications and M type stars account for19%(+/-6%). A small but significant number of X-ray sources areassociated with A type stars on the basis of positional coincidence.These results together with those of similar optical campaignsdemonstrate that the soft X-ray population of the Milky Way is largelydominated by active stars. We show that the density and distribution influx and spectral type of the active coronae detected in X-rays areconsistent with the picture drawn from current stellar population modelsand age dependent X-ray luminosity functions. The modelling of thispopulation suggests that most of the stars detected by ROSAT in thisdirection are younger than 1Gyr. This opens the possibility to extractin a novel way large samples of young stars from the ROSAT all-skysurvey. The small number of unidentified sources at low X-ray flux putrather strong constraints on the hypothetical X-ray emission from oldneutron stars accreting from the interstellar medium. Our observationsclearly rule out models which assume no dynamical heating for thispopulation and a total number of N_ns_=10^9^ neutron stars in theGalaxy. If accretion on polar caps is the dominant mode then our upperlimit may imply N_ns_=~10^8^. Among the non coronal identifications arethree white dwarfs, a Seyfert 1 active nucleus, two early type stars andone cataclysmic variable. We also report the discovery of a Me + WDclose binary system with P_orb_=~12h.
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