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The Third Signature of Granulation in Bright-giant and Supergiant Stars
We investigated third-signature granulation plots for 18 bright giantsand supergiants and one giant of spectral classes G0 to M3. These plotsreveal the net granulation velocities, averaged over the stellar disk,as a function of depth. Supergiants show significant differences fromthe "standard" shape seen for lower-luminosity stars. Most notable is astriking reversal of slope seen for three of the nine supergiants, i.e.,stronger lines are more blueshifted than weaker lines, opposite thesolar case. Changes in the third-signature plot of ? Sco (M1.5Iab) with time imply granulation cells that penetrate only the lowerportion of the photosphere. For those stars showing the standard shape,we derive scaling factors relative to the Sun that serve as afirst-order measure of the strength of the granulation relative to theSun. For G-type stars, the third-signature scale of the bright giantsand supergiants is approximately 1.5 times as strong as in dwarfs, butfor K stars, there in no discernible difference betweenhigher-luminosity stars and dwarfs. Classical macroturbulence, a measureof the velocity dispersion of the granulation, increases with thethird-signature-plot scale factors, but at different rates for differentluminosity classes.
| 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.
| First detection of a weak magnetic field on the giant Arcturus: remnants of a solar dynamo?
Context. Arcturus is the second closest K giant and among the brighteststars in the sky. It has not been found to have a magnetic field, eventhough Ca ii H&K lines as activity indicators imply that Arcturus ismagnetically active. Aims: We measure the mean longitudinalmagnetic field strengths and interpret them in terms of an intraseasonalactivity modulation. Methods: We apply our new Zeeman componentdecomposition (ZCD) technique to three single sets of Stokes I and Vspectra to measure the longitudinal component of the magnetic fieldresponsible for tiny Zeeman signatures detected in spectral lineprofiles. Results: For two of the spectra, we report thedetection of the Zeeman signature of a weak longitudinal magnetic fieldof 0.65 ± 0.26 G and 0.43 ± 0.16 G. The third measurementis less significant, but all the measurements closely reproduce arotationally modulated activity cycle with four active longitudes. Conclusions: For the first time, a magnetic field on Arcturus isdirectly detected. This field can be attributed to a diminishingsolar-type ??-dynamo acting in the deepening convection zoneof Arcturus. We demonstrate that our new method ZCD lowers the detectionlimit of very weak magnetic fields from spectropolarimetricmeasurements.
| A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| Systematic detection of magnetic fields in massive, late-type supergiants
We report the systematic detection of magnetic fields in massive (M >5Msolar) late-type supergiants, using spectropolarimetricobservations obtained with ESPaDOnS at the Canada-France-HawaiiTelescope. Our observations reveal detectable Stokes V Zeeman signaturesin least-squares deconvolved mean line profiles in one-third of theobserved sample of more than 30 stars. The signatures are sometimescomplex, revealing multiple reversals across the line. The correspondinglongitudinal magnetic field is seldom detected, although ourlongitudinal field error bars are typically 0.3 G (1?). Thesecharacteristics suggest topologically complex magnetic fields,presumably generated by dynamo action. The Stokes V signatures of sometargets show clear time variability, indicating either rotationalmodulation or intrinsic evolution of the magnetic field. We also observea weak correlation between the unsigned longitudinal magnetic field andthe CaII K core emission equivalent width of the active G2Iab supergiant? Dra and the G8Ib supergiant ? Gem.Based on observations obtained at the Canada-France-Hawaii Telescope(CFHT) which is operated by the National Research Council of Canada, theInstitut National des Sciences de l'Univers of the Centre National de laRecherche Scientifique of France and the University of Hawaii.E-mail: Jason.Grunhut@rmc.ca
| On Highly Clumped Magnetic Wind Models for Cool Evolved Stars
Recently, it has been proposed that the winds of non-pulsating andnon-dusty K and M giants and supergiants may be driven by some form ofmagnetic pressure acting on highly clumped wind material. While manyresearchers believe that magnetic processes are responsible for coolevolved stellar winds, existing MHD and Alfvén wave-driven windmodels have magnetic fields that are essentially radial and tied to thephotosphere. The clumped magnetic wind scenario is quite different inthat the magnetic flux is also being carried away from the star with thewind. We test this clumped wind hypothesis by computing continuum radiofluxes from the ? Aur semiempirical model of Baade et al., which isbased on wind-scattered line profiles. The radio continuum opacity isproportional to the electron density squared, while the line scatteringopacity is proportional to the gas density. This difference inproportionality provides a test for the presence of large clumpingfactors. We derive the radial distribution of clump factors (CFs) for? Aur by comparing the nonthermal pressures required to produce thesemiempirical velocity distribution with the expected thermal pressures.The CFs are ~5 throughout the sub-sonic inner wind region and thendecline outward. These implied clumping factors lead to excess radioemission at 2.0 cm, while at 6.2 cm it improves agreement with thesmooth unclumped model. Smaller clumping factors of ~2 lead to betteroverall agreement but also increase the discrepancy at 2 cm. Theseresults do not support the magnetic clumped wind hypothesis and insteadsuggest that inherent uncertainties in the underlying semiempiricalmodel probably dominate uncertainties in predicted radio fluxes.However, new ultraviolet line and radio continuum observations areneeded to test the new generations of inhomogeneous magnetohydrodynamicwind models.
| The star catalogue of Hevelius. Machine-readable version and comparison with the modern Hipparcos Catalogue
The catalogue by Johannes Hevelius with the positions and magnitudes of1564 entries was published by his wife Elisabeth Koopman in 1690. Weprovide a machine-readable version of the catalogue, and briefly discussits accuracy on the basis of comparison with data from the modernHipparcos Catalogue. We compare our results with an earlier analysis byRybka (1984), finding good overall agreement. The magnitudes given byHevelius correlate well with modern values. The accuracy of his positionmeasurements is similar to that of Brahe, with ? = 2´ forlongitudes and latitudes, but with more errors >5´ thanexpected for a Gaussian distribution. The position accuracy decreasesslowly with magnitude. The fraction of stars with position errors largerthan a degree is 1.5%, rather smaller than the fraction of 5% in thestar catalogue of Brahe.Star catalogue of Hevelius is only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/516/A29
| Three editions of the star catalogue of Tycho Brahe. Machine-readable versions and comparison with the modern Hipparcos Catalogue
Tycho Brahe completed his catalogue with the positions and magnitudes of1004 fixed stars in 1598. This catalogue circulated in manuscript form.Brahe edited a shorter version with 777 stars, printed in 1602, andKepler edited the full catalogue of 1004 stars, printed in 1627. Weprovide machine-readable versions of the three versions of thecatalogue, describe the differences between them and briefly discusstheir accuracy on the basis of comparison with modern data from theHipparcos Catalogue. We also compare our results with earlier analysesby Dreyer (1916, Tychonis Brahe Dani Scripta Astronomica, Vol. II) andRawlins (1993, DIO, 3, 1), finding good overall agreement. Themagnitudes given by Brahe correlate well with modern values, hislongitudes and latitudes have error distributions with widths of2´, with excess numbers of stars with larger errors (as comparedto Gaussian distributions), in particular for the faintest stars. Errorsin positions larger than ?10´, which comprise about 15% ofthe entries, are likely due to computing or copying errors.The full tables KeplerE and Variants (see Table 4) and the table withthe latin descriptions of the stars are available in electronic formonly at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/516/A28
| The PASTEL catalogue of stellar parameters
Aims: The PASTEL catalogue is an update of the [Fe/H] catalogue,published in 1997 and 2001. It is a bibliographical compilation ofstellar atmospheric parameters providing (T_eff, log g, [Fe/H])determinations obtained from the analysis of high resolution, highsignal-to-noise spectra, carried out with model atmospheres. PASTEL alsoprovides determinations of the one parameter T_eff based on variousmethods. It is aimed in the future to provide also homogenizedatmospheric parameters and elemental abundances, radial and rotationalvelocities. A web interface has been created to query the catalogue onelaborated criteria. PASTEL is also distributed through the CDS databaseand VizieR. Methods: To make it as complete as possible, the mainjournals have been surveyed, as well as the CDS database, to findrelevant publications. The catalogue is regularly updated with newdeterminations found in the literature. Results: As of Febuary2010, PASTEL includes 30151 determinations of either T_eff or (T_eff,log g, [Fe/H]) for 16 649 different stars corresponding to 865bibliographical references. Nearly 6000 stars have a determination ofthe three parameters (T_eff, log g, [Fe/H]) with a high qualityspectroscopic metallicity.The catalogue can be queried through a dedicated web interface at http://pastel.obs.u-bordeaux1.fr/.It is also available in electronic form at the Centre de DonnéesStellaires in Strasbourg (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/pastel),at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A111
| Masses and luminosities of O- and B-type stars and red supergiants
Massive stars are of interest as progenitors of supernovae, i.e.neutron stars and black holes, which can be sources of gravitationalwaves. Recent population synthesis models can predict neutron star andgravitational wave observations but deal with a fixed supernova rate oran assumed initial mass function for the population of massive stars. Here we investigate those massive stars, which are supernovaprogenitors, i.e. with O- and early B-type stars, and also allsupergiants within 3 kpc. We restrict our sample to those massive starsdetected both in 2MASS and observed by Hipparcos, i.e. only those starswith parallax and precise photometry. To determine the luminositieswe calculated the extinctions from published multi-colour photometry,spectral types, luminosity class, all corrected for multiplicity andrecently revised Hipparcos distances. We use luminosities andtemperatures to estimate the masses and ages of these stars usingdifferent models from different authors. Having estimated theluminosities of all our stars within 3 kpc, in particular for all O- andearly B-type stars, we have determined the median and mean luminositiesfor all spectral types for luminosity classes I, III, and V. Ourluminosity values for supergiants deviate from earlier results: Previouswork generally overestimates distances and luminosities compared to ourdata, this is likely due to Hipparcos parallaxes (generally moreaccurate and larger than previous ground-based data) and the fact thatmany massive stars have recently been resolved into multiples of lowermasses and luminosities. From luminosities and effective temperatureswe derived masses and ages using mass tracks and isochrones fromdifferent authors. From masses and ages we estimated lifetimes andderived a lower limit for the supernova rate of ?20 events/Myraveraged over the next 10 Myr within 600 pc from the sun. These data arethen used to search for areas in the sky with higher likelihood for asupernova or gravitational wave event (like OB associations).
| Evolution of intermediate and low mass binary systems
There are a number of binaries, fairly wide and with one or even twoevolved giant components, that do not agree very well with conventionalstellar evolution: the secondaries are substantially larger(‘oversized’) than they should be because their masses arequite low compared with the primaries. I discuss the possibility thatthese binaries are former triples, in which a merger has occurred fairlyrecently in a short-period binary sub-component.Some mergers areexpected, and may follow a phase of contact evolution. I suggest that incontact there is substantial transfer of luminosity between thecomponents due to differential rotation, of the character observed byhelioseismology in the Sun’s surface convection zone.
| Ellipsoidal Variable V1197 Orionis: Absolute Light-Velocity Analysis for Known Distance
V1197 Orionis light curves from a long-term observing program for redgiant binaries show ellipsoidal variation of small amplitude in the Vand RC bands, although not clearly in U and B. Eclipses arenot detected. All four bands show large irregular intrinsic variations,including fleeting quasi-periodicities identified by power spectra, thatdegrade analysis and may be caused by dynamical tides generated byorbital eccentricity. To deal with the absence of eclipses andconsequent lack of astrophysical and geometrical information, direct useis made of the Hipparcos parallax distance while the V and RClight curves and (older) radial velocity curves are analyzedsimultaneously in terms of absolute flux. The red giant's temperature isestimated from new spectra. This type of analysis, called InverseDistance Estimation for brevity, is new and can also be applied to otherellipsoidal variables. Advantages gained by utilization of definitedistance and temperature are discussed in regard to how radius,fractional lobe filling, and mass ratio information are expressed in theobservations. The advantages were tested in solutions of noisy syntheticdata. Also discussed and tested by simulations are ideas on the optimalnumber of light curves to be solved simultaneously under variousconditions. The dim companion has not been observed or discussed in theliterature but most solutions find its mass to be well below that of thered giant. Solutions show red giant masses that are too low forevolution to the red giant stage within the age of the Galaxy, althoughthat result is probably an artifact of the intrinsic brightnessfluctuations.
| A Catalog of Visual Double and Multiple Stars With Eclipsing Components
A new catalog of visual double systems containing eclipsing binaries asone component is presented. The main purpose of this catalog is tocompile a complete list of all known multiples of this variety, both forcurrent analysis and to highlight those in need of additionalobservations. All available photometric and astrometric data wereanalyzed, resulting in new orbits for eight systems and new times ofminimum light for a number of the eclipsing binaries. Some of thesystems in the catalog have acceptable solutions for their visualorbits, although in most cases their orbital periods are too long forsimultaneous analysis. Also included, however, are a number of systemswhich currently lack an orbital solution but which may be suitable forsimultaneous analysis in the future.
| Emission Lines in 32 Cygni
I identify the profusion of emission lines seen in IUE spectra of 32Cyg (K4-5 Ib+B6-7 IV-V) during total eclipse. With the exception of avery few weak lines, all of these are also seen in zeta Aur during itseclipse, and the stronger features appear in 31 Cyg. Seventy-fourpercent of these emission lines can be attributed to Fe II. Few areintrisically weaker than gf~0.01. Other spectra definitely present areC II, N I, O I, Si II, Mg II, S II, Cr II, Ni II, Al II, Al III, F III,Si IV, and C IV. No emission lines of the neutral metals, except forfluorescent Fe I UV44, are unambiguously detected; specifically, linesof C I, Si I, or S I were not detected in the spectrum.
| A Model for the Chromosphere/Wind of 31 Cygni and Its Implications for Single Stars
I develop a detailed empirical model for the chromosphere and wind of 31Cyg based on a previously published analysis of InternationalUltraviolet Explorer spectra from the 1993 eclipse and on thethermodynamics of how the wind must be driven. I then use this model tointerpret observations of single supergiant stars and to assess theevidence that their winds are fundamentally different from those ofsupergiants in binary systems. This model naturally predicts a certainlevel of clumping of the gas to balance the pressure that drives thewind. It also predicts that anisotropic turbulence, such as would resultfrom transverse displacements of Alfven waves directed along radialmagnetic flux lines, would not give the roughly Gaussian profiles ofemission lines seen in cool giant stars. Furthermore, it implies that CII] may not tell us much at all about general conditions inchromospheres. Finally, I speculate that chaotic magnetic fields, indynamical equilibrium with the gas of the wind, are the actual drivingmechanism.
| Polarimetric measures of selected variable stars
Aims. The purpose of this paper is to summarize and interpretunpublished optical polarimetry for numerous program stars that wereobserved over the past decades at the Flower and Cook Observatory (FCO),University of Pennsylvania. We also make the individual calibratedmeasures available for long-term comparisons with new data. Methods: Weemploy three techniques to search for intrinsic variability within eachdataset. First, when the observations for a given star and filter arenumerous enough and when a period has been determined previously viaphotometry or spectroscopy, the polarimetric measures are plotted versusphase. If a statistically significant pattern appears, we attribute itto intrinsic variability. Second, we compare means of the FCO data tomeans from other workers. If they are statistically different, weconclude that the object exhibits long-term intrinsic variability.Third, we calculate the standard deviation for each program star andfilter and compare it to the standard deviation estimated fromcomparable polarimetric standards. If the standard deviation of theprogram star is at least three times the value estimated from thepolarimetric standards, the former is considered intrinsically variable.All of these statements are strengthened when variability appears inmultiple filters. Results: We confirm the existence of anelectron-scattering cloud at L1 in the β Per system, andfind that LY Aur and HR 8281 possess scattering envelopes. Intrinsicpolarization was detected for Nova Cas 1993 as early as day +3. Wedetected polarization variability near the primary eclipse of 32 Cyg.There is marginal evidence for polarization variability of the βCepheid type star γ Peg. The other objects of this class exhibitedno variability. All but one of the β Cepheid objects (ES Vul) fallon a tight linear relationship between linear polarization and E(B-V),in spite of the fact that the stars lay along different lines of sight.This dependence falls slightly below the classical upper limit ofSerkowski, Mathewson, and Ford.The table, which contains the polarization observations of the programstars discussed in this paper, is only available in electronic form atthe 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/489/911
| A catalogue of multiplicity among bright stellar systems
We consider the multiplicity of stellar systems with (combined)magnitude brighter than 6.00 in Hipparcos magnitudes. We identify 4559such bright systems (including the Sun), and the frequencies ofmultiplicities 1, 2,..., 7 are found to be 2718, 1437, 285, 86, 20, 11and 2. We discuss the uncertainties, which are substantial. We alsoconsider the distributions of periods of orbits and suborbits. We notethat for even more restricted set of 478 systems with VH<= 4.00, the proportions of higher multiples up to sextuple areprogressively larger (213, 179, 54, 19, 8, 5), suggesting substantialincompleteness in even the reasonably well studied larger sample.This sample can be seen as relatively thoroughly studied formultiplicity, and reasonably representative of stars more massive thanthe Sun. But the restriction to VH <= 6 means that oursample contains hardly any systems where all components are low-massmain-sequence stars (K or M).Data on multiplicity are important as a constraint on (i) the starformation problem, (ii) the problem of the evolution of the Galacticstellar population and (iii) the interaction of dynamics and evolutionthrough the effect of Kozai cycles. We discuss these topics briefly.
| Orbits and Pulsations of the Classical ? Aurigae Binaries
We have derived new orbits for ? Aur, 32 Cyg, and 31 Cyg withobservations from the Tennessee State University (TSU) AutomaticSpectroscopic Telescope, and used them to identify nonorbital velocitiesof the cool supergiant components of these systems. We measure periodsin those deviations, identify unexpected long-period changes in theradial velocities, and place upper limits on the rotation of thesestars. These radial-velocity variations are not obviously consistentwith radial pulsation theory, given what we know about the masses andsizes of the components. Our concurrent photometry detected thenonradial pulsations driven by tides (ellipsoidal variation) in both? Aur and 32 Cyg, at a level and phasing roughly consistent withsimple theory to first order, although they seem to require moderatelylarge gravity darkening. However, the K component of 32 Cyg must beconsiderably bigger than expected, or have larger gravity darkening than? Aur, to fit its amplitude. However, again there is preciouslittle evidence for the normal radial pulsation of cool stars in ourphotometry. H? shows some evidence for chromospheric heating bythe B component in both ? Aur and 32 Cyg, and the three stars showamong them a meager ~2-3 outbursts in their winds of the sort seenoccasionally in cool supergiants. We point out two fundamental questionsin the interpretation of these stars: (1) whether it is appropriate tomodel the surface brightness as gravity darkening and (2) whether muchof the nonorbital velocity structure may actually represent changes inthe convective flows in the stars' atmospheres.
| 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.
| The Tennessee State University Automatic Spectroscopic Telescope: Data Processing and Velocity Variation of Cool Giants
This paper discusses data reduction for an echelle spectrograph we havedeveloped for an automatic telescope at Tennessee State University andare using to monitor radial velocities and line profiles of cool giantand supergiant stars. Although our approach to data reduction is ratherconventional, we discuss flat-fielding and extraction of velocities inways that should be of general interest, establish a transformation tothe IAU radial velocity system (+0.35 +/- 0.09 km s-1), anddetermine the external precision for measured velocities (0.10-0.11 kms-1). Also, we present results of the first 2-3 years ofmonitoring radial velocities in about 120 cool giants and compare thoseresults with the level of variability found with photometry. These newdata confirm the widely held understanding that K and M giants are allradial velocity variables at the level of 0.1 km s-1.
| Properties of the ? Aur-Type Binary System 22 Vul = QS Vul
The 22 Vul system is important for studying the winds and chromospheresof cool evolved stars because the G4 I component is rotating rapidly andprobably faster than synchronously. We discuss the system's physicalproperties in the context of a wide range of constraints on them andpropose values that may be marginally better than previous ones (see theend of § 3). We use H? spectroscopy to assess the variabilityof the cool star's wind, and archival IUE observations to measurevariation of density in the wind and rotation of the chromosphere. Weargue that the terminal velocity of the wind must be at least as greatas the edge velocity of Mg II and derive a new value ofv?>~208+/-5 km s-1. Directly measuredcolumn densities for hydrogen (from Ly?), combined with columndensities for metals, imply a ?~2.5 velocity law for the wind witha mass-loss rate of ~1.6×10-8 Msolaryr-1, about 4 times the surface flux of 31 Cyg. Excitationtemperatures and turbulent velocities in the inner 3R* of thewind are similar to those in other ? Aur binaries. The apparentfaster-than-synchronous rotation Griffin and coworkers found in theoptical persists in IUE spectra out to at least 2.5R(G4 I). This impliesthat the wind is locked to the star through magnetic fields or that thematerial in the wind is viscous enough to maintain approximatelysolid-body rotation.
| A critical test of empirical mass loss formulas applied to individual giants and supergiants
To test our new, improved Reimers-type mass-loss relation, given bySchröder & Cuntz in 2005 (ApJ, 630, L73), we take a look at thebest studied galactic giants and supergiants - particularly those withspatially resolved circumstellar shells and winds, obtained directly orby means of a companion acting as a probing light source. Together withwell-known physical parameters, the selected stars provide the mostpowerful and critical observational venues for assessing the validity ofparameterized mass-loss relations for cool winds not driven by moleculesor dust. In this study, star by star, we compare our previouslypublished relation with the original Reimers relation (1975, Mem. Roy.Soc. Liège 6. Ser. 8, 369), the Lamers relation (1981, ApJ, 245,593), and the two relations by de Jager and his group (1988, A&AS,72, 259; 1990, A&A, 231, 134). The input data, especially thestellar masses, have been constrained using detailed stellar evolutionmodels. We find that only the relationship by Schröder & Cuntzagrees, within the error bars, with the observed mass-loss rates for allgiants and supergiants.
| Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters(Teff, logg, [Fe/H]) for MILES, a new spectral stellarlibrary covering the range λλ 3525-7500Å at2.3Å (FWHM) spectral resolution. The library consists of 985 starsspanning a large range in atmospheric parameters, from super-metal-rich,cool stars to hot, metal-poor stars. The spectral resolution, spectraltype coverage and number of stars represent a substantial improvementover previous libraries used in population synthesis models. Theatmospheric parameters that we present here are the result of aprevious, extensive compilation from the literature. In order toconstruct a homogeneous data set of atmospheric parameters we have takenthe sample of stars of Soubiran, Katz & Cayrel, which has very welldetermined fundamental parameters, as the standard reference system forour field stars, and have calibrated and bootstrapped the data fromother papers against it. The atmospheric parameters for our clusterstars have also been revised and updated according to recent metallicityscales, colour-temperature relations and improved set of isochrones.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Medium-resolution Isaac Newton Telescope library of empirical spectra
A new stellar library developed for stellar population synthesismodelling is presented. The library consists of 985 stars spanning alarge range in atmospheric parameters. The spectra were obtained at the2.5-m Isaac Newton Telescope and cover the range λλ3525-7500 Å at 2.3 Å (full width at half-maximum) spectralresolution. The spectral resolution, spectral-type coverage,flux-calibration accuracy and number of stars represent a substantialimprovement over previous libraries used in population-synthesis models.
| 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.
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| VLA Observations of ζ Aurigae: Confirmation of the Slow Acceleration Wind Density Structure
Studies of the winds from single K and early M evolved stars indicatethat these flows typically reach a significant fraction of theirterminal velocity within the first couple of stellar radii. The mostdetailed spatially resolved information of the extended atmospheres ofthese spectral types comes from the ζ Aur eclipsing binaries.However, the wind acceleration inferred for the evolved primaries inthese systems appears significantly slower than for stars of similarspectral type. Since there are no successful theories for mass loss fromK and early M evolved stars, it is important to place strong empiricalconstraints on potential models and determine whether this difference inacceleration is real or an artifact of the analyses. We have undertakena radio continuum monitoring study of ζ Aurigae (K4 Ib + B5 V)using the Very Large Array to test the wind density model of Baade etal. that is based on Hubble Space Telescope (HST) Goddard HighResolution Spectrograph ultraviolet spectra. ζ Aur was monitored atcentimeter wavelengths over a complete orbital cycle, and fluxvariations during the orbit are found to be of similar magnitude tovariations at similar orbital phases in the adjacent orbit. Duringeclipse, the flux does not decrease, showing that the radio emissionoriginates from a volume substantially larger thanR3K~(150Rsolar)3 surroundingthe B star. Using the one-dimensional density model of the K4 Ibprimary's wind derived from HST spectral line profile modeling andelectron temperature estimates from previous optical and new HSTstudies, we find that the predicted radio fluxes are consistent withthose observed. Three-dimensional hydrodynamic simulations indicate thatthe accretion flow perturbations near the B star do not contributesignificantly to the total radio flux from the system, consistent withthe radio eclipse observations. Our radio observations confirm the slowwind acceleration for the evolved K4 Ib component. ζ Aur's velocitystructure does not appear to be typical of single stars with similarspectral types. This highlights the need for more comprehensivemultiwavelength studies for both single stars, which have been sadlyneglected, and other ζ Aur systems to determine if its windproperties are typical.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is 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/431/773
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Cygnus |
| Ascensió Recta: | 20h15m28.32s |
| Declinació: | +47°42'51.2" |
| Magnitud Aparent: | 3.999 |
| Moviment propi RA: | 1.8 |
| Moviment propi Dec: | 4.5 |
| B-T magnitude: | 5.907 |
| V-T magnitude: | 4.157 |
Catàlegs i designacions:
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