WIKISKY.ORG
 Главная Введение Выжить во Вселенной News@Sky Астрофотография Коллекция Форум Blog New! Помощь Пресса Войти

# β Sct

Оглавление

### Изображения

Загрузить ваше изображение

DSS Images   Other Images

### Публикации по объекту

 Lithium abundances and rotational behavior for bright giant starsAims.We study the links possibly existing between the lithium content ofbright giant stars and their rotational velocity. Methods: .Weperformed a spectral analysis of 145 bright giant stars (luminosityclass II) spanning the spectral range from F3 to K5. All these starshave homogeneous rotational velocity measurements available in theliterature. Results: .For all the stars of the sample, we provideconsistent lithium abundances (A_Li), effective temperatures (T_eff),projected rotational velocity (v sin i), mean metallicity ([Fe/H]),stellar mass, and an indication of the stellar multiplicity. The gradualdecrease in lithium abundance with T_eff is confirmed for bright giantstars, and it points to a dilution factor that is at least assignificant as in giant stars. From the F to K spectral types, the A_Lispans at least three orders of magnitude, reflecting the effects ofstellar mass and evolution on dilution. Conclusions: .We find thatthe behavior of A_Li as a function of v sin i in bright giant starspresents the same trend as is observed in giants and subgiants: starswith high A_Li are moderate or fast rotators, while stars with low A_Lishow a wide range of v sin i values. Shapes of Spectral Line Bisectors for Cool StarsThe shape of the line bisector for the prototype spectral line Fe Iλ6253 was measured for an array of 54 stars on the cool half ofthe HR diagram. These bisectors are given in tables along with theirerrors. The classic C shape is shown by only a rather restricted rangein effective temperature and luminosity. The detailed change in bisectorshape with effective temperature and luminosity is documented moreprecisely than in previous work. The most blueward point on the bisectorchanges its height systematically with luminosity and can be used as aluminosity or gravity discriminant. The wide range of bisector shapescontains significant information about the velocity fields in theatmospheres of these stars, but extracting that information may requireextensive modeling. Spectral Types for Four OGLE-III Transit Candidates: Could These Be Planets?We present spectral types for OGLE (Optical Gravitational LensingExperiment) transiting planet candidates OGLE-TR-134 through 137 basedon low-resolution spectra taken at Kitt Peak. Our main objective is toaid those planning radial velocity monitoring of transit candidates. Weobtain spectral types with an accuracy of 2 spectral subtypes, alongwith tentative luminosity classifications. Combining the spectral typeswith light-curve fits to the OGLE transit photometry, and with TwoMicron All Sky Survey counterparts in two cases, we conclude thatOGLE-TR-135 and 137 are not planetary transits, while OGLE-TR-134 and136 are good candidates and should be observed with precision radialvelocity monitoring to determine whether the companions are of planetarymass. OGLE-TR-135 is ruled out chiefly because a discrepancy between thestellar parameters obtained from the transit fit and those inferred fromthe spectra indicates that the system is a blend. OGLE-TR-137 is ruledout because the depth of the transit combined with the spectral type ofthe star indicates that the transiting object is stellar. OGLE-TR-134and 136, if unblended main-sequence stars, are each orbited by atransiting object with radius below 1.4 RJ. The caveats arethat our luminosity classification suggests that OGLE-TR-134 could be agiant (and therefore a blend), while OGLE-TR-136 shows a (much smaller)discrepancy of the same form as OGLE-TR-135, which may indicate that thesystem is a blend. However, since our luminosity classifications areuncertain at best, and the OGLE-TR-136 discrepancy can be explained ifthe primary is a slightly anomalous main-sequence star, the stars remaingood candidates. The Fine Guidance Sensor Orbit of the G4 Bright Giant HD 173764TRANS and POS mode observations of the G4 IIa star β Scuti (HD173764) have been made with a Hubble Space Telescope (HST) Fine GuidanceSensor (FGS3). This spectroscopic binary with a period of 833 days andan eccentricity of 0.36 offered hope of resolving the secondary stellarcomponent and inferring the orbital inclination, distance, and masses,thus contributing to comparisons with theory for rapidpost-main-sequence evolution. From analysis of IUE observations and thetotal UV-optical energy distribution, the secondary has a spectral classof B9 and a difference in visual luminosity of ~3 mag. Isochrone fittingusing this ΔV and temperatures from the spectral types yields ~26mas for the anticipated projected separation at apastron. The TRANS modedata demonstrate duplicity in the signal but fail to provide reliableseparations and position angles even near apastron. This separation isinstead no more than 22 mas. However, the parallax is probably smaller,by a similar factor, than that expected from initial isochrone fitting,and β Sct is more luminous than originally estimated. Analysis ofPOS mode data reveals the orbital inclination and the orientation on thesky for a semimajor axis of only 5.7+/-0.4 mas for the primary's orbitaround the center of mass. The parallax from POS mode observations isquite small, only consistent with isochrones at the 2 σ level.From all of the evidence, the system lies at 210+/-23 pc and the evolvedG-type primary has Mv~=-2.9. Astrometric orbits of SB^9 starsHipparcos 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. CHARM2: An updated Catalog of High Angular Resolution MeasurementsWe 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 Determination of fundamental characteristics for stars of the F, G, and K spectral types. The surface gravities and metallicity parameters.Not Available The Wilson-Bappu effect: A tool to determine stellar distancesWilson & Bappu (\cite{orig}) have shown the existence of aremarkable correlation between the width of the emission in the core ofthe K line of Ca II and the absolute visual magnitude of late-typestars.Here we present a new calibration of the Wilson-Bappu effect based on asample of 119 nearby stars. We use, for the first time, widthmeasurements based on high resolution and high signal to noise ratio CCDspectra and absolute visual magnitudes from the Hipparcos database.Our primary goal is to investigate the possibility of using theWilson-Bappu effect to determine accurate distances to single stars andgroups.The result of our calibration fitting of the Wilson-Bappu relationshipis MV=33.2-18.0 log W0, and the determinationseems free of systematic effects. The root mean square error of thefitting is 0.6 mag. This error is mostly accounted for by measurementerrors and intrinsic variability of W0, but in addition apossible dependence on the metallicity is found, which becomes clearlynoticeable for metallicities below [Fe/H] ~ -0.4. This detection ispossible because in our sample [Fe/H] ranges from -1.5 to 0.4.The Wilson-Bappu effect can be used confidently for all metallicitiesnot lower than ~ -0.4, including the LMC. While it does not provideaccurate distances to single stars, it is a useful tool to determineaccurate distances to clusters and aggregates, where a sufficient numberof stars can be observed.We apply the Wilson-Bappu effect to published data of the open cluster M67; the retrieved distance modulus is of 9.65 mag, in very goodagreement with the best distance estimations for this cluster, based onmain sequence fitting.Observations collected at ESO, La Silla. An updated review on microlensing experiments.Not Available Microlensing Maps for the Milky Way GalaxyAt any instant, there are ~1000 microlensing events to sources brighterthan 20 mag in the Milky Way. Large-scale maps of the microlensingoptical depth and the mean timescale are constructed for a number ofmodels of the Galactic bar and disk, incorporating the effects ofstreaming and spiral structure. Freudenreich's model can reproduce thehigh optical depths toward the bulge. It is also in good agreement withthe data toward the spiral arms (except for the field γ Norma).Spiral structure tends to increase the optical depth by <~20% and themean timescale by <~100%. Different bar morphologies givecharacteristically different shaped contours, especially at low Galacticlatitudes (|b|<2deg). These could be traced out with aK-band microlensing survey, consuming ~100 minutes per night on atelescope such as the Visible and Infrared Survey Telescope forAstronomy. CHARM: A Catalog of High Angular Resolution MeasurementsThe Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is 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/386/492, and from theauthors on CD-Rom. A Large Spectral Class Dependence of the Wilson-Bappu Effect among Luminous StarsThe striking correlation between Ca II K-line emission width andabsolute visual magnitude has not previously been well calibrated forstars more luminous than giants. From a sample of binary systems fit toisochrones, we find deviations of more than 2 mag, correlated withspectral class, between these binarity Mv values and theWilson-Bappu relation. Additional Mv values derived fromHipparcos parallaxes are used to explore the systematics. The spectralclass dependence vanishes for K-line parameterlogW0<=1.80. Linear spectral class corrections are derivedfor the more luminous stars, with logW0>=2.00, while atable is provided for the transition region. The dispersion from theserelations is about +/-0.6 mag. This recalibration extends thedemonstrated applicability of the Wilson-Bappu technique toMv~=-5 or distance ~20 kpc. Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statisticsThe Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521 The proper motions of fundamental stars. I. 1535 stars from the Basic FK5A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222 Near-Infrared Classification Spectroscopy: J-Band Spectra of Fundamental MK StandardsWe present a catalog of J-band spectra for 88 fundamental MK standardstars observed at a resolving power of R~3000. This contribution servesas a companion atlas to the K-band spectra recently published by Wallace& Hinkle and the H-band atlas by Meyer and coworkers. We report datafrom 7400 to 9550 cm-1 (1.05-1.34 μm) for stars ofspectral types O7-M6 and luminosity classes I-V as defined in the MKsystem. In reducing these data, special care has been taken to removetime-variable telluric features of water vapor. We identify atomic andmolecular indexes that are both temperature and luminosity sensitivethat aid in the classification of stellar spectra in the J band. Inaddition to being useful in the classification of late-type stars, the Jband contains several features of interest in the study of early-typestellar photospheres. These data are available electronically foranonymous FTP in addition to being served on the World Wide Web. Ca II activity and rotation in F-K evolved starsCa II H and K high resolution observations for 60 evolved stars in thefield and in 5 open clusters are presented. From these spectrachromospheric fluxes are derived, and a homogeneous sample of more than100 giants is built adding data from the literature. In addition, formost stars, rotational velocities were derived from CORAVELobservations. By comparing chromospheric emission in the cluster starswe confirm the results of Pasquini & Brocato (1992): chromosphericactivity depends on the stellar effective temperature, and mass, whenintermediate mass stars (M ~ 4 Msun) are considered. TheHyades and the Praesepe clump giants show the same level of activity, asexpected from stars with similar masses and effective temperatures. Adifference of up to 0.4 dex in the chromospheric fluxes among the Hyadesgiants is recorded and this sets a clear limit to the intrinsic spreadof stellar activity in evolved giants. These differences in otherwisevery similar stars are likely due to stellar cycles and/or differencesin the stellar initial angular momentum. Among the field stars none ofthe giants with (V-R)o < 0.4 and Ia supergiants observedshows a signature of Ca II activity; this can be due either to the realabsence of a chromosphere, but also to other causes which preclude theappearance of Ca II reversal. By analyzing the whole sample we find thatchromospheric activity scales linearly with stellar rotational velocityand a high power of stellar effective temperature: F'k ~Teff7.7 (Vsini)0.9. This result can beinterpreted as the effect of two chromospheric components of differentnature: one mechanical and one magnetic. Alternatively, by using theHipparcos parallaxes and evolutionary tracks, we divide the sampleaccording to the stellar masses, and we follow the objects along anevolutionary track. For each range of masses activity can simply beexpressed as a function of only one parameter: either theTeff or the angular rotation Omega , with laws F'k~ Omega alpha , because angular velocity decreases witheffective temperature along an evolutionary track. By using theevolutionary tracks and the observed Vsini we investigate the evolutionof the angular momentum for evolved stars in the range 1-5Msun. For the 1.6-3 solar mass stars the data are consistentwith the IOmega =const law while lower and higher masses follow a lawsimilar to IOmega 2=const, where I is the computed stellarmomentum of inertia. We find it intriguing that Vsini remains almostconstant for 1Msun stars along their evolution; if a similarbehavior is shared by Pop II stars, this could explain the relativelyhigh degree of activity observed in Pop II giants. Finally, through theuse of models, we have verified the consistency of the F'k ~Omega alpha and the IOmega beta = Const lawsderived, finding an excellent agreement. This representation, albeitcrude (the models do not consider, for instance, mass losses) representsthe evolution of Ca II activity and of the angular momentum in asatisfactory way in most of the portion of HR diagram analyzed.Different predictions could be tested with observations in selectedclusters. Based on observations collected at ESO, La Silla. Tables 1-3are only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html Observation of microlensing towards the galactic spiral arms. EROS II. 2 year surveyWe present the analysis of the light curves of 8.5 million starsobserved during two seasons by EROS (Expérience de Recherched'Objets Sombres), in the Galactic plane away from the bulge. Threestars have been found that exhibit luminosity variations compatible withgravitational microlensing effects due to unseen objects. Thecorresponding optical depth, averaged over four directions, is bar tau =0.38+0.53_-0.15 x 10-6. All three candidates havelong Einstein radius crossing times ( ~ 70 to 100 days). For one ofthem, the lack of evidence for a parallax or a source size effectenabled us to constrain the lens-source configuration. Another candidatedisplays a modulation of the magnification, which is compatible with thelensing of a binary source. The interpretation of the optical depthsinferred from these observations is hindered by the imperfect knowledgeof the distance to the target stars. Our measurements are compatiblewith expectations from simple galactic models under reasonableassumptions on the target distances. This work is based on observationsmade at the European Southern Observatory, La Silla, Chile. The CaII-M_v Correlation (Wilson-Bappu Effect) Calibrated by HIPPARCOS ParallaxesWe have used Hipparcos parallaxes to derive absolute visual magnitudesof G, K, and M stars with Ca II emission line widths previously measuredby O. C. Wilson. A linear relationship similar to the one derivedoriginally by Wilson & Bappu and improved by Lutz & Kelker wasfound from M_v=+7 to -2. For stars brighter than M_v=-2 a substantialnumber of stars show Ca II emission lines that are broader than expectedfrom the linear fit. Most of those stars are bright giants andsupergiants of type G. In appendices we show some sample Ca II profilesand identify emission lines of Fe II as well as the Hepsilon line insome stars. Determination of the characteristics of stars of spectral types F,G,K. The effective temperatures.Not Available Speckle Interferometry of New and Problem HIPPARCOS BinariesThe ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged G,''O,'' V,'' or X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as suspected nonsingle'' (flag S'' in field H61), thusyielding a total of 11,687 problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras. A catalog of rotational and radial velocities for evolved starsRotational and radial velocities have been measured for about 2000evolved stars of luminosity classes IV, III, II and Ib covering thespectral region F, G and K. The survey was carried out with the CORAVELspectrometer. The precision for the radial velocities is better than0.30 km s-1, whereas for the rotational velocity measurementsthe uncertainties are typically 1.0 km s-1 for subgiants andgiants and 2.0 km s-1 for class II giants and Ib supergiants.These data will add constraints to studies of the rotational behaviourof evolved stars as well as solid informations concerning the presenceof external rotational brakes, tidal interactions in evolved binarysystems and on the link between rotation, chemical abundance and stellaractivity. In this paper we present the rotational velocity v sin i andthe mean radial velocity for the stars of luminosity classes IV, III andII. Based on observations collected at the Haute--Provence Observatory,Saint--Michel, France and at the European Southern Observatory, LaSilla, Chile. Table \ref{tab5} also available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html Catalogs of temperatures and [Fe/H] averages for evolved G and K starsA catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html Spectral classifications in the near infrared of stars with composite spectra. III. Study of a sample of 137 objects with the Aurelie spectrographWe provide spectral classifications for a sample of 137 stars mentionedas having composite spectra. The classifications were carried out on 33Angstroms /mm spectra in the region 8370 - 8870 Angstroms. Of these 137objects, 115 correspond in the infrared to cool stars (G, K or M) ofluminosity classes III, II and I; for 22 stars, we find only hot spectraof types B, A, F or Am, so that they do not fulfil our definition ofcomposite spectra. We detect four new Am stars, and one Am star (HD70826) turns out to be a composite spectrum object. As in Paper II, thecool components of composite spectra show a strong concentration in thevicinity of G8III. Based upon observations carried out at Observatoirede Haute-Provence (OHP). Lithium abundance and massObservations of cool giants have shown that there exists a large rangein their lithium abundances even for apparently similar stars. Thedepletions are large in a majority of them, far in excess of thepredictions of the standard stellar evolution models. In order toexplore whether the large spread in Li abundances observed in giants canbe interpreted in terms of mass, moderately high resolution CCD spectraof the Li I line at 6707.8 Ä have been obtained in 65 subgiants,giants and supergiants and the lithium abundances derived. Theirabsolute magnitudes have been estimated from the Hipparcos data.Absolute magnitudes have also been determined for another 802 starswhose lithium abundances are already known from the availableliterature. All these stars have been plotted on the HR diagram andcompared with the theoretical evolutionary tracks of Bressan et al.(1993) with initial masses ranging from 1 M_sun to 9 M_sun for achemical composition typical of the solar neighbourhood: X=0.70, Y=0.28,Z=0.02. The stars of low mass of this sample, (<2M_sun), span a widerange in evolution (unmixed warm subgiants and mixed giants) andtherefore, show a correspondingly wide range of Li abundances, perhapsreminiscent of the large range in abundances observed on the mainsequence. The spread is further augmented by the effects of increasingdilution and mixing as the stars evolve to the right and up the redgiant branch. Higher mass stars show a different behaviour. Many of thegiants of masses between 2.5 and 4.0 M_sun observed in the present studyhave Li abundances close to what is predicted by the standard stellarmodels. On the other hand, there are several high mass giants (>2.5M_sun) cooler than Teff = 5000 K with Li abundances as low asthose of low mass stars of similar effective temperature. There must beparameters other than mass and evolutionary status, as implied by thestandard evolution model of a star, that control its Li abundance. Microlensing towards different Galactic targetsWe calculate the optical depth and the number of events due togravitational microlensing towards the Galactic bulge, the spiral armdirections gamma Scutum, beta Scutum, gamma Normae, vartheta Muscae andsome dwarf galaxies in the halo of the Galaxy. Using the events found bythe MACHO collaboration during their first year of observation towardsBaade's Window we estimate the mass functions for the bulge and diskpopulations following the mass moment method. We find that the massfunction can be described by a decreasing power-law with slope alpha =~2.0 in both cases and a minimal mass of ~ 0.01 Msun for thebulge and ~ 0.02 Msun for the disk, respectively. Assumingthat the obtained mass function for the disk is also valid in the spiralarms, we find that the expected number of events towards the spiral armsis in reasonable agreement with the observations. However, the smallnumber of observed events does not yet constrain much the differentparameters entering in the computation of the mass function. To studythe influence of the Magellanic Clouds on the shape and the velocitydispersion in the halo we perform a N-body simulation. We find thattheir presence induces a slight flattening of the halo (qH =~0.8). As a result the expected number of microlensing events towardssome targets in the halo, such as the LMC or the SMC, decreases by about20%, whereas due to the modification induced on the velocity dispersionthe event duration increases. Ultraviolet and Optical Studies of Binaries with Luminous Cool Primaries and Hot Companions. V. The Entire IUE SampleWe have obtained or retrieved IUE spectra for over 100 middle- andlate-type giant and supergiant stars whose spectra indicate the presenceof a hot component earlier than type F2. The hot companions areclassified accurately by temperature class from their far-UV spectra.The interstellar extinction of each system and the relative luminositiesof the components are derived from analysis of the UV and opticalfluxes, using a grid of UV intrinsic colors for hot dwarfs. We find thatthere is fair agreement in general between current UV spectralclassification and ground-based hot component types, in spite of thedifficulties of assigning the latter. There are a few cases in which thecool component optical classifications disagree considerably with thetemperature classes inferred from our analysis of UV and opticalphotometry. The extinction parameter agrees moderately well with otherdeterminations of B-V color excess. Many systems are worthy of furtherstudy especially to establish their spectroscopic orbits. Further workis planned to estimate luminosities of the cool components from the dataherein; in many cases, these luminosities' accuracies should becomparable to or exceed those of the Hipparcos parallaxes. Near-Infrared Classification Spectroscopy: H-Band Spectra of Fundamental MK StandardsWe present a catalog of H-band spectra for 85 stars of approximatelysolar abundance observed at a resolving power of 3000 with the KPNOMayall 4 m Fourier Transform Spectrometer. The atlas covers spectraltypes O7-M5 and luminosity classes I-V as defined in the MK system. Weidentify both atomic and molecular indices and line ratios that aretemperature and luminosity sensitive, allowing spectral classificationto be carried out in the H-band. The line ratios permit spectralclassification in the presence of continuum excess emission, which iscommonly found in pre-main-sequence or evolved stars. We demonstratethat with spectra of R = 1000 obtained at signal-to-noise ratio >50,it is possible to derive spectral types within +/-2 subclasses forlate-type stars. These data are available electronically through theAstronomical Data Center in addition to being served on the World WideWeb. Classification of Population II Stars in the Vilnius Photometric System. II. ResultsThe results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified. Classification and Identification of IRAS Sources with Low-Resolution SpectraIRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
Добавить новую статью

### Внешние ссылки

• - Внешних ссылок не найдено -
Добавить внешнюю ссылку

### Группы:

#### Наблюдательные данные и астрометрия

 Созвездие: Щит Прямое восхождение: 18h47m10.50s Склонение: -04Â°44'52.0" Видимая звёздная величина: 4.22 Расстояние: 211.416 парсек Собственное движение RA: -7 Собственное движение Dec: -16.9 B-T magnitude: 5.579 V-T magnitude: 4.337

Каталоги и обозначения:
 Собственные имена (Edit) Bayer β Sct HD 1989 HD 173764 TYCHO-2 2000 TYC 5122-1426-1 USNO-A2.0 USNO-A2 0825-12988247 BSC 1991 HR 7063 HIP HIP 92175 → Запросить дополнительные каталоги и обозначения от VizieR