Contents
Images
Upload your image
DSS Images Other Images
Related articles
Lithium abundances and rotational behavior for bright giant stars
Aims.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 Stars
The 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.
| Predicting accurate stellar angular diameters by the near-infrared surface brightness technique
I report on the capabilities of the near-infrared (near-IR) surfacebrightness technique to predict reliable stellar angular diameters asaccurate as <~2 per cent using standard broad-band Johnson photometryin the colour range -0.1 <= (V-K)O<= 3.7 includingstars of A, F, G, K spectral type. This empirical approach is fast toapply and leads to estimated photometric diameters in very goodagreement with recent high-precision interferometric diametermeasurements available for non-variable dwarfs and giants, as well asfor Cepheid variables. Then I compare semi-empirical diameters predictedby model-dependent photometric and spectrophotometric (SP) methods withnear-IR surface brightness diameters adopted as empirical referencecalibrators. The overall agreement between all these methods is withinapproximately +/-5 per cent, confirming previous works. However, on thesame scale of accuracy, there is also evidence for systematic shiftspresumably as a result of an incorrect representation of the stellareffective temperature in the model-dependent results. I also comparemeasurements of spectroscopic radii with near-IR surface brightnessradii of Cepheids with known distances. Spectroscopic radii are found tobe affected by a scatter as significant as >~9 per cent, which is atleast three times greater than the formal error currently claimed by thespectroscopic technique. In contrast, pulsation radii predicted by theperiod-radius (PR) relation according to the Cepheid period result aresignificantly less dispersed, indicating a quite small scatter as aresult of the finite width of the Cepheid instability strip, as expectedfrom pulsation theory. The resulting low level of noise stronglyconfirms our previous claims that the pulsation parallaxes are the mostaccurate empirical distances presently available for Galactic andextragalactic Cepheids.
| 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.
| 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
| Improved Baade-Wesselink surface brightness relations
Recent, and older accurate, data on (limb-darkened) angular diameters iscompiled for 221 stars, as well as BVRIJK[12][25] magnitudes for thoseobjects, when available. Nine stars (all M-giants or supergiants)showing excess in the [12-25] colour are excluded from the analysis asthis may indicate the presence of dust influencing the optical andnear-infrared colours as well. Based on this large sample,Baade-Wesselink surface brightness (SB) relations are presented fordwarfs, giants, supergiants and dwarfs in the optical and near-infrared.M-giants are found to follow different SB relations from non-M-giants,in particular in V versus V-R. The preferred relation for non-M-giantsis compared to the earlier relation by Fouqué and Gieren (basedon 10 stars) and Nordgren et al. (based on 57 stars). Increasing thesample size does not lead to a lower rms value. It is shown that theresiduals do not correlate with metallicity at a significant level. Thefinally adopted observed angular diameters are compared to thosepredicted by Cohen et al. for 45 stars in common, and there isreasonable overall, and good agreement when θ < 6 mas.Finally, I comment on the common practice in the literature to average,and then fix, the zero-point of the V versus V-K, V versus V-R and Kversus J-K relations, and then rederive the slopes. Such a commonzero-point at zero colour is not expected from model atmospheres for theV-R colour and depends on gravity. Relations derived in this way may bebiased.
| A Spectral Atlas of F and G Stars
We present an atlas of a group of bright stars in the range of spectralclasses F--G and luminosity classes I--V. The spectra were obtainedwith spectral resolution R 15,000 within spectral region4500--6620 Å. Typical spectra of stars with different metallicity[Fe/H] are included. We also show the digital version of the spectraldata in FITS format.
| Dynamical Mass Estimates for Five Young Massive Stellar Clusters
We have obtained high-dispersion spectra for four massive star clustersin the dwarf irregular galaxies NGC 4214 and NGC 4449, using the HIRESspectrograph on the Keck I telescope. Combining the velocity dispersionsof the clusters with structural parameters and photometry from imagestaken with the Hubble Space Telescope, we estimate mass-to-light (M/L)ratios and compare these with simple stellar population models in orderto constrain the stellar mass functions (MFs) of the clusters. For allclusters we find M/L values that are similar to or slightly higher thanfor a Kroupa MF and thereby rule out any MF that is deficient inlow-mass stars compared with a Kroupa-type MF. The four clusters havevirial masses ranging between 2.1×105 and1.5×106Msolar, half-light radii between 3.0and 5.2 pc, estimated core densities in the range 2×103to 2×105Msolarpc-3, and agesbetween 200 and 800 Myr. We also present new high-dispersionnear-infrared spectroscopy for a luminous young (~15 Myr) cluster in thenearby spiral galaxy NGC 6946, which we have previously observed withHIRES. The new measurements in the infrared agree well with previousestimates of the velocity dispersion for this cluster, yielding a massof about 1.7×106Msolar. Including animproved estimate of the reddening toward this cluster, the new datayield an M/L in excellent agreement with a Kroupa-type MF also for thiscluster. The properties of the clusters studied here are all consistentwith the clusters being young versions of the old globular clustersfound around all major galaxies.Based on data obtained at the W. M. Keck Observatory, which is operatedas a scientific partnership among the California Institute ofTechnology, the University of California, and the National Aeronauticsand Space Administration. Also based on observations with the HubbleSpace Telescope, obtained at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.
| High-Resolution Spectroscopy of FU Orionis Stars
High-resolution spectroscopy was obtained of the FU orionis stars FU Oriand V1057 Cyg between 1995 and 2002 with the SOFIN spectrograph at theNordic Optical Telescope and with HIRES at Keck I. During these years FUOri remained about 1 mag (in B) below its 1938-39 maximum brightness,but V1057 Cyg (B~10.5 at peak in 1970-1971) faded from about 13.5 to14.9 and then recovered slightly. Their photospheric spectra resemblethat of a rotationally broadened, slightly veiled supergiant of abouttype G0 Ib, with veqsini=70 km s-1 for FU Ori, and55 km s-1 for V1057 Cyg. As V1057 Cyg faded, P Cyg structurein Hα and the IR Ca II lines strengthened and a complexshortward-displaced shell spectrum of low-excitation lines of theneutral metals (including Li I and Rb I) increased in strength,disappeared in 1999, and reappeared in 2001. Several SOFIN runs extendedover a number of successive nights so that a search for rapid and cyclicchanges in the spectra was possible. These spectra show rapidnight-to-night changes in the wind structure of FU Ori at Hα,including clear evidence of sporadic infall. The equivalent width of theP Cyg absorption varied cyclically with a period of 14.8 days, withphase stability maintained over three seasons. This is believed to bethe rotation period of FU Ori. The internal structure of itsphotospheric lines also varies cyclically, but with a period of 3.54days. A similar variation may be present in V1057 Cyg, but the data aremuch noisier and that result uncertain. As V1057 Cyg has faded and thecontinuum level fallen, the emission lines of a preexistinglow-excitation chromosphere have emerged. Therefore we believe that the``line doubling'' in V1057 Cyg is produced by these central emissioncores in the absorption lines, not by orbital motion in an inclinedKeplerian disk. No convincing dependence of veqsini onwavelength or excitation potential was detected in either FU Ori orV1057 Cyg, again contrary to expectation for a self-luminous accretiondisk. It was found also that certain critical lines in the near infraredare not accounted for by synthetic disk spectra. It is concluded that arapidly rotating star near the edge of stability, as proposed by Larson,can better account for these observations. The possibility is alsoconsidered that FUor eruptions are not a property of ordinary T Tauristars but may be confined to a special subspecies of rapidly rotatingpre-main-sequence stars having powerful quasi-permanent winds.
| The ISO-SWS post-helium atlas of near-infrared stellar spectra
We present an atlas of near-infrared spectra (2.36 mu m-4.1 mu m) of ~300 stars at moderate resolution (lambda /delta lambda ~ 1500-2000). Thespectra were recorded using the Short-Wavelength Spectrometer aboard theInfrared Space Observatory (ISO-SWS). The bulk of the observations wereperformed during a dedicated observation campaign after the liquidhelium depletion of the ISO satellite, the so-called post-heliumprogramme. This programme was aimed at extending the MK-classificationto the near-infrared. Therefore the programme covers a large range ofspectral types and luminosity classes. The 2.36 mu m-4.05 mu m region isa valuable spectral probe for both hot and cool stars. H I lines(Bracket, Pfund and Humphreys series), He I and He II lines, atomiclines and molecular lines (CO, H2O, NH, OH, SiO, HCN,C2H2, ...) are sensitive to temperature, gravityand/or the nature of the outer layers of the stellar atmosphere(outflows, hot circumstellar discs, etc.). Another objective of theprogramme was to construct a homogeneous dataset of near-infraredstellar spectra that can be used for population synthesis studies ofgalaxies. At near-infrared wavelengths these objects emit the integratedlight of all stars in the system. In this paper we present the datasetof post-helium spectra completed with observations obtained during thenominal operations of the ISO-SWS. We discuss the calibration of the SWSdata obtained after the liquid helium boil-off and the data reduction.We also give a first qualitative overview of how the spectral featuresin this wavelength range change with spectral type. The dataset isscrutinised in two papers on the quantitative classification ofnear-infrared spectra of early-type stars ({Lenorzer} et al.\cite{lenorzer:2002a}) and late-type stars (Vandenbussche et al., inprep). Based on observations with ISO, an ESA project with instrumentsfunded by ESA Members States (especially the PI countries France,Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA. The full atlas is available inelectronic form at www.edpsciences.org Table 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?/A+A/390/1033
| Sodium enrichment of stellar atmospheres. I. Non-variable supergiants and bright giants
48 supergiants and bright giants have been observed in order toinvestigate the sodium enrichment of their atmospheres and itsconnection with stellar gravity. We present the equivalent widths of the6154 Å and 6160 Å Na I lines measured from the programspectra, the results of effective temperature determinations, the NLTEsodium abundances, and the derived relation between the sodiumoverabundance and surface gravity.
| CHARM: A Catalog of High Angular Resolution Measurements
The 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.
| Absolute spectrophotometry of late-type stars.
Not Available
| The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. II. Basic Parameters of Program Stars and the Role of Microturbulence
Paper I of this series presented precise MK spectral types for 372 lateA-, F-, and early G-type stars with the aim of understanding the natureof luminosity classification on the MK spectral classification systemfor this range of spectral types. In this paper, a multidimensionaldownhill simplex technique is introduced to determine the basicparameters of the program stars from fits of synthetic spectra andfluxes with observed spectra and fluxes from Strömgren uvbyphotometry. This exercise yields useful calibrations of the MK spectralclassification system but, most importantly, gives insight into thephysical nature of luminosity classification on the MK spectralclassification system. In particular, we find that in this range ofspectral types, microturbulence appears to be at least as important asgravity in determining the MK luminosity type.
| The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. I. Precise Spectral Types for 372 Stars
This is the first in a series of two papers that address the problem ofthe physical nature of luminosity classification in the late A-, F-, andearly G-type stars. In this paper, we present precise spectralclassifications of 372 stars on the MK system. For those stars in theset with Strömgren uvbyβ photometry, we derive reddenings andpresent a calibration of MK temperature types in terms of the intrinsicStrömgren (b-y)0 index. We also examine the relationshipbetween the luminosity class and the Strömgren c1 index,which measures the Balmer jump. The second paper will address thederivation of the physical parameters of these stars, and therelationships between these physical parameters and the luminosityclass. Stars classified in this paper include one new λ Bootisstar and 10 of the F- and G-type dwarfs with recently discoveredplanets.
| Non-axisymmetric accretion on the classical TTS RW Aur A
High-resolution spectroscopic monitoring of the exceptionally activeclassical T Tauri star (CTTS) RW Aur A was carried out in three seasonsof 1996, 1998 and 1999 with simultaneous B, V photometry. The highquality spectra revealed a multicomponent structure of the spectrum,which includes: 1) a veiled photospheric spectrum of a K1-K4 star, 2)broad emission lines of neutrals and ions, 3) narrow emission lines ofHe I and He Ii, 4) red-shifted accretion features of many lines, 5)shell lines at about the stellar velocity, 6) blue-shifted wind featuresand 7) forbidden lines. Periodic modulations in many spectral featureswere found. The photospheric absorption lines show sinusoidal variationsin radial velocity with an amplitude of +/-6 km s-1 and aperiod of about 2fd77 . The radial velocities of the narrow emissionlines of He vary with the same period but in anti-phase to thephotospheric lines. The equivalent widths of the narrow emissions varywith a phase-shift with respect to the velocity curve. The strength ofthe red-shifted accretion components of Na D and other lines is alsomodulated with the same period. The broad emission lines of metals varymostly with the double period of about 5fd5 . One unexpected result isthat no correlation was found between the veiling and the brightness,although both parameters varied in wide ranges. This is partly due to acontribution of the shell absorption to the photospheric line profiles,which make them vary in width and depth thus simulating lower veiling.The spectral lines of the accreting gas show two distinct components:one is formed at low velocity at the beginning of the accretion column,and the other at high velocity near the stellar surface. The lowvelocity components are strong in low excitation lines of neutrals,while the high velocity components are strong in high excitation linesof ions, thus showing the gradients of temperature and density along theaccretion column. Most of the observed features can be interpreted inthe framework of non-axisymmetric magnetospheric accretion, but theorigin of this asymmetry can be explained in different ways. We considertwo possible models. The first model suggests that RW Aur A is a binarywith a brown dwarf secondary in a nearly circular orbit with a period of2fd77 . The orbiting secondary generates a moving stream of enhancedaccretion from one side of the disk towards the primary. The other modelassumes that RW Aur A is a single star with a rotational period of 5fd5and with two footpoints of channeled accretion streams within a globalmagnetosphere which is tilted relative to the rotational axis orotherwise non-axisymmetric. Both models can explain qualitatively andquantitatively most of the observed variations, but there are somedetails which are less well accounted for. Based on observations madewith the Nordic Optical Telescope, operated on the island of La Palmajointly by Denmark, Finland, Iceland, Norway, and Sweden, in the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/367/297
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A 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
| On the Variability of A6 to F9 Supergiants
Hipparcos Satellite photometry of A6 to F9 supergiants reveals theiractivity. A few are especially quiescient. A0-A5II stars are examinedto help connect this study with that of earlier supergiants.
| Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over more than twocenturies and summarized in the FK5. Part I of the FK6 (abbreviatedFK6(I)) contains 878 basic fundamental stars with direct solutions. Suchdirect solutions are appropriate for single stars or for objects whichcan be treated like single stars. From the 878 stars in Part I, we haveselected 340 objects as "astrometrically excellent stars", since theirinstantaneous proper motions and mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,199 of the stars in Part I are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives in addition to the SI mode the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(I) proper motion in the single-star mode is 0.35 mas/year. This isabout a factor of two better than the typical HIPPARCOS errors for thesestars of 0.67 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(I) proper motions have atypical mean error of 0.50 mas/year, which is by a factor of more than 4better than the corresponding error for the HIPPARCOS values of 2.21mas/year (cosmic errors included).
| Excitation and visibility of high-degree modes in stars
Observational evidence for excitation of non-radial modes in stars isconfronted with the results of linear stability surveys for stellarmodels. We consider various types of pulsators on the upper mainsequence as well as stars in the Cepheid strip. Our stability surveycovers the whole range of spherical harmonic degrees, l, whereinstability is found. There is fair agreement between the theoreticalinstability strip and the location of ζ Oph stars, but the observedand calculated periods do not agree in some stars. We suggest thateither pulsation is not responsible for the ζ Oph phenomenon orelse there are serious errors in mode identification in these cases. Wedo not find instability at long periods for early B-type stars,supporting the idea that pulsation is not responsible for the periodicvariations in Be stars. The agreement between the observed andcalculated periods of high-degree modes in δ Sct stars is not verysatisfactory. This is attributed to problems in mode identification. Wediscuss unstable modes of high degree in Cepheid models as a possiblemechanism for the low-amplitude radial velocities seen in some starswithin the instability strip. We find, however, that the observedperiods are at least a factor of 2 longer than the calculated periods.Finally, we discuss the possibility of observing modes of high degreephotometrically. We suggest that a large number of high-degree modes maybecome detectable by future space-borne photometric missions. Theconfusion arising from these modes may greatly reduce the value of suchobservations for asteroseismology. However, they will be very importantin studying the mechanism of mode selection.
| Radii and Effective Temperatures for G, K, and M Giants and Supergiants
Interferometrically determined angular diameters obtained at the PalomarTestbed Interferometer (PTI) for 69 giant and supergiant stars arepresented. Spectral types of the 59 giant stars generally lie between G6and M6, although a B7 giant is included; the nine bright giants andsupergiants have spectral types between F5 and M5. Comparison of theresults to those from the IR Optical Telescope Array interferometerindicate no statistically significant difference between the two datasets. The use of Hipparcos parallaxes allows us to measure linear sizesdirectly for these stars, which range in size from 10 to 260 solarradii. In conjunction with previous results as reported by Dyck et al.,the total of 113 giant stars provides empirically determineddependencies of effective temperature and linear radius upon spectraltype and V-K color.
| A catalog of rotational and radial velocities for evolved stars
Rotational 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
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| A Precision Velocity Study of Photometrically Stable Stars in the Cepheid Instability Strip
Results of a precision Doppler velocity survey of 15 stars that lie inor near the Cepheid instability strip are presented. Previous studieshave shown that these stars are photometrically stable. Long-term radialvelocity precision of 15 m s-1 has been achieved with the use of aniodine absorption cell and a high-resolution cross-dispersed echellespectrometer. The stars show a variety of behavior from stability (atthe level of 30 m s-1) to variability from 50 m s-1 to a few km s-1.Periodograms of many of the program stars show significant peaks at50-80 days that are not associated with radial pulsation. Previouslyundetected binary companions have been found around two of the stars.Line profiles are compared to delta Cep.
| Increase of emission and shell features in the spectrum of the FUor V1057 CYG
High-resolution echelle spectra of the FUor V1057 Cyg were taken duringits minimum brightness in 1996-97. The spectra show the appearance ofstrong shell-components in the lines of low excitation, an increase ofthe splitting of the photospheric absorption lines, and the appearanceof weak emission lines. It is argued that the mysterious line splittingof the absorption lines in the spectrum of V1057 Cyg, which has beeninterpreted as originating from an accretion disk, can be explainedsimply by the presence of central emission cores in the broad absorptionlines. This emission spectrum of V1057 Cyg has increased in strengthrelative to the continuum as the star has faded. Based on observationsobtained at the 2.56m Nordic Optical Telescope, Roque de Los MuchachosObservatory, La Palma/Spain.
| Systematic Errors in the FK5 Catalog as Derived from CCD Observations in the Extragalactic Reference Frame.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..850S&db_key=AST
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| On the Determination of Empirical Stellar Flux Scales
Several studies have appeared in the literature describing methods forderiving stellar continuum fluxes as simple functions of Johnson colorindices. In previous papers, we have used similar relations to derive CaII H and K line core fluxes for dwarf stars on Lowell Observatory'sSolar-Stellar Spectrograph (SSS) program. Our desire is to present ourdata, and complementary data from the Mt. Wilson and National SolarObservatory stellar and solar programs, in terms of physical fluxes.However, our existing relations break down for mid-K and later stars andfor giant stars, which form an important element of our target list. Inthis work I have used a broader range of spectrophotometry and angulardiamters than in our previous work to derive empirical flux scales forspectral types A to early M, luminosity classes I to V, and for fourcolor indices, Johnson B-V, V-R, R-I, and Stromgren b-y. In this paper,I describe the methods I used and present the desired flux scales. Icompare the results with those from earlier studies and present examplesof the use of the flux scales. The data and results are available on theWorld Wide Web. (SECTION: Stars)
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | はくちょう座 |
| Right ascension: | 20h29m23.70s |
| Declination: | +30°22'07.0" |
| Apparent magnitude: | 4.01 |
| Distance: | 232.558 parsecs |
| Proper motion RA: | 5.7 |
| Proper motion Dec: | -1.1 |
| B-T magnitude: | 4.484 |
| V-T magnitude: | 4.044 |
Catalogs and designations:
|
