Contents
Images
Upload your image
DSS Images Other Images
Related articles
Cepheid Masses: FUSE Observations of S Muscae
S Mus is the Cepheid with the hottest known companion. The largeultraviolet flux means that it is the only Cepheid companion for whichthe velocity amplitude could be measured with the echelle mode of theHST GHRS. Unfortunately, the high temperature is difficult to constrainat wavelengths longer than 1200 Å because of the degeneracybetween temperature and reddening. We have obtained a FUSE spectrum inorder to improve the determination of the temperature of the companion.Two regions that are temperature sensitive near 16,000 K but relativelyunaffected by H2 absorption (940 Å and the Lyβwings) have been identified. By comparing FUSE spectra of S Mus B withspectra of standard stars, we have determined a temperature of17,000+/-500 K. The resulting Cepheid mass is 6.0+/-0.4Msolar. This mass is consistent with main-sequenceevolutionary tracks with a moderate amount of convective overshoot.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer satellite. FUSE is operated for NASA by JohnsHopkins University, under NASA contract NAS5-32985.
| A spectroscopic study of bright southern Cepheids - a high-resolution view of Cepheid atmospheres
We present high-resolution spectroscopic observations andspecies-by-species radial velocities of a number of southern Cepheids.The stars (BP Cir, V350 Sgr, AX Cir, V636 Sco, W Sgr, S Mus, β Dor,TT Aql, Y Oph, YZ Car, SW Vel, X Pup, T Mon and l Car) were observed aspart of a long-term programme at Mt John University Observatory. Radialvelocities were determined with the line bisector technique, and have aprecision of ~300 ms-1. Velocity differences as large as 30kms-1 were found for Hα and CaII when referenced to themetallic line velocity curves, but more subtle variations (of 1-2kms-1) were also detected in many other species. Pulsationalphase anticorrelations are found between lines of SiII and BaII,confirming the propagation time delay between line-forming layersproducing these two species. We find that the amplitude and phasedifferences between the various species increase with period.
| High-Mass Triple Systems: The Classical Cepheid Y Carinae
We have obtained a Hubble Space Telescope STIS ultraviolethigh-dispersion echelle-mode spectrum of the binary companion of thedouble-mode classical Cepheid Y Car. The velocity measured for the hotcompanion from this spectrum is very different from reasonablepredictions for binary motion, implying that the companion is itself ashort-period binary. The measured velocity changed by 7 kms-1 during the 4 days between two segments of theobservation, confirming this interpretation. We summarize ``binary''Cepheids that are in fact members of a triple system and find that atleast 44% are triples. The summary of information on Cepheids withorbits makes it likely that the fraction is underestimated.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc.
| Mean Angular Diameters and Angular Diameter Amplitudes of Bright Cepheids
We predict mean angular diameters and amplitudes of angular diametervariations for all monoperiodic PopulationI Cepheids brighter than=8.0 mag. The catalog is intended to aid selecting mostpromising Cepheid targets for future interferometric 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.
| 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
| The orbits of southern binary Cepheids
High-resolution spectroscopic observations have been made of a number ofsouthern Cepheids. The stars studied were part of a long-term programmeto observe southern variable stars and to complete a data base of radialvelocities over a long time interval. The radial velocities have aprecision of ~300 m s-1, allowing the detection of velocitydifferences of ~1 km s-1 with confidence. Our new dataprovide a consistent set of data against which other sources of data canbe compared.Masses were determined for two systems, the 9-d Cepheid S Mus (6.2 +/-0.2 Msolar) and the 5-d Cepheid V350 Sgr (6.0 +/- 0.9Msolar). For another seven Cepheids (Y Car, YZ Car, AX Cir,BP Cir, V636 Sco, W Sgr and T Mon), new or improved orbital solutionswere found.New results presented here include the first orbital solution for AXCir, a completely revised orbital solution for YZ Car, which establishedits eccentricity and orbital motion, and a new pulsation period (2.39819 d) for BP Cir. The pulsational mass determinations provide furtherconfirmation of the convergence of mass determinations between dynamicaland evolutionary methods.
| J - K DENIS photometry of a VLTI-selected sample of bright southern stars
We present a photometric survey of bright southern stars carried outusing the DENIS instrument equipped with attenuating filters. Theobservations were carried out not using the survey mode of DENIS, butwith individual target pointings. This project was stimulated by theneed to obtain near-infrared photometry of stars to be used in earlycommissioning observations of the ESO Very Large TelescopeInterferometer, and in particular to establish a network of brightcalibrator sources.We stress that near-infrared photometry is peculiarly lacking for manybright stars. These stars are saturated in 2MASS as well as in regularDENIS observations. The only other observations available for brightinfrared stars are those of the Two Micron Sky Survey dating from overthirty years ago. These were restricted to declinations above≈-30°, and thus cover only about half of the sky accessible fromthe VLTI site.We note that the final 2MASS data release includes photometry of brightstars, obtained by means of point-spread function fitting. However, thismethod only achieves about 30% accuracy, which is not sufficient formost applications.In this work, we present photometry for over 600 stars, each with atleast one and up to eight measurements, in the J and K filters. Typicalaccuracy is at the level of 0\fm05 and 0\fm04 in the J and K_s bands,respectively.Based on observations collected at the European Southern Observatory, LaSilla.Tables 1 and 2 are 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/413/1037
| New Period-Luminosity and Period-Color relations of classical Cepheids: I. Cepheids in the Galaxy
321 Galactic fundamental-mode Cepheids with good B, V, and (in mostcases) I photometry by Berdnikov et al. (\cite{Berdnikov:etal:00}) andwith homogenized color excesses E(B-V) based on Fernie et al.(\cite{Fernie:etal:95}) are used to determine their period-color (P-C)relation in the range 0.4~ 1.4). The latter effect is enhanced by asuggestive break of the P-L relation of LMC and SMC at log P = 1.0towards still shallower values as shown in a forthcoming paper.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/423
| Fundamental Parameters of Cepheids. V. Additional Photometry and Radial Velocity Data for Southern Cepheids
I present photometric and radial velocity data for Galactic Cepheids,most of them being in the southern hemisphere. There are 1250 Genevaseven-color photometric measurements for 62 Cepheids, the averageuncertainty per measurement is better than 0.01 mag. A total of 832velocity measurements have been obtained with the CORAVEL radialvelocity spectrograph for 46 Cepheids. The average accuracy of theradial velocity data is 0.38 km s-1. There are 33 stars withboth photometry and radial velocity data. I discuss the possiblebinarity or period change that these new data reveal. I also presentreddenings for all Cepheids with photometry. The data are availableelectronically. Based on observations obtained at the European SouthernObservatory, La Silla.
| Envelope Ejection: An Alternative Evolutionary Process for Some Early Case B Binaries
We discuss the evolution of binaries with moderately high masses (~10-30Msolar) and with periods of ~3-300 days, corresponding mostlyto early case B. These are usually thought to evolve either byreasonably conservative Roche lobe overflow, if the initial mass ratiois fairly mild, or else by highly nonconservative common-envelopeevolution, with spiral-in to short periods (hours, typically), if theinitial mass ratio is rather extreme. We discuss here a handful ofbinaries from part of this period range (~50-250 days), which appear tohave followed a different path: we argue that they must have lost alarge proportion of initial mass (~70%-80%) but without shortening theirperiods at all. We suggest that their behavior may be due to the factthat stars of such masses, when evolved also to rather large radii, arenot far from the Humphreys-Davidson limit, where single stars lose theirenvelopes spontaneously in P Cygni winds, and so have envelopes that areonly lightly bound to the core. These envelopes therefore may berelatively easily dissipated by the perturbing effect of a companion. Inaddition, some or all of the stars considered here may have been closeto the Cepheid instability strip when they filled their Roche lobes. Oneor the other, or both, of high luminosity and Cepheid instability, incombination with an appropriately close binary companion, may beimplicated.
| 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.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Photoelectric Observations of Southern Cepheids in 2001
A total of 2097 photometric observations in the BVIc systemare presented for 117 Cepheids located in the southern hemisphere. Themain purpose of the photometry is to provide new epochs of maximumbrightness for studying Cepheid period changes, as well as to establishcurrent light elements for the Cepheids.
| 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
| A photometric and spectroscopic study of the brightest northern Cepheids - III. A high-resolution view of Cepheid atmospheres
We present new high-resolution spectroscopic observations(λ/Δλ~40000) of 18 bright northern Cepheids carriedout at the David Dunlap Observatory in 1997. The measurements mainlyextend those presented in Paper I of this series, adding three morestars (AW Per, SV Vul, T Mon). The spectra were obtained in theyellow-red spectral region in the interval of 5900 and 6660Å,including strong lines of sodium D and Hα. New radial velocitiesdetermined with the cross-correlation technique and the bisectortechnique are presented. The new data are compared with those recentlypublished by several groups. We found systematic differences between thespectroscopic and CORAVEL-type measurements as large as1-3kms-1 in certain phases. We performed Baade-Wesselinkanalysis for CK Cam discovered by the Hipparcos satellite. The resultingradius is 31+/-1Rsolar, which is in very good agreement withrecent period-radius relation by Gieren, Moffett & Barnes III. It isshown that the systematic velocity differences do not affect theBaade-Wesselink radius more than 1per cent for CK Cam. Observationalpieces of evidence of possible velocity gradient affecting theindividual line profiles are studied. The full-width at half minimum(FWHM) of the metallic lines, similarly to the velocity differences,shows a very characteristic phase dependence, illustrating the effect ofglobal compression in the atmosphere. The smallest line widths alwaysoccur around the maximal radius, while the largest FWHM is associatedwith velocity reversal before the minimal radius. Three first overtonepulsators do not follow the general trend: the largest FWHM in SU Casand SZ Tau occurs after the smallest radius, during the expansion, whilein V1334 Cyg there are only barely visible FWHM variations. Thepossibility of a bright yellow companion of V1334 Cyg is brieflydiscussed. The observed line-profile asymmetries exceed the valuespredicted with a simple projection effect by a factor of 2-3. This couldbe associated with the velocity gradient, which is also supported by thedifferences between individual line velocities of different excitationpotentials.
| Astrophysical Quantities of Cepheid Variables Measured with the Navy Prototype Optical Interferometer
We present mean angular diameters for two Cepheid variables, α UMiand ζ Gem, determined with the Navy Prototype OpticalInterferometer (NPOI). We present linear radii for these Cepheids andtwo additional Cepheids, δ Cep and η Aql, previously observedat the NPOI. We find the limb-darkened angular diameters of α UMiand of ζ Gem to be 3.28+/-0.02 and 1.55+/-0.09 mas, respectively.Using trigonometric parallaxes, we find the linear radii of α UMi,ζ Gem, δ Cep, and η Aql to be 46+/-3,60+25-14, 45+8-6, and69+28-15 Rsolar, respectively. Wecompare the pulsation periods and linear radii of this sample ofCepheids, which range in period from 3 to 11 days, to theoretical andempirical period-radius and period-radius-mass relations found in theliterature. We find that the observed diameter of α UMi is inexcellent agreement with the predicted diameter as determined from bothsurface brightness techniques and theory only if α UMi is afirst-overtone pulsator.
| Galactic Cepheids. Catalogue of light-curve parameters and distances
We report a new version of the catalogue of distances and light-curveparameters for Galactic classical Cepheids. The catalogue listsamplitudes, magnitudes at maximum light, and intensity means for 455stars in BVRI filters of the Johnson system and (RI)_C filters of theCron-Cousins system. The distances are based on our new multicolour setof PL relations and on our Cepheid-based solution for interstellarextinction law parameters and are referred to an LMC distance modulus of18.25. The catalogue is only available in electronic form at the CDS viaanonymous ftp (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Direct calibration of the Cepheid period-luminosity relation
After the first release of Hipparcos data, Feast & Catchpole gave anew value for the zero-point of the visual Cepheid period-luminosityrelation, based on trigonometric parallaxes. Because of the largeuncertainties on these parallaxes, the way in which individualmeasurements are weighted is of crucial importance. We thereforeconclude that the choice of the best weighting system can be aided by aMonte Carlo simulation. On the basis of such a simulation, it is shownthat (i) a cut-off in π or in σ_ππ introduces a strongbias; (ii) the zero-point is more stable when only the brightestCepheids are used; and (iii) the Feast & Catchpole weighting givesthe best zero-point and the lowest dispersion. After correction, theadopted visual period-luminosity relation is=-2.77logP-1.44+/-0.05. Moreover, we extend this study to thephotometric I band (Cousins) and obtain=-3.05logP-1.81+/-0.09.
| Toward an Orbit for the High-Luminosity Cepheid T Monocerotis
We have obtained new velocities of the long-period Cepheid T Mon fromthe ground and velocities of its hot companion with the Hubble SpaceTelescope (HST) and the International Ultraviolet Explorer (IUE).Although observations do not cover a full orbit, both the maximum andminimum orbital velocities have now been obtained. We present apreliminary orbit and discuss the uncertainties in the orbitalparameters. The velocities for the companion appear to be inconsistentwith binary orbital motion, and it is likely that the companion isitself a binary in a short-period orbit. The HST spectrum of thecompanion shows that it is a chemically peculiar star, probablymagnetic. Because it is coupled with the more massive Cepheid, it mustbe very close to the zero-age main sequence. The well-determined massfunction from the preliminary orbit implies that the inclination of thelong-period system is close to 90 deg.
| I- and JHK-band photometry of classical Cepheids in the HIPPARCOS catalog
By correlating the \cite[Fernie et al. (1995)]{F95} electronic databaseon Cepheids with the ``resolved variable catalog'' of the hipparcosmission and the simbad catalog one finds that there are 280 Cepheids inthe hipparcos catalog. By removing W Vir stars (Type ii Cepheids),double-mode Cepheids, Cepheids with an unreliable solution in thehipparcos catalog, and stars without photometry, it turns out that thereare 248 classical Cepheids left, of which 32 are classified asfirst-overtone pulsators. For these stars the literature was searchedfor I-band and near-infrared data. Intensity-mean I-band photometry onthe Cousins system is derived for 189 stars, and intensity-mean JHK dataon the Carter system is presented for 69 stars.
| The bright southern Cepheid beta Doradus: the radial velocity curve, distance and size
A new high-accuracy velocity curve is presented for the bright southernCepheid beta Doradus (HR 1922), and an investigation into the long-termstability of the velocity curve is made. An upper limit of 0.57 kms^-1is placed on cycle-to-cycle variations. This work is compared with asimilar analysis previously applied to the long-period Cepheid l Carinae(HR 3884). Using a near-infrared variant of the Barnes-Evans method, themean radius of and distance to beta Dor are found to beR=67.8+/-0.7Rsolar and d=349+/-4pc. The systematic errors in theseparameters are less than 3 per cent. If these systematics can beresolved, through the development of advanced theoretical models and/orthe direct measurement of angular diameters, a calibration of the cosmicdistance scale to better than 1 per cent can be achieved.
| Spectroscopic survey of field Type II Cepheids
A sample of relatively bright, short- and intermediate-period (P=1-10d)Type II Cepheids in the Galactic field have been observedspectroscopically with an intermediate-resolution(lambda/Deltalambda=11000) spectrograph. The wavelength region was6500-6700A, including the Hα line and some photospheric ironlines. The signal-to-noise ratio (S/N) was usually between 50 and 100,depending on weather conditions and the brightness of target stars.Radial velocities were determined by cross-correlating the Cepheidspectra with those of selected IAU velocity standard stars having F-Gspectral types. The internal error of the velocity determination processwas calculated to be about 1 km s^-1. Hα emission and strong linesplitting were observed in BL Her during the expansion phase, but nosimilar phenomenon was detected in any other stars in this programme,except for AU Peg which has an unusual Hα line showing a PCygni-like profile. The velocity curve agrees well with recent CORAVELmeasurements. The velocity gradients in Cepheid atmospheres are studiedusing the Hα minus metallic velocities. Similar data are collectedfrom the literature. It seems that having large velocity differences(v_Hα-v_metal>40 km s^-1) is a characteristic feature of thevery short-period (P<1.5d) and longer period (P>10d) Cepheids.Between these period regions the Cepheid atmospheres exhibit smallervelocity differences. Most of the Type II Cepheids observed in thepresent study fall into this latter category. There might be a tendencyfor classical Cepheids of intermediate period to have larger maximumvelocity differences.
| The Mass of the Cepheid Binary V636 Scorpii
The mass-luminosity relation for Cepheids depends on the degree ofmixing in their main-sequence progenitors. Masses of Cepheids can beinferred by using different aspects of pulsation theory. These methodshave in the past led to diverging results, showing that something waswrong in either evolution theory or pulsation theory or both. For somebinary Cepheids dynamical masses, which are independent of pulsation andevolution theories, can be determined. V636 Sco is one of a handful ofCepheid binaries whose companions are bright enough in the ultravioletthat orbital radial velocities can be measured. We have here attemptedto determine the radial velocity of the companion V636 Sco B to theCepheid V636 Sco A by means of two Hubble Space Telescope (HST) spectrataken at phases of minimum and maximum Cepheid orbital velocities. Theratio of the orbital velocity of the companion and the Cepheid (which isthe inverse of their mass ratio) came out to be 1.25 +/- 0.17. V636 ScoB has a spectral type B9.5 V, for which we expect a stellar mass of 2.5M_ȯ. For the Cepheid we thus determine a mass of 3.1 +/- 0.4M_ȯ, which is surprisingly low. If true, such a low mass wouldindicate an extremely large amount of excess mixing, which is veryunlikely. We discuss the likely possibility that V636 Sco B may itselfbe a binary with an unseen secondary, in which case the mass derivedfrom the two measurements discussed above is not correct. Although theerror limits for the mass of each Cepheid are rather large, the combinedmass-luminosity relation for all Cepheids studied by us so far by meansof HST spectra indicates excess mixing corresponding to core convectiveovershoot by 0.25 to about 0.5 pressure scale height in themain-sequence progenitors of the Cepheids. Based on observations madewith the NASA/ESA Hubble Space Telescope, obtained at the SpaceTelescope Science Institute, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under NASA contractNASS-26555.
| Classical Cepheid Masses: U Aquilae
We have obtained medium-resolution spectra ( lambda / Delta lambda ~20,000) of the hot binary companion to the classical Cepheid U Aql withthe Goddard High Resolution Spectrograph on the Hubble Space Telescope(HST). These have been used to determine the orbital velocity amplitude.Combining this with the orbital velocity amplitude of the Cepheid fromthe ground-based orbit and the mass of the companion inferred from itsspectral type, we measure a mass of the Cepheid of 5.1 +/- 0.7 Mȯ.We discuss the full sample of Cepheids for which we have determinedmasses with HST (S Mus, V350 Sgr, Y Car, and U Aql) and also SU Cyg(mass from IUE). The HST masses are in agreement with the luminositiespredicted by recent evolutionary tracks with moderate overshoot. Thiscomparison, however, may be altered by reassessment of Cepheid distancesbased on Hipparcos parallaxes.
| The shape and scale of Galactic rotation from Cepheid kinematics
A catalog of Cepheid variables is used to probe the kinematics of theGalactic disk. Radial velocities are measured for eight distant Cepheidstoward l = 300 deg; these new Cepheids provide a particularly goodconstraint on the distance to the Galactic center, R0. We model the diskwith both an axisymmetric rotation curve and one with a weak ellipticalcomponent, and find evidence for an ellipticity of 0.043 +/- 0.016 nearthe sun. Using these models, we derive R0 = 7.66 +/- 0.32 kpc andv(circ) = 237 +/- 12 km/s. The distance to the Galactic center agreeswell with recent determinations from the distribution of RR Lyraevariables and disfavors most models with large ellipticities at thesolar orbit.
| Li-rich giants: A survey based on IRAS colours
In a previous work we studied the IRAS colours of known Li-rich redgiants and showed that they have flux ratiosF12/F25 and F25/F60 in welldefined ranges. By using this result as a selection criterion, weprepared a list of 280 IRAS Point Source candidates to be Li-rich giantstars. Up to the present we have obtained spectra for 57% of our targetlist. We identified five stars showing a strong LiI 670.079 nm line andsix ones with a Li line of medium strength. Most of the candidates showfeatures typical of normal giants having circumstellar dust, asindicated by their IRAS colours. Observations collected at theLaboratorio Nacional de Astrofisica - LNA, Brazil; Observatoire de HauteProvence - OHP, France; European Southern Observatory - ESO, Chile.
| The Mass of the Classical Cepheid V350 SGR
Two medium resolution spectra of the hot companion of the Cepheid V350Sgr have been obtained with the Goddard High Resolution Spectrographaboard the Hubble Space Telescope. Comparison of these spectra (in thewavelength range 1840 to 1880 \AA) with the spectrum of $\alpha$ Lyrshows that V350 Sgr B has a projected rotation velocity which may be ashigh as 150 km sec$^{-1}$. The velocity difference between the spectraof V350 Sgr B at two orbital phases is measured to be -23.1 $\pm$ 3.8 kmsec$^{-1}$. The error is dominated by the aperture centering. Whencombined with the orbital velocity variation of the Cepheid derived fromthe ground-based orbit and the mass of the companion deduced from IUEspectra, the mass of the Cepheid is found to be 5.2 $\pm$ 0.9 M$\sun$.The observed mass--luminosity combination of V350 Sgr A is a good matchto recent evolutionary calculations which use moderate convectiveovershoot near the main sequence, however, the blue loops do not extendto temperatures as hot as the Cepheid. (SECTION: Stars)
| Galactic kinematics of Cepheids from HIPPARCOS proper motions
The Hipparcos proper motions of 220 Galactic Cepheids, together withrelevant ground-based photometry, have been analyzed. The effects ofGalactic rotation are very clearly seen. Mean values of the Oortconstants, A = 14.82 +/- 0.84 km/s kpc, and B = -12.37 +/- 0.64 km/skpc, and of the angular velocity of circular rotation at the sun, 27.19+/- 0.87 km/s kpc, are derived. A comparison of the value of A withvalues derived from recent radial velocity solutions confirms, withinthe errors, the zero-points of the period-luminosity andperiod-luminosity-color relations derived directly from the Hipparcostrigonometrical parallaxes of the same stars. The proper motion resultssuggest that the Galactic rotation curve is declining slowly at thesolar distance from the Galactic Center (-2.4 +/- 1.2 km/s kpc). Thecomponent of the solar motion towards the North Galactic Pole is foundto be +7.61 +/- 0.64 km/s. Based on the increased distance scale deducedin the present paper, the distance to the Galactic Center derived in aprevious radial velocity study is increased to 8.5 +/- 0.5 kpc.
| The Mass of the Classical Cepheid S MUSCAE
A good determination of the mass-luminosity relation for evolved starson blue loops can determine the degree of excess mixing in the interiorsof their main-sequence companions. In this study we determine thedynamical mass of the Cepheid binary S Muscae. This can be combined withits known luminosity and be fitted on evolutionary tracks to determinethe amount of mixing in the main-sequence progenitor. Using the GoddardHigh Resolution Spectrograph on the Hubble Space Telescope we havemeasured the orbital radial velocity changes for the companion of theCepheid S Mus. Spectra taken at minimum and maximum orbital velocitieswere cross-correlated. The velocity difference was measured to be 30.6+/- 0.4 km s-1. The difference for the orbital velocities of the Cepheidfor the same phases was determined to be 26.9 km s-1 +/- 0.4 km s-1.This gives a velocity ratio of 1.14 +/- 0.02, which gives us the massratio for the companions. Adding possible centering errors of the targetin the entrance apertures the error limit would be increased to +/-0.06.The derived spectral types of the companion S Mus B range from B3 V toB5 V depending on the criterion used to determine it, with an averagespectral type B3.8 V. Using the average spectral type and themain-sequence mass-spectral type relation from Andersen & Harmanecwe find for S Mus B a mass of 5.2 +/- 0.2 Mȯ. With the newlydetermined mass ratio the mass for the Cepheid S Mus A comes out to be5.9^{+0.7}_{-0.6} Mȯ. Taking the mass of 5.9 Mȯ at face valueand adopting the absolute visual magnitude of Mv = -4.29 (log L/Lȯ= 3.62) for the Cepheid S Mus this indicates mixing in its main-sequenceprogenitor slightly in excess of the one assumed for the Maeder andMeynet evolutionary tracks. The present uncertainties in mass andluminosity prevent, however, a firm conclusion about the exact degree ofmixing.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | はえ座 |
| Right ascension: | 12h12m46.80s |
| Declination: | -70°09'07.0" |
| Apparent magnitude: | 6.17 |
| Distance: | 500 parsecs |
| Proper motion RA: | -7.1 |
| Proper motion Dec: | -0.2 |
| B-T magnitude: | 7.028 |
| V-T magnitude: | 6.169 |
Catalogs and designations:
|
