Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| 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.
| 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.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| 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.
| 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
| Multi-colour PL-relations of Cepheids in the bt HIPPARCOS catalogue and the distance to the LMC
We analyse a sample of 236 Cepheids from the hipparcos catalog, usingthe method of ``reduced parallaxes'' in V, I, K and the reddening-free``Wesenheit-index''. We compare our sample to those considered by Feast& Catchpole (1997) and Lanoix et al. (1999), and argue that oursample is the most carefully selected one with respect to completeness,the flagging of overtone pulsators, and the removal of Cepheids that mayinfluence the analyses for various reasons (double-mode Cepheids,unreliable hipparcos solutions, possible contaminated photometry due tobinary companions). From numerical simulations, and confirmed by theobserved parallax distribution, we derive a (vertical) scale height ofCepheids of 70 pc, as expected for a population of 3-10 Msunstars. This has consequences for Malmquist- and Lutz-Kelker (Lutz &Kelker 1973, Oudmaijer et al. 1998) type corrections which are smallerfor a disk population than for a spherical population. The V and I datasuggest that the slope of the Galactic PL-relations may be shallowerthan that observed for LMC Cepheids, either for the whole period range,or that there is a break at short periods (near log P_0 ~ 0.7-0.8). Westress the importance of two systematic effects which influence thedistance to the LMC: the slopes of the Galactic PL-relations andmetallicity corrections. In order to assess the influence of thesevarious effects, we present 27 distance moduli (DM) to the LMC. Theseare based on three different colours (V,I,K), three different slopes(the slope observed for Cepheids in the LMC, a shallower slope predictedfrom one set of theoretical models, and a steeper slope as derived forGalactic Cepheids from the surface-brightness technique), and threedifferent metallicity corrections (no correction as predicted by one setof theoretical models, one implying larger DM as predicted by anotherset of theoretical models, and one implying shorter DM based onempirical evidence). We derive DM between 18.45 +/- 0.18 and 18.86 +/-0.12. The DM based on K are shorter than those based on V and I andrange from 18.45 +/- 0.18 to 18.62 +/- 0.19, but the DM in K could besystematically too low by about 0.1 magnitude because of a bias due tothe fact that NIR photometry is available only for a limited number ofstars. From the Wesenheit-index we derive a DM of 18.60 +/- 0.11,assuming the observed slope of LMC Cepheids and no metallicitycorrection, for want of more information. The DM to the LMC based on theparallax data can be summarised as follows. Based on the PL-relation inV and I, and the Wesenheit-index, the DM is 18.60 ± 0.11(± 0.08 slope)(^{+0.08}_{-0.15} ;metallicity), which is ourcurrent best estimate. Based on the PL-relation in K the DM is ;;;;18.52 +/- 0.18 (± 0.03 ;slope) (± 0.06 ;metallicity)(^{+0.10}_{-0} ;sampling ;bias). The random error is mostly due to thegiven accuracy of the hipparcos parallaxes and the number of Cepheids inthe respective samples. The terms between parentheses indicate thepossible systematic uncertainties due to the slope of the GalacticPL-relations, the metallicity corrections, and in the K-band, due to thelimited number of stars. Recent work by Sandage et al. (1999) indicatesthat the effect of metallicity towards shorter distances may be smallerin V and I than indicated here. From this, we point out the importanceof obtaining NIR photometry for more (closeby) Cepheids, as for themoment NIR photometry is only available for 27% of the total sample.This would eliminate the possible bias due to the limited number ofstars, and would reduce the random error estimate from 0.18 to about0.10 mag. Furthermore, the sensitivity of the DM to reddening,metallicity correction and slope are smallest in the K-band. Based ondata from the ESA HP astrometry satellite.
| 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.
| Colour excesses of F-G supergiants and Cepheids from Geneva photometry.
A reddening scale for F-G supergiants and Cepheids is presented.Supergiants with low reddenings or in clusters form the basis of thecalibration. In this sense, it is entirely empirical. The data have beenobtained in the Geneva photometric system. Comparisons with otherreddening scales show no disagreement. The only problem is with Fernie'sscale for Cepheids (1990), where a systematic trend exists. Its originis not clear. It is suggested to extend the number of supergiants withindependently obtained colour excesses in order to test the existence ofa possible luminosity dependence of the calibration. A period-colourrelation for Cepheids is deduced, on the basis of the present reddeningcorrections. It gives strong support for V473 Lyr being a secondovertone pulsator.
| Photometric Parameters for Short-Period Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1313E&db_key=AST
| New method to recognize s-Cepheids
A new method of delineating sinusoidal or s-Cepheids is presented. Themethos uses the values of (V) (the mean intensity), V - Bar (the averagemagnitude), and Vmean (the value of the mean magnitude).Fourier coefficient data from galactic Cepheids is used to derive theseterms in the V band and the differences between the various terms showsystematic trends with increasing period. The Cepheids can be easilygrouped into 3 divisions-short period s-Cepheids, intermediate periodCepheids (P less than 9 days), and long period Cepheids (P greater than9 days). Cepheids previously designated as s-Cepheids by others arecompared to those found using the method outlined here. The method isalso applied to Cepheids in the Small Magellanic Cloud to examine itssuitability as a pulsation mode discriminator.
| Classical Cepheids with terminal age main-sequence companions: Constraints on evolution
Eight binaries containing a Cepheid and a hot companion evolved beyondthe ZAMS are studied using IUE spectra. The spectral types of these TAMS(terminal age main-sequence) companions are determined from the spectraand absolute magnitudes are determined from the magnitude differencebetween the two stars and the absolute magnitude of the Cepheid. Thesystems with Cepheids with periods less than 6 days (BP Cir, AX Cir, andV659 Cen) match isochrones with no core convective overshoot. The 12 dayCepheid SY Nor is better matched with an isochrone with mild overshoot.The 11 day Cepheid SV Per and the 16 day Cepheid RW Cam do not match anyavailable isochrone (with any overshoot value) because the companionsare cool enough to be at the very end of the main-sequence phase but themagnitude difference between the two stars is too large for thisscenarior. KN Cen and AW Per may be similar systems. These unusuallycool companions are common (up to half the sample) and distributedthroughout the Cepheid mass range. Rotation could explain thesecompanions. In this case, use of the main-sequence width to determinethe importance of convective overshoot would produce an overestimate ofconvective overshoot.
| The binary Cepheid BP CIR - A test of evolutionary tracks
Abstract image available at:http://adsabs.harvard.edu/abs/1992AJ....103.1638E
| The luminosity of the double-mode Cepheid Y Carinae
IUE spectra of the double-mode Cepheid Y Carinae have been used todetermine the spectral type of the binary companion. From the companionspectral type (B9.O V), the absolute magnitude of the Cepheid is foundto be -2.94 mag, with an estimated uncertainty of +/-0.3. Thisluminosity is in good agreement with that from theperiod-luminosity-color relation of Feast and Walker for the fundamentalmode. This agreement, together with the large magnitude differencebetween the B9.0 V star and the Cepheid, confirm that the Cepheid is anormal classical Cepheid with a mass much larger than that inferred fromthe ratio of the two periods (beat mass). The two double-mode Cepheidswith independently determined luminosities (Y Car and V 367 Sct) bothfall on the blue edge of the instability strip.
| A magnitude-limited survey of Cepheid companions in the ultraviolet
Results of a magnitude-limited survey of classic Cepheids brighter than8th mag carried out to search for hot main-sequence companions arepresented. Spectra of 76 stars obtained with the IUE satellite in the2000-3200-A region were compared with the spectra of nonvariablesupergiants and also the single Cepheid Delta Cep to search for excessflux at 2500 A from possible companions. Photometric companions werefound for 21 percent of the sample. When the Cepheids known to be binaryfrom either orbital motion or spectra in the 1200-2000-A region areincluded, the percentage of companions rises to 29 percent. If astatistical correction from stars with orbital motion is included, 34percent have companions. This percentage is compared with that found byAbt et al. (1990) for B2-B5 main-sequence stars. If only systems withperiods longer than a year and separations not more than 30 arcsec areconsidered, only 18 percent of the B stars will become Cepheids withcompanions.
| The calibration of the Stromgren photometric system for A, F and early G supergiants. I - The observational data
An empirical calibration of the Stromgren uvby-beta photometric systemfor the A, F, and early G supergiants is being derived. This paperexplains the observational program and the photometric reductiontechniques used and presents a catalog of new Stromgren photometry forover 600 A, F, and G supergiants.
| Physical parameters of pulsating variables with periods between one and three days. II - Fundamental parameters
On the basis of the Walraven VBLUW photometry data reported by Diethelm(1986) on 57 pulsating variables with periods between one and threedays, primary parameters (metallicity, log g, Teff, and the amount ofreddening) were deduced for 11 of these stars, using a semiempiricalapproach based on model atmosphere calculations. Results indicate thatboth the C-delta and the SA-class of the pulsating variables are youngstars of the disc-population pulsating either in the fundamental(C-delta) or in the first overtone mode (SA). The AHB1 stars, whichshowed a marked deficiency in metal abundance, are members of the halopopulaton. The stars of the AHB2 and AHB3 groups, which show anintermediate metallicity, must be considered as members of anintermediate stellar population.
| The separation of S-Cepheids from classical Cepheids and a new definition of the class
Fourier decomposition has been applied to a sample of 184 classical andS-Cepheids with P less than 8 d and a careful evaluation of errors inthe determination of the parameters has been made. The S-Cepheids starsare redefined by the authors as Population I Cepheids that do not followthe Hertzsprung progression, but have a progression of their own. In thephi(21)-P plane, the S- and classical Cepheids are characterized by twosequences well separated for P less than 5.5 d. In the period range Pbetween 3d and 5.5 d, two different progressions are also present in thephi(31)-P plane while a discriminating value R(21) = 0.20 can be seen inthe R(21)-P plane. The first overtone pulsation seems to be wellestablished for S-Cepheids with P less then 3.2 d; it is probable forall the stars of the redefined subclass. A discontinuity is clearlyvisible at about 3 d in the S-Cepheid sequence in the phi(21)-P plane;it is interpreted as a resonance effect. An apparent decrease in thenumber of stars is present in the classical sequence for P less than 3d.
| Color Excesses on a Uniform Scale for 328 Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990ApJS...72..153F&db_key=AST
| Milky Way rotation and the distance to the galactic center from Cepheid variables
The compiled photometry, reddenings, and radial velocities of GalacticCepheids are fit with an axisymmetric Galactic rotation model. R(0) =7.8 + or - 0.7 kpc and 2AR(0) = 228 + or - 19 km/s are derived. The LMCdistance modulus is 18.45 on the same absolute calibration. ObservedCepheid gamma velocities appear on average to be 30 + or - 1 km/s morenegative than the true corresponding center-of-mass velocities. Thetrend of increasing blueness toward larger Galactocentric radiusconfirms the radial metallicity gradient found spectroscopically.
| Cepheids as distance indicators
The current status of astronomical distance estimation based onobservations of Cepheids is surveyed. Consideration is given to theproblems of reddening and absorption correction, the forms of the BVIperiod-luminosity (PL) and period-luminosity-color (PLC) relations,abundance effects, the IR PL/PLC relations, PL/PLC relations at otherwavelengths, shortcut methods, PL/PLC zero points, long-period Cepheids,and Cepheid distances to galaxies. Diagrams, graphs, and extensivetables of numerical data are provided.
| Physical parameters of pulsating variables with periods between one and three days. I - Photometry and metallicities
Based on a new set of observations in the Walraven VBLUW system,obtained at the European Southern Observatory, La Silla, Chile,Fe/H(VBLU) values of 57 pulsating variables, mostly with periods betweenone and three days,. are determined. The distribution of the metalabundances is shown to be essentially bimodal. All the variables withFe/H ratios of less than -0.4 were classified by Diethelm (1983) as RRdstars. They are identified as the galactic field counterpart of theCepheids in the same period range found in globular clusters.
| Yellow supergiants with hot companions.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1986RMxAA..12..189A&db_key=AST
| Discovery of the Hot Companion to the Two-Day Cepheid HD129708
The Cepheid HD 129708 has been observed with the InternationalUltraviolet Explorer satellite, and a hot companion star (B4-5) has beendiscovered. Comparison of the observed energy distribution withtheoretical atmosphere models gives Te = 16,000±1000Kand log g = 4.0±0.5 for the hot companion. A visual magnitudedifference ΔV = 2m.4±0m.2 between thehot secondary and the Cepheid is calculated, which implies Mv≡ -3m.0±0m.3 for the Cepheid. Thisnumber is to be compared with Mv = -2m.8,predicted from the ridge line of the period-luminosity relationship,indicating that the Cepheid is pulsating in the fundamental mode.
| Intermediate-band and H-beta observations of short-period Cepheids
Intermediate-band and H-beta observations along with light and colorcurves for short-period Cepheids are presented. Although mainlysouthern, a few northern variables are included. Two of the variablesare briefly discussed.
| The period-luminosity-abundance relations for galactic Cepheids
The median photometric parameters from intermediate and H-betaphotometry of 106 Cepheids are used to test the Sandage-Tammann resultthat dispersions in the PL and PC relations are correlated with theamplitude of the light curves, as measured by the amplitude defect F(B).The correlation of both color and luminosity dispersions from mean PLand PC relations with F(B) are found to be the result of a correlationbetween abundance and amplitude. The short-period Cepheids (SPC) aredistinctly divided between type C and normal Cepheids, with type Cvariables defined by F(B). The C-type and normal SPC are separated by0.65 mag at a given period and abundance, or about 300 K at a givenluminosity, with the C-type Cepheids being fainter and bluer,respectively. The light curves of nine-day Cepheids with strong humpsmay be misinterpreted in that the hump has mistakenly been taken formaximum light.
| Cepheids and nonvariable supergiants
Photometric parameters for Cepheids in a previous paper are adapted foruse with nonvariable supergiants of similar temperature. The closecorrelation between the abundance and luminosity parameters forclassical, short-period Cepheids (SPC) confirms the nearlydispersionless luminosity temperature relation for these variables. Theassumptions that (1) the C-type variables are transiting the Cepheidtemperature for the first time, (2) the classical SPC are mostlytransiting for the second time, and (3) the long-period Cepheids (LPC)are a mixture of stars transiting for the first to third or fourth timesare found to be consistent with the various correlations of temperatureand luminosity parameters. The nonvariable supergiants with photometricparameters similar to those for the Cepheids are found to haveluminosities consistent with their spectroscopic luminosity class. Few,if any, nonvariable supergiants have temperatures and luminositiessimilar to the LPC.
| Physical parameters and pulsational mode of short-period small-amplitude Cepheids
Nine galactic short-period (P less than 8 days) small-amplitude Cepheidshave been the subject of a study to determine their physical parametersand pulsational properties. UBVRI photometry and radial velocities wereobtained in the same observing seasons. The wings of H-alpha were usedto determine effective temperatures. Empirical radii, luminosities, andmasses were determined. The short-period stars lie inside and seem to beon the red side of the observational Cepheid instability strip. It wasfound that these stars are likely pulsating in the radial fundamentalmode except HR 8084 (DT Cyg) which is suspected to be a first overtonepulsator. As the small-amplitude Cepheids in the LMC are thought to befirst overtone pulsators, it is suggested that small-amplitudesinusoidal variations are not the consequence of pulsation in the firstovertone, but rather the response to a more general amplitude trendacross the instability strip in a particular galactic system.
| Classification of intrinsic variables. IX - The Cepheid domain
The present H-beta, RI and intermediate band observations obtained for135 high mass, long- and short-period Cepheids (LPC and SPC) throughoutthe cycle of variation are combined with observations for 100 ultrashortperiod Cepheids in order to delineate the Cepheid domain in the (beta,/C1/) and (M-bol, log Te) planes. The independently derived luminositycalibrations for bright giants and supergiants previously published arefound to closely reproduce the luminosities derived from theSandage-Tammann (1968) PL relation for most variables. The majority ofthe LPC appear to be overabundant in metals by comparison to the sun,and reddening determinations for the LPC suggest a small systematiccorrection to previous results.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Pergel |
| Sað Açýklýk: | 14h46m41.98s |
| Yükselim: | -61°27'43.0" |
| Görünürdeki Parlaklýk: | 7.533 |
| Uzaklýk: | 7692.308 parsek |
| özdevim Sað Açýklýk: | -3.9 |
| özdevim Yükselim: | -1.9 |
| B-T magnitude: | 8.32 |
| V-T magnitude: | 7.598 |
Kataloglar ve belirtme:
|
