Contents
Images
Upload your image
DSS Images Other Images
Related articles
Photometry of Type II Cepheids. III. The Intermediate-Period Stars
We present 741 new photometric observations for 22 Cepheids with periodsbetween 3 and 8 days. Many of the stars are probable type II Cepheids,but we have included some type I Cepheids for comparison. The shapes andstability of the shapes of the light curves, the stability of theperiods, and the scatter of individual data points are discussed.Although none of these proves to be a reliable discriminator betweentype I and type II Cepheids, they do permit the identification ofseveral unusual stars.
| Sodium enrichment of the stellar atmospheres. II. Galactic Cepheids
The present paper is a continuation of our study of the sodium abundancein supergiant atmospheres (Andrievsky et al. 2002a). We present theresults on the NLTE abundance determination in Cepheids, and the derivedrelation between the sodium overabundance and their masses.
| The Spectra of Type II Cepheids. II. The Hα Line in Intermediate-Period Stars
We present 98 Hα profiles for 21 pulsating variable stars withperiods from 3 to 8 days. The strength, depth, and shape of Hαvary throughout the cycles of the stars in a way consistent with thetemperature changes. Otherwise, they are quite uniform among all thestars, with a single exception. In FM Del, Hα is weaker and has asmaller central depth than in the other stars. This and the wavelengthshifts of the core are attributed to incipient emission. Thedifferential velocity of Hα relative to the metal lines is lessthan 25 km s-1 for all the stars except QY Cyg, FM Del, andEF Tau. We suggest that this indicates that only these stars are type IICepheids despite the large distances of some of the others from theGalactic plane.Based in part on observations obtained with the Apache Point Observatory3.5 m telescope, which is owned and operated by the AstrophysicalResearch Consortium.
| The Cepheids of Population II and Related Stars
The Type II Cepheids include most intrinsic variables with periodsbetween 1 and about 50 days, except for the classical Cepheids and theshortest semiregular variables of type M. The Type II Cepheids may bedivided in groups by period, such that the stars with periods beween 1and 5 days (BL Her class), 10-20 days (W Vir class), and greater than 20days (RV Tau class) have differing evolutionary histories. The chemicalcomposition of Type II Cepheids reflects the material they were madefrom as modified by their internal nuclear evolution and mixing.Finally, RV Tau stars are affected by mass loss by dust and speciesattached to the dust. The populations to which the various classes ofType II Cepheids are assigned constitute important clues to the originand evolution of the halo of our Galaxy and the dwarf spheroidal systemsfrom which at least part of the halo seems to have been accreted.
| Using Cepheids to determine the galactic abundance gradient. I. The solar neighbourhood
A number of studies of abundance gradients in the galactic disk havebeen performed in recent years. The results obtained are ratherdisparate: from no detectable gradient to a rather significant slope ofabout -0.1 dex kpc-1. The present study concerns theabundance gradient based on the spectroscopic analysis of a sample ofclassical Cepheids. These stars enable one to obtain reliable abundancesof a variety of chemical elements. Additionally, they have welldetermined distances which allow an accurate determination of abundancedistributions in the galactic disc. Using 236 high resolution spectra of77 galactic Cepheids, the radial elemental distribution in the galacticdisc between galactocentric distances in the range 6-11 kpc has beeninvestigated. Gradients for 25 chemical elements (from carbon togadolinium) are derived. The following results were obtained in thisstudy. Almost all investigated elements show rather flat abundancedistributions in the middle part of galactic disc. Typical values foriron-group elements lie within an interval from ~-0.02 to ~-0.04 dexkpc-1 (in particular, for iron we obtainedd[Fe/H]/dRG =-0.029 dex kpc-1). Similar gradientswere also obtained for O, Mg, Al, Si, and Ca. For sulphur we have founda steeper gradient (-0.05 dex kpc-1). For elements from Zr toGd we obtained (within the error bars) a near to zero gradient value.This result is reported for the first time. Those elements whoseabundance is not expected to be altered during the early stellarevolution (e.g. the iron-group elements) show at the solargalactocentric distance [El/H] values which are essentially solar.Therefore, there is no apparent reason to consider our Sun as ametal-rich star. The gradient values obtained in the present studyindicate that the radial abundance distribution within 6-11 kpc is quitehomogeneous, and this result favors a galactic model including a barstructure which may induce radial flows in the disc, and thus may beresponsible for abundance homogenization. Based on spectra collected atMcDonald - USA, SAORAS - Russia, KPNO - USA, CTIO - Chile, MSO -Australia, OHP - France. Full Table 1 is only available in electronicform at http://www.edpsciences.org Table A1 (Appendix) is only, andTable 2 also, available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/32
| 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
| 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.
| Fourier Analysis of Hipparcos Photometry of Cepheid Variables
Fourier parameters have been computed for 240 field Cepheids observed bythe Hipparcos satellite. We have identified three new PopulationIovertone Cepheids: V411Lac, V898 Cen and V572 Aql. We have comparedFourier progressions of Population I and Population II Cepheids. Thepossibility of using Fourier parameters to distinguish between the twotypes is discussed.
| The intermediate-band approach to the surface-brightness method for Cepheid radii and distance determination
The surface-brightness parameter Fν is calibrated in termsof the Strömgren intermediate-band colour b-y. The relationFν-(b-y)o valid for Cepheids is calibratedusing accurate near-infrared radii and distances for selected Cepheids.We have obtained uvby photometry for non-Cepheid giant and supergiantstars with known angular diameters and compared the slope and zero-pointof their Fν-(b-y)o relation with the Cepheidcalibration. We found that the two calibrations are significantlydifferent. The theoretical models lie in between the two calibrations.It is remarked that Fν-colour relations derived fromnon-Cepheids and involving blue colours (e.g. B-V or b-y) are notapplicable to Cepheids, while those involving redder colours (e.g. V-R,V-K or V-J) also produce good radii for Cepheids. Selected Cepheids ascalibrators lead to the accurate relationFν=3.898(+/-0.003)-0.378(+/-0.006)(b-y)o, whichallowed the calculation of radii and distances for a sample of 59Galactic Cepheids. The uncertainties in the zero-point and slope of theabove relation are similar to those obtained from near-infrared colours,and determine the accuracies in radii and distance calculations. Whileinfrared light and colour curves for Cepheids may be superior inprecision, the intermediate-band b-y colour allows the recovery of meanradii with an accuracy comparable to those obtained from the infraredsolutions. The derived distances are consistent within the uncertaintieswith those predicted by a widely accepted period-luminosityrelationship. Likewise, the resulting period-radius relation from theintermediate-band approach is in better agreement with infrared versionsthan with optical versions of this law. It is highlighted that theintermediate-band calibration of the surface-brightness method in thiswork is of comparable accuracy to the near-infrared calibrations. Thepresent results stress the virtues of uvby in determining the physicalparameters of supergiant stars of intermediate temperature.
| Period Changes in Population II Cepheids: TX Del and W Vir
We have used the Hipparcos database of epoch photometry to study thevariability of two Population II Cepheids: TX Del and W Vir. We haveconstructed (O-c) diagrams for these stars, using the new data and datafrom the literature. The period of TX Del is decreasing, at a ratewhich is consistent with evolutionary predictions. THe periodchange ofW Vir is uncertain because of the many recent gaps in the data of thisstar. We urge AAVSO visual and photoelectric observers to monitorPopulation II Cepheids more systematically, since amny of these starshave unstable periods, and at least one has an unstable amplitude.
| Using BV Photometry to Distinguish between Type I and Type II Cepheids
We use Johnson BV photometry of Galactic type I and type II Cepheids ina variety of diagrams to see whether the two populations can beadequately separated. The diagrams include the Fourier parametersphi_21, phi_31, phi_41, R_21, R_31, R_41, the loop width in the V-(B-V)plane, the relative phasing of V and B-V extrema, and the amplituderatios of B-V to V, all versus period. We found the R_i1 diagramsuseless in this regard, while a plot of the phasing parameter versusamplitude ratio was best, closely followed by the phi_i1 diagrams. Amajor difficulty was arriving at a sample of Cepheids that could bereliably taken to be definitely type II. We found it necessary to useonly stars that would have been more than 2 kpc from the Galactic planehad they been type I for this sample, and even then it is uncertainwhether such overlap between types as we find in our diagrams is due toinadequacy of the tests or is due to type I stars' having contaminatedour type II sample. We point out evidence strongly suggesting that typeI stars can be found at least up to 2 kpc from the plane. Selectioneffects in our sample of type II Cepheids resulted in only one BLHerculis star (short-period type II) being included, so our conclusionsbasically apply only to W Virginis stars.
| Estimation of Stellar Metal Abundance. II. A Recalibration of the Ca II K Technique, and the Autocorrelation Function Method
We have recalibrated a method for the estimation of stellar metalabundance, parameterized as [Fe/H], based on medium-resolution (1-2Å) optical spectra (the majority of which cover the wavelengthrange 3700-4500 Å). The equivalent width of the Ca II K line (3933Å) as a function of [Fe/H] and broadband B-V color, as predictedfrom spectrum synthesis and model atmosphere calculations, is comparedwith observations of 551 stars with high-resolution abundances availablefrom the literature (a sevenfold increase in the number of calibrationstars that were previously available). A second method, based on theFourier autocorrelation function technique first described by Ratnatunga& Freeman, is used to provide an independent estimate of [Fe/H], ascalibrated by comparison with 405 standard-star abundances.Metallicities based on a combination of the two techniques for dwarfsand giants in the color range 0.30<=(B-V)_0<=1.2 exhibit anexternal 1 sigma scatter of approximately 0.10-0.20 dex over theabundance range -4.0<=[Fe/H]<=0.5. Particular attention has beengiven to the determination of abundance estimates at the metal-rich endof the calibration, where our previous attempt suffered from aconsiderable zero-point offset. Radial velocities, accurate toapproximately 10 km s^-1, are reported for all 551 calibration stars.
| UVBY beta Photometric Data and Fourier Coefficients for Galactic Population I and Population II Cepheids
Photometric data in the uvby beta system are presented for a sample of98 Population I Cepheids and seven W Virginis or Population II Cepheids.The importance of the Fourier decomposition technique in the study ofthe structure of pulsating stars is stressed. Mean values and Fourierdecomposition coefficients for the V, b - y, m1, and c1 variations arecalculated. Also, mean values of H beta are provided. New times ofmaximum V light are reported for the majority of the stars in thesample. Significant shifts of the light and color curves were found insome Cepheids; these are explained by their period variations. Thesestars are highlighted in the text.
| 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.
| A catalog of Cepheid radial velocities measured in 1995-1998 with the correlation spectrometer.
Not Available
| The radii of 62 classical Cepheids.
Not Available
| Monitoring the Evolution of Cepheid Variables
Described here are preliminary results of a pilot project to monitorchanges in the ephemerides of northern hemisphere Cepheid's using anSBIG camera attached to the 0.4-m telescope of the campus obversatory atSaint Mary's University. Epochs of maximum light for fifteen Cepheid'shave been derived using published light curves for each variable astemplates, and the results are being used to update the O-C ephemeridesfor the program stars. Results for BB Her are presented here. Periodchanges for Cepheid variables are demonstrated to be an excellent meansof pinpointing their evolutionary status, as well as for investigatingother peculiarities of the class.
| Baade-Wesselink Radius Determination of Type II Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113.1833B&db_key=AST
| Structural Properties of Pulsating Star Light Curves Through Fuzzy Divisive Hierarchical Clustering
Not Available
| ST Pup: a binary Type II Cepheid with a peculiar chemical composition
Analysis of recent photometric observations of the W Vir star ST Pupreveals that it has experienced one sudden period change in the last 35years. This is in sharp contrast to its erratic behaviour in the firsthalf of this century when the period changed much more frequently.Application of the surface brightness version of the Baade-Wesselinkmethod to the observations yields M_v=-3.86+/-0.2. Using spectroscopicobservations spanning almost 7yr, we have discovered that ST Pup is asingle-lined spectroscopic binary. The orbital period, 410.4+/-2.9d, isconsiderably longer than that of the other three known binary Type IICepheids, which average about 100d. It has a very low orbitaleccentricity, implying that orbital circularization and mass transferhave already taken place in this system. We estimate that[Fe/H]=-1.47+/-0.13 from a local thermodynamic equilibrium (LTE) fineanalysis of high-resolution spectra obtained near minimum light. Thevalue of C/O is 0.3, demonstrating that ST Pup is not a carbon star eventhough it displays strong CH and CN bands near minimum light. Most ofthe elements show an abundance pattern that correlates with condensationtemperature similar to that of diffuse interstellar clouds and peculiarhigh-latitude A-F supergiants, which have been interpreted as low-masspost-AGB stars that have undergone selective mass-loss via grainformation. However, the Ca/Ti abundance ratio in the atmosphere of STPup is too high to be consistent with this interpretation. The Caanomaly may have been caused by overionization of Ca^+ by Lyalphaphotons when the star was losing mass. An infrared excess is seen at theJHKL and IRAS bands, indicating the presence of dust spanning a largerange in distance from ST Pup.
| A spectroscopic study of the pulsating star BL Her.
Not Available
| A catalog of Cepheid radial velocities measured in 1992-1995 with a correlation spectrometer.
Not Available
| Mean radial velocities and binarity of Cepheids from 1987-1995 measurements.
Not Available
| Photoelectric Observations of Cepheids in 1994
Not Available
| Is TX Delphini a Population I (classical) Cepheid?
Not Available
| Spectroscopic Study of the Pulsating Star Tx-Delphini
Not Available
| A new approach to the surface brightness method for cepheid radii determination.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994RMxAA..29..148R&db_key=AST
| Study of the population II Cepheid AU Pegasi
New photoelectric B and V observations of the Population II Cepheid AUPeg are presented. The available photometric measurements are collectedfrom the literature and all data are analyzed with severalperiod-finding methods. The period variation has been found to benon-linear, and between 1986 and 1990 the period increase stopped andseems to reverse. Since this Cepheid is a member of a binary systemwhere proximity of the components is a deterministic factor, it isprobable that the pulsation is perturbed by the companion's tidal force.However, such a period variation can hardly be explained by tidalinteraction alone. The surface brightness analysis resulted in newabsolute parameters indicating that AU Peg is on the red edge of theinstability strip.
| Catalog of radial velocities for northern Cepheids measured with a correlation spectrometer
A catalog containing 1446 individual radial velocity values for 79 fieldCepheids and three Cepheids in globular clusters, and 32 averaged radialvelocities of the Cepheid Alpha UMi derived from 100 individual velocityparameters is presented. A table of gamma velocities for 30 Cepheidswith sufficiently good coverage of Vr curves is included. Radialvelocity observations of CE Cas A and CF Cas, which are photometricmembers of the open cluster NGC 7790, made it possible to estimate theradial velocity of the cluster (-78.0 km/s).
| Absolute magnitudes and kinematic properties of Cepheids
The relative solar motions, Oort constants, velocity ellipsoidparameters, and zero points of the PL and PLC relations are determinedby performing a maximum likelihood statistical parallax analysis ofclassical Cepheids. The analysis is based on 90 proper motions drawnfrom the list of Karimova and Pavlovskaya (1981) and on the analyticalapproach of Hawley et al. (1986). The results give a best estimate forthe mean absolute magnitude of Cepheids which, for the Cepheid absolutemagnitude zero point, is highly stable against refinements in themathematical technique and against additional Cepheid proper motion dataof quality similar to the existing proper motions. The solar motioncomponents along the axes of uncertainties less than + or - 2 km/s arealso determined.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Delphinus |
| Right ascension: | 20h50m12.69s |
| Declination: | +03°39'08.4" |
| Apparent magnitude: | 9.175 |
| Proper motion RA: | -3.4 |
| Proper motion Dec: | -6.8 |
| B-T magnitude: | 10.149 |
| V-T magnitude: | 9.256 |
Catalogs and designations:
|
