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Photometry of Type II Cepheids. II. The Short-Period Stars
We present 668 new photometric observations for 24 Cepheids with periodsless than 3 days. Most of the stars are probable type II Cepheids, butwe have included some type I Cepheids for comparison. A discussion ofthe Fourier parameters of the light curves leads to the conclusion thatthey can be used to distinguish among the several types of light curvesfound among the type II stars but are of limited usefulness fordistinguishing between type I and type II Cepheids. The pulsationalstability is investigated by searching for long-term changes in thelight-curve shapes, period changes, and light-curve scatter. In terms ofthese parameters, the pulsation is more stable than those that werefound for the long-period stars, but for each there are several starsthat show unusually large effects. However, there does not seem to beany obvious difference in light-curve stability of type II Cepheidscompared with type I Cepheids.
| The Spectra of Type II Cepheids. I. The Hα Line in Short-Period Stars
We present 88 Hα profiles for 24 pulsating variable stars withperiods between 1 and 3 days in order to explore the behavior of thisline in type II as compared with classical Cepheids. Surprisingly, largevelocity differences were found between Hα and the metal lines insome type II Cepheids. Strong emission was observed in three stars, VZAql, NW Lyr, and V439 Oph, while line filling by incipient emission ispresent in seven others. All of the stars with emission and most withincipient emission belong to Diethelm's AHB2 class, and the emission isassociated with the secondary bump on the rising branch of the lightcurve. Two stars, BF Ser and MQ Aql, show doubling of the core nearmaximum light, and asymmetry of the line is noted in some spectra.Based in part on observations obtained with the Apache Point Observatory3.5 m telescope, which is owned and operated by the AstrophysicalResearch Consortium.
| Astrophysics in 2002
This has been the Year of the Baryon. Some low temperature ones wereseen at high redshift, some high temperature ones were seen at lowredshift, and some cooling ones were (probably) reheated. Astronomerssaw the back of the Sun (which is also made of baryons), a possiblesolution to the problem of ejection of material by Type II supernovae(in which neutrinos push out baryons), the production of R CoronaeBorealis stars (previously-owned baryons), and perhaps found the missingsatellite galaxies (whose failing is that they have no baryons). A fewquestions were left unanswered for next year, and an attempt is made todiscuss these as well.
| Period Changes in Galactic Classical Cepheids. Slow Evolution of Long-Period Cepheids
We compared period changes derived from O-C diagrams for 63 classicalCepheids from our Galaxy with model calculations. We found that forCepheids with log P > 1.0 the observed changes are smaller thanpredicted values, except variable SZ Cas. However some of the firstovertone Cepheids, particularly EU Tau and Polaris, change its periodmuch faster than it follows from theory. Summary of the known data onperiod changes in Cepheids from the Galaxy and from the MagellanicClouds (previous papers) leads to conclusion that none of the 999Cepheids is undergoing the first crossing of the instability strip. Alsothe observed period changes for long-period Cepheids are a few timesslower than predicted by the models. These results imply that muchlarger fraction of helium is burned in the Cepheid stage than it ispredicted by models.
| Synergies in Variability Studies of Stars, Supernovae, and Active Galactic Nuclei
We introduce some basic concepts concerning multiband investigations ofvariable sources such as stars, supernovae, and active galactic nuclei.These topics have been widely discussed during the internationalworkshop Variability with Wide Field Imagers. We summarize the mainconclusions of this Workshop and briefly outline possible avenues forfuture broad collaborations.
| 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.
| Détermination des rayons de Céphéides. V. Vitesses radiales et dimensions de 22 Céphéides galactiques. Determination of the radii of Cepheids V. Radial velocities and dimensions of 22 galactic Cepheids
We present radial velocity data for 22 galactic Cepheid stars obtainedwith Coravel spectrometer. Continuous observation over several years hasenabled us to obtain 852 individual velocities covering all the phasesof the pulsation. The mean number of measurements per star is 39,ranging from 20 to 113. For each star radial velocity versus phasediagrams have been fitted by analytical relation, and the stellar radiusvariation has been derived by integration of this relation over thewhole period. Using recent ubv photometry of the literature and velocitycurves, we have calculated the radii of the stars using a method basedon the Baade-Wesselink concept. For these 22 Cepheids we give a linearlogarithmic period-radius relation with a range of 2,4 to 45 days. Lesobservations ont été effectuées àl'Observatoire de Haute-Provence (CNRS). Le tableau 1 est disponibleseulement sous forme électronique au CDS via ftp àcdsarc.u-strasbg.fr (130.79.128.5) ou viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Theoretical interpretation of the metallic line doubling phenomenon in the variable star RR Lyrae.
A series of nonlinear nonadiabatic models for the variable star RR Lyraeare calculated and FeII and BaII line profiles are reconstructed inorder to study the recently detected line doubling phenomenon. We foundthe doubling in both absorption lines, which is proved to be a result ofa shock passage through the line formation region (LFR), in agreementwith the Schwarzschild (1952) mechanism. It is shown that a number ofshock waves of different amplitudes and different physical origins formin the RR Lyrae atmosphere, but only the most strong one is responsiblefor the observed line doubling. In the FeII and BaII LFR, the associatedshock undergoes a very rapid acceleration, which provokes a suddenappearance of a new absorption component near zero velocity. It is foundthat the shock is first receding for the observer, then becomes almoststationary during the doubling phenomenon, and then advances. Thesethree phases of the shock evolution are well confirmed by recent highresolution observations (Chadid and Gillet, 1996A&A...308..481C),showing a similar complex doubling evolution of the line profile.
| H alpha profile variations in the long-period Cepheid L Carinae
We present Hα spectra of the 35.5d period Cepheid l Carinaethroughout several cycles during 1994 and 1995. A weak Hα emissionfeature is present at nearly all phases, which is unusual for classicalCepheids. This emission appears both redward and blueward of theabsorption feature at different phases.
| 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
| Linear and nonlinear models of the pulsating post-AGB star SAO 96709.
We have performed linear and nonlinear modelling of the pulsatingpost-AGB star SAO 96709 (=IRAS07134+1005=HD56126). A recentspectroscopic analysis of this object gives interesting information onthe atmospheric dynamics and propagation of shock waves, providing agood test of pulsational models. We show that adopting the photosphericand spectroscopic parameters inferred for this object, one can reproducethe main features observed and reconcile the presence of relativelystrong shock waves with small variations of the light curve.
| A first optical spectroscopic monitoring of the post-AGB star SAO 96709=IRAS 07134+1005: pulsation and shock waves.
We have performed a spectroscopic monitoring of the F5I "post-AGB" starSAO 96709 on the Hα and NaD spectral regions in order to studyatmospheric motions that could be associated with shock wave propagationthroughout the stellar atmosphere. Twenty-one Hα spectra andseventeen NaD spectra were obtained as regularly as possible, over a 14month interval. We find that the Hα, NaD, and other line profilesare strongly variable on a timescale of a few days. The 5853.688A BaIIand 6587.622A CI lines also reveal a variation in their radialvelocities. Fourier analysis of these variations yields one main periodof 27.3 days and three secondary ones of 32.9, 11.9 and 7.1 days. TheHα profiles and the velocity variations are good evidence forcomplex atmospheric dynamics that are related to shock wave propagationthroughout the atmospheric layers. These observed spectral features arein good agreement with the recently found photometric variability andpoint to a pulsating nature for SAO 96709 = HD 56126 = IRAS 07134+1005.
| Pulsating motions and turbulence in δ Cephei.
A nonlinear nonadiabatic pulsational model of the classical Cepheid starδ Cephei with an extended atmosphere was computed to firstlydetermine the dynamical structure of the atmosphere and secondly tointerpret the variation of FWHM with phase of the FeI lineλλ5576.0883. The presence of three bumps within theturbulence curve as put into evidence by Breitfellner and Gillet (1993),is examined. The effect of predicted shock waves crossing the FeI lineformation region is specified. Our detailed model shows that the truelevel of turbulence velocity is roughly two times smaller than the upperlimit given by these authors but is close to the microturbulencemeasured by van Paradijs (1971). The first peak observed just after theluminosity maximum (phase φ=0.0) in the FWHM is mainly theconsequence of large velocity gradients induced by the pulsating motionin presence of a strong shock wave which have been neglected in allprevious works. No additional small-scale motion field (microturbulence)is needed at this phase. The strongest peak of the FWHM curve (aroundφ=0.77) which occurs at the same time as the second large amplitudeshock, can only be interpreted by a strong increase of the turbulence.It seems that a large part of this turbulence increase is due to theatmospheric compression although a shock wave amplification effect isalso plausible. Our best fit of observed and theoretical FeI profilessuggests a rotational velocity v_rot_ sin i close to 7.5+/-2km/s.Moreover, because the FWHM is not affected by non-LTE effects, we haveonly one basic dependent parameter left: the turbulent velocity. Thusour result is strong in the framework of our semi-quantitative approach.
| A spectroscopic study of the pulsating star BL Her.
Not Available
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| The Period-Gravity Relation for Radially Pulsating Variable Stars
Abstract image available at:http://adsabs.harvard.edu/abs/1995AJ....110.2361F
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| The shock wave propagation effects in BL Herculis. II. Nonlinear model and theoretical profile of Hα
A full-amplitude pulsating model for BL Her is generated, and theHα formation in the shocked extended atmosphere is studied in thenon-LTE approximation. Theoretical profiles represent qualitatively wellthe observed Hα variation discovered recently by Gillet et al.(1994). Like the RR Lyr model, the BL Her model developed a veryextended atmosphere, periodically affected by a series of weak andstrong shock waves. Three of them, with amplitudes below 40km/s, mergenear the surface one by one into one strong shock with the totalamplitude {DELTA}U=~110km/s, which causes the observed line doubling.Just before this phase the shock heating provokes a short-livingemission. It is shown that in BL Her the shock, strong enough to producea prominent emission, forms deeper than in RR Lyr, but higher than in WVir model. This can explain why the observed emission strength in BL Heris intermediate between that in W Vir and RR Lyr stars.
| 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
| Summary of Delta S metallicity measurements for bright RR Lyrae variables observed at Lick Observatory and KPNO between 1972 and 1987
From 1972 to 1987 we conducted a survey of the metallicity of faint RRLyrae variables in the Galactic halo, using the 'Butler system' of DeltaS. As part of the calibration of this program, we made approximately 500observations of bright RR Lyraes as abundance standards. We summarizeall the observations of these bright field RR Lyraes and provideaveraged values for the metallicity parameter Delta S. These averagesrepresent the most precise definition of the Butler system for themeasurement of RR Lyrae metallicities. The typical mean error is 0.3units in Delta S, which corresponds to 0.05 dex in (Fe/H). We alsobriefly discuss the weaknesses in the determination of (Fe/H) from DeltaS.
| Post-main-sequence and POST red giant branch variables with pulsation periods less than one day
Post-main-sequence (mass 1 to 3 solar masses) and post-giant branch (0.5to 1 solar mass) pulsators are discussed on the basis of four color andH beta light curves published elsewhere. The post-main-sequencevariables, called ultrashort period cepheid (USPC) (delta Sct), pulsatein the fundamental and first harmonic modes of radial pulsation and, inmany cases, in nonradial modes. The variables for which photometryallows accurate, luminosity estimates and are known to pulsatesimultaneously in the fundamental and first harmonic or in thefundamental mode alone, define a PL relation (MV = -2.80 logP - 0.60, fundamental). It is notable that the slope of this relation isin the range of slopes found for classical cepheids. Accurate Vphotometry is lacking for many of the variables known as 'anomalouscepheids', but the available data divide them into low mass,pseudocepheids (BL Her and W Vir stars) and post-main-sequence USPC(delta Sct) variables. Four USPC in NGC 5053 and six in NGC 6466, forwhich accurate photometry is available, give remarkably consistentmoduli of 16.06 +/- 0.05 and 15.98 +/- 0.08 mag, respectively, for theclusters, in which they are blue stragglers similar to SX Phe inKapteyn's star group. The assumption that the four post-giant branchvariables, called VSPC (RR Lyr), S Ari, SU Dra, and ST Leo in Kapteyn'sstar group and RR Lyr in the Groombridge 1830 group, are physicalmembers of these groups and share their V-velocities, leads to acalibration of the photometry for the derivation of reddening,luminosity, and heavy element abundance of 45 field variables. Theresulting reddenings are consistent with values obtained by othermethods and the metallicities are consistent with the most accuratelyavailable spectroscopic determinations of delta S and of Ca II K. Theluminosities of the bulk of the variables confirm Sandage's (1993)relation between MV and (Fe/H). Four or five of the fieldvariables are probably binary, including BB Vir which Kinman &Carreta (1992) have independently noted as double. The PL relation forUSPC (delta Sct) variables intersects the horizontal branch (HB) near P= 0.3d and at least two field very short period cepheid (VSPC) (RR Lyr)star, FW Lup (0.484 d) and ST Pic (0.486 d) may be first overtonepulsators of the USPC (delta Sct) variety. A dozen field VSPC (RR Lyr)stars populate a (Fe/H), MV relation with the same slope asthe other stars but displaced 0.7 mag toward higher luminosities. Theonly cluster variable found to populate this diplaced relation is No. 9in 47 Tuc, although ST Vir, which may be a member of the Arcturus group,should also be considered. The elevated luminosities are unlikely to becaused by either evolution or errors in the photometric indices. Apossible source of these apparently young VSPC(RR Lyr) variables withhalo metallicity is in second (or third) generation globular clustersformed during an episodic collapse of the galaxy that produced metalpoor stars but in a dynamical situation that hastened the disruption ofthe clusters, currently formed, before the still older globularclusters, created under conditions that have kept them in a moredisruptive free environment.
| The shock wave propagation effects in BL Herculis. 1: The hydrogen alpha profile
For the first time, high spectral resolution observations of thehydrogen alpha profile of BL Her, obtained with a modern detector,during the whole pulsating period are presented. It clearly appears thatthe profile evolution is very similar to that observed in RR Lyrae starswhich are localized just below the BL Herculis stars in the PopulationII instability strip. No secondary emission is detected. The pulsationhas the form of a running wave. The shock wave associated with theemission is accelerated during its propagation between the photosphereand the region where the hydrogen line is formed. The effect of the 2:1resonance between the fundamental mode and the second overtone is wellobserved on the photospheric radius and acceleration curves.
| A photometric study of XX Virginis and V716 Ophiuchi
We present Stroemgren photometry of the two Population II variables XXVirginis and V716 Ophiuchi. An analysis of the photometry yields thefollowing physical parameters of the variables: for XX Vir average valueof Teff = 6410 K, (Fe/H) = -2.0, and average value of log g =1.95; for V716 OPH average value of Teff = 6450 K, (Fe/H) =-2.1, and average value of log g = 1.67. The average value of log gvalues of these two metal-poor variables are considerably smaller thanfor the metal-strong variable BL Herculis (average value of log g =2.37). The big surprise in this investigation is that the surfacegravity of V716 Oph (P = 1.12 days), the shorter-period variable, issmaller than the surface gravity of XX Vir (P = 1.35 days), the longerperiod variable. With the aid of the P x (square root of rho) = Qrelation we derive a semitheoretical P-L relation for the Type IICepheids of the form Mv = -1.88 log P + 0.13. This expressionis in rough agreement (within the uncertainties of many quantities usedin deriving the expression) with the observational data. The relativelygentle slope of the P-L relation (compared with the slope of the P-Lrelations of other pulsating stars) is probably a consequence of thefact that the masses of the Type II Cepheids are constant or nearlyconstant, independent of period, and a large variation of their M/Rvalues with period.
| Period-Radius and Period Luminosity Relations for the Classicla Cepheids. I.
The radii of 43 cepheids are computed by the method proposed by theauthor. A relation between the period and the radius for classicalcepheids is derived: log R = (11.9686 +/- 0.0216) + (0.7728 +/-0.197)*log P, where radius is in cm and period is in days.
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Osservazione e dati astrometrici
| Costellazione: | Ercole |
| Ascensione retta: | 18h01m09.22s |
| Declinazione: | +19°14'56.7" |
| Magnitudine apparente: | 10.23 |
| Moto proprio RA: | -4.7 |
| Moto proprio Dec: | -11.9 |
| B-T magnitude: | 10.603 |
| V-T magnitude: | 10.261 |
Cataloghi e designazioni:
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