Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
New homogeneous iron abundances of double-mode Cepheids from high-resolution echelle spectroscopy
Aims.We define the relationship between the double-mode pulsation ofCepheids and metallicity in a more accurate way, determine the empiricalmetallicities of double-mode Cepheids from homogeneous, high-resolutionspectroscopic data, and study of the period-ratio - metallicitydependence. Methods: The high S/N echelle spectra obtained with theFEROS spectrograph were analyzed using a self-developed IRAF script, andthe iron abundances were determined by comparing with synthetic spectraassuming LTE. Results: Accurate [Fe/H] values of 17 galactic beatCepheids were determined. All these stars have solar or slightlysubsolar metallicity. Their period ratio (P1 / P_0) showsstrong correlation with their derived [Fe/H] values. The correspondingperiod ratio - metallicity relation has been evaluated.Based on observations taken with the ESO 2.2-m telescope at La Silla,Chile (Proposal 073.D-0072) and the 1.82 m telescope at David DunlapObservatory, Canada.
| Cepheid parallaxes and the Hubble constant
Revised Hipparcos parallaxes for classical Cepheids are analysedtogether with 10 Hubble Space Telescope (HST)-based parallaxes. In areddening-free V, I relation we find that the coefficient of logP is thesame within the uncertainties in our Galaxy as in the Large MagellanicCloud (LMC), contrary to some previous suggestions. Cepheids in theinner region of NGC4258 with near solar metallicities confirm thisresult. We obtain a zero-point for the reddening-free relation and applyit to the Cepheids in galaxies used by Sandage et al. to calibrate theabsolute magnitudes of Type Ia supernova (SNIa) and to derive the Hubbleconstant. We revise their result for H0 from 62 to 70 +/-5kms-1Mpc-1. The Freedman et al. value is revisedfrom 72 to 76 +/- 8kms-1Mpc-1. These results areinsensitive to Cepheid metallicity corrections. The Cepheids in theinner region of NGC4258 yield a modulus of 29.22 +/- 0.03 (int.)compared with a maser-based modulus of 29.29 +/- 0.15. Distance modulifor the LMC, uncorrected for any metallicity effects, are 18.52 +/- 0.03from a reddening-free relation in V, I; 18.47 +/- 0.03 from aperiod-luminosity relation at K; 18.45 +/- 0.04 from aperiod-luminosity-colour relation in J, K. Adopting a metallicitycorrection in V, I from Macri et al. leads to a true LMC modulus of18.39 +/- 0.05.
| 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.
| Multiperiodicities from the Hipparcos epoch photometry and possible pulsation in early A-type stars
A selection criterion based on the relative strength of the largestpeaks in the amplitude spectra, and an information criterion are used incombination to search for multiperiodicities in Hipparcos epochphotometry. The method is applied to all stars which have beenclassified as variable in the Hipparcos catalogue: periodic, unsolvedand microvariables. Results are assessed critically: although there aremany problems arising from aliasing, there are also a number ofinteresting frequency combinations which deserve further investigation.One such result is the possible occurrence of multiple periods of theorder of a day in a few early A-type stars. The Hipparcos catalogue alsocontains a number of these stars with single periodicities: such starswith no obvious variability classifications are listed, and informationabout their properties (e.g., radial velocity variations) discussed.These stars may constitute a new class of pulsators.
| 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.
| Masses for Galactic Beat Cepheids
Accurate mass determinations for Cepheids may be used to determine thedegree of excess mixing in the interiors of their main-sequenceprogenitors: the larger the excess mixing, the larger the luminosity ofthe Cepheid of a given mass, or the smaller the mass of a Cepheid withgiven luminosity. Dynamical masses determined recently for a few Cepheidbinaries indicate excess mixing somewhat stronger than thatcorresponding to the convective overshoot models by Schaller et al. BeatCepheids can be used similarly to test main-sequence mixing in stellarinteriors. The period ratios for beat Cepheids depend on luminosity,Teff, heavy element abundance, and mass. By comparingpulsational models and the observationally derived luminosity,Teff, metallicities, and period ratios it is possible toobtain masses for these stars, the so-called beat masses. With the oldopacities masses much smaller than the evolutionary masses wereobtained. With the new OPAL opacities a beat mass close to the dynamicalmass was obtained for the binary beat Cepheid Y Carinae, showing that itis now possible to obtain reliable beat masses. In this paper, wedetermine beat masses for seven Galactic beat Cepheids for whichphotometric and spectroscopic data are available. We find an averagemass around 4.2+/-0.3 Msolar for these stars, though theactual error limits for each star may be larger mainly because ofuncertainties in E(B-V) and the heavy element abundances. (As derivedspectroscopically, beat Cepheids are in general metal-poor, with-0.4<~[Fe/H]<~0.0). The relation between the derived beat massesand the luminosities again indicates excess mixing that is somewhatlarger than that corresponding to the models by Schaller et al.
| 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.
| 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 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.
| 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.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The galactic double-mode Cepheids. II. Properties of the generalized phase differences.
By considering the least-squares fits of the double-mode Cepheid lightcurves discussed in Paper I we defined their properties by their Fourierparameters and generalized phase differences G_i,j_. When plotting thelatter quantities as a function of the order, the second order terms areconfined in the region just below 3π/2; the third order terms haveπ/2
| The galactic double-mode Cepheids. I. Frequency analysis of the light curves and comparison with single-mode Cepheids.
We submitted the available photometric V data of all the known galacticDouble Mode Cepheids (DMCs) to a careful frequency analysis with the aimof detecting in each case the importance of the harmonics and of thecross coupling terms. For each object, starting from different datasubsets, we progressively built a homogenous set of data, checking theconsistency of the results step by step. It was demonstrated that eachstar displays a different content, showing that no a priori fit can beapplied. Up to 4 harmonics were found for the fundamental radial mode(F); in every case, 2 harmonics were found for the first overtone radialmode (1O). We also proceeded to a preliminar analysis of the Fourierparameters of the DMC light curves and we found a very close similaritybetween i) the light curves of the classical Cepheids and those of theF-mode of the DMCs; ii) the light curves of the s-Cepheids and those ofthe 1O-mode of the DMCs. The analysis of DMC light curves offers thepossibility of unifying the light curves of classical and s-Cepheids.The case of the unique DMC CO Aur is also discussed.
| 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.
| Photoelectric Observations of Southern Cepheids in 1995
Not Available
| Photoelectric Ubvri/c Photometry of Southern Cepheids
Not Available
| Chemical composition of selected double-mode Cepheids and the P_1_/P_0_ - [Fe/H] relation.
We present the results of the detailed spectroscopic investigation ofthree double-mode Cepheids: EW Sct, VX Pup and BQ Ser. The abundanceanalysis has shown: (1) Carbon is deficient (the abundance normalized tothe iron content with respect to the solar value). (2) This carbondeficiency is accompanied by nitrogen overabundance and normal oxygencontent. (3) α - and iron group elements with little exceptionshow solar ratio [M/Fe]. (4) The heavy elements in EW Sct areunderabundant. (5) Normal iron abundance for EW Sct ([Fe/H]=-0.08) andmetal deficiency for VX Pup ([Fe/H]=-0.39) and BQ Ser ([Fe/H]=-0.36)strongly support the existence of a P_1_/P_0_-metallicity relation, asfirst discussed in work of Andrievsky et al. (1993).
| Nonlinear properties of double-mode pulsators
The generalized Fourier phase difference between the components of amultiperiodic oscillation is presented, and it is applied to thedouble-mode Cepheid light curve parameters. It is shown that thegeneralized phase difference of the combination frequency terms can giveuseful information on the nonlinear characteristics of the pulsation andon the possible presence of resonances between pulsation modes as in thecase of the classical phase differences used for single-mode pulsators.Furthermore, it is shown the utility of the qualitative interpretationof the main characteristics of the Fourier phases in the framework ofthe nonlinear adiabatic treatment of double-mode pulsation on theanalogy of single-mode pulsation.
| Opacity, metallicity, and Cepheid period ratios in the galaxy and Magellanic Clouds
Linear pulsation calculations are employed to reproduce the bump Cepheidresonance (P2/P0 = 0.5 at P0approximately equal to 10 days) and to model, individually, theP1/P0 period ratios for the dozen known Galacticbeat Cepheids. Convection is ignored. The results point to a range ofmetallicity among the Cepheids, perhaps as large as 0.01 approximatelyless than Z approximately less than 0.02, with no evidence for any starexceeding Z = 0.02. We find masses and luminosities which range from Mapproximately less than 4 solar mass, log(base 10) approximately lessthan 3.0 at P0 approximately equal to 3 days to Mapproximately less than 6 solar mass, log(base 10) L approximatelygreater than 3.5 at P0 approximately equal to 10 days.Similar parameters are indicated for the P0 approximatelyequal to 10 days Cepheids in the LMC and SMC, provided that theresonance for these stars occurs at a slightly longer period,P0 days, as has been suggested in the literature. Ourcalculations were performed mainly using OPAL opacities, but also withnew opacities from the Opacity project (OP). Only small differences werefound between the OPAL results and those from OP. Finally, somesuggestions are made for possible future work, including evolution andpulsation calculations, and more precise observations of Cepheids in theMagellanic Clouds.
| New radial velocities for classical cepheids. Local galactic rotation revisited
New centre-of-mass radial velocities are calculated for 107 classicalcepheids from CORAVEL observations. We generally determine thesevelocities from four to six measurements carefully spaced in phase, byfitting a "typical" radial velocity curve or the mirror image of thelight curve. A decomposition in Fourier series is used for stars withmore than 10 measurements. Distances are then computed through aperiod-luminosity-colour relation for 278 classical cepheids with knownradial velocity, and an axisymmetric galactic rotation model is appliedto the sample, using a generalised non-linear least square method withuncertainties on both the velocities and the distances. The bestresults, with a rotation curve modelled as a third order polynomial,are: Rsun_=8.09 +/-0.30 kpc, A=15.92 +/-0.34 km/s/kpc, 2ARsun_=257 +/-7 km/s, A2=d^2theta(R)/d R^2^=-3.38+/-0.38 km/s/kpc^2^, A3=d^3theta(R)/d R^3^=1.99 +/-0.62km/s/kpc^3^, u_0_=9.32 +/-0.80 km/s, v_0_=11.18 +/-0.65 km/s. The effectof modifying the distance scale of cepheids, the absorption coefficientor the fitting procedure algorithm are examined. It appears that theproduct 2 A Rsun_ is very robust towards these changes. Theextended sample of classical cepheids with known radial velocitypresented in this paper seems to imply a higher value for A thananterior studies. The radial velocity residuals show a systematic k-termof about 2 km/s. New evidence from cluster cepheids excludes anintrinsic cause for this shift, and a dynamical cause is proposed from acomparison with a N-body simulation of the Galaxy. The simulation showsthat a systematic bias of this magnitude is typical. The structure ofthe local residual velocity field is examined in some detail.
| An Investigation of the Double-Mode Cepheid Tu-Cassiopeiae - Part One - Atmospheric Parameters and Chemical Composition
Abstract image available at:http://adsabs.harvard.edu/abs/1993MNRAS.265..257A
| Color indices of double-mode Cepheids
Separate light curves of both oscillations are constructed for all thedouble-mode Cepheids. Analysis of 4600 photoelectric UBVRI observationsshows that the shape of the curves changes with a period equal to theperiod of the other oscillation. Data on amplitude variations of colorindices confirm an earlier conclusion that divided the group ofdouble-mode Cepheids into two subgroups.
| Amplitudes of light curves of double-mode Cepheids
Maximum and minimum amplitudes of both oscillations of all the 14 knowndouble-mode Cepheids (DMCs) are determined in B, V, R, and I filters.Mathematical and graphical relations between amplitudes, betweenamplitudes and periods, and between amplitudes and wavelength are given.Application of the method of principal components showed that the DMCgroup can be separated into two subgroups: long-period DMCs andshort-period DMCs, which are probably associated genetically withs-Cepheids and single-mode classical Cepheids, respectively.
| A catalogue of Fe/H determinations - 1991 edition
A revised version of the catalog of Fe/H determinations published by G.Cayrel et al. (1985) is presented. The catalog contains 3252 Fe/Hdeterminations for 1676 stars. The literature is complete up to December1990. The catalog includes only Fe/H determinations obtained from highresolution spectroscopic observations based on detailed spectroscopicanalyses, most of them carried out with model atmospheres. The catalogcontains a good number of Fe/H determinations for stars from open andglobular clusters and for some supergiants in the Magellanic Clouds.
| Light curves of double-mode Cepheids
Elements of the light variation of all known double-mode Cepheids arespecified on the basis of an analysis of about 4600 photoelectric UBVRIobservations. The separate light curves for each oscillation for all thedouble-mode Cepheids are obtained. The light curves for each oscillationof the double-mode Cepheids show significant systematic changes duringthe period of the other oscillation.
| Analyse des photometrischen Verhaltens von GZ Carinae.
The double mode cepheid GZ Car has been investigated by means ofphotographic observations on plates of the southern sky patrols ofBamberg and Sonneberg Observatories and photoelectric measurements takenfrom literature. The author estimates the long time behaviour of the twopulsation modes. The first overtone shows instabilities as compared tothe fundamental mode and incoherences of phase.
| 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
| Precise Fourier Decomposition Parameters for Classical Cepheids
Abstract image available at:http://adsabs.harvard.edu/abs/1988A&A...196..159A
| Classical Cepheids - Their distances and space distribution
A simplified method of calculating classical Cepheid distances isproposed. It is based on photometric data, without the use of thereddenings. By means of results obtained in this way the followingproblems are discussed: Cepheid double and more numerous aggregates andproperties of the cluster and association Cepheid.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Carena |
| Ascensione retta: | 10h20m20.37s |
| Declinazione: | -59°22'35.8" |
| Magnitudine apparente: | 10.206 |
| Moto proprio RA: | -4.1 |
| Moto proprio Dec: | 5 |
| B-T magnitude: | 11.39 |
| V-T magnitude: | 10.304 |
Cataloghi e designazioni:
|
