Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Delta Scuti, SX Phoenicis, and RR Lyrae Stars in Galaxies and Globular Clusters
The distances to four galaxies and two globular clusters which arederived with the aid of period-luminosity and period-color relations of? Scuti and SX Phe stars are compared to the distances derived byother methods, in particular RR Lyrae stars. We examine the luminositiesof horizontal branch or RR Lyrae stars in Oosterhoff I and II globularclusters. Observational data from a variety of sources indicate adiscontinuous jump of ~0.2 mag in the luminosities of RR Lyrae variablesat [Fe/H] ? -1.5 as we transition from Oosterhoff I to Oosterhoff IIclusters. If Oosterhoff I clusters have RR Lyrae variables with averageM V values of M V = 0.53 mag at [Fe/H] = -1.5, itimplies that RR Lyrae stars in Oosterhoff II clusters average MV values are ~0.34 mag. Unlike the Oosterhoff I clusterswhich show an increase in the V luminosity of RR Lyrae stars as [Fe/H]becomes smaller, little or no change in the V luminosity of RR Lyraevariables is evident in Oosterhoff II clusters in the interval of [Fe/H]from -1.5 to -2.2. We find distance moduli found with RR Lyrae variablesagree to <=0.04 mag with those found with the ? Scuti and/or SXPhe variables if the M V values of RR Lyrae stars above areadopted. We find evidence of recent star formation (presence of nearsolar-metallicity ? Scuti stars with ages of 150 Myr to 1 Gyr) inthe Large Magellanic Cloud (LMC), Small Magellanic Cloud, and thecentral region of the Fornax (dSph) galaxies. We also find an olderpopulation of metal-poor ? Scuti variables (SX Phe stars) in theLMC and Fornax galaxies. The Carina dSph is unique in that only an oldpopulation of metal-poor ? Scuti variables is evident. No evidenceof recent ? Scuti star formation is found. The minimum periodsobserved for the SX Phe variables (blue stragglers) in the globularclusters M55 and ? Cen indicate that they could have been formedin a burst of metal-poor single star formation in the last 2.9-6 Gyr. Ifformed by the more acceptable scenario of stellar mergers, it is likelythat the merged remnant resembles a normal star in a relatively advancedstage of main-sequence evolution with an enriched He core and ordinaryHe envelope. We present equations to calculate intrinsic-color indicesfor ? Scuti, SX Phe, and RR Lyrae stars at mean light. Finally, weshow that the fundamental-radial-pulsating stars (? Sct and SX Phevariables) have larger average light amplitudes than the first-overtonepulsating variables. The fundamental metal-poor variables (SX Phe stars)have the largest average and individual amplitudes.
| Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
| GSC 3203-0780 - A new Algol-type eclipsing binary.
Not Available
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Photoelectric Maxima of Selected Pulsating Stars
Not Available
| The Monoperiodic δ Scuti Star UY Camelopardalis: An Analog to SX Phoenicis and RR Lyrae Variables
We present the results of a 4 year photometric study of thehigh-amplitude δ Scuti (HADS) star UY Camelopardalis. Analysis ofthe available data from 1985 to 2003 shows that UY Cam is monoperiodic.Fourier solutions for individual data sets do not reveal period changesin the star. Although forced parabolic fits to the O-C residualsindicate a measurable period change, the distribution of the data pointsin the O-C diagram and the deviations between fits and observationssuggest that the existence of the period change still has not beenestablished. We demonstrate the presence of amplitude variations fromcycle to cycle and on longer timescales. The pulsation amplitude seemedto change from 1985 to the 2000s, but it remained constant in 2000-2003.UY Cam is located in the upper portion of the δ Scuti instabilityregion. Its photometric properties and estimated physical parametersreveal that UY Cam is an interesting object in terms of its poormetallicity, long period, high luminosity, low surface gravity, andlarge radius among the HADS stars. UY Cam could be a younger (0.7+/-0.1Gyr) Population I HADS star with low metal abundance (Z=0.004) evolvingon its post-main-sequence shell hydrogen burning evolutionary phase. UYCam intervenes among the Population I/II HADS and type c RR Lyraevariables. These characteristics suggest the star to be an analog ofHADS, SX Phoenicis, and RRc variables.
| On the Red Edge of the δ Scuti Instability Strip
The δ Scuti star catalogue is used to derive the observationallocations of such stars on the HR diagram. The theoretical andobservational instability strips are compared to check the theoreticalred edge obtained by considering non-local time-dependent convectiontheory. The observational instability strip almost overlaps with thetheoretical one, but the observed blue and red envelopes are hotter thanthe theoretical edges. The distribution of δ Scuti stars in thepulsation strip is not uniform.
| delta Scuti and related stars: Analysis of the R00 Catalogue
We present a comprehensive analysis of the properties of the pulsatingdelta Scuti and related variables based mainly on the content of therecently published catalogue by Rodríguez et al.(\cite{retal00a}, hereafter R00). In particular, the primaryobservational properties such as visual amplitude, period and visualmagnitude and the contributions from the Hipparcos, OGLE and MACHOlong-term monitoring projects are examined. The membership of thesevariables in open clusters and multiple systems is also analyzed, withspecial attention given to the delta Scuti pulsators situated ineclipsing binary systems. The location of the delta Scuti variables inthe H-R diagram is discussed on the basis of HIPPARCOS parallaxes anduvbybeta photometry. New borders of the classical instability arepresented. In particular, the properties of the delta Scuti pulsatorswith nonsolar surface abundances (SX Phe, lambda Boo, rho Pup, delta Deland classical Am stars subgroups) are examined. The Hipparcos parallaxesshow that the available photometric uvbybeta absolute magnitudecalibrations by Crawford can be applied correctly to delta Scutivariables rotating faster than v sin i ~ 100 km s{-1} withnormal spectra. It is shown that systematic deviations exist for thephotometrically determined absolute magnitudes, which correlate with vsin i and delta m1. The photometric calibrations are found tofit the lambda Boo stars, but should not be used for the group ofevolved metallic-line A stars. The related gamma Dor variables and thepre-main-sequence delta Scuti variables are also discussed. Finally, thevariables catalogued with periods longer than 0fd 25 are examined on astar-by-star basis in order to assign them to the proper delta Scuti, RRLyrae or gamma Dor class. A search for massive, long-period delta Scutistars similar to the triple-mode variable AC And is also carried out.
| 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.
| A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The delta Scuti Star GSC 2985-01044
GSC 2985-01044 is a delta Scuti star with a period of 0.0933584 days anda V-magnitude range of 11.85-12.05 its light curve is slightly variable.The location, space motion, and other properties of this star indicatethat it is a higher amplitude delta Scuti star (or ``dwarf Cepheid'')that is a member of the old disk population. The problem of determiningthe local space densities of the various populations of the higheramplitude delta Scuti stars is discussed.
| HIPPARCOS parallaxes and period-luminosity relations of high-amplitude delta Scuti stars
Hipparcos parallaxes of high-amplitude delta Scuti stars are used toderive a period-luminosity relation with a scatter of about +/-0.1 mag,which is independent from photometric calibrations to absoluteluminosities. Comparisons with several P-L relations from the literatureshow satisfactory agreement, and all deviations from the Hipparcos meanrelation can be explained by uncertainties in the data available beforeHipparcos. Hipparcos data for a few stars of relatively small anduncertain parallaxes indicate that they may have systematically very lowluminosity. However, briefly discussing Lutz-Kelker corrections andconsidering the full sample of high-amplitude delta Scuti stars, it isconcluded that this sample is homogeneous and has similar basic physicalproperties as the ``normal'' low-amplitude delta Scuti stars. It isemphasized that the Hipparcos P-L relation defines a new distance scalewhich is independent from those of the classical Cepheids and RR Lyraestars. Therefore, observations of high-amplitude delta Scuti stars canbe used to check fundamental distance determinations to e.g. globularclusters, the Galactic bulge and the Magellanic Clouds.
| Luminosities of SX Phoenicis, Large-Amplitude Delta Scuti, and RR Lyrae Stars
Strömgren _uvbyβ photometry of SX Phoenicis andlarge-amplitude δ Scuti variables is analyzed to determine themean temperatures, metal abundances, and surface gravities of the stars.The mean temperatures and fundamental periods are used in conjunctionwith the pulsation equation and stellar models to derive masses, radii,surface gravities, and M_bol of the variables. The stars exhibit aperiod-luminosity relation. With the aid of Hipparcos trigonometricparallaxes the zero-point of the M_v, p is set. We find M_v = -3.725 logP - 1.933. This P-L relation is utilized to find the M-v values of RRLyrae stars or horizontal-branch stars in globular clusters and theCarina galaxy-objects that contain both SX Phe, and RR Lyrae variables,or horizontal-branch stars. The M_v values of the metal-poor RR Lyraestars are found to be consistent with M_v [Fe/H] calibrations derived bySandage (1993) and by McNamara (1997) from revised Baade- Wesselink M_vvalues. At [Fe/H] = -1.9 M_v is 0.42. Feast and Catchpole (1997)suggestion that M_v = 0.25 at [Fe/H] = -1.9 for RR Lyrae is discussed.This M_v value is too luminous because it makes the (T_eff) of RR Lyraestoo high-well off any (T_eff) = _f (color index) calibration. (SECTION:Stars)
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Spectroscopic survey of delta Scuti stars. I. Rotation velocities and effective temperatures
Projected rotational velocities and effective temperatures for 68 deltaSct stars as well as 41 non-variable stars of similar spectral type andluminosity are presented here. The rotational velocities have beencalculated following the method developed in \cite[Gray (1992)]{ref38}and effective temperatures have been derived using the Balmer lineprofiles. The temperatures obtained from this method are shown to be inreasonable agreement with those calculated using the Infrared FluxMethod (IRFM) or spectrophotometric methods. This result has allowed usto use our temperatures to compare different uvby beta photometriccalibrations. We find that the calibration given by \cite[Moon \&Dworetsky (1985)]{ref72} is the most consistent. In the second part ofthis paper we have studied the relation between the pulsationalproperties (periods and amplitudes) and the physical parameters (v sin iand Teff). Where pulsation modes have been determined, thelow amplitude $\delta$ Scutis tend to be multimode (radial andnon-radial) pulsators, consistent with the theory that non-linearcoupling between modes acts to limit the amplitude in these stars. Wehave compared the distribution of v sin i for low amplitude $\delta$Scutis and non-variable stars. This shows the $\delta$ Scutis have abroader distribution in v sin i suggesting that a high rotation velocitymay favour pulsation. We find that the large amplitude delta Scuti starstend to have longer periods, cooler temperatures and lower rotationvelocities. Given that the large amplitude stars are also relativelyrare all the above are consistent with the hypothesis that these starsare more evolved (sub-giants) than the low amplitude delta Scutis (mainsequence or early post-main sequence).
| Accurate Positions for 38 Variables in a 5x5 deg Field Around BL Lac
Not Available
| Structural Properties of Pulsating Star Light Curves Through Fuzzy Divisive Hierarchical Clustering
Not Available
| Pulsation in high amplitude delta Scuti stars.
It has been pointed out by earlier authors that radial pulsation seemsto be the only type present in high amplitude δ Sct stars, atleast for monoperiodic stars. In order to confirm this or not, we havecollected all the multicolor data available for these stars in theStroemgren and Johnson photometric systems. Then, the type of pulsationhas been analysed on the basis of the phase shifts and amplitude ratiosbetween observed light and colour variations. The results indicate thatall the stars analysed, including both high amplitude δ Sct(Population I) and SX Phe (Population II) stars, are radial pulsators.This is also true for the monoperiodic medium amplitude δ Sctstars analysed.
| A catalogue of variable stars in the lower instability strip.
Identifications, positions, photometry, spectra, some pulsationalfeatures, other astrophysical parameters and literature for 302pulsating variable stars in the lower instability strip, near the ZAMS,are given. About 185 stars have near homogeneous photometric informationin the Stroemgren's uvby-β photometric system. Thiscatalogue/database covers information published until November 1993.
| δ Scuti stars: a new revised list
An extensive and up to date list of δ Sct stars is presented. Thiscatalogue is intended to be a comprehensive review of observationalcharacteristics of all the δ Sct stars known until now, includingstars contained in earlier catalogues together with other new discoveredvariables, covering information published until November 1993. Globalinformation in the form of histograms and diagrams are also shown.
| The visual surface brightness method and the radii of dwarf Cepheids
In order to determine the radii of dwarf Cepheids by applying the visualsurface brightness method, the empirical relationship between F(v) and(b - y) was derived. Seventeen stars of spectral type A to F, where bothangular diameters and uvby beta photometric data are available, wereselected from the literature. A theoretical F(v), (b-y) relation wasderived by using the Kurucz model atmospheres. It was found that thetheoretical relation is strongly dependent upon metallicity and surfacegravity. To demonstrate that the visual surface brightness method is aneffective way to determine the radii of dwarf Cepheids, both theoreticaland empirical relations were applied to seven dwarf Cepheids. The mostreliable result was obtained for AD CMi where the quality of the radialvelocity data is superior.
| Quasi-160-minute oscillation period of Delta Scuti stars
The resonance power spectrum (or commensurability spectrum) computed for217 Delta Scuti stars indicates that the dominant (most commensurate)period for the total set of oscillation periods of these stars is 162.2+ or - 2.8 min. Within the error limits, this period coincidesapproximately with the 160-min period of global oscillations of the sun.
| Fourier decomposition of the light curves of high amplitude Delta Scuti and SX Phe stars
The light curves of monoperiodic, high amplitude ? Scuti and SXPhe stars have been Fourier decomposed in order to study theirstructural properties. The computed phase differences show a trend toincrease with the period similar to the trend observed in short periodCepheids and RR Lyrae stars. There is some evidence of a separation ofthe light curves in two groups, which indicates the presence of twotypes of pulsation. The proposed separation is discussed taking alsointo account the amplitude-amplitude diagrams, and some comparisons withRR Lyrae star light curves are made. For the present there are noevident physical differences between the stars in the two groups whichcan explain the separation.
| Absolute magnitudes and kinematic properties of RR Lyrae stars
A maximum-likelihood statistical analysis of several subgroups of thefield RR Lyrae stars was performed to determine the relative solarmotion, velocity ellipsoid parameters, and mean absolute visualmagnitude for each group. The full sample of 159 stars was taken from arecent Chinese proper-motion survey, and new mean radial velocities wereused for 46 of the stars. A geometric minimization technique known assimplex optimization was used to apply a rigorous maximum-likelihoodmodel to the data. The best estimate for the mean absolute visualmagnitude is 0.76 + or - 0.14 mag for the entire RR ab-type sample.
| The rotational velocities of the dwarf Cepheids and related stars
The rotational velocities of the dwarf Cepheids are discussed, and someapparent differences between the dwarf Cepheids and the delta Scutivariables (other than light amplitude) are noted. For dwarf Cepheids,the rotational velocities are very small compared with the typicalrotational velocity of delta Scuti variables. The dwarf Cepheids,moreover, are restricted to a much more confined region in the H-Rdiagram. Unlike many typical delta Scuti variables, no dwarf Cepheidsare found near the ZAMS.
| Delta Scuti variables. II - Comparison of theoretical evolution sequences with observational data
Delta Scuti variable observational data concerning periods, periodratios, effective temperatures, gravities, radii, and metal abundancesare compared with novel theoretical stellar evolution sequences,including a pulsation analysis for models in the lower Cepheidinstability strip, in order to consider such physical properties asmasses, ages, composition parameters, and the occurrence ofhelium-depleted outer zones. It is established that the metal-rich, highamplitude Delta Scuti variables are shell hydrogen-burning stars, andthat the observed period ratios of double mode Delta Scuti variables canbe explained by means of homogeneous standard models (although somehelium depletion in surface zones is also possible). It is concludedthat all evidence is in agreement with the assumption that Delta Scutistars are evolving in accordance with standard stellar evolutionarytheory.
| Revised list of pulsating stars with ultra-short periods
A comprehensive list of 178 known Delta Scuti and RR Lyrae-stars ispresented. Using this revised list a HR diagram for these ultra shortperiod pulsating stars is plotted and the blue and red edges of theresultant instability strip are determined. Selection effects arediscussed, and the PLC relationship of Breger (1979) is tested usingdata from this list. Stars lying outside the defined instability regionare discussed.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Gyík |
| Rektaszcenzió: | 22h10m07.77s |
| Deklináció: | +40°55'10.6" |
| Vizuális fényesség: | 10.336 |
| RA sajátmozgás: | -2.4 |
| Dec sajátmozgás: | -4.7 |
| B-T magnitude: | 10.865 |
| V-T magnitude: | 10.38 |
Katalógusok és elnevezések:
|
INHABITED SKY
