תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
BV I c photometry of RR Lyrae stars
We have obtained 26 372 CCD frames in the B, V, and I c filters for 81 RR Lyrae stars in 2008-2010, using the 76-cm telescope ofthe South African Astronomical Observatory and the 40-cm telescope ofthe Cerro Armazones Observatory, North Catholic University (Chile) usingan SBIG ST-10XME CCD camera. For 12 of these RR Lyrae stars, we alsoobtained 337 brightness measurements in the B and V bands in 2000-2001using the 60-cm telescope of the High Altitude Mt. Maidanak Observatory(Republic of Uzbekistan). We present tables of observations, lightcurves, and improved light-curve elements for all these RR Lyrae stars.The Blazhko effect was detected for SU Hor.
| The luminosities and distance scales of type II Cepheid and RR Lyrae variables
Infrared and optical absolute magnitudes are derived for the type IICepheids κ Pav and VY Pyx using revised Hipparcos parallaxes andfor κ Pav, V553 Cen and SW Tau from pulsational parallaxes.Revised Hipparcos and HST parallaxes for RR Lyrae agree satisfactorilyand are combined in deriving absolute magnitudes. Phase-corrected J, Hand Ks mags are given for 142 Hipparcos RR Lyraes based onTwo-Micron All-Sky Survey observations. Pulsation and trigonometricalparallaxes for classical Cepheids are compared to establish the bestvalue for the projection factor (p) used in pulsational analyses.The MV of RR Lyrae itself is 0.16 +/- 0.12 mag brighter thanpredicted from an MV-[Fe/H] relation based on RR Lyrae starsin the Large Magellanic Cloud (LMC) at a modulus of 18.39 +/- 0.05 asfound from classical Cepheids. This is consistent with the prediction ofCatelan & Cortés that it is overluminous for its metallicity.The results for the metal- and carbon-rich Galactic disc stars, V553 Cenand SW Tau, each with small internal errors (+/-0.08 mag) have a meandeviation of only 0.02 mag from the period-luminosity (PL) relationestablished by Matsunaga et al. for type II Cepheids in globularclusters and with a zero-point based on the same LMC-scale. Comparingdirectly the luminosities of these two stars with published data on typeII Cepheids in the LMC and in the Galactic bulge leads to an LMC modulusof 18.37 +/- 0.09 and a distance to the Galactic Centre of R0= 7.64 +/- 0.21kpc. The data for VY Pyx agree with these results withinthe uncertainties set by its parallax. Evidence is presented thatκ Pav may have a close companion and possible implications of thisare discussed. If the pulsational parallax of this star is incorporatedin the analyses, the distance scales just discussed will be increased by~0.15 +/- 0.15 mag. V553 Cen and SW Tau show that at optical wavelengthsPL relations are wider for field stars than for those in globularclusters. This is probably due to a narrower range of masses in thelatter case.
| Multiperiodic Galactic field RR Lyrae stars in the ASAS catalogue
The All Sky Automated Survey (ASAS) monitors bright stars (8 < V <14 mag) south of declination +28°. The ASAS Catalogue of VariableStars (ACVS) presently contains 50099 objects; among them are 2212objects classified as RR Lyrae pulsating variables. We use ASASphotometric V-band data to search for multiperiodicity in those stars.We find that 73 of 1435 RRab stars and 49 of 756 RRc stars exhibit theBlazhko effect. We observe a deficiency of RRab Blazhko variables withmain pulsation periods greater than 0.65 d. The Blazhko periods of RRcstars exhibit a strongly bimodal distribution. During our study wediscovered the Blazhko effect with multiple periods in object ASAS050747-3351.9 = SU Col. Blazhko periods of 89.3 and 65.8 d and acandidate of 29.5 d were identified with periodogram peaks near thefirst three harmonics of the main pulsation. These observations mayinspire new models of the Blazhko effect, which has eluded a consistenttheory since its discovery about one hundred years ago. Long-term lightcurve changes were found in 29 stars. We also found 19 Galactic doublemode pulsators (RRd), of which four are new discoveries, raising thenumber of ASAS discoveries of such objects to 16, out of 27 known in thefield of our Galaxy.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Proper identification of RR Lyrae stars brighter than 12.5 mag
RR Lyrae stars are of great importance for investigations of Galacticstructure. However, a complete compendium of all RR-Lyraes in the solarneighbourhood with accurate classifications and coordinates does notexist to this day. Here we present a catalogue of 561 local RR-Lyraestars (V_max ≤ 12.5 mag) according to the magnitudes given in theCombined General Catalogue of Variable Stars (GCVS) and 16 fainter ones.The Tycho2 catalogue contains ≃100 RR Lyr stars. However, manyobjects have inaccurate coordinates in the GCVS, the primary source ofvariable star information, so that a reliable cross-identification isdifficult. We identified RR Lyrae from both catalogues based on anintensive literature search. In dubious cases we carried out photometryof fields to identify the variable. Mennessier & Colome (2002,A&A, 390, 173) have published a paper with Tyc2-GCVSidentifications, but we found that many of their identifications arewrong.
| RR Lyrae stars: kinematics, orbits and z-distribution
RR Lyrae stars in the Milky Way are good tracers to study the kinematicbehaviour and spatial distribution of older stellar populations. Arecently established well documented sample of 217 RR Lyr stars withV<12.5 mag, for which accurate distances and radial velocities aswell as proper motions from the Hipparcos and Tycho-2 catalogues areavailable, has been used to reinvestigate these structural parameters.The kinematic parameters allowed to calculate the orbits of the stars.Nearly 1/3 of the stars of our sample have orbits staying near the MilkyWay plane. Of the 217 stars, 163 have halo-like orbits fulfilling one ofthe following criteria: Θ < 100 km s-1, orbiteccentricity >0.4, and normalized maximum orbital z-distance>0.45. Of these stars roughly half have retrograde orbits. Thez-distance probability distribution of this sample shows scale heightsof 1.3±0.1 kpc for the disk component and 4.6±0.3 kpc forthe halo component. With our orbit statistics method we found a(vertical) spatial distribution which, out to z=20 kpc, is similar tothat found with other methods. This distribution is also compatible withthe ones found for blue (HBA and sdB) halo stars. The circular velocityΘ, the orbit eccentricity, orbit z-extent and [Fe/H] are employedto look for possible correlations. If any, it is that the metal poorstars with [Fe/H] <1.0 have a wide symmetric distribution aboutΘ=0, thus for this subsample on average a motion independent ofdisk rotation. We conclude that the Milky Way possesses a halo componentof old and metal poor stars with a scale height of 4-5 kpc having randomorbits. The presence in our sample of a few metal poor stars (thus partof the halo population) with thin disk-like orbits is statistically notsurprising. The midplane density ratio of halo to disk stars is found tobe 0.16, a value very dependent on proper sample statistics.
| 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.
| Kinematics of Metal-poor Stars in the Galaxy. II. Proper Motions for a Large Nonkinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected withoutkinematic bias and with available radial velocities, distance estimates,and metal abundances in the range -4.0<=[Fe/H]<=0.0. This updateof the 1995 Beers & Sommer-Larsen catalog includes newly derivedhomogeneous photometric distance estimates, revised radial velocitiesfor a number of stars with recently obtained high-resolution spectra,and refined metallicities for stars originally identified in the HKobjective-prism survey (which account for nearly half of the catalog)based on a recent recalibration. A subset of 1258 stars in this cataloghave available proper motions based on measurements obtained with theHipparcos astrometry satellite or taken from the updated AstrographicCatalogue (second epoch positions from either the Hubble Space TelescopeGuide Star Catalog or the Tycho Catalogue), the Yale/San Juan SouthernProper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog.Our present catalog includes 388 RR Lyrae variables (182 of which arenewly added), 38 variables of other types, and 1680 nonvariables, withdistances in the range 0.1 to 40 kpc.
| The absolute magnitudes of RR Lyraes from HIPPARCOS parallaxes and proper motions
We have used HIPPARCOS proper motions and the method of StatisticalParallax to estimate the absolute magnitude of RR Lyrae stars. Inaddition we used the HIPPARCOS parallax of RR Lyrae itself to determineit's absolute magnitude. These two results are in excellent agreementwith each other and give a zero-point for the RR Lyrae M_v,[Fe/H]relation of 0.77+/-0.15 at [Fe/H]=-1.53. This zero-point is in goodagreement with that obtained recently by several groups usingBaade-Wesselink methods which, averaged over the results from thedifferent groups, gives M_v = 0.73+/-0.14 at [Fe/H]=-1.53. Taking theHIPPARCOS based zero-point and a value of 0.18+/-0.03 for the slope ofthe M_v,[Fe/H] relation from the literature we find firstly, thedistance modulus of the LMC is 18.26+/-0.15 and secondly, the mean ageof the Globular Clusters is 17.4+/-3.0 GYrs. These values are comparedwith recent estimates based on other "standard candles" that have alsobeen calibrated with HIPPARCOS data. It is clear that, in addition toastrophysical problems, there are also problems in the application ofHIPPARCOS data that are not yet fully understood. Table 1, whichcontains the basic data for the RR Lyraes, is available only at CDS. Itmay be retrieved via anonymous FTP at cdsarc.u-strasbg.fr (130.79.128.5)or via the Web at http://cdsweb.u-strasbg.fr/Abstract.html
| Early evolution of the Galactic halo revealed from Hipparcos observations of metal-poor stars
The kinematics of 122 red giant and 124 RR Lyrae stars in the solarneighborhood are studied using accurate measurements of their propermotions obtained by the Hipparcos astrometry satellite, combined withtheir published photometric distances, metal abundances, and radialvelocities. A majority of these sample stars have metal abundances of(Fe/H) = -1 or less and thus represent the old stellar populations inthe Galaxy. The halo component, with (Fe/H) = -1.6 or less, ischaracterized by a lack of systemic rotation and a radially elongatedvelocity ellipsoid. About 16 percent of such metal-poor stars have loworbital eccentricities, and we see no evidence of a correlation between(Fe/H) and e. Based on the model for the e-distribution of orbits, weshow that this fraction of low-e stars for (Fe/H) = -1.6 or less isexplained by the halo component alone, without introducing the extradisk component claimed by recent workers. This is also supported by theabsence of a significant change in the e-distribution with height fromthe Galactic plane. In the intermediate-metallicity range, we find thatstars with disklike kinematics have only modest effects on thedistributions of rotational velocities and e for the sample at absolutevalue of z less than 1 kpc. This disk component appears to constituteonly 10 percent for (Fe/H) between -1.6 and -1 and 20 percent for (Fe/H)between -1.4 and -1.
| Structural Properties of Pulsating Star Light Curves Through Fuzzy Divisive Hierarchical Clustering
Not Available
| Kinematics of metal-poor stars in the galaxy
We discuss the kinematic properties of a sample of 1936 Galactic stars,selected without kinematic bias, and with abundances (Fe/H) is less thanor equal to -0.6. The stars selected for this study all have measuredradial velocities, and the majority have abundances determined fromspectroscopic or narrow-/intermediate-band photometric techniques. Incontrast to previous examinations of the kinematics of the metal-poorstars in the Galaxy, our sample contains large numbers of stars that arelocated at distances in excess of 1 kpc from the Galactic plane. Thus, amuch clearer picture of the nature of the metal-deficient populations inthe Galaxy can now be drawn.
| The metallicity of RR Lyrae stars in Baade's window
Metallicities are derived via the Delta S method for 59 RR Lyraevariables in the Baade's window field of the Galactic nuclear bulge.Both RRab and RRc variables have average Fe/H = -1.0. The metallicitydistribution for the whole sample is sharply peaked, with a dispersionin Fe/H of only 0.16 dex, far smaller than suggested by previousstudies. The narrow metallicity distribution does not permit the variouscurrent estimates of the magnitude of a luminosity/metallicity relationfor RR Lyrae stars to be distinguished. It is also found that the metalabundance of the globular cluster NGC 6522 in Baade's window is close tothat of the bulge RR Lyraes, which sets the reddening to the Baadewindow to be E(B - V) = 0.50 + or - 0.05 and the distance to thegalactic center to be 8.2 + or - 1 kpc.
| Population studies. II - Kinematics as a function of abundance and galactocentric position for (Fe/H) of -0.6 or less
A catalog is presented of some 1200 Galactic objects which have radialvelocities and (Fe/H) abundances of -0.6 or less. These data areanalyzed to yield information on the kinematic properties of the olderpopulations of the Galaxy and on the interdependence between kinematicsand abundance. It is found that the kinematics of the availablekinematically selected stars differ from those of the nonkinematicallyselected objects. No evidence is found for any significant difference inthe kinematic properties of the various halo subgroups, nor for anydependence of kinematics on abundance. While the rotation of the halo issmall at about 37 km/s for (Fe/H) of -1.2 or less, it rises quickly forhigher abundances to a value of about 160 km/s at (Fe/H) = 0.6. Objectsin the abundance range -0.9 to -0.6 appear to belong predominantly to apopulation possessing the kinematic characteristics of a thick disk. Theimplications of these findings for the suggestion that globular clustersbelong to the same population as the noncluster objects, for the originof the thick disk, and for the mass of the Galaxy are discussed.
| The light curves of RR Lyrae field stars
Fourier decompositions have been made of the light curves of a largesample of RR Lyrae field stars. The coefficients have been tabulated.Following the scheme of an earlier investigation of classical Cepheids,certain combinations of the low-order coefficients - phi21, R21, andphi31 - are plotted against period. The Bailey-type c pulsators standout from the type ab stars, particularly on the R21 plot which is foundto be a more sensitive discriminator of Bailey type than is thetraditionally employed amplitude-period diagram. The RR Lyrae plots ofphi21, R21, and phi31 are compared with those previously obtained forclassical Cepheids. It is noted that, while the Cepheid plots display atightly defined progression with period, reflecting the influence of amodal resonance, in the RR Lyrae case there is much more scatter.However, some evidence is shown to exist for a Cepheid-like progressionappearing among the longer period RR Lyrae pulsators and culminating inthe unique small-amplitude variable XZ Ceti.
| A spectroscopic study of the c-type RR Lyraes
Image tube scanner observations have been made for a sample of fieldc-type RR Lyraes. Using these spectra, it is shown how Preston's metalabundance indicator Delta-S can be applied to the RRc's to derive (Fe/H)on Butler's system. Mean temperatures for the field RRc's based onreddening free colors determined from the strength of the H-beta line.These abundances and temperatures allow the delineation of Oosterhoffgroups among field stars. It is shown that, as in clusters, theOosterhoff effect for field stars occurs star by star and not just formean properties of the group. There is a temperature region in thefield-star instability strip where the RRc's and RRab's can both existat the same temperature. Data on the temperature boundaries of theinstability strip provide no convincing case for helium abundancedifferences among field RR Lyraes with differing metal abundances.
| Reddening and blanketing of RR Lyrae stars
Based on complete light curves in the five channels of the WalravenVBLUW photometric system, a discussion is given of the determination ofblanketing and reddening for RR Lyrae stars. A photometric accuracy ofthe order of 0.005 mag has been reached. Blanketing derived from thereddening-free color index /B-L/ is shown to be equivalent to other waysof determining the metallicity of RR Lyrae stars, such as delta (u-B)s,m1, and delta S. Two independent ways to find the interstellar-reddeningcorrection are studied; they lead to identical results. A table is givenwith high-accuracy blanketing and reddening values for 73 RRab, 13 RRc,and a few short-period (RRs) variables. The relation between the presentobservations and those in other intermediate-band systems is considered.
| An atlas of light and colour curves of field RR Lyrae stars
An atlas is presented of light and color curves in the Walraven VBLUWphotometric system for 90 field RR Lyrae and short-period variables. Theobservational program and the reduction procedure are briefly described.Tables are presented containing the colors at mean and minimum light.
| Absolute magnitudes and motions of RR Lyrae stars
Absolute magnitudes are found by the use of statistical parallax for RRLyrae stars which have been grouped by period and by metal type. TheBailey c-type stars are treated independently. Solar motion solutionsare made using velocity data. Parameters of galactic orbits obtainedfrom space velocities show a relation to period. For the total a-stargroup the resultant mean light visual absolute magnitude is 0.49 mag,which corresponds to MB of 0.63 mag. Using this figure, thedistance to the galactic center is 9.3 kpc.
| Intermediate Band Photometry of BB Lyrae Stars. II. Colors of RR Lyrae and Ultra-Short Period Variables
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973ApJS...25..487J&db_key=AST
| Observations of southern RR Lyrae stars
Not Available
| Discussion of photo-electric five-colour observations of different types of pulsating variables
Not Available
| Bearbeitung des Lichtwechsels von 75 kurzperiodischen veranderlichen Sternen zwischen 25 und 90 sudlicher Deklination.
Not Available
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | טוקאן |
| התרוממות ימנית: | 01h18m30.63s |
| סירוב: | -67°55'05.0" |
| גודל גלוי: | 11.55 |
| תנועה נכונה: | 21.2 |
| תנועה נכונה: | -31.2 |
| B-T magnitude: | 12.09 |
| V-T magnitude: | 11.595 |
קטלוגים וכינוים:
|
INHABITED SKY
