Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
A catalogue of RR Lyrae stars from the Northern Sky Variability Survey
A search for RR Lyrae stars has been conducted in the publicly availabledata of the Northern Sky Variability Survey. Candidates have beenselected by the statistical properties of their variation; the standarddeviation, skewness and kurtosis with appropriate limits determined froma sample 314 known RRab and RRc stars listed in the General Catalogue ofVariable Stars. From the period analysis and light-curve shape of over3000 candidates 785 RR Lyrae have been identified of which 188 arepreviously unknown. The light curves were examined for the Blazhkoeffect and several new stars showing this were found. Six double-mode RRLyrae stars were also found of which two are new discoveries. Somepreviously known variables have been reclassified as RR Lyrae stars andsimilarly some RR Lyrae stars have been found to be other types ofvariable, or not variable at all.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Spectroscopy of QUEST RR Lyrae Variables: The New Virgo Stellar Stream
Eighteen RR Lyrae variables (RRLs) that lie in the ``12.4h clump''identified by the Quasar Equatorial Survey Team (QUEST) have beenobserved spectroscopically to measure their radial velocities and metalabundances. Ten blue horizontal branch (BHB) stars identified by theSloan Digital Sky Survey (SDSS) were added to this sample. Six of thenine stars in the densest region of the clump have a mean radialvelocity in the Galactic rest frame (Vgsr) of 99.8 andσ=17.3 km s-1, which is slightly smaller than theaverage error of the measurements. The whole sample contains eight RRLsand five BHB stars that have values of Vgsr suggestingmembership in this stream. For seven of these RRLs, the measurements of[Fe/H], which have an internal precision of 0.08 dex, yield<[Fe/H]>=-1.86 and σ=0.40. These values suggest that thestream is a tidally disrupted dwarf spheroidal galaxy of low luminosity.Photometry from the database of the SDSS indicates that this streamcovers at least 106 deg2 of the sky in the constellationVirgo. The name Virgo stellar stream is suggested.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
Not Available
| VLT Spectroscopy of RR Lyrae Stars in the Sagittarius Tidal Stream
Sixteen RR Lyrae variables from the QUEST survey that lie in the leadingarm of the tidal stream from the Sagittarius dSph galaxy have beenobserved spectroscopically to measure their radial velocities and metalabundances. The systemic velocities of 14 stars, which were determinedby fitting a standard velocity curve to the individual measurements,have a sharply peaked distribution with a mean of 33 km s-1and a standard deviation of only 25 km s-1. The [Fe/H]distribution of these stars has a mean of -1.76 and a standard deviationof 0.22. These measurements are in good agreement with previous onesfrom smaller samples of stars. The mean metallicity is consistent withthe age-metallicity relation that is observed in the main body of theSgr dSph galaxy. The radial velocities and the distances from the Sun ofthese stars are compared with recent numerical simulations of the Sgrstreams that assume different shapes for the dark matter halo. Modelsthat assume a oblate halo do not fit the data as well as ones thatassume a spherical or a prolate distribution. However, none of the fitsare completely satisfactory. Every model fails to reproduce the longextent of the stream in right ascension (36°) that is seen in theregion covered by the QUEST survey. Further modeling is required to seeif this and the other mismatches between theory and observation can beremoved by judicial choices for the model parameters or instead rule outa class of models.
| 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.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
Not Available
| A pulsational approach to near-infrared and visual magnitudes of RR Lyr stars
In this paper, we present an improved theoretical scenario concerningnear-infrared and visual magnitudes of RR Lyr variables, as based onup-to-date pulsating models. New relations connecting V and K absolutemagnitudes with periods, mass, luminosity and metal content arediscussed separately for fundamental and first-overtone pulsators. Wealso show that the V-K colours are predicted to supply tight constraintson the pulsator intrinsic luminosity. On this basis, we revisit the caseof the prototype variable RR Lyr, showing that the parallax inferred bythis new pulsational approach appears in close agreement with HubbleSpace Telescope absolute parallax. Moreover, available K and Vmeasurements for field and cluster RR Lyr variables with known reddeningand metal content are used to derive a relation connecting the Kabsolute magnitude to period and metallicity (MK-[Fe/H]-logP)as well as a new calibration of the MV-[Fe/H] relation. Thecomparison between theoretical prescriptions and observations suggeststhat RR Lyr stars in the field and in galactic globular clusters (GGCs)should have quite similar evolutionary histories. The comparison betweentheory and observations also discloses a general agreement that supportsthe reliability of the current pulsational scenario. On the contrary,current empirical absolute magnitudes based on the Baade-Wesselink (BW)method suggest relations with a zero-point which is fainter than ispredicted by pulsation models, together with a milder metallicitydependence. However, preliminary results based on a new calibration ofthe BW method provided by Cacciari et al. (2000) for RR Cet and SW Andappear in a much better agreement with the pulsational predictions.
| Revised [Fe/H] and Radial Velocities for 28 Distant RR Lyrae Stars
New abundances ([Fe/H] and radial velocities are given for 28 RR Lyraestars discovered by Kinman, Mahaffey and Wirtanen (1982) and by Saha(1984). The stars were observed with the IIDS scanner on the KPNO 2.1-mtelescope. The scans were calibrated by observing 18 nearby RR Lyraestars whose [Fe/H] have been given by Suntzeff et al. (1991).
| Ein Hoch auf die Hochs Helga und Liljana.
Not Available
| Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
Not Available
| Aus der "Kurzperiodische Pulsationssterne". T Sex.
Not Available
| 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.
| Metallicities for Double-Mode RR Lyrae Stars in the Large Magellanic Cloud
Metallicities for six double-mode RR Lyrae stars (RRd's) in the LargeMagellanic Cloud have been estimated using the ΔS method. Thederived [Fe/H] values are in the range [Fe/H]=-1.09 to -1.78 (or -0.95to -1.58, adopting a different calibration of [Fe/H] versus ΔS).Two stars in our sample are at the very metal-rich limit of all RRd'sfor which metal abundance has been estimated, either by direct measure(for field objects) or on the basis of the hosting system (for objectsin globular clusters or external galaxies). These metal abundances,coupled with mass determinations from pulsational models and thePetersen diagram, are used to compare the mass-metallicity distributionof field and cluster RR Lyrae variables. We find that field and clusterRRd's seem to follow the same mass-metallicity distribution, within theobservational errors, strengthening the case for uniformity ofproperties between field and cluster variables. At odds to what isusually assumed, we find no significant difference in mass for RR Lyraevariables in globular clusters of different metallicity and Oosterhofftypes, or there may even be a difference contrary to the commonlyaccepted one, depending on the metallicity scale adopted to derive themasses. This ``unusual'' result for the mass-metallicity relation isprobably due, at least in part, to the inclusion of updated opacitytables in the computation of metal-dependent pulsation models. Based onobservations collected at the European Southern Observatories, Chile.
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| 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 slope of the RR Lyrae Mv-(Fe/H) relation
We review the available observational data to show that the slope of theRR Lyrae Mv-(Fe/H) relation is 0.18 +/- 0.03. The recent claim by Feastthat, because of biases, the true slope is much steeper is notjustified.
| 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.
| 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
| The Absolute Magnitudes of the RR Lyrae Stars
We present a new calibration of the relationship between the absolutemagnitudes and metal abundances, [Fe/H], of RR Lyrae stars. Temperaturesinferred from optical and near infrared color indices and the new Kuruczmodels are utilized in conjunction with Baade-Wesselink solutions toderive absolute magnitudes. Temperature inferred from the optical andnear infrared photometry are $\sim$ 200K - 300K higher for the variablesthan those given from ($V-K$) color indices and the older Kurucz models.We find $M_v$ = 0.287 [Fe/H] + 0.964. This equation gives higherluminosities ($\sim$ 0.2 mag) for the metal-poor variables than previousB-W calibrations. The RR Lyrae stars in the Large Magellanic Cloud inconjunction with our calibration yield a distance modulus of 18.53.Thus, the Cepheids and RR Lyrae stars give identical distance moduli at$\leq$ 0.1 mag level. The repercussions of the higher temperatures andhigher luminosities of RR Lyrae stars on the distances and ages ofGlobular clusters, distance to the galactic center, the Hubble constantand age of the universe, and the masses of RR Lyrae stars are discussed.(SECTION: Stars)
| Structural Properties of Pulsating Star Light Curves Through Fuzzy Divisive Hierarchical Clustering
Not Available
| Radial velocities and iron abundances of field RR Lyraes. II.
This is the second of the papers devoted to derive radial velocities andiron abundances of field RR Lyraes observed by HIPPARCOS. Our abundancesshow good agreement with those in the literature obtained both fromphotometric (Delta S index) and spectroscopic methods. Binary candidatesand stars misclassified as RR Lyraes in the original HIPPARCOS list havebeen also identified. Appendix is only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u- strasbg.fr/Abstract.html
| Radial velocities and iron abundances of field RR Lyraes. I.
We present systemic velocities and iron abundances for 56 RR Lyraes, themajority of which have been observed by the HIPPARCOS satellite.Comparison between our systemic velocities and previous valuesidentifies several binary candidates only one of which, TU UMa, waspreviously suspected of being a binary. However, spectra of the unusualRR Lyrae BB Vir show no evidence of line doubling and hence do notsupport the recent claims that this star may have a Blue HorizontalBranch companion. Comparison between our abundances and previousdeterminations shows reasonable agreement except with the recent work of\cite[Layden (1994)]{Lay94} where we find systematic differences.Several of the stars included on the HIPPARCOS observing list as RRLyraes are shown to be mis-classified. Of particular interest are thestars V363 Cas and AT And which, by analogy with XZ Cet, may beanomalous Cepheids. The Appendix is available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Template K Light Curves for RR Lyrae Stars
We discuss a technique to compute using templates developed by fitting aFourier series to existing high-quality K light curves of field RRLyraes. We find that a series of order 2 is sufficient to model thelight curves of first-overtone RRc variables, but 4 different 6th-ordertemplates are needed for the fundamental RRab stars due to changes inthe light curves that appear to correlate with the B amplitude. Applyingthe appropriate template to single-phase observations yield estimatedvalues whose deviation from the true is randomly distributed over phase,and is of the same order of magnitude as the observational uncertainty,as long as the ephemeris phase is accurate. The addition of a secondpoint, separated by at least 0.2 in phase from the first, allows the useof template-shifting to remove deviations that may arise fromuncertainties in the ephemeris phase, and template and scaling factorselection, with final systematic errors reduced to less than 0.03 mag.We find that the use of templates yield superior results to thosederived using other techniques, which can produce values that showsystematic deviations over phase. (SECTION: Stars)
| The Chemical Composition of Field RR Lyrae Stars. I. Iron and Calcium
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..103..183L&db_key=AST
| Photometry of the RR Lyrae Variable U Comae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2142H&db_key=AST
| 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 Composition of HB Stars: RR Lyrae Variables
We used moderately high-resolution, high S/N spectra to study thechemical composition of 10 field ab-type RR Lyrae stars. A newtemperature scale was determined from literature Infrared Flux Methodmeasures of subdwarfs and the Kurucz (1992) model atmospheres, and usedto calibrate colors for both dwarfs and RR Lyraes. The applicability ofKurucz (1992) model atmospheres in the analysis of RR Lyraes at minimumlight was analyzed: we found that they are able to reproduce colors,excitation and ionization equilibria as well as the wings of Halpha. Wederived abundances for 21 species. The metal abundances of the programstars span the range -2.50<[Fe/H]<+0.17$. Lines of most elementsare found to form in LTE conditions. Fe lines satisfy very well theexcitation and ionization equilibria. RR Lyraes share the typicalabundance pattern of other stars of similar [Fe/H]: alpha-elements areoverabundant by about 0.4dex and Mn is underabundant by about 0.6dex instars with [Fe/H]<-1. Significant departures from LTE are found onlyfor a few species. We used our new [Fe/H] abundances, as well as valuesfrom Butler and coworkers (corrected to our system), and from highresolution spectroscopy of globular clusters giants, to obtain a newcalibration of the DeltaS index: [Fe/H]= -0.194(\pm 0.011)DeltaS-0.08(\pm 0.18) and to update the metallicity calibration of the Ca II Kline index: [Fe/H]= 0.65(\pm 0.17)W'(K) -3.49(\pm 0.39). Finally, ournew metallicity scale was used to revise the [Fe/H] dependence of theabsolute magnitude of RR Lyrae stars, Mv: Mv = 0.20(\pm 0.03)[Fe/H] +1.06(\pm 0.04).
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Sextans |
| Ascensió Recta: | 09h53m28.40s |
| Declinació: | +02°03'26.4" |
| Magnitud Aparent: | 10 |
| Moviment propi RA: | -19.8 |
| Moviment propi Dec: | -23.1 |
| B-T magnitude: | 10.271 |
| V-T magnitude: | 10.023 |
Catàlegs i designacions:
|
