תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Physical parameters of seven field RR Lyrae Stars in bootes
Strömgren uvby-? photometry is reported for the RR Lyrae starsAE, RS, ST, TV, TW, UU, and XX in Bootes. The physical parametersM/M_?, log(L/L_?), M_V, log T_{eff} and [Fe/H], have beenestimated from the Fourier decomposition of the light curves and theempirical calibrations developed for this type of stars. The obtained[Fe/H] values are compared with those calculated from the ? Sindex for some sample stars. It was found that reddening in the zone isnegligible compared to that shown by several objects in the same skyzone. From that, distance to the stars was calculated. The variation ofthe unreddened indexes (b-y)_0 and c_1 along the pulsational cycleallows the direct comparison with the theoretical grids and, hence, anindependent determination of T_{eff} and log g.
| 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.
| [Fe/H] relations for c-type RR Lyrae variables based upon Fourier coefficients
[Fe/H]-φ31-P relations are found for c-type RR Lyraestars in globular clusters. The relations are analogous to that found byJurcsik & Kovács for field ab-type RR Lyrae stars, where alonger period correlates with lower metallicity values for similarvalues of the Fourier coefficient φ31. The relationsobtained here are used to determine the metallicity of field c-type RRLyrae stars, those within ωCen, the Large Magellanic Cloud andtoward the galactic bulge. The results are found to compare favourablyto metallicity values obtained elsewhere.
| 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
| 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.
| How to make progress in the understanding of the Blazhko effect .
Almost a century after its discovery the Blazhko effect in RR Lyraestars remains a mystery. The Blazhko Project is an internationalcollaboration focusing at a better understanding of the phenomenon. Inthis short paper we summarize some of the results obtained so far, andpoint out some of the remaining challenges.
| 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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.
| 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.
| 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
| 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.
| 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
| 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)
| The Chemical Composition and Period Change Rate of the Anomalous Cepheid V19 in NGC 5466
A detailed model atmosphere and chemical composition analysis has beenmade of the brightest known anomalous Cepheid, V19 in the globularcluster NGC 5466. Our study is based on 30 minute CCD echellespectrograms (4300 <= lambda <= 6630 A) acquired in 1995 and 1996with the HIRES spectrograph on the 10 m Keck-I telescope. New CCDphotometric observations from 1992 to 1996 suggest that V19 was nearminimum light at the time each spectrum was acquired, a conclusion thatis also supported by spectral analyses using Kurucz model atmospheres.The line widths in the HIRES spectra are quite narrow, with v sin i<= 18 km s-1. Given that V19 is the first anomalous Cepheid (AC) tobe observed at such high spectroscopic resolution, the rotationalvelocity is significant in view of the hypothesis that ACs are coalescedbinaries. The upper limit on v sin i for V19 appears to contradict thishypothesis, unless sin i is very small. Radial velocities derived fromeach HIRES spectrogram, vr = +111.0 +/- 0.1 km s-1 in 1995 August and vr= +110.9 +/- 0.2 km s-1 in 1996 June, are smaller than would be expectedat minimum light based on previous, though much less precise, radialvelocity measurements. The lack of a detectable change in vr over 311days, if reinforced by continued monitoring, would also call intoquestion the evolutionary scenario that explains V19 as the result ofmass transfer in a close binary system presently composed of an AC plusa white dwarf, unless the orbit is in the plane of the sky. Theatmospheric parameters of V19 at the time of the 1995 HIRES observation( phi = 0.51 +/- 0.03) are estimated to have been Teff = 6450 +/- 50 K,log g = 2.55 +/- 0.15 dex, and microturbulence xi = 2.5 +/- 0.2 km s-1,in agreement with photometric light-cycle measurements near minimumlight. The spectroscopic estimates are based on theoretical line profilefits to the observed wings of the H I Balmer lines H gamma , H beta ,and H alpha , together with an investigation of the ionizationequilibria of Fe I:Fe II and Mg I:Mg II, taking into account the effectsof non-LTE. Adopting these atmospheric parameters and a distance modulusfor NGC 5466 of (m - M)0 = 16.01 +/- 0.10 gives a spectroscopic massestimate for V19 of 1.66^{+0.7}_{-0.5} Msolar , which issignificantly larger than the mass of the main-sequence turnoff stars inNGC 5466. Equivalent width measurements of 26 Fe II lines give an ironabundance of [Fe/H] = -1.92 +/- 0.05 dex. This value is consistent withprevious determinations of the mean metallicity for NGC 5466 fromintegrated spectra and from lower S/N echelle spectroscopy of individualred giant stars, to within the quoted uncertainties. The absence of thestrongest lines of Zn I suggests a possible underabundance of thiselement. No evidence is found for strong s-process enrichment, with[Ba/H] = -2.45 +/- 0.13 dex from four Ba II lines, consistent with ourupper limits [La/H] <= -1.93, [Ce/H] <= -1.69, and [Nd/H] <=-1.75, based on the marginal detections or absences of the strongest LaII, Ce II, and Nd II lines in the spectral regions recorded. Calcium isenhanced with respect to iron, with [Ca/Fe] = +0.22 dex derived from 16Ca I lines and 56 Fe I lines, under the assumption of LTE; other alpha-elements (e.g., Mg, Si, S, and Ti) are also enhanced relative to iron.In general, the abundance ratios to iron closely match the normal,well-established pattern for metal-poor stars. This result furtherconstrains evolutionary models attempting to explain anomalous Cepheidstars like V19 as the result of coalescence or mass transfer in anevolved binary system; unlike the velocity evidence, this abundanceconstraint applies regardless of inclination. Finally, the rate ofchange of V19's pulsation period was investigated using photometry ofnew CCD frames taken in 1995 and 1996 with the Dominion AstrophysicalObservatory 1.8 m telescope and taken in 1996 with the Hale 5 mtelescope at Palomar Observatory. This new photometry was combined withunpublished 1992 and 1993 data (courtesy of M. Corwin) and all earlierphotometry available from the literature. If the period is assumed to beconstant, then the new O-C diagram suggests a revised period of P =0d.821307. However, if the O-C data are fitted allowing P to changelinearly with time, then the derived period change rate, beta = dP/dt =-0d.28 +/- 0d.19 Myr-1, would imply that V19 is evolving toward hottertemperature, and its pulsation period at the present epoch (1996; JD =2,450,250) is instead P = 0d.8213010 +/- 0d.0000003. In either case, theresiduals in the O-C diagram suggest a possible long-term (Porb ~ 10,000day) binary motion. Any such companion would be far too distant to havecontributed to the mass of V19 through Roche lobe overflow.
| 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 Rotation of RR Lyrae Stars
We report upper limits to rotation from the measurement of line breadthsvia cross-correlation analysis for 27 RR Lyrae variables. The eightbest-observed stars of type RRab show the same variation of breadth withphase: the breadth peaks sharply during the rise to maximum light, dropsgradually, and reaches a broad minimum during the phase of maximumradius. During this phase the breadth is always narrow, consistent withinstrumental resolution and turbulence alone. For the threewell-observed RRc variables, the breadth is this narrow at all phasesexcept for a slight increase during the rise to maximum light. Theremaining stars also conform to these patterns, albeit with sparse phasecoverage and lower signal-to-noise ratio. We interpret these results asindicating that lines are broadened in RRab stars by shock-inducedplumes or turbulence during the rise to maximum light, and perhaps byother causes as well, but not by rotation in RR Lyrae stars of eithertype. We estimate an upper limit of v sin i < 10 km s-1 in all cases.This is in stark contrast to the rotation seen in field blue horizontalbranch stars, where v sin i > 10 km s-1 in three out of sixwell-studied field stars, and to the more rapid rotation, oftenexceeding 100 km s-1, of the Population I delta Scuti variables whichoccupy adjacent regions of the instability strip.
| 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 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).
| 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.
| 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.
| A revision to the absolute magnitudes of RR Lyrae stars from the Baade-Wesselink method
It is argued that the zero-point from the recent Baade-Wesselinkanalyses of RR Lyrae stars is 0.07 mags too faint due to aninappropriate value of the p factor having been used (this factorcorrects the observed pulsation velocity to the true pulsationvelocity). Adopting this brighter zero-point brings the Baade-Wesselinkcalibration of the RR Lyrae Absolute Magnitude - Metallicity relationinto closer agreement with theory and also the Baade-Wesselink RR Lyraedistance modulus to the Large Magellanic Cloud (LMC) into closeragreement with other distance indicators.
| AH Cam: A metal-rich RR Lyrae star with the shortest known Blazhko period
Analysis of 746 new V-band observations of the RR Lyrae star AH Camobtained during 1989 - 1992 clearly show that its light curve cannot bedescribed by a single period. In fact, at first glance, the Fourierspectrum of the photometry resembles that of a double-mode pulsator,with peaks at a fundamental period of 0.3686 d and an apparent secondaryperiod of 0.2628 d. Nevertheless, the dual-mode solution is a poor fitto the data. Rather, we believe that AH Cam is a single-mode RR Lyraestar undergoing the Blazhko effect: periodic modulation of the amplitudeand shape of its light curve. What was originally taken to be the periodof the second mode is instead the 1-cycle/d alias of a modulationsidelobe in the Fourier spectrum. The data are well described by amodulation period of just under 11 d, which is the shortest Blazhkoperiod reported to date in the literature and confirms the earliersuggestion by Goranskii. A low-resolution spectrum of AH Cam indicatesthat it is relatively metal rich, with delta-S less than or = 2. Itshigh metallicity and short modulation period may provide a critical testof at least one theory for the Blazhko effect. Moskalik's internalresonance model makes specific predictions of the growth rate of thefundamental model vs fundamental period. AH Cam falls outside the regimeof other known Blazhko variables and resonance model predictions, butthese are appropriate for metal-poor RR Lyrae stars. If the theorymatches the behavior of AH Cam for a metal-rich stellar model, thiswould bolster the resonance hypothesis.
| Temperature, mass, and luminosity of RR Lyrae stars as functions of metallicity at the blue fundamental edge. II
The calibration of the absolute magnitudes of average field RR Lyraestars from the pulsation equation is sought by finding the relationsbetween metallicity, period, and mass along the blue fundamental edge(BFE) on the basis of various types of observational data. It is shownin S93I that the Oosterhoff-Arp-Preston correlation of period andmetallicity at the BFE is steep at -0.122 +/- 0.02. The determination isindependent of reddening and of light curve amplitude. The (B-V) exp0mag color of the bluest field RR Lyrae in the field starsample of Blanco (1992) is independent of metallicity over the range of(Fe/H) from 0 to -2.1.
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
קטלוגים וכינוים:
|
