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The Chemical Compositions of Variable Field Horizontal-branch Stars: RR Lyrae Stars
We present a detailed abundance study of 11 RR Lyrae ab-type variables:AS Vir, BS Aps, CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WYAnt, XZ Aps, and Z Mic. High-resolution and high signal-to-noise ratioechelle spectra of these variables were obtained with the 2.5 m du Ponttelescope at the Las Campanas Observatory. We obtained more than 2300spectra, roughly 200 spectra per star, distributed more or lessuniformly throughout the pulsational cycles. A new method has beendeveloped to obtain the initial effective temperatures of our samplestars at a specific pulsational phase. We find that the abundance ratiosare generally consistent with those of similar metallicity field starsin different evolutionary states and throughout the pulsational cyclesfor RR Lyrae stars. TY Gru remains the only n-capture enriched staramong the RRab in our sample. A new relation is found betweenmicroturbulence and effective temperature among stars of thehorizontal-branch population. In addition, the variation ofmicroturbulence as a function of phase is empirically shown to besimilar to the theoretical variation. Finally, we conclude that thederived T eff and log g values of our sample stars follow thegeneral trend of a single mass evolutionary track.
| Radial Velocities and Pulsation Ephemerides of 11 Field RR Lyrae Stars
We present new radial velocities (RVs), improved pulsation periods, andreference epochs of 11 field RR Lyrae ab-type variables: AS Vir, BS Aps,CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WY Ant, XZ Aps, and ZMic. This study is based on high-resolution spectra obtained with theechelle spectrograph of the 2.5 m du Pont telescope at Las CampanasObservatory. We obtained ~200 spectra per star (i.e., a total of ~2300spectra), distributed more or less uniformly throughout their pulsationcycles. RV curves and photometric light curves phased to our newephemerides are presented for all program stars. In a subsequent paper,we will use these spectra to derive stellar atmospheric parameters andchemical compositions throughout the pulsational cycles, based purely onspectroscopic constraints.
| RR Lyrae Atmospherics: Wrinkles Old and New. A Preview
I report some results of an echelle spectroscopic survey of RR Lyraestars begun in 2006 that I presented in my Henry Norris Lecture of 2010January 4. Topics include (1) atmospheric velocity gradients, (2)phase-dependent envelope turbulence as it relates to Peterson'sdiscoveries of axial rotation on the horizontal branch and to Stothers'explanation of the Blazhko effect, (3) the three apparitions of hydrogenemission during a pulsation cycle, (4) the occurrence of He I lines inemission and absorption, (5) detection of He II emission and metallicline doubling in Blazhko stars, and finally (6) speculation about whathelium observations of RR Lyrae stars in omega Centauri might tell usabout the putative helium populations and the horizontal branch of thatstrange globular cluster.This paper preserves the substance and style of remarks that accompaniedthe author's PowerPoint presentation of the 2009 Henry Norris Russelllecture.
| Helium lines in RR Lyrae spectra
Context: During a comparative study of atmospheric phenomena that occurduring the pulsation cycles of 10 RRab stars I unexpectedly found heliumlines in emission and/or absorption in all 10 stars during rising light.The progression of events in the time-evolution of the helium spectrumdiffers in detail from star to star, but 9 of the 10 stars share anumber of general characteristics, illustrated approximately by thebehavior of RV Oct described in this Note. Aims: Mylong-term aim is to provide a comprehensive empirical description ofatmospheric phenomena that take place during the pulsation cycles ofRRab stars. The short-term goal of this paper is to inform readers thatmeasurements of helium lines place new constraints on shock-wave modelsfor RRab stars. Methods: Results presented here are based onmeasurements and analysis of observations made with the echellespectrograph of the du Pont 2.5-m telescope at Las CampanasObservatory. Results: A general pattern of behavior emergesalbeit with significant star-to-star variation. He I ? 5376 (D3)appears first as a pure emission feature, unlike the Balmer lines forwhich the emission profile is always overlain initially by strongredward-displaced absorption. The phase of maximum D3 emission coincidesapproximately with that of H?, but the duration of conspicuous D3emission (in excess of the local continuum) is less than 15 mn,approximately half the duration of similarly defined H? emission.The emission phase is followed by the appearance, first, ofredward-displaced absorption, and shortly thereafter by a secondviolet-displaced absorption component that strengthens with advancingphase. Both absorption components gradually weaken and disappear afterradial-velocity minimum, which lags luminosity maximum by no more than0.01P as discussed in Sect. 3. However, bona fide He I ? 5876emission flux in excess of the local continuum flux reappears nearmaximum light for some stars in the sample and persists for about 45 mn.The radial velocities of the initial and final He I ? 5876emission features differ little from the time-average value of themetallic-line radial velocities for RV Octantis. However, the absorptionfeatures appear to distort the location of the emission centroid, whenthey are strong.
| 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.
| 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.
| 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.
| 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 impact of HIPPARCOS on the RR Lyrae Distance Scale
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| Light Curves for 40 Field RR Lyrae Variables
Photoelectric photometry in the {\it BV} passbands is presented for 33nearby RR Lyrae stars. CCD frames are used to recalibrate thephotographic photometry of an additional 7 RR Lyraes to the Johnson $B$band. Light curves are presented for all 40 stars, along with derivedlight curve parameters. For one subset of stars, reddenings anddistances are computed from the observed colors at minimum light,periods, mean magnitudes, and spectroscopic metal abundances taken fromthe literature. For a second subset of stars, metal abundances,distances, and reddenings are determined via Fourier decomposition ofthe light curves. The results of the two methods are compared. (SECTION:Stars)
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