This catalog presents metal abundance, distance and radial velocity data on a sample of 302 ab-type RR Lyrae variables within about 2.5 kpc of the Sun. The metal abundance information was obtained from low-medium resolution spectra, using the pseudo-equivalent widths of the Ca II K line and the the H-delta, H-gamma and H-beta lines. The technique employed was similar to Preston's (1959ApJ...130..507P) {Delta}-S method, though significant differences exist; see the source reference for details. The data were calibrated to the Zinn & West (1984ApJS...55...45Z) globular cluster abundance scale. The photometry employed in the distance determinations was primarily taken from the General Catalog of Variable Stars (1985, hereafter GCVS4). Exceptions are noted in column 29; the letters match the footnotes in Table 10 of Layden (1994AJ....108.1016L). The minimum and maximum light photometry, and rise-time were combined following Barnes & Hawley (1986ApJ...307L...9B) to give an estimate of the intensity- averaged magnitude, i.e. the magnitude the star would have if it were not variable. When the GCVS4 quoted magnitudes in passbands other than V, the GCVS4 magnitudes were transformed to the V passband using the relations established in Layden (1994AJ....108.1016L). The interstellar absorption estimates are from Burstein & Heiles (1982AJ.....87.1165B), modified by a simple dust-distribution model. The distances were computed assuming the Mv(RR)-[Fe/H] relation of Carney, Storm & Jones (1992ApJ...386..663C). Radial velocities were measured from the spectra via cross-correlation with secondary velocity standards. The velocities from the individual spectra were fit with a standard radial velocity curve in the (phase, velocity) plane, to give an estimate of the systemic (center of mass) velocity of each star. The error in this value was estimated from the scatter about the best-fit velocity curve, and the quality of the spectra employed. Other methods were used to combine the individual velocities when the situation demanded (cm = 2,3 in column 70; see Layden (1994AJ....108.1016L) for details). The observed velocities were combined with values from the literature to produce a final, best estimate of the systemic radial velocity of each star, and its error.
A detailed analysis is presented of 33 RR Lyrae stars in Pisces observed with the Kepler space telescope over the 8.9-d long K2 Two-Wheel Concept Engineering Test. The sample includes not only fundamental-mode and first-overtone (RRab and RRc) stars but the first two double-mode (RRd) stars that Kepler detected and the only modulated first-overtone star ever observed from space so far. The precision of the extracted K2 light curves made it possible to detect low-amplitude additional modes in all subtypes. All RRd and non-modulated RRc stars show the additional mode at P_X_/P_1_~0.61 that was detected in previous space-based photometric measurements. A periodicity longer than the fundamental mode was tentatively identified in one RRab star that might belong to a gravity mode. We determined the photometric [Fe/H] values for all fundamental-mode stars and provide the preliminary results of our efforts to fit the double-mode stars with non-linear hydrodynamic pulsation models. The results from this short test run indicate that the K2 mission will be, and has started to be, an ideal tool to expand our knowledge about RR Lyrae stars. As a by-product of the target search and analysis, we identified 165 bona fide double-mode RR Lyrae stars from the Catalina Sky Survey observations throughout the sky, 130 of which are new discoveries.
We have used HIPPARCOS proper motions and the method of Statistical Parallax to estimate the absolute magnitude of RR Lyrae stars. In addition we used the HIPPARCOS parallax of RR Lyrae itself to determine it's absolute magnitude. These two results are in excellent agreement with 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 good agreement with that obtained recently by several groups using Baade-Wesselink methods which, averaged over the results from the different groups, gives M_v_=0.73+/-0.14 at [Fe/H]=-1.53. Taking the HIPPARCOS based zero-point and a value of 0.18+/-0.03 for the slope of the M_v_,[Fe/H] relation from the literature we find firstly, the distance modulus of the LMC is 18.26+/-0.15 and secondly, the mean age of the Globular Clusters is 17.4+/-3.0 GYrs. These values are compared with recent estimates based on other "standard candles" that have also been calibrated with HIPPARCOS data. It is clear that, in addition to astrophysical problems, there are also problems in the application of HIPPARCOS data that are not yet fully understood.
We present the first detailed study of the RR Lyrae variable population in the Local Group dSph/dIrr transition galaxy, Phoenix, using previously obtained HST/WFPC2 observations of the galaxy. We utilize template light curve fitting routines to obtain best fit light curves for RR Lyrae variables in Phoenix. Our technique has identified 78 highly probable RR Lyrae stars (54 ab-type; 24 c-type) with about 40 additional candidates. We find mean periods for the two populations of <P_ab_>=0.60+/-0.03 days and <P_c_>=0.353+/-0.002 days. We use the properties of these light curves to extract, among other things, a metallicity distribution function for ab-type RR Lyrae. Our analysis yields a mean metallicity of <[Fe/H]>=-1.68+/-0.06 dex for the RRab stars. From the mean period and metallicity calculated from the ab-type RR Lyrae, we conclude that Phoenix is more likely of intermediate Oosterhoff type; however the morphology of the Bailey diagram for Phoenix RR Lyraes appears similar to that of an Oosterhoff type I system. Using the RRab stars, we also study the chemical enrichment law for Phoenix. We find that our metallicity distribution is reasonably well fitted by a closed-box model. The parameters of this model are compatible with the findings of Hidalgo et al. (2009ApJ...705..704H; 2013ApJ...778..103H), further supporting the idea that Phoenix appears to have been chemically enriched as a closed-box-like system during the early stage of its formation and evolution.
We present systemic velocities and iron abundances for 56 RR Lyraes, the majority of which have been observed by the HIPPARCOS satellite. Comparison between our systemic velocities and previous values identifies several binary candidates only one of which, TU UMa, was previously suspected of being a binary. However, spectra of the unusual RR Lyrae BB Vir show no evidence of line doubling and hence do not support the recent claims that this star may have a Blue Horizontal Branch companion. Comparison between our abundances and previous determinations shows reasonable agreement except with the recent work of Layden (1994, Cat. <J/AJ/108/1016>) where we find systematic differences. Several of the stars included on the HIPPARCOS observing list as RR Lyraes are shown to be mis-classified. Of particular interest are the stars V363 Cas and AT And which, by analogy with XZ Cet, may be anomalous Cepheids.
This is the second of the papers devoted to derive radial velocities and iron abundances of field RR Lyraes observed by HIPPARCOS. Our abundances show good agreement with those in the literature obtained both from photometric ({DELTA}S index) and spectroscopic methods. Binary candidates and stars misclassified as RR Lyraes in the original HIPPARCOS list have been also identified.
We present an analysis of the substructure revealed by RR Lyraes in Sloan Digital Sky Survey Stripe 82, which covers 2.5{deg} in declination on the celestial equator over the right ascension range {alpha}=20.7h to 3.3h. We use the new public archive of light-motion curves in Stripe 82, published by Bramich et al. in 2008 (Cat. V/141), to identify a set of high-quality RR Lyrae candidates. Period estimates are determined to high accuracy using a string-length method. A subset of 178 RR Lyraes with spectrally derived metallicities are employed to derive metallicity-period-amplitude relations, which are then used, together with archive magnitude data and light-curve Fourier decomposition, to estimate metallicities and hence distances for the entire sample. The RR Lyraes lie 5-115kpc from the Galactic Centre, with distance estimates accurate to ~8%. The RR Lyraes are further divided into subsets of 316 RRab types and 91 RRc types based on their period, colour and metallicity. We fit a smooth density law to the distribution as a simple representation of the data. For Galactocentric radii 5-25kpc the number density of RR Lyraes falls as r^-2.4^, but beyond 25kpc, the number density falls much more steeply, as r^-4.5^. However, we stress that in practice the density distribution is not smooth, but dominated by clumps and substructure. Samples of 55 and 237 RR Lyraes associated with the Sagittarius Stream and the Hercules-Aquila Cloud, respectively, are identified. Hence, ~70% of the RR Lyraes in Stripe 82 belong to known substructure, and the sharp break in the density law reflects the fact that the dominant substructure in Stripe 82 - the Hercules-Aquila Cloud and the Sagittarius Stream - lie within 40kpc. In fact, almost 60% of all the RR Lyraes in Stripe 82 are associated with the Hercules-Aquila Cloud alone, which emphasizes the cloud's pre-eminence. Additionally, evidence of a new and distant substructure - the Pisces Overdensity - is found, consisting of 28 faint RR Lyraes centred on Galactic coordinates (l~80{deg}, b~-55{deg}), with distances of ~80kpc. The total stellar mass in the Pisces Overdensity is ~10^4^M_{sun}_ and its metallicity is [Fe/H]~-1.5.
With the increase of known RR Lyrae stars, it is reliable to create classifiers of RR Lyrae stars based on their photometric data or combined photometric and spectroscopic data. Nevertheless the total number of known RR Lyrae stars is still too small compared with the large survey databases. So classification of RR Lyrae stars and other sources belongs to imbalanced learning. Based on Sloan Digital Sky Survey (SDSS) photometric and spectroscopic data, we apply cost-sensitive Random Forests fit for imbalanced learning to preselect RR Lyrae star candidates. Only with photometric data, u-g,g-r,r-i,i-z is the best input pattern. While also considering physical parameters (Teff, [Fe/H], log(g)), the optimal input pattern is Teff, [Fe/H], log(g), u-g,g-r,r-i,i-z, at this moment for cost-sensitive Random Forests, the performance metrics of completeness, contamination, and Matthews correlation coefficient are 0.975, 0.019, and 0.975, respectively. It indicates that adding stellar physical parameters is helpful for identifying RR Lyrae stars from other stars. We apply the best classifiers on the SDSS photometric data and combined photometric data with physical parameters to select RR Lyrae star candidates. Finally 11,041 photometric candidates with spectral type A and F are obtained, and then 304 candidates with physical parameters are selected out. Among the 304 candidates, a small part are HB stars, BS stars, RGB stars, and peculiar stars, and the rest are unknown in the Simbad database. These candidates may be used as the input catalog for time-series follow-up observations.
We have performed the first study of the variable star population of Ursa Major I (UMa I), an ultra-faint dwarf satellite recently discovered around the Milky Way (MW) by the Sloan Digital Sky Survey. Combining time series observations in the B and V bands from four different telescopes, we have identified seven RR Lyrae stars in UMa I, of which five are fundamental-mode (RRab) and two are first-overtone pulsators (RRc). Our V, B-V color-magnitude diagram of UMa I reaches V~23mag (at a signal-to-noise ratio of ~6) and shows features typical of a single old stellar population. The mean pulsation period of the RRab stars <P_ab_>=0.628, {sigma}=0.071 days (or <P_ab_>=0.599, {sigma}=0.032 days, if V4, the longest period and brightest variable, is discarded) and the position on the period-amplitude diagram suggest an Oosterhoff-intermediate classification for the galaxy. The RR Lyrae stars trace the galaxy horizontal branch (HB) at an average apparent magnitude of <V(RR)>=20.43+/-0.02mag (average on six stars and discarding V4), giving in turn a distance modulus for UMa I of (m-M)_0_=19.94+/-0.13mag, distance d=97.3_-5.7_^+6.0^kpc, in the scale where the distance modulus of the Large Magellanic Cloud is 18.5+/-0.1mag. Isodensity contours of UMa I red giants and HB stars (including the RR Lyrae stars identified in this study) show that the galaxy has an S-shaped structure, which is likely caused by the tidal interaction with the MW. Photometric metallicities were derived for six of the UMa I RR Lyrae stars from the parameters of the Fourier decomposition of the V-band light curves, leading to an average metal abundance of [Fe/H]=-2.29dex ({sigma}=0.06dex, average on six stars) on the Carretta et al. (2009, J/A+A/505/117) metallicity scale.
RR Lyrae stars may be the best practical tracers of Galactic halo (sub-)structure and kinematics. The PanSTARRS1 (PS1) 3{pi} survey offers multi-band, multi-epoch, precise photometry across much of the sky, but a robust identification of RR Lyrae stars in this data set poses a challenge, given PS1's sparse, asynchronous multi-band light curves (<~12 epochs in each of five bands, taken over a 4.5yr period). We present a novel template fitting technique that uses well-defined and physically motivated multi-band light curves of RR Lyrae stars, and demonstrate that we get accurate period estimates, precise to 2s in >80% of cases. We augment these light-curve fits with other features from photometric time-series and provide them to progressively more detailed machine-learned classification models. From these models, we are able to select the widest (three-fourths of the sky) and deepest (reaching 120kpc) sample of RR Lyrae stars to date. The PS1 sample of ~45000 RRab stars is pure (90%) and complete (80% at 80kpc) at high galactic latitudes. It also provides distances that are precise to 3%, measured with newly derived period-luminosity relations for optical/near-infrared PS1 bands. With the addition of proper motions from Gaia and radial velocity measurements from multi-object spectroscopic surveys, we expect the PS1 sample of RR Lyrae stars to become the premier source for studying the structure, kinematics, and the gravitational potential of the Galactic halo. The techniques presented in this study should translate well to other sparse, multi-band data sets, such as those produced by the Dark Energy Survey and the upcoming Large Synoptic Survey Telescope Galactic plane sub-survey.
