Continued radial velocity observations over several years, have allowed to discover four spectroscopic binary systems among our sample of twenty five galactic Cepheids. Each system is composed by the Cepheid and an invisible probably hot dwarf star. A spectroscopic orbit has been determined for each system. The orbital periods for RX Cam, MW Cyg, Z Lac and U Vul are 1113, 439, 383 and 2510 days, respectively. For the pulsation motion, radial velocity versus phase diagram have been fitted by an analytic relation, formally similar to a Kepler motion. The stellar radius variation of each cepheid has been derived by integration of this relation over the whole pulsating period.
The catalogue contains 5905 individual radial velocity values for 126 Cepheids. 1446 individual radial velocity values for 79 fields Cepheids and three Cepheids in globular clusters were made in 1987-1991, 2140 individual radial-velocity measurements were made for 86 Cepheids between 1992 and 1995, and 2444 radial-velocity measurements for 108 Cepheids were made on the 1995-1998. The observations were made with the correlation spectrometer designed by A.A. Tokovinin.
We present new radial velocities (RVs), improved pulsation periods, and reference 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 Z Mic. This study is based on high-resolution spectra obtained with the echelle spectrograph of the 2.5m du Pont telescope at Las Campanas Observatory. We obtained ~200 spectra per star (i.e., a total of ~2300 spectra), distributed more or less uniformly throughout their pulsation cycles. RV curves and photometric light curves phased to our new ephemerides are presented for all program stars.
We present template radial velocity curves of ab-type RR Lyrae stars constructed from high-precision measurements of H{alpha}, H{beta}, and H{gamma} lines. Amplitude correlations between the Balmer line velocity curves, Johnson V band, and Sloan Digital Sky Survey (SDSS) g- and r-band light curves are also derived. Compared to previous methods, these templates and derived correlations reduce the uncertainty in measured systemic (center-of-mass) velocities of RR Lyrae stars by up to 15km/s, and will be of particular interest to wide-area spectroscopic surveys such as the SDSS and LAMOST Experiment for Galactic Understanding and Exploration.
We present here the appendix to the paper with the new high precision radial velocities for a sample of Galactic Cepheids. The stars are: SU Cas, EV Sct, del Cep, CV Mon, U Sgr, eta Aql, X Cyg, T Mon, RS Pup, and SV Vul.
We report 490 radial velocities for 16 Galactic Cepheid variables. The typical uncertainty of a single velocity is {+/-}0.40km/s. Comparison with published velocities shows excellent agreement. Two of the Cepheids (Z Lac, S Sge) are known binaries and exhibit orbital velocity changes in our observing interval.
All galaxies that have been adequately examined so far have shown an extended stellar halo. To search for such a halo in the LMC we have obtained low-resolution spectra for 100 LMC RR Lyrae stars, of which 87 are in the field and 13 in the clusters NGC 1835 and NGC 2019. We measured radial velocities for 87 LMC RR Lyrae stars, and metallicities for 78 RR Lyrae stars, nearly tripling the previous sample. These targets are located in 10 fields covering a wide range of distances, out to 2.5 degrees from the center of the LMC.
We present high-resolution spectroscopic observations and species-by-species radial velocities of a number of southern Cepheids. The stars (BP Cir, V350 Sgr, AX Cir, V636 Sco, W Sgr, S Mus, {beta} Dor, TT Aql, Y Oph, YZ Car, SW Vel, X Pup, T Mon and l Car) were observed as part of a long-term programme at Mt John University Observatory. Radial velocities were determined with the line bisector technique, and have a precision of ~300m/s. Velocity differences as large as 30km/s were found for H and Ca II when referenced to the metallic line velocity curves, but more subtle variations (of 12km/s) were also detected in many other species. Pulsational phase anticorrelations are found between lines of Si II and Ba II, confirming the propagation time delay between line-forming layers producing these two species. We find that the amplitude and phase differences between the various species increase with period.
Ruprecht 147 is a hitherto unappreciated open cluster that holds great promise as a standard in fundamental stellar astrophysics. We have conducted a radial velocity survey of astrometric candidates with Lick, Palomar, and MMT observatories and have identified over 100 members, including 5 blue stragglers, 11 red giants, and 5 double-lined spectroscopic binaries (SB2s). We estimate the cluster metallicity from spectroscopic analysis, using Spectroscopy Made Easy (SME), and find it to be [M/H]=+0.07+/-0.03. We have obtained deep CFHT/MegaCam g'r'i'z' photometry and fit Padova isochrones to the (g'-i') and Two Micron All Sky Survey (J-K_S_) color-magnitude diagrams, using the {tau}^2^ maximum-likelihood procedure of Naylor, and an alternative method using two-dimensional cross-correlations developed in this work. We find best fits for Padova isochrones at age t=2.5+/-0.25Gyr, m-M=7.35+/-0.1, and A_V_=0.25+/-0.05, with additional uncertainty from the unresolved binary population and possibility of differential extinction across this large cluster. The inferred age is heavily dependent on our choice of stellar evolution model: fitting Dartmouth and PARSEC models yield age parameters of 3Gyr and 3.25Gyr, respectively. At ~300pc and ~3Gyr, Ruprecht 147 is by far the oldest nearby star cluster.
