CORAVEL Radial Velocity Research Articles

Photometric membership and metallicities of red giant candidates in selected open clusters

AbstractAs part of a long‐term project to determine abundances and astrophysical properties of evolved red stars in open clusters, we present high‐precision DDO photoelectric observations for a sample of 33 red giant candidates projected in the fields of nine Galactic open clusters. These data are supplemented with UBV photoelectric photometry of 24 of these stars as well as with CORAVEL radial‐velocity observations for 13 red giant candidates in four of the clusters. We also present Washington photoelectric photometry of a small sample of red giant candidates of the open cluster Ruprecht 97. The likelihood of cluster membership for each star photometrically observed and for 23 additional red giant candidates with UBV and DDO data available in the literature, is evaluated by using two independent photometric criteria. Nearly 82% of the analysed stars are found to have a high probability of being cluster giants. Photometric membership probabilities show very good agreement with those obtained from CORAVEL radial velocities. While E (B –V) colour excesses were determined from combined B – V and DDO colours, calibrations of the DDO system were used to derive MK spectral types, effective temperatures and metallicities. The derived DDO metallicities range between values typical of moderately metal‐poor clusters ([Fe/H] = –0.19) to moderately metal‐rich ([Fe/H] = 0.25) ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

CCD BVI photometry and Coravel observations of stars in the open cluster NGC 2489

Abstract We present CCD BVI photometry for the southern open cluster NGC 2489 and its surrounding field. The sample consists of 2182 stars measured in an area of 13.6 × 13.6 arcmin2, extending down to V∼ 21.5. These data are supplemented with CORAVEL radial-velocity observations for seven red giant candidates. A cluster angular radius of 6.7 ± 0.6 arcmin, equivalent to 3.5 ± 0.3 pc, is estimated from star counts carried out inside and outside the cluster region. The comparison of the cluster colour–magnitude diagrams with isochrones of the Padova group yields E(B−V) = 0.30 ± 0.05, E(V−I) = 0.40 ± 0.05 and V−MV= 12.20 ± 0.25 for log t= 8.70 (t= 500+130−100 Myr) and Z= 0.019. NGC 2489 is then located at 1.8 ± 0.3 kpc from the Sun and 25 pc below the Galactic plane. The analysis of the kinematical data allowed us to confirm cluster membership for six red giants, one of them being a spectroscopic binary. A mean radial velocity of 38.13 ± 0.33 km s−1 was derived for the cluster red giants. The properties of a sample of open clusters aligned along the line of sight of NGC 2489 are examined.

Membership, binarity, reddening and metallicity of red giant candidates in three southern open clusters

37 potential members of the red-giant branches of NGC 6192, NGC 6208 and NGC 6268 were observed in the UBV system, while 22 of them were also observed in the DDO system. The observations were made at La Silla and Cerro Tololo Inter-American observatories (Chile), using pulse-counting photoelectric photometers. Coravel radial velocities (RVs) were obtained at La Silla for 24 red giant candidates in the three clusters. Five stars of NGC 6192 have RVs in the narrow range -8.8 km/s < VR < -6.4 km/s, including two new spectroscopic binaries (SBs). Three stars of NGC 6208 – including a new SB – and three stars of NGC 6268 show similar RVs so that their physical membership to NGC 6208 and NGC 6268, respectively, is highly probable. Mean radial velocities are: -7.7 ± 0.38 km/s (NGC 6192), -32.21 ± 0.28 km/s (NGC 6208) and -15.11 ± 0.08 km/s (NGC 6268). We have also derived the following mean E(B-V) values from Janes (1977) iterative method: 0.63 ± 0.02 (NGC 6192), 0.31 ± 0.02 (NGC 6208) and 0.43 ± 0.02 (NGC 6268).

Photometric and Coravel observations of red giant candidates in three open clusters: membership, binarity, reddening and metallicity

Aims. We present new CORAVEL radial-velocity observations and photoelectric photometry in the UBV and DDO systems for a sample of potential members of the red-giant branches of NGC 6192, NGC 6208 and NGC 6268, three open clusters projected close to the Galactic center direction. We also examine the properties of a sample of 42 inner disk open clusters projected towards almost the same direction as the three clusters. Methods. Cluster members and red field giants were discriminated by using the CORAVEL radial-velocity data and by applying two photometric criteria. Interstellar reddening and metal content of the clusters were derived from combined BV and DDO data. Results. Cluster membership for five red giants in NGC 6192, three in NGC 6208 and three in NGC 6268 has been confirmed by the analysis of the photometric and kinematic data. Photometric membership probabilities show very good agreement with those obtained from CORAVEL radial velocities. Three new spectroscopic binaries were discovered among the red giants of NGC 6192 and NGC 6208. Mean radial velocities and E(B − V) colour excesses were derived. Conclusions. The overall metallicities were found to be nearly solar for NGC 6208 and above solar for NGC 6192 and NGC 6268. Most of the clusters located closer than 2 kpc from the Sun in the considered direction are slightly more reddened than the absorption resulting from the Baade’s window absorption law.

Statistical Properties of Solar-Type Close Binaries

AbstractTwo Coravel radial velocity surveys dedicated to F7-K field dwarfs and to open clusters are merged in order to investigate the statistical properties of binaries with periods up to 10 years. Thanks to the accurate trigonometric parallaxes provided by Hipparcos, an unbiased sample of spectroscopic binaries (SB) is selected. After correction for the uncertainties of the measurements, the following results are obtained: 1. The distribution of mass ratios exhibits a peak for equal-mass binaries (twins), which is higher for short-period binaries than for long-period binaries. 2. Apart from the twins, the distribution of mass ratios exhibits a broad peak from 0.2 to 0.6. 3. The orbital eccentricities of twins are slightly smaller than those of other binaries. 4. An excess of SB is observed with periods shorter than about 50 days in comparison with the Duquennoy and Mayor log-normal distribution of periods. These features suggest that close binary stars are generated by two different processes. A possible difference could come from the accretion onto the binary, for instance from a common envelope or from a circumbinary disk. Alternatively, twins could come from dynamic evolution of multiple systems. It is not clear whether the formation models are already sufficiently elaborated to reproduce our statistics.

The relatively young, metal-poor and distant open cluster NGC 2324

We have obtained CCD photometry in the Johnson V, Kron-Cousins I and CT1 Washington systems for NGC 2324, a rich open cluster located ∼35 ◦ from the Galactic anticentre direction. We measured V magnitudes and V − I colours for 2865 stars and T1 magnitudes and C − T1 colours for 1815 stars in an area of 13. 6 × 13. 6. The comparison of the cluster colour-magnitude diagrams with isochrones of the Geneva group yield E(V − I) = 0.33 ± 0.07 and V − MV = 13.70 ± 0.15 for log t = 8.65 (t = 440 Myr) and Z = 0.008 ((Fe/H) = −0.40), and E(C − T1) = 0.40 ± 0.10 and T1 − MT 1 = 13.65 ± 0.15 for the same age and metallicity level. The resulting E(V − I) reddening value implies E(B − V) = 0.25 ± 0.05 and a distance from the Sun of (3.8 ± 0.5) kpc. Star counts carried out within and outside the cluster region allowed us to estimate the cluster angular radius as 5. 3 ± 0. 3 (5.9 pc). When using the E(B − V) reddening value here derived and the original Washington photometric data of Geisler et al. (1991) for the stars confirmed as red cluster giants from Coravel radial velocities, we found (Fe/H) = −0.31 ± 0.04, which is in good agreement with the best fits of isochrones. Therefore, NGC 2324 is found to be a relatively young, metal-poor and distant open cluster located beyond the Perseus spiral arm. A comparison of NGC 2324 with 10 well-known open clusters of nearly the same age shows that the cluster metal abundance and its position in the Galaxy are consistent with the existence of a radial abundance gradient of −0.07 dex kpc −1 in the Galactic disc.

Multicolour photometry and Coravel observations of stars in the southern open cluster IC 2488

We present new UBV photoelectric observations of 119 stars in the field of the southern open cluster IC 2488, supplemented by DDO and Washington photometry and Coravel radial velocities for a sample of red giant candidates. Nearly 50% of the stars sampled - including three red giants and one blue straggler - are found to be probable cluster members. Photometric membership probabilities of the red giant candidates show good agreement with those obtained from Coravel data. A mean radial velocity of ( 2.63 0.06) km s 1 is derived for the cluster giants. The reddening across the cluster is found to be uniform, the mean value being E(B V)= 0.24 0.04. IC 2488, located at a distance of (1250 120) pc from the Sun and 96 pc below the Galactic plane, is most probably not related to the planetary nebula ESO 166-PN21. A metal abundance (Fe/H)= 0.10 0.06 relative to the Sun is determined from DDO data of the red giant members, in good agreement with the (Fe/H) values derived from five independent Washington abundance indices. An age of 180 Myr is determined from the fitting of isochrones computed with convective overshooting for Z = 0.019. The isochrone for log t= 8.25 reproduces remarkably well not only the morphology of the upper main sequence but also the observed red giant pattern.

Multiplicity among solar–type stars

Two CORAVEL radial velocity surveys - one among stars in the solar neighbourhood, the other in the Pleiades and in Praesepe - are merged to derive the statistical properties of main-sequence binaries with spectral types F7 to K and with periods up to 10 years. A sample of 89 spectroscopic orbits was finally obtained. Among them, 52 relate to a free-of-bias selection of 405 stars (240 field stars and 165 cluster stars). The statistics corrected for selection eects yield the following results: (1) No discrepancy is found between the binaries among field stars and the binaries in open cluster. The distributions of mass ratios, of periods, the period-eccentricity diagram and the binary frequencies are all within the same error intervals. (2) The distribution of mass ratios presents two maxima: a broad peak from q 0: 2t oq 0:7, and a sharp peak for q> 0:8 (twins). Both are present among the early-type as well as among the late-type part of the sample, indicating a scale-free formation process. The peak for q> 0:8 gradually decreases when long-period binaries are considered. Whatever their periods, the twins have eccentricities significantly lower than the other binaries, confirming a dierence in the formation processes. Twins could be generated by in situ formation followed by accretion from a gaseous envelope, whereas binaries with intermediate mass ratios could be formed at wide separations, but they are made closer by migration led by interactions with a circumbinary disk. (3) The frequency of binaries with P< 10 years is about 14%. (4) About 0.3% of binaries are expected to appear as false positives in a planet search. Therefore, the frequency of planetary systems among stars is presently 7 +4%. The extension of the distribution of mass ratios in

Analysis of a δ Scuti spectroscopic binary: CQ Lyncis

CQ Lyn is a new double-lined spectroscopic binary, composed of an Am Scuti and a solar-like star, with an orbital period of 12.50736 d and a zero-eccentricity. Physical parameters of both stars are well constrained. The characteristics of the primary are the following: M = 1:714 M, Te = 6760 K, log L=L = 1:097 and logg = 3:85 dex. Power spectra of Hipparcos photometry and Coravel radial velocities show multi-period pulsation behaviour. Three frequencies are identified: f1 = 8:86725, f2 = 8:81150 and f3 = 8:91007 c/d and are assumed to be l = 2 f -modes split by rotation, considering their pulsation constants Q1= 0:0356, Q2= 0:0359 and Q3= 0:0355 d. Two combination oscillations are also present in the power spectrum at frequency f1+f2 and f2+f3.

Fundamental Parameters of Cepheids. V. Additional Photometry and Radial Velocity Data for Southern Cepheids

I present photometric and radial velocity data for Galactic Cepheids, most of them being in the southern hemisphere. There are 1250 Geneva seven-color photometric measurements for 62 Cepheids, the average uncertainty per measurement is better than 0.01 mag. A total of 832 velocity measurements have been obtained with the CORAVEL radial velocity spectrograph for 46 Cepheids. The average accuracy of the radial velocity data is 0.38 km s-1. There are 33 stars with both photometry and radial velocity data. I discuss the possible binarity or period change that these new data reveal. I also present reddenings for all Cepheids with photometry. The data are available electronically.

Structural Properties of s-Cepheid Velocity Curves: Constraining the Location of the ω4 = 2ω1 Resonance

AbstractThe light curves of the first overtone Pop I Cepheids (s-Cepheids) show a discontinuity in their ϕ21 vs. P diagram, near P = 3.2 d. This feature, commonly attributed to the 2:1 resonance between the first and the fourth overtones (ω4 ≈ 2ω1), is not reproduced by the hydrodynamical models (Antonello &amp; Aikawa 1995). With the goal of reexamining the resonance hypothesis, we have obtained new CORAVEL and CORALIE radial velocity curves for 17 overtone Cepheids. Together with 10 objects from Krzyt et al. (2000), the combined sample covers the whole range of overtone Cepheid periods. The velocity Fourier parameters display a strong characteristic resonant behavior. In striking contrast to photometric ones, they vary smoothly with the pulsation period and show no jump at 3.2 d. The existing radiative hydrodynamical models match very well the velocity parameters. The center of the ω4 = 2ω1 resonance is estimated to occur at Pr = 4.58 ± 0.04 d, i.e. at a period considerably longer than previously assumed (3.2 d). Five new s-Cepheids, with periods above 5 d, have been identified from the radial velocity curves morphology: V419 Cen, V659 Cen, MY Pup, GH Car and V440 Per. The data and the discussion can be found in Kienzle et al. (1999). Preprints and the data are available at: http://obswww.unige.ch/˜kienzle.

Membership, binarity and metallicity of red giants in the southern open cluster NGC 2354

We present new Coravel radial-velocity obser- vations and photoelectric photometry in the UBV,DDO and Washington systems for a sample of red giant can- didates in the eld of the intermediate-age open cluster NGC 2354. Photometric membership probabilities show very good agreement with those obtained from Coravel radial velocities. The analysis of the photometric and kine- matical data allow us to conrm cluster membership for 9 red giants, one of them being a spectroscopic binary, while 4 conrmed spectroscopic binaries appear to be proba- ble members. We have also discovered 4 spectroscopic bi- naries not belonging to the cluster. A mean radial ve- locity of (33.40 0.27) km s 1 and a mean reddening E(B V )=0 :13 0.03 were derived for the cluster giants. NGC 2354 has a mean ultraviolet excess = 0 :03 0.01, relative to the eld K giants, and a mean new cyanogen anomaly CN = 0:035 0.007, both im- plying (Fe/H) 0 :3. The moderately metal-poor char- acter of NGC 2354 is conrmed using ve dierent metal abundance indicators of the Washington system. The clus- ter giant branch is formed by a well dened clump of 7 stars and 4 stars with high membership probabilities seem to dene an ascending giant branch. The whole red giant locus cannot be reproduced by any theoretical track.

A CORAVEL radial-velocity monitoring of S stars: Symbiotic activity vs. orbital separation. III.

Orbital elements are presented for the Tc-poor S stars HR 363 (= HD 7351) and HD 191226. With an or- bital period of 4592 d (=12.6 y), HR 363 has the longest period known among S stars, and yet it is a strong X-ray source. Its X-ray flux is similar to that of HD 35155, an S star with one of the shortest orbital periods (640 d). This surprising result is put in perspective with other diagnos- tics of binary interaction observed in binary S stars. They reveal that there is no correlation between the level of bi- nary interaction and the orbital period. All these activity diagnostics moreover exhibit a strong time-variability. In the well-documented case of HR 1105, this time-variability appears to be a combination of orbital modulation and secular variation. A stream of gas from the red-giant wind, which is heated when funneled through the inner Lagrangian point, has been proposed as the source of the hard photons (Shcherbakov & Tuominen 1992). Dierent viewing angles of the stream during the orbital cycle ac- count for the orbital modulation, whereas long-term fluc- tuations of the mass-loss rate account for the secular vari- ations. Little dependence to the orbital separation is ex- pected for this kind of activity. If such streams are causing the activity observed in the other binary S stars as well, it would provide a natural explanation for the absence of correlation between orbital periods and activity levels, since the red-giant mass loss rate would be the dominant factor. The existence of such funneled streams is moreover predicted by smooth particle hydrodynamics simulations of mass transfer in detached binary systems.

A CORAVEL radial-velocity monitoring of giant Ba and S stars: Spectroscopic orbits and intrinsic variations. I.

With the aim of deriving the binary frequency among Ba and S stars, 56 new spectroscopic orbits (46 and 10, respectively) have been derived for these chemically- peculiar red giants monitored with the CORAVEL spec- trometers. These orbits are presented in this paper (38 or- bits) and in a companion paper (Udry et al. 1998, Paper II; 18 orbits). The results for 12 additional long-period binary stars (6 and 6, respectively), for which only minimum pe- riods (generally exceeding 10 y) can be derived, are also presented here (10) and in Paper II (2). The global analy- sis of this material, with a few supplementary orbits from the literature, is presented in Jorissen et al. (1998). For the subsample of Mira S, SC and (Tc-poor) C stars showing intrinsic radial-velocity variations due to at- mospheric phenomena, orbital solutions (when available) have been retained if the velocity and photometric pe- riods are dierent (3 stars). However, it is emphasized that these orbit determinations are still tentative. Three stars have been found with radial-velocity variations syn- chronous with the light variations. Pseudo-orbital solu- tions have been derived for those stars. In the case of RZ Peg, a line-doubling phenomenon is observed near maxi- mum light, and probably reflects the shock wave propa- gating through the photosphere.

Surface brightness distance determinations to the Large Magellanic Cloud Cepheid variables HV 899 and 2257*

We present new VRI light curves for the long-period LMC Cepheids HV899 and 2257 and combine these data with the CORAVEL radial velocity curves of Imbert to derive the distances to these variables using the surface brightness method. Assuming metallicities of [Fe/H]=(−0.4±0.2) for both supergiants, we find metallicity-corrected distances of (65.2±4.3) kpc for HV899 and (65.7±4.3) kpc for HV2257, which correspond to true distance moduli of (19.07±0.15) and (19.09±0.15) mag, respectively. These distance moduli are about 0.4 mag larger than those predicted for the LMC by the galactic Cepheid calibration of the surface brightness method of Gieren, Barnes & Moffett [which predicts μ 0 (LMC)∼18.65 mag]

Stellar kinematic groups. I - The Ursa Major group

The Ursa Major Group (UMaG) is studied as a test case for the authenticity of Stellar Kinematic Groups, using Coravel radial velocities, recent compilations of astrometric data, and new spectroscopic observations. Spectroscopic age indicators, particularly indices of the strength of chromospheric emission, are applied to solar-type candidate members of UMaG, and it is shown that stars that meet the spectroscopic criteria also have kinematics that agree better with the space motions of the nucleus of UMaG than does the starting sample as a whole. The primary limitation on the precision of kinematics is now parallaxes instead of radial velocities. These more restrictive kinematic criteria are then applied to other UMaG candidates and a list summarizing membership is presented. UMaG is also examined as a cluster, confirming its traditional age of 0.3 Gyr, and a mean Fe/H of -0.08 +/- 0.09 for those stars most likely to be bona fide members.

On the absolute magnitude of RR Lyrae stars - UU Ceti, RV Phoenicis, and W Tucanae

view Abstract Citations (71) References (70) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Absolute Magnitude of RR Lyrae Stars: UU Ceti, RV Phoenicis, and W Tucanae Cacciari, C. ; Clementini, G. ; Fernley, J. A. Abstract IR JHK light curves are presented for the RRab Lyrae stars UU Ceti, RV Phoenicis, and W Tucanae. These stars have similar periods and metallicities data, together with BVRI photometry and CORAVEL radial velocity data and Walraven photometry are used to derive absolute magnitudes for the stars using two formulations of the Baade-Wesselink method: (1) the infrared flux version and (2) the surface brightness version. The two methods are directly compared and their respective advantages and shortcomings are discussed. Finally, a comparison is made with previous results on the absolute magnitude of RR Lyrae variables. Publication: The Astrophysical Journal Pub Date: September 1992 DOI: 10.1086/171711 Bibcode: 1992ApJ...396..219C Keywords: Light Curve; Lyra Constellation; Stellar Magnitude; Stellar Oscillations; Variable Stars; Infrared Photometry; Metallicity; Radial Velocity; Astrophysics; STARS: FUNDAMENTAL PARAMETERS; STARS: OSCILLATIONS; STARS: VARIABLES: OTHER RR LYRAE full text sources ADS | data products SIMBAD (40)

The Luminosity-Metallicity Relation for RR Lyrae Stars and its Implications for the Astronomical Distance Scale

AbstractThe surface brightness version of the Baade-Wesselink method, has been applied to 7 field RR Lyrae stars with metallicity ranging from [Fe/H]= −0.2 to −1.5. V magnitudes, V-R and V-I colors and CORAVEL radial velocities were used, and the analysis was performed over a restricted phase range in order to avoid the complications caused by the pulsating atmospheres. The combination with previous results of the B-W method, which used comparable criteria (Jones, Carney, &amp; Latham, 1988, preprint; Jameson, Fernley, &amp; Longmore 1987, in press M.N.R.A.S; Cohen &amp; Gordon 1987, Ap.J., 318, 215) leads to the following relation between the absolute luminosity and metallicity:Mv = (1.0 ± 0.05) + (0.17 ± 0.05) [Fe/H]This relation is in very good agreement with the preliminary results found by Liu and Janes (this volume). The application of the above relation to the RR Lyraes in M31 and the Magellanic Clouds leads to distance moduli of (m–M)o= 24.21 ± 0.20 for M31, (m–M)o = 18.26 ± 0.20 for the LMC, and (m–M)o =18.85 ± 0.20 for the SMC, and the distance to the galactic center turns out to be approximately 7.2 kpc. From the absolute magnitude of the RR Lyraes and adopting a constant visual magnitude difference between the RR Lyraes and the turn-off ΔV = 3.55 (Buonanno 1986, Mem.S.A.It., 57, 333), we estimate ages of 18.8 and 15.7 Gyr for globular clusters of metallicity [Fe/H] = −2.2 (e.g. M92) and [Fe/H] = −0.8 (e.g. 47 Tuc) respectively, using the age-turnoff luminosity relation derived by Sandage (1982, Ap.J., 252, 553) or 20.9 and 16.9 Gyr using Buonanno’s relation.

The Absolute Luminosity of RR Lyrae Variables

We have taken UBVRI photoelectric photometry and CORAVEL radial velocities for 6 field RR Lyraes, i.e. SW And, YZ Cap, SW Dra, SS For, RV Phe and V440 Sgr, with the purpose of applying the Baade-Wesselink (B-W) method and determining their absolute magnitudes. The present improvements with respect to previous applications of the method are: a) the use of the (V-I) color, which shows the smallest sensitivity to gravity and metal abundance in the color-visual surface brightness plane. b) the use of a new grid of model atmospheres by Buser and Kurucz (1986), which include an improved treatment of opacity and convection. They provide a complete set of models for the relevant values of effective temperatures, gravities and metal abundances, thus avoiding the need of inaccurate interpolations or extrapolations.

Coravel Radial Velocities of Supergiants in the Small Magellanic Cloud

Kinematical studies of the Magellanic Clouds began more than half a century ago, when Wilson, in 1918, first interpreted the gradient of the 17 radial velocities of gazeous nebulae in the Large Cloud in terms of rotation. In the case of the Small Magellanic Cloud, the first real attempt to understand the velocity field of this galaxy was performed by the Radcliffe astronomers (Feast et al., 1960, 1961). Their study was based on radial velocities of 40 stars and 13 HII regions.With the installation by ESO of an objective-prisme astrograph in South Africa, in 1961, and then of several larger telescopes in Chile in 1968, the number of measurements significantly increased for Magellanic objects, in particular in the SMC. In this galaxy, the objective-prism observations resulted in about 100 stellar radial velocities (Florsch, 1972a) of probable members. A compilation by Maurice (1979) of all then known slit-spectrograph radial velocities gave velocities for 80 supergiants, 35 HII regions and 12 planetary nebulae.