Emilio Lapasset

Radial Velocities, Binarity, and Kinematic Membership in the Open Cluster NGC 2516*

We present echelle spectroscopic observations for 36 bright (V < 9.6) stars in the open cluster NGC 2516, including several blue straggler candidates and four red giants. Radial velocities are derived by cross-correlations using high signal-to-noise ratio standard spectra as templates. From 22 cluster members a mean cluster velocity of +22.0 ± 0.2 km s-1 was derived. Membership probabilities of the observed stars are computed on the basis of their distance to the cluster center and kinematic criteria. We report the discovery of three double-lined spectroscopic binaries and several probable binaries among main-sequence stars. A binary frequency of more than 26% is found among the high-mass main-sequence stars. The blue straggler HD 66341 is a slowly rotating cluster member with constant velocity, while HD 66194 is a fast-rotating Be star with probable variations in radial velocity. Other blue straggler candidates, such as HD 65663, 65950, 66066, and 65987, must be considered turnoff stars.

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.

Radial Velocities and Kinematic Membership in the Open Cluster NGC 3114

Echelle spectroscopic observations for 30 bright stars in the field of the sparse open cluster NGC 3114 are presented. The sample includes main-sequence stars, yellow and red giants, and blue straggler candidates. Radial velocities are derived by cross-correlations using high signal-to-noise ratio standard spectra as templates. The cluster mean velocity is well defined from eight giants and several main-sequence stars whose average is RV = -3.52 ± 0.25 km s-1. The membership probabilities of the observed stars are computed on the basis of the velocity distributions of the cluster and field stars, and the expected percentage of contamination at each position. We classified 19 cluster members and 10 nonmembers; the remaining star is a known spectroscopic binary for which no membership probability was assigned. Among the members, there is a bright yellow giant, seven red giants, and four blue straggler candidates, although they should be considered as turn-off stars. The location of two of them in the color-magnitude diagram (slightly blueward of the turn-off) can be explained by their low rotational velocities. No velocity variations were detected in the 16 stars measured more than once, which indicates that NGC 3114 possess an abnormally low binary frequency. From spectral types of cluster members, a distance modulus (V - Mv) = 9.8 ± 0.2 mag and a reddening E(B-V) = 0.07 ± 0.01 mag are derived. The cluster age is estimated to be 1.6 × 108 yr.

A REVISED EFFECTIVE TEMPERATURE CALIBRATION FOR THE DDO PHOTOMETRIC SYSTEM

A revised effective temperature calibration for the DDO photometric system is presented. Recently published photometric and spectroscopic observations of field and open cluster G and K stars allow a better definition of the solar-abundance fiducial relation in the DDO C0(45-48) vs C0(42-45) diagram. The ability of the DDO system to predict MK spectral types of G and K giants is demonstrated. The new DDO effective temperature calibration reproduces satisfactorily the infrared temperature scale of Bell and Gustafsson (1989). It is shown that Osborns (1979) calibration underestimates the effective temperatures of K giants by ~170 K and those of late-type dwarfs by ~150 K.

Spectroscopic Binaries and Kinematic Membership in the Open Cluster NGC 3532

We report spectroscopic observations for bright stars in the open cluster NGC 3532 up to 1 mag below the turnoff point. We compute radial velocities by cross-correlations and determine spectral types and rotational velocities. Using 21 stars identified as certain members, we derive a mean cluster velocity of +3.4 ± 0.3 km s-1. From radial velocities and angular distances to the cluster center, we compute membership probabilities for all but two stars that are radial velocity variables. Only one out of 34 program stars is a clear kinematic nonmember. Three spectroscopic binaries and three additional possible radial velocity variables are detected among the 23 stars measured more than once. We report the star HD 96609 as a double-lined spectroscopic binary. Using the two-dimensional cross-correlation technique TODCOR developed by Zucker & Mazeh, we derive the radial velocity curves for both components and obtain the orbital parameters with errors of 0.3% and 0.7% for the projected orbital semiaxis and masses, respectively. This system is composed of two main-sequence stars in a circular orbit, with a period of 8.19 days.

PHOTOMETRIC ANALYSIS OF THE CONTACT BINARY BF PAVONIS

We present UBV photoelectric observations of the W UMa star BF Pav obtained between 1987 and 1993. A minimum times study allows to detect a likely period increase of about 0.015 sec/year. The Wilson-Devinney code is employed to simultaneously model, the B and V light curves for several fixed values of mass-ratio q. From the quality-of-fit of the different solutions an approximate value of q=1.4 ± 0.2 is derived. Absolute values of masses, dimensions and luminosities are estimated by means of standard mass-luminosity relations for main sequence stars. The detected period variations determines a lower limit of 5 10-7 solar mass/year for the rate of mass transfer from the less massive to the more massive component. We speculate that BF Pav has recently become in contact and is now in a rapid phase of mass-transfer.

PHOTOMETRIC ANALYSES OF THE SHORT-PERIOD CONTACT BINARIES HY PAVONIS, AW VIRGINIS, AND BP VELORUM

We present BV light curve synthetic analyses of three short period contact (W UMa) binaries: HY Pavonis (P ~0.35 days), AW Virginis (P ~0.35 days), and BP Velorum (P ~0.26 days). Different possible configurations for a wide range of the mass ratio were explored in each case making use of the Wilson-Divinney code. The photometric parameters of the systems were determined from the synthetic light curve solutions that best fit the observations. AW Vir has two components of very similar temperatures and therefore the subtype (A or W) remains undetermined. HY Pav and BP Vel are best modeled by W-type configurations and the asymmetries in the light curves are reproduced by introducing cool spots on the more massive secondary components. Even when BP Vel lies in the region of the open cluster Cr 173, its distance modulus, in principle, rules it out as a cluster member.

COLLINDER 223: A MODERATELY YOUNG OPEN CLUSTER IN THE CARINA SPIRAL FEATURE

UBV photoelectric data for 110 stars and DDO data for seven stars are discussed originating in the field of the previously unstudied open cluster Collinder 223. These data show that Cr 223 is a genuine open cluster located at a distance of (2900 + or - 270) pc from the sun and 96 pc below the galactic plane. Nearly 40 percent of the sample stars - including one red giant, two blue stragglers, and two suspected variables - are found to be cluster members. The reddening across the cluster is not uniform, the mean value being E(B-V) = 0.26 + or - 0.03 (s.d.). An age of 3.6 x 10 to the 7th yr has been derived, which places Cr 223 within the IC 4665 age group.

UBV photometry of SN 1987A - Earliest photoelectric observations

This paper reports on the earliest known photoelectric photometry for Supernova 1987A, obtained just twenty-four hours after the IMB/Kamiokande-II neutrino detection. Values of V=4.78 (±0.05), B−V=0.00 (±0.06) and U−B= −0.78 (±0.06) were measured on Feb 24,336 UT 1987. This is twelve hours sooner than the next known reliable photoelectric observation

Orbital Solutions and Absolute Elements of the W UMa Binary MW Pavonis

We present differential UBV photoelectric photometry obtained by Williamon of the short-period A-type W UMa binary MW Pav. With the Wilson-Devinney analysis program, we obtained a simultaneous solution of these observations with the UBV photometry of Lapasset, the V measurements by the ASAS program, and the double-lined radial velocity measurements of Rucinski and Duerbeck. Our solution indicates that MW Pav is in an overcontact state, where both components exceed their critical Roche lobes. We derive masses of M1 = 1.514 ± 0.063 M⊙ and M2 = 0.327 ± 0.014 M⊙, and equal-volume radii of R1 = 2.412 ± 0.034 R⊙ and R2 = 1.277 ± 0.019 R⊙ for the primary and secondary, respectively. The system is assumed to have a circular orbit and is seen at an inclination of 86.39° ± 0.63°. The effective temperature of the primary was held fixed at 6900 K, whereas the secondarys temperature was found to be 6969 ± 10 K. The asymmetry of the light curves requires a large, single star spot on the smaller, less massive secondary component. A consistent base solution, with different spot characteristics for the Williamon, Lapasset, and ASAS data, was found. The modeled spot varied little during the 40-year range of photometric observations. The combined solution utilized a third light component and found that the period is changing at a rate of dP/dt = (6.50 ± 0.19) × 10-10.