Alejandra A. E. Milone

BVRI Light Curves for 22 Type 1a Supernovae

We present 1210 Johnson/Cousins B, V, R, and I photometric observations of 22 recent Type Ia supernovae (SNe Ia): SNe 1993ac, 1993ae, 1994M, 1994S, 1994T, 1994Q, 1994ae, 1995D, 1995E, 1995al, 1995ac, 1995ak, 1995bd, 1996C, 1996X, 1996Z, 1996ab, 1996ai, 1996bk, 1996bl, 1996bo, and 1996bv. Most of the photometry was obtained at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics in a cooperative observing plan aimed at improving the database for SNe Ia. The redshifts of the sample range from cz = 1200 to 37,000 km s-1 with a mean of cz = 7000 km s-1.

The Blue Straggler RS Canum Venaticorum Star S1082 in M67: A Detailed Light Curve and the Possibility of a Triple* **

Using both photometric and spectroscopic data, we present a picture of the very unusual blue straggler S1082 in the old open cluster M67 whose light is the sum of a close binary (P = 1.0677978 days) and another cluster member. The primary of the close binary and the third star are both blue stragglers in their own rights. Using relative photometry with millimagnitude accuracy, we provide a complete V-band light curve for the system and show a number of unusual features: brightness variations at the 0.01?0.03 mag level from month to month at all phases, a narrow primary and broad secondary eclipse, brightness differences between phases 0.25 and 0.75, and short duration (~1 hr) drops in brightness. Much of the light-curve variation appears to be because of spot activity on the cooler, fainter, nearly synchronized component of the close binary. We use spectra from several sources to constrain the temperatures of the three known components, the relative flux contributions, rotational velocities, and radial velocities. The data clearly show that the brightest star (narrow-line component) seen in the spectrum is on an orbit with period P = 1189 ? 7 days and eccentricity e = 0.57 ? 0.08, although we cannot prove that there is a dynamical link between it and the close binary. The systematic velocities of all of the stars indicate that they are members of the cluster. Our models of the system indicate that the cooler component of the close binary lies on the main sequence near the cluster turnoff, while the hotter component lies near an extension of the main sequence blueward of the turnoff, and thus qualifies as a blue straggler by itself. The reduction of the masses of the stars in the close binary compared with previous models indicates that it is possible that the more massive component of the close binary formed from a merger of just two turnoff-mass stars.

The new MMT

Originally commissioned in 1979, the Multiple Mirror Telescope was a highly innovative and successful facility that pioneered many of the technologies that are used in the new generation of 8 to 10 m class telescopes. After 19 years of operations the MMT was decommissioned in March of 1998: the enclosure was modified, the optics support structure was replaced, and a single 6.5-meter primary mirror was installed and aluminized in-situ. First light for the new MMT was celebrated on May 13, 2000. Operations began with an f/9 optical configuration compatible with existing instruments. Work has continued commissioning two new optical configurations that will serve a suite of new instruments: an f/15 deformable secondary mirror and adaptive optics facility that has obtained diffraction-limited images; and an f/5.4 secondary mirror and refractive corrector that provides a one-degree diameter field of view. The wide-field instrument suite includes two fiber-fed bench spectrographs, a robotic fiber positioner, and a wide-field imaging camera.

THE MEAN RADIAL VELOCITY OF THE OPEN CLUSTER NGC 6939

The systematic motion of NGC 6939 is redetermined in light of the signifiant discrepancies among the published values. Based on the monitoring of 26 evolved stars during two consecutive seasons and an average of almost 12 spectra per star, we find the clusters mean radial velocity to be -18.98 km s-1 with an error of ± 0.19 km s-1.

THE BLUE STRAGGLERS OF M67 AND OTHER OPEN CLUSTERS

Results are presented of a study aimed at establishing the frequency of spectroscopic binaries in a sample of blue stragglers, belonging to five old- and intermediate-age open clusters: NGC 752, NGC 2360, NGC 2420, NGC 2682 or M67, and NGC 7789. The observational material, which for the M67 subsample spans 10 years, consists of high-resolution, low signal-to-noise echelle spectra obtained with equivalent systmes at the Multiple Mirror Telescope and at the 1.5-m Tillinghast Reflector, both atop Mt. Hopkins (Arizona). In order to obtain reliable radial velocities for these early-type and/or rapidly rotating objects with the cross-correlation method, synthetic spectra matching the observed spectra were employed as templates. The goodness of the grid of computed spectra wsa estimated to be excellent judging from the degree of agreement in high-resolution, high signal-to-noise observed spectra of the Sun, Procyon, and Sirius with their theoretical counterparts. Using this technique it was possible to determine for the first time the spectroscopic orbit for the M67 blue straggler Fagerholm 190 (P 4.2 days). It is proposed that this is a case where mass transfer between the components has been involved, that the system is still in the final stages of mass transfer, and that the original primary--now the secondary--is an abnormal subgiant evolving towards a white dwarf. The rather large orbital eccentricity (e 0.21) remains an open question, since according to current theories a system with such a period should have been circularized by now. If the mass-transfer process that made F190 into a blue straggler started recently, by using the additional information provided by the turnoff mass we can put very strict limits on the original and current masses of both components. Very long-period variations (several thousand days) were detected in three other blue stragglers of M67; since only one of these has a preliminary orbit available, it is not clear whether these systems could also be explained by the mass-transfer mechanism, or a binary-binary interaction scenario should be invoked. Three large-amplitude spectroscopic binaries were discovered among the blue stragglers of the remaining clusters. Some blue stragglers do not show any signifianct variation at all. It is found that the contamination of the blue-straggler sample by field stars is significant in the case of NGC 7789, and to a lesser extent also for NGC 2420. The frequency of spectroscopic binaries among the blue stragglers studied exceeds 40%, approximately twice the current value accepted for the field or normal cluster members. Blue stragglers tend to be more concentrated towards the center of the clusters than single stars, where the frequency of binaries is expected to increase due to mass segregation; in that case, the derived value would be within the expected range. Nevertheless, more than one mechanism seems to be required to account for all the blue stragglers.

Spectroscopic Binaries in the Open Cluster M67

For almost 400 members of M67 we have accumulated about 5,000 precise radial velocities. Already we have orbital solutions for more than 32 spectroscopic binaries in M67. Many of these orbits were derived by combining the Palomar and CfA observations, thus extending the time coverage to more than 20 years. The distribution of eccentricity versus period shows evidence for tidal circularization on the main sequence. The transition from circular orbits is fairly clean. Excluding the blue stragglers, the first eccentric orbit has a period of 11.0 days, while the last circular orbit has a period of 12.4 days. For longer periods the distribution of eccentricity is the same as for field stars. The blue straggler S1284 has an eccentric orbit despite its short period of 4.2 days. In 1971 Roger Griffin and Jim Gunn began monitoring the radial velocities of most of the members brighter than the main-sequence turnoff in the old open cluster M67, primarily using the 200-inch Hale Telescope. In 1982, just as the sequence of observations at Palomar was ending, Dave Latham and Bob Mathieu began monitoring many of the same stars with the 1.5-m Tillinghast Reflector and the Multiple-Mirror Telescope on Mount Hopkins. The Palomar and Mount Hopkins data sets were successfully merged, together with some additional CORAVEL velocities kindly provided by Michel Mayor, to obtain 20 years of time coverage (e.g., see Mathieu et al. 1986). Based on these data, orbital solutions have been published (Mathieu et al. 1990) for 22 spectroscopic binaries. The M67 survey is now being extended to V = 15.5 with the telescopes at Mount Hopkins. Already we have 13 additional orbital solutions, with the promise of many more to come. In Table 1 we list the period and eccentricity for 34 spectroscopic binaries which are members of M67. For the binaries with circular orbits, Mathieu et al. (1990) adopted an eccentricity of 0.0. Here we have allowed the eccentricity to be a free parameter in the orbital solution, so that the estimated error in the eccentricity may be used to judge whether the eccentricity is significantly of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S025292110000628X Downloaded from https://www.cambridge.org/core. IP address: 54.70.40.11, on 09 Jun 2019 at 20:49:39, subject to the Cambridge Core terms