J. M. Fletcher

Performance of the Canada-France-Hawaii Telescope Adaptive Optics Bonnette

ABSTRACT Extensive results from the commissioning phase of PUEO, the adaptive optics instrument adaptor for the Canada‐France‐Hawaii Telescope (CFHT), are presented and discussed. Analyses of more than 750 images recorded with a CCD and a near‐IR camera on 16 nights in wavelengths from B to H are used to derive the properties of the compensated wavefront and images in a variety of conditions. The performance characteristics of the system are analyzed and presented in several ways, in terms of delivered Strehl ratios, full width half‐maxima (FWHM), and quantities describing the improvements of both. A qualitative description is given of how the properties of the corrected images result from the structure function of the compensated phase. Under median seeing conditions, PUEO delivers essentially diffraction‐limited images at H and K and images with FWHM ∼ 0 \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepac...

Spectroscopic Binaries in Globular Clusters. II. A Search for Long-Period Binaries in M22

A catalog of 383 radial velocities for red giants in the globular cluster M22 has been compiled from the literature and from new observations accumulated between 1972 and 1994. This 22-year baseline is the longest available for any sample of globular cluster stars. Using 333 repeat velocities for 109 cluster members, we have carried out a search for spectroscopic binaries with periods in the range 0.2 -- 40 years and with mass ratios between 0.1 and 1.0. Although the velocities for these evolved stars show clear evidence for atmospheric motions, no star is convincingly found to exhibit a velocity variation greater than 7 km/s. By comparing the observed velocity variations to those found in a series of Monte-Carlo simulations, we estimate the cluster binary fraction to be X = 0.01 (circular orbits) and X = 0.03 (thermal orbits). These results are to be compared to the corresponding binary fraction of X = 0.12 for nearby solar-type stars having similar mass ratios and periods. We speculate that both the relative abundances of short- and long-period binaries in globular clusters and the large differences in measured binary fractions for clusters with high binary ionization rates (M22, Omega Cen) compared to those for clusters with low ionization rates (M71, M4, NGC 3201) point to a frequency-period distribution in which soft binaries have been disrupted by stellar encounters. Finally, we note that none of the three CH stars in our survey shows evidence for velocity variations; this is in stark contrast to field CH stars, virtually all of which are binaries. We argue that binaries in M22 which have binding energies similar to field CH stars are unlikely to have been disrupted by stellar encounters and suggest that the cluster CH stars are otherwise normal red giants which lie in the carbon-enriched tail of the cluster metallicity

HRCam survey for closely spaced gravitational lenses

The CFHT image stabilizing camera HRCam was used to search for closely spaced images indicative of gravitational lensing among a sample of 101 apparently and intrinsically luminous quasars. No conclusive evidence of multiple imaging due to lensing was found. Although these results are in accord with recent predictions based on standard models of the universe. Turner (1990, ApJ, 365) points out that model universes dominated by a nonzero cosmological constant are not favored. No significant excess of galaxies near the quasars was found, in contrast to the results of Webster et al. (1988, Nature,336), and, more recently, by Drinkwater et al. (1991, ASP Conf. Ser., 21)

Mass-to-light ratios for globular clusters. I. The centrally concentrated clusters NGC 6624, M28 (NGC 6626), and M70 (NGC 6681)

Radial velocities accurate to about 1 km/s have been obtained for about 20 stars in each of the two cusp clusters NGC 6624 and M70 and in the centrally concentrated noncusped cluster M28. NGC 6624 and M70 are equally well fit by single and multicomponent King (1966) models with concentrations of greater than 2.0, and M28 is best fit by models with a concentration near 2.0. It is found that the M/L ratios of NGC 6624, M28, and M70 do not differ significantly from each other or from those of the cluster population as a whole, and that anisotropic models are poorer fits to the surface-brightness profiles than isotropic models. M28 and M70 are found to have less than about 25 percent of their mass in the form of remnants heavier than the giants, while NGC 6624 has less than about 10 percent in this form. 68 refs.

Dynamics of the globular cluster M2 (NGC 7089)

We have obtained radial velocities for 69 stars in the globular cluster M2 (NGC 7089). M2s rotation axis is, within sizeable uncertainties, perpendicular to the major axis determined by the flattening. The ratio of rotational to random kinetic energy agrees with that predicted from the ellipticity assuming an oblate figure and an isotropic velocity-dispersion tensor. We have fitted King-Michie models to determine M2s mass, the exponent of an assumed power-law mass function, and the anisotropy radius. The most significant sources of uncertainty in the modeling are the velocity dispersion, the distance, and the mass-luminosity relation for the cluster stars. The models favor mass functions similar to or shallower than the Salpeter initial-mass function and a moderate amount of velocity anisotropy.

A SPECTROSCOPIC ORBIT FOR HR 152.

HR 152, one of the four reference stars used to standardize radial-velocity observations made at Cambridge, has been shown by measurements made with the Dominion Astrophysical Observatory radial-velocity spectrometer to be a spectroscopic binary. The effects of its variability are traceable in the residuals of many spectroscopic-binary orbits based on Cambridge data. The orbit has a period of 576 days and a semiamplitude of 0.69±0.08 km s-1; this is the first plausible orbit to be published with a semiamplitude smaller than 1 km s-1.

A Survey of Globular Cluster Velocity Dispersions

We have used the Dominion Astrophysical Observatory radial velocity spectrometer on the 3.6m Canada-France-Hawaii telescope to obtain radial velocities, accurate to ∼0.8 km/s, for ∼20 stars in each of nine globular clusters. The stars are generally within three core radii of the cluster center. The cluster names and metallicities (the latter are averages of values in Zinn and West (1984), Pilachowski (1984), and Webbink (1985)) are given in Table I. This sample includes two clusters with cusps in their surface brightness profiles: NGC 6624 and 6681.

A REVISED SPECTROSCOPIC ORBIT FOR 93 LEONIS (HD 102509).

New high-dispersion spectrograms of 93 Leo provide the data for a revision of the orbital elements of this system which exhibits a composite spectrum (A7 + G5). The orbit is found to be circular and the new elements are: P = 71.6900 days, T0 = JD2443126.2, V0 = + 0.4 km/s, KG = 29.7 km/s, KA = 33.8 km/s. The mass-ratio has been determined for the first time by a spectrophotometric separation of the two spectra. The A-type component of the spectrum arises from the less-massive star, but it is nevertheless the stronger component of the composite spectrum in the normal photographic region - although, until now, no radial velocities have been derived from it. The minimum mass of the G-type star is 1.02 solar mass and of the A-type star 0.89 solar mass. The evolutionary status of the system is briefly discussed.

THE EVOLVED STELLAR SYSTEM SIGMA 2367

Visual and spectroscopic observations are employed to define the orbital elements of the binary Sigma 2367. The data were gathered with instrumentation at Cambridge, Mt. Palomar, and Victoria. A period of 33.528 days was determined for the binary system, with an absolute parallax of 0.0084 arcsec. The total mass of the two stars was set at 2.5 solar masses. A C component was identified as being physically related to the A and B components of the system.

Radial Velocity Spectrometers on the Dominion Astrophysical Observatory 1.2m and 0.4m Telescopes

A photoelectric radial velocity spectrometer has been in operation for several years at the coude focus of the 1.2m telescope of the Dominion Astrophysical Observatory (DAO). The design of this instrument has been described by Fletcher et al. (1982) and by McClure et al. (1984). These papers discuss the similarities and differences between this spectrometer and others of its type such as that constructed by Griffin and Gunn (1974) at Palomar. The spectrum mask in the present instrument consists of more than 700 transparent slots on an opaque background, representing the spectrum of a K giant star, plus a few slots to coincide with the argon lines in a cadmium-argon discharge tube for use in obtaining comparison arc velocities. By progressively tilting the slots an appropriate amount along the mask and scanning by moving the mask relative to the stellar spectrum at 45° to the dispersion it is possible to retain a spectral match at non-zero velocities. The masks are produced using a standard measuring engine modified with stepping motors controlled by a computer to position and tilt the slots. Since guiding errors are our major source of error we hope to make a significant improvement in this area in the following manner. By inserting an image rotating prism behind the slit a 180° rotation of the slit will occur when the prism is rotated.