Showing papers by "Dominion Astrophysical Observatory published in 1989"

Long-period radial-velocity variations of arcturus

Abstract: Precise measurements of the radial velocity of Arcturus were obtained on 43 occasions between 1981 and 1985. The measurements show a 500 m/s range, confirming the radial velocity variability of Arcturus. Multiperiod models which give a good representation of the velocities are derived using a least-squares technique. The models also fit the velocities of Smith et al. (1987). It is suggested that the small-amplitude short-period components of the models could be analogous to the solar five-minute oscillations. The best-fitting models require the largest-amplitude component to have a period of at least 640 days.

Radial velocities of more old open clusters

Abstract: Moderate-resolution CCD spectra in the Mg b region of red giants in 13 old or metal-poor open clusters were obtained with the kitt Peak 2.1-m telescope. Radial velocities for these giants, measured by cross-correlation techniques, are accurate to 10 km/s. For the six clusters in the sample with previous measurements, the velocities are in good agreement with published values. Results are presented for seven clusters (NGC 1193, NGC 1817, NGC 6819, NGC 7142, Be 21, King 8, IC 166) with no previous radial-velocity measurements. The majority of clusters in the sample, supplemented with ten more clusters older than 1 Gyr which have published velocities, show radial velocities which are consistent with those expected from the reflex of solar motion and simple galactic rotation. A few of the clusters, including the newly measured NGC 1193 and NGC 1817, show surprisingly large radial velocities, indicating significant deviation from the general rotation of the remaining old cluster system.

What is the difference between radio-loud and radio-quiet quasi-stellar objects

Abstract: Measures of the nuclear and host galaxy luminosities and colors and a morphological discussion of the host galaxies are presented for a sample of low-redshift, high-luminosity, radio-quiet QSOs whose redshift and luminosity distribution matches that of a radio-loud sample previously discussed. Radio-quiet QSOs are found to reside in galaxies which are smaller, fainter, and redder than the host galaxies of radio-loud QSOs. These properties are generally consistent with the suggestion that radio-quiet QSOs are located in spiral-type galaxies and radio-loud QSOs are located in more elliptical-type galaxies. Significantly less evidence is found for tidal interactions among the radio-quiet objects, although they appear to reside in somewhat richer environments in terms of nearby companions.

Evolution of radio quasars for z of less than 2

Abstract: A sample of 72 radio quasars is used to study the cosmic and individual evolution of quasars in the 1-2 redshift range. It is shown that the most luminous sources at all redshifts are unresolved, and that one-sided and two-sided structures correspond to progressively lower core (and total) luminosities. The sizes and fractional population of triple sources are found to fall steadily with increasing redshift to z of about 1.7. A correlation over many orders of magnitude is noted between the optical and maximum radio-core luminosity.

Life and death in the inner solar system

Abstract: Evidence for a causal relationhip between global extinctions and bolide impacts is reviewed. Results support the scenario of massive leaching of Sr-87 (found in high abundance at the K/T boundary) from continental rocks during a deluge of acid rain, and the occurrence of an extended period of greenhouse-effect-related high temperatures produced by the partial transfer of dissolved CO2 from the oceans to the atmosphere and the CO2 formed by a global conflagration. The probability that a supernova occurred within 5 pc of the sun during the last 10 to the 9th years is only 0.06.

A color gradient in the globular cluster M15

Abstract: A U-B color map of the central regions of the globular cluster M15 is constructed from data taken at the CFHT in subarcsec seeing Analysis of the color distribution of the pixels in this map unambiguously demonstrates that the area within 66 arcsec of the center of the cluster is bluer than surrounding regions The difference is apparently caused by a population of faint blue stars more prevalent in the core than elsewhere, and is consistent with post-core-collapse models which predict a centrally condensed distribution of cataclysmic variables

A search for closely spaced gravitational lenses

Abstract: The DAO/CFHT image stabilizing camera HRHR-Cam was used to search for closely spaced images resulting from gravitational lensing by foreground galaxies in a sample of 101 bright quasars. No convincing objects were found. Several widely-separated (1 – 6 arc-sec) point source companions were detected but half of these are known to be stars, and it is argued that the remainder are also likely to be stars. A slight excess of galaxy companions to the quasars is found when compared to a control sample of stars, but the difference is not statistically significant (galaxy companions to 17 quasars were found, similar companions were noted around 12 stars).

The Role of Binarity in the Evolution of Peculiar Red Giants

Abstract: There are several types of Peculiar Red Giants (PRG's) which have enhanced s-process elements and/or carbon, but which cannot be explained by mixing during helium shell-flashing in the late stages of Asymptotic Giant Branch (AGB) evolution. These are the Ball, CH, sgCH, and the hotter R-type carbon stars. All these PRG's have absolute magnitudes which range down to zero and fainter. The Ball stars (Bidelman & Keenan 1951) are G-K giants whose spectra have strong CN and CH bands, and in extreme cases bands of C 2 become noticeable. In addition they have strong lines of s-process elements such as Ball and SrII. The CH stars (Keenan 1942) are Population II equivalents of the Ball stars, and show similar spectral features, but with weaker metal lines, and usually stronger carbon bands. Bond (1974) introduced a new class of late F and G stars named the CH subgiants, which he suggests are fainter than the classical CH and Ball stars. They appear to be of mixed population (Luck & Bond 1982), and they are probably subgiants which will eventually evolve up the giant branch to become classical CH and Ball stars. The R-type carbon stars, at least the hotter (R0-R4) ones, differ from many of the other peculiar red giants in that they do not show enhanced s-process element abundances. The R stars have strong carbon bands, but relative to the N-type carbon stars they have less blue and ultraviolet absorption in their spectra. They range in absolute magnitude from near zero, similar to the Ball stars, up to several magnitudes brighter than this.

Mass Ejections from the G-Type Hypergiant HR 8752

Abstract: One of the most luminous stars in our Galaxy (Humphreys 1988) HR 8752 = HD 217476 (G0 Ia), is similar in some respects to Luminous Blue Variables. Studies by several authors (Sargent 1965; Smolinski 1971; Smolinski et al. 1977; Stickland and Harmer 1978; Lambert and Luck 1978; Lambert et al. 1981; Smolinski et al. 1986; Sheffer and Lambert 1987) have contributed to the understanding of activities in the atmosphere of this star, but its nature is still not well understood.