Dominion Astrophysical Observatory

About: Dominion Astrophysical Observatory is a facility organization based out in Victoria, British Columbia, Canada. It is known for research contribution in the topics: Galaxy & Stars. The organization has 244 authors who have published 554 publications receiving 20305 citations. The organization is also known as: DAO.

Discovery of a New Quadruple Lens HST 1411+5211

Abstract: Gravitational lensing is an important tool for probing the mass distribution of galaxies. In this Letter, we report the discovery of a new quadruple lens HST 1411+5211 found in archived Wide-Field Planetary Camera 2 images of the galaxy cluster CL 140933+5226. If the galaxy is a cluster member, then its redshift is z=0.46. The images of the source appear unresolved in the Wide-Field Camera, implying that the source is a quasar. We have modeled the lens as both a single galaxy and a galaxy plus a cluster. The latter model yields excellent fits to the image positions along with reasonable parameters for the galaxy and cluster, making HST 1411+5211 a likely gravitational lens. Determination of the source redshift and confirmation of the lens redshift would allow us to put strong constraints on the mass distribution of the lensing galaxy.

Two-Color CCD Photometry of Variable Stars in NGC 7006

Abstract: B and V CCD photometry from 1984 through 1994 is presented for 50 RR Lyrae stars and two red variable stars in the globular cluster NGC 7006. New determinations of pulsation periods and period change rates are given and used to plot B light curves. The new photometry is combined with previously published photometry obtained from photographic plates taken in the 1930s, the 1950s and 1984 and used to derive O - C diagrams and new period change rates. V light curves based on the CCD data are also displayed, and colors derived from mean values of B and V are given. Period-amplitude diagrams and the color-magnitude diagram for the variables are shown. The dereddened blue and red edges to the instability strip in the cluster are found to be at (B-V)0 = 0.14 and 0.38. The period change rates have been revised from those given in an earlier paper and the new median period change rate is found to be +0.03, close to that predicted by the Yale evolutionary models.

Optical imaging of the low redshift superluminous QSO 1821 + 643

Abstract: Optical imaging is presented of the luminous z = 0.3 QSO 1821 + 643, with resolution 1.0 and 0.4 arcsec. The host galaxy is resolved and seen to be large, featureless, and red, with slightly displaced outer isophotes. The nucleus is unusually red. There is a rich cluster of galaxies in the field which is probably at a much higher redshift, and extended nebulosity from a nearby star. These results and the IR properties are discussed in terms of a mature merger of a luminous galaxy in which there is still a considerable amount of central dust and molecular clouds.

Anchors for the cosmic distance scale: the Cepheids U Sagittarii, CF Cassiopeiae, and CEab Cassiopeiae

Abstract: New and existing X-ray, UB V JHKsW(1−4), and spectroscopic observations were analyzed to constrain fundamental parameters for M 25, NGC 7790, and dust along their sight-lines. The star clusters are of particular importance because they host the classical Cepheids U Sgr, CF Cas, and the visual binary Cepheids CEa and CEb Cas. Precise results from the multiband analysis, in tandem with a comprehensive determination of the Cepheids’ period evolution (dP/dt) from ∼140 years of observations, helped to resolve concerns raised regarding the clusters and their key Cepheid constituents. Specifically, the distances derived for members of M 25 and NGC 7790 are 630 ± 25 pc and 3.40 ± 0.15 kpc, respectively.

Classifications of the Host Galaxies of Supernovae

Abstract: Classifications on the DDO system are given for the host galaxies of 177 supernovae (SNe) that have been discovered since 1997 during the course of the Lick Observatory Supernova Search with the Katzman Automatic Imaging Telescope. Whereas SNe Ia occur in all galaxy types, it is found, at a high level of statistical confidence, that SNe Ib, Ic, and II are strongly concentrated in late-type galaxies. However, attention is drawn to a possible exception provided by SN 2001I. This SN IIn occurred in the E2 galaxy UGC 2836, which was not expected to harbor a massive young supernova progenitor.