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Stars, Interstellar Medium and the Galaxy

Dartmouth Scholarship

1998

Articles 1 - 6 of 6

Full-Text Articles in Physical Sciences and Mathematics

Cluster Versus Field Elliptical Galaxies And Clues On Their Formation, Mariangela Bernardi, Alvio Renzini, Luiz N. Da Costa, Gary Wegner Dec 1998

Cluster Versus Field Elliptical Galaxies And Clues On Their Formation, Mariangela Bernardi, Alvio Renzini, Luiz N. Da Costa, Gary Wegner

Dartmouth Scholarship

Using new observations for a sample of 931 early-type galaxies, we investigate whether the Mg2-σ0 relation shows any dependence on the local environment. The galaxies have been assigned to three different environments depending on the local overdensity (clusters, groups, and field); we used our complete redshift database to guide the assignment of galaxies. It is found that cluster, group, and field early-type galaxies follow almost identical Mg2-σ0 relations, with the largest Mg2 zero-point difference (clusters minus field) being only 0.007±0.002 mag. No correlation of the residuals is found with the morphological type or …

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Hubble Space Telescope Images And Spectra Of The Remnant Of Sn 1885 In M31, Robert A. Fesen, Christopher L. Gerardy, Kevin M. Mclin, Andrew J. S. Hamilton Oct 1998

Hubble Space Telescope Images And Spectra Of The Remnant Of Sn 1885 In M31, Robert A. Fesen, Christopher L. Gerardy, Kevin M. Mclin, Andrew J. S. Hamilton

Dartmouth Scholarship

Near-UV Hubble Space Telescope images of the remnant of SN 1885 (S And) in M31 show a 070±005 diameter absorption disk silhouetted against M31's central bulge, at SN 1885's historically reported position. The disk's size corresponds to a linear diameter of 2.5±0.4 pc at a distance of 725±70 kpc, implying an average expansion velocity of 11,000±2000 km s-1 over 110 yr. Low-dispersion Faint Object Spectrograph spectra over 3200-4800 Å reveal that the absorption arises principally from Ca II H and K (equivalent width 215 Å), with weaker absorption features of Ca I 4227 Å and Fe I 3720 Å. The …

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Hot White Dwarfs In The Extreme ‐ Ultraviolet Explorer Survey. Iv. Da White Dwarfs With Bright Companions, Stephane Vennes, Damian J. Christian, John R. Thorstensen Aug 1998

Hot White Dwarfs In The Extreme ‐ Ultraviolet Explorer Survey. Iv. Da White Dwarfs With Bright Companions, Stephane Vennes, Damian J. Christian, John R. Thorstensen

Dartmouth Scholarship

We present an analysis of optical, ultraviolet, and X-ray spectral properties of a sample of 13 hot hydrogen-rich (DA) white dwarfs, each paired with a luminous unresolved companion. Using low-dispersion International Ultraviolet Explorer spectra, ROSAT photometry, and Extreme-Ultraviolet Explorer photometry and spectroscopy, we estimate the effective temperature, mass, and distance of the white dwarfs. Additionally, we examine the question of their atmospheric composition. We establish orbital properties for most binaries by means of high-dispersion optical spectroscopy obtained with the Hamilton echelle spectrograph at Lick Observatory; the same data help uncover evidence of activity in some of the secondary …

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Aquila X-1: A Low-Inclination Soft X-Ray Transient, T. Shahbaz, J. R. Thorstensen, P. A. Charles, N. D. Sherman Jun 1998

Aquila X-1: A Low-Inclination Soft X-Ray Transient, T. Shahbaz, J. R. Thorstensen, P. A. Charles, N. D. Sherman

Dartmouth Scholarship

We have obtained I-band photometry of the neutron star X-ray transient Aql X-1 during quiescence. We find a periodicity at 2.487 cycles d−1, which we interpret as twice the orbital frequency (19.30±0.05 h). Folding the data on the orbital period, we model the light-curve variations as the ellipsoidal modulation of the secondary star. We determine the binary inclination to be 20°–30° (90 per cent confidence) and also determine the 95 per cent upper limits to the radial velocity semi-amplitude and rotational broadening of the secondary star to be 117 and 50 km s−1, respectively.

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Pg 1002+506: A Be Star Apparently At Z > +10 Kiloparsecs, F. A. Ringwald, W. R. J. Rolleston, R. A. Saffer, John R. Thorstensen Apr 1998

Pg 1002+506: A Be Star Apparently At Z > +10 Kiloparsecs, F. A. Ringwald, W. R. J. Rolleston, R. A. Saffer, John R. Thorstensen

Dartmouth Scholarship

PG 1002+506 is found to be a Be star, one of three found so far by the Palomar-Green survey. Its spectrum is classified as a B5 ± 1 Ve, with Teff = 14,900 ± 1200, log g = 4.2 ± 0.2, and v sin i = 340 ± 50 km s-1. At b = +51°, its height above the Galactic plane would therefore be z = +10.8 kpc, putting this apparently young, rapidly rotating star well into the Galactic halo. Its heliocentric radial velocity is found to be -2 ± 15 km s-1, consistent with …

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A Photometric And Spectroscopic Study Of The Cataclysmic Variable Sx Leonis Minoris In Quiescence And Superoutburst, R. Mark Wagner, John R. Thorstensen, R. K. Honeycutt, S. B. Howell Feb 1998

A Photometric And Spectroscopic Study Of The Cataclysmic Variable Sx Leonis Minoris In Quiescence And Superoutburst, R. Mark Wagner, John R. Thorstensen, R. K. Honeycutt, S. B. Howell

Dartmouth Scholarship

We present CCD imaging, CCD photometry on long and short timescales, and time-resolved spectroscopy of SX LMi, a new SU Ursae Majoris type dwarf nova. The quiescent optical spectrum shows broad double-peaked Balmer, He I, and He II emission lines, similar to other quiescent dwarf novae. Absorption lines from a late-type secondary are not detected. Time-resolved spectra obtained in quiescence reveal radial velocity variations of the Balmer emission lines on a period of 0.06717 ± 0.00011 days, or 96.72 ± 0.16 minutes, with only a slight possibility of a daily cycle-count error. Optical photometry obtained between 1987 and 1991 shows …

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