Physical Sciences and Mathematics Commons^™

Grb 021004: A Possible Shell Nebula Around A Wolf‐Rayet Star Gamma‐Ray Burst Progenitor, N. Mirabal, J. P. Halpern, Ryan Chornock, Alexei V. Filippenko, D. M. Terndrup, E. Armstrong, J. Kemp, J. R. Thorstensen, M. Tavarez, C. Espaillat

Dartmouth Scholarship

The rapid localization of GRB 021004 by the HETE-2 satellite allowed nearly continuous monitoring of its early optical afterglow decay, as well as high-quality optical spectra that determined a redshift of z_{3 =} 2.328 for its host galaxy, an active starburst galaxy with strong Ly emission and several absorption lines. Spectral observations show multiple absorbers at z_3A = 2.323, z_3B= 2.317, and z_3C = 2.293 blueshifted by ~450, ~990, and ~3155 km s^-1, respectively, relative to the host galaxy Lyα emission. We argue that these correspond to a fragmented shell nebula that has …

Spatially Resolved Spectroscopy Of Coma Cluster Early-Type Galaxies - Iii. The Stellar Population Gradients, D. Mehlert, D. Thomas, R. P. Saglia, R. Bender, G Wegner

Dartmouth Scholarship

Based on Paper I of this series (Mehlert et al. 2000), we derive central values and logarithmic gradients for the Hβ, Mg and Fe indices of 35 early-type galaxies in the Coma cluster. We find that pure elliptical galaxies have on average slightly higher velocity dispersions, lower Hβ, and higher metallic line-strengths than galaxies with disks (S0). The latter form two families, one comparable to the ellipticals and a second one with significantly higher Hβ, and weaker metallic lines. Our measured logarithmic gradients within the effective radius are ⟨△Mg b⟩ ≈ −0.037, ⟨△⟨Fe⟩⟩ ≈ −0.029, ⟨△Hβ⟩ ≈ +0.017 and ⟨△σ⟩ …

Redshift-Distance Survey Of Early-Type Galaxies: Circular-Aperture Photometry, M. V. Alonso, M. Bernardi, L. N. Da Costa, G. Wegner

Dartmouth Scholarship

We present R -band CCD photometry for 1332 early-type galaxies, observed as part of the ENEAR survey of peculiar motions using early-type galaxies in the nearby universe. Circular apertures are used to trace the surface brightness profiles, which are then fitted by a two-component bulge-disk model. From the fits, we obtain the structural parameters required to estimate galaxy distances using the Dn - and fundamental plane relations. We find that about 12% of the galaxies are well represented by a pure r1/4 law, while 87% are best fitted by a two-component model. There are 356 repeated observations of 257 galaxies …

Chandra Observations Of The Luminous, Oxygen‐Rich Supernova Remnants In The Irregular Galaxy Ngc 4449, Daniel J. Patnaude, Robert A. Fesen

Dartmouth Scholarship

An analysis of a 29 ks Chandra ACIS-S observation of the young, Cassiopeia A–like supernova remnant in the irregular galaxy NGC 4449 is presented. The observed 0.5–2.1 keV spectrum reveals the likely presence of several emission lines. A nonequilibrium ionization fit to the spectrum suggests an overabundance of oxygen around 20 times solar, consistent with the remnant’s UV and optical emission-line properties. We discuss the remnant’s approximate X-ray–derived elemental abundances and compare its X-ray spectrum and luminosity with other oxygen-rich remnants

Observational Constraints On General Relativistic Energy Conditions, Cosmic Matter Density And Dark Energy From X-Ray Clusters Of Galaxies And Type-La Supernovae, P. Schuecker, R. R. Caldwell, H. Böhringer, C. A. Collins

Dartmouth Scholarship

New observational constraints on the cosmic matter density Ωm and an effectively redshift-independent equation

of state parameter wx of the dark energy are obtained while simultaneously testing the strong and null energy conditions of

general relativity on macroscopic scales. The combination of REFLEX X-ray cluster and type-Ia supernova data shows that

for a flat Universe the strong energy condition might presently be violated whereas the null energy condition seems to be

fulfilled. This provides another observational argument for the present accelerated cosmic expansion and the absence of exotic

physical phenomena related to a broken null energy condition. The marginalization of …