Physical Sciences and Mathematics Commons^™

Parallaxes And Distance Estimates For 14 Cataclysmic Variable Stars, John R. Thorstensen

Dartmouth Scholarship

I used the 2.4 m Hiltner Telescope at MDM Observatory in an attempt to measure trigonometric parallaxes for 14 cataclysmic variable stars. Techniques are described in detail. In the best cases the parallax uncertainties are below 1 mas, and significant parallaxes are found for most of the program stars. A Bayesian method that combines the parallaxes together with proper motions and absolute magnitude constraints is developed and used to derive distance estimates and confidence intervals. The most precise distance derive here is for WZ Sge, for which I find 43: 3.1:6 1:5 pc. Six Luyten Half-Second stars with previous precise …

Stellar Pollution And [Fe/H] In The Hyades, Aaron Dotter, Brian Chaboyer

Dartmouth Scholarship

The Hyades open cluster presents a unique laboratory for planet formation and stellar pollution studies because all of the stars have essentially the same age and were born from the same cloud of gas. Furthermore, with an age of ~650 Myr, most of the intermediate- and low-mass stars are on the main sequence. Given these assumptions, the accretion of metal-rich material onto the surface of a star during and shortly after the formation of planetary systems should be evident via the enhanced metallicity of the star. Building on previous work, stellar evolution models that include the effects of stellar pollution …

A Model Of Zebra Emission In Solar Type Iv Radio Bursts, J. Labelle, R. A. Treumann, P. H. Yoon, M. Karlicky

Dartmouth Scholarship

Solar type IV radio bursts present a theoretical challenge because they are composed of both continuum emission and fine structures. The latter include "zebra bursts," which appear as harmonically spaced multiplets that shift in frequency with time. Similarities between these features and terrestrial auroral emissions suggest a new model to explain zebra-structured type IV emissions. In this model, the basic generation mechanism is identical with that proposed by Winglee and Dulk: mode conversion of Z-mode waves generated by the cyclotron maser mechanism under the condition fuh = Nfce, with N an integer; however, we propose a twist …

Early Quintessence In Light Of Thewilkinson Microwave Anisotropy Probe, Robert R. Caldwell, Michael Doran, Christian M. Mller, Gregor Schfer, Christof Wetterich

Dartmouth Scholarship

We examine the cosmic microwave background (CMB) anisotropy for signatures of early quintessence dark energy—a nonnegligible quintessence energy density during the recombination and structure formation eras. Only very recently does the quintessence overtake the dark matter and push the expansion into overdrive. Because the presence of early quintessence exerts an influence on the clustering of dark matter and the baryon-photon fluid, we may expect to find trace signals in the CMB and the mass fluctuation power spectrum. In detail, we demonstrate that suppressed clustering power on small length scales, as suggested by the combined Wilkinson Microwave Anisotropy Probe/CMB/large-scale structure …

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 …

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 …