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Articles 1 - 12 of 12
Full-Text Articles in Physical Sciences and Mathematics
Spintessence! New Models For Dark Matter And Dark Energy, Latham A. Boyle, Robert R. Caldwell, Marc Kamionkowski
Spintessence! New Models For Dark Matter And Dark Energy, Latham A. Boyle, Robert R. Caldwell, Marc Kamionkowski
Dartmouth Scholarship
We investigate a class of models for dark matter and/or negative-pressure, dynamical dark energy consisting of “spintessence”, a complex scalar field φ spinning in a U(1)-symmetric potential V(φ)=V(|φ|). As the Universe expands, the field spirals slowly toward the origin. The internal angular momentum plays an important role in the cosmic evolution and fluctuation dynamics. We outline the constraints on a cosmic spintessence field, describing the properties of the potential necessary to sustain a viable dark energy model, making connections with quintessence and self-interacting and fuzzy cold dark matter. Possible implications for the …
Spatially Resolved Spectroscopy Of Coma Cluster Early-Type Galaxies - Ii. The Minor Axis Dataset, G. Wegner, E. M. Corsini, R. P. Saglia, R. Bender
Spatially Resolved Spectroscopy Of Coma Cluster Early-Type Galaxies - Ii. The Minor Axis Dataset, G. Wegner, E. M. Corsini, R. P. Saglia, R. Bender
Dartmouth Scholarship
We present minor axis, offset major axis and one diagonal long slit spectra for 10 E and S0 galaxies of the Coma cluster drawn from a magnitude-limited sample studied before. We derive rotation curves, velocity dispersion profiles and the H3 and H4 coefficients of the Hermite decomposition of the line of sight velocity distribution. Moreover, we derive the line index profiles of Mg, Fe and Hβ line indices and assess their errors. The data will be used to construct dynamical models of the galaxies and study their stellar populations.
Extraordinary Late‐Time Infrared Emission Of Type Iin Supernovae, Christopher L. Gerardy, Robert A. Fesen, Ken-Ichi Nomoto, Peter M. Garnavich
Extraordinary Late‐Time Infrared Emission Of Type Iin Supernovae, Christopher L. Gerardy, Robert A. Fesen, Ken-Ichi Nomoto, Peter M. Garnavich
Dartmouth Scholarship
Near-infrared observations are presented for five Type IIn supernovae (SN 1995N, SN 1997ab, SN 1998S, SN 1999Z, and SN 1999el) that exhibit strong infrared excesses at late times (t > 100 days). H- and K-band emission from these objects is dominated by a continuum that rises toward longer wavelengths. The data are interpreted as thermal emission from dust, probably situated in a preexisting circumstellar nebula. The IR luminosities implied by single-temperature blackbody fits are quite large, >1041-1042 ergs s-1, and the emission evolves slowly, lasting for years after maximum light. For SN 1995N, the integrated energy release via …
Sensitivity Of The Cosmic Microwave Background Anisotropy To Initial Conditions In Quintessence Cosmology, Rahul Dave, R. R. Caldwell, Paul J. Steinhardt
Sensitivity Of The Cosmic Microwave Background Anisotropy To Initial Conditions In Quintessence Cosmology, Rahul Dave, R. R. Caldwell, Paul J. Steinhardt
Dartmouth Scholarship
We analyze the evolution of energy density fluctuations in cosmological scenarios with a mixture of cold dark matter and quintessence, in which the quintessence field is modeled by a constant equation of state. We obtain analytic expressions for the time evolution of the quintessence perturbations in models with light fields. The fluctuations behave analogously to a driven harmonic oscillator, where the driving term arises from the inhomogeneities in the surrounding cosmological fluid. We demonstrate that the homogeneous solution, determined by the initial conditions, is completely subdominant to the inhomogeneous solution for physically realistic scenarios. Thus we show that the cosmic …
The Warps Survey. Vi. Galaxy Cluster And Source Identifications From Phase I, Eric S. Perlman, Donald J. Horner, Laurence R. Jones, Caleb A. Scharf, Harald Ebeling, Gary Wegner, Matthew Malkan
The Warps Survey. Vi. Galaxy Cluster And Source Identifications From Phase I, Eric S. Perlman, Donald J. Horner, Laurence R. Jones, Caleb A. Scharf, Harald Ebeling, Gary Wegner, Matthew Malkan
Dartmouth Scholarship
We present in catalog form the optical identifications for objects from the first phase of the Wide Angle ROSAT Pointed Survey (WARPS). WARPS is a serendipitous survey of relatively deep, pointed ROSAT observations for clusters of galaxies. The X-ray source detection algorithm used by WARPS is Voronoi Tessellation and Percolation (VTP), a technique which is equally sensitive to point sources and extended sources of low surface brightness. WARPS-I is based on the central regions of 86 ROSAT PSPC fields, covering an area of 16.2 square degrees. We describe here the X-ray source screening and optical identification process for WARPS-I, which …
Infrared Spectra Of The Subluminous Type Ia Supernova Sn 1999by, Peter Hoflich, Christopher L. Gerardy, Robert A. Fesen, Shoko Sakai
Infrared Spectra Of The Subluminous Type Ia Supernova Sn 1999by, Peter Hoflich, Christopher L. Gerardy, Robert A. Fesen, Shoko Sakai
Dartmouth Scholarship
Near-infrared (NIR) spectra of the subluminous Type Ia supernova SN 1999by are presented that cover the time evolution from about 4 days before to 2 weeks after maximum light. Analysis of these data was accomplished through the construction of an extended set of delayed detonation (DD) models covering the entire range of normal to subluminous SNe Ia. The explosion, light curves, and time evolution of the synthetic spectra were calculated self-consistently for each model, with the only free parameters being the initial structure of the white dwarf and the description of the nuclear burning front during the explosion. From these, …
Measuring The Speed Of Sound Of Quintessence, Joel K. Erickson, R. R. Caldwell, Paul J. Steinhardt, C. Armendariz-Picon, V. Mukhanov
Measuring The Speed Of Sound Of Quintessence, Joel K. Erickson, R. R. Caldwell, Paul J. Steinhardt, C. Armendariz-Picon, V. Mukhanov
Dartmouth Scholarship
Quintessence, a time-varying energy component that may account for the accelerated expansion of the universe, can be characterized by its equation of state and sound speed. In this paper, we show that if the quintessence density is at least 1% of the critical density at the surface of last scattering the cosmic microwave background anisotropy can distinguish between models whose sound speed is near the speed of light versus near zero, which could be useful in distinguishing competing candidates for dark energy.
Theoretical Uncertainties In The Subgiant--Mass Age Relation And The Absolute Age Of Omega Cen, Brian Chaboyer, Lawrence M. Krauss
Theoretical Uncertainties In The Subgiant--Mass Age Relation And The Absolute Age Of Omega Cen, Brian Chaboyer, Lawrence M. Krauss
Dartmouth Scholarship
The theoretical uncertainties in the calibration of the relationship between the subgiant mass and age in metal-poor stars are investigated using a Monte Carlo approach. Assuming that the mass and iron abundance of a subgiant star are known exactly, uncertainties in the input physics used to construct stellar evolution models and isochrones lead to a Gaussian 1 σ uncertainty of ±2.9% in the derived ages. The theoretical error budget is dominated by the uncertainties in the calculated opacities. Observations by Kałużny et al. of detached double-lined eclipsing binary OGLEGC 17 in the globular cluster ω Centauri have found that the …
Optical And Ultraviolet Spectroscopy Of Sn 1995n: Evidence For Strong Circumstellar Interaction, Claes Fransson, Roger A. Chevalier, Alexei V. Filippenko, Bruno Leibundgut, Aaron J. Barth, Robert A. Fesen, Robert P. Kirshner, Douglas C. Leonard, Weidong Li, Peter Lundqvist, Jesper Sollerman, Schuyler D. Van Dyk
Optical And Ultraviolet Spectroscopy Of Sn 1995n: Evidence For Strong Circumstellar Interaction, Claes Fransson, Roger A. Chevalier, Alexei V. Filippenko, Bruno Leibundgut, Aaron J. Barth, Robert A. Fesen, Robert P. Kirshner, Douglas C. Leonard, Weidong Li, Peter Lundqvist, Jesper Sollerman, Schuyler D. Van Dyk
Dartmouth Scholarship
Optical and ultraviolet observations of the Type IIn supernova SN 1995N at epochs between 321 and 1799 days after the explosion show three distinct velocity components. The narrow lines come from circumstellar gas and show both low and high ionization. This component has a low filling factor and is photoionized by X-rays from the shock. The intermediate component, which is dominated by newly processed oxygen, originates in a shell with velocity of 2500-5000 km s-1 and most likely comes from the ejecta. The hydrogen- and helium-dominated gas has a low ionization, a high density, and velocities that extend out …
Are Stars With Planets Polluted?, N. Murray, B. Chaboyer
Are Stars With Planets Polluted?, N. Murray, B. Chaboyer
Dartmouth Scholarship
We compare the metallicities of stars with radial velocity planets to the metallicity of a sample of field dwarfs. We confirm recent work indicating that the stars-with-planets sample as a whole is iron-rich. However, the lowest mass stars tend to be iron-poor, with several having [Fe/H] < -0.2, demonstrating that high metallicity is not required for the formation of short-period Jupiter-mass planets. We show that the average [Fe/H] increases with increasing stellar mass (for masses below 1.2 M☉) in both samples, but that the increase is much more rapid in the stars-with-planets sample. The variation of metallicity with stellar age also differs between the two samples. We examine possible selection effects related to variations in the sensitivity of radial velocity surveys with stellar mass, apparent magnitude, and stellar metallicity, and …
The Qmap And Mat/Toco Experiments For Measuring Anisotropy In The Cosmic Microwave Background, A. Miller, J. Beach, S. Bradley, R. Caldwell, H. Chapman, M. J. Devlin, W. B. Devlin, W. B. Dorwart, T. Herbig, D. Jones, G. Monnelly, C. B. Netterfield, M. Nolta, L. A. Page, J. Puchalla, T. Robertson, E. Torbet, H. T. Tran, W. E. Vinje
The Qmap And Mat/Toco Experiments For Measuring Anisotropy In The Cosmic Microwave Background, A. Miller, J. Beach, S. Bradley, R. Caldwell, H. Chapman, M. J. Devlin, W. B. Devlin, W. B. Dorwart, T. Herbig, D. Jones, G. Monnelly, C. B. Netterfield, M. Nolta, L. A. Page, J. Puchalla, T. Robertson, E. Torbet, H. T. Tran, W. E. Vinje
Dartmouth Scholarship
We describe two related experiments that measured the anisotropy in the cosmic microwave background (CMB). QMAP was a balloon-borne telescope that flew twice in 1996, collecting data on degree angular scales with an array of six high electron mobility transistor-based amplifiers (HEMTs). QMAP used an interlocking scan strategy to directly produce high signal-to-noise ratio CMB maps over a limited region of sky. The QMAP gondola was then refitted for ground-based work as the MAT/TOCO experiment. Observations were made from 5200 m on Cerro Toco in Northern Chile in 1997 and 1998 using time domain beam synthesis. MAT/TOCO measured the rise …
The Afterglow And Complex Environment Of The Optically Dim Burst Grb 980613, Jens Hjorth, Bjarne Thomsen, Svend R. Nielsen, Michael I. Andersen, Stephen T. Holland, Johan U. Fynbo, Holger Pederson, Andreas O. Jaunsen, Jules P. Halpern, Robert Fesen, Javier Gorosabel, Alberto Castro-Tirado, Richard G. Mcmahon, Michael D. Hoenig, Gunnlaugur Bjornsson, Lorenzo Amati, Nial R. Tanvir, Priyamvada Natarajan
The Afterglow And Complex Environment Of The Optically Dim Burst Grb 980613, Jens Hjorth, Bjarne Thomsen, Svend R. Nielsen, Michael I. Andersen, Stephen T. Holland, Johan U. Fynbo, Holger Pederson, Andreas O. Jaunsen, Jules P. Halpern, Robert Fesen, Javier Gorosabel, Alberto Castro-Tirado, Richard G. Mcmahon, Michael D. Hoenig, Gunnlaugur Bjornsson, Lorenzo Amati, Nial R. Tanvir, Priyamvada Natarajan
Dartmouth Scholarship
We report the identification of the optical afterglow of GRB 980613 in R- and I-band images obtained between 16 and 48 hr after the gamma-ray burst. Early near-infrared (NIR) H and K' observations are also reported. The afterglow was optically faint (R ≈ 23) at discovery but did not exhibit an unusually rapid decay (power-law decay slope α < 1.8 at 2 σ). The optical/NIR spectral index (βRH < 1.1) was consistent with the optical-to-X-ray spectral index (βRX ≈ 0.6), indicating a maximal reddening of the afterglow of ≈0.45 mag in R. Hence, the dimness of the optical afterglow was mainly due to the fairly flat spectral shape rather than internal reddening …