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Articles 271 - 300 of 337

Full-Text Articles in Physical Sciences and Mathematics

A New Color-Magnitude Diagram For Palomar 11, Matthew S. Lewis, W. M. Liu, N. E. Q. Paust, Brian Chaboyer Jan 2006

A New Color-Magnitude Diagram For Palomar 11, Matthew S. Lewis, W. M. Liu, N. E. Q. Paust, Brian Chaboyer

Dartmouth Scholarship

We present new photometry for the Galactic thick-disk globular cluster Palomar 11 extending well past the main-sequence turnoff in the V and I bands. This photometry shows noticeable, but depleted, red giant and subgiant branches. The difference in magnitude between the red horizontal branch (red clump) and the subgiant branch is used to determine that Palomar 11 has an age of 10.4 ± 0.5 Gyr. The red clump is used to derive a distance d⊙ = 14.3 ± 0.4 kpc and a mean cluster reddening of E(V - I) = 0.40 ± 0.03. There is differential …

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Silicon Oxide Nanoparticles Reveal The Origin Of Silicate Grains In Circumstellar Environments, Peneé Armaize Clayborne Jan 2006

Silicon Oxide Nanoparticles Reveal The Origin Of Silicate Grains In Circumstellar Environments, Peneé Armaize Clayborne

Theses and Dissertations

The processes leading to the widespread presence of crystalline silicates throughout the galaxy and the origin of silicon nanoparticles thought to be responsible for the observed extended red emission in diffuse galactic background are still far from being understood. One of the most abundant oxygen bearing species in molecular astronomical regions is SiO. It has been conjectured that silicate formation probably proceeds via the agglomeration of these molecular species; however there are no studies to reveal the microscopic mechanism. We have used a synergistic approach combining experiments in molecular beams and first principles theoretical calculation to demonstrate that the passage …

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Is First J102347.6+003841 Really A Cataclysmic Binary?, John R. Thorstensen, Eve Armstrong Aug 2005

Is First J102347.6+003841 Really A Cataclysmic Binary?, John R. Thorstensen, Eve Armstrong

Dartmouth Scholarship

The radio source FIRST J102347.6+003841 was presented as the first radio-selected cataclysmic variable star. In the discovery paper, Bond et al. (2002) show a spectrum consistent with a magnetic AM Her–type system, or polar, featuring strong Balmer lines, He I and He II emission lines, and a light curve with rapid, irregular flickering. In contrast, Woudt, Warner, and Pretorius found a smoothly varying light curve with a period near 4.75 hr and one minimum per orbit, indicating that the state of the system had changed dramatically. We present time-resolved spectra showing a superficially normal, mid-G type photosphere, with no detectable …

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What Are The Building Blocks Of Our Universe?, Kameshwar C. Wali Nov 2004

What Are The Building Blocks Of Our Universe?, Kameshwar C. Wali

Physics - All Scholarship

We are told that we are living in a Golden Age of Astronomy. Cosmological Parameters are found with un precedented accuracy. Yet, the known form of matter forms only a small fraction of the total energy density of the universe. Also, a mysterious dark energy dominates the universe and causes acceleration in the rate of expansion.

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Cosmic Microwave Background And Supernova Constraints On Quintessence: Concordance Regions And Target Models, Robert R. Caldwell, Michael Doran Jun 2004

Cosmic Microwave Background And Supernova Constraints On Quintessence: Concordance Regions And Target Models, Robert R. Caldwell, Michael Doran

Dartmouth Scholarship

We perform a detailed comparison of the Wilkinson Microwave Anisotropy Probe (WMAP) measurements of the cosmic microwave background (CMB) temperature and polarization anisotropy with the predictions of quintessence cosmological models of dark energy. We consider a wide range of quintessence models, including: a constant equation-of-state; a simply-parametrized, time-evolving equation-of-state; a class of models of early quintessence; scalar fields with an inverse-power law potential. We also provide a joint fit to the CBI and ACBAR CMB data, and the type 1a supernovae. Using these select constraints we identify viable, target models for further analysis.

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Kinetics Of Binary Nucleation Of Vapors In Size And Composition Space, Sergey P. Fisenko, Gerald Wilemski Jan 2004

Kinetics Of Binary Nucleation Of Vapors In Size And Composition Space, Sergey P. Fisenko, Gerald Wilemski

Physics Faculty Research & Creative Works

We reformulate the kinetic description of binary nucleation in the gas phase using two natural independent variables: the total number of molecules g and the molar composition x of the cluster. The resulting kinetic equation can be viewed as a two-dimensional Fokker-Planck equation describing the simultaneous Brownian motion of the clusters in size and composition space. Explicit expressions for the Brownian diffusion coefficients in cluster size and composition space are obtained. For characterization of binary nucleation in gases three criteria are established. These criteria establish the relative importance of the rate processes in cluster size and composition space for different …

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Redshift-Distance Survey Of Early-Type Galaxies: Spectroscopic Data, G. Wegner, M. Bernardi, C. N. A. Willmer, L. N. Da Costa Nov 2003

Redshift-Distance Survey Of Early-Type Galaxies: Spectroscopic Data, G. Wegner, M. Bernardi, C. N. A. Willmer, L. N. Da Costa

Dartmouth Scholarship

We present central velocity dispersions and Mg2 line indices for an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984 had no previous measures. This sample contains the largest set of homogeneous spectroscopic data for a uniform sample of elliptical galaxies in the nearby universe. These galaxies were observed as part of the ENEAR project, designed to study the peculiar motions and internal properties of the local early-type galaxies. Using 523 repeated observations of 317 galaxies obtained during different runs, the data are brought to a common zero point. These multiple observations, taken during the many runs …

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Stellar Pollution And [Fe/H] In The Hyades, Aaron Dotter, Brian Chaboyer Oct 2003

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 …

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Gauge-Invariant Initial Conditions And Early Time Perturbations In Quintessence Universes, Michael Doran, Christian M. Müller, Gregor Schäfer, Christof Wetterich Sep 2003

Gauge-Invariant Initial Conditions And Early Time Perturbations In Quintessence Universes, Michael Doran, Christian M. Müller, Gregor Schäfer, Christof Wetterich

Dartmouth Scholarship

We present a systematic treatment of the initial conditions and evolution of cosmological perturbations in a universe containing photons, baryons, neutrinos, cold dark matter, and a scalar quintessence field. By formulating the evolution in terms of a differential equation involving a matrix acting on a vector comprised of the perturbation variables, we can use the familiar language of eigenvalues and eigenvectors. As the largest eigenvalue of the evolution matrix is fourfold degenerate, it follows that there are four dominant modes with a nondiverging gravitational potential at early times, corresponding to adiabatic, cold dark matter isocurvature, baryon isocurvature and neutrino isocurvature …

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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 Jun 2003

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 z3 = 2.328 for its host galaxy, an active starburst galaxy with strong Ly emission and several absorption lines. Spectral observations show multiple absorbers at z3A = 2.323, z3B= 2.317, and z3C = 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 …

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Effects Of The Sound Speed Of Quintessence On The Microwave Background And Large Scale Structure, Simon Dedeo, R. R. Caldwell, Paul J. Steinhardt May 2003

Effects Of The Sound Speed Of Quintessence On The Microwave Background And Large Scale Structure, Simon Dedeo, R. R. Caldwell, Paul J. Steinhardt

Dartmouth Scholarship

We consider how quintessence models in which the sound speed differs from the speed of light and varies with time affect the cosmic microwave background and the fluctuation power spectrum. Significant modifications occur on length scales related to the Hubble radius during epochs in which the sound speed is near zero and the quintessence contributes a non-negligible fraction of the total energy density. For the microwave background, we find that the usual enhancement of the lowest multipole moments by the integrated Sachs-Wolfe effect can be modified, resulting in suppression or bumps instead. Also, the sound speed can produce oscillations and …

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The Impact Of Pollution On Stellar Evolution Models, Aaron Dotter, Brian Chaboyer Jan 2003

The Impact Of Pollution On Stellar Evolution Models, Aaron Dotter, Brian Chaboyer

Dartmouth Scholarship

An approach is introduced for incorporating the concept of stellar pollution into stellar evolution models. The approach involves enhancing the metal content of the surface layers of stellar models. In addition, the surface layers of stars in the mass range of 0.5-2.0 M☉ are mixed to an artificial depth motivated by observations of lithium abundance. The behavior of polluted stellar evolution models is explored assuming the pollution occurs after the star has left the fully convective pre-main-sequence phase. Stellar models polluted with a few Earth masses (M⊕) of iron are significantly hotter than stars of the …

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Extraordinary Late‐Time Infrared Emission Of Type Iin Supernovae, Christopher L. Gerardy, Robert A. Fesen, Ken-Ichi Nomoto, Peter M. Garnavich Aug 2002

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 …

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Sensitivity Of The Cosmic Microwave Background Anisotropy To Initial Conditions In Quintessence Cosmology, Rahul Dave, R. R. Caldwell, Paul J. Steinhardt Jul 2002

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 …

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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 Feb 2002

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 …

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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 Jan 2002

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 …

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Fine-Tuning Solution For Hybrid Inflation In Dissipative Chaotic Dynamics, Rudnei O. Ramos Nov 2001

Fine-Tuning Solution For Hybrid Inflation In Dissipative Chaotic Dynamics, Rudnei O. Ramos

Dartmouth Scholarship

We study the presence of chaotic behavior in phase space in the preinflationary stage of hybrid inflation models. This is closely related to the problem of initial conditions associated with these inflationary types of model. We then show how an expected dissipative dynamics of fields just before the onset of inflation can solve or ease considerably the problem of initial conditions, driving the system naturally toward inflation. The chaotic behavior of the corresponding dynamical system is studied by computation of the fractal dimension of the boundary in phase space separating inflationary from noninflationary trajectories. The fractal dimension for this boundary …

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Redshifts For 2410 Galaxies In The Century Survey Region, Gary Wegner, John R. Thorstensen, Michael J. Kurtz, Warren R. Brown, Daniel G. Fabricant, Margaret J. Geller, John P. Huchra, Ronald O. Marzke, Shoko Sakai Aug 2001

Redshifts For 2410 Galaxies In The Century Survey Region, Gary Wegner, John R. Thorstensen, Michael J. Kurtz, Warren R. Brown, Daniel G. Fabricant, Margaret J. Geller, John P. Huchra, Ronald O. Marzke, Shoko Sakai

Dartmouth Scholarship

The Century Survey strip covers 102 deg2 within the limits 85 ≤ α ≤ 165, 290 ≤ δ ≤ 300, equinox B1950.0. The strip passes through the Corona Borealis supercluster and the outer region of the Coma cluster. Within the Century Survey region, we have measured 2410 redshifts that constitute four overlapping complete redshift surveys: (1) 1728 galaxies with Kron-Cousins Rph ≤ 16.13 covering the entire strip, (2) 507 galaxies with Rph ≤ 16.4 in right ascension range 8h32m ≤ α ≤ 10 h45m, equinox B1950.0, (3) 1251 galaxies with absorption- …

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Heavy‐Element Diffusion In Metal‐Poor Stars, Brian Chaboyer, W. H. Fenton, Jenica E. Nelan, D. J. Patnaude, Francesca E. Simon Aug 2001

Heavy‐Element Diffusion In Metal‐Poor Stars, Brian Chaboyer, W. H. Fenton, Jenica E. Nelan, D. J. Patnaude, Francesca E. Simon

Dartmouth Scholarship

Stellar evolution models that include the effect of helium and heavy-element diffusion have been calculated for initial iron abundances of [Fe/H] = -2.3, -2.1, -1.9, and -1.7. These models were calculated for a large variety of masses and three separate mixing lengths, α = 1.50, 1.75, and 2.00 (with α = 1.75 being the solar calibrated mixing length). The change in the surface iron abundance for stars of different masses was determined for the ages of 11, 13, and 15 Gyr. Iron settles out of the surface convection zone on the main sequence ; this iron is dredged back up …

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X‐Ray–Emitting Groups In The Infall Region Of Abell 2199, K. Rines, A. Mahdavi, M. J. Geller, A. Diaferio, J. J. Mohr, G. Wegner Jul 2001

X‐Ray–Emitting Groups In The Infall Region Of Abell 2199, K. Rines, A. Mahdavi, M. J. Geller, A. Diaferio, J. J. Mohr, G. Wegner

Dartmouth Scholarship

Using a large redshift survey covering 95 deg2, we demonstrate that the infall region of Abell 2199 contains Abell 2197, one or two X-ray-emitting groups, and up to five additional groups identified in redshift surveys. Our survey shows that the X-ray-emitting systems, located at projected radii of 14, 19, and 51 (2.2, 3.1, and 8.0 h-1 Mpc), are connected kinematically to A2199. A2197 is itself an optically rich cluster; its weak X-ray emission suggests that it is much less massive than A2199. The absence of a sharp peak in the infall pattern at the position of A2197 supports this …

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Shortcuts In The Fifth Dimension, Robert Caldwell, David Langlois Jul 2001

Shortcuts In The Fifth Dimension, Robert Caldwell, David Langlois

Dartmouth Scholarship

If our Universe is a three-brane embedded in a five-dimensional anti-de Sitter spacetime, in which matter is confined to the brane and gravity inhabits an infinite bulk space, then the causal propagation of luminous and gravitational signals is in general different. A gravitational signal traveling between two points on the brane can take a “shortcut” through the bulk, and appear quicker than a photon traveling between the same two points along a geodesic on the brane. Similarly, in a given time interval, a gravitational signal can propagate farther than a luminous signal. We quantify this effect, and analyze the impact …

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The Expansion Center And Dynamical Age Of The Galactic Supernova Remnant Cassiopeia A, John R. Thorstensen, Robert A. Fesen, Sidney Van Den Bergh Jul 2001

The Expansion Center And Dynamical Age Of The Galactic Supernova Remnant Cassiopeia A, John R. Thorstensen, Robert A. Fesen, Sidney Van Den Bergh

Dartmouth Scholarship

We present proper motions for 21 bright main shell and 17 faint, higher velocity, outer ejecta knots in the Cas A supernova remnant and use them to derive new estimates for the remnant's expansion center and age. Our study included 1951–1976 Palomar 5 m prime focus plates, 1988–1999 CCD images from the KPNO 4 m and MDM 2.4 m telescopes, and 1999 HST WFPC2 images. Measurable positions covered a 23 to 41 yr time span for most knots, with a few outer knots followed for almost 48 yr. We derive an expansion center of α(J2000) = 23h23m …

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Affinity For Scalar Fields To Dissipate, Arjun Berera, Rudnei O. Ramos Apr 2001

Affinity For Scalar Fields To Dissipate, Arjun Berera, Rudnei O. Ramos

Dartmouth Scholarship

The zero-temperature effective equation of motion is derived for a scalar field interacting with other fields. For a broad range of cases, involving interaction with as few as one or two fields, dissipative regimes are found for the scalar field system. The zero-temperature limit constitutes a baseline effect that will be prevalent in any general statistical state. Thus, the results found here provide strong evidence that dissipation is the norm not the exception for an interacting scalar field system. For application to inflationary cosmology, this provides convincing evidence that warm inflation could be a natural dynamics once proper treatment of …

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Near-Infrared Spectroscopy Of The Cassiopeia A And Kepler Supernova Remnants, Christopher L. Gerardy, Robert A. Fesen Feb 2001

Near-Infrared Spectroscopy Of The Cassiopeia A And Kepler Supernova Remnants, Christopher L. Gerardy, Robert A. Fesen

Dartmouth Scholarship

Near-infrared spectra (0.95 – 2.4 μm) of the Cassiopeia A and Kepler supernova remnants (SNRs) are presented. Low-dispersion (R ≈ 700) spectra were obtained for five bright fast-moving ejecta knots (FMKs) at two locations on the main shell and for three bright circumstellar knots (QSFs) near the southwest rim of Cas A. The main shell FMKs in Cas A exhibit a sparse near- infrared spectrum dominated by [S II] 1.03 μm emission with a handful of other, fainter emission lines. Among these are two high-ionization silicon lines, [Si VI] 1.96 μm and [Si X] 1.43 μm, which have been detected …

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A Desktop Universe For The Introductory Astronomy Laboratory, Laurence A. Marschall, Glenn A. Snyder, Paul Richard Cooper Dec 2000

A Desktop Universe For The Introductory Astronomy Laboratory, Laurence A. Marschall, Glenn A. Snyder, Paul Richard Cooper

Physics and Astronomy Faculty Publications

What is a well-intentioned astronomy instructor to do? There is no argument that experience with the real world is desirable in any astronomy course, especially the introductory classes that fulfill the science distribution requirements at many colleges and universities. Though it is a simple matter to take students out of doors, show them the motions of the Sun, Moon, and stars, and have them squint for a few seconds at Saturn's rings through a telescope, these activities represent only a small portion of the subject matter of modern astronomy. It is simply not possible, given the constraints of time, weather, …

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The Relative Age Of The Thin And Thick Galactic Disks, Wilson M. Liu, Brian Chaboyer Dec 2000

The Relative Age Of The Thin And Thick Galactic Disks, Wilson M. Liu, Brian Chaboyer

Dartmouth Scholarship

We determine the relative ages of the open cluster NGC 188 and selected Hipparcos field stars by isochrone fitting and compare them to the age of the thick-disk globular cluster 47 Tuc. The best-fit age for NGC 188 was determined to be 6.5 ± 1.0 Gyr. The solar-metallicity Hipparcos field stars yielded a slightly older thin-disk age, 7.5 ± 0.7 Gyr. Two slightly metal-poor ([Fe/H] = -0.22) field stars whose kinematic and orbital parameters indicate that they are members of the thin disk were found to have an age of 9.7 ± 0.6 Gyr. The age for 47 Tuc was …

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The Infall Region Of Abell 576: Independent Mass And Light Profiles, Kenneth Rines, Margaret J. Geller, Antonaldo Diaferio, Joseph J. Mohr, Gary A. Wegner Nov 2000

The Infall Region Of Abell 576: Independent Mass And Light Profiles, Kenneth Rines, Margaret J. Geller, Antonaldo Diaferio, Joseph J. Mohr, Gary A. Wegner

Dartmouth Scholarship

We describe observations of the nearby (cz = 11,487 km s-1) cluster of galaxies Abell 576 beyond the virial radius and into the infall region where galaxies are on their first or second pass through the cluster. Using 1057 redshifts, we use the infall pattern in redshift space to determine the mass profile of A576 to a radius of ~4 h-1 Mpc. This mass estimation technique makes no assumptions about the equilibrium state of the cluster. Within ~1 h-1 Mpc, the mass profile we derive exceeds that determined from X-ray observations by a factor of …

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Rosat Hri And Asca Observations Of The Spiral Galaxy Ngc 6946 And Its Northeast Complex Of Luminous Supernova Remnants, Eric M. Schlegel, William P. Blair, Robert A. Fesen Aug 2000

Rosat Hri And Asca Observations Of The Spiral Galaxy Ngc 6946 And Its Northeast Complex Of Luminous Supernova Remnants, Eric M. Schlegel, William P. Blair, Robert A. Fesen

Dartmouth Scholarship

Analysis of 80 ks ASCA and 60 ks ROSAT HRI observations of the face-on spiral galaxy NGC 6946 are presented. The ASCA image is the first observation of this galaxy above ~2 keV. Diffuse emission may be present in the inner ~4' extending to energies above ~2–3 keV. In the HRI data, 14 pointlike sources are detected, the brightest two being a source very close to the nucleus and a source to the northeast that corresponds to a luminous complex of interacting supernova remnants (SNRs). We detect a point source that lies ~30'' west of the SNR complex but with …

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Enear Redshift-Distance Survey: Cosmological Constraints, Stefano Borgani, Mariangela Bernardi, Luiz N. Da Costa, Gary Wegner Jul 2000

Enear Redshift-Distance Survey: Cosmological Constraints, Stefano Borgani, Mariangela Bernardi, Luiz N. Da Costa, Gary Wegner

Dartmouth Scholarship

We present an analysis of the ENEAR sample of peculiar velocities of field and cluster elliptical galaxies, obtained with Dn-σ distances. We use the velocity correlation function ψ1(r) to analyze the statistics of the field object's velocities, while the analysis of the cluster data is based on the estimate of their rms peculiar velocity Vrms. The results are compared with predictions from cosmological models using linear theory. The statistics of the model velocity field is parameterized by the amplitude η8 = σ8Ω and by the shape parameter Γ of the cold dark matter-like power spectrum. …

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Grb 991216 Joins The Jet Set: Discovery And Monitoring Of Its Optical Afterglow, J. P. Halpern, R. Uglesich, N. Mirabal, S. Kassin, J. Thorstenson, W. C. Keel, A. Diercks, J. S. Bloom, F. Harrison, J. Mattox, M. Eracleous Jun 2000

Grb 991216 Joins The Jet Set: Discovery And Monitoring Of Its Optical Afterglow, J. P. Halpern, R. Uglesich, N. Mirabal, S. Kassin, J. Thorstenson, W. C. Keel, A. Diercks, J. S. Bloom, F. Harrison, J. Mattox, M. Eracleous

Dartmouth Scholarship

The optical light curve of the energetic γ-ray burst GRB 991216 is consistent with jetlike behavior in which a power-law decay steepens from t-1.22+-0.04 at early times to t-1.53 +- 0.05 in a gradual transition at around 2 days. The derivation of the late-time decay slope takes into account the constant contribution of a host or intervening galaxy, which was measured 110 days after the event at R = 24.56 +- 0.14, although the light curve deviates from a single power law whether or not a constant term is included. The early-time spectral energy distribution of the afterglow …

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