Physical Sciences and Mathematics | Open Access Articles

Small-Scale X-Ray Variability In The Cassiopeia A Supernova Remnant, Daniel J. Patnaude, Robert A. Fesen

Dartmouth Scholarship

A comparison of X-ray observations of the Cassiopeia A supernova remnant taken in 2000, 2002, and 2004 with the Chandra ACIS-S3 reveals the presence of several small-scale features (≤10'') that exhibit significant intensity changes over a 4 yr time frame. Here we report on the variability of six features, four of which show count rate increases from ~10% to over 90%, and two of which show decreases of ~30%-40%. While extracted 1-4.5 keV X-ray spectra do not reveal gross changes in emission-line strengths, spectral fits using nonequilibrium-ionization, metal-rich plasma models indicate increased or decreased electron temperatures for features showing increasing …

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The Acs Survey Of Galactic Globular Clusters: M54 And Young Populations In The Sagittarius Dwarf Spheroidal Galaxy, Michael H. Siegel, Aaron Dotter, Steven R. Majewski, Ata Sarajedini, Brian Chaboyer, David L. Nidever, Jay Anderson, Antonio Martin-French, Alfred Rosenberg, Luigi R. Bedin, Antonio Aparicio, Ivan King, Giampolo Piotto, I. Neill Reid

Dartmouth Scholarship

As part of the ACS Survey of Galactic Globular Clusters, we present new Hubble Space Telescope photometry of the massive globular cluster M54 (NGC 6715) and the superposed core of the tidally disrupted Sagittarius (Sgr) dSph galaxy. Our deep (F606W ~ 26.5), high-precision photometry yields an unprecedentedly detailed color-magnitude diagram showing the extended blue horizontal branch and multiple main sequences of the M54+Sgr system. The distance and reddening to M54 are revised using both isochrone and main-sequence fitting to (m - M)₀ = 17.27 and E(B - V) = 0.15. Preliminary assessment finds the …

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Stellar Population Models And Individual Element Abundances. I. Sensitivity Of Stellar Evolution Models, Aaron Dotter, Brian Chaboyer, Jason W. Ferguson, Hyun-Chul Lee

Dartmouth Scholarship

Integrated light from distant galaxies is often compared to stellar population models via the equivalent widths of spectral features—spectral indices—whose strengths rely on the abundances of one or more elements. Such comparisons hinge not only on the overall metal abundance, but also on relative abundances. Studies have examined the influence of individual elements on synthetic spectra but little has been done to address similar issues in the stellar evolution models that underlie most stellar population models. Stellar evolution models will primarily be influenced by changes in opacities. In order to explore this issue in detail, 12 sets of stellar evolution …

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Dynamical Modelling Of Luminous And Dark Matter In 17 Coma Early-Type Galaxies, J. Thomas, R. O. Saglia, R. Bender, D. Thomas, J K. Gebhardt, J. Magorrian, E. M. Corsini, G. Wegner

Dartmouth Scholarship

Dynamical models for 17 early‐type galaxies in the Coma cluster are presented. The galaxy sample consists of flattened, rotating as well as non‐rotating early‐types including cD and S0 galaxies with luminosities between M_B=−18.79 and −22.56. Kinematical long‐slit observations cover at least the major‐axis and minor‐axis and extend to 1–4r_eff. Axisymmetric Schwarzschild models are used to derive stellar mass‐to‐light ratios and dark halo parameters. In every galaxy, the best fit with dark matter matches the data better than the best fit without. The statistical significance is over 95 per cent for eight galaxies, around 90 per …

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Mixing And Homogenization In The Early Solar System: Clues From Sr, Ba, Nd, And Sm Isotopes In Meteorites, Rasmus Andreasen, Mukul Sharma

Dartmouth Scholarship

High-precision barium isotopic compositions of large samples of an ordinary chondrite and a eucrite are identical to the terrestrial values. In contrast, the carbonaceous chondrites reveal excesses in ¹³⁵Ba and ¹³⁷Ba of around +39 and +22 parts per million (ppm), respectively; no anomalies are resolvable in ^130,132,138Ba. High-precision Sr isotopic compositions of all meteorites are identical within error. The data are consistent with the carbonaceous chondrites having an excess in the r-process ^135,137Ba with respect to Earth, eucrite parent bodies, and ordinary chondrites. The carbonaceous chondrites, however, display no variation in the r- and …

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A High-Resolution Ultraviolet Absorption Spectrum Of Supernova Ejecta In Sn1006, Andrew J. S. Hamilton, Robert A. Fesen, William P. Blair

Dartmouth Scholarship

We report a high-resolution, far-ultraviolet, Space Telescope Imaging Spectrograph (STIS) E140M spectrum of the strong, broad Siii, iii and iv features produced by the ejecta of the supernova of 1006 ad (SN1006) seen in absorption against the background Schweizer–Middleditch OB subdwarf star. The spectrum confirms the extreme sharpness of the red edge of the redshifted Si ii 1260 Å feature, supporting the idea that this edge represents the location of the reverse shock moving into the freely expanding Si-rich ejecta. The expansion velocity of ejecta at the reverse shock is measured to be 7026 ± 3(relative) ±10(absolute) km s^{−1 …}

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Constraints On A New Post-General Relativity Cosmological Parameter, Robert Caldwell, Asantha Cooray, Alessandro Melchiorri

Dartmouth Scholarship

A new cosmological variable is introduced to characterize the degree of departure from Einstein’s general relativity with a cosmological constant. The new parameter, ϖ, is the cosmological analog of γ, the parametrized post-Newtonian variable which measures the amount of spacetime curvature per unit mass. In the cosmological context, ϖ measures the difference between the Newtonian and longitudinal potentials in response to the same matter sources, as occurs in certain scalar-tensor theories of gravity. Equivalently, ϖ measures the scalar shear fluctuation in a dark-energy component. In the context of a vanilla, cosmological constant-dominated universe, a nonzero ϖ signals a departure from …

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The Acs Survey Of Galactic Globular Clusters. Ii. Stellar Evolution Tracks, Isochrones, Luminosity Functions, And Synthetic Horizontal-Branch Models, Aaron Dotter, Brian Chaboyer, Darko Jevremović, E. Baron

Dartmouth Scholarship

The ACS Survey of Galactic Globular Clusters, an HST Treasury Project, will deliver high-quality, homogeneous photometry of 65 globular clusters. This paper introduces a new collection of stellar evolution tracks and isochrones suitable for analyzing the ACS survey data. Stellar evolution models were computed at [Fe/H] = -2.5, -2.0, -1.5, -1.0, -0.5, and 0; [α/Fe] = -0.2, 0, 0.2, 0.4, 0.6, and 0.8; and three initial He abundances for masses from 0.1 to 1.8 M_⊙ and ages from 2 to 15 Gyr. Each isochrone spans a wide range in luminosity, from M_V ~ 14 up to the tip …

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Bvi Photometry And The Luminosity Functions Of The Globular Cluster M92, Nathaniel E. Q. Paust, Brian Chaboyer, Ata Sarajedini

Dartmouth Scholarship

We present new BVI ground-based photometry and VI space-based photometry for the globular cluster M92 (NGC 6341) and examine luminosity functions in B, V, and I containing over 50,000 stars ranging from the tip of the red giant branch to several magnitudes below the main-sequence turnoff. Once corrected for completeness, the observed luminosity functions agree very well with theoretical models and do not show stellar excesses in any region of the luminosity function. Using reduced-χ² fitting, the new M92 luminosity function is shown to be an excellent match to the previously published luminosity function for M30. These …

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The Chemical Distribution In A Subluminous Type Ia Supernova: Hubble Space Telescope Images Of The Sn 1885 Remnant, Robert A. Fesen, Peter A. Hoflich, Andrew J. S. Hamilton, Molly C. Hammell

Dartmouth Scholarship

SN 1885 was a probable subluminous SN Ia that occurred in the bulge of the Andromeda galaxy, M31, at a projected location 16'' from the nucleus. Here we present and analyze Hubble Space Telescope images of the SN 1885 remnant seen in absorption against the M31 bulge via the resonance lines of Ca I, Ca II, Fe I, and Fe II. Viewed in Ca II H and K line absorption, the remnant appears as a nearly black circular spot with an outermost angular radius of 0.40'' ± 0.025'', implying a maximum linear radius of 1.52 ± 0.15 pc at M31's …

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The Acs Survey Of Galactic Globular Clusters. I. Overview And Clusters Without Previoushubble Space Telescope Photometry, Ata Sarajedini, Luigi R. Bedin, Brian Chaboyer, Aaron Dotter, Michael H. Siegel, Jay Anderson, Antonio Aparicio, Ivan King, Steven R. Majewski, A. Marin-Franch, Giampolo Piotto, I. Neill Reid, Alfred Rosenberg

Dartmouth Scholarship

We present the first results of a large Advanced Camera for Surveys (ACS) survey of Galactic globular clusters. This Hubble Space Telescope (HST) Treasury project is designed to obtain photometry with S/N (signal-to-noise ratio) 10 for main-sequence stars with masses 0.2 M_⊙ in a sample of globulars using the ACS Wide Field Channel. Here we focus on clusters without previous HST imaging data. These include NGC 5466, NGC 6779, NGC 5053, NGC 6144, Palomar 2, E3, Lyngå 7, Palomar 1, and NGC 6366. Our color-magnitude diagrams (CMDs) extend reliably from the horizontal branch to as much as …

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A Time Delay For The Cluster‐Lensed Quasar Sdss J1004+4112, J. Fohlmeister, C. S. Kochanek, E. E. Falco, J. Wambsganss, N. Morgan, C.W. Morgan, E.O. Ofek, D. Maoz, C.R. Keeton, J.C. Barentine, G. Dalton, J. Dembicky, W. Ketzeback, R. Mcmillan, C.S. Peters

Dartmouth Scholarship

We present 426 epochs of optical monitoring data spanning 1000 days from 2003 December to 2006 June for the gravitationally lensed quasar SDSS J1004+4112. The time delay between the A and B images is tBA . 38: 42: 0 days (2 . 4) in the expected sense that B leads A and the overall time ordering is C-B-A-D-E. The measured delay invalidates all published models. The models probably failed because they neglected the perturbations from cluster member galaxies. Models including the galaxies can fit the data well, but conclusions about the clustermass distribution should await themeasurement of the longer, and …

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The Effect Of Cluster Environment On Galaxy Evolution In The Pegasus I Cluster, Lorenza Levy, James A. Rose, Jacqueline H. Van Gorkom, Brian Chaboyer

Dartmouth Scholarship

We present neutral hydrogen observations of 54 galaxies in the Pegasus Cluster. The observations include single-dish H I measurements, obtained with the Arecibo telescope for all 54 galaxies in the sample, as well as H I images obtained with the Very Large Array (VLA) for 10 of these. The Arecibo profiles reveal an overall H I deficiency in the cluster, with similar to 40% of the galaxies in the core of the cluster showing modest deficiencies of typically a factor of 2-3. The HI morphology of so me galaxies shows that the HI disk is smaller than the optical disk …

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The Wind‐Ism Interaction Of Α Tauri, Brian E. Wood, Graham M. Harper, Hans-Reinhard Muller, Jacob Heerikhuisen, Gary P. Zank

Dartmouth Scholarship

Ultraviolet spectra of α Tau (K5 III) obtained by the Hubble Space Telescope (HST) show many emission lines affected by broad absorption from the strong wind of this red giant star. For the Mg II h and k lines there is also a narrow absorption feature in the midst of the wind absorption that has been interpreted as being from α Tau's wind-interstellar medium (ISM) interaction region (i.e., its "astrosphere"). We try to reproduce this absorption using hydrodynamic models of the α Tau astrosphere, which show that stellar wind material heated, compressed, and decelerated at the wind's termination …

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Full-Text Articles in Physical Sciences and Mathematics

Small-Scale X-Ray Variability In The Cassiopeia A Supernova Remnant, Daniel J. Patnaude, Robert A. Fesen

Dartmouth Scholarship

Dartmouth Scholarship

Stellar Population Models And Individual Element Abundances. I. Sensitivity Of Stellar Evolution Models, Aaron Dotter, Brian Chaboyer, Jason W. Ferguson, Hyun-Chul Lee

Dartmouth Scholarship

Dynamical Modelling Of Luminous And Dark Matter In 17 Coma Early-Type Galaxies, J. Thomas, R. O. Saglia, R. Bender, D. Thomas, J K. Gebhardt, J. Magorrian, E. M. Corsini, G. Wegner

Dartmouth Scholarship

Mixing And Homogenization In The Early Solar System: Clues From Sr, Ba, Nd, And Sm Isotopes In Meteorites, Rasmus Andreasen, Mukul Sharma

Dartmouth Scholarship

A High-Resolution Ultraviolet Absorption Spectrum Of Supernova Ejecta In Sn1006, Andrew J. S. Hamilton, Robert A. Fesen, William P. Blair

Dartmouth Scholarship

Constraints On A New Post-General Relativity Cosmological Parameter, Robert Caldwell, Asantha Cooray, Alessandro Melchiorri

Dartmouth Scholarship

The Acs Survey Of Galactic Globular Clusters. Ii. Stellar Evolution Tracks, Isochrones, Luminosity Functions, And Synthetic Horizontal-Branch Models, Aaron Dotter, Brian Chaboyer, Darko Jevremović, E. Baron

Dartmouth Scholarship

Bvi Photometry And The Luminosity Functions Of The Globular Cluster M92, Nathaniel E. Q. Paust, Brian Chaboyer, Ata Sarajedini

Dartmouth Scholarship

The Chemical Distribution In A Subluminous Type Ia Supernova: Hubble Space Telescope Images Of The Sn 1885 Remnant, Robert A. Fesen, Peter A. Hoflich, Andrew J. S. Hamilton, Molly C. Hammell

Dartmouth Scholarship

Dartmouth Scholarship

A Time Delay For The Cluster‐Lensed Quasar Sdss J1004+4112, J. Fohlmeister, C. S. Kochanek, E. E. Falco, J. Wambsganss, N. Morgan, C.W. Morgan, E.O. Ofek, D. Maoz, C.R. Keeton, J.C. Barentine, G. Dalton, J. Dembicky, W. Ketzeback, R. Mcmillan, C.S. Peters

Dartmouth Scholarship

The Effect Of Cluster Environment On Galaxy Evolution In The Pegasus I Cluster, Lorenza Levy, James A. Rose, Jacqueline H. Van Gorkom, Brian Chaboyer

Dartmouth Scholarship

The Wind‐Ism Interaction Of Α Tauri, Brian E. Wood, Graham M. Harper, Hans-Reinhard Muller, Jacob Heerikhuisen, Gary P. Zank

Dartmouth Scholarship