Astrophysics and Astronomy Commons^™

A Multiwavelength Analysis Of The Halo Planetary Nebula Dddm‐1, R. B. C. Henry, K. B. Kwitter, R. J. Dufour, J. N. Skinner

Dartmouth Scholarship

We present new HST optical imagery as well as new UV and IR spectroscopic data obtained with the Hubble Space Telescope and Spitzer Space Telescope, respectively, of the halo planetary nebula DdDm-1. For the first time we present a resolved image of this object, which indicates that the morphology of DdDm-1 can be described as two orthogonal elliptical components in the central part surrounded by an extended halo. The extent of the emission is somewhat larger than was previously reported in the literature. We combine the spectral data with our own previously published optical measurements to derive nebular abundances …

Ages And Metallicities Of Early-Type Void Galaxies From Line Strength Measurements, Gary Wegner, Norman A. Grogin

Dartmouth Scholarship

We present spectroscopic observations of 26 galaxies of type E and S0, based on their blue morphologies, located in voids by the study of Grogin & Geller in 1999. Measurements of redshift, velocity dispersion, and four Lick line indices, Mg _b , Fe5270, Fe5335, and Hβ with their errors are given for all of these galaxies, along with Hβ, [O III], Hα, and [N II] emission line strengths for a subset of these objects. These sources are brighter than M* for low-density regions and tend to be bluer than their counterpart early-type objects in high-density regions. Using the models …

Large Scale Structure As A Probe Of Gravitational Slip, Scott F. Daniel, Robert R. Caldwell, Asantha Cooray, Alessandro Melchiorri

Dartmouth Scholarship

A new time-dependent, scale-independent parameter, ϖ, is employed in a phenomenological model of the deviation from general relativity in which the Newtonian and longitudinal gravitational potentials slip apart on cosmological scales as dark energy, assumed to be arising from a new theory of gravitation, appears to dominate the Universe. A comparison is presented between ϖ and other parametrized post-Friedmannian models in the literature. The effect of ϖ on the cosmic microwave background anisotropy spectrum, the growth of large-scale structure, the galaxy weak-lensing correlation function, and cross correlations of cosmic microwave background anisotropy with galaxy clustering are illustrated. Cosmological models with …

The Rapidly Flaring Afterglow Of The Very Bright And Energetic Grb 070125, Adria C. Updike, Josh B. Haislip, Melissa C. Nysewander, Andrew S. Fruchter, D. Alexander Kann, Sylvio Klose, Peter A. Milne, G. Grant Williams, Weikang Zheng, Carl W. Hergenrother, Jason X. Prochaska, Jules P. Halpern, Nestor Mirabal, John R. Thorstensen

Dartmouth Scholarship

We report on multiwavelength observations, ranging from X-ray to radio wave bands, of the IPN-localized gamma-ray burst GRB 070125. Spectroscopic observations reveal the presence of absorption lines due to O I, Si II, and C IV, implying a likely redshift of z = 1.547. The well-sampled light curves, in particular from 0.5 to 4 days after the burst, suggest a jet break at 3.7 days, corresponding to a jet opening angle of ~7.0°, and implying an intrinsic GRB energy in the 1-10,000 keV band of around E_γ = (6.3–6.9) × 10⁵¹ ergs (based on the fluences measured by …

Deep Advanced Camera For Surveys Imaging In The Globular Cluster Ngc 6397: The Cluster Color-Magnitude Diagram And Luminosity Function, Harvey B. Richer, Aaron Dotter, Jarrod Hurley, Jay Anderson

Dartmouth Scholarship

We present the color-magnitude diagram (CMD) from deep Hubble Space Telescope imaging in the globular cluster NGC 6397. The Advanced Camera for Surveys (ACS) was used for 126 orbits to image a single field in two colors (F814W, F606W) 5' SE of the cluster center. The field observed overlaps that of archival WFPC2 data from 1994 and 1997 which were used to proper motion (PM) clean the data. Applying the PM corrections produces a remarkably clean CMD which reveals a number of features never seen before in a globular cluster CMD. In our field, the main-sequence stars appeared to terminate …

The Nature Of The Ultraluminous Oxygen‐Rich Supernova Remnant In Ngc 4449, Dan Milisavljevic, Robert A. Fesen

Dartmouth Scholarship

Optical images and spectra, both ground based and taken by Hubble Space Telescope (HST), of the young, luminous O-rich supernova remnant in the irregular galaxy NGC 4449 are presented. HST images of the remnant and its local region were obtained with the ACS/WFC using filters F435W, F555W, F814W (B, V, and I, respectively), F502N ([O III]), F658N (Hα + [N II]), F660N ([N II]), and F550M (line-free continuum). These images show an unresolved remnant (FWHM < 0.05'') located within a rich cluster of OB stars which itself is enclosed by a nearly complete interstellar shell seen best in Hα + [N II] emission approximately 8'' × 6'' (150 pc × 110 pc ) in size. The remnant and its associated OB cluster are isolated …

Spatially Resolved Spectroscopy Of Coma Cluster Early‐Type Galaxies. Iv. Completing The Data Set, E. M. Corsini, G. Wegner, R. P. Saglia, J. Thomas

Dartmouth Scholarship

The long-slit spectra obtained along the minor axis, offset major axis, and diagonal axis are presented for 12 E and S0 galaxies of the Coma Cluster drawn from a magnitude-limited sample studied before. The rotation curves, velocity dispersion profiles, and the H₃ and H₄ coefficients of the Hermite decomposition of the line-of-sight velocity distribution are derived. The radial profiles of the Hβ, Mg, and Fe line strength indices are measured too. In addition, the surface photometry of the central regions of a subsample of four galaxies recently obtained with the Hubble Space Telescope is presented. The data will …

Comparing Various Multi-Component Global Heliosphere Models, H.-R. Müller, V. Florinski, J. Heerikhuisen, V. V. Izmodenov

Dartmouth Scholarship

Modeling of the global heliosphere seeks to investigate the interaction of the solar wind with the partially ionized local interstellar medium. Models that treat neutr al hydrogen self-consistently and in great detail, together with the plasma, but that neglect magnetic fields, constitute a sub-category within global heliospheric models. There are several different modeling strategies used for this sub-category in the literature. Differences and commonalities in the modeling results from different strategies are pointed out.

Comparison Of Birkeland Current Observations During Two Magnetic Cloud Events With Mhd Simulations, H Korth, B J. Anderson, J G. Lyon, M Wiltberger

Dartmouth Scholarship

Low altitude field-aligned current densities ob-

tained from global magnetospheric simulations are compared

with two-dimensional distributions of Birkeland currents at

the topside ionosphere derived from magnetic field observa-

tions by the constellation of Iridium satellites. We present the

analysis of two magnetic cloud events, 17–19 August 2003

and 19–21 March 2001, where the interplanetary magnetic

field (IMF) rotates slowly (∼10◦/h) to avoid time-aliasing in

the magnetic perturbations used to calculate the Birkeland

currents. In the August 2003 event the IMF rotates from

southward to northward while maintaining a negative IMF

By during much of the interval. During the March 2001 …

A New, Bright, Short-Period, Emission Line Binary In Ophiuchus, M. A. Stark, Richard A. Wade, John R. Thorstensen, Christopher S. Peters

Dartmouth Scholarship

The 11th magnitude star LS IV-08°3 has been classified previously as an OB star in the Luminous Stars survey, or alternatively as a hot subdwarf. It is actually a binary star. We present spectroscopy, spectroscopic orbital elements, and time-series photometry from observations made at the Kitt Peak National Observatory 2.1 m, Steward Observatory 2.3 m, MDM Observatory 1.3 m and 2.4 m, Hobby-Eberly 9.2 m, and Michigan State University 0.6 m telescopes. The star exhibits emission of varying strength in the cores of H and He I absorption lines. Emission is also present at 4686 Å (He II) and near …

De Canum Venaticorum: A Bright, Eclipsing Red Dwarf–White Dwarf Binary, E. J. M. Van Den Besselaar, R. Greimel, L. Morales-Rueda, G. Nelemans, J. R. Thorstensen

Dartmouth Scholarship

Close white dwarf - red dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarf - red dwarf binary with a relatively short (~8.7 hours) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters which we discuss in the frame work of common-envelope evolution. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average low-resolution spectrum of …

Optical Imaging And Spectroscopy Of The Galactic Supernova Remnant 3c 58 (G130.7+3.1), Robert Fesen, Gwen Rudie, Alan Hurford, Aljeandro Soto

Dartmouth Scholarship

We present a comprehensive imaging and spectroscopic survey of optical emission knots associated with the young Galactic supernova remnant 3C 58. Hα images show hundreds of clumpy filaments and knots arranged in a complex structure covering a nearly circular area roughly 400'' in diameter. A quite different emission structure is seen in [O III], where the brightest features are less clumpy and largely confined to the remnant's northwest quadrant. Measured radial velocities of over 450 knots reveal two distinct kinematic populations; one with average and peak expansion velocities of 770 and 1100 km s⁻¹, respectively, forming a thick …

Lower Limit To The Scale Of An Effective Quantum Theory Of Gravitation, R. R. Caldwell, Daniel Grin

Dartmouth Scholarship

An effective quantum theory of gravitation in which gravity weakens at energies higher than ∼10−3  eV is one way to accommodate the apparent smallness of the cosmological constant. Such a theory predicts departures from the Newtonian inverse-square force law on distances below ∼0.05  mm. However, it is shown that this modification also leads to changes in the long-range behavior of gravity and is inconsistent with observed gravitational lenses.

The Extinction Toward The Galactic Bulge From Rr Lyrae Stars, Andrea Kunder, Piotr Popowski, Kem H. Cook, Brian Chaboyer

Dartmouth Scholarship

We present mean reddenings toward 3525 RR0 Lyrae stars from the Galactic bulge fields of the MACHO Survey. These reddenings are determined using the color at minimum V-band light of the RR0 Lyrae stars themselves and are found to be in general agreement with extinction estimates at the same location obtained from other methods. Using 3256 stars located in the Galactic Bulge, we derive the selective extinction coefficient R_V,VR = A_V/E(V − R) = 4.3 ± 0.2. This value is what is expected for a standard extinction law with R …

Near Ultraviolet–Infrared Colours Of Red-Sequence Galaxies In Local Clusters, Timothy D. Rawle, Russell J. Smith, John R. Lucey, Michael J. Hudson, Gary A. Wegner

Dartmouth Scholarship

We present GALEX near‐ultraviolet (NUV) and Two‐Micron All‐Sky Survey J‐band photometry for red‐sequence galaxies in local clusters. We define quiescent samples according to a strict emission threshold, removing galaxies with very recent star formation. We analyse the NUV–J colour–magnitude relation (CMR) and find that the intrinsic scatter is an order of magnitude larger than for the analogous optical CMR (∼0.35 rather than 0.05 mag), in agreement with previous studies. Comparing the NUV–J colours with spectroscopically derived stellar population parameters, we find a strong (>5.5σ) correlation with metallicity, only a marginal trend with …

The Warps Survey. Vii. The Warps‐Ii Cluster Catalog, Donald J. Horner, Eric S. Perlman, Harald Ebeling, Laurence Jones, Caleb A. Scharf, Gary Wegner, Matthew Malkan, Ben Maughan

Dartmouth Scholarship

We present the galaxy cluster catalog from the second, larger phase of the Wide Angle ROSAT Pointed Survey (WARPS), an X-ray selected survey for high-redshift galaxy clusters. WARPS is among the largest deep X-ray cluster surveys and is being used to study the properties and evolution of galaxy clusters. The WARPS-II sample contains 125 clusters serendipitously detected in a survey of 301 ROSAT PSPC pointed observations and covers a sky area of 56.7 deg². Of these 125 clusters, 53 have not been previously reported in the literature. We have nearly complete spectroscopic follow-up of the clusters, which range …

First Results From Ideal 2-D Mhd Reconstruction: Magnetopause Reconnection Event Seen By Cluster, W. L. Teh, B. U. O. Sonnerup

Dartmouth Scholarship

We have applied a new reconstruction method (Sonnerup and Teh, 2008), based on the ideal single-fluid MHD equations in a steady-state, two-dimensional geometry, to a reconnection event observed by the Cluster-3 (C3) space- craft on 5 July 2001, 06:23 UT, at the dawn-side Northern- Hemisphere magnetopause. The event has been previously studied by use of Grad-Shafranov (GS) reconstruction, per- formed in the deHoffmann-Teller frame, and using the as- sumption that the flow effects were either negligible or the flow was aligned with the magnetic field. Our new method allows the reconstruction to be performed in the frame of reference moving …

The Crab Nebula's Dynamical Age As Measured From Its Northern Filamentary Jet, G. C. Rudie, R. A. Fesen, T. Yamada

Dartmouth Scholarship

We present a deep [O III] 4959,5007 image of the northern filamentary jet in the Crab Nebula taken with the 8.2m Subaru telescope. Using this image and an image taken with the KPNO 4m in 1988 (Fesen & Staker 1993), we have computed proper motions for 35 locations in the jet. The results suggest that when compared to the main body of the remnant, the jet experienced less outward acceleration from the central pulsar's rapidly expanding synchrotron nebula. The jet's apparent expansion rate yields an undecelerated explosion date for the Crab Nebula of 1055 plus or minus 24 C.E., a …

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 …

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 …

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 …

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 …

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 …

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 …}

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 …

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 …

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 …

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 …

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 …

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 …