Astrophysics and Astronomy Commons^™

Semi-Automated Extraction Of Digital Objective Prism Spectra, Coryn A.L. Bailer-Jones, Ted Von Hippel, Mike Irwin

Publications

We describe a method for the extraction of spectra from high dispersion objective prism plates. Our method is a catalogue driven plate solution approach, making use of the Right Ascension and Declination coordinates for the target objects. In contrast to existing methods of photographic plate reduction, we digitize the entire plate and extract spectra off-line. This approach has the advantages that it can be applied to CCD objective prism images, and spectra can be re-extracted (or additional spectra extracted) without having to re-scan the plate. After a brief initial interactive period, the subsequent reduction procedure is completely automatic, resulting in …

Measured Stark Widths And Shifts Of Several Niii Sectral Lines: Temperature Dependence, Stevan Djenize, Vladimir Milosavljevic

Articles

Stark parameters (width and shift) of four doubly ionized nitrogen spectral lines, that belong to 3s-3p and 3p-3d transitions (lower multiplets), have been measured in a linear pulsed, low pressure, arc discharge in the nitrogen-oxygen and helium-nitrogen-oxygen plasmas in a (30 000 - 54 000) K electron temperature and a (0.75 10²³ - 2.8 10²³) electron density ranges. The measured values have been compared to the existing experimental and calculated data.

Production Of Energy-Dependent Time Delays In Impulsive Solar Flare Hard X-Ray Emission By Short-Duration Spectral Index Variations, Ted N. La Rosa, Steven N. Shore

Faculty Articles

Cross-correlation techniques have been used recently to study the relative timing of solar flare hard X-ray emission at different energies. These studies find that for the majority of the impulsive flares observed with BATSE there is a systematic time delay of a few tens of milliseconds between low (approximate to 50 keV) and higher energy emission (approximate to 100 keV). These time delays have been interpreted as energy-dependent time-of-flight differences for electron propagation from the corona, where they are accelerated, to the chromosphere, where the bulk of the hard X-rays are emitted. We show in this paper that crosscorrelation methods …

Hot White Dwarfs In The Extreme ‐ Ultraviolet Explorer Survey. Iv. Da White Dwarfs With Bright Companions, Stephane Vennes, Damian J. Christian, John R. Thorstensen

Dartmouth Scholarship

We present an analysis of optical, ultraviolet, and X-ray spectral properties of a sample of 13 hot hydrogen-rich (DA) white dwarfs, each paired with a luminous unresolved companion. Using low-dispersion International Ultraviolet Explorer spectra, ROSAT photometry, and Extreme-Ultraviolet Explorer photometry and spectroscopy, we estimate the effective temperature, mass, and distance of the white dwarfs. Additionally, we examine the question of their atmospheric composition. We establish orbital properties for most binaries by means of high-dispersion optical spectroscopy obtained with the Hamilton echelle spectrograph at Lick Observatory; the same data help uncover evidence of activity in some of the secondary …

Statistics Of Active Galactic Nuclei In Rich Clusters Revisited, M. Way, R. Flores, H. Quintana

Physics Faculty Works

Using the spectrophotometry of a large sample of galaxies in 19 Abell clusters, we have selected 42 candidate active galactic nuclei (AGNs) using the criteria used by Dressler and coworkers in their analysis of the statistics of 22 AGNs in 14 rich cluster fields, which are based on the equivalent width of [O II] 3727 Å, Hβ, and [O III] 5007 Å emission. We have then discriminated AGNs from H II region-like galaxies (hereafter H II galaxies) in the manner developed by Veilleux & Osterbrock using the additional information provided by Hα and [N II] 6583 Å or Hα and …

Physical Properties Of The Binary Star 12 Persei, David J. Barlow, Colin D. Scarfe, Francis C. Fekel

Information Systems and Engineering Management Research Publications

We have obtained new radial velocities of the double-lined spectroscopic binary star 12 Persei, whose period is 331 days, and which has been resolved in recent years by speckle interferometry. We derive a solution for the orbital elements from the speckle and radial velocity data simultaneously, and find from that solution masses of 1.306 ± 0.035 and 1.172 ± 0.030 M☉ for the components, and an orbital parallax of 0farcs04224 ± 0farcs00056. We also determine spectroscopically the difference in magnitude between the components and, hence, their absolute magnitudes. We estimate their spectral types and individual colors by fitting standard-star colors …

Permitted Iron Emission Lines In The Classical T Tauri Star Dr Tauri, Georgina Beristain, Suzan Edwards, John Kwan

Astronomy: Faculty Publications

We present a study of permitted emission lines of Fe I and Fe II in the spectrum of the high-accretion rate classical T Tauri star DR Tau. Echelle spectra collected at the 4 m Mayall telescope at Kitt Peak National Observatory between 1988 and 1992 include four epochs with red spectral coverage (~5000-6800 Å) and three with blue spectral coverage (~4000-4950 Å). A total of 62 unblended Fe I and Fe II lines are identified, their profiles are examined, and ratios of line pairs that are sensitive to column density or temperature are analyzed.

The unblended Fe profiles exhibit a …

Broadband Optical Observations Of Bl Lacertae During The 1997 Outburst, Terry D. Oswalt, Daniel Marshall, Tim Robishaw

Aerospace, Physics, and Space Science Faculty Publications

We present BVRI observations of BL Lacertae during its recent outburst. These observations, made during a 3 month period, cover a significant portion of the optical flare. The reduced data are displayed as light curves and broadband spectra. Changes in the spectral index are analyzed, and the results are compared with previous BL Lac observations. We find that the variations are simultaneous in the optical bands, but the higher frequency bands show a higher amplitude of variability. The spectral index is variable during the active period, and there is marginal evidence that the spectrum flattens as the source gets brighter.

Aquila X-1: A Low-Inclination Soft X-Ray Transient, T. Shahbaz, J. R. Thorstensen, P. A. Charles, N. D. Sherman

Dartmouth Scholarship

We have obtained I-band photometry of the neutron star X-ray transient Aql X-1 during quiescence. We find a periodicity at 2.487 cycles d⁻¹, which we interpret as twice the orbital frequency (19.30±0.05 h). Folding the data on the orbital period, we model the light-curve variations as the ellipsoidal modulation of the secondary star. We determine the binary inclination to be 20°–30° (90 per cent confidence) and also determine the 95 per cent upper limits to the radial velocity semi-amplitude and rotational broadening of the secondary star to be 117 and 50 km s⁻¹, respectively.

A V And I Ccd Mosaic Survey Of The Ursa Minor Dwarf Spheroidal Galaxy, J. T. Kleyna, M. J. Geller, S. J. Kenyon, M. J. Kurtz, J. R. Thorstensen

Dartmouth Scholarship

We discuss a Johnson-Cousins V- and I-band CCD mosaic survey of the Ursa Minor dwarf spheroidal galaxy (dSph) to V ~ 22. We covered UMi with 27 105 × 105 overlapping CCD frames, each frame consisting of two 300 s exposures in each of V and I. We also observed several regions ~3° from UMi to obtain an estimate of contamination by galaxies and Galactic stars. We report the first H-R diagram of an entire dSph. Separation of dwarf stars from foreground stars by color allows a robust estimation of the structural parameters of UMi. We examine …

Search For A New Gauge Boson In Π0 Decays, Nomad Collaboration, J. Altegoer, D. Autiero, A. Baldisseri, M. Baldo-Ceolin, G. Ballocchi, M. Banner, S. Basa, G. Bassompierre, K. Benslama, N. Besson, I. Bird, B. Blumenfeld, F. Bobisut, J. Bouchez, S. Boyd, A. Bueno, S. Bunyatov, L. Camilleri, K. Zuber, Roberto Petti, Et. Al.

Faculty Publications

A search was made for a new light gauge boson X which might be produced in π⁰→γ+X decay from neutral pions generated by 450 GeV protons in the CERN SPS neutrino target. The X's would penetrate the downstream shielding and be observed in the NOMAD detector via the Primakoff effect, in the process of X→π⁰ conversion in the external Coulomb field of a nucleus. With 1.45×10¹⁸ protons on target, 20 candidate events with energy between 8 and 140 GeV were found from the analysis of neutrino data. This number is in …

Testing Modified Newtonian Dynamics With Low Surface Brightness Galaxies: Rotation Curve Fits, Stacy S. Mcgaugh

Faculty Scholarship

We present modified Newtonian dynamics (MOND) fits to 15 rotation curves of low surface brightness (LSB) galaxies. Good fits are readily found, although for a few galaxies minor adjustments to the inclination are needed. Reasonable values for the stellar mass-to-light ratios are found, as well as an approximately constant value for the total (gas and stars) mass-to-light ratio. We show that the LSB galaxies investigated here lie on the one, unique Tully-Fisher relation, as predicted by MOND. The scatter on the Tully-Fisher relation can be completely explained by the observed scatter in the total mass-to-light ratio. We address the question …

The Two-Dimensional Ising Model: Mean-Field And Monte Carlo Results For Equilibrium And Nonequilibrium Transitions, Kevin Scott Brown

Honors Capstones

No abstract provided.

Hubble Space Telescope Wide Field Planetary Camera 2 Imaging Of Ugc 12695: A Remarkably Unevolved Galaxy At Low Redshift, Stacy S. Mcgaugh

Faculty Scholarship

Utilizing the F814W and F300W filters, short-exposure Hubble Space Telescope Wide Field Planetary Camera 2 images were taken of UGC 12695, a nearby (z ∼ 0.021) low surface brightness disk galaxy. UGC 12695 has an unusual morphology, consisting of a Y-shaped nucleus surrounded by a faint spiral arm with a number of bright H II regions interspersed throughout the galaxy. Surface photometry indicates that the majority of recent star formation in this galaxy occurred in these very localized regions, most of which have a radius of ≲2″. This uneven stellar distribution, combined with the galaxy's overall extremely blue color and …

Radio Pulse Properties Of The Millisecond Pulsar Psr J0437-4715. I. Observations At 20 Centimeters, F. A. Jenet, S. B. Anderson, V. M. Kaspi, T. A. Prince, S. C. Unwin

Physics & Astronomy Faculty Publications

We present a total of 48 minutes of observations of the nearby, bright millisecond pulsar PSR J0437-4715 taken at the Parkes Observatory in Australia. The data were obtained at a central radio frequency of 1380 MHz using a high-speed tape recorder that permitted coherent Nyquist sampling of 50 MHz of bandwidth in each of two polarizations. Using the high time resolution available from this voltage recording technique, we have studied a variety of single-pulse properties, many for the first time in a millisecond pulsar. We show that individual pulses are broad band, have pulse widths ranging from ∼ 10 (∼ …

White Dwarf Cosmochronometry. I. Monte Carlo Simulations Of Proper-Motion And Magnitude-Limited Samples Using Schmidt's 1/Vmax Estimator, Matt A. Wood, Terry D. Oswalt

Aerospace, Physics, and Space Science Faculty Publications

Observationally, white dwarf stars are a remarkably homogeneous class with a minimum observed Teff ∼ 4000 K. Theoretically, the physics that determines their cooling timescales is relatively more straightforward than that which determines main-sequence evolutionary timescales. As a result, the white dwarf luminosity function has for the last decade been used as a probe of the age and star formation rate of the Galactic disk, providing an estimated local disk age of ∼ 10 Gyr with estimated total uncertainties of roughly 20%. A long-standing criticism of the technique is that the reality of the reported downturn in the luminosity function …

White Dwarf Cosmochronometry. I. Monte Carlo Simulations Of Proper-Motion ̶ And Magnitude-Limited Samples Using Schmidt’S 1/Vmax Estimator, Matt A. Wood, Terry D. Oswalt

Publications

Observationally, white dwarf stars are a remarkably homogeneous class with a minimum observed T_eff ~4000 K. Theoretically, the physics that determines their cooling timescales is relatively more straightforward than that which determines main-sequence evolutionary timescales. As a result, the white dwarf luminosity function has for the last decade been used as a probe of the age and star formation rate of the Galactic disk, providing an estimated local disk age of ~10 Gyr with estimated total uncertainties of roughly 20%. A long-standing criticism of the technique is that the reality of the reported downturn in the luminosity function (LF) …

Pg 1002+506: A Be Star Apparently At Z > +10 Kiloparsecs, F. A. Ringwald, W. R. J. Rolleston, R. A. Saffer, John R. Thorstensen

Dartmouth Scholarship

PG 1002+506 is found to be a Be star, one of three found so far by the Palomar-Green survey. Its spectrum is classified as a B5 ± 1 Ve, with T_eff = 14,900 ± 1200, log g = 4.2 ± 0.2, and v sin i = 340 ± 50 km s^-1. At b = +51°, its height above the Galactic plane would therefore be z = +10.8 kpc, putting this apparently young, rapidly rotating star well into the Galactic halo. Its heliocentric radial velocity is found to be -2 ± 15 km s^-1, consistent with …

Investigating The Formation Of Extra-Galactic Radio Jets, Casey R. Watson

Mahurin Honors College Capstone Experience/Thesis Projects

Jets of collimated particles are among the most intriguing characteristics of active galactic nuclei. In this paper two models of particle interactions in active galactic nuclei are used to explore a possible initial acceleration mechanism of the jets: charge separation. Model I ignores the effects of both collisions and electromagnetic forces and does not predict charge separation. Model II incorporates collisions and electromagnetic interactions, and, although it too predicts no charge separation, it provides a more physically sound model of active nucleus than does Model I.

Contribution Of White Dwarfs To Cluster Masses, Ted Von Hippel

Publications

I have undertaken a literature search through 1997 July 31 of white dwarfs (WDs) in open and globular clusters. I have tried to make a careful evaluation in each case of the likelihood that the object is a WD and that it is a cluster member. The results are presented for 13 open clusters and 11 globular clusters. Currently there are 36 single WDs and Ðve WDs in binaries known among the open clusters, and 340 single WDs and 11 WDs in binaries known among the globular clusters. From these data, I have calculated WD mass fractions for four open …

Contribution Of White Dwarfs To Cluster Masses, Ted Von Hippel

Publications

I have undertaken a literature search through 1997 July 31 of white dwarfs (WDs) in open and globular clusters. I have tried to make a careful evaluation in each case of the likelihood that the object is a WD and that it is a cluster member. The results are presented for 13 open clusters and 11 globular clusters. Currently there are 36 single WDs and Ðve WDs in binaries known among the open clusters, and 340 single WDs and 11 WDs in binaries known among the globular clusters. From these data, I have calculated WD mass fractions for four open …

Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xii. Ground-Based Monitoring Of 3c 390.3, M. Dietrich, Terry D. Oswalt, B. M. Peterson, P. Albrecht, M. Altmann, Et Al.

Publications

Results of a ground-based optical monitoring campaign on 3C 390.3 in 1994-1995 are presented. The broadband fluxes (B, V, R, and I), the spectrophotometric optical continuum flux and the F_λ(5177 Å),integrated emission-line fluxes of Hᵪ Hβ, Hᵧ, He I λ5876 and He II λ4686 all show a nearly monotonic increase with episodes of milder short-term variations superposed. The amplitude of the continuum variations increases with decreasing wavelength (4400-9000 Å). The optical continuum variations follow the variations in the ultraviolet and X-ray with time delays, measured from the centroids of the cross-correlation functions, typically around …

Semilocal String Formation In Two Dimensions, Ana Achúcarro, Julian Borrill, Andrew R. Liddle

Dartmouth Scholarship

We present a toy model for the investigation of the formation of semilocal strings, where a planar symmetry is employed to reduce the system to two dimensions. We approximate the symmetry breaking using an extension of the Vachaspati-Vilenkin algorithm, where we throw down random phases for the scalar fields and then find the gauge field configuration which minimizes gradient energy in this fixed scalar background. We show this procedure reproduces the standard estimate for the formation rate of cosmic strings. For semilocal strings the configurations generated by this method are ambiguous, and we numerically evolve the configurations forward in time …

How To Count Kinks. From The Continuum To The Lattice And Back, Marcelo Gleiser, Hans-Reinhard Muller

Dartmouth Scholarship

We investigate the matching between (1+1)-dimensional nonlinear field theories coupled to an external stochastic environment and their lattice simulations. In particular, we focus on how to obtain numerical results which are lattice-spacing independent, and on how to extract the correct effective potential which emerges from the simulations. As an application, we study the thermal production of kink-antikink pairs, obtaining a number density of pairs which is lattice-spacing independent and the

The Ultraviolet-Optical Albedo Of Broad Emission Line Clouds, Kirk Korista, Gary J. Ferland

Physics and Astronomy Faculty Publications

We explore the effective UV-optical albedos of a variety of types of broad emission line clouds, as well as their possible effects on the observed spectra of active galactic nuclei (AGNs). An important albedo source in moderately ionized ionization-bounded clouds is that which is due to neutral hydrogen: Rayleigh scattering of continuum photons off the extreme damping wings of Lyα. The photons resulting from this scattering mechanism may contribute significantly to the Lyα emission line, especially in the very broad wings. In addition, line photons emitted near 1200 Å (e.g., N V λ1240) that stream toward the neutral portion of …

Temperature Variations And N/O In The Orion Nebula From Hst Observations, R. H. Rubin, P. G. Martin, R. J. Dufour, Gary J. Ferland, J. A. Baldwin, J. J. Hester, D. K. Walter

Physics and Astronomy Faculty Publications

Using the Goddard High Resolution Spectrograph (GHRS) and the Faint Object Spectrograph (FOS) on the Hubble Space Telescope, we measured the flux of the N II] (2s2p^{3 5}S₂ --> 2s²2p^{2 3}P_2,1) lines at λ_vac = 2143.45, 2139.68 Å in the Orion Nebula--the first detection of these lines in an H II region. In order to assess the N⁺/O⁺ ratio, we also measured the flux of the [O II] (2p³²P^o_1/2,3/2-->2p³⁴S^o_3/2) lines at λ_{vac …}

Chromospherically Active Stars. Xvii. The Double-Lined Binary 54 Camelopardalis (Ae Lyncis), Francis C. Fekel, Joseph J. Eitter, José-Renan De Medeiros, J. Davy Kirkpatrick

Information Systems and Engineering Management Research Publications

New spectroscopic observations of the double-lined chromospherically active binary 54 Camelopardalis (=AE Lyncis) have been obtained, resulting in improved orbital elements and the determination of the fundamental properties of the system. 54 Cam has a period of 11.06794 days, an eccentricity of 0.125, and a mass ratio of 0.9945. The spectral types are F8 IV-V and G5 IV, positioning the components on opposite sides of the Hertzsprung gap. From a comparison with theoretical evolutionary tracks, the masses are estimated to be 1.60 and 1.59 M_⊙ for the G and F stars, respectively, while the radii are 3.7 and 3.2 R_⊙. …

Understanding The Cool Da White Dwarf Pulsator, G29-38, Scot J. Kleinman, Matt A. Wood

Aerospace, Physics, and Space Science Faculty Publications

The white dwarfs are promising laboratories for the study of cosmochronology and stellar evolution. Through observations of the pulsating white dwarfs, we can measure their internal structures and compositions, critical to understanding post-main-sequence evolution, along with their cooling rates, which will allow us to calibrate their ages directly. The most important set of white dwarf variables to measure are the oldest of the pulsators, the cool DA variables (DAVs), which have not been explored previously through asteroseismology due to their complexity and instability. Through a time-series photometry data set spanning 10 yr, we explore the pulsation spectrum of the cool …

Asteroseismology Of A Star Cooled By Neutrino Emission: The Pulsating Pre-White Dwarf Pg 0122 + 200, Marlea Sean O'Brien, Matt A. Wood

Aerospace, Physics, and Space Science Faculty Publications

Observation of g-rnode pulsations in the variable pre-white dwarf (GW Virginis) stars provides a unique means to probe their interiors and to study the late stages of stellar evolution. Multisite campaigns have in several cases proved highly successful in decoding pre-white dwarf light curves. Three previous attempts to untangle the pulsation spectrum of the coolest GW Virginis star, PG 0122+200, confirmed the existence of multiple g-modes but left the fundamental period spacing and therefore the star's mass and luminosity in doubt. We present an analysis based on new observations of PG 0122+200 obtained during a Whole Earth Telescope (WET) campaign …

The Warps Survey. Ii. The Log N –Log S Relation And The X‐Ray Evolution Of Low‐Luminosity Clusters Of Galaxies, L. R. Jones, C. Scharf, H. Ebeling, E. Perlman, G. Wegner, M. Malkan, D. Horner

Dartmouth Scholarship

The strong negative evolution observed in previous X-ray-selected surveys of clusters of galaxies is evidence in favor of hierarchical models of the growth of structure in the universe. A large recent survey has, however, contradicted the low-redshift results, finding no evidence for evolution at z < 0.3. Here we present the first results from an X-ray-selected, flux- and surface brightness-limited deep survey for high-redshift clusters and groups of galaxies based on ROSAT PSPC pointed data. The log N-log S relation of all clusters in this survey is consistent with that of most previous surveys, but it occupies a flux range not previously covered (greater than 6 × 10^-14 ergs cm^-2 s^-1 total flux in the 0.5-2 keV band). At high redshifts ( …