Physical Sciences and Mathematics Commons^™

Measured Stark Widths Of A 425,94 Nm Ari Spectral Line, Ljiljana Skuljan, Vladimir Milosavljevic, Aleksandar Sreckovic, Stevan Djenize

Articles

No abstract provided.

Locally Optimally Emitting Clouds And The Origin Of Quasar Emission Lines, Jack Baldwin, Gary J. Ferland, Kirk Korista, Dima Verner

Physics and Astronomy Faculty Publications

The similarity of quasar line spectra has been taken as an indication that the emission line clouds have preferred parameters, suggesting that the environment is subject to a fine-tuning process. We show here that the observed spectrum is a natural consequence of powerful selection effects. We computed a large grid of photoionization models covering the widest possible range of cloud gas density and distance from the central continuum source. For each line only a narrow range of density and distance from the continuum source results in maximum reprocessing efficiency, corresponding to "locally optimally emitting clouds" (LOCs). These parameters depend on …

Broad Ne Viii Λ744 Emission From The Quasar Pg 1148+549, Fred Hamann, Joseph C. Shields, Gary J. Ferland, Kirk T. Korista

Physics and Astronomy Faculty Publications

We discuss the probable detection of broad Ne VIII λ774 emission from the z_ɛ = 0.978 quasar PG 1148+549, and we use spectral synthesis calculations to study the physical conditions in the line-forming gas. The theoretical predictions and the measured line wavelength both support Ne VIII λ774 as the most likely identification.

Our calculations show that Ne VIII λ774 forms in hotter and more highly ionized gas than previously recognized in the broad emission line region. If the gas is photoionized by a standard active galactic nucleus continuum, the observed Ne VIII equivalent width, the Ne VIII/O VI flux …

An Automated Search For Variability In Chromospherically Active Stars, Gregory W. Henry, Francis C. Fekel, Douglas S. Hall

Information Systems and Engineering Management Research Publications

We have completed an automated photometric survey of 66 potential or known chromospherically active late-type stars with the 0.4 m Vanderbilt/Tennessee State robotic telescope. The precision of the observations from this telescope matches that predicted from photon and scintillation noise alone and represents a significant improvement in the precision of previous robotic telescope surveys of chromospherically active stars. Light variability has been detected and its period has been determined for 47 stars, 41 of which are newly discovered variables. The primary mechanism of variability is rotational modulation of a spotted surface. In addition we have detected eclipses in HD 62668 …

Observation Of Beam-Induced Changes In The Polarization Of Balmer-Α Radiation Emitted Following Beam--Tilted-Foil Transmission, Wang Qi, David D. Allred, Larry V. Knight, Douglas L. Harper, Royal G. Albridge, Norman H. Tolk

Faculty Publications

Measurements of the circular polarization of Balmer-α radiation emitted by excited hydrogen atoms, following the transmission of (20-50)-keV protons through thin, tilted amorphous carbon foils, exhibit markedly unexpected behavior as a function of exposure of the foil to the proton beam. Specifically, the circular polarization changes from an initially well understood tilt-angle dependence to a behavior which, for low tilt angles, gives the opposite handedness of circular polarization from that predicted. In addition, the degree of alignment, indicated by the linear Stokes parameter M/I, is enhanced also as a function of dose. These changes in the tilt-angle dependence of the …

The Lyman Continuum In Starburst Galaxies Observed With The Hopkins Ultraviolet Telescope, Claus Leitherer, Henry C. Ferguson, Timothy M. Heckman, James D. Lowenthal

Astronomy: Faculty Publications

The starburst galaxies IRAS 08339+6517, Mrk 1267, Mrk 66, and Mrk 496 (=NGC 6090) were observed with the Hopkins Ultraviolet Telescope (HUT) during the Astro-2 mission. All four galaxies have radial velocities larger than 5000 km s-1, permitting the measurement of their intrinsic Lyman continuum fluxes redward of the H I absorption edge in our Galaxy. The sample was selected on the basis of having the most favorable conditions for the escape of Lyman continuum photons. Two a upper limits of Fk < 7 X 10-16 ergs s-1 cm-2 A-1 were obtained for the flux around 900 A within the rest frame of each galaxy.A set of theoretical spectral energy distributions has been calculated. We show that there exists a tight correlation between the continuum luminosity at 900 A and the total number of photons emitted in the Lyman continuum, which is valid for high- and low-metallicity galaxies and essentially all relevant initial mass functions and star formation histories. Comparison with the observed values suggests that, on average, less than 3% of the intrinsic Lyman continuum photons escape from the program galaxies. Models for the ionization of the intergalactic medium at high 2 by young starbursts require a significant fraction of the ionizing radiation to escape from the galaxy. If the four galaxies observed by us have properties similar to young galaxies at redshift 2 2 3, such galaxies are not likely to provide Lyman continuum photons for the ionization of the early universe.

A Rosat Hri Observation Of The Supernova Remnant G109.1 – 1.0, Alan P. Hurford, Robert A. Fesen

Dartmouth Scholarship

We present results of a search using ROSAT HRI data for X-ray spatial substructures in the galactic supernova remnant G109.1 – 1.0 which might indicate a connection between the remnant’s bright X-ray blob and its X-ray pulsar, 1E2259 + 586. A 0.1 – 2.4 keV HRI image, created by combining separate 28- and 22-ks pointings, reveals the presence of a few small-scale X-ray features, including a NE-SW emission ridge in the remnant’s X-ray blob. Two diffuse knots in the X-ray blob, previously suggested as being aligned with the X-ray pulsar, appear to be statistical fluctuations in the Einstein HRI data. …

The Geometry And Kinematics Of The Broad-Line Region In Ngc 5548 From Hst And Iue Observations, Ignaz Wanders, Mike R. Goad, Kirk T. Korista, Bradley M. Peterson, Keith Horne, Gary J. Ferland, Anuradha P. Koratkar, Richard W. Pogge, Joseph C. Sheilds

Physics and Astronomy Faculty Publications

The spatial and radial velocity distribution of broad-line-emitting gas in the Seyfert 1 galaxy NGC 5548 is examined through the process of reverberation mapping, which is done by detailed comparison of continuum and emission-line variations. Recent spectroscopic monitoring of NGC 5548 with HST and IUE allows us to resolve the "transfer function" (TF) that relates the continuum and emission-line variability. We also examine the radial velocity-resolved TFs, and confirm that predominantly radial motions of the line-emitting clouds can be excluded. We find that a broad-line region comprised of clouds that are orbiting a central source of mass ~10⁸ M …

Aliasing Reduction In Staring Infrared Imagers Utilizing Subpixel Techniques, Joseph C. Gillette, Thomas M. Stadtmiller, Russell C. Hardie

Electrical and Computer Engineering Faculty Publications

We introduce and analyze techniques for the reduction of aliased signal energy in a staring infrared imaging system. A standard staring system uses a fixed two-dimensional detector array that corresponds to a fixed spatial sampling frequency determined by the detector pitch or spacing. Aliasing will occur when sampling a scene containing spatial frequencies exceeding half the sampling frequency. This aliasing can significantly degrade the image quality. The aliasing reduction schemes presented here, referred to as microscanning, exploit subpixel shifts between time frames of an image sequence. These multiple images are used to reconstruct a single frame with reduced aliasing. If …

Extended Molecular Gas Distribution In Mrk 273 And Merger-Luminosity Evolution, Min S. Yun, N Z. Scoville

Min S. Yun

We present the first interferometric measurement of CO emission (θ ~ 2'') from the ultraluminous infrared galaxy Mrk 273. A total H2 mass of 3.6 × 1010 Msun is inferred from the CO observations, half of which belongs to an extended component with deconvolved size 5.1 × 2.5 kpc. In addition, an unresolved molecular gas complex is found to be coincident with the optical nucleus. The inferred H2 mass, size (R ~ 380 pc), and mean surface mass density (ΣH2 ≥ 4 × 104 Msun pc-3) of this complex, as well as the IR luminosity, are very similar to those …

Imaging And Spectroscopy Of Damped Lyα Quasi-Stellar Object Absorption-Line Clouds, James Lowenthal, Craig J. Hogan, Richard F. Green, Bruce Woodgate, Adeline Caulet, Larry Brown, Jill Bechtold

Astronomy: Faculty Publications

We present the results of a multifaceted search for line emission from the vicinities of high-redshift quasi-stellar object (QSO) absorption-line clouds, most of them damped Lyα systems at z ≳ 2. Seven fields containing QSOs with known intervening damped Lyα absorbers were imaged with the GSFC Fabry-Perot Imager to search for diffuse redshifted Lyα. Apart from the one Lyα companion galaxy reported previously, no confirmed extended Lyα emission was detected down to 3 σ flux levels of around 3 x 10-17 ergs s-1 cm-2, corresponding to star formation rates ≲1 M⊙ yr-1, assuming case B recombination, a reasonable initial mass …

Development Of An Orthogonal-Stripe Cdznte Gamma Radiation Imaging Spectrometer, John R. Macri, Boris A. Apotovsky, J F. Butler, M L. Cherry, Brian K. Dann, A Drake, F P. Doty, T G. Guzik, K Larson, M Mayer, Mark L. Mcconnell, James M. Ryan

Space Science Center

We report performance measurements of a sub-millimeter resolution CdZnTe strip detector developed as a prototype for astronomical instruments operating with good efficiency in the 30-300 keV photon energy range. The prototype is a 1.4 mm thick, 64×64 contact stripe CdZnTe array of 0.375 mm pitch in both dimensions. Pulse height spectra were recorded in orthogonal-stripe coincidence mode which demonstrate room-temperature energy resolution <10 keV (FWHM) for 122 keV photons with a peak-to-valley ratio >5:1. Good response is also demonstrated at higher energies using a coplanar grid readout configuration. Spatial resolution capabilities finer than the stripe pitch are demonstrated. We present the image of a ¹³³Ba source viewed through a collimator …

Temperature Fluctuations In Photoionized Nebulae, J. B. Kingdon, Gary J. Ferland

Physics and Astronomy Faculty Publications

Recombination lines in gaseous nebulae frequently yield parent-ion abundances that are several times larger than abundances derived from forbidden lines. One possible explanation for this discrepancy is the presence of temperature fluctuations. We examine temperature fluctuations in model nebulae by utilizing Peimbert's t² parameter. We have run large grids of models, varying the stellar temperature and the total hydrogen density. We consider two abundance sets: The first uses "typical" planetary nebulae abundances, while the second examines the effect of increasing the metals and grains by a factor of 3. We also consider both a constant density distribution and one …

Large-Area Submillimeter Resolution Cdznte Strip Detector For Astronomy, James M. Ryan, John R. Macri, Mark L. Mcconnell, Brian K. Dann, M L. Cherry, T G. Guzik, F P. Doty, Boris A. Apotovsky, J F. Butler

Space Science Center

We report the first performance measurements of a sub-millimeter CdZnTe strip detector developed as a prototype for space-borne astronomical instruments. Strip detector arrays can be used to provide two-dimensional position resolution with fewer electronic channels than pixellated arrays. Arrays of this type and other candidate technologies are under investigation for the position-sensitive backplane detector for a coded-aperture telescope operating in the range of 30 - 300 keV. The prototype is a 1.4 mm thick, 64 multiplied by 64 stripe CdZnTe array of 0.375 mm pitch in both dimensions, approximately one square inch of sensitive area. Pulse height spectra in both …

Trajectory Mapping And Applications To Data From The Upper Atmosphere Research Satellite, Gary A. Morris, Mark R. Schoeberl, Lynn C. Sparling, Paul A. Newman, Leslie R. Lait, Lee Elson, Joe Waters, Robert A. Suttie, Aidan Roche, Jack Kumer, James M. Russell Iii

Physics and Astronomy Faculty Publications

The problem of creating synoptic maps from asynoptically gathered trace gas data has prompted the development of a number of schemes. Most notable among these schemes are the Kalman filter, the Salby-Fourier technique, and constituent reconstruction. This paper explores a new technique called "trajectory mapping." Trajectory mapping creates synoptic maps from asynoptically gathered data by advecting measurements backward or forward in time using analyzed wind fields. A significant portion of this work is devoted to an analysis of errors in synoptic trajectory maps associated with the calculation of individual parcel trajectories. In particular, we have considered (1) calculational errors; (2) …

Trajectory Mapping And Applications To Data From The Upper Atmosphere Research Satellite, Gary A. Morris, Mark R. Schoeberl, Lynn C. Sparling, Paul A. Newman, Leslie R. Lait, Lee Elson, Joe Waters, Robert A. Suttie, Aidan Roche, Jack Kumer, James M. Russell Iii

Gary A. Morris

The problem of creating synoptic maps from asynoptically gathered trace gas data has prompted the development of a number of schemes. Most notable among these schemes are the Kalman filter, the Salby-Fourier technique, and constituent reconstruction. This paper explores a new technique called "trajectory mapping." Trajectory mapping creates synoptic maps from asynoptically gathered data by advecting measurements backward or forward in time using analyzed wind fields. A significant portion of this work is devoted to an analysis of errors in synoptic trajectory maps associated with the calculation of individual parcel trajectories. In particular, we have considered (1) calculational errors; (2) …

Determination Of Malmquist Bias And Selection Effects From Monte Carlo Simulations, Wolfram Freudling, Luiz N. Da Costa, Gary Wegner, Riccardo Giovanelli

Dartmouth Scholarship

Maps of the peculiar velocity field derived from distance relations are affected by Malmquist type bias and selection effects. Because of the large number of interdependent effects, they are in most cases difficult to treat analytically. Monte Carlo simulations are used to understand and evaluate these effects. In these simulations the "true" spatial distribution and relevant properties of galaxies as well as selection effects and observational uncertainties are realistically modeled. The results of the simulation can be directly applied to correct observed peculiar velocity maps. The simulation is used to investigate biases in samples of measured peculiar velocities by Lynden-Bell …

Discovery Of Extreme-Ultraviolet Radiation From The Seyfert Galaxy Ton S180 (=Euve J0057−223), Stéphane Vennes, Elisha Polomski, Stuart Bowyer, John R. Thorstensen

Dartmouth Scholarship

We report the detection of intense EUV radiation from the Seyfert 1 galaxy Ton S180. The source EUVE J0057-223, discovered in the Extreme-Ultraviolet Explorer all-sky survey, is only 25'' away from its optical counterpart, well within the position error circle. We present a complete broadband energy distribution of Ton S180 using infrared (IRAS), optical, ultraviolet (IUE) and X-ray (ROSAT) flux measurements, and we find that the measured EUV flux, corrected for neutral hydrogen and helium absorption in the Galaxy, suggests the presence of a strong EUV to soft X-ray flux excess. We briefly discuss …

The Hubble Space Telescope Sample Of Radio-Loud Quasars: The LyΑ/HΒ Ratio, Hagai Netzer, M. S. Brotherton, Beverley J. Wills, Mingsheng Han, D. Wills, J. A. Baldwin, Gary J. Ferland, I. W. A. Browne

Physics and Astronomy Faculty Publications

We have used the first Hubble Space Telescope Faint Object Spectrograph spectra of our sample of radio- loud quasars, and quasi-simultaneous ground-based spectrophotometry, to investigate the intensity ratio Lyα/Hβ, whose small observed values are one of the outstanding problems of active galactic nuclei research. The present sample of 20 quasars with complete flux and profile data shows the first significant correlations of this ratio with other observed properties. The strongest correlations are with various continuum slope indicators: we find smaller Lyα/Hβ ratios in quasars whose continua rise more steeply into the red. The …

Binary Star Orbits From Speckle Interferometry. Vi. The Nearby Solar-Type Speckle-Spectroscopic Binary Hr 6697, Harold Mcalister, William I. Hartkopf, Brian D. Mason, Francis C. Fekel, Philip A. Ianna, Andrei A. Tokovinin, Roger F. Griffin, Roger B. Culver

Information Systems and Engineering Management Research Publications

Interferometric, spectroscopic, astrometric, and photometric observations are presented for the nearby solar-type binary HR 6697. The system consists of a G0-2 V primary and a K2-S V secondary. From a combined solution of the speckle and spectroscopic data the orbital period is 881 days or 2.41 yr, the semimajor axis is 2.1 A.U., the eccentricity is 0.42, and the inclination is 68°. The masses and luminosities are 1.16±0.12 Msun, 0.77±0.05 Msun, 1.61±0.15 Lsun, and 0.17±0.05 Lsun. Two independent determinations of the parallax, a trigonometric parallax of 0".0379±0".0030, and an orbital parallax of 0".0375±0".0014, are in excellent agreement and give a …

The Hubble Space Telescope Sample Of Radio-Loud Quasars: Ultraviolet Spectra Of The First 31 Quasars, Beverley J. Wills, Keith L. Thompson, Mingsheng Han, H. Netzer, D. Wills, J. A. Baldwin, Gary J. Ferland, I W. A. Browne, M. S. Brotherton

Physics and Astronomy Faculty Publications

We report the first results from a continuing program to investigate the multifrequency spectrophotometric and other properties of a sample of about 50 radio-loud quasars in the redshift range ˜0.3-1.3. Here we present spectrophotometric data of high signal-to-noise ratio (≳20 in the continuum) of the first 31 radio-loud quasars, over the wavelength range from below Lyα to an observed wavelength of 3250 or 4800 Å, obtained using the Faint Object Spectrograph on the Hubble Space Telescope. We have also made quasi-simultaneous observations to extend these spectra beyond the Balmer lines -- either Hβ or Hα -- …

Numerical Calculation Of Axisymmetric Electrostatic Modes For Cold Finite-Length Non-Neutral Plasmas, Johnny K. Jennings, Ross L. Spencer, K. C. Hansen

Faculty Publications

A numerical calculation of mode frequencies for cold, non-neutral plasmas is reported. The numerical method can be applied to any axisymmetric plasma shape in a trap. Here, it is used to study axisymmetric electrostatic modes in a long conducting cylinder. These modes were previously studied by Prasad and O'Neil [Phys. Fluids 26, 665 (1983)] and by Dubin [Phys. Rev. Lett. 66, 2076 (1991)]. In contrast to Dubin's calculation, the effects of a nearby cylindrical wall, including its influence on the shape of the plasma equilibrium, are considered. It is found that for plasmas with aspect ratios (length divided by diameter) …

Chromospherically Active Stars. Xiv. A Rediscussion Of The Properties And Evolutionary State Of Hd 181943, Francis C. Fekel, Gregory W. Henry, Douglas S. Hall

Information Systems and Engineering Management Research Publications

The chromospherically active single star HD 181943 was previously proposed as either a pre-main-sequence star seen pole-on or a post-main-sequence subgiant that evolved from an Ap star similar to 53 Cam. It also was found to be a variable star with a 385 day period. We have used new spectroscopic and photometric observations to reevaluate the properties and evolutionary state of this unusual system. We conclude that HD 181943 is a single K1 V star that has recently arrived on the ZAMS. Its emission line fluxes are nearly identical to those of HD 82558= LQ Hya, while its log lithium …

Infrared Emission And Dynamics Of Outlfows In Late-Type Stars, Željko Ivezić, Moshe Elitzur

Physics and Astronomy Faculty Publications

The dynamical structure and infrared emission of winds around late-type stars are studied in a self-consistent model that couples the equations of motion and radiative transfer. Thanks to its scaling properties, both the dynamics and IR spectrum of the solution are fully characterized by τ_F, the flux-averaged optical depth of the wind. Five types of dust grains are considered: astronomical silicate, crystalline olivine, graphite, amorphous carbon and SiC, as well as mixtures. Analysis of infrared signatures provides constraints on the grain chemical composition and indications for the simultaneous existence of silicate and carbon grains. The abundances of crystalline …

Transitions In Masculinity And Hemingway's Developed "Code", Daniel Polk

Honors Theses

The "Hemingway Code" is much more than two words that fit nicely together for a scholar's usage; the words signify a much deeper championing of masculinity, almost a haunting presence. For Ernest Hemingway living life every day, every moment with its fullest masculine fervor, became an obsession, a never-ending quest to be at one with the attitude of never complaining, never crying out, panicking, thinking too much, or regretting. To live a manly life in a series of tactical victories, performed with steadfast ritualistic mannerisms, is to embody masculinity, and therefore the "Hemingway Code."

Ubvri Photometry Of The Type Ia Sn 1994d In Ngc 4526, Michael W. Richmond, Richard R. Treffers, Alexei V. Filippenko, Schuyler D. Van Dyk, Young Paik, Chien Peng, Laurence A. Marschall, Bentley D. Laaksonen, Bruce Macintosh, Ian S. Mclean

Physics and Astronomy Faculty Publications

We present optical photometry for the type Ia SN 1994D in NGC 4526 from 1994 March 7 to June 4 starting 13 days before B-band maximum. The light curves of this SN resemble closely those of the "normal" type Ia events SNe 1989B and 1980N, differing only in a slightly faster decline after maximum in VRI. The optical absolute magnitudes of SN 1994D, however, are significantly brighter than those of its near twins, and brighter than those predicted by Phillips' [ApJ, 413, L105 (1993)] relationship between decline rate and luminosity. Our small amount of IR photometry of SN 1994D …

Collisional Effects In He I: An Observational Analysis, J. B. Kingdon, Gary J. Ferland

Physics and Astronomy Faculty Publications

Accurate and reliable helium abundances can test modern theories of galactic and primordial nucleosynthesis. Unfortunately, there is some question whether current theory can account for collisional contributions to He I. We present new observations of two planetary nebulae (PNs) in the range λ850-λ9650, which we use to assess the importance of collisonal effects in the He I spectrum. The first object, NGC 7027, is expected to show relatively strong collisional enhancement, while the second, NGC 7026, should display only small effects. We derive new collision-to-recombination correction factors, based on new collision strengths from the 29-state quantal calculation …

Starspot Evolution, Differential Rotation, And Magnetic Cycles In The Chromospherically Active Binaries Lambda Andromedae, Sigma Geminorum, Ii Pegasi, And V711 Tauri, Gregory W. Henry, Joel A. Eaton, Jamesia Hamer, Douglas S. Hall

Information Systems and Engineering Management Research Publications

We have analyzed 15-19 yr of photoelectric photometry, obtained manually and with automated telescopes, of the chromospherically active binaries lambda And, sigma Gem, II Peg, and V711 Tau. These observations let us identify individual dark starspots on the stellar surfaces from periodic dimming of the starlight, follow the evolution of these spots, and search for long-term cyclic changes in the properties of these starspots that might reveal magnetic cycles analogous to the Sun's 11 yr sunspot cycle. We developed a computer code to fit a simple two-spot model to our observed light curves that allows us to extract the most …

The Black-Hole Candidate Gro J0422+32: Mev Emission Measured With Comptel., R Van Dijk, K Bennett, W Collmar, R Diehl, W Hermsen, G G. Lichti, Mark L. Mcconnell, James M. Ryan, V. Schonfelder, A W. Strong, J Van Paradijs, C Winkler

Physics & Astronomy

On Aug. 5, 1992, BATSE detected the bright soft X-ray transient GRO J0422+32,also known as Nova Per 1992. The COMPTEL instrument (0.75-30MeV) aboard the Compton Gamma-Ray Observatory (CGRO) observed this black-hole candidate twice. During the first observation, which started when the X-ray flux was at its maximum, GRO J0422+32 was detected between 1 and 2MeV. The flux in this energy range was higher than expected from an extrapolation of the standard Sunyaev-Titarchuk Comptonisation model fits to the contemporaneous OSSE and SIGMA data. We discuss several models that may explain the total hard-X/γ-ray spectrum, including the generalised Comptonisation model from Titarchuk. …

Experiences Of Wfpc-2 Photometry And Psf Modelling, Nial Tanvir, David Robinson, Ted Von Hippel

Publications

The wide-field chips in WFPC-2 have ~0.0996 arcsec pixels, which is larger than the FWHM of the point spread function (PSF). This poor sampling of WFPC-2 images, means that simple stellar aperture photometry is competitive with profile fitting for moderately crowded fields. One of the problems which must be addressed with profile fitting photometry is that of allowing for variations of the PSF as a function of position on the image. The equivalent problem for aperture photometry is obtaining aperture corrections as a function of position. The aperture correction must be added to each aperture magnitude in order to account …