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Articles 901 - 930 of 1375

Full-Text Articles in Stars, Interstellar Medium and the Galaxy

Broad Relativistic Iron Emission Line Observed In Sax J1808.4-3658, E. M. Cackett, D. Altamirano, A. Patruno, J. M. Miller, M. Reynolds, M. Linares, R. Wijnands Mar 2009

Broad Relativistic Iron Emission Line Observed In Sax J1808.4-3658, E. M. Cackett, D. Altamirano, A. Patruno, J. M. Miller, M. Reynolds, M. Linares, R. Wijnands

Physics and Astronomy Faculty Research Publications

During the 2008 September-October outburst of the accreting millisecond pulsar SAX J1808.4-3658, the source was observed by both Suzaku and XMM-Newton approximately 1 day apart. Spectral analysis reveals a broad relativistic Fe Kα emission line which is present in both data sets, as has recently been reported for other neutron star low-mass X-ray binaries. The properties of the Fe K line observed during each observation are very similar. From modeling the Fe line, we determine the inner accretion disk radius to be 13.2 ± 2.5 GM c-2. The inner disk radius measured from the Fe K line suggests …

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Neutrosophic Logic, Wave Mechanics, And Other Stories: Selected Works 2005-2008, Florentin Smarandache, Victor Christianto Mar 2009

Neutrosophic Logic, Wave Mechanics, And Other Stories: Selected Works 2005-2008, Florentin Smarandache, Victor Christianto

Branch Mathematics and Statistics Faculty and Staff Publications

There is beginning for anything; we used to hear that phrase. The same wisdom word applies to us too. What began in 2005 as a short email on some ideas related to interpretation of the Wave Mechanics results in a number of papers and books up to now. Some of these papers can be found in Progress in Physics or elsewhere. It is often recognized that when a mathematician meets a physics-inclined mind then the result is either a series of endless debates or publication. In our story, we prefer to publish rather than perish. Therefore, our purpose with this …

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Discovery Of X-Ray Emission From The Wolf-Rayet Star Wr 142 Of Oxygen Subtype., L. Oskinova, W.-R. Hamann, A. Feldmeier, Richard Ignace, Y.-H. Chu Mar 2009

Discovery Of X-Ray Emission From The Wolf-Rayet Star Wr 142 Of Oxygen Subtype., L. Oskinova, W.-R. Hamann, A. Feldmeier, Richard Ignace, Y.-H. Chu

ETSU Faculty Works

We report the discovery of weak yet hard X-ray emission from the Wolf-Rayet (WR) star WR 142 with the XMM-Newton X-ray telescope. Being of spectral subtype WO2, WR 142 is a massive star in a very advanced evolutionary stage shortly before its explosion as a supernova or gamma-ray burst. This is the first detection of X-ray emission from a WO-type star. We rule out any serendipitous X-ray sources within approximate to 1 '' of WR 142. WR 142 has an X-ray luminosity of L(X) approximate to 7 x 10(30) erg s(-1), which constitutes only less than or similar to 10(-8) …

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Scattering Polarization Due To Light Source Anisotropy Ii. Envelope Of Arbitrary Shape., Richard Ignace, M. Al-Malki, J. Simmons, J. Brown, D. Clarke, J. Carson Mar 2009

Scattering Polarization Due To Light Source Anisotropy Ii. Envelope Of Arbitrary Shape., Richard Ignace, M. Al-Malki, J. Simmons, J. Brown, D. Clarke, J. Carson

ETSU Faculty Works

Aims. We consider the polarization arising from scattering in an envelope illuminated by a central anisotropic source. This work extends the theory introduced in a previous paper (Al-Malki et al. 1999) in which scattering polarization from a spherically symmetric envelope illuminated by an anisotropic point source was considered. Here we generalize to account for the more realistic expectation of a non-spherical envelope shape. Methods. Spherical harmonics are used to describe both the light source anisotropy and the envelope density distribution functions of the scattering particles. This framework demonstrates how the net resultant polarization arises from a superposition of three basic …

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The Dust Cloud Around The White Dwarf G 29-38. Ii. Spectrum From 5 To 40 Μm And Mid-Infrared Photometric Variability, William T. Reach, Ted Von Hippel, Et Al. Mar 2009

The Dust Cloud Around The White Dwarf G 29-38. Ii. Spectrum From 5 To 40 Μm And Mid-Infrared Photometric Variability, William T. Reach, Ted Von Hippel, Et Al.

Publications

We model the mineralogy and distribution of dust around the white dwarf G29-39 using the infrared spectrum from 1 to 35 μm. The spectral model for G29-38 dust combines a wide range of materials based on spectral studies of comets and debris disks. In order of their contribution to the mid-infrared emission, the most abundant minerals around G29-38 are amorphous carbon (λ < 8 μm), amorphous and crystalline silicates (5-40 μm), water ice (10-15 and 23-35 μm), and metal sulfides (18-28 μm). The amorphous C can be equivalently replaced by other materials (like metallic Fe) with featureless infrared spectra. The best-fitting crystalline silicate is Fe-rich pyroxene. In order to absorb enough starlight to power the observed emission, the disk must either be much thinner than the stellar radius (so that it can be heated from above and below) or it must have an opening angle wider than 2°. A "moderately optically thick" torus model fits well if the dust extends inward to 50 times the white dwarf radius, all grains hotter than 1100 K are vaporized, the optical depth from the star through the disk is τ∥ = 5, and the radial density profile ∝r –2.7; the total mass of this model disk is 2 × 1019 g. A physically thin (less than the white dwarf radius) and optically thick disk can contribute to the near-infrared continuum only; such a disk cannot …

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Infrared Spectroscopy Of Symbiotic Stars. Vii. Binary Orbit And Long Secondary Period Variability Of Ch Cygni, Kenneth H. Hinkle, Francis C. Fekel, Richard R. Joyce Feb 2009

Infrared Spectroscopy Of Symbiotic Stars. Vii. Binary Orbit And Long Secondary Period Variability Of Ch Cygni, Kenneth H. Hinkle, Francis C. Fekel, Richard R. Joyce

Information Systems and Engineering Management Research Publications

High-dispersion spectroscopic observations are used to refine orbital elements for the symbiotic binary CH Cyg. The current radial velocities, added to a previously published 13 year time series of infrared velocities for the M giant in the CH Cyg symbiotic system, more than double the length of the time series to 29 years. The two previously identified velocity periods are confirmed. The long period, revised to 15.6 ± 0.1 yr, is shown to result from a binary orbit with a 0.7 M☉ white dwarf and 2 M☉ M giant. Mass transfer to the white dwarf is responsible for the symbiotic …

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Veritas Observations Of A Very High Energy Gamma-Ray Flare From The Blazar 3c 66a, P. T. Reynolds, Et Al Feb 2009

Veritas Observations Of A Very High Energy Gamma-Ray Flare From The Blazar 3c 66a, P. T. Reynolds, Et Al

Physical Sciences Publications

The intermediate-frequency peaked BL Lacertae (IBL) object 3C 66A is detected during 2007-2008 in VHE (very high energy; E > 100 GeV) γ rays with the VERITAS stereoscopic array of imaging atmospheric Cherenkov telescopes. An excess of 1791 events is detected, corresponding to a significance of 21.2 standard deviations (σ), in these observations (32.8 hr live time). The observed integral flux above 200 GeV is 6% of the Crab Nebula's flux and shows evidence for variability on the timescale of days. The measured energy spectrum is characterized by a soft power law with photon index Γ = 4.1 ± 0.4stat ± …

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The Evolution Of Late-Time Optical Emission From Sn 1979c, Dan Milisavljevic, Robert A. Fesen, Robert P. Kirshner, Peter Challis Feb 2009

The Evolution Of Late-Time Optical Emission From Sn 1979c, Dan Milisavljevic, Robert A. Fesen, Robert P. Kirshner, Peter Challis

Dartmouth Scholarship

Optical spectra of the bright Type II-L supernova SN 1979C obtained in April 2008 with the 6.5 m Multiple Mirror Telescope are compared with archival late-time spectra to follow the evolution of its optical emission over the age range of 11-29 years. We estimate an Hα flux decrease of around 35% from 1993 to 2008 but noticeable increases in the strength of blueshifted emission of forbidden oxygen lines. While the maximum expansion of the broad ~6700 km s–1 Hα emission appears largely unchanged from 1993, we find a significant narrowing of the double-peaked emission profiles in the [O I] …

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A Deep Xmm-Newton Observation Of The Quasar 3c 287, G. Salvesen, J. M. Miller, E. Cackett, A. Siemiginowska Feb 2009

A Deep Xmm-Newton Observation Of The Quasar 3c 287, G. Salvesen, J. M. Miller, E. Cackett, A. Siemiginowska

Physics and Astronomy Faculty Research Publications

We report on an XMM-Newton observation of the z = 1.055 quasar and Gigahertz Peaked Spectrum (GPS) source 3C 287. Our 62.3 ks observation provides an exceptional X-ray view of a prominent member of this important subclass of active galactic nuclei (AGNs). The X-ray spectra of 3C 287 are consistent with a simple absorbed power law with a spectral index of Γ = 1.72 ± 0.02. Our fits imply a bolometric luminosity of L = 5.8 ± 0.2 × 1045 erg s-1 over the 0.3-10.0 keV band; this gives a mass lower limit of M BH min >= …

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Grb060602b = Swift J1749.4-2807: An Unusual Transiently Accreting Neutron-Star X-Ray Binary, R. Wijnands, E. Rol, E. Cackett, R. L. C. Starling, R. A. Remillard Feb 2009

Grb060602b = Swift J1749.4-2807: An Unusual Transiently Accreting Neutron-Star X-Ray Binary, R. Wijnands, E. Rol, E. Cackett, R. L. C. Starling, R. A. Remillard

Physics and Astronomy Faculty Research Publications

We present an analysis of the Swift Burst Alert Telescope (BAT) and X-ray telescope (XRT) data of GRB060602B, which is most likely an accreting neutron star in a binary system and not a gamma-ray burst. Our analysis shows that the BAT burst spectrum is consistent with a thermonuclear flash (type I X-ray burst) from the surface of an accreting neutron star in a binary system. The X-ray binary nature is further confirmed by the report of a detection of a faint point source at the position of the XRT counterpart of the burst in archival XMM-Newton data approximately six year …

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Spectropolarimetric Variability And Co-Rotating Structure In Hd 92207., Richard Ignace, S. Hubrig, M. Schöller Jan 2009

Spectropolarimetric Variability And Co-Rotating Structure In Hd 92207., Richard Ignace, S. Hubrig, M. Schöller

ETSU Faculty Works

We report on low resolution (R~3000) spectropolarimetry of the A0 supergiant star HD 92207. This star is well-known for significant spectral variability. The source was observed on seven different nights spanning approximately 3 months in time. With a rotation period of approximately 1 year, our data covers approximately a quarter of the star's rotational phase. Variability in the continuum polarization level is observed over this period of time. The polarization across the Halpha line on any given night is typically different from the degree and position angle of the polarization in the continuum. Interestingly, Hbeta is not in emission and …

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Absolute Magnitude Distribution And Light Curves Of Gamma-Ray Burst Supernovae., D. Richardson Jan 2009

Absolute Magnitude Distribution And Light Curves Of Gamma-Ray Burst Supernovae., D. Richardson

Faculty and Staff Publications

Photometry data were collected from the literature and analyzed for supernovae (SNe) that are thought to have a gamma-ray burst (GRB) association. There are several GRBs afterglow light curves that appear to have an SN component. For these light curves, the SN component was extracted and analyzed. An SN light-curve model was used to help determine the peak absolute magnitudes as well as estimates for the kinetic energy, ejected mass, and nickel mass in the explosion. The peak absolute magnitudes are, on average, brighter than those of similar SNe (stripped-envelope SNe) that do not have a GRB association, but this …

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A Search For Iron Emission Lines In The Chandra X-Ray Spectra Of Neutron Star Low-Mass X-Ray Binaries, E. M. Cackett, J. M. Miller, J. Homan, M. Van Der Klis, W. H. G. Lewin, M. Méndez, J. Raymond, D. Steeghs, R. Wijnands Jan 2009

A Search For Iron Emission Lines In The Chandra X-Ray Spectra Of Neutron Star Low-Mass X-Ray Binaries, E. M. Cackett, J. M. Miller, J. Homan, M. Van Der Klis, W. H. G. Lewin, M. Méndez, J. Raymond, D. Steeghs, R. Wijnands

Physics and Astronomy Faculty Research Publications

While iron emission lines are well studied in black hole systems, both in X-ray binaries and active galactic nuclei, there has been less of a focus on these lines in neutron star low-mass X-ray binaries (LMXBs). However, recent observations with Suzaku and XMM-Newton have revealed broad, asymmetric iron line profiles in three neutron star LMXBs, confirming an inner disk origin for these lines in neutron star systems. Here, we present a search for iron lines in six neutron star LMXBs. For each object we have simultaneous Chandra and RXTE observations at two separate epochs, allowing for both a high-resolution spectrum …

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General Search For Stars With Rapid Optical Variations: Test Fields, Elizabeth Fagg, Jieun Park, Kelly Pearson, Robert Kehoe Jan 2009

General Search For Stars With Rapid Optical Variations: Test Fields, Elizabeth Fagg, Jieun Park, Kelly Pearson, Robert Kehoe

Journal of Undergraduate Research

We present a search for stars exhibiting short time-scale optical lightvariations. Our search employs archival data taken by the ROTSE1 telephotoarray in two eight degree fields of view. This is a test study considering two fields which overlap fields previously mined for variables, but with different dataand search techniques. Each field was observed for approximately six continuous hours. We employ a general search strategy based on statistical properties of theobserved light curves for each object. The analysis is sensitive to sources with variations < 0.25 day and > 0.1 mag and with mean magnitudes between 9.5 magand 14 mag. We identify 42 variable stars with …

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Modeling Forbidden Line Emission Profiles From Colliding Wind Binaries., Richard Ignace, R. Bessey, C. Price Jan 2009

Modeling Forbidden Line Emission Profiles From Colliding Wind Binaries., Richard Ignace, R. Bessey, C. Price

ETSU Faculty Works

This paper presents calculations for forbidden emission-line profile shapes arising from colliding wind binaries. The main application is for systems involving a Wolf–Rayet (WR) star and an OB star companion. The WR wind is assumed to dominate the forbidden line emission. The colliding wind interaction is treated as an Archimedean spiral with an inner boundary. Under the assumptions of the model, the major findings are as follows. (i) The redistribution of the WR wind as a result of the wind collision is not flux conservative but typically produces an excess of line emission; however, this excess is modest at around …

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Statistical Analysis Of Stellar Evolution, David A. Van Dyk, Ted Von Hippel, Steven Degenarro, Nathan Stein, William Jefferys Jan 2009

Statistical Analysis Of Stellar Evolution, David A. Van Dyk, Ted Von Hippel, Steven Degenarro, Nathan Stein, William Jefferys

Publications

Color-Magnitude Diagrams (CMDs) are plots that compare the magnitudes (luminosities) of stars in different wavelengths of light (colors). High nonlinear correlations among the mass, color, and surface temperature of newly formed stars induce a long narrow curved point cloud in a CMD known as the main sequence. Aging stars form new CMD groups of red giants and white dwarfs. The physical processes that govern this evolution can be described with mathematical models and explored using complex computer models. These calculations are designed to predict the plotted magnitudes as a function of parameters of scientific interest, such as stellar age, mass, …

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The June 2008 Flare Of Markarian 421 From Optical To Tev Energies, P. T. Reynolds, Et Al Dec 2008

The June 2008 Flare Of Markarian 421 From Optical To Tev Energies, P. T. Reynolds, Et Al

Physical Sciences Publications

We present optical, X-ray, high-energy (30 GeV) and very high energy (100 GeV; VHE) observations of the high-frequency peaked blazar Mrk 421 taken between 2008 May 24 and June 23. A high-energy γ-ray signal was detected by AGILE with between June 9 and 15, with F(E>100 MeV) = 42+14 –12 × 10–8 photons cm–2 s–1. This flaring state is brighter than the average flux observed by EGRET by a factor of ~3, but still consistent with the highest EGRET flux. In hard X-rays (20-60 keV) SuperAGILE resolved a five-day flare (June 9-15) peaking at ~55 mCrab. SuperAGILE, …

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Discovery Of Very High-Energy Gamma-Ray Radiation From The Bl Lac 1es 0806+524, P. T. Reynolds, Et Al Dec 2008

Discovery Of Very High-Energy Gamma-Ray Radiation From The Bl Lac 1es 0806+524, P. T. Reynolds, Et Al

Physical Sciences Publications

The high-frequency-peaked BL Lacertae object 1ES 0806+524, at redshift z = 0.138, was observed in the very high energy (VHE) gamma-ray regime by VERITAS between 2006 November and 2008 April. These data encompass the two- and three-telescope commissioning phases, as well as observations with the full four-telescope array. 1ES 0806+524 is detected with a statistical significance of 6.3 standard deviations from 245 excess events. Little or no measurable variability on monthly timescales is found. The photon spectrum for the period 2007 November to 2008 April can be characterized by a power law with photon index 3.6 ± 1.0stat ± 0.3sys …

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Direct Distance Measurement To The Dusty White Dwarf Gd 362, Mukremin Kilic, John R. Thorstensen, D. Koester Dec 2008

Direct Distance Measurement To The Dusty White Dwarf Gd 362, Mukremin Kilic, John R. Thorstensen, D. Koester

Dartmouth Scholarship

We present trigonometric parallax observations of GD 362 obtained over seven epochs using the MDM 2.4m Hiltner Telescope. The existence of a dust disk around this possibly massive white dwarf makes it an interesting target for parallax observations. The measured parallax for GD 362 places it at a distance of 50.6 pc, which implies that its radius and mass are ~ 0.0106 Rsun and 0.71 Msun, respectively. GD 362 is not as massive as initially thought (1.2Msun). Our results are entirely consistent with the distance and mass estimates (52.2 pc and 0.73 Msun) by Zuckerman et al., who demonstrated that …

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Planetary Systems Around Close Binary Stars: The Case Of The Very Dusty, Sun-Like, Spectroscopic Binary Bd+20 307, Benjamin Zuckerman, Francis C. Fekel, Michael H. Williamson, Gregory W. Henry, Michael P. Muno Dec 2008

Planetary Systems Around Close Binary Stars: The Case Of The Very Dusty, Sun-Like, Spectroscopic Binary Bd+20 307, Benjamin Zuckerman, Francis C. Fekel, Michael H. Williamson, Gregory W. Henry, Michael P. Muno

Information Systems and Engineering Management Research Publications

Field star BD+20 307 is the dustiest known main-sequence star, based on the fraction of its bolometric luminosity, ~4%, that is emitted at infrared wavelengths. The particles that carry this large infrared luminosity are unusually warm, comparable to the temperature of the zodiacal dust in the solar system, and their existence is likely to be a consequence of a fairly recent collision of large objects such as planets or planetary embryos. Thus, the age of BD+20 307 is potentially of interest in constraining the era of terrestrial planet formation. The present project was initiated with an attempt to derive this …

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Multiwavelength Constraints On The Day–Night Circulation Patterns Of Hd 189733b, Heather Knutson, David Charbonneau, Nicolas B. Cowan, Jonathan J. Fortney, Adam P. Showman, Eric Agol, Gregory W. Henry, Mark E. Everett, Lori E. Allen Dec 2008

Multiwavelength Constraints On The Day–Night Circulation Patterns Of Hd 189733b, Heather Knutson, David Charbonneau, Nicolas B. Cowan, Jonathan J. Fortney, Adam P. Showman, Eric Agol, Gregory W. Henry, Mark E. Everett, Lori E. Allen

Information Systems and Engineering Management Research Publications

We present new Spitzer observations of the phase variation of the hot Jupiter HD 189733b in the MIPS 24 μm bandpass, spanning the same part of the planet's orbit as our previous observations in the IRAC 8 μm bandpass (Knutson et al. 2007). We find that the minimum hemisphere-averaged flux from the planet in this bandpass is 76% ± 3% of the maximum flux; this corresponds to minimum and maximum hemisphere-averaged brightness temperatures of 984 ± 48 K and 1220 ±  47 K, respectively. The planet reaches its maximum flux at an orbital phase of 0.396 ± 0.022, corresponding to …

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Cooling Of The Crust In The Neutron Star Low-Mass X-Ray Binary Mxb 1659-29, Edward M. Cackett, Rudy Wijnands, Jon M. Miller, Edward F. Brown, Nathalie Degenaar Nov 2008

Cooling Of The Crust In The Neutron Star Low-Mass X-Ray Binary Mxb 1659-29, Edward M. Cackett, Rudy Wijnands, Jon M. Miller, Edward F. Brown, Nathalie Degenaar

Physics and Astronomy Faculty Research Publications

In quasi-persistent neutron star transients, long outbursts cause the neutron star crust to be heated out of thermal equilibrium with the rest of the star. During quiescence, the crust then cools back down. Such crustal cooling has been observed in two quasi-persistent sources: KS 1731-260 and MXB 1659-29. Here we present an additional Chandra observation of MXB 1659-29 in quiescence, which extends the baseline of monitoring to 6.6 yr after the end of the outburst. This new observation strongly suggests that the crust has thermally relaxed, with the temperature remaining consistent over 1000 days. Fitting the temperature cooling curve with …

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Magnetic Field Measurements Of O Stars With Fors 1 At The Vlt., S. Hubrig, M. Schöller, R. Schnerr, J. González, Richard Ignace, H. Henrichs Nov 2008

Magnetic Field Measurements Of O Stars With Fors 1 At The Vlt., S. Hubrig, M. Schöller, R. Schnerr, J. González, Richard Ignace, H. Henrichs

ETSU Faculty Works

Context.The presence of magnetic fields in O-type stars has been suspected for a long time. The discovery of these fields would explain a wide range of well documented enigmatic phenomena in massive stars, in particular cyclical wind variability, Hα emission variations, chemical peculiarity, narrow X-ray emission lines, and non-thermal radio/X-ray emission. Aims.To investigate the incidence of magnetic fields in O stars, we acquired 38 new spectropolarimetric observations with FORS 1 (FOcal Reducer low dispersion Spectrograph) mounted on the 8-m Kueyen telescope of the VLT. Methods.Spectropolarimetric observations were obtained at different phases for a sample of 13 O …

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A Catalog Of Outer Ejecta Knots In The Cassiopeia A Supernova Remnant, Molly C. Hammell, Robert A. Fesen Nov 2008

A Catalog Of Outer Ejecta Knots In The Cassiopeia A Supernova Remnant, Molly C. Hammell, Robert A. Fesen

Dartmouth Scholarship

Hubble Space Telescope images of the core-collapse supernova remnant Cassiopeia A are used to identify high-velocity knots of ejecta located outside the remnant's main emission shell of expanding debris. These ejecta fragments are found near or ahead of the remnant's forward shock front and mostly lie from 120'' to 300'' in radial distance from the remnant's center of expansion. Filter flux ratios when correlated with published spectra show that these knots can be divided into three emission classes: (1) knots dominated by [N II] λλ6548, 6583 emissions, (2) knots dominated by [O II] λλ7319, 7330 emissions, and (3) …

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Parallax And Distance Estimates For Twelve Cataclysmic Variable Stars, John R. Thorstensen, Sébastien Lépine, Michael Shara Oct 2008

Parallax And Distance Estimates For Twelve Cataclysmic Variable Stars, John R. Thorstensen, Sébastien Lépine, Michael Shara

Dartmouth Scholarship

We report parallax and distance estimates for 12 more cataclysmic binaries and related objects observed with the 2.4 m Hiltner telescope at MDM Observatory. The final parallax accuracy is typically ~1 mas. Notable results include distances for V396 Hya (CE 315), a helium double degenerate with a relatively long orbital period, and for MQ Dra (SDSSJ155331+551615), a magnetic system with a very low accretion rate. We find that the Z Cam star KT Persei is physically paired with a K main-sequence star lying 15 arcsec away. Several of the targets have distance estimates in the literature that are based on …

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Chemical Analysis Of Five Red Giants In The Globular Cluster M10 (Ngc 6254), Sharina Haynes, Geoffrey Burks, Christian I. Johnson, Catherine A. Pilachowski Sep 2008

Chemical Analysis Of Five Red Giants In The Globular Cluster M10 (Ngc 6254), Sharina Haynes, Geoffrey Burks, Christian I. Johnson, Catherine A. Pilachowski

Information Systems and Engineering Management Research Publications

We have determined Al, α, Fe-peak, and neutron capture elemental abundances for five red-giant branch (RGB) stars in the Galactic globular cluster M10. Abundances were determined using equivalent width analyses of moderate-resolution (R ∼ 15,000) spectra obtained with the Hydra multifiber positioner and bench spectrograph on the WIYN telescope. The data sample the upper RGB from the luminosity level near the horizontal branch to about 0.5 mag below the RGB tip. We find, in agreement with previous studies, that M10 is moderately metal-poor with [Fe/H] = -1.45 (σ = 0.04). All stars appear enhanced in Al with 〈[Al/Fe]〉 = +0.33 …

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The Evolution Of Late‐Time Optical Emission From Sn 1986j, Dan Milisavljevic, Robert A. Fesen, Bruno Leibundgut, Robert P. Kirshner Sep 2008

The Evolution Of Late‐Time Optical Emission From Sn 1986j, Dan Milisavljevic, Robert A. Fesen, Bruno Leibundgut, Robert P. Kirshner

Dartmouth Scholarship

We present late-time optical images and spectra of the Type IIn supernova SN 1986J. HST ACS/WFC images obtained in 2003 February show it to be still relatively bright, with mF606W = 21.4 and mF814W = 20.0 mag. Compared to 1994 December HST WFPC2 images, SN 1986J shows a decline of only <1 mag in brightness over 8 years. Ground-based spectra taken in 1989, 1991, and 2007 show a 50% decline in Hα emission between 1989 and 1991, and an order of magnitude drop between 1991 and 2007, along with the disappearance of He I line emissions during the period 1991-2007. The object's [O I] λλ6300, 6364, [O II] λλ7319, 7330 and [O III] λλ4959, 5007 emission lines show two prominent peaks near –1000 and –3500 km s−1, with the more blueshifted component declining significantly in strength between 1991 and 2007. The observed spectral evolution suggests two different origins for SN 1986J's late-time optical emission: dense, shock-heated circumstellar material, which gave rise to the initially bright Hα, He I, and [N II] λ5755 …

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The Dartmouth Stellar Evolution Database, Aaron Dotter, Brian Chaboyer, Darko Jevremović, Veselin Kostov Sep 2008

The Dartmouth Stellar Evolution Database, Aaron Dotter, Brian Chaboyer, Darko Jevremović, Veselin Kostov

Dartmouth Scholarship

The ever-expanding depth and quality of photometric and spectroscopic observations of stellar populations increase the need for theoretical models in regions of age-composition parameter space that are largely unexplored at present. Stellar evolution models that employ the most advanced physics and cover a wide range of compositions are needed to extract the most information from current observations of both resolved and unresolved stellar populations. The Dartmouth Stellar Evolution Database is a collection of stellar evolution tracks and isochrones that spans a range of [Fe/H] from –2.5 to +0.5, [α/Fe] from –0.2 to +0.8 (for [Fe/H] ≤ 0) or +0.2 (for …

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Veritas Discovery Of > 200 Gev Gamma-Ray Emission From The Intermediate-Frequency-Peaked Bl Lacertae Object W Comae, P. T. Reynolds, Et Al Aug 2008

Veritas Discovery Of > 200 Gev Gamma-Ray Emission From The Intermediate-Frequency-Peaked Bl Lacertae Object W Comae, P. T. Reynolds, Et Al

Physical Sciences Publications

We report the detection of very high energy γ-ray emission from the intermediate-frequency-peaked BL Lacertae object W Comae (z = 0.102) by VERITAS. The source was observed between 2008 January and April. A strong outburst of γ-ray emission was measured in the middle of March, lasting for only 4 days. The energy spectrum measured during the two highest flare nights is fit by a power law and is found to be very steep, with a differential photon spectral index of Γ = 3.81 ± 0.35stat± 0.34syst. The integral photon flux above 200 GeV during those two nights corresponds to …

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The Effects Of Clumps In Explaining X-Ray Emission Lines From Hot Stars., J. Cassinelli, Richard Ignace, W. Waldron, J. Cho, N. Murphy, A. Lazarian Aug 2008

The Effects Of Clumps In Explaining X-Ray Emission Lines From Hot Stars., J. Cassinelli, Richard Ignace, W. Waldron, J. Cho, N. Murphy, A. Lazarian

ETSU Faculty Works

It is now well established that stellar winds of hot stars are fragmentary and that the X-ray emission from stellar winds has a strong contribution from shocks in winds. Chandra high spectral resolution observations of line profiles of O and B stars have shown numerous properties that had not been expected. Here we suggest explanations by considering the X-rays as arising from bow shocks that occur where the stellar wind impacts on spherical clumps in the winds. We use an accurate and stable numerical hydrodynamic code to obtain steady state physical conditions for the temperature and density structure in a …

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