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Articles 1 - 22 of 22
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Early-Time Chromatic Variations In The Wind-Swept Medium Of Grb 021211 And The Faintness Of Its Afterglow, M. C. Nysewander, D. E. Reichart, H.-S. Park, G. G. Williams, K. Kinugasa, D. Q. Lamb, A. A. Henden, S. Klose, T. Kato, A Harper, H Yamaoka, C Laws, K Torii, D G. York, J C. Barentine, J Dembicky, R J. Mcmillan, J A. Moran, Dieter H. Hartmann, B Ketzeback, M B. Bayliss, J A. Crain, A C. Foster, M Schwartz, P Holvorcem, P A. Price, R Canterna, G B. Crew, G R. Ricker, S D. Barthelmy
Early-Time Chromatic Variations In The Wind-Swept Medium Of Grb 021211 And The Faintness Of Its Afterglow, M. C. Nysewander, D. E. Reichart, H.-S. Park, G. G. Williams, K. Kinugasa, D. Q. Lamb, A. A. Henden, S. Klose, T. Kato, A Harper, H Yamaoka, C Laws, K Torii, D G. York, J C. Barentine, J Dembicky, R J. Mcmillan, J A. Moran, Dieter H. Hartmann, B Ketzeback, M B. Bayliss, J A. Crain, A C. Foster, M Schwartz, P Holvorcem, P A. Price, R Canterna, G B. Crew, G R. Ricker, S D. Barthelmy
Publications
We present Follow-Up Network for Gamma-Ray Bursts (FUN GRB) Collaboration observations of the optical afterglow of GRB 021211 made between 143 s and 102 days after the burst. Our unique data set includes the earliest filtered detections and color information for an afterglow in the pre-Swift era. We find that the afterglow is best described by (1) a propagation through a wind-swept medium, (2) a cooling break that is blueward of the observed optical frequencies, and (3) a hard electron energy distribution. However, superimposed on this ‘‘standard model’’ behavior we find, one and possibly two, significant chromatic variations during the …
Spitzer White Dwarf Planet Limits, F. Mullally, Ted Von Hippel, D. E. Winget
Spitzer White Dwarf Planet Limits, F. Mullally, Ted Von Hippel, D. E. Winget
Publications
We present preliminary limits on the presence of planets around white dwarf stars using the IRAC photometer on the Spitzer space telescope. Planets emit strongly in the mid-infrared which allows their presence to be detected as an excess at these wavelengths. We place limits of 5 MJ for 8 stars assuming ages of 1 Gyr, and 10 MJ for 23 stars.We describe our survey, present our results and comment on approaches to improve our methodology.
The Grb 060218/Sn 2006aj Event In The Context Of Other Gamma-Ray Burst Supernovae, P. Ferreo, D. A. Kann, A. Zeh, S. Klose, E. Pian, E. Palazzi, N. Masetti, Dieter H. Hartmann, J. Sollerman, J. Deng, A V. Filippenko, J Greiner, M A. Hughes, P Mazzali, W Li, E Rol, R J. Smith, N R. Tanvir
The Grb 060218/Sn 2006aj Event In The Context Of Other Gamma-Ray Burst Supernovae, P. Ferreo, D. A. Kann, A. Zeh, S. Klose, E. Pian, E. Palazzi, N. Masetti, Dieter H. Hartmann, J. Sollerman, J. Deng, A V. Filippenko, J Greiner, M A. Hughes, P Mazzali, W Li, E Rol, R J. Smith, N R. Tanvir
Publications
The supernova SN 2006aj associated with GRB 060218 is the second-closest GRB-SN observed to date (z =0.033). We present Very Large Telescope, Liverpool Telescope, and Katzman Automatic Imaging Telescope multi-color photometry of SN 2006aj. This super-nova is found to be subluminous and rapidly evolving. Its early light curve includes an additional wavelength-dependent component, which can be interpreted as shock break-out. We compare the photometric evolution of multi-band light curves with the corresponding properties of the present sample of more than 10 GRB-SNe with precisely known redshifts. Using host-galaxy extinction measure-ments, we derive extinction-corrected GRB-SN luminosities and place SN 2006aj in …
Cluster Observations Of Reconnection Due To The Kelvin-Helmholtz Instability At The Dawnside Magnetospheric Flank, K. Nykyri, A. Otto, B. Lavraud, C. Mouikis, L. M. Kistler, A. Balogh, H. Rème
Cluster Observations Of Reconnection Due To The Kelvin-Helmholtz Instability At The Dawnside Magnetospheric Flank, K. Nykyri, A. Otto, B. Lavraud, C. Mouikis, L. M. Kistler, A. Balogh, H. Rème
Publications
On 3 July 2001, the four Cluster satellites traversed along the dawnside magnetospheric flank and observed large variations in all plasma parameters. The estimated magnetopause boundary normals were oscillating in the z-direction and the normal component of the magnetic field showed systematic ~2–3 min bipolar variations for 1 h when the IMF had a small positive bz-component and a Parker-spiral orientation in the x, y-plane. Brief ~33 s intervals with excellent deHoffman Teller frames were observed satisfying the Wal´en relation. Detailed comparisons with 2- D MHD simulations indicate that Cluster encountered rotational discontinuities generated by Kelvin-Helmholtz instability. We estimate a …
Neutrino Oscillation Effects On Supernova Light Element Synthesis, Takashi Yoshida, Toshitaka Kajino, Hidekazu Yokomakura, Keichi Kimura, Akira Takamura, Dieter H. Hartmann
Neutrino Oscillation Effects On Supernova Light Element Synthesis, Takashi Yoshida, Toshitaka Kajino, Hidekazu Yokomakura, Keichi Kimura, Akira Takamura, Dieter H. Hartmann
Publications
Neutrion oscillations affect light-element synthesis through the v-process in supernova explosions. The 7Li and 11B yields produced in a supernova explosion of a 16.2 M ⊙ star model increase by factors of 1.9 and 1.3 in the case of the large mixing angle solution with a normal mass hierarchy of sin^2 2θ13 >~ 2x10^-3 compared with those without the oscillations. In the case of an inerted mass hierarchy or a nonadiabatic 1-3 mixing resonance, the increment of their yields is much smaller. Neutrino oscillations raise the reaction rates of charged-current v-process reactions in the region outside oxygen-rich layers. The number …
Signals For Lorentz Violation In Post-Newtonian Gravity, Quentin G. Bailey, V. Alan Kostelecký
Signals For Lorentz Violation In Post-Newtonian Gravity, Quentin G. Bailey, V. Alan Kostelecký
Publications
The pure-gravity sector of the minimal standard-model extension is studied in the limit of Riemann spacetime. A method is developed to extract the modified Einstein field equations in the limit of small metric fluctuations about the Minkowski vacuum, while allowing for the dynamics of the 20 independent coefficients for Lorentz violation. The linearized effective equations are solved to obtain the post-Newtonian metric. The corresponding post-Newtonian behavior of a perfect fluid is studied and applied to the gravitating many-body system. Illustrative examples of the methodology are provided using bumblebee models. The implications of the general theoretical results are studied for a …
Debris Disks Around White Dwarfs: The Daz Connection, Mukremin Kilic, Ted Von Hippel, Et Al.
Debris Disks Around White Dwarfs: The Daz Connection, Mukremin Kilic, Ted Von Hippel, Et Al.
Publications
We present near-infrared spectroscopic observations of 20 previously known DAZ white dwarfs obtained at the NASA Infrared Telescope Facility. Two of these white dwarfs (G29-38 and GD 362) are known to display significant K-band excesses due to circumstellar debris disks. Here we report the discovery of excess K-band radiation from another DAZ white dwarf WD0408041 (GD56). Using spectroscopic observations, we show that the excess radiation cannot be explained by a stellar or substellar companion, and is likely to be caused by a warm debris disk. Our observations strengthen the connection between the debris disk phenomena and the observed …
Inverting Color-Magnitude Diagrams To Access Precise Star Cluster Parameters: A Bayesian Approach, Ted Von Hippel, Et Al.
Inverting Color-Magnitude Diagrams To Access Precise Star Cluster Parameters: A Bayesian Approach, Ted Von Hippel, Et Al.
Publications
We demonstrate a new Bayesian technique to invert color-magnitude diagrams of main-sequence and white dwarf stars to reveal the underlying cluster properties of age, distance, metallicity, and line-of-sight absorption, as well as individual stellar masses. The advantages our technique has over traditional analyses of color-magnitude diagrams are objectivity, precision, and explicit dependence on prior knowledge of cluster parameters. Within the confines of a given set of often-used models of stellar evolution, a single mapping of initial to final masses, and white dwarf cooling, and assuming photometric errors that one could reasonably achieve with the Hubble Space Telescope, our technique …
Dust Stratification In Young Circumstellar Disks, Terrence Rettig, Sean D. Brittain, Theodore Simon, Erika Gibb, Dinshaw S. Balsara, David A. Tilley, Craig Kulesa
Dust Stratification In Young Circumstellar Disks, Terrence Rettig, Sean D. Brittain, Theodore Simon, Erika Gibb, Dinshaw S. Balsara, David A. Tilley, Craig Kulesa
Publications
We present high-resolution infrared spectra of four YSOs (T Tau N, T Tau S, RNO 91, and HL Tau). The spectra exhibit narrow absorption lines of 12CO, 13CO, and C18O, as well as broad emission lines of gas-phase 12CO. The narrow absorption lines of CO are shown to originate from the colder circumstellar gas. We find that the line-of-sight gas column densities resulting from the CO absorption lines are much higher than expected for the measured extinction for each source and suggest the gas/dust ratio is measuring the dust settling and/or grain coagulation in these extended disks. We provide a …
Book Review: Evolution Of Stars And Stellar Populations, T. D. Oswalt
Book Review: Evolution Of Stars And Stellar Populations, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of Evolution of Stars and Stellar Populations by Maurizio Salaris and Santi Cassisi Wiley, 2005 374p, 047009219X $150.00, 047009219X $60.00
Probing Cosmic Chemical Evolution With Gamma-Ray Bursts: Grb060206 At Z=4.048, J. P. U. Frynbo, R. L. C. Starling, C. Ledoux, K. Wiersema, C. C. Thöne, J. Sollerman, P. Jakobsson, J. Hjorth, D. Watson, P M. Vreeswijk, P Møller, E Rol, J Gorosabel, J Näränen, R.A.M.J. Wijers, G Björnsson, J M. Castro Cerón, P Curran, Dieter H. Hartmann, S T. Holland, B L. Jensen, A J. Levan, M Limousin, C Kouveliotou, G Nelemans, K Pedersen, R S. Priddey, N R. Tanvir
Probing Cosmic Chemical Evolution With Gamma-Ray Bursts: Grb060206 At Z=4.048, J. P. U. Frynbo, R. L. C. Starling, C. Ledoux, K. Wiersema, C. C. Thöne, J. Sollerman, P. Jakobsson, J. Hjorth, D. Watson, P M. Vreeswijk, P Møller, E Rol, J Gorosabel, J Näränen, R.A.M.J. Wijers, G Björnsson, J M. Castro Cerón, P Curran, Dieter H. Hartmann, S T. Holland, B L. Jensen, A J. Levan, M Limousin, C Kouveliotou, G Nelemans, K Pedersen, R S. Priddey, N R. Tanvir
Publications
Aims. We present early optical spectroscopy of the afterglow of the gamma-ray burst GRB 060206 with the aim of determining the metallicity of the GRB absorber and the physical conditions in the circumburst medium. We also discuss how GRBs may be important complementary probes of cosmic chemical evolution. Methods. Absorption line study of the GRB afterglow spectrum. Results. We determine the redshift of the GRB to be z =4.04795 ±0.00020. Based on the measurement of the neutral hydrogen column density from the damped Lyman-αline and the metal content from weak, unsaturated S ii lines we derive a metallicity of [S/H] …
Lp 400-22, A Very Low Mass And High-Velocity White Dwarf, Adela Kawka, Stephane Vennes, Terry D. Oswalt, J. Allyn Smith, Nicole M. Silvestri
Lp 400-22, A Very Low Mass And High-Velocity White Dwarf, Adela Kawka, Stephane Vennes, Terry D. Oswalt, J. Allyn Smith, Nicole M. Silvestri
Publications
We report the identification of LP 400-22 (WD 2234 + 222) as a very low mass and high-velocity white dwarf. The ultraviolet GALEX and optical photometric colors and a spectral line analysis of LP 400-22 show this star to have an effective temperature of 11,080 ± 140 K and a surface gravity of log g p 6.32 ± 0.08. Therefore, this is a helium-core white dwarf with a mass of 0.17 MꙨ. The tangential velocity of this white dwarf is 414 ± 43 km s-1, making it one of the fastest moving white dwarfs known. We …
The Mystery Deepens: Spitzer Observations Of Cool White Dwarfs, Mukremin Kilic, Ted Von Hippel, Et Al.
The Mystery Deepens: Spitzer Observations Of Cool White Dwarfs, Mukremin Kilic, Ted Von Hippel, Et Al.
Publications
We present 4.5 and 8 µm photometric observations of 18 cool white dwarfs obtained with the Spitzer Space Telescope. Our observations demonstrate that four white dwarfs with Teᶠᶠ < 6000 K show slightly depressed mid-infrared fluxes relative to white dwarf models. In addition, another white dwarf with a peculiar optical and near-infrared spectral energy distribution (LHS 1126) is found to display significant flux deficits in Spitzer observations. These mid-infrared flux deficits are not predicted by the current white dwarf models including collision-induced absorption due to molecular hydrogen. We postulate that either the collision-induced absorption calculations are incomplete or there are other unrecognized physical processes occurring in cool white dwarf atmospheres. The spectral energy distribution of LHS 1126 surprisingly fits a Rayleigh-Jeans spectrum in the infrared, mimicking a hot white dwarf with effective temperature well in excess of 105 K. This implies that the source of this flux deficit is probably not molecular absorption but some other process.
Are Ti44-Producing Supernovae Exceptional?, L.-S. The, Donald D. Clayton, R Diehl, Dieter H. Hartmann, A F. Iyudin, M D. Leising, B S. Meyer, Y Motizuki, V Schönfelder
Are Ti44-Producing Supernovae Exceptional?, L.-S. The, Donald D. Clayton, R Diehl, Dieter H. Hartmann, A F. Iyudin, M D. Leising, B S. Meyer, Y Motizuki, V Schönfelder
Publications
According to standard models supernovae produce radioactive 44Ti, which should be visible in gamma-rays following decay to 44Ca for a few centuries. 44Ti production is believed to be the source of cosmic 44Ca, whose abundance is well established. Yet, gamma-ray telescopes have not seen the expected young remnants of core collapse events. The 44Ti mean life of 89 y and the Galactic supernova rate of 3/100 y imply several detectable 44Ti gamma-ray sources, but only one is clearly seen, the 340-year-old Cas A SNR. Furthermore, supernovae which produce much 44Ti are expected …
Origin Of The Turbulent Spectra In The High-Altitude Cusp: Cluster Spacecraft Observations, K. Nykyri, B. Grison, P. J. Cargill, B. Lavraud, E. Lucek, I. Dandouras, A. Balogh, N. Cornilleau-Wehrlin, H. Reme
Origin Of The Turbulent Spectra In The High-Altitude Cusp: Cluster Spacecraft Observations, K. Nykyri, B. Grison, P. J. Cargill, B. Lavraud, E. Lucek, I. Dandouras, A. Balogh, N. Cornilleau-Wehrlin, H. Reme
Publications
High-resolution magnetic field data from Cluster Flux GateMagnetometer (FGM) and the Spatio-Temporal Analysis of Field Fluctuations (STAFF) instruments are used to study turbulent magnetic field fluctuations during the highaltitude cusp crossing on 17 March 2001. Despite the quiet solar wind conditions, the cusp was filled with magnetic field turbulence whose power correlates with the field-aligned ion plasma flux. The magnetic field wave spectra shows power law behavior with both double and single slopes with break in the spectra usually occurring in the vicinity of the local ion cyclotron frequency. Strong peaks in the wave power close to local ion cyclotron …
Post-Outburst Infrared Spectra Of V1647 Ori, The Illuminating Star Of Mcneil's Nebula, E L. Gibb, T W. Rettig, Sean D. Brittain, D Wasikowski, Theodore Simon, William D. Vacca, Michael C. Cushing, C Kulesa
Post-Outburst Infrared Spectra Of V1647 Ori, The Illuminating Star Of Mcneil's Nebula, E L. Gibb, T W. Rettig, Sean D. Brittain, D Wasikowski, Theodore Simon, William D. Vacca, Michael C. Cushing, C Kulesa
Publications
V1647 Ori is a low mass star in the L1630 star-forming region that underwent an outburst in late 2003/early 2004. We present post-outburst infrared spectra obtained with NIRSPEC (Keck II) and SpeX (IRTF) and compare these to spectra taken during the outburst. The results show that the temperature of the hot CO formed in the inner part of the disk has declined by ~800 K, while the water and CO ice and low-J CO gas features remained unchanged, consistent with previous assertions that the latter, low-temperature features arise in the foreground cloud. The P-Cygni profiles of the Paschen series that …
Growth Of Carbon Grains In Supernova Ejecta, Ethan A-N. Deneault, Donald D. Clayton, Bradley S. Meyer
Growth Of Carbon Grains In Supernova Ejecta, Ethan A-N. Deneault, Donald D. Clayton, Bradley S. Meyer
Publications
We present a chemical reaction network that describes the condensation chemistry of carbon dust grains in an expanding supernova shell. We assume that the region of interest consists solely of gaseous free carbon and oxygen atoms and that the buildup of CO is counteracted by the radioactive decay of 56Co, which breaks up the CO mol-ecule and allows C to condense into solids. Our chemical model takes C to first form linear chains, which, at some critical length, transition into ringed isomers. These isomers are more resistant to oxidation than linear chains. These ringed isomers form the nuclei for the …
The Clock Paradox In A Static Homogeneous Gravitational Field, Preston Jones, Lucas F. Wanex
The Clock Paradox In A Static Homogeneous Gravitational Field, Preston Jones, Lucas F. Wanex
Publications
The gedanken experiment of the clock paradox is solved exactly using the general relativistic equations for a static homogeneous gravitational field. We demonstrate that the general and special relativistic clock paradox solutions are identical and in particular that they are identical for finite acceleration. Practical expressions are obtained for proper time and coordinate time by using the destination distance as the key observable parameter. This solution provides a formal demonstration of the identity between the special and general relativistic clock paradox with finite acceleration and where proper time is assumed to be the same in both formalisms. By solving the …
Radioactive 26al And Massive Stars In The Galaxy, Roland Diehl, Hubert Halloin, Karsten Kretschmer, Giselher G. Lichiti, Volker Schönfelder, Andrew W. Strong, Andreas Von Kienlin, Wei Wang, Pierre Jean, Jürgen Knödlseder, Jean-Pierre Roques, Georg Weidenspointner, Stephane Schanne, Dieter H. Hartmann, Christoph Winkler, Cornelia Wunderer
Radioactive 26al And Massive Stars In The Galaxy, Roland Diehl, Hubert Halloin, Karsten Kretschmer, Giselher G. Lichiti, Volker Schönfelder, Andrew W. Strong, Andreas Von Kienlin, Wei Wang, Pierre Jean, Jürgen Knödlseder, Jean-Pierre Roques, Georg Weidenspointner, Stephane Schanne, Dieter H. Hartmann, Christoph Winkler, Cornelia Wunderer
Publications
Gamma-rays from radioactive 26Al (half life ~7.2 105 yr) provide a 'snapshot' view of ongoing nucleosynthesis in the Galaxy1. The Galaxy is relatively transparent to such gamma-rays, and emission has been found concentrated along the plane of the Galaxy2. This led to the conclusion1 that massive stars throughout the Galaxy dominate the production of 26Al. On the other hand, meteoritic data show locally-produced 26Al, perhaps from spallation reactions in the protosolar disk. Furthermore, prominent gamma-ray emission from the Cygnus region2,3 suggests that a substantial fraction of Galactic 26Al could originate in localized star-forming regions. Here we report high spectral resolution …
Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Jeffrey A. Munn, Hugh C. Harris, James W. Liebert, Ted Von Hippel, Kurtis A. Williams, Travis S. Metcalfe, D. E. Winget, Stephen E. Levine
Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Jeffrey A. Munn, Hugh C. Harris, James W. Liebert, Ted Von Hippel, Kurtis A. Williams, Travis S. Metcalfe, D. E. Winget, Stephen E. Levine
Publications
A reduced proper motion diagram utilizing Sloan Digital Sky Survey (SDSS) photometry and astrometry and USNO-B plate astrometry is used to separate cool white dwarf candidates from metal-weak, high-velocity, mainsequence Population II stars (subdwarfs) in the SDSS Data Release 2 imaging area. Follow-up spectroscopy using the Hobby-Eberly Telescope, the MMT, and the McDonald 2.7 m telescope is used to demonstrate that the white dwarf and subdwarf loci separate cleanly in the reduced proper motion diagram and that the contamination by subdwarfs is small near the cool white dwarf locus. This enables large, statistically complete samples of white dwarfs, particularly the …
The White Dwarf Luminosity Function From Sloan Digital Sky Survey Imaging Data, Hugh C. Harris, Jeffrey A. Munn, Mukremin Kilic, James W. Liebert, Kurtis A. Williams, Ted Von Hippel, Stephen E. Levine, David G. Monet, Daniel J. Eisenstein, S. J. Kleinman, T. S. Metcalfe, Atsuko Nikka, D. E. Winget, J. Brinkmann, Masataka Fukugita, G. R. Knapp, Robert H. Lupton, J. Allyn Smith, Donald P. Schneider
The White Dwarf Luminosity Function From Sloan Digital Sky Survey Imaging Data, Hugh C. Harris, Jeffrey A. Munn, Mukremin Kilic, James W. Liebert, Kurtis A. Williams, Ted Von Hippel, Stephen E. Levine, David G. Monet, Daniel J. Eisenstein, S. J. Kleinman, T. S. Metcalfe, Atsuko Nikka, D. E. Winget, J. Brinkmann, Masataka Fukugita, G. R. Knapp, Robert H. Lupton, J. Allyn Smith, Donald P. Schneider
Publications
A sample of white dwarfs is selected from the Sloan Digital Sky Survey (SDSS) Data Release 3 using their reduced proper motions, based on improved proper motions from combined SDSS and USNO-B data. Numerous SDSS and follow-up spectra (Kilic and coworkers) are used to quantify completeness and contamination of the sample; kinematicsmodels are used to understand and correct for velocity-dependent selection biases.A luminosity function is constructed covering the range 7 < Mbol < 16, and its sensitivity to various assumptions and selection limits is discussed. The white dwarf luminosity function based on 6000 stars is remarkably smooth and rises nearly monotonically to Mbol=15.3. It then drops abruptly, although the small number of low-luminosity stars in the sample and their unknown atmospheric composition prevent quantitative conclusions about this decline. Stars …
Book Review: The Amateur Astronomer's Introduction To The Celestial Sphere, T. D. Oswalt
Book Review: The Amateur Astronomer's Introduction To The Celestial Sphere, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of The Amateur Astronomer's Introduction to the Celestial Sphere by William Millar. Cambridge, 2006 299p, 052167123X $40.00, 9780521671231 $40.00.