Open Access. Powered by Scholars. Published by Universities.®

Astrophysics and Astronomy Commons™

Open Access. Powered by Scholars. Published by Universities.®

Clemson University

Articles 151 - 179 of 179

Full-Text Articles in Astrophysics and Astronomy

Online Resources For Late Additions To The Solar Nebula, Allen Parker Dec 2006

Online Resources For Late Additions To The Solar Nebula, Allen Parker

All Theses

The presence of an excess of short-lived radionuclides in the early protoplanetary disk has been inferred from studying how the distribution of the abundances, in materials like Ca-Al-rich inclusions, differ from the solar abundance distribution (SAD). The likely source of these radioactivites is a supernova that ejected material into the early solar system. This thesis will discuss the solar abundance distribution and how a supernova may have contributed a 'late addition' of material into the early solar system. In addition, we have constructed online resources for studying these topics. This thesis will outline the Solar Abundance Tool, which allows a …

Go to article

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 Nov 2006

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 …

Go to article

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 Oct 2006

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 …

Go to article

Neutrino Oscillation Effects On Supernova Light Element Synthesis, Takashi Yoshida, Toshitaka Kajino, Hidekazu Yokomakura, Keichi Kimura, Akira Takamura, Dieter H. Hartmann Sep 2006

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 …

Go to article

Dust Stratification In Young Circumstellar Disks, Terrence Rettig, Sean D. Brittain, Theodore Simon, Erika Gibb, Dinshaw S. Balsara, David A. Tilley, Craig Kulesa Jul 2006

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 …

Go to article

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 Jun 2006

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] …

Go to article

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 May 2006

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 …

Go to article

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 Apr 2006

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 …

Go to article

Growth Of Carbon Grains In Supernova Ejecta, Ethan A-N. Deneault, Donald D. Clayton, Bradley S. Meyer Feb 2006

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 …

Go to article

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 Jan 2006

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 …

Go to article

Chemical Composition In The Globular Cluster M71 From Keck Hires Spectra Of Turnoff Stars, Ann Merchant Boesgaard, Jeremy R. King, Ann Marie Cody, Alex Stephens, Constantine P. Deliyannis Aug 2005

Chemical Composition In The Globular Cluster M71 From Keck Hires Spectra Of Turnoff Stars, Ann Merchant Boesgaard, Jeremy R. King, Ann Marie Cody, Alex Stephens, Constantine P. Deliyannis

Publications

We have made observations with the Keck I telescope and HIRES at a resolution of ∼45,000 of five nearly identical stars at the turn-off of the metal-rich globular cluster M 71. Our mean Fe abundance, [Fe/H]=-0.80 +-0.02, is in excellent agreement with previous cluster determinations from both giants and near-turnoff stars. There is no clear evidence for any star-to-star abundance differences or correlations in our sample. Abundance ratios of the Fe-peak elements (Cr, Ni) are similar to Fe. The turn-off stars in M71 have remarkably consistent enhancements of 0.2 - 0.3 dex in [Si/Fe], [Ca/Fe] and [Ti/Fe] -- like the …

Go to article

Beryllium Enhancement As Evidence For Accretion In A Lithium-Rich F Dwarf, Johanna F. Ashwell, R D. Jeffries, Barry Smalley, C P. Deliyannis, Aaron Steinhauer, Jeremy R. King Aug 2005

Beryllium Enhancement As Evidence For Accretion In A Lithium-Rich F Dwarf, Johanna F. Ashwell, R D. Jeffries, Barry Smalley, C P. Deliyannis, Aaron Steinhauer, Jeremy R. King

Publications

The early F dwarf star ``J37'' in the open cluster NGC6633 shows an unusual pattern of photospheric abundances, including an order of magnitude enhancement of lithium and iron-peak elements, but an under-abundance of carbon. As a consequence of its thin convection zone these anomalies have been attributed to either radiative diffusion or the accretion of hydrogen-depleted material. By comparing high resolution VLT/UVES spectra of J37 (and other F stars in NGC 6633) with syntheses of the Be ii doublet region at 3131 Ang, we establish that J37 also has a Be abundance (A(Be)=3.0+/-0.5) that is at least ten times the …

Go to article

Co Line Emission And Absorption From The Hl Tauri Disk-Where Is All The Dust?, Sean D. Brittain, Terrence W. Rettig, Theodore Simon, Craig Kulesa Jun 2005

Co Line Emission And Absorption From The Hl Tauri Disk-Where Is All The Dust?, Sean D. Brittain, Terrence W. Rettig, Theodore Simon, Craig Kulesa

Publications

We present high-resolution infrared spectra of HL Tau, a heavily embedded young star. The spectra exhibit broad emission lines of 12CO gas-phase molecules, as well as narrow absorption lines of 12CO, 13CO, and C18O. The broad emission lines of vibrationally excited 12CO are dominated by the hot (T ~ 1500 K) inner disk. The narrow absorption lines of CO are found to originate from the circumstellar gas at a temperature of ~100 K. The 12CO column density for this cooler material [(7.5 ± 0.2) × 1018 cm-2] indicates a large column of absorbing gas along the line of sight. In …

Go to article

Grb 040403: A Faint X-Ray Rich Gamma-Ray Burst Discovered By Integral, S. Mereghetti, D. Götz, M. I. Andersen, A. Castro-Tirado, F. Frontera, F Frontera, J Gorosabel, Dieter H. Hartmann, J Hjorth, R Hudec, G Pizzichini, N Produit, A Tarana, M Topinka, P Ubertini, A Deugarte Apr 2005

Grb 040403: A Faint X-Ray Rich Gamma-Ray Burst Discovered By Integral, S. Mereghetti, D. Götz, M. I. Andersen, A. Castro-Tirado, F. Frontera, F Frontera, J Gorosabel, Dieter H. Hartmann, J Hjorth, R Hudec, G Pizzichini, N Produit, A Tarana, M Topinka, P Ubertini, A Deugarte

Publications

GRB 040403 is one of the faintest gamma-ray bursts for which a rapid and accurate localization has been obtained. Here we report on the gamma-ray properties of this burst, based on observations with the IBIS instrument aboard INTEGRAL, and the results of searches for its optical afterglow. The steep spectrum (power law photon index =1.9 in the 20–200 keV range) implies that GRB 040403 is most likely an X-ray rich burst. Our optical limit of R >24.2 at 16.5 h after the burst, indicates a rather faint afterglow, similar to those seen in other relatively soft and faint bursts.

Go to article

Integral/Spi Limits On Electron-Positron Annihilation Radiation From The Galactic Plane, B. J. Teegarden, K. Watanabe, P. Jean, J. Knödlseder, V. Lonjou, J. P. Roques, G. K. Skinner, P. Von Ballmoos, G. Weidenspointer, A Bazzano, Y M. Butt, A Decourchelle, A C. Fabian, A Goldwurm, M Gudel, D C. Hannikainen, Dieter H. Hartmann Mar 2005

Integral/Spi Limits On Electron-Positron Annihilation Radiation From The Galactic Plane, B. J. Teegarden, K. Watanabe, P. Jean, J. Knödlseder, V. Lonjou, J. P. Roques, G. K. Skinner, P. Von Ballmoos, G. Weidenspointer, A Bazzano, Y M. Butt, A Decourchelle, A C. Fabian, A Goldwurm, M Gudel, D C. Hannikainen, Dieter H. Hartmann

Publications

The center of our Galaxy is a known strong source of electron-positron 511 keV annihilation radiation. Thus far, however, there have been no reliable detection of annihilation radiation outside of the central radian of our Galaxy. One of the primary objectives of the INTEGRAL (International Gamma-Ray Astrophysics Laboratory mission, resolution, coded-apeture gamma-ray telescope with an unprecedented combination of sensitivity, angular resolution, and energy resolution. We resport results from the first 10 months of observation. During this period a significant fraction of the observing time was spent in or near the Galactic plan. No positive annihilation flux was detected outside of …

Go to article

Discovery Of Co Gas In The Inner Disk Of Tw Hydrae, Terrence W. Rettig, Joe Haywood, Theodore Simon, Sean D. Brittain, Erika Gibb Dec 2004

Discovery Of Co Gas In The Inner Disk Of Tw Hydrae, Terrence W. Rettig, Joe Haywood, Theodore Simon, Sean D. Brittain, Erika Gibb

Publications

We report the detection of rovibrationally excited CO emission from the inner disk of the classical T Tauri star (cTTS) TW Hya. We observe ~6 × 1021 g of CO gas with a rotational temperature of 430 ± 40 K. The linearity of the excitation plot suggests that the CO is optically thin. Atypical for cTTSs, hot CO was not detected, implying that TW Hya has cleared its inner disk region out to a radial distance of ~0.5 AU. We discuss implications for the structure of the disk as it relates to replenishment and planet formation.

Go to article

Discovery Of The Near-Ir Afterglow And Of The Host Of Grb 030528, A. Rau, J. Greiner, S. Klose, M. Salvato, J. M. Castro Cerón, Dieter H. Hartmann, A. Fruchter, A. Levan, N. R. Tanvir, J. Gorosabel Dec 2004

Discovery Of The Near-Ir Afterglow And Of The Host Of Grb 030528, A. Rau, J. Greiner, S. Klose, M. Salvato, J. M. Castro Cerón, Dieter H. Hartmann, A. Fruchter, A. Levan, N. R. Tanvir, J. Gorosabel

Publications

The rapid dissemination of an arcmin-sized HETE-2 localization of the long-duration X-ray flash GRB 030528 led to a ground-based multi-observatory follow-up campaign. We report the discovery of the near-IR afterglow, and also describe the detection of the underlying host galaxy in the optical and near-IR bands. The afterglow is classified as “optically dark” as it was not detected in the optical band. The K-band photometry presented here suggests that the lack of optical detection was simply the result of observational limitations (lack of rapid and deep observations plus high foreground extinction). Simple power law fits to the afterglow in the …

Go to article

Probing A Grb Progenitor At A Redshift Of Z=2: A Comprehensive Observing Campaign Of The Afterglow Of Grb 030226, S. Klose, J. Greiner, A. Rau, A. A. Henden, Dieter H. Hartmann, A. Zeh, C. Reis, N. Masetti, D. Malesani, E. Guenther Nov 2004

Probing A Grb Progenitor At A Redshift Of Z=2: A Comprehensive Observing Campaign Of The Afterglow Of Grb 030226, S. Klose, J. Greiner, A. Rau, A. A. Henden, Dieter H. Hartmann, A. Zeh, C. Reis, N. Masetti, D. Malesani, E. Guenther

Publications

We report results from a comprehensive follow-up observing campaign of the afterglow of GRB 030226, in-cluding VLTspectroscopy, VLT polarimetry, and Chandra X-ray observations. In addition, we present BOOTES-1 wide-field observations at the time of the occurrence of the burst. First observations at ESO started 0.2 days after the event when the gamma ray burst (GRB) afterglow was at a magnitude of R $19 and continued until the afterglow had faded below the detection threshold (R > 26). No underlying host galaxy was found. The optical light curve shows a break around 0.8 days after the burst, which is achromatic within the …

Go to article

The Correlation Of Lithium And Beryllium In F And G Cluster Dwarf Stars, Ann Merchant Boesgaard, Eric Armengaud, Constantine P. Deliyannis, Alex Stephens, Jeremy R. King Oct 2004

The Correlation Of Lithium And Beryllium In F And G Cluster Dwarf Stars, Ann Merchant Boesgaard, Eric Armengaud, Constantine P. Deliyannis, Alex Stephens, Jeremy R. King

Publications

Although Li has been extensively observed in main-sequence field and cluster stars, there are relatively fewer observations of Be. We have obtained Keck HIRES spectra of 36 late F and early G dwarfs in order to study the Li-Be correlation we found previously in the temperature regime of 5900–6650 K. The sample size for this temperature range with detectable and (usually) depleted Li and Be is now 88, including Li and Be abundances in both cluster and field stars. Therefore we can now investigate the influence of other parameters such as age, temperature, and metallicity on the correlation. The Be …

Go to article

Spin Mass Of An Electron Liquid, Zhixin Qian, Giovanni Vignale, D C. Marinescu Sep 2004

Spin Mass Of An Electron Liquid, Zhixin Qian, Giovanni Vignale, D C. Marinescu

Publications

We show that in order to calculate correctly the spin current carried by a quasiparticle in an electron liquid one must use an effective ‘‘spin mass’’ ms that is larger than both the band mass mb, which determines the charge current, and the quasiparticle effective mass m, which determines the heat capacity. We present two independent estimates of the spin mass enhancement, ms=mb, in two- and three-dimensional electron liquids, based on (i) previously calculated values of the Landau parameters and (ii) a recent theory of the dynamical local field factor in the spin channel. Both methods yield a significant spin …

Go to article

The Li Overabundance Of J37: Diffusion Or Accretion?, J F. Ashwell, R D. Jeffries, C P. Deliyannis, A Steinhauer, Jeremy R. King Aug 2004

The Li Overabundance Of J37: Diffusion Or Accretion?, J F. Ashwell, R D. Jeffries, C P. Deliyannis, A Steinhauer, Jeremy R. King

Publications

In September 2002 the discovery of a super Li-rich F-dwarf (J37) in NGC 6633, an iron poor analogue of the better studied Hyades and Praecepe open clusters, was announced. This unique star was thought to be the smoking gun for the action of diffusion, models of which predict a narrow ”Li-peak” at approximately the correct temperature. However, with more detailed studies into J37s abundance pattern this star provides firm evidence for the accretion of planetesimals or other material from the circumstellar environment of new born stars. Thanks to the specific predictions made about the behaviour of Be abundances, (the most …

Go to article

The Near-Infared Survey Of The N49 Region Around The Soft Gamma Repeater Sgr 0526-66, S. Klose, A. A. Henden, U. Geppert, J. Greiner, H. H. Guetter, Dieter H. Hartmann, C. Kouveliotou, C. B. Luginbuhl, B. Stecklum, F. J. Vrba Jul 2004

The Near-Infared Survey Of The N49 Region Around The Soft Gamma Repeater Sgr 0526-66, S. Klose, A. A. Henden, U. Geppert, J. Greiner, H. H. Guetter, Dieter H. Hartmann, C. Kouveliotou, C. B. Luginbuhl, B. Stecklum, F. J. Vrba

Publications

We report the results of a deep near-infrared survey with the Very Large Telescope/Infrared Spectrometer and Array Camera of the environment of the supernova remnant N49 in the Large Magellanic Cloud, which contains the soft gamma repeater SGR 0526-66. Two of the four confirmed SGRs are potentially associated with compact stellar clusters. We thus searched for a similar association of SGR 0526-66 and imaged a young stellar cluster at a projected distance of ∼30 pc from the SGR. This constitutes the third cluster–SGR link and lends support to scenarios in which SGR progenitors originate in young dusty clusters. If confirmed, …

Go to article

The Upper Limit For Ch4 In The Protostellar Disk Toward Hl Tauri, E L. Gibb, T Rettig, Sean D. Brittain, R Haywood, Theodore Simon, C Kulesa Jul 2004

The Upper Limit For Ch4 In The Protostellar Disk Toward Hl Tauri, E L. Gibb, T Rettig, Sean D. Brittain, R Haywood, Theodore Simon, C Kulesa

Publications

We used high-resolution infrared spectra of the heavily embedded T Tauri star HL Tau to search for evidence of absorption due to the R0, R1, and R2 gas-phase CH4 ν3 lines near 3.3 μm. From this, we report a 3 σ upper limit of 1.3 × 1015 cm-2 for the CH4 gas column density toward HL Tau. Our results are compared to those found for CO gas toward this source and to the recent model for chemistry in the inner (10 AU) disks around T Tauri stars by Markwick et al. We find that the upper limit of methane ice+gas …

Go to article

Interstellar H3+ Line Absorption Toward Lkhα 101, Sean D. Brittain, Theodore Simon, Craig Kulesa, Terrence W. Rettig May 2004

Interstellar H3+ Line Absorption Toward Lkhα 101, Sean D. Brittain, Theodore Simon, Craig Kulesa, Terrence W. Rettig

Publications

We present a detection of three lines of the H+3 ion in the near-infrared spectrum of the Herbig Be star LkHalpha 101. H+3 is the principal initiator of gas-phase chemistry in interstellar clouds and can be used to constrain the ionization rate or the path length through interstellar material along the line of sight. Essentially all of the observed H+3 column of (2.2+/-0.3)×1014 cm-2 toward LkHalpha 101 originates in the same dense, dark cloud; less than 1 mag of the ~11 total magnitudes of visual extinction is attributable to diffuse material. Constraints on the density [1×104cm-3

Go to article

Beryllium Abundances In F And G Dwarfs In Praesepe And Other Young Clusters From Keck Hires Observations, Ann Merchant Boesgaard, Eric Armengaud, Jeremy R. King Apr 2004

Beryllium Abundances In F And G Dwarfs In Praesepe And Other Young Clusters From Keck Hires Observations, Ann Merchant Boesgaard, Eric Armengaud, Jeremy R. King

Publications

The study of both Be and Li gives useful clues about stellar internal structure. Of particular interest is the study of these light elements in open clusters, which have a known age and metallicity. In this paper we present a study of Be abundances in 10 F-type stars in Praesepe and a comprehensive discussion about Be abundances in other open clusters: Hyades, Pleiades, Per, Coma, and UMa. We have made observations of the doublet of Be ii around 3130 A˚ in Praesepe stars, using the Keck I telescope and the High Resolution Echelle Spectrometer (HIRES). Beryllium abundances were derived from …

Go to article

Oxygen In Open Cluster Dwarfs: Pleiades And M34, Simon C. Schuler, Jeremy R. King, L M. Hobbs, Marc H. Pinsonneault Feb 2004

Oxygen In Open Cluster Dwarfs: Pleiades And M34, Simon C. Schuler, Jeremy R. King, L M. Hobbs, Marc H. Pinsonneault

Publications

We analyze the high-excitation O I lambda7774 triplet in high-resolution, moderate signal-to-noise ratio spectra of 15 Pleiades and eight M34 open cluster dwarfs over the effective temperature range of 5048-6172 K. Relative O abundances have been derived using model atmospheres interpolated from four different sets of ATLAS9 grids. In contrast to existing non-LTE (NLTE) predictions, a dramatic increase in the O I triplet abundance with decreasing temperature is seen for both clusters, regardless of the atmospheric model. S I abundances of three Pleiades stars derived from the high-excitation lambda6053 feature mimic the O I abundance behavior. O abundances have also …

Go to article

The Host Of Grb 030323 At Z=3.372: A Very High Column Density Dla System With A Low Metallicity, P. M. Vreeswijk, S. L. Ellison, C. Ledoux, R. A. M. J. Wijers, J. P. U. Fymbo, P. Møller, A. Henden, J. Hjorth, G. Masi Jan 2004

The Host Of Grb 030323 At Z=3.372: A Very High Column Density Dla System With A Low Metallicity, P. M. Vreeswijk, S. L. Ellison, C. Ledoux, R. A. M. J. Wijers, J. P. U. Fymbo, P. Møller, A. Henden, J. Hjorth, G. Masi

Publications

We present photometry and spectroscopy of the afterglow of GRB 030323. VLT spectra of the afterglow show damped Lyα(DLA) absorption and low- and high-ionization lines at a redshift z =3.3718 ±0.0005. The inferred neutral hy-drogen column density, log N(H i) =21.90±0.07, is larger than any (GRB- or QSO-) DLA H  column density inferred directly from Lyαin absorption. From the afterglow photometry, we derive a conservative upper limit to the host-galaxy extinction: AV <0.5 mag. The iron abundance is [Fe/H] =−1.47 ±0.11, while the metallicity of the gas as measured from sulphur is [S/H] =−1.26 ±0.20. We derive an upper limit on the H2 molecular fraction of 2N(H2)/(2N(H2) +N(H i)) <∼10−6.In the Lyαtrough, a Lyαemission line is detected, which corresponds to a star-formation rate (not corrected for dust extinction) of roughly 1 Myr−1. All these results are consistent with the host galaxy of GRB 030323 consisting of a low metallicity gas with a low dust content. We detect fine-structure lines of silicon, Si*, which have never been clearly detected in QSO-DLAs; this suggests that these lines are produced in the vicinity of the GRB explosion site. Under the assumption that these fine-structure levels are populated by particle collisions, we estimate the H  volume density to be nH i =102−104 cm−3.HST/ACS imaging 4 months after the burst shows an extended AB(F606W) =28.0 ±0.3 mag object at a distance of 0.14 (1 kpc) from the early afterglow location, which presumably is the host galaxy of GRB 030323.

Go to article

Supernova Reverse Shocks: Sic Growth And Isotopic Composition, Ethan A-N. Deneault, Donald D. Clayton, Alexander Heger Sep 2003

Supernova Reverse Shocks: Sic Growth And Isotopic Composition, Ethan A-N. Deneault, Donald D. Clayton, Alexander Heger

Publications

We present new mechanisms by which the isotopic compositions of X-type grains of presolar SiC are altered by reverse shocks in Type II supernovae. We address three epochs of reverse shocks: pressure wave from the H envelope near t ¼ 106 s, reverse shock from the presupernova wind near 108–109 s, and reverse shock from the interstellar medium near 1010 s. Using one-dimensional hydrodynamics we show that the first creates a dense shell of Si and C atoms near 106 s in which the SiC surely condenses. The second reverse shock causes precondensed grains to move rapidly forward through decelerated …

Go to article

Sic Particles From Asymptotic Giant Branch Stars: Mg Burning And The S-Process, Lawrence E. Brown, Donald D. Clayton Jun 1992

Sic Particles From Asymptotic Giant Branch Stars: Mg Burning And The S-Process, Lawrence E. Brown, Donald D. Clayton

Publications

The question of whether isotopically anomalous SiC particles found in meteorites originate in AGB stars is addressed. It is shown that if the peak helium shell flash temperatures of massive (6-9 solar masses) stars are about 10 percent larger than they are normally assumed to be, alpha particle reactions with the magnesium will become significant. Then the (Mg-29)(alpha, n)Si-29 reaction produces a large excess of Si-29. With a light element nuclear reaction network, the evolution of the silicon isotopic composition during AGB evolution is calculated. It is found that the experimentally determined correlation between excess Si-29 and excess Si-30 in …

Go to article

First Prev