Robert A. Fesen

Dartmouth College, Hanover, New Hampshire, United States

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Publications (291)1037.26 Total impact

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    ABSTRACT: SN 2012dn is a super-Chandrasekhar mass candidate in a purportedly normal spiral (SAcd) galaxy, and poses a challenge for theories of type Ia supernova diversity. Here we utilize the fast and highly parameterized spectrum synthesis tool, SYNAPPS, to estimate relative expansion velocities of species inferred from optical spectra obtained with six facilities. As with previous studies of normal SN Ia, we find that both unburned carbon and intermediate mass elements are spatially coincident within the ejecta near and below 14,000 km s−1. Although the upper limit on SN 2012dn's peak luminosity is comparable to some of the most luminous normal SN Ia, we find a progenitor mass exceeding ∼ 1.6 M⊙ is not strongly favored by leading merger models since these models do not accurately predict spectroscopic observations of SN 2012dn and more normal events. In addition, a comparison of light curves and host-galaxy masses for a sample of literature and Palomar Transient Factory SN Ia reveals a diverse distribution of SN Ia subtypes where carbon-rich material remains unburned in some instances. Such events include SN 1991T, 1997br, and 1999aa where trace signatures of C III at optical wavelengths are presumably detected.
    No preview · Article · Jan 2016 · Monthly Notices of the Royal Astronomical Society
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    Robert A. Fesen · Dan Milisavljevic
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    ABSTRACT: We present Hubble Space Telescope WFC3/IR images of the Cassiopeia A supernova remnant that survey its high-velocity, S-rich debris in the NE jet and SW counterjet regions through [S III] 9069, 9531 and [S II] 10,287 - 10,370 line emissions. We identify nearly 3400 sulfur emitting knots concentrated in ~120 degree wide opposing streams, almost triple the number previously known. The vast majority of these ejecta knots lie at projected distances well out ahead of the remnant's forward blast wave and main shell ejecta, extending to angular distance of 320" to the NE and 260" to the SW from the center of expansion. Such angular distances imply undecelerated ejecta knot transverse velocities of 15,600 and 12,700 km/s respectively, assuming an explosion date ~1670 AD and a distance of 3.4 kpc. Optical spectra of knots near the outermost tip of the NE ejecta stream show strong emission lines of S, Ca, and Ar. We estimate a total mass ~0.1 Msun and a kinetic energy of at least ~1 x10^50 erg for S-rich ejecta in the NE jet and SW counterjet. Although their broadness and kinetic energy argue against the Cas~A SN being a jet-induced explosion, the jets are kinematically and chemically distinct from the rest of the remnant. This may reflect an origin in a jet-like mechanism that accelerated interior material from a Si,S,Ar,Ca-rich region near the progenitor's core up through the mantle and H,He,N and O-rich outer layers with velocities that greatly exceeded that of the rapidly expanding photosphere.
    Preview · Article · Dec 2015 · The Astrophysical Journal
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    ABSTRACT: We present optical observations of supernova SN 2014C, which underwent an unprecedented slow metamorphosis from H-poor type Ib to H-rich type IIn over the course of one year. The observed spectroscopic evolution is consistent with the supernova having exploded in a cavity before encountering a massive shell of the progenitor star's stripped hydrogen envelope. Possible origins for the circumstellar shell include a brief Wolf-Rayet fast wind phase that overtook a slower red supergiant wind, eruptive ejection, or confinement of circumstellar material by external influences of neighboring stars. An extended high velocity Halpha absorption feature seen in near-maximum light spectra implies that the progenitor star was not completely stripped of hydrogen at the time of core collapse. Archival pre-explosion Subaru Telescope Suprime-Cam and Hubble Space Telescope Wide Field Planetary Camera 2 images of the region obtained in 2009 show a coincident source that is most likely a compact massive star cluster in NGC 7331 that hosted the progenitor system. By comparing the emission properties of the source with stellar population models that incorporate interacting binary stars we estimate the age of the host cluster to be 30 - 300 Myr, and favor ages closer to 30 Myr in light of relatively strong Halpha emission. SN 2014C is the best-observed member of a class of core-collapse supernovae that fill the gap between events that interact strongly with dense, nearby environments immediately after explosion and those that never show signs of interaction. Better understanding of the frequency and nature of this intermediate population can contribute valuable information about the poorly understood final stages of stellar evolution.
    No preview · Article · Nov 2015 · The Astrophysical Journal
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    ABSTRACT: Deep H$\alpha$ images of a faint emission complex 4.0 x 5.5 degrees in angular extent and located far off the Galactic plane at l = 70.0 degrees, b=-21.5 degrees reveal numerous thin filaments suggestive of a supernova remnant's shock emission. Low dispersion optical spectra covering the wavelength range 4500 - 7500 A show only Balmer line emissions for one filament while three others show a Balmer dominated spectrum along with weak [N I] 5198, 5200 A, [O I] 6300, 6364 A, [N II] 6583 A, [S II] 6716, 6731 A and in one case [O III] 5007 A line emission. Many of the brighter H$\alpha$ filaments are visible in near UV GALEX images presumably due to C III] 1909 A line emission. ROSAT All Sky Survey images of this region show a faint crescent shaped X-ray emission nebula coincident with the portion of the H$\alpha$ nebulosity closest to the Galactic plane. The presence of long, thin Balmer dominated emission filaments with associated UV emission and coincident X-ray emission suggests this nebula is a high latitude Galactic supernova remnant despite a lack of known associated nonthermal radio emission. Relative line intensities of the optical lines in some filaments differ from commonly observed [S II]/H$\alpha$ > 0.4 radiative shocked filaments and typical Balmer filaments in supernova remnants. We discuss possible causes for the unusual optical SNR spectra.
    Preview · Article · Aug 2015 · The Astrophysical Journal
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    Dan Milisavljevic · Robert A Fesen
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    ABSTRACT: The death of massive stars is believed to involve aspheric explosions initiated by the collapse of an iron core. The specifics of these catastrophic explosions remain uncertain, due partly to limited observational constraints on asymmetries deep inside the star. Here we present near-infrared observations of the young supernova remnant Cassiopeia A, descendant of a type IIb core-collapse explosion, and a three-dimensional map of its interior unshocked ejecta. The remnant's interior has a bubble-like morphology that smoothly connects to and helps explain the multiringed structures seen in the remnant's bright reverse-shocked main shell of expanding debris. This internal structure may originate from turbulent mixing processes that encouraged outwardly expanding plumes of radioactive (56)Ni-rich ejecta. If this is true, substantial amounts of its decay product, (56)Fe, may still reside in these interior cavities. Copyright © 2015, American Association for the Advancement of Science.
    Preview · Article · Jan 2015 · Science
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    ABSTRACT: We present Hubble Space Telescope (HST) ultraviolet Fe I and Fe II images of the remnant of Supernova 1885 (S And) which is observed in absorption against the bulge of the Andromeda galaxy, M31. We compare these Fe I and Fe II absorption line images to previous HST absorption images of S And, of which the highest quality and theoretically cleanest is Ca II H & K. Because the remnant is still in free expansion, these images provide a 2D look at the distribution of iron synthesized in this probable Type Ia explosion, thus providing insights and constraints for theoretical SN Ia models. The Fe I images show extended absorption offset to the east from the remnant's center as defined by Ca II images and is likely an ionization effect due to self-shielding. More significant is the remnant's apparent Fe II distribution which consists of four streams or plumes of Fe-rich material seen in absorption that extend from remnant center out to about 10,000 km/s. This is in contrast to the remnant's Ca II absorption, which is concentrated in a clumpy, roughly spherical shell at 3000 to 5000 km/s but which extends out to 12,500 km/s. The observed distributions of Ca and Fe rich ejecta in the SN 1885 remnant are consistent with delayed detonation white dwarf models. The largely spherical symmetry of the Ca-rich layer argues against a highly anisotropic explosion as might result from a violent merger of two white dwarfs.
    Preview · Article · Dec 2014 · The Astrophysical Journal
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    Christine S. Black · Robert A. Fesen
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    ABSTRACT: We present moderate resolution [O iii] λλ4959, 5007 line emission spectra of the Crab nebula's northern ejecta jet. These data along with an [O iii] image of the Crab nebula were used to build three-dimensional kinematic maps of the jet and adjacent remnant nebulosity to better understand the jet's properties and thus its likely origin. We find the jet's systemic velocity to be +170 ± 15 km s−1 with radial velocities ranging from −190 to +480 km s−1. Our data indicate that the jet consists of thin filamentary walls (Vexp ≃ 40–75 km s−1), is virtually hollow in [O iii] emission, and elliptical and funnel-like in shape rather than a straight cylindrical tube as previously thought. Examination of the Crab's 3D filamentary structure along the jet's base reveals a large and nearly emission-free opening in the remnant's thick outer ejecta shell. The jet's blueshifted and redshifted sides are surprisingly well defined and, like the jet's sharp western limb, appear radially aligned with the remnant's centre of expansion. These alignments, along with the opening in the nebula at the jet's base and proper motions indicating an expansion age in line with the 1054 supernova event, suggest a direct connection between the jet's formation and the Crab's radial expansion. While our analysis supports the scenario that the jet may simply represent the highest velocity material of the remnant's N–S bipolar expansion, the nature of this expansion asymmetry remains unclear.
    Preview · Article · Dec 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We present an observational study using high-resolution echelle spectroscopy of collisionless shocks in the Cygnus Loop supernova remnant. Measured H alpha line profiles constrain pre-shock heating processes resulting in narrow component broadening, cosmic-ray acceleration, and electron-proton equilibration. The shocks produce faint H alpha emission line profiles, which are characterized by narrow and broad components. The narrow component is representative of the pre-shock conditions, while the broad component is produced after charge transfer between neutrals entering the shock and protons in the post-shock gas, thus reflecting the properties of the post-shock gas. We observe a diffuse H alpha region extending about 2.5 arcmin ahead of the shock with line width about 29 km/s, while the H alpha profile of the shock itself consists of a broader than expected narrow (36 km/s) and a broad (250 km/s) component. The observed diffuse emission arises in a photoionization precursor heated to about 18,000 K by He I and He II emission from the shock, with additional narrow component broadening originating from a thin cosmic-ray precursor. Broad to narrow component intensity ratios of about 1.0 imply full electron-proton temperature equilibration (equal ion and electron temperatures) in the post-shock region. Broad component line widths indicate shock velocities of about 400 km/s. Combining the shock velocities with proper motions suggests the distance to the Cygnus Loop is about 890 pc, significantly greater than the generally accepted upper limit of 637 pc. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 1262851 and by the Smithsonian Institution. This work was partially supported by the grant HST-60-12885 to the Smithsonian Institution.
    No preview · Article · Aug 2014 · The Astrophysical Journal
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    ABSTRACT: We present ultraviolet, optical, and near-infrared observations of SN 2012ap, a broad-lined Type Ic supernova in the galaxy NGC 1729 that produced a relativistic and rapidly decelerating outflow without a gamma-ray burst signature. Photometry and spectroscopy follow the flux evolution from -13 to +272 days past the B-band maximum of -17.4 +/- 0.5 mag. The spectra are dominated by Fe II, O I, and Ca II absorption lines at ejecta velocities of 20,000 km/s that change slowly over time. Other spectral absorption lines are consistent with contributions from photospheric He I, and hydrogen may also be present at higher velocities (> 27,000 km/s). We use these observations to estimate explosion properties and derive a total ejecta mass of 2.7 Msolar, a kinetic energy of 1.0x10^{52} erg, and a 56Ni mass of 0.1-0.2 Msolar. Nebular spectra (t > 200d) exhibit an asymmetric double-peaked [OI] 6300,6364 emission profile that we associate with absorption in the supernova interior, although toroidal ejecta geometry is an alternative explanation. SN 2012ap joins SN 2009bb as another exceptional supernova that shows evidence for a central engine (e.g., black-hole accretion or magnetar) capable of launching a non-negligible portion of ejecta to relativistic velocities without a coincident gamma-ray burst detection. Defining attributes of their progenitor systems may be related to notable properties including above-average environmental metallicities of Z > Zsolar, moderate to high levels of host-galaxy extinction (E(B-V) > 0.4 mag), detection of high-velocity helium at early epochs, and a high relative flux ratio of [Ca II]/[O I] > 1 at nebular epochs. These events support the notion that jet activity at various energy scales may be present in a wide range of supernovae.
    Full-text · Article · Aug 2014 · The Astrophysical Journal
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    Daniel J. Patnaude · Robert A. Fesen
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    ABSTRACT: Broadband optical and narrowband Si XIII X-ray images of the young Galactic supernova remnant Cas A obtained over several decades are used to investigate spatial and temporal correlations on both large and small scales. The data consist of optical and near infrared ground-based and Hubble Space Telescope images taken between 1951 and 2011, and X-ray images from Einstein, ROSAT, and Chandra taken between 1979 and 2013. We find weak spatial correlations between the remnant's emission features on large scales, but several cases of good optical/X-ray correlations on small scales for features which have brightened due to recent interaction with the reverse shock. We also find instances where: (i) a time delay is observed between the appearance of a feature's optical and X-ray emissions, (ii) displacements of several arcseconds between a feature's X-ray and optical emission peaks and, (iii) regions showing no corresponding X-ray or optical emissions. To explain this behavior, we propose a inhomogeneous model for Cas A's ejecta consisting of small, dense optically emitting knots (n ~ 10^(2-3)/cm^(3)) and a much lower density (n ~ 0.1 - 1/cm^(3)) diffuse X-ray emitting component often spatially associated with optical emission knots. The X-ray emitting component is sometimes linked to optical clumps through shock induced mass ablation generating trailing material leading to spatially offset X-ray/optical emissions. A range of ejecta densities can also explain the observed X-ray/optical time delays since the remnant's 5000 km/s reverse shock heats dense ejecta clumps to temperatures around 3x10^4 K relatively quickly which then become optically bright while more diffuse ejecta become X-ray bright on longer timescales. Highly inhomogeneous ejecta as proposed here for Cas A may help explain some of the X-ray/opticalfeatures seen in other young core collapse SN remnants.
    Preview · Article · Mar 2014 · The Astrophysical Journal
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    ABSTRACT: The diffuse interstellar bands (DIBs) are absorption features observed in optical and near-infrared spectra that are thought to be associated with carbon-rich polyatomic molecules in interstellar gas. However, because the central wavelengths of these bands do not correspond with electronic transitions of any known atomic or molecular species, their nature has remained uncertain since their discovery almost a century ago. Here we report on unusually strong DIBs in optical spectra of the broad-lined Type Ic supernova SN 2012ap that exhibit changes in equivalent width over short (~30 days) timescales. The 4428 and 6283 Angstrom DIB features get weaker with time, whereas the 5780 Angstrom feature shows a marginal increase. These nonuniform changes suggest that the supernova is interacting with a nearby source of the DIBs and that the DIB carriers possess high ionization potentials, such as small cations or charged fullerenes. We conclude that moderate-resolution spectra of supernovae with DIB absorptions obtained within weeks of outburst could reveal unique information about the mass-loss environment of their progenitor systems and provide new constraints on the properties of DIB carriers.
    Full-text · Article · Jan 2014 · The Astrophysical Journal Letters
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    ABSTRACT: Observations spanning a large wavelength range, from X-ray to radio, of the Type IIb supernova (SN) 2011hs are presented, covering its evolution during the first year after explosion. The optical light curve presents a narrower shape and a fainter luminosity at peak than previously observed for Type IIb SNe. High expansion velocities are measured from the broad absorption H i and He i lines. From the comparison of the bolometric light curve and the time evolution of the photospheric velocities with hydrodynamical models, we found that SN 2011hs is consistent with the explosion of a 3–4 M⊙ He-core progenitor star, corresponding to a main-sequence mass of 12–15 M⊙, that ejected a mass of 56Ni of about 0.04 M⊙, with an energy of E = 8.5 × 1050 ERG. Such a low-mass progenitor scenario is in full agreement with the modelling of the nebular spectrum taken at ∼215 d from maximum. From the modelling of the adiabatic cooling phase, we infer a progenitor radius of ≈500–600 R⊙, clearly pointing to an extended progenitor star. The radio light curve of SN 2011hs yields a peak luminosity similar to that of SN 1993J, but with a higher mass-loss rate and a wind density possibly more similar to that of SN 2001ig. Although no significant deviations from a smooth decline have been found in the radio light curves, we cannot rule out the presence of a binary companion star.
    Full-text · Article · Jan 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: Two H-poor supernovae - SN 2012im and 2013ek - both originating from massive stripped-envelope progenitor stars have been found at virtually the same location (< 0.4 arcsec). Chance alignment of two completely independent supernovae of the same Type Ib/c class exploding within one year of each other from the same stellar cluster is statistically improbable. Thus, the two explosions may be physically related, and this has important ramifications in areas of high-mass binary star evolution and explosion mechanisms of core-collapse supernovae. Here we present optical photometry and spectra of SN 2013ek beginning shortly after outburst, as well as Hubble Space Telescope images that pin down the supernova's precise location and probe the stellar environment of the progenitor system.
    No preview · Article · Jan 2014
  • Dan Milisavljevic · Robert A. Fesen
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    ABSTRACT: Three-dimensional kinematic reconstructions of optically emitting ejecta in the young Galactic supernova remnant Cassiopeia A (Cas A) are discussed. The reconstructions encompass the remnant's faint outlying ejecta knots, including the exceptionally high-velocity NE and SW streams of debris often referred to as `jets'. The bulk of Cas A's ejecta are arranged in several circular rings with diameters between approximately 30'' (0.5 pc) and 2' (2 pc). We suggest that similar large-scale ejecta rings may be a common phenomenon of young core-collapse remnants and may explain lumpy emission line profile substructure sometimes observed in spectra of extragalactic core-collapse supernovae years after explosion. A likely origin for these large ejecta rings is post-explosion input of energy from plumes of radioactive 56Ni-rich ejecta that rise, expand, and compress non-radioactive material to form bubble-like structures.
    No preview · Article · Dec 2013 · Proceedings of the International Astronomical Union
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    Dan Milisavljevic · Robert A. Fesen
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    ABSTRACT: We present three-dimensional kinematic reconstructions of optically emitting material in the young Galactic supernova remnant Cassiopeia A (Cas A). These Doppler maps have the highest spectral and spatial resolutions of any previous survey of Cas A and represent the most complete catalog of its optically emitting material to date. We confirm that the bulk of Cas A's optically bright ejecta populate a torus-like geometry tilted approximately 30 degrees with respect to the plane of the sky with a -4000 to +6000 km/s radial velocity asymmetry. Near-tangent viewing angle effects and an inhomogeneous surrounding CSM/ISM environment suggest that this geometry and velocity asymmetry may not be faithfully representative of the remnant's true 3D structure or the kinematic properties of the original explosion. The majority of the optical ejecta are arranged in several well-defined and nearly circular ring-like structures with diameters between approximately 30 arcsec (0.5 pc) and 2 arcmin (2 pc). These ejecta rings appear to be a common phenomenon of young core-collapse remnants and may be associated with post-explosion input of energy from plumes of radioactive 56Ni-rich ejecta that rise, expand, and compress non-radioactive material. Our optical survey also encompassed Cas A's faint outlying ejecta knots and exceptionally high-velocity NE and SW streams of S-rich debris often referred to as `jets'. These outer knots, which exhibit a chemical make-up suggestive of an origin deep within the progenitor star, appear to be arranged in opposing and wide-angle outflows with opening half-angles of approximately 40 degrees.
    Preview · Article · Jun 2013 · The Astrophysical Journal
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    ABSTRACT: The double explosion of SN?2009ip in 2012 raises questions about our understanding of the late stages of massive star evolution. Here we present a comprehensive study of SN?2009ip during its remarkable rebrightenings. High-cadence photometric and spectroscopic observations from the?GeV to the radio band obtained from a variety of ground-based and space facilities (including the Very Large Array, Swift, Fermi, Hubble Space Telescope, and XMM) constrain SN?2009ip to be a low energy (E ~ 1050?erg for an ejecta mass ~0.5 M ?) and asymmetric explosion in a complex medium shaped by multiple eruptions of the restless progenitor star. Most of the energy is radiated as a result of the shock breaking out through a dense shell of material located at ~5 × 1014 cm with M ~ 0.1 M ?, ejected by the precursor outburst ~40?days before the major explosion. We interpret the NIR excess of emission as signature of material located further out, the origin of which has to be connected with documented mass-loss episodes in the previous years. Our modeling predicts bright neutrino emission associated with the shock break-out if the cosmic-ray energy is comparable to the radiated energy. We connect this phenomenology with the explosive ejection of the outer layers of the massive progenitor star, which later interacted with material deposited in the surroundings by previous eruptions. Future observations will reveal if the massive luminous progenitor star survived. Irrespective of whether the explosion was terminal, SN?2009ip brought to light the existence of new channels for sustained episodic mass loss, the physical origin of which has yet to be identified.
    Full-text · Article · May 2013 · The Astrophysical Journal
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    ABSTRACT: CBET 3506 available at Central Bureau for Astronomical Telegrams.
    No preview · Article · May 2013
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    ABSTRACT: We present optical and near-infrared observations of SN 2012au, a slow-evolving supernova (SN) with properties that suggest a link between subsets of energetic and H-poor SNe and superluminous SNe. SN 2012au exhibited conspicuous Type-Ib-like He I lines and other absorption features at velocities reaching ≈2 × 104 km s–1 in its early spectra, and a broad light curve that peaked at MB = –18.1 mag. Models of these data indicate a large explosion kinetic energy of ~1052 erg and 56Ni mass ejection of M Ni ≈ 0.3 M ☉ on par with SN 1998bw. SN 2012au's spectra almost one year after explosion show a blend of persistent Fe II P-Cyg absorptions and nebular emissions originating from two distinct velocity regions. These late-time emissions include strong [Fe II], [Ca II], [O I], Mg I], and Na I lines at velocities 4500 km s–1, as well as O I and Mg I lines at noticeably smaller velocities 2000 km s–1. Many of the late-time properties of SN 2012au are similar to the slow-evolving hypernovae SN 1997dq and SN 1997ef, and the superluminous SN 2007bi. Our observations suggest that a single explosion mechanism may unify all of these events that span –21 MB –17 mag. The aspherical and possibly jetted explosion was most likely initiated by the core collapse of a massive progenitor star and created substantial high-density, low-velocity Ni-rich material.
    Full-text · Article · Mar 2013 · The Astrophysical Journal Letters
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    ABSTRACT: Low-dispersion spectra (range 350-880 nm), obtained on March 10.9 UT with the 10-m SALT telescope (+ RSS), show PSN J08070669-2803101 to be a young type-II supernova not long after outburst. Fitting with the SYN++ software (Thomas et al. 2011, PASP, 123, 237) suggests that the broad P-Cyg features seen on a fairly blue continuum are associated with H_alpha, Na I, Ca II, and He I. Using a redshift of z = 0.0037 measured from narrow emission lines associated with a coincident H II region in the host galaxy ESO 430-020, we estimate the velocity of the H_alpha absorption feature to be approximately -18500 km/s.
    No preview · Article · Mar 2013
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    ABSTRACT: CBET 3437 available at Central Bureau for Astronomical Telegrams.
    No preview · Article · Mar 2013

Publication Stats

5k Citations
1,037.26 Total Impact Points


  • 1990-2015
    • Dartmouth College
      • • Department of Physics & Astronomy
      • • Division of Astrophysics
      Hanover, New Hampshire, United States
  • 2008
    • Arizona State University
      • Department of Physics
      Tempe, Arizona, United States
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 1993
    • Brigham Young University - Provo Main Campus
      Provo, Utah, United States
  • 1992
    • Universidad Casa Blanca
      Puebla, Mexico
  • 1985-1992
    • University of Colorado at Boulder
      • Center for Astrophysics and Space Astronomy
      Boulder, Colorado, United States
  • 1986-1989
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, MD, United States
  • 1988
    • University of California, Davis
      • Department of Physics
      Davis, California, United States
  • 1981-1986
    • NASA
      • Goddard Space Flight Centre
      Вашингтон, West Virginia, United States
  • 1982
    • University of Michigan
      Ann Arbor, Michigan, United States
  • 1978-1980
    • Concordia University–Ann Arbor
      Ann Arbor, Michigan, United States
  • 1979
    • Middlebury College
      • Department of Physics
      Middlebury, Indiana, United States