Browsing by Subject "supernovae:"

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Analytical Light Curve Models Of Superluminous Supernovae: Chi(2)-Minimization Of Parameter Fits
(2013-08) Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, Jozsef; Horvath, Z. L.; Nagy, A.; Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, Jozsef
We present fits of generalized semi-analytic supernova (SN) light curve (LC) models for a variety of power inputs including Ni-56 and Co-56 radioactive decay, magnetar spin-down, and forward and reverse shock heating due to supernova ejecta-circumstellar matter (CSM) interaction. We apply our models to the observed LCs of the H-rich superluminous supernovae (SLSN-II) SN 2006gy, SN 2006tf, SN 2008am, SN 2008es, CSS100217, the H-poor SLSN-I SN 2005ap, SCP06F6, SN 2007bi, SN 2010gx, and SN 2010kd, as well as to the interacting SN 2008iy and PTF 09uj. Our goal is to determine the dominant mechanism that powers the LCs of these extraordinary events and the physical conditions involved in each case. We also present a comparison of our semi-analytical results with recent results from numerical radiation hydrodynamics calculations in the particular case of SN 2006gy in order to explore the strengths and weaknesses of our models. We find that CS shock heating produced by ejecta-CSM interaction provides a better fit to the LCs of most of the events we examine. We discuss the possibility that collision of supernova ejecta with hydrogen-deficient CSM accounts for some of the hydrogen-deficient SLSNe (SLSN-I) and may be a plausible explanation for the explosion mechanism of SN 2007bi, the pair-instability supernova candidate. We characterize and discuss issues of parameter degeneracy.
CfAIR2: Near-Infrared Light Curves of 94 Type Ia Supernovae
(2015-09) Friedman, Andrew S.; Wood-Vasey, W. M.; Marion, G. H.; Challis, Peter; Mandel, Kaisey S.; Bloom, Joshua S.; Modjaz, Maryam; Narayan, Gautham; Hicken, Malcom; Foley, Ryan J.; Klein, Christopher R.; Starr, Dan L.; Morgan, Adam; Rest, Armin; Blake, Cullen H.; Miller, Adam A.; Falco, Emilio E.; Wyatt, William F.; Mink, Jessica; Skrutskie, Mmichael F.; Kirshner, Rrobert P.; Marion, G. H.
CfAIR2 is a large, homogeneously reduced set of near-infrared (NIR) light curves (LCs) for Type Ia supernovae (SNe Ia) obtained with the 1.3 m Peters Automated InfraRed Imaging TELescope. This data set includes 4637 measurements of 94 SNe Ia and 4 additional SNe Iax observed from 2005 to 2011 at the Fred Lawrence Whipple Observatory on Mount Hopkins, Arizona. CfAIR2 includes JHKs photometric measurements for 88 normal and 6 spectroscopically peculiar SN Ia in the nearby universe, with a median redshift of z similar to 0.021 for the normal SN Ia. CfAIR2 data span the range from -13 days to +127 days from B-band maximum. More than half of the LCs begin before the time of maximum, and the coverage typically contains similar to 13-18 epochs of observation, depending on the filter. We present extensive tests that verify the fidelity of the CfAIR2 data pipeline, including comparison to the excellent data of the Carnegie Supernova Project. CfAIR2 contributes to a firm local anchor for SN cosmology studies in the NIR. Because SN Ia are more nearly standard candles in the NIR and are less vulnerable to the vexing problems of extinction by dust, CfAIR2 will help the SN cosmology community develop more precise and accurate extragalactic distance probes to improve our knowledge of cosmological parameters, including dark energy and its potential time variation.
Dust And The Type II-Plateau Supernova 2004dj
(2011-05) Meikle, W. P. S.; Kotak, R.; Farrah, D.; Mattila, S.; Van Dyk, S. D.; Andersen, A. C.; Fesen, R.; Filippenko, Alexei V.; Foley, Ryan J.; Fransson, C.; Gerardy, C. L.; Hoflich, Peter A.; Lundqvist, P.; Pozzo, M.; Sollerman, Jesper; Wheeler, J. Craig; heeler, J. Craig
We present mid-infrared (MIR) spectroscopy of a Type II-plateau supernova, SN 2004dj, obtained with the Spitzer Space Telescope, spanning 106-1393 days after explosion. MIR photometry plus optical/near-IR observations are also reported. An early-time MIR excess is attributed to emission from non-silicate dust formed within a cool dense shell (CDS). Most of the CDS dust condensed between 50 days and 165 days, reaching a mass of 0.3 x 10(-5) M-circle dot. Throughout the observations, much of the longer wavelength (> 10 mu m) part of the continuum is explained as an IR echo from interstellar dust. The MIR excess strengthened at later times. We show that this was due to thermal emission from warm, non-silicate dust formed in the ejecta. Using optical/near-IR line profiles and the MIR continua, we show that the dust was distributed as a disk whose radius appeared to be shrinking slowly. The disk radius may correspond to a grain destruction zone caused by a reverse shock which also heated the dust. The dust-disk lay nearly face-on, had high opacities in the optical/near-IR regions, but remained optically thin in the MIR over much of the period studied. Assuming a uniform dust density, the ejecta dust mass by 996 days was (0.5 +/- 0.1) x 10(-4) M-circle dot and exceeded 10(-4) M-circle dot by 1393 days. For a dust density rising toward the center the limit is higher. Nevertheless, this study suggests that the amount of freshly synthesized dust in the SN 2004dj ejecta is consistent with that found from previous studies and adds further weight to the claim that such events could not have been major contributors to the cosmic dust budget.
Dust And The Type II-Plateau Supernova 2004et
(2009-10) Kotak, R.; Meikle, W. P. S.; Farrah, D.; Gerardy, C. L.; Foley, Ryan J.; Van Dyk, S. D.; Fransson, C.; Lundqvist, P.; Sollerman, Jesper; Fesen, R.; Filippenko, Alexei V.; Mattila, S.; Silverman, Jeffrey M.; Andersen, A. C.; Hoflich, Peter A.; Pozzo, M.; Wheeler, J. Craig; Wheeler, J. Craig
We present mid-infrared (MIR) observations of the Type II-plateau supernova (SN) 2004et, obtained with the Spitzer Space Telescope between 64 and 1406 days past explosion. Late-time optical spectra are also presented. For the period 300-795 days past explosion, we argue that the spectral energy distribution (SED) of SN 2004et comprises (1) a hot component due to emission from optically thick gas, as well as free-bound radiation; (2) a warm component due to newly formed, radioactively heated dust in the ejecta; and (3) a cold component due to an IR echo from the interstellar-medium dust of the host galaxy, NGC 6946. There may also have been a small contribution to the IR SED due to free-free emission from ionized gas in the ejecta. We reveal the first-ever spectroscopic evidence for silicate dust formed in the ejecta of a supernova. This is supported by our detection of a large, but progressively declining, mass of SiO. However, we conclude that the mass of directly detected ejecta dust grew to no more than a few times 10(-4) M(circle dot). We also provide evidence that the ejecta dust formed in comoving clumps of fixed size. We argue that, after about two years past explosion, the appearance of wide, box-shaped optical line profiles was due to the impact of the ejecta on the progenitor circumstellar medium and that the subsequent formation of a cool, dense shell was responsible for a later rise in the MIR flux. This study demonstrates the rich, multifaceted ways in which a typical core-collapse supernova and its progenitor can produce and/or interact with dust grains. The work presented here adds to the growing number of studies that do not support the contention that SNe are responsible for the large mass of observed dust in high-redshift galaxies.
Emission From Pair-Instability Supernovae With Rotation
(2015-01) Chatzopoulos, Emmanouil; van Rossum, Daniel R.; Wheeler, Craig J.; Whalen, Daniel J.; Smidt, Joseph; Wiggins, Brandon; Wheeler, Craig J.
Pair-instability supernovae (PISNe) have been suggested as candidates for some superluminous supernovae, such as SN 2007bi, and as one of the dominant types of explosion occurring in the early universe from massive, zero-metallicity Population III stars. The progenitors of such events can be rapidly rotating, therefore exhibiting different evolutionary properties due to the effects of rotationally induced mixing and mass-loss. Proper identification of such events requires rigorous radiation hydrodynamics and radiative transfer calculations that capture not only the behavior of the light curve but also the spectral evolution of these events. We present radiation hydrodynamics and radiation transport calculations for 90-300M(circle dot) rotating PISNe covering both the shock breakout and late light curve phases. We also investigate cases of different initial metallicity and rotation rate to determine the impact of these parameters on the detailed spectral characteristics of these events. In agreement with recent results on non-rotating PISNe, we find that for a range of progenitor masses and rotation rates these events have intrinsically red colors in contradiction with observations of superluminous supernovae. The spectroscopic properties of rotating PISNe are similar to those of non-rotating events with stripped hydrogen and helium envelopes. We find that the progenitor metallicity and rotation rate properties are erased after the explosion and cannot be identified in the resulting model spectra. It is the combined effects of pre-supernova mass-loss and the basic properties of the supernova ejecta such as mass, temperature, and velocity that have the most direct impact in the model spectra of PISNe.
Evidence For A Correlation Between The Si II Lambda 4000 Width And Type Ia Supernova Color
(2011-06) Nordin, Jakob; Ostman, Linda; Goobar, Ariel; Balland, C.; Lampeitl, Hubert; Nichol, Robert C.; Sako, Masao; Schneider, Donald P.; Smith, Mathew; Sollerman, Jesper; Wheeler, J. Craig; Wheeler, J. Craig
We study the pseudo-equivalent width of the Si II lambda 4000 feature of Type Ia supernovae (SNe Ia) in the redshift range 0.0024 <= z <= 0.634. We find that this spectral indicator correlates with the light curve color excess (SALT2c) as well as previously defined spectroscopic subclasses (Branch types) and the evolution of the Si II lambda 6150 velocity, i.e., the so-called velocity gradient. Based on our study of 55 objects from different surveys, we find indications that the Si II lambda 4000 spectral indicator could provide important information to improve cosmological distance measurements with SNe Ia.
Evidence For Type Ia Supernova Diversity From Ultraviolet Observations With The Hubble Space Telescope
(2012-04) Wang, Xiaofeng; Wang, Lifan; Filippenko, Alexei V.; Baron, Eddie; Kromer, Markus; Jack, Dennis; Zhang, Tianmeng; Aldering, Greg; Antilogus, Pierre; Arnett, W. David; Baade, Dietrich; Barris, Brian J.; Benetti, Stefano; Bouchet, Patrice; Burrows, Adam S.; Canal, Ramon; Cappellaro, Enrico; Carlberg, Raymond G.; di Carlo, Elisa; Challis, Peter J.; Crotts, Arlin P. S.; Danziger, John I.; Della Valle, Massimo; Fink, Michael; Foley, Ryan J.; Fransson, Claes; Gal-Yam, Avishay; Garnavich, Peter M.; Gerardy, Chris L.; Goldhaber, Gerson; Hamuy, Mario; Hillebrandt, Wolfgang; Hoeflich, Peter; Holland, Stephen T.; Holz, Daniel E.; Hughes, John P.; Jeffery, David J.; Jha, Saurabh W.; Kasen, Dan; Khokhlov, Alexei M.; Kirshner, Robert P.; Knop, Robert A.; Kozma, Cecilia; Krisciunas, Kevin; Lee, Brian C.; Leibundgut, Bruno; Lentz, Eric J.; Leonard, Douglas C.; Lewin, Walter H. G.; Li, Weidong; Livio, Mario; Lundqvist, Peter; Maoz, Dan; Matheson, Thomas; Mazzali, Paolo A.; Meikle, Peter; Miknaitis, Gajus; Milne, Peter A.; Mochnacki, Stefan W.; Nomoto, Ken'ichi; Nugent, Peter E.; Oran, Elaine S.; Panagia, Nino; Perlmutter, Saul; Phillips, Mark M.; Pinto, Philip; Poznanski, Dovi; Pritchet, Christopher J.; Reinecke, Martin; Riess, Adam G.; Ruiz-Lapuente, Pilar; Scalzo, Richard A.; Schlegel, Eric M.; Schmidt, Brian P.; Siegrist, James; Soderberg, Alicia M.; Sollerman, Jesper; Sonneborn, George; Spadafora, Anthony; Spyromilio, Jason; Sramek, Richard A.; Starrfield, Sumner G.; Strolger, Louis G.; Suntzeff, Nicholas B.; Thomas, Rollin C.; Tonry, John L.; Tornambe, Amedeo; Truran, James W.; Turatto, Massimo; Turner, Michael; Van Dyk, Schuyler D.; Weiler, Kurt W.; Wheeler, J. Craig; Wood-Vasey, Michael; Woosley, Stanford E.; Yamaoka, Hitoshi; Wheeler, J. Craig
We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This data set provides unique spectral time series down to 2000 angstrom. Significant diversity is seen in the near-maximum-light spectra (similar to 2000-3500 angstrom) for this small sample. The corresponding photometric data, together with archival data from Swift Ultraviolet/Optical Telescope observations, provide further evidence of increased dispersion in the UV emission with respect to the optical. The peak luminositiesmeasured in the uvw1/F250W filter are found to correlate with the B-band light-curve shape parameter Delta m(15)(B), but with much larger scatter relative to the correlation in the broadband B band (e.g., similar to 0.4 mag versus similar to 0.2 mag for those with 0.8 mag < Delta m(15)(B) < 1.7 mag). SN 2004dt is found as an outlier of this correlation (at > 3 sigma), being brighter than normal SNe Ia such as SN 2005cf by similar to 0.9 mag and similar to 2.0 mag in the uvw1/F250W and uvm2/F220W filters, respectively. We show that different progenitor metallicity or line-expansion velocities alone cannot explain such a large discrepancy. Viewing-angle effects, such as due to an asymmetric explosion, may have a significant influence on the flux emitted in the UV region. Detailed modeling is needed to disentangle and quantify the above effects.
The First Supernovae: Source Density And Observability Of Pair Instability Supernovae
(2012-09) Hummel, J. A.; Pawlik, A. H.; Milosavljevi, M.; Bromm, V.; Hummel, Jacob A.; Pawlik, Andreas H.; Milosavljević, Andreas H.; Bromm, Andreas H.
Theoretical models predict that some of the first stars ended their lives as extremely energetic Pair Instability Supernovae (PISNe). With energies approaching 10(53) erg, these supernovae are expected to be within the detection limits of the upcoming James Webb Space Telescope (JWST) allowing observational constraints to be placed on the properties of the first stars. We estimate the source density of PISNe using a semi-analytic Press-Schecter based approach informed by cosmological simulations, with an upper limit of similar to 0.2 PISNe visible per JWST field of view at any given time. We find that the main obstacle to observing PISNe is their scarcity rather than their faintness. Given this we suggest a mosaic style search strategy for detecting PISNe from the first stars.
Generalized Semi-Analytical Models Of Supernova Light Curves
(2012-02) Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, Jozsef; Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, Jozsef
We present generalized supernova (SN) light curve (LC) models for a variety of power inputs including the previously proposed ideas of radioactive decay of Ni-56 and Co-56 and magnetar spin-down. We extend those solutions to include finite progenitor radius and stationary photospheres as might be the case for SN that are powered by interaction of the ejecta with circumstellar matter (CSM). We provide an expression for the power input that is produced by self-similar forward and reverse shocks that efficiently convert their kinetic energy into radiation. We find that this ejecta-CSM interaction luminosity that we derive is in agreement with results from multi-dimensional radiation hydrodynamics simulations in the case of an optically thin CSM. We develop a semi-analytical model for the case of an optically thick CSM by invoking an approximation for the effects of radiative diffusion similar to that adopted by Arnett for SN II and compare this model to the results of numerical radiation hydrodynamics models. This model can give complex LCs, but for monotonically declining shock input, the LCs have a smooth rise, peak, and decline. In the context of this model, we provide predictions of the shock breakout of the forward shock from the optically thick part of the CSM envelope. We also introduce a hybrid LC model that incorporates ejecta-CSM interaction plus Ni-56 and Co-56 radioactive decay input. We fit this hybrid model to the LC of the super-luminous supernova (SLSN) 2006gy. We find that shock heating produced by ejecta-CSM interaction plus some contribution from radioactive decay provides a better fit to the LC of this event than previously presented models. We also address the relation between SN IIL and SN IIn with ejecta-CSM interaction models. The faster decline of SN IIL can be reproduced by the diffusion of previously deposited shock power if the shock power input to the diffusive component vanishes when the reverse shock sweeps up the whole ejecta and/or the forward shock propagates through the optically thick CSM. A CSM interaction with forward and reverse shock power input can produce the LCs of SN IIn in terms of duration, shape, and decline rate, depending on the properties of the CSM envelope and the progenitor star. This model can also produce LCs that are symmetric in shape around peak luminosity, which is the case for the observed LCs of some recently discovered peculiar transient events. We conclude that the observed LC variety of SN IIn and of some SLSNe is likely to be a byproduct of the large range of conditions relevant to significant ejecta-CSM interaction as a power source.
High-Velocity Line Forming Regions In The Type Ia Supernova 2009ig
(2013-11) Marion, G. H.; Vinko, Jozsef; Wheeler, J. Craig; Foley, Ryan J.; Hsiao, Eric Y.; Brown, Peter J.; Challis, Peter; Filippenko, Alexei V.; Garnavich, Peter; Kirshner, Robert P.; Landsman, Wayne B.; Parrent, Jerod T.; Pritchard, Tyler A.; Roming, Peter W. A.; Silverman, Jeffrey M.; Wang, Xiaofeng; Marion, G. H.; Vinko, Jozsef; Wheeler, J. Craig; Silverman, Jeffrey M.
We report measurements and analysis of high-velocity (HVF) (>20,000 km s(-1)) and photospheric absorption features in a series of spectra of the Type Ia supernova (SN) 2009ig obtained between -14 days and +13 days with respect to the time of maximum B-band luminosity (B-max). We identify lines of Si II, Si III, S II, Ca II, and Fe II that produce both HVF and photospheric-velocity (PVF) absorption features. SN 2009ig is unusual for the large number of lines with detectable HVF in the spectra, but the light-curve parameters correspond to a slightly overluminous but unexceptional SN Ia (M-B = -19.46 mag and Delta m(15)(B) = 0.90 mag). Similarly, the Si II lambda 6355 velocity at the time of B-max is greater than "normal" for an SN Ia, but it is not extreme (upsilon(Si) = 13,400 km s(-1)). The -14 days and -13 days spectra clearly resolve HVF from Si II lambda 6355 as separate absorptions from a detached line forming region. At these very early phases, detached HVF are prevalent in all lines. From -12 days to -6 days, HVF and PVF are detected simultaneously, and the two line forming regions maintain a constant separation of about 8000 km s(-1). After -6 days all absorption features are PVF. The observations of SN 2009ig provide a complete picture of the transition from HVF to PVF. Most SNe Ia show evidence for HVF from multiple lines in spectra obtained before -10 days, and we compare the spectra of SN 2009ig to observations of other SNe. We show that each of the unusual line profiles for Si II lambda 6355 found in early-time spectra of SNe Ia correlate to a specific phase in a common development sequence from HVF to PVF.
Late-Time Circumstellar Interaction In A Spitzer Selected Sample Of Type IIn Supernovae
(2013-07) Fox, Ori D.; Filippenko, Alexei V.; Skrutskie, Michael F.; Silverman, Jeffrey M.; Ganeshalingam, Mohan; Cenko, S. Bradley; Clubb, Kelsey I.; Silverman, Jeffrey M.
Type IIn supernovae (SNe IIn) are a rare (<10%) subclass of core-collapse SNe that exhibit relatively narrow emission lines from a dense, pre-existing circumstellar medium (CSM). In 2009, a warm Spitzer Space Telescope survey observed 30 SNe IIn discovered in 2003-2008 and detected 10 SNe at distances out to 175 Mpc with unreported late-time infrared emission, in some cases more than 5 yr post-discovery. For this single epoch of data, the warm-dust parameters suggest the presence of a radiative heating source consisting of optical and X-ray emission continuously generated by ongoing CSM interaction. Here we present multi-wavelength follow-up observations of this sample of 10 SNe IIn and the well-studied Type IIn SN 2010jl. A recent epoch of Spitzer observations reveals ongoing mid-infrared emission from nine of the SNe in this sample. We also detect three of the SNe in archival Wide-field Infrared Survey Explorer data, in addition to SNe 1987A, 2004dj, and 2008iy. For at least five of the SNe in the sample, optical and/or X-ray emission confirms the presence of radiative emission from ongoing CSM interaction. The two Spitzer nondetections are consistent with the forward shock overrunning and destroying the dust shell, a result that places upper limits on the dust-shell size. The optical and infrared observations confirm the radiative heating model and constrain a number of model parameters, including progenitor mass-loss characteristics. All of the SNe in this sample experienced an outburst on the order of tens to hundreds of years prior to the SN explosion followed by periods of less intense mass loss. Although all evidence points to massive progenitors, the variation in the data highlights the diversity in SN IIn progenitor evolution. While these observations do not identify a particular progenitor system, they demonstrate that future, coordinated, multi-wavelength campaigns can constrain theoretical mass-loss models.
Modeling The Light Curve Of The Transient Scp06F6
(2009-10) Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, Jozsef; Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, Jozsef
We consider simple models based on core collapse or pair-formation supernovae (SNe) to account for the light curve of the transient SCP06F6. A radioactive decay diffusion model provides estimates of the mass of the required radioactive nickel and the ejecta as functions of the unknown redshift. An opacity change such as by dust formation or a recombination front may account for the rapid decline from maximum. Within this class of model, the redshift must be less than z similar to 1 or the nickel mass would exceed the total mass of the ejecta; the radiated energy would exceed the kinetic energy, and kinematic and photometric estimates of the radius would disagree. We particularly investigate two specific redshifts: z = 0.143, for which Gaensicke et al. have proposed that the unidentified broad absorption features in the spectrum of SCP06F6 are C(2) Swan bands, and z = 0.57 based on a crude agreement with the Ca H& K and UV iron-peak absorption features that are characteristic of SNe of various types. For the lower redshift, we obtain a nickel mass of 0.3 M(circle dot) and an ejected envelope mass of similar to 38 M(circle dot), while for the latter case we find 4.8 M(circle dot) and 20 M(circle dot), respectively, for fiducial parameters. The kinetic energy of the ejecta, while dependent on uncertain parameters, is generally large, similar to 10(52) erg, throughout this range of redshift. The ejected masses and kinetic energies are smaller for a more tightly constrained model invoking envelope recombination. We also discuss the possibilities of circumstellar matter (CSM) shell diffusion and shock interaction models. In general, optically thick CSM diffusion models can fit the data with the underlying energy coming from an energetic buried SN. Models in which the CSM is of lower density so that the shock energy is both rapidly thermalized and radiated tend not to be self-consistent. We suggest that a model of SCP06F6 worth further exploration is one in which the redshift is similar to 0.57, the spectral features are Ca and iron-peak elements, and the light curve is powered by the diffusive release of a substantial amount of energy from nickel decay or from an energetic SN buried in the ejecta of an LBV-like event.
Near-Infrared Line Identification In Type Ia Supernovae During The Transitional Phase
(2014-09) Friesen, Brian; Baron, E.; Wisniewski, John P.; Parrent, Jerod T.; Thomas, R. C.; Miller, Timothy R.; Marion, G. H.; Marion, G. H.
We present near-infrared synthetic spectra of a delayed-detonation hydrodynamical model and compare them to observed spectra of four normal Type Ia supernovae ranging from day +56.5 to day +85. This is the epoch during which supernovae are believed to be undergoing the transition from the photospheric phase, where spectra are characterized by line scattering above an optically thick photosphere, to the nebular phase, where spectra consist of optically thin emission from forbidden lines. We find that most spectral features in the near-infrared can be accounted for by permitted lines of Fe II and Co II. In addition, we find that [Ni II] fits the emission feature near 1.98 mu m, suggesting that a substantial mass of Ni-58 exists near the center of the ejecta in these objects, arising from nuclear burning at high density.
On The Source Of The Dust Extinction In Type Ia Supernovae And The Discovery Of Anomalously Strong Na I Absorption
(2013-12) Phillips, Mark M.; Simon, Joshua D.; Morrell, Nidia; Burns, Christopher R.; Cox, Nick L. J.; Foley, Ryan J.; Karakas, Amanda I.; Patat, F.; Sternberg, Assaf; Williams, R. E.; Gal-Yam, Avishay; Hsiao, Eric Y.; Leonard, D. C.; Persson, Sven E.; Stritzinger, Maximilian; Thompson, Ian B.; Campillay, Abdo; Contreras, Carlos; Folatelli, Gaston; Freedman, Wendy L.; Hamuy, Mario; Roth, Miguel; Shields, Gregory A.; Suntzeff, Nicholas B.; Chomiuk, Laura; Ivans, Inese I.; Madore, Barry F.; Penprase, B. E.; Perley, Daniel; Pignata, G.; Preston, G.; Soderberg, Alicia M.; Shields, Gregory A.
High-dispersion observations of the Na I D lambda lambda 5890, 5896 and K I lambda lambda 7665, 7699 interstellar lines, and the diffuse interstellar band at 5780 angstrom in the spectra of 32 Type Ia supernovae are used as an independent means of probing dust extinction. We show that the dust extinction of the objects where the diffuse interstellar band at 5780 angstrom is detected is consistent with the visual extinction derived from the supernova colors. This strongly suggests that the dust producing the extinction is predominantly located in the interstellar medium of the host galaxies and not in circumstellar material associated with the progenitor system. One quarter of the supernovae display anomalously large Na I column densities in comparison to the amount of dust extinction derived from their colors. Remarkably, all of the cases of unusually strong Na I D absorption correspond to "Blueshifted" profiles in the classification scheme of Sternberg et al. This coincidence suggests that outflowing circumstellar gas is responsible for at least some of the cases of anomalously large Na I column densities. Two supernovae with unusually strong Na I D absorption showed essentially normal K I column densities for the dust extinction implied by their colors, but this does not appear to be a universal characteristic. Overall, we find the most accurate predictor of individual supernova extinction to be the equivalent width of the diffuse interstellar band at 5780 angstrom, and provide an empirical relation for its use. Finally, we identify ways of producing significant enhancements of the Na abundance of circumstellar material in both the single-degenerate and double-degenerate scenarios for the progenitor system.
SN 2008am: A Super-Luminous Type IIn Supernova
(2011-03) Chatzopoulos, Emmanouil; Wheeler, J. Craig; Vinko, Jozsef; Quimby, Robert; Robinson, Edward L.; Miller, A. A.; Foley, Ryan J.; Perley, D. A.; Yuan, F.; Akerlof, C.; Bloom, Joshua S.; Chatzopoulos, E.; Wheeler, J. Craig; Robinson, Edward L.
We present observations and interpretation of the Type IIn supernova SN 2008am discovered by the ROTSE Supernova Verification Project (RSVP). SN 2008am peaked at approximately -22.3 mag at a redshift of z = 0.2338, giving it a peak luminosity of similar to 3 x 10(44) erg s(-1) and making it one of the most luminous supernovae ever observed. The total radiated energy is similar or equal to 2 x 10(51) erg. The host galaxy appears to be an SB1 of normal luminosity (M-r' similar to -20) with metallicity Z similar to 0.4Z(circle dot). ROTSE upper limits and detections constrain the rise time to be similar to 34 days in the rest frame, significantly shorter than similar events, SN 2006gy and SN 2006tf. Photometric observations in the ultraviolet, optical, and infrared bands (J, H, K-s) constrain the spectral energy distribution evolution. We obtained six optical spectra of the supernova, five on the early decline from maximum light and a sixth nearly a year later plus a very late time spectrum (similar to 2 yr) of the host galaxy. The spectra show no evidence for broad supernova photospheric features in either absorption or emission at any phase. The spectra of SN 2008am show strong Balmer-line and He I lambda 5876 emission with intermediate widths (similar to 25 angstrom) in the first similar to 40 days after optical maximum. The width formally corresponds to a velocity of similar to 1000 km s(-1). We examine a variety of models for the line wings and conclude that multiple scattering is most likely, implying that our spectra contain no specific information on the bulk flow velocity. We examine a variety of models for the ROTSE light curve subject to the rise time and the nature of the spectra, including radioactive decay, shocks in optically thick and optically thin circumstellar media (CSMs) and a magnetar. The most successful model is one for which the CSM is optically thick and in which diffusion of forward shock-deposited luminosity gives rise to the observed light curve. The model suggests strong mass loss and a greater contribution from the interaction of the forward shock with optically thick CSM than from the reverse shock. Diffusion of the shock-deposited energy from the forward shock is found to be important in accounting for the rising part of the light curve. Although there are differences in detail, SN 2008am appears to be closely related to other super-luminous Type IIn supernovae, SN 2006gy, SN 2006tf, and perhaps SN 2008iy, that may represent the deaths of very massive luminous-blue-variable-type progenitors and for which the luminosity is powered by the interaction of the ejecta with a dense CSM.
Spectroscopic Observations Of Sn 2012fr: A Luminous, Normal Type Ia Supernova With Early High-Velocity Features And A Late Velocity Plateau
(2013-06) Childress, M. J.; Scalzo, R. A.; Sim, S. A.; Tucker, B. E.; Yuan, F.; Schmidt, Brian P.; Cenko, S. Bradley; Silverman, Jeffrey M.; Contreras, C.; Hsiao, Eric Y.; Phillips, M.; Morrell, N.; Jha, Saurabh W.; McCully, C.; Filippenko, Alexei V.; Anderson, J. P.; Benetti, S.; Bufano, F.; de Jaeger, T.; Forster, F.; Gal-Yam, Avishay; Le Guillou, L.; Maguire, K.; Maund, J.; Mazzali, P. A.; Pignata, G.; Smartt, S.; Spyromilio, J.; Sullivan, Mark; Taddia, F.; Valenti, S.; Bayliss, D. D. R.; Bessell, M.; Blanc, Guillermo A.; Carson, D. J.; Clubb, K. I.; de Burgh-Day, C.; Desjardins, T. D.; Fang, J. J.; Fox, O. D.; Gates, E. L.; Ho, I. T.; Keller, S.; Kelly, P. L.; Lidman, C.; Loaring, N. S.; Mould, J. R.; Owers, M.; Ozbilgen, S.; Pei, L.; Pickering, T.; Pracy, M. B.; Rich, J. A.; Schaefer, B. E.; Scott, N.; Stritzinger, Maximillian; Vogt, F. P. A.; Zhou, G.; Silverman, Jeffrey M.
We present 65 optical spectra of the Type Ia SN 2012fr, 33 of which were obtained before maximum light. At early times, SN 2012fr shows clear evidence of a high-velocity feature (HVF) in the Si lambda 6355 line that can be cleanly decoupled from the lower velocity "photospheric" component. This Si lambda 6355 HVF fades by phase - 5; subsequently, the photospheric component exhibits a very narrow velocity width and remains at a nearly constant velocity of similar to 12,000 km s(-1) until at least five weeks after maximum brightness. The Ca II infrared triplet exhibits similar evidence for both a photospheric component at v approximate to 12,000 km s(-1) with narrow line width and long velocity plateau, as well as an HVF beginning at v approximate to 31,000 km s(-1) two weeks before maximum. SN 2012fr resides on the border between the "shallow silicon" and "core-normal" subclasses in the Branch et al. classification scheme, and on the border between normal and high-velocity Type Ia supernovae (SNe Ia) in the Wang et al. system. Though it is a clear member of the "low velocity gradient" group of SNe Ia and exhibits a very slow light-curve decline, it shows key dissimilarities with the overluminous SN 1991T or SN 1999aa subclasses of SNe Ia. SN 2012fr represents a well-observed SN Ia at the luminous end of the normal SN Ia distribution and a key transitional event between nominal spectroscopic subclasses of SNe Ia.
A Unique Star in the Outer Halo of the Milky Way
(2009-05) Lai, David K.; Rockosi, Constance M.; Bolte, Michael; Johnson, Jennifer A.; Beers, Timothy C.; Lee, Young Sun; Prieto, Carlos Allende; Yanny, Brian; Prieto, Carlos Allende
As part of a program to measure abundance ratios in stars beyond 15 kpc from the Galactic center, we have discovered a metal-poor star in the outer halo with a unique chemical signature. We originally identified it in the Sloan Extension for Galactic Understanding and Exploration survey as a distant metal-poor star. We obtained a follow-up spectrum using the Echelle Spectrometer and Imager at the Keck 2 telescope, and measure [Fe/H] = -3.17, [Mg/Fe]= -0.10, and [Ca/Fe] = +1.11. This is one of the largest over-abundances of Ca measured in any star to date; the extremely low value of [Mg/Ca] = -1.21 is entirely unique. To have found such an unusual star in our small sample of 27 targets suggests that there may be previously unobserved classes of stars yet to be found in situ in the Galactic halo.