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ABSTRACT: Synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW are compared with spectra of the Type Ia SN 1994D that were obtained before the time of maximum brightness. Evidence is found for the presence of two-component Fe II and Ca II features, forming in high-velocity (≥20,000 km s-1) and lower velocity (≤16,000 km s-1) matter. Possible interpretations of these spectral splits, and implications for using early-time spectra of Type Ia supernovae to probe the metallicity of the progenitor white dwarf and the nature of the nuclear burning front in the outer layers of the explosion, are discussed.
The Astrophysical Journal 01/2009; 525(2):881. · 6.02 Impact Factor
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ABSTRACT: A systematic survey of ions that could be responsible for features in the optical spectra of supernovae is carried out. Six different compositions that could be encountered in supernovae are considered. For each composition, the LTE optical depth of one of the strongest optical lines of each ion is plotted against temperature. For each ion that can realistically be considered as a candidate for producing identifiable features in supernova spectra, a sample synthetic spectrum is displayed. The optical depth plots and the synthetic spectra can provide guidance for studies of line identifications in the optical spectra of all types of supernovae during their photospheric phases.
The Astrophysical Journal Supplement Series 01/2009; 121(1):233. · 13.46 Impact Factor
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Jennifer Millard,
David Branch,
E. Baron, Kazuhito Hatano,
Adam Fisher,
Alexei V. Filippenko,
R. P. Kirshner,
P. M. Challis,
Claes Fransson,
Nino Panagia,
M. M. Phillips,
George Sonneborn,
N. B. Suntzeff,
R. V. Wagoner,
and J. C. Wheeler
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ABSTRACT: Synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW are compared to observed photospheric-phase spectra of the Type Ic supernova SN 1994I. The observed optical spectra can be well matched by synthetic spectra that are based on the assumption of spherical symmetry. We consider the identification of the infrared absorption feature observed near 10250 Å, which previously has been attributed to He I λ10830 and regarded as strong evidence that SN 1994I ejected some helium. We have difficulty accounting for the infrared absorption with He I alone. It could be a blend of He I and C I lines. Alternatively, we find that it can be fitted by Si I lines without compromising the fit in the optical region. In synthetic spectra that match the observed spectra, from 4 days before to 26 days after the time of maximum brightness, the adopted velocity at the photosphere decreases from 17,500 to 7000 km s-1. Simple estimates of the kinetic energy carried by the ejected mass give values that are near the canonical supernova energy of 1051 ergs. The velocities and kinetic energies that we find for SN 1994I in this way are much lower than those that we find elsewhere for the peculiar Type Ic SNe 1997ef and 1998bw, which therefore appear to have been hyperenergetic.
The Astrophysical Journal 01/2009; 527(2):746. · 6.02 Impact Factor
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ABSTRACT: The Type Ia supernova (SN) 2000cx exhibited multiple peculiarities, including a lopsided B-band light-curve peak that does not conform to current methods for using shapes of light curves to standardize SN Ia luminosities. We use the parameterized SN synthetic-spectrum code SYNOW to study line identifications in the photospheric-phase spectra of SN 2000cx. Previous work established the presence of Ca II infrared triplet features forming above velocity ~20,000 km s-1, much higher than the photospheric velocity of ~10,000 km s-1. We find Ti II features forming at the same high velocity. High-velocity line formation is partly responsible for the photometric peculiarities of SN 2000cx: for example, B-band flux blocking by Ti II absorption features that decreases with time causes the B light curve to rise more rapidly and decline more slowly than it otherwise would. SN 2000cx contains an absorption feature near 4530 Å that may be Hβ, forming at the same high velocity. The lack of conspicuous Hα and Paα signatures does not necessarily invalidate the Hβ identification if the high-velocity line formation is confined to a clump that partly covers the photosphere and the Hα and Paα source functions are elevated relative to that of resonance scattering. The Hβ identification is tentative. If it is correct, the high-velocity matter must have come from a nondegenerate companion star.
The Astrophysical Journal 12/2008; 606(1):413. · 6.02 Impact Factor
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David Branch,
S. Benetti,
Daniel Kasen,
E. Baron,
David J. Jeffery, Kazuhito Hatano,
R. A. Stathakis,
Alexei V. Filippenko,
Thomas Matheson,
A. Pastorello,
G. Altavilla,
E. Cappellaro,
L. Rizzi,
M. Turatto,
Weidong Li,
Douglas C. Leonard,
and Joseph C. Shields
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ABSTRACT: Synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW are compared to photospheric-phase spectra of Type Ib supernovae (SNe Ib). Although the synthetic spectra are based on simplifying approximations, including spherical symmetry, they account well for the observed spectra. Our sample of SNe Ib obeys a tight relation between the velocity at the photosphere, as determined from the Fe II features, and the time relative to that of maximum light. From this we infer that the masses and the kinetic energies of the events in this sample were similar. After maximum light the minimum velocity at which the He I features form usually is higher than the velocity at the photosphere, but the minimum velocity of the ejected helium is at least as low as 7000 km s-1. Spectra of SN 2000H reveal the presence of hydrogen absorption features, and we conclude that hydrogen lines also were present in SNe 1999di and 1954A. Hydrogen appears to be present in SNe Ib in general, although in most events it becomes too weak to identify soon after maximum light. The hydrogen-line optical depths that we use to fit the spectra of SNe 2000H, 1999di, and 1954A are not high, so only a mild reduction in the hydrogen optical depths would be required to make these events look like typical SNe Ib. Similarly, the He I line optical depths are not very high, so a moderate reduction would make SNe Ib look like SNe Ic.
The Astrophysical Journal 12/2008; 566(2):1005. · 6.02 Impact Factor
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ABSTRACT: A comparison of the ratio of the depths of two absorption features in the spectra of Type Ia supernovae (SNe Ia) near the time of maximum brightness with the blueshift of the deep red Si II absorption feature 10 days after maximum shows that the spectroscopic diversity of SNe Ia is multidimensional. There is a substantial range of blueshifts at a given value of the depth ratio. We also find that the spectra of a sample of SNe Ia obtained a week before maximum brightness can be arranged in a "blueshift sequence" that mimics the time evolution of the pre-maximum-light spectra of an individual SN Ia, the well-observed SN 1994D. Within the context of current SN Ia explosion models, we suggest that some of the SNe Ia in our sample were delayed detonations while others were plain deflagrations.
The Astrophysical Journal 12/2008; 543(1):L49. · 6.02 Impact Factor
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ABSTRACT: We present 29 optical spectra of the normal Type Ia SN 1998aq, ranging from 9 days before to 241 days after the time of maximum brightness. This spectrocopic data set, together with photometric data presented elsewhere, makes SN 1998aq one of the best observed Type Ia supernovae at optical wavelengths. We use the parameterized supernova synthetic-spectrum code SYNOW to study line identifications in the early photospheric-phase spectra. The results include evidence for lines of singly ionized carbon, at ejection velocities as low as 11,000 km s-1. Implications for SN Ia explosion models are discussed.
The Astronomical Journal 12/2007; 126(3):1489. · 4.03 Impact Factor
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David Branch,
M. A. Troxel,
David J. Jeffery, Kazuhito Hatano,
Miriam Musco,
Jerod Parrent,
E. Baron,
Leann Chau Dang,
D. Casebeer,
Nicholas Hall,
Wesley Ketchum
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ABSTRACT: A comparative study of spectra of 21 Type Ia supernovae (SNe Ia) obtained about one week before maximum light, and 8 spectra obtained 11 or more days before maximum, is presented. To a large extent the premaximum spectra exhibit the defining characteristics of the four groups defined in Paper II (core-normal, broad-line, cool, and shallow-silicon). Comparisons with SYNOW synthetic spectra show that all strong features and most weak ones can be accounted for in a plausible way. The issues of detached high-velocity features, the possible ubiquity of carbon clumps, the maximum detectable ejecta velocities, and the possibility of blueshifted emission-line peaks are discussed. Comment: Accepted by PASP. 38 pages
06/2007;
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Peter M. Garnavich,
Alceste Z. Bonanos,
Kevin Krisciunas,
Saurabh Jha,
Robert P. Kirshner,
Eric M. Schlegel,
Peter Challis,
Lucas M. Macri, Kazuhito Hatano,
David Branch,
Gregory D. Bothun,
Wendy L. Freedman
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ABSTRACT: We present UBVRIJHK photometry and optical spectroscopy of the so-called 'peculiar' Type Ia supernova 1999by in NGC 2841. The observations began one week before visual maximum light which is well-defined by daily observations. The light curves and spectra are similar to those of the prototypical subluminous event SN 1991bg. We find that maximum light in B occurred on 1999 May 10.3 UT (JD 2,451,308.8 +/- 0.3) with B=13.66 +/- 0.02 mag and a color of B_max-V_max=0.51 +/- 0.03 mag. The late-time color implies minimal dust extinction from the host galaxy. Our photometry, when combined with the recent Cepheid distance to NGC 2841 (Macri et al. 2001), gives a peak absolute magnitude of M_B=-17.15 +/- 0.23 mag, making SN 1999by one of the least luminous Type Ia events ever observed. We estimate a decline rate parameter of dm15(B)=1.90 mag, versus 1.93 for SN 1991bg, where 1.10 is typical for so-called 'normal' events. We compare SN 1999by with other subluminous events and find that the B_max-V_max color correlates strongly with the decline rate and may be a more sensitive indicator of luminosity than the fading rate for these objects. We find a good correlation between luminosity and the depth of the spectral feature at 580 nm, which had been attributed solely to Si II. We show that in cooler photospheres the 580 nm feature is dominated by Ti II, which provides a simple physical explanation for the correlation. Using only subluminous Type Ia supernovae we derive a Hubble parameter of H_0=75 +12 -11 km/s Mpc, consistent with values found from brighter events.
06/2001;
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ABSTRACT: ABSTRACTA parametrized supernova synthetic-spectrum code is used to study line identifications in the photospheric-phase spectra of the peculiar Type Ia SN 1991T, and to extract some constraints on the composition structure of the ejected matter. The inferred composition structure is not like that of any hydrodynamical model for Type Ia supernovae. Evidence that SN 1991T was overluminous for a SN Ia is presented, and it is suggested that this peculiar event was probably a substantially super-Chandrasekhar explosion that resulted from the merger of two white dwarfs.
Monthly Notices of the Royal Astronomical Society 03/1999; 304(1):67 - 74. · 4.90 Impact Factor
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ABSTRACT: We construct a Monte Carlo code like that used by Dawson & Johnson
to study the observability of Galactic supernovae. In this paper we
adopt the Dawson & Johnson model for the distributions of supernova
progenitors and dust in the Galaxy, but vary the supernova luminosity
functions. Motivated by a paper by Schaefer in which the probable
existence of subluminous supernovae is stressed, we consider the
observability of a hypothesized population of ultra-dim supernovae
having M_V=-13 and sigma(M_V)=2. We estimate on the basis of six known
Galactic supernovae within the last 1000 years that the number of
ultra-dim supernovae is comparable to the number of `classical'
(luminous) supernovae, and that allowing for the possibility of
ultra-dim supernovae significantly raises the Galactic supernova rate as
inferred from the historical record. We also consider the observability
of supernovae in this model from the point of view of an external
observer, as a function of inclination angle. We find that this
particular model is not dusty enough to account by means of extinction
for a strong observational selection against the discovery of supernovae
in moderately inclined galaxies, and that it predicts the probability
distribution of extinction for Type Ia supernovae to be strongly peaked
near zero.
Monthly Notices of the Royal Astronomical Society 08/1997; 290:360-366. · 4.90 Impact Factor
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ABSTRACT: We use a Monte Carlo technique, together with a simple model for the
distribution of dust in the Galaxy, to investigate the observability,
spatial distribution and occurrence rate of Galactic classical novae. We
compare our model distributions of nova apparent magnitudes and
positions on the sky to the corresponding distributions for observed
classical novae in an updated version of the Duerbeck nova atlas. We
conclude that most Galactic novae come from the disc population, rather
than from the bulge as is often assumed, and we estimate the nova rate
to be 41+/-20 yr^-1. A suggestion for reducing the uncertainties in the
fraction of novae that is produced by the bulge, and in the nova rate,
is offered.
Monthly Notices of the Royal Astronomical Society 08/1997; 290:113-118. · 4.90 Impact Factor
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ABSTRACT: We use a Monte Carlo technique together with a simple model for the distribution of dust in M31 to investigate the observability and spatial distribution of classical novae in M31. Comment: 18 pages, AAStex, including 6 pages of figures. Submitted ApJ Letters (March 28)
04/1997;
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ABSTRACT: Li et al. presented extensive observational data on the peculiar Type Ia SN 1997br and showed that it resembled the well-known peculiar SN 1991T. We present some results of a direct analysis of the spectra of SN 1997br. We raise the question of whether the Fe III and Ni III features in the early spectra are produced by 54Fe and 58Ni rather than by 56Fe and 56Ni as usually assumed, and discuss the issue of whether SN 1991T-like events are more powerful versions of normal SNe Ia rather than a physically distinct subgroup of events.
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