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Showing papers by "Peter Nugent published in 2007"


Journal ArticleDOI
TL;DR: In this article, the diversity in spectral features of Type Ia supernova (SN Ia) surveys is considered and the authors present a template spectroscopic sequence near maximum light for further improvement on the K-correction estimate.
Abstract: With the advent of large dedicated Type Ia supernova (SN Ia) surveys, K-corrections of SNe Ia and their uncertainties have become especially important in the determination of cosmological parameters. While K-corrections are largely driven by SN Ia broadband colors, it is shown here that the diversity in spectral features of SNe Ia can also be important. For an individual observation, the statistical errors from the inhomogeneity in spectral features range from 0.01 (where the observed and rest-frame filters are aligned) to 0.04 (where the observed and rest-frame filters are misaligned). To minimize the systematic errors caused by an assumed SN Ia spectral energy distribution (SED), we outline a prescription for deriving a mean spectral template time series that incorporates a large and heterogeneous sample of observed spectra. We then remove the effects of broadband colors and measure the remaining uncertainties in the K-corrections associated with the diversity in spectral features. Finally, we present a template spectroscopic sequence near maximum light for further improvement on the K-correction estimate. A library of ~;;600 observed spectra of ~;;100 SNe Ia from heterogeneous sources is used for the analysis.

354 citations


Journal ArticleDOI
TL;DR: In this article, four spectra of the Type Ia supernova SN Ia 2006D were presented, extending from -7 to +13 days with respect to B-band maximum.
Abstract: We present four spectra of the Type Ia supernova SN Ia 2006Dextending from -7 to +13 days with respect to B-band maximum. The spectrainclude the strongest signature of unburned material at photosphericvelocities observed in a SN Ia to date. The earliest spectrum exhibits CII absorption features below 14,000 km/s, including a distinctive C IIlambda 6580 absorption feature. The carbon signatures dissipate as the SNapproaches peak brightness. In addition to discussing implications ofphotospheric-velocity carbon for white dwarf explosion models, we outlinesome factors that may influence the frequency of its detection before andaround peak brightness. Two effects are explored in this regard,including depopulation of the C II optical levels by non-LTE effects, andline-of-sight effects resulting from a clumpy distribution of unburnedmaterial with low volume-filling factor.

66 citations


Journal ArticleDOI
TL;DR: In this article, the strength of the absorption features in Type Ia supernova (SN Ia) spectra was measured and used to make a quantitative comparison between the spectra of SNe Ia at low and high redshifts.
Abstract: We develop a method to measure the strength of the absorption features in Type Ia supernova (SN Ia) spectra and use it to make a quantitative comparison between the spectra of Type Ia supernovae at low and high redshifts. In this case study, we apply the method to 12 high-redshift (0.212 ≤ z ≤ 0.912) SNe Ia observed by the Supernova Cosmology Project . Through measurements of the strengths of these features and of the blueshift of the absorption minimum in Ca ii H&K, we show that the spectra of the high-redshift SNe Ia are quantitatively similar to spectra of nearby SNe Ia (z < 0.15). One supernova in our high redshift sample, SN 2002fd at z=0.279, is found to have spectral characteristics that are associated with peculiar SN 1991T/SN 1999aa-like supernovae.

56 citations


Journal ArticleDOI
TL;DR: In this article, the strength of the absorption features in Type Ia supernova (SN Ia) spectra was measured and used to make a quantitative comparison between the spectra of SNe Ia at low and high redshifts.
Abstract: We develop a method to measure the strength of the absorption features in Type Ia supernova (SN Ia) spectra and use it to make a quantitative comparison between the spectra of Type Ia supernovae at low and high redshifts. In this case study, we apply the method to 12 high-redshift (0.212 < z < 0.912) SNe Ia observed by the Supernova Cosmology Project . Through measurements of the strengths of these features and of the blueshift of the absorption minimum in Ca II H&K, we show that the spectra of the high-redshift SNe Ia are quantitatively similar to spectra of nearby SNe Ia (z < 0.15). One supernova in our high redshift sample, SN 2002fd at z=0.279, is found to have spectral characteristics that are associated with peculiar SN 1991T/SN 1999aa-like supernovae.

53 citations


Journal Article
TL;DR: Quantitative comparison between Type Ia supernova spectra at low and high redshifts: A case study as mentioned in this paper was conducted to compare the supernova spectrum at different levels of redshift.
Abstract: Quantitative Comparison Between Type Ia Supernova Spectra at Low and High Redshifts: A Case Study

43 citations


Journal ArticleDOI
01 Jul 2007
TL;DR: In this article, a new generation of codes is being optimized for the four sub-problems, where and how often the burning is ignited in the convective core of an exploding white dwarf star, and how the subsonic burning makes a spontaneous transition to a detonation.
Abstract: At its heart, a Type Ia supernova is a problem in turbulent nuclear combustion. There are four sub-problems, each of which has eluded solution for decades, but which can be addressed by large scale simulation. First is the ignition – where and how often the burning is ignited in the convective core of an exploding white dwarf star. The outcome is sensitive to the initial conditions near the star's center, which may be chaotic. Second is the propagation of the flame. Until near the end, the flame is an unresolvably narrow sheet moved around by instabilities and the turbulence that its own motion produces, yet how fast it moves determines the strength and brightness of the explosion. Third is whether and how the subsonic burning makes a spontaneous transition to a detonation. Observations favor this outcome, but the physics of the transition is obscure. Fourth, is the radiation transport problem. Why does the supernova look the way it does and can its light curve be relied upon to do precision cosmology? Our Consortium has made genuine progress in each of these areas, as well as in planning, with observers, future observational strategies for SNAP/JDEM and LSST. A new generation of codes is being optimized for the four tasks.

39 citations


Journal ArticleDOI
01 Jul 2007
TL;DR: In this paper, Monte Carlo techniques for addressing multi-group time-dependent radiative transfer in 3D, rapidly expanding atmospheres were discussed, and the SEDONA code was developed to calculate detailed angle dependent light curves, spectra, and polarization.
Abstract: While the disruption of a star in a supernova explosion lasts only seconds, the ejected stellar material, much of it newly radioactive, continues to shine brightly for several months. Multi-physics simulations of supernova are now illuminating the physics of the stellar explosion itself, but further post-processing of models with a radiative transfer code is needed to predict the visible emission and compare directly to astronomical observations. Here we discuss Monte Carlo techniques for addressing multi-group time-dependent radiative transfer in 3-dimensional, rapidly expanding atmospheres. We have developed the SEDONA code, which calculates detailed angle dependent light curves, spectra, and polarization, and have applied it to study the nature and cosmological utility of supernovae. The code is scalable and is typically run on high-performance computers using 1024 processors.

7 citations



Journal ArticleDOI
TL;DR: In this article, the mean rest-frame ultraviolet (UV) spectrum of Type Ia supernovae (SNe Ia) and its dispersion using high signal-to-noise Keck-I/LRIS-B spectroscopy for a sample of 36 events at intermediate redshift (z=0.5) discovered by the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS).
Abstract: We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe Ia) and its dispersion using high signal-to-noise Keck-I/LRIS-B spectroscopy for a sample of 36 events at intermediate redshift (z=0.5) discovered by the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). We introduce a new method for removing host galaxy contamination in our spectra, exploiting the comprehensive photometric coverage of the SNLS SNe and their host galaxies, thereby providing the first quantitative view of the UV spectral properties of a large sample of distant SNe Ia. Although the mean SN Ia spectrum has not evolved significantly over the past 40% of cosmic history, precise evolutionary constraints are limited by the absence of a comparable sample of high quality local spectra. Within the high-redshift sample, we discover significant UV spectral variations and exclude dust extinction as the primary cause by examining trends with the optical SN color. Although progenitor metallicity may drive some of these trends, the variations we see are much larger than predicted in recent models and do not follow expected patterns. An interesting new result is a variation seen in the wavelength of selected UV features with phase. We also demonstrate systematic differences in the SN Ia spectral features with SN light curve width in both the UV and the optical. We show that these intrinsic variations could represent a statistical limitation in the future use of high-redshift SNe Ia for precision cosmology. We conclude that further detailed studies are needed, both locally and at moderate redshift where the rest-frame UV can be studied precisely, in order that future missions can confidently be planned to fully exploit SNe Ia as cosmological probes [ABRIDGED].

1 citations



02 Jul 2007
TL;DR: The Nearby Supernova Factory (SNfactory) as discussed by the authors is an international project to discover and study a large sample of type Ia supernovae in the redshift range 0.03 < z < 0.08.
Abstract: The Nearby Supernova Factory (SNfactory) is an international project to discover and study a large sample of type Ia supernovae in the redshift range 0.03 < z < 0.08. Follow-up spectro-photometric observations are performed using the dedicated Supernovae Integral-Field Spectrograph, mounted since 2004 on 2.2 m UH telescope. The goal is to acquire for each supernova and over its full life-time (more than 10 epochs) high spectro-photometric quality spectra over the extended optical range (320-1000 nm). I will present the current status of the SNfactory project, from search efficiency to first scientific results, with an emphasis on the spectro-photometric calibration issues and achievements.