Comparative Direct Analysis of Type Ia Supernova Spectra. III. Premaximum (original) (raw)

Comparative direct analysis of type Ia supernova spectra. II. Maximum light

Arxiv preprint astro-ph/ …, 2006

A comparative study of near-maximum-light optical spectra of 24 Type Ia supernovae (SNe Ia) is presented. The spectra are quantified in two ways, and assigned to four groups. Seven "core-normal" SNe Ia have very similar spectra, except for strong high-velocity Ca II absorption in SN 2001el. Seven SNe Ia are assigned to a "broad-line" group, the most extreme of which is SN 1984A. Five SNe Ia, including SN 1991bg, are assigned to a "cool" group. Five SNe Ia, including SN 1991T, are assigned to a "shallow-silicon" group. Comparisons with Synow synthetic spectra provide a basis for discussion of line identifications, and an internally consistent quantification of the maximum-light spectroscopic diversity among SNe Ia. The extent to which SN Ia maximum-light spectra appear to have a continuous distribution of properties, rather than consisting of discrete subtypes, is discussed.

Comparative Direct Analysis of Spectra of Type Ia Supernovae. I. SN 1994D

Arxiv preprint astro-ph/ …, 2005

As the first step in a comprehensive, comparative, direct analysis of the spectra of Type Ia supernovae (SNe Ia), we use the parameterized supernova synthetic-spectrum code, Synow, to interpret 26 spectra of the well-observed SN 1994D. Our results are consistent with the traditional view that the composition structure (element abundance fractions versus ejection velocity) is radially stratified. We find that resonance-scattering features due to permitted lines of Ca II, Na I, and Fe II persist to more than 100 days after explosion. The fitting parameters for SN 1994D, together with those to be determined for other SNe Ia, will provide an internally consistent quantification of the spectroscopic diversity among SNe Ia, and shed light on how the various manifestations of observational diversity are related to their physical causes.

Spectroscopy of Type Ia supernovae by the Carnegie Supernova Project

2013

This is the first release of optical spectroscopic data of low-redshift Type Ia supernovae (SNe Ia) by the Carnegie Supernova Project including 604 previously unpublished spectra of 93 SNe Ia. The observations cover a range of phases from 12 days before to over 150 days after the time of B-band maximum light. With the addition of 228 near-maximum spectra from the literature we study the diversity among SNe Ia in a quantitative manner. For that purpose, spectroscopic parameters are employed such as expansion velocities from spectral line blueshifts, and pseudo-equivalent widths (pW ). The values of those parameters at maximum light are obtained for 78 objects, thus providing a characterization of SNe Ia that may help to improve our understanding of the properties of the exploding systems and the thermonuclear flame propagation. Two objects, namely SNe 2005M and 2006is, stand out from the sample by showing peculiar Si II and S II velocities but otherwise standard velocities for the rest of the ions. We further study the correlations between spectroscopic and photometric parameters such as light-curve decline rate and color. In agreement with previous studies, we find that the pW of Si II absorption features are very good indicators of light-curve decline rate. Furthermore, we demonstrate that parameters such as pW 2 (Si II 4130) and pW 6 (Si II 5972) provide precise calibrations of the peak B-band luminosity with dispersions of ≈0.15 mag. In the search for a secondary parameter in the calibration of peak luminosity for SNe Ia, we find a ≈2-3-σ correlation between B-band Hubble residuals and the velocity at maximum light of S II and Si II lines.

THE FIRST MAXIMUM-LIGHT ULTRAVIOLET THROUGH NEAR-INFRARED SPECTRUM OF A TYPE Ia SUPERNOVA

The Astrophysical Journal, 2012

We present the first maximum-light ultraviolet (UV) through near-infrared (NIR) Type Ia supernova (SN Ia) spectrum. This spectrum of SN 2011iv was obtained nearly simultaneously by the Hubble Space Telescope at UV/optical wavelengths and the Magellan Baade telescope at NIR wavelengths. These data provide the opportunity to examine the entire maximum-light SN Ia spectral-energy distribution. Since the UV region of a SN Ia spectrum is extremely sensitive to the composition of the outer layers of the explosion, which are transparent at longer wavelengths, this unprecedented spectrum can provide strong constraints on the composition of the SN ejecta, and similarly the SN explosion and progenitor system. SN 2011iv is spectroscopically normal, but has a relatively fast decline (∆m 15 (B) = 1.69 ± 0.05 mag). We compare SN 2011iv to other SNe Ia with UV spectra near maximum light and examine trends between UV spectral properties, light-curve shape, and ejecta velocity. We tentatively find that SNe with similar light-curve shapes but different ejecta velocities have similar UV spectra, while those with similar ejecta velocities but different light-curve shapes have very different UV spectra. Through a comparison with explosion models, we find that both a solar-metallicity W7 and a zero-metallicity delayed-detonation model provide a reasonable fit to the spectrum of SN 2011iv from the UV to the NIR. Subject headings: supernovae: general -supernovae: individual (SN 2011iv) 1 Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-12592.

Spectroscopy of twelve type Ia supernovae at intermediate redshift

Astronomy and Astrophysics, 2006

We present spectra of twelve Type Ia supernovae obtained in 1999 at the William Herschel Telescope and the Nordic Optical Telescope during a search for Type Ia supernovae (SN Ia) at intermediate redshift. The spectra range from z = 0.178 to z = 0.493, including five high signal-to-noise ratio SN Ia spectra in the still largely unexplored range 0.15 ≤ z ≤ 0.3. Most of the spectra were obtained before or around restframe B-band maximum light. None of them shows the peculiar spectral features found in low-redshift over-or under-luminous SN Ia. Expansion velocities of characteristic spectral absorption features such as SiII at 6355 Å, SII at 5640 Å and CaII at 3945 Å are found consistent with their low-z SN Ia counterparts. Key words. cosmology:observations-supernovae:general 1 current high-statistics programs such as ESSENCE (www.ctio.noao.edu/∼wsen) or SNLS (cfht.hawaii.edu/SNLS) now target number statistics of well measured SN Ia well above the several hundreds in large multi-year projects

Spectra of High-Redshift Type Ia Supernovae and a Comparison with Their Low-Redshift Counterparts

The Astronomical Journal, 2005

We present spectra for 14 high-redshift (0.17 < z < 0.83) supernovae, which were discovered by the Supernova Cosmology Project as part of a campaign to measure cosmological parameters. The spectra are used to determine the redshift and classify the supernova type, essential information if the supernovae are to be used for cosmological studies. Redshifts were derived either from the spectrum of the host galaxy or from the spectrum of the supernova itself. We present evidence that these supernovae are of Type Ia by matching to spectra of nearby supernovae. We find that the dates of the spectra relative to maximum light determined from this fitting process are consistent with the dates determined from the photometric light curves, and moreover the spectral time-sequence for SNe Type Ia at low and high redshift is indistinguishable. We also show that the expansion velocities measured from blueshifted Ca H&K are consistent with those measured for low-redshift Type Ia supernovae. From these first-level quantitative comparisons we find no evidence for evolution in SNIa properties between these low-and high-redshift samples. Thus even though our samples may not be complete, we conclude that there is a population of SNe Ia at high redshift whose spectral properties match those at low redshift.

Direct Analysis of Spectra of Type Ib Supernovae

The Astrophysical Journal, 2002

Synthetic spectra generated with the parameterized supernova syntheticspectrum code SYNOW are compared with observed photospheric-phase optical spectra of the normal Type Ic SN 1994I and the peculiar Type Ic SNe 1997ef and 1998bw. The observed spectra can be matched fairly well with synthetic spectra that are based on spherical symmetry and that include lines of just a few ions that are expected to appear on the basis of LTE calculations. Spectroscopic estimates of the mass and kinetic energy of the line-forming layers of the ejected matter give conventional values for SN 1994I but high kinetic energy (∼ 30 × 10 51 erg) for SN 1997ef and even higher (∼ 60 × 10 51 erg) for SN 1998bw.

Near‐Infrared Spectra of Type Ia Supernovae

The Astrophysical Journal, 2003

We report near-infrared (NIR) spectroscopic observations of 12 '' branch-normal '' Type Ia supernovae (SNe Ia) that cover the wavelength region from 0.8 to 2.5 lm. Our sample more than doubles the number of SNe Ia with published NIR spectra within 3 weeks of maximum light. The epochs of observation range from 13 days before maximum light to 18 days after maximum light. A detailed model for a Type Ia supernovae is used to identify spectral features. The Doppler shifts of lines are measured to obtain the velocity and thus the radial distribution of elements. The NIR is an extremely useful tool to probe the chemical structure in the layers of SNe Ia ejecta. This wavelength region is optimal for examining certain products of the SNe Ia explosion that may be blended or obscured in other spectral regions. We identify spectral features from Mg ii, Ca ii, Si ii, Fe ii, Co ii, Ni ii, and possibly Mn ii. We find no indications for hydrogen, helium, or carbon in the spectra. The spectral features reveal important clues about the physical characteristics of SNe Ia. We use the features to derive upper limits for the amount of unburned matter, to identify the transition regions from explosive carbon to oxygen burning and from partial to complete silicon burning, and to estimate the level of mixing during and after the explosion. Elements synthesized in the outer layers during the explosion appear to remain in distinct layers. That provides strong evidence for the presence of a detonation phase during the explosion as it occurs in delayed detonation or merger models. Mg ii velocities are found to exceed 11,000-15,000 km s À1 , depending on the individual SNe Ia. That result suggests that burning during the explosion reaches the outermost layers of the progenitor and limits the amount of unburned material to less than 10% of the mass of the progenitor. Small residuals of unburned material are predicted by delayed detonation models but are inconsistent with pure deflagration or merger models. Differences in the spectra of the individual SNe Ia demonstrate the variety of these events.

The Spectroscopic Diversity of Type Ia Supernovae

2012

We present 2603 spectra of 462 nearby Type Ia supernovae (SN Ia) obtained during 1993-2008 through the Center for Astrophysics Supernova Program. Most of the spectra were obtained with the FAST spectrograph at the FLWO 1.5m telescope and reduced in a consistent manner, making data set well suited for studies of SN Ia spectroscopic diversity. We study the spectroscopic and photometric properties of SN Ia as a function of spectroscopic class using the classification schemes of Branch et al. and Wang et al. The width-luminosity relation appears to be steeper for SN Ia with broader lines. Based on the evolution of the characteristic Si II 6355 line, we propose improved methods for measuring velocity gradients, revealing a larger range than previously suspected, from ~0 to ~400 km/s/day considering the instantaneous velocity decline rate at maximum light. We find a weaker and less significant correlation between Si II velocity and intrinsic B-V color at maximum light than reported by Fol...