We present a complete sample of International Ultraviolet Explorer and Hubble Space Telescope ultraviolet (UV) spectra of Type Ia supernovae (SNe Ia) through 2004. We measure the equivalent width (EW) and blueshifted velocity of the minimum of the one strong UV feature, Fe II 3250. We also quantify the slope of the near-UV spectra using a new parameter, the ``UV ratio.'' We find that the velocity of the Fe II line does not correlate with light-curve shape, while the EW shows distinct behavior for the slow and fast-declining objects. Using precise Cepheid and surface brightness fluctuation distance measurements of 6 objects with UV spectra observed near maximum light (a total of 12 spectra), we determine that the UV ratio at maximum light is highly correlated with SN Ia luminosity. A larger sample of UV spectra is necessary to increase the statistical certainty of these luminosity indicators and whether they can be combined with light-curve shape to improve measured SN Ia distances.
The motivations to make ultraviolet (UV) studies of supernovae (SNe) are reviewed and discussed in the light of the results obtained so far by means of IUE and HST observations. It appears that UV studies of SNe can, and do lead to fundamental results not only for our understanding of the SN phenomenon, such as the kinematics and the metallicity of the ejecta, but also for exciting new findings in Cosmology, such as the tantalizing evidence for "dark energy" that seems to pervade the Universe and to dominate its energetics. The need for additional and more detailed UV observations is also cons…
The spectral properties of type Ia supernovae in the ultraviolet (UV) are investigated using the early-time spectra of SN 2001ep and SN 2001eh obtained using the Hubble Space Telescope (HST). A series of spectral models is computed with a Monte Carlo spectral synthesis code, and the dependence of the UV flux on the elemental abundances and the density gradient in the outer layers of the ejecta is tested. A large fraction of the UV flux is formed by reverse fluorescence scattering of photons from red to blue wavelengths. This process, combined with ionization shifts due to enhanced line blockin…
We present an empirical model of Type Ia supernovae spectro-photometric evolution with time. The model is built using a large data set including light-curves and spectra of both nearby and distant supernovae, the latter being observed by the SNLS collaboration. We derive the average spectral sequence of Type Ia supernovae and their main variability components including a color variation law. The model allows us to measure distance moduli in the spectral range 2500-8000 A with calculable uncertainties, including those arising from variability of spectral features. Thanks to the use of high-reds…
We present ultravioliet (UV) observations of supernovae (SNe) obtained with the UltraViolet/Optical Telescope (UVOT) on board the Swift spacecraft. This is the largest sample of UV light curves from any single instrument and covers all major SN types and most subtypes. The UV light curves of SNe Ia are fairly homogenous while SNe Ib/c and IIP show more variety in their light curve shapes. The UV-optical colors clearly differentiate SNe Ia and IIP, particularly at early times. The color evolution of SNe IIP, however, makes their colors similar to SNe Ia at about 20 days after explosion. SNe Ib/…
Long-term monitoring of the radio emission from supernovae with the Very Large Array (VLA) shows that the radio ``light curves'' evolve in a systematic fashion with a distinct peak flux density (and thus, in combination with a distance, a peak spectral luminosity) at each frequency and a well-defined time from explosion to that peak. Studying these two quantities at 6 cm wavelength, peak spectral luminosity (L_{6 cm peak}) and time after explosion date (t_0) to reach that peak (t_{6 cm peak} - t_0), we find that they appear related. In particular, based on two objects, Type Ib supernovae may b…
An explanation is given of the low value of $R_λ\equiv A_λ/E(B-V) $, the ratio of absolute to selective extinction deduced from Type Ia supernova observations. The idea involves scattering by dust clouds located in the circumstellar environment, or at the highest velocity shells of the supernova ejecta. The scattered light tends to reduce the effective $R_λ$ in the optical, but has an opposite effect in the ultraviolet. The presence of circumstellar dust can be tested by ultraviolet to near infrared observations and by multi-epoch spectropolarimetry of SNe Ia.
The possibility is investigated that the H$α$ luminosity at the nebular epoch may be an additional indicator of $^{56}$Ni mass in type II supernovae with plateau (SNe IIP), on the basis of available photometry and spectra. We first derive the $^{56}$Ni mass from the $M_V$ magnitude on the radioactive tail using a standard approach. A confirmation of the correlation between $^{56}$Ni mass and plateau $M_V$ magnitude found recently by Hamuy (2003) is evident. There is strong evidence of a correlation between steepness of the $V$ light curve slope at the inflection time and the $^{56}$Ni mass. If…
We present FUSE spectroscopy and supporting data for star-forming regions in nearby galaxies, to examine their massive-star content and explore the use of abundance and population indicators in this spectral range for high-redshift galaxies. New far-ultraviolet spectra are shown for four bright H II regions in M33 (NGC 588, 592, 595, and 604), the H II region NGC 5461 in M101, and the starburst nucleus of NGC 7714, supplemented by the very-low-metallicity galaxy I Zw 18. In each case, we see strong Milky Way absorption systems from H2, but intrinsic absorption within each galaxy is weak or und…
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 m…
Ultraviolet light curves are calculated for several thermonuclear supernova models using a multifrequency radiation hydrodynamic code. It is found that Chandrasekhar-mass models produce very similar light curves both for detonation and deflagration. Sub-Chandrasekhar-mass models essentially differ from ``normal'' Chandrasekhar ones regarding behaviour of their UV fluxes. Differences in absolute brightness and in shape of light curves of thermonuclear supernovae could be detectable up to 300 Mpc with modern UV space telescopes.
Large photometric surveys with the aim of identifying many Type Ia supernovae (SNe) at moderate redshift are challenged in separating these SNe from other SN types. We are motivated to identify Type Ia SNe based only on broadband photometric information, since spectroscopic determination of the SN type, the traditional method, requires significant amounts of time on large telescopes. We consider the possible observables provided by a large synoptic photometry survey. We examine the optical colors and magnitudes of many SN types from z=0.1 to z=1.0, using space-based ultraviolet spectra and gro…
We present ultraviolet and optical light curves in six broadband filters and grism spectra obtained by Swift's Ultraviolet/Optical Telescope for the Type Ia supernova SN2005am. The data were collected beginning about four days before the B-band maximum, with excellent coverage of the rapid decline phase and later observations extending out to 69 days after the peak. The optical and near UV light curve match well those of SN1992A. The other UV observations constitute the first set of light curves shorter than 2500 Angstroms and allow us to compare the light curve evolution in three UV bands. Th…
Type Ia supernovae (SNe) are the best standard candles available today in spite of an appreciable intrinsic variation of their luminosities at maximum phase, and of probably non-uniform progenitors. For an unbiased use of type Ia SNe as distance indicators it is important to know accurately how the decline rate and colour at maximum phase correlate with the peak brightness. In order to calibrate the Hubble diagram of type Ia SNe, i.e. to derive the Hubble constant, one needs to determine the absolute brightness of nearby type Ia SNe. Globular cluster systems of early type Ia host galaxies prov…
I use the largest available sample of Type II plateau supernovae to examine the previously reported luminosity-velocity relation. This study confirms such relation which permits one to standardize the luminosities of these objects from a spectroscopic measurement of their envelope velocities, and use them as extragalactic distance indicators. The "standard candle method" (SCM) yields a Hubble diagram with a dispersion of 0.3 mag, which implies that the SCM produces distances with a precision of 15%. Using two nearby supernovae with Cepheid distances I find Ho=81+/-10 km/s/Mpc, which compares w…
We study a possibility of detection of circumstellar absorption lines of Na I D$_{1,2}$ and Ca II H,K in spectra of type IIP supernovae at the photospheric epoch. The modelling shows that the circumstellar lines of Na I doublet will not be seen in type IIP supernovae for moderate wind density, e.g., characteristic of SN 1999em, whereas rather pronounced Ca II lines with P Cygni profile should be detectable. A similar model is used to describe Na I and Ca II circumstellar lines seen in SN 1998S, type IIL with a dense wind. We show that line intensities in this supernova are reproduced, if one a…
Double-peaked oxygen lines in the nebular spectra of two peculiar Type Ib/c Supernovae (SN Ib/c) have been interpreted as off-axis views of a GRB-jet or unipolar blob ejections. Here we present late-time spectra of 8 SN IIb, Ib and Ic and show that this phenomenon is common and should not be so firmly linked to extraordinary explosion physics. The line profiles are most likely caused by ejecta expanding with a torus- or disk-like geometry. Double-peaked oxygen profiles are not necessarily the indicator of a mis-directed GRB jet.
Type Ia supernovae have played a crucial role in the discovery of the dark energy, via the measurement of their light curves and the determination of the peak brightness via fitting templates to the observed lightcurve shape. Two spectroscopic indicators are also known to be well correlated with peak luminosity. Since the spectroscopic luminosity indicators are obtained directly from observed spectra, they will have different systematic errors than do measurements using photometry. Additionally, these spectroscopic indicators may be useful for studies of effects of evolution or age of the SNe …
The Supernova Acceleration Probe (SNAP) will use Type Ia supernovae (SNe Ia) as distance indicators to measure the effect of dark energy on the expansion history of the Universe. (SNAP's weak-lensing program is described in a companion White Paper.) The experiment exploits supernova distance measurements up to their fundamental systematic limit; strict requirements on the monitoring of each supernova's properties lead to the need for a space-based mission. Results from pre-SNAP experiments, which characterize fundamental SN Ia properties, will be used to optimize the SNAP observing strategy to…
The debate on the oxygen abundances of metal-poor stars has its origin in contradictory results obtained using different abundance indicators. To achieve a better understanding of the problem we have acquired high quality spectra with the Ultraviolet and Visual Echelle Spectrograph at VLT, with a signal-to-noise of the order of 100 in the near ultraviolet and 500 in the optical and near infrared wavelength range. Three different oxygen abundance indicators, OH ultraviolet lines around 310.0 nm, the [OI] line at 630.03 nm and the OI lines at 777.1-5 nm were observed in the spectra of 13 metal-p…
Supernova experiments to characterize dark energy require a well designed low redshift program; we consider this for both ongoing/near term (e.g. Supernova Legacy Survey) and comprehensive future (e.g. SNAP) experiments. The derived criteria are: a supernova sample centered near z=0.05 comprising 150-500 (in the former case) and 300-900 (in the latter case) well measured supernovae. Low redshift Type Ia supernovae play two important roles for cosmological use of the supernova distance-redshift relation: as an anchor for the Hubble diagram and as an indicator of possible systematics. An innate …
We present a novel investigation into the relationship between simple estimates of magnetic flux balance and the Ne VIII Doppler velocity partitioning of a large equatorial coronal hole observed by the Solar Ultraviolet Measurements of Emitted Radiation spectrometer (SUMER) on the Solar and Heliospheric Observatory (SOHO) in November 1999. We demonstrate that a considerable fraction of the large scale Doppler velocity pattern in the coronal hole can be qualitatively described by simple measures of the local magnetic field conditions, i.e., the relative unbalance of magnetic polarities and the …
In this paper, we make a comprehensive determination of the Hubble constant $H_0$ by using two parameters - the B-V color and the rate of decline $Δm_{15}$ - to simultaneously standardize the luminosities of all nearby Cepheid-calibrated type Ia supernovae (SNe Ia) and those of a larger, more distant sample of 29 SNe Ia. Each group is treated in as similar a manner as possible in order to avoid systematic effects. A simultaneous $χ^2$ minimization yields a standardized absolute luminosity of the Cepheid-calibrated supernovae as well as the Hubble constant obtained from the more distant sample.…
Photometry is the most easily acquired information about supernovae. The light curves constructed from regular imaging provide signatures not only for the energy input, the radiation escape, the local environment and the progenitor stars, but also for the intervening dust. They are the main tool for the use of supernovae as distance indicators through the determination of the luminosity. The light curve of SN 1987A still is the richest and longest observed example for a core-collapse supernova. Despite the peculiar nature of this object, as explosion of a blue supergiant, it displayed all the …
Type Ia supernovae, the thermonuclear explosions of white dwarf stars composed of carbon and oxygen, were instrumental as distance indicators in establishing the acceleration of the universe's expansion. However, the physics of the explosion are debated. Here we report a systematic spectral analysis of a large sample of well observed type Ia supernovae. Mapping the velocity distribution of the main products of nuclear burning, we constrain theoretical scenarios. We find that all supernovae have low-velocity cores of stable iron-group elements. Outside this core, nickel-56 dominates the superno…
We review the existing set of optical/UV/IR observations of Supernova 1993J, concentrating heavily on optical data because these are by far the most plentiful. Some results from theoretical modeling of the observations are also discussed. SN 1993J has provided the best observational evidence for the transformation of a SN from one spectral type to another, thereby providing a link between Type II and Type Ib supernovae (SNe). This has strengthened the argument that SNe Ib (and, by extension, SNe Ic) are core-collapse events. SN 1993J has remained relatively bright for 10 years; its late-time e…
We present an empirical method that uses multicolor light curve shapes (MLCS) to estimate the luminosity, distance, and total line-of-sight extinction of Type Ia supernovae (SN Ia). The empirical correlation between the MLCS and the luminosity is derived from a ``training set'' of nine SN Ia light curves with independent distance and reddening estimates. We find that intrinsically dim SN Ia are redder and have faster light curves than the bright ones which are slow and blue. By thirty-five days after maximum the intrinsic color variations become negligable. A formal treatment of extinction emp…
We consider the general theoretical problem of ultraviolet light from old stellar populations (t > 2 Gyr), and the interpretation of galaxy spectra at short wavelengths (lamda < 3200A) The sources believed to be responsible for the observed `ultraviolet upturn phenomenon' (UVX) are Post-AGB (P-AGB), extreme horizontal branch (EHB) and AGB-Manque (AGBM) stars. The production of EHB stars depends on mass loss on the red giant branch, which is poorly understood, making the far-UV flux problematical as an indicator of the gross properties, such as the age, of a given galaxy. We discuss the current…
Type Ia supernovae (SNe Ia) are one of the major tools to determine the cosmological parameters. Utilizing them as distance indicators, it is possible to geometrically survey the universe. To this end, the intrinsic scatter in the luminosities of these events needs to be calibrated using empirical relations between observables. A theoretical explanation for these relations is still lacking and can only be provided by a sound understanding of the mechanism of SNe Ia. Recently there has been significant progress in modeling SNe Ia. We report on numerical simulations of the explosion process, com…
The recent discovery of a very bright type Ia supernova, SNLS-03D3bb ($\equiv$ SN 2003fg), in the Supernova Legacy Survey (SNLS) has raised the question of whether super-Chandrasekhar-mass white dwarf stars are needed to explain such explosions. In principle, such a progenitor could form by the mergers of two rather massive white dwarfs. Binary systems of two white dwarfs in close orbit where their total mass significantly exceeds the Chandrasekhar mass, have not yet been found. Therefore SNLS-03D3bb could establish the first clear case of a double-degenerate progenitor of a (peculiar) type Ia…
We present the first results from our GALEX program designed to obtain ultraviolet (UV) spectroscopy of nearby core-collapse supernovae (SNe). Our first target, SN 2005ay in the nearby galaxy NGC 3938, is a typical member of the II-P SN subclass. Our spectra show remarkable similarity to those of the prototypical type II-P event SN 1999em, and resemble also Swift observations of the recent type II-P event SN 2005cs. Taken together, the observations of these three events trace the UV spectral evolution of SNe II-P during the first month after explosion, as required in order to interpret optical…
The use of Type Ia supernovae as distance indicators led to the discovery of the accelerating expansion of the universe a decade ago. Now that large second generation surveys have significantly increased the size and quality of the high-redshift sample, the cosmological constraints are limited by the currently available sample of ~50 cosmologically useful nearby supernovae. The Nearby Supernova Factory addresses this problem by discovering nearby supernovae and observing their spectrophotometric time development. Our data sample includes over 2400 spectra from spectral timeseries of 185 supern…
We investigate the extinction curves of young galaxies in which dust is supplied from Type II supernovae (SNe II) and/or pair instability supernovae (PISNe). Since at high redshift (z>5), low-mass stars cannot be dominant sources for dust grains, SNe II and PISNe, whose progenitors are massive stars with short lifetimes, should govern the dust production. Here, we theoretically investigate the extinction curves of dust produced by SNe II and PISNe, taking into account reverse shock destruction induced by collision with ambient interstellar medium. We find that the extinction curve is sensitive…
The methodology involved in deriving the Hubble Constant via the calibration of the corrected peak luminosities of Type Ia supernovae (SNe) is reviewed. We first present a re-analysis of the Calan-Tololo (C-T) and Center for Astrophysics (CfA) Type Ia SN surveys. Bivariate linear least squares and quadratic boot-strapped fits in peak apparent magnitude and light curve shape are employed to correct this heterogeneous sample of peak apparent magnitudes, resulting in an homogeneous (and excellent) secondary distance indicator: the so-called corrected peak luminosity. We next provide an empirical …
Optical and ultraviolet observations of the Type IIn supernova 1995N at epochs between 321 and 1799 days after the explosion show three distinct velocity components. The narrow lines come from circumstellar gas and show both low and high ionization. This component has a low filling factor, and is photoionized by X-rays from the shock. The intermediate component, which is dominated by newly processed oxygen, originates in a shell with velocity of 2500-5000 km/s, and most likely comes from the ejecta. The hydrogen- and helium-dominated gas has a low ionization, a high density, and velocities tha…
We create new U, B, V, R and I-band light curve templates of type Ia Supernovae (SNe Ia) and re-analyze 122 nearby (redshift < 0.11) SNe Ia using a new ``Multi-band Stretch method,'' which is a revised Stretch method (cf. Perlmutter et al. 1997; Goldhaber et al. 2001) extended to five bands. We find (i) our I-band template can fit about 90% of SNe Ia I-band light curves, (ii) relationships between luminosity, colours and stretch factors, (iii) possible sub-groups of SNe Ia, and (iv) the ratio of total to selective extinction R in other galaxies can be consistent with that in the Milky Way unde…
The remarkable uniformity of Type Ia supernovae (SNe Ia) has allowed astronomers to use them as distance indicators to measure the properties and expansion history of the Universe. However, SNe Ia exhibit intrinsic variation in both their spectra and observed brightness. To reduce these systematic uncertainties, we need a deeper understanding of the observed variations in SNe Ia. Toward this end, the Nearby Supernova Factory (SNfactory) has been designed to discover hundreds of SNe Ia in a systematic and automated fashion and study them in detail. A prototype run of the SNfactory search pipeli…
We study the properties of Type Ia Supernovae (SNe Ia) as functions of the radial distance from their host galaxy centers. Using a sample of 62 SNe Ia with reliable luminosity, reddening, and decline rate determinations, we find no significant radial gradients of SNe Ia peak absolute magnitudes or decline rates in elliptical+S0 galaxies, suggesting that the diversity of SN properties is not related to the metallicity of their progenitors. We do find that the range in brightness and light curve width of supernovae in spiral galaxies extends to brighter, broader values. These results are interpr…
