Darrin Alan Casebeer

A Comparative Study of the Absolute Magnitude Distributions of Supernovae

The Asiago Supernova Catalog is used to carry out a comparative study of supernova absolute magnitude distributions. An overview of the absolute magnitudes of the supernovae in the current observational sample is presented, and the evidence for subluminous and overluminous events is examined. The fraction of supernovae that are subluminous (MB > -15) appears to be higher (perhaps much higher) than but it remains very uncertain. The fraction that are overluminous (MB > -20) is lower (probably much lower) than 0.01. The absolute magnitude distributions for each supernova type, restricted to events within 1 Gpc, are compared. Although these distributions are affected by observational bias in favor of the more luminous events, they are useful for comparative studies. We find mean absolute blue magnitudes (for H0 = 60) of -19.46 for normal Type Ia supernovae (SNe Ia), -18.04 for SNe Ibc, -17.61 and -20.26 for normal and bright SNe Ibc considered separately, -18.03 for SNe II-L, -17.56 and -19.27 for normal and bright SNe II-L considered separately, -17.00 for SNe II-P, and -19.15 for SNe IIn.

Late-time spectroscopy of SN 2002cx: The prototype of a new subclass of Type Ia supernovae

We present Keck optical spectra of SN 2002cx, the most peculiar known Type Ia supernova (SN Ia), taken 227 and 277 days past maximum light. Astonishingly, the spectra are not dominated by the forbidden emission lines of iron that are a hallmark of thermonuclear SNe in the nebular phase. Instead, we identify numerous P Cygni profiles of Fe II at very low expansion velocities of ~700 km s-1, which are without precedent in SNe Ia. We also report the tentative identification of low-velocity O I in these spectra, suggesting the presence of unburned material near the center of the exploding white dwarf. SN 2002cx is the prototype of a new subclass of SNe Ia, with spectral characteristics that may be consistent with recent pure deflagration models of Chandrasekhar-mass thermonuclear SNe. These are distinct from the majority of SNe Ia, for which an alternative explosion mechanism, such as a delayed detonation, may be required.

EMERGENCE OF A BROAD ABSORPTION LINE OUTFLOW IN THE NARROW-LINE SEYFERT 1 GALAXY WPVS 007

We report results from a 2003 Far Ultraviolet Spectroscopic Explorer (FUSE) observation and reanalysis of a 1996 Hubble Space Telescope (HST) observation of the unusual X-ray transient Narrow-line Seyfert 1 galaxy WPVS 007. The HST Faint Object Spectrograph (FOS) spectrum revealed mini-BALs (broad absorption lines) with V max ~ 900 km s?1 and FWHM ~550 km s?1. The FUSE spectrum showed that an additional BAL outflow with V max ~ 6000 km s?1 and FWHM ~3400 km s?1 had appeared. WPVS 007 is a low-luminosity object in which such a high-velocity outflow is not expected; therefore, it is an outlier on the MV /v max relationship. Template spectral fitting yielded apparent ionic columns, and a Cloudy analysis showed that the presence of P V requires a high-ionization parameter log(U) ? 0 and high-column density log(N H) ? 23 assuming solar abundances and a nominal spectral energy distribution (SED) for low-luminosity NLS1s with ? ox = ?1.28. A recent long Swift observation revealed the first hard X-ray detection and an intrinsic (unabsorbed) ? ox ?1.9. Using this SED in our analysis yielded lower column density constraints (log(N H) ? 22.2 for Z = 1, or log(N H) ? 21.6 if Z = 5). The X-ray weak continuum, combined with X-ray absorption consistent with the UV lines, provides the best explanation for the observed Swift X-ray spectrum. The large column densities and velocities implied by the UV data in any of these scenarios could be problematic for radiative acceleration. We also point out that since the observed P V absorption can be explained by lower total column densities using an intrinsically X-ray weak spectrum, we might expect to find P V absorption preferentially more often (or stronger) in quasars that are intrinsically X-ray weak.

The Intrinsically X-Ray-weak Quasar PHL 1811. II. Optical and UV Spectra and Analysis

This is the second of two papers reporting observations and analysis of the unusually bright (mb = 14.4), luminous (MB = -25.5), nearby (z = 0.192) narrow-line quasar PHL 1811. The first paper reported that PHL 1811 is intrinsically X-ray-weak and presented a spectral energy distribution (SED). Here we present HST STIS optical and UV spectra, and ground-based optical spectra. The optical and UV line emission is very unusual. There is no evidence for forbidden or semiforbidden lines. The near-UV spectrum is dominated by very strong Fe II and Fe III, and unusual low-ionization lines such as Na I D and Ca II H and K are observed. High-ionization lines are very weak; C IV has an equivalent width of 6.6 ?, a factor of ~5 smaller than measured from quasar composite spectra. An unusual feature near 1200 ? can be deblended in terms of Ly?, N V, Si II, and C III* using the blueshifted C IV profile as a template. Photoionization modeling shows that the unusual line emission can be explained qualitatively by the unusually soft SED. Principally, a low gas temperature results in inefficient emission of collisionally excited lines, including the semiforbidden lines generally used as density diagnostics. The emission resembles that of high-density gas; in both cases this is a consequence of inefficient cooling. PHL 1811 is very unusual, but we note that quasar surveys may be biased against finding similar objects.

On the determination of N and O abundances in low-metallicity systems

We show that in order to minimize the uncertainties in the N and O abundances of low-mass, low-metallicity (O/H ≤ 1/5 solar) emission-line galaxies, it is necessary to employ separate parameterizations for inferring Te(N+) and Te(O+) from Te(O+2). In addition, we show that for the above systems, the ionization correction factor (ICF) for obtaining N/O from N+/O+, where the latter is derived from optical emission-line flux ratios, is = 1.08 ± 0.09. These findings are based on state-of-the-art single-star H II region simulations, employing our own modeled stellar spectra as input. Our models offer the advantage of having matching stellar and nebular abundances. In addition, they have O/H as low as 1/50 solar (lower than any past work), as well as log(N/O) and log(C/O) fixed at characteristic values of -1.46 and -0.7, respectively. The above results were used to rederive N and O abundances for a sample of 68 systems with 12 + log(O/H) ≤ 8.1, whose dereddened emission-line strengths were collected from the literature. The analysis of the log(N/O) versus 12 + log(O/H) diagram of the above systems shows that (1) the largest group of objects forms the well-known N/O plateau with a value for the mean (and its statistical error) of -1.43, (2) the objects are distributed within a range in log(N/O) of -1.54 to -1.27 in Gaussian fashion around the mean with a standard deviation of σ = , and (3) a χ2 analysis suggests that only a small amount of the observed scatter in log(N/O) is intrinsic.

FUSE Observation of the Narrow-Line Seyfert 1 Galaxy RE 1034+39: Dependence of Broad Emission Line Strengths on the Shape of the Photoionizing Spectrum

We present an analysis from simultaneous FUSE, ASCA, and EUVE observations, as well as a reanalysis of archival HST spectra, from the extreme narrow-line Seyfert 1 Galaxy RE 1034+39 (KUG 1031+398). RE 1034+39 has an unusually hard spectral energy distribution (SED) that peaks in the soft X-rays. Its emission lines are unusual in that they can all be modeled as a Lorentzian centered at the rest wavelength with only a small range in velocity widths. In order to investigate whether the unusual SED influences the emission-line ratios and equivalent widths, we present three complementary types of photoionization analysis. The FUSE spectrum was particularly important because it includes the high-ionization line O VI. First, we use the photoionization code CLOUDY and the SED developed from the coordinated observations to confirm that the emission lines are consistent with observed hard SED. The best model parameters were an ionization parameter log U ≈ -2 and a hydrogen number density log nH = 9.75 (cm-2). Second, we present a locally optimally emitting cloud model. This model produced enhanced O VI as observed, but also yielded far too strong Mg II. Third, we develop a series of semiempirical SEDs, run CLOUDY models, and compare the results with the measured values using a figure of merit (FOM). The FOM minimum indicates SED and gas properties similar to those inferred from the one-zone model using the RE 1034+39 continuum. Furthermore, the FOM increases sharply toward softer continua, indicating that a hard SED is required by the data in the context of a one-zone model.

Direct Analysis of Spectra of the Unusual Type Ib Supernova 2005bf

Synthetic spectra generated with the parameterized supernova synthetic spectrum code SYNOW are compared to spectra of the unusual Type Ib supernova 2005bf. We confirm the discovery by Folatelli et al. that very early spectra (~30 days before maximum light) contain both photospheric-velocity (~8000 km s–1) features of He i, Ca ii, and Fe ii, and detached high-velocity (~14,000 km s–1) features of Hα, Ca ii, and Fe ii. An early spectrum of SN 2005bf is an almost perfect match to a near-maximum-light spectrum of the Type Ib SN 1999ex. Although these two spectra were at very different times with respect to maximum light (20 days before maximum for SN 2005bf and 5 days after for SN 1999ex), they were for similar times after explosion—about 20 days for SN 2005bf and 24 days for SN 1999ex. The almost perfect match clinches the previously suggested identification of Hα in SN 1999ex and supports the proposition that many if not all Type Ib supernovae eject a small amount of hydrogen. The earliest available spectrum of SN 2005bf resembles a near-maximum-light spectrum of the Type Ic SN 1994I. These two spectra were also at different times with respect to maximum light (32 days before maximum for SN 2005bf and 4 days before for SN 1994I) but at similar times after explosion—about 8 days for SN 2005bf and 10 days for SN 1994I. The resemblance motivates us to consider a reinterpretation of the spectra of Type Ic supernovae, involving coexisting photospheric-velocity and high-velocity features. The implications of our results for the geometry of the SN 2005bf ejecta, which has been suggested as being grossly asymmetric, are briefly discussed.

Mount Wilson and Palomar Photographic Supernova Spectra

Fifty-one photographic spectra of 20 bright supernovae that were obtained by J. L. Greenstein, R. Minkowski, and F. Zwicky at the Mount Wilson and Palomar Observatories between 1954 and 1970 are presented and briefly discussed. Microphotometer transmission tracings of the photographic plates have been digitized and plotted on a common wavelength scale. These spectra are useful for classification purposes and for comparative studies of the blueshifts of absorption features.

Lick Observatory Photographic Supernova Spectra

Seventy-eight photographic spectra of 18 bright supernovae that were obtained by various observers at the Lick Observatory between 1937 and 1971 are presented and briefly discussed. Microphotometer transmission tracings of the photographic plates have been digitized and plotted on a common scale with a linear wavelength axis. The spectra were prismatic, with a nonlinear dispersion, in their original form. These spectra are useful for classification purposes and for comparative studies of the blueshifts of absorption features.

Probing the Nature of Type I Supernovae with SYNOW

SUSPECT is a web‐based database of supernova spectra (and photometry). As we thank observers who have contributed spectra to SUSPECT, we encourage them and other observers to develop the habit of sending spectra as they publish them. SYNOW is a simple resonance‐scattering supernova synthetic‐spectrum code that is used at the University of Oklahoma and elsewhere. A revised version of SYNOW that is now publicly available is briefly described. We offer an overview of our ongoing comparative direct analysis of spectra of Type Ia supernovae and a discussion (with some emphasis on the unusual Type Ib SN 2005bf) of the issue of whether Type Ib and perhaps even Type Ic supernovae eject hydrogen.