Richard R. Treffers

The Distance to SN 1999em in NGC 1637 from the Expanding Photosphere Method

ABSTRACT We present 30 optical spectra and 49 photometric epochs sampling the first 517 days after discovery of supernova (SN) 1999em and derive its distance through the expanding photosphere method (EPM). SN 1999em is shown to be a Type II‐plateau (II‐P) event, with a photometric plateau lasting until about 100 days after explosion. We identify the dominant ions responsible for most of the absorption features seen in the optical portion of the spectrum during the plateau phase. Using the weakest unblended absorption features to estimate photospheric velocity, we find the distance to SN 1999em to be \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfon...

A High Intrinsic Peculiarity Rate among Type Ia Supernovae

We have compiled a sample of 45 Type Ia supernovae (SNe Ia) discovered by the Lick Observatory Supernova Search (LOSS) and the Beijing Astronomical Observatory Supernova Survey (BAOSS), and determined the rate of spectroscopically peculiar SNe Ia (i.e., SN 1986G-like, SN 1991bg-like, and SN 1991T-like objects) and the luminosity function of SNe Ia. Because of the nature of the two surveys (distance-limited with small baselines and deep limiting magnitudes), nearly all SNe Ia have been discovered in the sample galaxies of LOSS and BAOSS; thus, the observed peculiarity rate and luminosity function of SNe Ia are intrinsic. We find that 36% ± 9% of nearby SNe Ia are peculiar; specifically, the luminosity function of SNe Ia consists of 20% SN 1991T-like, 64% normal, and 16% SN 1991bg-like objects. We have compared our results to those found by earlier studies, and to those found at high redshift. The apparent dearth of SN 1991T-like objects at high redshift may be due to extinction, and especially to the difficulty of recognizing them from spectra obtained past maximum brightness or from spectra with low signal-to-noise ratios. Implications of the high peculiarity rate for the progenitor systems of SNe Ia are also briefly discussed.

The Rise Time of Nearby Type Ia Supernovae

The work at the University of California, Berkeley, was supported by the Miller Institute for Basic Research in Science, by NSF grant AST 94-17213, and by grant GO-7505 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

The Type Ia Supernova 1998bu in M96 and the Hubble Constant

We present optical and near-infrared photometry and spectroscopy of the Type Ia SN 1998bu in the Leo I Group galaxy M96 (NGC 3368). The data set consists of 356 photometric measurements and 29 spectra of SN 1998bu between UT 1998 May 11 and July 15. The well-sampled light curve indicates the supernova reached maximum light in B on UT 1998 May 19.3 (JD 2450952.8 ± 0.8) with B = 12.22 ± 0.03 and V = 11.88 ± 0.02. Application of a revised version of the Multicolor Light Curve Shape (MLCS) method yields an extinction toward the supernova of AV = 0.94 ± 0.15 mag, and indicates the supernova was of average luminosity compared to other normal Type Ia supernovae. Using the HST Cepheid distance modulus to M96 and the MLCS fitted parameters for the supernova, we derive an extinction-corrected absolute magnitude for SN 1998bu at maximum, MV = -19.42 ± 0.22. Our independent results for this supernova are consistent with those of Suntzeff et al. Combining SN 1998bu with three other well-observed local calibrators and 42 supernovae in the Hubble flow yields a Hubble constant, H0 = 64 -->img1.gif km s-1 Mpc-1, where the error estimate incorporates possible sources of systematic uncertainty including the calibration of the Cepheid period-luminosity relation, the metallicity dependence of the Cepheid distance scale, and the distance to the LMC.

SN 1997bs in M66: Another Extragalactic η Carinae Analog?1

ABSTRACT We report on SN 1997bs in NGC 3627 (M66), the first supernova discovered by the Lick Observatory Supernova Search using the 0.75 m Katzman Automatic Imaging Telescope (KAIT). Based on its early‐time optical spectrum, SN 1997bs was classified as Type IIn. However, from the BVRI light curves obtained by KAIT early in the supernova’s evolution, and F555W and F814W light curves obtained from Hubble Space Telescope archival WFPC2 images at late times, we question the identification of SN 1997bs as a bona fide supernova. We believe that it is more likely a superoutburst of a very massive luminous blue variable star, analogous to η Carinae, and similar to SN 1961V in NGC 1058 (Filippenko et al. 1995 AJ, 110, 2261) and SN 1954J (“Variable 12”) in NGC 2403 (Humphreys & Davidson 1994 PASP, 106, 1025). The progenitor may have survived the outburst, since the SN is seen in early 1998 at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs}...

The Unique type Ia supernova 2000cx in NGC 524

ABSTRACT We present extensive photometric and spectroscopic observations of the Type Ia supernova (SN Ia) 2000cx in the S0 galaxy NGC 524, which reveal it to be peculiar. Photometrically, SN 2000cx is different from all known SNe Ia, and its light curves cannot be fitted well by the fitting techniques currently available. There is an apparent asymmetry in the B‐band peak, in which the premaximum brightening is relatively fast (similar to that of the normal SN 1994D), but the postmaximum decline is relatively slow (similar to that of the overluminous SN 1991T). The color evolution of SN 2000cx is also peculiar: the (B−V)0 color has a unique plateau phase and the (V−R)0 and (V−I)0 colors are very blue. Although the premaximum spectra of SN 2000cx are similar to those of SN 1991T–like objects (with weak Si ii lines), its overall spectral evolution is quite different. The Si ii lines that emerged near maximum B‐band brightness stay strong in SN 2000cx until about 3 weeks past maximum. The change in the excita...

Fabry-Perot H-alpha observations of Galactic H II regions

The radial velocity and linewidth of H-alpha emission from 284 objects listed in Galactic H II region catalogs were observed using a Fabry-Perot spectrometer. A few of these objects are supernova remnants or planetary nebula. The rest of this sample encompasses most of the H II regions that are visible optically from the Northern Hemisphere. These observations are compared to previous H-alpha observations as well as to radio recombination line and CO observations. The average radial-velocity difference V(CO) - V(H-alpha) is 0.50 + or - 0.48 km/s and the (1-sigma) dispersion is 6.44 km/s. The implications of these values are discussed in terms of a very simple kinematic and extinction H II region model. Total H-alpha luminosities for the sample are estimated, and the Galactic H II region luminosity function is compared to that recently found for other galaxies. 18 refs.

Multiwavelength Monitoring of the Narrow-Line Seyfert 1 Galaxy Arakelian 564. III. Optical Observations and the Optical-UV-X-Ray Connection

We present the results of a 2 yr long optical monitoring program of the narrow-line Seyfert 1 galaxy Ark 564. The majority of this monitoring project was also covered by X-ray observations (RXTE), and for a period of ~50 days, we observed the galaxy in UV (HST) and X-rays (RXTE and ASCA) simultaneously with the ground-based observations. Rapid and large-amplitude variations seen in the X-ray band, on a daily and hourly timescale, were not detected at optical and UV wavelengths, which in turn exhibited much lower variability either on short (1 day) or long (several months) timescales. The only significant optical variations can be described as two 2-4 day events with ~10% flux variations. We detect no significant optical line variations and thus cannot infer a reverberation size for the broad-line region. Similarly, the large X-ray variations seem to vanish when the light curve is smoothed over a period of 30 days. The UV continuum follows the X-rays with a lag of ~0.4 days, and the optical band lags the UV band by ~2 days. No significant correlation was found between the entire X-ray data set and the optical band. Focusing on a 20 day interval around the strongest optical event we detect a significant X-ray-optical correlation with similar events seen in the UV and X-rays. Our data are consistent with reprocessing models on the grounds of the energy emitted in this single event. However, several large X-ray flares produced no corresponding optical emission.

Detection of water vapor on Jupiter

High-altitude (12.4 km) spectroscopic observations of Jupiter at 5 microns from the NASA 91.5 cm airborne infrared telescope have revealed 14 absorptions assigned to the rotation-vibration spectrum of water vapor. Preliminary analysis indicates a mixing ratio about 1 millionth for the vapor phase of water. Estimates of temperature (greater than about 300 K) and pressure (less than 20 atm) suggest observation of water deep in Jupiters hot spots responsible for its 5 micron flux. Model-atmosphere calculations based on radiative-transfer theory may change these initial estimates and provide a better physical picture of Jupiters atmosphere below the visible cloud tops.

The spectrum of the planetary nebula NGC 7027 from 0.9 to 2.7 microns

The spectrum of the planetary nebula NGC 7027 is presented from 0.9 to 2.7 ..mu... Emission lines of the Brackett and Paschen series of hydrogen and of ionized helium have been detected, and the intensities are shown to be consistent with the theory of radiative recombination. Three lines of the 1-0 quadrupole spectrum of molecular hydrogen have been detected. Four lines of He I, including the 2 /sup 1/S/sup -/ 2 /sup 1/P line at 2.058 ..mu.., have been observed. It is concluded that the nebula is optically thick in the helium principal series. A tentative identification of an emission line in (P II) at 1.1898 ..mu.. has also been made. (AIP)