Timothy E. Pickering

MULTI-WAVELENGTH OBSERVATIONS OF SUPERNOVA 2011ei: TIME-DEPENDENT CLASSIFICATION OF TYPE IIb AND Ib SUPERNOVAE AND IMPLICATIONS FOR THEIR PROGENITORS

We present X-ray, UV/optical, and radio observations of the stripped-envelope, core-collapse supernova (SN) 2011ei, one of the least luminous SNe IIb or Ib observed to date. Our observations begin with a discovery within � 1 day of explosion and span several months afterward. Early optical spectra exhibit broad, Type II-like hydrogen Balmer profiles that subside rapidly and are replaced by Type Ib-like He-rich features on the timescale of one week. High-cadence monitoring of this transition suggests that absorption attributable to a high velocity (& 12,000 km s −1 ) H-rich shell is not rare in Type Ib events. Radio observations imply a shock velocity of v � 0.13c and a progenitor star mass-loss rate of u M � 1.4 × 10 −5 M⊙ yr −1 (assuming wind velocity vw = 10 3 km s −1 ). This is consistent with independent constraints from deep X-ray observations with Swift-XRT and Chandra. Overall, the multi-wavelength properties of SN2011ei are consistent with the explosion of a lower-mass (3 4 M⊙), compact (R∗ . 1 × 10 11 cm), He core star. The star retained a thin hydrogen envelope at the time of explosion, and was embedded in an inhomogeneous circumstellar wind suggestive of modest episodic mass-loss. We conclude that SN2011ei’s rapid spectral metamorphosis is indicative of time-dependent classifications that bias estimates of explosion rates for Type IIb and Ib objects, and that important information about a progenitor star’s evolutionary state and mass-loss immediately prior to SN explosion can be inferred from timely multi-wavelength observations. Subject headings: supernovae: general — supernova: individual (SN2011ei)

PySALT: the SALT science pipeline

PySALT is the python/PyRAF-based data reduction and analysis pipeline for the Southern African Large Telescope (SALT), a modern 10m class telescope with a large user community consisting of 13 partner institutions. The two first generation instruments on SALT are SALTICAM, a wide-field imager, and the Robert Stobie Spectrograph (RSS). Along with traditional imaging and spectroscopy modes, these instruments provide a wide range of observing modes, including Fabry-Perot imaging, polarimetric observations, and high-speed observations. Due to the large user community, resources available, and unique observational modes of SALT, the development of reduction and analysis software is key to maximizing the scientific return of the telescope. PySALT is developed in the Python/PyRAF environment and takes advantage of a large library of open-source astronomical software. The goals in the development of PySALT are: (1) Provide science quality reductions for the major operational modes of SALT, (2) Create analysis tools for the unique modes of SALT, and (3) Create a framework for the archiving and distribution of SALT data. The data reduction software currently provides support for the reduction and analysis of regular imaging, high-speed imaging, and long slit spectroscopy with planned support for multi-object spectroscopy, high-speed spectroscopy, Fabry-Perot imaging, and polarimetric data sets. We will describe the development and current status of PySALT and highlight its benefits through early scientific results from SALT.

The broad-lined type Ic SN 2012ap and the nature of relativistic supernovae lacking a gamma-ray burst detection

We present ultraviolet, optical, and near-infrared observations of SN 2012ap, a broad-lined Type Ic supernova in the galaxy NGC 1729 that produced a relativistic and rapidly decelerating outflow without a gamma-ray burst signature. Photometry and spectroscopy follow the flux evolution from –13 to +272 days past the B-band maximum of –17.4 ± 0.5 mag. The spectra are dominated by Fe II, O I, and Ca II absorption lines at ejecta velocities of v 20,000 km s–1 that change slowly over time. Other spectral absorption lines are consistent with contributions from photospheric He I, and hydrogen may also be present at higher velocities (v 27,000 km s–1). We use these observations to estimate explosion properties and derive a total ejecta mass of ~2.7 M ☉, a kinetic energy of ~1.0 × 1052 erg, and a 56Ni mass of 0.1-0.2 M ☉. Nebular spectra (t > 200 days) exhibit an asymmetric double-peaked [O I] λλ6300, 6364 emission profile that we associate with absorption in the supernova interior, although toroidal ejecta geometry is an alternative explanation. SN 2012ap joins SN 2009bb as another exceptional supernova that shows evidence for a central engine (e.g., black hole accretion or magnetar) capable of launching a non-negligible portion of ejecta to relativistic velocities without a coincident gamma-ray burst detection. Defining attributes of their progenitor systems may be related to notable observed properties including environmental metallicities of Z Z ☉, moderate to high levels of host galaxy extinction (E(B – V) > 0.4 mag), detection of high-velocity helium at early epochs, and a high relative flux ratio of [Ca II]/[O I] >1 at nebular epochs. These events support the notion that jet activity at various energy scales may be present in a wide range of supernovae.

Characterization of the nearby L/T Binary Brown Dwarf WISE J104915.57–531906.1 at 2 Pc from the Sun

WISE J104915.57–531906.1 is a L/T brown dwarf binary located 2 pc from the Sun. The pair contains the closest known brown dwarfs and is the third closest known system, stellar or sub-stellar. We report comprehensive follow-up observations of this newly uncovered system. We have determined the spectral types of both components (L8 ± 1, for the primary, agreeing with the discovery paper; T1.5 ± 2 for the secondary, which was lacking spectroscopic type determination in the discovery paper) and, for the first time, their radial velocities (V_(rad) ~ 23.1, 19.5 km s^(–1)) using optical spectra obtained at the Southern African Large Telescope and other facilities located at the South African Astronomical Observatory (SAAO). The relative radial velocity of the two components is smaller than the range of orbital velocities for theoretically predicted masses, implying that they form a gravitationally bound system. We report resolved near-infrared JHK_S photometry from the Infrared Survey Facility telescope at the SAAO which yields colors consistent with the spectroscopically derived spectral types. The available kinematic and photometric information excludes the possibility that the object belongs to any of the known nearby young moving groups or associations. Simultaneous optical polarimetry observations taken at the SAAO 1.9 m give a non-detection with an upper limit of 0.07%. For the given spectral types and absolute magnitudes, 1 Gyr theoretical models predict masses of 0.04-0.05 M _☉ for the primary, and 0.03-0.05 M _☉ for the secondary.

Spitzer Observations of Low-Luminosity Isolated and Low Surface Brightness Galaxies

We examine the infrared properties of five low surface brightness galaxies (LSBGs) and compare them with related but higher surface brightness galaxies, using Spitzer Space Telescope images and spectra. All the LSBGs are detected in the 3.6 and 4.5 μm bands, representing the stellar population. All but one are detected at 5.8 and 8.0 μm, revealing emission from hot dust and aromatic molecules, although many are faint or pointlike at these wavelengths. Detections of LSBGs at the far-infrared wavelengths of 24, 70, and 160 μm are varied in morphology and brightness, with only two detections at 160 μm, resulting in highly varied spectral energy distributions. Consistent with previous expectations for these galaxies, we find that detectable dust components exist for only some LSBGs, with the strength of dust emission dependent on the existence of bright star-forming regions. However, the far-infrared emission may be relatively weak compared with normal star-forming galaxies.

SN 2011hs: A fast and faint type IIb supernova from a supergiant progenitor

Observations spanning a large wavelength range, from X-ray to radio, of the Type IIb supernova (SN) 2011hs are presented, covering its evolution during the first year after explosion. The optical light curve presents a narrower shape and a fainter luminosity at peak than previously observed for Type IIb SNe. High expansion velocities are measured from the broad absorption H I and He I lines. From the comparison of the bolometric light curve and the time evolution of the photospheric velocities with hydrodynamical models, we found that SN 2011hs is consistent with the explosion of a 3–4 M⊙ He-core progenitor star, corresponding to a main-sequence mass of 12–15 M⊙, that ejected a mass of 56Ni of about 0.04 M⊙, with an energy of E = 8.5 × 1050 ERG. Such a low-mass progenitor scenario is in full agreement with the modelling of the nebular spectrum taken at ∼215 d from maximum. From the modelling of the adiabatic cooling phase, we infer a progenitor radius of ≈500–600 R⊙, clearly pointing to an extended progenitor star. The radio light curve of SN 2011hs yields a peak luminosity similar to that of SN 1993J, but with a higher mass-loss rate and a wind density possibly more similar to that of SN 2001ig. Although no significant deviations from a smooth decline have been found in the radio light curves, we cannot rule out the presence of a binary companion star.

Interaction Between the Broad-Lined Type Ic Supernova 2012ap and Carriers of Diffuse Interstellar Bands

The diffuse interstellar bands (DIBs) are absorption features observed in optical and near-infrared spectra that are thought to be associated with carbon-rich polyatomic molecules in interstellar gas. However, because the central wavelengths of these bands do not correspond with electronic transitions of any known atomic or molecular species, their nature has remained uncertain since their discovery almost a century ago. Here we report on unusually strong DIBs in optical spectra of the broad- lined Type Ic supernova SN2012ap that exhibit changes in equivalent width over short (. 30 days) timescales. The 4428 A and 6283 A DIB features get weaker with time, whereas the 5780 A feature shows a marginal increase. These nonuniform changes suggest that the supernova is interacting with a nearby source of the DIBs and that the DIB carriers possess high ionization potentials, such as small cations or charged fullerenes. We conclude that moderate-resolution spectra of supernovae with DIB absorptions obtained within weeks of outburst could reveal unique information about the mass-loss environment of their progenitor systems and provide new constraints on the properties of DIB carriers.

Abell 48 – a rare WN-type central star of a planetary nebula

A considerable fraction of the central stars of planetary nebulae (CSPNe) are hydrogendeficient. Almost all of these H-deficient central stars (CSs) display spectra with strong carbon and helium lines. Most of them exhibit emission-line spectra resembling those of massive WC stars. Therefore these stars are classed as CSPNe of spectral type [WC]. Recently, quantitative spectral analysis of two emission-line CSs, PB 8 and IC 4663, revealed that these stars do not belong to the [WC] class. Instead PB 8 has been classified as [WN/WC] type and IC 4663 as [WN] type. In this work we report the spectroscopic identification of another rare [WN] star, the CS of Abell 48. We performed a spectral analysis of Abell 48 with the Potsdam Wolf– Rayet (PoWR) models for expanding atmospheres. We find that the expanding atmosphere of Abell 48 is mainly composed of helium (85 per cent by mass), hydrogen (10 per cent) and nitrogen (5 per cent). The residual hydrogen and the enhanced nitrogen abundance make this object different from the other [WN] star IC 4663. We discuss the possible origin of this atmospheric composition.

Discovery of two new Galactic candidate luminous blue variables with Wide-field Infrared Survey Explorer

We report the discovery of two new Galactic candidate luminous blue variable (cLBV) stars via detection of circular shells (typical of known confirmed and cLBVs) and follow-up spectroscopy of their central stars. The shells were detected at 22 um in the archival data of the Mid-Infrared All Sky Survey carried out with the Wide-field Infrared Survey Explorer (WISE). Follow-up optical spectroscopy of the central stars of the shells conducted with the renewed Southern African Large Telescope (SALT) showed that their spectra are very similar to those of the well-known LBVs P Cygni and AG Car, and the recently discovered cLBV MN112, which implies the LBV classification for these stars as well. The LBV classification of both stars is supported by detection of their significant photometric variability: one of them brightened in the R- and I-bands by 0.68\pm0.10 mag and 0.61\pm0.04 mag, respectively, during the last 13-18 years, while the second one (known as Hen 3-1383) varies its B,V,R,I and K_s brightnesses by \simeq 0.5-0.9 mag on time-scales from 10 days to decades. We also found significant changes in the spectrum of Hen 3-1383 on a timescale of \simeq 3 months, which provides additional support for the LBV classification of this star. Further spectrophotometric monitoring of both stars is required to firmly prove their LBV status. We discuss a connection between the location of massive stars in the field and their fast rotation, and suggest that the LBV activity of the newly discovered cLBVs might be directly related to their possible runaway status.

Active optics and wavefront sensing at the upgraded 6.5-meter MMT

Shack-Hartmann wavefront sensors have been commissioned and are now in routine use at both of the optical foci (f/9 and f/5) of the converted MMT. Both units are of moderate resolution with 14x14 square apertures across the pupil for f/5 and 13x13 hexagonal apertures for f/9. They share a common software interface that fits a set of 19 Zernike polynomials to the wavefront errors. Zernike focus and coma are corrected by moving the secondary mirror, third order spherical by a combination of secondary motion and primary bending, and the rest by primary bending alone. In this paper we will describe the two wavefront sensor systems and how they have performed thus far.