J. Zolkower

Hydrogen-poor superluminous stellar explosions

Supernovae are stellar explosions driven by gravitational or thermonuclear energy that is observed as electromagnetic radiation emitted over weeks or more. In all known supernovae, this radiation comes from internal energy deposited in the outflowing ejecta by one or more of the following processes: radioactive decay of freshly synthesized elements (typically 56Ni), the explosion shock in the envelope of a supergiant star, and interaction between the debris and slowly moving, hydrogen-rich circumstellar material. Here we report observations of a class of luminous supernovae whose properties cannot be explained by any of these processes. The class includes four new supernovae that we have discovered and two previously unexplained events (SN 2005ap and SCP 06F6) that we can now identify as members of the same class. These supernovae are all about ten times brighter than most type Ia supernova, do not show any trace of hydrogen, emit significant ultraviolet flux for extended periods of time and have late-time decay rates that are inconsistent with radioactivity. Our data require that the observed radiation be emitted by hydrogen-free material distributed over a large radius (∼1015 centimetres) and expanding at high speeds (>104 kilometres per second). These long-lived, ultraviolet-luminous events can be observed out to redshifts z > 4.

Supernova PTF 09uj: A possible shock breakout from a dense circumstellar wind

Type-IIn supernovae (SNe IIn), which are characterized by strong interaction of their ejecta with the surrounding circumstellar matter (CSM), provide a unique opportunity to study the mass-loss history of massive stars shortly before their explosive death. We present the discovery and follow-up observations of an SN IIn, PTF 09uj, detected by the Palomar Transient Factory (PTF). Serendipitous observations by Galaxy Evolution Explorer (GALEX) at ultraviolet (UV) wavelengths detected the rise of the SN light curve prior to the PTF discovery. The UV light curve of the SN rose fast, with a timescale of a few days, to a UV absolute AB magnitude of about –19.5. Modeling our observations, we suggest that the fast rise of the UV light curve is due to the breakout of the SN shock through the dense CSM (n ≈ 10^(10) cm^(–3)). Furthermore, we find that prior to the explosion the progenitor went through a phase of high mass-loss rate (~0.1 M_⊙ yr^(–1)) that lasted for a few years. The decay rate of this SN was fast relative to that of other SNe IIn.

The palomar transient factory photometric calibration

The Palomar Transient Factory (PTF) provides multiple epoch imaging for a large fraction of the celestial sphere. Here, we describe the photometric calibration of the PTF data products that allows the PTF magnitudes to be related to other magnitude systems. The calibration process utilizes Sloan Digital Sky Survey (SDSS) r ∼ 16 mag point-source objects as photometric standards. During photometric conditions, this allows us to solve for the extinction coefficients and color terms and to estimate the camera illumination correction. This also enables the calibration of fields that are outside the SDSS footprint. We test the precision and repeatability of the PTF photometric calibration. Given that PTF is observing in a single filter each night, we define a PTF calibrated magnitude system for the R band and g band. We show that, in this system, ≈59% (47%) of the photometrically calibrated PTF R-band (g-band) data achieve a photometric precision of 0.02–0.04 mag and have color terms and extinction coefficients that are close to their average values. Given the objects’ color, the PTF magnitude system can be converted to other systems. Moreover, a night-by-night comparison of the calibrated magnitudes of individual stars observed on multiple nights shows that they are consistent to a level of ≈0.02 mag. Most of the data that were taken under nonphotometric conditions can be calibrated relative to other epochs of the same sky footprint obtained during photometric conditions. We provide a concise guide describing how to use the PTF photometric-calibration data products, as well as the transformations between the PTF magnitude system and the SDSS and Johnson-Cousins systems.

The Palomar Transient Factory Survey Camera: first year performance and results

The Palomar Transient Factory (PTF) is a new fully-automated, wide-field survey conducting a systematic exploration of the optical transient sky. The transient survey is performed using a new 8.1 square degree, 101 megapixel camera installed on the 48-inch Samuel Oschin Telescope at Palomar Observatory. The PTF Camera achieved first light at the end of 2008, completed commissioning in July 2009, and is now in routine science operations. The camera is based on the CFH12K camera, and was extensively modified for use on the 48-inch telescope. A field-flattening curved window was installed, the cooling system was re-engineered and upgraded to closed-cycle, custom shutter and filter exchanger mechanisms were added, new custom control software was written, and many other modifications were made. We here describe the performance of these new systems during the first year of Palomar Transient Factory operations, including a detailed and long term on-sky performance characterization. We also describe lessons learned during the construction and commissioning of the upgraded camera, the photometric and astrometric precision currently achieved with the PTF camera, and briefly summarize the first supernova results from the PTF survey.

Status of the PALM-3000 high-order adaptive optics system

The PALM-3000 upgrade to the Palomar Adaptive Optics system will deliver extreme adaptive optics correction to a suite of three infrared and visible instruments on the 5.1 meter Hale telescope. PALM-3000 uses a 3388-actuator tweeter and a 241-actuator woofer deformable mirror, a wavefront sensor with selectable pupil sampling, and an innovative wavefront control computer based on a cluster of 17 graphics processing units to correct wavefront aberrations at scales as fine as 8.1 cm at the telescope pupil using natural guide stars. Many components of the system, including the science instruments and a post-coronagraphic calibration wavefront sensor, have already been commissioned on the sky. Results from a laboratory testbed used to characterize the remaining new components and verify all interfaces are reported. Deployment to Palomar Observatory is planned August 2010, with first light expected in early 2011.

Debris Disk Science with the Palomar ExAO System : First Results

We present first imaging results from the PALM-3000 adaptive optics system and PHARO camera on the Hale 5 m telescope. Observations using a vector vortex coronagraph have given us direct detections of the two-ring dusty debris system around the star HD 141569. Our observations reveal the inner clearing in the disk to unprecedentedly small angular separations, and are the most sensitive yet at the H and K bands. We are for the first time able to measure and compare the colors of the scattered light in the inner and outer dust rings, and find that the outer ring is significantly bluer than the inner ring.

Initial performance of the Zwicky transient facility: a wide-fast time-domain survey (Conference Presentation)

Zwicky Transient Facility is an integrated, multi-band astronomical survey system optimized for sensitivity, observing cadence, and efficiency. The key subsystem consists of a 600 megapixel CCD focal plane mounted in a flat-fielding vacuum cryostat, located at the prime focus of the 1.2-meter Samuel Oschin Telescope at Palomar Observatory. Supporting subsystems include a new 2.4-meter optical shutter assembly, a 1.35-meter diameter aspheric corrector plate, a cryostat stabilizing hexapod, a commercial robotic arm-based exchanger, three 440 millimeter width filters, four guide/focus CCDs, and dedicated optics compensating individual field curvature over each of sixteen 6k x 6k science CCDs.To optimize ZTF efficiency, all telescope and dome drives were upgraded for higher speed and acceleration, fast readout electronics were implemented, and a sophisticated robotic control system has been implemented. We present for the first time on-sky results from the recently completed ZTF including its realized optical image quality, CCD noise, and observing efficiency performance and discuss engineering challenges that have been overcome. Early scientific results from the ZTF survey are also included.