Core-collapse Supernovae from the Palomar Transient Factory: Indications for a Different Population in Dwarf Galaxies

We use the first compilation of 72 core-collapse supernovae (SNe) from the Palomar Transient Factory (PTF) to study their observed subtype distribution in dwarf galaxies compared to giant galaxies. Our sample is the largest single-survey, untargeted, spectroscopically classified, homogeneous collection of core-collapse events ever assembled, spanning a wide host-galaxy luminosity range (down to M_r ≈ –14 mag) and including a substantial fraction (>20%) of dwarf (M_r ≥ –18 mag) hosts. We find more core-collapse SNe in dwarf galaxies than expected and several interesting trends emerge. We use detailed subclassifications of stripped-envelope core-collapse SNe and find that all Type I core-collapse events occurring in dwarf galaxies are either SNe Ib or broad-lined SNe Ic (SNe Ic-BL), while "normal" SNe Ic dominate in giant galaxies. We also see a significant excess of SNe IIb in dwarf hosts. We hypothesize that in lower metallicity hosts, metallicity-driven mass loss is reduced, allowing massive stars that would have appeared as "normal" SNe Ic in metal-rich galaxies to retain some He and H, exploding as Ib/IIb events. At the same time, another mechanism allows some stars to undergo extensive stripping and explode as SNe Ic-BL (and presumably also as long-duration gamma-ray bursts). Our results are still limited by small-number statistics, and our measurements of the observed N(Ib/c)/N(II) number ratio in dwarf and giant hosts (0.25^(+0.3)_(–0.15) and 0.23^(+0.11)_(–0.08), respectively; 1σ uncertainties) are consistent with previous studies and theoretical predictions. As additional PTF data accumulate, more robust statistical analyses will be possible, allowing the evolution of massive stars to be probed via the dwarf-galaxy SN population

Rapidly decaying supernova 2010X: A candidate ".Ia" explosion

We present the discovery, photometric, and spectroscopic follow-up observations of SN 2010X (PTF 10bhp). This supernova decays exponentially with τ_d = 5 days and rivals the current recordholder in speed, SN 2002bj. SN 2010X peaks at M_r = −17 mag and has mean velocities of 10,000 km s^(−1). Our light curve modeling suggests a radioactivity-powered event and an ejecta mass of 0.16M_⊙. If powered by Nickel, we show that the Nickel mass must be very small (≈0.02 M_⊙) and that the supernova quickly becomes optically thin to γ -rays. Our spectral modeling suggests that SN 2010X and SN 2002bj have similar chemical compositions and that one of aluminum or helium is present. If aluminum is present, we speculate that this may be an accretion-induced collapse of an O-Ne-Mg white dwarf. If helium is present, all observables of SN 2010X are consistent with being a thermonuclear helium shell detonation on a white dwarf, a “.Ia” explosion. With the 1 day dynamic-cadence experiment on the Palomar Transient Factory, we expect to annually discover a few such events

The CCAT 25m diameter submillimeter-wave telescope

CCAT will be a 25 m diameter telescope operating in the 2 to 0.2 mm wavelength range. It will be located at an altitude of 5600 m on Cerro Chajnantor in Northern Chile. The telescope will be equipped with wide-field, multi-color cameras for surveys and multi-object spectrometers for spectroscopic follow up. Several innovations have been developed to meet the <0.5 arcsec pointing error and 10 µm surface error requirements while keeping within the modest budget appropriate for radio telescopes

Evidence for an FU Orionis-like Outburst from a Classical T Tauri Star

We present pre- and post-outburst observations of the new FU Orionis-like young stellar object PTF 10qpf (also known as LkHα 188-G4 and HBC 722). Prior to this outburst, LkHα 188-G4 was classified as a classical T Tauri star (CTTS) on the basis of its optical emission-line spectrum superposed on a K8-type photosphere and its photometric variability. The mid-infrared spectral index of LkHα 188-G4 indicates a Class II-type object. LkHα 188-G4 exhibited a steady rise by ~1 mag over ~11 months starting in August 2009, before a subsequent more abrupt rise of >3 mag on a timescale of ~2 months. Observations taken during the eruption exhibit the defining characteristics of FU Orionis variables: (1) an increase in brightness by ≳ 4 mag, (2) a bright optical/near-infrared reflection nebula appeared, (3) optical spectra are consistent with a G supergiant and dominated by absorption lines, the only exception being Hα which is characterized by a P Cygni profile, (4) near-infrared spectra resemble those of late K-M giants/supergiants with enhanced absorption seen in the molecular bands of CO and H_(2)O, and (5) outflow signatures in H and He are seen in the form of blueshifted absorption profiles. LkHα 188-G4 is the first member of the FU Orionis-like class with a well-sampled optical to mid-infrared spectral energy distribution in the pre-outburst phase. The association of the PTF 10qpf outburst with the previously identified CTTS LkHα 188-G4 (HBC 722) provides strong evidence that FU Orionis-like eruptions represent periods of enhanced disk accretion and outflow, likely triggered by instabilities in the disk. The early identification of PTF 10qpf as an FU Orionis-like variable will enable detailed photometric and spectroscopic observations during its post-outburst evolution for comparison with other known outbursting objects

Know the Star, Know the Planet. III. A Stellar Companion to the Host Star of the Eccentric Exoplanet HD 8673b

HD 8673 hosts a massive exoplanet in a highly eccentric orbit (e = 0.723). Based on two epochs of speckle interferometry a previous publication identified a candidate stellar companion. We observed HD 8673 multiple times with the 10 m Keck II telescope, the 5 m Hale telescope, the 3.63 m Advanced Electro-Optical System telescope, and the 1.5 m Palomar telescope in a variety of filters with the aim of confirming and characterizing the stellar companion. We did not detect the candidate companion, which we now conclude was a false detection, but we did detect a fainter companion. We collected astrometry and photometry of the companion on six epochs in a variety of filters. The measured differential photometry enabled us to determine that the companion is an early M dwarf with a mass estimate of 0.33–0.45 M_☉. The companion has a projected separation of 10 AU, which is one of the smallest projected separations of an exoplanet host binary system. Based on the limited astrometry collected, we are able to constrain the orbit of the stellar companion to a semimajor axis of 35–60 AU, an eccentricity ≤0.5, and an inclination of 75°–85°. The stellar companion has likely strongly influenced the orbit of the exoplanet and quite possibly explains its high eccentricity

Evidence for an FU Orionis-like Outburst from a Classical T Tauri Star

We present pre- and post-outburst observations of the new FU Orionis-like young stellar object PTF 10qpf (also known as LkHa 188-G4 and HBC 722). Prior to this outburst, LkHa 188-G4 was classified as a classical T Tauri star on the basis of its optical emission-line spectrum superposed on a K8-type photosphere, and its photometric variability. The mid-infrared spectral index of LkHa 188-G4 indicates a Class II-type object. LkHa 188-G4 exhibited a steady rise by ~1 mag over ~11 months starting in Aug. 2009, before a subsequent more abrupt rise of > 3 mag on a time scale of ~2 months. Observations taken during the eruption exhibit the defining characteristics of FU Orionis variables: (i) an increase in brightness by > 4 mag, (ii) a bright optical/near-infrared reflection nebula appeared, (iii) optical spectra are consistent with a G supergiant and dominated by absorption lines, the only exception being Halpha which is characterized by a P Cygni profile, (iv) near-infrared spectra resemble those of late K--M giants/supergiants with enhanced absorption seen in the molecular bands of CO and H_2O, and (v) outflow signatures in H and He are seen in the form of blueshifted absorption profiles. LkHa 188-G4 is the first member of the FU Orionis-like class with a well-sampled optical to mid-infrared spectral energy distribution in the pre-outburst phase. The association of the PTF 10qpf outburst with the previously identified classical T Tauri star LkHa 188-G4 (HBC 722) provides strong evidence that FU Orionis-like eruptions represent periods of enhanced disk accretion and outflow, likely triggered by instabilities in the disk. The early identification of PTF 10qpf as an FU Orionis-like variable will enable detailed photometric and spectroscopic observations during its post-outburst evolution for comparison with other known outbursting objects.Comment: 14 pages, 11 figures, ApJ accepte

Know The Star, Know the Planet. IV. A Stellar Companion to the Host star of the Eccentric Exoplanet HD 8673b

HD 8673 hosts a massive exoplanet in a highly eccentric orbit (e=0.723). Based on two epochs of speckle interferometry a previous publication identified a candidate stellar companion. We observed HD 8673 multiple times with the 10 m Keck II telescope, the 5 m Hale telescope, the 3.63 m AEOS telescope and the 1.5m Palomar telescope in a variety of filters with the aim of confirming and characterizing the stellar companion. We did not detect the candidate companion, which we now conclude was a false detection, but we did detect a fainter companion. We collected astrometry and photometry of the companion on six epochs in a variety of filters. The measured differential photometry enabled us to determine that the companion is an early M dwarf with a mass estimate of 0.33-0.45 M?. The companion has a projected separation of 10 AU, which is one of the smallest projected separations of an exoplanet host binary system. Based on the limited astrometry collected, we are able to constrain the orbit of the stellar companion to a semi-major axis of 35{60 AU, an eccentricity ? 0.5 and an inclination of 75{85?. The stellar companion has likely strongly in uenced the orbit of the exoplanet and quite possibly explains its high eccentricity.Comment: Accepted to the Astronomical Journal, 6 Pages, 5 Figure

Rapidly Decaying Supernova 2010X: A Candidate ".Ia" Explosion

We present the discovery, photometric and spectroscopic follow-up observations of SN 2010X (PTF 10bhp). This supernova decays exponentially with tau_d=5 days, and rivals the current recordholder in speed, SN 2002bj. SN 2010X peaks at M_r=-17mag and has mean velocities of 10,000 km/s. Our light curve modeling suggests a radioactivity powered event and an ejecta mass of 0.16 Msun. If powered by Nickel, we show that the Nickel mass must be very small (0.02 Msun) and that the supernova quickly becomes optically thin to gamma-rays. Our spectral modeling suggests that SN 2010X and SN 2002bj have similar chemical compositions and that one of Aluminum or Helium is present. If Aluminum is present, we speculate that this may be an accretion induced collapse of an O-Ne-Mg white dwarf. If Helium is present, all observables of SN 2010X are consistent with being a thermonuclear Helium shell detonation on a white dwarf, a ".Ia" explosion. With the 1-day dynamic-cadence experiment on the Palomar Transient Factory, we expect to annually discover a few such events.Comment: 6 pages, 5 figures; Minor Changes; Note correction in Fig 4 caption; published by ApJ

PTF10fqs: A Luminous Red Nova in the Spiral Galaxy Messier 99

The Palomar Transient Factory (PTF) is systematically charting the optical transient and variable sky. A primary science driver of PTF is building a complete inventory of transients in the local Universe (distance less than 200 Mpc). Here, we report the discovery of PTF10fqs, a transient in the luminosity "gap" between novae and supernovae. Located on a spiral arm of Messier 99, PTF 10fqs has a peak luminosity of Mr = -12.3, red color (g-r = 1.0) and is slowly evolving (decayed by 1 mag in 68 days). It has a spectrum dominated by intermediate-width H (930 km/s) and narrow calcium emission lines. The explosion signature (the light curve and spectra) is overall similar to thatof M85OT2006-1, SN2008S, and NGC300OT. The origin of these events is shrouded in mystery and controversy (and in some cases, in dust). PTF10fqs shows some evidence of a broad feature (around 8600A) that may suggest very large velocities (10,000 km/s) in this explosion. Ongoing surveys can be expected to find a few such events per year. Sensitive spectroscopy, infrared monitoring and statistics (e.g. disk versus bulge) will eventually make it possible for astronomers to unravel the nature of these mysterious explosions.Comment: 12 pages, 12 figures, Replaced with published versio