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Haswell C.A.,Open University Milton Keynes | Fossati L.,Open University Milton Keynes | Ayres T.,University of Colorado at Boulder | France K.,University of Colorado at Boulder | And 14 more authors.
Astrophysical Journal | Year: 2012

Extended gas clouds have been previously detected surrounding the brightest known close-in transiting hot Jupiter exoplanets, HD 209458b and HD 189733b; we observed the distant but more extreme close-in hot Jupiter system, WASP-12, with Hubble Space Telescope (HST). Near-UV (NUV) transits up to three times deeper than the optical transit of WASP-12b reveal extensive diffuse gas, extending well beyond the Roche lobe. The distribution of absorbing gas varies between visits. The deepest NUV transits are at wavelength ranges with strong stellar photospheric absorption, implying that the absorbing gas may have temperature and composition similar to those of the stellar photosphere. Our spectra reveal significantly enhanced absorption (greater than 3σ below the median) at 200 individual wavelengths on each of two HST visits; 65 of these wavelengths are consistent between the two visits, using a strict criterion for velocity matching that excludes matches with velocity shifts exceeding 20 km s-1. Excess transit depths are robustly detected throughout the inner wings of the Mg II resonance lines independently on both HST visits. We detected absorption in Fe II λ2586, the heaviest species yet detected in an exoplanet transit. The Mg II line cores have zero flux, emission cores exhibited by every other observed star of similar age and spectral type are conspicuously absent. WASP-12 probably produces normal Mg II profiles, but the inner portions of these strong resonance lines are likely affected by extrinsic absorption. The required Mg+ column is an order of magnitude greater than expected from the interstellar medium, though we cannot completely dismiss that possibility. A more plausible source of absorption is gas lost by WASP-12b. We show that planetary mass loss can produce the required column. Our Visit2 NUV light curves show evidence for a stellar flare. We show that some of the possible transit detections in resonance lines of rare elements may be due instead to non-resonant transitions in common species. We present optical observations and update the transit ephemeris. © 2012. The American Astronomical Society. All rights reserved..

Creevey O.L.,Institute of Astrophysics of Canarias | Creevey O.L.,University of La Laguna | Metcalfe T.S.,High Altitude Observatory | Brown T.M.,Las Cumbres Observatory Global Telescope Network Inc. | And 3 more authors.
Astrophysical Journal | Year: 2011

Many stars exhibit stellar pulsations, favoring them for asteroseismic analyses. Interpreting the oscillations requires some knowledge of the oscillation mode geometry (spherical degree, radial, and azimuthal orders). The δ Scuti stars (1.5-2.5 M⊙) often show just one or few pulsation frequencies. Although this may promise a successful seismological analysis, we may not know enough about either the mode or the star to use the oscillation frequency to improve the determination of the stellar model or to probe the star's structure. For the observed frequencies to be used successfully as seismic probes of these objects, we need to concentrate on stars for which we can reduce the number of free parameters in the problem, such as binary systems or open clusters. We investigate how much our understanding of a δ Scuti star is improved when it is in a detached eclipsing binary system instead of being a single field star. We use singular value decomposition to explore the precision we expect in stellar parameters (mass, age, and chemical composition) for both cases. We examine how the parameter uncertainties propagate to the luminosity-effective temperature diagram and determine when the effort of obtaining a new measurement is justified. We show that for the single star, a correct identification of the oscillation mode is necessary to produce strong constraints on the stellar model properties, while for the binary system the observations without the pulsation mode provide the same or better constraints on the stellar parameters. In the latter case, the strong constraints provided by the binary system not only allow us to detect an incorrectly identified oscillation mode, but we can also constrain the oscillation mode geometry by comparing the distribution of possible solutions with and without including the oscillation frequency as a constraint. © 2011. The American Astronomical Society. All rights reserved..

Gomez H.L.,University of Cardiff | Vlahakis C.,Leiden University | Stretch C.M.,University of Cardiff | Dunne L.,University of Nottingham | And 5 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2010

Previous submillimetre (submm) observations detected 0.7 M. of cool dust emission around the luminous blue variable (LBV) star η Carinae. These observations were hindered by the low declination of η Carinae and contamination from free-free emission originating from the stellar wind. Here, we present deep submm observations with LABOCA at 870 μm, taken shortly after a maximum in the 5.5-year radio cycle. We find a significant difference in the submm flux measured here compared with the previous measurement: the first indication of variability at submm wavelengths. A comparison of the submm structures with ionized emission features suggests the 870 μm is dominated by emission from the ionized wind and not thermal emission from dust. We estimate 0.4 ±0.1 M. of dust surrounding η Carinae. The spatial distribution of the submm emission limits the mass loss to within the last thousand years, and is associated with mass ejected during the great eruptions and the pre-outburst LBV wind phase; we estimate that η Carinae has ejected >40 M. of gas within this time-scale. © 2009 RAS.

Adams J.J.,University of Texas at Austin | Blanc G.A.,University of Texas at Austin | Hill G.J.,University of Texas at Austin | Gebhardt K.,University of Texas at Austin | And 29 more authors.
Astrophysical Journal, Supplement Series | Year: 2011

We present a catalog of emission-line galaxies selected solely by their emission-line fluxes using a wide-field integral field spectrograph. This work is partially motivated as a pilot survey for the upcoming Hobby-Eberly Telescope Dark Energy Experiment. We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information for 397 emission-line galaxies detected over 169 □′ with a 3500-5800 Å bandpass under 5 Å full-width-half-maximum (FWHM) spectral resolution. The survey's best sensitivity for unresolved objects under photometric conditions is between 4 and 20 × 10-17 erg s-1 cm-2 depending on the wavelength, and Lya luminosities between 3 × 10 42 and 6 × 1042 erg s-1 are detectable. This survey method complements narrowband and color-selection techniques in the search of high-redshift galaxies with its different selection properties and large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS, and XMM-LSS areas are rich with existing, complementary data. We find 105 galaxies via their high-redshift Lya emission at 1.9 < z < 3.8, and the majority of the remainder objects are low-redshift [Oii]3727 emitters at z < 0.56. The classification between low-and high-redshift objects depends on rest-frame equivalent width (EW), as well as other indicators, where available. Based on matches to X-ray catalogs, the active galactic nuclei fraction among the Lya emitters is 6%. We also analyze the survey's completeness and contamination properties through simulations. We find five high-z, highly significant, resolved objects with FWHM sizes >44 □″ which appear to be extended Lyα nebulae. We also find three high-z objects with rest-frame Lya EW above the level believed to be achievable with normal star formation, EW0 > 240 Å. Future papers will investigate the physical properties of this sample. © 2011. The American Astronomical Society. All rights reserved. Printedin the U.S.A.

White C.J.,Princeton University | Kasliwal M.M.,Carnegie Institution for Science | Nugent P.E.,Lawrence Berkeley National Laboratory | Nugent P.E.,University of California at Berkeley | And 26 more authors.
Astrophysical Journal | Year: 2015

Since the discovery of the unusual prototype SN 2002cx, the eponymous class of Type I (hydrogen-poor) supernovae with low ejecta speeds has grown to include approximately two dozen members identified from several heterogeneous surveys, in some cases ambiguously. Here we present the results of a systematic study of 1077 Type I supernovae discovered by the Palomar Transient Factory, leading to nine new members of this peculiar class. Moreover, we find there are two distinct subclasses based on their spectroscopic, photometric, and host galaxy properties: "SN 2002cx-like" supernovae tend to be in later-type or more irregular hosts, have more varied and generally dimmer luminosities, have longer rise times, and lack a Ti II trough when compared to "SN 2002es-like" supernovae. None of our objects show helium, and we counter a previous claim of two such events. We also find that the occurrence rate of these transients relative to Type Ia supernovae is (90% confidence), lower compared to earlier estimates. Combining our objects with the literature sample, we propose that these subclasses have two distinct physical origins. © 2015. The American Astronomical Society. All rights reserved.

Kasliwal M.M.,California Institute of Technology | Kasliwal M.M.,Carnegie Institution for Science | Kulkarni S.R.,California Institute of Technology | Gal-Yam A.,Weizmann Institute of Science | And 28 more authors.
Astrophysical Journal | Year: 2012

From the first two seasons of the Palomar Transient Factory, we identify three peculiar transients (PTF09dav, PTF10iuv, and PTF11bij) with five distinguishing characteristics: peak luminosity in the gap between novae and supernovae (MR ≈ -15.5 to -16.5mag), rapid photometric evolution (t rise 12-15days), large photospheric velocities (6000-11,000km s-1), early spectroscopic evolution into nebular phase (1-3months), and peculiar nebular spectra dominated by calcium. We also culled the extensive decade-long Lick Observatory Supernova Search database and identified an additional member of this group, SN2007ke. Our choice of photometric and spectroscopic properties was motivated by SN2005E (Perets et al.). To our surprise, as in the case of SN2005E, all four members of this group are also clearly offset from the bulk of their host galaxy. Given the well-sampled early- and late-time light curves, we derive ejecta masses in the range of 0.4-0.7M ⊙. Spectroscopically, we find that there may be a diversity in the photospheric phase, but the commonality is in the unusual nebular spectra. Our extensive follow-up observations rule out standard thermonuclear and standard core-collapse explosions for this class of "calcium-rich gap" transients. If the progenitor is a white dwarf, we are likely seeing a detonation of the white dwarf core and perhaps even shock-front interaction with a previously ejected nova shell. If the progenitor is a massive star, a nonstandard channel specific to a low-metallicity environment needs to be invoked (e.g., ejecta fallback leading to black hole formation). Detection (or the lack thereof) of a faint underlying host (dwarf galaxy and cluster) will provide a crucial and decisive diagnostic to choose between these alternatives. © 2012. The American Astronomical Society. All rights reserved.

Price-Whelan A.M.,Columbia University | Agueros M.A.,Columbia University | Fournier A.P.,University of California at Santa Barbara | Fournier A.P.,Las Cumbres Observatory Global Telescope Network Inc. | And 7 more authors.
Astrophysical Journal | Year: 2014

Many photometric time-domain surveys are driven by specific goals, such as searches for supernovae or transiting exoplanets, which set the cadence with which fields are re-imaged. In the case of the Palomar Transient Factory (PTF), several sub-surveys are conducted in parallel, leading to non-uniform sampling over its ∼20,000 deg2 footprint. While the median 7.26 deg 2 PTF field has been imaged ∼40 times in the R band, ∼2300 deg2 have been observed >100 times. We use PTF data to study the trade off between searching for microlensing events in a survey whose footprint is much larger than that of typical microlensing searches, but with far-from-optimal time sampling. To examine the probability that microlensing events can be recovered in these data, we test statistics used on uniformly sampled data to identify variables and transients. We find that the von Neumann ratio performs best for identifying simulated microlensing events in our data. We develop a selection method using this statistic and apply it to data from fields with >10 R-band observations, 1.1 × 109 light curves, uncovering three candidate microlensing events. We lack simultaneous, multi-color photometry to confirm these as microlensing events. However, their number is consistent with predictions for the event rate in the PTF footprint over the survey's three years of operations, as estimated from near-field microlensing models. This work can help constrain all-sky event rate predictions and tests microlensing signal recovery in large data sets, which will be useful to future time-domain surveys, such as that planned with the Large Synoptic Survey Telescope. © 2014. The American Astronomical Society. All rights reserved.

Law N.M.,University of Toronto | Kraus A.L.,University of Hawaii at Manoa | Street R.,Las Cumbres Observatory Global Telescope Network Inc. | Fulton B.J.,Las Cumbres Observatory Global Telescope Network Inc. | And 24 more authors.
Astrophysical Journal | Year: 2012

We present three new eclipsing white-dwarf/M-dwarf binary systems discovered during a search for transiting planets around M-dwarfs. Unlike most known eclipsing systems of this type, the optical and infrared emission is dominated by the M-dwarf components, and the systems have optical colors and discovery light curves consistent with being Jupiter-radius transiting planets around early M-dwarfs. We detail the PTF/M-dwarf transiting planet survey, part of the Palomar Transient Factory (PTF). We present a graphics processing unit (GPU)-based box-least-squares search for transits that runs approximately 8 × faster than similar algorithms implemented on general purpose systems. For the discovered systems, we decompose low-resolution spectra of the systems into white-dwarf and M-dwarf components, and use radial velocity measurements and cooling models to estimate masses and radii for the white dwarfs. The systems are compact, with periods between 0.35 and 0.45days and semimajor axes of approximately 2 R ⊙ (0.01AU). The M-dwarfs have masses of approximately 0.35 M ⊙, and the white dwarfs have hydrogen-rich atmospheres with temperatures of around 8000K and have masses of approximately 0.5 M ⊙. We use the Robo-AO laser guide star adaptive optics system to tentatively identify one of the objects as a triple system. We also use high-cadence photometry to put an upper limit on the white-dwarf radius of 0.025 R ⊙ (95% confidence) in one of the systems. Accounting for our detection efficiency and geometric factors, we estimate that (90% confidence) of M-dwarfs are in these short-period, post-common-envelope white-dwarf/M-dwarf binaries where the optical light is dominated by the M-dwarf. The lack of detections at shorter periods, despite near-100% detection efficiency for such systems, suggests that binaries including these relatively low-temperature white dwarfs are preferentially found at relatively large orbital radii. Similar eclipsing binary systems can have arbitrarily small eclipse depths in red bands and generate plausible small-planet-transit light curves. As such, these systems are a source of false positives for M-dwarf transiting planet searches. We present several ways to rapidly distinguish these binaries from transiting planet systems. © 2012. The American Astronomical Society. All rights reserved.

Chen T.-W.,Queen's University of Belfast | Smartt S.J.,Queen's University of Belfast | Bresolin F.,Institute for Astronomy | Pastorello A.,National institute for astrophysics | And 6 more authors.
Astrophysical Journal Letters | Year: 2013

Super-luminous supernovae have a tendency to occur in faint host galaxies which are likely to have low mass and low metallicity. While these extremely luminous explosions have been observed from z = 0.1 to 1.55, the closest explosions allow more detailed investigations of their host galaxies. We present a detailed analysis of the host galaxy of SN 2010gx (z = 0.23), one of the best studied super-luminous type Ic supernovae. The host is a dwarf galaxy (M g = -17.42 ± 0.17) with a high specific star formation rate. It has a remarkably low metallicity of 12 + log (O/H) = 7.5 ± 0.1 dex as determined from the detection of the [O III] λ4363 line. This is the first reliable metallicity determination of a super-luminous stripped-envelope supernova host. We collected deep multi-epoch imaging with Gemini + GMOS between 240 and 560 days after explosion to search for any sign of radioactive 56Ni, which might provide further insights on the explosion mechanism and the progenitor's nature. We reach griz magnitudes of m AB ∼ 26, but do not detect SN 2010gx at these epochs. The limit implies that any 56Ni production was similar to or below that of SN 1998bw (a luminous type Ic SN that produced around 0.4 M⊙ of 56Ni). The low volumetric rates of these supernovae (∼10-4 of the core-collapse population) could be qualitatively matched if the explosion mechanism requires a combination of low-metallicity (below 0.2 Z ⊙), high progenitor mass (>60M) and high rotation rate (fastest 10% of rotators). © 2013. The American Astronomical Society. All rights reserved.

Saunders E.S.,Las Cumbres Observatory Global Telescope Network Inc. | Lampoudi S.,Liquid Robotics, Inc. | Lister T.A.,Las Cumbres Observatory Global Telescope Network Inc. | Norbury M.,Las Cumbres Observatory Global Telescope Network Inc. | Walker Z.,Las Cumbres Observatory Global Telescope Network Inc.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Las Cumbres Observatory Global Telescope (LCOGT) is developing a worldwide network of fully robotic optical telescopes dedicated to time-domain astronomy. Observatory automation, longitudinal spacing of the sites, and a centralised network scheduler enable a range of observing modes impossible with traditional manual observing from a single location. We discuss the design goals of the LCOGT network scheduler, and in particular examine the unique network characteristics we seek to exploit for novel observing. We present an analysis of the key design trade-offs informing the scheduling architecture and data model, with special emphasis on both the unusual capabilities we have implemented, and some of the limitations of our approach. Finally, we describe some of the lessons we have learnt as we have moved from the beta test phase into full operational deployment in 2014. © 2014 SPIE.

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