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Platais I.,Johns Hopkins University | Cudworth K.M.,University of Chicago | Kozhurina-Platais V.,US Space Telescope Science Institute | McLaughlin D.E.,Keele University | And 2 more authors.
Astrophysical Journal Letters | Year: 2011

We present comprehensive cluster membership and g′r′ photometry of the prototypical old, metal-rich Galactic star cluster NGC6791. The proper-motion catalog contains 58,901 objects down to g′ 24, limited to a circular area of radius 30′. The highest precision of the proper motions is 0.08 mas yr-1. Our proper motions confirm cluster membership of all main and also some rare constituents of NGC6791. The total number of probable cluster members down to g′ = 22 (MV +8) is 4800, corresponding to M tot 5000 M. New findings include an extended horizontal branch in this cluster. The angular radius of NGC6791 is at least 15′ (the effective radius is Rh ≃ 44 while the tidal radius is rt ≃ 23′). The luminosity function of the cluster peaks at 4.5 and then steadily declines toward fainter magnitudes. Our data provide evidence that differential reddening may not be ignored in NGC6791. © 2011. The American Astronomical Society. All rights reserved.

Morrison G.E.,University of Hawaii at Manoa | Morrison G.E.,Canada France Hawaii Telescope Corporation | Owen F.N.,U.S. National Radio Astronomy Observatory | Dickinson M.,National Optical Astronomy Observatory | And 3 more authors.
Astrophysical Journal, Supplement Series | Year: 2010

We describe deep, new, wide-field radio continuum observations of the Great Observatories Origins Deep Survey-North field. The resulting map has a synthesized beam size of ∼1.7 and an rms noise level of ∼3.9 μJy beam -1 near its center and ∼8 μJy beam -1 at 15′ from phase center. We have cataloged 1230 discrete radio emitters, within a 40′ × 40′ region, above a 5σ detection threshold of ∼20 μJy at the field center. New techniques, pioneered by Owen & Morrison, have enabled us to achieve a dynamic range of 6800:1 in a field that has significantly strong confusing sources. We compare the 1.4 GHz (20 cm) source counts with those from other published radio surveys. Our differential counts are nearly Euclidean below 100 μJy with a median source diameter of ∼1.2. This adds to the evidence presented by Owen & Morrison that the natural confusion limit may lie near 1 μJy. If the Euclidean slope of the counts continues down to the natural confusion limit as an extrapolation of our log N-log S, this indicates that the cutoff must be fairly sharp below 1 μJy else the cosmic microwave background temperature would increase above 2.7 K at 1.4 GHz. © 2010. The American Astronomical Society. All rights reserved.

Van Dyk S.D.,Spitzer Science Center Caltech | Cenko S.B.,University of California at Berkeley | Poznanski D.,Tel Aviv University | Arcavi I.,Weizmann Institute of Science | And 8 more authors.
Astrophysical Journal | Year: 2012

We report on the direct detection and characterization of the probable red supergiant (RSG) progenitor of the intermediate-luminosity TypeII-Plateau (II-P) supernova (SN) 2012aw in the nearby (10.0Mpc) spiral galaxy Messier 95 (M95; NGC3351). We have identified the star in both Hubble Space Telescope images of the host galaxy, obtained 17-18yr prior to the explosion, and near-infrared ground-based images, obtained 6-12yr prior to the SN. The luminous supergiant showed evidence for substantial circumstellar dust, manifested as excess line-of-sight extinction. The effective total-to-selective ratio of extinction to the star was R'V 4.35, which is significantly different from that of diffuse interstellar dust (i.e., RV = 3.1), and the total extinction to the star was therefore, on average, AV 3.1mag. We find that the observed spectral energy distribution for the progenitor star is consistent with an effective temperature of 3600K (spectral typeM3), and that the star therefore had a bolometric magnitude of -8.29. Through comparison with recent theoretical massive-star evolutionary tracks we can infer that the RSG progenitor had an initial mass 15 ≲ M ini(M ⊙) < 20. Interpolating by eye between the available tracks, we surmise that the star had initial mass 17-18 M ⊙. The circumstellar dust around the progenitor must have been destroyed in the explosion, as the visual extinction to the SN is found to be low (AV = 0.24mag with R V = 3.1). © 2012. The American Astronomical Society. All rights reserved.

Duc P.-A.,University Paris Diderot | Paudel S.,University Paris Diderot | McDermid R.M.,Gemini Observatory | Cuillandre J.-C.,Canada France Hawaii Telescope Corporation | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

It has recently been proposed that the dwarf spheroidal galaxies located in the Local Group discs of satellites (DoSs) may be tidal dwarf galaxies (TDGs) born in a major merger at least 5Gyr ago. Whether TDGs can live that long is still poorly constrained by observations. As part of deep optical and HI surveys with the Canada-France-Hawaii Telescope (CFHT) MegaCam camera and Westerbork Synthesis Radio Telescope made within the ATLAS3D project, and follow-up spectroscopic observations with the Gemini-North telescope, we have discovered old TDG candidates around several early-type galaxies. At least one of them has an oxygen abundance close to solar, as expected for a tidal origin. This confirmed pre-enriched object is located within the gigantic, but very low surface brightness, tidal tail that emanates from the elliptical galaxy, NGC 5557. An age of 4 Gyr estimated from its SED fitting makes it the oldest securely identified TDG ever found so far. We investigated the structural and gaseous properties of the TDG and of a companion located in the same collisional debris, and thus most likely of tidal origin as well. Despite several Gyr of evolution close to their parent galaxies, they kept a large gas reservoir. Their central surface brightness is low and their effective radius much larger than that of typical dwarf galaxies of the same mass. This possibly provides us with criteria to identify tidal objects which can be more easily checked than the traditional ones requiring deep spectroscopic observations. In view of the above, we discuss the survival time of TDGs and question the tidal origin of the DoSs. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Croll B.,University of Toronto | Lafreniere D.,University of Montreal | Albert L.,Canada France Hawaii Telescope Corporation | Jayawardhana R.,University of Toronto | And 2 more authors.
Astronomical Journal | Year: 2011

We present Ks, H, &J-band photometry of the very highly irradiated hot Jupiter WASP-12b using the Widefield Infrared Camera on the Canada-France-Hawaii telescope. Our photometry brackets the secondary eclipse of WASP-12b in the Ks and H bands, and in J band starts in mid-eclipse and continues until well after the end of the eclipse. We detect its thermal emission in all three near-infrared bands. Our secondary eclipse depths are 0.309 +0.013 -0.012% in Ks band (24σ), 0.176+0.016 -0.021% in H band (9σ), and 0.131+0.027 -0.029% in J band (4σ). All three secondary eclipses are best fit with a consistent phase, φ , that is compatible with a circular orbit: φ = 0.4998+0.0008 -0.0007. The limits on the eccentricity, e, and argument of periastron, ω, of this planet from our photometry alone are thus |ecos?| < 0.0040. By combining our secondary eclipse times with others published in the literature, as well as the radialvelocity and transit-timing data for this system, we show that there is no evidence that WASP-12b is precessing at a detectable rate and that its orbital eccentricity is likely zero. Our thermal-emission measurements also allow us to constrain the characteristics of the planet's atmosphere; our Ks-band eclipse depth argues strongly in favor of inefficient day to nightside redistribution of heat and a low Bond albedo for this very highly irradiated hot Jupiter. The J- and H-band brightness temperatures are slightly cooler than the Ks-band brightness temperature, and thus hint at the possibility of a modest temperature inversion deep in the atmosphere of WASP-12b; the high-pressure, deep atmospheric layers probed by our J- and H-band observations are likely more homogenized than the higher altitude layer probed by our Ks-band observations. Lastly, our best-fit Ks-band eclipse has a marginally longer duration than would otherwise be expected; this may be tentative evidence for material being tidally stripped from the planet-as was predicted for this system by Li and collaborators, and for which observational confirmation was recently arguably provided by Fossati and collaborators. © 2011. The American Astronomical Society.

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