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Sanchis-Ojeda R.,Massachusetts Institute of Technology | Rappaport S.,Massachusetts Institute of Technology | Winn J.N.,Massachusetts Institute of Technology | Levine A.,Mit Kavli Institute For Astrophysics And Space Research | And 3 more authors.
Astrophysical Journal | Year: 2013

We report the discovery of an Earth-sized planet (1.16 ± 0.19 R ⊕) in an 8.5 hr orbit around a late G-type star (KIC 8435766, Kepler-xx). The object was identified in a search for short-period planets in the Kepler database and confirmed to be a transiting planet (as opposed to an eclipsing stellar system) through the absence of ellipsoidal light variations or substantial radial-velocity variations. The unusually short orbital period and the relative brightness of the host star (m Kep = 11.5) enable robust detections of the changing illumination of the visible hemisphere of the planet, as well as the occultations of the planet by the star. We interpret these signals as representing a combination of reflected and reprocessed light, with the highest planet dayside temperature in the range of 2300 K-3100 K. Follow-up spectroscopy combined with finer sampling photometric observations will further pin down the system parameters and may even yield the mass of the planet. © 2013. The American Astronomical Society. All rights reserved.

Mineo S.,Harvard - Smithsonian Center for Astrophysics | Rappaport S.,Kavli Institute for Astrophysics and Space Research | Steinhorn B.,Harvard-MIT Division of Health Sciences and Technology | Levine A.,Mit Kavli Institute For Astrophysics And Space Research | And 3 more authors.
Astrophysical Journal | Year: 2013

The colliding galaxy pair NGC 2207/IC 2163, at a distance of ∼39 Mpc, was observed with Chandra, and an analysis reveals 28 well resolved X-ray sources, including 21 ultraluminous X-ray sources (ULXs) with LX ≳ 1039 erg s-1, as well as the nucleus of NGC 2207. The number of ULXs is comparable with the largest numbers of ULXs per unit mass in any galaxy yet reported. In this paper we report on these sources, and quantify how their locations correlate with the local star formation rates seen in spatially resolved star formation rate density images that we have constructed using combinations of GALEX FUV and Spitzer 24 μm images. We show that the numbers of ULXs are strongly correlated with the local star formation rate densities surrounding the sources, but that the luminosities of these sources are not strongly correlated with star formation rate density. © 2013. The American Astronomical Society. All rights reserved..

Mineo S.,Harvard - Smithsonian Center for Astrophysics | Mineo S.,Max Planck Institute for Astrophysics | Rappaport S.,Kavli Institute for Astrophysics and Space Research | Rappaport S.,Eureka Scientific Inc. | And 5 more authors.
Astrophysical Journal | Year: 2014

We present a comprehensive study of the total X-ray emission from the colliding galaxy pair NGC 2207/IC 2163, based on Chandra, Spitzer, and GALEX data. We detect 28 ultraluminous X-ray sources (ULXs), 7 of which were not detected previously because of X-ray variability. Twelve sources show significant long-term variability, with no correlated spectral changes. Seven sources are transient candidates. One ULX coincides with an extremely blue star cluster (B - V = -0.7). We confirm that the global relation between the number and luminosity of ULXs and the integrated star-formation rate (SFR) of the host galaxy also holds on local scales.We investigate the effects of dust extinction and age on the X-ray binary (XRB) population on subgalactic scales. The distributions of NX and LX are peaked at LIR/LNUV ∼ 1, which may be associated with an age of ∼ 10 Myr for the underlying stellar population. We find that approximately one-third of the XRBs are located in close proximity to young star complexes. The luminosity function of the XRBs is consistent with that typical for high-mass XRBs and appears unaffected by variability.We disentangle and compare the X-ray diffuse spectrum with that of the bright XRBs. The hot interstellar medium dominates the diffuse X-ray emission at E ≲ 1 keV and has a temperature kT = 0.28-0.04+0.05 keVand intrinsic 0.5-2 keV luminosity of 7.9 × 1040 erg s-1, a factor of ∼2.3 higher than the average thermal luminosity produced per unit SFR in local star-forming galaxies. The total X-ray output of NGC 2207/IC 2163 is 1.5 × 1041 erg s-1, and the corresponding total integrated SFR is 23.7M⊙ yr-1. © 2014. The American Astronomical Society. All rights reserved.

Carter J.A.,Mit Kavli Institute For Astrophysics And Space Research | Carter J.A.,Harvard - Smithsonian Center for Astrophysics | Rappaport S.,Mit Kavli Institute For Astrophysics And Space Research | Fabrycky D.,Harvard - Smithsonian Center for Astrophysics | Fabrycky D.,University of California at Santa Cruz
Astrophysical Journal | Year: 2011

We have found a system listed in the Kepler Binary Catalog (Porb = 3.273 days) that we have determined is comprised of a low-mass, thermally bloated, hot white dwarf orbiting an A star of about 2.3 M⊙. In this work, we designate the object, KIC 10657664, simply as "KHWD3" (Kepler Hot White Dwarf 3). We use the transit depth of ∼0.66%, the eclipse depth of ∼1.9%, and regular smooth periodic variations at the orbital frequency and twice the orbital frequency to analyze the system parameters. The smooth periodic variations are identified with the classical ellipsoidal light variation (ELV) and illumination (ILL) effects, and the newly utilized Doppler boosting (DB) effect. Given the measured values of R/a and inclination angle of the binary, both the ELV and DB effects are mostly sensitive to the mass ratio, q = M2/M1, of the binary. The two effects yield values of q which are somewhat inconsistent-presumably due to unidentified systematic effects-but which nonetheless provide a quite useful set of possibilities for the mass of the white dwarf (either 0.26 ± 0.04 M⊙ or 0.37 ± 0.08 M⊙). All of the other system parameters are determined fairly robustly. In particular, we show that the white dwarf has a radius of 0.15 ± 0.01 R⊙, which is extremely bloated over the radius it would have as a fully degenerate object, and an effective temperature Teff ≈ 14,500 K. Binary evolution scenarios and models for this system are discussed. We suggest that the progenitor binary was comprised of a primary of mass ∼2.2 M⊙ (the progenitor of the current hot white dwarf) and a secondary of mass ∼1.4 M⊙ (the progenitor of the current A star in the system). We compare this new system with three other white dwarfs in binaries that likely were formed via stable Roche-lobe overflow (KOI-74, KOI-81, and the inner Regulus binary). © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

Matt G.,Third University of Rome | Bianchi S.,Third University of Rome | Bianchi S.,National institute for astrophysics | Guainazzi M.,European Space Agency | And 8 more authors.
Astronomy and Astrophysics | Year: 2011

Context. In about half of the Seyfert galaxies, the X-ray emission is absorbed by an optically thin, ionized medium, the so-called "warm absorber", whose origin and location is still a matter of debate. Aims. The aim of this paper is to constrain the warm absorber further by studying its variability. Methods. We analyzed the X-ray spectra of a Seyfert 1 galaxy, Mrk 704, which was observed twice, three years apart, by XMM-Newton. Results. The spectra were well fitted with a two-zones absorber, which possibly covers the source only partially. The parameters of the absorbing matter - column density, ionization state, covering factor - changed significantly between the two observations. Possible explanations for the more ionized absorber are a torus wind (the source is a polar scattering one) or, in the partial covering scenario, an accretion disk wind. The less ionized absorber is possibly composed of orbiting clouds in the surroundings of the nucleus, similarly to what was already found in other sources, most notably NGC 1365. © ESO, 2011.

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