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Diaz Trigo M.,ESO | Sidoli L.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Boirin L.,11 Rue Of Luniversite | Parmar A.N.,ESAC
Astronomy and Astrophysics | Year: 2012

We analysed data from five XMM-Newton observations of GX 13 + 1 to investigate the variability of the photo-ionised absorber in this source. We fitted EPIC and RGS spectra obtained from the "least-variable" intervals with a model consisting of disc-blackbody and blackbody components together with a Gaussian emission feature at ∼6.55-6.7 keV modified by absorption due to cold and photo-ionised material. We found a significant correlation between the hard, ∼6-10 keV, flux, the ionisation and column density of the absorber and the equivalent width of the broad iron line. We interpret the correlation in a scenario in which a disc wind is thermally driven at large, ∼1010 cm, radii and the broad line results from reprocessed emission in the wind and/or hot atmosphere. The breadth of the emission line is naturally explained by a combination of scattering, recombination and fluorescence processes. We attribute the variations in the absorption and emission along the orbital period to the view of different parts of the wind, possibly located at slightly different inclination angles. We constrain the inclination of GX 13 + 1 to be between 60 and 80° from the strong absorption in the line of sight, which obscures up to 80% of the total emission in one observation, and the absence of eclipses. We conclude that either a disc wind and/or a hot atmosphere can explain the current observations of narrow absorption and broad iron emission features in neutron star low-mass X-ray binaries as a class. © 2012 ESO.

Trigo M.D.,ESO | Boirin L.,11 Rue Of Luniversite
Acta Polytechnica | Year: 2013

We review the current status of studies of disc atmospheres and winds in low mass X-ray binaries. We discuss the possible wind launching mechanisms and compare the predictions of the models with the existent observations. We conclude that a combination of thermal and radiative pressure (the latter being relevant at high luminosities) can explain the current observations of atmospheres and winds in both neutron star and black hole binaries. Moreover, these winds and atmospheres could contribute significantly to the broad iron emission line observed in these systems. © Czech Technical University in Prague, 2013.

Halbwachs J.-L.,11 Rue Of Luniversite | Mayor M.,Observatoire de Geneva | Udry S.,Observatoire de Geneva
Monthly Notices of the Royal Astronomical Society | Year: 2012

Wide binaries are tracers of the gravity field of the Galaxy, but their study requires some caution. A large list of common proper motion stars selected from the third Astronomischen Gesellschaft Katalog (AGK3) was monitored with the CORAVEL (for COrrelation RAdial VELocities) spectrovelocimeter, in order to prepare a sample of physical binaries with very wide separations. 66 stars received special attention, since their radial velocities (RV) seemed to be variable. These stars were monitored over several years in order to derive the elements of their spectroscopic orbits. In addition, 10 of them received accurate RV measurements from the SOPHIE spectrograph of the T193 telescope at the Observatory of Haute-Provence. For deriving the orbital elements of double-lined spectroscopic binaries (SB2), a new method was applied, which assumed that the RV of blended measurements are linear combinations of the RV of the components. 13 SB2 orbits were thus calculated. The orbital elements were eventually obtained for 52 spectroscopic binaries (SB), two of them making a triple system. 40 SB received their first orbit and the orbital elements were improved for 10 others. In addition, 11 SB were discovered with very long periods for which the orbital parameters were not found. The median period of the 40 first orbits is 1yr, and several SB should be resolved or should receive an astrometric orbit in future, providing the masses of the components. In addition, it appeared that HD153252 has a close companion, which is a candidate brown dwarf with a minimum mass of 50 Jupiter masses. The final selection of wide binaries and the derivation of their statistical properties will be presented in a second paper. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Mouhcine M.,Liverpool John Moores University | Ibata R.,11 Rue Of Luniversite | Rejkuba M.,European Southern Observatory
Astrophysical Journal Letters | Year: 2010

Recent panoramic observations of the dominant spiral galaxies of the Local Group have revolutionized our view of how these galaxies assemble their mass. However, it remains completely unclear whether the properties of the outer regions of the Local Group large spirals are typical. Here, we present the first panoramic view of a spiral galaxy beyond the Local Group, based on the largest, contiguous, ground-based imaging survey to date resolving the stellar halo of the nearest prime analog of the Milky Way, NGC 891 (D ≈ 10 Mpc). The low surface brightness outskirts of this galaxy are populated by multiple, coherent, and vast substructures over the ∼ 90 kpc × ∼ 90 kpc extent of the survey. These include a giant stream, the first to be resolved into stars beyond the Local Group using ground-based facilities, that loops around the parent galaxy up to distances of ∼ 50 kpc. The bulge and the disk of the galaxy are found to be surrounded by a previously undetected large, flat, and thick cocoon-like stellar structure at vertical and radial distances of up to ∼ 15 kpc and ∼ 40 kpc, respectively. © 2010. The American Astronomical Society.

Dovciak M.,Czech Republic Astronomical Institute | Muleri F.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Goosmann R.W.,11 Rue Of Luniversite | Karas V.,Czech Republic Astronomical Institute | Matt G.,Third University of Rome
Astrophysical Journal | Year: 2011

We discuss a model of an X-ray illuminating source above an accretion disk of a rotating black hole. Within the so-called lamp-post scheme we compute the expected (observed) polarization properties of the radiation reaching an observer. We explore the dependences on model parameters, employing Monte Carlo radiation transfer computations of the X-ray reflection on the accretion disk and taking general relativity effects into account. In particular, we discuss the role of the black hole spin, of the observer viewing angle, and of the primary X-ray source distance from the black hole. We give several examples of the resulting polarization degree for two types of exemplary objects - active galactic nuclei and Galactic black holes. In order to assess potential observability of the polarization features, we assume the sensitivity of the proposed New Hard X-ray Mission (NHXM). We examine the energy range from several keV to ∼50 keV, so the iron line complex and the Compton hump are included in our model spectra. We find the resultant polarization degree to increase at the higher end of the studied energy band, i.e., at ≳20 keV. Thus, the best results for polarimetry of reflection spectra should be achieved at the Compton hump energy region. We also obtain a higher polarization degree for large spin values of the black hole, small heights of the primary source, and low inclination angles of the observer. © 2011. The American Astronomical Society. All rights reserved.

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