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Saint-Rémy-de-Provence, France

Galliano E.,Observatorio Nacional | Kissler-Patig M.,European Southern Observatory | Alloin D.,Observatoire de Haute Provence | Telles E.,Observatorio Nacional
Astronomy and Astrophysics | Year: 2012

This paper presents and examines new near-infrared integral field observations of the three so-called "embedded star clusters" located in the nuclear region of NGC 1365. Adaptive-optics-corrected K-band data cubes were obtained with the ESO/VLT instrument SINFONI. The continuum in the K-band and emission lines such as He I, Brγ, and several H2 lines were mapped at an achieved angular resolution of 0.2′ over a field of 3 × 3′2 around each source. We find that the continuum emission of the sources is spatially resolved. This means that they are indeed cluster complexes confined to regions of about 50 pc extension. We performed robust measurements of the equivalent width of the CO absorption band at 2.3 μm and of Brγ. For the main mid-infrared bright sources, the data only allow us to determine an upper limit to the equivalent width of the CO bands. Under the assumption of an instantaneously formed standard initial mass function Starburst99 model, the new measurements are found to be incompatible with previously published mid-infrared line ratios. We show that an upper mass limit of 25 to 30 M·, lower than the typically assumed 100 M ·, allows one to simply remove this inconsistency. For such a model, the measurements are consistent with ages in the range of 5.5 Myr to 6.5 Myr, implying masses in the range from 3 to 10 × 106 M ·. We detect extended gas emission both in H ii and H 2. We argue that the central cluster complexes are the sources of excitation for the whole nebulae, through ionisation and shock heating. We detect a blue wing on the Brγ emission profile, suggesting the existence of gas outflows centred on the cluster complexes. We do not find any evidence for the presence of a lower mass cluster population, which would fill up a "traditional" power law cluster mass function. © 2012 ESO.

Coward D.M.,University of Western Australia | Heary A.,University of Western Australia | Venville G.,University of Western Australia | Todd M.,Curtin University Australia | And 5 more authors.
Advances in Space Research | Year: 2011

This paper describes plans for employing a new fully robotic optical telescope in Western Australia, the Zadko telescope, for evaluating education-outreach. A key feature of the telescope is the optimized observation-scheduling program, developed by our French collaborators who operate the TAROT robotic telescope network. It provides a simple interface for requesting observation time remotely, and has the potential for school students to participate in real astronomical research. The University of Western Australia and Curtin University are commencing a study for evaluating changes in student perceptions of science by participation in our astronomy research. Other areas of interest include broadening the program to include access of students from European countries, and exploring how remote access astronomy can be used to encourage awareness between different cultures. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.

Coward D.M.,University of Western Australia | Gendre B.,Science Data Center | Sutton P.J.,University of Cardiff | Howell E.J.,University of Western Australia | And 6 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2011

Observations of an optical source coincident with gravitational wave emission detected from a binary neutron star coalescence will improve the confidence of detection, provide host galaxy localization and test models for the progenitors of short gamma-ray bursts. We employ optical observations of three short gamma-ray bursts, 050724, 050709 and 051221, to estimate the detection rate of a coordinated optical and gravitational wave search of neutron star mergers. ModelR-band optical afterglow light curves of these bursts that include a jet-break are extrapolated for these sources at the sensitivity horizon of an Advanced LIGO/Virgo network. Using optical sensitivity limits of three telescopes, namely TAROT (m= 18), Zadko (m= 21) and an 8-10m class telescope (m= 26), we approximate detection rates and cadence times for imaging. We find a median coincident detection rate of 4yr-1 for the three bursts. GRB 050724 like bursts, with wide opening jet angles, offer the most optimistic rate of 13 coincident detections per year, and would be detectable by Zadko up to 5d after the trigger. Late-time imaging tom= 26 could detect off-axis afterglows for GRB 051221 like bursts several months after the trigger. For a broad distribution of beaming angles, the optimal strategy for identifying the optical emissions triggered by gravitational wave detectors is rapid response searches with robotic telescopes followed by deeper imaging at later times if an afterglow is not detected within several days of the trigger. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Fabas N.,Montpellier University | Lebre A.,Montpellier University | Gillet D.,Observatoire de Haute Provence
Astronomy and Astrophysics | Year: 2011

Context. In the spectra of variable pulsating stars, especially Mira stars, the detection of intense hydrogen emission lines has been explained by the presence of a radiative and hypersonic shock wave, periodically propagating throughout the stellar atmosphere. Previous observation of the Mira star o Ceti around one of its brightest maximum light led to the detection of a strong level of linear polarization associated to Balmer emissions, although the origin of this phenomenon is not fully explained yet. Aims. With the help of spectropolarimetry, we propose to investigate the nature of shock waves propagating throughout the stellar atmosphere and present, for o Ceti (the prototype of Mira stars), a full observational study of hydrogen emission lines formed in the radiative region of such a shock. Methods. Using the instrument NARVAL mounted on the Télescope Bernard Lyot (TBL) in Pic du Midi Observatory (France), we performed a spectropolarimetric monitoring of o Ceti during three consecutive pulsation cycles. For this survey, the four Stokes parameters (I for intensity, Q and U for linear polarization, and V for circular polarization) were systematically collected, with a particular emphasis on the maxima of luminosity, i.e. when a radiative shock wave is supposed to emerge from the photosphere and starts to propagate outward. Results. On hydrogen Balmer lines, over a large part of the luminosity cycle, we report clear detection of polarimetric structures in Q and U Stokes spectra (and also in V Stokes spectra but to a lesser extent). We report a temporal evolution of these spectropolarimetric signatures, which appear strongly correlated to the presence of an intense shock wave responsible for the hydrogen emission lines. We establish that the hydrogen lines are polarized by a physical process inherent to the mechanism responsible for the emission line formation: the shock wave itself. Two mechanisms are thus considered: a global one that implies a polarization induced by some giant convective cells located around the photosphere and a local one that implies a charge separation due to the passage of the shock wave, inducing an electrical current. Combined with the existing turbulence, this may generate a magnetic field, hence polarization. © 2011 ESO.

Coward D.M.,University of Western Australia | Todd M.,Curtin University Australia | Vaalsta T.P.,University of Western Australia | Laas-Bourez M.,University of Western Australia | And 16 more authors.
Publications of the Astronomical Society of Australia | Year: 2010

The new 1m f/4 fast-slew Zadko Telescope was installed in June 2008 about 70km north of Perth, Western Australia. It is the only metre-class optical facility at this southern latitude between the east coast of Australia and South Africa, and can rapidly image optical transients at a longitude not monitored by other similar facilities. We report on first imaging tests of a pilot program of minor planet searches, and Target of Opportunity observations triggered by the Swift satellite. In 12 months, 6gamma-ray burst afterglows were detected, with estimated magnitudes; two of them, GRB 090205 (z=4.65) and GRB 090516 (z=4.11), are among the most distant optical transients imaged by an Australian telescope. Many asteroids were observed in a systematic 3-month search. In September 2009, an automatic telescope control system was installed, which will be used to link the facility to a global robotic telescope network; future targets will include fast optical transients triggered by high-energy satellites, radio transient detections, and LIGO gravitational wave candidate events. We also outline the importance of the facility as a potential tool for education, training, and public outreach. © Astronomical Society of Australia 2010.

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