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Rigaut F.O.,Australian National University | Neichel B.,Gemini Observatory | Boccas M.,Gemini Observatory | d'Orgeville C.,Australian National University | And 26 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The Gemini multiconjugate adaptive optics system (GeMS) at the Gemini South telescope in Cerro Pachón is the first sodium-based multilaser guide star (LGS) adaptive optics system. It uses five LGSs and two deformable mirrors to measure and compensate for atmospheric distortions. The GeMS project started in 1999, and saw first light in 2011. It is now in regular operation, producing images close to the diffraction limit in the near-infrared, with uniform quality over a field of view of two square arcminutes. This paper is the first one in a two-paper review of GeMS. It describes the system, explains why and how it was built, discusses the design choices and trade-offs, and presents the main issues encountered during the course of the project. Finally, we briefly present the results of the system first light. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Podio L.,Institute Of Planetologie Et Dastrophysique Of Grenoble | Podio L.,Kapteyn Institute | Kamp I.,Kapteyn Institute | Flower D.,Durham University | And 9 more authors.
Astronomy and Astrophysics | Year: 2012

Context. Observations of the atomic and molecular line emission associated with jets and outflows emitted by young stellar objects provide sensitive diagnostics of the excitation conditions, and can be used to trace the various evolutionary stages they pass through as they evolve to become main sequence stars. Aims. To understand the relevance of atomic and molecular cooling in shocks, and how accretion and ejection efficiency evolves with the evolutionary state of the sources, we will study the far-infrared counterparts of bright optical jets associated with Class I and II sources in Taurus (T Tau, DG Tau A, DG Tau B, FS Tau A+B, and RW Aur). Methods. We have analysed Herschel/PACS observations of a number of atomic ([O i]63 μm, 145 μm, [C ii]158 μm) and molecular (high-J CO, H 2O, OH) lines, collected within the open time key project GASPS (PI: W. R. F. Dent). To constrain the origin of the detected lines we have compared the obtained FIR emission maps with the emission from optical-jets and millimetre-outflows, and the measured line fluxes and ratios with predictions from shock and disk models. Results. All of the targets are associated with extended emission in the atomic lines; in particular, the strong [O≠i] 63 μm≠emission is correlated with the direction of the optical jet/mm-outflow. The line ratios suggest that the atomic lines can be excited in fast dissociative J-shocks occurring along the jet. The molecular emission, on the contrary, originates from a compact region, that is spatially and spectrally unresolved, and lines from highly excited levels are detected (e.g., the o-H 2O 8 18-7 07 line, and the CO J = 36-35 line). Disk models are unable to explain the brightness of the observed lines (CO and H 2O line fluxes up to 10 -15-6 × 10 -16 W m -2). Slow C-or J-shocks with high pre-shock densities reproduce the observed H 2O and high-J CO lines; however, the disk and/or UV-heated outflow cavities may contribute to the observed emission. Conclusions. Similarly to Class 0 sources, the FIR emission associated with Class I and II jet-sources is likely to be shock-excited. While the cooling is dominated by CO and H 2O lines in Class 0 sources, [O i] becomes an important coolant as the source evolves and the environment is cleared. The cooling and mass loss rates estimated for Class II and I sources are one to four orders of magnitude lower than for Class 0 sources. This provides strong evidence to indicate that the outflow activity decreases as the source evolves. © 2012 ESO. Source

Dent W.R.F.,ALMA
Revista Mexicana de Astronomia y Astrofisica: Serie de Conferencias | Year: 2010

ALMA is a millimeter/submillimeter interferometer currently under constuction at 5000m altitude in northern Chile. When completed in 2012, it will provide more than an order of magnitude increase in sensitivity, resolution as well as image fidelity compared with existing facilities. This will enable significant breakthroughs in many areas of astronomy, including the study of hot stars. The capabilities of ALMA are described, along with some of the potential areas of impact on hot star research. © 2010: Instituto de Astronomía, UNAM. Source

Day-Jones A.C.,University of Chile | Day-Jones A.C.,University of Hertfordshire | Marocco F.,University of Hertfordshire | Pinfield D.J.,University of Hertfordshire | And 13 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present a new sample of mid-L to mid-T dwarfs with effective temperatures of 1100-1700 K selected from the UKIDSS Large Area Survey (LAS) and confirmed with infrared spectra from X-shooter/Very Large Telescope. This effective temperature range is especially sensitive to the formation history of Galactic brown dwarfs and allows us to constrain the form of the sub-stellar birth rate, with sensitivity to differentiate between a flat (stellar like) birth rate and an exponentially declining form. We present the discovery of 63 new L and T dwarfs from the UKIDSS LAS DR7, including the identification of 12 likely unresolved binaries, which form the first complete sub-set from our programme, covering 495 square degrees of sky, complete to J = 18.1. We compare our results for this sub-sample with simulations of differing birth rates for objects of masses 0.10-0.03 M⊙and ages 1-10 Gyr. We find that the more extreme birth rates (e.g. a halo type form) can likely be excluded as the true form of the birth rate. In addition, we find that although there is substantial scatter we find a preference for a mass function, with a power-law index α in the range -1 < α <0 that is consistent (within the errors) with the studies of late T dwarfs. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Donaldson J.K.,University of Maryland University College | Roberge A.,NASA | Chen C.H.,US Space Telescope Science Institute | Augereau J.-C.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | And 9 more authors.
Astrophysical Journal | Year: 2012

We present Herschel PACS photometry of 17 B- to M-type stars in the 30Myr old Tucana-Horologium Association. This work is part of the Herschel Open Time Key Programme "Gas in Protoplanetary Systems". 6 of the 17 targets were found to have infrared excesses significantly greater than the expected stellar IR fluxes, including a previously unknown disk around HD30051. These six debris disks were fitted with single-temperature blackbody models to estimate the temperatures and abundances of the dust in the systems. For the five stars that show excess emission in the Herschel PACS photometry and also have Spitzer IRS spectra, we fit the data with models of optically thin debris disks with realistic grain properties in order to better estimate the disk parameters. The model is determined by a set of six parameters: surface density index, grain size distribution index, minimum and maximum grain sizes, and the inner and outer radii of the disk. The best-fitting parameters give us constraints on the geometry of the dust in these systems, as well as lower limits to the total dust masses. The HD105 disk was further constrained by fitting marginally resolved PACS 70 μm imaging. © 2012. The American Astronomical Society. All rights reserved.. Source

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