Time filter

Source Type

Dougados C.,Laboratoire Dastrophysique Of Grenoble | Bacciotti F.,National institute for astrophysics | Cabrit S.,French National Center for Scientific Research | Nisini B.,National institute for astrophysics
Lecture Notes in Physics | Year: 2010

We review in this course diagnostics for the physical conditions in the atomic component of the flow (electronic densities nê, electronic temperatures T e and hydrogen ionization fraction x e ) based on the most prominent optical and near-infrared forbidden emission lines. We discuss both diagnostics independent of the excitation process and methods based on the comparison with radiative shock models. We then detail the different techniques used to derive jet mass-loss rates, an important parameter for launching models, and their associated uncertainties. Finally, we describe important biases introduced by projection and convolution effects which can critically affect the translation of observed quantities into meaningful physical quantities of the flow. © 2010 Springer-Verlag Berlin Heidelberg.

Korkiakoski V.,University Utrecht | Verinaud C.,Laboratoire Dastrophysique Of Grenoble
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

EPICS is a project for a high contrast imaging instrument dedicated to direct imaging of exopianets with the European Extremely Large Telescope. Its conceptual design study phase has finished. at the early 2010, and we show here its end-to-end extreme adaptive optics simulation results. The simulations have been made using conventional, well-known but numerically intensive computation techniques (full Fourier diffraction model of a WFS and wavefront reconstruction with matrix-vector-multiplication). Many error sources important for XAO are considered: chromaticity effects, Ml segment mis-figure, pupil rotation, WFS misregistration, telescope jitter and spiders. The results confirm that a raw contrast of 10-5 is reached at 20 mas, and 10-7...... 10-6 at 200-500 mas. This is in agreement with our analytic estimations and EPICS top-level requirements. © 2010 SPIE.

Manoj P.,University of Rochester | Watson D.M.,University of Rochester | Neufeld D.A.,Johns Hopkins University | Megeath S.T.,University of Toledo | And 14 more authors.
Astrophysical Journal | Year: 2013

We present far-infrared (57-196 μm) spectra of 21 protostars in the Orion molecular clouds. These were obtained with the Photodetector Array Camera and Spectrometer (PACS) on board the Herschel Space observatory as part of the Herschel Orion Protostar Survey program. We analyzed the emission lines from rotational transitions of CO, involving rotational quantum numbers in the range Jup = 14-46, using PACS spectra extracted within a projected distance of ≲2000 AU centered on the protostar. The total luminosity of the CO lines observed with PACS (LCO) is found to increase with increasing protostellar luminosity (Lbol). However, no significant correlation is found between LCO and evolutionary indicators or envelope properties of the protostars such as bolometric temperature, Tbol, or envelope density. The CO rotational (excitation) temperature implied by the line ratios increases with increasing rotational quantum number J, and at least 3-4 rotational temperature components are required to fit the observed rotational diagram in the PACS wavelength range. The rotational temperature components are remarkably invariant between protostars and show no dependence on Lbol, Tbol, or envelope density, implying that if the emitting gas is in local thermodynamic equilibrium, the CO emission must arise in multiple temperature components that remain independent of Lbol over two orders of magnitudes. The observed CO emission can also be modeled as arising from a single-temperature gas component or from a medium with a power-law temperature distribution; both of these require sub-thermally excited molecular gas at low densities (n(H2) ≲ 106 cm -3) and high temperatures (T ≳ 2000 K). Our results suggest that the contribution from photodissociation regions, produced along the envelope cavity walls from UV-heating, is unlikely to be the dominant component of the CO emission observed with PACS. Instead, the "universality" of the rotational temperatures and the observed correlation between LCO and Lbol can most easily be explained if the observed CO emission originates in shock-heated, hot (T ≳ 2000 K), sub-thermally excited (n(H2) ≲ 106 cm-3) molecular gas. Post-shock gas at these densities is more likely to be found within the outflow cavities along the molecular outflow or along the cavity walls at radii ≳ several 100-1000 AU. © 2013. The American Astronomical Society. All rights reserved.

Morales-Calderon M.,California Institute of Technology | Stauffer J.R.,California Institute of Technology | Hillenbrand L.A.,California Institute of Technology | Gutermuth R.,Smith College | And 36 more authors.
Astrophysical Journal | Year: 2011

We present initial results from time-series imaging at infrared wavelengths of 0.9 deg2 in the Orion Nebula Cluster (ONC). During Fall 2009 we obtained 81 epochs of Spitzer 3.6 and 4.5 μm data over 40 consecutive days. We extracted light curves with ∼3% photometric accuracy for ∼2000 ONC members ranging from several solar masses down to well below the hydrogen-burning mass limit. For many of the stars, we also have time-series photometry obtained at optical (Ic ) and/or near-infrared (JK s) wavelengths. Our data set can be mined to determine stellar rotation periods, identify new pre-main-sequence eclipsing binaries, search for new substellar Orion members, and help better determine the frequency of circumstellar disks as a function of stellar mass in the ONC. Our primary focus is the unique ability of 3.6 and 4.5 μm variability information to improve our understanding of inner disk processes and structure in the Class I and II young stellar objects (YSOs). In this paper, we provide a brief overview of the YSOVAR Orion data obtained in Fall 2009 and highlight our light curves for AA-Tau analogs - YSOs with narrow dips in flux, most probably due to disk density structures passing through our line of sight. Detailed follow-up observations are needed in order to better quantify the nature of the obscuring bodies and what this implies for the structure of the inner disks of YSOs. © 2011. The American Astronomical Society. All rights reserved..

Sonnentrucker P.,Johns Hopkins University | Neufeld D.A.,Johns Hopkins University | Phillips T.G.,California Institute of Technology | Gerin M.,French National Center for Scientific Research | And 46 more authors.
Astronomy and Astrophysics | Year: 2010

We discuss the detection of absorption by interstellar hydrogen fluoride (HF) along the sight line to the submillimeter continuum sources W49N and W51. We have used Herschel's HIFI instrument in dual beam switch mode to observe the 1232.4762 GHz J = 1-0 HF transition in the upper sideband of the band 5a receiver. We detected foreground absorption by HF toward both sources over a wide range of velocities. Optically thin absorption components were detected on both sight lines, allowing us to measure-as opposed to obtain a lower limit on-the column density of HF for the first time. As in previous observations of HF toward the source G10.6-0.4, the derived HF column density is typically comparable to that of water vapor, even though the elemental abundance of oxygen is greater than that of fluorine by four orders of magnitude. We used the rather uncertain N(CH)-N(H2) relationship derived previously toward diffuse molecular clouds to infer the molecular hydrogen column density in the clouds exhibiting HF absorption. Within the uncertainties, we find that the abundance of HF with respect to H2 is consistent with the theoretical prediction that HF is the main reservoir of gas-phase fluorine for these clouds. Thus, hydrogen fluoride has the potential to become an excellent tracer of molecular hydrogen, and provides a sensitive probe of clouds of small H 2 column density. Indeed, the observations of hydrogen fluoride reported here reveal the presence of a low column density diffuse molecular cloud along the W51 sight line, at an LSR velocity of ∼24 km s-1, that had not been identified in molecular absorption line studies prior to the launch of Herschel. © 2010 ESO.

Discover hidden collaborations