615 research outputs found
The circumstellar environment of low-mass protostars
We present a complete 1.3 mm continuum mapping survey of the embedded
young stellar objects (YSOs) in the Taurus molecular cloud. We have
also imaged several isolated Bok globules, as well as protostellar
objects in the Perseus cluster. Our maps, taken with the IRAM 30 m
telescope and the MPIfR bolometer arrays, are sensitive to the column
density structure of the sources on spatial scales ranging from
1 500-5 000 AU to > 15 000-50 000 AU. For the protostellar
envelopes mapped in Taurus, the results are roughly consistent with
the predictions of the self-similar inside-out collapse model of Shu
and collaborators. The envelopes observed in Bok globules are also
qualitatively consistent with these predictions, providing the effects
of magnetic pressure are included in the model. By contrast, the
envelopes of Class 0 protostars in Perseus have finite radii ≾ 10 000 AU and are a factor of 3 to 12 denser than is predicted by
the standard model. In cluster-forming regions, individual
protostellar collapse thus appears to be induced in compact
condensations resembling more finite-sized Bonnor-Ebert condensations
than singular isothermal spheres. Accordingly, the beginning of
protostellar evolution is suggested to be more violent, with larger
accretion rates, in protoclusters compared to regions of distributed
star formation like Taurus. Follow-up line observations of the
envelopes' velocity fields are required to confirm this suggestion. We also find that roughly half of the Class I infrared sources of
Taurus are either at the very end of the main accretion phase or
already in the pre-main sequence phase. These sources are surrounded
by only remnant, finite-sized envelopes (Menv4200 AU ≾ 0.01 M⊙ and
Rout ≾ 1 500 AU). Lastly, our 1.3 mm continuum images reveal
the presence of new candidate pre-stellar condensations and/or Class 0
protostars in the close environment of 8 Taurus Class I YSOs, 2 Bok
globules, and 3 Perseus protostars
A multi-scale, multi-wavelength source extraction method: getsources
We present a multi-scale, multi-wavelength source extraction algorithm called
getsources. Although it has been designed primarily for use in the far-infrared
surveys of Galactic star-forming regions with Herschel, the method can be
applied to many other astronomical images. Instead of the traditional approach
of extracting sources in the observed images, the new method analyzes fine
spatial decompositions of original images across a wide range of scales and
across all wavebands. It cleans those single-scale images of noise and
background, and constructs wavelength-independent single-scale detection images
that preserve information in both spatial and wavelength dimensions. Sources
are detected in the combined detection images by following the evolution of
their segmentation masks across all spatial scales. Measurements of the source
properties are done in the original background-subtracted images at each
wavelength; the background is estimated by interpolation under the source
footprints and overlapping sources are deblended in an iterative procedure. In
addition to the main catalog of sources, various catalogs and images are
produced that aid scientific exploitation of the extraction results. We
illustrate the performance of getsources on Herschel images by extracting
sources in sub-fields of the Aquila and Rosette star-forming regions. The
source extraction code and validation images with a reference extraction
catalog are freely available.Comment: 31 pages, 27 figures, to be published in Astronomy & Astrophysic
Pierre Brulé, La Grèce d’à côté. Réel et imaginaire en miroir en Grèce antique
Cet historien de l’Antiquité (qu’on ne présente pas aux familiers de la religion grecque) rassemble ici une vingtaine d’études dont la plupart ont déjà été publiées entre 1992 et 2006, deux d’entre elles étant encore à paraître, une étant inédite, et qui sont réparties entre les sept parties de l’ouvrage correspondant à autant de thématiques distinctes; les intitulés de chacun des articles sont présentés en détail plus loin (p. 1). Une solide préface met en perspective les études réunies et l..
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