667 research outputs found
Identification of new transitional disk candidates in Lupus with Herschel
New data from the Herschel Space Observatory are broadening our understanding
of the physics and evolution of the outer regions of protoplanetary disks in
star forming regions. In particular they prove to be useful to identify
transitional disk candidates. The goals of this work are to complement the
detections of disks and the identification of transitional disk candidates in
the Lupus clouds with data from the Herschel Gould Belt Survey. We extracted
photometry at 70, 100, 160, 250, 350 and 500 m of all spectroscopically
confirmed Class II members previously identified in the Lupus regions and
analyzed their updated spectral energy distributions. We have detected 34 young
disks in Lupus in at least one Herschel band, from an initial sample of 123
known members in the observed fields. Using the criteria defined in Ribas et
al. (2013) we have identified five transitional disk candidates in the region.
Three of them are new to the literature. Their PACS-70 m fluxes are
systematically higher than those of normal T Tauri stars in the same
associations, as already found in T Cha and in the transitional disks in the
Chamaeleon molecular cloud. Herschel efficiently complements mid-infrared
surveys for identifying transitional disk candidates and confirms that these
objects seem to have substantially different outer disks than the T Tauri stars
in the same molecular clouds.Comment: Accepted for publication in A&A. 16 pages, 9 figures, 7 table
First results from the CALYPSO IRAM-PdBI survey. I. Kinematics of the inner envelope of NGC1333-IRAS2A
The structure and kinematics of Class 0 protostars on scales of a few hundred
AU is poorly known. Recent observations have revealed the presence of Keplerian
disks with a diameter of 150-180 AU in L1527-IRS and VLA1623A, but it is not
clear if such disks are common in Class 0 protostars. Here we present
high-angular-resolution observations of two methanol lines in NGC1333-IRAS2A.
We argue that these lines probe the inner envelope, and we use them to study
the kinematics of this region. Our observations suggest the presence of a
marginal velocity gradient normal to the direction of the outflow. However, the
position velocity diagrams along the gradient direction appear inconsistent
with a Keplerian disk. Instead, we suggest that the emission originates from
the infalling and perhaps slowly rotating envelope, around a central protostar
of 0.1-0.2 M. If a disk is present, it is smaller than the disk of
L1527-IRS, perhaps suggesting that NGC1333-IRAS2A is younger.Comment: Accepted for publication in A&A letter
First results from the CALYPSO IRAM-PdBI survey - III. Monopolar jets driven by a proto-binary system in NGC1333-IRAS2A
Context: The earliest evolutionary stages of low-mass protostars are
characterised by hot and fast jets which remove angular momentum from the
circumstellar disk, thus allowing mass accretion onto the central object.
However, the launch mechanism is still being debated. Aims: We would like to
exploit high-angular (~ 0.8") resolution and high-sensitivity images to
investigate the origin of protostellar jets using typical molecular tracers of
shocked regions, such as SiO and SO. Methods: We mapped the inner 22" of the
NGC1333-IRAS2A protostar in SiO(5-4), SO(65-54), and the continuum emission at
1.4 mm using the IRAM Plateau de Bure interferometer in the framework of the
CALYPSO IRAM large program. Results: For the first time, we disentangle the
NGC1333-IRAS2A Class 0 object into a proto-binary system revealing two
protostars (MM1, MM2) separated by ~ 560 AU, each of them driving their own
jet, while past work considered a single protostar with a quadrupolar outflow.
We reveal (i) a clumpy, fast (up to |V-VLSR| > 50 km/s), and blueshifted jet
emerging from the brightest MM1 source, and (ii) a slower redshifted jet,
driven by MM2. Silicon monoxide emission is a powerful tracer of
high-excitation (Tkin > 100 K; n(H2) > 10^5 cm-3) jets close to the launching
region. At the highest velocities, SO appears to mimic SiO tracing the jets,
whereas at velocities close to the systemic one, SO is dominated by extended
emission, tracing the cavity opened by the jet. Conclusions: Both jets are
intrinsically monopolar, and intermittent in time. The dynamical time of the
SiO clumps is < 30-90 yr, indicating that one-sided ejections from protostars
can take place on these timescales.Comment: Astronomy & Astrophysics Letter, in pres
Subnanosecond spectral diffusion of a single quantum dot in a nanowire
We have studied spectral diffusion of the photoluminescence of a single CdSe
quantum dot inserted in a ZnSe nanowire. We have measured the characteristic
diffusion time as a function of pumping power and temperature using a recently
developed technique [G. Sallen et al, Nature Photon. \textbf{4}, 696 (2010)]
that offers subnanosecond resolution. These data are consistent with a model
where only a \emph{single} carrier wanders around in traps located in the
vicinity of the quantum dot
Defect in lung growth Comparative study of three diagnostic criteria.
Traduction anglaise de l'article Arch Pediatr. 2004 Jun;11(6):515-7 Référence pubmed : 15158815A systematic analysis was made of the autopsies of 74 newborns and fetuses (49 pathological cases and 25 controls) to detect defects in lung growth. In each case lung/body (L/B) weight ratio was calculated, and radial alveolar (RA) count and histological assessment were performed. The L/B ratio is of diagnostic value when lower than 0.012 but not when there is intercurrent disease. RA count is low in lung hypoplasia but is not an entirely reliable diagnostic criterion since it change throughout pregnancy and the earlier the gestational age the wider the range of variation. Histological assessment showed an abnormally high number of bronchi and bronchi in distal location with in some cases delayed differentiation of distal airways. If any one of the above three critera fails to determine lung hypoplasia the other two can be used to arrive at diagnosis
Witnessing the fragmentation of a filament into prestellar cores in Orion B/NGC 2024
Recent Herschel observations of nearby clouds have shown that filamentary
structures are ubiquitous and that most prestellar cores form in filaments.
Probing the density () and velocity () structure of filaments is crucial
for the understanding of the star formation process. To characterize both the
and the field of a fragmenting filament, we mapped NGC2024. 13CO, C18O,
and H13CO+ trace the filament seen in the data. The radial profile
from the data shows ~0.081 pc, which is similar to the
Herschel findings. The from 13CO and C18O are broader, while the
from H13CO+ is narrower, than from Herschel. These results
suggest that 13CO and C18O trace only the outer part of the filament and H13CO+
only the inner part. The H13CO+ map reveals gradients along
both filament axis, as well as oscillations with a period ~0.2 pc
along the major axis. Comparison between the and the distribution shows
a tentative /4 shift in H13CO+ or C18O. This /4 shift is not
simultaneously observed for all cores in any single tracer but is tentatively
seen in either H13CO+ or C18O. We produced a toy model taking into account a
transverse gradient, a longitudinal gradient, and a longitudinal
oscillation mode caused by fragmentation. Examination of synthetic data shows
that the oscillation component produces an oscillation pattern in the velocity
structure function (VSF) of the model. The H13CO+ VSF shows an oscillation
pattern, suggesting that our observations are partly tracing core-forming
motions and fragmentation. We also found that the mean corresponds
to the effective in the filament. This is consistent with a scenario
in which higher-mass cores form in higher line-mass filaments.Comment: accepted in A&
A multi-wavelength census of star formation activity in the young embedded cluster around Serpens/G3-G6
Aims. The aim of this paper is to characterise the star formation activity in
the poorly studied embedded cluster Serpens/G3-G6, located ~ 45' (3 pc) to the
south of the Serpens Cloud Core, and to determine the luminosity and mass
functions of its population of Young Stellar Objects (YSOs).
Methods. Multi-wavelength broadband photometry was obtained to sample the
near and mid-IR spectral energy distributions to separate YSOs from field stars
and classify the YSO evolutionary stage. ISOCAM mapping in the two filters LW2
(5-8.5 um) and LW3 (12-18 um) of a 19' x 16' field was combined with JHKs data
from 2MASS, Ks data from Arnica/NOT, and L' data from SIRCA/NOT. Continuum
emission at 1.3 mm (IRAM) and 3.6 cm (VLA) was mapped to study the cloud
structure and the coldest/youngest sources. Deep narrow band imaging at the
2.12 um S(1) line of H2 from NOTCam/NOT was obtained to search for signs of
bipolar outflows.
Results. We have strong evidence for a stellar population of 31 Class II
sources, 5 flat-spectrum sources, 5 Class I sources, and two Class 0 sources.
Our method does not sample the Class III sources. The cloud is composed of two
main dense clumps aligned along a ridge over ~ 0.5 pc plus a starless core
coinciding with absorption features seen in the ISOCAM maps. We find two
S-shaped bipolar collimated flows embedded in the NE clump, and propose the two
driving sources to be a Class 0 candidate (MMS3) and a double Class I (MMS2).
For the Class II population we find a best age of ~ 2 Myr and compatibility
with recent Initial Mass Functions (IMFs) by comparing the observed Class II
luminosity function (LF), which is complete to 0.08 L_sun, to various model LFs
with different star formation scenarios and input IMFs.Comment: 18 pages, 16 figures, 3 online tables, accepted by A&
Results from the First Field Tests of the WISDOM GPR (2018 ExoMars Mission)
International audienceIntroduction: The WISDOM (Water Ice Subsur- face Deposit Observation on Mars) Ground Penetrating Radar (GPR) is one of the instruments that have been selected as part of the Pasteur payload of ESA’s 2018 ExoMars Rover mission[1]. The Pasteur payload actu- ally consists of two different sets of instruments: the Panoramic Instruments, which include a wide angle camera and the WISDOM radar, that will be used to perform large-scale scientific investigations of the landing site and the Analytical Laboratory Instruments that will analyze the core samples obtained by the sub- surface drill. WISDOM will help identify the location of sedimentary layers, where organic molecules are the most likely to be found and well-preserved. WISDOM has been designed to investigate the near subsurface environment down to a depth of ~2-3 m with a vertical resolution of a few centimeters [2]. WISDOM is a step frequency radar operating over a wide frequency band between 0.5 and 3 GHz. Particular attention was paid to the design of the antenna system, which needs to be able to conduct polarimetric measurements over the whole bandwidth without significant distortion [3]
Profiling filaments: comparing near-infrared extinction and submillimetre data in TMC-1
Interstellar filaments are an important part of star formation. To understand
the structure of filaments, cross-section profiles are often fitted with
Plummer profiles. This profiling is often done with submm studies, such as
Herschel. It would be convenient if filament properties could also be studied
using groundbased NIR data. We compare the filament profiles obtained by NIR
extinction and submm observations to find out if reliable profiles can be
derived using NIR data. We use J-, H-, and K-band data of a filament north of
TMC-1 to derive an extinction map from colour excesses of background stars. We
compare the Plummer profiles obtained from extinction maps with Herschel dust
emission maps. We present 2 methods to estimate profiles from NIR: Plummer
profile fits to median Av of stars or directly to the Av of individual stars.
We compare the methods by simulations. In simulations extinction maps and the
new methods give correct results to within ~10-20 for modest densities. Direct
fit to data on individual stars gives more accurate results than extinction
map, and can work in higher density. In profile fits to real observations,
values of Plummer parameters are generally similar to within a factor of ~2.
Although parameter values can vary significantly, estimates of filament mass
usually remain accurate to within some tens of per cent. Our results for TMC-1
are in agreement with earlier results. High resolution NIR data give more
details, but 2MASS data can be used to estimate profiles. NIR extinction can be
used as an alternative to submm observations to profile filaments. Direct fits
of stars can also be a valuable tool. Plummer profile parameters are not always
well constrained, and caution should be taken when making fits. In the
evaluation of Plummer parameters, one can use the independence of dust emission
and NIR data and the difference in the shapes of the confidence regions.Comment: accepted to Astronomy & Astrophysics; abstract has been shortened for
astrop
Identification of transitional disks in Chamaeleon with Herschel
Transitional disks are circumstellar disks with inner holes that in some
cases are produced by planets and/or substellar companions in these systems.
For this reason, these disks are extremely important for the study of planetary
system formation. The Herschel Space Observatory provides an unique opportunity
for studying the outer regions of protoplanetary disks. In this work we update
previous knowledge on the transitional disks in the Chamaeleon I and II regions
with data from the Herschel Gould Belt Survey. We propose a new method for
transitional disk classification based on the WISE 12 micron-PACS 70 micron
color, together with inspection of the Herschel images. We applied this method
to the population of Class II sources in the Chamaeleon region and studied the
spectral energy distributions of the transitional disks in the sample. We also
built the median spectral energy distribution of Class II objects in these
regions for comparison with transitional disks. The proposed method allows a
clear separation of the known transitional disks from the Class II sources. We
find 6 transitional disks, all previously known, and identify 5 objects
previously thought to be transitional as possibly non-transitional. We find
higher fluxes at the PACS wavelengths in the sample of transitional disks than
those of Class II objects. We show the Herschel 70 micron band to be an
efficient tool for transitional disk identification. The sensitivity and
spatial resolution of Herschel reveals a significant contamination level among
the previously identified transitional disk candidates for the two regions,
which calls for a revision of previous samples of transitional disks in other
regions. The systematic excess found at the PACS bands could be a result of the
mechanism that produces the transitional phase, or an indication of different
evolutionary paths for transitional disks and Class II sources.Comment: Accepted for publication in A&A: 11 March 2013 11 pages, 15 figure
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