206 research outputs found
Hot and dense water in the inner 25 AU of SVS13-A
In the context of the ASAI (Astrochemical Surveys At IRAM) project, we
carried out an unbiased spectral survey in the millimeter window towards the
well known low-mass Class I source SVS13-A. The high sensitivity reached (3-12
mK) allowed us to detect at least 6 HDO broad (FWHM ~ 4-5 km/s) emission lines
with upper level energies up to Eu = 837 K. A non-LTE LVG analysis implies the
presence of very hot (150-260 K) and dense (> 3 10^7 cm-3) gas inside a small
radius ( 25 AU) around the star, supporting, for the first time, the
occurrence of a hot corino around a Class I protostar.
The temperature is higher than expected for water molecules are sublimated
from the icy dust mantles (~ 100 K). Although we cannot exclude we are observig
the effects of shocks and/or winds at such small scales, this could imply that
the observed HDO emission is tracing the water abundance jump expected at
temperatures ~ 220-250 K, when the activation barrier of the gas phase
reactions leading to the formation of water can be overcome. We derive X(HDO) ~
3 10-6, and a H2O deuteration > 1.5 10-2, suggesting that water deuteration
does not decrease as the protostar evolves from the Class 0 to the Class I
stage.Comment: MNRAS Letter
Italian Science Case for ALMA Band 2+3
The Premiale Project "Science and Technology in Italy for the upgraded ALMA
Observatory - iALMA" has the goal of strengthening the scientific,
technological and industrial Italian contribution to the Atacama Large
Millimeter/submillimeter Array (ALMA), the largest ground based international
infrastructure for the study of the Universe in the microwave. One of the main
objectives of the Science Working Group (SWG) inside iALMA, the Work Package 1,
is to develop the Italian contribution to the Science Case for the ALMA Band 2
or Band 2+3 receiver. ALMA Band 2 receiver spans from ~67 GHz (bounded by an
opaque line complex of ozone lines) up to 90 GHz which overlaps with the lower
frequency end of ALMA Band 3. Receiver technology has advanced since the
original definition of the ALMA frequency bands. It is now feasible to produce
a single receiver which could cover the whole frequency range from 67 GHz to
116 GHz, encompassing Band 2 and Band 3 in a single receiver cartridge, a so
called Band 2+3 system. In addition, upgrades of the ALMA system are now
foreseen that should double the bandwidth to 16 GHz. The science drivers
discussed below therefore also discuss the advantages of these two enhancements
over the originally foreseen Band 2 system.Comment: 43 pages, 21 figure
The census of interstellar complex organic molecules in the Class I hot corino of SVS13-A
We present the first census of the interstellar Complex Organic Molecules
(iCOMs) in the low-mass Class I protostar SVS13-A, obtained by analysing data
from the IRAM-30m Large Project ASAI (Astrochemical Surveys At IRAM). They
consist of an high-sensitivity unbiased spectral survey at the 1mm, 2mm and 3mm
IRAM bands. We detected five iCOMs: acetaldehyde (CHCHO), methyl formate
(HCOOCH), dimethyl ether (CHOCH), ethanol (CHCHOH) and
formamide (NHCHO). In addition we searched for other iCOMs and ketene
(HCCO), formic acid (HCOOH) and methoxy (CHO), whose only ketene was
detected. The numerous detected lines, from 5 to 37 depending on the species,
cover a large upper level energy range, between 15 and 254 K. This allowed us
to carry out a rotational diagram analysis and derive rotational temperatures
between 35 and 110 K, and column densities between and
cm on the 0."3 size previously determined by
interferometric observations of glycolaldehyde. These new observations clearly
demonstrate the presence of a rich chemistry in the hot corino towards SVS13-A.
The measured iCOMs abundances were compared to other Class 0 and I hot corinos,
as well as comets, previously published in the literature. We find evidence
that (i) SVS13-A is as chemically rich as younger Class 0 protostars, and (ii)
the iCOMs relative abundances do not substantially evolve during the
protostellar phase.Comment: 24 pages, MNRAS in pres
Associations of water and methanol masers at milli-arcsec angular resolution in two high-mass young stellar objects
Most previous high-angular (<0.1 arcsec) resolution studies of molecular
masers in high-mass star forming regions (SFRs) have concentrated mainly on
either water or methanol masers. While high-angular resolution observations
have clarified that water masers originate from shocks associated with
protostellar jets, different environments have been proposed in several sources
to explain the origin of methanol masers. Tha aim of the paper is to
investigate the nature of the methanol maser birthplace in SFRs and the
association between the water and methanol maser emission in the same young
stellar object. We have conducted phase-reference Very Long Baseline
Interferometry (VLBI) observations of water and methanol masers toward two
high-mass SFRs, Sh 2-255 IR and AFGL 5142. In Sh 2-255 IR water masers are
aligned along a direction close to the orientation of the molecular outflow
observed on angular scales of 1-10 arcsec, tracing possibly the disk-wind
emerging from the disk atmosphere. In AFGL 5142 water masers trace expansion at
the base of a protostellar jet, whilst methanol masers are more probably
tracing infalling than outflowing gas. The results for AFGL 5142 suggest that
water and methanol masers trace different kinematic structures in the
circumstellar gas.Comment: 11 pages, 3 figures, accepted for publication in Astronomy &
Astrophysic
Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B
Aims. The aim of this paper is to study deuterated water in the solar-type
protostars NGC1333 IRAS4A and IRAS4B, to compare their HDO abundance
distribution with other star-forming regions, and to constrain their HDO/H2O
ratios. Methods. Using the Herschel/HIFI instrument as well as ground-based
telescopes, we observed several HDO lines covering a large excitation range
(Eup/k=22-168 K) towards these protostars and an outflow position. Non-LTE
radiative transfer codes were then used to determine the HDO abundance profiles
in these sources. Results. The HDO fundamental line profiles show a very broad
component, tracing the molecular outflows, in addition to a narrower emission
component and a narrow absorbing component. In the protostellar envelope of
NGC1333 IRAS4A, the HDO inner (T>100 K) and outer (T<100 K) abundances with
respect to H2 are estimated at 7.5x10^{-9} and 1.2x10^{-11}, respectively,
whereas, in NGC1333 IRAS4B, they are 1.0x10^{-8} and 1.2x10^{-10},
respectively. Similarly to the low-mass protostar IRAS16293-2422, an absorbing
outer layer with an enhanced abundance of deuterated water is required to
reproduce the absorbing components seen in the fundamental lines at 465 and 894
GHz in both sources. This water-rich layer is probably extended enough to
encompass the two sources as well as parts of the outflows. In the outflows
emanating from NGC1333 IRAS4A, the HDO column density is estimated at about
(2-4)x10^{13} cm^{-2}, leading to an abundance of about (0.7-1.9)x10^{-9}. An
HDO/H2O ratio between 7x10^{-4} and 9x10^{-2} is derived in the outflows. In
the warm inner regions of these two sources, we estimate the HDO/H2O ratios at
about 1x10^{-4}-4x10^{-3}. This ratio seems higher (a few %) in the cold
envelope of IRAS4A, whose possible origin is discussed in relation to formation
processes of HDO and H2O.Comment: 16 pages, 13 figure
A Catalogue of Optically Selected Cores
We present a new catalogue of 406 dense cores optically selected by using the
STScI Digitized Sky Survey (DSS). In this catalogue 306 cores have neither an
Embedded YSO (EYSO) nor a Pre-Main-Sequence (PMS) star, 94 cores have EYSOs (1
core has both an EYSO and a PMS star), and 6 cores have PMS star only. Our
sample of dense cores in the catalogue is fairly complete within a category of
northern Lynds class 5, 6 clouds, and southern Hartley et al. (1986)'s class A
clouds, providing a database useful for the systematic study of dense cores.
Most of the cores listed in the catalogue have diameters between
pc with a mean of pc. The sizes ( pc in the mean) of
cores with EYSOs are found to be usually larger than the sizes ( pc
in the mean) of starless cores. The typical mean gas density of the cores is
. Most of the cores are more likely elongated than
spherical (mean aspect ratio: ). The ratio of the number of cores
with EYSOs to the number of starless cores for our sample is about 0.3,
suggesting that the typical lifetime of starless cores is Myr, about
3 times longer than the duration of the Class 0 and Class I phases. This
lifetime is shorter than expected from models of ambipolar diffusion, by
factors of 2-44.Comment: 22 pages, 8 figures, 3 tables, and to appear in ApJS.
Harvard-Smithsonian Center for Astrophysic
A Search for H2CO 6cm Emission toward Young Stellar Objects III: VLA Observations
We report the results of our third survey for formaldehyde (H2CO) 6cm maser
emission in the Galaxy. Using the Very Large Array, we detected two new H2CO
maser sources (G23.01-0.41 and G25.83-0.18), thus increasing the sample of
known H2CO maser regions in the Galaxy to seven. We review the characteristics
of the G23.01-0.41 and G25.83-0.18 star forming regions. The H2CO masers in
G23.01-0.41 and G25.83-0.18 share several properties with the other known H2CO
masers, in particular, emission from rich maser environments and close
proximity to very young massive stellar objects.Comment: Accepted for publication in the Astrophysical Journal Supplement
Serie
Rotating molecular outflows: the young T Tauri star in CB26
The disk-outflow connection is thought to play a key role in extracting
excess angular momentum from a forming proto-star. Though jet rotation has been
observed in a few objects, no rotation of molecular outflows has been
unambiguously reported so far. We report new millimeter-interferometric
observations of the edge-on T Tauri star - disk system in the isolated Bok
globule CB26. The aim of these observations was to study the disk-outflow
relation in this 1Myr old low-mass young stellar object. The IRAM PdBI array
was used to observe 12CO(2-1) at 1.3mm in two configurations, resulting in
spectral line maps with 1.5 arcsec resolution. We use an empirical
parameterized steady-state outflow model combined with 2-D line radiative
transfer calculations and chi^2-minimization in parameter space to derive a
best-fit model and constrain parameters of the outflow. The data reveal a
previously undiscovered collimated bipolar molecular outflow of total length
~2000 AU, escaping perpendicular to the plane of the disk. We find peculiar
kinematic signatures that suggest the outflow is rotating with the same
orientation as the disk. However, we could not ultimately exclude jet
precession or two misaligned flows as possible origin of the observed peculiar
velocity field. There is indirect indication that the embedded driving source
is a binary system, which, together with the youth of the source, could provide
the clue to the observed kinematic features of the outflow. CB26 is so far the
most promising source to study the rotation of a molecular outflow. Assuming
that the outflow is rotating, we compute and compare masses, mass flux, angular
momenta, and angular momentum flux of disk and outflow and derive disk
dispersal timescales of 0.5...1 Myr, comparable to the age of the system.Comment: 14 pages, 6 figures, to appear in Astronomy & Astrophysic
School self-efficacy is affected by gender and motor skills: findings from an Italian study
Background: Perceived school self-efficacy (SE) is an important variable in students' activities as it affects their motivation and learning. Further, self-efficacy might represent a good predictor of performance, persistence and perseverance. Motor skills and other physical health determinants are extensively debated and linked to cognitive function in children of developmental age. However, inconclusive evidence supports a definitive relationship between perceived school SE and motor skills among schoolchildren. We conducted a cross-sectional study on 6-11-year-old schoolchildren to evaluate the extent by which perceived school SE and physical health determinants were related. Methods: A SE questionnaire and motor performance battery tests were administered to primary school pupils recruited from 154 sampled schools of northwest Italy. Perceived SE at school was assessed via 12 items from the Caprara's questionnaire. Motor performance scores were obtained from motor skill tests: 4 Ă 10 m shuttle run test, SRT; standing broad jump, SBJ; six-minute walking test, 6MWT. Results: A total of 3,962 children (M = 2,019; F = 1943) were studied and 68% were normal weight. Overall, a 58% of the sample perceived a high SE, while, as to gender differences, a greater percentage of females perceived high levels of school SE with respect to any other level (Ï2 = 38.93, p < 0.0001). Results from multinomial logistic regression analysis revealed that: (i) females perceived higher SE compared to males; (ii) children who performed better in SRT and 6MWT showed higher levels of perceived school SE; (iii) no significant effect was registered for the body weight. Alternative strategies are encouraged to enhance SE through physical education: structured interventions might enhance both complex motor skills and high-order cognitive skills, like SE, in young children
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