1,465 research outputs found
High-spatial-resolution CN and CS observation of two regions of massive star formation
Molecular line CN, CS and mm continuum observations of two intermediate- to
high-mass star-forming regions - IRAS20293+3952 and IRAS19410+2336 - obtained
with the Plateau de Bure Interferometer at high spatial resolution reveal
interesting characteristics of the gas and dust emission. In spite of the
expectation that the CN and CS morphology might closely follow the dense gas
traced by the dust continuum, both molecules avoid the most central cores.
Comparing the relative line strengths of various CN hyperfine components, this
appears not to be an opacity effect but to be due to chemical and physical
effects. The CN data also indicate enhanced emission toward the different
molecular outflows in the region. Regarding CS, avoiding the central cores can
be due to high optical depth, but the data also show that the CS emission is
nearly always associated with the outflows of the region. Therefore, neither CS
nor CN appear well suited for dense gas and disk studies in these two sources,
and we recommend the use of different molecules for future massive disk
studies. An analysis of the 1 and 3mm continuum fluxes toward IRAS20293+3952
reveals that the dust opacity index beta is lower than the canonical value of
2. Tentatively, we identify a decreasing gradient of beta from the edge of the
core to the core center. This could be due to increasing optical depth toward
the core center and/or grain growth within the densest cores and potential
central disks. We detect 3mm continuum emission toward the collimated outflow
emanating from IRAS20293+3952. The spectral index of alpha ~ 0.8 in this region
is consistent with standard models for collimated ionized winds.Comment: 5 pages, 2 tables, 9 figures, accepted for Ap
The structure of molecular clumps around high-mass young stellar objects
We have used the IRAM 30-m and FCRAO 14-m telescopes to observe the molecular
clumps associated with 12 ultracompact (UC) HII regions in the J=6-5, 8-7 and
13-12 rotational transitions of methyl-acetylene (CH3C2H). Under the assumption
of LTE and optically thin emission, we have derived temperature estimates
ranging from 30 to 56 K. We estimate that the clumps have diameters of 0.2-1.6
pc, H_2 densities of 10^5-10^6 {cm^{-3}}, and masses of 10^2-2 10^4 M_\odot. We
compare these values with those obtained by other authors from different
molecular tracers and find that the H_2 density and the temperature inside the
clumps vary respectively like n_{H_2} ~ R^{-2.6} and T ~ R^{-0.5}, with R
distance from the centre. We also find that the virial masses of the clumps are
~3 times less than those derived from the CH3C2H column densities: we show that
a plausible explanation is that magnetic fields play an important role to
stabilise the clumps, which are on the verge of gravitational collapse.
Finally, we show that the CH3C2H line width increases for decreasing distance
from the clump centre: this effect is consistent with infall in the inner
regions of the clumps. We conclude that the clumps around UC HII regions are
likely to be transient (~10^(5) yr) entities, remnants of isothermal spheres
currently undergoing gravitational collapse: the high mass accretion rates
(~10^{-2} M_\odot yr^{-1}) lead to massive star formation at the centre of such
clumps.Comment: 15 pages, 11 figures, A & A in pres
A High-Mass Protobinary System in the Hot Core W3(H2O)
We have observed a high-mass protobinary system in the hot core W3(H2O) with
the BIMA Array. Our continuum maps at wavelengths of 1.4mm and 2.8mm both
achieve sub-arcsecond angular resolutions and show a double-peaked morphology.
The angular separation of the two sources is 1.19" corresponding to 2.43X10^3
AU at the source distance of 2.04 kpc. The flux densities of the two sources at
1.4mm and 2.8mm have a spectral index of 3, translating to an opacity law of
kappa ~ nu. The small spectral indices suggest that grain growth has begun in
the hot core. We have also observed 5 K components of the CH3CN (12-11)
transitions. A radial velocity difference of 2.81 km/s is found towards the two
continuum peaks. Interpreting these two sources as binary components in orbit
about one another, we find a minimum mass of 22 Msun for the system. Radiative
transfer models are constructed to explain both the continuum and methyl
cyanide line observations of each source. Power-law distributions of both
density and temperature are derived. Density distributions close to the
free-fall value, r^-1.5, are found for both components, suggesting continuing
accretion. The derived luminosities suggest the two sources have equivalent
zero-age main sequence (ZAMS) spectral type B0.5 - B0. The nebular masses
derived from the continuum observations are about 5 Msun for source A and 4
Msun for source C. A velocity gradient previously detected may be explained by
unresolved binary rotation with a small velocity difference.Comment: 38 pages, 9 figures, accepted by The Astrophysical Journa
Chemical Segregation in Hot Cores With Disk Candidates: An investigation with ALMA
In the study of high-mass star formation, hot cores are empirically defined
stages where chemically rich emission is detected toward a massive YSO. It is
unknown whether the physical origin of this emission is a disk, inner envelope,
or outflow cavity wall and whether the hot core stage is common to all massive
stars. We investigate the chemical make up of several hot molecular cores to
determine physical and chemical structure. We use high spectral and spatial
resolution Cycle 0 ALMA observations to determine how this stage fits into the
formation sequence of a high mass star. We observed the G35.20-0.74N and
G35.03+0.35 hot cores at 350 GHz. We analyzed spectra and maps from four
continuum peaks (A, B1, B2 and B3) in G35.20, separated by 1000-2000 AU, and
one continuum peak in G35.03. We made all possible line identifications across
8 GHz of spectral windows of molecular emission lines and determined column
densities and temperatures for as many as 35 species assuming local
thermodynamic equilibrium. In comparing the spectra of the four peaks, we find
each has a distinct chemical composition expressed in over 400 different
transitions. In G35.20, B1 and B2 contain oxygen- and sulfur-bearing organic
and inorganic species but few nitrogen-bearing species whereas A and B3 are
strong sources of O, S, and N-bearing species (especially those with the
CN-bond). CHDCN is clearly detected in A and B3 with D/H ratios of 8 and
13, respectively, but is much weaker at B1 and undetected at B2. No
deuterated species are detected in G35.03, but similar molecular abundances to
G35.20 were found in other species. We also find co-spatial emission of HNCO
and NHCHO in both sources indicating a strong chemical link between the two
species. The chemical segregation between N-bearing organic species and others
in G35.20 suggests the presence of multiple protostars, surrounded by a disk or
torus.Comment: 14 pages with 13 figures main text, 54 pages appendi
First ALMA maps of HCO, an important precursor of complex organic molecules, towards IRAS 16293-2422
The formyl radical HCO has been proposed as the basic precursor of many
complex organic molecules such as methanol (CHOH) or glycolaldehyde
(CHOHCHO). Using ALMA, we have mapped, for the first time at high angular
resolution (1, 140 au), HCO towards the Solar-type
protostellar binary IRAS 162932422, where numerous complex organic molecules
have been previously detected. We also detected several lines of the chemically
related species HCO, CHOH and CHOHCHO. The observations revealed
compact HCO emission arising from the two protostars. The line profiles also
show redshifted absorption produced by foreground material of the circumbinary
envelope that is infalling towards the protostars. Additionally, IRAM 30m
single-dish data revealed a more extended HCO component arising from the common
circumbinary envelope. The comparison between the observed molecular abundances
and our chemical model suggests that whereas the extended HCO from the envelope
can be formed via gas-phase reactions during the cold collapse of the natal
core, the HCO in the hot corinos surrounding the protostars is predominantly
formed by the hydrogenation of CO on the surface of dust grains and subsequent
thermal desorption during the protostellar phase. The derived abundance of HCO
in the dust grains is high enough to produce efficiently more complex species
such as HCO, CHOH, and CHOHCHO by surface chemistry. We found that
the main formation route of CHOHCHO is the reaction between HCO and
CHOH.Comment: Accepted in Monthly Notices of the Royal Astronomical Society; 19
pages, 12 figures, 7 table
On the chemical ladder of esters. Detection and formation of ethyl formate in the W51 e2 hot molecular core
The detection of organic molecules with increasing complexity and potential
biological relevance is opening the possibility to understand the formation of
the building blocks of life in the interstellar medium. One of the families of
molecules with astrobiological interest are the esters, whose simplest member,
methyl formate, is rather abundant in star-forming regions. The next step in
the chemical complexity of esters is ethyl formate, CHOCHO. Only two
detections of this species have been reported so far, which strongly limits our
understanding of how complex molecules are formed in the interstellar medium.
We have searched for ethyl formate towards the W51 e2 hot molecular core, one
of the most chemically rich sources in the Galaxy and one of the most promising
regions to study prebiotic chemistry, especially after the recent discovery of
the PO bond, key in the formation of DNA. We have analyzed a spectral line
survey towards the W51 e2 hot molecular core, which covers 44 GHz in the 1, 2
and 3 mm bands, carried out with the IRAM 30m telescope. We report the
detection of the trans and gauche conformers of ethyl formate. A Local
Thermodynamic Equilibrium analysis indicates that the excitation temperature is
7810 K and that the two conformers have similar source-averaged column
densities of (2.00.3)10 cm and an abundance of
10. We compare the observed molecular abundances of ethyl formate
with different competing chemical models based on grain surface and gas-phase
chemistry. We propose that grain-surface chemistry may have a dominant role in
the formation of ethyl formate (and other complex organic molecules) in hot
molecular cores, rather than reactions in the gas phase.Comment: Accepted in A&A; 11 pages, 6 figures, 7 Table
New signposts of massive star formation in the S235A-B region
We report on new aspects of the star-forming region S235AB revealed through
high-resolution observations at radio and mid-infrared wavelengths. Using the
Very Large Array, we carried out sensitive observations of S235AB in the cm
continuum (6, 3.6, 1.3, and 0.7) and in the 22 GHz water maser line. These were
complemented with Spitzer Space Telescope Infrared Array Camera archive data to
clarify the correspondence between radio and IR sources. We made also use of
newly presented data from the Medicina water maser patrol, started in 1987, to
study the variability of the water masers found in the region. S235A is a
classical HII region whose structure is now well resolved. To the south, no
radio continuum emission is detected either from the compact molecular core or
from the jet-like structure observed at 3.3 mm, suggesting emission from dust
in both cases. We find two new compact radio continuum sources (VLA-1 and
VLA-2) and three separate maser spots. VLA-1 coincides with one of the maser
spots and with a previously identified IR source (M1). VLA-2 lies towards S235B
and represents the first radio detection from this peculiar nebula that may
represent an ionized wind from a more evolved star. The two other maser spots
coincide with an elongated structure previously observed within the molecular
core in the C34S line. This structure is perpendicular to a bipolar molecular
outflow observed in HCO+(1-0) and may trace the associated equatorial disk. The
Spitzer images reveal a red object towards the molecular core. This is the most
viable candidate for the embedded source originating the outflow and maser
phenomenology. The picture emerging from these and previous data shows the
extreme complexity of a small (< 0.5 pc) star-forming region where widely
different stages of stellar evolution are present.Comment: 15 pages, 16 figures, to be published in Astronomy & Astrophysic
New strategic goals and organizational solutions in large R&D labs: lessons from Centro Ricerche Fiat and Telecom Italia Lab
The issue of corporate R&D management has become particularly relevant during the last decade, since many industrial sectors experienced growing complexity in their research areas and increasing constraints in budgets devoted to R&D activities. This paper discusses the cases of the ICT and automotive sectors, exploring the changes in managerial procedures and strategies that two of the largest corporate research centres in Italy (Telecom Italia Lab and Centro Ricerche Fiat) adopted during a delicate phase of transition. Both cases are characterized by a growing pressure towards the effective integration of short-term and long-term perspectives, i.e. towards a balance between valorization of research results and competencies, and exploration of new technological trajectories. The solutions adopted by the two organizations are explored and discussed. Specifically, while TiLab focused on the promotion of controlled spin-off companies, CRF has been very active in local technology transfer, especially in favour of SMFs
New light on the S235A-B star forming region
The S235A-B star forming region has been extensively observed in the past
from the radio to the near-IR, but what was happening in the immediate
surroundings of the water maser, placed in between the two nebulosities, was
still unclear because of insufficient resolution especially in the spectral
range from the Far-IR to the mm, even though there were sound indications that
new young stellar objects (YSOs) are being formed there. We present here new
high resolution maps at mm wavelengths in different molecules (HCO+, C34S,
H2CS, SO2 and CH3CN), as well as in the 1.2 and 3.3 mm continuum obtained with
the Plateau de Bure interferometer, and JCMT observations at 450 micron and 850
micron that unambiguously reveal the presence of new YSOs placed in between the
two HII regions S235A and S235B and associated with the water maser. A
molecular core and an unresolved source in the mm and in the sub-mm are centred
on the maser, with indication of mass infall onto the core. Two molecular
bipolar outflows and a jet originate from the same position. Weak evidence is
found for a molecular rotating disk perpendicular to the direction of the main
bipolar outflow. The derived parameters indicate that one of the YSOs is an
intermediate luminosity object (L~1000 Lsun) in a very early evolutionary
phase, embedded in a molecular core of ~100 Msun, with a temperature of 30 K.
The main source of energy for the YSO could come from gravitational infall,
thus making of this YSO a rare example of intermediate luminosity protostar
representing a link between the earliest evolutionary phases of massive stars
and low mass protostars of class 0-I.Comment: 19 pages, 22 figures, to be published in Astronomy & Astrophysic
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