61 research outputs found
Exploring molecular complexity in the Galactic Center with ALMA
The search for complex organic molecules (COMs) in the ISM has revealed
chemical species of ever greater complexity. This search relies heavily on the
progress made in the laboratory to characterize the rotational spectra of these
molecules. Observationally, the advent of ALMA with its high angular resolution
and sensitivity has allowed to reduce the spectral confusion and detect
low-abundance molecules that could not be probed before. We present results of
the EMoCA survey conducted with ALMA toward the star-forming region Sgr B2(N).
This spectral line survey aims at deciphering the molecular content of Sgr
B2(N) in order to test the predictions of astrochemical models and gain insight
into the chemical processes at work in the ISM. We report on the tentative
detection of N-methylformamide, on deuterated COMs, and on the detection of a
branched alkyl molecule. Prospects for probing molecular complexity in the ISM
even further are discussed at the end.Comment: Invited contribution to appear in "Astrochemistry VII -- Through the
Cosmos from Galaxies to Planets", proceedings of the IAU Symposium No. 332,
2017, Puerto Varas, Chile. M. Cunningham, T. Millar and Y. Aikawa, eds. (12
pages, 8 figures
Observation of rotation in star forming regions: clouds, cores, disks, and jets
Angular momentum plays a crucial role in the formation of stars and planets.
It has long been noticed that parcels of gas in molecular clouds need to reduce
their specific angular momentum by 6 to 7 orders of magnitude to participate in
the building of a typical star like the Sun. Several physical processes on
different scales and at different stages of evolution can contribute to this
loss of angular momentum. In order to set constraints on these processes and
better understand this transfer of angular momentum, a detailed observational
census and characterization of rotation at all stages of evolution and over all
scales of star forming regions is necessary. This review presents the main
results obtained in low-mass star forming regions over the past four decades in
this field of research. It addresses the search and characterization of
rotation in molecular clouds, prestellar and protostellar cores, circumstellar
disks, and jets. Perspectives offered by ALMA are briefly discussed.Comment: 43 pages, 8 figures. To appear in the Proceedings of the Evry
Schatzman School 2012 of PNPS and CNRS/INSU on the "Role and mechanisms of
angular momentum transport during the formation and early evolution of
stars", Eds. P.Hennebelle and C.Charbonne
Widening of Protostellar Outflows: an Infrared Outflow Survey in Low Luminosity Objects
We present an outflow survey toward 20 Low Luminosity Objects (LLOs), namely
protostars with an internal luminosity lower than 0.2 Lsun. Although a number
of studies have reported the properties of individual LLOs, the reasons for
their low luminosity remain uncertain. To answer this question, we need to know
the evolutionary status of LLOs. Protostellar outflows are found to widen as
their parent cores evolve, and therefore, the outflow opening angle could be
used as an evolutionary indicator. The infrared scattered light escapes out
through the outflow cavity and highlights the cavity wall, giving us the
opportunity to measure the outflow opening angle. Using the
Canada-France-Hawaii Telescope, we detected outflows toward eight LLOs out of
20 at Ks band, and based on archival Spitzer IRAC1 images, we added four
outflow-driving sources from the remaining 12 sources. By fitting these images
with radiative transfer models, we derive the outflow opening angles and
inclination angles. To study the widening of outflow cavities, we compare our
sample with the young stellar objects from Arce & Sargent 2006 and Velusamy et
al. 2014 in the plot of opening angle versus bolometric temperature taken as an
evolutionary indicator.Our LLO targets match well the trend of increasing
opening angle with bolometric temperature reported by Arce & Sargent and are
broadly consistent with that reported by Velusamy et al., suggesting that the
opening angle could be a good evolutionary indicator for LLOs. Accordingly, we
conclude that at least 40% of the outflow-driving LLOs in our sample are young
Class 0 objects.Comment: Accepted for publication in AJ, 13 pages, 9 figure
Strongly triggered collapse model confront observations
Detailed modelling of individual protostellar condensations, is important to
test the various theories. Here we present comparisons between strongly induced
collapse models with one young class-0, IRAS4A in the Perseus cloud and one
prestellar cloud observed in the Coalsack molecular cloud.Comment: IAU 237, Triggering of star formation in turbulent molecular clouds,
eds B. Elmegreen and J. Palou
A 500 pc filamentary gas wisp in the disk of the Milky Way
Star formation occurs in molecular gas. In previous studies, the structure of
the molecular gas has been studied in terms of molecular clouds, but has been
overlooked beyond the cloud scale. We present an observational study of the
molecular gas at 49.5 degree <l<52.5 degree and -5.0 km/s <v_lsr <17.4 km/s.
The molecular gas is found in the form of a huge (>= 500 pc) filamentary gas
wisp. This has a large physical extent and a velocity dispersion of ~5 km/s.
The eastern part of the filamentary gas wisp is located ~130 pc above the
Galactic disk (which corresponds to 1.5-4 e-folding scale-heights), and the
total mass of the gas wisp is >= 1 X 10^5 M_sun. It is composed of two
molecular clouds and an expanding bubble. The velocity structure of the gas
wisp can be explained as a smooth quiescent component disturbed by the
expansion of a bubble. That the length of the gas wisp exceeds by much the
thickness of the molecular disk of the Milky Way is consistent with the
cloud-formation scenario in which the gas is cold prior to the formation of
molecular clouds. Star formation in the filamentary gas wisp occurs at the edge
of a bubble (G52L nebula), which is consistent with some models of triggered
star formation.Comment: Accepted for publication in A&
Detection of a branched alkyl molecule in the interstellar medium: iso-propyl cyanide
The largest non-cyclic molecules detected in the interstellar medium (ISM)
are organic with a straight-chain carbon backbone. We report an interstellar
detection of a branched alkyl molecule, iso-propyl cyanide (i-C3H7CN), with an
abundance 0.4 times that of its straight-chain structural isomer. This
detection suggests that branched carbon-chain molecules may be generally
abundant in the ISM. Our astrochemical model indicates that both isomers are
produced within or upon dust grain ice mantles through the addition of
molecular radicals, albeit via differing reaction pathways. The production of
iso-propyl cyanide appears to require the addition of a functional group to a
non-terminal carbon in the chain. Its detection therefore bodes well for the
presence in the ISM of amino acids, for which such side-chain structure is a
key characteristic.Comment: This is the author's version of the work. It is posted here by
permission of the AAAS for non-commercial use. The definitive version was
published in Science 345, 1584 (2014), doi:10.1126/science.125667
Properties of the Molecular Cores of Low Luminosity Objects
We present a survey toward 16 Low Luminosity Objects (LLOs with an internal
luminosity, Lint, lower than 0.2 Lsun) with N2H+ (1-0), N2H+ (3-2), N2D+ (3-2),
HCO+ (3-2) and HCN (3-2) using the Arizona Radio Observatory Kitt Peak 12m
Telescope and Submillimeter Telescope. Our goal is to probe the nature of these
faint protostars which are believed to be either very low mass or extremely
young protostars. We find that the N2D+/N2H+ column density ratios of LLOs are
similar to those of typical starless cores and Class 0 objects. The N2D+/N2H+
column density ratios are relatively high (> 0.05) for LLOs with kinetic
temperatures less than 10 K in our sample. The distribution of N2H+ (1-0) line
widths spreads between that of starless cores and young Class 0 objects. If we
use the line width as a dynamic evolutionary indicator, LLOs are likely young
Class 0 protostellar sources. We further use the optically thick tracers, HCO+
(3-2) and HCN (3-2), to probe the infall signatures of our targets. We derive
the asymmetry parameters from both lines and estimate the infall velocities by
fitting the HCO+ (3-2) spectra with two-layer models. As a result, we identify
eight infall candidates based on the infall velocities and seven candidates
have infall signatures supported by asymmetry parameters from at least one of
HCO+ (3-2) and HCN (3-2).Comment: 15 pages, 8 figures, accepted to Ap
EXPLORING MOLECULAR COMPLEXITY IN THE INTERSTELLAR MEDIUM WITH ALMA
The search for complex organic molecules (COMs) in the interstellar medium _x000d_
(ISM) relies heavily on the progress made in the laboratory to record and _x000d_
characterize the rotational spectra of these molecules. Almost 200 different _x000d_
molecules have been identified in the ISM so far, in particular thanks to _x000d_
millimeter-wavelength observations of the star-forming molecular cloud core _x000d_
Sgr B2(N) in the Galactic Center region. The advent of the Atacama Large _x000d_
Millimeter/submillimeter Array (ALMA) has recently opened a new door to _x000d_
explore the molecular complexity of the ISM. Thanks to its high angular _x000d_
resolution, the spectral confusion of star-forming cores can be reduced, and _x000d_
its tremendous sensitivity allows astronomers to detect molecules of low _x000d_
abundance that could not be probed by previous generations of telescopes. _x000d_
_x000d_
I will present results of the EMoCA survey conducted toward Sgr B2(N) with _x000d_
ALMA. The main goal of this spectral line survey is to decipher the molecular _x000d_
content of Sgr B2(N) in order to test the predictions of astrochemical _x000d_
numerical simulations and gain insight into the chemical processes at work in _x000d_
the ISM. I will in particular report on the tentative detection of _x000d_
N-methylformamide\footnote{A. Belloche, A.~A. Meshcheryakov, R.~T. Garrod et _x000d_
al. 2017, A\&A, in press, DOI: 10.1051/0004-6361/201629724}, on the deuterium _x000d_
fractionation of COMs\footnote{A. Belloche, H.~S.~P. M\"uller, R.~T. Garrod, _x000d_
and K.~M. Menten 2016, A\&A, 587, A91}, and on the detection of a branched _x000d_
alkyl molecule in the ISM\footnote{A. Belloche, R.~T. Garrod, H.~S.~P. _x000d_
M\"uller, and K.~M. Menten 2014, Science, 345, 1584}\footnote{R.~T. Garrod, _x000d_
A. Belloche, H.~S.~P. M\"uller, and K.~M. Menten 2017, A\&A, in press, DOI: _x000d_
10.1051/0004-6361/201630254}. _x000d_
The latter detection has unveiled a new domain in the structures _x000d_
available to the chemistry of star-forming regions and established a further _x000d_
connection to the COMs found in meteorites. _x000d
Complex organic molecules in the interstellar medium: IRAM 30 m line survey of Sagittarius B2(N) and (M)
The discovery of amino acids in meteorites and the detection of glycine in
samples returned from a comet to Earth suggest that the interstellar chemistry
is capable of producing such complex organic molecules. Our goal is to
investigate the degree of chemical complexity that can be reached in the ISM.
We performed an unbiased, spectral line survey toward Sgr B2(N) and (M) with
the IRAM 30m telescope in the 3mm window. The spectra were analyzed with a
simple radiative transfer model that assumes LTE but takes optical depth
effects into account. About 3675 and 945 spectral lines with a peak
signal-to-noise ratio higher than 4 are detected toward N and M, i.e. about 102
and 26 lines per GHz, respectively. This represents an increase by about a
factor of 2 over previous surveys of Sgr B2. About 70% and 47% of the lines
detected toward N and M are identified and assigned to 56 and 46 distinct
molecules as well as to 66 and 54 less abundant isotopologues of these
molecules, respectively. We also report the detection of transitions from 59
and 24 catalog entries corresponding to vibrationally or torsionally excited
states of some of these molecules, respectively. Excitation temperatures and
column densities were derived for each species but should be used with caution.
Among the detected molecules, aminoacetonitrile, n-propyl cyanide, and ethyl
formate were reported for the first time in space based on this survey, as were
5 rare isotopologues of vinyl cyanide, cyanoacetylene, and hydrogen cyanide. We
also report the detection of transitions from within 12 new vib. or tors.
excited states of known molecules. Although the large number of unidentified
lines may still allow future identification of new molecules, we expect most of
these lines to belong to vib. or tors. excited states or to rare isotopologues
of known molecules for which spectroscopic predictions are currently missing.
(abridged)Comment: Accepted for publication in A&A. 266 pages (39 pages of text), 111
tables, 8 figure
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