1,525 research outputs found
Starless Cores
Dense low mass cores in nearby clouds like Taurus and Auriga are some of the
simplest sites currently forming stars like our Sun. Because of their
simplicity and proximity, dense cores offer the clearest view of the different
phases of star formation, in particular the conditions prior to the onset of
gravitational collapse. Thanks to the combined analysis of the emission from
molecular lines and the emission/absorption from dust grains, the last several
years have seen a very rapid progress in our understanding of the structure and
chemical composition of starless cores. Previous contradictions between
molecular tracers are now understood to arise from core chemical
inhomogeneities, which are caused by the selective freeze out of molecules onto
cold dust grains. The analysis of the dust emission and absorption, in
addition, has allowed us to derive accurate density profiles, and has made
finally possible to carry out self consistent modeling of the internal
structure of starless cores. In this paper I briefly review the evolution of
core studies previous to the current golden age, and show how multi-tracer
emission can now be modeled in a systematic manner. Finally I show how we can
start to reconstruct the early history of core formation taking advantage of
the chemical changes in the gas.Comment: 16 pages, 7 figures. Review article to appear in the proceedings of
the "Cores to Clusters" meeting held in Porto, Portugal, October 200
HH 114 MMS: a new chemically active outflow
Context. A small group of bipolar protostellar outflows display strong
emission from shock-tracer molecules such as SiO and CH3OH, and are generally
referred to as "chemically active." The best-studied outflow from this group is
the one in L 1157. Aims. We study the molecular emission from the bipolar
outflow powered by the very young stellar object HH 114 MMS and compare its
chemical composition with that of the L1157 outflow. Methods. We have used the
IRAM 30m radio telescope to observe a number of transitions from CO, SiO,
CH3OH, SO, CS, HCN, and HCO+ toward the HH 114 MMS outflow. The observations
consist of maps and a two-position molecular survey. Results. The HH 114 MMS
outflow presents strong emission from a number of shock-tracer molecules that
dominate the appearance of the maps around the central source. The abundance of
these molecules is comparable to the abundance in L 1157. Conclusions. The
outflow from HH 114 MMS is a spectacular new case of a chemically active
outflow.Comment: 4 pages, 3 figures. Accepted for publication in Astronomy &
Astrophysic
Molecules in Bipolar Outflows
Bipolar outflows constitute some of the best laboratories to study shock
chemistry in the interstellar medium. A number of molecular species have their
abundance enhanced by several orders of magnitude in the outflow gas, likely as
a combined result of dust mantle disruption and high temperature gas chemistry,
and therefore become sensitive indicators of the physical changes taking place
in the shock. Identifying these species and understanding their chemical
behavior is therefore of high interest both to chemical studies and to our
understanding of the star-formation process. Here we review some of the recent
progress in the study of the molecular composition of bipolar outflows, with
emphasis in the tracers most relevant for shock chemistry. As we discuss, there
has been rapid progress both in characterizing the molecular composition of
certain outflows as well as in modeling the chemical processes likely involved.
However, a number of limitations still affect our understanding of outflow
chemistry. These include a very limited statistical approach in the
observations and a dependence of the models on plane-parallel shocks, which
cannot reproduce the observed wing morphology of the lines. We finish our
contribution by discussing the chemistry of the so-called extremely high
velocity component, which seems different from the rest of the outflow and may
originate in the wind from the very vicinity of the protostar.Comment: 15 pages, 7 figures. Contribution to the IAU Conference "The
Molecular Universe" held in Toledo in June 201
Fibers in the NGC1333 proto-cluster
Are the initial conditions for clustered star formation the same as for
non-clustered star formation? To investigate the initial gas properties in
young proto-clusters we carried out a comprehensive and high-sensitivity study
of the internal structure, density, temperature, and kinematics of the dense
gas content of the NGC1333 region in Perseus, one of the nearest and best
studied embedded clusters. The analysis of the gas velocities in the
Position-Position-Velocity space reveals an intricate underlying gas
organization both in space and velocity. We identified a total of 14
velocity-coherent, (tran-)sonic structures within NGC1333, with similar
physical and kinematic properties than those quiescent, star-forming (aka
fertile) fibers previously identified in low-mass star-forming clouds. These
fibers are arranged in a complex spatial network, build-up the observed total
column density, and contain the dense cores and protostars in this cloud. Our
results demonstrate that the presence of fibers is not restricted to low-mass
clouds but can be extended to regions of increasing mass and complexity. We
propose that the observational dichotomy between clustered and non-clustered
star-forming regions might be naturally explained by the distinct spatial
density of fertile fibers in these environments.Comment: 25 pages, 17 figures; Accepted for publication in A&
Chemical modeling of the L1498 and L1517B prestellar cores: CO and HCO+ depletion
Prestellar cores exhibit a strong chemical differentiation, which is mainly
caused by the freeze-out of molecules onto the grain surfaces. Understanding
this chemical structure is important, because molecular lines are often used as
probes to constrain the core physical properties. Here we present new
observations and analysis of the C18O (1-0) and H13CO+ (1-0) line emission in
the L1498 and L1517B prestellar cores, located in the Taurus-Auriga molecular
complex. We model these observations with a detailed chemistry network coupled
to a radiative transfer code. Our model successfully reproduces the observed
C18O (1-0) emission for a chemical age of a few 10^5 years. On the other hand,
the observed H13CO+ (1-0) is reproduced only if cosmic-ray desorption by
secondary photons is included, and if the grains have grown to a bigger size
than average ISM grains in the core interior. This grain growth is consistent
with the infrared scattered light ("coreshine") detected in these two objects,
and is found to increase the CO abundance in the core interior by about a
factor four. According to our model, CO is depleted by about 2-3 orders of
magnitude in the core center.Comment: Accepted for publication in A&
Entrevista a Raimund Herder, director de Herder Editorial
Entrevista a Raimund Herder, director de Herder Editorial.Interview with Raimund Herder, Herder Editorial’s director.Entrevista a Raimund Herder, director de Herder Editorial
The Aesthetic Appreciation of Animals in Zoological Parks
Can we appreciate in a serious and deep way the aesthetic qualities of wild species in exemplars held captive for exhibition in the artificial installations of a zoo? To answer this question I invoke theories concerning the aesthetic appreciation of nature propounded by Yuriko Saito and Allen Carlson. I then argue that zoos impose their story on animals, thereby preventing us from appreciating the animals on their own terms. I claim that captivity and its effects on the health, behavior, and appearance of animals make serious and deep appreciation of the aesthetic qualities of wild species impossible
Detection of interstellar HCS and its metastable isomer HSC: new pieces in the puzzle of sulfur chemistry
We present the first identification in interstellar space of the thioformyl
radical (HCS) and its metastable isomer HSC. These species were detected toward
the molecular cloud L483 thanks to observations carried out with the IRAM 30m
telescope in the 3 mm band. We derive beam-averaged column densities of 7e12
cm-2 for HCS and 1.8e11 cm-2 for HSC, which translate to fractional abundances
relative to H2 of 2e-10 and 6e-12, respectively. Although the amount of sulfur
locked by these radicals is low, their detection allows to put interesting
constraints on the chemistry of sulfur in dark clouds. Interestingly, the
H2CS/HCS abundance ratio is found to be quite low, around 1, in contrast with
the oxygen analogue case, in which the H2CO/HCO abundance ratio is around 10 in
dark clouds. Moreover, the radical HCS is found to be more abundant than its
oxygen analogue, HCO. The metastable species HOC, the oxygen analogue of HSC,
has not been yet observed in space. These observational constraints are
confronted with the outcome of a recent model of the chemistry of sulfur in
dark clouds. The model underestimates the fractional abundance of HCS by at
least one order of magnitude, overestimates the H2CS/HCS abundance ratio, and
does not provide an abundance prediction for the metastable isomer HSC. These
observations should prompt a revision of the chemistry of sulfur in
interstellar clouds.Comment: Accepted for publication in A&A Letter
El ressorgiment de l'estètica de la natura
L'estètica de la natura, la disciplina que estudia com apreciem la bellesa d'un paisatge, un animal, una planta o fins i tot el firmament, va ser expulsada de la filosofia acadèmica a principis del segle XIX per Hegel, que va considerar que l'estètica s'havia de limitar a estudiar l'art que, en ser una creació humana, era superior a la bellesa natural. Durant els anys 60 del segle XX i amb el sorgiment de la consciència ecologista, va reaparèixer la sensibilitat per aquesta disciplina, que va ser introduïda de nou a l'acadèmia, de manera independent, per dos autors, l'alemany Theodor W. Adorno i el brità nic Ronald Hepburn. Aquesta investigació és un estudi comparatiu dels que van ser els dos articles fundacionals d'aquesta nova etapa de la disciplina, i una reivindicació de la necessitat de dià leg entre les tradicions brità nica i germà nica. L'estètica de la naturalesa defensa que una major consciència de la bellesa del món natural ens donarà motius per protegir-lo.La estética de la naturaleza, la disciplina que estudia cómo apreciamos la belleza de un paisaje, un animal, una planta o incluso el firmamento, fue expulsada de la filosofÃa académica a principios del siglo XIX porHegel, quien consideró que la estética debÃa limitarse a estudiar el arteque, al ser una creación humana, era superior a la belleza natural. Durante los años 60 del siglo XX y con el surgimiento de la conciencia ecologista, reapareció la sensibilidad por esta disciplina, que fue introducida de nuevo en la academia, de forma independiente, por dos autores, el alemán Theodor W. Adorno y el británico Ronald Hepburn. Esta investigación es un estudio comparativo de los que fueron los dos artÃculos fundacionales de esta nueva etapa de la disciplina, y una reivindicación de la necesidad de diálogo entre las tradiciones británica ygermánica. La estética de la naturaleza defiende que una mayor conciencia de la belleza del mundo natural nos dará motivos paraprotegerlo
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