1,319 research outputs found
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
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
Teaching about Madrid: A Collaborative Agents-Based Distributed Learning Course
Interactive art courses require a huge amount of computational resources to be running on real time. These computational resources are even bigger if the course has been designed as a Virtual Environment with which students can interact. In this paper, we present an initiative that has been develop in a close collaboration between two Spanish Universities: Universidad Politécnica de Madrid and Universidad Rey Juan Carlos with the aim of join two previous research project: a Collaborative Awareness Model for Task-Balancing-Delivery (CAMT) in clusters and the “Teaching about Madrid” course, which provides a cultural interactive background of the capital of Spain
A high resolution study of complex organic molecules in hot cores
We present the results of a line identification analysis using data from the
IRAM Plateau de Bure Inferferometer, focusing on six massive star-forming hot
cores: G31.41+0.31, G29.96-0.02, G19.61-0.23, G10.62-0.38, G24.78+0.08A1 and
G24.78+0.08A2. We identify several transitions of vibrationally excited methyl
formate (HCOOCH) for the first time in these objects as well as transitions
of other complex molecules, including ethyl cyanide (CHCN), and
isocyanic acid (HNCO). We also postulate a detection of one transition of
glycolaldehyde (CH(OH)CHO) in two new hot cores. We find G29.96-0.02,
G19.61-0.23, G24.78+0.08A1 and 24.78+0.08A2 to be chemically very similar.
G31.41+0.31, however, is chemically different: it manifests a larger chemical
inventory and has significantly larger column densities. We suggest that it may
represent a different evolutionary stage to the other hot cores in the sample,
or it may surround a star with a higher mass. We derive column densities for
methyl formate in G31.41+0.31, using the rotation diagram method, of
10 cm and a T of 170 K. For G29.96-0.02,
G24.78+0.08A1 and G24.78+0.08A2, glycolaldehyde, methyl formate and methyl
cyanide all seem to trace the same material and peak at roughly the same
position towards the dust emission peak. For G31.41+0.31, however,
glycolaldehyde shows a different distribution to methyl formate and methyl
cyanide and seems to trace the densest, most compact inner part of hot cores.Comment: Accepted to MNRA
Dissecting a hot molecular core: The case of G31.41+0.31
We made a detailed observational analysis of a well known hot molecular core
lying in the high-mass star-forming region G31.41+0.31. This core is believed
to contain deeply embedded massive stars and presents a velocity gradient that
has been interpreted either as rotation or as expansion, depending on the
authors. Our aim was to shed light on this question and possibly prepare the
ground for higher resolution ALMA observations which could directly detect
circumstellar disks around the embedded massive stars. Observations at
sub-arcsecond resolution were performed with the Submillimeter Array in methyl
cyanide, a typical hot molecular core tracer, and 12CO and 13CO, well known
outflow tracers. We also obtained sensitive continuum maps at 1.3 mm. Our
findings confirm the existence of a sharp velocity gradient across the core,
but cannot confirm the existence of a bipolar outflow perpendicular to it. The
improved angular resolution and sampling of the uv plane allow us to attain
higher quality channel maps of the CH3CN lines with respect to previous studies
and thus significantly improve our knowledge of the structure and kinematics of
the hot molecular core. While no conclusive argument can rule out any of the
two interpretations (rotation or expansion) proposed to explain the velocity
gradient observed in the core, in our opinion the observational evidence
collected so far indicates the rotating toroid as the most likely scenario. The
outflow hypothesis appears less plausible, because the dynamical time scale is
too short compared to that needed to form species such as CH3CN, and the mass
loss and momentum rates estimated from our measurements appear too high.Comment: Astronomy and Astrophysics, in pres
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
The hyperyoung HII region in G24.78+0.08 A1
Context. G24.78+0.08 A1 is a 20 Msun star surrounded by a hypercompact (HC)
HII region, driving a CO bipolar outflow, and located at the center of a
massive rotating toroid undergoing infall towards the HC region. Recent water
maser observations suggest that the HC region is expanding and accretion onto
the star is halted. Aims. This study aims to confirm the expansion scenario
proposed for the HC region on the basis of recent H2O maser observations.
Methods. We carried out continuum VLA observations at 1.3cm and 7mm with the A
array plus Pie Town configuration to map the HC region towards G24 A1. Results.
The emission of the HC region has been resolved and shows a ring shape
structure. The profiles of the emission obtained by taking slices at different
angles passing through the barycenter of the HC region confirm the shell
structure of the emission. The ratio between the inner and the outer radius of
the shell, Ri/Ro, derived fitting the normalized brightness temperature profile
passing through the peak of the 7mm emission, is 0.9, which indicates that the
shell is thin. The deconvolved outer radius estimated from the fit is 590 AU.
These results imply that the HC region in G24 A1 cannot be described in terms
of a classical, homogeneous HII region but is instead an ionized shell. This
gives support to the model of an expanding wind-driven, ionized shell suggested
by the kinematics and distribution of the H2O masers associated with the HC
region. According to this model, the HC region is expanding on very short times
scales, 21-66 yr.Comment: 4 pages, 5 figures. Accepted for publication by A&A Lette
Habilidades de visualización de estudiantes de primaria en actividades de geometría espacial
La forma de usar la visualización ayuda a caracterizar a los estudiantes con talento matemático (Ramírez, 2012). Los investigadores adoptan varios puntos de vista para analizar esta relación (Riu y otros, 2007). Entendiendo la visualización como “el tipo de razonamiento basado en el uso de elementos visuales o espaciales, tanto mentales como físicos” (Gutiérrez, 1996, p. 9), planteamos dos objetivos de investigación: i) analizar las habilidades de visualización (Del Grande, 1990) puestas en juego por un grupo natural de 21 estudiantes de 6º de Primaria, con diferentes grados de talento matemático, al resolver un bloque de actividades de manipulación de cubos y ii) relacionar el uso de esas habilidades con el talento matemático de los alumnos, evaluado mediante los tests PMA (Thurstone, 2005) y PEM (Benavides, 2008)
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