1,926 research outputs found
Orbital parameters and evolutionary status of the highly-peculiar binary system HD 66051
The spectroscopic binary system HD 66051 (V414 Pup) consists of a highlypeculiar CP3 (HgMn) star and an A-type component. It also shows out-of-eclipsevariability that is due to chemical spots. This combination allows thederivation of tight constraints for the testing of time-dependent diffusionmodels. We analysed radial velocity and photometric data using two differentmethods to determine astrophysical parameters and the orbit of the system.Appropriate isochrones were used to derive the age of the system. The orbitalsolution and the estimates from the isochrones are in excellent agreement withthe estimates from a prior spectroscopic study. The system is very close to thezero-age main sequence and younger than 120 Myr. HD 66051 is a most importantspectroscopic binary system that can be used to test the predictions of thediffusion theory explaining the peculiar surface abundances of CP3 stars.Fil: Paunzen, E.. Masaryk University; República ChecaFil: Fedurco, M.. Masaryk University; República ChecaFil: Helminiak, K.G.. Masaryk University; República ChecaFil: Pintado, Olga Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentin
The largest oxigen bearing organic molecule repository
We present the first detection of complex aldehydes and isomers in three
typical molecular clouds located within 200pc of the center of our Galaxy.
We find very large abundances of these complex organic molecules (COMs) in
the central molecular zone (CMZ), which we attribute to the ejection of COMs
from grain mantles by shocks. The relative abundances of the different COMs
with respect to that of CH3OH are strikingly similar for the three sources,
located in very different environments in the CMZ. The similar relative
abundances point toward a unique grain mantle composition in the CMZ. Studying
the Galactic center clouds and objects in the Galactic disk having large
abundances of COMs, we find that more saturated molecules are more abundant
than the non-saturated ones. We also find differences between the relative
abundance between COMs in the CMZ and the Galactic disk, suggesting different
chemical histories of the grain mantles between the two regions in the Galaxy
for the complex aldehydes. Different possibilities for the grain chemistry on
the icy mantles in the GC clouds are briefly discussed. Cosmic rays can play an
important role in the grain chemistry. With these new detections, the molecular
clouds in the Galactic center appear to be one of the best laboratories for
studying the formation of COMs in the Galaxy.Comment: 20 pages, 4 figures, accepted in Ap
The role of low-mass star clusters in massive star formation. The Orion Case
To distinguish between the different theories proposed to explain massive
star formation, it is crucial to establish the distribution, the extinction,
and the density of low-mass stars in massive star-forming regions. We analyze
deep X-ray observations of the Orion massive star-forming region using the
Chandra Orion Ultradeep Project (COUP) catalog. We studied the stellar
distribution as a function of extinction, with cells of 0.03 pc x 0.03 pc, the
typical size of protostellar cores. We derived stellar density maps and
calculated cluster stellar densities. We found that low-mass stars cluster
toward the three massive star-forming regions: the Trapezium Cluster (TC), the
Orion Hot Core (OHC), and OMC1-S. We derived low-mass stellar densities of
10^{5} stars pc^{-3} in the TC and OMC1-S, and of 10^{6} stars pc^{-3} in the
OHC. The close association between the low-mass star clusters with massive star
cradles supports the role of these clusters in the formation of massive stars.
The X-ray observations show for the first time in the TC that low-mass stars
with intermediate extinction are clustered toward the position of the most
massive star, which is surrounded by a ring of non-extincted low-mass stars.
This 'envelope-core' structure is also supported by infrared and optical
observations. Our analysis suggests that at least two basic ingredients are
needed in massive star formation: the presence of dense gas and a cluster of
low-mass stars. The scenario that better explains our findings assumes high
fragmentation in the parental core, accretion at subcore scales that forms a
low-mass stellar cluster, and subsequent competitive accretion. Finally,
although coalescence does not seem a common mechanism for building up massive
stars, we show that a single stellar merger may have occurred in the evolution
of the OHC cluster, favored by the presence of disks, binaries, and gas
accretion.Comment: 17 pages, 11 figures, 3 Tables. Accepted for publication in A&
A probable pre-main sequence chemically peculiar star in the open cluster Stock 16
We used the Ultraviolet and Visual Echelle Spectrograph of the ESO-Very Large
Telescope to obtain a high resolution and high signal-to-noise ratio spectrum
of Stock 16-12, an early-type star which previous Delta-a photometric
observations suggest being a chemically peculiar (CP) star. We used spectral
synthesis to perform a detailed abundance analysis obtaining an effective
temperature of 8400 +/- 400 K, a surface gravity of 4.1 +/- 0.4, a
microturbulence velocity of 3.4 +0.7/-0.3 km/s, and a projected rotational
velocity of 68 +/- 4 km/s. We provide photometric and spectroscopic evidence
showing the star is most likely a member of the young Stock 16 open cluster
(age 3-8 Myr). The probable cluster membership, the star's position in the
Hertzsprung-Russell diagram, and the found infrared excess strongly suggest the
star is still in the pre-main-sequence (PMS) phase. We used PMS evolutionary
tracks to determine the stellar mass, which ranges between 1.95 and 2.3 Msun,
depending upon the adopted spectroscopic or photometric data results.
Similarly, we obtained a stellar age ranging between 4 and 6 Myr, in agreement
with that of the cluster. Because the star's chemical abundance pattern
resembles well that known of main sequence CP metallic line (Am) stars, the
object sets important constraints to the diffusion theory. Additional
spectroscopic and spectropolarimetric data allowed us to conclude that the
object is probably a single non-magnetic star.Comment: Accepted for publication in MNRAS; 8 pages, 5 figures, 1 tabl
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
A Molecular Counterpart to the Herbig-Haro 1-2 Flow
We present high angular resolution (12"-24") and high sensitivity 12CO and
13CO J=2-1 and J=1-0 observations of the HH 1-2 outflow. The observations show
the molecular counterpart, moving with a velocity of approx. 30 km/s, of the
optical bipolar system driven by the VLA 1 embedded source. Along the optical
jet there are certain regions where the molecular gas reaches deprojected
velocities of 100-200 km/s, and that we interpret as the molecular jet. The
bipolar CO outflow has a length of approx. 260" with a curved morphology
towards the North where it extends beyond the HH 1 object (approx. 120") .
Two new molecular outflows have been detected, one arising from IRAS
05339-0647 which excites the HH 147 optical flow and another powered by VLA 2
which drives the HH 144 optical outflow. The molecular outflow driven by the
VLA 3 source is also clearly detected and spatially resolved from the VLA 1
main outflow.Comment: 14 pages, 4 figures, accepted ApJLet
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