1,188 research outputs found
Methanol detection in M82
We present a multilevel study of the emission of methanol, detected for the
first time in this galaxy, and discuss the origin of its emission. The high
observed methanol abundance of a few 10^-9 can only be explained if injection
of methanol from dust grains is taken into account. While the overall
[CH3OH]/[NH3] ratio is much larger than observed towards other starbursts, the
dense high excitation component shows a similar value to that found in NGC 253
and Maffei 2. Our observations suggest the molecular material in M 82 to be
formed by dense warm cores, shielded from the UV radiation and similar to the
molecular clouds in other starbursts, surrounded by a less dense
photodissociated halo. The dense warm cores are likely the location of recent
and future star formation within M 82.Comment: Accepted for publication in A&A Letter
Extragalactic CS survey
We present a coherent and homogeneous multi-line study of the CS molecule in
nearby (D10Mpc) galaxies. We include, from the literature, all the available
observations from the to the transitions towards NGC 253, NGC
1068, IC 342, Henize~2-10, M~82, the Antennae Galaxies and M~83. We have, for
the first time, detected the CS(7-6) line in NGC 253, M~82 (both in the
North-East and South-West molecular lobes), NGC 4038, M~83 and tentatively in
NGC 1068, IC 342 and Henize~2-10. We use the CS molecule as a tracer of the
densest gas component of the ISM in extragalactic star-forming regions,
following previous theoretical and observational studies by Bayet et al.
(2008a,b and 2009). In this first paper out of a series, we analyze the CS data
sample under both Local Thermodynamical Equilibrium (LTE) and non-LTE (Large
Velocity Gradient-LVG) approximations. We show that except for M~83 and Overlap
(a shifted gas-rich position from the nucleus NGC 4039 in the Antennae
Galaxies), the observations in NGC 253, IC 342, M~82-NE, M~82-SW and NGC 4038
are not well reproduced by a single set of gas component properties and that,
at least, two gas components are required. For each gas component, we provide
estimates of the corresponding kinetic temperature, total CS column density and
gas density.Comment: 17 pages, 16 figures, 3 tables, Accepted to Ap
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
A new intermediate mass protostar in the Cepheus A HW2 region
We present the discovery of the first molecular hot core associated with an
intermediate mass protostar in the CepA HW2 region. The hot condensation was
detected from single dish and interferometric observations of several high
excitation rotational lines (from 100 to 880K above the ground state) of SO2 in
the ground vibrational state and of HC3N in the vibrationally excited states
v7=1 and v7=2. The kinetic temperature derived from both molecules is 160K. The
high-angular resolution observations (1.25'' x 0.99'') of the SO2
J=28(7,21)-29(6,24) line (488K above the ground state) show that the hot gas is
concentrated in a compact condensation with a size of 0.6''(430AU), located
0.4'' (300AU) east from the radio-jet HW2. The total SO2 column density in the
hot condensation is 10E18cm-2, with a H2 column density ranging from 10E23 to 6
x 10E24cm-2. The H2 density and the SO2 fractional abundance must be larger
than 10E7cm-3 and 2 x 10E-7 respectively. The most likely alternatives for the
nature of the hot and very dense condensation are discussed. From the large
column densities of hot gas, the detection of the HC3N vibrationally excited
lines and the large SO2 abundance, we favor the interpretation of a hot core
heated by an intermediate mass protostar of 10E3 Lo. This indicates that the
CepA HW2 region contains a cluster of very young stars
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
The spectral type of CHS7797 - an intriguing very low mass periodic variable in the Orion Nebula Cluster
We present the spectroscopic characterization of the unusual high-amplitude
very low mass pre-main-sequence periodic variable CHS7797. This study is based
on optical medium-resolution (R=2200) spectroscopy in the 6450-8600 A range,
carried out with GMOS-GEMINI-S in March 2011. Observations of CHS7797 have been
carried out at two distinct phases of the 17.8d period, namely at maximum and
four days before maximum. Four different spectral indices were used for the
spectral classification at these two phases, all of them well-suited for
spectral classification of young and obscured late M dwarfs. In addition, the
gravity-sensitive NaI (8183/8195 A) and KI (7665/7699 A) doublet lines were
used to confirm the young age of CHS7797. From the spectrum obtained at maximum
light we derived a spectral type (SpT) of M6.05, while for the spectrum taken
four days before maximum the derived SpT is M5.75. The derived SpTs confirm
that CHS7797 has a mass in the stellar-substellar boundary mass range. In
addition, the small differences in the derived SpTs at the two observed phases
may provide indirect hints that CHS7797 is a binary system of similar mass
components surrounded by a tilted circumbinary disk, a system similar to KH15D.Comment: 6 pages, accepted for publication A&
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