524 research outputs found
Ammonia observations in the LBV nebula G79.29+0.46. Discovery of a cold ring and some warm spots
The surroundings of Luminous Blue Variable (LBV) stars are excellent
laboratories to study the effects of their high UV radiation, powerful winds,
and strong ejection events onto the surrounding gas and dust. The LBV
G79.29+0.46 powered two concentric infrared rings which may interact with the
infrared dark cloud (IRDC) G79.3+0.3. The Effelsberg 100m telescope was used to
observe the NH_3 (1,1), (2,2) emission surrounding G79.29+0.46 and the IRDC. In
addition, we observed particular positions in the (3,3) transition toward the
strongest region of the IRDC. We report here the first coherent shell-like
structure of dense NH_3 gas associated with an evolved massive star. The shell,
two or three orders of magnitude more tenuous than the IRDC, is well traced in
both ammonia lines, and surrounds the ionized nebula. The NH_3 emission in the
IRDC is characterized by a low and uniform rotational temperature (T_rot ~ 10
K) and moderately high opacities in the (1,1) line. The rest of the observed
field is spotted by warm or hot zones (T_rot > 30 K) and characterized by
optically thin emission of the (1,1) line. The NH_3 abundances are about
10^{-8} in the IRDC, and 10^{-10}-10^{-9} elsewhere. The warm temperatures and
low abundances of NH_3 in the shell suggest that the gas is being heated and
photo-dissociated by the intense UV field of the LBV star. An outstanding
region is found to the south-west (SW) of the LBV star within the IRDC. The
NH_3 (3,3) emission at the centre of the SW region reveals two velocity
components tracing gas at temperatures > 30K. The northern edge of the SW
region agrees with the border of the ring nebula and a region of continuum
enhancement; here, the opacity of the (1,1) line and the NH_3 abundance do not
decrease as expected in a typical clump of an isolated cold dark cloud. This
strongly suggests some kind of interaction between the ring nebula and the
IRDC.Comment: 15 pages, 13 figures, accepted by A&A. Note the change of title with
respect to previous versio
A search for water maser emission toward obscured post-AGB star and planetary nebula candidates
Water maser emission at 22 GHz is a useful probe to study the transition
between the nearly spherical mass-loss in the AGB to a collimated one in the
post-AGB phase. In their turn, collimated jets in the post-AGB phase could
determine the shape of planetary nebulae (PNe) once photoionization starts. We
intend to find new cases of post-AGB stars and PNe with water maser emission,
including water fountains or water-maser-emitting PNe. We observed water maser
emission in a sample of 133 objects, with a significant fraction being post-AGB
and young PN candidate sources with strong obscuration. We detected this
emission in 15 of them, of which seven are reported here for the first time. We
identified three water fountain candidates: IRAS 17291-2147, with a total
velocity spread of ~96 km/s in its water maser components and two sources (IRAS
17021-3109 and IRAS 17348-2906) that show water maser emission outside the
velocity range covered by OH masers. We have also identified IRAS 17393-2727 as
a possible new water-maser-emitting PN. The detection rate is higher in
obscured objects (14%) than in those with optical counterparts (7%), consistent
with previous results. Water maser emission seems to be common in objects that
are bipolar in the near-IR (43% detection rate). The water maser spectra of
water fountain candidates like IRAS 17291-2147 show significantly less maser
components than others (e.g., IRAS 18113-2503). We speculate that most
post-AGBs may show water maser emission with wide enough velocity spread (> 100
km/s) when observed with enough sensitivity and/or for long enough periods of
time. Therefore, it may be necessary to single out a special group of "water
fountains", probably defined by their high maser luminosities. We also suggest
that the presence of both water and OH masers in a PN is a better tracer of its
youth, rather than the presence of just one of these species.Comment: To be published in Astronomy & Astrophysics. 16 pages, 1 figure
(spanning 5 pages). This version includes some minor language corrections and
fixes some errors in Table
Quantum Hall resistance standards from graphene grown by chemical vapor deposition on silicon carbide
Replacing GaAs by graphene to realize more practical quantum Hall resistance
standards (QHRS), accurate to within in relative value, but operating
at lower magnetic fields than 10 T, is an ongoing goal in metrology. To date,
the required accuracy has been reported, only few times, in graphene grown on
SiC by sublimation of Si, under higher magnetic fields. Here, we report on a
device made of graphene grown by chemical vapour deposition on SiC which
demonstrates such accuracies of the Hall resistance from 10 T up to 19 T at 1.4
K. This is explained by a quantum Hall effect with low dissipation, resulting
from strongly localized bulk states at the magnetic length scale, over a wide
magnetic field range. Our results show that graphene-based QHRS can replace
their GaAs counterparts by operating in as-convenient cryomagnetic conditions,
but over an extended magnetic field range. They rely on a promising hybrid and
scalable growth method and a fabrication process achieving low-electron density
devices.Comment: 12 pages, 8 figure
The NH2D/NH3 ratio toward pre-protostellar cores around the UCHII region in IRAS 20293+3952
The deuterium fractionation, Dfrac, has been proposed as an evolutionary
indicator in pre-protostellar and protostellar cores of low-mass star-forming
regions. We investigate Dfrac, with high angular resolution, in the cluster
environment surrounding the UCHII region IRAS 20293+3952. We performed high
angular resolution observations with the IRAM Plateau de Bure Interferometer
(PdBI) of the ortho-NH2D 1_{11}-1_{01} line at 85.926 GHz and compared them
with previously reported VLA NH3 data. We detected strong NH2D emission toward
the pre-protostellar cores identified in NH3 and dust emission, all located in
the vicinity of the UCHII region IRAS 20293+3952. We found high values of
Dfrac~0.1-0.8 in all the pre-protostellar cores and low values, Dfrac<0.1,
associated with young stellar objects. The high values of Dfrac in
pre-protostellar cores could be indicative of evolution, although outflow
interactions and UV radiation could also play a role.Comment: 5 pages, 3 figures. Accepted for publication in Astronomy and
Astrophysics Letter
First detection of thermal radio jets in a sample of proto-brown dwarf candidates
We observed with the JVLA at 3.6 and 1.3 cm a sample of 11 proto-brown dwarf
candidates in Taurus in a search for thermal radio jets driven by the most
embedded brown dwarfs. We detected for the first time four thermal radio jets
in proto-brown dwarf candidates. We compiled data from UKIDSS, 2MASS, Spitzer,
WISE and Herschel to build the Spectral Energy Distribution (SED) of the
objects in our sample, which are similar to typical Class~I SEDs of Young
Stellar Objects (YSOs). The four proto-brown dwarf candidates driving thermal
radio jets also roughly follow the well-known trend of centimeter luminosity
against bolometric luminosity determined for YSOs, assuming they belong to
Taurus, although they present some excess of radio emission compared to the
known relation for YSOs. Nonetheless, we are able to reproduce the flux
densities of the radio jets modeling the centimeter emission of the thermal
radio jets using the same type of models applied to YSOs, but with
corresponding smaller stellar wind velocities and mass-loss rates, and
exploring different possible geometries of the wind or outflow from the star.
Moreover, we also find that the modeled mass outflow rates for the bolometric
luminosities of our objects agree reasonably well with the trends found between
the mass outflow rates and bolometric luminosities of YSOs, which indicates
that, despite the "excess" centimeter emission, the intrinsic properties of
proto-brown dwarfs are consistent with a continuation of those of very low mass
stars to a lower mass range. Overall, our study favors the formation of brown
dwarfs as a scaled-down version of low-mass stars.Comment: 18 pages, 8 figures, 14 tables, accepted by the Astrophysical Journa
Three intermediate-mass YSOs with different properties emerging from the same natal cloud in IRAS 00117+6412
We observed with the VLA, PdBI, and SMA the centimeter and millimeter
continuum, N2H+(1-0), and CO(2-1) emission associated with a dusty cloud
harboring a nascent cluster with intermediate-mass protostars. At centimeter
wavelengths we found a strong source, tracing a UCHII region, at the eastern
edge of the dusty cloud, with a shell-like structure, and with the
near-infrared counterpart falling in the center of the shell. This is
presumably the most massive source of the forming cluster. About 15'' to the
west of the UCHII region and well embedded in the dusty cloud, we detected a
strong millimeter source, MM1, associated with centimeter and near-infrared
emission. MM1 seems to be driving a prominent high-velocity CO bipolar outflow,
and is embedded in a ridge of dense gas traced by N2H+. We estimated that MM1
is an intermediate-mass source in the Class 0/I phase. About 15'' to the south
of MM1, and still more deeply embedded in the dusty cloud, we detected a
compact millimeter source, MM2, with neither centimeter nor near-infrared
emission, but with water maser emission. MM2 is associated with a clump of
N2H+, whose kinematics reveal a clear velocity gradient and additionally we
found signposts of infall motions. MM2, being deeply embedded within the dusty
cloud, with an associated water maser but no hints of CO outflow emission, is
an intriguing object, presumably of intermediate mass. In conclusion, the UCHII
region is found at the border of a dusty cloud which is currently undergoing
active star formation. Two intermediate-mass protostars in the dusty cloud seem
to have formed after the UCHII region and have different properties related to
the outflow phenomenon.Comment: accepted to Astronomy and Astrophysic
Release of trace elements during bioreductive dissolution of magnetite from metal mine tailings: Potential impact on marine environments
Adverse impacts of mine tailings on water and sediments quality are major worldwide environmental problems. Due to the environmental issues associated with the deposition of mine tailings on land, a controversial discussed alternative is submarine tailings disposal (STD). However, Fe(III) bioreduction of iron oxides (e.g., magnetite) in the tailings disposed might cause toxic effects on coastal environments due to the release of different trace elements (TEs) contained in the oxides. To study the extent and kinetics of magnetite bioreduction under marine conditions and the potential release of TEs, a number of batch experiments with artificial seawater (pH 8.2) and a marine microbial strain (Shewanella loihica) were performed using several magnetite ore samples from different mines and a mine tailings sample. The elemental composition of the magnetite determined in the tailings showed relatively high amounts of TEs (e.g., Mn, Zn, Co) compared with those of the magnetite ore samples (LA-ICP-MS and EMPA analyses). The experiments were conducted at 10 °C in the dark for up to 113 days. Based on the consumption of lactate and production of acetate and aqueous Fe(II) over time, the magnitude of Fe(III) bioreduction was calculated using a geochemical model including Monod kinetics. Model simulations reproduced the release of iron and TEs observed throughout the experiments, e.g., Mn (up to 203 μg L−1), V (up to 79 μg L−1), As (up to 17 μg L−1) and Cu (up to 328 μg L−1), suggesting a potential contamination of pore water by STD. Therefore, the results of this study can help to better evaluate the potential impacts of STD
Phenotypic and molecular characterization of Phaseolus vulgaris plants from non-cryopreserved and cryopreserved seeds
The objective of this work was to evaluate if cryostorage of Phaseolus vulgaris L. seeds induced variations in regenerated plants at the phenotypic and molecular levels. A series of agricultural traits was measured on plants grown from control, non-cryopreserved and cryopreserved seeds, and the genetic stability of plants of the second generation was analysed at selected microsatellite loci. The phenotype of the second generation plants was evaluated as well. No statistically significant phenotypic differences were observed for the parameters measured, neither in the first nor in the second generations. Averaging both treatments, about 76% of the seeds had germinated 10 days after sowing. At harvest we recorded plants with about 73 cm in height, 13 stem internodes, 25 fruits, 103 grains and 4 grains per fruit. One hundred seeds weighted about 26 g. The genetic analyses performed on the second generation plants using six nuclear Simple Sequences Repeats (SSR) markers revealed no changes in microsatellite length between control and cryopreserved samples, implying that there was no effect of seed liquid nitrogen exposure on genome integrity. The phenotypic and molecular results reported here confirm that cryostorage is an efficient and reliable technique to conserve P. vulgaris seeds and regenerate true-to-type plants
Star formation in the vicinity of the IC 348 cluster
Aims. We present molecular line observations of the southwestern part of the
IC 348 young cluster, and we use them together with NIR and mm continuum data
to determine the distribution of dense gas, search for molecular outflows, and
analyze the ongoing star formation activity in the region. Methods. Our
molecular line data consists of C18O(1--0) and N2H+(1--0) maps obtained with
the FCRAO telescope at a resolution of about 50'' and CO(2--1) data obtained
with the IRAM 30m telescope at a resolution of 11''. Results. The dense gas
southwest of IC 348 is concentrated in two groups of dense cores, each of them
with a few solar masses of material and indications of CO depletion at high
density. One of the core groups is actively forming stars, while the other
seems starless. There is evidence for at least three bipolar molecular outflows
in the region, two of them powered by previously identified Class 0 sources,
while the other one is powered by a still not well characterized low-luminosity
object. The ongoing star formation activity is producing a small stellar
subgroup in the cluster. Using the observed core characteristics and the star
formation rate in the cluster we propose that that similar episodes of stellar
birth may have produced the subclustering observed in the halo of IC 348.Comment: 10 pages, 6 figures, A&A accepte
IRAS 21391+5802: The Molecular Outflow and its Exciting Source
We present centimeter and millimeter observations of gas and dust around IRAS
21391+5802, an intermediate-mass source embedded in the core of IC 1396N.
Continuum observations from 3.6 cm to 1.2 mm are used to study the embedded
objects and overall distribution of the dust, while molecular line observations
of CO, CS, and CH3OH are used to probe the structure and chemistry of the
outflows in the region. The continuum emission at centimeter and millimeter
wavelengths has been resolved into three sources separated about 15 arcsec from
each other, and with one of them, BIMA 2, associated with IRAS 21391+5802. The
dust emission around this source shows a very extended envelope, which accounts
for most of the circumstellar mass of 5.1 Msun. This source is powering a
strong molecular outflow, elongated in the E--W direction, which presents a
complex structure and kinematics. While at high outflow velocities the outflow
is clearly bipolar, at low outflow velocities the blueshifted and redshifted
emission are highly overlapping, and the strongest emission shows a V-shaped
morphology. The outflow as traced by CS and CH3OH exhibits two well
differentiated and clumpy lobes, with two prominent northern blueshifted and
redshifted clumps. The curved shape of the clumps and the spectral shape at
these positions are consistent with shocked material. In addition, CS and CH3OH
are strongly enhanced toward these positions with respect to typical quiescent
material abundances in other star-forming regions.Comment: 41 pages, including 11 figures, accepted for publication in ApJ (July
1); available at http://www.am.ub.es/~robert/Papers.html#las
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