401 research outputs found
First evidence of quasi-periodic magnetic intraday activity from SiO emission in the atmosphere of two Mira stars
accepté A&A 2008During the phase when stars appear in the Hertzsprung-Russell-Diagram in the upper asymptotic giant branch (AGB), they loose, due to a wind driven by pulsations, at least half of their mass. The inner part of the envelop thus formed, also called extended atmosphere, is expected to bear complex magneto-hydrodynamic phenomena, due to the interaction of the wind with the previously expulsed matter and, possibly, with Jovian or terrestial planets. As in the solar system, fluctuations of the magnetic field ("space weather" about a mean value can be expected, but the observational evidence is still lacking. Here we show that for a narrow range of velocities the circular polarization of SiO masers, tracing the magnetic field in the extended atmosphere of AGB stars, varies in two stars with a period of a few hours. Previous multi-epoch observations of SiO masers were neither polarimetric nor critically sampled to detect such intraday magnetic fluctuations. Because statistically significant fluctuations are seemingly rare and localized in the extended atmosphere, they are expected to be due to a variety of phenomena. Coronal flux loops, magnetic clouds or Jovian magnetospheres provide suitable explanations. Our study opens the way to future observations combining intensive full polarization monitoring of SiO masers, sampling at least once per hour, with high spatial resolution. This will ultimately allow us to distinguish between the proposed scenarios and to investigate the fate of inner planetary systems around solar-type stars entering their AGB phase
Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B
Aims. The aim of this paper is to study deuterated water in the solar-type
protostars NGC1333 IRAS4A and IRAS4B, to compare their HDO abundance
distribution with other star-forming regions, and to constrain their HDO/H2O
ratios. Methods. Using the Herschel/HIFI instrument as well as ground-based
telescopes, we observed several HDO lines covering a large excitation range
(Eup/k=22-168 K) towards these protostars and an outflow position. Non-LTE
radiative transfer codes were then used to determine the HDO abundance profiles
in these sources. Results. The HDO fundamental line profiles show a very broad
component, tracing the molecular outflows, in addition to a narrower emission
component and a narrow absorbing component. In the protostellar envelope of
NGC1333 IRAS4A, the HDO inner (T>100 K) and outer (T<100 K) abundances with
respect to H2 are estimated at 7.5x10^{-9} and 1.2x10^{-11}, respectively,
whereas, in NGC1333 IRAS4B, they are 1.0x10^{-8} and 1.2x10^{-10},
respectively. Similarly to the low-mass protostar IRAS16293-2422, an absorbing
outer layer with an enhanced abundance of deuterated water is required to
reproduce the absorbing components seen in the fundamental lines at 465 and 894
GHz in both sources. This water-rich layer is probably extended enough to
encompass the two sources as well as parts of the outflows. In the outflows
emanating from NGC1333 IRAS4A, the HDO column density is estimated at about
(2-4)x10^{13} cm^{-2}, leading to an abundance of about (0.7-1.9)x10^{-9}. An
HDO/H2O ratio between 7x10^{-4} and 9x10^{-2} is derived in the outflows. In
the warm inner regions of these two sources, we estimate the HDO/H2O ratios at
about 1x10^{-4}-4x10^{-3}. This ratio seems higher (a few %) in the cold
envelope of IRAS4A, whose possible origin is discussed in relation to formation
processes of HDO and H2O.Comment: 16 pages, 13 figure
Conversion of Cerrado into agricultural land in the south-western amazon: carbon stocks and soil fertility.
Mudanças de uso da terra e práticas de manejo modificam a dinâmica do C e a fertilidade do solo. Este estudo avaliou as implicações dos sistemas de cultivo (NT e CT) nos estoques de C e de nutrientes e identificou inter-relações entre estes estoques e outros atributos da fertilidade do solo em Latossolo após a mudança do uso da terra no cerrado amazônico. Os estoques de C e de nutrientes (P, K, Ca e Mg) ajustados pela massa equivalente do solo sob cerrado (CE), foram maiores principalmente sob NT. Após a adoção do NT, exceto em 2NT, os estoques de C foram maiores em relação às demais áreas avaliadas. Correlações entre estoques de C e de nutrientes revelaram algumas correlações positivas com Ca e Mg nas áreas sob NT, devido ao uso continuo de calcário, à maior quantidade de resíduos culturais e ao não revolvimento do solo, associado à correlações positivas com CTC, saturação por bases e pH. A correlação positiva (r = 0,91, p < 0,05) entre estoques de C e CTC em CE indica a importante contribuição da MOS na CT de solos tropicais, embora os sítios de troca estejam ocupados principalmente por H + Al. Estoques de P e K mostraram correlações positivas com estoques de C em CE (0,81 e 0,82; respectivamente), indicando a alta relação de P e K com a MOS em ecossistemas naturais. A alta variabilidade espacial associada à aplicação de fertilizantes (P e K) no sulco de plantio pode ter mascarado os resultados dos estoques. A principal fonte destes nutrientes para o solo foi o fertilizante aplicado e não a MOS
High-mass star formation in the Southern Hemisphere sky
We report on a multi-wavelength (IR to cm) and multi-resolution (1 mas to 20
arcsec) exploration of high-mass star formation regions in the Galactic plane,
at longitudes observable from the Southern Hemisphere. Our source sample was
originally identified through methanol masers in the Galactic plane, which
exclusively trace high-mass star-forming regions. (Sub)millimetre continuum and
molecular line observations were carried out with SEST/SIMBA, JCMT/SCUBA and
ATNF/Mopra mm-wave telescopes and have allowed us to identify massive (
M) and luminous ( L) clumps in each star-forming
region. We have also constrained the SED with additional archival IR data, the
physical conditions (, , ) and the chemical composition of each
massive clump. Several types of objects were characterised based on the
ratio, the dust temperature and the molecular line
properties, ranging from class 0-like YSO clusters (,
T=30 K) to hot molecular clumps (, K).
Preliminary high-angular resolution observations for a subset of the sample
with the ATNF/ATCA at 3 mm, the VLA at 15, 22 and 43 GHz and Gemini in MIR have
revealed that several (proto)stellar objects are embedded in the massive
clumps: massive protostars, hot cores and hyper-compact HII regions. We have
thus identified protoclusters of massive YSOs, which are the precursors of the
OB associations. This sample of Southern Hemisphere star-forming regions will
be extremely valuable for the scientific preparation of the ALMA and HSO
observations.Comment: 4 pages, 3 figures, conference proceeding
Transcriptional Rewiring of the Sex Determining dmrt1 Gene Duplicate by Transposable Elements
Control and coordination of eukaryotic gene expression rely on transcriptional and posttranscriptional regulatory networks. Evolutionary innovations and adaptations often require rapid changes of such networks. It has long been hypothesized that transposable elements (TE) might contribute to the rewiring of regulatory interactions. More recently it emerged that TEs might bring in ready-to-use transcription factor binding sites to create alterations to the promoters by which they were captured. A process where the gene regulatory architecture is of remarkable plasticity is sex determination. While the more downstream components of the sex determination cascades are evolutionary conserved, the master regulators can switch between groups of organisms even on the interspecies level or between populations. In the medaka fish (Oryzias latipes) a duplicated copy of dmrt1, designated dmrt1bY or DMY, on the Y chromosome was shown to be the master regulator of male development, similar to Sry in mammals. We found that the dmrt1bY gene has acquired a new feedback downregulation of its expression. Additionally, the autosomal dmrt1a gene is also able to regulate transcription of its duplicated paralog by binding to a unique target Dmrt1 site nested within the dmrt1bY proximal promoter region. We could trace back this novel regulatory element to a highly conserved sequence within a new type of TE that inserted into the upstream region of dmrt1bY shortly after the duplication event. Our data provide functional evidence for a role of TEs in transcriptional network rewiring for sub- and/or neo-functionalization of duplicated genes. In the particular case of dmrt1bY, this contributed to create new hierarchies of sex-determining genes
Molecular line survey of the high-mass star-forming region NGC 6334I with Herschel/HIFI and the SMA
We aim at deriving the molecular abundances and temperatures of the hot
molecular cores in the high-mass star-forming region NGC 6334I and consequently
deriving their physical and astrochemical conditions. In the framework of the
Herschel guaranteed time key program CHESS, NGC 6334I is investigated by using
HIFI aboard the Herschel Space Observatory. A spectral line survey is carried
out in the frequency range 480-1907 GHz, and auxiliary interferometric data
from the SMA in the 230 GHz band provide spatial information for disentangling
the different physical components contributing to the HIFI spectrum. The
spectral lines are identified with the aid of former surveys and spectral line
catalogs. The observed spectrum is then compared to a simulated synthetic
spectrum with XCLASS, assuming local thermal equilibrium, and best fit
parameters are derived using the model optimization package MAGIX. A total of
46 molecules are identified, with 31 isotopologues, resulting in about 4300
emission and absorption lines. High- energy levels of the dominant emitter
methanol and vibrationally excited HCN are detected. The number of unidentified
lines remains low with 75, or less than 2 percent of the lines detected. The
modeling suggests that several spectral features need two or more components to
be fitted properly. Other components could be assigned to cold foreground
clouds or to outflows, most visible in the SiO emission. A chemical variation
between the two embedded hot cores is found, with more N-bearing molecules
identified in SMA1 and O-bearing molecules in SMA2. Spectral line surveys give
powerful insights into the study of the interstellar medium. Different
molecules trace different physical conditions like the inner hot core, the
envelope, the outflows or the cold foreground clouds. The derived molecular
abundances provide further constraints for astrochemical models.Comment: 30 pages including appendix, 49 figures, accepted for publication in
Astronomy and Astrophysic
S-bearing molecules in massive dense cores
Context. Although few in number, high-mass stars play a major role in the interstellar energy budget and the shaping of the Galactic environment; however, the formation of high-mass stars is not well understood, because of their large distances, short time scales, and heavy extinction.
Aims. The chemical composition of the massive cores forming high-mass stars can put some constraints on the time scale of the massive star formation: sulfur chemistry is of specific interest thanks to its rapid evolution in warm gas and because the abundance of sulfur-bearing species increases significantly with the temperature.
Methods. Two mid-infrared quiet and two brighter massive cores were observed in various transitions (E_(up) to 289 K) of CS, OCS, H_2S, SO, and SO_2 and of their ^(34)S isotopologues at mm wavelengths with the IRAM 30m and CSO telescopes. The 1D modeling of the dust continuum is used to derive the density and temperature laws, which were then applied in the RATRAN code to modeling the observed line emission and to deriving the relative abundances of the molecules.
Results. All lines are detected, except the highest energy SO_2 transition. Infall (up to 2.9 km s^(-1)) may be detected towards the core W43MM1. The inferred mass rate is 5.8–9.4 10^(-2) M_⊙/yr. We propose an evolutionary sequence of our sources (W43MM1 → IRAS18264-1152 → IRAS05358+3543 → IRAS18162-2048), based on the SED analysis. The analysis of the variations in abundance ratios from source to source reveals that the SO and SO_2 relative abundances increase with time, while CS and OCS decrease.
Conclusions. Molecular ratios, such as [OCS/H_2S], [CS/H_2S], [SO/OCS], [SO_2/OCS], [CS/SO], and [SO_2/SO] may be good indicators of evolution, depending on layers probed by the observed molecular transitions. Observations of molecular emission from warmer layers, so that involving higher upper energy levels must be included
Master crossover behavior of parachor correlations for one-component fluids
The master asymptotic behavior of the usual parachor correlations, expressing
surface tension as a power law of the density difference
between coexisting liquid and vapor, is analyzed for a
series of pure compounds close to their liquid-vapor critical point, using only
four critical parameters , , and ,
for each fluid.
... The main consequences of these theoretical estimations are discussed in
the light of engineering applications and process simulations where parachor
correlations constitute one of the most practical method for estimating surface
tension from density and capillary rise measurements
S-bearing molecules in Massive Dense Cores
Chemical composition of the massive cores forming high-mass stars can put
some constrains on the time scale of the massive star formation: sulphur
chemistry is of specific interest due to its rapid evolution in warm gas and
because the abundance of sulphur bearing species increases significantly with
the temperature. Two mid-infrared quiet and two brighter massive cores are
observed in various transitions (E_up up to 289K) of CS, OCS, H2S, SO, SO2 and
of their isotopologues at mm wavelengths with the IRAM 30m and CSO telescopes.
1D modeling of the dust continuum is used to derive the density and temperature
laws, which are then applied in the RATRAN code to model the observed line
emission, and to derive the relative abundances of the molecules. All lines,
except the highest energy SO2 transition, are detected. Infall (up to 2.9km/s)
may be detected towards the core W43MM1. The inferred mass rate is 5.8-9.4
10^{-2} M_{\odot}/yr. We propose an evolutionary sequence of our sources
(W43MM1-IRAS18264-1152-IRAS05358+3543-IRAS18162-2048), based on the SED
analysis. The analysis of the variations in abundance ratios from source to
source reveals that the SO and SO2 relative abundances increase with time,
while CS and OCS decrease. Molecular ratios, such as [OCS/H2S], [CS/H2S],
[SO/OCS], [SO2/OCS], [CS/SO] and [SO2/SO] may be good indicators of evolution
depending on layers probed by the observed molecular transitions. Observations
of molecular emission from warmer layers, hence involving higher upper energy
levels are mandatory to include.Comment: 24 pages, accepted for publicatio
Fluctuations of elastic interfaces in fluids: Theory and simulation
We study the dynamics of elastic interfaces-membranes-immersed in thermally
excited fluids. The work contains three components: the development of a
numerical method, a purely theoretical approach, and numerical simulation. In
developing a numerical method, we first discuss the dynamical coupling between
the interface and the surrounding fluids. An argument is then presented that
generalizes the single-relaxation time lattice-Boltzmann method for the
simulation of hydrodynamic interfaces to include the elastic properties of the
boundary. The implementation of the new method is outlined and it is tested by
simulating the static behavior of spherical bubbles and the dynamics of bending
waves. By means of the fluctuation-dissipation theorem we recover analytically
the equilibrium frequency power spectrum of thermally fluctuating membranes and
the correlation function of the excitations. Also, the non-equilibrium scaling
properties of the membrane roughening are deduced, leading us to formulate a
scaling law describing the interface growth, W^2(L,T)=L^3 g[t/L^(5/2)], where
W, L and T are the width of the interface, the linear size of the system and
the temperature respectively, and g is a scaling function. Finally, the
phenomenology of thermally fluctuating membranes is simulated and the frequency
power spectrum is recovered, confirming the decay of the correlation function
of the fluctuations. As a further numerical study of fluctuating elastic
interfaces, the non-equilibrium regime is reproduced by initializing the system
as an interface immersed in thermally pre-excited fluids.Comment: 15 pages, 11 figure
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