7,387 research outputs found
Evidence for episodic warm outflowing CO gas from the intermediate mass young stellar object IRAS 08470-4321
We present a R=10,000 M-band spectrum of LLN19 (IRAS 08470-4321), a heavily
embedded intermediate-mass young stellar object located in the Vela Molecular
Cloud, obtained with VLT-ISAAC. The data were fitted by a 2-slab cold-hot model
and a wind model. The spectrum exhibits deep broad ro-vibrational absorption
lines of 12CO v=1<-0 and 13CO v=1<-0. A weak CO ice feature at 4.67 micron is
also detected. Differences in velocity indicate that the warm gas is distinct
from the cold millimeter emitting gas, which may be associated with the
absorption by cooler gas (45K). The outflowing warm gas at 300-400K and with a
mass-loss rate varying between 0.48E-7 and 4.2E-7 MSun /yr can explain most of
the absorption. Several absorption lines were spectrally resolved in subsequent
spectra obtained with the VLT-CRIRES instrument. Multiple absorption
substructures in the high-resolution (R=100,000) spectra indicate that the
mass-loss is episodic with at least two major events that occurred recently
(<28 years). The discrete mass-loss events together with the large turbulent
width of the gas (dv=10-12 km/s) are consistent with the predictions of the
Jet-Bow shock outflow and the wide-angle wind model. The CO gas/solid column
density ratio of 20-100 in the line-of-sight confirms that the circumstellar
environment of LLN~19 is warm. We also derive a 12C/13C ratio of 67 +/- 3,
consistent with previous measurements in local molecular clouds but not with
the higher ratios found in the envelope of other young stellar objects.Comment: 16 pages, 12 figures, accepted for publication in MNRA
Impurity effect of Lambda hyperon on collective excitations of atomic nuclei
Taking the ground state rotational band in Mg as an example, we
investigate the impurity effect of hyperon on collective excitations
of atomic nuclei in the framework of non-relativistic energy density functional
theory. To this end, we take into account correlations related to the
restoration of broken symmetries and fluctuations of collective variables by
solving the eigenvalue problem of a five-dimensional collective Hamiltonian for
quadrupole vibrational and rotational degrees of freedom. The parameters of the
collective Hamiltonian are determined with constrained mean-field calculations
for triaxial shapes using the SGII Skyrme force. We compare the low-spin
spectrum for Mg with the spectrum for the same nucleus inside
Mg. It is found that the hyperon stretches the
ground state band and reduces the value by
, mainly by softening the potential energy surface towards the
spherical shape, even though the shrinkage effect on the average proton radius
is only .Comment: 16 pages, 5 figures, and 1 tabl
FUV and X-ray irradiated protoplanetary disks: a grid of models I. The disk structure
Context. Planets are thought to eventually form from the mostly gaseous (~99%
of the mass) disks around young stars. The density structure and chemical
composition of protoplanetary disks are affected by the incident radiation
field at optical, FUV, and X-ray wavelengths, as well as by the dust
properties.
Aims. The effect of FUV and X-rays on the disk structure and the gas chemical
composition are investigated. This work forms the basis of a second paper,
which discusses the impact on diagnostic lines of, e.g., C+, O, H2O, and Ne+
observed with facilities such as Spitzer and Herschel.
Methods. A grid of 240 models is computed in which the X-ray and FUV
luminosity, minimum grain size, dust size distribution, and surface density
distribution are varied in a systematic way. The hydrostatic structure and the
thermo-chemical structure are calculated using ProDiMo.
Results. The abundance structure of neutral oxygen is stable to changes in
the X-ray and FUV luminosity, and the emission lines will thus be useful
tracers of the disk mass and temperature. The C+ abundance distribution is
sensitive to both X-rays and FUV. The radial column density profile shows two
peaks, one at the inner rim and a second one at a radius r=5-10 AU. Ne+ and
other heavy elements have a very strong response to X-rays, and the column
density in the inner disk increases by two orders of magnitude from the lowest
(LX = 1e29 erg/s) to the highest considered X-ray flux (LX = 1e32 erg/s). FUV
confines the Ne+ ionized region to areas closer to the star at low X-ray
luminosities (LX = 1e29 erg/s). H2O abundances are enhanced by X-rays due to
higher temperatures in the inner disk and higher ionization fractions in the
outer disk. The line fluxes and profiles are affected by the effects on these
species, thus providing diagnostic value in the study of FUV and X-ray
irradiated disks around T Tauri stars. (abridged)Comment: 47 pages, accepted by Astronomy and Astrophysics, a high resolution
version of the paper is located at
http://www.astro.rug.nl/~meijerink/disk_paperI_xrays.pd
Treatment of multidrug-resistant tuberculosis in a remote, conflict-affected area of the Democratic Republic of Congo.
The Democratic Republic of Congo is a high-burden country for multidrug-resistant tuberculosis. Médecins Sans Frontières has supported the Ministry of Health in the conflict-affected region of Shabunda since 1997. In 2006, three patients were diagnosed with drug-resistant TB (DR-TB) and had no options for further treatment. An innovative model was developed to treat these patients despite the remote setting. Key innovations were the devolving of responsibility for treatment to non-TB clinicians remotely supported by a TB specialist, use of simplified monitoring protocols, and a strong focus on addressing stigma to support adherence. Treatment was successfully completed after a median of 24 months. This pilot programme demonstrates that successful treatment for DR-TB is possible on a small scale in remote settings
The effects of dust evolution on disks in the mid-IR
In this paper, we couple together the dust evolution code two-pop-py with the
thermochemical disk modelling code ProDiMo. We create a series of
thermochemical disk models that simulate the evolution of dust over time from
0.018 Myr to 10 Myr, including the radial drift, growth, and settling of dust
grains. We examine the effects of this dust evolution on the mid-infrared gas
emission, focussing on the mid-infrared spectral lines of C2H2, CO2, HCN, NH3,
OH, and H2O that are readily observable with Spitzer and the upcoming E-ELT and
JWST.
The addition of dust evolution acts to increase line fluxes by reducing the
population of small dust grains. We find that the spectral lines of all species
except C2H2 respond strongly to dust evolution, with line fluxes increasing by
more than an order of magnitude across the model series as the density of small
dust grains decreases over time. The C2H2 line fluxes are extremely low due to
a lack of abundance in the infrared line-emitting regions, despite C2H2 being
commonly detected with Spitzer, suggesting that warm chemistry in the inner
disk may need further investigation. Finally, we find that the CO2 flux
densities increase more rapidly than the other species as the dust disk
evolves. This suggests that the flux ratios of CO2 to other species may be
lower in disks with less-evolved dust populations.Comment: 13 pages, 9 figures, accepted in A&
Floquet stroboscopic divisibility in non-Markovian dynamics
We provide a general discussion of the Liouvillian spectrum for a system
coupled to a non-Markovian bath using Floquet theory. This approach is suitable
when the system is described by a time-convolutionless master equation with
time-periodic rates. Surprisingly, the periodic nature of rates allow us to
have a stroboscopic divisible dynamical map at discrete times, which we refer
to as Floquet stroboscopic divisibility. We illustrate the general theory for a
Schr\"odinger cat which is roaming inside a non-Markovian bath, and demonstrate
the appearance of stroboscopic revival of the cat at later time after its
death. Our theory may have profound implications in entropy production in
non-equilibrium systems.Comment: We changed the title and explained in more detail the definition of
non-Markovian dynamics used in the manuscrip
Results from a VLT-ISAAC survey of ices and gas around young stellar objects
General results from a 3-5 micron spectroscopic survey of nearby low-mass
young stellar objects are presented. L and M-band spectra have been obtained of
\~50 low mass embedded young stars using the ISAAC spectrometer mounted on
UT1-Antu at Paranal Observatory. For the first time, a consistent census of the
CO, H2O ices and the minor ice species CH3OH and OCN- and warm CO gas present
around young stars is obtained, using large number statistics and resolving
powers of up to R=10000. The molecular structure of circumstellar CO ices, the
depletion of gaseous CO onto grains in protoplanetary disks, the presence of
hot gas in the inner parts of circumstellar disks and in outflows and infalls
are studied. Furthermore, the importance of scattering effects for the
interpretation of the spectra have been addressed.Comment: To appear in the proceedings of the conference "Chemistry as a
Diagnostic of Star Formation", University of Waterloo, Canada, 21-23 August
200
Grain size limits derived from 3.6 {\mu}m and 4.5 {\mu}m coreshine
Recently discovered scattered light from molecular cloud cores in the
wavelength range 3-5 {\mu}m (called "coreshine") seems to indicate the presence
of grains with sizes above 0.5 {\mu}m. We aim to analyze 3.6 and 4.5 {\mu}m
coreshine from molecular cloud cores to probe the largest grains in the size
distribution. We analyzed dedicated deep Cycle 9 Spitzer IRAC observations in
the 3.6 and 4.5 {\mu}m bands for a sample of 10 low-mass cores. We used a new
modeling approach based on a combination of ratios of the two background- and
foreground-subtracted surface brightnesses and observed limits of the optical
depth. The dust grains were modeled as ice-coated silicate and carbonaceous
spheres. We discuss the impact of local radiation fields with a spectral slope
differing from what is seen in the DIRBE allsky maps. For the cores L260,
ecc806, L1262, L1517A, L1512, and L1544, the model reproduces the data with
maximum grain sizes around 0.9, 0.5, 0.65, 1.5, 0.6, and > 1.5 {\mu}m,
respectively. The maximum coreshine intensities of L1506C, L1439, and L1498 in
the individual bands require smaller maximum grain sizes than derived from the
observed distribution of band ratios. Additional isotropic local radiation
fields with a spectral shape differing from the DIRBE map shape do not remove
this discrepancy. In the case of Rho Oph 9, we were unable to reliably
disentangle the coreshine emission from background variations and the strong
local PAH emission. Considering surface brightness ratios in the 3.6 and 4.5
{\mu}m bands across a molecular cloud core is an effective method of
disentangling the complex interplay of structure and opacities when used in
combination with observed limits of the optical depth.Comment: 23 pages, 18 figures, accepted for publication in A&
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