5,179 research outputs found
HST FUV C IV observations of the hot DG Tauri jet
Protostellar jets are tightly connected to the accretion process and regulate
the angular momentum balance of accreting star-disk systems. The DG Tau jet is
one of the best-studied protostellar jets and contains plasma with temperatures
ranging over three orders of magnitude within the innermost 50 AU of the jet.
We present new Hubble Space Telescope (HST) far ultraviolet (FUV) long-slit
spectra spatially resolving the C IV emission (T~1e5 K) from the jet for the
first time, and quasi-simultaneous HST observations of optical forbidden
emission lines ([O I], [N II], [S II] and [O III]) and fluorescent H2 lines.
The C IV emission peaks at 42 AU from the stellar position and has a FWHM of 52
AU along the jet. Its deprojected velocity of around 200 km/s decreases
monotonically away from the driving source. In addition, we compare our HST
data with the X-ray emission from the DG Tau jet. We investigate the
requirements to explain the data by an initially hot jet compared to local
heating. Both scenarios indicate a mass loss by the T~1e5 K jet of ~1e-9
Msun/year, i.e., between the values for the lower temperature jet (T~1e4 K) and
the hotter X-ray emitting part (T>1e6 K). However, a simple initially hot wind
requires a large launching region (~1 AU), and we therefore favor local
heating.Comment: 5 pages, 2 figures, accepted by A&A letter
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Emission of volatile halogenated organic compounds over various Dead Sea landscapes
Volatile halogenated organic compounds (VHOCs), such as methyl halides (CH3X; X is Br, Cl and I) and very short-lived halogenated substances (VSLSs; bromoform-CHBr3, dibromomethane-CH2Br2, bromodichloromethane-CHBrCl2, trichloroethylene-C2HCl3, chloroform-CHCl3- A nd dibromochloromethane-CHBr2Cl) are well known for their significant influence on ozone concentrations and oxidation capacity of the troposphere and stratosphere and for their key role in aerosol formation. Insufficient characterization of the sources and the emission rate of VHOCs limits our ability to understand and assess their impact in both the troposphere and stratosphere. Over the last two decades, several natural terrestrial sources for VHOCs, including soil and vegetation, have been identified, but our knowledge of emission rates from these sources and their responses to changes in ambient conditions remains limited. Here we report measurements of the mixing ratios and fluxes of several chlorinated and brominated VHOCs from different landscapes and natural and agricultural vegetated sites at the Dead Sea during different seasons. Fluxes were generally positive (emission into the atmosphere), corresponding to elevated mixing ratios, but were highly variable. Fluxes (and mixing ratios) for the investigated VHOCs ranged as follows: CHBr3 from 79 to 187 nmolm2 d1 (1.9 to 22.6 pptv), CH2Br2 from 55 to 71 nmolm2 d1 (0.7 to 19 pptv), CHBr2Cl from 408 to 768 nmolm2 d1 (0.4 to 11 pptv), CHBrCl2 from 29 to 45 nmolm2 d1 (0.5 to 9.6 pptv), CHCl3 from 577 to 883 nmolm2 d1 (15 to 57 pptv), C2HCl3 from 74 to 884 nmolm2 d1 (0.4 to 11 pptv), methyl chloride (CH3Cl) from-5300 to 10,800 nmolm2 d1 (530 to 730 pptv), methyl bromide (CH3Br) from 111 to 118 nmolm2 d1 (7.5 to 14 pptv) and methyl iodide (CH3I) from 25 to 17 nmolm2 d1 (0.4 to 2.8 pptv). Taking into account statistical uncertainties, the coastal sites (particularly those where soil is mixed with salt deposits) were identified as sources of all VHOCs, but this was not statistically significant for CHCl3. Further away from the coastal area, the bare soil sites were sources for CHBrCl2, CHBr2Cl, CHCl3, and probably also for CH2Br2 and CH3I, and the agricultural sites were sources for CHBr3, CHBr2Cl and CHBrCl2. In contrast to previous reports, we also observed emissions of brominated trihalomethanes, with net molar fluxes ordered as follows: CHBr2Cl > CHCl3 > CHBr3 > CHBrCl2 and lowest positive flux incidence for CHCl3 among all trihalomethanes; this finding can be explained by the soil's enrichment with Br. Correlation analysis, in agreement with recent studies, indicated common controls for the emission of CHBr2Cl and CHBrCl2 and likely also for CHBr3. There were no indications for correlation of the brominated trihalomethanes with CHCl3. Also in line with previous reports, we observed elevated emissions of CHCl3 and C2HCl3 from mixtures of soil and different salt-deposited structures; the flux correlations between these compounds and methyl halides (particularly CH3I) suggested that at least CH3I is also emitted via similar mechanisms or is subjected to similar controls. Overall, our results indicate elevated emission of VHOCs from bare soil under semiarid conditions. Along with other recent studies, our findings point to the strong emission potential of a suite of VHOCs from saline soils and salt lakes and call for additional studies of emission rates and mechanisms of VHOCs from saline soils and salt lakes
Nuclear Photonics
With new gamma-beam facilities like MEGa-ray at LLNL (USA) or ELI-NP at
Bucharest with 10^13 g/s and a bandwidth of Delta E_g/E_g ~10^-3, a new era of
g-beams with energies <=20 MeV comes into operation, compared to the present
world-leading HIGS facility (Duke Univ., USA) with 10^8 g/s and Delta
E_g/E_g~0.03. Even a seeded quantum FEL for g-beams may become possible, with
much higher brilliance and spectral flux. At the same time new exciting
possibilities open up for focused g-beams. We describe a new experiment at the
g-beam of the ILL reactor (Grenoble), where we observed for the first time that
the index of refraction for g-beams is determined by virtual pair creation.
Using a combination of refractive and reflective optics, efficient
monochromators for g-beams are being developed. Thus we have to optimize the
system of the g-beam facility, the g-beam optics and g-detectors. We can trade
g-intensity for band width, going down to Delta E_g/E_g ~ 10^-6 and address
individual nuclear levels. 'Nuclear photonics' stresses the importance of
nuclear applications. We can address with g-beams individual nuclear isotopes
and not just elements like with X-ray beams. Compared to X rays, g-beams can
penetrate much deeper into big samples like radioactive waste barrels, motors
or batteries. We can perform tomography and microscopy studies by focusing down
to micron resolution using Nucl. Reson. Fluorescence for detection with eV
resolution and high spatial resolution. We discuss the dominating M1 and E1
excitations like scissors mode, two-phonon quadrupole octupole excitations,
pygmy dipole excitations or giant dipole excitations under the new facet of
applications. We find many new applications in biomedicine, green energy,
radioactive waste management or homeland security. Also more brilliant
secondary beams of neutrons and positrons can be produced.Comment: 8 pages, 3 figures, 2 table
Reproduction affects immune defenses in the guinea pig even under ad libitum food
Reproduction is one of the costliest processes in the life of an animal. Life history theory assumes that when resources are limiting allocation to reproduction will reduce allocation to other essential processes thereby inducing costs of reproduction. The immune system is vital for survival. If reproduction reduces investment in immune function, this could increase the risk of disease, morbidity and mortality. We here test in the guinea pig, if even under ad libitum food conditions, pregnancy and lactation reduce the activity of the adaptive and innate immune system compared to the reaction of non-reproducing animals. In response to a challenge with keyhole limpet haemocyanin the antibody-mediated adaptive immunity during (pregnancy and) lactation was reduced. Pregnant and lactating females showed higher levels of bacterial killing activity, an integrated measure of innate immunity, than non-reproducing females. However, two major effectors of the innate immunity, the natural antibody and the complement of pregnant and lactating females showed lower levels than in non-reproducing females. Pregnant and lactating females did not differ significantly in the expressed levels of innate immunity. Our results indicate that changes in the immune response during reproduction are physiological adjustments to predictable allocation problems, because they happen even under ad libitum food availability
MOST photometry of the enigmatic PMS pulsator HD 142666
We present precise photometry of the pulsating Herbig Ae star HD 142666
obtained in two consecutive years with the MOST (Microvariability & Oscilations
of STars) satellite.
Previously, only a single pulsation period was known for HD 142666. The MOST
photometry reveals that HD 142666 is multi-periodic. However, the unique
identification of pulsation frequencies is complicated by the presence of
irregular variability caused by the star's circumstellar dust disk. The two
light curves obtained with MOST in 2006 and 2007 provided data of unprecedented
quality to study the pulsations in HD 142666 and also to monitor the
circumstellar variability.
We attribute 12 frequencies to pulsation. Model fits to the three frequencies
with the highest amplitudes lie well outside the uncertainty box for the star's
position in the HR diagram based on published values.
The models suggest that either (1) the published estimate of the luminosity
of HD 142666, based on a relation between circumstellar disk radius and stellar
luminosity, is too high and/or (2) additional physics such as mass accretion
may be needed in our models to accurately fit both the observed frequencies and
HD 142666's position in the HR diagram.Comment: 10 pages, 11 figures, accepted for publication by Astronomy and
Astrophysic
Spectropolarimetry of the Classical T Tauri Star TW Hydrae
We present high resolution (R ~ 60,000) circular spectropolarimetry of the
classical T Tauri star TW Hydrae. We analyze 12 photospheric absorption lines
and measure the net longitudinal magnetic field for 6 consecutive nights. While
no net polarization is detected the first five nights, a significant
photospheric field of Bz = 149 \pm 33 G is found on the sixth night. To rule
out spurious instrumental polarization, we apply the same analysis technique to
several non-magnetic telluric lines, detecting no significant polarization. We
further demonstrate the reality of this field detection by showing that the
splitting between right and left polarized components in these 12 photospheric
lines shows a linear trend with Lande g-factor times wavelength squared, as
predicted by the Zeeman effect. However, this longitudinal field detection is
still much lower than that which would result if a pure dipole magnetic
geometry is responsible for the mean magnetic field strength of 2.6 kG
previously reported for TW Hya. We also detect strong circular polarization in
the He I 5876 and the Ca II 8498 emission lines, indicating a strong field in
the line formation region of these features. The polarization of the Ca II line
is substantially weaker than that of the He I line, which we interpret as due
to a larger contribution to the Ca II line from chromospheric emission in which
the polarization signals cancel. However, the presence of polarization in the
Ca II line indicates that accretion shocks on Classical T Tauri stars do
produce narrow emission features in the infrared triplet lines of Calcium.Comment: One tar file. The paper has 22 pages, 5 figures. Accepted by AJ on
Sep 10, 200
- A tool for multiband light curve modeling of planetary transits and stellar spots
Several studies have shown that stellar activity features, such as occulted
and non-occulted starspots, can affect the measurement of transit parameters
biasing studies of transit timing variations and transmission spectra. We
present , which we designed to model multiband transit
light curves showing starspot anomalies, inferring both transit and spot
parameters. The code follows a pixellation approach to model the star with its
corresponding limb darkening, spots, and transiting planet on a two dimensional
Cartesian coordinate grid. We combine with an MCMC
framework to study and derive exoplanet transmission spectra, which provides
statistically robust values for the physical properties and uncertainties of a
transiting star-planet system. We validate 's performance
by analyzing eleven synthetic light curves of four different star-planet
systems and 20 transit light curves of the well-studied WASP-41b system. We
also investigate the impact of starspots on transit parameters and derive
wavelength dependent transit depth values for WASP-41b covering a range of
6200-9200 , indicating a flat transmission spectrum.Comment: 17 pages, 22 figures; accepted for publication in Astronomy &
Astrophysic
Measuring the Magnetic Field on the Classical T Tauri Star TW Hydrae
We present infrared (IR) and optical echelle spectra of the Classical T Tauri
star TW Hydrae. Using the optical data, we perform detailed spectrum synthesis
to fit atomic and molecular absorption lines and determine key stellar
parameters: Teff = 4126 \pm 24 K, log g = 4.84 \pm 0.16, [M/H] = -0.10 \pm
0.12, vsini = 5.8 \pm 0.6 km/s. The IR spectrum is used to look for Zeeman
broadening of photospheric absorption lines. We fit four Zeeman sensitive Ti I
lines near 2.2 microns and find the average value of the magnetic field over
the entire surface is 2.61 \pm 0.23 kG. In addition, several nearby
magnetically insensitive CO lines show no excess broadening above that produced
by stellar rotation and instrumental broadening, reinforcing the magnetic
interpretation for the width of the Ti I lines. We carry out extensive tests to
quantify systematic errors in our analysis technique which may result from
inaccurate knowledge of the effective temperature or gravity, finding that
reasonable errors in these quantities produce a 10% uncertainty in the mean
field measurement.Comment: The tar file includes one Tex file and four .eps figures. The paper
is accepted and tentatively scheduled for the ApJ 1 December 2005, v634, 2
issue. ApJ manuscript submission # 6310
A new European plant-specific emission inventory of biogenic volatile organic compounds for use in atmospheric transport models
We present a new European plant-specific emission inventory for isoprene, monoterpenes, sesquiterpenes and oxygenated VOC (OVOC), on a spatial resolution of 0.089&times;0.089 degrees, for implementation in atmospheric transport models. The inventory incorporates more accurate data on foliar biomass densities from several litterfall databases that became available in the last years for the main tree species in Europe. A bioclimatic correction factor was introduced to correct the foliar biomass densities of trees and crops for the different plant growth conditions that can be found in Pan-Europe. Long-term seasonal variability of agriculture and forest emissions was taken into account by implementing a new growing season concept. The 2004–2005 averaged annual total biogenic volatile organic compound (BVOC) emissions for the Pan-European domain are estimated to be about 12 Tg with a large contribution from the OVOC class of about 4.5 Tg and from monoterpenes of about 4 Tg. Annual isoprene emissions are found to be about 3.5 Tg, insensitive to the chosen emission algorithm. Emissions of OVOC were found to originate to a large extent from agriculture. Further experiments on crop emissions should be carried out to check the validity of the applied standard emission factors. The new inventory aims at a fully transparent and verifiable aggregation of detailed land use information and at the inclusion of plant-specific emission data. Though plant-specific land use data is available with relatively high accuracy, a lack of experimental biomass densities and emission data on terpenes, sesquiterpenes and oxygenated VOC, in particular for agricultural plants, currently limits the setup of a highly accurate plant-specific emission inventory
Confirmation of the Planet Hypothesis for the Long-period Radial Velocity Variations of Beta Geminorum
We present precise stellar radial velocity measurements for the K giant star
Beta Gem spanning over 25 years. These data show that the long period low
amplitude radial velocity variations found by Hatzes & Cochran (1993) are
long-lived and coherent. An examination of the Ca II K emission, spectral line
shapes from high resolution data (R = 210,000), and Hipparcos photometry show
no significant variations of these quantities with the RV period. These data
confirm the planetary companion hypothesis suggested by Hatzes & Cochran
(1993). An orbital solution assuming a stellar mass of 1.7 M_sun yields a
period, P = 589.6 days, a minimum mass of 2.3 M_Jupiter, and a semi-major axis,
and a = 1.6 AU. The orbit is nearly circular (e = 0.02). Beta Gem is the
seventh intermediate mass star shown to host a sub-stellar companion and
suggests that planet-formation around stars much more massive than the sun may
common.Comment: 10 pages, 9 figures, Astronomy and Astrophysics, in pres
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