10 research outputs found
Determination of the position angle of stellar spin axes
Measuring the stellar position angle provides valuable information on binary
stellar formation or stellar spin axis evolution. We aim to develop a method
for determining the absolute stellar position angle using spectro-astrometric
analysis of high resolution long-slit spectra. The method has been designed in
particular for slowly rotating stars. We investigate its applicability to
existing dispersive long-slit spectrographs, identified here by their plate
scale, and the size of the resulting stellar sample. The stellar rotation
induces a tilt in the stellar lines whose angle depends on the stellar position
angle and the orientation of the slit. We developed a rotation model to
calculate and reproduce the effects of stellar rotation on unreduced high
resolution stellar spectra. Then we retrieved the tilt amplitude using a
spectro-astrometric extraction of the position of the photocentre of the
spectrum. Finally we present two methods for analysing the position spectrum
using either direct measurement of the tilt or a cross-correlation analysis.
For stars with large apparent diameter and using a spectrograph with a small
plate scale, we show that it is possible to determine the stellar position
angle directly within 10deg with a signal-to-noise ratio of the order of 6.
Under less favourable conditions, i.e. larger plate scale or smaller stellar
diameter, the cross-correlation method yields comparable results. We show that
with the currently existing instruments, it is possible to determine the
stellar position angle of at least 50 stars precisely, mostly K-type giants
with apparent diameter down to 5 milliarcseconds. If we consider errors of
around 10deg still acceptable, we may include stars with apparent diameter down
to 2 mas in the sample that then comprises also some main sequence stars.Comment: 10 pages, 9 figures, A&A (in press
Infrared Observations During the Secondary Eclipse of HD 209458b: I. 3.6-Micron Occultation Spectroscopy Using the VLT
We search for an infrared signature of the transiting extrasolar planet HD
209458b during secondary eclipse. Our method, which we call `occultation
spectroscopy,' searches for the disappearance and reappearance of weak spectral
features due to the exoplanet as it passes behind the star and later reappears.
We argue that at the longest infrared wavelengths, this technique becomes
preferable to conventional `transit spectroscopy'. We observed the system in
the wing of the strong nu-3 band of methane near 3.6 microns during two
secondary eclipses, using the VLT/ISAAC spectrometer at a spectral resolution
of 3300. Our analysis, which utilizes a model template spectrum, achieves
sufficient precision to expect detection of the spectral structure predicted by
an irradiated, low-opacity (cloudless), low-albedo, thermochemical equilibrium
model for the exoplanet atmosphere. However, our observations show no evidence
for the presence of this spectrum from the exoplanet, with the statistical
significance of the non-detection depending on the timing of the secondary
eclipse, which depends on the assumed value for the orbital eccentricity. Our
results reject certain specific models of the atmosphere of HD 209458b as
inconsistent with our observations at the 3-sigma level, given assumptions
about the stellar and planetary parameters.Comment: 26 pages, 8 figures Accepted to Astrophysical Journa
Prolastin, a pharmaceutical preparation of purified human α1-antitrypsin, blocks endotoxin-mediated cytokine release
BACKGROUND: α1-antitrypsin (AAT) serves primarily as an inhibitor of the elastin degrading proteases, neutrophil elastase and proteinase 3. There is ample clinical evidence that inherited severe AAT deficiency predisposes to chronic obstructive pulmonary disease. Augmentation therapy for AAT deficiency has been available for many years, but to date no sufficient data exist to demonstrate its efficacy. There is increasing evidence that AAT is able to exert effects other than protease inhibition. We investigated whether Prolastin, a preparation of purified pooled human AAT used for augmentation therapy, exhibits anti-bacterial effects. METHODS: Human monocytes and neutrophils were isolated from buffy coats or whole peripheral blood by the Ficoll-Hypaque procedure. Cells were stimulated with lipopolysaccharide (LPS) or zymosan, either alone or in combination with Prolastin, native AAT or polymerised AAT for 18 h, and analysed to determine the release of TNFα, IL-1β and IL-8. At 2-week intervals, seven subjects were submitted to a nasal challenge with sterile saline, LPS (25 μg) and LPS-Prolastin combination. The concentration of IL-8 was analysed in nasal lavages performed before, and 2, 6 and 24 h after the challenge. RESULTS: In vitro, Prolastin showed a concentration-dependent (0.5 to 16 mg/ml) inhibition of endotoxin-stimulated TNFα and IL-1β release from monocytes and IL-8 release from neutrophils. At 8 and 16 mg/ml the inhibitory effects of Prolastin appeared to be maximal for neutrophil IL-8 release (5.3-fold, p < 0.001 compared to zymosan treated cells) and monocyte TNFα and IL-1β release (10.7- and 7.3-fold, p < 0.001, respectively, compared to LPS treated cells). Furthermore, Prolastin (2.5 mg per nostril) significantly inhibited nasal IL-8 release in response to pure LPS challenge. CONCLUSION: Our data demonstrate for the first time that Prolastin inhibits bacterial endotoxin-induced pro-inflammatory responses in vitro and in vivo, and provide scientific bases to explore new Prolastin-based therapies for individuals with inherited AAT deficiency, but also for other clinical conditions
Solar Hidden Photon Search
The Solar Hidden Photon Search (SHIPS) is a joint astroparticle project of the Hamburger Sternwarte and DESY. The main target is to detect the solar emission of a new species of particles, so called Hidden Photons (HPs). Due to kinetic mixing, photons and HPs can convert into each other as they propagate. A small number of solar HPs - originating from photon to HP oscillations in the interior of the Sun - can be converted into photons in a long vacuum pipe pointing to the Sun - the SHIPS helioscope
The proposed giant planet orbiting VB 10 does not exist
We present high-precision relative radial velocities of the very low mass star VB 10 that were obtained over a time span of 0.61 years as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the Very Large Telescope with an ammonia gas cell. The typical internal precision of the measurements is 10 m s(-1). These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB 10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo & Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the similar to 1 km s(-1) radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with M-p > 3 M-Jup and the orbital period and inclination suggested by Pravdo & Shaklan at better than 5 sigma confidence. We conclude that the planet detection claimed by Pravdo & Shaklan is spurious on the basis of this result. Although the outcome of this work is a non-detection, it illustrates the potential of using ammonia cell radial velocities to detect planets around very low mass stars