Infrared Spectra of Meteoritic SiC Grains

We present here the first infrared spectra of meteoritic SiC grains. The mid-infrared transmission spectra of meteoritic SiC grains isolated from the Murchison meteorite were measured in the wavelength range 2.5--16.5 micron, in order to make available the optical properties of presolar SiC grains. These grains are most likely stellar condensates with an origin predominately in carbon stars. Measurements were performed on two different extractions of presolar SiC from the Murchison meteorite. The two samples show very different spectral appearance due to different grain size distributions. The spectral feature of the smaller meteoritic SiC grains is a relatively broad absorption band found between the longitudinal and transverse lattice vibration modes around 11.3 micron, supporting the current interpretation about the presence of SiC grains in carbon stars. In contrast to this, the spectral feature of the large (> 5 micron) grains has an extinction minimum around 10 micron. The obtained spectra are compared with commercially available SiC grains and the differences are discussed. This comparison shows that the crystal structure (e.g., beta-SiC versus alpha-SiC) of SiC grains plays a minor role on the optical signature of SiC grains compared to e.g. grain size.Comment: 7 pages, 6 figures. To appear in A&

Are Coronae of Magnetically Active Stars Heated by Flares? III. Analytical Distribution of Superimposed Flares

(abridged) We study the hypothesis that observed X-ray/extreme ultraviolet emission from coronae of magnetically active stars is entirely (or to a large part) due to the superposition of flares, using an analytic approach to determine the amplitude distribution of flares in light curves. The flare-heating hypothesis is motivated by time series that show continuous variability suggesting the presence of a large number of superimposed flares with similar rise and decay time scales. We rigorously relate the amplitude distribution of stellar flares to the observed histograms of binned counts and photon waiting times, under the assumption that the flares occur at random and have similar shapes. Applying these results to EUVE/DS observations of the flaring star AD Leo, we find that the flare amplitude distribution can be represented by a truncated power law with a power law index of 2.3 +/- 0.1. Our analytical results agree with existing Monte Carlo results of Kashyap et al. (2002) and Guedel et al. (2003). The method is applicable to a wide range of further stochastically bursting astrophysical sources such as cataclysmic variables, Gamma Ray Burst substructures, X-ray binaries, and spatially resolved observations of solar flares.Comment: accepted for publication in Ap

A New Version of Reimers' law of Mass Loss Based on a Physical Approach

We present a new semi-empirical relation for the mass loss of cool stellar winds, which so far has frequently been described by "Reimers' law". Originally, this relation was based solely on dimensional scaling arguments without any physical interpretation. In our approach, the wind is assumed to result from the spill-over of the extended chromosphere, possibly associated with the action of waves, especially Alfven waves, which are used as guidance in the derivation of the new formula. We obtain a relation akin to the original Reimers law, but which includes two new factors. They reflect how the chromospheric height depends on gravity and how the mechanical energy flux depends, mainly, on effective temperature. The new relation is tested and sensitively calibrated by modelling the blue end of the Horizontal Branch of globular clusters. The most significant difference from mass loss rates predicted by the Reimers relation is an increase by up to a factor of 3 for luminous late-type (super-)giants, in good agreement with observations.Comment: 12 pages, 4 figures, accepted by ApJ Letter

The composition and nature of the dust shell surrounding the binary AFGL 4106

We present infrared spectroscopy and imaging of AFGL~4106. The 2.4-5 micron ISO-SWS spectrum reveals the presence of a cool, luminous star (T_eff ~ 3750 K) in addition to an almost equally luminous F star (T_eff ~ 7250 K). The 5-195 micron SWS and LWS spectra are dominated by strong emission from circumstellar dust. We find that the dust consists of amorphous silicates, with a minor but significant contribution from crystalline silicates. The amorphous silicates consist of Fe-rich olivines. The presence of amorphous pyroxenes cannot be excluded but if present they contain much less Fe than the amorphous olivines. Comparison with laboratory data shows that the pure Mg-end members of the crystalline olivine and pyroxene solid solution series are present. In addition, we find strong evidence for simple oxides (FeO and Al2O3) as well as crystalline H2O ice. Several narrow emission features remain unidentified. Modelling of the dust emission using a dust radiation transfer code shows that large grains (~1 micron) must be present and that the abundance of the crystalline silicates is between 7 and 15% of the total dust mass, depending on the assumed enstatite to forsterite ratio, which is estimated to be between 1 and 3. The amorphous and crystalline dust components in the shell do not have the same temperature, implying that the different dust species are not thermally coupled. We find a dust mass of ~3.9 x 10^-2 M_sol expelled over a period of 4 x 10^3 years for a distance of 3.3 kpc. The F-star in the AFGL~4106 binary is likely a post-red-supergiant in transition to a blue supergiant or WR phase.Comment: 22 pages (including 12 figures), accepted by Astronomy and Astrophysic

UV and X-Ray Monitoring of AG Draconis During the 1994/1995 Outbursts

The recent 1994-1995 active phase of AG Draconis has given us for the first time the opportunity to follow the full X-ray behaviour of a symbiotic star during two successive outbursts and to compare with its quiescence X-ray emission. With \ros observations we have discovered a remarkable decrease of the X-ray flux during both optical maxima, followed by a gradual recovering to the pre-outburst flux. In the UV the events were characterized by a large increase of the emission line and continuum fluxes, comparable to the behaviour of AG Dra during the 1980-81 active phase. The anticorrelation of X-ray/UV flux and optical brightness evolution is shown to very likely be due to a temperature decrease of the hot component. Such a temperature decrease could be produced by an increased mass transfer to the burning compact object, causing it to slowly expand to about twice its original size.Comment: 12 pages postscript incl. figures, Proc. of Workshop on Supersoft X-Ray Sources, to appear in Lecture Notes in Physics vol. 472 (1996

Low energy kaon photoproduction from nuclei

We study $K^+$-meson production in $\gamma{A}$ interaction at energies below the reaction threshold in free space. The Thomas-Fermi and spectral function approaches are used for the calculations of the production process. It is found that the measurement of the differential spectra may allow to reconstruct the production mechanism and to investigate the dispersion relations entering the production vertex. It is shown that the contribution from secondary pion induced reactions to the total kaon photoproduction is negligible for $E_\gamma{<}$1.2 GeV so that strangeness production at low energies is sensitive to the nuclear spectral function.Comment: 20 pages, espcrc1, including 12 figures, to appear in Nucl. Phys.

Two populations of X-ray pulsars produced by two types of supernovae

Two types of supernova are thought to produce the overwhelming majority of neutron stars in the Universe. The first type, iron-core collapse supernovae, occurs when a high-mass star develops a degenerate iron core that exceeds the Chandrasekhar limit. The second type, electron-capture supernovae, is associated with the collapse of a lower-mass oxygen-neon-magnesium core as it loses pressure support owing to the sudden capture of electrons by neon and/or magnesium nuclei. It has hitherto been impossible to identify the two distinct families of neutron stars produced in these formation channels. Here we report that a large, well-known class of neutron-star-hosting X-ray pulsars is actually composed of two distinct sub-populations with different characteristic spin periods, orbital periods and orbital eccentricities. This class, the Be/X-ray binaries, contains neutron stars that accrete material from a more massive companion star. The two sub-populations are most probably associated with the two distinct types of neutron-star-forming supernovae, with electron-capture supernovae preferentially producing system with short spin period, short orbital periods and low eccentricity. Intriguingly, the split between the two sub-populations is clearest in the distribution of the logarithm of spin period, a result that had not been predicted and which still remains to be explaine

Serological identification and expression analysis of gastric cancer-associated genes

Serological identification of tumour antigens by recombinant expression cloning has proved to be an effective strategy for the identification of cancer-associated genes having a relevance to cancer aetiology and progression, and for defining possible targets for immunotherapeutic intervention. In the present study we applied this technique to identify immunogenic proteins for gastric cancer that resulted in isolation of 14 distinct serum-reactive antigens. In order to evaluate their role in tumourigenesis and assess the immunogenicity of the identified antigens, we characterised each cDNA clone by DNA sequence analysis, mRNA tissue distribution, comparison of mRNA levels in cancerous and adjacent non-cancerous tissues and the frequency of antibody responses in allogeneic patient and control sera. Previously unknown splice variants of TACC1 and an uncharacterised gene Ga50 were identified. The expression of a newly identified TACC1 isoform is restricted to brain and gastric cancer tissues. Comparison of mRNA levels by semi-quantitative RT–PCR revealed a relative overexpression of three genes in cancer tissues, including growth factor granulin and Tbdn-1 – an orthologue of the mouse acetyltransferase gene which is associated with blood vessel development. An unusual DNA polymorphism – a three-nucleotide deletion was found in NUCB2 cDNA but its mRNA level was consistently decreased in gastric tumours compared with that in the adjacent non-cancerous tissues. This study has revealed several new gastric cancer candidate genes; additional studies are required to gain a deeper insight into their role in the tumorigenesis and their potential as therapeutic targets

THE HIALINE PROJECT: ALLERGEN RELEASE FROM POLLEN ACROSS 10 EUROPEAN COUNTRIES

Exposure to allergens is one of severa1 factors determining sensitization and allergic symptoms in individuals. Exposure to aeroallergens from pollen is assessed by counting allergenic pollen in ambient air. However, proof is lacking that pollen count is representative for allergen exposure. We therefore monitored simultaneously birch, grass and olive pollen counts and their corresponding major pollen allergens Bet v 1, Phl p 5 and Ole e 1 across Europe. Already at one location in Europe in Munich, Germany, it has been found that the same amount of pollen from different years, different trees and even different days released up to lO-fold different amounts of Bet v 1. Thus exposure to allergen is poorly monitored by only monitoring pollen countl-2. Monitoring the allergen itself in ambient air might be an improvement in allergen exposure assessment. The objective of the HIALINE-project is to evaluate if these effects found in Munich, Germany are also measurable over a bigger geographic area like Europe, and at the same time implement an outdoor allergen early warning network, in addition to the pollen forecasts. Climatic factors that influence allergen exposure will be extracted and will be used to calculate the effect of climate change on local airborne allergen exposure. The major allergens from the top 3 airborne allergens in Europe (grasses, birch and olive) are sampled with a cascade impactor, extracted and analyzed by allergen specific ELISA 's. Pollen counts are measured by standard pollen traps and correlated with the weather data. Allergen forecast will be calculated by incorporating the SILAM chemical transport model and compared with the observations of HIALINE aiming at a comprehensive parameterization of the allergen release and transport. Expected outcomes are the implementation of a network of European outdoor allergen measurements to better predict allergic symptoms. Also the climatic factors that govern allergen exposure in outdoor air will be established. These can be used to calculate the effect of climate change on the health effects of airborne allergens The research leading to these results has received funding from the Executive Agency for Health and Consumers under grant agreement No 2008 11 07