[en] The detection of circular polarization in R Mon and NGC 2261 is reported. This detection implies that the mechanism responsible for the linear and circular polarization is most likely multiple scattering in a flattened distribution. It replaces the previously suggested scenario where dichroic extinction by elongated dust grains aligned by a toroidal magnetic field was producing the polarization. The multiple scattering interpretation of linear polarization maps also means that these maps now provide direct evidence for a circumstellar disk around R Mon and possibly around many other young stellar objects

[en] A thorough radiological assessment of the impact of the 1949 to 1982 dumping of low- and intermediate- level radioactive waste in the deep North-East Atlantic is performed with the numerical compartmental REJMAR model. The calculations include the assessment of the dose equivalent to the individuals of a theoretical critical group through a large set of pathways, and the collective dose to mankind through the ingestion pathways. The complete dumping performed in the deep North-East Atlantic is taken into account. The assumptions of biological short-circuit through marin food chains are tested. The order of magnitude of the dose delivered to marine organisms living near the dumping site is assessed

[en] Polarization maps obtained during the past few years of regions around young stellar objects associated with optical jets and/or bipolar outflows and/or cometary nebulas show, in many cases, a centrosymmetric pattern usually attributed to scattering of radiation from the central sources by dust grains in their vicinity. In other cases, a pattern of aligned polarization vectors is observed close to the central object; dichroic extinction by aligned grains has been proposed for their interpretation. This paper explores different ways to explain such a pattern without invoking aligned grains. It is found that multiple scattering alone with an optically thick disk and optically thin polar lobes can explain most, if not all, polarization maps so far observed. If this interpretation is correct, aligned grains and magnetic fields are no longer required. However, this does not disprove the presence of magnetic fields around young stars; it only shows that they are not efficient at aligning grains in the circumstellar environment of premain-sequence stars. 41 references

[en] Linear polarization maps of young stellar objects in which a pattern of aligned polarization vectors are observed close to the central object have been interpreted recently in terms of multiple scattering in flattened, optically thick, structures (Bastien and Menard). These patterns provide direct evidence for circumstellar disks around young stellar objects. Circular polarization, which is predicted by this model, has been detected in a few stars already; however, it cannot be accounted for by a competing suggestion in which the pattern of aligned vectors is due to dichroic extinction by aligned nonspherical grains. This fact and many other objections lead us to reject aligned grains as a suitable model for the observations. This paper uses the results of the model calculations to derive some parameters which represent best the observations. In particular, the size of the optically thick part of the disks, and their inclination to the line of sight is determined for published polarization maps. The distribution of inclination angles is consistent with the expected distribution. Inclination angles and disk sizes compare well with values obtained by other methods for the objects in common. 96 refs

[en] In vitro binding assays with ¹²⁵I-[8-methoxy-2-[N-propyl-N-(3'-iodo-4'-hydroxyphenyl)-propionamido -N'- propylamino] tetralin] (¹²⁵I-BH-8-MeO-N-PAT), a ¹²⁵I-labeled derivative of the potent serotonin (5-HT) agonist 8-hydroxy-2-[di-n-propylamino]tetralin [(³H]-8-OH-DPAT), showed that this compound recognized specific sites with nanomolar affinity for 5-HT and 5-HT1A ligands such as spiroxatrine, ipsapirone, buspirone and gepirone in rat hippocampal membranes. Comparison of the binding characteristics of ¹²⁵I-BH-8-MeO-N-PAT with those of [³H]-8-OH-DPAT revealed striking similarities: at the hippocampal level, both binding sites exhibited nanomolar affinity for their respective ligands and the same Bmax; their pharmacological profiles defined by the inhibition of each bound ligand by a series of 26 serotonin, dopamine- or norepinephrine-related agonists and antagonists were identical; and their regional distributions examined by membrane binding assays and autoradiography of labeled brain sections were highly correlated. These observations indicate that ¹²⁵I-BH-8-MeO-N-PAT is the first ¹²⁵I-reversible ligand for the selective labeling of 5-HT1A sites in the rat central nervous system

[en] New optical linear polarization maps are presented of the star-forming regions near L1506 in Taurus, L1755 in Ophiuchus, and the complex of dark cloud which extends from L1448 in B5 in Perseus. The former two show a well-defined peak magnetic field direction in the plane of the sky with a finite dispersion about that peak which is smaller than would be expected for a random distribution of field distributions. The dispersion in the position angle of filamentary clouds within these complexes implies that clouds which appear elongated on the plane of the sky are not all associated with a pattern of polarization vectors particularly parallel or perpendicular to their geometry. Instead, clouds tend to be oriented at the angle formed by their axis and the mean direction of the local large-scale field. For the dark cloud complex, a bimodal distribution of the polarization vector angle is taken to result from at least two distributions of gas along the line of sight which appear as a complex in projection. 55 refs

[en] Water is an important species that has a large influence on the chemical and physical structure of protoplanetary disks. Unfortunately, its main isotope is difficult to observe from the ground because of Earth's atmosphere, with the exception of a few maser lines. A viable alternative is offered by its isotopologue HDO, for which several lines are observable (and observed) with ground telescopes. In addition, observations of the HDO lines permit us to estimate the HDO/H₂O ratio, which can be a powerful diagnostic of the past history of the disk. In this Letter, we present a theoretical study of the HDO lines. We show that a few HDO lines are bright enough to be observable with ground-based telescopes. Among them, the 225 GHz line is the brightest because of a maser effect taking place in the inner dense and warm regions of the disk. The high-frequency lines are all in absorption, with absorption that can reach almost the totality of the continuum. We discuss how the line spectra arise from a delicate equilibrium between emission and absorption and are, therefore, highly dependent on the assumed physical and chemical structure. We also show that the HDO/H₂O ratio can not be derived with a simple prescription but it requires multi-frequency observations coupled with careful modeling.

[en] Water is a key species in many astrophysical environments, but it is particularly important in protoplanetary disks. So far, observations of water in these objects have been scarce, but the situation should soon change thanks to the Herschel satellite. We report here a theoretical study of the water line spectrum of a protoplanetary disk surrounding Ae stars. We show that several lines will be observable with the HIFI instrument onboard the Herschel Space Observatory. We predict that some maser lines also could be observable with ground telescopes and we discuss how the predictions depend not only on the adopted physical and chemical model but also on the set of collisional coefficients used and on the H₂ ortho-to-para ratio through its effect on collisional excitation. This makes the water line observations a powerful, but dangerous-if misused-diagnostic tool.

No abstract available

[en] We present high-resolution spectroscopic mid-infrared observations of the circumstellar (CS) disk around the Herbig Ae star HD 97048 obtained with the VLT Imager and Spectrometer for the Mid-InfraRed. We conducted observations of mid-infrared pure rotational lines of molecular hydrogen (H₂) as a tracer of warm gas in the disk surface layers. In a previous paper, we reported the detection of the S(1) pure rotational line of H₂ at 17.035 μm, and argued that it is arising from the inner regions of the disk around the star. We used the VISIR on the VLT for a more comprehensive study based on complementary observations of the other mid-infrared molecular transitions, namely S(2) and S(4) at 12.278 μm and 8.025 μm respectively, to investigate the physical properties of the molecular gas in the CS disk around HD 97048. We do not detect either the S(2) line or the S(4) H₂ line from the disk of HD 97048, but we derive upper limits on the integrated line fluxes which allows us to estimate an upper limit on the gas excitation temperature, T _ex < 570 K. This limit on the temperature is consistent with the assumptions previously used in the analysis of the S(1) line, and allows us to set stronger constraints on the mass of warm gas in the inner regions of the disk. Indeed, we estimate the mass of warm gas to be lower than 0.1 M _Jup. We also discuss the probable physical mechanisms which could be responsible for the excitation of H₂ in the disk of HD 97048.