Molecular line study of the very young protostar IRAM 04191 in Taurus: Infall, rotation, and outflow

We present a detailed millimeter line study of the circumstellar environment of the low-luminosity Class 0 protostar IRAM 04191+1522 in the Taurus molecular cloud. New line observations demonstrate that the ~14000 AU radius protostellar envelope is undergoing both extended infall and fast, differential rotation. Radiative transfer modeling of multitransition CS and C34S maps indicate an infall velocity v_inf ~ 0.15 km/s at r ~ 1500 AU and v_inf ~ 0.1 km/s up to r ~ 11000 AU, as well as a rotational angular velocity Omega ~ 3.9 x 10^{-13} rad/s, strongly decreasing with radius beyond 3500 AU down to a value Omega ~ 1.5-3 x 10^{-14} rad/s at ~ 11000 AU. Two distinct regions, which differ in both their infall and their rotation properties, therefore seem to stand out: the inner part of the envelope (r ~< 2000-4000 AU) is rapidly collapsing and rotating, while the outer part undergoes only moderate infall/contraction and slower rotation. These contrasted features suggest that angular momentum is conserved in the collapsing inner region but efficiently dissipated due to magnetic braking in the slowly contracting outer region. We propose that the inner envelope is in the process of decoupling from the ambient cloud and corresponds to the effective mass reservoir (~0.5 M_sun) from which the central star is being built. Comparison with the rotational properties of other objects in Taurus suggests that IRAM 04191 is at a pivotal stage between a prestellar regime of constant angular velocity enforced by magnetic braking and a dynamical, protostellar regime of nearly conserved angular momentum. The rotation velocity profile we derive for the inner IRAM 04191 envelope should thus set some constraints on the distribution of angular momentum on the scale of the outer Solar system at the onset of protostar/disk formation.Comment: 23 pages, 16 figures, 1 table, Accepted by Astronomy & Astrophysic

Observations of cometary parent molecules with the IRAM radio telescope

Several rotational transitions of HCN, H2S, H2CO, and CH3OH were detected in comets P/Brorsen-Metcalf 1989 X, Austin (1989c1) and Levy (1990c) with the Institute for Millimeter Radioastronomy (IRAM) 30-m radio telescope. This allows us to determine the production rates of these molecules and to probe the physical conditions of the coma

Ethylene glycol in comet C/1995 O1 (Hale-Bopp)

We report the detection of ethylene glycol (HOCH_2CH_2OH) in comet C/1995 O1 (Hale-Bopp) from the analysis of archival radio spectra. Its production rate is ≈0.25% that of water, making it one of the most abundant organic molecules in cometary ices. This detection strengthens the similarity between interstellar and cometary material

The composition of ices in comet C/1995 O1 (Hale-Bopp) from radio spectroscopy - Further results and upper limits on undetected species

From radio spectroscopic observations of comets, more than 22 molecules, radicals and ions, plus several isotopologues, were detected, the majority of them being recently revealed in comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp). Among them, 6 molecules were detected for the first time (Bockelée-Morvan et al. [CITE]) in the course of a spectral survey conducted at radio wavelengths in comet Hale-Bopp with the CSO, the IRAM 30-m telescope and Plateau de Bure interferometer. In addition, many species were searched for unsuccessfully, some of them with stringent upper limits. We present here a review of these observations and further analysis of their results. This include: (i) confirmed detection of acetaldehyde (CH_3CHO); (ii) limits on small molecules such as ketene (H_2CCO) or methanimine (CH_2NH); (iii) limits on the abundance ratios in homologous series such as HC_5N/HC_3N, ethanol/methanol, acetic acid/formic acid; (iv) searches for precursors of key cometary species such as atomic Na and HNC; (v) constraints on more exotic species ranging from water dimer (H_2O)_2 to glycine; (vi) detection of the H_2^(34)S isotopic species and independent observations of HDO and DCN; (vii) limits on several other deuterated species; (viii) limits on several radicals and ions and a tentative detection of the C_2H radical; (ix) the presence of unidentified lines. Typical abundance upper limits of 2–5 x 10^(-4) relative to water are achieved for many species. Better upper limits are obtained for some linear molecules with high dipole moments. But more complex molecules such as dimethyl ether or glycine are poorly constrained. These results should give important clues to the chemical composition of cometary ices, to the formation mechanisms of cometary material, and to the chemical processes which occur in the inner coma

Use of Supplements for Increasing Performances of Suckling Martinik Ewes When Fed Tropical Forages

Experiments have been carried out to determine the effects of supplementation upon milk production and growing performances with hair sheep Martinik ewes weighing 48 ± 4 kg liveweight (LW). In a first trial, 6 single bearing ewes (group GS) were offered individually a daily 0.5 kg of commercial pellets. They were compared to the control group (GN; 6 ewes) with no supplement during 10 weeks of lactation. Basal diet was chopped Digitaria decumbens grass ad libitum. In a second trial, level of supplementation was adapted to the ewes’ litter size: 6 twins bearing ewes (TW) and 6 single (SI). Mean milk production (oxytocin method) reached 1186 and 940 g.d-1 (P\u3c 0.05) for GS and GN ewes, respectively. Body condition score (BCS) of GS ewes maintained during lactation while those of GN ewes slightly decreased (P\u3c 0.05). No difference was recorded for lambs daily weight gain (DWG). Milk production varied significantly (P\u3c 0.05) according to the litter size: 926 and 1246 g.d-1 for SI and TW, respectively. The BCS of TW ewes decreased more than those of SI ewes (-1.4 vs –1.0). Individual DWG were different (P\u3c 0.01): 216 and 150 g.d-1 for single and twin lamb, respectively. It is concluded that use of supplements is necessary in intensive breeding conditions (high reproduction frequency and productivity), in order to allow high levels of performances when ewes are fed tropical forages

Detection of Cold Atomic Clouds in the Magellanic Bridge

We report a detection of cold atomic hydrogen in the Magellanic Bridge using 21-cm absorption spectroscopy toward the radio source B0312-770. With a column density of N_HI=1.2E20 cm^-2, a maximum absorption optical depth of tau=0.10 and a maximum 21-cm emission brightness temperature of 1.4 K, this line of sight yields a spin temperature, T_s, between 20 K and 40 K. H I 21-cm absorption and emission spectroscopy toward 7 other low column density sightlines on the periphery of the LMC and SMC reveal absorption toward one additional background radio source behind the SMC with tau=0.03. The data have typical sensitivities of sigma_tau=0.005 to 0.070 in absorption and sigma_{T_B}=0.03 K in emission. These data demonstrate the presence of a cold atomic phase which is probably accompanied by molecular condensations in the tenuous interstellar medium of the Bridge region. Young OB stars observed in the Magellanic Bridge could form "in situ" from these cold condensations rather than migrate from regions of active star formation in the main body of the SMC. The existence of cold condensations and star formation in the Magellanic Bridge might be understood as a small scale version of the mechanism that produces star formation in the tidal tails of interacting galaxies.Comment: 25 pages, uses AASTeX and psfig; Accepted for Publication in the Astronomical Journa

Djerba

Située à l’extrémité sud-est du Golfe de Gabès, la Petite Syrte des Anciens, Djerba est la plus grande – avec 538 km2 de superficie – et surtout la plus célèbre des îles du littoral d’Afrique du Nord. Elle n’est séparée du continent que par deux étroits passages – celui entre Adjim et Djorf à l’ouest et celui d’El Kantara à l’est -qui encadrent la mer de Bou Grara*. Une zone de hauts-fonds qui l’enveloppe entièrement, une marée dont l’amplitude est ici de 1,30 m en période de vives eaux, rend..

Djerba

Située à l’extrémité sud-est du Golfe de Gabès, la Petite Syrte des Anciens, Djerba est la plus grande – avec 538 km2 de superficie – et surtout la plus célèbre des îles du littoral d’Afrique du Nord. Elle n’est séparée du continent que par deux étroits passages – celui entre Adjim et Djorf à l’ouest et celui d’El Kantara à l’est -qui encadrent la mer de Bou Grara*. Une zone de hauts-fonds qui l’enveloppe entièrement, une marée dont l’amplitude est ici de 1,30 m en période de vives eaux, rend..

Interferometric imaging of carbon monoxide in comet C/1995 O1 (Hale-Bopp): evidence for a strong rotating jet

Observations of the CO J(1-0) 115 GHz and J(2-1) 230 GHz lines in comet C/1995 O1 (Hale-Bopp) were performed with the IRAM Plateau de Bure interferometer on 11 March, 1997. The observations were conducted in both single-dish (ON-OFF) and interferometric modes with 0.13 km s-1 spectral resolution. Images of CO emission with 1.7 to 3" angular resolution were obtained. The ON-OFF and interferometric spectra show a velocity shift with sinusoidal time variations related to the Hale-Bopp nucleus rotation of 11.35 h. The peak position of the CO images moves perpendicularly to the spin axis direction in the plane of the sky. This suggests the presence of a CO jet, which is active night and day at about the same extent, and is spiralling with nucleus rotation. The high quality of the data allows us to constrain the characteristics of this CO jet. We have developed a 3-D model to interpret the temporal evolution of CO spectra and maps. The CO coma is represented as the combination of an isotropic distribution and a spiralling gas jet, both of nucleus origin. Spectra and visibilities (the direct output of interferometric data) analysis shows that the CO jet comprises ~40% the total CO production and is located at a latitude ~20 degrees North on the nucleus surface. Our inability to reproduce all observational characteristics shows that the real structure of the CO coma is more complex than assumed, especially in the first thousand kilometres from the nucleus. The presence of another moving CO structure, faint but compact and possibly created by an outburst, is identified.Comment: 20 pages, 26 figures. Accepted for publication in Astronomy & Astrophysic

Fezzân

Fezzân et Phazania (P. Trousset) Bien que le nom actuel du Fezzân qui désigne une des trois régions de la Libye contemporaine tire son origine de celui de la Phazania antique, les deux toponymes ne s’appliquent pas en réalité à la même aire géographique et ce glissement spatial depuis l’Antiquité doit être attribué aux géographes arabes. Pour Ibn Hawkal et pour Al Idrisi, par exemple, le Fāzāz (Fezzân) « où sont les villes de Djarma et de Tasawa », est bien à l’emplacement que nous lui connai..