Observatoire Aquitain des Sciences de l'Univers

A quasi-inertial reference frame is defined based on the radio positions of 212 extragalactic sources distributed over the entire sky. The positional accuracy of these sources is better than about 1 mas in both coordinates. The radio positions are based upon a general solution for all applicable dual-frequency 2.3 and 8.4 GHz Mark III very long baseline interferometry data available through the middle of 1995, consisting of 1.6 million pairs of group delay and phase delay rate observations. Positions and details are also given for an additional 396 objects that either need further observation or are currently unsuitable for the definition of a high-accuracy reference frame. The final orientation of the frame axes has been obtained by a rotation of the positions into the system of the International Celestial Reference System and is consistent with the FK5 J2000.0 optical system, within the limits of the link accuracy. The resulting International Celestial Reference Frame has been adopted by the International Astronomical Union as the fundamental celestial reference frame, replacing the FK5 optical frame as of 1998 January 1.

We provide a first look at the results of the Herschel Gould Belt survey toward the IC 5146 molecular cloud and present a preliminary analysis of the filamentary structure in this region. The column density map, derived from our 70–500 μm Herschel data, reveals a complex network of filaments and confirms that these filaments are the main birth sites of prestellar cores. We analyze the column density profiles of 27 filaments and show that the underlying radial density profiles fall off as r-1.5 to r-2.5 at large radii. Our main result is that the filaments seem to be characterized by a narrow distribution of widths with a median value of 0.10 ± 0.03 pc, which is in stark contrast to a much broader distribution of central Jeans lengths. This characteristic width of ~0.1 pc corresponds to within a factor of ~2 to the sonic scale below which interstellar turbulence becomes subsonic in diffuse gas, which supports the argument that the filaments may form as a result of the dissipation of large-scale turbulence.

<i>Aims. <i/>This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's <i>Herschel<i/> Space Observatory in May 2009. <i>Methods. <i/>The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480–1250 GHz with SIS mixers and the 1410–1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s<sup>-1<sup/>.<i>Results. <i/>After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations.

While warm dense gas is prevalent around low-mass protostars, the presence of complex saturated molecules-the chemical inventory characteristic of hot cores-has remained elusive in such environments. Here we report the results of an IRAM 30 m study of the molecular composition associated with the low-mass protostar IRAS 16293-2422. Our observations highlight an extremely rich organic inventory in this source with abundant amounts of complex O- and N-bearing molecules such as formic acid, HCOOH, acetaldehyde, CH3CHO, methyl formate, CH3OCHO, dimethyl ether, CH3OCH3, acetic acid, CH3COOH, methyl cyanide, CH3CN, ethyl cyanide, C2H5CN, and propyne, CH3CCH. We compare the composition of the hot core around this low-mass young stellar object with those around massive protostars and address the chemical processes involved in molecular complexity in regions of star formation.

Aims.The gas-phase abundance of methanol in dark quiescent cores in the interstellar medium cannot be explained by gas-phase chemistry. In fact, the only possible synthesis of this species appears to be production on the surfaces of dust grains followed by desorption into the gas. Yet, evaporation is inefficient for heavy molecules such as methanol at the typical temperature of 10 K. It is necessary then to consider non-thermal mechanisms for desorption. But, if such mechanisms are considered for the production of methanol, they must be considered for all surface species.

This review examines the state-of-the-art knowledge of high-mass star and massive cluster formation, gained from ambitious observational surveys, which acknowledges the multiscale characteristics of these processes. After a brief overview of theoretical models and main open issues, we present observational searches for the evolutionary phases of high-mass star formation, first among high-luminosity sources and more recently among young massive protostars and the elusive high-mass prestellar cores. We then introduce the most likely evolutionary scenario for high-mass star formation, which emphasizes the link of high-mass star formation to massive cloud and cluster formation. Finally, we introduce the first attempts to search for variations of the star-formation activity and cluster formation in molecular cloud complexes in the most extreme star-forming sites and across the Milky Way. The combination of Galactic plane surveys and high–angular resolution images with submillimeter facilities such as Atacama Large Millimeter Array (ALMA) are prerequisites to make significant progress in the forthcoming decade.

This article reviews our current understanding of terrestrial planet formation. The focus is on computer simulations of the dynamical aspects of the accretion process. Throughout the review, we combine the results of these theoretical models with geochemical, cosmochemical, and chronological constraints to outline a comprehensive scenario of the early evolution of our solar system. Given that the giant planets formed first in the protoplanetary disk, we stress the sensitive dependence of the terrestrial planet accretion process on the orbital architecture of the giant planets and on their evolution. This suggests a great diversity among the terrestrial planet populations in extrasolar systems. Issues such as the cause for the different masses and accretion timescales between Mars and Earth and the origin of water (and other volatiles) on our planet are discussed in depth.

We present STELIB, a new spectroscopic stellar library, available at http://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneous library of 249 stellar spectra in the visible range (3200 to 9500 Å), with an intermediate spectral resolution (3 Å) and sampling (1 Å). This library includes stars of various spectral types and luminosity classes, spanning a relatively wide range in metallicity. The spectral resolution, wavelength and spectral type coverage of this library represents a substantial improvement over previous libraries used in population synthesis models. The overall absolute photometric uncertainty is 3%.

We present a database of 908 spectra of 709 stars obtained with the ELODIE spectrograph at the Observatoire de Haute-Provence. 52 orders of the echelle spectra have been carefully fitted together to provide continuous, high-resolution spectra in the wavelength range nm. The archive provides a large coverage of the space of atmospheric parameters: Teff from 3700 K to 13 600 K, from 0.03 to 5.86 and [Fe/H] from -2.8 to +0.7. At the nominal resolution, , the mean signal-to-noise ratio is 150 per pixel. The spectra given at this resolution are normalized to their pseudo-continuum and are intended to serve for abundance studies, spectral classification and tests of stellar atmosphere models. A lower resolution version of the archive, at , is calibrated in physical flux with a broad-band photometric precision of 2.5% and narrow-band precision of 0.5% . It is well suited to stellar population synthesis of galaxies and clusters, and to kinematical investigations of stellar systems. The archive is distributed in FITS format through the HYPERCAT and CDS databases.

We present PEGASE-HR, a new stellar population synthesis program generating high resolution spectra () over the optical range = 400–680 nm. It links the spectro-photometric model of galaxy evolution PEGASE.2 (Fioc & Rocca-Volmerange 1997) to an updated version of the ELODIE library of stellar spectra observed with the 193 cm telescope at the Observatoire de Haute-Provence [CITE]. The ELODIE star set gives a fairly complete coverage of the Hertzprung-Russell (HR) diagram and makes it possible to synthesize populations in the range to +0.4. This code is an exceptional tool for exploring signatures of metallicity, age, and kinematics. We focus on a detailed study of the sensitivity to age and metallicity of the high-resolution stellar absorption lines and of the classical metallic indices proposed until now to solve the age-metallicity degeneracy. Validity tests on several stellar lines are performed by comparing our predictions for Lick indices to the models of other groups. The comparison with the lower resolution library BaSeL [CITE] confirms the quality of the ELODIE library when used for single stellar populations (SSPs) from 107 to yr. Predictions for the evolved populations of globular clusters and elliptical galaxies are given and compared to observational data. Two new high-resolution indices are proposed around the Hγ line. They should prove useful in the analysis of spectra from the new generation of telescopes and spectrographs.

<i>Context. <i/>The formation of massive stars is a highly complex process in which it is unclear whether the star-forming gas is in global gravitational collapse or an equilibrium state supported by turbulence and/or magnetic fields. In addition, magnetic fields may play a decisive role in the star-formation process since they influence the efficiency of gas infall onto the protostar.<i>Aims. <i/>By studying one of the most massive and dense star-forming regions in the Galaxy at a distance of less than 3 kpc, i.e. the filament containing the well-known sources DR21 and DR21(OH), we attempt to obtain observational evidence to help us to discriminate between these two views.<i>Methods. <i/>We use molecular line data from our <sup>13<sup/>CO 1 0, CS 2 1, and N<sub>2<sub/>H<sup>+<sup/> 1 0 survey of the Cygnus X region obtained with the FCRAO and high-angular resolution observations in isotopomeric lines of CO, CS, HCO<sup>+<sup/>, N<sub>2<sub/>H<sup>+<sup/>, and H<sub>2<sub/>CO, obtained with the IRAM 30 m telescope, to investigate the distribution of the different phases of molecular gas. Gravitational infall is identified by the presence of inverse P Cygni profiles that are detected in optically thick lines, while the optically thinner isotopomers are found to reach a peak in the self-absorption gap.<i>Results. <i/>We observe a complex velocity field and velocity dispersion in the DR21 filament in which regions of the highest column-density, i.e., dense cores, have a lower velocity dispersion than the surrounding gas and velocity gradients that are not (only) due to rotation. Infall signatures in optically thick line profiles of HCO<sup>+<sup/> and <sup>12<sup/>CO are observed along and across the whole DR21 filament. By modelling the observed spectra, we obtain a typical infall speed of ~0.6 km s<sup>-1<sup/> and mass accretion rates of the order of a few 10<sup>-3<sup/> yr<sup>-1<sup/> for the two main clumps constituting the filament. These massive clumps (4900 and 3300 at densities of around 10<sup>5<sup/> cm<sup>-3<sup/> within 1 pc diameter) are both gravitationally contracting (with free-fall times much shorter than sound crossing times and low virial parameter <i>α<i/>). The more massive of the clumps, DR21(OH), is connected to a sub-filament, apparently “falling” onto the clump. This filament runs parallel to the magnetic field.<i>Conclusions. <i/>All observed kinematic features in the DR21 filament (velocity field, velocity dispersion, and infall), its filamentary morphology, and the existence of (a) sub-filament(s) can be explained if the DR21 filament was formed by the convergence of flows on large scales and is now in a state of global gravitational collapse. Whether this convergence of flows originated from self-gravity on larger scales or from other processes cannot be determined by the present study. The observed velocity field and velocity dispersion are consistent with results from (magneto)-hydrodynamic simulations where the cores lie at the stagnation points of convergent turbulent flows.

Context. Proto-planetary disks are thought to provide the initial environment for planetary system formation. The dust and gas distribution and its evolution with time is one of the key elements in the process. Aims. We attempt to characterize the radial distribution of dust in disks around a sample of young stars from an observational point of view, and, when possible, in a model-independent way, by using parametric laws. Methods. We used the IRAM PdBI interferometer to provide very high angular resolution (down to 0.4 in some sources) observations of the continuum at 1.3 mm and 3 mm around a sample of T Tauri stars in the Taurus-Auriga region. The sample includes single and multiple systems, with a total of 23 individual disks. We used track-sharing observing mode to minimize the biases. We fitted these data with two kinds of models: a "truncated power law" model and a model presenting an exponential decay at the disk edge ("viscous" model).

Context. To calibrate automatic pipelines that determine atmospheric parameters of stars, one needs a sample of stars, or "benchmark stars", with well-defined parameters to be used as a reference. Aims. We provide detailed documentation of the iron abundance determination of the 34 FGK-type benchmark stars that are selected to be the pillars for calibration of the one billion Gaia stars. They cover a wide range of temperatures, surface gravities, and metallicities. Methods. Up to seven different methods were used to analyze an observed spectral library of high resolutions and high signal-to-noise ratios. The metallicity was determined by assuming a value of effective temperature and surface gravity obtained from fundamental relations; that is, these parameters were known a priori and independently from the spectra. Results. We present a set of metallicity values obtained in a homogeneous way for our sample of benchmark stars. In addition to this value, we provide detailed documentation of the associated uncertainties. Finally, we report a value of the metallicity of the cool giant Phe for the first time.

Stellar nucleosynthesis of heavy elements such as carbon allowed the formation of organic molecules in space, which appear to be widespread in our Galaxy. The physical and chemical conditions—including density, temperature, ultraviolet (UV) radiation and energetic particles—determine reaction pathways and the complexity of organic molecules in different space environments. Dense interstellar clouds are the birth sites of stars of all masses and their planetary systems. During the protostellar collapse, interstellar organic molecules in gaseous and solid phases are integrated into protostellar disks from which planets and smaller solar system bodies form. After the formation of the planets 4.6 billion years ago, our solar system, including the Earth, was subjected to frequent impacts for several hundred million years. Life on Earth may have emerged during or shortly after this heavy bombardment phase, perhaps as early as 3.90–3.85 billion years ago, but the exact timing remains uncertain. A prebiotic reducing atmosphere, if present, predicts that building blocks of biopolymers—such as amino acids, sugars, purines and pyrimidines—would be formed in abundance. Recent modelling of the Earth's early atmosphere suggests, in contrast, more neutral conditions (e.g. H2O, N2, CO2), thus, precluding the formation of significant concentrations of prebiotic organic compounds. Moreover, even if the Earth's atmosphere were reducing, the presence of UV photons would readily destroy organic compounds unless they were quickly sequestered away in rocks or in the prebiotic ocean. Other possible sources of organic compounds would be high temperature vent chemistry, although the stability of such compounds (bases, amino acids) in these environments remains problematic. Finally, organic compounds may have been delivered to the Earth by asteroids, comets and smaller fragments, such as meteorites and interplanetary dust particles.

We present STELIB, a new spectroscopic stellar library, available at http://webast.ast.obs-mip.fr/stelib . STELIB consists of an homogeneous library of 249 stellar spectra in the visible range (3200 to 9500A), with an intermediate spectral resolution (~3A) and sampling (1A). This library includes stars of various spectral types and luminosity classes, spanning a relatively wide range in metallicity. The spectral resolution, wavelength and spectral type coverage of this library represents a substantial improvement over previous libraries used in population synthesis models. The overall absolute photometric uncertainty is 3%.

The ELODIE archive contains the complete collection of high-resolution echelle spectra accumulated over the last decade using the ELODIE spectrograph at the Observatoire de Haute-Provence 1.93-m telescope. This article presents the different data products and the facilities available on the web to re-process these data on-the-fly. Users can retrieve the data in FITS format from

We present the results of the first extensive mid-infrared (IR) imaging survey of the ρ Ophiuchi embedded cluster, performed with the ISOCAM camera on board the ISO satellite. The main ρ Ophiuchimolecular cloud L1688, as well as the two secondary clouds L1689N and L1689S, have been completely surveyed for point sources at 6.7 μm and 14.3 μm. A total of 425 sources are detected in ~0.7 deg2, including 16 Class I, 123 Class II, and 77 Class III young stellar objects (YSOs). Essentially all of the mid-IR sources coincide with near-IR sources, but a large proportion of them are recognized for the first time as YSOs. Our dual-wavelength survey allows us to identify essentially all the YSOs with IR excess in the embedded cluster down to ~ 10-15 mJy. It more than doubles the known population of Class II YSOs and represents the most complete census to date of newly formed stars in the ρ Ophiuchi central region. There are, however, reasons to believe that several tens of Class III YSOs remain to be identified below . The mid-IR luminosities of most (~65% ) Class II objects are consistent with emission from purely passive circumstellar disks. The stellar luminosity function of the complete sample of Class II YSOs is derived with good accuracy down to . It is basically flat (in logarithmic units) below , exhibits a possible local maximum at , and sharply falls off at higher luminosities. A modeling of the luminosity function, using available pre-main sequence tracks and plausible star formation histories, allows us to derive the mass distribution of the Class II YSOs which arguably reflects the initial mass function (IMF) of the embedded cluster. After correction for the presence of unresolved binary systems, we estimate that the IMF in ρ Ophiuchiis well described by a two-component power law with a low-mass index of , a high-mass index of -1.7 (to be compared with the Salpeter value of -1.35), and a break occurring at . This IMF is flat with no evidence for a low-mass cutoff down to at least ~.

The close approach to the Earth of Comet C/1996 B2 (Hyakutake) in March 1996 allowed searches for minor volatile species outgassed from the nucleus. We report the detection of deuterated water (HDO) through its 101–000rotational transition at 464.925 GHz using the Caltech Submillimeter Observatory. We also present negative results of a sensitive search for theJ(5–4) line of deuterated hydrogen cyanide (DCN) at 362.046 GHz. Simultaneous observations of two rotational lines of methanol together with HDO in the same spectrum allow us to determine the average gas temperature within the telescope beam to be 69 ± 10 K. We are thus able to constrain the excitation conditions in the inner coma and determine reliably the HDO production rate as (1.20 ± 0.28) × 1026s−1on March 23–24, 1996. Available IR, UV, and radio measurements led to a water production rate of (2.1 ± 0.5) × 1029s−1at the time of our HDO observations. The resulting D/H ratio in cometary water is thus (29 ± 10) × 10−5, in good agreement with the values of (30.8+3.8−5.3) × 10−5(H. Balsigeret al., 1995,J. Geophys. Res.100, 5827–5834). and (31.6 ± 3.4) × 10−5(P. Eberhardet al., 1995,Astron. Astrophys.302, 301–316) determined in Comet P/Halley fromin situion mass spectra. The inferred 3σ upper limit for the D/H ratio in HCN is 1%. Deuterium abundance is a key parameter for studying the origin and the early evolution of the Solar System and of its individual bodies. Our HDO measurement confirms that, in cometary water, deuterium is enriched by a factor of at least 10 relative to the protosolar ratio, namely the D/H ratio in H2in the primitive Solar Nebula which formed from the collapse of the protosolar cloud. This indicates that cometary water has preserved a major part of the high D/H ratio acquired in this protosolar cloud through ion–molecule isotopic exchanges or grain-surface reactions and was not re-equilibrated with H2in the Solar Nebula. However, there are strong presumptions that interstellar grains were partly mixed in the early nebula prior to cometary formation with water reprocessed in the warm inner part of the nebula and transported by turbulent diffusion. Scenarios of formation of comets consistent with these results are discussed.

The catalogue presented here is a compilation of published atmospheric parameters (T eff , log g, [Fe/H]) obtained from high resolution, high signal-to-noise spectroscopic observations. This new edition has changed compared to the five previous versions. It is now restricted to intermediate and low mass stars (F, G and K stars). It contains 6354 determinations of (T eff , log g, [Fe/H]) for 3356 stars, including 909 stars in 79 stellar systems. The literature is complete between January 1980 and December 2000 and includes 378 references. The catalogue is made up of two tables, one for field stars and one for stars in galactic associations, open and globular clusters and external galaxies. The catalogue is distributed through the CDS database. Access to the catalogue with cross-identification to other sets of data is also possible with VizieR (Ochsenbein et al. 2000).

Aims. In this paper the calibration and in-orbit performance of the Heterodyne Instrument for the Far-Infrared (HIFI) is described. Methods. The calibration of HIFI is based on a combination of ground and in-flight tests. Dedicated ground tests to determine those instrument parameters that can only be measured accurately using controlled laboratory stimuli were carried out in the instrument level test (ILT) campaign. Special in-flight tests during the commissioning phase (CoP) and performance verification (PV) allowed the determination of the remaining instrument parameters. The various instrument observing modes, as specified in astronomical observation templates (AOTs), were validated in parallel during PV by observing selected celestial sources. Results. The initial calibration and in-orbit performance of HIFI has been established. A first estimate of the calibration budget is given. The overall in-flight instrument performance agrees with the original specification. Issues remain at only a few frequencies.