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Riviere-Marichalar P.,CSIC - National Institute of Aerospace Technology | Riviere-Marichalar P.,NOVA Kapteyn Astronomical Institute | Barrado D.,CSIC - National Institute of Aerospace Technology | Montesinos B.,CSIC - National Institute of Aerospace Technology | And 13 more authors.
Astronomy and Astrophysics | Year: 2014

Context. Debris discs are thought to be formed through the collisional grinding of planetesimals, and then can be considered as the outcome of planet formation. Understanding the properties of gas and dust in debris discs can help us comprehend the architecture of extrasolar planetary systems. Herschel Space Observatory far-infrared (IR) photometry and spectroscopy have provided a valuable dataset for the study of debris discs gas and dust composition. This paper is part of a series of papers devoted to the study of Herschel-PACS observations of young stellar associations. Aims. This work aims at studying the properties of discs in the beta Pictoris moving group (BPMG) through far-IR PACS observations of dust and gas. Methods. We obtained Herschel-PACS far-IR photometric observations at 70, 100, and 160 μm of 19 BPMG members, together with spectroscopic observations for four of them. These observations were centred at 63.18 μm and 157 μm, aiming to detect [OI] and [CII] emission. We incorporated the new far-IR observations in the SED of BPMG members and fitted modified blackbody models to better characterise the dust content. Results. We have detected far-IR excess emission towards nine BPMG members, including the first detection of an IR excess towards HD 29391.The star HD 172555, shows [OI] emission, while HD 181296 shows [CII] emission, expanding the short list of debris discs with a gas detection. No debris disc in BPMG is detected in both [OI] and [CII]. The discs show dust temperatures in the range 55-264 K, with low dust masses (<6.6 × 10-5 M ⊕ to 0.2 M⊕) and radii from blackbody models in the range 3 to ~82 AU. All the objects with a gas detection are early spectral type stars with a hot dust component. © 2014 ESO.

Walsh C.,Leiden University | Juhasz A.,Leiden University | Pinilla P.,Leiden University | Harsono D.,Leiden University | And 12 more authors.
Astrophysical Journal Letters | Year: 2014

HD 100546 is a well-studied Herbig Be star-disk system that likely hosts a close-in companion with compelling observational evidence for an embedded protoplanet at 68 AU. We present Atacama Large Millimeter/Submillimeter Array observations of the HD 100546 disk which resolve the gas and dust structure at (sub)millimeter wavelengths. The CO emission (at 345.795 GHz) originates from an extensive molecular disk (390 ± 20 AU in radius) whereas the continuum emission is more compact (230 ± 20 AU in radius), suggesting radial drift of the millimeter-sized grains. The CO emission is similar in extent to scattered light images indicating well-mixed gas and micrometer-sized grains in the disk atmosphere. Assuming azimuthal symmetry, a single-component power-law model cannot reproduce the continuum visibilities. The visibilities and images are better reproduced by a double-component model: a compact ring with a width of 21 AU centered at 26 AU and an outer ring with a width of 75 ± 3 AU centered at 190 ± 3 AU. The influence of a companion and protoplanet on the dust evolution is investigated. The companion at 10 AU facilitates the accumulation of millimeter-sized grains within a compact ring, ≈20-30 AU, by ≈10 Myr. The injection of a protoplanet at 1 Myr hastens the ring formation (≈1.2 Myr) and also triggers the development of an outer ring (≈100-200 AU). These observations provide additional evidence for the presence of a close-in companion and hint at dynamical clearing by a protoplanet in the outer disk. © 2014. The American Astronomical Society. All rights reserved.

Lebreton J.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | Augereau J.-C.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | Thi W.-F.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | Roberge A.,NASA | And 23 more authors.
Astronomy and Astrophysics | Year: 2012

Context. HD 181327 is a young main sequence F5/F6 V star belonging to the β Pictoris moving group (age ∼12 Myr). It harbors an optically thin belt of circumstellar material at radius ∼90 AU, presumed to result from collisions in a population of unseen planetesimals. Aims. We aim to study the dust properties in the belt in details, and to constrain the gas-to-dust ratio. Methods. We obtained far-infrared photometric observations of HD 181327 with the PACS instrument onboard the Herschel Space Observatory*, complemented by new 3.2 mm observations carried with the ATCA** array. The geometry of the belt is constrained with newly reduced HST/NICMOS scattered light images that allow the degeneracy between the disk geometry and the dust properties to be broken. We then use the radiative transfer code GRaTeR to compute a large grid of models, and we identify the grain models that best reproduce the spectral energy distribution (SED) through a Bayesian analysis. We attempt to detect the oxygen and ionized carbon fine-structure lines with Herschel/PACS spectroscopy, providing observables to our photochemical code ProDiMo. Results. The HST observations confirm that the dust is confined in a narrow belt. The continuum is detected with Herschel/PACS completing nicely the SED in the far-infrared. The disk is marginally resolved with both PACS and ATCA. A medium integration of the gas spectral lines only provides upper limits on the [OI] and [CII] line fluxes. We show that the HD 181327 dust disk consists of micron-sized grains of porous amorphous silicates and carbonaceous material surrounded by an important layer of ice, for a total dust mass of ∼0.05 M ⊕ (in grains up to 1 mm). We discuss evidences that the grains consists of fluffy aggregates. The upper limits on the gas atomic lines do not provide unambiguous constraints: only if the PAH abundance is high, the gas mass must be lower than ∼17 M +. Conclusions. Despite the weak constraints on the gas disk, the age of HD 181327 and the properties of the dust disk suggest that it has passed the stage of gaseous planets formation. The dust reveals a population of icy planetesimals, similar to the primitive Edgeworth-Kuiper belt, that may be a source for the future delivery of water and volatiles onto forming terrestrial planets. © 2012 ESO.

Riviere-Marichalar P.,CSIC - National Institute of Aerospace Technology | Menard F.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | Thi W.F.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | Kamp I.,NOVA Kapteyn Astronomical Institute | And 14 more authors.
Astronomy and Astrophysics | Year: 2012

Line spectra of 68 Taurus T Tauri stars were obtained with the Herschel-PACS (Photodetector Array Camera and Spectrometer) instrument as part of the GASPS (GAS evolution in Protoplanetary Systems) survey of protoplanetary discs. A careful examination of the linescans centred on the [OI] 63.18 μm fine-structure line unveiled a line at 63.32 μm in some of these spectra. We identify this line with the 8 18 → 7 07 transition of ortho-water. It is detected confidently (i.e., >3σ) in eight sources, i.e., ∼24% of the sub-sample with gas-rich discs. Several statistical tests were used to search for correlations with other disc and stellar parameters such as line fluxes of [O I] 6300 Å and 63.18 μm; X-ray luminosity and continuum levels at 63 μm and 850 μm. Correlations are found between the water line fluxes and the [O I] 63.18 μm line luminosity, the dust continuum, and possibly with the stellar X-ray luminosity. This is the first time that this line of warm water vapour has been detected in protoplanetary discs. We discuss its origins, in particular whether it comes from the inner disc and/or disc surface or from shocks in outflows and jets. Our analysis favours a disc origin, with the observed water vapour line produced within 2-3 AU from the central stars, where the gas temperature is of the order of 500-600 K. © 2012 ESO.

Riviere-Marichalar P.,CSIC - National Institute of Aerospace Technology | Barrado D.,CSIC - National Institute of Aerospace Technology | Barrado D.,Centro Astronomico Hispano Aleman | Augereau J.-C.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | And 16 more authors.
Astronomy and Astrophysics | Year: 2012

Context. HD 172555 is a young A7 star belonging to the β Pictoris moving group that harbours a debris disc. The Spitzer/IRS spectrum of the source showed mid-IR features such as silicates and glassy silica species, indicating the presence of a warm dust component with small grains, which places HD 172555 among the small group of debris discs with such properties. The IRS spectrum also shows a possible emission of SiO gas. Aims. We aim to study the dust distribution in the circumstellar disc of HD 172555 and to asses the presence of gas in the debris disc. Methods. As part of the GASPS open time key programme, we obtained Herschel/PACS photometric and spectroscopic observations of the source. We analysed PACS observations of HD 172555 and modelled the spectral energy distribution with a modified blackbody and the gas emission with a two-level population model with no collisional de-excitation. Results. We report for the first time the detection of [OI] atomic gas emission at 63.18 μm in the HD 172555 circumstellar disc. We detect excesses due to circumstellar dust toward HD 172555 in the three photometric bands of PACS (70, 100, and 160 μm). We derive a large dust particle mass of (4.8 ± 0.6) × 10 -4 M ⊕ and an atomic oxygen mass of 2.5 × 10 -2R 2 M ⊕, where R in AU is the separation between the star and the inner disc. Thus, most of the detected mass of the disc is in the gaseous phase. © ESO, 2012.

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