| 1. |
- Greaves, J. S., et al.
(författare)
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Extreme Conditions in a Close Analog to the Young Solar System: Herschel Observations of ∈ Eridani
- 2014
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 791:1
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Tidskriftsartikel (refereegranskat)abstract
- Far-infrared Herschel images of the is an element of Eridani system, seen at a fifth of the Sun's present age, resolve two belts of debris emission. Fits to the 160 mu m PACS image yield radial spans for these belts of 12-16 and 54-68 AU. The south end of the outer belt is approximate to 10% brighter than the north end in the PACS+SPIRE images at 160, 250, and 350 mu m, indicating a pericenter glow attributable to a planet "c" From this asymmetry and an upper bound on the offset of the belt center, this second planet should be mildly eccentric (e(c) approximate to 0.03-0.3). Compared to the asteroid and Kuiper Belts of the young Sun, the is an element of Eri belts are intermediate in brightness and more similar to each other, with up to 20 km sized collisional fragments in the inner belt totaling approximate to 5% of an Earth mass. This reservoir may feed the hot dust close to the star and could send many impactors through the Habitable Zone, especially if it is being perturbed by the suspected planet is an element of Eri b, at semi-major axis approximate to 3 AU.
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| 2. |
- Acke, B., et al.
(författare)
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Herschel images of Fomalhaut An extrasolar Kuiper belt at the height of its dynamical activity
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 540, s. Article Number: A125 -
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Tidskriftsartikel (refereegranskat)abstract
- Context. Fomalhaut is a young (2 +/- 1 x 10(8) years), nearby (7.7 pc), 2 M-circle dot star that is suspected to harbor an infant planetary system, interspersed with one or more belts of dusty debris. Aims. We present far-infrared images obtained with the Herschel Space Observatory with an angular resolution between 5.7 '' and 36.7 '' at wavelengths between 70 mu m and 500 mu m. The images show the main debris belt in great detail. Even at high spatial resolution, the belt appears smooth. The region in between the belt and the central star is not devoid of material; thermal emission is observed here as well. Also at the location of the star, excess emission is detected. We aim to construct a consistent image of the Fomalhaut system. Methods. We use a dynamical model together with radiative-transfer tools to derive the parameters of the debris disk. We include detailed models of the interaction of the dust grains with radiation, for both the radiation pressure and the temperature determination. Comparing these models to the spatially resolved temperature information contained in the images allows us to place strong constraints on the presence of grains that will be blown out of the system by radiation pressure. We use this to derive the dynamical parameters of the system. Results. The appearance of the belt points toward a remarkably active system in which dust grains are produced at a very high rate by a collisional cascade in a narrow region filled with dynamically excited planetesimals. Dust particles with sizes below the blow-out size are abundantly present. The equivalent of 2000 one-km-sized comets are destroyed every day, out of a cometary reservoir amounting to 110 Earth masses. From comparison of their scattering and thermal properties, we find evidence that the dust grains are fluffy aggregates, which indicates a cometary origin. The excess emission at the location of the star may be produced by hot dust with a range of temperatures, but may also be due to gaseous free-free emission from a stellar wind.
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| 3. |
- de Vries, B. L., et al.
(författare)
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Comet-like mineralogy of olivine crystals in an extrasolar proto-Kuiper belt
- 2012
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 490:7418, s. 74-76
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Tidskriftsartikel (refereegranskat)abstract
- Some planetary systems harbour debris disks containing planetesimals such as asteroids and comets(1). Collisions between such bodies produce small dust particles(2), the spectral features of which reveal their composition and, hence, that of their parent bodies. A measurement of the composition of olivine crystals (Mg2-2xFe2xSiO4) has been done for the protoplanetary disk HD 100546 (refs 3, 4) and for olivine crystals in the warm inner parts of planetary systems. The latter compares well with the iron-rich olivine in asteroids(5,6) (x approximate to 0.29). In the cold outskirts of the beta Pictoris system, an analogue to the young Solar System, olivine crystals were detected(7) but their composition remained undetermined, leaving unknown how the composition of the bulk of Solar System cometary olivine grains compares with that of extrasolar comets(8,9). Here we report the detection of the 69-micrometre-wavelength band of olivine crystals in the spectrum of beta Pictoris. Because the disk is optically thin, we can associate the crystals with an extrasolar proto-Kuiper belt a distance of 15-45 astronomical units from the star (one astronomical unit is the Sun-Earth distance), determine their magnesium-rich composition (x = 0.01 +/- 0.001) and show that they make up 3.6 +/- 1.0 per cent of the total dust mass. These values are strikingly similar to those for the dust emitted by the most primitive comets in the Solar System(8-10), even though beta Pictoris is more massive and more luminous and has a different planetary system architecture.
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| 4. |
- Hartogh, P., et al.
(författare)
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HIFI observations of water in the atmosphere of comet C/2008 Q3 (Garradd)
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L150
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution far-infrared and sub-millimetre spectroscopy of water lines is an important tool to understand the physical and chemical properties of cometary atmospheres. We present observations of several rotational ortho- and para-water transitions in comet C/2008 Q3 (Garradd) performed with HIFI on Herschel. These observations have provided the first detection of the 2(12)-1(01) (1669 GHz) ortho and 1(11)-0(00) (1113 GHz) para transitions of water in a cometary spectrum. In addition, the ground-state transition 1(10)-1(01) at 557 GHz is detected and mapped. By detecting several water lines quasi-simultaneously and mapping their emission we can constrain the excitation parameters in the coma. Synthetic line profiles are computed using excitation models which include excitation by collisions, solar infrared radiation, and radiation trapping. We obtain the gas kinetic temperature, constrain the electron density profile, and estimate the coma expansion velocity by analyzing the map and line shapes. We derive water production rates of 1.7-2.8 x 10(28) s(-1) over the range r(h) = 1.83-1.85 AU.
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| 5. |
- Khouri, T., et al.
(författare)
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The wind of W Hydrae as seen by Herschel I. The CO envelope
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 561, s. Article no. A5-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Asymptotic giant branch (AGB) stars lose their envelopes by means of a stellar wind whose driving mechanism is not understood well. Characterizing the composition and thermal and dynamical structure of the outflow provides constraints that are essential for understanding AGB evolution, including the rate of mass loss and isotopic ratios. Aims. We characterize the CO emission from the wind of the low mass-loss rate oxygen-rich AGB star W Hya using data obtained by the HIFI, PACS, and SPIRE instruments on board the Herschel Space Observatory and ground-based telescopes. (CO)-C-12 and (CO)-C-13 lines are used to constrain the intrinsic C-12/C-13 ratio from resolved HIFI lines. Methods. We combined a state-of-the-art molecular line emission code and a dust continuum radiative transfer code to model the CO lines and the thermal dust continuum. Results. The acceleration of the outflow up to about 5.5 km s(-1) is quite slow and can be represented by a beta-type velocity law with index beta = 5. Beyond this point, acceleration up the terminal velocity of 7 km s(-1) is faster. Using the J = 10-9, 9-8, and 6-5 transitions, we find an intrinsic C-12/C-13 ratio of 18 +/- 10 for W Hya, where the error bar is mostly due to uncertainties in the (CO)-C-12 abundance and the stellar flux around 4.6 mu m. To match the low-excitation CO lines, these molecules need to be photo-dissociated at similar to 500 stellar radii. The radial dust emission intensity profile of our stellar wind model matches PACS images at 70 mu m out to 20 '' (or 800 stellar radii). For larger radii the observed emission is substantially stronger than our model predicts, indicating that at these locations there is extra material present. Conclusions. The initial slow acceleration of the wind may imply inefficient dust formation or dust driving in the lower part of the envelope. The final injection of momentum in the wind might be the result of an increase in the opacity thanks to the late condensation of dust species. The derived intrinsic isotopologue ratio for W Hya is consistent with values set by the first dredge-up and suggestive of an initial mass of 2 M-circle dot or more. However, the uncertainty in the isotopologic ratio is large, which makes it difficult to set reliable limits on W Hya's main-sequence mass.
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| 6. |
- Sibthorpe, B., et al.
(författare)
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The Vega debris disc: A view from Herschel
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L130
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Tidskriftsartikel (refereegranskat)abstract
- We present five band imaging of the Vega debris disc obtained using the Herschel Space Observatory. These data span a wavelength range of 70-500 mu m with full-width half-maximum angular resolutions of 5.6-36.9 ''. The disc is well resolved in all bands, with the ring structure visible at 70 and 160 mu m. Radial profiles of the disc surface brightness are produced, and a disc radius of 11 '' (similar to 85AU) is determined. The disc is seen to have a smooth structure thoughout the entire wavelength range, suggesting that the disc is in a steady state, rather than being an ephemeral structure caused by the recent collision of two large planetesimals.
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| 7. |
- Vandenbussche, B., et al.
(författare)
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The beta Pictoris disk imaged by Herschel PACS and SPIRE
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L133
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Tidskriftsartikel (refereegranskat)abstract
- We obtained Herschel PACS and SPIRE images of the thermal emission of the debris disk around the A5V star beta Pic. The disk is well resolved in the PACS filters at 70, 100, and 160 mu m. The surface brightness profiles between 70 and 160 mu m show no significant asymmetries along the disk, and are compatible with 90% of the emission between 70 and 160 mu m originating in a region closer than 200 AU to the star. Although only marginally resolving the debris disk, the maps obtained in the SPIRE 250-500 mu m filters provide full-disk photometry, completing the SED over a few octaves in wavelength that had been previously inaccessible. The small far-infrared spectral index (beta = 0.34) indicates that the grain size distribution in the inner disk (
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