* Astronomy

Blobrana · L

RE: Beta Pictoris

Blobrana · L

Title: Comet-like mineralogy of olivine crystals in an extrasolar proto-Kuiper belt
Authors: B. L. de Vries, B. Acke, J. A. D. L. Blommaert, C. Waelkens, L. B. F. M. Waters, B. Vandenbussche, M. Min, G. Olofsson, C. Dominik, L. Decin, M. J. Barlow, A. Brandeker, J. Di Francesco, A. M. Glauser, J. Greaves, P. M. Harvey, W. S. Holland, R. J. Ivison, R. Liseau, E. E. Pantin, G. L. Pilbratt, P. Royer, B. Sibthorpe

Some planetary systems harbour debris disks containing planetesimals such as asteroids and comets. Collisions between such bodies produce small dust particles, the spectral features of which reveal their composition and, hence, that of their parent bodies. A measurement of the composition of olivine crystals has been done for the protoplanetary disk HD100546 and for olivine crystals in the warm inner parts of planetary systems. The latter compares well with the iron-rich olivine in asteroids (x<0.29). In the cold outskirts of the Beta Pictoris system, an analogue to the young Solar System, olivine crystals were detected 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. 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, even though Beta Pictoris is more massive and more luminous and has a different planetary system architecture.

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Blobrana · L

Comet crystals found in a nearby planetary system

Pristine material that matches comets in our own Solar System have been found in a dust belt around the young star Beta Pictoris by ESA's Herschel space observatory.
Twelve-million-year-old Beta Pictoris resides just 63 light-years from Earth and hosts a gas giant planet along with a dusty debris disc that could, in time, evolve into a torus of icy bodies much like the Kuiper Belt found outside the orbit of Neptune in our Solar System.
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Blobrana · L

Title: VLT imaging of the beta Pictoris gas disk
Authors: R. Nilsson, A. Brandeker, G. Olofsson, K. Fathi, Ph. Thébault, R. Liseau

Circumstellar debris disks older than a few Myr should be largely devoid of primordial gas remaining from the protoplanetary disk phase. Tracing the origin of observed atomic gas in Keplerian rotation in the edge-on debris disk surrounding the ~12 Myr old star beta Pictoris requires more detailed information about its spatial distribution than has previously been acquired by limited slit spectroscopy. Especially indications of asymmetries and presence of Ca II gas at high disk latitudes call for additional investigation. We set out to recover a complete image of the Fe I and Ca II gas emission around beta Pic by spatially resolved, high-resolution spectroscopic observations to better understand the morphology and origin of the gaseous disk component. The multiple fibre facility FLAMES/GIRAFFE at the VLT, with the large IFU ARGUS, was used to obtain spatially resolved optical spectra in four regions covering the northeast and southwest side of the disk. Emission lines from Fe I and Ca II were mapped and could be used to fit a parametric function for the disk gas distribution, using a gas-ionisation code for gas-poor debris disks. Both Fe I and Ca II emission are clearly detected, with the former dominating along the disk midplane, and the latter revealing vertically more extended gas. The surface intensity of the Fe I emission is lower but more extended in the northeast (reaching the 210 AU limit of our observations) than in the southwest, while Ca II shows the opposite asymmetry. The modelled Fe gas disk profile shows a linear increase in scale height with radius, and a vertical profile that suggests dynamical interaction with the dust. We also qualitatively demonstrate that the Ca II emission profile can be explained by optical thickness in the disk midplane, and does not require Ca to be spatially separated from Fe.

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Blobrana · L

Title: Soft coronal X-rays from beta Pictoris
Authors: H. M. Günther, S. J. Wolk, J. J. Drake, C. M. Lisse, J. Robrade, J. H. M. M. Schmitt

A type stars are expected to be X-ray dark, yet weak emission has been detected from several objects in this class. We present new Chandra/HRC-I observations of the A5 V star beta Pictoris. It is clearly detected with a flux of 9±2 10^{-4} counts/s. In comparison with previous data this constrains the emission mechanism and we find that the most likely explanation is an optically thin, collisionally dominated, thermal emission component with a temperature around 1.1 MK. We interpret this component as a very cool and dim corona, with \log L_X/L_{bol}=-8.2 (0.2-2.0 keV). Thus, it seems that beta Pictoris shares more characteristics with cool stars than previously thought.

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Blobrana · L

Title: A background galaxy in the field of the beta Pic debris disk
Authors: S. Regibo, B. Vandenbussche, C. Waelkens, B. Acke, B. Sibthorpe, M. Nottebaere, K. Voet, J. Di Francesco, M. Fridlund, W.K. Gear, R.J. Ivison, G. Olofsson

Herschel images in six photometric bands show the thermal emission of the debris disk surrounding beta Pic. In the three PACS bands at 70 micron, 100 micron and 160 micron and in the 250 micron SPIRE band, the disk is well-resolved, and additional photometry is available in the SPIRE bands at 350 micron and 500 micron, where the disk is only marginally resolved. The SPIRE maps reveal a blob to the southwest of beta Pic, coinciding with submillimetre detection of excess emission in the disk. We investigated the nature of this blob. Our comparison of the colours, spectral energy distribution and size of the blob, the disk and the background sources shows that the blob is most likely a background source with a redshift between z =1.0 and z = 1.6.

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Blobrana · L

Title: Constrains on planets around beta Pic with Harps radial velocity data
Authors: A.-M. Lagrange, K. De Bondt, N. Meunier, M. Sterzik, H. Beust, F. Galland

Context. The beta Pictoris system with its debris disk and a massive giant planet orbiting at \simeq 9 AU represents an ideal laboratory to study giant planet formation and evolution as well as planet-disk interactions. beta Pic b can also help testing brightness-mass relations at young ages. Other planets, yet undetected, may of course be present in the system.
Aims. We aim at putting direct constrains on the mass of beta Pic b and at searching for additional jovian planets on orbits closer than typically 2 AU.
Methods. We use high precision Harps data collected over 8 years since 2003 to measure and analyse beta Pic radial velocities.
Results. We show that the true mass of beta Pic b is less than 10, 12, 15.5, 20 and 25 Jupiter masses if orbiting respectively at 8, 9, 10, 11 and 12 AU. This is the first direct constraint on the mass of an imaged planet. The upper mass found is well in the range predicted by brightness-mass relations provided by current "hot start" models. We also exclude the presence of giant planets more massive than 2.5 Jupiter masses with periods less than 100 days (hot Jupiters), more massive than 9 Jupiter masses for periods in the range 100-500 days. In the 500-1000 day range, the detection limit is in the brown dwarf domain. Beyond the intrinsic interest for beta Pic, these results show the possibilities of precise RV measurements of early type, rapidly rotating stars.

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Blobrana · L

Title: Orbital characterisation of the Beta Pictoris b giant planet
Authors: G. Chauvin, A.-M. Lagrange, H. Beust, M. Bonnefoy, A. Boccaletti, D. Apai, F. Allard, D. Ehrenreich, J. H. V. Girard, D. Mouillet, D. Rouan

In June 2010, we confirmed the existence of a giant planet in the disk of the young star Beta Pictoris, located between 8 AU and 15 AU from the star. This young planet offers the rare opportunity to monitor a large fraction of the orbit using the imaging technique over a reasonably short timescale. Using the NAOS-CONICA adaptive-optics instrument (NACO) at the Very Large Telescope (VLT), we obtained repeated follow-up images of the Bpic system in the Ks and L' filters at four new epochs in 2010 and 2011. Complementing these data with previous measurements, we conduct a homogeneous analysis, which covers more than eight yrs, to accurately monitor the Bpic b position relative to the star. On the basis of the evolution of the planet's relative position with time, we derive the best-fit orbital solutions for our measurements. More reliable results are found with a Markov-chain Monte Carlo approach. The solutions favour a low-eccentricity orbit e greater than 0.17, with semi-major axis in the range 8--9 AU corresponding to orbital periods of 17--21 yrs. Our solutions favour a highly inclined solution with a peak around i=88.5±1.7 deg, and a longitude of ascending node tightly constrained at Omega = -147.5±1.5 deg. These results indicate that the orbital plane of the planet is likely to be above the midplane of the main disk, and compatible with the warp component of the disk being tilted between 3.5 deg and 4.0 deg. This suggests that the planet plays a key role in the origin of the inner warped-disk morphology of the Bpic disk. Finally, these orbital parameters are consistent with the hypothesis that the planet is responsible for the transit-like event observed in November 1981, and also linked to the cometary activity observed in the Bpic system.

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Blobrana · L

Title: beta Pic b position relative to the Debris Disk
Authors: A.-M. Lagrange, A. Boccaletti, J. Milli, G. Chauvin, M. Bonnefoy, D. Mouillet, J. C. Augereau, J. H. Girard, S. Lacour, D. Apai

Context. We detected in 2009 a giant, close-by planet orbiting beta Pic, a young star surrounded with a disk, extensively studied for more than 20 years. We showed that if located on an inclined orbit, the planet could explain several peculiarities of beta Pictoris system. However, the available data did not permit to measure the inclination of beta Pic b with respect to the disk, and in particular to establish in which component of the disk - the main, extended disk or the inner inclined component/disk-, the planet was located. Comparison between the observed planet position and the disk orientation measured on previous imaging data was not an option because of potential biases in the measurements.
Aims. Our aim is to measure precisely the planet location with respect to the dust disk using a single high resolution image, and correcting for systematics or errors that degrades the precision of the disk and planet relative position measurements.
Methods. We gathered new NaCo data at Ks band, with a set-up optimised to derive simultaneously the orientation(s) of the disk(s) and that of the planet.
Results. We show that the projected position of beta Pic b is above the midplane of the main disk. With the current data and knowledge on the system, this implies that beta Pic b cannot be located in the main disk. The data rather suggest the planet being located in the inclined component.

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Blobrana · L

An astronomer in New Zealand claims to have captured the first amateur pictures of another solar system from a tiny telescope in his back yard.
Rolf Olsen, a New Zealand-based astrophotographer, has published the first non-professional pictures of the disk of debris and dust swirling around Beta Pictoris, a very young solar system.
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