Brenda C. Matthews

Discovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager

An exoplanet extracted from the bright Direct imaging of Jupiter-like exoplanets around young stars provides a glimpse into how our solar system formed. The brightness of young stars requires the use of next-generation devices such as the Gemini Planet Imager (GPI). Using the GPI, Macintosh et al. discovered a Jupiter-like planet orbiting a young star, 51 Eridani (see the Perspective by Mawet). The planet, 51 Eri b, has a methane signature and is probably the smallest exoplanet that has been directly imaged. These findings open the door to understanding solar system origins and herald the dawn of a new era in next-generation planetary imaging. Science, this issue p. 64; see also p. 39 The Gemini Planet Imager detects a Jupiter-like exoplanet orbiting the young star 51 Eridani. [Also see Perspective by Mawet] Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10−6 and an effective temperature of 600 to 750 kelvin. For this age and luminosity, “hot-start” formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the “cold-start” core-accretion process that may have formed Jupiter.

Discovery of a Large Dust Disk Around the Nearby Star AU Microscopii

We present the discovery of a circumstellar dust disk surrounding AU Microscopii (AU Mic, GJ 803, HD 197481). This young M star at 10 parsec has the same age and origin as β Pictoris, another nearby star surrounded by a dust disk. The AU Mic disk is detected between 50 astronomical units (AU) and 210 AU radius, a region where dust lifetimes exceed the present stellar age. Thus, AU Mic is the nearest star where we directly observe the solid material required for planet formation. Because 85% of stars are M-type, the AU Mic disk provides new clues on how the majority of planetary systems might form and evolve.

Molecular Gas Clumps from the Destruction of Icy Bodies in the β Pictoris Debris Disk

One-Sided Story from Disk In young analogs of the solar system, the ongoing erosion of comets and nascent planets produces dusty debris that is eventually expelled by the host star. Gas should also be released in this process when volatile ices sublimate, but it is detected less often. Using the Atacama Large Millimeter/Submillimeter Array, Dent et al. (p. 1490, published online 6 March; see the Perspective by Brandeker) mapped a highly asymmetric disk of dust and carbon monoxide orbiting the planet-hosting star, β Pictoris. The distribution of gas and dust is consistent with two proposed scenarios: In one, an outward-migrating planet has resonantly trapped dust-yielding bodies in two clumps opposite the star. In another, the entire debris mass is the result of a single recent collision of Mars-sized bodies. An asymmetric disk of dust and carbon monoxide indicates a recent large-scale collision or shepherding by an unseen planet. [Also see Perspective by Brandeker] Many stars are surrounded by disks of dusty debris formed in the collisions of asteroids, comets, and dwarf planets, but is gas also released in such events? Observations at submillimeter wavelengths of the archetypal debris disk around β Pictoris show that 0.3% of a Moon mass of carbon monoxide orbits in its debris belt. The gas distribution is highly asymmetric, with 30% found in a single clump 85 astronomical units from the star, in a plane closely aligned with the orbit of the inner planet, β Pictoris b. This gas clump delineates a region of enhanced collisions, either from a mean motion resonance with an unseen giant planet or from the remnants of a collision of Mars-mass planets.

Resolved debris discs around a stars in the herschel DEBRIS survey

The majority of debris discs discovered so far have only been detected through infrared excess emission above stellar photospheres. While disc properties can be inferred from unresolved photometry alone under various assumptions for the physical properties of dust grains, there is a degeneracy between disc radius and dust temperature that depends on the grain size distribution and optical properties. By resolving the disc we can measure the actual location of the dust. The launch of Herschel, with an angular resolution superior to previous far-infrared telescopes, allows us to spatially resolve more discs and locate the dust directly. Here we present the nine resolved discs around A stars between 20 and 40 pc observed by the DEBRIS survey. We use these data to investigate the disc radii by tting narrow ring models to images at 70, 100 and 160 m and by tting blackbodies to full spectral energy distributions. We do this with the aim of nding an improved way of estimating disc radii for unresolved systems. The ratio between the resolved and blackbody radii varies between 1 and 2.5. This ratio is inversely correlated with luminosity and any remaining discrepancies are most likely explained by dierences to the minimum size of grain in the size distribution or dierences in composition. We nd that three of the systems are well t by a narrow ring, two systems are borderline cases and the other four likely require wider or multiple rings to fully explain the observations, reecting the diversity of planetary systems.

The James Clerk Maxwell telescope legacy survey of nearby star-forming regions in the gould belt

This paper describes a James Clerk Maxwell Telescope (JCMT) legacy survey that has been awarded roughly 500 hr of observing time to be carried out from 2007 to 2009. In this survey, we will map with SCUBA-2 (Submillimetre Common-User Bolometer Array 2) almost all of the well-known low-mass and intermediate-mass star-forming regions within 0.5 kpc that are accessible from the JCMT. Most of these locations are associated with the Gould Belt. From these observations, we will produce a flux-limited snapshot of star formation near the Sun, providing a legacy of images, as well as point-source and extended-source catalogs, over almost 700 deg(2) of sky. The resulting images will yield the first catalog of prestellar and protostellar sources selected by submillimeter continuum emission, and should increase the number of known sources by more than an order of magnitude. We will also obtain with the array receiver HARP (Heterodyne Array Receiver Program) CO maps, in three CO isotopologues, of a large typical sample of prestellar and protostellar sources. We will then map the brightest hundred sources with the SCUBA-2 polarimeter (POL-2), producing the first statistically significant set of polarization maps in the submillimeter. The images and source catalogs will be a powerful reference set for astronomers, providing a detailed legacy archive for future telescopes, including ALMA, Herschel, and JWST.

A Submillimeter Search of Nearby Young Stars for Cold Dust: Discovery of Debris Disks around Two Low-Mass Stars

We present results from a James Clerk Maxwell Telescope/SCUBA 850 � m search for cold dust around eight nearby young stars belonging to thePic (t � 12 Myr) and the Local Association (t � 50 Myr) moving groups. Unlike most past submillimeter studies, our sample was chosen solely on the basis of stellar age. Our observations achieve about an order of magnitude greater sensitivity in dust mass compared to previous work in this age range. We detected two of the three M dwarfs in our sample at 850 � m, GJ 182 and GJ 803 (M� � 0:5 M� ), with inferred dust masses of only � 0:01 0:03 M� . GJ 182 may also possess a 25 � m excess, which is indicative of warm dust in the inner few AU of its disk. For GJ 803 (AU Mic; HD 197481), submillimeter mapping finds that the 850 � m emission is unresolved. A nondetection of the CO 3-2 line indicates the system is gas-poor, and the spectral energy distribution suggests the presence of a large inner disk hole (� 17 AU ¼ 1B7 in radius for blackbody grains). These are possible indications that planets at large separations can form around M dwarfs within � 10 Myr. In a companion paper, we confirm the existence of a dust disk around GJ 803 using optical coronagraphic imaging. Given its youthfulness, proximity, and detectability, the GJ 803 disk will be a valuable system for studying disk, and perhaps planet, formation in great detail. Overall, submillimeter measurements of debris disks point to a drop in dust mass by a factor of � 10 3 within the first � 10 Myr, with the subsequent decline in the masses of submillimeter-detected disks consistent with t � 0:5 -t � 1 . Subject headings: circumstellar matter — planetary systems: formation — planetary systems: protoplanetary disks — stars: late-type

The Signature of Primordial Grain Growth in the Polarized Light of the AU Microscopii Debris Disk

We have used the Hubble Space Telescope Advanced Camera for Surveys coronagraph to make the first polarization maps of the AU Microscopii debris disk. The polarization rises from 5% at 20 AU to 40% at 80 AU. The polarization is perpendicular to the disk, indicating that the scattered light originates from micron-sized grains in an optically thin disk. Disk models show that interior to the ‘‘birth ring’’ (40Y50 AU) there is a hole in the dust distribution where micron-sized dust is depleted by a factor of more than 300. The disk is collision dominated, and grains that fall inward due to drag forces undergo a destructive collision. The presence of this hole implies that the localized enhancements in surface brightness that occur at projected radii interior to the birth ring are caused by nonaxisymmetric structures in the outer disk. The grains exhibit strong forward scattering and high polarization. Spherical grains composed of conventional materials cannot reproduce these optical properties. A Mie/MaxwellGarnett analysis demands highly porous (91%Y94%) particles. In the inner solar system, porous particles form in cometary dust, where the sublimation of ices leaves a ‘‘bird’s nest’’ of refractory material. In AU Mic, the grain porosity may be primordial, because the dust birth ring lies beyond the ice sublimation point. The observed porosities span the range of values implied by laboratory studies of particle coagulation by ballistic clustercluster aggregation. To avoid compactification, the upper size limit for the parent bodies is in the decimeter range, in agreement with theoretical predictions based on collisional lifetime arguments. Consequently, AU Mic may exhibit thesignatureoftheprimordialagglomerationprocesswherebyinterstellargrainsfirstassembledtoformmacroscopic objects. Subject headingg circumstellar matter — dust, extinction — planetary systems: formation — polarization — stars: individual (AU Mic, GJ 803)

The Spitzer Gould Belt Survey of Large Nearby Interstellar Clouds: Discovery of a Dense Embedded Cluster in the Serpens-Aquila Rift

We report the discovery of a nearby, embedded cluster of young stellar objects, associated filamentary infrared dark cloud, and 4.5 μm shock emission knots from outflows detected in Spitzer IRAC mid-infrared imaging of the Serpens-Aquila Rift obtained as part of the Spitzer Gould Belt Legacy Survey. We also present radial velocity measurements of the region from molecular line observations obtained with the Submillimeter Array (SMA) that suggest the cluster is comoving with the Serpens Main embedded cluster 3° to the north. We therefore assign it the same distance, 260 pc. The core of the new cluster, which we call Serpens South, is composed of an unusually large fraction of protostars (77%) at high mean surface density (>430 pc−2) and short median nearest neighbor spacing (3700 AU). We perform basic cluster structure characterization using nearest neighbor surface density mapping of the YSOs and compare our findings to other known clusters with equivalent analyses available in the literature.

Resolving debris discs in the far-infrared: Early highlights from the DEBRIS survey

We present results from the earliest observations of DEBRIS, a Herschel Key Programme to conduct a volume- and flux-limited survey fo r debris discs in A-type through M-type stars. PACS images (from chop/nod or scan-mode observations) at 100 and 160� m are presented toward two

Herschel imaging of 61 Vir: implications for the prevalence of debris in low-mass planetary systems

This paper describes Herschel observations of the nearby (8.5pc) G5V multi-exoplanet host star 61Vir at 70, 100, 160, 250, 350 and 500m carried out as part of the DEBRIS survey. These observations reveal emission that is significantly extended out to a distance of >15arcsec with a morphology that can be fitted by a nearly edge-on (77° inclination) radially broad (from 30au out to at least 100au) debris disc of fractional luminosity 2.7 × 10 -5, with two additional (presumably unrelated) sources nearby that become more prominent at longer wavelengths. Chance alignment with a background object seen at 1.4GHz provides potential for confusion, however, the stars 1.4arcsecyr -1 proper motion allows archival Spitzer 70m images to confirm that what we are interpreting as disc emission really is circumstellar. Although the exact shape of the discs inner edge is not well constrained, the region inside 30au must be significantly depleted in planetesimals. This is readily explained if there are additional planets outside those already known (i.e. in the 0.5-30au region), but is also consistent with collisional erosion. We also find tentative evidence that the presence of detectable debris around nearby stars correlates with the presence of the lowest mass planets that are detectable in current radial velocity surveys. Out of an unbiased sample of the nearest 60G stars, 11 are known to have planets, of which six (including 61Vir) have planets that are all less massive than Saturn, and four of these have evidence for debris. The debris towards one of these planet hosts (HD20794) is reported here for the first time. This fraction (4/6) is higher than that expected for nearby field stars (15per cent), and implies that systems that form low-mass planets are also able to retain bright debris discs. We suggest that this correlation could arise because such planetary systems are dynamically stable and include regions that are populated with planetesimals in the formation process where the planetesimals can remain unperturbed over Gyr time-scales.