Molecular Hydrogen emission from disks in the eta Chamaeleontis cluster

Disks in the 6 Myr old cluster eta Chamaeleontis were searched for emission from hot H2. Around the M3 star ECHAJ0843.3-7905 we detect circumstellar gas orbiting at ~2 AU. If the gas is UV-excited, the ro-vibrational line traces a hot gas layer supported by a disk of mass ~0.03Msolar, similar to the minimum mass solar nebula. Such a gas reservoir at 6 Myr would promote the formation and inwards migration of gas giant planets.Comment: Accepted for publication in MNRAS. 9 page

The Geminga pulsar wind nebula in the mid-infrared and submillimetre

The nearby middle-aged Geminga pulsar has crossed the Galactic plane within the last ∼0.1 Myr. We present archival data from Wide-field Infrared Survey Explorer and from SCUBA and SCUBA-2 on the James Clerk Maxwell Telescope to assess whether any midinfrared and submillimetre emission arises from interaction of the pulsar wind nebula with the interstellar medium. A candidate shell and bow shock are reported. Given the low pulsar velocity and local density, dust grains appear able to penetrate into the nebula. A compact source seen towards the pulsar is fitted with a dust spectrum. If confirmed as a real association at higher resolution, this could be a circum-pulsar disc of at least a few Earth-masses, in which future planets could form

Sub-arcsecond high sensitivity measurements of the DG~Tau jet with e-MERLIN

We present very high spatial resolution deep radio continuum observations at 5 GHz (6 cm) made with e-MERLIN of the young stars DG Tau A and B. Assuming it is launched very close (~=1 au) from the star, our results suggest that the DG Tau A outflow initially starts as a poorly focused wind and undergoes significant collimation further along the jet (~=50 au). We derive jet parameters for DG Tau A and find an initial jet opening angle of 86 degrees within 2 au of the source, a mass-loss rate of 1.5x10^-8 solar masses/yr for the ionised component of the jet, and the total ejection/accretion ratio to range from 0.06-0.3. These results are in line with predictions from MHD jet-launching theories.Comment: Accepted MNRAS Letter

Single-dish 1-cm-band radio photometry of protoplanetary discs: few centimetre-sized dust grains?

Radio-wavelength observations of protoplanetary discs can show whether large dust grains (pebbles) have formed on the pathway to aggregation of planetary cores. The 100-m Green Bank Telescope was used to make a four-subband (26–40 GHz) photometric survey of the Taurus and Ophiuchus regions, which is nearly complete for class II systems above fixed millimetre-flux thresholds. There is evidence of anomalous microwave emission in 40 per cent of the systems, indicating that radio observations of protoplanetary discs need good spectral coverage to distinguish the presence of dust. At most, one-quarter of the systems are seen to host pebbles, of radii as large as 1 cm. The lack of pebble-dominated systems suggests that this is a short-lived phase in particle size evolution, and/or that pebbles only grow in limited areas of the disc. Either case supports models where grains of centimetre size rapidly fragment and/or drift towards the star, potentially feeding growing planets. In the best-fitting systems, including the 26–40 GHz data raises the detected dust mass by up to an order of magnitude, and the mass distribution of the discs may be flatter. Both of these phenomena could help to solve the ‘missing mass’ problem, where the solid budget in protoplanetary discs is compared with the substantial requirements of extrasolar-planet systems

New sub-millimeter limits on dust in the 55 Cancri planetary system

We present new, high-sensitivity sub-millimeter observations towards 55 Cancri, a nearby G8 star with one, or possibly two, known planetary companion(s). Our 850 $\mu$m map, obtained with the SCUBA instrument on the James Clerk Maxwell Telescope, shows three peaks of emission at the 2.5 mJy level in the vicinity of the star's position. However, the observed peaks are 25\arcsec--40\arcsec away from the star and a deep $R$-band optical image reveals faint point sources that coincide with two of the sub-millimeter peaks. Thus, we do not find evidence for dust emission spatially associated with 55 Cancri. The excess 60 $\mu$m emission detected with ISO may originate from one or more of the 850 $\mu$m peaks that we attribute to background sources. Our new results, together with the HST/NICMOS coronographic images in the near-infrared, place stringent limits on the amount of dust in this planetary system, and argue against the existence of a detectable circumstellar dust disk around 55 Cnc.Comment: 11 pages, 2 PostScript figures, to appear in The Astrophysical Journal Letter

Dust in the 55 Cancri planetary system

The presence of debris disks around $\sim$ 1-Gyr-old main sequence stars suggests that an appreciable amount of dust may persist even in mature planetary systems. Here we report the detection of dust emission from 55 Cancri, a star with one, or possibly two, planetary companions detected through radial velocity measurements. Our observations at 850$\mu$m and 450$\mu$m imply a dust mass of 0.0008-0.005 Earth masses, somewhat higher than that in the the Kuiper Belt of our solar system. The estimated temperature of the dust grains and a simple model fit both indicate a central disk hole of at least 10 AU in radius. Thus, the region where the planets are detected is likely to be significantly depleted of dust. Our results suggest that far-infrared and sub-millimeter observations are powerful tools for probing the outer regions of extrasolar planetary systems.Comment: 8 pages and 2 figures, to appear in the Astrophysical Journa

New constraints on the millimetre emission of six debris discs

The presence of dusty debris around main-sequence stars denotes the existence of planetary systems. Such debris discs are often identified by the presence of excess continuum emission at infrared and (sub-)millimetre wavelengths, with measurements at longer wavelengths tracing larger and cooler dust grains. The exponent of the slope of the disc emission at submillimetre wavelengths, ‘q’, defines the size distribution of dust grains in the disc. This size distribution is a function of the rigid strength of the dust producing parent planetesimals. As a part of the survey ‘PLAnetesimals around TYpical Pre-main seqUence Stars’, we observed six debris discs at 9 mm using the Australian Telescope Compact Array. We obtain marginal (∼3σ) detections of three targets: HD 105, HD 61005 and HD 131835. Upper limits for the three remaining discs, HD 20807, HD 109573 and HD 109085 provide further constraint of the (sub-)millimetre slope of their spectral energy distributions. The values of q (or their limits) derived from our observations are all smaller than the oft-assumed steady-state collisional cascade model (q = 3.5), but lie well within the theoretically expected range for debris discs q ∼ 3–4. The measured q values for our targets are all <3.3, consistent with both collisional modelling results and theoretical predictions for parent planetesimal bodies being ‘rubble piles’ held together loosely by their self-gravity

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 fitting narrow ring models to images at 70, 100 and 160 {\mu}m and by fitting blackbodies to full spectral energy distributions. We do this with the aim of finding 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 differences to the minimum size of grain in the size distribution or differences in composition. We find that three of the systems are well fit by a narrow ring, two systems are borderline cases and the other four likely require wider or multiple rings to fully explain the observations, reflecting the diversity of planetary systems.Comment: 19 pages, 13 figures, 6 tables. Accepted for publication in MNRA