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Dust emission around the nearby star ǫ Eridani has been imaged using a new submillimetre camera (SCUBA at the JCMT). At 850 µm wavelength a ring of dust is seen, peaking at 60 AU from the star and with much lower emission inside 30 AU. The mass of the ring is at least ∼ 0.01 M ⊕ in dust, while an upper limit of 0.4 M ⊕ in molecular gas is imposed by CO observations. The total mass is comparable to the estimated amount of material, 0.04-0.3 M ⊕ , in comets orbiting the Solar System.The most probable origin of the the ring structure is that it is a young analogue to the Kuiper Belt in our Solar System, and that the central region has been partially cleared by the formation of grains into planetesimals. Dust clearing around ǫ Eri is seen within the radius of Neptune's orbit, and the peak emission at 35-75 AU lies within the estimated Kuiper Belt zone of 30-100 AU radius. ǫ Eri is a main-sequence star of type K2V (0.8 M ⊙ ) with an estimated age of 0.5-1.0 Gyr, so this interpretation is consistent with the early history of the Solar System where heavy bombardment occurred up to ≈ 0.6 Gyr. An unexpected discovery is substructure within the ring, and these asymmetries could be due to perturbations by planets.

We present results from a 2300 arcmin 2 survey of the Orion A molecular cloud at 450 and 850 µm using the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope. The region mapped lies directly south of the OMC1 cloud core and includes OMC4, OMC5, HH1/2, HH34, and L1641N. We identify 71 independent clumps in the 850 µm map and compute size, flux, and degree of central concentration in each. Comparison with isothermal, pressure-confined, self-gravitating Bonnor-Ebert spheres implies that the clumps have internal temperatures T d ∼ 22 ± 5 K and surface pressures log(k −1 P cm −3 K) = 6.0 ± 0.2. The clump masses span the range 0.3 − 22 M ⊙ assuming a dust temperature T d ∼ 20 K and a dust emissivity κ 850 = 0.02 cm 2 g −1 . The distribution of clump masses is well characterized by a power-law N(M) ∝ M −α with α = 2.0 ± 0.5 for M > 3.0 M ⊙ , indicating a clump mass function steeper than the stellar Initial Mass Function. Significant incompleteness makes determination of the slope at lower masses difficult. A comparison of the submillimeter emission map with an H 2 2.122 µm survey of the same region is performed. Several new Class 0 sources are revealed and a correlation is found between both the column density and degree of concentration of the submillimeter sources and the likelihood of coincident H 2 shock emission.

New submillimeter images have been obtained of the dust disk around the nearby K2 V star e Eridani, with the total data set now spanning 5 yr. These images show the distribution of dusty debris generated by comet collisions, reflecting clearing and perturbations by planets, and may give insights to early conditions in the solar system. The structure seen around e Eri at 850 mm and published in 1998 is confirmed in the new observations, and the same structure is also seen in an image obtained for the first time at 450 mm. The disk is inclined by ≈25Њ to the sky plane, with emission peaking at 65 AU, a 105 AU radius outer edge, and an inner cavity fainter by a factor of ≈2. The structure within the dust ring suggests perturbations by a planet orbiting at tens of AU, and long-term tracking of these features will constrain its mass and location. A preliminary analysis shows that two clumps and one arc appear to follow the stellar motion (i.e., are not background objects) and have tentative evidence of counterclockwise rotation of ∼1Њ yr Ϫ1 . Within the ring, the mass of colliding comets is estimated at 5-9 M , similar to the primordial Kuiper Belt, and so any inner terrestrial planets may be undergoing an epoch of heavy bombardment.

We report the discovery of a radio counterpart to GRB 990123. In contrast to previous well-studied radio afterglows which rise to peak flux on a timescale of a week and then decay over several weeks to months, the radio emission from this GRB was clearly detected one day after the burst, after which it rapidly faded away. The simplest interpretation of this ``radio flare'' is that it arises from the reverse shock. In the framework of the afterglow models discussed to date, a forward shock origin for the flare is ruled out by our data. However, at late times, some radio afterglow emission (commensurate with the observed late-time optical emission, the optical afterglow) is expected from the forward shock. The relative faintness of the observed late-time radio emission provides an independent indication for a jet-like geometry in this GRB. We use the same radio observations to constrain two key parameters of the forward shock, peak flux and peak frequency, to within a factor of two. These values are inconsistent with the notion advocated by several authors that the prompt optical emission detected by ROTSE smoothly joins the optical afterglow emission. Finally, with hindsight we now recognize another such radio flare and this suggests that one out of eight GRBs has a detectable radio flare. This abundance coupled with the reverse shock interpretation suggests that the radio flare phenomenon has the potential to shed new light into the physics of reverse shocks in GRBs.Comment: pages including 2 figures. Accepted by the Astrophys. J. (Letters