When viewed in optical starlight scattered by dust, the nearly edge-on debris disk surrounding the A5V star beta Pictoris (distance 19.3 pc; ref. 1) extends farther than 1,450 au from the star. Its large-scale complexity has been well characterized, but the detailed structure of the disk's central approximately 200-au region has remained elusive. This region is of special interest, because planets may have formed there during the star's 10-20-million-year lifetime, perhaps resulting in both the observed tilt of 4.6 degrees relative to the large-scale main disk and the partial clearing of the innermost dust. A peculiarity of the central disk (also possibly related to the presence of planets) is the asymmetry in the brightness of the 'wings', in which the southwestern wing is brighter and more extended at 12 microm than the northeastern wing. Here we present thermal infrared images of the central disk that imply that the brightness asymmetry results from the presence of a bright clump composed of particles that may differ in size from dust elsewhere in the disk. We suggest that this clump results from the collisional grinding of resonantly trapped planetesimals or the cataclysmic break-up of a planetesimal.

We present a time series of 8 -13 µm spectra and photometry for SN 2014J obtained 57, 81, 108, and 137 d after the explosion using CanariCam on the Gran Telescopio Canarias. This is the first mid-IR time series ever obtained for a Type Ia supernova. These observations can be understood within the framework of the delayed detonation model and the production of ∼0.6 M ⊙ of 56 Ni, consistent with the observed brightness, the brightness decline relation, and the γ-ray fluxes. The [Co III] line at 11.888 µm is particularly useful for evaluating the time evolution of the photosphere and measuring the amount of 56 Ni and thus the mass of the ejecta. Late-time line profiles of SN 2014J are rather symmetric and not shifted in the rest frame. We see Argon emission, which provides a unique probe of mixing in the transition layer between incomplete burning and nuclear statistical equilibrium. We may see [Fe III] and [Ni IV] emission, both of which are observed to be substantially stronger than indicated by our models. If the latter identification is correct, then we are likely observing stable Ni, which might imply central mixing. In addition, electron capture, also required for stable Ni, requires densities larger than ∼1 × 10 9 g cm −3 , which are expected to be present only in white dwarfs close to the Chandrasekhar limit. This study demonstrates that mid-IR studies of Type Ia supernovae are feasible from the ground and provide unique information, but it also indicates the need for better atomic data.Subject headings: supernovae: general -supernovae: individual (SN 2014J) -midinfrared: spectra INTRODUCTIONType Ia supernovae (SNe Ia) have proven invaluable in cosmological studies, understanding the origin of the elements, and as laboratories for probing the physics of flames, instabilities, radiation transport, non-equilibrium systems, and nuclear and high energy physics. There is general agreement that SNe Ia are the thermonuclear explosions of C/O white dwarfs (WDs) and that the competition between nuclear burning and hydrodynamical time scales determines the result of the explosion. To first order, the outcome hardly depends on details of the physics, the scenario, or the progenitor evolution ("stellar amnesia"), because nuclear physics governs the structure of the progenitor and the explosion, and radioactive 56 Ni powers the light curves, which we subsequently observe as SNe Ia (Höflich et al. 2003). As a result, the apparent homogeneity of SNe Ia does not imply homogeneous classes of either progenitors or explosion scenarios. However, advances in observations and computational methods are allowing detailed studies of secondary effects (e.g., Branch 1999), which can be crucial for distinguishing among alternatives. For example, with time, the expanding envelope becomes increasingly transparent and, thus, spectral time series can probe the structure of the envelope and the corresponding radial structure of the exploding object. The inferred distribution of products of explosive C burning (O/Mg/Ne), incomplete burning (...

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Magnetic fields (B-fields) play a key role in the formation and evolution of protoplanetary disks, but their properties are poorly understood due to the lack of observational constraints. Using CanariCam at the 10.4-m Gran Telescopio Canarias, we have mapped out the mid-infrared polarization of the protoplanetary disk around the Herbig Ae star AB Aur. We detect ∼0.44% polarization at 10.3 µm from AB Aur's inner disk (r < 80 AU), rising to ∼1.4% at larger radii. Our simulations imply that the mid-infrared polarization of the inner disk arises from dichroic emission of elongated particles aligned in a disk B-field. The field is well ordered on a spatial scale commensurate with our resolution (∼50 AU), and we infer a poloidal shape tilted from the rotational axis of the disk. The disk of AB Aur is optically thick at 10.3 µm, so polarimetry at this wavelength is probing the B-field near the disk surface. Our observations therefore confirm that this layer, favored by some theoretical studies for developing magneto-rotational instability and its resultant viscosity, is indeed very likely to be magnetized. At radii beyond ∼80 AU, the mid-infrared polarization results primarily from scattering by dust grains with sizes up to ∼1 µm, a size indicating both grain growth and, probably, turbulent lofting of the particles from the disk mid-plane.

Context. The formation of dust gaps in protoplanetary disks is one of the most important signs of disk evolution and might indicate the formation of planets. Aims. We aim to characterize the flaring disk structure around the Herbig Ae/Be stars HD 100453 and HD 34282. Their spectral energy distributions (SEDs) show an emission excess between 15−40 µm, but very weak (HD 100453) and no (HD 34282) signs of the 10 and 20 µm amorphous silicate features. We investigate whether this implies the presence of large dust gaps. Methods. We investigated spatially resolved mid-infrared Q-band images taken with Gemini North/MICHELLE. We performed radiative transfer modeling and examined the radial distribution of dust. We simultaneously fit the Q-band images and SEDs of HD 100453 and HD 34282. Results. Our solutions require that the inner halos and outer disks be separated by large dust gaps that are depleted with respect to the outer disk by a factor of 1000 or more. The inner edges of the outer disks of HD 100453 and HD 34282 have temperatures of ∼160 ± 10 K and ∼60 ± 5 K, respectively. Because of the high surface brightness of these walls, they dominate the emission in the Q band. Their radii are constrained at 20 +2 −2 AU and 92 +31 −17 AU, respectively. Conclusions. HD 100453 and HD 34282 most likely have disk dust gaps. The upper limit of the dust mass in each gap is estimated to be about 10 −7 M . We find that the locations and sizes of disk dust gaps are connected to the SED, as traced by the mid-infrared flux ratio F 30 /F 13.5 . We propose a new classification scheme for the Meeus groups based on the F 30 /F 13.5 ratio. The absence of amorphous silicate features in the observed SEDs is caused by the depletion of small ( 1 µm) silicate dust at temperatures above 160 K, which could be related to the presence of a dust gap in that region of the disk.