We present Keck LWS images of the Orion BN/KL star forming region obtained in the first multi-wavelength study to have 0. ′′ 3-0. ′′ 5 resolution from 4.7µm to 22µm. The young stellar objects designated infrared source n and radio source I are believed to dominate the BN/KL region. We have detected extended emission from a probable accretion disk around source n but infer a stellar luminosity on the order of only 2000 L ⊙ . Although source I is believed to be more luminous, we do not detect an infrared counterpart even at the longest wavelengths. However, we resolve the closeby infrared source, IRc2, into an arc of knots ∼ 10 3 AU long at all wavelengths. Although the physical relation of source I to IRc2 remains ambiguous, we suggest these sources mark a high density core (10 7 -10 8 pc −3 over ∼ 10 3 AU) within the larger BN/KL star forming cluster. The high density may be a consequence of the core being young and heavily embedded. We suggest the energetics of the BN/KL region may be dominated by this cluster core rather than one or two individual sources.

Observations of oscillations of temperature and wind in planetary atmospheres provide a means of generalizing models for atmospheric dynamics in a diverse set of planets in the Solar System and elsewhere. An equatorial oscillation similar to one in the Earth's atmosphere 1,2 has been discovered in Jupiter 3-6 . Here we report the existence of similar oscillations in Saturn's atmosphere, from an analysis of over two decades of spatially resolved observations of its 7.8-mm methane and 12.2-mm ethane stratospheric emissions, where we compare zonal-mean stratospheric brightness temperatures at planetographic latitudes of 3.66 and 15.56 in both the northern and the southern hemispheres. These results support the interpretation of vertical and meridional variability of temperatures in Saturn's stratosphere 7 as a manifestation of a wave phenomenon similar to that on the Earth and in Jupiter. The period of this oscillation is 14.8 6 1.2 terrestrial years, roughly half of Saturn's year, suggesting the influence of seasonal forcing, as is the case with the Earth's semi-annual oscillation 1 .These conclusions are based on a sequence of filtered mid-infrared maps or images of Saturn, through narrow-to medium-band spectral filters that are sensitive to upwelling radiance emerging from Saturn's stratosphere. As in our study of Jupiter 6 , we preferred to use the emission of stratospheric methane at wavelengths of around 7.8 mm to detect the stratospheric temperature field near the 20-mbar pressure level in the atmosphere, because methane is expected to be well mixed in Saturn's stratosphere. Thus, all variations in the thermal radiance must be attributed to variations in temperature, rather than in the methane abundance. However, because 7.8-mm methane emission is much fainter for Saturn than it is for Jupiter, most of our earliest observations with lengthy raster scans consist only of observations of much brighter stratospheric emission from ethane at wavelengths of around 12.2 mm (see the Supplementary Information), because only these images had sufficient signal-to-noise ratios to be useful. Figure 1 shows examples of 7.8-mm methane emission observed from the NASA Infrared Telescope Facility (IRTF) in two different phases of the oscillation. Details of the observations are given in the Supplementary Information.The angular resolution of scans and images at the IRTF was limited by diffraction to no better than 0.7 arcsec (at latitude 4u) for 7.8-mm methane emission and 1.1 arcsec (at latitude 7u) for 12.2-mm ethane emission, with some additional blurring arising from seeing (that is, distortion due to terrestrial atmospheric turbulence). (Here and below, latitude values without an explicit attribution refer to either the northern or the southern hemisphere.) It is possible to resolve differences between emission at planetographic latitudes of 3.6u and 15.5u (planetocentric latitudes of 3.0u and 13.0u) in all the images used in this study, which is a requirement for this investigation. We ignored regions of the planet that ...

Context. The massive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*) is, in relative terms, the weakest accreting black hole accessible to observations. It has inspired the theoretical models of radiatively inefficient accretion. Unfortunately, our knowledge of the mean SED and source structure of Sgr A* is very limited owing to numerous observational difficulties. At the moment, the mean SED of Sgr A* is only known reliably in the radio to mm regimes. Aims. The goal of this paper is to provide constraints on the mean emission from Sgr A* in the near-to-mid infrared. Methods. Sensitive images of the surroundings of Sgr A* at 8.6 μm, 4.8 μm , and 3.8 μm were produced by combining large quantities of imaging data. Images were produced for several observing epochs. Excellent imaging quality was reached in the MIR by using speckle imaging combined with holographic image reconstruction, a novel technique for this kind of data. Results. No counterpart of Sgr A* is detected at 8.6 μm. At this wavelength, Sgr A* is located atop a dust ridge, which considerably complicates the search for a potential point source. An observed 3σ upper limit of ∼10 mJy is estimated for the emission of Sgr A* at 8.6 μm, a tighter limit at this wavelength than in previous work. The de-reddened 3σ upper limit, including the uncertainty of the extinction correction, is ∼84 mJy . Based on the available data, it is argued that, with currently available instruments, Sgr A* cannot be detected in the MIR, not even during flares. At 4.8 μm and 3.8 μm, on the other hand, Sgr A* is detected at all times, at least when considering timescales of a few up to 13 min. We derive well-defined time-averaged, de-reddened flux densities of 3.8 ± 1.3 mJy at 4.8 μm and 5.0 ± 0.6 mJy at 3.8 μm. Observations with NIRC2/Keck and NaCo/VLT from the literature provide good evidence that Sgr A* also has a fairly well-defined de-reddened mean flux of 0.5−2.5 mJy at wavelengths of 2.1−2.2 μm. Conclusions. We present well-constrained anchor points for the SED of Sgr A* on the high-frequency side of the Terahertz peak. The new data are in general agreement with published theoretical SEDs of the mean emission from Sgr A*, but we expect them to have an appreciable impact on the model parameters in future theoretical work.

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