We determine and tabulate A [λ] /A K , the wavelength dependence of interstellar extinction, in the Galactic plane for 1.25µm ≤ λ ≤ 8.0µm along two lines of sight: l = 42 • and l = 284 • . The first is a relatively quiescent and unremarkable region; the second contains the giant H II region RCW 49 as well as a "field" region unrelated to the cluster and nebulosity. Areas near these Galactic longitudes were imaged at J, H, and K bands by 2MASS and at 3-8µm by Spitzer for the GLIMPSE Legacy program. We measure the mean values of the color excess ratios (A [λ] − A K )/(A J − A K ) directly from the color distributions of observed stars. The extinction ratio between two of the filters, e.g. A J /A K , is required to calculate A [λ] /A K from those measured ratios. We use the apparent JHK magnitudes of giant stars along our two sightlines, and fit the reddening as a function of magnitude (distance) to determine A J /kpc, A K /kpc, and A J /A K . Our values of A [λ] /A K show a flattening across the 3-8µm wavelength range, roughly consistent with the Lutz et al. (1996) extinction measurements derived for the sightline toward the Galactic center.

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We present a multiwavelength study of the infrared dark cloud MSXDC G034.43+00.24. Dust emission, traced by millimeter/submillimeter images obtained with the IRAM, JCMT, and CSO telescopes, reveals three compact cores within this infrared dark cloud with masses of 170--800 Msun and sizes < 0.5 pc. Spitzer 3.6-8.0 um images show slightly extended emission toward these cores, with a spectral enhancement at 4.5 um that probably arises from shocked H2. In addition, the broad line widths (Delta V ~ 10 km/s) of HCN (4-3), and CS (3-2), and the detection of SiO (2-1), observed with the JCMT and IRAM telescopes, also indicate active star formation. Spitzer 24 um images reveal that each of these cores contains a bright, unresolved continuum source; these sources are most likely embedded protostars. Their millimeter to mid-IR continuum spectral energy distributions reveal very high luminosities, 9000-32,000 Lsun. Because such large luminosities cannot arise from low-mass protostars, MSXDC G034.43+00.24 is actively forming massive (~ 10 Msun) stars.Comment: 6 pages, 3 figures (1 colour), accepted ApJ

The Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey aims to characterise the physical and chemical evolution of high-mass star-forming clumps. Exploiting the unique broad frequency range and on-the-fly mapping capabilities of the Australia Telescope National Facility Mopra 22 m single-dish telescope 1 , MALT90 has obtained 3 × 3 maps towards ß2 000 dense molecular clumps identified in the ATLASGAL 870 μm Galactic plane survey. The clumps were selected to host the early stages of high-mass star formation and to span the complete range in their evolutionary states (from prestellar, to protostellar, and on to H II regions and photodissociation regions). Because MALT90 mapped 16 lines simultaneously with excellent spatial (38 arcsec) and spectral (0.11 km s −1 ) resolution, the data reveal a wealth of information about the clumps' morphologies, chemistry, and kinematics. In this paper we outline the survey strategy, 1 The Mopra radio telescope is part of the Australia Telescope National Facility which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO.

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