Silicate absorption in heavily obscured galaxy nuclei Roche, Patrick F.; Packham, Christopher; Aitken, David K. ...
Monthly notices of the Royal Astronomical Society,
02/2007, Letnik:
375, Številka:
1
Journal Article
We present the first mid-IR detection of the linear polarization toward the star CygOB2-12, a luminous blue hypergiant that, with Av of ~10 mag of foreground extinction, is a benchmark in the study ...of the properties of dust in the diffuse interstellar medium. The 8-13 micrometer spectropolarimetry, obtained with the CanariCam multi-mode camera at the Gran Telescopio Canarias (GTC), shows clear trends with wavelength characteristic of silicate grains aligned in the interstellar magnetic field. The maximum polarization, detected with 7.8 statistical significance near 10.2 micrometers, is (1.24 +/- 0.28) % with position angle (126 +/- 8) deg. We comment on these measurements in the context of recent models for the dust composition in the diffuse interstellar medium.
Ground-based mid-infrared (MIR) astronomical observations require the removal of the fast time variable components of (a) sky/background variation and (b) array background. Typically, this has been ...achieved through oscillating the telescope's secondary mirror a few times a second, a process termed "chopping". However, chopping reduces on-object photon collection time, imposes stringent demands on the secondary mirror, requires nodding of the telescope to remove the radiative offset imprinted by the chopping, and relies on an often-fixed chop-frequency regardless of the sky conditions in the actual observations. In the 30m telescope era, secondary mirror chopping is impracticable. However, if the sky and background is sufficiently stable, drift scanning holds the promise to remove the necessity of chopping. In this paper we report our encouraging drift scanning results using the CanariCam MIR instrument on the 10.4m Gran Telescopio Canarias and the implications to future instruments and experiments.
We present the first subarcsecond-resolution images at multiple mid-IR wavelengths of the thermally emitting dust around the A0 star HD 32297. Our observations with T-ReCS at Gemini South reveal a ...nearly edge-on resolved disk at both 11.7 and 18.3 mu m that extends similar to 150 AU in radius. The mid-IR is the third wavelength region in which this disk has been resolved, following coronagraphic observations by others of the source at optical and near-IR wavelengths. The global mid-IR colors and detailed consideration of the radial colortemperature distribution imply that the central part of the disk out to similar to 80 AU is relatively deficient in dust.
We present 0.4 arcsec-resolution imaging polarimetry at 8.7, 10.3, and 12.5 microns, obtained with CanariCam at the Gran Telescopio Canarias, of the central region of W51 IRS2. The polarization, as ...high as 14 percent, arises from silicate particles aligned by the interstellar magnetic field. We separate, or unfold, the polarization of each sightline into emission and absorption components, from which we infer the morphologies of the corresponding projected magnetic fields that thread the emitting and foreground-absorbing regions. We conclude that the projected magnetic field in the foreground material is part of the larger-scale ambient field. The morphology of the projected magnetic field in the mid-IR emitting region spanning the cometary HII region W51 IRS2W is similar to that in the absorbing region. Elsewhere, the two magnetic fields differ significantly with no clear relationship between them. The magnetic field across the W51 IRS2W cometary core appears to be an integral part of a champagne outflow of gas originating in the core and dominating the energetics there. The bipolar outflow, W51north jet, that appears to originate at or near SMA1/N1 coincides almost exactly with a clearly demarcated north-south swath of lower polarization. While speculative, comparison of mid-IR and submm polarimetry on two different scales may support a picture in which SMA1/N1 plays a major role in the magnetic field structure across W51 IRS2.
Mid-infrared (MIR) observations are typically accomplished from the ground through oscillating the secondary mirror a few times a second. This chopping serves to remove the fast time variable ...components of (a) sky variation and (b) array background. However, there is a significant price to pay for this, including reduced on-object photon collection time, stringent demands on the secondary mirror, nodding the telescope to remove the radiative offset imprinted by the chopping, and an often-fixed chop-frequency regardless of the sky conditions in the actual observations. Worse, in the era of 30m telescopes it is wholly impracticable to chop the secondary mirror. If the array is stable enough, drift scanning holds the promise to remove the necessity of chopping. In this paper we report our experiments using the CanariCam MIR instrument on the 10.4m GranTeCan and the implications to future instruments and experiments.
We present spatially resolved mid-infrared spectroscopy of the Class I/flat-spectrum protostellar binary system SVS 20 in the Serpens cloud core. The spectra were obtained with the mid-infrared ...instrument T-ReCS on Gemini South. SVS 20-South, the more luminous of the two sources, exhibits a mid-infrared emission spectrum peaking near 11.3 km, while SVS 20-North exhibits a shallow amorphous silicate absorption spectrum with a peak optical depth of t 6 0.3. After removal of the line-of-sight extinction by the molecular common envelope, the "protostar-only" spectra are found to be dominated by strong amorphous olivine emission peaking near 10 km. We also find evidence for emission from crystalline forsterite and enstatite associated with both SVS 20-S and SVS 20-N. The presence of crystalline silicate in such a young binary system indicates that the grain processing found in more evolved Herbig Ae/Be and T Tauri pre-main-sequence stars likely begins at a relatively young evolutionary stage, while mass accretion is still ongoing.
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