Showing papers by "Roger H. Hildebrand published in 1989"
TL;DR: In this paper, the polarization of far-infrared emission from dust in nine molecular clouds was measured in Mon R2, in the Kleinmann-low (KL) nebula in Orion, and in Sgr A.
Abstract: The paper reports measurements of the polarization of far-infrared emission from dust in nine molecular clouds. Detections were obtained in Mon R2, in the Kleinmann-Low (KL) nebula in Orion, and in Sgr A. Upper limits were set for six other clouds. A comparison of the 100 micron polarization of KL with that previously measured at 270 microns provides new evidence that the polarization is due to emission from magnetically aligned dust grains. Comparing the results for Orion with measurements at optical wavelengths, it is inferred that the magnetic field direction in the outer parts of the Orion cloud is the same as that in the dense core. This direction is nearly perpendicular to the ridge of molecular emission and is parallel to both the molecular outflow in KL and the axis of rotation of the cloud core. In Mon R2, the field direction which the measurements imply does not agree withthat derived from 0.9-2.2 micron polarimetry. The discrepancy is attributed to scattering in the near-infrared. In Orion and Sgr A, where comparisons are possible, the measurements are in good agreement with 10 micron polarization measurements.
35 citations
TL;DR: An analysis of systematic errors in an apparatus for measuring linear polarization in far-infrared observations of astrophysical objects and modifications to the apparatus are described which have reduced the effect to almost negligible levels.
Abstract: We present an analysis of systematic errors in an apparatus for measuring linear polarization in far-infrared observations of astrophysical objects. In particular, we examine a systematic effect which has until now limited the accuracy of measurement of spatially extended sources. We describe modifications to the apparatus which have reduced the effect to almost negligible levels.
11 citations
01 Jan 1989
TL;DR: In this article, it was shown that the magnetic fields in dense clouds would be sufficiently greater than those in the intercloud medium to overcome the higher rate at which gas collisions would destroy alignment, and if sufficient locally, would have enough large-scale order to give measurable polarization in far-infrared observations with large beams and large column depths.
Abstract: At the beginning of this decade what we knew about polarization of far-infrared emission from dense clouds was that some very good observers had looked for it and had not found it. Gull et at. (1978) had shown that the degree of polarization in Orion was not more than 2%. That information provided an important guide but very little encouragement for later efforts. There was reason to doubt whether the mechanisms invoked to explain the alignment of dust grains in the diffuse intercloud medium would operate in dense clouds; whether the strengths of the magnetic fields in dense clouds would be sufficiently greater than those in the intercloud medium to overcome the higher rate at which gas collisions would destroy alignment; and whether the field, if sufficient locally, would have enough large-scale order to give measurable polarization in far-infrared observations with large beams and large column depths.
10 citations
TL;DR: In this article, the design and performance of the 100-micron polarimeter proposed for use on the NASA Kuiper Airborne Observatory was considered. But the polarimeter design and data reduction techniques are based on the work of Hildebrand et al.
Abstract: Consideration is given to the design and performance of the 100-micron polarimeter proposed for use on the NASA Kuiper Airborne Observatory. The polarimeter specifications are listed. The polarimeter design and data reduction techniques are based on the work of Hildebrand et al. (1984) and Dragovan (1986). The polarimeter has an improved signal-to-noise ratio and systematic measurement errors below 0.2 percent.
9 citations