Engineering topics

Crutcher, R. M.

Publications and source records attributed to Crutcher, R. M..

7 records

DOE OSTI2016

ORION’S VEIL: MAGNETIC FIELD STRENGTHS AND OTHER PROPERTIES OF A PDR IN FRONT OF THE TRAPEZIUM CLUSTER

We present an analysis of physical conditions in the Orion Veil, an atomic photon-dominated region (PDR) that lies just in front (≈2 pc) of the Trapezium stars of Orion. This region offers an unusual opportunity to study the properties of PDRs, including the magnetic field. We have obtained 21 cm H i and 18 cm (1665 and 1667 MHz) OH Zeeman effect data that yield images of the line-of-sight magnetic field strength B {sub los} in atomic and molecular regions of the Veil. We find B {sub los} ≈ −50 to −75 μ G in the atomic gas across much of the Veil (25″ resolution) and B {sub los} ≈ −350 μ G at one position in the molecular gas (40″ resolution). The Veil has two principal H i velocity components. Magnetic and kinematical data suggest a close connection between these components. They may represent gas on either side of a shock wave preceding a weak-D ionization front. Magnetic fields in the Veil H i components are 3–5 times stronger than they are elsewhere in the interstellar medium where N (H) and n (H) are comparable. The H i components are magnetically subcritical (magnetically dominated), like the cold neutral medium, although they are about 1 dex denser. Comparatively strong fields in the Veil H i components may have resulted from low-turbulence conditions in the diffuse gas that gave rise to OMC-1. Strong fields may also be related to magnetostatic equilibrium that has developed in the Veil since star formation. We also consider the location of the Orion-S molecular core, proposing a location behind the main Orion H{sup +} region.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

TESTING MAGNETIC FIELD MODELS FOR THE CLASS 0 PROTOSTAR L1527

For the Class 0 protostar L1527 we compare 131 polarization vectors from SCUPOL/JCMT, SHARP/CSO, and TADPOL/CARMA observations with the corresponding model polarization vectors of four ideal-MHD, nonturbulent, cloud core collapse models. These four models differ by their initial magnetic fields before collapse; two initially have aligned fields (strong and weak) and two initially have orthogonal fields (strong and weak) with respect to the rotation axis of the L1527 core. Only the initial weak orthogonal field model produces the observed circumstellar disk within L1527. This is a characteristic of nearly all ideal-MHD, nonturbulent, core collapse models. In this paper we test whether this weak orthogonal model also has the best agreement between its magnetic field structure and that inferred from the polarimetry observations of L1527. We found that this is not the case; based on the polarimetry observations, the most favored model of the four is the weak aligned model. However, this model does not produce a circumstellar disk, so our result implies that a nonturbulent, ideal-MHD global collapse model probably does not represent the core collapse that has occurred in L1527. Our study also illustrates the importance of using polarization vectors covering a large area of a cloud core to determine the initial magnetic field orientation before collapse; the inner core magnetic field structure can be highly altered by a collapse, and so measurements from this region alone can give unreliable estimates of the initial field configuration before collapse.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1987

The CO J = 2-1 emission from the interstellar gas toward Zeta Ophiuchi

Measurements of the J = 2-1 transition of (C-12)O have been obtained with a high signal-to-noise ratio. Two distinct velocity components are seen, one at the velocity of the strongest optically observed atomic lines and a weaker, second component at the velocity of the CH(+) absorption line. This second component has a full width at half-intensity of about 0.4 km/s, considerably narrower than the CH(+) line.These new observations place severe constraints on the shock models used to reproduce the CH(+) abundance.

Crutcher, R. M.↗

NASA NTRS1984

NGC 2024: Multi-wavelength Infrared and Radio Observations

A series of far-infrared maps obtained on the KAO find the total IR luminosity of NGC 2024 is to the 4th power L, and show a peak in flux density and optical depth about 1' south of IRS 2. High resolution spectra of IRS 2 in Brackett alfa and Pfund gamma indicate the presence of an optically thick wind with M approx. 7 x 10 to the minus 7 power M sub yr to minus 1 power, from which we infer that IRS 2 is unable to supply the luminosity observed. A six centimeter continuum map peaks near the location of the far-infrared peak and confirms it as a likely site for a source to provide this luminosity. Maps in HCN, CS, and H2CO show the gas is dense in the direction of the far IR peak. Velocity analysis shows the H2 region created by the far IR source and IRS 2 forms an expanding bubble in front of which the H2CO is seen in absorption, and which is bounded in the south and behind by dense material.

Smith, H. A.↗

NASA NTRS1984

Distances of Local Clouds from Optical Line Observations

The interstellar D-line of Na 1 toward 49 stars were observed in order to determine the distance (125 plus or minus 25 pc) to a cold H 1 cloud. This sheet of gas may be part of the back side of the shell formed by the Loop I supernova.

Crutcher, R. M.↗

NASA NTRS1982

The local interstellar medium

Analysis of the velocities of optical interstellar lines shows that the sun is immersed in a coherently moving local interstellar medium whose velocity vector agrees with that of the interstellar wind observed through backscatter of solar H Ly-alpha and He lambda 584 photons. The local interstellar medium consists of both cool clouds and warm intercloud medium gas, has a mass of perhaps approximately 30 solar masses, does not have severe depletion of trace elements from the gas phase, and appears to be material which has been shocked and accelerated by stellar winds and supernovae associated with the Sco-Oph OB association.

Crutcher, R. M.↗

NASA NTRS1981

A search for interstellar molecules in the spectra of highly reddened stars

A total of ten stars were observed with cameras of the International Ultraviolet Explorer (IUE) in both high and low dispersion. One star, X Persei (HD 24534, 6.0 BE), was analyzed in detail. Ultraviolet observations of the column densities of CO match those derived from the radio to within a factor of 4, with the difference probably due to the larger beam size of the radio measurement and the assumption of a thermal population in the rotational levels of CO. Upper limits are given to the log column densities for OH, HCl, and CH2 of 14.0, 12.3 and 12.8. The carbon abundance was found to be about solar with a possible depletion of about a factor of 2. With precautions concerning both noise and correct background, the IUE can be used for studies of interstellar molecules.

Lien, D.↗