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At least 271 records · Page 15
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NASA NTRS1986

The Orion star-forming region - Far-infrared and radio molecular observations

New J = 1-0 CO and far-infrared maps of the Orion star-forming region are presented and discussed. The total infrared luminosity of the Orion star-forming ridge is 250,000 solar luminosities. The material that is emitting strongly at 60 microns is traced and found to be highly centrally concentrated. However, the majority of the extended emission from this region comes from dust that is ultimately heated by the visible Trapezium cluster stars. The luminosity of IRc 2, the most luminous member of the infrared cluster, is estimated to be 40,000-50,000 solar luminosities. A schematic drawing of the Ori MC 1 region is presented.

Thronson, H. A., Jr.↗
NASA NTRS1986

CO mapping of the Orion molecular cloud: The influence of star formation on cloud structure

Regions of massive star formation have long been believed to have a profound influence on the structure of their surrounding molecular clouds. The ways in which massive star formation has altered the structure and kinematics of the Orion Molecular Cloud are discussed. The data to be discussed consists of a large scale map of the CO J=1-0 emission from approximately 3 square degrees of OMC-1. During 1985, the Five College Radio Astronomy Observatory 14M antenna was used to map a 2 deg x 1 deg region centered on alpha(1950) = 5(h)33(m)00(s) delta(1950) = -5 deg 30 min. The region mapped in 1985 covers the well known HII regions M42, M43, and NGC1977, and the CO map contains abundant evidence of the interaction between these regions and the molecular cloud. Indeed, the global structure of the cloud appears to have been strongly influenced by the continuous formation of massive stars within the cloud. Individual instances of some of these features are discussed. There appear to be two classes of features which are indicative of this interaction: CO bright rims and CO holes. During 1986, we have undertaken further mapping of OMC-1 to the south of the region covered by the 1985 map. This portion of the cloud contains significant regions of star formation, but O star formation has not occured and large HII regions have not developed to alter the appearance of the cloud. A detailed map of this region is thus an opportunity to view the structure of the molecular cloud before it has been altered by massive star formation. Preliminary analysis of data obtained in this region suggests that the structure and kinematics of the southern portion of the Orion cloud are indeed dramatically different from those of the region previously mapped. Comparison of the two regions thus supports models of the development of structure in molecular clouds through interaction with the HII regions formed within them.

Schloerb, F. P.↗
NASA NTRS1986

Point sources in the Orion complex

Point sources identified in Orion with the IRAS are discussed to illustrate methods of using the IRAS Catalog. The present survey revealed 54 new objects. The Catalog was employed to find companion stars for the observed sources, discern those sources which were predominantly IR cirrus clouds, and separate sources with 12 and 25 microns emissions that were both detected at 60 and 100 microns. Attention is also given to usage of the Catalog to determine which sources were galaxies in Orion and which were galaxies in nearby Gemini. Color-color diagrams are provided for 12, 25 and 60 microns emissions to demonstrate how the data permit identification pre-main sequence stars, stars with circumstellar disks, very young stars, stars with cool photospheres, and hot cirrus clouds.

Beichman, C. A.↗
NASA NTRS1987

Interpretation of rotationally excited far-infrared OH emission in Orion-KL

The 2Pi(1/2) OH 163-micron J = 3/2-1/2 rotational transitions in Orion-KL were observed and an upper limit was set to the line strength of the 2II(1/2) OH 56-micron J = 9/2-7/2 doublet in this source. The 163-micron line intensities were modeled, along with the previously measured 2II(3/2) 119 and 84-micron rotational line emission and it is found that the gas in the Orion-KL postshocked region can produce OH 119-micron line emission of the same strength as measured; however, the resultant 84 and 163-micron line intensities would be weaker than observed. Shocked gas plus a second component which experiences strong radiative excitation can reproduce the observations.

Melnick, G. J.↗
NASA NTRS1989

Observations of the rotational transitions of OH from the Orion molecular cloud

A summary of observed rotationally excited, far infrared OH line emissions from Orion-KL made using the Kuiper Airborne Observatory is given, together with a list of the resulting publications, talks, and lectures based on this data. In addition, a paper is appended, particularly addressing the (16)OH and (18)OH emission from Orion-KL. The first detections of the (16)OH (2)pi(1/2) to (2)pi(3/2) J = 3/2(-) to 3/2(+) rotational cross-ladder transition (53.351 micrometer) and the (18)OH (2)pi(3/2) J = 5/2(+) to 3/2(-) rotational ground-state transition (120.1719 micrometer). It is found that both of these lines exhibit a P-Cygni profile.

Melnick, Gary J.↗
NASA NTRS1988

On the origin of the Orion and Monoceros molecular cloud complexes

A detailed model for the origin of the Orion and Monoceros cloud complexes is presented, showing that a single high-velocity H I cloud-galaxy collision can explain their main observed features. The collision generates massive shocked layers, and self-gravity can then provide the conditions for the transformation of these layers into molecular clouds. The clouds formed by the collision maintain the motion of their parental shocked gas and reach positions located far away from the plane. According to this model, both the Orion and Monoceros complexes were formed some 60 million yr ago, when the original shocked layer was fragmented by Galactic tidal forces.

Franco, J.↗
NASA NTRS1989

The constancy of the ratio of the molecular hydrogen lines at 3.8 microns in Orion

The 1-0 O(7) and 0-0 S(13) lines of H2, at 3.807 and 3.846 microns, have been mapped over the region of the Orion molecular outflow. The intensity ratio of these lines is found to be independent of position in the outflow. From this it is inferred that the structure of the shocks and their cooling flows in Orion may be more akin to hydrodynamic shocks than the low-temperature C-shocks that are currently favored.

Brand, P. W. J. L.↗
NASA NTRS1989

Millimeter- and submillimeter-wave surveys of Orion A emission lines in the ranges 200.7-202.3, 203.7-205.3, and 330-360 GHz

A continuous spectral line survey of the Orion A position from 330.5 to 360.1 GHz was carried out. This survey covers nearly the entire 870 micron atmospheric window accessible from ground-based observations. Approximately 160 distinct spectral features composed of about 180 lines were detected, 29 of which could not be readily identified. In addition, Orion A from 200.7 to 202.3 GHz and from 203.7 to 205.3 GHz and 42 distinct new spectral lines were detected, including four that are unidentified at present. These data sets are the first thorough survey results in these spectral regions. The new interstellar lines in the survey bands are tabulated and displayed graphically. Moreover, the data are being made available to the Astronomical Data Center at the Goddard Space Flight Center for distribution by request to the astronomical community.

Jewell, P. R.↗
NASA NTRS1989

Dust clouds in Orion and the interstellar neutral hydrogen distribution

According to published examples of the far IR observations in the Orion and its surroundings, several well defined dust clouds of different sizes and structure are present. For comparison of these clouds with the neutral hydrogen distribution on the area of approx. 1000 sq degs, the data from Pulkovo Sky Survey in the interstellar neutral Hydrogen Radio Line as well as special observations with the RATAN-600 telescope in 21 cm line were used. From the materials of Pulkovo HI Survey, the data were taken near the line emission at ten velocities between -21.8 and +25.6 km/s LSR for the structural component of the interstellar hydrogen emission. The results given concern mainly the Orion's Great Dust Cloud and the Lambda Orionis region where the information about the situation with the dust and interstellar hydrogen is very essential for interpretation.

Bystrova, N. V.↗
NASA NTRS1991

Observations of forbidden Si II (35 microns) and Si I (25 microns) in Orion - Evidence of a wind shock near IRc2

Forbidden Si II and Si I line emission from Orion's BN-KL was measured using a cryogenic grating spectrometer aboard NASA's Kuiper Airborne Observatory. It is believed that the bulk of the forbidden Si II emission in Orion originates in photodissociated gas at the interface between the H II region and its parent molecular cloud. There is, however, a twofold enhancement in forbidden Si II emission near IRc2, which is attributed to fast dissociative J-shock where the wind from IRc2 impact slower moving material. Model fits suggest a silicon gas-phase depletion near ITc2 of 0.3-1.0 relative to solar. The spatial distribution of the forbidden Si II emission has a centralized peak.

Haas, Michael R.↗
NASA NTRS1993

N2H(+) in the Orion ambient ridge - Cloud clumping versus rotation

The IRAM 30-m telescope is used to obtain spectra of the J = 1 yields 0 transition of N2H(+) over a 2 x 2 arcsec area toward the Orion-KL/IRc2 star-forming region with 26-arcsec angular resolution. The N2H(+) emission, which exclusively traces the ridge gas, exhibits multiple radial velocities which appear to arise from the presence of at least four clouds of quiescent material. It is argued that the velocity structure of N2H(+) does not uniformly change across OMC-1 and, consequently, is inconsistent with the presence of large-scale differential rotation of the extended ridge along the SW-NE axis about IRc2. The coincidence of the two larger clouds with star-forming activity in Orion-KL suggests that either the quiescent gas is being pushed apart or that the star formation may have been triggered by a cloud-cloud interaction.

Womack, Maria↗
NASA NTRS1993

A multi-transition study of carbon monoxide in the Orion A molecular cloud. II - C(O-18)

We present an analysis of density, temperature, and excitation conditions in a one half square degree region around BN/KL in Orion A using new C(O-l8) J = 1 yields 0 and J = 2 yields 1 data. This paper extends a previous study of Orion A, based on a multitransition analysis of (C-13)O, to the optically thinner C(O-18) species that traces better the dense inner regions of giant molecular clouds. From the C(O-18) maps we identify several condensations and are able to derive their size, linewidth, average density, mass, and virial mass.

Dutrey, A.↗
NASA NTRS1994

Orion: Design of a system for assured low-cost human access to space

In recent years, Congress and the American people have begun to seriously question the role and importance of future manned spaceflight. This is mainly due to two factors: a decline in technical competition caused by the collapse of communism, and the high costs associated with the Space Shuttle transportation system. With these factors in mind, the ORION system was designed to enable manned spaceflight at a low cost, while maintaining the ability to carry out diverse missions, each with a high degree of flexibility. It is capable of performing satellite servicing missions, supporting a space station via crew rotation and resupply, and delivering satellites into geosynchronous orbit. The components of the system are a primary launch module, an upper stage, and a manned spacecraft capable of dynamic reentry. For satellite servicing and space station resupply missions, the ORION system utilizes three primary modules, an upper stage, and the spacecraft, which is delivered to low earth orbit and used to rendezvous, transfer materials, and make repairs. For launching a geosynchronous satellite, one primary module and an upper stage are used to deliver the satellite, along with an apogee kick motor, into orbit. The system is designed with reusability and modularity in mind in an attempt to lower cost.

Elvander, Josh↗
NASA NTRS1995

ORION: A Supersynchronous Transfer Orbit mission

ORION F1 was launched on 29th November 1994 on an Atlas IIA launch vehicle. It was designed, built and delivered in-orbit by Matra Marconi Space Systems Plc and was handed over to ORION Satellite Corporation on 20th January 1995 at its on-station longitude of 37.5 deg W. The mission differed significantly from that of any other geostationary communications satellite in that the Transfer Orbit apogee altitude of 123,507 km was over three times geosynchronous (GEO) altitude and one third of the way to the moon. The SuperSynchronous Transfer Orbit (SSTO) mission is significantly different from the standard Geostationary Transfer Orbit (GTO)mission in a number of ways. This paper discusses the essential features of the mission design through its evolution since 1987 and the details of the highly successful mission itself including a detailed account of the attitude determination achieved using the Galileo Earth and Sun Sensor (ESS).

Walters, I. M.↗
NASA NTRS1993

The spectrum of Orion-KL at 2 millimeters (150-160 GHz)

A spectral survey of Orion-KL has been carried out in the 2 mm atmospheric window in the frequency range 149.6-159.6 GHz, using the FCRAO 14 m telescope. Typical sensitivities achieved were T(sub A sup *) approximately 0.03-0.1 K, peak-to-peak. Over 180 spectral lines were detected, including approximately 45 unidentified features. The spectra were measured with a single-sideband receiver and, even at levels of T(sub A sup *) approximately 30 mK, are far from being confusion-limited. Fifteen known species were conclusively identified in Orion in this spectral region, with the largest numbers of lines arising from methyl formate, ethyl cyanide, methanol, and dimethyl ether. These species have beam-averaged column densities of N(sub tot) approximately 0.5-8 x 10(exp 15)/sq cm. Several other species have been tentatively observed, including acetaldehyde, C2S, and possibly EtOH. The large organic species, however, appear to arise from different regions. For example, CH3CCH and (CH3)2O come primarily from the extended ridge, while EtCN and VyCN exclusively arise in the hot core. This survey clearly demonstrates that the 2 mm window is rich in spectral lines. It also suggests there is much chemical selectivity in the formation of large organic interstellar molecules.

Ziurys, L. M.↗
NASA NTRS1995

Gamma-ray lines from the Orion complex

We show that the 4.44 and 6.13 MeV line emission observed with the Compton Telescope (COMPTEL) from Orion is consistent with gamma-ray spectra consisting of a mixture of narrow and broad lines or spectra containing only broad lines. We employed several accelerated particle compositions and showed that the current COMPTEL data in the 3-7 MeV region alone cannot distinguish between the various possibilities. However, the COMPTEL upper limits in the 1-3 MeV band favor a composition similar to that of the winds of Wolf-Rayet stars of spectral type WC. The power dissipated by the accelerated particles at Orion is about 4 x 10(exp 38) ergs/s. These particles are not expected to produce significant amounts of Al-26.

Ramaty, Reuven↗
NASA NTRS1994

The abundance of interstellar oxygen toward Orion: Evidence for recent infall?

We present high S/N (greater than 800) Goddard High-Resolution Spectrograph (GHRS) observations of the weak interstellar O I lambda 1356 absorption in the low-density sight lines toward iota Ori and kappa Ori. By comparing these data with observations toward more reddened stars, we find no evidence of density-dependent depletion from the gas phase for oxygen. The derived total oxygen abundance (gas plus grains) towards iota Ori and kappa Ori is consistent with stellar and nebular determinations in Orion at a level that is one-half the solar value. We speculate that the O/H abundance ratio is lower in Orion compared to the Sun because the local Milky Way has suffered a recent infall of metal-poor material, perhaps from the Magellanic Stream.

Meyer, David M.↗