Studies of interstellar vibrationally-excited molecules

Several molecules thus far have been detected in the ISM in vibrationally-excited states, including H2, SiO, HC3N, and CH3CN. In order for vibrational-excitation to occur, these species must be present in unusually hot and dense gas and/or where strong infrared radiation is present. In order to do a more thorough investigation of vibrational excitation in the interstellar medium (ISM), studies were done of several mm-wave transitions originating in excited vibrational modes of HCN, an abundant interstellar molecule. Vibrationally-excited HCN was recently detected toward Orion-KL and IRC+10216, using a 12 meter antenna. The J=3-2 rotational transitions were detected in the molecule's lowest vibrational state, the bending mode, which is split into two separate levels, due to l-type doubling. This bending mode lies 1025K above ground state, with an Einstein A coefficient of 3.6/s. The J=3-2 line mode of HCN, which lies 2050K above ground state, was also observed toward IRC+10216, and subsequently in Orion-KL. Further measurements of vibrationally-excited HCN were done using a 14 meter telescope, which include the observations of the (0,1,0) and (0,2,0) modes towards Orion-KL, via their J=3-2 transitions at 265-267 GHz. The spectrum of the J=3-2 line in Orion taken with the 14 meter telescope, is shown, along with a map, which indicates that emission from vibrationally-excited HCN arises from a region probably smaller than the 14 meter telescope's 20 arcsec beam

The molecular gas in the supernova remnant IC443

Although a few highly perturbed regions characterized by gas motions with velocities larger than 20 km/s have been discovered during the last several years in the supernova remnant (SNR) IC 443, the nature of these perturbed clumps and their relationship to the quiescent molecular gas near the SNR remains unknown. In part, this is due to a lack of large-scale, high angular resolution observations. Therefore, a systematic survey of this SNR in the CO (J=1 yields 0) line has been conducted, covering a roughly 50' x 50' region spaced by 2'. The observations were made with the 14 m telescope of the Five College Radio Astronomy Observatory (FCRAO), which has a resolution of 45" and a single sideband receiver temperature of 200 K at 2.6 mm wavelength. Five new clumps were discovered, bringing the total number of known perturbed regions to eight. To study the physical structure of these clumps in more detail, more complete maps of the clumps have been made in both the CO(J=1 yields 0) and (J=2 yields 1) transitions with the FCRAO telescope. These maps show that the extent of perturbed gas in a typical clump is several arcmin, or a few pc at a distance of 1.5 kpc

CO Abundance Variations in the Orion Molecular Cloud

Infrared stellar photometry from 2MASS and spectral line imaging observations of 12CO and 13CO J = 1-0 line emission from the FCRAO 14m telescope are analysed to assess the variation of the CO abundance with physical conditions throughout the Orion A and Orion B molecular clouds. Three distinct Av regimes are identified in which the ratio between the 13CO column density and visual extinction changes corresponding to the photon dominated envelope, the strongly self-shielded interior, and the cold, dense volumes of the clouds. Within the strongly self-shielded interior of the Orion A cloud, the 13CO abundance varies by 100% with a peak value located near regions of enhanced star formation activity. The effect of CO depletion onto the ice mantles of dust grains is limited to regions with AV > 10 mag and gas temperatures less than 20 K as predicted by chemical models that consider thermal-evaporation to desorb molecules from grain surfaces. Values of the molecular mass of each cloud are independently derived from the distributions of Av and 13CO column densities with a constant 13CO-to-H2 abundance over various extinction ranges. Within the strongly self-shielded interior of the cloud (Av > 3 mag), 13CO provides a reliable tracer of H2 mass with the exception of the cold, dense volumes where depletion is important. However, owing to its reduced abundance, 13CO does not trace the H2 mass that resides in the extended cloud envelope, which comprises 40-50% of the molecular mass of each cloud. The implied CO luminosity to mass ratios, M/L_{CO}, are 3.2 and 2.9 for Orion A and Orion B respectively, which are comparable to the value (2.9), derived from gamma-ray observations of the Orion region. Our results emphasize the need to consider local conditions when applying CO observations to derive H2 column densities.Comment: Accepted for publication in MNRAS. 21 pages, 14 figure

Discovery Of A Molecular Outflow in the Haro 6-10 Star-Forming Region

We present high sensitivity 12CO and 13CO (1-0) molecular line maps covering the full extent of the parsec scale Haro~6-10 Herbig-Haro (HH) flow. We report the discovery of a molecular CO outflow along the axis of parsec-scale HH flow. Previous molecular studies missed the identification of the outflow probably due to their smaller mapping area and the confusing spectral features present towards the object. Our detailed molecular line study of the full 1.6 pc extent of the optical flow shows evidence for both blueshifted and redshifted gas set in motion by Haro~6-10 activity. The molecular outflow is centered at Haro~6-10, with redshifted gas being clumpy and directed towards the northeast, while blueshifted gas is in the southwest direction. The molecular gas terminates well within the cloud, short of the most distant HH objects of the optical flow. Contamination from an unrelated cloud along the same line of sight prevents a thorough study of the blueshifted outflow lobe and the mass distribution at the lowest velocities in both lobes. The cloud core in which Haro~6-10 is embedded is filamentary and flattened in the east-west direction. The total cloud mass is calculated from 13CO(1-0) to be ~200Msun. The lower limit of the mass associated with the outflow is ~0.25Msun.Comment: ApJ Accepted; 9 pages, 8 figures. For high resolution ps file use: http://www.astro.umass.edu/~irena/haro.p

Validation of magnetophonon spectroscopy as a tool for analyzing hot-electron effects in devices

It is shown that very high precision hot-electron magnetophonon experiments made on n+n−n+-GaAs sandwich device structures which are customized for magnetoresistance measurements can be very accurately modeled by a new Monte Carlo technique. The latter takes account of the Landau quantization and device architecture as well as material parameters. It is proposed that this combination of experiment and modeling yields a quantitative tool for the direct analysis of spatially localized very nonequilibrium electron distributions in small devices and low dimensional structures

Striations in the Taurus molecular cloud: Kelvin-Helmholtz instability or MHD waves?

The origin of striations aligned along the local magnetic field direction in the translucent envelope of the Taurus molecular cloud is examined with new observations of 12CO and 13CO J=2-1 emission obtained with the 10~m submillimeter telescope of the Arizona Radio Observatory. These data identify a periodic pattern of excess blue and redshifted emission that is responsible for the striations. For both 12CO and 13CO, spatial variations of the J=2-1 to J=1-0 line ratio are small and are not spatially correlated with the striation locations. A medium comprised of unresolved CO emitting substructures (cells) with a beam area filling factor less than unity at any velocity is required to explain the average line ratios and brightness temperatures. We propose that the striations result from the modulation of velocities and the beam filling factor of the cells as a result of either the Kelvin-Helmholtz instability or magnetosonic waves propagating through the envelope of the Taurus molecular cloud. Both processes are likely common features in molecular clouds that are sub-Alfvenic and may explain low column density, cirrus-like features similarly aligned with the magnetic field observed throughout the interstellar medium in far-infrared surveys of dust emission.Comment: 11 pages, 4 figures. Accepted for publication in MNRA

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

Flight Control System Design with Rate Saturating Actuators

Actuator rate saturation is an important factor adversely affecting the stability and performance of aircraft flight control systems. It has been identified as a catalyst in pilot-induced oscillations, some of which have been catastrophic. A simple design technique is described that utilizes software rate limiters to improve the performance of control systems operating in the presence of actuator rate saturation. As described, the technique requires control effectors to be ganged such that any effector is driven by only a single compensated error signal. Using an analysis of the steady-state behavior of the system, requirements are placed upon the type of the loop transmissions and compensators in the proposed technique. Application of the technique to the design of a multi-input/multi-output, lateral-directional control system for a simple model of a high-performance fighter is demonstrated as are the stability and performance improvements that can accrue with the technique

Robust, Decoupled, Flight Control Design with Rate Saturating Actuators

Techniques for the design of control systems for manually controlled, high-performance aircraft must provide the following: (1) multi-input, multi-output (MIMO) solutions, (2) acceptable handling qualities including no tendencies for pilot-induced oscillations, (3) a tractable approach for compensator design, (4) performance and stability robustness in the presence of significant plant uncertainty, and (5) performance and stability robustness in the presence actuator saturation (particularly rate saturation). A design technique built upon Quantitative Feedback Theory is offered as a candidate methodology which can provide flight control systems meeting these requirements, and do so over a considerable part of the flight envelope. An example utilizing a simplified model of a supermaneuverable fighter aircraft demonstrates the proposed design methodology