Engineering topics

Harvey, P. M.

Publications and source records attributed to Harvey, P. M..

At least 37 records · Page 2

NASA NTRS1989

Observations of 40-70 micron bands of ice in IRAS 09371+1212 and other stars

The observations of the M giant star, IRAS 09371+1212, in the 40 to 70 microns emission bands, are reported. This star has a circumstellar CO envelope, and a unique infrared color, attributed to ice emission bands. The observations performed in February 1988, using grating spectrometer, showed that the far infrared bands of ice are the strongest known in the sky, and that its dust temperature (50K) is the lowest known for a circumstellar envelope. The 43 microns band of ice is also detected in several very cold circumstellar envelopes.

Omont, A.↗

NASA NTRS1987

Far-infrared continuum emission from the nucleus, starburst, and extended spiral arms of NGC 1068

Far-infrared slit scans across NGC 1068 are used to better define the contribution of the active nucleus, starburst disk, and extended spiral arms in the luminous output of this bright Seyfert 2 galaxy. The decomposition of the emission from the bright, inner 3 kpc of this galaxy suggests that at 50 microns, about half the emission is from star formation in a starburst disk and half from the compact, centrally heated circumnuclear cloud. The 100-micron profile of the starburst disk is asymmetric with respect to the nucleus. This appears to be the result of an extraordinary star-forming complex about a kiloparsec away from the center. With the application of maximum entropy deconvolution to the scans, evidence is found for 100-micron emission from the extended spiral arms of the galaxy. The far-infrared emission from the starburst region is distinguished from that of the extended spiral arms. In terms of both total luminosity and surface brightness, the extended spiral arms of NGC 1068 are at the bright end of the range of far-infrared emission from quiescent, noninteracting spirals.

Lester, D. F.↗

NASA NTRS1987

A near-infrared study of the NGC 6334-IV region

High-angular-resolution, high-sensitivity maps at 1.2, 1.65, and 2.2 microns have been made of the NGC 6334-IV region. These maps show that the diffuse, bipolar 2-micron emission associated with a bipolar source in the region is probably excited by two sources between the lobes. The first is a highly obscured protostar with a luminosity of about 100,000 solar luminosities. The second possible source of excitation is the scattered free-free and bound-free emission from an H II region surrounding a second young star. The extinction to both these objects must be much higher along the line of sight from earth to them than from them to the bipolar lobes. This is consistent with an earlier interpretation of FIR observations (Harvey and Gatley, 1983) which suggested the presence of an edge-on dust disk around the two central luminosity sources. A rich cluster of lower luminosity IR sources has also been found associated with the two most luminous objects.

Harvey, P. M.↗

NASA NTRS1986

Airborne photometry of Comet Halley from 40 to 160 microns

Far infrared photometry of comet Halley was obtained from NASA's Kuiper Airborne Observatory. The brightness of the comet decreases by nearly a factor of two on the second day in phase with the variability observed in blue light by IUE during the same time period. The energy distribution also varies significantly with a shallower (cooler) spectrum on the second day indicating fewer small particles on that day. Observations 30 and 60 arcsec away from the nuclear condensation show lower 50 to 100 microns color temperatures on both dates. This is consistent with observations by Giotto and Vega which indicate a higher proportion of large particles away from the nucleus.

Campins, H.↗

NASA NTRS1986

Image restoration and superresolution as probes of small scale far-IR structure in star forming regions

Far-infrared continuum studies from the Kuiper Airborne Observatory are described that are designed to fully exploit the small-scale spatial information that this facility can provide. This work gives the clearest picture to data on the structure of galactic and extragalactic star forming regions in the far infrared. Work is presently being done with slit scans taken simultaneously at 50 and 100 microns, yielding one-dimensional data. Scans of sources in different directions have been used to get certain information on two dimensional structure. Planned work with linear arrays will allow us to generalize our techniques to two dimensional image restoration. For faint sources, spatial information at the diffraction limit of the telescope is obtained, while for brighter sources, nonlinear deconvolution techniques have allowed us to improve over the diffraction limit by as much as a factor of four. Information on the details of the color temperature distribution is derived as well. This is made possible by the accuracy with which the instrumental point-source profile (PSP) is determined at both wavelengths. While these two PSPs are different, data at different wavelengths can be compared by proper spatial filtering. Considerable effort has been devoted to implementing deconvolution algorithms. Nonlinear deconvolution methods offer the potential of superresolution -- that is, inference of power at spatial frequencies that exceed D lambda. This potential is made possible by the implicit assumption by the algorithm of positivity of the deconvolved data, a universally justifiable constraint for photon processes. We have tested two nonlinear deconvolution algorithms on our data; the Richardson-Lucy (R-L) method and the Maximum Entropy Method (MEM). The limits of image deconvolution techniques for achieving spatial resolution are addressed.

Lester, D. F.↗

NASA NTRS1986

Near-infrared spectroscopy of planetary nebulae: How strong is the H2 emission?

In an effort to understand the systematics of the H2 emission from planetary nebulae, a program of near-infared spectroscopy using the University of Texas infrared reticon spectrometer was started. This instrument has a 1x32 element InSb photodiode array as a detector. All of the observations reported were made on the McDonald Observatory 2.7 m telescope, with spectra resolving power lambda/delta lambda = 600. The spectral coverage allows the measurement strengths of Brackett gamma He I 2.113 microns, HE II 2.189 microns and the v = 1=0 S(1) line of H2 at 2.122 microns. One of the most important advantages of this instrument is that we are able to resolve H2 from the adjacent He I line. Most previous observations of planetaries have been made at spectral resolving powers of about 100, which blend these lines. The contribution of the He I line has generally been dismissed as being unimportant, but we show that this may not be valid. Our higher resolving power also improves the line-to-continuum contrast; in some cases, the continuum is the limiting factor in detecting faint lines.

Dinerstein, H. L.↗

NASA NTRS1986

Far-infrared image restoration analysis of the protostellar cluster in S140

Image restoration techniques are applied to one-dimensional scans at 50 and 100 microns of the protostellar cluster in S140. These measurements resolve the surrounding nebula clearly, and Fourier methods are used to match the effective beam profiles at these wavelengths. This allows the radial distribution of temperature and dust column density to be derived at a diffraction limited spatial resolution of 23 arcsec (0.1 pc). Evidence for heating of the S140 molecular cloud by a nearby ionization front is established, and the dissociation of molecules inside the ionization front is spatially well correlated with the heating of the dust. The far-infrared spectral distribution of the three near-infrared sources within 10 arcsesc of the cluster center is presented.

Lester, D. F.↗

NASA NTRS1986

The far-infrared and optical structure of Arp 220

The spatial structure of the luminous peculiar galaxy Arp 220 has been investigated in the far infrared. The results reveal that most of the luminosity is from a source less than 3 kpc in extent, located in the nuclear region of the galaxy. The size constraints yield a lower limit of 0.05 for the 100 micron optical depth, implying a hydrogen column density over 5 x 10 to the 22nd/sq cm. New optical images confirm that the double-lobed optical appearance results from strong absorption across the true nucleus. Arp 220 exhibits three primary features which provide strong evidence for an external source of energy: (1) a chaotic and highly asymmetric galactic halo; (2) a large internal velocity dispersion in CO and H I; and (3) extreme compression of gas and dust. These features are natural consequences of previously proposed models which invoke a direct galactic collision and merger, and are unlikely to result from a long-range tidal interaction with the neighboring galaxy IC 4554.

Joy, M.↗

NASA NTRS1986

The spatial structure of IRC + 10216 and NGC 7027 in the far-infrared

Spatial scans of IRC + 10216 and NGC 7027 were made at 50 and 100 microns using a diffraction-limited slit. Maximum entropy deconvolution techniques were applied to the data and, in effect, the structure of these sources was probed down to a scale far smaller than previously achieved at these wavelengths. IRC + 10216 was unresolved on a spatial scale of several arcsecs and a low upper limit to either the dust-gas ratio or the bulk emissivity of the grains was implied for the large molecular envelope surrounding the star. NGC 7027 was easily resolved in the scans, with far-infrared emission distribution corresponding closely with the distribution of ionized gas and shorter wavelength infrared emission.

Lester, D. F.↗

NASA NTRS1986

Far-infrared structure in the nuclear region of M51

Far-infrared (100-micron) scans across the nucleus of M51 are presented. These scans show that much of the far-infrared luminosity of this galaxy comes from a small, sharply bounded region within a 30 arcsec radius (700 pc) of the nucleus. This radius corresponds to the innermost spiral structure, as well as that estimated from dynamical models for the radius of the inner Lindblad resonance. The results of a nonlinear image restoration analysis of the data are presented. This analysis, carried out with two different algorithms, yields information on the spatial structure of star formation near the nucleus that exceeds the diffraction limit of the telescope at this wavelength. This 'superresolution' treatment shows that star formation is enhanced at the outer edge of this region compared to the nucleus, which appears to be relatively devoid of young stars. This ring of active star formation may be produced in the same way as that seen in our own Galaxy at a galactocentric radius of 4-5 kpc and may indicate that the region near the nucleus has been swept clean of material by violent processes.

Lester, D. F.↗

NASA NTRS1986

Far-infrared photometry of low-mass pre-main-sequence stars with broad CO wings

A sample of 14 low-mass premain-sequence stars were studied in the far-infrared. There is evidence for outflowing material around twelve of these stars; in most cases the evidence includes broad wings on the profiles of the CO J = 2 to 1 line. Ten of the objects were detected (5 sigma) at 100 micros, and seven were mapped at 50 and 100 micros. The far-infrared emission makes a significant contribution to the total luminosity of the objects. It is found that the force available from radiation pressure is not sufficient to drive the outflows. Any process which taps the same energy source as does the present stellar luminosity must have high efficiency.

Evans, N. J., II↗

NASA NTRS1986

Infrared studies of the Herbig-Haro object 1-2 region

Far-infrared (50-100 micrometers) photometric mapping and near-infrared spectroscopic mapping of the Herbig-Haro 1-2 region are presented. Both lobes of the double-lobed far-infrared source in this region are found to be nearly coincident with recently discovered radio continuum sources. The dust temperature structure around each peak is not spherically symmetric, suggesting either that the far-infrared sources are centrally heated or that the dust column density is highly nonspherically symmetric. The results are consistent with a picture in which each far-infrared lobe contains a highly obscured young star surrounded by a highly nonspherically symmetric dust cloud. A complementary study by Strom et al. (1985) is pointed out.

Harvey, P. M.↗

NASA NTRS1986

High angular resolution infrared mapping of the compact H II regions W51 and DR 21/W75

Far-infrared maps of W51/G49.5-0.4, W51/G49.4-0.3, and the DR 21 W75 S regions are presented. The simultaneous 50 and 100 micron maps enable a determination of the dust temperature and density structure in these areas. In G49.5-0.4 a luminosity and dust column-density peak at the position of the W51-Main maser is found, suggesting that this is the dominant luminosity source in W51. In G49.4-0.3 three components associated with the three known 2.7 GHz sources are resolved. A comparison of the total far-infrared luminosity with the radio continuum brightness in both G49.5-0.4 and G49.4-0.3 shows that the ratio of Lyman continuum to total luminosity of the exciting stars in not consistent with excitation by a single ZAMS star if most of the Lyman continuum photons are being absorbed bay gas rather than dust. In DR 21 micron far-infrared data and some new 2-20 micron results reveal a region of hot dust associated with the 2 micron H2 emission to the east and west of DR 21. Finally, a new 1.5-100 micron 'protostellar' source 2 deg north of W75 S at the position of a 1 mm continuum peak is reported.

Harvey, P. M.↗

NASA NTRS1986

Molecular clouds in the outer galaxy 1: Far infrared observations

From the Kuiper Airborne Observatory, far infrared emission were detected from 4 molecular clouds in the outer galaxy. Eleven areas in 6 clouds were observed at 50 and 100 microns. The far-infrared luminosities indicate the presence of stars with spectral types ranging from B3 to O7. Therefore, despite the fact that these clouds have lower CO line temperatures than comparable clouds in the inner galaxy, they are giving birth to massive stars.

Mead, K. N.↗

NASA NTRS1985

Star formation in the inner galaxy: A far-infrared and radio study of two H2 regions

Far-infrared and radio continuum maps have been made of the central 6' of the inner-galaxy H II regions G30.8-0.0 (in the W43 complex) and G25.4-02., along with radio and molecular line measurements at selected positions. An effort is made to understand far infrared wavelingths allow the dust temperature structures and total far infrared fluxes to be determined. Comparison of the radio and infrared maps shows a close relationship between the ionized gas and the infrared-emitting material. There is evidence that parts of G30.8 are substantially affected by extinction, even at far-infrared wavelengths. For G25.4-0.2, the radio recombination line and CO line data permit resolution of the distance ambiguity for this source. The confusion in distance determination is found to result from an extraordinary near-superposition of two bright H II regions. Using revised distances of 4.3 kpc for G26.4SE and 12 kpc for G25.4NW, that the latter, which is apparently the fainter of the two sources, is actually the more luminous. Though it is not seen on the Palomar Sky Survey, G25.4SE is easily visible in the 9532A line of S III and is mapped in this line. The ratio of total luminosity to ionizing luminosity is very similar to that of H II regions in the solar circle. Assuming a coeval population of ionizing stars, a normal initial mass function is indicated.

Lester, D. F.↗

NASA NTRS1985

An infrared study of the NGC 1977 H II region/molecular cloud interface

The results of an infrared study of the H II region NGC 1977 and the adjacent dense molecular cloud are reported. Extensive far-infrared maps with 45 arcsec resolution allow the spatial structure of the dust temperature and optical depth variations across the ionization front to be delineated. Analysis of the dust energetics indicates that the only significant energy source is the B1 V star HD 37018 which ionizes the H II region. This result, together with a favorable geometry, provides a good opportunity to determine the ratio of ultraviolet absorption efficiency to far-infrared emission efficiency, 790 + 460 or - 180. Analysis of the gas energetics indicates that collisions with warm dust grains can explain the observed gas temperatures.

Makinen, P.↗

NASA NTRS1985

Far-infrared observations of young clusters embedded in the R Coronae Austrinae and RHO Ophiuchi dark clouds

Multicolor far infrared maps in two nearby dark clouds, R Coronae Austrinae and rho Ophiuchi, were made in order to investigate the individual contribution of low mass stars to the energetics and dynamics of the surrounding gas and dust. Emission from cool dust associated with five low mass stars in Cr A and four in rho Oph was detected; their far infrared luminosities range from 2 far infrared luminosities L. up to 40 far infrared luminosities. When an estimate of the bolometric luminosity was possible, it was found that typically more than 50% of the star's energy was radiated longward of 20 micrometers. meaningful limits to the far infrared luminosities of an additional eleven association members in Cr A and two in rho Oph were also obtained. The dust optical depth surrounding the star R Cr A appears to be asymmetric and may control the dynamics of the surrounding molecular gas. The implications of the results for the cloud energetics and star formation efficiency in these two clouds are discussed.

Wilking, B. A.↗

NASA NTRS1985

Star formation in the inner Galaxy - A far-infrared and radio study of two H II regions

Far-infrared and radio continuum maps have been made of two inner-Galaxy H II region complexes, G30.8-0.0 and G25.4-0.2, along with radio and molecular line measurements at selected positions. The far-IR emission from each region is dominated by two sources. For both G25.4 and G30.8, the distribution of the emission is similar to that of the radio emission, indicating that OB stars provide most of the heating. There is evidence that extinction plays an important role in G30.8, even in the far-IR. A near-IR point source has been detected in G30.8 at the position of peak far-IR color temperature. This source may be the ionizing star for the core of G30.8. Measurement of forbidden S III 9532 A from G25.4SE indicates that the extinction toward this source is very low, which is difficult to reconcile with previously determined distance measurements to this source.

Lester, D. F.↗