Engineering topics

Townes, C. H.

Publications and source records attributed to Townes, C. H..

At least 37 records · Page 2

NASA NTRS1989

Far infrared, submm and mm spectroscopy of the galactic center: Radio arc and +20/+50 km s (exp -1) clouds

The observations of the par improved spectroscopy and the molecular clouds at the galactic center are reported. The results show: the spatial distributions of C(II) 158 microns and molecular line radiation and of the thermal radio continuum emission in the arched filaments of the radio arc are similar; about 2 x 10(exp 4) of the solar mass, or 10 percent of the total gas mass in the radio arc, are contained in C(+) regions; the H(+)/C(+) regions are probably located at the surfaces of the dense molecular clouds in the arc. Profiles, fluxes and spatial distributions of the C(II) fine structure and CO rotational lines are reported. It is demonstrated that the data does not fit models in which the neutral interstellar clouds in the arc are ionized by shocks or by magnetohydrodynamic phenomena. Moreover, that the high temperatures and densities derived previously from NH3 and CS observations may not be characteristic of the bulk of the molecular gas.

Genzel, R.↗

NASA NTRS1989

C II forbidden line emission from spiral galaxies

Measurements of 158-micron forbidden emission taken from a sample of 13 gas-rich galaxies are analyzed. The new data are combined with the previous sample of six infrared-bright galaxies. The 158-micron line emission line is bright in all of the galaxies detected, amounting to between 0.1 and 0.2 percent of the total nuclear far-infrared luminosity, and is therefore one of the primary gas coolants in these regions. A close association between 158-micron line emission and CO line emission is noted, with the integrated 158-micron/CO line intensity ratio being substantially less in galaxies than in Galactic star-formation regions. However, for the starburst galaxies the integrated line intensity ratio is the same as that for star-formation regions in the Galaxy.

Stacey, G. J.↗

NASA NTRS1988

High spatial resolution 10 micron imaging of IRC + 10216

Precise high-resolution 10-micron images of the carbon star IRC + 10216 have been obtained with a scanned linear array. The low noise and high dynamic range of these images permit deconvolution of the telescope point-spread function, revealing the radial brightness distribution of the circumstellar dust shell: approximate reflection symmetry is found in west-east scans, with a distinct division into two components of diameter about 0.40 and 2.2 arcsec. It is shown that this morphology is consistent with published interferometric data that had cast doubt upon an earlier, idealized two-component model. The observed brightness distribution implies that the circumstellar dust density may deviate substantially from the 1/r squared radial dependence expected for spherically symmetric outflow with constant velocity and constant rate of mass loss.

Bloemhof, E. E.↗

NASA NTRS1988

High-resolution forbidden Ne II observations of the ionized filaments in the Galactic center

The forbidden Ne II 12.8 micron emission from the central 10 arcsec of the Galaxy has been observed with 1.5 arcsec resolution. The broad lines previously observed in this region are resolved into separate features associated with the filaments and knots of radio continuum emission present. The radial velocity varies rapidly and continuously with position along the filaments, with gradients of up to 30 km/s. The emission along the 'eastern arm' is mapped. The velocities are consistent with streams of gas orbiting about the center. A simple model of gravitationally dominated orbits fits the data; the masses estimated to lie within the orbits suggest the presence of a central mass of about 2.5 million solar. The implications of this model and possible objections to it are considered.

Serabyn, E.↗

NASA NTRS1987

Physical conditions, dynamics and mass distribution in the center of the galaxy

Investigations of the central 10 pc of the Galaxy, and conclusions on energetics, dynamics, and mass distribution derived from X and gamma ray measurements and from infrared and microwave studies, especially from spectroscopy, high resolution imaging, and interferometry are reviewed. Evidence for and against a massive black hole is analyzed.

Genzel, R.↗

NASA NTRS1987

Physical conditions, dynamics, and mass distribution in the center of the Galaxy

Recent observations and theoretical models of the Galactic center (GC) are reviewed. An overview of phenomena seen in the GC is given, including the stellar cluster, radio continuum emission and interstellar clouds, the Sgr A complex, and X-ray and gamma emission. Also discussed are the energetics and physical conditions in the central 4 pc (star burst or central source?); the circumnuclear ring, ionized streamers, and relativistic and hot gas in the cavity; the mass distribution and the possibility of a massive black hole, and the central 0.1 pc (Sgr A and IRS 16). Diagrams, graphs, photographs, and tables of numerical data are provided.

Genzel, R.↗

NASA NTRS1986

C II forbidden-line 158 micron mapping in Sagittarius A Rotation curve and mass distribution in the galactic center

Based on data obtained with the NASA Kuiper Airborne Observatory 91.4 cm telescope, the 158-micron fine structure line emission of C(+) is mapped near the galactic center. The strongest emission comes from a 10-pc FWHM diameter disk centered on Sgr A West whose dominant motion is rotation. Extended C(+) emission is also found from the +50 km/s galactic center molecular cloud, and a second cloud at v(LSR) of about -35 km/s. The rotation curve and mass distribution within 10 pc of the galactic center are derived, and the C(+) profiles show a drop-off of rotation velocity between 2 and 10 pc. A mass model is suggested with 2-4 million solar masses in a central point mass, and a M/L ratio of the central stellar cluster of 0.5 solar masses/solar luminosities, suggesting a large abundance of giants and relatively recent star formation in the center.

Lugten, J. B.↗

NASA NTRS1986

Diffraction-limited 10 microns imaging with 3 meter telescopes

An IR imaging system that achieves diffraction-limited spatial resolution (about 0.8 arcsec) at 10 microns on 3-meter ground-based telescopes. The system uses a linear array of sensitive HgCdTe photodiodes, scanned in the direction perpendicular to the array axis, to form two-dimensional images. Scans are completed rapidly enough to freeze atmospheric fluctuations. Individual detectors are small compared to the diameter of the Airy disk, and images are oversampled heavily in the scan direction. This method has a number of advantages for studying small fields with very high spatial resolution, and has been applied successfully to the problem of directly imaging faint circumstellar dust shells.

Bloemhof, E. E.↗

NASA NTRS1985

Rapid variation in the circumstellar 10 micron emission of Alpha Orionis

The spatial distribution of 10 micron continuum flux around the supergiant star Alpha Orionis was measured on two occasions separated by an interval of 1 yr. A significant change in the infrared radiation pattern on the subarcsecond scale was observed. This change cannot be explained plausibly by macroscopic motion but may be due to a change in the physical properties of the circumstellar dust.

Bloemhof, E. E.↗

NASA NTRS1985

Far-infrared emission lines of CO and OH in the Orion-KL molecular shock

Observations of far infrared rotational emission lines which arise in the shocked gas associted with Orion-Kl are presented, including detections of the CO J = 34 yields 33, J = 31 yields 30, J = 26 yields 25, and OH sup 2 PI sub (3/2) J sup P = 7/2(-) yields 5/2(+) emission lines, as well as improved measurements of the CO J = 22 yields 21 and OH sup 2 PI sub (3/2) J = 5/2 yields 3/2 lines. These lines are observed to have velocity widths of Del V approx. 20 to 30 km/sec, somewhat less than either the 2 micro H sub 2 lines or the high velocity plateau component of the millimeter wave CO lines seen in this object. An H sub 2 column density of aprox. 3 x 10 to the 21st power, a total mass of approx. 1 solar mass and characteristic temperature and density T approx. 750 K and approx. 2 x 10 to the 6th power per cu cm can be derived from the CO intensities. The density is too low by at least an order of magnitude for the observed infrared H sub 2 and far infrared CO emission to be accounted for by a purely hydrodynamic shock, and support is lent to hydromagnetic shock models. From the present measurements, the relative abundance of CO is estimated to be CO H sub 2 = 1.2 x .0001, corresponding to 20 percent of the cosmic abundance of C existing in the form of CO. The average relative abundance of OH in the shocked gas is O/H sub 2 or = 5 x 10 to the -7th power. An upper limit to the intensity of the HD J - 1 yields 0 line is used to derive an upper limit of tau or = 3 for the D/H relative abundance in the Orion cloud core.

Watson, D. M.↗

NASA NTRS1985

The neutral-gas disk around the galactic center

The mapping of far-infrared C(+) and O(0) fine-structure lines and the first detection of far-infrared CO and OH rotational line emission and OH absorption toward the Galactic center are reported. These measurments are compared with far-infrared and radio continuum maps, with recent observations of the 12.8 micron forbidden Ne II line, and with measurements of CO 2.6 mm emission and H I 21 cm absorption. The new observations clearly show that there is a 10 pc diameter neutral gas disk or torus of several times 10,000 solar masses surrounding the inner ionized cavity. The disk has an inner radius of 1.7 pc, is inclined by about 20 deg to the Galactic plane, and may be quite thin. The atomic gas in the neutral disk is dense and fills less than 10 percent of the volume. The disk rotates about the Galactic center about an axis remarkably similar to that of the Galactic rotation at much larger scales.

Genzel, R.↗

NASA NTRS1985

Far-infrared emission lines of CO and OH in the Orion-KL molecular shock

Observations of far infrared rotational emission lines which arise in the shocked gas associated with Orion-Kl are presented, including detections of the CO J = 34 yields 33, J = 31 yields 30, J = 26 yields 25, and OH sup 2 PI sub (3/2) J sup P = 7/2(-) yields 5/2(+) emission lines, as well as improved measurements of the CO J = 22 yields 21 and OH sup 2 PI sub (3/2) J = 5/2 yields 3/2 lines. These lines are observed to have velocity widths of Del V approx. 20 to 30 km/sec, somewhat less than either the 2 micro H sub 2 lines or the high velocity plateau component of the millimeter wave CO lines seen in this object. An H sub 2 column density of approx. 3 x 10 to the 21st power, a total mass of approx. 1 solar mass and characteristic temperature and density T approx. 750 K and approx. 2 x 10 to the 6th power per cu cm can be derived from the CO intensities. The density is too low by at least an order of magnitude for the observed infrared H sub 2 and far infrared CO emission to be accounted for by a purely hydrodynamic shock, and support is lent to hydromagnetic shock models. From the present measurements, the relative abundance of CO is estimated to be CO H sub 2 = 1.2 x .0001, corresponding to 20% of the cosmic abundance of C existing in the form of CO. The average relative abundance of OH in the shocked gas is O/H sub 2 or = 5 x 10 to the -7th power. An upper limit to the intensity of the HD J = 1 yields 0 line is used to derive an upper limit of tau or = 3 for the D/H relative abundance in the Orion cloud core.

Watson, D. M.↗

NASA NTRS1985

Mass distribution in the galactic centre

New infrared and submillimeter spectroscopic measurements of the gas dynamics in the central 10 pc of the Galaxy make a convincing case that the mass distribution at the center of the Galaxy is more concentrated than a spherical isothermal stellar cluster. The measurements fit a point mass of about 4 million solar masses, but are also consistent with a cluster where stellar density decreases with radius (R) at least as fast as R to the -2.7, or a combination of a point mass and a stellar cluster. The dynamical information combined with previous 2-micron observations favor a large point mass, which is presumably a massive black hole.

Crawford, M. K.↗

NASA NTRS1985

Far-infrared spectroscopy of galaxies - The 158 micron C(+) line and the energy balance of molecular clouds

Observations of the 158 microns fine-structure line of C(+) toward the nuclei of six gas-rich galaxies are presented. The observations are compared with observations of the CO J = 1-0 and H I 21 cm lines, observations of far-IR continuum emission, and observations of forbidden C II emission with the Galaxy. The forbidden C II line comes from dense, warm gas in UV-illuminated photodissociation regions at the surfaces of molecular clouds. This line is probably optically thin in all but the brightest of galactic sources. The variation of forbidden C II brightness from source to source and its ratio to the integrated infrared continuum intensity agree well with the theoretical prediction that UV absorption by dust controls the C(+) column density. The forbidden C II line is a tracer of molecular clouds, especially those near intense sources of UV radiation.

Crawford, M. K.↗

NASA NTRS1984

Far-infrared Spectroscopy of Galaxies: the 158 Micron C(+) Line

The C II 158 micron fine structure line in six gas rich galaxies was investigated. These data are combined with other measurements of the C II line (in various galactic sources) and are compared to studies of the CO J = approaches O rotational line at 2.6 mm, the H I 21 cm line, and the far infrared continuum emission in the same objects.

Crawford, M. K.↗

NASA NTRS1984

Detection of shocked atomic gas in the Kleinmann-Low nebula

The 63 micrometer (3)P(1)-(3)P(2) fine structure line emission of neutral atomic oxygen at the center of the Orion nebula with a resolution of 30'' is presented. There are three main emission peaks. One is associated with the region of strongest thermal radio continuum radiation close to the Trapezium cluster, and probably arises at the interface between the H II region and the dense Orion molecular cloud. The other two line emission peaks, associated with the Kleinmann-Low nebula, are similar in both distribution and velocity to those of the 2 micrometer S(1) line of molecular hydrogen and of the high velocity wings of rotational CO emission. The OI emission from the KL nebula can be produced in the shocked gas associated with the mass outflows in this region and is an important coolant of the shocked gas.

Werner, M. W.↗

NASA NTRS1984

Detection of shocked atomic gas in the Kleinmann-Low nebula

The 63 micrometer (3)p(1)-(3)P(2) fine structure line emission of neutral atomic oxygen at the center of the Orion nebula with a resolution of 30" is presented. There are three main emission peaks. One is associated with the region of strongest thermal radio continuum radiation close to the Trapezium cluster, and probably arises at the interface between the HII region and the dense Orion molecular cloud. The other two line emission peaks, associated with the Kleinmann Low nebula, are similar in both distribution and velocity to those of the 2 micrometer S(1) line of molecular hydrogen and of the high velocity wings of rotational CO emission. The OI emission from the KL nebula can be produced in the shocked gas associated with the mass outflows in this region and is an important coolant of the shocked gas.

Werner, M.↗

NASA NTRS1984

Detection of far-infrared forbidden O I and forbidden O III emission from the galaxy M82

Observations in M82 of the lowest-lying transitions of neutral and doubly ionized oxygen, forbidden O I 63.2 microns and forbidden O III 88.4 microns, which have wavelengths at which the extinction toward M82 is negligible, are reported. For O III, the +220 km/s velocity of the line center with respect to the local standard of rest, the 300 km/s intrinsic line width, and the asymmetry of the profile are consistent with the systemic velocity and rotational broadening seen in other ionic lines in the nucleus of M82. The fraction of oxygen that is present in doubly ionized form, indicates that the ionization state is similar to that found in H II regions in the disk of the Milky Way Galaxy. The central velocity of the O I line is +130 km/s, and no broadening in excess of instrumental resolution is seen. This result appears to rule out association of this emission with the periphery of the central H II region.

Watson, D. M.↗