Engineering topics

Stanford, S. A.

Publications and source records attributed to Stanford, S. A..

23 records · Page 2

NASA NTRS1990

Imaging and two-dimensional spectra of the IR-bright galaxy NGC 2146 - A recent low-energy merger?

New data are presented on the IR-luminous galaxy NGC 2146 from several sources: direct imaging in B, R, and H-alpha; IR imaging in the J, H, and K bands; long-slit spectroscopy at optical and IR wavelengths; and scanning etalon observations in H-alpha. The results allow measurement of the interstellar extinction in the dust lane, and estimation of the true luminosity of the galaxy and nuclear regions. The spectra indicate that there is no active nucleus, and measure the changing ratio of forbidden to permitted lines across the galaxy. IR images and colors indicate the existence of a significant population of hot young stars in the central regions of the system. The H-alpha velocity maps show the full radial-velocity pattern, and suggest that the system consists of a disturbed disk and a merging or interacting arm which connects to the inner dust and radio structures. Outer H-alpha and H I structures appear to be the earlier remnants of this spiraling merger.

Hutchings, J. B.↗

NASA NTRS1990

CO aperture synthesis of NGC 4038/9 (ARP 244)

Researchers present high-resolution (approx. 6 seconds) CO observations of the merging galaxies NGC 4038/9 made with the Owens Valley Radio Observatory (OVRO) Millimeter Wave Interferometer. The CO observations of Arp 244 were obtained between April and June 1988 using the OVRO Millimeter Wave Interferometer. Two fields with phase centers near the NGC 4039 nucleus and near the NGC 4038 nucleus were observed. The size of the synthesized beam is approximately 6.5 x 7 seconds at PA=72 degrees. The rms in a single cleaned channel map is 0.06 Jy beam(exp -1), corresponding to a brightness temperature of 0.12 K over the synthesized beam. Contour maps of the integrated CO intensity for both interferometer fields are shown. Three CO concentrations are evident. Two are centered near the nuclei of NGC 4038 and NGC 4039, closely correlated with H alpha and radio continuum maxima. A third CO emission region lies about 25 seconds northeast of the NGC 4039 nucleus. A number of radio continuum, H alpha, and 10 micron emission knots appear in this region. The total integrated intensity at the northern nuclear source, 302 K km/s, leads to a molecular mass of 8.3 by 10 to the 8th power solar mass assuming a Galactic CO to H2 conversion factor of 3.0 x 10 to the 20th power H2 cm(-2) (K km/s)(-1). The integrated CO intensity of the southern nuclear source leads to a molecular mass of 2.4 x 10 to the 8th solar mass. The extranuclear CO concentration contains 1.2 x 10 to the 9th power solar mass of molecular gas, extending over 170 km/s, and is resolved in a number of channels. Its large size, mass, and morphology strongly suggest that it is an agglomeration of several clumps.

Stanford, S. A.↗

NASA NTRS1990

CO aperture synthesis of NGC 4038/39 (ARP 244)

High-resolution CO observations of the merging galaxies NGC 4038/39 (the 'Antennae') have been made with the Owens Valley Millimeter Wave Interferometer. Three concentrations of CO emission were detected. In addition to masses of a few x 100 million solar masses at each nucleus, approximately 1.2 x 10 to the 9th solar masses of molecular gas was discovered in a 32 arcsec x 22 arcsec region where the two galaxies overlap. Within this region are four distinct clumps. These coincide with H-alpha, 10 microns, and radio continuum peaks, suggesting that they are extremely active sites of star formation. The galaxy interaction appears to have concentrated gas at the nuclei of NGC 4038 and NGC 4039 and to have engendered enhanced star formation activity in the region where their disks overlap. From estimates of the SFR in this overlap region, it is suggested that the gas will be completely depleted in 240 million yr.

Stanford, S. A.↗

NASA NTRS1989

A single rotating disk of H I in Arp 299 (NGC 3690/IC 694)

Ten-arcsec resolution 21-cm spectral line observations of the merging galaxies NGC 3690/IC 694 are presented. Strong H I absorption was seen at three sites of activity identified previously by Gehrz, Sramek, and Weedman (1983), and regions of weak emission were found extending from the optical edges of the system. The absorption data set lower limits on the neutral hydrogen mass contained in the nuclei and in the overlap region. The emission shows evidence of a single rotating disk of H I surrounding the system out to a radius twice that of the optical radius. This single H I disk morphology indicates that IC 694 and NGC 3690 are coverage of Arp 299 which now spans from the UV to radio regimes, thus making it possible to compare the distribution and kinematics of atomic hydrogen with previous observations, and offering new insight into the effect of a collision on a progenitor's interstellar medium.

Stanford, S. A.↗

NASA NTRS1988

R Coronae Borealis dust ejections - A preferred plane?

Spectropolarimetric observations of R Coronae Borealis obtained during the brightness minimum of 1986 are presented. When combined with previous polarization observations of brightness minima, the distribution of observations in the Q-U plane suggests that ejections of dust clouds occur in a preferred plane about the star, in contrast to the standard model for the R CrB-type stars, which holds that clouds are ejected from all parts of the stellar surface. The possibility of an ejection mechanism connected with nonradial pulsations is discussed as the most likely explanation of the preferred plane.

Stanford, S. A.↗