Engineering topics

Labonte, Barry J.

Publications and source records attributed to Labonte, Barry J..

5 records

NASA NTRS1991

The Mees CCD imaging spectrograph

The Mees CCD (MCCD0 instrument is an imaging spectroscopy device which uses the 25-cm coronagraph telescope and the 3.0-m Coude spectrograph at Mees Solar Observatory on Haleakala, Maui. The instrument works with resolving power up to about 200,000 with significant throughput from 3934 A (Ca II K) to about 10,000 A. A fast guiding active mirror stabilizes the image during observations. A rapidly writing magnetic tape storage system allows observations to be recorded at 256 kbytes/s. Currently, the MCCD is used for imaging spectroscopy of solar flares at 6563 A (H-alpha), and velocity measurements of umbral oscillations; future plans include emission line studies of active region coronae, and photospheric studies of solar oscillations.

Penn, Matthew J.↗

NASA NTRS1991

Can the starpatch on Xi Bootis A be explained by using tangential flows?

It is demonstrated that a modification of the starpatch model of Toner and Gray (1988), using tangential flows instead of an enhanced granulation velocity dispersion within the patch, is very successful at reproducing both the observed line asymmetry and the line broadening variations observed in the G8 dwarf Xi Boo A. Areal coverage of 10 percent + or - 3 percent of the visible disk, latitude 30 deg + or - 4 deg, mean brightness 0.85 + or - 0.05 relative to the 'quiet' photosphere, mean tangential flow velocities of 8.0 + or - 1.5 km/s, and dispersions about the mean of 8/0 + or - 2.0 km/s are inferred for the patch. A feature at a latitude of about 30 deg is inferred which covers about 10 percent of the visible disk and is 10-20 percent fainter than the rest of the photosphere. It is inferred that 70-80 percent of the patch is penumbra.

Toner, Clifford G.↗

NASA NTRS1988

Mass and energy flow near sunspots. I - Observations of moat properties

New measurements of the velocities of moving magnetic features (MMFs) are made from spectroheliograms and filtergrams. The sample includes 200 MMFs found in the moats surrounding 7 different sunspots. Our data are compiled with the data from other authors to uncover common properties of moats. The moat radius is roughly twice the penumbral radius. No significant correlation between the average moat velocity or angular extent and any noted property of the spot or moat (size, age, stage of development) is found. Individual MMFs move radially outward with a constant speed, but nearby MMFs may have quite different speeds. The average moat speed is twice the supergranule flow speed. The speed of MMFs in moats is equal on average to the surface gas flow speed. A large bias is found in much of the existing observations of moat speeds from MMFs.

Brickhouse, Nancy S.↗

NASA NTRS1988

Mass and energy flow near sunspots

Sunspots block the flow of energy to the solar surface. The blocked energy heats the volume beneath the spot, producing a pressure excess which drives an outflow of mass. Linear numerical models of the mass and energy flow around spots were constructed to estimate the predictions of this physical picture against the observed properties of sunspot bright rings and moat flows. The width of the bright ring and moat are predicted to be proportional to the depth of the spot penumbra, in conflict with the observed proportionality of the moat width to the spot diameter. Postulating that spot depths are proportional to spot diameters would bury the moat flow too deeply to be observed, because the radial velocity at the surface is found to be inversely proportional to the depth of the spot penumbra. The radial velocity at the surface is of order a few hundred meters per second after 1 day, in agreement with the observed excess of moat velocities over supergranule velocities.

Nye, Alan↗

NASA NTRS1987

Ground-based photometric measurements

Resolution in space, time, magnetic field strength, intensity variance, and wavelength all are used to isolate the signals from sunspots, plage, network, and nonmagnetic areas. Ground data has demonstrated the dominance of sunspots in causing irradiance variance on time scales of hours to months, the near balance of spot deficit and facular excess emission, and the low level of irradiance variation caused by nonmagnetic regions. Present techniques limit the accuracy of comparison with direct irradiance measures, and improvements should be made. Goals for ground-based photometry for the next cycle are suggested.

Labonte, Barry J.↗