Engineering topics

Schoolman, S. A.

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

11 records

NASA NTRS1982

Low-resolution Mg II h and k observations of solar type stars

Observations with the International Ultraviolet Explorer (IUE) have made possible a comparison between chromospheric radiative loss rates in the Mg II h and k lines and the Ca II H and K lines. Observations made by Stencel et al. (1980) confirm the findings of Linsky et al. (1979) that the chromospheric radiative loss rates in h and k and H and K are about equal for supergiants, but the h and k loss rate is greater than the H and K loss rate in giants. It is pointed out that this may result from physical differences between the lower chromospheres of giants and supergiants. The present investigation has the objective to explore the possibility of determining relative chromospheric radiative loss rates in F and G dwarf stars with low-resolution IUE spectra. It is found that this is possible. Cluster stars were selected to provide two temperature sequences at two slightly different metal abundances.

Barry, D. C.↗

NASA NTRS1981

H-alpha flare spectra

More than 1000 H-alpha flare profiles from 24 solar flares of Class 1 or brighter recorded with the multislit spectrograph of the Lockheed Solar Observatory are examined. It is found that the profiles can be classified in terms of whether or not they show central self-reversals, whether or not they have extended wings, and whether or not they are asymmetric. The profile groupings are not correlated with the size (class) of the flares, nor do they seem to be correlated with the type of chromospheric flare structure from which they are emitted. Although different flare points within the same overall event may show profiles of different types, any given element (bright patch) can usually be described in terms of a single combination of the profile descriptors.

Schoolman, S. A.↗

NASA NTRS1981

Observations of the 1980 April 30 limb flare by the ultraviolet spectrometer and polarimeter on the Solar Maximum Mission

Observations of the M2 limb flare of 1980 April 30 by the ultraviolet spectrometer and polarimeter in the C IV 1548 A line are described and compared with observations from other SMM instruments and with ground-based H-alpha data. Events observed during the 18 minutes leading up to the flare impulsive phase include the filling of a small loop with material moving at about 20 km/s, followed by a rapid brightening in C IV, H-alpha, and hard X-rays, with a subsequent brightening of a higher set of loops. The rapid brightening appears to be at the junction of the small loop with the overlying magnetic structures, which suggests the flare may be caused by their interaction.

Woodgate, B. E.↗

NASA NTRS1980

Radiative energy output of the 5 September 1973 flare

Measurements of the radiative energy output of the solar flare of Sept. 5, 1973, over a wavelength range of more than ten decades, from below 1 A to above 1 m are presented. Observations of soft X-rays (0.5-20 A), XUV and EUV lines (171-1863 A) and EUV continua (1400-1960 A), H alpha radiation, visible lines and continua (3700-8700 A) and radio emission (centimeter to meter wavelengths) were obtained concurrently by Skylab and ground-based instruments. Estimates of power output at flare maximum are obtained for the observed wavelengths with uncertainty of at least half an order of magnitude, due to corresponding uncertainties in EUV and visible fluxes. Taking into account energy radiated at unobserved wavelengths and the characteristic time of the best-reduced data (the soft X-ray), calculations indicate a total radiated flare energy of approximately 4 x 10 to the 29th erg.

Canfield, R. C.↗

NASA NTRS1977

On the size, structure, and strength of the small-scale solar magnetic field

High-resolution magnetograms place an upper limit of 0.33 arcsec on the smallest magnetic-field structures. These magnetograms show that the active-region field is organized into roughly cellular patterns 2-3 arcsec in diameter and that the field structures occur in the centers of 'abnormal' granules. Comparison of these data and other magnetograms with high signal-to-noise ratio indicates that there exists another component of the field that is diffuse on the scale of an arc second and has a maximum strength of less than 500 gauss.

Ramsey, H. E.↗

NASA NTRS1976

The dark component of the photospheric network

We examine a high quality Zeeman-analyzed lambda-scan through Ca I 6103, using a 0.1 A filter. We find that filter shifts of 0.01 A produce substantial changes in the contrast seen in the photospheric network in the core of the line, implying that the Doppler velocity in the network is constant to within 0.25 km/sec or less. Relative line profiles constructed from the lambda-scan indicate that the bright network points have smaller equivalent widths than does the background photosphere and are systematically Doppler shifted toward the red. However, we also find numerous small dark points within the magnetic network which exhibit increased equivalent widths. We infer these to be due to magnetic flux tubes which are highly inclined through the photosphere.

Schoolman, S. A.↗

NASA NTRS1976

Development of birefringent filters for spaceflight

The critical problem for flight of a birefringent filter is the shock mounting of the calcite. The design presented here bonds the calcite block with silicon rubbers to the calcite holder. The calcite together with its all necessary polarizers and rotating achromatic plates are mounted together in units called a filter module. By using a set of modules containing calcite crystals of differing lengths, a filter can be produced. A description of the modules is given. Also described is a container for the filter modules, which can be used both to hermetically seal the system or contain an index matching oil. The response of a filter element while being controlled by the Lockheed Temperature Control is described and the determination of the wavelength sensitivity to temperature of calcite is explained. Operation of the filter using a software control algorithm instead of a hardware temperature controller is shown. Some radiation considerations of filter systems are given.

Title, A. M.↗

NASA NTRS1976

Recent advances in birefringent filters

In the past several years, important developments have been made in the construction and theory of birefringent filters. Tunable filters that operate from 4500 to 7000 A with full widths at half maximum of 0.05 A and maximum transmissions of almost 20 percent have been constructed. Inexpensive large-aperture (at least 15 cm) achromatic waveplates have been fabricated which allow full use of resolution-solid angle products that are 100 times that of Fabry-Perots and 10,000 times that of grating systems.

Title, A. M.↗

NASA NTRS1975

Height of helium emission in the chromosphere

Filtergrams of the limb show the He I D3 chromosphere as a shell which is separated from the limb by a gap. The height of maximum D3 contribution occurs at about 1350 km above the limb and is independent of the intensity of the D3 emission. We interpret this effect as the height to which coronal EUV radiation is capable of penetrating the atmosphere.

Pope, T.↗

NASA NTRS1973

Videomagnetograph studies of solar magnetic fields. II - Field changes in an active region

Using the Caltech videomagnetograph, we obtained a 6.5-hr movie of the magnetic fields in a young active region. The major contribution to the short term magnetic evolution of the region was provided by many discrete magnetic points which move in apparently random directions with typical velocities of 0.4 - 1.0 km/sec. The majority of these features appear to be footpoints of new EFR's, which emerge at an observed rate of one to two per hour. The pattern of the motions suggests that the magnetic evolution of a growing region cannot be principally due to photospheric convective cells.

Schoolman, S. A.↗

NASA NTRS1973

Contrast elements in birefringent filters.

Calculations were made to determine the effects which contrast elements of various thicknesses have in Lyot filters. A filter which is significantly narrower than the line at which it is looking produces the best results. Therefore, if the filter is broad the addition of as thick an element as possible is desired. However, if the filter is already narrow, a contrast element whose thickness equals that of the second Lyot element will produce the best performance.

Schoolman, S. A.↗