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Maran, S. P.

Publications and source records attributed to Maran, S. P..

At least 55 records · Page 3
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NASA NTRS1978

Stellar model chromospheres. VII - Capella /G5 III +/, Pollux /K0 III/, and Aldebaran /K5 III/

Data from high-resolution SEC vidicon spectroscopy with a ground-based telescope (for the Ca II K line) and from spectral scans made with the BUSS ultraviolet balloon spectrograph (for the Mg II h and k lines) are used to derive models of the chromospheres and upper photospheres of three G-K giants. The models are based on partial-redistribution analyses of the Ca II K line wings and cores and on the fluxes in the Mg II lines. The photospheres thus computed are hotter than predicted by radiative-equilibrium models. The minimum-to-effective temperature ratio is found to decrease with decreasing effective temperature, while the mass column density at the top of the chromosphere increases with decreasing stellar surface gravity. The computed pressure at the chromosphere top in the primary member of the Capella spectroscopic binary system is 70 times smaller than the transition-region pressure derived by Haisch and Linsky (1976), which suggests that additional terms must be included in the transition-region energy equations for giant stars. Estimates of the Ca II and hydrogen column densities are made for the circumstellar envelope of Aldebaran.

Kelch, W. L.↗
NASA NTRS1978

Cygnus A at 99 GHz - Observations of the three principal components and interpretation of the central source

The three principal emission components of Cygnus A have been observed at 99 GHz, the highest frequency at which radio measurements of this source have been accomplished. The observations show no definite indication of a high-frequency cutoff in the spectrum of the compact central component, which perhaps may be attributed to an optically thin synchrotron source that peaks at a frequency of several hundred GHz.

Hobbs, R. W.↗
NASA NTRS1978

Development of the Equatorial Infrared Catalogue from satellite data

More than 40,000 infrared measurements of stellar sources have been obtained since November, 1976 during the ongoing process of compiling an Equatorial Infrared Catalogue. Because of the problem of eliminating spurious sources, which has affected earlier space surveys, an extensive effort is being made to verify the sources by means of (1) repetitive observations by satellite sensors, (2) cross correlation with a large data base developed from ground-based and space surveys at other wavelengths, and (3) investigation of a significant subset of the sources with a ground-based infrared telescope. As sources are verified, they are transferred from a working list to a screened preliminary version of the catalogue. The catalogue comprises the only survey of a significant area of the sky that has been accomplished (or is presently planned) with positional accuracies of a few arc seconds at a wavelength of not less than 2 microns.

Heinsheimer, T. F.↗
NASA NTRS1977

Microwave continuum radiation from comet West 1975n

Continuum emission at wavelength 3.71 cm was observed from the nuclear region of comet West 1975n on March 5, 1976. The flux density was 0.040 Jy, which is uncertain by 25% due to calibration. Assuming that the source was a uniformly illuminated disk, the diameter was no more than about 1100 km and the brightness temperature was at least 330 + or - 85 K. On March 4, 1976, similar observations yielded only an upper limit (two standard deviations) to the flux density of 0.010 Jy. Thus it appears that the source turned on with a time scale of 1 day or less, at about the time that the short-lived cometary daughter nucleus 'C' split from the main nucleus 'A'. Similar emission was observed from comet Kohoutek 1973f. In each case, it appears that the microwave emission can be interpreted as thermal radiation from a temporarily enhanced icy-grain halo (IGH). If this interpretation is correct, then the actual temperature (which is assumed to be approximately equal to the nuclear surface temperature) must be in the range 200-250 K, roughly compatible with the observations, in order to satisfy the IGH models of Delsemme (1973).

Hobbs, R. W.↗
NASA NTRS1977

Cygnus A at 99 GHz: Observations of the three principal components and interpretation of the central source

The three principal emission components of Cygnus A were observed at 99 GHz, the highest frequency at which radio measurements of this source have been accomplished. The observations show no definite indication of a high-frequency cutoff in the spectrum of the compact central component, which perhaps may be attributed to an optically thin synchrotron source that peaks at a frequency of several hundred GHz.

Hobbs, R. W.↗
NASA NTRS1977

Satellite observations of new infrared sources

Preliminary results are reported for satellite observations of about 1000 IR sources at a wavelength of 2.7 microns. The observations were made in the declination zone between +10 and -10 deg to a limiting flux of 4 by 10 to the -16th power W/sq cm per micron. Of 83 previously unobserved sources, twenty are identified with late-type stars having visual magnitudes of 6 to 9. The nine sources with available luminosity classifications are found to be giant stars, and flux densities at 2.2 and 3.6 microns are predicted for four unreddened stars among these. Three other detected sources are positively identified with red variable stars; twenty more are tentatively identified as such. It is suggested that some of the 40 blank-field 2.7-micron sources detected at high galactic latitude may be Mira variables with thick dust shells located at large distances from the galactic plane.

Heinsheimer, T. F.↗
NASA NTRS1977

High-resolution stellar vidicon spectrophotometry. I - Variable mass loss from Arcturus and the hypothesis of giant convective elements

High-resolution spectrophotometry of the variable Ca II K line in the K2 IIIp star Alpha Boo was performed with the McMath Solar Telescope at Kitt Peak National Observatory and an experimental SEC vidicon camera. The results are compared with Copernicus observations of the Mg II h and k lines and with earlier Ca II data. It is found that either of two states may typically occur in the Arcturus chromosphere. From comparison with the results of model calculations for expanding chromospheres, it is concluded that these correspond respectively to a 'normal' state in which the mass loss is less than one billionth of a solar mass per year and an 'abnormal' state in which the mass loss is about 8 billionths of a solar mass per year. In the latter case, the expansion velocity is around 13 km/s at optical depth unity in the K-line, which exceeds the local sound speed. It is suggested that the abnormal state represents the rise to the photosphere of a very large convective element, as hypothesized for red giants by Schwarzschild (1975).

Chiu, H. Y.↗
NASA NTRS1977

High-precision infrared sky survey at wavelength 2.7 microns

Preliminary results of an infrared survey of the equatorial sky zone (declinations 10 S to 10 N) with U.S. Air Force satellite sensors show that positions of previously unknown infrared sources are measured with an rms accuracy of 4 arc seconds, which is six times better than the best previous infrared survey. The search area per source for further study is thus 36 times smaller, so that identification of the infrared sources with optical objects in catalogs and sky photographs is facilitated, as is reacquisition of the sources with ground-based infrared telescopes. The survey extends the content of near-infrared source catalogs to lower flux densities and adds information at a wavelength not observable from the ground. Objects found in the survey include cool giants and supergiants, long-period and semi-regular variable stars, and sources identified with faint red stars visible on the Palomar Observatory Sky Survey.

Sweeney, L. H.↗
NASA NTRS1976

Coordinated X-ray optical and radio observations of YZ Canis Minoris

Coordinated X ray, optical, and radio observations of the flare star YZ CMi are reported. Twenty-two minor optical flares and twelve radio events were recorded. No major optical flares, greater than 3 magnitudes, were observed. Although no flare related X ray emission was observed, the measured upper limits in this band enable meaningful comparisons with published flare star models. Three of the five models predicting the relative X ray to optical or radio flare luminosities are in serious disagreement with the observations. For the largest optical flare with coincident X ray coverage, the 3 sigma upper limit on X ray emission in the 0.15 to 0.8 keV band is 8.7 x 10 to the 28th power erg/s, corresponding to a ratio of X ray to B-band luminosity of less than 0.3. Based on the present results, the contribution of the flares UV Ceti flare stars to the galactic component of the diffuse soft X ray background is less than 0.2 percent.

Karpen, J. T.↗
NASA NTRS1976

The origin of OB associations and extended regions of high-energy activity in the Galaxy through supernova cascade processes

A number of observed characteristics of OB associations, including their positive total energies and subgroup structure, are explained by the hypothesis that an association is composed of stars formed by compression of interstellar clouds in blast waves of several generations of supernovae. The later-generation supernovae are simply the most massive stars formed by this mechanism in the earlier generations. This supernova cascade process may also be responsible for giant loops such as the North Polar Spur. Enhanced high-energy gamma-ray emission is expected from the loops.

Ogelman, H. B.↗
NASA NTRS1976

Long-term infrared monitoring of stellar sources from earth orbit

A program is discussed which involved monitoring the photometric activity of 18 bright variable IR stars at 2.7 microns with satellite- and rocket-borne instrumentation in the period from 1971 to 1975. The stellar sample includes 3 Lb variables, 8 semiregular variables, 5 Mira-type variables, and 2 previously unknown and unclassified IR variables. Detailed light curves of many of these stars were determined for intervals of 3 yr or more; spectra from 2.7 to 20 microns were constructed for nine of them using data obtained entirely with instruments above the atmosphere. Photometric IR light curves and other data are presented for SW Virginis, R Aquilae, S Scuti, IRC 00265, RT Hydrae, S Orionis, S Canis Minoris, Omicron Ceti, and R Leonis. Several hypotheses concerning the interpretation of the IR data are examined.

Maran, S. P.↗
NASA NTRS1976

Telescopes and space exploration

The necessity for different types of telescopes for astronomical investigations is discussed. Major findings in modern astronomy by ground-based and spaceborne telescopes are presented. Observations of the Crab Nebula, solar flares, interstellar gas, and the Black Hole are described. The theory of the oscillating universe is explored. Operating and planned telescopes are described.

Brandt, J. C.↗
NASA NTRS1976

Characteristics of IR variable stars as observed from orbit

A selection of infrared variable stars was studied at wavelength 2.7 microns during 1971-1975 with data from U.S. Air Force satellites. Stars observed in this program are classified as long-period variable stars, semiregular variables, and irregular variables and are among the strongest stellar sources at this wavelength. In addition, a few new, as yet unclassified variable stars were identified during the course of the investigation. Time scales of reproducible variations range from a few weeks to a few years, and amplitudes of variation are as large as a factor of three for stars with periods of order one year. The minimum infrared flux density of a long-period star repeats accurately from one cycle to the next, whereas the maximum flux density was found to be unstable. The correlation of 2.7 micron and radio emission line data from one, well-studied long-period variable is consistent with the hypothesis that the H2O and OH circumstellar masers are saturated, if pumped by the stellar infrared flux near 2.7 microns.

Maran, S. P.↗
NASA NTRS1975

Microwave continuum radiation from comet Kohoutek 1973f - Emission from the icy-grain halo

Cometary emission was measured at 3.71 cm on January 10-11, 1974. A possible detection at 2.8 cm and an upper limit at 11.1 cm are also reported. Interferometer measurements at 3.71 cm show that the angular diameter is less than 1.4 arc sec or less than 850 km at the comet. The corresponding disk brightness temperature is greater than 313 + or - 80 K. The radiation presumably originates in the icy-grain halo postulated by Delsemme.

Hobbs, R. W.↗
NASA NTRS1975

The last OSO satellite

Missions planned for OSO-8 are outlined. Instruments to be included on the satellite comprise a multichannel UV spectrometer, a high-resolution UV spectrometer, an X-ray crystal spectrometer and polarimeter, a hard X-ray telescope, a celestial X-ray spectrometer, a mapping X-ray heliometer, an extrasolar extreme UV monitor, and a soft X-ray telescope. The instruments make up a scientific payload that is larger, transmits data at a greater rate, can be pointed with higher accuracy, and has much better spatial and spectral resolution over a wider range of wavelengths than any payload carried by previous OSO satellites.

Maran, S. P.↗
NASA NTRS1975

Possible relationships between solar activity and meteorological phenomena

A symposium was conducted in which the following questions were discussed: (1) the evidence concerning possible relationships between solar activity and meteorological phenomena; (2) plausible physical mechanisms to explain these relationships; and (3) kinds of critical measurements needed to determine the nature of solar/meteorological relationships and/or the mechanisms to explain them, and which of these measurements can be accomplished best from space.

Bandeen, W. R.↗
NASA NTRS1974

Astronomical demonstration of an infrared upconverter

An upconverter has been used to convert infrared photons from astronomical sources to higher frequency quanta that were detected with a pulse-counting photomultiplier photometer. It is pointed out that these observations represent the first successful astronomical demonstration of infrared upconversion. Upconversion is carried out in an optically nonlinear medium, which in the upconverter described is a lithium iodate crystal. A 0.6943-micrometer high peak power ruby laser pump was developed for the demonstration.

Gurski, T. R.↗