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Hobbs, R. W.

Publications and source records attributed to Hobbs, R. W..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
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 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

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

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

Intercomparison of ground based and satellite pictures of the sun

Using NASA facilities in space (OSO-7) and on the ground (Goddard multi-channel spectrophotometer at Sacramento Peak, New Mexico) an active region has been mapped. By combining these ultraviolet, X-ray, and visible data, a physical picture of this structured region was constructed from the photosphere to the corona, corresponding to temperature regimes from 4500 K to 4,000,000 K. The morphology of the active region was studied by comparing grey-shaded images in which fine details stand out more clearly than in the contour plots. One result of the study is that gross similarities persist from the low photosphere up to high in the transition region, while some changes occur in the corona.

Chapman, R. D.↗
NASA NTRS1973

A short-lived chromospheric flare-point with a lifetime of 20 seconds and rise and fall times of 5 seconds

We have observed a chromospheric brightening in the H alpha and Ca II K lines with a diameter of about 1 arc second. The time structure of this event, obtained with a relative resolution of 1 second, shows the rise time to be 4 seconds, the lifetime (FWHM) to be 20 seconds, and the decay time to be 5 seconds. This imposes new constraints on flare-point models. These restrictions can be accommodated easily by either an infall-impact flare model or a model invoking the precipitation of high-energy particles from the corona.

Hyder, C. L.↗
NASA NTRS1973

Kohoutek - A great comet coming.

Passing inside the earth's orbit in late November, the comet Kohoutek will travel through the inner solar system during a unique period in the history of the space program, when Skylab and Mariner Venus-Mercury are in operation and the new C-141 Airborne Infrared Observatory is ready for flight. It is planned to investigate comprehensively the nature and evolution of the coma and tails of the comet. The detailed goals of the investigation include the identification of the parent molecules of the gases observed in comets, the determination of the processes that break down the parent molecules, the study of the physical nature of transient events in the comet, and the measurement of the solar-wind velocity in the inner solar system.

Maran, S. P.↗
NASA NTRS1973

High resolution radio observations of the sun at 3.71 and 11.1 cm.

The results of observations of the sun performed at 3.71 and 11.1 cm on Jan. 14, 1972, using the NRAO three-element interferometer in the 2.7-1.8-0.9 km configuration, are reported. A flare of importance 1 N observed in the active region 693 near the east limb at about 1530 UT is discussed.

Hobbs, R. W.↗
NASA NTRS1973

High radio frequency observations of the Omega nebula.

Observations of M17 at 0.955, 1.65, and 2.73 cm yield flux densities of 575 plus or minus 80, 644 plus or minus 64, and 644 plus or minus 64 flux units. We conclude that M17, although having a very complex angular structure over approximately one square degree of the sky, is composed of sources with thermal spectra.

Johnston, K. J.↗
NASA NTRS1973

Astronomical observations with an SEC vidicon system.

Description of the design and operation of an SEC vidicon camera system, and review of some of the astronomical observations performed with it. Following a discussion of the main system and instrumentation features and a delineation of present and future software tasks, the preliminary series of observations obtained in conjunction with the 36-inch telescope at Kitt Peak National Observatory is briefly surveyed. These observations include (1) exposures on the Orion Nebula through various narrow-band interference filters, and (2) exposures on the galaxy Messier 82 in white light and with medium band filters.

Chiu, H.-Y.↗
NASA NTRS1972

Electronic systems for the new multichannel spectrometer at Sacramento Peak.

Description of the design features and operation of a new multichannel solar spectrometer to be used for ground-based observations of active regions whose X-ray and EUV emissions are studied by the OSO-H and other satellites. The electronic systems associated with the instrument include (1) an electrooptical guider controlled by a punched paper tape capable of making raster scans of selected portions of the solar disk, (2) a programmer unit that applies paper-tape commands to various portions of the instrument, (3) a closed-loop servosystem for the vacuum heliostat, (4) stepping motor controls for spectral scans, (5) a 40-channel photomultiplier readout, and (6) a magnetometer. Preliminary solar observations indicate satisfactory performance of the system.

Hobbs, R. W.↗