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At least 271 records · Page 15
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NASA NTRS1982

H1409-45 - A recurrent soft X-ray transient

Satellite observations of the soft X-ray variable H1409-45 and observations of a promising optical counterpart are reviewed. It is shown that the source appears to have several types of X-ray variability, ranging from rapid flickering on time scales of seconds to changes between states of different intrinsic luminosity on time scales of months to years, and that the source's X-ray spectrum appears to be softer in its high-luminosity state. The observations indicate that H1409-45 may be a white dwarf accreting mass from a close binary companion and that the X-ray and optical properties most closely resemble the AM Her variables.

Jensen, K. A.↗
NASA NTRS1983

Recurrent pulse trains in the solar hard X-ray flare of 1980 June 7

This study presents a detailed examination of the solar hard X-ray and gamma-ray flare of 1980 June 7 as seen by the Hard X-Ray Burst Spectrometer on SMM. The hard X-ray profile is most unusual in that it is characterized by an initial pulse train of seven intense hard X-ray spikes. However, the event is unique among the 6300 events observed by HXRBS in that the temporal signature of this pulse train recurs twice during the flare. Examinations of the hard X-ray data in conjunction with radio and gamma-ray observations show that the 28-480 keV X-ray emission is simultaneous with the 17 GHz microwave fluxes within 128 ms and that the 3.5-6.5 MeV prompt gamma-ray line emission is coincident with secondary maxima of the microwave and X-ray fluxes. Although the absence of spatially resolved hard X-ray observations leaves other possibilities open, a parameterization of the event as a set of seven sequentially firing loops is presented that offers many satisfying explanations of the observations.

Kiplinger, A. L.↗
NASA NTRS1985

A study of periodicities and recurrences in solar activity and cosmic ray modulation

The 154d periodicity was found in the cosmic ray intensity (RE) vs Flares, and some other peaks of coherency in the RC vs aa sub I, that when interpreted as aliased values, might correspond to recurring interplanetary magnetic field structures and solar wind streams. It cannot be excluded, however, that some of the correspondence with aa are of terrestrial origin. This study cannot be considered exhaustive due to the fact that other solar variables, such as polar hole size, are possibly correlated to cosmic ray intensities. However, the number of observations is small so that the interpretation of the results is very difficult.

Attolini, M. R.↗
NASA NTRS1984

Dynamic evolution of recurrent mass ejections observed in H-alpha and C IV lines

The mass ejections of 1 September, 1980 are studied from observations obtained with the MSDP spectrograph and with the Ultraviolet Spectrometer and Polarimeter aboard the Solar Maximum Mission satellite. The analysis is focused on observations in the chromospheric H-alpha line and the transition region C IV 1548 A line. It is noted that cold and hot material had the same projection, although the upward C IV velocity structure was more extended than the H-alpha one. It is shown that the observed contrast of the H-alpha absorbing structure can be interpreted in terms of a dynamic cloud model overlying the chromosphere. Radial velocities of 25-30 km/s and -40 km/s are estimated for the first and second phases of ejection, respectively.

Schmieder, B.↗
NASA NTRS1985

On the long term evolution of white dwarfs in cataclysmic variables and their recurrence times

The relevance of the long term quasi-static evolution of accreting white dwarfs to the outbursts of Z Andromeda-like symbiotics; the masses and accretion rates of classical nova white dwarfs; and the observed properties of white dwarfs detected optically and with IUE in low M dot cataclysmic variables is discussed. A surface luminosity versus time plot for a massive, hot white dwarf bears a remarkable similarity to the outburst behavior of the hot blue source in Z Andromeda. The long term quasi-static models of hot accreting white dwarfs provide convenient constraints on the theoretically permissible parameters to give a dynamical (nova-like) outburst of classic white dwarfs.

Sion, E. M.↗
NASA NTRS1987

The development and implementation of cockpit resource management in UAL recurrent training

Line Oriented Flight Training (LOFT) for United Airlines started in 1976. At that time it was basically no more than a line-simulated training function conducted in a full-mission simulator with no attention or stress on its human factor content. Very soon after the implementation of the LOFT program concerns were voiced about certain crew behavioral situations they were observing in the flight crew's execution of cockpit duties. These duties involved emergency procedures as well as irregular and normal procedures and situations. It was evident that new information was surfacing concerning crew interaction, or its lack thereof, in the cockpit and its effect on satisfactory performance. These observations naturally raised the question of how this information translated into the safety of aircraft operations. A training system had to be repetitive, the crew interactive, and the training had to be conducted under the crew concept. The foundation had to have two other factors: (1) it was necessary to have adequate human factor content, and (2) an advanced state-of-the-art simulator and appropriate electronic devices were required. These concepts are further discussed.

Shroyer, David H.↗
NASA NTRS1987

Recurrent episodic mass loss in a B2e star - 66 Ophiuchi, 1982-1985

The results of three intensive ultraviolet monitoring campaigns for 66 Oph in September-October 1982, September 1983, and September 1984, supplemented by the available IUE archival data from April, 1982 to June, 1985 are reported. The stellar wind went through at least two and probably three episodes of weak-wind absorption. At wind minimum, the resonance profiles and equivalent widths of C IV, Si IV, Si III, and Al III are similar to those observed in normal B stars of comparable luminosity, effective temperature, and v sin i. The strong-wind absorption profiles show one or more shortward-shifted discrete components superposed upon the weak-wind absorption profiles. Significant profile variations are seen on time scales spanning over two orders of magnitude, ranging from small-amplitude changes detected on time scales of hours to the transitions from wind minimum to maximum, which take months.

Grady, C. A.↗
NASA NTRS1988

The recurrence behaviour of X-ray bursts from 4U/MXB 1735-44

During about 80 h of uninterrupted observations of the X-ray burst source 4 U/MXB 1735-44, made in August 1985 with Exosat, five bursts were observed. The bursts occur at irregular intervals, ranging between 30 min and 36 h. The burst sizes do not scale with the intervals preceding the bursts; in particular the energy in a burst which occurred after an interval of 50 min was only 30 percent less than that of a burst which occurred after more than 20 h. Due to the long uninterrupted observations possible with Exosat, this is the first time for 1735-44 that the burst intervals and the burst characteristics (e.g., fluence) can be compared. The observations show that the model recently proposed by Fujimoto et al. (1987) to explain irregular burst intervals, is not applicable to 1735-44. The amplitude of periodic X-ray flux variations at the 4.65 h orbital period is less than 4 percent.

Van Paradijs, J.↗
NASA NTRS1988

Recurrent shell infall events in a B0.5e star: HD 58978 1979-1988

Infall from the circumstellar envelope onto the bright B0.5 IVe star, HD 58978 was studied. The IUE data indicate that the star was surrounded by a low and moderately ionized circumstellar shell at least 12 times between 1979 and 1988. During 6 of these episodes, the signatures of cool circumstellar material were redshifted with respect to the photosphere by 20 to 80 km/sec. The data indicate that the transition from infall to minimal shell absorption can occur in under 10 days, and are consistent either with infall phases lasting up to 6 months, or with infall episodes shorter than 10 to 15 days. The long term behavior of the shell episodes is compared with variability in the stellar wind.

Grady, C. A.↗
NASA NTRS1992

The photometric period of the recurrent Nova T Pyxidis

The paper presents 1713 photometric measurements of T Pyx from 1966 to 1990. The light curve of T Pyx shows roughly sinusoidal variations with a typical amplitude of 0.09 mag and a time scale of 2 hr. Discrete Fourier transforms of data from individual nights and runs reveal a highly significant periodic modulation. This modulation is proven to be coherent only on time scales shorter than from 6 d to under 1 d. The present period for the modulation is 0.07616 +/- 0.00017 d. Since other stars have variable photometric periods (possibly related to the superhump phenomenon) which are slightly different from the orbital period, an orbital period of about 0.073 d for T Pyx is suggested.

Schaefer, Bradley E.↗
NASA NTRS1991

The impact of initial and recurrent cockpit resource management training on attitudes

It is noted that previous analyses of the boomerang effect (attitude change as a result of training in the direction opposite of that intended) in aviation training environments were limited in that each subscale of the cockpit management attitudes questionnaire (CMAQ) was examined independently. This study develops and utilizes a new algorithm for grouping subjects such that a global attitude change score is derived from the attitude change scores on each CMAQ subscale. By evaluating global attitude change in addition to the more specific attitude change on each subscale, it might be possible to better comprehend the effects of crew resource management training on pilot attitudes.

Irwin, Cheryl M.↗
NASA NTRS1993

Recurrent burst activity from the soft gamma-ray repeater SGR 1900 + 14

Three short very soft gamma-ray (SGR) transient events from a location consistent with that of the SGR 1900 + 14, first described by Mazets et al. (1979), were detected by the Burst and Transient Source Experiment. The results of observations of the temporal and spectral properties of the SGR 1900 + 14 suggest that the SGR phase lasts at least 13 years, lending support to the suggestion by Kouveliotou et al. (1987) and Fishman et al. (1989) that SGRs are related to galactic (possibly population I) objects, perhaps neutron stars.

Kouveliotou, C.↗
NASA NTRS1939

A recurrence formula for shear-lag problems

The analysis of the bending action in box beams with appreciable shear deformation of the flanges becomes very difficult in the general case of variable cross section and loading. This paper presents a convenient method of solving the problem by the familiar method of dividing the beam into a number of bays that can be assumed to have constant cross section and loading. Application of formerly derived shear-lag formulas leads to a general equation closely analogous in form to the well-known three-moment equation. A numerical example and two comparisons between calculation and experimental results are included.

Kuhn, Paul↗
NASA NTRS1993

Models of Neptune's smooth recurrent radio emission

The quantitative response of the Planetary Radio Astronomy (PRA) instrument to a wave with polarization ellipse of arbitrary shape and orientation, arriving at the antennas from any direction, can be determined. This capability is used to model the time variation of intensity and circular polarization over a range of radio frequencies for proposed radio-source locations and emission characteristics at Neptune. At frequencies below 400 kHz the observed variation of intensity, polarization, and phase are closely simulated in an offset tilted dipole magnetic field by conjugate sources at midlatitude with filled emission cones. The phase of emission at higher frequencies is reproduced by sources at lower latitude. Modeled wide-cone emission does not reach the spacecraft at the observed phase nor have the polarization sense observed before closest approach. Source-surface maps of apparent polarization for the period before closest approach when instrumental response is especially sensitive to source location is presented. The method is capable of extension to more realistic models of the magnetic field.

Sawyer, Constance↗
NASA NTRS1995

Ulysses high energy particle observation of the effects of recurrent high speed streams

Since June 1992 The Kiel Electron Telescope on board Ulysses measures variations of more than 10% in the fluxes of high energy H and He showing a periodicity of about 27 days, which are coincident with the passage of corotating interaction refios (CIR). At low energies MeV protons are accelerared at the shocks of the CIRs. These effects were observed up to high southern latitudes, where the signature of time of the conference Ulysses will have passed the solar equator and climbed up to 70 deg N at solar distance of 1.7 AU. In this paper we study the intensity variations with latitude as a function of magnetic rigidity.

Droege, W.↗