Engineering topics

Tuohy, I. R.

Publications and source records attributed to Tuohy, I. R..

34 records · Page 2

NASA NTRS1981

Low-energy X-ray line emission from IC 443

HEAO 1 observations of the spectrum of the supernova remnant IC 443 in the energy range of 0.4-3 keV reveal the presence of a complex structure suggestive of emission from Fe XVIII-XX, S XV-XVI, and Si XIII-XIV ions. The best electron temperature in the band for simple model fits is about (6-11) x 10 to the 6th K. Raymond and Smith collisional equilibrium emission models do not adequately fit the data. These results are discussed in terms of possible nonequilibrium effects in the remnant.

Charles, P. A.↗

NASA NTRS1981

Pointed soft X-ray observations of AM Herculis from HEAO 1

Extensive soft X-ray (0.1-1.5 keV) observations of AM Herculis are reported. The data, acquired during two pointed observations by HEAO 1 in 1978, span four binary cycles and reveal considerable detail in the 3.09 hour light curve. Rapid X-ray flickering is evident throughout the bright section of the light curve and is characterized by an average e-folding autocorrelation time of about 10 s. Analysis of the spectral data indicates a 30% variability; on occasion the X-ray spectrum becomes softer as the source intensity decreases. The current understanding of AM Her as an accreting magnetic white dwarf is discussed, and various models are related to the present HEAO-1 data.

Tuohy, I. R.↗

NASA NTRS1980

A 5.57 hr modulation in the optical counterpart of 2S 1822-371

A periodic 5.57 hr modulation has been observed in the optical counterpart of the X-ray source 2S 1822-371. Two alternative periods are consistent with the data: P = 0.232114d and P = 0.232191d, with statistical uncertainties of 0.000015d in each case. Minimum light occurred at JD 2,444,105.668 + or - 0.005. The amplitude of the modulation is about 1 mag, independent of UBV color, and no variability exceeding the 2% level other than the 5.57 hr effect is found on time scales down to a few seconds. The light curve of the star can be understood in terms of a highly inclined close binary system which contains a relatively large, luminous accretion disk that is periodically occulted by a companion star and an associated gas stream. On the assumption that the companion is a main-sequence star, the distance of the system is found to be more than 600 pc, based on the absence of color variations commensurate with the 5.57 hr intensity cycle.

Mason, K. O.↗

NASA NTRS1980

AM Herculis - Simultaneous X-ray, optical, and near-IR coverage

A 6 hour X-ray pointing at AM Her using the HEAO 1 satellite is correlated with simultaneous broadband V and I photometry and visual circular polarimetry. The absence of correlations on either a flickering or an orbital time scale implies distinct regions for the visual and X-ray emission. Significant changes in the light curves are observed from one binary cycle to the next.

Szkody, P.↗

NASA NTRS1980

X-ray line emission from the supernova remnant G292.0 + 1.8

The Solid State Spectrometer on the Einstein Observatory has detected line emission from Mg, Si and S in the thermal X-ray spectrum of the supernova remnant G292.0 + 1.8. An over-abundance of sulfur and a probable under-abundance of iron relative to their solar values is indicated by the data. The X-ray and optical data for this object support an interpretation of emission originating in ejecta from the comparatively recent explosion of a massive (about 20-solar-mass) progenitor star.

Clark, D. H.↗

NASA NTRS1980

Soft X-ray observations of the supernova remnants HB 3 and 3C 58

The HEAO 1 A-2 low energy detectors have discovered soft X-ray emission from a source positionally coincident with the supernova remnant HB 3. The flux in the energy range 0.3-2.2 keV is about 6 x 10 to the -11th ergs per sq cm s. The spectral data are fitted to a hydrogen thermal bremsstrahlung model, and the physical parameters of the supernova remnant are estimated. The age derived is about 21,000 years, and the initial blast energy is about 3.1 x 10 to the 50th ergs. Upper limits to the soft X-ray flux and the luminosity of the supernova remnant 3 C 58 are also derived.

Galas, C. M. F.↗

NASA NTRS1980

Soft X-ray pulsations from SS Cygni

Pulsed soft X-rays (0.1 to 0.5 keV) with a period of 9 sec and a pulsed fraction that varies between 0 and 100% were detected from the dwarf nova SS Cygni at the peak of an optical outburst. This detection confirms for the first time the supposed high energy origin of optical pulsations seen in erupting dwarf novae. The pulse shape is remarkably sinusoidal for such a large-amplitude oscillation. The X-ray pulsation observed in this outburst is not coherent, in contrast to previous claims for the related optical oscillations.

Cordova, F. A.↗

NASA NTRS1980

X-ray line emission from the Tycho supernova remnant

The A-2 experiment onboard HEAO 1 has observed the X-ray spectrum of the Tycho supernova remnant in the energy range 0.5-20 keV. The spectrum reveals four significant line features: the K(alpha) lines of silicon, sulfur, and iron; and the L lines of iron. Comparisons between the silicon and sulfur equivalent widths and K(alpha) iron line energies of Tycho and Cas A suggest that the X-ray emitting plasma in Tycho is further from collisional ionization equilibrium than that in Cas A.

Pravdo, S. H.↗

NASA NTRS1979

Observation of soft X-ray emission from the supernova remnant HB9

The number of known X-ray emitting supernova remnants in our galaxy has significantly grown as a result of the soft X-ray survey by the HEAO-1 spacecraft. The HEAO-1 A-2 experiment has observed soft X-ray emission from the old supernova remnant HB9 which lies close to the previously identified X-ray source, Capella. Spectral data and the low optical obscuration in the direction of the remnant suggest that HB9 is a good candidate for detecting Fe XIV coronal forbidden-line emission. Mapping of the coronal line emission in association with the imaging X-ray data expected from HEAO-2 would allow the temperature profile of the emitting shell to be determined in a manner similar to that used by Tuohy, Nousek, and Garmire (1979) for the Cygnus Loop, which is in a similar evolutionary phase to HB9.

Tuohy, I. R.↗

NASA NTRS1979

Imaging X-ray observations and the temperature structure of the Cygnus Loop

Imaging X-ray observations of the northeast portion of the Cygnus Loop (NGC 6992) reveal that X-ray emission extends 5 arc min beyond the optical filaments. Comparison with Fe XIV 5303 forbidden line measurements across the emitting shell is consistent with a temperature gradient across the shell from 10 to the 6.1 K (outside) to 10 to the 6.3 K (inside). Both X-ray and Fe XIV forbidden line intensity and spatial structure can be explained by a Sedov adiabatic blast wave with a shock velocity of 290 plus or minus 15 km/s.

Tuohy, I. R.↗

NASA NTRS1979

X-ray line emission from the Tycho supernova remnant

The observation of the X-ray spectrum of the Tycho supernova remnant in the energy range 0.5 to 20 keV is discussed. Four significant line features in the spectrum: The K alpha lines of silicon, sulphur, and iron; and the L lines of iron are examined. Comparisons between the silicon and sulphur equivalent widths and K alpha iron line energies of Tycho and Cas A are discussed. Suggest that the X-ray emitting plasma in Tycho is further from collisional ionization equilibrium than that of Cas A.

Pravdo, S. H.↗

NASA NTRS1979

Discovery of X-ray emission from two southern supernova remnants

Two soft X-ray sources positionally coincident with the supernova remnants PKS 1209-52 and RCW 103 have been discovered by using the A-2 experiment on HEAO 1. Their measured fluxes are, respectively, about 1.4 x 10 to the -10th erg/cm-sec (0.2-1.0 keV) and about 1.8 x 10 to the -10th erg/cm-sec (0.6-2.0 keV). Spectral data are used to derive physical parameters for each remnant. For PKS 1209-52 the parameters are suggestive of the remnant's being in an advanced evolutionary phase, with shock-heated interstellar material producing the soft X-ray emission. RCW 103, in contrast, is known from radio and optical data to be in an earlier evolutionary phase, and the soft X-ray flux is most likely due to emission originating in a reflected shock wave or in plasma evaporated from shock-heated interstellar clouds.

Tuohy, I. R.↗

NASA NTRS1979

Evidence for X-ray emission from Kepler's supernova remnant

Evidence for weak soft X-ray emission from the remnant of Kepler's supernova has been acquired by the low energy detectors of the A 2 experiment on HEAO 1. A soft X-ray source has been detected using a narrow field of view sensitive to X rays between 0.2 and 3 keV and is found to be the only constant X-ray source within the error box containing Kepler's supernova remnant. The intensity of the X-ray source is calculated to be about 6.3 x 10 to the -2 counts/sq cm sec, with an intrinsic X-ray luminosity in the energy range 0.3 to 3 keV of about 28 x 10 to the 35 erg/sec if, as is widely believed, the remnant is at a distance of 4 kpc. Observations from HEAO 2 will allow the detection to be confirmed, the source to be imaged and its spectrum to be determined.

Tuohy, I. R.↗

NASA NTRS1979

HEAO-1 observations of AM Herculis between 0.1 and 3 keV

Results are reported for HEAO A2 scanning observations of AM Her in the energy range from 0.1 to 3 keV. A light curve of AM Her is plotted, a typical flux of 8 x 10 to the -10th erg/sq cm-sec in the 0.15-0.5-keV range at X-ray maximum is estimated, and no pronounced spectral variation with phase is detected. It is found that both a 0.025-keV blackbody spectrum and an exponential spectrum with an energy-dependent Gaunt factor provide an acceptable fit to the data. It is concluded that the spectrum of the radiation from the plasma at the surface of the strongly magnetic and relatively massive white dwarf in AM Her consists of three components: (1) a high-temperature (about 100 million to 1 billion K) component produced by electron-ion bremsstrahlung in the hot postshock plasma; (2) a blackbody component of about 100,000 to 1 million K produced by the heated surface of the white dwarf; and (3) a still softer component produced by optically thick electron cyclotron emission in the postshock region.

Tuohy, I. R.↗

NASA NTRS1978

New evidence on the nature of the soft X-ray source in AM Herculis from HEAO 1

Results are reported for scanning observations of AM Herculis from HEAO 1 during the period September 22-October 12, 1977. The soft X-ray light curve constructed from the observations shows considerable scatter in intensity, together with clear evidence for a residual flux during X-ray minimum. At X-ray maximum the flux in the energy range 0.15-0.5 keV is typically 8 x 10 to the -10th power erg/sq cm per sec. The spectrum of AM Her is characterized by a sharp turnover at 0.2 keV and is well described by a blackbody model with absorption. There is no appreciable change in the spectrum with binary phase. The present observations, when combined with theoretical models, imply that the soft X-rays are produced by the heated surface of the degenerate dwarf component, and that the surface has a temperature of approximately 400,000 K and a luminosity about 30 times that observed at optical or hard X-ray wavelengths. AM Her is predicted to be a spectacular UV source, with an intrinsic UV luminosity comparable to that in soft X-rays.

Tuohy, I. R.↗

NASA NTRS1976

Pulsed X-ray observations of Cen X-3 from Ariel-5

The 4.8 second X-ray pulsations from Centaurus X-3 were monitored by the MSSL collimated proportional counter on board Ariel-5 between 18-27 January 1975. Analysis of the source Doppler effect shows that the pulsation period of Cen X-3 decreased by 3.70 + or - 0.04 milliseconds during the preceding 2.3 years. The Doppler analysis also yields updated values for the binary phase and period of Cen X-3. Phase zero occurred at JD 2442438.628 + or - 0.003, and the average heliocentric binary period between October 1972 and January 1975 was 2.087129 + or - 0.000007 days. Light curves of the 4.8 second pulsations in the 3-9 keV band are characterized by two pronounced peaks, in contrast with the single peak profiles observed by Uhuru.

Tuohy, I. R.↗