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The line energy, equivalent width, binary phase dependence, and intrinsic width of the iron line emission feature observed in the low state sepctrum of Hercules X-1 are examined. Deductions are made concerning secondary X-ray emission from this binary system.
SAS 3 observations reveal a pulsation period of 3.61 sec for the transient X-ray source 4U0115+63. Positional measurement is accurate to approximately 30 arc s, and has led to the likely identification of an optical counterpart. The intensity of the pulses, as reported on 5.9 January 1978, is given as approximately 1.7 times that of the Crab Nebula (1-27 keV). Spectral information was also obtained from the ratios of counting rates in the first three energy channels of the center slat collimator detector (1-27 keV). Two classes of models are proposed to explain the transient nature of the X-ray sources: (1) episodic mass transfer in a binary system, and (2) eccentric binary orbits.
A soft X-ray spectrum of Capella has been obtained with the HEAO 1 satellite. Only models which include intense line emission at 0.85 keV can adequately explain the data. The spectrum is consistent with emission from an isothermal solar-abundance plasma with a temperature of 10.5 million (+ or - 2.8 million) K. It is also consistent with a blend of temperatures between 4 and 20 million K. The intensity of the X-ray emission is constant over 2 days and similar to the intensity observed by ANS.
The optical counterpart of 4U 1735-44, X-ray burst source MXB 1735-44, was studied with the 1.5-m telescope at Cerro Tololo, and by SAS 3, during the period between June 1 and 3, 1978. Explanations for the optical activity are discussed in terms of accretion instabilities onto a neutron star, or thermonuclear flashes on the neutron star itself. Attention is given to the timing of the bursts, which indicate that the burst source probably is located in a region within 1-2 light seconds from the X-ray source. In the binary case, it is noted that the optical emission is probably removed from the X-ray heated stellar atmosphere of the possible companion.
SAS 3 observations of a complete orbital cycle (about 3.5 days) of the X-ray source 4U 1700-37 are presented. A persistent, approximately sinusoidal modulation of about 60% amplitude is present in the data at 97 minutes. Satellite orbital effects are ruled out by using other detectors pointed away from the source but sampled at the same time. The effect of such a long rotation period (if indeed the period is rotational) on current ideas involving accretion torques and stellar wind is discussed.
During an extensive program of direct imagery of emission nebulae, arcuate structures were found around two stars. A well-defined shock-like structure was found about the T-Orionis variable LL Orionis, located to the side of the Orion Nebula. A less extensive shock-like structure was also found about the runaway star zeta Ophiuchus. These structures can best be described in terms of distorted interstellar bubbles. A direct consequence of this interpretation is an independent estimate of the rates of mass loss for these stars.
The Viking spacecraft are described as well as the instruments carried to accomplish the combined goal of studying the atmosphere and geology of the entire planet, and to analyze the Martian soil and search for life in two specific locations. Imagery received from the spacecraft illustrate discussions of the planetary surface, composition, and winds. Suggestions for further reading are included along with a list of available NASA film. Experiments and activities for classroom use are described.
Results are reported for HEAO 1 observations of Her X-1 which confirm the existence of the iron line-emission feature discovered with OSO 8 in the high-state spectrum and also reveal an iron emission feature in the low-state spectrum. The iron line-emission feature in the low-state spectrum was detected at a significance level greater than 5 sigmas and is characterized by a line energy of 6.4 keV, an equivalent width larger than that of the high-state line, a binary phase dependence of the line intensity, and a line width that is intrinsically narrow in contrast to the broad high-state line. The observed line energy and narrow line width are shown to be consistent with an interpretation in terms of fluorescence emission due to X-ray heating. It is suggested that HZ Her contributes no more than about 10% of the predicted line flux, that this emission is reflected from a highly ionized plasma, and that a hot coronal gas is an important source of the low-state X-rays.
Following the suggestion by Jura and Jacoby (1976), linearly polarized blue continuum starlight scattered by the dust shell around the M2 Iab star Alpha Orionis (Betelgeuse) has been discovered. The polarization has been traced in the NE, NW, SE, and SW directions and has positive (tangential) orientation. Some asymmetry of the optical depth in the shell exists 15 and 30 arcsec from the star. In the NE direction the polarization was measured as far as 90 arcsec (17,000 AU) from the star. The dependence of the average intensity of the scattered light from the nebula on angular distance from the star is more consistent with an inverse-square density law than with inverse 1.5 or inverse-cube laws. Assuming that the density is proportional to the inverse square of distance from the star, the scattering optical depth in blue light along a radius of 0.03 arcsec is no more than 0.15 + or - 0.05. Future observations of the wavelength dependence of polarization will allow a determination of grain size.
During April 1976 a soft X-ray flux was detected with SAS 3 from the vicinity of 2A 1102+384. The average flux densities were 4.3 x 10 to the -11th and 14 x 10 to the -11th erg/sq cm per sec in the energy bands 0.1-0.28 keV and 1-6 keV, respectively. There is an indication of variability over about 0.5 day in the lowest energy band. An upper limit of 3 x 10 to the 20th H atoms per sq cm is found for the gas column density to the X-ray source. In May 1978, observations with the modulation collimators of SAS 3 yielded an accurate (40 arcsec error radius) position for the X-ray source (2-6 keV) at right ascension 11 h 1 m 39.7 s, declination + 38 deg 28 min 51 sec (equinox 1950). The earlier tentative identification by Ricketts et al. (1976) with the BL Lacertae object B2 1101+38 = Markarian 421 is thus confirmed.
Data are presented from a HEAO 1 scanning observation of the Virgo cluster in December 1977. The L-shell iron lines at 1.1 keV have been observed in the spectrum of this source. The iron abundance derived is consistent with previous determinations from the 6.7-keV line. The HEAO data also indicate that the source is extended with FWHM of about 1 deg of arc.
Results are reported for far-IR, CO, 8-GHz, 15-GHz, H2O, and near-IR observations of a compact far-IR source (designated IR 12.4+0.5) in the M17 molecular cloud, as well as for CO and near-IR observations of a CO peak (designated MC 12.8+0.5) 24 arcmin to the NE of IR 12.4+0.5. The observed far-IR signal from IR 12.4+0.5 is found to correspond to a flux of 2400 Jy at 69 microns for a color temperature of 70 K, and the FWHM size of the source is estimated to be about 36 arcsec. The CO data for both sources and the observed reddening of background giants are shown to indicate high column densities; the existence of internal heat sources is inferred from the measured CO temperatures and the far-IR emission. It is concluded that the two sources are probably sites of very recent or ongoing star formation and that IR 12.4+0.5 is consistent with the 'cocoon star' model of early star formation.
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.
'Slow-moving Object Kowal' was discovered as an asteroidal object of photographic magnitude about 18 on photographic plates made on October 18 and 19, 1977 with the 122-cm Schmidt telescope at Palomar Observatory. It was determined that the object was located between 14 and 17 AU from the earth in a low-inclination, near-circular orbit. Examination of subsequent plates and earlier observations of the area allowed a more exact calculation of the orbital elements, which suggest the object to be in 3:5 resonance with Saturn at a perihelion of 8.5 AU. The object's orbital behavior suggests that of an inactive comet perturbed by Saturn from a previous orbit, however its magnitude is uncharacteristically large for a comet. It is proposed that object Kowal was once an ordinary minor planet that was deflected into its present orbit by collisions with other minor planets and a series of encounters with Jupiter and Saturn. The object has received the minor planet number (2060) and the name of Chiron has been proposed.
Two volcanic plumes were discovered on an image of Io taken as part of the Voyager optical navigation effort. This is the first evidence of active volcanism on any body in the solar system other than earth.
The HEAO 1 modulation-collimator data associate the X-ray emission from the Cygnus A region (4U 1957 + 40) with a small area including the radio galaxy. The source appears to be extended, with a size of about 2 arcmin; it may have a complex geometry. Any point-source component must have a flux no greater than 1.3 UFU. A lower limit of 1 microgauss is placed on the magnetic field in the radio lobes, based on the upper limit on the X-ray flux due to inverse Compton scattering of radio electrons on the 2.7-K microwave background radiation. The X-ray emission is more likely due to driven accretion of the intercluster gas onto the giant cD radio galaxy. Therefore this source appears to be similar to the Virgo and Perseus clusters. The density derived for the X-ray-emitting gas is too small for its thermal pressure to confine the radio source.
During an extensive program of direct imagery of emission nebulae, arcuate structures have been found around two stars. A well-defined shocklike structure is found about the T Orionis variable LL Ori, located to the side of the Orion Nebula. A less extensive shocklike structure is also found about the runaway star Zeta Oph. These structures can be best described in terms of distorted interstellar bubbles. A direct consequence of this interpretation is an independent estimate of the rates of mass loss for these stars.
The detection of a point source of soft X-rays (H0405-08) consistent with the position of the nearby triple star system 40 Eridani is reported. The source, which has a temperature near 10 million K, has a flux of 3 x 10 to the -11th erg/sqcm-sec at earth, implying a luminosity of 9(+ or -3) x 10 to the 28th erg/s at the distance of 40 Eridani. The likely source of the bulk of the X-rays is considered, including the K1 dwarf, the DA white dwarf, the dwarf M4 flare star, or accretion onto the white dwarf.