Volume 7, Issue 3
September 1986, pages 131-240
pp 131-139 September 1986
Radio recombination lines are known to be observable at positions along the galactic ridge which are free of discrete continuum sources. Based on the results of a recent survey of H272α lines it is shown that most of the observed galactic ridge recombination lines can be explained as emission from outer low-density envelopes of normal Hn regions. The distribution of low-density ionized gas and discrete HII regions as a function of the distance from the galactic centre is also derived.
pp 141-153 September 1986
Observations of the H272α recombination line towards the galactic centre show features near VLSR= 0, −50 and + 36 kms−1. We have combined the parameters of these features with the available H166α measurements to obtain the properties of the ionized gas present along the line of sight and also in the ‘3 kpc arm’. For the line-of-sight ionized gas we get an electron density around 7 cm−3 and a pathlength through it ∼ 10–60 pc. The emission measure and the electron temperature are in the range 500–2900 pc cm−6 and 2000–6000 K. respectively. The ionized gas in the 3 kpc arm has an electron density of 30 cm−3 and extends over 9 pc along the line of sight if we assume an electron temperature of 104 K. Using the available upper limit to the intensity of the H351α recombination line, we show that the distributed ionized gas responsible for the dispersion of pulsar signals should have a temperature >4500 K. and a minimum filling factor of 20 per cent. We also show that recombination lines from the ‘warm ionized’ gas proposed by McKee & Ostriker (1977) should be detectable in the frequency range 100–150 MHz towards the galactic centre with the sensitivity available at present.
pp 155-170 September 1986
We present a detailed study of the inhomogeneous Stephani-Krasinski solution with time-dependent curvature index. In general, the cosmological behaviour of the models depends on six arbitrary functions of time. Such models are termed ‘private universes’ and cannot be in accord with observation in the most general case. Two simple models with changing topology are considered as illustrating examples. In one of these models the pressure turns out to be negative and hence a violation of the weak energy condition in the singularity theorems is possible. A brief review of other inhomogeneous cosmologies is included for the sake of clarity. It is shown that the geodesic equation can be reduced to a complicated differential equation, which depends on the three arbitrary functions involved. Therefore, it is difficult to obtain explicit formulas for the various observational relations.
pp 171-194 September 1986
Spectrophotometric and spectroscopic observations of CQ Cep — the shortest-period binary with WN component — are presented. Excepting the NV λ4603, the fluxes of all other emission lines show enhancement at minima. They can be explained by the Roche surfaces that take into account the strong wind of the WN7 component. Various radial velocity curves for emission and absorption give different orbital solutions with a general positive shift of λ axes. Although N IV λ4058 represents the true motion of the WN7 component, its flux variations are influenced by geometric effects. There is no signature of the companion. The extent of the atmosphere of CQ Cephei appears larger than in V444Cyg, another eclipsing binary with a Wolf-Rayet component.
pp 195-223 September 1986
Composite-spectrum binary stars generally consist of a late-type giant and a main-sequence star of type A or B. Their spectra are therefore rather confusing; but by a technique of digital subtraction of the spectra of appropriate single late-type giants, composite spectra can be split into their individual components. In favourable cases the radial velocities of both components can be measured and the mass ratio determined. The procedures are illustrated by reference to HR 6902, a fifth-magnitude composite-spectrum binary. Its components are shown to have spectral types of G9 II and B8 V, with a mass ratio of 1.31, and its orbit is determined. There is some evidence that the system shows eclipses. If it does, the masses of the components are 3.9 and 3.0M⊙ respectively, and HR 6902 becomes the sixth known member of the important class ofζ Aur binaries.
pp 225-236 September 1986
New observations of the jet in 3C 273 support and refine our earlier interpretation that (i) the mapped jet is 106±0.3 yr old and grows at 0.6 to 0.75 times the speed of light, at an average angle θ of (20 ± 10)‡ with respect to the line of sight; (ii) its twin is not seen yet because arriving signals were emitted when it was some 100.6±0.2 times younger; (iii) the fluid moving in the jet is an extremely relativistice±-pair plasma, of bulk Lorentz factor γ >102; (iv) the beam has swung in projection through some 10‡; and (v) the small excursions (wiggles) of the jet around its average propagation direction result from a self-stabilizing interaction with the nonstatic ambient plasma. All other interpretations of which we are aware depend heavily on the (‘beaming’) assumption that the jet material radiates isotropically in some (comoving) Lorentz frame, an assumption which we consider unrealistic.
pp 237-240 September 1986
The source IRAS 03134 + 5958 identified by Iyengar & Verma (1984) on the Palomar Observatory Sky Survey (POSS) prints with a nonstellar optical object with [P – R]≃ 5.3 ± 1.5 is near the edge of Lynds dark cloud No. 1384 and is either embedded in or behind the cloud. The galactic latitude of this source (bII = 2‡.3), its positionvis-a-vis the Lynds dark cloud, its nonstellar appearance, high [P – R] colour and its far-infrared spectrum, all suggest the possibility of its being a Herbig-Haro (HH) object. To test this possibility we undertook measurements of its proper motion and variability (two of the characteristic properties of HH objects). These yield μa = (3.6 ± 2.3) arcsec/century and μδ= (−1.2 ± 2.0) arcsec/century for its proper motion. The source reveals large variation in brightness between 1950 and 1954. Optical line studies of the source are required to confirm its classification as an HH object.
Volume 41, 2020
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