The Flux Density Scale for radio Sources at 81·5 MHzScott, P., F.;Shakeshaft, J., R.
doi: 10.1093/mnras/154.1.19Ppmid: N/A
Abstract The flux densities at 81.5 MHz of 13 radio sources have been carefully measured with respect to those of Cas A and Cyg A. It is found that the flux densities of the weaker sources are systematically larger, by 22.5 per cent on average, than the values interpolated from the spectra listed by Kellermann, Pauliny-Toth and Williams. This is consistent with earlier suggestions that the KPW scale is too low for frequencies less than 750 MHz and implies that the apparent flattening of the spectra of the majority of sources at about this frequency may be largely removed. This content is only available as a PDF. © 1971 Royal Astronomical Society. Provided by the NASA Astrophysics Data System
A Compact Radio Component in M82Wilkinson, P., N.
doi: 10.1093/mnras/154.1.1Ppmid: N/A
Abstract Recent radio-link interferometer observations at J odrell Bank have shown that the nearby galaxy M82 contains a small radio component |$(\lt\,{0}^{\prime{}\prime}\,.7)$| , emitting ≈7 per cent of the total radio flux at 1423 MHz, whose spectrum exhibits a low frequency cut off. Several explanations for the cut off in the spectrum are considered. M82 appears to be another example of a galaxy having an ‘ active ’ core in Heeschen's definition. This content is only available as a PDF. © 1971 Royal Astronomical Society. Provided by the NASA Astrophysics Data System
On the V / Vm test Applied to Quasi-Stellar Radio Sources Rees, M., J.;Schmidt,, M.
doi: 10.1093/mnras/154.1.1pmid: N/A
Abstract The V / Vm test for a sample of quasi-stellar radio sources complete to given radio and optical flux densities has been recently discussed critically by Longair and Scheuer. Contrary to their claims, we argue that. (i) Proper inclusion of the optical limit increases the significance of the derived non-uniformity of the distribution of 3CR quasars very markedly. (ii) The test was devised to include the effect of unavoidable simultaneous selection according to radio and optical flux density of QSSs. The fact that the test depends little upon the association of a particular redshift with a particular QSS is incidental. (iii) |$\langle V/{V}_{m}\rangle$| for those sources in the sample that are radio limited is a measure of the non-uniformity of the space distribution of sources with a maximum value of |${F}_\text{rad}/{F}_\text{opt}$| —it is not a measure of the evolution of the radio properties of the QSSs. (iv) Longair's 1966 paper contains essentially no valid information on the evolution of QSSs. This content is only available as a PDF. © 1971 Royal Astronomical Society. Provided by the NASA Astrophysics Data System
Radiative Transfer in spherically symmetricsystems—II: The Non-Conservative case and Linearly Polarized RadiationCassinelli, J., P.;Hummer, D., G.
doi: 10.1093/mnras/154.1.9pmid: N/A
Abstract The method for the solution of transfer problems in spherically symmetric systems developed recently by Hummer and Rybicki is here generalized to the non-conservative case. This procedure, which depends on the iterative determination of the Eddington factor f = K / J , handles in a natural way the outward peaking of the radiation field which occurs in extended atmospheres. To illustrate the present extension of this method, solutions are obtained for the problem of scattering of linearly polarized radiation by an extended electron-scattering atmosphere. Although the transfer of radiation through such an atmosphere is conservative, each of the component equations is not. For opacity laws of the form |$k\rho \,=\,{r}^{-n},\,o\,\lt\,r\,\lt\,R,\,n\,=2\,\text{and}\,3$| , very large values of the polarization are found as a general feature arising from the strong peaking of the radiation field. It is found that the temperature distribution in such extended electron-scattering atmospheres differs negligibly from that computed on the assumption of isotropic scattering, with the neglect of polarization. The procedure used for the polarization problem can also be applied directly to problems with a non-grey opacity involving many frequencies simultaneously. This content is only available as a PDF. © 1971 Royal Astronomical Society. Provided by the NASA Astrophysics Data System
Quantitative Results of Stellar Evolution and Pulsation TheoriesFricke,, K.;Stobie, R., S.;Strittmatter, P., A.
doi: 10.1093/mnras/154.1.23pmid: N/A
Abstract The discrepancy between the masses of Cepheid variables deduced from evolution theory ( Mev ) and pulsation theory |$({M}_\text{Q},\,{M}_{\phi })$| is examined. It is shown that plausible systematic errors in interior opacity, distance calibration and the |${T}_\text{eff}-B-V$| relation can cause substantial errors in the derived masses. The mass Mϕ obtained for certain Cepheids from the non-linear pulsation theory through the pulsation period and phase of the secondary hump in the velocity curve is shown to provide a potentially strong constraint on allowable systematic errors in luminosity and effective temperature; some doubts as to the reliability of Mϕ and the predictions of the non-linear theory generally are, however, raised. While it appears unlikely that the entire Cepheid mass anomaly can be ascribed to a unique source, there is no difficulty in reconciling the mass discrepancy within the likely errors in physical and empirical data, particularly if doubts about Mϕ are substantiated. Although mass loss from Cepheid variables may indeed occur it is thus not ‘ required ’ by the data. The effects of the above systematic errors in other astrophysical contexts (e.g. solar neutrinos, Hyades mass–luminosity relation) are examined and the reliability of previously derived quantities discussed. The extreme sensitivity to input physical data of the evolutionary tracks in the post red giant phase is emphasized. In particular the length of the second crossing track is shown to depend strongly on the hydrogen abundance profile in the neighbourhood of the shell source. This content is only available as a PDF. © 1971 Royal Astronomical Society. Provided by the NASA Astrophysics Data System
Stars Without Circulation The Effect of Slight Differential Rotation in the Convective Core of Upper Main Sequence StarsMonaghan, J., J.
doi: 10.1093/mnras/154.1.47pmid: N/A
Abstract The effect of relaxing the usual, but poorly justified assumption, that convective regions in stars rotate rigidly, is examined by considering rotating stars with no circulation. Upper main sequence stars are examined in detail and the differential rotation in the radiative envelope is found to depend sensitively on the differential rotation in the convective core. A 0 . 5 per cent change in the angular velocity in the core from the value for rigid rotation may result in a 30 per cent change in the angular velocity on the equator. Some models are constructed which have zero angular velocity at the equator but they are found to be unstable near the edge of the star. This content is only available as a PDF. © 1971 Royal Astronomical Society. Provided by the NASA Astrophysics Data System
The Site of the Helium FlashOwen, Peter, Russell
doi: 10.1093/mnras/154.1.59pmid: N/A
Abstract Calculations have been made, using the Henyey method, of evolutionary sequences of stars approaching and at the time of the helium flash. Any hydrodynamical effects have been neglected. These calculations have been made for both Population I and Population II compositions. The effects of nitrogen burning and neutrino energy losses have been considered by constructing sequences both with and without these processes. For the Population I composition |$({X}_\text{CNO}\,=\,0.02)$| the flash is in a shell if there are neutrino losses whereas for Population II |$({X}_\text{CNO}\,=\,0.001)$| the flash is initially in a shell but is soon shifted to the centre, even though there are neutrino losses. As a result, if there are neutrino losses, the character of the flash is different in the two stellar populations. This may result in different evolution subsequently and in different H–R diagrams. The boundary between the two cases is at an initial composition in the range |$({X}_\text{CNO}\,=\,0.002)\,\text{to}\,0.003$| . This shift of the flash to the centre for Population II stars is a property of the nitrogen burning; it does not occur if nitrogen burning is neglected. Neglect of neutrinos puts the flash at the centre. Observed luminosities of stars at the peak of the red giant branch of globular clusters are consistent with theoretical predictions if these stars are making their first ascent of the giant branch. This content is only available as a PDF. © 1971 Royal Astronomical Society. Provided by the NASA Astrophysics Data System