Search

We have compared the results of a number of published class I methanol maser surveys with the catalogue of high-mass outflow candidates identified from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire survey (known as extended green objects or EGOs). We find class I methanol masers associated with approximately two-thirds of EGOs. Although the association between outflows and class I methanol masers has long been postulated on the basis of detailed studies of a small number of sources, this result demonstrates the relationship for the first time on a statistical basis. Despite the publication of a number of searches for class I methanol masers, a close physical association with another astrophysical object which could be targeted for the search is still lacking. The close association between class I methanol masers and EGOs therefore provides a large catalogue of candidate sources, most of which have not previously been searched for class I methanol masers. Interstellar masers and outflows have both been proposed to trace an evolutionary sequence for high-mass star formation, therefore a better understanding of the relationship between class I methanol masers and outflow offers the potential for comparison and amalgamation of these two evolutionary sequences.

A solar Stokes spectrum telescope has been built and is routinely used to measure full Stokes spectra of solar surface features. Its optical and electronic systems are outlined while the polarization analyzer is described in detail. The observations carried out by this telescope are sampled and the performance parameters are given. The measured Stokes spectra during solar cycle 23 show that the measurement accuracy of Stokes polarization components can reach an r.m.s. noise level of less than 9.0×10−4 with short time integration for an active region and 5.0×10−4 with long time integration for a weak field region without smoothing.

The D3 emission lines observed on a prominence over the solar east limb on 1984 May 5, which were found to consist of two components, i.e. the main and the broadened components, have been successfully calculated using the two-cloud model method with the multiplet of helium (3 D-3(3,2,1)-2 P-3(2,1,0)) taken into account. The results obtained show that the ejecta in front of the prominence are formed by the intermittent ejections of the matter from the plage region around the prominence, because there exist at least three distinguishable phases of the line-of-sight velocity, increasing during the observations. The turbulent velocity of the ejecta is rather large, about 29 km s(-1). The Doppler width of the ejecta is mainly the result of the non-thermal effect, and the thermal effect can be neglected compared with the non-thermal effect. The prominence is quiet and characterized by typical properties.

A new method of deriving the three-dimensional structures of the solar vector magnetic field and thermodynamic parameters from Stokes profiles is presented in this paper. Assuming scattering and atomic polarization can be ignored, the method consists of three coupled operations, which have different functions and act upon the Stokes profiles of one or two adjacent layers of the solar atmosphere. Applying the set of operations to various points of a chosen grid throughout the various layers of the atmosphere gives the 3D field structure and thermodynamic parameters of the area. A flow chart and detailed descriptions of the three operations are presented, and fitting of the theoretical profiles was made using a simplified program. The result shows that this method can yield rather satisfactorily the 3D spatial field structure, particularly the field intensity, while the derivation of the thermodynamic parameters needs further improvement.

We study the full evolution of low-mass white dwarfs with helium and oxygen cores. We revisit the age dichotomy observed in many white dwarf companions to millisecond pulsar on the basis of white dwarf configurations derived from binary evolution computations. We evolve 11 dwarf sequences for helium cores with final masses of 0.1604, 0.1869, 0.2026, 0.2495, 0.3056, 0.3333, 0.3515, 0.3844, 0.3986, 0.4160 and 0.4481 M⊙. In addition, we compute the evolution of five sequences for oxygen cores with final masses of 0.3515, 0.3844, 0.3986, 0.4160 and 0.4481 M⊙. A metallicity of Z = 0.02 is assumed. Gravitational settling, chemical and thermal diffusion are accounted for during the white dwarf regime. Our study reinforces the result that diffusion processes are a key ingredient in explaining the observed age and envelope dichotomy in low-mass helium-core white dwarfs, a conclusion we arrived at earlier on the basis of a simplified treatment for the binary evolution of progenitor stars. We determine the mass threshold where the age dichotomy occurs. For the oxygen white dwarf sequences, we report the occurrence of diffusion-induced, hydrogen-shell flashes, which, as in the case of their helium counterparts, strongly influence the late stages of white dwarf cooling. Finally, we present our results as a set of white dwarf mass-radius relations for helium and oxygen cores., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata