Correlation between Infrared Colors and Intensity Ratios of SiO Maser Lines

We present the results of SiO millimeter-line observations of a sample of known SiO maser sources covering a wide dust-temperature range. A cold part of the sample was selected from the SiO maser sources found in our recent SiO maser survey of cold dusty objects. The aim of the present research is to investigate the causes of the correlation between infrared colors and SiO maser intensity ratios among different transition lines. In particular, the correlation between infrared colors and SiO maser intensity ratio among the J=1-0 v=1, 2, and 3 lines are mainly concerned in this paper. We observed in total 75 SiO maser sources with the Nobeyama 45m telescope quasi-simultaneously in the SiO J=1-0 v=0, 1, 2, 3, 4 and J=2-1 v=1, 2 lines. We also observed the sample in the 29SiO J=1-0 v=0 and J=2-1 v=0, and 30SiO J=1-0 v=0 lines, and the H2O 6(1,6)-5(2,3) line. As reported in previous papers, we confirmed that the intensity ratios of the SiO J=1-0 v=2 to v=1 lines clearly correlate with infrared colors. In addition, we found possible correlation between infrared colors and the intensity ratios of the SiO J=1-0 v=3 to v=1&2 lines. Two overlap lines of H2O (i.e., 11(6,6) nu_2=1 -> 12(7,5) nu_2=0 and 5(0,5) nu_2=2 -> 6(3,4) nu_2=1) might explain these correlation if these overlap lines become stronger with increase of infrared colors, although the phenomena also might be explained by more fundamental ways if we take into account the variation of opacity from object to object.Comment: 49 pages, 7 figures, 3 tables, accepted for publication in ApJ. Full resolution version available at http://www.asiaa.sinica.edu.tw/~junichi/paper

Do Water Fountain Jets Really Indicate the Onset of the Morphological Metamorphosis of Circumstellar Envelopes?

The small-scale bipolar jets having short dynamical ages from "water fountain (WF)" sources are regarded as an indication of the onset of circumstellar envelope morphological metamorphosis of intermediate-mass stars. Such process usually happens at the end of the asymptotic giant branch (AGB) phase. However, recent studies found that WFs could be AGB stars or even early planetary nebulae. This fact prompted the idea that WFs may not necessarily be objects at the beginning of the morphological transition process. In the present work, we show that WFs could have different envelope morphologies by studying their spectral energy distribution profiles. Some WFs have spherical envelopes that resembles usual AGB stars, while others have aspherical envelopes which are more common to post-AGB stars. The results imply that WFs may not represent the earliest stage of the morphological metamorphosis. We further argue that the dynamical age of a WF jet, which can be calculated from maser proper motions, may not be the real age of the jet. The dynamical age cannot be used to justify the moment when the envelope begins to become aspherical, nor to tell the concrete evolutionary status of the object. A WF jet could be the innermost part of a larger well-developed jet, which is not necessarily a young jet.Comment: 21 pages, 4 figures, accepted for publication in MNRA

The Crystallography of Aluminum and its Alloys

This chapter begins with pure aluminium and a discussion of the form of the crystal structure and different unit cells that can be used to describe the crystal structure. Measurements of the face-centred cubic lattice parameter and thermal expansion coefficient in pure aluminium are reviewed and parametrisations given that allow the reader to evaluate them across the full range of temperatures where aluminium is a solid. A new concept called the vacancy triangle is introduced and demonstrated as an effective means for determining vacancy concentrations near the melting point of aluminium. The Debye-Waller factor, quantifying the thermal vibration of aluminium atoms in pure aluminium, is reviewed and parametrised over the full range of temperatures where aluminium is a solid. The nature of interatomic bonding and the history of its characterisation in pure aluminium is reviewed with the unequivocal conclusion that it is purely tetrahedral in nature. The crystallography of aluminium alloys is then discussed in terms of all of the concepts covered for pure aluminium, using prominent alloy examples. The electron density domain theory of solid-state nucleation and precipitate growth is introduced and discussed as a new means of rationalising phase transformations in alloys from a crystallographic point of view.Comment: 93 pages, 21 figures, 4 tables and 4 tabular appendices, 465 reference

CO in OH/IR stars close to the Galactic centre

Aims: A pilot project has been carried out to measure circumstellar CO emission from three OH/IR stars close to the Galactic centre. The intention was to find out whether it would be possible to conduct a large-scale survey for mass-loss rates using, for example, the Atacama Large Millimeter Array (ALMA). Such a survey would increase our understanding of the evolution of the Galactic bulge. Methods: Two millimetre-wave instruments were used: the Nobeyama Millimeter Array at 115 GHz and the Submillimeter Array at 230 GHz. An interferometer is necessary as a `spatial filter' in this region of space because of the confusion with interstellar CO emission. Results: Towards two of the stars, CO emission was detected with positions and radial velocities coinciding within the statistical errors with the corresponding data of the associated OH sources. However, for one of the stars the line profile is not what one expects for an unresolved expanding circumstellar envelope. We believe that this CO envelope is partially resolved and that this star therefore is a foreground star not belonging to the bulge. Conclusions: The results of the observations have shown that it is possible to detect line profiles of circumstellar CO from late-type stars both within and in the direction of the Galactic bulge. ALMA will be able to detect CO emission in short integrations with sensitivity sufficient to estimate mass-loss rates from a large number of such stars.Comment: 5 pages, 3 figure