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Register a new userObserved relationship between CO2-1 and dust emission during post-AGB phase
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A CO,2-1 line survey is performed toward a sample of 58 high Galactic latitude post-AGB (pAGB) stars. To complement the observations, a compilation of literature CO,2-1 line data of known pAGB stars is done. After combining the datasets, CO,2-1 line data are available for 133 pAGB stars (about 34 per cent of known pAGB stars) among which 44 are detections. The CO line strengths are compared with infrared dust emission for these pAGB stars by defining a ratio between the integrated CO,2-1 line flux and {it IRAS} 25,mu flux density (CO-IR ratio). The relationship between the CO-IR ratio and the {it IRAS} color C23 (defined with the 25 and 60,mu flux densities) is called here the CO-IR diagram. The pAGB objects are found to be located between AGB stars and planetary nebulae (PNe), and segregate into three distinctive groups (I, II and III) on the CO-IR diagram. By analyzing their various properties such as chemical types, spectral types, binarity, circumstellar envelope expansion velocities, and pAGB sub-types on the CO-IR diagram, it is argued that the group-I objects are mainly intermediate mass C-rich pAGB stars in early pAGB stage (almost all of the considered carbon rich `21,mu stars belong to this group); the group-II objects are massive or intermediate mass pAGB stars which already follow the profound trend of PNe; and the group-III objects are mainly low mass binary pAGB stars with very weak CO,2-1 line emission (almost all of the considered RV,Tau variables belong to this group). The CO-IR diagram is proven to be a powerful tool to investigate the co-evolution of circumstellar gas and dust during the short pAGB stage of stellar evolution.
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Measuring molecular gas mass is vital for understanding the evolution of galaxies at high redshifts (z$geq$1). Most measurements rely on CO as a tracer, but dependences on metallicity, dynamics and surface density lead to systematic uncertainties in high-z galaxies, where these physical properties are difficult to observe, and where the physical environments can differ systematically from those at z=0. Dust continuum emission provides a potential alternative assuming a known dust/gas ratio, but this must be calibrated on a direct gas tracer at z$geq$1. In this paper we consider the [CI] 492-GHz emission line, which has been shown to trace molecular gas closely throughout Galactic clouds and has the advantages of being optically thin in typical conditions (unlike CO), and being observable at accessible frequencies at high redshifts (in contrast to the low-excitation lines of CO). We use the Atacama Large Millimetre/submillimetre Array (ALMA) to measure [CI], CO(4-3) and dust emission in a representative sample of star-forming galaxies at z=1, and combine these data with multi-wavelength spectral energy distributions to study relationships between dust and gas components of galaxies. We uncover a strong [CI]-dust correlation, suggesting that both trace similar phases of the gas. By incorporating other samples from the literature, we show that this correlation persists over a wide range of luminosities and redshifts up to z$sim$4. Finally we explore the implications of our results as an independent test of literature calibrations for dust as a tracer of gas mass, and for predicting the CI abundance.
There is ample evidence for strong magnetic fields in the envelopes of (Post-)Asymptotic Giant Branch (AGB) stars as well as supergiant stars. The origin and role of these fields are still unclear. This paper updates the current status of magnetic field observations around AGB, post-AGB stars and describes their possible role during these stages of evolution. The discovery of magnetically aligned dust around a supergiant star is also highlighted. In our search for the origin of the magnetic fields, recent observations show the signatures of possible magnetic activity and rotation, indicating that the magnetic fields might be intrinsic to the AGB stars.
We present the results of our search for low- and intermediate mass evolved stars in the outer Galaxy using AllWISE catalogue photometry. We show that the [3.4]-[12] versus [4.6]-[22] colour-colour diagram is most suitable for separating C-rich/O-rich AGB and post- AGB star candidates. We are able to select 2,510 AGB and 24,821 post-AGB star candidates. However, the latter are severely mixed with the known young stellar objects in this diagram.
This review presents the latest advances in the nebular studies of post-AGB objects. Post-AGB stars are great tools to test nucleosynthesis and evolution models for stars of low and intermediate masses, and the evolution of dust in harsh environment. I will present the newly discovered class of post-RGB stars, formed via binary interaction on the RGB. Binary systems can also lead to the formation of two class of aspherical post-AGB, the Proto-Planetary Nebulae and the naked post-AGBs (dusty RV Taus , a.k.a. Van Winckels stars).
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