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Abstract.We present the results of our studies of Be stars within the Magellanic Clouds. We have studied the Be population within four young populous clusters, NGC 330 in the SMC, NGC 1818, 2004 and 2100 in the LMC as well as the field population around NGC 2004. The Be fraction within each cluster is seen to peak towards the luminosity of the main sequence turnoff. The field, which exhibits a large spread of ages, has a Be fraction more uniformly distributed in luminosity. We interpret this difference as evidence for an evolutionary enhancement of the Be phenomenon that occurs towards the end of the main sequence lifetime.

Carbon stars have always been amongst the most intriguing of stars which show grossly non-solar abundances. All such stars raise the questions:(a) at what stage of stellar evolution does this peculiar abundance phase occur?(b) do all stars pass through this stage?(c) is the phase significant in the overall picture of galactic nucleosynthesis?

White dwarfs fall in two main categories (1) the group with H-rich atmospheres (DA) the most numerous, and (2) the group with He-rich atmospheres (DB, DC, DF, DG, λ4670). Calculations of element separation (via gravitational settling) and convective mixing in white dwarf models have been made by Koester (1976) and Vauclair and Reisse (1977) in order to understand the existence and maintenance of these distinct groups and to predict at what stage during the cooling of the white dwarf some connection may occur between the two groups. Over the last few years, Wickramasinghe, Bessell and Cottrell (Wickramasinghe et al., 1977; Cottrell et al., 1977; Bessell and Wickramasinghe, 1979; Bessell, 1978 and Wickramasinghe and Bessell, 1979) have investigated the properties of cool (T < 6000K white dwarfs observationally and theoretically. We have attempted to establish at what temperature mixing does occur in DA white dwarfs, whether cool white dwarfs could be confused with G, K and M dwarfs, and if one can discriminate spectroscopically cool He and H-rich white dwarfs. In this paper we will discuss the spectra and colors of the coolest (Te < 5000K white dwarfs and compare them with model atmosphere calculations.

We have investigated the interstellar reddening law of young open clusters within 3kpc from the Sun using optical, near-IR 2MASS, and Spitzer IRAC data. The total-to-selective extinction ratio R V of 162 young open clusters (log t age 7.3) listed in the open cluster database WEBDA is determined from the color excess ratios. The young open clusters in the Sgr-Car arm show a relatively higher R V , those in the Per arm and in the Cygnus region of the local arm show a relatively smaller value, and those in the Mon-CMa region of the local arm show a normal value (R V ≈ 3.1).

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