We have obtained high-resolution images of two carbon-rich objects that are undergoing the transition from post-AGB star to planetary nebula: IRAS 21282+5050 (hereafter IRAS 21282), a young planetary nebula, and AFGL 3068, a post-AGB star with a high mass-loss rate. Detailed structure is seen in IRAS 21282. A torus of dust, with its polar axis in the N-S direction, surrounds the central star, i...

the interacting two winds model and a spherical density distribution function are introduced to study the dynamical and ionization structure of the planetary nebula ic 418. a fast wind with a mechanical luminousity  2/34×1034erg.s-1 of interacts with a super wind with a mass-loss rate of  2×10-5m(°)yr-1 and  a velocity of 10 , and produces a dense and luminous medium.   in this model, the expan...

We study the chemistry in the slow wind during the transition from AGB star to pre-planetary nebula (PPN) and planetary nebula (PN). We show that there is a very rich chemistry of degradation products created by photoprocessing, driven by the gradually hardening radiation field of the central star. Most of these products are, however, photodissociated during the PPN phase if the wind is smooth....

We have observed with the 30-m IRAM telescope, the CSO telescope and the ISO satellite (Infrared Space Observatory) the rotational lines of CO at millimeter, submillimeter and far infrared wavelengths in the direction of C-rich stellar objects at different stages of evolution : CRL 2688 (a very young Proto-Planetary Nebula), CRL 618 (a Proto-Planetary Nebula), and NGC 7027 (a young Planetary Ne...

We have observed Sakurai’s object in the S(1)λ2.121 line of H2 and in the J = 2 → 1 line of 12CO. We give upper limits on the H2 and 12CO emission from the planetary nebula associated with this object. Assuming a distance of 3.8 kpc, we obtain an upper limit on the mass of molecular hydrogen in the planetary nebula of 1.8 10−4 M for an excitation temperature of 1000 K and, for an excitation tem...

The [O III] λ5007 planetary nebula luminosity function (PNLF) occupies an important place on the extragalactic distance ladder: it is the only standard candle that can be applied to all the large galaxies of the Local Supercluster. We review the method’s precision, and use it to show that the distance scale defined by Cepheids and the Surface Brightness Fluctuation method is likely too large by...

Everything that became part of the primitive solar nebula first passed through the interstellar medium and the dense molecular cloud from which the nebula collapsed. We begin with a brief discussion of the connection between dense molecular clouds and the formation of solar-type stars. We then review processes that occur in these environments in order to constrain the chemical and physical prop...