Related papers: Abell 30 -- A Binary Central Star Among the Born-A…

We present observations proving the close binary nature of the central stars belonging to the planetary nebulae (PNe) NGC 6326 and NGC 6778. Photometric monitoring reveals irradiated lightcurves with orbital periods of 0.372 and 0.1534…

We present the analysis of OGLE-2016-BLG-0613, for which the lensing light curve appears to be that of a typical binary-lens event with two caustic spikes but with a discontinuous feature on the trough between the spikes. We find that the…

Previous work indicates that about 10% of planetary-nebula nuclei (PNNi) are photometrically variable short-period binaries with periods of hours to a few days. These systems have most likely descended from common-envelope (CE) interactions…

Hot subdwarf B stars (sdBs) in close binary systems are assumed to be formed via common envelope ejection. According to theoretical models, the amount of energy and angular momentum deposited in the common envelope scales with the mass of…

Due to thermal pulses, asymptotic giant branch (AGB) stars experience periods of convective mixing that provide ideal conditions for slow neutron-capture nucleosynthesis. These processes are affected by large uncertainties and are still not…

During an analysis of optical spectra of 80 young star clusters in several nearby spiral galaxies, [O III] and [N II] emission lines were noted in some cases. Three of these emission line sources are identified as likely planetary nebula…

We measure the Balmer decrements of 23 of the brightest planetary nebulae (PNe) in the inner bulge ($r \lesssim 3$ arcmin) of M31 and de-redden the bright end of the region's [O III] $\lambda 5007$ planetary nebula luminosity function. We…

Our ongoing spectroscopic survey of faint planetary-nebula nuclei (PNNi) has revealed 30 new hydrogen-deficient central stars. The majority of them (21) belong to the PG1159 spectral class (having He-C-O-dominated atmospheres). They…

AGB stars are responsible for producing a variety of elements, including carbon, nitrogen, and the heavy elements produced in the slow neutron-capture process ($s$-elements). There are many uncertainties involved in modelling the evolution…

Close binarity can play a significant role in the shaping of planetary nebulae (PNe) as the system evolves through the common-envelope phase. We present the detection of two of the shortest orbital periods among PN binary central stars.…

We present the discovery of a 3h5m orbital-period binary star at the heart of the planetary nebula M 3-1 - the shortest period photometrically-variable central star known and second only to V458 Vul, in general. Combined modelling of light…

Planetary nebulae are formed by the matter ejected by low-to-intermediate mass stars (~0.8-8 times the mass of the Sun) towards the end of their lives. As hydrogen and then helium fuel sources run out, stars expand. During these giant…

A project which aims to understand the abundance patterns of He, C, N, O, Ne, S, and Ar for a small sample of planetary nebulae is described. Abundance ratios of O/H, C/O, and N/O especially show a broad range relative to their solar…

We present constraints on the variability and binarity of young stars in the central 10 arcseconds (~0.4 pc) of the Milky Way Galactic Center (GC) using Keck Adaptive Optics data over a 12 year baseline. Given our experiment's photometric…

Multiplicity is ubiquitous among massive stars. While the stellar components usually display similar masses, some binaries with extremely low mass ratios were also observed. Some of them are primordial, while others arise from binary…

A sample of bright contact binary stars (W UMa-type or EW, and related: with beta Lyr light curves, EB, and ellipsoidal, ELL - in effect, all but the detached, EA), to the limit of Vmax = 7.5 magnitude is deemed to include all discoverable…

Planetary nebulae represent a potential late stage of stellar evolution, however the central stars (CSPNe) are relatively faint and therefore pertinent information is merely available for <20% of the Galactic sample. Consequently, the…

The results of long-term surveys of radial velocities of cool Ap and Am stars are presented. There are two samples, one of about 100 Ap stars and the other of 86 Am stars. Both have been observed with the CORAVEL scanner from Observatoire…

We present the results of optical spectroscopic observations of 54 candidate evolved massive stars revealed through the detection of mid-infrared nebulae of various shapes surrounding them with the {\it Spitzer Space Telescope} and {\it…

Almost all massive stars have bound stellar companions, existing in binaries or higher-order multiples. While binarity is theorized to be an essential feature of how massive stars form, essentially all information about such properties is…