Stavros Akras

A morpho-kinematic and spectroscopic study of the bipolar nebulae: M 2−9, Mz 3, and Hen 2−104

Context. Complex bipolar shapes can be generated either as a planetary nebula or a symbiotic system. The origin of the material ionised by the white dwarf is very different in these two scenarios, and it complicates the understanding of the morphologies of planetary nebulae. Aims. The physical properties, structure, and dynamics of the bipolar nebulae, M 2-9, Mz 3, and Hen 2-104, are investigated in detail with the aim of understanding their nature, shaping mechanisms, and evolutionary history. Methods. Long-slit optical echelle spectra are used to investigate the morpho-kinematics of M 2-9, Mz 3, and Hen 2-104. Near-infrared (NIR) data, as well as optical, spectra are used to separate Galactic symbiotic-type nebulae from genuine planetary nebulae by means of a 2MASS J-H/H-Ks diagram and a {\lambda}4363/H{\gamma} vs. {\lambda}5007/H\b{eta} diagnostic diagram, respectively. Results. The best-fitted 3-D models for M 2-9, Mz 3, and Hen 2-104 provide invaluable kinematical information on the expansion velocity of its nebular components by means of synthetic spectra. Kinematical ages of the different structures of M 2-9 and Mz 3 have also been determined. Both diagnostic diagrams show M 2-9 and Hen 2-104 to fall well within the category of having a symbiotic source, whereas Mz 3 borders the region of symbiotic and young planetary nebulae in the optical diagram. The optical diagnostic diagram is shown to successfully separate the two types of nebulae. Conclusions. The morphology, kinematics, and evolutionary history of M 2-9, Mz 3, and Hen 2-104 are better understood using the interactive 3-D modelling tool shape. The optical and NIR diagnostic diagrams used are important techniques for separating Galactic symbiotic-type nebulae from genuine planetary nebulae.

Deciphering the bipolar planetary nebula Abell 14 with 3D ionization and morphological studies

Abell 14 is a poorly studied object despite being considered a born again planetary nebula. We performed a detailed study of its 3D morphology and ionization structure using the SHAPE and MOCASSIN codes. We found that Abell 14 is a highly evolved, bipolar nebula with a kinematical age of

H2in low-ionization structures of planetary nebulae

\sim

Discovery of true, likely and possible symbiotic stars in the dwarf spheroidal NGC 205★

19,400 yr for a distance of 4 kpc. The high He abundance, and N/O ratio indicate a progenitor of 5

The bow-shock and high-speed jet in the faint, 40 arcmin diameter, outer halo of the evolved Helix planetary nebula (NGC 7293)

M_{\odot}

Proof of shock-excited H2 in low-ionization structure of PNe

that has experienced the third dredge-up and hot bottom burning phases. The stellar parameters of the central source reveal a star at a highly evolved stage near to the white dwarf cooling track, being inconsistent with the born again scenario. The nebula shows unexpectedly strong [N I]

Distance mapping technique and the 3-D structure of BD +30°3639

\lambda 5200

Low-ionization structures in planetary nebulae - I: physical, kinematic and excitation properties

and [O I]

Evidence for a [WR] or WEL-type binary nucleus in the bipolar planetary nebula Vy 1-2

\lambda 6300

Modelling the structure and kinematics of the Firework nebula: The nature of the GK Persei nova shell and its jet-like feature

emission lines indicating possible shock interactions. Abell 14 appears to be a member of a small group of highly evolved, extreme Type-I PNe. The members of this group lie at the lower-left corner of the PNe regime on the [N II]/H