PyNeb is a Python package widely used to model emission lines in gaseous nebulae. We take advantage of its object-oriented architecture, class methods, and historical atomic database to structure a practical environment for atomic data assessment. Our aim is to reduce the uncertainties in parameter space (line-ratio diagnostics, electron density

For more than six decades, the quest to understand the formation of hot (about 20,000-30,000 K) extreme horizontal branch (EHB) stars in Galactic globular clusters has remained one of the most elusive in stellar evolutionary theory. Here we report on two discoveries that challenge the idea of the stable luminosity of EHB stars. The first mode of

PHOEBE 2 is a Python package for modeling the observables of eclipsing star systems, but until now it has focused entirely on the forward model—that is, generating a synthetic model given fixed values of a large number of parameters describing the system and the observations. The inverse problem, obtaining orbital and stellar parameters given

We present the discovery and characterisation of the post-common-envelope central star system in the planetary nebula PN G283.7-05.1. Deep images taken as part of the POPIPlaN survey indicate that the nebula may possess a bipolar morphology similar to other post-common-envelope planetary nebulae. Simultaneous light and radial velocity curve

We present a detailed study of the binary central star of the planetary nebula ETHOS 1 (PN G068.1+11.0). Simultaneous modelling of light and radial velocity curves reveals the binary to comprise a hot and massive pre-white dwarf with an M-type main-sequence companion. A good fit to the observations was found with a companion that follows expected

We compile published spectroscopic data and [O III] magnitudes of almost 500 extragalactic planetary nebulae (PNe) in 13 galaxies of various masses and morphological types. This is the first paper of a series that aims to analyse the PN populations and their progenitors in these galaxies. Although the samples are not complete or homogeneous, we

Eight planetary nebulae have been identified as 'born-again', a class of object typified by knotty secondary ejecta having low masses (${\sim}10^{-4}$ M ☉) with nearly no hydrogen. Abell 30, the archetype of the class, also belongs to a small subset of planetary nebulae that exhibit extreme abundance discrepancy factors (where Abell 30 is the most

The long-standing difference in chemical abundances determined from optical recombination lines and collisionally excited lines raises questions about our understanding of atomic physics, as well as the assumptions made when determining physical conditions and chemical abundances in astrophysical nebulae. Here, we study the recombination

We present a reassessment of the radial abundance gradients of C, N, O, Ne, S, Cl, and Ar in the Milky Way using deep spectra of 33 H II regions gathered from the literature, covering Galactocentric distances from 6 to 17 kpc. The distances of the objects have been revised using Gaia parallaxes. We recalculate the physical conditions and ionic

It has long been suspected that tidal forces in close binary stars could modify the orientation of the pulsation axis of the constituent stars. Such stars have been searched for, but until now never detected. Here we report the discovery of tidally trapped pulsations in the ellipsoidal variable HD 74423 in Transiting Exoplanet Survey Satellite

We determine the radial abundance gradient of helium in the disc of the Galaxy from published spectra of 19 H II regions and ring nebulae surrounding massive O-type stars. We revise the Galactocentric distances of the objects considering Gaia DR2 parallaxes (Gaia Collaboration 2018) and determine the physical conditions and the ionic abundance of

The INT Galactic Plane Survey (IGAPS) is the merger of the optical photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. Here, we present the IGAPS point source catalogue. It contains 295.4 million rows providing photometry in the filters, i, r, narrow-band Hα, g, and U RGO. The

CO Cam (TIC 160268882) is the second 'single-sided pulsator' to be discovered. These are stars where one hemisphere pulsates with a significantly higher amplitude than the other side of the star. CO Cam is a binary star comprised of an Am δ Sct primary star with T eff = 7070 ± 150 K, and a spectroscopically undetected G main-sequence secondary star

Context. AT 2019abn was discovered in the nearby M51 galaxy by the Zwicky Transient Facility at more than two magnitudes and around three weeks prior to its optical peak. Aims: We aim to conduct a detailed photometric and spectroscopic follow-up campaign for AT 2019abn, with early discovery allowing for significant pre-maximum observations of an

Traditionally, the effects of interstellar extinction on binary star light curves have been treated as a uniform reduction in the observed brightness of the system that is independent of the orbital phase. However, unless the orbital plane of the system coincides with the plane of the sky, or if the two stars are completely identical and present

Context. It has become clear in recent years that binarity plays a crucial role in many aspects of planetary nebulae (PNe), particularly with regard to the striking morphologies they exhibit. To date, there are nearly 60 known binary central stars of PNe (bCSPNe). However, both theory and observation indicate that this figure represents only the

Fulfilling the goals of space-based exoplanetary transit surveys, like Kepler and TESS, is impossible without ground-based spectroscopic follow-up. In particular, the first-step vetting of candidates could easily necessitate several hundreds of hours of telescope time—an area where 2 m class telescopes can play a crucial role. Here, we describe the

We present deep spectrophotometry of 18 H II regions in the nearby massive spiral galaxies M 101 and M 31. We have obtained direct determinations of electron temperature in all the nebulae. We detect the C II 4267 Å line in several H II regions, permitting to derive the radial gradient of C/H in both galaxies. We also determine the radial gradients

Recent studies have indicated that triple-star systems may play a role in the formation of an appreciable number of planetary nebulae, however, only one triple central star is known to date (and that system is likely too wide to have had much influence on the evolution of its component stars). Here, we consider the possibility that Sh 2-71 was

We report the first unambiguous observational evidence of Rydberg Enhanced Recombination (RER), a potentially important recombination mechanism that has hitherto been unexplored in low-temperature photoionized plasmas. RER shares similarities with dielectronic recombination, with the difference that the electron is captured into a highly excited