We report deep spectroscopy of 10 planetary nebulae (PNe) in the Andromeda Galaxy (M31) using the 10.4 m Gran Telescopio Canarias (GTC). Our targets reside in different regions of M31, including halo streams and the dwarf satellite M32, and kinematically deviate from the extended disk. The temperature-sensitive [O III] λ4363 line is observed in all

The characterization of stellar streams in the Milky Way halo can provide important observational constraints on the ΛCDM cosmological model, which posits that galaxies form via the accretion of smaller satellites. One such stream, the 300 km/s stellar stream near the dwarf galaxy Segue 1 (300S), was detected in narrow-field spectroscopic surveys

To better understand how galaxy clusters form, we look at their progenitors which have not yet virialized: protoclusters. We use the Planck Collaboration (2016) published list of 2,151 protocluster candidate sources to explore further characterization as bonafide protoclusters or other extragalactic phenomena. We investigate the correlation of

Supermassive black holes, with masses more than a million times that of the Sun, seem to inhabit the centres of all massive galaxies. Cosmologically motivated theories of galaxy formation require feedback from these supermassive black holes to regulate star formation. In the absence of such feedback, state-of-the-art numerical simulations fail to

The combination of asteroseismologically measured masses with abundances from detailed analyses of stellar atmospheres challenges our fundamental knowledge of stars and our ability to model them. Ancient red-giant stars in the Galactic thick disc are proving to be most troublesome in this regard. They are older than 5 Gyr, a lifetime corresponding

In contrast to the situation in a laboratory, the study of the solar atmosphere has to be pursued without direct access to the physical conditions of interest. Information is therefore incomplete and uncertain and inference methods need to be employed to diagnose the physical conditions and processes. One of such methods, solar atmospheric