Creatures
Massive Stars
Massive stars (Mini > 8 Mo) stand as powerful cosmic engines, which play a major role in the evolution of galaxies throughout the history of the Universe. During their short lifetime, they enrich the interstellar medium with elements synthesized in the stellar interior and provide large amounts of mechanical energy, which shapes the surroundings via steady powerful winds, massive eruptions or, on a larger scale, supernova explosions. Spending most of their life as core hydrogen burning OB-type stars, massive stars radiate much of their energy in the ultraviolet regime ionizing the circumstellar gas and heating the circumstellar dust, which in turn, gives rise to the energy output of galaxies in the infrared. The rarity of massive stars is compensated by their high luminosity, which renders them ideal observational beacons valuable for investigating the stellar evolution in diverse environments in the Local Group galaxies and beyond.
Yellow Hypergiants
Yellow hypergiants (YHGs) constitute a short-term and poorly-understood state of evolved massive stars, which have survived a red supergiant (RSG) phase and exhibit a blueward evolution towards the hot upper region of the Hertzsprung-Russell diagram. They are characterized by extended atmospheric structures and high mass loss rates, while they are shown to display outbursts when approaching the cool limit of the instability zone known as the 'Yellow Void'. Due to their rarity, less than fifteen YHGs have been reported in the Galaxy and the Magellanic Clouds, as well as Var A in M33. In my latest article, I exploit the wealth of archival data along with spectroscopy obtained with the Gran Telescopio Canarias to suggest the discovery of a strong YHG candidate and several dusty post-RSG stars in M33, which are proposed for follow-up spectroscopic investigation and monitoring.
Massive eclipsing binaries
Eclipsing binaries are stellar systems of two or more components occulting each other's light due to the high inclination of their orbital plane with respect to the observer. Such systems provide a geometrical method for deriving accurate fundamental parameters of stars. Photometry combined with spectroscopy yields the physical radii of the systems, individual masses, and therefore, the surface gravities. Furthermore, effective temperatures and luminosities can be estimated, enabling an accurate and direct determination of the reddening and the distance to OB-type stars within the Galaxy and the galaxies of the Local Group. As part of my research, I studied the properties of a massive dust-obscured system located in the Galactic Danks 2 cluster and inferred masses of 22-25 Mo for the stellar components. Accurate radii measurements allowed determination of the distance to the system of 3.52 kpc, which is the most precise distance measurement to the cluster and the host complex, accurate to 2%. In addition, as part of my first published work I reported the discovery of 101 eclipsing binaries in the Small Magellanic Cloud, which are accessible through the VizieR.
Be stars
Be stars are massive stars of mainly early B-type. As a result of their fast rotation possibly along with non-radial pulsations, they establish a gaseous, circumstellar, equatorial disk, the modulation of which results in spectroscopic and photometric variability. The occurrence of the phenomenon is highly associated with metallicity, yielding a higher fraction of Be stars in low-metallicity environments. Such a dependency is also confirmed in my first published work on the Small Magellanic Cloud using long-term photometry, infering 30% of the spectroscopically confirmed early B-type stars to display the Be phenomenon.
