My main research interests include different classes of hydrogen rich transients, which share the peculiarity of being underluminous compared to standard type II supernovae (SNe II). I am particularly keen on the modeling and physical interpretation of light curves and spectra obtained in the ultraviolet, optical and infrared domains. The starting point of my studies was a category of faint SNe:

• Low luminosity type II-plateau supernovae (LL SNe IIP) have been a subject of extensive study within the Padova SN group (e.g. Pastorello et al. 2004, MNRAS, Spiro et al. 2014, MNRAS, 439, 2873, Reguitti et al. 2021, MNRAS, 501, 1059, Valerin et al. 2022, MNRAS, 513, 4983), also thanks to the valuable hydrodynamical modelling provided by M. L. Pumo. A body of mounting evidence indicates that LL SNe IIP originate from the explosion of low mass red supergiants, which eject material at lower velocity, release less energy in the form of radiation, and synthesise less ⁵⁶Ni compared to standard SNe IIP. However, there is no sharp separation between the two classes: they form a continuous distribution of events, with LL SNe IIP making up the low energy tail of this spectrum of stellar explosions.

In the past twenty years we discovered a growing number of objects with peak luminosity intermediate between those of classical novae and faint core-collapse SNe. These events were dubbed Gap Transients, but they are far from being a homogeneous family. Among Gap Transients we can find violent stellar eruptions, non-degenerate stellar mergers, and possibly even extremely faint SNe (Cai, Valerin et al. 2022, Univ, 8, 493). I delved into the study of two sub-classes of Gap Transients:

• Intermediate Luminosity Red Transients (ILRTs) are objects characterised by narrow lines spectra dominated by hydrogen and calcium features. Their single peaked light curves settle on a linear decline at late time, similar to classical SNe. Late time monitoring in the mid-infrared domain corroborate the scenario of an explosion which destroys the star, possibly producing a compact object. Finally, whenever a progenitor star was identified for an ILRT, it was compatible with a super asymptotic giant branch star. The low energy released during these events, their terminal nature, and their peculiar progenitor make ILRTs appealing electron capture SN candidates (Valerin et al. to be submitted to ApJ).


• During the photospheric phase, Luminous Red Novae (LRNe) present spectra that are quite similar to those of ILRTs, dominated by narrow hydrogen lines. At late times, however, molecular bands erode the optical and near-infrared continuum of LRNe, becoming a valuable hallmark for the correct identification of these objects. The nature of LRNe is known thanks to the detailed analysis of nearby objects, nearby V838 Monocerotis and V1309 Scorpii. In this last case in particular it was possible to infer the evolution of a binary system of non-degenerate stars going through a common envelope phase, the subsequent coalescence of the stars, the ejection of the common envelope and its interaction with the surrounding circumstellar medium (CSM). This complex sequence of events is reflected in the light curve of LRNe, often characterised by a double peak in luminosity (Pastorello A., Valerin G. et al. 2021, A&A, 646, A119, Pastorello A., Valerin G. et al. 2021, A&A, 647, A93).

I have led two consecutive long-term proposals at the Telescopio Nazionale Galileo and Rapid-Eye Mount telescope with the goal of monitoring and studying Gap Transients as well as SNe interacting with CSM. I am also a member of prolific international collaborations such as NUTS2 and ePESSTO+. In these context, I contributed to the observations and analysis of SNe IIn and other more classical SNe events.

List of publications (personal ADS library)

My Curriculum Vitae