Padova-Asiago Supernova Group
Faint SNe

Type Iax Supernovae

In the last decade, the discovery of several peculiar Type Ia SNe has drawn the attention both to the photometric and spectroscopic diversity among this class of otherwise homogeneous transients. SNe Iax are the largest class of peculiar thermonuclear SNe (over 50 members known) and the main characteristics are:
- low luminosities (-13 > MV > -19) and fast rise (~10 to 20 days) to maximum;
- lower ejecta velocity (~2-6000 km/s) compared to normal Type Ia;
- early spectra dominated by Fe-group elements (strong FeII, FeIII; CoII in the JHK-bands); IMEs Si, S, Ca present but with less strength than in normal Ia.
See Jha 2017, Handbook of Supernovae (Springer) for a review.

Type Iax are unique among all SNe in their late-time spectra, showing both permitted and forbidden emission features, never becoming fully nebular. Regarding the progenitors, pre-explosion HST deep images for SN 2012Z (McCully et al. 2014, Nature, 512) show a luminous and blue source consistent with an He-star companion to a C/O WD system; progenitor non-detection for 2014ck (Tomasella et al. 2016, MNRAS 459), SNe 2008ge and 2014dt (Foley et al. 2010, AJ, 140; 2015, ApJ, 798) rules out the most luminous/massive stars. However, the diversity within this class of transients cannot be reduced to a one-parameter description and this may imply that distinct progenitors and/or explosion mechanisms are involved, despite the overall similarity of the main observables.

The figure shows the NIR spectral sequence of SN 2014ck (Tomasella et al. 2016, MNRAS 459, 1018) obtained with the Gemini N Telescope (+GNIRS). Phases, labelled on the left, are relative to V-band maximum. Spectra at +19d and later are strongly dominated by Co II lines, which provide a clear link to SNe Ia.

Faint and slow Type II SNe

Faint and slow type II SNe is a group of core-collapse SNe showing this specific properties:
- They are faint at all phases (-13 > MV > -15);
- they have low velocity ejecta (i.e. low kinetic energy, < 1050 erg);
- they eject low amounts of 56Ni (of the order of few 10-3 Msun).

Besides the low-luminosity (LL) Type II-P events (Pastorello et al. 2004, MNRAS, 347, 74; Spiro et al. 2014, MNRAS, 439, 2873),several slow and intermediate-luminosity Type IIP (2008in, 2009N, 2009js, 2009ib, 2010id, 2012A, 2013am, 2013K, etc.) are bridging the gap between normal and LL SNe. The cause of the spread of parameters among LL, intermediate and standard SNe remains unclear. Comparison of progenitor mass estimates is a key point.

The main focus of this project is the characterization of the different types of faint and slow (in the sense of extremely low ejecta velocities) SNe on the basis of their observational parameters (photometric monitoring, spectroscopic evolution, and information on the progenitors).

Research group
People directly involved in this project:
Lina Tomasella (INAF-OAPd), Stefano Benetti (INAF-OAPd), Enrico Cappellaro (INAF-OAPd), Nancy Elias-Rosa (INAF-OAPd), Andrea Pastorello (INAF-OAPd), Massimo Turatto (INAF-OAPd)

Other researchers involved:
Maximilian Stritzinger (Aarhus Univ. Denmark), Luca Zampieri (INAF-OAPd), Maria Letizia Pumo (Univ. Catania)