Intermediate-luminosity red transients: Spectrophotometric properties and connection to electron-capture supernova explosions

We present the spectroscopic and photometric study of five intermediate-luminosity red transients (ILRTs), namely AT 2010dn, 2012jc, 2013la, 2013lb, 2018aes. They share common observational properties belong to a family objects similar prototypical ILRT SN 2008S. These events have rise time that is less than 15 days absolute peak magnitudes between ?11.5 ?14.5 mag. Their pseudo-bolometric light curves in range 0.5–9.0 × 10 40 erg s ?1 their total radiated energies are on order (0.3–3) 47 erg. After maximum brightness, show monotonic decline or plateau, resembling those faint supernovae IIL IIP, respectively. At late phases, flatten, roughly following slope 56 Co decay. If late-time power source indeed radioactive decay, these produce Ni masses ?4 ?3 M ? . The spectral energy distribution our sample, extending from optical mid-infrared (MIR) domain, reveals clear IR excess soon after explosion non-negligible MIR emission at very phases. spectra prominent H lines with typical velocity few hundred km , along Ca II features. In particular, [Ca ] ? 7291,7324 doublet visible all times, which characteristic feature for this transients. identified progenitor 2008S, luminous archival Spitzer images, suggests an intermediate-mass precursor star embedded dusty cocoon. propose super-asymptotic giant branch forming electron-capture supernova as plausible explanation events.