2022ApJ...927...61K

We report results of optical imaging and low-resolution spectroscopic monitoring of supernova (SN) 2017iro that occurred in the nearby (∼31 Mpc) galaxy NGC 5480. The He I λ5876 feature present in the earliest spectrum (-7 days) classified it as a Type Ib SN. The follow-up observations span from -7 to +266 days with respect to the B-band maximum. With a peak absolute magnitude in V band M _ V _ = -17.76 ± 0.15 mag and bolometric luminosity log₁₀ L = 42.39 ± 0.09 erg s^–1, SN 2017iro is a moderately luminous Type Ib SN. The overall light-curve evolution of SN 2017iro is similar to that of SN 2012au and SN 2009jf during the early (up to ∼100 days) and late phases (>150 days), respectively. The line velocities of both Fe II λ5169 and He I λ5876 are ∼9000 km s^–1 near the peak. The analysis of the nebular phase spectrum (∼+209 days) indicates an oxygen mass of ∼0.35 M _☉. The smaller [O I]/[Ca II] flux ratio of ∼1 favors a progenitor with a zero-age main-sequence mass in the range ∼13-15 M _☉, most likely in a binary system, similar to the case of iPTF13bvn. The explosion parameters are estimated by applying different analytical models to the quasi-bolometric light curve of SN 2017iro. ⁵⁶Ni mass synthesized in the explosion has a range of ∼0.05-0.10 M _☉, ejecta mass ∼1.4-4.3 M _☉, and kinetic energy ∼(0.8-1.9) x 10⁵¹ erg.