shock breaks out of optically thick material. Produces early shock cooling emission. Shock breakout ionizes optically thin region at ~ 1014 cm. Produces narrow emission lines of CSM material. See Gal-Yam+ 2014, Yaron+ 2017 7/17
MS star - He star binary First Type Ib/c SN MS star - neutron star (NS) binary High mass X-ray binary Common envelope spiral in He star - NS binary Double NS system ?? Observations of galactic double neutron star systems suggest they were created in a low ejecta mass, low energy explosion (Piran+ 2006; Dewi+ 2005)
MS star - He star binary First Type Ib/c SN MS star - neutron star (NS) binary High mass X-ray binary Common envelope spiral in He star - NS binary He star (stable/unstable) RLO. Most He is ejected from the system Stripped He star + NS Intense mass loss forms expanding envelope. iPTF 14gqr: Ultra-stripped SN inside He-rich envelope Double NS system
km/s, RCSM ~ 5e+13 cm Mass loss rate ~ 10-4 M⊙ yr -1 +14 d, Photospheric phase: Helium-rich, no hydrogen Mg II in UV (interaction) +85 d, Late time: Both narrow (~300 km/s) And intermediate-width (~2000 km/s) emission (similar to SN Ibn)
~0.24 M ⊙ ~ 0.7 M ⊙ ~ 0.6 M ⊙ M Ni ~ 0.017 M ⊙ ~ 0.08 M ⊙ ~ 0.02—0.07 M ⊙ ~ 0.02 M ⊙ R env ~ 170 R ⊙ ~ 860 R ⊙ ~ 130—1500 R ⊙ ~ 350 R ⊙ M env ~ 0.1 M ⊙ ~ 0.03 M ⊙ ~ 0.05 M ⊙ ~ 0.1 M ⊙ R CSM ~ 700 R ⊙ ~ 8500 R ⊙ ~ 14000 R ⊙ — Type SN Ib (?) SN Ic (Ca) SN IIb (Ca) SN Ib (Ca) Summary of observations Rate: 2%--12% of CCSNe
helium stars appear to always expand before the explosion • Evidence of extended CSM produced by pre-explosion mass loss • High [Ca II]/[O I] in the nebular phase -- consistent with low O nucleosynthesis for lower CO core masses • Striking similarities to thermonuclear Ca-rich transients, but these appear exclusively in star forming galaxies.
emission) bound to the progenitor? The inferred R env almost exceeds the maximum photospheric radius reached by low-mass helium stars, challenging the assertion of Case BB mass transfer. • The inferred mass loss rates are too high to be sustained over a long time -- do low mass helium stars undergo intense pre-explosion mass loss? • What range of binary companions (MS, WD, NS, BH?) can produce the extremely stripped stars we see in the data? Relative rates? • Prospects for progenitor searches -- Extreme helium stars radiative mostly in the ultraviolet! Problematic for Galactic extinction + low UV sensitivity • Calcium ‘richness’ -- is the [O I] lines a reliable tracer of the progenitor mass for low mass progenitors? What role does mixing play? • How to distinguish from fast thermonuclear explosions: Can white dwarfs contain large amounts of hydrogen (> 0.01 solar masses) at explosion?