\citet{Reilly_2017} FORS2 Optical specpol for SN 2009ip during the 2012 outbursts.
About SN 2009ip
- First detected in 2009 August, before reclassified as an LBV outburst
- Preexplosion HST image -> 50-60 solar mass start
- Two spectacular outbursts in 2012, July 24 at M = -14 and Sep 23 at M = -18.5
- The 2012b outburst is believed to be terminal, but it's still under debate.
Polarimetric observations by FORS2 on the VLT, 35, 42, 64, 68, 73, and 83 days after the 2012b outburst
- ISP determined by assuming that the core of H\(\alpha\) emission line is unpolarized since the opacity is high and the emission comes from outside.
- Continuum polarization (bands without lines): 0.7% at 45\(^{\circ}\) at 35-64d, then ~60\(^{\circ}\) rotation around ~70d, which is also when the bolometric lightcurve dips. (Though they didn't say why)
- Broad line polarization, focused on H\(\alpha\): depolarization (found by removing continuum contribution by fitting 2nd order polynomial to cont. flux to then remove cont. polarization)
- Low-velocity narrow lines polarization (low v = not far from main peak): H\(\alpha\), \(\beta\) and He I have absorption component at -1500 km/s. Generally 0.5-1% polarized at 30-40\(^{\circ}\). All lines seem to come from the same line forming region.
- Intermediate and high-velocity narrow lines polarization: similar degree of polarization, but different angle (~100-120\(^{\circ}\)). Lines at similar velocity from different lines share similar polarimetry, again, these share the same line forming region, which is different from the low velocity one.
Interpretation of polarimetry
II-P