Rogue waves from parametric resonance in pulsating white dwarfs Key takeaway: outbursts are not rare in coolest pulsating WDs - only requirement seems to be high mode density for coupling - expression of energy transfer via nonlinear mode coupling
A Visual Guide to Outbursts in Pulsating White Dwarfs Keaton Bell 2017 (PhD thesis) outbursts seen in at least 13 DAVs (this is not a rare phenomenon!) none of the outbursts in pulsating WDs are periodic; appear chaotic each color is a different DAV
1000 s 200 s 500 s 125 s white dwarfs: g-modes, not all modes are observed excited model: 11,245 K, 0.632 M¤ , 10-4.12 MH /MWD (Romero et al. 2012) l=1 l=2 n=5 n=10 n>20 n>35
Spectroscopy Yields Effective Temperatures and Masses SDSS 4.2m SOAR Telescope our workhorse we have obtained and analyzed SOAR spectra of 62 of the first 65 DAVs observed by K2 so far: first 27 at k2wd.org WDs Evolve (Cool) à Blue: Observed by Kepler Open: Ground-based fits via Pier-Emmanuel Tremblay
Outbursting DAVs are Among the Coolest DAVs Blue: Observed by Kepler Red: Outbursting DAV Open: Ground-based more than 50% of DAVs from 11,200-10,600 K show outbursts in ~70 days of K2 monitoring
Outbursting DAVs are Among the Coolest DAVs Blue: Observed by Kepler Red: Outbursting DAV Open: Ground-based GD 1212 friendly bet: Josh Fuchs (formerly UNC) thought GD 1212 should pulsate based on his fits to SOAR spectra of DAVs
13/65 (20% of) DAVs with Kepler Data Show Outbursts Blue: Observed by Kepler Red: Outbursting DAV Open: Ground-based we expect all non-magnetic white dwarfs to pulsate at the appropriate temperature, and it appears most (all?) outburst at some point, too outbursts are likely a new phase of stellar evolution uncovered by Kepler/K2
Should Other Pulsating Stars Show Outbursts? DBVs (He-atmosphere WDs) have very similar structures to DAVs, and thus similar mode densities so far 7 DBVs observed by Kepler: none show outbursts (but so far none with dominant periods >1000 s) See poster by Zach Vanderbosch
Key Takeaways: Outbursts in the Coolest Pulsating WDs Blue: Observed by Kepler Red: Outbursting DAV Open: Ground-based - outbursts are not rare in coolest pulsating WDs - this is a common (universal?) phase of stellar evolution! - only requirement seems to be high mode density for coupling - nonlinear resonances expressed as outbursts are very likely responsible for the cessation of pulsations at the red edge of the DAV instability strip
Should Other Pulsating Stars Show Outbursts? the well-studied DBV GD 358 showed pulsation changes and got ~20-30% brighter during 2006 WET run for just one day nicknamed the ‘sforzando’ or often the ‘whoopsie’ GD 358: Montgomery et al. 2010
oDAV1 10860 K 0.70 M¤ oDAV2 11060 K 0.64 M¤ oDAV3 10570 K 0.56 M¤ oDAV4 11190 K 0.62 M¤ oDAV5 10850 K 0.53 M¤ 3rd & 4th: Bell et al. 2016, ApJ, arXiv: 1607.01392
1000 s 500 s 360 s 1400 s oDAV1 10860 K 0.70 M¤ oDAV2 11060 K 0.64 M¤ oDAV3 10570 K 0.56 M¤ oDAV4 11190 K 0.62 M¤ oDAV5 10850 K 0.53 M¤ 800 s 3rd & 4th: Bell et al. 2016, ApJ, arXiv: 1607.01392