Outrigger modes in pulsating white dwarfs J.J. Hermes + Bart Dunlap (UT-Austin) Madi VanWyngarden (BU) Chris Clemens (UNC) Ben Kaiser (UNC) 

What Exactly Am I on About with “Outrigger” Modes? SDSS J084055.72+130329.5 is one of the richest DAVs observed in K2 Two of the strongest modes look like l=3 septuplets with m=±1 components missing (e.g., i = 60°) 

What Exactly Am I on About with “Outrigger” Modes? SDSS J084055.72+130329.5 is one of the richest DAVs observed in K2 Two of the strongest modes look like l=3 septuplets with m=±1 components missing But the ν spacings are 19σ incompatible with l=3 modes 

What Exactly Am I on About with “Outrigger” Modes? Phenomenologically these appear as outriggers to an internal l=1 mode 

FUV-to-Optical Amplitudes Incompatible with l=3 Modes HST Program 14691 We tested changing geometric cancellation from limb-darkening based on six HST orbits with COS 

FUV-to-Optical Amplitudes Incompatible with l=3 Modes We tested changing geometric cancellation from limb-darkening based on six HST orbits with COS: likely l < 3 for highest-amplitude modes 

There Are Significant Nonlinearities in the Light Curve f 1 f 2 f 3 f 1 + f 1 f 1 + f 3 f 1 - f 3 The UV light curve reminds us that the pulse shape is highly non-sinusoidal 

There Are Significant Nonlinearities in the Light Curve 

There Are Significant Nonlinearities in the Light Curve 

There Are Significant Nonlinearities in the Light Curve 3-day sliding window There is significant amplitude/phase modulation, likely from resonant mode coupling see also, e.g., Zong et al. 2016 

There Appear to Be Four Main Outrigger Modes f 1 f 3 f 9 All four outrigger modes are separated from the nearest mode by exactly 2.4969±0.0017 μHz 

Re-Observations in K2 Campaign 16 (2.6 years later) f 1 f 3 f 9 All four outrigger modes are separated from the nearest mode by exactly 2.4741±0.0015 μHz 

More Observations in K2 Campaign 18 (0.4 years later) f 1 f 3 f 9 All four outrigger modes are separated from the nearest mode by exactly 2.4010±0.0048 μHz 

What Exactly Are “Outrigger” Modes in DAVs? Mode identification via pattern recognition is complicated in the richest K2 DAV UV amplitudes and imperfect splittings suggest this is not an l=3 septuplet Is it at all possible these modes sample multiple distinct cavities? 

What Exactly Are “Outrigger” Modes in DAVs? Is it possible outrigger modes are purely nonlinear artifacts? If so, how are they generated? Are there further useful tests or numerology to explore? In the spirit of a T/KASC workshop, I would love any thoughts or input you may have! 

Extra Slides 

He P.I. zone (30-20 kK) H P.I. zone (13-10 kK) N2 L l 2 DAV Propagation Diagram Core Surface p-modes σ2 > Ll 2, N2 convection zone log σ2 (s-2) g-modes σ2 < Ll 2, N2 DBV: aka V477 Her DAV: aka ZZ Ceti Fontaine & Brassard 2008 

a) shortest-period modes show long-term stability b) amplitudes start to increase as periods increase c) modes > 800 s feel effects of changing convection zone, as more nonlinearities seen d) mode coupling leads to dramatic outbursts e) amplitudes die off strongly at 10,500 K Hermes et al. 2017, ApJS 

1000 s 200 s 500 s 125 s m = +1 m = +1 m = 0 345.3 s l = 1 n = 6 Prot = 0.9 ± 0.2 day l = 1 n = 5 316.8 s actual data: KIC 4357037 Most hotter DAVs have symmetric dipole splittings