# Summary of K2 Program GO10018

Title: K2 Observations of Variable White Dwarfs in Fields 8 and 10

PI: Hermes, James J (Astronomy Group)
CoIs: Kawaler, Steven; Montgomery, Mike; Gentile Fusillo, Nicola; Raddi, Roberto; Gaensicke, Boris Teddy; Bell, Keaton; Winget, D. E.

We propose observations of variable white dwarfs in Fields 8 & 10 of the K2 mission. We propose short-cadence observations of known and high-probability pulsating white dwarfs within the empirical DAV instability strip. We additionally propose observations of known magnetic and convective-atmosphere white dwarfs to constrain magnetic activity in these stars.

As they cool, white dwarf stars with hydrogen-dominated atmospheres pulsate as DAVs (a.k.a. ZZ Ceti stars) when they reach the appropriate effective temperature to foster a hydrogen partial-ionization zone, which efficiently drives global oscillations. This range of temperatures empirically spans roughly 12,600-11,100 K for typical-mass (0.6 Msun), log g = 8.0 white dwarfs (Gianninas et al. 2011, ApJ, 743, 138). Pulsating white dwarfs provide an important glimpse into the interior of the future of the vast majority (> 97%) of all stars in our Galaxy, including our Sun, allowing us to probe the masses and compositions of their electron-degenerate cores, as well as of their non-degenerate envelopes; to determine their internal rotation profiles; and to detect weak magnetic fields (see reviews by Winget & Kepler 2008 (ARA&A, 46, 157) and Fontaine & Brassard 2008 (PASP, 120, 1043).

Since the DAV instability strip is defined by temperature, color selection is an excellent predictor of variability. Our team discovered all DAVs in the original Kepler mission, which has led to exquisite insight into white dwarf interiors. We have applied the same photometric selection methods to K2 Fields 8 & 10 using the SDSS, and have identified 15 excellent candidate white dwarfs on silicon in each field with colors consistent with the empirical DAV instability strip. Additionally, there are five previously known, confirmed pulsating white dwarfs in Field 8 (SDSS J0052-0051, GD 842, SDSS J1112+0009, WD J0050-0023, WD J0111+0018) and three in Field 10 (PG 1159-035, WD J1200-0251, and WD J1244-0221). Notably, PG1159-035 (V=15.0 mag) was the subject of one of the first Whole Earth Telescope runs -- a coordinated global multi-site campaign in 1989 March (Winget et al. 1991, ApJ, 378, 326) -- and is one of the best-studied and richest pulsating white dwarfs known.

Every new pulsating white dwarf we can observe with Kepler adds value, since it brings us that much closer to statistically significant studies of white dwarfs with ensemble asteroseismology (e.g. Chaplin et al. 2011, Science, 332, 213). With typical pulsations ranging from 100-1400 s, we require short-cadence observations of these white dwarfs. Minute-cadence K2 observations have the added benefit of catching transits/eclipses of the white dwarf, revealing any unresolved double-degenerate binaries or even planetary companions.

Additionally, we propose observations of multiple convective and/or possibly magnetic white dwarfs in Fields 8 and 10 to carry out the first in-depth study into the magnetic activity of the endpoints of stellar evolution. These long-baseline photometric observations will test white dwarf variability on a large scale and in a completely new regime.

# Targets requested by this program that have been observed (97)
EPIC ID, RA (J2000) [deg], Dec (J2000) [deg], magnitude, Investigation IDs
201107802, 183.150154, -6.371596, 17.515, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10048_SC
201214472, 180.441568, -3.761279, 14.907, GO10018_LC|GO10076_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10018_SC|GO10076_SC|GO10048_SC|GO10011_SC
201273498, 180.227291, -2.851947, 18.246, GO10018_LC|GO10019_LC|GO10006_LC|GO10018_SC
201283111, 181.315866, -2.706304, 18.752, GO10018_LC|GO10019_LC|GO10006_LC
201290806, 181.118658, -2.587333, 18.33, GO10018_LC|GO10019_LC
201291506, 183.038068, -2.576451, 18.69, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
201292141, 183.735043, -2.5675, 18.293, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10018_SC|GO10048_SC
201296279, 181.85738, -2.50685, 18.175, GO10018_LC|GO10005_LC|GO10048_LC|GO10052_LC|GO10048_SC
201312533, 183.191336, -2.264993, 18.693, GO10018_LC|GO10019_LC|GO10006_LC
201316574, 182.299731, -2.205326, 17.395, GO10018_LC|GO10048_LC|GO10048_SC
201386994, 181.068307, -1.156932, 18.688, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
201396979, 181.579675, -1.007601, 18.784, GO10018_LC|GO10052_LC
201421856, 182.460173, -0.626875, 18.77, GO10018_LC|GO10019_LC|GO10006_LC|GO10018_SC
201426361, 181.742261, -0.560223, 18.297, GO10018_LC|GO10019_LC|GO10006_LC|GO10011_LC
201429828, 181.517212, -0.510964, 17.548, GO10018_LC|GO10019_LC|GO10006_LC|GO10011_LC
201433263, 181.493944, -0.461105, 18.159, GO10018_LC|GO10019_LC|GO10006_LC
201438289, 180.947615, -0.386389, 15.276, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10048_SC
201452746, 181.559309, -0.179916, 18.441, GO10018_LC|GO10019_LC|GO10006_LC
201453267, 182.113431, -0.172129, 18.973, GO10018_LC|GO10019_LC|GO10006_LC
201648341, 184.204337, 2.790499, 14.039, GO10018_LC|GO10004_LC|GO10007_LC|GO10004_SC|GO10007_SC
228773807, 191.148574, -7.884629, 18.193, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10048_SC
228779074, 192.361015, -7.660107, 18.948, GO10018_LC|GO10019_LC|GO10006_LC
228782059, 191.409232, -7.527324, 18.424, GO10018_LC|GO10006_LC|GO10048_LC|GO10048_SC
228796212, 191.194356, -6.940515, 18.83, GO10018_LC|GO10006_LC
228822395, 190.410753, -5.839766, 17.814, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
228823722, 190.544926, -5.787047, 18.657, GO10018_LC|GO10019_LC
228828420, 188.906686, -5.59364, 16.582, GO10018_LC|GO10019_LC|GO10006_LC|GO10011_LC|GO10018_SC
228851681, 190.670625, -4.621505, 18.873, GO10018_LC|GO10019_LC|GO10006_LC
228876899, 187.922242, -3.668794, 18.861, GO10018_LC|GO10006_LC|GO10052_LC
228877473, 189.557229, -3.659143, 17.796, GO10045_LC|GO10018_LC|GO10014_LC|GO10019_LC|GO10048_LC|GO10045_SC|GO10048_SC
228881795, 186.661616, -3.588337, 18.791, GO10018_LC|GO10052_LC
228886332, 188.733151, -3.513083, 17.996, GO10902_LC|GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10902_SC|GO10048_SC
228900584, 187.768631, -3.266015, 17.253, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
228904088, 192.107817, -3.203336, 18.856, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
228904396, 185.008193, -3.198422, 18.839, GO10018_LC|GO10006_LC|GO10052_LC
228908905, 183.242538, -3.120528, 17.962, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10048_SC
228914323, 193.12336, -3.02492, 15.761, GO10018_LC|GO10004_LC|GO10006_LC|GO10007_LC|GO10031_LC|GO10004_SC|GO10007_SC
228931507, 184.477561, -2.723171, 18.693, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
228938232, 193.557443, -2.602363, 18.309, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
228939929, 193.128904, -2.5716, 17.463, GO10018_LC|GO10019_LC|GO10006_LC
228944520, 192.21376, -2.490206, 18.615, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10018_SC|GO10048_SC
228952212, 191.161559, -2.352106, 18.46, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10018_SC|GO10048_SC
228953047, 187.93748, -2.337051, 18.554, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
228954599, 193.741991, -2.310498, 16.691, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10048_SC
228960704, 189.589527, -2.203192, 18.488, GO10018_LC|GO10006_LC|GO10048_LC|GO10048_SC
228960916, 192.74455, -2.199854, 17.961, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10048_SC
228974142, 193.190753, -1.956497, 17.846, GO10018_LC|GO10019_LC|GO10006_LC
228979673, 189.269588, -1.85638, 17.399, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
228982746, 184.107644, -1.801273, 18.782, GO10018_LC
228989483, 189.546484, -1.679589, 18.09, GO10018_LC|GO10019_LC|GO10048_LC|GO10048_SC
228997493, 187.893777, -1.5357, 14.541, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10028_LC|GO10048_SC
229002689, 185.239517, -1.445102, 18.649, GO10018_LC|GO10006_LC|GO10048_LC|GO10048_SC
229005867, 187.141266, -1.386564, 17.631, GO10018_LC
229009797, 191.119054, -1.316083, 14.066, GO10018_LC|GO10006_LC|GO10048_LC|GO10048_SC
229011123, 185.515905, -1.29128, 18.17, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
229012313, 190.712891, -1.268782, 18.73, GO10018_LC
229013546, 187.784663, -1.243987, 17.902, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10048_SC
229016181, 191.953853, -1.186465, 16.843, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10048_SC
229021507, 191.065966, -1.074921, 18.294, GO10018_LC|GO10005_LC|GO10052_LC
229021782, 193.545259, -1.068994, 17.723, GO10018_LC|GO10006_LC
229022713, 192.91579, -1.048361, 18.442, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10018_SC|GO10048_SC
229023601, 184.748871, -1.028917, 18.831, GO10018_LC|GO10006_LC|GO10052_LC
229035574, 189.636899, -0.758303, 18.449, GO10018_LC|GO10019_LC|GO10006_LC
229037256, 186.849962, -0.721189, 18.618, GO10018_LC|GO10019_LC|GO10006_LC
229039143, 189.651451, -0.678407, 17.633, GO10018_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10048_SC
229041065, 187.297918, -0.637343, 18.343, GO10018_LC
229041897, 190.02648, -0.616911, 18.217, GO10902_LC|GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10902_SC|GO10048_SC
229056690, 187.49675, -0.287366, 17.513, GO10902_LC|GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10902_SC|GO10048_SC
229061365, 186.974004, -0.180778, 18.164, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10048_SC
229103879, 189.582366, 0.880096, 18.881, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
229111512, 189.434957, 1.075722, 18.579, GO10018_LC|GO10005_LC|GO10052_LC
229119187, 191.410978, 1.271584, 16.64, GO10018_LC|GO10019_LC|GO10006_LC
229128833, 186.96005, 1.497341, 16.836, GO10018_LC
229137289, 191.727898, 1.697639, 18.842, GO10018_LC|GO10019_LC|GO10006_LC
229146138, 187.539675, 1.907036, 18.476, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
229149295, 191.292546, 1.984334, 18.468, GO10018_LC|GO10006_LC|GO10018_SC
229152706, 189.708233, 2.070921, 18.672, GO10018_LC|GO10019_LC|GO10006_LC
229154226, 185.415792, 2.110634, 18.504, GO10018_LC|GO10019_LC|GO10006_LC
229154640, 190.872655, 2.121335, 18.34, GO10018_LC|GO10019_LC|GO10018_SC
229155531, 184.182204, 2.143309, 18.729, GO10018_LC|GO10006_LC
229156039, 189.869301, 2.155567, 18.843, GO10018_LC|GO10052_LC
229163519, 189.055881, 2.360268, 18.276, GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10018_SC|GO10048_SC
229165995, 189.537969, 2.426821, 18.928, GO10902_LC|GO10018_LC|GO10019_LC|GO10006_LC|GO10902_SC
229167100, 184.324272, 2.458804, 17.409, GO10018_LC
248368922, , , , GO10018_LC|GO10005_LC|GO10019_LC|GO10048_LC|GO10048_SC
248368947, , , , GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
248368953, , , , GO10018_LC|GO10019_LC|GO10006_LC
248368956, , , , GO10018_LC|GO10019_LC|GO10006_LC|GO10011_LC
248368957, , , , GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10048_SC
248368959, , , , GO10018_LC|GO10006_LC
248368967, , , , GO10018_LC|GO10019_LC|GO10006_LC|GO10048_LC|GO10011_LC|GO10018_SC|GO10048_SC|GO10011_SC
248369124, , , , GO10018_LC
248369125, , , , GO10018_LC|GO10048_LC|GO10048_SC
248369126, , , , GO10018_LC|GO10019_LC
248369127, , , , GO10018_LC|GO10019_LC
248369128, , , , GO10018_LC
248369129, , , , GO10018_LC|GO10019_LC