# Summary of K2 Program GO13040

Title: K2 Observations of Variable White Dwarfs in Fields 11, 12 and 13

PI: Hermes, James J (University Of North Carolina, Chapel Hill)
CoIs: Clemens, Chris; Gaensicke, Boris Teddy; Dennihy, Erik; Montgomery, Mike; Gentile Fusillo, Nicola; Fuchs, Josh; Kawaler, Steven; Barlow, Brad Newton; Winget, D. E.; Raddi, Roberto; Bell, Keaton

We propose observations of variable white dwarfs (WDs) in Fields 11-13 of the K2 mission. We propose short-cadence observations of known and high-probability pulsating WDs. We additionally propose short-cadence observations of known magnetic and metal-polluted white dwarfs to constrain magnetic activity in these stars, and to search for possible transits in around stars with known evolved planetary systems.

As they cool, WDs 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) WDs. Pulsating WDs 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.

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 is leading to exquisite insight into white dwarf interiors. We have applied the same photometric selection methods to K2 Fields 11-13 using the SDSS, VST/ATLAS, and VPHAS+ multiwavelength surveys, and have identified 75 excellent candidate white dwarfs on silicon in the three fields with colors consistent with the empirical DAV and DBV instability strips. Additionally, there are three previously published pulsating white dwarfs in Field 12. We have used ground-based resources to refine the atmospheric parameters of many of these candidates, confirming than a large number fall within the empirical ZZ Ceti instability strip. Additionally, we have confirmed pulsations in two new white dwarfs using ground-based high-speed photometry. With typical pulsations ranging from 100-1400 s, we require short-cadence observations of these white dwarfs.

Every new DAV we can observe with K2 adds significant legacy value, since it brings us that much closer to statistically significant studies of white dwarfs with ensemble asteroseismology. There were only six pulsating white dwarfs in the original Kepler mission, but that number has grown to at least 20 with K2, and will continue to grow as the extended mission progresses.

Additionally, we propose long-cadence observations of all other WD candidates in these fields, to continue our in-depth study into rotation, magnetic activity, planetary systems, and binarity in the endpoints of stellar evolution. These observations simultaneously allow for serendipitous discoveries, including possible eclipses or transits, as demonstrated by the unique disintegrating planetesimal orbiting a WD in K2 Campaign 1 (Vanderburg et al. 2015, Nature, 526, 546).

# Targets requested by this program that have been observed (39)
EPIC ID, RA (J2000) [deg], Dec (J2000) [deg], magnitude, Investigation IDs
210600298, 67.162621, 16.969976, 17.911, GO13040_LC|GO13040_SC
210682034, 66.685656, 18.109754, 19.431, GO13040_LC
210755204, 67.847842, 19.189495, 16.372, GO13040_LC|GO13037_LC|GO13040_SC|GO13037_SC
210765616, 66.444482, 19.34736, 19.222, GO13040_LC
210766332, 67.913469, 19.357669, 17.477, GO13040_LC|GO13027_LC|GO13037_LC|GO13040_SC|GO13037_SC
210768799, 66.690243, 19.394236, 18.286, GO13040_LC
210844962, 65.379, 20.553683, 17.401, GO13040_LC|GO13027_LC|GO13040_SC
210857535, 66.89617, 20.739412, 18.818, GO13040_LC|GO13027_LC|GO13037_LC
210899098, 66.092786, 21.377074, 18.728, GO13040_LC|GO13027_LC
210935777, 65.523064, 21.956092, 18.739, GO13040_LC
246723035, 75.829204, 14.857469, 18.855, GO13040_LC|GO13027_LC|GO13040_SC
246808113, 76.830501, 15.828171, 18.314, GO13040_LC|GO13040_SC
246885975, 77.755863, 16.617522, 17.965, GO13040_LC|GO13027_LC|GO13040_SC
247296400, 69.906169, 20.519141, 17.752, GO13040_LC|GO13027_LC|GO13037_LC|GO13040_SC|GO13037_SC
247333314, 69.383357, 20.843541, 18.26, GO13040_LC
247426706, 71.774134, 21.614242, 18.616, GO13040_LC|GO13027_LC|GO13037_LC|GO13040_SC|GO13037_SC
247510898, 67.913246, 22.279218, 18.688, GO13040_LC|GO13037_LC
247559069, 71.505412, 22.648632, 17.816, GO13040_LC|GO13007_LC|GO13027_LC|GO13037_LC|GO13040_SC|GO13037_SC
247637336, 74.366224, 23.247383, 17.471, GO13040_LC|GO13002_LC|GO13027_LC|GO13037_LC|GO13040_SC|GO13037_SC
247644144, 74.882948, 23.298087, 17.801, GO13040_LC|GO13027_LC|GO13037_LC|GO13040_SC|GO13037_SC
247710612, 73.537932, 23.787513, 18.928, GO13040_LC|GO13027_LC|GO13037_LC|GO13040_SC|GO13037_SC
247747914, 75.748219, 24.046868, 17.511, GO13040_LC|GO13027_LC|GO13037_LC|GO13040_SC|GO13037_SC
247895901, 75.775183, 25.064634, 16.395, GO13040_LC|GO13027_LC|GO13037_LC|GO13040_SC|GO13037_SC
247938111, 75.713265, 25.359201, 18.044, GO13040_LC|GO13040_SC
247940917, 75.556005, 25.379295, 18.346, GO13040_LC|GO13027_LC|GO13037_LC
247943447, 68.11238, 25.397036, 18.036, GO13040_LC
247947876, 71.176996, 25.428837, 17.274, GO13040_LC|GO13027_LC|GO13037_LC|GO13040_SC|GO13037_SC
251456975, , , , GO13040_LC|GO13037_LC|GO13040_SC|GO13037_SC
251456976, , , , GO13040_LC|GO13040_SC
251456977, , , , GO13040_LC|GO13040_SC
251456978, , , , GO13040_LC|GO13040_SC
251456979, , , , GO13040_LC|GO13040_SC
251456980, , , , GO13040_LC
251456981, , , , GO13040_LC
251456982, , , , GO13040_LC
251456983, , , , GO13040_LC
251456984, , , , GO13040_LC
251456985, , , , GO13040_LC
251456986, , , , GO13040_LC