# Summary of K2 Program GO12027

Title: Eclipses, transits and variability of white dwarf stars with the K2 Mission

PI: Burleigh, Matt R. (University of Leicester)
CoIs: Barstow, Martin Adrian; Lawrie, Katherine Anne; Holberg, Jay B; Braker, Ian Peter

Matt Burleigh(1)(PI), Jay Holberg(2)(Co-I), Martin Barstow(1)(Co-I), Ian Braker(1)(Graduate Student), Katherine Lawrie(1)(Co-I)

(1) Dept. Physics and Astronomy, University of Leicester, Leicester, UK.
(2) Lunar and Planetary Laboratory, Sonnett Space Sciences Bld., University of Arizona, Tucson, AZ 85721, USA

The small size of a white dwarf (WD) star (approx. 1 Earth radii) implies that any sub-stellar or gas giant companion at suitable orbital inclination will completely eclipse it, while terrestrial bodies smaller than the Moon, including asteroids, will still produce transits that are detectable in high signal/noise light-curves.

Whether such planets actually exist around WDs is an open question. Those caught within the expanding envelope of an AGB star will be destroyed. However, the presence of debris disks around a few % of WDs (Farihi et al. 2011, Barber et al. 2012), and accreted metals in the photospheres of a surprisingly large fraction of such stars (approx. 25% at circa 1Gyr, Zuckerman et al.2003) demonstrates that surviving asteroids and terrestrial planets must be perturbed into orbits that take them close to the central WD, where they are tidally disrupted. Even so, it appears dynamically difficult, though not impossible, to perturb them into stable, circularised orbits within the WD HZ. Alternatively, 2nd generation planets may be created from material ejected after the AGB phase.

The Kepler 2 mission is an ideal opportunity to search the HZs of a statistically significant (500 to 1000) sample of WDs for terrestrial planets. Any discovery would provide vital data and a significant challenge to dynamicists and theoreticians, just as the unexpected discovery of hot Jupiters did in the 1990s. A single detection would then open the exciting possibility of studying the atmosphere of a nearby terrestrial world through spectroscopy with JWST (Loeb & Maoz 2013).

A Kepler survey of WDs opens up other serendipitous science than just the exciting, but perhaps tantalising prize of a terrestrial planet. Besides pulsating WDs, which can be studied in exquisite detail with high cadence mode observations, other variable examples will be discovered. Recently, Beuermann et al.(2013) discovered the first eclipsing, detached WD + brown dwarf (BD) system, and Casewell et al.(2012) found probably the lowest mass close companion to a white dwarf (25 - 30 Jupiter masses). Both BDs likely survived common envelope evolution, but what is the lowest mass object that can do so, and will it be revealed through eclipses of the WD?

This survey will also reveal the full population of optically variable WDs at accuracies undetectable from the Earth. We have detected low level variability in circa 50% of the WDs in the Kepler and K2 Campaign 0 fields. These could be due to star spots or accretion of dust from disrupted asteroids onto poles of low level magnetic WDs. It is likely more unexpected variables await discovery. 

The total eclipse of an Earth-sized WD by a Jovian or BD sized companion in a few hour orbit will last around 5 mins. In a 30 min long cadence (LC) observation this will be diluted to 17%. An eclipse by an Earth terrestrial companion in the HZ would last approximately 2.5 min, diluted to circa 8% in a LC datapoint. These can be compared to the expected Kepler 2 mission sensitivity at magnitude 19.0 of circa 50,000ppm(5%). Even at this faint magnitude, the Jovian sized object would be comfortably visible at 3 sigma confidence in a single datapoint, while the Earth-sized object would also be detectable, especially if many such eclipses/transits are observed and suitably phase-folded.

We estimate that our target list will be made up of 1, 222  and 22 WDs (campaigns 11, 12 and 13), that have been spectroscopically identified or are deemed to have a 90% or greater probability of being a WD (Fusillo et al. 2015), and which are brighter than Kepler Magnitude 19.5 from the McCook & Sion and SDSS catalogues.

# Targets requested by this program that have been observed (141)
EPIC ID, RA (J2000) [deg], Dec (J2000) [deg], magnitude, Investigation IDs
206437239, 343.947637, -6.014018, 15.126, GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC|GO12037_SC|GO12040_SC
206439828, 343.863942, -5.973186, 18.783, GO12027_LC|GO12040_LC
245949270, 351.608088, -10.876391, 18.704, GO12037_LC|GO12027_LC|GO12040_LC
245955120, 354.425848, -10.695595, 17.376, GO12027_LC|GO12007_LC|GO12040_LC
245970451, 356.300941, -10.267382, 17.813, GO12027_LC|GO12007_LC|GO12040_LC
245973600, 355.084299, -10.179422, 19.037, GO12027_LC|GO12040_LC
245978450, 348.006994, -10.050092, 18.151, GO12027_LC|GO12040_LC
245979486, 355.690671, -10.022499, 18.41, GO12027_LC|GO12040_LC
245987518, 354.743991, -9.804461, 19.51, GO12027_LC|GO12040_LC|GO12040_SC
245988152, 355.492701, -9.787958, 17.726, GO12027_LC|GO12002_LC|GO12007_LC
245993663, 349.122381, -9.645988, 18.736, GO12037_LC|GO12027_LC|GO12040_LC
245995295, 351.476502, -9.606235, 17.806, GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC|GO12037_SC
245995521, 348.330991, -9.600378, 18.002, GO12037_LC|GO12027_LC|GO12040_LC|GO12040_SC
246002141, 351.03554, -9.430223, 17.712, GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC|GO12037_SC
246025269, 349.91817, -8.843679, 19.016, GO12037_LC|GO12027_LC|GO12040_LC
246027988, 357.677168, -8.771933, 18.582, GO12027_LC|GO12040_LC
246028825, 350.497135, -8.750243, 18.886, GO12037_LC|GO12027_LC|GO12040_LC
246032115, 345.729261, -8.668247, 16.763, GO12027_LC|GO12007_LC|GO12040_LC
246039590, 356.456351, -8.491899, 18.875, GO12037_LC|GO12027_LC|GO12040_LC
246043452, 355.345672, -8.403264, 17.664, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246048259, 350.803854, -8.29538, 18.132, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246049962, 346.095891, -8.256515, 18.034, GO12027_LC|GO12007_LC|GO12040_LC
246051402, 347.911752, -8.223742, 18.965, GO12037_LC|GO12027_LC|GO12040_LC
246055467, 353.616731, -8.1317, 17.998, GO12037_LC|GO12027_LC|GO12040_LC
246057496, 345.841474, -8.083975, 18.602, GO12027_LC|GO12040_LC|GO12040_SC
246057529, 352.948756, -8.082941, 18.564, GO12037_LC|GO12027_LC|GO12040_LC|GO12040_SC
246057757, 358.36573, -8.07757, 18.101, GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC|GO12903_LC
246059117, 352.625783, -8.0457, 18.126, GO12037_LC|GO12027_LC|GO12040_LC
246061387, 346.578686, -7.994157, 18.172, GO12037_LC|GO12027_LC|GO12040_LC
246064616, 346.24304, -7.920215, 19.011, GO12027_LC|GO12040_LC
246064698, 345.866376, -7.91798, 18.317, GO12027_LC
246064789, 345.867358, -7.916082, 18.318, GO12027_LC|GO12040_LC|GO12040_SC
246070215, 354.699077, -7.795855, 17.561, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246074853, 354.711392, -7.688892, 13.34, GO12037_LC|GO12027_LC|GO12039_LC|GO12007_LC|GO12040_LC|GO12902_LC|GO12903_LC|GO12037_SC|GO12007_SC|GO12040_SC
246074959, 355.907074, -7.686676, 18.81, GO12037_LC|GO12027_LC|GO12040_LC
246077697, 354.803389, -7.624999, 18.578, GO12037_LC|GO12027_LC|GO12040_LC
246080155, 348.679401, -7.571645, 15.524, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246083440, 349.163355, -7.500779, 18.981, GO12037_LC|GO12027_LC|GO12040_LC
246083492, 349.627282, -7.499446, 18.899, GO12037_LC|GO12027_LC|GO12040_LC
246083909, 352.051649, -7.489563, 16.545, GO12037_LC|GO12027_LC|GO12040_LC
246084714, 348.870203, -7.472157, 17.126, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246090450, 354.818988, -7.349278, 18.652, GO12037_LC|GO12027_LC|GO12040_LC
246097647, 356.898644, -7.192873, 16.827, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC
246105313, 346.079541, -7.024085, 17.121, GO12037_LC|GO12027_LC|GO12007_LC|GO12014_LC|GO12037_SC
246105735, 347.018259, -7.014599, 18.973, GO12037_LC|GO12027_LC|GO12040_LC|GO12040_SC
246119563, 348.734155, -6.713315, 18.708, GO12037_LC|GO12027_LC|GO12040_LC
246127319, 348.603985, -6.547115, 15.387, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC
246130279, 353.874208, -6.482791, 18.569, GO12037_LC|GO12027_LC|GO12040_LC|GO12040_SC
246137493, 346.548426, -6.328871, 18.683, GO12037_LC|GO12027_LC|GO12040_LC
246141115, 346.176369, -6.249831, 18.772, GO12037_LC|GO12027_LC|GO12040_LC
246142616, 349.788018, -6.21823, 17.837, GO12027_LC
246143534, 348.121912, -6.199417, 18.064, GO12037_LC|GO12027_LC|GO12040_LC|GO12040_SC
246145395, 348.651099, -6.161077, 18.139, GO12037_LC|GO12027_LC|GO12040_LC
246151427, 351.193452, -6.030138, 19.231, GO12037_LC|GO12027_LC|GO12040_LC
246159261, 351.891276, -5.866534, 18.787, GO12037_LC|GO12027_LC|GO12040_LC
246164560, 345.713514, -5.752851, 18.543, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246168339, 351.273756, -5.674744, 16.945, GO12037_LC|GO12027_LC|GO12015_LC|GO12014_LC|GO12040_LC|GO12037_SC|GO12040_SC
246173840, 344.646249, -5.559429, 17.643, GO12027_LC|GO12040_LC|GO12040_SC
246185677, 344.957219, -5.318591, 18.834, GO12027_LC|GO12040_LC|GO12040_SC
246192083, 351.464352, -5.18361, 18.646, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246197803, 350.894633, -5.066885, 17.141, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246198340, 347.935523, -5.056086, 18.677, GO12037_LC|GO12027_LC|GO12040_LC
246198765, 347.968109, -5.047349, 19.01, GO12037_LC|GO12027_LC|GO12040_LC
246199999, 350.783321, -5.022957, 18.783, GO12037_LC|GO12027_LC|GO12040_LC|GO12040_SC
246215654, 353.974574, -4.70393, 15.779, GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC|GO12903_LC|GO12037_SC|GO12040_SC
246222349, 358.176826, -4.575146, 18.745, GO12027_LC
246228158, 348.293629, -4.463106, 18.218, GO12037_LC|GO12027_LC|GO12040_LC
246228541, 353.377054, -4.455894, 18.103, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC
246237452, 352.031903, -4.286688, 18.698, GO12037_LC|GO12027_LC|GO12040_LC
246237505, 347.429541, -4.285705, 19.111, GO12037_LC|GO12027_LC|GO12040_LC
246239242, 358.280759, -4.252904, 19.155, GO12027_LC
246239524, 349.899284, -4.247307, 18.749, GO12037_LC|GO12027_LC|GO12040_LC
246240280, 347.909939, -4.232937, 17.865, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC
246251189, 346.527281, -4.024971, 18.879, GO12037_LC|GO12027_LC|GO12040_LC
246252491, 354.527134, -3.99872, 17.09, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246253703, 349.910897, -3.97627, 18.617, GO12037_LC|GO12027_LC|GO12040_LC
246262784, 350.364286, -3.805912, 18.282, GO12037_LC|GO12027_LC|GO12040_LC|GO12040_SC
246264433, 349.849094, -3.775409, 17.033, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC
246282932, 350.037632, -3.405803, 17.329, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC
246286733, 354.211549, -3.332703, 18.093, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246306620, 358.46214, -2.934413, 19.063, GO12027_LC
246306676, 358.132325, -2.933134, 18.256, GO12027_LC
246308959, 358.134604, -2.885903, 17.048, GO12027_LC|GO12007_LC|GO12040_LC|GO12040_SC
246317680, 350.726242, -2.708014, 15.237, GO12037_LC|GO12027_LC|GO12123_LC|GO12040_LC|GO12037_SC
246319946, 346.931155, -2.663971, 18.427, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246330296, 353.886697, -2.461208, 19.449, GO12027_LC|GO12901_LC
246345042, 346.219539, -2.169693, 19.074, GO12027_LC|GO12040_LC
246359507, 348.146112, -1.885431, 18.598, GO12037_LC|GO12027_LC|GO12040_LC
246361569, 349.664128, -1.844919, 18.513, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246369658, 347.926053, -1.688928, 16.691, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC
246369780, 353.015396, -1.686724, 19.009, GO12037_LC|GO12027_LC|GO12040_LC|GO12040_SC
246370259, 346.989756, -1.677276, 18.552, GO12027_LC
246371026, 350.574642, -1.663329, 19.372, GO12027_LC|GO12901_LC
246387809, 348.689283, -1.327004, 18.163, GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
246394334, 349.167409, -1.16432, 18.661, GO12027_LC|GO12901_LC|GO12901_SC
246405291, 349.755158, -0.830471, 19.284, GO12027_LC|GO12013_LC|GO12002_LC|GO12040_LC|GO12040_SC
246407622, 351.151104, -0.760033, 18.286, GO12027_LC|GO12002_LC
246430458, 346.970542, -0.035403, 19.263, GO12027_LC
246449947, 349.561462, 0.574999, 18.401, GO12027_LC|GO12002_LC|GO12901_LC
246466836, 349.965509, 1.152471, 18.452, GO12027_LC|GO12013_LC|GO12040_LC
246479464, 350.685433, 1.508291, 17.79, GO12027_LC|GO12040_LC|GO12040_SC
246483959, 349.886693, 1.629577, 19.2, GO12027_LC|GO12901_LC
246485489, 350.994526, 1.67408, 14.122, GO12027_LC|GO12044_LC|GO12007_LC|GO12040_LC
246495334, 349.677279, 1.949854, 19.158, GO12027_LC|GO12040_LC
246506598, 350.832066, 2.291042, 19.09, GO12027_LC|GO12040_LC
251455484, , , , GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC|GO12037_SC|GO12007_SC|GO12040_SC
251455486, , , , GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC|GO12037_SC
251455487, , , , GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC|GO12040_SC
251455488, , , , GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC
251455489, , , , GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC|GO12037_SC
251455490, , , , GO12027_LC|GO12007_LC|GO12040_LC
251455491, , , , GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC|GO12037_SC
251455493, , , , GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC|GO12037_SC
251455494, , , , GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC
251455495, , , , GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC
251455496, , , , GO12037_LC|GO12027_LC|GO12007_LC|GO12040_LC
251456055, , , , GO12037_LC|GO12027_LC|GO12013_LC
251456057, , , , GO12027_LC|GO12013_LC
251456058, , , , GO12037_LC|GO12027_LC|GO12013_LC
251456362, , , , GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
251456363, , , , GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC
251456364, , , , GO12027_LC|GO12040_LC|GO12040_SC
251456365, , , , GO12027_LC|GO12040_LC
251456366, , , , GO12027_LC|GO12040_LC
251456367, , , , GO12037_LC|GO12027_LC|GO12040_LC|GO12037_SC|GO12040_SC
251456368, , , , GO12037_LC|GO12027_LC|GO12040_LC
251456370, , , , GO12037_LC|GO12027_LC|GO12040_LC|GO12040_SC
251456371, , , , GO12027_LC|GO12040_LC
251456373, , , , GO12027_LC|GO12040_LC|GO12040_SC
251456374, , , , GO12037_LC|GO12027_LC|GO12040_LC
251456375, , , , GO12027_LC
251456376, , , , GO12037_LC|GO12027_LC|GO12040_LC
251456377, , , , GO12037_LC|GO12027_LC|GO12040_LC
251456378, , , , GO12037_LC|GO12027_LC|GO12040_LC
251456379, , , , GO12037_LC|GO12027_LC|GO12040_LC
251456380, , , , GO12027_LC
251456381, , , , GO12027_LC|GO12040_LC
251456383, , , , GO12027_LC|GO12901_LC
251456384, , , , GO12037_LC|GO12027_LC
251456386, , , , GO12027_LC
251456388, , , , GO12027_LC