# Summary of K2 Program GO11125

Title: The age of Galactic Bulge/Thick disk field stars in the metal-poor metallicity distribution tail

PI: Valentini, Marica (Kepler Guest Observer Office)
CoIs: Miglio, Andrea; Chiappini, Cristina; Anders, Friedrich; Montalban, Josefina; Barbuy, Beatriz

MOTIVATION: The detection of chemical imprints left by the first stars has a key role in the understanding the chemical and physical conditions of the early Universe. Most of the current observational efforts in finding the chemical imprints left by the first stars have focused on the most metal-poor stars found in the MW halo. However, studies based on the chemical and kinematic properties of stars in the different MW components have shown that not only the halo, but also the bulge and thick disk are potential hosts of the oldest stars in our Galaxy.
By studying the heavy element content of few stars in the oldest MW GC NGC6522, located in the Galactic Bulge, Chiappini et al. (2001) and Barbuy et al. (2014) suggested that Bulge stars at moderately low metallicites are as old as the oldest halo stars, which are 100 times more metal poor ([Fe/H] = -3).
 Obviously, no age measurements are available for any of the red giants studied in these works.
 As the correspondence between age and metallicity is strongly dependent on the star formation history of the particular studied component, it is crucial to confirm that moderately metal poor Bulge stars are very old and hence born from an interstellar medium essentially enriched by the first stellar generations of massive stars. This confirmation can be performed by measuring with high precision the ages and abundances of field red giants in the Bulge. As only asteroseismic measurements will be able to provide precise ages for these distant red giants, this is an opportunity not to be missed by K2. The feasibility and the impact of the use of asteroseismology coupled with spectroscopy have been confirmed by recent works in the field of Galactic Archeology (i.e. Chiappini et al. 2015).

RELEVANCE: The derivation of precise and accurate abundances and ages for Bulge field stars is hampered by the difficulties of observing in such obscured region (Eb-V reaching 1) and of determining ages for red giants (difficulties in determining atmospheric parameters plus degeneracies in the HR diagram in the RG locus). A dedicated program combining asteroseismology with K2 and spectroscopy will avoid such limitations, providing an ambitious and new dataset where to look for the imprints of first stars. This will be the only opportunity to confirm/discard the old ages of distant field Red Giant Bulge stars. So far, ages of bulge field stars were obtained only for lensed dwarf stars (Bensby et al. 2013). If confirmed that bulge stars of moderate low metallicity (1/10th solar) are indeed very old, this will open a new window into the study of the fossil records containing the chemical imprints of the first stellar generations.

AIM: We selected our targets from the APOGEE DR13 catalog. By applying a selection in gravity (following K-2 performances, Stello et al. 2015) and in metallicity ([M/H]<-0.5), we identified 30 field Red Giants useful for our project. The light curves obtained from this campaign, will led us to obtain fundamental seismic information. With this data we aim to a) confirm that Bulge stars of moderately low metallicities are very old objects, as old as the oldest halo stars observed; and b) analyse the chemical pattern of the oldest objects in order to establish if there are imprints left by the first stellar generations . 

METHOLOGY: The K2 data will be used to determine the radius and the mass of each stars using asteroseismology. This information will be complemented by already secured ground-based spectroscopy with APOGEE. With this it will be possible to determine accurate distances, reddening and model-dependent ages.  Finally, the inferred ages together with key abundance indicators will be combined in order to identify possible imprints of the first stellar generations left in the oldest stars in the Galactic Bulge.

# Targets requested by this program that have been observed (88)
EPIC ID, RA (J2000) [deg], Dec (J2000) [deg], magnitude, Investigation IDs
204338067, 254.65113, -22.728104, 13.362, GO11123_LC|GO11125_LC
204339408, 254.537637, -22.72273, 13.423, GO11123_LC|GO11125_LC
204386383, 255.056902, -22.538536, 12.577, GO11123_LC|GO11125_LC
204433876, 254.933827, -22.352498, 13.73, GO11123_LC|GO11125_LC
204543889, 254.753993, -21.905931, 12.598, GO11123_LC|GO11125_LC
204550905, 253.385731, -21.87671, 13.897, GO11123_LC|GO11125_LC
204562835, 253.340918, -21.825976, 13.755, GO11123_LC|GO11125_LC
204564308, 254.823769, -21.819701, 14.042, GO11123_LC|GO11125_LC
204577683, 253.637108, -21.763564, 12.524, GO11123_LC|GO11125_LC
204588368, 253.016087, -21.71891, 13.405, GO11123_LC|GO11125_LC
204594915, 254.965169, -21.691487, 13.651, GO11123_LC|GO11125_LC
204596317, 253.05349, -21.685452, 13.827, GO11123_LC|GO11125_LC
204597246, 254.236562, -21.68165, 13.193, GO11123_LC|GO11125_LC
204597517, 253.403435, -21.680466, 13.445, GO11123_LC|GO11125_LC
204630018, 253.194432, -21.543679, 13.044, GO11123_LC|GO11048_LC|GO11125_LC
204645301, 252.835542, -21.4793, 12.015, GO11123_LC|GO11125_LC
204651697, 252.943625, -21.451988, 13.865, GO11123_LC|GO11125_LC
204652777, 254.3583, -21.447306, 13.706, GO11123_LC|GO11125_LC
204664797, 253.57588, -21.39598, 12.988, GO11123_LC|GO11125_LC
204674255, 252.833525, -21.355682, 13.27, GO11123_LC|GO11125_LC
204674302, 252.905231, -21.355507, 13.304, GO11123_LC|GO11125_LC
204683960, 254.199045, -21.313748, 13.326, GO11123_LC|GO11125_LC
204686477, 254.386756, -21.303267, 12.533, GO11123_LC|GO11125_LC
204711515, 254.547517, -21.194168, 13.435, GO11123_LC|GO11125_LC
204720374, 254.510407, -21.155073, 12.725, GO11123_LC|GO11048_LC|GO11125_LC
204722708, 254.17599, -21.145012, 11.364, GO11123_LC|GO11125_LC
204726572, 254.339632, -21.127999, 13.501, GO11123_LC|GO11125_LC
204770467, 253.766406, -20.938421, 11.363, GO11071_LC|GO11122_LC|GO11125_LC
204777654, 252.757065, -20.906656, 13.748, GO11123_LC|GO11125_LC
204785972, 254.180909, -20.86962, 12.405, GO11123_LC|GO11125_LC
204787769, 254.085847, -20.86149, 12.325, GO11049_LC|GO11122_LC|GO11125_LC
204788857, 254.494557, -20.856326, 13.733, GO11123_LC|GO11125_LC
222924691, 266.725955, -26.781009, 10.783, GO11123_LC|GO11125_LC
223009644, 266.446055, -26.653049, 13.635, GO11123_LC|GO11125_LC
224053677, 267.24501, -24.937603, 13.184, GO11123_LC|GO11125_LC
224498808, 262.775807, -24.137516, 13.187, GO11123_LC|GO11125_LC
224569547, 262.715649, -24.01356, 12.895, GO11123_LC|GO11125_LC
224693227, 263.029487, -23.799403, 14.924, GO11123_LC|GO11125_LC
224738405, 263.257086, -23.723343, 13.114, GO11123_LC|GO11125_LC
224738459, 262.730063, -23.723266, 13.335, GO11123_LC|GO11125_LC
224866988, 262.465, -23.507461, 13.263, GO11123_LC|GO11125_LC
226203879, 264.070625, -21.065002, 14.023, GO11123_LC|GO11125_LC
226852010, 263.367869, -19.588331, 14.624, GO11123_LC|GO11125_LC
227280660, 263.474384, -18.542379, 14.082, GO11123_LC|GO11125_LC
227449454, 263.472211, -18.124708, 13.993, GO11123_LC|GO11125_LC
227579751, 263.38789, -17.791637, 13.238, GO11123_LC|GO11125_LC
227653459, 262.638964, -17.595451, 13.442, GO11123_LC|GO11125_LC
227729334, 263.401635, -17.379856, 13.176, GO11123_LC|GO11125_LC
227732408, 263.264105, -17.371086, 13.02, GO11123_LC|GO11125_LC
227738032, 263.152498, -17.354137, 12.629, GO11123_LC|GO11125_LC
227799134, 263.114868, -17.169012, 10.531, GO11123_LC|GO11125_LC
227945945, 262.955103, -16.698863, 13.403, GO11123_LC|GO11125_LC
230490368, 255.815996, -21.975184, 13.531, GO11123_LC|GO11125_LC
230492642, 255.675489, -21.953373, 13.165, GO11123_LC|GO11125_LC
230536555, 255.683954, -21.536991, 11.923, GO11123_LC|GO11125_LC
230538371, 255.646475, -21.520193, 12.929, GO11123_LC|GO11125_LC
230542745, 255.601004, -21.479928, 12.942, GO11123_LC|GO11125_LC
230545915, 255.650522, -21.449913, 12.967, GO11123_LC|GO11125_LC
231357535, 255.933651, -22.92814, 13.595, GO11123_LC|GO11125_LC
231387632, 255.817665, -22.643575, 13.897, GO11123_LC|GO11125_LC
231418011, 255.856989, -22.34115, 11.668, GO11123_LC|GO11125_LC
231424251, 255.848919, -22.280704, 14.292, GO11123_LC|GO11125_LC
231436327, 256.03273, -22.159806, 15.073, GO11123_LC|GO11125_LC
234936593, 258.25649, -24.919823, 13.885, GO11123_LC|GO11125_LC
234957435, 258.445514, -24.831556, 14.407, GO11123_LC|GO11125_LC
234996860, 258.507421, -24.661525, 14.474, GO11123_LC|GO11125_LC
235020353, 258.042641, -24.557653, 14.517, GO11123_LC|GO11125_LC
235023473, 258.148357, -24.54394, 14.152, GO11123_LC|GO11125_LC
235032202, 258.468172, -24.504366, 12.996, GO11123_LC|GO11125_LC
235052965, 261.742497, -24.4062, 13.394, GO11123_LC|GO11125_LC
235132769, 259.426647, -24.009121, 14.993, GO11123_LC|GO11125_LC
235153847, 258.381464, -23.91342, 14.603, GO11123_LC|GO11125_LC
235870896, 258.752419, -29.101667, 13.485, GO11123_LC|GO11125_LC
235977292, 259.979972, -28.768204, 13.64, GO11123_LC|GO11125_LC
236238729, 258.971914, -27.921299, 14.139, GO11123_LC|GO11125_LC
236275431, 260.374907, -27.800308, 13.077, GO11123_LC|GO11125_LC
236322794, 260.715766, -27.639852, 14.399, GO11123_LC|GO11125_LC
236405713, 259.851772, -27.348786, 13.214, GO11123_LC|GO11125_LC
236419080, 261.829481, -27.301126, 13.364, GO11125_LC
236439141, 260.021397, -27.229917, 13.129, GO11123_LC|GO11048_LC|GO11125_LC
240252225, 263.793562, -29.997039, 12.865, GO11123_LC|GO11125_LC
240512147, 262.627501, -29.098002, 13.676, GO11123_LC|GO11125_LC
240522766, 264.184626, -29.060964, 13.016, GO11123_LC|GO11125_LC
240547251, 264.507132, -28.974476, 13.565, GO11123_LC|GO11125_LC
240554986, 263.769185, -28.946587, 13.433, GO11123_LC|GO11125_LC
240592204, 264.503805, -28.806894, 13.261, GO11123_LC|GO11048_LC|GO11125_LC
240748341, 263.753604, -28.134756, 13.524, GO11125_LC
240978776, 262.227023, -26.903269, 13.415, GO11123_LC|GO11125_LC