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Szabo G.M.,ELTE Gothard Astrophysical Observatory | Szabo G.M.,Hungarian Academy of Sciences | Szabo G.M.,Gothard Lendulet Research Team | Simon A.,Hungarian Academy of Sciences | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

Kepler-13b is a most intriguing exoplanet system due to the rapid precession rate, exhibiting several exotic phenomena.We analysed Kepler short cadence data up to Quarter 14, with a total time-span of 928 d, to reveal changes in transit duration, depth, asymmetry and identify the possible signals of stellar rotation and low-level activity.We investigated long-term variations of transit light curves testing for duration, peak depth and asymmetry. We also performed cluster analysis on Kepler quarters. We computed the autocorrelation function of the out-oftransit light variations. Transit duration, peak depth and asymmetry evolve slowly, due to the slowly drifting transit path through the stellar disc. The detected transit shapes will map the stellar surface on the time-scale of decades. We found a very significant clustering pattern with 3-orbit period. Its source is very probably the rotating stellar surface, in the 5:3 spin- orbit resonance reported in a previous study. The autocorrelation function of the out-of-transit light variations, filtered to 25.4 h and harmonics, shows slow variations and a peak around 300-360 d period, which could be related to the activity cycle of the host star. © 2013 The Authors. Source

Carlberg J.K.,Carnegie Institution of Washington | Smith V.V.,National Optical Astronomy Observatory | Cunha K.,Observatorio Nacional | Cunha K.,University of Arizona | And 18 more authors.
Astrophysical Journal | Year: 2015

A Li-rich red giant (RG) star (2M19411367+4003382) recently discovered in the direction of NGC 6819 belongs to the rare subset of Li-rich stars that have not yet evolved to the luminosity bump, an evolutionary stage where models predict Li can be replenished. The currently favored model to explain Li enhancement in first-ascent RGs like 2M19411367+4003382 requires deep mixing into the stellar interior. Testing this model requires a measurement of 12C/13C, which is possible to obtain from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra. However, the Li-rich star also has abnormal asteroseismic properties that call into question its membership in the cluster, even though its radial velocity and location on color-magnitude diagrams are consistent with membership. To address these puzzles, we have measured a wide array of abundances in the Li-rich star and three comparison stars using spectra taken as part of the APOGEE survey to determine the degree of stellar mixing, address the question of membership, and measure the surface gravity. We confirm that the Li-rich star is a RG with the same overall chemistry as the other cluster giants. However, its is significantly lower, consistent with the asteroseismology results and suggestive of a very low mass if the star is indeed a cluster member. Regardless of the cluster membership, the 12C/13C and C/N ratios of the Li-rich star are consistent with standard first dredge-up, indicating that Li dilution has already occurred, and inconsistent with internal Li enrichment scenarios that require deep mixing. © 2015. The American Astronomical Society. All rights reserved.. Source

Martell S.L.,University of New South Wales | Shetrone M.D.,University of Texas at Austin | Lucatello S.,National institute for astrophysics | Schiavon R.P.,Liverpool John Moores University | And 6 more authors.
Astrophysical Journal | Year: 2016

We present new identifications of five red giant stars in the Galactic halo with chemical abundance patterns that indicate they originally formed in globular clusters. Using data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) Survey available through Sloan Digital Sky Survey (SDSS) Data Release 12, we first identify likely halo giants, and then search those for the well-known chemical tags associated with globular clusters, specifically enrichment in nitrogen and aluminum. We find that 2% of the halo giants in our sample have this chemical signature, in agreement with previous results. Following the interpretation in our previous work on this topic, this would imply that at least 13% of halo stars originally formed in globular clusters. Recent developments in the theoretical understanding of globular cluster formation raise questions about that interpretation, and we concede the possibility that these migrants represent a small fraction of the halo field. There are roughly as many stars with the chemical tags of globular clusters in the halo field as there are in globular clusters, whether or not they are accompanied by a much larger chemically untaggable population of former globular cluster stars. © 2016. The American Astronomical Society. All rights reserved. Source

Tayar J.,Ohio State University | Ceillier T.,University Paris Diderot | Garcia-Hernandez D.A.,Institute of Astrophysics of Canarias | Garcia-Hernandez D.A.,University of La Laguna | And 23 more authors.
Astrophysical Journal | Year: 2015

We investigate the occurrence rate of rapidly rotating (ν sin i >10 km s-1), low-mass giant stars in the Apache Point Observatory Galaxy Evolution Experiment-Kepler (APOKASC) fields with asteroseismic mass and surface gravity measurements. Such stars are likely merger products and their frequency places interesting constraints on stellar population models. We also identify anomalous rotators, i.e., stars with 5 km s-1 < ν sin i < 10 km s-1 that are rotating significantly faster than both angular momentum evolution predictions and the measured rates of similar stars. Our data set contains fewer rapid rotators than one would expect given measurements of the Galactic field star population, which likely indicates that asteroseismic detections are less common in rapidly rotating red giants. The number of low-mass moderate (5-10 km s-1) rotators in our sample gives a lower limit of 7% for the rate at which low-mass stars interact on the upper red giant branch because single stars in this mass range are expected to rotate slowly. Finally, we classify the likely origin of the rapid or anomalous rotation where possible. KIC 10293335 is identified as a merger product and KIC 6501237 is a possible binary system of two oscillating red giants. © 2015. The American Astronomical Society. All rights reserved. Source

Hayden M.R.,New Mexico State University | Bovy J.,Institute for Advanced Study | Holtzman J.A.,New Mexico State University | Nidever D.L.,University of Michigan | And 40 more authors.
Astrophysical Journal | Year: 2015

Using a sample of 69,919 red giants from the SDSS-III/APOGEE Data Release 12, we measure the distribution of stars in the [/Fe] versus [Fe/H] plane and the metallicity distribution functions (MDFs) across an unprecedented volume of the Milky Way disk, with radius 3 < R < 15 kpc and height kpc. Stars in the inner disk (R < 5 kpc) lie along a single track in [/Fe] versus [Fe/H], starting with -enhanced, metal-poor stars and ending at [/Fe] ∼ 0 and [Fe/H] ∼ +0.4. At larger radii we find two distinct sequences in [/Fe] versus [Fe/H] space, with a roughly solar- sequence that spans a decade in metallicity and a high- sequence that merges with the low- sequence at super-solar [Fe/H]. The location of the high- sequence is nearly constant across the disk. Source

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