@article{SchaffenrothCasewellSchneideretal.2020,
  author    = {Schaffenroth, Veronika and Casewell, Sarah L. and Schneider, D. and Kilkenny, David and Geier, Stephan and Heber, Ulrich and Irrgang, Andreas and Przybilla, Norbert and Marsh, Thomas R. and Littlefair, Stuart P. and Dhillon, Vik S.},
  title     = {A quantitative in-depth analysis of the prototype sdB plus BD system SDSS J08205+0008 revisited in the Gaia era},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {501},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {3},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/staa3661},
  pages     = {3847 -- 3870},
  year      = {2020},
  abstract  = {Subdwarf B stars are core-helium-burning stars located on the extreme horizontal branch (EHB). Extensive mass loss on the red giant branch is necessary to form them. It has been proposed that substellar companions could lead to the required mass loss when they are engulfed in the envelope of the red giant star. J08205+0008 was the first example of a hot subdwarf star with a close, substellar companion candidate to be found. Here, we perform an in-depth re-analysis of this important system with much higher quality data allowing additional analysis methods. From the higher resolution spectra obtained with ESO-VLT/XSHOOTER, we derive the chemical abundances of the hot subdwarf as well as its rotational velocity. Using the Gaia parallax and a fit to the spectral energy distribution in the secondary eclipse, tight constraints to the radius of the hot subdwarf are derived. From a long-term photometric campaign, we detected a significant period decrease of -3.2(8) x 10(-12) dd(-1). This can be explained by the non-synchronized hot subdwarf star being spun up by tidal interactions forcing it to become synchronized. From the rate of period decrease we could derive the synchronization time-scale to be 4 Myr, much smaller than the lifetime on EHB. By combining all different methods, we could constrain the hot subdwarf to a mass of 0.39-0.50 M-circle dot and a radius of R-sdB = 0.194 +/- 0.008 R-circle dot, and the companion to 0.061-0.071 M-circle dot with a radius of R-comp = 0.092 +/- 0.005 R-circle dot, below the hydrogen-burning limit. We therefore confirm that the companion is most likely a massive brown dwarf.},
  language  = {en}
}
@article{GrunerBarnes2020,
  author    = {Gruner, David and Barnes, Sydney A.},
  title     = {Rotation periods for cool stars in the open cluster Ruprecht 147 (NGC 6774) Implications for gyrochronology},
  series = {Astronomy and astrophysics : an international weekly journal},
  volume    = {644},
  journal   = {Astronomy and astrophysics : an international weekly journal},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {0004-6361},
  doi       = {10.1051/0004-6361/202038984},
  pages     = {40},
  year      = {2020},
  abstract  = {Context: Gyrochronology allows the derivation of ages for cool main sequence stars based on their observed rotation periods and masses, or a suitable proxy thereof. It is increasingly well-explored for FGK stars, but requires further measurements for older ages and K - M-type stars. Aims: We study the 2.7 Gyr-old open cluster Ruprecht 147 to compare it with the previously-studied, but far more distant, NGC 6819 cluster, and especially to measure cooler stars than was previously possible there. Methods: We constructed an inclusive list of 102 cluster members from prior work, including Gaia DR2, and for which light curves were also obtained during Campaign 7 of the Kepler/K2 space mission. We placed them in the cluster color-magnitude diagram and checked the related information against appropriate isochrones. The light curves were then corrected for data systematics using Principal Component Analysis on all observed K2 C07 stars and subsequently subjected to periodicity analysis. Results: Periodic signals are found for 32 stars, 21 of which are considered to be both highly reliable and to represent single, or effectively single, Ru 147 stars. These stars cover the spectral types from late-F to mid-M stars, and they have periods ranging from 6 d - 33 d, allowing for a comparison of Ruprecht 147 to both other open clusters and to models of rotational spindown. The derived rotation periods connect reasonably to, overlap with, and extend to lower masses the known rotation period distribution of the 2.5 Gyr-old cluster NGC 6819. Conclusions: The data confirm that cool stars lie on a single surface in rotation period-mass-age space, and they simultaneously challenge its commonly assumed shape. The shape at the low mass region of the color-period diagram at the age of Ru 147 favors a recently-proposed model which requires a third mass-dependent timescale in addition to the two timescales required by a former model, suggesting that a third physical process is required to model rotating stars effectively.},
  language  = {en}
}
@article{WellsPoppenhaegerWatson2019,
  author    = {Wells, Robert and Poppenh{\"a}ger, Katja and Watson, C. A.},
  title     = {Validation of a temperate fourth planet in the K2-133 multiplanet system},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {487},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {2},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stz1334},
  pages     = {1865 -- 1873},
  year      = {2019},
  abstract  = {We present follow-up observations of the K2-133 multiplanet system. Previously, we announced that K2-133 contained three super-Earths orbiting an M1.5V host star - with tentative evidence of a fourth outer-planet orbiting at the edge of the temperate zone. Here, we report on the validation of the presence of the fourth planet, determining a radius of 1.73+0.14-0.13 R⊕. The four planets span the radius gap of the exoplanet population, meaning further follow-up would be worthwhile to obtain masses and test theories of the origin of the gap. In particular, the trend of increasing planetary radius with decreasing incident flux in the K2-133 system supports the claim that the gap is caused by photo-evaporation of exoplanet atmospheres. Finally, we note that K2-133 e orbits on the edge of the star's temperate zone, and that our radius measurement allows for the possibility that this is a rocky world. Additional mass measurements are required to confirm or refute this scenario.},
  language  = {en}
}
@article{ZhangLideGrijsetal.2015,
  author    = {Zhang, Chaoli and Li, Chengyuan and de Grijs, Richard and Bekki, Kenji and Deng, Licai and Zaggia, Simone and Rubele, Stefano and Piatti, Andres E. and Cioni, Maria-Rosa L. and Emerson, Jim and For, Bi-Qing and Ripepi, Vincenzo and Marconi, Marcella and Ivanov, Valentin D. and Chen, Li},
  title     = {The vmc survey. XVIII. radial dependence of the Low-Mass, 0.55-0.82M(circle dot) stellar mass function in the galactic globular cluster 47 tucanae},
  series = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
  volume    = {815},
  journal   = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
  number    = {2},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {0004-637X},
  doi       = {10.1088/0004-637X/815/2/95},
  pages     = {9},
  year      = {2015},
  language  = {en}
}