The K2 Bright Star Survey. I. Methodology and data release
Astrophysical Journal Supplement American Astronomical Society 245 (2019) 8
Abstract:
While the Kepler mission was designed to look at tens of thousands of faint stars (V gsim 12), brighter stars that saturated the detector are important because they can be and have been observed very accurately by other instruments. By analyzing the unsaturated scattered-light "halo" around these stars, we retrieved precise light curves of most of the brightest stars in K2 fields from Campaign 4 onward. The halo method does not depend on the detailed cause and form of systematics, and we show that it is effective at extracting light curves from both normal and saturated stars. The key methodology is to optimize the weights of a linear combination of pixel time series with respect to an objective function. We test a range of such objective functions, finding that lagged Total Variation, a generalization of Total Variation, performs well on both saturated and unsaturated K2 targets. Applying this to the bright stars across the K2 Campaigns reveals stellar variability ubiquitously, including effects of stellar pulsation, rotation, and binarity. We describe our pipeline and present a catalog of the 161 bright stars, with classifications of their variability, asteroseismic parameters for red giants with well-measured solar-like oscillations, and remarks on interesting objects. These light curves are publicly available as a High Level Science Product from the Mikulski Archive for Space Telescopes (footnote 17).A ghost in the toast: TESS background light produces a false “transit” across τ Ceti
Research Notes of the AAS American Astronomical Society 3:10 (2019) 145
An 11 Earth-mass, Long-period Sub-Neptune Orbiting a Sun-like Star
ASTRONOMICAL JOURNAL American Astronomical Society 158:4 (2019) ARTN 165
Abstract:
© 2019. The American Astronomical Society. All rights reserved.. Although several thousands of exoplanets have now been detected and characterized, observational biases have led to a paucity of long-period, low-mass exoplanets with measured masses and a corresponding lag in our understanding of such planets. In this paper we report the mass estimation and characterization of the long-period exoplanet Kepler-538b. This planet orbits a Sun-like star (V = 11.27) with M∗ =0.892-0.035+0.051 and R∗ = 0.8717-0.0061+0.0064 R o. Kepler-538b is a 2.215-0.034+0.040 R ⊕ sub-Neptune with a period of P = 81.73778 ± 0.00013 days. It is the only known planet in the system. We collected radial velocity (RV) observations with the High Resolution Echelle Spectrometer (HIRES) on Keck I and High Accuracy Radial velocity Planet Searcher in North hemisphere (HARPS-N) on the Telescopio Nazionale Galileo (TNG). We characterized stellar activity by a Gaussian process with a quasi-periodic kernel applied to our RV and cross-correlation function FWHM observations. By simultaneously modeling Kepler photometry, RV, and FWHM observations, we found a semi-amplitude of K = 1.68-0.38+0.39 m s-1 and a planet mass of Mp = 10.6-2.4+2.5 M ⊕. Kepler-538b is the smallest planet beyond P = 50 days with an RV mass measurement. The planet likely consists of a significant fraction of ices (dominated by water ice), in addition to rocks/metals, and a small amount of gas. Sophisticated modeling techniques such as those used in this paper, combined with future spectrographs with ultra high-precision and stability will be vital for yielding more mass measurements in this poorly understood exoplanet regime. This in turn will improve our understanding of the relationship between planet composition and insolation flux and how the rocky to gaseous transition depends on planetary equilibrium temperature.An 11 Earth-mass, long-period Sub-Neptune orbiting a Sun-like star
Astronomical Journal American Astronomical Society 158:4 (2019) 165-165
Abstract:
Although several thousands of exoplanets have now been detected and characterized, observational biases have led to a paucity of long-period, low-mass exoplanets with measured masses and a corresponding lag in our understanding of such planets. In this paper we report the mass estimation and characterization of the long-period exoplanet Kepler-538b. This planet orbits a Sun-like star (V = 11.27) with = - M + 0.892 0.035 0.051* Me and R =* - + 0.8717 0.0061 0.0064 Re. Kepler-538b is a - + 2.215 0.034 0.040 R⊕ sub-Neptune with a period of P = 81.73778 ± 0.00013 days. It is the only known planet in the system. We collected radial velocity (RV) observations with the High Resolution Echelle Spectrometer (HIRES) on Keck I and High Accuracy Radial velocity Planet Searcher in North hemisphere (HARPS-N) on the Telescopio Nazionale Galileo (TNG). We characterized stellar activity by a Gaussian process with a quasi-periodic kernel applied to our RV and cross-correlation function FWHM observations. By simultaneously modeling Kepler photometry, RV, and FWHM observations, we found a semi-amplitude of = -+ K 1.68 0.38 0.39 m s−1 and a planet mass of = - M + p 10.6 2.4 2.5 M⊕. Kepler-538b is the smallest planet beyond P = 50 days with an RV mass measurement. The planet likely consists of a significant fraction of ices (dominated by water ice), in addition to rocks/metals, and a small amount of gas. Sophisticated modeling techniques such as those used in this paper, combined with future spectrographs with ultra high-precision and stability will be vital for yielding more mass measurements in this poorly understood exoplanet regime. This in turn will improve our understanding of the relationship between planet composition and insolation flux and how the rocky to gaseous transition depends on planetary equilibrium temperature.Radial velocity confirmation of K2-100b: a young, highly irradiated, and low-density transiting hot Neptune
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY Oxford University Press (OUP) 490:1 (2019) 698-708