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1/06 - 2021 |
Using the Hamilton Échelle Spectrograph at Lick Observatory, we have obtained precise radial velocities (RVs) of a sample of 373 G- and K-giant stars over more than 12 years, leading to the discovery of several single and multiple planetary systems. The RVs of the long-period spectroscopic binary ε Cyg (HIP 102488) are found to exhibit additional regular variations with a much shorter period. We intend to improve the orbital solution of the ε Cyg system, and attempt to identify the cause of...
4/04 - 2021 |
Aims. To study the spot evolution and differential rotation in the magnetically-active cool K-type giant star $\sigma$ Gem from broad-band photometry and continuous spectroscopic observations spanning 150 nights.Methods. We use high-resolution, high signal-to-noise ratio spectra obtained with the Hertzsprung SONG telescope to reconstruct surface (photospheric) temperature maps with Doppler imaging techniques. The 303 observations span 150 nights and allow for a detailed analysis of the spot...
18/02 - 2021 |
Eclipsing binary stars provide the means to derive accurate and precise masses and radii, from which insights into their evolution may be obtained. When they reside in star clusters, basic properties of even higher precision, along with additional information, can be extracted. Asteroseismology of solar-like oscillations offers similar possibilities for single stars. We wish to improve the previously established properties of the Hyades eclipsing binary HD 27130 and re-asses the...
14/10 - 2020 |
We have been monitoring the metal-poor Population II giant, HD 122563, for radial velocity variations since 2016 using the SONG telescope on Tenerife. We have detected the global seismic quantity $\nu_{\rm max}$ which provides information related to the stellar parameters. By combining these data with complementary data, we derive a new precise surface gravity, radius and distance to the star. Our results are corroborated by using the parallax from Gaia DR2. We present these results and some...
29/07 - 2020 |
The study of planet occurrence as a function of stellar mass is important for a better understanding of planet formation. Estimating stellar mass, especially in the red giant regime, is difficult. In particular, stellar masses of a sample of evolved planet-hosting stars based on spectroscopy and grid-based modelling have been put to question over the past decade with claims they were overestimated. Although efforts have been made in the past to reconcile this dispute using asteroseismology,...
12/07 - 2020 |
We report the discovery of a second planet orbiting the K-giant star 7 CMa based on 166 high-precision radial velocities obtained with Lick, HARPS, UCLES and SONG. The periodogram analysis reveals two periodic signals of approximately 745 and 980 d, associated to planetary companions. The double-Keplerian orbital fit of the data suggests possible strong interaction between the planets. The system is consistent with two Jupiter-like planets with minimum masses $m_b\sin i \sim 2...
29/04 - 2020 |
We report the detection of a Saturn-size exoplanet orbiting HD 332231 (TOI 1456) in light curves from the Transiting Exoplanet Survey Satellite (TESS). HD 332231—an F8 dwarf star with a $V$-band magnitude of 8.56—was observed by TESS in Sectors 14 and 15. We detect a single-transit event in the Sector 15 presearch data conditioning (PDC) light curve. We obtain spectroscopic follow-up observations of HD 332231 with the Automated Planet Finder, Keck I, and SONG...
28/04 - 2020 |
We present new Doppler images of both components of the double-lined binary $\sigma^{2}$ CrB, based on the high-resolution spectroscopic data collected during 11 nights in 2015 March–April. The observed spectra form two independent data sets with sufficient phase coverage. We apply the least-squares deconvolution to all observed spectra to obtain high signal-to-noise mean profiles, from which we derive the Doppler images of both components of $\sigma^{2}$ CrB simultaneously. The surfaces of...
8/11 - 2019 |
We present an in-depth analysis of the bright subgiant star HR 7322 (KIC 10005473) using Kepler short-cadence photometry, optical interferometry from CHARA, high-resolution spectroscopy using SONG spectra, and stellar modelling using garstec grids and the Bayesian grid-fitting algorithm basta. HR 7322 is only the second subgiant with high-quality Kepler asteroseismology for which we also have interferometric data. We find a limb-darkened angular diameter of $0.443 \pm...
20/09 - 2019 |
The nearby red giant Aldebaran is known to host a gas giant planetary companion from decades of ground-based spectroscopic radial velocity measurements. Using Gaussian Process-based Continuous Auto-Regressive Moving Average models, we show that these historic data also contain evidence of acoustic oscillations in the star itself, and verify this result with further dedicated ground-based spectroscopy using the SONG telescope and space-based photometry with the Kepler Space Telescope. From...
