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16 Publications visible to you, out of a total of 16
Improved asteroseismic inversions for red-giant surface rotation rates

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Context: Asteroseismic observations of internal stellar rotation have indicated a substantial lack of angular momentum transport in theoretical models of subgiant and red-giant stars. Accurate core and … surface rotation rate measurements are therefore needed to constrain the internal transport processes included in the models. Aims: We eliminate substantial systematic errors of asteroseismic surface rotation rates found in previous studies. Methods: We propose a new objective function for the optimally localised averages method of rotational inversions for red-giant stars, which results in more accurate envelope rotation rate estimates obtained from the same data. We use synthetic observations from stellar models across a range of evolutionary stages and masses to demonstrate the improvement. Results: We find that our new inversion technique allows us to obtain estimates of the surface rotation rate that are independent of the core rotation. For a star at the base of the red-giant branch, we reduce the systematic error from about 20% to a value close to 0, assuming constant envelope rotation. We also show the equivalence between this method and the method of linearised rotational splittings. Conclusions: Our new rotational inversion method substantially reduces the systematic errors of red-giant surface rotation rates. In combination with independent measures of the surface rotation rate, this will allow better constraints to be set on the internal rotation profile. This will be a very important probe for further constraining the internal angular momentum transport along the lower part of the red-giant branch.

Authors: F. Ahlborn, E. P. Bellinger, S. Hekker, S. Basu, D. Mokrytska

Date Published: 1st Dec 2022

Publication Type: Journal

Companions to Kepler giant stars: A long-period eccentric sub-stellar companion to KIC 3526061 and a stellar companion to HD 187878

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Context: Our knowledge of populations and the occurrence of planets orbiting evolved intermediate-mass stars is still incomplete. In 2010 we started a planet search programme among 95 giant stars … observed by the Kepler mission to increase the sample of giant stars with planets and with reliable estimates of stellar masses and radii. Aims: We present the two systems from our planet search programme whose companions we were able to characterise: KIC 3526061 and HD 187878. Methods: We used precise stellar radial velocity measurements taken with four different echelle spectrographs to derive an orbital solution. We used Gaia astrometric measurements to obtain the inclination of the HD 187878 system and Kepler photometric observations to estimate the stellar mass and radius. Results: We report the discovery of a sub-stellar companion and a stellar companion around two intermediate-mass red giant branch stars. KIC 3526061 b is most likely a brown dwarf with a minimum mass of 18.15 ± 0.44 M Jupiter in a long-period eccentric orbit, with orbital period 3552−135+158d and orbital eccentricity e= 0.85 ± 0.01. It is the most evolved system found having a sub-stellar companion with such a high eccentricity and wide separation. HD 187878 B has a minimum mass of 78.4 ± 2.0 M Jupiter. Combining the spectroscopic orbital parameters with the astrometric proper motion anomaly, we derived an orbital inclination i=9.8−0.6+0.4deg, which corresponds to the companion’s mass in the stellar regime of 0.51−0.02+0.04M⊙. Conclusions: A sub-stellar companion of KIC 3526061 extends the sample of known red giant branch stars with sub-stellar companions on very eccentric wide orbits, and might provide a probe of the dynamical evolution of such systems over time.

Authors: Marie Karjalainen, Raine Karjalainen, Artie P. Hatzes, Holger Lehmann, Pierre Kervella, Saskia Hekker, Hans Van Winckel, Jakub Überlauer, Michaela Vítková, Marek Skarka, Petr Kabáth, Saskia Prins, Andrew Tkachenko, William D. Cochran, Alain Jorissen

Date Published: 1st Dec 2022

Publication Type: Journal

Jupiter’s inhomogeneous envelope

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Context: While Jupiter’s massive gas envelope consists mainly of hydrogen and helium, the key to understanding Jupiter’s formation and evolution lies in the distribution of the remaining (heavy) elements. … Before the Juno mission, the lack of high-precision gravity harmonics precluded the use of statistical analyses in a robust determination of the heavy-element distribution in Jupiter’s envelope. Aims: In this paper, we assemble the most comprehensive and diverse collection of Jupiter interior models to date and use it to study the distribution of heavy elements in the planet’s envelope. Methods: We apply a Bayesian statistical approach to our interior model calculations, reproducing the Juno gravitational and atmospheric measurements and constraints from the deep zonal flows. Results: Our results show that the gravity constraints lead to a deep entropy of Jupiter corresponding to a 1 bar temperature that is 515 K higher than traditionally assumed. We also find that uncertainties in the equation of state are crucial when determining the amount of heavy elements in Jupiter’s interior. Our models put an upper limit to the inner compact core of Jupiter of 7 M_Earth, independently of the structure model (with or without a dilute core) and the equation of state considered. Furthermore, we robustly demonstrate that Jupiter’s envelope is inhomogeneous, with a heavy-element enrichment in the interior relative to the outer envelope. This implies that heavy-element enrichment continued through the gas accretion phase, with important implications for the formation of giant planets in our Solar System and beyond.

Authors: Y. Miguel, M. Bazot, T. Guillot, S. Howard, E. Galanti, Y. Kaspi, W. B. Hubbard, B. Militzer, R. Helled, S. K. Atreya, J. E. P. Connerney, D. Durante, L. Kulowski, J. I. Lunine, D. Stevenson, S. Bolton

Date Published: 1st Jun 2022

Publication Type: Journal

TESS asteroseismology of the Kepler red giants

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ABSTRACT Red giant asteroseismology can provide valuable information for studying the Galaxy as demonstrated by space missions like CoRoT and Kepler. However, previous observations have been limited …d to small data sets and fields of view. The TESS mission provides far larger samples and, for the first time, the opportunity to perform asteroseimic inference from full-frame images full-sky, instead of narrow fields and pre-selected targets. Here, we seek to detect oscillations in TESS data of the red giants in the Kepler field using the 4-yr Kepler results as a benchmark. Because we use 1–2 sectors of observation, our results are representative of the typical scenario from TESS data. We detect clear oscillations in ∼3000 stars with another ∼1000 borderline (low S/N) cases. In comparison, best-case predictions suggest ∼4500 detectable oscillating giants. Of the clear detections, we measure Δν in 570 stars, meaning a ∼20 per cent Δν yield (14 per cent for one sector and 26 per cent for two sectors). These yields imply that typical (1–2 sector) TESS data will result in significant detection biases. Hence, to boost the number of stars, one might need to use only νmax as the seismic input for stellar property estimation. However, we find little bias in the seismic measurements and typical scatter is about 5–6 per cent in νmax and 2–3 per cent in Δν. These values, coupled with typical uncertainties in parallax, Teff, and [Fe/H] in a grid-based approach, would provide internal uncertainties of 3 per cent in inferred stellar radius, 6 per cent in mass, and 20 per cent in age for low-luminosity giant stars. Finally, we find red giant seismology is not significantly affected by seismic signal confusion from blending for stars with Tmag ≲ 12.5.

Authors: Dennis Stello, Nicholas Saunders, Sam Grunblatt, Marc Hon, Claudia Reyes, Daniel Huber, Timothy R Bedding, Yvonne Elsworth, Rafael A García, Saskia Hekker, Thomas Kallinger, Savita Mathur, Benoit Mosser, Marc H Pinsonneault

Date Published: 1st May 2022

Publication Type: Journal

Asteroseismic Inference of the Central Structure in a Subgiant Star

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Asteroseismic measurements enable inferences of the underlying stellar structure, such as the density and the speed of sound at various points within the interior of the star. This provides an opportunity … to test stellar evolution theory by assessing whether the predicted structure of a star agrees with the measured structure. Thus far, this kind of inverse analysis has only been applied to the Sun and three solar-like main-sequence stars. Here we extend the technique to stars on the subgiant branch, and apply it to one of the best-characterized subgiants of the Kepler mission, HR 7322. The observation of mixed oscillation modes in this star facilitates inferences of the conditions of its inert helium core, nuclear-burning hydrogen shell, and the deeper parts of its radiative envelope. We find that despite significant differences in the mode frequencies, the structure near to the center of this star does not differ significantly from the predicted structure.

Authors: Earl P. Bellinger, Sarbani Basu, Saskia Hekker, Jørgen Christensen-Dalsgaard, Warrick H. Ball

Date Published: 13th Jul 2021

Publication Type: Journal

TOI-257b (HD 19916b): a warm sub-saturn orbiting an evolved F-type star

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We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to … be of planetary origin based on radial velocity observations. An analysis of the TESS photometry, the MINERVA-Australis, FEROS, and HARPS radial velocities, and the asteroseismic data of the stellar oscillations reveals that TOI-257b has a mass of MP = 0.138 ± 0.023 MJ (43.9 ± 7.3 M⊕ ), a radius of RP = 0.639 ± 0.013 RJ (7.16 ± 0.15 R⊕ ), bulk density of 0.65+0.12−0.11 (cgs), and period 18.38818+0.00085−0.00084 days . TOI-257b orbits a bright (V = 7.612 mag) somewhat evolved late F-type star with M* = 1.390 ± 0.046 Msun , R* = 1.888 ± 0.033 Rsun , Teff = 6075 ± 90 K , and vsin i = 11.3 ± 0.5 km s-1. Additionally, we find hints for a second non-transiting sub-Saturn mass planet on a ∼71 day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars (∼100) that have been characterized with asteroseismology. Warm sub-Saturns are rare in the known sample of exoplanets, and thus the discovery of TOI-257b is important in the context of future work studying the formation and migration history of similar planetary systems.

Authors: Brett C Addison, Duncan J Wright, Belinda A Nicholson, Bryson Cale, Teo Mocnik, Daniel Huber, Peter Plavchan, Robert A Wittenmyer, Andrew Vanderburg, William J Chaplin, Ashley Chontos, Jake T Clark, Jason D Eastman, Carl Ziegler, Rafael Brahm, Bradley D Carter, Mathieu Clerte, Néstor Espinoza, Jonathan Horner, John Bentley, Andrés Jordán, Stephen R Kane, John F Kielkopf, Emilie Laychock, Matthew W Mengel, Jack Okumura, Keivan G Stassun, Timothy R Bedding, Brendan P Bowler, Andrius Burnelis, Sergi Blanco-Cuaresma, Michaela Collins, Ian Crossfield, Allen B Davis, Dag Evensberget, Alexis Heitzmann, Steve B Howell, Nicholas Law, Andrew W Mann, Stephen C Marsden, Rachel A Matson, James H O’Connor, Avi Shporer, Catherine Stevens, C G Tinney, Christopher Tylor, Songhu Wang, Hui Zhang, Thomas Henning, Diana Kossakowski, George Ricker, Paula Sarkis, Martin Schlecker, Pascal Torres, Roland Vanderspek, David W Latham, Sara Seager, Joshua N Winn, Jon M Jenkins, Ismael Mireles, Pam Rowden, Joshua Pepper, Tansu Daylan, Joshua E Schlieder, Karen A Collins, Kevin I Collins, Thiam-Guan Tan, Warrick H Ball, Sarbani Basu, Derek L Buzasi, Tiago L Campante, Enrico Corsaro, L González-Cuesta, Guy R Davies, Leandro de Almeida, Jose-Dias do Nascimento, Rafael A García, Zhao Guo, Rasmus Handberg, Saskia Hekker, Daniel R Hey, Thomas Kallinger, Steven D Kawaler, Cenk Kayhan, James S. Kuszlewicz, Mikkel N Lund, Alexander Lyttle, Savita Mathur, Andrea Miglio, Benoit Mosser, Martin B Nielsen, Aldo M Serenelli, Victor Silva Aguirre, Nathalie Themeßl

Date Published: 1st Apr 2021

Publication Type: Journal

Asteroseismology of luminous red giants with Kepler – II. Dependence of mass-loss on pulsations and radiation

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Mass-loss by red giants is an important process to understand the final stages of stellar evolution and the chemical enrichment of the interstellar medium. Mass-loss rates are thought to be controlled … by pulsation-enhanced dust-driven outflows. Here, we investigate the relationships between mass-loss, pulsations, and radiation, using 3213 luminous Kepler red giants and 13 5000 ASAS-SN semiregulars and Miras. Mass-loss rates are traced by infrared colours using 2MASS and Wide-field Infrared Survey Explorer(WISE) and by observed-to-model WISE fluxes, and are also estimated using dust mass-loss rates from literature assuming a typical gas-to-dust mass ratio of 400. To specify the pulsations, we extract the period and height of the highest peak in the power spectrum of oscillation. Absolute magnitudes are obtained from the 2MASS Ks band and the Gaia DR2 parallaxes. Our results follow. (i) Substantial mass-loss sets in at pulsation periods above ∼60 and ∼100 d, corresponding to Asymptotic-Giant-Branch stars at the base of the period-luminosity sequences C' and C. (ii) The mass-loss rate starts to rapidly increase in semiregulars for which the luminosity is just above the red-giant-branch tip and gradually plateaus to a level similar to that of Miras. (iii) The mass-loss rates in Miras do not depend on luminosity, consistent with pulsation-enhanced dust-driven winds. (iv) The accumulated mass-loss on the red giant branch consistent with asteroseismic predictions reduces the masses of red-clump stars by 6.3 per cent, less than the typical uncertainty on their asteroseismic masses. Thus mass-loss is currently not a limitation of stellar age estimates for galactic archaeology studies.

Authors: Jie Yu, Saskia Hekker, Timothy R Bedding, Dennis Stello, Daniel Huber, Laurent Gizon, Shourya Khanna, Shaolan Bi

Date Published: 1st Mar 2021

Publication Type: Journal

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