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

Abstract (Expand)

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

Abstract (Expand)

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

Asteroseismic inference of subgiant evolutionary parameters with deep learning

Abstract (Expand)

With the observations of an unprecedented number of oscillating subgiant stars expected from NASA's TESS mission, the asteroseismic characterization of subgiant stars will be a vital task for stellar … population studies and for testing our theories of stellar evolution. To determine the fundamental properties of a large sample of subgiant stars efficiently, we developed a deep learning method that estimates distributions of fundamental parameters like age and mass over a wide range of input physics by learning from a grid of stellar models varied in eight physical parameters. We applied our method to four Kepler subgiant stars and compare our results with previously determined estimates. Our results show good agreement with previous estimates for three of them (KIC 11026764, KIC 10920273, KIC 11395018). With the ability to explore a vast range of stellar parameters, we determine that the remaining star, KIC 10005473, is likely to have an age 1 Gyr younger than its previously determined estimate. Our method also estimates the efficiency of overshooting, undershooting, and microscopic diffusion processes, from which we determined that the parameters governing such processes are generally poorly constrained in subgiant models. We further demonstrate our method's utility for ensemble asteroseismology by characterizing a sample of 30 Kepler subgiant stars, where we find a majority of our age, mass, and radius estimates agree within uncertainties from more computationally expensive grid-based modelling techniques.

Authors: Marc Hon, Earl P Bellinger, Saskia Hekker, Dennis Stello, James S Kuszlewicz

Date Published: 1st Dec 2020

Publication Type: Journal

A Layered Approach to Robust Determination of Asteroseismic Parameters

Abstract (Expand)

We describe here a layered approach to the robust determination of the broad characteristics of the asteroseismic signal from red-giant stars. No single stringent test can exclude all false results. … The use of multiple, weak tests not only provides robust results but also avoids over-constraining the parameter space.

Authors: Yvonne Elsworth, Nathalie Themeßl, Saskia Hekker, William Chaplin

Date Published: 1st Oct 2020

Publication Type: Misc

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