ORCID Profile
0000-0002-5496-365X
Current Organisations
Aarhus University
,
University of Bristol
,
University of Birmingham
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Publisher: American Astronomical Society
Date: 17-09-2019
Publisher: American Astronomical Society
Date: 30-05-2019
Publisher: American Astronomical Society
Date: 21-09-2023
Publisher: Springer Science and Business Media LLC
Date: 28-06-2023
Publisher: American Astronomical Society
Date: 29-01-2020
Publisher: Oxford University Press (OUP)
Date: 12-08-2019
Abstract: We present an in-depth analysis of the bright subgiant HR 7322 (KIC 10005473) using Kepler short-cadence photometry, optical interferometry from CHARA, high-resolution spectra from SONG, 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 ± 0.007 mas, which, combined with a distance derived using the parallax from Gaia DR2 and a bolometric flux, yields a linear radius of 2.00 ± 0.03 R⊙ and an effective temperature of 6350 ± 90 K. HR 7322 exhibits solar-like oscillations, and using the asteroseismic scaling relations and revisions thereof, we find good agreement between asteroseismic and interferometric stellar radius. The level of precision reached by the careful modelling is to a great extent due to the presence of an avoided crossing in the dipole oscillation mode pattern of HR 7322. We find that the standard models predict a stellar radius systematically smaller than the observed interferometric one and that a sub-solar mixing length parameter is needed to achieve a good fit to in idual oscillation frequencies, interferometric temperature, and spectroscopic metallicity.
Publisher: Oxford University Press (OUP)
Date: 07-06-2022
Abstract: The Milky Way was shaped by the mergers with several galaxies in the past. We search for remnant stars that were born in these foreign galaxies and assess their ages in an effort to put upper limits on the merger times and thereby better understand the evolutionary history of our Galaxy. Using 5D-phase space information from Gaia eDR3, radial velocities from Gaia DR2 and chemical information from apogee DR16, we kinematically and chemically select 21 red giant stars belonging to former dwarf galaxies that merged with the Milky Way. With added asteroseismology from Kepler and K2 , we determine the ages of the 21 ex situ stars and 49 in situ stars with an average σage/age of ∼31 per cent. We find that all the ex situ stars are consistent with being older than 8 Gyr. While it is not possible to associate all the stars with a specific dwarf galaxy, we classify eight of them as Gaia-Enceladus/Sausage stars, which is one of the most massive mergers in our Galaxy’s history. We determine their mean age to be 9.5 ± 1.3 Gyr consistent with a merger time of 8–10 Gyr ago. The rest of the stars are possibly associated with Kraken, Thamnos, Sequoia, or another extragalactic progenitor. The age determination of ex situ stars paves the way to more accurately pinning down when the merger events occurred and hence provide tight constraints useful for simulating how these events unfolded.
Publisher: American Astronomical Society
Date: 08-2021
Publisher: Oxford University Press (OUP)
Date: 17-10-2020
Abstract: The Transiting Exoplanet Survey Satellite (TESS) is recording short-cadence, high duty-cycle timeseries across most of the sky, which presents the opportunity to detect and study oscillations in interesting stars, in particular planet hosts. We have detected and analysed solar-like oscillations in the bright G4 subgiant HD 38529, which hosts an inner, roughly Jupiter-mass planet on a $14.3\\, \\mathrm{d}$ orbit and an outer, low-mass brown dwarf on a $2136\\, \\mathrm{d}$ orbit. We combine results from multiple stellar modelling teams to produce robust asteroseismic estimates of the star’s properties, including its mass $M=1.48\\pm 0.04\\, \\mathrm{M}_\\odot {}$, radius $R=2.68\\pm 0.03\\, \\mathrm{R}_\\odot {}$, and age $t=3.07\\pm 0.39\\, \\mathrm{Gyr}{}$. Our results confirm that HD 38529 has a mass near the higher end of the range that can be found in the literature and also demonstrate that precise stellar properties can be measured given shorter timeseries than produced by CoRoT, Kepler, or K2.
Publisher: Oxford University Press (OUP)
Date: 11-10-2021
Abstract: We introduce the public version of the BAyesian STellar Algorithm (BASTA), an open-source code written in Python to determine stellar properties based on a set of astrophysical observables. BASTA has been specifically designed to robustly combine large data sets that include asteroseismology, spectroscopy, photometry, and astrometry. We describe the large number of asteroseismic observations that can be fit by the code and how these can be combined with atmospheric properties (as well as parallaxes and apparent magnitudes), making it the most complete analysis pipeline available for oscillating main-sequence, subgiant, and red giant stars. BASTA relies on a set of pre-built stellar isochrones or a custom-designed library of stellar tracks, which can be further refined using our interpolation method (both along and across stellar tracks or isochrones). We perform recovery tests with simulated data that reveal levels of accuracy at the few percent level for radii, masses, and ages when in idual oscillation frequencies are considered, and show that asteroseismic ages with statistical uncertainties below 10 per cent are within reach if our stellar models are reliable representations of stars. BASTAis extensively documented and includes a suite of ex les to support easy adoption and further development by new users.
Publisher: EDP Sciences
Date: 02-2019
DOI: 10.1051/0004-6361/201834461
Abstract: Context . The search for twins of the Sun and Earth relies on accurate characterization of stellar and the exoplanetary parameters age, mass, and radius. In the modern era of asteroseismology, parameters of solar-like stars are derived by fitting theoretical models to observational data, which include measurements of their oscillation frequencies, metallicity [Fe/H], and effective temperature T eff . Furthermore, combining this information with transit data yields the corresponding parameters for their associated exoplanets. Aims . While values of [Fe/H] and T eff are commonly stated to a precision of ∼0.1 dex and ∼100 K, the impact of systematic errors in their measurement has not been studied in practice within the context of the parameters derived from them. Here we seek to quantify this. Methods . We used the Stellar Parameters in an Instant (SPI) pipeline to estimate the parameters of nearly 100 stars observed by Kepler and Gaia , many of which are confirmed planet hosts. We adjusted the reported spectroscopic measurements of these stars by introducing faux systematic errors and, separately, artificially increasing the reported uncertainties of the measurements, and quantified the differences in the resulting parameters. Results . We find that a systematic error of 0.1 dex in [Fe/H] translates to differences of only 4%, 2%, and 1% on average in the resulting stellar ages, masses, and radii, which are well within their uncertainties (∼11%, 3.5%, 1.4%) as derived by SPI. We also find that increasing the uncertainty of [Fe/H] measurements by 0.1 dex increases the uncertainties of the ages, masses, and radii by only 0.01 Gyr, 0.02 M ⊙ , and 0.01 R ⊙ , which are again well below their reported uncertainties (∼0.5 Gyr, 0.04 M ⊙ , 0.02 R ⊙ ). The results for T eff at 100 K are similar. Conclusions . Stellar parameters from SPI are unchanged within uncertainties by errors of up to 0.14 dex or 175 K. They are even more robust to errors in T eff than the seismic scaling relations. Consequently, the parameters for their exoplanets are also robust.
Publisher: Springer Science and Business Media LLC
Date: 13-01-2020
Publisher: Wiley
Date: 09-2023
DOI: 10.1111/BPH.16204
Abstract: Ticagrelor is labelled as a reversible, direct‐acting platelet P2Y 12 receptor (P2Y 12 R) antagonist that is indicated clinically for the prevention of thrombotic events in patients with acute coronary syndrome (ACS). As with many antiplatelet drugs, ticagrelor therapy increases bleeding risk in patients which in emergency situations requires platelet transfusion although there is ongoing debate on its effectiveness following ticagrelor therapy. The aim of this study was to further examine the reversibility of ticagrelor at the P2Y 12 R. Studies were performed in human platelets with both P2Y 12 R‐stimulated GTPase activity and platelet aggregation assessed. Cell‐based bioluminescence resonance energy transfer (BRET) assays were also undertaken to assess G protein subunit activation downstream of P2Y 12 R activation. Initial studies revealed a range of P2Y 12 R ligands including ticagrelor displayed inverse agonist activity at the P2Y 12 R. Of these only ticagrelor was resistant to wash‐out. In both human platelets and cell‐based assays, washing failed to reverse ticagrelor‐dependent inhibition of ADP‐stimulated P2Y 12 R function in contrast to other P2Y 12 R antagonists. The P2Y 12 R agonist 2MeSADP, which was also resistant to wash‐out, was able to effectively compete with ticagrelor. In silico docking revealed that ticagrelor and 2MeSADP penetrated more deeply into the orthosteric binding pocket of the P2Y 12 R than other P2Y 12 R ligands. Ticagrelor binding to the P2Y 12 R is prolonged and more akin to that of an irreversible antagonist especially versus the endogenous P2Y 12 R agonist ADP. This study highlights the potential clinical need for novel ticagrelor reversal strategies in patients with spontaneous major bleeding and bleeding associated with urgent invasive procedures.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Amalie Stokholm.