82 citations · 598 across the 37 of their papers we have counts for
37 papers · 1 filter
Towards understanding stellar variability at the sub m/s level: granulation-induced variability across the optical spectrum
Cis Lagae, Ginger Frame, Heather M. Cegla +5
Detecting the radial velocity signal of Earth-mass exoplanets requires the characterisation and removal of granulation-induced radial velocity variability from spectroscopic observ…
The Fe I 4377 Å Line as a Solar Faculae Indicator: Insights from Spectral Ratio Analysis
Katlyn L. Hobbs, Christopher A. Watson, Jean C. Costes +21
Faculae are a dominant source of stellar activity noise in radial velocity measurements, yet their low contrast and broad surface distribution make them difficult to track in disc-…
Effect of surface magnetic fields on limb darkening in main-sequence stars
N. Kostogryz, A. I. Shapiro, V. Witzke +5
Context.Stellar limb darkening encodes the thermal and radiative structure of stellar photospheres and is a key ingredient in modeling transit light curves and transmission spectra…
The Curious Case of Dark Faculae on M Dwarf Stars
Alexander~I. ~Shapiro, Sara~Seager, Sami~K. ~Solanki +6
The study of exoplanet atmospheres has brought a renewed interest in stellar astrophysics. Specifically, stellar magnetic activity from the host star contaminates exoplanet atmosph…
Decoding the Radial Velocity Signatures of Solar Faculae with 3D MHD Simulations
Florian Kröll, Sowmya Krishnamurthy, Alexander Shapiro +8
We model the solar radial velocity (RV) signal induced by faculae, the dominant contributor to RV variability in Sun-like stars. We use a representative case of a facular patch tra…
Sensitivity of spectral lines to granulation: from the Sun to K-type stars
V. Vasilyev, K. Sowmya, A. I. Shapiro +7
Stellar granulation produces radial-velocity (RV) jitter at the 1 m/s level in Sun-like stars, limiting Earth-analog detection. A route beyond this limit is to weight spectral line…
Synthetic disk-integrated absorption lines isolating stellar granulation for high-precision RV studies
Ginger Frame, Heather Cegla, Cis Lagae +6
We present a novel method for constructing high-accuracy, time-varying disk-integrated stellar absorption line profiles that isolate the effects of granulation alone. This framewor…
Simulations of facular magnetic fields on cool stars I: Main sequence stars with solar metallicity
Tanayveer Singh Bhatia, Robert H. Cameron, Sami K. Solanki +4
Stellar convection in the presence of magnetic field affects the emergent intensity, as well as the structure and evolution of cool main-sequence dwarfs. We aim to understand the e…
Overestimated Pressure Broadening Misleads Model Spectra in Cool M Dwarf Stars
Ana Glidden, Veronika Witzke, Alexander I. Shapiro +1
Available one-dimensional stellar models fail to reproduce the observed spectrum of the ultracool M dwarf TRAPPIST-1. In particular, current models predict strong iron hydride (FeH…
Molecular hydrogen controls the temperatures of flares on TRAPPIST-1
Alexander I. Shapiro Nadiia Kostogryz Sara Seager Veronika Witzke Julien de Wit Valeriy Vasilyev Astrid M. Veronig Robert Cameron Hardi Peter Sami K. Solanki
Early JWST observations of TRAPPIST-1 have revealed an unexpected puzzle: energetic white-light flares ( erg) reach temperatures of only 3500--4000\,K, ne…
Sensitivity of spectral lines to granulation: The Sun
K. Sowmya, A. I. Shapiro, V. Vasilyev +3
The intrinsic variability of stars, due to acoustic oscillations, surface granulation, and magnetic activity, introduces radial velocity (RV) jitter in spectral lines, obscuring tr…
The effect of stellar magnetic activity on measurements of morning and evening asymmetry of planetary terminator
N. Kostogryz, A. I. Shapiro, L. Carone +9
Differences in the ingress and egress shapes of transit light curves can indicate morning-evening temperature contrasts on transiting planets. Here, we pinpoint an alternative mech…
Modeling HMI observables for the study of solar oscillations
D. Fournier, N. M. Kostogryz, L. Gizon +4
Context: Helioseismology aims to infer the properties of the solar interior by analyzing observations of acoustic oscillations. The interpretation of the helioseismic data is howev…
Towards understanding stellar variability at the sub m/s level: Isolating granulation signals in synthetic spectral lines
Ginger Frame, Heather M. Cegla, Veronika Witzke +5
Granulation in the photospheres of FGK-type stars induces variability in absorption lines, complicating exoplanet detection via radial velocities and characterisation via transmiss…
First Calculations of Starspot Spectra based on 3D Radiative Magnetohydrodynamics Simulations
H. N. Smitha, Alexander I. Shapiro, Veronika Witzke +6
Accurate calculations of starspot spectra are essential for multiple applications in astronomy. The current standard is to represent starspot spectra by spectra of stars that are c…
Stellar Surface Magnetic Fields Impact Limb Darkening
Nadiia M. Kostogryz, Alexander I. Shapiro, Veronika Witzke +8
Stars appear darker at their limbs than at their disk centers because at the limb we are viewing the higher and cooler layers of stellar photospheres. Limb darkening derived from s…
Testing MURaM and MPS-ATLAS against the quiet solar spectrum
Veronika Witzke, Alexander I. Shapiro, Nadiia M. Kostogryz +8
Three-dimensional (3D) radiative magnetohydrodynamics (MHD) simulations are the only way to model stellar atmospheres without any ad hoc parameterisations. Several 3D radiative MHD…
Spectral variability of photospheric radiation due to faculae II: Facular contrasts for cool main-sequence stars
Charlotte M. Norris, Yvonne C. Unruh, Veronika Witzke +5
Magnetic features on the surface of stars, such as spots and faculae, cause stellar spectral variability on time-scales of days and longer. For stars other than the Sun, the spectr…
MPS-ATLAS library of stellar model atmospheres and spectra
N. Kostogryz, A. I Shapiro, V. Witzke +5
Stellar spectra contain a large amount of information about the conditions in stellar atmospheres. However, extracting this information is challenging and demands comprehensive num…
Can 1D radiative equilibrium models of faculae be used for calculating contamination of transmission spectra?
Veronika Witzke, Alexander I. Shapiro, Nadiia M. Kostogryz +5
The reliable characterization of planetary atmospheres with transmission spectroscopy requires realistic modeling of stellar magnetic features, since features that are attributable…
Small-scale dynamo in cool main sequence stars. II. The effect of metallicity
V. Witzke, H. B. Duehnen, A. I. Shapiro +4
All cool main sequence stars including our Sun are thought to have magnetic fields. Observations of the Sun revealed that even in quiet regions small-scale turbulent magnetic field…
Stellar limb darkening. A new MPS-ATLAS library for Kepler, TESS, CHEOPS, and PLATO passbands
N. M. Kostogryz, V. Witzke, A. I. Shapiro +4
The detection of the first exoplanet paved the way into the era of transit photometry space missions with a revolutionary photometric precision that aim at discovering new exoplane…
Small-scale Dynamo in Cool Stars: I. Changes in stratification and near-surface convection for main-sequence spectral types
Tanayveer S. Bhatia, Robert H. Cameron, Sami K. Solanki +4
Some of the small-scale solar magnetic flux can be attributed to a small-scale dynamo (SSD) operating in the near-surface convection. The SSD fields have consequences for solar gra…
Chromospheric Extension of the MURaM Code
D. Przybylski, R. Cameron, S. K. Solanki +5
Detailed numerical models of chromosphere and corona are required to understand the heating of the solar atmosphere. An accurate treatment of the solar chromosphere is complicated…