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3 results on '"Cegla, HM [0000-0001-8934-7315]"'

1. Unsigned magnetic flux as a proxy for radial-velocity variations in sun-like stars

Author

R. D. Haywood, T. W. Milbourne, S. H. Saar, A. Mortier, D. Phillips, D. Charbonneau, A. Collier Cameron, H. M. Cegla, N. Meunier, M. L. Palumbo III, Science & Technology Facilities Council, University of St Andrews. School of Physics and Astronomy, University of St Andrews. St Andrews Centre for Exoplanet Science, Haywood, RD [0000-0001-9140-3574], Saar, SH [0000-0001-7032-8480], Mortier, A [0000-0001-7254-4363], Phillips, D [0000-0001-5132-1339], Charbonneau, D [0000-0002-9003-484X], Cameron, AC [0000-0002-8863-7828], Cegla, HM [0000-0001-8934-7315], Iii, MLP [0000-0002-4677-8796], and Apollo - University of Cambridge Repository

Subjects
Earth and Planetary Astrophysics (astro-ph.EP), Solar faculae, Radial velocity, astro-ph.SR, Sunspots, FOS: Physical sciences, Astronomy and Astrophysics, Quiet sun, 3rd-DAS, Solar cycle, Active sun, QC Physics, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, astro-ph.EP, Astronomy data analysis, Astrophysics::Solar and Stellar Astrophysics, Exoplanet detection methods, QB Astronomy, Astrophysics::Earth and Planetary Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), QC, Astrophysics - Earth and Planetary Astrophysics, QB
Abstract

We estimate disc-averaged RV variations of the Sun over the last magnetic cycle, from the single Fe I line observed by SDO/HMI, using a physical model for rotationally modulated magnetic activity that was previously validated against HARPS-N solar observations. We estimate the disc-averaged, unsigned magnetic flux and show that a simple linear fit to it reduces the RMS of RV variations by 62%, i.e. a factor of 2.6. We additionally apply the FF' method, which predicts RV variations based on a star's photometric variations. At cycle maximum, we find that additional physical processes must be at play beyond suppression of convective blueshift and velocity imablances resulting from brightness inhomogeneities, in agreement with recent studies of solar RV variations. By modelling RV variations over the magnetic cycle using a linear fit to the unsigned magnetic flux, we recover injected planets at an orbital period of about 300 days with RV semi-amplitudes down to 0.3 m/s. To reach semi-amplitudes of 0.1 m/s, we will need to identify and model additional physical phenomena that are not well traced by the unsigned magnetic flux or FF'. The unsigned magnetic flux is an excellent proxy for rotationally modulated, activity-induced RV variations, and could become a key tool in confirming and characterising Earth analogs orbiting Sun-like stars. The present study motivates ongoing and future efforts to develop observation and analysis techniques to measure the unsigned magnetic flux at high precision in slowly rotating, relatively inactive stars like the Sun., 25 pages, 11 figures, 3 tables, submitted to ApJ

Published
2022

2. The EXPRES Stellar Signals Project II. State of the field in disentangling photospheric velocities

Author

Lily L. Zhao, Debra A. Fischer, Eric B. Ford, Alex Wise, Michaël Cretignier, Suzanne Aigrain, Oscar Barragan, Megan Bedell, Lars A. Buchhave, João D. Camacho, Heather M. Cegla, Jessi Cisewski-Kehe, Andrew Collier Cameron, Zoe L. de Beurs, Sally Dodson-Robinson, Xavier Dumusque, João P. Faria, Christian Gilbertson, Charlotte Haley, Justin Harrell, David W. Hogg, Parker Holzer, Ancy Anna John, Baptiste Klein, Marina Lafarga, Florian Lienhard, Vinesh Maguire-Rajpaul, Annelies Mortier, Belinda Nicholson, Michael L. Palumbo, Victor Ramirez Delgado, Christopher J. Shallue, Andrew Vanderburg, Pedro T. P. Viana, Jinglin Zhao, Norbert Zicher, Samuel H. C. Cabot, Gregory W. Henry, Rachael M. Roettenbacher, John M. Brewer, Joe Llama, Ryan R. Petersburg, Andrew E. Szymkowiak, Apollo-University Of Cambridge Repository, Zhao, LL [0000-0002-3852-3590], Fischer, DA [0000-0003-2221-0861], Ford, EB [0000-0001-6545-639X], Wise, A [0000-0002-5013-5769], Cretignier, M [0000-0002-2207-0750], Aigrain, S [0000-0003-1453-0574], Barragan, O [0000-0003-0563-0493], Bedell, M [0000-0001-9907-7742], Buchhave, LA [0000-0003-1605-5666], Camacho, JD [0000-0001-5121-5560], Cegla, HM [0000-0001-8934-7315], Cisewski-Kehe, J [0000-0002-9656-2272], Collier Cameron, A [0000-0002-8863-7828], De Beurs, ZL [0000-0002-7564-6047], Dodson-Robinson, S [0000-0002-8796-4974], Dumusque, X [0000-0002-9332-2011], Faria, JP [0000-0002-6728-244X], Gilbertson, C [0000-0002-1743-3684], Haley, C [0000-0003-3996-773X], Harrell, J [0000-0001-8936-6276], Hogg, DW [0000-0003-2866-9403], Holzer, P [0000-0001-8936-6276], John, AA [0000-0002-1715-6939], Klein, B [0000-0003-0637-5236], Lafarga, M [0000-0002-8815-9416], Lienhard, F [0000-0003-4047-0771], Maguire-Rajpaul, V [0000-0001-7576-6703], Mortier, A [0000-0001-7254-4363], Nicholson, B [0000-0003-1360-4404], Palumbo, ML [0000-0002-4677-8796], Ramirez Delgado, V [0000-0001-8183-459X], Shallue, CJ [0000-0002-7585-9974], Vanderburg, A [0000-0001-7246-5438], Viana, PTP [0000-0003-1572-8531], Zhao, J [0000-0001-5290-2952], Zicher, N [0000-0001-6143-2905], Cabot, SHC [0000-0001-9749-6150], Henry, GW [0000-0003-4155-8513], Roettenbacher, RM [0000-0002-9288-3482], Brewer, JM [0000-0002-9873-1471], Llama, J [0000-0003-4450-0368], Petersburg, RR [0000-0003-2168-0191], Szymkowiak, AE [0000-0002-4974-687X], Apollo - University of Cambridge Repository, Zhao, Lily L. [0000-0002-3852-3590], Fischer, Debra A. [0000-0003-2221-0861], Ford, Eric B. [0000-0001-6545-639X], Wise, Alex [0000-0002-5013-5769], Cretignier, Michaël [0000-0002-2207-0750], Aigrain, Suzanne [0000-0003-1453-0574], Barragan, Oscar [0000-0003-0563-0493], Bedell, Megan [0000-0001-9907-7742], Buchhave, Lars A. [0000-0003-1605-5666], Camacho, João D. [0000-0001-5121-5560], Cegla, Heather M. [0000-0001-8934-7315], Cisewski-Kehe, Jessi [0000-0002-9656-2272], Collier Cameron, Andrew [0000-0002-8863-7828], de Beurs, Zoe L. [0000-0002-7564-6047], Dodson-Robinson, Sally [0000-0002-8796-4974], Dumusque, Xavier [0000-0002-9332-2011], Faria, João P. [0000-0002-6728-244X], Gilbertson, Christian [0000-0002-1743-3684], Haley, Charlotte [0000-0003-3996-773X], Harrell, Justin [0000-0001-8936-6276], Hogg, David W. [0000-0003-2866-9403], Holzer, Parker [0000-0001-8936-6276], John, Ancy Anna [0000-0002-1715-6939], Klein, Baptiste [0000-0003-0637-5236], Lafarga, Marina [0000-0002-8815-9416], Lienhard, Florian [0000-0003-4047-0771], Maguire-Rajpaul, Vinesh [0000-0001-7576-6703], Mortier, Annelies [0000-0001-7254-4363], Nicholson, Belinda [0000-0003-1360-4404], Palumbo, Michael L., III [0000-0002-4677-8796], Ramirez Delgado, Victor [0000-0001-8183-459X], Shallue, Christopher J. [0000-0002-7585-9974], Vanderburg, Andrew [0000-0001-7246-5438], Viana, Pedro T. P. [0000-0003-1572-8531], Zhao, Jinglin [0000-0001-5290-2952], Zicher, Norbert [0000-0001-6143-2905], Cabot, Samuel H. C. [0000-0001-9749-6150], Henry, Gregory W. [0000-0003-4155-8513], Roettenbacher, Rachael M. [0000-0002-9288-3482], Brewer, John M. [0000-0002-9873-1471], Llama, Joe [0000-0003-4450-0368], Petersburg, Ryan R. [0000-0003-2168-0191], Szymkowiak, Andrew E. [0000-0002-4974-687X], Science & Technology Facilities Council, University of St Andrews. School of Physics and Astronomy, and University of St Andrews. St Andrews Centre for Exoplanet Science

Subjects
Radial velocity, astro-ph.SR, FOS: Physical sciences, QB Astronomy, Exoplanet detection methods, Astrophysics::Solar and Stellar Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), Solar and Stellar Astrophysics (astro-ph.SR), QC, Stellar activity, QB, Earth and Planetary Astrophysics (astro-ph.EP), MCC, Spectrometers, The Solar System, Exoplanets, and Astrobiology, Astronomy and Astrophysics, 3rd-DAS, QC Physics, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, astro-ph.EP, Planet hosting stars, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - Instrumentation and Methods for Astrophysics, astro-ph.IM, Astrophysics - Earth and Planetary Astrophysics
Abstract

Measured spectral shifts due to intrinsic stellar variability (e.g., pulsations, granulation) and activity (e.g., spots, plages) are the largest source of error for extreme precision radial velocity (EPRV) exoplanet detection. Several methods are designed to disentangle stellar signals from true center-of-mass shifts due to planets. The EXPRES Stellar Signals Project (ESSP) presents a self-consistent comparison of 22 different methods tested on the same extreme-precision spectroscopic data from EXPRES. Methods derived new activity indicators, constructed models for mapping an indicator to the needed RV correction, or separated out shape- and shift-driven RV components. Since no ground truth is known when using real data, relative method performance is assessed using the total and nightly scatter of returned RVs and agreement between the results of different methods. Nearly all submitted methods return a lower RV RMS than classic linear decorrelation, but no method is yet consistently reducing the RV RMS to sub-meter-per-second levels. There is a concerning lack of agreement between the RVs returned by different methods. These results suggest that continued progress in this field necessitates increased interpretability of methods, high-cadence data to capture stellar signals at all timescales, and continued tests like the ESSP using consistent data sets with more advanced metrics for method performance. Future comparisons should make use of various well-characterized data sets -- such as solar data or data with known injected planetary and/or stellar signals -- to better understand method performance and whether planetary signals are preserved., 33 pages (+12 pages of Appendix), 10 figures, 8 tables, accepted for publication in AJ

Published
2022

3. Detection Limits of Low-mass, Long-period Exoplanets Using Gaussian Processes Applied to HARPS-N Solar Radial Velocities

Author

Christopher A. Watson, M. Lopez-Morales, Massimo Cecconi, L. Malavolta, R. D. Haywood, Timothy Milbourne, M. Gonzalez, Dimitar Sasselov, David F. Phillips, Xavier Dumusque, J. Maldonado, Ken Rice, H. M. Cegla, S. H. Saar, Stéphane Udry, Rosario Cosentino, D. W. Latham, N. Buchschacher, Elisa Molinari, Ronald L. Walsworth, Adriano Ghedina, Giuseppina Micela, Francesco Pepe, Alessandro Sozzetti, C. H. Li, Susan E. Thompson, D. Charbonneau, E. Poretti, Annelies Mortier, Nicholas Langellier, A. Collier Cameron, Marcello Lodi, Langellier, N [0000-0003-2107-3308], Milbourne, TW [0000-0001-5446-7712], Phillips, DF [0000-0001-5132-1339], Haywood, RD [0000-0001-9140-3574], Saar, SH [0000-0001-7032-8480], Mortier, A [0000-0001-7254-4363], Malavolta, L [0000-0002-6492-2085], Thompson, S [0000-0002-8039-194X], Cameron, AC [0000-0002-8863-7828], Dumusque, X [0000-0002-9332-2011], Cegla, HM [0000-0001-8934-7315], Latham, DW [0000-0001-9911-7388], Maldonado, J [0000-0002-2218-5689], Buchschacher, N [0000-0002-3697-1541], Cecconi, M [0000-0001-5701-2529], Charbonneau, D [0000-0002-9003-484X], Cosentino, R [0000-0003-1784-1431], Ghedina, A [0000-0003-4702-5152], Lodi, M [0000-0002-5432-9659], López-Morales, M [0000-0003-3204-8183], Micela, G [0000-0002-9900-4751], Molinari, E [0000-0002-1742-7735], Poretti, E [0000-0003-1200-0473], Rice, K [0000-0002-6379-9185], Sasselov, D [0000-0001-7014-1771], Sozzetti, A [0000-0002-7504-365X], Udry, S [0000-0001-7576-6236], Walsworth, RL [0000-0003-0311-4751], Apollo - University of Cambridge Repository, Science & Technology Facilities Council, University of St Andrews. School of Physics and Astronomy, and University of St Andrews. St Andrews Centre for Exoplanet Science

Subjects
Radial velocity, astro-ph.SR, Solar activity, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, 010309 optics, symbols.namesake, Long period, 0103 physical sciences, QB Astronomy, Astrophysics::Solar and Stellar Astrophysics, Gaussian regression, 010303 astronomy & astrophysics, Gaussian process, QC, Astrophysics::Galaxy Astrophysics, QB, Physics, Detection limit, Exoplanets, DAS, Astronomy and Astrophysics, Exoplanet, QC Physics, 13. Climate action, Space and Planetary Science, astro-ph.EP, symbols, Astrophysics::Earth and Planetary Astrophysics, Low Mass, astro-ph.IM
Abstract

Funding: A.C.C. acknowledges support from the Science and Technology Facilities Council (STFC) consolidated grant No. ST/R000824/1. Radial velocity (RV) searches for Earth-mass exoplanets in the habitable zone around Sun-like stars are limited by the effects of stellar variability on the host star. In particular, suppression of convective blueshift and brightness inhomogeneities due to photospheric faculae/plage and starspots are the dominant contribution to the variability of such stellar RVs. Gaussian process (GP) regression is a powerful tool for statistically modeling these quasi-periodic variations. We investigate the limits of this technique using 800 days of RVs from the solar telescope on the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) spectrograph. These data provide a well-sampled time series of stellar RV variations. Into this data set, we inject Keplerian signals with periods between 100 and 500 days and amplitudes between 0.6 and 2.4 m s−1. We use GP regression to fit the resulting RVs and determine the statistical significance of recovered periods and amplitudes. We then generate synthetic RVs with the same covariance properties as the solar data to determine a lower bound on the observational baseline necessary to detect low-mass planets in Venus-like orbits around a Sun-like star. Our simulations show that discovering planets with a larger mass (~0.5 m s−1) using current-generation spectrographs and GP regression will require more than 12 yr of densely sampled RV observations. Furthermore, even with a perfect model of stellar variability, discovering a true exo-Venus (~0.1 m s−1) with current instruments would take over 15 yr. Therefore, next-generation spectrographs and better models of stellar variability are required for detection of such planets. Postprint

Published
2021

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