DOCSLIB.ORG

Characterizing Exoplanet Transits and Stellar Activity with Scalable Gaussian Processes

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Characterizing Exoplanet Transits and Stellar Activity with Scalable Gaussian Processes Universiteit van Amsterdam MSc Artificial Intelligence Master Thesis Characterizing Exoplanet Transits and Stellar Activity with Scalable Gaussian Processes by Victoria Foing 11773391 October 17, 2020 36 ECTS February 2020 - October 2020 Main Supervisor: Ana M. Heras (European Space Agency) Co-Supervisor: Patrick Forré (University of Amsterdam) Abstract Exoplanets are planets orbiting around stars other than our sun. The field of exoplanet science has boomed since the 1990s [1]. Space missions like CoRoT, Kepler and TESS, and ground-based observatories have collected millions of lightcurves and detected more than 3,200 exoplanets using transit photometry, an approach that involves measuring the brightness of a star over time and looking for periodic dips in the brightness caused by a planet repeatedly passing in front of the star. Once a transit is detected, astronomers seek to characterize the transit signal in the lightcurve to learn about properties of the planet. This can be challenging due to noise from stellar activity, namely rotational modulation patterns in the lightcurve caused by starspots and plages appearing in and out of view as the host star rotates. In the past decade, Gaussian Processes have become popular models for modelling both instrumental and astrophysical noise in lightcurves to aid the detection and characterization of exoplanet transits. Gaussian Processes are well-suited to this task because they are flexible, interpretable, and probabilistic estimates of the model parameters can be obtained with Markov Chain Monte Carlo sampling. However, they have been disadvantaged by slow computation speeds which has precluded their application to the vast datasets provided by Kepler and TESS. Recently, a new software, celerite, has introduced special kernel functions that are not only well-suited to model stellar activity but also scale linearly with the dataset by taking advantage of semi-separable matrices [2]. In this work, we apply scalable Gaussian Process models using the software celerite in order to characterize exoplanet transits and stellar activity in Kepler and TESS lightcurves. By "charac- terizing", we mean the retrieval of accurate transit and rotation parameters, with a focus on the radius of the planet and the rotation period of the star. We develop a pipeline for preprocessing the lightcurves, defining prior distributions using Physics techniques, building a Gaussian Process model with a transit mean function and a quasi-periodic Rotation kernel and a noise kernel, and sampling from the model with Markov Chain Monte Carlo. To assess the benefits of jointly mod- elling the rotation and the transits, we compare the performances of three Gaussian Process models: RotGP (only rotation), ExoGP (only transit), and ExoRotGP (rotation and transit). The mod- els are applied to 15 TESS stars and 9 Kepler stars with confirmed planets and rotation periods, and the parameter estimates obtained are compared to those from refereed publications. For the lightcurves classified as having unambiguous rotation periods by previous authors, our best GP models obtain rotation periods within one one day of the reference rotation periods. For four of the TESS lightcurves classified as having ambiguous rotation periods by previous authors, the GP models are able to find rotation periods, outperforming the analysis of other researchers using tra- ditional techniques. For the recovery of planet radii, our best GP models are able to estimate the planet radii within one standard deviation of the radii for all Kepler planets and all but two TESS planets. Moreover, we highlight the importance of preprocessing decisions, demonstrating that the pipeline correction method can worsen the retrieval of the rotation period and temporal binning can dramatically worsen the retrieval of planet radii. Finally, we discover that joint modelling improves rotation period estimates for a few stars, due to the extra noise kernel, but only marginally improves the planet radii estimates, suggesting that celerite’s noise kernel can be effective for removing stellar activity. Our results further indicate that the joint model could be a promising tool for the charac- terisation of small exoplanets, with sizes between Neptune and Earth. Our method provides a solid basis for a future application and extension of the model to these objects. Code: https://github.com/victoriafoing/ExoRotGP 1 Acknowledgements I would like to express my sincere gratitude to my supervisor at the European Space Agency, Ana M. Heras, for her wonderful guidance and excellent support throughout the research project. I would also like to thank my supervisor at the University of Amsterdam, Patrick Forre, for the great feedback about the Artificial Intelligence side of the project. I would like to thank my family for their unwavering support and advice, in particular Bernard Foing. Furthermore, I would like to thank the authors of celerite software, which I used throughout the project, in particular Dan Foreman-Mackey, who was very helpful in answering my questions and guiding me in the right direction. Lastly, I would like to thank my boyfriend Adam, my friends, and my classmates in the AI masters program for teaching me a lot throughout the AI master and making this experience very enjoyable. 2 Contents 1 Executive Summary 5 2 Introduction 7 2.1 Problem Statement . .7 2.2 Motivation . .7 2.3 Research questions . .8 2.4 History of Exoplanet Science . .9 2.4.1 Exoplanet Transits . 10 2.4.2 Stellar activity . 10 2.5 Challenges . 11 2.5.1 Detection of Signals . 11 2.5.2 Noise: photon, instrumental, astrophysical . 11 2.5.3 Stellar Limb Darkening . 11 3 Literature Review 12 3.1 Traditional Methods in Physics . 12 3.1.1 Transit Fitting . 12 3.1.2 Recovering Rotation Periods . 13 3.2 Applications in Machine Learning . 14 3.2.1 Gaussian Processes . 14 3.3 Position in the State of the Art . 15 4 Methodology 16 4.1 Bayesian Inference . 16 4.2 Gaussian Processes . 17 4.3 Celerite . 17 4.3.1 Stochastically-Driven Dampled Harmonic Oscillator (SHO) Kernel . 19 4.3.2 Rotation Kernel . 19 4.3.3 Semi-Separable Matrics . 20 4.4 Transit models . 22 4.5 Markov Chain Monte Carlo . 23 5 Algorithm 24 5.1 Algorithm . 24 5.1.1 Initial estimates . 24 5.1.2 Three Models: ExoGP, RotGP, ExoRotGP . 26 5.1.3 Sampling . 30 6 Experiments 31 6.1 Data . 31 6.2 Selection of Targets . 31 6.3 Preprocessing . 32 6.4 Experimental Design . 35 6.5 Experimental Evaluation . 36 7 Results and Discussion 38 7.1 Simulated Experiment . 38 7.2 Rotation Periods . 39 7.2.1 Kepler . 39 7.2.2 TESS . 40 7.2.3 Observation Window . 42 3 CONTENTS CONTENTS 7.3 Transit Characterization . 43 7.3.1 Kepler . 43 7.3.2 TESS . 44 7.4 Computation Time . 46 7.5 Discussion . 47 7.5.1 Kepler vs. TESS . 48 7.5.2 How could our method be improved? . 48 7.5.3 Challenges . 49 8 Conclusion and Future Work 50 8.1 Contributions . 50 8.2 Future work . 51 8.3 Concluding Remarks . 52 References 54 Appendix A 59 A.1 Summary Statistics . 59 A.2 Power spectrum of Celerite kernel and SHO . 60 A.3 Example of Document Outputted by Pipeline: WASP-173 A . 60 CHAPTER 1 Executive Summary In this work, we apply scalable Gaussian Process models using the software celerite in order to characterize exoplanet transits and stellar activity in Kepler and TESS lightcurves. Our goal is to use this machine learning method to obtain accurate characteristics of the planet and its orbit, and of the stellar light variations, with a focus on the radius of the planet and the rotation period of the star. We begin by presenting our research questions: (1) How accurately can we model the stellar activity with Gaussian processes in Kepler and TESS lightcurves? (2) How accurately can we model the exoplanet transits with Gaussian processes in Kepler and TESS lightcurves? (3) Does joint modelling improve the characterization of rotation and transit parameters in Kepler and TESS lightcurves? In the motivation section, we outline the motivation for studying the transit signals and rotation signals in Kepler and TESS lightcurves. The motivation is to help astronomers study and understand the planetary systems observed by these missions and to investigate one of the most fundamental questions in science: is our solar system unique? We further highlight how important finding accurate transit parameters is for deriving the properties of planets, which can give clues about the habitability of the planet. Modelling stellar activity can provide valuable insights about stellar physics (i.e. the evolution, age, and magnetic fields of stars) and the potential habitability of orbiting planets. Stellar activity models can also be used to detrend lightcurves, which can improve the detection of smaller Earth-sized planets, which are more likely to be habitable, and improve the characterization of transit parameters. Next, we explore the motivation for using Gaussian Process to solve the problem of finding accurate transit and rotation parameters. In the past decade, Gaussian Processes have become popular models for modelling both instrumental and astrophysical noise in lightcurves because they are flexible and interpretable. However, they have been largely limited by slow computation speeds. Recently, a new software, celerite, has introduced special kernel functions that are not only well-suited to model stellar activity but also scale linearly with the dataset by taking advantage of semi-separable matrices [2]. We provide a brief summary of the history of exoplanet science and an introduction of the two astronomy concepts that we will study with.
Load more

Recommended publications
  • Evans.2013.HD189733.Albedo.Pdf
    ORE Open Research Exeter TITLE The Deep Blue Color of HD 189733b: Albedo Measurements with Hubble Space Telescope/Space Telescope Imaging Spectrograph at Visible Wavelengths AUTHORS Evans, T.M.; Pont, F.; Sing, David K.; et al. JOURNAL Astrophysical Journal DEPOSITED IN ORE 15 December 2014 This version available at http://hdl.handle.net/10871/16042 COPYRIGHT AND REUSE Open Research Exeter makes this work available in accordance with publisher policies. A NOTE ON VERSIONS The version presented here may differ from the published version. If citing, you are advised to consult the published version for pagination, volume/issue and date of publication The Astrophysical Journal Letters, 772:L16 (5pp), 2013 August 1 doi:10.1088/2041-8205/772/2/L16 C 2013. The American Astronomical Society. All rights reserved. Printed in the U.S.A. THE DEEP BLUE COLOR OF HD 189733b: ALBEDO MEASUREMENTS WITH HUBBLE SPACE TELESCOPE/SPACE TELESCOPE IMAGING SPECTROGRAPH AT VISIBLE WAVELENGTHS Thomas M. Evans1,Fred´ eric´ Pont2,DavidK.Sing2, Suzanne Aigrain1, Joanna K. Barstow1, Jean-Michel Desert´ 3,7, Neale Gibson4, Kevin Heng5, Heather A. Knutson3, and Alain Lecavelier des Etangs6 1 Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK; [email protected] 2 School of Physics, University of Exeter, EX4 4QL Exeter, UK 3 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA 4 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany 5 University of Bern, Center for Space and Habitability, Sidlerstrasse 5, CH-3012 Bern, Switzerland 6 Institut d’Astrophysique de Paris, UMR7095 CNRS, Universite Pierre et Marie Curie, 98 bis Boulevard Arago, F-75014 Paris, France Received 2013 May 31; accepted 2013 June 15; published 2013 July 11 ABSTRACT We present a secondary eclipse observation for the hot Jupiter HD 189733b across the wavelength range 290–570 nm made using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope.
    [Show full text]
  • Suzanne Aigrain on Behalf of the Corot Exoplanet Science Team Why Space?
    Suzanne Aigrain on behalf of the CoRoT exoplanet science team Why space? • Atmosphere limits precision photometry from the ground • Scintillation limit ~2 mmag • Representative transit depths for Sun-like star • Jupiter: 10 mmag • Neptune: 1.3 mmag • Earth: 0.1 mmag • Weather and daytime limit temporal coverage from the ground • Many sources of noise transit timescales removed • colour dependent differential extinction, seeing, etc... 27 December 2006 The satellite • PI: Annie Baglin, LESIA, Meudon • CNES PROTEUS bus • 27cm aperture telescope • Soyuz II-1b launcher from Baikonour • Polar orbit • 2.5 year minimum lifetime Payload 27cm telescope layout focal box Full images, windowing and target selection Focal planeSeismology detector (Vincent Lapeyrere) Exopplnat detector (Farid Karioty) • Sismo field • 5 windows / CCD • 5.7 < mV < 9.5 • 32s sampling (1s on request) • frame transfer mode • used for astrometry 2.8° • 10 bright stars • 10 background windows • 11600 faint stars • 400 background windows CoRoT_Booklet_talks_summer2007 2 seismo exo SCAO Pointing stability Barycenter X of the stellar image x-coord of stellar image barycenter Stability performances : x axis: rms 0.12 pixel y axis: rms 0.15 pixel ~ 0RMS.3 a stability:rc sec. 0.12 pixel in x 0.15 pixel in y ~0.3 arcsec Vibrations due to the entrance and exit form ecclipses vibrations due to Earth eclipse ingress and egress CoRoT_Booklet_talks_summer2007 3 Exo field 2.8° • Exo field • up to 6000 LCs / CCD • 11.5 < mV < 16 • 512s sampling (32s for 500 objects / CCD) • 3 colours for
    [Show full text]
  • Cvetoje- Vic, Anthony Cheetham, Frantz Martinache, Barnaby Norris, Peter Tuthill
    Dr Benjamin Pope Lecturer in Astrophysics and DECRA Fellow Advisor: Prof. David Hogg Affiliation: School of Mathematics & Physics University of Queensland, St Lucia, QLD 4072, Australia and Centre for Astrophysics University of Southern Queensland, West Street, Toowoomba, QLD 4350, Australia Homepage: benjaminpope.github.io email: [email protected] orcid: 0000-0003-2595-9114 Education and Previous Positions 2017-2020 NASA Sagan Fellow, New York University Advisor: Prof. David Hogg 2017 Postdoctoral Research Associate, University of Sydney Advisor: Prof. Peter Tuthill 2013-2017 Doctor of Philosophy in Astrophysics, University of Oxford Thesis: “Observing Bright Stars and their Planets from the Earth and from Space” Balliol College | Supervisors: Prof. Suzanne Aigrain, Prof. Patrick Roche 2013-14 Master of Science in Astrophysics, University of Sydney Thesis: “Vision and Revision: Wavefront Sensing from the Image Domain” Supervisor: Prof. Peter Tuthill 2012 Bachelor of Science (Advanced) with Honours in Physics, University of Sydney First Class Honours, with the University Medal Thesis: “Dancing in the Dark: Kernel Phase Interferometry of Ultracool Dwarfs” Supervisors: Prof. Peter Tuthill, Dr. Frantz Martinache 2010-2011 Study Abroad at the University of California, Berkeley Research project with Prof. Charles H. Townes, Infrared Spatial Interferometer. Grants ARC Discovery Early Career Research Award (DECRA) AUD $444,075.00 NASA TESS Cycle 3 Guest Investigator USD $50,000 TESS Cycle 2 Guest Investigator USD $50,000 Balliol Balliol Interdisciplinary Institute Research Grant College GBP £3,000 Teaching 2021 Extragalactic Astrophysics & Cosmology, University of Queensland 2019 Master of Data Science Guest Lecturer, NYU Center for Data Science 2017 Bayesian Reasoning Honours Lecturer, University of Sydney 2017 Honours Project Supervisor, University of Sydney Supervised Alison Wong and Matthew Edwards, both to First Class Honours and PhD acceptance.
    [Show full text]
  • Nawal Husnoo, Frédéric Pont, David Sing, Kevin Heng, Suzanne Aigrain, Leigh Fletcher, Jaemin Lee, Tom Evans
    Opacity and spectra in hot Jupiters Nawal Husnoo, Frédéric Pont, David Sing, Kevin Heng, Suzanne Aigrain, Leigh Fletcher, Jaemin Lee, Tom Evans. Contact: [email protected]. We are developing a set of tools for generating absorption coeffcients for hot Jupiter atmospheres. We focus on the visible spectrum, where we plan to use the routines for generating "frst guess" models for the upcoming transmission spectra of hot Jupiters (HST program in progress, PI: Sing). We also plan to study the atmospheric temperature-pressure profle of hot Jupiters (Heng et al. 2011)[1], with a focus on the effects of various types of clouds. The transmission spectrum of an exoplanet allows us to probe the atmosphere for elemental and molecular species. In the visible spectrum, sodium, potassium, titanium oxide and vanadium oxide are expected to be dominant [2], (depending on the composition and temperature). Absorption due to clouds/hazes can also be relevant [3]. In this project, we seek "frst guess" models to guide the ongoing observations of transmission spectra of transiting planets with HST. We seek to link the transmission spectrum with the "refection spectrum" in the visible, and compare the effects of scattering due to grains and absorption due to gasses. Transmission spectrum We perform fnite element integration for visible light rays that travel in a grazing geometry through the planet's atmosphere to generate the transmission spectrum. Absorption from the radiatively active species in the atmosphere causes wavelength-selective dimming in the light. Figure 1 shows an example of a transmission spectrum (HD 189733b), where we have plotted a model that includes the sodium D lines, Figure 1: Plot showing the latest reduction of the transmission spectroscopy for HD 189733b (our and Mie scattering for small particles (r<<λ), giving the Rayleigh regime.
    [Show full text]
  • Today Oxford
    www.oxfordtoday.ox.ac.uk Michaelmas Term 2010 Volume 23 No 1 OX FOR D TODAY THE UNIVERSITY MAGAZINE 20 | WILFRED THESIGER AFRICA SEEN THROUGH HIS LENS 30 | SCIENCE WHEN TO SHARE GENE DATA? 45 | GEOFFREY HILL SEAMUS PERRY ON OUR GREATEST LIVING POET PRIME MINISTERS Why has Oxford produced so many? OXF01.cover 1 8/10/10 3:37:5 pm FROM HOME Since 1821 the Oxfordand Cambridge Club has provided alumni of both universities with an exclusive home from home in the heartofthe Capital. Todaymembers can relax, dine and meetfriends in supremely elegant surroundings thatalso featurewell stocked libraries,sports facilities and first-class bedroom accommodation. Reciprocal clubs welcome members of the Oxfordand Cambridge Club in 35 countriesaround the world. Formoreinformation, please contact: [email protected] or call +44 (0)20 7321 5110 Oxfordand Cambridge Club,71Pall Mall,LondonSW1Y 5HD www.oxfordandcambridgeclub.co.uk OX FOR D TODAY EDITOR: Dr Richard Lofthouse DEPUTY ART EDITOR: Steven Goldring DESIGNER: Victoria Ford HEAD OF PUBLICATIONS AND WEB OFFICE: Anne Brunner-Ellis PRODUCTION EDITOR: Kate Lloyd SUB EDITOR: Elizabeth Tatham PICTURE EDITOR: Joanna Kay DESIGN DIRECTOR: Dylan Channon Thanks to Simon Kirrane, Esther Woodman, Helen Cox, Emma Swift EDITORIAL ENQUIRIES: Janet Avison Public Affairs Directorate Tel: 01865 280545 Fax: 01865 270178 [email protected] www.oxfordtoday.ox.ac.uk ALUMNI ENQUIRIES, INCLUDING CHANGE OF ADDRESS: Claire Larkin Alumni Offi ce Tel: 01865 611610 Michaelmas [email protected] COVER IMAGE: HARRY BORDEN/CORBIS OUTLINE, ROB JUDGES www.alumni.ox.ac.uk Term 2010 University of Oxford, University Offi ces, Wellington Square, Oxford OX1 2JD ADVERTISING ENQUIRIES: Marie Longstaff Future Plus, Beaufort Court, 30 Monmouth Street, Bath BA1 2BW Tel: 01225 822849 [email protected] www.futureplc.com Oxford Today is published in February, June and October.
    [Show full text]
  • Gaussian Processes
    Gaussian processes: the next step in exoplanet data analysis Suzanne Aigrain (University of Oxford) Neale Gibson, Tom Evans, Amy McQuillan Steve Roberts, Steve Reece, Mike Osborne ... let the data speak Gaussian processes: the next step in exoplanet data analysis Suzanne Aigrain (University of Oxford) Neale Gibson, Tom Evans, Amy McQuillan Steve Roberts, Steve Reece, Mike Osborne Gaussian processes for modelling systematics 5 high precision time-series stochastic correlated disentangle noise Figure 1. The ‘raw’ HD 189733 NICMOS dataset used as an example for our Gaussian process model. Left: Raw light curves of HD 189733 for each of the 18 wavelength channels, from 2.50µmto1.48µmtoptobottom.Right:Theopticalstateparametersextracted from the spectra plotted as a time series. These are used as the input parameters for our GP model. The red lines represent a GP regression on the input parameters, used to remove the noise and test how this effects the GP model. the noisy input parameters. We also checked that the choice wavelength channels. In this example, only orbits 2, 3 and 5 of hyperprior length scale had little effect on the results, by are used to determine the parameters and hyperparameters setting them to large values, and repeating the procedure of the GP (or ‘train’ the GP), and are shown by the red with varying length scales ensuring the transmission spec- points4. Orbit 4 (green points) was not used... in the traininglet the data speak tra were not significantly altered. set. Predictive distributions were calculated for orbits 2–5, and are shown by the grey regions, which plot the 1 and 2σ confidence intervals.
    [Show full text]
  • Statistics and Exoplanets
    FM 8: Statistics and Exoplanets Downloaded from https://www.cambridge.org/core. IP address: 170.106.202.8, on 29 Sep 2021 at 23:15:31, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921316002726 Astronomy in Focus, Volume 1, Focus Meeting 8 XXIXth IAU General Assembly, August 2015 c International Astronomical Union 2016 Piero Benvenuti, ed. doi:10.1017/S1743921316002726 Introduction Suzanne Aigrain1 and Eric Feigelson2 1 Department of Physics, University of Oxford, Keble Road, Oxford, OX3 9UU, UK email: [email protected] 2 TBD email: Department of Astronomy & Astrophysics and Center for Astrostatistics, Penn State University, 525 Davey Laboratory, University Park PA 16802 USA Abstract. The IAU’s Statistics and Exoplanets Focus Meeting brings together observers, mod- elers and methodologists to discuss the intricate challenges of extracting and interpreting faint planetary signals from dominant starlight. Initiated by the IAU’s new groups concentrating on astroinformatics and astrostatistics, the meeting stimulated the wider exoplanetary community as well as experts in data and science analysis. This proceedings presented selected papers from the Focus Meeting. Keywords. methods: data analysis, methods: statistical, (stars:) planetary systems 1. Motivation The discovery and characterization of exoplanets requires both superbly accurate in- strumentation and sophisticated statistical methods, to extract weak planetary signals from dominant starlight, very large samples and noisy datasets. While numerous exo- planet conferences take place each year, these mostly focus on observational results, their physical implications, and current or future instrument developments; the statistical as- pects of the papers presented, while important, are not usually central to the program.
    [Show full text]
  • Suzanne Aigrain: Refereed Publications
    Suzanne Aigrain: Refereed publications 1. Bayesian detection of planetary transits: A modified version of the Gregory-Loredo method for periodic signal detection, S. Aigrain & F. Favata, Astronomy & Astrophysics, 395, 625 (2002) 2. The photospheric abundances of active binaries - I: Detailed analysis of HD 113816 (IS Vir) and HD 119285 (V851 Cen), D. Katz, F. Favata, S. Aigrain & G. Micela, Astronomy & Astrophysics, 397, 747 (2003) 3. Detecting planetary transits in the presence of stellar variability: Optimal filtering and the use of colour information, S. Carpano, S. Aigrain & F. Favata, Astronomy & Astrophysics, 401, 743 (2003) 4. Characterising stellar micro-variability for planetary transit searches, S. Aigrain, F. Favata & G. Gilmore, Astronomy & Astrophysics, 414, 1139 (2004) 5. Practical planet prospecting, S. Aigrain & M. Irwin, Monthly Notices of the Royal Astronomical Society, 350, 331 (2004) 6. Comparative blind test of five planetary transit detection algorithms on realistic synthetic light curves, C. Moutou, F. Pont, P. Barge, S. Aigrain, M. Auvergne, D. Blouin, R. Cautain, A. R. Erikson, V. Guis, P. Guterman, M. Irwin, A. F. Lanza, D. Queloz, H. Rauer, H. Voss & S. Zucker, Astronomy & Astrophysics, 437, 355 (2005) 7. The Monitor project: rotation of low mass stars in the open cluster M34, J. M. Irwin, S. Aigrain, S. T. Hogkin, M. J. Irwin, J. Bouvier, C. Clarke, L. Hebb & E. Moraux, Monthly Notices of the Royal Astronomical Society, 370, 954 (2006) 8. The Monitor project: Searching for occultations in young open clusters, S. Aigrain, S. T. Hogkin, J. M. Irwin, L. Hebb, M. J. Irwin, F. Favata, E. Moraux & F. Pont, Monthly Notices of the Royal Astronomical Society, 375, 29 (2007) 9.
    [Show full text]
  • The Effects of Stellar Activity on Detecting and Characterising Exoplanets
    The effects of stellar activity on detecting and characterising exoplanets Suzanne Aigrain R. Angus, J. Barstow, V. Rajpaul, E. Gillen, H. Parviainen, B. Pope, S. Roberts, A. McQuillan, N. Gibson, T. Mazeh, F. Pont, S. Zucker Timescales Solar irradiance (SoHO/VIRGO) Transits are easy to separate from Active regions photometric variations due to star spots … up to a point! Activity-induced variability is more problematic for: - transmission spectroscopy - radial velocity planet searches - phase curve studies Granulation Orbit Transits Oscillations (Aigrain, Favata & Gilmore 2004) Filtering activity to detect transits Iterative non-linear filter followed by least-squares box-shaped transit search (Aigrain & Irwin 2004) P ~ 20h, depth 0.0003, Rplanet ~ 2 REarth (CoRoT-7b, Leger et al. 2009) When does activity matter for transit searches? Transit SNR = sqrt(Ntransits) x depth / sigma(Ttransit) where: Intrinsic stellar variability on 6 hour time- - Ntransits is number of transits scales from Kepler (Gilliland et al. 2011) - Ttransit is duration of transit Activity means Kepler would have needed 7 rather than 4 years to reach SNR of 10 for Earth-like planets in the Sun habitable zone of Sun-like stars This can be addressed, at least partially, by modelling the activity-induced variations simultaneously with the transits Modelling stellar signals and instrumental systematics jointly using Gaussian Processes (GPs) Model activity as a quasi-periodic a Gaussian process. Example from K2 Campaign 7 Simultaneously model pointing-related systematics K2SC pipeline - Aigrain et al. 2016. Code and LCs available - talk to Hannu Parviainen First planet candidate catalog: Pope et al. (2016, on arXiv this week) Activity in transit spectra • In any kind of high precision transit studies, need to worry about spots (see e.g.
    [Show full text]
  • 30Th March – 1St April 2016 University of Exeter
    30th March – 1st April 2016 University of Exeter 2 Welcome to the third UK Exoplanet Community Meeting taking place at the University of Exeter Local Organising Committee (green*) Scientific Organising Committee (orange*) Emma Way Isabelle Baraffe Ben Drummond David Sing Tiffany Kataria Sasha Hinkley Hannah Wakeford Nathan Mayne Tom Evans Didier Queloz Felix Sainsbury-Martinez Don Pollacco Sam Morrell Christiane Helling David Skålid Amundsen Jayesh Goyal Elisabeth Matthews Florian Debras *LOC and SOC members will be identifiable by the coloured dots on their name badges 3 Scientific Programme Wednesday 30th March 09:30 – 10:15 Welcome / Registration / Tea & Coffee 10:15 – 10:25 Introduction I Baraffe Session I Detection & statistics 10:30 – 11:05 (Invited) D Ségransan (Geneva) Title: TBC 11:05 – 11:30 A Triaud (Cambridge, Postdoc) The many reasons to search for circumbinary planets 11:30 – 11:55 H Osborn (Warwick, PhD) Single transit detections in the era of high-precision photometry 11:55 – 12:10 Tea / Coffee 12:10 – 12:35 S Durkan (Queen’s Belfast, PhD) High constrast imaging with Spitzer: Constraining the frequency of giant planets out to 1000 AU 12:35 – 13:00 H Celga (Queen’s Belfast, Postdoc) The Rossiter McLaughlin effect reloaded: Convective problems and new solutions 13:00 – 14:00 Lunch / Posters 14:00 – 14:25 M Bonavita (Edinburgh, Postdoc) Constraints on the frequency of sub-stellar companions on wide circumbinary orbits 14:25 – 14:50 S Aigrain (Oxford, Staff) K2SC: Unleashing the potential of K2 for active stars Session II
    [Show full text]
  • Suzanne Aigrain Exoplanets - 30/01/08 Off the Cuff List
    Some interesting things to do with transits Suzanne Aigrain Exoplanets - 30/01/08 Off the cuff list • True mass and radius • Rossiter effect • Detection of small planets • Atmospheric studies • Transit timing True massM. Gillo n et&al.: De tectradiusion of transits of the nearby hot Neptune GJ 436 b L15 Table 1. Parameters for the GJ 436 system, host star and transiting planet. Star (very) inflated planets - additional heat source? Stellar mass [M ] 0.44 ( 0.04)∗ dense planets - corSteel lmass?ar radius [R! ] 0.44 (± 0.04) neptune-mass and smaller planets! - composition?± can we really tell? Planet Period [days] 2.64385 0.00009∗ ± Eccentricity 0.16 0.02∗ ± Orbital inclination [◦] 86.5 0.2 Radius ratio 0.082± 0.005 Planet mass [M ] 22.6 ±1.9 Planet radius [R⊕ ] 3.95+±0.41 ⊕ 0.28 − +2600 [km] 25 200 1800 − T [BJD] 2 454 222.616 0.001 tr ± ∗ From M07. photometry, or using the lower-accuracy data from St.-Luc and Wise, leads to changes of 5% in the radius ratio. If the stellar radius is lef∼t as a free parameter in the lightcurve fit, the best-fit values are R = 0.46 R , Rpl = 26 500 km, and ! i = 86◦. This is an independent indication that the radius deter- mination of the primary is basically correct. 4. Discussion The measured radius of GJ 436 b is comparable to that of Neptune and Uranus. Figure 3 places it in the context of the mass-http://obsradius dwwwiagra.unigem for.ch/~pont/simpleTSolar System planABLE.datets and transiting ex- oplanets.
    [Show full text]
  • Download the May 2021 Newsletter
    Volume26 Issue 9 NWASNEWS MAY 2021 Newsletter for the Wiltshire, Swindon, BLACK HOLE EDITION Beckington, Bath Astronomical Societies I’m am sorry I may have confused our provided the first image of a black hole has speaker topic for this evening, several rea- been further refined and magnetic streams sons, but it will not be Black Holes. have been seen around the black hole Wiltshire Society Page 2 (Asterisms talk by Martin was booked to event horizon. Also discovery of one of the Swindon Stargazers 3 replace one about the Big Bang—but dur- smallest black holes ever detected has ing a talk about the Spanish Observatory been found a mere 1200 light years away Beckington AS and Star Quest Astronomy 4 and memories coming up on Facebook I (not close enough to affect us). Group page. thought it was asterisms and the speaker With this in mind I thought it was time to replied Big Bang. Either way our speaker is Black Holes 5-15 take a look at where science is with the eminently capable, and is awaiting publica- theories around black holes, hence a spe- tion of has observational book from Spring- SPACE NEWS 16-30 cial edition, and further confusion for me. 4th flight for Ingenuity er about lesser known stellar asterisms, Russia to build own space station had had taught astronomy of the Big Bang. April also saw a few transits of the Sun by Ingenuity images Perseverance the International Space Station. While few To add to my personal confusion whilst Astronomers ask UN to protect skies April night passes were visible this means it Mysterious Sun Corona heat source? putting together the space news section of was passing in the day time and close to Black Hole Neutron Star Collisions this bumper 44 page newsletter two topics the Sun’s declination.
    [Show full text]