Flares on Active M-Type Stars Observed with XMM-Newton and Chandra

Total Page:16

File Type:pdf, Size:1020Kb

Flares on Active M-Type Stars Observed with XMM-Newton and Chandra Flares on active M-type stars observed with XMM-Newton and Chandra Urmila Mitra Kraev Mullard Space Science Laboratory Department of Space and Climate Physics University College London A thesis submitted to the University of London for the degree of Doctor of Philosophy I, Urmila Mitra Kraev, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. Abstract M-type red dwarfs are among the most active stars. Their light curves display random variability of rapid increase and gradual decrease in emission. It is believed that these large energy events, or flares, are the manifestation of the permanently reforming magnetic field of the stellar atmosphere. Stellar coronal flares are observed in the radio, optical, ultraviolet and X-rays. With the new generation of X-ray telescopes, XMM-Newton and Chandra , it has become possible to study these flares in much greater detail than ever before. This thesis focuses on three core issues about flares: (i) how their X-ray emission is correlated with the ultraviolet, (ii) using an oscillation to determine the loop length and the magnetic field strength of a particular flare, and (iii) investigating the change of density sensitive lines during flares using high-resolution X-ray spectra. (i) It is known that flare emission in different wavebands often correlate in time. However, here is the first time where data is presented which shows a correlation between emission from two different wavebands (soft X-rays and ultraviolet) over various sized flares and from five stars, which supports that the flare process is governed by common physical parameters scaling over a large range. (ii) As it is impossible to spatially resolve any but a very few giant stars, the only information on spatial dimensions as well as the magnetic field strength of stellar coronae has to come from indirect measurements. Using wavelet analysis, I isolated the first stellar X-ray flare oscillation. Interpreting it as a standing coronal flare loop oscillation, I derived a flare loop length as well as the magnetic field strength for this X-ray flare. 3 ABSTRACT 4 (iii) The high-resolution soft X-ray spectra of Chandra and XMM-Newton allow us to determine temperatures, densities and abundances of the stellar coronae. De- spite a low signal-to-noise ratio because of the relatively short duration of a flare, we find that, if adding up the photons of several flares, certain density sensitive spectral lines change significantly between quiescent and flaring states. This project led on to investigate the flaring spectrum further, and it is found that the plasma is no longer in collisional ionisation equilibrium, but that it is dominated by recombinations. Acknowledgments First and foremost, I would like to thank my supervisor Louise Harra for her en- during support and guiding me on my way to become an independent researcher. My grateful thanks also go to my co-supervisors Graziella Branduardi-Raymont and Keith Mason for giving me the opportunity to work with XMM-Newton data and for their valuable contributions, in particularly regarding instrumentation and data analysis. My thanks also go to all my collaborators and colleagues at MSSL: Hilary Kay, for sharing her knowledge on stars and the Sun in general and XMM-Newton data analysis in particular; David Williams, for passing on his knowledge on coronal waves and IDL programming; Lidia van Driel-Gesztelyi, for her everlasting enthusi- asm for solar and stellar physics; Alex Blustin, for introducing me to XMM-Newton data analysis and spectral fitting with SPEX, and many other contemporary col- leagues at MSSL for answering questions, and discussing solar- and astrophysics. I am also gratefully indebted to my collaborators from other institutions, namely: Manuel G¨udel, for introducing me to and passing on his excitement for stellar coro- nal physics, fruitful collaboration and discussions; Marc Audard and Ton Raassen for much valued contributions; Jan-Uwe Ness, for introducing me to Chandra data analysis and enthusiastic discussions about flare spectra; and last but not least my husband Egor Kraev, for his patience, constant support, and sharing his mathemat- ical insight, in particular about wavelet analysis and error statistics. Special thanks also go to my examiners Valery Nakariakov and Mihalis Mathioudakis. And finally I would like to thank everyone who supported me patiently on my journey. 5 Contents Abstract 3 Acknowledgments 5 List of Tables 10 List of Figures 11 1 Introduction 17 1.1 Mdwarfs ................................. 17 1.1.1 Generalproperties . 17 1.1.2 Magnetic activity . 20 1.1.3 Features of the dMe stars treated in this work . 23 1.2 Flares ................................... 27 1.2.1 Stellar flare observations . 27 1.2.2 The standard flare model: Magnetic reconnection and chro- mosphericevaporation . 27 1.2.3 Flaredimensions ......................... 31 1.3 Magneto-hydrodynamicwaves . 31 1.4 X-rayspectroscopy ............................ 32 1.4.1 Temperatures and densities from line ratios . 33 1.4.2 Non-ionisation equilibria . 35 1.5 Openquestions .............................. 36 6 CONTENTS 7 1.6 Overview.................................. 37 2 Instrumentation 38 2.1 XMM-Newton ............................. 39 2.2 Chandra ................................. 42 3 Flares in X-rays and ultraviolet 43 3.1 Summary ................................. 43 3.2 Introduction................................ 43 3.3 Observations................................ 46 3.4 Results................................... 48 3.4.1 Lightcurves............................ 48 3.4.1.1 Determining the luminosity . 48 3.4.1.2 Cross-correlation between the UV and X-ray flux . 51 3.4.1.3 Flare identification . 53 3.4.2 The UV–X-ray relationship in flares . 53 3.5 Discussion................................. 55 3.6 Conclusions ................................ 60 4 X-ray flare oscillation 62 4.1 Summary ................................. 62 4.2 Introduction................................ 63 4.3 TargetandObservation . 65 4.4 Analysis .................................. 67 4.4.1 Datapreparation . 67 4.4.2 Continuous wavelet transform and frequency band decompo- sition................................ 68 4.4.3 CWTerroranalysis. 72 4.5 Results................................... 73 4.5.1 Magneto-acoustic waves . 74 CONTENTS 8 4.5.2 Loop length from radiative cooling times . 76 4.5.3 Pressure balance scaling laws . 76 4.6 Discussionandconclusions . 77 5 High-density flares on EV Lacertae 81 5.1 Summary ................................. 81 5.2 Introduction................................ 82 5.3 Datareduction .............................. 85 5.4 Analysisandresults............................ 86 5.4.1 Lightcurveandspectra . 87 5.4.2 Statisticalassessment. 90 5.4.3 ResultsofotherdMestars . 94 5.5 Discussion................................. 97 5.5.1 Temperature and densities from line ratios . 97 5.5.2 Resonantscattering. 99 5.5.3 Transient recombination . 100 5.5.4 Flaringvolume .. .. .. ... .. .. .. .. .. ... .. ..101 5.6 Conclusions ................................102 6 The recombining X-ray flare spectrum of EV Lac 104 6.1 Summary .................................104 6.2 Introduction................................105 6.3 Resultsanddiscussion . .107 6.3.1 Spectrallines ...........................118 6.3.2 Overalltrends. .118 6.3.3 TheHe-liketransitions . .119 6.3.4 The H-like Lyman-series . 121 6.3.5 Photoionisation? . .122 6.4 Conclusions ................................124 CONTENTS 9 7 Conclusions and outlook 126 7.1 Conclusions ................................126 7.2 Outlook ..................................129 Bibliography 131 List of Tables 1.1 Terminology................................ 18 1.2 Targetsandtheirproperties . 24 1.2 Targets and their properties – continued . 25 1.3 Solarparameters ............................. 25 2.1 Key instrument spectral X-ray features of XMM-Newton and Chan- dra .................................... 40 3.1 Observational Parameters and Results . 47 3.2 Relationship Parameters for log(X-ray) = κ log(UV) + c ....... 55 · 3.3 Neupert Relationship Parameters: = 10c κ ............ 57 Lx · Euv 4.1 Comparison of values derived for the indicated models . ...... 78 5.1 EV Lac line count rates. In bold are significant changes. 97 5.2 EV Lac line ratios and derived densities and temperatures. In bold are ratios which show significant changes. 98 6.1 Chandra HETG fluxes of EV Lac during quiescence and flares . 108 6.2 Collisional ionisation and recombination equilibration timescales τ . 120 10 List of Figures 1.1 Chromospheric evaporation. From the corona, a non-thermal electron beam is accelerated along a magnetic loop down toward the photo- sphere. The relativistic electrons gyrate along the magnetic field lines and emit gyro-synchrotron radiation in the radio frequency. When they reach the chromosphere, they collide with the dense plasma, ex- citing the ions and emitting hard X-ray bremsstrahlung. Thus, the plasma gets heated and flows up into the corona. Eventually, the plasma cools again and emits soft X-rays (SXR) from recombination processes. Subsequently, the material sort of condenses, falls down- ward, gets denser still and thus radiates even more SXR. 29 1.2 The f/i-ratio as a function of density for He-like ions at their respec- tive maximum emission temperature, calculated with CHIANTI. 34 11 LIST OF FIGURES 12 3.1 The light curves (left panels) and their cross-correlations (right pan- els) of EV Lac
Recommended publications
  • The Agb Newsletter
    THE AGB NEWSLETTER An electronic publication dedicated to Asymptotic Giant Branch stars and related phenomena Official publication of the IAU Working Group on Red Giants and Supergiants No. 276 — 1 July 2020 https://www.astro.keele.ac.uk/AGBnews Editors: Jacco van Loon, Ambra Nanni and Albert Zijlstra Editorial Board (Working Group Organising Committee): Marcelo Miguel Miller Bertolami, Carolyn Doherty, JJ Eldridge, Anibal Garc´ıa-Hern´andez, Josef Hron, Biwei Jiang, Tomasz Kami´nski, John Lattanzio, Emily Levesque, Maria Lugaro, Keiichi Ohnaka, Gioia Rau, Jacco van Loon (Chair) Figure 1: The Cat’s Eye Planetary Nebula imaged by Mark Hanson at Stan Watson Observatory with a 24′′ f6.7 teelescope. It includes 23 hours worth of [O iii]. The best known part, the “eye” is just the small object in the middle, while the messy halo extends much further. Notice also the bowshock on the right. (Suggestion by Sakib Rasool.) 1 Editorial Dear Colleagues, It is a pleasure to present you the 276th issue of the AGB Newsletter. Note that IAU Symposium 366 (”The Origin of Outflows in Evolved Stars”) has been postponed until November next year, while in June 2021 there will be a 4-week programme of workshops on stellar astrophysics in the Gaia era, in Munich (Germany). See the announcements for both meetings at the end of the newsletter. Unfortunately our proposal for a Focus Meeting at next year’s IAU General Assembly was not successful. One of the reasons given was: ”Some evaluators commented that Most of the topics in this proposal could have been made 10 or 20 years ago.
    [Show full text]
  • Antony Hewish
    PULSARS AND HIGH DENSITY PHYSICS Nobel Lecture, December 12, 1974 by A NTONY H E W I S H University of Cambridge, Cavendish Laboratory, Cambridge, England D ISCOVERY OF P U L S A R S The trail which ultimately led to the first pulsar began in 1948 when I joined Ryle’s small research team and became interested in the general problem of the propagation of radiation through irregular transparent media. We are all familiar with the twinkling of visible stars and my task was to understand why radio stars also twinkled. I was fortunate to have been taught by Ratcliffe, who first showed me the power of Fourier techniques in dealing with such diffraction phenomena. By a modest extension of existing theory I was able to show that our radio stars twinkled because of plasma clouds in the ionosphere at heights around 300 km, and I was also able to measure the speed of ionospheric winds in this region (1) . My fascination in using extra-terrestrial radio sources for studying the intervening plasma next brought me to the solar corona. From observations of the angular scattering of radiation passing through the corona, using simple radio interferometers, I was eventually able to trace the solar atmo- sphere out to one half the radius of the Earth’s orbit (2). In my notebook for 1954 there is a comment that, if radio sources were of small enough angular size, they would illuminate the solar atmosphere with sufficient coherence to produce interference patterns at the Earth which would be detectable as a very rapid fluctuation of intensity.
    [Show full text]
  • Detecting Reflected Light from Close-In Extrasolar Giant Planets with the Kepler Photometer
    Accepted for publication by the Astrophysical Journal 05/2003 Detecting Reflected Light from Close-In Extrasolar Giant Planets with the Kepler Photometer Jon M. Jenkins SETI Institute/NASA Ames Research Center, MS 244-30, Moffett Field, CA 94035 [email protected] and Laurance R. Doyle SETI Institute, 2035 Landings Drive, Mountain View, CA 94043 [email protected] ABSTRACT NASA’s Kepler Mission promises to detect transiting Earth-sized planets in the habitable zones of solar-like stars. In addition, it will be poised to detect the reflected light component from close-in extrasolar giant planets (CEGPs) similar to 51 Peg b. Here we use the DIARAD/SOHO time series along with models for the reflected light signatures of CEGPs to evaluate Kepler’s ability to detect arXiv:astro-ph/0305473v1 24 May 2003 such planets. We examine the detectability as a function of stellar brightness, stellar rotation period, planetary orbital inclination angle, and planetary orbital period, and then estimate the total number of CEGPs that Kepler will detect over its four year mission. The analysis shows that intrinsic stellar variability of solar-like stars is a major obstacle to detecting the reflected light from CEGPs. Monte Carlo trials are used to estimate the detection threshold required to limit the total number of expected false alarms to no more than one for a survey of 100,000 stellar light curves. Kepler will likely detect 100-760 51 Peg b-like planets by reflected light with orbital periods up to 7 days. Subject headings: planetary systems — techniques: photometry — methods: data analysis –2– 1.
    [Show full text]
  • Simultaneous Multiwavelength Flare Observations of Ev Lacertae
    Draft version August 19, 2021 Typeset using LATEX twocolumn style in AASTeX61 SIMULTANEOUS MULTIWAVELENGTH FLARE OBSERVATIONS OF EV LACERTAE Rishi R. Paudel,1, 2 Thomas Barclay,1, 3 Joshua E. Schlieder,3 Elisa V. Quintana,3 Emily A. Gilbert,4, 5, 6, 3 Laura D. Vega,7, 3, 2 Allison Youngblood,8 Michele Silverstein,3 Rachel A. Osten,9 Michael A. Tucker,10, ∗ Daniel Huber,10 Aaron Do,10 Kenji Hamaguchi,11, 1 D. J. Mullan,12 John E. Gizis,12 Teresa A. Monsue,3 Knicole D. Colon,´ 3 Patricia T. Boyd,3 James R. A. Davenport,13 and Lucianne Walkowicz6 1University of Maryland, Baltimore County, Baltimore, MD 21250, USA 2CRESST II and Exoplanets and Stellar Astrophysics Laboratory, NASA/GSFC, Greenbelt, MD 20771, USA 3NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 4Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave, Chicago, IL 60637, USA 5University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA 6The Adler Planetarium, 1300 South Lakeshore Drive, Chicago, IL 60605, USA 7Department of Astronomy, University of Maryland, College Park, MD 20742, USA 8Laboratory for Atmospheric and Space Physics, 1234 Innovation Dr, Boulder, CO 80303, USA 9Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 10Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA 11CRESST II and X-ray Astrophysics Laboratory NASA/GSFC, Greenbelt, MD, USA 12Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA 13Department of Astronomy, University of Washington, Seattle, WA 98195, USA ABSTRACT We present the first results of our ongoing project conducting simultaneous multiwavelength observations of flares on nearby active M dwarfs.
    [Show full text]
  • Research at the Belgrade Astronomical Observatory
    ASTRONOMY AND SPACE SCIENCE eds. M.K. Tsvetkov, L.G. Filipov, M.S. Dimitrijevic,´ L.C.ˇ Popovic,´ Heron Press Ltd, Sofia 2007 Influence of Collisional Processes on the Astrophysical Plasma Spectra – Research at the Belgrade Astronomical Observatory M.S. Dimitrijevic´ Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia Abstract. Activities on the project “Influence of collisional processes on the astrophysical plasma spectra”, supported by the Ministry of Science and Envi- ronment protection from 1st January 2002 up to 31st December 2005 are re- viewed, including other scientific results of the project participants. 1 Research on the Influence of Collisional Processes on the Astro- physical Plasma Spectra on Belgrade Astronomical Observatory From 1. January 2002, activities on investigation of the influence of collisional processes on the astrophysical plasma spectra are organized at Belgrade astronomical observatory within the frame of the project with the same name, supported by the Ministry of Science and Environment protection of Serbia. Investigations made within the frame of the Project concern plasma in astrophysics, lab- oratory and technology and the corresponding modelling, determination and research of atomic and molecular processes, optical properties and spectra, with a particular accent on the role of collisional processes. The particular attention has been paid to the inves- tigation of spectral line profiles, broadened by collisions with charged particles (Stark effect). Such investigations are of interest for the diagnostics and modelling of stellar plasma, plasma in laboratory and technological plasma. Semiclasical perturbation and Modified semiempirical methods were used, tested and investigated. Stark broadening parameters, line width and shift, were determined for a large number of spectral lines of Ag I, Ar I, Cd I, Ga I, Ge I, Kr I, Ne I, F II, In II, Ne II, Ti II, Be III, Cd III, Co III, Cu III, F III, S III, Si III, Zn III, and Si IV.
    [Show full text]
  • X-Ray Properties of Active M Dwarfs As Observed by XMM-Newton
    A&A 435, 1073–1085 (2005) Astronomy DOI: 10.1051/0004-6361:20041941 & c ESO 2005 Astrophysics X-ray properties of active M dwarfs as observed by XMM-Newton J. Robrade and J. H. M. M. Schmitt Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: [email protected] Received 2 September 2004 / Accepted 8 February 2005 Abstract. We present a comparative study of X-ray emission from a sample of active M dwarfs with spectral types M3.5–M4.5 using XMM-Newton observations of two single stars, AD Leonis and EV Lacertae, and two unresolved binary systems, AT Microscopii and EQ Pegasi. The light curves reveal frequent flaring during all four observations. We perform a uniform spectral analysis and determine plasma temperatures, abundances and emission measures in different states of activity. Applying multi-temperature models with variable abundances separately to data obtained with the EPIC and RGS detectors we are able to investigate the consistency of the results obtained by the different instruments onboard XMM-Newton. We find that the X-ray properties of the sample M dwarfs are very similar, with the coronal abundances of all sample stars following a trend of increasing abundance with increasing first ionization potential, the inverse FIP effect. The overall metallicities are below solar photospheric ones but appear consistent with the measured photospheric abundances of M dwarfs like these. A significant increase in the prominence of the hotter plasma components is observed during flares while the cool plasma component is only marginally affected by flaring, pointing to different coronal structures.
    [Show full text]
  • Publications Ofthe Astronomical Society Ofthe Pacific 99:490-496, June 1987
    Publications ofthe Astronomical Society ofthe Pacific 99:490-496, June 1987 RADIAL VELOCITIES OF M DWARF STARS GEOFFREY W. MARCY,* VICTORIA LINDSAY,* AND KAREN WILSON Department of Physics and Astronomy, San Francisco State University, San Francisco, California 94132 Received 1987 February 26, revised 1987 March 28 ABSTRACT Radial velocities for 72 M dwarfs have been obtained having internal errors of about 0.1 km s1 and external errors of about 0.4 km s_1. Multiple velocity measurements of ten dMe stars have yielded a set of six which have no stellar companions, providing confirmation that the dMe phenomenon can occur in single stars. These single dMe stars have low space motions indicative of relative youth. Four stars from the entire survey were found to have double-line spectra and two were found to be single-line spectroscopic binaries of low amplitude. The zero point of the velocity scale is found to agree well with that of O. C. Wilson (1967) and differences are noted among other radial-velocity studies. Most of the stars in this study have velocities sufficiently well determined to constitute potential radial-velocity standards. Key words: K-M dwarfs-radial velocities I. Introduction atic difference between their velocities and O. C. 1 Accurate measurements of radial velocities for M Wilson's of —1.7 km s , a discrepancy not explainable by dwarfs are used to address a number of astrophysical the random errors of the two studies. problems such as the age dependence of the kinematics of Thus, it is not known at present which zero point is to the Galaxy (cf.
    [Show full text]
  • THE VALLEY SKYWATCHER Volume 47 Number 3 Summer 2010
    THE VALLEY SKYWATCHER Volume 47 Number 3 Summer 2010 The Valley Skywatcher is the official publication of the Chagrin Valley Astronomical Society, founded 1963. Our mailing address is PO Box 11, Chagrin Falls, OH 44022 More information can be found on our web site: www.chagrinvalleyastronomy.org Editor: Dan Rothstein Table of Contents: A Few Summer Double Stars George Gliba Constellation Quiz Dan Rothstein Discovery History and Recent Light Curves for 1700 Zvezdara Ron Baker Astronomical Alignments in Ireland Dan Rothstein A Few Summer Double Stars - by G.W. Gliba There are many fine double stars available in the Summer sky that can be split in a small refractor or medium size reflector this time of the year. One of my favorite is Xi Bootids, because it was originally thought to be the radiant to a solo minor meteorite shower, which is now known to be a complex of several radiants, now recognized by the IAU as the Bootid-Corona Borealis Complex. It can be split with a good 2.4-inch refractor. The components consists of a 4.8 magnitude primary star that is a G8V with a 7th magnitude companion of K5V spec. type, which appears yellow and orange respectively to an observer. This star system is 22 light years distant. The G8V component is also a variable star of low amplitude know as a BY Draconis type star, which varies from 4.52 to 4.67 over 10.137 days. However, this variability can't be noticed visually. Much easier and more colorful is the nice pair Epsilon Bootis nearby, also known as Izar.
    [Show full text]
  • FLARES on the Dme FLARE STAR EV LACERTAE Rachel A
    The Astrophysical Journal, 621:398–416, 2005 March 1 # 2005. The American Astronomical Society. All rights reserved. Printed in U.S.A. FROM RADIO TO X-RAY: FLARES ON THE dMe FLARE STAR EV LACERTAE Rachel A. Osten1, 2 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903; [email protected] Suzanne L. Hawley2 Astronomy Department, Box 351580, University of Washington, Seattle, WA 98195; [email protected] Joel C. Allred Physics Department, Box 351560, University of Washington, Seattle, WA 98195; [email protected] Christopher M. Johns-Krull2 Department of Physics and Astronomy, Rice University, 6100 Main Street, Houston, TX 77005; [email protected] and Christine Roark3 Department of Physics and Astronomy, University of Iowa, 203 Van Allen Hall, Iowa City, IA 52245 Received 2004 June 23; accepted 2004 November 5 ABSTRACT We present the results of a campaign to observe flares on the M dwarfflare star EV Lacertae over the course of two days in 2001 September, utilizing a combination of radio continuum, optical photometric and spectroscopic, ultraviolet spectroscopic, and X-ray spectroscopic observations to characterize the multiwavelength nature offlares from this active, single, late-type star. We find flares in every wavelength region in which we observed. A large radio flare from the star was observed at both 3.6 and 6 cm and is the most luminous example of a gyrosynchrotron flare yet observed on a dMe flare star. The radio flare can be explained as encompassing a large magnetic volume, comparable to the stellar disk, and involving trapped electrons that decay over timescales of hours.
    [Show full text]
  • Gaia Data Release 2 Special Issue
    A&A 623, A110 (2019) Astronomy https://doi.org/10.1051/0004-6361/201833304 & © ESO 2019 Astrophysics Gaia Data Release 2 Special issue Gaia Data Release 2 Variable stars in the colour-absolute magnitude diagram?,?? Gaia Collaboration, L. Eyer1, L. Rimoldini2, M. Audard1, R. I. Anderson3,1, K. Nienartowicz2, F. Glass1, O. Marchal4, M. Grenon1, N. Mowlavi1, B. Holl1, G. Clementini5, C. Aerts6,7, T. Mazeh8, D. W. Evans9, L. Szabados10, A. G. A. Brown11, A. Vallenari12, T. Prusti13, J. H. J. de Bruijne13, C. Babusiaux4,14, C. A. L. Bailer-Jones15, M. Biermann16, F. Jansen17, C. Jordi18, S. A. Klioner19, U. Lammers20, L. Lindegren21, X. Luri18, F. Mignard22, C. Panem23, D. Pourbaix24,25, S. Randich26, P. Sartoretti4, H. I. Siddiqui27, C. Soubiran28, F. van Leeuwen9, N. A. Walton9, F. Arenou4, U. Bastian16, M. Cropper29, R. Drimmel30, D. Katz4, M. G. Lattanzi30, J. Bakker20, C. Cacciari5, J. Castañeda18, L. Chaoul23, N. Cheek31, F. De Angeli9, C. Fabricius18, R. Guerra20, E. Masana18, R. Messineo32, P. Panuzzo4, J. Portell18, M. Riello9, G. M. Seabroke29, P. Tanga22, F. Thévenin22, G. Gracia-Abril33,16, G. Comoretto27, M. Garcia-Reinaldos20, D. Teyssier27, M. Altmann16,34, R. Andrae15, I. Bellas-Velidis35, K. Benson29, J. Berthier36, R. Blomme37, P. Burgess9, G. Busso9, B. Carry22,36, A. Cellino30, M. Clotet18, O. Creevey22, M. Davidson38, J. De Ridder6, L. Delchambre39, A. Dell’Oro26, C. Ducourant28, J. Fernández-Hernández40, M. Fouesneau15, Y. Frémat37, L. Galluccio22, M. García-Torres41, J. González-Núñez31,42, J. J. González-Vidal18, E. Gosset39,25, L. P. Guy2,43, J.-L. Halbwachs44, N. C. Hambly38, D.
    [Show full text]
  • The Coronal X-Ray – Age Relation and Its Implications for the Evaporation of Exoplanets
    Mon. Not. R. Astron. Soc. 000, 1–20 (2011) Printed 24 October 2018 (MN LATEX style file v2.2) The coronal X-ray – age relation and its implications for the evaporation of exoplanets Alan P. Jackson1,2⋆, Timothy A. Davis1,3⋆ and Peter J. Wheatley4 1Sub-Department of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford, UK, OX1 3RH 2Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, UK, CB3 0HA 3European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748, Garching bei Muenchen, Germany 4Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, UK, CV4 7AL Submitted 2011 ABSTRACT We study the relationship between coronal X-ray emission and stellar age for late-type stars, and the variation of this relationship with spectral type. We select 717 stars from 13 open clusters and find that the ratio of X-ray to bolometric luminosity during the saturated phase of coronal emission decreases from 10−3.1 for late K-dwarfs to 10−4.3 for early F-type stars (across the range 0.29 6 (B − V )0 < 1.41). Our determined saturation timescales vary between 107.8 and 108.3 years, though with no clear trend across the whole FGK range. We apply our X-ray emission – age relations to the investigation of the evaporation history of 121 known transiting exoplanets using a simple energy-limited model of evaporation and taking into consideration Roche lobe effects and different heating/evaporation efficiencies. We confirm that a linear cut-off of the planet distribution in the M 2/R3 versus a−2 plane is an expected result of population modification by evaporation and show that the known transiting exoplanets display such a cut-off.
    [Show full text]
  • Observations of Variable Stars from Holomon Astronomical Station A
    Observations of variable stars from Holomon Astronomical Station A. Kokori1, 2; A. Tsiaras3; M. Aspridis4; K. Karpouzas4; J. H. Seiradakis4 & S. Avgoloupis5 1 Faculty of Humanities and Social Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland 2 Blackrock Castle Observatory, Cork Institute of Technology, Castle Rd, Blackrock, T12 YW52 Co. Cork, Ireland 3 Department of Physics & Astronomy, University College London, Gower Street, WC1E6BT London, United Kingdom 4 Department of Physics, Section of Astrophysics, Astronomy and Mechanics, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece 5 Department of Primary Education, Faculty of Education, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece ABSTRACT EV Lacertae is a young (300 million years), M3.5 red dwarf star with strong flare activity. We observed EV Lac in the optical, for three consecutive nights in August 2016. The data obtained were analysed using the Holomon Photometric software and revealed three flares, one for each night. The first, increased the stellar flux by approximately 15% while the following two by approximately 5%. EV Lacertae (EV Lac, Gliese 873, HIP 112460) is a spectral type M3.5 red dwarf star, 16.5 light years away and lies in the constellation Lacerta. It is the nearest star to the Sun in that region of the sky. It is a flare star that emits X-rays and on 25 April 2008, NASA’S Swift satellite recorded a flare which was thousands of times more powerful than the largest observed solar flare. Mavridis and Avgoloupis (1986) were the first who suggested the existence of an activity cycle of 5 years.
    [Show full text]