Variability of a Stellar Corona on a Time Scale of Days Evidence for Abundance Fractionation in an Emerging Coronal Active Region

Total Page:16

File Type:pdf, Size:1020Kb

Variability of a Stellar Corona on a Time Scale of Days Evidence for Abundance Fractionation in an Emerging Coronal Active Region A&A 550, A22 (2013) Astronomy DOI: 10.1051/0004-6361/201220491 & c ESO 2013 Astrophysics Variability of a stellar corona on a time scale of days Evidence for abundance fractionation in an emerging coronal active region R. Nordon1,2,E.Behar3, and S. A. Drake4 1 Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach 1312 85741 Garching, Germany 2 School of Physics and Astronomy, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, 69978 Tel-Aviv, Israel e-mail: [email protected] 3 Physics Department, Technion Israel Institute of Technology, 32000 Haifa, Israel e-mail: [email protected] 4 NASA/GSFC, Greenbelt, 20771 Maryland, USA e-mail: [email protected] Received 3 October 2012 / Accepted 1 December 2012 ABSTRACT Elemental abundance effects in active coronae have eluded our understanding for almost three decades, since the discovery of the first ionization potential (FIP) effect on the sun. The goal of this paper is to monitor the same coronal structures over a time interval of six days and resolve active regions on a stellar corona through rotational modulation. We report on four iso-phase X-ray spectroscopic observations of the RS CVn binary EI Eri with XMM-Newton, carried out approximately every two days, to match the rotation period of EI Eri. We present an analysis of the thermal and chemical structure of the EI Eri corona as it evolves over the six days. Although the corona is rather steady in its temperature distribution, the emission measure and FIP bias both vary and seem to be correlated. An active region, predating the beginning of the campaign, repeatedly enters into our view at the same phase as it rotates from beyond the stellar limb. As a result, the abundances tend slightly, but consistently, to increase for high FIP elements (an inverse FIP effect) with phase. We estimate the abundance increase of high FIP elements in the active region to be of about 75% over the coronal mean. This observed fractionation of elements in an active region on time scales of days provides circumstantial clues regarding the element enrichment mechanism of non-flaring stellar coronae. Key words. stars: atmospheres – stars: coronae – stars: abundances – X-rays: stars – stars: individual: EI Eridani 1. Introduction micro-flaring, which is observed on the sun, but perhaps with different statistics (e.g., Caramazza et al. 2007). The best studied cool-star corona is that of our own sun, which Solar coronal chemical abundances are different from the also provides the only spatially resolved stellar coronal source solar photospheric composition. The solar corona itself is non- of extreme ultraviolet (EUV) and X-rays. From X-ray images uniform in that respect. While in coronal holes, the abundances of the sun we know that the solar corona in its active state is are close to photospheric, abundances in active regions and in non-uniform and that a significant fraction of the emission in the solar wind are significantly different. The abundance pat- these bands comes from magnetic loop structures concentrated terns depend on the first ionization potential (FIP; Meyer 1985; in active regions around photospheric sun-spots. Evidently, these Feldman 1992; Sheeley 1995). Elements with FIP < 10 eV structures evolve in brightness on time scales of hours. The mor- (low FIP) are enriched in the corona relative to elements with phology as well as the metal abundances vary on longer time FIP > 12 eV (high FIP). Averaging over the entire solar disk, scales of days. Coronal structures on the Sun may survive for the enrichment factor is about 4 (Feldman & Widing 2002,and a few weeks, although tracking them continuously from the references therein). Such a FIP bias, in varying intensities, has ground is difficult due to the ∼24.5 day solar rotation period. been reported for many coronal structures, from closed magnetic Active coronae of other cool stars can be up to five orders loops to streamers (see reviews by Kohl et al. 2006; Doschek & of magnitude more luminous and an order of magnitude hot- Feldman 2010). Currently there is no generally accepted model ter than the solar corona. Although unresolved, they show many that explains the FIP bias. characteristics similar to those of the solar corona, and are there- The FIP effect became even more puzzling when high reso- fore believed to be structured and to evolve in a similar way. For lution X-ray spectra from XMM-Newton and Chandra revealed the most part, late-type stars have envelopes in which convec- that active stellar coronae do not follow the solar FIP pattern. In tion and differential rotation interact to drive a dynamo, which some cases, the high-FIP elements are even enriched compared produces magnetic flux tubes. The flux tubes float into the up- to the low-FIP ones, an effect labeled the inverse-FIP (IFIP) ef- per atmosphere and eventually the corona. It is generally un- fect (Brinkman et al. 2001). Later studies revealed that FIP and clear, however, whether stellar coronae actually have larger cov- IFIP biases are correlated with coronal activity (and age): Highly ering of their stellar photosphere, or even qualitatively different active stars show an IFIP effect, while less active coronae have a morphologies, such as inter-binary magnetic structures. Stellar solar FIP bias (Audard et al. 2003; Telleschi et al. 2005), imply- coronae show high variability, often attributed to continuous ing a transition on stellar-evolution time scales of Gyr. Article published by EDP Sciences A22, page 1 of 9 A&A 550, A22 (2013) Table 1. Observing log. Obs. ID Start time End time Exposure [ks] 060317201 2009-08-01T00:02:50 2009-08-01T09:13:05 32.84 060317301 2009-08-02T23:06:16 2009-08-03T09:24:46 36.92 060317401 2009-08-04T22:20:49 2009-08-05T07:42:41 33.54 060317501 2009-08-06T20:59:39 2009-08-07T07:31:30 37.48 On the face of it, the correlation with activity supported pre- M4-5 secondary, with a possible 19-year orbit of a third body vious suggestions that abundances may be linked to flares (e.g., (Washuettl et al. 2009a). Güdel et al. 1999, 2004; Osten et al. 2003; Nordon et al. 2006). Long term photometric monitoring of EI Eri seemed to indi- However, direct systematic measurements of abundance varia- cate a ∼11 yr brightness cycle that was conjectured to be an ana- tions during flares show that regardless of coronal FIP/IFIP bias, log of the solar activity cycle (Oláh & Strassmeier 2002), but un- during large flares the abundances tend to photospheric values like the sun, long term Doppler imaging of EI Eri by Washuettl (Nordon & Behar 2007, 2008). The mechanism for FIP/IFIP is, et al. (2009b) shows little variability of its cool starspots therefore, related either to the long-term evolution of coronal over 11 yr. As for the hot corona, Osten et al. (2002) observed structures, or to the continuous micro-flaring that produces the EI Eri with ASCA (and EUVE) and fitted its spectrum with a quiescence emission, but not to large flares. 2T model of kT = 0.72 keV and 2.2 keV, but the abundances In recent years, a model has been proposed in which abun- could not be tightly constrained with ASCA. The XMM-Newton dance fractionation is driven by magneto hydrodynamics(MHD) CCD spectra of a short flare on EI Eri on 2009-08-06 during the waves (Laming 2004, 2009, 2012). This “pondermotive” force is present campaign was analyzed by Pandey & Singh (2012), who controlled by the energy density of MHD waves at the bases of suggested the flare originated from a loop the size of ∼R∗ (pri- the coronal loops. Wood et al. (2012) studied a sample of X-ray mary), which is about a tenth of the binary separation distance. 29 −1 faint (LX < 10 erg s ) dwarfs and found no correlation with X-ray luminosity or surface flux, but a good correlation with spectral type instead. According to this relation M dwarfs are 2. Observations, data, and analysis IFIP biased while early G dwarfs are FIP biased. Wood et al. In Table 1 we list the log of the four XMM-Newton observations (2012) claim that this shift from FIP to IFIP can be explained of EI Eri. Note the start times for each observation, which are by the inversion of the pondermotive force at certain conditions. separated by approximately the EI Eri orbital period of 168.5 ks. The latter study is limited to X-ray faint dwarfs and may not be applicable to the typical highly active binaries from other stud- ies that are more than two order of magnitude more luminous in 2.1. Data reduction X-rays, emitted mostly by a giant or sub-giant star (RSCVn type XMM-Newton data were reduced using the Science Analysis systems). Software (SAS – ver. 10.0.0) in the standard processing chains Despite the assumed similarity between solar and stellar as described in the ABC Guide to XMM-Newton Data Analysis1, coronae, we have lacked a study of the evolution of a stellar and using the most updated calibration files (date 22.06.2010). corona on time scales of days, which is the relevant time for Pileup was checked using the epatplot routine of the SAS soft- coronal loop evolution on the sun. The goal of the observations ware package. No significant pileup was detected in either of the presented in this paper is to seek and measure the variability of EPIC instruments and thus events from single to quadruple were temperatures and abundances in an active corona over several retained.
Recommended publications
  • Coronal Structure of Pre-Main Sequence Stars
    **FULL TITLE** ASP Conference Series, Vol. **VOLUME**, **YEAR OF PUBLICATION** **NAMES OF EDITORS** Coronal Structure of Pre-Main Sequence Stars Moira Jardine SUPA, School of Physics and Astronomy, North Haugh, St Andrews, Fife, KY16 9SS, UK Abstract. The study of pre-main sequence stellar coronae is undertaken in many different wavelength regimes, with apparently conflicting results. X-ray studies of T Tauri stars suggest the presence of loops with a range of sizes ranging from less than a stellar radius to 10 stellar radii. Some of these stars show a clear rotational modulation in X-rays, but many do not and indeed the nature of this emission and its dependence on stellar mass and rotation rate is still a matter of debate. Some component of it may come from the accretion shock, but the location and extent of the accretion funnels (inferred from optical and UV observations) is as much of a puzzle as the mass accretion rate that they carry. Mass and angular momentum are not only gained by the star in the process of accretion, but also lost in either jets or winds. Linking all these different features is the magnetic field. Recent observations suggest the presence of structure on many scales, with a complex, multipolar field on small scales near the surface co-existing with a much simpler field structure on the larger scales at which the stellar field may be linking onto a surrounding disk. Some recent models suggest that the open field lines which are responsible for carrying gas escaping in winds and jets may also be responsible for much of the infalling accretion flow.
    [Show full text]
  • 15 Stellar Winds
    15 Stellar Winds Stan Owocki Bartol Research Institute, Department of Physics and Astronomy, University of Colorado, Newark, DE, USA 1IntroductionandBackground....................................... 737 2ObservationalDiagnosticsandInferredProperties....................... 740 2.1 Solar Corona and Wind ................................................ 740 2.2 Spectral Signatures of Dense Winds from Hot and Cool Stars ................. 742 2.2.1 Opacity and Optical Depth ............................................. 742 2.2.2 Doppler-Shi!ed Line Absorption ........................................ 744 2.2.3 Asymmetric P-Cygni Pro"les from Scattering Lines ......................... 745 2.2.4 Wind-Emission Lines .................................................. 748 2.2.5 Continuum Emission in Radio and Infrared ................................ 750 3GeneralEquationsandFormalismforStellarWindMassLoss.............. 751 3.1 Hydrostatic Equilibrium in the Atmospheric Base of Any Wind ............... 751 3.2 General Flow Conservation Equations .................................... 752 3.3 Steady, Spherically Symmetric Wind Expansion ............................ 753 3.4 Energy Requirements of a Spherical Wind Out#ow .......................... 753 4CoronalExpansionandSolarWind................................... 754 4.1 Reasons for Hot, Extended Corona ....................................... 754 4.1.1 $ermal Runaway from Density and Temperature Decline of Line-Cooling ...... 754 4.1.2 Coronal Heating with a Conductive $ermostat ...........................
    [Show full text]
  • Detecting Differential Rotation and Starspot Evolution on the M Dwarf GJ 1243 with Kepler James R
    Western Washington University Masthead Logo Western CEDAR Physics & Astronomy College of Science and Engineering 6-20-2015 Detecting Differential Rotation and Starspot Evolution on the M Dwarf GJ 1243 with Kepler James R. A. Davenport Western Washington University, [email protected] Leslie Hebb Suzanne L. Hawley Follow this and additional works at: https://cedar.wwu.edu/physicsastronomy_facpubs Part of the Stars, Interstellar Medium and the Galaxy Commons Recommended Citation Davenport, James R. A.; Hebb, Leslie; and Hawley, Suzanne L., "Detecting Differential Rotation and Starspot Evolution on the M Dwarf GJ 1243 with Kepler" (2015). Physics & Astronomy. 16. https://cedar.wwu.edu/physicsastronomy_facpubs/16 This Article is brought to you for free and open access by the College of Science and Engineering at Western CEDAR. It has been accepted for inclusion in Physics & Astronomy by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. The Astrophysical Journal, 806:212 (11pp), 2015 June 20 doi:10.1088/0004-637X/806/2/212 © 2015. The American Astronomical Society. All rights reserved. DETECTING DIFFERENTIAL ROTATION AND STARSPOT EVOLUTION ON THE M DWARF GJ 1243 WITH KEPLER James R. A. Davenport1, Leslie Hebb2, and Suzanne L. Hawley1 1 Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA; [email protected] 2 Department of Physics, Hobart and William Smith Colleges, Geneva, NY 14456, USA Received 2015 March 9; accepted 2015 May 6; published 2015 June 18 ABSTRACT We present an analysis of the starspots on the active M4 dwarf GJ 1243, using 4 years of time series photometry from Kepler.
    [Show full text]
  • Starspot Temperature Along the HR Diagram
    Mem. S.A.It. Suppl. Vol. 9, 220 Memorie della c SAIt 2006 Supplementi Starspot temperature along the HR diagram K. Biazzo1, A. Frasca2, S. Catalano2, E. Marilli2, G. W. Henry3, and G. Tasˇ 4 1 Department of Physics and Astronomy, University of Catania, via Santa Sofia 78, 95123 Catania, e-mail: [email protected] 2 INAF - Catania Astrophysical Observatory, via S. Sofia 78, 95123 Catania, Italy 3 Tennessee State University - Center of Excellence in Information Systems, 330 10th Ave. North, Nashville, TN 37203-3401 4 Ege University Observatory - 35100 Bornova, Izmir˙ , Turkey Abstract. The photospheric temperature of active stars is affected by the presence of cool starspots. The determination of the spot configuration and, in particular, spot temperatures and sizes, is important for understanding the role of the magnetic field in blocking the convective heating flux inside starspots. It has been demonstrated that a very sensitive di- agnostic of surface temperature in late-type stars is the depth ratio of weak photospheric absorption lines (e.g. Gray & Johanson 1991, Catalano et al. 2002). We have shown that it is possible to reconstruct the distribution of the spots, along with their sizes and tempera- tures, from the application of a spot model to the light and temperature curves (Frasca et al. 2005). In this work, we present and briefly discuss results on spot sizes and temperatures for stars in various locations in the HR diagram. Key words. Stars: activity - Stars: variability - Stars: starspot 1. Introduction Table 1. Star sample. Within a large program aimed at studying the behaviour of photospheric surface inhomo- Star Sp.
    [Show full text]
  • Abstracts Connecting to the Boston University Network
    20th Cambridge Workshop: Cool Stars, Stellar Systems, and the Sun July 29 - Aug 3, 2018 Boston / Cambridge, USA Abstracts Connecting to the Boston University Network 1. Select network ”BU Guest (unencrypted)” 2. Once connected, open a web browser and try to navigate to a website. You should be redirected to https://safeconnect.bu.edu:9443 for registration. If the page does not automatically redirect, go to bu.edu to be brought to the login page. 3. Enter the login information: Guest Username: CoolStars20 Password: CoolStars20 Click to accept the conditions then log in. ii Foreword Our story starts on January 31, 1980 when a small group of about 50 astronomers came to- gether, organized by Andrea Dupree, to discuss the results from the new high-energy satel- lites IUE and Einstein. Called “Cool Stars, Stellar Systems, and the Sun,” the meeting empha- sized the solar stellar connection and focused discussion on “several topics … in which the similarity is manifest: the structures of chromospheres and coronae, stellar activity, and the phenomena of mass loss,” according to the preface of the resulting, “Special Report of the Smithsonian Astrophysical Observatory.” We could easily have chosen the same topics for this meeting. Over the summer of 1980, the group met again in Bonas, France and then back in Cambridge in 1981. Nearly 40 years on, I am comfortable saying these workshops have evolved to be the premier conference series for cool star research. Cool Stars has been held largely biennially, alternating between North America and Europe. Over that time, the field of stellar astro- physics has been upended several times, first by results from Hubble, then ROSAT, then Keck and other large aperture ground-based adaptive optics telescopes.
    [Show full text]
  • 10. Scientific Programme 10.1
    10. SCIENTIFIC PROGRAMME 10.1. OVERVIEW (a) Invited Discourses Plenary Hall B 18:00-19:30 ID1 “The Zoo of Galaxies” Karen Masters, University of Portsmouth, UK Monday, 20 August ID2 “Supernovae, the Accelerating Cosmos, and Dark Energy” Brian Schmidt, ANU, Australia Wednesday, 22 August ID3 “The Herschel View of Star Formation” Philippe André, CEA Saclay, France Wednesday, 29 August ID4 “Past, Present and Future of Chinese Astronomy” Cheng Fang, Nanjing University, China Nanjing Thursday, 30 August (b) Plenary Symposium Review Talks Plenary Hall B (B) 8:30-10:00 Or Rooms 309A+B (3) IAUS 288 Astrophysics from Antarctica John Storey (3) Mon. 20 IAUS 289 The Cosmic Distance Scale: Past, Present and Future Wendy Freedman (3) Mon. 27 IAUS 290 Probing General Relativity using Accreting Black Holes Andy Fabian (B) Wed. 22 IAUS 291 Pulsars are Cool – seriously Scott Ransom (3) Thu. 23 Magnetars: neutron stars with magnetic storms Nanda Rea (3) Thu. 23 Probing Gravitation with Pulsars Michael Kremer (3) Thu. 23 IAUS 292 From Gas to Stars over Cosmic Time Mordacai-Mark Mac Low (B) Tue. 21 IAUS 293 The Kepler Mission: NASA’s ExoEarth Census Natalie Batalha (3) Tue. 28 IAUS 294 The Origin and Evolution of Cosmic Magnetism Bryan Gaensler (B) Wed. 29 IAUS 295 Black Holes in Galaxies John Kormendy (B) Thu. 30 (c) Symposia - Week 1 IAUS 288 Astrophysics from Antartica IAUS 290 Accretion on all scales IAUS 291 Neutron Stars and Pulsars IAUS 292 Molecular gas, Dust, and Star Formation in Galaxies (d) Symposia –Week 2 IAUS 289 Advancing the Physics of Cosmic
    [Show full text]
  • Spectroscopy of Variable Stars
    Spectroscopy of Variable Stars Steve B. Howell and Travis A. Rector The National Optical Astronomy Observatory 950 N. Cherry Ave. Tucson, AZ 85719 USA Introduction A Note from the Authors The goal of this project is to determine the physical characteristics of variable stars (e.g., temperature, radius and luminosity) by analyzing spectra and photometric observations that span several years. The project was originally developed as a The 2.1-meter telescope and research project for teachers participating in the NOAO TLRBSE program. Coudé Feed spectrograph at Kitt Peak National Observatory in Ari- Please note that it is assumed that the instructor and students are familiar with the zona. The 2.1-meter telescope is concepts of photometry and spectroscopy as it is used in astronomy, as well as inside the white dome. The Coudé stellar classification and stellar evolution. This document is an incomplete source Feed spectrograph is in the right of information on these topics, so further study is encouraged. In particular, the half of the building. It also uses “Stellar Spectroscopy” document will be useful for learning how to analyze the the white tower on the right. spectrum of a star. Prerequisites To be able to do this research project, students should have a basic understanding of the following concepts: • Spectroscopy and photometry in astronomy • Stellar evolution • Stellar classification • Inverse-square law and Stefan’s law The control room for the Coudé Description of the Data Feed spectrograph. The spec- trograph is operated by the two The spectra used in this project were obtained with the Coudé Feed telescopes computers on the left.
    [Show full text]
  • The High Resolution Camera
    CXC Newsletter The High Resolution Camera To create a source catalog of the M31 center and search for time variability of the sources, we includ- Ralph Kraft, Hans Moritz Guenther (SAO), and ed 23 observations from November 1999 to February Wolfgang Pietsch (MPE) 2005 (adding about 250 ks exposure time). We detected 318 X-ray sources and created long term light curves It has been another quiet, but successful year for for all of them. We classified sources as highly variable HRC operations. The instrument performs well with or outbursting (with subclasses short vs. long outbursts no significant anomalies or instrumental issues. The and activity periods). 129 sources could be classified as HRC continues to be used for a wide variety of astro- X-ray binaries due to their position in globular clusters physical investigations. In this chapter, we briefly de- or their strong time variability (see Fig. 2). We detected scribe two such science studies. First, a collaboration seven supernova remnants, one of which is a new can- led by Dr. Wolfgang Pietsch of MPE used the HRC to didate, and also resolved the first X-rays from a known study the X-ray state of the nova population in M31 radio supernova remnant (see Hofmann et al. 2013). in conjunction with XMM-Newton and optical studies. In a second study, Guenther et al. used the HRC to They found that there is a strong correlation between determine the origin of the X-ray emission from β Pic, the optical and X-ray properties of these novae. Sec- a nearby star with a dusty disk.
    [Show full text]
  • Variability of a Stellar Corona on a Time Scale of Days Evidence for Abundance Fractionation in an Emerging Coronal Active Region
    A&A 550, A22 (2013) Astronomy DOI: 10.1051/0004-6361/201220491 & c ESO 2013 Astrophysics Variability of a stellar corona on a time scale of days Evidence for abundance fractionation in an emerging coronal active region R. Nordon1,2,E.Behar3, and S. A. Drake4 1 Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach 1312 85741 Garching, Germany 2 School of Physics and Astronomy, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, 69978 Tel-Aviv, Israel e-mail: [email protected] 3 Physics Department, Technion Israel Institute of Technology, 32000 Haifa, Israel e-mail: [email protected] 4 NASA/GSFC, Greenbelt, 20771 Maryland, USA e-mail: [email protected] Received 3 October 2012 / Accepted 1 December 2012 ABSTRACT Elemental abundance effects in active coronae have eluded our understanding for almost three decades, since the discovery of the first ionization potential (FIP) effect on the sun. The goal of this paper is to monitor the same coronal structures over a time interval of six days and resolve active regions on a stellar corona through rotational modulation. We report on four iso-phase X-ray spectroscopic observations of the RS CVn binary EI Eri with XMM-Newton, carried out approximately every two days, to match the rotation period of EI Eri. We present an analysis of the thermal and chemical structure of the EI Eri corona as it evolves over the six days. Although the corona is rather steady in its temperature distribution, the emission measure and FIP bias both vary and seem to be correlated.
    [Show full text]
  • Arxiv:1812.04626V2 [Astro-Ph.HE] 27 Jan 2019
    Draft version January 29, 2019 Preprint typeset using LATEX style emulateapj v. 12/16/11 OPTICAL SPECTROSCOPY AND DEMOGRAPHICS OF REDBACK MILLISECOND PULSAR BINARIES Jay Strader1, Samuel J. Swihart1, Laura Chomiuk1, Arash Bahramian2, Christopher T. Britt3, C. C. Cheung4, Kristen C. Dage1, Jules P. Halpern5, Kwan-Lok Li6, Roberto P. Mignani7,8, Jerome A. Orosz9, Mark Peacock1, Ricardo Salinas10, Laura Shishkovsky1, Evangelia Tremou11 Draft version January 29, 2019 ABSTRACT We present the first optical spectroscopy of five confirmed (or strong candidate) redback millisecond pulsar binaries, obtaining complete radial velocity curves for each companion star. The properties of these millisecond pulsar binaries with low-mass, hydrogen-rich companions are discussed in the context of the 14 confirmed and 10 candidate field redbacks. We find that the neutron stars in redbacks have a median mass of 1:78 ± 0:09M with a dispersion of σ = 0:21 ± 0:09. Neutron stars with masses in excess of 2M are consistent with, but not firmly demanded by, current observations. Redback companions have median masses of 0:36 ± 0:04M with a scatter of σ = 0:15 ± 0:04M , and a tail possibly extending up to 0.7{0:9M . Candidate redbacks tend to have higher companion masses than confirmed redbacks, suggesting a possible selection bias against the detection of radio pulsations in these more massive candidate systems. The distribution of companion masses between redbacks and the less massive black widows continues to be strongly bimodal, which is an important constraint on evolutionary models for these systems. Among redbacks, the median efficiency of converting the pulsar spindown energy to γ-ray luminosity is ∼ 10%.
    [Show full text]
  • Spot Activity of the RS Canum Venaticorum Star Σ Geminorum⋆
    A&A 562, A107 (2014) Astronomy DOI: 10.1051/0004-6361/201321291 & c ESO 2014 Astrophysics Spot activity of the RS Canum Venaticorum star σ Geminorum P. Kajatkari1, T. Hackman1,2, L. Jetsu1,J.Lehtinen1, and G.W. Henry3 1 Department of Physics, PO Box 64, 00014 University of Helsinki, 00014 Helsinki, Finland e-mail: [email protected] 2 Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland 3 Center of Excellence in Information Systems, Tennessee State University, 3500 John A. Merritt Blvd., Box 9501, Nashville, TN 37209, USA Received 14 February 2013 / Accepted 6 November 2013 ABSTRACT Aims. We model the photometry of RS CVn star σ Geminorum to obtain new information on the changes of the surface starspot distribution, that is, activity cycles, differential rotation, and active longitudes. Methods. We used the previously published continuous period search (CPS) method to analyse V-band differential photometry ob- tained between the years 1987 and 2010 with the T3 0.4 m Automated Telescope at the Fairborn Observatory. The CPS method divides data into short subsets and then models the light-curves with Fourier-models of variable orders and provides estimates of the mean magnitude, amplitude, period, and light-curve minima. These light-curve parameters are then analysed for signs of activity cycles, differential rotation and active longitudes. d Results. We confirm the presence of two previously found stable active longitudes, synchronised with the orbital period Porb = 19.60, and found eight events where the active longitudes are disrupted. The epochs of the primary light-curve minima rotate with a shorter d period Pmin,1 = 19.47 than the orbital motion.
    [Show full text]
  • Bayesian Analysis on Gravitational Waves And
    The Pennsylvania State University The Graduate School Department of Physics BAYESIAN ANALYSIS ON GRAVITATIONAL WAVES AND EXOPLANETS A Dissertation in Physics by Xihao Deng c 2015 Xihao Deng Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy May 2015 ii The dissertation of Xihao Deng was read and approved1 by the following: Lee Samuel Finn Professor of Physics Dissertation Advisor Chair of Committee Chad Hanna Assistant Professor of Physics Stephane Coutu Professor of Physics Aleksander Wolszczan Professor of Astronomy and Astrophysics Nitin Samarth Professor of Physics Head of the Department of Physics 1Signatures on file in the Graduate School. iii Abstract Attempts to detect gravitational waves using a pulsar timing array (PTA), i.e., a collection of pulsars in our Galaxy, have become more organized over the last several years. PTAs act to detect gravitational waves generated from very distant sources by observing the small and correlated effect the waves have on pulse arrival times at the Earth. In this thesis, I present advanced Bayesian analysis methods that can be used to search for gravitational waves in pulsar timing data. These methods were also applied to analyze a set of radial velocity (RV) data collected by the Hobby- Eberly Telescope on observing a K0 giant star. They confirmed the presence of two Jupiter mass planets around a K0 giant star and also characterized the stellar p-mode oscillation. The first part of the thesis investigates the effect of wavefront curvature on a pulsar’s response to a gravitational wave. In it we show that we can assume the gravitational wave phasefront is planar across the array only if the source luminosity distance 2πL2/λ, where L is the pulsar ≫ distance to the Earth ( kpc) and λ is the radiation wavelength ( pc) in the PTA waveband.
    [Show full text]