DOCSLIB.ORG

Are Rotational Axes Perpendicular to Orbital Planes in Binary Systems. III. Main Sequence and Short-Period RS Cvn Stars. R

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Are Rotational Axes Perpendicular to Orbital Planes in Binary Systems. III. Main Sequence and Short-Period RS Cvn Stars. R ACTA ASTRONOMICA Vol. 45 (1995) pp. 725±745 Are Rotational Axes Perpendicular to Orbital Planes in Binary Systems. III. Main Sequence and Short-Period RS CVn Stars. by R. GøeÎbocki Institute of Theoretical Physics and Astrophysics, University of GdaÂnsk, ul. Wita Stwosza 57, 80-952 GdaÂnsk, Poland e-mail: ®[email protected] and A. Stawikowski N. Copernicus Astronomical Center, ul. RabiaÂnska 8, 87-100 ToruÂn, Poland e-mail: [email protected] Received November 24, 1995 ABSTRACT Inclinations of the rotational axes, irot , are determined for 46 main sequence binaries of F, G, K and M spectral type and short period RS CVn systems. Seven binaries are asynchronous. The i inclinations irot are then compared with the orbital inclinations, orb , to test the alignment between the equatorial and orbital planes. In all 39 cases of synchronous rotators irot is equal or nearly equal to iorb . In a sample of seven asynchronous systems, at least six, and perhaps all, are non-coplanar. Key words: Stars: rotation-binaries: general-Stars: late-type 1. Introduction Chromospherically active stars with spots present a unique possibility to de- V i termine rotational period, Prot , and with independently measured rot sin rot to evaluate inclination of rotational axis, irot . In late type binaries it allows for com- parison of inclination of rotational axes to the orbital plane. Our previous analyses (Stawikowski and GøeÎbocki 1994 a,b called hereinafterPaperIandPaperII)showed that in long-period RS CVn stars an assumption of coplanarity of the equatorial ro- = i tational and orbital planes ( irot orb ) is justi®ed for synchronous systems only. In asynchronous binaries the rotational axes are not perpendicularto the orbital plane. 726 A. A. It contradicts generally accepted assumption and requires revision of time-scales of circularization and synchronization for non-coplanar systems. In the present study we analyze main sequence F, G, K and M binaries and short-period RS CVn stars with orbital periods smaller than about 10 days. The observational data were collected from all recently available publications, but in most cases they are based on the second edition of "A catalog of chromospherically active binary stars" Strassmeier et al. (1993), hereinafter called CABS. ThemethodoftheanalysisisthesameasinPaperIandII. Becausethe accuracy of determination of irot is crucialfor®nalconclusions,specialattention is paid tothe determination of stellar temperatures and absolute magnitudes in¯uencing directly error in stellar radii and in consequence error in irot . In Chapter 2 we discuss calibration and errors of our temperature and absolute magnitude scales for main sequence F, G, K and M stars. A de®nition of synchronismin binary systems is not unique. A simple criterion = P of Porb rot is useless because of differential rotation and "pseudo synchro- nism" for highly eccentric orbits. Tan Huisong et al. (1993) suggest a parameter = j(P P )P j S S orb rot orb as a measure of synchronism, where 0 01 means S synchronism and S 0 04 means asynchronism. The case of 0 01 0 04 means either a slight asynchronism or a highly differential rotation. We use this parameter for discriminating asynchronous systems. It should be stressed that we = P assume Prot phot and we include in our analysis only stars with directly deter- V mined values of Pphot (either from periodic variations of obs or from "migration waves" in eclipsing binaries). The values of Pphot show small seasonal variations due to differential rotation, but the observed changes are smaller than 4%. i In Section 3 we present the results ± our values of stellar parameters: iorb , rot = ji i j and i orb rot . The discussion of errors is made individually for each star in Comments to Tables 2±5. 2. Observational Data We have found 69 binary systems (short-period RS CVn or main sequenceF, G, V i K,Mspectraltypebinaries)withknown Pphot and rot sin rot full®ling our selection criteria. Unfortunately, only for 46 systems other stellar and orbital parameters were i known with accuracy good enough for determination of iorb and rot . They are listed in Tables 2±5. In this sample, 21 systems are eclipsing binaries providing accurate orbital inclinations, 22 non-eclipsing objects are the SB2 systems with reliable parameters for both components. For three non-eclipsing SB1 systems (EI Eri, V833 Tau and DM UMa) evaluation of orbital inclination was possible (m) i because of extremely low value of the mass function, f . In such a case orb q is low and insensitive to the adopted values of mass, M , and mass ratio, (see Paper I). Vol. 45 727 When both (or at least one) components of the binary are main sequence stars, the evaluation of iorb is made using stellar masses determined from the mass- luminosity relation. We used the relation given in Lang (1992) compendium, which is based on careful discussion of Popper (1980). Our results were always very close to that presented in CABS. Accuracies of iorb determination in most cases are better than 2 and not worse than 5 . Binary systems for which errors in iorb exceed 5 were excluded from the sample. An interesting case of II Peg for which iorb is very uncertain but spots have been observed (and modeled) by many authors is described in Section 3. Inclinations of rotational axes were determined from the ratio of the observed i V V projected rotational velocity, Vrot sin rot , to the rotational velocity, rot , with rot obtained from rotational period, Prot , using the formula = R P Vrot 50 61 rot R P V where is radius in R , rot in days and rot in km/s. As in previous papers P only Prot based on direct phot measurements (or equivalent "migration wave" observations) have been used in the analysis. We are warning again that some authors are publishing Prot based on the a priori assumption of synchronism, especially for short-period systems. It could lead to serious errors (e.g., for VY Ari = P = P = P = Porb 13 2 while phot 16 4 or LR Hya with orb 6 86 and phot 3 14). There are two main sources of errors in the determination of irot : inaccuracy i R of Vrot sin rot measurements and evaluation of . In the estimation of error of i individual Vrot sin rot values we must rely on accuracies published in original papers. Sometimes a few independent measurements are available. If our estimate i indicates that the error of Vrot sin rot exceeds 15% we exclude such star from the sample. The stellar radius, R , was obtained from the estimation of the effective T M temperature, eff , and the absolute magnitude, v . To minimize this error special attention was paid to the calibration of the temperature scale. Fortunately, most of stars in our sample are the F, G, K, M dwarfs not very distant from the Sun. For some of them very accurate trigonometric parallaxes were available. Otherwise M T M v v was estimated from the spectral type. The scales and errors in eff and are described in the following subsection. 2.1. Effective Temperature and Absolute Magnitude Calibration Most accurate estimation of Teff can be obtained from a multicolor infrared photometry. ForF,GandK typesubgiantsandgiantsformulae found by McWilliam = f (CI ) (1990) (see his Table 6), in his extensive analysis of Teff for the BVRI photometry, provide the most reliable values of Teff . We used these formulae for all stars with the luminosity class IV, IV-III and III. Using Table 12 of McWilliam = f ( ) (1990) we have constructed a relation Teff sp type . The adopted values for Teff are the average values obtained from each color index and spectral type of a star. 728 A. A. There are many relations of Teff versus spectral type or color index for main sequence stars, e.g.,Johnson (1966), Novotny (1973), Bohm-Vitense (1981) Gray (1992) and most frequently used Landolt-Bernstein (1982). When comparing these relations some discrepanciesand systematic shifts become evident. With increasing accuracy and number of infrared observations many independent determinations of Teff for individual stars have been published. We used the following sources = f ( ) T = f (CI ) for redetermination of Teff sp type and eff for late type dwarfs: Leggett et al. (1986), Blackwell et al. (1991), Buser and Kurucz (1992), Blackwell and Lynas-Gray (1994) and Taylor (1994). Additionally we included independent Teff estimations used for the [Fe/H] determinations and published in the catalogue of Cayrel de Strobel et al. (1992). We analyzed only stars within the luminosity class V and present in the Bright Star Catalogue to avoid interstellar reddening effects. If more than one determination of temperature was available for a given star, an average value was calculated with the weight equal 2 given to Taylor's (1994) data, and the ®nal weight equal to the number of independent determinations of Teff . Information about spectral types was obtained from SIMBAD, and the most = f ( ) frequently cited ones were adopted. The resulting relation of Teff sp type for F, G, K and M main sequencestars is presented in columns 1 and 2 of Table 1. The catalogue of multicolor photometry of Lanz (1986) allowed to determine relations between effective temperature and BVRI color indices in the same way. T = f (CI ) B V V R For BS stars with known Teff the best relations eff for , , I V I R and color indices were found. They are presented in columns 3, 4, 5 and 6 of Table 1. We believe that with known spectral type and infrared color indices our calibration provides Teff with the accuracy of 50 K. Unfortunately V for 18 analyzed binary systems only spectral type and B are known.
Load more

Recommended publications
  • Starspot Photometry with Robotic Telescopes
    SUPPLEMENT SERIES Astron. Astrophys. Suppl. Ser. 125, 11-63 (1997) Starspot photometry with robotic telescopes Continuous UBV and V (RI)C photometry of 23 stars in 1991–1996 K.G. Strassmeier1, J. Bartus1,2, G. Cutispoto3, and M. Rodon´o3 1 Institut f¨ur Astronomie, Universit¨at Wien, T¨urkenschanzstraße 17, A-1180 Wien, Austria [email protected] 2 Konkoly Observatory, Hungarian Academy of Sciences, H-1525 Budapest, Hungary [email protected] 3 Catania Astrophysical Observatory, V.le A. Doria 6, I-95125 Catania, Italy [email protected], [email protected] Received September 23; accepted December 16, 1996 Abstract. We report on the progress of our ongoing pho- 1. Introduction: Starspot photometry tometric monitoring program of spotted late-type stars with automatic photoelectric telescopes (APTs) on Mt. Photometry of late-type stars with inhomogeneous sur- Hopkins in Arizona and on Mt. Etna in Sicily. We present face brightness distributions revealed distinct light-curve 9 250 differential UBV and/or V (RI)C observations for variations modulated with the stellar rotation period. altogether 23 chromospherically active stars, singles and Numerous papers dealt with this phenomenology since the binaries, pre main sequence and post main sequence, taken early seventies, starting with the first interpretations by between 1991 and 1996. The variability mechanism of our Kron (1947, 1952), Hoffmeister (1965), Chugainov (1966), target stars is mostly rotational modulation by an asym- Catalano & Rodon´o (1967) and Hall (1972) and finally cul- metrically spotted stellar surface. Therefore, precise rota- minating in the use of fully automatic telescopes for con- tional periods and their seasonal variations are determined tinuously monitoring RS CVn- and even solar-type stars using baselines between 3 years for HD 129333 to 34 years (e.g.
    [Show full text]
  • Arxiv:0705.4290V2 [Astro-Ph] 23 Aug 2007
    DRAFT VERSION NOVEMBER 11, 2018 Preprint typeset using LATEX style emulateapj v. 08/13/06 THE GEMINI DEEP PLANET SURVEY – GDPS∗ DAVID LAFRENIÈREA,RENÉ DOYONA , CHRISTIAN MAROISB ,DANIEL NADEAUA, BEN R. OPPENHEIMERC,PATRICK F. ROCHED , FRANÇOIS RIGAUTE, JAMES R. GRAHAMF ,RAY JAYAWARDHANAG,DOUG JOHNSTONEH,PAUL G. KALASF ,BRUCE MACINTOSHB, RENÉ RACINEA Draft version November 11, 2018 ABSTRACT We present the results of the Gemini Deep Planet Survey, a near-infrared adaptive optics search for giant planets and brown dwarfs around nearby young stars. The observations were obtained with the Altair adaptive optics system at the Gemini North telescope and angular differential imaging was used to suppress the speckle noise of the central star. Detection limits for the 85 stars observed are presented, along with a list of all faint point sources detected around them. Typically, the observations are sensitive to angular separations beyond 0.5′′ with 5σ contrast sensitivities in magnitude difference at 1.6 µm of 9.5 at 0.5′′, 12.9 at 1′′, 15.0 at 2′′, and 16.5 at 5′′. For the typical target of the survey, a 100 Myr old K0 star located 22 pc from the Sun, the observations are sensitive enough to detect planets more massive than 2 MJup with a projected separation in the range 40–200 AU. Depending on the age, spectral type, and distance of the target stars, the detection limit can be as low as 1 MJup. Second epoch observations of 48 stars with candidates (out of 54) have confirmed that all candidates are∼ unrelated background stars. A detailed statistical analysis of the survey results, yielding upper limits on the fractions of stars with giant planet or low mass brown dwarf companions, is presented.
    [Show full text]
  • Where Are All the Sirius-Like Binary Systems?
    Mon. Not. R. Astron. Soc. 000, 1-22 (2013) Printed 20/08/2013 (MAB WORD template V1.0) Where are all the Sirius-Like Binary Systems? 1* 2 3 4 4 J. B. Holberg , T. D. Oswalt , E. M. Sion , M. A. Barstow and M. R. Burleigh ¹ Lunar and Planetary Laboratory, Sonnett Space Sciences Bld., University of Arizona, Tucson, AZ 85721, USA 2 Florida Institute of Technology, Melbourne, FL. 32091, USA 3 Department of Astronomy and Astrophysics, Villanova University, 800 Lancaster Ave. Villanova University, Villanova, PA, 19085, USA 4 Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK 1st September 2011 ABSTRACT Approximately 70% of the nearby white dwarfs appear to be single stars, with the remainder being members of binary or multiple star systems. The most numerous and most easily identifiable systems are those in which the main sequence companion is an M star, since even if the systems are unresolved the white dwarf either dominates or is at least competitive with the luminosity of the companion at optical wavelengths. Harder to identify are systems where the non-degenerate component has a spectral type earlier than M0 and the white dwarf becomes the less luminous component. Taking Sirius as the prototype, these latter systems are referred to here as ‘Sirius-Like’. There are currently 98 known Sirius-Like systems. Studies of the local white dwarf population within 20 pc indicate that approximately 8 per cent of all white dwarfs are members of Sirius-Like systems, yet beyond 20 pc the frequency of known Sirius-Like systems declines to between 1 and 2 per cent, indicating that many more of these systems remain to be found.
    [Show full text]
  • Exploring the Brown Dwarf Desert with Hipparcos J
    Exploring the brown dwarf desert with Hipparcos J. L. Halbwachs, Frédéric Arenou, M. Mayor, S. Udry, D. Queloz To cite this version: J. L. Halbwachs, Frédéric Arenou, M. Mayor, S. Udry, D. Queloz. Exploring the brown dwarf desert with Hipparcos. Astronomy and Astrophysics - A&A, EDP Sciences, 2000, 355, pp.581-594. hal- 02055170 HAL Id: hal-02055170 https://hal.archives-ouvertes.fr/hal-02055170 Submitted on 3 Mar 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Astron. Astrophys. 355, 581–594 (2000) ASTRONOMY AND ASTROPHYSICS Exploring the brown dwarf desert with Hipparcos? J.L. Halbwachs1, F. Arenou2, M. Mayor3, S. Udry3, and D. Queloz3,4 1 Equipe “Populations stellaires et evolution galactique”, Observatoire Astronomique de Strasbourg (UMR 7550), 11 rue de l’Universite,´ 67 000 Strasbourg ([email protected]) 2 DASGAL, Observatoire de Paris–Meudon, bat 11, 5 place J. Janssen, 92195 Meudon Cedex, France ([email protected]) 3 Geneva Observatory, 51 chemin des Maillettes, 1290 Sauverny, Switzerland ([email protected]; [email protected]; [email protected]) 4 Jet Propulsion Lab., 4800 Oak Grove Drive, Pasadena, CA 91109, USA Received 5 July 1999 / Accepted 16 November 1999 Abstract.
    [Show full text]
  • I110-00 1..9999
    PLANETARY SCIENCE THE SCIENCE OF PLANETS AROUND STARS PLANETARY SCIENCE THE SCIENCE OF PLANETS AROUND STARS George H A Cole Department of Physics, University of Hull, UK Michael M Woolfson Department of Physics, University of York, UK Institute of Physics Publishing Bristol and Philadelphia # IOP Publishing Ltd 2002 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher. Multiple copying is permitted in accordance with the terms of licences issued by the Copyright Licensing Agency under the terms of its agreement with Universities UK (UUK). British Library Cataloguing-in-Publication Data A catalogue record of this book is available from the British Library. ISBN 0 7503 0815 X Library of Congress Cataloging-in-Publication Data are available Commissioning Editor: John Navas Production Editor: Simon Laurenson Production Control: Sarah Plenty Cover Design: Fre de rique Swist Published by Institute of Physics Publishing, wholly owned by The Institute of Physics, London Institute of Physics Publishing, Dirac House, Temple Back, Bristol BS1 6BE, UK US Oce: Institute of Physics Publishing, The Public Ledger Building, Suite 1035, 150 South Independence Mall West, Philadelphia, PA 19106, USA Typeset by Academic Technical, Bristol Printed in the UK by Bookcraft, Midsomer Norton, Somerset CONTENTS INTRODUCTION xix A REVIEW OF THE SOLAR SYSTEM 1 THE UNITY OF THE UNIVERSE 1 1.1. Cosmic abundance of the chemical elements 1 1.2. Some examples 2 Problem 1 4 2 THE SUN AND OTHER STARS 6 2.1.
    [Show full text]
  • Download This Article in PDF Format
    A&A 593, A38 (2016) Astronomy DOI: 10.1051/0004-6361/201628231 & c ESO 2016 Astrophysics SPOTS: The Search for Planets Orbiting Two Stars II. First constraints on the frequency of sub-stellar companions on wide circumbinary orbits M. Bonavita1; 2, S. Desidera2, C. Thalmann3, M. Janson4, A. Vigan5, G. Chauvin6, and J. Lannier6 1 Institute for Astronomy, The University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK e-mail: [email protected] 2 INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy 3 Institute for Astronomy, ETH Zurich, Wolfgang-Pauli Strasse 27, 8093 Zurich, Switzerland 4 Department of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden 5 Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France 6 Institut de Planétologie et d’Astrophysique de Grenoble, UJF, CNRS, 414 rue de la piscine, 38400 Saint-Martin-d’Hères, France Received 1 February 2016 / Accepted 12 May 2016 ABSTRACT A large number of direct imaging surveys for exoplanets have been performed in recent years, yielding the first directly imaged planets and providing constraints on the prevalence and distribution of wide planetary systems. However, like most of the radial velocity ones, these generally focus on single stars, hence binaries and higher-order multiples have not been studied to the same level of scrutiny. This motivated the Search for Planets Orbiting Two Stars (SPOTS) survey, which is an ongoing direct imaging study of a large sample of close binaries, started with VLT/NACO and now continuing with VLT/SPHERE.
    [Show full text]
  • Université De Montréal Relevé De Planètes Géantes Autour D'étoiles
    Université de Montréal Relevé de planètes géantes autour d’étoiles proches par imagerie directe et optimisation d’une technique d’imagerie multibande par David Lafrenière Département de physique Faculté des arts et des sciences Thèse présentée à la Faculté des études supérieures en vue de l’obtention du grade de Philosophiœ Doctor (Ph.D.) en physique Avril, 2007 © David Lafrenière, 2007. o o Université (III de Montréal Direction des bib1othèques AVIS L’auteur a autorisé l’Université de Montréal à reproduire et diffuser, en totalité ou en partie, par quelque moyen que ce soit et sur quelque support que ce soit, et exclusivement à des fins non lucratives d’enseignement et de recherche, des copies de ce mémoire ou de cette thèse. L’auteur et les coauteurs le cas échéant conservent la propriété du droit d’auteur et des droits moraux qui protègent ce document. Ni la thèse ou le mémoire, ni des extraits substantiels de ce document, ne doivent être imprimés ou autrement reproduits sans l’autorisation de l’auteur. Afin de se conformer à la Loi canadienne sur la protection des renseignements personnels, quelques formulaires secondaires, coordonnées ou signatures intégrées au texte ont pu être enlevés de ce document. Bien que cela ait pu affecter la pagination, il n’y a aucun contenu manquant. NOTICE The author of this thesis or dissertation has granted a nonexciusive license allowing Université de Montréal to reproduce and publish the document, in part or in whole, and in any format, solely for noncommercial educationaT and research purposes. The author and co-authors if applicable retain copyright ownership and morel rights in this document.
    [Show full text]
  • Classification of Population Ii Stars in the Vilnius Photometric System. I
    Baltic Astronomy, vol. 5, 1-82, 1996. CLASSIFICATION OF POPULATION II STARS IN THE VILNIUS PHOTOMETRIC SYSTEM. I. METHODS A. Bartkevicius1 and R. Lazauskaite1'2 1 Institute of Theoretical Physics and Astronomy, Gostauto 12, Vilnius 2600, Lithuania 2 Department of Theoretical Physics, Vilnius Pedagogical University, Studenty, 39, Vilnius 2340, Lithuania Received February 7, 1996. Abstract. The methods used for classification of Population II stars in the Vilnius photometric system are described. An exten- sive set of standards with known astrophysical parameters compiled from the literature sources is given. These standard stars are classi- fied in the Vilnius photometric system using the methods described. The accuracy of classification is evaluated by a comparison of the as- trophysical parameters derived from the Vilnius photometric system with those estimated from spectroscopic studies as well as from pho- tometric data in other systems. For dwarfs and subdwarfs, we find a satisfactory agreement between our reddenings and those estimated in the uvby/3 system. The standard deviation of [Fe/H] determined in the Vilnius system is about 0.2 dex. The absolute magnitude for dwarfs and subdwarfs is estimated with an accuracy of <0.5 mag. Key words: techniques: photometric - stars: fundamental para- meters (classification) - stars: Population II 1. INTRODUCTION The first attempt to classify Population II stars and to estimate their astrophysical parameters by using the Vilnius photometric sys- tem was made by Bartkevicius & Straizys (1970a, b, c). Later on, Straizys & Bartkevicius (1982) demonstrated a possibility to deter- mine, from photometry alone, the metallicities, temperatures and color excesses of metal-deficient giants. The most detailed calibration 2 A.
    [Show full text]
  • Arxiv:Astro-Ph/0606009V2 2 Jan 2007 E Words
    Astronomy & Astrophysics manuscript no. paperfinal c ESO 2007 January 3, 2007 The eccentricity-mass distribution of exoplanets: signatures of different formation mechanisms? Ignasi Ribas1 and Jordi Miralda-Escud´e1,2 1 Institut de Ci`encies de l’Espai (CSIC-IEEC), Campus UAB, Facultat de Ci`encies, Torre C5 - parell - 2a planta, 08193 Bellaterra, Spain e-mail: [email protected], [email protected] 2 Instituci´oCatalana de Recerca i Estudis Avanc¸ats, Barcelona, Spain ABSTRACT We examine the distributions of eccentricity and host star metallicity of exoplanets as a function of their mass. Planets with M sin i & 4 MJ have an eccentricity distribution consistent with that of binary stars, while planets with M sin i . 4 MJ are less eccentric than binary stars and more massive planets. In addition, host star metallicities decrease with planet mass. The statistical significance of both of these trends is only marginal with the present sample of exoplanets. To account for these trends, we hypothesize that there are two populations of gaseous planets: the low-mass population forms by gas accretion onto a rock-ice core in a circumstellar disk and is more abundant at high metallicities, and the high-mass population forms directly by fragmentation of a pre-stellar cloud. Planets of the first population form in initially circular orbits and grow their eccentricities later, and may have a mass upper limit from the total mass of the disk that can be accreted by the core. The second population may have a mass lower limit resulting from opacity-limited fragmentation. This would roughly divide the two populations in mass, although they would likely overlap over some mass range.
    [Show full text]
  • Analysis of the Hipparcos Observations of the Extrasolar
    July 19th, 2001 Analysis of the Hipparcos Observations of the Extrasolar Planets and the Brown-Dwarf Candidates Shay Zucker and Tsevi Mazeh School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel [email protected], [email protected] accepted for publication by the Astrophysical Journal ABSTRACT We analyzed the Hipparcos astrometric observations of 47 stars that were discovered to harbor giant planets and 14 stars with brown-dwarf secondary can- didates. The Hipparcos measurements were used together with the corresponding stellar radial-velocity data to derive an astrometric orbit for each system. To find out the significance of the derived astrometric orbits we applied a “permutation” technique by which we analyzed the permuted Hipparcos data to get false or- bits. The size distribution of these false orbits indicated the range of possibly random, false orbits that could be derived from the true data. These tests could not find any astrometric orbit of the planet candidates with significance higher than 99%, suggesting that most if not all orbits are not real. Instead, we used the Hipparcos data to set upper limits on the masses of the planet candidates. The lowest derived upper limit is that of 47 UMa — 0.014 M⊙, which confirms arXiv:astro-ph/0107124v2 20 Jul 2001 the planetary nature of its unseen companion. For 13 other planet candidates the upper limits exclude the stellar nature of their companions, although brown- dwarf secondaries are still an option. These negate the idea that all or most of the extrasolar planets are disguised stellar secondaries.
    [Show full text]
  • Starspot Photometry with Robotic Telescopes. $UBV(RI) {\Rm C}$ And
    ASTRONOMY & ASTROPHYSICS NOVEMBER II 1999,PAGE29 SUPPLEMENT SERIES Astron. Astrophys. Suppl. Ser. 140, 29–53 (1999) Starspot photometry with robotic telescopes. UBV (RI)C and by light curves of 47 active stars in 1996/97? K.G. Strassmeier, E. Serkowitsch, and Th. Granzer Institut f¨ur Astronomie, Universit¨at Wien, T¨urkenschanzstraße 17, A-1180 Wien, Austria e-mail: [email protected], [email protected], [email protected] Received March 15; accepted September 3, 1999 Abstract. We present continuous multicolor photometry their appearance and disappearance marking the begin- for 47 stars from October 1996 through June 1997. ning and ending of a spot cycle similar to the Sun’s 11-year Altogether, 7073 V (RI)c, UBV,andby data points, each cycle. the average of three individual readings, were acquired In the past decade several studies were presented that with three automatic photoelectric telescopes (APTs) at attempted to model long-term light-curve variations with Fairborn Observatory in southern Arizona. Most of our an evolving spot distribution on the basis of one stellar ro- targets are chromospherically active single and binary tation to the next. Much literature could be cited here but stars of spectral type G to K but there are also four instead let us selflessly draw your attention to our own se- pre-main-sequence objects and three pulsating stars ries of papers on “Time-series photometric spot modeling” in our sample. The light variability is generally due and the many references therein. Paper I on the RS CVn to rotational modulation of an asymmetrically spotted binary VY Ari (Strassmeier & Bopp 1992) included a de- stellar surface and therefore precise rotational periods scription of the modeling technique and were followed by and their seasonal variations are determined from Fourier Strassmeier et al.
    [Show full text]
  • SPOTS: the Search for Planets Orbiting Two Stars
    Astronomy & Astrophysics manuscript no. MBonavita_SPOTS_II_final c ESO 2016 May 16, 2016 SPOTS: The Search for Planets Orbiting Two Stars II. First constraints on the frequency of sub-stellar companions on wide circumbinary orbits M. Bonavita1, 2, S. Desidera2, C. Thalmann3, M. Janson4, A. Vigan5, G. Chauvin6, and J. Lannier6 1 Institute for Astronomy, The University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, U.K. 2 INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122, Padova, Italy 3 Institute for Astronomy, ETH Zurich, Wolfgang-Pauli Strasse 27, 8093 Zurich, Switzerland 4 Department of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden 5 Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388, Marseille, France 6 Institut de Planétologie et d’Astrophysique de Grenoble, UJF, CNRS, 414 rue de la piscine, 38400 Saint Martin d’Hères, France Received / Accepted ABSTRACT A large number of direct imaging surveys for exoplanets have been performed in recent years, yielding the first directly imaged planets and providing constraints on the prevalence and distribution of wide planetary systems. However, like most of the radial velocity ones, these surveys generally focus on single stars, hence binaries and higher-order multiples have not been studied to the same level of scrutiny. This motivated the SPOTS (Search for Planets Orbiting Two Stars) survey, which is an ongoing direct imaging study of a large sample of close binaries, started with VLT/NACO and now continuing with VLT/SPHERE. To complement this survey, we have identified the close binary targets in 24 published direct imaging surveys.
    [Show full text]