WHITE DWARFS

ASTROPHYSICS AND SPACE SCIENCE LIBRARY

VOLUME 214

Executive Committee W. B. BURTON, Sterrewacht, Leiden, The Netherlands

J. M. E. KUIJPERS, Faculty o/Science, Nijmegen, The Netherlands E. P. 1. V AN DEN HEUVEL, Astronomical Institute, University 0/ Amsterdam,

The Netherlands H. V AN DER LAAN, Astronomical Institute, University 0/ Utrecht,

The Netherlands

Editorial Board I. APPENZELLER, Landessternwarte Heidelberg-Konigstuhl, Germany

J. N. BAHCALL, The Institute/or Advanced Study, Princeton, U.S.A. F. BERTOLA, Universita di Padova, Italy

W. B. BURTON, Sterrewacht, Leiden, The Netherlands 1. P. CASSINELLI, University o/Wisconsin, Madison, U.S.A.

C. J. CESARSKY, Centre d'Etudes de Saclay, Gif-sur-Yvette Cedex, France O. ENGVOLD, Institute o/Theoretical Astrophysics, University 0/ Oslo, Norway

J. M. E. KUIJPERS, Faculty o/Science, Nijmegen, The Netherlands R. McCRAY, University o/Colorado, JILA, Boulder, U.S.A.

P. G. MURDIN, Royal Greenwich Observatory, Cambridge, UK F. PACINI, Istituto Astronomia Arcetri, Firenze, Italy

V. RADHAKRISHNAN, Raman Research Institute, Bangalore, India F. H. SHU, University o/California, Berkeley, U.S.A.

B. V. SOMOV, Astronomical Institute, Moscow State University, Russia R. A. SUNY AEV, Space Researchlnstitute, Moscow, Russia

S. TREMAINE, CITA, University o/Toronto, Canada Y. TANAKA, Institute 0/ Space & Astronautical Science, Kanagawa, Japan

E. P. 1. VAN DEN HEUVEL, Astronomical:Institute, University 0/ Amsterdam, The Netherlands

H. VANDER LAAN, Astronomical Institute, University o/Utrecht, The Netherlands

N. O. WEISS, University o/Cambridge, U.K.

WHITE DWARFS Proceedings of the 10th European Workshop on White Dwarfs,

held in Blanes, Spain, 17-21 June 1996

Edited by

J.ISERN Institut d' Estudis Espacials de Catalunya, CSIC,

Barcelona, Spain

M.HERNANZ Institut d' Estudis Espacials de Catalunya, CSIC,

Barcelona, Spain

and

E. GARCIA-BERRO Universitat Politecnica de Catalunya,

Barcelona, Spain

SPRINGER SCIENCE+BUSINESS MEDIA, B.V.

A C.I.P. Catalogue record for this book is available from the Library of Congress

ISBN 978-94-010-6334-0 ISBN 978-94-011-5542-7 (eBook) DOI 10.1007/978-94-011-5542-7

Cover picture: White Dwarf Stars in M4. HST. WFPC2.

PRC95-32. ST Sci opo. August 28, 1995. H Bond (ST Scl), NASA.

Printed on acid-free paper

All Rights Reserved © 1997 Springer Science+Business Media Dordrecht

Originally published by Kluwer Academic Publishers in 1997 Softcover reprint of the hardcover 1st edition 1997

No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical,

including photocopying, recording or by any information storage and retrieval system, without written permission from the copyright owner.

TABLE OF CONTENTS

Preface ................................................................................. xiii

List of Participants ..................................................................... xv

1. Structure and Evolution ...................................................... l

The empirical white dwarf mass-radius relation H. Schmidt ... ........................................................................... 3

What we have learned about white dwarfs from studies of novae S. Starr field .......................................................................... " 11

The redistribution of carbon and oxygen in crystallizing white dwarfs R. Mochkovitch .... ..................................................................... 19

The cooling of white dwarfs and their internal composition M. Salaris, M. Hemanz, J. Isem, 1. Dominguez fj E. Garcia-Berro ..................... 27

Theoretical models of white dwarfs with helium-rich interiors J.M. Aparicio fj G. Fontaine ............................................................ 35

The electrostatic screening of thermonuclear reactions in astrophysical plasmas N.J. Shaviv fj G. Shaviv .... ............................................................ 43

The possible white dwarf-neutron star connection R. Canal fj J. Gutierrez ................................................................ 49

The impact of evolutionary envelope masses on the evolution of white dwarfs T. Blocker, F. Herwig, T. Driebe, H. Bramkamp fj D. Schonbemer ..... ................. 57

The progenitors of high-mass white dwarfs F. Herwig .............................................................................. 63

The multi periodic, short-period variations of WZ Sge J.L. Provencal fj R.E. Nather ........................................................... 67

Limits on gravities of evolved stars, from infrared photometry and binary companions P. Thejll fj A. Ulla ..................................................................... 71

R.otat.ion: CO white dwarfs near the Chandrasekhar limiting mass 1. Dominguez, O. Straniero, A. Tomambe fj J. Isem ... ................................. 75

The Accretion-Induced Collapse of white dwarfs revisited in 3D D. Garda-Senz fj E. Bravo .. ........................................................... 79

vi

II. Luminosity Functions and Populations ................................ 83

Towards a luminosity function of hot DA white dwarfs 1. Liebert, T.A. Fleming, J.B. Holberg, P. Bergeron fj R. Saffer . ........................ 85

White dwarfs in M67 T.A. Fleming, J. Liebert, P. Bergeron fj A. Beauchamp . ................................ 91

Monte Carlo simulations of the kinematics and luminosity function of white dwarfs E. Garcia-Berro fj S. Torres ............................................................ 97

Monte Carlo simulations of the white dwarf population and luminosity function M.A. Wood ............................................................................ 105

Halo white dwarfs: a conservative point of view 1. Is ern, M. Hernanz, E. Garcia-Berro, N. Itoh fj R. Mochkovitch ..................... 113

Halo white dwarfs: a non conventional scenario G. Chabrier, L. Segretain fj D. Mera .............................. ..................... 121

HST observations of white dwarfs in the globular cluster NGC 6397 A.M. Cool, C. Sosin fj I.R. King ....................................................... 129

The distance and age of the globular cluster NGC 6752 measured by HST observations of cluster and field white dwarfs A. Bragaglia, F.R. Ferraro, A. Renzini, R. Gilmozzi, J.B. Holberg, J. Liebert, S. Ortolani, F. Wesemael fj R. Bohlin . ................................................ 135

DA white dwarfs in the Montreal-Cambridge-Tololo survey R. Lamontagne, F. Wesemael, G. Fontaine, S. Demers, P. Bergeron, M.J. Irwin fj w.E. Kunkel. ....................................................................... 143

Cool white dwarf survey using stacked digitised Schmidt plates R. Knox fj M.R.S. Hawkings ........................................................... 149

III. Atmospheres ................................................................ 153

Chemical evolution of cool white dwarf's atmospheres M.T. Ruiz, P. Bergeron fj S.K. Leggett ........ ......................................... 155

The chemical evolution of white dwarf stars: what the observations tell us H.L. Shipman .... ..................................................................... 165

A critical look at the question of thick vs thin hydrogen and helium envelopes in white dwarfs G. Fontaine fj F. Wesemael ........................................................... 173

Polyatomic carbon molecules in very cool helium-rich white dwarfs I. Bues fj T. Asian . ................................................................... 193

Analysis of optical, UV and EUV observations of G 191-B2B B. Wolff, D. Koester fj A. Vidal-Mad jar ............................................... 199

New results on PG 1159 stars and ultrahigh-excitation DO white dwarfs K. Werner, S. Dreizler, U. Heber fj T. Rauch ........ .................................. 207

vii

Non-LTE analyses of DO white dwarfs S. Dreizler & K. Werner ............................................................... 213

New spectral analyses of pre-white dwarfs T. Rauch, S. Dreizler & K. Werner .................................................... 221

The sphericity effects in the NLTE model atmospheres of white dwarfs J. Kubat ............................................................................... 229

Heavy elements in white dwarf envelopes M.A. Barstow, J.B. Holberg, 1. Hubeny & T. Lanz ...................................... 237

Lyman spectra of hot DA white dwarfs D.S. Finley, D. Koester, J. W. Kruk, R.A. Kimble & N.F. Allard ................. ....... 245

Diffusion of silicon in the envelopes of hot DA white dwarfs P. Chayer, G. Fontaine & C. Pelletier .............................. ................... 253

Time-dependent diffusion calculations for hot pre-white dwarfs K. Unglaub & 1. Bues ... ............................................................... 259

Evolutionary calculations of carbon dredge-up in helium envelope white dwarfs J. MacDonald, M. Hernanz & J. Jose ................................. ................. 265

Analysis of optical and ultraviolet spectroscopy of the DAZ white dwarf G 74-7 M. Billeres, F. Wesemael, A. Beauchamp & P. Bergeron ................ ............... 269

Modeling extreme ultraviolet spectra of white dwarfs with high-metallicity LTE models P. Chayer, S. Vennes, J. Dupuis, P. Thejll & A.K. Pmdhan ............................ 273

Extreme ultraviolet spectroscopy of EUVE J0720-317 and EUVE J0723-277 J. Dupuis, S. Vennes & S. Bowyer ..... ................................................ 277

A new dithered EUVE spectrum of PG 1234+482 S. Jordan, D. Koester & D.S. Finley ...... ............ '" .............................. 281

Line of sight H and He ionization fractions in the local interstellar medium P.D. Dobbie & M.A. Barstow .. ........................................................ 285

An instrument for observations of EUV opacity sources in G 191-B2B K. Gunderson, J. Green & R. McLean ................................................. 289

Metals in the variable DA G 29-38 D. Koester, J.L. Provencal & H.L. Shipman ...................... ...................... 293

IV. White Dwarfs in Binaries ........... .................................... 297

In search of the double degenerate progenitors of Type Ia Supernovae R.A. Saffer & M. Livia .... ........................ , ................................... 299

The double degenerate population M. Hernanz, J. Isern & M. Salaris ........................................ ............. 307

White dwarf+M dwarf systems: a new infrared search A. G. Gemma .......................................................................... 315

viii

The EC 14026 stars: a new class of pulsating star D.E. Q'Donoghue, C. Koen, D. Kilkenny, R.S. Stobie, A.E. Lynas-Gray f3 S.D. Kawaler .......... ................................................................ 321

Hot white dwarfs in non-interacting binaries from the ROSAT EUV survey M Burleigh f3 M.A. Barstow . .................................. '" .................... 329

HST observations of AM Canum Venaticorum l.E. Solheim, l.L. Provencal f3 E.M Sion .............................................. 337

Effects of irradiation on the secondary star in a tight binary system, exemplified by AM Canum Venaticorum T.K. Nymark .. ........................................................................ 345

White dwarfs in AM Herculis systems B. T. Giinsicke, K. Beuermann, D.de Martino f3 S. lordan .... ........ " ............... 353

HST synthetic spectral analysis of U Gem in early and late quiescence: a heated white dwarf and accretion belt PH Cheng, E.M Sion, K. Horne, 1. Hubeny, M Huang f3 S.D. Vrtilek ................ 359

WFPC2 observations of Procyon B l.L. Provencal, HL. Shipman, P Wesemael, P. Bergeron, HE. Bond, l. Liebert f3 E.M Sion . .................................. '" .......................... 367

Extreme ultraviolet light curve and phase-resolved spectroscopy of the hot white dwarf in V 471 Tauri J. Dupuis, S. Vennes, P. Chayer, S. Cully f3 T. Rodriguez-Bell .. ..................... , 375

Unique white dwarfs accompanying recycled pulsars MH Van Kerkwijk .................................................................... 383

Merging of different mass ratio white dwarfs: first moments of the 0.4-1.2 M0 case 1. Guerrero, J. Is ern, W. Benz, E. Garcia-Berro f3 R. Mochkovitch .................... 391

V. Magnetic White Dwarfs ................................................... 395

New results of magnetic white dwarf spectroscopy S. Jordan .............................................................................. 397

I-D and 2-D calculations of dynamo-generated magnetic fields in white dwarfs l.A. Markiel, J.H. Thomas f3 H.M. Van, Horn .......................................... 405

Magnetic field survey of DC white dwarfs A. Putney . ............................................................................ 413

New IDE-spectra of the magnetic white dwarf Grw +70°8247 and their interpretation D. Engelhardt f3 1. Bues ........ ....................................................... 421

VI. Pulsating White Dwarfs ................................................. 427

Convection and the ZZ Ceti instability strip D. Koester f3 G. Vauclair .............................................................. 429

ix

WET observations of the DAY variable HL Tau 76: first results N. Dolez fj s.J. Kleinman ............................................................. 437

Preliminary asteroseismology of G 29-38 P. Bradley fj S. J. Kleinman ... ............................................ , ........... 445

Recent advances in the theoretical determination of the ZZ Ceti instability strip P. Brassard fj G. Fontaine ... .......................................................... 451

Cool DAY asteroseismology S.J. Kleinman ... ...................................................................... 459

Overstability of g-modes in ZZ Ceti variables y. Wu ................................................................................. 467

A continuing spectroscopic study of the instability strip of the pulsating DB (Y 777 Her) white dwarfs: the view in the optical F. Wesemael, A. Beauchamp, P. Bergeron, G. Fontaine, R.A. Saffer fj J. Liebert .. ..... 473

The potential of asteroseismology for hot, B sub dwarfs: a new class of pulsating stars? S. Charpinet, G. Fontaine, P. Brassard fj B. Dorman .. ................................ 477

Modeling time-resolved spectra of ZZ Ceti stars H. Viith, D. Koester, S.O. Kepler fj E.L. Robinson ..................................... 481

Discovery of two new ZZ Ceti variables N. Dolez, G. Vauclair, J.N. Fu fj M. Chevreton ..................... , .................. 485

Non-pulsating DA white dwarfs in the DAY region R. Silvotti, C. Bartolini, G. Cosentino, A. Guarnieri fj A. Piccioni .................. ,.489

PREFACE

The study of white dwarfs has been steadily growing during the last years and now is a mature field extending its influence over many others. Since white dwarfs are long lived objects, they can be used to obtain information about the history of the Galaxy. The simplicity of their structures enables them to act as precise particle physics laboratories and the extreme con­ditions reached at their surfaces allow us to test the equation of state and to study the behavior of matter under conditions impossible to be reached in terrestrial laboratories. Nevertheless, white dwarfs are still challenging astrophysicists. Many questions, ranging from the determination of funda­mental parameters to the evolution of their outer layers, are still waiting for a satisfactory answer.

The European Workshop series on White Dwarfs started in 1974 as a con­sequence of the effort and enthusiasm of Professor Volker Weidemann. The existing proceedings of these meetings, together with those corresponding to the lAU Colloquia held in Rochester (1979) and in Hanover (1988), provide a unique opportunity to follow the development of this field. We hope that the present volume will provide a representative snapshot of the state of the art in 1996. In this sense we are very indebted to all the participants that have sent their contributions according to the instructions (this clearly excludes everybody beyond three sigmas from the standards).

We are very indebted to all of our colleagues of the Scientific Organizing Committee: M. Barstow, F. D'Antona, G. Fontaine, 1. Iben, D. Koester, J. Liebert, R. Mochkovitch, G. Shaviv, P. Thejll, H. Van Horn, and G. Vau­clair. We want also to express our recognition to Carme Arenillas, Pilar Camps and Evilio del Rio for their enthusiastic support. We are specially grateful to our colleagues at the Centre d'Estudis Avanyats de Blanes for their support anf for showing us that not all in science is Astrophysics. We also thank the Consell Comarcal de la Selva for logistic support and the Blanes City Hall for their hospitality. Finally we acknowledge the financial support received from the Direcci6n General de Investigaci6n Cientifica y Tecnica (D.G.I.C.Y.T.), the Comissi6 Interdepertamental de Recerca i In-

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xiv

novaci6 Tecnologia (C.I.R.I.T.), the Consejo Superior de Investigaciones Cientificas (C.S.I.C.), the Universitat Politecnica de Catalunya (U.P.C.) and the Fundaci6 Catalana per a la Recerca (F.C.R.).

Barcelona, January 1997

Jordi Isern and Margarida Hernanz Institut d'Estudis Espacials de Catalunya

(C.S.I.C. Research Unit)

Enrique Garcia-Berro Universitat Politecnica de Catalunya

List of Participants

xvi

D. ALVAREZ, (64)

F. ALLARD, (28)

J.M. APARICIO, (67)

M.A. BARSTOW, ( 2)

T. BLOCKER, (52)

P.A. BRADLEY, (46)

A. BRAGAGLlA, (59)

P. BRASSARD, (61)

I. BUES, (58)

Dept. d'Astronomia i Meteorologia, Universitat de Barcelona, Marti i Franques, 1, 08028 Barcelona, SPAIN e-mail: dalvarez@mizar.am.ub.es

Dept. of Physics, Wichita State UniversitY,1845 Fairmount, Wichita KS 67260-0032, USA e-mail: allard@eureka.physics.twsu.edu

Departement de Physique, Universite de Montreal, C.P. 6128, Succ. Centre-Ville, Montreal, Quebec, CANADA H3C 3J7 e-mail: aparicio@astro.umontreal.ca

Dept. of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK e-mail: mab@star.le.ac. uk

Astrophysikalisches Institut Potsdam, Telegrafenberg A27, 0-14473 Potsdam, GERMANY e-mail: tbloecker@aip.de

Los Alamos National Laboratory, XTA MS B220, Los Alamos NM 87545, USA e-mail: pbradley@lanl.gov

Osservatorio Astronomico di Bologna, Via Zamboni 33,1-40126 Bologna, ITALY e-mail: angela@astb03.bo.astro.it

Dept. de Physique, Universite de Montreal, C.P. 6128, Succ. Centre-Ville, Montreal, Quebec, CANADA H3C 3J7 e-mail: brassard@astro.umontreal.ca

Astronomisches Institut der Universitaet Erlangen, Remeis-Sternwarte Bamberg, Sternwartstrasse 7, 0-96049 Bamberg, GERMANY e-mail: bues@sternwarte.uni-erlangen.d400.de

M. BURLEIGH, (49)

R. CANAL, (31)

AM. COOL, (16)

L. CUCURULL, ( 7)

G. CHABRIER, (32)

P. CHAYER, (25)

P.O. DOBBIE, (57)

N. DOLEZ, (10)

I. DOMiNGUEZ, (

xvii

Physics and Astronomy Department, University of Leicester, Leicester LE1 7RH, UK e-mail: mbu@star.le.ac.uk

Dept. d'Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal, 647, 08028 Barcelona, SPAIN e-mail: ramon@mizar.am.ub.es

Astronomy Department, University of California, 601 Campbell Hall, Berkeley, CA 94720-3411, USA e-mail: cool@spark.berkeley.edu

IEEC, Edifici Nexus -104, Gran Capita 2-4,08034 Barcelona, SPAIN e-mail: cucurull@ieec.fcr.es

Laboratoire de Physique, Ecole Normale Superieure de Lyon, 46 Allee d'italie, 69364 Lyon Cedex 07, FRANCE e-mail: chabrier@cral.ens-Iyon.fr

Center for EUV Astronphysics, 2150 Kitteredge Street, Berkeley, California 94720, USA e-mail: chayer@cea.berkeley.edu

X-Ray Astronomy Group, Dept. of Physics and Astronomy, University of Leicester, University Road, Leicester, LE17RH, UK e-mail: pdd@star.le.ac.uk

Observatoire Midi-Pyrenees, 14 Avenue Edouard Belin, 31400 Toulouse, FRANCE e-mail: dolez@obs-mip.fr

Fisica te6rica y del cosmos, Universidad de Granada, c/ Fuentenueva 18002, Granada, SPAIN e-mail: inma@ugr.es

xviii

S. DREIZLER, (24)

J. DUPUIS, (14)

D.S. FINLEY, (38)

TA FLEMING, (36)

G. FONTAINE, (8)

B.T. GANSICKE, (15)

Institut fOr Astronomie und Astrophysik, Universitat Kiel, 0-24098 Kiel, GERMANY e-mail: dreizler@astrophysic.uni-kiel.de

Center for EUV Astrophysics, 2150 Kittredge Street, Berkeley CA 94720, USA e-mail: jdupuis@cea.berkeley.edu

Eureka Scientific, Inc, 2452 Delmer St., Oakland CA 94602, USA e-mail: david@cea.berkeley.edu

University of Arizona, Steward Observatory, Tucson, AZ 85721, USA e-mail: taf@as.arizona.edu

Departement de Physique, Universite de Montreal, C.P. 6128, Succ. Centre-Ville, Montreal, Quebec, CANADA H3C 3J7 e-mail: fontaine@astro.umontreal.ca

Universitats-Sternwarte G6ttingen, Geismarlandstrasse 11, 0-37083 G6ttingen, GERMANY e-mail: boris@uni-sw.gwdg.de

E. GARCiA-BERRO, (6) Dept. de Ffsica Aplicada, Universitat Politecnica de Catalunya, Jordi Girona sIn, M6dul B-4, 08034 Barcelona, SPAIN e-mail: garcia@rigel.upc.es

D. GARCIA-SENZ, (60) Universitat Politecnica de Catalunya, Dept. Ffsica i Enginyeria Nuclear, UPC - Campus Nord, Sor Eulalia de Anzizu sIn - MOd. 84, 08034 Barcelona, SPAIN

A. GEMMO, (12)

e-mail: domingo@polux.upc.es

Dipartimento di Astronomia, Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio,5, 1-35122 Padova ITALY e-mail: gemmo@astrpd.pd.astro.it

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J. G6MEZ, ( ) IEEC, Edifici Nexus - 104, Gran Capita 2-4, 08034 Barcelona, SPAIN e-mail: gomez@ieec.fcr.es

J. GREEN, (66) CAS A, University of Colorado, 1255 38th Street -Campus Box 593, Boulder, Colorado 80309, USA e-mail: jgreen@casa.colorado.edu

J. GUERRERO, (54) IEEC, Edifici Nexus -104, Gran Capita 2-4, 08034 Barcelona, SPAIN e-mail: guerrero@ieec.fcr.es

K. GUNDERSON, (68) Astrophysics Research Laboratory, University of Colorado, 1255 38th Street, Boulder, CO 80303, USA

J. GUTIERREZ, (63)

M. HERNANZ, (18)

F. HERWIG, (43)

J.B. HOLBERG, (39)

I. IBEN, (21)

J. ISERN, ( 1)

e-mail: gunderso@casa.colorado.edu

Dept. d'Astronomia i Meteorologia, Universitat de Barcelona, Marti i Franques, 1, 08028 Barcelona, SPAIN e-mail: jgutier@mizar.am.ub.es

IEEC, Edifici Nexus - 104, Gran Capita 2-4, 08034 Barcelona, SPAIN e-mail: hernanz@ieec.fcr.es

Astrophysikalisches Institut Potsdam, Telegraphenberg A 27, D-14473 Potsdam, GERMANY e-mail: fherwig@aip.de

Lunar and Planetary Laboratory-west, University of Arizona, Gould-Simpson Building, Tucson AZ 85721, USA e-mail: holberg@argus.lpl.arizona.edu

Astronomy Department, University of Illinois, 1002 West Green St., URBANA, IL 61801, USA e-mail: icko@astro.uiuc.edu

IEEC, Edifici Nexus -104, Gran Capita 2-4,08034 Barcelona, SPAIN

xx

S. JORDAN, (44)

S. KAWALER, (34)

I. R. KING, ( 9)

S.J. KLEINMAN, (33)

R. KNOX, (47)

D. KOESTER, (29)

J. KUBAT, (40)

e-mail: isern@ieec.fcr.es

Institut fOr Astronomie und Astrophysik, Universitat Kiel, 0- 24098 Kiel, GERMANY e-mail: jordan@astrophysik.uni-kiel.de

Dept. of Physics and Astronomy, Iowa State University, Ames IA 50011, USA e-mail: sdk@iastate.edu

Astronomy Department, University of California, Berkeley, CA 94720-3411, USA e-mail: king@glob.berkeley.edu

Astronomy Dept., University of Texas, Austin, TX 78712, USA e-mail: sjk@bullwinkle.as.utexas.edu

Institute of Astronomy, University of Edinburgh Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK e-mail: rak@roe.ac.uk

Institut fOr Astronomie und Astrophysik, Universitat Kiel, 0-24098 Kiel, GERMANY e-mail: koester@astrophysik.uni-kiel.d400.de

Astronomicky ustav, Akademie ved Ceske Republiky, Fricova 1, 251 65 Ondrejov, CZECH REPUBLIC e-mail: kubat@sunstel.asu.cas.cz

R. LAMONTAGNE, (30) Departement de Physique, Universite de Montreal, C.P. 6128, Succ. Centre-ville, Montreal, Quebec, CANADA H3C 3J7

J. LIEBERT, ( 3)

e-mail: lamont@astro.umontreal.ca

University of Arizona, Steward Observatory, Tucson, AZ 85721, USA e-mail: liebert@as.arizona.edu

JA MARKIEL, (42) Dept. of Physics and Astronomy, University of Rochester, Rochester, NY 14627, USA e-mail: markiel@callisto.pas.rochester.edu

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C. MASSACAND, (23) IMR - Nordlysobservatoriet, University of Tromso, N-9037 Tromso, NORWAY e-mail: xtophe@lie.uit.no

R. McLEAN, (70) CASA, University of Colorado, Boulder, ARLl1255 38th St., Boulder, CO, USA e-mail: mclean@casa.colorado.edu

R. MOCHKOVITCH, (41) C N R S, Institut d'Astrophysique de Paris, 98 bis, Blvd. Arago, 75014 Paris, FRANCE e-mail: mochko@iap.fr

T.K. NYMARK, (17) The Auroral Observatory, University of Tromso, 9037 Tromso, NORWAY e-mail: tanja@lie.uit.no

D. O'DONOGHUE, (19) Dept. of Astronomy, University of Cape Town, Rondebosch 7700, Cape Town, SOUTH AFRICA e-mail: dod@uctvms.uct.ac.za

J. PROVENCAL, (26) Dept. of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA e-mail: jlp@chopin.udel.edu

A. PUTNEY, (11) California Institute ofTechnology, 105-24, Pasadena, CA 91125, USA e-mail: axp@astro.caltech.edu

T. RAUCH, (45) Institut fOr Astronomie und Astrophysik, Universitat Kiel, D-24098 Kiel, GERMANY e-mail: rauch@astrophysik.uni-kiel.de

M.T. RUIZ, (27) Department of Astronomy, Universidad de Chile, Casilla 36-D, Santiago, CHILE e-mail: mtruiz@das.uchile.cI

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P. RUIZ-LAPUENTE. (35) Dept. Astronomia i Meteorologia. Universitat de Barcelona. Diagonal 647. 08028 Barcelona. SPAIN e-mail: pilar@mizar.am.ub.es

R.A. SAFFER. (51)

M. SALARIS. (65)

H. SCHMIDT. (50)

G. SHAVIV. (22)

Space Telescope Science Institute. 3700 San Martin Drive. Baltimore MD 21218. USA e-mail: saffer@stsci.edu

IEEC. Edifici Nexus - 104. Gran Capita 2-4. 08034 Barcelona. SPAIN e-mail: maurizio@mpa-garching.mpg.de

Institut fOr Astronomie und Astrophysik. Universitat Kiel. D- 24098 Kiel. GERMANY e-mail: schmidt@astrophysik.uni-kiel.d400.de

Asher Space Research Institute and Dept. of Physics. Israel Institute of Technology. Haifa. ISRAEL 32000 e-mail: gioras@physics.technion.ac.il

H. SHIPMAN. (4) Physics and Astronomy Department University of Delaware Sharp Laboratory Newark - Delaware 19716 USA e-mail: harrys@udel.edu

E.M. SION. ( ) Dept. of Astronomy and Astrophysics Villanova University Villanova. PA 19085 USA e-mail: emsion@ucis.vill.edu

J.E. SOLHEIM. (56) Institute of Mathematical and Physical Sciences University of Tromso Auroral Observatory N-9037 Tromso NORWAY a-mail: janerik@mack.uit.no

S. STARRFIELD. (13) Physics & Astronomy Arizona State University P.O Box 871504 Tempe. AZ 85287-1504 USA e-mail: sumner.starrfield@asu.edu

S. TORRES.( ) Universitat Politecnica de Catalunya EUP Matar6 Av. Puig i Cadafalch. 101-111 08303 MATAR6 e-mail: santi@benard.fa.upc.es

A. ULLA, ( )

K. UNGLAUB, (62)

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Instituto de Astroflsica de Canarias cl Via Lactea sIn 38200 La Laguna SPAIN e-mail: aulla@ILiac.es

Astronomisches Institut der Universitaet Erlangen Remeis-Sternwarte Bamberg Sternwartstrasse 7 0-96049 Bamberg GERMANY e-mail: unglaub@sternwarte.uni-erlangen.d400.de

M. VAN KERKWIJK, (69) Dept. of Astronomy, m.s. 105-24 California Institute ofTechnology Pasadena, CA 91125 USA e-mail: mhvk@astro.caltech.edu

H. VATH, (48)

V. WEIDEMANN, (20)

F. WESEMAEL, (53)

B. WOLFF, ( 5)

M. WOOD, (55)

Y. WU, (37)

Institut fOr Astronomie und Astrophysik Universitat Kiel 0-24098 Kiel GERMANY e-mail: supas097@astrophysik.uni-kiel.de

Institut fOr Astronomie und Astrophysik Universitat Kiel 0-24098 Kiel GERMANY e-mail: supas058@astrophysik.uni-kiel.de

Oepartement de Physique Universite de Montreal C.P. 6128, Succ. Centre-Ville Montreal - QUEBEC CANADA H3C 3J7 e-mail: wesemael@astro.umontreal.ca

Institut fOr Astronomie und Astrophysik Universitat Kiel 0-24098 Kiel GERMANY e-mail: supas089@astrophysik.uni-kiel.d400.de

Dept. Physics and Space Sciences Florida Institute of Technology 150. W. University Blvd. Melbourne, FL 32901-6988 USA e-mail: wood@kepler.pss.fit.edu

Theoretical Astrophysics, 130-33 California Institute of Technology Pasadena, CA 91125 USA e-mail: wyq@tapir.caltech.edu