Table Of Content

THE ASTROPHYSICAL JOURNAL Founded in 1895 by George E. Hale and James E. Keeler HELMUT A. ABT Editor-in-Chief Kitt Peak National Observatory A. DALGARNO EUGENE H. AVRETT Letters Editor Deputy Letters Editor Center for Astrophysics Center for Astrophysics JULES P. HALPERN ANNEILA I. SARGENT JOSEPH I. SILK Associate Letters Editor Associate Letters Editor Associate Letters Editor Columbia University California Institute of Technology University of California, Berkeley AAS PUBLICATIONS BOARD ROBERT J. HANISCH (1996-1999), Chairperson Space Telescope Science Institute MOSHE ELITZUR (1995-1998) KAREN S. BJORKMAN (1996-1999) DIMITRI M. MIHALAS (1996-1999) University of Kentucky University of Toledo University of Illinois SUSAN TEREBEY (1997-2000) BRUCE ELMEGREEN (1998-2001) ALYSSA A. GOODMAN (1998-2001) California Institute of Technology IBM TJ Watson Research Center Harvard University Publication Manager: JULIE STEFFEN Production Manager: Kim LANGFORD Chief Manuscript Editor. GERALDINE BRADY Manuscript Editors: WALTER G. GLascorF III, BETH GARRISON, THAD A. Doria, PAUL RUICH, SHARON JENNINGS, STEPHANIE O. NEVINS, BAHARE RASHIDI, ELIZABETH Huyck, PETER M. RIvARD, Mary ALICE HINSHAW, ELISSA PARK, SHARON C. BRINKMAN, AND DANIEL J. SMITH Production Staff: CINDY GARRETT, SUCHITRA GURURAJ, ABIGAIL C. FAcToR, JAMES LAFOREST, AND AIMEE BALDRIDGE Cambridge Editorial Office: CAROLANN BARRETT, ANGELA BRowN, LAURIE ELLIS, MARY GUILLEMETTE, DAviID LOBRON, AND KRISTA WOODBRIDGE VOLUME 497, PART 2 1998 APRIL 10 AND APRIL 20 PUBLISHED BY THE UNIVERSITY OF CHICAGO PRESS FOR THE AMERICAN ASTRONOMICAL SOCIETY © 1998 BY THE AMERICAN ASTRONOMICAL SOCIETY. ALL RIGHTS RESERVED. PUBLISHED THREE TIMES A MONTH COMPOSED BY THE UNIVERSITY OF CHICAGO PRESS, CHICAGO, ILLINOIS, U.S.A. PRINTED BY CAPITAL CITY PRESS, INC., MONTPELIER, VERMONT, U.S.A. THE ASTROPHYSICAL JOURNAL LETTERS CONTENTS OF VOLUME 497, PART 2 1998 APRIL 10, Number 1 ABUNDANCES IN SPIRAL GALAXIES: EVIDENCE FOR PRIMARY NITROGEN PRODUCTION Liese van Zee, John J. Salzer, & Martha P. Haynes WHAT IS THE TRUE COVERING FACTOR OF ABSORBING MATTER IN BALQSOs? J. H. Krolik & G. M. Voit WHERE IS THE CORONAL LINE REGION IN ACTIVE GALACTIC NUCLEI? Takashi Murayama & Yoshiaki Taniguchi OPTICAL FOLLOW-UP OF GRB 970508 T. J. Galama, P. J. Groot, J. van Paradijs, C. Kouveliotou, R. G. Strom, R. A. M. J. Wijers, N. Tanvir, J. Bloom, M. Centurion, J. Telting, R. G. M. Rutten, P. Smith, C. Mackey, S. Smartt, C. Benn, J. Heise, & J. in’t Zand SPECTRA AND LIGHT CURVES OF GAMMA-RAY BURST AFTERGLOWS Re’em Sari, Tsvi Piran, & Ramesh Narayan EUCLIDEAN VERSUS NON-EUCLIDEAN GAMMA-RAY BURSTS M. Tavani DISCOVERY OF TeV GAMMA RAYS FROM SN 1006: FURTHER EVIDENCE FOR THE SUPERNOVA REMNANT ORIGIN OF COSMIC RAYS T. Tanimori, Y. Hayami, S. Kamei, S$. A. Dazeley, P. G. Edwards, S. Gunji, S. Hara, T. Hara, J. Holder, A. Kawachi, T. Kifune, R. Kita, T. Konishi, A. Masaike, Y. Matsubara, T. Matsuoka, Y. Mizumoto, M. Mori, M. Moriya, H. Muraishi, Y. Muraki, T. Naito, K. Nishijima, S. Oda, S. Ogio, J. R. Patterson, M. D. Roberts, G. P. Rowell, K. Sakurazawa, T. Sako, Y. Sato, R. Susukita, A. Suzuki, R. Suzuki, T. Tamura, G. J. Thornton, S. Yanagita, T. Yoshida, & T. Yoshikoshi X-RAY EMISSION FROM THE RADIO PULSAR PSR J1105—6107 E. V. Gotthelf & V. M. Kaspi SIDEBANDS DUE TO QUASI-PERIODIC OSCILLATIONS IN 4U 1626-67 Jefferson M. Kommers, Deepto Chakrabarty, & Walter H. G. Lewin INFRARED SPECTROSCOPY OF GX 1+4/V2116 OPHIUCHI: EVIDENCE FOR A FAST RED GIANT WIND? Deepto Chakrabarty, Marten H. van Kerkwijk, & James E. Larkin ON THE THEORETICAL PERIOD-RADIUS RELATION OF CLASSICAL CEPHEIDS Giuseppe Bono, Filippina Caputo, & Marcella Marconi A BROWN DWARF CANDIDATE IN THE PRAESEPE OPEN CLUSTER A. Magazziu, R. Rebolo, M. R. Zapatero Osorio, E. L. Martin, & S. T. Hodgkin SOLAR TACHOCLINE REVISITED V. M. Canuto ERRATUM EVIDENCE FOR MAGNETIC FIELD Decay IN RX J0720.4—3125 John C. L. Wang INSTRUCTIONS TO AUTHORS OF LETTERS, AND RECENT LETTERS ABSTRACTS AND OTHER Inside Back Cover BIBLIOGRAPHICAL SERVICES INSTRUCTIONS FOR ELECTRONIC MANUSCRIPT SUBMISSION Back Cover CONTENTS 1998 APRIL 20, Number 2 TYPE Ia SUPERNOVA COUNTS AT HIGH z: SIGNATURES OF COSMOLOGICAL MODELS AND PROGENITORS P. Ruiz-Lapuente & R. Canal WEAK LENSING BY TWO z ~ 0.8 CLUSTERS OF GALAXIES D. Clowe, G. A. Luppino, N. Kaiser, J. P. Henry, & 1. M. Gioia DISK MODELS FOR MCG —06-30-15: THE VARIABILITY CHALLENGE J. W. Sulentic, P. Marziani, & M. Calvani VLBA CONTINUUM OBSERVATIONS OF NGC 4258: CONSTRAINTS ON AN ADVECTION-DOMINATED ACCRETION FLOW J. R. Herrnstein, L. J. Greenhill, J. M. Moran, P. J. Diamond, M. Inoue, N. Nakai, & M. Miyoshi THE TROUBLE WITH HUBBLE TYPES IN THE VIRGO CLUSTER Rebecca A. Koopmann & Jeffrey D. P. Kenney MASS FUNCTION GRADIENTS AND THE NEED FOR DARK MATTER Jason A. Taylor COSMIC-RAY *°Al AND ITS DECAY IN THE GALAXY J. A. Simpson & J. J. Connell THE VARIABLE GAMMA-RAY SOURCE 2CG 135+01 M. Tavani, D. Kniffen, J. R. Mattox, J. M. Paredes, & R. S. Foster CORRELATION BETWEEN FAST QUASI-PERIODIC OSCILLATIONS AND X-RAY SPECTRAL SHAPE IN ATOLL SOURCES Philip Kaaret, Wenfei Yu, Eric C. Ford, & S. N. Zhang POPULATION SYNTHESIS OF MILLISECOND AND SUBMILLISECOND PULSARS Andrea Possenti, Monica Colpi, Nichi D’Amico, & Luciano Burderi RAPID ROTATION AND NONRADIAL PULSATIONS: k-MECHANISM EXCITATION OF g-MODES IN B STARS Greg Ushomirsky & Lars Bildsten THERMAL WATER VAPOR EMISSION FROM SHOCKED REGIONS IN ORION Martin Harwit, David A. Neufeld, Gary J. Melnick, & Michael J. Kaufman PHOTOSPHERIC MAGNETIC FIELD CHANGES ASSOCIATED WITH TRANSITION REGION EXPLOSIVE EVENTS L109 Jongchul Chae, Haimin Wang, Chik-Yin Lee, Philip R. Goode, & Udo Schiihle CALIBRATION OF THE SERTS-95 SPECTROGRAPH FROM IRON LINE INTENSITY RATIOS Jeffrey W. Brosius, Joseph M. Davila, & Roger J. Thomas HCO* IMAGING OF COMET HALE-BOPP (C/1995 O1) Amy J. Lovell, F. Peter Schloerb, James E. Dickens, Christopher H. DeVries, Matthew C. Senay, & William M. Irvine INSTRUCTIONS TO AUTHORS OF LETTERS, AND RECENT LETTERS ABSTRACTS AND OTHER Inside Back Cover BIBLIOGRAPHICAL SERVICES INSTRUCTIONS FOR ELECTRONIC MANUSCRIPT SUBMISSION Back Cover S h set Bees pie