Interacting Binaries No

Interacting Binaries No. 6, March, 2001 An Electronic Newsletter Editors: Boris T. Gansic¨ ke, Jens Kube Universitats-Ster¨ nwarte, Geismar Landstraße 11, D-37083 Gottingen¨ [email protected] http://www.uni-sw.gwdg.de/ibnews

Contents

1 Editorial 2 – IBNews #06 Gansic¨ ke & Kube ...... 2

2 Abstracts of refereed papers 3 – Z Cam stars: A particular response to a general phenomenon Buat-Menar´ d et al...... 3 – Repetitive Rebrightening of EG Cancri: Evidence for Viscosity Decay in Quiescent Disk? Osaki et al. 3 – The standstill luminosity in Z Cam systems Stehle et al...... 4 – On the nature of superoutbursts in dwarf novae Truss et al...... 4 – On Echo Outbursts and ER UMa Supercycles in SU UMa-type Cataclysmic Variables Hellier . . . . . 4 – NLTE accretion disc models for the AM Canum Venaticorum systems Nasser et al...... 5 – A ROSAT WFC observation of SW UMa: the EUV behaviour of dwarf novae in superoutburst explained Burleigh et al...... 5 – Phase-resolved HST/STIS spectroscopy of the exposed white dwarf in the high-ﬁeld polar AR UMa Gansic¨ ke et al...... 6 – Optical Photometry of the Double-lined Cataclysmic Variable Phoenix 1 Hoard et al...... 6 – Hubble Space Telescope spectroscopy of the dwarf nova RX Andromeda I: The underlying white dwarf Sion et al...... 7 – X-ray and Optical Spectra of the Unusual Cataclysmic Variables LS Peg and T Leo Szkody et al. . . . 7 – Spectroscopic Discovery of Brown Dwarf-like Secondary Stars in the Cataclysmic Variables LL Andromedae and EF Eridani Howell & Ciardi ...... 8 – The early X-ray emission from V382 Velorum (=Nova Vel 1999): An internal shock model Mukai & Ishida ...... 8 – Superhumps in Cataclysmic Binaries. XIX. DV Ursae Majoris Patterson et al...... 9 – Superhumps in Cataclysmic Binaries. XX. V751 Cygni Patterson et al...... 9 – Superhumps in Cataclysmic Binaries. XVIII. IY Ursae Majoris Patterson et al...... 10 – Accretion-Disk Precession and Substellar Secondaries in Cataclysmic Variables Patterson ...... 11 – Optical studies of the X-ray transient XTE J2123-058 - II. Phase-resolved spectroscopy Hynes et al. . 11 – IR spectra of the microquasar GRS 1915+105 during a low state Harlaftis et al...... 12 – A ‘superoutburst’ in XTE J1118+480 Kuulkers ...... 12 – Black hole X-ray transients: mass accumulation in the disk - constraints for the viscosity Meyer- Hofmeister & Meyer ...... 13 – Applications of Indirect Imaging techniques in X-ray binaries Harlaftis ...... 13

– The “Twin Jet” Planetary Nebula M2 9 Livio & Soker ...... 13 – Properties and nature of Be stars XX. Binary nature and orbital elements of γ Cas Harmanec et al...... 14 1 EDITORIAL 2

– On the duration of the subsonic propeller state of neutron stars in wind-fed mass-exchange close binary systems Ikhsanov ...... 14 – Tidal evolution of eccentric orbits in massive binary systems II. Coupled resonance locking for two rotating main sequence stars Witte & Savonije ...... 15 – Population synthesis for double white dwarfs I. Close detached systems Nelemans et al...... 15 – Population synthesis for double white dwarfs II. Semi-detached systems: AM CVn stars Nelemans et al. 16

3 Other abstracts 17 – Outburst activity in magnetic cataclysmic variables BY Cam and QQ Vul Halevin et al...... 17 – A self-regulating braking mechanism in black hole X-ray binaries Meyer & Meyer-Hofmeister . . . . 17

4 Miscellaneous announcements 18 – OpenGL code to draw pictures and animations of cataclysmic variables Beardmore ...... 18 – Free copies of 2 Proceedings Volumes Greiner ...... 18 – Cataclysmic Variable Stars: How and why they vary Hellier ...... 18 – Book review: Cataclysmic Variable Stars: How and why they vary Gansic¨ ke ...... 19

5 Conference announcements 19 – The International Conference on Variable Star Research M. Zejda & Z. Mikulasek ...... 19 – Stellar atmospheric modeling Werner ...... 20 – The physics of cataclysmic variables and related objects, August 5–10, 2001, Georg-August- Universitat¨ Gottingen,¨ Germany ...... 21

6 Jobs and positions 21 – Research Associate, Univ. of Leicester – Available from 1 October 2001 for 2 years ...... 21

1 Editorial IBNews #06 B. T. Gansic¨ ke & J. Kube Universitats-Sternw¨ arte Gottingen,¨ Geismar Landstraße 11, D-37083 Gottingen,¨ Germany

Dear IB friends, we celebrate with this issue the ﬁrst anniversary of the Interacting Binary Newsletter, so it’s time for us to thank all of you for the steady inﬂow of contributions. The next issue of IBnews is planned for May 31 and we will remind you a week ahead with a call for abstracts. Happy reading, Boris Gansick¨ e & Jens Kube

Download/Website: http://www.uni-sw.gwdg.de/ibnews Contact: [email protected] 2 ABSTRACTS OF REFEREED PAPERS 3

2 Abstracts of refereed papers Z Cam stars: A particular response to a general phenomenon V. Buat-Menar´ d 1, J.-M. Hameury 1 and J.-P. Lasota 1 1 UMR 7550 du CNRS, Observatoire de Strasbourg, 11 rue de l’Universite,´ F-67000 Strasbourg, France 2 Institut d’Astrophysique de Paris, 98bis Boulevard Arago, 75014 Paris, France Astronomy & Astrophysics, in press (astro-ph/0101329)

We show that the disc instability model can reproduce all the observed properties of Z Cam stars if the energy equation includes heating of the outer disc by the mass-transfer stream impact and by tidal torques, and if the mass-transfer rate from the secondary varies by about 30% around the value critical for stability. In particular the magnitude difference between outburst maxima and standstills corresponds to observations, all outbursts are of the inside-out type and can be divided into two classes: long (wide) and short (narrow) outbursts, as observed. Mass transfer rate ﬂuctuations should occur in other dwarf novae but one can exclude variations similar to those observed in magnetic systems (AM Her’s and some DQ Her’s) and some nova-like systems (VY Scl’s), in which M˙ become very small during low states; these would produce mini-outbursts which, although detectable, have never been observed. Download/Website: http://xxx.lpthe.jussieu.fr/ps/astro-ph/0101329 Contact: [email protected]

Repetitive Rebrightening of EG Cancri: Evidence for Viscosity Decay in Quiescent Disk? Yoji Osaki1, Friedrich Meyer2, Emmi Meyer-Hofmeister2 1 Faculty of Education, Nagasaki University, Nagasaki 852-8521, Japan 2 Max-Planck-Institut fur¨ Astrophysik, Karl-Schwarzschild Str. 1, D-85740 Garching, Germany Astronomy & Astrophysics, in press(astro-ph/0102335)

A WZ Sge-type dwarf nova, EG Cancri, exhibited six consecutive mini-outbursts with a mean interval of about seven days after the end of the main outburst in 1996/1997. The most unusual was that the star entered abruptly into a deep faint minimum after such frantic activities. We propose that this peculiar phenomenon may be understood in terms of viscosity decay in the cold disk in which the disk viscosity is produced by MHD turbulence due to the magneto-rotational instability (the Balbus-Hawley instability). In this picture, the viscosity dies down exponentially with time when the disk becomes cold because the magnetic fields decay due to finite conductivity in the cold disk, a mechanism suggested by Gammie and Menou (1998), but it is refreshed to a high value every time when a mini- outburst occurs (i.e., the disk becomes hot again). It is argued that a sudden cessation of repetitive mini-outbursts may be brought about by a very small reduction in viscosity or a small increase in its decay rate, which may in turn be produced most likely by stochastic fluctuations of magnetic fields. Numerical simulations based on a simple model are presented which can reproduce observed light curve of EG Cancri very well. Some discussions are made for possible causes why the reflare after the main outburst occurs mostly in the WZ Sge-type stars. Contact: [email protected] 2 ABSTRACTS OF REFEREED PAPERS 4

The standstill luminosity in Z Cam systems R. Stehle, A.R. King, C. Rudge Theoretical Astrophysics Group, Department of Physics & Astronomy, University of Leicester, Leicester LE1 7RH, U.K. Monthly Notices of the Royal Astronomical Society, in press (astro-ph/0012379)

We consider accretion discs in close binary systems. We show that heating of a disc at the impact point of the accretion stream contributes signiﬁcantly to the local energy budget at its outer edge. As a result the thermal balance relation between local accretion rate and surface density (the ‘S–curve’) changes; the critical mass transfer rate above which no dwarf nova outbursts occur can be up to 40% smaller than without impact heating. Standstills in Z Cam systems thus occur at smaller mass transfer rates than otherwise expected, and are rather fainter than the peak luminosity during the dwarf nova phase as a result. Contact: [email protected]

On the nature of superoutbursts in dwarf novae M.R. Truss, J.R. Murray, G.A. Wynn Astronomy Group, University of Leicester, University Road, Leicester, LE1 7RH Monthly Notices of the Royal Astronomical Society Letters, in press

We present the ﬁrst detailed hydrodynamic simulation of a superoutburst to incorporate the full tidal potential of a binary system. A two-dimensional smoothed particle hydrodynamics code is used to simulate a superoutburst in a binary with the parameters of the SU UMa system Z Chamaeleontis. The simulated light curves shows all the features observed in such systems. Analysis of the mass ﬂux through the disc and the growth rate of the superhumps and disc eccentricity show that the superoutburst-superhump phenomenon is a direct result of tidal instability. No enhanced mass transfer from the secondary is required to initiate or sustain these phenomena. Comparisons of superoutbursts with normal outbursts are made and we show that the model can be reconciled with the behavior of U Geminorum type dwarf novae, which show no superoutbursts.

Download/Website: http://www.star.le.ac.uk/ ¡ mtr Contact: [email protected]

On Echo Outbursts and ER UMa Supercycles in SU UMa-type Cataclysmic Variables Coel Hellier Department of Physics, Keele University, Staffordshire ST5 5BG, U.K. PASP, in press (astro-ph/0101102)

I present a variation on Osaki’s tidal-thermal-instability model for SU UMa behavior. I suggest that in systems with the lowest mass ratios, the angular-momentum dissipation in an eccentric disk is unable to sustain the disk on the hot side of the thermal instability. This decoupling of the tidal and thermal instabilities in systems with q ¢ 0.07 allows a better explanation of the ‘echo’ outbursts of EG Cnc and the short supercycles of RZ LMi and DI UMa. The idea might also apply to the soft X-ray transients.

Download/Website: http://www.astro.keele.ac.uk/ ¡ ch Contact: [email protected] 2 ABSTRACTS OF REFEREED PAPERS 5

NLTE accretion disc models for the AM Canum Venaticorum systems Mosab R. Nasser1, Jan-Erik Solheim1 & D. A. Semionoff2 1 University of Tromsø, Department of Physics, N-9037 Tromsø, Norway 2 University of Vilnus, Institute of Theoretical Physics and Astronomy, A. Gostautoˇ 12, Vilnus 2600, Lithuania Astronomy & Astrophysics, in press

We present models of the optical spectra of two types of accretion disc atmospheres: a pure helium model and a H-He model, in a low mass ratio, helium transferring, interacting binary white dwarfs system. The computations are restricted to stationary discs in LTE and NLTE cases. We also investigate the inﬂuence on the spectra of some of the disc parameters such as the mass accretion rate, the angle of inclination, the H/He mass ratio, and the inner and outer radius of the disc. Departures from LTE are also investigated in order to assess the necessity of computing more complicated and more time consuming models. We ﬁnd for some models a difference which ranges between 10 to more than 40 percent between equivalent width values for a line computed with LTE and NLTE. Finally we compare our disc models with 4 of the AM CVn systems observed with the Nordic Optical Telescope: AM CVn, HP Lib, V803 Cen and CR Boo to determine parameters as mass transfer rate and inclination of their discs. Contact: [email protected]

A ROSAT WFC observation of SW UMa: the EUV behaviour of dwarf novae in superoutburst explained Matt Burleigh, John Pye, Stuart Poulton, Keith Sohl, Pete Wheatley, Graham Wynn Dept. of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK Monthly Notices of the Royal Astronomical Society, in press

During re-processing and analysis of the entire ROSAT Wide Field Camera (WFC) pointed observations database, we discovered a serendipitous, off-axis detection of the cataclysmic variable SW UMa at the onset of its 1997

October superoutburst. Although long outbursts in this SU UMa-type system are known to occur every ¡ 450 days, none had ever been previously observed in the extreme ultra-violet (EUV) by ROSAT. The WFC observations

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¤ ¥ began just £ 13 hr after the optical rise was detected. With a peak count rate of 4 5 count s in the S1 ﬁlter,

SW UMa was temporarily the third brightest object in the sky in this waveband. Over the next £ 19 hr the measured ¢

1 ¡ EUV ﬂux dropped to 2 count s ¥ , while the optical brightness remained essentially static at mv 11. Similar behaviour has also been recently reported in the EUV light curve of the related SU UMa-type binary OY Car during superoutburst (Mauche and Raymond 2000). In contrast, U Gem-type dwarf novae show no such early EUV dip during normal outbursts. Therefore, this feature may be common in superoutbursts of SU UMa-like systems. We offer an explanation for this behaviour by examining the interplay between the thermal and tidal instabilities which affect the accretion disks in these systems. Download/Website: http://ledas-www.star.le.ac.uk/Preprint Contact: [email protected] 2 ABSTRACTS OF REFEREED PAPERS 6

Phase-resolved HST/STIS spectroscopy of the exposed white dwarf in the high-ﬁeld polar AR UMa Boris T. Gansic¨ ke1, Gary D. Schmidt2, Stefan Jordan3, Paula Szkody4 1 Universitats-Sternw¨ arte Gottingen,¨ Geismar Landstraße 11, D-37083 Gottingen,¨ Germany 2 Steward Observatory, University of Arizona, Tucson, AZ 85721 3 Institut fur¨ Astronomie und Astrophysik, Universitat¨ Kiel, 24098 Kiel, Germany 4 Astronomy Department, University of Washington, Seattle, WA 98195 The Astrophysical Journal, in press (astro-ph/0103131)

Phase-resolved HST/STIS ultraviolet spectroscopy of the high-field polar AR UMa confirms that the white dwarf ¦ photospheric Lyα Zeeman features are formed in a magnetic field of ¡ 200 MG. In addition to the Lyα π and σ

components, we detect the forbidden hydrogen 1s0 § 2s0 transition, which becomes “enabled” in the presence of both strong magnetic and electric ﬁelds. Overall, the combined ultraviolet and optical low state spectrum is similar to that of the single white dwarf PG 1031+234, in that the optical continuum has a steeper slope than the ultraviolet continuum and that the depth of the Lyα Zeeman lines reaches only 30 50 % of the continuum level. Our attempt in ﬁtting the low state data with single temperature magnetic white dwarf models remains rather unsatisfactory,

indicating either a shortcoming in the present models or a new physical process acting in AR UMa. As a result, © our estimate of the white dwarf temperature remains somewhat uncertain, Twd ¨ 20000 5000 K. We detect a broad emission bump centered at ¡ 1445 A˚ and present throughout the entire binary orbit, and a second bump near ¡ 1650 A,˚ which appears only near the inferior conjunction of the secondary star. These are suggestive of

¡ 13 1

¥ low harmonic cyclotron emission produced by low-level (M˙ 10 ¥ M yr ) accretion onto both magnetic poles.

However, there is no evidence in the power spectrum of light variations for accretion in gas blobs. The derived ﬁeld

¡ ¡ strengths are B 240 MG and B 160 MG for the northern and the southern pole, respectively, broadly consistent with the ﬁeld derived from the Zeeman lines. The observed Lyα emission line shows a strong phase dependence with

φ ¡ maximum ﬂux and redshift near orbital phase 0 ¤ 3, strongly indicating an origin on the trailing hemisphere of the

α α ¡ 1 secondary star. An additional Ly absorption feature with similar phasing as the Ly emission, but a 700 kms ¥ blueshift could tentatively be ascribed to absorption of white dwarf emission in a moderately fast wind. Finally, the high signal-to-noise STIS data provide important information on the intergalactic absorption toward AR UMa.

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We derive a column density of neutral hydrogen of NH ¨ 1 1 1 0 10 cm , the lowest of any known polar, making AR UMa an excellent candidate for further EUV observations. Download/Website: http://xxx.lanl.gov/abs/astro-ph/0103131 Contact: [email protected]

Optical Photometry of the Double-lined Cataclysmic Variable Phoenix 1

D. W. Hoard1, S. Wachter1, J. Kim-Quijano2 3 1 Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile 2 1999 CTIO Research Experiences for Undergraduates program participant 3 Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD, 21218, USA PASP, in press was We have obtained 7 nights of time-resolved VI photometry of the double-lined cataclysmic variable Phoenix 1. We detect two candidate orbital periods, 0.1344 d and 0.2683 d. The former, which would correspond to a single modulation caused by viewing the irradiated face of the secondary star, is the less favored choice based on the folded light curves. The latter, which would correspond to a double modulation with unequal minima depths caused by ellipsoidal variation of the secondary star, is inconsistent with the observed late spectral type (M2–5) of the secondary star. However, we discuss some recent results from the literature that may make it possible to reconcile 2 ABSTRACTS OF REFEREED PAPERS 7 the longer orbital period and later spectral type. Some ambiguity remains as to which of these two periods is the true orbital period. information/data Contact: [email protected]

Hubble Space Telescope spectroscopy of the dwarf nova RX Andromeda I: The underlying white dwarf Edward M. Sion1, Paula Szkody2, Boris Gansic¨ ke3, F.H. Cheng1, C. LaDous4, & B. Hassall5 1 Department of Astronomy & Astrophysics, Villanova University, Villanova, PA 19085 2 Department of Astronomy, University of Washington, Seattle, WA 98195 3 Universitats-Sternw¨ arte, Gottingen,37083¨ Germany 4 Webergasse 21, D-96450 Coburg, Germany 5 Dept. of Physics, Astronomy & Mathematics, Univ. of Central Lancashire, U.K., PR1 2HE The Astrophysical Journal, in press

We obtained Hubble GHRS phase-resolved spectroscopic observations of the dwarf nova RX Andromeda at three times in its outburst cycle: (1) near the end of an extraordinarily deep and long dwarf nova quiescence, 3 months after the last previous outburst; (2) during the rise to outburst and; (3) near the end of a decline from outburst. The spectral wavelength range covered was 1149A˚ to 1435A.˚ All of the spectra are dominated by absorption lines with

weak to moderately strong emission wings due to the continued presence of disk material. Uncertainities in line

¤ © ¤ ¨ velocities preclude a K1 determination or mass information. Our best ﬁtting model yielded Twd 1000 34 0 0 1

¦ 200

¤ © ¤ ¨ K, log g ¨ 8 0 0 1, and Vrot 600 100 km/s. The Te f f value is very similar to the Te f f of the white dwarf in U Gem, but the rotational velocity appears¥ to be higher than U Gem’s value. We report approximate subsolar chemical abundances of Carbon and Silicon for RX And with C being 0.05 x solar and Si = 0.1 x solar while other elements are at essentially their solar values. However, accurate abundances are complicated by line emission and we cannot exclude that the abundances of all species are essentially at the solar values. We see no evidence of thermonuclear-

processed abundance ratios. If the white dwarf mass is 0.8 M (Ritter 1999), then the corresponding white dwarf 6 cooling age, 4 10 years, is a lower limit to the age of this CV. If the peculiar line features seen in the spectrum on the late decline from outburst are inverse P Cygni in nature, then infall velocities of ¡ 2000 km/s are indicated during the decline from outburst. We compare the surface properties of the RX And white dwarf with the properties of other CV degenerates studied to date with HST, HUT and IUE. Contact: [email protected]

X-ray and Optical Spectra of the Unusual Cataclysmic Variables LS Peg and T Leo P. Szkody, K. Nishikida1, K. S. Long2, R. Fried3 1 Department of Astronomy Box 351580, University of Washington, Seattle, WA 98195 2 STScI, 3700 San Martin Drive, Baltimore, MD 21218 3 Braeside Observatory, P. O. Box 906, Flagstaff AZ 86002 Astronomical Journal, in press (May)

We obtained ASCA observations of the cataclysmic variables LS Peg and T Leo in order to refine the X-ray characteristics of these two systems with unusual stream behaviors and search for orbital features that might signify the presence of material above the orbital plane. Simultaneous (LS Peg) and contemporaneous (T Leo) optical observations showed the systems undergoing their typical stream behaviors (absorption, high velocity component, QPOs in LS Peg; stream flow to the far side of the disk in T Leo). The X-ray light curve of LS Peg shows a low but constant count rate throughout its orbit. To fit the spectrum with a reasonable temperature requires a 7 keV partial 2 ABSTRACTS OF REFEREED PAPERS 8

22 2 ¥ absorber model with high column (6 10 cm ). This may be evidence for material thrown high above the disk by the disk-stream interaction or a magnetic accretion funnel sometimes suggested to explain other SW Sex stars.

20 2 ¥ The spectrum of T Leo is consistent with a simple 4-6 keV thermal model with lower column (3-5 10 cm ) and a small contribution from a cooler 1 keV component. Its light curve shows enhanced ﬂux between phases 0.8-1.0, which is not due to a change in temperature or column. The difference in behavior of this light curve from that of U Gem may be due to the lower accretion in this shorter period system. Contact: [email protected]

Spectroscopic Discovery of Brown Dwarf-like Secondary Stars in the Cataclysmic Variables LL Andromedae and EF Eridani S. Howell1, D. Ciardi2 1 Astrophysics Group, Planetary Science Institute 2 Department of Astronomy, University of Florida The Astrophysical Journal Letters, in press (astro/ph 0101572)

[X] refereed journal Infrared spectroscopic observations of LL Andromedae and EF Eridani are presented. Our K

band spectrum of LL Andromedae reveals the presence of methane absorption in the secondary star indicating an ¢ effective temperature ¡ 1300K, similar to a “T” type methane brown dwarf. The secondary star in EF Eridani is seen to be warmer with an effective temperature of ¡ 1650K and a spectroscopic classiﬁcation consistent with an L4-5

star. Both secondaries have theoretical mass estimates of 0.04-0.055 M (40-55 MJupiter). Our IR spectroscopic observations of LL And and EF Eri provide the ﬁrst direct proof of the theoretical prediction that post-period minimum cataclysmic variables contain brown dwarf-like secondary stars. Contact: [email protected]

The early X-ray emission from V382 Velorum (=Nova Vel 1999): An internal shock model

Koji Mukai1 2, Manabu Ishida3 1 Code 662, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA. 2 Universities Space Research Association 3 Institute of Space and Astronautical Science, 3-3-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan. The Astrophysical Journal, in press

We present the results of ASCA and RXTE observations of the early X-ray emission from the classical nova

¡ 23 2 V382 Velorum. Its ASCA spectrum was hard (kT 10 keV) with a strong (10 cm ¥ ) intrinsic absorption. In the subsequent RXTE data, the spectra became softer both due to a declining temperature and a diminishing column. We argue that this places the X-ray emission interior to the outermost ejecta produced by V382 Vel in 1999, and therefore must have been the result of a shock internal to the nova ejecta. The weakness of the Fe Kα lines probably indicates that the X-ray emitting plasmas are not in ionization equilibrium. Download/Website: ftp://lheaftp.gsfc.nasa.gov/pub/mukai/PP/v382vel.ps.gz Contact: [email protected] 2 ABSTRACTS OF REFEREED PAPERS 9

Superhumps in Cataclysmic Binaries. XIX. DV Ursae Majoris J. Patterson1, T. Vanmunster2, D. Skillman3, L. Jensen4, J. Stull5, B. Martin6, L. Cook7, J. Kemp8 1, C. Knigge9 1 1 Columbia University, Department of Astronomy 2 Center for Backyard Astrophysics (Belgium) 3 Center for Backyard Astrophysics (East) 4 Center for Backyard Astrophysics (Denmark) 5 Alfred University, Division of Physical Sciences 6 King’s University College, Department of Physics 7 Center for Backyard Astrophysics (Concord) 8 Joint Astronomy Centre 9 University of Southampton, Department of Physics and Astronomy PASP, published (2000PASP..112.1584P)

DV Ursae Majoris is a deeply eclipsing dwarf nova which shows very powerful superhumps when it attains superoutburst. We report detailed observations of the 1997 and 1999 eruptions. Some of the results reproduce what has been learned from other eclipsing dwarf novae: that the disk becomes very large in outburst, that superhumps develop in a few days, and that superhumps remain strong even after the disk has shrunk by more than 30%. The

5 ¥

mean superhump period was 0.08870(8) d, but in both eruptions the period decreased with P ¨ 6 10 . Global- ly distributed coverage of the 1997 eruption revealed two other interesting features: a transient modulation at the orbital period at the peak of eruption, and intricate ﬁne structure in the harmonics of the main superhump signal. In

particular, we found that the second harmonic occurred not at 3ω 3Ω as expected (where ω and Ω are respectively the orbital and “precessionfrequencies), but at 3ω 2Ω and 3ω Ω. The strong orbital modulation may have arisen from enhanced mass transfer from the secondary.

We also report photometry at quiescence, which separates the luminous contributions of the white dwarf, accretion

disk, and secondary star. We estimate a distance of 350 120 pc. Analysis of the eclipses suggests i ¨ 84 0 0 8 ,

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¨ ¨ q ¨ 0 155 0 015, M2 0 14 0 02M , M1 0 90 0 13M . Download/Website: http://cba.phys.columbia.edu/publications/ Contact: [email protected], [email protected]

Superhumps in Cataclysmic Binaries. XX. V751 Cygni J. Patterson1, J. Thorstensen2, R. Fried3, D. Skillman4, L. Cook5, L. Jensen6 1 Columbia University, Department of Astronomy 2 Dartmouth College, Department of Physics and Astronomy 3 Center for Backyard Astrophysics (Flagstaff) 4 Center for Backyard Astrophysics (East) 5 Center for Backyard Astrophysics (Concord) 6 Center for Backyard Astrophysics (Denmark) PASP, published (2001PASP..113...72P)

We report photometric and spectroscopic observations of the novalike variable V751 Cygni. The radial velocities indicate an underlying binary period of 0.1445(2) d; the long-term cycle count is not ﬁrmly decided but the best choice implies a period of 0.144464(1) d. The star shows a moderately low-excitation spectrum with transient P Cygni absorption suggestive of a wind origin, occasionally seen in cataclysmic variables accreting at a high rate.

Curiously, the P Cygni absorption appears correlated with binary phase in our two most extensive data sets. A

¤ photometric wave with P ¨ 0 1394 1 d, slightly shorter than Porb, rumbles through the light curve, as well as a low-frequency wiggle at 3.94(6) d. We identify the former as a “negative superhump”, and the latter as the wobble 2 ABSTRACTS OF REFEREED PAPERS 10 period of a tilted accretion disk. These characteristics all suggest classiﬁcation as an ordinary, accretion-powered cataclysmic variable of the VY Scl class. We discuss possible origins for the observed soft X-rays at quiescence. Download/Website: http://cba.phys.columbia.edu/publications/ Contact: [email protected], [email protected]

Superhumps in Cataclysmic Binaries. XVIII. IY Ursae Majoris

J. Patterson1, J. Kemp2 1, L. Jensen3, T. Vanmunster4, D. Skillman5, B. Martin6, R. Fried7, J. Thorstensen8 1 Columbia University, Department of Astronomy 2 Joint Astronomy Centre 3 Center for Backyard Astrophysics (Denmark) 4 Center for Backyard Astrophysics (Belgium) 5 Center for Backyard Astrophysics (East) 6 King’s University College, Department of Physics 7 Center for Backyard Astrophysics (Flagstaff) 8 Dartmouth College, Department of Physics and Astronomy PASP, published (2000PASP..112.1567P)

We report photometric and spectroscopic observations of the eclipsing dwarf nova IY Ursae Majoris (= Takamizawa V85). During its January 2000 superoutburst, the star ﬂashed superhumps with a period of 0.07583 d, 2.6% longer than the true orbital period. These waves rumbled through the light curve for ¡ 20 days. They appeared compatible with their common interpretation as the lower precessional sideband of the orbital clock: at a frequency ωo Ω,

where ωo is the orbital frequency and Ω is the accretion disk’s assumed precessional frequency. But the power

spectrum of the superhumps showed additional complexity, including signals at 3ωo Ω, 4ωo Ω, and 5ωo Ω. The latter probably arise from gravitational perturbation of more complex but still resonant (e.g., spiral) structures in the disk.

During eruption, the light curve across eclipse showed a large, bright accretion disk. But timings of minima and

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eclipse contacts revealed that the disk was quite eccentric, with e ¨ 0 29 0 06, and that this eccentric shape moved around with the putative precession period of 2.9 d. As the eruption faded, the eclipses began to reveal the signature of the white dwarf and the hot spot at the disk’s edge. “Lateßuperhumps raged at high amplitude for another ¡ 10 days, although the disk had seemingly contracted by ¡ 30%. Spectroscopy in quiescence showed strong doubled emission lines, typical of low-M˙ dwarf novae, and an S-wave with a semiamplitude of 750 km/s. The travelling knife-edge of the secondary’s limb made it possible to separate all the important light sources: white dwarf, secondary star, hot spot, accretion disk. The ingress and egress phases of the white-dwarf eclipse were very

brief, declining from ¡ 40 s to 25 s. The brightness of the white dwarf also varied, rapidly at ﬁrst and then slowly.

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Eclipse measurements in quiescence lead to estimates for the fundamental parameters of the binary: q ¨ 0 13 0 02,

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¨ ¨ M2 ¨ 0 12 0 02M , M1 0 86 0 11M , i 86 8 1 5 . We estimate a distance of 190 60 pc. With a small distance, a high inclination, vigorous superhumps, bright emission lines, and clear lines of sight to the central object, IY UMa furnishes a promising new laboratory for studying accretion-disk physics. Download/Website: http://cba.phys.columbia.edu/publications/ Contact: [email protected], [email protected] 2 ABSTRACTS OF REFEREED PAPERS 11

Accretion-Disk Precession and Substellar Secondaries in Cataclysmic Variables J. Patterson Columbia University, Department of Astronomy PASP, in press (2001 June)

The mass-losing secondaries in cataclysmic binaries are progressively whittled away by the ongoing loss of angular

momentum. The expected rate of evolution implies that the binaries should spend most of their lives at very short

¢ orbital period, with light secondaries ( 0 ¤ 08M ). But compared to the nearby white dwarf and accretion disk, these secondaries are effectively dark; so it has been quite difﬁcult to learn anything about them from observation. Here we show that for dwarf novae, the majority species, the mass ratios can be measured from simple photometric observations of “superhumps”, using equipment commonly possessed by amateur astronomers. The technique basically involves measuring the apsidal precession rate of the accretion disk, and thus has the merit of being purely dynami- cal, requiring no actual detection of light from the secondary. The results reafﬁrm what we have known for a long

time — that most secondaries are near the main sequence — but also show that near the end of the main sequence at 0 ¤ 08M , the secondaries are signiﬁcantly larger. This bloating, possibly due to an extra angular momentum sink

in the binary, sets the value of the minimum orbital period for H-rich binaries to be 76 80 minutes. Seven stars are

¤ found with secondaries in the mass range 0 ¤ 014 0 06M . Download/Website: http://cba.phys.columbia.edu/publications/ Contact: [email protected], [email protected]

Optical studies of the X-ray transient XTE J2123-058 - II. Phase-resolved spectroscopy R.I. Hynes1 3, P.A. Charles2 3, C.A. Haswell1, J. Casares4, C. Zurita4, M. Serra-Ricart4 1 Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK 2 Astrophysics, Nuclear and Astrophysics Laboratory, Keble Road, Oxford, OX1 3RH, UK 3 Department of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK 4 Instituto de Astrof´ısica de Canarias, 38200 La Laguna, Tenerife, Spain Monthly Notices of the Royal Astronomical Society, in press (astro-ph/0101104)

We present time-resolved spectroscopy of the soft X-ray transient XTE J2123–058 in outburst. A useful spectral coverage of 3700–6700 A˚ was achieved spanning two orbits of the binary, with single epoch coverage extending to

¡ 9000 A.˚ The optical spectrum approximates a steep blue power-law, consistent with emission on the Rayleigh- Jeans tail of a hot black body spectrum. The strongest spectral lines are HeII 4686 A˚ and CIII/NIII 4640 A˚ (Bowen blend) in emission. Their relative strengths suggest that XTE J2123–058 was formed in the Galactic plane, not in the halo. Other weak emission lines of HeII and CIV are present and Balmer lines show a complex structure, blended with HeII. HeII 4686 A˚ proﬁles show a complex multiple S-wave structure with the strongest component appearing at low velocities in the lower-left quadrant of a Doppler tomogram. Hα shows transient absorption between phases 0.35–0.55. Both of these effects appear to be analogous to similar behaviour in SW Sex type cataclysmic variables. We therefore consider whether the spectral line behaviour of XTE J2123–058 can be explained by the same models invoked for those systems. Contact: [email protected] 2 ABSTRACTS OF REFEREED PAPERS 12

IR spectra of the microquasar GRS 1915+105 during a low state

Emilios T. Harlaftis1, V. R. Dhillon2, A. Castro-Tirado3 4 1 Institute of Astronomy and Astrophysics, National Observatory of Athens, P.O.Box 20048, Thession, Athens - 11810, Greece 2 Department of Physics and Astronomy, University of Shefﬁeld, Shefﬁeld S3 7RH, UK 3 Instituto de Astrof´ısica de Andaluc´ıa (IAA-CSIC), P.O. Box 03004, E-18080 Granada, Spain 4 Laboratorio de Astrof´ısica Espacial y F´ısica Fundamental (LAEFF-INTA), P.O. Box 50727, E-28080 Madrid, Spain Astronomy & Astrophysics, in press (astro-ph/0012513)

There is controversy regarding the nature of the suspected donor star to the microquasar GRS 1915+105, and hence whether GRS 1915+105 is a high mass X-ray binary (HMXB) or a low-mass X-ray binary (LMXB). In order to clarify this issue, we obtained an infrared (J, H and K) spectrum of GRS 1915+105 in its low state which shows a steeper continuum than the prototype X-ray binary Sco X-1. We did not detect any HeII emission at 2.189 microns from GRS 1915+105 in our quiescent spectrum, indicating that the line is transient and is only observed during episodes of high X-ray activity. For our instrument conﬁguration, there is no detection of the 12CO lines which are characteristic of late-type stars either in GRS1915+105 or Sco X-1 Download/Website: http://xxx.soton.ac.uk/abs/astro-ph/0101391 Contact: [email protected]

A ‘superoutburst’ in XTE J1118+480

Erik Kuulkers1 2 1 Space Research Organization Netherlands (SRON), Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands 2 Astronomical Institute, Utrecht University, P.O. Box 80000, 3507 TA Utrecht, The Netherlands Astronomische Nachrichten, in press (astro-ph/0102066)

I propose that the properties of the two outbursts observed in the X-ray transient XTE J1118+480 in 2000 are akin to superoutbursts of SU UMa stars. In these systems a ‘normal’ outburst immediately precedes a 5–10 times longer (‘super’)outburst. The optical light curve of the outbursts of XTE J1118+480 is remarkably similar to that seen in

some SU UMa stars, such as UV Per and T Leo, where the precursor outburst is distinct from the superoutburst, but ¡ the time scales are a factor of ¡ 15 different. The ﬁrst outburst of XTE J1118+480 was relatively short ( 1 month) while the second outburst was ¡ 5 times longer. During the second outburst superhumps were seen, a feature characteristic for superoutbursts. The gap of about a month between the two outbursts is longer in X-rays with respect to the optical, a feature not previously recognized for X-ray transients. Also in SU UMa stars the precursor outburst becomes more distinct at shorter wavelengths. Finally, I show that the time of appearance of the superhumps in XTE J1118+480 is consistent with the expected superhump growth time, if the superhump mechanism was trigge- red during the ﬁrst outburst. I conclude that the similarity in outburst behaviour in the two types of systems provides further support that a common mechanism is at work to start the long (‘super’)outbursts. Download/Website: http://arXiv.org/abs/astro-ph/?0102066 Contact: [email protected] 2 ABSTRACTS OF REFEREED PAPERS 13

Black hole X-ray transients: mass accumulation in the disk - constraints for the viscosity E. Meyer-Hofmeister1, F. Meyer1 1 Max-Planck-Institut fur¨ Astrophysik, Karl Schwarzschildstr. 1, D-85740 Garching, Germany Astronomy & Astrophysics, in press (astro-ph/0103166)

The outburst cycles of black hole X-ray transients are now generally understood as caused by a thermal instability in the accretion disk, the same mechanism as in dwarf novae outbursts. During quiescence the accretion occurs via a cool disk in the outer region but changes to a coronal ﬂow/ADAF in the inner region. The transition to the coronal ﬂow is caused by evaporation of matter from the cool disk. This process is an important feature for the disk evolution. We point out that if the disk is depleted during the outburst, e.g. by irradiation, its evolution during quiescence is independent of the detailed outburst luminosity decline. The mass accumulation during quiescence has to meet several constraints as the accretion rate, the recurrence time and the total outburst energy. We present a critical discussion of different ways to model X-ray transient outburst cycles and compare with the requirements from observations. For the case of only little mass left over after the outburst the observations indicate a frictional parameter in the cool disk of order alpha(cold) =0.05, similar to that in dwarf nova disks during quiescence, with no need to resort to much lower alpha values of order 0.005. Contact: [email protected]

Applications of Indirect Imaging techniques in X-ray binaries Emilios T. Harlaftis1 1 Institute of Astronomy and Astrophysics, National Observatory of Athens, P.O.Box 20048, Thession, Athens - 11810, Greece Astro Tomography - An International Workshop on Indirect Imaging, eds. D. Steeghs, H. Bofﬁn, J. Cuypers, Lecture Notes in Physics series, Springer-Verlag, in press (astro-ph/0012513)

A review is given on aspects of indirect imaging techniques in X-ray binaries which are used as diagnostics tools for probing the X-ray dominated accretion disc physics. These techniques utilize observed properties such as the emission line proﬁle variability, the time delays between simultaneous optical/X-ray light curves curves, the light curves of eclipsing systems and the pulsed emission from the compact object in order to reconstruct the accretion disc’s line emissivity (Doppler tomography), the irradiated disc and heated secondary (echo mapping), the outer disc structure (modiﬁed eclipse mapping) and the accreting regions onto the compact object, respectively. Download/Website: http://xxx.soton.ac.uk/abs/astro-ph/0012513 Contact: [email protected]

The “Twin Jet” Planetary Nebula M2 9 Mario Livio1, Noam Soker2 1 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 2 Department of Physics, University of Haifa at Oranim, Oranim, Tivon 36006, Israel The Astrophysical Journal, in press

We present a model for the structure, temporal behavior, and evolutionary status of the bipolar nebula M2 9. According to this model the system consists of an AGB or post-AGB star and a hot white dwarf companion, with an orbital period of about 120 years. The white dwarf has undergone a symbiotic nova eruption about 1200 years ago, followed by a supersoft x-ray source phase. The positional shift of the bright knots in the inner nebular lobes 2 ABSTRACTS OF REFEREED PAPERS 14 is explained in terms of a revolving ionizing source. We show that the interaction between the slow, AGB star’s wind, and a collimated fast wind from the white dwarf clears a path for the ionizing radiation in one direction, while the radiation is attenuated in others. This results in the mirror-symmetric (as opposed to the more common point-symmetric) shift in the knots. We show that M2 9 provides an important evolutionary link among planetary nebulae with binary central stars, symbiotic systems, and supersoft x-ray sources. Contact: [email protected]

Properties and nature of Be stars

XX. Binary nature and orbital elements of γ Cas

P. Harmanec1 2, P. Habuda3, S. Steﬂˇ 2, P. Hadrava2, D. Korcˇak´ ova´4 2, P. Koubsky´2, J. Krtickaˇ 4 2, J. Kubat´ 2, P. Skˇ oda2, M. Slecˇ hta2, M. Wolf1 1 Astronomical Institute of the Charles University, V Holesoˇ vickˇ ach´ 2, CZ-180 00 Praha 8, Czech Republic 2 Astronomical Institute of the Academy of Sciences, CZ-251 65 Ondˇrejov, Czech Republic 3 Faculty of Mathematics and Physics of the Charles University, Ke Karlovu 3, CZ-121 16 Praha 2, Czech Republic 4 Department of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University, CZ-611 37 Brno, Czech Republic Astronomy & Astrophysics, published (2000A&A...364L..85H)

An analysis of accurate radial velocities (RVs) of the Be star γ Cas from 295 Reticon spectrograms secured between October 1993 and May 2000 allowed us to prewhiten the RVs for the long-term changes and to obtain the ﬁrst orbital RV curve of this star. The orbital period is 203.59d and the orbit has an eccentricity of 0.26. The orbital motion is detectable even in the published velocities, based on photographic spectra. This implies that γ Cas is a primary

component of a spectroscopic binary. The secondary has a mass of about 1 M , appropriate for a white dwarf or a neutron star, but it could also be a normal late-type dwarf. The ultimate solution of the dispute whether the observed X-ray emission is associated with the secondary or with the primary will need further dedicated studies. Contact: [email protected]

On the duration of the subsonic propeller state of neutron stars in wind-fed mass-exchange close binary systems N.R. Ikhsanov Max-Planck-Institut fur¨ Radioastronomie, Auf dem Hugel¨ 69, D-53121 Bonn, Germany Astronomy and Astrophysics Letters, published (ADS-Bibcode: 2001A&A...368L...5I)

The condition for the subsonic propeller § accretor state transition of neutron stars in wind-fed mass-exchange binary systems is discussed. I show that the value of the break period, at which the neutron star change its state to

accretor, presented by Davies & Pringle (1981, MNRAS 196, 209) is underestimated by a factor of 7.5. The correct

16 21 5 7

4 21 ¥

˙ ¥ value is Pbr 450 µ30 M15 M M s. This result forced us to reconsider some basic conclusions on the efﬁciency of the propeller spindown mechanism. Download/Website: http://www.mpifr-bonn.mpg.de/div/ir-interferometry/publications.html Contact: [email protected] 2 ABSTRACTS OF REFEREED PAPERS 15

Tidal evolution of eccentric orbits in massive binary systems II. Coupled resonance locking for two rotating main sequence stars M.G. Witte, G.J. Savonije Astronomical Institute ‘Anton Pannekoek’, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands Astronomy & Astrophysics, published (2001A&A...366..840W)

We extend our study of the tidal evolution of elliptic binary systems to the case of a system consisting of two

10M uniformly rotating main sequence stars. Previous work showed that in a system consisting of a 1 ¤ 4M

compact object in orbit about a 10M main sequence star stellar oscillation modes were prone to be excited nearly resonantly for prolonged periods of time. This resonance locking was shown to constitute an effective mechanism for orbital decay in moderately eccentric orbits. In this work we investigate in what ways the locking mechanism is altered if also the companion is tidally perturbed, also inducing orbital changes and potentially also being locked in resonance. We show that simultaneous locking can intensify the tidal excitations, and that resonance locking is a common phenomenon during the tidal evolution of eccentric double main sequence binary systems which speeds up the secular evolution signiﬁcantly. Download/Website: http://www.astro.uva.nl/ marnix/h2437.ps.gz Contact: [email protected]

Population synthesis for double white dwarfs I. Close detached systems

G. Nelemans1, L. R. Yungelson1 2, S. F. Portegies Zwart3 and F. Verbunt4 1 Astronomical Institute “Anton Pannekoek”, Kruislaan 403, NL-1098 SJ Amsterdam, the Netherlands 2 Institute of Astronomy of the Russian Academy of Sciences, 48 Pyatnitskaya Str., 109017 Moscow, Russia 3 Department of Physics and Center for Space Research, MIT, 77 Massachusetts Avenue, Cambridge MA 02139 USA 4 Astronomical Institute, Utrecht University, P.O.Box 80000, NL-3508 TA Utrecht, the Netherlands 11, Astronomy & Astrophysics, published (2001A&A...365..491N)

We model the population of double white dwarfs in the Galaxy and find a better agreement with observations compared to earlier studies, due to two modifications. The first is the treatment of the first phase of unstable mass transfer and the second the modelling of the cooling of the white dwarfs.

A satisfactory agreement with observations of the local sample of white dwarfs is achieved if we assume that the

¡ initial binary fraction is 50 % and that the lowest mass white dwarfs (M 0 ¤ 3M ) cool faster than the most recently published cooling models predict. 1 With this model we ﬁnd a Galactic birth rate of close double white dwarfs of 0.05 yr ¥ , a birth rate of AM CVn 1 systems of 0.005 yr ¥ , a merger rate of pairs with a combined mass exceeding the Chandrasekhar limit (which may

1 1 ¥ be progenitors of SNe Ia) of 0.003 yr ¥ and a formation rate of planetary nebulae of 1 yr . We estimate the total 8

number of double white dwarfs in the Galaxy as 2.5 10 . ¡

In an observable sample with a limiting magnitude Vlim ¨ 15 we predict the presence of 855 white dwarfs of which ¡ 220 are close pairs. Of these 10 are double CO white dwarfs of which one has a combined mass exceeding the Chandrasekhar limit and will merge within a Hubble time. Download/Website: http://www.edpsciences.fr/articles/aa/pdf/2001/03/aah2305.pdf Contact: [email protected] 2 ABSTRACTS OF REFEREED PAPERS 16

Population synthesis for double white dwarfs II. Semi-detached systems: AM CVn stars

G. Nelemans1, S. F. Portegies Zwart2, F. Verbunt3 and L. R. Yungelson1 4 1 Astronomical Institute “Anton Pannekoek”, Kruislaan 403, NL-1098 SJ Amsterdam, the Netherlands 2 Department of Physics and Center for Space Research, MIT, 77 Massachusetts Avenue, Cambridge MA 02139 USA 3 Astronomical Institute, Utrecht University, P.O.Box 80000, NL-3508 TA Utrecht, the Netherlands 4 Institute of Astronomy of the Russian Academy of Sciences, 48 Pyatnitskaya Str., 109017 Moscow, Russia Astronomy & Astrophysics, published (2001A&A...368..939N)

We study two models for AM CVn stars: white dwarfs accreting (i) from a helium white dwarf companion and (ii) from a helium-star donor. We show that in the ﬁrst model possibly no accretion disk forms at the onset of mass transfer. The stability and the rate of mass transfer then depend on the tidal coupling between the accretor and the orbital motion. In the second model the formation of AM CVn stars may be prevented by detonation of the CO white dwarf accretor and the disruption of the system. With the most favourable conditions for the formation of AM

3 1 3 1

¥ ¥ ¥ ¥

¤ CVn stars we ﬁnd a current Galactic birth rate of 6 ¤ 8 10 yr . Unfavourable conditions give 1 1 10 yr .

7 7

¤ The expected total number of the systems in the Galaxy is 9 ¤ 4 10 and 1 6 10 , respectively. We model very simple selection effects to get some idea about the currently expected observable population and discuss the (quite good) agreement with the observed systems. Download/Website: http://www.edpsciences.fr/articles/aa/ps/2001/12/aah2552.ps.gz Contact: [email protected] 3 OTHER ABSTRACTS 17

3 Other abstracts Outburst activity in magnetic cataclysmic variables BY Cam and QQ Vul A.V. Halevin1, N.M. Shakhovskoy2, I.L. Andronov1, S. V. Kolesnikov3 1 Astronomy Department, Odessa National University, Odessa, Ukraine 2 Crimean Astrophysical Observatory, Nauchni, Crimea, Ukraine 3 Astronomical Observatory Odessa National University, Odessa, Ukraine Proceedings of the conference “ASTRONOMY IN UKRAINE - 2000 AND BEYOND”, Kinemat.Phys.Celest.Bodies, spec. issue, in press

Flare properties in magnetic cataclysmic variables BY Cam and QQ Vul are determined based on the observations obtained at AZT-11 and the Shain mirror telescope of the Crimean Astrophysical Observatory. The UBVRI AZT-11 photometry demonstrates a wide range of color properties of these events. There are significant differencies between the flare amplitudes in BY Cam and QQ Vul. The correlation coefficient between the flare amplitude and smoothed brightness variations of QQ Vul is about 0.83. Similar dependence for the flares of BY Cam is not detected. Some values of the cross-correlation “brightness-polarization” are as large as 0.7. There are no significant differences between the colors of observed flares, as for instance, one could expect for possible “accretion” and “red dwarf” flares. Contact: [email protected]

A self-regulating braking mechanism in black hole X-ray binaries F. Meyer1, E. Meyer-Hofmeister1 1 Max-Planck-Institut fur¨ Astrophysik, Karl Schwarzschildstr. 1, D-85740 Garching, Germany Conference Proc., in press

The outbursts of black hole X-ray transients can be understood as caused by a limit cycle instability in the accretion disk, similar to dwarf nova outbursts. For adequately low mass overflow rates from the companion star long outburst recurrence times are expected. But the fact that we find predominantly long recurrence times or that only one X-ray nova outburst was detected at all poses a problem. The question arises whether any braking mechanism could act in a way that long recurrence times are favored. We suggest that a circumbinary disk exists and brakes the orbital motion of the binary stars by tidal interaction. The irradiation during an outburst leads to mass loss by winds from the circumbinary disk, releaving the braking force until the removed matter is refilled by diffusion from outer parts. We show that this reduction of braking will self-adjust the mass transfer to the marginal rate that gives long recurrence times. Download/Website: http://www.mpa-garching.mpg.de/Binary/pre 2001.html Contact: [email protected] 4 MISCELLANEOUS ANNOUNCEMENTS 18

4 Miscellaneous announcements OpenGL code to draw pictures and animations of cataclysmic variables Andrew Beardmore Dept. of Physics, Keele Universtiy, Staffordshire, ST5 5BG, UK A OpenGL code is made availabe which draws relatively pretty pictures of CVs (polars, IPs, DNs). The secondary, disc, & magnetosphere are texture mapped with ßtarspots”, shadow from the disc, and plasma¨ımages. The code can be used to create images and animations that can be used in talks, public understanding of science work, etc.

Download/Website: http://www.astro.keele.ac.uk/ ¡ apb/OGL CV/oglcv.html Contact: [email protected]

Free copies of 2 Proceedings Volumes Jochen Greiner Astrophysical Institute Potsdam As the editor of the proceedings, the Springer publisher has sent me all unsold copies of

1. Proceedings of the IAU Colloquium 151: Flares and Flashes. IAU Coll was held in Sonneberg/Germany, Dec. 5-9, 1994 published in Lecture Notes in Physics, vol. 454 (1995), Springer. eds. Jochen Greiner, Hilmar W. Duerbeck, Roald E. Gershberg ISBN 3-540-60057-4 2. Proceedings of the Workshop on Supersoft X-ray Sources. The workshop was held at MPE Garching, Feb. 28 - Mar. 1, 1996 published in Lecture Notes in Physics, vol. 472 (1996), Springer. ed. Jochen Greiner ISBN 3-540-6139-0

Anybody who still is interested in getting a copy should contact me. Jochen Greiner

Download/Website: http://www.aip.de/¡ jcg/proceed.html Contact: [email protected]

Cataclysmic Variable Stars: How and why they vary Coel Hellier Department of Physics, Keele University, Staffordshire ST5 5BG, U.K.

A new book “Cataclysmic Variable Stars: How and why they vary” by Coel Hellier has just been published by Springer-Verlag UK. This is an introductory book, deliberately at a lower level than Warner’s CV book. It is thus aimed primarily at undergraduates, masters or 1st-year PhD students, researchers in adjacent areas, and advanced amateur astronomers. The book discusses the behaviour of CVs, with 154 illustrations, and emphasises the reasons for the variability. The 13 chapters are: 1. Observing cataclysmic variables; 2. The orbital cycle; 3. Spectral characteristics; 4. The evolution of cataclysmic variables; 5. Discs and outbursts; 6. Elliptical discs and superoutbursts; 7. Siphons, winds and streams; 8. Magnetic cataclysmic variables I: AM Her stars; 9. Magnetic cataclysmic variables II: intermediate polars; 10. Flickering and oscillations; 11. The nova eruption; 12. Secondary star variations; 13. Variations on the theme. 5 CONFERENCE ANNOUNCEMENTS 19

The book is a 210-page paperback with an ISBN of 1-85233-211-5, and can be ordered from internet book stores such as www.amazon.co.uk. However, the UK ofﬁce of Springer-Verlag is offering a 15% discount for orders sent direct to them, using the order form at http://www.springer.co.uk/or form.htm (or contact [email protected]). The prices (with discount) are £20, $34 or DM 68 depending on geographical location, plus £2 postage (make sure to claim the discount on the form).

Download/Website: http://www.astro.keele.ac.uk/ ¡ ch Contact: [email protected]

Book review: Cataclysmic Variable Stars: How and why they vary B. Gansic¨ ke Universitats-Sternw¨ arte Gottingen,¨ Geismar Landstraße 11, D-37083 Gottingen,¨ Germany

Cataclysmic Variable Stars: How and why they vary by Coel Hellier provides a good overview of the present state of CV research – including some of the unresolved problems – somewhat weighted from the point of view of an observer. The topic of CVs is embedded between an introduction to CCD photometry of variable stars and a short overview of related systems, such as X-ray binaries, AGN and YSO. A large amount of well-prepared figures supports the text. Each chapter is supplemented with a number of “boxes” that give additional details about observation techniques, essential equations, or analysis methods. The book addresses an incredible number aspects. In fact, I found that almost every keyword coming to my mind in the context of CV reasearch is mentioned. This breadth is of course paid by a lack of depth – the entire text is kept on ¡ 200 pages. As a consequence, penetrating some of the involved physics might at times be difficult for a young researcher. A more extended bibliography, especially pointing to a larger number of relevant non-CV papers, would have helped to prevent this shortcoming. Summing up, Cataclysmic Variable Stars: How and why they vary is a crash course in CV research that brings the unfamiliar reader into the field within the shortest time, and prepares him/her for the lecture of more comprehensive overviews, such as e.g. Warner’s book, or Frank, King & Raine’s text on the theoretical aspects of accretion.

5 Conference announcements The International Conference on Variable Star Research M. Zejda & Z. Mikulasek The International Conference on Variable Star Research 8 - 11th, November 2001 N. Copernicus Observatory and Planetarium, Brno, Czech Republic Preliminary topics of the conference:

1. The role of amateur observers in contemporary and future research of variable stars 2. Violently interacting close binaries. Cataclysmic variable stars 3. Light elements of periodic variable stars. Construction of true (O-C) diagram, problems of light elements determination. Changes of light elements of periodic variable stars and their causes. Aperiodic phenomena, their plausibility, possible explanations

Further information available by e-mail: [email protected] and [email protected], of Zdenek Mikulasek (SOC) and Miloslav Zejda (LOC), respectively. 5 CONFERENCE ANNOUNCEMENTS 20

Stellar atmospheric modeling Klaus Werner

We are pleased to announce an international workshop on STELLAR ATMOSPHERIC MODELING to be held at Tubingen,¨ Germany, on September 17-21, 2001. The workshop will be hosted by the Institute for Astronomy and Astrophysics at the University of Tubingen.¨ The rationale for organizing this workshop is as follows. In the last decade we have witnessed an enormous progress of computer power and consequent power of computing more and more realistic model atmospheres, relaxing more and more former approximations that plagued earlier models. But such a progress was earned by a hard and pain- staking work of those brave individuals who build and upgrade stellar atmospheres and general radiative transfer computer programs. The groups of modelers are few, and are scattered over the world. When such modelers get together, they always proﬁt very much from exchanging notes about how exactly avoid such and such convergence problems, how to make things more efﬁcient, and generally how to deal with a host of everyday problems modelers have to face but the rest of community doesn’t very much care about. In this spirit, we envisage a workshop for a highly motivated audience of experienced modelers and anyone who wants to learn more about making models, not just about using them. The workshop is essentially a method-oriented, as opposed to a standard, results-oriented, meeting. The actual model results have their chance to be presented on other meetings, while there is usually not much space for discussing methods during typical, object- or instrument- oriented conferences. We plan to have a number of topics and sessions; each session will be introduced by two invited keynote speakers, and followed by more or less informal, but registered, contributions on the given subject. Actual results may be presented on posters.

Topic Keynote Speakers Basic Accelerated Lambda Iteration (ALI) in Plane-parallel Atmosphe- Auer, Hubeny res and Formal solvers Model Photospheres with ALI Hubeny, Werner Basic ALI in Moving Atmospheres Hamann, Hoeﬂich Rate Equations with ALI Koesterke, Hillier Temperature Correction Schemes Dreizler, Hauschildt Parallelization Hauschildt, Hoeﬂich Basic Multi-D Radiative Transfer Paletou, Fabiani-Bendicho Basic Radiation Hydrodynamics Mihalas, TBD Numerical Multi-D Radiation (Magneto-) Hydrodynamics Carlsson, Stein Polarization Trujillo-Bueno, Nagendra Handling of Atomic Data Lanz, Rauch Molecular, Grain and Dust Opacities Alexander, TBD

Scientiﬁc Organizing Committee: L.S. Anderson (USA), M. Carlsson (Norway), S. Dreizler (Germany), W.R. Ha- mann (Germany), I. Hubeny (USA, Co-Chair, [email protected]), T. Lanz (USA), D. Mihalas (USA), J. Trujillo-Bueno (Spain), K. Werner (Germany, Co-Chair, [email protected])

Local Organizing Committee: A. Heynen, H. Oberndoerffer, T. Rauch (Chair, [email protected])

For REGISTRATION and detailed INFORMATION see our Workshop Website: http://astro.uni-tuebingen.de/ ¡ rauch/ATMOS 2001 index.html 6 JOBS AND POSITIONS 21

The physics of cataclysmic variables and related objects, August 5–10, 2001, Georg-August-Universitat¨ Gotting¨ en, Germany

Next deadline: May 01, 2001 – early registration Download/Website: http://www.uni-sw.gwdg.de/CVConference Contact: [email protected]

6 Jobs and positions Research Associate, Univ. of Leicester – Available from 1 October 2001 for 2 years Theoretical Astrophysics Group, Department of Physics & Astronomy, University of Leicester, Leicester LE1 7RH, U.K. Applications are invited for this post-doctoral position, which is supported by a PPARC rolling grant for theoretical astrophysics. The successful candidate will be expected to develop a strong research programme com- plementing and extending the activities of the research group in areas such as accretion disc structure and stability, and close binary evolution. The Theoretical Astrophysics Group currently comprises four permanent staff (Prof A.R. King, Drs G.A. Wynn, M.B. Davies, and J.R. Murray), one fixed-term lectureship, five postdoctoral positions, and four support staff. It benefits from considerable and growing in-house supercomputing resources, and hosts the UK Astrophysical Fluids Facility (a 128-CPU national supercomputer facility for astrophysical fluid calculations). There are close links with the large X-ray Astronomy Group in the same department. Candidates should have (or be about to complete) a PhD, and have a good background in theoretical astrophysics. Applicants are encouraged to make informal enquiries concerning this position to Professor A.R. King, Dept of Physics and Astronomy, e-mail [email protected], telephone +44 (0)116 252 2072. Application forms and further particulars are available from the Personnel Office, tel 0116 252 5114, fax 0116 252 5140, e-mail [email protected]. Closing Date: 30 March 2001 Download/Website: http://www.le.ac.uk/personnel/jobs/r9283a.htm Contact: [email protected]