The Be Star Newsletter, Volume 33, June 1998

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Abstracts

Photometric Monitoring of Bright Be Stars. III. 1988-89 and 1992-95

John R. Percy, Jason Harlow, Katharine A.S. Hayhoe, Inese I. Ivans, Matthew Lister, Rene Plume, Tara Rosebery, Sarah Thompson, and David Yeung
Erindale College and Department of Astronomy, University of Toronto, Mississauga, Ontario, Canada L5L 1C6

We report long-term photometric (BV) observations of 23 bright, active Be stars made in 1988 and 1989 and 1992 to 1995 with the 0.4m telescope at the University of Toronto. Cumulative light curves, including observations made earlier at the University of Toronto, and with the Automatic Photometric Telescope Service in Arizona, are presented for several of the stars. Many of the stars show cyclic variations of up to 0.2 in V and B on time scales of a few years, as well as variations on time scales of about a day.

1997, PASP, 109, 1215

On the spectacular variations of $\gamma$ Cas: Evidence for a temporarily tilted circumstellar disk

W. Hummel
Universitätssternwarte München, Scheinerstr. 1, D-81679 München, Germany

A new explanation for the spectacular emission line variations occuring in the Be stars $\gamma$ Cas and 59 Cyg is presented. We propose a circumstellar Keplerian disk, tilted with respect to the equatorial plane. The precessing nodal and apsidal line causes a variation in the emission line widths and profile shapes. In particular the sequence of alternating shell-phases and narrow single-peak phases is proposed to be due to an apparent variation in the disk inclination.

1998, A&A, 330, 243

Long-term visual spectrophotometric behaviour of Be stars

A. Moujtahid,¹, J. Zorec², A.M. Hubert¹, A. Garcia² and D.G. Burki³
¹Observatoire de Paris-Meudon, DASGAL, F-92195 Meudon Principal Cedex, France
²Institut d'Astrophysique de Paris, C.N.R.S. - 98^bis, bd. Arago, F-75014 Paris, France
³Observatoire de Genève, CH-1290 Sauverny, Switzerland

The long-term spectrophotometric variations of 49 Be stars are studied using the U and V magnitudes of the UBV system, the total Balmer discontinuity D and the visible gradient $\Phi _{\rm rb}$ . BCDspectrophotometric and photometric data in five different photometric systems, obtained in most cases since 1950 and reduced to the BCD system, were used. The (U,D), (V,D), ( $\Phi _{\rm rb},D$ ) and ( $\Phi _{\rm rb},V$ ) correlations obtained differ from star to star and they can be single or double-valued. They differ clearly for Be phases or Be-shell phases. Be stars with small $V\!\sin i$ showing the "spectrophotometric shell behaviour": D > D_*, were found. This finding implies either that strongly flattened models of circumstellar envelopes are in doubt for these stars, or that not all Be stars are rapid rotators. Comparison of observed variations with those predicted for model Be stars with spherical circumstellar envelopes of variable densities and dimensions implies that spectrophotometric patterns of Be phases are due to circumstellar envelopes in low opacity regimes, while those of spectrophotometric shell phases are due to circumstellar envelopes in high opacity regimes. In a given star, the envelope regions responsible for the observed variations of D and $\Phi _{\rm rb}$ in spectrophotometric shell phases seem to be smaller and denser than those producing the observed variations of these parameters in spectrophotometric Be phases. The high positive RV found in strong shell phases might favor the formation of compact circumstellar layers near the star.

1998, A&AS, 129, 289

The optical counterparts to Be/X-ray binaries in the Magellanic Clouds

J.B.Stevens¹, M.J.Coe¹ and D.A.H.Buckley²
¹Dept. of Physics and Astronomy, University of Southampton, Highfield
²South African Astronomical Observatory, P.O. Box 9, Observatory, 7935, South Africa

The fields of 8 X-ray sources in the Magellanic Clouds believed to be Be/X-ray binaries have been searched for possible Be star counterparts. BVR and H $\alpha$ CCD imaging was employed to identify early type emission stars through colour indices and H $\alpha$ fluxes. Follow up H $\alpha$ spectroscopy of 5 sources confirms the presence of H $\alpha$ emission in each case. Based on the positional coincidence of emission line objects with the X-ray sources, we identify Be star counterparts to the ROSAT sources RX J0032.9-7348, RX J0049.1-7250, RX J0054.9-7226 and RX J0101.0-7206, and to the recently discovered ASCA source AX J0051-722. We confirm the Be star nature of the counterparts to the EXOSAT source EXO0531.1-6609, and the HEAO1 source H0544-665. In the field of the ROSAT source RX J0051.8-7231 we find three possible counterparts, each showing evidence for H $\alpha$ emission.

Submitted to MNRAS
Preprints from jbs@astro.soton.ac.uk

HIGH STATE OF H $\alpha$ EMISSION ACTIVITY OF THE HERBIG Be STAR HD 200775

Anatoly S. Miroshnichenko¹, Christopher L. Mulliss¹, Karen S. Bjorkman¹, Nancy D. Morrison¹, Yuri V. Glagolevskij², Georgij A. Chountonov²
¹Ritter Observatory, Dept. of Physics & Astronomy, The University of Toledo, Toledo, OH 43606-3390, USA
²Special Astrophysical Observatory of the Russian Academy of Sciences, Karachai-Cherkess Republic, Nizhnyi Arkhyz, 357147, Russia

We present the results of high-resolution spectroscopic observations of the pre-main-sequence Herbig Be star HD 200775 obtained between September 1994 and February 1998. Strong variations of the H $\alpha$ line associated with an extended period of strong emission during summer and fall 1997 have been observed. The line equivalent width took on the highest value reported in the last 20 years. Evidence of a strong stellar wind followed by enhanced accretion of circumstellar matter onto the star, as suggested previously by Beskrovnaya et al. (1994, A&A, 287, 564), is confirmed. A review of the observational literature dating back to 1977 indicates periodic behavior of the H $\alpha$ equivalent width with a period of 3.68 years. The next high emission state is predicted to occur in the first half of 2001. We emphasize the importance of coordinated photometric and high-resolution spectroscopic observations for further understanding of the star's behavior.

Submitted to PASP
For preprints, contact anatoly@physics.utoledo.edu or by anonymous ftp to ftp.physics.utoledo.edu /users/anatoly/hd200775

Evidence for one-armed oscillations in the equatorial disk of $\zeta$ Tau from GI2T spectrally resolved interferometry

F. Vakili¹, D. Mourard¹, Ph. Stee¹, D. Bonneau¹, P. Berio¹, O. Chesneau¹, N. Thureau¹, F. Morand¹, A. Labeyrie², and I. Tallon-Bosc³
¹GI2T, Fresnel, Observatoire de la Côte d'Azur, F-06740 Caussols, France
²Observatoire de Haute Provence, 04870 Saint Michel l'Observatoire, France
³Centre de Recherche Astronomique de Lyon, UMR CNRS 5574, 9 avenue Charles André, 69561 St Genis Laval Cedex, France

We report sub-mas observations of the Be Shell star $\zeta$ Tau with the Grand Interféromètre à 2 Télescopes (GI2T) on November '93 and October '94. In '93, the H $\alpha$ line presented a V/R ratio of 0.57 with a central absorption shell component. On October '94 the H $\alpha$ line presented a reversed V/R ratio of 1.26 with a shallower absorption component. For both epochs we analysed the amplitude and phase of the fringe signal relative to the local continuum as a function of Doppler-shift across H $\alpha$ . We clearly resolve the H $\alpha$ emitting envelope on October '93. We find that the bulge of the emission which occurs around RV=+130 km.s^-1 has a N-S projected position of 0.7 mas to the South of the continuum source. This value corresponds to a linear separation of 3.6 photospheric radii. For October 94, the same analysis shows that the projected position of this bulge, occuring around RV=-70 km.s^-1 has moved to 0.5 mas, i.e. 2.6 photospheric radii, North of the continuum source. On account of the opposite V/R values between 93 and 94 and the long term H $\alpha$ cyclic variability of $\zeta$ Tau this apparent motion corresponds to the first interferometric detection of an axi-asymmetric envelope around a Be star that we interpret as direct evidence for a prograde one-armed oscillation of its equatorial disk.

Accepted by Astronomy & Astrophysics, Main Journal, March 1998
Preprints from vakili@obs-azur.fr

Stellar and circumstellar activity of the Be star $\mu$ Cen I. Line emission outbursts

Th. Rivinius¹, D. Baade², S. Stefl³, O. Stahl³, B. Wolf³, and A. Kaufer³
¹Landessternwarte Königstuhl, Heidelberg, Germany
²European Southern Observatory, Garching bei München, Germany
³Astronomical Institute, Academy of Sciences, Ondrejov, Czech Republic

With a total of 408 echelle spectra obtained with HEROS (Heidelberg Extended Range Optical Spectrograph) during 6 observing runs covering 355 nights in 4 years and the spectral range from 3450 to 8620Å at a resolving power of 20000, this study is based on one of the most extensive homogeneous observational records of the short-, medium-, and long-term variability of any Be star. One week worth of low-resolution spectra with very high temporal sampling was additionally obtained. Three dense series of very high-resolution low-noise profiles of He I $\lambda$ 6678 observed in 1985-1987 (309 spectra) and one of Si III $\lambda$ 4553 obtained in 1995 (27 spectra) simultaneously to the low-resolution data could also be relied upon for verification purposes.

The star was found to be in the process of continued gradual recovery of the H $\alpha$ emitting disk which had been lost from 1977-1989. During the monitoring period numerous line emission outbursts were observed. A detailed generalized pattern of an outburst cycle is derived from observations of different circumstellar lines at times of various levels of emission from the disk. Relative quiescence, precursor, outburst, and subsequent relaxation can be distinguished as the main constituing phases, even though there are distinct differences between different groups of spectral lines.

Outbursts are preceded by a significant decline in the peak height of all circumstellar emission lines, which only lasts a few days. The outbursts proper are characterized by the occurrence within 1-3 days of (i) broad emission wings, (ii) rapid cyclic variability of the violet-to-red (V/R) emission peak ratio, (iii) temporary high velocity absorptions, (iv) transient sharp absorption spikes at the edges of photospheric lines, (v) an increase in the separation of emission peaks, and (vi) an increase of emission strength as the burst goes on. Particularly the V/R activity may be accompanied by relatively short-lived narrow, blueshifted high-velocity absorption components. The relaxation phase following the outburst exhibits a slow but steady decline from these sudden enhancements and ultimately returns to the pre-outburst state of relative quiescence. Outbursts can differ in amplitude and duration by a factor of a few, and the larger an outburst is, the more time it takes relative quiescence to be reached. At times the frequency of outbursts is so high, or the amplitude of an outburst is so large, that the next outburst takes place before the previous pre-outburst state has been re-established.

Based on this empirical phenomenology, a schematic picture of the associated ejection of matter into a near-stellar orbit is sketched.

1998, A&A, 333, 125

Stellar and circumstellar activity of the Be star $\mu$ Cen II. Multiperiodic low-order line-profile variability

Th. Rivinius¹, D. Baade², S. Stefl³, O. Stahl¹, B. Wolf¹, and A. Kaufer¹
¹Landessternwarte Heidelberg, Königstuhl, D-69117 Heidelberg, Germany, email: T.Rivinius@lsw.uni-heidelberg.de
²European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching b. München, Germany, e-mail: dbaade@eso.org
³Astronomical Institute, Academy of Sciences, CZ-25165 Ondrejov, Czech Republic, e-mail: sstefl@sunstel.asu.cas.cz

After the study in Paper I of the morphology of the line emission outbursts of this bright Be star, the same database is analyzed for the temporal characteristics of the photospheric variability.

In the 1992-1997 spectra, separate time series analyses were performed for the mean radial velocities of two groups of lines, He I and Si III, which were selected for their being the least contaminated by emission components. A period search with iterative pre-whitening revealed six periods which maintained phase coherence over the entire time interval covered. Four of them are close to the previously reported 0.505-day period (and, in fact, constitute it). Their relative frequency spacings are about 1.8%, 0.9%, and again 1.8% and cannot be resolved in single-season data strings. The other two periods, which were not found in the Si III lines, are near 0.28 day. Additionally, the radial velocity variations of the single line He I $\lambda$ 6678 were studied. This data set extends from 1985 to 1997 thereby permitting a refinement of the periods found in the other lines.

Similar time series analyses of the flux contained in 5 $\rm km\,s^{-1}$ wide line-profile bins of the 1995-1997 spectra found periods that are identical to those of the radial velocities to within 4 decimal places. However, not all periods are detected in all 21 lines studied.

Within either group of periods, the line-profile variability patterns are indistinguishable from one another whereas the difference between the two groups is highly significant. This implies that there are also two different stellar surface patterns associated with the two groups. Their analysis is deferred to the third paper in this series.

Numerous different tests were performed to check the genuineness of the multiperiodicity. None of them could disprove the reality of any of the periods which seems to be well founded on many observational facts.

At times of enhanced V/R variability, an additional line-profile modulation with period $\sim 0.505$ day may develop. It consists of narrow absorption spikes at $\pm \sim 0.7 v \sin i$ and, in the respective opposite wing, a very extended ramp-like ascent of the profile to the adjacent continuum.

Finally, a series of 348 low-resolution spectra obtained during 8 nights, which coincided with a line-emission outburst, indicates cyclic variations of the radial velocity of Balmer and He I lines with a time scale of 0.58 day. The same time scale was also present in the V/R ratio of the two emission peaks in H $\beta$ .

Submitted to Astronomy & Astrophysics
Preprints will be available from the first author after the paper has been accepted for publication.

Multiperiodic line-profile variability and a tentative ephemeris for line-emission outbursts of the Be star $\mu$ Cen

Between 1992 and 1997 the bright Be star $\mu$ Cen was monitored spectroscopically with a high-resolution echelle spectrograph. A thorough period analysis of the stellar radial velocity could resolve the previously suspected 0.505-day period into 3 distinct, closely spaced periods. The line-profile variations associated with all three periods are about the same and can be best described as a roughly sinusoidal low-order modulation of the line profiles. A fourth mode with higher frequency in both the spatial and temporal domain was also detected. Qualitatively, low-order NRP g-modes of (different) high radial degree can readily serve as a possible interpretation. This might open meaningful asteroseismological opportunities.

From the phases and mean amplitudes of the three 0.5-day periods the times of maximal amplitude superposition were re-constructed which correlate well with the times of the observed increases of the emission line strength. This may lead to a revival of the notion of pulsationally driven outbursts of Be stars.

To appear in: ``A Half Century of Stellar Pulsation Interpretations: A Tribute to Arthur N. Cox'' held in Los Alamos in June 1997, eds. P.A. Bradley and J.A. Guzik.

Preprints from T.Rivinius@lsw.uni-heidelberg.de or on the web at http://www.lsw.uni-heidelberg.de/~ triviniu/Bestars.html

Circumstellar quasi-periods accompanying stellar periods of Be stars

S. Stefl¹, D. Baade², Th. Rivinius³, O. Stahl³, B. Wolf³, and A. Kaufer³
¹Astronomical Institute, Academy of Sciences, Ondrejov, Czech Republic
²European Southern Observatory, Garching bei München, Germany
³Landessternwarte Königstuhl, Heidelberg, Germany

Several hundred high spectral and temporal resolution spectra (345-862 nm) of three southern Be stars obtained in three seasons were used for time series analyses of line profiles. The periodicity pattern differs significantly: ( I) across a given line-profile, ( II) between different spectral lines, and ( III) between different phases of an emission outburst cycle. In some seasons, newly discovered transient periods co-exist with the main stellar periods which maintain long-term stability and phase coherence. They differ typically by $\sim$ 10% from the main periods, less from transient periods at other epochs, and are not present in purely photospheric lines, but can be dominant in the lines formed in the upper parts of the extended atmosphere. The nature of the phenomenon and concerns about implications for studies of rapid variability are discussed.

To appear in: ``A Half Century of Stellar Pulsation Interpretations: A Tribute to Arthur N. Cox'' held in Los Alamos in June 1997, eds. P.A. Bradley and J.A. Guzik.

Preprints from sstefl@sunstel.asu.cas.cz or on the web at http://www.lsw.uni-heidelberg.de/~ triviniu/Bestars.html

Weak and Post T Tauri Stars around B-type members of the Sco-Cen OB association

E.L. Martín^1,2
¹Astronomy Department, University of California, Berkeley, CA 94720
²Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain

I report medium-resolution (FWHM=1.9 Å) spectroscopic observations of six H $_\alpha$ emission stars proposed by Meyer et al. (1993) to be T Tauri stars formed in the vicinity of the B1 giant $\sigma$ Sco, a bright member of the Sco-Cen OB association. Using spectroscopic criteria (spectral types, H $_\alpha$ and LiI equivalent widths), which are distance-independent, I classify these stars in different PMS classes. Taking data from the literature, a number of stars detected by X-ray observations around other B-type members of Sco-Cen are also classified. The current census of ``bona-fide'' low-mass PMS stars identified in about 9 deg.² in Sco-Cen is 2 CTTS, 18 WTTS and 10 PTTS. The presence of a mixture of T Tauri and post T Tauri stars implies that previous results based on isochrone fitting that indicated an extremely young age ( $\sim$ 1 Myr) for the Sco-Cen PMS low-mass population are incorrect. A distance of about 125 pc for Sco-Cen, instead of the 160 pc used in previous works, is consistent with the Hipparcos parallaxes for many of the B-type stars and would lead to older H-R diagram ages. Taking into account that PTTS are generally fainter and harder to identify than WTTS, I argue that the WTTS/PTTS ratio in Sco-Cen may be of order of unity. This result suggests that the low-mass stars of the OB association span an age range similar to the B-type members (5-15 Myrs), i.e. the low and high-mass star populations are essentially coeval. Sco-Cen appears to be indeed a promising place to find many PTTSs in future surveys.

Coupled long-term photometric and V/R variations in Be stars: evidence for prograde global one-armed disk oscillations

R.E. Mennickent ¹, C. Sterken² and N. Vogt³
¹Dpto. de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Concepción, Casilla 4009, Concepción, Chile.
²University of Brussels (VUB), Pleinlaan 2, 1050 Brussels, Belgium.
³Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 104, Santiago 22, Chile and Sternwarte Sonneberg, Sternwartenstr. 32, D-96515 Sonneberg, Germany.

We review theoretical work on global oscillations of Be star disks and summarize possible observational tests. In addition, we analyze existing records on photometric data and V/R ratio for a sample of 6 V/R variable Be stars. Five stars showed coupled long-term photometric-V/R variations. In all cases the photometric extrema coincided with times of V = R transits, the fainter state being followed by a V < R phase. V1294 Aql, 48Lib and MXPup showed anticorrelated c₁ and b-y colors during light cycles, the stars being redder in b-y when brightest. 48Lib shows a complex color behaviour, exhibiting two minima during a V/R cycle and a pronounced b-y drop just at maximum light. In addition, this star shows enigmatic, non-periodic, eclipse-like features in its light curve. In general, the V/R-photometric observations can be grouped in three main groups, depending on the degree of correlation exhibited by the V/R ratio and the photometric fluxes and the rate of change of the uflux. These groups are compatible with prograde global disk oscillations observed under different system inclinations.

1997, A&A, 326, 1167

Long-Term Photometry of Be stars III: Evidence for periodic outbursts of $\lambda$ Eri and photometric activity in HR2142.

R.E. Mennickent¹, C. Sterken², N. Vogt^3,4
¹Dpto. de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Concepción, Casilla 4009, Concepción, Chile.
²University of Brussels (VUB), Pleinlaan 2, 1050 Brussels, Belgium.
³Grupo de Astrofísica, Universidad Católica de Chile, Casilla 314, Santiago, Chile.
⁴Sternwarte Sonneberg, Sternwartenstr. 32, D-96515 Sonneberg, Germany.

Strömgren differential uvby photometry of $\lambda$ Eri and HR2142 is analyzed. The data were taken during the time interval 1983-1994 in the framework of the Long-Term Photometry of Variables project at La Silla. $\lambda$ Eri exhibited four photometric events (probably associated with line emission episodes) that last several months and which were characterized by a common pattern of change in all passbands ( $\sim \pm 10^{-3}$ mag/day) along with an apparent decrease of the amplitude of the short-term variability and an increase of the stellar temperature. A search for periodicities reveals that these events fit a 486d recurrence time. On the other hand, HR2142 showed a relatively ``quiet" long-term photometric behaviour, the orbital period being detected only marginally in the photometric data set. In contrast, a 344d period optimally fits the data. We discuss the possibility of an internal ``clock" regulating the outburst activity of $\lambda$ Eri and show that the photometric variability of HR2142 can hardly be explained by its interacting binary nature. We also discuss an empirical relationship found between $\frac{\partial c_{1}}{\partial u}$ and v sini in a sample of 11 Be stars.

1998, A&A, 330, 631

On the inner envelope of the Be star Gamma Cas

Ph. Stee, F. Vakili, D. Bonneau and D. Mourard
GI2T, Fresnel, Observatoire de la Côte d'Azur, F-06740 Caussols, France

We report the first spectrally-resolved observations of the Be star $\gamma$ Cas in the He I $\lambda 6678$ and H $\beta$ emission lines using the Grand Interféromètre à 2 Télescopes in the southern France. Milliarcsecond angular resolution measurements were carried in both lines and their neighbouring continuum during October and November 1993. The He I $\lambda 6678$ and H $\beta$ maximum emissions correspond respectively to 1.05 and 1.5 of the local continuum level. The interferometric baselines ranged from 15 m to 51 m on the sky which correspond to angular resolutions of 9 to 3 mas at HeI $\lambda 6678$ and 6.5 to 2 mas at H $\beta$ wavelengths. We compare these values to predicted extents of H $\beta$ and He I $\lambda 6678$ components of the circumstellar gas from models of radiative transfer in these lines. We conclude that the emitting region must be smaller than 8.5 stellar radius in H $\beta$ and close to 2.3 stellar radius in He I $\lambda 6678$ which is, for He I $\lambda 6678$ , smaller than the nearby continuum extent. These results confirm $\gamma$ Cas basic parameters for this star obtained by Stee et al. in 1993 from their model constrained by GI2T observations in the H $\alpha$ line.

1998, A&A, 332, 268

The Equatorial Disc of the Be Star X Persei

J.H. Telting^1,2, L.B.F.M. Waters¹, P. Roche³, A.C.A. Boogert⁴, J.S. Clark⁵, D. de Martino^6,7, and P. Persi⁸
¹Astronomical Institute Anton Pannekoek, University of Amsterdam, and Center for High Energy Astrophysics, Kruislaan 403, 1098 SJ Amsterdam, Netherlands
²Isaac Newton Group of Telescopes, ASTRON/NFRA, Apartado 321, 38780 Santa Cruz de La Palma, Spain
³Astronomy Centre, CPES, University of Sussex, Falmer, Brighton, BN1 9QH, UK
⁴Kapteyn Institute, p.o. box 800, NL-9700 AV Groningen, Netherlands
⁵Physics Department, University of Southampton, Southampton, SO17 1BJ, UK
⁶ESA IUE Observatory, VILSPA, Villafranca, Apartado 50727, 28080 Madrid, Spain
⁷Osservatorio Astronomico di Capodimonte, via Moiariello 16, I-80131 Napoli, Italy
⁸Instituto di Astrofisica Spaziale CNR, C.P. 67, I-00044 Frascati, Italy

We have studied the long-term behaviour of the equatorial disc of the Be/X-ray binary X Persei, combining new low-resolution IUE spectra and IR photometry with UV, optical and IR observations collected from the literature.

We find that the near-UV continuum level of X Per varies along with the optical brightness. From the UV observations we find that during optical high states the flux excess due to the intrinsic stellar variability and/or electron scattering in the disc is at most 15-20% of the photospheric flux.

>From the data taken in discless and near-discless states (optical low states) we derive that the stellar photosphere can be modelled with $\rm T_{eff}$ =31,000K and log(g)=4. With this model we derive E(B-V)=0.39 and estimate the distance to X Per as 950(200) parsec (assuming $\rm R_{*} = 9 R_{\odot}$ ).

We fit the (quasi-)simultaneous optical and IR photometry with a simple disc model including free-bound and free-free radiation. We find that the density of the disc at the photosphere of the star varies along with the brightness of X Per, and that in optical high states the disc in X Per is among the densest of all Be stars: $\rm\rho_{0} = 1.5(0.3) \times 10^{-10} g cm^{3}$ . The disc density at the photosphere varies by a factor of at least 20 from optical high to low states.

During disc build-up and break-down phases, and also in phases when the disc is relatively stable, we find a very steep radial density gradient of the disc of X Per. This may reflect the limitations of some of the assumptions in our model.

We find that in a disc-loss event the disc loses mass at a rate of about $\rm 5 \times 10^{-9} M_{\odot}/year$ . For a disc build-up phase we find a disc-mass growth rate of about $\rm 4 \times 10^{-9} M_{\odot}/year$ . This growth rate is consistent with a model that feeds the disc from the ``ordinary'' mass loss of the star, but we cannot exclude that other phenomena contribute to the disc growth as well.

1998, MNRAS, 296, 785

The Development and Behavior of an Active Region On/Near the Photosphere of the B2e Star $\mu$ Centauri

Geraldine J. Peters
Space Sciences Center, University of Southern California, University Park, Los Anglees, CA 90089-1341, USA

An unusual mass loss event observed in the B2e star $\mu$ Cen during the course of 5 days in 1994 April is described and discussed within the framework of contemporary ideas on the Be phenomenon. The onset of the activity occurred in less than $\rm 1^{d}$ and was characterized by variable emission in He I $\lambda$ 6678 that displayed a distinctive character. Unlike the transient microemission in He I that frequently occurs in $\mu$ Cen and other Be stars, the emission line variations seen in this event took place more slowly in three discrete velocity intervals. On two occasions, violet (v) and red (r)-shifted emission components declined on a time scale of < 2 hr, while the emission at/near the line center increased. The short time scale and observed velocity behavior suggest the site of the activity was near the photosphere. The possible importance of nonradial pulsations and magnetic fields in precipitating the event is discussed. A scenario is suggested to explain the observations in which material originating from an active site on the photosphere is injected into a slab. Layers in the active region become visible in He I $\lambda$ 6678 as the prevailing density builds to values favorable for the production of this emission line. It is estimated that the slab covered $\sim$ 30% of the star. A 22% increase in the H $\alpha$ emission strength by the final day of the observations indicates that the activity did indeed add material to the circumstellar disk.

Accepted by Astrophysical Journal Letters
Preprints from gjpeters@mucen.usc.edu

B[e] stars. IV. HD 45677=MWC 142

Yvette Andrillat¹, Carlos Jaschek², and Mercedes Jaschek³
¹Laboratoire d'Astronomie (072), Université de Montpellier - URA 1280 et 1981, CNRS, Place Eugne Bataillon, F-34095 Montpellier, France
²Observatoire de Strasbourg - URA 1280, CNRS-11, rue de l'Université, F-67000,Strasbourg, France
³deceased

On the basis of spectroscopic CCD material obtained at the Haute Provence Observatory, we provide line identifications and equivalent width measurements in the wavelength regions 3750-5112 and 7065-10212 A of the spectrum of HD 45677 Over 235 features are identified and a comparison of our results with those of other authors is provided. We also discuss the variability of the lines using equivalent widths and the line spectrum. We conclude that the gaseous shell surrounding the star has a temperature of the order of 7000 K and that its distance to the star is less than ten stellar radii. We discuss the similarity of this star to other stars previously analyzed.

1997, A&AS, 124, 441

B[e] stars V. HD 50138=MWC 158

Carlos Jaschek¹, Yvette Andrillat²
¹Observatoire de Strasbourg, URA 1280, CNRS-11, rue de l'Université, F-67000,Strasbourg, France
²Laboratoire d'Astronomie (072), Université de Montpellier - URA 1280 et 1981, CNRS, Place Eugne Bataillon, F-34095 Montpellier, France

On the basis of spectroscopic CCD material obtained at the Haute Provence Observatory, we provide line identifications and equivalent width measurements in the wavelength region 3738 -10232 Åof the spectrum of HD 50138 Over two hundred features are identified and a comparison of our results with those of other authors is provided. We also discuss the variability of the lines using equivalent widths and descriptions of the line spectrum. We attribute as a best compromise a spectral type of B5 III. We conclude that the gaseous shell surrounding the star has a temperature of the order of 10,000 K and that its distance to the star is of the order of two stellar radii. We discuss the relation of this star to others previously analyzed and warn against hasty generalizations.

1998, A&AS, 128, 475

On the nature of the Be phenomenon 1. The case of Omega CMa

P. Harmanec
Astronomical Institute, Academy of Sciences, CZ 251 65 Ondrejov, Czech Republic
Internet: hec@sunstel.asu.cas.cz, hec@mbox.cesnet.czls

The main purpose of this paper is to demonstrate the extreme complexity of the observed variations of Be stars on the example of a well-observed bright Be star $\omega$ CMa. A detailed analysis of all published radial velocities and a representative set of photometric and spectral observations of this star led to the following firm conclusions:

At least three and possibly four different time scales of variability of $\omega$ CMa, ranging from 1.37 d to more than 40 years, could be identified.
The correct mean period of the RV and line-profile changes is 1.371906 d, not 1.3667 d as derived earlier.
The brightness of the object and the strength of the Balmer emission vary in an apparent cycle of several thousands of days. The long-term brightness and emission-line changes can be understood as consequences of the formation and gradual dispersal of a gaseous envelope which is flattened and seen more face-on than equator-on. During each episode, the envelope grows from an optically thick pseudophotosphere to a more extended and optically thin envelope.
Existence of much smaller episodes of light brightening which can have the same cause (though on a more limited scale) has clearly been demonstrated.
The amplitude of the 1.37 d RV curve varies on a time scale somewhere between 10 and 300 d.

The following conclusions are less certain and represent possible alternatives to be tested by future, systematic and homogeneous observations:

Some evidence is presented that the amplitude of the 1.372 d RV variations, local mean RV and brightness of the object, prewhitened for the long-term changes, all vary on a time scale of about 35 d, possibly with a period of 34.675 d.
The O-C deviations of the local epochs of RV maxima from a linear ephemeris for the 1.372 d period seem to be undergoing a slow and probably cyclic variation in time, being shortest at times when the star is brightest and when a new Be envelope begins to grow. However, the same O-C deviations can also be reconciled with the 34.675 d period. Whatever the true timescale of the O-C deviations is, their behaviour can also be simulated as an interference of several periods, the second most significant period being close to 1.35 d. Several reasons are given why the explanation in terms of one variable period appears more probable.
With the help of both, real and artificial data it is demonstrated that the slow variation of the 1.3719 d period -- if unrecognized -- may be misinterpreted for a multiperiodic variation with several close periods between 1.3 d and 1.45 d. This constitutes a methodological warning for the period analyses of data on some Bn, Be and ``slowly pulsating" B stars.
The cause(s) of the variations with the 1.37 (and 1.345) period(s) and/or the 35 d cycle remain unexplained. It is obvious, however, that these three periods are not mutually independent. The 34.675 d period may be either a real physical period or a beat period between the 1.372 d and 1.345 d periods. In the former case, $\omega$ CMa could be a 34.7 d binary in an eccentric orbit and the periods twice longer than the two periods near 1.4 d would represent the sidereal and synodic rotational periods of the Be primary.
Finally, some speculations are offered in terms of a hierarchical multiple system of three or even four stars.

Investigation of the variability of bright Be stars using Hipparcos photometry

A.M. Hubert and M. Floquet
Observatoire de Paris-Meudon, D.A.S.G.A.L., URA 335 du CNRS, F-92195 Meudon Cedex, France

The high accuracy and the homogeneity of Hipparcos data for bright stars have allowed us to quantify the degree of variability of Be stars. This degree has been found to be highly dependent on the temperature of the star. Rapid variability is the main feature of 86% of early Be and less than 20% of late Be stars taking into account the limit of detection considered. In addition to the Be stars reported in the Hipparcos catalogue (ESA 1997) as short-period variables, we have been able to enlarge the number of detections as well as to confirm periods previously determined. Be stars that show larger amplitude rapid variations are proposed as candidates for a search of multi-periodicity, i.e., as non-radial pulsators. We have also searched for the presence of outbursts and fading events in the Hipparcos data. Outbursts have been frequently and preferentially detected in early Be stars with rather low to moderate $V \sin i$ while fading events seem to be more conspicuous in stars with higher $V \sin i$ . Mid-term and long-term variations have also been investigated. Several stars have shown some evidence of quasi-periodic oscillations ranging between 10 and 200 days. Finally information concerning long-term variations is reported. Cycles shorter than or equal to the Hipparcos mission have mainly been detected in stars earlier than B6. Long-term time scales of late Be stars are confirmed to be longer by far.

Accepted by A&A
Preprints from Anne-Marie.Hubert@obspm.fr

Luminous Magnetic Rotator Theory

J. P. Cassinelli
Department of Astronomy, University of Wisconsin, 475 N. Charter St., Madison, WI 53706, U.S.A.

This paper decsribes the development of a wind theory that combines forces associated with magnetic rotators with those operating in line driven winds. It has relevance to cyclic variability because if a rotating star has a magnetic field that changes from one longitude sector to the next, the wind speed can also change and this could lead to fast/slow wind co-rotating interaction region. This paper focuses on effects that can increase the radial velocity of a line driven wind within a sector.

To appear in ESO Workshop on `Cyclical Variability in Stellar Winds'
Preprints from cassinelli@madraf.astro.wisc.edu

Large-scale perturbations in the circumstellar envelopes of Be/X-ray binaries

I. Negueruela^1,2, P. Reig², M. J. Coe², & J. Fabregat³
¹Astrophysics Research Institute, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, U.K.
²Physics and Astronomy Department, Southampton University, Southampton, SO17 1BJ, U.K.
³Departmento de Astronomia y Astrofisica, Universidad de Valencia, 46100, Burjassot, Valencia, Spain

We investigate the spectroscopic characteristics of the optical components of Be/X-ray binary systems, using data collected during our seven-year monitoring campaign. We find examples of major changes in the emission line profiles associated with Type II X-ray outbursts, later developing into V/R variability cycles. We show that the time-scales for V/R variability in Be/X-ray transients extend from a few weeks to years and interpret all these changes as due to the presence of global disruptions of the axisymmetric density distribution in the extended envelopes of the Be stars in these systemes. The association between X-ray outbursts and V/R variability, the occurrence of very fast changes and very short quasi-periods of variability displayed by the Be/X-ray binaries lead us to conclude that the presence of the neutron star is an important factor affecting the dynamics of disc-like envelopes. The interaction between the compact companion and the disc would explain the correlation between H $\alpha$ strength and orbital period recently found. The characteristics of the V/R cycles are, however, mainly independent of the binary parameters.

A&A, in press
Preprints from ind@staru1.livjm.ac.uk

Last modified: August 17, 1998

David McDavid
dam3ma@virginia.edu

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