Evolution of the symbiotic star AS 338 after its strong outburst in 1983

The photometric UBV observations of AS 338 that we began after its outburst in 1983 are presented. They were accompanied by yearly spectroscopic observations and by occasional estimations of the star’s infrared JHKL magnitudes. In June 1993, the star’s optical spectrum was extended to the ultraviolet via IUE observations of AS 338. Collectively, the above observations make it possible to trace the evolution of stellar activity over a period of 15 years in various spectral ranges. In particular, a short-time return of the hot component of AS 338 to the state when He II lines reappeared in the star’s spectrum was noted in 1993. At this time, a blend of the C IV λλ5802 and 5812 lines, which is typical of Wolf-Rayet spectra, was detected in it. In June 1993, the temperature of the hot component was T _h ≈ 8.8 × 10⁴ K, and the ratio of its bolometric flux to that of the red giant was F _{h, bol}/F _{g, bol} ≈ 1.0. In August, its temperature increased to ～1.0×10⁵ K, while the bolometric flux dropped by a factor of ～1.5(F _{h, bol}/F _{g, bol} ≈ 0.7). In the B-V, U diagram, the points referring to this so-called quiescent state form a separate group shifted in B-V from all the remaining ones located in a horizontal strip with $\Delta U \approx 3\mathop .\limits^m 5$ and $\Delta (B - V) \approx 0\mathop .\limits^m 4$ . This allows us to diagnose the state of the hot component without spectroscopic observations of the star. In October 1993, the hot component flared up again. The main brightness rise took no more than 19 days. The outburst occurred shortly before eclipse egress of the hot component, whose duration was ～0.01P _orb. In December 1993, F _{h, bol}/F _{g, bol}≤1.5 at maximum light. During the recurrent, even stronger outburst in April 1995, F _{h, bol}/F _{g, bol}≤3.4. The Hαline during outbursts has a P Cyg profile and broad wings stretching to velocities of ±1500 km s^?1. The color temperature of the active hot component at short optical wavelengths and in the ultraviolet lies in the range of effective temperatures for hot supergiants. Nevertheless, it always produces an H II region in the circumstellar envelope that is larger in size than this binary system.     

A minor outburst during the quiescent period of the symbiotic star CH Cygni

We have studied a few optical spectra of the symbiotic star CH Cygni obtained in the period January 1990-June 1991, which indicate that a mild increase of activity occurred between July and December 1990. This increase of activity is confirmed by the IUE observations made in the same period. In fact, in this period of time, we have observed an increase of intensity of all the emission lines both in the optical and ultraviolet ranges and of the continuous ultraviolet flux.Based on observations obtained at the Observatory of Haute Provence (OHP) and on observations by the International Ultraviolet Explorer (IUE) collected at the Villafranca Satellite Tracking Station.     

The far UV spectrum of the Be star AX Monocerotis

In this paper we study the main features of the far UV spectrum of the binary star AX Mon, observed with the IUE satellite at phase 0.568.Ions indicating a large range of ionization stages, going fromCi,Oi,Ni toSiv,Civ,Nv are present.The spectrum is dominated by shell absorption lines of Feii, Feiii, Siiii,Cii, Alii, Mgii and Niii.Two satellite components are clearly indicated in all these lines except for Niii which presents only one. Their mean velocities are +10±5 km s^–1, –75±10 km s^–1, and –260±15 km s^–1.Red emission wings are observed in the Mgii resonant doublet at 2800 Å, which shows a P Cygni profile. Each of the absorption lines of the Mgii doublet is formed by a narrow component, which is blended with the Mgii interstellar line and a broad component, which shows a complex structure.Broad and asymmetrical profiles are observed for the Siiv,Civ, andNv resonance lines with blue edge velocities about –700±30 km s^–1.     

A study of the close binary star TU Monocerotis

New photometric elements,i=89°.5,r _a =0.24,r _b =0.25 andL _a =0.82(Y), 0.88(B), 0.94(U), are deduced for the eclipsing system TU Mon, using the incomplete Fourier method for the analysis of its light curve. They are based upon three-colour photoelectric observations obtained in 1966–68 with the 36-inch reflector of the Okayama Astrophysical Observatory. From discussion combined with the spectroscopic data byDeutsch (1945) and byPopper (1967), it seems fair to conclude that TU Mon is an ordinary semi-detached close binary system consisting of a detached brighter B5V star and an A5 subgiant in contact at its Roche limit.     

Periodic variations in the symbiotic star spectra

Periodic variations of emission line intensities and radial velocities in three S-type symbiotic stars: BF Cyg, CI Cyg and AX Per are presented and discussed. The behavior of emission lines is different in these objects and suggests that significant differences in physical conditions and geometry may occur in these seemingly similar systems.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

The pulsating hydrogen-deficient star LSS 3184 (BX Cir)

We present extensive photometry and spectroscopy of the extremely hydrogen-deficient star, LSS 3184, recently discovered to be a rapid variable (period ∼0.1066 d) strikingly similar to V652 Her. Over 95 h of photometry confirms the reported variability, which is of rather low amplitude (Δ V ∼0.03 mag), defines the light curve with greater precision and establishes a much more accurate ephemeris (period ∼0.106 578 4 d) to form a basis for detecting period change. Attention is drawn to the usefulness of a period-finding technique that fits harmonic components to the photometric observations. Spectroscopy shows a peak-to-peak variation in radial velocity of about 30 km s⁻¹, which, when combined with the photometric observations, confirms the pulsational nature of the variability and strongly indicates that the pulsations are radial in nature.     

UV observations of the symbiotic star EG And

EG And is a S-type symbiotic star. Here is present UV observations made by IUE from 1978 to 1991. From these observations the electronic density and the electronic temperature were obtained. The size of He II emitting region was estimated as 7.3R . Line and continuum variations confirm the binary nature of EG And.     

Orbital eccentricity of the symbiotic star MWC 560

We present projected rotational velocity measurements of the red giant in the symbiotic star MWC 560, using the high‐resolution spectroscopic observations with the FEROS spectrograph. We find that the projected rotational velocity of the red giant is v sin i = 8.2 ± 1.5 km s^–1, and estimate its rotational period tobe P_rot = 144–306 days. Using the theoretical predictions of tidal interaction and pseudosynchronization, we estimate the orbital eccentricity e = 0.68–0.82. We briefly discuss the connection of our results with the photometric variability of the object (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

UV observations of the symbiotic star EG And

EG And is a S-type symbiotic star. Presented are UV observations made by IUE from 1978 to 1991. From these observations the electron density and the electron temperature were obtained. The size of the Heii emitting region was estimated as 7.3R. Line and continuum variations confirm the binary nature of EG And.     

Eclipsing phenomena of the symbiotic star CH Cygni

Eclipsing phenomena of the inner binary with a period of 756 d in the triple symbiotic system CH Cyg may have been detected in detailed spectrophotometric observations. The eclipse of the hot component by the red giant started on 1994 October 11 and finished between 1995 January 8 and 18. The ingress duration was less than one day. The radius of the red giant is estimated to be 288 ± 15 R⊙ from the duration of the eclipse. Assuming the bolometric correction of the red giant (M7 III) as 4, the distance to this object is estimated to be 307 ± 32 pc, which agrees well with that obtained in the observations by Hipparcos . The interstellar extinction in the direction of this object may be much lower than that in the nearby areas. It has been suggested that the outer binary system with an orbital period of about 15 yr is an eclipsing one. It seems unlikely, however, that the variation of the activity of this object with a time-scale of more than 10 yr was a result of eclipses.     

Rapid mass accretion in the symbiotic star AG Dra

The mass accretion process onto the hot component of AG Dra and its explosive phenomena are discussed. The hot component seems to be a massive white dwarf (M>1 M). The mass accretion rate is estimated to be about 10^–7M/year. Many properties of the explosive phenomena agree with those of mild hydrogen flashes expected from this rapid mass accretion.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

The 2016 outburst of the unique symbiotic star MWC 560 (= V694 Mon), its long-term BVRI evolution and a marked 331 days periodicity

After 26 years from the major event of 1990, in early 2016 the puzzling symbiotic binary MWC 560 has gone into a new and even brighter outburst. We present our tight BVR_CI_C photometric monitoring of MWC 560 (451 independent runs distributed over 357 different nights), covering the 2005–2016 interval, and the current outburst in particoular. A stricking feature of the 2016 outburst has been the suppression of the short term chaotic variability during the rise toward maximum brightness, and its dominance afterward with an amplitude in excess of 0.5 mag. Similar to the 1990 event when the object remained around maximum brightness for ∼6 months, at the time Solar conjunction prevented further observations of the current outburst, MWC 560 was still around maximum, three months past reaching it. We place our observations into a long term contex by combining with literature data to provide a complete 1928–2016 lightcurve. Some strong periodicities are found to modulate the optical photometry of MWC 560. A period of 1860 days regulate the occourence of bright phases at BVR_C bands (with exactly 5.0 cycles separating the 1990 and 2016 outbursts), while the peak brightness attained during bright phases seems to vary with a ∼9570 days cycle. A clean 331 day periodicity modulate the I_C lightcurve, where the emission from the M giant dominates, with a lightcurve strongly reminiscent of an ellipsoidal distortion plus irradiation from the hot companion. Pros and cons of 1860 and 331 days as the system orbital period are reviewed, waiting for a spectroscopic radial velocity orbit of the M giant to settle the question (provided the orbit is not oriented face-on).     

Reticon observations of the yellow symbiotic star AG Draconis

Reticon spectroscopic observations of the yellow symbiotic star AG Draconis are reported. Small rapid (15–30 min) changes in the intensities of the Hei λ5015 Å and Hei λ6678 Å singlet lines, and of the Hγ line are observed. The first observational evidence of presence of the unidentified band at 7088 Å in this star is also reported.     

A model for symbiotic star Z Andromedae

An analysis of the results of observations of the symbiotic star Z And has shown that no definite model can be derived at present on their basis. If the hot component is essentially an accreting white dwarf with a hydrogen-burning shell source, then the gas envelope must be optically thin for Lc-emission and itsT _e must be in the neighborhood of 2.6×10⁴K. And if the hot component is a Main-Sequence star with an accretion disk around it, then it is classified with red dwarfs. The electron temperature of the gas envelope must be 1.5×10⁴K. The luminosity of the hot component at the minimum of its visual brightness is only a few times lower than its Eddington limit. Therefore, as the accretion rate goes up, the initial increase in its brightness (U1 ^m .5), unaccompanied by any perceptible changes in the spectrum of Z And, will be followed by disintegration of the regular disk and flare of the star in the visible range. In the same model, partial eclipses of the hot source must occur. They seem to be observable on the star's light curve in theU band. Substitution of a solar-type star for the first-named component in the binary red dwarf + red giant system will lead to a significant decrease in the excitation of the combination spectrum.     

Circumstellar matter in the symbiotic binary CH cyg during its current outburst

We present optical high-resolution spectroscopy and UBV photometry of the symbiotic binary CH Cyg during the current outburst which began in 1992 February.