Infrared measurements of faint symbiotic stars

Far infrared IRAS measurements and near infrared observational data of nineteen faint symbiotic stars are presented in this paper. From their flux distributions and the near infrared and far infrared colours an attempt is made to study the type of these stars. The colour temperature, dust temperature and mass-loss rates are estimated from the far infrared flux ratios and compared to those of known S and D type symbiotic stars. Probably nine of them are S type, two of them are D type and three of them are D type symbiotic stars. But it is difficult to suggest the type of five stars from the information available.     

Evidence of nebula produced by mass injection from the massive component of a symbiotic star

The analysis of Balmer emission line profiles can provide abundant evidence on the complexity of the CS environment of symbiotic stars. In this work, we have studied the Hγ and Hδ Balmer lines of CH Cygni at four different dates in the period 1991–1995, taken from shortly before the beginning till the decline of the 1992–1994 activity. Because of rapid changes in physical conditions in the emitting region, which lead to striking line-shape variability on very short time scales, we investigated the profiles in the context of the published data, referring to larger time intervals around the dates of our spectra. The results of our spectroscopic observations are given without an assumption of a unique model.     

A comprehensive variability study of the enigmatic WN8 stars: final results

As a conclusion of our all-sky variability survey of the 'enigmatic' variable WN8 stars, we have carried out coordinated multisite photometric and spectroscopic observations of WN8 stars in 1989 and 1994–1995. We confirm the leading role of the stellar core in restructuring the whole wind. This emerges as a statistical trend: the higher the level of the ∼continuum (i.e. ∼core) light variations, the higher the variability of the P Cygni edges of the optical emission lines. However, the form of the correlation between the light and profile variations is generally different for each individual star. The high level of activity of WN8 stars may be supported/induced by pulsational instability.     

Atlas of M7III Spectral Features in the Optical

The difficulties encountered in attempts to study the spectra of very late stars inspired us to prepare this spectral atlas containing essentially spectral features of M7III stars in the optical spectral region. As representative star we took the cool component of the binary symbiotic CH Cygni during one of its quiescent phases. Total number of 920 atomic lines and molecular bands have been identified with different degrees of reliability. This revised version was published online in July 2006 with corrections to the Cover Date.     

ISO Observations of Symbiotic Stars

A number of symbiotic stars have been observed with ISO. In addition to a number of emission lines, SWS observations of the symbiotic novae RR Tel and V1016 Cyg reveal prominent, broad 10 & 18 μm silicate dust features. The 10 μm features are similar to the crystalline silicate profiles seen in classical novae. There is some evidence that the silicate brightness in V1016 Cyg varies with Mira-component phase. However, the silicate feature in RR Tel also showed some variation even though observations were made at very similar Mira-component phases. PHT observations of S-type symbiotic stars show the IR emission to be dominated by the red-giant component. However, an excess in the PHT-P filters from 10 to 15 μm is evident in all the stars, and there may be a broad 3.2 μm absorption feature or a broad 3.8 μm emission feature. At this time we have no adequate physical explanations for any of these features. This revised version was published online in August 2006 with corrections to the Cover Date.     

Palomar Testbed Interferometer Observations of Young Stellar Objects

We present observations of a sample of Herbig AeBe stars, as well as the FU Orionis object V1057 Cygni. Our K-band (2.2μm) observations from the Palomar Testbed Interferometer (PTI) used baselines of 110 m and 85 m, resulting in fringe spacings of ∼4 mas and 5 mas, respectively. Fringes were obtained for the first time on V1057 Cygnias well as V594 Cas. Additional measurements were made of MWC147, while upper limits to visibility-squared are obtained for MWC297, HD190073, and MWC614. These measurements are sensitive to the distribution of warm, circumstellar dust in these sources. If the circumstellar infrared emission comes from warm dust in a disk, the inclination of the disk to the line of sight implies that the observed interferometric visibilities should depend upon hour angle. Surprisingly, the observations of Millan-Gabet, Schloerb and Traub (2001)(hereafter MST) did not show significant variation with hour angle. However, limited sampling of angular frequencies on the sky was possible with the IOTA interferometer, motivating us to study a subset of their objects to further constrain these systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optimization analysis of the light curves of eccentric eclipsing binary systems

The iterative optimization procedures described in a previous paper by the author have been extended to cover unrectified light curves of eccentric eclipsing binary systems. Two stars have been studied in detail: namely, Coronae Borealis and V477 Cygni. In both cases improved element sets have been obtained. Moreover, in the case of V477 Cygni the obtained values of the longitude of periastron for three different light curves are found to provide a useful basis for discussion of the apsidal motion of this system.     

The masses and radii of the components of symbiotic stars

The physical parameters of both the components of fifteen symbiotic stars have been estimated statistically. Data obtained are compared with data available in the literature from photometric and spectroscopic observations. It is found that the mass-radius relations for close binary systems can be applicable for the giant and accreting main-sequence components of symbiotic binaries. Amass-radius relation for the white dwarf components is derived from the linear variation of masses and radii data obtained from observation. These statistical relations can be used to get a rough estimate of masses and radii of the components of symbiotic stars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spectral classification of the cool components of symbiotic stars

We have made near infrared spectroscopic observations of 10 symbiotic and 27 K-M comparison stars. For stars later than M3, we found the band depth of the triple-headed TiO absorption band to be sensitive to temperature and insensitive to gravity. We fitted the spectral type to the band depth with a standard error of 0.22 of a subtype and derived the spectral types for 6 symbiotic stars. We measured the EW of a large number of lines including the CaII lines (very sensitive to luminosity), the FeI and TiO lines (moderately sensitive) and the NaI lines (not sensitive). The EW of these lines vary with the spectral type, particularly for stars later than M3, both spectral type and luminosity effects must be considered. We give the luminosity classes for 10 of the brighter symbiotic stars, they are all giant stars, showing no features of bright giants or supergiants.     

Observational aspects of wind variability

The observational methods to derive information about the instability and variability of winds of hot stars are discussed. The expected effects of blobs and shells in the winds on the P Cygni profiles of the UV resonance lines and on the wind emission lines such as H are described. The evidence for the variability and instability of the winds is derived from the UV observations of Discrete Absorption Components and their variability, the X-ray flickering in compact binaries and the H variations. The evidence for wind variations in Wolf-Rayet stars and Luminous Blue Variables is discussed briefly, as well as a possible explanation for the V/R variations of Be stars.     

Variability of the HeIλ5876 Å line in early type chemically peculiar stars. II

To try to understand the behavior of helium variability in Chemically Peculiar stars, we continued our on‐going observational campaign started by Catanzaro, Leone & Catalano (1999). In this paper we present a new set of time resolved spectroscopic observations of the HeI5876 Å line for a sample of 10 stars in the spectral range B3 ‐ A2 and characterized by different overabundances. This line does not show variability in two stars: HD77350 and HD175156. It shows instead an equivalent width variation in phase with the Hipparcos light curve for two stars: HD79158 and HD196502. Antiphase variations have been found in 4 stars of our sample, namely: HD35502, HD124224, HD129174 and HD142990. Nothing we can say about HD115735 because of the constancy of Hipparcos photometric data, while no phase relation has been observed for HD90044. In the text we discuss the case of HD175156, according to photometric calibration and our spectroscopic observations we rule out the membership of this star to the main sequence chemically peculiar stars. We confirm the results obtained in the previous paper for which phase relations between light, spectral and magnetic variations are not dependent on stellar spectral type or peculiarity subclass.     

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 symbiotic system CH Cygni: An analysis of the shocked nebulae at different epochs

We analyse the line and continuum spectra of the symbiotic system CH Cygni. We adopt the colliding‐wind model to explain the symbiotic system at different phases. Peculiar observed features such as flickering, radio variation, X‐ray emission, as well as the distribution of the nebulae and shells throughout the system are investigated by modelling the spectra at different epochs. The models account consistently for shock and photoionization and are constrained by absolute fluxes. We find that the reverse shock between the stars leads to the broad lines observed during the active phases, as well as to radio and hard X‐ray emission, while the expanding shock is invoked to explain the data particularly during the transition phases (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Infrared photometry for variable stars of selected types in 1978–1999

We present and discuss IR observations for 35 stars of different variability types averaged over many years. These include about twenty symbiotic stars, four W Ser stars and one Algol, six Miras, etc.     

Fast optical variability of SS 433

We study the variability of the optical flux from the peculiar Galactic source SS 433 based on observations with the Russian-Turkish 1.5-m telescope. We describe in detail the technique of highquality photometric measurements with a time resolution of 0.3–1 s using an ordinary CCD. Through test observations of nonvariable stars, we show that atmospheric turbulence introduces no significant distortions into the light curves. Therefore, such data are well suited for studying the aperiodic variability of various objects.     

On the radio spectrum of CI Cygni: a test of popular models for symbiotic stars

We have determined the spectral energy distribution at wavelengths between 6 cm and 850 μm for the prototypical S(stellar)-type symbiotic star, CI Cygni, during quiescence. Data were obtained simultaneously with the Very Large Array and the SCUBA submillimetre (sub-mm) camera on the James Clerk Maxwell Telescope. The data have allowed us to determine the free–free turnover frequency of the ionized component, facilitating a model-dependent estimate of the binary separation to compare with the known orbital parameters of CI Cyg and to critically test the known models for radio emission from symbiotic stars. In particular, our data rule out the two most popular models: ionization of the giant wind by Lyman continuum photons from its hot companion, and emission resulting from the interaction of winds from the two binary components.     

The Na i D resonance lines in main-sequence late-type stars

We study the sodium D lines (D1: 5895.92 Å; D2: 5889.95 Å) in late-type dwarf stars. The stars have spectral types between F6 and M5.5 ( B − V between 0.457 and 1.807) and metallicity between  [Fe/H]=−0.82  and 0.6. We obtained medium-resolution echelle spectra using the 2.15-m telescope at the Argentinian observatory Complejo Astronómico El Leoncito (CASLEO). The observations have been performed periodically since 1999. The spectra were calibrated in wavelength and in flux. A definition of the pseudo-continuum level is found for all our observations. We also define a continuum level for calibration purposes. The equivalent width of the D lines is computed in detail for all our spectra and related to the colour index ( B − V ) of the stars. When possible, we perform a careful comparison with previous studies. Finally, we construct a spectral index  ( R '_D)  as the ratio between the flux in the D lines and the bolometric flux. We find that, once corrected for the photospheric contribution, this index can be used as a chromospheric activity indicator in stars with a high level of activity. Additionally, we find that combining some of our results, we obtain a method to calibrate in flux stars of unknown colour.     

The physical properties of the Hα-emission line stars: CD-42°11721, KK Oph and XX Oph

By use of the data found in the literature, observed at the ESO and taken from the IRAS point source catalogue, the physical properties of the H-emission stars: CD-42°11721, KK Oph and XX Oph were studied photometrically and spectroscopically. The results can be summarized as follows: (a) Feii and [Feii] emission lines show that these stars have a gaseous envelope of which part is of low density. (b) P Cygni profiles in the spectral lines of XX Oph indicate the existence of rapid gaseous motions in its atmosphere. The presence of P Cygni profiles in the spectra of the other two stars is not certain. (c) In the outer atmosphere of CD-42°11721 and KK Oph at least two circumstellar concentrations of dust grains seems to be present; the temperatures of these dust shells are, for both stars, about 1200 and 250 K. (d) XX Oph has an M6III companion causing the infrared excess. Furthermore, we have studied the physical properties of the dust shells. The distances to the central star, the chemical composition and the masses of each shell were estimated. It is recommended to study above stars further with high dispersion spectroscopy and simultaneous long-term photometry.Based partly on data obtained at the ESO, La Silla, Chile and with the Infrared Astronomical Satellite (IRAS).     

Intrinsic properties of carbon stars. I. Effective temperature scale of N-type carbon stars

It is shown that the infrared flux method for determining stellar effective temperatures (Blackwell and Shallis 1977; Blackwell, Petford and Shallis 1980) can be applied to cool carbon stars. Although the spectra of cool carbon stars are highly line blanketed, the spectral region between 3 and 4 μm (L-band in the infrared photometry system) is found to be relatively free from strong line absorption. The ratioR _L of bolometric flux toL flux can then be used as a measure of effective temperature. On the basis of the predicted line-blanketed flux based on model atmospheres, with an empirical correction for the effect of 3 μm absorption due to polyatomic species (HCN, C₂H₂), it is shown thatR _L is roughly proportional to T³ _eff. The high sensitivity ofR _L to T_eff makes it a very good measure of effective temperature, and the usual difficulty due to differential line blanketing effect in the analyses of photometric indices of cool carbon stars can be minimized. It is found that the majority of N-type carbon stars with small variability (SRb and Lb variables) are confined to the effective temperature range between 2400 and 3200 K, in contrast to M-giant stars (M0 III - M6 III, including SRb and Lb variables) that are confined to the effective temperature range between 3200 and 3900 K. The effective temperatures based on the infrared flux method show good agreement with those derived directly from angular diameter measurements of 5 carbon stars. On the basis of the new effective temperature scale for carbon stars, it is shown that the well known C-classification does not represent a temperature sequence. On the other hand, colour temperatures based on various photometric indices all show good correlations with our derived effective temperatures. An erratum to this article is available at .     

Optical properties of the carbon dust grains in the envelopes around asymptotic giant branch stars

We have investigated the optical properties of the carbon dust grains in the envelopes around carbon-rich asymptotic giant branch stars, paying close attention to the infrared observations of the stars and the laboratory-measured optical data of the candidate dust grain materials. We have compared the radiative transfer model results with the observed spectral energy distributions of the stars including IRAS Point Source Catalog and IRAS Low Resolution Spectrograph data. We have deduced an opacity function of amorphous carbon dust grains from model fitting with infrared carbon stars. From the opacity function, we have derived the optical constants of the AMC grains. The optical constants satisfy the Kramers–Kronig relation and produce the opacity function that fits the observations of infrared carbon stars better than previous works in the wide wavelength range 1–1000 μm. We have used simple mixtures of the AMC and silicon carbide grains for modelling. We have compared the contributions that AMC and SiC grains make to the opacity for the cases of simple mixtures of them and spherical core–mantle type grains consisting of a SiC core and an AMC mantle .