S-type Symbiotic Stars Research Articles

Density asymmetry and wind velocities in the orbital plane of the symbiotic binary EG Andromedae

Context. Non-dusty late-type giants without a corona and large-scale pulsations represent objects that do not fulfil the conditions under which standard mass-loss mechanisms can be applied efficiently. Despite the progress during the past decades, the driving mechanism of their winds is still unknown. Aims. One of the crucial constraints of aspiring wind-driving theories can be provided by the measured velocity and density fields of outflowing matter. The main goal of this work is to match the radial velocities of absorbing matter with a depth in the red giant (RG) atmosphere in the S-type symbiotic star EG And. Methods. We measured fluxes and radial velocities of ten Fe I absorption lines from spectroscopic observations with a resolution of ≈30 000. At selected orbital phases, we modelled their broadened profiles, including all significant broadening mechanisms. Results. The selected Fe I absorption lines at 5151–6469 Å originate at a radial distance ≈1.03 RG radii from its centre. The corresponding radial velocity is typically ≈1 km s−1, which represents a few percent of the terminal velocity of the RG wind. The high scatter of the radial velocities of several km s−1 in the narrow layer of the stellar atmosphere points to the complex nature of the near-surface wind mass flow. The average rotational velocity of 11 km s−1 implies that the rotation of the donor star can contribute to observed focusing the wind towards the orbital plane. The orbital variability of the absorbed flux indicates the highest column densities of the wind in the area between the binary components, even though the absorbing neutral material is geometrically more extended from the opposite side of the giant. This wind density asymmetry in the orbital plane region can be ascribed to gravitational focusing by the white dwarf companion. Conclusions. Our results suggest that both gravitational and rotational focusing contribute to the observed enhancement of the RG wind towards the orbital plane, which makes mass transfer by the stellar wind highly efficient.

DeGaPe 35: Amateur discovery of a new southern symbiotic star

In this work, we present the discovery and characterization of a new southern S-type symbiotic star, DeGaPe 35. We have obtained the low-resolution spectroscopic observations and supplemented them with the photometry from Gaia DR3 and other surveys. The optical spectra of this target show prominent emission lines, including highly ionized [Fe VII] and O VI lines. The cool component of this symbiotic binary is an M4-5 giant with Teff∼3380 – 3470K and luminosity ∼3×103L⊙ (for the adopted distance of 3kpc), the hot component is a shell-burning white dwarf. The photometric observations of the Gaia satellite, published recently in the Gaia DR3 suggested the variability with the period of about 700–800 days, that we tentatively attributed to the orbital motion of the binary.

Optical Time-series Photometry of the Symbiotic Nova V1835 Aquilae

We present time-series CCD photometry in the BVRI passbands of the recently identified symbiotic nova V1835 Aquilae (NSV 11749) over an interval of 5.1 yr with 7–14 day cadence, observed during its quiescence. We find slow light variations with a range of ∼0.9 mag in V and ∼0.3 mag in I. Analysis of these data show strong periodicity at 419 ± 10 days, which we interpret to be the system’s orbital period. A dip in the otherwise-sinusoidal phased light curve suggests a weak ellipsoidal effect due to tidal distortion of the giant star, which in turn opens the possibility that V1835 Aql transfers some of its mass to the hot component via Roche lobe overflow rather than via a stellar wind. We also find evidence that V1835 Aql is an S-type symbiotic star, relatively free of circumstellar dust, and include it among the nuclear burning group of symbiotics. Finally, we provide photometry, periods, and light curve classifications for 22 variable stars in the field around V1835 Aql, about half of which are newly identified.

Formation of the Asymmetric Accretion Disk from Stellar Wind Accretion in an S-type Symbiotic Star

The accretion process in a typical S-type symbiotic star, targeting AG Draconis, is investigated through 3D hydrodynamical simulations using the FLASH code. Regardless of the wind velocity of the giant star, an accretion disk surrounding the white dwarf is always formed. In models where the wind is faster than the orbital velocity of the white dwarf, the disk size and accretion rate are consistent with the predictions under Bondi–Hoyle–Lyttleton (BHL) conditions. In slower-wind models, unlike the BHL predictions, the disk size does not grow, and the accretion rate increases to a considerably higher level, up to >20% of the mass-loss rate of the giant star. The accretion disk in our fiducial model is characterized by a flared disk with a radius of 0.16 au and a scale height of 0.03 au. The disk mass of ∼5 × 10−8 M ⊙ is asymmetrically distributed, with the density peak toward the giant star being about 50% higher than the density minimum in the disk. Two inflowing spiral features are clearly identified, and their relevance to the azimuthal asymmetry of the disk is pointed out. The flow in the accretion disk is found to be sub-Keplerian, at about 90% of the Keplerian speed, which indicates a caveat of overestimating the O vi emission region from the spectroscopy of Raman-scattered O vi features at 6825 and 7082 Å.

Gaia18aen: First symbiotic star discovered by Gaia

Context. Besides the astrometric mission of the Gaia satellite, its repeated and high-precision measurements also serve as an all-sky photometric transient survey. The sudden brightenings of the sources are published as Gaia Photometric Science Alerts and are made publicly available, allowing the community to photometrically and spectroscopically follow up on the object. Aims. The goal of this paper is to analyze the nature and derive the basic parameters of Gaia18aen, a transient detected at the beginning of 2018. This object coincides with the position of the emission-line star WRAY 15-136. The brightening was classified as a “nova?” on the basis of a subsequent spectroscopic observation. Methods. We analyzed two spectra of Gaia18aen and collected the available photometry of the object covering the brightenings in 2018 and also the preceding and following periods of quiescence. Based on this observational data, we derived the parameters of Gaia18aen and discussed the nature of the object. Results. Gaia18aen is the first symbiotic star discovered by Gaia satellite. The system is an S-type symbiotic star and consists of an M giant of a slightly super-solar metallicity, where Teff ∼ 3500 K, a radius of ∼230 R⊙, and a high luminosity L ∼ 7400 L⊙. The hot component is a hot white dwarf. We tentatively determined the orbital period of the system ∼487 d. The main outburst of Gaia18aen in 2018 was accompanied by a decrease in the temperature of the hot component. The first phase of the outburst was characterized by the high luminosity L ∼ 27 000 L⊙, which remained constant for about three weeks after the optical maximum, later followed by the gradual decline of luminosity and increase of temperature. Several re-brightenings have been detected on the timescales of hundreds of days.

Broad Wings around Hα and Hβ in the Two S-type Symbiotic Stars Z Andromedae and AG Draconis

Abstract Symbiotic stars often exhibit broad wings around Balmer emission lines, whose origin is still controversial. We present high-resolution spectra of the S type symbiotic stars Z Andromedae and AG Draconis obtained with the ESPaDOnS and the 3.6 m Canada–France–Hawaii Telescope to investigate the broad wings around Hα and Hβ. When Hα and Hβ lines are overplotted in the Doppler space, it is noted that Hα profiles are overall broader than Hβ in these two objects. Adopting a Monte Carlo approach, we consider the formation of broad wings of Hα and Hβ through Raman scattering of far-UV radiation around Lyβ and Lyγ and Thomson scattering by free electrons. Raman scattering wings are simulated by choosing an H i region with a neutral hydrogen column density N H i and a covering factor CF. For Thomson wings, the ionized scattering region is assumed to fully cover the Balmer emission nebula and is characterized by the electron temperature T e and the electron column density N e. Thomson wings of Hα and Hβ have the same width that is proportional to . However, Raman wings of Hα are overall three times wider than Hβ counterparts, which is attributed to different cross sections for Lyβ and Lyγ. Normalized to have the same peak values and presented in the Doppler factor space, Hα wings of Z And and AG Dra are observed to be significantly wider than their Hβ counterparts, favoring the Raman scattering origin for broad Balmer wings.

Wind asymmetry imprint in the UV light curves of the symbiotic binary SY Mus

Context: Light curves (LCs) of some symbiotic stars show a different slope of the ascending and descending branch of their minimum profile. The origin of this asymmetry is not understood well. Aims: We explain this effect in the ultraviolet LCs of the symbiotic binary SY Mus. Methods: We model the continuum fluxes in the spectra obtained by the International Ultraviolet Explorer at 10 wavelengths, from 1280 to 3080 \AA. We consider that the white dwarf radiation is attenuated by $H^0$ atoms, $H^-$ ions and free electrons in the red giant wind. Variation in the nebular component is approximated by a sine wave along the orbit as suggested by spectral energy distribution models. The model includes asymmetric wind velocity distribution and the corresponding ionization structure of the binary. Results: We determined distribution of the $H^0$ and $H^+$, as well as upper limits of $H^-$ and $H^0$ column densities in the neutral and ionized region at the selected wavelengths as functions of the orbital phase. Corresponding models of the LCs match well the observed continuum fluxes. In this way, we suggested the main UV continuum absorbing (scattering) processes in the circumbinary environment of S-type symbiotic stars. Conclusions: The asymmetric profile of the ultraviolet LCs of SY Mus is caused by the asymmetric distribution of the circumstellar matter at the near-orbital-plane area.

Indication of The High Mass-Transfer Ratio In S-Type Symbiotic Binaries

By modelling H$^0$ column densities in eclipsing S-type symbiotic stars EG And and SY Mus, we derived the wind velocity profile and the corresponding mass-loss rate from their giants. Our analysis revealed a strong enhancement of the wind at the orbital plane.

SS 383: A NEW S-TYPE YELLOW SYMBIOTIC STAR?

Symbiotic stars are key objects in understanding the formation and evolution of interacting binary systems, and are probably the progenitors of Type Ia supernovae. However, the number of known symbiotic stars is much lower than predicted. We aim to search for new symbiotic stars, with particular emphasis on the S-type yellow symbiotic stars, in order to determine their total population, evolutionary timescales, and physical properties. The Two Micron All Sky Survey (2MASS) (J ? H) versus (H ? K s) color-color diagram has been previously used to identify new symbiotic star candidates and show that yellow symbiotics are located in a particular region of that diagram. Candidate symbiotic stars are selected on the basis of their locus in the 2MASS (J ? H) versus (H ? K s) diagram and the presence of H? line emission in the Stephenson & Sanduleak H? survey. This diagram separates S-type yellow symbiotic stars from the rest of the S-type symbiotic stars, allowing us to select candidate yellow symbiotics. To establish the true nature of the candidates, intermediate-resolution spectroscopy is obtained. We have identified the H? emission line source SS?383 as an S-type yellow symbiotic candidate by its position in the 2MASS color-color diagram. The optical spectrum of SS?383 shows Balmer, He I, He II, and [O III] emission lines, in combination with TiO absorption bands that confirm its symbiotic nature. The derived electron density (108-9?cm?3), He I emission line intensity ratios, and position in the [O III] ?5007/H? versus [O III] ?4363/H? diagram indicate that SS?383 is an S-type symbiotic star, with a probable spectral type of K7-M0 deduced for its cool component based on TiO indices. The spectral type and the position of SS?383 (corrected for reddening) in the 2MASS color-color diagram strongly suggest that SS?383 is an S-type yellow symbiotic. Our result points out that the 2MASS color-color diagram is a powerful tool in identifying new S-type yellow symbiotics.

Discovery of the first symbiotic star in NGC 6822★

We report the discovery of the first symbiotic star (V= 21.6, KS= 15.8 mag) in the Local Group dwarf irregular galaxy NGC 6822. This star was identified during a spectral survey of Hα emission-line objects using the Southern African Large Telescope during its performance-verification phase. The observed strong emission lines of H i and He ii suggest a high electron density and T* < 130 000 K for the hot companion. The infrared colours allow us to classify this object as an S-type symbiotic star, comprising a red giant losing mass to a compact companion. The red giant is an asymptotic giant branch (AGB) carbon star, and a semiregular variable, pulsating in the first overtone with a period of 142 d. Its bolometric magnitude is Mbol=−4.4 mag. We review what is known about the luminosities of extragalactic symbiotic stars, showing that most, possibly all, contain AGB stars. We suggest that a much larger fraction of Galactic symbiotic stars may contain AGB stars than was previously realized.

Rotational velocities of the giants in symbiotic stars - II. Are S-type symbiotics synchronized?★

We have measured the projected rotational velocities (v sin i) of the mass donors for 29 S-type symbiotic stars using high resolution spectroscopic observations and the cross-correlation function (CCF) method. The results of the CCF have been controlled with synthetic spectra. The typical rotational velocity of the K and M giants in S-type symbiotics appeared to be 4.5 99%) only for the recurrent nova RS Oph. For 22 S-type symbiotics we give clues as to what their orbital periods could be.

Disentangling the composite continuum of symbiotic binaries

We describe a method of disentangling the composite, 0.12-5 µm continuum of symbiotic binaries. The ob- served SED is determined by the IUE/HST archival spectra and flux-points corresponding to the optical UBVRI and infrared JHKLM photometric measurements. The modeled SED is given by superposition of fluxes from the cool giant, hot stellar source and nebula including the effect of the Rayleigh scattering process and considering influence of the iron curtain absorptions. We applied this method to 21 S-type symbiotic stars during quiescence, activity and eclipses. We isolated four main components of radiation and determined their properties. (i) Stellar radiation from the giant corresponds to a unique luminosity class - normal giants. Characteristic luminosities are 1600 ± 200 and 290 ± 30 Lfor red and yellow giants, respectively in our sample of objects. (ii) Hot object radiation during quiescence consists of the nebular and stellar component. The former radiates at a mean electron temperature of 19 000 K and its amount of emission suggests a mass-loss rate from giants via the wind at u MW = af ew× 10 −7 Myr −1 . Radiation of the latter conforms well with that of a black-body photosphere at a characteristic temperature of 105 000 K. The corresponding effective radii are a factor of ∼10 larger than those of white dwarfs, which thus precludes observing the accretor's surface. Extreme cases of AX Per and V443 Her, for which the hot star temperature from the fit is not capable of producing the nebular emission, signal a disk-like structure of the hot stellar source even during quiescence. (iii) Hot object radiation during activity consists of three components - the stellar and the low- and high-temperature nebular radiation. The stellar radiation satisfies that of a black-body photosphere at a low characteristic temperature of ∼22 000 K (we call it the 1st type of outbursts) or at a very high characteristic temperature of ≈165 000 K (2nd type of outbursts). All the active objects with a high orbital inclination show features of the 1st-type of outbursts (here Z And, AE Ara, CD − 43 ◦ 14304, TX CVn, BF Cyg, CH Cyg, CI Cyg, AR Pav, AX Per), while AG Dra represents the 2nd-type. The presence of a two-temperature type of UV spectrum and an enlargement of effective radii of the stellar source by a factor of ∼10 with respect to the quiescent values during the 1st-type of outburst suggest an expansion of an optically thick medium at the orbital plane in the form of a disk. The low-temperature nebula radiates at a mean electron temperature of 14 000 K and is subject to eclipses, while the high-temperature nebula, which is seen during eclipses as the only component, is characterized by Te > 30 000 K. Radiative and geometric properties of the main sources of radiation allowed us to reconstruct a basic structure of the hot object during the 1st-type of outburst. There is an edge-on disk around the accretor. Its outer flared rim represents a warm pseudopho- tosphere of the hot stellar source, whose radiation is Rayleigh attenuated and affected by the iron curtain absorptions in the neutral gas concentrated at the orbital plane. The low-temperature nebula is placed just above/below the disk with a concentra- tion at its edge as to be subject to eclipses and to see well the central ionizing source. High above/below the orbital plane, there is a hot nebular emitting region.

Spectral and luminosity classification for the cool components in symbiotic stars

The near infrared spectra of 12 S-type symbiotic stars and 78 comparison stars have been observed with moderate dispersion in five runs from 1992 to 1997, the resolving power being R = lambda/Delta lambda > 2000, with a signal to noise ratio SIN > 100. The triple-headed absorption band of TiO (lambda lambda 8432, 8422 and 8452 Angstrom) emerges when a star is later than M2, and the depth of the TiO absorption band is very sensitive to the spectral type (ST) and insensitive to the luminosity class of the star. We fit a curve of spectral type against the index of the absorption depth of this band with a standard deviation sigma = 0.37 of a subdivision of one spectral type. The IR all triplet (lambda lambda 8498, 8542, 8662 Angstrom); Fe I 8689 Angstrom: and Fe I 8675 Angstrom are good luminosity indicators although the equivalent widths (EWs) of these lines clearly decrease fora star later than M3. When the star is a supergiant the lines have a smaller central residual intensity and broader wings than in the case of a normal giant. The Ca II 8662 Angstrom/Fe I 8675 Pi and Fe I 8689 Angstrom/Fe I 8675 A ratios are also good luminosity indicators for Ii-type giants. The latter is particularly useful when there are abundance anomalies. The metal-poor symbiotic star AG Dra is classified as a Ib or II giant, as is TX CVn, on the basis of Fe I 8689 Angstrom/Fe I 8675 Angstrom. 9 other symbiotic stars containing M-type cool components are classified as giants by direct comparison and quantitative analysis. Due to there being no known good ratio indicator of luminosity for M-type stars in the band studied and because there is no metal abundance data for the symbiotic stars studied by us except for AG Dra, the results for these 9 symbiotic stars are only preliminary. The infrared Ca II triplet of most symbiotic stars clearly varies between the different observing runs. The different luminosity classes given to the same symbiotic star are probably caused by the variability of the lines of ionized elements,: while in some cases they are affected by a low metal abundance.

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.

Infrared observations of symbiotic stars

Near infrared measurements in the J, H and K bands have been carried out for a number of symbiotic stars with the 1.5 m telescope at the Rothney Astrophysical Observatory (RAO). A comparison with the earlier observations shows that the S-type symbiotic stars do not have any significant variation in the infrared flux over the past five years. However a small variation ~ 0·3 magnitude in the infrared flux has been detected for CH Cygni. The observations of HM Sagittae show large decreases in the infrared flux compared to the previous measurements. The variability in the infrared fluxes of both these objects could be attributed to a variation in the temperature due to the cooling of the dust shell. The variability observed for V1016 Cygni is found consistent with the previous measurements.

Ultraviolet observations of the symbiotic star AS 296

AS 296 is a well-known S-type symbiotic star which underwent an optical outburst during 1988. In this paper, UV data based on IUE observations obtained both during the quiescent and outburst stages are presented and discussed, correlating them to observations made in the optical region. It is concluded that the object is a symbiotic nova, in which the outburst is due to a thermonuclear runaway produced in the hydrogen-burning shell of a white dwarf with M of about 0.5 solar masses, accreting from the late-type giant at a rate M(acc) of about 9.7 x 10 exp -9 solar mass/year. It is not possible to determine from the observations if the hydrogen flash is degenerate or nondegenerate.

A discussion on the classification and evolution of symbiotic stars

A H-R diagram is drawn from the bolometric luminosities and effective temperatures of 24 symbiotic stars and compared with theoretical evolutionary tracks of Population I metal-rich stars. It is shown that the S-type and D-type symbiotic stars are classified very clearly in course of their evolution and it is suggested that it depends on their cool components, whether it is a normal giant or an asymptotic giant branch star. The recurrent novae are less evolved than classical novae or symbiotic novae.

Properties Of Cool Stellar Components in S-Type Symbiotic Stars

In 1975 Webster and Allen (1975) divided all symbiotic stars into two groups-those in which the 1-4μm continuum show only the presence of a cool star (type S),and those in which dust emission dominates (type D). With the exception of some of yellow symbiotic stars, the dust presence in others correlates with the spectral type of their cool components. That is why one can say that S-type symbiotics contain red giants with spectral type earlier than M6-M7.At the IAU Colloq. N 7Q Allen (1982) noted that it is difficult to escape the conclusion that symbiotic stars contain normal cool giants. Nowadays it is certaiu to be correct because the modern observations of S-type symbiotic stars have not yet discovered any specific distinctions between their cool stellar components and normal red giants. At the same time it should be noted that some of these, for example, Z And, CI Cyg may be interacting binaries in which the cool component apparently fields its Roche lobe and unstable accretion of gas from the red giant onto its hot companion leads to the out bursts of the latter (Kenyon and Webbink 1984; Yudin 1987).

Periodic Variations in the Symbiotic Star Spectra

AbstractPeriodic 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.