Symbiotic Stars

Aims: We are performing a search for symbiotic stars using IPHAS, the INT Hα survey of the northern Galactic plane, and follow-up observations.
Methods: Candidate symbiotic stars are selected on the basis of their IPHAS and near-IR colours, and spectroscopy and photometry are obtained to determine their nature. We present here observations of the symbiotic star candidate IPHAS J205836.43+503307.2.
Results: The optical spectrum shows the combination of a number of emission lines, among which are the high-excitation species of [O iii], He ii, [Ca v], and [Fe vii], and a red continuum with the features of a star at the cool end of the carbon star sequence. The nebular component is spatially resolved: the analysis of the spatial profile of the [N ii]6583 line in the spectrum indicates a linear size of ~ 2.5 arcsec along the east-west direction. Its velocity structure suggests an aspherical morphology. The near-infrared excess of the source, which was especially strong in 1999, indicated that a thick circumstellar dust shell was also present in the system. The carbon star has brightened in the last decade by two to four magnitudes at red and near-infrared wavelengths. Photometric monitoring during a period of 60 days from November 2010 to January 2011 reveals a slow luminosity decrease of 0.2 mag.
Conclusions: From the observed spectrophotometric properties and variability, we conclude that the source is a new Galactic symbiotic star of the D-type, of the rare kind that contains a carbon star, likely a carbon Mira. Only two other systems of this type are known in the Galaxy.
Based on observations obtained with the 2.5 m INT and the 4.2 m WHT telescopes of the Isaac Newton Group of Telescopes and the 1.5 m Carlos Sanchez Telescope, operating on the islands of La Palma and Tenerife at the Spanish Observatories of the Roque de Los Muchachos and Teide of the Instituto de Astrofísica de Canarias; the 2.1 m telescope at San Pedro Martir, Mexico; and the GAPC 0.7 m Ritchey-Chrétien telescope at La Polse di Cougnes, Udine, Italy.

Context. The study of symbiotic stars is essential to understand important aspects of stellar evolution in interacting binaries. Their observed population in the Galaxy is however poorly known, and is one to three orders of magnitudes smaller than the predicted population size. Aims. IPHAS, the INT Photometric Hα survey of the Northern Galactic plane, gives us the opportunity to make a systematic, complete search for symbiotic stars in a magnitude-limited volume, and discover a significant number of new systems. Methods. A method of selecting candidate symbiotic stars by combining IPHAS and near-IR (2MASS) colours is presented. It allows us to distinguish symbiotic binaries from normal stars and most of the other types of Hα emission line stars in the Galaxy. The only exception are T Tauri stars, which can however be recognized because of their concentration in star forming regions. Results. Using these selection criteria, we discuss the classification of a list of 4338 IPHAS stars with Hα in emission. 1500 to 2000 of them are likely to be Be stars. Among the remaining objects, 1183 fulfill our photometric constraints to be considered candidate symbiotic stars. The spectroscopic confirmation of three of these objects, which are the first new symbiotic stars discovered by IPHAS, proves the potential of the survey and selection method.

Because dwarf galaxies are the most abundant type of galaxy, they are crucial for our understanding of the formation and evolution of galaxies. Abundance ratios and their variations as a result of star formation are key constraints in chemical evolution models. Thus, the determination of these abundances in the dwarf galaxies of the Local Universe is extremely important. However, these objects are intrinsically faint, and observational constraints to their evolution can be obtained only for very nearby galaxies. NGC 185 is one of the four brightest dwarf companions of M31. However, unlike the other three -NGC 147, 205 and 221 (M32) -it has an important content of gas and dust. We have obtained deep spectroscopic observations of the Hα emitting population of NGC 185 using the Gemini multi-object spectrograph at the Gemini North telescope. As a result, in addition to the bright planetary nebulae (PNe) previously found in the galaxy and reported in the literature, we have found other, much fainter, PNe. We have then recalculated the electron temperatures and chemical abundances of the brightest PNe and, for the first time, we have derived their electron densities. Our characterization of the population properties of the PNe is interpreted in terms of the chemical evolution of NGC 185, which suggests that it has suffered a significant chemical enrichment within the last ∼8 Gyr. We have also discovered the first symbiotic star in the galaxy and we have determined the properties of a known supernova remnant located close to the centre of NGC 185.

In this Letter, we report the detection of an emission feature around 6545Å in the spectra of the bipolar planetary nebula M2-9 and the symbiotic stars RR Telescopii and He 2-106 and propose to identify it as the He II Raman scattered feature. This feature was predicted by Nussbaumer, Schmid & Vogel (1989), who suggested that it is formed through Raman scattering by atomic hydrogen of He II n = 6 → n = 2 photons with slightly shorter wavelength than that of Lyβ. The scattering cross section ∼ 10 −20 cm 2 for this process implies the existence of a neutral hydrogen component with a column density N HI ∼ 10 20 cm −2 around the He II emission regions in these objects, which are believed to be associated with the mass loss process in the late stage of stellar evolution. Brief discussions on the astrophysical implications of Raman scattering in these objects are presented.

Important similarities between the objects M1-92, a proto-planetary nebula of bipolar morphology, and MWC 560, a symbiotic star with a jet, have been found. A brief review of the previous studies for both objects is presented for the purpose of proposing mechanisms that best explain these similarities, since up to now both objects have been studied independently. From the comparison of the spectra of both objects, the existence of a jet is confirmed for the proto-planetary nebula M1-92, as well as its binary nature and the existence of a circumnuclear disk. Finally, an evolutionary sequence is proposed for the two objects where M1-92 is ~900 yr more evolved than MWC 560.

Variable Star Network (VSNET) is a global professional-amateur network of researchers in variable stars and related objects, particularly in transient objects, such as cataclysmic variables, black hole binaries, supernovae and gamma-ray bursts. The VSNET has been playing a pioneering role in establishing the field of transient object astronomy, by effectively incorporating modern advance in observational astronomy and global electronic network, as well as collaborative progress in theoretical astronomy and astronomical computing. The VSNET is now one of the best-featured global networks in this field of astronomy. We review on the historical progress, design concept, associated technology, and a wealth of scientific achievements powered by the VSNET.

We report observations of the flickering variability of the recurrent nova RS Oph at quiescence on the basis of simultaneous observations in five bands (UBVRI). RS Oph has a flickering source with (U - B)0 = -0.62 +/- 0.07, (B - V)0 = 0.15 +/- 0.10 and (V - R)0 = 0.25 +/- 0.05. We find for the flickering source a temperature Tfl ~ 9500 +/- 500K, and luminosity Lfl ~ 50-150Lsolar (using a distance of d = 1.6kpc). We also find that on a (U - B) versus (B - V) diagram, the flickering of the symbiotic stars differs from that of the cataclysmic variables. The possible source of the flickering is discussed. The data are available upon request from the authors. Based on data from Bulgarian observatories Rozhen and Belogradchik.

Detection of close binary central stars with periods of less than a day is now well-tested and routinely possible via photometric monitoring. For wide binary central stars with periods of weeks to years detection techniques are still in their infancy. Radial velocity monitoring programs are yet to be applied to very large samples and the method suffers from large systematic errors as well as intrinsic wind variability. One alternative we are exploring is the detection of dense circumstellar nebulae residing around a wide companion. The archetype of this class is EGB6 as revealed by HST imaging (Bond 2009). Here we present spectroscopic evidence for other EGB6-like central stars and discuss their relationship to symbiotic stars. A probable 12.5-day irradiated binary is also presented to demonstrate the limits of the photometric monitoring technique.

Aims:In this paper, we analyse the spectra of D-type SS H1-36 within a colliding-wind scenario. We aim to analyse the properties of this object by taking the observational data along the whole electromagnetic spectrum into account, in order to derive a self-consistent picture able to interpret the nature of the system as a whole.
Methods: After constraining the relative physical conditions by modelling more than 40 emission lines from radio to UV, we are able to explain the continuum spectral energy distribution by considering all the emitting contributions arising from both the stars, the dust shells, and the gaseous nebulæ.
Results: A comprehensive model of the radio spectra allows reproduction of the different slopes of the radio profile and the turnover frequency, as well as the different sizes of the observed shocked envelope at different frequencies in the light of the contributions from the expanding and reverse nebulæ. The IR continuum unveils the presence of two dust shells with different radii and temperatures, which might be a distinctive feature of D-type symbiotic systems as a class of objects. The broad profiles of IR lines direct us to investigate whether an X-ray jet may be present.
Conclusions: This insight leads us to indicate H1-36 as a promising X-ray target and to encourage observations and studies that consistently take the complex nature of symbiotic stars into account throughout the whole electromagnetic spectrum.

Aims. We investigate the dynamics of the nebula around the symbiotic star Hen 2-147, determine its expansion parallax, and compare it with the distance obtained via the period-luminosity relation for its Mira variable. Methods. A combination of multi-epoch HST images and VLT integral field high-resolution spectroscopy is used to study the nebular dynamics both along the line of sight and in the plane of the sky. These observations allow us to build a 3D spatio-kinematical model of the nebula, which, together with the measurement of its apparent expansion in the plane of the sky over a period of 3 years, provides the expansion parallax for the nebula. Additionally, SAAO near-infrared photometry obtained over 25 years is used to determine the Mira pulsation period and derive an independent distance estimation via the period-luminosity relationship for Mira variables.

New electron density diagnostic line ratios are presented for the O IV 2s 2 2p 2 P-2s2p 2 4 P and S IV 3s 2 3p 2 P-3s3p 2 4 P intercombination lines around 1400Å. A comparison of these with observational data for the symbiotic star RR Telescopii (RR Tel), obtained with the Space Telescope Imaging Spectrograph (STIS), reveals generally very good agreement between theory and observation. However the S IV 2 P 3/2 -4 P 1/2 transition at 1423.824Å is found to be blended with an unknown feature at 1423.774Å. The linewidth for the latter indicates that the feature arises from a species with a large ionization potential. In addition, the S IV 2 P 1/2 -4 P 3/2 transition at 1398.044Å is identified for the first time (to our knowledge) in an astrophysical source other than the Sun, and an improved wavelength of 1397.166Å is measured for the O IV 2 P 1/2 -4 P 3/2 line. The O IV and S IV line ratios in a sunspot plume spectrum, obtained with the Solar Ultraviolet Measurements of the Emitted Radiation (SUMER) instrument on the Solar and Heliospheric Observatory, are found to be consistent, and remove discrepancies noted in previous comparisons of these two ions.

Symbiotic stars are long-orbital-period interacting binaries characterized by extended emission over the whole electromagnetic range and by complex photometric and spectroscopic variability. In this paper, the first of a series, we present Optical Gravitational Lensing Experiment (OGLE) light curves of all the confirmed symbiotic stars in the Large Magellanic Cloud, with one exception. By careful visual inspection and combined time series analysis techniques, we investigate for the first time in a systematic way the photometric properties of these astrophysical objects, trying in particular to distinguish the nature of the cool component (e.g. semiregular Variable versus OGLE small-amplitude red giant), to provide its first-order pulsational ephemerides and to link all this information with the physical parameters of the binary system as a whole. Among the most interesting results, there is the discovery of a 20 yr-long steady fading of Sanduleak's star, a peculiar symbiotic star known to produce the largest stellar jet ever discovered. We discuss by means of direct examples the crucial need for long-term multi-band observations to get a real understanding of symbiotic and other interacting binary stars. We eventually introduce BOMBOLO, a multi-band simultaneous imager for the Southern Astrophysical Research 4 m Telescope, whose design and construction we are currently leading.

We give a brief summary of common basic characteristics of active phases during the whole (1963-2000) observed symbiotic life of CH Cygni. We identify two types of outbursts: (1) those with pronounced signatures of a high-velocity mass outflow, and (2) those displaying signatures of only a mass inflow to the central star. On the basis of the observed Hα emission, we investigate mass loss from the active star during the period from when radio jets appeared (1984.6) to the most recent activity (1998-2000). A simple expression, which relates the observed Hα luminosity to the mass-loss rate, is derived. We obtained mass-loss rates oḟ

Abell 70 (PN G038.1−25.4, hereafter A 70) is a planetary nebula (PN) known for its diamond ring appearance due a superposition with a background galaxy. The previously unstudied central star is found to be a binary consisting of a G8IV-V secondary at optical wavelengths and a hot white dwarf (WD) at UV wavelengths. The secondary shows Ba II and Sr II features enhanced for its spectral type that, combined with the chromospheric Hα emission and possible 20-30 km/s radial velocity amplitude, firmly classifies the binary as a Barium star. The proposed origin of Barium stars is intimately linked to PNe whereby wind accretion pollutes the companion with dredged-up material rich in carbon and s-process elements when the primary is experiencing thermal pulses on the Asymptotic Giant Branch (AGB). A 70 provides further evidence for this scenario together with the other very few examples of Barium central stars. The nebula is found to have Type-I chemical abundances with helium and nitrogen enrichment, which when combined with future abundance studies of the central star, will establish A 70 as a unique laboratory for studying s-process AGB nucleosynthesis. We also discuss guidelines to discover more binary central stars with cool secondaries in large orbits that are required to balance our knowledge of binarity in PNe against the currently better studied post common-envelope binary central stars.

It is the purpose of this paper to rediscuss the circumstellar properties of S stars and to put these properties in perspective with our current understanding of the evolutionary status of S stars, in particular the intrinsic/extrinsic dichotomy. This dichotomy states that only Tc-rich ('intrinsic') S stars are genuine thermally-pulsing asymptotic giant branch stars, possibly involved in the M-S-C evolutionary sequence. Tc-poor S stars are referred to as 'extrinsic' S stars, because they are the cooler analogs of barium stars, and like them, owe their chemical peculiarities to mass transfer across their binary system. Accordingly, an extensive data set probing the circumstellar environment of S stars (IRAS flux densities, maser emission, CO rotational lines) has been collected and critically evaluated. This data set combines new observations (9 stars have been observed in the CO J = 2 − 1 line and 3 in the CO J = 3 − 2 line, with four new detections) with existing material (all CO and maser observations of S stars published in the literature). The IRAS flux densities of S stars have been re-evaluated by co-adding the individual scans, in order to better handle the intrinsic variability of these stars in the IRAS bands, and possible contamination by Galactic cirrus.

We report the discovery of the first known symbiotic star in IC10, a starburst galaxy belonging to the Local Group, at a distance of ∼750 kpc. The symbiotic star was identified during a survey of emission-line objects. It shines at V =24.62±0.04, V −R C =2.77±0.05 and R C −I C =2.39±0.02 and suffers from E B−V =0.85±0.05 reddening. The spectrum of the cool component well matches that of solar neighborhood M8III giants. The observed emission lines belong to Balmer series, [SII], [NII] and [OIII]. They suggest a low electronic density, negligible optical depth effects and 35,000<T eff <90,000 K for the ionizing source. The spectrum of the new symbiotic star in IC10 is an almost perfect copy of that of Hen 2-147, a well known Galactic symbiotic star and Mira.

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We present photometric and spectroscopic observations of a peculiar slow nova (designated DASCH J075731.1+201735 or J0757) discovered using digitized scans from our DASCH project of the Harvard College Observatory archival photographic plates. The source brightened by about 1.5 magnitudes in B within a year starting in 1942, and then slowly faded back to its pre-outburst brightness from 1943 to ~1950s.

There are some fundamental aspects of the "symbiotic phenomenon" which are poorly understood. Modern technology now allows to observe faint stars with efficient very high resolution spectrographs, such as the SARG mounted at TNG, which will be crucial for our understanding of the nature and evolutionary stage of symbiotic stars and related sytems. Of great importance will be the determination of luminosity, rotation, mass loss, chemical composition of the cool stellar components which is basic for settling the mass transfer in the system and tracing back its past history. High resolution observations are also needed to derive the velocity, temperature and abundance gradients in the nebula, and to unveil peculiar excitation processes.

Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce X-ray emission but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable gamma-ray (0.1-10 GeV) emission from the recently-detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary, and that particles can be accelerated effectively to produce pi0 decay gamma-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.

We report strong evidence for a ∼ 304-day periodicity in the spin history of the accretion-powered pulsar GX 1+4 that is most probably associated with the orbital period of the system. We have used data from the Burst and Transient Source Experiment on the Compton Gamma Ray Observatory to show a clear periodic modulation of the pulsar frequency from 1991 to date, in excellent agreement with the ephemeris proposed by Cutler, Dennis & Dolan (1986). Our results indicate that the orbital period of GX 1+4 is 303.8±1.1 days, making it the widest known low-mass X-ray binary system by more than one order of magnitude and putting this long-standing question to rest. A likely scenario for this system is an elliptical orbit in which the neutron star decreases its spin-down rate (or even exhibits a momentary spin-up behavior) at periastron passages due to the higher torque exerted by the accretion disk onto the magnetosphere of the neutron star. These results are not inconsistent with both the X-ray pulsed flux light curve measured by BATSE during the same epoch and the X-ray flux history from the All-Sky Monitor (ASM) onboard the Rossi X-Ray Timing Explorer.

This paper addresses the question of why metal-deficient barium stars are not yellow symbiotic stars (YSyS). Samples of (suspected) metaldeficient barium (mdBa) stars and YSyS have been collected from the literature, and their properties reviewed. It appears in particular that the barium nature of the suspected mdBa stars needs to be ascertained by detailed abundance analyses. Abundances are therefore derived for two of them, HD 139409 and HD 148897, which reveal that HD 148897 should not be considered a barium star. HD 139409 is a mild barium star, with overabundances observed only for elements belonging to the first s-process peak (Y and Zr). It is only moderately metal-poor ([Fe/H] = −0.4). The evidence for binarity among mdBa stars is then reviewed, using three different methods: (i) radial-velocity variations (from CORAVEL observations), (ii) Hipparcos astrometric data, and (iii) a method based on the comparison between the Hipparcos and Tycho-2 proper motions. An orbit is obtained for HIP 55852, whereas evidence for the (so far unknown) binary nature of HIP 34795, HIP 76605, HIP 97874 and HIP 107478 is presented. No conclusion regarding the binary nature of HIP 11595, HIP 25161 could be reached. Two stars with no evidence for binarity whatsoever (HIP 58596 and BD +3 • 2688) are candidates low-metallicity thermally-pulsing asymptotic giant branch stars, as inferred from their large luminosities. The reason why mdBa stars are not YSyS is suggested to lie in their different orbital period distributions: mdBa stars have on average longer orbital periods than YSyS, and hence their companion accretes matter at a lower rate, for a given mass loss rate of the giant star. The definite validation of this explanation should nevertheless await the determination of the orbital periods for the many mdBa stars still lacking periods, in order to make the comparison more significant.

We discuss the three periods during which the Mira component was heavily obscured by dust as observed in the different wavelength bands. A change in the correlations of J with other infrared magnitudes was observed with the colour becoming redder after JD2446000. Generally, J-K was comparable, while K-L was larger than typical values for single Miras. A distance estimate of 2.5 kpc, based on the IR data, is given. A larger flux decrease for the permitted than for the forbidden Fe II lines, during the obscuration episode studied, has been found. There is no evidence for other correlations with line properties, in particular with wavelength, which suggests obscuration due to separate optically thick clouds in the outer layers.

The rates of proton-and alpha-capture reactions on unstable proton-rich nuclei are needed to understand the energy generation and element synthesis occurring in novae, X-ray bursts, and other explosions. Direct measurements of the cross sections of some of these reactions are now possible with radioactive beams and a recoil separator. A new device for such measurements, the Separator for CApture Reactions [SECAR], is being designed for use at the Facility for Rare Isotope Beams (FRIB). The specifications and preliminary conceptual design will be discussed along with plans for the first set of measurements.

We have analyzed the optical spectra of 67 symbiotic stars and objects suspected of being symbiotic, and found 18 new symbiotic systems. This is the largest homogeneous set of optical spectrophotometric data for symbiotic binaries ever studied. We have derived the reddenings and distances for all systems, estimated the IR classes (S and D) for the new systems, and determined the location of the hot components in the Hertzsprung-Russell diagram.

Barium stars and technetium-poor, extrinsic S stars are binary systems with a white dwarf companion, and with orbital elements similar to those of symbiotic systems. One may thus wonder whether these various families of binary systems involving red giant stars are somehow related. This question is actually twofold: (i) Do barium and binary S stars exhibit some symbiotic activity? (ii) Do symbiotic systems exhibit overabundances of s-process elements like barium and S stars? This paper reviews the current situation regarding these two questions.

Aims:We present a comprehensive and self-consistent modelling of the D' type symbiotic star (SS) HD 330036 from radio to UV.
Methods: Within a colliding-wind scenario, we analyse the continuum, line, and dust spectra by means of SUMA, a code that simulates the physical conditions of an emitting gaseous cloud under the coupled effect of ionisation from an external radiation source and shocks.
Results: We find that the UV lines are emitted from high-density gas between thestars downstream of the reverse shock, while the optical lines are emitted downstream of the shock propagating outwards from the system. As regards the continuum SED, three shells are identified in the IR, at 850 K, 320 K, and 200 K with radii r = 2.8 × 1013 cm, 4 × 1014 cm, and 1015 cm, respectively, after adopting a distance to Earth of d=2.3 kpc. Interestingly, all these shells appear to be circumbinary. Analysis of the unexploited ISO-SWS spectrum reveals that both PAHs and crystalline silicates coexist in HD 330036, with PAHs associated to the internal shell at 850 K, and crystalline silicates stored in the cool shells at 320 K and 200 K. Strong evidence that crystalline silicates are shaped in a disk-like structure is derived on the basis of the relative band strengths. Finally, we suggest that shocks can be a reliable mechanism for activating the annealing and the consequent crystallisation processes.
Conclusions: We show that a consistent interpretation of gas and dust spectra emitted by SS can be obtained by models that account for the coupled effect of the photoionising flux and of shocks. The VLTI/MIDI proposal recently accepted by ESO aims to verify and better constrain some of our results by means of IR interferometric observations.

This paper addresses the question of why metal-deficient barium stars are not yellow symbiotic stars (YSyS). Samples of (suspected) metal-deficient barium (mdBa) stars and YSyS have been collected from the literature, and their properties reviewed. It appears in particular that the barium nature of the suspected mdBa stars needs to be ascertained by detailed abundance analyses. Abundances are therefore derived for two of them, HD 139409 and HD 148897, which reveal that HD 148897 should not be considered a barium star. HD 139409 is a mild barium star, with overabundances observed only for elements belonging to the first s-process peak (Y and Zr). It is only moderately metal-poor ([Fe/H] = −0.4). The evidence for binarity among metal-deficient barium stars is then reviewed, using three different methods: (i) radial-velocity variations (from CORAVEL observations), (ii) Hipparcos astrometric data, and (iii) a method based on the comparison between the Hipparcos and Tycho-2 proper motions. An orbit is obtained for HIP 55852, whereas evidence for the (so far unknown) binary nature of HIP 34795, HIP 76605, HIP 97874 and HIP 107478 is presented. No conclusion regarding the binary nature of HIP 11595, HIP 25161 could be reached. Two stars with no evidence for binarity whatsoever (HIP 58596 and BD +3 • 2688) are candidates low-metallicity thermally-pulsing asymptotic giant branch stars, as inferred from their large luminosities. The reason why mdBa stars are not YSyS is suggested to lie in their different orbital period distributions: mdBa stars have on average longer orbital periods than YSyS, and hence their companion accretes matter at a lower rate, for a given mass loss rate of the giant star. The definite validation of this explanation should nevertheless await the determination of the orbital periods for the many mdBa stars still lacking periods, in order to make the comparison more significant.

Symbiotic stars are binary systems consisting of a hot star, typically a white dwarf, and a cool giant companion. The wind from the cool star is ionized by the radiation from the hot star, resulting in the characteristic combination of sharp nebular emission lines and stellar molecular absorption bands in the optical spectrum. Most of the emission lines are readily identiÐable with common ions. However, two strong, broad emission lines at 6825 and 7082 deÐed identiÐcation with known atoms and ions. In A 1989 Schmid made the case that these long unidentiÐed emission lines resulted from the Raman scattering of the O VI resonance photons at 1032, 1038 by neutral hydrogen. A We present contemporaneous far-UV and optical observations of direct and Raman-scattered O VI lines for nine symbiotic stars obtained with the Hopkins Ultraviolet Telescope (Astro-2) and various ground-based optical telescopes. The O VI emission lines are present in every instance in which the jj6825, 7082 lines are present, in support of the Schmid Raman-scattering model. We calculate the scattering efficiencies and discuss the results in terms of the Raman-scattering model. Additionally, we measure the Ñux of the Fe II Ñuorescence line at 1776 which is excited by the O VI line at 1032 and A , A , calculate the Ðrst estimates of the conversion efficiencies for this process.

Eleven objects that have been reported as proto-planetary nebula or as young planetary nebulae that show very extended Hα wings are presented. The extension of these wings is larger than 800 km s −1. Data for two symbiotic stars that show this same characteristic is also presented. Raman scattering is the mechanism that best explains the wings in 10 of the PNe and in the 2 symbiotic stars. In the PN IRAS 20462+3416 the wing profile can be explained by very intense stellar wind.

The photometric variations of the symbiotic binary AG Dra have been analyzed. Changes in the U band variations in quiescence between orbital cycles are most easily explained by changes in the cool component wind. The small variations of B and V in quiescence seem to require an additional mechanism. Period analysis of the data from the quiescent stage between two outbursts (1986 - 1994) gave a value for the period in the U band near the orbital period. However new periods were detected with the values of 356 and 350 days in the B and V bands respectively, which is strikingly close to the interval between the two large maxima in B and V, seen during activity.

We report results of a spectrophotometric study of SBS 1150+599A and discuss the nature of this object based upon our data. Our study shows that SBS 1150+599A is most probably a planetary nebula located in the Galactic halo and not a cataclysmic variable as originally proposed by the authors of the Second Byurakan Survey from low resolution spectroscopy. We have further elaborated on the properties of SBS 1150+599A (now becoming PN G135.9+55.9) with tools used for planetary nebula analysis. Our photoionization models show that, in order to match the observational constraints, the oxygen abundance in the nebula is probably extremely low, around 1/500 solar, which is one order of magnitude lower than the most oxygen-poor planetary nebulae known so far. This finding has strong implications on our understanding of the formation of planetary nebulae and of the evolution of the Galactic halo.

We present orfeus spectra of the O vi lambda lambda 1032,1038 emission lines in the symbiotic stars AG Dra, V1016 Cyg, RR Tel, CD-43(deg) 14304, AG Peg and Z And. The O vi emission lines can convert into broad and highly polarized emission lines at lambda 6825 and lambda 7082 in a Raman scattering process by neutral hydrogen. From a comparison of direct and Raman scattered radiation we extract new information on the scattering geometry in symbiotic systems. The nebular O vi emission lines are in all objects redshifted by about +40 km s(-1) . This can be explained as a radiative line transfer effect in a slowly expanding emission region. A comparable redshift is measured in the Raman scattered O vi lines. In AG Peg the O vi emissions show beside a narrow nebular line a broad component from a fast stellar wind outflow. Many interstellar absorption lines of molecular hydrogen are detected, particularly near the O vi lambda 1038 component. With model calculations we investigate their im...

We have calculated relative element abundances for a sample of 43 symbiotic stars. Helium abundances and the relative elemental abundances N/O, Ne/O, Ar/O were derived from new spectra collected in the optical range through low dispersion spectroscopy. The He ionic abundances were derived taking into account self-absorption effects in Balmer lines. We found that the symbiotic stars in the galactic bulge have heavy element abundances showing the same wide distribution as other bulge objects. In the galactic disk, the symbiotic stars follow the abundance gradient as derived from different kinds of objects.

We present the results of an extensive campaign of coordinated X-ray (ROSAT) and UV (IUE) observations of the symbiotic star AG Dra during a long period of quiescence (1990-1993) followed by two optical outbursts in 1994 and 1995. The hot component (i.e. X-ray emitting compact object) turns out to be very luminous during the quiescent phase: (9.5+/-1.5)*10^36 (D/2.5 kpc)^2 erg/s. This suggests that the compact object is burning hydrogen-rich matter on its surface even in the quiescent (as defined optically) state at a rate of (3.2+/-0.5)*10^-8 (D/2.5 kpc)^2 M_sun/yr. Assuming a steady state, i.e. burning at precisely the accretion supply rate, this high rate suggests a Roche lobe filling cool companion though Bondi-Hoyle accretion from the companion wind cannot be excluded. We have discovered a remarkable decrease of the X-ray flux during both optical maxima. In the UV these events were characterized by a large increase of the emission line and continuum fluxes. The anticorrelation ...

A highly and rapidly variable bipolar mass outflow from StHα 190 has been discovered, the first time in a yellow symbiotic star. Permitted emission lines are flanked by symmetrical jet features and multi-component P-Cyg profiles, with velocities up to 300 km s −1. Given the high orbital inclination of the binary, if the jets leave the system nearly perpendicular to the orbital plane, the de-projected velocity equals or exceeds the escape velocity (1000 km s −1). StHα 190 looks quite peculiar in many other respects: the hot component is an O-type sub-dwarf without an accretion disk or a veiling nebular continuum and the cool component is a G7 III star rotating at a spectacular 105 km s −1 , unseen by a large margin in field G giants.

We report an identification of the lithium resonance doublet LiI 6708Å in the spectrum of V407 Cyg, a symbiotic Mira with a pulsation period of about 745 days. The resolution of the spectra used was R = λ/∆λ ≈ 18500 and the measured equivalent width of the line is ∼ 0.34Å. It is suggested that the lithium enrichment is due to hot bottom burning in the intermediate mass AGB variable, although other possible origins cannot be totally ruled out. In contrast to lithium-rich AGB stars in the Magellanic clouds, ZrO 5551Å, 6474Å absorption bands were not found in the spectrum of V407 Cyg. These are the bands used to classify the S-type stars at low-resolution. Although we identified weak ZrO 5718Å, 6412Å these are not visible in the low-resolution spectra, and we therefore classify the Mira in V407 Cyg as an M type. This, together with other published work, suggests lithium enrichment can precede the third dredge up of s-process enriched material in galactic AGB stars.

Infrared and optical photometric and spectroscopic observations of the symbiotic nova RR Tel are used to study the effects and properties of dust in symbiotic binaries containing a cool Mira component, as well as showing "obscuration events" of increased absorption, which are typical for such Miras. A set of photometric observations of the symbiotic nova RR Tel in different wavelength bands -visual from 1949 to 2002 and near-infrared (JHKL) from 1975 to 2002 -are presented. The variability due to the normal Mira pulsation was removed from the JHKL data, which were then compared with the American Association of Variable Star Observers' (AAV SO) visual light curve. The changes of the Fe II emission line fluxes during the 1996-2000 obscuration episode were studied in the optical spectra taken with the Anglo-Australian telescope. We discuss the three periods during which the Mira component was heavily obscured by dust as observed in the different wavelength bands. A change in the correlations of J with other infrared magnitudes was observed with the colour becoming redder after JD2446000. Generally, J-K was comparable, while K-L was larger than typical values for single Miras. A distance estimate of 2.5 kpc, based on the IR data, is given. A larger flux decrease for the permitted than for the forbidden Fe II lines, during the obscuration episode studied, has been found. There is no evidence for other correlations with line properties, in particular with wavelength, which suggests obscuration due to separate optically thick clouds in the outer layers.

We report on a BeppoSAX observation of the transient X-ray source XTE J0421+560 during quiescence performed ∼150 days after the 1998 April outburst. The source had an unabsorbed 0.5-10 keV flux of 6.7 × 10 −12 erg cm −2 s −1 and was still remarkably soft with most of the emission below 2 keV. The X-ray spectrum can be fit with the same twotemperature model as the outburst observations. There is evidence for the presence of an Iron emission feature at ∼7 keV. We report also on a series of optical observations performed using the 72 cm Teramo-Normale Telescope (TNT) of the Teramo Observatory, and the 1.5 m Loiano Telescope of the Bologna Observatory. The optical spectrum includes very strong Balmer emission lines, He I, [Fe II], and [O I] features. From the observed L x /L opt ∼ 10 −3 the quiescent optical emission cannot be due to re-processing of the X-rays, but has to be generated in the optical companion or the circumstellar material. Moreover, the quiescent X-ray luminosity cannot be due to the optical star if it is of spectral type OB. Although the nature of the compact object present in the XTE J0421+560/CI Cam system cannot be firmly established, we speculate that it is most probably a white dwarf.

Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce X-ray emission but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable gamma-ray (0.1-10 GeV) emission from the recently-detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary, and that particles can be accelerated effectively to produce pi0 decay gamma-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.