RW Hya Research Articles

High-resolution Optical Spectroscopic Observations of Four Symbiotic Stars: AS 255, MWC 960, RW Hya, and StHα 32*

Abstract We report on the analysis of high-resolution optical spectra of four symbiotic stars: AS 255, MWC 960, RW Hya, and StHα32. We employ the local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral analysis code moog to analyze the spectra. The abundance of barium and carbon was derived using the spectral synthesis technique. The chemical composition of the atmospheres of AS 255 and MWC 960 show that they are metal-poor K giants with metallicities of −1.2 and −1.7 respectively. StHα32 is a CH star and also a low-metallicity object (−1.4). AS 255 and MWC 960 are yellow symbiotic stars and, like other previously studied yellow symbiotics, are s-process enriched. StHα32, like other CH stars, is also an s-process and carbon-enriched object. RW Hya has a metallicity of −0.64, a value in accordance with previous determinations, and is not s-process enriched. Based on its position in the 2MASS diagram, we suggest that RW Hya is at an intermediate position between yellow symbiotics and classical S-type symbiotics. We also discuss whether the dilution effect was the mechanism responsible for the absence of the s-process elements overabundance in RW Hya. The luminosity obtained for StHα32 is below the luminosity of the asymptotic giant branch (AGB) stars that started helium burning (via thermal pulses) and became self-enriched in neutron-capture elements. Therefore, its abundance peculiarities are due to mass transfer from the previous thermally pulsing AGB star (now the white dwarf) that was overabundant in s-process elements. For the stars AS 255 and MWC 960, the determination of their luminosities was not possible due to uncertainties in their distance and interstellar absorption. AS 255 and MWC 960 have a low galactic latitude and could be bulge stars or members of the inner halo population. The heavy-element abundance distribution of AS 255 and MWC 960 is similar to that of the other yellow symbiotics previously analyzed. Their abundance patterns follow that of the thick disk population for RW Hya and of the halo population for AS 255, MWC 960, and StHα32. We also determined the rotational velocities of these four symbiotic stars and compare our results with those of single field stars.

FUSE Spectroscopy of the Accreting Hot Components in Symbiotic Variables.

We have conducted a spectroscopic analysis of the far ultraviolet archival spectra of four symbiotic variables, EG And, AE Ara, CQ Dra and RW Hya. RW Hya and EG And have never had a recorded outburst while CQ Dra and AE Ara have outburst histories. We analyze these systems while they are in quiescence in order to help reveal the physical properties of their hot components via comparisons of the observations with optically thick accretion disk models and NLTE model white dwarf photospheres. We have extended the wavelength coverage down to the Lyman Limit with FUSE spectra. We find that the hot component in RW Hya is a low mass white dwarf with a surface temperature of 160,000K. We re-examine whether or not the symbiotic system CQ Dra is a triple system with a red giant transferring matter to a hot component made up of a cataclysmic variable in which the white dwarf has a surface temperature as low as ∼20,000K. The very small size of the hot component contributing to the shortest wavelengths of the FUSE spectrum of CQ Dra agrees with an optically thick and geometrically thin (∼4% of the WD surface) hot (∼ 120, 000K) boundary layer. Our analysis of EG And reveals that its hot component is a hot, bare, low mass white dwarf with a surface temperature of 80-95,000K, with a surface gravity log(g) = 7.5. For AE Ara, we also find that a low gravity (log(g) ∼ 6) hot (T ∼ 130, 000K) WD accounts for the hot component.

Chemical abundance analysis of symbiotic giants – I. RW Hya and SY Mus

The study of symbiotic systems is of considerable importance in our understanding of binary system stellar evolution in systems where mass-loss or transfer takes place. Elemental abundances are of special significance since they can be used to track mass exchange. However, there are few symbiotic giants for which the abundances are fairly well determined. Here, we present for the first time a detailed analysis of the chemical composition for the giants in the RW Hya and SY Mus systems. The analysis is based on high-resolution (R ∼ 50 000), high signal-to-noise (S/N), near-IR spectra. Spectrum synthesis employing standard local thermal equilibrium (LTE) analysis and atmosphere models was used to obtain photospheric abundances of CNO and elements around the iron peak (Sc, Ti, Fe, and Ni). Our analysis reveals a significantly sub-solar metallicity, [Fe/H] ∼ −0.75, for the RW Hya giant confirming its membership in the Galactic halo population and a near-solar metallicity for the SY Mus giant. The very low 12C/13C isotopic ratios, ∼6–10, derived for both objects indicate that the giants have experienced the first dredge-up.

UV emission line shifts of symbiotic binaries

Relative and absolute emission line shifts have been previously found for symbiotic binaries, but their cause was not clear. This work aims to better understand the emission line shifts. Positions of strong emission lines were measured on archival UV spectra of Z And, AG Dra, RW Hya, SY Mus and AX Per and relative shifts between the lines of different ions compared. Profiles of lines of RW Hya and Z And were also examined. The reality of the relative shift between resonance and intercombination lines of several times ionised atoms was clearly shown except for AG Dra. This redshift shows a well defined variation with orbital phase for Z And and RW Hya. In addition the intercombination lines from more ionised atoms and especially OIV are redshifted with respect to those from less ionised atoms. Other effects are seen in the profiles. The resonance-intercombination line shift variation can be explained in quiescence by P Cygni shorter wavelength component absorption, due to the wind of the cool component, which is specially strong in inferior conjunction of this cool giant. The velocity stratification permits absorption of line emission. The relative intercombination line shifts may be connected with varying occultation of line emission near an accretion disk, which is optically thick in the continuum.

Notices to investigation of symbiotic binaries IV. Optical light curves from the near-ultraviolet

The aim of this note is to reconstruct optical light curves (LC) from the near-UV fluxes of the ultraviolet spectra of symbiotic binaries during their quiescent phases. The method is based on the fact that the nebular component of radiation dominates the near-UV during quiescent phases and represents the main source of the light variability in the optical. We demonstrate this approach on example of two quiet symbiotic stars, SY Mus and RW Hya. Using their IUE spectra we determined U and B magnitudes in the standard Johnson system. Values derived from the near-ultraviolet are fainter then those measured photometrically by Δ U ≈ 0.2 and Δ B ≈ 0.4 . This difference is due to emission lines.

Fe II Fluorescence in Symbiotic Stars

AbstractFe II fluorescence by PAR has been investigated in eight symbiotic stars having a wide range in temperature of the hot component and orbital period. The data used are spectra obtained from the IUE archive. All pumping lines investigated in this work are in the short wavelength region of IUE (1200-2000 Å), except for He ɪɪ λ1084.942 and O VI λ1032.041. The resulting Fe ɪɪ fluorescence lines are mainly in the long wavelength region (2000-3300 Å), but a few fall in the same region as the pumping lines. The aim is to understand the optimal conditions for formation of Fe ɪɪ fluorescence lines caused by PAR. Three of the selected systems, RR Tel, AG Peg and V1016 Cyg, have 10-30 active Fe ɪɪ channels. Two conditions connect those systems to each other: The hot component is a white dwarf of extreme temperature (80·103-150·103 K) and all three systems are so called symbiotic novae and have had outbursts during the last 150 years. Three systems, AG Dra, RW Hya and R Aqr, have only 2-3 active Fe ɪɪ channels. In the two remaining systems, CI Cyg and T CrB, Fe ɪɪ fluorescence lines were totally absent. These two systems have two features in common: The emission strength of highly ionized elements is less than in most symbiotic systems, and the hot component is suspected to be an accreting main sequence star rather than a white dwarf.

An [ITAL]IUE[/ITAL] and [ITAL]HST[/ITAL] Archival Study of the Hot White Dwarf in the Symbiotic Variable RW Hydrae

We have carried out an ultraviolet spectroscopic study of the hot white dwarf in the eclipsing S-type symbiotic variable RW Hydrae (Porb = 370.2 days). Our study used orbital phase–resolved IUE archival low-resolution and high-resolution spectra and Hubble Space Telescope archival spectra, including all available images obtained at inferior conjunction (when the accreting hot white dwarf is in front of the red giant). This system is one of less than a handful of symbiotic variables in which the photospheric continuum from the hot white dwarf is the dominant source of light in the far-UV. We have found N V features characteristic of an outflow with velocity of approximately 170 km s-1, almost certainly associated with outflow from the white dwarf, as they are present only in those phases in which the white dwarf is visible. We have also performed the first model atmosphere synthetic spectral fit to the white dwarf–dominated far-UV continuum and found that the best fit was provided by a model with solar abundances, log g = 8, and a temperature of 41,000 K, considerably cooler than estimates of the temperature based on Zanstra techniques. We cannot exclude the possibility that the hot component is hidden by an accretion curtain and that our temperature does not characterize the accreting white dwarf's true photospheric temperature. For a measured red giant wind mass-loss rate of 1 × 10-7 M⊙ yr-1 and a wind accretion efficiency of 7%, we estimate = 7 × 10-9 M⊙ yr-1. The heating at this rate of accretion cannot maintain the white dwarf surface temperature even close to what we have derived. At the surface luminosity implied by our fitting, the required accretion rate for steady nuclear burning is a factor of 20 lower than the above accretion rate. Based on these results, we conclude that the hot component of RW Hya is a young (lower limit age of 1.6 Myr), accretion-heated white dwarf, very likely with nuclear shell burning, on its final cooling track.

3D Hydrodynamical Simulations of Colliding Wind Binaries: TheoryConfronts Observations

The link between gas dynamical models and observations is crucial. The general progress in numerical simulations must be accompanied by predictions for observable quantities, which not only allow to test the models or parts of them against observations but which also improve the understanding of observational data. In this paper we focus on predictions for observations, for three examples of 3Dhydrodynamical simulations of binary star systems, and the techniques required for their derivation. The examples include synthetic, optically thin Doppler broadened line profiles for colliding wind symbiotic binaries, the UV light curve of an accretion model for the symbiotic binary RW Hya, and the X-ray light curve of the WR+O binaryγ Velorum. The main purpose is to emphasize the importance of such studies and to illustrate the capabilities of the emploiedtools. The tools are all contained in the A-MAZE code package we have developed and are publicly available.

Orbital Radial Velocity Curves of Symbiotic Stars

AbstractFor the past 6 years we have been measuring the radial velocity of the M-giant component of Symbiotics Stars with high dispersion echelle spectrographs. Because these velocities are based on the absorption line spectrum of the M-star, very reliable orbital radial velocity curves can be constructed. The orbital solutions derived from these velocity curves allow the approximate size of the binary to be determined, and also provide insight into the origin of the photometric variations seen in these stars. For most of the stars, the photometric variations are due to eclipse or reflection effects (two notable exceptions are Z And and RW Hya). Stars which may be near to filling their Roche lobes are TX CVn, Z And, EG And, UV Aur, and CI Cyg. Stars which do not appear to fill their Roche lobes are AG Dra, RW Hya, and AG Peg.

Spectroscopic observations of the symbiotic binary RW Hydrae

view Abstract Citations (21) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectropscopic Observations of the Symbiotic Binary RW Hydrae Kenyon, Scott J. ; Fernandez-Castro, Telmo Abstract Ultraviolet/optical spectrophotometry and infrared photometry show that the symbiotic binary RW Hya is comprised of an M giant (with L of about 1000 solar luminosities) and a compact object (with L of about 200 solar luminosities) which resembles the central star of a planetary nebula. The luminosity of the hot component is produced by a nuclear shell source which is replenished by the wind of the red giant at a rate of about 10 to the -8th solar mass/yr. Results indicate that the binary is surrounded by an H II region (of radius of about 10 AU) which gives rise to the observed emission lines and radio emission. The He(2+) and O(2+) regions are found to be confined to the immediate vicinity of the hot component. Publication: The Astrophysical Journal Pub Date: May 1987 DOI: 10.1086/165211 Bibcode: 1987ApJ...316..427K Keywords: Binary Stars; Spectral Energy Distribution; Stellar Physics; Stellar Spectra; Stellar Spectrophotometry; Symbiotic Stars; H Ii Regions; Infrared Photometry; Red Giant Stars; Stellar Temperature; Ultraviolet Spectroscopy; Visible Spectrum; Astrophysics; STARS: BINARIES; STARS: SYMBIOTIC full text sources ADS | data products SIMBAD (3) MAST (1) INES (1)

Symbiotic star UV emission and theoretical models

Observations of symbiotic stars in the far UV have provided important information on the nature of these objects. The canonical spectrum of a symbiotic star, e.g. RW Hya, Z And, AG Peg, is dominated by strong allowed and semiforbidden lines of a variety of at least twice ionized elements. Weaker emission from neutral and singly ionized species is also present. The Mg II doublet is usually very strong and may be associated with the M giant primary. A continuum may or may not be present in the 1200 - 2000 A range but is generally present in the range 2000 - 3200 A range, the latter arising from free-free and bound-free emission in the same nebula that is responsible for the UV line emission (CI Cyg, RW Hya, RX Pup). The suspected hot subdwarf continuum is seen in some cases in the range 1200 - 2000 A (RW Hya, AG Peg, SY Mus).

IUE observations of RW Hydrae /gM2 + pec/

Analysis of the intense UV continuum observed between 1100 and 2000 A suggested that observations of the late type star RW Hya is a binary system in which the secondary is the central star of a planetary nebula. The UV spectrum is characterized by semiforbidden and allowed transition lines, of which the C IV doublet is particularly strong. Tidal interaction from the M giant is proposed as a method of forming a nebula with the characteristic densities inferred from the UV line analysis. RW Hya is suggested as a possible source of soft X-ray emission if material is accreting onto the surface of the secondary.

IUE observations of the hot components in two symbiotic stars

Recent IUE observations reveal striking differences in the UV spectra of two symbiotic stars, R Aqr and RW Hya. RW Hya is found to be an unexpectedly intense source of UV radiation. The measurements reported here demonstrate the presence of a hot component in each star, supporting the view that each is a binary system with a luminous red primary and a hot, sub-luminous companion. In one case, the hot companion manifests itself by exciting a compact nebulosity; in the other case we believe that the continuous spectrum of the hot star is directly detected, while the continuum of nebulosity excited by the hot star is detected at longer wavelengths.

Symbiotic Stars at Optical, Infrared and Radio Wavelengths

No paper of this nature should begin without a definition of symbiotic stars. It was Paul Merrill who, borrowing on his botanical background, coined the termsymbioticto describe apparently single stellar systems which combine the TiO absorption of M giants (temperature regime ≲ 3500 K) with He II emission (temperature regime ≳ 100,000 K). He and Milton Humason had in 1932 first drawn attention to three such stars: AX Per, CI Cyg and RW Hya. At the conclusion of the Mount Wilson Ha emission survey nearly a dozen had been identified, and Z And had become their type star. The numbers slowly grew, as much because the definition widened to include lower-excitation specimens as because new examples of the original type were found. In 1970 Wackerling listed 30; this was the last compendium of symbiotic stars published.

Spectroscopic Observations of AX Persei, RW Hydrae, CI Cygni, and Z Andromedae.

view Abstract Citations (29) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopic Observations of AX Persei, RW Hydrae, CI Cygni, and Z Andromedae. Merrill, Paul W. Abstract Data concerning the intensities and displacements of the chief bright lines in the blue-violet portion of the combination spectra of AX Per 013053, RW Hya 132824, CI Cyg 194635, and Z And 232848 are re- ported in considerable detail. Lines observed include those of H, He i, He u, N m, [0 ni], [Ne m], Fe U, [Fe v}, and [Fe vu]. Bright-line stars with absorption spectra of late type may be arranged in five groups. Those charac- terized by bright lines of He ii and/or [0 ml, [Ne iii] are called "combination spectra." Data concern- ing probable periodic variations in the displacements of the bright lines in six combination spectra are summarized. Tentative generalizations are: (1) The displacements of most, if not all, of the lines are variable. (2) A typical range is 30 km/sec. Permitted lines exhibit smaller ranges than forbidden lines. (3) The fluctuations are of long period (one to three years). (4) Maxima and minima of the forbidden lines occur about one-fifth of the period after the corresponding phases of permitted lines Publication: The Astrophysical Journal Pub Date: January 1944 DOI: 10.1086/144586 Bibcode: 1944ApJ....99...15M full text sources ADS | Related Materials (1) Reprint: 1944CMWCI.688....1M