A barium central star binary in the Type I diamond ring planetary nebula Abell 70

Abell 70 (PN G038.1−25.4, hereafter A 70) is a planetary nebula known for its diamond ring appearance due to 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 at ultraviolet 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 −1 radial velocity amplitude, firmly classifies the binary as a Barium star. The proposed origin of Barium stars is intimately linked to planetary nebulae (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 needed to balance our knowledge of binarity in PNe against the currently better studied post-common-envelope binary central stars.

[1]  R. Corradi,et al.  Discovery of close binary central stars in the planetary nebulae NGC 6326 and NGC 6778 , 2011, 1105.5731.

[2]  C. Corbally,et al.  FIRST DIRECT EVIDENCE THAT BARIUM DWARFS HAVE WHITE DWARF COMPANIONS , 2011 .

[3]  T. Rauch,et al.  The influence of binarity on dust obscuration events in the planetary nebula M 2-29 and its analogues , 2011, 1101.4959.

[4]  Lena Danaia,et al.  K 1-6: An Asymmetric Planetary Nebula with a Binary Central Star , 2010, Publications of the Astronomical Society of Australia.

[5]  R. Corradi,et al.  Prediction of close binarity based on planetary nebula morphology , 2010, 1009.2890.

[6]  Sub-Arcsecond Morphology of Planetary Nebulae , 2010, Publications of the Astronomical Society of Australia.

[7]  Q. Parker,et al.  Planetary Nebulae: Observational Properties, Mimics and Diagnostics , 2010, Publications of the Astronomical Society of Australia.

[8]  A. Karakas,et al.  Heavy Element Abundances in Planetary Nebulae: A Theorist's Perspective , 2009, Publications of the Astronomical Society of Australia.

[9]  R. Davies,et al.  Astronomical Society of the Pacific Conference Series , 2010 .

[10]  Leicester,et al.  A survey for post-common-envelope binary stars using GALEX and SDSS photometry , 2009, 0908.2916.

[11]  A. Acker,et al.  Binary planetary nebulae nuclei towards the Galactic bulge - II. A penchant for bipolarity and low-ionisation structures , 2009, 0907.2463.

[12]  J. Farihi,et al.  The WD perspective on the PN binary hypothesis , 2009 .

[13]  U. Kolb,et al.  A comprehensive population synthesis study of post‐common envelope binaries , 2009, 0903.4152.

[14]  O. Marco The Origin and Shaping of Planetary Nebulae: Putting the Binary Hypothesis to the Test , 2009, 0902.1137.

[15]  A. Acker,et al.  Binary planetary nebulae nuclei towards the Galactic bulge - I. Sample discovery, period distribution, and binary fraction , 2009, 0901.4419.

[16]  M. V. van Raai,et al.  NUCLEOSYNTHESIS PREDICTIONS FOR INTERMEDIATE-MASS ASYMPTOTIC GIANT BRANCH STARS: COMPARISON TO OBSERVATIONS OF TYPE I PLANETARY NEBULAE , 2008, 0809.1456.

[17]  A. Schwope,et al.  Post-common envelope binaries from SDSS – III. Seven new orbital periods , 2008, 0808.2148.

[18]  R. Sahai,et al.  Binarity in Cool Asymptotic Giant Branch Stars: A GALEX Search for Ultraviolet Excesses , 2008, 0807.1944.

[19]  L. Stanghellini,et al.  The Magellanic Cloud Calibration of the Galactic Planetary Nebula Distance Scale , 2008, 0807.1129.

[20]  K. Cunha,et al.  High-resolution spectroscopic observations of the peculiar planetary nebula Me 1-1 , 2008 .

[21]  A. Szalay,et al.  The Calibration and Data Products of GALEX , 2007 .

[22]  R. Méndez,et al.  Planetary Nebulae in our Galaxy and Beyond , 2007 .

[23]  A. Acker,et al.  Chemical compositions and plasma parameters of planetary nebulae with Wolf-Rayet and wels type central stars , 2006, astro-ph/0611149.

[24]  Q. Parker,et al.  Two new evolved bipolar planetary nebulae in the solar neighbourhood , 2006 .

[25]  L. Lucy,et al.  Spectroscopic binaries with components of similar mass , 2006, astro-ph/0607225.

[26]  M. Skrutskie,et al.  The Two Micron All Sky Survey (2MASS) , 2006 .

[27]  H. Dinerstein,et al.  The Abundances of Light Neutron-Capture Elements in Planetary Nebulae. II. s-Process Enrichments and Interpretation , 2005, Proceedings of the International Astronomical Union.

[28]  M. Peimbert,et al.  Planetary nebulae in our Galaxy and beyond , 2006 .

[29]  Thomas G. Barnes,et al.  Cosmic Abundances as Records of Stellar Evolution and Nucleosynthesis in honor of David L. Lambert , 2005 .

[30]  N. Hambly,et al.  The AAO/UKST SuperCOSMOS Hα survey , 2005, astro-ph/0506599.

[31]  S. Udry,et al.  On metal-deficient barium stars and their link with yellow symbiotic stars , 2005, astro-ph/0506592.

[32]  A. Szalay,et al.  The Galaxy Evolution Explorer: A Space Ultraviolet Survey Mission , 2004, astro-ph/0411302.

[33]  K. Cunha,et al.  High-resolution spectroscopic observations of the D${'}$-type symbiotic stars HD 330036 and AS 201 , 2005 .

[34]  I. J. Danziger,et al.  Me 1-1: A PN containing a cool star , 2004 .

[35]  I. Hook,et al.  The Gemini–North Multi‐Object Spectrograph: Performance in Imaging, Long‐Slit, and Multi‐Object Spectroscopic Modes , 2004 .

[36]  L. Morbidelli,et al.  A reanalysis of chemical abundances in galactic PNe and comparison with theoretical predictions , 2004 .

[37]  Matthew Colless,et al.  The 6dF Galaxy Survey: Samples, observational techniques and the first data release , 2004, astro-ph/0403501.

[38]  C. Ledoux,et al.  The UVES Paranal Observatory Project: A Library of High- Resolution Spectra of Stars across the Hertzsprung-Russell Diagram , 2003 .

[39]  Hans Van Winckel,et al.  Post-AGB Stars , 2003 .

[40]  A. Sandage,et al.  The Age of the Oldest Stars in the Local Galactic Disk from Hipparcos Parallaxes of G and K Subgiants , 2003, astro-ph/0307128.

[41]  B. Gaensicke,et al.  The age, life expectancy, and space density of Post Common Envelope Binaries , 2003, astro-ph/0305531.

[42]  H. E. Schwarz,et al.  Angular dimensions of planetary nebulae , 2003, astro-ph/0304433.

[43]  R. Corradi,et al.  Symbiotic Stars Probing Stellar Evolution , 2003 .

[44]  R. Webbink,et al.  WeBo 1: A Young Barium Star Surrounded by a Ringlike Planetary Nebula , 2002, astro-ph/0209418.

[45]  A. Gawryszczak,et al.  Morphology of planetary nebulae with binary cores - The effect of gravitational focusing by the companion to the mass-losing star , 2002 .

[46]  H. Bond,et al.  HST Observations of Sakurai's Object (V4334 Sgr) and Related Stars , 2002 .

[47]  R. Corradi,et al.  Low-Ionization Structures in Planetary Nebulae: Confronting Models with Observations , 2000, astro-ph/0010282.

[48]  R. Wing The Carbon Star Phenomenon , 2000 .

[49]  A. Robin,et al.  An absolute calibration of DENIS (deep near infrared southern sky survey) , 2000 .

[50]  M. Morris,et al.  Bipolar Pre-Planetary Nebulae: Hydrodynamics of Dusty Winds in Binary Systems. II. Morphology of the Circumstellar Envelopes , 1999 .

[51]  R. Ciardullo,et al.  A HUBBLE SPACE TELESCOPE Survey for Resolved Companions of Planetary Nebula Nuclei , 1999, astro-ph/9904043.

[52]  J. Lattanzio,et al.  The eccentricities of the barium stars , 2000 .

[53]  M. Dopita,et al.  Detection of new emission structures around planetary nebulae , 1998 .

[54]  A. Pickles A Stellar Spectral Flux Library: 1150–25000 Å , 1998 .

[55]  Michael J. Kurtz,et al.  RVSAO 2.0: Digital Redshifts and Radial Velocities , 1998, astro-ph/9803252.

[56]  L. Kohoutek Search for envelopes of some stellar planetary nebulae, symbiotic stars and further emission-line objects , 1997 .

[57]  R. Jeffries,et al.  Wind-accretion induced rapid rotation and a new class of active star , 1996 .

[58]  A. Jorissen,et al.  Wind accretion in binary stars — II. Accretion rates , 1996, astro-ph/9602089.

[59]  P. Podsiadlowski,et al.  The formation of bipolar planetary nebulae and close white dwarf binaries , 1995 .

[60]  M. Barlow,et al.  Elemental abundances for a sample of southern galctic planetary nebulae , 1994 .

[61]  M. Livio,et al.  The formation of binary and single nuclei of planetary nebulae , 1993 .

[62]  M. Livio,et al.  COMMON ENVELOPES IN BINARY STAR EVOLUTION , 1993 .

[63]  Robin Ciardullo,et al.  The Abell 35-Type Planetary Nuclei , 1993 .

[64]  A. Duquennoy,et al.  Binaries as tracers of star formation. Proceedings. , 1992 .

[65]  A. Jorissen,et al.  Evidences for interaction among wide binary systems: to Ba or not to Ba? , 1992 .

[66]  H. R. Johnson,et al.  An interactive companion to the S star HD 35155 , 1991 .

[67]  R. Shaw,et al.  Large planetary nebulae and their significance to the late stages of stellar evolution , 1990 .

[68]  M. Livio,et al.  Morphologies of Planetary Nebulae Ejected by Close-Binary Nuclei , 1990 .

[69]  J. B. Oke Faint Spectrophotometric Standard Stars , 1990 .

[70]  R. Mcclure,et al.  The Binary Nature of the Barium and CH Stars. III. Orbital Parameters , 1990 .

[71]  J. Mathis,et al.  The relationship between infrared, optical, and ultraviolet extinction , 1989 .

[72]  G. Jacoby,et al.  Central star temperatures of optically thick planetary nebulae and a distance-independent test of dredge-up theory , 1989 .

[73]  P. Wood,et al.  A study of some southern planetary nebulae , 1988 .

[74]  A. King The evolution of compact binaries , 1988 .

[75]  J. Kaler The evolution of large planetary nebulae and their central stars , 1983 .

[76]  I. Howarth LMC and galactic extinction , 1983 .

[77]  P. K. Lu,et al.  A catalog of spectral classification and photometry of Barium stars. , 1983 .

[78]  G. Danielson,et al.  Halos around planetary nebulae , 1982 .

[79]  R. Mcclure,et al.  The binary nature of the barium stars. , 1980 .

[80]  G. Abell,et al.  Properties of Some Old Planetary Nebulae , 1966 .

[81]  P. C. Keenan,et al.  The Ba II Stars. , 1951 .

[82]  Vol Xiii,et al.  Astronomical Society of the Pacific , 1937, Nature.