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Post Info TOPIC: Nova RS Ophiuchi


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RE: Nova RS Ophiuchi
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Explosions of small stars, long thought to create stellar dust, actually sweep dust away, scientists discovered.
For years, researchers have observed swirling dust clouds around systems called recurring novas, which periodically explode. New images of a distant nova have now overturned astronomers' long-standing assumption that the dust originates in the blasts.
Scientists recently observed the RS Ophiuchi system, where a small white dwarf star and large red giant orbit each other. Over time, the giant sheds its outer layer of gas, which the dwarf sweeps up. The little star's mass grows gradually, eventually reaching a tipping point, when the top layer ignites in a thermonuclear explosion and expels the surface into space. The process then starts over astronomers have already seen this system "go nova" in 1898, 1933, 1958, 1967 and 1985.

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Title: Historic mass loss from the RS Ophiuchi system
Authors: Jacco Th. van Loon (Keele University, UK)

Dust has been detected in the recurrent nova RS Ophiuchi on several occasions. I model the historical mid-infrared photometry and a recent Spitzer Space Telescope spectrum taken only half a year after the 2006 eruption. The dust envelope is little affected by the eruptions. I show evidence that the eruptions and possibly the red giant wind of RS Oph may sculpt the interstellar medium, and show similar evidence for the recurrent dwarf nova T Pyxidis.

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RS Ophiuchi.kmz
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Title: GMRT Observations of the 2006 outburst of the Nova RS Ophiuchi: First detection of emission at radio frequencies < 1.4 GHz
Authors: N. G. Kantharia (1), G. C. Anupama (2), T. P. Prabhu (2), S. Ramya (2), M. F. Bode (3), S. P. S. Eyres (4), T. J. O'Brien (5) ((1) National Centre for Radio Astrophysics (TIFR), Pune (2) Indian Institute of Astrophysics, Bangalore (3) Liverpool John Moores University (4) University of Central Lancashire (5) Jodrell Bank Observatory, University of Manchester)

The first low radio frequency (<1.4 GHz) detection of the outburst of the recurrent nova RS Ophiuchi is presented in this letter. Radio emission was detected at 0.61 GHz on day 20 with a flux density of ~48 mJy and at 0.325 GHz on day 38 with a flux density of ~ 44 mJy. This is in contrast with the 1985 outburst when it was not detected at 0.327 GHz even on day 66. The emission at low radio frequencies is clearly non-thermal and is well-explained by a synchrotron spectrum of index alpha ~ -0.8 (S propto nu^alpha) suffering foreground absorption due to the pre-existing, ionised, warm, clumpy red giant wind. The absence of low frequency radio emission in 1985 and the earlier turn-on of the radio flux in the current outburst are interpreted as being due to higher foreground absorption in 1985 compared to that in 2006, suggesting that the overlying wind densities in 2006 are only ~30% of those in 1985.

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Title: Hubble Space Telescope Imaging of the Expanding Nebular Remnant of the Recurrent Nova RS Ophiuchi (2006)
Authors: M.F. Bode (1), D.J. Harman (1), T.J. O'Brien (2), H.E. Bond (3), S. Starrfield (4), M.J. Darnley (1), A. Evans (5), S.P.S. Eyres (6) ((1) Liverpool John Moores University, (2) Jodrell Bank Observatory, University of Manchester, (3) Space Telescope Science Institute, (4) Arizona State University, (5) Keele University, (6) University of Central Lancashire)

We report Hubble Space Telescope imaging obtained 155 days after the 2006 outburst of RS Ophiuchi. We detect extended emission in both [O III] and [Ne V] lines. In both lines, the remnant has a double ring structure. The E-W orientation and total extent of these structures (580 50 AU at d=1.6kpc) is consistent with that expected due to expansion of emitting regions imaged earlier in the outburst at radio wavelengths. Expansion at high velocity appears to have been roughly constant in the E-W direction (v_{exp} = 3200 300 km/s in the plane of the sky), with tentative evidence of deceleration N-S. We present a bipolar model of the remnant whose inclination is consistent with that of the central binary. The true expansion velocities of the polar components are then v = 5600 1100 km/s. We suggest that the bipolar morphology of the remnant results from interaction of the outburst ejecta with a circumstellar medium that is significantly denser in the equatorial regions of the binary than at the poles. This is also consistent with observations of shock evolution in the X-ray and the possible presence of dust in the infrared. Furthermore, it is in line with models of the shaping of planetary nebulae with close binary central systems, and also with recent observations relating to the progenitors of Type Ia supernovae, for which recurrent novae are a proposed candidate. Our observations also reveal more extended structures to the S and E of the remnant whose possible origin is briefly discussed.

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Title: The SSS phase of RS Ophiuchi observed with Chandra and XMM-Newton I.: Data and preliminary Modelling
Authors: J.-U. Ness, S. Starrfield, A.P. Beardmore, M.F. Bode, J.J. Drake, A. Evans, R.D. Gehrz, M.R. Goad, R. Gonzalez-Riestra, P. Hauschildt, J. Krautter, T.J. O'Brien, J.P. Osborne, K.L. Page, R.A. Schoenrich, C.E. Woodward
(Version v2)

The phase of Super-Soft-Source (SSS) emission of the sixth recorded outburst of the recurrent nova RS Oph was observed twice with Chandra and once with XMM-Newton. The observations were taken on days 39.7, 54.0, and 66.9 after outburst. We confirm a 35-sec period on day 54.0 and found that it originates from the SSS emission and not from the shock. We discus the bound-free absorption by neutral elements in the line of sight, resonance absorption lines plus self-absorbed emission line components, collisionally excited emission lines from the shock, He-like intersystem lines, and spectral changes during an episode of high-amplitude variability. We find a decrease of the oxygen K-shell absorption edge that can be explained by photoionisation of oxygen. The absorption component has average velocities of -1286 267 km/s on day 39.7 and of -771 65 km/s on day 66.9. The wavelengths of the emission line components are consistent with their rest wavelengths as confirmed by measurements of non-self absorbed He-like intersystem lines. We have evidence that these lines originate from the shock rather than the outer layers of the outflow and may be photoexcited in addition to collisional excitations. We found collisionally excited emission lines that are fading at wavelengths shorter than 15A that originate from the radiatively cooling shock. On day 39.5 we find a systematic blue shift of -526 114 km/s from these lines. We found anomalous He-like f/i ratios which indicates either high densities or significant UV radiation near the plasma where the emission lines are formed. During the phase of strong variability the spectral hardness light curve overlies the total light curve when shifted by 1000sec. This can be explained by photoionisation of neutral oxygen in the line of sight if the densities of order 10^{10}-10^{11} cm^{-3}.

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Title: VLTI/AMBER interferometric observations of the recurrent Nova RS Oph 5.5 days after outburst
Authors: Olivier Chesneau (LG), N. Nardetto (LG), F. Millour (LUAN, LAOG), Ch. Hummel (ESO), A. Domiciano De Souza (LUAN), D. Bonneau (LG), M. Vannier (ESO), F.T. Rantakyro (ESO), A. Spang (LG), F. Malbet (LUAN), D. Mourard (LG), M.F. Bode, T.J. O'brien, G. Skinner (CESR), R. Petrov (LUAN), Ph. Stee (LG), E. Tatulli, F. Vakili (LUAN)

We report on interferometric AMBER/VLTI observations of the recurrent nova RS Oph five days after its outburst on 2006 Feb 12. Using three baselines from 44 to 86m, and a spectral resolution of 1500, we measured the extension of the emission in the K band continuum and in the BrG and HeI2.06 micron lines. The continuum visibilities were interpreted by fitting simple geometric models consisting of uniform and Gaussian ellipses, ring and binary models. The visibilities and differential phases in the BrG line were interpreted using skewed ring models aiming to perform a limited parametric reconstruction of the extension and kinematics of the line forming region. The limited uv coverage does not allow discrimination between filled models and rings. Binary models are discarded because the measured closure phase in the continuum is close to zero. The visibilities in the lines are at a low level compared to their nearby continuum, consistent with a more extended line forming region for HeI2.06 than BrG. The ellipse models for the continuum and for the lines are highly flattened and share the same position angle. Two radial velocity fields are apparent in the BrG line: a 'slow' expanding ring-like structure (v~1800km/s), and a 'fast' structure extended in the E-W direction (v~2500-3000km/s). These results confirm the basic fireball model, contrary to the conclusions of other interferometric observations conducted by Monnier et al. (2006).

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Title: The Hydrogen Burning Turn-off of RS Ophiuchi 2006
Authors: Izumi Hachisu (Univ. of Tokyo), Mariko Kato (Kieo Univ.), Seiichiro Kiyota, Katsuaki Kubotera, Hiroyuki Maehara, Kazuhiro Nakajima (VSOLJ), Yuko Ishii, Mari Kamada, Sahori Mizoguchi, Shinji Nishiyama, Naoko Sumitomo, Ken'ichi Tanaka, Masayuki Yamanaka, Kozo Sadakane (Osaka Kyoiku Univ.)

We report a coordinated multi-band photometry of the RS Oph 2006 outburst and highlight the emission line free y-band photometry that shows a mid-plateau phase at y ~ 10.2 mag from day 40 to day 75 after the discovery followed by a sharp drop of the final decline. Such mid-plateau phases are observed in other two recurrent novae, U Sco and CI Aql, and are interpreted as a bright disk irradiated by the white dwarf. We have calculated theoretical light curves based on the optically thick wind theory and have reproduced the observed light curves including the mid-plateau phase and the final sharp decline. This final decline is identified with the end of steady hydrogen shell-burning, which turned out the day ~80. This turnoff date is consistent with the end of a supersoft X-ray phase observed with Swift. Our model suggests a white dwarf mass of 1.35 0.01 solar masses, which indicates that RS Oph is a progenitor of Type Ia supernovae. We strongly recommend the y-filter observation of novae to detect both the presence of a disk and the hydrogen burning turn-off.

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Title: No Expanding Fireball: Resolving the Recurrent Nova RS Ophiuchi with Infrared Interferometry
Authors: J.D. Monnier (1), R.K. Barry (2,12), W.A. Traub (7,8), B.F. Lane (3), R.L. Akeson (6), S. Ragland (4), P.A. Schuller (7), H.Le Coroller (11), J.P. Berger (5), R. Millan-Gabet (6), E. Pedretti (1), F.P. Schloerb (9), C. Koresko (6), N.P. Carleton (7), M.G. Lacasse (7), P. Kern (5), F. Malbet (5), K. Perraut (5), M.J. Kuchner (12), M.W. Muterspaugh (10) ((1) Michigan, (2) Johns-Hopkins, (3) MIT, (4) Keck Obs., (5) Grenoble, (6) Michelson Science Center, (7) CfA, (8) JPL, (9) UMass, (10) Caltech, (11) Obs. de Haute-Provence, (12) NASA-GSFC)


Following the recent outburst of the recurrent nova RS Oph on 2006 Feb 12, we measured its near-infrared size using the IOTA, Keck, and PTI Interferometers at multiple epochs. The characteristic size of ~3 milliarcseconds hardly changed over the first 60 days of the outburst, ruling out currently-popular models whereby the near-infrared emission arises from hot gas in the expanding shock. The emission was also found to be significantly asymmetric, evidenced by non-zero closure phases detected by IOTA. The physical interpretation of these data depend strongly on the adopted distance to RS Oph. Our data can be interpreted as the first direct detection of the underlying RS Oph binary, lending support to the recent ''reborn red giant'' models of Hachisu & Kato. However, this result hinges on an RS Oph distance of ~< 540 pc, in strong disagreement with the widely-adopted distance of ~1.6 kpc. At the farther distance, our observations imply instead the existence of a non-expanding, dense and ionised circumbinary gaseous disk or reservoir responsible for the bulk of the near-infrared emission. Longer-baseline infrared interferometry is uniquely suited to distinguish between these models and to ultimately determine the distance, binary orbit, and component masses for RS Oph, one of the closest-known (candidate) SNIa progenitor systems.

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Title: An asymmetric shock wave in the 2006 outburst of the recurrent nova RS Ophiuchi
Authors: T. J. O'Brien, M. F. Bode, R. W. Porcas, T. W. B. Muxlow, S. P. S. Eyres, R. J. Beswick, S. T. Garrington, R. J. Davis, A. Evans

Nova outbursts take place in binary star systems comprising a white dwarf and either a low-mass Sun-like star or, as in the case of the recurrent nova RS Ophiuchi, a red giant. Although the cause of these outbursts is known to be thermonuclear explosion of matter transferred from the companion onto the surface of the white dwarf, models of the previous (1985) outburst of RS Ophiuchi failed to adequately fit the X-ray evolution and there was controversy over a single-epoch high-resolution radio image, which suggested that the remnant was bipolar rather than spherical as modelled.
Here researchers report the detection of spatially resolved structure in RS Ophiuchi from two weeks after its 12 February 2006 outburst. They track an expanding shock wave as it sweeps through the red giant wind, producing a remnant similar to that of a type II supernova but evolving over months rather than millennia.
As in supernova remnants, the radio emission is non-thermal (synchrotron emission), but asymmetries and multiple emission components clearly demonstrate that contrary to the assumptions of spherical symmetry in models of the 1985 explosion, the ejection is jet-like, collimated by the central binary whose orientation on the sky can be determined from these observations.

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