Stellar evolution - Supernovae and interacting binaries


Novae and Interacting binaries

The 1.82m telescope in Asiago offers a flexible tool for monitoring outbursts and for surveys. Every year the Asiago observatory contributes to the studies of interacting binaries in outburst and in quiescence, with a large number of refereed papers, circulars and conference reports. In addition to this, the plate archive of the Asiago 40/50 and 67/92 Schmidt telescopes offers the opportunity to reconstruct the past variability history of some of the most interesting among such variables. Archival research is frequently carried out in a coordinated effort with the Harvard, Pulkovo and Sonnenberg plate archives. The research carried out by OAPD astronomers and their collaborators is described below (but see also the High Energy Astrophysics section).

WD single degenerate binaries as SN Ia progenitors

The most extreme single degenerate systems containing a white dwarf are characterized by high mass accretion rates and a very large, near-Eddington supersoft X-ray luminosity. This group of objects includes some classical novae and recurrent novae, symbiotic binaries, and the so called supersoft X-ray binaries in which the white dwarf accretes and burns hydrogen rich material at the high rate (mdot~10(-7) M(sun)/year) that allows radiating all the energy of the CNO cycle as it is produced. The two major ongoing projects focus on bright Galactic systems, and on X-ray binaries in external, nearby galaxies.

Hunting for SN Ia progenitors in our Galactic backyard.

 binaries fig1

Figure 1: The spectrum of RS Oph observed on 2007 April 20 observed with the Chandra LETG grating (in black). The fit with a preliminary model calculated by Rauch for Nova V4743 Sgr with enhanced nitrogen is shown in red, while the model in green is a similar model with solar abundances. The models can clearly discriminate between different abundances. The effective temperature of the white dwarf was about 800,000 K, compatible only with a very compact and massive white dwarf, very close to the Chandrasekhar mass (Nelson et al. 2007, ApJ, submitted)


When a near-by nova explodes and the intervening column of absorbing neutral hydrogen is not too large, it is often observed as a luminous supersoft X-tray source and a bright ultraviolet object. This happens whenever there is residual hydrogen rich material burning on the white dwarf, after the ejection of layers of the accreted envelope, while the white dwarf atmosphere shrinks again. For several years we have been obtaining X-ray observations of hot and luminous post-outburst novae. With the high resolution spectroscopy done with the grating spectrographs of Chandra and XMM-Newton we can derive the effective gravity (hence the mass if the distance is known) and an estimate the abundances. The abundances are really critical to understand whether the white dwarf retains material after the outburst or not, since the burning material at times is also eroded, or dredged up, from outer layers of the inert white dwarf core. Post-outburst novae white dwarfs are special objects, that allow studying the characteristics of hydrogen burning at high rate. eventually leading also to SNe Ia. Regardless of whether they actually are candidate type Ia SN progenitors or not, post-novae offer a glimpse into the physical process that leads to SNe Ia. There has been a very special object in outburst in 2006, the recurrent nova and symbiotic binary RS Oph, that proved to be so hot, luminous and massive that eventually it may really end with a supernova outburst in the next few thousand years (Nelson et al. 2007, ApJ, submitted). In-depth analysis of these amazing results is still continuing, while new objects are also being observed.

XRB populations in the Local Group.

We try to classify and monitor a statistically number of SSS in the XRB stellar populations of the Local Group. Statistics of "on-off" times and knowledge of persistent sources help define the nature of the SNe Ia progenitors. Recent work on M31 (Orio 2006) is being continued in a collaboraton with a group group at the Harvard-Smithsonian center for astrophysics, using HST archival data to determine possible counterparts of the sources in the galactic core, or at least the type of population in which they reside. Ground based imaging to detect short and long term variations, possibly orbital in nature, have been being done for M31 with the WIYN telescope for sources that are not located in the central core. We also used the Galex archival data of M31. Only few of the X-ray supersoft sources in M31 away from the core (where the Galex spatial resolution is not sufficient) are also bright UV sources. We have also obtained deep WIYN images with different optical filters of supersoft X-ray sources in M33 and in nearby galaxies outside the Local Group. We combine data of Magellanic Cloud sources at different wavelengths and epochs to follow the long term evolution of these sources. Most recently, we observed the dwarph spheroidal galaxy Leo I in X-rays. These observations are not only very significant for population studies in genral, but they also allow us to complete the census of supersoft X-ray sources in the Local Group.


The outbursts of classical and recurrent novae, are investigated with intensive photometrically and spectroscopically (high and low resolution), all the way through the final decline. Our data sets are among the most complete and detailed to reconstruct the history of outbursts. Energetics, ejecta velocity field and ionized/neutral mass, dust characteristics and mass, reddening and galactic kinematics, nebular parameters and chemical abundances are derived (Munari et al. 2006a, 2006b, Iijima 2006). Reconstruction of pre-outburst photometric evolution is also attempted using the plate archives. Global properties and statistical re-analysis of the nova population are under investigation using the huge amount of new multi-band data collected on the novae that erupted over the last few years. Among the novae in outburst in 2006-07, we are intensively monitoring Nova Cyg 2006 (V2362 Cyg), Nova Cyg 2007 (V2467 Cyg), RS Oph, Nova Sco 2007 N.1 (V1280 Sco) and N.2 (V1281 Sco), Nova Oph 2007 (V2615 Oph), Nova Sgr 2007 (V5558 Sgr), Nova Vul 2007 (V458 Vul), and Nova 2007-1 in M33.

  Symbiotic binaries

binaries fig2
Figure 2: Evolution of Halpha and HeI 5876 profiles of Hen 3-1341 during 1989-2004 outburst from Asiago 1.82m Echelle observations, which prove the feeding of collimated, bi-polar jets (seen in Halpha, jet mass 2.5x10(-7) M(sun) and kinetic energy 1.7x10(42) erg/sin i) by the wind from the central engine (see P-Cyg absorption in HeI lines), which was powered by a sustained TNR (Munari et al. 2005)

  Most symbiotic stars are powered by stable H-burning at the surface of a white dwarf accreting from a cool giant donor, and as such they are observed as super-soft X-ray sources when the local self-absorption by massive circumstellar cocoons is below a critical threshold (super-soft symbiotics are observed as far as Draco dwarf galaxy and the SMC, Orio et al. 2007). The symbiotic star SMC 3 in the SMC is abright supersoft X-ray source that we are currently monitoring (Orio et al. 2009, in preparation).The lack of significant amounts of nuclear processed material in the circumstellar environment, the recently discovery of wind Roche lobe filling mechanism (spatially resolved by interferometry in Mira A+B) and the large population of symbiotic stars discovered in recent surveys of galaxies of the Local Group, have rekindled the interest in symbiotic stars as precursors of SN Ia (Munari & Renzini 1992), especially in the subclass of recurrent novae. In addition to long-term spectroscopic and photometric investigations of symbiotic stars aimed at deriving their binary orbits and physical parameters, characterize their nebular regions and derive chemical abundances, follow their outburst and constrain the energetics, we are also focusing on the relation of symbiotics with binary nuclei of planetary nebulae and their pulsation instabilities (Siviero et al. 2007). By making use of spatio-kinematical models, we derive expansion parallaxes and map the expanding shocks of the circumstellar nebulae with HST and with the VLT (Santander-Garcia et al. 2007). We also study the origin, feeding and collimation mechanism of the bipolar jets of symbiotics (e.g. Munari et al. 2006a ). During a thermonuclear outburst, the evolution of white dwarf radius, temperature and luminosity are derived by eclipse mapping (e.g. Siviero et al. 2007). We also have an ungoing projet with the REM robotic telescope of INAF in Cile, systematic monitoring of the Magellanic Clouds symbiotics, with the aim of measuring orbital periods in the whole sample. Being at known distance he MC supersoft X-ray sources are extremely interesting to us to derive general properties of symbiotics. Additional projects concern post common-envelope systems with donor giants rotating close to break-up velocities. Finally, we also study the metallicity and possible chemical anomalies of some symbiotics, because ultimately we want to link these intriguing systems with their parent Galactic population and investigate enrichment/depletion processes (e.g. Wallerstein et al. 2006).

People: M. Orio, U. Munari, T. Iijima, A. Siviero, M. Valentini 

Collaboration: A. Bianchini (Padova Univ.), A. Henden (USNO), R. Corradi and M. Santander-Garcia (ING, La Palma) R. DiStefano, J. Lu, F. Primini and A. Zezas (CfA, USA), G. Wallerstein and J. Lutz (Washington Univ., USA), J. Gallagher, D. Harbek and L. Nigra (Wisconsin Univ., USA), J. Greiner (MPI fuer Extraterrestrische Physik, Germany), T. Rauch (Universitaet Tuebingen, Germany), T. Zwitter (Ljubljana Univ., Slovenia), E. Leibowitz (Tel Aviv Univ. Israel), P. Whitelock (SAAO), M. Livio (STScI), T. Nelson

 Publications: Orio et al. (2007), ApJ 661,1105; Santander-García et al. (2007), A&A 465,481


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