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