133 research outputs found
The Henize sample of S stars: IV. New symbiotic stars
The properties of the few symbiotic stars detected among the 66 binary S
stars from the Henize sample are discussed. Two stars (Hen 18 and Hen 121)
exhibit both a strong blue-violet continuum and strong H_alpha emission (FWHM
of 70 km/s), whereas Hen 134 and 137 exhibit weak H_alpha emission. The H_alpha
profiles are typical of non-dusty symbiotic stars belonging to class S-3 as
defined by Van Winckel et al. (1993, A&AS 102, 401). In that class as in the
Henize symbiotic S stars, He I, [N II] or [S II] emission lines are absent,
suggesting that the nebular density is high but the excitation rather low. The
radial velocity of the centre of the H_alpha emission is identical to that of
the companion star (at least for Hen 121 where this can be checked from the
available orbital elements), thus suggesting that the H_alpha emission
originates from gas moving with the companion star. For Hen 121, this is
further confirmed by the disappearance of the ultraviolet Balmer continuum when
the companion is eclipsed by the S star. Hen 121 is thus the second eclipsing
binary star discovered among extrinsic S stars (the first one is HD 35155). A
comparison of the available data on orbital periods and H_alpha emission leads
to the conclusion that H_alpha emission in S stars seems to be restricted to
binary systems with periods in the range 600 - 1000 d, in agreement with the
situation prevailing for red symbiotic stars (excluding symbiotic novae).
Symbiotic S stars are found among the most evolved extrinsic S stars.Comment: 10 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
Discovery of the eclipse in the symbiotic binary Z Andromedae
Our photometric observations of the symbiotic binary Z And during its recent
(2000 -- 2003) active phase revealed a minimum in the U, B and V light curves
(LC) at the position of the inferior conjunction of its cool component (the
orbital phase 'phi' = 0). This fact and the behaviour of colour indices suggest
that the minimum was due to the eclipse of the active hot object by the red
giant. Physically plausible fit of the eclipse profile and a precise analysis
of the spectral energy distribution (SED) in the ultraviolet continuum suggest
a disk-like structure for the hot object during active phases. The present
knowledge of fundamental parameters of the system limits the orbital
inclination 'i' to 76 - 90 deg. The presence of the Rayleigh attenuated far-UV
continuum at 'phi' around 0 during quiescent phase confirms the very high
inclination of the Z And orbit.Comment: 4 pages, 3 figures, accepted for Astronomy and Astrophysics as a
Lette
Mm/submm observations of symbiotic binary stars: implications for the mass loss and mass exchange
We discuss mm/submm spectra of a sample of symbiotic binary systems, and
compare them with popular models proposed to account for their radio emission.
We find that radio emission from quiescent S-type systems originates from a
conical region of the red giant wind ionized by the hot companion (the STB
model), whereas more complicated models involving winds from both components
and their interaction are required to account for radio emission of active
systems. We also find that the giant mass-loss rates derived from our
observations are systematically higher than those for single cool giants. This
result is in agreement with conclusions derived from IRAS observations and with
requirements of models for the hot component.Comment: 7 pages, 8 figures. Paper presented at COSPAR 2000 "New results in
FIR and Submm Astronomy", to be published in Advances in Space Researc
High resolution spectroscopy of symbiotic stars. VI. Orbital and stellar parameters for AR Pav
We present new dynamical parameters of the AR Pav binary system.
Ourobservations consist of a series of high resolution optical/NIR spectra from
which we derive the radial velocity curve of the red giant as well as its
rotation velocity. Assuming co-rotation, we determine the stellar radius (130
R_solar) of the red giant. Based on this we derive the red giant's luminosity
and mass (2.0 M_solar) as well as the distance of the system (4.9 kpc). The
binary mass function finally yields the companion's mass (0.75 M_solar) and the
binary separation (1.95 AU). We find that the red giant does not fill its Roche
lobe. We review the radial velocity data of Thackeray and Hutchings (1974), and
compare it with our red giant's orbit. We find that their RV curves of the blue
absorption system and the permitted emission lines are in anti-phase with the
red giant, and that the forbidden emission lines are shifted by a quarter of a
period. The blue absorptions and the permitted emission lines are associated
with the hot companion but not in a straightforward way. The blue absorption
system only tracks the hot component's orbital motion whilst it is in front of
the red giant, whereas at other phases line blanketing by interbinary material
leads to perturbations. We finally present UV light curves based on IUE archive
spectra. We clearly detect eclipses in the continuum at all wavelengths. The
eclipse light curves are unusual in that they show a slow and gradual decline
prior to eclipse which is followed by a sharp increase after eclipse.Comment: 9 pages, 5 figure
DASCH Discovery of A Possible Nova-like Outburst in A Peculiar Symbiotic Binary
We present photometric and spectroscopic observations of a peculiar variable
(designated DASCH J075731.1+201735 or J0757) discovered from our DASCH project
using the digitized Harvard College Observatory archival photographic plates.
It brightened by about 1.5 magnitudes in B within a year starting in 1942, and
then slowly faded back to its pre-outburst brightness from 1943 to the 1950s.
The mean brightness level was stable before and after the outburst, and
ellipsoidal variations with a period of days are seen,
suggesting that the star is tidally distorted. Radial-velocity measurements
indicate that the orbit is nearly circular () with a
spectroscopic period that is the same as the photometric period. The binary
consists of a M0III star, and a
companion, very likely a white dwarf (WD). Unlike other symbiotic binaries,
there is no sign of emission lines or a stellar wind in the spectra. With an
outburst timescale of ~10 years and estimated B band peak luminosity M_B~0.7,
J0757 is different from any other known classic or symbiotic novae. The most
probable explanation of the outburst is Hydrogen shell-burning on the WD,
although an accretion-powered flare cannot be ruled out.Comment: 12 pages, 6 figures, accepted for publication in Ap
The secondary minimum in YY Her: Evidence for a tidally distorted giant
We present and analyze quiescent UBVRI light curves of the classical
symbiotic binary YY Her. We show that the secondary minimum, which is clearly
visible only in the quiescent VRI light curves, is due to ellipsoidal
variability of the red giant component. Our simple light curve analysis, by
fitting of the Fourier cosine series, resulted in a self-consistent
phenomenological model of YY Her, in which the periodic changes can be
described by a combination of the ellipsoidal changes and a sinusoidal changes
of the nebular continuum and line emission.Comment: 5 pages, 2 figures, to appear in Astronomy & Astrophysic
A multi-epoch spectrophotometric atlas of symbiotic stars
A multi-epoch, absolute-fluxed spectral atlas extending from about 3200 to
9000 Ang is presented for 130 symbiotic stars, including members of the LMC,
SMC and Draco dwarf galaxies. The fluxes are accurate to better than 5% as
shown by comparison with Tycho and ground-based photometric data. The spectra
of 40 reference objects (MKK cool giant standards, Mira and Carbon stars,
planetary nebulae, white dwarfs, hot sub-dwarfs, Wolf-Rayet stars, classical
novae, VV Cep and Herbig Ae/Be objects) are provided to assist the
interpretation of symbiotic star spectra. Astrometric positions and
counterparts in astrometric catalogues are derived for all program symbiotic
stars.Comment: A&A, in press (264 pages, 3 tables, 256 figures). The spectra are
available in electronic form from the authors. Only a sample of the whole
paper is given here. The full text can be downloaded from
http://ulisse.pd.astro.it/symbio-atlas/ where the spectra in electronic form
of the 40 reference objects can be found to
High-resolution X-ray Spectra Of The Symbiotic Star SS73 17
SS73 17 was an innocuous Mira-type symbiotic star until Integral and Swift
discovered its bright hard X-ray emission, adding it to the small class of
"hard X-ray emitting symbiotics." Suzaku observations in 2006 then showed it
emits three bright iron lines as well, with little to no emission in the 0.3-2
keV bandpass. We present here followup observations with the Chandra HETG and
Suzaku that confirm the earlier detection of strong emission lines of Fe Kalpha
fluorescence, Fe XXV and Fe XXVI but also show significantly more soft X-ray
emission. The high resolution spectrum also shows emission lines of other
highly ionized ions as Si XIV and possibly S XVI. In addition, a reanalysis of
the 2006 Suzaku data using the latest calibration shows that the hard (15-50
keV) X-ray emission is brighter than previously thought and remains constant in
both the 2006 and 2008 data.
The G ratio calculated from the Fe XXV lines shows that these lines are
thermal, not photoionized, in origin. With the exception of the hard X-ray
emission, the spectra from both epochs can be fit using thermal radiation
assuming a differential emission measure based on a cooling flow model combined
with a full and partial absorber. We show that acceptable fits can be obtained
for all the data in the 1-10 keV band varying only the partial absorber. Based
on the temperature and accretion rate, the thermal emission appears to be
arising from the boundary layer between the accreting white dwarf and the
accretion disk.Comment: 7 pages, 5 figures. Accepted by the Astrophysical Journa
The historical light curve of the symbiotic star AG Draconis: intense, magnetically induced cyclic activity
We analyze an optical light curve of the symbiotic system AG Draconis
covering the last 120 years of its history. During the first 32 years the
system was in a quiescence state. Around the year 1922 the star's quiescence
luminosity brightened by 0.29 mag. The last 82 years of the light curve (LC)
are characterized by a series of outbursts of 1-2 magnitude in brightness and
about 100 days in duration. The outbursts are distributed along the time axis
in 6 clusters with a quasi-periodic cycle of some 5300 days. The time intervals
among the outbursts themselves are integral numbers of the period 373.5 days.
During quiescence states the LC oscillates with the binary period of the system
of 550 d. The LC contains also a weak periodic signal with a period of 350 d,
attributed to pulsations of the giant star. Another period of 1160 d is also
present in the light curve, being the sidereal rotation period of the giant
star. We suggest that the outbursts are events of intense mass transfer from
the giant onto the hot component. These are modulated by an interplay between a
solar-like magnetic dynamo cycle operating in the outer layers of the giant,
and a tidal deformation of these layers that circulates the surface of the
giant with the synodic diurnal period of 373.5 Earth days. AG Dra is the 5th
symbiotic system with a light curve that reflects such an intense magnetic and
magnetically modulated activity. (Abridged)Comment: 10 pages, 4 figures. Accepted for publication in MNRA
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