28 research outputs found
The O I] 1641A line as a probe of symbiotic star winds
The neutral oxygen resonance 1302A line can, if the optical depth is
sufficiently high, de-excite by an intercombination transition at 1641A to a
metastable state. This has been noted in a number of previous studies but never
systematically investigated as a diagnostic of the neutral red giant wind in
symbiotic stars and symbiotic-like recurrent novae. We used archival high
resolution, and GHRS and STIS medium and high resolution, spectra to study a
sample of symbiotic stars. The integrated fluxes were measured, where possible,
for the O I 1302A and O I] 1641A lines. The intercombination 1641A line is
detected in a substantial number of symbiotic stars with optical depths that
give column densities comparable with direct eclipse measures (EG And) and the
evolution of the recurrent nova RS Oph 1985 in outburst. In four systems (EG
And, Z And, V1016 Cyg, and RR Tel), we find that the O I] variations are
strongly correlated with the optical light curve and outburst activity. This
transition can also be important for the study of a wide variety of sources in
which an ionization-bounded H II region is imbedded in an extensive neutral
medium, including active galactic nuclei, and not only for evaluations of
extinction.Comment: accepted for publication in Astronomy and Astrophysics (2010 Feb.
23), in press, NASA-GSFC-Code 66
The central binary and surrounding nebula of the symbiotic star V1016 Cygni
We present HST/WFPC2 images of the symbiotic star V1016 Cyg which, for the
first time, directly explore the inner regions of the nebula to AU scales at
optical wavelengths. They also suggest that the [OIII] 4959,5007 emission takes
place in a bipolar outflow. We use these images to determine the position of
the two stars and hence a projected binary separation of 84 AU (assuming a
distance of 2 kpc) and a position angle of 143.5 degrees. Furthermore, we
combine our images with VLA radio imaging which enables diagnostic tests to be
applied and properties of the circumstellar nebula to be determined. Finally we
have obtained archive HST/STIS spectra of V1016 Cyg with which we were able to
spatially resolve the source at various positions in the nebula. This enabled
discovery of the ultraviolet counterpart to the ~25 arcsec extended emission
found by Bang et al. (1992).Comment: Accepted for publication in Ap
The spectral energy distribution of D-type symbiotic stars: the role of dust shells
We have collected continuum data of a sample of D-type symbiotic stars. By
modelling their spectral energy distribution in a colliding-wind theoretical
scenario we have found the common characteristics to all the systems: 1) at
least two dust shells are clearly present, one at \sim 1000 K and the other at
\sim 400 K; they dominate the emission in the IR; 2) the radio data are
explained by thermal self-absorbed emission from the reverse shock between the
stars; while 3) the data in the long wavelength tail come from the expanding
shock outwards the system; 4) in some symbiotic stars, the contribution from
the WD in the UV is directly seen. Finally, 5) for some objects soft X-ray
emitted by bremsstrahlung downstream of the reverse-shock between the stars are
predicted. The results thus confirm the validity of the colliding wind model
and the important role of the shocks. The comparison of the fluxes calculated
at the nebula with those observed at Earth reveals the distribution throughout
the system of the different components, in particular the nebulae and the dust
shells. The correlation of shell radii with the orbital period shows that
larger radii are found at larger periods. Moreover, the temperatures of the
dust shells regarding the sample are found at 1000 K and <=400 K, while, in the
case of late giants, they spread more uniformly throughout the same range.Comment: 14 pages, 7 figures, 5 tables. Accepted for publication in MNRA
On the nature of the candidate T-Tauri star V501 Aurigae
We report new multi-colour photometry and high-resolution spectroscopic
observations of the long-period variable V501 Aur, previously considered to be
a weak-lined T-Tauri star belonging to the Taurus-Auriga star-forming region.
The spectroscopic observations reveal that V501 Aur is a single-lined
spectroscopic binary system with a 68.8-day orbital period, a slightly
eccentric orbit (e ~ 0.03), and a systemic velocity discrepant from the mean of
Taurus-Auriga. The photometry shows quasi-periodic variations on a different,
~55-day timescale that we attribute to rotational modulation by spots. No
eclipses are seen. The visible object is a rapidly rotating (vsini ~ 25 km/s)
early K star, which along with the rotation period implies it must be large (R
> 26.3 Rsun), as suggested also by spectroscopic estimates indicating a low
surface gravity. The parallax from the Gaia mission and other independent
estimates imply a distance much greater than the Taurus-Auriga region,
consistent with the giant interpretation. Taken together, this evidence
together with a re-evaluation of the LiI~6707 and H lines
shows that V501 Aur is not a T-Tauri star, but is instead a field binary with a
giant primary far behind the Taurus-Auriga star-forming region. The large mass
function from the spectroscopic orbit and a comparison with stellar evolution
models suggest the secondary may be an early-type main-sequence star.Comment: 13 pages, 7 figures. Accepted to MNRA
Properties of a cool component in the symbiotic nova V1016 Cyǧ
Abstract. Analysis of all available infrared JHK photometry was performed to determine interstellar extinction, distance and basic parameters of the cool component in the symbiotic nova V1016 Cyg. The cool component is a Mira variable of the spectral type M 7 and pulsation period 474 ± 2 days. Its mass is 0.81 ± 0.20 M , mean radius 485 ± 40 R , mean effective temperature 2450 ± 150 K and luminosity 7600 ± 100 L . The distance to symbiotic system was determined to be 2.93 ± 0.75 kpc
OBSERVATIONS OF CATACLYSMIC VARIABLES AT KOLONICA OBSERVATORY
We present a small sample of our observations of cataclysmic variable stars obtained at Kolonica Observatory, The presented data for CI UMa, MR UMa and SW UM were obtained in 2006 and 2007. Our observations demonstrate that also the small telescopes with low cost CCD camera could be used for a serious and useful observations
KOROAPS - SYSTEM FOR A LARGE SCALE MONITORING AND VARIABLE STARS SEARCHING
We give an introduction information about the KOROAPS (KOsice ROztoky Automatic Photometry System). It is a system for a large scale automatic multicolor monitoring and variable stars searching. It is in a development at Safarik University in Kosice in cooperation with Roztoky Observatory . The system is now in a test operation at Roztoky Observatory . System consists of Nikkor photolense 2/200 equipped with SBIG ST8 CCD camera and set of the standard VRI photometric filters. It is placed on Celestron’s CG-5 Advanced mount. We give description of the basic properties of the instrument, data reduction pipeline and operational modes of the instrument
Pulsational properties of ten new slowly pulsating B stars
Context. Slowly pulsating B (SPB) stars are upper main-sequence multi-periodic pulsators that show non-radial g-mode oscillations driven by the κ mechanism acting on the iron bump. These multi-periodic pulsators have great asteroseismic potential and can be employed for the calibration of stellar structure and evolution models of massive stars.
Aims. We collected a sample of ten hitherto unidentified SPB stars with the aim of describing their pulsational properties and identifying pulsational modes.
Methods. Photometric time series data from various surveys were collected and analyzed using diverse frequency search algorithms. We calculated astrophysical parameters and investigated the location of our sample stars in the log Teff vs. log L/L⊙ diagram. Current pulsational models were calculated and used for the identification of pulsational modes in our sample stars. An extensive grid of stellar models along with their g-mode eigenfrequencies was calculated and subsequently cross-matched with the observed pulsational frequencies. The best-fit models were then used in an attempt to constrain stellar parameters such as mass, age, metallicity, and convective overshoot.
Results. We present detected frequencies, corresponding g-mode identifications, and the masses and ages of the stellar models producing the best frequency cross-matches. We partially succeeded in constraining stellar parameters, in particular concerning mass and age. Where applicable, rotation periods have been derived from the spacing of triplet component frequencies. No evolved SPB stars are present in our sample. We identify two candidate high-metallicity objects (HD 86424 and HD 163285), one young SPB star (HD 36999), and two candidate young SPB stars (HD 61712 and HD 61076).
Conclusions. We demonstrate the feasibility of using ground-based observations to perform basic asteroseismological analyses of SPB stars. Our results significantly enlarge the sample of known SPB stars with reliable pulsational mode identifications, which provides important input parameters for modeling attempts aiming to investigate the internal processes at work in upper main-sequence stars