24 research outputs found
Evidence for bipolar jets from the optical spectra of the prototypical symbiotic star Z Andromedae
We have studied optical spectra of the symbiotic star Z And, obtained during
its latest outburst started in April 2006, with the aim of finding changes in
the spectrum yielding clues to the nature of the hot component and its
outbursts. The spectroscopic observations of Z And have been made using the
1.5-meter telescope at the Tartu Observatory, Estonia, and processed in a
standard way. We have found high velocity satellites to the hydrogen Balmer
emission lines. Starting from July 30, 2006, weak additional emission
components at velocities of about +/-1150 km/s were detected. Their appearance
near the outburst maximum and similarity to the emission features in another
symbiotic star Hen 3-1341 imply fast collimated outflows from the hot component
of Z And. This finding is consistent with the earlier results by several
authors that symbiotic stars can emit bipolar jets at certain stages of their
outbursts. A significant decrease in the temperature of the hot component in
initial stages of the outburst was detected by the disappearance of the high
excitation emission line from the spectrum.Comment: 4 pages, 6 figures, accepted for publication by A&A Letter
Spectroscopy of the symbiotic star CH Cygni from 1996 to 2007
We monitored a set of emission lines in the optical spectra of CH Cyg using
the 1.5-m telescope at the Tartu Observatory, Estonia. Most of the spectra were
registered in the H alpha region, but other Balmer lines and lines of He, N, O,
and Fe were also investigated in terms of their equivalent widths, radial
velocities, and absolute fluxes. The spectra indicate different stages that CH
Cyg has been through in the course of our observations. During quiescence, the
strength of the line profiles changes in opposite phase with the star's
luminosity. The H alpha profile becomes double-peaked at times, which may point
to the temporary presence of some disk-like structure, but also to absorption
in neutral gas surrounding the area of the formation of the emission component.
In 1999, when a periastron passage is assumed according to the 5700-day model,
the Balmer lines strengthen considerably, as might be expected due to an
increase in the accretion rate. The eclipse in 2001, however, is not noticed.
At certain episodes, the controversial 756-day period of CH Cyg is seen in our
data.Comment: 10 pages, 12 figure
Discovery of Raman-scattered lines in the massive luminous emission-line star LHA 115-S 18
LHA 115-S 18 is a very peculiar emission-line star exhibiting the B[e]
phenomenon. Located in the Small Magellanic Cloud, its spectrum shows features
of an extremely wide range of excitation and ionization stages, extending from
highly ionized atomic lines (Si IV, C IV, He II) in the UV and optical regions
to molecular emission bands of CO and TiO in the optical and IR regions. The
most distinguishing spectral characteristic of LHA 115-S 18 is the high
variability detected in the He II {\lambda}4686 emission line, which can be a
very conspicuous or completely invisible feature.
In this work, we report on another peculiarity of LHA 115-S 18. From
high-resolution optical spectra taken between 2000 and 2008, we discovered the
appearance and strengthening of two emission features at {\lambda}6825 \AA, and
{\lambda}7082 \AA,, which we identified as Raman-scattered lines. This is the
first time these lines have been detected in the spectrum of a massive luminous
B[e] star. As the classification of LHA 115-S 18 is highly controversial, we
discuss how the discovery of the appearance of Raman-scattered lines in this
peculiar star might help us to solve this puzzle.Comment: Letter accepted for publication in MNRAS. 5 pages, 3 figure
Large interferometer for exoplanets (LIFE). I. Improved exoplanet detection yield estimates for a large mid-infrared space-interferometer mission
Stars and planetary system
News from AG Draconis
AG Dra is a classical symbiotic star that undergoes major outbursts at intervals between 12-15 years. We present spectroscopic observations of four emission lines (Hα, Hβ, He II 4686 Å, Raman scattered OVI 6825 Å) before, during and after the major outburst that started in 2006. Interesting strengthenings of the emission lines took place in late 2005 and in early 2008. the latter was followed by a very deep minimum in the line strengths in 2008–2009