42 research outputs found
Distinguishing between symbiotic stars and planetary nebulae
Number of known symbiotic stars (SySt) is still significantly lower than
their predicted population. One of the main problems in finding complete
population of SySt is the fact that their spectrum can be confused with other
objects, such as planetary nebulae (PNe) or dense H II regions. The problem is
reinforced by a fact that in significant fraction of established SySt the
emission lines used to distinguish them from other objects are not present. We
aim at finding new diagnostic diagrams that could help separate SySt from PNe.
Additionally, we examine known sample of extragalactic PNe for candidate SySt.
We employed emission line fluxes of known SySt and PNe from the literature. We
found that among the forbidden lines in the optical region of spectrum, only
the [O III] and [N II] lines can be used as a tool for distinguishing between
SySt and PNe, which is consistent with the fact that they have the highest
critical densities. The most useful diagnostic that we propose is based on He I
lines which are more common and stronger in SySt than forbidden lines. All
these useful diagnostic diagrams are electron density indicators that better
distinguishes PNe and ionized symbiotic nebulae. Moreover, we found six new
candidate SySt in the Large Magellanic Cloud and one in M81. If confirmed, the
candidate in M81 would be the furthest known SySt thus far.Comment: 7 pages, 7 figures, submitted to A&
Variability of the symbiotic X-ray binary GX 1+4: Enhanced activity near periastron passage
Context. GX 1+4 belongs to a rare class of X-ray binaries with red giant
donors, symbiotic X-ray binaries. The system has a history of complicated
variability on multiple timescales in the optical light and X-rays. The nature
of this variability remains poorly understood. Aims. We study variability of GX
1+4 on long time-scale in X-ray and optical bands. Methods. The presented X-ray
observations are from INTEGRAL Soft Gamma-Ray Imager and RXTE All Sky Monitor.
The optical observations are from INTEGRAL Optical Monitoring Camera. Results.
The variability of GX 1+4 both in optical light and hard X-ray emission (>17
keV) is dominated by ~50-70d quasi-periodic changes. The amplitude of this
variability is highest during the periastron passage, while during the
potential neutron star eclipse the system is always at minimum, which confirms
the 1161d orbital period that has had been proposed for the system based on
radial velocity curve. Neither the quasi-periodic variability or the orbital
period are detected in soft X-ray emission (1.3-12.2 keV), where the binary
shows no apparent periodicity.Comment: 8 pages, 7 figures, accepted for publication in A&