Vsge V Sagittae stars

- Stars of this type are often classified as novalike cataclysmic variables but, in fact, they do not fit into any of the patterns established for this class. The nature of these stars is still not clear, but there seems to be a consensus in the literature that they are binary systems with an evolved component. The nature of this component, however, has not been clearly established. Ideas involving a subdwarf, white dwarf, neutron star,

Figure 5.10. Light curve of RX And |UGZ). Data provided by the VSNET. Used with Permission.

Figure 5.10. Light curve of RX And |UGZ). Data provided by the VSNET. Used with Permission.

1995 1997 1999 2001

4Sagitta (pronounced SAH-jit-a), the Arrow, is recognized as the arrow Hercules shot eastwards, still in flight, and also as Cupid's arrow.

and a black hole plus a He (helium) main-sequence star have been considered, not recognized within the GCVS

The variable star V Sagittae has defied classification despite much attention from photometric observers since its discovery in 1902. It has often been classified as a novalike cataclysmic variable but, in fact, does not fit into any of the patterns established for this class.

V Sge was discovered in 1902 as a variable star but it wasn't until 1965 that it was discovered to be a binary system with an orbital period of 12.3. Since then it has remained a puzzle among the variable stars. There are a small number of stars, however, that show properties quite similar to those of V Sge.

The nature of these stars is still not clear but there seems to be a consensus in the literature that they are binary systems with an evolved component. The nature of this component, however, has not been clearly established. Ideas involving a subdwarf, white dwarf, neutron star, and a black hole along with an He main sequence star have been considered for V Sge.

V Sge is the first object of its class to be identified and studied in detail. It has been shown that this star is a double spectroscopic binary. V Sge is also a faint and soft Einstein5 source. The long-term photometric behavior of this system is based on observations made over a period of 70 years. It has been shown that an optical brightness variation exists, including high and low states separated by up to 2™0. A semiregular period of ~240d has also been claimed.

It is important to establish the basic structure and evolutionary status of this new class of binaries; in particular, the nature of the compact star is of fundamental importance to the understanding of these objects. To this point there has been no agreement in the literature of the nature of the compact, more evolved, component of the binary system.

The hypothesis of a white dwarf as the compact star has been discussed as one of the possibilities for V Sge, the other two possibilities being a neutron star or a black hole. The most popular model for explaining the supersoft X-ray sources seems to be hydrostatic nuclear burning on the surface of a white dwarf. This can occur when a massive white dwarf accretes at rates approach sThc second of NASA's three High Energy Astrophysical Observatories, HEAO-2, renamed Einstein after launch.

ing 10 solar masses per year. The progenitor stars should be in the range of 6-8 solar masses. According to this idea, about 100-200 such objects are expected to exist in the Galaxy.

The neutron star hypothesis has also been raised for V Sge stars. It can be shown that under some circumstances, accretion onto a neutron star may produce a supersoft X-ray binary.

Observation

Mixed stars

^ Small amplitudes p. Mixed periods <§> Visual, CCD/PEP

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