Sxphe Sx Phoenicis stars

- Phenomenologically, these variables resemble S SCT variables and are pulsating subdwarfs of the spherical component, or old disk galactic population, with spectral types in the range A2-F5. They may show several simultaneous periods of oscillation, generally in the range -ff!08, with variable amplitude light changes that may reach 0".'7 in V. Theses stars are present in globular cluster. SXPHE(B) (subtype) not a recognized subtype within the GCVS. GCVS

SX Phoenicis14 variable stars are found within spectral types A2-F5 stars on the HR diagram. They display periods that are similar to the S Scuti stars, however in comparison, their photometric amplitudes are greater, generally ranging from to 0".'8. Upon closer examination, metal abundance as well as space motion for these stars are typical of the Population II stars.

Population I and II classifications were originally made by Walter Baade to characterize two different groups of stars that are distinguished by their velocities (kinematically distinct), relative to the Sun. Population I stars posses velocities that are low when compared to Population II stars., relative to the Sun. Also, Population I stars are predominantly found in the disk of the galaxy whereas Population II stars are found above or below the disk.

Is has been suggested that SX Phoenicis stars are blue stragglers15 in the post-main-sequence stage of evolution. The interesting thing about this suggestion is that one of the theories describing blue straggler evolution proposes that they are formed from coalescing binary stars; in other words, two stars that once orbited each other have come together to form a single star.

The discovery of SX Phoenicis stars among the blue stragglers in globular clusters marks the beginning of an exciting new age in the study of globular clusters. Like RR Lyrae stars and Cepheids, SX Phoenicis stars are useful as distance indicators, as probes of their respective stellar evolution phases, and for studying stellar population problems. Furthermore, since globular cluster SX Phe stars can be identified more easily than their field star counterparts, and the metal content and distances of the parent systems tend to be known, their relatively large numbers provide a basis for studying statistical relationships.

Observation

"jAr Bright stars fitj Mixed amplitude

Mixed periods 0> CCD or PEP

uNamed for "Phoenix" the mythical creature which, after being incinerated, grew again from its own ashes to fly away.

,sBlue stragglers are a group of stars which show a reluctance to evolve off the main sequence due to some unusual aspect of their evolution. The cause may be mass exchange with a binary star or some process of internal chemical mixing that provides more hydrogen fuel in the core.

The light, color, and radial velocity curves of SX Phe stars are similar to those of RR Lyrae and Cepheid variables. At maximum light (phase = 0), the observed visual brightness is greatest, primarily because the star is hottest. The radius is increasing at the maximum expansion speed, having just been at maximum compression during the rise to maximum light. At minimum light, when the star is at its coolest, the radius of the star is at its minimum.

0 0

Post a comment