Using The Pulsation To Detect The Companions Of Short Period Pulsation Variable And The Related Evolution Discussion

In the present paper, the main objects of study are short period pulsation variables, including RR Lyrae stars, Delta Scuti stars and SX Phoenicis stars,and the contents of the study are using the pulsation to detect the companions of short period pulsation variable. We ?rst give a brief overview of the research in RR Lyrae stars, including the number and distribution, the characteristics as standard candles, the Oosterho group, the long term changes of the pulsation period and the Blazhko effect, discuss the observational fact of that RR Lyrae stars are rarely found in binary systems, and then introduce the evolution properties of SX Phoenicis stars. By using the photometric data of Kepler space telescope, ground surveys and our small telescopes, we use the O-C method and other methods to detect the companions of short period pulsation stars, and obtain the results as follow:1. Long cadence corrected PDC ?uxes of FN Lyr(KIC 6936115) and V894Cyg(KIC 9591503), observed continuously by Kepler mission, spanning over 1470 d are used to determine hundreds of times of maximum and minimum for analysis of O- C residuals. The clear variations in the O- C diagrams are interpreted to be caused by the light-travel-time effect due to additional companions.The mass functions of the companions are f(M) =(3.94 ± 0.82) × 10-6and(2.01 ± 0.22) × 10-4M⊙. Assuming that the orbital plane inclination follows a random distribution, the companions to both stars can be constrained to be substellar objects(brown dwarf, or giant planet), with 89.4% and 59.4% probability,respectively. Under the assumption that the orbital inclination equals 90?, the distances between the companions and the central RR Lyrae stars at periastron should be 1.03 and 0.50 AU, respectively. In addition, the orbital periods are794.8 and 1084.4 d for FN Lyr and V894 Cyg, respectively. Comparing these orbital parameters with those of B subdwarf stars in binary systems yields strong hints that horizontal branch stars may have different evolution histories. The long-term pulsation period changes are also discussed. Based on our studies, RRLyrae stars in binary systems are not rare, at least among binary systems with wider separations.2. the O- C diagrams of other 19 Non-Blazhko RRab-type stars in Kepler?eld also show some variations, including the parabolic variations and irregular variations. The parabolic variations mean that the pulsation periods are changing linearly with time. However, the observed β values are slightly larger than those predicted by theoretical models. Considering that the data observed by Kepler are not enough for the research of long term pulsation period, more photometric observations are needed in the future to check the changes. Moreover, the O-C diagrams of some stars show irregular variations or semi-periodic changes,indicating that some unknown mechanism may in?uence the O- C values.3. We determine forty-two new times of light maximum from our photometry observations and WASP project, and collect all the times of light maximum observed between 1961 and 2013 to calculate the orbital elements of the SZ Lyn binary system and secular change of the pulsation period with the classical O- C method. We con?rm the decrease of longitude of the periastron passage with a rate of(-1.15 ± 0.25)?yr-1, and discuss the causative mechanism. The results show that the precession of the star’s orbit is due to a close binary system, which means that SZ Lyn system is actually a triple star system. We use the Hipparcos Intermediate Astrometric Data to obtain the complete orbital elements of SZ Lyn system and ?nd that the inclination i and parallax are 39.5±17.7?and 2.61±0.98mas(corresponds to 380 ± 140 pc), respectively. We reanalyze the mean radial velocities of SZ Lyn given by Bardin & Imbert(1984)[18], and notice a weak variation existing in the residuals from a single-Keplerian ?t. We suggest that more detailed high-precision spectroscopic observations are de?nitely needed in the future to check this short periodic change.4. DW Psc is a high-amplitude SX Phe-type variable with a period of pulsation of 0.05875 days. Using a few newly determined times of maximum light together with those collected from the literature, the changes in the O- C diagram are analyzed. It is discovered that the O- C curve of DW Psc shows a cyclic variation with a period of 6.08 years and a semi-amplitude of 0.0066 days. The periodic variation is analyzed for the light travel time effect, which is due to the presence of a stellar companion(M2sin i 0.45(±0.03)M⊙). The two-component stars in the binary system are orbiting each other in an eccentric orbit(e 0.4) at an orbital separation of about 2.7(±0.3) AU. The detection of a close stellar companion to an SX Phe-type star supports the idea that SX Phe-type pulsating stars are blue stragglers that were formed from the merging of close binaries. The stellar companion has played an important role in the merging of the original binary by removing angular momentum from the central binary during early dynamical interaction or/and late dynamical evolution. After the more massive component in DW Psc evolves into a red giant, the cool close companion should help to remove the giant envelope via possible critical Rochelobe over?ow, and the system may be a progenitor of a cataclysmic variable.The detection of a close stellar companion to DW Psc makes it a very interesting system to study in the future.