Possible third body effects in the period changes of four Algol binaries: RY Aqr, SZ Her, RV Lyr and V913 Oph

Abstract

An investigation of the orbital period changes of the neglected eclipsing binaries, RY Aqr, SZ Her, RV Lyr and V913 Oph, is presented based on all published minima times. Although the explanation of magnetic activity on the surface of the secondaries of the studied Algols is still open, the preferred light-time effect due to the unseen components around the systems seems more plausible in explaining the tilted sinusoidal variations with relatively high-amplitudes. The minimal mass values of possible tertiary components have been estimated to be about 1.06, 0.25, 0.78 and 2.85 M for RY Aqr, SZ Her, RV Lyr and V913 Oph, respectively and the results indicate that their contributions to the total light of the eclipsing pairs are measurable with high accuracy photometric and spectroscopic data, if they exist. Applegate's (1992) model has been discussed as an alternative mechanism assuming that the cooler components have magnetic cycles. It is found that the model parameters of RY Aqr and V913 Oph are consistent with the required values in Applegate's model. In addition to the first detailed orbital study on these systems, a statistical survey on the character of the O − C variations of classical Algols has revealed that about 50 percent of the systems show cyclic behavior. This means that the presence of possible third bodies around classical Algols should be tested with careful analysis using new data.

The Algol System Sz Herculis: Physical Nature and Orbital Behavior

“…Previous researchers (Székely 2003;Soydugan 2008) have suggested that the period variations of SZ Her can be represented using an LITE caused by the presence of a third body in the system.…”

“…They reported that the period change can be described using either a sine curve or a single light-time effect (LITE) ephemeris due to a third body with implied periods of 66 and 71 yr, respectively. Soydugan (2008) also suggested that the timing residuals from the LITE fit indicate an additional short-term oscillation with a period within about 20 yr. More than one thousand eclipse timings, spanning ∼ 110 yr, should be sufficient to resolve the confusion regarding the orbital behavior of SZ Her. Nonetheless, the period variation of this system has not yet been studied as conclusively as required.…”

“…Although the orbital period of SZ Her has been examined several times (Kreiner 1971;Mallama 1980;Zavala et al 2002), a detailed study of its orbital period was made by Székely (2003) and Soydugan (2008). They reported that the period change can be described using either a sine curve or a single light-time effect (LITE) ephemeris due to a third body with implied periods of 66 and 71 yr, respectively.…”

Period Changes of the Algol System SZ Herculis

“…The former reported that the period change can be fitted to a sine curve with a period of 66 yr, while the latter concluded that it can be represented by a single light-time-travel (LTT) ephemeris, caused mainly by a third body with a cycle length of 72 yr and a minimum mass of 0.25 M . Soydugan (2008) also suggested that the timing residuals from the LTT fit indicate an additional short-term oscillation with a period within about 20 yr. Nonetheless, the period variation still has not been studied as conclusively as can be desired.…”

“…Although the orbital period of SZ Her has been examined several times, its detailed study was made by Szekely (2003) and Soydugan (2008). The former reported that the period change can be fitted to a sine curve with a period of 66 yr, while the latter concluded that it can be represented by a single light-time-travel (LTT) ephemeris, caused mainly by a third body with a cycle length of 72 yr and a minimum mass of 0.25 M .…”