Apsidal Motion Studies: Eccentric Eclipsing Binaries



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Apsidal Motion Studies: Eccentric Eclipsing Binaries

A new apsidal motion determination of the eccentric eclipsing binary V1143 was carried out by J. Burns (USAF), Guinan, and student J. Marshall. The eclipsing binary V1143 Cyg (HR 7484, HD 185912, BD+542193; ) consists of a pair of F5V stars moving in an eccentric orbit (e=0.54) and having an orbital period of . The system is detached with both components residing well inside their respective Roche lobes. The orbital and stellar properties of V1143 Cyg are very well determined from the careful study of Andersen et al.. One of the interesting aspects of this binary is that its U,V, W space velocity components, as given by Andersen of +31, -16, -2 km/s are very close to those of the Hyades cluster (+40, -17, -3). Although the similarity between the space motions of the binary and the Hyades Moving group could be a coincidence, it is more likely that V1143 Cyg is a member. If this is true, then the binary would be coeval with the Hyades, thus having an age of about 600 Myr. Knowing the age of a binary vastly increases its importance for testing stellar structure, opacity laws, and evolution models.

Photoelectric photometry of V1143 Cyg was conducted with the Jenkins 38-cm reflector at Villanova Un. Obs. These observations were made on the nights of 17 and 19 Oct 1987 UT, using intermediate-bandpass blue (Å) and yellow Å) interference filters. The secondary and primary minima occurred respectively on these nights. These timings were combined with the photoelectric eclipse timings already available up to 1994. Independent linear least squares solutions were made of the primary and secondary eclipses respectively, yielding periods of and . The period determination from the primary eclipses is better determined than secondary eclipses because the primary eclipse has twice as many timings. The analysis of all available timings yielded an apsidal motion rate of yr. This value is nearly identical to those previously determined. More timings, in particular of secondary eclipses, are necessary to define the apsidal motion rate more precisely, so additional photometry will take place during 1997. This work was supported by NSF grant AST 93-153665 and made use of the SIMBAD data base, operated at CDS, Strasbourg, Fr.

Beginning in Spring 1995, UBVR photoelectric photometry of V541 Cyg has been conducted on the Villanova-Fairborn 0.8M APT at Mt. Hopkins by Guinan, McCook and students J. Maley and J. Marshall. During 1995, differential photometry of the star was obtained on 63 nights. Nearly complete light curves have been obtained and new eclipse timings have been made from these data. V541 Cyg is a detached eclipsing binary consisting of a pair of B9.5 V stars having an eccentric orbit (e=0.4740) and an orbital period of d. Khaliullin was the first to show that this binary could be an important test case for General Relativity (GR) because the apsidal motion expected from GR is significantly larger than the classical apsidal motion arising from the tidal and rotational distortions of the component stars. Using updated values for the internal structure constant from Claret & Giménez, theory predicts a relativistic effect of yr/100yr and classical effects of yryr. This result is particularly interesting because in V541 Cyg most of the apsidal motion is expected to arise from GR.

A new determination of apsidal motion was made using timings recorded with the APT along with timings reported in the literature. The analysis yielded an apsidal motion rate of yr /100yr. This apsidal motion is nearly the same as one found by M. Wolf. These studies confirm that V541 Cyg has an observed rate of apsidal motion significantly less than the theoretically expected apsidal motion. This discrepancy is as difficult to explain as those found for two other eclipsing binaries, DI Her and AS Cam. The plan is to continue photometry of the star with the APT during 1997 to complete the UBVR light curves, in particular, to cover fully the primary eclipse. Spectroscopic radial velocity observations of V541 Cyg are currently being conducted by Etzel (SDSU). Once the light and radial velocity curves are complete, a more thorough study of this important binary can be made. This study is supported by NSF grants AST-861362 and AST-9315365 which we gratefully acknowledge. The reduction and analysis of the IUE observations were supported by NASA NAG 5-2160. A preliminary report can be found in IBVS 4362.



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Next: Apsidal Motion Studies: Up: CURRENT RESEARCH Previous: Eclipsing Binaries: Magellanic



Astronomy
Fri Nov 8 13:37:39 EST 1996