The binary system X Ophiuchi.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The binary system X Ophiuchi. Fernie, J. D. Abstract X Ophiuchi is a visual binary, the components of which are a long-period variable of period 337 days, spectrum M6e and a normal K giant, K2 III. The period of the binary is probably of the order of 500 years or more, but 120 observations since 1900 define a 500 arc of the apparent orbit. Five widely differing ellipses have been found to fit this arc to within the errors of observation, but among all five orbits deduced from these ellipses, the value of (a3/P2) is constant to within a factor of two. The parallax of the system has been derived principally through accurate spe etrophotometric analysis of the K star (Oke 1957). The apparent distance modulus so obtained agrees closely with that derived from the long-period variable, employing the absolute magnitude versus period relation given by Wilson and Merrill (1942). Allowance for interstellar absorption has been made from consideration of the reddening of nearby stars. Radial velocity data for both components are available for mean epochs in 1921 and 1957. Wilson's (1941) method was applied to obtain the mass ratio of the system, but the velocity changes were found to be too small to be able to distinguish among the five visual orbits. Collation of the above data leads to a formal solution for the masses of the individual components, as follows: K star ~ = 1.2 ~O Variable ~ = o.8 ~o The position of the K star on the H-R diagram suggests that it is very similar to the K giants of M 67. Applying Sandage's (1957) evolutionary tracks to this object, one deduces that its mass is 1.2 ~ O, which agrees with the formal solution of the data described above. From a discussion of the errors involved it is concluded that the mass of the long-period variable is definitely greater than 0.4 ~o, and while no upper limit can be assigned free from all doubt, there exists a high degree of probability that the mass of the variable is less than 2 ~ O. This result is to be compared with the mass 13 ~ 0 previously supposed on the basis of the mass-luminosity law. The mass o.8 ~Th 0 for the long-period variable is consistent with Deutsch's (1957) work on Mira, and leads to close agreement with the pulsation constant P (p) predicted from theory. Since the K companion is similar to the K giants of M67, it is concluded that the long- period variables, stars of periods about 300 days, are old objects. Deutsch, A. J. 1957, A. J. 63, 49. Oke, J. B. 1957, Ap. J. 126, 509. Sandage, A. 1957, Ap. J. 126, 326. Wilson, O. C. 1941, Ap. J. 93, 29. Wilson, R. E. and Merrill, P. W. 1942, Ap. J. 95, 248. Goethe Link Observatory. Indiana University, Bloomington, Ind. Publication: The Astronomical Journal Pub Date: September 1958 DOI: 10.1086/107753 Bibcode: 1958AJ.....63..305F full text sources ADS | data products SIMBAD (1)