i Bootis B, 44 Bootis B

Eclipsing Binary Variable i Boo B (Boss 3846), of W Ursae Majoris type, in Bootes

Right Ascension 15 : 03.8 (h:m)
Declination +47 : 39 (deg:m)
Distance 42 (ly)
Visual brightness 5.80 .. 6.39 (mag)
Period 0.268 (days)
Spectra type G2V + G2V

William Herschel had discovered and identified this star as the fainter component of a visual binary in 1781; he noted in his observing book (Herschel 1782):

[I.] 15. i Bootis, Fl. 44
August 17. 1781. Double, considerably unequal. Both W [white]. With 227 [power] they seem almost to touch or at most 1/4 diameter of S (southernmost star) asunder, with 460, 1/2 or 3/4 diameter of S. This is a fine object to try a telescope, and a miniature of alpha Geminorum.
This star had been cataloged as i Bootis (according to Bayer) or 44 Bootis (according to Flamsteed). Herschel cataloged it as double star I.15, i.e., No. 15 in his first class of double stars. It was included in Lewis Boss' Preliminary General Catalogue as No. 3846 or Boss 3846 (component B) and 3847 (A), Boss (1910).

The variability, suspected already in the later 19th century, was found in the 1910 (Hertzsprung), but judged as erroneous. It was eventually established in the 1920s: Mt. Wilson astronomers found its spectrum to resemble W Ursae Majoris (W UMa), i.e., a contact system. It is a short-period variable with rotationally broadened spectral lines (Adams et.al. 1921), and from spectra taken in 1926, its rotation period was found to be a bit more than a quarter of a day (Schilt 1926); a modern value is 6.42758 hours.

A concise description of the system is given in Eggen (1948).

The variable is the fainter componenti, 44 i Boo B of variable mag 5.8..6.4, the primary component, 44 i Boo A, is of about mag 5.19, so that the combined visual magnitude varies between 4.70..4.88 mag. The components orbit each other, or their center of mass, every 209.8 years in an orbit of about 46 AU average distance, but considerably high excentricity taking them between 22 and 69 AU away from each other. Because of the inclination against the line of view, the components seem to come apparently very close on mid-course, e.g. in the 1960s and 2020s (significantly below 1"), and go out to about 2" near periastron (2000s) and about 4" near apastron (1880s, 2090s). From Kepler's laws, a total mass of about 2.2 solar masses could be derived, with A: 1.13 solar masses, and the eclipsing binary pair B about the same total mass, so each of the two White Dwarf stars in B having about 0.55 .. 0.6 solar masses.


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Hartmut Frommert
Christine Kronberg