Astronomy Now - January 2021

S

Bob Argyle

Double star of the month: 88 Tauri

ix-and-a-half degrees due south of Aldebaran (alpha [α] Tauri) lies the wide and unequal pair 88
Tauri. First catalogued by William Herschel in 1780, it was recorded by the great astronomer as
H 6 31. He gave the separation of the components as 70.6 arcseconds, but noted that this was “a
little inaccurate”. When I measured the pair in the autumn of 2013, using the Cambridge 200mm
(eight-inch) refractor, the distance was 69.1 arcseconds.

e stars are magnitude +4.3 (SAO 6h 6 94026) and +7.8, making it an easy pair for small apertures.
Admiral Smyth saw colours of bluish-white and blue, as did I with a 210mm (~8.3-inch) reector.

88 Tauri is a sextuple system, like Castor (alpha Gem). e A component is actually two pairs of
stars about 0.2 arcsecond apart that revolve around each other in 18 years, with the components of
the pairs having periods of 3.57 and 7.89 days.

Astrometric observations of these close pairs have been made using the Palomar High-precision
Astrometric Search for Exoplanet Systems (PHASES) instrument, which consists of three 400mm
apertures separated by baselines of 86 and 110 metres, and is capable of resolving bright, stellar
sources less than one milliarcsecond apart. Spectra taken in 1987 tentatively show lines of ve
different components, but later studies have not conrmed this. Component B is also a spectroscopic
binary with a period of 1,347 days and moves through space with the stars that make up component
A.

Gaia DR2 puts the stars at a distance of 175 light years, some 23 light years beyond the mean
distance of the Hyades open cluster.

88 Tauri is a multiple star that lies south of Aldebaran in Taurus.

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Double star of the month: 88 Tauri

January 2021

Astronomy Now