alpha Draconis ?

alpha Draconis is a star well placed in the sky for observers in the northern hemisphere during the whole spring and part of the summer.


The equatorial coordinates (2000.0) are :
Right ascension: 14 04 23.35
Declination: +64 22 33.06

Spectroscopic interest

The spectroscopic duplicity of alpha Draconis is known for a long time (Harper, 1907), initially as a SB1 system (Single-lined Spectroscopic Binary). It is also an eclipsing binary. A recent study (Pavlovski et al, 2021 - reveals a SB2 (Double-lined Spectsospic Binary) system.

The lines of the second component of the pair have so far gone unnoticed because the star that produces them shines with a brightness 5.3 times weaker than the main one and it is a fast rotator, producing very broad and blunt lines.


The period of the system is 51.41891 days, which means that it is possible to build the complete cycle of radial velocity variation in a small month. The amplitude (Kprimary) for the primary component is about 48.52 km/s, i.e. a displacement of the lines of +/-1 angstrom with respect to their average position.

The amplitude in radial velocity for the secondary component (Ksecondary), known since the study of 2021, is 63.58 +/- 0.41 km/s.