CASTOR: a six-star system
αGEM
Σ 1110
RA
07 35
Dec
31 53
Castor was discovered in 1678 by G.D. Cassini and formally classified as a true
“binary” in 1803 by William Herschel. The system lies at a distance of about 52
light years and is a six star system.
The AB components comprise two blue-white stars separated by 5 arc seconds
with magnitudes 1.9, 3.0 and spectral types A1V and A2V and an orbital period
of 467 years. These are, in turn, spectroscopic binaries giving a four-star
configuration.
In addition, a faint orange companion C star (magnitude 8.9 – 9.60) at a
separation of 70.5” can be seen. This is, in fact, two orange dwarf stars
(Spectral types M0V) that orbit one another in less than a day and is an
eclipsing binary to our line of sight known as YY Gem.
The orbital period of the AB to C system is unknown but is thought to be of the
order of 10,000 years.
An amazing six-star system!!
REGULUS
αLEO
Σ II 6
RA
10 08
Dec
11 58
Regulus is a four star system comprising two stellar pairs. The blue-white
primary (B7V, 3.8 solar masses) pairs with a yet to be visually observed
hypothesised White Dwarf star of 0.3 solar masses (detected via spectroscopy).
These orbit over a short 40 day period. Regulus is observed to be spinning
rapidly with a distorted shape (possible due to gravitational interaction with
the white dwarf?).
At a separation of 177 arc seconds lies the secondary which is also a contained
binary common proper motion pair with an orbital period of 2000 years. The
two components have spectral types K2V and M4V with magnitudes 8.14 and
13.5.
Mizar and Alcor
RA
13 23 55.5
Dec
54 55 31
Mizar (magnitude 2.23, spectral class A1V) was the first double star to be seen
through a telescope in 1650. Its companion can be seen clearly at a separation
0f 14 arc seconds. Mizar A was also the first star found to be a double via
spectroscopy and later its companion B was also shown to be a spectroscopic
binary making Mizar a quadruple system.
At a larger separation of 707 arc seconds lies Alcor (3.99, A5V) which is also a
spectroscopic binary with a red dwarf companion.
Mizar and Alcor’s proper motions have long been observed to be similar but as
they are part of the Ursa Major moving group a true gravitational connection
between the two was in doubt. However, it has recently been proven (2009) by
two separate teams that Mizar and Alcor represent a true binary system at a
distance of about 83 light years.
Algieba
Gamma LEO
RA
10 19 58
Dec
19 50 29
Algieba is a true double star comprising two giants at an angular separation of
4 arc seconds.
The primary star (K0III, 2.28) has a surface temperature of 4, 470 K, a
luminosity 180 x that of the Sun and a diameter 23 x the Sun.
The companion star has a temperature of 4, 980 K a luminosity of 50 Suns and
a diameter 10 times the Sun.
The orbital period is 500 years.
Iota Cancri
RA
08 46 42
Dec
28 45 36
The A component lies at a distance of 298 light years and is a G8II spectral type
with apparent magnitude 4.02. This yellow/orange star has evolved off the
Main Sequence and has a high Fe abundance.
Its companion is a blue-white Main Sequence star (A3V) with magnitude 6.57
and lies at a distance of 2800 A.U.
The angular separation is 30.6 arc seconds and the orbital period is a
staggering 65, 000 years!
The pair are often referred to as the “Spring Albireo”.
Cor Caroli
RA
12 56 02
Dec
38 19 06
Cor Caroli (Charles’ Heart) was named in honour of Charles I (or II?) in 1660
and is a binary system at a distance of 110 light years with an angular
separation of 19.6 arc seconds.
The primary is an A0 “chemically peculiar” star whose magnitude varies
between 2.84 and 2.98 over a period of 5.47 days. This variability is thought to
be due to a powerful magnetic field (5000x that of the Earth) giving rise to
starspots that vary in intensity during the star’s rotation period.
The secondary is an F-type Main Sequence star of magnitude 5.60.
Virtually no change has been observed in the system’s configuration since 1830
leading to a calculated large orbital period of 7, 900 years.