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 sextuple 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 first seen visually by Castelli in 1617 and
through a telescope in 1650. It was one of the first double stars to be photographed by
Bond in 1857. 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 (1889) and later its companion
B (also A class) 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 with yellow-white colourations at an
angular separation of 4 arc seconds. It was first observed by William Herschel in 1782.
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 (G5111, 3.64) 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 first observed by William Herschel and named in honour of
Charles I (or II?) in 1660. It 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.
It is suspected that each component may also be a spectroscopic binary.
Virtually no change has been observed in the system’s configuration since 1830 leading to a
calculated large orbital period of 7, 900 years.
Iota Bootis
RA
14 16
DEC
51 22
Iota Bootis (Asellus Secundus: Second Donkey Colt??) lies at an approximate distance of 97
light years and is a true double with a third very faint unrelated member,
The primary is an A-type Main Sequence dwarf that is a Delta Scuti variable star. Precise
measurements are needed but the magnitude varies between 4.73 and 4.78 over separate
pulsation periods of 38.22 and 30.55 minutes.
B is a A2 type star of apparent magnitude 8.27 (7.5).
Kappa Bootis
RA
14 13
DEC
51 47
Kappa Bootis (Asellus Tertius: third donkey colt) lies at a distance of 155 light years and is a
triple star system.
The primary is an A7 subgiant (magnitude 4.54) with a surface temperature of 7830K. It is
about to end its H-core burning phase and swell to a Red Giant. It is classified as a Delta
Scuti variable with a period of 1.56 hours and has a faint binary companion (combined
orbital period of 4.9 years).
The secondary (magnitude 6.6) is an F1V dwarf star with an estimated surface temperature
of 6835K.
The primary and secondary orbit over at least 6,000 (from observed partial orbit) to 8,700
(theoretical) years.
Mu Bootis
RA
15 24
DEC
37 23
Mu Bootis/Alkalurops (“club”, “shepherd’s Staff”) is a triple system at a distance of 121 light
years.
The primary is a yellow-white magnitude 4.31, F-type subgiant that is suspected to be
variable and to have an orbiting companion.
At a separation of 109.4 arc-seconds lies the main binary secondary system of two G1 Dwarf
stars (magnitudes 7.2, 7.8) orbiting over a 260 year period at an average separation of 2.2
arc-seconds.
Delta Cyg
RA
19 45
DEC
45 08
The dominant primary is a late Main Sequence B class supergiant star of magnitude 2.9, with
a luminosity 180 x the Sun, a radius of 4.7 solar radii and a mass of 3.5 solar masses. It is
known to be spinning rapidly (135 km/s at the stellar equator) producing an ellipsoidal
shape.
The secondary is a yellow-white F-class star with a luminosity 6x the Sun and a mass of 1.5
solar masses. Its magnitude is 6.3 and as it is only 2.5 arc seconds from the primary it can be
a challenge requiring steady, clear seeing! The position angle is 217 degrees.
A further two companion stars have been reported consisting of two pairing each 3 arcseconds apart lying at distances of 42 and 148 arc seconds from the primary. Other sources
report a single orange companion however??
AB has an orbital period of 918 years and lies at a distance of 170 light-years.
Albireo (Beta Cyg)
RA
19 30
DEC
27 57
A classic “showcase double” Albireo is actually a triple (or maybe quintuple) system and was
first observed by Flamsteed in 1691.
The primary is an orange class K helium fusing star with a temperature of 4400 K, a
luminosity 950 x the Sun, a radius of 50 solar radii and a mass 5x that of the Sun. Spectral
analysis revealed it to have a varying radial velocity and a companion was clarified by
speckle interferometry. It is a late class B9 dwarf star with a temperature of 11,000 K, a
luminosity 0f 100 Suns and a mass 3.2 x that of the Sun. Partial orbit measurements have led
to period estimates ranging from 100 – 213 years. The two stars are separated by 0.4 arcseconds.
The secondary blue star is a B8 dwarf with a temperature of 12,100 K, a luminosity of 190
Suns and a mass of 3.3 Suns. It is a rapid rotator (250 km/s at the equator) completing an
orbit in 0.6 Earth days. This gives rise to a surrounding disc of gas.
It is not certain that Albireo is a true “binary system” but, if it is, it has an orbital period of
around 100,000 years.
Epsilon Lyra: “Double-Double”
RA
18 44
DEC
39 40
This system consists of four A-class white stars organised into two pairs of binaries.
Epsilon 1 has two stars of magnitudes 4.7 and 6.2 separated by 2.6 arc-seconds orbiting one
another in around 1200 years.
Epsilon 2 has stars of magnitudes 5.1 and 5.3 orbiting in a period of 600 years (less precise).
The two systems are thought to orbit one another in about 1000 years and are currently
separated by 208 arc seconds.
Precise measurements only began in the 1980s but in 1986 a further companion star was
revealed by interferometry giving a five-star system.
However, it is thought that other surrounding faint stars could be part of the system and
that the total count could be ten revealing a complex, fascinating gravitational world.
Rasalgethi (α Her)
RA
17 14
DEC
14 23
Rasalgethi (Emperor’s Seat) is a triple (quintuple?) system lying 380 light years away.
The primary (magnitude 3.5) is a M5IIvar red bright giant that varies by a magnitude over a
14 year period. It is near the end of its life and undergoing mass-loss giving it an extended
gaseous envelope. Speckle interferometry has further hinted at a very close companion star.
The secondary is a double star consisting of a primary yellow giant (G5III) and a secondary
yellow-white dwarf (F2V) with a combined magnitude of 5.4).
The overall orbit is around 3600 years.
Nu Draco
RA
17 32
DEC
55 11
Nu Draco consists of two white dwarf stars (A6V, A4m both magnitude 4.9) at a distance of
99 light years and separated by 63.4 arc seconds.
The secondary is also a spectroscopic binary with a low mass companion completing an orbit
every 38.6 days.
The overall system has an orbital period of 44,000 years.
61 Cyg
RA
21 07
DEC
38 45
61 Cyg was the first system apart from the Sun to have its stellar parallax and distance
measured. The distance measurement of 10.3 light years made by Friedrich Wilhelm Bessel
is remarkably close to the current accepted value of 11.4 light years. As the stars are
separated by 31 arc-seconds the true binary nature was open to question until 1934 when
the orbital parameters were accurately measured confirming the true binary status.
The two stars are orange dwarf main sequence stars (K5V, K7V) with magnitudes 5.2 and
6.05 and a combined orbit of 659 years.
Star A is a BY Draconis variable star and B is a flare type variable star with a measured 11.7
year cycle. Both exhibit notable flare activity with B being 25% more active.
Almaach (γ And)
RA
02 04
DEC
42 20
This double star is actually a quadruple system lying at a distance of 355 light years.
Component A is a bright golden yellow giant star (K3IIb) of magnitude 2.2 separated from an
indigo-blue companion (magnitude 4.84) by 9.6 arc seconds and position angle 63 degrees.
However, Wilhelm Struve observed B to be a double in 1842 with the components
separated by less than an arc-second. Further spectroscopic analysis between 1957 and
1959 revealed a third star.
B is now known to consist of two B9.5V stars (magnitude 5.5) that orbit in 2.67 days and an
A0V star (magnitude 6.3). The two B9.5V stars and the A0V orbit in 64 years.
It is possible that fainter surrounding stars also belong to the system.
95 Her
RA
18 02
DEC
21 36
This is a true binary system with an orbit of about 11,000 years lying at a distance of 470
light years and separated by 6.3 arc-seconds.
Component A is a white A5 giant star (magnitude 4.96) with a temperature 0f 8000K a
luminosity of 67 Suns, a diameter of 6.8 Suns and a mass of 2.8 solar masses.
B is a yellow-white giant star (G8) with a temperature of 4900K, a diameter of 19.4 Suns and
a mass o £.2 solar masses.
A, due to its smaller size, is the more rapid rotator and is in the transition stage between H
and He core burning whereas B has already reached the He burning phase.
Delta Cephei
RA
22 29
DEC
58 25
Delta Cephei lies at a distance of 887 light years and is a triple system (possibly quadruple).
It was discovered by John Goodricke in 1784 and its pale orange primary is the prototype for
the Cepheid Variables: vital for distance measurements. It is the second closest Cepheid to
the Sun (Polaris being the closest) and varies from magnitude 3.5 – 4.4 over a 5.3 day
period. Recent radial velocity measurements revealed a spectroscopic companion B with a
tenth of the mass of A. This AB system orbits over a 6 year period.
The visual blue companion C is separated from A by an easy 41 arc-seconds and is strongly
suspected to also be a spectroscopic binary. Confirmation is needed but would give Delta
Cephei the status of a quadruple system.
56 And
RA
01 56
DEC
37 15
56 And lies at a distance of 360 Light Years and can be found on the SW border of the Open
Cluster NGC 752 (distance 1,200 Light Years and unrelated to 56 And).
The primary A is a K0 giant star separated from the M0 giant secondary B by 207 arc
seconds (PA 298 degrees). Burnham noticed the large proper motion of A and observed a
further C star (magnitude 11.9 at 18 arc seconds, PA 77 degrees). In addition, there is a
further star D of magnitude 9.77 lying at 204 arc seconds from A (PA 258 degrees).
The present magnitudes of A and B are 5.7 and 5.9 but there has been dispute in the past as
to which is the primary in this system implying some magnitude variations and possibly
variable-like activity?
However, A and B are not physically connected and are an Optical Double star system.
ɳ Persei
RA
02 51
DEC
55 54
The primary of this multiple star system is a K3 (originally reported as M3?) orange-yellow
supergiant (magnitude 3.8) with a luminosity of 13, 000 Suns and an estimated radius of 210
solar radii. Also known as “Miram” it lies at 1, 300 Light years and its light will have
undergone significant dust absorption due to its location deep in the Milky Way. It has at
least five companions although all are probably line of sight coincidences.
The secondary is a B9 dwarf star of magnitude 8.5 and its blue hue together with the yellow
tints of the primary make this a “mini-Albireo”. If this is a true binary system then the orbital
period would be a staggering 350,000 years which makes a true binary connection unlikely.
Ʃ 2816
RA
21 39
DEC
57 29
This, at first sight, appears to be a neat triple system found in the heart of the nebulous H11
Open Cluster (IC 1396).
However, things are far more complex and the following systems are now verified:
A (a magnitude 5.73 06F star) and C (magnitude 7.48) are separated by 11.8 arc-seconds (PA
120 degrees)
A and D (magnitude 7.53) are separated by 19.8 arc seconds (POA 338 degrees).
D and E (magnitude 13.19) are separated by 55.2 degrees (PA 351 degrees).
Another B star of magnitude 13.3 was identified by Burnham in 1889 and is separated from
A by 1.7 arc-seconds (PA 320 degrees).
Very high resolution observations revealed a further companion to A at a distance 0f 0.1 arc
seconds…………..and this is further shown to be a spectroscopic binary making A on its own a
very close triple system.
I think that makes Ʃ 2816 a seven-star system……..at least!!
And, close by is the double Ʃ 2819 system consisting of magnitude 7.4, 8.6 stars separated
by 13 arc seconds.
A multiple star feast!!!