Corona Borealis
Transit Date of principal star: 16 May
MYTHOLOGY

Corona Borealis, or the Northern Crown, is the crown Ariadne wore at her wedding. It was made by the supreme goldsmith, Hephaestus, at his underwater smithy.

The story is connected to a more notable myth, of the Minotaur and of Theseus, who was destined to kill it. To do so, he needed Ariadne's help. This beautiful young maiden was the daughter of Minos, king of Crete. She was also the half-sister to the Minotaur, the half-man half-bull which lived at the centre of a labyrinth.

Every year Minos ordered seven young men and seven maidens from Athens to be served up to the Minotaur. The current hero in Athens was Theseus, son of Poseidon, and heir to the Athenian throne. Only a young man, Theseus had already proved himself by a variety of heroic deeds. Then time came for the yearly tribute to Crete. Theseus volunteered to be one of the seven young men.

As he arrived in Crete, Theseus was met by Minos, who challenged the young man to prove he was indeed the son of Poseidon. Minos threw a gold ring into the sea, and told Theseus to fetch it.

Theseus dove into the deep, and was met by dolphins which escorted him to the palace of the Nereids. Thetis, one of the Nereid sisters (or sea nymphs), gave Theseus a jewelled crown that Hephaestus had made. With the gold ring and the crown, Theseus swam back to Crete. This feat received the loving admiration of Ariadne.

Ariadne had a magic ball of twine that could roll out by itself and follow the path to the centre of the labyrinth, where the Minotaur was kept. She promised to help Theseus kill the Minotaur if he would marry her and take her back to Athens. Theseus agreed, so she gave him the ball of twine. Theseus followed the rolling twine to the centre of the labyrinth and promptly killed the Minotaur.

Unfortunately he forgot his promise. Or, some say, he did marry Ariadne, giving her the jewelled crown as a wedding present. And then he later abandoned her on the isle of Naxos, on the way to Athens.

Others have it that Theseus sailed off, leaving a sleeping Ariadne to pine for her loss. She implored her father, Zeus, to make amends. Zeus took pity and sent Dionysus to comfort his daughter.

Another version has Dionysus visiting Naxos and falling in love with Ariadne, so he cast a spell on Theseus. Theseus then forgot all about Ariadne and sailed off for Athens. In any case, Dionysus took her for his bride and placed the jewelled crown of Hephaestus on her head.

They raised four sons and `lived happily ever after'. When Ariadne died Dionysus took the wedding crown and placed it in the heavens between Hercules and Bootes.

LOCATION
The constellation Corona Borealis is found nearly midway between Arcturus and Vega; a little closer to the first of these stars.From Arcturus move up to Izar (epsilon Bootis) and then east fifteen degrees to alpha CrB.


The seven stars that make up the crown are not terribly bright, except for Gemma, or Alphecca (alpha Coronae Borealis), which is a 2.2 magnitude star 75 light years away.


The rest of the Bayer stars vary from three to six magnitude. The constellation includes several fine binaries, an unusual variable, and an extremely faint cluster of galaxies.

Both alpha Coronae Borealis and beta Coronae Borealis are spectroscopic binaries, with periods of 17.36 days and 10.5 years respectively. Gamma CrB is also a spectroscopic binary (period uncertain) as well as a very close visual binary (see below). Zeta CrB is actually two stars which form a splendid binary (see below). The two are approximately 220 light years away, given their parallax of 0.015".
DOUBLE STARS IN CORONA BOREALIS
Gamma CrB (Struve 1967) is a close binary with an orbit of 91 years. The PA is 265º and separation about 0.2".
Eta CrB (Struve 1937) is a fine binary with orbit of 41.5 years. Presently the companion can be found at PA 47º and separation 0.9".
Zeta2 and zeta1 CrB (Struve 1965): a pleasant pair of blue-white stars with 5.0 and 6.0 magnitudes; PA 305º, separation 6.3". Note that zeta2 is the primary.
Sigma CrB (Struve 2032) is a slow binary, with a period of a thousand years. Currently the companion is at PA 236º and separation 7.03"
Nu1 and nu2 CrB (Struve I 29) form a very wide (but only optical) pair of orange giants, quite suitable for binoculars: PA 166º, separation 372".
VARIABLE STARS IN CORONA BOREALIS
Alpha CrB is an EA variable: 2.21 to 2.32 with period of 17.36 days.
Beta CrB is an aCV type variable: 3.65-3.72, period 18.487 days.
Gamma CrB is a delta Sct variable: 3.80-3.86, period 0.03 days (=43 minutes, 12 seconds).
Delta CrB: RS variable, 4.57-4.69.
SigmaA CrB is an RS and delta Sct variable with period of 1.14 days.
R CrB is the most interesting variable here; an unusual RCB type variable with a range from 5.71 to 14.8.
The star maintains its maximum for most of the time, perhaps several years. Then it will start to fade, perhaps down to 8 or 9 visual magnitude, or as faint as 14 or 15. It fluctuates for some time, not maintaining any constant magnitude, and then years later will once again brighten to its maximum.
DEEP SKY OBJECTS IN CORONA BOREALIS
The only deep sky object is the Corona Borealis Galaxy Cluster.
This group is very faint but quite spectacular for those with the proper equipment.
The cluster is comprised of over four hundred galaxies in an area of about one degree (the width of your thumb). The galaxies are extremely distant, over a billion light years away, and consequently are very faint. The brightest of the group are 16.5 visual magnitude.
To find the cluster, move two degrees west of alpha CrB and north almost a full degree. In the same field, southwest, is the sixth magnitude binary Struve 1932 (PA 57, separation 1") with a period of 203 years.
CORONA BOREALIS - 5alp CrB (Alphekka)

Identification Data
Common Name Alphekka
Constellation Corona Borealis
Star Name 5alp CrB
Skymap Number 15340114
Henry Draper (HD) Number 139006
Harvard Revised (HR) Number 5793
SAO Number 83893
Durchmusterung (DM) Number BD+27 2512
Washington Double Stars (WDS) Number
Positional Data
Position and Proper Motion (PPM) Number 104146
Right Ascension (RA) J2000 15h 34m 41.268s
Declination (Dec) J2000 +26° 42' 52.895"
Position Uncertainty 0.0067s
Proper Motion in RA(J2000) /cos(Dec) +0.00898
Proper Motion in Dec(J2000) -0.089466
Radial Velocity +001.7km s-1
Trigonometric Parallax +0.04365s
Trigonometric Parallax Uncertainty 0.00079s
GCI Unit Vector in X (J2000) -0.529172
GCI Unit Vector in Y (J2000) -0.719641
GCI Unit Vector in Z (J2000) 0.449548
Galactic Longitude 41.87°
Galactic Latitude 53.77°
Observational Data
Observed Visual Magnitude (V) 2.22
Derived Visual Magnitude
Derived Visual Magnitude or Observed Visual Magnitude Uncertainty 0.003
Observed B Magnitude 2.25
Observed B-V Colour +0.028
Observed B Magnitude or (B-V) Magnitude Uncertainty 0.003
Observed U Magnitude
Observed U-B Colour
Observed U Magnitude or (U-B) Magnitude Uncertainty
Observed Photovisual Magnitude 2.3
Observed Photographic Magnitude
Morgan Keenan (MK) Spectral Type A0V+G5V
One-Dimensional Spectral Class A0
Position Angle
Year of Observation AD
Data Source
SKY2000 - Master Star Catalog - Star Catalog Database, Version 2.
Sande C.B., Warren Jr. W.H., Tracewell D.A., Home A.T., Miller A.C.
(Goddard Space Flight Center, Flight Dynamics Division (1998))
CORONA BOREALIS - Star Stats
CARBON STARS
Spectral class R stars are carbon stars. They are cool giants with strong absorption bands in their spectra due to C2, CN, and CH. Technicium is observed; and since there are no stable isotopes of technicium, and the longest half-life is only a few million years, nucleosynthesis products must be being brought to the surface. These stars are believed to be highly evolved stars with masses over three times that of the sun.

How is carbon produced by nucleosynthesis?
The term nucleosynthesis means the creation of new elements in nuclear reactions. These reactions occur in stars, where nuclear fusion joins the basis elements present in the Universe initially to produce heavier elements. The stars which produce these new elements are in the main sequence; they are producing energy by nuclear fusion. Although the consumption of the nuclear fuel in this way is generally referred to as burning, it is not combustion or chemical burning. It is the production of heavier elements by a nuclear joining. Hydrogen, present in about 75% in the universe initially, produces helium by two processes in stars. The two main processes which occur for the production of helium are the 4p chain (or proton-proton chain) and the CNO cycle. The 4p chain is the lower energy process, and the CNO chain also produces helium by the use of 4 protons , but occurs at higher energies by using carbon, nitrogen and oxygen as "catalysts". Once helium has been synthesized, then in higher mass stars, carbon can also be synthesized in the core, by the tri-alpha process.
The carbon stars must be higher mass stars if helium has been synthesized into carbon.
The initial nucleosynthesis process of hydrogen to helium is the 4p chain and has 3 stages;-

Stage 3 needs stages 1 and 2 to occur twice to produce 2 deuterium.
There is therefore 6 protons in; and 2 protons out. So 4 protons are used; hence the name 4p chain.

This nucleo-synthesis of hydrogen to helium occurs at lower temperatures; at higher temperatures the CNO process can occur:-


When hydrogen burning ceases in the core, the radiation pressure in a main sequence star no longer balances the gravitation attraction, and matter is pulled inwards in the core. In smaller stars, the core is condensed to form a white dwarf, while the outer layers expand and the star forms a red giant star. In larger mass stars, such as the "carbon stars" of the Corona Borealis, the contraction of the core raises the core temperature by such an extent, when gravitational energy is converted to heat, that fusion of the helium is able to take place. This process is called the tri-alpha, or triple alpha process.

The carbon is produced in the core of stars. In the carbon stars of the Corona Borealis, the carbon appears to be transported to the surface, as is seen by their spectra.

The Thomas Hardye School, Dorchester, UK.