Procyon and the Constellation Canis Minor

Introduction – Canis Minor

Canis Minor in the Classroom

Procyon – Introduction

Procyon – Composition

Procyon B


From December until April, the constellation Canis Minor (The Little Dog) can be seen in the Northern Hemisphere. It represents the smaller of Orion’s two hunting dogs and, when visible, appears to stand on the back of Monoceros, the unicorn. (See Fig.1)

Canis Minor can be relatively easily found, it is situated to the left of Orion

Canis Minor image map  Fig 1.

According to myth, Canis Minor was placed in the sky by the gods who were touched by a magnificent display by a dog called Mera. Mera showed complete loyalty and love for its master Icarus and for his family.

Its main star Procyon, meaning ‘before the dog’ is so named because it rises before Sirius (the dog star) and in total is consists of over 40 stars, however only four other main ones, they are Gomeisa (Beta Canis Minoris), and others similarly named, Gamma, 6 and Epsilon Canis Minoris (See Appendix 1 ).

Unlike, for example, the majority of stars in the Constellation Orion, the stars in Canis Minor are not close together. Procyon is 11.31 light years distant from the Earth, and the nearest in its constellation after that is 112.32 light years distant. This ‘distance’ is calculated by first determining the annual parallax 1 , and converting this into a distance (See Appendix 2 ). The distances of each of the five stars are shown below:


Annual Parallax (arc seconds)

Distance (light years/pc)



11.31 / 3.472



171.44 / 52.632



171.44 / 52.632



112.32 / 34.383



407.17 / 125

1 – Annual Parallax is half the angle through which the direction of a star shifts as the Earth moves from one side of its orbit to the other.

2 – Apparent Magnitude is the magnitude of a star as it appears to the observer


Although the distance between these stars is great some of the further ones are actually brighter in terms of absolute magnitude, if they were all 10pc from the Earth, Procyon would not be the brightest.  If we take the visual magnitudes of the stars, i.e. apparent magnitudes 2 it is a simple matter to determine the absolute magnitudes of the stars ( Appendix 3 ):


Apparent Magnitude

Absolute Magnitude


+ 0.38

+ 2.68


+ 2.9

- 0.71


+ 4.32

+ 0.71


+ 4.54

+ 1.85


+ 4.99

- 0.50

            As you can see, the brightest star is Gomeisa, however the great distance that it is further back from Procyon (160 ly) makes it appear dimmer. These distances and magnitudes when coupled with some declination information form the basis for a practical, classroom model.

Canis Minor in a Classroom


X (metres)

Y (metres)

Height above floor (metres)

Alpha (Procyon)




Beta (Gomeisa)




















Plan View of Average Classroom:





Using data collected/calculated we can calculate the position of each star when scaled down into a classroom. By using simple trigonometry, the x and y co-ordinates and the height was calculated (from declination etc. information). Setting up the model in the classroom gives a reasonable size picture of what is actually out there.

Use LED’s and suspend them from the ceiling.  Alternatively, the LED’s can be held in place using retort stands. The next stage is to use resistors to vary the brightness of each LED, these can be set approximately as per the absolute magnitudes of each star.

If you now look at the model from the viewpoint it appears that the constellation is ‘flat’ and that Procyon is the brightest, however, if you then walk around you then begin to see the distances involved, just how different the arrangement of the stars seems from outer space and that infact Procyon isn’t as bright as you first thought.


Procyon is a binary star system; this means that it is made up of two stars.  The main star is Procyon A and the other is known as Procyon B.  Procyon A is the brightest of the constellation, being the eighth brightest star in the sky. It is a yellow-white star with a spectral class of F5IV-V, so it is a subgiant-main sequence star with a surface temperature between 6300 and 7800K, unlike our Sun, which is of spectral class G5 and as such a main sequence star with a temperature of about 5000K.  The spectral classes of the stars are shown by the Hertzsprung-Russell diagram:

It can be seen from the diagram that Procyon A has about 7 times the intrinsic brightness of the Sun. The actual figure is about 7.5, this means that it is 7.5 times more luminous.

Using the mass-luminosity relation which has been shown to exist for main sequence stars it can be roughly deduced that the mass of Procyon A is 1.75 that of the Sun, which fits in with information found during research.

This extra mass (compared to the Sun) means that the force exerted on a body equidistant between the Sun and Procyon A by Procyon A is greater than that of the Sun. This means that the region in which planets can stay in orbit around Procyon A is different to the Sun, and also is the habitable range, especially with the greater heat on Procyon.




        Procyon is a star of spectral type F5. Being stable for about 6 billion years, this represents the upper limit for advanced, mammal-like forms of life. A hypothetical, habitable planet within the Procyon system would be a sunnier place than most regions on Earth. Not only does Procyon emit more visible light, this is also true for ultraviolet radiation. Life on Procyon (planet) would require either more protective pigments in their cells or a highly efficient mechanism for DNA repair.


       A further obstacle for life in the Procyon system is the presence of a White Dwarf. When Procyon B became a Red Giant some hundred million years ago, the increase in brightness would have severely stressed the climate on the planet. If it survived the disaster, the world of Procyon would be a desert planet now. Any surviving creatures would huddle around the last reservoirs of water.



The constitution of Procyon A can be determined from analysis of its emission spectra.  From X-ray spectroscopy data taken using the Chandra and XMM-Newton telescopes 1 the graphs below display intensity of EM radiation detected per second plotted against wavelength of that detected radiation.

            The wavelength is recorded in angstroms (1 angstrom =10 -10 m) and the graph shows a range of wavelengths of 36-174 Ǻ.

1 - Taken from paper researched by members of SORN (National Institute for space research), The Netherlands; Paul Scherrer Institut, Switzerland; Columbia Astrophysics Laboratory, USA; Mullard Space Laboratory, UK and  Universitat Hamburg, Germany. April 2002


The spectra show clear traces (labeled on graphs) for elements and isotopes of the elements Oxygen, Nitrogen, Iron, Silicon, Magnesium, Carbon, Nitrogen and Argon.

Procyon A can be shown to have a core temperature greater than 16x10 6 Kelvin and be more massive than the Sun by the presence of Carbon, Nitrogen and Oxygen as part of its composition. This is a process of stellar energy generation, starting with the thermonuclear fusion of a proton with the nucleus of 12 C. This process occurs in tandem with the Proton-Proton chain in stars with a core temperature exceeding 16 million Kelvin. (While as star of the Sun’s mass is only hot enough to enable the proton-proton chain).

This process is called the CNO cycle (See Appendix 4 ) and accounts for the Carbon, Nitrogen and Oxygen peaks on the spectra above.

Being a subgiant (a star evolving off the Main Sequence in the process of becoming a Giant star) Procyon is coming to the end of its main sequence life. Therefore the presence of the heavier elements could be explained by Procyon having undergone stellar nucleosynthesis. Forming the Ar, Mg, Si and Fe, with S- and R-processes forming the heavier Ni. However the mass of Procyon is only 1.75 M SUN (Irwin et al, 1992) and therefore does not have the minimum 3M SUN that is required to enable Stellar Nucleosynthesis as the Core Temperature reaches a higher level.

Two possible explanations present themselves as to the presence of these heavier elements within Procyon:

Firstly the Binary partner of Procyon, Procyon B, may have been over the Chandrasekhar limit. When Hydrostatic equilibrium ceased to maintain the stars’ stability it would collapse. The massive increase in temperature and pressure would enable the synthesis of heavier elements, before a type II supernova that would eject these heavier elements into the ISM (interstellar medium). If sufficient matter was ejected the mass of the star would drop below the Chandasekhar limit and so a Procyon B would become a White Dwarf (as seen at the present day) opposed to a Neutron Star. Meanwhile because of the close proximity to Procyon α much of the ejected synthesized elements would be attracted to by its gravitational field and so the heavier elements would go to add to the mass of Procyon A. So enabling Procyon to have these heavy elements.

Alternatively the binary pair could have originally consisted of a red Giant of mass greater than 3M SUN and a white dwarf. The mass of the Red Giant would be sufficient to enable the nucleosynthesis of the heavier elements seen in the spectrum analysis. As the Red Giant expands matter could flow from the Red Giant to the White Dwarf in a Roche Lobe. As Hydrogen is collected and was compressed as an accretion disc onto the surface of the white dwarf (Procyon B). The temperature would rise because of the increase in pressure and if greater than 10 6 K would ignite the envelope to cause a Nova. Though matter would be ejected the white dwarf would continue as a white dwarf (Procyon B as seen today). Also the mass of the red giant would have greatly reduced because of the mass-transfer streaming between the two stars and so it would have reduced to the present 1.75M SUN , below the nuclear synthesis level, but it would still contain heavy elements and as a smaller Subgiant proceed (as Procyon A does today) towards becoming a Giant again.

Procyon B

Procyon B is the White Dwarf of the binary star system Procyon and orbits Procyon A at a distance of 14.9AU on average, that it about 16 times the distance from the Earth to the Sun; this would be like having a white dwarf orbiting our Sun in an orbit between that of Saturn and Uranus.

Procyon B is not visible to the naked eye and was not detected visually until 1896 by John M. Schaeberle.  Although it was not visually detected, Arthur J. G. F. von Auswers first detected Procyon B in 1840, due to the irregularities observed in the proper motion of Procyon A, and deduced that it was a faint but massive companion.  This much dimmer star has a spectral class of A-FVII, and due to the closeness of its orbit with that of it’s companion have made observations of its luminosity, colours and spectrum difficult to determine.

Procyon B is massive, it has 60% of the Sun’s mass, but about only 2% of the Suns diameter, and possibly may have a diameter only 30% that of Earth’s.



Appendix 1 – Star Names

There are many systems used for naming stars as shown in the table below the stars that we are investigating, however, some stars are not named using all the systems, the full table of names is as thus:


Proper Name












































Names used in our text are either proper name, Bayer or Flamsteed.


Appendix 2 – Trigonometrical Parallax

· Trigonometrical Parallax is a method of determining stellar distances by using the surveying technique of triangulation. It is based on the fact that nearby stars appear to move relative to more distant ones as the earth orbits the sun.

· To determine the annual parallax record the position of the nearby star at two points on the Earth’s orbit separated by a time interval of six months. As stated earlier the nearby star appears to move relative to distant ones, using simple trigonometry the distance can be found.


d = 1AU/tan p

However, for small angles tan p = p, and 1 radian = 206264.81 AU (= 1 pc), therefore

d = 1/p” pc

Converting to light years is a simple matter of multiplying by 3.257. The main source of error in this calculation method is due to proper motion, the fact that the distant stars also move during the 6 month period.




Appendix 3 – Conversion from Apparent to Absolute Magnitude

In 1856 Norman Pogson (1829 – 91), a British astronomer formulated Hipparchus’ scale into a precise mathematical equation, and it is this that enables the simple conversion from apparent magnitude to absolute magnitude:

M = m + 5 log (10/d)

M = Absolute Magnitude, m = apparent magnitude and d = distance (in parsecs)

Appendix 4 – The CNO Cycle

The CNO Cycle is one of the methods of hydrogen burning, and occurs in stars with a mass of more than our Sun’s, i.e. Procyon A.

Step 1)             Carbon atom and Proton fuse to form an isotope of N and a γ ray:

12 C + 1 H           à         13 N + γ

Step 2)             The isotope of N decays to an isotope of C with the emission of a positron and a neutrino:                     13 N                        à        13 C + e + +ν                  (positron decay)

Step 3)             The C isotope fuses with a proton to form N with the emission of a γ ray:

                        13 C + 1 H            à        14 N + γ

Step 4)             The N fuses with another proton to form an isotope of O and with the emission of a γ ray :                                 14 N + 1 H           à        15 O + γ

Step 5)             The isotope of O decays to form an isotope of N with the emission of a positron and a ν:                                   15 O                   à        15 N + e + + ν                 (positron decay)

Step 6)             Finally the isotope of N fuses with a final proton to form an atom of C and an atom of He:                                  15 N + 1 H          à        12 C + 4 He

The net result of the CNO Cycle is that 4 protons combine to form a Helium nucleus, two positrons and two neutrinos.


Main Sources:


“Astrophysics and Cosmology” Rodger Muncaster

ISBN 07487 2865 1

“Astrophysics” Christopher Bishop

ISBN 07195 8590 2

Other small parts from various other internet sites

Project Compiled by : Ben R.Dubock, Katie Hassell and Charles W.D. Marsh