NEW STARS OR NOVAE.

Hawera Star, Volume XLVII, 14 April 1928, Page 3

NEW STARS OR NOVAE.

BY F.G-. — (F.R.A.S., MEMBEE DE LA SOCiETE ASXKONOMIQDE DE FRANCE.) (Written for ‘'Tlie Star.”) in the Chinese records of Ala-tuan-lin is to be found the earliest reference to temporary or new stars, known to astronomers as novae, and the first definite record of sucn a star was made in the year 134. Jl.O. The elder i'Jiny was of thei opinion that stimulated by observations of this star Hipparchus was led to complete Ins star catalogue. Hipparchus not only gave astronomers the first star catalogue of reasonable accuracy, but we credit to him tne invention of trigonometry, tue discovery of the precession of the equinoxes and, what was even more important still, lie placed the science of astronomy on n truly scientific basis by his introduction of orderly and scientific methods of observation and investigation. The new star in the constellation of Cassiopeia was the most famous newstar of what might be termed pretelescopic days. Tliis star burst into brilliance in 1572, and had the effect of attracting back to the study of astronomy tne great Danish pioneer— Tycho Brahe. This star is recorded to have been brighter than Sirius — the largest star in the heavens at the present time —and is almost overhead just after sunset when at its maximum brightness. It was seen in the daytime, and remained for 15 months ■visible l to the naked eye. With greater telescopic power and equipment it is only reasonable to suppose that a greater numter of “new stars” would 1)0' detected by observers in recent years, and no less than five; have been observed with the naked eye since the beginning of this century. In 1901 Nova Persei was discovered by Bov. T. D. Anderson on February 21. At discovery this star was of the magnitude 2.7. Tw-enty-seven hours before its discovery it was fainter than magnitude 11.0” and 3S hours after its discovery it had increased to a star of magnitude 0.1, or brighter than Alpha Centauri (the outside pointer to the Southern Cross). It then decreased in brightness, first rapidly and then with a series of oscillations of brightness with, of course, accompanying change® of spectral type. In 1912 11 no bo, of Pombaas, Norway, discovered Nova Geminorujn. When discovered this star was of magnitude 4.2, and evidence proved that it had increased in brightness during the preceding 23 hours by 6.5 magnitudes. It reached, before slowly fading with marked fluctuations, a magnitude of 3.4. In June of 1918 a star in the constellation of Aquila, and now known as Nova Aquilae, burst into a star of magnitude —l, becoming for a time the brightest star in the northern sky. When discovered on June 8 of that year it had reached a magnitude of 0.8. Apparently this star had l been known as a slightly variable star for 30 years. In 1920 on August 20 Nova Cigni was discovered. This star when discovered, was of magnitude 3.5, and at its maximum brightness rose 1 to 1.8 magnitude. In 1925 Nova Pictoris made its appearance, and followed the same course in general as the others referred to above. This star reached a maximum brightness of a. star of the first magnitude, and then faded away with fluctuations of brightness. The nova discovered a fortnight ago by Mr. A. C. Crust, D.Sc., of Scientific Bescarch Department, whilst making observations at Windsor, near Oamaru, is not so far visible to the naked eye. From spectroscopic examination of recent novae wo have gained what appears to be the normal sequence of changes in the spectra of tfiese new stars. In the early stages the predominating elements are hydrogen and ionized iron, titanium and calcium. The displacement of the dark lines towards the violet end of the spectrum and varies as the wave length, thus suggesting motion of the absorbing gases, towards the observer, with increasing or decreasing velocity of approach. We can best explain this implied motion towards an observer by the supposition that the absorbing gases are in the form of a shell of gas driven out from the disturbed central area. In the second stage the spectrum of a new star reveals the presence of companions on the red side of the absorption lines, thus indicating the presence of other elements which are unable at first to reveal themselves owing to theirj disorganised state. At this stage generally the lines corresponding with the presence of carbon, oxygen, nitrogen and helium appear. The final stage seeing to be in the direction of that of what is understood as a Wolf-Bayet star of varying brightness. There are various explanations as to the origin of new stars. The natural suggestion of two stars colliding and causing violent upheavals was inferred from the dark and bright line spectra being simultaneously present. But further investigation lias proved that more than two bodies would be required to cause the observed changes in the varying spectra. Prof. Bickerton advanced the theory of a third body is formed by the tremendous tidal action of one star on the other. In this way a portion of each star is torn off and according to tliis theory it is the nnstability of the elements in this third body that causes the hidden outbursts of light. This third body, being in an unstable condition wouid light up the space between the two passing stars, but being small it would soon cool and reach a. state of equilibrium, thus rapidly diminishing in brightness and leaving the original stars revealed as separate bodies. Thus it would seem this happened in the recently reported case of Nova Pictoris, and commented on by Mr. P. o’Dea T.8.A.5., «f Hawera. Sccligcr and Halm hate developed the theory of the collision, a. star, or a. binary star system, with some extensive nebulosity. .In this theory the brilliant outburst is caused by the radiation of tho star’s light becoming intensified whilst passing through the tenuous matter of a small nebulor which is not dense enough to radiate enough light on its own account to be observed.