Recurrent Novae
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| FOREWORD. The night of August 30, 1975 was
so typical of Florida in late summer. The weather was sultry and muggy.
Not a breath of air moved. Even the sea breeze had stopped as if too hot
to move! And without the cooling sea breeze the house was quickly becoming
unbearable. After supper the kids had gone down the street to play with the other neighborhood kids. Bill (my late husband) was busy catching up on his article writing, paying bills, etc. So, I thought I would go out and sit on the front steps to cool off and watch the traffic go by. Yes, the mosquitoes were sure to be out looking for their evening meal, but staying inside held no appeal for me! The neighborhood was quiet except for an occasional passing car and the usual screams and yells of excited kids playing in the street. Absentmindedly I looked up into the night sky. While the glare from the mercury vapor streetlight did its best to obliterate many of the summer stars as possible, I could still make out the brighter stars in the constellation of Cygnus (The Swan). After a short time, I noticed that something just did not look right. At first, I thought I was seeing a jet or satellite slowly making its way through the constellation, but then I noticed the bright object was not moving. After a few more seconds, I decided that something WAS indeed amiss! Thoughts flew through my mind! A new comet perhaps? Or, maybe even better yet...A NOVA?!!! Immediately I jumped up and went back indoors. Quickly I made some notes in my logbook. I jotted down the approximate brightness of the object (which I estimated to be 1.5 magnitude) and its location. After referring to Norton's Star Atlas, I thought maybe a star designated on the map as Nova 1876 had decided to do a repeat performance, but the location was just not right. A few days later, while chatting with a neighbor, I learned that indeed a nova had been spotted several days earlier! Knowing that piece of information confirmed my observation, but WAS the new star Nova 1876 springing back to life? As it turned out, the nova was not Nova 1876, but another star that received the distinction of being called Nova Cygni 1975 and was located near 63 Cygni. The newcomer had reached a visual magnitude of 1.8 on August 30-31. By late September the star had faded to slightly more than 7th magnitude before disappearing. (NOTE: More information on Nova Cygni 1975 can be found in the October, November, and December 1975 issues of Sky and Telescope. In addition, the reader may wish to refer to the 3rd Edition of The Cambridge Atlas of Astronomy, by Jean Audouze and Guy Israel (1994) pages 282-283 and/or The Cambridge Encyclopedia of Astronomy, edited by Simon Mitton (1977) page 81 and 83.) RECURRENT NOVAE. As far as astronomers are concerned Nova Cygni 1975 was just an ordinary or classical nova as opposed to a recurrent nova. Recurrent novae are simply cataclysmic variable stars the have a history of undergoing more than one violent outburst in their lifetime. On average, these nova-like outbursts can occur from 10, 15 to 80 years apart and are typical of the red giant and small white dwarf binary systems. Then there is another class of novae called dwarf novae that also undergo frequent nova-like outbursts, but do so on a smaller scale. Here, the period is much shorter and the difference in magnitude change is much less.. For instance, U Geminorum type stars undergo outbursts every few weeks or even months with a maximum brightness that lasts a few days. The change in magnitude is usually on the order of 3 to 6 magnitudes. A prime example of this type star is SS Cygni that maintains a maximum brightness for about a day and then slowly returns to minimum. Z Camelopardalis type stars (also dwarf novae) can stay bright some 10 to 25 days. The magnitude change is between 2 to 4 magnitudes after which the star basically stops its activity and begins to oscillate in brightness. Finally, the SU Ursae Majoris type stars that undergo super outbursts every few months and which last longer than two weeks. Three other attributes set the recurrent novae apart from the classical novae: * The spectra of the recurrent novae undergo a change during the outburst stage. Unlike the classical novae spectra, the coronal lines show extreme excitation. * The magnitude range for a recurrent nova is smaller than the classical nova. This range appears to be about 7 magnitudes, whereas, a classical nova may increase 12 or 13 magnitudes in brightness. * A recurrent nova (a red giant star and a very old star) has a small white dwarf for a companion. In such a binary system, hydrogen gas is transferred from the red giant star to the small white dwarf star. Over a period of decades, a white dwarf accumulates such an excess of hydrogen that a thermonuclear explosion ensues. A SHORT LIST OF RECURRENT NOVAE. Following are three recurrent novae that the amateur astronomer might like to try and observe: * T Coronae Borealis (known as the Blaze Star) flared up in 1866 and 1946.. * RS Ophiuchi flared up in 1901, 1933, 1958, and 1967. * T Pyxidis has quite a record for flaring up and did so in 1890, 1902, 1920, 1944, and 1965. The following are also recurrent novae, but lack dates: N2 Sagittae, N5 Sagittarii, U Scorpii, and V616 Monocerotis. A SUGGESTION. Should you find yourself getting even mildly interested in observing recurrent novae or variable stars in general, I would highly recommend the following books for your bookshelf: Observing Variable Stars, by David H. Levy (1998) Variable Stars, by Michel Petit (1987) Variable Stars, by John S. Glasby (1969) The Study of Variable Stars Using Small Telescopes, by John R. Percy (1986) SUMMARY. While the heavens may declare the glory of God, it takes a nova or two to keep things interesting is a seemingly unchanging Universe! And while the average person may get excited about a passing comet or an extraordinarily pretty grouping of several planets, along with the Moon, there is nothing quite like the appearance of a nova to set the heart and mind racing! Nancy L. Thomas 2/25/2000 "Humble Before The Stars."
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