VARIABLE STARS & NOVAE
slightest doubt this is the most know and widespread monitoring activity
in which amateurs are involved for decades. This is probably the biggest
area where amateurs own the field and use rigorous methods.
are grouped in two main categories depending of the nature of their
Extrinsic variables which light variation is inducted by the eclipse
of a small companion (Algol case) or by an effect of the stellar
Intrinsic variables which vary most of the time regularly, resulting
of physical changes inside the star or its atmosphere (pulses, plasma
ejections), effects that contract and expand the superficial layers of
the star. This later category is subdivided in some major classes:
Long period variable stars like Mira Ceti which brightness
slowly varies over several years
Irregular variable stars like Betelgeuse which exhibit no defined
Eruptive variable stars which light rises up to four magnitudes in a
few seconds (Wolf 424 AB, UV Ceti, Eta Carina).
that we also find in external galaxies and globular clusters are also
variables stars. The relation that links their luminosity to their
fluctuation is known with accuracy. Their absolute brightness is
inversed proportional to the square of their distance.
member of an AAVSO local section, you will receive a list of
variable stars to survey. The first time you have to test your ability to
accurately appreciate magnitudes. Nowadays however you can use
photometers to automate this process without to forget to zero your
device and optional filters system.
results of this monitoring are light curves accurate to 1/10th of a
magnitude or more in best cases. These reports are sent to the local
section of AAVSO for analysis that in exchange spares with amateurs
results of his researches.
are also variable stars that professionals divided in several subcategories
Fast novae which brightness may rise of 10 magnitudes in a few days
Slow novae which light increases regularly on a period of around 15 days
with a maximum that may last several months (Nova Herculis 1934)
Recurrent novae which presents light blasts at intervals of a few dozen
years, like T Corona Borealis (1866, 1946) or RS Ophiuchus (1958, 1967)
Dwarf novae which are cataclysmic variable stars. Their brightness rises
irregularly of several magnitudes in some hours (U Geminorum). This
event is the most spectacular evolution a variable star may know.
Novae-X which brightness mainly rise in X-light. This emission can
overpass the more intenses galactical X sources in two weeks. Most are
associated to faint stars of 16th magnitude.