Visual Variable Star Observing Michael Kohl, BBSAG

BBSAG Bulletins

The BBSAG Bulletins are compiled by Roger Diethelm and offered electronicaly as Rich Text Files.
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The Purpose of Amateur Variable Star Observing

Variable stars are important because they supply us with much information on specific stellar states. Dependent on the type we learn about their mass, radii, temperature, luminosity, inner and outer structure, composition, distance and evolution. Professionals are not able to observe all known variable stars. Therefore amateur astronomers can provide important scientific data. In the last years confidence in amateur work grew among professionals; data requests on specific object increased steadily. One of the most important concerns is the long-time behaviour of particular stars. This is the only way to arrange specific observations in other wavelenghts.

Classification of Variable Stars

Each variable star is designated with a name and a number. Names are issued in the order of discovery in a particular constellation. For historical reasons the first variable discovered gets an R, the second an S down to Z. The 10th star is RR, followed by RS, RT ... to RZ; SS, ST ... to SZ etc. After that, the naming continues with AA, AB, AC and so on. The letter J is omitted. The constellation Sagittarius counts today far more than 4000 variables. After QZ (the 334th variable star) they become V335, V336 etc. which sets no limits to the number of stars. Although recent mass-dicoveries of variables in globular clusters and other galaxies by satellites questions this naming system.

Types

There are two major groups of variable stars: the intrinsic and the 'apparent' variables. The most important types are:

Pulsation Variables:

• Cepheids (yellow stars, periods between 1 and 70 days, amplitudes of 0.1 to 2 mag)
• RR Lyrae Stars (white giant stars, periods of 0.05 to 1.2 days, amplitudes of 1 to 2 mag)
• RV Tauri Stars (yellow supergiant stars, periods of 30 to 150 days, sometimes superimposed periods of 500 to 9000 days, amplitudes up to 3 mag)

Longperiod Variables:

• Mira Stars (amplitudes of 2 to 9 mag, Red Giants with quite regular periods of 80 to 1000 days)
• Semi-Regular Variables: Quite regular periods of 30 to 1000 days, interrupted by phases of irregular brightness, amplitudes up to 2 mag.
• Irregular variables
• Light curve shows no or very little periodicity.

Erruptive variables:

• Supernovae (amplitudes up to 20 mag! 2 types in general)
• Novae (close binary stars with mass transfer resluting in heavy outbursts)
• Reccurent Novae (like novae but several outburst historically recorded)
• Dwarf Novae (similar to novae but periods of 10 to 1000 days, smaller amplitudes (3-6 mag))
• Symbiotic Stars (similar to novae but amplitudes only up to 3 mag)
• Flare Stars (violent sudden outbursts with amplitudes of 1 to 6 mag, duration only minutes!)
• R Corona Borealis Stars ('inverse novae': most of the time on maximum brightness, then fading of up to 9 magnitudes, most probably due to condensating carbon)

'Apparent' variables

• Eclipsing Binaries (binary systems whose orbital plane lies in our line-of-sight, which causes the eclipses when on star is passing in front of the other one)
• Rotating Variables (stars with spots (bright or dark))

Data Archive

Each organization has its own data administration (unfortunately) and therefore its own rules for transmitting and acquiring data. To enable exchange of the results on an international level, indication of reference comparision stars is important. These stars are used for estimating the visual magnitude of the variable. Some organizations use finder and comparision charts which are readily distributed to the interested amateur.

BBSAG

The group of eclipsing binary observers of the Swiss Astronomical Society (BBSAG) acquires data of minima-times of eclipsing binary systems. Estimation of the magnitude itself is usually not required. The aim is trying to determine most exactly the time of maximum eclipse i.e. the time of minimum brightness. Long-term observations allow to make statements on the evolution of such a system. Observations take several hours a night to cover an entire eclipse.
Finder Charts will be available soon on astro!nfo and can now be requested at:

last modified: 27-April-1998 (ab)
BBSAG / astro!nfo-Team / barmettler@astroinfo.org