[vsnet-be 25] gamma Cas; delta Sco; V862 Sco; Be stars

[no name <crawl@zoom.co.uk>]

For those not afeared of biasing themselves, the lightcurve history of
gamma Cas is well and concisely summarised in Burnham's Celestial
Handbook volume 1.  Other well known gCas type stars are X Per and BU
Tau [the Pleiad Pleione]

Both gamma Cas and delta Sco are ROSAT bright sources, and IRAS
sources...

...for gamma Cas some suspect the xrays to mean a compact companion
[neutron star], such that it is actually a gCas+XP type star like X Per.

gamma Cas and delta Sco are also both "zeta Oph" type Be stars...
...this is a criterion based on behaviour of spectral absorption lines.

V862 Sco is probably a "lambda Eridani" type Be star: these stars can
show very short timescale flaring that is possibly generated by surface
magnetic field effects.

Be stars are main sequence to giant stars of spectral type "late" O, B
or "early" A. betaCep=betaCMa stars are giant to bright giant stars of
type B.  Some bCep stars can be Be stars... ...some Be stars have
non-radial pulsations... ...some Be stars are zeta Ophiuchi stars,
lambda Eridani is also a zOph star on occasions! zOph stars are high
order nonradial pulsators, lEri are low order nrp.  There are also 53
Per stars...

Be stars that undergo optical outbursts become gCas stars... ...best
known examples are gamma Cas, X Per, BU Tau and [NOW] del Sco.

Be stars are sometimes called shell stars because of their spectra...
...Be stars are sometimes called shell stars because they are surrounded
by a circumstellar shell... ...Be stars can be shell stars _and_ shell
stars, or can be shell stars _without_ being shell stars, or can be
shell stars sometimes, not at others, or whatever...

In fact, Be stars can exhibit several contemporaneous types, just one,
or none at all.

Be stars are rapid rotators with a wide spread of v sin i due to
orientation effects. Many people think that orientation effects can help
to explain various aspects of the above.

Be stars can exhibit all or any of the above at any time,
contemporaneously or sequentially, and then stop exhibiting such
behaviour(s), and possibly or possibly not start doing so all over
again! Be stars can stop being one sort of Be star and start being
another.

Be stars are confusing taxonomically...

gCas Be stars undergo a hot outburst which is followed by cooling before
things return to the pre-outburst situation, hence the character of
their lightcurves... ...and it takes a while.  A spectroscopic
diagnostic is the independent behaviour of the violet and red wings of
the selfabsorbed hydrogen emission line[s].

John

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