[vsnet-alert 130] trouble in the jungle

[jop@carmen.phys.columbia.edu (Joe Patterson)]

     There has been much mention of "TOADs" in this forum, and I thought it
was worth entering a dissent on this term -- which it seems to me is
astronomically and zoologically poor.  Dwarf nova fans are familiar with the
term "SU UMa stars", and the meaning is clear: dwarf novae whose eruptions
divide very distinctly into long and short, and which show superhumps in their
long eruptions.  Some people also use the term "WZ Sge stars" to refer to the
subset of SU UMas which either: (a) show the longest outburst intervals, (b)
have few or no short outbursts, or (c) qualify according to both (a) and (b).
Because this is somewhat vague, and because Nature provides no dividing line,
many of us either do not use the term "WZ Sge stars" or use it only as a
convenient shorthand for a more cumbersome phrase - "the most infrequently
erupting SU UMa stars".  At least it refers to an actual star; whether it is
a useful subclass is harder to say.

     Now comes this term TOADs.  To my mind this has no meaning, at least none
which bears any relation to the groupings suggested by Nature or physics.
Outburst amplitudes of dwarf novae range smoothly from 2 to 9 mag with no
breaks or suggestions of any dichotomy.  Nor is there any distinction in the
physics known, suspected, or alleged to be involved in the outburst -- they
all seem to be powered by gravitational energy released by unstable mass
flows through the accretion disk.  Most stars receiving this label are WZ Sge
stars, which are in turn basically just SU UMa stars which don't erupt much.
Most SU UMas are intrinsically faint in quiescence and therefore have fairly
large outburst amplitudes -- and the more intrinsically faint, the lower the
accretion rate and hence the longer the outburst interval (as predicted in
standard accretion disk theory).  In all such properties the SU UMas form a
smooth continuum, not suggestive of even an OBSERVATIONAL dichotomy, much
less any true distinction in the underlying physics.

     I strongly urge use of traditional variable-star nomenclature, lest we
dissipate much energy trying to understand each other's favorite animal
acronyms.  "SU UMa stars" with the optional subclass "WZ Sge" seems like the
best way to go.

     TOADs, in this context, are also an offense against zoology.  Toads
move forward by a series of very short hops, whereas FROGS leap.  But stars
like WZ Sge and AL Com are distinguished for their leaps, and for having
few or no short hops.  Thus if we want a name from the animal kingdom, we
might consider Fabulously Robust Outbursting Gravity-powered Stars.

     But anyone who does so should be shot at sunrise.

joe patterson

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