[vsnet-unknown 12] re LO Cep and CT Vul

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

The "contextual" positions of these variables seems consistent with
their IA and IS: variability classifications.

The first lies near large regions of dark and light nebulosity amidst
Cep OB2, the second amongst regions of dark and light nebulosity amidst
Vul OB1.

It seems that the type IS is suggestive of rapid flickering, where
nonesuch is seen in type IA. Subtypes ISA and ISB are a split of early
and late spectral types, apparently unknown in CT Vul's case.

INA variables, ie "early Orion variables", are said to have occasional
abrupt fadings. Possibly LO Cep is only classed as IA because it has no
specific nebulosity associated with it.  Certainly bright nebulosity on
the edge of Sharpless 129 is not too distant.

There is a thin borderline twixt type ISA & INA, for eg.

Re the cause of variability: swirling clouds of protostellar material
occasionally occulting these YSOs?????????  That'd fit the short
timescales, and the quasiRCB nature of the fadings...

John

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