[vsnet-chat 557] eta Carinae

["STAN WALKER" <astroman@voyager.co.nz>]

Greetings, All,

I'm a little puzzled by the comments that eta Carinae changes by 0.4
magnitudes on a timescale of days. At a distance of 2000 parsecs or so the
object we see visually (about 10" in diameter?) is about 20,000 AUs across
which gives a light travel time of over a hundred days. Presuming  the
Homunculus is more or less spherical there is a light travel lag of several
weeks between the edge and the centre as we see it. So any central event
which causes the visible object to brighten by 40% should be seen initially
as a bright central spot at least twice the brightness of the edges. As the
centre dimmed the edges would then brighten to appear ringlike. Noone
reports anything like this - or have I missed it? Or is my thinking
muddled?

Regards,
Stan Walker

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