[vsnet-chat 5348] Re: On UY Cen fading

["Sebastian Otero" <varsao@fullzero.com.ar>]

> On UY Cen fading
>
>     According to BAA VSS Circular 112, 3 (J. Toone), UY Cen is reported to
> have undergone a deep minimum (mag 10) in 2002 February to March.  Such
> a deep fading may have been compared to a RCB-type fading.

In no way...
I am sure we are dealing again with different color response and observing
technics.
A proof of that is the comparison between Peter Williams' observations and
mine.
There is approximately a 1.3 mag. difference for a given time. There is also
some scatter due to the difficult task that is to estimate such a red star
(B-V 2.7 - 3.5). But this huge difference is for sure the source of the
discrepant comments.
The star is ACTUALLY very dim comparing with previous activity (as Colin
reported).
The GCVS lists a range 9.22 - 11.2 in B.
We know its color index so it means more or less 6.5 - 7.7 in V.
And recently it has been much fainter than that, it's true.
But I can't see any similarity with an RCB event.

The event is more likely similar to that of L2 Puppis in the last couple of
years: its mean magnitude has been fainter than the catalogued values. L2
Puppis got as faint as 7.0 (0.8 mag. fainter than "official") and this one
may have done such a thing in a more important fashion.
Future monitoring will reveal it but -although faint- the star's behaviour
has nothing strange. It is very stable around 8.5 - 9.1.


> Colin Henshaw (BAA VSS) in February 2002 that UY Cen was the faintest he
> had seen in many years.

Maybe Colin can inform us WHEN this low state started.

Peter asked:

> Perhaps the difference in reported magnitudes relates to resolution of the
> companion star or a different comparison sequence?

I used a 8" and the star is correctly identified.
The cause arises in the deep red color as mentioned before.
Sequences (specially if they are V based) can not account for such a
difference.
Check my chart of UY Centauri at:
http://ar.geocities.com/varsao/Carta_UY_Cen.htm

And this is a comparison between Peter observations and mine:
http://ar.geocities.com/varsao/Curva_UY_Centauri.htm
You can see our different color response there.

Regards,
Sebastian.


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