[vsnet-chat 3656] Re: Overobserving

[Taichi Kato <tkato>]

Re: Overobserving

> Is it possible to correct for various observers' errors? The word systematic
> is frequently used but I don't know that this is a fair description. We're
> talking about Miras and so forth so the subjective errors which are
> associated with CVs and RCrBs don't come into it.

   As I wrote in the preceding post, I understand that constant offsets
caused by various reasons are major (and correctable) cause of observers'
errors.  And I just brought R CrB into discussion to exemplify how
"unbiased" look into visual estimates could extract signatures, since
the amplitude of pulsation in R CrB is usually considered below the
detection limit of visual observations.  This analysis was made possible
because the conventional observing strategy allowed to monitor R CrB stars
every night -- the same comparison is usually impossible for most of LPVs
and semiregulars.  In the usual sense of observing low-amplitude SR stars,
this situation is undoubtedly "obserobserving".

> What are you achieving by analysing visual measures of stars like RY Sgr,
> etc? It's easy enough to derive a period using DFT or something but this
> period is not particularly accurate. Whereas you can get a good seasonal
> sample from pep the visual measures give a value about 20-50 times less
> reliable. Take a Cepheid such as R Crucis - the pep measures will give an
> epoch +/- 10 minutes, the visual ones about 10 hours. So the error bars are
> much greater than the suspected period change.

   What do you think if some particular CCD/PEP observers will become
no longer interested in keeping track on these particular stars?
Some eclipsing variables have large gaps of PEP observations, but are
partly filled by visual observations, albeit lower accuracy.
I know at least one visual observer keep tracking on period changes
in bright eclipsers and pulsators, whose detectability of period changes
have been truly comparable to PEP observations.  [And the recent detection
of delta Sco outburst by S. Otero also outlines the achievable accuracy
of experienced visual observers.]

> I look in the GCVS and it
> tells me that BF Arae is a UGSS which generally have a longish period, no
> superhumps or orbital signatures and relatively uninteresting outbursts.

   You may be overrelying on the GCVS type.  There have been many examples
of UGSS/UGZ stars which turned out to be UGSU stars.  On the display
of my computer at the telescope, I kept looking at "V452 Cas UGSS"
while observing the current superoutburst.  [BF Ara: as I suggested
several times in VSNET lists, this star could be a good candidate
for the first southern ER UMa-like star -- well, ER UMa itself was
first cataloged as a "not particularly variable" novalike CV, but I must
note that its dwarf nova-type variablity was detected visually by Iida,
see the corresponding Name List -- this is already what visual observers
could do better than less frequent professional observations.]

> Perhaps it's significant that
> until superhumps were recognised about 1974  from pep measures the visual
> people, in spite of thousands of measures, didn't notice these. There was
> then an abortive attempt to prove that these could be tracked visually.

   If visual observers had not been advised to observe cataclysmic variables
once per night, the situation might have been different.  There are a couple
of recent detections of superhumps by visual observers: yes, they can be
detected visually.

> I'm unclear about the 'dips'. What was the time scale? Are we talking about
> a decrease covering several orbits or just something lasting part of a
> cycle? This brings up something which I've been thinking about for a time.

   In calling 'dips' in SS Cyg stars, I mention temporary fadings during
outbursts.  This phenomenon is rarely documented, nor followed by PEP/CCD,
at least some outburst (non-superoutburst in the usual sense) seem
to exhibit it.  In the Disk Instability Workshop, E. Kuulkers presented
a light curve of U Gem compiled from visual observations, which seems to
show such a temporary fading, which had been regarded as a phenomenon
associated with superoutbursts (as you mentioned).

> Maybe what I'm saying here is that the dense observing of CV stars is
> unplanned and consequently doesn't prove much. It's easy enough to find
> periodicities in visual data if the pep and CCD people have already
> established that these exist. But there are few good examples of the visual
> people making the discovery.

> In conclusion, I'm still not convinced that all this visual attention to CVs
> during outbursts produces anything of value.

   Perhaps you may have (by chance) little encountered these discoveries.
The SU UMa-type nature of AQ Eri was revealed by visual observations,
and was confirmed by photographic follow-up observations.  The first
independent detection of T Leo superhumps was also done by visual
observations.  Most recently, the discovery of a queer microquasar
V4641 Sgr (aka "old" GM Sgr) is triggered by visual observations.
If Berto Monard didn't make "overobserving" on the preceding night
of the event, this transient outburst could have been even missed.

Regards,
Taichi Kato

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