[vsnet-chat 1264] Re: From the "A Guide to Dwarf Novae Observing" - "How to observe faint stars"

[Taichi Kato <tkato>]

Re: [vsnet-chat 1256] From the "A Guide to Dwarf Novae Observing" - "How to observe faint stars"

   Please note the article was written in 1988, more than ten years ago,
when there was no CCDs available, and I was an amatuer variable star observer
(even not a student of astronomy).

   The following comments are from my experience of that time.

> I doubt if there are observers with "CCD-eyes"

   Some observers were indeed called to have "CCD-eyes" (or II-eyes, where
II = image intensifier ;-).  An observer used to resolve WZ Sge from the
companinon using a 10-cm telescope, and was able to observe many OVV-QSO's
at minimum.

> In my opinion it is impossible to detect a few photons of a faint star in
> the avalanche of backgroundphotons.

   I experienced a very interesting phenomenon.  Under the same dark-adaptation
level, my right eye perceived the sky background "smooth" and the left eye
perceived "too noisy".  The right eye could detect much fainter objects than
the left eye.  There must have been some sort of "noise suppression" working
in the natural neural network (?) somewhere between the retina and the brain.
It may be even possible some sort of PSF-sensitive or faint-star-sensitive
neurons existed.  Canals on Mars might have been a work of similar sort of
pattern recognition, e.g. detecting linear-shaped signals etc.

   Under bright citylight, CCDs can easily detect these faint stars even in
the presence of the bright background light.  The reasoning of the object's
signal being overwhelmed by the backgound photons doesn't always seem to
be substantiated.  This clearly depends on the image processing ability
of the individual.

> the archives of VSNET itself clearly demonstrate that observers make
> mistakes with some regularity.

   I must note mistakes of this kind have been mostly categorized into a
few: confusion with the nearby star (most frequent), inadequate chart,
omission of faint companions or distorted patterns.  In CVs realm, this
kind of confusion is minimized since there are already good POSS-based
and CCD-based charts (presently) available.  Another factor is that dwarf
novae, which were the main targets of this limiting magnitude challenge,
are not always concentrated around the Milky Way field.  There are many
objects at high galactic lattitudes, making confusion less likely.  Confusions
in CVs tended to occur in novae cases, esp. such having close companions.

> Therefore, my advise is to be careful, and leave the variables close or at
> the limiting-magnitude to the larger telescopes!

   One of my motivatations at that time was that the magnitude scale is
logarithmic.  In order to gain 1 more mag, it would be easy to grade up the
telescope to 10 cm to 16 cm.  Possibly affordable 16 cm to 25 cm, difficult
to 40cm, impossible to 64cm ...  If one were able to gain 1 mag by some
training, it was thought to be a less expensive choice.  One was used to
be advised to avoid daylight, avoid moonlight, avoid planet and bright
stars -- when locating the field using a finder, observers were advised
not to use bright stars.  Observers were advised not to be lured to look
at bright stars, like Pleiades or famous double stars, even when one was
asked to show such objects.  A rumor was that signals from such bright stars
will destruct the subtle recongition system adapted to faint objects --
the similarty to I.I. was in it ;-)  Observers were recommended not to read
books or charts in a bright room, but to train to read them under starlight
(with the help of the scattering light, I didn't have to use a pen light
to see charts).  We know some observers actually attained this degree of
faintness adaptation, but they also confessed they became deadly exhausted
after observation ... ;-)

Regards,
Taichi Kato

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp