[vsnet-chat 5868] Re: GSC vs Tyc2

["Stan Walker" <astroman@xtra.co.nz>]

Hi Arne,

Indeed, I did compare my results against your photometry and spent a lot of
time thinking about the answers. One of the most frustrating was a star
which Guide 6 describes as 6846 174. It's description in that puts it down
as a white dwarf but I don't think that's correct. Using a Meade 8" f6.3
telescope and the ST6 this comes out as a single star but a bit ragged. Your
photometry makes it into three stars and explains why my magnitude and
colour was different. When I add the intensities derived from your
photometry I get a reasonable match. I think Guide 6 uses the distance from
one of the fainter components to get the absolute magnitude of the brighter
object but that's only a guess and may be wrong. It's irrelevant in this
context. I am using a set of filters from Mike Bessell and they came through
the Auckland Observatory with the message that they were designed to match
the ST6 to the standard BVRI system. In my naivete I assumed that the system
transformations would be tiny and was surprised by their size!

Some years ago you mentioned the idea of using multiple comparisons and I
did this in this field with the stars of interest. It improved the values
quite dramatically and it's a technique that I'll continue to use.

When I did the check of Tycho values and transformations against E Region
stars it was not necessarily the faintest stars which had the largest
deviations. But the very bright ones were good in V.

I'm OK with the idea of always stating how the magnitudes and colours are
determined but along the way the descriptions often get mislaid. So I'm a
great believer in getting everything as close to the standard system as
possible right from the start. This means a bit more work in initial
calibration but it also gives photometrists a greater understanding and feel
for what they're doing. I remember reading in my first ever Norton's Star
Atlas something along the lines of "that photoelectric photometric was a
great step forward except that there were no standard systems and the
magnitudes were meaningless!" Now we're beginning to see many star measures
published in the VSNet messages with quite non-standard magnitude
descriptions - reminiscent of pep in the 1950s - not that I was doing it
then, but it's interesting - if that's the right word - to try to match some
of the early measures.

Regards,
Stan


----- Original Message -----
From: "Arne Henden" <aah@nofs.navy.mil>
To: "Stan Walker" <astroman@xtra.co.nz>
Cc: <vsnet-chat@ooruri.kusastro.kyoto-u.ac.jp>
>

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