----- Original Message ----
> From: luzius.thuerlemann <[email protected]>
>
> Hello there,
> Studying the double cluster NGC 884/869 while comparing to
> my recently developed picture on conventional negative-film, I found in the
> environment (north of OCL 365 and south of OCL 362/NGC 957) the following
> star:
> ASCC 170585.
I don't have that catalog. Google suggests it's the "All-sky Compiled
Catalogue".
> When I zoom out so that I see the double cluster and the two
> smaller OCL-clusters mentioned above, the bright star disappears and becomes
> a
> normal star like all the others in the neighbourhood. So I zoomed in and
> found
> that there is a second star displayed next to ASCC 170585 (visual mag 11.05)
> :
> 1425-03538941 with red-mag and blue-mag 0.00, color index and field number
> 0.00
> etc etc. This star disappears when I deactivate the USNO-A-catalog activated
> on
> Stars2 under catalog settings.
I don't have USNO-A2.0 either (it's huge), but if you give me the coordinates I
could use the "online resources" to get USNO-A for that star field.
Well I just tried that but there are too many USNO-A stars in the field to find
one particular star without more precise coordinates. And I don't think CdC
will search for USNO stars.
OK, I searched for it at Vizier. It appears to be the mag 10.57 GSC star
GSC3695.1339. It's also the Tycho-2 star TYC3695-01339-1 (listed as visual
magnitude 11.14).
Stars that bright won't have accurate magnitudes listed in the USNO-A catalog,
since it's designed for much fainter stars. I think CdC misinterpreted an odd
mag listing in the USNO-A catalog for this star (listed as R mag 0.1), so it's
displayed very bright. When you zoom out, the USNO catalog is no longer
"active" for the wider field, so it shows correctly as listed in smaller
catalogs of brighter stars.
The deep catalogs have many goofs like this, since they were prepared almost
entirely by computer from digital scans of the Palomar Sky Survey plates.
There are far too many stars to check even a small fraction of them all
manually, so, for example, dust specks or scratches on the plates, or
diffraction spikes, also get listed as stars.
>This is only one strange star
> appearance!
>The following star appears in the middle of NGC 1266/PGC 12131:
> QSO NGC 1266 (visual mag: 0.00, Mabs: 0.00, U-B: 0.00 etc etc).
Also in the
> constellation Leo: QSO RXS J10292+2729 on position Date: RA 10h 29m 47.01s
> DEC +27° 26' 48.7" .
> I guess the following star in the southern
> hemisphere is also such an "artificial" star: QSO Q 2138-4432 (position
> Date: RA 21h 42m 33.49s DEC -44° 15' 46.8").
"QSO" is "quasi stellar object", or "quasar", so these aren't stars.
CdC uses a different symbol for quasars, and since these are all very faint, it
uses a different size scale to indicate magnitude.
> Sometimes I also
> found a strange very bright star opposite of the sun on the
> ecliptic.
Here's one possibility: remember CdC shows dates as "YYYY MM DD". I think in
Europe it's more common to list the date first, then the month. So if you
adjust the date and get it wrong by 6 months, the sun would be half-way around
the ecliptic from where it should be.
-John
