[vsnet-chat 1258] Re: H/T chart vs. VT mags...

["Fraser Farrell" <fraserf@dove.net.au>]

G'day all,


On Wed, 02 Sep 1998 08:02:00 +0200, Berto Monard wrote:

> If I read you correctly you are about to make a blunder. Guide 6 and a
> number of other charting software use GSC magnitudes. These are
> inferior magnitudes and should be avoided.

Robert Fidrich wrote earlier:

> In the spring I dowloaded all the H/T charts (HIPGIF and HIPGIF2) from
> the VSNET.
> I thougth these chart were made using the Hipparchos and Tycho
> catalgues, but the sequences show large differences compared with the
> VT mags or Hp mags. from the Guide6.


Previous Guide versions used the GSC mags, but Guide 6 _can_ use 
the Johnson V magnitudes from Tycho for stars brighter than 11th mag. 
All the necessary data is on the Guide 6 CD-ROM.

It would seem that both Robert and Berto -- like me -- bought their 
Guide 6's as soon as they were released.  These "early" Guide 6's 
do not show Tycho's Johnson V magnitudes.

But if you download the updated Guide 6 program files from Project 
Pluto (http://vsnet.projectpluto.com/update6.htm) you will discover that
the "later" Guide 6's now show Johnson V mags.  Plus the very useful B-V
They will also still show the VT and Hp mags in the "More Info" display;
and for variable stars a maximum, minimum and mean magnitude (but these
are _Hp_ mags).


From my experience, the relationship between VT, Hp and V mags is 
colour dependent.  But to get an approximate visual range (according 
to Hipparcos) for a variable in Guide 6 you can:

(1) From the "More Info" display, note the Johnson V mag and the 
maximum, minimum and mean Hpmags.
(2) Knowing that the V mag is calculated from the mean Hpmag, calculate 
the "offset" as:  offset = (V - Hpmag[mean])
(3) Add the "offset" value to the Hpmag[maximum] and to the Hpmag[minimum] 
to get the approximate visual max and min.

This procedure (naively) assumes that the colour doesn't change between 
max and min.  Also note that Hipparcos missed observing the full range 
of many variables.  So if it's in the GCVS just page down to the GCVS
details displayed in "More Info" and hope that the GCVS mags aren't
photographic.


If you have the Windows or 386-DOS versions of Guide 6 then I highly 
recommend a download from Project Pluto's website.  The latest releases
have lots of new capabilities such as using RealSky South, using the
USNO ACT Reference Catalog, the improved ELP Lunar Theory, showing
ground tracks for asteroid occultations, "locked target" animations, the
ability to run reduced installations without the CD-ROM,....



cheers,
Fraser Farrell

http://vsnet.dove.net.au/~fraserf/  email: fraserf@dove.net.au
traditional: PO Box 332, Christies Beach, SA 5165, Australia

VSNET Home Page

Return to Daisaku Nogami

---

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