[Aavso-photometry] [AAVSO-DIS] True Chart Confessions

[Wolfgang Renz]

Hello

Using geometric shapes for the stars in charts will IMO severely
degrade the readability of the charts for visual observers. I even
didn't like old charts from other sources that used "just" differing
numbers of line or triangular spikes to distinguish different bright-
ness levels. 

As the newly processed charts should in general just use comps in
a limited B-V range, one won't gain much in using special shapes
for the stars/comps on the chart. And getting a chart with mostly
square stars/comps won't help me much. For charts with comps
with severely differing colors, one could e.g. add an option to ap-
pend a cmag B-V color index to the the cmag V values in the charts
(like Sebastian is doing it on his charts) or a letter code.

But it is IMO a good idea to mark the comp stars in the field photo-
metry table (e.g. by a one letter/number code) according to their
color as calculating a color index from the band mags is a time
consuming task just to get an idea for the colors of the comps.

In crowded or wide fields there are often many comps (often also
with the same V cmag values) so that it gets difficult to find a spe-
cial one quickly just by guessing from the coordinates in the field
photometry list. Adding a relative position like e.g. "4.5' SSW"
would make this task really much easier.

What is also missing is an approximate mean color index of the
var itself. Without this one will have no good idea which comps
are closest in color. The spectral type is partially given, but this
doesn't allow a good mapping to a color index. Especially not
in reddened fields.

And an other one especially for CCD observers:
Right now the AAVSO VSP charts serve primarily visual obs.
The VSD table is a good first step for CCD observers. But as
they just contain recommended comp stars with sufficient large
stemps in mag for visual observing, they don't support CCD ob-
servers well. These will limit the comps to as close as possible
and as color matching as possible comps that are in their FOV
and as bright or a bit brighter than the var (of course just if possi-
ble). So it would be good for these to add more of these stars to
the field photometry table. For brighter vars it would be also good
to add some fainter close of such color matching comps to support
ensemble photometry if no sufficient bright one is present. One
could solve this also via a switch in the VSP form. But anyway it
would be good to especially mark recommended comp stars for
CCD observers.

Clear skies
 Wolfgang

-- 
Wolfgang Renz, Karlsruhe, Germany



----- Original Message ----- 
From: "Michael Linnolt" 
To: "Richard Huziak"
Cc: "Aavso-Discussion" <aavso-discussion at mira.aavso.org>
Sent: Wednesday, July 22, 2009 10:01 PM
Subject: Re: [AAVSO-DIS] True Chart Confessions

> I think an equally important issue is not knowing the colors of the
> comp stars, when using a new chart, or at first glance. Choosing
> the best color is as important as finding suitably bracketed ones.
> I manually go to the photometry table and mark them on the chart,
> which is time consuming. Printing the charts in color probably won't
> help, if most observers use red lights in the dark, so I would like to
> suggest we use a geometric shape for the comp stars, based upon
> their B-V. For example:
> 
> B-V range       comp star shape
> ________        _____________
> 0.0 - +0.5         Solid circle
> +0.5 - +1.0       Solid square
> +1.0 - +1.5       Solid triangle
>> +1.5              X shape
> 
> Basically, the best color comps could have similar shapes to the
> other stars, with the more "angular" and obviously startling shapes
> to signify the more and more red comp stars, which should be
> avoided if possible.
> 
> Mike L.
> 
> 
> 
> ----- Original Message -----
> From: Richard Huziak
> Date: Wednesday, July 22, 2009 7:48 am
> Subject: Re: [AAVSO-DIS] True Chart Confessions
> To: Aavso-Discussion <aavso-discussion at mira.aavso.org>
> 
>> Hi Bob and Geoff et al,
>> 
>> Early versions of the charts had the 'photometry table' printed at
>> the bottom right of the chart, but even a basic one with just V mags 
>> took up a significant portion of the chart.  But just a 'row of mags
>> that appear on the chart' might be a way to uncrowd this idea.
>> However, I'd want to see it as a print option and not a standard fea-
>> ture on all charts because in my application, I want as much chart
>> area as possible. 
>> 
>> But best to submit the idea now and let the chart team make the 
>> call.  (I have several ideas they should implement soon, too) :-)
>> 
>> rick
>> 
>> -- 
>> * * * * * * * * * * * * *
>> Richard Huziak
>> Manufacturing Engineering
>> SED Systems
>> Saskatoon, SK, Canada
>> tel. (306) 933-1676
>> <huziak at SEDSystems.ca>
>> * * * * * * * * * * * * * 
>> 
>> 
>> 
>> Geoff Gaherty wrote:
>> > Bob Stine wrote:
>> >> Here's a mistake I've frequently made: I make a visual observation 
>> >> under the dark sky and dim red light, using what I think are the two
>> >> closest comp stars.  Only later do I find out that somewhere on the
>> >> chart was a comp star even closer in brightness that I failed to notice
>> >> in a crowded field in the dark.
>> >>
>> >> Has this happened to anyone else?  If it's only me, then stop reading
>> >> here. But if this is a common issue, then I have an idea to fix it.  When
>> >> one prints a chart using the AAVSO Variable Star Plotter (VSP) and
>> >> one selects the "Table of Photometry" option, lo and behold, there is
>> >> a column containing the magnitudes of the comparison stars in de-
>> >> scending order.  What if we could have that column printed along, say,
>> >> the right margin of the chart?  That would give us a "Table of Contents"
>> >> of all the comps in the sequence for that chart.
>> >>
>> >> So, let's say our variable is around 11.5 and we see a comp at 10.8
>> >> and another at 12.3.  We ask ouselves at the eyepiece,  "I wonder if 
>> >> there are comps perhaps in the 11 th magnitude range.  We could
>> >> then glance at our handy index.  If there were no comps listed between
>> >> 10.8 and 12.3, then we have our answer: there is a sequence gap -
>> >> deal with it.  But if there is a comp(s) between 10.8 and 11.3, then we
>> >> know to go on an "Easter Egg Hunt" to find them in the field.
>> >>
>> >> If this idea has any merit and there is some interest out there in it, then
>> >> I will submit it to HQ as a possible future VSP enhancement.  But if 
>> >> it's just me with the problem, I'll take my licking publicly and drop "the
>> >> cause".
>> >
>> > That is an _excellent_ idea!  I often have the same experience.
>> >
>> > Geoff [GHT]