I have mentioned this issue several times before. There needs to be at least an option in VSP to allow printing the star comp labels to 2 decimal places on the face of the chart. Rounding to the nearest tenth adds up to 0.05 of systematic error to the estimates, for no good reason! For example, the charts for HL Cma, the "120" comp is actually V=11.952, should be labelled "1195". The "130" comp is actually V=13.042, and should be labelled "1304". The systematic error incorporated in this rough rounding adds almost 0.1 magnitude error when using these two principal comp stars as bracketing!
I know you can get the precise values by selecting the "photometry table" option, but it is a needless and time consuming step to do it every time for each new chart, and pencil in the correct magnitudes manually.
The solution in the plotting code would be nearly trivial, just add one more digit to the output, add another option block to the "advanced" section.
I really hope someone could take care of this small request...
Thanks,
Mike
Hi Mike,
I just print the entire photometry table on the back side of the chart :-)
You are missing a lot of useful information by just looking at the V magnitudes, the error in the measurements & color information for example!
-Emery (EEY)
Hi Mike,
I discussed this with the chart team not long ago in the contect of visual measures of large amplitude Cepheids, say 1.0 to 1.5 range. I'm not too sure that it matters much with Miras but many of the lower amplitude targets would benefit from this idea. My only concern was that it tends to clutter the chart. Cepheid comparisons also need to be close in magnitude - say about 0.2 or 0.3 at the most.
I also saw Emery's comment. The photometry tables are not perfect - I had cause to check stars which appeared in the list for BH Crucis and which differed from the Hipparcos values by 0.3 in a couple of cases. The answer was startling - for completeness the fainter stars were based on photographic values - and if you've worked with those as I have at times they're often less reliable than visual magnitudes. Hipparcos values might be doubtful at that level but they're certainly better than the old SPv and SPg values from more than 60 years ago!
Glenn Schrader of Variable Stars South also experimented with some ideas to improve the accuracy of visual estimates. They take a little more time but worked quite well. With many people wishing to extend observing into variable types other than Miras perhaps we should be examining how it's all done and ensuring that the comparisons are adequate for the task,
Regards, Stan
[quote=Stan Walker]
I'm not too sure that it matters much with Miras but many of the lower amplitude targets would benefit from this idea. My only concern was that it tends to clutter the chart. Cepheid comparisons also need to be close in magnitude - say about 0.2 or 0.3 at the most.
[/quote]
Yes, That's the main "argument" I have heard against extending comp labels to 2 decimals - "clutter". Well, to me its just adding one numeric character to a short string! Typically from 3 to 4 digits printed on the face. If its really such a big deal, the font could be changed a few points smaller!
[quote=Stan Walker]
I also saw Emery's comment. The photometry tables are not perfect - I had cause to check stars which appeared in the list for BH Crucis and which differed from the Hipparcos values by 0.3 in a couple of cases. The answer was startling - for completeness the fainter stars were based on photographic values - and if you've worked with those as I have at times they're often less reliable than visual magnitudes. Hipparcos values might be doubtful at that level but they're certainly better than the old SPv and SPg values from more than 60 years ago!
[/quote]
Well, I think with most new comp stars coming from APASS, these old issues of comp star accuracy will be going away.
[quote=Stan Walker]
Glenn Schrader of Variable Stars South also experimented with some ideas to improve the accuracy of visual estimates. They take a little more time but worked quite well.
[/quote]
I am curious what ideas Glenn came up with?
BTW, Emery's issue with colors of comps does need to be addressed as well. Why not print charts in color? In my own homemade photometry charting program (C++), I can plot the stars colors (B-V). I typically use Red for stars with B-V > +1.0, Yellow for B-V between +0.6 to +1.0, Green for B-V between +0.2 to +0.6, White for B-V between -0.2 and +0.2, and Blue for B-V below -0.2
Mike
Mike, I for one would have problems with charts being in colour. Colours tend to do funny things under red light.
Kind regards
Stephen [HSP]
In the VSP form under ADVANCED OPTIONS > MISCELLANEOUS OPTIONS, have 3 radio buttons that the user can select one, two, or three decimal places (default would be one).
Michael