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VSP single sequence option request

wbs's picture
wbs
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Joined: 2010-09-05

I'd like to see a radio button option in VSP to limit the labeling of comparison stars to one for each magnitude, the one closest to the variable.

In crowded areas like Cygnus, this would help declutter the charts and would make it easier for us to find the comparison stars we're really looking for.  It would also serve to direct everybody's attention to the same sequence of comparison stars.  This would even be helpful when plotting a binocular chart for an area that overlaps the comparison stars for a neighboring binocular star.

I would expect to turn this option off only when observing multiple variables on the same chart or when too many of the closest comparison stars are too close to brighter stars to use with binoculars.

I'm not sure which section is the best place to post this request.  Please feel free to move it to another section.

Dick

VSP option
HQA's picture
HQA
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Joined: 2010-05-10

Hi Dick,

VSP depends on a database of comparison stars called VSD (Variable Star Database).  It was developed through the efforts of many volunteers, spearheaded by Vance Petriew.  The fundamental decision was made that each comparison star stands by itself, based on its RA/DEC coordinates.  It is NOT tied to any specific variable star, since crowded fields might show multiple variables, with the single comparison common to several different sequences.

What you ask is a reversal of this: choosing a set of comparison stars to display for a specific variable, rather than all of the comparison/sequence stars that fall within your selected field of view and selected magnitude range.  I can think of a few problems with your scheme, including the fact that most sequences are developed using guidelines that specify approximately one sequence star per 0.3mag step, so one star per magnitude defeats the guidelines.

Crowded fields can be a pain, whether you are dealing with binocular variables or telescopic ones.  Probably your best choice is some up-front work, such as underlining on a printed finding chart those sequence stars that you intend to use with your target.  I can't think of an easy way for VSP to handle it, but we should keep your idea around for a future version of VSP.

Arne

VSP option
wbs's picture
wbs
Offline
Joined: 2010-09-05

Hi Arne,

Oops!  What I meant to say was, one labeled comparison star per magnitude value (in tenths) -- in other words, labels should be printed for all of the comparison stars "intended" to be used with the variable plus the nearest other comparison stars that fill in the gaps in the sequence.

Underlining or circling a sequence by hand on the chart works in some cases, but there are some fields where I'm inclined to print a binocular chart, which will turn off most or all comp star labels, and then copy selected comp star labels from another version of the same chart on which all comp are stars labeled.  I'm lazy enough to want a computer to do this for me.

Thinning the labels automatically would require VSP to make a list of all comp stars to be labeled, calculate the distance from each comp star to the center of the chart (some spherical trig, similar in complexity to the spherical trig involved in placing each star on the chart), and sort and thin the list of labels before plotting them.  I assume this would be done in or near the part of the present VSP code that places the labels so they don't overlap each other or the stars -- thinning could be easy or very hard to add depending on whether user option settings and the necessary position information are visible to this part of the code.

Thanks to everyone who has made VSP what it is today, and especially for providing the binocular chart option and for fixing the problem with missing stars along the poleward boundary.

Dick

single sequence
HQA's picture
HQA
Online
Joined: 2010-05-10

Hi Dick,

That probably could be done, with a bunch of caveats.  Crowded fields are an interesting problem.  We have been discussing what the next generation VSP would look like, and we might consider adding some
intelligence in the comparison star plotting.  Thanks for your suggestion!

Arne

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