Hi all!
It was a very long time ago I did some variable star work, but want to get at it again. However, two things puzzles me:
If a VSP-chart are missing magnitudes on comparison stars (i.e magnitudes completely missing, regardless FOV), what to do?
I request a VSP-chart for visual observations, but in the chart header (top left corner) max and min magnitudes are for example listed in “B-mags” - does that mean that the comparison stars are in B-magnitudes as well?
Many thanks,
Found the answer to question number 1. But number 2 is unsolved. Tnx again.
#2, The chart magnitudes for the comparison stars are Johnson V I believe if you select “visual” orientation. However, if you select “binocular” in the “advanced Options” section as well you get a subset of stars marked as comparisons. The magnitudes indicated come from a variety of source catalogs but for visual use are all OK.
The information in the chart header specifies the magnitude range and in what color/filter the range was observed with. Other information such as the J2000 coordinates, name, chart ID, variability type are also shown.
Here is a grab from today from Variable Star Plotter (VSP) of the R Leo ‘A’ scale chart. name, J2000 coordinates for telescope/planetarium program use, the chart epoch which is important for stars that may have large proper motion, Max, Min in the Johnson V filter, period is the long-term average in days, type is M (Mira-long period variable) and the spectral type.
Jim (DEY)
Greatly appreciated, thanks. If I understand you correctly, it doesn’t matter what type of min/max magnitudes are listed in the header. As long as I have chosen a chart for visual application, the comparison stars will be V-mag, or roughly visual?
Hi Bjorn,
If you pick a visual (as opposed to CCD) chart, the mags are all visual, so 74 = 7.4m visual. It is in the range values of the variable itself that you need to be a little bit wary Sometimes, especially with the red stars like Mira and similar types, you will see a range given in’p’ or ‘pg’ which means ‘photographic’. As the older style photographic plates were relatively insensitive to red light, the photographic range of a red star would have a fainter value than the visual. To determine the visual range, as a ballpark figure make the range brighter by about a mag and a half - so a star with a range of 10-14 pg would have a visual range of about 8.5-12.5 - but I stress again that this relates only to the range in brightness of the variable. The comparison star magnitudes are a different ‘kettle of fish’ entirely - or as an astronomer I used to know would say ‘a different crater of pisces’.
The variation range and its stability depend on the variable type. The color indicated for the variation will give you an idea of what to expect to measure when you observe. Long-period Mira types will vary their max, mins from cycle to cycle usually for example.
If you select a visual orientation chart the magnitudes shown for the comparison stars are what you want to use for eye-based estimates, either naked eye, binocular or telescope using your eye as sensor.
Which star is giving you B for the variation color in the header?
Jim (DEY)
