Affiliation
American Association of Variable Star Observers (AAVSO)
Mon, 01/12/2015 - 18:24
In VSX, the magnitude range of most stars is specified as: x.xx-y.yy, but, occasionally, one finds the form: x.xx (z.zz). Eg: "7.43 (0.08)" for V2314 Oph. What is the interpretation of this "range"?
Tom
Hi Tom,
when you find such a thing it means that the amplitude of variations is 0.08 mag.
The maximum magnitude field in these cases refers to a magnitude that may not actually be a maximum.
In the case of EA-type variables it will be the maximum magnitude because it is the typical magnitude of the star but for other types it will usually be a mean magnitude value.
Cheers,
Sebastian
I also asked about this a while back. Several stars on my observing list have brackets including a number of RCB eg V1135 Sco, Y Mus, MACHO 135.27132.51, MACHO 401.48170.2237. So Y Mus is shown as10.14 (1.6:)p. So is the range 8.5-11.7? LCG shows a visual range of 9.8-11.6
There are several CVs as well. Consider CSS 080404:213309+155004 which is shown as 15.67 (5.33)clear. So does this mean 15.67 is the mean and that this UG ranges from 10-20. There are quite a few CSS and SSS UGs that also have brackets included in their range.
If the given figure is a mean, one assumes that that the mean is found by adding the observed values and dividing by the number of observations. This would give the range? Or is it, especially with CVs that this is the mean magnitude when they are observed when in quiescence? That would make sense to me (with my limited knowledge).
Stephen [HSP]
Hi Stephen,
No, the mean magnitude is not related to the amplitude. The amplitude given is the total amplitude.
In the case of RCBs, they behave more like EAs, staying most of the time at maximum, so the maximum magnitude would usually be an actual maximum. That is the case with Y Mus (maximum magnitude 10.14 V) which, btw, hasn't shown any minima in recent times.
In the case of CSS CVs, the maximum magnitude is the outburst discovery magnitude plus the total amplitude so the range for the star in your example should be 15.67 - 20 CV.
The mean magnitudes can be found for instance when the magnitude is obtained from a photometric source (APASS, GCPD, etc) and the study of the star only gives differential magnitudes, thus an amplitude is taken from the paper but the mean magnitude is taken form another source.
There is no simple answer to the question...
Cheers,
Sebastian