Affiliation
American Association of Variable Star Observers (AAVSO)
Wed, 11/28/2018 - 09:33
Hello everyone, I'm trying to get the phase of a variable, but my measurements leave me puzzled. I found a value that shows me the variation both in the data obtained from my shots, both in those of ASAS-SN, but between the two there is a difference both in time and in light intensity, although both are in V. The difference It is so great that at one point I even suspected that it was two different stars, but after careful scrutiny I can rule out this hypothesis. In the same field there are other variable stars that do not have this discrepancy with the ASAS-SN measurements.
I am attaching the phase plot graph as it appears to me with current data. What do you think?
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Maybe the light is blended in ASAS-SN from a nearby star. There is one 13 mag star 19" from your target. Blended light can explain why the amplitude is lesser and the target is brighter in ASAS-SN.
The best periods I got from the ASAS-SN data was 0.477555. Try to find a period in this vicinity that makes yours and the ASAS-SN curve synched.
I also found a period of 0.477247 that seems possible.
What is weird about this phase plot is that the eclipses don't line up between your data and ASAS-SN. There can be a generic offset, depending on whether one dataset was acquired at a different time than another, but the dips should occur with the same phase difference in the cycle.
One thing that is missing is error bars. Your personal data has a lot of scatter, so I wonder what the signal/noise is for each point; what your aperture size was; what your seeing was like; etc.. Otherwise, I agree with Thomas, in that blending is often a big problem and definitely could be the cause for the differing amplitude between your data and ASAS-SN.
Arne
I believe that the fact that a neighboring star can contaminate the ASAS-SN observations may make sense for the difference in amplitude, but not for the phase difference. I enclose a chart with the error bars and also the measured data on my shots.
I have looked at your data, but did not manage to get the two datasets in phase with each other. Maybe you should doublecheck the time in your set so there is no problem there. The period for both sets seems almost identical, but I could not get the minima synched between the sets or see the same shift between the primary/secondary minima in the ASAS-SN that your set have.
Hi Cervini,
Can you share me the two light curves data sets (HJD and magnitude) .If I get these data sets then I can try to find out the period using PDM in IRAF and then try to fit these data sets to the tff code of Geza Kovacs.
Pradip
I checked again and I do not think there are any errors. To convince you I show this phase curve of another variable star that is in the same field of recovery. I got this data from the same set of shots and I used the stars to compare and check. As you can see here there is a good correspondence with the ASAS-SN data both in terms of magnitude and period. This leads me to exclude a problem, for example, in the observatory PC clock. Among other things, it seems to me that even in my observations the curves do not coincide well, as if the period of this star was not regular.
If evererthing seems right you should try to get more data to see how the star behave over a longer period. For example to see if there are any phase shifts or other irregularities. I have no better ideas why your and the ASAS-SN lightcurves differ. Your other example has, as you says, a good similarity.