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DU Cep

MJB
Affiliation
American Association of Variable Star Observers (AAVSO)
Wed, 05/18/2016 - 18:54

This star is classified as a ISB.  It looks to me to be an SR. J-K is 1.377 and it plainly pulsates. Problem is to submit it to VSX I need a chart with the period shown.  I have rudamentary familiarity with vstar and this particular star's curve is complex.  Looks like there is more than one process going as any period chosen will drift.  About 57.2 is the best fit I can get.  See attached.  Any thoughts on how to chart this would be welcome.  Thanks.

File Upload
DU Cep-ISB.png40.26 KB
DU Cep-ISB_.png45.74 KB
Sebastian Otero
Affiliation
American Association of Variable Star Observers (AAVSO)
Wed, 05/18/2016 - 22:57
VSX revision

Hi James,

As in the case of V1912 Cyg, you are right.
This one is an SRB (J-K= 1.39 and B-V= 2.04 according to APASS), more than one period going on here, that's why your plot looks more scattery.
The phase plot you uploaded is okay for a VSX submission.

You may try to find a secondary period in this light curve to add that in the VSX remarks.
It looks like there are several red giants hidden among potential YSOs...

Cheers,
Sebastian

David Benn
Affiliation
Astronomical Society of South Australia (ASSAU)
Thu, 05/19/2016 - 13:49
Model with two periods

Hi James, Sebastian

I loaded all DU Cep data from AID, ran DCDFT on Johnson V with a period range of 40 to 400 and a resolution of 0.01 days. There are two top hits around 57 (as you say) and 361. If you select both in the top hits pane, then click the Create Model button, you'll see a dialog with 2 periods. Have a look at the resulting model.

You may also want to play around with a different number of harmonics per period when creating a model.

Then, look at the residuals and apply DCDFT to those if there still appears to not only be noise.

David

MJB
Affiliation
American Association of Variable Star Observers (AAVSO)
Thu, 05/19/2016 - 17:09
DU Cep

Big help.  But if you turn a multi-period model into a phase plot the model gets scrambled.  So in reporting this to VSX do I assume I would supply a phase plot for 57.08 and list the secondary phase as 361?  The third phase is pretty stout as well.  Would one consider listing a third phase in remarks?

Thanks

David Benn
Affiliation
Astronomical Society of South Australia (ASSAU)
Fri, 05/20/2016 - 00:13
Multiple periods

Hi James

I suspect the answer comes back to what Sebastian has said, i.e. that multiple periods can be submitted. It's a good question as to which is the primary/main and which is the second period. I'm thinking that this is a question for Sebastian and the VSX team.

There would seem to be at least 3 ways to view the primary vs secondary vs tertiary ... period question:

  • Which is most "prominent" in the periodogram?
    • It may be that the dataset contains more data that reveal a short period and very little of the data to reveal the longer period.
    • In some cases, the strongest signal may actually be an annual observation gap.
    • So this is probably not a good guide.
  • Which period "modifies" which other period(s)?
    • Thinking about your light curve, I suppose you could say that the short period (~57 days) is modified or modulated by the longer period (~361 days), even when we just visually inspect it.
    • But I suppose the converse could also be thought a reasonable statement.
  • Knowledge about the physical nature of the system itself. For that, presumably spectral information must be combined with the light curve data.

There are people who know a great deal more about this kind of thing than I do, but if you'd like someone else to bounce ideas off with respect to analysing further periods etc, please let me know. I'd be happy to help.

David