Affiliation
American Association of Variable Star Observers (AAVSO)
Tue, 06/06/2017 - 21:08
Hi all
Looking at the light curve of U Lyrae seems that sometimes this variable not only develops humps, but also shows something similar to a dual-maxima.
This behavior on JD 2451600-2456525-2456900 it's real or we are seeing an artifact ?
Regards.
Alfredo
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U Lyr 2451600.png25.35 KB
U Lyr 2456525.png28.65 KB
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U Lyr phase plot.png71.58 KB
Greetings,
Much as I'd like to see another dual maxima Miras, particularly in the north, this doesn't look likely. I looked at the electronic measures, V, B, R and I. Many of these are very erratic and there may be consistent errors with some observers. For example, a V-R value of ~0.1 magnitudes as one observer has consistently is not real. I've struck this problem with other Mira measures. At other times there are two sets of V measures differing by half to one magnitude.
Turning to the visual measures.these show little indication of a dual maxima object. What is noticeable is the instability of the mean value of the star - this ranges over a couple of magnitudes although the amplitude reains near 3 magnitudes - typical of carbon Miras. The GCVS quotes a companion of B = 13 at 8" which may affect some measures near minimum.
In this context Matt Templeton mentioned a northern DMM star but I've lost track of the email - I don't think it was U CMi ot T Cas which is a Mira with a very wide maximum which may well be dual. Can anyone offer an idea? Regarding T Cas - some well-transformed V measures, together with BVRI would be very useful. But keep looking Alfredo, there must be some good examples in the north not yet recognised.
Regards,
Stan
Thanks a lot Stan.
I always suspected that the behavior shown was due to the scatter present in the light curve.I wonder if there is some case of a mira star that has transformed or evoluted from humps to a dual-maxima in the light curve or vice versa.
Alfredo
Alfredo,
BH Cru had a strong Dual-Maxima when it was discovered in 1969 and continued with that behavior until about cycle 13 then changed to having a "hump" on the rising light curve. I wrote an article about BH Cru for this month's LPV of the month which can be found at https://www.aavso.org/lpv-month. Stan Walker wrote an excellent paper on BH Cru which gives a LOT more detail about this aspect of BH Cru. The following is information about the paper Stan wrote: W.S. G. Walker, “BH Crucis: Period, Magnitude, and Color Changes”, 2009, JAAVSO, Volume 37, Pages 87-95
Stan also has a number of update about BH Cru in articles in the "Variable Stars South" newsletter at www.variablestarssouth.org. I hope he finds time to comment on BH Cru here!
Frank Schorr (SFRA)
Thanks Frank
I'll read your article in detail.
I'm looking for more information about these kind of stars, and i agree that the articles of Stan are a good source for the study of the dual maxima miras.
Regards
Alfredo
Hi Stan,
I remember an email with you and Matt about LX Cyg in 2009, but looking at the light curve right now, it doesn't look like a DMM to me.
The visual observers did a good job in finding most of the stars with odd light curves with large deviations. As more observers use more precise techniques, we're seeing an increase in the number of LPVs with odd light curves. Often B-band observations do the best job in highlighting these fluctuations. They are interesting stars!
Arne
Hi Arne, Alfredo et al,
The star I was trying to identify is CT Lacertae about which Matt Templeton and others published a paper - JAAVSO 2014 42,260T.
This is classed as SR but is reasonably regular with a period ~562 days and recently has been showing a more regular duality. Earlier it was more erratic but the data were sparse. I note a GCVS spectrum of C6- and a range of 10.6-17.2 pg but this is mainly due to fades in the mean brightness. Maybe this is a star which has changed from a low amplitude carbon Mira with humps to a DMM star.
In 2013 I presented a Ppt address at an RASNZ conference about some of these stars - I can forward it to anyone interested (I'm astroman@paradise.net.nz) but I'd like to draw attention from this to T Cas which looks very much like R Nor but with a shorter period of 445 days. It could use some good quality measures at maximum to determine the exact light curve there.
One of the interesting things about these DMM stars is that they are mostly in one small area of the southern sky - an interesting finding by John Greaves - but this must surely be a statistical result of a rare type of object. But this odd distribution is supported by another one found down this way recently.
Regards,
Stan