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LPVs for CCD observers

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StefanUtt's picture
StefanUtt
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Joined: 2011-05-24

Dear LPV observers,

I would like to suggest two exciting objects for the CCD observers among you: RU Vul and T UMi. Both strongly decreased their pulsation period and amplitude in the past decades, and are therefore candidates for having undergone a helium shell flash (aka thermal pulse) in the recent past.


RU Vul used to be an SRa variable with P~155d and a full amplitude of 2mag when it was discovered, but the period and amplitude decreased substaintaly in the past decades. Nowadays the amplitude is too low to be detected by visual observations, so it would be required to be observed with a CCD camera to safely detect its light variation (pulsation). The last detected period was 108 days, so one observation every five days would be required to get a good light curve. At this time of the year, RU Vul rises in the East in the evening, so it is entering a phase of good observabilty. There is the possibility that the pulsation period and amplitude recover again in the near future, it would be very interesting to see the onset of period and amplitude increase.


The other star, T UMi, used to be a Mira variable with a period of 315d that started to sharply decrease in the 1980ies, for no apparent reason. Today, the period is about 113d (!), and the amplitude is below the classical definition limit for Miras of 2.5 mag. At the moment, its light variation can still be detected by visual observations, but if the amplitude decreases further, it could become a difficult target for visual observers. Hence, CCD observers are also encouraged to follow the exciting evolution of that star. As for RU Vul, there is the possibility that the period and amplitude start to increase again in the next few years, continued monitoring is very important.

Just to illustrate for what kind of science these observations are useful, I would like to point you to a recent paper by me, where these two stars are discussed amongst others: http://arxiv.org/abs/1105.2198 RU Vul and T UMi are candidates for a recent helium shell flash, so it is possible that we are witnessing real-time stellar evolution in these cases! Continued monitoring of these stars is of paramount importance to understand these objects.


Please let me know if there is someone among you who is going to observe these stars.

Cheers,

Stefan

only scatter in the visual light curve of RU Vul
StefanUtt's picture
StefanUtt
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Joined: 2011-05-24

OK, I just see that T UMi is being followed by CCD observers from time to time, but not so RU Vul. In fact, I only see scatter in the visual estimates of that star. CCD observations over one or two observing seasons would be good to see if there is any real variability left in this star! So, please observe this target! And, if the helium shell flash hypothesis is correct, we should see the pulsation re-appearing in the next few years.


Thanks,

Stefan

CCD observations of RU Vul needed!
StefanUtt's picture
StefanUtt
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Joined: 2011-05-24

Dear Wolfgang,
thanks for sharing the mean light curves. It just confirms what I said about RU Vul: lots of scatter, V band observations of that star are badly needed!
On the other hand, the pulsation of T UMi is well detectable by visual observations. Maybe my call for CCD V band observations was a shot from the hip, nevertheless please continue observing this exciting object!

Please let me know your opinion!

Cheers,
Stefan

RU Vul and T UMi
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robinriordan
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Joined: 2011-03-02

Hi Stefan,

I have been observing short period variables for the past half year in order to develop my techniques and gain confidence in my myself and equipment. I have worked with Tim Crawfoerd during this period. I now feel competent to contribute. I will add RU Vul and T UMi to my list of program stars.

Robin Riordan

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484