SW Crt – RR Lyrae star

Some background information on SW Crt, from the paper by Vogt.
Ref.: 1983A&AS…53. (Mati Morel)

“..21V [Astron. Astrophys. Suppl. Ser. 53,21-27 (1983)].
Vogt says, regarding SW Crt :
1147-23 SW Crt. Dorodnaya and Kholopov (1977) described SW Crt=SVS 2147 as a new Z Cam star. The magnitude in table II could refer to the standstill. The colours, however, are not typical for a cataclysmic variable. A spectrogram obtained by the author only shows Balmer absorption lines of an A star, compatible with the UBV colours. SW Crt is probably not a dwarf nova. >From Table II, one observation (only) of SW Crt.
V = 16.41 B-V = 0.40 U-B = 0.22”

Taichi Kato (cf. vsnet-alert 11114 SW Crt bright) noted the object has been classified as a non-CV, and Christlieb et al. (A&A 431, 143) included it in a catalog of horizontal-branch stars.

YYYYMMDD(UT)   mag  observer
20090316.2787 15.278V  (ASAS (Pojmanski, G. 2002, Acta Astron. 52,397))
20090319.507  <154  (Rod Stubbings)
20090320.465   154  (Rod Stubbings)
20090320.648   153  (Rod Stubbings)
20090321.547   152  (Rod Stubbings)

Following this alert I paid close attention and nightly monitoring on SW Crt. I noticed a variation of about 0.7 mag over 6 hours. The range was from 15.0 to 15.8, so it was quite faint. As there were no proper sequence available all estimates were by eyeball, but the variation I observed was there.

I sent my data on to Stan Walker and John Greaves to see what they could find and John Greaves found a period about 0.3264 days as shown by the light curve.

A new sequence was provided by Arne Henden and further observations were obtained  over the following weeks. With the new sequence my estimates came in a lot fainter and this showed a 0.494 day period and more like a RRAB Lyrae star. The light curve below based on the new sequence.

In June 2009 Taichi Kato (cf. vsnet-chat 7452 Re: SW Crt) commented:

“I came across the article of SW Crt: http://adsabs.harvard.edu/abs/1977PZP…..3..274D
The authors stated that an attempt to find a period between 0.3 and 50 days was unsuccessful.  I tried the data with a modern computer.    There appear to be several candidate periods (assuming the RR Lyr classification).  The periods include 0.48505 d and 0.32633 d.
The light curves are well-expressed except “standstill-like” apparently
constant segments.
cf. vsnet-alert 11114 SW Crt bright”

Conformation of an RRAB Lyrae Star

Over the next three years I continued to monitor SW Crt in which all observations were entered into the AAVSO data base. In April 2012 I recieved an unexpected email from Sebastian Otero, VSX Team, American Association of Variable Star Observers regarding the conformation of SW Crt as a RRAB Lyr star.

“SW Crt is given as SR:/M: in the Z Cam page and as RRAB: in VSX because it
is an A-type star with rapid variations according to just a few observations
in the Catalina Sky Survey.
Amazingly there is visual data in the AAVSO database by just one observer,
Rod Stubbings, and his dataset shows it is an RRAB with a period of 0.493164
d.!!!
After having found the period I added data from CRTS for only 6 nights and
indeed, the period was confirmed (impossible to find a period with the CRTS
data only because there were too few datapoints).
This is a nice example of how useful visual data may be.”

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