Let's observe RCB stars!

Thanks, Thom! But the effort was 99% Robert's!

I am working my way through Geoff Clayton's 68-entry spectroscopically-confirmed R CrB list from his recent eJAAVSO review paper to determine which stars have sequences and which do not. So I expect that there will be more charts and sequences in the not too distant future. Unfortunately, most of the spectroscopically-confirmed R CrBs are in the south. Patrick Tisserand's set of candidates from WISE (infrared) colors is all-sky, but either spectroscopy or photometry needs to be available to narrow the candidate list to highly-probable R CrBs. See:

http://arxiv.org/abs/1110.6579

Cheers,

Doug

Hi Sebastian

Great work to do! I'll have a look at this ASAS southern one. The shallow-ish fade event reminds me of V2552 Oph.

Best. Alan.

A new sequence has been uploaded into VSD, so this RCB candidate ASAS J122658-6824.2 can be observed from now. Thanks, Sebastian for proposing this star!

Clear skies for the southern hemisphere observers,

Robert Fidrich (FRF)

Hi Sebastian, I believe the last observed decline of Y Mus was in 1889, see http://adsabs.harvard.edu/full/1928BHarO.861...11P . I began observing Y Mus in 1987 - just missed it!  I am not aware of any other decline seen for this star.  Tks.  Peter Williams.

Upstream Gustav mentions Mike's blog addressing the behavior of a number of the better observed RCB-type stars. To that I would like to add some personal insight into their activity.

DY PER is likely a variable on fringes of the RCB class, if indeed any member of the group at all. Its rather regular variability cycle (see the LCG plot) is unlike just about any other star in the RCB classification. In fact, DY PER varies through its brightness cycles in almost perfect step with its  orbital period, rather than in any truly irregular manner. This has recently led several researchers to classify it as other than a true RCB-type object in their papers, regardless of its spectral characteristics.

U AQR Like DY PER, U AQR might also be regarded as somewhat of a weird duck. For decades it was classified in the GCVS as a Mira-type star, rather than an RCB. I was among those that pointed out that its activity was distinctly different from any other Miras, back in Director Margaret Mayall's days at the helm of the AAVSO. Subsequently, the star's classification was altered. 

MV SGR Mike cites this object's seemingly semi-regular variations, at least according the AAVSO's lightcurve. However, this seems to be a case where examining a combined data lightcurve does not serve a researcher's best interests.

I my opinion the seemingly 1.5 magnitude amplitude and short, more-or-less yearly cycle of the star, is nothing more than a reflection of observational scatter and the use of differing sequences among the observers. I've followed MV SGR for two decades and never seen it change by more than 0.2 magnitudes and recent CCD data reflects the same situation. This is an instance where I feel consulting the observations of different individuals separately would be a far better approach than simply taking the combined lightcurve at face value.

UV CAS As Mike points out, this is another example of a star that shows little activity. However, it does point up the absolute necessity of attempting to be totally unbiased in one's observations. Back in 2005, and again in 2007, UV did a distinct dip in brightness. Unfortunately, for some folks who had been lulled into reporting essentially the same "at-maximum" magnitude for years, they went right on seeing it that way! Please don't hurry through your observing program and sacrifice accuracy for just numbers.

V1157 SGR This is another star that I'm currently rather uncomfortable about regarding as a true RCB at the moment. So far my visual observations (and those made by others via CCD) suggest something perhaps akin to the cyclic variations shown by DY PER. In fact, I have seen this star classed as a Mira. However, a few more seasons of observation are necessary to better define the lightcurve and ascertain just what sort of variability, or cycle, is being displayed.

All in all, watching the RCB stars - very carefully - can be a lot of fun and a situation where one truly cannot predict, or even anticipate, what the next night's observations will indicate.

J.Bortle   (BRJ)

Yes, an interesting paper! One notes, for example, that several of the RCBs and DYPers discussed in section 5 have actually been known as variables for decades, in some cases since the 1920's, but were not recognised as RCBs. Typically, they were discovered in photographic surveys, were given a classification and became an entry into catalogues such as GCVS, but were actually not very well studied.

Probably, more RCBs are hidden in the catalogues as known but understudied or outright neglected variables labelled as M, semiregulars or irregulars. ... (A point made by Percy in the RCB chapter in Understanding variable stars.) Z UMi is another example; it was only in the 1990's that its status as an RCB was discovered, by Priscilla Benson, Geoffrey Clayton and others, while it had been known as a variable star since the 1930's. And V532 Oph was classified as an eclipsing binary star in 1942 on the basis of a large drop in brightness in 1928, while Clayton and others, using ASAS-3 data from 2001-2009, found out that it was an RCB.

20th century astronomy was very good at discovering new variables harvested from photographic surveys with large blink comparators, perhaps not as good in following up the discoveries.

That might be changing with the new photometric surveys and automated classification technologies, of which the paper by Miller et al is an example. But can amateurs also play a role here by developing projects that aims at studying neglected variables? Just for the sake of argument, say that a semi-large number of neglected variables from the GCVS were studied for a year or two, who knows what would be found?

I just saw this. I obtained images of T CrB early this morning. Did not think to check R CrB. It has dropped a magnitude in 1 week.

Barbara