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Let's observe RCB stars!

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Doug Welch mentioned in the AAVSO Legacy Stars LPVS topic[1] that, "there are also newly discovered and confirmed R CrB stars that need to have sequences defined and monitoring started!"

I think this is a good idea, but quite offtopic on the Legacy LPVs topic, so it's time to start a new topic for RCB variables.

After some discussion with Doug I made sequence for two new RCB stars:

ASAS J190640-1623.9: listed as ASAS-RCB-8 in Clayton's paper[1]. This is a 10.89V star in maximum, and a 1.38 magnitude fading was observed by ASAS-3 around 2001-2002. T Sgr and R Sgr lie not far from this star, so LPV fans can easily include this star into their programme.

NSV 8353: This star can be found in Ophiuchus, at -21 degress, so especially southern observers can monitor NSV 8353. According to VSX the amplitude of this RCB variable is: 12.6 - <14.1V. The light curve of ASAS-3 show some fadings down to 14.1V. 

[1] http://www.aavso.org/aavso-legacy-stars-lpvs
[2] What Are the R Coronae Borealis Stars? http://www.aavso.org/sites/default/files/jaavso/ej201.pdf

Clear skies,

Robert Fidrich (FRF)

Virtually all the stars on my
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Virtually all the stars on my visual program are either RCB or NL stars, and I've run out of stars in the AUID that arre accessible with my telescope, so I really appreciate knowing about these new ones.  A separate forum for RCB stars would be real interesting!  Bravo Robert and Doug!

Thom

Thanks, Thom! But the effort
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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

Thank you!
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Hello Robert and Doug,

       Many thanks to you both for the R CrB forum idea/implementation.  (Didn't mean to leave you out,

Robert - this forum stuff is great, but it's sometimes confusing who posted what to where!)

 

Cheers,

Thom

New RCB candidate
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Hi, all,
I've always liked RCB stars and the recent papers and RCB fever caused by them made me go and look for some more candidates. I have updated most of the RCB stars in VSX and changed some of the types for them. Y Mus has no documented fading (if you have proof it has ever been faint, then show it!) so it has been classified as a hydrogen deficient PVTELIII star. Also LV TrA is in the same situation and it is also even less variable.
I am now checking the entire CGCS catalogue searching for some missing RCB. I am focused on carbon stars formerly classified as R, which is where RCB stars live.
I found a nice candidate:
http://www.astrouw.edu.pl/cgi-asas/asas_variable/122658-6824.2,asas3,69.2,2085,440,270,0

It shows a 69.2 d. pulsation and it underwent a 1.5 mag. fading event around JD 2452800. IRAS source and R-type spectrum. It would be a nice target to monitor. The R-type spectrum seems to preclude a DYPER classification but new spectral observations would be of help.

The star is ASAS J122658-6824.2:
http://www.aavso.org/vsx/index.php?view=detail.top&oid=94989

Cheers,
Sebastian

 

I also like RCB stars and
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I also like RCB stars and would like to participate - I only have an 8 inch reflector under urban skies, though, for visual observations, so I can't go very faint - in whatever projects the AAVSO community can build around these interesting objects. Mike Simonsen's blog post on RCB stars is inspiring.

/Gustav Holmberg, HGUA

Possible Musca RCB
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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.

Further On Some Specific RCB Stars
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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)

DY Per stars
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Hi, John,
DY Persei has been in fact used as the prototype of a new class of variables, not related with the double degenerate merger or final helium flash.
These are carbon-rich giants and not supergiants as the RCB stars, thus they are 10 times fainter.
it is not easy to distinguish them without spectroscopic information or without knowing their actual distances (to infer their luminosity) but their fadings are usually of smaller amplitue than those of the RCB stars and also more symmetric (the RCB recoveries are slower than the fadings)

V1157 Sgr's ASAS-3 light curve supports the RCB clasification:

http://www.astrouw.edu.pl/cgi-asas/asas_variable/191011-2029.7,asas3,0,0,500,0,0

Cheers,
Sebastian

ASAS J122658-6824.2 new sequence
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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)

Y Mus decline
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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.

DY PER Stars, et al.
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Sebastian Otero wrote:

Hi, John,
DY Persei has been in fact used as the prototype of a new class of variables, not related with the double degenerate merger or final helium flash.
These are carbon-rich giants and not supergiants as the RCB stars, thus they are 10 times fainter.
it is not easy to distinguish them without spectroscopic information or without knowing their actual distances (to infer their luminosity) but their fadings are usually of smaller amplitue than those of the RCB stars and also more symmetric (the RCB recoveries are slower than the fadings)

V1157 Sgr's ASAS-3 light curve supports the RCB clasification:

http://www.astrouw.edu.pl/cgi-asas/asas_variable/191011-2029.7,asas3,0,0,500,0,0
Cheers,
Sebastian

Good morning, Sebastian. Indeed, I was aware from reading the literature of DY PER's "reclassification" and it's becoming the prototype for a newly recognized class of variables, although such things tend to leave me still wondering about just how meaningful/correct they may actually be when it comes to real oddities. As justification for this outlook let me relate a couple of stories from my past.

Back more than 45 years ago, when I was still something of a fledgling variable star observer, I began perusing the pages of the then current GCVS for "unusual" stars to add to my expanding observing program. The GCVS indicated quite a number of variables classified as Z AND? and R CRB?, far more than today, and those particularly caught my interest. From questioning the Director and some longtime VSO friends of mine like Ed Oravec and Wayne Lowder I came to learn that, at the time, any star with truly unusual behavior would be almost automatically dumped into one, or the other, of those two classes! Needless to say, most eventually got reclassified as something else, but even to this day I regard some assignments as likely more speculative than truly accurate. One from that era that still comes to mind is V348 Sgr, a real odd-ball if there ever was one. It is still an oddity among oddities! I would add that a reclassification also often proves to be a temporary state of affairs as the latest ideas and theories change with time. And that leads me to a second little story.

On one of my regular visits to Harvard/Smithsonian and the AAVSO HQ to talk with colleagues I was in a discussion with Dr. Brian Marsden of the IAU Central Bureau for Astronomical Telegrams. As our conversation shifted back and forth between comets and variable stars, Brian made a most profound statement that has stayed with me and encouraged me ever since. He related, "John, theories and explanations of phenomena come and go with time. The only things of any real lasting value are the observations themselves." Better and more learned advice I've never received in my long career. ;)

J.Bortle   (BRJ)

RCB stars
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This is an interesting paper...

  http://arxiv.org/abs/1204.4181

My observations of DY Per since 1992 reveal a period of ~793d.  Light curve here...

 http://www.garypoyner.pwp.blueyonder.co.uk/DYPer.html

Gary

PYG

Yes, an interesting paper!
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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?

V2331 Sgr: a possible RCB star
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Another possible RCB star found matching Tisserand's catalogue and VSX: V2331 Sgr.

The OGLE light curve of this star:

http://ogledb.astrouw.edu.pl/~ogle/photdb/getobj.php?field=BUL_SC13&star...

We have just recently created a new sequence for V2331 Sgr.

Clear skies,

Robert Fidrich (FRF)

RCB's and WD merging
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This appeared on Astro-ph today.  Hot topic in RCB research...

"Do R Coronae Borealis Stars Form from Double White Dwarf Mergers"  Staff et al...

 http://arxiv.org/abs/1208.0732

Gary (PYG)

A possible DY Per star
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Continuing with the search for RCB or related objects in the CGCS catalogue, I found a star showing small amplitude fadings. The fadings are symmetric and that is consistent with the DYPer classification But the interesting thing is that the spectroscopic studies remark that C13 is strong. This is the spectrocopic signature of DYPer stars. So maybe in the future this star may surprise us with a fading deepr than the 0.9 mag. events that has displayed since the ASAS discovery.

The star is ASAS J094200-0852.3 and it is in the constellation Sextans:
http://www.aavso.org/vsx/index.php?view=detail.top&oid=89967

This is its ASAS-3 light curve:
http://www.astrouw.edu.pl/cgi-asas/asas_variable/094200-0852.3,asas3,56.55,4460.0000,440,270,0

Cheers,
Sebastian

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