Special Notice #145: R Coronae Borealis at or near faintest recorded minimum

AAVSO Special Notice #145

R Coronae Borealis at or near faintest recorded minimum
January 28, 2009

R Coronae Borealis, the prototype of the R CrB class, is apparently at or near historic minimum; a number of observers have put this star below m(vis)=14.0 since early November 2008, and both visual and instrumental measures are now indicating R CrB is near or below V=14.5.  R CrB began its current fading episode around JD 2454288 (2007 July 6 +/- 1 day), and faded from m(vis) ~ 6.0 to below m(vis) ~ 12.0 by JD 2454325 (2007 August 12).  The star has continued to fade for the past 17 months. Current visual observations by a number of AAVSO visual observers estimate the star to be around m(vis) 14.3-14.5, and V-band CCD observations suggest the star may be at or near V=15.0.  BAAVSS observer J. Toone also visually estimated the star is at m(vis) ~ 14.9 (via baavss-alert).  Both visual estimates and instrumental photometry of R CrB are strongly encouraged at this time.

The duration of the current episode and its depth are similar to that observed during the previous extreme fading episode which began circa JD 2438200 (June 1963) and continued with only one brief interruption until circa JD 2439100 (December 1965).  During the 1963-1965 event, a few AAVSO observers estimated that R CrB reached m(vis) around 14.9-15.0, although the average visual estimate remained around 14.2-14.3 at minimum. The current episode seems to have reached the same depth; there is no way to tell whether the fade will continue, although the light curve has been flat or trending weakly downward for several months. As J. Toone pointed out, the current magnitude is very close to if not fainter than the historic minimum for this star.

The following observations were made during the past week and submitted to the AAVSO: m(vis) < 13.4, JD 2454853.97361 (2009 Jan 22.4736; L. Shotter, Uniontown, PA, United States); m(vis) = 14.5, JD 2454855.7050 (2009 JAN 24.205; G. Poyner, Birmingham, England); m(vis) = 14.0, JD 2454856.68056 (2009 JAN 25.1806; K. Wenzel, Grossostheim, Germany); m(vis) < 13.5, JD 2454856.9167 (2009 Jan 25.4167; M. Komorous, London, ON, Canada); m(vis) < 13.4, JD 2454856.94861 (2009 JAN 25.4486; L. Shotter); V = 14.98 +/- 0.02, JD 2454857.01564 (2009 JAN 25.5156; W. Dillon, Missouri City, TX, United States); m(vis) = 14.4:, JD 2454857.6507 (2009 JAN 26.1507; W. Kriebel, Walkenstetten, Germany); and m(vis) < 13.5, JD 2454857.9458 (2009 JAN 26.4458; M. Komorous).

R CrB is located at the following (J2000) coordinates:

RA: 15 48 34.40 , Dec: +28 09 24.0

Charts for R CrB may be plotted using VSP at the following URL: http://www.aavso.org/observing/charts/vsp/index.html?pickname=R%20CrB

Please promptly submit all observations to the AAVSO using the name "R CRB".

This AAVSO Special Notice was prepared by M. Templeton.

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