The Macho project LMC variable star inventory. X. The R Coronae Borealis stars

C. Alcock, Lawrence Livermore National Laboratory
R. A. Allsman, The Australian National University
D. R. Alves, Space Telescope Science Institute
T. S. Axelrod, The Australian National University
A. Becker, University of Washington
D. P. Bennett, Lawrence Livermore National Laboratory
Geoffrey C. Clayton, Louisiana State University
K. H. Cook, Lawrence Livermore National Laboratory
N. Dalal, University of California, Berkeley
A. J. Drake, Lawrence Livermore National Laboratory
K. C. Freeman, The Australian National University
M. Geha, Lawrence Livermore National Laboratory
K. D. Gordon, The University of Arizona
K. Griest, University of California, Berkeley
D. Kilkenny, The University of Arizona
M. J. Lehner, The University of Sheffield
S. L. Marshall, Lawrence Livermore National Laboratory
D. Minniti, Lawrence Livermore National Laboratory
K. A. Misselt, NASA Goddard Space Flight Center
C. A. Nelson, Lawrence Livermore National Laboratory
B. A. Peterson, The Australian National University
P. Popowski, Lawrence Livermore National Laboratory
M. R. Pratt, University of Washington
P. J. Quinn, European Southern Observatory
C. W. Stubbs, University of California, Berkeley
W. Sutherland, University of Oxford
A. Tomaney, University of Washington
T. Vandehei, University of California, Berkeley
D. L. Welch, McMaster University


We report the discovery of eight new R Coronae Borealis (RCB) stars in the Large Magellanic Cloud (LMC) using the MACHO project photometry database. The discovery of these new stars increases the number of known RCB stars in the LMC to thirteen. We have also discovered four stars similar to the Galactic variable DY Per. These stars decline much more slowly and are cooler than the RCB stars. The absolute luminosities of the Galactic RCB stars are unknown since there is no direct measurement of the distance to any Galactic RCB star. Hence, the importance of the LMC RCB stars. We find a much larger range of absolute magnitudes (MV = - 2.5 to - 5 mag) than inferred from the small pre-MACHO sample of LMC RCB stars. It is likely that there is a temperature-MV relationship with the cooler stars being intrinsically fainter. Cool (∼ 5000 K) RCB stars are much more common than previously thought based on the Galactic RCB star sample. Using the fairly complete sample of RCB stars discovered in the MACHO fields, we have estimated the likely number of RCB stars in the Galaxy to be ∼ 3200. The SMC MACHO fields were also searched for RCB stars, but none were found.