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Session 96 - Cepheids and Supergiant Variable Stars.
Display session, Thursday, January 16
Metropolitan Ballroom,

[96.14] The MACHO Project LMC Variable Star Inventory: How Bright Are the R Coronae Borealis Stars?

G. C. Clayton (LSU), D. L. Welch (McMaster), D. Kilkenny (SAAO), C. Alcock, D. Alves, K. H. Cook, S. L. Marshall, D. Minniti (LLNL/CfPA), D. P. Bennett (Notre Dame/CfPA), R. A. Allsman (ANU), A. Becker, M. R. Pratt, C. W. Stubbs (UW/CfPA), T. S. Axelrod, K. C. Freeman, B. A. Peterson, A. W. Rodgers (MSSSO), P. J. Quinn (ESO), K. Griest, J. A. Guern, M. J. Lehner (CfPA/UCSD), W. Sutherland (Oxford)

We report the discovery of several new R Coronae Borealis (RCB) stars in the Large Magellanic Cloud (LMC) using the MACHO project photometry database. The identification of at least six new stars has now been confirmed spectroscopically. Five are cool RCB stars (T_eff\sim 5000 K) characterized by very strong Swan bands of C_2 and violet bands of CN, and weak or absent Balmer lines, G-band and ^12C^13C bands. The sixth star is an example of a hot RCB star of which only 3 were previously known to exist in the Galaxy and none in the LMC. All of the stars have shown deep declines of \Delta V \ge 4 mag in brightness. The discovery of these new stars triples the number of known RCB stars in the LMC to nine and demonstrates the utility of the MACHO photometric database for the discovery of new RCB stars. Two interesting trends are present in the characteristics of the new stars. First, they are significantly fainter at maximum light than the three previously known LMC RCB stars. They seem to have absolute luminosities, M_V, about a magnitude fainter than the other three stars. Second, the stars discovered thus far are all members of the cool or hot subgroups of the RCB stars. RCB stars have a wide range of temperatures but they can be divided simply into three subgroups, cool (5000 K), warm (7000 K) and hot (20,000 K). Most RCB stars in the Galaxy fall in the warm subgroup. Cool and hot RCB stars are quite rare in the Galaxy.

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Program listing for Thursday