The macho project large magellanic cloud variable star inventory. IV. New R coronae borealis stars

We report the discovery of two new R Coronae Borealis (RGB) stars in the LMC using the MACHO project photometry database. The identification of both stars has been confirmed spectroscopically. One is a cool RGB star (T_eff ∼ 5000 K), characterized by very strong Swan bands of C2 and violet bands of CN, and weak or absent Bahner lines, G band, and ¹²C¹³C bands. The second star is an example of a hot RGB star, of which only three were previously known to exist in the Galaxy and none in the LMC. Its spectrum is characterized by several G n lines in emission. Both stars have shown deep declines of Δ F ≥ 4 mag in brightness. The new stars are significantly fainter at maximum light than the three previously known LMC RGB stars. The amount of reddening toward these stars is somewhat uncertain, but both seem to have absolute magnitudes, M_V, ∼0.5 mag fainter than the other three stars. Estimates of M_bol find that the hot RGB star lies in the range of the other three stars, while the cool RGB star is fainter. The two cool LMC RGB stars are the faintest at M_bol. The discovery of these two new stars brings to five the number of known RGB stars in the LMC, and it demonstrates the utility of the MACHO photometric database for the discovery of new RGB stars.