CCD Photometry of Variable Stars in the Orion Nebula Cluster

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Session 62 -- Very Young Stars
Display presentation, Thursday, 9:20-4:00, Pauley Room

[62.12] CCD Photometry of Variable Stars in the Orion Nebula Cluster

G.R.Keenan, W.Herbst (Wesleyan), C.F.Prosser, J.R.Stauffer (CfA)

CCD photometry of the Orion Nebula Cluster has been obtained in the Cousins I band on twelve nights during the 1991/1992 observing season at Mt. Hopkins and at CTIO. More than fifty images were obtained of a field centered on the Trapezium. The data are particularly well suited to studying shorter timescale variations and fainter stars than previous studies (Mandel \& Herbst 1991 ApJ 383, L75; Attridge \& Herbst, ApJ 398, L61.). Approximately 30\% of the stars show significant variations. The distribution of the images in time is such that an independent search for periodicities greater than three days was not fruitful. As Attridge and Herbst discussed, the periods they found for stars in the short period peak of the bimodal frequency distribution could be aliases and we show that, in fact, the true period of JW 526 is probably only 0.63 days, making it one of the shortest period T Tauri stars known. Since short period T Tauri stars appear not to have circumstellar disks (Edwards et al. 1993, AJ, preprint the brighter members of the ONC.

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