S. B. Holmes, P. Massey (Lowell Observatory) Detections Using data obtained with the MOSAIC 8k x 8k CCD at the 4-m Mayall telescope at KPNO, we have been able to sample the entire galaxy much deeper than earlier studies. New candidates, once spectroscopically confirmed, might then alter the WC/WN ratio. The IC10 field was observed using three different filters in order to determine Wolf-Rayet candidacy. Filters used include: the WC filter ( 4650), the WN filter ( 4690), & the CT filter ( 4750). Respectively, the filters detect the CIII 4650 line, the HeII 4686 line, & a clean continuum. A set of three, dithered images were taken in each of the three filters. The exposure time for each image was 30 minutes; i.e., 1.5 hrs per filter. The seeing was XXXX Purpose Acknowledgements Observations Analysis Future Work This research is supported by the National Science Foundation under grant AST We plan to spectroscopically observe our new Wolf-Rayet candidates. Spectra will indicate which candidates are definite WC or WN stars, possibly changing the WC/WN ratio, and either bringing it into better accord with more normal galaxies, or telling us that the WC/WN ratio is high in starbursts. Figure 2. Potential WR candidates: Asterisks indicate new detections, squares are spectroscopically confirmed WR stars and diamonds are the “control field”. The smallest ellipse contains likely non-WR stars. Progressing in size, the next region contains 25 questionable candidates, followed by a larger region containing an additional 10 probable WR candidates. The largest region contains 6 high significance candidates. Figure 1. The WC/WN ratios for Local Group Galaxies: IC10 has a high WC/WN ratio based on the survey done by Massey & Armandoff (1995). Figure 3. Spatial distribution of candidates in IC10: Based on fig. 2, red denotes spectroscopically confirmed WR stars, light blue indicates the location of the 6 high significance candidates, dark blue denotes the 10 probable candidates, and green represents the 25 questionable candidates. The Discovery of New Wolf-Rayet Star Candidates in the Starburst Galaxy IC10 Photometry of the galaxy was done using the IRAF/daophot package and our own scripts and code. In order to preserve the photometric integrity of the individual chips within a Mosaic frame, chips were analyzed separately. In the case of IC10, the galaxy was confined to a single chip. An additional chip was used as a “control field”. We selected candidates based upon the magnitude differences between the continuum and emission-line filters. We used the photometric errors to judge if a magnitude difference was significant or not. Multiple detections were also considered a plus in constructing our final candidate list. All spectroscopically confirmed Wolf-Rayet stars were found. In addition, we have confirmed the candidacy of several stars proposed to be Wolf-Rayets by Royer et al (2001 A & A 366, L1) based upon their own interference filter imaging but never confirmed spectroscopically. The exceptions are their “WC9" candidates; none of these were detected in our survey, causing us to question their surprising result that late-type WCs were to be found in such a low metallicity system. Comparing our final numbers against the control field, we have found a minimum of 6 & a maximum of 41 new Wolf- Rayet stars (Figures 2 & 3). IC10 is a Local Group dwarf irregular galaxy described by Hubble (1936) as ``one of the most curious objects in the sky". Massey and Armandoff (1995) proposed that it is currently undergoing a starburst: despite its small size, it contains 15 spectroscopically confirmed Wolf-Rayet stars, which is a galaxy- averaged surface density that is as high as that found in young, massive OB associations. This is consistent with a comparison of the Hα luminosity to HI mass or blue light luminosity (Hunter and Gallagher 1986, Hunter 1993), which suggests a star- formation rate comparable to that of NGC 1569, a classical starburst irregular. However, the relative number of WC-type and WN-type Wolf-Rayet stars is surprising high given the galaxy's low metallicity (Figure 1). Does this suggest a peculiar initial mass function, or an extremely short burst of star formation? Or could previous studies simply missed some of the weaker-lined WNs? IC10 stacked image: Hα is denoted by red, V is denoted by green, B is denoted by blue.