AAS 206th Meeting, 29 May - 2 June 2005
Session 7 Star Formation
Poster, Monday, 9:20am-6:30pm, Tuesday, 10:00am-7:00pm, May 30, 2005, Ballroom A

## [7.04] NICMOS Paschen Alpha Imaging Survey of "Proplyd" Candidates in NGC 2024

D.C. Hines (Space Science Institute), K.R. Stapelfeldt, P.G. Wannier, R. Sahai, H.W. Yorke (JPL)

We report the results of a narrowband imaging survey of 16 young stars, which are members of the embedded young cluster NGC 2024 and associated with its H II region. The goal of our study is to detect and spatially resolve externally illuminated circumstellar material (proplyds"), as prior studies have done in the case of the Trapezium cluster in M42. The targets were selected from VLA 3.6 cm continuum maps, and all possess compact regions of ionized gas emission coincident with an obscured infrared star. Images were taken in the Pa\alpha line and adjacent narrowband continuum, using the Hubble Space Telescope NICMOS 2 camera and the F187N and F190N filters. Pa\alpha emission line images of each target were constructed from the difference of the two calibrated filter images. The results show extended Pa\alpha emission in 2 (probably 3) of the targets. Two of the objects have emission extending about an arcsecond around the star, and one has a head-tail morphology reminiscent of a proplyd. Three additional stars show significant, unresolved Pa\alpha emission, most likely from stellar activity. In addition to the 16 prime targets, we find evidence for unresolved Pa\alpha emission from 15 of 53 stars serendipitously imaged in the fields of view of the primary targets. We also find one object among these 53 stars that exhibits proplyd morphology. No disk silhouettes are seen in any of the sources. The results provide further evidence of the uniqueness of the "proplyds" in M42.

Support for this work was provided by NASA through grant number GO-9424 from STScI, operated by the Association of Universities for Research in Astronomy Incorporated, under NASA contract NAS5-26555.