X‐Rays and Protostars in the Trifid Nebula

Abstract

The Tri—d Nebula is a young H II region, recently rediscovered as a ii pre-Orion ˇˇ star-forming region, containing protostars undergoing violent mass ejections visible in optical jets as seen in images from the Infrared Space Observatory and the Hubble Space Telescope. We report the —rst X-ray observations of the Tri—d Nebula using ROSAT and ASCA. The ROSAT image shows a dozen X-ray sources, with the brightest X-ray source being the O7 star, HD 164492, which provides most of the ionization in the nebula. We also identify 85 T Tauri star and young, massive star candidates from near-infrared colors using the color-color diagram from the Two-Micron All-Sky Survey (2MASS). Ten X-ray sources JHK s have counterpart near-infrared sources. The 2MASS stars and X-ray sources suggest there are potentially numerous protostars in the young H II region of the Tri—d. ASCA moderate-resolution spectroscopy of the brightest source shows hard emission up to 10 keV with a clearly detected Fe K line. The best model —t is a two-temperature (T 1.2 ] 106 K and 39 ] 106 K) thermal model with additional warm absorbing media. The hotter component has an unusually high temperature for either an O star or an H II region; a typical Galactic H II region could not be the primary source for such hot temperature plasma and the Fe XXV line emission. We suggest that the hotter component originates in either the interaction of the wind with another object (a companion star or a dense region of the nebula) or from —ares from deeply embedded young stars. . . . . . . . . . . . . . . . . . . . . .