The ionizing star of the North America and Pelican nebulae

Abstract

We present the results of a search for the ionizing star of the North America (NGC 7000) and the Pelican (1C 5070) nebulae complex. The application of adequate selection criteria to the 2MASS JHKs broad-band photometry allows us to narrow the search down to 19 preliminary candidates in a circle of 0°5 radius containing most of the L935 dark cloud that separates both nebulae. Follow-up near-infrared spectroscopy shows that most of these objects are carbon stars and mid-to-late-type giants, including some AGB stars. Two of the three remaining objects turn out to be later than spectral type B and thus cannot account for the ionization of the nebula, but a third object, 2MASS J205551.25+435224.6, has infrared properties consistent with it being a mid O-type star at the distance of the nebulae complex and reddened by Av ≃ 9.6. We confirm its 05V spectral type by means of visible spectroscopy in the blue. This star has the spectral type required by the ionization conditions of the nebulae and photometric properties consistent with the most recent estimates of their distance. Moreover, it lies close to the geometric center of the complex that other studies have proposed as the most likely location for the ionizing star, and is also very close to the position inferred from the morphology of cloud rims detected in radio continuum. Given the fulfillment of all the conditions and the existence of only one star in the whole search area that satisfies them, we thus propose 2MASS J205551.25+435224. 6 as the ionizing star of the North America/Pelican complex.