The true nature of the alleged planetary nebula w16-185.

• Grant number: 07/02868-7
• Support Opportunities: Regular Research Grants - Publications - Scientific article
• Start date: June 01, 2007
• End date: August 31, 2007
• Field of knowledge: Physical Sciences and Mathematics - Astronomy - Astrophysics of the Interstellar Medium
• Principal Investigator: Zulema Abraham
• Grantee: Zulema Abraham
• Host Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

We report the discovery of a small cluster of massive stars embedded in a NIR nebula in the direction of the IRAS 15411-5352 point source, which is related to the alleged planetary nebula W16-185. The majority of the stars present large NIR excess characteristic of young stellar objects and have bright counterparts in the Spitzer IRAC images; the most luminous star (IRS 1) is the NIR counterpart of the IRAS source. We found very strong unresolved Brγ emission at the IRS 1 position and more diluted and extended emission across the continuum nebula. From the sizes and electron volume densities we concluded that they represent ultracompact and compact H II regions, respectively. Comparing the Brγ emission with the 7 mm free-free emission, we estimated that the visual extinction ranges between 14 and 20 mag. We found that only one star (IRS 1) can provide the number of UV photons necessary to ionize the nebula. (AU)