Shadows and photoevaporated flows from neutral clumps exposed to two ionizing sources

 

A. H. Cerqueira,^1,2 J. Cantó,³ A. C. Raga,² and M. J. Vasconcelos^1,2

 

¹ LATO-DCET, UESC, Rodovia Ilhéus-Itabuna, km 16, Ilhéus, Bahia, Brasil, CEP 45662-000 (hoth@uesc.br, mjvasc@uesc.br).

² Instituto de Ciencias Nucleares, UNAM, Apdo. Postal 70-543, 04510, México, D. F., México (raga@nucleares.unam.mx).

³ Instituto de Astronomía, UNAM, Apdo. Postal 70-264, 04510, México, D. F., México.

 

Received, 2005 October 11
Accepted 2006 April 28

 

RESUMEN

Glóbulos neutros sumergidos en regiones H II se encuentran frecuentemente en regiones de formación estelar. En este trabajo investigamos la formación de regiones de sombra detrás de glóbulos neutros iluminados por el flujo ionizante directo de dos estrellas. Utilizamos una aproximación analítica, la cual nos permite hacer estimaciones de la geometríca de las sombras detrás de los glóbulos neutros para distintas configuraciones geométricas iniciales, y también simulaciones numéricas tridimensionales. Encontramos un buen acuerdo entre los cálculos analíticos y los numéricos. Una aplicación de particular relevancia pueden ser los 'proplyds' ubicados en el cúmulo del Trapecio en Orión, los cuales están siendo fotoevaporados por la radiación de las estrellas O θ¹ Ori C y θ² Ori A.

 

ABSTRACT

Neutral clumps immersed in H II regions are frequently found in star formation regions. We investigate here the formation of tails of neutral gas, which are not reached by the direct ionizing flux coming from two massive stars, using both an analytical approximation that allows us to estimate the shadow geometry behind the clumps for different initial geometric configurations, and three-dimensional numerical simulations. We find a good agreement between both approaches to this theoretically interesting problem. A particularly important application could be the proplyds that are found in the Trapezium cluster in Orion, which are being photoevaporated primordially by the O θ¹ Ori C y θ² Ori A.

Key Words: HYDRODYNAMICS - H II REGIONS - STARS: FORMATION - STARS: PRE-MAIN SEQUENCE.

 

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Acknowledgements

We would like to thank the anonymous referee for suggestions which improved substantially the presentation of the paper. A.H.C. acknowledges Brazilian agency CAPES for a post-doctoral fellowship (process BEX 0285/05-6). A.H.C. and M.J.V. would like to thank P. Velázquez and the staff of the ICN-UNAM (Mexico), for their warm hospitality and also for partial financial support during our visit. This work is funded in part by the Brazilian agencies PROPP-UESC (220.1300.327) and CNPq (62.0053/01-1-PADCT III/Milenio, 470185/2003-1 and 306843/2004-8). This work was also supported by CONACYT grants 41320-F, 43103-F and 46828 and the DGAPA (UNAM) project IN 113605.

 

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