A Possible Origin of the H-H Objects in Young Stellar Outflows

Details A Possible Origin of the H-H Objects in Young Stellar Outflows A Possible Origin of the H-H Objects in Young Stellar Outflows

Nov 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990rmxaa..21..477d&link_type=abstract

Revista Mexicana de Astronomia y Astrofisica, 21, 477

Astronomy and Astrophysics

Astronomy

1

Scientific paper

RESUMEN. La presencIa de flujos coljmados asocjados con objetos estelares j6venes es un fen6meno comun en reglones de formacI6n estelar. Estos chorros frecuentemente muestran una cadena de reglones de lineas de emjsI6n, a varIas de las cuales se les conoce desde bace mucho tlempo objetos HerbIg-Haro (HAl). En el presente trabajo examjnamos la poslbIlI dad de que estos nudos sean condensaciones producIdas por inestabilidad termica en un plasma que se se expande sujeto a `bremsstrahlung' reco - binaci6n y perdida por radjacj5n en lineas de emjsj6n. Nostramos que el valor minimo de = P0/PN0 bajo condjcjones Isobaricas para el crecimien to de la inestabilidad termica es = (6/5) [9/(STc\)e) - 3/2]; en donde P0 es la presi6n de particulas, PM0 la presi6n magnetica, `)e la tasa de expansI5n y Tc el tiempo de enfriatniento radiativo en el flujo (3eI plasma ambiente. Haciendo calculos no lineales, encontratnos que l9s flujos colitnados de temperatura K, tasas de perdida de masa `4 = 10-6 - lO 8 Ne y velocidades de flujo VJ = 100-400 km/s, resultan favorables para la formacl6n de condensaciones por inestabilidad termica con contrastes de densidad Pp/ .3 -2.0 creados en intervalos de tiempo mas cortos que el tiempo estirnado de expansl6n en los chorros, en donde Pp(Po) es la densidad en la regi5n (ambiente) perturbada. ABSTRACT. The presence of collimated outflows associated with young stellar objects is a common phenomenon in star-fortning regions. These jets frequently show a chain of emission-line regions several of which have long been known as Herbig-Haro (H-H) objects. In this paper we examine the possibility that these knots are condensations produced by thermal instability in an expanding plasma , recombination and emission-line radiation losses. We show that the minimum value of = P /PNo under isobaric conditions for the growth of a thermal instability 0is = (6/5)1 [9/(STcN)e) - 3/2]; where P0 is the particle pressure, NQ tWe magnetic pressure, N) the expansion rate and Tc the radiative cooling time of the ambient plasma flow.Performing nonlinear calculations, we found that collimated flows of temperature T0 %% iOS K, mass-loss rates N = iO-6 - 10-8 Ne yr-1, and flow velocities VJ = 100-400 km/s, are favorable to the formation of condensations by thermal instability with density contrasts Pp/P0 1.3 - 2.0 created in time irr%ervals shorter than the estimated expansion time scales of the jets, where Pp(Po) is the density at the perturbed (ambient) region. Key : HERBIG-HARO OBJECTS - STARS-MASS LOSS

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