A comparison of the radio and optical time-evolution of HH 1 and 2

Abstract

We present a comparison between the time-evolution over the past ∼ 20 years of the radio continuum and Hα emission of HH 1 and 2. We find that the radio continuum and the Hα emission of both objects show very similar trends, with HH 1 becoming fainter and HH 2 brightening quite considerably (about a factor of 2). We also find that the F Hα /F f f (Hα to free-free continuum) ratio of HH 1 and 2 has higher values than the ones typically found in planetary nebulae (PNe), which we interpret as an indication that the Hα and free-free emission of HH 1/2 is produced in emitting regions with lower temperatures (∼ 2000 K) than the emission of PNe (with ∼ 10 4 K).Presentamos una comparaci´on entre la evoluci´on temporal en los pasados ≈ 20 a˜nos de la emisi´on de radio continuo y de H α de HH 1 y 2. Encontramos que el radio continuo y H α de los dos objetos muestran evoluciones similares, con HH 1 debilit´andose y HH 2 volvi´endose considerablemente m´as brillante (aproximadamente un factor de 2). Tambi´en encontramos que el cociente FHα/Fff (entre Hα y el radio continuo) de HH 1 y 2 tiene valores mayores que los encontrados t´ıpicamente en nebulosas planetarias (PNe), lo cual interpretamos como una indicaci´on de que la emisi´on libre-libre y de H α de HH 1/2 se produce en regiones emisoras con temperaturas menores (≈ 2000 K) que la emisi´on de las PNe (con ≈ 104 K).