Collisionally excited filaments in HST H$\alpha$ and H$\beta$ images of HH~1/2

Abstract

We present new H$\alpha$ and H$\beta$ images of the HH~1/2 system, and we find that the H$\alpha$/H$\beta$ ratio has high values in ridges along the leading edges of the HH~1 bow shock and of the brighter condensations of HH~2. These ridges have H$\alpha$/H$\beta =4\to 6$, which is consistent with collisional excitation from the $n=1$ to the $n=3$ and 4 levels of hydrogen in a gas of temperatures $T=1.5\to 10\times 10^4$~K. This is therefore the first direct proof that the collisional excitation/ionization region of hydrogen right behind Herbig-Haro shock fronts is detected.

arXiv comment13 pages, 5 figures, ApJL accepted

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• Balmer-Dominated Shocks: A Concise Review
• Fluid Dynamics of Stellar Jets in Real Time: Third Epoch HST Images of HH 1, HH 34, and HH 47
• Studies of NGC 6720 with Calibrated HST WFC3 Emission-Line Filter Images--I: Structure and Evolution
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• Effects of Pre-ionisation in Radiative Shocks II: Application to the Herbig-Haro Objects
• A New Diagnostic of Magnetic Field Strengths in Radiatively-Cooled Shocks
• The UV Perspective of Low-Mass Star Formation
• Illuminating the Tadpole's metamorphosis I: MUSE observations of a small globule in a sea of ionizing photons
• The time evolution of HH 1 from four epochs of HST images
• The time evolution of HH~2 from four epochs of HST images