Temperature Variations from HST Spectroscopy of NGC 1976

Details Temperature Variations from HST Spectroscopy of NGC 1976 Temperature Variations from HST Spectroscopy of NGC 1976

Sep 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003rmxac..18..113r&link_type=abstract

The Eight Texas-Mexico Conference on Astrophysics (Eds. M. Reyes-Ruiz & E. Vázquez-Semadeni) Revista Mexicana de Astronomía y As

Astronomy and Astrophysics

Astrophysics

H Ii Regions, Ism: Abundances, Ism: Individual (Orion Nebula)

Scientific paper

We present HST/STIS long-slit spectroscopy of NGC 1976. Our goal is to measure the intrinsic line flux ratio [O III] 4364/5008 and thereby evaluate the electron temperature (T[e]) and the fractional mean-square T[e] variation (t[A]^2) across the nebula. We also measure the intrinsic line flux ratio [N II] 5756/6585 in order to estimate T[e] and t[A]^2 in the N+ region. The interpretation of the [N II] data is not as clear cut as the [O III] data because of a higher sensitivity to knowledge of the electron density (N[e]). We present results from binning the data along the various slits into tiles that are 0.5'' square. The average [O III] temperature for our four HST/STIS slits varies from 7678 K to 8358 K; t[A]^2 varies from 0.00682 to 0.0176. When we use N[e] of 8000 (for slits 1 and 2) and 3000 cm-3 (for slits 4 and 5) with Lennon & Burke (1994) collision strengths, the average [N II] temperature for each of the four slits varies from 8979 K to 9761 K; t[A]^2 varies from 0.00551 to 0.0172. The measurements of T[e] reported here are an average along each line of sight. Therefore, despite finding remarkably low t[A]^2, we cannot rule out significantly larger temperature fluctuations along the line of sight. The result that the average [N II] T[e] exceeds the average [O III] T[e] confirms what has been previously found for Orion and what is expected on theoretical grounds.

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