Open AccessTemperature variations from Hubble Space Telescope spectroscopy of the Orion Nebula
Author(s) -
Rubin R. H.,
Martin P. G.,
Dufour R. J.,
Ferland G. J.,
Blagrave K. P. M.,
Liu X.W.,
Nguyen J. F.,
Baldwin J. A.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06185.x
Subject(s) - physics , astrophysics , orion nebula , line of sight , spectroscopy , hubble space telescope , line (geometry) , doubly ionized oxygen , nebula , planetary nebula , electron density , emission spectrum , astronomy , electron , spectral line , stars , geometry , mathematics , quantum mechanics
We present Hubble Space Telescope ( HST )/STIS long‐slit spectroscopy of NGC 1976. Our goal is to measure the intrinsic line ratio [O iii ] 4364/5008 and thereby evaluate the electron temperature ( T e ) and the fractional mean‐square T e variation ( t 2 A ) across the nebula . We also measure the intrinsic line ratio [N ii ] 5756/6585 in order to estimate T e and t 2 A 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 as well as a possible contribution to the [N ii ] 5756 emission by recombination (and cascading). We present results from binning the data along the various slits into tiles that are 0.5 arcsec square (matching the slit width). The average [O iii ] temperature for our four HST /STIS slits varies from 7678 K to 8358 K; t 2 A varies from 0.00682 to at most 0.0176. For our preferred solution, the average [N ii ] temperature for each of the four slits varies from 9133 to 10 232 K; t 2 A varies from 0.00584 to 0.0175. The measurements of T e reported here are an average along each line of sight. Therefore, despite finding remarkably low t 2 A , 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. Observations of the proplyd P159‐350 indicate: large local extinction associated; ionization stratification consistent with external ionization by θ 1 Ori C; and indirectly, evidence of high electron density.