Measurements of [O [CSC]i[/CSC]] λ6300/Hα Line Intensity Ratios for Four O Star H [CSC]ii[/CSC] Regions

Abstract

We have used the Wisconsin H Mapper facility to measure the [O i] 6300/H line intensity ratios for four O star H ii regions: S27 (observation coordinates l = 6=3, b = +23=6), S252 (l = 190=1, b = +0=6), S261 (l = 194=1, b = À1=9), and S264 (l = 195=1, b = À12=0). We find that the ratios range from 0.0015 to 0.0053. These results are roughly a factor of 10 lower than measured [O i]/H ratios in directions that sample the warm ionized component of the interstellar medium. This difference implies a significantly lower hydrogen ionization ratio n(H +)/n(H 0) or higher electron temperature in the diffuse ionized gas compared with that in the bright discrete O star H ii regions.

G192.8-1.1: A Candidate of an Evolved Thermal Composite Supernova Remnant Reignited by Nearby Massive Stars

“…The spectroscopic or photometric distances to the star within S261 are 1.4 kpc (Georgelin & Georgelin 1976) and 1.5 kpc (Garmany et al 1982), which are close to that of S255. The radial velocity of the Hα line emission of S261, v LSR = +5.6 km s ¡1 (Hausen et al 2002) is close to the lower limit of those of S254 -S258, v LSR = +6.0 -+11.1 km s ¡1 , measured in CO and Hα lines. On the other hand, S259, which overlaps with G192, seems separated from the rest of the Hii regions in the field.…”

“…The expected count rate per EM is 8 ¢ 10 ¡4 counts s ¡1 arcmin ¡2 at T 5 ¢ 10 6 K in band 5 (0.56 -1.21 keV), for example, when a maximum extinction of N H 10 22 cm ¡2 is assumed (see Figure 7 of Snowden et al 1997). The count rate of G192, for an EM = 190 cm ¡6 pc, would be 0.16 counts s ¡1 arcmin ¡2 , while, the rms of the G192 a Optical size (Sharpless 1959) b Hα emission line radial velocity (Fich et al 1990), except S261, which is from Hausen et al (2002). c CO radial velocity (Blitz et al 1982).…”

The warm ionized medium in spiral galaxies

“…Nevertheless, high-sensitivity, high-resolution spectroscopic measurements with WHAM have managed to resolve the Galactic emission from atmospheric emission to provide reliable measurements in a few select directions. These observations indicate that H + /H > 90% for T > 8000 K (Hausen et al, 2002;Reynolds et al, 1998).…”

A Multiwavelength Optical Emission Line Survey of Warm Ionized Gas in the Galaxy

“…The similar first ionization potentials of N and H (14.5 and 13.6 eV, respectively), along with N-H charge exchange, mean that in the WIM the ionization fraction of N + /N is expected to be similar to H + /H. The fraction H + /H is observed to be near unity in the WIM Hausen et al 2002a), and the high second ionization potential of N (29.6 eV ) means that little N is likely to be in the form of N ++ . This is supported by the weak [O iii]/ H ratios in the WIM (see below) and by photoionization modeling (e.g., Sembach et al 2000), which have shown that N þ /N % 0:8 over a wide range of input spectra and ionization parameters.…”