Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990mnras.245..701w&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Vol. 245, NO.4/AUG15, P. 701, 1990
Astronomy and Astrophysics
Astronomy
14
Scientific paper
We have used the Cerro Tololo 1-m telescope and two-dimensional Frutti spectrograph to obtain long-slit spectra near 17 early-type stars, whose interstellar absorption spectra had been studied with both the Copernicus and IUE satellites, in the direction of the Vela remnant to study the emission lines from hot gas associated with the remnant. All the observations were reduced to absolute fluxes in each emission line. Most fields showed nearly uniform illumination along the 176 arcsec slit but bright discrete clouds were observed near two stars, HD 72088 and 73658.
The clouds fall into two groups: those with Hβ stronger than 4959 of [O III], and those with λ4959 stronger than Hβ. The latter are unique because of their high temperature as indicated by the ratio of λ4959 + λ5007/λ4363. Both type of clouds show [Fe III] while the clouds with Hβ > λ4959 also show [Fe II]. Electron densities as obtained from [O II] and [S II] are at or below the low density limit, 100 cm-3.
The data are rather well-modelled by the calculations of shocked cloud emission by Raymond et al. and show some characteristics similar to Herbig-Haro 1 and Burnham's nebula near T Tauri, as well as shocked gas in Seyfert nuclei. The high-excitation clouds fit models with shock velocities near 90 km s-1, while the low-excitation clouds are best modelled with a shock velocity near 65 km s-1 and hydrogen (and perhaps helium) pre-ionized by the ambient radiation field.
Finally, a comparison is made with absorption data obtained with the Copernicus satellite. We find that the combined data and the models of Raymond et al. indicate a total column density of log NH = 18.0-18.5. For a density of 100 cm-3 such clouds would be about 200 AU in size and 4 arcsec in projected size.
Balick Bruce
Wallerstein George
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