The SMC compact blob N 81 : a detailed multi-wavelength investigation.
Abstract
This paper is devoted to an extensive investigation of the compact Small Magellanic Cloud H II region N81. Several observational techniques with various telescopes at ESO have been employed to acquire a multi-aspect view of the physical characteristics of this interesting nebula: CCD, IDS and Reticon high, medium and low resolution spectroscopy (range 3700-10000 A), CCD imaging using 17 different filters, optical and infrared photometry at UBVRI and JHK. We also use the H I emission observations reported in the literature. The nebula N81 is probably excited by one star of about 60 M_sun_, (T_eff_ = 47500 K) accompanied by a cluster of about 10 B0 stars (M = 15 M_sun_, T_eff_ = 32000 K). We derive the absolute visual magnitude of the exciting star to be -5.1, corresponding to a bolometric magnitude of M_bol_= -9.1 and a luminosity of 3.5 10^5^ L_sun_. This nebula is a young H II region. From the equivalent width of the Hβ emission line we derive an age of 2.5 10^6^yr for N81. We stress the importance of correcting the continuum emission around Hβ for the nebular contribution. We derive the gas electron density and temperature and compute the chemical abundances of He, O, N, Ne, S, and Ar. The results are compared with the mean values available for the SMC. The high resolution profile of N81 at Hβ was decomposed into its various components. We find the most probable three dimensional turbulent velocity in N81 to be about 3 km s^-1^. We observationally confirm the proposition by Koornneef and Israel (1985) that the H_2_ emission may be produced by the action of a mild shock moving through the ambient cloud of this nebula. Interestingly, unlike other representatives of this category of H II regions in the Magellanic Clouds, N81 is not affected by the local dust. The nebula N81 is associated with the SMC H I cloud of radial velocity +167 km s^-1^, observed by McGee and Newton (1981). The neighboring H II complexes N83 are associated with a density peak of this H I cloud. N 88 A, another SMC H II blob, lying in the vicinity of N 81, is associated with another H I cloud. We speculate that N 81 and N 88 A may have been formed due to a collision between these two clouds.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- April 1988
- Bibcode:
- 1988A&A...195..230H
- Keywords:
-
- Charge Coupled Devices;
- H Beta Line;
- H Ii Regions;
- Interstellar Matter;
- Magellanic Clouds;
- O Stars;
- Abundance;
- Infrared Photometry;
- Ubv Spectra;
- Velocity Distribution;
- Astrophysics