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A Comprehensive Look at LH72 in the Context of Supergiant Shell LMC-4 | Knut A.G. Olsen
; Sungeun Kim
; Jeremy F. Buss
; | Date: |
26 Feb 2001 | Subject: | astro-ph | Affiliation: | CTIO), Sungeun Kim (CfA), and Jeremy F. Buss (U. Wisc./Oshkosh | Abstract: | Stellar spectroscopy, UBV photometry, H$alpha$ imaging, and analysis of data from the ATCA ion{H}{1} survey of the LMC are combined in a study of the LMC OB association LH 72 and its surroundings. LH 72 lies on the rim of a previously identified ion{H}{1} shell, SGS-14, and in the interior of LMC-4, one of the LMC’s largest known supergiant shells. Our analysis of the ion{H}{1} data finds that SGS-14 is expanding with velocity $v_{exp}sim15$ km s$^{-1}$, giving it an expansion age of $sim$15 Myr. Through the stellar spectroscopy and photometry, we find similar ages for the oldest stars of LH 72, $sim15-$30 Myr. We confirm that LH 72 contains an age spread of $sim15-$30 Myr, similar to the range in ages of stars derived for the entire surrounding supergiant shell. Combining analysis of the O and B stars with H$alpha$ imaging of the ion{H}{2} region DEM 228, we find that DEM 228 accounts for only 60% of the available ionizing Lyman continuum photons. Comparing the distribution of ionized gas with that of the ion{H}{1}, we find that DEM 228 and LH 72 are offset by $sim1-2arcmin$ from the peak 21-cm emission, towards the interior of SGS-14. Taken together, these results imply that SGS-14 has cleared its interior of gas and triggered the formation of LH 72. On the basis of our results, we suggest that LMC-4 was not formed as unit but by overlapping shells such as SGS-14, and that LH 72 will evolve to produce a stellar arc similar to others seen within LMC-4. | Source: | arXiv, astro-ph/0102444 | Services: | Forum | Review | PDF | Favorites |
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