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Register a new userThe feedback of massive stars on the ISM: XMM-Newton view of the LMC superbubble N51D
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Dominik J. Bomans
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N51D (= DEM L 192) appears at first glance as a nearly circular, 120pc diameter bubble of ionized gas around the LMC OB association LH 54. A deeper look reveals a complex web of filaments and deviations from radial expansion. Using a deep XMM-Newton X-ray pointing centered on N51D we find that diffuse soft X-ray emitting gas fills the whole superbubble as delineated by the H-alpha filaments. Contrary to recent findings for galactic winds, the correlation between H-alpha and X-ray surface brightness is not good. The X-ray spectrum of this diffuse gas cannot be fitted with the LMC abundance pattern, but implies an overabundance of at least oxygen and neon, consistent with recent enrichment from supernovae type II. Some indications for enhanced mixing at the brightest region of the H-alpha shell and for a beginning outflow of the hot gas were also detected.
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Using Spitzer Space Telescope and Hubble Space Telescope observations of the superbubble N51D, we have identified three young stellar objects (YSOs) in dust globules, and made the first detection of a Herbig-Haro object outside the Galaxy. The spectral energy distributions of these YSOs suggest young massive stars with disk, envelope, and outflow cavities. The interstellar conditions are used to assess whether the star formation was spontaneous or induced by external pressure.
Clusters or associations of early-type stars are often associated with a superbubble of hot gas. The formation of such superbubbles is caused by the feedback from massive stars. The complex N206 in the Large Magellanic Cloud exhibits a superbubble and a rich massive star population. We observed these massive stars using the FLAMES multi-object spectrograph at ESO-VLT. Available UV spectra from HST, IUE, and FUSE are also used. The spectral analysis is performed with Potsdam Wolf-Rayet (PoWR) model atmospheres. We present the stellar and wind parameters of the OB stars and the two WR binaries in the N206 complex. Twelve percent of the sample show Oe/Be type emission lines, although most of them appear to rotate far below critical. We found eight runaway stars based on their radial velocity. The wind-momentum luminosity relation of our OB sample is consistent with the expectations. The HRD of the OB stars reveals a large age spread (1-30 Myr), suggesting different episodes of star formation in the complex. The youngest stars are concentrated in the inner part of the complex, while the older OB stars are scattered over outer regions. We derived the present day mass function for the entire N206 complex as well as for the cluster NGC2018. Three very massive Of stars are found to dominate the feedback among 164 OB stars in the sample. The two WR winds alone release about as much mechanical luminosity as the whole OB star sample. The cumulative mechanical feedback from all massive stellar winds is comparable to the combined mechanical energy of the supernova explosions that likely occurred in the complex. Accounting also for the WR wind and supernovae, the mechanical input over the last five Myr is ~$2.3times10^{52}$ erg, which exceeds the current energy content of the complex by more than a factor of five. The morphology of the complex suggests a leakage of hot gas from the superbubble.
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