A dissection of 30 Doradus and a discussion of other Magellanic Cloud OB associations

I Present the results of ground-based and Hubble Space Telescope photometry and spectroscopy of the stars in the central region (roughly 7×7 arcmin) of 30 Doradus in the Large Magellanic Cloud (LMC). Using photometric data for over 2400 stars (complete toV18 mag), and spectroscopic observations of over 150 stars in the region, the best estimate of the initial mass function (IMF) yields a slope of =–1.5±0.2 for masses > 12M, where the Salpeter slope is =–1.35. I compare these results to other measurements of the IMF for OB associations in the Magellanic Clouds.     

Wind asymmetries in massive stars

We are in the process of surveying the linear polarization in luminous, early-type stars. We here report on new observations of the B [e] stars S 18 and R 50, and of the Luminous Blue Variables HR Car, R 143, and HD 160529. Together with previously published data, these observations provide clear evidence for the presence of intrinsic polarization in 1 B[e] star (HD 34664) and in 5 LBVs ( Car, P Cyg, R 127, AG Car, and HR Car). The data indicate that anisotropic stellar winds are a common occurrence among massive stars in these particular evolutionary stages. For such stars, mass-loss rates estimated using the assumption of a spherical, homogeneous and stationary outflow may be in error.     

Spectral properties of Lake Superior banded iron formation: application to Martian hematite deposits

Several locations have been identified on Mars that expose bulk, coarsely crystalline gray hematite. These deposits have been interpreted as being sedimentary and formed in aqueous environments. Lake Superior Type (LST) banded iron formation (BIF) was investigated as a spectral and possible process analog to these deposits. In northern Michigan, LST BIF formed in a sedimentary, continental shelf or shallow basin environment under stable tectonic conditions, and the oxide facies contains gray, crystalline hematite. These deposits are Proterozoic in age and contain microfossils associated with the early diversification of life on Earth. Samples of the hematite-bearing oxide facies, as well as the carbonate facies, were collected and analyzed for their spectral and geochemical characteristics. Sample spectra were measured in the visible, near-infrared, and thermal infrared for comparison with remote and in situ spectra obtained at Mars. Thin section analysis, as well as X-ray diffraction and scanning electron microscopy measurements, were performed to determine detailed geochemistry. There is no evidence for BIF at Opportunity's Meridiani landing site, and the results of this work will provide useful data for determining whether BIFs exist elsewhere on Mars and are, thus, relevant to current and future Mars exploration missions.     

Interplanetary scintillation observations of the high-latitude solar wind

Until the ULYSSES spacecraft reached the polar regions of the solar wind, the only high-latitude measurements available were from indirect techniques. The most productive observations in regions of the solar wind between 5R and 200R have been the family of radio scattering techniques loosely referred to as Interplanetary Scintillation (IPS) (Coles, 1978). Useful observations can be obtained using a variety of radio sources, for example spacecraft beacons, planetary radar echoes and compact cosmic sources (quasars, active galactic nuclei, pulsars, galactic masers, etc.). However for measurement of the high-latitude solar wind cosmic sources provide the widest coverage and this review will be confined to such observations. IPS observations played a very important role in establishing that polar coronal holes (first observed in soft x-ray emission) were sources of fast solar wind streams which occasionally extend down to the equatorial region and are observed by spacecraft. Here I will review the IPS technique and show the variation of both the velocity and the turbulence level with latitude over the last solar cycle. I will also outline recent work and discuss comparisons that we hope to make between IPS and ULYSSES observations.     

Be stars in young clusters in the Magellanic Clouds

A substantial fraction (typically 10%) of Galactic B stars consists of Be stars. While Galactic Be stars have been fairly well investigated, very little is known about the Be star content of the Magellanic Clouds (MCs). We present a refined method of Be star identification by CCD photometry and apply it to four young clusters and associations in the MCs. We find NGC 330 in the SMC to be exceptionally rich in Be stars, while the fraction is clearly lower in the similarly aged LMC clusters NGC 2004 and NGC 1818. NGC 2044, a very young region in the LMC, contains almost no Be stars. Among very early-type B stars in the investigated MC clusters we find the largest number of Be stars, while in the Milky Way this is shifted to somewhat later types. In the LMC, there may be a second frequency peak around B6.Based on observations obtained at the 2.2m MPIA telescope at ESO, La Silla, Chile, partly on time granted by the MPIA, Heidelberg.