1,748 research outputs found
Low-excitation blobs in the Magellanic Clouds
Aims : We study an unknown, or very poorly known, interstellar HII component
in the Magellanic Clouds. This is the first study ever devoted to this class of
objects, which we call Low-excitation blobs (LEBs).
Methods : We used low-dispersion spectroscopy carried out at ESO to obtain
emission line intensities of Ha, Hb, and [OIII] (4959+5007) for 15 objects in
the Large Magellanic Cloud and 14 objects in the Small Magellanic Cloud.
Results are displayed in excitation ([oiii]/Hb ratio) versus Hb luminosity
diagrams.
Results : We show the presence of an LEB component in the Magellanic Clouds
and study its relationship with the already known class of high-excitation
blobs (HEBs). The newly found LEBs are lower excitation counterparts of HEBs
and are powered by less massive exciting stars. Further study of LEBs is
expected to provide new pieces of information for a better understanding the
low mass end of the upper initial mass function in the Magellanic Clouds.Comment: Accepted in A&
Spitzer Mid-infrared Study of Compact HII Regions in the Magellanic Clouds
We present a study of the mid-infrared properties and dust content of a
sample of 27 HII ``blobs'', a rare class of compact HII regions in the
Magellanic Clouds. A unique feature of this sample is that even though these
HII regions are of high and low excitation they have nearly the same physical
sizes ~1.5-3 pc. We base our analysis on archival 3-8 microns infrared imagery
obtained with the Infrared Array Camera (IRAC) on board the Spitzer Space
Telescope. We find that despite their youth, sub-solar metallicity and varied
degrees of excitation, the mid-infrared colors of these regions are similar to
those of typical HII regions. Higher excitation ``blobs'' (HEBs) display
stronger 8 micron emission and redder colors than their low-excitation
counterparts (LEBs).Comment: 8 pages, 4 figures, Accepted for publication in Astronomy &
Astrophysics (higher resolution version is available in
http://www.physics.uoc.gr/~vassilis/papers/blobs_spitzer.pdf
STIS spectroscopy of newborn massive stars in SMC N81
Using Hubble Space Telescope observations with STIS, we study the main
exciting stars of N81, a high excitation compact Hii region in the Small
Magellanic Cloud (SMC). These far UV observations are the first spectroscopic
measurements of stars in such a region and reveal features characteristic of an
O6-O8 stellar type. The astonishing weakness of their wind profiles and their
sub-luminosity (up to ~ 2 mag fainter in Mv than the corresponding dwarfs) make
these stars a unique stellar population in the Magellanic Clouds. Our analysis
suggests that they are probably in the Hertzsprung-Russell diagram locus of a
particularly young class of massive stars, the so-called Vz luminosity class,
as they are arriving on the zero age main sequence.Comment: 9 pages, 3 figure
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