from model atmosphere analyses of the spectra of b-type stars in young clusters, we have found zero galactic abundance gradients for the solar neighbourhood (i.e. within 3 kpc of the sun). at larger galactocentic distances, we find considerable abundance variations over relatively small distance scales (i.e. virgul1 kpc). these results are significantly different from those deduced from h ii region observations. however our discussion of these discrepancies has been compromised by the lack of data for both the b-type stars and their associated h ii regions. we therefore plan to observe with iso the h ii regions directly associated with early-type stars that we have previously analysed viz. s 208, s 212 and s 285 for a spring and the first two only for an autumn launch. the iso observations will be supplemented with our existing optical data for the h ii regions plus new observations, which will be obtained using time recently awarded to us on the 4.2 m william herschel telescope. the nebular abundances will be compared with the b-type stellar values, which will allow us to investigate if the discrepancies discussed above are due to: (a) errors in (probably) the h ii region analyses, (b) variations in their dust content, and/or (c) the stellar observations identifying abundance variations on a small spatial scale beyond those seen in the h ii region results. as h ii regions are used extensively to map abundances in external galaxies, it is important that these discrepancies are understood.
Instrument
LWS01 , SWS02
Temporal Coverage
1998-03-02T21:09:56Z/1998-03-02T22:23:24Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, DUFTON et al., 1999, 'H II REGIONS ASSOCIATED WITH YOUNG GALACTIC CLUSTERS: COMPARISON OF STELLAR AND NEBULAR CHEMICAL COMPOSITIONS.', 1.0, European Space Agency, https://doi.org/10.5270/esa-zm3eqey
