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BEGIN:VEVENT
DTSTART;TZID=Atlantic/Canary:20111020T000000
DTEND;TZID=Atlantic/Canary:20111020T010000
UID:iactalks-313
X-WR-CALNAME: IAC Talks: Open Astronomy Seminars
X-ORIGINAL-URL: /iactalks/Talks/view/313
CREATED:2011-10-20T00:00:00+01:00
X-WR-CALDESC: IAC Talks upcomming talks
SUMMARY:Facing the Abundance Discrepancy in the Orion Nebula 
DESCRIPTION:Facing the Abundance Discrepancy in the Orion Nebula \nDr. Adal
  Mesa\n\nThe spectral analysis of HII regions allows one to determine the 
  chemical composition of the ionized gas phase of the interstellar medium 
  (ISM) from the solar neighborhood to the high-redshift galaxies.  Therefo
 re, it stands as an essential tool for our knowledge of the  chemical evol
 ution of the Universe. However, it turns out that chemical  abundances of 
 heavy-element ions determined from the bright  collisionally excited lines
  (CELs) are systematically lower than the  abundances derived from the fai
 nt recombination lines (RLs) emitted by  the same ions. Today, this contro
 versial issue is known as abundance  discrepancy problem and it is far fro
 m negligible. In the analysis of  Galactic and extragalactic HII regions t
 he O2+/H+ ratio calculated from  the OII RLs is between 0.10 and 0.35 dex 
 higher than that obtained from  the [OIII] CELs. In this talk, we will fac
 e this problem in the  benchmark object of the solar vicinity, the Orion N
 ebula. Due to its  high surface brightness and proximity, the Orion Nebula
  is an ideal lab,  which allows us to study in detail the possible role of
  its rich and  well-resolved internal structure (such as Herbig-Haro objec
 ts,  protoplanetary disks or bars) on the abundance discrepancy.
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