10 research outputs found
The Integral Field View of the Orion Nebula
This paper reviews the major advances achieved in the Orion Nebula through
the use of integral field spectroscopy (IFS). Since the early work of
Vasconcelos and collaborators in 2005, this technique has facilitated the
investigation of global properties of the nebula and its morphology, providing
new clues to better constrain its 3D structure. IFS has led to the discovery of
shock-heated zones at the leading working surfaces of prominent Herbig-Haro
objects as well as the first attempt to determine the chemical composition of
Orion protoplanetary disks, also known as proplyds. The analysis of these
morphologies using IFS has given us new insights into the abundance discrepancy
problem, a long-standing and unresolved issue that casts doubt on the
reliability of current methods used for the determination of metallicities in
the universe from the analysis of H II regions. Results imply that high-density
clumps and high-velocity flows may play an active role in the production of
such discrepancies. Future investigations based on the large-scale IFS mosaic
of Orion will be very valuable for exploring how the integrated effect of
small-scale structures may have impact at larger scales in the framework of
star-forming regions.Comment: 15 pages, 8 figures. Review paper published in Advances in Astronomy
as part of the special issue "Metals in 3D: A Cosmic View from Integral Field
Spectroscopy". More information: http://dx.doi.org/10.1155/2014/27932
Keck HIRES Spectroscopy of Extragalactic HII Regions: C and O Abundances from Recombination Lines
We present very deep spectrophotometry of 14 bright extragalactic HII regions
belonging to spiral, irregular, and blue compact galaxies. The data for 13
objects were taken with the HIRES echelle spectrograph on the Keck I telescope.
We have measured CII recombination lines in 10 of the objects and OII
recombination lines in 8 of them. We have determined electron temperatures from
line ratios of several ions, specially of low ionization potential ones. We
have found a rather tight linear empirical relation between Te([NII]) and
Te([OIII]). We have found that OII lines give always larger abundances than
[OIII] lines. Moreover, the difference of both O++ abundance determinations
--the so-called abundance discrepancy factor-- is very similar in all the
objects, with a mean value of 0.26+/-0.09 dex, independently of the properties
of the HII region and of the parent galaxy. Using the observed recombination
lines, we have determined the O, C, and C/O radial abundance gradients for 3
spiral galaxies: M33, M101, and NGC2403, finding that C abundance gradients are
always steeper than those of O, producing negative C/O gradients accross the
galactic disks. This result is similar to that found in the Milky Way and has
important implications for chemical evolution models and the nucleosynthesis of
C.Comment: Accepted for publication in ApJ, 54 pages, 4 figure