Other
Scientific paper
May 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...194.4702b&link_type=abstract
American Astronomical Society, 194th AAS Meeting, #47.02; Bulletin of the American Astronomical Society, Vol. 31, p.888
Other
Scientific paper
The light isotope of helium, (3) He, can serve as a probe of cosmology, the evolution of low mass stars, and the chemical evolution of the Galaxy. Its abundance can be determined via measurements of the 3.46 cm hyperfine transition of (3) He(+) . Potentially observable sources of ionized gas include H ii regions and planetary nebulae. The selection of (3) He targets is counter-intuitive because the (3) He(+) hyperfine line strength is proportional to the source density, while one usually thinks of H ii regions in terms of radio continuum or recombination line strength both of which depend on the square of the density. The (3) He(+) line strength depends on the (3) He(+) abundance ratio and a number of other factors: $ TL(A}({) (3) He(+)) ~ frac {N((3) He(+)}{N() H(+)}) frac {({TC(A}}D)({1/2)) Te(1/4) (theta_obs (2) - theta_beam (2})({3/4}}{Delta {v}({)) (3) He(+)) [ln(5.717 x 10(-3}Te({3/2})]^{1/2)) theta_obs } where T_L^A and Delta v are the antenna temperature and FWHM of the ^3He^+ line, D is the nebular distance, T_C^A and theta_obs are the antenna temperature and observed FWHM angular size of the continuum emission, theta_beam is the telescope's FWHM beam, and Te is the nebular electron temperature. For H {sc ii} regions much larger than the telescope beam we can select targets using the criterion: TLA(^3He^+)\sim\sqrt{TCA D\theta_obs}. This is the case since we can neglect the weak dependence on T_e and because we do not know either ^3He^{+}/H^+ or Delta v. Thus big, distant H ii regions could be potential ^3He^+ targets even if their continuum emission is weak. Armed with this knowledge we included H ii regions like S209 in our early observing list along with more famous sources like W43. Still we did not have the temerity to push this reasoning to the limit. We have now found, however, that this selection criterion is valid for even the wimpiest known H ii regions. Here we report on the detection of ^3He^+$ emission in 8 distant, low density H ii regions.
Balser Dana S.
Bania Thomas M.
Rood Robert T.
No associations
LandOfFree
3-Helium in Obscure H II Regions does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with 3-Helium in Obscure H II Regions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and 3-Helium in Obscure H II Regions will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1120427