Bibcode
Madonna, S.; Bautista, Manuel; Dinerstein, Harriet L.; Sterling, N. C.; García-Rojas, J.; Kaplan, Kyle F.; del Mar Rubio-Díez, Maria; Castro-Rodríguez, N.; Garzón, F.
Bibliographical reference
The Astrophysical Journal Letters, Volume 861, Issue 1, article id. L8, 7 pp. (2018).
Advertised on:
7
2018
Citations
18
Refereed citations
17
Description
We have identified two new near-infrared (NIR) emission lines in the
spectra of planetary nebulae arising from heavy elements produced by
neutron-capture reactions: [Te III] 2.1019 μm and [Br V] 1.6429
μm. [Te III] was detected in both NGC 7027 and IC 418, while [Br V]
was seen in NGC 7027. The observations were obtained with the
medium-resolution spectrograph Espectrógrafo Multiobjeto
Infra-Rojo (EMIR) on the 10.4 m Gran Telescopio Canarias at La Palma,
and with the high-resolution Immersion GRating INfrared Spectrometer
(IGRINS) on the 2.7 m Harlan J. Smith telescope at McDonald Observatory.
New calculations of atomic data for these ions, specifically A-values
and collision strengths, are presented and used to derive ionic
abundances of Te2+ and Br4+. We also derive ionic
abundances of other neutron-capture elements detected in the NIR
spectra, and estimate total elemental abundances of Se, Br, Kr, Rb, and
Te after correcting for unobserved ions. Comparison of our derived
enrichments to theoretical predictions from asymptotic giant branch
(AGB) evolutionary models shows reasonable agreement for solar
metallicity progenitor stars of ∼2–4 M ⊙. The
spectrally isolated [Br V] 1.6429 μm line has advantages for
determining nebular Br abundances over optical [Br III] emission lines
that can be blended with other features. Finally, measurements of Te are
of special interest because this element lies beyond the first peak of
the s-process, and thus provides new leverage on the abundance pattern
of trans-iron species produced by AGB stars.
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