2023A&A...671L...1L


Query : 2023A&A...671L...1L

2023A&A...671L...1L - Astronomy and Astrophysics, volume 671, L1-6 (2023/3-1)

First detection of radio recombination lines of ions heavier than helium.

LIU X., LIU T., SHEN Z., GOLDSMITH P.F., EVANS II N.J., QIN S.-L., LUO Q., CHENG Y., LIU S.-Y., ZHU F., TATEMATSU K., LIU M., YANG D., LI C., CHEN L., LI J., LU X., GU Q., ZHAO R., LI B., WU Y., ZHONG W., ZHAO Z., WANG J., LIU Q., XIA B., FU L., YAN Z., ZHANG C., WANG L., YE Q., LIU H., ZHANG C., XU F. and SAHU D.

Abstract (from CDS):

We report the first detection of radio recombination lines (RRLs) of ions heavier than helium. In a highly sensitive multi-band (12-50 GHz) line survey toward Orion KL with the TianMa 65-m Radio Telescope (TMRT), we successfully detected more than fifteen unblended α lines of RRLs of singly ionized species (XII) recombined from XIII. The Ka-band (26-35 GHz) spectrum also shows tentative signals of β lines of ions. The detected lines can be successfully crossmatched with the rest frequencies of RRLs of C II and/or O II. This finding greatly expands the scope of our understanding of ion RRLs, since prior to this work, only two blended lines (105α and 121α) of He II had been reported. Our detected lines can be fitted simultaneously under assumption of local thermodynamic equilibrium (LTE). An abundance of C III and O III of 8.8×10–4 was obtained, avoiding the complexities of optical and infrared observations and the blending of RRLs of atoms. It is consistent with but approaches the upper bound of the value (10–4-10–3) estimated from optical and infrared observations. The effects of dielectronic recombination may contribute to enhancing the level populations even at large n. We expect future observations using radio interferometers could break the degeneracy between C and O, while also helping to reveal the ionization structure and dynamical evolution of various ionized regions.

Abstract Copyright: © The Authors 2023

Journal keyword(s): HII regions - radio lines: ISM - line: identification - stars: formation - ISM: abundances

Simbad objects: 6

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Number of rows : 6
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 NAME Orion-KL SFR 05 35 14.16 -05 22 21.5           ~ 2299 1
2 [RLK73] IRc 2 IR 05 35 14.51548 -05 22 30.5943           ~ 641 1
3 * tet01 Ori C SB* 05 35 16.4662967280 -05 23 22.921811880 4.20 5.15 5.13 4.91 4.73 O7Vp 1406 1
4 M 42 HII 05 35 17 -05 23.4           ~ 4083 0
5 NGC 6302 PN 17 13 44.5 -37 06 11           O-rich 797 1
6 NGC 7027 PN 21 07 01.571952 +42 14 10.47120   10.358 8.831 10.157   ~ 2462 1

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