2010A&A...521L..10N

Query : 2010A&A...521L..10N

2010A&A...521L..10N - Astronomy and Astrophysics, volume 521, L10-10 (2010/10-1)

Herschel/HIFI observations of interstellar OH⁺ and H₂O⁺ towards W49N: a probe of diffuse clouds with a small molecular fraction.

NEUFELD D.A., GOICOECHEA J.R., SONNENTRUCKER P., BLACK J.H., PEARSON J., YU S., PHILLIPS T.G., LIS D.C., DE LUCA M., HERBST E., RIMMER P., GERIN M., BELL T.A., BOULANGER F., CERNICHARO J., COUTENS A., DARTOIS E., KAZMIERCZAK M., ENCRENAZ P., FALGARONE E., GEBALLE T.R., GIESEN T., GODARD B., GOLDSMITH P.F., GRY C., GUPTA H., HENNEBELLE P., HILY-BLANT P., JOBLIN C., KOLOS R., KRELOWSKI J., MARTIN-PINTADO J., MENTEN K.M., MONJE R., MOOKERJEA B., PERAULT M., PERSSON C., PLUME R., SALEZ M., SCHLEMMER S., SCHMIDT M., STUTZKI J., TEYSSIER D., VASTEL C., CROS A., KLEIN K., LORENZANI A., PHILIPP S., SAMOSKA L.A., SHIPMAN R., TIELENS A.G.G.M., SZCZERBA R. and ZMUIDZINAS J.

Abstract (from CDS):

We report the detection of absorption by interstellar hydroxyl cations and water cations, along the sight-line to the bright continuum source W49N. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 972GHz N=1-0 transition of OH⁺ and the 1115GHz 1₁₁-0₀₀ transition of ortho-H₂O⁺. The resultant spectra show absorption by ortho-H₂O⁺, and strong absorption by OH⁺, in foreground material at velocities in the range 0 to 70km/s with respect to the local standard of rest. The inferred OH⁺/H₂O⁺ abundance ratio ranges from ∼3 to ∼15, implying that the observed OH⁺ arises in clouds of small molecular fraction, in the 2-8% range. This conclusion is confirmed by the distribution of OH⁺ and H₂O⁺ in Doppler velocity space, which is similar to that of atomic hydrogen, as observed by means of 21cm absorption measurements, and dissimilar from that typical of other molecular tracers. The observed OH⁺/H abundance ratio of a fewx10^–8 suggests a cosmic ray ionization rate for atomic hydrogen of 0.6-2.4x10^–16s^–1, in good agreement with estimates inferred previously for diffuse clouds in the Galactic disk from observations of interstellar H₃⁺ and other species.

Abstract Copyright: ∼

Journal keyword(s): ISM: molecules - submillimeter: ISM - astrochemistry - molecular processes

Simbad objects: 10

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Number of rows : 10

N	Identifier	Otype	ICRS (J2000) RA	ICRS (J2000) DEC	Mag B	Mag V	Sp type	#ref 1850 - 2023	#notes
1	Mrk 231	Sy1	12 56 14.2341182928	+56 52 25.238373852	14.68	13.84	~	1956	3
2	NAME NGC 6334-I	Cl*	17 20 53.35	-35 47 01.5			~	333	0
3	NAME Sgr B2	MoC	17 47 20.4	-28 23 07			~	2199	1
4	NAME Sgr B2 Main	Rad	17 47 20.5	-28 23 06			~	390	1
5	W 31c	HII	18 10 29.1	-19 56 05			~	336	0
6	W 49n	HII	19 10 13.2	+09 06 12			~	461	3
7	W 49a	SFR	19 10 15.7	+09 06 05			~	298	2
8	W 49	SFR	19 10 20	+09 07.7			~	566	1
9	DR 21	SFR	20 39 01.6	+42 19 38			O4.5	1036	0
10	NAME dze Per Cloud	Cld	~	~			~	21	0

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