TY  - JOUR
A1  - Zhang, Heshou
A1  - Yan, Huirong
A1  - Richter, Philipp
T1  - The influence of atomic alignment on absorption and emission spectroscopy
JF  - Monthly notices of the Royal Astronomical Society
N2  - Spectroscopic observations play essential roles in astrophysics. They are crucial for determining physical parameters in our Universe, providing information about the chemistry of various astronomical environments. The proper execution of the spectroscopic analysis requires accounting for all the physical effects that are compatible to the signal-to-noise ratio. We find in this paper the influence on spectroscopy from the atomic/ground state alignment owing to anisotropic radiation and modulated by interstellar magnetic field, has significant impact on the study of interstellar gas. In different observational scenarios, we comprehensively demonstrate how atomic alignment influences the spectral analysis and provide the expressions for correcting the effect. The variations are even more pronounced for multiplets and line ratios. We show the variation of the deduced physical parameters caused by the atomic alignment effect, including alpha-to-iron ratio ([X/Fe]) and ionization fraction. Synthetic observations are performed to illustrate the visibility of such effect with current facilities. A study of Photodissociation regions in rho Ophiuchi cloud is presented to demonstrate how to account for atomic alignment in practice. Our work has shown that due to its potential impact, atomic alignment has to be included in an accurate spectroscopic analysis of the interstellar gas with current observational capability.
KW  - magnetic fields
KW  - submillimetre: ISM
KW  - ultraviolet: ISM
KW  - ISM: abundances
KW  - ISM: lines and bands
KW  - techniques: spectroscopic
Y1  - 2018
U6  - https://doi.org/10.1093/mnras/sty1594
SN  - 0035-8711
SN  - 1365-2966
VL  - 479
IS  - 3
SP  - 3923
EP  - 3935
PB  - Oxford Univ. Press
CY  - Oxford
ER  -