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http://dx.doi.org/10.5303/JKAS.2017.50.6.185

TEMPORAL VARIATION OF HCO+ 1-0 GALACTIC ABSORPTION LINES TOWARD NRAO 150 AND BL LAC  

Han, Junghwan (School of Integrated Technology, Yonsei University)
Yun, Youngjoo (Korea Astronomy and Space Science Institute)
Park, Yong-Sun (Department of Physics and Astronomy, Seoul National University)
Publication Information
Journal of The Korean Astronomical Society / v.50, no.6, 2017 , pp. 185-190 More about this Journal
Abstract
We present observations of $HCO^+$ 1-0 absorption lines toward two extragalactic compact radio sources, NRAO 150 and BL Lac with the Korean VLBI Network in order to investigate their time variation over 20 years by Galactic foreground clouds. It is found that the line shape of $-17kms^{-1}$ component changed marginally during 1993-1998 period and has remained unaltered thereafter for NRAO 150. Its behavior is different from that of $H_2CO$ $1_{10}-1_{11}$, suggesting chemical differentiation on ~ 20 AU scale, the smallest ever seen. On the other hand, BL Lac exhibits little temporal variation for the $HCO^+$ and $H_2CO$ lines. Our observation also suggests that Korea VLBI Network performs reliably in the spectrum mode in that the shapes of the new $HCO^+$ 1-0 spectra are in good agreement with the previous ones to an accuracy of a few percent except the time varying component toward NRAO 150.
Keywords
ISM: abundance; ISM: molecules; quasars: individual (NRAO 150, BL Lac); technique: interferometric;
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