Journal of The Korean Astronomical Society (천문학회지)

The Korean Astronomical Society (한국천문학회)
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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)
  • Received : 2017.08.14
  • Accepted : 2017.12.04
  • Published : 2017.12.31
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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.

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References

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