TEMPORAL VARIATION OF HCO+ 1_0 GALACTIC ABSORPTION LINES TOWARD NRAO 150 AND BL LAC

• Published in: Journal of the Korean Astronomical Society, 50(6) pp. 185 - 190
• Main Authors: 한정환, 윤영주, 박용선
• Format: Journal Article
• Language: English
• Published: 한국천문학회 01.12.2017
• Subjects: 천문학
• ISSN: 1225-4614; 2288-890X
• DOI: 10.5303/JKAS.2017.50.6.185

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 --17 km s$^{-1}$ component changed marginally during 1993--1998 period and has remained unaltered thereafter for NRAO~150. Its behavior is different from that of H$_2$CO 1$_{10}$--1$_{11}$, suggesting chemical differentiation on $\sim 20$ AU scale, the smallest ever seen. On the other hand, BL~Lac exhibits little temporal variation for the HCO$^+$ and H$_2$CO 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. KCI Citation Count: 0