We observed the symbiotic star AG Dra for a total of 61 nights between April 2004 and December 2021 using the 1.8-m telescope and the high-resolution Echelle spectrograph BOES at the Bohyunsan Optical Astronomy Observatory and obtained 355 frames of spectroscopic data to investigate the variations in its spectral lines. Overnight short-term and long-term changes in prominent emission lines are examined. No short-term changes are found in the line profiles. However, the peak intensity of the Hα emission line exhibits very small variation. In the long-term period, many emission lines including He I λ5875, λ6678, λ7065 and Fe II λ5018 are found to vary reflecting the symbiotic outburst activities. It is noted that He II λ4686 and Raman-scattered O VI λ6830, λ7088 are exceptions, where no significant variations are discernible. One of the noticeable lines is the λ5018 line. Its appearance and disappearance pattern are different from other emission lines, and the line is found to appear in outburst states. The Hα and Hβ lines remain very similar in our spectroscopic monitoring campaign.

ABSTRACT
1. INTRODUCTION
2. OBSERVATION
3. ANALYSIS AND RESULTS
    3.1. Overnight Variations in AG Dra Emission Lines
    3.2. Long-term Variations in AG Dra Emission Lines
4. DISCUSSION
    4.1. Overnight Variations
    4.2. Long-term Variations
5. CONCLUSIONS
ACKNOWLEDGMENT
REFERENCES

• SOO HYUN KIM(Kyungpook National University, Daegu 41566, Korea)
• TAE SEOG YOON(Kyungpook National University, Daegu 41566, Korea) Corresponding author
• HYUNG-IL OH(Kyungpook National University,Korea Astronomy and Space Science Institute)