ENR CTIO 1.5-m 2025-02-28

1. We are puzzled by the variations of the mean counts of ThAr and quartz frames in fiber and slicer mode. I have put together two plots to show not only the day-to-day variations, but the frame-to-frame variation within a night.

Sorry about not having time to beatuify the plots, but these two plots are available at www.astro.gsu.edu/~jao/fiber.png and www.astro.gsu.edu/~jao/slicer.png.

Data shown here are taken between 2024-08-19 to 2025-02-27. Each dot represents the mean count for calibration frames in 24xxxx/25xxxx folders using settings like, quartz+fiber, ThAr+fiber, quartz+slicer, and ThAr+slicer. The error bar is the standard deviation for all those frames . Only a setting with more than 2 frames is shown here. For example, ThAr+fiber only has two frames in 2025-02-26, and it is not shown here.

Three obvious features can be seen. The first one is the sudden increase of counts since 2025/02/14. We have checked our RV standard star taken on 2025-02-20, and its RV and H-alpha is stable as data acquired two years ago. Hence, the high counts is less a conern for now. The second is the relatively large error bars on 2025-02-26, especially for the quartz lamp. As I reported on 02-26, the last four ThAr images taken after the science star were also visibly fainter than ThAr taken earlier that night. This shows a large frame-to-frame variation in a night.  The last feature is the drop on 2027-02-27. Although it is not a historically low, the magnitude is quite large. 

Are these red flags for more sever problems in the future? Or it has already been problems.

2. A star at DEC=+25 is observed this morning. Without pressing any button on the hand paddle to move the star in the guiding box, the telescope keeps drifting south itself.