Y -band is a broad passband that is centered at ~1 μm. It is becoming a new, popular window for extragalactic study especially for observations of red objects thanks to recent CCD technology de- velopments. In order to better understand the general characteristics of objects in Y -band, and to investigate the promise of Y -band observations with small telescopes, we carried out imaging observa- tions of several extragalactic fields, brown dwarfs, and high redshift quasars with Y -band filter at the Mt. Lemmon Optical Astronomy Observatory and the Maidanak observatory. From our observations, we constrain the bright end of the galaxy and the stellar number counts in Y -band. We also test the usefulness of high redshift quasar (z >6) selection via i − z − Y color-color diagram, to demonstrate that the i − z − Y color-color diagram is effective for the selection of high redshift quasars even with a conventional optical CCD camera installed at a 1-m class telescope.

ABSTRACT
1. INTRODUCTION
2. Y -BAND FILTER AND OBSERVATION
    2.1 Y -band Filters
    2.2 LOAO Observation
    2.3 Maidanak Observation
3. DATA REDUCTION
    3.1 Image Reduction and Stacking
    3.2 Photometry Calibration
    3.3 Astrometry Calibration
    3.4 Source Detection and Extraction
4. RESULTS
    4.1 Number Counts
    4.2 Completeness Test
    4.3 High Redshift Quasar Selection
5. DISCUSSION
    5.1 Detection Limits of LOAO and Maidanak Telescopes
    5.2 Promises of Y -band Imaging with Small Telescopes
6. SUMMARY
REFERENCES

• MANSUR IBRAHIMOV(Ulugh Beg Astronomical Institute)
• YISEUL JEON(CEOU/Astronomy Program, Department of Physics and Astronomy, Seoul National University)
• MYUNGSHIN IM(CEOU/Astronomy Program, Department of Physics and Astronomy, Seoul National University) Corresponding Author
• CHANGSU CHOI(CEOU/Astronomy Program, Department of Physics and Astronomy, Seoul National University)