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The wavelength range around 1.4 μm is highly opaque on the ground due to water vapor absorption in the Earth’s atmosphere. However, this range becomes nearly transparent at Dome A, Antarctica, where the precipitable water vapor (PWV) is exceptionally low, measuring only ∼0.1 mm. Consequently, the observation efficiency is significantly enhanced in this band, allowing for the accurate observation of spectral features within this region. Notably, dwarfs with spectral types of M6 and later, also known as ultracool dwarfs, exhibit absorption features in this band due to the presence of water vapor in their atmospheres. Later spectral type star has deeper water absorption. Accordingly, Allers et al. (2020) introduced a filter named the W band, centered at 1.45 μm. By combining photometry in the J, W, and H bands, it becomes possible to differentiate these dwarfs from early-type reddened background stars that lack water absorption. This filter was successfully implemented on the UH 88-inch telescope at Mauna Kea, resulting in the discovery of several young substellar objects. In this study, we aim to tailor the W-band filter design specifically for Dome A, Antarctica, with the expectation of achieving enhanced accuracy and efficiency. By utilizing spectra of 141 late-type dwarfs, along with typical atmospheric transmission, we will calculate synthetic photometry in the J, W, and H bands, respectively. Through adjusting the wavelength center and width of the W band, we will determine the optimized configuration that yields the lowest uncertainty in determining spectral types. It is important to note that this design is derived considering the typical atmospheric transmission at Dome A, characterized by a typical PWV. Furthermore, we investigate the impact of PWV fluctuations at Dome A on the performance of our filter.
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