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tokens: two very weak periods were also detected, at 20 minutes and 90 minutes, but cannot be confirmed. Figure 10. Multiband PDM analysis of the oscillatory variation on a timescale of days. A period of 3.9 ± 0.005 days is clearly detected (upper panel) from light curves based on the superposition of two independent observations. The bottom panel is the phased light curves folded with the detected 3.9 day period, in which the symbols are the same as in Figure 2 , revealing a sinusoidally shaped light curve. Figure 11. Variability of HO Pup down to a timescale of hours. Panel (a) presents the SLT r -band photometric data taken from 2019 December to 2020 March. The blue curve represents the 3.9 day cycle fitted with a sinusoidal function (see Figure 10 ). To uncover the variability shorter than one day, a sinusoidal function of 3.9 days has been subtracted from this light curve and the residuals are displayed in panel (b). After removing the 3.9 day cyclic variations, we found a new cycle of 50 minute variations using Lomb–Scargle periodogram analysis, based on the light-curve data taken from 2019 December to 2020 January, as shown in panel (c). As can be seen from this panel, the variation signal is well above the false-alarm probability (FAP, indicated by the red and cyan dashed lines for the 95% and 99% FAPs, respectively). The variability with 50 minute period can be easily seen in the phased light curve as presented in panel (e). However, the 50 minute variations were barely resolved or undetected for the data collected between 2020 February and March, as evident in panels (d) and (f). Instead, complicated variations can be seen in the nightly chunks of light-curve data during this period of observations. 3.6. Polarization Variation We have also observed variations in polarization for HO Pup. Based on polarization level P and position angle θ measured from Lulin Observatory (see Table 3 ), a small and yet significant polarization was observed on 2018 October 24 and 26. However, the polarization drops back to an insignificant value on 2018 October 25 and 2018 October 28. The observed variation in polarization suggested that HO Pup exhibits intrinsic polarization. 4. Discussion 4.1. Spectral-energy-distribution Fitting Prior to our work, classification of HO Pup in the literature was done via inspection of its light curves, either as a Be star with GCAS-type variability (Samus et al. 2017 ) or as an IW And-type DN (Kimura et al. 2020a ). Here, we first estimated its spectral and luminous class using spectral-energy-distribution fitting together with distance estimation based on the parallax measurement from Gaia Data Release 2 (DR2) (1.6165 ± 0.0311 mas, or d = 618.6 pc, Gaia Collaboration et al. 2018 ). The observed SED of HO Pup was constructed using available broadband photometry covering from near-UV (NUV) to mid-infrared. In Table 5 we list all available broadband photometric data on HO Pup queried within 1′′ radius using the VizieR