HO Puppis: Not a Be Star but a Newly Confirmed IW And-Type Star

TL;DR

HO Puppis was previously thought to be a Be star but is now confirmed as an IW And-type star based on its light curve, spectral features, and polarization, revealing its true nature through multi-faceted observational analysis.

Contribution

This study provides the first spectroscopic confirmation and detailed variability analysis that reclassifies HO Puppis as an IW And-type star, not a Be star.

Findings

HO Pup's light curve resembles IW And-type stars with characteristic phases.

Spectroscopic data show Balmer emission lines and Bowen fluorescence, supporting IW And classification.

Polarization measurements indicate significant intrinsic polarization in HO Pup.

Abstract

HO Puppis (HO Pup) was considered as a Be-star candidate based on its gamma-Cassiopeiae-type light curve, but lacked spectroscopic confirmation. Using distance measured from Gaia Data Release 2 and the spectral-energy-distribution (SED) fit on broadband photometry, the Be-star nature of HO Pup is ruled out. Furthermore, based on the 28,700 photometric data points collected from various time-domain surveys and dedicated intensive-monitoring observations, the light curves of HO Pup closely resemble IW And-type stars (as pointed out in Kimura et al. 2020a), exhibiting characteristics such as quasi-standstill phase, brightening, and dips. The light curve of HO Pup displays various variability timescales, including brightening cycles ranging from 23 to 61 days, variations with periods between 3.9 days and 50 minutes during the quasi-standstill phase, and a semi-regular ~14-day period for the dip events. We have also collected time-series spectra (with various spectral resolutions), in which Balmer emission lines and other expected spectral lines for an IW And-type star were detected (even though some of these lines were also expected to be present for Be stars). We detect Bowen fluorescence near the brightening phase, and that can be used to discriminate between IW And-type stars and Be stars. Finally, despite only observing for four nights, the polarization variation was detected, indicating that HO Pup has significant intrinsic polarization.