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

Creators: Lee, Chien-De; Ou, Jia-Yu; Yu, Po-Chieh; Ngeow, Chow-Choong; Huang, Po-Chieh; Ip, Wing-Huen; Hambsch, Franz-Josef; Sung, Hyun-il; van Roestel, Jan; Dekany, Richard; Drake, Andrew J.; Graham, Matthew J.; Duev, Dmitry A.; Kaye, Stephen; Kupfer, Thomas; Laher, Russ R.; Masci, Frank J.; Mróz, Przemek; Neill, James D.; Riddle, Reed; Rusholme, Ben; Walters, Richard

Abstract

HO Puppis (HO Pup) was considered as a Be-star candidate based on its γ Cassiopeiae-type light curve, but lacked spectroscopic confirmation. Using distance measured from Gaia Data Release 2 and the spectral-energy-distribution 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 those of IW And-type stars (as pointed out by Kimura et al.), exhibiting characteristics such as a 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 semiregular ~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 spectral lines expected 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.

Additional Information

© 2021. The American Astronomical Society. Received 2020 August 6; revised 2021 February 17; accepted 2021 February 18; published 2021 April 15. This work is partly supported by the Ministry of Science and Technology (Taiwan) under grants of 104-2923-M-008-004-MY5, 107-2119-M-008-014-MY2, 107-2119-M-008-012, 108-2811-M-008-546, and 109-2112-M-155-001. We thank Abert Kong for pointing out the DASCH light curve. We are also grateful for the discussions with Yi Chou, Wen-Ping Chen, Shih-Yun Tang, Michihiro Takami, Chi-Hung Yan, Paula Szkody, and Melissa Graham on this work, as well as suggestions from an anonymous referee to improve the manuscript. Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171 This work was partly supported by the GROWTH (Global Relay of Observatories Watching Transients Happen) project funded by the National Science Foundation under PIRE grant No. 1545949. GROWTH is a collaborative project among California Institute of Technology (USA), University of Maryland College Park (USA), University of Wisconsin Milwaukee (USA), Texas Tech University (USA), San Diego State University (USA), University of Washington (USA), Los Alamos National Laboratory (USA), Tokyo Institute of Technology (Japan), National Central University (Taiwan), Indian Institute of Astrophysics (India), Indian Institute of Technology Bombay (India), Weizmann Institute of Science (Israel), The Oskar Klein Centre at Stockholm University (Sweden), Humboldt University (Germany), Liverpool John Moores University (UK), and University of Sydney (Australia). This research relied on the SIMBAD and VizieR catalog access tool and the Aladin plot tool at CDS, Strasbourg (France), and NASA ADS bibliographic services. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. We also made use of data collected at Lulin Observatory, partly supported by MoST grant 108-2112-M-008-001. We sincerely thank the staff and queue observers (Chi-Sheng Lin, Hsiang-Yao Hsaio, and Wei-Jie Hou) at the Lulin Observatory for carrying out the observations with the SLT telescope. We thank the observer at the P200 Telescope, Marianne Heida, for taking the P200/DBSP spectrum. We also thank staffs of BOAO. We appreciate the achievements and online catalogs provided by ASAS-SN, AAVSO, and Pan-STARRS, making this investigation possible for much longer baseline and/or better time coverage. The DASCH project at Harvard is grateful for partial support from NSF grants AST-0407380, AST-0909073, and AST-1313370.

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