{"issue":"10","date_created":"2025-11-02T23:01:34Z","oa_version":"Published Version","abstract":[{"lang":"eng","text":"In this second paper on our variability survey of central stars of planetary nebulae (CSPNe) using the Zwicky Transient Facility (ZTF), we report 11 long-timescale variables with variability timescales ranging from months to years. We also present preliminary analyses based on spectroscopic and/or photometric follow-up observations for six of them. Among them is NGC 6833, which shows a 980 days periodic variability with strange characteristics: “triangle-shaped” brightening in r, i, and WISE bands but almost coincidental shallow dips in the g-band. The most plausible explanation is a wide binary with the photometric period being the orbital period. Long-period near-sinusoidal variability was detected in two other systems, NGC 6905 and Kn 26, with periods of 700 days and 230 days, respectively, making them additional wide-binary candidates. The latter also shows a short period at 1.18 hr. We then present CTSS 2 and K 3-5, which show brightening and significant reddening over the whole ZTF baseline. A stellar model fit to the optical spectrum of CTSS 2 reveals it to be one of the youngest post-AGB CSPNe known. Both show high-density emission-line cores. We propose these to be late-thermal-pulse candidates, currently evolving towards the AGB phase. We then present recent HST/COS ultraviolet spectroscopy of the known wide-binary candidate LoTr 1, showing that the hot star is a spectroscopic twin of the extremely hot white dwarf in UCAC2 46706450. Similar to this object, LoTr 1 also has a fast rotating wide subgiant companion. We suggest that the long photometric period of 11 yr is the binary orbital period. Finally, we briefly discuss the ZTF light curves of the remaining variables, namely Tan 2, K 3-20, WHTZ 3, Kn J1857+3931, and IPHAS J1927+0814. With these examples, we present the effectiveness of the von Neumann statistics and Pearson Skew-based metric space in searching for long-timescale variables."}],"month":"10","acknowledgement":"This work is 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 Nos. AST-1440341 and AST-2034437 and a collaboration including current partners Caltech, IPAC, the Oskar Klein Center at Stockholm University, the University of Maryland, University of California, Berkeley, the University of Wisconsin at Milwaukee, University of Warwick, Ruhr University Bochum, Cornell University, Northwestern University, and Drexel University. Operations are conducted by COO, IPAC, and UW.\r\n\r\nThis work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular, the institutions participating in the Gaia Multilateral Agreement.\r\n\r\nWe are grateful to the staffs of Palomar Observatory and the Hobby-Eberly Telescope for assistance with the observations and data management. The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council.\r\n\r\nThe Low-Resolution Spectrograph 2 (LRS2) on HET was developed and funded by the University of Texas at Austin McDonald Observatory and Department of Astronomy, and by Pennsylvania State University. We thank the Leibniz-Institut für Astrophysik Potsdam (AIP) and the Institut für Astrophysik Göttingen (IAG) for their contributions to the construction of the integral field units. We acknowledge the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing high performance computing, visualization, and storage resources that have contributed to the results reported within this paper.\r\n\r\nThe Isaac Newton Telescope is operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias\r\n\r\nS.B. thanks Frank J. Masci and Zachary P. Vanderbosch for useful discussions and suggestions regarding solving the issues with ZTF forced photometry on extended sources. S.B. also thanks Jim Fuller, Charles C. Steidel, Lynne Hillenbrand, and Adolfo Carvalho for useful discussions on methods and science. S.B. acknowledges financial support from the Wallace L. W. Sargent Graduate Fellowship during the first year of his graduate studies at Caltech. N.C. was supported through the Cancer Research UK grant A24042.\r\n\r\nN.R. is supported by the Deutsche Forschungsgemeinschaft (DFG) through grant RE3915/2-1.\r\n\r\nD.J. acknowledges support from the Agencia Estatal de Investigación del Ministerio de Ciencia, Innovación y Universidades (MICIU/AEI) under grant “Nebulosas planetarias como clave para comprender la evolución de estrellas binarias” and the European Regional Development Fund (ERDF) with reference PID-2022-136653NA-I00 (DOI:10.13039/501100011033). D.J. also acknowledges support from the Agencia Estatal de Investigación del Ministerio de Ciencia, Innovación y Universidades (MICIU/AEI) under grant “Revolucionando el conocimiento de la evolución de estrellas poco masivas” and the the European Union NextGenerationEU/PRTR with reference CNS2023-143910 (DOI:10.13039/501100011033).\r\n\r\nWe have used Python packages Numpy (Harris et al. 2020), SciPy (Virtanen et al. 2020), Matplotlib (Hunter 2007), Pandas (pandas development team 2020), Astropy (Astropy Collaboration et al. 2013, 2018), and Astroquery (Ginsburg et al. 2019) at various stages of this research.","publisher":"IOP Publishing","type":"journal_article","language":[{"iso":"eng"}],"date_published":"2025-10-01T00:00:00Z","scopus_import":"1","isi":1,"title":"Variability of central stars of planetary nebulae with the Zwicky Transient Facility. II. Long-timescale variables including wide binary and late thermal pulse candidates","article_processing_charge":"Yes (in subscription journal)","file":[{"creator":"dernst","access_level":"open_access","success":1,"checksum":"cc7d00c349d48458accb0d3df67e4879","content_type":"application/pdf","file_name":"2025_PASP_BhattacharjeeS.pdf","file_size":12677603,"file_id":"20599","date_created":"2025-11-04T08:26:39Z","date_updated":"2025-11-04T08:26:39Z","relation":"main_file"}],"_id":"20588","intvolume":"       137","has_accepted_license":"1","file_date_updated":"2025-11-04T08:26:39Z","citation":{"chicago":"Bhattacharjee, Soumyadeep, Nicole Reindl, Howard E. Bond, Klaus Werner, Gregory R. Zeimann, David Jones, Kareem El-Badry, et al. “Variability of Central Stars of Planetary Nebulae with the Zwicky Transient Facility. II. Long-Timescale Variables Including Wide Binary and Late Thermal Pulse Candidates.” <i>Publications of the Astronomical Society of the Pacific</i>. IOP Publishing, 2025. <a href=\"https://doi.org/10.1088/1538-3873/ae051e\">https://doi.org/10.1088/1538-3873/ae051e</a>.","ieee":"S. Bhattacharjee <i>et al.</i>, “Variability of central stars of planetary nebulae with the Zwicky Transient Facility. II. Long-timescale variables including wide binary and late thermal pulse candidates,” <i>Publications of the Astronomical Society of the Pacific</i>, vol. 137, no. 10. IOP Publishing, 2025.","short":"S. Bhattacharjee, N. Reindl, H.E. Bond, K. Werner, G.R. Zeimann, D. Jones, K. El-Badry, N. Mackensen, N. Chornay, S.R. Kulkarni, I. Caiazzo, J. Van Roestel, A.C. Rodriguez, T.A. Prince, B. Rusholme, R.R. Laher, R. Smith, Publications of the Astronomical Society of the Pacific 137 (2025).","ama":"Bhattacharjee S, Reindl N, Bond HE, et al. Variability of central stars of planetary nebulae with the Zwicky Transient Facility. II. Long-timescale variables including wide binary and late thermal pulse candidates. <i>Publications of the Astronomical Society of the Pacific</i>. 2025;137(10). doi:<a href=\"https://doi.org/10.1088/1538-3873/ae051e\">10.1088/1538-3873/ae051e</a>","apa":"Bhattacharjee, S., Reindl, N., Bond, H. E., Werner, K., Zeimann, G. R., Jones, D., … Smith, R. (2025). Variability of central stars of planetary nebulae with the Zwicky Transient Facility. II. Long-timescale variables including wide binary and late thermal pulse candidates. <i>Publications of the Astronomical Society of the Pacific</i>. IOP Publishing. <a href=\"https://doi.org/10.1088/1538-3873/ae051e\">https://doi.org/10.1088/1538-3873/ae051e</a>","mla":"Bhattacharjee, Soumyadeep, et al. “Variability of Central Stars of Planetary Nebulae with the Zwicky Transient Facility. II. Long-Timescale Variables Including Wide Binary and Late Thermal Pulse Candidates.” <i>Publications of the Astronomical Society of the Pacific</i>, vol. 137, no. 10, 104206, IOP Publishing, 2025, doi:<a href=\"https://doi.org/10.1088/1538-3873/ae051e\">10.1088/1538-3873/ae051e</a>.","ista":"Bhattacharjee S, Reindl N, Bond HE, Werner K, Zeimann GR, Jones D, El-Badry K, Mackensen N, Chornay N, Kulkarni SR, Caiazzo I, Van Roestel J, Rodriguez AC, Prince TA, Rusholme B, Laher RR, Smith R. 2025. Variability of central stars of planetary nebulae with the Zwicky Transient Facility. II. Long-timescale variables including wide binary and late thermal pulse candidates. Publications of the Astronomical Society of the Pacific. 137(10), 104206."},"OA_place":"publisher","arxiv":1,"status":"public","author":[{"last_name":"Bhattacharjee","full_name":"Bhattacharjee, Soumyadeep","first_name":"Soumyadeep"},{"full_name":"Reindl, Nicole","first_name":"Nicole","last_name":"Reindl"},{"last_name":"Bond","first_name":"Howard E.","full_name":"Bond, Howard E."},{"last_name":"Werner","full_name":"Werner, Klaus","first_name":"Klaus"},{"full_name":"Zeimann, Gregory R.","first_name":"Gregory R.","last_name":"Zeimann"},{"full_name":"Jones, David","first_name":"David","last_name":"Jones"},{"last_name":"El-Badry","full_name":"El-Badry, Kareem","first_name":"Kareem"},{"full_name":"Mackensen, Nina","first_name":"Nina","last_name":"Mackensen"},{"full_name":"Chornay, Nicholas","first_name":"Nicholas","last_name":"Chornay"},{"first_name":"S. R.","full_name":"Kulkarni, S. R.","last_name":"Kulkarni"},{"first_name":"Ilaria","full_name":"Caiazzo, Ilaria","last_name":"Caiazzo","id":"8ae5b6e7-2a03-11ee-914d-b58ed7a3b47d","orcid":"0000-0002-4770-5388"},{"last_name":"Van Roestel","first_name":"Jan","full_name":"Van Roestel, Jan"},{"last_name":"Rodriguez","first_name":"Antonio C.","full_name":"Rodriguez, Antonio C."},{"last_name":"Prince","full_name":"Prince, Thomas A.","first_name":"Thomas A."},{"last_name":"Rusholme","first_name":"Ben","full_name":"Rusholme, Ben"},{"full_name":"Laher, Russ R.","first_name":"Russ R.","last_name":"Laher"},{"first_name":"Roger","full_name":"Smith, Roger","last_name":"Smith"}],"publication_status":"published","external_id":{"isi":["001595690000001"],"arxiv":["2502.18651"]},"article_number":"104206","day":"01","article_type":"original","oa":1,"publication":"Publications of the Astronomical Society of the Pacific","ddc":["520"],"PlanS_conform":"1","date_updated":"2025-12-01T15:13:50Z","publication_identifier":{"issn":["1538-3873"]},"year":"2025","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","volume":137,"tmp":{"image":"/images/cc_by.png","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"doi":"10.1088/1538-3873/ae051e","quality_controlled":"1","OA_type":"hybrid","department":[{"_id":"IlCa"}]}