Morphological study of the nested planetary nebula Hubble 12^★

¹ State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau
e-mail: chhsia@must.edu.mo
² CNSA Macau Centre for Space Exploration and Science, Macau
³ School of Physics and Astronomy, Sun Yat-Sen University, 2 Da Xue Road, Tangjia, Zhuhai 519000, Guangdong Province, PR China
e-mail: zhangyong5@mail.sysu.edu.cn
⁴ Laboratory for Space Research, Faculty of Science, Department of Physics, The University of Hong Kong, Hong Kong
e-mail: abdi1374@connect.hku.hk
⁵ Nantong Academy of Intelligent Sensing, Nantong 226000, PR China

Received: 10 June 2021
Accepted: 26 August 2021

Abstract

We present a visible-infrared imaging study of young planetary nebula (PN) Hubble 12 (Hb 12; PN G111.8-02.8) obtained with Hubble Space Telescope (HST) archival data and our own Canada-France-Hawaii Telescope (CFHT) measurements. Deep HST and CFHT observations of this nebula reveal three pairs of bipolar structures and an arc-shaped filament near the western waist of Hb 12. The existence of nested bipolar lobes together with the presence of H₂ knots suggests that these structures originated from several mass-ejection events during the pre-PN phase. To understand the intrinsic structures of Hb 12, a three-dimensional model enabling the visualisation of this PN at various orientations was constructed. The modelling results show that Hb 12 may resemble other nested hourglass nebulae, such as Hen 2-320 and M 2-9, suggesting that this type of PN may be common and the morphologies of PNs are not so diverse as is shown by their visual appearances. The infrared spectra show that this PN has a mixed chemistry. We discuss the possible material that may cause the unidentified infrared emissions. The analyses of the infrared spectra and the spectral energy distribution suggest the existence of a cool companion in the nucleus of this object.