The Curious Long-term Photometric and Dust Evolution of Born-again Planetary Nebulae HuBi 1

We reveal post-VLTP stellar recovery, dust formation, obscuration and evolution of born-again planetary nebula HuBi 1 by combining archival plates, optical photometry, and infrared observations from the 1890s to 2025. These revealed a century long, linear brightening interpreted as the post-VLTP recovery phase where central star contraction and reheating shifts emergent flux toward shorter wavelengths, while enhanced nebular ionization strengthened blue-band emission. The subsequent optical decline from 1986, provides a tight constraint for dust obscuration and formation onset. The infrared SED shows that HuBi 1 remained dust-emitting throughout and that it cannot come from a single dust component but requires at least two dust-emitting regions associated with the compact inner shell and extended outer nebula. A two-shell Cloudy model favors amorphous carbon as the dominant dust species. In our model the infrared dust evolution is driven by the compact inner shell, whose dust temperature declines from 587 to 462 K between 1986 and 2025, while inferred dust mass increases from 1.412 × 10 −6 to 1.023 × 10 −5 M ⊙ . We interpret this as continued evolution of the dust reservoir in the born-again ejecta, rather than uniform dust formation under the shell-averaged modeled conditions. These results provide the clearest observational link between preobscuration brightening, dust formation/obscuration onset, and subsequent infrared dust evolution in HuBi 1 and indeed for any PN. They yield tight observational constraints for theoretical models for a brief stellar evolutionary stage, making HuBi 1 a valuable laboratory and benchmark for testing models of late helium-shell flashes, post-VLTP reheating, and transition toward a compact hot central star.