The Persistent Eruption of UGC~2773-OT: Finally, a Decade-Long Extragalactic Eta Carinae Analog
Nathan Smith, Jennifer E. Andrews, Jon C. Mauerhan, WeiKang Zheng,, Alexei V. Filippenko, Melissa L. Graham, and Peter Milne

TL;DR
This paper presents a decade-long eruption of UGC 2773-OT, an extragalactic transient that closely resembles eta Carinae's historic eruption, providing new insights into long-duration stellar eruptions and their spectral features.
Contribution
It reports the first long-term observation of an eta Car analog with a persistent eruption lasting over a decade, including detailed spectroscopic analysis and evidence of bipolar nebula ejection.
Findings
UGC 2773-OT's eruption lasted over 6 years with a slow fade.
Spectroscopy shows bipolar nebula ejection similar to eta Car's Homunculus.
Late-time spectra indicate strong circumstellar interaction.
Abstract
While SN impostors resemble the Great Eruption of eta Car in the sense that their spectra show narrow H lines and they have typical peak absolute magnitudes of -13 to -14 mag, most extragalactic events observed so far are quite different from eta Car in duration. Their bright phases typically last for 100~d or less, rather than persisting for several years. The transient object UGC2773-OT had a similar peak absolute magnitude to other SN impostors, but with a gradual 5-yr prediscovery rise. In the 6 yr since discovery, it has faded very slowly (0.26 mag/yr). Overall, we suggest that its decade-long eruption is so far the best known analog of eta Car's 19th century eruption. We discuss extensive spectroscopy of the ongoing eruption. The spectra show interesting changes in velocity and line shape that we discuss in detail, including an asymmetric Halpha emission line that we show is…
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