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  1. Free, publicly-accessible full text available September 1, 2023
  2. Abstract We present Hubble Space Telescope (HST) imaging of the site of SN 2015bh in the nearby spiral galaxy NGC 2770 taken between 2017 and 2019, nearly four years after the peak of the explosion. In 2017–2018, the transient fades steadily in optical filters before declining more slowly to F814W = −7.1 mag in 2019, ≈4 mag below the level of its eruptive luminous blue variable (LBV) progenitor observed with HST in 2008–2009. The source fades at a constant color of F555W − F814W = 0.4 mag until 2018, similar to SN 2009ip and consistent with a spectrum dominated by interaction of the ejecta with circumstellar material (CSM). A deep optical spectrum obtained in 2021 lacks signatures of ongoing interaction ( L H α ≲ 10 38 erg s −1 for broadened emission ≲2000 km s −1 ), but indicates the presence of a nearby H ii region (≲300 pc). The color evolution of the fading source makes it unlikely that emission from a scattered-light echo or binary OB companion of the progenitor contributes significantly to the flattening of the late-time light curve. The remaining emission in 2019 may plausibly be attributed an evolved/inflated companion or an unresolved (≲3 pc),more »young stellar cluster. Importantly, the color evolution of SN 2015bh rules out scenarios in which the surviving progenitor is obscured by nascent dust and does not clearly indicate a transition to a hotter, optically faint state. The simplest explanation is that the massive progenitor did not survive. SN 2015bh likely represents a remarkable example of the terminal explosion of a massive star preceded by decades of end-stage eruptive variability.« less
    Free, publicly-accessible full text available August 1, 2023
  3. Free, publicly-accessible full text available August 22, 2023
  4. Free, publicly-accessible full text available July 1, 2023
  5. Abstract We present the discovery of an exceptional dimming event in a cool supergiant star in the Local Volume spiral M51. The star, dubbed M51-DS1, was found as part of a Hubble Space Telescope (HST) search for failed supernovae (SNe). The supergiant, which is plausibly associated with a very young (≲6 Myr) stellar population, showed clear variability (amplitude Δ F 814 W ≈ 0.7 mag) in numerous HST images obtained between 1995 and 2016, before suddenly dimming by >2 mag in F 814 W sometime between late 2017 and mid-2019. In follow-up data from 2021, the star rebrightened, ruling out a failed supernova. Prior to its near-disappearance, the star was luminous and red ( M F 814 W ≲ − 7.6 mag, F 606 W − F 814 W = 1.9–2.2 mag). Modeling of the pre-dimming spectral energy distribution of the star favors a highly reddened, very luminous ( log [ L / L ⊙ ] = 5.4 –5.7) star with T eff ≈ 3700–4700 K, indicative of a cool yellow or post-red supergiant (RSG) with an initial mass of ≈26–40 M ⊙ . However, the local interstellar extinction and circumstellar extinction are uncertain, and could be lower: the near-IRmore »colors are consistent with an RSG, which would be cooler ( T eff ≲ 3700 K) and slightly less luminous ( log [ L / L ⊙ ] = 5.2 –5.3), giving an inferred initial mass of ≈19–22 M ⊙ . In either case, the dimming may be explained by a rare episode of enhanced mass loss that temporarily obscures the star, potentially a more extreme counterpart to the 2019–2020 “Great Dimming” of Betelgeuse. Given the emerging evidence that massive evolved stars commonly exhibit variability that can mimic a disappearing star, our work highlights a substantial challenge in identifying true failed SNe.« less
    Free, publicly-accessible full text available May 1, 2023
  6. Free, publicly-accessible full text available December 1, 2022
  7. Free, publicly-accessible full text available June 1, 2023
  8. Free, publicly-accessible full text available January 1, 2023