The FUor outburst of PR Ori B

ATel #16776; Carlos Contreras Pena (Department of Physics and Astronomy, Seoul National University), Gregory Herczeg (Kavli Institute for Astronomy and Astrophysics, Peking University), Jeong-Eun Lee (Department of Physics and Astronomy, Seoul National University), Doug Johnstone (NRC Herzberg Astronomy and Astrophysics), Ho-Gyu Lee (Korea Astronomy and Space Science Institute), Jessy Jose (Indian Institute of Science Education and Research Tirupati), Mizna Ashraf (Indian Institute of Science Education and Research Tirupati), Min Fang (Purple Mountain Observatory, Chinese Academy of Sciences)
on 16 Aug 2024; 02:35 UT
Credential Certification: Carlos Contreras Peña (cecontrep@gmail.com)

Tweet

We report the discovery of a new FUOr eruption of PR Ori B (α=05:36:24.8, δ =-06:17:31), a well-studied object in the L1641-N cluster in Orion. The high-amplitude brightening, absorption-dominated near-IR spectrum and association with a reflection nebula are all consistent with the FUor classification of PR Ori B. The PR Ori system is comprised of PR Ori A, itself a close (0.077”) binary, and PR Ori B at a separation of 3.5” (see Reipurth et al. 2018). Excess infrared and sub-mm emission are both produced by a circumstellar disk around PR Ori B, while PR Ori A is diskless (Fang et al. 2013, Reipurth et al. 2018, van Terwisga et al. 2022). PR Ori B is also the driver of HH305, with many shocks that may indicate past bursts (Reipurth et al. 2018).

PR Ori was identified as a stochastic variable in the mid-IR by Park et al. (2021), analysing NEOWISE data obtained before MJD=59200. Since then, PR Ori has had two brightening events with Δ W1=0.5, Δ W2=0.6 mag, and Δ W1=2, Δ W2=2.2 mag respectively. The centroid of the mid-IR emission shifts to PR Ori B as the system gets brighter, indicating that the brightening is associated with PR Ori B.

A 3-4 mag brightening of PR Ori B was published by the Gaia Science Alerts as Gaia21arx (Hodgkin et al. 2021). PR Ori A remains nearly constant during the observations covered by Gaia DR3. The ASAS-SN g and V, and AAVSO B, V, R and I-band data, resulting from the combined emission of the A and B components, also display variability that follows the Gaia photometry of PR Ori B. The amplitude is damped in unresolved observations because PR Ori A dominates emission when PR Ori B is in a quiescent state.

During the Gaia coverage, PR Ori B displays two significant brightening events. The first brightening is already ongoing at the start of Gaia observations. The source fades and reaches the faintest point of the light curve at MJD=58241 d. The source then rises by 3.8 mag over 700 days, reaches G=12.6, then rises at a slower rate over the next 1400 days, reaching G=11.3 mag in the latest epoch provided by the Gaia alerts. A fading event during this slow rise lasted about 600 days and with Delta G=0.8 mag. The latest ASAS-SN photometry, with g=11.48 on 2024 Aug 14, demonstrates a sustained burst.

Visual inspection of r-band images provided by the Zwicky Transient Facility survey, shows a clear brightening of the system with time, along with the appearance of a reflection nebula around the September 2020 observations. The nebula is still apparent in the latest available images from March 2024 observations.

The IRTF/Spex spectrum of PR Ori B (using the 0.5” slit, covering 0.7-2.5 μm at R= 2000), obtained on 23 December 2023 (program 2023B079, PI: Contreras Peña), displays several features associated with FUors (see descriptions in Connelley & Reipurth 2018), including a triangular shape in the H-band, strong ¹²CO (Δ ν=2) ro-vibrational absorption bands, and weak absorption from Na I (2.21 μm) and Ca I (2.26 μm). The equivalent widths of Na I+Ca I versus ¹²CO of PR Ori B are consistent with those of known FUors. Several Paschen lines (including Pa β, γ and δ) and Brγ are seen in absorption, though He I 10830 is seen in emission. The FU Ori features in this new spectrum differ from the late-K photosphere and Paβ emission seen in a near-IR spectrum obtained on 2012 Feb 04 (Reipurth et al. 2018). We also identify absorption lines commonly associated with outflows in FUors, including the Ca II triplet (0.850, 0.854, and 0.866 μm) and O I (0.77 and 0.84 μm) lines.

The relevant figures (light curves, spectrum) can be found in the following link