The 2022–2023 accretion outburst of the young star V1741 Sgr

Michael Kuhn, Lynnee A. Hillenbrand, Michael S. Connelley, R. Michael Rich, Bart Staels, Adolfo S. Carvalho, Philip Lucas, Christoffer Fremling, Viraj R. Karambelkar, Ellen Lee, Tomás Ahumada, Emille E.~O. Ishida, Kishalay De, Rafael S. de Souza, Mansi M. Kasliwal

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Abstract

V1741 Sgr (= SPICY 71482/Gaia22dtk) is a Classical T Tauri star on the outskirts of the Lagoon Nebula. After at least a decade of stability, in mid-2022, the optical source brightened by ∼3 mag over 2 months, remained bright until early 2023, then dimmed erratically over the next 4 months. This event was monitored with optical and infrared spectroscopy and photometry. Spectra from the peak (October 2022) indicate an EX Lup-type (EXor) accretion outburst, with strong emission from H I, He I, and Ca II lines and CO bands. At this stage, spectroscopic absorption features indicated a temperature of T ∼ 4750 K with low-gravity lines (e.g. Ba II and Sr II). By April 2023, with the outburst beginning to dim, strong TiO absorption appeared, indicating a cooler T ∼ 3600 K temperature. However, once the source had returned to its pre-outburst flux in August 2023, the TiO absorption and the CO emission disappeared. When the star went into outburst, the source’s spectral energy distribution became flatter, leading to bluer colours at wavelengths shorter than ∼1.6
m and redder colours at longer wavelengths. The brightening requires a continuum emitting area larger than the stellar surface, likely from optically thick circumstellar gas with cooler surface layers producing the absorption features. Additional contributions to the outburst spectrum may include blue excess from hotspots on the stellar surface, emission lines from diffuse gas, and reprocessed emission from the dust disc. Cooling of the circumstellar gas would explain the appearance of TiO, which subsequently disappeared once this gas had faded and the stellar spectrum reemerged.
Original languageEnglish
Article numberstae205
Pages (from-to)2630-2646
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Volume529
Issue number3
Early online date18 Jan 2024
DOIs
Publication statusPublished - 1 Apr 2024

Keywords

  • accretion, accretion discs
  • stars: pre-main-sequence
  • stars: individual: V1741 Sgr
  • stars: variables: T Tauri, Herbig Ae/Be
  • techniques: spectroscopic

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