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Published March 2022 | Submitted + Published
Journal Article Open

LkHα 225 (V1318 Cyg) South in Outburst


Magakian et al. called attention to the current bright state of LkHα 225 South, a well-known highly embedded, intermediate-mass young stellar object that over the past two decades has brightened visually from >20^m to <13^m. We present recent optical photometric monitoring showing colorless, nonsinusoidal, periodic brightness oscillations occurring every 43 days with amplitude ∼0.7 mag. We also present new flux-calibrated optical and near-infrared spectroscopy, which we model in terms of a Keplerian accretion disk, and high-dispersion spectra that demonstrate similarity to some categories of "mixed-temperature" accretion-outburst objects. At blue wavelengths, LkHα 225 South has a pure absorption spectrum and is a good spectral match to the FU Ori stars V1515 Cyg and V1057 Cyg. At red optical and infrared wavelengths, however, the spectrum is more similar to Gaia 19ajj, showing emission in TiO, CO, and metals. Sr II absorption indicates a low-surface-gravity atmosphere. There are also signatures of a strong wind/outflow. LkHα 225 South was moderately bright in the early 1950s as well as in the late 1980s, with evidence for deep fades during intervening epochs. The body of evidence suggests that LkHα 225 South is another case of a source with episodically enhanced accretion that causes brightening by orders of magnitude, and development of a hot absorption spectrum and warm wind. It is similar to Gaia 19ajj, but also reminiscent in its long brightening time and brightness oscillation near peak to the embedded sources L1634 IRS7 and ESO Ha 99.

Additional Information

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2020 November 17; revised 2021 December 28; accepted 2021 December 29; published 2022 February 7. We acknowledge the work of former Caltech undergraduate Sirin Caliskan, who produced the photometry and astrometry for the Keck/LRIS images. We acknowledge with thanks the AAVSO International Database, which allowed us to connect with coauthor D.R.P. We thank Roc Cutri for consultation regarding whether the saturated photometry of LkHα 225 South could be recovered in NEOWISE data. We thank Kishaley De for checking on the source in Gattini data. Andrew Howard facilitated the first Keck/HIRES spectrum. Erik Petigura and Trevor David kindly obtained the first Keck/NIRSPEC data set; Jessica Spake kindly allowed for the second. We thank Richard Larson for his interest in this system, and for his suggestions regarding the 43 day quasiperiodicity. We also thank the referee for a careful and insightful review of our work. Facilities: IPHaS - , PanSTARRS - , AAVSO - , Gaia - , PO: 1.2m (PTF) - , PO: 1.2m (ZTF) - , IRSA - , ASAS - , PO: Hale (DBSP) - , Keck:I (HIRES) - , Keck:II (NIRSPEC) - , IRTF (SpeX) - , Gemini (NIRI). -

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Published - Hillenbrand_2022_AJ_163_115.pdf

Submitted - 2108.05406.pdf


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August 22, 2023
October 23, 2023