# PTF 14jg: The Remarkable Outburst and Post-Burst Evolution of a Previously Anonymous Galactic Star

## TL;DR

This paper reports on the unique outburst and post-burst evolution of PTF 14jg, a previously unstudied star, exhibiting characteristics of a hot FU Ori-like event with atypical features, suggesting a potential new class of young star outbursts.

## Contribution

It presents detailed observations of PTF 14jg's outburst, highlighting its unusual hot spectrum and lightcurve, and proposes it as a possible new category of young star outbursts.

## Key findings

- Outburst lasted over five years with a peak brightness increase of 6-7 magnitudes.
- Spectral features indicate a hot, low-gravity star with high-velocity outflows.
- The event shows characteristics similar to FU Ori objects but with notable differences, suggesting a new outburst class.

## Abstract

We report the outbursting source PTF 14jg, which prior to the onset of its late 2013 eruption, was a faint, unstudied, and virtually uncatalogued star. The salient features of the PTF 14jg outburst are: (i) projected location near the W4 HII region and radial velocity consistent with physical association; (ii) a lightcurve that underwent a $\sim$6-7 mag optical (R-band) through mid-infrared (L-band) brightening on a few month time scale, that peaked and then faded by $\sim$3 mag, but plateaued still $>$3.5 mag above quiescence by $\sim$8 months post-peak, lasting to at least five years after eruption; (iii) strong outflow signatures, with velocities reaching -530 km/s; (iv) a low gravity and broad ($\sim$100-150 km/s FWHM) optical absorption line spectrum that systematically changes its spectral type with wavelength; (v) lithium; and (vi) ultraviolet and infrared excess. We tentatively identify the outburst as exhibiting characteristics of a young star FU Ori event. However, the burst would be unusually hot, with an absorption spectrum exhibiting high-excitation ($\sim$11,000-15,000 K) lines in the optical, and no evidence of CO in the near-infrared, in addition to exhibiting an unusual lightcurve. We thus also consider alternative scenarios including various forms of novae, nuclear burning instabilities, massive star events, and mergers -- finding them all inferior to the atypically hot FU Ori star classification. The source eventually may be interpreted as a new category of young star outburst with larger amplitude and shorter rise time than most FU Ori-like events. Continued monitoring of the lightcurve and spectral evolution will reveal its true nature.