Gaia 17bpi: An FU Ori–type Outburst

Abstract

We report on the source Gaia 17bpi and identify it as a new, ongoing FU Ori type outburst, associated with a young stellar object. The optical lightcurve from Gaia exhibited a 3.5 mag rise with the source appearing to plateau in mid/late 2018. Mid-infrared observations from NEOWISE also show a >3 mag rise that occurred in two stages, with the second one coincident with the optical brightening, and the first one preceding the optical brightening by ∼1.5 years. We model the outburst as having started between October and December of 2014. This wavelength-dependent aspect of young star accretion-driven outbursts has never been documented before. Both the mid-infrared and the optical colors of the object become bluer as the outburst proceeds. Optical spectroscopic characteristics in the outburst phase include: a GK-type absorption spectrum, strong wind/outflow in e.g. Mgb, NaD, Hα, K I, O I, and Ca II profiles, and detection of Li I 6707Å. The infrared spectrum in the outburst phase is similar to that of an M-type spectrum, notably exhibiting prominent H 2 O and 12 CO (2-0) bandhead absorption in the K-band, and likely He I wind in the Y-band. The new FU Ori source Gaia 17bpi is associated with a little-studied dark cloud in the galactic plane, located at a distance of 1.27 kpc.

A Comparison of the X-Ray Properties of FU Ori-type Stars to Generic Young Stellar Objects

“…G53.2: Gaia 17bpi is a probable member of the G53.2 region. The median parallax to probable members of this region is found to be 0.79 mas (Hillenbrand et al 2018), from which we calculate a distance of 1200 +80 −70 pc.…”

“…However, probable ranges for pre-outburst N H and L X can be estimated from statistical relations between X-ray properties and stellar properties for T Tauri stars. The pre-outburst spectral energy distribution (SED) of Gaia 17bpi could be fit by a variety of reddened stellar photospheric models with A V ranging from 1 to 5 mag and corresponding T eff ranging from 2900 to 4500 K (Hillenbrand et al 2018), with a preferred model with T eff = 3500 K and A V = 3 mag (see also Appendix C). From these ranges, we derive extinction-corrected bolometric luminosities of L bol ≈ 4 × 10 32 -2 × 10 33 erg s −1 for the pre-outburst star using bolometric and color corrections from Pecaut & Mamajek (2013).…”

“…Our procedure is similar to that described by Hillenbrand et al (2018); we obtain a catalog of probable association members from the literature, match these stars to Gaia DR2 sources, discard stars with parallaxes that are discrepant by >3σ, and find the median parallax of the resulting sample.…”

“…C. OPTICAL AND ULTRAVIOLET PHOTOMETRY Figure 6 shows the SED of Gaia 17bpi during its eruption using photometry from Hillenbrand et al (2018) with the XMM Newton OM U V W 1, U , and V -band photometry newly added here. The sources is clearly more luminous in U and V than it would have been in its pre-outburst state (shown for comparison).…”

Gaia 19ajj: A Young Star Brightening Due to Enhanced Accretion and Reduced Extinction

“…No error estimates are provided but we adopt 0.05 mag uncertainty. We include an iPHaS/VPHaS ) r-band measurement that has been approximately converted to the Gaia photometric system (using the procedure described in Hillenbrand et al 2018). Also shown is the V-band and g-band data available from ASAS (Shappee et al 2014).…”