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We present pre- and post-outburst observations of the new FU Orionis-likeyoung stellar object PTF 10qpf (also known as LkHa 188-G4 and HBC 722). Priorto this outburst, LkHa 188-G4 was classified as a classical T Tauri star on thebasis of its optical emission-line spectrum superposed on a K8-typephotosphere, and its photometric variability. The mid-infrared spectral indexof LkHa 188-G4 indicates a Class II-type object. LkHa 188-G4 exhibited a steadyrise by ~1 mag over ~11 months starting in Aug. 2009, before a subsequent moreabrupt rise of > 3 mag on a time scale of ~2 months. Observations taken duringthe eruption exhibit the defining characteristics of FU Orionis variables: (i)an increase in brightness by > 4 mag, (ii) a bright optical/near-infraredreflection nebula appeared, (iii) optical spectra are consistent with a Gsupergiant and dominated by absorption lines, the only exception being Halphawhich is characterized by a P Cygni profile, (iv) near-infrared spectraresemble those of late K--M giants/supergiants with enhanced absorption seen inthe molecular bands of CO and H_2O, and (v) outflow signatures in H and He areseen in the form of blueshifted absorption profiles. LkHa 188-G4 is the firstmember of the FU Orionis-like class with a well-sampled optical to mid-infraredspectral energy distribution in the pre-outburst phase. The association of thePTF 10qpf outburst with the previously identified classical T Tauri star LkHa188-G4 (HBC 722) provides strong evidence that FU Orionis-like eruptionsrepresent periods of enhanced disk accretion and outflow, likely triggered byinstabilities in the disk. The early identification of PTF 10qpf as an FUOrionis-like variable will enable detailed photometric and spectroscopicobservations during its post-outburst evolution for comparison with other knownoutbursting objects.

Evidence for an FU Orionis-like Outburst from a Classical T Tauri Star