Evidence for an Fu Orionis-Like Outburst From a Classical T Tauri Star

Abstract

We present pre-and post-outburst observations of the new FU Orionis-like young stellar object PTF 10qpf (also known as LkHα 188-G4 and HBC 722). Prior to this outburst, LkHα 188-G4 was classified as a classical T Tauri star on the basis of its optical emission-line spectrum superposed on a K8-type photosphere, and its photometric variability. The mid-infrared spectral index of LkHα 188-G4 indicates a Class II-type object. LkHα 188-G4 exhibited a steady rise by ∼1 mag over ∼11 months starting in Aug. 2009, before a subsequent more abrupt rise of > 3 mag on a time scale of ∼2 months. Observations taken during the eruption exhibit the defining characteristics of FU Orionis variables: (i) an increase in brightness by 4 mag, (ii) a bright optical/near-infrared reflection nebula appeared, (iii) optical spectra are consistent with a G supergiant and dominated by absorption lines, the only exception being Hα which is characterized by a P Cygni profile, (iv) near-infrared spectra resemble those of late K-M giants/supergiants with enhanced absorption seen in the molecular bands of CO and H 2 O, and (v) outflow signatures in H and He are seen in the form of blueshifted absorption profiles. LkHα 188-G4 is the first member of the FU Orionis-like class with a well-sampled optical to mid-infrared spectral energy distribution in the pre-outburst phase. The association of the PTF 10qpf outburst with the previously identified classical T Tauri star LkHα 188-G4 (HBC 722) provides strong evidence that FU Orionis-like eruptions represent periods of enhanced disk accretion and outflow, likely triggered by instabilities in the disk. The early identification of PTF 10qpf as an FU Orionislike variable will enable detailed photometric and spectroscopic observations during its post-outburst evolution for comparison with other known outbursting objects.

MULTIWAVELENGTH OBSERVATIONS OF V2775 Ori, AN OUTBURSTING PROTOSTAR IN L 1641: EXPLORING THE EDGE OF THE FU ORIONIS REGIME

“…Of the other young stellar objects with both documented outbursts and FU Orionis-like near-infrared spectra (Reipurth & Aspin 2010;Semkov et al 2010;Miller et al 2011;Reipurth et al 2012), most have luminosities of at least 100 L . V2493 Cyg is the only one with a post-outburst luminosity (12 L ; Miller et al 2011) similar to or lower than the 28 L found for V2775 Ori. V2493 Cyg was a known classical T Tauri star prior to its outburst and has no protostellar envelope (Green et al 2011), making V2775 Ori the least luminous documented FU Orionis outburster with an envelope.…”

“…Greene et al (2008) distinguish between sources in which an outburst was actually observed and those that merely have outburst-like spectra, pointing to the importance of time monitoring to unambiguously classify each putative outburster and determine the frequency of these events. Since the advent of large-scale optical and IR monitoring programs, several young stellar objects have been observed to undergo significant increases in luminosity; e.g., V733 Cep (Reipurth et al 2007), V2492 Cyg ), V2493 Cyg (Semkov et al 2010;Miller et al 2011), V2494 Cyg (Aspin et al 2009), V2495 Cyg (Movsessian et al 2006), V900 Mon (Reipurth et al 2012), and V1647 Ori (Reipurth & Aspin 2004; Abrahám et al 2004;Briceño et al 2004), allowing a more thorough understanding of the range of outburst types and their frequencies.…”

A wide-field near-infrared H22.122μm line survey of the Braid Nebula star formation region in Cygnus OB7

“…An FU Ori object may experience hundreds of outbursts Miller et al 2011). During these outbursts the central object may gain as much as 10% to 25% of its final mass (Greene et al 2008;Hartmann & Kenyon 1996;Herbig 1977).…”

Long-term photometric observations of pre-main sequence objects in the field of North America/Pelican Nebula

“…Adding to this, observations of PMS stars are usually made difficult by their faintness in quiescence and by the disturbance from sometimes heavy dust extinction, either surrounding the star or diffuse through the star forming region. Therefore, the rare outbursts of PMS stars always attract considerable interest, especially when they are long lasting, as in the case of new FUor objects (from the name of the prototype of this class, FU Ori), with one of the most recent and spectacular cases being that of HBC 722 = V2493 Cyg (Semkov et al 2010;Miller et al 2011;Munari et al 2010;Leoni et al 2010;Kóspál et al 2011;Armond et al 2011;Green et al 2011).…”