Large Amplitude Brightening of the Young Stellar Object iPTF 15afq

ATel #7428; A. A. Miller (JPL/Caltech), L. A. Hillenbrand, P. Bilgi, Y. Cao, G. Duggan (Caltech), I. Arcavi, G. Hosseinzadeh, D. A. Howell, C. McCully (UCSB/LCOGT), on behalf of the intermediate Palomar Transient Factory
on 21 Apr 2015; 22:10 UT
Credential Certification: Adam Miller (amiller@astro.caltech.edu)

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The content of this ATel is identical to the previously submitted ATel#7427. This posting is an update to include the correct Title and Author List.

We report the detection of a rapid photometric rise identified via automated processing of intermediate Palomar Transient Factory (iPTF; Atel#4807) observations. The variable star, named iPTF 15afq, was discovered on 2015-03-13.19 UT with R = 17.7 mag. In historical iPTF images collected over the past 1.5 yr, the source has shown small amplitude (~0.25 mag) variations around a mean brightness of R ~ 19 mag. Prior to the current ongoing outburst, the brightest recorded measurements of iPTF 15afq in iPTF imaging is R = 18.7 mag. Following identification of the outburst, the source continued to rise over the following 3 weeks, peaking on 2015-04-01.17 UT at R = 16.5 mag. After peak, the source has remained bright, plateauing at approximately R = 16.7 mag.

The source is relatively isolated and can be associated with counterparts within 1-2" in USNO, 2MASS, Akari, and WISE. The infrared (IR) observations show a clear and strong IR-excess, and our early analysis suggests the source spectral energy distribution was consistent with a Class I classical T Tauri star prior to outburst.

An initial low-resolution classification spectrum was obtained with the Faulkes Telescope/FLOYDS on 2015-04-05 UT. That spectrum shows strong and narrow Halpha and Ca II IRT emission. A follow-up spectrum obtained on 2015-04-16 UT with Keck/DEIMOS shows a series of forbidden emission lines, including [O I], [S II], [Fe I] and [Ca II], in addition to Halpha and the Ca II IRT and other weak emission from FeI and FeII. There is also a strong absorption associated with Na I D, KI 7665, 7699, and OI 7773 which are often blueshifted and attributed to strong winds in young stars. The DEIMOS spectrum shows a remarkable similarity to PTF 10nvg, in particular, the very unusual presence of apparent TiO and VO emission in the red part of the spectrum. PTF 10nvg is another Class I young star that exhibited large amplitude optical variations (Covey et al. 2011, AJ, 141, 40; Hillenbrand et al. 2013, AJ, 145, 59).

The variable source is located at R.A. Dec = 07:09:21.40 -10:29:34.4 (J2000), near the Galactic plane (b = -0.84 deg). It lies in the direction of the Canis Majoris OB1 association and is several arcmin south of the O7 III member star HD 54662, within a dark area suggesting a cloud filament, to the west of CMa R1. iPTF 15afq appears to be one of the reddest sources associated with a previously unstudied embedded cluster that is seen in WISE and Spitzer/GLIMPSE images. The strong IR excess in conjunction with the low-amplitude historical variability and spatial location of iPTF 15afq, unambiguously identifies this source as a young stellar object (YSO). The current outburst, which shows a ~2.5 mag amplitude in the R band and a rich emission line spectrum, suggests this source is a new member of the EX Lupi-like class of YSO outbursts that are interpreted as accretion events driven by disk instabilities. Further monitoring is ongoing, and complementary observations -- particularly IR spectra and high dispersion optical spectra -- are encouraged. The DEIMOS spectrum, and future observations, are available here: http://www.astro.caltech.edu/~lah/ptf15afq/.