Gaia 19ajj: A Young Star Brightening Due to Enhanced Accretion + Reduced Extinction. (arXiv:1910.05790v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hillenbrand_L/0/1/0/all/0/1">Lynne A. Hillenbrand</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reipurth_B/0/1/0/all/0/1">Bo Reipurth</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Connelley_M/0/1/0/all/0/1">Michael Connelley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cutri_R/0/1/0/all/0/1">Roc M. Cutri</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Isaacson_H/0/1/0/all/0/1">Howard Isaacson</a>
We report on the source Gaia 19ajj, identifying it as a young star associated
with a little-studied star-forming region seen along a complex line-of-sight
through the Gum Nebula. The optical lightcurve recently recorded by Gaia
exhibits a slow and unsteady 5.5 mag rise over about 3 years, while the
mid-infrared lightcurve from NEOWISE over the same time period shows a 1.2 mag
rise having similar structure. Available color information is inconsistent with
pure extinction reduction as the cause for the photometric brightening. Optical
spectroscopic characteristics in the current bright phase include: little in
the way of absorption except for the hallmark Li I 6707 A signature of youth
plus weak e.g. Ca I and notably Ba II; strong wind/outflow in Ca II, Mg I b, Na
I D, Halpha, K I, O I; jet signatures in [O I], [S II], [Ca II], [Fe II], and
[Ni II]; and narrow rest-velocity emission in neutral species such as Fe I, Ni
I, and Mg I. The infrared spectrum is also characterized by outflow and
emission, including: a hot He I wind, jet lines such as [Fe II] and H2; and
weak narrow rest-velocity atomic line emission. The 12CO bandheads are weakly
in emission, but there is also broad H2O absorption. Gaia 19ajj exhibited a
previous bright state in the 2010-2012 time frame. The body of photometric and
spectroscopic evidence suggests that the source bears resemblance to V2492 Cyg
(PTF 10nvg) and PV Cep, both of which similarly experience bright phases that
recur on long timescales, with large-amplitude photometric variations and
emission-dominated spectra. We interpret the behavior of Gaia 19ajj as caused
by cycles of enhanced disk accretion accompanied by reduced extinction.
We report on the source Gaia 19ajj, identifying it as a young star associated
with a little-studied star-forming region seen along a complex line-of-sight
through the Gum Nebula. The optical lightcurve recently recorded by Gaia
exhibits a slow and unsteady 5.5 mag rise over about 3 years, while the
mid-infrared lightcurve from NEOWISE over the same time period shows a 1.2 mag
rise having similar structure. Available color information is inconsistent with
pure extinction reduction as the cause for the photometric brightening. Optical
spectroscopic characteristics in the current bright phase include: little in
the way of absorption except for the hallmark Li I 6707 A signature of youth
plus weak e.g. Ca I and notably Ba II; strong wind/outflow in Ca II, Mg I b, Na
I D, Halpha, K I, O I; jet signatures in [O I], [S II], [Ca II], [Fe II], and
[Ni II]; and narrow rest-velocity emission in neutral species such as Fe I, Ni
I, and Mg I. The infrared spectrum is also characterized by outflow and
emission, including: a hot He I wind, jet lines such as [Fe II] and H2; and
weak narrow rest-velocity atomic line emission. The 12CO bandheads are weakly
in emission, but there is also broad H2O absorption. Gaia 19ajj exhibited a
previous bright state in the 2010-2012 time frame. The body of photometric and
spectroscopic evidence suggests that the source bears resemblance to V2492 Cyg
(PTF 10nvg) and PV Cep, both of which similarly experience bright phases that
recur on long timescales, with large-amplitude photometric variations and
emission-dominated spectra. We interpret the behavior of Gaia 19ajj as caused
by cycles of enhanced disk accretion accompanied by reduced extinction.
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