New eruptive variable(s) in the RAFGL 7009S H ii region

Abstract

ABSTRACT Eruptions of young stellar objects (YSOs) are rare events, therefore a new outburst is always noteworthy. We present two new high-amplitude variable YSOs, J183421.85−055951.0 (#1) and J183421.39−055937.7 (#2), in the RAFGL 7009S star-forming region. We find them in the United Kingdom Infrared Telescope Infrared Deep Sky Survey Galactic Plane Survey data base, and supplement these data with archived infrared and millimetre photometric and spectral images and data from the Spitzer Infrared Array Camera, the K-band Multi-Object Spectrograph, and the Atacama Large Millimeter/submillimeter Array data bases. The outburst in #1 occurred in the period 2007–2011, during which the brightness increased by ∼2.7 mag in the K band and by ∼2.5 mag in the 3.6 μm band. The colour indices indicate a YSO in Class I/II evolutionary stage. After outburst, the K-band spectrum shows the CO band, Brγ, Mg i in absorption and H2 in emission – characteristics associated with a FU Orionis (FUors)-type eruptive variable. Object #1 is associated with an outflow detected in the near-infrared and millimetre ranges, mainly in the H2, SiO, HCO+, and HCN lines. Object #2 only shows high-amplitude variability in the K band (ΔK  =  2.0 mag) while its colour indices before outburst indicate a YSO at an early evolutionary stage. There is no obvious outflow activity associated with this object. We classify #1 as a FUor-type eruptive variable based on the obtained data. The limited information on #2 makes it difficult to draw definite conclusions about the nature of its variability.