Near-infrared brightening of IRAS18305-0826 hints at an accretion burst
ATel #16312; Bringfried Stecklum (TLS Tautenburg), Alessio Caratti o Garatti (INAF Naples), Ana Guijarro (CAHA), Hendrik Linz (MPIA Heidelberg), and Sol Molina (CAHA)
on 29 Oct 2023; 10:34 UT
Credential Certification: Bringfried Stecklum (stecklum@tls-tautenburg.de)
Subjects: Infra-Red, Variables, Young Stellar Object
Tanabe & Yonekura (ATel #16303) reported on recent flare activity of 6.668 GHz Class II methanol masers, known by Simbad as [HMW2016] G023.389+00.185. These masers are associated with the massive young stellar object (MYSO) IRAS18305-0826. Due to their radiative pumping, a luminosity increase caused by enhanced accretion will lead to flaring. This connection has been recently established for four MYSO accretion bursts (Caratti o Garatti et al. 2017; Hunter et al. 2017; Stecklum et al. 2021; Wolf et al., in prep.). Thus, we attempted near-infrared (NIR) imaging of the object to verify a possible brightness increase.
For this purpose, the Omega2000 camera (Bizenberger et al. 1998) at the 3.5-m telescope of the Calar Alto Observatory (CAHA), Spain, was used on 2023 October 25 for director's discretionary time observations. Exposures were taken using the J, H, and NB2144 filters. The latter has a bandwidth of 1% and was applied to prevent detector saturation from the bright target in order to yield precise photometry. The 2MASS catalog (Skrutskie et al. 2006) served for photometric calibration and comparison. We assumed that the tiny difference in effective wavelengths between the 2.144 µm narrowband and Ks filters is negligible. A preliminary analysis revealed the brightening of the source by 1.36±0.25, 1.20±0.07, and 0.66±0.03 magnitudes in the three bands over the 2MASS values. The color changes indicate that part of the brightening may be due dust clearing, leading to reduced extinction, similar as for the emergence of McNeils nebula (Reipurth & Aspin 2004).
Although the brightness increase is less than that observed for the S255IR-NIRS3 burst (Stecklum et al., ATel #8732), it nonetheless indicates that a possible mild accretion burst is going on in IRAS18305-0826. This source is located at 4.8 kpc (Reid et al. 2019). Scaling the luminosity from the Red MSX Source (RMS) survey (Lumsden et al. 2013) to this distance yields 2.7E4 L☉.
Follow-up measurements are highly encouraged, since the target visibility in the night sky will end soon.
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