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Mid-Term Near-Infrared Variability of the Massive Young Stellar Object RAFGL 7009S associated with G25.65+1.05

ATel #10842; Bringfried Stecklum (TLS Tautenburg), Alessio Caratti o Garatti (DIAS Dublin), Sylvio Klose (TLS Tautenburg), Phil Wiseman (MPE Garching)
on 11 Oct 2017; 19:49 UT
Credential Certification: Bringfried Stecklum (stecklum@tls-tautenburg.de)

Subjects: Infra-Red, Transient, Variables, Young Stellar Object

A bright rapid 22.235 GHz water maser flare from the ultracompact HII region G25.65+1.05 was recently reported by Volvach et al. (ATel #10728). It was accompanied by a moderate flux rise of the associated Class II 6.7 GHz methanol masers (Sugiyama et al. ATel #10757). Qualitative conclusions on the near-infrared (NIR) variability of G25.65+1.05 were drawn by Sobolev et al. (ATel #10788), based on the comparison of their K-band image obtained on 2017 Sep 21 to UKIDSS data.

To assess the brightness change of RAFGL 7009S we obtained JHKs imaging with GROND (Greiner et al. 2008) on Sep. 11.97 UT at the La Silla MPG 2.2-m telescope, and Ks-band imaging with PANIC (Baumeister et al. 2008) at the Calar Alto 2.2-m telescope on Sep 12.80 UT. In addition, the two UKIDSS K-band images (epochs: 2007-08-27, 2011-09-18) and archival ESO-SOFI Ks-band imaging (epoch 2002-08-15) were retrieved. Unlike Sobolev et al. (ATel #10788) we do not describe the changes in brightness and morphology with reference to the 2MASS sources assigned to the object. 2MASS resolved the source into two components only while the images at hand clearly show three brightness peaks, marked by circles in the image provided below. The northernmost represents the MYSO since it coincides with the IR source seen in Spitzer/GLIMPSE data at longer wavelengths. The two features south of it may be scattering peaks. The GROND Ks-band image taken in twilight is shallower than those from the other facilities, and not shown for comparison. A close-up view of RAFGL 7009S on the four images taken within ~15 years can be seen at this URL

ftp://ftp.tls-tautenburg.de/pub/stecklum/G25.png

All images were photometrically calibrated using 2MASS. The photometry revealed that the source brightened from 2002 to 2011 by about half a magnitude and faded since then. However, the variability is different for the various components, causing a change of the morphology over time. In 2011, the northern component, i.e., RAFGL 7009S, was brightest but diminished by ~0.4 mag since then while the southernmost shows a steady rise. The inherent variability of embedded YSOs (Contreras Peña et al. 2014) makes it difficult to conclude whether the observed changes are related to the maser activity. Proper motion measurements of the water masers are required to see whether their kinematic age is in the time range of the NIR variability. Kinematic ages of water maser outflows as small as 40 yr have been estimated using this method (Torrelles et al. 2014). For what concerns the group of Class II methanol maser spots (marked by the cross) north of RAFGL 7009S, it is difficult to reconcile the rise of their flux and the dimming of the MYSO in the NIR. We note that there are two variable stars to the NE and SW of the source, respectively.