Flares and proper motions of ground-state OH masers in W75N

Abstract

The star‐forming region W75N hosts bright OH masers that are observed to be variable. We present observations taken in 2008 of the ground‐state OH maser transitions with the Very Long Baseline Array and the Multi‐Element Radio‐Linked Interferometer Network and with the Nançay Radio Telescope in 2011. Several of the masers in W75N were observed to be flaring, with the brightest 1720‐MHz maser in excess of 400 Jy. The 1720‐MHz masers appear to be associated with the continuum source VLA 1, unlike the bright flaring 1665‐ and 1667‐MHz masers, which are associated with VLA 2. The 1720‐MHz masers are located in an outflow traced by water masers and are indicative of very dense molecular material near the H ii region. The magnetic field strengths are larger in the 1720‐MHz maser region than in most regions hosting only main‐line OH masers. The density falls off along the outflow, and the order of appearance of different transitions of OH masers is consistent with theoretical models. The 1665‐ and 1667‐MHz VLBA data are compared against previous epochs over a time baseline of over 7 years. The median maser motion is 3.5 km s−1 with a scatter that is comparable to thermal turbulence. The general pattern of maser proper motions observed in the 1665‐ and 1667‐MHz transitions is consistent with previous observations.

Monitoring of the polarized H2O maser emission around the massive protostars W75N(B)-VLA 1 and W75N(B)-VLA 2

“…The great interest that W75N(B) has aroused in the past is also due to the presence of several maser species (OH, CH 3 OH, and H 2 O) around the two sources VLA 1 and VLA 2 (e.g., Haschick et al 1981;Hunter et al 1994;Torrelles et al 1997;Lekht & Krasnov 2000;Minier et al 2000;Surcis et al 2009;Fish et al 2011;Kang et al 2016;Colom et al 2018Colom et al , 2021. OH masers are distributed throughout the region with the majority of the maser spots associated with VLA 1 (Hutawarakorn et al 2002;Fish et al 2005).…”

Masers in star forming regions

“…They detected a long-term variability with an average period of 14 years and two series of flares that are likely associated with some cyclic activity of the protostar in the UC H II. 1720 MHz OH masers towards W75N also showed flaring, possibly related to the very dense molecular material that is excited and slowly accelerated by the outflow (Fish et al 2011a). A surprising event was registered in IRAS18566+0408 by Araya et al (2010): the 4.8 GHz H 2 CO maser showed flaring and a period correlated with the 6.7 GHz methanol outbursts.…”

Powerful flare phenomena in water vapor maser lines in the emerging protostellar system with protoplanetary disks IRAS 16293-2422

“…Strong water masers may arise in a turbulent medium. This environment can see as a real source of collisional pumping of a water maser ("at least those corresponding to the lowvelocity core of the spectrum") [36][37][38]. H 2 O masers can arise in star-forming regions due to regular movements of turbulent gas and dust matter during its expansion or accretion as it rotates around protostars.…”