Quasi-Periodic Formaldehyde Maser Flares in the Massive Protostellar Object Iras 18566+0408

Abstract

We report results of an extensive observational campaign of the 6 cm formaldehyde maser in the young massive stellar object IRAS 18566+0408 (G37.55+0.20) conducted from 2002 to 2009. Using Arecibo, VLA, and GBT, we discovered quasi-periodic formaldehyde flares (P ∼ 237 days). Based on Arecibo observations, we also discovered correlated variability between formaldehyde (H 2 CO) and methanol (CH 3 OH) masers. The H 2 CO and CH 3 OH masers are not spatially coincident, as demonstrated by different line velocities and high angular resolution MERLIN observations. The flares could be caused by variations in the infrared radiation field, possibly modulated by periodic accretion onto a young binary system.

The shortest periodic and flaring flux variability of a methanol maser emission at 6.7 GHz in G 014.23−00.50

“…Patterns of the variability have been classified into two categories: the sinusoidal one, and the intermittent one with a quiescent phase. Such periodic flux variability was also observed in other masers, i.e., silicon monoxide in Orion Kleinmann-Low (KL) (Ukita et al 1981), formaldehyde in IRAS 18556+0408 (Araya et al 2010), hydroxyl in G 012.88+00.48 (Green et al 2012a), and water in IRAS 22198+6336 (Szymczak et al 2016), and variations of these lines except for the silicon monoxide were synchronized with the variations of methanol masers in the same sources. The periodic variability, therefore, must be a common phenomenon at around high-mass (proto-)stars, but appears in limited conditions.…”

“…The derived period of 23.9 days is the shortest one observed in the masers at around high-mass YSOs so far, compared to 29.5 days in methanol ), ∼2 yrs in silicon monoxide (Ukita et al 1981), 237 days in formaldehyde (Araya et al 2010), 25-30 days in hydroxyl (Green et al 2012a), and 34.4 days in water (Szymczak et al 2016). …”

“…Therefore, the periodic flares in G 014.23 that occurred only on one component G showing the intermittent pattern cannot be explained by the pulsation model. The circumbinary disk model is also proposed to explain the periodic variability in some methanol sources through variations of the dust temperature (Araya et al 2010). However, this model is not suited to the periodic flares in G 014.23 since it is difficult to cause periodic variations toward only one in seven spectral components as in the case of the pulsation model.…”

“…Four models have been proposed for interpretations of the periodic flux variability, in the point of view that variations of (multiple) spectral components are synchronized with 1-14 days' delay in some sources, possibly caused by global variation on a central engine: a colliding-wind binary (CWB: van der ; van der Walt 2011), a stellar pulsation (Inayoshi et al 2013;Sanna et al 2015), a circumbinary accretion disk (Araya et al 2010), and a rotation of spiral shocks within a gap region in a circumbinary disk (Parfenov & Sobolev 2014). The first model is based on changes in the flux of seed photons, while the remaining three ones are based on changes in the temperature of dust grains at the masing regions.…”

Discovery of four periodic methanol masers and updated light curve for a further one

“…Specifically, a colliding-wind binary (CWB) could produce a periodic pulse in the ionising radiation that changes the electron density and periodically modulates the free-free emission from the H ii region against which the maser clouds are projected. In another model, the periodic maser variation is related to the flux of infrared emission that could be regulated by periodic accretion of material from the circumbinary disc onto a protostar or accretion disc (Araya et al 2010). Recently, Parfenov & Sobolev (2014) proposed that the dust temperature variations in the circumbinary accretion disc are caused by rotation of hot and dense material of the spiral shock wave in the disc central gap.…”