Water maser variability in a high-mass YSO outburst -- VERA and ALMA observations of S255 NIRS 3

Abstract

We carried out observations of the 22 GHz H2O masers in a high-mass protostar S255 NIRS 3 by using VERA. We measured the proper motions of the 22 GHz H2O masers associated with a bipolar outflow. The expansion velocity of the blueshifted bow shock traced by the 22 GHz H2O masers was 28 km s-1 corresponding to a dynamical timescale of 60 years. The direction of the maser outflow is slightly tilted compared with the radio jet, which could suggest a more recent ejection episode during the accretion burst event. The total flux density of the 22 GHz H2O masers has gradually increased from early 2017 and has become almost constant in 2018. For the first time, we reveal extended H2O maser emission at 22 GHz in a star forming region, which is partly resolved out by VERA and even by the most extended VLA configurations. We find that the flux variation of such an extended component is similar to that of the unresolved maser emission. We also conducted observations of the submillimeter continuum and the 321 GHz H2O masers with ALMA at Band 7. The continuum emission does not show significant variations compared with the previous observations performed 5 months before. We mapped the 321 GHz H2O masers in S255 NIRS 3 providing the fourth example, for this maser, of the spatial distribution in a high-mass star-forming region. The lower ratio of the 22 GHz/321 GHz maser luminosity in the blueshifted bow shock suggests a temperature (>1000 K), higher than for the other maser features in this region. We conclude that the bow shock structure traced by the 22 GHz H2O maser features is unlikely to be originating at the interface between the radio jet powered by the recent accretion outburst and the surrounding medium. The brightening of the 22 GHz H2O masers could be due to radiative excitation by photons form the infrared outburst escaping along the cavity created by the newly ejected material.

19 pages, 28 figures, accepted for publication in Astronomy & Astrophysics

References in corpus (10)

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• An extraordinary outburst in the massive protostellar system NGC6334I-MM1: quadrupling of the millimeter continuum
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• ALMA sub-mm maser and dust distribution of VY Canis Majoris
• Detection of new methanol maser transitions associated with G358.93-0.03
• Discovery of six new class II methanol maser transitions, including the unambiguous detection of three torsionally excited lines toward G358.931-0.030
• Associations of water and methanol masers at milli-arcsec angular resolution in two high-mass young stellar objects
• VERA and ALMA Observations of the H2O Supermaser Burst in Orion KL
• Submillimeter Array Observations of 321 GHz Water Maser Emission in Cepheus A
• Near-infrared Monitoring of the Accretion Outburst in the MYSO S255-NIRS3

Cited by in corpus (9)

• Dissecting the different components of the modest accretion bursts of the very young protostar HOPS 373
• The evolution of the H2O maser emission in the accretion burst source G358.93-0.03
• High energy gamma-ray emission powered by a young protostar: the case of S255 NIRS 3
• Ammonia mapping observations toward the Galactic massive star-forming region Sh 2-255 and Sh 2-257
• Fine structure and kinematics of the ionized and molecular gas in the jet and disk around S255IR NIRS3 from high resolution ALMA observations
• Spectral survey of a Hot core with an Eruptive Accretion in S255IR NIRS3 (SHEA): The discovery of class I and class II millimeter methanol maser transitions
• Study of the high-mass star-forming region S255IR at various scales
• Identifying the Mechanisms of Water Maser Variability During the Accretion Burst in NGC6334I
• Digging into the Massive Protostar S255IR NIRS3: A Study of Nitrogen-Bearing Molecules and Their Prebiotic Chemistry