Protostellar Outflows at the EarliesT Stages (POETS)

Abstract

Context. Although recent observations and theoretical simulations have pointed out that accretion disks and jets can be essential for the formation of stars with a mass of up to at least 20 M⊙, the processes regulating mass accretion and ejection are still uncertain. Aims. The goal of the Protostellar Outflows at the EarliesT Stages (POETS) survey is to image the disk-outflow interface on scales of 10–100 au in a statistically significant sample (36) of luminous young stellar objects (YSO), targeting both the molecular and ionized components of the outflows. Methods. The outflow kinematics is studied at milliarcsecond scales through very long baseline interferometry (VLBI) observations of the 22 GHz water masers, which are ideal test particles to measure the three-dimensional (3D) motion of shocks owing to the interaction of winds and jets with ambient gas. We employed the Jansky Very Large Array (JVLA) at 6, 13, and 22 GHz in the A- and B-Array configurations to determine the spatial structure and the spectral index of the radio continuum emission, and address its nature. Results. In about half of the targets, the water masers observed at separation ≤1000 au from the YSOs trace either or both of these kinematic structures: (1) a spatially elongated distribution oriented at close angle with the direction of collimation of the maser proper motions (PM), and (2) a linear local standard of rest (LSR) velocity (VLSR) gradient across the YSO position. The kinematic structure (1) is readily interpreted in terms of a protostellar jet, as confirmed in some targets via the comparison with independent observations of the YSO jets, in thermal (continuum and line) emissions, reported in the literature. The kinematic structure (2) is interpreted in terms of a disk-wind (DW) seen almost edge-on on the basis of several pieces of evidence: first, it is invariably directed perpendicular to the YSO jet; second, it agrees in orientation and polarity with the VLSR gradient in thermal emissions (when reported in the literature) identifying the YSO disk at scales of ≤1000 au; third, the PMs of the masers delineating the VLSR gradients hint at flow motions at a speed of 10–20 km s−1 directed at large angles with the disk midplane. In the remaining targets, the maser PMs are not collimated but rather tend to align along two almost perpendicular directions. To explain this peculiar PM distribution, and in light of the observational bias strongly favoring masers moving close to the plane of sky, we propose that, in these sources, the maser emission could originate in DW-jet systems slightly inclined (≤30°) with respect to edge-on. Magneto-centrifugally driven DWs could in general account for the observed velocity patterns of water masers.

Multi-scale view of star formation in IRAS 21078+5211: from clump fragmentation to disk wind

“…The water masers show a SW-NE elongated distribution at radii between 100 au and 300 au from the peak of the compact 1.3 cm JVLA continuum, corresponding to the core of the radio jet and the YSO-1 position. The elongation, at PA ≈ 38 • , of the maser spatial distribution, and the average direction of the proper motions, PA ≈ 49 • (Moscadelli et al 2019, see Table A1), are in good agreement with the orientation, PA ≈ 43 • , of the double-component radio jet (see Fig. 5).…”

Protostellar Outflows at the EarliesT Stages (POETS)

“…Sanna et al (2018; hereafter Paper I) reported on and interpreted the radio continuum data of the whole sample, while Sanna et al (2019a; hereafter Paper II) examined the radio synchrotron jet associated with the high-mass YSO G035.02+0.35. Moscadelli et al (2019a; hereafter Paper III) completed the combined analysis of the radio continuum and water maser observations for all the targets, with a particular focus on the water maser kinematics. The main result of Paper III is that the 3D-velocity distribution of the water masers near the YSO in all the sources of the sample can be interpreted in terms of a single physical scenario: a disk-wind (DW).…”

Clustered star formation towards Berkeley 87 / ON2. I. Multi-wavelength census and the population overlap problem

“…The main components of ON 2S are the G75.77+0.34 Hii region and the Cygnus 2N site of massive star formation. The later hosts several water masers whose distances have been measured by Ando et al (2011); Xu et al (2013); Moscadelli et al (2019) through trigonometric parallaxes, yielding (3.83 ± 0.13) kpc, 3.56 +0.49 −0.38 kpc, and (3.72 ± 0.43) kpc, respectively.…”