With the advent of high-resolution high-sensitivity observations, spiral patterns have been revealed around several asymptotic giant branch (AGB) stars. Such patterns can provide possible evidence for the existence of central binary stars embedded in outflowing circumstellar envelopes. Here, we suggest the viability of explaining the previously observed incomplete ring-like patterns with the spiral-shell structure due to the motion of (unknown) binary components viewed at an inclination with respect to the orbital plane. We describe a method of extracting such spiral-shells from an incomplete ring-like pattern to place constraints on the characteristics of the central binary stars. The use of gas kinematics is essential in facilitating a detailed modeling for the three-dimensional structure of the circumstellar pattern. We show that a hydrodynamic radiative transfer model can reproduce the structure of the HC 3 N molecular line emission of the extreme carbon star, CIT 6. This method can be applied to other sources in the AGB phase and to the outer ring-like patterns of pre-planetary nebulae for probing the existence of embedded binary stars, which are highly anticipated with future observations using the Atacama Large Millimeter/submillimeter Array.

Preplanetary nebulae (pPNe) and planetary nebulae (PNe) are evolved, mass-losing stellar objects that show a wide variety of morphologies. Many of these nebulae consist of outer structures that are nearly spherical (spiral/shell/arc/halo) and inner structures that are highly asymmetric (bipolar/multipolar) [1,2]. The coexistence of such geometrically distinct structures is enigmatic because it hints at the simultaneous presence of both wide and close binary interactions, a phenomenon that has been attributed to stellar binary systems with eccentric orbits [3]. Here we report new high-resolution molecular-line observations of the circumstellar spiral-shell pattern of AFGL 3068, an asymptotic giant branch (AGB) star transitioning to the pPN phase. The observations clearly reveal that the dynamics of the mass loss is influenced by the presence of an eccentric-orbit binary. This quintessential object opens a new window on the nature of deeply embedded binary stars through the circumstellar spiral-shell patterns that reside at distances of several thousand Astronomical Units (AU) from the stars.AFGL 3068, an extreme carbon star at the tip of the AGB evolutionary phase, is a remarkable source with the best-characterized, complete spiral pattern in its circumstellar envelope (CSE). This unambiguous spiral pattern was the first ever revealed surrounding an evolved star in a dust-scattered light image in the optical band (at 0.6 µm) of the Hubble Space Telescope (HST) [4,5]. The striking discovery of the presence of this very well-defined pattern has prompted new research on how binarity can affect mass outflows during late stages of stellar evolution (AGB, pPN, and PN). In particular, recent theoretical investigations have shown that such patterns can naturally be explained by the orbital motion of a mass-losing star in a binary system [6][7][8][9][10]. In the case of AFGL 3068, there are indeed two point-like sources in its central region detected with Keck adaptive optics near-infrared imaging, revealing a projected binary separation of 109 AU [4]. Constraints on its binary parameters have been derived on the basis of these HST and Keck images, assuming a circular orbit [9]. This further indicated that the degeneracy imposed by the two-dimensional image of the three-dimensional structure can be lifted by high-resolution molecular line observations.Our new observations of AFGL 3068 taken with the Atacama Large Millimeter/submillimeter Array (ALMA; see Methods for details on observations and data calibrations) unveil exceptionally detailed features in its CSE (Fig. 1; individual molecular lines are presented in Supplementary Figs 1-3). A

The massive young stellar object S255IR NIRS3 embedded in the star-forming core SMA1 has been recently observed with a luminosity burst, which is conjectured as a disk-mediated variable accretion event. In this context, it is imperative to characterize the gas properties around the massive young stellar object. With this in mind, we carried out high angular resolution observations with the Atacama Large Millimeter/submillimeter Array and imaged the 900 μm dust continuum and the CH3CN J = 19−18 K = 0−10 transitions of S255IR SMA1. The integrated CH3CN emission exhibits an elongated feature with an extent of 1800 au in the northwest–southeast direction at a position angle of 165°, which is nearly perpendicular to the bipolar outflow. We confirm the presence of dense (a few cm−3) and hot (∼400 K) gas immediately surrounding the central protostar. The CH3CN emission features a velocity gradient along the elongated ridge, and by modeling the gas kinematics based on features in the position–velocity diagram, we infer that the gas is best described by a flattened rotating infalling envelope (or pseudo-disk). A mass infall rate of a few × 10−4 M ⊙ yr−1 is derived. If there exists a putative Keplerian disk directly involved in the mass accretion onto the star and jet/outflow launching, it is likely smaller than 125 au and unresolved by our observations. We show qualitative resemblances between the gas properties (such as density and kinematics) in 255IR SMA1 inferred from our observations and those in a numerical simulation particularly tailored for studying the burst mode of massive star formation.

Probing magnetic fields in self-gravitating molecular clouds are generally difficult even with the use of the polarimetry. Based on the properties of magneto-hydrodynamic (MHD) turbulence and turbulent reconnection, Velocity Gradient Technique (VGT) provides a new way in tracing magnetic field orientation and strength based on the spectroscopic data. Our study tests the applicability of VGT in various molecular tracers, e.g. 12 CO, 13 CO, and C 18 O. By inspecting synthetic molecular line maps of CO isotopologue generated through radiative transfer calculations, we show that the VGT method can be successfully applied in probing the magnetic field direction in the diffuse interstellar medium as well as in self-gravitating molecular clouds.

We present our analysis of the magnetic field structures from 6000 au to 100 au scales in the Class 0 protostar B335 inferred from our JCMT POL-2 observations and the ALMA archival polarimetric data. To interpret the observational results, we perform a series of (non-)ideal MHD simulations of the collapse of a rotating nonturbulent dense core, whose initial conditions are adopted to be the same as observed in B335, and generate synthetic polarization maps. The comparison of our JCMT and simulation results suggests that the magnetic field on a 6000 au scale in B335 is pinched and well aligned with the bipolar outflow along the east-west direction. Among all our simulations, the ALMA polarimetric results are best explained with weak magnetic field models having an initial mass-to-flux ratio of 9.6. However, we find that with the weak magnetic field, the rotational velocity on a 100 au scale and the disk size in our simulations are larger than the observational estimates by a factor of several. An independent comparison of our simulations and the gas kinematics in B335 observed with the SMA and ALMA favors strong magnetic field models with an initial mass-to-flux ratio smaller than 4.8. We discuss two possibilities resulting in the different magnetic field strengths inferred from the polarimetric and molecular-line observations, (1) overestimated rotational-to-gravitational energy in B335 and (2) additional contributions in the polarized intensity due to scattering on a 100 au scale.