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
We present ALMA and VLA observations of the molecular and ionized gas at 0.1-0.3 ′′ resolution in the Class 0 protostellar system IRAS 16293-2422. These data clarify the origins of the protostellar outflows from the deeply embedded sources in this complex region. Source A2 is confirmed to be at the origin of the well known large scale north-east-south-west flow. The most recent VLA observations reveal a new ejection from that protostar, demonstrating that it drives an episodic jet. The central compact part of the other known large scale flow in the system, oriented roughly east-west, is well delineated by the CO(6-5) emission imaged with ALMA and is confirmed to be driven from within component A. Finally, a one-sided blueshifted bubble-like outflow structure is detected here for the first time from source B to the north-west of the system. Its very short dynamical timescale (∼ 200 yr), low velocity, and moderate collimation support the idea that source B is the youngest object in the system, and possibly one of the youngest protostars known.
We present sensitive, high angular resolution (∼ 0.2 arcsec) submillimeter continuum and line observations of IRAS 16293-2422B made with the Atacama Large Millimeter/Submillimeter Array (ALMA). The 0.45 mm continuum observations reveal a single and very compact source associated with IRAS 16293-2422B. This submillimeter source has a deconvolved angular size of about 400 milli-arcseconds (50 AU), and does not show any inner structure inside of this diameter. The H 13 CN, HC 15 N, and CH 3 OH line emission regions are about twice as large as the continuum emission and reveal a pronounced inner depression or "hole" with a size comparable to that estimated for the submillimeter continuum. We suggest that the presence of this inner depression and the fact that we do not see inner structure (or a flat structure) in the continuum is produced by very optically thick dust located in the innermost parts of IRAS 16293-2422B. All three lines also show pronounced inverse P-Cygni profiles with infall and dispersion velocities larger than those recently reported from observations at lower frequencies, suggesting that we are detecting faster, and more turbulent gas located closer to the central object. Finally, we report a small east-west velocity gradient in IRAS 16293-2422B that suggests that its disk plane is likely located very close to the plane of the sky.
We present JCMT SCUBA-2 450µm and 850µm observations of 14 Asymptotic Giant Branch (AGB) stars (9 O-rich, 4 C-rich and 1 S-type) and one Red Supergiant (RSG) in the Solar Neighbourhood. We combine these observations with Herschel /PACS observations at 70µm and 160µm and obtain azimuthally-averaged surface-brightness profiles and their PSF subtracted residuals. The extent of the SCUBA-2 850 µm emission ranges from 0.01 to 0.16 pc with an average of ∼ 40% of the total flux being emitted from the extended component. By fitting a modified black-body to the four-point SED at each point along the radial profile we derive the temperature (T ), spectral index of dust emissivity (β) and dust column density (Σ) as a function of radius. For all the sources, the density profile deviates significantly from what is expected for a constant mass-loss rate, showing that all the sources have undergone variations in mass-loss during this evolutionary phase. In combination with results from CO line emission, we determined the dust-to-gas mass ratio for all the sources in our sample. We find that, when sources are grouped according to their chemistry, the resulting average dust-to-gas ratios are consistent with the respective canonical values. However we see a range of values with significant scatter which indicate the importance of including spatial information when deriving these numbers.
Aims. The protoplanetary disk around HL Tau is so far the youngest candidate of planet formation, and it is still embedded in a protostellar envelope with a size of thousands of au. In this work, we study the gas kinematics in the envelope and its possible influence on the embedded disk. Methods. We present our new ALMA cycle 3 observational results of HL Tau in the 13 CO (2-1) and C 18 O (2-1) emission at resolutions of 0 ′′ . 8 (110 au), and we compare the observed velocity pattern with models of different kinds of gas motions. Results. Both the 13 CO and C 18 O emission lines show a central compact component with a size of 2 ′′ (280 au), which traces the protoplanetary disk. The disk is clearly resolved and shows a Keplerian motion, from which the protostellar mass of HL Tau is estimated to be 1.8±0.3 M ⊙ , assuming the inclination angle of the disk to be 47• from the plane of the sky. The 13 CO emission shows two arc structures with sizes of 1000-2000 au and masses of 3 × 10 −3 M ⊙ connected to the central disk. One is blueshifted and stretches from the northeast to the northwest, and the other is redshifted and stretches from the southwest to the southeast. We find that simple kinematical models of infalling and (counter-)rotating flattened envelopes cannot fully explain the observed velocity patterns in the arc structures. The gas kinematics of the arc structures can be better explained with three-dimensional infalling or outflowing motions. Nevertheless, the observed velocity in the northwestern part of the blueshifted arc structure is ∼60-70% higher than the expected free-fall velocity. We discuss two possible origins of the arc structures: (1) infalling flows externally compressed by an expanding shell driven by XZ Tau and (2) outflowing gas clumps caused by gravitational instabilities in the protoplanetary disk around HL Tau.
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