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Register a new userKinematics of the Envelope and Two Bipolar Jets in the Class 0 Protostellar System L1157
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Woojin Kwon
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A massive envelope and a strong bipolar outflow are the two main structures characterizing the youngest protostellar systems. In order to understand the physical properties of a bipolar outflow and the relationship with those of the envelope, we obtained a mosaic map covering the whole bipolar outflow of the youngest protostellar system L1157 with about $5$ angular resolution in CO J=2-1 using the Combined Array for Research in Millimeter-wave Astronomy. By utilizing these observations of the whole bipolar outflow, we estimate its physical properties and show that they are consistent with multiple jets. We also constrain a preferred precession direction. In addition, we observed the central envelope structure with $2$ resolution in the $lambda=1.3$ and 3 mm continua and various molecular lines: C$^{17}$O, C$^{18}$O, $^{13}$CO, CS, CN, N$_2$H$^+$, CH$_3$OH, H$_2$O, SO, and SO$_2$. All the CO isotopes and CS, CN, and N$_2$H$^+$ have been detected and imaged. We marginally detected the features that can be interpreted as a rotating inner envelope in C$^{17}$O and C$^{18}$O and as an infalling outer envelope in N$_2$H$^+$. We also estimated the envelope and central protostellar masses and found that the dust opacity spectral index changes with radius.
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We present a characterization of the protostar embedded within the BHR7 dark cloud, based on both photometric measurements from the near-infrared to millimeter and interferometric continuum and molecular line observations at millimeter wavelengths. We find that this protostar is a Class 0 system, the youngest class of protostars, measuring its bolometric temperature to be 50.5~K, with a bolometric luminosity of 9.3~L$_{odot}$. The near-infrared and textit{Spitzer} imaging show a prominent dark lane from dust extinction separating clear bipolar outflow cavities. Observations of $^{13}$CO ($J=2rightarrow1$), C$^{18}$O ($J=2rightarrow1$), and other molecular lines with the Submillimeter Array (SMA) exhibit a clear rotation signature on scales $<$1300~AU. The rotation can be traced to an inner radius of $sim$170~AU and the rotation curve is consistent with an R$^{-1}$ profile, implying that angular momentum is being conserved. Observations of the 1.3~mm dust continuum with the SMA reveal a resolved continuum source, extended in the direction of the dark lane, orthogonal to the outflow. The deconvolved size of the continuum indicates a radius of $sim$100~AU for the continuum source at the assumed distance of 400~pc. The visibility amplitude profile of the continuum emission cannot be reproduced by an envelope alone and needs a compact component. Thus, we posit that the resolved continuum source could be tracing a Keplerian disk in this very young system. If we assume that the continuum radius traces a Keplerian disk (R$sim$120~AU) the observed rotation profile is consistent with a protostar mass of 1.0~$M_{odot}$.
We present the first detection of polarization around the Class 0 low-mass protostar L1157-mm at two different wavelengths. We show polarimetric maps at large scales (10 resolution at 350 um) from the SHARC-II Polarimeter and at smaller scales (1.2-4.5 at 1.3 mm) from the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The observations are consistent with each other and show inferred magnetic field lines aligned with the outflow. The CARMA observations suggest a full hourglass magnetic field morphology centered about the core; this is only the second well-defined hourglass detected around a low-mass protostar to date. We apply two different methods to CARMA polarimetric observations to estimate the plane-of-sky magnetic field magnitude, finding values of 1.4 and 3.4 mG.
We have observed the Class I protostellar source Elias 29 with Atacama Large Millimeter/submillimeter Array (ALMA). We have detected CS, SO, $^{34}$SO, SO$_2$, and SiO line emissions in a compact component concentrated near the protostar and a ridge component separated from the protostar by 4arcsec ($sim 500$ au). The former component is found to be abundant in SO and SO$_2$ but deficient in CS. The abundance ratio SO/CS is as high as $3^{+13}_{-2} times 10^2$ at the protostar, which is even higher than that in the outflow-shocked region of L1157 B1. However, organic molecules (HCOOCH$_3$, CH$_3$OCH$_3$, CCH, and c-C$_3$H$_2$) are deficient in Elias 29. We attribute the deficiency in organic molecules and richness in SO and SO$_2$ to the evolved nature of the source or the relatively high dust temperature (protectraisebox{-0.7ex}{$:stackrel{textstyle >}{sim}:$} 20 K) in the parent cloud of Elias 29. The SO and SO$_2$ emissions trace rotation around the protostar. Assuming a highly inclined configuration ($i geq 65$degr; 0degr for a face-on configuration) and Keplerian motion for simplicity, the protostellar mass is estimated to be (0.8 -- 1.0) Msun. The $^{34}$SO and SO$_2$ emissions are asymmetric in their spectra; the blue-shifted components are weaker than the red-shifted ones. Although this may be attributed to the asymmetric molecular distribution, other possibilities are also discussed.
[abridged] Understanding how the infalling gas redistribute most of its initial angular momentum inherited from prestellar cores before reaching the stellar embryo is a key question. Disk formation has been naturally considered as a possible solution to this angular momentum problem. However, how the initial angular momentum of protostellar cores is distributed and evolves during the main accretion phase and the beginning of disk formation has largely remained unconstrained up to now. In the framework of the IRAM CALYPSO survey, we used high dynamic range C$^{18}$O (2-1) and N$_2$H$^+$ (1-0) observations to quantify the distribution of specific angular momentum along the equatorial axis in a sample of 12 Class 0 protostellar envelopes from scales ~50 to 10000 au. The radial distributions of specific angular momentum in the CALYPSO sample suggest two distinct regimes within protostellar envelopes: the specific angular momentum decreases as $j propto r^{1.6 pm 0.2}$ down to ~1600 au and then tends to become relatively constant around 6 $times$ 10$^{-4}$ km s$^{-1}$ pc down to ~50 au. The values of specific angular momentum measured in the inner Class 0 envelopes, namely that of the material directly involved in the star formation process ($<$1600 au), is on the same order of magnitude as what is inferred in small T-Tauri disks. Thus, disk formation appears to be a direct consequence of angular momentum conservation during the collapse. Our analysis reveals a dispersion of the directions of velocity gradients at envelope scales $>$1600 au, suggesting that they may not be related to rotational motions of the envelopes. We conclude that the specific angular momentum observed at these scales could find its origin in core-forming motions (infall, turbulence) or trace an imprint of the initial conditions for the formation of protostellar cores.
Context: The protostellar envelopes, outflow and large-scale chemistry of Class~0 and Class~I objects have been well-studied, but while previous works have hinted at or found a few Keplerian disks at the Class~0 stage, it remains to be seen if their presence in this early stage is the norm. Likewise, while complex organics have been detected toward some Class~0 objects, their distribution is unknown as they could reside in the hottest parts of the envelope, in the emerging disk itself or in other components of the protostellar system, such as shocked regions related to outflows. Aims: In this work, we aim to address two related issues regarding protostars: when rotationally supported disks form around deeply embedded protostars and where complex organic molecules reside in such objects. Methods: We observed the deeply embedded protostar, L483, using Atacama Large Millimeter/submillimeter Array (ALMA) Band~7 data from Cycles~1 and 3 with a high angular resolution down to $sim$~0.1$^{primeprime}$ (20~au) scales. Results: We find that the kinematics of CS~$J=7$--$6$ and H$^{13}$CN~$J=4$--$3$ are best fitted by the velocity profile from infall under conservation of angular momentum and not by a Keplerian profile. The spatial extents of the observed complex organics are consistent with an estimated ice sublimation radius of the envelope at $sim$~50~au, suggesting that the complex organics exist in the hot corino of L483. Conclusions: We find that L483 does not harbor a Keplerian disk down to at least $15$~au in radius. Instead, the innermost regions of L483 are undergoing a rotating collapse. This result highlights that some Class~0 objects contain only very small disks, or none at all, with the complex organic chemistry taking place on scales inside the hot corino of the envelope, in a region larger than the emerging disk.
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