ALMA Super-resolution Imaging of T Tau: r = 12 au Gap in the Compact Dust Disk around T Tau N

Based on Atacama Large Millimeter/submillimeter Array (ALMA) observations, compact protoplanetary disks with dust radii of r ≲ 20–40 au were found to be dominant in nearby low-mass star formation regions. However, their substructures have not been investigated because of the limited spatial resolution achieved so far. We apply a newly developed super-resolution imaging technique utilizing sparse modeling (SpM) to explore several au-scale structures in such compact disks. SpM imaging can directly solve for the incomplete sampling of visibilities in the spatial frequency and potentially improve the fidelity and effective spatial resolution of ALMA images. Here we present the results of the application to the T Tau system. We use the ALMA 1.3 mm continuum data and achieve an effective spatial resolution of ∼30% (5 au) compared with the conventional CLEAN beam size at a resolution of 17 au. The reconstructed image reveals a new annular gap structure at r = 12 au in the T Tau N compact disk, with a dust radius of 24 au, and resolves the T Tau Sa and Sb binary into two sources. If the observed gap structure in the T Tau N disk is caused by an embedded planet, we estimate a Saturn-mass planet when the viscous parameter of the disk is 10−3. Ultimately, ALMA observations with enough angular resolution and sensitivity should be able to verify the consistency of the super-resolution imaging and definitely confirm the existence of this disk substructure.

VELOCITY SEGREGATION IN A CLUMP-LIKE OUTFLOW WITH A NON-TOP HAT VELOCITY CROSS-SECTION

High velocity clumps joined to the outflow source by emission with a “Hubble law” ramp of linearly increasing radial velocity vs. distance are observed in some planetary nebulae and in some outflows in star formation regions. We propose a simple model in which a “clump” is ejected from a source over a period τ0, with a strong axis to edge velocity stratification. This non-top hat cross section results in the production of a highly curved working surface (initially being pushed by the ejected material, and later coasting along due to its inertia). From both analytic models and numerical simulations we find that this working surface has a linear velocity vs. position ramp, and therefore reproduces in a qualitative way the “Hubble law clumps” in planetary nebulae and outflows from young stars.

NH3 (1,1) hyperfine intensity anomalies in the Orion A molecular cloud

Ammonia (NH3) inversion lines, with their numerous hyperfine components, are a common tracer used in studies of molecular clouds (MCs). In local thermodynamical equilibrium, the two inner satellite lines (ISLs) and the two outer satellite lines (OSLs) of the NH3(J, K) = (1,1) transition are each predicted to have equal intensities. However, hyperfine intensity anomalies (HIAs) are observed to be omnipresent in star formation regions, a characteristic which is still not fully understood. In addressing this issue, we find that the computation method of the HIA by the ratio of the peak intensities may have defects, especially when used to process the spectra with low-velocity dispersions. Therefore, we defined the integrated HIAs of the ISLs (HIAIS) and OSLs (HIAOS) by the ratio of their redshifted to blueshifted integrated intensities (unity implies no anomaly) and developed a procedure to calculate them. Based on this procedure, we present a systematic study of the integrated HIAs in the northern part of the Orion A MC. We find that integrated HIAIS and HIAOS are commonly present in the Orion A MC and no clear distinction is found at different locations of the MC. The medians of the integrated HIAIS and HIAOS are 0.921 ± 0.003 and 1.422 ± 0.009, respectively, which is consistent with the HIA core model and inconsistent with the collapse or expansion (CE) model. In the selection of those 170 positions, where both integrated HIAs deviate by more than 3σ from unity, most (166) are characterized by HIAIS < 1 and HIAOS > 1, which suggests that the HIA core model plays a more significant role than the CE model. The remaining four positions are consistent with the CE model. We compare the integrated HIAs with the para-NH3 column density (N(para-NH3)), kinetic temperature (TK), total velocity dispersion (σv), non-thermal velocity dispersion (σNT), and the total opacity of the NH3(J, K) = (1,1) line (τ0). The integrated HIAIS and HIAOS are almost independent of N(para-NH3). The integrated HIAIS decreases slightly from unity (no anomaly) to about 0.7 with increasing TK, σv, and σNT. The integrated HIAOS is independent of TK and reaches values close to unity with increasing σv and σNT. The integrated HIAIS is almost independent of τ0, while the integrated HIAOS rises with τ0, thus showing higher anomalies. These correlations cannot be fully explained by either the HIA core nor the CE model.

The diffuse gamma-ray emission toward the Galactic mini starburst W43

In this paper we report the Fermi Large Area Telescope (Fermi-LAT) detection of the γ-ray emission toward the young star forming region W43. Using the latest source catalog and diffuse background models, the extended γ-ray excess is detected with a significance of ~16σ. The γ-ray emission has a spectrum with a photon index of 2.3 ± 0.1. We also performed a detailed analysis of the gas content in this region by taking into account the opacity correction to the HI gas column density. The total cosmic-ray (CR) proton energy is estimated to be on the order of 1048 erg, assuming the γ-rays are produced from the interaction of the accelerated protons and nuclei with the ambient gas. Comparing this region to the other star formation regions in our Galaxy, we find that the CR luminosity is better correlated with the wind power than the star formation rate (SFR). This result suggests that CRs are primarily accelerated by stellar wind in these systems.

On the Thermal Regime and Density in the Star-Forming Regions

We developed an automatic code to determine some physical parameters describing the radiation of a simple one-temperature black body model and implemented it to calculating the temperatures and masses of molecular clouds in several star formation regions, using the observed IR emission fluxes for the chosen sources. Calculations show that the used commonly simplifications need to study in more detail for estimating the accuracy of computing results.