Millimeter Dust Emission in the GQ Lup System

We present Submillimeter Array observations of the GQ Lup system at 1.3 millimeters wavelength with 0\farcs4 ($\sim$60 AU) resolution. Emission is detected from the position of the primary star, GQ Lup A, and is marginally resolved. No emission is detected from the substellar companion, GQ Lup B, 0\farcs7 away. These data, together with models of the spectral energy distribution, suggest a compact disk around GQ Lup A with mass $\sim 3$ M$_{Jup}$, perhaps truncated by tidal forces. There is no evidence for a gap or hole in the disk that might be the signature of an additional inner companion body capable of scattering GQ Lup B out to $\sim100$ AU separation from GQ Lup A. For GQ Lup B to have formed {\it in situ}, the disk would have to have been much more massive and extended.Comment: 16 pages, 2 figures, accepted to A

Infall, Outflow, Rotation, and Turbulent Motions of Dense Gas within NGC 1333 IRAS 4

Millimeter wavelength observations are presented of NGC 1333 IRAS 4, a group of highly-embedded young stellar objects in Perseus, that reveal motions of infall, outflow, rotation, and turbulence in the dense gas around its two brightest continuum objects, 4A and 4B. These data have finest angular resolution of approximately 2" (0.0034 pc) and finest velocity resolution of 0.13 km/s. Infall motions are seen from inverse P-Cygni profiles observed in H2CO 3_12-2_11 toward both objects, but also in CS 3-2 and N2H+ 1-0 toward 4A, providing the least ambiguous evidence for such motions toward low-mass protostellar objects. Outflow motions are probed by bright line wings of H2CO 3_12-2_11 and CS 3-2 observed at positions offset from 4A and 4B, likely tracing dense cavity walls. Rotational motions of dense gas are traced by a systematic variation of the N2H+ line velocities, and such variations are found around 4A but not around 4B. Turbulent motions appear reduced with scale, given N2H+ line widths around both 4A and 4B that are narrower by factors of 2 or 3 than those seen from single-dish observations. Minimum observed line widths of approximately 0.2 km/s provide a new low, upper bound to the velocity dispersion of the parent core to IRAS 4, and demonstrate that turbulence within regions of clustered star formation can be reduced significantly. A third continuum object in the region, 4B', shows no detectable line emission in any of the observed molecular species.Comment: LateX, 51 pages, 9 figures, accepted by Ap

An evolved disk surrounding the massive main sequence star MWC 297?

We present the results of the interferometric observations of the circumstellar disk surrounding MWC 297 in the continuum at 230 GHz (1.3 mm) and in the (J=2-1) rotational transitions of $^{12}$CO,$^{13}$CO and C$^{18}$O using the Submillimeter Array. At a distance of 250 pc, MWC 297 is one of the closest, young massive stars (M$_{\star}$ $\sim$10 M$_{\odot}$) to us. Compact continuum emission is detected towards MWC 297 from which we estimate a disk mass (gas+dust) of 0.07 M$_{\odot}$ and a disk radius of $\le$ 80 AU. Our result demonstrates that circumstellar disks can survive around massive stars well into their main sequence phase even after they have become optically visible. Complementing our observations with the data compiled from the literature, we find the submm dust opacity index $\beta$ to be between 0.1 and 0.3. If the emission is optically thin, the low value of $\beta$ indicates the presence of relatively large grains in the disk, possibly because of grain growth. We do not detect any CO emission associated with the continuum source. We argue that the $^{13}$CO emission from the disk is likely optically thin, in which case, we derive an upper limit to the gas mass which implies significant depletion of molecular gas in the disk. The mass of this disk and the evolutionary trends observed are similar to those found for intermediate mass Herbig Ae stars and low mass T Tauri stars.Comment: 4 pages, 3 Figures, accepted for publication in ApJ

Molecular Evolution in Collapsing Prestellar Cores

We have investigated the evolution and distribution of molecules in collapsing prestellar cores via numerical chemical models, adopting the Larson-Penston solution and its delayed analogues to study collapse. Molecular abundances and distributions in a collapsing core are determined by the balance among the dynamical, chemical and adsorption time scales. When the central density n_H of a prestellar core with the Larson-Penston flow rises to 3 10^6 cm^{-3}, the CCS and CO column densities are calculated to show central holes of radius 7000 AU and 4000 AU, respectively, while the column density of N2H+ is centrally peaked. These predictions are consistent with observations of L1544. If the dynamical time scale of the core is larger than that of the Larson-Penston solution owing to magnetic fields, rotation, or turbulence, the column densities of CO and CCS are smaller, and their holes are larger than in the Larson-Penston core with the same central gas density. On the other hand, N2H+ and NH3 are more abundant in the more slowly collapsing core. Therefore, molecular distributions can probe the collapse time scale of prestellar cores. Deuterium fractionation has also been studied via numerical calculations. The deuterium fraction in molecules increases as a core evolves and molecular depletion onto grains proceeds. When the central density of the core is n_H=3 10^6 cm^{-3}, the ratio DCO+/HCO+ at the center is in the range 0.06-0.27, depending on the collapse time scale and adsorption energy; this range is in reasonable agreement with the observed value in L1544.Comment: 21 pages, 17 figure

Macro-scale ore-controlling faults revealed by micro-geochemical anomalies

Whereas the mechanism of fluid flow, and thus structural control, linked with mineral deposit formation is quite understood, the specific structures that likely provided controls on mineralization at certain geographic scales are not readily known for a given region unless it is well-explored. This contributes uncertainty in mineral prospectivity analysis in poorly-explored regions (or greenfields). Here, because the spatial distribution of mineral deposits has been postulated to be fractals (i.e., the patterns of these features are self-similar across a range of spatial scales), we show for the first time that micro-geochemical anomalies (as proxies of micro-scale patterns of ore minerals), from few discrete parts of the Sossego iron-oxide copper-gold (IOCG) deposit in the Carajas Mineral Province (CMP) of Brazil, exhibit trends of macro-scale faults that are known to have controlled IOCG mineralization in the CMP. The methodology described here, which led to this novel finding, would help towards detecting mineral exploration targets as well as help towards understanding structural controls on mineralization in greenfields9CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2014-9/401316; 2017-3/3097122015/11186-3FAPESP (Sao Paulo Research Foundation)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2015/11186-3]; CNPq (Brazilian National Council for Scientific and Technological Development)National Council for Scientific and Technological Development (CNPq) [2014-9/401316, 2017-3/309712]; Vale Compan

Constraint on ion-neutral drift velocity in the Class 0 protostar B335 from ALMA observations

Ambipolar diffusion can cause a velocity drift between ions and neutrals. This is one of the non-ideal MHD effects proposed to enable the formation of Keplerian disks with sizes of tens of au. To observationally study ambipolar diffusion in collapsing protostellar envelopes, we compare gas kinematics traced by the H13CO+ (3-2) and C18O (2-1) lines in the Class 0 protostar B335 obtained with our ALMA observations. A central compact (~1"-2") component that is elongated perpendicular to the outflow direction and exhibits a clear velocity gradient along the outflow direction is observed in both lines and most likely traces the infalling flattened envelope. We constructed kinematical models to fit the observed velocity structures and to measure the infalling velocities of the ionized and neutral gas on a 100 au scale in B335. The infalling velocities in the H13CO+ and C18O emission are both measured to be 0.85+/-0.2 km/s at a radius of 100 au, suggesting that the velocity drift between the ionized and neutral gas is at most 0.3 km/s at a radius of 100 au. The Hall parameter for H13CO+ is estimated to be >>1 on a 100 au scale in B335, so that H13CO+ is expected to be attached to the magnetic field. Our non-detection or upper limit of the velocity drift between ions and neutrals could suggest that the magnetic field remains rather well coupled to the bulk neutral material on a 100 au scale in this source, and that any significant field-matter decoupling, if present, likely occurs only on a smaller scale, leading to an accumulation of magnetic flux and thus efficient magnetic braking in the inner envelope. However, because of our limited angular resolution, we cannot rule out a significant ambipolar drift only in the midplane of the infalling envelope. Future observations with higher angular resolutions (~0.1") are needed to examine this possibility and ambipolar diffusion on a smaller scale.Comment: Accepted by A&

PROSAC: A Submillimeter Array Survey of Low-Mass Protostars. I. Overview of Program: Envelopes, Disks, Outflows and Hot Cores

This paper presents a large spectral line and continuum survey of 8 deeply embedded, low-mass protostellar cores using the Submillimeter Array. Each source was observed in high excitation lines of some of the most common molecular species, CO, HCO+, CS, SO, H2CO, CH3OH and SiO. Line emission from 11 species originating from warm and dense gas have been imaged at high angular resolution (1-3"; typically 200-600 AU) together with continuum emission at 230 GHz (1.3 mm) and 345 GHz (0.8 mm). Compact continuum emission is observed for all sources which likely originates in marginally optically thick circumstellar disks, with typical lower limits to their masses of 0.1 M_sun (1-10% of the masses of their envelopes) and having a dust opacity law with beta approximately 1. Prominent outflows are present in CO 2-1 observations in all sources: the most diffuse outflows are found in the sources with the lowest ratios of disk-to-envelope mass, and it is suggested that these sources are in a phase where accretion of matter from the envelope has almost finished and the remainder of the envelope material is being dispersed by the outflows. Other characteristic dynamical signatures are found with inverse P Cygni profiles indicative of infalling motions seen in the 13CO 2-1 lines toward NGC1333-IRAS4A and -IRAS4B. Outflow-induced shocks are present on all scales in the protostellar environments and are most clearly traced by the emission of CH3OH in NGC1333-IRAS4A and -IRAS4B. These observations suggest that the emission of CH3OH and H2CO from these proposed "hot corinos" are related to the shocks caused by the protostellar outflows. Only one source, NGC1333-IRAS2A, has evidence for hot, compact CH3OH emission coincident with the embedded protostar.Comment: Accepted for publication in ApJ (52 pages; 9 figures). Abstract abridge