27 research outputs found
Facing differences with an open mind: Openness to Experience, salience of intra-group differences, and performance of diverse groups.
This study examined how the performance of diverse teams is affected by member openness to experience and the extent to which team reward structure emphasizes intragroup differences. Fifty-eight heterogeneous four-person teams engaged in an interactive task. Teams in which reward structure converged with diversity (i.e., "faultline" teams) performed more poorly than teams in which reward structure cut across differences between group members or pointed to a "superordinate identity." High openness to experience positively influenced teams in which differences were salient (i.e., faultline and "cross-categorized" teams) but not teams with a superordinate identity. This effect was mediated by information elaboration
ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris
Context. At the end of their lives, most stars lose a significant amount of mass through a stellar wind. The specific physical and chemical circumstances that lead to the onset of the stellar wind for cool luminous stars are not yet understood. Complex geometrical morphologies in the circumstellar envelopes prove that various dynamical and chemical processes are interlocked and that their relative contributions are not easy to disentangle. Aims. We aim to study the inner-wind structure (R< 250 R⋆) of the well-known red supergiant VY CMa, the archetype for the class of luminous red supergiant stars experiencing high mass loss. Specifically, the objective is to unravel the density structure in the inner envelope and to examine the chemical interaction between gas and dust species. Methods. We analyse high spatial resolution (~0.̋24×0.̋13) ALMA science verification (SV) data in band 7, in which four thermal emission lines of gaseous sodium chloride (NaCl) are present at high signal-to-noise ratio. Results. For the first time, the NaCl emission in the inner wind region of VY CMa is spatially resolved. The ALMA observations reveal the contribution of up to four different spatial regions. The NaCl emission pattern is different compared to the dust continuum and TiO2 emission already analysed from the ALMA SV data. The emission can be reconciled with an axisymmetric geometry, where the lower density polar/rotation axis has a position angle of ~50° measured from north to east. However, this picture cannot capture the full morphological diversity, and discrete mass ejection events need to be invoked to explain localized higher-density regions. The velocity traced by the gaseous NaCl line profiles is significantly lower than the average wind terminal velocity, and much slower than some of the fastest mass ejections, signalling a wide range of characteristic speeds for the mass loss. Gaseous NaCl is detected far beyond the main dust condensation region. Realising the refractory nature of this metal halide, this hints at a chemical process that prevents all NaCl from condensing onto dust grains. We show that in the case of the ratio of the surface binding temperature to the grain temperature being ~50, only some 10% of NaCl remains in gaseous form while, for lower values of this ratio, thermal desorption efficiently evaporates NaCl. Photodesorption by stellar photons does not seem to be a viable explanation for the detection of gaseous NaCl at 220 R⋆ from the central star, so instead, we propose shock-induced sputtering driven by localized mass ejection events as an alternative. Conclusions. The analysis of the NaCl lines demonstrates the capabilities of ALMA to decode the geometric morphologies and chemical pathways prevailing in the winds of evolved stars. These early ALMA results prove that the envelopes surrounding evolved stars are far from homogeneous, and that a variety of dynamical and chemical processes dictate the wind structure
ATOMIUM: Probing the inner wind of evolved O-rich stars with new, highly excited HO and OH lines
Water and the hydroxyl radical are major constituents of the envelope of
O-rich late-type stars. Transitions involving energy levels that are highly
excited have been observed in both HO and OH. These and more recently
discovered transitions can now be observed at a high sensitivity and angular
resolution with the ALMA Array. Spectra and maps of HO and OH observed with
an angular resolution of 20 to 200 mas were obtained at two epochs with
the ALMA array. Observations with the Compact Array were also used to check for
time variability of water transitions. Radiative transfer models of water were
revisited to characterize masing conditions and up-to-date chemical models were
used for comparison with our observations. Ten rotational transitions of HO
with energies up to 9000 K were observed in various vibrational states. All but
one are new detections in space, and from these we have derived accurate rest
frequencies. Hyperfine split -doubling transitions in v = 0, J = 27/2
and 29/2 levels of the state and, and 35/2 of the
state of OH with excitation energies up to 8900 K were also
observed. Four of these transitions are new detections in space. Combining our
measurements with earlier observations of OH, the v = 0 and v = 1
-doubling frequencies have been improved. Our HO maps show compact
emission and extensions up to twelve stellar radii or more. The 268.149 GHz
emission line of water in the v = 2 state is time variable, tends to be
masing with dominant radiative pumping, and is widely excited. The widespread
but weaker 262.898 GHz water line in v = 1 also shows signs of maser
emission. Emission and absorption of both HO and OH reveal an infall of
matter and complex kinematics influenced by binarity. From our observed column
densities, we derived OH/HO abundance ratios in a few stars.Comment: 41 pages with references and 25 figures in main text. 4 Tables in
Appendix A. 10 figures in Appendix B. 2 figures in Appendix C. 14 figures in
Appendix D. 5 figures in Appendix E. 2 figures in Appendix
ALMA spectrum of the extreme OH/IR star OH 26.5+0.6
We present ALMA band 7 data of the extreme OH/IR star, OH 26.5+0.6. In addition to lines of CO and its isotopologues, the circumstellar envelope also exhibits a number of emission lines due to metal-containing molecules, e.g., NaCl and KCl. A lack of C18O is expected, but a non-detection of C17O is puzzling given the strengths of H217O in Herschel spectra of the star. However, a line associated with Si17O is detected. We also report a tentative detection of a gas-phase emission line of MgS. The ALMA spectrum of this object reveals intriguing features which may be used to investigate chemical processes and dust formation during a high mass-loss phase...