- Published on Tuesday, 05 December 2017 08:00
In section 1. Letters
Detection of CS in Neptune’s atmosphere from ALMA observations
Evidence is mounting that Nepune, like Jupiter did with comet Shoemaker-Levy 9, suffered a large cometary impact that polluted its stratosphere in CO, CS and HCN. In the case of Neptune however, the comet was large (~4 km diameter) and the impact must have occurred ~1000 years ago. Moreno et al. use ALMA to detect for the first time the presence of CS in Neptune's stratosphere, and show that it is strongly depleted with respect to CO. Because of its different chemical properties, CS can stick to aerosols in the deeper stratosphere and be progressively lost. The timescale to diffuse to these regions and lead to the observed depletion is estimated to be ~1000 years.
- Published on Wednesday, 29 November 2017 08:00
In section 4. Extragalactic astronomy
An ALMA survey of submillimeter galaxies in the COSMOS field: Multiwavelength counterparts and redshift distribution
Submillimeter galaxies (SMGs) represent a key population of high redshift star-forming galaxies shedding light on the epoch of galaxy assembly and peak star formation. Surveys of SMGs began in 1997 with sensitive bolometers such as SCUBA, but on single dish telescopes with wide beams, leading to confusion of sources. Recently several SMG surveys in the southern hemisphere with ALMA have shown how previous sources may split into several objects. Their redshift distributions varied from one to six, with a median of around two but with large variations due to different selection biases. This work presents ALMA observations of 129 fields in the COSMOS region at 1.25 mm, detecting 152 galaxies. The sources were selected from a sample of 129 SMGs that were initially discovered with the AzTEC camera on ASTE telescope, and are now identified with high resolution 1.25 mm ALMA imaging. Together with the multiwavelength photometric data available in COSMOS, this survey can now identify SMG counterparts and determine their photometric redshifts. The results are consistent with several previous submillimeter galaxy surveys, and show a median redshift of z=2.48. In addition, 33 AzTEC sources have been resolved into multi-component systems and our redshifts suggest that nine of them are likely to be physically associated.
- Published on Tuesday, 28 November 2017 08:00
In section 2. Astrophysical processes
Dissipation of the striped pulsar wind
The formation and development of pulsar winds, and their associated energization and particle acceleration have been daunting theoretical problems for decades. This paper presents a massive, self-consistent calculation of the time development of the wind current sheet of a split dipole magnetic field extending from the neutron star surface. Reconnection is seen throughout the stripping, especially close to thelight cylinder. Trace particle trajectories are shown to illustrate thestochastic and bulk dynamics. Radial acceleration profiles are providedand, in one of the truly novel features of the paper, spectral emissivities, and pulse profiles and their fine structure are recoveredfrom the simulations.
- Published on Monday, 13 November 2017 08:00
In section 6. Interstellar and circumstellar matter
Search for hydrogen-helium molecular species in space
The search for helium in molecular form has been a long standing challenge in astrophysics. Searches for HeH+ have repeatedly come up empty-handed although hydrogenated heavier noble gases have been detected in the interstellar medium. This study proposes an alternative candidate,HeH3+, based on the ubiquitous presence of the H3+ ion in cosmic environments. The authors compute the binding energy, vibrational states, and radiative association rates through two channels. They propose that the HeH+ + H2 dominates by more than four orders of magnitude over the He + H3+ under a wide range of temperatures. Thepaper also provides frequencies to aid in the search for this intriguing molecule whose presence may be important in the context of early universe chemistry.
- Published on Monday, 06 November 2017 08:00
In section 6. Interstellar and circumstellar medium
Interferometric view of the circumstellar envelopes of northern FU Orionis-type stars
The FU Ori stage of protostar formation is one of intense photometric and spectroscopic variability, lasting decades, and indicating a phase of enhanced mass transfer onto the forming protostar. The outbursts should also involve enhanced stellar outflows, This paper presents thefirst comprehensive spectrophotometric-interferometric millimeter wavelength study using the IRAM telescopes of the circumstellar environments of these stars including the peripheral regions of their accretion disks and the envelope in superb dynamical and spatial detailin two optically thin isotopes of CO. Outflow was detected in only three stars, but these were all well resolved. Compact structures were seen in 5/8 of the sample stars and the structures produced in channel maps. The combination of star and/or inner disk-like signatures and those of themore extended envelope are consistent with the picture of the FU Ori objects as the transition between completely enshrouded central objectsand the T Tau stage in which the central star dominates the disk.
- Published on Tuesday, 24 October 2017 08:00
In section 6. Interstellar and circumstellar matter
Fibers in the NGC 1333 proto-cluster
The authors carried out a high-sensitivity study of the internal structure, density, temperature, and kinematics of the dense gas content in the Perseus embedded cluster NGC1333 to investigate the initial gas properties in young proto-clusters. They identified 14 velocity-coherent, (tran-)sonic structures within NGC1333, with physical and kinematic properties that are similar to those of quiescent, star-forming fibers previously identified in low-mass star-forming clouds. These fibers are arranged in a complex spatial network, build-up the observed total column density, and contain the dense cores and protostars in this cloud. From a comparison with Taurus, they propose that the observational dichotomy between clustered and non-clustered star-forming regions might be naturally explained by the distinct spatial density of star-forming fibers in these environments.