1,149 research outputs found
FAUST VIII. The protostellar disk of VLA 1623-2417 W and its streamers imaged by ALMA
More than 50% of solar-mass stars form in multiple systems. It is therefore
crucial to investigate how multiplicity affects the star and planet formation
processes at the protostellar stage. We report continuum and CO (2-1)
observations of the VLA 1623-2417 protostellar system at 50 au angular
resolution as part of the ALMA Large Program FAUST. The 1.3 mm continuum probes
the disks of VLA 1623A, B, and W, and the circumbinary disk of the A1+A2
binary. The CO emission reveals, for the first time, the gas in the
disk-envelope of VLA 1623W. We estimate the dynamical mass of VLA 1623W,
M, and the mass of its disk, M. CO also reveals streamers that
extend up to 1000 au, spatially and kinematically connecting the envelope and
outflow cavities of the A1+A2+B system with the disk of VLA 1623W. The presence
of the streamers, as well as the spatial (1300 au) and velocity
(2.2 km/s) offset of VLA 1623W suggest that either sources W and A+B
formed in different cores, interacting between them, or that source W has been
ejected from the VLA 1623 multiple system during its formation. In the latter
case, the streamers may funnel material from the envelope and cavities of VLA
1623AB onto VLA 1623W, thus concurring to set its final mass and chemical
content.Comment: 10 pages, 5 figures, accepted by MNRA
A Triple Protostar System Formed via Fragmentation of a Gravitationally Unstable Disk
Binary and multiple star systems are a frequent outcome of the star formation
process, and as a result, almost half of all sun-like stars have at least one
companion star. Theoretical studies indicate that there are two main pathways
that can operate concurrently to form binary/multiple star systems: large scale
fragmentation of turbulent gas cores and filaments or smaller scale
fragmentation of a massive protostellar disk due to gravitational instability.
Observational evidence for turbulent fragmentation on scales of 1000~AU has
recently emerged. Previous evidence for disk fragmentation was limited to
inferences based on the separations of more-evolved pre-main sequence and
protostellar multiple systems. The triple protostar system L1448 IRS3B is an
ideal candidate to search for evidence of disk fragmentation. L1448 IRS3B is in
an early phase of the star formation process, likely less than 150,000 years in
age, and all protostars in the system are separated by 200~AU. Here we
report observations of dust and molecular gas emission that reveal a disk with
spiral structure surrounding the three protostars. Two protostars near the
center of the disk are separated by 61 AU, and a tertiary protostar is
coincident with a spiral arm in the outer disk at a 183 AU separation. The
inferred mass of the central pair of protostellar objects is 1 M,
while the disk surrounding the three protostars has a total mass of 0.30
M_{\sun}. The tertiary protostar itself has a minimum mass of 0.085
M. We demonstrate that the disk around L1448 IRS3B appears susceptible
to disk fragmentation at radii between 150~AU and 320~AU, overlapping with the
location of the tertiary protostar. This is consistent with models for a
protostellar disk that has recently undergone gravitational instability,
spawning one or two companion stars.Comment: Published in Nature on Oct. 27th. 24 pages, 8 figure
Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV
The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8 TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum
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