1,841 research outputs found
A multiple system of high-mass YSOs surrounded by disks in NGC7538 IRS1
NGC7538 IRS1 is considered the best high-mass accretion disk candidate around
an O-type young star in the northern hemisphere. We investigated the 3D
kinematics and dynamics of circumstellar gas with very high linear resolution,
from tens to 1500 AU, with the ultimate goal of building a comprehensive
dynamical model for this YSO. We employed four different observing epochs of
EVN data at 6.7 GHz, spanning almost eight years, which enabled us to measure,
besides line-of-sight (l.o.s.) velocities and positions, also l.o.s.
accelerations and proper motions of methanol masers. In addition, we imaged
with the JVLA-B array highly-excited ammonia inversion lines, from (6,6) to
(13,13), which enabled us to probe the hottest molecular gas very close to the
exciting source(s). We found five 6.7 GHz maser clusters which are distributed
over a region extended N-S across ~1500 AU and are associated with three peaks
of the radio continuum. We proposed that these maser clusters identify three
individual high-mass YSOs, named IRS1a, IRS1b, and IRS1c. We modeled the maser
clusters in IRS1a and IRS1b in terms of edge-on disks in centrifugal
equilibrium. In the first case, masers may trace a quasi-Keplerian thin disk,
orbiting around a high-mass YSO, IRS1a, of up to 25 solar masses. This YSO
dominates the bolometric luminosity of the region. The second disk is both
massive (<16 Msun within ~500 AU) and thick, and the mass of the central YSO,
IRS1b, is constrained to be at most a few solar masses. In summary, we present
compelling evidence that NGC7538 IRS1 is not forming just one single high-mass
YSO, but consists of a multiple system of high-mass YSOs, which are surrounded
by accretion disks, and are probably driving individual outflows. This new
model naturally explains all the different orientations and disk/outflow
structures proposed for the region in previous models.Comment: 34 pages, 18 figures, accepted for publication in Astronomy &
Astrophysic
Does your surname affect the citability of your publications?
Prior investigations have offered contrasting results on a troubling
question: whether the alphabetical ordering of bylines confers citation
advantages on those authors whose surnames put them first in the list. The
previous studies analyzed the surname effect at publication level, i.e. whether
papers with the first author early in the alphabet trigger more citations than
papers with a first author late in the alphabet. We adopt instead a different
approach, by analyzing the surname effect on citability at the individual
level, i.e. whether authors with alphabetically earlier surnames result as
being more cited. Examining the question at both the overall and discipline
levels, the analysis finds no evidence whatsoever that alphabetically earlier
surnames gain advantage. The same lack of evidence occurs for the subpopulation
of scientists with very high publication rates, where alphabetical advantage
might gain more ground. The field of observation consists of 14,467 scientists
in the sciences
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