880 research outputs found
A revised distance to IRAS 162932422 from VLBA astrometry of associated water masers
IRAS 16293-2422 is a very well studied young stellar system seen in
projection towards the L1689N cloud in the Ophiuchus complex. However, its
distance is still uncertain with a range of values from 120 pc to 180 pc. Our
goal is to measure the trigonometric parallax of this young star by means of
HO maser emission. We use archival data from 15 epochs of VLBA observations
of the 22.2 GHz water maser line. By modeling the displacement on the sky of
the HO maser spots, we derived a trigonometric parallax of mas,
corresponding to a distance of pc. This new distance is in
good agreement with recent values obtained for other magnetically active young
stars in the L1689 cloud. We relate the kinematics of these masers with the
outflows and the recent ejections powered by source A in the system.Comment: 14 pages, 6 tables, 8 figures. Accepted to be published in Astronomy
\& Astrophysic
Site selection of the Colombian antarctic research station based on fuzzy-topsis algorithm
By 2025 the Republic of Colombia aims to be an advisory member
of the Antarctic Treaty System (ATS) and the installation of a scientific station is
necessary to upscale the scientific capabilities. The aim of this paper is showing
the results of the implementation of a Fuzzy TOPSIS algorithm for site selection
of the Colombian Antarctic Scientific Station. A three-phase methodology was AQ1
proposed, and the obtained results allowed to identify the optimum location for
the station, considering key success factors and regulatory constraints
A global view on star formation: The GLOSTAR Galactic plane survey VIII. Formaldehyde absorption in Cygnus~X
Cygnus X is one of the closest and most active high-mass star-forming regions
in our Galaxy, making it one of the best laboratories for studying massive star
formation. As part of the GLOSTAR Galactic plane survey, we performed large
scale simultaneous HCO (1-1) spectral line and radio
continuum imaging observations toward Cygnus X at 6 cm with the
Karl G. Jansky Very Large Array and the Effelsberg-100 m radio telescope. Our
Effelsberg observations reveal widespread HCO (1-1)
absorption with a spatial extent of 50 pc in Cygnus~X for the first
time. On large scales of 4.4 pc, the relative orientation between local
velocity gradient and magnetic field tends to be more parallel at H
column densities of 1.8~cm. On the smaller
scale of 0.17 pc, our VLA+Effelsberg combined data reveal HCO absorption
only toward three bright H{\scriptsize II} regions. Our observations
demonstrate that HCO (1-1) is commonly optically thin.
Kinematic analysis supports the assertion that molecular clouds generally
exhibit supersonic motions on scales of 0.17-4.4 pc. We show a non-negligible
contribution of the cosmic microwave background radiation in producing extended
absorption features in Cygnus X. Our observations suggest that HCO
() can trace molecular gas with H column densities of
cm. The ortho-HCO fractional abundance
with respect to H has a mean value of 7.0. A comparison
of velocity dispersions on different linear scales suggests that the dominant
km s velocity component in the prominent DR21 region has nearly
identical velocity dispersions on scales of 0.17-4.4 pc, which deviates from
the expected behavior of classic turbulence.Comment: 27 pages, 23 figures, accepted for publication in A&
A global view on star formation: The GLOSTAR Galactic plane survey. VII. Supernova remnants in the Galactic longitude range
Context. While over 1000 supernova remnants (SNRs) are estimated to exist in
the Milky Way, only less than 400 have been found to date. In the context of
this apparent deficiency, more than 150 SNR candidates were recently identified
in the D-configuration Very Large Array (VLA-D) continuum images of the 4--8
GHz global view on star formation (GLOSTAR) survey, in the Galactic longitude
range . Aims. We attempt to find evidence of nonthermal
synchrotron emission from 35 SNR candidates in the region of Galactic longitude
range , and also to study the radio continuum emission
from the previously confirmed SNRs in this region. Methods. Using the
short-spacing corrected GLOSTAR VLA-D+Effelsberg images, we measure
GHz total and linearly polarized flux densities of the SNR candidates and the
SNRs that were previously confirmed. We also attempt to determine the spectral
indices by measuring flux densities from complementary Galactic plane surveys
and from the temperature-temperature plots of the GLOSTAR-Effelsberg images.
Results. We provide evidence of nonthermal emission from four candidates that
have spectral indices and polarization consistent with a SNR origin, and,
considering their morphology, we are confident that three of these
(G28.36+0.21, G28.78-0.44, and G29.38+0.10) are indeed SNRs. However, about
of the candidates have spectral index measurements that indicate thermal
emission, and the rest of them are too faint to have a good constraint on the
spectral index yet. Conclusions. Additional observations at longer wavelengths
and higher sensitivities will shed more light on the nature of these
candidates. A simple Monte-Carlo simulation reiterates the view that future
studies must persist with the current strategy of searching for SNRs with small
angular size to solve the problem of the Milky Way's missing SNRs.Comment: To be published in A&A. 21 pages, 15 figure
Blind separation of overlapping partials in harmonic musical notes using amplitude and phase reconstruction
The importance of conserving Mexico's tomato agrodiversity to research plant biochemistry under different climates
Tomatoes are important to agriculture, human nutrition and cuisines globally. However, many commercial tomato varieties, including the saladette that dominates the North American market, are highly sensitive to environmental changes that impact yields and critical biochemical pathways including carotenoids and isoprenoids that influence nutritional content and flavour. We highlight the potential of tomato agrodiversity, notably its genetic diversity, as an undervalued research tool for understanding environmental regulation of plant biochemistry under different climates. Yet, tomato genetic diversity in Mexico, the major centre of tomato domestication, is not formally described or protected. We propose that transdisciplinary efforts are essential to identify, conserve and research these globally significant genetic resources
Charge separation relative to the reaction plane in Pb-Pb collisions at TeV
Measurements of charge dependent azimuthal correlations with the ALICE
detector at the LHC are reported for Pb-Pb collisions at TeV. Two- and three-particle charge-dependent azimuthal correlations in
the pseudo-rapidity range are presented as a function of the
collision centrality, particle separation in pseudo-rapidity, and transverse
momentum. A clear signal compatible with a charge-dependent separation relative
to the reaction plane is observed, which shows little or no collision energy
dependence when compared to measurements at RHIC energies. This provides a new
insight for understanding the nature of the charge dependent azimuthal
correlations observed at RHIC and LHC energies.Comment: 12 pages, 3 captioned figures, authors from page 2 to 6, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/286
Transverse sphericity of primary charged particles in minimum bias proton-proton collisions at , 2.76 and 7 TeV
Measurements of the sphericity of primary charged particles in minimum bias
proton--proton collisions at , 2.76 and 7 TeV with the ALICE
detector at the LHC are presented. The observable is linearized to be collinear
safe and is measured in the plane perpendicular to the beam direction using
primary charged tracks with GeV/c in . The
mean sphericity as a function of the charged particle multiplicity at
mid-rapidity () is reported for events with different
scales ("soft" and "hard") defined by the transverse momentum of the leading
particle. In addition, the mean charged particle transverse momentum versus
multiplicity is presented for the different event classes, and the sphericity
distributions in bins of multiplicity are presented. The data are compared with
calculations of standard Monte Carlo event generators. The transverse
sphericity is found to grow with multiplicity at all collision energies, with a
steeper rise at low , whereas the event generators show the
opposite tendency. The combined study of the sphericity and the mean with multiplicity indicates that most of the tested event generators
produce events with higher multiplicity by generating more back-to-back jets
resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with
tune PERUGIA-2011 exhibits a noticeable improvement in describing the data,
compared to the other tested generators.Comment: 21 pages, 9 captioned figures, 3 tables, authors from page 16,
published version, figures from
http://aliceinfo.cern.ch/ArtSubmission/node/308
Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at = 5.02 TeV
Two-particle angular correlations between unidentified charged trigger and
associated particles are measured by the ALICE detector in p-Pb collisions at a
nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum
range 0.7 5.0 GeV/ is examined,
to include correlations induced by jets originating from low
momen\-tum-transfer scatterings (minijets). The correlations expressed as
associated yield per trigger particle are obtained in the pseudorapidity range
. The near-side long-range pseudorapidity correlations observed in
high-multiplicity p-Pb collisions are subtracted from both near-side
short-range and away-side correlations in order to remove the non-jet-like
components. The yields in the jet-like peaks are found to be invariant with
event multiplicity with the exception of events with low multiplicity. This
invariance is consistent with the particles being produced via the incoherent
fragmentation of multiple parton--parton scatterings, while the yield related
to the previously observed ridge structures is not jet-related. The number of
uncorrelated sources of particle production is found to increase linearly with
multiplicity, suggesting no saturation of the number of multi-parton
interactions even in the highest multiplicity p-Pb collisions. Further, the
number scales in the intermediate multiplicity region with the number of binary
nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation.Comment: 23 pages, 6 captioned figures, 1 table, authors from page 17,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/161
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