502 research outputs found
Testing the Disk Regulation Paradigm with Spitzer Observations. II. A Clear Signature of Star-Disk Interaction in NGC 2264 and the Orion Nebula Cluster
Observations of PMS star rotation periods reveal slow rotators in young
clusters of various ages, indicating that angular momentum is somehow removed
from these rotating masses. The mechanism by which spin-up is regulated as
young stars contract has been one of the longest-standing problems in star
formation. Attempts to observationally confirm the prevailing theory that
magnetic interaction between the star and its circumstellar disk regulates
these rotation periods have produced mixed results. In this paper, we use the
unprecedented disk identification capability of the Spitzer Space Telescope to
test the star-disk interaction paradigm in two young clusters, NGC 2264 and the
Orion Nebula Cluster (ONC). We show that once mass effects and sensitivity
biases are removed, a clear increase in the disk fraction with period can be
observed in both clusters across the entire period range populated by cluster
members. We also show that the long-period peak (P 8 days) of the bimodal
distribution observed for high-mass stars in the ONC is dominated by a
population of stars possessing a disk, while the short-period peak (P 2
days) is dominated by a population of stars without a disk. Our results
represent the strongest evidence to date that star-disk interaction regulates
the angular momentum of these young stars. This study will make possible
quantitative comparisons between the observed period distributions of stars
with and without a disk and numerical models of the angular momentum evolution
of young stars.Comment: 31 pages, 7 figures, 2 tables. Accepted for publication in Ap
Pair of Heavy-Exotic-Quarks at LHC
We study the production and signatures of heavy exotic quarks pairs at LHC in
the framework of the vector singlet model (VSM), vector doublet model (VDM) and
fermion-mirror-fermion (FMF) model. The pair production cross sections for the
electroweak and strong sector are computed.Comment: 7 pages, 6 figures. accept at Int. Jour. of Mod. Phy
Recommended from our members
PPAR gamma pro12Ala polymorphism and type 2 diabetes: a study in a spanish cohort
Type 2 diabetes (T2D) is a disease whose occurrence is increasing prevalent in westernized civilizations and is responsible for the proliferation in the morbidity and total mortality of patients with cardiovascular diseases, worldwide. However, the complexity in the treatment and prevention of T2D arises from the intricacy of the many physical and biological factors involved in its etiology. Impaired pathways for insulin signaling have been implicated as one the many factors in the development of T2D Individual peroxisome proliferator-activated receptors (PPARs) have previously exhibited associations with alterations of lipid profiles, fat tissue and T2D and displayed complications derived from high levels of glucose. However, PPARgamma has not yet been associated with the development or developmental pathways of T2D. We performed an observational study a Spanish cohort in order to better understand the association between the SNP PPARgamma polymorphism Pro12Ala in our patients and the incidence of T2D and other cardiovascular complications. We study did not find a statistically significant relationship between the Pro12Ala and T2D development in our cohort, future observations will help us to know the association with vascular disease in patients with T2D
The ALMA Early Science View of FUor/EXor objects. III. The Slow and Wide Outflow of V883 Ori
We present Atacama Large Millimeter/ sub-millimeter Array (ALMA) observations
of V883 Ori, an FU Ori object. We describe the molecular outflow and envelope
of the system based on the CO and CO emissions, which together
trace a bipolar molecular outflow. The CO emission traces the rotational
motion of the circumstellar disk. From the CO blue-shifted emission, we
estimate a wide opening angle of 150 for the outflow
cavities. Also, we find that the outflow is very slow (characteristic velocity
of only 0.65 km~s), which is unique for an FU Ori object. We calculate
the kinematic properties of the outflow in the standard manner using the
CO and CO emissions. In addition, we present a P Cygni profile
observed in the high-resolution optical spectrum, evidence of a wind driven by
the accretion and being the cause for the particular morphology of the
outflows. We discuss the implications of our findings and the rise of these
slow outflows during and/or after the formation of a rotationally supported
disk.Comment: 12 pages, 7 figures, 2 tables. Accepte
HD 169142 in the eyes of ZIMPOL/SPHERE
We present new data of the protoplanetary disc surrounding the Herbig Ae/Be
star HD 169142 obtained in the very broad-band (VBB) with the Zurich imaging
polarimeter (ZIMPOL), a sub-system of the Spectro-Polarimetric High-contrast
Exoplanet REsearch instrument (SPHERE) at the Very Large Telescope (VLT). Our
Polarimetric Differential Imaging (PDI) observations probe the disc as close as
0.03" (3.5au) to the star and are able to trace the disc out to ~1.08"
(~126au). We find an inner hole, a bright ring bearing substructures around
0.18" (21au), and an elliptically shaped gap stretching from 0.25" to 0.47"
(29-55au). Outside of 0.47", the surface brightness drops off, discontinued
only by a narrow annular brightness minimum at ~0.63"-0.74" (74-87au). These
observations confirm features found in less-well resolved data as well as
reveal yet undetected indications for planet-disc interactions, such as
small-scale structures, star-disk offsets, and potentially moving shadows.Comment: Accepted for publication in MNRA
A census of Oph candidate members from Gaia DR2
The Ophiuchus cloud complex is one of the best laboratories to study the
earlier stages of the stellar and protoplanetary disc evolution. The wealth of
accurate astrometric measurements contained in the Gaia Data Release 2 can be
used to update the census of Ophiuchus member candidates. We seek to find
potential new members of Ophiuchus and identify those surrounded by a
circumstellar disc. We constructed a control sample composed of 188 bona fide
Ophiuchus members. Using this sample as a reference we applied three different
density-based machine learning clustering algorithms (DBSCAN, OPTICS, and
HDBSCAN) to a sample drawn from the Gaia catalogue centred on the Ophiuchus
cloud. The clustering analysis was applied in the five astrometric dimensions
defined by the three-dimensional Cartesian space and the proper motions in
right ascension and declination. The three clustering algorithms systematically
identify a similar set of candidate members in a main cluster with astrometric
properties consistent with those of the control sample. The increased
flexibility of the OPTICS and HDBSCAN algorithms enable these methods to
identify a secondary cluster. We constructed a common sample containing 391
member candidates including 166 new objects, which have not yet been discussed
in the literature. By combining the Gaia data with 2MASS and WISE photometry,
we built the spectral energy distributions from 0.5 to 22\microm for a subset
of 48 objects and found a total of 41 discs, including 11 Class II and 1 Class
III new discs. Density-based clustering algorithms are a promising tool to
identify candidate members of star forming regions in large astrometric
databases. If confirmed, the candidate members discussed in this work would
represent an increment of roughly 40% of the current census of Ophiuchus.Comment: A&A, Accepted. Abridged abstrac
Submillimeter Array Observations of the RX J1633.9-2442 Transition Disk: Evidence for Multiple Planets in the Making
We present continuum high resolution Submillimeter Array (SMA) observations
of the transition disk object RX J1633.9-2442, which is located in the
Ophiuchus molecular cloud and has recently been identified as a likely site of
ongoing giant planet formation. The observations were taken at 340 GHz (880
micron) with the SMA in its most extended configuration, resulting in an
angular resolution of 0.3" (35 AU at the distance of the target). We find that
the disk is highly inclined (i ~50 deg) and has an inner cavity ~25 AU in
radius, which is clearly resolved by our observations. We simultaneously model
the entire optical to millimeter wavelength spectral energy distribution (SED)
and SMA visibilities of RX J1633.9-2442 in order to constrain the structure of
its disk. We find that an empty cavity ~25 AU in radius is inconsistent with
the excess emission observed at 12, 22, and 24 micron. Instead, the mid-IR
excess can be modeled by either a narrow, optically thick ring at ~10 AU or an
optically thin region extending from ~7 AU to ~25 AU. The inner disk (r < 5 AU)
is mostly depleted of small dust grains as attested by the lack of detectable
near-IR excess. We also present deep Keck aperture masking observations in the
near-IR, which rule out the presence of a companion up to 500 times fainter
than the primary star (in K-band) for projected separations in the 5-20 AU
range. We argue that the complex structure of the RX J1633.9-2442 disk is best
explained by multiple planets embedded within the disk. We also suggest that
the properties and incidence of objects such as RX J1633.9-2442, T Cha, and
LkCa 15 (and those of the companions recently identified to these two latter
objects) are most consistent with the runaway gas accretion phase of the core
accretion model, when giant planets gain their envelopes and suddenly become
massive enough to open wide gaps in the disk.Comment: Accepted for publication in Ap
t-channel production of heavy charged leptons
We study the pair production of heavy charged exotic leptons at e+ e-
colliders in the SU(2)_L x SU(2)_I x U(1)_Y model. This gauge group is a
subgroup of the grand unification group E6; SU(2)_I commutes with the electric
charge operator, and the three corresponding gauge bosons are electrically
neutral. In addition to the standard photon and Z boson contributions, we also
include the contributions from extra neutral gauge bosons. A t-channel
contribution due to W_I-boson exchange, which is unsuppressed by mixing angles,
is quite important. We calculate the left-right and forward-backward
asymmetries, and discuss how to differentiate different models.Comment: Increased discussion of experimental signatures. Version accepted by
PR
The inner environment of Z~CMa: High-Contrast Imaging Polarimetry with NaCo
Context. Z\,CMa is a binary composed of an embedded Herbig Be and an FU Ori
class star separated by au. Observational evidence indicate a complex
environment in which each star has a circumstellar disk and drives a jet, and
the whole system is embedded in a large dusty envelope.
Aims. We aim to probe the circumbinary environment of Z\,CMa in the inner 400
au in scattered light.
Methods. We use high contrast imaging polarimetry with VLT/NaCo at and
bands.
Results. The central binary is resolved in both bands. The polarized images
show three bright and complex structures: a common dust envelope, a sharp
extended feature previously reported in direct light, and an intriguing bright
clump located 0\farcs3 south of the binary, which appears spatially connected
to the sharp extended feature.
Conclusions.We detect orbital motion when compared to previous observations,
and report a new outburst driven by the Herbig star. Our observations reveal
the complex inner environment of Z\,CMa with unprecedented detail and contrast.Comment: Accepted for publication in A&A Letter
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