461 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
The Masses of Transition Circumstellar Disks: Observational Support for Photoevaporation Models
We report deep Sub-Millimeter Array observations of 26 pre-main-sequence
(PMS) stars with evolved inner disks. These observations measure the mass of
the outer disk (r ~20-100 AU) across every stage of the dissipation of the
inner disk (r < 10 AU) as determined by the IR spectral energy distributions
(SEDs). We find that only targets with high mid-IR excesses are detected and
have disk masses in the 1-5 M_Jup range, while most of our objects remain
undetected to sensitivity levels of M_DISK ~0.2-1.5 M_Jup. To put these results
in a more general context, we collected publicly available data to construct
the optical to millimeter wavelength SEDs of over 120 additional PMS stars. We
find that the near-IR and mid-IR emission remain optically thick in objects
whose disk masses span 2 orders of magnitude (~0.5-50 M_Jup). Taken together,
these results imply that, in general, inner disks start to dissipate only after
the outer disk has been significantly depleted of mass. This provides strong
support for photoevaporation being one of the dominant processes driving disk
evolution.Comment: Accepted for publication by ApJL, 4 pages and 3 figure
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
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
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