191 research outputs found
Universality of Regge and vibrational trajectories in a semiclassical model
The orbital and radial excitations of light-light mesons are studied in the
framework of the dominantly orbital state description. The equation of motion
is characterized by a relativistic kinematics supplemented by the usual funnel
potential with a mixed scalar and vector confinement. The influence of finite
quark masses and potential parameters on Regge and vibrational trajectories is
discussed. The case of heavy-light mesons is also presented.Comment: 12 page
Young "Dipper" Stars in Upper Sco and Oph Observed by K2
We present ten young (10 Myr) late-K and M dwarf stars observed in
K2 Campaign 2 that host protoplanetary disks and exhibit quasi-periodic or
aperiodic dimming events. Their optical light curves show 10-20 dips in
flux over the 80-day observing campaign with durations of 0.5-2 days and
depths of up to 40%. These stars are all members of the Ophiuchus
(1 Myr) or Upper Scorpius (10 Myr) star-forming regions. To
investigate the nature of these "dippers" we obtained: optical and
near-infrared spectra to determine stellar properties and identify accretion
signatures; adaptive optics imaging to search for close companions that could
cause optical variations and/or influence disk evolution; and
millimeter-wavelength observations to constrain disk dust and gas masses. The
spectra reveal Li I absorption and H emission consistent with stellar
youth (<50 Myr), but also accretion rates spanning those of classical and
weak-line T Tauri stars. Infrared excesses are consistent with protoplanetary
disks extending to within 10 stellar radii in most cases; however, the
sub-mm observations imply disk masses that are an order of magnitude below
those of typical protoplanetary disks. We find a positive correlation between
dip depth and WISE-2 excess, which we interpret as evidence that the dipper
phenomenon is related to occulting structures in the inner disk, although this
is difficult to reconcile with the weakly accreting aperiodic dippers. We
consider three mechanisms to explain the dipper phenomenon: inner disk warps
near the co-rotation radius related to accretion; vortices at the inner disk
edge produced by the Rossby Wave Instability; and clumps of circumstellar
material related to planetesimal formation.Comment: Accepted to ApJ, 19 pages, 10 figure
Auxiliary fields and hadron dynamics
The relations existing between the auxiliary field (einbein field) formalism
and the spinless Salpeter equation are studied in the case of two particles
with the same mass, interacting via a confining potential. The problem of
non-orthogonality for radial excited states in the auxiliary field formalism is
discussed and found to be non-crucial. It is shown that the classical equations
of motion of the rotating string model, derived from the QCD lagrangian, reduce
exactly to the classical equations of motion of the phenomenological
semirelativistic flux tube model, provided all auxiliary fields are eliminated
correctly from the rotating string hamiltonian
EPIC 220204960: A Quadruple Star System Containing Two Strongly Interacting Eclipsing Binaries
We present a strongly interacting quadruple system associated with the K2
target EPIC 220204960. The K2 target itself is a Kp = 12.7 magnitude star at
Teff ~ 6100 K which we designate as "B-N" (blue northerly image). The host of
the quadruple system, however, is a Kp = 17 magnitude star with a composite
M-star spectrum, which we designate as "R-S" (red southerly image). With a 3.2"
separation and similar radial velocities and photometric distances, 'B-N' is
likely physically associated with 'R-S', making this a quintuple system, but
that is incidental to our main claim of a strongly interacting quadruple system
in 'R-S'. The two binaries in 'R-S' have orbital periods of 13.27 d and 14.41
d, respectively, and each has an inclination angle of >89 degrees. From our
analysis of radial velocity measurements, and of the photometric lightcurve, we
conclude that all four stars are very similar with masses close to 0.4 Msun.
Both of the binaries exhibit significant ETVs where those of the primary and
secondary eclipses 'diverge' by 0.05 days over the course of the 80-day
observations. Via a systematic set of numerical simulations of quadruple
systems consisting of two interacting binaries, we conclude that the outer
orbital period is very likely to be between 300 and 500 days. If sufficient
time is devoted to RV studies of this faint target, the outer orbit should be
measurable within a year.Comment: 20 pages, 18 figures, 7 tables; accepted for publication in MNRA
Kepler's Last Planet Discoveries: Two New Planets and One Single-Transit Candidate from K2 Campaign 19
The Kepler space telescope was responsible for the discovery of over 2,700
confirmed exoplanets, more than half of the total number of exoplanets known
today. These discoveries took place during both Kepler's primary mission, when
it spent 4 years staring at the same part of the sky, and its extended K2
mission, when a mechanical failure forced it to observe different parts of the
sky along the ecliptic. At the very end of the mission, when Kepler was
exhausting the last of its fuel reserves, it collected a short set of
observations known as K2 Campaign 19. So far, no planets have been discovered
in this dataset because it only yielded about a week of high-quality data.
Here, we report some of the last planet discoveries made by Kepler in the
Campaign 19 dataset. We conducted a visual search of the week of high-quality
Campaign 19 data and identified three possible planet transits. Each planet
candidate was originally identified with only one recorded transit, from which
we were able to estimate the planets' radii and estimate the semimajor axes and
orbital periods. Analysis of lower-quality data collected after low fuel
pressure caused the telescope's pointing precision to suffer revealed
additional transits for two of these candidates, allowing us to statistically
validate them as genuine exoplanets. We also tentatively confirm the transits
of one planet with TESS. These discoveries demonstrate Kepler's exoplanet
detection power, even when it was literally running on fumes.Comment: 14 pages, 9 figures, 4 tables. Accepted for publication in MNRA
Zodiacal Exoplanets In Time (ZEIT) I: A Neptune-sized planet orbiting an M4.5 dwarf in the Hyades Star Cluster
Studying the properties of young planetary systems can shed light on how the dynamics and structure of planets evolve during their most formative years. Recent K2 observations of nearby young clusters (10–800 Myr) have facilitated the discovery of such planetary systems. Here we report the discovery of a Neptune-sized planet transiting an M4.5 dwarf (K2-25) in the Hyades cluster (650–800 Myr). The light curve shows a strong periodic signal at 1.88 days, which we attribute to spot coverage and rotation. We confirm that the planet host is a member of the Hyades by measuring the radial velocity of the system with the high-resolution near-infrared spectrograph Immersion Grating Infrared Spectrometer. This enables us to calculate a distance based on K2-25's kinematics and membership to the Hyades, which in turn provides a stellar radius and mass to ≃ 5%–10%, better than what is currently possible for most Kepler M dwarfs (12%–20%). We use the derived stellar density as a prior on fitting the K2 transit photometry, which provides weak constraints on eccentricity. Utilizing a combination of adaptive optics imaging and high-resolution spectra, we rule out the possibility that the signal is due to a bound or background eclipsing binary, confirming the transits' planetary origin. K2-25b has a radius (3.43}_(-0.31)^(+0.95)R_⊕) much larger than older Kepler planets with similar orbital periods (3.485 days) and host-star masses (0.29 M_⊙). This suggests that close-in planets lose some of their atmospheres past the first few hundred million years. Additional transiting planets around the Hyades, Pleiades, and Praesepe clusters from K2 will help confirm whether this planet is atypical or representative of other close-in planets of similar age
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