353 research outputs found
Employing a New BVIc Photometric Survey of IC 4665 to Investigate the Age of this Young Open Cluster
We present a new, BVIc photometric survey of the young open cluster IC4665,
which improves on previous studies of this young cluster by incorporating a
rigorous standardization procedure, thus providing high-fidelity colors and
magnitudes for cluster members. We use this new photometric dataset to
reevaluate the properties (age and distance) of IC4665. Namely, using a
statistical approach incorporating Tau^2 CMD modeling, we measure a
pre-main-sequence isochrone age and distance of 36+-9 Myr and 360+-12 pc, as
well as a upper-main-sequence turn-off age and distance of 42+-12 Myr and
357+-12 pc. These ages and distances are highly dependent on the isochrone
model and color used for the fitting procedure, with a possible range of ~10-20
Myr in age and ~20 pc in distance. This spread in calculated ages and distances
seen between colors and models is likely due to limitations in the individual
membership catalogs and/or systematic differences in the predicted stellar
parameters from the different sets of models. Interestingly, when we compare
the isochrone ages for IC4665 to the published lithium depletion boundary age,
28+-5 Myr, we observe that this cluster does not appear to follow the trend of
isochrone ages being 1.5 times smaller than lithium depletion boundary ages. In
addition, comparing the overall magnetic activity (X-ray and H-alpha emission)
in IC4665 with other well studied open clusters, we find the observed activity
distributions for this young cluster are best characterized by assuming an age
of 30-40 Myr, thus in agreement with our pre-main-sequence and turn-off
isochrone ages for IC4665. Overall, although some age discrepancies do exist,
particularly in the ages measured from pre-main-sequence isochrones, the range
of possible IC4665 ages derived from the various dating techniques employed
here is relatively small compared to that found for other well studied open
clusters.Comment: 17 pages, 13 figures, 6 tables; Accepted for publication in the
Astronomical Journa
Exploiting kinematics and UBVIc photometry to establish high fidelity membership of the open cluster Blanco 1
We present the results of a wide-field, high-precision UBVIc CCD photometric survey of the Galactic open cluster Blanco 1. Standardized photometry was acquired using the Y4Kcam on the SMARTS 1m telescope at CTIO. We have also determined new high-precision proper motions (σμ = 0.3 mas yr−1) over an eight square degree area down to V = 16.5. Combined with 1D kinematic data, our survey yields a complete list of cluster members down to ~ 0.5 M and new high-fidelity color-magnitude diagrams are presented for Blanco 1. Having established a bona fide membership catalog, astrophysical characteristics of solar-type cluster members such as X-ray activity and lithium abundance have been studied to gain more insights in the process of internal mixing and convection. Our new results should also help to better understand its peculiar location in the Milky Way and to unravel its dynamical histor
The Factory and The Beehive II. Activity and Rotation in Praesepe and the Hyades
Open clusters are collections of stars with a single, well-determined age,
and can be used to investigate the connections between angular-momentum
evolution and magnetic activity over a star's lifetime. We present the results
of a comparative study of the relationship between stellar rotation and
activity in two benchmark open clusters: Praesepe and the Hyades. As they have
the same age and roughly solar metallicity, these clusters serve as an ideal
laboratory for testing the agreement between theoretical and empirical
rotation-activity relations at 600 Myr. We have compiled a sample of
720 spectra --- more than half of which are new observations --- for 516
high-confidence members of Praesepe; we have also obtained 139 new spectra for
130 high-confidence Hyads. We have collected rotation periods () for
135 Praesepe members and 87 Hyads. To compare emission, an indicator
of chromospheric activity, as a function of color, mass, and Rossby number
, we first calculate an expanded set of values, with which we can
obtain the to bolometric luminosity ratio, ,
even when spectra are not flux-calibrated and/or stars lack reliable distances.
Our values cover a broader range of stellar masses and colors (roughly
equivalent to spectral types from K0 to M9), and exhibit better agreement
between independent calculations, than existing values. We find no difference
between the two clusters in their equivalent width or
distributions, and therefore take the merged
and data to be representative of 600-Myr-old stars. Our analysis
shows that activity in these stars is saturated for
. Above that value activity declines as a
power-law with slope , before dropping off rapidly
at ...Comment: 17 pages, 15 figures, Accepted by Ap
FSL-BM: Fuzzy Supervised Learning with Binary Meta-Feature for Classification
This paper introduces a novel real-time Fuzzy Supervised Learning with Binary
Meta-Feature (FSL-BM) for big data classification task. The study of real-time
algorithms addresses several major concerns, which are namely: accuracy, memory
consumption, and ability to stretch assumptions and time complexity. Attaining
a fast computational model providing fuzzy logic and supervised learning is one
of the main challenges in the machine learning. In this research paper, we
present FSL-BM algorithm as an efficient solution of supervised learning with
fuzzy logic processing using binary meta-feature representation using Hamming
Distance and Hash function to relax assumptions. While many studies focused on
reducing time complexity and increasing accuracy during the last decade, the
novel contribution of this proposed solution comes through integration of
Hamming Distance, Hash function, binary meta-features, binary classification to
provide real time supervised method. Hash Tables (HT) component gives a fast
access to existing indices; and therefore, the generation of new indices in a
constant time complexity, which supersedes existing fuzzy supervised algorithms
with better or comparable results. To summarize, the main contribution of this
technique for real-time Fuzzy Supervised Learning is to represent hypothesis
through binary input as meta-feature space and creating the Fuzzy Supervised
Hash table to train and validate model.Comment: FICC201
The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
The size of a planet is an observable property directly connected to the
physics of its formation and evolution. We used precise radius measurements
from the California-Kepler Survey (CKS) to study the size distribution of 2025
planets in fine detail. We detect a factor of 2 deficit
in the occurrence rate distribution at 1.5-2.0 R. This gap splits
the population of close-in ( < 100 d) small planets into two size regimes:
R < 1.5 R and R = 2.0-3.0 R, with few planets in
between. Planets in these two regimes have nearly the same intrinsic frequency
based on occurrence measurements that account for planet detection
efficiencies. The paucity of planets between 1.5 and 2.0 R supports
the emerging picture that close-in planets smaller than Neptune are composed of
rocky cores measuring 1.5 R or smaller with varying amounts of
low-density gas that determine their total sizes.Comment: Paper III in the California-Kepler Survey series, accepted to the
Astronomical Journa
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