9,384 research outputs found
They might be giants: luminosity class, planet frequency, and planet-metallicity relation of the coolest Kepler target stars
We estimate the stellar parameters of late K and early M type Kepler target
stars. We obtain medium resolution visible spectra of 382 stars with Kp-J>2
(~K5 and later spectral type). We determine luminosity class by comparing the
strength of gravity-sensitive indices (CaH, K I, Ca II, and Na I) to their
strength in a sample of stars of known luminosity class. We find that giants
constitute 96+-% of the bright (Kp<14) Kepler target stars, and 7+-3% of dim
(Kp>14) stars, significantly higher than fractions based on the stellar
parameters quoted in the Kepler Input Catalog (KIC). The KIC effective
temperatures are systematically (110 +15 -35} K) higher than temperatures we
determine from fitting our spectra to PHOENIX stellar models. Through Monte
Carlo simulations of the Kepler exoplanet candidate population, we find a
planet occurrence of 0.36+-0.08 when giant stars are properly removed, somewhat
higher than when a KIC log(g)>4 criterion is used (0.27+-0.05). Lastly, we show
that there is no significant difference in g-r color (a probe of metallicity)
between late-type Kepler stars with transiting Earth-to-Neptune sized exoplanet
candidates and dwarf stars with no detected transits. We show that a previous
claimed offset between these two populations is most likely an artifact of
including a large number of misidentified giants.Comment: Accepted to Ap
The role of the RACK1 ortholog Cpc2p in modulating pheromone-induced cell cycle arrest in fission yeast
The detection and amplification of extracellular signals requires the involvement of multiple protein components. In mammalian cells the receptor of activated C kinase (RACK1) is an important scaffolding protein for signal transduction networks. Further, it also performs a critical function in regulating the cell cycle by modulating the G1/S transition. Many eukaryotic cells express RACK1 orthologs, with one example being Cpc2p in the fission yeast Schizosaccharomyces pombe. In contrast to RACK1, Cpc2p has been described to positively regulate, at the ribosomal level, cells entry into M phase. In addition, Cpc2p controls the stress response pathways through an interaction with Msa2p, and sexual development by modulating Ran1p/Pat1p. Here we describe investigations into the role, which Cpc2p performs in controlling the G protein-mediated mating response pathway. Despite structural similarity to Gβ-like subunits, Cpc2p appears not to function at the G protein level. However, upon pheromone stimulation, cells overexpressing Cpc2p display substantial cell morphology defects, disorientation of septum formation and a significantly protracted G1 arrest. Cpc2p has the potential to function at multiple positions within the pheromone response pathway. We provide a mechanistic interpretation of this novel data by linking Cpc2p function, during the mating response, with its previous described interactions with Ran1p/Pat1p. We suggest that overexpressing Cpc2p prolongs the stimulated state of pheromone-induced cells by increasing ste11 gene expression. These data indicate that Cpc2p regulates the pheromone-induced cell cycle arrest in fission yeast by delaying cells entry into S phase
Kepler Input Catalog: Photometric Calibration and Stellar Classification
We describe the photometric calibration and stellar classification methods
used to produce the Kepler Input Catalog (KIC). The KIC is a catalog containing
photometric and physical data for sources in the Kepler Mission field of view;
it is used by the mission to select optimal targets. We derived atmospheric
extinction corrections from hourly observations of secondary standard fields
within the Kepler field of view. Repeatability of absolute photometry for stars
brighter than magnitude 15 is typically 2%. We estimated stellar parameters
Teff, log(g), log (Z), E_{B-V} using Bayesian posterior probability
maximization to match observed colors to Castelli stellar atmosphere models. We
applied Bayesian priors describing the distribution of solar-neighborhood stars
in the color-magnitude diagram (CMD), in log (Z)$, and in height above the
galactic plane. Comparisons with samples of stars classified by other means
indicate that in most regions of the CMD, our classifications are reliable
within about +/- 200 K and +/- 0.4 dex in log (g). It is difficult to assess
the reliability of our log(Z) estimates, but there is reason to suspect that it
is poor, particularly at extreme Teff. Of great importance for the Kepler
Mission, for Teff <= 5400 K, the distinction between main-sequence stars and
giants has proved to be reliable with better than 98% confidence. The KIC is
available through the MAST data archive.Comment: 77 pages, 12 figures, 1 Table. Accepted by Astronomical Journal 24
July 201
Gaugino Condensation in N=1 Supergravity Models with Multiple Dilaton-Like Fields
We study supersymmetry breaking by hidden-sector gaugino condensation in N=1
D=4 supergravity models with multiple dilaton-like moduli fields. Our work is
motivated by Type I string theory, in which the low-energy effective Lagrangian
can have different dilaton-like fields coupling to different sectors of the
theory. We construct the effective Lagrangian for gaugino condensation and use
it to compute the visible-sector gaugino masses. We find that the gaugino
masses can be of order the gravitino mass, in stark contrast to heterotic
string models with a single dilaton field.Comment: LaTeX, 17 pages, 2 eps figure
Distributional National Accounts (DINA) with Household Survey Data: Methodology and Results for European Countries
The paper builds Distributional National Accounts (DINA) using household survey data. We present a transparent and reproducible methodology to construct DINA whenever administrative tax data are not available for research and apply it to various European countries. By doing so, we build synthetic microdata files which cover the entire distribution, include all income components individually aligned to national accounts, and preserve the detailed socioeconomic information available in the surveys. The methodology uses harmonized and publicly available data sources (SILC, HFCS) and provides highly comparable results. We discuss the methodological steps and their impact on the income distribution. In particular, we highlight the effects of imputations and the adjustment of the variables to national accounts totals. Furthermore, we compare different income concepts of both the DINA and EG-DNA approach of the OECD in a consistent way. Our results confirm that constructing DINA is crucial to get a better picture of the income distribution. Our methodology is well suited to build synthetic microdata files which can be used for policy evaluation like social impact analysis and microsimulation.Series: INEQ Working Paper Serie
Selection, Prioritization, and Characteristics of Kepler Target Stars
The Kepler Mission began its 3.5-year photometric monitoring campaign in May
2009 on a select group of approximately 150,000 stars. The stars were chosen
from the ~half million in the field of view that are brighter than 16th
magnitude. The selection criteria are quantitative metrics designed to optimize
the scientific yield of the mission with regards to the detection of Earth-size
planets in the habitable zone. This yields more than 90,000 G-type stars on or
close to the Main Sequence, >20,000 of which are brighter than 14th magnitude.
At the temperature extremes, the sample includes approximately 3,000 M-type
dwarfs and a small sample of O and B-type MS stars <200. Small numbers of
giants are included in the sample which contains ~5,000 stars with surface
gravities log(g) < 3.5. We present a brief summary of the selection process and
the stellar populations it yields in terms of surface gravity, effective
temperature, and apparent magnitude. In addition to the primary,
statistically-derived target set, several ancillary target lists were manually
generated to enhance the science of the mission, examples being: known
eclipsing binaries, open cluster members, and high proper-motion stars.Comment: Submitted to Astrophysical Journal Letter
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