1,647 research outputs found
Testing the Radio-Selection Method of Dual Active Galactic Nuclei in the Stripe 82 Field
We test the merger-induced dual active galactic nuclei (dAGN) paradigm using
a sample of 35 radio galaxy pairs from the SDSS Stripe 82 field. Using Keck
optical spectroscopy, we confirm 21 pairs have consistent redshifts,
constituting kinematic pairs; the remaining 14 pairs are line-of-sight
projections. We classify the optical spectral signatures via emission line
ratios, equivalent widths, and excess of radio power above star-formation
predicted outputs. We find 6 galaxies are classified as LINERs and 7 are
AGN/starburst composites. Most of the LINERs are retired galaxies, while the
composites likely have AGN contribution. All of the kinematic pairs exhibit
radio power more than 10 above the level expected from just
star-formation, suggestive of a radio AGN contribution. We also analyze
high-resolution (0.3") imaging at 6 GHz from the NSF's Karl G. Jansky Very
Large Array for 17 of the kinematic pairs. We find 6 pairs (2 new, 4 previously
known) host two separate radio cores, confirming their status as dAGNs. The
remaining 11 pairs contain single AGNs, with most exhibiting prominent
jets/lobes overlapping their companion. Our final census indicates a dAGN duty
cycle slightly higher than predictions of purely stochastic fueling, although a
larger sample (potentially culled from VLASS) is needed to fully address the
dAGN fraction. We conclude that while dAGNs in the Stripe 82 field are rare,
the merger process plays some role in their triggering and it facilitates low
to moderate levels of accretion.Comment: 26 pages, 10 figures, resubmitted to ApJ after addressing referee
report, supplemental figures/data to be included in online journa
CRISPR/Cas9 interrogation of the mouse Pcdhg gene cluster reveals a crucial isoform-specific role for Pcdhgc4.
The mammalian Pcdhg gene cluster encodes a family of 22 cell adhesion molecules, the gamma-Protocadherins (γ-Pcdhs), critical for neuronal survival and neural circuit formation. The extent to which isoform diversity-a γ-Pcdh hallmark-is required for their functions remains unclear. We used a CRISPR/Cas9 approach to reduce isoform diversity, targeting each Pcdhg variable exon with pooled sgRNAs to generate an allelic series of 26 mouse lines with 1 to 21 isoforms disrupted via discrete indels at guide sites and/or larger deletions/rearrangements. Analysis of 5 mutant lines indicates that postnatal viability and neuronal survival do not require isoform diversity. Surprisingly, given reports that it might not independently engage in trans-interactions, we find that γC4, encoded by Pcdhgc4, is the only critical isoform. Because the human orthologue is the only PCDHG gene constrained in humans, our results indicate a conserved γC4 function that likely involves distinct molecular mechanisms
A First Comparison of Kepler Planet Candidates in Single and Multiple Systems
In this letter we present an overview of the rich population of systems with
multiple candidate transiting planets found in the first four months of Kepler
data. The census of multiples includes 115 targets that show 2 candidate
planets, 45 with 3, 8 with 4, and 1 each with 5 and 6, for a total of 170
systems with 408 candidates. When compared to the 827 systems with only one
candidate, the multiples account for 17 percent of the total number of systems,
and a third of all the planet candidates. We compare the characteristics of
candidates found in multiples with those found in singles. False positives due
to eclipsing binaries are much less common for the multiples, as expected.
Singles and multiples are both dominated by planets smaller than Neptune; 69
+2/-3 percent for singles and 86 +2/-5 percent for multiples. This result, that
systems with multiple transiting planets are less likely to include a
transiting giant planet, suggests that close-in giant planets tend to disrupt
the orbital inclinations of small planets in flat systems, or maybe even to
prevent the formation of such systems in the first place.Comment: 13 pages, 13 figures, submitted to ApJ Letter
Transit Timing Observations from Kepler: III. Confirmation of 4 Multiple Planet Systems by a Fourier-Domain Study of Anti-correlated Transit Timing Variations
We present a method to confirm the planetary nature of objects in systems
with multiple transiting exoplanet candidates. This method involves a
Fourier-Domain analysis of the deviations in the transit times from a constant
period that result from dynamical interactions within the system. The
combination of observed anti-correlations in the transit times and mass
constraints from dynamical stability allow us to claim the discovery of four
planetary systems Kepler-25, Kepler-26, Kepler-27, and Kepler-28, containing
eight planets and one additional planet candidate.Comment: Accepted to MNRA
Planetary Candidates Observed by Kepler, III: Analysis of the First 16 Months of Data
New transiting planet candidates are identified in sixteen months (May 2009 -
September 2010) of data from the Kepler spacecraft. Nearly five thousand
periodic transit-like signals are vetted against astrophysical and instrumental
false positives yielding 1,091 viable new planet candidates, bringing the total
count up to over 2,300. Improved vetting metrics are employed, contributing to
higher catalog reliability. Most notable is the noise-weighted robust averaging
of multi-quarter photo-center offsets derived from difference image analysis
which identifies likely background eclipsing binaries. Twenty-two months of
photometry are used for the purpose of characterizing each of the new
candidates. Ephemerides (transit epoch, T_0, and orbital period, P) are
tabulated as well as the products of light curve modeling: reduced radius
(Rp/R*), reduced semi-major axis (d/R*), and impact parameter (b). The largest
fractional increases are seen for the smallest planet candidates (197% for
candidates smaller than 2Re compared to 52% for candidates larger than 2Re) and
those at longer orbital periods (123% for candidates outside of 50-day orbits
versus 85% for candidates inside of 50-day orbits). The gains are larger than
expected from increasing the observing window from thirteen months (Quarter 1--
Quarter 5) to sixteen months (Quarter 1 -- Quarter 6). This demonstrates the
benefit of continued development of pipeline analysis software. The fraction of
all host stars with multiple candidates has grown from 17% to 20%, and the
paucity of short-period giant planets in multiple systems is still evident. The
progression toward smaller planets at longer orbital periods with each new
catalog release suggests that Earth-size planets in the Habitable Zone are
forthcoming if, indeed, such planets are abundant.Comment: Submitted to ApJS. Machine-readable tables are available at
http://kepler.nasa.gov, http://archive.stsci.edu/kepler/results.html, and the
NASA Exoplanet Archiv
Accretion of Planetary Material onto Host Stars
Accretion of planetary material onto host stars may occur throughout a star's
life. Especially prone to accretion, extrasolar planets in short-period orbits,
while relatively rare, constitute a significant fraction of the known
population, and these planets are subject to dynamical and atmospheric
influences that can drive significant mass loss. Theoretical models frame
expectations regarding the rates and extent of this planetary accretion. For
instance, tidal interactions between planets and stars may drive complete
orbital decay during the main sequence. Many planets that survive their stars'
main sequence lifetime will still be engulfed when the host stars become red
giant stars. There is some observational evidence supporting these predictions,
such as a dearth of close-in planets around fast stellar rotators, which is
consistent with tidal spin-up and planet accretion. There remains no clear
chemical evidence for pollution of the atmospheres of main sequence or red
giant stars by planetary materials, but a wealth of evidence points to active
accretion by white dwarfs. In this article, we review the current understanding
of accretion of planetary material, from the pre- to the post-main sequence and
beyond. The review begins with the astrophysical framework for that process and
then considers accretion during various phases of a host star's life, during
which the details of accretion vary, and the observational evidence for
accretion during these phases.Comment: 18 pages, 5 figures (with some redacted), invited revie
KOI-126: A Triply-Eclipsing Hierarchical Triple with Two Low-Mass Stars
The Kepler spacecraft has been monitoring the light from 150,000 stars in its
primary quest to detect transiting exoplanets. Here we report on the detection
of an eclipsing stellar hierarchical triple, identified in the Kepler
photometry. KOI-126 (A,(B, C)), is composed of a low-mass binary (masses M_B =
0.2413+/-0.0030 M_Sun, M_C = 0.2127+/-0.0026 M_Sun; radii R_B = 0.2543+/-0.0014
R_Sun, R_C = 0.2318+/-0.0013 R_Sun; orbital period P_1 = 1.76713+/-0.00019
days) on an eccentric orbit about a third star (mass M_A = 1.347+/-0.032 M_Sun;
radius R_A = 2.0254+/-0.0098 R_Sun; period of orbit around the low-mass binary
P_2 = 33.9214+/-0.0013 days; eccentricity of that orbit e_2 = 0.3043+/-0.0024).
The low-mass pair probe the poorly sampled fully-convective stellar domain
offering a crucial benchmark for theoretical stellar models.Comment: To be published in Science on 2/4/2011. Announced at Jan. 2011 AAS
meeting and made available on Science Express. Includes Supporting Online
Materia
Architecture and Dynamics of Kepler's Candidate Multiple Transiting Planet Systems
About one-third of the ~1200 transiting planet candidates detected in the
first four months of \ik data are members of multiple candidate systems. There
are 115 target stars with two candidate transiting planets, 45 with three, 8
with four, and one each with five and six. We characterize the dynamical
properties of these candidate multi-planet systems. The distribution of
observed period ratios shows that the vast majority of candidate pairs are
neither in nor near low-order mean motion resonances. Nonetheless, there are
small but statistically significant excesses of candidate pairs both in
resonance and spaced slightly too far apart to be in resonance, particularly
near the 2:1 resonance. We find that virtually all candidate systems are
stable, as tested by numerical integrations that assume a nominal mass-radius
relationship. Several considerations strongly suggest that the vast majority of
these multi-candidate systems are true planetary systems. Using the observed
multiplicity frequencies, we find that a single population of planetary systems
that matches the higher multiplicities underpredicts the number of
singly-transiting systems. We provide constraints on the true multiplicity and
mutual inclination distribution of the multi-candidate systems, revealing a
population of systems with multiple super-Earth-size and Neptune-size planets
with low to moderate mutual inclinations.Comment: 27 pages, 19 figures, 8 tables, emulateapj style. Accepted to ApJ.
This version includes several minor changes to the tex
Masses, radii, and orbits of small Kepler planets : The transition from gaseous to rocky planets
We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm-3, suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than 2 R ⊕. Larger planets evidently contain a larger fraction of low-density material (H, He, and H2O).Peer reviewedFinal Accepted Versio
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