676 research outputs found
Generation of Polarization Squeezing with Periodically Poled KTP at 1064 nm
We report the experimental demonstration of directly produced polarization
squeezing at 1064 nm from a type I optical parametric amplifier (OPA) based on
a periodically poled KTP crystal (PPKTP). The orthogonal polarization modes of
the polarization squeezed state are both defined by the OPA cavity mode, and
the birefringence induced by the PPKTP crystal is compensated for by a second,
but inactive, PPKTP crystal. Stokes parameter squeezing of 3.6 dB and anti
squeezing of 9.4 dB is observed.Comment: 4 pages, 2 figure
The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars
The detailed chemical composition of most metal-poor halo stars has been
found to be highly uniform, but a minority of stars exhibit dramatic
enhancements in their abundances of heavy neutron-capture elements and/or of
carbon. The key question for Galactic chemical evolution models is whether
these peculiarities reflect the composition of the natal clouds, or if they are
due to later mass transfer of processed material from a binary companion. If
the former case applies, the observed excess of certain elements was implanted
within selected clouds in the early ISM from a production site at interstellar
distances. Our aim is to determine the frequency and orbital properties of
binaries among these chemically peculiar stars. This information provides the
basis for deciding whether mass transfer from a binary companion is necessary
and sufficient to explain their unusual compositions. This paper discusses our
study of a sample of 17 moderately (r-I) and highly (r-II) r-process-element
enhanced VMP and EMP stars. High-resolution, low signal-to-noise spectra of the
stars were obtained at roughly monthly intervals over 8 years with the FIES
spectrograph at the Nordic Optical Telescope. From these spectra, radial
velocities with an accuracy of ~100 m/s were determined by cross-correlation
against an optimized template. 14 of the programme stars exhibit no significant
RV variation over this period, while 3 are binaries with orbits of typical
eccentricity for their periods, resulting in a normal binary frequency of
~18+-6% for the sample. Our results confirm our preliminary conclusion from
2011, based on partial data, that the chemical peculiarity of the r-I and r-II
stars is not caused by any putative binary companions. Instead, it was
imprinted on the natal molecular clouds of these stars by an external, distant
source. Models of the ISM in early galaxies should account for such mechanisms.Comment: 14 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
The role of binaries in the enrichment of the early Galactic halo. II. Carbon-Enhanced Metal-Poor Stars - CEMP-no stars
The detailed composition of most metal-poor halo stars has been found to be
very uniform. However, a fraction of 20-70% (increasing with decreasing
metallicity) exhibit dramatic enhancements in their abundances of carbon - the
so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic
chemical evolution models is whether this non-standard composition reflects
that of the stellar natal clouds, or is due to local, post-birth mass transfer
of chemically processed material from a binary companion; CEMP stars should
then all be members of binary systems. Our aim is to determine the frequency
and orbital parameters of binaries among CEMP stars with and without
over-abundances of neutron-capture elements - CEMP-s and CEMP-no stars,
respectively - as a test of this local mass-transfer scenario. This paper
discusses a sample of 24 CEMP-no stars, while a subsequent paper will consider
a similar sample of CEMP-s stars. Most programme stars exhibit no statistically
significant radial-velocit variation over this period and appear to be single,
while four are found to be binaries with orbital periods of 300-2,000 days and
normal eccentricity; the binary frequency for the sample is 17+-9%. The single
stars mostly belong to the recently-identified ``low-C band'', while the
binaries have higher absolute carbon abundances. We conclude that the
nucleosynthetic process responsible for the strong carbon excess in these
ancient stars is unrelated to their binary status; the carbon was imprinted on
their natal molecular clouds in the early Galactic ISM by an even earlier,
external source, strongly indicating that the CEMP-no stars are likely bona
fide second-generation stars. We discuss potential production sites for carbon
and its transfer across interstellar distances in the early ISM, and
implications for the composition of high-redshift DLA systems. Abridged.Comment: 16 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
Spin orbit alignment for KELT-7b and HAT-P-56b via Doppler tomography with TRES
We present Doppler tomographic analyses for the spectroscopic transits of
KELT-7b and HAT-P-56b, two hot-Jupiters orbiting rapidly rotating F-dwarf host
stars. These include analyses of archival TRES observations for KELT-7b, and a
new TRES transit observation of HAT-P-56b. We report spin-orbit aligned
geometries for KELT-7b (2.7 +/- 0.6 deg) and HAT-P-56b (8 +/- 2 deg). The host
stars KELT-7 and HAT-P-56 are among some of the most rapidly rotating
planet-hosting stars known. We examine the tidal re-alignment model for the
evolution of the spin-orbit angle in the context of the spin rates of these
stars. We find no evidence that the rotation rates of KELT-7 and HAT-P-56 have
been modified by star-planet tidal interactions, suggesting that the spin-orbit
angle of systems around these hot stars may represent their primordial
configuration. In fact, KELT-7 and HAT-P-56 are two of three systems in
super-synchronous, spin-orbit aligned states, where the rotation periods of the
host stars are faster than the orbital periods of the planets.Comment: 9 pages, accepted for publication in MNRA
Constraining planet structure from stellar chemistry: the cases of CoRoT-7, Kepler-10, and Kepler-93
We explore the possibility that the stellar relative abundances of different
species can be used to constrain the bulk abundances of known transiting rocky
planets. We use high resolution spectra to derive stellar parameters and
chemical abundances for Fe, Si, Mg, O, and C in three stars hosting low mass,
rocky planets: CoRoT-7, Kepler-10, and Kepler-93. These planets follow the same
line along the mass-radius diagram, pointing toward a similar composition. The
derived abundance ratios are compared with the solar values. With a simple
stoichiometric model, we estimate the iron mass fraction in each planet,
assuming stellar composition. We show that in all cases, the iron mass fraction
inferred from the mass-radius relationship seems to be in good agreement with
the iron abundance derived from the host star's photospheric composition. The
results suggest that stellar abundances can be used to add constraints on the
composition of orbiting rocky planets.Comment: A&A Letters, in pres
A Transiting Jupiter Analog
Decadal-long radial velocity surveys have recently started to discover
analogs to the most influential planet of our solar system, Jupiter. Detecting
and characterizing these worlds is expected to shape our understanding of our
uniqueness in the cosmos. Despite the great successes of recent transit
surveys, Jupiter analogs represent a terra incognita, owing to the strong
intrinsic bias of this method against long orbital periods. We here report on
the first validated transiting Jupiter analog, Kepler-167e (KOI-490.02),
discovered using Kepler archival photometry orbiting the K4-dwarf KIC-3239945.
With a radius of , a low orbital eccentricity
() and an equilibrium temperature of K,
Kepler-167e bears many of the basic hallmarks of Jupiter. Kepler-167e is
accompanied by three Super-Earths on compact orbits, which we also validate,
leaving a large cavity of transiting worlds around the habitable-zone. With two
transits and continuous photometric coverage, we are able to uniquely and
precisely measure the orbital period of this post snow-line planet
( d), paving the way for follow-up of this mag
target.Comment: 14 pages, 10 figures. Accepted to ApJ. Posteriors available at
https://github.com/CoolWorlds/Kepler-167-Posterior
HAT-P-25b: a Hot-Jupiter Transiting a Moderately Faint G Star
We report the discovery of HAT-P-25b, a transiting extrasolar planet orbiting
the V = 13.19 G5 dwarf star GSC 1788-01237, with a period P = 3.652836 +/-
0.000019 days, transit epoch Tc = 2455176.85173 +/- 0.00047 (BJD), and transit
duration 0.1174 +/- 0.0017 days. The host star has mass of 1.01 +/- 0.03
M(Sun), radius of 0.96 +(0.05)-(0.04) R(Sun), effective temperature 5500 +/- 80
K, and metallicity [Fe/H] = +0.31 +/- 0.08. The planetary companion has a mass
of 0.567 +/- 0.022 M(Jup), and radius of 1.190 +(0.081)-(0.056) R(Jup) yielding
a mean density of 0.42 +/- 0.07 g cm-3. Comparing these observations with
recent theoretical models, we find that HAT-P-25b is consistent with a
hydrogen-helium dominated gas giant planet with negligible core mass and age
3.2 +/- 2.3 Gyr. The properties of HAT-P-25b support several previously
observed correlations for planets in the mass range 0.4 < M < 0.7 M(Jup),
including those of core mass vs. metallicity, planet radius vs. equilibrium
temperature, and orbital period vs. planet mass. We also note that HAT-P-25b
orbits the faintest star found by HATNet to have a transiting planet to date,
and is one of only a very few number of planets discovered from the ground
orbiting a star fainter than V = 13.0.Comment: 11 pages, 8 figures, 5 tables, submitted to Ap
HAT-P-27b: A hot Jupiter transiting a G star on a 3 day orbit
We report the discovery of HAT-P-27b, an exoplanet transiting the moderately
bright G8 dwarf star GSC 0333-00351 (V=12.214). The orbital period is 3.039586
+/- 0.000012 d, the reference epoch of transit is 2455186.01879 +/- 0.00054
(BJD), and the transit duration is 0.0705 +/- 0.0019 d. The host star with its
effective temperature 5300 +/- 90 K is somewhat cooler than the Sun, and is
more metal-rich with a metallicity of +0.29 +/- 0.10. Its mass is 0.94 +/- 0.04
Msun and radius is 0.90 +/- 0.04 Rsun. For the planetary companion we determine
a mass of 0.660 +/- 0.033 MJ and radius of 1.038 +0.077 -0.058 RJ. For the 30
known transiting exoplanets between 0.3 MJ and 0.8 MJ, a negative correlation
between host star metallicity and planetary radius, and an additional
dependence of planetary radius on equilibrium temperature are confirmed at a
high level of statistical significance.Comment: Submitted to ApJ on 2011-01-18. 12 pages, 7 figures, 7 table
The Detection and Characterization of a Nontransiting Planet by Transit Timing Variations
The Kepler Mission is monitoring the brightness of ~150,000 stars searching
for evidence of planetary transits. As part of the "Hunt for Exomoons with
Kepler" (HEK) project, we report a planetary system with two confirmed planets
and one candidate planet discovered using the publicly available data for
KOI-872. Planet b transits the host star with a period P_b=33.6d and exhibits
large transit timing variations indicative of a perturber. Dynamical modeling
uniquely detects an outer nontransiting planet c near the 5:3 resonance
(P_c=57.0d) of mass 0.37 times that of Jupiter. Transits of a third planetary
candidate are also found: a 1.7-Earth radius super-Earth with a 6.8d period.
Our analysis indicates a system with nearly coplanar and circular orbits,
reminiscent of the orderly arrangement within the solar system.Comment: Accepted for publication in Science. Published online on May 10,
2012. Main Text and supplemental information included in a single merged
file, 58 page
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