266 research outputs found
Candidate exoplanet host HD131399A: a nascent Am star
Direct imaging suggests that there is a Jovian exoplanet around the primary
A-star in the triple-star system HD131399. We investigate a high-quality
spectrum of the primary component HD131399A obtained with FEROS on the ESO/MPG
2.2m telescope, aiming to characterise the star's atmospheric and fundamental
parameters, and to determine elemental abundances at high precision and
accuracy. The aim is to constrain the chemical composition of the birth cloud
of the system and therefore the bulk composition of the putative planet. A
hybrid non-local thermal equilibrium (non-LTE) model atmosphere technique is
adopted for the quantitative spectral analysis. Comparison with the most recent
stellar evolution models yields the fundamental parameters. The atmospheric and
fundamental stellar parameters of HD131399A are constrained to Teff=9200+-100
K, log g=4.37+-0.10, M=1.95+0.08-0.06 Msun, R=1.51+0.13-0.10 Rsun, and log
L/Lsun=1.17+-0.07, locating the star on the zero-age main sequence. Non-LTE
effects on the derived metal abundances are often smaller than 0.1dex, but can
reach up to ~0.8dex for individual lines. The observed lighter elements up to
calcium are overall consistent with present-day cosmic abundances, with a C/O
ratio of 0.450.07 by number, while the heavier elements show mild
overabundances. We conclude that the birth cloud of the system had a standard
chemical composition, but we witness the onset of the Am phenomenon in the
slowly rotating star. We furthermore show that non-LTE analyses have the
potential to solve the remaining discrepancies between observed abundances and
predictions by diffusion models for Am stars. Moreover, the present case allows
mass loss, not turbulent mixing, to be identified as the main transport process
competing with diffusion in very young Am stars.Comment: 5 pages + 3 pages appendix, 3 figures. Accepted for publication in
A&
On the transport and thermodynamic properties of quasi-two-dimensional purple bronzes AMoO (A=Na, K)
We report a comparative study of the specific heat, electrical resistivity
and thermal conductivity of the quasi-two-dimensional purple bronzes
NaMoO and KMoO, with special emphasis on
the behavior near their respective charge-density-wave transition temperatures
. The contrasting behavior of both the transport and the thermodynamic
properties near is argued to arise predominantly from the different
levels of intrinsic disorder in the two systems. A significant proportion of
the enhancement of the thermal conductivity above in
NaMoO, and to a lesser extent in KMoO, is
attributed to the emergence of phason excitations.Comment: 8 pages, 6 figures, To appear in Physical Review
Peeking beneath the precision floor -- II. Probing the chemo-dynamical histories of the potential globular cluster siblings, NGC 288 and NGC 362
The assembly history of the Milky Way (MW) is a rapidly evolving subject,
with numerous small accretion events and at least one major merger proposed in
the MW's history. Accreted alongside these dwarf galaxies are globular clusters
(GCs), which act as spatially coherent remnants of these past events. Using
high precision differential abundance measurements from our recently published
study, we investigate the likelihood that the MW clusters NGC 362 and NGC 288
are galactic siblings, accreted as part of the Gaia-Sausage-Enceladus (GSE)
merger. To do this, we compare the two GCs at the 0.01 dex level for 20+
elements for the first time. Strong similarities are found, with the two
showing chemical similarity on the same order as those seen between the three
LMC GCs, NGC 1786, NGC 2210 and NGC 2257. However, when comparing GC abundances
directly to GSE stars, marked differences are observed. NGC 362 shows good
agreement with GSE stars in the ratio of Eu to Mg and Si, as well as a clear
dominance in the r- compared to the s-process, while NGC 288 exhibits only a
slight r-process dominance. When fitting the two GC abundances with a GSE-like
galactic chemical evolution model, NGC 362 shows agreement with both the model
predictions and GSE abundance ratios (considering Si, Ni, Ba and Eu) at the
same metallicity. This is not the case for NGC 288. We propose that the two are
either not galactic siblings, or GSE was chemically inhomogeneous enough to
birth two similar, but not identical clusters with distinct chemistry relative
to constituent stars.Comment: Second paper in a series. Accepted for publication by MNRAS, 17
pages, 11 figure
Direct Imaging discovery of a second planet candidate around the possibly transiting planet host CVSO 30
We surveyed the 25 Ori association for direct-imaging companions. This association has an age of only few million years. Among other targets, we observed CVSO 30, which has recently been identified as the first T Tauri star found to host a transiting planet candidate. We report on photometric and spectroscopic high-contrast observations with the Very Large Telescope, the Keck telescopes, and the Calar Alto observatory. They reveal a directly imaged planet candidate close to the young M3 star CVSO 30. The JHK-band photometry of the newly identified candidate is at better than 1 sigma consistent with late-type giants, early-T and early-M dwarfs, and free-floating planets. Other hypotheses such as galaxies can be excluded at more than 3.5 sigma. A lucky imaging z' photometric detection limit z'= 20.5 mag excludes early-M dwarfs and results in less than 10 MJup for CVSO 30 c if bound. We present spectroscopic observations of the wide companion that imply that the only remaining explanation for the object is that it is the first very young (Publisher PDFPeer reviewe
YETI observations of the young transiting planet candidate CVSO 30 b
CVSO 30 is a unique young low-mass system, because, for the first time, a
close-in transiting and a wide directly imaged planet candidates are found
around a common host star. The inner companion, CVSO 30 b, is the first
possible young transiting planet orbiting a previously known weak-lined T-Tauri
star. With five telescopes of the 'Young Exoplanet Transit Initiative' (YETI)
located in Asia, Europe and South America we monitored CVSO 30 over three years
in a total of 144 nights and detected 33 fading events. In two more seasons we
carried out follow-up observations with three telescopes. We can confirm that
there is a change in the shape of the fading event between different
observations and that the fading event even disappears and reappears. A total
of 38 fading event light curves were simultaneously modelled. We derived the
planetary, stellar, and geometrical properties of the system and found them
slightly smaller but in agreement with the values from the discovery paper. The
period of the fading event was found to be 1.36 s shorter and 100 times more
precise than the previous published value. If CVSO 30 b would be a giant planet
on a precessing orbit, which we cannot confirm, yet, the precession period may
be shorter than previously thought. But if confirmed as a planet it would be
the youngest transiting planet ever detected and will provide important
constraints on planet formation and migration time-scales.Comment: 14 pages (20 with appendix), 7 figures (16 with appendix), 6 tables
(7 with appendix
BICEP2 II: Experiment and Three-Year Data Set
We report on the design and performance of the BICEP2 instrument and on its
three-year data set. BICEP2 was designed to measure the polarization of the
cosmic microwave background (CMB) on angular scales of 1 to 5 degrees
(=40-200), near the expected peak of the B-mode polarization signature of
primordial gravitational waves from cosmic inflation. Measuring B-modes
requires dramatic improvements in sensitivity combined with exquisite control
of systematics. The BICEP2 telescope observed from the South Pole with a 26~cm
aperture and cold, on-axis, refractive optics. BICEP2 also adopted a new
detector design in which beam-defining slot antenna arrays couple to
transition-edge sensor (TES) bolometers, all fabricated on a common substrate.
The antenna-coupled TES detectors supported scalable fabrication and
multiplexed readout that allowed BICEP2 to achieve a high detector count of 500
bolometers at 150 GHz, giving unprecedented sensitivity to B-modes at degree
angular scales. After optimization of detector and readout parameters, BICEP2
achieved an instrument noise-equivalent temperature of 15.8 K sqrt(s). The
full data set reached Stokes Q and U map depths of 87.2 nK in square-degree
pixels (5.2 K arcmin) over an effective area of 384 square degrees within
a 1000 square degree field. These are the deepest CMB polarization maps at
degree angular scales to date. The power spectrum analysis presented in a
companion paper has resulted in a significant detection of B-mode polarization
at degree scales.Comment: 30 pages, 24 figure
First Season QUIET Observations: Measurements of CMB Polarization Power Spectra at 43 GHz in the Multipole Range 25 <= ell <= 475
The Q/U Imaging ExperimenT (QUIET) employs coherent receivers at 43GHz and
95GHz, operating on the Chajnantor plateau in the Atacama Desert in Chile, to
measure the anisotropy in the polarization of the CMB. QUIET primarily targets
the B modes from primordial gravitational waves. The combination of these
frequencies gives sensitivity to foreground contributions from diffuse Galactic
synchrotron radiation. Between 2008 October and 2010 December, >10,000hours of
data were collected, first with the 19-element 43GHz array (3458hours) and then
with the 90-element 95GHz array. Each array observes the same four fields,
selected for low foregrounds, together covering ~1000deg^2. This paper reports
initial results from the 43GHz receiver which has an array sensitivity to CMB
fluctuations of 69uK sqrt(s). The data were extensively studied with a large
suite of null tests before the power spectra, determined with two independent
pipelines, were examined. Analysis choices, including data selection, were
modified until the null tests passed. Cross correlating maps with different
telescope pointings is used to eliminate a bias. This paper reports the EE, BB
and EB power spectra in the multipole range ell=25-475. With the exception of
the lowest multipole bin for one of the fields, where a polarized foreground,
consistent with Galactic synchrotron radiation, is detected with 3sigma
significance, the E-mode spectrum is consistent with the LCDM model, confirming
the only previous detection of the first acoustic peak. The B-mode spectrum is
consistent with zero, leading to a measurement of the tensor-to-scalar ratio of
r=0.35+1.06-0.87. The combination of a new time-stream double-demodulation
technique, Mizuguchi-Dragone optics, natural sky rotation, and frequent
boresight rotation leads to the lowest level of systematic contamination in the
B-mode power so far reported, below the level of r=0.1Comment: 19 pages, 14 figures, higher quality figures are available at
http://quiet.uchicago.edu/results/index.html; Fixed a typo and corrected
statistical error values used as a reference in Figure 14, showing our
systematic uncertainties (unchanged) vs. multipole; Revision to ApJ accepted
version, this paper should be cited as "QUIET Collaboration et al. (2011)
The QUIET Instrument
The Q/U Imaging ExperimenT (QUIET) is designed to measure polarization in the
Cosmic Microwave Background, targeting the imprint of inflationary
gravitational waves at large angular scales (~ 1 degree). Between 2008 October
and 2010 December, two independent receiver arrays were deployed sequentially
on a 1.4 m side-fed Dragonian telescope. The polarimeters which form the focal
planes use a highly compact design based on High Electron Mobility Transistors
(HEMTs) that provides simultaneous measurements of the Stokes parameters Q, U,
and I in a single module. The 17-element Q-band polarimeter array, with a
central frequency of 43.1 GHz, has the best sensitivity (69 uK sqrt(s)) and the
lowest instrumental systematic errors ever achieved in this band, contributing
to the tensor-to-scalar ratio at r < 0.1. The 84-element W-band polarimeter
array has a sensitivity of 87 uK sqrt(s) at a central frequency of 94.5 GHz. It
has the lowest systematic errors to date, contributing at r < 0.01. The two
arrays together cover multipoles in the range l= 25-975. These are the largest
HEMT-based arrays deployed to date. This article describes the design,
calibration, performance of, and sources of systematic error for the
instrument
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