85 research outputs found
First On-Sky High Contrast Imaging with an Apodizing Phase Plate
We present the first astronomical observations obtained with an Apodizing
Phase Plate (APP). The plate is designed to suppress the stellar diffraction
pattern by 5 magnitudes from 2-9 lambda/D over a 180 degree region. Stellar
images were obtained in the M' band (4.85 microns) at the MMTO 6.5m telescope,
with adaptive wavefront correction made with a deformable secondary mirror
designed for low thermal background observations. The measured PSF shows a halo
intensity of 0.1% of the stellar peak at 2 lambda/D (0.36 arcsec), tapering off
as r^{-5/3} out to radius 9 lambda/D. Such a profile is consistent with
residual errors predicted for servo lag in the AO system.
We project a 5 sigma contrast limit, set by residual atmospheric
fluctuations, of 10.2 magnitudes at 0.36 arcsec separation for a one hour
exposure. This can be realised if static and quasi-static aberrations are
removed by differential imaging, and is close to the sensitivity level set by
thermal background photon noise for target stars with M'>3. The advantage of
using the phase plate is the removal of speckle noise caused by the residuals
in the diffraction pattern that remain after PSF subtraction. The APP gives
higher sensitivity over the range 2-5 lambda/D compared to direct imaging
techniques.Comment: 22 pages, 5 figures, 1 table, ApJ accepte
First Results of the Laser-Interferometric Detector for Axions (LIDA)
We present the operating principle and the first observing run of a novel kind of direct detector for axions and axionlike particles in the galactic halo. Sensitive to the polarisation rotation of linearly polarised laser light induced by an axion field, our experiment is the first detector of its kind collecting scientific data. We discuss our peak sensitivity of 1.51×10−10  GeV−1 (95% confidence level) to the axion-photon coupling strength in the axion mass range of 1.97–2.01 neV which is, for instance, motivated by supersymmetric grand-unified theories. We also report on effects that arise in our high-finesse in-vacuum cavity at an unprecedented optical continuous-wave intensity of 4.7  MW/cm2. Our detector already belongs to the most sensitive direct searches within its measurement band, and our results pave the way towards surpassing the current sensitivity limits even of astrophysical observations in the mass range from 10−8 down to 10−16  eV via quantum-enhanced laser interferometry, especially with the potential of scaling our detector up to kilometer length
First results of the Laser-Interferometric Detector for Axions (LIDA)
We present the operating principle and the first observing run of a novel
kind of direct detector for axions and axion-like particles in the galactic
halo. Our experiment is sensitive to the polarisation rotation of linearly
polarised laser light induced by an axion field, and the first detector of its
kind collecting science data. We discuss our current peak sensitivity of
GeV (95 % confidence level) to the axion-photon
coupling strength in the axion mass range of 1.97-2.01 neV which is, for
instance, motivated by supersymmetric grand-unified theories. We also report on
effects that arise in our high-finesse in-vacuum cavity at unprecedented
optical continuous-wave intensity. Our detector already belongs to the most
sensitive direct searches within its measurement band, and our first results
pave the way towards surpassing the current sensitivity limits in the mass
range from eV down to eV via quantum-enhanced laser
interferometry
Thermal Infrared MMTAO Observations of the HR 8799 Planetary System
We present direct imaging observations at wavelengths of 3.3, 3.8 (L',band),
and 4.8 (M band) microns, for the planetary system surrounding HR 8799. All
three planets are detected at L'. The c and d component are detected at 3.3
microns, and upper limits are derived from the M band observations. These
observations provide useful constraints on warm giant planet atmospheres. We
discuss the current age constraints on the HR 8799 system, and show that
several potential co-eval objects can be excluded from being co-moving with the
star. Comparison of the photometry is made to models for giant planet
atmospheres. Models which include non-equilibrium chemistry provide a
reasonable match to the colors of c and d. From the observed colors in the
thermal infrared we estimate T_eff < 960 K for b, and T_eff=1300 and 1170 K for
c and d, respectively. This provides an independent check on the effective
temperatures and thus masses of the objects from the Marois 2008 results.Comment: 16 pages, 6 figures, accepted to Ap
Discovery of a Faint Companion to Alcor Using MMT/AO 5 m Imaging
We report the detection of a faint stellar companion to the famous nearby A5V
star Alcor (80 UMa). The companion has M-band ( = 4.8 m)
magnitude 8.8 and projected separation 1".11 (28 AU) from Alcor. The companion
is most likely a low-mass (0.3 \msun) active star which is responsible
for Alcor's X-ray emission detected by ROSAT (L 10
erg/s). Alcor is a nuclear member of the Ursa Major star cluster (UMa; d
25 pc, age 0.5 Gyr), and has been occasionally mentioned as a
possible distant (709") companion of the stellar quadruple Mizar ( UMa).
Comparing the revised Hipparcos proper motion for Alcor with the mean motion
for other UMa nuclear members shows that Alcor has a peculiar velocity of 1.1
km/s, which is comparable to the predicted velocity amplitude induced by the
newly-discovered companion (1 km/s). Using a precise dynamical parallax
for Mizar and the revised Hipparcos parallax for Alcor, we find that Mizar and
Alcor are physically separated by 0.36 0.19 pc (74 39 kAU; minimum
18 kAU), and their velocity vectors are marginally consistent (
probability 6%). Given their close proximity and concordant motions we suggest
that the Mizar quadruple and the Alcor binary be together considered the 2nd
closest stellar sextuplet. The addition of Mizar-Alcor to the census of stellar
multiples with six or more components effectively doubles the local density of
such systems within the local volume (d 40 pc).Comment: 28 pages, 2 figures, AJ, in press; emulateapj short version at
http://www.pas.rochester.edu/~emamajek/alcor.pd
Observation of Parametric Instability in Advanced LIGO
Parametric instabilities have long been studied as a potentially limiting
effect in high-power interferometric gravitational wave detectors. Until now,
however, these instabilities have never been observed in a kilometer-scale
interferometer. In this work we describe the first observation of parametric
instability in an Advanced LIGO detector, and the means by which it has been
removed as a barrier to progress
Aberrant salience network functional connectivity in auditory verbal hallucinations::a first episode psychosis sample
Auditory verbal hallucinations (AVH) often lead to distress and functional disability, and are frequently associated with psychotic illness. Previously both state and trait magnetic resonance imaging (MRI) studies of AVH have identified activity in brain regions involving auditory processing, language, memory and areas of default mode network (DMN) and salience network (SN). Current evidence is clouded by research mainly in participants on long-term medication, with chronic illness and by choice of seed regions made 'a priori'. Thus, the aim of this study was to elucidate the intrinsic functional connectivity in patients presenting with first episode psychosis (FEP). Resting state functional MRI data were available from 18 FEP patients, 9 of whom also experienced AVH of sufficient duration in the scanner and had symptom capture functional MRI (sc fMRI), together with 18 healthy controls. Symptom capture results were used to accurately identify specific brain regions active during AVH; including the superior temporal cortex, insula, precuneus, posterior cingulate and parahippocampal complex. Using these as seed regions, patients with FEP and AVH showed increased resting sb-FC between parts of the SN and the DMN and between the SN and the cerebellum, but reduced sb-FC between the claustrum and the insula, compared to healthy controls.It is possible that aberrant activity within the DMN and SN complex may be directly linked to impaired salience appraisal of internal activity and AVH generation. Furthermore, decreased intrinsic functional connectivity between the claustrum and the insula may lead to compensatory over activity in parts of the auditory network including areas involved in DMN, auditory processing, language and memory, potentially related to the complex and individual content of AVH when they occur
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