334 research outputs found
Detection and Quantification of Fluorescent Cell Clusters in Cryo-Imaging
We developed and evaluated an algorithm for enumerating fluorescently labeled cells (e.g., stem and cancer cells) in mouse-sized, microscopic-resolution, cryo-image volumes. Fluorescent cell clusters were detected, segmented, and then fit with a model which incorporated a priori information about cell size, shape, and intensity. The robust algorithm performed well in phantom and tissue imaging tests, including accurate (<2% error) counting of cells in mouse. Preliminary experiments demonstrate that cryo-imaging and software can uniquely analyze delivery, homing to an organ and tissue distribution of stem cell therapeutics
Overview of the spectrometer optical fiber feed for the Habitable-zone Planet Finder
The Habitable-zone Planet Finder (HPF) is a highly stabilized fiber fed
precision radial velocity (RV) spectrograph working in the Near Infrared (NIR):
810 - 1280 nm . In this paper we present an overview of the preparation of the
optical fibers for HPF. The entire fiber train from the telescope focus down to
the cryostat is detailed. We also discuss the fiber polishing, splicing and its
integration into the instrument using a fused silica puck. HPF was designed to
be able to operate in two modes, High Resolution (HR- the only mode mode
currently commissioned) and High Efficiency (HE). We discuss these fiber heads
and the procedure we adopted to attach the slit on to the HR fibers.Comment: Presented at 2018 SPIE Astronomical Telescopes + Instrumentation,
Austin, Texas, USA. 18 pages, 25 figures, and 2 table
Towards Space-like Photometric Precision from the Ground with Beam-Shaping Diffusers
We demonstrate a path to hitherto unachievable differential photometric
precisions from the ground, both in the optical and near-infrared (NIR), using
custom-fabricated beam-shaping diffusers produced using specialized
nanofabrication techniques. Such diffusers mold the focal plane image of a star
into a broad and stable top-hat shape, minimizing photometric errors due to
non-uniform pixel response, atmospheric seeing effects, imperfect guiding, and
telescope-induced variable aberrations seen in defocusing. This PSF reshaping
significantly increases the achievable dynamic range of our observations,
increasing our observing efficiency and thus better averages over
scintillation. Diffusers work in both collimated and converging beams. We
present diffuser-assisted optical observations demonstrating
ppm precision in 30 minute bins on a nearby bright star
16-Cygni A (V=5.95) using the ARC 3.5m telescope---within a factor of 2
of Kepler's photometric precision on the same star. We also show a transit of
WASP-85-Ab (V=11.2) and TRES-3b (V=12.4), where the residuals bin down to
ppm in 30 minute bins for WASP-85-Ab---a factor of 4 of
the precision achieved by the K2 mission on this target---and to 101ppm for
TRES-3b. In the NIR, where diffusers may provide even more significant
improvements over the current state of the art, our preliminary tests have
demonstrated ppm precision for a star on the 200"
Hale Telescope. These photometric precisions match or surpass the expected
photometric precisions of TESS for the same magnitude range. This technology is
inexpensive, scalable, easily adaptable, and can have an important and
immediate impact on the observations of transits and secondary eclipses of
exoplanets.Comment: Accepted for publication in ApJ. 30 pages, 20 figure
Evidence for He I 10830 \AA~ absorption during the transit of a warm Neptune around the M-dwarf GJ 3470 with the Habitable-zone Planet Finder
Understanding the dynamics and kinematics of out-flowing atmospheres of hot
and warm exoplanets is crucial to understanding the origins and evolutionary
history of the exoplanets near the evaporation desert. Recently, ground based
measurements of the meta-stable Helium atom's resonant absorption at 10830
\AA~has become a powerful probe of the base environment which is driving the
outflow of exoplanet atmospheres. We report evidence for the He I 10830 \AA~in
absorption (equivalent width \AA) in the exosphere of
a warm Neptune orbiting the M-dwarf GJ 3470, during three transits using the
Habitable Zone Planet Finder (HPF) near infrared spectrograph. This marks the
first reported evidence for He I 10830 \AA\, atmospheric absorption for a
planet orbiting an M-dwarf. Our detected absorption is broad and its
blueshifted wing extends to -36 km/sec, the largest reported in the literature
to date. We modelled the state of Helium atoms in the exosphere of GJ3470b
based on assumptions on the UV and X-ray flux of GJ 3470, and found our
measurement of flux-weighted column density of meta-stable state Helium
, derived from our transit
observations, to be consistent with model, within its uncertainties. The
methodology developed here will be useful to study and constrain the
atmospheric outflow models of other exoplanets like GJ 3470b which are near the
edge of the evaporation desert.Comment: Accepted in Ap
Solar Contamination in Extreme-precision Radial-velocity Measurements: Deleterious Effects and Prospects for Mitigation
Solar contamination, due to moonlight and atmospheric scattering of sunlight, can cause systematic errors in stellar radial velocity (RV) measurements that significantly detract from the ~10 cm s−1 sensitivity required for the detection and characterization of terrestrial exoplanets in or near habitable zones of Sun-like stars. The addition of low-level spectral contamination at variable effective velocity offsets introduces systematic noise when measuring velocities using classical mask-based or template-based cross-correlation techniques. Here we present simulations estimating the range of RV measurement error induced by uncorrected scattered sunlight contamination. We explore potential correction techniques, using both simultaneous spectrometer sky fibers and broadband imaging via coherent fiber imaging bundles, that could reliably reduce this source of error to below the photon-noise limit of typical stellar observations. We discuss the limitations of these simulations, the underlying assumptions, and mitigation mechanisms. We also present and discuss the components designed and built into the NEID (NN-EXPLORE Exoplanet Investigations with Doppler spectroscopy) precision RV instrument for the WIYN 3.5 m telescope, to serve as an ongoing resource for the community to explore and evaluate correction techniques. We emphasize that while "bright time" has been traditionally adequate for RV science, the goal of 10 cm s−1 precision on the most interesting exoplanetary systems may necessitate access to darker skies for these next-generation instruments
Persistent starspot signals on M dwarfs: multi-wavelength Doppler observations with the Habitable-zone Planet Finder and Keck/HIRES
Young, rapidly-rotating M dwarfs exhibit prominent starspots, which create
quasiperiodic signals in their photometric and Doppler spectroscopic
measurements. The periodic Doppler signals can mimic radial velocity (RV)
changes expected from orbiting exoplanets. Exoplanets can be distinguished from
activity-induced false positives by the chromaticity and long-term incoherence
of starspot signals, but these qualities are poorly constrained for
fully-convective M stars. Coherent photometric starspot signals on M dwarfs may
persist for hundreds of rotations, and the wavelength dependence of starspot RV
signals may not be consistent between stars due to differences in their
magnetic fields and active regions. We obtained precise multi-wavelength RVs of
four rapidly-rotating M dwarfs (AD Leo, G 227-22, GJ 1245B, GJ 3959) using the
near-infrared (NIR) Habitable-zone Planet Finder, and the optical Keck/HIRES
spectrometer. Our RVs are complemented by photometry from Kepler, TESS, and the
Las Cumbres Observatory (LCO) network of telescopes. We found that all four
stars exhibit large spot-induced Doppler signals at their rotation periods, and
investigated the longevity and optical-to-NIR chromaticity for these signals.
The phase curves remain coherent much longer than is typical for Sunlike stars.
Their chromaticity varies, and one star (GJ 3959) exhibits optical and NIR RV
modulation consistent in both phase and amplitude. In general, though, we find
that the NIR amplitudes are lower than their optical counterparts. We conclude
that starspot modulation for rapidly-rotating M stars frequently remains
coherent for hundreds of stellar rotations, and gives rise to Doppler signals
that, due to this coherence, may be mistaken for exoplanets.Comment: Accepted for publication in the Astrophysical Journa
Ghosts of NEID's Past
The NEID spectrograph is a R 120,000 resolution fiber-fed and highly
stabilized spectrograph for extreme radial velocity (RV) precision. It is being
commissioned at the 3.5 m WIYN telescope in Kitt Peak National Observatory with
a desired instrumental precision of better than 30 \cms{}. NEID's bandpass of
380 -- 930 nm enables the simultaneous wavelength coverage of activity
indicators from the Ca HK lines in the blue to the Ca IR triplet in the IR. In
this paper we will present our efforts to characterize and mitigate optical
ghosts in the NEID spectrograph during assembly, integration and testing, and
highlight several of the dominant optical element contributors such as the
cross dispersion prism and input optics. We shall present simulations of the
2-D spectrum and discuss the predicted ghost features on the focal plane, and
how they may impact the RV performance for NEID. We also present the mitigation
strategy adopted for each ghost which may be applied to future instrument
designs. This work will enable other instrument builders to potentially avoid
some of these issues, as well as outline mitigation strategies.Comment: Conference Proceeding from SPIE Astronomical Telescopes +
Instrumentation (2020): 12 page
The NEID spectrometer: fibre injection system design
NEID is a high resolution echelle spectrograph designed to enable extremely precise Doppler radial velocity observations of stars in the 380-930nm wavelength range1. It has recently been installed at the 3.5m WIYN telescope at Kitt Peak National Observatory, and is currently being commissioned. The design is based on a white pupil layout with a monolithic parabolic primary mirror and a 195mm pupil size on the R4 Echelle grating. Here we describe the optical and mechanical design, assembly, and alignment of the fiber injection system which converts the native focal ratio of the sky, calibration, and science fibers to the focal ratio required to form the 195mm collimated beam
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