75 research outputs found
Modeling the e-APD SAPHIRA/C-RED ONE camera at low flux level: An attempt to count photons in the near-infrared with the MIRC-X interferometric combiner
This is the final version. Available on open access from EDP Sciences via the DOI in this recordContext. We implement an electron avalanche photodiode (e-APD) in the MIRC-X instrument, upgrade of the 6-telescope nearinfrared imager MIRC, at the CHARA array. This technology should improve the sensitivity of near-infrared interferometry.
Aims. We characterize a near-infrared C-RED ONE camera from First Light Imaging (FLI) using an e-APD from Leonardo (previously SELEX).
Methods. We first used the classical Mean-Variance analysis to measure the system gain and the amplification gain. We then developed
a physical model of the statistical distribution of the camera output signal. This model is based on multiple convolutions of the Poisson
statistic, the intrinsic avalanche gain distribution, and the observed distribution of the background signal. At low flux level, this model
constraints independently the incident illumination level, the total gain, and the excess noise factor of the amplification.
Results. We measure a total transmission of 48 ± 3% including the cold filter and the Quantum Efficiency. We measure a system
gain of 0.49 ADU/e, a readout noise of 10 ADU, and amplification gains as high as 200. These results are consistent between the two
methods and therefore validate our modeling approach. The measured excess noise factor based on the modeling is 1.47 ± 0.03, with
no obvious dependency with flux level or amplification gain.
Conclusions. The presented model allows measuring the characteristics of the e-APD array at low flux level independently of preexisting calibration. With < 0.3 electron equivalent readout noise at kilohertz frame rates, we confirm the revolutionary performances of
the camera with respect to the PICNIC or HAWAII technologies. However, the measured excess noise factor is significantly higher
than the one claimed in the literature (<1.25), and explains why counting multiple photons remains challenging with this camera.European Union Horizon 2020Labex OSUG@2020CNRS/INS
MYSTIC: Michigan Young STar Imager at CHARA
We present the design for MYSTIC, the Michigan Young STar Imager at CHARA.
MYSTIC will be a K-band, cryogenic, 6-beam combiner for the Georgia State
University CHARA telescope array. The design follows the image-plane
combination scheme of the MIRC instrument where single-mode fibers bring
starlight into a non-redundant fringe pattern to feed a spectrograph. Beams
will be injected in polarization-maintaining fibers outside the cryogenic dewar
and then be transported through a vacuum feedthrough into the ~220K cold volume
where combination is achieved and the light is dispersed. We will use a C-RED
One camera (First Light Imaging) based on the eAPD SAPHIRA detector to allow
for near-photon-counting performance. We also intend to support a 4-telescope
mode using a leftover integrated optics component designed for the VLTI-GRAVITY
experiment, allowing better sensitivity for the faintest targets. Our primary
science driver motivation is to image disks around young stars in order to
better understand planet formation and how forming planets might influence disk
structures.Comment: Presented at the 2018 SPIE Astronomical Telescopes + Instrumentation,
Austin, Texas, US
Astronomical interferometry with near-IR e-APD at CHARA: characterization, optimization and on-sky operation
We characterize a near-infrared C-RED ONE camera from First Light Imaging
(FLI). This camera uses a SAPHIRA electron avalanche photo-diode array (e-APD)
from Leonardo (previously Selex). To do so, we developed a model of the signal
distribution. This model allows a measurement of the gain and the Excess Noise
Factor (ENF) independently of preexisting calibration such as the system gain.
The results of this study show a gain which is 0.53 +/- 0.04 times the gain
reported by the manufacturer. The measured ENF is 1.47 +/- 0.03 when we
expected 1.25. For an avalanche gain of 60 and a frame rate larger than 100 Hz,
the total noise can be lower than 1 e-/frame/pixel. The lowest dark current
level is 90e-/s/pixel, in agreement with the expected H-band background passing
through the camera window. These performance values provide a significant
improvement compared to earlier-generation PICNIC camera and allowed us to
improve the performance of the Michigan infrared combiner (MIRC) instrument at
the Center for High Angular Resolution Astronomy (CHARA), as part of our MIRC-X
instrumentation project.Comment: 18 pages, 15 figures, presented at SPIE Astronomical Telescopes +
Instrumentation 2018, Austin, Texas, US
MYSTIC: Michigan Young STar Imager at CHARA
This is the final version of the article. Available from SPIE via the DOI in this record.We present the design for MYSTIC, the Michigan Young STar Imager at CHARA. MYSTIC will be a K-band, cryogenic, 6-beam combiner for the Georgia State University CHARA telescope array. The design follows the image-plane combination scheme of the MIRC instrument where single-mode fibers bring starlight into a non-redundant fringe pattern to feed a spectrograph. Beams will be injected in polarization-maintaining fibers outside the cryogenic dewar and then be transported through a vacuum feedthrough into the ~220K cold volume where combination is achieved and the light is dispersed. We will use a C-RED One camera (First Light Imaging) based on the eAPD SAPHIRA detector to allow for near-photon-counting performance. We also intend to support a 4-telescope mode using a leftover integrated optics component designed for the VLTI-GRAVITY experiment, allowing better sensitivity for the faintest targets. Our primary science driver motivation is to image disks around young stars in order to better understand planet formation and how forming planets might influence disk structures.MYSTIC is funded by the USA National Science Foundation (PI: Monnier, NSF-ATI 1506540) while the MIRC-X project is funded by the European Research Council (PI: Kraus, ERC, Grant # 639889)
The MIRC-X 6-telescope imager: Key science drivers, instrument design and operation
This is the final version of the article. Available from SPIE via the DOI in this recordMIRC-X is a new beam combination instrument at the CHARA array that enables 6-telescope interferometric imaging on object classes that until now have been out of reach for milliarcsecond-resolution imaging. As part of an instrumentation effort lead by the University of Exeter and University of Michigan, we equipped the MIRC instrument with an ultra-low read-noise detector system and extended the wavelength range to the J and H-band. The first phase of the MIRC-X commissioning was successfully completed in June 2017. In 2018 we will commission polarisation control to improve the visibility calibration and implement a 'cross-talk resiliant' mode that will minimise visibility cross-talk and enable exoplanet searches using precision closure phases. Here we outline our key science drivers and give an overview about our commissioning timeline. We comment on operational aspects, such as remote observing, and the prospects of co-phased parallel operations with the upcoming MYSTIC combiner.MIRC-X is funded by a Starting Grant from the European Research Council (ERC; grant agreement No. 639889,
PI: Kraus) and funds from the University of Exeter. The project builds on earlier investments from the University
of Michigan and the National Science Foundation (NSF, PI: Monnier)
MIRC-X/CHARA: sensitivity improvements with an ultra-low noise SAPHIRA detector
This is the final version of the article. Available from Society of Photo Optical Instrumentation Engineers (SPIE) via the DOI in this record.MIRC-X is an upgrade of the six-telescope infrared beam combiner at the CHARA telescope array, the world's largest baseline interferometer in the optical/infrared, located at the Mount Wilson Observatory in Los Angeles. The upgraded instrument features an ultra-low noise and fast frame rate infrared camera (SAPHIRA detector) based on e-APD technology. We report the MIRC-X sensitivity upgrade work and first light results in detail focusing on the detector characteristics and software architecture.MIRC-X is funded, in parts, by a Starting Grant from the European Research Council (ERC; grant agreement No. 639889, PI: Kraus) and builds on earlier investments from the University of Michigan and the National Science Foundation (NSF, PI: Monnier). This research has made use of the Jean-Marie Mariotti Center OIFits Explorer service (http://www.jmmc.fr/oifitsexplorer)
The Small Separation A-Star Companion Population: First Results with CHARA/MIRC-X
We present preliminary results from our long-baseline interferometry (LBI)
survey to constrain the multiplicity properties of intermediate-mass A-type
stars within 80pc. Previous multiplicity studies of nearby stars exhibit
orbital separation distributions well-fitted with a log-normal with peaks >
15au, increasing with primary mass. The A-star multiplicity survey of De Rosa
et al. (2014), sensitive beyond 30au but incomplete below 100 au, found a
log-normal peak around 390au. Radial velocity surveys of slowly-rotating,
chemically peculiar Am stars identified a significant number of very close
companions with periods 5 days, ~ 0.1au, a result similar to surveys of
O- and B-type primaries. With the improved performance of LBI techniques, we
can probe these close separations for normal A-type stars where other surveys
are incomplete. Our initial sample consists of 27 A-type primaries with
estimated masses between 1.44-2.49M and ages 10-790Myr, which we
observed with the MIRC-X instrument at the CHARA Array. We use the open source
software CANDID to detect five companions, three of which are new, and derive a
companion frequency of 0.19 over mass ratios 0.25-1.0 and
projected separations 0.288-5.481 au. We find a probability of 10 that
our results are consistent with extrapolations based on previous models of the
A-star companion population, over mass ratios and separations sampled. Our
results show the need to explore these very close separations to inform our
understanding of stellar formation and evolution processes.Comment: 14 pages, 3 figures, Accepted to the Astrophysical Journal on Nov. 2,
202
Characterising the orbit and circumstellar environment of the high-mass binary MWC 166 A
Context: Stellar evolution models are highly dependent on accurate mass
estimates, especially for high-mass stars in the early stages of evolution. The
most direct method for obtaining model-independent masses is derivation from
the orbit of close binaries. Aims: To derive the first astrometric+RV orbit
solution for the single-lined spectroscopic binary MWC 166 A, based on CHARA
and VLTI near-infrared interferometry over multiple epochs and ~100 archival
radial velocity measurements, and to derive fundamental stellar parameters from
this orbit. We also sought to model circumstellar activity in the system from
K-band spectral lines. Methods: We geometrically modelled the dust continuum to
derive astrometry at 13 epochs and constrain individual stellar parameters. We
used the continuum models as a base to examine differential phases,
visibilities and closure phases over the Br- and He-I emission lines.
Results: Our orbit solution suggests a period of d, twice as long
as found with previous RV orbit fits, subsequently constraining the component
masses to and . The
line-emitting gas was found to be localised around the primary and is spatially
resolved on scales of ~11 stellar radii, with the spatial displacement between
the line wings consistent with a rotating disc. Conclusions: The large radius
and stable orientation of the line emission are inconsistent with
magnetospheric or boundary-layer accretion, but indicate an ionised inner gas
disk around MWC 166 Aa. We observe line variability that could be explained
either with generic line variability in a Herbig star disc or V/R variations in
a decretion disc. We also constrained the age of the system to
~ yr, consistent with the system being comprised of a
main-sequence primary and a secondary still contracting towards the main
sequence.Comment: 24 pages, 19 figures, 7 tables, 1 appendix. Accepted in A&
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