104 research outputs found
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
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
AC Her: Evidence of the first polar circumbinary planet
We examine the geometry of the post-asymptotic giant branch (AGB) star binary
AC Her and its circumbinary disk. We show that the observations describe a
binary orbit that is perpendicular to the disk with an angular momentum vector
that is within of the binary eccentricity vector, meaning that the
disk is close to a stable polar alignment. The most likely explanation for the
very large inner radius of the dust is a planet within the circumbinary disk.
This is therefore both the first reported detection of a polar circumbinary
disk around a post-AGB binary and the first evidence of a polar circumbinary
planet. We consider the dynamical constraints on the circumbinary disk size and
mass. The polar circumbinary disk feeds circumstellar disks with gas on orbits
that are highly inclined with respect to the binary orbit plane. The resulting
circumstellar disk inclination could be anywhere from coplanar to polar
depending upon the competition between the mass accretion and binary torques.Comment: Accepted for publication in ApJ
A Low Cost Auto-filling and Refrigeration Rate Regulated Liquid Nitrogen Controller for Near Infrared Instruments
Liquid Nitrogen is one of the key refrigerating elements in cooling near infrared science instruments to reduce the dark, readout noises and thermal emissions in the near infrared originated from the instrument structure. Usually, a small liquid nitrogen tank connected to the near infrared instrument is auto filled from a large Dewar in order to maintain required low temperatures during the experiment for several hours. The detectors used in these instruments are quite expensive and they need to be cooled down steadily (< 2K/min) to avoid mechanical damage. The steady state cooling of the detector is the key requirement to be considered while cooling down the detector. In this paper, a controller is developed to auto-fill the liquid nitrogen tank and also to keep the refrigeration rate of the detector below 2K/min. A systematic survey of auto-filling controllers is studied. The auto-filling of liquid nitrogen from Dewar to tank is implemented with a standard on-off controller. To address the critical refrigeration rate of the detector, two approaches are studied: a) by fixed time pumping; b) by feedback the detector cooling rate. In this work we have used inexpensive equipment to develop this controller. It is very successfully used for GRAVITY acquisition camera, a near infrared instrument for European Southern Observatory. This controller has been stable and efficient for our experiment. This low cost controller can be used for any student laboratory and research
The GRAVITY instrument software / High-level software
GRAVITY is the four-beam, near- infrared, AO-assisted, fringe tracking,
astrometric and imaging instrument for the Very Large Telescope Interferometer
(VLTI). It is requiring the development of one of the most complex instrument
software systems ever built for an ESO instrument. Apart from its many
interfaces and interdependencies, one of the most challenging aspects is the
overall performance and stability of this complex system. The three infrared
detectors and the fast reflective memory network (RMN) recorder contribute a
total data rate of up to 20 MiB/s accumulating to a maximum of 250 GiB of data
per night. The detectors, the two instrument Local Control Units (LCUs) as well
as the five LCUs running applications under TAC (Tools for Advanced Control)
architecture, are interconnected with fast Ethernet, RMN fibers and dedicated
fiber connections as well as signals for the time synchronization. Here we give
a simplified overview of all subsystems of GRAVITY and their interfaces and
discuss two examples of high-level applications during observations: the
acquisition procedure and the gathering and merging of data to the final FITS
file.Comment: 8 pages, 7 figures, published in Proc. SPIE 9146, Optical and
Infrared Interferometry IV, 91462
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,
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