32 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
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
MIRC-X: a highly-sensitive six telescope interferometric imager at the CHARA Array
MIRC-X (Michigan InfraRed Combiner-eXeter) is a new highly-sensitive
six-telescope interferometric imager installed at the CHARA Array that provides
an angular resolution equivalent of up to a 330 m diameter baseline telescope
in J and H band wavelengths ( milli-arcseconds). We
upgraded the original MIRC (Michigan InfraRed Combiner) instrument to improve
sensitivity and wavelength coverage in two phases. First, a revolutionary
sub-electron noise and fast-frame rate C-RED ONE camera based on a SAPHIRA
detector was installed. Second, a new-generation beam combiner was designed and
commissioned to (i) maximize sensitivity, (ii) extend the wavelength coverage
to J-band, and (iii) enable polarization observations. A low-latency and
fast-frame rate control software enables high-efficiency observations and
fringe tracking for the forthcoming instruments at CHARA Array. Since mid-2017,
MIRC-X has been offered to the community and has demonstrated best-case H-band
sensitivity down to 8.2 correlated magnitude. MIRC-X uses single-mode fibers to
coherently combine light of six telescopes simultaneously with an image-plane
combination scheme and delivers a visibility precision better than 1%, and
closure phase precision better than . MIRC-X aims at (i) imaging
protoplanetary disks, (ii) detecting exoplanets with precise astrometry, and
(iii) imaging stellar surfaces and star-spots at an unprecedented angular
resolution in the near-infrared. In this paper, we present the instrument
design, installation, operation, and on-sky results, and demonstrate the
imaging and astrometric capability of MIRC-X on the binary system Peg.
The purpose of this paper is to provide a solid reference for studies based on
MIRC-X data and to inspire future instruments in optical interferometry.Comment: 31 pages, 29 figures, accepted for publication in The Astronomical
Journa
Imaging the warped dusty disk wind environment of SU Aurigae with MIRC-X
SU Aurigae is a widely studied T Tauri star and here we present original
state-of-the-art interferometric observations with better uv and baseline
coverage than previous studies. We aim to investigate the characteristics of
the circumstellar material around SU Aur, constrain the disk geometry,
composition and inner dust rim structure. The MIRC-X instrument at CHARA is a 6
telescope optical beam combiner offering baselines up to 331 m. We undertook
image reconstruction for model-independent analysis, and fitted geometric
models such as Gaussian and ring distributions. Additionally, the fitting of
radiative transfer models constrains the physical parameters of the disk. Image
reconstruction reveals a highly inclined disk with a slight asymmetry
consistent with inclination effects obscuring the inner disk rim through
absorption of incident star light on the near-side and thermal
re-emission/scattering of the far-side. Geometric models find that the
underlying brightness distribution is best modelled as a Gaussian with a FWHM
of at an inclination of and minor
axis position angle of . Radiative transfer modelling shows a
flared disk with an inner radius at 0.16 au which implies a grain size of assuming astronomical silicates and a scale height of 9.0 au at
100 au. In agreement with literature, only the dusty disk wind successfully
accounts for the NIR excess by introducing dust above the mid-plane. Our
results confirm and provide better constraints than previous inner disk studies
of SU Aurigae. We confirm the presence of a dusty disk wind in the cicumstellar
environment, the strength of which is enhanced by a late infall event which
also causes very strong misalignments between the inner and outer disks.Comment: arXiv admin note: substantial text overlap with arXiv:2111.06205,
arXiv:1905.1190
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&
The Orbits and Dynamical Masses of the Castor System
Castor is a system of six stars in which the two brighter objects, Castor A
and B, revolve around each other every 450 yr and are both short-period
spectroscopic binaries. They are attended by the more distant Castor C, which
is also a binary. Here we report interferometric observations with the CHARA
array that spatially resolve the companions in Castor A and B for the first
time. We complement these observations with new radial velocity measurements of
A and B spanning 30 yr, with the Hipparcos intermediate data, and with existing
astrometric observations of the visual AB pair obtained over the past three
centuries. We perform a joint orbital solution to solve simultaneously for the
three-dimensional orbits of Castor A and B as well as the AB orbit. We find
that they are far from being coplanar: the orbit of A is nearly at right angles
(92 degrees) relative to the wide orbit, and that of B is inclined about 59
degrees compared to AB. We determine the dynamical masses of the four stars in
Castor A and B to a precision better than 1%. We also determine the radii of
the primary stars of both subsystems from their angular diameters measured with
CHARA, and use them together with stellar evolution models to infer an age for
the system of 290 Myr. The new knowledge of the orbits enables us to measure
the slow motion of Castor C as well, which may assist future studies of the
dynamical evolution of this remarkable sextuple system.Comment: 17 pages in emulateapj format, including figures and tables. Accepted
for publication in The Astrophysical Journa
Multiplicity of northern bright O-type stars with optical long baseline interferometry
The study of the multiplicity of massive stars gives hints on their formation
processes and their evolutionary paths, which are still not fully understood.
Large separation binaries (>50 milliseconds of arc, mas) can be probed by
adaptive-optics-assisted direct imaging and sparse aperture masking, while
close binaries can be resolved by photometry and spectroscopy. However, optical
long baseline interferometry is mandatory to establish the multiplicity of
Galactic massive stars at the separation gap between 1 and 50 mas. In this
paper, we aim to demonstrate the capability of the new interferometric
instrument MIRC-X, located at the CHARA Array, to study the multiplicity of
O-type stars and therefore probe the full range of separation for more than 120
massive stars (H<7.5 mag). We initiated a pilot survey of bright O-type stars
(H<6.5mag) observable with MIRC-X. We observed 29 O-type stars, including two
systems in average atmospheric conditions around a magnitude of H=7.5 mag. We
systematically reduced the obtained data with the public reduction pipeline of
the instrument. We analyzed the reduced data using the dedicated python
software CANDID to detect companions. Out of these 29 systems, we resolved 19
companions in 17 different systems with angular separations between ~0.5 and 50
mas. This results in a multiplicity fraction fm=17/29=0.59+/-0.09, and an
average number of companions fc=19/29=0.66+/-0.13. Those results are in
agreement with the results of the SMASH+ survey in the Southern Hemisphere.
Thirteen of these companions have been resolved for the first time, including
the companion responsible for the nonthermal emission in Cyg OB2-5 A and the
confirmation of the candidate companion of HD 47129 suggested by SMASH+. A
large survey on more than 120 northern O-type stars (H<7.5) is possible with
MIRC-X and will be fruitful.Comment: 15 pages, 9 figures, 5 tables, accepted in A&
Refining the Stellar Parameters of Ceti: a Pole-on Solar Analog
To accurately characterize the planets a star may be hosting, stellar
parameters must first be well-determined. Ceti is a nearby solar analog
and often a target for exoplanet searches. Uncertainties in the observed
rotational velocities have made constraining Ceti's inclination
difficult. For planet candidates from radial velocity (RV) observations, this
leads to substantial uncertainties in the planetary masses, as only the minimum
mass () can be constrained with RV. In this paper, we used new
long-baseline optical interferometric data from the CHARA Array with the MIRC-X
beam combiner and extreme precision spectroscopic data from the Lowell
Discovery Telescope with EXPRES to improve constraints on the stellar
parameters of Ceti. Additional archival data were obtained from a
Tennessee State University Automatic Photometric Telescope and the Mount Wilson
Observatory HK project. These new and archival data sets led to improved
stellar parameter determinations, including a limb-darkened angular diameter of
mas and rotation period of days. By combining
parameters from our data sets, we obtained an estimate for the stellar
inclination of . This nearly-pole-on orientation has implications
for the previously-reported exoplanets. An analysis of the system dynamics
suggests that the planetary architecture described by Feng et al. (2017) may
not retain long-term stability for low orbital inclinations. Additionally, the
inclination of Ceti reveals a misalignment between the inclinations of
the stellar rotation axis and the previously-measured debris disk rotation axis
().Comment: 14 pages, 3 figures, 4 tables, 1 appendix, accepted for publication
to A