31 research outputs found
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
Probing the Inner Disk Emission of the Herbig Ae Stars HD 163296 and HD 190073
The physical processes occurring within the inner few astronomical units of
proto-planetary disks surrounding Herbig Ae stars are crucial to setting the
environment in which the outer planet-forming disk evolves and put critical
constraints on the processes of accretion and planet migration. We present the
most complete published sample of high angular resolution H- and K-band
observations of the stars HD 163296 and HD 190073, including 30 previously
unpublished nights of observations of the former and 45 nights of the latter
with the CHARA long-baseline interferometer, in addition to archival VLTI data.
We confirm previous observations suggesting significant near-infrared emission
originates within the putative dust evaporation front of HD 163296 and show
this is the case for HD 190073 as well. The H- and K-band sizes are the same
within for HD 163296 and within for HD 190073. The
radial surface brightness profiles for both disks are remarkably Gaussian-like
with little or no sign of the sharp edge expected for a dust evaporation front.
Coupled with spectral energy distribution analysis, our direct measurements of
the stellar flux component at H and K bands suggest that HD 190073 is much
younger (<400 kyr) and more massive (~5.6 M) than previously thought,
mainly as a consequence of the new Gaia distance (891 pc).Comment: 19 pages, 6 figure
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
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
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
The orbit and stellar masses of the archetype colliding-wind binary WR 140
We present updated orbital elements for the Wolf-Rayet (WR) binary WR 140 (HD
193793; WC7pd + O5.5fc). The new orbital elements were derived using previously
published measurements along with 160 new radial velocity measurements across
the 2016 periastron passage of WR 140. Additionally, four new measurements of
the orbital astrometry were collected with the CHARA Array. With these
measurements, we derive stellar masses of
and . We also include a discussion of the
evolutionary history of this system from the Binary Population and Spectral
Synthesis (BPASS) model grid to show that this WR star likely formed primarily
through mass loss in the stellar winds, with only a moderate amount of mass
lost or transferred through binary interactions.Comment: 10 pages, 5 figure