827 research outputs found
Near-IR imaging of T Cha: evidence for scattered-light disk structures at solar system scales
T Chamaeleontis is a young star surrounded by a transitional disk, and a
plausible candidate for ongoing planet formation. Recently, a substellar
companion candidate was reported within the disk gap of this star. However, its
existence remains controversial, with the counter-hypothesis that light from a
high inclination disk may also be consistent with the observed data. The aim of
this work is to investigate the origin of the observed closure phase signal to
determine if it is best explained by a compact companion. We observed T Cha in
the L and K s filters with sparse aperture masking, with 7 datasets covering a
period of 3 years. A consistent closure phase signal is recovered in all L and
K s datasets. Data were fit with a companion model and an inclined
circumstellar disk model based on known disk parameters: both were shown to
provide an adequate fit. However, the absence of expected relative motion for
an orbiting body over the 3-year time baseline spanned by the observations
rules out the companion model. Applying image reconstruction techniques to each
dataset reveals a stationary structure consistent with forward scattering from
the near edge of an inclined disk.Comment: 6 pages, 3 figures, accepted for publication in MNRAS Letter
Unveiling the near-infrared structure of the massive-young stellar object NGC 3603 IRS 9A with sparse aperture masking and spectroastrometry
Contemporary theory holds that massive stars gather mass during their initial
phases via accreting disk-like structures. However, conclusive evidence for
disks has remained elusive for the most massive young objects. This is mainly
due to significant observational challenges. Incisive studies, even targeting
individual objects, are therefore relevant to the progression of the field. NGC
3603 IRS 9A* is a young massive stellar object still surrounded by an envelope
of molecular gas. Previous mid-infrared observations with long-baseline
interferometry provided evidence for a disk of 50 mas diameter at its core.
This work aims at a comprehensive study of the physics and morphology of IRS 9A
at near-infrared wavelengths. New sparse aperture masking interferometry data
taken with NACO/VLT at Ks and Lp filters were obtained and analysed together
with archival CRIRES spectra of the H2 and BrG lines. The calibrated
visibilities recorded at Ks and Lp bands suggest the presence of a partially
resolved compact object of 30 mas at the core of IRS 9A, together with the
presence of over-resolved flux. The spectroastrometric signal of the H2 line
shows that this spectral feature proceeds from the large scale extended
emission (300 mas) of IRS 9A, while the BrG line appears to be formed at the
core of the object (20 mas). This scenario is consistent with the brightness
distribution of the source for near- and mid-infrared wavelengths at various
spatial scales. However, our model suffers from remaining inconsistencies
between SED modelling and the interferometric data. Moreover, the BrG
spectroastrometric signal indicates that the core of IRS 9A exhibits some form
of complexity such as asymmetries in the disk. Future high-resolution
observations are required to confirm the disk/envelope model and to flesh out
the details of the physical form of the inner regions of IRS 9A.Comment: Accepted to be published in Astronomy & Astrophysics, 13 pages, 14
figure
B606: An Economic Study of the Beef Cattle Industry in Maine
This study was designed to determine the nature and location of the beef cattle industry of Maine, to investigate its economic aspects and to ascertain the conditions under which a beef enterprise would most likely succeed. This information should be useful to both present and prospective beef enterprise operators.https://digitalcommons.library.umaine.edu/aes_bulletin/1077/thumbnail.jp
A low cost scheme for high precision dual-wavelength laser metrology
A novel method capable of delivering relative optical path length metrology
with nanometer precision is demonstrated. Unlike conventional dual-wavelength
metrology which employs heterodyne detection, the method developed in this work
utilizes direct detection of interference fringes of two He-Ne lasers as well
as a less precise stepper motor open-loop position control system to perform
its measurement. Although the method may be applicable to a variety of
circumstances, the specific application where this metrology is essential is in
an astrometric optical long baseline stellar interferometer dedicated to
precise measurement of stellar positions. In our example application of this
metrology to a narrow-angle astrometric interferometer, measurement of
nanometer precision could be achieved without frequency-stabilized lasers
although the use of such lasers would extend the range of optical path length
the metrology can accurately measure. Implementation of the method requires
very little additional optics or electronics, thus minimizing cost and effort
of implementation. Furthermore, the optical path traversed by the metrology
lasers is identical with that of the starlight or science beams, even down to
using the same photodetectors, thereby minimizing the non-common-path between
metrology and science channels.Comment: 17 pages, 4 figures, accepted for publication in Applied Optic
A complex relationship between immunity and metabolism in Drosophila diet-induced insulin resistance
Spatially Resolved Mid-IR Imaging of the SR 21 Transition Disk
We present mid-IR observations from Gemini/TReCS that spatially resolve the
dust emission around SR 21. The protoplanetary disk around SR 21 is believed to
have a cleared gap extending from stellocentric radii of ~0.5 AU to ~20 AU,
based on modeling of the observed spectral energy distribution. Our new
observations resolve the dust emission, and our data are inconsistent with the
previous model. We require the disk to be completely cleared within ~10 AU,
without the hot inner disk spanning ~0.25-0.5 AU posited previously. To fit the
SED and mid-IR imaging data together, we propose a disk model with a large
inner hole, but with a warm companion--possibly surrounded by circumstellar
material of its own--residing near the outer edge of the cleared region. We
also discuss a model with a narrow ring included in a large cleared inner disk
region, and argue that it is difficult to reconcile with the data.Comment: 13 pages, including 3 figures. Accepted for publication by ApJ
Letter
Long-Baseline Interferometric Multiplicity Survey of the Sco-Cen OB Association
We present the first multiplicity-dedicated long baseline optical
interferometric survey of the Scorpius-Centaurus-Lupus-Crux association. We
used the Sydney University Stellar Interferometer to undertake a survey for new
companions to 58 Sco-Cen B- type stars and have detected 24 companions at
separations ranging from 7-130mas, 14 of which are new detections. Furthermore,
we use a Bayesian analysis and all available information in the literature to
determine the multiplicity distribution of the 58 stars in our sample, showing
that the companion frequency is F = 1.35 and the mass ratio distribution is
best described as a power law with exponent equal to -0.46, agreeing with
previous Sco-Cen high mass work and differing significantly from lower-mass
stars in Tau-Aur. Based on our analysis, we estimate that among young B-type
stars in moving groups, up to 23% are apparently single stars. This has strong
implications for the understanding of high-mass star formation, which requires
angular momentum dispersal through some mechanism such as formation of multiple
systems.Comment: 7 figures, 5 tables, accepted for publication in MNRA
NACO/SAM observations of sources at the Galactic Center
Sparse aperture masking (SAM) interferometry combined with Adaptive Optics
(AO) is a technique that is uniquely suited to investigate structures near the
diffraction limit of large telescopes. The strengths of the technique are a
robust calibration of the Point Spread Function (PSF) while maintaining a
relatively high dynamic range. We used SAM+AO observations to investigate the
circumstellar environment of several bright sources with infrared excess in the
central parsec of the Galaxy. For our observations, unstable atmospheric
conditions as well as significant residuals after the background subtraction
presented serious problems for the standard approach of calibrating SAM data
via interspersed observations of reference stars. We circumvented these
difficulties by constructing a synthesized calibrator directly from sources
within the field-of-view. When observing crowded fields, this novel method can
boost the efficiency of SAM observations because it renders interspersed
calibrator observations unnecessary. Here, we presented the first NaCo/SAM
images reconstructed using this method.Comment: 8 pages, 10 figures, proceedings of the conference "Astrophysics at
High Angular Resolution" (AHAR-2011
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