59 research outputs found
12 and 18 micron images of dust surrounding HD 32297
We present the first subarcsecond-resolution images at multiple mid-IR
wavelengths of the thermally-emitting dust around the A0 star HD 32297. Our
observations with T-ReCS at Gemini South reveal a nearly edge-on resolved disk
at both 11.7 microns and 18.3 microns that extends ~150 AU in radius. The
mid-IR is the third wavelength region in which this disk has been resolved,
following coronagraphic observations by others of the source at optical and
near-IR wavelengths. The global mid-IR colors and detailed consideration of the
radial color-temperature distribution imply that the central part of the disk
out to ~80 AU is relatively deficient in dust.Comment: 4 pages, 3 figures; accepted for publication in ApJ
High-spatial-resolution imaging of thermal emission from debris disks
We have obtained sub-arcsec mid-IR images of a sample of debris disks within
100 pc. For our sample of nineteen A-type debris disk candidates chosen for
their IR excess, we have resolved, for the first time, five sources plus the
previously resolved disk around HD 141569. Two other sources in our sample have
been ruled out as debris disks since the time of sample selection. Three of the
six resolved sources have inferred radii of 1-4 AU (HD 38678, HD 71155, and HD
181869), and one source has an inferred radius ~10-30 AU (HD 141569). Among the
resolved sources with detections of excess IR emission, HD 71155 appears to be
comparable in size (r~2 AU) to the solar system's asteroid belt, thus joining
Zeta Lep (HD 38678, reported previously) to comprise the only two resolved
sources of that class. Two additional sources (HD 95418 and HD 139006) show
spatial extent that implies disk radii of ~1-3 AU, although the excess IR
fluxes are not formally detected with better than 2-sigma significance. For the
unresolved sources, the upper limits on the maximum radii of mid-IR disk
emission are in the range ~1-20 AU, four of which are comparable in radius to
the asteroid belt. We have compared the global color temperatures of the dust
to that expected for the dust in radiative equilibrium at the distances
corresponding to the observed sizes or limits on the sizes. In most cases, the
temperatures estimated via these two methods are comparable, and therefore, we
see a generally consistent picture of the inferred morphology and the global
mid-IR emission. Finally, while our sample size is not statistically
significant, we notice that the older sources (>200 Myr) host much warmer dust
(T > 400 K) than younger sources (in the 10s of Myr).Comment: 46 pages, 12 figure
An active asteroid belt causing the UX Ori phenomenon in RZ Psc
We report the discovery of mid-infrared excess emission in the young object
RZ Psc. The excess constitutes ~8% of its Lbol, and is well fit by a single
500K black-body implying a dust free region within 0.7AU for optically thick
dust. The object displays dust obscuration events (UXOR behaviour) with a
time-scale that suggests dusty material on orbits of 0.5AU. We also report a
12.4 year cyclical photometric variability which can be interpreted as due to
perturbations in the dust distribution. The system is characterized by a high
inclination, marginal extinction (during bright photometric states), a single
temperature for the warm dust, and an age estimate which puts the star beyond
the formation stage. We propose that the dust occultation events present a
dynamical view of an active asteroid belt whose collisional products
sporadically obscure the central star.Comment: Accepted for A&A letter
Twenty-five subarcsecond binaries discovered by lunar occultations
We report on 25 subarcsecond binaries, detected for the first time by means of lunar occultations in the near-infrared (near-IR) as part of a long-term program using the ISAAC instrument at the ESO Very Large Telescope. The primaries have magnitudes in the range K = 3.8–10.4, and the companions in the range K = 6.4–12.1. The magnitude differences have a median value of 2.8, with the largest being 5.4. The projected separations are in the range 6–748 mas and with a median of 18 mas, or about three times less than the diffraction limit of the telescope. Among our binary detections are a pre-main-sequence star and an enigmatic Mira-like variable previously suspected to have a companion. Additionally, we quote an accurate first-time near-IR detection of a previously known wider binary. We discuss our findings on an individual basis as far as made possible by the available literature, and we examine them from a statistical point of view. We derive a typical frequency of binarity among field stars of ≈10%, in the resolution and sensitivity range afforded by the technique (≈0farcs003 to ≈0farcs5, and K ≈ 12 mag, respectively). This is in line with previous results using the same technique but we point out interesting differences that we can trace up to sensitivity, time sampling, and average distance of the targets. Finally, we discuss the prospects for further follow-up studies
A catalog of near-ir sources found to be unresolved with milliarcsecond resolution
Calibration is one of the long-standing problems in optical interferometric measurements, particularly with long baselines which demand stars with angular sizes on the milliarcsecond scale and no detectable companions. While systems of calibrators have been generally established for the near-infrared in the bright source regime (K ≲ 3 mag), modern large interferometers are sensitive to significantly fainter magnitudes. We aim to provide a list of sources found to be unresolved from direct observations with high angular resolution and dynamic range, which can be used to choose interferometric calibrators. To this purpose, we have used a large number of lunar occultations recorded with the ISAAC instrument at the Very Large Telescope to select sources found to be unresolved and without close companions. An algorithm has been used to determine the limiting angular resolution achieved for each source, taking into account a noise model built from occulted and unocculted portions of the light curves. We have obtained upper limits on the angular sizes of 556 sources, with magnitudes ranging from Ks ≈ 4 to 10, with a median of 7.2 mag. The upper limits on possible undetected companions (within ≈0farcs5) range from Ks ≈ 8 to 13, with a median of 11.5 mag. One-third of the sources have angular sizes ⩽1 mas, and two-thirds have sizes ⩽2 mas. This list of unresolved sources matches well the capabilities of current large interferometric facilities. We also provide available cross-identifications, magnitudes, spectral types, and other auxiliary information. A fraction of the sources are found to be potentially variable. The list covers parts of the Galactic Bulge and in particular the vicinity of the Galactic Center, where extinction is very significant and traditional lists of calibrators are often insufficient
Resolving the terrestrial planet forming regions of HD113766 and HD172555 with MIDI
We present new MIDI interferometric and VISIR spectroscopic observations of
HD113766 and HD172555. Additionally we present VISIR 11um and 18um imaging
observations of HD113766. These sources represent the youngest (16Myr and 12Myr
old respectively) debris disc hosts with emission on <<10AU scales. We find
that the disc of HD113766 is partially resolved on baselines of 42-102m, with
variations in resolution with baseline length consistent with a Gaussian model
for the disc with FWHM of 1.2-1.6AU (9-12mas). This is consistent with the
VISIR observations which place an upper limit of 0."14 (17AU) on the emission,
with no evidence for extended emission at larger distances. For HD172555 the
MIDI observations are consistent with complete resolution of the disc emission
on all baselines of lengths 56-93m, putting the dust at a distance of >1AU
(>35mas). When combined with limits from TReCS imaging the dust at ~10um is
constrained to lie somewhere in the region 1-8AU. Observations at ~18um reveal
extended disc emission which could originate from the outer edge of a broad
disc, the inner parts of which are also detected but not resolved at 10um, or
from a spatially distinct component. These observations provide the most
accurate direct measurements of the location of dust at 1-8AU that might
originate from the collisions expected during terrestrial planet formation.
These observations provide valuable constraints for models of the composition
of discs at this epoch and provide a foundation for future studies to examine
in more detail the morphology of debris discs.Comment: 22 pages, 19 figures, accepted for publication in MNRA
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