584 research outputs found
Imaging the asymmetric dust shell around CI Cam with long baseline optical interferometry
We present the first high angular resolution observation of the B[e]
star/X-ray transient object CI Cam, performed with the two-telescope Infrared
Optical Telescope Array (IOTA), its upgraded three-telescope version (IOTA3T)
and the Palomar Testbed Interferometer (PTI). Visibilities and closure phases
were obtained using the IONIC-3 integrated optics beam combiner. CI Cam was
observed in the near-infrared H and K spectral bands, wavelengths well suited
to measure the size and study the geometry of the hot dust surrounding CI Cam.
The analysis of the visibility data over an 8 year period from soon after the
1998 outburst to 2006 shows that the dust visibility has not changed over the
years. The visibility data shows that CI Cam is elongated which confirms the
disc-shape of the circumstellar environment and totally rules out the
hypothesis of a spherical dust shell. Closure phase measurements show direct
evidence of asymmetries in the circumstellar environment of CI Cam and we
conclude that the dust surrounding CI Cam lies in an inhomogeneous disc seen at
an angle. The near-infrared dust emission appears as an elliptical skewed
Gaussian ring with a major axis a = 7.58 +/- 0.24 mas, an axis ratio r = 0.39
+/- 0.03 and a position angle theta = 35 +/- 2 deg.Comment: 9 pages, 5 figures, accepted MNRA
Strong Near-Infrared Emission Interior to the Dust-Sublimation Radius of Young Stellar Objects MWC275 and AB Aur
Using the longest optical-interferometeric baselines currently available, we
have detected strong near-infrared (NIR) emission from inside the
dust-destruction radius of Herbig Ae stars MWC275 and AB Aur. Our
sub-milli-arcsecond resolution observations unambiguously place the emission
between the dust-destruction radius and the magnetospheric co-rotation radius.
We argue that this new component corresponds to hot gas inside the
dust-sublimation radius, confirming recent claims based on spectrally-resolved
interferometry and dust evaporation front modeling.Comment: 12 pages, 4 figures, Accepted for publication in ApJ
First L-band Interferometric Observations of a Young Stellar Object: Probing the Circumstellar Environment of MWC 419
We present spatially-resolved K- and L-band spectra (at spectral resolution R
= 230 and R = 60, respectively) of MWC 419, a Herbig Ae/Be star. The data were
obtained simultaneously with a new configuration of the 85-m baseline Keck
Interferometer. Our observations are sensitive to the radial distribution of
temperature in the inner region of the disk of MWC 419. We fit the visibility
data with both simple geometric and more physical disk models. The geometric
models (uniform disk and Gaussian) show that the apparent size increases
linearly with wavelength in the 2-4 microns wavelength region, suggesting that
the disk is extended with a temperature gradient. A model having a power-law
temperature gradient with radius simultaneously fits our interferometric
measurements and the spectral energy distribution data from the literature. The
slope of the power-law is close to that expected from an optically thick disk.
Our spectrally dispersed interferometric measurements include the Br gamma
emission line. The measured disk size at and around Br gamma suggests that
emitting hydrogen gas is located inside (or within the inner regions) of the
dust disk.Comment: Accepted for publication in Ap
Mid-infrared size survey of Young Stellar Objects: Description of Keck segment-tilting experiment and basic results
The mid-infrared properties of pre-planetary disks are sensitive to the
temperature and flaring profiles of disks for the regions where planet
formation is expected to occur. In order to constrain theories of planet
formation, we have carried out a mid-infrared (wavelength 10.7 microns) size
survey of young stellar objects using the segmented Keck telescope in a novel
configuration. We introduced a customized pattern of tilts to individual mirror
segments to allow efficient sparse-aperture interferometry, allowing full
aperture synthesis imaging with higher calibration precision than traditional
imaging. In contrast to previous surveys on smaller telescopes and with poorer
calibration precision, we find most objects in our sample are partially
resolved. Here we present the main observational results of our survey of 5
embedded massive protostars, 25 Herbig Ae/Be stars, 3 T Tauri stars, 1 FU Ori
system, and 5 emission-line objects of uncertain classification. The observed
mid-infrared sizes do not obey the size-luminosity relation found at
near-infrared wavelengths and a companion paper will provide further modelling
analysis of this sample. In addition, we report imaging results for a few of
the most resolved objects, including complex emission around embedded massive
protostars, the photoevaporating circumbinary disk around MWC 361A, and the
subarcsecond binaries T Tau, FU Ori and MWC 1080.Comment: Accepted by Astrophysical Journal. 38 pages. 9 figure
Spatially and Spectrally Resolved Hydrogen Gas within 0.1 AU of T Tauri and Herbig Ae/Be Stars
We present near-infrared observations of T Tauri and Herbig Ae/Be stars with
a spatial resolution of a few milli-arcseconds and a spectral resolution of
~2000. Our observations spatially resolve gas and dust in the inner regions of
protoplanetary disks, and spectrally resolve broad-linewidth emission from the
Brackett gamma transition of hydrogen gas. We use the technique of
spectro-astrometry to determine centroids of different velocity components of
this gaseous emission at a precision orders of magnitude better than the
angular resolution. In all sources, we find the gaseous emission to be more
compact than or distributed on similar spatial scales to the dust emission. We
attempt to fit the data with models including both dust and Brackett
gamma-emitting gas, and we consider both disk and infall/outflow morphologies
for the gaseous matter. In most cases where we can distinguish between these
two models, the data show a preference for infall/outflow models. In all cases,
our data appear consistent with the presence of some gas at stellocentric radii
of ~0.01 AU. Our findings support the hypothesis that Brackett gamma emission
generally traces magnetospherically driven accretion and/or outflows in young
star/disk systems.Comment: 48 pages, including 17 figures. Accepted for publication by Ap
Spatially Resolved Circumstellar Structure of Herbig Ae/Be Stars in the Near-Infrared
We have conducted the first systematic study of Herbig Ae/Be stars using the
technique of long baseline stellar interferometry in the near-infrared. The
principal result of this paper is that the IOTA interferometer resolves the
source of infrared excess in 11 of the 15 systems surveyed.
The visibility data for all the sources has been interpreted within the
context of four simple models which represent a range of plausible
representations for the brightness distribution of the source of excess
emission: a Gaussian, a narrow uniform ring, a flat blackbody disk with a
single temperature power law, and an infrared companion. We find that the
characteristic sizes of the near-infrared emitting regions are larger than
previously thought (0.5-5.9 AU, as given by the FWHM of the Gaussian
intensity). A further major result of this paper is that the sizes measured,
when combined with the observed spectral energy distributions, essentially rule
out accretion disk models represented by blackbody disks with the canonical
radial temperature law with exponent -3/4. We also find that, within the range
observed in this study, none of the sources (except the new binary) shows
varying visibilities as the orientation of the interferometer baseline changes.
Taken as an ensemble, with no clear evidence in favor of axi-symmetric
structure, the observations favor the interpretation that the circumstellar
dust is distributed in spherical envelopes (the Gaussian model) or thin shells
(the ring model).Comment: Accepted for publication by The Astrophysical Journa
Science with the Keck Interferometer ASTRA Program
The ASTrometric and phase-Referenced Astronomy (ASTRA) project will provide
phase referencing and astrometric observations at the Keck Interferometer,
leading to enhanced sensitivity and the ability to monitor orbits at an
accuracy level of 30-100 microarcseconds. Here we discuss recent scientific
results from ASTRA, and describe new scientific programs that will begin in
2010-2011. We begin with results from the "self phase referencing" (SPR) mode
of ASTRA, which uses continuum light to correct atmospheric phase variations
and produce a phase-stabilized channel for spectroscopy. We have observed a
number of protoplanetary disks using SPR and a grism providing a spectral
dispersion of ~2000. In our data we spatially resolve emission from dust as
well as gas. Hydrogen line emission is spectrally resolved, allowing
differential phase measurements across the emission line that constrain the
relative centroids of different velocity components at the 10 microarcsecond
level. In the upcoming year, we will begin dual-field phase referencing (DFPR)
measurements of the Galactic Center and a number of exoplanet systems. These
observations will, in part, serve as precursors to astrometric monitoring of
stellar orbits in the Galactic Center and stellar wobbles of exoplanet host
stars. We describe the design of several scientific investigations capitalizing
on the upcoming phase-referencing and astrometric capabilities of ASTRA.Comment: Published in the proceedings of the SPIE 2010 conference on "Optical
and Infrared Interferometry II
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