33 research outputs found
A VLA Survey For Faint Compact Radio Sources in the Orion Nebula Cluster
We present Karl G. Janksy Very Large Array (VLA) 1.3 cm, 3.6 cm, and 6 cm
continuum maps of compact radio sources in the Orion Nebular Cluster. We
mosaicked 34 square arcminutes at 1.3 cm, 70 square arcminutes at 3.6 cm and
109 square arcminutes at 6 cm, containing 778 near-infrared detected YSOs and
190 HST-identified proplyds (with significant overlap between those
characterizations). We detected radio emission from 175 compact radio sources
in the ONC, including 26 sources that were detected for the first time at these
wavelengths. For each detected source we fit a simple free-free and dust
emission model to characterize the radio emission. We extrapolate the free-free
emission spectrum model for each source to ALMA bands to illustrate how these
measurements could be used to correctly measure protoplanetary disk dust masses
from sub-millimeter flux measurements. Finally, we compare the fluxes measured
in this survey with previously measured fluxes for our targets, as well as four
separate epochs of 1.3 cm data, to search for and quantify variability of our
sources.Comment: 13 pages, 6 figures, 4 tables, ApJ, in pres
AB Aurigae Resolved: Evidence for Spiral Structure
We obtained high angular resolution (~2") images of the 13CO(J=1-0) line and
2.7 millimeter continuum emission, and slightly lower resolution images of
12CO(J=1-0) and C18O(J=1-0) line emission toward the Herbig Ae star AB Aurigae.
We resolve a circumstellar disk of diameter 780 AU (FWHM) with a velocity
pattern consistent with a purely rotational disk at inclination 21.5 degrees
and position angle 58.6 degrees. Using Keplerian disk models, we find a central
source dynamical mass of 2.8+-0.1 Msun and a cutoff radius of 615 AU for the
13CO emission. Inclination, mass, and radius determined from 12CO and C18O
observations agree with those values, given optical depth and abundance
effects. As a result of the high angular resolution of our observations, we
confirm the existence of spiral structure suggested by near-IR scattered light
images and show that the spiral arms represent density contrasts in the disk.Comment: 11 pages, 3 figures, accepted ApJ Letter
Simultaneous Exoplanet Characterization and deep wide-field imaging with a diffractive pupil telescope
High-precision astrometry can identify exoplanets and measure their orbits
and masses, while coronagraphic imaging enables detailed characterization of
their physical properties and atmospheric compositions through spectroscopy. In
a previous paper, we showed that a diffractive pupil telescope (DPT) in space
can enable sub-microarcsecond accuracy astrometric measurements from wide-field
images by creating faint but sharp diffraction spikes around the bright target
star. The DPT allows simultaneous astrometric measurement and coronagraphic
imaging, and we discuss and quantify in this paper the scientific benefits of
this combination for exoplanet science investigations: identification of
exoplanets with increased sensitivity and robustness, and ability to measure
planetary masses to high accuracy. We show how using both measurements to
identify planets and measure their masses offers greater sensitivity and
provides more reliable measurements than possible with separate missions, and
therefore results in a large gain in mission efficiency. The combined
measurements reliably identify potentially habitable planets in multiple
systems with a few observations, while astrometry or imaging alone would
require many measurements over a long time baseline. In addition, the combined
measurement allows direct determination of stellar masses to percent-level
accuracy, using planets as test particles. We also show that the DPT maintains
the full sensitivity of the telescope for deep wide-field imaging, and is
therefore compatible with simultaneous scientific observations unrelated to
exoplanets. We conclude that astrometry, coronagraphy, and deep wide-field
imaging can be performed simultaneously on a single telescope without
significant negative impact on the performance of any of the three techniques.Comment: 15 pages, 6 figures. This second paper, following the paper
describing the diffractive pupil telescope (DPT) astrometric technique, shows
how simultaneous astrometry and coronagraphy observations, enabled by the DPT
concept, constrain the orbital parameters and mass of exoplanet
Isolating Dust and Free-Free Emission in ONC Proplyds with ALMA Band 3 Observations
The Orion Nebula Cluster (ONC) hosts protoplanetary disks experiencing
external photoevaporation by the cluster's intense UV field. These ``proplyds"
are comprised of a disk surrounded by an ionization front. We present ALMA Band
3 (3.1 mm) continuum observations of 12 proplyds. Thermal emission from the
dust disks and free-free emission from the ionization fronts are both detected,
and the high-resolution (0.057") of the observations allows us to spatially
isolate these two components. The morphology is unique compared to images at
shorter (sub)millimeter wavelengths, which only detect the disks, and images at
longer centimeter wavelengths, which only detect the ionization fronts. The
disks are small ( = 6.4--38 au), likely due to truncation by ongoing
photoevaporation. They have low spectral indices ()
measured between Bands 7 and 3, suggesting the dust emission is optically
thick. They harbor tens of Earth masses of dust as computed from the millimeter
flux using the standard method, although their true masses may be larger due to
the high optical depth. We derive their photoevaporative mass-loss rates in two
ways: first, by invoking ionization equilibrium, and second using the
brightness of the free-free emission to compute the density of the outflow. We
find decent agreement between these measurements and = 0.6--18.4
10 yr. The photoevaporation timescales are
generally shorter than the 1 Myr age of the ONC, underscoring the known
``proplyd lifetime problem." Disk masses that are underestimated due to being
optically thick remains one explanation to ease this discrepancy.Comment: 17 pages, 12 figures, accepted for publication in Ap
Imaging protoplanets: observing transition disks with non-redundant masking
Transition disks, protoplanetary disks with inner clearings, are promising
objects in which to directly image forming planets. The high contrast imaging
technique of non-redundant masking is well posed to detect planetary mass
companions at several to tens of AU in nearby transition disks. We present
non-redundant masking observations of the T Cha and LkCa 15 transition disks,
both of which host posited sub-stellar mass companions. However, due to a loss
of information intrinsic to the technique, observations of extended sources
(e.g. scattered light from disks) can be misinterpreted as moving companions.
We discuss tests to distinguish between these two scenarios, with applications
to the T Cha and LkCa 15 observations. We argue that a static,
forward-scattering disk can explain the T Cha data, while LkCa 15 is best
explained by multiple orbiting companions.Comment: SPIE conference proceedin
Astrometry with the Keck-Interferometer: the ASTRA project and its science
The sensitivity and astrometry upgrade ASTRA of the Keck Interferometer is
introduced. After a brief overview of the underlying interferometric
principles, the technology and concepts of the upgrade are presented. The
interferometric dual-field technology of ASTRA will provide the KI with the
means to observe two objects simultaneously, and measure the distance between
them with a precision eventually better than 100 uas. This astrometric
functionality of ASTRA will add a unique observing tool to fields of
astrophysical research as diverse as exo-planetary kinematics, binary
astrometry, and the investigation of stars accelerated by the massive black
hole in the center of the Milky Way as discussed in this contribution.Comment: 22 pages, 10 figures (low resolution), contribution to the
summerschool "Astrometry and Imaging with the Very Large Telescope
Interferometer", 2 - 13 June, 2008, Keszthely, Hungary, corrected authorlis