153 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
Temporal Variation In Fecundity And Spawning In The Eastern Oyster, Crassostrea Virginica, In The Piankatank River, Virginia
Oysters of the genus Crassostrea are considered good examples of an r-selected marine invertebrate with small egg size, high fecundity, and multiple spawning events per year, each characterized by significant individual weight loss. Historical (decadal) data for the Virginia portion of the Chesapeake Bay support these generalities. We present recent (subdecadal) data, collected for natural Crassostrea virginica broodstock of populations in the Piankatank River, Virginia. The relationship is described between oyster size, fecundity, spawning periodicity, and egg viability for natural broodstock. Oysters collected throughout the summers of 2010 through 2012 and induced to spawn by thermal cycling released viable eggs on 7 dates (n = 119 oysters, 35male, 84 female; shell length (SL) range, 58-113 mm). Oysters were opened to examine sex ratio on four additional dates (total n = 242 oysters, 82 male, 160 female). Fecundity varied in the range 10(5)-1.2x10(8) eggs. When all data are considered in unison, no strong relationship with SL is evident; however, when eliminating the artifact of data corresponding to minimal egg release, a much stronger relationship, comparable with that reported in older literature, emerges. Female fraction (Female/(Female + Male)) was consistently more than 1 in oysters larger than 60 mm in SL (estimated age, \u3e= 2 y), generally in accordance with recently published literature on the species in themid-Atlantic. The size-versus-fecundity relationship does not appear to be greatly influenced by disease prevalence/intensity. The temporal sequence of spawning activity was not observed to continue after midsummer and is not commensurate with a cumulative degree-day estimator during the latter half of the well-documented historical spawning season. A size-fecundity estimator for the Piankatank River oysters provides a basis to estimate the disproportionate value of larger/older (\u3e= 3 y) oysters in the system, and provides additional input to the fine-tuning of a previously developed rotational harvest schedule for the river stock. The possible impact of recent changes in water quality, seasonal occurrence of dinoflagellate blooms, and/or long-term impacts of changing regimes were not examined in detail in this study but are suggested as worthy lines of future investigation
Protoplanetary Disk Masses in the Young NGC 2024 Cluster
We present the results from a Submillimeter Array survey of the 887 micron
continuum emission from the protoplanetary disks around 95 young stars in the
young cluster NGC 2024. Emission was detected from 22 infrared sources, with
flux densities from ~5 to 330 mJy; upper limits (at 3sigma) for the other 73
sources range from 3 to 24 mJy. For standard assumptions, the corresponding
disk masses range from ~0.003 to 0.2Msolar, with upper limits at
0.002--0.01Msolar. The NGC 2024 sample has a slightly more populated tail at
the high end of its disk mass distribution compared to other clusters, but
without more information on the nature of the sample hosts it remains unclear
if this difference is statistically significant or a superficial selection
effect. Unlike in the Orion Trapezium, there is no evidence for a disk mass
dependence on the (projected) separation from the massive star IRS2b in the NGC
2024 cluster. We suggest that this is due to either the cluster youth or a
comparatively weaker photoionizing radiation field.Comment: ApJ, in pres
ALMA Observations of the Largest Proto-Planetary Disk in the Orion Nebula, 114-426: A CO Silhouette
We present ALMA observations of the largest protoplanetary disk in the Orion
Nebula, 114-426. Detectable 345 GHz (856 micron) dust continuum is produced
only in the 350 AU central region of the ~1000 AU diameter silhouette seen
against the bright H-alpha background in HST images. Assuming optically thin
dust emission at 345 GHz, a gas-to-dust ratio of 100, and a grain temperature
of 20 K, the disk gas-mass is estimated to be 3.1 +/- 0.6 Jupiter masses. If
most solids and ices have have been incorporated into large grains, however,
this value is a lower limit. The disk is not detected in dense-gas tracers such
as HCO+ J=4-3, HCN J=4-3, or CS =7-6. These results may indicate that the
114-426 disk is evolved and depleted in some light organic compounds found in
molecular clouds. The CO J=3-2 line is seen in absorption against the bright 50
to 80 K background of the Orion A molecular cloud over the full spatial extent
and a little beyond the dust continuum emission. The CO absorption reaches a
depth of 27 K below the background CO emission at VLSR ~6.7 km/s about 0.52
arcseconds (210 AU) northeast and 12 K below the background CO emission at VLSR
~ 9.7 km/s about 0.34 arcseconds (140 AU) southwest of the suspected location
of the central star, implying that the embedded star has a mass less than 1
Solar mass .Comment: 20 pages, 4 figure
ALMA Observations of the Orion Proplyds
We present ALMA observations of protoplanetary disks ("proplyds") in the
Orion Nebula Cluster. We imaged 5 individual fields at 856um containing 22
HST-identified proplyds and detected 21 of them. Eight of those disks were
detected for the first time at submillimeter wavelengths, including the most
prominent, well-known proplyd in the entire Orion Nebula, 114-426. Thermal dust
emission in excess of any free-free component was measured in all but one of
the detected disks, and ranged between 1-163 mJy, with resulting disk masses of
0.3-79 Mjup. An additional 26 stars with no prior evidence of associated disks
in HST observations were also imaged within the 5 fields, but only 2 were
detected. The disk mass upper limits for the undetected targets, which include
OB stars, theta1Ori C and theta1Ori F, range from 0.1-0.6 Mjup. Combining these
ALMA data with previous SMA observations, we find a lack of massive (>3 Mjup)
disks in the extreme-UV dominated region of Orion, within 0.03 pc of O-star
theta1Ori C. At larger separations from theta1Ori C, in the far-UV dominated
region, there is a wide range of disk masses, similar to what is found in
low-mass star forming regions. Taken together, these results suggest that a
rapid dissipation of disk masses likely inhibits potential planet formation in
the extreme-UV dominated regions of OB associations, but leaves disks in the
far-UV dominated regions relatively unaffected.Comment: ApJ, in pres
A Submillimeter Array Survey of Protoplanetary Disks in the Orion Nebula Cluster
We present the full results of our 3-year long Submillimeter Array survey of
protoplanetary disks in the Orion Nebula Cluster. We imaged 23 fields at 880
microns and 2 fields at 1330 microns, covering an area of ~6.5 arcmin^2 and
containing 67 disks. We detected 42 disks with fluxes between 6-135 mJy and at
rms noise levels between 0.6 to 5.3 mJy/beam. Thermal dust emission above any
free-free component was measured in 40 of the 42 detections, and the inferred
disk masses range from 0.003-0.07 Msolar. We find that disks located within 0.3
pc of theta^1 Ori C have a truncated mass distribution, while disks located
beyond 0.3 pc have masses more comparable to those found in low-mass star
forming regions. The disk mass distribution in Orion has a distance dependence,
with a derived relationship max(M_(disk)) = 0.046Msolar(d/0.3pc)^0.33 for the
maximum disk masses. We found evidence of grain growth in disk 197-427, the
only disk detected at both 880 microns and 1330 microns with the SMA. Despite
the rapid erosion of the outer parts of the Orion disks by photoevaporation,
the potential for planet formation remains high in this massive star forming
region, with approximately 18% of the surveyed disks having masses greater than
or equal to 0.01 Msolar within 60 AU.Comment: Accepted for publication in ApJ, 36 pages, 10 figure
ALMA Observations of Asymmetric Molecular Gas Emission from a Protoplanetary Disk in the Orion Nebula
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations
of molecular line emission from d216-0939, one of the largest and most massive
protoplanetary disks in the Orion Nebula Cluster (ONC). We model the spectrally
resolved HCO (4--3), CO (3--2), and HCN (4--3) lines observed at 0\farcs5
resolution to fit the temperature and density structure of the disk. We also
weakly detect and spectrally resolve the CS (7--6) line but do not model it.
The abundances we derive for CO and HCO are generally consistent with
expected values from chemical modeling of protoplanetary disks, while the HCN
abundance is higher than expected. We dynamically measure the mass of the
central star to be which is inconsistent with the
previously determined spectral type of K5. We also report the detection of a
spatially unresolved high-velocity blue-shifted excess emission feature with a
measurable positional offset from the central star, consistent with a Keplerian
orbit at . Using the integrated flux of the feature in
HCO (4--3), we estimate the total H gas mass of this feature to be at
least , depending on the assumed temperature. The
feature is due to a local temperature and/or density enhancement consistent
with either a hydrodynamic vortex or the expected signature of the envelope of
a forming protoplanet within the disk.Comment: 19 pages, 12 figures, accepted for publication in A
The Circumstellar Disk Mass Distribution in the Orion Trapezium Cluster
We present the results of a submillimeter interferometric survey of
circumstellar disks in the Trapezium Cluster of Orion. We observed the 880
micron continuum emission from 55 disks using the Submillimeter Array, and
detected 28 disks above 3sigma significance with fluxes between 6-70 mJy and
rms noise between 0.7-5.3 mJy. Dust masses and upper limits are derived from
the submillimeter excess above free-free emission extrapolated from longer
wavelength observations. Above our completeness limit of 0.0084 solar masses,
the disk mass distribution is similar to that of Class II disks in
Taurus-Auriga and rho Ophiuchus but is truncated at 0.04 solar masses. We show
that the disk mass and radius distributions are consistent with the formation
of the Trapezium Cluster disks ~1 Myr ago and subsequent photoevaporation by
the ultraviolet radiation field from Theta-1 Ori C. The fraction of disks which
contain a minimum mass solar nebula within 60 AU radius is estimated to be
11-13% in both Taurus and the Trapezium Cluster, which suggests the potential
for forming Solar Systems is not compromised in this massive star forming
region.Comment: Accepted for publication in ApJL (2009 Feb 3
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