276 research outputs found
The Arizona Radio Observatory CO Mapping Survey of Galactic Molecular Clouds: III. The Serpens Cloud in CO J=2-1 and 13CO J=2-1 Emission
We mapped 12CO and 13CO J = 2-1 emission over 1.04 square deg of the Serpens
molecular cloud with 38 arcsec spatial and 0.3 km/s spectral resolution using
the Arizona Radio Observatory Heinrich Hertz Submillimeter telescope. Our maps
resolve kinematic properties for the entire Serpens cloud. We also compare our
velocity moment maps with known positions of Young Stellar Objects (YSOs) and
1.1 mm continuum emission. We find that 12CO is self-absorbed and 13CO is
optically thick in the Serpens core. Outside of the Serpens core, gas appears
in filamentary structures having LSR velocities which are blue-shifted by up to
2 km/s relative to the 8 km/s systemic velocity of the Serpens cloud. We show
that the known Class I, Flat, and Class II YSOs in the Serpens core most likely
formed at the same spatial location and have since drifted apart. The spatial
and velocity structure of the 12CO line ratios implies that a detailed
3-dimensional radiative transfer model of the cloud will be necessary for full
interpretation of our spectral data. The starless cores region of the cloud is
likely to be the next site of star formation in Serpens.Comment: 41 pages, 15 figure
CO Line Emission and Absorption from the HL Tau Disk: Where is all the dust?
We present high-resolution infrared spectra of HL Tau, a heavily embedded
young star. The spectra exhibit broad emission lines of hot CO gas as well as
narrow absorption lines of cold CO gas. The column density for this cooler
material (7.5+/-0.2 x 10^18 cm-2) indicates a large column of absorbing gas
along the line of sight. In dense interstellar clouds, this column density of
CO gas is associated with Av~52 magnitudes. However, the extinction toward this
source (Av~23) suggests that there is less dust along the line of sight than
inferred from the CO absorption data. We discuss three possibilities for the
apparent paucity of dust along the line of sight through the flared disk: 1)
the dust extinction has been underestimated due to differences in circumstellar
grain properties, such as grain agglomeration; 2) the effect of scattering has
been underestimated and the actual extinction is much higher; or (3) the line
of sight through the disk is probing a gas-rich, dust-depleted region, possibly
due to the stratification of gas and dust in a pre-planetary disk.Comment: To be published in The Astrophysical Journa
Sampling distributions and the bootstrap
The bootstrap can be used to assess uncertainty of sample estimates
On a model mechanism for the spatial patterning of teeth primordia in the Alligator
We propose a model mechanism for the initiation and spatial positioning of teeth primordia in the alligator,Alligator mississippiensis. Detailed embryological studies by Westergaard & Ferguson (1986, 1987, 1990) show that jaw growth plays a crucial role in the developmental patterning of the tooth initiation process. Based on biological data we develop a reaction-diffusion mechanism, which crucially includes domain growth. The model can reproduce the spatial pattern development of the first seven teeth primordia in the lower half jaw ofA. mississippiensis. The results for the precise spatio-temporal sequence compare well with detailed developmental experiments
Buoyancy waves in Pluto's high atmosphere: Implications for stellar occultations
We apply scintillation theory to stellar signal fluctuations in the
high-resolution, high signal/noise, dual-wavelength data from the MMT
observation of the 2007 March 18 occultation of P445.3 by Pluto. A well-defined
high wavenumber cutoff in the fluctuations is consistent with viscous-thermal
dissipation of buoyancy waves (internal gravity waves) in Pluto's high
atmosphere, and provides strong evidence that the underlying density
fluctuations are governed by the gravity-wave dispersion relation.Comment: Accepted 18 June 2009 for publication in Icaru
Where is the best site on Earth? Domes A, B, C and F, and Ridges A and B
The Antarctic plateau contains the best sites on earth for many forms of
astronomy, but none of the existing bases was selected with astronomy as the
primary motivation. In this article, we try to systematically compare the
merits of potential observatory sites.We include South Pole, Domes A, C, and F,
and also Ridge B (running northeast from Dome A), and what we call "Ridge A"
(running southwest from Dome A). Our analysis combines satellite data,
published results, and atmospheric models, to compare the boundary layer,
weather, aurorae, airglow, precipitable water vapor, thermal sky emission,
surface temperature, and the free atmosphere, at each site. We find that all
Antarctic sites are likely to be compromised for optical work by airglow and
aurorae. Of the sites with existing bases, Dome A is easily the best overall;
but we find that Ridge A offers an even better site. We also find that Dome F
is a remarkably good site. Dome C is less good as a thermal infrared or
terahertz site, but would be able to take advantage of a predicted "OH hole"
over Antarctica during spring.Comment: Revised version. 16 pages, 21 figures (22 in first version).
Submitted to PASP 16/05/09, accepted 13/07/09; published 20/08/0
Molecular Line Emission from Gravitationally Unstable Protoplanetary Disks
In the era of high resolution submillimeter interferometers, it will soon be
possible to observe the neutral circumstellar medium directly involved in gas
giant planet (GGP) formation at physical scales previously unattainable. In
order to explore possible signatures of gas giant planet formation via disk
instabilities, we have combined a 3D, non-local thermodynamic equilibrium (LTE)
radiative transfer code with a 3D, finite differences hydrodynamical code to
model molecular emission lines from the vicinity of a 1.4 M_J self-gravitating
proto-GGP. Here, we explore the properties of rotational transitions of the
commonly observed dense gas tracer, HCO+. Our main results are the following:
1. Very high lying HCO+ transitions (e.g. HCO+ J=7-6) can trace dense planet
forming clumps around circumstellar disks. Depending on the molecular
abundance, the proto-GGP may be directly imageable by the Atacama Large
Millimeter Array (ALMA). 2. HCO+ emission lines are heavily self-absorbed
through the proto-GGP's dense molecular core. This signature is nearly
ubiquitous, and only weakly dependent on assumed HCO+ abundances. The
self-absorption features are most pronounced at higher angular resolutions.
Dense clumps that are not self-gravitating only show minor self-absorption
features. 3. Line temperatures are highest through the proto-GGP at all assumed
abundances and inclination angles. Conversely, due to self-absorption in the
line, the velocity-integrated intensity may not be. High angular resolution
interferometers such as the Submillimeter Array (SMA) and ALMA may be able to
differentiate between competing theories of gas giant planet formation.Comment: 10 pages, 13 figures; Accepted by Ap
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