468 research outputs found
A "Starless" Core that Isn't: Detection of a Source in the L1014 Dense Core with the Spitzer Space Telescope
We present observations of L1014, a dense core in the Cygnus region previously thought to be starless, but data from the Spitzer Space Telescope show the presence of an embedded source. We propose a model for this source that includes a cold core, heated by the interstellar radiation field, and a low-luminosity internal source. The low luminosity of the internal source suggests a substellar object. If L1014 is representative, other "starless" cores may turn out to harbor central sources
7-Li(p,n) Nuclear Data Library for Incident Proton Energies to 150 MeV
We describe evaluation methods that make use of experimental data, and
nuclear model calculations, to develop an ENDF-formatted data library for the
reaction p + Li7 for incident protons with energies up to 150 MeV. The
important 7-Li(p,n_0) and 7-Li(p,n_1) reactions are evaluated from the
experimental data, with their angular distributions represented using Lengendre
polynomial expansions. The decay of the remaining reaction flux is estimated
from GNASH nuclear model calculations. The evaluated ENDF-data are described in
detail, and illustrated in numerous figures. We also illustrate the use of
these data in a representative application by a radiation transport simulation
with the code MCNPX.Comment: 11 pages, 8 figures, LaTeX, submitted to Proc. 2000 ANS/ENS
International Meeting, Nuclear Applications of Accelerator Technology
(AccApp00), November 12-16, Washington, DC, US
The Spitzer c2d Survey of Nearby Dense Cores: VI. The Protostars of Lynds Dark Nebula 1221
Observations of Lynds Dark Nebula 1221 from the Spitzer Space Telescope are
presented. These data show three candidate protostars towards L1221, only two
of which were previously known. The infrared observations also show signatures
of outflowing material, an interpretation which is also supported by radio
observations with the Very Large Array. In addition, molecular line maps from
the Five College Radio Astronomy Observatory are shown.
One-dimensional dust continuum modelling of two of these protostars, IRS1 and
IRS3, is described. These models show two distinctly different protostars
forming in very similar environments. IRS1 shows a higher luminosity and larger
inner radius of the envelope than IRS3. The disparity could be caused by a
difference in age or mass, orientation of outflow cavities, or the impact of a
binary in the IRS1 core.Comment: accepted for publication in Ap
SCUBA Mapping of Spitzer c2d Small Clouds and Cores
We present submillimeter observations of dark clouds that are part of the
Spitzer Legacy Program, From Molecular Cores to Planet-Forming Disks (c2d). We
used the Submillimetre Common User's Bolometer Array to map the regions
observed by Spitzer by the c2d program to create a census of dense molecular
cores including data from the infrared to the submillimeter. In this paper, we
present the basic data from these observations: maps, fluxes, and source
attributes. We also show data for an object just outside the Perseus cloud that
was serendipitously observed in our program. We propose that this object is a
newly discovered, evolved protostar.Comment: 37 pages, accepted to The Astronomical Journa
Evolutionary Signatures in the Formation of Low-Mass Protostars. II. Towards Reconciling Models and Observations
A long-standing problem in low-mass star formation is the "luminosity
problem," whereby protostars are underluminous compared to the accretion
luminosity expected both from theoretical collapse calculations and arguments
based on the minimum accretion rate necessary to form a star within the
embedded phase duration. Motivated by this luminosity problem, we present a set
of evolutionary models describing the collapse of low-mass, dense cores into
protostars, using the Young & Evans (2005) model as our starting point. We
calculate the radiative transfer of the collapsing cores throughout the full
duration of the collapse in two dimensions. From the resulting spectral energy
distributions, we calculate standard observational signatures to directly
compare to observations. We incorporate several modifications and additions to
the original Young & Evans model in an effort to better match observations with
model predictions. We find that scattering, 2-D geometry, mass-loss, and
outflow cavities all affect the model predictions, as expected, but none
resolve the luminosity problem. A cycle of episodic mass accretion, however,
can resolve this problem and bring the model predictions into better agreement
with observations. Standard assumptions about the interplay between mass
accretion and mass loss in our model give star formation efficiencies
consistent with recent observations that compare the core mass function (CMF)
and stellar initial mass function (IMF). The combination of outflow cavities
and episodic mass accretion reduce the connection between observational Class
and physical Stage to the point where neither of the two common observational
signatures (bolometric temperature and ratio of bolometric to submillimeter
luminosity) can be considered reliable indicators of physical Stage.Comment: 27 pages. Accepted for publication in Ap
Discovery of a Low Mass Bipolar Molecular Outflow from L1014-IRS with the Submillimeter Array
Using the Submillimeter Array we report the discovery of a compact low mass
bipolar molecular outflow from L1014-IRS and confirm its association with the
L1014 dense core at 200 pc. Consequently, L1014-IRS is the lowest luminosity (L
\~0.09 Lsun) and perhaps the lowest mass source known to be driving a bipolar
molecular outflow, which is one of the smallest known in size (~500 AU), mass
(< 10^{-4} Msun), and energetics (e.g., force < 10^{-7} Msun km/s/yr).Comment: 11 pages, 3 figures, to appear in ApJ Letter
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