1,199 research outputs found
Debris Disk Radiative Transfer Simulation Tool (DDS)
A WWW interface for the simulation of spectral energy distributions of
optically thin dust configurations with an embedded radiative source is
presented. The density distribution, radiative source, and dust parameters can
be selected either from an internal database or defined by the user. This tool
is optimized for studying circumstellar debris disks where large grains are
expected to determine the far-infrared through millimeter dust reemission
spectral energy distribution. The tool is available at
http://aida28.mpia-hd.mpg.de/~swolf/ddsComment: Comp. Phys. Comm, 2005, in pres
The Stellar Populations of Praesepe and Coma Berenices
We present the results of a stellar membership survey of the nearby open
clusters Praesepe and Coma Berenices. We have combined archival survey data
from the SDSS, 2MASS, USNOB1.0, and UCAC-2.0 surveys to compile proper motions
and photometry for ~5 million sources over 300 deg^2. Of these sources, 1010
stars in Praesepe and 98 stars in Coma Ber are identified as candidate members
with probability >80%; 442 and 61 are identified as high-probability candidates
for the first time. We estimate that this survey is >90% complete across a wide
range of spectral types (F0 to M5 in Praesepe, F5 to M6 in Coma Ber). We have
also investigated the stellar mass dependence of each cluster's mass and radius
in order to quantify the role of mass segregation and tidal stripping in
shaping the present-day mass function and spatial distribution of stars.
Praesepe shows clear evidence of mass segregation across the full stellar mass
range; Coma Ber does not show any clear trend, but low number statistics would
mask a trend of the same magnitude as in Praesepe. The mass function for
Praesepe (t~600 Myr; M~500 Msun) follows a power law consistent with that of
the field present-day mass function, suggesting that any mass-dependent tidal
stripping could have removed only the lowest-mass members (<0.15 Msun). Coma
Ber, which is younger but much less massive (t~400 Myr; M~100 Msun), follows a
significantly shallower power law. This suggests that some tidal stripping has
occurred, but the low-mass stellar population has not been strongly depleted
down to the survey completeness limit (~0.12 Msun).Comment: Accepted to AJ; 14 pages, 10 figures, 5 tables + 2 online-only table
An Optical Survey of the Partially Embedded Young Cluster in NGC 7129
NGC 7129 is a bright reflection nebula located in the molecular cloud complex
near l=105.4, b=+9.9, about 1.15 kpc distant. Embedded within the reflection
nebula is a young cluster dominated by a compact grouping of four early-type
stars: BD+65 1638 (B3V), BD+65 1637 (B3e), SVS 13 (B5e), and LkH-alpha 234
(B8e). About 80 H-alpha emission sources brighter than V~23 are identified in
the region, many of which are presumably T Tauri star members of the cluster.
We also present deep (V~23), optical (VRI) photometry of a field centered on
the reflection nebula and spectral types for more than 130 sources determined
from low dispersion, optical spectroscopy. The narrow pre-main sequence evident
in the color-magnitude diagram suggests that star formation was rapid and
coeval. A median age of about 1.8 Myr is inferred for the H-alpha and
literature-identified X-ray emission sources having established spectral types,
using pre-main sequence evolutionary models. Our interpretation of the
structure of the molecular cloud and the distribution of young stellar objects
is that BD+65 1638 is primarily responsible for evacuating the blister-like
cavity within the molecular cloud. LkH-alpha 234 and several embedded sources
evident in near infrared adaptive optics imaging have formed recently within
the ridge of compressed molecular gas. The compact cluster of low-mass stars
formed concurrently with the early-type members, concentrated within a central
radius of ~0.7 pc. Star formation is simultaneously occurring in a
semi-circular arc some ~3 pc in radius that outlines remaining dense regions of
molecular gas. High dispersion, optical spectra are presented for BD+65 1638,
BD+65 1637, SVS 13, LkH-alpha 234, and V350 Cep. These spectra are discussed in
the context of the circumstellar environments inferred for these stars.Comment: 45 pages, 20 figures, accepted for publication in the Astronomical
Journa
A full-scale fire program to evaluate new furnishings and textile materials developed by the National Aeronautics and Space Administration
A program of experimental fires was carried out to establish the advantages offered by new materials for improved fire safety. Four full-scale bedrooms, differing only in the materials used to furnish them, were built and burned to provide comparative data on the fire hazards produced. Cost and availability differences were not considered. The visual evidence provided by TV and photographic coverage of the four experimental room fires showed clearly that the rooms responded very differently to a common ignition condition. Resistance to the ignition and spread of fire was substantially improved in the rooms furnished completely or partially with the new materials
Constraining the Sub-AU-Scale Distribution of Hydrogen and Carbon Monoxide Gas around Young Stars with the Keck Interferometer
We present Keck Interferometer observations of T Tauri and Herbig Ae/Be stars
with a spatial resolution of a few milliarcseconds and a spectral resolution of
~2000. Our observations span the K-band, and include the Br gamma transition of
Hydrogen and the v=2-0 and v=3-1 transitions of carbon monoxide. For several
targets we also present data from Keck/NIRSPEC that provide higher spectral
resolution, but a seeing-limited spatial resolution, of the same spectral
features. We analyze the Br gamma emission in the context of both disk and
infall/outflow models, and conclude that the Br gamma emission traces gas at
very small stellocentric radii, consistent with the magnetospheric scale.
However some Br gamma-emitting gas also seems to be located at radii of >0.1
AU, perhaps tracing the inner regions of magnetically launched outflows. CO
emission is detected from several objects, and we generate disk models that
reproduce both the KI and NIRSPEC data well. We infer the CO spatial
distribution to be coincident with the distribution of continuum emission in
most cases. Furthermore the Br gamma emission in these objects is roughly
coincident with both the CO and continuum emission. We present potential
explanations for the spatial coincidence of continuum, Br gamma, and CO
overtone emission, and explore the implications for the low occurrence rate of
CO overtone emission in young stars. Finally, we provide additional discussion
of V1685 Cyg, which is unusual among our sample in showing large differences in
emitting region size and spatial position as a function of wavelength.Comment: Accepted for publication in MNRA
Mass Function of Newly Formed Stars
The topic of the stellar âoriginal mass functionâ has a nearly 50 year history, dating to the publication in 1955 of Salpeterâs seminal paper. In this review I discuss the many more recent results that have emerged on the initial mass function (IMF), as it is now called, from studies over the last decade of resolved populations in star forming regions and young open clusters
Two Wide Planetary-mass Companions to Solar-type Stars in Upper Scorpius
At wide separations, planetary-mass and brown dwarf companions to solar-type stars occupy a curious region of
parameter space not obviously linked to binary star formation or solar system scale planet formation. These
companions provide insight into the extreme case of companion formation (either binary or planetary), and
due to their relative ease of observation when compared to close companions, they offer a useful template
for our expectations of more typical planets. We present the results from an adaptive optics imaging survey
for wide (~50â500 AU) companions to solar-type stars in Upper Scorpius. We report one new discovery of a
~14 M_J companion around GSC 06214â00210and confirm that the candidate planetary-mass companion 1RXS
J160929.1â210524 detected by Lafrenière et al. is in fact comoving with its primary star. In our survey, these
two detections correspond to ~4% of solar-type stars having companions in the 6â20 M_J mass and ~200â500 AU
separation range. This figure is higher than would be expected if brown dwarfs and planetary-mass companions
were drawn from an extrapolation of the binary mass function. Finally, we discuss implications for the formation
of these objects
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