4,090 research outputs found
Cross-language Wikipedia Editing of Okinawa, Japan
This article analyzes users who edit Wikipedia articles about Okinawa, Japan,
in English and Japanese. It finds these users are among the most active and
dedicated users in their primary languages, where they make many large,
high-quality edits. However, when these users edit in their non-primary
languages, they tend to make edits of a different type that are overall smaller
in size and more often restricted to the narrow set of articles that exist in
both languages. Design changes to motivate wider contributions from users in
their non-primary languages and to encourage multilingual users to transfer
more information across language divides are presented.Comment: In Proceedings of the SIGCHI Conference on Human Factors in Computing
Systems, CHI 2015. AC
A Dusty Disk Around GD 362, a White Dwarf With a Uniquely High Photospheric Metal Abundance
Eighteen years after an infrared excess was discovered associated with the
white dwarf G29-38, we report ground-based measurements (JHKL'N') with
mJy-level sensitivity of GD 362 that show it to be a second single white dwarf
with an infrared excess. As a first approximation, the excess around GD 362,
which amounts to about 3% of the total stellar luminosity, can be explained by
emission from a passive, flat, opaque dust disk that lies within the Roche
radius of the white dwarf. The dust may have been produced by the tidal
disruption of a large parent body such as an asteroid. Accretion from this
circumstellar disk could account for the remarkably high abundance of metals in
the star's photosphere.Comment: 12 pages, 2 figures. ApJ Letters, in pres
Warm dust in the terrestrial planet zone of a sun-like Pleiad: collisions between planetary embryos?
Only a few solar-type main sequence stars are known to be orbited by warm
dust particles; the most extreme is the G0 field star BD+20 307 that emits ~4%
of its energy at mid-infrared wavelengths. We report the identification of a
similarly dusty star HD 23514, an F6-type member of the Pleiades cluster. A
strong mid-IR silicate emission feature indicates the presence of small warm
dust particles, but with the primary flux density peak at the non-standard
wavelength of ~9 micron. The existence of so much dust within an AU or so of
these stars is not easily accounted for given the very brief lifetime in orbit
of small particles. The apparent absence of very hot (>~1000 K) dust at both
stars suggests the possible presence of a planet closer to the stars than the
dust. The observed frequency of the BD+20 307/HD 23514 phenomenon indicates
that the mass equivalent of Earth's Moon must be converted, via collisions of
massive bodies, to tiny dust particles that find their way to the terrestrial
planet zone during the first few hundred million years of the life of many
(most?) sun-like stars. Identification of these two dusty systems among
youthful nearby solar-type stars suggests that terrestrial planet formation is
common.Comment: ApJ in press, 19 pages including 3 figures and 2 tables, minor
changes to the tables and figure
SACY - a Search for Associations Containing Young stars
The scientific goal of the SACY (Search for Associations Containing
Young-stars) was to identify possible associations of stars younger than the
Pleiades Association among optical counterparts of the ROSAT X-ray bright
sources. High-resolution spectra for possible optical counterparts later than
G0 belonging to HIPPARCOS and/or TYCHO-2 catalogs were obtained in order to
assess both the youth and the spatial motion of each target. More than 1000
ROSAT sources were observed, covering a large area in the Southern Hemisphere.
The newly identified young stars present a patchy distribution in UVW and XYZ,
revealing the existence of huge nearby young associations. Here we present the
associations identified in this survey.Comment: 8 pages, 2 figures, to appear in the Proceedings of Open Issues in
Local Formation and Early Stellar Evolution, Ouro Preto, Brazi
On k-Column Sparse Packing Programs
We consider the class of packing integer programs (PIPs) that are column
sparse, i.e. there is a specified upper bound k on the number of constraints
that each variable appears in. We give an (ek+o(k))-approximation algorithm for
k-column sparse PIPs, improving on recent results of and
. We also show that the integrality gap of our linear programming
relaxation is at least 2k-1; it is known that k-column sparse PIPs are
-hard to approximate. We also extend our result (at the loss
of a small constant factor) to the more general case of maximizing a submodular
objective over k-column sparse packing constraints.Comment: 19 pages, v3: additional detail
Stellar Companions and the Age of HD 141569 and its Circumstellar Disk
We investigate the stellar environment of the Beta Pictoris-like star HD
141569 with optical spectroscopy and near infrared imaging. The B9.5Ve primary,
and an M2 and an M4 type star both located in projection less than nine
arseconds away have the same radial velocity and proper motion and therefore
almost certainly form a triple star system. From their x-ray flux, lithium
absorption and location on pre-main-sequence evolutionary tracks, the
companions appear to be 5 Myr old. HD 141569 A is now one of the few stars with
a circumstellar disk that has a well-determined age. The circumstellar disk is
composed of secondary debris material (Fisher et al. 2000), thus placing an
upper limit on the time needed for disk processing. These three stars may be
part of an association of young stars.Comment: 18 pages incl. 7 ps figures, aastex v5.0, accepted for publication in
Ap
HST and Spitzer Observations of the HD 207129 Debris Ring
A debris ring around the star HD 207129 (G0V; d = 16.0 pc) has been imaged in
scattered visible light with the ACS coronagraph on the Hubble Space Telescope
and in thermal emission using MIPS on the Spitzer Space Telescope at 70 microns
(resolved) and 160 microns (unresolved). Spitzer IRS (7-35 microns) and MIPS
(55-90 microns) spectrographs measured disk emission at >28 microns. In the HST
image the disk appears as a ~30 AU wide ring with a mean radius of ~163 AU and
is inclined by 60 degrees from pole-on. At 70 microns it appears partially
resolved and is elongated in the same direction and with nearly the same size
as seen with HST in scattered light. At 0.6 microns the ring shows no
significant brightness asymmetry, implying little or no forward scattering by
its constituent dust. With a mean surface brightness of V=23.7 mag per square
arcsec, it is the faintest disk imaged to date in scattered light.Comment: 28 pages, 8 figure
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