4,246 research outputs found
A 22 Degree Tidal Tail for Palomar 5
Using Data Release 4 of the Sloan Digital Sky Survey, we have applied an
optimal contrast, matched filter technique to trace the trailing tidal tail of
the globular cluster Palomar 5 to a distance of 18.5 degrees from the center of
the cluster. This more than doubles the total known length of the tail to some
22 degrees on the sky. Based on a simple model of the Galaxy, we find that the
stream's orientation on the sky is consistent at the 1.7 sigma level with
existing proper motion measurements. We find that a spherical Galactic halo is
adequate to model the stream over its currently known length, and we are able
to place new constraints on the current space motion of the cluster.Comment: 10 pages, 3 figures, accepted for publication in ApJ Letter
Accretion Disks around Young Stars: Lifetimes, Disk Locking and Variability
We report the findings of a comprehensive study of disk accretion and related
phenomena in four of the nearest young stellar associations spanning 6-30
million years in age, an epoch that may coincide with the late stages of planet
formation. We have obtained ~650 multi-epoch high-resolution optical spectra of
100 low-mass stars that are likely members of the eta Chamaeleontis (~6 Myr),
TW Hydrae (~8 Myr), beta Pictoris (~12 Myr) and Tucanae-Horologium (~30 Myr)
groups. Our data were collected over 12 nights between 2004 December - 2005
July on the Magellan Clay 6.5m telescope. Based on H line profiles,
along with a variety of other emission lines, we find clear evidence of
on-going accretion in three out of 11 eta Cha stars and two out of 32 TW Hydrae
members. None of the 57 beta Pic or Tuc-Hor members shows measurable signs of
accretion. Together, these results imply significant evolution of the disk
accretion process within the first several Myr of a low-mass star's life. While
a few disks can continue to accrete for up to ~10 Myr, our findings suggest
that disks accreting for beyond that timescale are rather rare. This result
provides an indirect constraint on the timescale for gas dissipation in inner
disks and, in turn, on gas giant planet formation. All accretors in our sample
are slow rotators, whereas non-accretors cover a large range in rotational
velocities. This may hint at rotational braking by disks at ages up to ~8 Myr.
Our multi-epoch spectra confirm that emission-line variability is common even
in somewhat older T Tauri stars, among which accretors tend to show
particularly strong variations. Thus, our results indicate that accretion and
wind activity undergo significant and sustained variations throughout the
lifetime of accretion disks.Comment: to appear in The Astrophysical Journa
Reduction of quantum noise in optical interferometers using squeezed light
We study the photon counting noise in optical interferometers used for
gravitational wave detection. In order to reduce quantum noise a squeezed
vacuum state is injected into the usually unused input port. Here, we
specifically investigate the so called `dark port case', when the beam splitter
is oriented close to 90{\deg} to the incoming laser beam, such that nearly all
photons go to one output port of the interferometer, and only a small fraction
of photons is seen in the other port (`dark port'). For this case it had been
suggested that signal amplification is possible without concurrent noise
amplification [R.Barak and Y.Ben-Aryeh, J.Opt.Soc.Am.B25(361)2008]. We show
that by injection of a squeezed vacuum state into the second input port,
counting noise is reduced for large values of the squeezing factor, however the
signal is not amplified. Signal strength only depends on the intensity of the
laser beam.Comment: 8 pages, 1 figur
UKIDSS detections of cool brown dwarfs - proper motions of 14 known T5 dwarfs and discovery of three new T5.5-T6 dwarfs
AIMS: We contribute to improving the census of cool brown dwarfs (late-T and
Y dwarfs) in the immediate solar neighbourhood. METHODS: By combining
near-infrared (NIR) data of UKIDSS with mid-infrared WISE and other available
NIR (2MASS) and red optical (SDSS -band) multi-epoch data we detect high
proper motion (HPM) objects with colours typical of late spectral types
(T5). We use NIR low-resolution spectroscopy for the classification of new
candidates. RESULTS: We determined new proper motions for 14 known T5.5-Y0
dwarfs, many of them being significantly (2-10 times) more accurate than
previous ones. We detected three new candidates, ULAS J0954+0623, ULAS
J1152+0359, and ULAS J1204-0150, by their HPMs and colours. Using previously
published and new UKIDSS positions of the known nearby T8 dwarf WISE J0254+0223
we improved its trigonometric parallax to 16520 mas. For the three new
objects we obtained NIR spectroscopic follow-up with LBT/LUCIFER classifying
them as T5.5 and T6 dwarfs. With their estimated spectroscopic distances of
about 25-30 pc, their proper motions of about 430-650 mas/yr lead to tangential
velocities of about 50-80 km/s typical of the Galactic thin disk population.Comment: 5 pages, 2 figures, plus 3 pages with 5 tables (online material),
accepted for publication in Astronomy and Astrophysic
Upper Columbia United Tribes Fisheries Center Fisheries Technical Report No. 12
Predicting the Effect of Reduced Streamflow on Rainbow Trout, Brown Trout, and Sculpin Populations in Chamokane Creek Using the Instream Flow Incremental Methodology (IFIM
Subjective perceptions as prognostic factors of time to fitness for work during a 4-year period after inpatient rehabilitation for orthopaedic trauma.
INTRODUCTION: Time to fitness for work (TFW) was measured as the number of days that were paid as compensation for work disability during the 4 years after discharge from the rehabilitation clinic in a population of patients hospitalised for rehabilitation after orthopaedic trauma. The aim of this study was to test whether some psychological variables can be used as potential early prognostic factors of TFW.
MATERIAL AND METHODS: A Cox proportional hazards model was used to estimate the associations between predictive variables and TFW. Predictors were global health, pain at hospitalisation and pain decrease during the stay (all continuous and standardised by subtracting the mean and dividing by two standard deviations), perceived severity of the trauma and expectation of a positive evolution (both binary variables).
RESULTS: Full data were available for 807 inpatients (660 men, 147 women). TFW was positively associated with better perceived health (hazard ratio [HR] 1.16, 95% confidence interval [CI] 1.13-1.19), pain decrease (HR 1.46, 95% CI 1.30-1.64) and expectation of a positive evolution (HR 1.50, 95% CI 1.32-1.70) and negatively associated with pain at hospitalisation (HR 0.67, 95% CI 0.59-0.76) and high perceived severity (HR 0.72, 95% CI 0.61-0.85).
DISCUSSION: The present results provide some evidence that work disability during a four-year period after rehabilitation may be predicted by prerehabilitation perceptions of general health, pain, injury severity, as well as positive expectation of evolution
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