3,230 research outputs found
Fabry-Perot Measurements of the Dynamics of Globular Cluster Cores: M15 (NGC~7078)
We report the first use of the Rutgers Imaging Fabry-Perot Spectrophotometer
to study the dynamics of the cores of globular clusters. We have obtained
velocities for cluster stars by tuning the Fabry-Perot to take a series of
narrow-band images at different wavelengths across one of the Na D (5890 AA)
absorption lines. Measuring the flux in every frame yields a short portion of
the spectrum for each star simultaneously. This proves to be a very efficient
method for obtaining accurate stellar velocities; in crowded regions we are
able to measure hundreds of velocities in 3-4 hours of observing time. We have
measured velocities with uncertainties of less than 5 km/s for 216 stars within
1.5' of the center of the globular cluster M15 (NGC 7078). The paper is a
uuencoded compressed postscript file
MoleculeâInduced Radical Formation (MIRF) ReactionsâA Reappraisal
Radical chain reactions are commonly initiated through the thermal or photochemical activation of purposeâbuilt initiators, through photochemical activation of substrates, or through wellâdesigned redox processes. Where radicals come from in the absence of these initiation strategies is much less obvious and are often assumed to derive from unknown impurities. In this situation, moleculeâinduced radical formation (MIRF) reactions should be considered as wellâdefined alternative initiation modes. In the most general definition of MIRF reactions, two closedâshell molecules react to give a radical pair or biradical. The exact nature of this transformation depends on the Ïâ or Ïâbonds involved in the MIRF process, and this Minireview specifically focuses on reactions that transform two Ïâbonds into two radicals and a closedâshell product molecule
Ultra-Transparent Antarctic Ice as a Supernova Detector
We have simulated the response of a high energy neutrino telescope in deep
Antarctic ice to the stream of low energy neutrinos produced by a supernova.
The passage of a large flux of MeV-energy neutrinos during a period of seconds
will be detected as an excess of single counting rates in all individual
optical modules. We update here a previous estimate of the performance of such
an instrument taking into account the recent discovery of absorption lengths of
several hundred meters for near-UV photons in natural deep ice. The existing
AMANDA detector can, even by the most conservative estimates, act as a galactic
supernova watch.Comment: 9 pages, Revtex file, no figures. Postscript file also available from
http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-888.ps.Z or from
ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-888.ps.
Hydration Status Response to Bolus Frequency and Volume Intake During Exercise in Heat
Click the PDF icon to download the abstract
A proper motion study of the globular cluster M55
We have derived the absolute proper motion (PM) of the globular cluster M55
using a large set of CCD images collected with the du Pont telescope between
1997 and 2008. We find (PM_RA*cos(DEC), PM_DEC) = (-3.31 +/- 0.10, -9.14 +/-
0.15) mas/yr relative to background galaxies. Membership status was determined
for 16 945 stars with 14<V<21 from the central part of the cluster. The PM
catalogue includes 52 variables of which 43 are probable members of M55. This
sample is dominated by pulsating blue straggler stars but also includes 5
eclipsing binaries, three of which are main sequence objects. The survey also
identified several candidate blue, yellow and red straggler stars belonging to
the cluster. We detected 15 likely members of the Sgr dSph galaxy located
behind M55. The average PM for these stars was measured to be (PM_RA*cos(DEC),
PM_DEC)=(-2.23 +/- 0.14, -1.83 +/- 0.24) mas/yr.Comment: 12 figures and 4 tables, accepted for publication in MNRAS Main
Journal; full PM catalogue (Table 3) at http://case.camk.edu.p
Proper motions and membership probabilities of stars in the region of globular cluster NGC 6809
NGC 6809 is a luminous metal-poor halo globular cluster that is relatively
easy to study due to its proximity and low concentration. Because of its high
Galactic latitude (b = -23deg), interstellar reddening and contamination is not
very high. We aim to determine the relative proper motion and membership
probability of the stars in the wide area of globular cluster NGC 6809. To
target cluster members reliably during spectroscopic surveys and both spatial
and radial distributions in the cluster outskirts without including field
stars, a good proper motion and membership probability catalogue of NGC 6809 is
required.The archival data of two epochs with a time-base line of 7.1 years
have been collected with Wide Field Imager (WFI) mounted on the 2.2m MPG/ESO
telescope. The CCD images of both epochs have been reduced using the
astrometric techniques as described in Anderson et al. (2006). The calibrated
UBVI magnitudes have been derived using Stetson's secondary standard stars. We
derived the relative proper motion and membership probabilities for \sim 12600
stars in the field of globular cluster NGC 6809. The measurement error in
proper motions for the stars of V \sim 17 mag is 2.0 mas/yr, gradually
increasing up to \sim 3 mas/yr at V = 20 mag. We also provide the membership
probability for the published different types of sources in NGC 6809. An
electronic catalogue with proper motion and membership probability for the
stars will be available to the astronomical community.Comment: Accepted for publication in The A&A. 11 pages. 11 figures,5 Table
- âŠ