8,171 research outputs found
An evaluation of aft-end ignition for solid propellant rocket motors
Performance evaluation of solid propellant rocket motor ignition to determine igniter design and parameters to avoid overpressurizatio
Seasonal and interannual variability of North American isoprene emissions as determined by formaldehyde column measurements from space
Formaldehyde (HCHO) columns measured from space by solar UV backscatter allow mapping of reactive hydrocarbon emissions. The principal contributor to these emissions during the growing season is the biogenic hydrocarbon isoprene, which is of great importance for driving regional and global tropospheric chemistry. We present seven years (1995-2001) of HCHO column data for North America from the Global Ozone Monitoring Experiment (GOME), and show that the general seasonal and interannual variability of these data is consistent with knowledge of isoprene emission. There are some significant regional discrepancies with the seasonal patterns predicted from current isoprene emission models, and we suggest that these may reflect flaws in the models. The interannual variability of HCHO columns observed by GOME appears to follow the interannual variability of surface temperature, as expected from current isoprene emission models
DN Tauri - coronal activity and accretion in a young low-mass CTTS
We present a deep XMM-Newton observation of DN Tau, a young M0-type accreting
CTTS and investigate its X-ray properties and X-ray generating mechanisms.
Specifically we examine the presence of X-ray emission from magnetic activity
and accretion shocks and compare our new X-ray data with UV data taken
simultaneously and with X-ray/UV observations performed before. We find that
the X-ray emission from DN Tau is dominated by coronal plasma generated via
magnetic activity, but also clearly detect a contribution of the accretion
shocks to the cool plasma component at about 2 MK as consistently inferred from
density and temperature analysis. Typical phenomena of active coronae like
flaring, the presence of very hot plasma at 30 MK and an abundance pattern
showing the inverse FIP effect are seen on DN Tau. Strong variations in the
emission measure of the cooler plasma components between the 2005 and 2010 XMM
data point to accretion related changes. The UV light curve taken
simultaneously is in general not related to the X-ray brightness, but exhibits
clear counterparts during the observed X-ray flares. The X-ray properties of DN
Tau are similar to those of more massive CTTS, but its low mass and large
radius shift the accretion shocks to lower temperatures, reducing their imprint
in the X-ray regime.Comment: 11 pages, 8 figures, accepted for publication in A&
A low-mass stellar companion of the planet host star HD75289
We report on the detection of a new low-mass stellar companion of HD75289, a
G0V star that harbors one known radial-velocity planet (Udry et al. 2000).
Comparing an image of 2MASS with an image we obtained with SofI at the ESO
3.58m NTT three years later, we detected a co-moving companion located
21.465+-0.023arcsecs (621+-10AU at 29pc) east of HD75289. A second SofI image
taken 10 months later confirmed the common proper motion of HD75289B with its
host star. The infrared spectrum and colors of the companion are consistent
with an M2 to M5 main-sequence star at the distance of HD75289. No further
(sub)stellar companion down to H = 19mag could be detected. With the SofI
detection limit we can rule out additional stellar companions beyond 140AU and
substellar companions with masses m > 0.050Msun from 400AU up to 2000AU.Comment: accepted in A&
A magnetic cycle of tau Bootis? The coronal and chromospheric view
Tau Bootis is a late F-type main sequence star orbited by a Hot Jupiter.
During the last years spectropolarimetric observations led to the hypothesis
that this star may host a global magnetic field that switches its polarity once
per year, indicating a very short activity cycle of only one year duration. In
our ongoing observational campaign, we have collected several X-ray
observations with XMM-Newton and optical spectra with TRES/FLWO in Arizona to
characterize tau Boo's corona and chromosphere over the course of the supposed
one-year cycle. Contrary to the spectropolarimetric reconstructions, our
observations do not show indications for a short activity cycle.Comment: 4 pages, 2 figures, appeared in Astronomical Notes 333, 1, 26-29
(2012
Combined chips for atom-optics
We present experiments with Bose-Einstein condensates on a combined atom
chip. The combined structure consists of a large-scale "carrier chip" and
smaller "atom-optics chips", containing micron-sized elements. This allows us
to work with condensates very close to chip surfaces without suffering from
fragmentation or losses due to thermally driven spin flips. Precise
three-dimensional positioning and transport with constant trap frequencies are
described. Bose-Einstein condensates were manipulated with submicron accuracy
above atom-optics chips. As an application of atom chips, a direction sensitive
magnetic field microscope is demonstrated.Comment: 9 pages, 9 figure
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