1,673 research outputs found
Negatively Charged Strangelet Search using the E864 Spectrometer at the AGS
We provide a status report on the progress of searching for negatively
charged strangelets using the E864 spectrometer at the AGS. About 200 million
recorded events representing approximately 14 billion 10% central interactions
of Au + Pt at 11.5 GeV/c taken during the 1996-1997 run of the experiment are
used in the analysis. No strangelet candidates are seen for charges Z=-1 and
Z=-2, corresponding to a 90% confidence level for upper limits of strangelet
production of ~1 x 10^{-8} and ~4 x 10^{-9} per central collision respectively.
The limits are nearly uniform over a wide range of masses and are valid only
for strangelets which are stable or have lifetimes greater than ~50 ns.Comment: 6 pages, 4 figures; Talk at SQM'98, Padova, Italy (July 20-24, 1998
Discovery of two infrared supernovae: a new window on the SN search
We report the discovery of two supernovae (SN 1999gw and SN 2001db) obtained
within the framework of an infrared monitoring campaign of Luminous Infrared
Galaxies, aimed at detecting obscured supernovae. SN 2001db, extinguished by
Av~5.5 mag, is the first supernova discovered in the infrared which has
received the spectroscopic confirmation. This result highlights the power of
infrared monitoring in detecting obscured SNe and indicates that optical
surveys are probably missing a significant fraction of SNe, especially in
obscured systems such as starburst galaxies. The preliminary estimate of SN
rate in LIRG galaxies is about an order of magnitude higher than that expected
from optical surveys.Comment: 9 pages, 7 figures, accepted for publication in A&
CO emission and variable CH and CH+ absorption towards HD34078: evidence for a nascent bow shock ?
The runaway star HD34078, initially selected to investigate small scale
structure in a foreground diffuse cloud has been shown to be surrounded by
highly excited H2. We first search for an association between the foreground
cloud and HD34078. Second, we extend previous investigations of temporal
absorption line variations (CH, CH+, H2) in order to better characterize them.
We have mapped the CO(2-1) emission at 12 arcsec resolution around HD34078's
position, using the 30 m IRAM antenna. The follow-up of CH and CH+ absorption
lines has been extended over 5 more years. In parallel, CH absorption towards
the reddened star Zeta Per have been monitored to check the homogeneity of our
measurements. Three more FUSE spectra have been obtained to search for N(H2)
variations. CO observations show a pronounced maximum near HD34078's position,
clearly indicating that the star and diffuse cloud are associated. The optical
spectra confirm the reality of strong, rapid and correlated CH and CH+
fluctuations. On the other hand, N(H2, J=0) has varied by less than 5 % over 4
years. We also discard N(CH) variations towards Zeta Per at scales less than 20
AU. Observational constraints from this work and from 24 micron dust emission
appear to be consistent with H2 excitation but inconsistent with steady-state
bow shock models and rather suggest that the shell of compressed gas
surrounding HD34078, is seen at an early stage of the interaction. The CH and
CH+ time variations as well as their large abundances are likely due to
chemical structure in the shocked gas layer located at the stellar wind/ambient
cloud interface. Finally, the lack of variations for both N(H2, J=0) towards
HD34078 and N(CH) towards Zeta Per suggests that quiescent molecular gas is not
subject to pronounced small-scale structure.Comment: 19 pages, 15 figures, accepted for publication in A&
A Candidate Protoplanet in the Taurus Star Forming Region
HST/NICMOS images of the class I protostar TMR-1 (IRAS04361+2547) reveal a
faint companion with 10.0" = 1400 AU projected separation. The central
protostar is itself resolved as a close binary with 0.31" = 42 AU separation,
surrounded by circumstellar reflection nebulosity. A long narrow filament seems
to connect the protobinary to the faint companion TMR-1C, suggesting a physical
association. If the sources are physically related then we hypothesize that
TMR-1C has been ejected by the protobinary. If TMR-1C has the same age and
distance as the protobinary then current models indicate its flux is consistent
with a young giant planet of several Jovian masses.Comment: 16 pages, 1 figure, Accepted by Astrophysical Journal Letters,
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E-BOSS: an Extensive stellar BOw Shock Survey. I: Methods and First Catalogue
Context: Bow shocks are produced by many astrophysical objects where shock
waves are present. Stellar bow shocks, generated by runaway stars, have been
previously detected in small numbers and well-studied. Along with progress in
model development and improvements in observing instruments, our knowledge of
the emission produced by these objects and its origin can now be more clearly
understood. Aims: We produce a stellar bow-shock catalogue by applying uniform
search criteria and a systematic search process. This catalogue is a starting
point for statistical studies, to help us address fundamental questions such
as, for instance, the conditions under wich a stellar bow shock is detectable.
Methods: By using the newest infrared data releases, we carried out a search
for bow shocks produced by early-type runaway stars. We first explored whether
a set of known IRAS bow shock candidates are visible in the most recently
available IR data, which has much higher resolution and sensitivity. We then
carried out a selection of runaway stars from the latest, large runaway
catalogue available. In this first release, we focused on OB stars and searched
for bow-shaped features in the vicinity of these stars. Results: We provide a
bow-shock candidate survey that gathers a total of 28 members which we call the
Extensive stellar BOw Shock Survey (E-BOSS). We derive the main bow-shock
parameters, and present some preliminary statistical results on the detected
objects. Conclusions: Our analysis of the initial sample and the newly detected
objects yields a bow-shock detectability around OB stars of 10 per cent.
The detections do not seem to depend particularly on either stellar mass, age
or position. The extension of the E-BOSS sample, with upcoming IR data, and by
considering, for example, other spectral types as well, will allow us to
perform a more detailed study of the findings.Comment: A&A accepted (25-NOV-2011), 15 pages, 4 tables, 11 figure
Longitudinal T1 relaxation rate (R1) captures changes in short-term Mn exposure in welders
We demonstrated recently that the T1 relaxation rate (R1) captured short-term Mn exposure in welders with chronic, relatively low exposure levels in a cross-sectional study. In the current study, we used a longitudinal design to examine whether R1 values reflect the short-term dynamics of Mn exposure
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