124 research outputs found
Photoassociative creation of ultracold heteronuclear 6Li40K* molecules
We investigate the formation of weakly bound, electronically excited,
heteronuclear 6Li40K* molecules by single-photon photoassociation in a
magneto-optical trap. We performed trap loss spectroscopy within a range of 325
GHz below the Li(2S_(1/2))+K(4P_(3/2)) and Li(2S_(1/2))+K(4P_(1/2)) asymptotic
states and observed more than 60 resonances, which we identify as rovibrational
levels of 7 of 8 attractive long-range molecular potentials. The long-range
dispersion coefficients and rotational constants are derived. We find large
molecule formation rates of up to ~3.5x10^7s^(-1), which are shown to be
comparable to those for homonuclear 40K_2*. Using a theoretical model we infer
decay rates to the deeply bound electronic ground-state vibrational level
X^1\Sigma^+(v'=3) of ~5x10^4s^(-1). Our results pave the way for the production
of ultracold bosonic ground-state 6Li40K molecules which exhibit a large
intrinsic permanent electric dipole moment.Comment: 6 pages, 4 figures, submitted to EP
Seasonal H1N1 2007 influenza virus infection is associated with elevated preâexposure antibody titers to the 2009 pandemic influenza A (H1N1) virus
AbstractThe new influenza strain detected in humans in April 2009 has caused the first influenza pandemic of the 21st century. A crossâreactive antibody response, in which antibodies against seasonal H1N1 viruses neutralized the 2009 pandemic influenza A (H1N1) virus (2009 pH1N1), was detected among individuals aged >60âyears. However, factors other than age associated with such a crossâreactive antibody response are poorly documented. Our objective was to examine factors potentially associated with elevated preâexposure viroâneutralization and hemagglutinationâinhibition antibody titers against the 2009 pH1N1. We also studied factors associated with antibody titers against the 2007 seasonal H1N1 virus. One hundred subjects participating in an influenza cohort were selected. Sera collected in 2008 were analysed using hemagglutination inhibition and viroâneutralization assays for the 2009 pH1N1 virus and the 2007 seasonal H1N1 virus. Viroâneutralization results were explored using a linear mixedâeffect model and hemagglutinationâinhibition results using linearâregression models for intervalâcensored data. Elevated antibody titers against 2009 pH1N1 were associated with seasonal 2007 H1N1 infection (viroâneutralization, pâ0.006; hemagglutinationâinhibition, pâ0.018). Elevated antibody titers were also associated with age in the viroâneutralization assay (pâ<0.0001). Seasonal 2007 H1N1 infection is an independent predictor of elevated preâexposure antibody titers against 2009 pH1N1 and may have contributed to lowering the burden of the 2009 pH1N1 pandemic
The 35Cl/37Cl isotopic ratio in dense molecular clouds: HIFI observations of hydrogen chloride towards W3A
We report on the detection with the HIFI instrument on board the Herschel
satellite of the two hydrogen chloride isotopologues, H35Cl and H37Cl, towards
the massive star-forming region W3A. The J=1-0 line of both species was
observed with receiver 1b of the HIFI instrument at 625.9 and 624.9 GHz. The
different hyperfine components were resolved. The observations were modeled
with a non-local, non-LTE radiative transfer model that includes hyperfine line
overlap and radiative pumping by dust. Both effects are found to play an
important role in the emerging intensity from the different hyperfine
components. The inferred H35Cl column density (a few times 1e14 cm^-2), and
fractional abundance relative to H nuclei (~7.5e^-10), supports an upper limit
to the gas phase chlorine depletion of ~200. Our best-fit model estimate of the
H35Cl/H37Cl abundance ratio is ~2.1+/-0.5, slightly lower, but still compatible
with the solar isotopic abundance ratio (~3.1). Since both species were
observed simultaneously, this is the first accurate estimation of the
[35Cl]/[37Cl] isotopic ratio in molecular clouds. Our models indicate that even
for large line opacities and possible hyperfine intensity anomalies, the H35Cl
and H37Cl J=1-0 integrated line-intensity ratio provides a good estimate of the
35Cl/37Cl isotopic abundance ratio.Comment: Accepted for publication in Astronomy and Astrophysics (Herschel
special issue
Herschel/HIFI deepens the circumstellar NH3 enigma
Circumstellar envelopes (CSEs) of a variety of evolved stars have been found
to contain ammonia (NH3) in amounts that exceed predictions from conventional
chemical models by many orders of magnitude. The observations reported here
were performed in order to better constrain the NH3 abundance in the CSEs of
four, quite diverse, oxygen-rich stars using the NH3 ortho J_K = 1_0 - 0_0
ground-state line. We used the Heterodyne Instrument for the Far Infrared
aboard Herschel to observe the NH3 J_K = 1_0 - 0_0 transition near 572.5 GHz,
simultaneously with the ortho-H2O J_Ka,Kc = 1_1,0 -1_0,1 transition, toward VY
CMa, OH 26.5+0.6, IRC+10420, and IK Tau. We conducted non-LTE radiative
transfer modeling with the goal to derive the NH3 abundance in these objects'
CSEs. For the latter two stars, Very Large Array imaging of NH3
radio-wavelength inversion lines were used to provide further constraints,
particularly on the spatial extent of the NH3-emitting regions. Results. We
find remarkably strong NH3 emission in all of our objects with the NH3 line
intensities rivaling those obtained for the ground state H2O line. The NH3
abundances relative to H2 are very high and range from 2 x 10-7 to 3 x 10-6 for
the objects we have studied. Our observations confirm and even deepen the
circumstellar NH3 enigma. While our radiative transfer modeling does not yield
satisfactory fits to the observed line profiles, it leads to abundance
estimates that confirm the very high values found in earlier studies. New ways
to tackle this mystery will include further Herschel observations of more NH3
lines and imaging with the Expanded Very Large Array.Comment: 4+2 page
Strong CH+ J=1-0 emission and absorption in DR21
We report the first detection of the ground-state rotational transition of
the methylidyne cation CH+ towards the massive star-forming region DR21 with
the HIFI instrument onboard the Herschel satellite. The line profile exhibits a
broad emission line, in addition to two deep and broad absorption features
associated with the DR21 molecular ridge and foreground gas. These observations
allow us to determine a CH+ J=1-0 line frequency of 835137 +/- 3 MHz, in good
agreement with a recent experimental determination. We estimate the CH+ column
density to be a few 1e13 cm^-2 in the gas seen in emission, and > 1e14 cm^-2 in
the components responsible for the absorption, which is indicative of a high
line of sight average abundance [CH+]/[H] > 1.2x10^-8. We show that the CH+
column densities agree well with the predictions of state-of-the-art C-shock
models in dense UV-illuminated gas for the emission line, and with those of
turbulent dissipation models in diffuse gas for the absorption lines.Comment: Accepted for publication in A&
Large atom number dual-species magneto-optical trap for fermionic 6Li and 40K atoms
We present the design, implementation and characterization of a dual-species
magneto-optical trap (MOT) for fermionic 6Li and 40K atoms with large atom
numbers. The MOT simultaneously contains 5.2x10^9 6Li-atoms and 8.0x10^9
40K-atoms, which are continuously loaded by a Zeeman slower for 6Li and a
2D-MOT for 40K. The atom sources induce capture rates of 1.2x10^9 6Li-atoms/s
and 1.4x10^9 40K-atoms/s. Trap losses due to light-induced interspecies
collisions of ~65% were observed and could be minimized to ~10% by using low
magnetic field gradients and low light powers in the repumping light of both
atomic species. The described system represents the starting point for the
production of a large-atom number quantum degenerate Fermi-Fermi mixture
Nitrogen hydrides in the cold envelope of IRAS16293-2422
Nitrogen is the fifth most abundant element in the Universe, yet the
gas-phase chemistry of N-bearing species remains poorly understood. Nitrogen
hydrides are key molecules of nitrogen chemistry. Their abundance ratios place
strong constraints on the production pathways and reaction rates of
nitrogen-bearing molecules. We observed the class 0 protostar IRAS16293-2422
with the heterodyne instrument HIFI, covering most of the frequency range from
0.48 to 1.78~THz at high spectral resolution. The hyperfine structure of the
amidogen radical o-NH2 is resolved and seen in absorption against the continuum
of the protostar. Several transitions of ammonia from 1.2 to 1.8~THz are also
seen in absorption. These lines trace the low-density envelope of the
protostar. Column densities and abundances are estimated for each hydride. We
find that NH:NH2:NH3=5:1:300. {Dark clouds chemical models predict steady-state
abundances of NH2 and NH3 in reasonable agreement with the present
observations, whilst that of NH is underpredicted by more than one order of
magnitude, even using updated kinetic rates. Additional modelling of the
nitrogen gas-phase chemistry in dark-cloud conditions is necessary before
having recourse to heterogen processes
The origin of the [C II] emission in the S140 PDRs - new insights from HIFI
Using Herschel's HIFI instrument we have observed [C II] along a cut through
S140 and high-J transitions of CO and HCO+ at two positions on the cut,
corresponding to the externally irradiated ionization front and the embedded
massive star forming core IRS1. The HIFI data were combined with available
ground-based observations and modeled using the KOSMA-tau model for photon
dominated regions. Here we derive the physical conditions in S140 and in
particular the origin of [C II] emission around IRS1. We identify three
distinct regions of [C II] emission from the cut, one close to the embedded
source IRS1, one associated with the ionization front and one further into the
cloud. The line emission can be understood in terms of a clumpy model of
photon-dominated regions. At the position of IRS1, we identify at least two
distinct components contributing to the [C II] emission, one of them a small,
hot component, which can possibly be identified with the irradiated outflow
walls. This is consistent with the fact that the [C II] peak at IRS1 coincides
with shocked H2 emission at the edges of the outflow cavity. We note that
previously available observations of IRS1 can be well reproduced by a
single-component KOSMA-tau model. Thus it is HIFI's unprecedented spatial and
spectral resolution, as well as its sensitivity which has allowed us to uncover
an additional hot gas component in the S140 region.Comment: accepted for publication in Astronomy and Astrophysics (HIFI special
issue
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