647 research outputs found
The Kinematics of HH 34 from HST Images with a Nine-year Time Baseline
We study archival HST [S II] 6716+30 and Hα images of the HH 34 outflow, taken in 1998.71 and in 2007.83. The ~9 yr time baseline and the high angular resolution of these observations allow us to carry out a detailed proper-motion study. We determine the proper motions of the substructure of the HH 34S bow shock (from the [S II] and Hα frames) and of the aligned knots within ~30'' from the outflow source (only from the [S II] frames). We find that the present-day motions of the knots along the HH 34 jet are approximately ballistic, and that these motions directly imply the formation of a major mass concentration in ~900 yr, at a position similar to the one of the present-day HH 34S bow shock. In other words, we find that the knots along the HH 34 jet will merge to form a more massive structure, possibly resembling HH 34S
Strongly driven quantum pendulum of the OCS molecule
We demonstrate and analyze a strongly driven quantum pendulum in the angular
motion of stateselected and laser aligned OCS molecules. Raman-couplings during
the rising edge of a 50-picosecond laser pulse create a wave packet of pendular
states, which propagates in the confining potential formed by the
polarizability interaction between the molecule and the laser field. This
wave-packet dynamics manifests itself as pronounced oscillations in the degree
of alignment with a laser-intensity dependent period.Comment: 6 pages, 4 figure
A Spitzer Study of the Mass Loss Histories of Three Bipolar Pre-Planetary Nebulae
We present the results of far-infrared imaging of extended regions around
three bipolar pre-planetary nebulae, AFGL 2688, OH 231.8+4.2, and IRAS
163423814, at 70 and 160 m with the MIPS instrument on the Spitzer
Space Telescope. After a careful subtraction of the point spread function of
the central star from these images, we place constraints on the existence of
extended shells and thus on the mass outflow rates as a function of radial
distance from these stars. We find no apparent extended emission in AFGL 2688
and OH 231.8+4.2 beyond 100 arcseconds from the central source. In the case of
AFGL 2688, this result is inconsistent with a previous report of two extended
dust shells made on the basis of ISO observations. We derive an upper limit of
M yr and M
yr for the dust mass loss rate of AFGL 2688 and OH 231.8, respectively,
at 200 arcseconds from each source. In contrast to these two sources, IRAS
163423814 does show extended emission at both wavelengths, which can be
interpreted as a very large dust shell with a radius of 400 arcseconds
and a thickness of 100 arcseconds, corresponding to 4 pc and 1 pc,
respectively, at a distance of 2 kpc. However, this enhanced emission may also
be galactic cirrus; better azimuthal coverage is necessary for confirmation of
a shell. If the extended emission is a shell, it can be modeled as enhanced
mass outflow at a dust mass outflow rate of M
yr superimposed on a steady outflow with a dust mass outflow rate of
M yr. It is likely that this shell has swept
up a substantial mass of interstellar gas during its expansion, so these
estimates are upper limits to the stellar mass loss rate.Comment: 31 pages, 12 figures, accepted to A
Strongly aligned molecules inside helium droplets in the near-adiabatic regime
Iodine (I) molecules embedded in He nanodroplets are aligned by a 160 ps
long laser pulse. The highest degree of alignment, occurring at the peak of the
pulse and quantified by , is measured as a
function of the laser intensity. The results are well described by calculated for a gas of isolated molecules each
with an effective rotational constant of 0.6 times the gas-phase value, and at
a temperature of 0.4 K. Theoretical analysis using the angulon quasiparticle to
describe rotating molecules in superfluid helium rationalizes why the alignment
mechanism is similar to that of isolated molecules with an effective rotational
constant. A major advantage of molecules in He droplets is that their 0.4 K
temperature leads to stronger alignment than what can generally be achieved for
gas phase molecules -- here demonstrated by a direct comparison of the droplet
results to measurements on a 1 K supersonic beam of isolated molecules.
This point is further illustrated for more complex system by measurements on
1,4-diiodobenzene and 1,4-dibromobenzene. For all three molecular species
studied the highest values of achieved in
He droplets exceed 0.96.Comment: 11 pages, 8 figure
Laboratory Determination of the Infrared Band Strengths of Pyrene Frozen in Water Ice: Implications for the Composition of Interstellar Ices
Broad infrared emission features (e.g., at 3.3, 6.2, 7.7, 8.6, and 11.3
microns) from the gas phase interstellar medium have long been attributed to
polycyclic aromatic hydrocarbons (PAHs). A significant portion (10%-20%) of the
Milky Way's carbon reservoir is locked in PAH molecules, which makes their
characterization integral to our understanding of astrochemistry. In molecular
clouds and the dense envelopes and disks of young stellar objects (YSOs), PAHs
are expected to be frozen in the icy mantles of dust grains where they should
reveal themselves through infrared absorption. To facilitate the search for
frozen interstellar PAHs, laboratory experiments were conducted to determine
the positions and strengths of the bands of pyrene mixed with H2O and D2O ices.
The D2O mixtures are used to measure pyrene bands that are masked by the strong
bands of H2O, leading to the first laboratory determination of the band
strength for the CH stretching mode of pyrene in water ice near 3.25 microns.
Our infrared band strengths were normalized to experimentally determined
ultraviolet band strengths, and we find that they are generally ~50% larger
than those reported by Bouwman et al. based on theoretical strengths. These
improved band strengths were used to reexamine YSO spectra published by Boogert
et al. to estimate the contribution of frozen PAHs to absorption in the 5-8
micron spectral region, taking into account the strength of the 3.25 micron CH
stretching mode. It is found that frozen neutral PAHs contain 5%-9% of the
cosmic carbon budget, and account for 2%-9% of the unidentified absorption in
the 5-8 micron region.Comment: Accepted for publication in ApJ on 14 Feb 201
Manipulating the torsion of molecules by strong laser pulses
A proof-of-principle experiment is reported, where torsional motion of a
molecule, consisting of a pair of phenyl rings, is induced by strong laser
pulses. A nanosecond laser pulse spatially aligns the carbon-carbon bond axis,
connecting the two phenyl rings, allowing a perpendicularly polarized, intense
femtosecond pulse to initiate torsional motion accompanied by an overall
rotation about the fixed axis. The induced motion is monitored by femtosecond
time-resolved Coulomb explosion imaging. Our theoretical analysis accounts for
and generalizes the experimental findings.Comment: 4 pages, 4 figures, submitted to PRL; Major revision of the
presentation of the material; Correction of ion labels in Fig. 2(a
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