959 research outputs found
Laser cooling with electromagnetically induced transparency: Application to trapped samples of ions or neutral atoms
A novel method of ground state laser cooling of trapped atoms utilizes the
absorption profile of a three (or multi-) level system which is tailored by a
quantum interference. With cooling rates comparable to conventional sideband
cooling, lower final temperatures may be achieved. The method was
experimentally implemented to cool a single Ca ion to its vibrational
ground state. Since a broad band of vibrational frequencies can be cooled
simultaneously, the technique will be particularly useful for the cooling of
larger ion strings, thereby being of great practical importance for
initializing a quantum register based on trapped ions. We also discuss its
application to different level schemes and for ground state cooling of neutral
atoms trapped by a far detuned standing wave laser field.Comment: 9 pages, 13 figures, submitted to Appl Phys B 200
The spectral type of CHS7797 - an intriguing very low mass periodic variable in the Orion Nebula Cluster
We present the spectroscopic characterization of the unusual high-amplitude
very low mass pre-main-sequence periodic variable CHS7797. This study is based
on optical medium-resolution (R=2200) spectroscopy in the 6450-8600 A range,
carried out with GMOS-GEMINI-S in March 2011. Observations of CHS7797 have been
carried out at two distinct phases of the 17.8d period, namely at maximum and
four days before maximum. Four different spectral indices were used for the
spectral classification at these two phases, all of them well-suited for
spectral classification of young and obscured late M dwarfs. In addition, the
gravity-sensitive NaI (8183/8195 A) and KI (7665/7699 A) doublet lines were
used to confirm the young age of CHS7797. From the spectrum obtained at maximum
light we derived a spectral type (SpT) of M6.05, while for the spectrum taken
four days before maximum the derived SpT is M5.75. The derived SpTs confirm
that CHS7797 has a mass in the stellar-substellar boundary mass range. In
addition, the small differences in the derived SpTs at the two observed phases
may provide indirect hints that CHS7797 is a binary system of similar mass
components surrounded by a tilted circumbinary disk, a system similar to KH15D.Comment: 6 pages, accepted for publication A&
Testing evolutionary tracks of Pre-Main Sequence stars: the case of HD113449
Evolutionary tracks are of key importance for the understanding of star
formation. Unfortunately, tracks published by various groups differ so that it
is fundamental to have observational tests. In order to do this, we intend to
measure the masses of the two components of the Pre-Main Sequence binary
HD113449 by combining radial velocity measurements taken with HARPS, with
infrared interferometric data using AMBER on the VLTI. The spectroscopic orbit
that has already been determined, combined with the first AMBER measurement,
allows us to obtain a very first estimation of the inclination of the binary
system and from this the masses of the two stars. More AMBER measurements of HD
113449 are needed to improve the precision on the masses: in the ESO period P82
two new measurements are scheduled.Comment: 4 pages, 3 figures; to appear in proceedings of Cool Star 15
conference, St.Andrews 200
Physical properties of the jet from DG Tauri on sub-arcsecond scales with HST/STIS
We derive the physical properties at the base of the jet from DG Tau both
along and across the flow and as a function of velocity. We analysed seven
optical spectra of the DG Tau jet, taken with the Hubble Space Telescope
Imaging Spectrograph. The spectra were obtained by placing a long-slit parallel
to the jet axis and stepping it across the jet width. The resulting
position-velocity diagrams in optical forbidden emission lines allowed access
to plasma conditions via calculation of emission line ratios.
We find at the base of the jet high electron density, 10, and
very low ionisation, , which combine to give a total
density up to 3 10. This analysis confirms previous reports of
variations in plasma parameters along the jet, (i.e. decrease in density by
several orders of magnitude, increase of from 0.05 to a plateau at 0.7
downstream at 2 from the star). Furthermore, a spatial coincidence is
revealed between sharp gradients in the total density and supersonic velocity
jumps. This strongly suggests that the emission is caused by shock excitation.
The position-velocity diagrams indicate the presence of both fast accelerating
gas and slower, less collimated material. We derive the mass outflow rate,
, in the blue-shifted lobe in different velocity channels, that
contribute to a total of 8 4 10 M
yr. We estimate that a symmetric bipolar jet would transport at the low
and intermediate velocities probed by rotation measurements, an angular
momentum flux of 2.9 1.5 10 M yr
AU km s.
The derived properties of the DG Tau jet are demonstrated to be consistent
with magneto-centrifugal theory. However, non-stationary modelling is required
in order to explain all of the features revealed at high resolution.Comment: 16 pages, 18 figure
Proper Motions of the Jets in the Region of HH 30 and HL/XZ Tau. Evidence for a Binary Exciting Source of the HH 30 Jet
We present [SII] images of the HH 30 and HL/XZ Tau region obtained at two
epochs, as well as long-slit optical spectroscopy of the HH 30 jet. We measured
proper motions of about 100-300 km/s for the HH 30 jet and counterjet, and of
about 120 km/s for the HL Tau jet. Inclination angles with respect to the plane
of the sky are 0-40 deg for the HH 30 jet and 60 deg for the HL Tau jet.
Comparison with previous observations suggests that most of the jet knots
consist of persisting structures. Also, we corroborate that the HH 30-N knots
correspond to the head of the HH 30 jet. The overall HH 30 jet structure can be
well described by a wiggling ballistic jet, arising either by the orbital
motion of the jet source around a primary or by precession of the jet axis
because of the tidal effects of a companion. In the first scenario, the orbital
period would be 53 yr and the total mass 0.25-2 solar masses. In the precession
scenario, the mass of the jet source would be 0.1-1 solar masses, the orbital
period <1 yr, and the mass of the companion less than a few times 0.01 solar
masses, thus being a substellar object or a giant exoplanet. In both scenarios
a binary system with a separation <18 AU (<0.13 arcsec) is required. Since the
radius of the flared disk observed with the HST is about 250 AU, we conclude
that this disk appears to be circumbinary rather than circumstellar, suggesting
that the search for the collimating agent of the HH 30 jet should be carried
out at much smaller scales.Comment: 42 pages, 7 figures, 5 tables. To Appear in The Astronomical Journal,
Vol. 133 No. 6 (June 2007
HST/STIS observations of the RW Aurigae bipolar jet: mapping the physical parameters close to the source
We present the results of new spectral diagnostic investigations applied to
high-resolution long-slit spectra of the RW Aur bipolar jet obtained with
HST/STIS. The spectra include the forbidden doublets [O I] 6300,6363 \AA, [S
II] 6716,6731 \AA, and [N II] 6548, 6583 \AA that we utilized to determine
electron density, electron temperature, hydrogen ionisation fraction, total
hydrogen density, radial velocity and the mass outflow rate. We were able to
extract the parameters as far as 3".9 in the red- and 2".1 in the blueshifted
beam. The RW Aur jet appears to be the second densest outflow from a T Tauri
star studied so far, but its other properties are quite similar to those found
in other jets from young stars. The overall trend of the physical parameters
along the first few arcseconds of the RW Aur jet is similar to that of HH 30
and DG Tau and this can reflect analogies in the mechanisms operating in that
region, suggesting the same engine is accelerating the jets in the T Tauri
stars with outflows. Our study of the RW Aur jet indicates for the first time
that, despite the detected marked asymmetries in physical and kinematic
properties between the two lobes, the mass outflow rates in the two lobes are
similar. This appears to indicate that the central engine has constraining
symmetries on both sides of the system, and that the observed asymmetries are
probably due to different environmental conditions.Comment: 24 pages, 10 figures, accepted for publication in the Astronomy and
Astrophysic
Experiments towards quantum information with trapped Calcium ions
Ground state cooling and coherent manipulation of ions in an rf-(Paul) trap
is the prerequisite for quantum information experiments with trapped ions. With
resolved sideband cooling on the optical S1/2 - D5/2 quadrupole transition we
have cooled one and two 40Ca+ ions to the ground state of vibration with up to
99.9% probability. With a novel cooling scheme utilizing electromagnetically
induced transparency on the S1/2 - P1/2 manifold we have achieved simultaneous
ground state cooling of two motional sidebands 1.7 MHz apart. Starting from the
motional ground state we have demonstrated coherent quantum state manipulation
on the S1/2 - D5/2 quadrupole transition at 729 nm. Up to 30 Rabi oscillations
within 1.4 ms have been observed in the motional ground state and in the n=1
Fock state. In the linear quadrupole rf-trap with 700 kHz trap frequency along
the symmetry axis (2 MHz in radial direction) the minimum ion spacing is more
than 5 micron for up to 4 ions. We are able to cool two ions to the ground
state in the trap and individually address the ions with laser pulses through a
special optical addressing channel.Comment: Proceedings of the ICAP 2000, Firenz
Two-photon interaction between trapped ions and cavity fields
In this paper, we generalize the ordinary two-photon Jaynes-Cummings model
(TPJCM) by considering the atom (or ion) to be trapped in a simple harmonic
well. A typical setup would be an optical cavity containing a single ion in a
Paul trap. Due to the inclusion of atomic vibrational motion, the atom-field
coupling becomes highly nonlinear what brings out quite different behaviors for
the system dynamics when compared to the ordinary TPJCM. In particular, we
derive an effective two-photon Hamiltonian with dependence on the number
operator of the ion's center-of-mass motion. This dependence occurs both in the
cavity induced Stark-shifs and in the ion-field coupling, and its role in the
dynamics is illustrated by showing the time evolution of the probability of
occupation of the electronic levels for simple initial preparations of the
state of the system.Comment: 9 pages, 10 figure
High Angular Resolution Radio Observations of the HL/XZ Tau Region: Mapping the 50 AU Protoplanetary Disk around HL Tau and Resolving XZ Tau S into a 13 AU Binary
We present new 7 mm and archive 1.3 cm high angular resolution observations
of the HL/XZ Tau region made with the VLA. At 7 mm, the emission from HL Tau
seems to be arising in a clumpy disk with radius of order 25 AU. The 1.3 cm
emission from XZ Tau shows the emission from a binary system with 0"3 (42 AU)
separation, known from previous optical/IR observations. However, at 7 mm, the
southern radio component resolves into a binary with 0"09 (13 AU) separation,
suggesting that XZ Tau is actually a triple star system. We suggest that the
remarkable ejection of gas from the XZ Tau system observed with the HST may be
related to a periastron passage of this newly discovered close binary system.Comment: Accepted by The Astrophysical Journal Letters (23 Jan 2009
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