20,656 research outputs found
Threaded pilot insures cutting tool alignment
Threaded pilot allows machining of a port component, or boss, after the reciprocating hole has been threaded. It is used to align cutting surfaces with the boss threads, thus insuring precision alignment
On the structure of the BBGKY hierarchy for a Boltzmann gas
Structure of BBGKY hierarchy for Boltzmann gas and particle distribution
Parallax measurements of cool brown dwarfs
Accurate parallax measurements allow us to determine physical properties of
brown dwarfs, and help us to constrain evolutionary and atmospheric models,
break the age-mass degeneracy and reveal unresolved binaries.
We measured absolute trigonometric parallaxes and proper motions of 6 cool
brown dwarfs using background galaxies to establish an absolute reference
frame. We derive the absolute J-mag. The six T brown dwarfs in our sample have
spectral types between T2.5 and T7.5 and magnitudes in J between 13.9 and 18.0,
with photometric distances below 25 pc.
The observations were taken in the J-band with the Omega-2000 camera on the
3.5 m telescope at Calar Alto, during a time period of 27 months, between March
2011 and June 2013. The number of epochs varied between 11 and 12 depending on
the object. The reduction of the astrometric measurements was carried out with
respect to the field stars. The relative parallax and proper motions were
transformed into absolute measurements using the background galaxies in our
fields.
We obtained absolute parallaxes for our six brown dwarfs with a precision
between 3 and 6 mas. We compared our results in a color-magnitude diagram with
other brown dwarfs with determined parallax and with the BT-Settl 2012
atmospheric models. For four of the six targets we found a good agreement in
luminosity with objects of similar spectral types. We obtained an improved
accuracy in the parallaxes and proper motions in comparison to previous works.
The object 2MASS J11061197+2754225 is more than 1 mag overluminous in all bands
pointing to binarity or high order multiplicity.Comment: 9 pages, 15 figures. Astronomy & Astrophysics, 201
Realization of uniform synthetic magnetic fields by periodically shaking an optical square lattice
Shaking a lattice system, by modulating the location of its sites
periodically in time, is a powerful method to create effective magnetic fields
in engineered quantum systems, such as cold gases trapped in optical lattices.
However, such schemes are typically associated with space-dependent effective
masses (tunneling amplitudes) and non-uniform flux patterns. In this work we
investigate this phenomenon theoretically, by computing the effective
Hamiltonians and quasienergy spectra associated with several kinds of
lattice-shaking protocols. A detailed comparison with a method based on moving
lattices, which are added on top of a main static optical lattice, is provided.
This study allows the identification of novel shaking schemes, which
simultaneously provide uniform effective mass and magnetic flux, with direct
implications for cold-atom experiments and photonics.Comment: 15 pages, 10 eps figure
Spectroscopic and photometric studies of white dwarfs in the Hyades
The Hyades cluster is known to harbour ten so-called classical white dwarf
members. Numerous studies through the years have predicted that more than twice
this amount of degenerate stars should be associated with the cluster. Using
the PPMXL catalog of proper motions and positions, a recent study proposed 17
new white dwarf candidates. We review the membership of these candidates by
using published spectroscopic and photometric observations, as well as by
simulating the contamination from field white dwarfs. In addition to the ten
classical Hyades white dwarfs, we find six white dwarfs that may be of Hyades
origin and three more objects that have an uncertain membership status due to
their unknown or imprecise atmospheric parameters. Among those, two to three
are expected as field stars contamination. Accurate radial velocity
measurements will confirm or reject the candidates. One consequence is that the
longstanding problem that no white dwarf older than ~340 Myr appears to be
associated with the cluster remains unsolved.Comment: 14 pages, 9 figures, accepted for publication in the Astronomy and
Astrophysics journa
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