1,363 research outputs found
MMTF: The Maryland-Magellan Tunable Filter
This paper describes the Maryland-Magellan Tunable Filter (MMTF) on the
Magellan-Baade 6.5-meter telescope. MMTF is based on a 150-mm clear aperture
Fabry-Perot (FP) etalon that operates in low orders and provides transmission
bandpass and central wavelength adjustable from ~5 to ~15 A and from ~5000 to
over ~9200 A, respectively. It is installed in the Inamori Magellan Areal
Camera and Spectrograph (IMACS) and delivers an image quality of ~0.5" over a
field of view of 27' in diameter (monochromatic over ~10'). This versatile and
easy-to-operate instrument has been used over the past three years for a wide
variety of projects. This paper first reviews the basic principles of FP
tunable filters, then provides a detailed description of the hardware and
software associated with MMTF and the techniques developed to observe with this
instrument and reduce the data. The main lessons learned in the course of the
commissioning and implementation of MMTF are highlighted next, before
concluding with a brief outlook on the future of MMTF and of similar facilities
which are soon coming on line.Comment: 38 pages, 12 figures, 3 tables, now accepted for publication to the
Astronomical Journa
Spin and Charge Transport on the Surface of a Topological Insulator
We derive diffusion equations, which describe spin-charge coupled transport
on the helical metal surface of a three-dimensional topological insulator. The
main feature of these equations is a large magnitude of the spin-charge
coupling, which leads to interesting and observable effects. In particular, we
predict a new magnetoresistance effect, which manifests in a nonohmic
correction to a voltage drop between a ferromagnetic spin-polarized electrode
and a nonmagnetic electrode, placed on top of the helical metal. This
correction is proportional to the cross-product of the spin polarization of the
ferromagnetic electrode and the charge current between the two electrodes. We
also demonstrate tunability of this effect by applying a gate voltage, which
makes it possible to operate the proposed device as a transistor.Comment: 4 pages, 1 figure; published versio
Tomography of high-redshift clusters with OSIRIS
High-redshift clusters of galaxies are amongst the largest cosmic structures.
Their properties and evolution are key ingredients to our understanding of
cosmology: to study the growth of structure from the inhomogeneities of the
cosmic microwave background; the processes of galaxy formation, evolution, and
differentiation; and to measure the cosmological parameters (through their
interaction with the geometry of the universe, the age estimates of their
component galaxies, or the measurement of the amount of matter locked in their
potential wells). However, not much is yet known about the properties of
clusters at redshifts of cosmological interest. We propose here a radically new
method to study large samples of cluster galaxies using microslits to perform
spectroscopy of huge numbers of objects in single fields in a narrow spectral
range-chosen to fit an emission line at the cluster redshift. Our objective is
to obtain spectroscopy in a very restricted wavelength range (~100 A in width)
of several thousands of objects for each single 8x8 square arcmin field.
Approximately 100 of them will be identified as cluster emission-line objects
and will yield basic measurements of the dynamics and the star formation in the
cluster (that figure applies to a cluster at z~0.50, and becomes ~40 and ~20
for clusters at z~0.75 and z~1.00 respectively). This is a pioneering approach
that, once proven, will be followed in combination with photometric redshift
techniques and applied to other astrophysical problems.Comment: 4 pages, 3 figures. Proceedings of "Science with the GTC", Granada
(Spain), February 2002, RMxAA in pres
Is it possible to reveal the lost siblings of the Sun?
We present the results of our numerical experiments on stellar scattering in
the galactic disc under the influence of the perturbed galactic gravitation
field connected with the spiral density waves and show that the point of view
according to which stars do not migrate far from their birthplace, in general,
is incorrect. Despite close initial locations and the same velocities after 4.6
Gyrs members of an open cluster are scattered over a very large part of the
galactic disc. If we adopt that the parental solar cluster had
stars, it is unlikely to reveal the solar siblings within 100 pc from the Sun.
The problem stands a good chance to be solved if the cluster had
stars.
We also demonstrate that unbound open clusters disperse off in a short period
of time under the influence of spiral gravitation field. Their stars became a
part of the galactic disc. We have estimated typical times of the cluster
disruption in radial and azimuth directions and the corresponding diffusion
coefficients.Comment: 7 pages, 12 figure
The Taurus Tunable Filter Field Galaxy Survey: Sample Selection and Narrowband Number-Counts
Recent evidence suggests a falling volume-averaged star-formation rate (SFR)
over z ~ 1. It is not clear, however, the extent to which the selection of such
samples influences the measurement of this quantity. Using the Taurus Tunable
Filter (TTF) we have obtained an emission-line sample of faint star-forming
galaxies over comparable lookback times: the TTF Field Galaxy Survey. By
selecting through emission-lines, we are screening galaxies through a quantity
that scales directly with star-formation activity for a given choice of initial
mass function. The scanning narrowband technique furnishes a galaxy sample that
differs from traditional broadband-selected surveys in both its volume-limited
nature and selection of galaxies through emission-line flux. Three discrete
wavelength intervals are covered, centered at H-alpha redshifts z = 0.08, 0.24
and 0.39.
Galaxy characteristics are presented and comparisons made with existing
surveys of both broadband and emission-line selection. When the number-counts
of emission-line objects are compared with those expected on the basis of
existing H-alpha surveys, we find an excess of ~ 3 times at the faintest
limits. While these detections are yet to be independently confirmed,
inspection of the stronger subsample of galaxies detected in both the line and
continuum (line-on-continuum subsample; 13 %) is sufficient to support an
excess population. This increase in the emission-line field population implies
higher star-formation densities over z ~ 0.4. However, further study in the
form of multi-object spectroscopic follow-up is necessary to quantify this and
confirm the faintest detections in the sample.Comment: 48 pages, 12 figures. To appear in the Astrophysical Journal. An
abridged version of the Abstract is shown her
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