7,726 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
Threshold Resummation for W-Boson Production at RHIC
We study the resummation of large logarithmic perturbative corrections to the
partonic cross sections relevant for the process pp -> W^+- X at the BNL
Relativistic Heavy Ion Collider (RHIC). At RHIC, polarized protons are
available, and spin asymmetries for this process will be used for precise
measurements of the up and down quark and anti-quark distributions in the
proton. The corrections arise near the threshold for the partonic reaction and
are associated with soft-gluon emission. We perform the resummation to
next-to-leading logarithmic accuracy, for the rapidity-differential cross
section. We find that resummation leads to relatively moderate effects on the
cross sections and spin asymmetries.Comment: 25 pages, 15 figures as eps files. One reference added and typo
correcte
Tunable-filter imaging of quasar fields at z ~ 1. II. The star-forming galaxy environments of radio-loud quasars
We have scanned the fields of six radio-loud quasars using the Taurus Tunable
Filter to detect redshifted [OII] 3727 line-emitting galaxies at redshifts 0.8
< z < 1.3. Forty-seven new emission-line galaxy (ELG) candidates are found.
This number corresponds to an average space density about 100 times that found
locally and, at L([OII]) < 10^{42} erg s^{-1} cm^{-2}, is 2 - 5 times greater
than the field ELG density at similar redshifts, implying that radio-loud
quasars inhabit sites of above-average star formation activity. The implied
star-formation rates are consistent with surveys of field galaxies at z ~ 1.
However, the variation in candidate density between fields is large and
indicative of a range of environments, from the field to rich clusters. The ELG
candidates also cluster -- both spatially and in terms of velocity -- about the
radio sources. In fields known to contain rich galaxy clusters, the ELGs lie at
the edges and outside the concentrated cores of red, evolved galaxies,
consistent with the morphology-density relation seen in low-redshift clusters.
This work, combined with other studies, suggests that the ELG environments of
powerful AGN look very much the same from moderate to high redshifts, i.e. 0.8
< z < 4.Comment: 18 pages, 18 figures, uses emulateapj.cls. Accepted for publication
in A
The large scale distribution of warm ionized gas around nearby radio galaxies with jet-cloud interactions
Deep, narrow-band Halpha observations taken with the TAURUS Tunable Filter
(TTF) on the 4.2m WHT telescope are presented for two nearby radio galaxies
with strong jet-cloud interactions. Although the brightest emission line
components are closely aligned with the radio jets --- providing nearby
examples of the ``alignment effect'' most commonly observed in high redshift (z
> 0.5) radio galaxies --- lower surface brightness emission line structures are
detected at large distances (10's of kpc) from the radio jet axis. These latter
structures cannot be reconciled with anisotropic illumination of the ISM by
obscured quasar-like sources, since parts of the structures lay outside any
plausible quasar ionization cones. Rather, the distribution of the emission
lines around the fringes of the extended radio lobes suggests that the gas is
ionized either by direct interaction with the radio components, or by the
diffuse photoionizing radiation fields produced in the shocks generated in such
interactions. These observations serve to emphasise that the ionizing effects
of the radio components can extend far from the radio jet axes, and that deep
emission line imaging observations are required to reveal the true distribution
of warm gas in the host galaxies. We expect future deep imaging observations to
reveal similar structures perpendicular to the radio axes in the high-z radio
galaxies.Comment: 18 pages, 4 figures, to be published in MNRA
Instability of Rotationally Tuned Dipolar Bose-Einstein Condensates
The possibility of effectively inverting the sign of the dipole-dipole
interaction, by fast rotation of the dipole polarization, is examined within a
harmonically trapped dipolar Bose-Einstein condensate. Our analysis is based on
the stationary states in the Thomas-Fermi limit, in the corotating frame, as
well as direct numerical simulations in the Thomas-Fermi regime, explicitly
accounting for the rotating polarization. The condensate is found to be
inherently unstable due to the dynamical instability of collective modes. This
ultimately prevents the realization of robust and long-lived rotationally tuned
states. Our findings have major implications for experimentally accessing this
regime.Comment: 9 pages with 5 figure
The hydrogen isotopic composition of fossil micrometeorites: Implications for the origin of water on Earth.
Accepted versio
NGC 300: an extremely faint, outer stellar disk observed to 10 scale lengths
We have used the Gemini Multi-object Spectrograph (GMOS) on the Gemini South
8m telescope in exceptional conditions (0.6" FWHM seeing) to observe the outer
stellar disk of the Sculptor group galaxy NGC 300 at two locations. At our
point source detection threshold of r' = 27.0 (3-sigma) mag, we trace the
stellar disk out to a radius of 24', or 2.2 R_25 where R_25 is the 25
mag/arcsec**2 isophotal radius. This corresponds to about 10 scale lengths in
this low-luminosity spiral (M_B = -18.6), or about 14.4 kpc at a cepheid
distance of 2.0 +/- 0.07 Mpc. The background galaxy counts are derived in the
outermost field, and these are within 10% of the mean survey counts from both
Hubble Deep Fields. The luminosity profile is well described by a nucleus plus
a simple exponential profile out to 10 optical scale lengths. We reach an
effective surface brightness of 30.5 mag/arcsec**2 (2-sigma) at 55%
completeness which doubles the known radial extent of the optical disk. These
levels are exceedingly faint in the sense that the equivalent surface
brightness in B or V is about 32 mag/arcsec**2. We find no evidence for
truncation of the stellar disk. Only star counts can be used to reliably trace
the disk to such faint levels, since surface photometry is ultimately limited
by nonstellar sources of radiation. In the Appendix, we derive the expected
surface brightness of one such source: dust scattering of starlight in the
outer disk.Comment: ApJ accepted -- 30 pages, 13 figures -- see
ftp://www.aao.gov.au/pub/local/jbh/astro-ph/N300 for full resolution figures
and preprin
Discrete emotion-congruent false memories in the DRM paradigm
Research has shown that false memory production is enhanced for material that is emotionally congruent with the mood of the participant at the time of encoding. So far this research has only examined the influence of generic negative affective mood states and generic negative stimuli on false memory production. In addition, much of the research is limited as it focuses on valence and arousal dimensions, and fails to take into account the more comprehensive nature of emotions. The current study demonstrates that this effect goes beyond general negative or positive moods and acts at a more discrete emotional level. Participants underwent a standard emotion induction procedure before listening to negative emotional or neutral associative word lists. The emotions induced, negative word lists and associated non-presented critical lures, were related to either fear or anger, two negative valence emotions that are also both high in arousal. Results showed that when valence and arousal are controlled for, false memories are more likely to be produced for discrete emotionally congruent compared to incongruent materials. These results support spreading activation theories of false remembering and add to our understanding of the adaptive nature of false memory production
Statistical analysis of the primary outcome in acute stroke trials
Common outcome scales in acute stroke trials are ordered categorical or pseudocontinuous in structure but most have been analyzed as binary measures. The use of fixed dichotomous analysis of ordered categorical outcomes after stroke (such as the modified Rankin Scale) is rarely the most statistically efficient approach and usually requires a larger sample size to demonstrate efficacy than other approaches. Preferred statistical approaches include sliding dichotomous, ordinal, or continuous analyses. Because there is no best approach that will work for all acute stroke trials, it is vital that studies are designed with a full understanding of the type of patients to be enrolled (in particular their case mix, which will be critically dependent on their age and severity), the potential mechanism by which the intervention works (ie, will it tend to move all patients somewhat, or some patients a lot, and is a common hazard present), a realistic assessment of the likely effect size, and therefore the necessary sample size, and an understanding of what the intervention will cost if implemented in clinical practice. If these approaches are followed, then the risk of missing useful treatment effects for acute stroke will diminish
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