300 research outputs found
Asymmetric Drift and the Stellar Velocity Ellipsoid
We present the decomposition of the stellar velocity ellipsoid using stellar
velocity dispersions within a 40 deg wedge about the major-axis (sigma_maj),
the epicycle approximation, and the asymmetric drift equation. Thus, we employ
no fitted forms for sigma_maj and escape interpolation errors resulting from
comparisons of the major and minor axes. We apply the theoretical construction
of the method to integral field data taken for NGC 3949 and NGC 3982. We derive
the vertical-to-radial velocity dispersion ratio (sigma_z / sigma_R) and find
(1) our decomposition method is accurate and reasonable, (2) NGC 3982 appears
to be rather typical of an Sb type galaxy with sigma_z / sigma_R = 0.73
(+0.13/-0.11) despite its high surface brightness and small size, and (3) NGC
3949 has a hot disk with sigma_z / sigma_R = 1.18 (+0.36/-0.28).Comment: 4 pages including 3 figures, to appear in "Island Universes:
Structure and Evolution of Disk Galaxies", Terschelling, Netherlands, July
3-8, 200
Impact of surface-polish on the angular and wavelength dependence of fiber focal ratio degradation
We present measurements of how multimode fiber focal-ratio degradation (FRD)
and throughput vary with levels of fiber surface polish from 60 to 0.5 micron
grit. Measurements used full-beam and laser injection methods at wavelengths
between 0.4 and 0.8 microns on 17 meter lengths of Polymicro FBP 300 and 400
micron core fiber. Full-beam injection probed input focal-ratios between f/3
and f/13.5, while laser injection allowed us to isolate FRD at discrete
injection angles up to 17 degrees (f/1.6 marginal ray). We find (1) FRD effects
decrease as grit size decreases, with the largest gains in beam quality
occurring at grit sizes above 5 microns; (2) total throughput increases as grit
size decreases, reaching 90% at 790 nm with the finest polishing levels; (3)
total throughput is higher at redder wavelengths for coarser polishing grit,
indicating surface-scattering as the primary source of loss. We also quantify
the angular dependence of FRD as a function of polishing level. Our results
indicate that a commonly adopted micro-bending model for FRD is a poor
descriptor of the observed phenomenon.Comment: 10 pages, 7 figures, presented at SPIE Astronomical Telescopes and
Instrumentation, July 201
An X-ray Survey in SA 57 with XMM-Newton
The maximum number density of Active Galactic Nuclei (AGNs), as deduced from
X-ray studies, occurs at z<~1, with lower luminosity objects peaking at smaller
redshifts. Optical studies lead to a different evolutionary behaviour, with a
number density peaking at z~2 independently of the intrinsic luminosity, but
this result is limited to active nuclei brighter than the host galaxy. A
selection based on optical variability can detect low luminosity AGNs (LLAGNs),
where the host galaxy light prevents the identification by non-stellar colours.
We want to collect X-ray data in a field where it exists an optically-selected
sample of "variable galaxies'', i.e. variable objects with diffuse appearance,
to investigate the X-ray and optical properties of the population of AGNs,
particularly of low luminosity ones, where the host galaxy is visible. We
observed a field of 0.2 deg^2 in the Selected Area 57, for 67ks with
XMM-Newton. We detected X-ray sources, and we correlated the list with a
photographic survey of SA 57, complete to B_J~23 and with available
spectroscopic data. We obtained a catalogue of 140 X-ray sources to limiting
fluxes 5x10^-16, 2x10^-15 erg/cm^2/s in the 0.5-2 keV and 2-10 keV
respectively, 98 of which are identified in the optical bands. The X-ray
detection of part of the variability-selected candidates confirms their AGN
nature. Diffuse variable objects populate the low luminosity side of the
sample. Only 25/44 optically-selected QSOs are detected in X-rays. 15% of all
QSOs in the field have X/O<0.1.Comment: 13 pages, 6 figures, 4 tables, A&A in pres
SparsePak Observations of Diffuse Ionized Gas Halo Kinematics in NGC 891
We present WIYN SparsePak observations of the diffuse ionized gas (DIG) halo
of NGC 891. Preliminary results of an analysis of the halo velocity field
reveal a clear gradient of the azimuthal velocity with z which agrees with
results for the neutral gas. The magnitude of the gradient has been determined,
using two independent methods, to be approximately 15 km/s/kpc.Comment: 4 pages, 3 figures; to appear in the proceedings of the Island
Universes conference held in Terschelling, Netherlands, July 2005, ed. R. de
Jon
The Rapidly Fading Optical Afterglow of GRB 980519
GRB 980519 had the most rapidly fading of the well-documented GRB afterglows,
consistent with t^{-2.05 +/- 0.04} in BVRI as well as in X-rays during the two
days in which observations were made. We report VRI observations from the MDM
1.3m and WIYN 3.5m telescopes, and we synthesize an optical spectrum from all
of the available photometry. The optical spectrum alone is well fitted by a
power law of the form nu^{-1.20 +/- 0.25}, with some of the uncertainty due to
the significant Galactic reddening in this direction. The optical and X-ray
spectra together are adequately fitted by a single power law nu^{-1.05 +/-
0.10}. This combination of steep temporal decay and flat broad-band spectrum
places a severe strain on the simplest afterglow models involving spherical
blast waves in a homogeneous medium. Instead, the rapid observed temporal decay
is more consistent with models of expansion into a medium of density n(r)
proportional to r^{-2}, or with predictions of the evolution of a jet after it
slows down and spreads laterally. The jet model would relax the energy
requirements on some of the more extreme GRBs, of which GRB 980519 is likely to
be an example because of its large gamma-ray fluence and faint host galaxy.Comment: 13 pages, submitted to ApJ Letter
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