2,048 research outputs found
The Haar Wavelet Transform of a Dendrogram: Additional Notes
We consider the wavelet transform of a finite, rooted, node-ranked, -way
tree, focusing on the case of binary () trees. We study a Haar wavelet
transform on this tree. Wavelet transforms allow for multiresolution analysis
through translation and dilation of a wavelet function. We explore how this
works in our tree context.Comment: 37 pp, 1 fig. Supplementary material to "The Haar Wavelet Transform
of a Dendrogram", http://arxiv.org/abs/cs.IR/060810
The SED Machine: a robotic spectrograph for fast transient classification
Current time domain facilities are finding several hundreds of transient
astronomical events a year. The discovery rate is expected to increase in the
future as soon as new surveys such as the Zwicky Transient Facility (ZTF) and
the Large Synoptic Sky Survey (LSST) come on line. At the present time, the
rate at which transients are classified is approximately one order or magnitude
lower than the discovery rate, leading to an increasing "follow-up drought".
Existing telescopes with moderate aperture can help address this deficit when
equipped with spectrographs optimized for spectral classification. Here, we
provide an overview of the design, operations and first results of the Spectral
Energy Distribution Machine (SEDM), operating on the Palomar 60-inch telescope
(P60). The instrument is optimized for classification and high observing
efficiency. It combines a low-resolution (R100) integral field unit (IFU)
spectrograph with "Rainbow Camera" (RC), a multi-band field acquisition camera
which also serves as multi-band (ugri) photometer. The SEDM was commissioned
during the operation of the intermediate Palomar Transient Factory (iPTF) and
has already proved lived up to its promise. The success of the SEDM
demonstrates the value of spectrographs optimized to spectral classification.
Introduction of similar spectrographs on existing telescopes will help
alleviate the follow-up drought and thereby accelerate the rate of discoveries.Comment: 21 pages, 20 figure
The Host Galaxy of GRB 990712
We present a comprehensive study of the z=0.43 host galaxy of GRB 990712,
involving ground-based photometry, spectroscopy, and HST imaging. The
broad-band UBVRIJHKs photometry is used to determine the global spectral energy
distribution (SED) of the host galaxy. Comparison with that of known galaxy
types shows that the host is similar to a moderately reddened starburst galaxy
with a young stellar population. The estimated internal extinction in the host
is Av=0.15+/-0.1 and the star-formation rate (SFR) from the UV continuum is
1.3+/-0.3 M_sun/yr, (not corrected for the effects of extinction). Other galaxy
template spectra than starbursts failed to reproduce the observed SED. We also
present VLT spectra leading to the detection of Halpha from the GRB host
galaxy. A SFR of 2.8+/-0.7 M_sun/yr, is inferred from the Halpha line flux, and
the presence of a young stellar population is supported by a large equivalent
width. Images from HST/STIS show that the host has two separate knots, which
could be two distinct star-forming regions.Comment: 11 pages, accepted for publication in Astronomy and Astrophysic
Mapping the Polarization of the Radio-Loud Ly Nebula B3 J2330+3927
Lya nebulae, or "Lya blobs", are extended (up to ~100 kpc), bright (L[Lya] >
10^43 erg/s) clouds of Lya emitting gas that tend to lie in overdense regions
at z ~ 2--5. The origin of the Lya emission remains unknown, but recent
theoretical work suggests that measuring the polarization might discriminate
among powering mechanisms. Here we present the first narrowband, imaging
polarimetry of a radio-loud Lya nebula, B3 J2330+3927 at z=3.09, with an
embedded active galactic nucleus (AGN). The AGN lies near the blob's Lya
emission peak and its radio lobes align roughly with the blob's major axis.
With the SPOL polarimeter on the 6.5m MMT telescope, we map the total (Lya +
continuum) polarization in a grid of circular apertures of radius 0.6"
(4.4kpc), detecting a significant (>2sigma) polarization fraction P in nine
apertures and achieving strong upper-limits (as low as 2%) elsewhere. P
increases from <2% at ~5kpc from the blob center to ~17% at ~15-25kpc. The
detections are distributed asymmetrically, roughly along the nebula's major
axis. The polarization angles theta are mostly perpendicular to this axis.
Comparing the Lya flux to that of the continuum, and conservatively assuming
that the continuum is highly polarized (20-100%) and aligned with the total
polarization, we place lower limits on the polarization of the Lya emission
P(Lya) ranging from no significant polarization at ~5 kpc from the blob center
to ~ 3--17% at 10--25kpc. Like the total polarization, the Lya polarization
detections occur more often along the blob's major axis.Comment: 9 pages, 7 figures, accepted for publication in Ap
Spatiotemporal evolution of radio wave pump-induced ionospheric phenomena near the fourth electron gyroharmonic
On 12 November 2001, the European Incoherent Scatter (EISCAT) high-frequency (HF) radio wave transmitter facility, operating in O-mode at 5.423 MHz with 550 MW effective radiated power, produced artificial optical rings which appeared immediately at transmitter turn-on and collapsed into blobs after ∼60 s while descending in altitude. A similar descent in altitude was observed in the EISCAT ultra high frequency (UHF) ion line enhancements. Likewise, the stimulated electromagnetic emission (SEE) spectra changed as the pump frequency approached the fourth electron gyroharmonic due to pump-induced variations in electron concentration. Optical recordings were made from Skibotn at 630.0 and 557.7 nm and from Ramfjord in white light. The altitude of the initial optical ring and steady state blob has been estimated by triangulation. The evolution in altitude of the optical emissions, ion line enhancements, and SEE spectra all show a similar morphology but are generally not at exactly the same height. Typically, the optical height is close to and a few kilometers below that of the radar backscatter but sometimes above it, both of which are above the SEE generation altitude. There is evidence that upper hybrid (UH) waves, which propagate perpendicular to the magnetic field line, and Langmuir (L) waves, which propagate parallel to the magnetic field line, act simultaneously to accelerate electrons even in the steady state
Suppression of the near-infrared OH night sky lines with fibre Bragg gratings - first results
The background noise between 1 and 1.8 microns in ground-based instruments is
dominated by atmospheric emission from hydroxyl molecules. We have built and
commissioned a new instrument, GNOSIS, which suppresses 103 OH doublets between
1.47 - 1.7 microns by a factor of ~1000 with a resolving power of ~10,000. We
present the first results from the commissioning of GNOSIS using the IRIS2
spectrograph at the AAT. The combined throughput of the GNOSIS fore-optics,
grating unit and relay optics is ~36 per cent, but this could be improved to
~46 per cent with a more optimal design. We measure strong suppression of the
OH lines, confirming that OH suppression with fibre Bragg gratings will be a
powerful technology for low resolution spectroscopy. The integrated OH
suppressed background between 1.5 and 1.7 microns is reduced by a factor of 9
compared to a control spectrum using the same system without suppression. The
potential of low resolution OH suppressed spectroscopy is illustrated with
example observations.
The GNOSIS background is dominated by detector dark current below 1.67
microns and by thermal emission above 1.67 microns. After subtracting these we
detect an unidentified residual interline component of ~ 860 +/ 210
ph/s/m^2/micron/arcsec^2. This component is equally bright in the suppressed
and control spectra. We have investigated the possible source of the interline
component, but were unable to discriminate between a possible instrumental
artifact and intrinsic atmospheric emission. Resolving the source of this
emission is crucial for the design of fully optimised OH suppression
spectrographs. The next generation OH suppression spectrograph will be focussed
on resolving the source of the interline component, taking advantage of better
optimisation for a FBG feed. We quantify the necessary improvements for an
optimal OH suppressing fibre spectrograph design.Comment: Accepted for publication in MNRAS. 15 pages, 18 figure
The XMM Cluster Outskirts Project (X-COP): Physical conditions to the virial radius of Abell 2142
Context. Galaxy clusters are continuously growing through the accretion of
matter in their outskirts. This process induces inhomogeneities in the gas
density distribution (clumping) which need to be taken into account to recover
the physical properties of the intracluster medium (ICM) at large radii. Aims.
We studied the thermodynamic properties in the outskirts (R > R500) of the
massive galaxy cluster Abell 2142 by combining the Sunyaev Zel'dovich (SZ)
effect with the X-ray signal. Methods. We combined the SZ pressure profile
measured by Planck with the XMM-Newton gas density profile to recover radial
profiles of temperature, entropy and hydrostatic mass out to 2R500. We used a
method that is insensitive to clumping to recover the gas density, and we
compared the results with traditional X-ray measurement techniques. Results.
When taking clumping into account, our joint SZ/X-ray entropy profile is
consistent with the predictions from pure gravitational collapse, whereas a
significant entropy flattening is found when the effect of clumping is
neglected. The hydrostatic mass profile recovered using joint X-ray/SZ data
agrees with that obtained from spectroscopic X-ray measurements and with mass
reconstructions obtained through weak lensing and galaxy kinematics.
Conclusions. We found that clumping can explain the entropy flattening observed
by Suzaku in the outskirts of several clusters. When using a method insensitive
to clumping for the reconstruction of the gas density, the thermodynamic
properties of Abell 2142 are compatible with the assumption that the thermal
gas pressure sustains gravity and that the entropy is injected at accretion
shocks, with no need to evoke more exotic physics. Our results highlight the
need for X-ray observations with sufficient spatial resolution, and large
collecting area, to understand the processes at work in cluster outer regions.Comment: 22 pages, 32 figures, accepted in the journal A&
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