788 research outputs found
COSMOSOMAS Observations of the CMB and Galactic Foregrounds at 11 GHz: Evidence for anomalous microwave emission at high Galactic Latitude
We present observations with the new 11 GHz radiometer of the COSMOSOMAS
experiment at the Teide Observatory (Tenerife). The sky region between 0 deg <=
RA <= 360 deg and 26 deg <= DEC 49 deg (ca. 6500 square degrees) was observed
with an angular resolution of 0.9 deg. Two orthogonal independent channels in
the receiving system measured total power signals from linear polarizations
with a 2 GHz bandwidth. Maps with an average sensitivity of 50 microK per beam
have been obtained for each channel. At high Galactic latitude (|b|>30deg) the
11 GHz data are found to contain the expected cosmic microwave background as
well as extragalactic radiosources, galactic synchrotron and free-free
emission, and a dust-correlated component which is very likely of galactic
origin. At the angular scales allowed by the window function of the experiment,
the dust-correlated component presents an amplitude \Delta T aprox. 9-13 microK
while the CMB signal is of order 27 microK. The spectral behaviour of the
dust-correlated signal is examined in the light of previous COSMOSOMAS data at
13-17 GHz and WMAP data at 22-94 GHz in the same sky region. We detect a
flattening in the spectral index of this signal below 20 GHz which rules out
synchrotron radiation as being responsible for the emission. This anomalous
dust emission can be described by a combination of free-free emission and
spinning dust models with a flux density peaking around 20 GHz.Comment: 17 pages, 10 tables, 20 figures. Details on the COSMOSOMAS experiment
can be found at http://www.iac.es/project/cmb/cosmosomas
CMB observations with the Jodrell Bank - IAC interferometer at 33 GHz
The paper presents the first results obtained with the Jodrell Bank - IAC
two-element 33 GHz interferometer. The instrument was designed to measure the
level of the Cosmic Microwave Background (CMB) fluctuations at angular scales
of 1 - 2 degrees. The observations analyzed here were taken in a strip of the
sky at Dec = +41 deg with an element separation of 16.7 lambda, which gives a
maximum sensitivity to ~1.6 deg structures on the sky. The data processing and
calibration of the instrument are described. The sensitivity achieved in each
of the two channels is 7 micro K per resolution element. A reconstruction of
the sky at Dec = +41 deg using a maximum entropy method shows the presence of
structure at a high level of significance. A likelihood analysis, assuming a
flat CMB spatial power spectrum, gives a best estimate of the level of CMB
fluctuations of Delta Tl = 43 (+13,-12) micro K for the range l = 109 +/- 19;
the main uncertainty in this result arises from sample variance. We consider
that the contamination from the Galaxy is small. These results represent a new
determination of the CMB power spectrum on angular scales where previous
results show a large scatter; our new results are in agreement with the
theoretical predictions of the standard inflationary cold dark matter models.Comment: 11 pages, 11 figures. Web site at
http://www.jb.man.ac.uk/research/cmb/ Accepted for publication in MNRA
The optical system of the Tenerife Microwave Spectrometer: a window for observing the 10-20 GHz sky spectra
The TMS optical system is based on a decentered dual-reflector system in a
Gregorian configuration to observe with an angular resolution of less than
. The primary goal of the present study is to evaluate the final
design and verify that it satisfies the design requirements. We aim for low
cross-polarization (-30 dB), low sidelobe (-25 dB) levels, and a stable beam in
terms of shape (low ellipticity) and size over a full octave bandwidth (10-20
GHz). We performed both ray-tracing and full-wave simulations using the CST
Studio software in order to investigate the system behaviour. We gave special
attention to the beam frequency variation and polarization leakage. We have
characterized the effects on the radiation pattern produced by the cryostat
window. We present the final design of the TMS optical system, as well as a
complete study of the system's performance in terms of cross-polarization,
sidelobes, ellipticity and beamwidth. We discuss the effects of sidelobes and
study the need for a baffle.Comment: 30 pages, 15 figures. Accepted for publication in JINS
QUIJOTE Scientific Results. II. Polarisation Measurements of the Microwave Emission in the Galactic molecular complexes W43 and W47 and supernova remnant W44
We present Q-U-I JOint TEnerife (QUIJOTE) intensity and polarisation maps at
10-20 GHz covering a region along the Galactic plane 24<l<45 deg, |b|<8 deg.
These maps result from 210 h of data, have a sensitivity in polarisation of ~40
muK/beam and an angular resolution of ~1 deg. Our intensity data are crucial to
confirm the presence of anomalous microwave emission (AME) towards the two
molecular complexes W43 (22 sigma) and W47 (8 sigma). We also detect at high
significance (6 sigma) AME associated with W44, the first clear detection of
this emission towards a SNR. The new QUIJOTE polarisation data, in combination
with WMAP, are essential to: i) Determine the spectral index of the synchrotron
emission in W44, beta_sync =-0.62 +/-0.03, in good agreement with the value
inferred from the intensity spectrum once a free-free component is included in
the fit. ii) Trace the change in the polarisation angle associated with Faraday
rotation in the direction of W44 with rotation measure -404 +/- 49 rad/m2. And
iii) set upper limits on the polarisation of W43 of Pi_AME <0.39 per cent (95
per cent C.L.) from QUIJOTE 17~GHz, and <0.22 per cent from WMAP 41 GHz data,
which are the most stringent constraints ever obtained on the polarisation
fraction of the AME. For typical physical conditions (grain temperature and
magnetic field strengths), and in the case of perfect alignment between the
grains and the magnetic field, the models of electric or magnetic dipole
emissions predict higher polarisation fractions.Comment: Accepted for publication in MNRA
Polarization Observations of the Anomalous Microwave Emission in the Perseus Molecular Complex with the Cosmosomas Experiment
The anomalous microwave emission detected in the Perseus molecular complex by
Watson \ea has been observed at 11 GHz through dual orthogonal polarizations
with the COSMOSOMAS experiment. Stokes U and Q maps were obtained at a
resolution of \sim 0.9deg. for a 30deg. X 30deg. region including the Perseus
molecular complex. A faint polarized emission has been measured; we find Q=-0.2
% \pm1.0%, while U=-3.4^{+1.8}_{-1.4}% both at the 95% confidence level with a
systematic uncertainty estimated to be lower than 1% determined from tests of
the instrumental performance using unpolarized sources in our map as null
hypothesis. The resulting total polarization level is \Pi = 3.4^{+1.5}_{-1.9}%.
These are the first constraints on the polarization properties of an anomalous
microwave emission source. The low level of polarization seems to indicate that
the particles responsible for this emission in the Perseus molecular complex
are not significantly aligned in a common direction over the whole region, as a
consequence of either a high structural symmetry in the emitting particle or a
low-intensity magnetic field. Our weak detection is fully consistent with
predictions from electric dipole emission and resonance relaxation at this
frequency.Comment: 11 pages, 1 figure, accepted ApJL. A better control of systematics
allows a clear polarization detection. Details on the COSMOSOMAS experiment
can be found at http://www.iac.es/project/cmb/cosmosoma
New Cosmological Structures on Medium Angular Scales Detected with the Tenerife Experiments
We present observations at 10 and 15 GHz taken with the Tenerife experiments
in a band of the sky at Dec.=+35 degrees. These experiments are sensitive to
multipoles in the range l=10-30. The sensitivity per beam is 56 and 20 microK
for the 10 and the 15 GHz data, respectively. After subtraction of the
prediction of known radio-sources, the analysis of the data at 15 GHz at high
Galactic latitude shows the presence of a signal with amplitude Delta Trms ~ 32
microK. In the case of a Harrison-Zeldovich spectrum for the primordial
fluctuations, a likelihood analysis shows that this signal corresponds to a
quadrupole amplitude Q_rms-ps=20.1+7.1-5.4 microK, in agreement with our
previous results at Dec.+=40 degrees and with the results of the COBE DMR.
There is clear evidence for the presence of individual features in the RA range
190 degrees to 250 degrees with a peak to peak amplitude of ~110 microK. A
preliminary comparison between our results and COBE DMR predictions for the
Tenerife experiments clearly indicates the presence of individual features
common to both. The constancy in amplitude over such a large range in frequency
(10-90 GHz) is strongly indicative of an intrinsic cosmological origin for
these structures.Comment: ApJ Letters accepted, 13 pages Latex (uses AASTEX) and 4 encapsulated
postscript figures
Detection of anomalous microwave emission in the Perseus molecular cloud with the COSMOSOMAS experiment
We present direct evidence for anomalous microwave emission in the Perseus
molecular cloud, which shows a clear rising spectrum from 11 to 17 GHz in the
data of the COSMOSOMAS experiment. By extending the frequency coverage using
WMAP maps convolved with the COSMOSOMAS scanning pattern we reveal a peak flux
density of 42 (+/-) 4 Jy at 22 GHz integrated over an extended area of 1.65 x
1.0 deg centered on RA = 55.4 (+/-) 0.1 deg and Dec = 31.8 (+/-) 0.1 deg
(J2000). The flux density that we measure at this frequency is nearly an order
of magnitude higher than can be explained in terms of normal galactic emission
processes (synchrotron, free-free and thermal dust). An extended IRAS dust
feature G159.6-18.5 is found near this position and no bright unresolved source
which could be an ultracompact HII region or gigahertz peaked source could be
found. An adequate fit for the spectral density distribution can be achieved
from 10 to 50 GHz by including a very significant contribution from electric
dipole emission from small spinning dust grains.Comment: 5 pages, 2 postscript figures, accepted ApJ Let
HMM based scenario generation for an investment optimisation problem
This is the post-print version of the article. The official published version can be accessed from the link below - Copyright @ 2012 Springer-Verlag.The Geometric Brownian motion (GBM) is a standard method for modelling financial time series. An important criticism of this method is that the parameters of the GBM are assumed to be constants; due to this fact, important features of the time series, like extreme behaviour or volatility clustering cannot be captured. We propose an approach by which the parameters of the GBM are able to switch between regimes, more precisely they are governed by a hidden Markov chain. Thus, we model the financial time series via a hidden Markov model (HMM) with a GBM in each state. Using this approach, we generate scenarios for a financial portfolio optimisation problem in which the portfolio CVaR is minimised. Numerical results are presented.This study was funded by NET ACE at OptiRisk Systems
Observations of the Cosmic Microwave Background and Galactic Foregrounds at 12-17 GHz with the COSMOSOMAS Experiment
(Abridged) We present the analysis of the first 18 months of data obtained
with the COSMOSOMAS experiment at the Teide Observatory (Tenerife). Three maps
have been obtained at 12.7, 14.7 and 16.3 GHz covering 9000 square degrees each
with a resolution of ~1 degree and with sensitivities 49, 59 and 115 muK per
beam respectively. These data in conjuction with the WMAP first year maps have
revealed that the Cosmic Microwave Background (CMB) is the dominant
astronomical signal at high galatic latitude in the three COSMOSOMAS channels
with an average amplitude of 29.7+/- 1.0 \muK (68% c.l. not including
calibration errors). This value is in agreement with the predicted CMB signal
in the COSMOSOMAS maps using the best fit Lambda-CDM model to the WMAP power
spectrum. Cross-correlation of COSMOSOMAS data with the DIRBE map at 100 \mu m
shows the existence of a common signal with amplitude 7.4+/- 1.1, 7.5+/- 1.1,
and 6.5+/-2.3 muK in the 12.7, 14.7 and 16.3 GHz COSMOSOMAS maps at
|b|>30^\deg. Using the WMAP data we find this DIRBE correlated signal rises
from high to low frequencies flattening below ~20 GHz. At higher galactic
latitudes the average amplitude of the correlated signal with the DIRBE maps
decreases slightly. The frequency behaviour of the COSMOSOMAS/WMAP correlated
signal with DIRBE is not compatible with the expected tendency for thermal
dust. A study of the H-alpha emission maps do not support free-free as a major
contributor to that signal. Our results provide evidence of a new galactic
foreground with properties compatible with those predicted by the spinning dust
models.Comment: 11 pages, 21 figures. Submitted to MNRAS. For paper with figures at
full resolution, see http://www.iac.es/project/cmb/cosmosomas
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