415,825 research outputs found
Comets at radio wavelengths
Comets are considered as the most primitive objects in the Solar System.
Their composition provides information on the composition of the primitive
solar nebula, 4.6 Gyr ago. The radio domain is a privileged tool to study the
composition of cometary ices. Observations of the OH radical at 18 cm
wavelength allow us to measure the water production rate. A wealth of molecules
(and some of their isotopologues) coming from the sublimation of ices in the
nucleus have been identified by observations in the millimetre and
submillimetre domains. We present an historical review on radio observations of
comets, focusing on the results from our group, and including recent
observations with the Nan\c{c}ay radio telescope, the IRAM antennas, the Odin
satellite, the Herschel space observatory, ALMA, and the MIRO instrument aboard
the Rosetta space probe.Comment: Proceedings of URSI France scientific days, "Probing Matter with
Electromagnetic Waves", 24-25 March 2015, Paris. To be published in C. R.
Physiqu
Flexible metamaterials at visible wavelengths
We report on the fabrication and characterization of plasmonic structures on flexible substrates (Metaflex) and demonstrate the optical properties of a single layer of Metaflex. The layer exhibits a plasmonic resonance in the visible region around 620 nm. We show experimental and numerical results for both nano-antennas and fishnet geometries. We anticipate the use of Metaflex as a building block for flexible metamaterials in the visible range.Publisher PDFPeer reviewe
Pulsar observations at millimetre wavelengths
Detecting and studying pulsars above a few GHz in the radio band is
challenging due to the typical faintness of pulsar radio emission, their steep
spectra, and the lack of observatories with sufficient sensitivity operating at
high frequency ranges. Despite the difficulty, the observations of pulsars at
high radio frequencies are valuable because they can help us to understand the
radio emission process, complete a census of the Galactic pulsar population,
and possibly discover the elusive population in the Galactic Centre, where
low-frequency observations have problems due to the strong scattering. During
the decades of the 1990s and 2000s, the availability of sensitive
instrumentation allowed for the detection of a small sample of pulsars above
10GHz, and for the first time in the millimetre band. Recently, new
attempts between 3 and 1mm (86300GHz) have resulted in the
detections of a pulsar and a magnetar up to the highest radio frequencies to
date, reaching 291GHz (1.03mm). The efforts continue, and the advent of
new or upgraded millimetre facilities like the IRAM 30-m, NOEMA, the LMT, and
ALMA, warrants a new era of high-sensitivity millimetre pulsar astronomy in the
upcoming years.Comment: 4 pages. Published in the Proceedings of the IAU Symposium 337 Pulsar
Astrophysics - The Next 50 Year
Gravitational Lensing at Millimeter Wavelengths
With today's millimeter and submillimeter instruments observers use
gravitational lensing mostly as a tool to boost the sensitivity when observing
distant objects. This is evident through the dominance of gravitationally
lensed objects among those detected in CO rotational lines at z>1. It is also
evident in the use of lensing magnification by galaxy clusters in order to
reach faint submm/mm continuum sources. There are, however, a few cases where
millimeter lines have been directly involved in understanding lensing
configurations. Future mm/submm instruments, such as the ALMA interferometer,
will have both the sensitivity and the angular resolution to allow detailed
observations of gravitational lenses. The almost constant sensitivity to dust
emission over the redshift range z=1-10 means that the likelihood for strong
lensing of dust continuum sources is much higher than for optically selected
sources. A large number of new strong lenses are therefore likely to be
discovered with ALMA, allowing a direct assessment of cosmological parameters
through lens statistics. Combined with an angular resolution <0.1", ALMA will
also be efficient for probing the gravitational potential of galaxy clusters,
where we will be able to study both the sources and the lenses themselves, free
of obscuration and extinction corrections, derive rotation curves for the
lenses, their orientation and, thus, greatly constrain lens models.Comment: 69 pages, Review on quasar lensing. Part of a LNP Topical Volume on
"Dark matter and gravitational lensing", eds. F. Courbin, D. Minniti. To be
published by Springer-Verlag 2002. Paper with full resolution figures can be
found at ftp://oden.oso.chalmers.se/pub/tommy/mmviews.ps.g
- …