12,811 research outputs found
Ground-based NIR emission spectroscopy of HD189733b
We investigate the K and L band dayside emission of the hot-Jupiter HD
189733b with three nights of secondary eclipse data obtained with the SpeX
instrument on the NASA IRTF. The observations for each of these three nights
use equivalent instrument settings and the data from one of the nights has
previously reported by Swain et al (2010). We describe an improved data
analysis method that, in conjunction with the multi-night data set, allows
increased spectral resolution (R~175) leading to high-confidence identification
of spectral features. We confirm the previously reported strong emission at
~3.3 microns and, by assuming a 5% vibrational temperature excess for methane,
we show that non-LTE emission from the methane nu3 branch is a physically
plausible source of this emission. We consider two possible energy sources that
could power non-LTE emission and additional modelling is needed to obtain a
detailed understanding of the physics of the emission mechanism. The validity
of the data analysis method and the presence of strong 3.3 microns emission is
independently confirmed by simultaneous, long-slit, L band spectroscopy of HD
189733b and a comparison star.Comment: ApJ accepte
Molecular Signatures in the Near Infrared Dayside Spectrum of HD 189733b
We have measured the dayside spectrum of HD 189733b between 1.5 and 2.5
microns using the NICMOS instrument on the Hubble Space Telescope. The emergent
spectrum contains significant modulation, which we attribute to the presence of
molecular bands seen in absorption. We find that water (H2O), carbon monoxide
(CO), and carbon dioxide (CO2) are needed to explain the observations, and we
are able to estimate the mixing ratios for these molecules. We also find
temperature decreases with altitude in the ~0.01 < P < ~1 bar region of the
dayside near-infrared photosphere and set an upper limit to the dayside
abundance of methane (CH4) at these pressures.Comment: 13 pages, 3 figures. accepted in Astrophysical Journal Letter
Phase-dependent spectra in a driven two-level atom
We propose a method to observe phase-dependent spectra in resonance
fluorescence, employing a two-level atom driven by a strong coherent field and
a weak, amplitude-fluctuating field. The spectra are similar to those which
occur in a squeezed vacuum, but avoid the problem of achieving squeezing over a
solid angle. The system shows other interesting features, such as
pronounced gain without population inversion.Comment: 4 pages and 4 figures. Submitted to Phys. Rev. Let
Elemental abundances and minimum mass of heavy elements in the envelope of HD 189733b
Oxygen (O) and carbon (C) have been inferred recently to be subsolar in
abundance from spectra of the atmosphere of the transiting hot Jupiter HD
189733b. Yet, the mass and radius of the planet coupled with structure models
indicate a strongly supersolar abundance of heavy elements in the interior of
this object. Here we explore the discrepancy between the large amount of heavy
elements suspected in the planet's interior and the paucity of volatiles
measured in its atmosphere. We describe the formation sequence of the icy
planetesimals formed beyond the snow line of the protoplanetary disk and
calculate the composition of ices ultimately accreted in the envelope of HD
189733b on its migration pathway. This allows us to reproduce the observed
volatile abundances by adjusting the mass of ices vaporized in the envelope.
The predicted elemental mixing ratios should be 0.15--0.3 times solar in the
envelope of HD 189733b if they are fitted to the recent O and C determinations.
However, our fit to the minimum mass of heavy elements predicted by internal
structure models gives elemental abundances that are 1.2--2.4 times oversolar
in the envelope of HD189733b. We propose that the most likely cause of this
discrepancy is irradiation from the central star leading to development of a
radiative zone in the planet's outer envelope which would induce gravitational
settling of elements. Hence, all strongly irradiated extrasolar planets should
present subsolar abundances of volatiles. We finally predict that the
abundances of nitrogen (N), sulfur (S) and phosphorus (P) are of , and relative to
H, respectively in the atmosphere of HD 189733b.Comment: Accepted for publication in Astronomy & Astrophysic
Coupling and tuning of modal frequencies in direct current biased microelectromechanical systems arrays
Understanding the coupling of different modal frequencies and their tuning mechanisms has become essential to design multi-frequency MEMS devices. In this work, we fabricate a MEMS beam with fixed boundaries separated from two side electrodes and a bottom electrode. Subsequently, we perform experiments to obtain the frequency variation of in-plane and out-of-plane mechanical modes of the microbeam with respect to both DC bias and laser heating. We show that the frequencies of the two modes coincide at a certain DC bias, which in turn can also be varied due to temperature. Subsequently, we develop a theoretical model to predict the variation of the two modes and their coupling due to a variable gap between the microbeam and electrodes, initial tension, and fringing field coefficients. Finally, we discuss the influence of frequency tuning parameters in arrays of 3, 33, and 40 microbeams, respectively. It is also found that the frequency bandwidth of a microbeam array can be increased to as high as 25 kHz for a 40 microbeam array with a DC bias of 80 V
Probing the Higgs Field Using Massive Particles as Sources and Detectors
In the Standard Model, all massive elementary particles acquire their masses
by coupling to a background Higgs field with a non-zero vacuum expectation
value. What is often overlooked is that each massive particle is also a source
of the Higgs field. A given particle can in principle shift the mass of a
neighboring particle. The mass shift effect goes beyond the usual perturbative
Feynman diagram calculations which implicitly assume that the mass of each
particle is rigidly fixed. Local mass shifts offer a unique handle on Higgs
physics since they do not require the production of on-shell Higgs bosons. We
provide theoretical estimates showing that the mass shift effect can be large
and measurable, especially near pair threshold, at both the Tevatron and the
LHC.Comment: 6 pages, no figures; Version 2 corrects some typographical errors of
factors of 2 in equations 14, 17, 18 and 19 (all of the same origin) and
mentions a linear collider as an interesting place to test the results of
this pape
Quantum interference in optical fields and atomic radiation
We discuss the connection between quantum interference effects in optical
beams and radiation fields emitted from atomic systems. We illustrate this
connection by a study of the first- and second-order correlation functions of
optical fields and atomic dipole moments. We explore the role of correlations
between the emitting systems and present examples of practical methods to
implement two systems with non-orthogonal dipole moments. We also derive
general conditions for quantum interference in a two-atom system and for a
control of spontaneous emission. The relation between population trapping and
dark states is also discussed. Moreover, we present quantum dressed-atom models
of cancellation of spontaneous emission, amplification on dark transitions,
fluorescence quenching and coherent population trapping.Comment: To be published in Journal of Modern Optics Special Issue on Quantum
Interferenc
Water in HD 209458b's atmosphere from 3.6 - 8 microns IRAC photometric observations in primary transit
The hot Jupiter HD 209458b was observed during primary transit at 3.6, 4.5,
5.8 and 8.0 microns using the Infrared Array Camera (IRAC) on the Spitzer Space
Telescope. We detail here the procedures we adopted to correct for the
systematic trends present in the IRAC data. The light curves were fitted
including limb darkening effects and fitted using Markov Chain Monte Carlo and
prayer-bead Monte Carlo techniques, finding almost identical results. The final
depth measurements obtained by a combined Markov Chain Monte Carlo fit are at
3.6 microns, 1.469 +- 0.013 % and 1.448 +- 0.013 %; at 4.5 microns, 1.478 +-
0.017 % ; at 5.8 microns, 1.549 +- 0.015 % and at 8.0 microns 1.535 +- 0.011 %.
Our results clearly indicate the presence of water in the planetary atmosphere.
Our broad band photometric measurements with IRAC prevent us from determining
the additional presence of other other molecules such as CO, CO2 and methane
for which spectroscopy is needed. While water vapour with a mixing ratio of
10^-4-10^-3 combined with thermal profiles retrieved from the day-side may
provide a very good fit to our observations, this data set alone is unable to
resolve completely the degeneracy between water abundance and atmospheric
thermal profile.Comment: 14 pages, 6 tables, 10 figures, Accepted for publication in MNRA
- …