22 research outputs found
Collective waves in dense and confined microfluidic droplet arrays
Excitation mechanisms for collective waves in confined dense one-dimensional
microfluidic droplet arrays are investigated by experiments and computer
simulations. We demonstrate that distinct modes can be excited by creating
specific `defect' patterns in flowing droplet trains. Excited longitudinal
modes exhibit a short-lived cascade of pairs of laterally displacing droplets.
Transversely excited modes obey the dispersion relation of microfluidic phonons
and induce a coupling between longitudinal and transverse modes, whose origin
is the hydrodynamic interaction of the droplets with the confining walls.
Moreover, we investigate the long-time behaviour of the oscillations and
discuss possible mechanisms for the onset of instabilities. Our findings
demonstrate that the collective dynamics of microfluidic droplet ensembles can
be studied particularly well in dense and confined systems. Experimentally, the
ability to control microfluidic droplets may allow to modulate the refractive
index of optofluidic crystals which is a promising approach for the production
of dynamically programmable metamaterials.Comment: 13 pages, 17 figure
Observed spectral energy distribution of the thermal emission from the dayside of WASP-46b
We aim to construct a spectral energy distribution (SED) for the emission
from the dayside atmosphere of the hot Jupiter WASP-46b and to investigate its
energy budget. We observed a secondary eclipse of WASP-46b simultaneously in
the g'r'i'z'JHK bands using the GROND instrument on the MPG/ESO 2.2m telescope.
Eclipse depths of the acquired light curves were derived to infer the
brightness temperatures at multibands that cover the SED peak. We report the
first detection of the thermal emission from the dayside of WASP-46b in the K
band at 4.2-sigma level and tentative detections in the H (2.5-sigma) and J
(2.3-sigma) bands, with flux ratios of 0.253 +0.063/-0.060%, 0.194 +/- 0.078%,
and 0.129 +/- 0.055%, respectively. The derived brightness temperatures (2306
+177/-187K, 2462 +245/-302K, and 2453 +198/-258K, respectively) are consistent
with an isothermal temperature profile of 2386K, which is significantly higher
than the dayside-averaged equilibrium temperature, indicative of very poor heat
redistribution efficiency. We also investigate the tentative detections in the
g'r'i' bands and the 3-sigma upper limit in the z' band, which might indicate
the existence of reflective clouds if these tentative detections do not arise
from systematics.Comment: 8 pages, 7 figures, accepted for publication in A&
Ground-based detection of the near-infrared emission from the dayside of WASP-5b
(Abridged) WASP-5b is a highly irradiated dense hot Jupiter orbiting a G4V
star every 1.6 days. We observed two secondary eclipses of WASP-5b in the J, H
and K bands simultaneously. Thermal emission of WASP-5b is detected in the J
and K bands. The retrieved planet-to-star flux ratios in the J and K bands are
0.168 +0.050/-0.052% and 0.269+/-0.062%, corresponding to brightness
temperatures of 2996 +212/-261K and 2890 +246/-269K, respectively. No thermal
emission is detected in the H band, with a 3-sigma upper limit of 0.166%,
corresponding to a maximum temperature of 2779K. On the whole, our J, H, K
results can be explained by a roughly isothermal temperature profile of ~2700K
in the deep layers of the planetary dayside atmosphere that are probed at these
wavelengths. Together with Spitzer observations, which probe higher layers that
are found to be at ~1900K, a temperature inversion is ruled out in the range of
pressures probed by the combined data set. While an oxygen-rich model is unable
to explain all the data, a carbon-rich model provides a reasonable fit but
violates energy balance.Comment: 13 pages, 9 figures, accepted for publication in A&
Broad-band transmission spectrum and K-band thermal emission of WASP-43b as observed from the ground
(Abridged) We observed one transit and one occultation of the hot Jupiter
WASP-43b simultaneously in the g'r'i'z'JHK bands using the GROND instrument on
the MPG/ESO 2.2-meter telescope. From the transit event, we have independently
derived WASP-43's system parameters with high precision, and improved the
period to be 0.81347437(13) days. No significant variation in transit depths is
detected, with the largest deviations coming from the i', H, and K bands. Given
the observational uncertainties, the broad-band transmission spectrum can be
explained by either a flat featureless straight line that indicates thick
clouds, synthetic spectra with absorption signatures of atomic Na/K or
molecular TiO/VO that indicate cloud-free atmosphere, or a Rayleigh scattering
profile that indicates high-altitude hazes. From the occultation event, we have
detected planetary dayside thermal emission in the K-band with a flux ratio of
0.197 +/- 0.042%, which confirms previous detections obtained in the 2.09
micron narrow band and Ks-band. The K-band brightness temperature 1878
+108/-116 K favors an atmosphere with poor day- to night-side heat
redistribution. We also have a marginal detection in the i'-band (0.037
+0.023/-0.021%), which is either a false positive, a signature of non-blackbody
radiation at this wavelength, or an indication of reflective hazes at high
altitude.Comment: 14 pages, 9 figures, accepted for publication in A&
Very accurate cryogenic mechanisms for CRIRES+
After 5 years of operation on the VLT, a large upgrade of CRIRES (the ESO Cryogenic InfraRed Echelle Spectrograph) was decided mainly in order to increase the efficiency. Using a cross dispersion design allows better wavelength coverage per exposure. This means a complete re-design of the cryogenic pre-optic which were including a predispersion stage with a large prism as dispersive element. The new design requires a move of the entrance slit and associated decker toward the first intermediate focal plane right behind the window. Implement 2 functions with high positioning accuracy in a pre-defined and limited space was a real challenge. The design and the test results recorded in the ESO Cryogenic Test Facility are reported in this paper. The second critical function is the grating wheel which positions the 6 cross disperser gratings into the beam. The paper describes the design of the mechanism which includes a detente system in order to guaranty the 5 arc sec positioning reproducibility requested. The design includes also feedback system, based on switches, in order to ensure that the right grating is in position before starting a long exposure. The paper reports on the tests carried out at cryogenic temperature at the sub-system level. It also includes early performances recorded in the instrument along the first phases of the system test
The "+" for CRIRES: enabling better science at infrared wavelength and high spectral resolution at the ESO VLT
The adaptive optics (AO) assisted CRIRES instrument is an IR (0.92 - 5.2 μm) high-resolution spectrograph was in operation from 2006 to 2014 at the Very Large Telescope (VLT) observatory. CRIRES was a unique instrument, accessing a parameter space (wavelength range and spectral resolution) up to now largely uncharted. It consisted of a single-order spectrograph providing long-slit (40 arcsecond) spectroscopy with a resolving power up to R=100 000. However the setup was limited to a narrow, single-shot, spectral range of about 1/70 of the central wavelength, resulting in low observing efficiency for many scientific programmes requiring a broad spectral coverage. The CRIRES upgrade project, CRIRES+, transforms this VLT instrument into a cross-dispersed spectrograph to increase the simultaneously covered wavelength range by a factor of ten. A new and larger detector focal plane array of three Hawaii 2RG detectors with 5.3 μm cut-off wavelength will replace the existing detectors. For advanced wavelength calibration, custom-made absorption gas cells and an etalon system will be added. A spectro-polarimetric unit will allow the recording of circular and linear polarized spectra. This upgrade will be supported by dedicated data reduction software allowing the community to take full advantage of the new capabilities offered by CRIRES+. CRIRES+ has now entered its assembly and integration phase and will return with all new capabilities by the beginning of 2018 to the Very Large Telescope in Chile. This article will provide the reader with an update of the current status of the instrument as well as the remaining steps until final installation at the Paranal Observatory
A unique infrared spectropolarimetric unit for CRIRES+
High-resolution infrared spectropolarimetry has many science applications in astrophysics. One of them is measuring weak magnetic fields using the Zeeman effect. Infrared domain is particularly advantageous as Zeeman splitting of spectral lines is proportional to the square of the wavelength while the intrinsic width of the line cores increases only linearly. Important science cases include detection and monitoring of global magnetic fields on solar-type stars, study of the magnetic field evolution from stellar formation to the final stages of the stellar life with massive stellar winds, and the dynamo mechanism operation across the boundary between fully- and partially-convective stars. CRIRES+ (the CRIRES upgrade project) includes a novel spectropolarimetric unit (SPU) based on polar- ization gratings. The novel design allows to perform beam-splitting very early in the optical path, directly after the tertiary mirror of the telescope (the ESO Very Large Telescope, VLT), minimizing instrumental polariza- tion. The new SPU performs polarization beam-splitting in the near-infrared while keeping the telescope beam mostly unchanged in the optical domain, making it compatible with the adaptive optics system of the CRIRES+ instrument. The SPU consists of four beam-splitters optimized for measuring circular and linear polarization of spectral lines in YJ and HK bands. The SPU can perform beam switching allowing to correct for throughput in each beam and for variations in detector pixel sensitivity. Other new features of CRIRES+, such as substantially increased wavelength coverage, stability and advanced data reduction pipeline will further enhance the sensitivity of the polarimetric mode. The combination of the SPU, CRIRES+ and the VLT is a unique facility for making major progress in understanding stellar activity. In this article we present the design of the SPU, laboratory measurements of individual components and of the whole unit as well as the performance prediction for the operation at the VLT