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The gaseous component in disks of spiral galaxies generally shows strong metallicity gradients of about 0.2 dex per scale length of the disk (e.g. Edmunds and Pagel 1984, MNRAS 211,507). Current models explain these gradients by a radially varying ratio of stellar density to gas density, possibly coupled with infall of gas from outside and radial gas flows in the disk (Lacey and Fall 1985, Ap.J. 290,154). It follows from these models that the final metallicity gradient (i.e. the gradient after infall has ceased and all gas has been locked into stars) should be quite shallow.
CARMENES is a pair of high-resolution (R ≳ 80, 000) spectrographs covering the wavelength range from 0.52 to 1.71 μm with only small gaps. The instrument has been optimized for precise radial velocity measurements. It was installed and commissioned at the 3.5 m telescope of the Calar Alto observatory in Southern Spain in 2015. The first large science program of CARMENES is a survey of ~300 M dwarfs, which started on Jan 1, 2016. We present an overview of the instrument, and provide a few examples of early science results.
The Ofpe/WN9 stars R84 and S61 of the LMC have been studied with high-dispersion spectroscopy in the optical and satellite-UV range. The high resolution and high S/N spectra in the optical range are particularly distinguished by strong emission lines of H, HeI and [NII]. The comparison of R84 with S61 shows that the peculiar emission line spectrum is not caused by the previously found late type companion of R84. We find that the UV spectra of both stars closely resemble those of late O-supergiants but all absorption lines are violet-shifted by about 250 km s−1 (R84) and about 200 km s−1 (S61). The absorption lines are stronger than in normal O-type stars. The UV-resonance lines indicate low terminal wind velocities of ≈ 900 km s−1 only. Unlike to normal O-type stars the AlIII-resonance lines also show pronounced P Cygni profiles with an even lower edge velocity (vedge ≈ 400 km s−1). Tne mass loss rates (>6.10−6 Mo yr−1) are comparable to rates found in normal luminous hot stars. However, the wind appears to be much more gradually accelerated similar to the wind of the galactic supergiant P Cygni. It is suggested that the Ofpe/WN9 transition type stars are the hotter counterparts of the early B-type P Cygni stars.
We investigate the polarization characteristics of optical emission from young pulsars. In a first attempt we search for polarization in images without time resolution in order to select suitable candidates for time-resolved studies. Polarization information constrains the nature of the faint optical emission of pulsars and will eventually allow to derive the topology of the field in those areas were optical radiation is emitted. We determine the polarization of the time-integrated optical emission of the SMC pulsar B0540-69 and the Vela pulsar B0833-45. We identify a new candidate optical counterpart for the young pulsar B1509-58 and find that the old candidate is unpolarized. The polarization of these three sources is rather high in view of the assumption that averaging over a putative swing of the polarization angle through 180 degrees will lead to depolarisation in the pulse-averaged signal.
We also detect high degrees of polarization in the synchrotron nebula surrounding the LMC pulsar B0540-69, indicating even further similarity to the Crab.
The University Observatories of München and Göttingen and the Landessternwarte Heidelberg are building in cooperation with ESO two almost identical FOcal Reducer /low-dispersion Spectrographs (FORS) for the ESO Very Large Telescopes. FORS allows low-dispersion multiobject spectroscopy (19 slits) and longslit spectroscopy in the wavelength range of 330 to 1100 nm. A set of standard grisms with reciprocal dispersions of 45 ...230 Å/mm working in the first order are foreseen. With a slitwidth of 1 arcsec the resulting spectral resolutions range from 180 to 1800.
For further FORS details see Appenzeller and Rupprecht (1992) and Seifert et al. (1994).
The standard grisms are located in a grism wheel in the parallel beam between the collimator and the camera. Seven of eight positions are available for grisms. The free diameter of the grisms is 135 mm to cover the whole field of view of FORS. To avoid reflection ghosts the entrance surfaces are all tilted by .
Focal reducers are nowadays widely used on large telescopes as multi-mode instruments. Some general aspects of the design of focal reducers are discussed. FORS, the focal reducer/low-dispersion spectrograph for the ESO VLT is presented as an example for such a multi-mode instrument on a large telescope.
As a follow-up to the most successful Hipparcos mission we have suggested a mini-satellite. The instrument DIVA is a pair of two small Fizeau interferometers with a fixed angular separation scanning the entire sky in a Hipparcos-type fashion. Despite its small apertures the very efficient opticaldesign and the use of CCD detectors will allow a significant increase in performance compared to the Hipparcos mission. Introducing objective prisms in front of the beam combiners will generate dispersed fringes which will allow a more accurate astrometry and much more detailed spectro-photometric information than filtered, undispered fringes. A complete optical system was
designed which is suitable to achieve the desired goal and may be expanded to the size of GAIA. Likewise, several options exists to improve the capabilities and the depth of the DIVA mission.
CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) is a new instrument currently undergoing commissioning at the 3.5 m telescope of the Calar Alto Observatory. It has been constructed by a consortium of eleven Spanish and German institutions. The scientific goal of the project is a 600-night radial-velocity survey targeting 300 M dwarfs with sufficient precision to detect terrestrial planets in their habitable zones. The CARMENES instrument consists of two separate échelle spectrographs covering the wavelength range from 0.55 to 1.7 μm at a spectral resolution of R = 82,000, fed by fibers from the Cassegrain focus of the telescope. Both spectrographs are housed in a temperature-stabilized environment in vacuum tanks, to enable a long-term radial velocity precision of 1 m s−1. The wavelength calibration will be done with Th-Ne and U-Ne emission line lamps, and with Fabry-Pérot etalons.
CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) will conduct a radial-velocity survey of ~ 300 M dwarfs with the 3.5m telescope at the Calar Alto Observatory. The CARMENES instrument is currently under construction; it consists of two independent échelle spectrographs, which together cover the wavelength range 0.55 – 1.7μm at a spectral resolution of R = 82,000. The spectrographs and the fiber input are designed with a goal of 1m/s radial velocity precision using simultaneous calibration with emission-line lamps.
Rapid thermal annealing was shown by EBIC to increase the minority-carrier diffusion length in cast polycrystalline silicon. The beneficial effect is due to a deactivation of intragrain defects (mainly dislocations) and is stable against post-RTA annealing up to at least 600 °C/ 10 min.
CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) is a next-generation instrument under construction for the 3.5 m telescope at the Calar Alto Observatory by a consortium of eleven Spanish and German institutions. The scientific goal of the project is a five-year exoplanet survey targeting 300 M stars with the completed instrument. The CARMENES hardware consists of two separate échelle spectrographs covering the wavelength range from 0.55 to 1.7 μm at a spectral resolution of R = 82,000, fed by fibers from the Cassegrain focus of the telescope. Both spectrographs are housed in a temperature-stabilized environment in vacuum tanks, to enable a long-term radial velocity precision of 1 m s−1 employing a simultaneous calibration with Th-Ne and U-Ne emission line lamps.
Within the framework of a new optimization strategy based on self-compatible thermoelectric elements, the ability to reach maximum performance is discussed. For the efficiency of a thermogenerator and the coefficient of performance of a Peltier cooler, the constraint z T = ko = const. turned out to provide a suitable criterion for judging maximum performance. In this paper ko is calculated as an average of the temperature dependent figure of merit z T.
The study discusses the mineralogical, geochemical and thermometric properties of rock-forming blue quartz from eight worldwide occurrences. Compared to non-blue quartz, blue quartz contains significant amounts of submicron-sized (1 μm—100 nm) and nanometre-sized (<100 nm) inclusions. Mica, ilmenite and rutile constitute the most abundant submicron-sized inclusions, and are formed probably by syngenetic precipitation in the boundary layer between quartz and melt (entrapment model). Nanometre-sized rutile possibly originated by epigenetic exsolution of Ti from the quartz structure (exsolution model). Rayleigh scattering of light by nano-particulate inclusions best explains the origin of the blue colour. Blue quartz is generally Ti-rich (∼100—300 ppm) and formed at high temperatures (∼700°C—900°C). The large number, and high spatial density, of tiny xenocrystic inclusions of Ti-bearing minerals make calculations of crystallization temperatures using the Ti-in-quartz thermometer unreliable. The geological significance of blue quartz remains obscure.
Experimentally observed blue shifts of the peak position of the luminescence from quantum-well-wire and -dot structures are often significantly larger than the calculated shifts induced by lateral confinement in the structures. In this work we have used high-quality InGaAsAnP multi-quantum-wells for the fabrication of wires. The quantum wells are in the range 3 to 17 monolayers (ML) nominally. The thinnest well, 3 ML, shows a clearly resolved split into two luminescence peaks from areas with a thickness difference of 1 ML. In the case of the wires, the luminescence from the thicker wells show a blue shift, as well a significant broadening. However, the thinnest well shows no blue shift, but a different ratio of the two peaks, with the high energy peak favoured in the wire case. We interpret these effects in terms of a reduced transfer of excitons from thinner to thicker areas of the well in the wire as compared to the unpattemed areas. This due to a reduction of the transfer from 2 dimensional to 1 dimensional in the wires. The peaks originating in areas of different ML thicknesses are not spectrally resolved in the thicker wells and the reduced transfer therefore results in a blue shift as well as a broadening of the luminescence peak.
Temperature-dependent (80 … 300 K) measurements of dislocation recombination activity by the electron-beam-induced-current (EBIC) technique are reported. Controlled Cu contamination (ppb to ppm range), chemomechanical polishing and hydrogenation treatments were applied to alter dislocation properties. Increasing Cu level is found not only to increase the electrical activity of misfit dislocations in SiGe/Si structures at 300 K, but also to change its dependence on temperature. At low contamination, shallow centres control dislocation activity while deep centres are characteristic at higher Cu levels. Heavy Cu contamination results in very strong recombination activity which is attributed to precipitates. Chemomechanical polishing has an effect which is analogous to medium Cu contamination. Hydrogenation was found to passivate recombination activity at 300 K, but did not show pronounced effects on activity at low temperature.
Single strained layers of GaAs grown on InP have been studied using different optical techniques. Absorption has been measured on these structure which are believed to be type II. The absorption is found to increase slowly close to the threshold and the spectral shape is very similar to photoluminescence excitation spectra. No sharp excitonic peaks were found. The absorption has been modelled using K.p-theory including strain and confinement. The agreement with experiments is good with respect to the shape of the spectra but differs a factor of three with respect to the magnitude of the absorption. The strain and composition of the samples have been measured by a combination of photoluminescence and Raman spectroscopy.
It is a well-known phenomenon that the luminescence energies of nominally n monolayer (1 ML = 0.239 nm) thick QWs of GalnAs in InP are shifted to longer wavelengths in comparison to calculated values. The reason is seen in the formation of (Ga)InAs(P)-interfaces, one or a few ML thick, which contribute to the effective potential of the QW.Based on a comparison of MBE and MOVPE and on properties of QW structures grown by MOVPE under different conditions we conclude that high AsH3 pressures and low growth temperatures favour the formation of arsenic multilayers on the surface, which act as the main arsenic source for the formation of graded InAsxP1−x interface layers.
In order to study their applicability as the active base material in Si thin crystalline film solar cell technology, SiGe relaxed layers grown by Liquid Phase Epitaxy (LPE) and Chemical Vapor Deposition (CVD) on Si substrates are investigated by optical and electrical measurements (TEM, EXD, PL, EBIC). The main results of this work is to point out the improvement of the SiGe active base layer by using smooth Ge graded SiGe buffer layer and remote plasma hydrogenation. TEM, EXD, PL experiments show the effect of the Ge graded buffer layer grown using LPE, by confining the threading dislocations in the SiGe buffer layer close to the Si/SiGe interface. EBIC measurements reveal low recombination activity of dislocations at 300 K providing the diffusion length exceeds the 15 μm layer thickness The enhanced luminescence of SiGe near bandgap indicates that remote plasma hydrogenation induces a decrease of the non-radiative recombination pathways due to dislocations on CVD layers where defect recombinations dominate as indicated by EBIC measurements.
This study points out the importance of controlling relaxed SiGe layers with good minority carrier recombination quality as a key issue for the optimization of new SiGe/Si based solar cells.