1,723,580 research outputs found
The International Year of Astronomy 2009 in the Netherlands
No full textWe briefly discuss public outreach and education ideas for IYA2009 at the national level and a project at the Kapteyn Astronomical Institute that focuses on the infrared Universe and also takes place in 2009
Automatic Observation Rendering (AMORE). I. On a synthetic stellar population's colour-magnitude diagram
Get PDFA new method, AMORE – based on a genetic algorithm optimizer, is presented for the automated study of colourmagnitude
diagrams. The method combines several stellar population synthesis tools developed in the last decade by or in
collaboration with the Padova group. Our method is able to recover, within the uncertainties, the parameters – distance, extinction,
age, metallicity, index of a power-law initial mass function and the index of an exponential star formation rate – from a
reference synthetic stellar population. No a priori information is inserted to recover the parameters, which is done simultaneously
and not one at a time. Examples are given to demonstrate and to better understand biases in the results, if one of the input
parameters is deliberately set fixed to a non-optimum value
High optical efficiency and photon noise limited sensitivity of microwave kinetic inductance detectors using phase readout
Get PDFWe demonstrate photon noise limited performance in both phase and amplitude readout in microwave kinetic inductance detectors (MKIDs) consisting of NbTiN and Al, down to 100 fW of optical power. We simulate the far field beam pattern of the lens-antenna system used to couple radiation into the MKID and derive an aperture efficiency of 75%. This is close to the theoretical maximum of 80% for a single-moded detector. The beam patterns are verified by a detailed analysis of the optical coupling within our measurement setup.QN/Quantum NanoscienceApplied Science
The non-equilibrium response of a superconductor to pair-breaking radiation measured over a broad frequency band
Get PDFWe have measured the absorption of terahertz radiation in a BCS superconductor over a broad range of frequencies from 200 GHz to 1.1 THz, using a broadband antenna-lens system and a tantalum microwave resonator. From low frequencies, the response of the resonator rises rapidly to a maximum at the gap edge of the superconductor. From there on, the response drops to half the maximum response at twice the pair-breaking energy. At higher frequencies, the response rises again due to trapping of pair-breaking phonons in the superconductor. In practice, this is a measurement of the frequency dependence of the quasiparticle creation efficiency due to pair-breaking in a superconductor. The efficiency, calculated from the different non-equilibrium quasiparticle distribution functions at each frequency, is in agreement with the measurements.QN/Quantum NanoscienceApplied Science
Keys to the Stars — A Unique Experience
Get PDFThe International Year of Astronomy 2009 saw the birth of a remarkable arts and science collaboration, between a piano duo and an astronomer. Since 2009, the Dutch Grieg Piano Duo, consisting of the professional pianists Elles van der Heiden and Siebert Nix, and the author have performed together in their project Keys to the Stars. The astronomer accompanies the fourhand piano music played by the Duo with an astronomical video, projected onto a large screen behind the grand piano. The trio has performed compositions by the Estonian composer Urmas Sisask (born in 1960) and Franz Schubert (1797-1828) in several concert halls in the Netherlands during 2009 and 2010 with great success
The International Year of Astronomy 2009 in the Netherlands
No full textWe briefly discuss public outreach and education ideas for IYA2009 at the national level and a project at the Kapteyn Astronomical Institute that focuses on the infrared Universe and also takes place in 2009
Sunspot positions and sizes for 1825-1867 from the observations by Samuel Heinrich Schwabe
Get PDF<p>Samuel Heinrich Schwabe made 8486 drawings of the solar disc with sunspots in the period from 1825 November 5 to 1867 December 29. We have measured sunspot sizes and heliographic positions on digitized images of these drawings. A total of about 135 000 measurements of individual sunspots are available in a data base. Positions are accurate to about 5 per cent of the solar radius or to about 3 degrees in heliographic coordinates in the solar-disc centre. Sizes were given in 12 classes as estimated visually with circular cursor shapes on the screen. Most of the drawings show a coordinate grid aligned with the celestial coordinate system. A subset of 1168 drawings have no indication of their orientation. We have used a Bayesian estimator to infer the orientations of the drawings as well as the average heliographic spot positions from a chain of drawings of several days, using the rotation profile of the present Sun. The data base also includes all information available from Schwabe on spotless days.</p>
Non-parametric foreground subtraction for 21-cm epoch of reionization experiments
Get PDFOne of the problems facing experiments designed to detect redshifted 21-cm emission from the epoch of reionization (EoR) is the presence of foregrounds which exceed the cosmological signal in intensity by orders of magnitude. While fitting them so that they can be removed, we must be careful to minimize 'overfitting', in which we fit away some of the cosmological signal, and 'underfitting', in which real features of the foregrounds cannot be captured by the fit, polluting the signal reconstruction. We argue that in principle it would be better to fit the foregrounds non-parametrically - allowing the data to determine their shape - rather than selecting some functional form in advance and then fitting its parameters. Non-parametric fits often suffer from other problems, however. We discuss these before suggesting a non-parametric method, Wp smoothing, which seems to avoid some of them. After outlining the principles of Wp smoothing, we describe an algorithm used to implement it. Some useful results for implementing an alternative algorithm are given in an appendix. We apply Wp smoothing to a synthetic data cube for the Low Frequency Array (LOFAR) EoR experiment. This cube includes realistic models for the signal, foregrounds, instrumental response and noise. The performance of Wp smoothing, measured by the extent to which it is able to recover the variance of the cosmological signal and to which it avoids the fitting residuals being polluted by leakage of power from the foregrounds, is compared to that of a parametric fit, and to another non-parametric method (smoothing splines). We find that Wp smoothing is superior to smoothing splines for our application, and is competitive with parametric methods even though in the latter case we may choose the functional form of the fit with advance knowledge of the simulated foregrounds. Finally, we discuss how the quality of the fit is affected by the frequency resolution and range, by the characteristics of the cosmological signal and by edge effects
The Environment and Nature of the Class I Protostar Elias 29 : Molecular Gas Observations and the Location of Ices
Get PDFPublished in: Astrophys. J. 570 (2002) 708-723
citations recorded in [Science Citation Index]
Abstract: A (sub-)millimeter line and continuum study of the class I protostar Elias 29 in the Rho Ophiuchi molecular cloud is presented, whose goals are to understand the nature of this source, and to locate the ices that are abundantly present along this line of sight. Within 15-60" beams, several different components contribute to the line emission. Two different foreground clouds are detected, an envelope/disk system and a dense ridge of HCO+ rich material. The latter two components are spatially separated in millimeter interferometer maps. We analyze the envelope/disk system by using inside-out collapse and flared disk models. The disk is in a relatively face-on orientation (<60 degrees), which explains many of the remarkable observational features of Elias 29, such as its flat SED, its brightness in the near infrared, the extended components found in speckle interferometry observations, and its high velocity molecular outflow. It cannot account for the ices seen along the line of sight, however. A small fraction of the ices is present in a (remnant) envelope of mass 0.12-0.33 Msun, but most of the ices (~70%) are present in cool (T<40 K) quiescent foreground clouds. This explains the observed absence of thermally processed ices (crystallized H2O) toward Elias 29. Nevertheless, the temperatures could be sufficiently high to account for the low abundance of apolar (CO, N2, O2) ices. This work shows that it is crucial to obtain spectrally and spatially resolved information from single-dish and interferometric molecular gas observations in order to determine the nature of protostars and to interpret infrared ISO satellite observations of ices and silicates along a pencil beam.
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