Center-to-limb variation of spectral lines and their effect on full-disk observations

An accurate description of the center-to-limb variation (CLV) of stellar spectra is becoming an increasingly critical factor in both stellar and exoplanet characterization. In particular, the CLV of spectral lines is extremely challenging as its characterization requires highly detailed knowledge of the stellar physical conditions. To this end, we present the Numerical Empirical Sun-as-a-Star Integrator (NESSI) as a tool for translating high-resolution solar observations of a partial field of view into disk-integrated spectra that can be used to test common assumptions in stellar physics.Comment: Conference proceeding for IAU Symposium 365: "Dynamics of Solar and Stellar Convection Zones and Atmospheres

The coronagraphic Modal Wavefront Sensor: a hybrid focal-plane sensor for the high-contrast imaging of circumstellar environments

The raw coronagraphic performance of current high-contrast imaging instruments is limited by the presence of a quasi-static speckle (QSS) background, resulting from instrumental non-common path errors (NCPEs). Rapid development of efficient speckle subtraction techniques in data reduction has enabled final contrasts of up to 10-6 to be obtained, however it remains preferable to eliminate the underlying NCPEs at the source. In this work we introduce the coronagraphic Modal Wavefront Sensor (cMWS), a new wavefront sensor suitable for real-time NCPE correction. This pupil-plane optic combines the apodizing phase plate coronagraph with a holographic modal wavefront sensor, to provide simultaneous coronagraphic imaging and focal-plane wavefront sensing using the science point spread function. We first characterise the baseline performance of the cMWS via idealised closed-loop simulations, showing that the sensor successfully recovers diffraction-limited coronagraph performance over an effective dynamic range of +/-2.5 radians root-mean-square (RMS) wavefront error within 2-10 iterations. We then present the results of initial on-sky testing at the William Herschel Telescope, and demonstrate that the sensor is able to retrieve injected wavefront aberrations to an accuracy of 10nm RMS under realistic seeing conditions. We also find that the cMWS is capable of real-time broadband measurement of atmospheric wavefront variance at a cadence of 50Hz across an uncorrected telescope sub-aperture. When combined with a suitable closed-loop adaptive optics system, the cMWS holds the potential to deliver an improvement in raw contrast of up to two orders of magnitude over the uncorrected QSS floor. Such a sensor would be eminently suitable for the direct imaging and spectroscopy of exoplanets with both existing and future instruments, including EPICS and METIS for the E-ELT.Comment: 14 pages, 12 figures: accepted for publication in Astronomy & Astrophysic

Why every observatory needs a disco ball

Commercial disco balls provide a safe, effective and instructive way of observing the Sun. We explore the optics of solar projections with disco balls, and find that while sunspot observations are challenging, the solar disk and its changes during eclipses are easy and fun to observe. We explore the disco ball's potential for observing the moon and other bright astronomical phenomena.Comment: 6 pages, 7 figures. Submitted to Physics Education. Comments welcom

Spectral Background-Subtracted Activity Maps

High-resolution solar spectroscopy provides a wealth of information from photospheric and chromospheric spectral lines. However, the volume of data easily exceeds hundreds of millions of spectra on a single observation day. Therefore, methods are needed to identify spectral signatures of interest in multidimensional datasets. Background-subtracted activity maps (BaSAMs) have previously been used to locate features of solar activity in time series of images and filtergrams. This research note shows how this method can be extended and adapted to spectral data.Comment: 3 pages, 1 figure, initial version submitted to Research Notes of the AA

Physical properties of chromospheric features : Plage, peacock jets, and calibrating it all

The chromosphere is a complex and dynamic layer of the solar atmosphere, largely dominated by the local magnetic field configuration. It acts as an important interface between the photosphere below it and the hot corona above. However, studying this layer is not straightforward, as it is largely transparent in optical wavelengths. On top of that most of its observable radiation is formed in conditions far from thermodynamic equilibrium, and thus only partially sensitive to local plasma conditions. Observations of the active features found in the chromosphere such as plage, fibrils, and jets, are therefore more difficult to interpret than emission from active features in the photosphere. This thesis focuses on plage and peacock-jets, two types of chromospheric features. Additionally, I study the quiet solar atmosphere for calibration purposes. In all three cases, I utilize high-resolution spectral and spectro-polarimetric data from the Swedish 1-m Solar Telescope (SST) in order to constrain the physical parameters of these regions and to create high-resolution reference profiles of the quiet regions. In the first paper, the magnetic field vector of a plage region is inferred using STiC, a spectro-polarimetric inversion code, which is achieved after applying several methods to improve the signal-to-noise ratio. In the second paper, a peacock jet near an X9.3-class flare is studied. The expanding flare ribbon moves under the jet and inhibits new material from being accelerated upwards. This coupled with back-lighting from the heavily broadened line profile of the flare ribbon that can be approximated as quasi-continuum, allowed us to estimate its density and mass by using a cloud model.   The third paper is an observational study of the center-to-limb variations of ten spectral lines commonly used for solar diagnostics

Physical properties of chromospheric features : Plage, peacock jets, and calibrating it all

The chromosphere is a complex and dynamic layer of the solar atmosphere, largely dominated by the local magnetic field configuration. It acts as an important interface between the photosphere below it and the hot corona above. However, studying this layer is not straightforward, as it is largely transparent in optical wavelengths. On top of that most of its observable radiation is formed in conditions far from thermodynamic equilibrium, and thus only partially sensitive to local plasma conditions. Observations of the active features found in the chromosphere such as plage, fibrils, and jets, are therefore more difficult to interpret than emission from active features in the photosphere. This thesis focuses on plage and peacock-jets, two types of chromospheric features. Additionally, I study the quiet solar atmosphere for calibration purposes. In all three cases, I utilize high-resolution spectral and spectro-polarimetric data from the Swedish 1-m Solar Telescope (SST) in order to constrain the physical parameters of these regions and to create high-resolution reference profiles of the quiet regions. In the first paper, the magnetic field vector of a plage region is inferred using STiC, a spectro-polarimetric inversion code, which is achieved after applying several methods to improve the signal-to-noise ratio. In the second paper, a peacock jet near an X9.3-class flare is studied. The expanding flare ribbon moves under the jet and inhibits new material from being accelerated upwards. This coupled with back-lighting from the heavily broadened line profile of the flare ribbon that can be approximated as quasi-continuum, allowed us to estimate its density and mass by using a cloud model.   The third paper is an observational study of the center-to-limb variations of ten spectral lines commonly used for solar diagnostics

The electronics, trigger and data acquisition system for the liquid argon time projection chamber of the DarkSide-50 search for dark matter

FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPThe DarkSide-50 experiment at the Laboratori Nazionali del Gran Sasso is a search for dark matter using a dual phase time projection chamber with 50 kg of low radioactivity argon as target. Light signals from interactions in the argon are detected by a system of 38 photo-multiplier tubes (PMTs), 19 above and 19 below the TPC volume inside the argon cryostat. We describe the electronics which processes the signals from the photo-multipliers, the trigger system which identifies events of interest, and the data-acquisition system which records the data for further analysis. The electronics include resistive voltage dividers on the PMTs, custom pre-amplifiers mounted directly on the PMT voltage dividers in the liquid argon, and custom amplifier/discriminators (at room temperature). After amplification, the PMT signals are digitized in CAEN waveform digitizers, and CAEN logic modules are used to construct the trigger; the data acquisition system for the TPC is based on the Fermilab artdaq software. The system has been in operation since early 2014.12126FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2016/09084-0The DarkSide-50 Collaboration thanks the LNGS laboratory and its staff for their invaluable technical and logistical support. We particularly wish to thank our Fermilab colleagues Dr. Jin-Yuan Wu for his contributions to the FPGA firmware, Dr. Don Holmgren for his advice on the selection and procurement of the computing and networking hardware, Engineer Sten Hansen for his work on designing the PMT divider and his help with the V1495 firmware, and Engineer Ron Rechenmacher for resolving issues with Infiniband and our raid disk arrays. DarkSide-50 has been supported by the Italian Istituto Nazionale di Fisica Nucleare, the U.S. National Science Foundation under grant Nos. 1004051, 1242571, 1314268, 1314479, 1314483, 1314501, 1314507 & 1314752, the US Department of Energy under contracts DE-AC02-07CH11359 and DE-FG02-91ER40671, the Polish NCN (Grant UMO-2014/15/B/ST2/02561), and the Russian Science Foundation Grant No. 16-12-10369. We also acknowledge financial support from the UnivEarthS Labex program of Sorbonne Paris Cité (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02) and from the São Paulo Research Foundation (FAPESP) grant No. 2016/09084-0. Development of the in-liquid pre-amplifier was supported by the INFN CSN-V(5) QUPID-R&D grant