Instrumental Point Spread Function Research Articles

Stellar angular momentum of intermediate-redshift galaxies in MUSE surveys

We quantify the stellar rotation of galaxies by computing the λR parameter, a proxy for the stellar angular momentum in a sample of 106 intermediate-redshift galaxies (0.1 < z < 0.8). The sample is located in the CANDELS/GOODS-S and CANDELS/COSMOS regions, and it was observed by various MUSE surveys. We created spatially resolved stellar velocity and velocity dispersion maps using a full-spectrum fitting technique, covering spatially ∼2Re for the galaxies. The sample spans stellar masses from ∼107.5 M⊙ to 1011.8 M⊙ with star formation rates (SFRs) from log10(SFR)≈ − 3 M⊙ yr−1 to ≈1.7 M⊙ yr−1 over a range of 6 Gyr in cosmic time. We studied how the atmospheric seeing, introduced by the instrumental point spread function (PSF), affects the measured spin parameter, and we applied corrections when pertinent. Through the analysis of the λR − ϵ diagram, we note that the fraction of round and massive galaxies increases with redshift. We did not measure any galaxy with λR < 0.1 in the sample, and we found only one potential (but uncertain) low-mass slow rotator at z ∼ 0.3, more similar to the z = 0 low-mass slow rotators characterized by counter-rotation than to massive ellipticals. Moreover, we do not see an evident evolution or trend in the stellar angular momentum with redshift. We characterized the galaxy environment using two different indicators: a local estimator based on the Voronoi tesselation method, and a global estimator derived by the use of the friends-of-friends (FoF) algorithm. We find no correlation between the environment and λR given that we are not probing dense regions or massive galaxy structures. We also analysed the kinematic maps of the sample finding that about 40% of the galaxies are consistent with being regular rotators (RRs), having rotating stellar discs with flat velocity dispersion maps, while ∼20% have complex velocity maps and can be identified as non-regular rotators in spite of their λR values. For the remaining galaxies the classification is uncertain. As we lack galaxies with λR < 0.1 in the sample, we are not able to identify when galaxies lose their angular momentum and become slow rotators within the surveyed environments, area, and redshift range.

The Basic Iterative Deconvolution: A Fast Instrumental Point-Spread Function Deconvolution Method That Corrects for Light That Is Scattered Out of the Field of View of a Detector

The Basic Iterative Deconvolution: A Fast Instrumental Point-Spread Function Deconvolution Method That Corrects for Light That Is Scattered Out of the Field of View of a Detector

PSF-Radon transform algorithm: Measurement of the point-spread function from the Radon transform of the line-spread function.

In this article, we present a new method called point spread function (PSF)-Radon transform algorithm. This algorithm consists on recovering the instrument PSF from the Radon transform (in the line direction axis) of the line spread function (i.e., the image of a line). We present the method and tested with synthetic images, and real images from macro lens camera and microscopy. A stand-alone program along with a tutorial is available, for any interested user, in Martinez (PSF-Radon transform algorithm, standalone program). RESEARCH HIGHLIGHTS: Determining the instrument PSF is a key issue. Precise PSF determinations are mandatory if image improvement is performed numerically by deconvolution. Much less exposure time to achieve the same performance than a measurement of the PSF from a very small bead. Does not require having to adjust the PSF by an analytical function to overcome the noise uncertainties.

Unbiased CLEAN for STIX in Solar Orbiter

CLEAN is an iterative deconvolution method for radio and hard-X-ray solar imaging. In a specific step of its pipeline, CLEAN requires the convolution between an idealized version of the instrumental point-spread function (PSF), and a map collecting point sources located at positions from where most of the flaring radiation is emitted. This step has highly heuristic motivations and the shape of the idealized PSF, which depends on the user’s choice, impacts the shape of the reconstruction. This study introduces a user-independent release of CLEAN for image reconstruction from observations recorded by the Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter. Specifically, we show here that this unbiased release of CLEAN outperforms the standard version of the algorithm, with reconstructions in line with the ones offered by other imaging methods developed in the STIX framework.

Characterization of instrumental PSF in neutron imaging experiments using logarithmic power spectral plot method

In this work, we investigated an experimental method for estimating the point spread function (PSF) of neutron tomography images from their Fourier domain properties and compared it to another well-known methodology based on the Fourier ring correlation. The logarithmic power spectral plot approach is based on the concept that, in the most general sense, overall blurring effects may be approximated with a Gaussian distribution function. The PSF measured using this approach compares favourably to that obtained using typical microfabricated neutron phantoms, validating the hypothesis of the Gaussian distribution PSF model and providing a credible way for estimating it in the context of neutron imaging using reconstructed data.

GaiaData Release 3

Context.GaiaData Release 3 (GaiaDR3) contains the second release of the combined radial velocities. It is based on the spectra collected during the first 34 months of the nominal mission. The longer time baseline and the improvements of the pipeline made it possible to push the processing limit fromGRVS = 12 inGaiaDR2 toGRVS = 14 mag.Aims.We describe the new functionalities implemented forGaiaDR3, the quality filters applied during processing and post-processing, and the properties and performance of the published velocities.Methods.ForGaiaDR3, several functionalities were upgraded or added to the spectroscopic pipeline. The calibrations were improved in order to better model the temporal evolution of the straylight and of the instrumental point spread function (PSF). The overlapped spectra, which were mostly discarded inGaiaDR2, are now handled by a dedicated module. The hot star template mismatch, which prevented publication of hot stars inGaiaDR2, is largely mitigated now, down toGRVS = 12 mag. The combined radial velocity of stars brighter than or equal toGRVS = 12 mag is calculated in the same way as inGaiaDR2, that is, as the median of the epoch radial velocity time series. The combined radial velocity of the fainter stars is measured from the average of the cross-correlation functions.Results.GaiaDR3 contains the combined radial velocities of 33 812 183 stars. With respect toGaiaDR2, the temperature interval has been expanded fromTeff ∈ [3600, 6750] K toTeff ∈ [3100, 14 500] K for the bright stars (GRVS ≤ 12 mag) and [3100, 6750] K for the fainter stars. The radial velocities sample a significant part of the Milky Way: they reach a few kiloparsecs beyond the Galactic centre in the disc and up to about 10−15 kpc vertically into the inner halo. The median formal precision of the velocities is 1.3 km s−1atGRVS = 12 and 6.4 km s−1atGRVS = 14 mag. The velocity zeropoint exhibits a small systematic trend with magnitude that starts aroundGRVS = 11 mag and reaches about 400 m s−1atGRVS = 14 mag. A correction formula is provided that can be applied to the published data. TheGaiaDR3 velocity scale agrees satisfactorily with APOGEE, GALAH, GES, and RAVE; the systematic differences mostly remain below a few hundred m s−1. The properties of the radial velocities are also illustrated with specific objects: open clusters, globular clusters, and the Large Magellanic Cloud. For example, the precision of the data allows mapping the line-of-sight rotational velocities of the globular cluster 47 Tuc and of the Large Magellanic Cloud.

Image-to-image translation for wavefront and point spread function estimation

We develop and evaluate a new approach to phase estimation for observational astronomy that can be used for accurate point spread function reconstruction. Phase estimation is required where a terrestrial observatory uses an adaptive optics (AO) system to assist astronomers in acquiring sharp, high-contrast images of faint and distant objects. Our approach is to train a conditional adversarial artificial neural network architecture to predict phase using the wavefront sensor data from a closed-loop AO system. We present a detailed simulation study under different turbulent conditions, using the retrieved residual phase to obtain the point spread function of the simulated instrument. Compared to the state-of-the-art model-based approach in astronomy, our approach is not explicitly limited by modeling assumptions, e.g., independence between terms, such as bandwidth and anisoplanatism—and is conceptually simple and flexible. We use the open-source COMPASS tool for end-to-end simulations. On key quality metrics, specifically the Strehl ratio and Halo distribution in our application domain, our approach achieves results better than the model-based baseline.

Data reduction and restoration of spectropolarimetric microlensed hyperspectral imager data

Context. A microlensed hyperspectral imager (MiHI) is an integral field spectrograph based on a double-sided microlens array.Aims. To convert the raw data frames of such an instrument to hyperspectral cubes, and restore them to high-resolution science-ready Stokes data, a new kind of data reduction procedure is required.Methods. An optimized ad hoc transfer map of a MiHI prototype was used to convert the raw data into raw hyperspectral form. The transfer map was modified to match the position of the image on the detector, which was found to drift considerably during the course of an observing day. The determination of this position was used to move the recorded flat-field images to the position of the observation, which was found to be a critical step in the accurate gain correction of the raw data cubes. The converted data were found to be suitable for image restoration but still contained unwanted polarimetric structure that needed to be removed.Results. The extracted and restored data were found to be of a similar spatial resolution as the equivalent data from the context imager, while retaining a spectral resolution of approximately 300 000. The noise properties of the raw data were determined by the photon statistics and were found to be consistent with the estimated transparency of the instrument and the integration time of the image sensor. As for all image-restored data, the noise properties of the restored data were found to be dependent on the instrumental and atmospheric point spread function. An attempt to compare the data to other similar data suggested that the data had a spectral and spatial information content comparable to that of a Hinode spectro-polarimetric scan, but with a higher spatial resolution and a temporal cadence of approximately 10s.

The 700 ks Chandra Spiderweb Field

Aims. We present the X-ray imaging and spectral analysis of the diffuse emission around the radio galaxy J1140-2629 (the Spiderweb galaxy) at z = 2.16 and of its nuclear emission, based on a deep (700 ks) Chandra observation. Methods. We obtained a robust characterization of the unresolved nuclear emission, and carefully computed the contamination in the surrounding regions due to the wings of the instrument point spread function. Then, we quantified the extended emission within a radius of 12 arcsec. We used the Jansky Very Large Array radio image to identify the regions overlapping the jets, and performed X-ray spectral analysis separately in the jet regions and in the complementary area. Results. We find that the Spiderweb galaxy hosts a mildly absorbed quasar, showing a modest yet significant spectral and flux variability on a timescale of ∼1 year (observed frame). We find that the emission in the jet regions is well described by a power law with a spectral index of Γ ∼ 2 − 2.5, and it is consistent with inverse-Compton upscattering of the cosmic microwave background photons by the relativistic electrons. We also find a roughly symmetric, diffuse emission within a radius of ∼100 kpc centered on the Spiderweb galaxy. This emission, which is not associated with the jets, is significantly softer and consistent with thermal bremsstrahlung from a hot intracluster medium (ICM) with a temperature of kT = 2.0−0.4+0.7 keV, and a metallicity of Z < 1.6 Z⊙ at 1σ c.l. The average electron density within 100 kpc is ne = (1.51 ± 0.24 ± 0.14) × 10−2 cm−3, corresponding to an upper limit for the total ICM mass of ≤(1.76 ± 0.30 ± 0.17) × 1012 M⊙ (where error bars are 1σ statistical and systematic, respectively). The rest-frame luminosity L0.5 − 10 keV = (2.0 ± 0.5) × 1044 erg s−1 is about a factor of 2 higher than the extrapolated L − T relation for massive clusters, but still consistent within the scatter. If we apply hydrostatic equilibrium to the ICM, we measure a total gravitational mass M(<100 kpc) = (1.5−0.3+0.5) × 1013 M⊙ and, extrapolating at larger radii, we estimate a total mass M500 = (3.2−0.6+1.1) × 1013 M⊙ within a radius of r500 = (220 ± 30) kpc. Conclusions. We conclude that the Spiderweb protocluster shows significant diffuse emission within a radius of 12 arcsec, whose major contribution is provided by inverse-Compton scattering associated with the radio jets. Outside the jet regions, we also identified thermal emission within a radius of ∼100 kpc, revealing the presence of hot, diffuse baryons that may represent the embryonic virialized halo of the forming cluster.

Redundant apodization for direct imaging of exoplanets

Context. Telescope pupil fragmentation from spiders generates specific aberrations that have been observed at various telescopes and are expected on the 30-meter class telescopes under construction. This is known as the island effect, and it induces differential pistons, tips, and tilts on the pupil petals, deforming the instrumental point spread function (PSF); it is one of the main limitations to the direct detection of exoplanets with high-contrast imaging. These petal-level aberrations can have different origins such as the low-wind effect or petaling errors in the adaptive optics reconstruction. Aims. In this paper, we propose a method for alleviating the impact of the aberrations induced by island effects on high-contrast imaging by adapting the coronagraph design in order to increase its robustness to petal-level aberrations. Methods. Following a method first developed and applied on robustness to errors due to primary mirror segmentation (e.g., segment phasing errors, missing segments), we developed and tested redundant apodized pupils (RAP): apodizers designed at the petal-scale, then duplicated and rotated to mimic the pupil petal geometry. Results. We applied this concept to the ELT architecture, made of six identical petals, to yield a 10−6 contrast in a dark region from 8 to 40λ/D. Both amplitude and phase apodizers proposed in this paper are robust to differential pistons between petals, with minimal degradation to their coronagraphic PSFs and contrast levels. In addition, they are also more robust to petal-level tip-tilt errors than classical apodizers designed for the whole pupil, with which the limit of contrast of 10−6 in the coronagraph dark zone is achieved for constraints up to 2 rad RMS of these petal-level modes. Conclusions. In this paper the RAP concept proves its robustness to island effects (low-wind effect and post-adaptive optics petaling), with an application to the ELT architecture. It can also be considered for other 8- to 30-m class ground-based units such as VLT/SPHERE, Subaru/SCExAO, GMT/GMagAO-X, and TMT/PSI.

A knock-on deuteron imager for measurements of fuel and hotspot asymmetry in direct-drive inertial confinement fusion implosions (invited).

A knock-on deuteron imager (KoDI) has been implemented to measure the fuel and hotspot asymmetry of cryogenic inertial confinement fusion implosions on OMEGA. Energetic neutrons produced by D-T fusion elastically scatter ("knock on") deuterons from the fuel layer with a probability that depends on ρR. Deuterons above 10MeV are produced by near-forward scattering, and imaging them is equivalent to time-integrated neutron imaging of the hotspot. Deuterons below 6MeV are produced by a combination of side scattering and ranging in the fuel, and encode information about the spatial distribution of the dense fuel. The KoDI instrument consists of a multi-penumbral aperture positioned 10-20cm from the implosion using a ten-inch manipulator and a detector pack at 350cm from the implosion to record penumbral images with magnification of up to 35×. Range filters and the intrinsic properties of CR-39 are used to distinguish different charged-particle images by energy along the same line of sight. Image plates fielded behind the CR-39 record a 10keV x-ray image using the same aperture. A maximum-likelihood reconstruction algorithm has been implemented to infer the source from the projected penumbral images. The effects of scattering and aperture charging on the instrument point-spread function are assessed. Synthetic data are used to validate the reconstruction algorithm and assess an appropriate termination criterion. Significant aperture charging has been observed in the initial experimental dataset, and increases with aperture distance from the implosion, consistent with a simple model of charging by laser-driven EMP.

Extended far-ultraviolet emission in distant dwarf galaxies.

Blue compact dwarf (BCD) galaxies are low-luminosity (absolute K-band magnitude,MK > -21 mag)1, metal-poor (1/50 ≤ Z/Z⊙ ≤ 1/2,where Z is the metallicity in terms of the solar metallicityZ⊙)2, centrally concentrated3 galaxies with bright clumps of star formation4. Cosmological surface-brightness dimming5 and the small size of BCDs limit their detection at high redshifts, making their formation process difficult to observe. Observations of BCDs are needed at intermediate redshifts, where they are still young enough to show their formative stages, particularly in the outer regions where cosmic gas accretion should drive evolution. Here we report the observation of excess far-ultraviolet (FUV) emission in the outer regions of 11 BCDs in the GOODS South field at redshifts between 0.1 and 0.24, corresponding to look-back times of 1.3-2.8 billion years in standard cosmology. These observations were made by the Ultra-Violet Imaging Telescope6 on AstroSat7. For ten BCDs, the radial profiles of the intrinsic FUV emission, corrected for the instrument point spread function, have larger scale lengths than their optical counterparts observed with the Hubble Space Telescope. Such shallow FUV profiles suggest extended star formation in cosmically accreting disks. Clumpy structure in the FUV also suggests that the outer FUV disks are gravitationally unstable. Dynamical friction on the clumps drives them inwards at an average rate exceeding 106 solar masses per billion years.

The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope

We provide an overview of the capabilities and performance of the Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope when used in its multi-object spectroscopy (MOS) mode employing a novel Micro Shutter Array (MSA) slit device. The MSA consists of four separate 98″ × 91″ quadrants each containing 365 × 171 individually addressable shutters whose open areas on the sky measure 0.20″ × 0.46″ on a 0.27″ × 0.53″ pitch. This is the first time that a configurable multi-object spectrograph has been available on a space mission. The levels of multiplexing achievable with NIRSpec MOS mode are quantified and we show that NIRSpec will be able to observe typically fifty to two hundred objects simultaneously with the pattern of close to a quarter of a million shutters provided by the MSA. This pattern is fixed and regular, and we identify the specific constraints that it yields for NIRSpec observation planning. In particular, the roll angle at which a given NIRSpec MSA observation will be executed will, in most cases, not be known before the observation is actually scheduled. As a consequence, NIRSpec users planning MOS mode observations cannot at the proposal stage know precisely which subset of their intended targets will be observable, and will therefore need to intentionally oversize their submitted target catalogues accordingly. We also present the data processing and calibration steps planned for the NIRSpec MOS data. The significant variation in size of the mostly diffraction-limited instrument point spread function over the large wavelength range of 0.6–5.3 µm covered by the instrument, combined with the fact that most targets observed with the MSA cannot be expected to be perfectly centred within their respective slits, makes the spectrophotometric and wavelength calibration of the obtained spectra particularly complex. This is reflected by the inclusion of specific steps such as the wavelength zero-point correction nd the relative path loss correction in the NIRSpec data processing and calibration flow. The processing of spectra of morphologically extended targets will require additional attention and development. These challenges notwithstanding, the sensitivity and multiplexing capabilities anticipated of NIRSpec in MOS mode are unprecedented, and should enable significant progress to be made in addressing a wide range of outstanding astrophysical problems.

Uncertainty Propagation in Quantitative Magnetic Force Microscopy Using a Monte-Carlo Method

A Monte-Carlo (MC)-type method is utilized for the propagation of uncertainties in quantitative magnetic force microscopy (qMFM). In qMFM, quantitative magnetic field distributions are inferred from magnetic force microscopy (MFM) raw data using a calibration of the instrument point spread function and a subsequent inversion process. The two stages of calibration and measurement may be subject to a variety of uncertainties that naturally arise in practice. Identifying these sources of uncertainties and quantifying their impact on the reconstruction of the measurand is crucial for reliable quantitative studies of nanomagnetic materials and devices. So far, the propagation of variance method has been applied to determine the uncertainty budget for a complete calibration and measurement process. In this work, we are able to improve the uncertainty description in terms of structure and magnitude by application of an MC method. We demonstrate the importance of correlations and show possible side effects of model linearizations.

Probing Intra-Halo Light with Galaxy Stacking in CIBER Images

Abstract We study the stellar halos of 0.2 ≲ z ≲ 0.5 galaxies with stellar masses spanning M * ∼ 1010.5 to 1012 M ⊙ (approximately L * galaxies at this redshift) using imaging data from the Cosmic Infrared Background Experiment (CIBER). A previous CIBER fluctuation analysis suggested that intra-halo light (IHL) contributes a significant portion of the near-infrared extragalactic background light (EBL), the integrated emission from all sources throughout cosmic history. In this work, we carry out a stacking analysis with a sample of ∼30,000 Sloan Digital Sky Survey (SDSS) photometric galaxies from CIBER images in two near-infrared bands (1.1 and 1.8 μm) to directly probe the IHL associated with these galaxies. We stack galaxies in five sub-samples split by brightness and detect an extended galaxy profile beyond the instrument point-spread function (PSF) derived by stacking stars. We jointly fit a model for the inherent galaxy light profile plus large-scale one- and two-halo clustering to measure the extended galaxy IHL. We detect nonlinear one-halo clustering in the 1.8 μm band at a level consistent with numerical simulations. By extrapolating the fraction of extended galaxy light we measure to all galaxy mass scales, we find ∼30%/15% of the total galaxy light budget from galaxies is at radius r > 10/20 kpc, respectively. These results are new at near-infrared wavelengths at the L * mass scale and suggest that the IHL emission and one-halo clustering could have appreciable contributions to the amplitude of large-scale EBL background fluctuations.

RHAPSODIE: Reconstruction of High-contrAst Polarized SOurces and Deconvolution for cIrcumstellar Environments

Context. Polarimetric imaging is one of the most effective techniques for the high-contrast imaging and characterization of circumstellar environments. These environments can be characterized through direct-imaging polarimetry at near-infrared wavelengths. The Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE)/IRDIS instrument, installed on the Very Large Telescope (VLT) in its dual-beam polarimetric imaging mode, offers the capability to acquire polarimetric images at high contrast and high angular resolution. However, dedicated image processing is needed to eliminate the contamination from the stellar light, instrumental polarization effects, and blurring from the instrumental point spread function. Aims. We aim to reconstruct and deconvolve the near-infrared polarization signal from circumstellar environments. Methods. We used observations of these environments obtained with the high-contrast imaging infrared polarimeter SPHERE-IRDIS at the VLT. We developed a new way to extract the polarimetric signal using an inverse approach method that benefits from the additional knowledge of the detected signal formation process. The method includes a weighted data fidelity term and smooth penalization, and it takes the instrumental polarization into account. Results. This method enables us to accurately measure the polarized intensity and angle of linear polarization of circumstellar disks by taking into account the noise statistics and the convolution by the instrumental point spread function. It has the capacity to use incomplete polarimetry cycles, which enhance the sensitivity of the observations. The method improves the overall performances in particular for instances of both low signal-to-noise (S/N) and small polarized flux compared to standard methods. Conclusions. By increasing the sensitivity and including deconvolution, our method will allow for more accurate studies of these disks morphology, especially in the innermost regions. It also will enable more accurate measurements of the angle of linear polarization at low S/N, which would lead to in-depth studies of dust properties. Finally, the method will enable more accurate measurements of the polarized intensity, which is critical for the construction of scattering phase functions.

Spectral unmixing for exoplanet direct detection in hyperspectral data

Context. The direct detection of faint exoplanets with high-contrast instruments can be boosted by combining it with high spectral resolution. For integral field spectrographs yielding hyperspectral data, this means that the majority of the field of view consists of diffracted starlight spectra and a spatially localized planet. Observation analysis usually relies on classic cross-correlation with theoretical spectra, maximized at the position and with the properties of the planet. In a purely blind-search context, this supervised strategy can be biased with model mismatch and/or be computationally inefficient. Aims. Using an approach that is inspired by the analysis of hyperspectral data within the remote-sensing community, we aim to propose an alternative to cross-correlation that is fully data-driven, which decomposes the data into a set of individual spectra and their corresponding spatial distributions. This strategy is called spectral unmixing. Methods. We used an orthogonal subspace projection to identify the most distinct spectra in the field of view. Their spatial distribution maps were then obtained by inverting the data. These spectra were then used to break the original hyperspectral images into their corresponding spatial distribution maps via non-negative least squares. A matched filter with the instrument point-spread function (or visual inspection) was then used to detect the planet on one of the maps. The performance of our method was evaluated and compared with a cross-correlation using simulated hyperspectral data with medium resolution from the ELT/HARMONI integral field spectrograph. Results. We show that spectral unmixing effectively leads to a planet detection solely based on spectral dissimilarities at significantly reduced computational cost. The extracted spectrum holds significant signatures of the planet while being not perfectly separated from residual starlight. The sensitivity of the supervised cross-correlation is three to four times higher than with unsupervised spectral unmixing, the gap is biased toward the former because the injected and correlated spectrum match perfectly. The algorithm was furthermore vetted on real data obtained with VLT/SINFONI of the β Pictoris system. This led to the detection of β Pictoris b with a signal-to-noise ratio of 28.5. Conclusions. Spectral unmixing is a viable alternative strategy to a cross-correlation to search for and characterize exoplanets in hyperspectral data in a purely data-driven approach. The advent of large data from the forthcoming IFS on board JWST and future ELTs motivates further algorithm development along this path.

A new spectroscopic method for measuring the temperature gradient in the solar photosphere

Context. The contribution of quiet-Sun regions to the solar irradiance variability is currently unclear. Certain solar-cycle variations of the quiet-Sun’s physical structure, such as the temperature gradient, might affect the irradiance. Accurate measurements of this quantity over the course of the activity cycle would improve our understanding of long-term irradiance variations. Aims. In a previous work, we introduced and successfully tested a new spectroscopic method for measuring the photospheric temperature gradient directly on a geometric scale in the case of non-magnetic regions. In this paper, we generalize this method for moderately magnetized regions that may be encountered in the quiet solar photosphere. Methods. To simulate spectroscopic observations, we used synthetic Stokes profiles I and V of the magnetic FeI 630.15 nm line and intensity profiles of the non-magnetic FeI 709 nm line computed from realistic three-dimensional magneto-hydrodynamical simulations of the photospheric granulation and line radiative transfer under local thermodynamical equilibrium conditions. We then obtained maps at different levels in the line-wings by convolution with the instrumental point spread function (PSF) under various conditions of atmospheric turbulence – with and without correction by an adaptive optics (AO) system. The PSF were obtained with the PAOLA software and the AO performance is inspired by the system that will be operating on the Daniel K. Inouye Solar Telescope. Results. We considered different conditions of atmospheric turbulence and photospheric regions with different mean magnetic strengths of 100 G and 200 G. As in non-magnetic cases studied in our previous work, the image correction by the AO system is mandatory for obtaining accurate measurements of the temperature gradient. We show that the non-magnetic line at 709 nm may be safely used in all the cases we have investigated. However, the intensity profile of the magnetic-sensitive line is broadened by the Zeeman effect, which would bias our temperature-gradient measurement. We thus implemented a correction procedure of the line profile for this magnetic broadening in the case of weakly magnetized regions. In doing so, we remarked that in the weak-field regime, the right- and left-hand (I + V and I − V) components have similar shapes, however, they are shifted in opposite directions due to the Zeeman effect. We thus reconstructed the intensity profile by shifting back the I + V and I − V profiles and by adding the re-centered profiles. The measurement then proceeds as in the non-magnetic case. We find that this correction procedure is efficient in regions where the mean magnetic strength is smaller or on the order of 100 G. Conclusions. The new method we implement here may be used to measure the temperature gradient in the quiet Sun from ground-based telescopes equipped with an efficient AO system. We stress that we derive the gradient on a geometrical scale and not on an optical-depth scale as we would do with other standard methods. This allows us to avoid any confusion due to the effect of temperature variations on the continuum opacity in the solar photosphere.

A versatile tool for cluster lensing source reconstruction – I. Methodology and illustration on sources in the Hubble Frontier Field Cluster MACS J0717.5+3745

ABSTRACT We describe a general-purpose method to reconstruct the intrinsic properties of sources lensed by the gravitational potential of foreground clusters of galaxies. The tool lenstruction is implemented in the publicly available multipurpose gravitational lensing software lenstronomy, in order to provide an easy and fast solution to this common astrophysical problem. The tool is based on forward modelling the appearance of the source in the image plane, taking into account the distortion by lensing and the instrumental point spread function. For singly imaged sources, a global lens model in the format of the Hubble Frontier Fields (HFF) lensing maps is required as a starting point. For multiply imaged sources, the tool can also fit and apply first- (deflection), second- (shear, convergence), and third-order (flexion) corrections to the local gravitational potential to improve the reconstruction, depending on the quality of the data. We illustrate the performance and features of the code with two examples of multiply imaged systems taken from the HFF, starting from five different publicly available cluster models. We find that, after our correction, the relative magnification – and other lensing properties – between the multiple images becomes robustly constrained. Furthermore, we find that scatter between models of the reconstructed source size and magnitude is reduced. The code and Jupyter notebooks are publicly available.

End-of-mission calibration of the Cassini Imaging Science Subsystem

We provide an end-of-mission update to the in-flight calibration of the Imaging Science Subsystem cameras on the Cassini spacecraft, resolving discrepancies in our previous analyses from 2004 to 2010, incorporating data through the end of the mission, adding a correction for the weak but measurable camera sensitivity decline over time, and providing new transmission values for polarizing filters. In the new analysis, we add full-disk photometry of Jupiter and the Saturnian icy satellites Rhea, Dione and Enceladus to the previous measurements, which had consisted primarily of standard star targets, while the stellar photometry is updated to include a correction for light lost to the extended wings of the instrumental point spread function. The resulting absolute flux corrections differ considerably from those previously reported, shifting measured radiance by close to 10% in most broadband filters, and bringing agreement between star and satellite targets to within 3%. We also detail improvements to the narrow-angle camera flat field correction, and provide updates to the filter-by-filter point spread functions, hot pixel correction, and polarizer calibration. For the latter, we present new measurements of Titan’s polarization from near-UV to near-IR, including three methane bands and nearby spectral windows.