Precision Of Photometry Research Articles

Lossy Compression of Integer Astronomical Images Preserving Photometric Properties* *This work was supported in part by the Spanish Ministry of Science and Innovation (MICINN) and by the European Regional Development Fund (FEDER), funded by MCIN/AEI/10.13039/501100011033/FEDER, UE, under grant PID2021-125258OB-I00; also by the Catalan Government under grant SGR2021-00643; and also by the “PhotSat” project under the Institute for Space Studies of

Observatories are producing astronomical image data at quickly increasing rates. As a result, the efficiency of the compression methods employed is critical to meet the storage and distribution requirements of both observatories and scientists. This paper presents a novel lossy compression technique that is able to preserve the results of photometry analysis with high fidelity while improving upon the state of the art in terms of compression performance. The proposed compression pipeline combines a flexible bi-region quantization scheme with the lossless, dictionary-based, LPAQ9M encoder. The quantization process allows compression performance and photometric fidelity to be precisely tailored to different scientific requirements. A representative data set of 16-bit integer astronomical images produced by telescopes from all around the world has been employed to empirically assess its compression-fidelity trade-offs, and compare them to those of the de facto standard Fpack compressor. In these experiments, the widespread SExtractor software is employed as the ground truth for photometric analysis. Results indicate that after lossy compression with our proposed method, the decompressed data allows consistent detection of over 99% of all astronomical objects for all tested telescopes, maintaining the highest photometric fidelity (as compared to state of the art lossy techniques). When compared to the best configuration of Fpack (Hcompress lossy using 1 quantization parameter) at similar compression rates, our proposed method provides better photometry precision: 7.15% more objects are detected with magnitude errors below 0.01, and 9.13% more objects with magnitudes below SExtractor’s estimated measurement error. Compared to the best lossless compression results, the proposed pipeline allows us to reduce the compressed data set volume by up to 38.75% and 27.94% while maintaining 90% and 95%, respectively, of the detected objects with magnitude differences lower than 0.01 mag; and up to 18.93% while maintaining 90% of the detected objects with magnitude differences lower than the photometric measure error.

Analysis of the Precision of CSST Time-domain Photometric Observation

The Chinese Space Station Telescope (CSST) is the first space optical survey telescope of China. It will perform scientific observations and yield important scientific results, e.g. multi-color photometry to find and characterize exoplanets. The precision of time-domain photometry affected by various astrophysical and instrument noises is crucial for exoplanet detection and characterization. This paper constructs a time-domain model to simulate the stellar signal and various noises based on the main technical parameters of CSST published so far. The precision of photometry is analyzed by modeling the signal and noises for an example of the gazing mode in the i-band. We investigate and discuss the contribution of various noise sources in aperture photometry, especially the jitter noise caused by pointing jitter and pixel response inhomogeneity. The test results also provide the recommended aperture sizes for photometry. Jitter noise can be suppressed by reducing jitter amplitude, uniforming pixels, or using differential photometry with reference stars. Our simulation results have broad applications, including precision predictions for time-domain photometry, the refinement of CSST instrumental specifications, the evaluation of exoplanet detection capabilities, and improvements in data reduction progress for CSST.

Pushing point-spread function reconstruction to the next level: application to SPHERE/ZIMPOL

ABSTRACT Point-spread function (PSF) reconstruction (PSF-R) is a well-established technique to determine the PSF reliably and accurately from adaptive optics (AO) control-loop data. We have successfully applied this technique to improve the precision of photometry and astrometry for observations of NGC 6121 obtained with the Spectro Polarimetric High-contrast Exoplanet REsearch (SPHERE)/Zurich IMaging POLarimeter (ZIMPOL), which will be presented in a forthcoming Letter. First, we present the methodology we followed to reconstruct the PSF by combining pupil-plane and focal-plane measurements using our PSF-R method PRIME (PSF Reconstruction and Identification for Multiple-source characterization Enhancement), with upgrades of both the model and best-fitting steps compared with previous articles. Secondly, we highlight that PRIME allows us to maintain the PSF fitting residual below 0.2 per cent over 2 hours of observation and using only 30 s of AO telemetry, which may have important consequences for telemetry storage for PSF-R purposes on future 30–40 m class telescopes. Finally, we deploy PRIME in a more realistic regime using faint stars, so as to identify the precision needed on the initial-guess parameters to ensure convergence towards the optimal solution.

Photometry of near earth asteroid Florence (3122)

Purpose. The purpose of this work is investigation of asteroid period of own rotation in moment of its close approach to Earth. Increased brightness of the object create an opportunity to find hidden new aspects of asteroid surface based on higher signal noise ratio and better precision of photometry. Methods . In this work we use methods of CCD photometry. Observations were made on two telescopes with diameter 40 and 35 cm at different observatories. Results. Photometry of near Earth asteroid Florence (3122) is performed during two nights in August and two nights in September 2017 from observatories in west of Ukraine — Laboratory of space research of Uzhhorod National University and amateur observatory in Ternopil. Brief overview of Florence period determination by other authors is given. Light curves obtained from observation data are presented. Periods of asteroid rotation were defined by MPO Canopus software. Conclusions. Determined periods of rotation confirm previously published values. Presented period precisions are better than published before. Two different periods obtained on two observation sessions. Reasons of these results are described. No hidden aspects of asteroid surface were identified because of too fast phase angle change, also two light curves is not enough for such task salvation.

The effects of the WISE/GALEX photometry for the SED-fitting with M31 star clusters and candidates

Spectral energy distribution (SED) fitting of stellar population synthesis models is an important and popular way to constrain the physical parameters ---e.g., the ages, metallicities, masses for stellar population analysis. The previous works suggest that both blue-bands and red-bands photometry works for the SED-fitting. Either blue-domained or red-domained SED-fitting usually lead to the unreliable or biased results. Meanwhile, it seems that extending the wavelength coverage could be helpful. Since the Galaxy Evolution Explorer ({\it GALEX}) and Wide-field Infrared Survey Explorer (WISE) provide the FUV/NUV and mid-infrared $W1$/$W2$ band data, we extend the SED-fitting to a wider wavelength coverage. In our work, we analyzed the effect of adding the FUV/NUV and $W1$/$W2$ band to the optical and near-infrared $UBVRIJHK$ bands for the fitting with the Bruzual \& Charlot 2003 (BC03) models and {\sc galev} models. It is found that the FUV/NUV bands data affect the fitting results of both ages and metallicities much more significantly than that of the WISE $W1$/$W2$ band with the BC03 models. While for the {\sc galev} models, the effect of the WISE $W1$/$W2$ band for the metallicity fitting seems comparable to that of {\it GALEX} FUV/NUV bands, but for age the effect of the $W1$/$W2$ band seems less crucial than that of the FUV/NUV bands. Thus we conclude that the {\it GALEX} FUV/NUV bands are more crucial for the SED-fitting of ages and metallicities, than the other bands, and the high-quality UV data (with high photometry precision) are required.

PSF modelling for very wide-field CCD astronomy

One of the possible approaches to detecting optical counterparts of GRBs requires monitoring large parts of the sky. This idea has gained some instrumental support in recent years, such as with the "Pi of the Sky" project. The broad sky coverage of the "Pi of the Sky" apparatus results from using cameras with wide-angle lenses (20x20 deg field of view). Optics of this kind introduce significant deformations of the point spread function (PSF), increasing with the distance from the frame centre. A deformed PSF results in additional uncertainties in data analysis. Our aim was to create a model describing highly deformed PSF in optical astronomy, allowing uncertainties caused by image deformations to be reduced. Detailed laboratory measurements of PSF, pixel sensitivity, and pixel response functions were performed. These data were used to create an effective high quality polynomial model of the PSF. Finally, tuning the model and tests in applications to the real sky data were performed. We have developed a PSF model that accurately describes even very deformed stars in our wide-field experiment. The model is suitable for use in any other experiment with similar image deformation, with a simple tuning of its parameters. Applying this model to astrometric procedures results in a significant improvement over standard methods, while basic photometry precision performed with the model is comparable to the results of an optimised aperture algorithm. Additionally, the model was used to search for a weak signal -- namely a possible gamma ray burst optical precursor -- showing very promising results. Precise modelling of the PSF function significantly improves the astrometric precision and enhances the discovery potential of a wide-field system with lens optics.

KEPLER MISSION STELLAR AND INSTRUMENT NOISE PROPERTIES

Kepler Mission results are rapidly contributing to fundamentally new discoveries in both the exoplanet and asteroseismology fields. The data returned from Kepler are unique in terms of the number of stars observed, precision of photometry for time series observations, and the temporal extent of high duty cycle observations. As the first mission to provide extensive time series measurements on thousands of stars over months to years at a level hitherto possible only for the Sun, the results from Kepler will vastly increase our knowledge of stellar variability for quiet solar-type stars. Here we report on the stellar noise inferred on the timescale of a few hours of most interest for detection of exoplanets via transits. By design the data from moderately bright Kepler stars are expected to have roughly comparable levels of noise intrinsic to the stars and arising from a combination of fundamental limitations such as Poisson statistics and any instrument noise. The noise levels attained by Kepler on-orbit exceed by some 50% the target levels for solar-type, quiet stars. We provide a decomposition of observed noise for an ensemble of 12th magnitude stars arising from fundamental terms (Poisson and readout noise), added noise due to the instrument and that intrinsic to the stars. The largest factor in the modestly higher than anticipated noise follows from intrinsic stellar noise. We show that using stellar parameters from galactic stellar synthesis models, and projections to stellar rotation, activity and hence noise levels reproduces the primary intrinsic stellar noise features.

High-precision K-band photometry of the secondary eclipse of HD 209458

Recently, mid-infrared Spitzer observations have been presented that show the light decrement due to the passage of a planet behind its host star. These measurements of HD209458b and TrES-1 are the first detections of direct light from an extra-solar planet. Interpretation of these results in terms of planet equipartition temperature and bond albedo is however strongly model dependent and require additional observations at shorter wavelengths. Here we report on two attempts to detect the secondary eclipse of HD209458b from the ground in K-band, using the UK InfraRed Telescope (UKIRT). A photometry precision of 0.12% relative to two nearby reference stars was reached during both occasions, but no firm detection of the eclipses were obtained. The first observation shows a flux decrement of -0.13+-0.18%, and the second of -0.10+-0.10%. A detailed description of the observing strategy, data reduction and analysis is given, and a discussion on how the precision in ground-based K-band photometry could be further improved. In addition we show that the relative photometry between the target and the reference stars between the two epochs is consistent down to the <0.1% level, which is interesting in the light of possible near-infrared surveys to search for transiting planets around M and L dwarfs.

SIGNAL-TO-NOISE CONSIDERATIONS FOR SKY-SUBTRACTED CCD DATA

ABSTRACT The standard equation for calculating the uncertainty of photometry obtained from CCDs does not correctly consider the random errors, or 'noise', introduced into observations by procedures used in reducing the data. This paper presents a thorough derivation of the theoretical error equation that considers the contributions from all internal noise sources in the signal-to-noise ratio (S/N) of a sky-subtracted image. A simplified version used for estimating the internal errors from empirical data is also derived. The propagation of noise through the data-reduction process is illustrated through a series of equations for the change in S/N that results from a variety of different operations performed on a CCD frame. Comparing these effects with the results expected for an observation made with an ideal detector suggests a number of ways to improve the precision of photometry through the practices employed in obtaining and reducing the observations.

Photometric Studies of Asteroids. VIII. Additional Photographic Magnitudes.

view Abstract Citations (4) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometric Studies of Asteroids. VIII. Additional Photographic Magnitudes. Gehrels, T. ; Carstens, J. R. ; Peters, J. G. ; Peters, L. S. Abstract In the Yerkes-McDonald Asteroid Survey, photographic magnitudes were determined brighter than P0 = 16.5. For fainter asteroids and for some with large inclination and eccentricity additional magnitudes are reported in this paper. The work was done as a part of the regular Indiana Asteroid Program, supplemented by plates taken in South Africa. Aspect variation and its effects on the precision of photometry are discussed. The axes of rotation of the asteroids are apparently fixed in space. Asteroids may be used in order to transfer the zero point of the U, B, V system from the northern to the southern hemispheres. Publication: The Astrophysical Journal Pub Date: July 1960 DOI: 10.1086/146917 Bibcode: 1960ApJ...132..232G full text sources ADS | Related Materials (12) Part 1: 1954ApJ...120..200G Part 2: 1954ApJ...120..529G Part 3: 1954ApJ...120..547S Part 4: 1954ApJ...120..551A Part 5: 1956ApJ...123..331G Part 6: 1957ApJ...125..550G Part 7: 1958ApJ...127..253V Part 8: 1960PGLO...37...53G Part 10: 1960ApJ...132..915G Part 11: 1962ApJ...135..906G Part 12: 1962PGLO...46..906G Part 13: 1963PGLO...53.1279W