Photometric System Research Articles

Design and performance of a collimated beam projector for telescope transmission measurement using a broad-band light source

Abstract Type Ia supernovae are the most direct cosmological probe to study dark energy in the recent Universe, for which the photometric calibration of astronomical instruments remains one major source of systematic uncertainties. To address this, recent advancements introduce collimated beam projectors (CBPs), aiming to enhance calibration by precisely measuring a telescope’s throughput as a function of wavelength. This work describes the performance of a prototype portable CBP. The experimental set-up consists of a broad-band Xenon light source replacing a more customary but much more demanding high-power laser source, coupled with a monochromator emitting light inside an integrating sphere monitored with a photodiode and a spectrograph. Light is injected at the focus of the CBP telescope projecting a collimated beam onto a solar cell whose quantum efficiency has been obtained by comparison with a NIST-calibrated photodiode. The throughput and signal-to-noise ratio achieved by comparing the photocurrent signal in the CBP photodiode with the one in the solar cell are computed. We prove that the prototype, in its current state of development, is capable of achieving 1.2 per cent and 2.3 per cent precision on the integrated g and r bands of the Zwicky Transient Facility photometric filter system, respectively, in a reasonable amount of integration time. Central wavelength determination accuracy is kept below ∼0.91 and ∼0.58 nm for g and r bands, respectively. The expected photometric uncertainty caused by filter throughput measurement is approximately 5 mmag on the zero-point magnitude. Several straightforward improvement paths are discussed to upgrade the current set-up.

Astrometric and Photometric Calibrators for the 4-m International Liquid Mirror Telescope

The International Liquid Mirror Telescope (ILMT) is a 4-meter class survey telescope. It achieved its first light on 29th April 2022 and is now undergoing the commissioning phase. It scans the sky in a fixed wide strip centred at the declination of and works in Time Delay Integration (TDI) mode. We present a full catalog of sources in the ILMT strip derived by crossmatching Gaia DR3 with SDSS DR17 and PanSTARRS-1 (PS1) to supplement the catalog with apparent magnitudes of these sources in g, r, and i filters. These sources can serve as astrometric calibrators. The release of Gaia DR3 provides synthetic photometry in popular broadband photometric systems, including the SDSS g, r, and i bands for ∼220 million sources across the sky. We have used this synthetic photometry to verify our crossmatching performance and, in turn, create a subset of the catalog with accurate photometric measurements from two reliable sources.

Robust point light source calibration method for near-field photometric stereo using feature points selection

In this paper, we present a robust method for nonisotropic point light source calibration through feature points selection. By analyzing the relationship between the observed surface and its image intensity under near-field lighting, the feature points selection method is first developed to effectively address the noisy observations and improve calibration robustness. Afterward, to enhance efficiency and accuracy of the calibration, a cost function of l p -norm is established based on the above relationship, and an improved Newton method-based iteration process is applied to calculate the light source parameters. The simulations demonstrate that the proposed method is capable of achieving robust calibration results with the estimation error less than 2.7 mm and 0.8°, even though the image intensities are corrupted by Gaussian white noise with standard deviation up to 0.4. The experimental validation is performed using a self-designed photometric stereo system, where the calibration of point light sources is conducted, and measurements are taken on a standard sphere and compressor blade based on the obtained calibration results, which demonstrates the effectiveness of what we believe to be a new method.

A novel three-dimensional surface reconstruction method for fabric appearance evaluation

Traditional fabric appearance evaluation method mainly relies on subjective and manual operation, which is not uniform and time-consuming. In this paper, one set of self-developed 3D reconstruction system and method based on photometric stereo is proposed for objective fabric appearance evaluation. A photometric stereo image acquisition system equipped with multi-directional lighting sources is developed for the 3D surface reconstruction. Lighting and camera calibration is conducted to obtain the position of light sources and the intrisic parameters of digital camera. Our experimental results show that 3D fabric surface could be reconstructed effectively based on photometric stereo vision method, it has the potential to be used for fabric appearance evaluation.

COLOR-INDEX DETERMINATION OF LEO SATELLITES USING COLOR IP-CAMERAS

The study is devoted to determining the color characteristics of the structural surfaces of artificial satellites. Observations of satellites were carried out in automatic mode using software for detection fast moving object, developed at RI “MAO”. The satellite observations equipment consists of Canon EF 85mm f/1.8 USM photographic lens and professional VIVOTEK IP816A-HP network camera. The camera is directed to the zenith and has a field of view (4.9°х2.8°). The camera has progressive CMOS sensor with Bayer color filter⁰₀ array for producing RGB color image. Coordinate and photometric processing of saved images is carried out using SExtractor and Astrometry.net software along with additional Python scripts. In this paper, we present first results of our LEO satellites observations using network IP-cameras with RGB Bayer filter. To convert the instrumental magnitudes from RGB Bayer system into standard bp/rp magnitudes of the Gaia EDR3 photometric system, a system of equations was solved, where the calculated magnitudes in the bp/rp photometric system were represented as functions of magnitudes and colors in the instrumental RGB system. The mean differences between the calculated magnitudes and the catalog magnitudes are (0.03±0.15)mag and (0.01±0.16)mag for bp and rp band, respectively. The calculated Brjb_bp and Rrjb_rp magnitudes using obtained transformation coefficients show a good linear correlation with the bp and rp Gaia EDR3 magnitudes. Only main sequence’s stars in the range of (5-13)mag were used as reference stars for determining the transformation coefficients. The results of determining the color indexes (Brjb_bp - Rrjb_rp) for 8 LEO satellites with the obtained transformation coefficients were received. The average accuracy of the obtained values of color indexes is about 0.2mag.

TWO TOOLS FOR ESTIMATING STAR CLUSTER PARAMETERS

A star cluster is a composition of stars held together by the overall gravitational field of the whole cluster. The stars of a given cluster are born in a giant molecular cloud and, as such, can be regarded as objects with almost equal ages. Furthermore, assuming that the initial material in the cloud is perfectly mixed, we may also say that the metallicity of all cluster members is the same. Four parameters (distance, extinction or reddening, age, and metallicity) are standardly used to describe star clusters. Their knowledge is essential for studying galaxies’ local and global properties (especially our own Galaxy). However, deriving these parameters may take time and effort. Thanks to the Gaia mission’s parallax measurements, we can determine the distances of stars (and clusters) within our Galaxy with unprecedented precision. Therefore, we can remove the distance from the list of free parameters. We developed two different tools for estimating cluster parameters: 1) Metalcode, an automatic tool focused on deriving metallicities of open clusters, and 2) Stellar Isochrone Fitting Tool (StIFT), a tool for fitting a grid of isochrones for any photometric system available. We present both tools in more detail.

Empirical 2MASS–WFC3/IR Filter Transformations Across the H-R Diagram from Synthetic Photometry

Near-infrared bandpasses on spaceborne observatories diverge from their ground-based counterparts as they are free of atmospheric telluric absorption. Available transformations between respective filter systems in the literature rely on theoretical stellar atmospheres, which are known to have difficulties reproducing the observed spectral energy distributions of cool giants. We present new transformations between the Two Micron All Sky Survey JHK S and Hubble Space Telescope WFC3/IR F110W, F125W, and F160W photometric systems based on synthetic photometry of empirical stellar spectra from four spectral libraries. This sample comprises over 1000 individual stars, which together span nearly the full H-R diagram and sample stellar populations from the solar neighborhood out to the Magellanic Clouds, covering a broad range of ages, metallicities, and other relevant stellar properties. In addition to global color-dependent transformations, we examine band-to-band differences for cool, luminous giant stars in particular, including multiple types of primary distance indicators.

Validation of a commercially available photometric analytical system for assessment of plasma oxidative status in healthy horses

Reactive oxygen species (ROS) are the end-products of physiologic functions in health. Oxidative stress occurs when endogenous antioxidants are insufficient to neutralize ROS in the system. As a result, ROS can damage DNA, RNA, proteins, lipids, and cell organelles. To obtain accurate measurements of plasma oxidative stress, levels of both oxidants and antioxidants must be measured. This study validates a commercially available, semi-quantitative, photometric analytical system that measures systemic determinants of reactive oxygen metabolites (dROM) and plasma antioxidant capacity (PAC) in stored equine plasma. The objectives of this work were: 1) to validate a photometric analytical system to quantify dROM and PAC in equine plasma; and 2) to determine expected results for these tests in healthy adult horses. We hypothesized that this system would reliably and reproducibly assess dROM and PAC in equine plasma. We observed expected, dose-dependent increases in dROM generated by adding increasing concentrations of H2O2 or ascorbic acid to equine plasma to provide samples containing a known quantity of oxidants or antioxidants respectively. Mean dROM value in healthy horses was 103.3 ±20.7 U. Carr and mean PAC was 2881.0 ± 313.9 U. Cor. This system reliably and reproducibly quantified dROM and PAC in equine plasma samples.

Period Change Analysis of a W UMa-type Binary: V417 Aquilae

Light curve analysis investigated the orbital period variations of the short period, overcontact eclipsing binary system, and V417 Aquilae (V417 Aql). The system was observed using a 0.70-meter telescope with a CCD photometric system using B and V filters at the Regional Observatory for the Public, Songkhla, Thailand, on 2 July 2021 UT. The light curve constructed by the photometric method for each filter was analyzed to find the period change of the system. It is found that the V417 Aql system is undergoing a long-term decrease of rate 0.00251 seconds/year. The reduction in the period showed that the distance between the stars was decreased according to Angular Momentum Loss (AML) theory. V417 Aql residuals tend to be periodic, indicating there might be a third body in the system. The calculation shows that the third body’s distance, period, and mass function are about 1.97 AU, 47.7 years, and 0.19Mʘ, respectively.

How Tycho Brahe’s recordings in 1572 support SN 1572 as a type I(a) supernova

The 450th anniversary of the discovery of the SN 1572 supernova event was celebrated in 2022. A closer look at the historical development of the field of supernova astronomy reveals the scientific importance of Tycho Brahe’s 1572 observations of this “new star.” In their quest to learn more about the new type of stellar explosion and subsequent evolution, the initial protagonists in this field (Baader and Zwicky among others) gradually turned their attention to the final remnant state of these supernova events. Since the remnant object thought to be associated with the extragalactic supernova event was found to be very dim, the focus quickly shifted toward nearby galactic events. It is at this point where Tycho Brahe’s observations played an important and often overlooked role in the context of the development of stellar evolution as a scientific field. Tycho Brahe’s meticulous and detailed recordings of the change in brightness of the new star not only allowed modern astronomers to classify SN 1572 as a supernova event but also helped them pinpoint the exact astrometric location of SN 1572. These findings helped to empirically link extragalactic supernova events to nearby past supernova remnants in the Milky Way. This enabled subsequent observations allowing further characterization. Transforming the historical recordings to a standardized photometric system also allowed the classification of SN 1572 as a type I supernova event.

An UBVRI calibration method based on Pan-STARRS photometric survey

The Landolt’s standard stars catalog is the most widely utilized for CCD astronomy in the UBVRI broad band photometry system. The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) is one of the usage of the newly grizy photometric system. In this work, the main objective of this paper is to calibrate observations in the U, B, V, R, and I bands by utilizing data in the g, r, and i bands from the literature. First, the machine learning based method XGBoost is employed to train a model for selecting objects with linear relations between the two catalogs. Then, the color transformation method is utilized to convert objects with gri magnitudes of Pan-STARRS1 (PS1) catalog to the UBVRI system, and a set of transformation coefficients is presented. A photometric calibration system is developed and the color based calibration method is implemented in the system. The typical calibration errors of standard field GD279 from instrumental magnitudes to those of standard UBVRI system are derived as 0.173mag, 0.053mag, 0.024mag, 0.019mag, 0.020mag, respectively. Furthermore, the light curve comparison of SN 2017hpa of a large number of observations from different nights suggests that this method can be qualified for various astrometric observations.

Benchmarking Gaia DR3 Apsis with the Hyades and Pleiades open clusters

Context. The Gaia astrophysical parameters inference system (Apsis) provides astrophysical parameter estimates for several to hundreds of millions of stars. Aims. We aim to benchmark Gaia DR3 Apsis. Methods. We compiled approximately 1500 bona fide single stars in the Hyades and Pleiades open clusters for validation of PARSEC isochrones, and for comparison with Apsis estimates. PARSEC stellar isochrones in the Gaia photometric system enable us to assign average ages and metallicities to the clusters, and mass, effective temperature, luminosity, and surface gravity to the individual stars. Results. Apsis does not recover the single-age, single-metallicity characteristic of the cluster populations. Ages assigned to cluster members seemingly follow the input template for Galactic populations, with earlier-type stars being systematically assigned younger ages than later-type stars. Cluster metallicities are underestimated by 0.10–0.2 dex. Effective temperature estimates are in general reliable. Surface gravity estimates reveal strong systematic errors for specific ranges of the Gaia BP − RP colours. Conclusions. We caution that Gaia DR3 Apsis estimates can be subject to significant systematic uncertainties. Some of the Apsis estimates, such as metallicity, might only be meaningful for statistical studies of the time-averaged Galactic stellar population, but are not recommended to be used for individual stars.

An astrometric approach to measuring the colour of an object

ABSTRACT The colour of a star is a critical feature to reflect its physical property such as the temperature. The colour index is usually obtained via absolute photometry, which is demanding for weather conditions and instruments. In this work, we present an astrometric method to measure the catalogue-matched colour index of an object based on the effect of differential colour refraction (DCR). Specifically, we can observe an object using only one filter or alternately using two different filters. Through the difference of the DCR effect compared with reference stars, the catalogue-matched colour index of an object can be conveniently derived. Hence, we can perform DCR calibration and obtain its accurate and precise positions even if observed with Null filter during a large range of zenith distances, by which the limiting magnitude and observational efficiency of the telescope can be significantly improved. This method takes advantage of the DCR effect and builds a link between astrometry and photometry. In practice, we measure the colour indices and positions of Himalia (the sixth satellite of Jupiter) using 857 CCD frames over 8 nights by two telescopes. Totally, the mean colour index BP − RP (Gaia photometric system) of Himalia is 0.750 ± 0.004 mag. Through the rotational phased colour index analysis, we find two places with their colour indices exceeding the mean ± 3σ.

Color Transformations of Photometric Measurements of Galaxies in Optical and Near-infrared Wide-field Imaging Surveys* *An online color transformation calculator is available at: https://colors.voxastro.org/.

Over the past 2 decades, wide-field photometric surveys in optical and infrared domains reached a nearly all-sky coverage thanks to numerous observational facilities operating in both hemispheres. However, subtle differences among exact realizations of Johnson and SDSS photometric systems require one to convert photometric measurements into the same system prior to analysis of composite data sets originating from multiple surveys. It turns out that the published photometric transformations lead to substantial biases when applied to integrated photometry of galaxies from the corresponding catalogs. Here we present photometric transformations based on piece-wise linear approximations of integrated photometry of galaxies in the optical surveys SDSS, DECaLS, BASS, MzLS, DES, DELVE, KiDS, VST ATLAS, and the near-infrared surveys UKIDSS, UHS, VHS, and VIKING. We validate our transformations by constructing k-corrected color–magnitude diagrams of non-active galaxies and measuring the position and tightness of the “red sequence.” We also provide transformations for aperture magnitudes and show how they are affected by the image quality difference among the surveys. We present the implementation of the derived transformations in python and idl and also a web-based color transformation calculator for galaxies. By comparing DECaLS and DES, we identified systematic issues in DECaLS photometry for extended galaxies, which we attribute to the photometric software package used by DECaLS. As an application of our method, we compiled two multi-wavelength photometric catalogs for over 200,000 low- and intermediate-redshift galaxies originating from CfA FAST and Hectospec spectral archives.

Period–Luminosity Relations for Galactic Classical Cepheids in the Sloan Bands* * Based on data from the Las Cumbres Observatory.

We present the first period–luminosity (PL) and period–Wesenheit (PW) relations in the Sloan–Pan-STARRS g P1 r P1 i P1 bands for classical fundamental-mode Cepheids in the Milky Way. We used a relatively modest number of 76 stars for the PL and 84−85 stars for the PW relations calibration. The data for the project were collected with the network of 40 cm telescopes of the Las Cumbres Observatory, and Gaia Data Release 3 parallaxes were used for the calculations. These gri-band PL and PW relations calibrations will be a useful tool for distance determinations in the era of large sky surveys using the Sloan photometric system, especially with the near-future start of the Large Synoptic Survey of Space and Time.

A Blueprint for the Milky Way’s Stellar Populations. IV. A String of Pearls—the Galactic Starburst Sequence

We continue our series of papers on phase-space distributions of stars in the Milky Way based on photometrically derived metallicities and Gaia astrometry, with a focus on the halo−disk interface in the local volume. To exploit various photometric databases, we develop a method of empirically calibrating synthetic stellar spectra based on a comparison with observations of stellar sequences and individual stars in the Sloan Digital Sky Survey, the SkyMapper Sky Survey, and the Pan-STARRS1 surveys, overcoming band-specific corrections employed in our previous work. In addition, photometric zero-point corrections are derived to provide an internally consistent photometric system with a spatially uniform metallicity zero-point. Using our phase-space diagrams, we find a remarkably narrow sequence in the rotational velocity (v ϕ ) versus metallicity ([Fe/H]) space for a sample of high proper-motion stars (>25 mas yr−1), which runs along Gaia Sausage/Enceladus (GSE) and the Splash substructures and is linked to the disk, spanning nearly 2 dex in [Fe/H]. Notably, a rapid increase of v ϕ from a nearly zero net rotation to ∼180 km s−1 in a narrow metallicity interval (−0.6 ≲ [Fe/H] ≲ −0.4) suggests that some of these stars emerged quickly on a short gas-depletion timescale. Through measurements of a scale height and length, we argue that these stars are distinct from those heated dynamically by mergers. This chain of high proper-motion stars provides additional support for recent discoveries suggesting that a starburst took place when the young Milky Way encountered the gas-rich GSE progenitor, which eventually led to the settling of metal-enriched gas onto the disk.

The IAU recommended photometric system for ultraviolet astronomy

In the current era when access to space is becoming easier and at a lower cost thanks to the standardised cubesat technology, numerous missions are expected to be launched to observe, particularly, at ultraviolet wavelengths. Given the reduced dimensions of the telescope that a cubesat can carry, most of these missions will be focused on photometric surveys of a reduced sample of targets of interest, and therefore each mission will define their own photometric bands according to their scientific objectives and orbital constraints. However, in order to provide a coherent view of the ultraviolet sky, the data should be post-processed under a common framework. In 2017, the IAU working group on ultraviolet astronomy identified the need to define such a common framework for the upcoming ultraviolet missions, and coordinated the definition of a standard set of photometric bands that could serve for homogenizing the current and future data. This paper presents the procedure adopted by the working group for the definition of the standard photometric system, that was approved by the IAU during the General Assembly Business Sessions held in August, 2021. The photometric system consists of seven bands, denoted as UV1-UV7, all included in the range 115 - 400 nm. Some of these bands are based on existing filters, while others have been defined as theoretical bands with constant throughput. This system is to be regarded as a set of synthetic bands for post-processing the data of any mission, and an example of its application to the SPARCS cubesat is also included. The photometric bands are publicly available and can be downloaded from https://www.nuva.eu/uv-photometry/.

Photometric flow system for the determination of serum lactate dehydrogenase activity

The routine method for LDH (Lactate dehydrogenase) activity determination is to monitor the increase of NADH concentration at 340 nm. There are some inconvenience in taking measurements in the near-UV region, especially in the case of serum samples analysis. In this work, two modifications of the routine LDH activity assay based on the use of reducing properties of NADH have been compared. Both methods involved the reduction of compounds that can be easily determined by well-known methods, ferric ion (with ferrozine) and nitrotetrazolium blue (NBT). A fully-mechanized Multicommutated Flow Analysis-Paired Emitter Detector Diode (MCFA-PEDD) system based on solenoid devices was developed and applied for both methods. The linear ranges obtained for Fe-ferrozine and NBT methods are 6.0–200.0 U L−1 and 10.0–250.0 U L−1 with estimated detection limits at 0.2 U L−1 and 4.5 U L−1, respectively. The low LOQ values enabled 10-fold sample dilutions, which is advantageous for samples with limited available volume. The Fe-ferrozine method is more selective for LDH activity in the presence of glucose, ascorbic acid, albumin, bilirubin, copper and calcium ions than NBT method. To confirm the analytical usefulness of the proposed flow system, the analysis of real human serum samples was carried out. The statistic tests showed satisfactory correlation between the results obtained for both developed methods and those received using the reference method.

The Study of Helium Variations in Star Clusters Using China Space Station Telescope

The China Space Station Telescope (CSST) is a 2 m space-based optical-UV telescope. Its primary goal is to carry out a high-resolution photometric imaging survey of a 17,500 square degree sky area using the on board Survey Camera. With its wide field of view (1.1 square degrees) and a mosaic imager containing 640 million pixels, studying the different populations of stars within star clusters is highly feasible. The aim of this study is to assess the CSST’s ability to distinguish between stellar populations with varying helium abundance levels, with the help of Modules for Experiments in Stellar Astrophysics. The results of the CSST’s photometry for these different populations are presented by transferring the models into the CSST Survey Camera photometric system. The findings confirm that helium-enriched stellar populations will have unique patterns in the color–magnitude diagrams under the CSST photometric system, compared to normal stellar populations. The CSST, with its filters and wide field of view of the Survey Camera, provides a new avenue for the study of multiple populations in star clusters.

Сolor transformation between photometric systems of 2MASS catalog and ASTRONIRCAM of SAI MSU 2.5-m telescope

In this paper, we consider a method for determining the coefficients of the transformation equations between different photometric systems based on the photometry of all field stars recorded during observations of the primary standards of one of the photometric systems. Using this method, the coefficients of color transformation equations between the photometric system of ASTRONIRCAM of the 2.5-m telescope KGO SAI MSU and the 2MASS all-sky survey catalog photometric system are obtained.