Photometric Model Research Articles

Detection of Polarization due to Cloud Bands in the Nearby Luhman 16 Brown Dwarf Binary

Abstract Brown dwarfs exhibit patchy or spatially varying banded cloud structures that are inferred through photometric and spectroscopic variability modeling techniques. However, these methods are insensitive to rotationally invariant structures, such as the bands seen in Jupiter. Here, we present H-band Very Large Telescope/NaCo linear polarization measurements of the nearby Luhman 16 L/T transition binary, which suggest that Luhman 16A exhibits constant longitudinal cloud bands. The instrument was operated in pupil tracking mode, allowing us to unambiguously distinguish between a small astrophysical polarization and the ∼2% instrumental linear polarization. We measure the degree and angle of linear polarization of Luhman 16A and B to be p A = 0.031% ± 0.004% and ψ A = −32° ± 4°, and p B = 0.010% ± 0.004% and , respectively. Using known physical parameters of the system, we demonstrate that an oblate homogeneous atmosphere cannot account for the polarization measured in Luhman 16A, but could be responsible for that of the B component. Through a nonexhaustive search of banded cloud morphologies, we demonstrate a two-banded scenario that can achieve a degree of linear polarization of p = 0.03% and conclude that the measured polarization of the A component must be predominantly due to cloud banding. For Luhman 16B, either oblateness or cloud banding could be the dominant source of the measured polarization. The misaligned polarization angles of the two binary components tentatively suggest spin–orbit misalignment. These measurements provide new evidence for the prevalence of cloud banding in brown dwarfs while at the same time demonstrating a new method—complementary to photometric and spectroscopic variability methods—for characterizing the cloud morphologies of substellar objects without signs of variability.

TESS photometry of the asynchronous polar CD Ind: A short period analog of BY Cam

We present a time-series analysis of the asynchronous polar CD Ind, using fast cadence TESS photometry. A similar analysis is performed using ground based photometry of BY Cam. These asynchronous polars show remarkably similar light curves and enigmatic timing characteristics. A pair of competing models for the assignment of the white dwarf spin period have been presented for both binaries. TESS allows for the breaking of this degeneracy by providing continuous coverage over several beat-cycles. The CD Ind light curve displays a super-orbital period of 7.2 days due to beat-phased modulation of the accretion rate onto a permanently visible spot. This (main) accretion region is active for 3/4 of the beat-cycle. The dominant photometric signal is at 109.654(4) min and is identified as a side-band related to the white dwarf spin and the binary orbit, analogous to that found in BY Cam. We obtain the white dwarf spin period of CD Ind as 110.820(5) min and an orbital period of 111.952(8) min. The TESS light curve supports a pole-switching scenario for CD Ind, with a total of 4 alternating, and oppositely positioned accretion regions. This inclination of CD Ind is estimated as i = 65°±10°. One accretion region remains in view of the observer at all times. In addition, two pulsed accretion spots each accrete for just less than 1/2 of the beat-cycle. These alternating spots are orthogonal to the main accretion region (which is always in view), and are found to be roughly 180° apart in longitude. Finally, since the mean flux drops by a factor of 2 for about 1/4 of the beat-cycle and the dominant accretion region turns off during this time, we hypothesize the existence of a fourth (permanently hidden) accretion region opposite to the one permanently in view. Photometric models for the 2- and 4-pole accretion configurations are developed and only the 4-pole model is consistent with the observed periodogram for CD Ind. We conclude that complex magnetic fields affect accretion flow onto these white dwarf stars. In particular, the magnetic field of the white dwarf in both of these binaries is inconsistent with either a centered or an offset dipole configuration.

ZTF J1901+5309: a 40.6-min orbital period eclipsing double white dwarf system

ABSTRACT The Zwicky Transient Facility has begun to discover binary systems with orbital periods that are less than 1 h. Combined with dedicated follow-up systems, which allow for high-cadence photometry of these sources, systematic confirmation and characterization of these sources are now possible. Here, we report the discovery of ZTF J190125.42+530929.5, a 40.6-min orbital period, eclipsing double white dwarf binary. Both photometric modelling and spectroscopic modelling confirm its nature, yielding an estimated inclination of $i = 86.2^{+0.6}_{-0.2}\, \rm deg$ and primary and secondary effective temperatures of $\textrm{{T}}_\textrm{eff} = 28\,000^{+500}_{-500}$ and $17\,600^{+400}_{-400}\, \mathrm{ K}$, respectively. This system adds to a growing list of sources for future gravitational-wave detectors and contributes to the demographic analysis of double degenerates.

Disk-resolved photometric modeling and properties of asteroid (101955) Bennu

OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) is a NASA mission to return a sample of asteroid (101955) Bennu. Photometric modeling of Bennu's surface is a key element of both sample site characterization and our broader scientific understanding of the asteroid. Bennu's heterogeneous surface presents substantial variation in reflectance and produces a scattered dataset that poses a challenge to photometric modeling. We show that the resolution of the shape model with which we calculate photometric angles strongly affects the accuracy of the analysis, as well as the efficacy of subsequent photometric corrections. We use global imaging data to fit empirical photometric models of the surface. These models represent the average behavior of Bennu's surface and can be used beyond this work to photometrically correct panchromatic and color basemaps of Bennu and perform albedo analyses of individual features on Bennu's surface. Bennu's global photometry reveals a moderate opposition effect and detectable phase reddening, both of which suggest a macroscopically rough surface, which is confirmed by centimeter-scale images of the asteroid.

Apsidal motion in the massive binary HD 152248

Context. The eccentric massive binary HD 152248 (also known as V1007 Sco), which hosts two O7.5 III-II(f) stars, is the most emblematic eclipsing O-star binary in the very young and rich open cluster NGC 6231. Its properties render the system an interesting target for studying tidally induced apsidal motion. Aims. Measuring the rate of apsidal motion in such a binary system gives insight into the internal structure and evolutionary state of the stars composing it. Methods. A large set of optical spectra was used to reconstruct the spectra of the individual binary components and establish their radial velocities using a disentangling code. Radial velocities measured over seven decades were used to establish the rate of apsidal motion. We furthermore analysed the reconstructed spectra with the CMFGEN model atmosphere code to determine stellar and wind properties of the system. Optical photometry was analysed with the Nightfall binary star code. A complete photometric and radial velocity model was constructed in PHOEBE 2 to determine robust uncertainties. Results. We find a rate of apsidal motion of (1.843−0.083+0.064)° yr−1. The photometric data indicate an orbital inclination of (67.6−0.1+0.2)° and Roche-lobe filling factors of both stars of about 0.86. Absolute masses of 29.5−0.4+0.5 M⊙ and mean stellar radii of 15.07−0.12+0.08 R⊙ are derived for both stars. We infer an observational value for the internal structure constant of both stars of 0.0010 ± 0.0001. Conclusions. Our in-depth analysis of the massive binary HD 152248 and the redetermination of its fundamental parameters can serve as a basis for the construction of stellar evolution models to determine theoretical rates of apsidal motion to be compared with the observational one. In addition, the system hosts two twin stars, which offers a unique opportunity to obtain direct insight into the internal structure of the stars.

Variability and transient search in the SUDARE–VOICE field: a new method to extract the light curves

ABSTRACT The VLT Survey Telescope (VST) Optical Imaging of the CDFS and ES1 Fields Survey, in synergy with the SUDARE survey, is a deep optical ugri imaging of the CDFS and ES1 fields using the VST. The observations for the CDFS field comprise about 4.38 deg2 down to r ∼ 26 mag. The total on-sky time spans over 4 yr in this field, distributed over four adjacent sub-fields. In this paper, we use the multiepoch r-band imaging data to measure the variability of the detected objects and search for transients. We perform careful astrometric and photometric calibrations and point spread function modelling. A new method, referring to as differential running-average photometry, is proposed to measure the light curves of the detected objects. With the method, the difference of PSFs between different epochs can be reduced, and the background fluctuations are also suppressed. Detailed uncertainty analysis and detrending corrections on the light curves are performed. We visually inspect the light curves to select variable objects, and present some objects with interesting light curves. Further investigation of these objects in combination with multiband data will be presented in our forthcoming paper.

Photometric Analyses of Saturn’s Small Moons: Aegaeon, Methone, and Pallene Are Dark; Helene and Calypso Are Bright

Abstract We examine the surface brightnesses of Saturn’s smaller satellites using a photometric model that explicitly accounts for their elongated shapes and thus facilitates comparisons among different moons. Analyses of Cassini imaging data with this model reveal that the moons Aegaeon, Methone, and Pallene are darker than one would expect given trends previously observed among the nearby mid-sized satellites. On the other hand, the trojan moons Calypso and Helene have substantially brighter surfaces than their co-orbital companions Tethys and Dione. These observations are inconsistent with the moons’ surface brightnesses being entirely controlled by the local flux of E-ring particles, and therefore strongly imply that other phenomena are affecting their surface properties. The darkness of Aegaeon, Methone, and Pallene is correlated with the fluxes of high-energy protons, implying that high-energy radiation is responsible for darkening these small moons. Meanwhile, Prometheus and Pandora appear to be brightened by their interactions with the nearby dusty F ring, implying that enhanced dust fluxes are most likely responsible for Calypso’s and Helene’s excess brightness. However, there are no obvious structures in the E ring that would preferentially brighten these two moons, so there must either be something subtle in the E-ring particles’ orbital properties that leads to asymmetries in the relevant fluxes, or something happened recently to temporarily increase these moons’ brightnesses.

The performance of photometric reverberation mapping at high redshift and the reliability of damped random walk models

ABSTRACT Accurate methods for reverberation mapping using photometry are highly sought after since they are inherently less resource intensive than spectroscopic techniques. However, the effectiveness of photometric reverberation mapping for estimating black hole masses is sparsely investigated at redshifts higher than z ≈ 0.04. Furthermore, photometric methods frequently assume a damped random walk (DRW) model, which may not be universally applicable. We perform photometric reverberation mapping using the javelin photometric DRW model for the QSO SDSS-J144645.44+625304.0 at z = 0.351 and estimate the Hβ lag of $65^{+6}_{-1}$ d and black hole mass of $10^{8.22^{+0.13}_{-0.15}}\, \mathrm{M_{\odot }}$. An analysis of the reliability of photometric reverberation mapping, conducted using many thousands of simulated CARMA process light curves, shows that we can recover the input lag to within 6 per cent on average given our target’s observed signal-to-noise of >20 and average cadence of 14 d (even when DRW is not applicable). Furthermore, we use our suite of simulated light curves to deconvolve aliases and artefacts from our QSO’s posterior probability distribution, increasing the signal-to-noise on the lag by a factor of ∼2.2. We exceed the signal-to-noise of the Sloan Digital Sky Survey Reverberation Mapping Project (SDSS-RM) campaign with a quarter of the observing time per object, resulting in a ∼200 per cent increase in signal-to-noise efficiency over SDSS-RM.

The Black Hole–Bulge Mass Relation Including Dwarf Galaxies Hosting Active Galactic Nuclei

Abstract We present a new relationship between central black hole (BH) mass and host galaxy stellar bulge mass extending to the lowest BH masses known in dwarf galaxies (M BH ≲ 105 M ⊙; M ⋆ ∼ 109 M ⊙). We have obtained visible and near-infrared Hubble Space Telescope imaging of seven dwarf galaxies with optically selected broad-line active galactic nuclei (AGNs) and BH mass estimates from single-epoch spectroscopy. We perform 2D photometric modeling with GALFIT to decompose the structure of these galaxies and find that the majority have an inner bulge/pseudo-bulge component with an exponential disk that dominates the total stellar mass. Using the modeling results and color-dependent mass-to-light ratios, we determine the stellar mass of each photometric component in each galaxy. We determine the M BH–M bulge relation using a total of 12 dwarf galaxies hosting broad-line AGNs, along with a comparison sample of 88 galaxies with dynamical BH masses and 37 reverberation-mapped AGNs. We find a strong correlation between BH mass and bulge mass with . The near-linear slope and normalization are in good agreement with correlations found previously when only considering higher-mass systems. This work has quadrupled the number of dwarf galaxies on the BH–bulge mass relation, with implications for BH seeding and predictions for gravitational wave detections of merging BHs at higher redshifts with LISA.

The bidirectional and directional hemispheric reflectance of Apollo 11 and 16 soils: Laboratory and Diviner measurements

We have acquired a comprehensive laboratory bidirectional measurements of Apollo 11 and Apollo 16 lunar soil samples and have successfully fit photometric models to the laboratory data and have determined the solar spectrum averaged hemispheric reflectance as a function of incidence angle. The Apollo 11 (sample 10,084) and 16 (sample 68,810) soil samples are two representative end member samples from the Moon, dark lunar maria and bright lunar highlands. We used our solar spectrum averaged albedos in a thermal model and compared our model-calculated normal bolometric infrared emission curves with those measured by the LRO Diviner Lunar Radiometer Experiment. We found excellent agreement at the Apollo 11 site, but at the Apollo 16 site, we found that the albedos we measured in the laboratory were 33% brighter than those required to fit the Diviner infrared data. We attribute this difference at Apollo 16 to increased compaction and decreased maturity of the laboratory sample relative to the natural lunar surface, and to local variability in surface albedos at the Apollo 16 field area that are below the spatial resolution of Diviner.

Generation of photoclinometric DTMs for application to transient changes on the surface of comet 67P/Churyumov-Gerasimenko

Context. The wide spatial and temporal coverage of 67P/Churyumov-Gerasimenko (67P) by the Rosetta mission has revealed a surface created by scattered large-scale changes and numerous small-scale changes. The many small-scale changes are of particular interest because they are unexpected and ubiquitous. As their topographic relief is often smaller than one meter, which is below the resolution of any shape models, we need higher resolution topography to analyze them properly. Aims. We describe a photoclinometry method that is able to retrieve surface elevations for a single OSIRIS image of the surface of 67P. With this method, we can provide accurate measures, along with error estimates, of the centimeter-scale topography of observed transient changes. Methods. Photoclinometry, or shape-from-shading, estimates heights by examining the light reflection of the surface as dictated by a photometric model under a specified set of viewing geometries. Assuming a standard photometric model for 67P, we can recreate the shading of a surface under specified viewing geometries. The output is a high-resolution height map that matches the original image pixel by pixel. We then provide estimates of the error in the retrieved heights and ensure that our method is valid with a series of checks. Results. We generate digital terrain models (DTMs) with a vertical resolution comparable to or smaller than the pixel scale. This allows us to accurately measure changes in the surface topography on centimeter scales. We find that most changes within the smooth terrains involve the transport or removal of material thinner than one meter.

Modelling Kepler eclipsing binaries: homogeneous inference of orbital and stellar properties

Abstract We report on the properties of eclipsing binaries (EBs) from the Kepler mission with a newly developed photometric modelling code, which uses the light curve, spectral energy distribution of each binary, and stellar evolution models to infer stellar masses without the need for radial velocity (RV) measurements. We present solutions and posteriors to orbital and stellar parameters for 728 systems, forming the largest homogeneous catalogue of full Kepler binary parameter estimates to date. Using comparisons to published RV measurements, we demonstrate that the inferred properties (e.g. masses) are reliable for well-detached main-sequence (MS) binaries, which make up the majority of our sample. The fidelity of our inferred parameters degrades for a subset of systems not well described by input isochrones, such as short-period binaries that have undergone interactions, or binaries with post-MS components. Additionally, we identify 35 new systems which show evidence of eclipse timing variations, perhaps from apsidal motion due to binary tides or tertiary companions. We plan to subsequently use these models to search for and constrain the presence of circumbinary planets in Kepler EB systems.

Bi-directional reflectance and polarization measurements of pulse-laser irradiated airless body analog materials

Space weathering (SW) processes including solar wind irradiation and micrometeorite bombardment produce nano-phase iron (npFe) and amorphous layers that redden and darken the visible and near-infrared (VNIR) reflectance spectra of the surface of airless bodies. To understand how SW may affect the directional reflectance and polarization properties of regolith layers, we carried out pulsed laser irradiation experiments to simulate micrometeorite bombardment process on olivine (OL), orthopyroxene (OPX), anorthosite (AN), ilmenite (ILM), and JSC-1A Lunar Regolith Simulant (LRS). All samples have been equalized with a size distribution of (<45 μm) and the unsieved LRS with (<1 mm) was also used. Depending on each sample's difficulty level of weathering, 2 to 8 irradiations with single pulse energy of 50 mJ were used in the irradiations. We measured the spectral reflectance from 0.5 to 25 μm, bi-directional reflectance distribution function (BRDF) and polarization phase curves at 0.633 μm of the samples before and after irradiations. Scanning electron microscopic images show that the irradiated samples become rougher with produced melts and agglutinates. The VNIR reflectance spectra of all irradiated samples show prominent darkening and reddening, except for the unsieved LSR sample which shows spectral blueing. Compared to that of the original samples, the BRDF of irradiated OL and OPX have both enhanced back- and forward-scattering components, while the other 4 samples have enhanced backscattering but nearly unchanged (AN, ILM, JSC-1A (<45 μm)) or decreased (JSC-1A (<1 mm)) forward scattering. In general, the irradiated samples have larger positive polarization values DOPmax as compared to the original samples, consistent with the Umov law prediction. Within measurement uncertainties, the irradiated samples did not show systematic changes in the minimum polarization value DOPmin and the polarization inversion angle αinv. Using OL as an example, numerical radiative transfer computations verified that, the BRDF of olivine grains with npFe distributed uniformly inside the grains or coated with npFe have enhanced back- and forward scattering components as compared with that of the original grains, consistent with measurement results. A 5-parameter Hapke photometric model inversion has shown that all sample grains except OPX have become more backscattering (with smaller asymmetry parameters) upon the strongest irradiation as compared with the original ones. These results indicate that the directional reflectance properties of space weathered regolith grains of airless bodies may be more backscattering than that of fresh materials.

Core Cosmology Library: Precision Cosmological Predictions for LSST

Abstract The Core Cosmology Library (CCL) provides routines to compute basic cosmological observables to a high degree of accuracy, which have been verified with an extensive suite of validation tests. Predictions are provided for many cosmological quantities, including distances, angular power spectra, correlation functions, halo bias, and the halo mass function through state-of-the-art modeling prescriptions available in the literature. Fiducial specifications for the expected galaxy distributions for the Large Synoptic Survey Telescope (LSST) are also included, together with the capability of computing redshift distributions for a user-defined photometric redshift model. A rigorous validation procedure, based on comparisons between CCL and independent software packages, allows us to establish a well-defined numerical accuracy for each predicted quantity. As a result, predictions for correlation functions of galaxy clustering, galaxy–galaxy lensing, and cosmic shear are demonstrated to be within a fraction of the expected statistical uncertainty of the observables for the models and in the range of scales of interest to LSST. CCL is an open source software package written in C, with a Python interface and publicly available at https://github.com/LSSTDESC/CCL.

New Horizons Photometry of Pluto's Moon Charon

Abstract The New Horizons spacecraft extended the range in solar phase angle coverage for Pluto’s moon Charon from 1.°8—the maximum observable from Earth—to 170°. This extraordinary expansion in range has enabled photometric modeling and a robust determination of Charon’s phase integral and Bond albedo at visible wavelengths. Photometric modeling shows that Charon is similar in its photometric properties to other icy moons, except that its single particle phase function is more isotropic, suggesting the Kuiper Belt may represent a new regime for surface alteration processes. Charon’s phase integral is 0.70 ± 0.04 and its Bond albedo is 0.29 ± 0.05.

Light Curve Investigation: BN Ari Eclipsing Binary

Investigation of changes in the light of a binary star with plotted light curves, which shows the variation of light during a periodic time, helps us to obtain useful information about the binary systems. In this article, by R-band photometric light curve modeling of BN Ari binary star (in 2015) which is located in Aries constellation, we plot related light curve, obtain new period for the system and calculate the rate of period changes. We also calculate a new ephemeris of such system by fitting a quadratic curve to the O–C values. Finally, we use the Wilson–Devinney code as implemented in the PHOEBE to simulate such a system, and obtain its specific geometrical and physical parameters.

Retrieving soil surface roughness with the Hapke photometric model: Confrontation with the ground truth

Surface roughness can be defined as the mean slope angle integrated over all scales from the grain size to the local topography. It controls the energy balance of bare soils, in particular the angular distribution of scattered and emitted radiation. This provides clues to understand the intimate structure and evolution of planetary surfaces over ages. In this article we investigate the capacity of the Hapke photometric model, the most widely used in planetary science, to retrieve surface roughness from multiangular reflectance data. Its performance is still a question at issue and we lack validation experiments comparing model retrievals with ground measurements. To address this issue and to show the potentials and limits of the Hapke model, we compare the mean slope angle determined from very high resolution digital elevation models of volcanic and sedimentary terrains sampled in the Asal-Ghoubbet rift (Republic of Djibouti), to the photometric roughness estimated by model inversion on multiangular reflectance data measured on the ground (Chamelon field goniometer) and from space (Pleiades images). The agreement is good on moderately rough surfaces, in the domain of validity of the Hapke model, and poor on others.

Assessing Effects of Azimuthally Oriented Roughness on Directional Reflectance of Sand

We measured and compared hyperspectral bidirectional reflectance factors of a sand sample of varying roughness levels using the Goniometer of the Rochester Institute of Technology-Two. We developed a geotechnical routine to generate sand samples of approximately constant density and grain size distribution, but varying roughness levels. In addition, we developed sand samples of two different classes of surface roughness: wave-like and normally distributed. The samples exhibiting normally distributed roughness met several criterion outlined by Hapke in the roughness correction to his photometric model for a smooth sediment surface. We developed a method to empirically forward model the photometric model for a rough surface using roughness metrics derived from digital elevation models of the surface. Our results from empirically forward modeling the correction factor indicate that Hapke's shadowing function does not adequately describe the effects of macroscopic roughness at a subcentimeter scale. In addition, we also performed experiments in which we oriented the surface waves of the wave-like roughness profiles in different orientations to the principal plane of illumination. These results indicate that future photometric models of wave-like roughness should include a description of how multiple scattering increases reflectance within cavities, reducing the effects of shadowing within the cavities. Our results also suggest that since Hapke's model correction for macroscopic roughness assumes that the underlying distribution of surface slopes does not depend on azimuth, it cannot adequately characterize surface roughness when it is both structured and has a preferred orientation.

A Model of Eclipsing Binary System V525 Sgr From CCD Photometry

New BVRI CCD photometry of eclipsing binary system V525 Sgr is presented. It is found that the light curves of V525 Sgr show a typical Eb-type light variation with an O’Connell effect. Photometric solutions and model of V525 Sgr were derived by qualitative fitting method using a Wilson-Devinney program. It showed that the mass ratio, q, of V525 Sgr is 0.55 and it is one of the near-contact binary in which the primary fills its Roche lobe. As the result of light curve fitting. We propose that the O’Connell effect may be attributed to the gas impacts of mass transferring in the system which is represented as a hot spot on the secondary star.

Фотометрическая модель звёздного датчика ориентации

Фотометрическая модель звёздного датчика ориентации