Photometric Profiles Research Articles

A Study of the Comets with Large Perihelion Distances C/2019 L3 (ATLAS) and C/2019 O3 (Palomar)

This work analyzes the photometric data of the Oort spike comets C/2019 L3 (ATLAS) and C/2019 O3 (Palomar) obtained between 2016 and 2023 by the ATLAS network and the Belgian Olmen Observatory. The comets Palomar and ATLAS have a typical and unusually high activity level, respectively, based on the Afρ parameter corrected to phase angle zero at perihelion. The absolute magnitude of comets ATLAS and Palomar in the o-band is 4.71 ± 0.05 and 4.16 ± 0.02 respectively. The cometary activity of comets ATLAS and Palomar probably began at r > 13 au before perihelion and will end at r >14 au after perihelion, which means that they could remain active until the second half of 2026. The nucleus of comet ATLAS has a minimum radius of 7.9 km, and the nucleus of comet Palomar could be a little larger. The c − o colors of the comets ATLAS and Palomar are redder and bluer, respectively, at perihelion than the solar twin YBP 1194. These comets showed a bluish trend in the coma color with decreasing heliocentric distance. Comet Palomar probably had two outbursts after its perihelion, each releasing about 108 kg of dust. The slopes of the photometric profile of the comae of these comets were between 1 and 1.5, indicating a steady state during the observation campaign.

Numerical simulations of exocomet transits: Insights from β Pic and KIC 3542116

In recent years, the topic of existence and exploration of exocomets has been gaining increasing attention. The asymmetrical decrease in the star’s brightness due to the passage of a comet-like object in front of the star was successfully predicted. It was subsequently confirmed on the basis of the light curves of stars observed by Kepler and TESS orbital telescopes. Since then, there have been successful attempts to fit the asymmetrical dips observed in the stars’ light curves utilizing a simple 1D model of an exponentially decaying optically thin dust tail. In this work, we propose fitting the photometric profiles of some known exocomet transits based on a Monte Carlo approach to build up the distribution of dust particles in a cometary tail. As the exocomet prototypes, we used the physical properties of certain Solar System comets belonging to the different dynamical groups and moving at heliocentric distances of 0.6 au, 1.0 au, 5.0 au, and 5.5 au. We obtained a good agreement between the observed and modeled transit light curves. We also show that the physical characteristics of dust particles, such as the particle size range, the power index of dust size distribution, the particle terminal velocity, and distance to the host star affect the shape of the transit light curve, while the dust productivity of the comet nucleus and the impact parameter influence its depth and duration. The estimated dust production rates of the transiting exocomets are at the level of the most active Solar System comets.

A photometric study of centaurs 29P/Schwassmann–Wachmann and (2060) Chiron

ABSTRACT This study presents the analysis of forced photometry data in the o and c filters of centaurs 29P/Schwassmann–Wachmann and (2060) Chiron obtained by the ATLAS network between 2015 and 2022. Centaur 29P had 24 outbursts with a median peak brightness of −3.0 and a range of −3.7 mag, regardless of spectral band. Some of these outbursts exhibited an asymmetric light curve with respect to peak brightness, with brightness decreases ranging from −0.22 to −7.6 mag h−1 and durations from 2.8 min to 1.4 d. The slope m of the photometric profile of the coma after/before and during an outburst was ≤1 and >1, respectively, reflecting an increase in brightness at the optocenter of the object. Without the outbursts, 29P has an absolute magnitudes H0 of 9.3 ± 0.2 and 9.10 ± 0.01 in the c and o filters, respectively, and activity indices of n = 11.56 ± 0.08 and 2.1 ± 0.1. Using the Lomb–Scargle periodogram, a periodicity of 0.97 d was found in the c magnitudes after perihelion, probably related to nuclear rotation. The absolute magnitude of Chiron in the HG1G2 system in the o filter is nearly constant between 2017 and 2020, with a weighted mean of 5.35 ± 0.03. In 2021, the brightness increases to H = 4.54 ± 0.03 and decreases to 5.04 ± 0.04 in 2022. This increase in 2021 is not due to outbursts that did not occur during the entire observing campaign, but is related to the increase in opposition effect.

Photometric BVR Observations of (65803) Didymos after DART

The near-Earth binary asteroid Didymos was observed by robotic telescopes in Australia, Chile, and the United States three to five weeks after its impact with the DART spacecraft. The B − R spectral slope of the Didymos system was 13% ± 1%/100 nm, redder than that of the Sun, active comets, and its previously measured colors. The dust cloud around the Didymos system caused a mean drop of 0.29 ± 0.08 mag and had an optical thickness of 0.27 ± 0.07, based on observations from October 27.743 and 28.740 UT. The mean FWHM of the photometric profile of the Didymos system was 1.1 ± 0.1 larger than that of the unsaturated field stars in the R band during our observing campaign. According to our results, the B − R color index was the best parameter to detect the activity of this asteroid in the visible range.

Radial stellar populations, kinematics, and photometry of the cD galaxy NGC 6086 in Abell 2162

ABSTRACT We present a full study of deep optical long-slit spectroscopy and deep broad-band photometry of NGC 6086. We cover up to at least 3re in spectroscopy and 5re in photometry (re ≈ 22 arcsec in our V-band photometry). The envelope first appears in the photometric profile around 23 arcsec, and the velocity dispersion, age, metallicity, and Mg2 indices all show changes starting at about this radius suggesting that we are seeing two separate structures (ellipsoid and envelope) with different properties in the data. We do not find the kinematically decoupled core reported in Carter et al. The velocity dispersion profile rises from 300 km s−1 in the centre to 600 km s−1 at 40 arcsec, a similar tendency to that previously observed in NGC 6166. Populations indicate a trend from old metal-rich stars to younger metal-poorer ones as the radius increases. Line-index analysis indicates that the α-element proportion is high at all radii and that the Mg2 index declines relatively steeply with radius. The photometry shows the extended envelope with a Sérsic index of 0.6 and flat colour gradients. Previous measurements of the velocity dispersion of the galaxies in the cluster A2162 are in the range 300–420 km s−1 for only around 40 member galaxies, but there appears to be a radial discontinuity in the distribution of galaxies and a flattish distribution in radial velocity, implying that the kinematics of this cluster requires further investigation.

Photometric study of the C/2014 Q2 (Lovejoy) comet plasma tails

Observations of C/2014 Q2 (Lovejoy) comet were carried out on 7th February, 2015, at the observation station in Mayaki village (No. 583 – Odesa-Mayaki observatory). The integrated-light photometry of the comet was conducted using RC-800 telescope (D = 80 cm; F = 214.0 cm) with FLI MicroLine 9000 CCD camera. The photometric primary reductions included dark-frame subtraction and flat-field correction. The photometric study of the comet plasma tails was performed using an interactive program to construct a series of longitudinal and transverse profiles of individual tail rays. The Shulman diffusion model was applied to interpret the calculated photometric profiles. The comparison of the experimental profiles and those calculated theoretically from the diffusion model enabled us to estimate the following physical parameters of the comet plasma tail: acceleration a = 176 m/sec2 and lifetime of fluorescent ions τ = 2.7⋅103 s; longitudinal and transverse diffusion coefficients, and magnetic flux density B = 97 ± 5.3 nT.

Photometric Intensity Profiles Analysis for Thick Segment Recognition and Geometric Measures

AbstractThe segmentation or the geometric analysis of specular objects is known as a difficult problem in the computer vision domain. It is also true for the problem of line detection where the specular reflection implies numerous false positive line detection or missing lines located on the dark parts of the object. This limitation reduces its potential use for concrete industrial applications where metallic objects are frequent. In order to overcome this limitation, a new strategy to detect thick segment is proposed. It is not based on the image gradient as usually, but rather exploits the image intensity profile defined inside a parallel strip primitive. Associated to a digital straight segment recognition algorithmwhich is robust to noise, this strategy was implemented to track metallic tubular objects in gray-level images. The efficiency of the proposed method is demonstrated through extensive tests using an actual industrial application. An alternate release intended to overcome the possible impact of the digitization process on the achieved performance is also introduced. Both strategies are discussed at the end of the article.

GHASP: an Hα kinematic survey of spiral galaxies – X. Surface photometry, decompositions and the Tully–Fisher relation in theRcband

We present Rc-band surface photometry for 170 of the 203 galaxies in GHASP, Gassendi H-Alpha survey of SPirals, a sample of late-type galaxies for which high-resolution Fabry-Perot H{\alpha} maps have previously been obtained. Our data set is constructed by new Rc-band observations taken at the Observatoire de Haute-Provence (OHP), supplemented with Sloan Digital Sky Survey (SDSS) archival data, obtained with the purpose of deriving homogeneous photometric profiles and parameters. Our results include Rc-band surface brightness profiles for 170 galaxies and $ugriz$ profiles for 108 of these objects. We catalogue several parameters of general interest for further reference, such as total magnitude, effective radius and isophotal parameters -- magnitude, position angle, ellipticity and inclination. We also perform a structural decomposition of the surface brightness profiles using a multi-component method in order to separate disks from bulges and bars, and to observe the main scaling relations involving luminosities, sizes and maximum velocities. We determine the Rc-band Tully Fisher relation using maximum velocities derived solely from H$\alpha$ rotation curves for a sample of 80 galaxies, resulting in a slope of $-8.1 \pm 0.5$, zero point of $-3.0 \pm 1.0$ and an estimated intrinsic scatter of $0.28 \pm 0.07$. We note that, different from the TF-relation in the near-infrared derived for the same sample, no change in the slope of the relation is seen at the low-mass end (for galaxies with $V_{max} < 125$ km/s). We suggest that this different behaviour of the Tully Fisher relation (with the optical relation being described by a single power-law while the near-infrared by two) may be caused by differences in the stellar mass to light ratio for galaxies with $V_{max} < 125$ km/s.

The dynamics of a gas–dust cloud expansion in the upper atmosphere at a shutdown of solid-propellant rocket engines

The velocity of spherical gas–dust cloud expansion in the situation when the stages of solid-propellant rocket separate in the upper atmosphere have been determined. The measured velocity vary from 2.5 to 7.5 km/s. The dispersed component accelerates at the front of a shock that develops at engine-thrust shutdown. The model calculations of the gas–dust cloud luminosity intensity qualitatively coincide with the photometric profiles of object images. Such formations can vary from almost homogeneous ball-shaped clouds to rather thin spherical shells depending on the gas–dust cloud mass and the matter distribution within this cloud.

Does the stellar disc flattening depend on the galaxy type?

We analyse the dependence of the stellar disc flatness on the galaxy morphological type using 2D decomposition of galaxies from the reliable subsample of the Edge-on Galaxies in SDSS catalogue. Combining these data with the retrieved models of the edge-on galaxies from the Two Micron All Sky Survey and the Spitzer Survey of Stellar Structure in Galaxies catalogue, we make the following conclusions. (1) The disc relative thickness z0/h in the near- and mid-infrared passbands correlates weakly with morphological type and does not correlate with the bulge-to-total luminosity ratio B/T in all studied bands. (2) Applying a 1D photometric profile analysis overestimates the disc thickness in galaxies with large bulges making an illusion of the relationship between the disc flattening and the

Segmentation of brain magnetic resonance images based on multi-atlas likelihood fusion: testing using data with a broad range of anatomical and photometric profiles.

We propose a hierarchical pipeline for skull-stripping and segmentation of anatomical structures of interest from T1-weighted images of the human brain. The pipeline is constructed based on a two-level Bayesian parameter estimation algorithm called multi-atlas likelihood fusion (MALF). In MALF, estimation of the parameter of interest is performed via maximum a posteriori estimation using the expectation-maximization (EM) algorithm. The likelihoods of multiple atlases are fused in the E-step while the optimal estimator, a single maximizer of the fused likelihoods, is then obtained in the M-step. There are two stages in the proposed pipeline; first the input T1-weighted image is automatically skull-stripped via a fast MALF, then internal brain structures of interest are automatically extracted using a regular MALF. We assess the performance of each of the two modules in the pipeline based on two sets of images with markedly different anatomical and photometric contrasts; 3T MPRAGE scans of pediatric subjects with developmental disorders vs. 1.5T SPGR scans of elderly subjects with dementia. Evaluation is performed quantitatively using the Dice overlap as well as qualitatively via visual inspections. As a result, we demonstrate subject-level differences in the performance of the proposed pipeline, which may be accounted for by age, diagnosis, or the imaging parameters (particularly the field strength). For the subcortical and ventricular structures of the two datasets, the hierarchical pipeline is capable of producing automated segmentations with Dice overlaps ranging from 0.8 to 0.964 when compared with the gold standard. Comparisons with other representative segmentation algorithms are presented, relative to which the proposed hierarchical pipeline demonstrates comparative or superior accuracy.

The connection between shape and stellar population in early-type galaxies

AbstractWe comment on the observed connection between the shape of the photometric profiles and the stellar population content in early-type galaxies.

Physical conditions in the chromosphere of a two-strand solar flare with ejection

Chromosphere layers of solar flares were investigated according to the observed profiles of the Hα line. A two-strand flare was observed on September 4, 1990. Spectra were obtained with the ATsU-26 solar horizontal telescope at Terskol Peak Observatory (3100 m). Spectra photometry is performed for two bright nodes of one strand of the flare. Some profiles are superposed to the ejection. The observed profiles are characterized by high emissions in the wings of the Hα line (up to 10–12 A) under relatively low intensity in the center of Hα (r = 0.35–0.6). To explain such profile behavior we calculated flare models with two or three components. Separate components of the model correspond to unresolved details in the flare area and therefore the averaged profile is calculated. Emission in the far wings is explained by model components with deep heating of chromosphere layers. These occupy 5–12% of the total area. Noticeable emission asymmetry is explained by ray velocities of up to 70 km/s and more. The models are determined by agreement of the observed and calculated profiles. We processed several photometric profiles for seven observations. The temperature in the models with deep heating in the lower cromosphere is increased by 1000–2500 K with respect to the model with an undisturbed chromosphere VAL-C. The second feature of the observed profiles is their high asymmetry and shift with respect to the undisturbed profiles. This can be explained by the opposite motion of the material. We revealed that for the most of the profiles the line-of-sight velocities were directed to the observer in the upper chromosphere (10–100 km/s) and from the observer in the lower chromosphere (5–20 km/s).

THE CATALOG OF EDGE-ON DISK GALAXIES FROM SDSS. I. THE CATALOG AND THE STRUCTURAL PARAMETERS OF STELLAR DISKS

We present a catalog of true edge-on disk galaxies automatically selected from the Seventh Data Release (DR7) of the Sloan Digital Sky Survey. A visual inspection of the $g$, $r$ and $i$ images of about 15000 galaxies allowed us to split the initial sample of edge-on galaxy candidates into 4768 (31.8% of the initial sample) genuine edge-on galaxies, 8350 (55.7%) non-edge-ons, and 1865 (12.5%) edge-on galaxies not suitable for simple automatic analysis because these objects show signs of interaction, warps, or nearby bright stars project on it. We added more candidate galaxies from RFGC, EFIGI, RC3, and Galaxy Zoo catalogs found in the SDSS footprints. Our final sample consists of 5747 genuine edge-on galaxies. We estimate the structural parameters of the stellar disks (the stellar disk thickness, radial scale length, and central surface brightness) in the galaxies by analyzing photometric profiles in each of the g, r, and i images. We also perform simplified 3-D modeling of the light distribution in the stellar disks of edge-on galaxies from our sample. Our large sample is intended to be used for studying scaling relations in the stellar disks and bulges and for estimating parameters of the thick disks in different types of galaxies via the image stacking. In this paper we present the sample selection procedure and general description of the sample.

The intrinsic shape of galaxies in SDSS/Galaxy Zoo

By modelling the axis ratio distribution of SDSS DR8 galaxies we find the intrinsic 3D shapes of spirals and ellipticals. We use morphological information from the Galaxy Zoo project and assume a non-parametric distribution intrinsic of shapes, while taking into account dust extinction. We measure the dust extinction of the full sample of spiral galaxies and find a smaller value than previous estimations, with an edge-on extinction of $E_0 = 0.284^{+0.015}_{-0.026}$ in the SDSS r band. We also find that the distribution of minor to major axis ratio has a mean value of $ 0.267 \pm 0.009 $, slightly larger than previous estimates mainly due to the lower extinction used; the same affects the circularity of galactic discs, which are found to be less round in shape than in previous studies, with a mean ellipticity of $0.215 \pm 0.013$. For elliptical galaxies, we find that the minor to major axis ratio, with a mean value of $0.584 \pm 0.006$, is larger than previous estimations due to the removal of spiral interlopers present in samples with morphological information from photometric profiles. These interlopers are removed when selecting ellipticals using Galaxy Zoo data. We find that the intrinsic shapes of galaxies and their dust extinction vary with absolute magnitude, colour and physical size. We find that bright elliptical galaxies are more spherical than faint ones, a trend that is also present with galaxy size, and that there is no dependence of elliptical galaxy shape with colour. For spiral galaxies we find that the reddest ones have higher dust extinction as expected, due to the fact that this reddening is mainly due to dust. We also find that the thickness of discs increases with luminosity and size, and that brighter, smaller and redder galaxies have less round discs.

WSRT observations and surface photometry of two unusual spiral galaxies

We discuss the results of a mass decomposition of two spiral galaxies, NGC 6824 and UGC 11919. In a previous analysis of the Hyperleda catalog, the galaxies were identified as having a peculiar dynamical $M/L$. The aim of this study is to confirm or disprove the preliminary findings, indicating a non-standard stellar initial mass function (IMF) for the galaxies. The surface photometry in B, V, and R bands was carried out with the Apache Point 0.5-m telescope and the \ion{H}{I} data cubes were obtained with the Westerbork Synthesis Radio Telescope (WSRT). Photometric profiles were decomposed into bulge and exponential disk components. Using the obtained \ion{H}{I} data cubes, rotation curves of both galaxies were constructed. Employing the photometric profiles, the mass distribution of the galaxies was decomposed into mass components: bulge, stellar disk, gas, and pseudo-isothermal dark halo. We conclude that NGC 6824 possesses a stellar disk with mass-to-light ratio $(M/L_B)_{\rm disk} = 2.5$, in agreement with its color $(B-V)_0$. On the contrary, UGC 11919 appears to have a very lightweight disk. Its dynamically estimated mass corresponds to a low stellar disk mass-to-light ratio $(M/L_B)_{\rm disk} \approx 0.5$. Under standard assumptions, this ratio does not agree with the relatively red color of the disk, while a bottom light stellar initial mass function is needed to explain the observations.

A dynamical study of Galactic globular clusters under different relaxation conditions

We perform a systematic combined photometric and kinematic analysis of a sample of globular clusters under different relaxation conditions, based on their core relaxation time (as listed in available catalogs), by means of two well-known families of spherical stellar dynamical models. Systems characterized by shorter relaxation time scales are expected to be better described by isotropic King models, while less relaxed systems might be interpreted by means of non-truncated, radially-biased anisotropic f^(\nu) models, originally designed to represent stellar systems produced by a violent relaxation formation process and applied here for the first time to the study of globular clusters. The comparison between dynamical models and observations is performed by fitting simultaneously surface brightness and velocity dispersion profiles. For each globular cluster, the best-fit model in each family is identified, along with a full error analysis on the relevant parameters. Detailed structural properties and mass-to-light ratios are also explicitly derived. We find that King models usually offer a good representation of the observed photometric profiles, but often lead to less satisfactory fits to the kinematic profiles, independently of the relaxation condition of the systems. For some less relaxed clusters, f^(\nu) models provide a good description of both observed profiles. Some derived structural characteristics, such as the total mass or the half-mass radius, turn out to be significantly model-dependent. The analysis confirms that, to answer some important dynamical questions that bear on the formation and evolution of globular clusters, it would be highly desirable to acquire larger numbers of accurate kinematic data-points, well distributed over the cluster field.

Estimating the standard uncertainty contribution of the straight-line fit algorithm used to determine the position and the width of a graduation line

We propose an implementation of the straight-line fit algorithm to evaluate data obtained as part of measurements of line structures, e.g. a grating line, which allows us to determine, at a conventional threshold value, the coordinates of the edges, the position and the width of its photometric profile as well as the related standard uncertainty contribution. These are derived for the (1 − α)100% confidence intervals with α ∊ [0, 1]. The implementation is demonstrated using data obtained by the PTB Nanometer Comparator (Fluegge and Köning 2001 Proc. SPIE 4401 275–83). The investigation revealed that large parts of the uncertainty of the position and the width of the line are due to the choice of the fit interval and the uncertainty of the determination of the minimum and maximum level of the photoelectric signal of the line.

Constrain the stellar population gradient of elliptical galaxies with SED

AbstractWe use multiple wavelength photometric data, from Optical to NIR, to determine the radial gradient of stellar populations of nearby elliptical galaxies. Empirical model, such as the Sersic profile, is assumed to describe the radial stellar distribution, and the metallicity gradient is parameterlized in this model. The PSF effects of different wavebands are also involved to predict the photometric profiles which can be compared with observational surface brightness profile directly. For most of elliptical galaxies, they have negative gradients, which means their central parts is metal rich than outer parts. We also found the gradient is significantly correlated to the stellar mass of the whole galaxy. More massive elliptical galaxies have shallower gradients. But for our sample galaxies, their is no correlations between Sersic n and mass, and between Sersic n and gradient can be found.

A Morphological Study of UV-Bright Stars and Emission Nebulae in a Selection of Star Formation Regions in M31

ABSTRACTUsing the data from the NOAO Local Group Survey, we have measured the Hα fluxes of 291 nebulae associated with 21 of the van den Bergh OB associations. We have combined these data together with six-color HST WFPC2 photometry, in order to identify the most UV-bright stars in the region. The simple purpose of this article is to explore the spatial relationships between these components. We find that there are basically three types of Hα-hot star morphology. One type consists of a very bright H II region, with a tightly spaced group of hot stars at or near its center; we refer to these as monolithic structures. A second common arrangement is that of a ringlike bubble structure with an often-empty central area, where the hot stars are concentrated. We construct simple models of these objects, which show that their photometric profiles are like those of spherical shells. We refer to these as bubble structures A third morphology is a scattered distribution of small nebulae with a few hot stars that are widely spaced; these are called dispersed structures. We suggest that this sequence may be an evolutionary one.