Photometric Colors Research Articles

The Pristine survey – IX. CFHT ESPaDOnS spectroscopic analysis of 115 bright metal-poor candidate stars

ABSTRACT A chemo-dynamical analysis of 115 metal-poor candidate stars selected from the narrow-band Pristine photometric survey is presented based on CFHT high-resolution ESPaDOnS spectroscopy. We have discovered 28 new bright (V < 15) stars with [Fe/H] < −2.5 and 5 with [Fe/H] < −3.0 for success rates of 40 (28/70) and 19 per cent (5/27), respectively. A detailed model atmosphere analysis is carried out for the 28 new metal-poor stars. Stellar parameters were determined from SDSS photometric colours, Gaia DR2 parallaxes, MESA/MIST stellar isochrones, and the initial Pristine survey metallicities, following a Bayesian inference method. Chemical abundances are determined for 10 elements (Na, Mg, Ca, Sc, Ti, Cr, Fe, Ni, Y, and Ba). Most stars show chemical abundance patterns that are similar to the normal metal-poor stars in the Galactic halo; however, we also report the discoveries of a new r-process-rich star, a new CEMP-s candidate with [Y/Ba] > 0, and a metal-poor star with very low [Mg/Fe]. The kinematics and orbits for all of the highly probable metal-poor candidates are determined by combining our precision radial velocities with Gaia DR2 proper motions. Some stars show unusual kinematics for their chemistries, including planar orbits, unbound orbits, and highly elliptical orbits that plunge deeply into the Galactic bulge (Rperi < 0.5 kpc); also, eight stars have orbital energies and actions consistent with the Gaia-Enceladus accretion event. This paper contributes to our understanding of the complex chemo-dynamics of the metal-poor Galaxy, and increases the number of known bright metal-poor stars available for detailed nucleosynthetic studies.

Color speckle measurement of white laser beam emitted from fiber output of RGB laser modules

Color speckle metrics of an RGB-combined white laser beam emitted from an optical fiber output of two types of RGB laser module are measured. A new method for eliminating the effects of a fiber far field pattern from the measured 2D speckle data is employed to calculate the speckle metrics with a statistical accuracy. In this method, unspeckled 2D data of the far field pattern can be directly measured by opening the iris of the speckle measurement equipment. As a result, white photometric speckle contrast and color speckle distribution in CIE1931 chromaticity diagram are, for the first time, successfully obtained by eliminating the far field pattern effects.

On the inclinations of the Jupiter Trojans

Jupiter Trojans are a resonant asteroidal population characterised by photometric colours that are compatible with trans-Neptunian objects, high inclinations, and an asymmetric distribution of the number of asteroids between the two swarms. Different models have been proposed to explain the high inclination of the Trojans and to interpret their relation with the Trans-Neptunian objects, but none of these models can also satisfactorily explain the asymmetry ratio between the number of asteroids in the two swarms. It has recently been found that the asymmetry ratio can arise if Jupiter has migrated inwards through the protoplanetary disc by at least a few astronomical units during its growth. The more numerous population of the leading swarm and the dark photometric colours of the Trojans are natural outcomes of this new model, but simulations with massless unperturbed disc particles led to a flat distribution of the Trojan inclinations and a final total mass of the Trojans that was 3–4 orders of magnitude larger than the current mass. We here investigate the possible origin of the peculiar inclination distribution of the Trojans in the scenario where Jupiter migrates inwards. We analyse different possibilities: (a) the secular evolution of an initially flat Trojan population, (b) the presence of planetary embryos among the Trojans, and (c) capture of the Trojans from a pre-stirred planetesimal population in which Jupiter grows and migrates. We find that the secular evolution of the Trojans and secular perturbations from Saturn do not affect the inclination distribution of the Trojans appreciably, nor is there any significant mass depletion over the age of the Solar System. Embryos embedded in the Trojan swarms, in contrast, can stir the Trojans to their current degree of excitation and can also deplete the swarms efficiently, but it is very difficult to remove all of the massive bodies in 4.5 Gyr of evolution. We propose that the disc where Jupiter’s core was forming was already stirred to high inclination values by other planetary embryos competing in the feeding zone of Jupiter’s core. We show that the trapped Trojans preserve their high inclination through the gas phase of the protoplanetary disc and that Saturn’s perturbations are more effective on highly inclined Trojans, leading to a lower capture efficiency and to a substantial depletion of the swarms during 4.5 Gyr of evolution.

ON THE FON ASTROPLATE PROJECT ACCOMPLISHMENT

The plan of the photographic survey of the northern sky (FON) was proposed in 1976 in Golosiiv ob- servatory (now MAO NAS of Ukraine) by I. Kolchinsky and A. Onegina. The final project of the Compiled FONAC catalog (FON Astrographic Catalog) is based on the digital data of photographic plates exposed at four observatories. They are MAO NAS of Ukraine (Kyiv, Ukraine), Kitab astronomical observatory (Tashkent, Uzbekistan), Hissar astronomical observatory (Dushanbe, Tajikistan), and Bal- done observatory (Latvia)). The total amount of plates is 5700. The result is expected to be the catalog of positions and B-magnitudes of stars covered the declination area from -20 to 90 degrees. The estimated mean epoch of the catalog is ~1987. The limiting B-magnitude is ~17.5 m . The reference system for positions is Tycho-2. B-magnitudes are being obtained in the system of photoelectric standards. The resulted data of photometric reduction are corrected for the photometric color equation in B magnitudes. The com- plement for the photometric content of the catalog is U and V magnitudes of stars being obtained from the processing of 5400 plates from the glass collection of 1.2 m Schmidt telescope in Baldone. Photometric data of bright stars with V < 8.5 m U, B,V magnitudes cannot be obtained from pho- tographic material, so those objects will gain photometric data from photoelectric catalogs. The catalog will be com- plemented with proper motions from GAIA.

The completeness of Gaia-selected samples of white dwarfs

AbstractThe Gaia DR2 has dramatically increased the ability to detect faint nearby white dwarfs. The census of the local white dwarf population has recently been extended from 25 pc to 50 pc, effectively increasing the sample by roughly an order of magnitude. Here we examine the completeness of this new sample as a function of variables such as apparent magnitude, distance, proper motion, photometric color index, unresolved components, etc.

Faint solar analogues at the limit of no reddening

Context. The flux distribution of solar analogues is required for calculating the spectral albedo of solar system bodies such as asteroids and trans-Neptunian objects. Ideally a solar analogue should be comparatively faint as the target of interest, but very few analogues fainter than V = 9 mag have been identified so far. Only atmospheric parameters equal to solar guarantee a flux distribution equal to solar as well, while only photometric colours equal to solar do not. Reddening is also a factor to consider when selecting faint analogue candidates. Aims. Our aim is to implement the methodology for identifying faint analogues at the limit of precision allowed by the current spectroscopic surveys. We quantify the precision attainable for the atmospheric parameters of effective temperature (Teff), metallicity ([Fe/H]), and surface gravity (log g) when derived from moderately low-resolution (R = 8000) spectra with S∕N ~ 100. We estimate the significance of reddening at 100–300 pc from the Sun. Methods. We used the less precise photometry in the HIPPARCOS catalogue to select potential analogues with V ~ 10.5 mag (located at ~135 pc). We calibrated Teff and [Fe/H] as functions of equivalent widths of spectral indices by means of the principal component analysis regression. We derived log g, mass, radius, and age from the atmospheric parameters, Gaia parallaxes, and evolutionary tracks. We evaluated the presence of reddening for the candidates by underestimations of photometric Teff with respect to those derived by spectral indices. These determinations were validated with extinction maps. Results. We obtained the atmospheric parameters Teff, [Fe/H], and log g with precision of 97 K, 0.06 dex, 0.05 dex, respectively. From 21 candidates analysed, we identify five solar analogues: HIP 991, HIP 5811, and HIP 69477 have solar parameters within 1σ errors, and HIP 55619 and HIP 61835 within 2σ errors. Six other stars have Teff close to solar, but slightly lower [Fe/H]. Our analogues show no evidence of reddening except for four stars, that present E(B−V) ≥ 0.06 mag, translating to at least a 200 K decrease in photometric Teff.

A classifier to detect elusive astronomical objects through photometry

ABSTRACT The application of machine learning principles in the photometric search of elusive astronomical objects has been a less-explored frontier of research. Here, we have used three methods, the neural network and two variants of k-nearest neighbour, to identify brown dwarf candidates using the photometric colours of known brown dwarfs. We initially check the efficiencies of these three classification techniques, both individually and collectively, on known objects. This is followed by their application to three regions in the sky, namely Hercules (2° × 2°), Serpens (9° × 4°), and Lyra (2° × 2°). Testing these algorithms on sets of objects that include known brown dwarfs show a high level of completeness. This includes the Hercules and Serpens regions where brown dwarfs have been detected. We use these methods to search and identify brown dwarf candidates towards the Lyra region. We infer that the collective method of classification, also known as ensemble classifier, is highly efficient in the identification of brown dwarf candidates.

Milky Way Tomography with the SkyMapper Southern Survey. I. Atmospheric Parameters and Distances of One Million Red Giants

Abstract Accurate determinations of atmospheric parameters (effective temperature T eff, surface gravity log g, and metallicity [Fe/H]) and distances for large complete samples are of vital importance for various Galactic studies. We have developed a photometric method to select red giant stars and estimate their atmospheric parameters from the photometric colors provided by SkyMapper Southern Survey (SMSS) data release (DR) 1.1, using stars in common with the LAMOST Galactic spectroscopic surveys as a training set. Distances are estimated with two different approaches: one based on the Gaia DR2 parallaxes for nearby (d ≤ 4.5 kpc) bright stars and another based on the absolute magnitudes predicted by intrinsic color (g − i)0 and photometric metallicity [Fe/H] for distant (d &gt; 4.5 kpc) faint stars. Various tests show that our method is capable of delivering atmospheric parameters with a precision of ∼80 K for T eff, ∼ 0.18 dex for [Fe/H], and ∼0.35 dex for log g but with a significant systematic error at log g ∼ 2.3. For distances delivered from (g − i)0 and photometric [Fe/H], our test with the member stars of globular clusters show a median uncertainty of 16% with a negligible zero-point offset. Using this method, the atmospheric parameters and distances of nearly one million red giant stars are derived from SMSS DR1.1. Proper motion measurements from Gaia DR2 are available for almost all of the red giant stars, and radial velocity measurements from several large spectroscopic surveys are available for 44% of these. This sample will be accessible at https://yanghuang0.wixsite.com/yangh/research.

Judd-Ofelt analysis on pH sensitive Eu(tta)3bipy and Eu(dmh)3phen hybrid organic complexes in various organic solvents for solution processed OLEDs

Extremely luminescent Eu(tta)3bipy and Eu(dmh)3phen complexes were synthesized by encapsulating the lanthano-ion Eu(III) with β-diketonates ligands (tta: thenoyltrifluoroacetone and dmh: 2,6-dimethyl-3,5-heptanedione) and neutral ligands (bipy: 2,2′ bipyridine and phen: 1,10 phenanthroline) so as to investigate their photo physical parameters in various organic solvents. Various UV-absorbance based transition parameters, Stokes shift and its dependence on solvent polarity were explored by Lippert-Mataga plot. Judd-Ofelt emissive parameters Ω2 and Ω4 (pH: ranging from 6.0 to 8.0) and photoluminescence quantum yield (PLQY) were calculated in different organic solvents. These architechered complexes, when dissolved in different organic solvents maintained their emission in reddish-orange region, irrespective of polarity of solvents. Photometric parameters-CIE coordinates, dominant wavelength, color purity and Color co-related temperature (CCT) were determined. These results reflect their versatility in the manufacture of solution processed electroluminescent devices such as OLEDs, flat panel displays and solid state lighting technology, wherever reddish-orange emission is highly essential.

Using the Agile software development lifecycle to develop a standalone application for generating colour magnitude diagrams

Virtual observatories allow the means by which an astronomer is able to discover, access, and process data seamlessly, regardless of its physical location. However, steep learning curves are often required to become proficient in the software employed to access, analyse and visualise this trove of data. It would be desirable, for both research and educational purposes, to have applications which allow users to visualise data at the click of a button. Therefore, we have developed a standalone application (written in Python) for plotting photometric Colour Magnitude Diagrams (CMDs) - one of the most widely used tools for studying and teaching about astronomical populations. The CMD Plot Tool application functions "out of the box" without the need for the user to install code interpreters, additional libraries and modules, or to modify system paths; and it is available on multiple platforms. Interacting via a graphical user interface (GUI), users can quickly and easily generate high quality plots, annotated and labelled as desired, from various data sources. This paper describes how CMD Plot Tool was developed using Object Orientated Programming and a formal software design lifecycle (SDLC). We highlight the need for the astronomical software development culture to identify appropriate programming paradigms and SDLCs. We outline the functionality and uses of CMD Plot Tool, with examples of star cluster photometry. All results plots were created using CMD Plot Tool on data readily available from various online virtual observatories, or acquired from observations and reduced with IRAF/PyRAF.

Rainbow cosmic shear: Optimization of tomographic bins

In this paper, we address the problem of finding optimal cosmic shear tomographic bins. We generalize the definition of a cosmic shear tomographic bin to be a set of commonly labeled voxels in photometric color space; rather than bins defined directly in redshift. We explore this approach by using a self-organizing map to define the multidimensional color space, and a we define a ``label space'' of connected regions on the self-organizing map using overlapping elliptical disks. This allows us to then find optimal labeling schemes by searching the label space. We use a metric that is the signal-to-noise ratio of a dark energy equation of state measurement, and in this case we find that for up to five tomographic bins the optimal color-space labeling is an approximation of an equally spaced binning in redshift; that is in all cases the best configuration. We also show that such a redefinition is more robust to photometric redshift outliers than a standard tomographic bin selection.

The color and binarity of (486958) 2014 MU69 and other long-range New Horizons Kuiper Belt targets

The Hubble Space Telescope (HST) measured the colors of eight Kuiper Belt Objects (KBOs) that will be observed by the New Horizons spacecraft including its 2019 close fly-by target the Cold Classical KBO (486958) 2014 MU69. We find that the photometric colors of all eight objects are red, typical of the Cold Classical dynamical population within which most reside. Because 2014 MU69 has a similar color to that of other KBOs in the Cold Classical region of the Kuiper Belt, it may be possible to use the upcoming high-resolution New Horizons observations of 2014 MU69 to draw conclusions about the greater Cold Classical population. Additionally, HST found none of these KBOs to be binary within separations of ~0.06 arcsec (~2000 km at 44 AU range) and Δm ≤ 0.5. This conclusion is consistent with the lower fraction of binaries found at relatively wide separations. A few objects appear to have significant photometric variability, but our observations are not of sufficient signal-to-noise or time duration for further interpretation.

NLTE Stellar Population Synthesis of Globular Clusters Using Synthetic Integrated Light Spectra. II. Expanded Photometry and Sensitivity of Near-IR Spectral Features to Cluster Age and Metallicity

Abstract We present an expanded investigation of the library of globular cluster (GC) synthetic integrated light (IL) spectra of Young &amp; Short, focusing on the impact of non-local thermodynamic equilibrium (NLTE) modeling effects on cluster parameters derived from photometric colors and sensitivity of near-IR spectral features to cluster age and metallicity. Johnson–Cousins–Bessel UBVIJK photometric colors are produced for 910 synthetic IL spectra with two degrees of α enhancement, in both NLTE and local thermodynamic equilibrium (LTE). These color values are used to investigate the GC age–metallicity degeneracy and compare NLTE and LTE derived [M/H] values for NGC 104, NGC 5139, and NGC 6205. For a given age, derived [M/H] values are shown to increase by up to 0.05 dex when modeled in NLTE. A total of 86 spectral lines in the range λ = 12000–22000 Å, representing 14 different atomic species, were identified as sensitive to either cluster age or metallicity, 12 of which were identified as sensitive to both. Equivalent widths of the lines are measured in NLTE and LTE spectra, with NLTE effects changing the widths by up to Å depending on the atomic species.

A High Space Density of L* Active Galactic Nuclei at z ∼ 4 in the COSMOS Field

Abstract Identifying the source population of ionizing radiation, responsible for the reionization of the universe, is currently a hotly debated subject with conflicting results. Studies of faint, high-redshift star-forming galaxies, in most cases, fail to detect enough escaping ionizing radiation to sustain the process. Recently, the capacity of bright quasi-stellar objects to ionize their surrounding medium has been confirmed also for faint active galactic nuclei (AGNs), which were found to display an escaping fraction of ∼74% at z ∼ 4. Such levels of escaping radiation could sustain the required UV background, given the number density of faint AGNs is adequate. Thus, it is mandatory to accurately measure the luminosity function of faint AGNs (L ∼ L*) in the same redshift range. For this reason we have conducted a spectroscopic survey, using the wide field spectrograph IMACS at the 6.5 m Baade Telescope, to determine the nature of our sample of faint AGN candidates in the COSMOS field. This sample was assembled using photometric redshifts, color, and X-ray information. We ended up with 16 spectroscopically confirmed AGNs at down to a magnitude of i AB = 23.0 for an area of 1.73 deg2. This leads to an AGN space density of (corrected) at z ∼ 4 for an absolute magnitude of M 1450 = −23.5. This is higher than previous measurements and seems to indicate that AGNs could make a substantial contribution to the ionizing background at z ∼ 4. Assuming that AGN physical parameters remain unchanged at higher redshifts and fainter luminosities, these sources could be regarded as the main drivers of cosmic reionization.

The radius inflation problem in short-period low-mass binaries: a large sample analysis

Due to the recent increase in the availability of photometric time-series databases, the characterisation of low-mass eclipsing binaries for the study of their orbital and physical parameters is now possible in large samples and with good precision. We have identified and photometrically characterised a sample of 230 detached close-orbiting eclipsing binaries with low-mass main-sequence components in the Catalina Sky Survey. These low-mass stars have masses of $M \leq 1.0\ M_{\odot}$ and orbital periods shorter than $2$ days. The adopted method provided a robust estimate of stellar parameters (as mass and fractional radius) by using only light curves and photometric colours, since no spectroscopic information was available for these objects. A SDSS-2MASS ten-colour grid of composite synthetic and observed colours and the K-Nearest Neighbours method were employed to identify main-sequence stars and to estimate their effective temperatures, typically of $T_{\rm eff}\leq 5720$ K. Each light curve was modelled with the JKTEBOP code together with an asexual genetic algorithm to obtain the most coherent values for the fitted parameters. The present work provides an unprecedented number of homogeneous estimates of main stellar parameters in short-period low-mass binary systems. The distribution of the components of the investigated detached eclipsing binaries in the mass-radius diagram supports a trend of radius inflation on low-mass main-sequence stars. A relative increase of inflation for lower masses is also found and our results suggest that the secondaries are more inflated, i.e. they present larger radii than the primary components of same mass, when compared to stellar evolutionary models.

Searching for the Lowest-metallicity Galaxies in the Local Universe

Abstract We report a method of identifying candidate low-metallicity blue compact dwarf galaxies (BCDs) from the Sloan Digital Sky Survey (SDSS) imaging data, and present 3 m Lick Observatory and 10 m W.M. Keck Observatory optical spectroscopic observations of 94 new systems that have been discovered with this method. The candidate BCDs are selected from Data Release 12 (DR12) of SDSS on the basis of their photometric colors and morphologies. Using the Kast spectrometer on the 3 m telescope, we confirm that the candidate low-metallicity BCDs are emission-line galaxies, and we make metallicity estimates using the empirical R and S calibration methods. Follow-up observations on a subset of the lowest-metallicity systems are made at Keck using the Low Resolution Imaging Spectrometer, which allow for a direct measurement of the oxygen abundance. We determine that 45 of the reported BCDs are low-metallicity candidates with 12 + log(O/H) ≤ 7.65, including six systems which are either confirmed or projected to be among the lowest-metallicity galaxies known, at 1/30 of the solar oxygen abundance, or 12 + log(O/H) ∼ 7.20.

Extended scale invariant local binary pattern for background subtraction

Background subtraction based on change detection is the first step in many video surveillance systems, an effective background subtraction algorithm should distinguish foreground from the background sensitively, and adapt to the variation of background scenes robustly. In this study, the authors propose a robust background subtraction algorithm which takes advantages of local texture features represented by an extended scale invariant local binary pattern and colour intensities to characterise pixel representations. Local texture features achieve good tolerance against illumination variations in rich texture regions but not so efficiently on uniform regions, so a photometric invariant colour measurement is proposed to overcome its limitation. Both quantitative and qualitative evaluations carried out on a well-known change detection dataset are provided to demonstrate the effectiveness of the proposed algorithm.

Planetary nebula distances in Gaia DR2

Context. Planetary nebula distance scales often suffer from model-dependent solutions. Model-independent trigonometric parallaxes have been rare. Space-based trigonometric parallaxes are now available for a larger sample using the second Data Release of Gaia. Aims. We aim to derive a high-quality approach for selection criteria of trigonometric parallaxes for planetary nebulae and discuss possible caveats and restrictions in the use of this Data Release. Methods. A few hundred sources from previous distance scale surveys were manually cross-identified with data from the second Gaia Data Release (DR2) because coordinate-based matching does not work reliably. The data were compared with the results of previous distance scales and to the results of a recent similar study that used the first Data Release Gaia DR1. Results. While the few available previous ground-based trigonometric parallaxes as well as those obtained with the Hubble Space Telescope perfectly match the new data sets, older statistical distance scales, reaching larger distances, do show small systematic differences. When we restrict the comparison to the central stars for which the photometric colors of Gaia show a negligible contamination by the surrounding nebula, the difference is negligible for statistical distances based on radio flux, while those derived from Hα surface brightness still show minor differences. The DR2 study significantly improves the previous recalibration of the statistical distance scales using DR1/TGAS.

Using the CIFIST grid of CO5BOLD 3D model atmospheres to study the effects of stellar granulation on photometric colours

Aims. We studied the influence of convection on the spectral energy distributions (SEDs), photometric magnitudes, and colour indices of different types of stars across the H–R diagram. Methods. The 3D hydrodynamical CO5BOLD, averaged ⟨3D⟩, and 1D hydrostatic LHD model atmospheres were used to compute SEDs of stars on the main sequence (MS), main sequence turn-off (TO), subgiant branch (SGB), and red giant branch (RGB), in each case at two different effective temperatures and two metallicities, [M∕H] = 0.0 and − 2.0. Using the obtained SEDs, we calculated photometric magnitudes and colour indices in the broad-band Johnson-Cousins UBVRI and 2MASS JHKs, and the medium-band Strömgren uvby photometric systems. Results. The 3D–1D differences in photometric magnitudes and colour indices are small in both photometric systems and typically do not exceed ± 0.03 mag. Only in the case of the coolest giants located on the upper RGB are the differences in the U and u bands able reach ≈−0.2 mag at [M∕H] = 0.0 and ≈−0.1 mag at [M∕H] = −2.0. Generally, the 3D–1D differences are largest in the blue-UV part of the spectrum and decrease towards longer wavelengths. They are also sensitive to the effective temperature and are significantly smaller in hotter stars. Metallicity also plays a role and leads to slightly larger 3D–1D differences at [M∕H] = 0.0. All these patterns are caused by a complex interplay between the radiation field, opacities, and horizontal temperature fluctuations that occur due to convective motions in stellar atmospheres. Although small, the 3D–1D differences in the magnitudes and colour indices are nevertheless comparable to or larger than typical photometric uncertainties and may therefore cause non-negligible systematic differences in the estimated effective temperatures.

Surface Ice and Tholins on the Extreme Centaur 2012 DR30

Abstract 2012 is one of the known solar system objects with the largest aphelion distance, exceeding 2200 au, on a high inclination orbit (i = 78°). It has been recognized to be either a borderline representative of high inclination, high perihelion distance (HiHq) objects, or even a new class of bodies, similar to HiHq objects for orbit but with an aphelion in the inner Oort Cloud. Here, we present photometry using long-term data from 2000 to 2013 taken by the SDSS sky survey, ESO MPG 2.2 m and McDonald 2.1 m telescopes, and a visual+near-infrared spectrum taken with the Southern Astrophysical Research Telescope and Magellan telescopes, providing insights into the surface composition of this body. Our best fit suggests that the surface contains 60% of complex organics (30% of Titan and 30% of Triton tholins) with a significant fraction of ice (30%, including pure water and water with inclusions of complex organics) and 10% silicates. The models also suggest a low limit of amorphous carbons, and hence the fragmentation of long-chained complex organics is slower than their rate of generation. 2012 just recently passed the perihelion, and the long-term photometry of the object suggested ambiguous signs of activity, since the long-term photometric scatter well exceeded the supposed measurement errors and the expected brightness variation related to rotation. Photometric colors put 2012 exactly between dark neutral and red objects, thus it either can be in a transition phase between the two classes or have differing surface properties from these populated classes.