Color Diagrams Research Articles

Relativistic X-ray reflection and photoionized absorption in the neutron star low-mass X-ray binary GX 13+1

ABSTRACT We analysed a dedicated NuSTAR observation of the neutron star low-mass X-ray binary Z-source GX 13+1 to study the timing and spectral properties of the source. From the colour–colour diagram, we conclude that during that observation the source transitioned from the normal branch to the flaring branch. We fitted the spectra of the source in each branch with a model consisting of an accretion disc, a Comptonized blackbody, relativistic reflection (relxillNS), and photoionized absorption (warmabs). Thanks to the combination of the large effective area and good energy resolution of NuSTAR at high energies, we found evidence of relativistic reflection in both the Fe K line profile and the Compton hump present in the 10–25 keV energy range. The inner disc radius is Rin ≲ 9.6 rg , which allowed us to further constrain the magnetic field strength to B ≲ 1.8 × 108 G. We also found evidence for the presence of a hot wind leading to photoionized absorption of Fe and Ni, with a Ni overabundance of ∼6 times solar. From the spectral fits, we find that the distance between the ionizing source and the slab of ionized absorbing material is ∼4–40 × 105 km. We also found that the width of the boundary layer extends ∼3 km above the surface of a neutron star, which yielded a neutron star radius RNS ≲ 16 km. The scenario inferred from the spectral modelling becomes self-consistent only for high electron densities in the accretion disc, ne ∼ 1022 − 1023 cm−3, as expected for a Shakura–Sunyaev disc, and significantly above the densities provided by relxillNS models. These results have implications for our understanding of the physical conditions in GX 13+1.

PAH Emission from Star-forming Galaxies in JWST Mid-infrared Imaging of the Lensing Cluster SMACS J0723.3-7327

The mid-infrared spectra of star-forming galaxies (SFGs) are characterized by characteristic broad polycyclic aromatic hydrocarbon (PAH) emission features at 3–20 μm. As these features are redshifted, they are predicted to dominate the flux at specific mid-infrared wavelengths, leading to substantial redshift-dependent color variations in broadband photometry. The advent of JWST for the first time allows the study of this effect for normal SFGs. Based on spectral energy distribution templates, we here present tracks in mid-infrared (4.4, 7.7, 10, 15, and 18 μm) color–color diagrams describing the redshift dependence of SFG colors. In addition, we present simulated color–color diagrams by populating these tracks using the cosmic star formation history and the star formation rate function. Depending on redshift, we find that SFGs stand out in the color–color diagrams by several magnitudes. We provide the first observational demonstration of this effect for galaxies detected in the JWST Early Release Observations of the field toward the lensing cluster SMACS J0723.3−7327. While the distribution of detected galaxies is consistent with the simulations, the numbers are substantially boosted by lensing effects. The PAH emitter with the highest spectroscopic redshift, detected in all bands, is a multiply imaged galaxy at z = 1.45. There is also a substantial number of cluster members that do not exhibit PAH emission except for one SFG at z = 0.38. Future wider-field observations will further populate mid-infrared color–color diagrams and provide insight into the evolution of typical SFGs.

Identifying and characterising the population of hot sub-luminous stars with multi-colour MeerLICHT data

Context. Colour–magnitude diagrams reveal a population of blue (hot) sub-luminous objects with respect to the main sequence. These hot sub-luminous stars are the result of evolutionary processes that require stars to expel their obscuring, hydrogen-rich envelopes to reveal the hot helium core. As such, these objects offer a direct window into the hearts of stars that are otherwise inaccessible to direct observation. Aims. MeerLICHT is a wide-field optical telescope that collects multi-band photometric data in six band filters (u, g, r, i, z, and q), whose primary goals are to study transient phenomena, gravitational wave counterparts, and variable stars. We showcase MeerLICHT’s capabilities of detecting faint hot subdwarfs and identifying the dominant frequency in the photometric variability of these compact hot stars, in comparison to their Gaia DR3 data. We hunt for oscillations, which will be an essential ingredient for accurately probing stellar interiors in future asteroseismology. Methods. Comparative MeerLICHT and Gaia colour–magnitude diagrams are presented as a way to select hot subdwarfs from our sample. A dedicated frequency determination technique is developed and applied to the selected candidates to determine their dominant variability using time-series data from MeerLICHT and Gaia DR3. We explore the power of both datasets in determining the dominant frequency. Results. Using the g − i colour, MeerLICHT offers a colour–magnitude diagram that is comparable in quality to that of Gaia DR3. The former, however, is more sensitive to fainter objects. The MeerLICHT colour–colour diagrams allow for the study of different stellar populations. The frequency analysis of MeerLICHT and Gaia DR3 data demonstrates the superiority of our MeerLICHT multi-colour photometry in estimating the dominant frequency compared to the sparse Gaia DR3 data. Conclusions. MeerLICHT’s multi-band photometry leads to the discovery of high-frequency faint subdwarfs. Continued observations tuned to asteroseismology will allow for mode identification using the method of amplitude ratios. Our MeerLICHT results are a proof-of-concept of the capacity of the BlackGEM instrument currently in the commissioning stage at ESO’s La Silla Observatory in Chile.

AGN candidates in the VVV near-IR galaxy catalogue

ABSTRACTThe goal of this work is to search for Active Galactic Nuclei (AGN) in the Galactic disc at very low latitudes with |b| < 2°. For this, we studied the five sources from the VVV near-infrared (IR) galaxy catalogue that have also WISE counterparts and present variability in the VIrac VAriable Classification Ensemble (VIVACE) catalogue. In the near-IR colour–colour diagrams, these objects have in general redder colours compared to the rest of the sources in the field. In the mid-IR ones, they are located in the AGN region, however, there is a source that presents the highest interstellar extinction and different mid-IR colours to be a young stellar object (YSO). We also studied the source variability using two different statistical methods. The fractional variability amplitude σrms ranges from 12.6 to 33.8, being in concordance with previous results found for type-1 AGNs. The slopes of the light curves are in the range (2.6 − 4.7) × 10−4 mag d–1, also in agreement with results reported on quasars variability. The combination of all these results suggest that four galaxies are type-1 AGN candidates, whereas the fifth source likely a YSO candidate.

Development of a 3D Color Diagram for Improved Visual Grading System of Cotton

Development of a 3D Color Diagram for Improved Visual Grading System of Cotton

Synthesis and characterization of europium (III), terbium (III) complexes and their mixture for making white light emission powder

The enhanced luminescence of lanthanide complexes coordinated to antenna ligands has potential applications for developing devices like screens and lamps. Herein, three β-diketone antenna ligands were incorporated into Eu(III) and Tb(III) metals to synthesize five complexes. Their luminescence properties in solid state and the energy levels of the electronic states for the ligands and the metals were recorded and probed by UV–vis and fluorescence spectroscopies. Under UV light, a white-light emission powder was observed by mixing red-emission europium and green-emission terbium complexes, with blue-emission laundry powder. The powder composition was tuned by using spectroscopic analysis and CIE 1931 color diagram.

Investigation of the connection between X-ray binaries and compact star clusters in NGC 628

ABSTRACTWe investigated for a possible connection between the types of X-ray binaries (XRBs) and the properties of compact star clusters in the nearby galaxy NGC 628. Using Chandra archival data covering the years 2001–2018, 75 X-ray sources were detected within the field of view of observations. A total of 69 XRBs, one of which is an ultraluminous X-ray source (ULX), were found to be in the luminosity range of 3 × 1036 ≤ LX ≤ 2 × 1039 erg s−1. We identified the optical counterpart(s) of 15 of the 42 XRBs that coincide with the HST field of view via improved astrometry. We classified 15 of them as HMXBs based on the presence of the optical counterparts. The remaining sources with no optical counterparts were classified as LMXBs. We also search compact star clusters in this galaxy using the multiband optical images drawn from HST archives. 864 compact star clusters were identified and their ages and masses were determined by applying the best-fit SSP (Simple Stellar Population) model to their colour–colour diagram. We found that in NGC 628, HMXBs are associated with younger star clusters and LMXBs with older ones. Our findings support a connection between different types of XRBs and cluster ages, already known to exist for other galaxies.

Early JWST Imaging Reveals Strong Optical and NIR Color Gradients in Galaxies at z ∼ 2 Driven Mostly by Dust

Recent studies have shown that galaxies at cosmic noon are redder in the center and bluer in the outskirts, mirroring results in the local universe. These color gradients could be caused by gradients in either the stellar age or dust opacity; however, distinguishing between these two causes is impossible with rest-frame optical photometry alone. Here we investigate the underlying causes of the gradients from spatially resolved rest-frame U − V versus V − J color–color diagrams measured from early observations with the James Webb Space Telescope. We use 1–4 μm NIRCam photometry from the CEERS survey of a sample of 54 galaxies with at redshifts 1.7 < z < 2.3 selected from the 3D-HST catalog. We model the light profiles in the F115W, F200W, and F356W NIRCam bands using imcascade, a Bayesian implementation of the multi-Gaussian expansion technique that flexibly represents galaxy profiles using a series of Gaussians. We construct resolved rest-frame U − V and V − J color profiles. The majority of star-forming galaxies have negative gradients (i.e., redder in the center, bluer in the outskirts) in both U − V and V − J colors consistent with radially decreasing dust attenuation. A smaller population (roughly 15%) of star-forming galaxies have positive U − V but negative V − J gradients implying centrally concentrated star formation. For quiescent galaxies, we find a diversity of UVJ color profiles, with roughly one-third showing star formation in their center. This study showcases the potential of JWST to study the resolved stellar populations of galaxies at cosmic noon.

Multi-primary human-centric lighting based on the optical power ratio and the CCT super-smooth switching algorithms

The discovery of intrinsically photosensitive retinal ganglion cells related to circadian rhythms has led to an increased research focus on the physiological and psychological effects of artificial lighting sources, with the emerging concept of human-centric lighting. This study tuned the spectra of a six-primary lighting source based on pulse width modulation to obtain the best visual and non-visual performances in work, leisure, and daytime indoor applications. The adopted method uses indicators, including the circadian action factor, goodness-of-fit coefficient, color rendering index, and correlated color temperature (CCT). Among these, a CCT super-smooth switching algorithm has been proposed to achieve the change trajectory of the chromaticity coordinates in the Commission Internationale de L'Eclairage color diagram close to the blackbody radiation curve during the CCT switching process in different cases. Finally, this study can provide useful guidance for improving light qualities and achieving human-centric lighting based on a six-primary lighting source with light-emitting diodes.

The Relation between Globular Cluster Systems and Supermassive Black Holes in Spiral Galaxies. III. The Link to the M •–M * Correlation

We continue to explore the relationship between the total number of globular clusters (GCs), N GC, and the central black hole mass, M •, in spiral galaxies. We present here results for the Sab galaxies NGC 3368, NGC 4736 (M94), and NGC 4826 (M64), and the Sm galaxy NGC 4395. The GC candidate selection is based on the (u* – ) versus ( – K s ) color–color diagram, and -band shape parameters. We determine the M • versus N GC correlation for these spirals, plus NGC 4258, NGC 253, M104, M81, M31, and the Milky Way. We also redetermine the correlation for the elliptical sample in Harris et al., with updated galaxy types from Sahu et al. Additionally, we derive the total stellar galaxy mass, M *, from its two-slope correlation with N GC, and fit M • versus M * for both spirals and ellipticals. We obtain log M • ∝ (1.01 ± 0.13) log N GC for ellipticals, and log M • ∝ (1.64 ± 0.24) log N GC for late-type galaxies (LTGs). The linear M • versus N GC correlation in ellipticals could be due to statistical convergence through mergers, unlike the much steeper correlation for LTGs. However, in the M • versus total stellar mass (M *) parameter space, with M * derived from its correlation with N GC, M • ∝ (1.48 ± 0.18) log M * for ellipticals, and M • ∝ (1.21 ± 0.16) log M * for LTGs. The observed agreement between ellipticals and LTGs in this parameter space may imply that black holes and galaxies coevolve through calm accretion, active galactic nuclei feedback, and other secular processes.

Machine Learning to Search for Accreting Neutron Star Binary Candidates Using Chinese Space Station Telescope Photometric System

Accreting neutron star binary (ANSB) systems can provide some important information about neutron stars (NSs), especially on the structure and the equation of state of NSs. However, only a few ANSBs are known so far. The upcoming Chinese Space Station Telescope (CSST) provides an opportunity to search for a large number of ANSB candidates. We aim to investigate whether or not a machine learning method may efficiently search for ANSBs based on CSST photometric system. In this paper, we generate some ANSBs and normal binaries under CSST photometric system by binary evolution and binary population synthesis method and use a machine learning method to train a classification model. We consider the classical multi-color disk and the irradiated accretion disk, then compare their effects on the classification results. We find that no matter whether the X-ray reprocessing effect is included or not, the machine learning classification accuracy is always very high, i.e., higher than 96%. If a significant magnitude difference exists between the accretion disk and the companion of an ANSB, machine learning may not distinguish it from some normal stars such as massive main sequence stars, white dwarf binaries, etc. False classifications of the ANSBs and the normal stars highly overlap in a color–color diagram. Our results indicate that machine learning would be a powerful way to search for potential ANSB candidates from the CSST survey.

XGAPS: a sub-arcsec cross-match of galactic plane surveys

ABSTRACT We present a sub-arcsec cross-match of Gaia Data Release 3 (DR3) against the INT Galactic Plane Surveys (IGAPS) and the United Kingdom Infrared Deep Sky Survey (UKIDSS). The resulting cross-match of Galactic Plane Surveys (XGAPS) provides additional precise photometry (URGO, g, r, i, Hα, J, H, and K) to the Gaia photometry. In building the catalogue, proper motions given in Gaia DR3 are wound back to match the epochs of the IGAPS constituent surveys (INT Photometric HαSurvey of the Northern Galactic Plane, IPHAS, and the UV-Excess Survey of the Northern Galactic Plane, UVEX) and UKIDSS, ensuring high-proper motion objects are appropriately cross-matched. The catalogue contains 33 987 180 sources. The requirement of &amp;gt;3σ parallax detection for every included source means that distances out to 1–1.5 kpc are well covered. In producing XGAPS, we have also trained a Random Forest classifier to discern targets with problematic astrometric solutions. Selection cuts based on the classifier results can be used to clean colour-magnitude and colour–colour diagrams in a controlled and justified manner, as well as producing subsets of astrometrically reliable targets. We provide XGAPS as a 111 column table. Uses of the catalogue include the selection of Galactic targets for multi-object spectroscopic surveys as well as identification of specific Galactic populations.

Investigation of photoluminescence properties and energy transfer in Sm3+ and Eu3+ co-doped Na2Ca(SO4)2 nanophosphors prepared by combustion technique

A series of Na2Ca(SO4)2 nano phosphors doped singly with Sm3+(1 mol%) and Eu3+ (1 mol%) ions and co-doped with Sm3+(1 mol%) and Eu3+(x)(where x = 0.5, 1.0 and 1.5 mol%) ions were synthesized using a chemical combustion method. Structural, morphological and optical properties of prepared nanophosphors were studied using X-ray diffraction (XRD), Field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), Diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) characterization techniques. XRD results confirmed that prepared nanophosphors are crystalized in a monoclinic phase with space groups of C2/c. Surface morphological studies indicate that the addition of dopants into the Na2Ca(SO4)2 phosphors could have influenced the particle sizes and shapes and their agglomeration. Optical band gap energy values were calculated from the Kubelka-Munk theory using the reflection spectra data. All of the Na2Ca(SO4)2 nanophosphors series were excited with different ultraviolet (UV) excitation such as 403 nm and 394 nm wavelength to investigate the PL features of the Sm3+ and Eu3+ ions, respectively. When Sm3+ ions excited were under 404 nm wavelength, it is observed that in addition to Sm3+ ions, Eu3+ ion emission was found in the PL spectra. This was due to the energy transfer from Sm3+ ions to the Eu3+ ions in the Na2Ca(SO4)2: Sm3+, Eu3+ (1.5 mol%) nanophosphors. Using the PL data, Commission Internationale de l'Elcairage (CIE) color coordinates were obtained. Using the CIE color diagram these coordinates were found to be lying in the orange and red color region. For increasing Eu3+ ion concentration, a color shift from orange to red was obtained and found to be tunable in the pure red color emission for an increasing Eu3+ ion concentration in the Na2Ca(SO4)2 nanophosphors. From all the results, it is noticed that Sm3+ and Eu3+co-doped Na2Ca(SO4)2 materials are potential candidates for efficient orange and red emitting luminescent phosphors for application in white light emitting diodes (W-LEDs).

The concentration effect of Ce3+ ions on the photoluminescence properties of the host sensitized NaMPO4-Ce3+ (M = Mg and Ca) phosphors via solid-state reaction method

A series of Ce3+ doped NaMPO4 (M = Mg and Ca) nanophosphors were prepared using the solid-state reaction route, annealed at 900 °C for 4 h (except for NaMgPO4 which was annealed at 780 °C for 4 h). In this study, the concentration effects of Ce3+ ions for x = 0.0, 0.1, 0.5, 1.0, 1.5 and 2.0 mol% were investigated for its structural and photoluminescence (PL) properties. The structural and PL properties of the NaMPO4:xCe3+ compounds were analyzed using different characterization techniques, such as X-Ray diffraction (XRD), Field Emission Scanning Microscopy (FE-SEM), UV–vis diffuse reflection spectroscopy (DRS), Fourier Transform Infrared Spectroscopy (FTIR), PL and International Commission on Illumination (CIE) colour coordinates. XRD results confirm the prepared phosphors were crystallized into monoclinic (NaMgPO4) and orthorhombic (NaCaPO4) structures. SEM results confirm that all prepared samples were formed in the micrometer dimension range, with different sizes and shapes. Energy dispersive X-ray spectroscopy (EDS) spectra confirm the presence of chemical elements in the prepared nanophosphors. The presence of all phosphate (PO43−) and other structural groups were confirmed through FTIR measurements. UV–vis DRS measurements were used to calculate the optical band gap energy values via the Kubelka-Munk function theory. The PLE spectra of the NaMPO4:xCe3+ phosphors were measured in the 200–300 nm range by monitoring their peak at the 385 nm emission wavelength. Using 281 nm excitation wavelength, the PL spectra were measured and a high intensity emission band was found at the 385 nm wavelength (violet colour region). Using PL data of all NaMPO4:xCe3+ ion nanophosphors, the CIE colour coordinates were calculated and were found to lie in the violet colour region of the CIE colour diagram. From all the PL results, it is noticed that enhanced violet colour emissions were observed for all NaMPO4:xCe3+ compounds with increasing Ce3+ ion concentrations, implying that NaMPO4:xCe3+ phosphors are potential candidates for violet colour emitting technologies in display systems.

Maxwell's color box: Retracing the path of color matching experiments

In his 1860 paper On the theory of compound colours, James Clerk Maxwell described an instrument used to obtain a direct comparison between daylight and a mixture of three selected spectral colors. This investigation was part of Maxwell's study of human color vision, color perception, and color representation, and it encompasses his main achievements in the field. The working principle underlying this device provided the basis from which color diagrams have been derived, beginning with the standard chromaticity diagram proposed by the International Commission on Illumination in 1931. We describe a reconstruction of Maxwell's original version of the color box. Constructing and analyzing data obtained with such a replica could serve as a semester project for advanced optics students.

Aging of galaxies along the morphological sequence, marked by bulge growth and disk quenching

Aims. We revisit the color bimodality of galaxies using the extensive EFIGI morphological classification of nearby galaxies. Methods. The galaxy profiles from the Sloan Digital Sky Survey (SDSS) gri images were decomposed as a bulge and a disk by controlled profile modeling with the Euclid SourceXtractor++ software. The spectral energy distributions from our resulting gri SDSS photometry complemented with Galaxy Evolution Explorer (GALEX) NUV photometry were fitted with the ZPEG software and PEGASE.2 templates in order to estimate the stellar masses and specific star formation rates (sSFR) of whole galaxies as well as their bulge and disk components. Results. The absolute NUV−r color versus stellar mass diagram shows a continuous relationship between the present sSFR of galaxies and their stellar mass, which spans all morphological types of the Hubble sequence monotonously. Irregular galaxies to intermediate-type Sab spirals make up the “Blue Cloud” across 4 orders of magnitude in stellar mass but a narrow range of sSFR. This mass build-up of spiral galaxies requires major mergers, in agreement with their frequently perturbed isophotes. At high mass, the Blue Cloud leads to the “Green Plain”, dominated by S0a and Sa early-type spirals. It was formerly called the “Green Valley”, due to its low density, but we rename it because of its wide stretch and nearly flat density over ∼2 mag in NUV−r color (hence sSFR), despite a limited range of stellar mass (1 order of magnitude). The Green Plain links up the “Red Sequence”, containing all lenticular and elliptical galaxies with a 2 order of magnitude mass interval, and systematically higher masses for the ellipticals. We confirm that the Green Plain cannot be studied using u − r optical colors because it is overlayed by the Red Sequence, hence NUV data are necessary. Galaxies across the Green Plain undergo a marked growth by a factor 2 to 3 in their bulge-to-total mass ratio and a systematic profile change from pseudo to classical bulges, as well as a significant reddening due to star formation fading in their disks. The Green Plain is also characterized by a maximum stellar mass of 1011.7 M⊙ beyond which only elliptical galaxies exist, hence supporting the scenario of ellipticals partly forming by major mergers of massive disk galaxies. Conclusions. The EFIGI attributes indicate that dynamical processes (spiral arms and isophote distortions) contribute to the scatter of the Main Sequence of star-forming galaxies (Blue Cloud), via the enhancement of star formation (flocculence, HII regions). The significant bulge growth across the Green Plain confirms that it is a transition region, and excludes a predominantly quick transit due to rapid quenching. The high frequency of bars for all spirals as well as the stronger spiral arms and flocculence in the knee of the Green Plain suggest that internal dynamics, likely triggered by flybys or (mainly minor) mergers, may be the key to the bulge growth of massive disk galaxies, which is a marker of the aging of galaxies from star forming to quiescence. The Hubble sequence can then be considered as an inverse sequence of galaxy physical evolution.

AstroSat view of ‘Clocked’ burster GS 1826-238: broad-band spectral nature of persistent and burst emission during soft state

ABSTRACT In this paper, we have carried out a detailed study of the ‘Clocked’ burster GS 1826 − 238 using ∼ 90 ks broad-band (0.7–60.0 keV) data obtained with AstroSat observatory. The source was observed during a soft spectral state and traced a ‘banana’ type track in the colour–colour diagram (CCD). We find that a combination of thermal component (multi-colour disc/bbodyrad) and Comptonized component is statistically good description for all the sections of the track in the CCD. The corona becomes optically thick (τ increases from ∼ 5 to 21) and cooler (kTe decreases from ∼ 4.8 to 2.2 keV) as the source moves up in the ‘banana’ branch. Probably cooling is caused by increase in the supply of soft-seed photons from the disc/boundary-layer. Reflection signature is observed at upper ‘banana’ branch of the source. Two type-I X-ray bursts are detected during the AstroSat observations. During the bursts, hard X-rays increased unlike previous observations where a reduction in hard X-rays is observed during the bursts. Decrease in the electron temperature and increase in the optical depth are observed during the bursts. The power spectral density of all the sections of the CCD can be represented by a pure power-law component. The strength of this component increases from ∼ 1 per cent to 4.5 per cent as the source moves up in the ‘banana’ track. Search for burst oscillations gave a null result. We discuss the implications of our results in the context of previous findings.

Signature of a chemical spread in the open cluster M37

ABSTRACT Recent Gaia photometry of the open cluster M37 has disclosed the existence of an extended main sequence turn-off – like in Magellanic clusters younger than about 2 Gyr – and a main sequence that is broadened in colour beyond what is expected from the photometric errors, at magnitudes well below the region of the extended turn-off, where neither age differences nor rotation rates (the candidates to explain the extended turn-off phenomenon) are expected to play a role. Moreover, not even the contribution of unresolved binaries can fully explain the observed broadening. We investigated the reasons behind this broadening by making use of synthetic stellar populations and differential colour–colour diagrams, using a combination of Gaia and Sloan filters. From our analysis, we have concluded that the observed colour spread in the Gaia colour–magnitude diagram can be reproduced by a combination of either a metallicity spread $\Delta \rm [Fe/H] \sim 0.15$ plus a differential reddening across the face of the cluster spanning a total range ΔE(B − V) ∼ 0.06, or a spread of the initial helium mass fraction ΔY ∼ 0.10 plus a smaller range of reddening ΔE(B − V) ∼ 0.03. High-resolution differential abundance determinations of a sizeable sample of cluster stars are necessary to confirm or exclude the presence of a metal abundance spread. Our results raise the possibility that also individual open clusters, like globular clusters and massive star clusters, host stars born with different initial chemical compositions.

Searching for nascent planetary nebulae: OHPNe candidates in the SPLASH survey

ABSTRACT The evolution of asymptotic giant branch stars from the spherical symmetry into the diverse shapes of planetary nebulae (PNe) is a topic of intensive research. Young PNe provide a unique opportunity to characterize the onset of this transitional phase. In particular, OH maser-emitting PNe (OHPNe) are considered nascent PNe. In fact, only six OHPNe have been confirmed to date. In order to identify and characterize more OHPNe, we processed the unpublished continuum data of the interferometric follow-up of the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH). We then matched the interferometric positions of OH maser and radio continuum emission, considering the latter as a possible tracer of free–free emission from photoionized gas, characteristic of PNe. We report eight objects with a positive coincidence, four of which are classified as candidate OHPNe here for the first time (IRAS 16372–4808, IRAS 17494–2645, IRAS 18019–2216, and OH 341.6811+00.2634). Available evidence strongly indicates that they are evolved stars, while the comparison with confirmed OHPNe indicates that they are likely to be PNe. Their final confirmation as bona fide PNe, however, requires optical/infrared spectroscopy. The obtained spectral indices of the radio continuum emission (between ≃0.4–1.3) are consistent with partially optically thick free–free emission from photoionized gas. Also, they cluster in the same region of a WISE colour–colour diagram as that of the confirmed OHPNe ($9.5\lesssim[3.4]{-}[22]\lesssim13.5$, and $4.0\lesssim[4.6]{-}[12] \lesssim7.0$), thus this diagram could help to identify more OHPNe candidates in the future.

Large-scale vivid metasurface color printing using advanced 12-in. immersion photolithography

Nanostructures exhibiting optical resonances (so-called nanoantennas) have strong potential for applications in color printing and filtering with sub-wavelength resolution. While small scale demonstrations of these systems are interesting as a proof-of-concept, their large scale and volume fabrication requires deeper analysis and further development for industrial adoption. Here, we evaluate the color quality produced by large size nanoantenna arrays fabricated on a 12-in. wafer using deep UV immersion photolithography and dry etching processes. The color reproduction and quality are analyzed in context of the CIE color diagram, showing that a vivid and vibrant color palette, almost fully covering the sRGB color space, can be obtained with this mass-manufacturing-ready fabrication process. The obtained results, thus, provide a solid foundation for the potential industrial adoption of this emerging technology and expose the limits and challenges of the process.