[en] The compound diffractive telescope is a novel space optical system which combines the structure of compound eyes with diffractive optics and so it has a lighter weight, a wider field of view (FOV), a lower cost as well as looser fabrication tolerance. In this paper, the design of a compound diffractive telescope composed of one primary lens and twenty-one eyepieces is introduced. Then the influence of diffraction orders on the performance of the system is analysed. A modified phase function model of diffractive optics is proposed to analyse the modulation transfer function (MTF) curves for 0deg FOV, which provides a more accurate prediction of the performance of the system. In addition, an optimized mechanism is also proposed to suppress stray light. The star image and resolution tests show that the system can achieve diffraction limit imaging within deg 2deg of FOV and deg 4 mm of eccentricity. Finally, a series of pictures of an object are taken from different channels, and the splicing of pictures from adjacent FOVs is demonstrated. In summary, the designed system has been proved to have great potential applications. (general)

[en] In this paper we present our studies on the stellar populations and star formation histories (SFHs) for the Reines et al. sample of 136 dwarf galaxies that host active galactic nuclei (AGNs), selected from the Sloan Digital Sky Survey Data Release 8. We derive stellar populations and reconstruct SFHs for these AGN-host dwarfs using the stellar population synthesis code STARLIGHT. Our results suggest that these AGN-host dwarfs have assembled their stellar masses within a narrow period of time with the stellar mass-weighted ages in the range of 10⁹–10¹⁰ yr, but show a wide diversity of SFHs with the luminosity-weighted stellar ages in the range of 10⁷–10¹⁰ yr. The old population (t > 10⁹ yr) contributes most to the galaxy light for the majority of the sample; the young population (t < 10⁸ yr) also appears in significant but widely varying fractions, while the intermediate-age population (10⁸ < t < 10⁹ yr) in general contributes less to the optical continuum at 4020 Å. We also find that these dwarfs follow a similar mass–metallicity relation to normal star-forming galaxies, indicating that AGNs have little effect on the chemical evolution of the host galaxy. We further investigate the relation between the derived SFHs and morphology of the host galaxy, and find no correlation. Comparing the SFHs with the luminosity of the [O iii] λ5007 line ($L_{[\mathrm{O}\mathrm{I}\mathrm{I}\mathrm{I}]}$), we find a mild correlation exists when $L_{[\mathrm{O}\mathrm{I}\mathrm{I}\mathrm{I}]}><!--\; >\; -->{10}^{39}$ erg s⁻¹, indicating a physical connection between star formation and AGN activities in these dwarf galaxies.

[en] In an effort to probe the origin of surface brightness profile (SBP) breaks widely observed in nearby disk galaxies, we carry out a comparative study of stellar population profiles of 635 disk galaxies selected from the Mapping Nearby Galaxies at Apache Point Observatory spectroscopic survey. We classify our galaxies into single exponential (Ti), down-bending (Tii), and up-bending (Tiii) SBP types and derive their spin parameters and radial profiles of age/metallicity-sensitive spectral features. Most Tii (Tiii) galaxies have down-bending (up-bending) star formation rate (SFR) radial profiles, implying that abrupt radial changes of SFR intensities contribute to the formation of both Tii and Tiii breaks. Nevertheless, a comparison between our galaxies and simulations suggests that stellar migration plays a significant role in weakening down-bending Σ_⋆ profile breaks. While there is a correlation between the break strengths of SBPs and age/metallicity-sensitive spectral features for Tii galaxies, no such correlation is found for Tiii galaxies, indicating that stellar migration may not play a major role in shaping Tiii breaks, as is also evidenced by a good correspondence between the break strengths of Σ_⋆ and SBPs of Tiii galaxies. We do not find evidence for galaxy spin being a relevant parameter for forming different SBP types, nor do we find significant differences between the asymmetries of galaxies with different SBP types, suggesting that environmental disturbances or satellite accretion in the recent past do not significantly influence the break formation. By dividing our sample into early and late morphological types, we find that galaxies with different SBP types follow nearly the same tight stellar mass–$R_{25}$ relation, which makes the hypothesis that stellar migration alone can transform SBP types from Tii to Ti and then to Tiii highly unlikely.

[en] We present a study on the radial profiles of the D4000, luminosity-weighted stellar ages τ _L, and luminosity-weighted stellar metallicities [Z/H]_L of 3654 nearby galaxies (0.01 < z < 0.15) using the IFU spectroscopic data from the MaNGA survey available in the SDSS DR15, in an effort to explore the connection between median stellar population radial gradients (i.e., ∇D4000, ∇τ _L, ∇[Z/H]_L) out to ∼1.5 R _e and various galaxy properties, including stellar mass (M _⋆), specific star formation rate (sSFR), morphologies, and local environment. We find that M _⋆ is the single most predictive physical property for ∇D4000 and ∇[Z/H]_L. The most predictive properties for ∇τ _L are sSFR and, to a lesser degree, M _⋆. The environmental parameters, including local galaxy overdensities and central–satellite division, have virtually no correlation with stellar population radial profiles for the whole sample, but the ∇D4000 of star-forming satellite galaxies with M _⋆ ≲ 10¹⁰ M _⊙ exhibit a significant positive correlation with galaxy overdensities. Galaxies with lower sSFR have on average steeper negative stellar population gradients, and this sSFR dependence is stronger for more massive star-forming galaxies. The negative correlation between the median stellar population gradients and M _⋆ are best described largely as segmented relationships, whereby median gradients of galaxies with log M _⋆ ≲ 10.0 (with the exact value depending on sSFR) have much weaker mass dependence than galaxies with higher M _⋆. While the dependence of the radial gradients of ages and metallicities on T-Types and central stellar mass surface densities are generally not significant, galaxies with later T-Types or lower central mass densities tend to have significantly lower D4000, younger τ _L, and lower [Z/H]_L across the radial ranges probed in this study.

[en] Highlights: • The Fe₃O₄@TiO₂ nanocomposite was prepared with the in-situ synthesis coating process. • It has finished at low temperature not to recur to calcination to form the coating layer. • The core and shell are linked with the chemical bond Ti-O-Fe. • The magnetic nanocomposite has the high whiteness and the outstanding dispersibility.

[en] We investigate the on-average properties for 28 star-forming ultra-diffuse galaxies (UDGs) located in low-density environments, by stacking their spectra from the Sloan Digital Sky Survey. These relatively isolated UDGs, with stellar masses of ${\mathrm{l}\mathrm{o}\mathrm{g}}_{10}(M_{\ast <!--\; ???\; -->}/M_{\odot <!--\; ???\; -->})\sim <!--\; ???\; -->8.57\pm <!--\; ??\; -->0.29$, have the on-average total stellar metallicity [M/H] ∼ −0.82 ± 0.14, iron metallicity [Fe/H] ∼ −1.00 ± 0.16, stellar age t _* ∼ 5.2 ± 0.5 Gyr, α-enhancement [α/Fe] ∼ 0.24 ± 0.10, and oxygen abundance 12+log(O/H) ∼ 8.16 ± 0.06, as well as central stellar velocity dispersion 54 ± 12 km s⁻¹. On the star formation rate versus stellar mass diagram, these UDGs are located lower than the extrapolated star-forming main sequence from the massive spirals, but roughly follow the main sequence of low-surface-brightness dwarf galaxies. We find that these star-forming UDGs are not particularly metal-poor or metal-rich for their stellar masses, as compared with the metallicity–mass relations of the nearby typical dwarfs. With the UDG data of this work and previous studies, we also find a coarse correlation between [Fe/H] and magnesium-element enhancement [Mg/Fe] for UDGs: [Mg/Fe] ≃ −0.43(±0.26) [Fe/H] −0.14(±0.40).

[en] We explore the environmental dependence of star formation timescales in low-mass galaxies using the [α/Fe] abundance ratio as an evolutionary clock. We present integrated [α/Fe] measurements for 11 low-mass ($M_{\star <!--\; ???\; -->}\sim <!--\; ???\; -->{10}^9{M}_{\odot <!--\; ???\; -->}$) early-type galaxies (ETGs) with a large range of cluster-centric distance in the Virgo Cluster. We find a gradient in [α/Fe], where the galaxies closest to the cluster center (the cD galaxy, M87) have the highest values. This trend is driven by galaxies within a projected radius of 0.4 Mpc (0.26 times the virial radius of Virgo A), all of which have super-solar [α/Fe]. Galaxies in this mass range exhibit a large scatter in the [α/Fe]–σ diagram, and do not obviously lie on an extension of the relation defined by massive ETGs. In addition, we find a correlation between [α/Fe] and globular cluster specific frequency (S_N), suggesting that low-mass ETGs that formed their stars over a short period of time were also efficient at forming massive star clusters. The innermost low-mass ETGs in our sample have [α/Fe] values comparable to that of M87, implying that environment is the controlling factor for star formation timescales in dense regions. These low-mass galaxies could be the surviving counterparts of the objects that have already been accreted into the halo of M87, and may be the link between present-day low-mass galaxies and the old, metal-poor, high-[α/Fe], high-S_N stellar populations seen in the outer halos of massive ETGs.

[en] Determining the shape of dwarf irregular (dIrr) galaxies is controversial because if one assumes that these objects are disks and if these disks are randomly distributed over the sky, then their projected minor-to-major axis ratios should follow a particular statistical distribution, which is not observed. Thus, different studies have led to different conclusions. Some believe that the observed distributions can be explained by assuming the dIrrs are thick disks while others have concluded that dIrrs are triaxial. Fortunately, the central stellar velocity dispersion, σ_z,0, combined with maximum rotation speed, V_max, provides a kinematic measure, V_max/σ_z,0, which gives the three-dimensional shape of a system. In this work, we present the stellar and gas kinematics of DDO 46 and DDO 168 from the Local Irregulars That Trace Luminosity Extremes; The H i Nearby Galaxy Survey (LITTLE THINGS) and determine their respective V_max/σ_z,0 values. We used the Kitt Peak National Observatory's Mayall 4 m telescope with the Echelle spectrograph as a long-slit spectrograph, which provided a two-dimensional, 3′-long slit. We acquired spectra of DDO 168 along four position angles (PAs) by placing the slit over the morphological major and minor axes and two intermediate PAs. However, due to poor weather conditions during our observing run for DDO 46, we were able to extract only one useful data point from the morphological major axis. We determined a central stellar velocity dispersion perpendicular to the disk, σ_z,0, of 13.5 ± 8 km s⁻¹ for DDO 46 and $⟨<!--\; ???\; -->{\mathrm{\sigma <!--\; ??\; -->}}_{z,0}⟩<!--\; ???\; -->$ of 10.7 ± 2.9 km s⁻¹ for DDO 168. We then derived the maximum rotation speed in both galaxies using the LITTLE THINGS H i data. We separated bulk motions from non-circular motions using a double Gaussian decomposition technique and applied a tilted-ring model to the bulk velocity field. We corrected the observed H i rotation speeds for asymmetric drift and found a maximum velocity, V_max, of 77.4 ± 3.7 and 67.4 ± 4.0 for DDO 46 and DDO 168, respectively. Thus, we derived a kinematic measure, V_max/σ_z,0, of 5.7 ± 0.6 for DDO 46 and 6.3 ± 0.3 for DDO 168. Comparing these values to ones determined for spiral galaxies, we find that DDO 46 and DDO 168 have V_max/σ_z,0 values indicative of thin disks, which is in contrast to minor-to-major axis ratio studies.

[en] As one of the three payloads for the Advanced Space-based Solar Observatory (ASO-S) mission, the Lyman-alpha (Lyα) Solar Telescope (LST) is composed of three instruments: a Solar Corona Imager (SCI), a Lyα Solar Disk Imager (SDI) and a full-disk White-light Solar Telescope (WST). When working in-orbit, LST will simultaneously perform high-resolution imaging observations of all regions from the solar disk to the inner corona up to 2.5 R_⊙ (R_⊙ stands for the mean solar radius) with a spatial resolution of 4.8″ and 1.2″ for coronal and disk observations, respectively, and a temporal resolution of 30 – 120 s and 1 – 120 s for coronal and disk observations, respectively. The maximum exposure time can be up to 20 s due to precise pointing and image stabilization function. Among the three telescopes of LST, SCI is a dual-waveband coronagraph simultaneously and independently observing the inner corona in the HI Lyα (121.6±10 nm) line and white light (WL) (700±40 nm) wavebands by using a narrowband Lyα beam splitter and has a field of view (FOV) from 1.1 to 2.5 R_⊙. The stray-light suppression level can attain <10⁻⁶ B_⊙ (B_⊙ is the mean brightness of the solar disk) at 1.1 R_⊙ and ≤5×10⁻⁸ B_⊙ at 2.5 R_⊙. SDI and WST are solar disk imagers working in the Lyα line and 360.0 nm wavebands, respectively, which adopt an off-axis two-mirror reflective structure with an FOV up to 1.2 R_⊙, covering the inner coronal edge area and relating to coronal imaging. We present the up-to-date design for the LST payload. (paper)

[en] A dual-functional nanosysterm is developed by means of Chlorin e6 (Ce6) as photosensitizer and 1,3-Diphenylisobenzofuran (DPBF) as fluorescent singlet oxygen (¹O₂) probe. Under 660 nm laser irradiation, Ce6 exhibites efficient ¹O₂ generation, and subsequently the production of ¹O₂ is assessed by the ratiometric fluorescence of PFO and DPBF under one-photon and two-photon excitation mode. The nanoparticles with excellent biocompatibility can be internalized into Hela cells and applied for tumor treatment. For intracellular PDT, the nanoparticles perform a high phototoxicity, while the PDT proccess can be evaluated in time by monitoring fluorescence signals of DPBF. This theranostic nanosysterm provides a facile strategy to fabricate ¹O₂-detection PDT, which can realize accurate and efficient photodynamic therapy based on singlet oxygen detection. (paper)