Near-ultraviolet Band Research Articles

Simultaneous Far-ultraviolet and Near-ultraviolet Observations of T Tauri Stars with UVIT/AstroSat: Probing the Accretion Process in Young Stars

We present results from simultaneous far-ultraviolet (FUV) and near-ultraviolet (NUV) observations of T Tauri stars (TTSs) in the Taurus molecular cloud with UVIT/AstroSat. This is the very first UVIT study of TTSs. From the spectral energy distribution of TTSs from FUV to IR, we show that classical TTSs (CTTSs) emit significantly higher UV excess compared to weak-line TTSs (WTTSs). The equivalent blackbody temperatures corresponding to the UV excess in CTTSs (>104 K) are also found to be relatively higher than those in WTTSs (<9250 K). From the UV excess, we have reclassified two WTTSs (BS Tau and V836 Tau) as CTTSs, which has been supported by the follow-up optical spectroscopic study using the Himalayan Chandra Telescope, showing strong Hα line emission. We find that CTTSs show strong excess emission in both the FUV (>107) and NUV (>103) bands, while WTTSs show strong excess only in the FUV (≲105), suggesting that excess emission in the NUV can be used as a tool to classify the TTSs. We also find a linear correlation between UV luminosity (a primary indicator of mass accretion) and Hα luminosity (a secondary indicator of mass accretion) with a slope of 1.20 ± 0.22 and intercept of 2.16 ± 0.70.

Discovery of an extended horizontal branch in the Large Magellanic Cloud globular cluster NGC 1835

We present a high-angular-resolution multi-wavelength study of the massive globular cluster NGC 1835 in the Large Magellanic Cloud. Thanks to a combination of optical and near-ultraviolet images acquired with the WFC3 on board the HST, we performed a detailed inspection of the stellar population in this stellar system, adopting a ‘UV-guided search’ to optimize the detection of relatively hot stars. This allowed us to discover a remarkably extended horizontal branch (HB): it spans more than 4.5 mag in both the optical and the near-ultraviolet bands, and its colour (temperature) ranges from the region redder than the instability strip up to effective temperatures of 30 000 K. This is the first time that such a feature has been detected in an extragalactic cluster, demonstrating that the physical conditions responsible for the formation of extended HBs are ubiquitous. The HB of NGC 1835 includes a remarkably large population of RR Lyrae (67 confirmed variables and 52 new candidates). The acquired dataset was also used to redetermine the cluster distance modulus, reddening, and absolute age: (m − M)0 = 18.58, E(B − V) = 0.08, and t = 12.5 Gyr.

On the Performances of Estimating Stellar Atmospheric Parameters from CSST Broad-band Photometry

Deriving atmospheric parameters of a large sample of stars is of vital importance to understand the formation and evolution of the Milky Way. Photometric surveys, especially those with near-ultraviolet filters, can offer accurate measurements of stellar parameters, with the precision comparable to that from low/medium resolution spectroscopy. In this study, we explore the capability of measuring stellar atmospheric parameters from Chinese Space Station Telescope (CSST) broad-band photometry (particularly in the near-ultraviolet bands), based on synthetic colors derived from model spectra. We find that colors from the optical and near-ultraviolet filter systems adopted by CSST show significant sensitivities to the stellar atmospheric parameters, especially the metallicity. According to our mock data tests, the precision of the photometric metallicity is quite high, with typical values of 0.17 and 0.20 dex for dwarf and giant stars, respectively. The precision of the effective temperature estimated from broad-band colors are within 50 K.

Stellar Loci. VII. Photometric Metallicities of 5 Million FGK Stars Based on GALEX GR6+7 AIS and Gaia EDR3

We combine photometric data from GALEX GR6+7 All-Sky Imaging Survey and Gaia Early Data Release 3 with stellar parameters from the SAGA and PASTEL catalogs to construct high-quality training samples for dwarfs (0.4 < BP − RP < 1.6) and giants (0.6 < BP − RP < 1.6). We apply careful reddening corrections using empirical temperature- and extinction-dependent extinction coefficients. Using the two samples, we establish a relationship between stellar loci (near-ultraviolet (NUV)−BP versus BP − RP colors), metallicity, and M G . For a given BP − RP color, a 1 dex change in [Fe/H] corresponds to an approximately 1 magnitude change in NUV − BP color for solar-type stars. These relationships are employed to estimate metallicities based on NUV − BP, BP − RP, and M G . Thanks to the strong metallicity dependence in the GALEX NUV band, our models enable a typical photometric-metallicity precision of approximately σ [Fe/H] = 0.11 dex for dwarfs and σ [Fe/H] = 0.17 dex for giants, with an effective metallicity range extending down to [Fe/H] = −3.0 for dwarfs and [Fe/H] = −4.0 for giants. We also find that the NUV-band-based photometric-metallicity estimate is not as strongly affected by carbon enhancement as previous photometric techniques. With the GALEX and Gaia data, we have estimated metallicities for about 5 million stars across almost the entire sky, including approximately 4.5 million dwarfs and 0.5 million giants. This work demonstrates the potential of the NUV band for estimating photometric metallicities, and sets the groundwork for utilizing the NUV data from space telescopes such as the upcoming Chinese Space Station Telescope.

Detection of X-ray/UV delay in NGC 4051 using AstroSat observations

ABSTRACT We study the connection between the variations in the far-ultraviolet (FUV), near-ultraviolet (NUV), and X-ray band emission from NGC 4051 using 4 d long AstroSat observations performed during 5–9 June 2016. NGC 4051 showed rapid variability in all three bands with the strongest variability amplitude in the X-ray band ($F_{\mathrm{ var}} \sim 37~{{\ \rm per\ cent}}$) and much weaker variability in the UV bands ($F_{\mathrm{ var}} \sim 3{\!-\!}5~{{\ \rm per\ cent}}$). Cross-correlation analysis performed using interpolated cross-correlation functions and discrete cross-correlation functions revealed a robust correlation (∼0.75) between the UV and X-ray light curves. The variations in the X-ray band are found to lead those in the FUV and NUV bands by ∼7.4 ks and ∼24.2 ks, respectively. The UV lags favour the thermal disc reprocessing model. The FUV and NUV bands are strongly correlated (∼0.9) and the variations in the FUV band lead those in the NUV band by ∼13 ks. Comparison of the UV lags found using the AstroSat observations with those reported earlier and the theoretical model for thermal reverberation timelag suggests a possible change in either the geometry of the accretion disc/corona or the height of the corona.

The haloes and environments of nearby galaxies (HERON) – III. A 45-kpc spiral structure in the GLSB galaxy UGC 4599

ABSTRACT We use a 0.7-m telescope in the framework of the Halos and Environments of Nearby Galaxies (HERON) survey to probe low surface brightness (LSB) structures in nearby galaxies. One of our targets, UGC 4599, is usually classified as an early-type galaxy surrounded by a blue ring making it a potential Hoag’s Object analogue. Prior photometric studies of UGC 4599 were focused on its bright core and the blue ring. However, the HERON survey allows us to study its faint extended regions. With an 8-h integration, we detect an extremely faint outer disc with an extrapolated central surface brightness of μ0, d(r) = 25.5 mag arcsec−2 down to 31 mag arcsec−2 and a scale length of 15 kpc. We identify two distinct spiral arms of pitch angle ∼6○ surrounding the ring. The spiral arms are detected out to ∼45 kpc in radius and the faint disc continues to ∼70 kpc. These features are also seen in the GALEX far- and near-ultraviolet bands, in a deep u-band image from the 4.3-m Lowell Discovery Telescope (which reveals inner spiral structure emerging from the core), and in H i. We compare this galaxy to ordinary spiral and elliptical galaxies, giant low surface brightness (GLSB) galaxies, and Hoag’s Object itself using several standard galaxy scaling relations. We conclude that the pseudo-bulge and disc properties of UGC 4599 significantly differ from those of Hoag’s Object and of normal galaxies, pointing toward a GLSB galaxy nature and filamentary accretion of gas to generate its outer disc.

Auxiliary Diagnosis of Papillary Thyroid Carcinoma Based on Spectral Phenotype.

Thyroid cancer, a common endocrine malignancy, is one of the leading death causes among endocrine tumors. The diagnosis of pathological section analysis suffers from diagnostic delay and cumbersome operating procedures. Therefore, we intend to construct the models based on spectral data that can be potentially used for rapid intraoperative papillary thyroid carcinoma (PTC) diagnosis and characterize PTC characteristics. To alleviate any concerns pathologists may have about using the model, we conducted an analysis of the used bands that can be interpreted pathologically. A spectra acquisition system was first built to acquire spectra of pathological section images from 91 patients. The obtained spectral dataset contains 217 spectra of normal thyroid tissue and 217 spectra of PTC tissue. Clinical data of the corresponding patients were collected for subsequent model interpretability analysis. The experiment has been approved by the Ethics Review Committee of the Wuhu Hospital of East China Normal University. The spectral preprocessing method was used to process the spectra, and the preprocessed signal respectively optimized by the first and secondary informative wavelengths selection was used to develop the PTC detection models. The PTC detection model using mean centering (MC) and multiple scattering correction (MSC) has optimal performance, and the reasons for the good performance were analyzed in combination with the spectral acquisition process and composition of the test slide. For model interpretable analysis, the near-ultraviolet band selected for modeling corresponds to the location of amino acid absorption peak, and this is consistent with the clinical phenomenon of significantly lower amino acid concentrations in PTC patients. Moreover, the absorption peak of hemoglobin selected for modeling is consistent with the low hemoglobin index in PTC patients. In addition, the correlation analysis was performed between the selected wavelengths and the clinical data, and the results show: the reflection intensity of selected wavelengths in normal cells has a moderate correlation with cell arrangement structure, nucleus size and free thyroxine (FT4), and has a strong correlation with triiodothyronine (T3); the reflection intensity of selected bands in PTC cells has a moderate correlation with free triiodothyronine (FT3).

CEERS: Spatially Resolved UV and Mid-infrared Star Formation in Galaxies at 0.2 < z < 2.5: The Picture from the Hubble and James Webb Space Telescopes

We present the mid-infrared (MIR) morphologies for 64 star-forming galaxies (SFGs) at 0.2 < z < 2.5 with stellar mass M * > 109 M ⊙ using James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) observations from the Cosmic Evolution Early Release Science survey. The MIRI bands span the MIR (7.7–21 μm), enabling us to measure the effective radii (R eff) and Sérsic indexes of these SFGs at rest-frame 6.2 and 7.7 μm, which contains strong emission from Polycyclic aromatic hydrocarbon (PAH) features, a well-established tracer of star formation in galaxies. We define a “PAH band” as the MIRI bandpass that contains these features at the redshift of the galaxy. We then compare the galaxy morphologies in the PAH bands to those in the rest-frame near-ultraviolet (NUV) using Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)/F435W or ACS/F606W and optical/near-IR using HST WFC3/F160W imaging from UVCANDELS and CANDELS. The R eff of galaxies in the PAH band are slightly smaller (∼10%) than those in F160W for galaxies with M * ≳ 109.5 M ⊙ at z ≤ 1.2, but the PAH band and F160W have similar fractions of light within 1 kpc. In contrast, the R eff of galaxies in the NUV band are larger, with lower fractions of light within 1 kpc compared to F160W for galaxies at z ≤ 1.2. Using the MIRI data to estimate the SFRIR surface density, we find that the correlation between the SFRIR surface density and stellar mass has a steeper slope than that of the SFRUV surface density and stellar mass, suggesting more massive galaxies having increasing amounts of obscured fraction of star formation in their inner regions. This paper demonstrates how the high-angular resolution data from JWST/MIRI can reveal new information about the morphology of obscured star formation.

UVIT Observations of the Small Magellanic Cloud: Point-source Catalog

Three fields in the outskirts of the Small Magellanic Cloud were observed by the UltraViolet Imaging Telescope (UVIT) on board AstroSat, between 2017 December 31 and 2018 January 1. The observations were carried out on a total of seven filters, three in the far-ultraviolet (FUV; 1300–1800 Å) band and four in the near-ultraviolet (NUV; 2000–3000 Å) band. We carried out photometry of these observations that have a spatial resolution better than 1.″5. We present here the first results of this work, which is a matched catalog of 11,241 sources detected in three FUV and four NUV wavelengths. We make the catalog available online, which would be of use to the astronomical community to address a wide variety of astrophysical problems. We provide an expression to estimate the total count rate in the full point-spread function of UVIT that also incorporates the effect of saturation.

High-Density Near-Ultraviolet Silicon Photomultipliers: Characterization of photosensors for Cherenkov light detection

In recent years, Silicon Photomultipliers (SiPMs) have proven to be highly suitable devices for applications where high sensitivity to low-intensity light and fast responses are required. Among their many advantages are their low operational voltage when compared with classical photomultiplier tubes, mechanical robustness, and increased photon detection efficiency (PDE).Here we present a full characterization of a SiPM device technology developed in Italy by Fondazione Bruno Kessler, which is suitable for Cherenkov light detection in the Near-Ultraviolet (NUV) band. This device is a High-Density (HD) NUV SiPM, based on a microcell of 40μm×40μm and with an area of 6 × 6mm2, providing low levels of dark noise and high PDE peaking in the NUV band. This particular device has been selected to equip a part of the focal plane of the Schwarzschild–Couder Telescope (SCT) prototype proposed for the Cherenkov Telescope Array (CTA) Observatory.

Investigation of Electronic and Optical Properties of (Cs, Br, Cs-Br) Doped Mono-Layer Hexagonal Boron Nitride Using First Principles

Research on the effect of alternative doping on the photoelectric properties of boron nitride is still at an early stage. In particular, research on hexagonal boron nitride’s diatomic co-doping is still rarely studied. In this work, first-principles calculations are selected as the main method to investigate the electronic structure and optical properties of different atoms used to dope hexagonal boron nitride (h-BN). The band gap value of intrinsic h-BN is 4.66 eV. The band gap was changed after Cs, Br, and Cs-Br doping. The results show that the band gap is 4.61 eV when the Br atom replaces the N atom, while the band gap of h-BN doped with Cs is 3.52 eV. Additionally, the band gap width can be reduced to a typical narrower band gap width of 3.19 eV when Cs-Br is used for doping. At the same time, the complex dielectric function representing the optical properties is calculated after Cs, Br, and Cs-Br doping. The optical absorption peaks of Cs-Br-doped h-BN are weaker at low-frequency conditions. The optical absorption of h-BN can be modified by Cs doping, Br doping, and Cs-Br co-doping in the near-infrared, visible, or portion of the near-ultraviolet bands, which makes the doped material more suited for photoelectric detectors in the relevant frequency bands.

UVIT view of Centaurus A: a detailed study on positive AGN feedback

ABSTRACT Supermassive black holes at the centre of active galactic nuclei (AGNs) produce relativistic jets that can affect the star formation characteristics of the AGN hosts. Observations in the ultraviolet (UV) band can provide an excellent view of the effect of AGN jets on star formation. Here, we present a census of star formation properties in the Northern Star-forming Region (NSR) that spans about 20 kpc of the large radio source Centaurus A hosted by the giant elliptical galaxy NGC 5128. In this region, we identified 352 UV sources associated with Cen A using new observations at an angular resolution of &amp;lt;1.5 arcsec observed with the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat. These observations were carried out in one far-ultraviolet (FUV; λmean = 1481 Å) and three near-ultraviolet (NUV; with λmean of 2196, 2447, and 2792 Å, respectively) bands. The star-forming sources identified in UV tend to lie in the direction of the jet of Cen A, thereby suggesting jet triggering of star formation. Separating the NSR into Outer and Inner regions, we found the stars in the Inner region to have a relatively younger age than the Outer region, suggesting that the two regions may have different star formation histories. We also provide the UVIT source catalogue in the NSR.

Enhanced luminescence efficiency and thermal stability via introduction of non-rare earth Bi3+ in Gd5Si2BO13:Eu3+

A series of Gd5Si2BO13:Eu3+ and non-rare earth Bi3+ ions doped Gd5Si2BO13:Eu3+ phosphors was successfully synthesized via high-temperature solid-state method, and the as-obtained phosphors were studied on their phase structures, luminescence characteristics, thermal stability and luminescence lifetime. Transient fluorescence spectroscopy data show that the addition of Bi3+ can obviously enhance the emission intensity of Eu3+ in the near-ultraviolet band owing to energy transfer from Bi3+ to Eu3+. Besides, the addition of Bi3+ can improve the thermal stability of a single-doped phosphor Gd5Si2BO13:0.35Eu3+ from 70.33% to 87.45% at 150 °C and the quantum yield from 58.80% to 78.61% at room temperature. Finally, Gd5Si2BO13:Eu3+,Bi3+ was used to encapsulate white light-emitting diodes (WLEDs) with green ((Ba,Sr)2SiO4:Eu2+) and blue (BaMgAl10O17:Eu2+) commercial phosphors. The color rendering index of WLEDs was calculated to be larger than 90, and the color temperature was estimated to be 4300–4500 K, which demonstrate that Gd5Si2BO13:Eu3+,Bi3+ can be regarded as a red phosphor with great potential application. This paper can provide a new insight into design of high-efficiency phosphors by introducing non-rare earth Bi3+ ions via energy transfer from Bi3+ to Eu3+.

Near-Ultraviolet to Near-Infrared Band Thresholds Cloud Detection Algorithm for TANSAT-CAPI

Cloud and aerosol polarization imaging detector (CAPI) is one of the important payloads on the China Carbon Dioxide Observation Satellite (TANSAT), which can realize multispectral polarization detection and accurate on-orbit calibration. The main function of the instrument is to identify the interference of clouds and aerosols in the atmospheric detection path and to improve the retrieval accuracy of greenhouse gases. Therefore, it is of great significance to accurately identify the clouds in remote sensing images. However, in order to meet the requirement of lightweight design, CAPI is only equipped with channels in the near-ultraviolet to near-infrared bands. It is difficult to achieve effective cloud recognition using traditional visible light to thermal infrared band spectral threshold cloud detection algorithms. In order to solve the above problem, this paper innovatively proposes a cloud detection method based on different threshold tests from near ultraviolet to near infrared (NNDT). This algorithm first introduces the 0.38 μm band and the ratio of 0.38 μm band to 1.64 μm band, to realize the separation of cloud pixels and clear sky pixels, which can take advantage of the obvious difference in radiation characteristics between clouds and ground objects in the near-ultraviolet band and the advantages of the band ratio in identifying clouds on the snow surface. The experimental results show that the cloud recognition hit rate (PODcloud) reaches 0.94 (ocean), 0.98 (vegetation), 0.99 (desert), and 0.86 (polar), which therefore achieve the application standard of CAPI data cloud detection The research shows that the NNDT algorithm replaces the demand for thermal infrared bands for cloud detection, gets rid of the dependence on the minimum surface reflectance database that is embodied in traditional cloud recognition algorithms, and lays the foundation for aerosol and CO2 parameter inversion.

Universal Conditional Distribution Function of [O ii] Luminosity of Galaxies, and Prediction for the [O ii] Luminosity Function at Redshift z &lt; 3

Abstract The star-forming emission line galaxies (ELGs) with a strong [O ii] doublet are one of the main spectroscopic targets for the ongoing and upcoming fourth-generation galaxy redshift surveys. In this work, we measure the [O ii] luminosity L [O II] and the absolute magnitude in the near-ultraviolet (NUV) band M NUV for a large sample of galaxies in the redshift range 0.6 ≤ z &lt; 1.45 from the Public Data Release 2 (PDR-2) of the VIMOS Public Extragalactic Redshift Survey (VIPERS). We aim to construct the intrinsic relationship between L [O II] and M NUV through Bayesian analysis. In particular, we develop two different methods to properly correct for the incompleteness effect and observational errors in the [O ii] emission line measurement. Our results indicate that the conditional distribution of L [O II] at a given M NUV can be well described by a universal probability distribution function (PDF), which is independent of M NUV and redshift. Convolving the L [O II] conditional PDF with the NUV luminosity function (LF) available in the literature, we make a prediction for [O ii] LFs at z &lt; 3. The predicted [O ii] LFs are in good agreement with the observational results from the literature. Finally, we utilize the predicted [O ii] LFs to estimate the number counts of [O ii] emitters for the Subaru Prime Focus Spectrograph survey. This universal conditional PDF of L [O II] provides a novel way to optimize the source targeting strategy for [O ii] emitters in future galaxy redshift surveys, and to model [O ii] emitters in theories of galaxy formation.

GALEX absolute calibration and extinction coefficients based on white dwarfs

ABSTRACT We use 1837 DA white dwarfs with high signal-to-noise ratio spectra and Gaia parallaxes to verify the absolute calibration and extinction coefficients for the Galaxy Evolution Explorer (GALEX). We use white dwarfs within 100 pc to verify the linearity correction to the GALEX data. We find that the linearity correction is valid for magnitudes brighter than 15.95 and 16.95 for the far-ultraviolet (FUV) and near-ultraviolet (NUV) bands, respectively. We also use DA white dwarfs beyond 250 pc to calculate extinction coefficients in the FUV and NUV bands: RFUV = 8.01 ± 0.07 and RNUV = 6.72 ± 0.04. These are consistent with the predicted extinction coefficients for Milky Way-type dust in the FUV, but smaller than predictions in the NUV. With well understood optical spectra and state-of-the-art model atmosphere analysis, these white dwarfs currently provide the best constraints on the extinction coefficients for the GALEX data.

Learning Transient Universe in Near-ultraviolet by Wide-angle Cameras

We perform a detailed analysis and simulations on the transient detection capability in the near-ultraviolet (NUV) band by focusing on some major local transient events. These events include the tidal disruption event due to a supermassive black hole, the shock breakout of a core-collapse supernova and the flare of a late-type star. Our simulations show that a set of small, wide-angle NUV cameras can allow us to detect and study numerous galactic and extragalactic transient events. Based on the analysis and simulations, here we propose a space-based NUV sky patrol mission by updating the proposal that was originally submitted to the Chinese Space Station mission in 2011. The mission proposed here is composed of a set of eight small wide-field NUV cameras each with a diameter of 20 cm. The total sky area simultaneously covered by the NUV cameras is as large as . The survey cadence ranges from 30 to 300 s. The transient events are required to be detected by a dedicated onboard software in real time.

Multi-wavelength correlation studies of diffuse emission from the Aquila Rift

We present a multi-wavelength correlation study of diffuse ultraviolet radiation using GALEX observations towards the Aquila Rift. Apart from airglow and zodiacal emissions, we find a diffuse background of 1300 - 3700 \photu\ in the far-ultraviolet (FUV: 1350 - 1750 \AA) band and 1300 - 2800 \photu\ in the near-ultraviolet (NUV: 1750 - 2850 \AA) band. The observed diffuse UV emissions are saturated with total as well as neutral hydrogen column density in the region due to high optical depth in UV ($\tau$: 0.91-23.38). Higher values of FUV/NUV ratio in the region, greater than the threshold value of 0.6, along with the positive correlation between the ratio and FUV intensity are due to excess emission in the FUV band which is absent in the NUV band. We estimated the excess emission to be in the range $\sim$ 400 - 2700 \photu, plausibly due to H$_2$ fluorescence, ion line emissions and two-photon continuum emissions from the region in the FUV band, which also shows saturation in optically thick regions with N(H$_{2}$) as well as H$\alpha$ emissions. Since N(H$_{2}$) and H$\alpha$ emissions spread all over the region, the excess emission from the field is composite in nature and a detailed spectroscopic analysis is needed to disentangle the contribution from individual components.

Ultraviolet stellar population of the old open cluster M67 (NGC 2682)

We present the results of ultraviolet (UV) photometry of the old open cluster M67 obtained using Galaxy Evolution Explorer (GALEX) in far-ultraviolet (FUV) and near-ultraviolet (NUV) bands. UV detections of 18 blue straggler stars (BSSs), 3 white dwarfs (WDs), 4 yellow straggler stars, 2 sub-subgiants, and 25 X-ray sources are presented (along with an online catalog). We demonstrate the capability of UV colour magnitude diagrams (CMDs) along with the UV isochrones to identify potential stars which defy standard stellar evolution in this well studied cluster. We also detect a few main sequence turn-off and subgiant branch stars with excess flux in the FUV and/or NUV. UV continuum excess as well as Mg II $\it h$ +$\it k$ emission lines from the IUE archival spectra for 2 red giants are detected, suggestive of their chromospheric activity. We suggest that a large number of stars in this cluster are chromospherically active, whereas the bright BSS are unlikely to be active. We also estimate the fundamental parameters L/L$_{\odot}$, R/R$_{\odot}$ and T$_{eff}$ of the BSSs and 15 FUV bright stars by constructing the spectral energy distribution (SED) using multi-wavelength data. We identify three groups among the BSSs, based on their properties. The H-R diagram of BSSs with isochrones suggests that the BSSs in M67 are formed in the last 2.5 Gyr - 400 Myr, more or less continuously. We identify 7 potential MS+WD candidates based on large UV excess from a probable 11, based on SEDs.

Purification and thermochemical properties of dihydromyricetin

This work reports the purification of dihydromyricetin (abbreviation: DMY) by the recrystallization method, with a yield of secondary recrystallization of up to 77 %. The products were confirmed by element and spectral analysis. The results showed a sharp R-bond absorption peak located around the near-ultraviolet band, which is close to K-bond absorption, illustrating the occurrence of a large conjugation of carbonyl with adjacent phenol and hydroxyl. This was further confirmed by the infrared (IR) spectrum, i.e., the carbonyl stretching vibration peaks were red-shifted from 1700 to 1641 cm−1. The standard thermodynamic energy was determined to be ΔcUmθ[DMY(s), 298.15 K] = −(5437.44 ± 5.14) kJ mol−1 by an oxygen bomb calorimeter. Furthermore, the standard molar enthalpy of combustion was calculated to be ΔcHmθ[DMY(s), 298.15 K] = −(5434.96 ± 5.14) kJ mol−1, and the standard molar formation enthalpy of DMY was estimated to be ΔfHmθ[DMY(s), 298.15 K] = −(2182.67 ± 5.33) kJ mol−1.