The VST Photometric Ha Survey of the Southern Galactic Plane and Bulge (VPHAS+) is surveying the southern Milky Way in u, g, r, i and Hα at ~1 arcsec angular resolution. Its footprint spans the ...Galactic latitude range -5... < b < +5... at all longitudes south of the celestial equator. Extensions around the Galactic Centre to Galactic latitudes ±10... bring in much of the Galactic bulge. This European Southern Observatory public survey, begun on 2011 December 28, reaches down to ~20th magnitude (10s) and will provide single-epoch digital optical photometry for ~300 million stars. The observing strategy and data pipelining are described, and an appraisal of the segmented narrow-band Hα filter in use is presented. Using model atmospheres and library spectra, we compute main-sequence (u - g), (g - r), (r - i) and (r - Hα) stellar colours in the Vega system. We report on a preliminary validation of the photometry using test data obtained from two pointings overlapping the Sloan Digital Sky Survey. An example of the (u - g, g - r) and (r - Hα, r - i) diagrams for a full VPHAS+ survey field is given. Attention is drawn to the opportunities for studies of compact nebulae and nebular morphologies that arise from the image quality being achieved. The value of the u band as the means to identify planetary-nebula central stars is demonstrated by the discovery of the central star of NGC 2899 in survey data. Thanks to its excellent imaging performance, the VLT Survey Telescope (VST)/OmegaCam combination used by this survey is a perfect vehicle for automated searches for reddened early-type stars, and will allow the discovery and analysis of compact binaries, white dwarfs and transient sources. (ProQuest: ... denotes formulae/symbols omitted.)
Cyclohexene to adipic acid synthesis using heterogeneous polyoxometalate catalysts.
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•Catalysts act on both the decomposition of H2O2 and oxidation of diol to adipic acid.•Direct ...relationship between acidity and catalytic activity.•High yield to adipic acid without addition of organic or inorganic acids.•High thermal resistance and catalytic performance of K3PW12O40, even after reuse.
Polyoxometalates prepared with W or Mo precursors, have been used together with H2O2 as homogeneous and heterogeneous catalysts for the adipic acid synthesis from cyclohexene. In this context, the K3PMo12O40, Cs3PMo12O40, K3PW12O40 and Cs3PW12O40 heteropolysalts were synthesized and calcined at 600 °C, characterized by XRD, acid-base titration, Raman Spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, SEM-EDX and evaluated in the cyclohexene oxidation to adipic acid. The XRD and FT-IR analyzes showed that the polyoxometalates structures were stable even after calcination at 600 °C. The thermogravimetric results showed that the heteropolysalts present superior thermal resistance compared to heteropolyacids. However, the acidities of the heteropolysalts are lower than the heteropolyacids. The K3PW12O40 catalyst presented the best performance in the catalytic tests (77% yield in adipic acid) associated with its higher total acid sites density. The catalytic performance of this recycled catalyst was evaluated and the yield in adipic acid was maintained.
•Thermal treatment affects Keggin catalysts performance in the cyclohexene oxidation.•Reaction temperature affects conversion and selectivity in the cyclohexene oxidation.•Density of acidic sites ...influences oxidation/hydrolysis in the reaction mechanism.•Thermal treatment increases Keggin catalysts settling and facilitates separation.
The use of heteropolysalts in the cyclohexene oxidation reaction has shown good results, but there is still a significant solubility of this catalyst in the aqueous phase of the reaction medium which is not discussed in most articles dealing with this subject. A thermal treatment, such as calcination step, can significantly affect the properties of a catalyst, including its solubility, sedimentation and acidity. These effects are very important in batch reaction processes and frequently neglected. Thus, the main objective of this work was to study the effect of different calcination temperatures (200 and 600 °C) on the solubility and the acidity of Keggin-type catalysts (K3PW12O40). In addition, the effect of reaction temperature (65, 75 and 85 °C) on the conversion and distribution of products in the oxidation of cyclohexene with these two catalysts was analyzed. The heteropolysalts were characterized using XRD, Raman spectroscopy, N2 physisorption, SEM-EDS, acid-base titration and NH3-TPD. XRD and Raman results showed that the catalysts synthesis was carried out successfully and the thermal treatments did not affect the polyanion structures, even at the highest temperature (600 °C). When compared to the catalyst treated at 600 °C, the KPW-200 catalyst showed greater solubility in the reaction medium. However, it achieved 100% conversion and the highest yield of adipic acid (89%) at 75 °C, in addition to the highest density of acid sites. Tests were performed using the aqueous phase of the post-reaction solution to evaluate the occurrence of homogeneous catalysis under the same conditions. The results showed that, despite the solubilization of the catalyst, there was no adipic acid formation, only of intermediate compounds. Thus, the contribution of homogeneous catalysis in the synthesis of adipic acid is discarded, and the acidity of the catalyst seems to be the determining parameter in the formation of this product. Acidity can influence both the oxidation and hydrolysis steps present in the reaction mechanism and can justify these results.
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Context.
The characterization of white dwarf atmospheres is crucial for accurately deriving stellar parameters such as effective temperature, mass, and age. However, the inclusion of physical ...processes such as convective mixing and convective dilution in current white dwarf atmospheric models offers a prediction of the spectral evolution of these objects. To constrain these models, accurate observational data and analyses are necessary.
Aims.
We aim to classify the population of white dwarfs up to 500 pc into hydrogen-rich or hydrogen-deficient atmospheres based on
Gaia
spectra and to derive an accurate spectral type-temperature distribution, namely, the ratio between the number of non-DAs to the total number of white dwarfs as a function of the effective temperature for the largest observed unbiased sample of these objects.
Methods.
We took advantage of the recent
Gaia
low-resolution spectra available for 76 657 white dwarfs up to 500 pc. We calculated the synthetic J-PAS narrow-band photometry and fit the spectral energy distribution of each object with up-to-date models for hydrogen-rich and helium-rich white dwarf atmospheres. We estimated the probability for a white dwarf to have a hydrogen-rich atmosphere and validated the results using the Montreal White Dwarf Database. Finally, precise effective temperature values were derived for each object using La Plata evolutionary models.
Results.
We successfully classified a total of 65 310 white dwarfs (57 155 newly classified objects) into DAs and non-DAs with an accuracy of 94%. An unbiased subsample of nearly 34 000 objects was built, from which we computed a precise spectral distribution spanning an effective temperature range from 5500 to 40 000 K, while accounting for potential selection effects.
Conclusions.
Some characteristic features of the spectral evolution, such as the deficit of helium-rich stars at
T
eff
≈ 35 000 − 40 000 K and in the range of 22 000 ≲
T
eff
≲ 25 000 K, as well as a gradual increase from 18 000 K to
T
eff
≈ 7000 K, where the non-DA stars percentage reaches its maximum of 41%, followed by a decrease for cooler temperatures, are statistically significant. These findings will provide precise constraints for the proposed models of spectral evolution.
Context.
We present our findings on 18 previously known ZZ Ceti stars observed by the TESS space telescope in 120 s cadence mode during the survey observation of the southern ecliptic hemisphere.
...Aims.
We focus on the frequency analysis of the space-based observations, comparing the results with findings of previous ground-based measurements. The frequencies detected by the TESS observations can serve as inputs for future asteroseismic analyses.
Methods.
We performed standard pre-whitening of the data sets to derive the possible pulsation frequencies of the different targets. In some cases, we fit Lorentzians to the frequency groups that emerged as the result of short-term amplitude or phase variations that occurred during the TESS observations.
Results.
We detected more than 40 pulsation frequencies in seven ZZ Ceti stars observed in the 120 s cadence by TESS, with precision better than 0.1
μ
Hz. We found that HE 0532−5605 may be a new outbursting ZZ Ceti. Ten targets do not show any significant pulsation frequencies in their Fourier transforms, due to a combination of their intrinsic faintness and/or crowding on the large TESS pixels. We also detected possible amplitude or phase variations during the TESS observations in some cases. Such behaviour in these targets was not previously identified from ground-based observations.
We present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using the accurate parallax measurements from the Gaia space mission data ...release 3 (DR3). The sample comprises a total of 397 members, with 305 (~77%) identified as hot subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 (~58%) are hydrogen-rich sdBs, 65 are sdOBs (~21%), 32 are sdOs (~11%), and 30 are He-sdO/Bs (~10%). Among them, 48 (~16%) exhibit an infrared excess in their spectral energy distribution fits, suggesting a composite binary system. The hot subdwarf population is estimated to be 90% complete, assuming that most missing systems are these composite binaries located within the main sequence (MS) in the Gaia colour-magnitude diagram. The remaining sources in the sample include cataclysmic variables, blue horizontal branch stars, hot white dwarfs, and MS stars. We derived the mid-plane density ρ 0 and scale height h z for the non-composite hot subdwarf star population using a hyperbolic sechant profile (sech 2 ). The best-fit values are ρ 0 = 5.17 ± 0.33 × 10 −7 stars pc −3 and h z = 281 ± 62 pc. When accounting for the composite-colour hot subdwarfs and their estimated completeness, the mid-plane density increases to ρ 0 = 6.15 −0.53 +1.16 × 10 −7 stars pc −3 . This corrected space density is an order of magnitude lower than predicted by population synthesis studies, supporting previous observational estimates.
We present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using the accurate parallax measurements from the Gaia space mission data ...release 3 (DR3). The sample comprises a total of 397 members, with 305 (~77%) identified as hot subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 (~58%) are hydrogen-rich sdBs, 65 are sdOBs (~21%), 32 are sdOs (~11%), and 30 are He-sdO/Bs (~10%). Among them, 48 (~16%) exhibit an infrared excess in their spectral energy distribution fits, suggesting a composite binary system. The hot subdwarf population is estimated to be 90% complete, assuming that most missing systems are these composite binaries located within the main sequence (MS) in the Gaia colour-magnitude diagram. The remaining sources in the sample include cataclysmic variables, blue horizontal branch stars, hot white dwarfs, and MS stars. We derived the mid-plane density ρ0 and scale height hz for the non-composite hot subdwarf star population using a hyperbolic sechant profile (sech2). The best-fit values are ρ0 = 5.17 ± 0.33 × 10−7 stars pc−3 and hz = 281 ± 62 pc. When accounting for the composite-colour hot subdwarfs and their estimated completeness, the mid-plane density increases to ρ0 = 6.15−0.53+1.16 × 10−7 stars pc−3. This corrected space density is an order of magnitude lower than predicted by population synthesis studies, supporting previous observational estimates.
Solid acid catalysts are largely used in several industrial processes, and the development of materials with high activity, selectivity and reusability is a subject of study of research groups around ...the world. The improvement of oxide acidity could be performed by phosphation with phosphoric acid but the investigation of phosphated niobia is still incipient. In this work, niobia was treated with phosphoric acid solutions to generate catalysts with higher esterification activity at mild condition. The phosphated catalysts were obtained and characterized by XRD, N.sub.2 adsorption, NH.sub.3 and pyridine chemisorption and FTIR, and were tested in the esterification of acetic acid with ethanol at 60 °C and RT. DFPT calculations indicated that H.sub.2PO.sub.4 group was the predominant phosphate species on the hydroxylated surface. Theoretical results also show that ethanol adsorbs preferentially at H.sub.2PO.sub.4 acidic sites on the phosphated catalyst as compared to acetic acid. Graphic
Context. We present our findings on 18 previously known ZZ Ceti stars observed by the TESS space telescope in 120 s cadence mode during the survey observation of the southern ecliptic hemisphere. ...Aims. We focus on the frequency analysis of the space-based observations, comparing the results with findings of previous ground-based measurements. The frequencies detected by the TESS observations can serve as inputs for future asteroseismic analyses. Methods. We performed standard pre-whitening of the data sets to derive the possible pulsation frequencies of the different targets. In some cases, we fit Lorentzians to the frequency groups that emerged as the result of short-term amplitude or phase variations that occurred during the TESS observations. Results. We detected more than 40 pulsation frequencies in seven ZZ Ceti stars observed in the 120 s cadence by TESS, with precision better than 0.1 μHz. We found that HE 0532−5605 may be a new outbursting ZZ Ceti. Ten targets do not show any significant pulsation frequencies in their Fourier transforms, due to a combination of their intrinsic faintness and/or crowding on the large TESS pixels. We also detected possible amplitude or phase variations during the TESS observations in some cases. Such behaviour in these targets was not previously identified from ground-based observations.
The influence of the calcination procedure on the catalytic activity of Pt/HZSM-5 was investigated for propane aromatization. The TPR, CO chemisorption and XPS measurements showed significant ...differences due to the existence of different platinum species after calcination procedures and reduction step, that could explain the differences on catalytic behavior. High calcination temperature promoted a great reduction of Pt
+2 to Pt
0 and a surprisingly high dispersion, consistent with the increasing catalytic activity.
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