IR AND UV-VISIBLE SPECTRA OF IRON(II) PHTHALOCYANINE COMPLEXES WITH PHOSPHINE OR PHOSPHITE

We have prepared and studied by vibrational and electronic spectrometry of a series of ferrophthalocyanine complexes with phosphine or phosphite axial ligands [PMe3, P(OMe)3, PPh3, P(OPh)3, PPh(OMe)3 and POH(OEt)2]. With PMe3, P(OMe)3 as ligands, only hexacoordinated complexes are obtained but with PPh3, P(OPh)3 and POH(OEt)2 as ligands, the coordination number depends on the FePc:ligand ratio in the reaction mixture. In the ratio 1:1 the complexes thus formed are pentacoordinated and in the ratio 1:2 hexacoordinated complexes are obtained. In the electronic spectra of hexacoordinated complexes, two charge-transfer transition bands, one at ~375 nm and the other at ~421 nm can be observed. We attribute the band at 375 nm to charge-transfer from axial ligand to macrocycle (CT Lax ® Pc) and the band at 421 nm to charge-transfer from metal to axial ligand (CT Fe ® Lax). In the IR spectra, the position of the n FeN4 band is linked to the coordination number; in the spectra of pentacoordinated complexes, its frequency is almost the same as that in the FePc spectrum but in hexacoordinated complexes, it moves to high frequencies. (Received September 10, 2001; revised February 26, 2002) Bull. Chem. Soc. Ethiop. 2002, 16(1), 73-79

A sequential regularization method for time-dependent incompressible Navier--Stokes equations

The objective of the paper is to present a method, called sequential regularization method (SRM), for the nonstationary incompressible Navier-Stokes equations from the viewpoint of regularization of differential-algebraic equations (DAEs) , and to provide a way to apply a DAE method to partial differential-algebraic equations (PDAEs). The SRM is a functional iterative procedure. It is proved that its convergence rate is O(ffl m ), where m is the number of the SRM iterations and ffl is the regularization parameter. The discretization and implementation issues of the method are considered. In particular, a simple explicit difference scheme is analyzed and its stability is proved under the usual step size condition of explicit schemes. It appears that the SRM formulation is new in the Navier-Stokes context. Unlike other regularizations or pseudo-compressibility methods in the Navier-Stokes context, the regularization parameter ffl in the SRM need not be very small, and the regularized..

Radiological Impact Assessment of Farm Soils and Ofada rice (Oryza sativa japonica) from Three Areas in Nigeria

            يزرع الارز الاسيوي والمسمى ب (ارز اوفادا )في مجتمعات المسماة (أراموكو ، وأباكاليكي وأوفادا) ويستهلكها كل من الفقراء والأغنياء في نيجيريا على حد سواء . تم تحديد ما مجموعه عشرين مزرعة من أراضي الأرز في كل منطقة من مناطق الدراسة ، وتم جمع عينات من الأرز بشكل عشوائي ، وتم خلطها بشكل دقيق لتقديم عينة من كل أرض زراعية. تم جمع عينات التربة في كل مزرعة على عمق 5-15 سم من ثماني نقاط مختلفة على الأقل وتم خلطها معًا لتشكيل العينة. تم التحليل الطيفي لهذه العينات. تم استخدام كاشف أشعة كاما NaI (Tl) ذو معايرة جيدة في التحليل الطيفي للعينات واستخدمت الإحصاءات الوصفية لتحليل النتائج.لقد كان متوسط التركيز الاشعاعي للعناصر  40K,232Th,238U , هو 261.8±52.5Bq/kg      و   9.6±1.2Bq/kg و 8.7±1.0Bq/kg (أوفادا)،257.3±39.0Bq/kg،9.3±1.1Bq/kg و 7.8±1.8Bq/kg (أباكاليكي) و 248.2±54.8Bq/kg،9.3±0.9Bq/kg،7.6±1.5Bq/kg (أراموكو) على التوالي اما تراكيز النشاط الاشعاعي في التربة للعناصر  40K,232Th,238U ,كانت 333.9±62.8Bq/kg،11.1±1.1Bq/kg و 11.0±1.4Bq/kg (اوفادا) ،306.8±36.0Bq/kg،10.7±0.8Bq/kg و 9.4±1.8 Bq/kg (أباكاليكي) و 321.8±42.4Bq/kg،10.9±0.5Bq/kg و9.5±0.6Bq/kg (أراموكو). تم تسجيل أعلى متوسط جرعة 106.0±8.0µSv/y والجرعة الفعالة في الهواء الطلق البالغة32.4±3.40µSv/y في  Ofada. وان أعلى معدل لخطر الاصابة بسرطان قدره (0.33±0.004) x10-3 تم تسجيله في (أراموكو). أشارت النتائج إلى أن جرعة  النويدات المشعة أقل بكثير من الحد العالمي البالغ   290µSv/y  ومخاطر انخفاض السرطان عن الحد الذي أوصى به UNSCEAR وهو 0.29x10-3 ، وبالتالي فإن استهلاك الأرز ofada من المناطق قد لا يشكل أي تأثير صحي خطير.Oryza sativa japonica (ofada rice) is largely grown in Aramoko, Abakaliki and Ofada are communities and consumed by both the poor and rich in Nigeria. A total of twenty ofada rice farmlands were identified in each study area and rice samples were randomly collected, thoroughly mixed to make a representative sample from each farmland. Soil samples were collected in each farm to a depth of 5-15cm from at least eight different points and thoroughly mixed together to form a representative sample. The samples were thereafter taken to the laboratory for preparation and spectroscopic analysis. A well-calibrated NaI(Tl) gamma-ray detector was used in spectrometric analysis of the samples and descriptive statistics was used to analyze the results. The respective mean 40K, 238U and 232Th activity concentrations in the rice were 261.8±52.5Bq/kg, 9.6±1.2Bq/kg and 8.7±1.0Bq/kg (Ofada); 257.3±39.0Bq/kg, 9.3±1.1Bq/kg and 7.8±1.8Bq/kg (Abakaliki); and 248.2±54.8Bq/kg, 9.3±0.9Bq/kg and 7.6±1.5Bq/kg (Aramoko). The respective mean 40K, 238U and 232Th activity concentrations in the soils were 333.9±62.8Bq/kg, 11.1±1.1Bq/kg and 11.0±1.4Bq/kg (Ofada); 306.8±36.0Bq/kg, 10.7±0.8Bq/kg and 9.4±1.8 Bq/kg (Abakaliki) and 321.8±42.4Bq/kg, 10.9±0.5Bq/kg and 9.5±0.6Bq/kg (Aramoko). The highest mean ingestion dose of 106.0±8.0µSv/y and outdoor effective dose of 32.4±3.40µSv/y were recorded in Ofada community. The highest mean ingestion cancer risk of (0.33±0.004) x10-3was recorded in Aramoko. The results indicated significantly lower radionuclide ingestion dose than the world limit value of 290µSv/y and lower cancer risks than the UNSCEAR recommended limit of 0.29x10-3, therefore consumption of ofada rice from the areas may not pose any serious health impact

Near-infrared photometry of WISE J085510.74-071442.5

Indexación: Web of ScienceAims. We aim at obtaining near-infrared photometry and deriving the mass, age, temperature, and surface gravity of WISE J085510.74 071442.5 (J0855 0714), which is the coolest object beyond the solar system currently known. Methods. We used publicly available data from the archives of the Hubble Space Telescope (HST) and the Very Large Telescope (VLT) to determine the emission of this source at 1.153 mu m (F110W) and 1.575 mu m (CH4-o ff). J0855 0714 was detected at both wavelengths with a signal-to-noise ratio of approximate to 10 (F110W) and approximate to 4 (CH4-off) at the peak of the corresponding point-spread-functions. Results. This is the first detection of J0855 0714 in the H-band wavelengths. We measured 26.31 +/- 0.10 and 23.22 +/- 0.35 mag in F110W and CH4-o ff (Vega system). J0855 0714 remains unresolved in the HST images that have a spatial resolution of 0.22 0 0. Companions at separations of 0.5 AU (similar mass and brightness) and at similar to 1 AU approximate to 1 mag fainter in the F110W filter) are discarded. By combining the new data with published photometry, including non-detections, we build the spectral energy distribution of J0855 0714 from 0.89 through 22.09 mu m, and contrast it against current solar-metallicity models of planetary atmospheres. We determine that the best spectral fit yields a temperature of 225 250 K, a bolometric luminosity of log L/L-circle dot = 8 : 57, and a high surface gravity of log g = 5 : 0 (cm s(2)), which suggests an old age although a gravity this high is not fully compatible with evolutionary models. After comparing our data with the cooling theory for brown dwarfs and planets, we infer a mass in the interval 2 10 MJup for ages of 1 12 Gyr and high atmospheric gravities of log g greater than or similar to 3.5 (cm s(2)). If it had the age of the Sun, J0855 0714 would be a approximate to 5-M-Jup free-floating planetary-mass object. Conclusions. J0855 0714 meets the mass values previously determined for free-floating planetary-mass objects discovered in starforming regions and young stellar clusters. Based on extrapolations of the substellar mass functions of young clusters to the field, as many J0855 0714-like objects as M5-L2 stars may be expected to populate the solar neighborhood.http://www.aanda.org/articles/aa/pdf/2016/08/aa28662-16.pd

Is there really a debris disc around ζ2 Reticuli\zeta^2\,\mathrm{Reticuli} ?

The presence of a debris disc around the Gyr-old solar-type star $\zeta^2\,\mathrm{Reticuli}$ was suggested by the $\mathit{Spitzer}$ infrared excess detection. Follow-up observations with $\mathit{Herschel}$/PACS revealed a double-lobed feature, that displayed asymmetries both in brightness and position. Therefore, the disc was thought to be edge-on and significantly eccentric. Here we present ALMA/ACA observations in Band 6 and 7 which unambiguously reveal that these lobes show no common proper motion with $\zeta^2\,\mathrm{Reticuli}$. In these observations, no flux has been detected around $\zeta^2\,\mathrm{Reticuli}$ that exceeds the $3\sigma$ levels. We conclude that surface brightness upper limits of a debris disc around $\zeta^2\,\mathrm{Reticuli}$ are $5.7\,\mathrm{\mu Jy/arcsec^2}$ at 1.3 mm, and $26\,\mathrm{\mu Jy/arcsec^2}$ at 870 microns. Our results overall demonstrate the capability of the ALMA/ACA to follow-up $\mathit{Herschel}$ observations of debris discs and clarify the effects of background confusion.Comment: 6 pages, 2 figures, 2 table

SPITZER: Accretion in Low Mass Stars and Brown Dwarfs in the Lambda Orionis Cluster

We present multi-wavelength optical and infrared photometry of 170 previously known low mass stars and brown dwarfs of the 5 Myr Collinder 69 cluster (Lambda Orionis). The new photometry supports cluster membership for most of them, with less than 15% of the previous candidates identified as probable non-members. The near infrared photometry allows us to identify stars with IR excesses, and we find that the Class II population is very large, around 25% for stars (in the spectral range M0 - M6.5) and 40% for brown dwarfs, down to 0.04 Msun, despite the fact that the H(alpha) equivalent width is low for a significant fraction of them. In addition, there are a number of substellar objects, classified as Class III, that have optically thin disks. The Class II members are distributed in an inhomogeneous way, lying preferentially in a filament running toward the south-east. The IR excesses for the Collinder 69 members range from pure Class II (flat or nearly flat spectra longward of 1 micron), to transition disks with no near-IR excess but excesses beginning within the IRAC wavelength range, to two stars with excess only detected at 24 micron. Collinder 69 thus appears to be at an age where it provides a natural laboratory for the study of primordial disks and their dissipation.Comment: ApJ, in pres

Temperature constraints on the coldest brown dwarf known WISE 0855-0714

Context. Nearby isolated planetary mass objects are beginning to be discovered, but their individual properties are poorly constrained because their low surface temperatures and strong molecular self-absorption make them extremely faint. Aims. We aimed to detect the near infrared emission of the coldest brown dwarf (BD) found so far, WISE0855$-$0714, located $\sim$2.2 pc away, and to improve its temperature estimate (T$_{\rm eff}$= 225-260 K) from a comparison with state-of-the-art models of BD atmospheres. Methods. We observed the field containing WISE0855-0714 with HAWK-I at the VLT in the $Y$ band. For BDs with T$_{\rm eff}<$500\,K theoretical models predict strong signal (or rather less molecular absorption) in this band. Results. WISE0855-0714 was not detected in our Y-band images, thus placing an upper limit on its brightness to Y>24.4 mag at 3-$\sigma$ level, leading to Y-[4.5]>10.5. Combining this limit with previous detections and upper limits at other wavelengths, WISE0855$-$0714 is confirmed as the reddest BD detected, further supporting its status as the coldest known brown dwarf. We applied spectral energy distribution fitting with collections of models from two independent groups for extremely cool BD atmospheres leading to an effective temperature of T$_{\rm eff}<$250\,K,.Comment: 4 pages, 4 figures. A&A letter Accepte

YSOVAR: Mid-IR variability in the star forming region Lynds 1688

The emission from young stellar objects (YSOs) in the mid-IR is dominated by the inner rim of their circumstellar disks. We present an IR-monitoring survey of about 800 objects in the direction of the Lynds 1688 (L1688) star forming region over four visibility windows spanning 1.6 years using the \emph{Spitzer} space telescope in its warm mission phase. Among all lightcurves, 57 sources are cluster members identified based on their spectral-energy distribution and X-ray emission. Almost all cluster members show significant variability. The amplitude of the variability is larger in more embedded YSOs. Ten out of 57 cluster members have periodic variations in the lightcurves with periods typically between three and seven days, but even for those sources, significant variability in addition to the periodic signal can be seen. No period is stable over 1.6 years. Non-periodic lightcurves often still show a preferred timescale of variability which is longer for more embedded sources. About half of all sources exhibit redder colors in a fainter state. This is compatible with time-variable absorption towards the YSO. The other half becomes bluer when fainter. These colors can only be explained with significant changes in the structure of the inner disk. No relation between mid-IR variability and stellar effective temperature or X-ray spectrum is found.Comment: accepted by ApJ, 24 pages, 17 figure

<i>Herschel</i> observations of the debris disc around HIP 92043

Context. Typical debris discs are composed of particles ranging from several micron sized dust grains to km sized asteroidal bodies, and their infrared emission peaks at wavelengths 60-100 μm. Recent Herschel DUNES observations have identified several debris discs around nearby Sun-like stars (F, G and K spectral type) with significant excess emission only at 160 μm. Aims. We observed HIP 92043 (110 Her, HD 173667) at far-infrared and sub-millimetre wavelengths with Herschel PACS and SPIRE. Identification of the presence of excess emission from HIP 92043 and the origin and physical properties of any excess was undertaken through analysis of its spectral energy distribution (SED) and the PACS images. Methods. The PACS and SPIRE images were produced using the HIPE photProject map maker routine. Fluxes were measured using aperture photometry. A stellar photosphere model was scaled to optical and near infrared photometry and subtracted from the far-infared and sub-mm fluxes to determine the presence of excess emission. Source radial profiles were fitted using a 2D Gaussian and compared to a PSF model based on Herschel observations of α Boo to check for extended emission. Results. Clear excess emission from HIP 92043 was observed at 70 and 100 μm. Marginal excess was observed at 160 and 250 μm. Analysis of the images reveals that the source is extended at 160 μm. A fit to the source SED is inconsistent with a photosphere and single temperature black body. Conclusions. The excess emission from HIP 92043 is consistent with the presence of an unresolved circumstellar debris disc at 70 and 100 μm, with low probability of background contamination. The extended 160 μm emission may be interpreted as an additional cold component to the debris disc or as the result of background contamination along the line of sight. The nature of the 160 μm excess cannot be determined absolutely from the available data, but we favour a debris disc interpretation, drawing parallels with previously identified cold disc sources in the DUNES sample

Young Stellar Object Variability (YSOVAR): Long Timescale Variations in the Mid-Infrared

The YSOVAR (Young Stellar Object VARiability) Spitzer Space Telescope observing program obtained the first extensive mid-infrared (3.6 & 4.5 um) time-series photometry of the Orion Nebula Cluster plus smaller footprints in eleven other star-forming cores (AFGL490, NGC1333, MonR2, GGD 12-15, NGC2264, L1688, Serpens Main, Serpens South, IRAS 20050+2720, IC1396A, and Ceph C). There are ~29,000 unique objects with light curves in either or both IRAC channels in the YSOVAR data set. We present the data collection and reduction for the Spitzer and ancillary data, and define the "standard sample" on which we calculate statistics, consisting of fast cadence data, with epochs about twice per day for ~40d. We also define a "standard sample of members", consisting of all the IR-selected members and X-ray selected members. We characterize the standard sample in terms of other properties, such as spectral energy distribution shape. We use three mechanisms to identify variables in the fast cadence data--the Stetson index, a chi^2 fit to a flat light curve, and significant periodicity. We also identified variables on the longest timescales possible of ~6 years, by comparing measurements taken early in the Spitzer mission with the mean from our YSOVAR campaign. The fraction of members in each cluster that are variable on these longest timescales is a function of the ratio of Class I/total members in each cluster, such that clusters with a higher fraction of Class I objects also have a higher fraction of long-term variables. For objects with a YSOVAR-determined period and a [3.6]-[8] color, we find that a star with a longer period is more likely than those with shorter periods to have an IR excess. We do not find any evidence for variability that causes [3.6]-[4.5] excesses to appear or vanish within our data; out of members and field objects combined, at most 0.02% may have transient IR excesses.Comment: Accepted to AJ; 38 figures, 93 page