ABSTRACT
We present a study based on the high-resolution spectroscopy and K2 space photometry of five chemically peculiar stars in the region of the open cluster M44. The analysis of the ...high-precision photometric K2 data reveals that the light variations in HD 73045 and HD 76310 are rotational in nature and caused by spots or cloud-like co-rotating structures, which are non-stationary and short-lived. The time-resolved radial velocity measurements, in combination with the K2 photometry, confirm that HD 73045 does not show any periodic variability on time-scales shorter than 1.3 d, contrary to previous reports in the literature. In addition to these new rotational variables, we discovered a new heartbeat system, HD 73619, where no pulsational signatures are seen. The spectroscopic and spectropolarimetric analyses indicate that HD 73619 belongs to the peculiar Am class, with either a weak or no magnetic field, considering the 200-G detection limit of our study. The least-squares deconvolution profiles for HD 76310 indicate a complex structure in its spectra, suggesting that this star is either part of a binary system or surrounded by a cloud shell. When placed in the Hertzsprung–Russell diagram, all studied stars are evolved from the main sequence and situated in the δ Scuti instability strip. This work is relevant for further detailed studies of chemically peculiar stars, for example on inhomogeneities (including spots) in the absence of magnetic fields and the origin of the pulsational variability in heartbeat systems.
Kepler observations of the open cluster NGC 6819 Balona, L. A; Medupe, T; Abedigamba, O. P ...
Monthly Notices of the Royal Astronomical Society,
04/2013, Letnik:
430, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Using photometry from the Kepler Input Catalogue, we determine the distance and age of NGC 6819 using several different methods. From isochrone fitting we find the age of the cluster to be about 2.5 ...Gyr. There are many different types of variables in the field, including eight δ Scuti stars, at least three γ Dor variables and several eclipsing binaries of various types. We derive masses, radii and luminosities from 63 red giants with solar-like oscillations, including 28 stars with no previous measurements, from which we obtain an unreddened distance modulus of 12.20 ± 0.06 mag. We measured rotation periods of 129 stars which showed variations attributable to starspots. There is a correlation between the rotation period and the colour which extends to stars with temperatures equivalent to late A-type. This implies that starspots are present in stars which are much hotter than previously supposed. We also discuss several eclipsing binaries and the variability of stars which are blue straggler candidates and discuss X-ray sources found in the cluster.
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•Ho3+-doped NiO nanophosphor-based sensor was reported for the first time.•Upon increasing the exposure time, the response improved by almost 6 times.•Exposure time and applied bias ...voltage play a vital role in sensing performance.
The incorporation of rare earths (REs) into semiconducting metal oxides is advantageous for creating surface defects and manipulating electronic structures. Therefore, the hydrothermal method fabricated p-type NiO nanostructures with various holmium (Ho3+) ion concentrations of 0, 1, 2, 3, and 4 wt% are investigated. The gas sensing features of the Ho3+-doped NiO sensors were conducted at different bias voltages and exposure times. At the bias voltage of 1 V with the exposure time of 5 min, the Ho3+-doped NiO sensors displayed a relatively high response of 36.35%, detection limit and sensitivity of 449 ppb and 0.749 ppm−1, respectively towards 60 ppm toluene at 100 °C. Upon increasing the exposure time to 1 h, at the applied bias voltage of 0.5 V, the response improved by almost 6 times (Rg/Ra ∼ 201%) towards 60 ppm of toluene, showing the outstanding toluene selectivity against benzene, xylene, ethyl-benzene and acetone vapours. The gas sensing findings proved that an appropriate concentration of Ho3+ doping, exposure time and applied bias voltage have a significant influence on the sensing performances. Further tuning of these features could result in an improved sensing response. The increased sensing mechanism is assigned to the creation of oxygen vacancies.
Access to safe drinking water is a basic human right in South Africa. Therefore, the accurate measurement of water quality is critical in ensuring the safety of water prior to its intended use. ...Proficiency testing schemes (PTSs) are a recognised form of assessing the technical competence of laboratories performing these analyses. There are over 200 water testing laboratories in South Africa, with only 51 being accredited for testing some or all parameters (physical, chemical and microbiological content) prescribed in SANS 241. Only a limited number of laboratories test for organic contaminants, as this requires advanced, costly analytical instrumentation, such as GC-FID/ECD/MS and LC-UV/MS, as well as skilled staff. These laboratories are either looking at selected organic contaminants listed in the World Health Organisation (WHO) drinking water guidelines or performing the minimum requirements, as stipulated in SANS 241, for phenols, atrazine, trihalomethanes and total dissolved organic content. Whereas several local PTS providers are addressing the competent assessment of microbiological, physical and inorganic chemical testing of water, a clear need for a South African PTS provider for organic contaminant analysis in water was identified by NMISA (National Metrology Institute of South Africa) in 2012. The key drivers for the coordination of a local PTS stem mainly from the limited stability of analytes in the samples for analysis and the high cost and logistics of international PTS participation. During 2012 and 2013, NMISA conducted a PTS trial round, a workshop and 2 additional PTS rounds for organochlorine pesticides in water, for South African laboratories, and also several international participants from other countries in Africa. This paper will highlight some of the challenges faced by laboratories when analysing organochlorine pesticides at the ng/l concentration level. Issues surrounding the comparability of measurement results, traceability, method validation and measurement uncertainty are also discussed.
Limited studies have been undertaken with regard to virus complexes contributing to the aetiology of sweet potato virus disease (SPVD) in South Africa (SA). In this study, a metagenomic approach was ...adopted to reveal the genetic diversity of viruses infecting sweet potato. In order to undertake a comprehensive analysis of viral sequences, total RNA was isolated from 17 asymptomatic and symptomatic sweet potato plants that were collected from the Eastern (EC) and Western Cape (WC) provinces of SA. DNase-treated total RNA was depleted of ribosomal RNA (rRNA) and deep-sequenced using the Illumina MiSeq platform. Genomic DNA, isolated from the same plants, underwent rolling circle amplification (RCA) and deep sequencing. Sequence reads were analysed with the CLC Bio Genomics Workbench. Both de novo and reference-guided assemblies were performed resulting in four near full-length RNA virus genomes. BLAST searches using de novo assembled sequences against published virus genomes confirmed the presence of previously detected begomoviruses in the Western Cape (WC) province, namely Sweet potato mosaic virus (SPMaV) and Sweet potato leaf curl Sao Paulo virus (SPLCSPV). The begomoviruses were detected in mixed infections with two major disease-causing RNA viruses, Sweet potato feathery mottle virus (SPFMV) and Sweet potato chlorotic stunt virus (SPCSV). The sequence data further demonstrated mixed infections of RNA and DNA viruses from 11 of the 17 sequenced samples. Metagenomics is a reliable diagnostic tool for virus diversity detection, in particular virus-complexes and synergies affecting disease aetiology.
•Detection of sweet potato viruses using a metagenomic approach and next generation sequencing (NGS).•Assembled full-length and near full-length genomes of six viruses•A distinct SPCSV RNA 1 segment, which suggests a reassortment.•Mixed virus infections of begomoviruses, a Potyvirus and a Crinivirus in individual plants•Design of virus specific primers for South African sweet potato isolates
We reviewed the implementation of isoniazid preventive therapy (IPT) in South Africa from January 2010 to March 2011. The South African National Department of Health distributed revised IPT ...guidelines in May 2010 to increase IPT use in eligible human immunodeficiency virus (HIV) infected patients. We found a dramatic increase in the absolute numbers of patients reported to have been initiated on IPT (from 3309 in January-March 2010 to 49 130 in January-March 2011), representing an increase in the proportion (1.0-10.5%) of potentially eligible HIV-infected patients started on IPT.
Nanostructured Zn- and Al-doped cobalt spinel ferrites Zn
x
Co
1-
x
Fe
2-
x
Al
x
O
4
(0 ≤
x
≤ 1.0) with particle size in the range of 7–13 nm were synthesized by glycol-thermal reaction. XRD ...analysis confirmed single-phase cubic spinel structure with no impurity phases. The Mössbauer spectra for Zn- and Al-substituted fine powders could be resolved into two quadrupole doublets associated with
57
Fe nuclei in paramagnetic spin phase. An unusual reducing magnetization with increasing particle size has been observed. The field cooled and zero field cooled magnetization measurements show superparamagnetic nanoparticles in the compounds investigated. The blocking temperatures (
T
B
) are sensitive to particle size. Larger particles are blocked at higher temperatures compared to smaller particles at the same field.
We present a study based on the high-resolution spectroscopy and K2 space photometry of five chemically peculiar stars in the region of the open cluster M44. The analysis of the high-precision ...photometric K2 data reveals that the light variations in HD 73045 and HD 76310 are rotational in nature and caused by spots or cloud-like co-rotating structures, which are non-stationary and short-lived. The time-resolved radial velocity measurements, in combination with the K2 photometry, confirm that HD 73045 does not show any periodic variability on timescales shorter than 1.3 d, contrary to previous reports in the literature. In addition to these new rotational variables, we discovered a new heartbeat system, HD 73619, where no pulsational signatures are seen. The spectroscopic and spectropolarimetric analyses indicate that HD 73619 belongs to the peculiar Am class, with either a weak or no magnetic field considering the 200 G detection limit of our study. The Least-Squares Deconvolution (LSD) profiles for HD 76310 indicate a complex structure in its spectra suggesting that this star is either part of a binary system or surrounded by a cloud shell. When placed in the Hertzsprung-Russell diagram, all studied stars are evolved from main-sequence and situated in the \(\delta\) Scuti instability strip. The present work is relevant for further detailed studies of CP stars, such as inhomogeneities (including spots) in the absence of magnetic fields and the origin of the pulsational variability in heartbeat systems.
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