Abstract
We report on a detailed abundance study of six bright, mostly southern, slowly rotating late B-stars: HD 1279 (B8III), HD 99803 (B9V), HD 123445 (B9V), HD 147550 (B9V), HD 171961 (B8III), ...and HD 202671 (B5II/III), hitherto reported as normal stars. We compare them to the two classical HgMn stars
μ
Lep and
β
Scl, and to the superficially normal star
ν
Cap. In the spectra of the six stars, the Hg
ii
line at 3984 Å line is clearly seen and numerous lines of P, Ti, Mn, Fe, Ga, Sr, Y, and Zr appear to be strong absorbers. A comparison of newly acquired and archival spectra of these objects with a grid of synthetic spectra for selected unblended lines reveals large overabundances of P, Ti, Cr, Mn, Sr, Y, Zr, Ba, Pt, and Hg, and underabundances of He, Mg, Sc, and Ni. The effective temperatures, surface gravities, low projected rotational velocities, and the peculiar abundance patterns of the six investigated stars show that they are new chemically peculiar stars, mostly new HgMn stars, and are reclassified as such. The evolutionary status of these stars has been inferred, and their ages and masses estimated. The two most massive objects, HD 1279 and HD 202671, might have evolved away from the main sequence recently, the other stars are main-sequence objects. HD 99803A is a sharp lined HgMn star with grazing eclipses. From TESS and MASCARA photometry, we determine an orbital period of
P
orb
= 26.12022 ± 0.00004 day.
Linearity of P–N junction photodiodes under pulsed irradiation Stuik, Remko; Bijkerk, Fred
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2002, Letnik:
489, Številka:
1
Journal Article
Recenzirano
The dependence of the sensitivity on the radiation pulse length for a P–N junction photodiode has been investigated over an extended range of pulse lengths, from 170
ns to 1.2
ms. The power incident ...on the diode surface was varied between 1.6 and 118
mW.
A novel method was used to generate the light pulses with variable length, while keeping the temporal pulse shape and the intensity constant. The method consists of using a rotating mirror in combination with a DC light source, in our case at 633 and 532
nm. In this way, the pulse shape only depends on the geometry of the setup, with the pulse length solely determined by the rotation frequency of the mirror. No further calibration is needed for determination of the pulse intensity and shape. Accuracies obtained are better than 2%, mainly determined by instabilities in the setup.
The sensitivity of an IRD AXUV-100 photodiode was studied, both with and without a reverse bias voltage applied. At unbiased conditions and irradiation levels well below the saturation intensity, the photodiode had a constant, frequency-independent sensitivity over the full range of pulse lengths investigated. The sensitivity decreased at irradiation levels approaching saturation, with the largest decrease at longer pulse lengths. This decrease was fully accounted for by electron–hole recombination at a typical time scale of 15±5
μs.
Under biased conditions and pulse lengths below 5
μs, the diode sensitivity remained constant for all incident power levels investigated. At longer pulse lengths a decrease in sensitivity was observed, both at low and high power. This second type of decrease is attributed to the frequency response of the bias electronics.
An extrapolation of the results to other wavelength ranges is given, including the extreme ultraviolet (EUV) and soft X-ray ranges.
The Multi-site All-Sky CAmeRA, MASCARA, is an instrument currently in the design phase, that is aimed to find the brightest transiting planet systems In the sky. It will consist of several stations ...across the globe, each monitoring the near-entire sky using a battery of CCD-detectors plus wide-field lenses, targeting stars in the V = 4 ? 8 magnitude range. MASCARA will be able to detect individual transits from Jupiter-size planets over this whole magnitude range, while smaller planets will be found by co-adding transit events. We expect to discover up to a dozen bright transit systems In this way. These will be extremely valuable for atmospheric follow-up studies.
The β Pictoris system is the closest known stellar system with directly detected gas giant planets, an edge-on circumstellar disc, and evidence of falling sublimating bodies and transiting exocomets. ...The inner planet, β Pictoris c, has also been indirectly detected with radial velocity (RV) measurements. The star is a known δ Scuti pulsator, and the long-term stability of these pulsations opens up the possibility of indirectly detecting the gas giant planets through time delays of the pulsations due to a varying light travel time. We search for phase shifts in the δ Scuti pulsations consistent with the known planets β Pictoris b and c and carry out an analysis of the stellar pulsations of β Pictoris over a multi-year timescale. We used photometric data collected by the BRITE-Constellation, bRing, ASTEP, and TESS to derive a list of the strongest and most significant δ Scuti pulsations. We carried out an analysis with the open-source python package maelstrom to study the stability of the pulsation modes of β Pictoris in order to determine the long-term trends in the observed pulsations. We did not detect the expected signal for β Pictoris b or β Pictoris c. The expected time delay is 6 s for β Pictoris c and 24 s for β Pictoris b. With simulations, we determined that the photometric noise in all the combined data sets cannot reach the sensitivity needed to detect the expected timing drifts. An analysis of the pulsational modes of β Pictoris using maelstrom showed that the modes themselves drift on the timescale of a year, fundamentally limiting our ability to detect exoplanets around β Pictoris via pulsation timing.
ABSTRACT
We have found that the 2+2 quadruple star system BU CMi is currently the most compact quadruple system known, with an extremely short outer period of only 121 d. The previous record holder ...was TIC 219006972 (Kostov et al.), with a period of 168 d. The quadruple nature of BU CMi was established by Volkov, Kravtsova & Chochol, but they misidentified the outer period as 6.6 yr. BU CMi contains two eclipsing binaries (EBs), each with a period near 3 d, and a substantial eccentricity of ≃0.22. All four stars are within ∼0.1 M⊙ of 2.4 M⊙. Both binaries exhibit dynamically driven apsidal motion with fairly short apsidal periods of ≃30 yr, due to the short outer orbital period. The outer period of 121 d is found both from the dynamical perturbations, with this period imprinted on the eclipse timing variations curve of each EB by the other binary, and by modelling the complex line profiles in a collection of spectra. We find that the three orbital planes are all mutually aligned to within 1 deg, but the overall system has an inclination angle near 83.5°. We utilize a complex spectro-photodynamical analysis to compute and tabulate all the interesting stellar and orbital parameters of the system. Finally, we also find an unexpected dynamical perturbation on a time-scale of several years whose origin we explore. This latter effect was misinterpreted by Volkov et al. and led them to conclude that the outer period was 6.6 yr rather than the 121 d that we establish here.
The European Extremely Large Telescope (ELT) is a 39m large, ground-based optical and near- to mid-infrared telescope under construction in the Chilean Atacama desert. Operation is planned to start ...around the middle of the next decade. All first light instruments will come with wavefront sensing devices that allow control of the ELT’s intrinsic M4 and M5 wavefront correction units, thus building an adaptive optics (AO) system. To take advantage of the ELT’s optical performance, full diffraction-limited operation is required and only a high performance AO system can deliver this. Further technically challenging requirements for the AO come from the exoplanet research field, where the task to resolve the very small angular separations between host star and planet, has also to take into account the high-contrast ratio between the two objects. We present in detail the results of our simulations and their impact on high-contrast imaging in order to find the optimal wavefront sensing device for the METIS instrument. METIS is the mid-infrared imager and spectrograph for the ELT with specialised high-contrast, coronagraphic imaging capabilities, whose performance strongly depends on the AO residual wavefront errors. We examined the sky and target sample coverage of a generic wavefront sensor in two spectral regimes, visible and near-infrared, to pre-select the spectral range for the more detailed wavefront sensor type analysis. We find that the near-infrared regime is the most suitable for METIS. We then analysed the performance of Shack-Hartmann and pyramid wavefront sensors under realistic conditions at the ELT, did a balancing with our scientific requirements, and concluded that a pyramid wavefront sensor is the best choice for METIS. For this choice we additionally examined the impact of non-common path aberrations, of vibrations, and the long-term stability of the SCAO system including high-contrast imaging performance.
The bRing robotic observatory network was built to search for circumplanetary material within the transiting Hill sphere of the exoplanet β Pic b across its bright host star β Pic. During the bRing ...survey of β Pic, it simultaneously monitored the brightnesses of thousands of bright stars in the southern sky (V 4-8, δ −30°). In this work, we announce the discovery of δ Scuti pulsations in the A-type star HD 156623 using bRing data. HD 156623 is notable as it is a well-studied young star with a dusty and gas-rich debris disk, previously detected using ALMA. We present the observational results on the pulsation periods and amplitudes for HD 156623, discuss its evolutionary status, and provide further constraints on its nature and age. We find strong evidence of frequency regularity and grouping. We do not find evidence of frequency, amplitude, or phase modulation for any of the frequencies over the course of the observations. We show that HD 156623 is consistent with other hot and high-frequency pre-main sequence and early zero-age main sequence (ZAMS) δ Scutis as predicted by theoretical models and corresponding evolutionary tracks, although we observe that HD 156623 lies hotter than the theoretical blue edge of the classical instability strip. This, coupled with our characterization and Sco-Cen membership analyses, suggests that the star is most likely an outlying ZAMS member of the ∼16 Myr Upper Centaurus-Lupus subgroup of the Sco-Cen association.
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