165 research outputs found
Fast photodetectors and their role in measuring star diameters with the MAGIC intensity interferometer
No full textA few years ago MAGIC Stellar Intensity Interferometer (MAGIC-SII) was implemented by applying adjustments to the existing MAGIC IACT array. One of the key parts of the instrument are the photodetectors. Improved photodetector properties as a higher PDE or a better SPTR could increase the sensitivity of the interferometer. This could be achieved, for instance, if the PMTs were replaced by SiPMs thanks to their excellent SPTR. Probably the main drawback of SiPMs is their limited area. I worked on two approaches that aimed at overcoming this limitation: LASiP and Photo-Trap. The first one sums the current of several SiPMs into a single output. We built and characterized a LASiP prototype that used an ASIC called MUSIC to sum the output of 8 SiPMs of 6 mm 6 mm. I explored the feasibility of using LASiPs in SPECT, which is an application in which one needs to cover a large area (50 40 cm) with a limited amount of readout channels (typically 100). I showed that it was possible to reconstruct simple images with an energy resolution of 11.6 \% and an intrinsic spatial resolution of 2 mm (comparable to standard SPECT cameras). Using SiPMs would allow reducing by at least 50 \% the volume of a SPECT camera which would result in a compact and lighter camera. A few LASiPs are also present in one of the MAGIC cameras. These pixels could be a good starting point for testing the feasibility of using SiPMs in intensity interferometry.\\
Photo-Trap provides a different solution to build large SiPM pixels, combining a WLS plastic and a dichroic filter with a commercial SiPM. We built four prototypes using WLS plastics of 20~~20~mm or 40~~40~mm and SiPMs of 3~~3 mm or 3~~12~mm. One of those prototypes is, as far as I know, the largest existing SiPM pixel with single-phe resolution at room temperature. One of the main advantages of Photo-Trap is that it is easily scalable to larger sizes. The prototypes achieved a trapping efficiency of (which corresponds to a peak PDE of ) with a time resolution of ~ns (FWHM).
My main contribution to the MAGIC-SII was the development of the analysis chain which was used to analyze the data of multiple calibration campaigns. The calibration results of the MAGIC-SII showed that the current MAGIC-SII is a working and reliable instrument. MAGIC-SII has so far measured the diameter of over 25 stars. The diameters of several of them were measured for the first time by MAGIC-SII, at least in its wavelength band (412-438 nm). Since some of them are variable stars, they appear as interesting targets to study their oblateness and might be candidates for asteroseismology studies. Observations of these types of targets may contribute to improving our knowledge of stellar structure and evolution
Meioneta canariensis Wunderlich 1987
No full textMeioneta canariensis (Wunderlich, 1987) Taxonomy & Ecology, 1: 151–152 Paratypes. Canary Islands. Tenerife, Anaga Montains: 1♂ 1 ♀ 2 subadult ♂ IV J. Wunderlich leg. (DZUL 24652). Current status: valid species, originally described as Agyneta canariensis (see Platnick 1989). Additional notes: these paratypes were collected by J. Wunderlich and originally published as deposited in his collection (SJW), but were subsequently assigned by the author and kept at DZUL.Published as part of Reboleira, Ana Sofia P. S., Pérez, Antonio José, López, Heriberto, Hernández, Nuria Macías -, Cruz, Salvador De La & Oromí, Pedro, 2012, Catalogue of the type material in the entomological collection of the University of La Laguna (Canary Islands, Spain). I. Arachnida, pp. 61-79 in Zootaxa 3556 on pages 73-74, DOI: 10.5281/zenodo.21283
Tenuiphantes canariensis Wunderlich 1987
No full textTenuiphantes canariensis (Wunderlich, 1987) Taxonomy & Ecology, 1: 157–158 Paratypes. Canary Islands. La Palma, without locality: 3♂ 3 ♀ VII J. Wunderlich leg. (DZUL 24643). Current status: valid species, originally described as Lepthyphantes canariensis (see Saaristo & Tanasevitch 1996). Additional notes: these paratypes were collected by J. Wunderlich and originally published as deposited in his collection (SJW), but were subsequently assigned by the author and kept at DZUL.Published as part of Reboleira, Ana Sofia P. S., Pérez, Antonio José, López, Heriberto, Hernández, Nuria Macías -, Cruz, Salvador De La & Oromí, Pedro, 2012, Catalogue of the type material in the entomological collection of the University of La Laguna (Canary Islands, Spain). I. Arachnida, pp. 61-79 in Zootaxa 3556 on page 74, DOI: 10.5281/zenodo.21283
Spatiator martensi Wunderlich, 2006, n. sp.
No full textSpatiator martensi n. sp. Figs 1 –3, 5 Type material: Male holotype in Baltic amber, its origin is most probably the region of Kaliningrad (Königsberg), F 1688 /BB/AR/ CJW, SMF. Derivatio nominis: This species is dedicated to Prof. Jochen Martens, University of Mainz, who discovered numerous arachnids which were new to science; I had the pleasure to describe some of the spiders which were collected by J. Martens in Nepal. J. Martens and the present author have been in close and best contact for 35 years. Diagnosis ( ♂; Ψ unknown ): Close to Spatiator praeceps, but embolus in S. martensi n. sp. not that slender, forming a large triangle, and tips of embolus and conductor separated (Fig. 3). Description ( ♂ ): Measurements (in mm): Body length 4.3, prosomal length 2.1, opisthosoma: Length 1.9, width 1.3; leg I: Femur 1.3, patella 1.7, tibia 1.15, metatarsus 0.85, tarsus 0.8, tibia IV 1.5, its diameter 0.14. Color: Body and legs dark brown, opisthosoma yellow brown. Prosoma (Figs 1, 5) ca. 1.7 times longer than wide, cephalic part distinctly raised, thoracic fissure long, setae indistinct, mostly short, cuticula fairly rugose. 8 eyes in two rows, anterior median eyes distinctly largest, posterior row distinctly procurved. Basal cheliceral articles large, retrolaterally with a large field of stridulatory files, fangs short, peg teeth hidden. Gnathocoxae converging above the labium which is long and slender. Sternum finely rugose, prolongated between the coxae IV. Petiolus is long and apparently symmetrically bipartite. Legs fairly long and slender, order IV/I/II/III, bristles absent, setae short and indistinct Tibia and metatarsus I slightly bent, bearing some prodorsal to prolateral spatulate setae, tarsi I–II bear a weak ventral pseudoscopula, metatarsus III bears a dense field of long ventral preening setae in the distal half. Opisthosoma (Figs 1, 5) oval, 1.45 times longer than wide, dorsally covered with short setae and hardened (apparently leathery) along its whole length. Epigaster sclerotized, lung covers hairless, small; epiandrous gland spigots absent. Spinnerets short and partly hidden. Pedipalpus (Figs 2–3) fairly small, with stout articles, tibia with a short prodorsal bristle and at least one dorsal trichobothrium. Cymbium wide, enclosing the bulbus, with few strong prodorsal setae besides long normal setae, bulbus long, tegulum large, embolus in a retroventral position, conductor distinctly separate from the embolus and in a more prolateral position and bent distally to the embolus, sperm duct easily recognizable. Female: unknown. Relationships: Only a single congeneric species has been described previously: Spatiator praeceps. The holotype of S. praeceps is a female. I described a male which I regarded as conspecific with the holotype, see Wunderlich (2004: 768, 807, fig. 56) (in this figure I probably mistook the embolus for the conductor). This male is probably conspecific with the female holotype of S. praeceps but — according to the distinctly different structures of their bulbi — it is not conspecific with S. martensi n. sp. No somatic differences are known to exist between these three specimens. This case reflects a fundamental problem in the taxonomy of numerous congeneric — fossil species: (a) the generotype is known from one sex only (or is juvenile), (b) no somatic differences between different species are known and (c) it is not likely to find both sexes in the same piece of amber: How do deal with different congeneric species of the other sex? Occasionally — for practical reasons — fossil specimens from the other sex were described as different species (in contrast to extant species), e.g. by Petrunkevitch (1942). So it would be consequent to designate a new name for Spatiator praeceps sensu Wunderlich (2004) but this is not a matter of this paper. I found no somatic differences between the present holotype and the material of praeceps sensu Wunderlich (2004) but the bulbus structures are clearly different (and in my opinion surely not caused by circumstances of the preservation): embolus and conductor are in close contact in the male of S. praeceps (Fig. 4) in contrast to S. martensi n. sp. (Fig. 3). Distribution: Early Tertiary (Eocene) Baltic amber forest. Preservation: The spider is situated at the corner of a yellow piece of amber which has a size of 3.1 x 2.0 x 0.9 mm. Legs and pedipalpi are completely and well preserved, some parts are darkened apparently by heating, the ventral side is weakly covered with a white emulsion, the opisthosoma has a low longitudinal depression dorsally (probably the result of a blow), a bubble is situated close to the left cymbium, but distinctly separated from the cymbial cuticula. Syninclusions: Four Formicidae, workers (body length 1.3, 2.4, 2.4 and 4.3 mm), remains of the abdomen of an ant (two parts, 1.4 mm long) 2 mm right of the spider in the same layer of the amber, an adult Acari (body length 1 mm), few tiny to small larvae of Acari (body length up to 0.5 mm), numerous stellate hairs of plants, numerous small bubbles and bubbleshaped particles which are dried out as well as particles of detritus. Notes: (a) Myrmecophagy: Remains of an ant — two parts of an abdomen — near the spider's body may be remains of the spider's prey, but this presumption is quite tentative: Most relatives of the Spatiatoridae, e. g. Archaeidae and Palpimanidae, are araneophages. The complete ants in the same piece of amber are apparently not injured. (b) Myrmecomorphy: The silvery glancing cuticle in most congeneric specimens (S. praeceps) which are preserved in pieces of amber which were not heated, the slender body and legs as well as the raised cephalic part — which give the illusion of a tripartite body of the spider — may be hints that these spiders were only weakly antshaped. We do not know the behavior of the fossil spiders, and a saddleshaped inclination of the opisthosoma is absent. Therefore I am not sure about the actual antmimicry of these fossil spiders. The largest ant which is embedded together with the spider has the same body size as the spider and may have been a model of a probable Batesian mimicry. The small ants may have been the model of conspecific juveniles.Published as part of Wunderlich, Jörg, 2006, Spatiator martensi n. sp., a second species of the extinct spider family Spatiatoridae in Eocene Baltic amber (Araneae), pp. 313-318 in Zootaxa 1325 on pages 314-317, DOI: 10.5281/zenodo.17402
Investigating the accuracy achievable in reconstructing the angular sizes of stars through stellar intensity interferometry observations
No full textContext. In recent years, stellar intensity interferometry has seen renewed interest from the astronomical community because it can be efficiently applied to Cherenkov telescope arrays.
Aims. We have investigated the accuracy that can be achieved in reconstructing stellar sizes by fitting the visibility curve measured on the ground. The large number of expected available astronomical targets, the limited number of nights in a year, and the likely presence of multiple baselines will require careful planning of the observational strategy to maximise the scientific output.
Methods. We studied the trend of the error on the estimated angular size, considering the uniform disk model, by varying several parameters related to the observations, such as the total number of measurements, the integration time, the signal-to-noise ratio, and different positions along the baseline.
Results. We found that measuring the value of the zero-baseline correlation is essential to obtain the best possible results. Systems that can measure this value directly or for which it is known in advance will have better sensitivity. We also found that to minimise the integration time, it is sufficient to obtain a second measurement at a baseline half-way between 0 and that corresponding to the first zero of the visibility function. This function does not have to be measured at multiple positions. Finally, we obtained some analytical expressions that can be used under specific conditions to determine the accuracy that can be achieved in reconstructing the angular size of a star in advance. This is useful to optimise the observation schedule
Evaluation of temperature influence on ultrasound velocity in concrete by coda wave interferometry
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