153 research outputs found
Statistical analysis of lightcurves of active stars
Over the last thirty years more than five thousand exoplanets have been discovered around a wide variety of stellar objects. Most exoplanets have been discovered using the transit method, which relies on observing the periodic brightness changes of stars as their planet transits in front of them. The discovery efficiency of these planets has been strongly enhanced with the advent of space telescopes dedicated to the discovery of planets using the transit method.
Planetary signals in the photometric data of active stars can be challenging to find, as the surface features of the stars combined with their rotation might produce signals which are orders of magnitude stronger than those caused by the planetary transit.
The question of what statistical methods should be applied to account for the innate variability of stars in order to identify the transits of exoplanets in the lightcurves of active stars is being investigated in this thesis.
I test a number of statistical methods in order to combat stellar activity and to identify planetary transit signals. The rotation period of the star is investigated using the Lomb-Scargle and likelihood ratio periodograms.
Starspot induced variability is approximated with a number of sinusoids, with periods based on the star's rotation period. Additional stellar activity is filtered out using autoregressive and moving average models.
Model fittings are performed with least squares fitting, and using samples generated by the Adaptive Metropolis algorithm. After the lightcurve has been detrended for stellar activity, the likelihoods of planetary transit signals are assessed with a box-fitting algorithm. Models are compared with the Bayesian and Akaike information criteria. Planetary characteristics are then estimated by modeling the shape of the transit lightcurve.
These methods are tested and performed on the lightcurve of HD~110082, a highly active young star with one confirmed planetary companion, based on the observations of the TESS space telescope. I find that stellar activity is sufficiently filtered out with a model containing four sinusoid signals. The signal corresponding to the planet is confirmed by the box fitting algorithm, agreeing with results available in scientific literature
Design and Performance of the Data Acquisition System for the NA61/SHINE Experiment at CERN
This paper describes the hardware, firmware and software systems used in data
acquisition for the NA61/SHINE experiment at the CERN SPS accelerator. Special
emphasis is given to the design parameters of the readout electronics for the
40m^3 volume Time Projection Chamber detectors, as these give the largest
contribution to event data among all the subdetectors: events consisting of
8bit ADC values from 256 timeslices of 200k electronic channels are to be read
out with ~100Hz rate. The data acquisition system is organized in "push-data
mode", i.e. local systems transmit data asynchronously. Techniques of solving
subevent synchronization are also discussed.Comment: 14 pages, 13 figure
Protoplanetary and Transitional Disks in the Open Stellar Cluster IC 2395
We present new deep UBVRI images and high-resolution multi-object optical
spectroscopy of the young (~ 6 - 10 Myr old), relatively nearby (800 pc) open
cluster IC 2395. We identify nearly 300 cluster members and use the photometry
to estimate their spectral types, which extend from early B to middle M. We
also present an infrared imaging survey of the central region using the IRAC
and MIPS instruments on board the Spitzer Space Telescope, covering the
wavelength range from 3.6 to 24 microns. Our infrared observations allow us to
detect dust in circumstellar disks originating over a typical range of radii ~
0.1 to ~ 10AU from the central star. We identify 18 Class II, 8 transitional
disk, and 23 debris disk candidates, respectively 6.5%, 2.9%, and 8.3% of the
cluster members with appropriate data. We apply the same criteria for
transitional disk identification to 19 other stellar clusters and associations
spanning ages from ~ 1 to ~ 18 Myr. We find that the number of disks in the
transitional phase as a fraction of the total with strong 24 micron excesses
([8] - [24] > 1.5) increases from 8.4 +\- 1.3% at ~ 3 Myr to 46 +\- 5% at ~ 10
Myr. Alternative definitions of transitional disks will yield different
percentages but should show the same trend.Comment: accepted by the Astrophysical Journa
The mass and density of the dwarf planet (225088) 2007 OR10
The satellite of (225088) 2007 OR10 was discovered on archival Hubble Space
Telescope images and along with new observations with the WFC3 camera in late
2017 we have been able to determine the orbit. The orbit's notable
eccentricity, e0.3, may be a consequence of an intrinsically eccentric
orbit and slow tidal evolution, but may also be caused by the Kozai mechanism.
Dynamical considerations also suggest that the moon is small, D 100
km. Based on the newly determined system mass of 1.75x10 kg, 2007 OR10
is the fifth most massive dwarf planet after Eris, Pluto, Haumea and Makemake.
The newly determined orbit has also been considered as an additional option in
our radiometric analysis, provided that the moon orbits in the equatorial plane
of the primary. Assuming a spherical shape for the primary this approach
provides a size of 123050 km, with a slight dependence on the satellite
orbit orientation and primary rotation rate chosen, and a bulk density of
1.750.07 g cm for the primary. A previous size estimate that
assumed an equator-on configuration (1535 km) would provide a
density of 0.92 g cm, unexpectedly low for a 1000
km-sized dwarf planet.Comment: Accepted for publication in Icaru
Surface Analysis by Secondary Ion Mass Spectrometry (SIMS): Principles and Applications from Swiss laboratories
Secondary Ion Mass Spectrometry (SIMS) extracts chemical, elemental, or isotopic information about a localized area of a solid target by performing mass spectrometry on secondary ions sputtered from its surface by the impact of a beam of charged particles. This primary beam sputters ionized atoms and small molecules (as well as many neutral particles) from the upper few nanometers of the sample surface. The physical basis of SIMS has been applied to a large range of applications utilizing instruments optimized with different types of mass analyzer, either dynamic SIMS with a double focusing mass spectrometer or static SIMS with a Time of Flight (TOF) analyzer. Here, we present a short review of the principles and major applications of three different SIMS instruments located in Switzerland
Altered Potassium Ion Homeostasis in Hearing Loss
Connexins, Kv-type ion channels, and pannexins have a dominant role in maintaining the potassium ion homeostasis in the cochlea. The cellular background currents are sustained by Kir2.1 ion channels; however, their involvement in the hearing system is less clear. In this study, the mutations of gap junction proteins beta 2 (GJB2), beta 3 (GJB3) and beta 6 (GJB6) were screened in the white Caucasian population in Hungary using gene mapping and immunofluorescence methods from translated proteins of these genes—connexins on blood cells. Expression of connexins and Kir2.1 ion channels was investigated in the blood cells of deaf patients prior to cochlear implantation, and the results show significantly decreased amounts of connexin26 and connexin43. In addition, the coexpression of Kir2.1 ion channels with synapse-associated 97 proteins was partially impaired. Our investigation revealed a reduced level of Kir2.1 channels in deaf patients indicating a crucial role for the functional Shaker superfamily of K+ channels in the non-diseased hearing system
Promoter analysis of the rabbit POU5F1 gene and its expression in preimplantation stage embryos
Background: The POU5F1 gene encodes the octamer-binding transcription factor-4 (Oct4). It is crucial in the regulation of pluripotency during embryonic development and widely used as molecular marker of embryonic stem cells (ESCs). The objective of this study was to identify and to analyse the promoter region of rabbit POU5F1 gene; furthermore to examine its expression pattern in preimplantation stage rabbit embryos. [br/] Results: The upstream region of rabbit POU5F1 was subcloned sequenced and four highly conserved promoter regions (CR1-4) were identified. The highest degree of similarity on sequence level was found among the conserved domains between rabbit and human. Among the enhancers the proximal enhancer region (PE-1A) exhibited the highest degree of homology (96.4%). Furthermore, the CR4 regulator domain containing the distal enhancer (DE-2A) was responsible for stem cell-specific expression. Also, BAC library screen revealed the existence of a processed pseudogene of rabbit POU5F1. The results of quantitative real-time PCR experiments showed that POU5F1 mRNA was abundantly present in oocytes and zygotes, but it was gradually reduced until the activation of the embryonic genome, thereafter a continuous increase in POU5F1 mRNA level was observed until blastocyst stage. By using the XYClone laser system the inner cell mass (ICM) and trophoblast portions of embryos were microdissected and examined separately and POU5F1 mRNA was detected in both cell types. [br/] Conclusion: In this study we provide a comparative sequence analysis of the regulatory region of rabbit POU5F1 gene. Our data suggest that the POU5F1 gene is strictly regulated during early mammalian development. We proposed that the well conserved CR4 region containing the DE-2A enhancer is responsible for the highly conserved ESC specific gene expression. Notably, we are the first to report that the rabbit POU5F1 is not restricted to ICM cells only, but it is expressed in trophoblast cells as well. This information may be well applicable to investigate further the possible phylogenetic role and the regulation of POU5F1 gene
- …