Nachbeobachtungen von Transitkandidaten und jungen bedeckungsveränderlichen Doppelsternen in der scheinbaren Umgebung des offenen Sternhaufens Trumpler 37

Seit der Entdeckung des ersten Exoplaneten 1995 wurden bisher über 1000 Planeten gefunden. Dadurch hat sich das Verständnis von Planeten- und Sternentstehung stark verbessert. Es ist nötig möglichst viele Parameter der Planeten und Sterne (Masse, Radius, Alter) direkt zu bestimmen um diese Werte mit Modellen vergleichen zu können. Bisher wurden vorwiegend Planeten älter als 100 Mio. Jahre untersucht. In dieser Arbeit wurde mit Hilfe der Transitmethode nach jungen Exoplaneten im 4 Mio. Jahre jungen Sternhaufen Trumpler 37 gesucht. Die Region des Sternhaufens wurde dabei mit dem Teleskop des "Astrophysikalischen Instituts und Universitäts-Sternwarte" Jena, sowie anderen Teleskopen des YETI (Young Exoplanet Transit Initiative) Netzwerkes in 188 Nächten über einen Zeitraum von drei Jahren beobachtet. Aus den korrigierten Aufnahmen wurden für über 17000 Sterne (Mitgliedssterne, sowie Vorder- und Hintergrundsterne) die Lichtkurven extrahiert. Dabei kam differentielle Photometrie zum Einsatz. In den Lichtkurven wurde nach Periodizität sowie typischen Transitsignalen gesucht. Es wurden über 400 variable Sterne gefunden, darunter zwei transitartige. Für diese Sterne wurden Nachbeobachtungen durchgeführt um andere, falsch-positive Ursachen auszuschließen. Es zeigte sich, dass beide Signale von Doppelsternen verursacht wurden. Das eine System besteht aus einem sonnenartigen und einem sehr massearmen Stern, während es sich bei dem anderen System um zwei Sternen ähnlicher Größe und Leuchtkraft handelt, bei welchen sich jedoch ein weiterer Stern innerhalb der optischen Punktbidfunktion des Doppelsterns befindet. Im letzten Teil der Arbeit wurden die in Trumpler 37 gefundenen Doppelsterne spektroskopisch untersucht und die Lichtkurven und Radialgeschwindigkeitsdaten gemeinsam modelliert. Dadurch konnten unter anderem Massen und Radien der beiden Komponenten eines Systems bestimmt werden, welche im Anschluss mit verschiedenen Modellen zur Sternentstehung verglichen wurden

EXOhSPEC folded design optimization and performance estimation

The EXOplanet high resolution SPECtrograph (EXOhSPEC) instrument is an echelle spectrograph dedicated to the detection of exoplanets by using the radial velocity method using 2m class telescopes. This spectrograph is specified to provide spectra with a spectral resolution R < 70, 000 over the spectral range from 400 to 700 nm and to reach a shortterm radial velocity precision of 3 m/s. To achieve this the separation between two adjacent spectral orders is specified to be greater than 30 pixels and to enable a wide range of targets the throughput of the instrument is specified to be higher than 4%. We present the results of the optimization of the spectrograph collimator performed and initial tests of its optical performance. First, we consider the spectrograph design and we estimate its theoretical performance. We show that the theoretical image quality is close to the diffraction limit. Second, we describe the method used to perform the tolerancing analyzes using ZEMAX software to estimate the optical performance of the instrument after manufacturing, assembly and alignment. We present the results of the performance budget and we show that the estimated image quality performance of EXOhSPEC are in line with the specifications. Third, we present the results of the stray light analysis and we show that the minimum ratio between the scientific signal and the stray light halo signal is higher than 1,000. Finally, we provide a status on the progress of the EXOhSPEC project and we show the first results obtained with a preliminary version of the prototype.Final Accepted Versio

Transmission properties of tapered optical fibres: Simulations and experimental measurements

© 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license. https://creativecommons.org/licenses/by-nc-nd/4.0/We measured the transmission of tapered and untapered optical fibres as a function of input beam numerical aperture at 635 nm. The tapered fibres were fabricated with an adiabatic tapering process from graded and step-index fibres with 50 m core diameters to form a 100 mm long taper with 5:1 taper ratio. We tested tapered graded-index and step-index fibres fabricated from commercial Thorlabs products and a custom graded-index taper. The 5:1 tapered graded-index fibre can give a transmission greater than 0.4 for Thorlabs and 0.6 for the custom taper. We simulated the transmission of the tapered fibres and found reasonable agreement with the measured graded-index tapered fibre results across the numerical aperture range of interest. Experimentally, step-index tapered fibres performed relative poorly and considerably below modelling expectations. Based on our examinations this arises because the properties of step-index fibre were not robust to the tapering process. Suitably tapered graded-index fibres may offer a new route for efficient focal ratio reduction of fibre optic signals, e.g., in fibre-fed spectrographs, though we stress that our measurements have been limited to monochromatic light in this work.Peer reviewe

A small actively-controlled high-resolution spectrograph based on off-the-shelf components

© 2021. The Astronomical Society of the Pacific. The original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. https://creativecommons.org/licenses/by/3.0/We present the design and testing of a prototype in-plane echelle spectrograph based on an actively controlled fiber-fed double-pass design. This system aims to be small and efficient with the minimum number of optical surfaces—currently a collimator/camera lens, cross-dispersing prism, grating and a reflector to send light to the detector. It is built from catalog optical components and has dimensions of approximately 20 × 30 cm. It works in the optical regime with a resolution of >70,000. The spectrograph is fed by a bifurcated fiber with one fiber to a telescope and the other used to provide simultaneous Thorium Argon light illumination for wavelength calibration. The positions of the arc lines on the detector are processed in real time and commercial auto-guiding software is used to treat the positions of the arc lines as guide stars. The guiding software sends any required adjustments to mechanical piezo-electric actuators which move the mirror sending light to the camera removing any drift in the position of the arc lines. The current configuration using an sCMOS detector provides a precision of 3.5 milli-pixels equivalent to 4 ms −1 in a standard laboratory environment.Peer reviewe

HiFLEx – a highly flexible package to reduce cross-dispersed Echelle spectra

© 2020 The Astronomical Society of the Pacific. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence (https://creativecommons.org/licenses/by/3.0/). Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.We describe a flexible data reduction package for high resolution cross-dispersed echelle data. This open-source package is developed in Python and includes optional GUIs for most of the steps. It does not require any pre-knowledge about the form or position of the echelle-orders. It has been tested on cross-dispersed echelle spectrographs between 13k and 115k resolution (bifurcated fiber-fed spectrogaph ESO-HARPS and single fiber-fed spectrograph TNT-MRES). HiFLEx can be used to determine radial velocities and is designed to use the TERRA package but can also control the radial velocity packages such as CERES and SERVAL to perform the radial velocity analysis. Tests on HARPS data indicates radial velocities results within ±3ms−1 of the literature pipelines without any fine tuning of extraction parameters.Peer reviewe

YETI – search for young transiting planets******

We present our search for young transiting planets at ages of 2 to 20 Myr. Towards this goal, we monitor a number of young open clusters with the YETI network. YETI consists of 0.4-2 m-sized telescopes at different longitudes that observe continuously over timescales much longer than a night. In our first cluster Trumpler 37 we found more than 350 variable stars. Also two transiting candidates were found so far, for which follow-up is partly done. The first candidate turned out to be an eclipsing binary with an M-type companion. We describe the research done on these two transiting candidates

Interferometric nulling of four channels with integrated optics

Nulling interferometry has been identified as a competitive technique for the detection of extrasolar planets. In its basic form, the technique consists of combining out-of-phase a single pair of telescopes to effectively null the light of a bright star and reveal the dim glow of the companion. However, in order to mitigate the effect of the stellar leaks through the interferometer, a broad angular central null is required. The hierarchical combination of several pairs of telescopes can accomplish this task. We have manufactured and tested with monochromatic light an integrated optics component, which combines a linear array of four telescopes in the nulling mode envisaged by Angel and Woolf [Astroph. J. 475, 373 -379 (1997).]. By simulating in the laboratory the motion of a star in the sky, we could measure the expected angular transmission of the four-telescope nuller. Moreover, the tests have demonstrated a broad nulling scaling as the fourth power of the baseline delay. (C) 2015 Optical Society of Americ

YETI – search for young transiting planets

We present our search for young transiting planets at ages of 2 to 20 Myr. Towards this goal, we monitor a number of young open clusters with the YETI network. YETI consists of 0.4-2 m-sized telescopes at different longitudes that observe continuously over timescales much longer than a night. In our first cluster Trumpler 37 we found more than 350 variable stars. Also two transiting candidates were found so far, for which follow-up is partly done. The first candidate turned out to be an eclipsing binary with an M-type companion. We describe the research done on these two transiting candidates