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Radial Velocity Measurements for White-Dwarf/Brown-Dwarf Binarie Candidates and Development of an Active Mirror Control for the 11 M Hobby-Eberly-Telescope

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Ludwig-Maximilians-Universität München Radial velocity measurements for white-dwarf/brown-dwarf binarie candidates and development of an active mirror control for the 11 m Hobby-Eberly-Telescope. Dissertation Marco Häuser Ludwig-Maximilians-Universität München Dissertation: Radial velocity measurements for white-dwarf/brown-dwarf binarie candidates and development of an active mirror control for the 11 m Hobby-Eberly-Telescope. Candidate: Date: Reviewer: Marco Häuser 27th of June Supervisor: 2019 Prof. Dr. Ralf Bender Ludwig-Maximilians-Universität 2nd Referee: Prof. Gary Hill Ph.D. University of Texas at Austin Wendelstein Observatorium: Where it all began.... Credit: M. Kluge “Der Ziellose erleidet sein Schicksal - der Zielbewusste gestaltet es.” Immanuel Kant Dissertation an der Fakultät für Physik der Ludwig-Maximilians-Universität München Radialgeschwindigkeitsmessungen von Weißer-Zwerg/Brauner-Zwerg Binärsystem Kandidaten und Entwicklung einer aktiven Primärspiegelkontrolle für das 11 m Hobby-Eberly-Telescope. Vorgelegt von Marco Häuser München, 27 Juni 2019 Erstgutachter: Prof. Dr. Ralf Bender Zweitgutachter: Prof. Gary Hill Ph.D. Datum der mündlichen Prüfung: 6. August 2019 Zusammenfassung Diese Dissertation präsentiert die Ergebnisse von Radialgeschwindigkeitsmes- sungen für potentielle Weißer-Zwerg (WD) / Brauner-Zwerg (BD) Binärsys- teme. Weiterhin wird im zweiten Teil dieser Arbeit das Upgrade der Primär- spiegelkontrolle des 11m Hobby-Eberly-Telescope (HET) des McDonald Ob- servatories in Texas geschildert. Als methodisches Fazit unserer Arbeit stellen zeigt sich, dass die getestete Methode zur Bestätigung von WD-BD unter Nutzung von nieder auflösender Spektroskopie bedingt funktionsfähig ist. Die Auswahl der Testkandidaten beruht auf den nicht klassifizierten Objekten einer ursprünglichen Kandidatenliste von Steele et al. [86], welcher einen Kandidaten als WD-BD bestätigen konnte. Zunächst zeigt sich, dass die reale Leistungsfähigkeit und Stabilität des ES2 Spektrograhen unter Berücksichtigung aller notwendigen Kalibrationen nicht zur sicheren Klassi- fikation von WD-BD Binärsystemen ausreicht. Dem gegenüber erreicht der deutlich modernere LRS2 Spektrograph grundsätzlich seine Spezifikationen und ist somit für die Selektion von Kandidatenlisten für die Nachverfolgung mit noch aufwendigeren Instrumenten geeignet. Alle Kandidaten werden durch Ihre Spektren als Spezialfälle von F-Sternkonstallationen und nicht als als WD-BD Binärsystem klassifiziert. Diese Einschätzung wird durch die inzwischen verfügbaren Distanzmessungen der Gaia-Satellitenmission [30][29] bestätigt. Diese Studie zeigt, dass niederauflösende und somit kostengünstige Spektroskopie ein probates Mittel zur Vorselektion von deutlich aufwendi- geren Multi-Instrument Beobachtungen sein kann. Der zweite Teil dieser Dissertation behandelt das Design der neuen aktiven Hauptspiegelsteuerung des optischen Großteleskopes HET. Ziel dieses Upgrade ist die Langzeitperformance sowie die Gesamteffizienz des HET nachhaltig zu steigern. Die verbesserte Systemleistung in Hinsicht auf die Stabilität und Abwärme sind in Form eines verbesserten Seeings Gegen- stand aktueller und zukünftiger Messungen. Zunächst wird die Vorgänger Studie in welcher für das 4MOST- Projekt der Prototyp eines Glasfaserpositionierer mit 27 µm absoluter Po- sitioniergenauigkeit bei 1σ = 14 µm Standardabweichung entwickelt wurde, präsentiert. Aufbauend auf dieser Entwicklung wurde die Hauptspiegelsteuerung des HET durch unseren maßgeschneiderte HET Segment Motion Controller ersetzt und in Zusammenarbeit mit dem technischen Team des HET die Inbetriebnahme begonnen. Seit dem 5 Juni 2019 wird der Hauptspiegel des HET nun im wissenschaftlichem Betrieb von SCS2 gesteuert. Summary In a nutshell: The work presented in this thesis observationally tests the evolutionary scenarios which can yield a binary system, consisting of a highly evolved stellar remnant of an intermediate to low mass star and an almost unevolved very low mass star, which most probably formed together. The partsI andII of this thesis each cover their individual aspects independently and can be read and understood separately from each other. Detailed abstract: This thesis is separated into two major parts. Both, the radial velocity measurements of WD-BD candidates in partI as well as the detailed design of the active mirror control for the HET in part II can be read independently, since the HET hardware upgrade is not directly linked to the scientific study presented in this work. The telescope upgrade rather improves the whole facility, which hence benefits all research aided by HET data, such as this radial velocity measurements of binary systems. We present the follow-up study for candidates, resulting from the WFCAM Transit Survey [80]. The targets have been proposed by a P. Steele as binaries, consisting of a White-Dwarf (WD) with a Brown-Dwarf (BD) companion. In 2013, Steele et al. [86] published his only confirmation NLTT 5306, which they characterized as the shortest period detached WD-BD bi- nary known at that time and also being the fourth of only seven confirmed such binary systems until today. In contrast to these cases, we try to confirm the remaining targets which were not ruled out by Steele, using lower resolu- tion spectroscopy. Generally surveys leave plenty of targets of unclear nature, which in order to confirm them, have to be followed up extensively. We make use of time efficient but less resolving spectroscopy to see if the technique is feasible to reduce the observation time for this and further targets like those three which we test: • For our first target SDSS193144, the spectra disproved the WD-BD theory and the major component is classified as F8 star with around Teff. ≈ 6000 K. However the gathered radial velocity data allowed to compare the real performance of two used low resolution spectrographs, for the specific task of faint rv follow up observations. • For the second target SDSS70433, we find a upper limit for the targets radial velocity semiamplitude of K = 35.0 km/s. The primary part- ner is identified as a F6 star (Teff. ≈ 6400) in a distance of about r = 2.6 kpc. The measured 4 % transit as well as the period of p ≈ 4.6 d are consistent with a M-dwarf companion, which would cause a maximum radial velocity variability of ∆vapp. = 22.7 km/s. • The nature of our third target SDSS070428 remains unknown as we did not get enough data to derive a proper limit to the radial ve- locity variability. The measured spectra hint a F5 V host star with Teff. = 6380 K, which is either orbitally affected by a companion or composed of a blended, eclipsing binary. While, additional obser- vations could shed some light on the true nature on the target, this thesis’ assumption has been to refute. In conclusion, we show that our low resolution attempt is a reasonable first step of a follow up study. Short exposure time campaigns with resolution R ≤ 2000, using unassigned schedule holes or mediocre weather periodes during a night can hence be of value for the community by prefiltering such follow up samples. In our case, none of the targets ends up as the rare WD-BD type, as it is consistent with the little known number of such binaries. Finally, the most recent data release of the Gaia-project has delivered inevitable indication against WD-BD binaries as all three targets have proven to be too far away for the expected combined luminosity and thereby supports our stellar classifications. Nowadays, most results of observational astrophysics are gained via the data of a few, outstanding observatories respectively surveys. Each of these projects and facilities, such as the Very Large Telescope, requires enormous initial financial investments, as well as enough budget for instruments, long term maintenance and the according staff. Thus, only a few such leading research facilities exist and the available observation time is limited. Therefore, it is important to test the lower limits of required instrumentation power for follow up observations such as presented in this work. The technical part of the thesis starts with the proof of concept for a fiber-positioner, which was proposed to ESO for their upcoming multi object spectrograph 4MOST. Hence, we present a CAN-Bus-controlled, Θ − Φ-style fiber-positioner prototype, which points without iterations or a metrology system. This design provides an overlapping patrol disc of 17.3 mm diameter and reaches a filling factor of 100 %. Given a mechanical reference point measured by stall detection, the absolute accuracy is 27 µm (1σ = 14 µm) and pointings are repeatable with 7 µm (1σ = 4 µm). Better positioning is reachable with optional calibration. This precursor laid the foundation for the later SCS2 upgrade of the primary mirror control for the 11m Hobby-Eberly-Telescope (HET), which is presented in the second project in this thesis. Together with the ongoing major instrument upgrade, we present the up- grade of the HET Segment Control System (SCS) to SCS2. Because HET’s primary mirror is segmented into 91 individual 1-meter hexagonal mirrors the SCS is essential to maintain the mirror alignment throughout an entire night of observations. The new motion control for SCS2 further increases the systems efficiency, precision and reliability. HET’s 91 mirror segments are aligned to micron precision using in- ductive edge sensors to probe the relative position on a sub-micron level. The system corrects for external influences, such as steep temperature changes and mechanical stress, while tracking the telescope
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