京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18079号 / 理博第3957号 / 新制||理||1570(附属図書館) / 30937 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 嶺重 慎, 准教授 前田 啓一, 教授 長田 哲也 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

In this work, we investigate the presence of stellar companions around hot Jupiter systems using data sets from the Clio and VISAO instruments on the Magellan Telescope. We observed eighteen targets of which eleven have known spin-orbit obliquity measurements. We detected eleven candidate companions of which five are new discoveries, five involved the validation and confirmation of previous studies, and one candidate proved to be a background star not bound to the transiting planet system. Out of eleven systems with known spin-orbit obliquity, seven systems have candidate companions. Due to the size of the sample, we could not find any correlation between the spin-orbit obliquity and the presence of a stellar companion. As future work, we will do follow up observations on the targets with candidate companions. We will increase our sample to one hundred systems to investigate if there is a correlation between spin-orbit obliquity and the presence of a distant stellar companion.

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Wie seit schon einigen Jahrzehnten bekannt ist, werden akustische Oszillationen durch stellare Aktivität beeinflusst. Die globalen akustischen Moden in der Sonne weisen eine Variation mit dem 11-jährigen Sonnenzyklus auf. Ein ähnliches Phänomen konnte auch in anderen Sternen mit Hilfe von Asteroseismologie nachgewiesen werden. In dieser Arbeit erforsche ich den Einfluss von großen Sternflecken auf globale Oszillationen mit niedrigem Grad ℓ. Als wichtigstes Werkzeug benutze ich hierfür den GLASS Kode, der die Ausbreitung von linearen akustischen Wellen im Sterninneren in 3D simuliert. Zunächst habe ich das Problem der konvektiven Stabilisierung betrachtet, welches bei jedem linearen Oszillationskode im Zeitbereich auftritt. Ich präsentiere eine allgemeine Methode um konvektiv stabile Hintergrundsmodelle für ein vorgegebenes Sternmodell zu erzeugen. Dabei werden wichtige Eigenschaften des ursprünglichen Modells beibehalten, beispielsweise das hydrostatische Gleichgewicht. Ich schlage einen störungstheoretischen Ansatz vor, um das akustische Wellenfeld in dem ursprünglichen instabilen Sternmodell näherungsweise zu erlangen. Tests zeigen, dass für Moden mit niedrigem Grad ℓ und einer Frequenz um 3 mHz die korrigierten Frequenzen mit einer Genauigkeit von 1 μHz mit den exakten Werten übereinstimmen. Zweitens habe ich mit Hilfe des GLASS Kodes den Einfluss einer am Nordpol des Sterns lokalisierten Störung der Schallgeschwindigkeit auf radiale, dipolare und quadrupolare Oszillationsmoden untersucht. Diese Studie zeigt auf, dass die axialsymmetrischen Moden dadurch am stärksten beeinflusst werden und im Falle von großen Sternflecken können ihre Frequenzen nicht mit der linearen Theorie berechnet werden. Die Form der Eigenfunktionen der Moden weicht von reinen Kugelflächenfunktionen ab und werden mit Kugelflächenfunktionen mit unterschiedlichem Grad ℓ vermischt. Dies könnte die korrekte Identifikation der Moden in der spektralen Leistungsdichte beeinflussen. Drittens habe ich den beobachtbaren Einfluss eines großen Sternflecks auf Moden mit Grad ℓ betrachtet. Im Falle einer aktiven Region, die mit dem Stern rotiert (und sich nicht am Pol befindet), ist die Störung nicht stabil, wenn sie in einem Inertialsystem betrachtet wird. Der kombinierte Einfluss von Rotation und Sternfleck veranlasst jede Mode, in der beobachteten spektralen Leistungsdichte als (2ℓ + 1)² Peaks aufzutreten. Die Einhüllende der spektralen Leistungsdichte eines Multipletts ist also komplex und hängt von dem Breitengrad ab, wo sich die aktive Region befindet, und vom Inklinationswinkel des Sterns. Ich berechne die spektrale Leistungsdichte für einige Beispiele sowohl mit Störungstheorie als auch mit Hilfe von GLASS. Diese Arbeit soll dazu beitragen, die spektrale Leistungsdichte von oszillierenden Sternen, die Sternflecken aufweisen, zu interpretieren.

In this thesis, I focus on the physical and chemical evolution at the earliest stages of low-mass star formation. I report results from the Spitzer Space Telescope and molecular line observations of 9 species toward the dark cloud L43, a survey of 10 Class 0 and 6 Class I protostars with 8 molecular lines, and a survey of 9 Very Low Luminosity Objects (VeLLOs) with 11 molecular lines. From the observational results, CO depletion is extensively observed with C¹⁸O(2-1) maps. A general evolutionary trend is also seen toward the Class 0 and I samples: higher deuterium fractionation at higher CO depletion. For the VeLLO candidates and starless cores with N₂D⁺(3-2) detection, we found the deuterium ratio of N₂D⁺/N₂H⁺ is higher comparing with the Class 0 and I samples. We use DCO⁺(3-2) maps to trace the velocity structures. Also, HCO⁺(3-2) blue profiles are seen toward the VeLLO candidate L328, indicating possible infall. To test theoretical models and to interpret the observations, we adopt a modeling sequence with self-consistent calculations of dust radiative transfer, gas energetics, chemistry, and line radiative transfer. In the L43 region described in Chapter 2, a starless core and a Class I protostar are evolving in the same environment. We modeled both sources with the same initial conditions to test the chemical characteristics with and without protostellar heating. The physical model consists of a series of Bonner-Ebert spheres describing the pre-protostellar (PPC) stages following by standard inside-out collapse (Shu 1977). The model best matches the observed lines suggests a longer total timescale at the PPC stage, with faster evolution at the later steps with higher densities. In Chapter 3, we modeled the entire group of Class 0 and I protostars. The trend of decreasing deuterium ratio can be seen after the temperature is high enough for CO to evaporate. After the evaporation, the history of heavy depletion (e.g, from longer PPC timescales or different grain surface properties) no longer affects the line intensities of gas-phase CO. The HCO⁺ blue profiles, which are used as infall indicators, are predicted to be observed when infall is beyond the CO evaporation front. The low luminosity of VeLLOs cannot be explained by standard models with steady accretion, and we tested an evolutionary model incorporating episodic accretion to investigate the thermal history and chemical behaviors. We tested a few chemical parameters to compare with the observations and the results from Chapter 2 and 3. The modeling results from episodic accretion models show that CO and N₂ evaporate from grain mantle surfaces at the accretion bursts and can freeze back onto grain surfaces during the long periods of quiescent phases. Deuterated species, such as N₂D⁺ and H₂D⁺, are most sensitive to the temperature. Possible good tracers for the thermal history include the line intensities of gas-phase N₂H+ relative to CO, as well as CO₂ and CO ice features. / text

We conduct a broad investigation about stellar mass and population diagnostics in order to formulate novel constraints related to the formation and evolution of galaxies from a nearby cluster environment. Our work is powered by the use of stellar population models which transform galaxy colours and/or absorption line strengths into estimates of its stellar properties. As input to such models, we assemble an extensive compilation of age and chemical abundance information for Galactic globular clusters. This compilation allows a confident expansion of these models into new regions of parameter space that promise to refine our knowledge of galactic chemical evolution. We then draw upon a state-of-the-art spectroscopic and photometric survey of the Virgo galaxy cluster in order to constrain spatial variations of the stellar ages, metallicities, and masses within its member galaxies, and their dynamical masses. We interpret these data in the context of the histories of star formation, chemical enrichment, and stellar mass assembly to formulate a broad picture of the build-up of this cluster’s content over time. In it, the giant early-type galaxies formed through highly dissipational processes at early times that built up most of their stellar mass and drew significant amounts of dark matter within their optical radii. Conversely, dwarf early-types experienced environmental processes that quenched their star formation during either the early stages of cluster assembly or upon infall at later times. Somewhat perplexing is our finding that the internal dynamics of these galaxies are largely explained by their stellar masses. Lastly, Virgo spirals also suffer from their dense environment, through ram pressure stripping and/or tidal harrassment. In addition to quenching, these effects leave an imprint on their internal dynamical evolution too. Late-type spirals exhibit evidence of having ejected significant amounts of baryons from their inner regions, likely via energetic feedback events. Rich as our picture of the history of the Virgo cluster has become, real progress in our understanding of this system will truly benefit from future high-resolution cosmological and hydrodynamic simulations of this environment. Such simulations are still in their infancy, but the data assembled here should soon provide their most direct validation. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-09-30 23:32:48.575

Star formation in the Milky Way is confined to star-forming regions (OB association, HII regions, and open clusters) in the Galactic plane. It is usually assumed that these regions are found preferably along spiral arms, as is observed in other spiral galaxies. However, young early-type stars are often found at high Galactic latitudes, far away from their birthplaces in the Galactic disc. These stars are called runaway stars, and it is believed that they were ejected from their birth- places early in their lifetimes by one of two mechanisms: ejection from a binary system following the destruction of the massive companion in a supernova type II event (the binary ejection mechanism), or ejection from a dense cluster following a close gravitational encounter between two close binaries (the dynamical ejection mechanism). The aims of our study were: to improve the current understanding of the nature of high Galactic latitude runaway stars, in particular by investigating whether the theoretical ejection mechanisms could explain the more extreme cases; to show the feasibility of using high Galactic latitude stars as tracers of the spiral arms. The main technique used in this investigation was the tracing of stellar orbits back in time, given their present positions and velocities in 3D space. This technique allowed the determination of the ejection velocities, flight times and birthplaces of a sample of runaway stars. In order to obtain reasonable velocity estimates several recent catalogues of proper motion data were used. We found that the evolutionary ages of the vast majority of runaway stars is consistent with the disc ejection scenario. However, we identified three outliers which would need flight times much larger then their estimated ages in order to reach their present positions in the sky. Moreover, the ejection velocity distribution appears to be bimodal, showing evidence for two populations of runaway stars: a “low” velocity population (89 per cent of the sample), with a maximum ejection velocity of about 300 kms−1, and a “high” velocity population, with ejection velo- cities of 400 – 500 kms−1. We argue that the observed bimodality and maximum ejection velocity of 500 kms−1 can be interpreted as a natural consequence of a variation of the binary ejection mechanism. A possible connection between the “high” velocity population and the so-called hypervelocity stars is also explored, resulting in the conclusion that some stars previously identified as hypervelocity may be in fact runaway stars. The feasibility of using stars as tracers of the spiral arms was tested on a local sample, in order to obtain better quality data and larger numbers. We found that the spiral arms pattern speeds estimated from this sample (24.9±5.2 kms−1 kpc−1) and from a selected sample of runaways (22.8 ± 7.8 kms−1 kpc−1) are consistent within the errors and also consistent with other published estimates. We concluded that our estimates combined with the ones obtained in other studies suggest a value in the range 20 − 25 kms−1 kpc−1 for the pattern speed. Moreover, we concluded that an adequate representation of the spiral arms is obtained given the former pattern speed estimate, even when applied to the sample of runaway stars.

In this dissertation, we conduct a census and assessment of the nearest young Sun-like stars and investigate the potential for finding giant planets orbiting spotted stars using the radial velocity (RV) method at optical and near-infrared wavelengths. Based in part on new spectroscopic measurements conducted here, we have assembled a complete list of 129 young (<150 >Myr), nearby Sun-like stars and their fundamental parameters, including rotational and multiplicity information. We also provide a statistical analysis of their stellar parameters, including projected rotational velocity and inclination. Sixteen of these stars have no close companions and have low projected rotational velocities (vsini/s) that are ideal for precision RV planet searches. Seven of these rotate nearly edge-on and are ideal targets for upcoming transiting planet searches, assuming low obliquity. We conduct precision RV planet search of 7 young Sun-like stars using the TRES spectrograph, mounted on the 1.5-m Tillinghast Reflector at the Fred L. Whipple Observatory, and with the SOPHIE spectrograph, mounted on the 1.93-m Telescope at the Observatoire de Haute Provence; we achieve a precision of 10 m/s for both. Four stars are identified as having larger RV variations that are periodic, possibly caused by an orbiting companion. However, the RV variations are correlated with asymmetries in the spectral absorption features, which instead suggests that the variations are caused by spots. Nevertheless our observations provide new independent measures of the rotation periods of these stars. Through this analysis we tentatively confirm the planetary companion around BD+20 1790 in the presence of activity. We additionally investigate the use of comparing red orders of the optical spectrum to the blue orders in order to distinguish spots from planets; we find that this method can be effective for observations that span the full wavelength range of the optical. We also investigate our detection limits at optical wavelengths and find that we are sensitive to over 90% of short period giant planets. Next, we assemble the stellar jitter measurements of our stars with previous studies of all Sun-like stars younger than 1 Gyr to investigate how stellar jitter declines with stellar age. We find that stellar jitter decreases with stellar age as t^(0.53±0.13), similar to the relationship between stellar rotation period and stellar age. The implication is that it will be diffcult to find planets orbiting stars younger than 100 Myr without using techniques that mitigate star spot noise. Furthermore, we present a near-infrared RV search for giant planets orbiting 8 stars observed with CSHELL at the NASA Infrared Telescope Facility (IRTF). Because of the limited wavelength coverage (29 ̊A) and older (1980s) detector technology, the achieved precision of 200 m/s inhibits finding the majority of exoplanets, but is nevertheless sufficient to identify short-period brown dwarfs for these stars. We also analyze our detection limits at IR wavelengths and find that we are only sensitive to roughly 50% of short period giant planets. Finally, we present a new orbital solution for V835 Her, a spectroscopic binary with a 3 day orbital period.