## 天文学教室談話会(2015年度)

last-update:2016/12/14

### 第1554回 2015年4月14日(火)

OGLEやMACHOプロジェクトによって、大小マゼラン星雲では多くのred giant variablesが見つかってきた。その結果少なくともsequence A’~Fまでの8本(8系列)の周期光度関係が存在することが明らかになっている(e.g. Soszynski+ 2013)。異なる系列は変光の起源の違いを反映し、周期の短い6本の系列は星の脈動が起源の変光である。一方周期のばらつきが大きいsequence Eは食連星やellipsoidal variablesが起源である。最も長周期のsequence Dの周期はlong secondary periods(LSPs)と呼ばれ、その変光の原因は未だにわかっていない。

### 第1555回 2015年4月21日(火)

Precise and fast computation of　generalized Fermi-Dirac integral by parameter polynomial approximation
Toshio FUKUSHIMA (NAOJ)

The generalized Fermi-Dirac integral, $F_k(\eta,\beta)$, is approximated by a group of polynomials of $\beta$ as $F_k(\eta,\beta) \approx \sum_{j=0}^J g_j \beta^j F_{k+j} (\eta)$ where $J=1(1)10$. Here $F_k(\eta)$ is the Fermi-Dirac integral of order $k$ while $g_j$ are the numerical coefficients of the single and double precision minimax polynomial approximations of the generalization factor as $\sqrt{1+x/2} \approx \sum_{j=0}^J g_j x^j$. If $\beta$ is not so large, an appropriate combination of these approximations computes $F_k(\eta,\beta)$ precisely when $\eta$ is too small to apply the optimally truncated Sommerfeld expansion (Fukushima, 2014, Appl. Math. Comp., 234, 417). For example, a degree 8 single precision polynomial approximation guarantees the 24 bit accuracy of $F_k(\eta,\beta)$ of the orders, $k=-1/2(1)5/2$, when $-\infty < \eta \le 8.92$ and $\beta \le 0.2113$. Also, a degree 7 double precision polynomial approximation assures the 15 digit accuracy of $F_k(\eta,\beta)$ of the same orders when $-\infty < \eta \le 29.33$ and $0 \le \beta \le 3.999 \times 10^{-3}$. Thanks to the piecewise minimax rational approximations of $F_k(\eta)$ (Fukushima, 2015, Appl. Math. Comp., 259, 708), the averaged CPU time of the new method is only 0.9--1.4 times that of the evaluation of the integrand of $F_k(\eta,\beta)$. Since most of $F_k(\eta)$ are commonly used in the approximation of $F_k(\eta,\beta)$ of multiple contiguous orders, the simultaneous computation of $F_k(\eta,\beta)$ of these orders is further accelerated by the factor 2--4. As a result, the new method runs 70-450 times faster than the direct numerical integration in practical applications requiring $F_k(\eta, \beta)$.

### 第1556回 2015年4月28日(火)

Magnetic fields of cosmic bodies generated and maintained by dynamos
Karl-Heinz Raedler (Astrophysical Institute Potsdam, Germany)

The focus of the lecture is on the mean-field dynamo theory of cosmic magnetic fields. The central element of this theory is the mean electromotive force due to the velocity and magnetic field fluctuations in turbulent electrically conducting fluids, which depends in general in a nonlinear way on the mean velocity and the mean magnetic field. Within this framework several types of dynamo models applying to cosmic objects have been developed. Considerable progress has been achieved in the last years in determining the mean electromotive force in realistic situations and so in the elaboration of mean-field dynamo models.

### 第1558回 2015年5月19日(火)

The Shape and Survival of High-velocity Clouds
Gerhard Hensler（ウィーン大）

Since several decades it became observationally manifested that our Milky Way (MW) is steadily bombarded by infalling gas clouds over a large velocities range. For those with velocities lower than the MW escape velocity their origin is still under debate, if of galactic origin as a fountain or intergalactic.

In fact, high-velocity clouds (HVCs) must originate from the intergalactic space. Various questions can be addressed to these HVCs from cosmological to plasmaphysical problems.

Since these infalling extragalactic clouds contain highly subsolar metallicity they could represent the cosmological building blocks which assemble to larger galaxies in the hierarchical structure-formation scenario of CDM cosmology. But then they are expected to be hosted by Dark Matter (DM) subhalos. From the Magellanic Stream, on the other hand, HVCs are stripped off and rain down towards the MW which cannot contain DM. How can one distinguish between DM-supported and DM-free HVCs? What can we learn from their shapes and metal content? Do HVCs passing the hot galactic halo gas survive and reach the MW disk?

This talk will address these problems by numerical models in comparison with observed HVCs and will discuss consequences for our astrophysical understanding.

### 第1559回 2015年5月26日(火)

また、我々はダークハローの平均面密度を用いたダークマター理論への制限に対する新たな手法を考案した。この面密度は矮小銀河から楕円銀河までの広い範囲の質量スケールにおいて一定の値をとることがわかり、この普遍性はCDM理論では自然に再現できる事がわかった。しかし一方で3keV以下の温かい暗黒物質(WDM)では、矮小銀河スケールにおいて再現することができず、WDM粒子質量の下限値を与えることができた。

### 第1560回 2015年6月2日(火)

1＜z＜2における銀河の低温ガス量の進化: ガスを残しつつ星形成を止めるフィードバックの必要性

### 第1561回 2015年6月9日(火)

Gauging the Universe with Classical Cepheids: from galactic structures to the cosmic acceleration
Laura Inno

Classical Cepheids are the most precise stellar distance indicators to date: they play a fundamental role in the calibration of the cosmic distance ladder and in the determination of the local expansion rate of the Universe. However, we still lack a firm understanding and control of the systematics affecting the Cepheid distance estimates. In this talk, I will review the physics underlying the Cepheid Period-Luminosity (PL) and Period-Wesenheit (PW) relations, which are generally adopted to determine Cepheid distances. In particular, I will show that near-infrared (NIR) PW relations are reddening independent, minimally affected by metallicity, and linear over the entire period range, with a very low dispersion. These relations are then the best suited tool to derive Cepheid distances to high precision. For this reason, we recently developed new light-curve templates that provide accurate mean magnitudes form single-epoch observations in the NIR bands. By applying these new templates and by adopting the PW we derived, it is possible to obtain Cepheids distances with an accuracy which is only limited by the method itself. I will then discuss an application of the templates to IRSF/SIRIUS data for Magellanic Cloud Cepheids, in order to derive the geometry and the three-dimensional distribution of the young stellar populations of the Magellanic Clouds, as prototype of interacting dwarf galaxies. Cepheids are indeed perfect tracers of the young stellar population, because their evolutionary status is well known and their age can be precisely determined on the basis of period-age relations. This feature, together with their use as standard candles, make Cepheids a perfect tool to probe the Galactic structure and to provide constraints on the recent Galactic chemo-dynamical evolution. I will then present the main results on this topics recently obtained by our group. Finally, I will discuss the major role that Cepheids are going to play in the light of GAIA, not only for our understanding of the Milky Way but also for establishing the nature of the Universe itself.

### 第1563回　2015年7月10日(金)

The Planck 2015 release: general overview of the Planck results and news from the CMB at large angular scales
Anna Mangilli (パリ天体物理研究所・フランス)

Planck is the ESA telescope that surveyed with unprecedented precision the Cosmic Microwave Background (CMB), providing with the highest resolution measurements so far of the CMB temperature and polarization anisotropies. In this talk I will go through a brief introduction about the CMB -in particular the CMB polarization- and I will give an overview of the Planck 2015 results, focusing on the improvement of the constraints on the cosmological parameters thanks to the new full mission and polarization data. Also, I will give the status of the Planck analysis on the CMB at large angular scales. The high precision measurement of the CMB polarization at large angular scales is in fact one of the main challenge left for the present and the future CMB experiments. The reionization bump in the CMB polarization EE and BB power spectra encodes unique informations about the reionization history of the Universe and the inflationary epoch. Such valuable information can be accessed only with an unprecedented accuracy and care on each step of the data analysis and its interpretation. I will show how the EE and BB spectra at low-l can be used to improve the constraints on the cosmological parameters, in particular those related to the reionization history (tau) and the amount of tensor modes (r).

### 第1564回　 2015年7月14日(火)

Ana Lopez Sepulcre (東京大学・物理学専攻)
Broadband spectral-line surveys of star-forming regions: unveiling all the molecular secrets

The past few years have witnessed a huge progress in the development of sensitive broadband (sub-)millimetre receivers, especially at single-dish telescopes. Thanks to this, it is now possible to carry out large spectral-line surveys that homogeneously cover tens and even hundreds of GHz in modest amounts of time, thus providing a unique, very powerful, tool to explore the molecular composition of the region under study. As a result, a new and very promising road in molecular astrophysics is opening, in particular in star formation research. I will introduce two recent large observational campaigns I am taking part in, ASAI and CHESS, entirely based on broadband spectral-line surveys of star-forming regions, and I will illustrate the huge potential of this approach with some selected results on complex organics, molecular ions, and isotopic anomalies. Finally, I will briefly introduce the importance of applying this technique also with (sub-)millimetre interferometers, where the (hopefully near) future of unbiased spectral-line surveys lies.

### 第1565回　 2015年7月21日(火)

VLBI位置天文観測で探る、天の川銀河の3次元構造と3次元運動

2000年代以降、人類史上最高の空間分解能が電波の波長域におけるVLBI技術によって達成され、太陽近傍($\sim$100~pc)に限られていた位置天文研究が(e.g., Hipparcos衛星, Perryman 1989)、銀河系円盤サイズ($\sim$20~kpc)まで拡張された。\\本講演では、VLBI位置天文観測の原理を簡単に紹介すると共に(e.g., Reid and Honma 2014)、特に銀河系渦状腕に関する位置天文観測の結果を紹介する(Sakai et al. 2012)。また、銀河系渦状腕で見られた系統的な非円運動を説明する為に、密度波理論(Lin and Shu 1964)に準拠した解析解との比較も行ったので、それらの結果も併せて紹介する(Sakai et al. 2015)。今後10年はGaia衛星による星の位置天文観測の結果も新たに加わり、銀河系位置天文研究が大きく進展する事が期待される。最後に時間が許せば、Gaia時代における銀河系位置天文研究の展望をご紹介したい。

### 第1566回　 2015年7月28日(火)

Future Observational Prospects at Thermal-IR Wavelengths and The AGN Torus
Chris Packham（The University of Texas at San Antonio）

A thermal-infrared imager and spectrometer is being investigated for possible construction in the early operation of the Thirty Meter Telescope (TMT). Combined with the mid-infrared adaptive optics (AO) system (MIRAO), the instrument will afford $\sim 15$~times higher sensitivity and $\sim 4$~times better spatial resolution (0.07$^{\prime\prime}$) with a greatly improved and stable Strehl ratio at 10~$\mu$m compared to the images delivered by 8m-class telescopes. Through exploiting the large collecting area of the TMT, a high-dispersion spectroscopy mode unrivaled by other ground- and space-based facilities is planned. Such capabilities offer the possibility for breakthrough science, as well as ‘workhorse’ observing modes of imaging and low/moderate spectral resolution. In this presentation I detail the approach we followed to initially define the instrument and some of the science cases enabled, with a particular focus on the AGN torus.

### 第1567回 2015年9月1日(火)

The Dust Properties of the Nearby Universe, in the Herschel Era
Frederic Galliano（Service d’Astrophysique – Laboratoire AIM）

The electromagnetic emission from a galaxy contains information about the variety of physical conditions experienced in its interstellar medium. In star forming regions, particularly, most of the power is reradiated by dust grains in the infrared. The knowledge of the grain properties (their chemical composition, size distribution and abundances) is therefore crucial to interpret observations of star forming galaxies, nearby and distant. However, these dust properties are known to evolve with their environment, and this evolution is currently poorly constrained. In this talk, I will review several studies, based on Herschel observations of nearby galaxies, aimed at constraining several of these evolutionary processes.

After a general introduction, I will first discuss the general evolution of the dust content of galaxies, as a function of their elemental enrichment, comparing recent observations and theoretical models. Then, I will present the revision of the grain opacities that Herschel and Planck allowed us to reveal, in the Large Magellanic Cloud and in the Milky Way. Finally, I will present the modeling of spectral energy distributions with hierarchical Bayesian inference, and demonstrate its relevance for the study of infrared observations. I will show the application of this technique to derive maps of the dust properties in two massive star forming regions of the Magellanic clouds (LMC-N44 and SMC-N66).

### 第1568回 2015年9月16日(水)

A new distance measure using the correlation between CO luminosity and its line width

Does the dark energy vary over cosmic time? To answer this question, we need to map the expansion of the Universe over a large span of the cosmic time. Type Ia supernovae have been used to measure distances to $z \sim 1.7$, but beyond this, no reliable distance measure has been established. We propose a new distance measure using sub-millimeter (submm) galaxies to determine distances out to $z \sim 6$. Using a large sample of submm galaxies compiled from the literature, we show there exists a significant correlation between the CO luminosity ($L^\prime _{\rm CO}$) and the CO line width (FWHM) of submm galaxies. We use this correlation to measure intrin- sic luminosity of submm galaxies, based on the observed FWHM. Through comparison with their observed brightness, we measure their luminosity distance, and construct the Hubble diagram to $z \sim 6$. Submm galaxies are detected all across the history of the Universe, including some at $z>6$. With the advent of ALMA, it is expected that large numbers of distant submm galaxies will be discovered in the near future. This method is suitable for such an era, providing a new opportunity to constrain the earliest cosmic expansion. (http://arxiv.org/abs/1505.00013).

### 第1569回　2015年9月29日(火)

The evolution of stellar rotation

### 第1570回　2015年10月13日(火)

Binary systems at high energies

The small source class of gamma-ray binaries consists at present of six known objects with different orbital periods ranging from days up to several years. One of the best studied gamma-ray binary across all frequencies, LS I +61 303, is highly variable at any given orbital phase and was lately discovered to show on top of orbital also superorbital variability at high energies. In contrary, the other famous binary, LS 5039, shows no variations apart from those related to the orbital period. The other unresolved mystery in most of these sources is the nature of their compact object. Both neutron star (e.g. PSR B1259-63) and probable black hole (microquasar, e.g., Cyg X-3) binary systems have been detected at GeV energies, hence both types of compact object are viable in the undetermined systems. In this talk I will present the recent findings on the known gamma-ray binaries up to now and discuss their behavior at high and very high energies.

### 第1571回　2015年10月27日(火)

Combining IRIS/Hinode observations and modelling: a pathfinder for coronal heating
Patrick Antolin (国立天文台)

The combination of imaging and spectroscopic instruments with multiple temperature diagnostics at high spatial, temporal and spectral resolution can allow to recover the 3D plasma flow and thermodynamic evolution associated to specific coronal heating mechanisms. Although very hard considering the complexity of the solar atmosphere, this approach is becoming possible now through combination of instruments such as IRIS and Hinode, and with proper guiding from advanced numerical simulations and forward modelling. In this talk I will focus on a particular example of this approach, a recently published case study, that serves as a pathfinder in the search for the dominant coronal heating mechanism. In this case, resonant absorption, a long hypothesised wave-related energy conversion mechanism is spotted in action for the first time, and is characterised by a peculiar 3D motion of the plasma. With the help of 3D MHD numerical simulations and forward modelling the observational signatures of resonant absorption are characterised, matching very well the observational results. The process through which this mechanism can lead to observed significant heating in the solar corona is further identified: the resonant flow becomes turbulent, following dynamic instabilities, and heats the plasma. I will show how this resonance and instability dual process is expected in different scenarios of the solar atmosphere (the corona, prominences and spicules) and can potentially explain several observed features that remain so far unexplained.

### 第1572回 2015年11月10日(火)

Surface chemistry in astrochemical models
Emeric Bron (パリ天文台)

With the advent of the new generation of mm and sub-mm detectors (ALMA, NOEMA), molecules are detected in a large variety of galactic and extra-galactic interstellar environments. These molecules are unique probes to investigate the physical and chemical processes in interstellar gas and on grains. State-of-the-art astrochemical models have to take into account consistently both gas phase and surface chemistry to interpret observations and, to do so, they must rely on theoretical and laboratory experiments results. However, surface chemistry is complex to implement in astrophysical codes, in which grain models are necessarily simplified.

We have implemented surface chemistry for H, C, and O bearers in a new version of the Meudon PDR code, one of the state-of-the-art public astrochemical code (http://ism.obspm.fr). In particular, H2 formation on grains is a complex process, highly dependent on grain temperature. Small grains, the largest contributors, undergo temperature fluctuations caused by the absorption of UV photons. These fluctuations can significantly affect surface processes, such as H2 formation or ortho/para conversion of H2. We have thus developed several formalisms to simulate H2 formation mechanisms on grains in the Meudon PDR code. In particular, I have developed a new statistical formalism based on a master equation approach to compute the average efficiency of surface processes perturbed by fluctuations of the grain temperature.

In this talk, I will first demonstrate the critical influence of H2 formation on emission lines in PDR, and in particular show that the high-J CO ladders observed by Herschel are signatures of high H2 formation efficiency at the edge of PDRs. I will discuss how this efficiency can be explained by the Eley-Rideal mechanism. I will then present a new stochastic formalism for surface processes with dust temperature fluctuations, and demonstrate its application to both H2 formation and ortho-para conversion of H2 on grains, in relation to observations of H2 rotational emission in PDRs. I will finally discuss how the relation between H3+ abundance and the cosmic ray ionization rate in the Galactic Center is highly dependant on H2 formation efficiency.If time allows, I will also present the modelling of C and O surface chemistry in the Meudon PDR code, in relation to observations of organic molecules such as methanol in the Horsehead nebula.

### 第1574回 2015年12月1日(火)

Probing the nature of the compact object in the gamma-ray binaries

The gamma-ray binaries, the recently identified subclass of the X-ray binaries, show variable emissions in the wide range band, from radio to the TeV gamma-rays. Currently, 5 systems are classified as the gamma-ray binaries, among which 4 systems have the compact object of unknown nature, whilst their optical counterparts are well-known as massive stars (M > 10 M_sun). There are two competing models, the pulsar wind model and the microquasar model, is proposed to explain the gamma-ray binaries. Although a plenty of both theoretical and observational studies have been done, the nature of the compact object is still under discussion for four systems. Hence the mechanisms for particle acceleration and very high energetic emissions are still one of the big challenge of the this field. We have monitored two gamma-ray binaries, LS I +61 303 and HESS J0632+057, to probe the nature of the compact object. The optical counterpart in the two systems is a Be star, a B-type star with geometrically thin circumstellar disk. We focus on the interaction between the optical star, in particular the circumstellar disk, and the compact object, which effects on the structure of the disk. Our high-dispersion spectroscopic and polarimetric monitoring shows the evidence for that the compact object is pulsar in these systems.

### 第1575回 2015年12月8日(火)

Near-infrared diffuse interstellar bandsの観測的研究

### 第1576回 2015年12月16日(水)

Stellar Dynamics Informing Stellar Evolution
Harvey Richer (University of British Columbia)

Using recent Hubble Space Telescope data, I will demonstrate in this talk how to use stellar dynamics in a globular star cluster to learn about stellar evolution. The key element is to use the radial distributions of stars in various stages of evolution to learn about their mass. A few surprises are presented.

### 第1577回 2015年12月22日(火)

SPHシミュレーションによるIa型超新星爆発の研究

Ia型超新星(SNIa)は炭素酸素からなる白色矮星(COWD)の爆発である. しかし, その爆発の引き金が, 主系列星や赤色巨星からの質量降着(SDシナリオ)か, 別のCOWD との合体(DDシナリオ)か, 決着がついていない. 近年, SN2011feやSN2014Jの爆発直後の光度曲線が観測されており, その親星の大きさに強い制限が課された. 親星の半径を考える際に注意する必要があるのは,親星の星周物質も親星の半径として寄与することである. 我々はDDシナリオを星周物質の観点から検証した. 星周物質の構造を調べるために, 我々はSPHシミュレーションを用いて, 質量が1.1太陽質量と1.0太陽質量の2つのCOWDの合体を追った. その結果, 合体の前後でこの系は爆発するが, 爆発直前の星周物質の構造は, SN2011feやSN2014Jの星周物質の構造には合わない可能性があることが明らかになった. 最後に, 現在開発中のSPHシミュレーションコードを紹介し, そのコードを適用できるサイエンスについて紹介する.

### 第1578回 2016年1月12日(火)

ブラックホール・中性子星連星からの質量放出と電磁波対応天体

### 第1579回 2016年1月26日(火)

N-body simulations of stellar systems: star clusters and disk galaxies

N-body simulations are a powerful tool to investigate the dynamical evolution of stellar systems such as star clusters and galaxies. I will show my recent works on 1. the formation of star clusters and 2. the dynamical evolution of galactic disks. For star cluster simulations, we developed a new method to construct initial conditions which resemble observed star forming regions. Using this method, we show the formation processes of observed star clusters and associations. For disk galaxies, we performed a numerical survey of stellar disks with a wide range of parameters. Our simulations were preformed with the largest number of particles using GPU clusters. We found that swing amplification describes the formation of spiral arms and bars of galactic disks.

### 第1580回 2016年2月2日(火)

New constraint on gravity theory at z~1.4 from the Subaru FMOS galaxy redshift survey (FastSound)

I will present a cosmological result obtained from a spectroscopic sample of ~2800 emission line galaxies from the FastSound survey. The survey, which uses the Subaru Telescope and covers the redshift ranges of 1.19

### 第1581回 2016年2月16日(火)

Rotation curve of M33 explained by dark matter disc

We developed a numerical method to compute the gravitational field of an infinitely-thin axisymmetric disc with an arbitrary profile of the surface mass density. We evaluate the gravitational potential by a split quadrature using the double exponential rule and obtain the acceleration vector by numerically differentiating the potential by Ridder’s algorithm. The new method is of around 12 digit accuracy and sufficiently fast because requiring only one-dimensional integration. By using the new method, we show the rotation curve of some non-trivial discs: (i) truncated power-law discs, (ii) discs with a non-negligible center hole, (iii) truncated Mestel discs with edge-softening, (iv) double power-law discs, (v) exponentially-damped power-law discs, and (vi) an exponential disc with a sinusoidal modulation of the density profile. Also, we present a couple of model fittings to the observed rotation curve of M33: (i) the standard deconvolution by assuming a spherical distribution of the dark matter and (ii) a direct fit of infinitely-thin disc mass with a double power-law distribution of the surface mass density. Although the number of free parameters is a little larger, the latter model provides a significantly better fit. The determined profile of the surface mass density of the disc is significantly larger than those of the observed stars and gas. This hints a disc-like distribution of the dark matter.

### 第1582回 2016年2月23日(火)

Richard Armstrong (Univ. Oxford/Univ. Cape Town)

Extreme astrophysical phenomena, such as relativistic flows, cataclysmicexplosions and all types of accretion onto black holes, are a key area for astrophysics in the 21st century. The extremes of physics, density, temperature, pressure, velocity, gravitational and magnetic fields experienced in these environments are beyond anything achievable experimentally on Earth, and provide a unique glimpse of the laws of physics operating in extraordinary regimes. Nearly all such phenomena are associated with transient radio emission, a tracer of the acceleration of particles to relativistic energies by their interaction with the local magnetic field. However, in order to probe the dynamic radio sky, we have thus far relied on 1.) biased triggers from instruments at other wavelengths, and 2.) archival searches of data, obviating the possibility of multi-wavelength follow-up and classification to resolve the inevitable ambiguities.

MeerKAT, which will be the world’s most sensitive radio telescope once science operations begin at the end of next year, enables an unrivalled view of the deep radio sky. Yet it will also push the boundaries of transient searches in both temporal resolution (cadence of images) and completeness (time-on-sky); in this talk, I will discuss my own project, the fast imaging system for MeerKAT, which will detect transient radio emission in real-time, and will operate commensally with all other science observations, allowing MeerKAT to be unprecedentedly sensitive to extreme phenomena.

### 第1583回 2016年3月9日(水)

Formation and Compositions of Planet Interiors and Atmospheres: Discoveries from Kepler, K2, and Beyond.
Erik Petigura (Hubble Fellow/Caltech)

I will give an overview of the current state of exoplanet astronomy, highlighting some of the major achievements of the recently completed Kepler mission. Today, K2 is building upon that rich legacy by surveying 14x more sky than Kepler, casting a wide net for planets around nearby bright stars that are more amenable to precise characterization. I will present some of my group’s latest K2 efforts, including a program to study sub-Saturns: a mysterious class of planets between Neptune and Saturn size, not present in our Solar System. These planets have mean densities ranging from 2.0 g/cc (concrete) to 0.05 g/cc (Styrofoam) and offer an intriguing window into the processes that form and sculpt planetary systems.

### 第1584回 2016年3月22日(火)

Near-Infrared Linear and Circular Polarimetry in Star Forming Regions
Kwon Jungmi (天文学教室)

Polarimetry is a unique tool for studying the physical processes in the interstellar medium, including star-forming regions. However, it has been much less explored than conventional photometry and spectroscopy. Infrared polarimetry provides very valuable information about the distribution of matter of young stellar objects and the configuration of magnetic fields within molecular clouds. Compared with linear polarization (LP), only a few near-infrared circular polarization (CP) observations were reported so far (before our survey). I have conducted a first systematic polarization survey of star forming regions in both LP and CP. In this presentation, I present our investigation for roles of magnetic fields in cluster formation using linear polarimetry as well as new information of magnetic and scattering fields obtained by the circular polarimetry survey.

### 第1585回 2016年3月29日(火)

Asteroseismic detection of planets and other companions to intermediate-mass stars
Simon Murphy (天文学教室)

The Kepler Space Telescope has revolutionised the fields of exoplanet detection and asteroseismology. With over 1000 confirmed planets and thousands more planet candidates, it is now the most successful planet-finding mission to date. But its entire planet tally has been found via transits, or perturbations to the timing of those transits. Only a small fraction of all planets may be observed to transit their host star. Further, the transit probability falls off rapidly with increasing orbital period. The second most successful method for finding planets is the radial velocity method, which does not require transits but also has a detection rate that decreases with orbital period. In this talk, I present a new method of finding planets and other companions. The method utilises asteroseismic data from the Kepler Mission, namely the phases of stellar oscillations, to detect changes in the path length between Earth and the observed star due to motion in a binary system. I will show how the sensitivity of the method increases with orbital period, which allows the detection of planetary companions that have orbital periods on the order of 1000 d. The companions detected with this method include planets, brown dwarfs, main-sequence stars with masses between 0.1 and 2.5 Msun, and possible compact objects such as neutron stars and black holes. Statistically robust distributions of eccentricity with orbital period are also discussed.