Neutron stars possess the densest matter and strongest gravitational fields that are accessible to observations. In this talk, I will discuss how precise measurements of neutron star radii, masses, and spins not only open a window onto the poorly known neutron star interior but can also be used to probe their formation mechanism, their recycling to millisecond periods, and their connection to the formation of low-mass black holes.

The physical origin of high-frequency QPOs (HFQPOs) in black-hole X-ray binaries remains an enigma despite many years of detailed observational studies. Although there exists a number of models for HFQPOs, many of these are simply “notions” or “concepts” without actual calculation derived from fluid or disk physics. Future progress requires a combination of numerical simulations and semi-analytic studies to extract physical insights. We review recent works on global oscillation modes in black-hole accretion disks, and explain how, with the help of general relativistic effects, the energy stored in the disk differential rotation can be pumped into global spiral density modes in the disk, making these modes grow to large amplitudes under certain conditions (“corotational instability”). These modes are robust in the presence of disk magnetic fields and turbulence. The computed oscillation mode frequencies are largely consistent with the observed values for HFQPOs in BH X-ray binaries. The approximate 2:3 frequency ratio is also expected from this model. The connection of HFQPOs with other disk properties (such as production of episodic jets) is also discussed.

We study how the solar magnetic field evolves from antisymmetric (dipolar) to symmetric (quadrupolar) state during the course of its 11-yr cycle. We show that based on equatorial symmetries of the induction equation, flux transport solar mean field dynamo models excite mostly the antisymmetric (dipolar) family whereas a decomposition of the solar magnetic field data reveals that both families should be excited to similar amplitude levels. We propose an alternative solar dynamo solution based on North-South asymmetry of the meridional circulation to better reconcile models and observations.

The Large Area Telescope (LAT) on the Fermi satellite is the first γ-ray instrument to discover pulsars directly via their γ-ray emission. Roughly one third of the 117 γ-ray pulsars detected by the LAT in its first three years were discovered in blind searches of γ-ray data and most of these are undetectable with current radio telescopes. I review some of the key LAT results and highlight the specific challenges faced in γ-ray (compared to radio) searches, most of which stem from the long, sparse data sets and the broad, energy-dependent point-spread function (PSF) of the LAT. I discuss some ongoing LAT searches for γ-ray millisecond pulsars (MSPs) and γ-ray pulsars around the Galactic Center. Finally, I outline the prospects for future γ-ray pulsar discoveries as the LAT enters its extended mission phase, including advantages of a possible modification of the LAT observing profile.

We have examined solar polar fields during the solar cycles 21–23 using both ground and space based synoptic magnetograms. It has been shown that the unsigned polar fields in the latitude range (78°–90°) show a steady decline starting ~1995–1996 till the maximum of cycle 23. We also find that the long term changes in the unsigned polar fields at higher latitudes are well correlated with changes in the surface meridional flow speed that have been reported for the cycle 23.

GM Cephei is an active T Tauri star in the young open cluster Trumpler 37, showing abrupt UX Orionis type of photometric variability. Its light curves exhibit frequent, sporadic brightening events, each of <0.5 mag and lasting for days, which must have been originated from unsteady circumstellar accretion. In addition, the star undergoes a brightness drop up to ~1 mag lasting for about a month, during which the star became bluer when fainter. Moreover, the brightness drops seem to have a recurrence timescale of about 300 days. It is proposed that the brightness drop arises from obscuration of the central star by an orbiting dust concentration, exemplifying disk inhomogeneity in transition between grain coagulation and planetesimal formation in a young circumstellar disk. GM Cep was found to show a few percent polarization in the optical wavelengths, and an enhanced level of polarization during the occultation phase.

We select ten passively evolving and massive galaxies at redshift z ~ 2 from the Cluster Lensing And Supernova survey with Hubble (CLASH). We derive the stellar properties of these galaxies using the multiwavelength HST WFC3 and ACS data, together with Spitzer IRAC observations. We also analyze the optical rest-frame morphology of these high redshift objects by using the GALFIT package (Peng et al. 2002). The observed near-IR images, obtained with the HST/WFC3 camera with high spatial resolution and amplified by the foreground clusters, provide us with a good chance to study the structures of such systems. Six out of ten galaxies have on average a four times smaller effective radius, in agreement with previous works at redshift z ~ 2.

The environments surrounding nine Wolf-Rayet stars were studied in molecular emission. Expanding shells were detected surrounding these WR stars (see left panels of Figure 1). The average masses and radii of the molecular cores surrounding these WR stars anti-correlate with the WR stellar wind velocities (middle panels of Figure 1), indicating the WR stars has great impact on their environments. The number density of Young Stellar Objects (YSOs) is enhanced in the molecular shells at ∼5 arcmin from the central WR star (lower-right panel of Figure 1). Through detailed studies of the molecular shells and YSOs, we find strong evidences of triggered star formation in the fragmented molecular shells (Liu et al. 2010).

Direct imaging and spectroscopy of exoplanets is a key element for understanding planet formation and migration. Such direct detections and characterizations remains technologically challenging, since a very high contrast ratio and small angular separation are involved, and futhermore speckle noise limits the high-contrast imaging performance. We further discuss a speckle subtraction and suppression technique that fully takes advantage of spectral and time-domain information on quasi-static speckles to measure the highest-fidelity photometry as well as accurate astrometry of detected companions.

Our team was awarded 108 orbits of Hubble Space Telescope time to obtain parallaxes and photometry of nine metal-poor stars with [Fe/H] < −1.5 dex. The parallaxes are obtained from observations with the Fine Guidance Sensor (FGS 1r; 11 orbits per star) and photometry was obtained with the Advanced Camera for Surveys (one orbit per star). The first data were obtained in October 2008, and the data collection is ongoing. It is anticipated that the observations will be complete in June 2013. Preliminary data reduction has been completed for five of our target stars. The parallax errors vary from 0.12 to 0.16 milli-arcseconds, and the parallaxes are at least an order of magnitude more accurate than existing Hipparcos parallaxes for these stars. The errors in the true distance modulus range from 0.02 to 0.03 mag. Ground-based high-resolution spectra have been analyzed to obtain accurate abundances for three stars. The properties of the two stars with accurate abundances and parallaxes are in excellent agreement with those predicted by stellar evolution models.

Observations of quiescent prominences show rising plumes, dark in chromospheric lines, that propagate from large bubbles. In this paper we present a method that may be used to determine the plasma β (ratio of gas pressure to magnetic pressure) from the rising plumes. Using the classic fluid dynamic solution for flow around a circular cylinder, the compression of the prominence material can be estimated. Application to a prominence gave an estimate of the plasma β as β=0.47−1.13 for a ratio of specific heats of γ=1.4−1.7.

Detecting neutrinos associated with the still enigmatic sources of cosmic rays has reached a new watershed with the completion of IceCube, the first detector with sensitivity to the anticipated fluxes. In this review, we will briefly revisit the rationale for constructing kilometer-scale neutrino detectors and summarize the status of the field.

The interaction between a hot corona and a cold thin disk can drive cold gas evaporating into the corona or hot gas condensing into the thin disk. The evaporation is caused by heat conduction downwards to the disk; while condensation is caused by overcooling of corona gas through inverse Compton scattering. Evaporation occurs at low accretion rates when the corona cannot efficiently radiate the viscous heat, thereby part of which is conducted down and heats up gas. Condensation occurs at high accretion rates when the Compton cooling of disk photons is strong enough to efficiently cool the corona gas. An important consequence of the evaporation is complete removal of the disk at a certain distances. In contrast, condensation can lead to a weak corona or complete collapse of the corona. This causes the observed transitions between various spectral states, at which the accretion flows are dominated respectively by ADAF, disk+ corona, and thin disk from low to high accretion rates, providing a natural explanation to the low, intermediate and high spectral states in BHXRBs, as well as their transitions. The same process can also be applied to accretion around supermassive black holes.

Class II methanol masers are known to be tracers of an early phase of massive star formation. The 6.7- and 12.2-GHz methanol maser transitions can show a significant amount of variability, including periodic variations. Studying maser variability can lead to important insights into conditions in the maser environment but first the maser time-series need to be characterised. The results of long-term monitoring of 8 regularly-varying sources will be presented and methods of period-search discussed.

It is now clear that the epoch when the Universe was half of its current age is a crucial period during which galaxies assembled their mass and evolved into the galaxies we observe in the local Universe. However, so far only very few direct studies of mass assembly in action, hence galaxy merging, were conducted over z=1 and usually relied on very small or biased samples. Based on very deep near infrared survey data, the latest UKIDSS-UDS DR8, combined with the optical data conducted by Subaru and CFHT and Spitzer IRAC observations, we explored the evolution of the merging rate up to z = 2, over the largest volume of the Universe at 0.4<z<2 ever sampled. The pair fraction is found to decrease by a factor of two during this period, and wet (gas rich) mergers dominate largely. The dry mergers are very rare, ruling it out as the main mechanism for the mass assembly of passive massive galaxies. Also while massive galaxies undergo a decrease of their pair fraction during this period, less massive systems follow an increase during the same period.

Observations of pulsars with the Large Area Telescope (LAT) on the Fermi satellite have revolutionized our view of the gamma-ray pulsar population. For the first time, a large number of young gamma-ray pulsars have been discovered in blind searches of the LAT data. More generally, the LAT has discovered many new gamma-ray sources whose properties suggest that they are powered by unknown pulsars. Radio observations of gamma-ray sources have been key to the success of pulsar studies with the LAT. For example, radio observations of LAT-discovered pulsars provide constraints on the relative beaming fractions, which are crucial for pulsar population studies. Also, radio searches of LAT sources with no known counterparts have been very efficient, with the discovery of over forty millisecond pulsars. I review radio follow-up studies of LAT-discovered pulsars and unidentified sources, and discuss some of the implications of the results.

The Magellan Adaptive Optics (MagAO) system saw first light in November 2012 at Las Campanas Observatory (LCO) on the 6.5m Clay telescope. Here we present an introduction to MagAO's visible wavelength diffraction limited imager, VisAO. VisAO delivers Strehl ratios greater than 30% from 0.62 microns (r') through 1 micron, where Strehl is even higher, and achieved resolutions as small as 20 milli-arcseconds. We took advantage of the excellent performance of MagAO/VisAO to conduct high contrast observations of an exoplanet in the optical. With VisAO, we are, for the first time, able to begin characterizing exoplanet atmospheres in the optical from the ground.

We present our preliminary results on the application of dendrogram statistics to the carbon monoxide PPV map of the giant molecular cloud G333. We obtain the dendrograms at various merging levels and found the clustering of branches is independent from the merging levels. The statistics of intensity distributions show gravity is possibly significant in this cloud and the gas may be sonic. Application of this method to other molecular lines data are required for further analysis of the cloud properties.

The emission of steady compact jets observed in the hard spectral state of X-ray binaries is likely to be powered by internal shocks caused by fluctuations of the outflow velocity. The dynamics of the internal shocks and the resulting spectral energy distribution (SED) of the jet is very sensitive to the shape of the Power Spectral Density (PSD) of the fluctuations of the jet Lorentz factor. I use Monte-Carlo simulations to investigate this dependence. It turns out that Lorentz factor fluctuations injected at the base of the jet with a flicker noise power spectrum (i.e. P(f) ∝ 1/f) naturally produce the canonical flat SED observed from radio to IR band in X-ray binary systems in the hard state. This model also predicts a strong, wavelength dependent, variability that resembles the observed one. In particular, strong sub-second variability is predicted in the infrared and optical bands.

Studying the amazingly diverse planet zoo provides us with unprecedented opportunities for understanding planet Earth and ultimately ourselves. An assessment of a planet's “habitability” reflects our Earth-centric prejudice and can serve to prioritise targets to actually search for signatures of life similar to ours. The probability for life beyond Earth to exist however remains unknown, and studies on habitability or statistics of planetary systems do not change this. But we can leave speculation behind, and embark on a journey of exploration. A sample of detected cosmic habitats would provide us with insight on the conditions for life to emerge, develop, and sustain, but disentangling the biota fraction from the duration of the biotic era would depend particularly on our knowledge about the dynamics of planetary systems. Apart from the fact that planets usually do not come alone, we also must not forget that the minor bodies in the Solar system vastly outnumber the planets. A focus on just what we might consider “habitable” planets is too narrow to understand their formation and evolution. While uniqueness prevents understanding, we need to investigate the context and embrace diversity. A comprehensive picture of planet populations can only arise by exploiting a variety of different detection techniques, where not only Kepler but also gravitational microlensing can now enter hitherto uncharted territory below the mass or size of the Earth. There is actually no shortage of planets, the Milky Way alone may host hundreds of billions, and so far we have found only about 1000.