Resolved stellar spectroscopy can obtain knowledge about chemical enrichment processes back to the earliest times, when the oldest stars were formed. In this contribution I will review the early (chemical) evolution of the Milky Way halo from an observational perspective. In particular, I will discuss our understanding of the origin of the peculiar abundance patterns in various subclasses of extremely metal-poor stars, taking into account new data from our abundance and radial velocity monitoring programs, and their implications for our understanding of the formation and early evolution of both the Milky Way halo and the satellite dwarf galaxies therein. I conclude by presenting the “Pristine” survey, a program on the Canada-France-Hawaii Telescope to study this intriguing epoch much more efficiently.

Early-type galaxies (ETGs) host a hot ISM produced mainly by stellar winds, and heated by Type Ia supernovae and the thermalization of stellar motions. High resolution 2D hydrodynamical simulations showed that ordered rotation in the stellar component results in the formation of a centrifugally supported cold equatorial disc. In a recent numerical investigation we found that subsequent generations of stars are formed in this cold disc; this process consumes most of the cold gas, leaving at the present epoch cold masses comparable to those observed. Most of the new stellar mass formed a few Gyrs ago, and resides in a disc.

Models of galaxy formation in a hierarchical universe predict substantial scatter in the halo-to-halo stellar properties, owing to stochasticity in galaxies' merger histories. Currently, only few detailed observations of stellar halos are available, mainly for the Milky Way and M31. We present the stellar halo color/metallicity and density profiles of red giant branch stars out to ~60 kpc along the minor axis of six massive nearby Milky Way-like galaxies beyond the Local Group from the Galaxy Halos, Outer disks, Substructure, Thick disks and Star clusters (GHOSTS) HST survey. This enlargement of the sample of galaxies with observations of stellar halo properties is needed to understand the range of possible halo properties, i.e. not only the mean properties but also the halo-to-halo scatter, what a ‘typical’ halo looks like, and how similar the Milky Way halo is to other halos beyond the Local Group.

Rocky planets are built through a series of highly energetic accretionary impacts. The accreting bodies are thought to carry small amounts of water to the growing planet, but it is debated whether the planet can retain this water through the accretionary process, or if water needs to be added largely after the planet is complete and cooled. Most of the relatively few measurements of deuterium to hydrogen in cometary water do not match Earths water, though the single example of 103P/Hartley 2 is a good match (Mumma & Charnley 2011, Hartogh et al. 2011). Alexander et al. (2012) point out, however, that organic materials in comets have far higher D/H than does their water, so in bulk no comet matches Earths D/H ratio, not even comet Hartley. Meteorites provide evidence that the material that built planets had small but sufficient amounts of water, and analysis of its isotopic composition demonstrates that water from rocky material, and not comets, provided water to the Earth (Alexander et al. 2012). This current evidence that Earths water came from rocky asteroidal material does not solve the question of whether this material was the accreting material that built the planet, or if it was added later. Mission data from the Moon and Mercury demonstrates that those bodies are not completely devoid of volatiles (McCubbin et al. 2010, Saal et al. 2008, Peplowski et al. 2011). The Moon, in particularly, has small amounts of internal water that survived its energetic origins (Hauri et al. 2011). Thus, the giant accretionary impacts that build planets do not completely dry them, and the water from their initial building blocks can be retained. If volatiles are delivered and partly retained during accretion, then the initial habitability of a young planet may be set by degassing of a magma ocean. Models predict that cooling can result in liquid water oceans within ten or tens of millions of years (Abe and Matsui 1986, Elkins-Tanton 2011). Thus, rocky planets in solar systems similarly composed to our own have a good chance of forming with water oceans, and of being habitable, at least for some period of time.

Late-type stars with thick convective zones and rapid rotations exhibit magnetic activity phenomena, such as starspots, plages, and flares. However, in many such kinds of eclipsing binaries, the details of the active phenomena are not well understood. In order to improve our understanding of stellar magnetic activities, we are carrying out an extensive study of the magnetic activities of eclipsing binaries by multi-color CCD photometry using several telescopes (SARA 90cm at KPNO, and NAOC 85cm and 60 cm telescopes at Xinglong). In this paper, we will present our preliminary results with revised orbital parameters, starspot parameters, and stellar flare events on DV Psc and BX Tri.

The stellar content of young massive star clusters emit large amounts of Lyman continuum photons and inject momentum into the inter stellar medium (ISM) by the strong stellar winds of the most massive stars in the cluster. When the most massive stars explode as supernovae, large amounts of mechanical energy are injected in the ISM. A detailed study of the ISM around these massive cluster provides insights on the effect of cluster feedback.

We present high quality integral field spectroscopy taken with VLT/MUSE of two starburst galaxies: ESO 338-IG04 and Haro 11. Both galaxies contain a significant number of super star clusters. The MUSE data provide us with an unprecedented view of the state and kinematics of the ionized gas in the galaxy allowing us to study the effect of stellar feedback on small and large spatial scales. We present our recent results on studying the ISM state of these two galaxies. The data of both galaxies show that the mechanical and ionization feedback of the super star clusters in the galaxy modify the state and kinematics of the ISM substancially by creating highly ionized bubbles around the cluster, making the central part of the galaxy highly ionized. This shows that the HII regions around the individual clusters are density bounded, allowing the ionizing photons to escape and ionize the ISM further out.

Most ultra-compact dwarf galaxies (UCDs) and very massive globular clusters reside in nearby galaxy clusters or around nearby giant galaxies. Due to their distance (> 4 Mpc) and compactness (r eff < 100 pc) they are barely resolved, and thus it is difficult to obtain their internal properties. Here I present our most recent attempts to constrain the mass function, stellar content and dynamical state of UCDs in the Fornax cluster. Thanks to radial velocity membership assignment of ~ 950 globular clusters (GCs) and UCDs in the core of Fornax, the shape of their mass function is well constrained. It is consistent with the ‘standard’ Gaussian mass function of GCs. Our recent simulations on the disruption process of nucleated dwarf galaxies in cluster environments showed that ~ 40% of the most massive UCDs should originate from nuclear star clusters. Some Fornax UCDs actually show evidence for this scenario, as revealed by extended low surface brightness disks around them and onsets of tidal tails. Multi-band UV to optical imaging as well as low to medium resolution spectroscopy revealed that there exist UCDs with youngish ages, (sub-)solar [α/Fe] abundances, and probably He-enriched populations.

The preliminary results of an analysis of the red giant star KIC 5701829 observed for 29 days in short-cadence mode with the Kepler satellite are reported. The oscillation spectrum of this star is characterized by the presence of a well-defined solar-like oscillation pattern due to acoustic modes. The characterization of the power spectrum has been performed following three basics steps commonly used in the analysis of solar-like oscillations: fitting and correcting for the background, estimating the frequency of maximum power (νmax) and the large separation (Δν), and extracting individual frequencies. We have found that the frequency of maximum oscillation power, νmax, and the mean large frequency separation, Δν, are around, 143 and 12 μHz, respectively. The global asteroseismic parameters along with atmospheric parameters from the literature allow us to infer about evolutionary status of the star.

I review theoretical models of star formation and how they apply across the stellar mass spectrum. Several distinct theories are under active study for massive star formation, especially Turbulent Core Accretion, Competitive Accretion and Protostellar Mergers, leading to distinct observational predictions. These include the types of initial conditions, the structure of infall envelopes, disks and outflows, and the relation of massive star formation to star cluster formation. Even for Core Accretion models, there are several major uncertainties related to the timescale of collapse, the relative importance of different processes for preventing fragmentation in massive cores, and the nature of disks and outflows. I end by discussing some recent observational results that are helping to improve our understanding of these processes.

We present a measurement of the spatial clustering of massive compact galaxies at 1 ≤ z ≤ 3 in CANDELS/3D-HST. We obtain the correlation length and characteristic DM halo masses for compact quiescent galaxies (cQGs) at z ~ 1.5 and compact starforming galaxies (cSFGs) at z ~ 2.5. By comparison with extended starforming galaxies (eSFGs), our result indicates that eSFGs are less possible to be the progenitors of cQGs at lower redshift. Our results indicates that cQGs at z ~ 1.5 could be the progenitors of local luminous ETGs and the descendants of cSFGs and SMGs at z > 2.

The strong similarities between the flares observed on the Sun and in low mass stars has raised question regarding dynamo in these stars. Using the Sun as a prototype, one may be able to address this. In this paper, we present an analysis of 30 intense X-ray flares observed from AB Dor. These flares detected in XMM-Newton data show a rapid rise (500-3000 s) and a slow decay (1000-6000 s). Our studies suggest that the scaling law between the flare peak emission measure and the flare peak temperature for all the flares observed on AB Dor is very similar to the relationship followed by solar flares. Furthermore, we obtain the frequency distribution of flare energies which is a crucial diagnostic to calculate the overall energy residing in a flare. Our results of this study indicate that the large flare (1033 ≤ E ≤ 1034 erg) may not contribute to the heating of the corona.

Turbulence in the interstellar medium is ubiquitous. The turbulent energy density in the gas is significant, and comparable to energy densities of magnetic fields and cosmic rays. Studies of the turbulent interstellar gas in the Milky Way have mostly focused on the neutral gas component, since various spectral lines can give velocity information. Probing turbulent properties in the ionized gas, let alone in magnetic fields, is observationally more difficult. A number of observational methods are discussed below which provide estimates of the maximum scale of fluctuations, the Mach number and other turbulence characteristics.

Outer-halo globular clusters show large half-light radii and flat stellar mass functions, depleted in low-mass stars. Using N-body simulations of globular clusters on eccentric orbits within a Milky Way-like potential, we show how a cluster’s half-mass radius and its mass function develop over time. The slope of the central mass function flattens proportionally to the amount of mass a cluster has lost, and the half-mass radius grows to a size proportional to the average strength of the tidal field. The main driver of these processes is mass segregation of dark remnants. We conclude that the extended, depleted clusters observed in the Milky Way must have had small half-mass radii in the past, and that they expanded due to the weak tidal field they spend most of their lifetime in. Moreover, their mass functions must have been steeper in the past but flattened significantly as a cause of mass segregation and tidal mass loss.

The Kepler Mission has discovered thousands of planets with radii <4 R ⊕, paving the way for the first statistical studies of super-Earth dynamics, formation, and evolution. These calculations often require planetary masses, and yet the vast majority of Kepler planet candidates do not have theirs measured. A key concern is therefore how to map the measured radii to mass estimates in a size range that lacks Solar System analogs. While previous works have derived one-to-one relationships between radius and mass, a realistic mass-radius (M-R) relation should account for the range of compositions that we expect within the population. This compositional diversity creates astrophysical scatter in the relation, which we quantify here.

Spectrometer/Telescope for Imaging X-rays (STIX) is a part of Solar Orbiter (SO) science payload. SO will be launched in October 2018, and after three years of cruise phase, it will reach orbit with perihelion distance of 0.3 a.u. STIX is a Fourier imager equipped with pairs of grids that comprise the flare hard X-ray tomograph. Similar imager types were already used in the past (eq. RHESSI, Yohkoh/HXT), but STIX will incorporate Moiré modulation and a new type of pixelized detectors with CdTe sensor. We developed a method of modeling these detectors' response matrix (DRM) using the Geant4 simulations of X-ray photons interactions with CdTe crystals. Taking into account known detector effects (Fano noise, hole tailing etc.) we modeled the resulting spectra with high accuracy. Comparison of Caliste-SO laboratory measurements of 241Am decay spectrum with our results shows a very good agreement. The modeling based on the Geant4 simulations significantly improves our understanding of detector response to X-ray photons. Developed methodology gives opportunity for detailed simulation of whole instrument response with complicated geometry and secondary radiation from cosmic ray particles taken into account. Moreover, we are developing the Geant4 simulations of aging effects which decrease detector's performance.

We present the results of our search for planets around subdwarf B stars. We look for wobbles of the sdB stars seen as sinusoidal variations of the pulsation periods. For a p-mode dominated pulsating sdB star we did not find any signatures of a companion and we marked KIC 10139564 to be a single star. In the case of the g-mode dominated objects the method turned out to inefficient not leading to any conclusion on the planet existence.

New CO J=1–0 observations with NANTEN and NANTEN2 reveal that extensive collisions between two molecular clouds at relative velocity of 15 km s−1 triggered the O star formation in the Galactic mini-starbursts NGC 6357 and NGC 6334. Correlated/anti-correlated gas distributions and intermediate velocity features between the two clouds lend support for the cloud-cloud collision scenario. The timescale of the collision and high-mass star formation is as short as less than 0.5 Myrs, suggesting rapid O star formation.

For the last 3 decades, infrared and microwave techniques have enabled the detection of up to 27 parent molecules in the coma of comets. Several molecules have been detected in over 40 different comets. A large diversity of composition is seen in the sample, comprising comets of various dynamical origins. Abundances relative to water for the molecules can vary by a factor 3 to more than 10. The taxonomic study of a sample of comets in which the abundance of several molecules (e.g., HCN, CH3OH, CO, CH4, C2H6, H2S, H2CO, CH3CN, CS, . . .) has been measured does not show any clear grouping. Except for fragments of a common parent comet, every observed comet shows a different composition. The absence of any clear correlation between the volatile content of the comets and their dynamical origin (Kuiper Belt versus Oort Cloud) is consistent with a common origin for these two populations. Their diversity in composition may also suggest that radial and temporal mixing in the early proto-planetary nebula may have played an important role.

The underlying population of exoplanets around stars in the Kepler sample can be inferred by a simulation that includes binning the Kepler planets in radius and period, invoking an empirical noise model, assuming a model exoplanet distribution function, randomly assigning planets to each of the Kepler target stars, asking whether each planet's transit signal could be detected by Kepler, binning the resulting simulated detections, comparing the simulations with the observed data sample, and iterating on the model parameters until a satisfactory fit is obtained. The process is designed to simulate the Kepler observing procedure. The key assumption is that the distribution function is the product of separable functions of period and radius. Any additional suspected biases in the sample can be handled by adjusting the noise model or selective editing of the range of input planets. An advantage of this overall procedure is that it is a forward calculation designed to simulate the observed data, subject to a presumed underlying population distribution, minimizing the effect of bin-to-bin fluctuations. Another advantage is that the resulting distribution function can be extended to values of period and radius that go beyond the sample space, including, for example, application to estimating eta-sub-Earth, and also estimating the expected science yields of future direct-imaging exoplanet missions such as WFIRST-AFTA.

Since the first detection of intracluster planetary nebulae in 1996, imaging and spectroscopic surveys identified such stars to trace the radial extent and the kinematics of diffuse light in clusters. This topic of research is tightly linked with the studies of galaxy formation and evolution in dense environment, as the spatial distribution and kinematics of planetary nebulae in the outermost regions of galaxies and in the cluster cores is relevant for setting constraints on cosmological simulations. In this sense, extragalactic planetary nebulae play a very important role in the near-field cosmology, in order to measure the integrated mass as function of radius and the orbital distribution of stars in structures placed in the densest regions of the nearby universe.