The single-degenerate (SD) model is currently a favourable progenitor scenario for the production of type Ia supernovae (SNe Ia). The companion in the SD model would survive after the SN explosion. In this work, we obtained the velocity distribution of the surviving companion stars from different SD scenarios in the Galaxy, which can be verified by future observations.

With modern large scale spectroscopic surveys, such as the SDSS and LSS-GAC, Galactic astronomy has entered the era of millions of stellar spectra. Taking advantage of the huge spectroscopic database, we propose to use a “standard pair" technique to a) Estimate multi-band extinction towards sightlines of millions of stars; b) Detect and measure the diffuse interstellar bands in hundreds of thousands SDSS and LAMOST low-resolution spectra; c) Search for extremely faint emission line nebulae in the Galaxy; and d) Perform photometric calibration for wide field imaging surveys. In this contribution, we present some results of applying this technique to the SDSS data, and report preliminary results from the LAMOST data.

Chemical and kinematical information is needed in order to understand and trace the formation history of our Galaxy. In the homogeneous large sample of F and G stars in the survey by Nordström et al. (2004), groups of stars with orbital parameters different from field stars were found by Helmi et al. (2006). Simulations of disrupted satellites showed that the groups had similar properties as infalling dwarf satellites would have after several Gyr. From high resolution spectra, we analyse elemental abundances of stars in 3 such groups with conserved kinematic properties. Here we present first results of s- and r- process element abundances in two such groups and compare with average field stars.

Anomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 Å are found in absorption along the line of sight to Herschel 36, an O star system next to the bright Hourglass nebula of the Hii region Messier 8. Excited lines of CH and CH+ are seen as well. We show that the region is very compact and itemize other anomalies of the gas. An infrared-bright star within 400 AU is noted. The combination of these effects produces anomalous DIBs, interpreted by Oka et al. (2013, see also this volume) as being caused predominantly by infrared pumping of rotational levels of relatively small molecules.

Studies of gas phase ion-neutral reactions provide insight into many areas of astrochemistry, including the elusive characterization of the Diffuse Interstellar Bands (DIBs). This presentation gives an overview of our experimental studies of several classes of positive and negative ions, using the flowing afterglow-selected ion flow tube and a newly modified ion trap. Earlier studies of carbon chain anions and polycyclic aromatic hydrocarbon (PAH) cations, both of which have been suggested as carriers of the DIBs, are described. More recent work including isomeric PAHs, nitrogen-containing PAHs, negative ions of PAHs, and negative ions of 5-membered heterocyclic rings are discussed. Finally, the study of quantitative thermochemistry by coupling our results with data from Photoelectron Spectroscopy is described.

Resonances with spiral density waves or the Galactic bar can cause structure in local velocity distributions (also known as phase space). Because resonances are narrow, it is possible to place tight constraints on a pattern speed or the shape of the underlying gravitational potential.

Interference between multiple spiral patterns can cause localized bursts of star formation and discontinuities or kinks in the spiral arm morphology. Numerical simulations suggest that boundaries between different dominant patterns in the disk can manifest in local velocity distributions as gaps that are associated with specific orbital periods or angular momentum values. Recent studies have detected age gradients that may be associated with the appearance of spiral features such as armlets and spurs.

When patterns grow or vary in speed, resonances can be swept through the disk causing changes in the velocity distributions. Evidence of resonance capture or resonance crossing can be used to place constraints on the past history of patterns in the disk. The X-shaped Galactic bulge may have been caused by stars captured into vertical resonance with the Bar.

Disturbances in the Galactic disk, such as from a past merger, can cause an uneven distribution of disk stars in action angles. Subsequently the stellar distribution becomes more tightly wound in phase space. Phase wrapping can cause a series of shell like features in either real space or in a local velocity distribution. The spacing between features is dependent on the time since the disturbance.

Given a parametrized model of the Galactic potential, the best-fit parameters can be obtained by maximizing the Kullback-Leibler divergence of the action distribution of a set of stars initially clustered in action space (e.g. stars in tidal streams). This method will allow us to map the Milky Way's gravitational potential by simultaneously fitting multiple tidal streams without requiring stream membership information. With 20 streams of at least 20 stars each, including observational errors consistent with predictions for Gaia, this technique recovers the input potential parameters to a precision of 10-60% and an accuracy of 10%. With all the observed streams in our mock stellar halo (about 40) that fit the error criteria, the precision improves to 10%.

A short review of the profiles of diffuse interstellar bands and their possible interpretation is given, largely from the perspective of absorption by gas-phase molecules. Potentially a crucial source of information on the nature of the diffuse band carriers, profile studies provide a promising avenue of research towards finding the solution to their identification. Detection and modelling of fine structure in particular offers a valuable benchmark against which any proposed carriers(s) can be tested.

Solar oxygen abundance is a key parameter for the studies of solar physics. Oxygen abundances of cool stars with different metallicities are important for understanding the galactic chemical evolution. We present non-LTE calculations for O I with the classical plane-parallel (1D) model atmospheres for a set of stellar parameters corresponding to stars of spectral types from A to K. Non-LTE leads to strengthening the O I lines, and the difference between the non-LTE and LTE abundances (non-LTE correction) is negative. The departures from LTE grow toward higher effective temperature and lower surface gravity. In the entire temperature range and log g = 4, the non-LTE correction does not exceed 0.05 dex in absolute value for lines of O I in the visible spectral range. The non-LTE corrections are significantly larger for the infrared O I 7771-5, 8446 Å lines and reach an order of magnitude for A-type stars. To differentiate the effects of inelastic collisions with electrons and neutral hydrogen atoms on the statistical equilibrium (SE) of O I, we derived the oxygen abundance for the five well studied A-type stars. For each star, non-LTE largely removes the difference between the infrared and visible lines found in LTE. In the case of cool stars (Sun and Procyon), inelastic collisions with H I affect the SE of O I, and agreement between the abundances from different lines is achieved when using the Drawin's formalism for collisional rates calculations. The solar mean oxygen abundance from the six lines is ϵ = 8.74 ± 0.05, when using the MAFAGS-OS solar model atmosphere and ϵ = 8.78 ± 0.03, when applying the 3D corrections taken from the literature. The non-LTE abundances of oxygen are derived for the sample of cool dwarfs with various metallicities on high-resolution spectra observed in the Lick observatory.

We present the results of special tests of the automatic procedure for atmospheric parameters determination based on spectroscopy.

We use 63,774 F/G dwarf stars from the LAMOST pilot survey to explore the velocity distribution in the solar neighborhood. The intrinsic UV distribution is reconstructed with a 20-Gaussian model using extreme deconvolution. We find at least two arcs, one extending from (−106, −3) to (94, −27) km/s and the other from (29, −9) to (78, −51) km/s. The arcs are qualitatively consistent with numerical simulations of the resonance induced by the Galactic bar and can be used to constrain its dynamical properties.

Variable stars have a unique part to play in Galactic astronomy. Among the most important of these variables are the Cepheids (types I and II), the RR Lyraes and the Miras (O- and C-rich). The current status of the basic calibration of these stars in their roles as distance, structure and population indicators is outlined and some examples of recent applications of these stars to Galactic and extragalactic problems are reviewed. The expected impact of Gaia on this type of work is discussed and the need for complementary ground based observations, particularly large scale near-infrared photometry, is stressed.

The statistical equilibrium of neutral and ionized silicon in the atmospheres of cool stars is discussed. Non-local thermodynamic equilibrium effects (NLTE) are investigated. It is found that the NLTE effects for Si are important, in particular for warm metal-poor stars. For warm metal-poor stars, the NLTE abundance correction reaches ~0.2 dex relative to standard LTE calculations.

I summarizes the main characteristics of a cosmological hydro-dynamical model which includes chemical evolution. In the last decade, galaxy formation models have made important progress which contribute to understand observations although there are still many open questions to be answered. Current chemo-dynamical cosmological simulations are able to reproduce global trends. They provide a suitable route to underpin physical events responsible of determining observed chemical patterns.

We briefly summarize the method of kinematic distances of Galactic radio objects and discuss the ambiguity in this method. Both Hi absorption and Hi self-absorption are effective tools to solve the kinematic distance ambiguity. We build the 21 cm Hi absorption spectrum of the complex G35.6-0.5, and suggest SNR G35.6-0.4, one component of the complex, is located at the near side distance of about 3.6 kpc.

A knowledge of the three dimensional distribution of interstellar dust is critical in interpreting all observations of the sky, particularly in the understanding of the structure and morphology of our Galaxy. It has been much easier to map the integrated dust extinction through the Galaxy, which is needed in modeling extragalactic sources, but this yields an overestimate of reddening to Galactic objects. Massive surveys, such as Gaia, present both a problem in that the distribution of interstellar dust must be known in order to model the internal structure of the Galaxy and an opportunity in that multi-color data may be used to deconvolve the dust distribution. I will present the current state of the modeling, which is yet in its early stages.

We report on the discovery and characterization of a possibly new signature related to the formation of the Milky Way stellar local halo.

We obtained the chemical abundances of more than 20 Barium (Ba) stars by analysing high resolution echelle spectra. They show obvious overabundances of neutron capture process elements, such as Y, Zr, Ba, La and Eu. Their abundance pattern can be explained by binary accretion through stellar wind, where the Ba stars have accreted the ejecta from the companion stars which were in AGB stages at that time and now evolve as white dwarfs.

We present our recent measurement of the kinematics of the Milky Way stellar halo (Light Side) and the derived mass of the dark matter halo (Dark Side) using the Jeans analysis. A tangential dip in the velocity anisotropy profile at r ~ 17 kpc (Kafle et al. 2012), and a distinct difference of ~65 kms−1 in the mean azimuthal velocity and the r.m.s dispersion of the most metal-rich and the metal-poor Blue Horizontal Branch stars we find (Kafle et al. 2013) are reported. The implications of this on the current controversial issue of an existence of the two-components in the halo are also discussed.

Aided with the kinematic measurements of the light side, we demonstrate how we infer the dynamical property of the dark side. Considering a realistic three component galaxy model (Hernquist bulge, Miyamoto-Nagai disk and NFW halo), we estimate the virial mass of the Galaxy to be Mvir = 1.2+0.5−0.4 × 1012M⊙ (Kafle et al. 2012). We also show that the rotation curve of the Galaxy has undulations similar to what have also been seen in the studies of the HI gas (Sofue et al. 2009).

We use the stellar population synthesis code SeBa (Portegies Zwart & Verbunt (1996), Toonen, Nelemans & Portegies Zwart (2012)) to study the halo white dwarf population. Here we assume a Kroupa initial mass function and compare 4 models, varying two parameters: the star formation (SF) history of the halo (either continuous SF during 2.5 Gyr, which started 13.2 Gyr ago, or a SF burst during 360 Myr, which started 12.9 Gyr ago – see the left panel of the figure) and the binary fraction of the halo (either 100% single stars, or 100% binaries). White dwarf cooling models (Althaus et al. (2009) and Renedo et al. (2010)) allow us to plot the halo white dwarf luminosity function for these 4 models, as is done in the right panel of the figure. Combined with an assumption about the density distribution of halo stars, we will study which of these white dwarfs Gaia can see, and what that can tell us about the initial parameter distributions in the halo. In the near future, we plan to use the Munich-Groningen semi-analytical galaxy formation model (Starkenburg et al. (2013)), to obtain key ingredients for the population synthesis modeling, such as a realistic star formation history (see the left panel of the figure).