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In order to investigate the origin of multiple stellar populations in the halo and bulge of the Milky Way, we have constructed chemical evolution models for the low-mass proto-Galactic subsystems such as globular clusters (GCs). Unlike previous studies, we assume that supernova blast waves undergo blowout without expelling the pre-enriched gas, while relatively slow winds of massive stars (WMS), together with the winds and ejecta from low and intermediate mass asymptotic-giant-branch stars (AGBs), are all locally retained in these less massive systems. We find that the observed Na-O anti-correlations in metal-poor GCs can be reproduced, when multiple episodes of starbursts are allowed to continue in these subsystems. A specific form of star formation history (SFH) with decreasing time intervals between the stellar generations, however, is required to obtain this result, which is in good agreement with the parameters obtained from our stellar evolution models for the horizontal-branch. The “mass budget problem” is also much alleviated by our models without ad-hoc assumptions on star formation efficiency (SFE) and initial mass function (IMF). We also applied these models to investigate the origin of super-helium-rich red clump stars in the metal-rich bulge as recently suggested by Lee et al. (2015). We find that chemical enrichments by the WMS can naturally reproduce the required helium enhancement (ΔY/ΔZ = 6) for the second generation stars. Disruption of proto-GCs in a hierarchical merging paradigm would have provided helium enhanced stars to the bulge field.
The Milky Way (MW) is interacting with its satellite galaxies and the tidal remnants of satellite galaxies have been observed especially in the MW halo. Understanding the spatial and velocity distributions of stars stripped from satellite galaxies will be of particular importance when interpreting the data from upcoming observations, such as Gaia, Subaru-HSC and PFS. We study tidal stripping events of satellite galaxies with various internal structures using high resolution N-body simulations. The dynamics of satellite galaxies is dominated by dark matter halos, but their density structure is still uncertain. The simulations reveal satellite galaxies with more tightly bound dark matter halos are more robust against the tidal force of the MW and have longer lifetimes than loosely bound ones (Ogiya et al., in prep.). Density scratches on the MW caused by the gravitational force of satellite galaxies and the observability are also discussed (Ogiya & Burkert 2016).
It is well known that the energy for solar eruptions comes from magnetic fields in solar active regions. Magnetic energy storage and dissipation are regarded as important physical processes in the solar corona. With incomplete theoretical modeling for eruptions in the solar atmosphere, activity forecasting is mainly supported with statistical models. Solar observations with high temporal and spatial resolution continuously from space well describe the evolution of activities in the solar atmosphere, and combined with three dimensional reconstruction of solar magnetic fields, makes numerical short-term (within hours to days) solar activity forecasting possible. In the current report, we propose the erupting frequency and main attack direction of solar eruptions as new forecasts and present the prospects for numerical short-term solar activity forecasting based on the magnetic topological framework in solar active regions.
Stars observed in the field of an open cluster are ideal for a controlled test of chemical tagging. Using chemical tagging, one should identify the cluster members, i.e., those stars of similar chemical composition, if their composition is indeed different from that of all the non-member stars of the field. Moreover, the abundance-based membership can be checked against membership based on radial velocities and proper motions. Here, I report preliminary results of such an experiment using data from the Gaia-ESO Survey. Although the three membership criteria usually agree, a few interesting examples of discrepant membership classification have been found. In addition, the mean composition of each open cluster was compared to a sample of 1 600 Gaia-ESO field stars. Some cases of field stars with abundances matching those of the open clusters were identified. This experiment suggests that open clusters do not necessarily have unique abundance patterns that set them apart from all other clusters.
In the recent years it has been generally accepted that seismic parameters add an important observational constraint for the study of stellar populations and galaxy evolution. Padova-Trieste (PARSEC) evolutionary tracks are widely used to characterise stellar objects and stellar populations. Stellar models at the base of these studies suffer from uncertainties and, more important, degeneracy among different input parameters: stellar mass, chemical composition, central chemical mixing, age, etc. Adding seismic properties to the classic parameters for stars at different evolutionary states, from the H main-sequence to the asymptotic giant branch, is a powerful tool to calibrate physical processes in stellar models, and hence to improve our interpretation of Galactic and extra-Galactic observations.
In studying Galactic open clusters based on LAMOST DR3, we deliberately selected several nearby cluster, which have relatively large projection area and reliable proper motion measurements. For each cluster, we firstly determine the typical proper motion distribution profiles in the cluster-core and the outskirt region, respectively, and perform field-star decontamination on the cluster area. We then calculate kinematic membership probability for each star in the cluster area and cross-match the highly probable members with LAMOST DR3 spectral catalog. Based on enhanced signal of cluster-member radial velocity distribution emerging from the whole field, we have also obtained reliable radial velocity membership probability for each star. Finally, we perform isochrones fitting with MCMC technique to study basic properties of these cluster, including age, metallicity, and distance modulus.
We describe the DR14 APOGEE-TGAS catalogue, a new SDSS value-added catalogue that provides precise astrophysical parameters, chemical abundances, astro-spectro- photometric distances and extinctions, as well as orbital parameters for ~30, 000 APOGEE-TGAS stars, among them ~5, 000 high-quality giant stars within 1 kpc.
We report on a technique to construct a flux rope (FR) from eruption data at the Sun. The technique involves line-of-sight magnetic fields, post-eruption arcades in the corona, and white-light coronal mass ejections (CMEs) so that the FR geometric and magnetic properties can be fully defined in addition to the kinematic properties. We refer to this FR as FRED (Flux Rope from Eruption Data). We illustrate the FRED construction using the 2012 July 12 eruption and compare the coronal and interplanetary properties of the FR. The results indicate that the FRED input should help make realistic predictions of the components of the FR magnetic field in the heliosphere.
The 5th RAVE data release is based on 520,781 spectra (R ≈ 7500 in the CaT region at 8410 - 8795Å) of 457,588 unique stars. RAVE DR5 provides radial velocities, stellar parameters and individual abundances for up to seven elements and distances found using isochrones for a considerable subset of these objects. In particular, RAVE DR5 has 255,922 stellar observations that also have parallaxes and proper motions from the Tycho-Gaia astrometric solution (TGAS) in Gaia DR1. The combination of RAVE and TGAS thus provides the currently largest overlap of spectroscopic and space-based astrometric data and thus can serve as a formidable preview of what Gaia is going to deliver in coming data releases. Basic properties of the RAVE+TGAS survey and its derived data products are presented as well as first applications w.r.t wave-like patterns in the disk structure. An outlook to the 6th RAVE data release is given.
We investigate the geomagnetic field variations recorded by INTERMAGNET geomagnetic observatories. We confirm that the effect of solar eclipse can be seen over an interval of 180 minutes centered at the time of maximum eclipse on a site of a geomagnetic observatory. It is found that the effect of the solar eclipse on the geomagnetic field becomes conspicuous as the magnitude of a solar eclipse becomes larger. The effect of solar eclipses is more evident in the second half of the path of Moon’s shadow. We also find that the effect can be overwhelmed, more sensitively by geomagnetic disturbances than by solar activity of solar cycle.
We present our latest 3D model atmospheres for carbon-enhanced metal-poor (CEMP) stars computed with the CO5BOLD code. The stellar parameters are representative of hot turn-off objects (Teff ~ 6250 K, log g = 4.0, [Fe/H]=−3). The main purpose of these models is to investigate the role of 3D effects on synthetic spectra of the CH G-band (4140-4400 Å), the CN BX-band (3870-3890 Å), and several UV OH transitions (3122-3128 Å). By comparison with the synthetic spectra from standard 1D model atmospheres (assuming local thermodynamic equilibrium, LTE), we derive 3D abundance corrections for carbon and oxygen of up to −0.5 and −0.7 dex, respectively.
The study of extremely metal-poor (EMP; [Fe/H] <−3.0) and ultra metal-poor (UMP; [Fe/H] <−4.0) stars is crucial for better understanding first-star nucleosynthesis and constraining the initial mass function in the early Universe. However, UMP stars discovered in the past 25 years only number ~25. A few recent theoretical studies have pointed out that there is likely to exist large numbers of EMP and UMP stars in the periphery of the Galactic halo, at distances exceeding 30-50 kpc. We present identifications of several new EMP/UMP stars and introduce a survey to expedite discovering hundreds to thousands of EMP/UMP stars in the outermost halo (as well as in the local volume) over the next few years, which could revolutionize chemical-evolution studies of the Galaxy.
The four main findings about the age and abundance structure of the Milky Way bulge based on microlensed dwarf and subgiant stars are: (1) a wide metallicity distribution with distinct peaks at [Fe/H] = -1.09, -0.63, -0.20, +0.12, +0.41; (2) a high fraction of intermediate-age to young stars where at [Fe/H] > 0 more than 35 % are younger than 8 Gyr, (3) several episodes of significant star formation in the bulge 3, 6, 8, and 11 Gyr ago; (4) the ‘knee’ in the α-element abundance trends of the sub-solar metallicity bulge appears to be located at a slightly higher [Fe/H] (about 0.05 to 0.1 dex) than in the local thick disk.
We present the concept of a novel facility dedicated to massively-multiplexed spectroscopy. The telescope has a very wide field Cassegrain focus optimised for fibre feeding. With a Field of View (FoV) of 2.5 degrees diameter and a 11.4m pupil, it will be the largest etendue telescope. The large focal plane can easily host up to 16.000 fibres. In addition, a gravity invariant focus for the central 10 arc-minutes is available to host a giant integral field unit (IFU). The 3 lenses corrector includes an ADC, and has good performance in the 360-1300 nm wavelength range. The top level science requirements were developed by a dedicated ESO working group, and one of the primary cases is high resolution spectroscopy of GAIA stars and, in general, how our Galaxy formed and evolves. The facility will therefore be equipped with both, high and low resolution spectrographs. We stress the importance of developing the telescope and instrument designs simultaneously. The most relevant R&D aspect is also briefly discussed.
Radiation environment of near-Earth space is one of the most important factors of space weather. Space Monitoring Data Center of Moscow State University provides operational monitor and forecast of radiation conditions both at Geostationary Orbits (GEO) and at Low Earths Orbits (LEO) of the near-Earth space using data of recent space missions (Vernov, CORONAS series) and current (Lomonosov, Meteor-M, Electro-L) ones. Internet portal of Space Monitoring Data Center of Skobeltsyn Institute of Nuclear Physics of Lomonosov Moscow State University (SINP MSU - [swx.sinp.msu.ru]) provides possibilities to monitor and analyze the space radiation conditions in the real time mode together with the geomagnetic and solar activity including hard X-ray and gamma-emission of solar flares.
It is known that the poloidal field is at its maximum during solar minima, and that the behaviour during this time acts as a strong predictor of the strength of the following solar cycle. This relationship relies on the action of differential rotation (the Omega effect) on the poloidal field, which generates the toroidal flux observed in sunspots and active regions. We measure the helicity flux into both the northern and southern hemispheres using a model that takes account of the omega effect, which we find offers a strong quantification of the above relationship. We find that said helicity flux offers a strong prediction of solar activity up to 5 years in advance of the next solar cycle.
The heliospheric modulation model HelMod solves the transport-equation for Galactic Cosmic Ray propagation through the heliosphere down to Earth. It is based on a 2-D Monte Carlo approach that includes a general description of the symmetric and antisymmetric parts of the diffusion tensor, thus properly treating the particle drift effects as well as convection within the solar wind and adiabatic energy loss. The model was tuned in order to fit 1) the data observed outside the ecliptic plane at several distances from the Earth and 2) the spectra observed near the Earth for both, high and low solar activity periods. Great importance was given to description of polar regions of the heliosphere. We present the flux for protons, antiprotons and helium nuclei computed for solar cycle 23-24 in comparison with experimental observations and prediction for the full solar cycle 24.
The Global Muon Detector Network (GMDN) is composed by four ground cosmic ray detectors distributed around the Earth: Nagoya (Japan), Hobart (Australia), Sao Martinho da Serra (Brazil) and Kuwait city (Kuwait). The network has operated since March 2006. It has been upgraded a few times, increasing its detection area. Each detector is sensitive to muons produced by the interactions of ~50 GeV Galactic Cosmic Rays (GCR) with the Earth′s atmosphere. At these energies, GCR are known to be affected by interplanetary disturbances in the vicinity of the earth. Of special interest are the interplanetary counterparts of coronal mass ejections (ICMEs) and their driven shocks because they are known to be the main origins of geomagnetic storms. It has been observed that these ICMEs produce changes in the cosmic ray gradient, which can be measured by GMDN observations. In terms of applications for space weather, some attempts have been made to use GMDN for forecasting ICME arrival at the earth with lead times of the order of few hours. Scientific space weather studies benefit the most from the GMDN network. As an example, studies have been able to determine ICME orientation at the earth using cosmic ray gradient. Such determinations are of crucial importance for southward interplanetary magnetic field estimates, as well as ICME rotation.
We have studied the consequences of interacting coronal mass ejections (CMEs) of June 13-14, 2012 which were directed towards Earth and caused a moderate geomagnetic storm with Dst index ~ −86 nT. We analysed the in-situ observations of the solar wind plasma and magnetic field parameters obtained from the OMNI database for these CMEs. The in-situ observations show that the interacting CMEs arrive at Earth with the strongest (~ 150 nT) Sudden Storm Commencement (SSC) of the solar cycle 24. We compared these interacting CMEs to a similar interaction event which occurred during November 9-10, 2012. This occurred in the same phase of the solar cycle 24 but resulted in an intense geomagnetic storm (Dst ~ −108 nT), as reported by Mishra et al. (2015). Our analysis shows that in the June event, the interaction led to a merged structure at 1 AU while in the case of November 2012 event, the interacted CMEs arrived as two distinct structures at 1 AU. The geomagnetic signatures of the two cases reveal that both resulted in a single step geomagnetic storm.