Untangling the Galaxy. III. Photometric Search for Pre-main-sequence Stars with Deep Learning

A reliable census of pre-main-sequence stars with known ages is critical to our understanding of early stellar evolution, but historically there has been difficulty in separating such stars from the field. We present a trained neural network model, Sagitta, that relies on Gaia DR2 and 2 Micron All-Sky Survey photometry to identify pre-main-sequence stars and to derive their age estimates. Our model successfully recovers populations and stellar properties associated with known star-forming regions up to five kpc. Furthermore, it allows for a detailed look at the star-forming history of the solar neighborhood, particularly at age ranges to which we were not previously sensitive. In particular, we observe several bubbles in the distribution of stars, the most notable of which is a ring of stars associated with the Local Bubble, which may have common origins with Gould’s Belt.

Separation of stellar properties using SDSS, 2MASS magnitudes

В работе описан и апробирован на выборке размером ∼ 300 звезд теоретико-вероятностный подход, который на основе блеска в полосах ugriz и JHK s позволяет вынести суждение о значениях атмосферных характеристик звезды и полном поглощении. Подход основан на методе максимального правдоподобия с использованием поискового индекса по типу k - d дерева, для создания которого использовались результаты вычислений моделей звездных атмосфер Куруца. We present a probability-theoretic approach to separation of stellar properties using SDSS, 2MASS magnitudes. The approach is based on the maximum likelihood method using a search index of the type k - d tree. Using synthetic photometry of Kurucz model spectra, the search index is constructed and the approach is tested on sample of ∼ 300 stars.

New Clues to Reveal Origins of Hot- and Warm-Jupiter: Mutual Occurrence Rate of Hot Jupiter，Warm Jupiter and Cold Jupiter

Many works based on the correlations between the occurrence rate of various giant planets and stellar properties of their hosts have provided clues revealing planetary formation processes. However, few researches have focused on the mutual occurrence rate of different type of planets and their dependency upon the stellar properties, which may help to provide an insight into the dynamics evolution history of planetary systems. To investigate the mutual occurrence rates, first we define three types of giant planets, i.e. cold Jupiter(CJ), warm Jupiter(WJ) and hot Jupiter(HJ), according to their position normalized by the snow-line in the system, ap > asnow, 0:1asnow < ap ≤ asnow and ap ≤ 0:1asnow, respectively. Then, we derive their occurrence rates(ηHJ,ηwJ,ηcJ) considering completeness correction caused by different detection methods (RV and transit) and surveys (HARPS& CORALIE and Kepler). Finally, we investigate the correlation between the relative occurrence rates, i.e. ηcJ/ηwJ or ηwJ/ηHJ, and various stellar properties, e.g. stellar metallicity and effective temperature Teff . We find that ηWJ from RV and transit surveys show a similar increasing trend with the increasing stellar effective temperature when Teff ≤ 6100K. While ηcJ from RV samples is almost flat within Teff in (4600K;6100K], and ηHJ from transit samples is increasing with increasing stellar effective temperature within 3600K < Te f f < 7100K. Further more, we find that the mutual occurrence rate between CJ and WJ, i.e. ηcJ/ηwJ , shows a decreasing trend with the increasing stellar effective temperature. In contrary, the ratio ηwJ/ηHJ is reversely depends on the stellar effective temperature. After a series of consistency tests, our results suggest the in-situ hypothesis can be excluded from the formation process of both WJ and HJ. However, the origin and evolution history of HJ may be quite different from that of WJ.

Fundamentals of Astrophysics

This concise textbook, designed specifically for a one-semester course in astrophysics, introduces astrophysical concepts to undergraduate science and engineering students with a background in college-level, calculus-based physics. The text is organized into five parts covering: stellar properties; stellar structure and evolution; the interstellar medium and star/planet formation; the Milky Way and other galaxies; and cosmology. Structured around short easily digestible chapters, instructors have flexibility to adjust their course's emphasis as it suits them. Exposition drawn from the author's decade of teaching his course guides students toward a basic but quantitative understanding, with 'quick questions' to spur practice in basic computations, together with more challenging multi-part exercises at the end of each chapter. Advanced concepts like the quantum nature of energy and radiation are developed as needed. The text's approach and level bridge the wide gap between introductory astronomy texts for non-science majors and advanced undergraduate texts for astrophysics majors.

Comprehensive list of semi-detached double-lined eclipsing binaries with Gaia DR2 data

Semi-detached eclipsing systems play an important role in our understanding of stellar properties. In the present study, we have cross-matched a previously compiled comprehensive list of SD double-lined eclipsing binaries, containing 119 systems, with Gaia DR2 and analyze the result. A special analysis is conducted for systems with controversial data on parallaxes. It is shown that Gaia DR2 effective temperatures should be used with caution, as they do not describe hot SD systems well. We have also compiled an empirical relation between the temperature of the accretor and the donor.

Deciphering the Origin of Ionized Gas in IC 1459 with VLT/MUSE

IC 1459 is an early-type galaxy (ETG) with a rapidly counter-rotating stellar core, and is the central galaxy in a gas-rich group of spirals. In this work, we investigate the abundant ionized gas in IC 1459 and present new stellar orbital models to connect its complex array of observed properties and build a more complete picture of its evolution. Using the Multi-Unit Spectroscopic Explorer (MUSE), the optical integral field unit (IFU) on the Very Large Telescope (VLT), we examine the gas and stellar properties of IC 1459 to decipher the origin and powering mechanism of the galaxy’s ionized gas. We detect ionized gas in a non-disk-like structure rotating in the opposite sense to the central stars. Using emission-line flux ratios and velocity dispersion from full-spectral fitting, we find two kinematically distinct regions of shocked emission-line gas in IC 1459, which we distinguished using narrow (σ ≤ 155 km s−1) and broad (σ &gt; 155 km s−1) profiles. Our results imply that the emission-line gas in IC 1459 has a different origin than that of its counter-rotating stellar component. We propose that the ionized gas is from late-stage accretion of gas from the group environment, which occurred long after the formation of the central stellar component. We find that shock heating and AGN activity are both ionizing mechanisms in IC 1459 but that the dominant excitation mechanism is by post-asymptotic giant branch stars from its old stellar population.

FROM GLOBAL TO SPATIALLY RESOLVED IN LOW-REDSHIFT GALAXIES

Our understanding of the structure, composition and evolution of galaxies hasstrongly improved in the last decades, mostly due to new results based on large spectro-scopic and imaging surveys. In particular, the nature of ionized gas, its ionization mech-anisms, its relation with the stellar properties and chemical composition, the existence ofscaling relations that describe the cycle between stars and gas, and the corresponding evo-lution patterns have been widely explored and described. More recently, the introduction ofadditional techniques, in particular integral field spectroscopy, and their use in large galaxysurveys, have forced us to re-interpret most of those recent results from a spatially resolvedperspective. This review is aimed to complement recent efforts to compile and summarizethis change of paradigm in the interpretation of galaxy evolution. To this end we replicatepublished results, and present novel ones, based on the largest compilation of IFS data ofgalaxies in the nearby universe to date.

HAYDN

In the last decade, the Kepler and CoRoT space-photometry missions have demonstrated the potential of asteroseismology as a novel, versatile and powerful tool to perform exquisite tests of stellar physics, and to enable precise and accurate characterisations of stellar properties, with impact on both exoplanetary and Galactic astrophysics. Based on our improved understanding of the strengths and limitations of such a tool, we argue for a new small/medium space mission dedicated to gathering high-precision, high-cadence, long photometric series in dense stellar fields. Such a mission will lead to breakthroughs in stellar astrophysics, especially in the metal poor regime, will elucidate the evolution and formation of open and globular clusters, and aid our understanding of the assembly history and chemodynamics of the Milky Way’s bulge and a few nearby dwarf galaxies.