Various white-dwarf (WD) binary scenarios have been proposed trying to understand the nature and the diversity of type Ia supernovae (SNe Ia). In this work, we study the evolution of carbon–oxygen WD—red giant (RG) binaries (including the role of magnetic confinement) as possible SN Ia progenitors (the so-called symbiotic progenitor channel). Using the mesa stellar evolution code, we calculate the time dependence of the structure of the RG star, the wind mass loss, the Roche lobe-overflow mass-transfer rate, the polar mass-accretion rate (in the case of magnetic confinement), and the orbital and angular-momentum evolution. We consider cases where the WD is nonmagnetic and cases where the magnetic field is strong enough to force accretion onto the two small polar caps of the WD. Confined accretion onto a small area allows for more efficient hydrogen burning, potentially suppressing nova outbursts. This makes it easier for the WD to grow in mass toward the Chandrasekhar-mass limit and explode as a SN Ia. With magnetic confinement, the initial parameter space of the symbiotic channel for SNe Ia is shifted toward shorter orbital periods and lower donor masses compared to the case without magnetic confinement. Searches for low-mass He WDs or relatively low-mass giants with partially stripped envelopes that survived the supernova explosion and are found in SN remnants will provide crucial insights for our understanding of the contribution of this symbiotic channel.

Most neutron stars (NSs) and black holes (BHs) are believed to be the final remnants in the evolution of massive stars. In this study, we propose a new formation channel for the formation of BHs and peculiar NSs (specifically, magnetars and Thorne-$\dot{\rm Z}$ytkow objects [T$\dot{\rm Z}$Os]), which we refer to as the core merger-induced collapse (CMIC) model. This model involves the merger at the end of a common-envelope phase of an oxygen/neon/magnesium composition white dwarf and the core of a hydrogen-rich or helium-rich non-degenerate star, leading to the creation of peculiar new types of objects. The results of binary population synthesis simulations show that the CMIC channel could make important contributions to the populations of (millisecond) pulsars, T$\dot{\rm Z}$Os, magnetars and BHs. The possibility of superluminous supernovae powered by T$\dot{\rm Z}$Os, magnetars and BHs formed through the CMIC model is also being investigated. Magnetars with immediate matter surroundings formed after the CMIC might be good sources for fast radio bursts.

Ultra-diffuse galaxies are objects that have very extended morphology and faint central surface brightness. Most UDGs are discovered in galaxy clusters and groups, but some are also found in low-density environments. The diffuse morphology and faint surface brightness make them difficult to distinguish from the sky background. Several previous works have suggested that at least some UDGs are consistent with exponential surface brightness profiles). The surface brightness of exponential disks is enhanced in edge-on systems, so searching for edge-on systems may be an efficient way to select UDGs. In this paper, we focus on searching for edge-on H i -bearing ultra-diffuse sources (HUDS) from the 40% Arecibo Legacy Fast ALFA (ALFALFA) catalog, based on Sloan Digital Sky Survey g - and r -band images. After correcting the observed central surface brightness to a face-on perspective, we discover 11 edge-on HUDS candidates. All these newly discovered HUDS candidates are blue and H i -bearing, similar to other HUDS in 70% ALFALFA catalog, and different from UDGs in clusters.

We present the ultraviolet magnitudes for over three million stars in the LAMOST survey, in which 2,202,116 stars are detected by GALEX. For 889,235 undetected stars, we develop a method to estimate their upper limit magnitudes. The distribution of (FUV NUV) shows that the color declines with increasing effective temperature for stars hotter than 7000 K in our sample, while the trend disappears for the cooler stars due to upper atmosphere emission from the regions higher than their photospheres. For stars with valid stellar parameters, we calculate the UV excesses with synthetic model spectra, and find that the (FUV - NUV) versus R-FUV' can be fitted with a linear relation and late-type dwarfs tend to have high UV excesses. There are 87,178 and 1,498,103 stars detected more than once in the visit exposures of GALEX in the FUV and NUV, respectively. We make use of the quantified photometric errors to determine statistical properties of the UV variation, including intrinsic variability and the structure function on the timescale of days. The overall occurrence of possible false positives is below 1.3% in our sample. UV absolute magnitudes are calculated for stars with valid parallaxes, which could serve as a possible reference frame in the NUV. We conclude that the colors related to UV provide good criteria to distinguish between M giants and M dwarfs, and the variability of RR Lyrae stars in our sample is stronger than that of other A and F stars.

We have obtained CO(J=2-1) spectra of nine face-on low surface brightness galaxies(LSBGs) using the JCMT 15-meter telescope and observed Hα images using the 2.16-meter telescope of NAOC. As no CO has been detected, only upper limits on the H2 masses are given. The upper limits of total molecular hydrogen masses are about (1.2-82.4) × 10M⊙. Their star formation rates are mainly lower than 0.4 M⊙ yr −1 and star formation efficiencies are lower than 1.364 × 10 yr. Our results show that the absence of molecular gas content is the direct reason for the low star formation rate. The low star formation efficiency probably resulted from the low efficiency of HI gas transforming to H2 gas. Subject headings: galaxies: molecules — galaxies: evolution —galaxies: star formation rate Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, P.R. China; twcao@bao.ac.cn School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing, P.R. China; hwu@bao.ac.cn Chinese Academy of Sciences South America Center for Astronomy, China-Chile Joint Center for Astronomy,Camino El Observatorio 1515, Las Condes, Santiago, Chile East Asian Observatory, 660 N. Aohoku Place, University Park, Hilo, Hawaii 96720, USA School of Space Science and Physics, Shandong University at Weihai, Weihai, Shandong 264209, China

Using a Bayesian technology, we derived distances and extinctions for over 100 000 red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey by taking into account spectroscopic constraints from the APOGEE stellar parameters and photometric constraints from Two Micron All-Sky Survey, as well as a prior knowledge on the Milky Way. Derived distances are compared with those from four other independent methods, the Hipparcos parallaxes, star clusters, APOGEE red clump stars, and asteroseismic distances from APOKASC and Stromgren survey for Asteroseismology and Galactic Archaeology catalogues. These comparisons covers four orders of magnitude in the distance scale from 0.02 to 20 kpc. The results show that our distances agree very well with those from other methods: the mean relative difference between our Bayesian distances and those derived from other methods ranges from -4.2 per cent to +3.6 per cent, and the dispersion ranges from 15 per cent to 25 per cent. The extinctions towards all stars are also derived and compared with those from several other independent methods: the Rayleigh-Jeans Colour Excess (RJCE) method, Gonzalez's 2D extinction map, as well as 3D extinction maps and models. The comparisons reveal that, overall, estimated extinctions agree very well, but RJCE tends to overestimate extinctions for cool stars and objects with low log g.

The distance to the Large Magellanic Cloud (LMC) represents a key local rung of the extragalactic distance ladder yet the galaxy's distance modulus has long been an issue of contention, in particular in view of claims that most newly determined distance moduli cluster tightly-and with a small spread-around the "canonical" distance modulus, (m - M)(0) = 18.50 mag. We compiled 233 separate LMC distance determinations published between 1990 and 2013. Our analysis of the individual distance moduli, as well as of their two-year means and standard deviations resulting from this largest data set of LMC distance moduli available to date, focuses specifically on Cepheid and RR Lyrae variable-star tracer populations, as well as on distance estimates based on features in the observational Hertzsprung-Russell diagram. We conclude that strong publication bias is unlikely to have been the main driver of the majority of published LMC distance moduli. However, for a given distance tracer, the body of publications leading to the tightly clustered distances is based on highly non-independent tracer samples and analysis methods, hence leading to significant correlations among the LMC distances reported in subsequent articles. Based on a careful, weighted combination, in a statistical sense, of the main stellar population tracers, we recommend that a slightly adjusted canonical distance modulus of (m - M)(0) = 18.49 +/- 0.09 mag be used for all practical purposes that require a general distance scale without the need for accuracies of better than a few percent.

We explore correlations between extinction-corrected Hα, Hβ and ${\rm [O\,{II}]_{double}}$ luminosities versus 12- and 22-μm band luminosities, based on matching samples from the Sloan Digital Sky Survey (SDSS) and the Wide-field Infrared Survey Explorer (WISE). All the coefficients show strong correlations between Balmer lines and mid-infrared (MIR) luminosities, while the extinction-corrected ${...

Upon their formation, dynamically cool (collapsing) star clusters will, within only a few million years, achieve stellar mass segregation for stars down to a few solar masses, simply because of gravitational two-body encounters. Since binary systems are, on average, more massive than single stars, one would expect them to also rapidly mass segregate dynamically. Contrary to these expectations and based on high-resolution Hubble Space Telescope observations, we show that the compact, 15-30 Myr-old Large Magellanic Cloud cluster NGC 1818 exhibits tantalizing hints at the >= 2 sigma level of significance (> 3 sigma if we assume a power-law secondary-to-primary mass-ratio distribution) of an increasing fraction of F-star binary systems (with combined masses of 1.3-1.6 Msun) with increasing distance from the cluster center, specifically between the inner 10 to 20" (approximately equivalent to the cluster's core and half-mass radii) and the outer 60 to 80". If confirmed, this will offer support of the theoretically predicted but thus far unobserved dynamical disruption processes of the significant population of 'soft' binary systems—with relatively low binding energies compared to the kinetic energy of their stellar members—in star clusters, which we have access to here by virtue of the cluster's unique combination of youth and high stellar density.

We study the rest-frame 3.4 mu m band infrared luminosity as an indicator of the stellar masses of galaxies. We cross-match the Wide-field Infrared Survey Explorer All-Sky catalogue with the MPA-JHU Sloan Digital Sky Survey catalogue to produce a sample of 542 757 galaxies. We find that up to z similar to 0.35, the stellar mass (log(10)M(*)) is strongly correlated with the rest-frame 3.4 mu m luminosity [log(10)nu L-nu(3.4 mu m)]. We have derived the formulae for using the log(10)nu L-nu(3.4 mu m) to calculate the stellar mass of the total galaxy sample. We can improve the calculation of stellar mass by classifying the sample into H ii galaxies, composite galaxies, AGNs, absorption line galaxies and low-signal-to-noise (S/N) emission line galaxies, or by classifying the sample into early-type galaxies and late-type galaxies. The composite galaxies, AGNs, absorption galaxies and low-S/N emission line galaxies have similar peak values of log(10)M(*)/nu L-nu(3.4 mu m) as early-type galaxies have. H ii galaxies and late-type galaxies also have similar peak values. For the same luminosity, slightly higher stellar mass estimates will result for composite galaxies, AGNs, absorption line galaxies and low-S/N emission line galaxies than for H ii galaxies. Similarly, the mass estimates for early-type galaxies are higher than for late-type galaxies. The mass-to-luminosity ratio, log(10)M(*)/nu L-nu(3.4 mu m), correlates with [22]-[3.4] mu m colour, g - r and u - r colour in the rest frame. We give the quadratic regression fitting of these quantities, which can also be used to estimate the stellar mass. The ratio also has a relationship with EQW(H alpha) and weaker relationships with log(10)nu L-nu(22 mu m), oxygen abundances, the intrinsic extinction of galaxies and the strength of AGN features.

Stellar clusters are regularly used to study the evolution of their host galaxy. Except for a few nearby galaxies, these studies rely on the interpretation of integrated cluster properties, especially integrated photometry observed using multiple filters (i.e., the spectral energy distribution, SED). To allow interpretation of such observations, we present a large set of GALEV cluster models using the realistic approach of adopting stochastically sampled stellar initial mass functions. We provide models for a wide range of cluster masses (10(3)-2 x 10(5) M-circle dot), metallicities (-2.3 <= [Fe/H] <= + 0.18 dex), foreground extinction, and 184 regularly used filters. We analyze various sets of stochastic cluster SEDs by fitting them with non-stochastic models, which is the procedure commonly used in this field. We identify caveats and quantify the fitting uncertainties associated with this standard procedure. We show that this can yield highly unreliable fitting results, especially for low-mass clusters.

With the goal of investigating the degree at which the MIR luminosity in the Wide-field Infrared Survey Explorer (WISE) traces the SFR, we analyse 3.4, 4.6, 12 and 22 μ m data in a sample of ~140,000 star-forming galaxies or star-forming regions covering a wide range in metallicity 7.66 < 12 + log(O/H)<9.46, with redshift z < 0.4. These star-forming galaxies or star-forming regions are selected by matching the WISE Preliminary Release Catalog with the star-forming galaxy Catalog in SDSS DR8 provided by JHU/MPA 1 . We study the relationship between the luminosity at 3.4, 4.6, 12 and 22 μ m from WISE and H α luminosity in SDSS DR8. From these comparisons, we derive reference SFR indicators for use in our analysis. Linear correlations between SFR and the 3.4, 4.6, 12 and 22 μ m luminosity are found, and calibrations of SFRs based on L(3.4), L(4.6), L(12) and L(22) are proposed. The calibrations hold for galaxies with verified spectral observations. The dispersion in the relation between 3.4, 4.6, 12 and 22 μ m luminosity and SFR relates to the galaxy’s properties, such as 4000 Å break and galaxy color.

Our purpose is to find which is the most reliable one among various oxygen abundance determination methods. We will test the validity of several different oxygen abundance determination methods using methods of modern statistics. These methods include Bayesian analysis and information scoring. We will analyze a sample of ∼ 6000 Hii galaxies from the Sloan Digital Sky Survey (SDSS) spectroscopic observations data release four. All methods that we used drew the same conclusion that the T e method is a more reliable oxygen abundance determination method than the Bayesian metallicity method under the existing telescope ability. The ratios of the likelihoods between the different kinds of methods tell us that the T e , P, and O3N2 methods are consistent with each other because the P and O3N2 methods are calibrated by T e method. The Bayesian and R 23 methods are consistent with each other because both are calibrated by a galaxy model. In either case, the N2 method is an unreliable method.