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The properties of the young pulsars and their relations to the supernova remnants (SNRs) have been the interesting topics. At present, 383 SNRs in the Milky Way galaxy have been published, which are associated with 64 radio pulsars and 46 pulsars with high energy emissions. However, we noticed that 630 young radio pulsars with spin periods of less than half a second have been not yet observed the SNRs surrounding or nearby them, which arises a question of that could the two types of young radio pulsars with/without SNRs hold distinctive characteristics? Here, we employ the statistical tests on the two groups of young radio pulsars with (52) and without (630) SNRs to reveal if they share different origins. Kolmogorov-Smirnov (K-S) and Mann-Whitney-Wilcoxon (M-W-W) tests indicate that the two samples have the different distributions with parameters of spin period ($P$), derivative of spin period ($\dot P$), surface magnetic field strength ($B$), and energy loss rate ($\dot E$). Meanwhile, the cumulative number ratio between the pulsars with and without SNRs at the different spindown ages decreases significantly after $\rm10-20\,Kyr$. So we propose that the existence of the two types of supernovae (SNe), corresponding to their SNR lifetimes, which can be roughly ascribed to the low-energy and high-energy SNe. Furthermore, the low-energy SNe may be formed from the $\rm8-12\,M_{\odot}$ progenitor, e.g., possibly experiencing the electron capture, while the main sequence stars of $\rm12-25\,M_{\odot}$ may produce the high-energy SNe probably by the iron core collapse., Comment: 8 pages, 10 figures, 3 tables. Published in MNRAS

For the last two decades we have been observing a huge increase in discoveries of long-period comets (LPCs), especially those with large-perihelion distances. We collected data for a full sample of LPCs discovered over the 1801-2017 period including their osculating orbits, discovery moments (to study the discovery distances), and original semimajor axes (to study the number ratio of large-perihelion to small-perihelion LPCs in function of 1/a-original, and to construct the precise distribution of an 1/a-original). To minimize the influence of parabolic comets on these distributions we determined definitive orbits (which include eccentricities) for more than 20 LPCs previously classified as parabolic comets. We show that the percentage of large-perihelion comets is significantly higher within Oort spike comets than in a group of LPCs with a

Nearby star-forming galaxies offer a unique environment to study the populations of young (<100 Myr) accreting binaries. These systems are tracers of past populations of massive stars that heavily affect their immediate environment and parent galaxies. Using a Chandra X-ray Visionary program, we investigate the young neutron-star binary population in the low metallicity of the Small Magellanic Cloud (SMC) by reaching quiescent X-ray luminosity levels (~few times 1032 erg/s). We present the first measurement of the formation efficiency of high-mass X-ray binaries (HMXBs) as a function of the age of their parent stellar populations by using 3 indicators: the number ratio of HMXBs to OB stars, to the SFR, and to the stellar mass produced during the specific star-formation burst they are associated with. In all cases, we find that the HMXB formation efficiency increases as a function of time up to ~40–60 Myr, and then gradually decreases.

The goal of this paper is to characterise the light variation properties of Mira variables in the Small Magellanic Cloud. We have investigated a combined optical and near infrared multi-epoch dataset of Mira variables based on our monitoring data obtained over 15 years. Bolometric correction relations are formulated for various near-infrared colours. We find that the same bolometric correction equation holds for both the bolometricly brightest and faintest pulsation phases. Period-bolometric magnitude relations and period-colour relations were derived using time-averaged values. Phase lags between bolometric phase and optical and near-infrared phases were detected from the O-rich (the surface C/O number ratio is below unity) Mira variables, while no significant systematic lags were observed in most of the C-rich (the C/O ratio is over unity) ones. Some Miras show colour phase inversions, e.g., $H-K_{\rm s}$ at its bluest while $J-H$ and $J-K_{\rm s}$ are at their reddest values at about the bolometricly brightest phase. Their occurrence conditions were studied but no clear direct or indirect trigger was found. A large NIR colour change unassociated with stellar pulsation was observed in Miras with long secondary periods, and its possible explanation is described., Comment: 20 pages, 22 figures, accepted for publication in MNRAS

We construct a sample of 10,680 wall galaxies and 3,064 void galaxies with $M_R \lesssim -20$ by cross referencing a void catalog from literature with Baryon Oscillation Spectroscopic Survey (BOSS) CMASS and WiggleZ galaxies, where the CMASS survey targets redder galaxies and the WiggleZ survey targets bluer galaxies. Comparing the density profiles of the red and blue galaxies as a function of the void radius, we find that the number ratio of red-to-blue galaxies increases with distances from the void centers, suggesting a deficit of luminous and normal red galaxies in voids. We find a mean (g -- r) magnitude color of 1.298 and 1.210 for the wall and void galaxies, respectively, when considering the combined red and blue sample, which is found to be a significant difference. However, when considering the blue and red samples separately, we find no significant color difference. We conclude that the constituents galaxies of each population, rather than intrinsic color difference, is the main driver in the apparent average color difference of galaxies in voids and walls, indicating a deficit of luminous and normal red galaxies in voids. Our analysis suggests that the primary environmental-dependence effect on galaxy evolution for normal and luminous galaxies between void and wall regions is manifested in the number of red galaxies, which depends on the environmental-dependent merger history. Using a semi-analytic simulation model, we can successfully reproduce the apparent color difference between the void and wall galaxies., Comment: 11 pages, 10 figures, accepted to MNRAS

We have investigated the brown dwarf (BD) and stellar disc fractions in the Upper Scorpius OB Association (USco) and compared them with several other young regions. We have compiled the most complete sample of of all spectroscopically confirmed BDs in USco, and have made use of the WISE catalog to identify the disc candidates. We report on the discovery of 12 new BD discs in USco, with spectral type (SpT) between M6 and M8.5. The WISE colors for the new discs are similar to the primordial (transition) discs earlier detected in USco. Combining with previous surveys, we find the lowest inner disc fractions (~20-25%) for a wide range in stellar masses (~0.01-4.0 Msun) in the USco association. The low disc fractions for high-mass stars in USco (and the other clusters) are consistent with an evolutionary decline in inner disc frequency with age. However, BD disc fractions are higher than those for the stars in 1-3 Myr clusters, but very low in the ~5 Myr old USco. Also, primordial BD discs are still visible in the ~10 Myr TW Hydrae association, whereas the higher mass stars have all transitioned to the debris stage by this age. The disc frequencies for BDs do not show any dependence on the stellar density or the BD/star number ratio in a cluster. We suggest that the large differences in the observed BD disc fractions between regions may well be due to different BD formation mechanisms and therefore different initial disc fractions/properties. We also present a WISE SED classification scheme, based on the Ks and WISE bands of 3.4-12micron, to distinguish between the Class I/II and the Class III sequence. Our work includes a comparison of the sensitivities of WISE and Spitzer disc surveys. We estimate that WISE can be incomplete for discs at SpT later than M8 in distant clusters such as SOri. WISE should be able to recover the M8-M9 discs in the nearby young clusters.

SN 2002cx-like and SN Ia-CSM objects show similar early spectra and both belong to a young stellar population, suggesting that they could share the same progenitor origin. Adopting the framework of the common-envelope-wind (CEW) model developed in \citet{MENGXC17}, we here propose that both subclasses of SNe Ia are caused by the explosion of hybrid carbon-oxygen-neon white dwarfs (CONe WDs) in single-degenerate systems, where SNe Ia-CSM explode in systems with a massive common envelope (CE) of $\sim1~M_{\odot}$, while SN 2002cx-like events correspond to those events where most of the CE has been lost in a wind. Using binary-population-synthesis (BPS) calculations, we estimate a number ratio of SNe Ia-CSM to SN 2002cx-like objects between $\frac{1}{3}$ and $\frac{2}{3}$, consistent with observational constraints, and an overall contribution from hybrid CONe WDs to the total SN Ia population that also matches the observed number from these peculiar objects. Our model predicts a statistical sequence of CSM density from SN Ia-CSM to SN 2002cx-like events and normal SNe Ia, consistent with existing radio constraints. We also find a new subclass of hybrid SNe which share the properties of Type II and Type Ia SNe, consistent with some observed SNe, which do not have a surviving companion. In some cases these could even produce SNe Ia from apparently single WDs., 15 pages, 5 figures, accepted for publication in ApJ

We have analyzed ACS/WFC and WFPC2 images from HST, as well as ground-based data to study the radial distribution of the double sub-giant branch (SGB) recently discovered in the Galactic globular cluster NGC 1851. We found that the SGB split can be followed all the way from the cluster center out to at least 8\arcmin from the center. Beyond this distance out to the tidal radius at $\sim 11.7$ arcmin, there are simply too few SGB stars to dentify the sequences. The number ratio of the bright SGB to the faint SGB stars shows no significant radial trend. Furthermore, we have found that the ratio of blue horizontal-branch (HB) stars plus RR Lyrae to the red HB stars also remains constant from the cluster center to the outer envelope., Comment: 11 pages, 10 figures, accepted for pubblication in A&A

We have carried out a detailed study of Mira symbiotic stars by means of a population synthesis code. We estimate the number of Mira symbiotic stars in the Galaxy as 1700-3100 and the Galactic occurrence rate of Mira symbiotic novae as from similar to 0.9 to 6.0 yr(-1), depending on the model assumptions. The distributions of the orbital periods, the masses of the components, mass-loss rates of cool components, mass-accretion rates of hot components and Mira pulsation periods in Mira symbiotic stars are simulated. By a comparison of the number ratio of Mira symbiotic stars to all symbiotic stars, we find the model with the stellar wind model of Winters et al. to be reasonable.

We derive the luminosity functions in three bands (BVR) for the rich galaxy cluster ABCG 209 at z=0.21. The data cover an area of ~78 arcmin^2 in the B and R bands, while a mosaic of three pointings was obtained in the V band, covering an area of approximately 160 arcmin^2. The galaxy sample is complete to B = 22.8 (N_gal = 339), V = 22.5 (N_gal = 1078) and R = 22.0 (N_gal = 679). Although the fit of a single Schechter function cannot be rejected in any band, the luminosity functions are better described by a sum of two Schechter functions for bright and faint galaxies, respectively. There is an indication for a presence of a dip in the luminosity functions in the range V = 20.5--21.5 and R = 20.0--21.0. We find a marked luminosity segregation, in the sense that the number ratio of bright--to--faint galaxies decreases by a factor 4 from the center to outer regions. Our analysis supports the idea that ABCG 209 is an evolved cluster, resulting from the merger of two or more sub--clusters., 18 pages, 7 figures. A&A in press

We have carried out a large grid of N-body simulations in order to investigate if mass-loss as a result of primordial gas expulsion can be responsible for the large fraction of second generation stars in globular clusters (GCs) with multiple stellar populations (MSPs). Our clusters start with two stellar populations in which $10\%$ of all stars are second generation stars. We simulate clusters with different initial masses, different ratios of the half-mass radius of first to second generation stars, different primordial gas fractions and Galactic tidal fields with varying strength. We then let our clusters undergo primordial gas-loss and obtain their final properties such as mass, half-mass radius and the fraction of second generation stars. Using our N-body grid we then perform a Monte Carlo analysis to constrain the initial masses, radii and required gas expulsion time-scales of GCs with MSPs. Our results can explain the present-day properties of GCs only if (1) a substantial amount of gas was present in the clusters after the formation of second generation stars and (2) gas expulsion time-scales were extremely short ($\lesssim 10^5$ yr). Such short gas expulsion time-scales are in agreement with recent predictions that dark remnants have ejected the primordial gas from globular clusters, and pose a potential problem for the AGB scenario. In addition, our results predict a strong anti-correlation between the number ratio of second-generation stars in GCs and the present-day mass of GCs. So far, the observational data show only a significantly weaker anti-correlation, if any at all., Comment: 14 pages, 6 figures, 3 tables, typos corrected. Accepted for publication in MNRAS

In this paper, we calculate new line lists and opacities for the 12 bands of the A$^6\Sigma^{+}$ -- X$^6\Sigma^{+}$ transitions of the CrH molecule. Identified in objects of the new L dwarf spectroscopic class (many of which are brown dwarfs), as well as in sunspots, the CrH molecule plays an important role in the diagnosis of low-temperature atmospheres. As a tentative first application of these opacities, we employ our new theoretical CrH data in an atmospheres code to obtain a CrH/H$_2$ number ratio for the skin of the L5 dwarf 2MASSI J1507038-151648 of $\sim 2-4\times 10^{-9}$, in rough agreement with chemical equilibrium expectations. Since in previous compilations the oscillator strength was off by more than an order of magnitude, this agreement represents a modest advance. However, in order to determine the CrH abundance in an L dwarf atmosphere, silicate clouds need to be incorporated into the model, and cloud modeling is still in a primitive stage of development. Nevertheless, one important step in L dwarf modeling is a reliable CrH opacity and this is what we have here attempted to provide., Comment: Includes 3 color figures (in .gif format). Accepted to the Astrophysical Journal

We present subarcsecond resolution observations of the star-forming region W49N made with the Berkeley-Illinois-Maryland Association array at 1.4 mm wavelength in the continuum and CH3CN J = 12-11 lines. The continuum image, at a resolution of 018 (2000 AU), shows many of the previously identified ultracompact H II regions and at least one new source whose steep spectrum to short wavelengths indicates dust emission. This compact dust concentration also shows the strongest CH3CN emission in the region. Additional peaks of CH3CN emission likely mark hot cores produced by other deeply embedded young massive stars that may be precursors to O-type stars like those that power the ultracompact H II regions. The number ratio of hot cores to ultracompact H II regions found in W49N provides a measure of the relative timescales of these early evolutionary phases. Although the samples are small, the source counts suggest that the hot core lifetime is most likely shorter than, but comparable to, the ultracompact H II region lifetime.

Using integral field spectroscopy, we detected the broad features of massive Wolf-Rayet stars in the core of three Seyfert galaxies. The observed high value of the WR/O number ratio is a clear signature of a young and powerful starburst. The star-forming regions are distributed in an arc/ring-like structure around the AGN, at a distance of about 200 pc. These are the first spatially-resolved detections of massive starbursts so close of an AGN.

We report the discovery of a starburst-driven wind (superwind) from the starburst nucleus galaxy Mrk 1259. The estimated number ratio of Wolf-Rayet (WR) to O stars amounts to 0.09. While the nuclear emission-line region is due to the usual photoionization by massive stars, the circumnuclear emission-line regions show anomalous line ratios that can be due to cooling shocks. Since the host galaxy seems to be a face-on disk galaxy and the excitation conditions of the circumnuclear emission-line regions show spatial symmetry, we consider that we are seeing the superwind nearly from a pole-on view. Cooling shock models may explain the observed emission-line ratios of the circumnuclear regions, although a factor of 2 overabundance of nitrogen is necessary. All these suggest that the high-mass-enhanced starburst occurred ~5 × 106 yr ago in the nuclear region of Mrk 1259.

The first calibrated broadband UBVI time-series photometry is presented for the RR Lyrae variable stars in NGC6656 (M22), with observations spanning a range of twenty-two years. We have also redetermined the variability types and periods for the RR Lyrae stars identified previously by photographic observations, revising the number of fundamental-mode RR Lyrae variables (RR0) to 10 and the number of first-overtone variables (RR1) to 16. The mean periods of the RR0 and RR1 variables are _{RR0}=0.66 \pm 0.02 d and _{RR1}=0.33 \pm 0.01 d, respectively, supporting an Oosterhoff II classification for the cluster. The number ratio of RR1- to all RR-type variables is N_1/N_{RR}=0.61, also consistent with an Oosterhoff II designation. Both the RR Lyrae stars' minimum light colors and the blue edge of the RR Lyrae instability strip suggest E(B-V)=0.36 \pm 0.02 mag toward M22. Regarding the HB morphology of M22, we find (B-R)/(B+V+R)=+0.97 \pm 0.1 and at least one "gap" located in an unusual part of the blue HB, in the middle of the so-called hot HB stars., Comment: accepted to AJ

In this paper we study the long-term dynamical evolution of multiple-population clusters, focusing on the evolution of the spatial distributions of the first- (FG) and second-generation (SG) stars.In previous studies we have suggested that SG stars formed from the ejecta of FG AGB stars are expected initially to be concentrated in the cluster inner regions. Here, by means of N-body simulations, we explore the time scales and the dynamics of the spatial mixing of the FG and the SG populations and their dependence on the SG initial concentration.Our simulations show that, as the evolution proceeds, the radial profile of the SG/FG number ratio, NSG/NFG, is characterized by three regions: 1) a flat inner part; 2) a declining part in which FG stars are increasingly dominant; and 3) an outer region where the NSG/NFG profile flattens again (the NSG/NFG profile may rise slightly again in the outermost cluster regions). The radial variation of NSG/NFG implies that the fraction of SG stars determined by observations covering a limited range of radial distances is not, in general, equal to the SG global fraction, (NSG/NFG)glob. The distance at which NSG/NFG equals (NSG/NFG)glob is approximately between 1 and 2 cluster half-mass radii. The results of our simulations suggest that in many Galactic globular clusters the SG should still be more spatially concentrated than the FG.[abridged], 10 pages 9 figures. Accepted for publication in MNRAS

We present a photometric study of the globular clusters (GCs) in the Virgo giant elliptical galaxy M86 based on Washington CT1 images. The colors of the GCs in M86 show a bimodal distribution with a blue peak at (C -T1) = 1.30 and a red peak at (C -T1) = 1.72. The spatial distribution of the red GCs is elongated similarly to that of the stellar halo, while that of the blue GCs is roughly circular. The radial number density profile of the blue GCs is more extended than that of the red GCs. The radial number density profile of the red GCs is consistent with the surface brightness profile of the M86 stellar halo. The GC system has a negative radial color gradient, which is mainly due to the number ratio of the blue GCs to the red GCs increasing as galactocentric radius increase. The bright blue GCs in the outer region of M86 show a blue tilt: the brighter they are, the redder their mean colors get. These results are discussed in comparison with other Virgo giant elliptical galaxies., Comment: 15 pages, 13 figures, Accepted by Journal of the Korean Astronomical Society

We studied the temperature and abundance distributions of intra-cluster medium (ICM) in the Abell 262 cluster of galaxies observed with Suzaku. Abell 262 is a bright, nearby poor cluster with ICM temperature of ~2 keV, thus providing useful information about the connection of ICM properties between groups and clusters of galaxies. The observed spectrum of the central region was well-represented by two temperature models, and the spectra for the outer regions were described by single temperature model. With the XIS instrument, we directly measured not only Si, S, and Fe lines but also O and Mg lines and obtained those abundances to an outer region of ~0.43 r_180 for the first time. We found steep gradients for Mg, Si, S, and Fe abundances, while O showed almost flat abundance distribution. Abundance ratios of alpha-elements to Fe were found to be similar to those of the other clusters and groups. We calculated the number ratio of type II to type Ia supernovae for the ICM enrichment to be 3.0 +- 0.6 within 0.1 r_180, and the value was consistent with those for other clusters and groups. We also calculated metal mass-to-light ratios (MLRs) for Fe, O and Mg (IMLR, OMLR, MMLR) with B-band and K-band luminosities of the member galaxies of Abell 262. The derived MLRs were comparable to those for other clusters with kT = 3-4 keV., 12 pages, 8 figures, accepted for publication in PASJ

The search-volume corrected period distribution of contact binaries of the W UMa type appears to reflect primarily the constant number ratio of ~1/500 to the number of stars along the Main Sequence; there exist no evidence for angular momentum evolution. The maximum in contact binary numbers is located at shorter periods than estimated before, P ~ 0.27 d. The drop in numbers towards the cut-off at P ~ 0.215 - 0.22 d still suffers from the small number statistics while the cut-off itself remains unexplained. Only one out of seven short-period ASAS variables with P, accepted by MNRAS

Aims: Ices in dense star-forming cores contain the bulk of volatile molecules apart from H2 and thus represent a large fraction of dark cloud chemistry budget.To directly constrain the freeze-out profile of CO, the formation route of CO2 and the carrier of the 6.8 micron band, the spatial distribution of the CO/CO2 ice system and the 6.8 micron band carrier are measured in a nearby dense core. Methods: VLT-ISAAC, ISOCAM-CVF and Spitzer-IRS archival mid-infrared (3-20 micron) spectroscopy of young stellar objects is used to construct a map of the abundances of CO and CO2 ices in the Oph-F star-forming core, probing core radii from 2 10^3 to 14 10^3 AU or densities from 5 10^4 to 5 10^5 cm^-3 with a resolution of ~ 3000 AU. Results: The line-of-sight averaged abundances relative to water ice of both CO and CO2 ices increase monotonously with decreasing distance to the core center. The map traces the shape of the CO abundance profile between freeze-out ratios of 5-60% and shows that the CO2 ice abundance increases by a factor of 2 as the CO freezes out. It is suggested that this indicates a formation route of CO2 on a CO ice surface to produce a CO2 component dilute in CO ice, in addition to a fraction of the CO2 formed at lower densities along with the water ice mantle. It is predicted that the CO2 bending mode band profile should reflect a high CO:CO2 number ratio in the densest parts of dark clouds. In contrast to CO and CO2, the abundance of the carrier of the 6.8 micron band remains relatively constant throughout the core. A simple freeze-out model of the CO abundance profile is used to estimate the binding energy of CO on a CO ice surface to 814+/-30 K., Comment: 5 pages, accepted for publication in A&A letters

The recent VIIth Catalogue of Galactic Wolf-Rayet Stars lists 227 Population I WR stars, comprising 127 WN, 87 WC, 10 WN/WC and 3 WO stars. Additional discoveries bring the census to 234 WR stars. A re-determination of the optical photometric distances and the galactic distribution of WR stars shows in the solar neighbourhood a projected surface density of 2.7 WR stars per kpc2, a N WC/N WN number ratio of 1.3, and a WR binary frequency of 40%. The galactocentric distance (R WR) distribution per subtype shows R WN and R WC decreasing with WN and WC subtypes.

It has been recognized that the arc statistics of gravitational lensing is a useful probe of the density profile of clusters of galaxies. We examine several systematic effects which are important in predicting the number of arcs, with particular attention to the difference between tangential and radial arcs. First we derive an analytic expression of the cross section for radial arcs taking account of the source size and find that the moderate source size enhances the cross section for radial arcs while larger source size (\gtrsim 1'' in our example) suppresses the number of radial arcs. On the other hand, tangential arcs are much less sensitive to the source size. Next we numerically calculate the cross section for arcs considering the lens and source ellipticities. We find that the numbers of both tangential and radial arcs are highly enhanced by both ellipticities, by one or two orders of magnitude. The number ratio of radial to tangential arcs is, however, not so affected if the threshold axis ratio of arcs is large (\gtrsim 7). The number ratio therefore still remains good statistics which probe the density profile of the lens objects, if the source size effect is correctly taken into account., Comment: 8 pages, 9 figures, emulateapj5, accepted for publication in ApJ; minor typos corrected

The statistics of gravitationally lensed arcs, which can be used for a variety of cosmological tests, are sensitive to the intrinsic shapes of the source galaxies. I present an analytic formalism that makes it simple to include elliptical sources in analytic calculations of lens statistics. For cuspy lens models, sources with an axis ratio of 2:1 enhance the total number of arcs longer than 10:1 by a factor of order two, while modestly decreasing the number ratio of radial arcs to tangential arcs. Source ellipticity is therefore an important systematic effect in detailed quantitative studies, but it should not hinder cosmological applications such as attempts to constrain cluster dark matter profiles with arc statistics., Comment: 4 pages, emulateapj5; accepted in ApJ

Stellar evolution sequences of models of spherical stars were very successful in the late 1950’s and early 1960’s in outlining the major stages and even many of the details of the stellar life cycle. Since then, we have continued to modify the physics and model properties to explain discrepancies as new observations became available. For the most part this has been successful, but there remain some pieces of the puzzle which either do not fit or must be tortured into place. One might divide these into three particular classes - surface abundances of elements show peculiarities for which traditional stellar evolution does not easily account, observed global properties such as the masses of massive main sequence stars do not agree with stellar evolution calculations, and regions of the H-R diagram are not populated either at all or to the extent that observations indicate (such as the number ratio of blue to red supergiants, the region between the end of core hydrogen burning and the beginning of core helium burning in massive stars, and the location of blue loops for some intermediate mass stars).

We have applied our empirical-PSF-based photometric techniques on a large number of calibration-related WFC3/UVIS UV-B exposures of the core of {\omega} Cen, and found a well-defined split in the right part of the white-dwarf cooling sequence (WDCS). The redder sequence is more populated by a factor of ~2. We can explain the separation of the two sequences and their number ratio in terms of the He-normal and He-rich subpopulations that had been previously identified along the cluster main sequence. The blue WDCS is populated by the evolved stars of the He-normal component (~0.55 Msun CO-core DA objects) while the red WDCS hosts the end-products of the He-rich population (~0.46 Msun objects, ~10% CO-core and ~90% He-core WDs). The He-core WDs correspond to He-rich stars that missed the central He-ignition, and we estimate their fraction by analyzing the population ratios along the cluster horizontal branch., Comment: 6 pages, 4 figures, accepted for publication in ApJ Letters. Fixed a typo in the metadata

The durations (T90) of 315 GRBs detected with Fermi/GBM (8-1000 keV) by 2011 September are calculated using the Bayesian Block method. We compare the T90 distributions between this sample and those derived from previous/current GRB missions. We show that the T90 distribution of this GRB sample is bimodal, with a statistical significance level being comparable to those derived from the BeppoSAX/GRBM sample and the Swift/BAT sample, but lower than that derived from the CGRO/BATSE sample. The short-to-long GRB number ratio is also much lower than that derived from the BATSE sample, i.e., 1:6.5 vs 1:3. We measure T90 in several bands, i.e., 8-15, 15-25, 25-50, 50-100, 100-350, and 350-1000 keV, to investigate the energy-dependence effect of the bimodal T90 distribution. It is found that the bimodal feature is well observed in the 50-100 and 100-350 keV bands, but is only marginally acceptable in the 25-50 keV and 350-1000 keV bands. The hypothesis of the bimodality is confidently rejected in the 8-15 and 15-25 keV bands. The T90 distributions in these bands are roughly consistent with those observed by missions with similar energy bands. The parameter T90 as a function of energy follows \bar T90 \propto E^{-0.20\pm 0.02} for long GRBs. Considering the erratic X-ray and optical flares, the duration of a burst would be even much longer for most GRBs. Our results, together with the observed extended emission of some short GRBs, indicate that the central engine activity time scale would be much longer than T90} for both long and short GRBs and the observed bimodal T90 distribution may be due to an instrumental selection effect., Comment: 29 pages, 2 tables, 9 figures, accepted for publication in ApJ

We study the color-magnitude red sequence and blue fraction of 72 X-ray selected galaxy clusters at z=0.04-0.07 from the WINGS survey, searching for correlations between the characteristics of the red sequence and the environment. We consider the slope and scatter of the red sequence, the number ratio of red luminous-to-faint galaxies, the blue fraction and the fractions of ellipticals, S0s and spirals that compose the red sequence. None of these quantities correlate with the cluster velocity dispersion, X-ray luminosity, number of cluster substructures, BCG prevalence over next brightest galaxies and spatial concentration of ellipticals. Instead, the properties of the red sequence depend strongly on local galaxy density. Higher density regions have a lower RS scatter, a higher luminous-to-faint ratio, a lower blue fraction, and a lower spiral fraction on the RS. Our results highlight the prominent effect of the local density in setting the epoch when galaxies become passive and join the red sequence, as opposed to the mass of the galaxy host structure., Accepted for publication in A&A

Intermediate helium stars are defined bynHe/nHbeing the number ratio of He over H. The upper bound which separates the intermediates from the extremes is well-defined (see Sect. 7), whereas the lower bound is rather soft.The first intermediate helium star discovered was Sigma Ori E (Greenstein and Wallerstein, 1956). Since then, 23 intermediates with V ≤ 1lmhave been found (see the list of Walborn, 1983 and also the Annex), mostly through surveys such as that by McConnell et al. (1970) and McConnell (1972). (To this list, the newly discovered object SB 939, Langhans and Heber, 1985, should be added.) It is anticipated that a substantial fraction has as yet escaped detection. The spectral type centres around B2V while nHe/nHis typically of the order of unity.

We discuss optical and infrared photometric properties of stars matched in the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) commissioning data for similar to 50 deg(2) of sky along the celestial equator centered at l = 150 degrees, b = -60 degrees. About 98% (similar to 63,000) of objects listed in the 2MASS Point Source Catalog in the analyzed area are matched within 2 " to an SDSS source. The matched sources represent 8% of the similar to 800,000 SDSS sources in this area. They are predominantly red sources, as expected, and 15% of them are resolved in SDSS imaging data although they are detected as point sources in 2MASS data. The distribution of positional discrepancies for the matched sources and the astrometric statistics for the multiply observed SDSS sources imply that the astrometric accuracy of both surveys is about 0."1 per coordinate (rms). For about 14,000 stars with the smallest photometric errors (less than or similar to 10%) in both surveys, we present optical and infrared color-magnitude and color-color diagrams. We use optical (SDSS) colors to identify the stellar spectral sequence and show that stars of different spectral types can have similar infrared colors, thus making the classification of stars based on only 2MASS data very difficult. However, a broad separation into "early" and "late" spectral types (relative to type KO) is possible with a reliability of similar to 95% even with 2MASS colors alone. The distributions of matched sources in color-magnitude and color-color diagrams are compared with the predictions of a stellar population synthesis code. We find that the models are in fair overall agreement with the data. In particular, the total number counts agree to better than 10%, and the morphologies of the color-magnitude and color-color diagrams appear similar. The most significant discrepancies are found for the number ratio of "early" to "late" type stars (by about a factor of 2) and in the colors of M stars (up to 0.2 mag). The first disagreement indicates that some parameters of the standard Galactic structure model and/or initial mass function can be improved, and the second disagreement emphasizes known difficulties with the modeling of stellar atmospheres for cool stars.

Using the Owens Valley and Nobeyama Radio Observatory interferometers, we carried out an unbiased search for hot molecular cores and ultracompact UC HII regions toward the high-mass star forming region G19.61--0.23. In addition, we performed 1.2 mm imaging with SIMBA, and retrieved 3.5 and 2 cm images from the VLA archive data base. The newly obtained 3 mm image brings information on a cluster of high-mass (proto)stars located in the innermost and densest part of the parsec scale clump detected in the 1.2 mm continuum. We identify a total of 10 high-mass young stellar objects: one hot core (HC) and 9 UC HII regions, whose physical parameters are obtained from model fits to their continuum spectra. The ratio between the current and expected final radii of the UC \HII regions ranges from 0.3 to 0.9, which leaves the possibility that all O-B stars formed simultaneously. Under the opposite assumption -- namely that star formation occurred randomly -- we estimate that HC lifetime is less than $\sim$1/3 of that of UCHII regions on the basis of the source number ratio between them., Comment: 13 pages, 2 figs, including a color fig