The spin rates and spin evolution of the O components in WR+O binaries

Despite 50 years of extensive binary research we have to conclude that the Roche lobe overflow/mass transfer process that governs close binary evolution is still poorly understood. It is the scope of the present paper to lift a tip of the veil by studying the spin-up and spin-down processes of the O-type components of WR+O binaries. We critically analyze the available observational data of rotation speeds of the O-type components in WR+O binaries. By combining a binary evolutionary code and a formalism that describes the effects of tides in massive stars with an envelope in radiative equilibrium, we compute the corresponding rotational velocities during the Roche lobe overflow of the progenitor binaries. In all the studied WR+O binaries, we find that the O-type stars were affected by accretion of matter during the RLOF of the progenitor. This means that common envelope evolution which excludes any accretion onto the secondary O-star, has not played an important role to explain the WR+O binaries. Moreover, although it is very likely that the O-type star progenitors were spun-up by the mass transfer, many ended the RLOF/mass transfer phase with a rotational velocity that is significantly smaller than the critical rotation speed. This may indicate that during the mass transfer phase there is a spin-down process which is of the same order as, although significantly less than that of the spin-up process. We propose a Spruit-Tayler type dynamo spin-down suggested in the past to explain the rotation speeds of the mass gainers in long-period Algols.Comment: 6 pages, accepted for publication in A&A; accepted versio

Symbiotic stars in the Local Group of Galaxies

Preliminary results of the ongoing search for symbiotic binary stars in the Local Group of Galaxies are presented and discussed.Comment: Proceedings of Physics of Evolved Stars 2015: A Conference Dedicated to the Memory of Olivier Chesneau, Nice, 8-12 June 201

Stellar Populations and Variable Stars in the Core of the Globular Cluster M5

We report the discovery of a variable blue straggler in the core of the globular cluster M5, based on a 12-hour long series of images obtained with the Planetary Camera aboard the Hubble Space Telescope. In addition, we present the light curves of 28 previously unknown or poorly studied large-amplitude variable stars (all but one are RR Lyrae) in the cluster core. A (V, U-I) color-magnitude diagram shows 24 blue stragglers within 2 core radii of the cluster center. The blue straggler population is significantly more centrally concentrated than the horizontal branch and red giant stars.Comment: 22 pages, 18 postscript figures, 1 postscript table, AJ, in press (Feb 1998

The diffusion-induced nova scenario. CK Vul and PB 8 as possible observational counterparts

We propose a scenario for the formation of DA white dwarfs with very thin helium buffers. For these stars we explore the possible occurrence of diffusion-induced CNO- flashes, during their early cooling stage. In order to obtain very thin helium buffers, we simulate the formation of low mass remnants through an AGB final/late thermal pulse (AFTP/LTP scenario). Then we calculate the consequent white dwarf cooling evolution by means of a consistent treatment of element diffusion and nuclear burning. Based on physically sounding white dwarf models, we find that the range of helium buffer masses for these diffusion-induced novas to occur is significantly smaller than that predicted by the only previous study of this scenario. As a matter of fact, we find that these flashes do occur only in some low-mass (M < 0.6M) and low metallicity (Z_ZAMS <0.001) remnants about 10^6 - 10^7 yr after departing from the AGB. For these objects, we expect the luminosity to increase by about 4 orders of magnitude in less than a decade. We also show that diffusion-induced novas should display a very typical eruption lightcurve, with an increase of about a few magnitudes per year before reaching a maximum of M_V ~ -5 to -6. Our simulations show that surface abundances after the outburst are characterized by logNH/NHe ~ -0.15...0.6 and N>C>O by mass fractions. Contrary to previous speculations we show that these events are not recurrent and do not change substantially the final H-content of the cool (DA) white dwarf. (Abridged)Comment: 16 pages, 8 figures, 3 tables. Replaced to match the final version published by MNRAS. The definitive version is available at http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291365-296

The Early Palomar Program (1950-1955) for the Discovery of Classical Novae in M81: Analysis of the Spatial Distribution, Magnitude Distribution, and Distance Suggestion

Data obtained in the 1950-1955 Palomar campaign for the discovery of classical novae in M81 are set out in detail. Positions and apparent B magnitudes are listed for the 23 novae that were found. There is modest evidence that the spatial distribution of the novae does not track the B brightness distribution of either the total light or the light beyond an isophotal radius that is 70\arcsec from the center of M81. The nova distribution is more extended than the aforementioned light, with a significant fraction of the sample appearing in the outer disk/spiral arm region. We suggest that many (perhaps a majority) of the M81 novae that are observed at any given epoch (compared with say $10^{10}$ years ago) are daughters of Population I interacting binaries. The conclusion that the present day novae are drawn from two population groups, one from low mass white dwarf secondaries of close binaries identified with the bulge/thick disk population, and the other from massive white dwarf secondaries identified with the outer thin disk/spiral arm population, is discussed. We conclude that the M81 data are consistent with the two population division as argued previously from (1) the observational studies on other grounds by Della Valle et al. (1992, 1994), Della Valle & Livio (1998), and Shafter et al. (1996) of nearby galaxies, (2) the Hatano et al. (1997a,b) Monte Carlo simulations of novae in M31 and in the Galaxy, and (3) the Yungelson et al. (1997) population synthesis modeling of nova binaries. Two different methods of using M81 novae as distance indicators give a nova distance modulus for M81 as $(m-M)_0 = 27.75$, consistent with the Cepheid modulus that is the same value.Comment: 24 pages, 7 figures, accepted to PAS

A Far-Ultraviolet Survey of 47 Tucanae.II The Long-Period Cataclysmic Variable AKO 9

We present time-resolved, far-ultraviolet (FUV) spectroscopy and photometry of the 1.1 day eclipsing binary system AKO 9 in the globular cluster 47 Tucanae. The FUV spectrum of AKO 9 is blue and exhibits prominent C IV and He II emission lines. The spectrum broadly resembles that of long-period, cataclysmic variables in the galactic field. Combining our time-resolved FUV data with archival optical photometry of 47 Tuc, we refine the orbital period of AKO 9 and define an accurate ephemeris for the system. We also place constraints on several other system parameters, using a variety of observational constraints. We find that all of the empirical evidence is consistent with AKO 9 being a long-period dwarf nova in which mass transfer is driven by the nuclear expansion of a sub-giant donor star. We therefore conclude that AKO 9 is the first spectroscopically confirmed cataclysmic variable in 47 Tuc. We also briefly consider AKO 9's likely formation and ultimate evolution. Regarding the former, we find that the system was almost certainly formed dynamically, either via tidal capture or in a 3-body encounter. Regarding the latter, we show that AKO 9 will probably end its CV phase by becoming a detached, double WD system or by exploding in a Type Ia supernova.Comment: 40 pages, 11 figures, to appear in the Dec 20 issue of ApJ; minor changes to match final published versio

A dwarf nova in the globular cluster M13

Dwarf novae in globular clusters seem to be rare with only 13 detections in the 157 known Galactic globular clusters. We report the identification of a new dwarf nova in M13, the 14th dwarf nova identified in a globular cluster to date. Using the 2m Faulkes Telescope North, we conducted a search for stars in M13 that show variability over a year (2005-2006) on timescales of days and months. This led to the detection of one dwarf nova showing several outbursts. A Chandra X-ray source is coincident with this dwarf nova and shows both a spectrum and variability consistent with that expected from a dwarf nova, thus supporting the identification. We searched for a counterpart in Hubble Space Telescope ACS/WFC archived images and found at least 11 candidates, of which we could characterize only the 7 brightest, including one with a 3 sigma H-alpha excess and a faint blue star. The detection of one dwarf nova when more could have been expected likely indicates that our knowledge of the global Galactic population of cataclysmic variables is too limited. The proportion of dwarf novae may be lower than found in catalogs, or they may have a much smaller duty cycle in general as proposed by some population synthesis models and recent observations in the field.Comment: Accepted for publication in ApJ, 12 pages, 12 figures, 5 tables (v2 contains corrections of the proofs

The origin of intergalactic thermonuclear supernovae

The population synthesis method is used to study the possibility of explaining the appreciable fraction (20^+12_15%) of the intergalactic (no-host) type Ia supernovae observed in galaxy clusters (Gal-Yam ete al. 2003) by binary whote dwarf merginngs in the cores of globular clusters. In a typical globular cluster, the number of merging double white dwarfs is fount to be smaller than 10^{-13} per year per average cluster star during the entire evolution of the cluster, which is a factor of 3 higher than in a Milky-Way-type galaxy. From 5 to 30% of the merging white dwarfs are dynamically expelled from the cluster with barycenter velocities up to 150 km/s. SN Ia explosions during the mergers of binary white dwarfs in dense star clusters may account for \sim 1% of the total rate of SN Ia in the central parts of galaxy clusters if the baryon mass fraction in such star clusters is \sim 0.3%.Comment: 8 pages, 3 figs. Astronomy Letters (in press

RetroSpective cohort stUdy of PD-L1 expression in REcurrent and/or MEtastatic squamous cell carcinoma of the head and neck (SUPREME-HN)

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