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One of the mysteries of nebulae in the vicinity of bright stars is theappearance of bright emission spectral lines of ions, which imply fairlyhigh excitation temperatures. We suggest that an ion formationmechanism, based on resonance-enhanced two-photon ionization (RETPI) byintense H Lyman alpha radiation (wavelength of 1215 angstroms) trappedinside optically thick nebulae, can produce these spect
Based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan telescopes we present detailed elemental abundances for 64 red giant stars in the inner and outer Galactic disk. For the inner disk sample (4-7 kpc from the Galactic centre) we find that stars with both thin and thick disk abundance patterns are present while for Galactocentric distances beyond 10 kpc, we only fin
Book abstract: The book reviews recent observations of non-evolved and evolved binary populations in clusters and the field with special emphasis on statistical biases, incompleteness and distribution functions. Different binary types are considered: cataclysmic variables, super-soft X-ray sources, double degenerate binaries, Algol-type binaries, Be binaries, X-ray binaries, and Wolf-Rayet binarie
We consider the implications of a model for long-duration gamma-ray bursts in which the progenitor is spun up in a close binary by tidal interactions with a massive black-hole companion. We investigate a sample of such binaries produced by a binary population synthesis, and show that the model predicts several common features in the accretion on to the newly formed black hole. In all cases, the ac
Aims. This paper presents a new homogeneous catalogue of blue straggler stars ( BSS) in Galactic open clusters. Methods. Photometric data for 216 clusters were collected from the literature and 2782 BSS candidates were extracted from 76 of them. Results. We found that the anticorrelation of BSS frequency vs. total magnitude identified in similar studies conducted on Galactic globular clusters exte
The formation of beryllium in the early Galaxy is discussed. It is shown that if spallation occurs predominantly in regions rich in heavy elements, i.e., close to supernovae, the linear relation recently obtained by Gilmore et al. (1992) between beryllium and oxygen abundances for Population II stars may be reproduced. Estimates of relevant timescales for mixing show that the decisive factor, the
A method is presented for estimating the long exposure point spreadfunction (PSF) degradation due to tilt anisoplanatism in alaser-guide-star-based multiconjugate adaptive optics systems fromcontrol loop data. The algorithm is tested in numerical Monte Carlosimulations of the separately driven low-order null-mode system, and isshown to be robust and accurate with less than 10 relative error inboth
We have discovered four extremely surprising emission lines of strontiumin ejecta near eta Carinae. Hubble Space Telescope (HST) SpaceTelescope Imaging Spectrograph (STIS) observations made in 1999 show twonarrow features whose wavelengths correspond to the forbiddentransitions of Sr II, and we have found no other plausibleidentification for these lines. The identifications are confirmed by newHST
Dissipation of acoustic waves may be an efficient heating mechanism forthe lower and middle chromosphere of the quiet Sun. The basic idea isthat turbulent motions at the top of the solar convection zone generateacoustic waves which propagate upwards and dissipate in the lower andmiddle chromosphere, transporting energy into the higher layers. Butstill the question remains if this amount of energy
We report a search for gravitational waves from the inspiral, merger and ringdown of binary black holes (BBH) with total mass between 25 and 100 solar masses, in data taken at the LIGO and Virgo observatories between July 7, 2009 and October 20, 2010. The maximum sensitive distance of the detectors over this period for a (20, 20)M-circle dot coalescence was 300 Mpc. No gravitational wave signals w
The space mission PLATO will usher in a new era of exoplanetary science by expanding our current inventory of transiting systems and constraining host star ages, which are currently highly uncertain. This capability might allow PLATO to detect changes in planetary system architecture with time, particularly because planetary scattering due to Lagrange instability may be triggered long after the sy
We present the first results of the EMBLA survey (Extremely Metal-poor BuLge stars with AAOmega), aimed at finding metal-poor stars in the Milky Way bulge, where the oldest stars should now preferentially reside. EMBLA utilizes SkyMapper photometry to pre-select metal-poor candidates, which are subsequently confirmed using AAOmega spectroscopy. We describe the discovery and analysis of four bulge
We consider the origin of the anomalously high intensity of theultraviolet Fe II lambda 2507/2509 A lines observed with high spatialand spectral resolutions from gas blobs (GBs) near Carinae. This rareeffect in stellar spectra is attributable to a combination of severalfactors: (1) the high hydrogen density (>10^{8} cm^{-3}) that ensuresthe blocking of the Lyman continuum by GBs and, accordingly,
The hyperfine structure of a large number of transitions in Al II cannot be described using A and B hyperfine constants and the hyperfine structure is therefore said to be anomalous. In this paper, we have studied the hyperfine structure of a few transitions in Al II, 3s5s(3)S-3s5p(3)P, 3s4d(3)D-3s5p(3)P and 3s5p(3)P-3s5d(3)D, by combining theory and experiment. It is shown that the anomalous hype
Spectroscopy with the high spatial resolution of the Hubble Space Telescope (HST) reveals narrow absorption in the hydrogen Balmer lines in spectra of Eta Carinae and the nearby nebular-scattered starlight. While hydrogen Balmer absorption lines are seen in stellar photospheres and winds, we are not aware of such being seen in galactic nebulae. This exceptional case is caused by intense stellar UV
A set of equations are put into a code forming a procedure to derive intensities of fluorescence lilies based on both physical properties of the fluorescent plasma and its location relative to the origin of the pumping emission. In a first test, the code is applied to symbiotic stars, and effort is made to explain the circumstances under which the two known Fell channels pumped by C IV are activat
Investigating the Galactic center offers unique insights into the buildup and history of our Galaxy and is a stepping stone to understand galaxies in a larger context. It is reasonable to expect that the stars found in the Galactic center might have a different composition compared to stars found in the local neighborhood around the Sun. It is therefore quite exciting when recently there were repo
Observed FeO/MgO ratios in the Moon and Earth are inconsistent with simulations done with a single homogeneous silicate layer. In this paper we use a newly developed equation of state to perform smoothed particle hydrodynamics simulations on the lunar-forming impact, testing the effect of a primordial magma ocean on Earth. This is investigated using the impact parameters of both the canonical case
Sizeable number of stellar-mass black holes (BHs) in globular clusters (GCs) can strongly influence the dynamical evolution and observational properties of their host cluster. Using results from a large set of numerical simulations, we identify the key ingredients needed to sustain a sizeable population of BHs in GCs up to a Hubble time. We find that while BH natal kick prescriptions are essential
