Search Publications
The low-mass initial mass function in the young cluster NGC6611
van Loon, J. Th.; Jeffries, R. D.; Oliveira, J. M.
NGC6611 is the massive young cluster (2-3Myr) that ionizes the Eagle Nebula. We present very deep photometric observations of the central region of NGC6611 obtained with the Hubble Space Telescope and the following filters: ACS/WFC F775W and F850LP and NIC2 F110W and F160W, loosely equivalent to ground-based IZJH filters. This survey reaches down …
Spectroscopic orbits for K giants β Reticuli and ν Octantis: what is causing a low-amplitude radial velocity resonant perturbation in ν Oct?
Pourbaix, D.; Ramm, D. J.; Hearnshaw, J. B. +1 more
New astrometric-spectroscopic orbital solutions for the single-line K-giant binaries β Reticuli (P ~ 5.2yr, e = 0.3346 +/- 0.0004) and ν Octantis (P ~ 2.9yr, e = 0.2358 +/- 0.0003) have been derived based on high-precision spectroscopic radial velocities (RVs) and the Hipparcos astrometry. For the case of ν Oct, the simultaneous solution is partic…
VLT/SINFONI time-resolved spectroscopy of the central, luminous, H-rich WN stars of R136
Chené, A. -N.; Moffat, A. F. J.; Schnurr, O. +2 more
Using the Very Large Telescope's Spectrograph for INtegral Field Observation in the Near-Infrared, we have obtained repeated adaptive-optics-assisted, near-infrared spectroscopy of the six central luminous, Wolf-Rayet (WR) stars in the core of the very young (~1 Myr), massive and dense cluster R136, in the Large Magellanic Cloud (LMC). We also de-…
Long-term photometry and periods for 261 nearby pulsating M giants
Kjeldsen, H.; Kiss, L. L.; Bedding, T. R. +3 more
We present the results of a 5.5-yr CCD photometric campaign that monitored 261 bright, southern, semiregular variables (SRVs) with relatively precise Hipparcos parallaxes. The data are supplemented with independent photoelectric observations of 34 of the brightest stars, including 11 that were not part of the CCD survey, and a previously unpublish…
A model of the TeV flare of Cygnus X-1: electron acceleration and extended pair cascades
Bednarek, W.; Zdziarski, Andrzej A.; Malzac, Julien
We consider theoretical models of emission of TeV photons by Cyg X-1 during a flare discovered by the Major Atmospheric Gamma Imaging Cherenkov Telescope (MAGIC) detector. We study acceleration of electrons to energies sufficient for TeV emission, and find the emission site is allowed to be close to the black hole. We then consider pair absorption…
Discovery of a broad iron line in the black hole candidate Swift J1753.5-0127, and the disc emission in the low/hard state revisited
Mostafa, Reham; Hiemstra, Beike; Soleri, Paolo +3 more
We analysed simultaneous archival XMM-Newton and Rossi X-ray Timing Explorer observations of the X-ray binary and black hole candidate Swift J1753.5-0127. In a previous analysis of the same data, a soft thermal component was found in the X-ray spectrum, and the presence of an accretion disc extending close to the innermost stable circular orbit wa…
PHL 1092 as a transient extreme X-ray weak quasar
Brandt, W. N.; Fabian, A. C.; Boller, Th. +2 more
We report a dramatic variability event in the X-ray history of the narrow-line quasar PHL 1092 (z = 0.396). Our latest 2008 XMM-Newton observation reveals a flux drop of ~200 with respect to the previous observation performed about 4.5 yr earlier, and a drop of ~135 with respect to its historical flux. Despite the huge X-ray variation, the UV flux…
Optical spectroscopy of X-Mega targets in the Carina nebula - VII. On the multiplicity of Tr16-112, HD93343 and HD93250
Gosset, E.; Nazé, Y.; Rauw, G. +4 more
We present the results of a spectroscopic monitoring campaign devoted to three O-type stars in the Carina nebula. We derive the full SB2 orbital solution of the binary system Tr16-112, an exceptional dissymmetrical system consisting of an O5.5-6V((f+?p)) primary and a B2V-III secondary. We also report on low-amplitude brightness variati…
A new determination of the orbit and masses of the Be binary system δ Scorpii
Tuthill, P. G.; Davis, J.; Tango, W. J. +5 more
The binary star δ Sco (HD143275) underwent remarkable brightening in the visible in 2000, and continues to be irregularly variable. The system was observed with the Sydney University Stellar Interferometer (SUSI) in 1999, 2000, 2001, 2006 and 2007. The 1999 observations were consistent with predictions based on the previously published orbital ele…
Quiet but still bright: XMM-Newton observations of the soft gamma-ray repeater SGR0526-66
Tiengo, A.; Götz, D.; Mereghetti, S. +7 more
SGR0526-66 was the first soft gamma-ray repeater from which a giant flare was detected in 1979 March, suggesting the existence of magnetars, i.e. neutron stars powered by the decay of their extremely strong magnetic field. Since then, very little information has been obtained on this object, mainly because it has been burst inactive since 1983 and…