Aqueous Sample Preparation by FMS

Scientific conference (2010, April)

Deviations from a uniform period spacing of gravity modes in a massive star

in Nature (2010), 464

The life of a star is dominantly determined by the physical processes in the stellar interior. Unfortunately, we still have a poor understanding of how the stellar gas mixes near the stellar core ... [more ▼]

The life of a star is dominantly determined by the physical processes in the stellar interior. Unfortunately, we still have a poor understanding of how the stellar gas mixes near the stellar core, preventing precise predictions of stellar evolution. The unknown nature of the mixing processes as well as the extent of the central mixed region is particularly problematic for massive stars. Oscillations in stars with masses a few times that of the Sun offer a unique opportunity to disentangle the nature of various mixing processes, through the distinct signature they leave on period spacings in the gravity mode spectrum. Here we report the detection of numerous gravity modes in a young star with a mass of about seven solar masses. The mean period spacing allows us to estimate the extent of the convective core, and the clear periodic deviation from the mean constrains the location of the chemical transition zone to be at about 10 per cent of the radius and rules out a clear-cut profile. [less ▲]

Dynamical evolution of titanium, strontium, and yttrium spots on the surface of the HgMn star HD 11753

in Astronomy and Astrophysics (2010), 511

<BR /> Aims: We gathered about 100 high-resolution spectra of three typical HgMn (mercury-manganese) stars, <ASTROBJ>HD 11753</ASTROBJ>, <ASTROBJ>HD 53244</ASTROBJ>, and <ASTROBJ>HD 221507</ASTROBJ>, to ... [more ▼]

<BR /> Aims: We gathered about 100 high-resolution spectra of three typical HgMn (mercury-manganese) stars, <ASTROBJ>HD 11753</ASTROBJ>, <ASTROBJ>HD 53244</ASTROBJ>, and <ASTROBJ>HD 221507</ASTROBJ>, to search for slowly pulsating B-like pulsations and surface inhomogeneous distribution of various chemical elements. <BR /> Methods: Classical frequency analysis methods were used to detect line profile variability and to determine the variation period. Doppler imaging reconstruction was performed to obtain abundance maps of chemical elements on the stellar surface. <BR /> Results: For <ASTROBJ>HD 11753</ASTROBJ>, which is the star with the most pronounced variability, distinct spectral line profile changes were detected for Ti, Sr, Y, Zr, and Hg, whereas for <ASTROBJ>HD 53244</ASTROBJ> and <ASTROBJ>HD 221507</ASTROBJ> the most variable line profiles belong to the elements Hg and Y, respectively. We derived rotation periods for all three stars from the variations of radial velocities and equivalent widths of spectral lines belonging to inhomogeneously distributed elements: P[SUB]rot[/SUB] (<ASTROBJ>HD 11753</ASTROBJ>) = 9.54 d, P[SUB]rot[/SUB] (<ASTROBJ>HD 53244</ASTROBJ>) = 6.16 d, and P[SUB]rot[/SUB] (<ASTROBJ>HD 221507</ASTROBJ>) = 1.93 d. For <ASTROBJ>HD 11753</ASTROBJ> the Doppler imaging technique was applied to derive the distribution of the most variable elements Ti, Sr, and Y using two datasets separated by ~65 days. Results of Doppler imaging reconstruction revealed noticeable changes in the surface distributions of Ti II, Sr II, and Y II between the datasets, indicating the hitherto not well understood physical processes in stars with radiative envelopes that cause a rather fast dynamical chemical spot evolution. Based on observations obtained with the CORALIE Echelle Spectrograph on the 1.2-m Euler Swiss telescope, situated at La Silla, Chile.Postdoctoral Fellow of the Fund for Scientific Research, Flanders. [less ▲]

CoRoT photometry and high-resolution spectroscopy of the interacting eclipsing binary AU Monocerotis

in Monthly Notices of the Royal Astronomical Society (2010), 401

Analyses of very accurate CoRoT space photometry, past Johnson V photoelectric photometry and high-resolution echelle spectra led to the determination of improved and consistent fundamental stellar ... [more ▼]

Analyses of very accurate CoRoT space photometry, past Johnson V photoelectric photometry and high-resolution echelle spectra led to the determination of improved and consistent fundamental stellar properties of both components of AU Monocerotis. We derived new, accurate ephemerides for both the orbital motion (with a period of ) and the long-term, overall brightness variation (with a period of ) of this strongly interacting Be + G semi-detached binary. It is shown that this long-term variation must be due to attenuation of the total light by some variable circumbinary material. We derived the binary mass ratio M[SUB]G[/SUB]/M[SUB]B[/SUB] = 0.17 +/- 0.03 based on the assumption that the G-type secondary fills its Roche lobe and rotates synchronously. Using this value of the mass ratio as well as the radial velocities of the G-star, we obtained a consistent light curve model and improved estimates of the stellar masses, radii, luminosities and effective temperatures. We demonstrate that the observed lines of the B-type primary may not be of photospheric origin. We also discover rapid and periodic light changes visible in the high-quality residual CoRoT light curves. AU Mon is put into perspective by a comparison with known binaries exhibiting long-term cyclic light changes. Based on photometry collected by the CoRoT space mission as well as spectroscopy obtained with the FEROS spectrograph attached to the 2.2-m telescope at European Southern Observatory (ESO), La Silla, Chile, under the ESO Large Programme LP178.D-0361, and with the SOPHIE spectrograph of the Observatoire de Haute-Provence (France). The CoRoT space mission was developed and is operated by the French space agency CNES, with the participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany and Spain. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). E-mail: maarten.desmet@ster.kuleuven.be [less ▲]

A ‘cook book’ method for dioxin analysis

in Book of abstract (2010, January)

GCxGC with TOFMS and qMS for POP Analyses

Scientific conference (2009, December)

Advanced approaches in POPs analysis

in RAFA 2009 Book of abstract (2009, November)

Post-AGB stars with hot circumstellar dust: binarity of the low-amplitude pulsators

in Astronomy and Astrophysics (2009), 505

Context: The influence of binarity on the late stages of stellar evolution remains an open issue. <BR />Aims: While the first binary post-AGB stars were serendipitously discovered, the distinct ... [more ▼]

Context: The influence of binarity on the late stages of stellar evolution remains an open issue. <BR />Aims: While the first binary post-AGB stars were serendipitously discovered, the distinct characteristics of their spectral energy distribution (SED) allowed us to launch a more systematic search for binaries. We selected post-AGB objects, which exhibit a broad dust excess starting either at H or K, pointing to the presence of a gravitationally bound dusty disc in the system. We initiated an extensive multiwavelength study of those systems and here report on our radial velocity and photometric monitoring results for six stars of early F type, which are pulsators of small amplitude. <BR />Methods: To determine the radial velocity of low signal-to-noise ratio time-series data, we constructed dedicated autocorrelation masks based on high signal-to-noise ratio spectra, used in our published chemical studies. The radial velocity variations were analysed in detail to differentiate between pulsational variability and variability caused by orbital motion. When available, the photometric monitoring data were used to complement the time series of radial velocity data and to establish the nature of the pulsation. Finally, orbital minimalisation was performed to constrain the orbital elements. <BR />Results: All of the six objects are binaries with orbital periods ranging from 120 to 1800 days. Five systems have non-circular orbits. The mass functions range from 0.004 to 0.57 M[SUB]&sun;[/SUB] and the companions are probably unevolved objects of (very) low initial mass. We argue that these binaries must have evolved through a phase of strong binary interaction when the primary was a cool supergiant. Although the origin of the circumstellar disc is not well understood, the disc is generally believed to have formed during this strong interaction phase. The eccentric orbits of these highly evolved objects remain poorly understood. In one object, the line-of-sight grazes the edge of the puffed-up inner rim of the disc. <BR />Conclusions: These results corroborate our earlier statement that evolved objects in binary stars create a Keplerian dusty circumbinary disc. With the measured orbits and mass functions, we conclude that the circumbinary discs seem to have a major impact on the evolution of a significant fraction of binary systems. based on observations collected with the Flemish 1.2 m Mercator telescope at Roque de los Muchachos (Spain), the Swiss 1.2 m Euler telescope at La Silla (Chile) and the 0.5 m and 0.75 m telescopes at SAAO (South-Africa). Tables [see full textsee full text]-[see full textsee full text] are only available in electronic form at http://www.aanda.org Postdoctoral fellow of the Fund for Scientific Research, Flanders. Ph.D. student of the Fund for Scientific Research, Flanders. [less ▲]

Total Solution for Rapid Sample Preparation Procedure

Scientific conference (2009, August)

Artistes en milieu de soin psychiatrique : une approche de la médiation par les pratiques professionnelles

Scientific conference (2009, June 25)