Structure of the outer layers of cool standard stars

Context: Among late-type red giants, an interesting change occurs in the structure of the outer atmospheric layers as one moves to later spectral types in the Hertzsprung-Russell diagram: a chromosphere is always present, but the coronal emission diminishes and a cool massive wind steps in. Aims: Where most studies have focussed on short-wavelength observations, this article explores the influence of the chromosphere and the wind on long-wavelength photometric measurements. Methods: The observational spectral energy distributions are compared with the theoretical predictions of the MARCS atmosphere models for a sample of 9 K- and M-giants. The discrepancies found are explained using basic models for flux emission originating from a chromosphere or an ionized wind. Results: For 7 out of 9 sample stars, a clear flux excess is detected at (sub)millimeter and/or centimeter wavelengths. The precise start of the excess depends upon the star under consideration. The flux at wavelengths shorter than about 1 mm is most likely dominated by an optically thick chromosphere, where an optically thick ionized wind is the main flux contributor at longer wavelengths. Conclusions: Although the optical to mid-infrared spectrum of the studied K- and M-giants is well represented by a radiative equilibrium atmospheric model, the presence of a chromosphere and/or ionized stellar wind at higher altitudes dominates the spectrum in the (sub)millimeter and centimeter wavelength ranges. The presence of a flux excess also has implications on the role of these stars as fiducial spectrophotometric calibrators in the (sub)millimeter and centimeter wavelength range.Comment: 13 pages, 6 figures, 7 pages of online material, submitted to A&

Towards ensemble asteroseismology of the young open clusters Chi Persei and NGC 6910

As a result of the variability survey in Chi Persei and NGC6910, the number of Beta Cep stars that are members of these two open clusters is increased to twenty stars, nine in NGC6910 and eleven in Chi Persei. We compare pulsational properties, in particular the frequency spectra, of Beta Cep stars in both clusters and explain the differences in terms of the global parameters of the clusters. We also indicate that the more complicated pattern of the variability among B type stars in Chi Persei is very likely caused by higher rotational velocities of stars in this cluster. We conclude that the sample of pulsating stars in the two open clusters constitutes a very good starting point for the ensemble asteroseismology of Beta Cep-type stars and maybe also for other B-type pulsators.Comment: 4 pages, Astronomische Nachrichten, HELAS IV Conference, Arecife, Lanzarote, Feb 2010, submitte

Photometric multi-site campaign on the open cluster NGC 884 I. Detection of the variable stars

CONTEXT: Recent progress in the seismic interpretation of field beta Cep stars has resulted in improvements of the physics in the stellar structure and evolution models of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. AIMS: To improve our comprehension of the beta Cep stars, we studied the young open cluster NGC 884 to discover new B-type pulsators, besides the two known beta Cep stars, and other variable stars. METHODS: An extensive multi-site campaign was set up to gather accurate CCD photometry time series in four filters (U, B, V, I) of a field of NGC884. Fifteen different instruments collected almost 77500 CCD images in 1286 hours. The images were calibrated and reduced to transform the CCD frames into interpretable differential light curves. Various variability indicators and frequency analyses were applied to detect variable stars in the field. Absolute photometry was taken to deduce some general cluster and stellar properties. RESULTS: We achieved an accuracy for the brightest stars of 5.7 mmag in V, 6.9 mmag in B, 5.0 mmag in I and 5.3 mmag in U. The noise level in the amplitude spectra is 50 micromag in the V band. Our campaign confirms the previously known pulsators, and we report more than one hundred new multi- and mono-periodic B-, A- and F-type stars. Their interpretation in terms of classical instability domains is not straightforward, pointing to imperfections in theoretical instability computations. In addition, we have discovered six new eclipsing binaries and four candidates as well as other irregular variable stars in the observed field.Comment: Accepted for publication in Astronomy and Astrophysics, 21 pages, 14 figures, 4 tables. The full appendix is available at http://www.ster.kuleuven.be/~sophies/Appendix.pdf (74 MB, 169 pages, 343 figures, 1 table

Baseline psychosocial predictors of survival in localised breast cancer

Despite the large number of studies on the impact of psychosocial factors on breast cancer progression, there is no certainty about the contributing factors or processes involved. We investigated the relative impacts of socioeconomic, psychological, and psychosocial factors on survival in breast cancer. A consecutive sample of 102 patients (participation 82%) under 72 years of age with locoregional breast cancer completed validated questionnaires on coping with cancer, emotional expression (anger), perceived available support, noncancer life stresses, and quality of life 3−4 months after diagnosis. Survival times were measured from the date of diagnosis to the date of relapse and further to the date of death or date of last follow-up. Cumulative Cox regression analyses were carried out. After controlling for biological prognostic factors, age, and baseline treatment, longer survival was predicted by a long education and a minimising-related coping, while shorter survival was predicted by emotional defensiveness (antiemotionality), behavioural-escape coping, and a high level of perceived support. A shorter event-free time was also predicted by unemployment and depressive symptoms. Cancer survival is affected by a complex combination of psychosocial factors, among which minimising predicts a favourable prognosis and anger nonexpression and escape behaviour an unfavourable prognosis. Higher socioeconomic status is associated with longer survival. High scores in well-being scales may reflect emotional nonexpression

Detection of ‘parent ’ molecules from the inner wind of AGB stars as tracers of non-equilibrium chemistry

Context. Asymptotic Giant Branch (AGB) stars are typified by strong dust-driven, molecular outflows. For long, it was believed that the molecular setup of the circumstellar envelope of AGB stars is primarily determined by the atmospheric C/O ratio. However, recent observations of molecules such as HCN, SiO, and SO reveal gas-phase abundances higher than predicted by thermodynamic equilibrium (TE) models. UV-photon initiated dissociation in the outer envelope or non-equilibrium formation by the effect of shocks in the inner envelope may be the origin of the anomolous abundances. Aims. We aim at detecting (i) a group of ‘parent ’ molecules (CO, SiO, HCN, CS), predicted by the non-equilibrium study of Cherchneff (2006) to form with almost constant abundances independent of the C/O ratio and the stellar evolutionary stage on the Asymptotic Giant Branch (AGB), and (ii) few molecules, such as SiS and SO, which are sensitive to the O- or C-rich nature of the star. Methods. Several low and high excitation rotational transitions of key molecules are observed at mm and sub-mm wavelengths with JCMT and APEX in four AGB stars: the oxygen-rich Mira WX Psc, the S star W Aql, and the two carbon stars V Cyg and II Lup. A critical density analysis is performed to determine the formation region of the high-excitation molecular lines

Spectroscopy of the ODD-ODD nucleus 76As and its supersymmetric description

Gamma rays and conversion electrons following thermal-neutron capture in 75As have been measured using the Ge pair spectrometer PN4, the bent crystal spectrometers GAMS and the β-spectrometer BILL at the ILL. Coincident γ-rays were recorded at the CEN/SCK Mol, and average resonance capture at En = 2 and 24 keV has been studied at the HFBR of BNL. The neutron binding energy in 76As was determined to be 7328.498 ± 0.075 keV. The resulting level scheme for 76As greatly improves the knowledge on this odd-odd nucleus. The low-lying positive-parity states are discussed in the U(5) limit of the Uv(6/12)⊗Uπ(6/12) supersymmetry using the same hamiltonian to describe the quartet 76Se-77Se-75As-76As having the same total number of bosons plus fermions

The ongoing 2005 -- 2006 campaign on beta Cephei stars in NGC 6910 and chi Persei (NGC 884)

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