Doppler imaging an X-ray flare on the ultrafast rotator BO Mic - A contemporaneous multiwavelength study using XMM-Newton and VLT

We present an analysis of contemporaneous photospheric, chromospheric and coronal structures on the highly active K-dwarf star BO Mic (Speedy Mic). We localize a moderate flare in the stellar atmosphere and study its energetics, size and thermal behaviour. The analysis is based on strictly simultaneous X-ray, UV- and optical observations carried out by XMM-Newton and the VLT. We use Doppler imaging and related methods for the localization of features. Based on X-ray spectroscopy we study the the coronal plasma in and outside the flare. The flare emits in X-rays and UV, but is not detected in white light; it is located at intermediate latitude between an extended spot group and the weakly spotted pole. We estimate its height below 0.4 stellar radii making it clearly distinct in longitude and height from the prominences found about two stellar radii above the surface. While BO Mic's photospheric brightness is modulated due to extended starspots, neither the chromospheric nor the X-ray emission show a pronounced rotational modulation.Comment: Accepted by A&

A planetary eclipse map of CoRoT-2a. Comprehensive lightcurve modeling combining rotational-modulation and transits

We analyze the surface structure of the planet host star CoRoT-2a using a consistent model for both the `global' (i.e., rotationally modulated) lightcurve and the transit lightcurves, using data provided by the CoRoT mission. Selecting a time interval covering two stellar rotations and six transits of the planetary companion CoRoT-2b, we adopt a `strip' model of the surface to reproduce the photometric modulation inside and outside the transits simultaneously. Our reconstructions show that it is possible to achieve appropriate fits for the entire sub-interval using a low-resolution surface model with 36 strips. The surface reconstructions indicate that the brightness on the eclipsed section of the stellar surface is (6 +/- 1) % lower than the average brightness of the remaining surface. This result suggests a concentration of stellar activity in a band around the stellar equator similar to the behavior observed on the Sun.Comment: accepted by A&A on 12/09/200

The center-to-limb variation across the Fraunhofer lines of HD 189733; Sampling the stellar spectrum using a transiting planet

The center-to-limb variation (CLV) describes the brightness of the stellar disk as a function of the limb angle. Across strong absorption lines, the CLV can vary quite significantly. We obtained a densely sampled time series of high-resolution transit spectra of the active planet host star HD 189733 with UVES. Using the passing planetary disk of the hot Jupiter HD 189733 b as a probe, we study the CLV in the wings of the Ca II H and K and Na I D1 and D2 Fraunhofer lines, which are not strongly affected by activity-induced variability. In agreement with model predictions, our analysis shows that the wings of the studied Fraunhofer lines are limb brightened with respect to the (quasi-)continuum. The strength of the CLV-induced effect can be on the same order as signals found for hot Jupiter atmospheres. Therefore, a careful treatment of the wavelength dependence of the stellar CLV in strong absorption lines is highly relevant in the interpretation of planetary transit spectroscopy.Comment: Accepted in A&

Time-resolved UVES observations of a stellar flare on the planet host HD 189733 during primary transit

HD 189733 is an exoplanetary system consisting of a transiting hot Jupiter and an active K2V-type main sequence star. We aim to use VLT/UVES high resolution echelle spectra to study a stellar flare. We have performed simultaneous analyses of the temporal evolution in several chromospheric stellar lines, namely, the Ca II H and K lines, Halpha, Hbeta, Hgamma, Hdelta, Hepsilon, the Ca II infrared triplet line, and He I D3. Observations were carried out with a time resolution of approximately 1 min for a duration of four hours, including a complete planetary transit. We determine the energy released during the flare in all studied chromospheric lines combined to be about 8.7e31 erg, which puts this event at the upper end of flare energies observed on the Sun. Our analysis does not reveal any significant delay of the flare peak observed in the Balmer and Ca II H and K lines, although we find a clear difference in the temporal evolution of these lines. The He I D3 shows additional absorption possibly related to the flare event. Based on the flux released in Ca II H and K lines during the flare, we estimate the soft X-ray flux emission to be 7e30 erg. The observed flare can be ranked as a moderate flare on a K-type star and confirms a rather high activity level of HD 189733 host star. The cores of the studied chromospheric lines demonstrate the same behavior and let us study the flare evolution. We demonstrate that the activity of an exoplanet host star can play an important role in the detection of exoplanet atmospheres, since these are frequently discovered as an additional absorption in the line cores. A possible star-planet interaction responsible for a flare occurrence during a transit can neither be confirmed nor ruled out.Comment: 12 pages, 9 figures, accepted for publication in A&

Investigation of Low-Density Symmetry Energy via Nucleon and Fragment Observables

With stochastic transport simulations we study in detail central and peripheral collisions at Fermi energies and suggest new observables, sensitive to the symmetry energy below normal density. As such we identify on one hand the isospin imbalance ratio, i.e. the relative amount of isospin equilibration in binary, peripheral reactions of nuclei with different isospin, as a function of the energy loss, which is sensitive to isospin diffusion; on the other hand the isospin asymmetry of an intermediate mass fragment (IMF) in symmetric collisions in ternary reactions, or more particularly, the ratio of the IMF to the residue asymmetry, which is sensitive to isospin migration.Comment: 6 pages, 6 figures; Contrib. to Int. Symp. on Exotic States of Nuclear Matter (EXOCT2007), Catania, Italy, June 2007, World Scientifc styl

Fired and pregnant: gender differences in job flexibility outcomes after job loss

We study whether women and men cope with job loss differently, focusing on the importance of workers’ job flexibility and household setting. Our empirical analysis is based on Dutch administrative monthly micro data over the period 2006-2017 using a quasi-experimental design involving job loss following firm bankruptcy. We find for displaced women, but not for displaced men, a persistence in job flexibilities involving limited working hours and short commutes. Importantly, job loss results in a smaller loss in hourly wages and longer unemployment for women, narrowing the gender wage gap but widening the gender employment gap. Also, we show that female workers who are pregnant when job loss occurs experience large losses in employment and conditional on re-employment take up a flexible job. Policy advice is to put a safety net in place to protect pregnant women against the long-term consequences of job loss

Planetary eclipse mapping of CoRoT-2a. Evolution, differential rotation, and spot migration

The lightcurve of CoRoT-2 shows substantial rotational modulation and deformations of the planet's transit profiles caused by starspots. We consistently model the entire lightcurve, including both rotational modulation and transits, stretching over approximately 30 stellar rotations and 79 transits. The spot distribution and its evolution on the noneclipsed and eclipsed surface sections are presented and analyzed, making use of the high resolution achievable under the transit path. We measure the average surface brightness on the eclipsed section to be (5\pm1) % lower than on the noneclipsed section. Adopting a solar spot contrast, the spot coverage on the entire surface reaches up to 19 % and a maximum of almost 40 % on the eclipsed section. Features under the transit path, i.e. close to the equator, rotate with a period close to 4.55 days. Significantly higher rotation periods are found for features on the noneclipsed section indicating a differential rotation of $\Delta \Omega > 0.1$. Spotted and unspotted regions in both surface sections concentrate on preferred longitudes separated by roughly 180 deg.Comment: Paper accepted by A&A 17/02/2010. For a better resolution paper please visit my homepage: http://www.hs.uni-hamburg.de/EN/Ins/Per/Huber/index.htm