Publications

Lithium in the active sub-giant HD123351. A quantitative analysis with 3D and 1D model atmospheres using different observed spectra

Here we present a spectroscopic comparative analysis of the Li doublet region of HD 123351, an active sub-giant star of solar metallicity. We fit the Li profile in three observed spectra characterized by different qualities: two very-high resolution spectra (Gecko@CFHT, R=120 000, SNR=400 and PEPSI@LBT, R=150 000, SNR=663) and a high-resolution SOPHIE@OHP spectrum (R=40 000, SNR=300). We adopt a set of model atmospheres, both 3D and 1D, having different stellar parameters (T_{eff} and log g). The 3D models are taken from the CIFIST grid of COBOLD model atmospheres and departures from LTE are considered for the lithium components. For the blends other than the lithium in this wavelength region we adopt the linelist of Melendez et al. (2012, A&A, 543, 29). We find consistent results for all three observations and an overall good fit with the selected list of atomic and molecular lines, indicating a high 6Li content.

The presence of 6Li is not expected in cool stellar atmospheres. Its detection is of crucial importance for understanding mixing processes in stars and external lithium production mechanisms, possibly related to stellar activity or planetray accretion of 6Li-rich material.

Comparison of observed spectra of the Li doublet region of HD 123351 around 670.8 nm. The Gecko (blue dotted line), SOPHIE (red dashed line) and PEPSI (green dashed-dotted line) spectra are superimposed on the Solar flux atlas by Kurucz (2005) (black continuous line) for a comparison. The locations of the Li I components and the dominant blends attributed to Fe  and CN are also indicated.

 

Read more:  Mott, Steffen, Caffau, & Strassmeier 2017, MemSAI 88, 68

 

First light, Publications

CoRoT photometry and STELLA spectroscopy of an eccentric, eclipsing, and spotted HgMn binary with sub-synchronized rotation

Context. We report the discovery and analysis of very narrow transits in the eccentric spectroscopic binary HSS 348 (IC 4756).
Aims: The aim is to characterize the full HSS 348 system.
Methods: We obtained high-precision CoRoT photometry over two long runs and multi-epoch high-resolution échelle spectroscopy and imaging with STELLA and first PEPSI spectra.
Results: HSS 348 is found to be an eccentric (e = 0.18) double-lined spectroscopic binary with a period of 12.47 d in which at least the primary component is a peculiar B star of the HgMn class. The orbital elements are such that the system undergoes a grazing eclipse with the primary in front but no secondary eclipse. The out-of-eclipse light variations show four nearly equidistant but unequal minima stable in shape and amplitude throughout our observations. Their individual photometric periods are all harmonics of the same fundamental period which happens to agree with the transit period to within the errors. We interpret the fundamental period to be the rotation period of at least one if not both stars due to surface inhomogeneities. Due to the non-zero eccentricity of the orbit the two components are rotating sub-synchronously.
Conclusions: It appears that HSS 348 is not a member of the IC 4756 cluster but a background B8+B8.5 binary system. Its sharp eclipses every 12.47 days just mimic a small-body transit but are in reality the grazing eclipses of a B-star binary and thus a classical false positive. The system seems to be pre-main sequence with the primary possibly just arrived on the ZAMS. The light curve with four unequal minima can be explained with four cool spots of different size equidistantly positioned in longitude. Our data do not allow to uniquely assign the spots to either of the two stars.

PEPSI spectrum showing a series of Mn II lines from the primary of HSS348 in IC4756.

Read more: Strassmeier et al. 2017, A&A 597, A55