HD 188101: A Spotted B Star with Abundance Anomalies

Abstract

Based on spectroscopic and photometric observations, we have determined the fundamental parameters of the poorly studied star HD 188101 with a weak magnetic field. Its effective temperature $T_{\rm eff} = 14200 \pm 990$ K and surface gravity log g = 3.70 $\pm$ 0.16 are typical for main-sequence B9 stars. The He, C, O, Mg, Si, Ti, and Sr abundances have been determined by taking into account the departures from local thermodynamic equilibrium. Overabundances of Si, Ti, and Sr relative to their solar abundances have been revealed. The He abundance is lower than the solar one, but the difference is within the error limits. In addition to the photometric variability known from Kepler data, we have found changes in absorption for He I, Mg II, Si II, Si III, Ti II, and Fe II lines, with different He I and Mg II lines giving different abundances for the same phase of observations. The star HD 188101 is shown to belong to the group of chemically peculiar He-weak SiTiSr stars.

Figures (10)

• Figure 1: Changes in the equivalent widths of the Mg II and He I lines in HD 188101 with rotation phase.
• Figure 2: Changes in the equivalent widths of the Si III, Ti II, and Fe II lines in HD 188101 with rotation phase.
• Figure 3: Energy levels in themodel He I atom. The dashes indicate the transitions in which the lines involved in determining the He abundance are formed (the wavelengths are in Å).
• Figure 4: The $b$--factors of He I and He II levels as a function of the depth in the 17 500/3.8 ($\iota$ Her, the upper panel) and 10 400/3.5 (21 Peg, the lower panel) model atmospheres. The formation depths of the He I 4437 and 5875 Å line cores are indicated.
• Figure 5: The deviations of the theoretical fluxes from the observed ones (in magnitudes) for different $T_{\rm eff}$ and E(B-V) are indicated by the shading with different intensities. The solid and dashed red straight lines mark the derived E(B-V) and $T_{\rm eff}$ with their errors.