2006A&A...455..673B

The λ Bootis stars are a small spectroscopic subgroup of Population I A-type stars and show significant underabundances of metals. Many are δ Scuti pulsators. HD 210111 was selected for a detailed multisite pulsation study to determine whether its pulsation properties differ from those of normal A stars. 262 h of high-precision photometry were obtained at the SAAO and SSO observatories. 13 statistically significant pulsation frequencies were detected with very small photometric amplitudes from 1 to 7 millimag in the visual. A comparison with earlier 1994 measurements indicates a small increase in amplitude. As a byproduct, one of the comparison stars, HD 210571, was discovered to be a millimag variable with a frequency of 1.235c/d and is probably a new γ Doradus variable. The observed wide range of excited frequencies from 12 to 30c/d in HD 210111 can be explained with both the single- and double-star hypothesis. HD 210111 is in a similar evolutionary status to FG Vir, which also shows a wide range of excited frequencies with a similar frequency spacing near 4c/d. This is interpreted as successive radial orders of the excited nonradial modes. In the double-star hypothesis previously evoked for HD 210111, the low and the high frequencies originate in different stars: here HD 210111 would resemble θ² Tau. The pulsation of the λ Bootis star HD 210111 does not differ from that of normal δ Scuti stars.