A rival for Babcock's star: the extreme 30-kG variable magnetic field in the Ap star HD 75049

TL;DR

HD75049 is a highly magnetic Ap star with a 30kG surface magnetic field, exhibiting variability and a near-zero-age main sequence status, making it a strong rival to Babcock's star in magnetic strength.

Contribution

This study provides detailed measurements of HD75049's magnetic field, rotation, and chemical abundances, establishing it as the second most magnetic main sequence star after Babcock's star.

Findings

Magnetic field modulus reaches 30kG at maximum.

Star's rotation period is 4.049 days.

Surface magnetic field modeled as a centered dipole.

Abstract

The extraordinary magnetic Ap star HD75049 has been studied with data obtained with the ESO VLT and 2.2-m telescopes. Direct measurements reveal that the magnetic field modulus at maximum reaches 30kG. The star shows photometric, spectral and magnetic variability with a rotation period of 4.049d. Variations of the mean longitudinal magnetic field can be described to first order by a centred dipole model with an inclination i = 25 degrees, an obliquity beta = 60 degrees, and a polar field B_p = 42kG. The combination of the longitudinal and surface magnetic field measurements imply a radius of R = 1.7 R sun, suggesting the star is close to the zero-age main sequence. HD75049 displays moderate overabundances of Si, Ti, Cr, Fe and large overabundances of rare earth elements. This star has the second strongest magnetic field of any main sequence star after Babcock's star, HD215441, which it rivals.