HD 65949: the highest known mercury excess of any CP star?

Free access article

Issue		A&A Volume 455, Number 2, August IV 2006


Page(s)		L21 - L24
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20065799

A&A 455, L21-L24 (2006)
DOI: 10.1051/0004-6361:20065799

Letter

HD 65949: the highest known mercury excess of any CP star?

C. R. Cowley¹, S. Hubrig², G. F. González³ and N. Nuñez⁴

¹ Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1090, USA
    e-mail: cowley@umich.edu
² European Southern Observatory, Casilla 19001, Santiago 19, Chile
    e-mail: shubrig@eso.org
³ Complejo Astronómico El Leoncito, Casilla 467, 5400 San Juan, Argentina
    e-mail: fgonzalez@casleo.gov.ar
⁴ Departamento de Geofísica y Astronomía, Facultad de Ciencias Exactas Físicas y Naturales, Universidad Nacional de San Juan, Argentina

(Received 10 June 2006 / Accepted 29 June 2006 )

Abstract
ESO spectra of HD 65949 show it to be unlike any of the well-known types within its temperature range $\approx$ 13 600 K. It is neither a silicon, nor a mercury-manganese star, though it has a huge Hg II line at $\lambda$ 3984. We estimate $\log\,({\rm Hg/H}) + 12.0 \approx 7.4$ . This is higher than any published stellar mercury abundance. HD 65949 is a member of a nearby open cluster, NGC 2516, which is only slightly older than the Pleiades, and has been of recent interest because of its numerous X-ray emission stars, including HD 65949 itself, or a close companion. A longitudinal magnetic field of the order of -290 Gauss at the 4.7 $\sigma$ level was very recently diagnosed from accurate circular spectropolarimetric observations with FORS 1 at the VLT.

The spectral lines are sharp, allowing a thorough identification study. Second spectra of Ti, Cr, and Fe are rich. Mn II is well identified but not unusually strong. Numerous lines of S II and P II are found, but not Ga II. The resonance lines of Sr II are strong. While many Y II lines are identified, and Nb II is very likely present, no Zr II lines were found. Xe II is well identified. Strong absorptions from the third spectra of the lanthanides Pr, Nd, and Ho are present, but lines from the second spectra of lanthanides are extremely weak or absent. Among lines from the heavier elements, those of Pt II are clearly present, and the heaviest isotope, ¹⁹⁸Pt, is indicated. The uncommon spectrum of Re II is certain, while Os II and Te II are highly probable. Several of the noted anomalies are unusual for a star as hot as HD 65949.

Key words: stars: chemically peculiar -- stars: abundances -- stars: individual: HD 65949

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