M. Netopil, L. Fossati, E. Paunzen, K. Zwintz, O. I. Pintado and S. Bagnulo

A probable pre-main sequence chemically peculiar star in the open cluster Stock 16

Figure 2.Top panel: comparison between the observed Hγ and Hβ line profile (black solid line) and synthetic profiles calculated with the final adopted parameters (dash-dotted green line) and with the parameters which were found to best fit the hydrogen line profiles (dashed red line). The Hγ line profile was rigidly shifted downwards by 0.2. The wavelength dimension has been converted in velocity and centred at the laboratory wavelength of the Hβ and Hγ lines, respectively. Bottom panel: difference between the synthetic and observed Hγ and Hβ line profiles rigidly shifted respectively downwards and upwards by 0.05. The line colours and styles are as for the top panel.

Abstract

We used the Ultraviolet and Visual Echelle Spectrograph of the ESO-Very Large Telescope to obtain a high resolution and high signal-to-noise ratio spectrum of Stock 16-12, an early-type star which previous Δa photometric observations suggest being a chemically peculiar (CP) star. We used spectral synthesis to perform a detailed abundance analysis obtaining an effective temperature of 8400±400 K, a surface gravity of 4.1±0.4, a microturbulence velocity of 3.4+0.7 kms−1, and a projected rotational velocity of 68±4kms−1. We provide photometric and spectroscopic evidence showing the star is most likely a member of the young Stock 16 open cluster (age 3–8 Myr). The probable cluster membership, the star’s position in the Hertzsprung-Russell diagram, and the found infrared excess strongly suggest the star is still in the pre-main-sequence (PMS) phase. We used PMS evolutionary tracks to determine the stellar mass, which ranges between 1.95 and 2.3M, depending upon the adopted spectroscopic or photometric data results. Similarly, we obtained a stellar age ranging between 4 and 6 Myr, in agreement with that of the cluster. Because the star’s chemical abundance pattern resembles well that known of main sequence CP metallic line (Am) stars, the object sets important constraints to the diffusion theory. Additional spectroscopic and spectropolarimetric data allowed us to conclude that the object is probably a single non-magnetic star.

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Last Revised: 2014 September 18th