HR 8844: a new transition object between the Am stars and the HgMn stars ?

TL;DR

This study identifies HR 8844 as a chemically peculiar star with a unique abundance pattern, suggesting it is a transitional object between Am and HgMn stars, based on high-resolution spectral analysis.

Contribution

The paper presents the discovery and detailed spectral analysis of HR 8844 as a new transition object between Am and HgMn stars, highlighting its distinctive chemical abundance pattern.

Findings

HR 8844 shows underabundances of He, C, O, Mg, Ca, Sc.

HR 8844 exhibits enhancements in heavy elements like Sr, Y, Zr, Ba, La, Pr, Sm, Eu, Hg.

Chemical pattern indicates it is a transition between HgMn and Am stars.

Abstract

While monitoring a sample of apparently slowly rotating superficially normal early A stars, we have discovered that HR 8844 (A0 V), is actually a new Chemically Peculiar star. We have first compared the high resolution spectrum of HR 8844 to that of four slow rotators near A0V ($\nu$ Cap, $\nu$ Cnc , Sirius A and HD 72660) to highlight similarities and differences. The lines of Ti II, Cr II, Sr II and Ba II are conspicuous features in the high resolution high signal-to-noise SOPHIE spectra of HR 8844 and much stronger than in the spectra of the normal star $\nu$ Cap. The Hg II line at 3983.93 \AA\ is also present in a 3.5 \% blend. Selected unblended lines of 31 chemical elements from He up to Hg have been synthesized using model atmospheres computed with ATLAS9 and the spectrum synthesis code SYNSPEC48 including hyperfine structure of various isotopes when relevant. These synthetic spectra have been adjusted to the mean SOPHIE spectrum of HR 8844, and high resolution spectra of the comparison stars. Chisquares were minimized in order to derive abundances or upper limits to the abundances of these elements for HR 8844 and the comparison stars. HR 8844 is found to have underabundances of He, C, O, Mg, Ca and Sc, mild enhancements of Ti, V, Cr, Mn and distinct enhancements of the heavy elements Sr, Y, Zr, Ba, La, Pr, Sm, Eu and Hg, the overabundances increasing steadily with atomic number. This chemical pattern suggests that HR 8844 may actually be a new transition object between the coolest HgMn stars and the Am stars.