Absolute Parameters of Young Stars: NO Puppis

Abstract

The southern early-type, young, eccentric-orbit eclipsing binary NO Puppis forms the A component of the multiple star Gaia DR3 552\-8147999779517568. The B component is an astrometric binary now at a separation of about 8.1 arcsec. There may be other fainter stars in this interesting but complex stellar system. We have combined several lines of evidence, including TESS data from 4 sectors, new ground-based BVR photometry, HARPS (ESO) and HERCULES (UCMJO) high-resolution spectra and astrometry of NO Pup. We derive a revised set of absolute parameters with increased precision. Alternative optimal curve-fitting programs were used in the analysis, allowing a wider view of modelling and parameter uncertainties. The main parameters are as follows: $M_{Aa}=3.58\pm 0.11$, $M_{Ab}=1.68\pm 0.09$ (M${}_{\odot }$); $R_{Aa}=2.17\pm 0.03$, $R_{Ab}=1.51\pm 0.06$ (R${}_{\odot }$), and $T_{\mathrm{eAa}}=13300\pm 500$, $T_{\mathrm{eAb}}=7400\pm 500$ (K). We estimate approximate masses of the wide companions, Ba and Bb, as $M_{Ba}=2.0$ and $M_{Bb}=1.8$ (M${}_{\odot }$). The close binary's orbital separation is $a=8.51\pm 0.05$ (R${}_{\odot }$); its age is approximately $20$ Myr and distance $172\pm 1$ pc. The close binary's secondary (Ab) appears to be the source of low amplitude $\delta$ Scuti-type oscillations, although the form of these oscillations is irregular and unrepetitive. Analysis of the $\lambda$ 6678 He I profile of the primary show synchronism of the mean bodily and orbital rotations. The retention of significant orbital eccentricity, in view of the closeness of the A-system components, is unexpected and poses challenges for the explanation that we discuss.

22 pages, 21 figures, 13 tables, accepted for publication in PASA

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