Simultaneous optical speckle masking and NIR adaptive optics imaging of the 126 mas Herbig Ae/Be binary star NX Puppis

Abstract

We present simultaneous optical and near-infrared high angular resolution observations of the close Herbig Ae/Be binary star NX Pup which is associated with cometary globule~1. The reconstructed images have a diffraction--limited resolution of 62 mas in V, 75 mas in R (speckle masking reconstruction), and 115 mas in H, 156 mas in K (adaptive optics + post--processing). Compared to previous results we were able to derive better estimates on spectral type and luminosity and hence put better constraints on the evolutionary status (mass & age) of NX Pup A and B: with NX Pup A of spectral type F0-F2 we estimate the spectral type of NX Pup B in the range F7-G4, masses of 2 M$_\odot$ and 1.6--1.9 M$_\odot$, respectively, and an age of 3--5~Myr for both stars. We discuss the implication of the new age determination on the physical relation between NX Pup and the cometary globule. The dynamical lifetime of $\approx$ 10$^6$ yr for cometary globule 1 suggests that cometary globule 1 and the nearby cometary globule 2 represent transient phenomena and are left overs of a larger molecular cloud which in turn was the parental cloud of NX~Pup A and B and finally got dispersed by photoevaporation. The IR excess of NX Pup A can be modeled by a viscous accretion disk, which is cut off at $\approx$ 20 AU from the star. NX Pup B has a smaller IR excess which indicates that there is less circumstellar material present than around the primary.