Revealing the inclined circumstellar disk in the UX Orionis system KK Ophiuchi

A Kreplin,V Grinin,K.-H Hofmann,Ph Stee,G Weigelt,M Kishimoto,D Schertl,J.-M Clausse,S Kraus,L Tambovtseva,F Massi,K Perraut

doi:10.1051/0004-6361/201220806

Abstract

Aims. We study the inner sub-AU region of the circumstellar environment of the UX Ori-type star KK Oph with near-infrared VLTI/AMBER interferometry. We are particularly interested in the inclination of the star-disk system, and we use this information to test the current standard picture for UX Ori stars. Methods. We recorded spectrally dispersed (R 35) interferograms in the near-infraredH andK bands with the VLTI/AMBER instrument. The derived visibilities, closure phases, and the spectral energy distribution of KK Oph were compared with two-dimensional geometric and radiative transfer models (RADMC). Results. We obtained visibilities at four di erent position angles. Using two-dimensional geometric models, we derive an axis ratio 3:0 corresponding to an inclination of 70 . A fitted inclined ring model leads to a ring radius of 2:8 0:2 mas, corresponding to 0:44 0:03 AU at a distance of 160 pc, which is larger than the dust sublimation radius of 0:1 AU predicted for a dust sublimation temperature of 1500 K. Our derived two-dimensional RADMC model consists of a circumstellar disk with an inclination angle of 70 and an additional dust envelope. Conclusions. The finding of an 70 inclined disk around KK Oph is consistent with the prediction that UX Ori objects are seen under large inclination angles, and orbiting clouds in the line of sight cause the observed variability. Furthermore, our results suggest that the orbit of the companion KK Oph B and the disk plane are coplanar.

Highlights

UX Ori stars (UXORs) are young stars showing irregular brightness variations
We presented the first near-infrared interferometric measurements of the UX Ori star KK Oph
The star was observed with the Very Large Telescope Interferometer (VLTI)/AMBER instrument at four different position angle (PA)

Summary

Introduction

UX Ori stars (UXORs) are young stars showing irregular brightness variations. A typical decrease of two to three magnitudes in the V band is observed for a few days to a couple of weeks. One of the current theories links these brightness variations to obscurations of the central star by orbiting dust clouds in an almost edge-on disk (Grinin et al 1994; Natta & Whitney 2000; Grinin et al 1991; Natta et al 1997). KK Oph A, for simplicity hereafter referred to as KK Oph, is a highly irregular variable star located near the dark cloud B56 (Swope 1928; Herbst & Shevchenko 1999). We present the first near-infrared interferometric observations of the UX Ori-type star KK Oph. In Sect. From the 2009 data (data set A; see Table 1), we could extract H- and K-band visibilities between 1.6−1.8 μm and 2.0−2.4 μm. Due to poor seeing of 1.3 arcsec during the night of 2012-02-23, we could only extract K-band data from data sets B and C (Table 1). We complemented our near-infrared AMBER data with existing mid-infrared MIDI data of KK Oph (Leinert et al 2004)

Modeling

Observations and data reduction

Two-dimensional radiative transfer model of a disk and an envelope

Findings

Discussion

Summary and conclusion