SPECTRO-INTERFEROMETRY OF THE Be STAR δ Sco: NEAR-INFRARED CONTINUUM AND GAS EMISSION REGION SIZES IN 2007

Abstract

We present near-infrared H and K-band spectro-interferometric observations of the gaseous disk around the primary Be star in the δ Sco binary system, obtained in 2007 (between periastron passages in 2000 and 2011). Observations using the CHARA/MIRC instrument at H-band resolve an elongated disk with a Gaussian FWHM 1.18 × 0.91 mas. Using the Keck Interferometer, the source of the K-band continuum emission is only marginally spatially resolved, and consequently we estimate a relatively uncertain K-band continuum disk FWHM of 0.7 ± 0.3 mas. Line emission on the other hand, He I λ2.0583 µm and Brγ λ2.1657 µm, is clearly detected, with ∼ 10% lower visibilities than those of the continuum. When taking into account the continuum/line flux ratio this translates into much larger sizes for the line emission regions: 2.2 ± 0.4 mas and 1.9 ± 0.3 mas for He I and Brγ respectively. Our KI data also reveal a relatively flat spectral differential phase response, ruling out significant off-center emission.We expect these new measurements will help constrain dynamical models being actively developed in order to explain the disk formation process in the δ Sco system and Be stars in general.a Consistent with the companion location relative to the FOV for each instrument, in the above flux ratios the H-band total flux (F T ) includes the secondary star, but the K-band total flux does not. b D = 14R .c Only needed to determine the continuum disk size, not the line sizes.

The binary Be starδScorpii at high spectral and spatial resolution

“…a Brγ = 3.6 ± 0.6 R and a HeI = 4.2 ± 0.8 R . Moreover, the size of the Hα emission obtained from our CHARA/VEGA measurements is also roughly compatible with the Millan-Gabet et al (2010) estimation using the line EW, i.e., 14.9 R . Consequently, it seems that the disk did not grow or shrink during the 2007-2010 period.…”

“…Modeled as a Gaussian distribution, the respective FWHM are a Hα = 9.0 ± 3.0 R , a Brγ = 5.5 ± 1 R , and a HeI = 4.5±0.5 R . The disk extensions in the infrared lines are compatible with those derived by Millan-Gabet et al (2010) from 2007 Keck-Interferometer measurements, i.e. a Brγ = 3.6 ± 0.6 R and a HeI = 4.2 ± 0.8 R .…”

“…These lines are formed at various distances from the central star as already measured for γ Cas in the Hα, Hβ, and He i 6678 lines by Stee et al (1998) and as seen in the previous section where we found φ Hα > φ He i > φ Brγ . But compared to Stee et al (1998) and other recent work (Carciofi et al 2006;Millan-Gabet et al 2010) we now have a direct access to the kinematics within each lineforming region with a velocity resolution of about 25 km s −1 . We see from Fig.…”

Binaries and Multiple Systems Observed with the CHARA, NPOI, SUSI and VLTI Interferometric Eyes

“…δ Sco is also a binary Be star already observed by Millan-Gabet et al (2010) in 2007 with CHARA and resolved in the H continuum, Brγ, HeI and Hα lines. This is an interesting system since the companion passage at periastron is so close that tidal effects have strong effects on the formation/dissipation of the circumstellar disk around the primary.…”

Recent progress at the Keck interferometer

“…The Be star delta Sco was studied by combining KI and CHARA observations 21 . These authors found the K-band continuum emission was only marginally spatially resolved, while line emission from He I λ2.0583 μm and Br γ λ2.1657 μm was clearly detected with ~10% lower visibilities than those of the continuum.…”