Multi-Epoch VLBA Observations of the Compact Wind-Collision Region in the Quadruple System Cyg OB2 #5

Abstract

We present multi--epoch VLBA observations of the compact wind collision region in the Cyg OB2 #5 system. These observation confirm the arc-shaped morphology of the emission reported earlier. The total flux as a function of time is roughly constant when the source is "on", but falls below the detection limit as the wind collision region approaches periastron in its orbit around the contact binary at the center of the system. In addition, at one of the "on" epochs, the flux drops to about a fifth of its average value. We suggest that this apparent variation could result from the inhomogeneity of the wind that hides part of the flux rather than from an intrinsic variation. We measured a trigonometrical parallax, for the most compact radio emission of 0.61 $\pm$ 0.22 mas, corresponding to a distance of 1.65 ${}_{-0.44}^{+0.96}$ kpc, in agreement with recent trigonometrical parallaxes measured for objects in the Cygnus X complex. Using constraints on the total mass of the system and orbital parameters previously reported in the literature, we obtain two independent indirect measurements of the distance to the Cyg OB2 #5 system, both consistent with 1.3--1.4 kpc. Finally, we suggest that the companion star responsible for the wind interaction, yet undetected, is of spectral type between B0.5 to O8.

manuscript format, 24 pages, 5 figures, accepted for publication in The Astrophysical Journal

References in corpus (5)

• VLBA determination of the distance to nearby star-forming regions I. The distance to T Tauri with 0.4% accuracy
• Radio, X-ray, and gamma-ray Emission Models of the Colliding Winds Binary WR 140
• Non-thermal emission processes in massive binaries
• A multiwavelength investigation of the massive eclipsing binary Cyg OB2 #5
• The Distance and Size of the Red Hypergiant NML Cyg from VLBA and VLA Astrometry

Cited by in corpus (22)

• Micro-Arcsecond Radio Astrometry
• The Massive Star Population of Cygnus OB2
• OB associations and their origins
• Comparison of Gaia DR2 Parallaxes of Stars with VLBI Astrometry
• Predicting Gaia's Parallax Distance to the Cygnus OB2 Association with Eclipsing Binaries
• Wind collisions in three massive stars of Cyg OB2
• A global view on star formation: The GLOSTAR Galactic plane survey III. 6.7 GHz methanol maser survey in Cygnus X
• Galactic Kinematics from a Sample of Young Massive Stars
• Search for magnetic fields in particle-accelerating colliding-wind binaries
• A global view on star formation: The GLOSTAR Galactic plane survey VIII. Formaldehyde absorption in Cygnus~X
• Bow shocks, bow waves, and dust waves. II. Beyond the rip point
• The compact, time-variable radio source projected inside W3(OH): Evidence for a Photoevaporated Disk?
• A global view on star formation: The GLOSTAR Galactic plane survey X. Galactic HII region catalog using radio recombination lines
• Searching for compact radio sources associated to UCHII regions
• Megahertz emission of massive early-type stars in the Cygnus region
• Non-thermal radio emission from O-type stars. V. 9 Sgr
• Parameters of the Link between the Optical and Radio Frames from Gaia DR2 Data and VLBI Measurements
• Very Large Array and Jansky Very Large Array observations of the compact radio sources in M8
• A Massive Young Runaway Star in W49 North
• Residual HCRF Rotation relative to the Inertial Coordinate System
• Quest for the tertiary component in Cyg OB2 #5
• Dynamical masses of YSOs with the VLBA: DYNAMO VLBA: Trigonometric parallaxes and proper motions of YSOs in Orion