A Pulsed, Precessing Jet in Cepheus A

Abstract

We present near-infrared H 2 , radio CO, and thermal infrared observations of the nearby massive star-forming region Cepheus A (Cep A). From H 2 bow shocks arranged along four distinct jet axes, we infer that the massive protostellar source HW2 drives a pulsed, precessing jet that has changed its orientation by about 45• in roughly 10 4 years. The current HW2 radio jet represents the most recent event in this time series of eruptions. This scenario is consistent with the recent discovery of a disk around HW2, perpendicular to the current jet orientation, and with the presence of companions at projected distances comparable to the disk radius. We propose that the Cep A system formed by the disk-assisted capture of a sibling star by HW2. We present a numerical model of a 15 M star with a circumstellar disk, orbited by a companion in an inclined, eccentric orbit. Close passages of the companion through or near the disk result in periods of enhanced accretion and mass loss, as well as forced precession of the disk and associated orientation changes in the jet. The observations reveal a second powerful outflow that emerges from radio source HW3c or HW3d. This flow is associated with blueshifted CO emission and a faint H 2 bow shock to the east, and with HH 168 to the west. A collision between the flows from HW2 and HW3c/d may be responsible for X-ray and radio continuum emission in Cep A West.

The Chandra X-ray view of the power sources in Cepheus A

“…This sources lies close to the connecting line of an H 2 emission complex in the west associated with HH 168 and an H 2 complex at the eastern side. Cunningham et al (2009) estimated the distance of the connecting line to be 5-10 arcsec south of HW 2, which is exactly the value of X6. Thus, X6 is possibly driving the HH 168 outflow.…”

Millimetre spectral line mapping observations towards four massive star-forming H ii regions

“…The bolometric luminosity of this region is 2.5 × 10 4 L with a mass of ∼330 M (Evans et al 1981;Narayanan & Walker 1996). Our mapping centre of Cep A is located in the radio source HW2, which is a massive protostar (Cunningham, Moeckel & Bally 2009;Dzib et al 2011), with a mass of ∼18 M (Torrelles et al 2011). There is a fast, bipolar, highly collimated radio jet ejected from the HW2 young stellar object (YSO), with well-aligned NE-SW direction and a scale of ∼1500 au (Curiel et al 2006).…”

Observations of Winds, Jets, and Turbulence Generation in GMCs

“…Velocities >60 km s −1 dissociate and ionize hydrogen. Charge exchange and collisional Cunningham et al (2009) proposed that HW2 and its disk captured a moderate-mass companion into an eccentric orbit inclined with respect to the disk. The companion passes through the disk twice during each orbit, triggering a mass accretion and ejection event.…”

“…A collision between the two flows may be responsible for the bright HH 168 complex. Taken from Cunningham, Moeckel, & Bally (2009). excitation at the shock form thin zones that radiate only in hydrogen recombination lines, producing "Balmer filaments". In fast shocks, the thin (about one mean-free-path) Balmer filament is followed by a thicker layer of fully ionized hydrogen and highly ionized trace elements.…”

“…Figure 2 shows the L ≈ 2 × 10 4 L Cepheus A (Cep A) region in the near-infrared (Cunningham, Moeckel, & Bally 2009). The most luminous object HW2 appears to be a 15 M protostar which has trapped its ionizing radiation.…”