Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA Highly Collimated Jet from the Red Square Nebula, MWC 922
60
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Deep, narrow-band Ha and 6584 AA [Nii ] CCD images of the peculiar, infrared excess B[e] star MWC~922 reveal a collimated, bipolar jet orthogonal to the previously detected extended nebula. The jet consists of a pair of $sim$0.15 pc segments on either side of MWC~922 separated by gaps. The most distant jet segments disappear $sim$0.6 pc from the star. The northwest beam points to a faint emission-line feature 1.65 pc from MWC~922 that may be a terminal bow shock where the jet rams the ambient medium. The narrow opening-angle of the jet combined with an estimated internal sound speed of $sim$10 kms implies a jet speed $sim$500 kms . The previously detected nebula extends up to 0.6~pc to the southwest of MWC~922 at right angles to the jet and appears to be an extension of the compact, edge-on disk surrounding the star. It points toward the HII region Messier 16 located $sim$1degr ($sim$30 pc in projection) to the southwest. This nebula and jet appear to be externally ionized by the ambient Lyman continuum radiation field and have electron densities of n$_e sim$ 50 to 100 cm$^{-3}$. The southwest nebula and jet have similar surface brightness in Ha and [Nii ]. Faint 70 $mu$m emission traces the southwest ejecta that likely originates from $sim$50 K dust embedded in the photo-ionized plasma which may shadow the dimmer ejecta northeast of MWC~922. MWC~922 may be a massive member of the Serpens OB1 or OB2 associations surrounding Messier 16 and Sh2-54.
rate research
Read More
We present Very Large Array C, X, and Q-band continuum observations, as well as 1.3 mm continuum and CO(2-1) observations with the Submillimeter Array toward the high-mass protostellar candidate ISOSS J23053+5953 SMM2. Compact cm continuum emission was detected near the center of the SMM2 core with a spectral index of 0.24 between 6 and 3.6 cm, and a radio luminosity of 1.3 mJy kpc$^2$. The 1.3 mm thermal dust emission indicates a mass of the SMM2 core of 45.8 Msun. The CO(2-1) observations reveal a large, massive molecular outflow centered on the SMM2 core. This fast outflow ($>$ 50 km/s from the cloud systemic velocity) is highly collimated, with a broader, lower-velocity component. The large values for outflow mass (45.2 Msun), and momentum rate (6 x 10$^{-3}$ Msun km/s/yr) derived from the CO emission are consistent with those of flows driven by high-mass YSOs. The dynamical timescale of the flow is between 1.5 - 7.2 x 10$^4$ yr. We also found from the C18O to thermal dust emission ratio that CO is depleted by a factor of about 20, possibly due to freeze out of CO molecules on dust grains. Our data are consistent with previous findings that ISOSS J23053+5953 SMM2 is an emerging high-mass protostar in an early phase of evolution, with an ionized jet, and a fast, highly collimated, and massive outflow.
Highly-collimated gas ejections are among the most dramatic structures in the Universe, observed to emerge from very different astrophysical systems - from active galactic nuclei down to young brown dwarf stars. Even with the huge span in spatial scales, there is convincing evidence that the physics at the origin of the phenomenon, namely the acceleration and collimation mechanisms, is the same in all classes of jets. Here we report on the discovery of a giant, highly-collimated jet from Sanduleaks star in the Large Magellanic Cloud (LMC). With a physical extent of 14 parsecs at the distance of the LMC, it represents the largest stellar jet ever discovered, and the first resolved stellar jet beyond the Milky Way. The kinematics and extreme chemical composition of the ejecta from Sanduleaks star bear strong resemblance with the low-velocity remnants of SN1987A and with the outer filaments of the most famous supernova progenitor candidate, i.e., eta Carinae. Moreover, the precise knowledge of the jets distance implies that it will be possible to derive accurate estimates of most of its physical properties. Sanduleaks bipolar outflow will thus become a crucial test-bed for future theoretical modeling of astrophysical jets.
We present interferometric observations with the Atacama Large Millimeter Array (ALMA) of the free-free continuum and recombination line emission at 1 and 3mm of the Red Square Nebula surrounding the B[e]-type star MWC922. The unknown distance to the source is usually taken to be d=1.7-3 kpc. The unprecedented angular resolution (up to ~0.02arcsec) and exquisite sensitivity of these data unveil, for the first time, the structure and kinematics of the emerging, compact ionized region at its center. We imaged the line emission of H30a and H39a, previously detected with single-dish observations, as well as of H51epsilon, H55gamma, and H63delta, detected for the first time in this work. The line emission is seen over a full velocity range of ~180 km/s arising in a region of diameter <0.14arcsec (less than a few hundred au) in the maser line H30a, which is the most intense transition reported here. We resolve the spatio-kinematic structure of a nearly edge-on disk rotating around a central mass of ~10Msun (d=1.7 kpc) or ~18Msun (d=3 kpc), assuming Keplerian rotation. Our data also unveil a fast (~100 km/s) bipolar ejection (a jet?) orthogonal to the disk. In addition, a slow (<15km/s) wind may be lifting off the disk. Both, the slow and the fast winds are found to be rotating in a similar manner to the ionized layers of the disk. This represents the first empirical proof of rotation in a bipolar wind expanding at high velocity (~100 km/s). (abridged)
The active young protostar DG Tau has an extended jet that has been well studied at radio, optical, and X-ray wavelengths. We report sensitive new VLA full-polarization observations of the core and jet between 5 GHz and 8 GHz. Our high angular resolution observation at 8 GHz clearly shows an unpolarized inner jet with a size 42 AU (0.35) extending along a position angle similar to the optical-X ray outer jet. Using our nearly coeval 2012 VLA observations, we find a spectral-index=+0.46+/-0.05, which combined with the lack of polarization, is consistent with bremsstrahlung (free-free) emission, with no evidence for a non-thermal coronal component. By identifying the end of the radio jet as the optical depth unity surface, and calculating the resulting emission measure, we find our radio results are in agreement with previous optical line studies of electron density and consequent mass-loss rate. We also detect a weak radio knot at 5 GHz located 7 from the base of the jet, coincident with the inner radio knot detected by Rodriguez et al. (2012) in 2009 but at lower surface brightness. We interpret this as due to expansion of post-shock ionized gas in the three years between observations.
Radio emission from protostellar jets is usually dominated by free-free emission from thermal electrons. However, in some cases, it has been proposed that non-thermal emission could also be present. This additional contribution from non-thermal emission has been inferred through negative spectral indices at centimeter wavelengths in some regions of the radio jets. In the case of HH 80-81, one of the most powerful protostellar jets known, linearly polarized emission has also been detected, revealing that the non-thermal emission is of synchrotron nature from a population of relativistic particles in the jet. This result implies that an acceleration mechanism should be taking place in some parts of the jet. Here, we present new high sensitivity and high angular resolution radio observations at several wavelengths (in the 3-20 cm range) of the HH80-81 radio jet. These new observations represent an improvement in sensitivity and angular resolution by a factor of $sim$10 with respect to previous observations. This allows us to resolve the morphology of the radio jet, and to study the different emission mechanisms involved through spectral index maps. We conclude that synchrotron emission in this jet arises from an extended component detected at low frequencies and from the termination points of the jet, where strong shocks against the ambient medium can produce efficient particle acceleration.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
