High resolution CO observations of S88-B

CO J = 2-1 and 13CO J = 2-1 and 1-0 observations have been made of the H II region S88-B, using the 15-m James Clerk Maxwell telescope in Hawaii and the 20-m telescope at Onsala. The core of the cloud is resolved into a horseshoelike structure which surrounds a diffuse reflection nebula. The central core has a mass of ≥ 1000 M⊙, with 400 M⊙ in the horseshoe structure. The gas in the horse in the horseshoe appears highly fragmented, and has a kinetic temperature of ≈ 60 K, suggesting it is closely coupled to the dust temperature. A recently formed high mass star appears to be in the process of evacuating a cavity, possibly through a large molecular outflow that is found to show an accelerated component in its blue-shifted lobe. A velocity gradient across the horseshoe structure suggest ordered motion, and could represent rotation in the parental cloud

High signal/noise ¹³CO observations of the bipolar outflow in L1551

New high-signal/noise 13CO observations of the bipolar outflow in the molecular cloud L1551 are reported. Contrary to earlier observations of CO J = 1-0 and 2-1, no strong spatial dependence is found for the velocity profile of these spectra. The implications of these observations are such that the model of an empty shell for this source is less likely, and a model consisting of a shell which contains significant amounts of outflowing molecular gas inside the swept-up cavity walls is suggested

Discovery of X-ray emission from the proto-stellar jet L1551 IRS5 (HH 154)

We have for the first time detected X-ray emission associated with a proto-stellar jet, on the jet emanating from L1551 IRS5. The IRS5 proto-star is hidden beyond a very large absorbing column density, making the direct observation of the jet's emission possible. The observed X-ray emission is likely associated with the shock ``working surface'', i.e. the interface between the jet and the circumstellar medium. The X-ray luminosity emanating from the jet is moderate, at LX ~ 3 times 10^29 erg/s, a significant fraction of the luminosity normally associated with the coronal emission from young stars. The spectrum of the X-ray emission is compatible with thermal emission from a hot plasma, with T ~ 0.5 MK, fully compatible with the temperature expected (on the basis of the jet's velocity) for the shock front produced by the jet hitting the circumstellar medium.Comment: To appear in "Stellar Coronae in the Chandra and XMM Era", ASP Conference Series in press, F. Favata & J. Drake ed

The discovery of an expanding X-ray source in the HH 154 protostellar jet

We have performed, in October 2005, a deep Chandra X-ray observation of HH 154. Comparison with the previous (2001) Chandra observation allows to detect proper motion down to the level predicted by models of X-ray emitting shocks in the jet. The 2005 Chandra observation of HH 154 shows unexpected morphological changes of the X-ray emission in comparison with the 2001 data. Two components are present: a stronger, point-like component with no detectable motion and a weaker component which has expanded in size by approximately 300 AU over the 4 years time base of the two observations. This expansion corresponds to approximately 500 km/s, very close to the velocity of the X-ray emitting shock in the simple theoretical models. The 2005 data show a more complex system than initially thought (and modeled), with multiple components with different properties. The observed morphology is possibly indicating a pulsed jet propagating through a non-homogeneous medium, likely with medium density decreasing with distance from the driving source. Detailed theoretical modeling and deeper X-ray observations will be needed to understand the physics of this fascinating class of sources.Comment: Accepted for publication in A&A Letter

High Angular Resolution, Sensitive CS J=2-1 and J=3-2 Imaging of the Protostar L1551 NE: Evidence for Outflow-Triggered Star Formation ?

High angular resolution and sensitive aperture synthesis observations of CS ($J=2-1$) and CS ($J=3-2$) emissions toward L1551 NE, the second brightest protostar in the Taurus Molecular Cloud, made with the Nobeyama Millimeter Array are presented. L1551 NE is categorized as a class 0 object deeply embedded in the red-shifted outflow lobe of L1551 IRS 5. Previous studies of the L1551 NE region in CS emission revealed the presence of shell-like components open toward L1551 IRS 5, which seem to trace low-velocity shocks in the swept-up shell driven by the outflow from L1551 IRS 5. In this study, significant CS emission around L1551 NE was detected at the eastern tip of the swept-up shell from $V_{\rm{lsr}}$ = 5.3 km s$^{-1}$ to 10.1 km s$^{-1}$, and the total mass of the dense gas is estimated to be 0.18 $\pm$ 0.02 $M_\odot$. Additionally, the following new structures were successfully revealed: a compact disklike component with a size of $\approx$ 1000 AU just at L1551 NE, an arc-shaped structure around L1551 NE, open toward L1551 NE, with a size of $\sim 5000$ AU, i.e., a bow shock, and a distinct velocity gradient of the dense gas, i.e., deceleration along the outflow axis of L1551 IRS 5. These features suggest that the CS emission traces the post-shocked region where the dense gas associated with L1551 NE and the swept-up shell of the outflow from L1551 IRS 5 interact. Since the age of L1551 NE is comparable to the timescale of the interaction, it is plausible that the formation of L1551 NE was induced by the outflow impact. The compact structure of L1551 NE with a tiny envelope was also revealed, suggesting that the outer envelope of L1551 NE has been blown off by the outflow from L1551 IRS 5.Comment: 29 pages, 12 figures, Accepted for Publication in the Astrophysical Journa

Transmission measurement at 10.6 microns of Te2As3Se5 rib-waveguides on As2S3 substrate

The feasibility of chalcogenide rib waveguides working at lambda = 10.6 microns has been demonstrated. The waveguides comprised a several microns thick Te2As3Se5 film deposited by thermal evaporation on a polished As2S3 glass substrate and further etched by physical etching in Ar or CF4/O2 atmosphere. Output images at 10.6 microns and some propagation losses roughly estimated at 10dB/cm proved that the obtained structures behaved as channel waveguides with a good lateral confinement of the light. The work opens the doors to the realisation of components able to work in the mid and thermal infrared up to 20 microns and even more.Comment: The following article appeared in Vigreux-Bercovici et al., Appl. Phys. Lett. 90, 011110 (2007) and may be found at http://link.aip.org/link/?apl/90/01111

The X-ray puzzle of the L1551 IRS 5 jet

Protostars are actively accreting matter and they drive spectacular, dynamic outflows, which evolve on timescales of years. X-ray emission from these jets has been detected only in a few cases and little is known about its time evolution. We present a new Chandra observation of L1551 IRS 5's jet in the context of all available X-ray data of this object. Specifically, we perform a spatially resolved spectral analysis of the X-ray emission and find that (a) the total X-ray luminosity is constant over almost one decade, (b) the majority of the X-rays appear to be always located close to the driving source, (c) there is a clear trend in the photon energy as a function of the distance to the driving source indicating that the plasma is cooler at larger distances and (d) the X-ray emission is located in a small volume which is unresolved perpendicular to the jet axis by Chandra. A comparison of our X-ray data of the L1551 IRS 5 jet both with models as well as X-ray observations of other protostellar jets shows that a base/standing shock is a likely and plausible explanation for the apparent constancy of the observed X-ray emission. Internal shocks are also consistent with the observed morphology if the supply of jet material by the ejection of new blobs is sufficiently constant. We conclude that the study of the X-ray emission of protostellar jet sources allows us to diagnose the innermost regions close to the acceleration region of the outflows.Comment: A&A accepted, 14 pages, 9 figure