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Star formation in the Vela Molecular Clouds: A new protostar powering a bipolar jet
We have performed a detailed study of the star-forming region associatedwith the IRAS source 08448-4343 in the cloud D of the Vela MolecularRidge. Our investigation covers a wide spectral range from the near IR,through the thermal IR to the mm-band exploiting both imaging andspectroscopic facilities in each spectral regime. A picture emerges of adust structure which hosts a near IR cluster and multiplewell-collimated H2 jets; these jets originate from different sourceslying in a compact region at the cluster centre. The peak of the 1.2 mmmap does not coincide with the IRAS peak, thus tracing a less evolvedand denser region with a colder dust with respect to that traced byIRAS. This view is also confirmed by the observations of CS transitionsfrom J=2-1 to J=7-6. The mm peak can be associated with the position ofa red object, already proposed in previous studies as the driving sourceof the main jet in the field. This jet, extended along more than 0.3 pc,is composed of individual knots whose radial velocities decrease withincreasing distance from the central source, which is resolved into atleast six 2 μm peaks. The reddest and coldest of these peaks is wellaligned with the inner knots of the jet. The spectral energydistribution of the central source resembles that of an intermediateluminosity, Class I protostar, whose youth is discussed in terms of theefficiency of the energy transfer into the jet.
| Physical and kinematical properties of a newly discovered star cluster and its associated jet in the Vela Molecular Clouds
The star forming region associated with IRAS 08211-4158 and located inthe Vela Molecular Ridge (VMR) has been investigated with low (R ≈600) and high resolution (R ≈ 9000) near infrared spectroscopy (1-2.5μm) together with narrow band ([Fe II] and H2) and broadband (H, K, L, M) imaging. The photometric results allow us to identifyfor the first time a young cluster with the less evolved star lyingtoward its center. Our results confirm that the most massive stars foundin the clusters of the VMR do not form before the low mass ones. Inparticular, the only bipolar jet detected across the investigated fieldis driven by the most massive object which lacks an optical counterpart.Such a jet is composed of individual knots showing several H2and [Fe II] emission lines indicative of a coexistence of differentshocks responsible for their excitation. Physical parameters of theemitting gas such as electron density, extinction and temperature havebeen derived from the low resolution spectroscopy. Some knots arealready thermalized, while other present a stratification of temperatureup to values of 5000 K. Through high resolution spectroscopy the [Fe II]lines profile for the majority of the knots can be resolved in a doublepeaked structure which is consistent with bow shock model predictions.Moreover, the radial velocity component is determined for differentknots. Finally, by comparing [Fe II] images taken in different epochs,we have been able to derive the proper motion for some knots, hence toevaluate their total velocity (˜300 km s-1), thedynamical age and the jet inclination with respect to the plane of thesky.Based on observations collected at the European Southern Observatory,Paranal and La Silla, Chile (65.I-0150, 66.C-0158, 68.C-0020).Table 2 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/141Tables 3-6 are only available in electronic form athttp://www.edpsciences.org
| Near-infrared and optical emission-line structure of the Keyhole Nebula in NGC 3372
Narrow-band infrared and optical images of the Keyhole Nebula in NGC3372 reveal which structures are caused by extinction, and show theunderlying morphology of photoionized and shock-excited gas. Dark cloudsconspire with ionized gas to create the apparent keyhole shape, which isprominent at blue wavelengths and less apparent in the infrared. ThePaβ/Hα line ratio shows the spatial distribution offoreground extinction. The wavelength dependence of this extinctionindicates a reddening law with R~4.8, different from the normalinterstellar medium. This confirms previous estimates of reddeningtoward the Carina Nebula determined from stellar photometry, and revealsthat the anomalous extinction is patchy and within the HII region. Themorphology of the ionized gas is different from the extinction clouds;it shows an edge-on ionization front running NE to SW, with alimb-brightened indentation that forms the upper outline of the keyholeshape. A fast polar wind from η Carinae may have punctured theionization front, since the indentation is directly along a projectionof the polar axis of the star. This is supported by the morphology ofshock-excited gas revealed by a high [SII]/Hα ratio.High-excitation gas emitting [OIII] and HeI has a smoother distribution.Molecular clumps in the region are also discussed.
| A Deep Near-Infrared Survey of the Chamaeleon I Dark Cloud Core
We have carried out a deep near-infrared imaging survey to search forlow-mass young stellar objects (YSOs) in the densest star-forming coreof the Chamaeleon I dark cloud. Our observations cover an area of 30arcmin2, including an early B9 star (HD 97300) and an outflowsource (HM 23). The 10 σ limiting magnitudes are 18.1, 17.0, and16.2 mag at J, H, and K, respectively, which is sensitive enough toprovide a census of the embedded stellar population down to substellarobjects in the cloud. Source classification is performed based on thenear-infrared (NIR) color-color diagram. Many of the YSO candidates withNIR excesses are more than 7 mag fainter than typical T Tauri stars inthe same cloud. Some of them are even fainter than the known browndwarfs in the Pleiades. The luminosities of newly identified YSOcandidates and the recent evolutionary models for very low mass objectssuggest that they appear to be substellar, if their typical age isassumed to be similar to that of classic T Tauri stars or, namely, 1 Myrwith an upper limit of 10 Myr. Therefore it is highly likely that youngbrown dwarfs form in this molecular cloud core. The J-band luminosityfunction of the YSO candidates does not appear to turn over down to thecompleteness limit. In the Chamaeleon I dark cloud core, stars form in aclustered mode characterized by both a high star formation efficiencyand high stellar density such as in the ρ Oph core.
| The MSSSO near-infrared photometric system
The JHKL photometric system currently used at the Mount Stromlo andSiding Spring Observatories (MSSSO) is described via an extensive listof standard-star values and filter transmission curves. At JHK thissystem is identical to the Mount Stromlo Observatory (MSO) systemdefined by Jones and Hyland (1982), except for small zero-pointdifferences which we impose here. Transformations are given between theMSSSO system and several near-infrared photometric systems in use inother observatories and the homogenized JHKL system proposed by Besselland Brett (1988).
| JHKLM standard stars in the ESO system
A list of 199 standard stars suitable for the ESO standard photometricsystem at JHKLM is given. Faint stars (although brighter than K = 7.7)to be used on larger telescopes are included. This list is based on ananalysis of all infrared photometric observations carried out at LaSilla from 1979 until 1989 inclusive. The accuracy of the data (about0.02 mag. at J, H, K, L, and M) is similar to the one achieved at SAAOand CTIO. Comparisons with these systems, as well as with the AAO andMSSO systems, are made: it is shown that the ESO system is very close tothe other ones, with the exception of CTIOs.
| Southern JHKL standards
The basis for the current SAAO standard photometric system at JHKL isgiven. This depends on an extensive investigation involving 230 starsdistributed around the sky. The accuracy is estimated at + or - 0.02 magfor J, H and K and + or - 0.05 mag for L.
| Comparison of the Mt. Stromlo/AAO and Caltech/Tololo infrared photometric systems
The transformations between the Mt. Stromlo/AAO and the Caltech/Tololoinfrared photometric systems have been determined by means ofobservations of 21 stars with both systems. A small zero-pointdifference but no color term is found at K; color terms are found forthe J - K, J - H, and H - K colors. All scatter in the transformationscan be attributed to the random errors in the observations.
| Infrared standard stars
The results of an observational program aimed at setting up a network offaint near-infrared standards of sufficient accuracy are reported. Thenetwork covers both northern and southern hemispheres and includesstandards red enough to provide at least a limited check on colortransformations. The standards are set up at J (1.2 micron), H (1.6micron), K (2.2 microns), and L (3.5 microns), and their H2O and COmolecular absorption indices are determined. The problem of colortransformations between observatories is discussed briefly. Allmagnitudes presented are transformed to the natural system defined bythe CIT observations.
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