Tigran Khanzadyan

An unbiased search for the signatures of protostars in the ρ Ophiuchi molecular cloud , II. Millimetre continuum observations

The dense cores which conceive and cradle young stars can be explored through continuum emission from associated dust grains. We have performed a wide field survey for dust sources at 1.2 millimetres in the ρ Ophiuchi molecular cloud, covering more than 1 square degree in an unbiased fashion. We detect a number of previously unknown sources, ranging from extended cores over compact, starless cores to envelopes surrounding young stellar objects of Class 0, Class I, and Class II type. We analyse the mass distribution, spatial distribution and the potential equilibrium of the cores. For the inner regions, the survey results are consistent with the findings of previous narrower surveys. The core mass function resembles the stellar initial mass function, with the core mass function shifted by a factor of two to higher masses (for the chosen opacity and temperature). In addition, we find no statistical variation in the core mass function between the crowded inner regions and those in more isolated fields except for the absence of the most massive cores in the extended cloud. The inner region contains compacter cores. This is interpreted as due to a medium of higher mean pressure although strong pressure variations are evident in each region. The cores display a hierarchical spatial distribution with no preferred separation scale length. However, the frequency distribution of nearest neighbours displays two peaks, one of which at 5000 AU can be the result of core fragmentation. The orientations of the major axes of cores are consistent with an isotropic distribution. In contrast, the relative orientations of core pairs are preferentially in the NW-SE direction on all separation scales. These results are consistent with core production and evolution in a turbulent environment. Finally, we report the discovery of a new, low-mass Class 0 object candidate and its CO outflow.

The Earliest Phases of Star Formation (EPoS): a Herschel key project - The thermal structure of low-mass molecular cloud cores

Context. The temperature and density structure of molecular cloud cores are the most important physical quantities that determine the course of the protostellar collapse and the properties of the stars they form. Nevertheless, density profiles often rely either on the simplifying assumption of isothermality or on observationally poorly constrained model temperature profiles. The instruments of the Herschel satellite provide us for the first time with both the spectral coverage and the spatial resolution that is needed to directly measure the dust temperature structure of nearby molecular cloud cores. Aims. With the aim of better constraining the initial physical conditions in molecular cloud cores at the onset of protostellar collapse, in particular of measuring their temperature structure, we initiated the guaranteed time key project (GTKP) The Earliest Phases of Star Formation (EPoS) with the Herschel satellite. This paper gives an overview of the low-mass sources in the EPoS project, the Herschel and complementary ground-based observations, our analysis method, and the initial results of the survey. Methods. We study the thermal dust emission of 12 previously well-characterized, isolated, nearby globules using FIR and submm continuum maps at up to eight wavelengths between 100 mu m and 1.2 mm. Our sample contains both globules with starless cores and embedded protostars at different early evolutionary stages. The dust emission maps are used to extract spatially resolved SEDs, which are then fit independently with modified blackbody curves to obtain line-of-sight-averaged dust temperature and column density maps. Results. We find that the thermal structure of all globules (mean mass 7 M-circle dot) is dominated by external heating from the interstellar radiation field and moderate shielding by thin extended halos. All globules have warm outer envelopes (14-20 K) and colder dense interiors (8-12 K) with column densities of a few 10(22) cm(-2). The protostars embedded in some of the globules raise the local temperature of the dense cores only within radii out to about 5000 AU, but do not significantly affect the overall thermal balance of the globules. Five out of the six starless cores in the sample are gravitationally bound and approximately thermally stabilized. The starless core in CB 244 is found to be supercritical and is speculated to be on the verge of collapse. For the first time, we can now also include externally heated starless cores in the L-smm/L-bol vs. T-bol diagram and find that T-bol <25 K seems to be a robust criterion to distinguish starless from protostellar cores, including those that only have an embedded very low-luminosity object.

UWISH2 -- The UKIRT Widefield Infrared Survey for H2

The definitive version can be found at : http://onlinelibrary.wiley.com/ Copyright Wiley-Blackwell

An outbursting protostar of the FU Orionis type in the Cygnus OB7 molecular cloud

Context. To follow the early evolution of stars we need to understand how young stars accrete and eject mass. It is generally assumed that the FU Orionis phenomenon is related to the variations in the disk accretion, but many questions remain still open, in particular because of the rarity of FU Ori type stars. Aims. We explore here the characteristics of the outburst and of the environment of one new object, discovered recently in the active star formation region containing RNO 127, within the Cygnus OB7 dark cloud complex. Methods. We present an extensive optical and near-infrared study of a new candidate of FU Orionis object, including its direct imaging, spectroscopy and scanning Fabry-Perot interferometry. Results. The source, associated with the variable reflection nebula, underwent prodigious outburst. The “Braid” nebula, which appeared in 2000, as is indicated by its name, consists of two intertwined features, illuminated by the outburst. Subsequent NIR observations revealed the bright source, which was not visible on 2MASS images, and its estimated brightening was more than 4 mag. Optical and infrared spectral data show features, which are necessary for the system to be referred to as a FUor object. The bipolar optical flow directed by the axis of nebula also was found. Various estimates give the November/December 1999 as the most probable date for the eruption.

A near-infrared study of the bow shocks within the L1634 protostellar outflow

The L1634 bright-rimmed globule contains an intriguing arrangement of shock structures: two series of aligned molecular shock waves associated with the Herbig-Haro flows HH 240 and HH 241. We present near-infrared spectroscopy and narrow-band imaging in the (1, 0) S(1) and (2, 1) S(1) emission lines of molecular hydrogen. These observations yield the spatial distributions of both the molecular excitation and velocity, which demonstrate distinct properties for the individual bow shocks. Bow shock models are applied, varying the shock physics, geometry, speed, density and magnetic field properties to fit two prominent bow shocks. The models predict that both bows move at 60 ◦ to the plane of the sky. High magnetic fields and low molecular fractions are implied. The advancing compact bow HH 240C is interpreted as a J-type bow (frozen-in magnetic field) with the flanks in transition to C-type (field diffusion). It is a paraboloidal bow of speed ∼42 km s −1 entering a medium of quite high density (2 × 10 4 cm −3 ). The following bow HH 240A is faster despite a lower excitation, moving through a lower density medium. We find a C-type bow shock model to fit all the data for HH 240A. The favoured bow models are then tested comprehensively against published H2 emission line fluxes and CO spectroscopy. We conclude that, while the CO emission originates from cloud gas directly set in motion, the H2 emission is generated from shocks sweeping through an outflow. Also considering optical data, we arrive at a global outflow model involving episodic slow-precessing twin jets.

An optical and near-infrared exploration of the star formation region in Cygnus surrounding RNO 127

We investigate a relatively unstudied star formation region in Cygnus centered on RNO 127, finding numerous Herbig-Haro flows, many identified in optical (SII), Hα, and near-infrared H2 tracers of shock waves. Several protostars and young stars are thus located, including one conspicuously brightened object, which illuminates a variable reflection nebula. In total, the coordinates of 17 optical HH knots and jets, 4 associated cometary nebulae and 3 NIR objects are given. Individual structures are discussed including a central complex which has the characteristics of superposed HH flows. This star-forming cloud is not isolated but is part of a much larger region of distributed star formation, including HH 380 and HH 381.

An unbiased search for the signatures of protostars in the

We present an unbiased search for molecular hydrogen emission in the L1688 cloud within the ρ u2009Ophiuchi molecular cloud complex. Our near-infrared survey covers a connected region of extent 35´u2009

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Ophiuchi A molecular cloud - I. Near-infrared observations

u200935´. We detect several new H 2 flows but the total number of detected outflows is low and is consistent with the paucity of Classu20090 and Classu20091 sources in the molecular cloud. From the spatial distribution, their collimation and the individual shapes of the bow shocks, we suggest possible candidates for the outflow sources. Most of the candidate driving sources are deeply embedded in dense cores of the molecular cloud. Axa0very young outflow arises from the newly discovered Classxa00 source MMSxa0126. Two major outflows in the NE–SW direction arise from the YLWxa015 and YLWxa016 Classxa0I sources. Three additional outflows, which both extend over several arcminutes, arise from the Classxa0I sources YLWxa031 and YLWxa052. Flow directions are generally NE–SW, perpendicular to the elongation directions of the cloud filaments. The apparent extents of molecular flows are related to either the widths of cloud filaments or to the separation between filaments. The estimated jet power needed to continuously drive and excite the detected portions of the shocked H 2 xa0outflows lies in the range 0.02-0.2u2009

A wide-field near-infrared H2 2.122 μm line survey of the Braid Nebula star formation region in Cygnus OB7

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