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Tigran Yu. Magakian,
Elena H. Nikogossian,
Tigran Movsessian,
Alexei Moiseev,
Colin Aspin,
Chris J. Davis,
Tae-Soo Pyo,
Tigran Khanzadyan,
Dirk Froebrich, Michael D. Smith,
Gerald H. Moriarty-Schieven,
Tracy L. Beck
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ABSTRACT: A photometric and spectral study of the variable star V2494 Cyg in the L 1003 dark cloud is presented. The brightness of the star, formerly known as HH 381 IRS, increased by 2.5 mag in R (probably in the 1980s) and since then has remained nearly constant. Since the brightness increase, V2494 Cyg has illuminated a bipolar cometary nebula. The stellar spectrum has several features typical of the FU Ori type, plus it exhibits very strong Halpha and forbidden emission lines with high-velocity components. These emission lines
originate in the HH jet near the star. The kinematic age of the jet is consistent with it forming at the time of the outburst leading to the luminosity increase. V2494 Cyg also produces a rather extended outflow; it is
the first known FUor with both an observed outburst and a parsec-sized HH flow. The nebula, illuminated by V2494 Cyg, possesses similar morphological and spectral characteristics to Hubble's Variable Nebula (R Monocerotis/NGC 2261).
Monthly Notices of the Royal Astronomical Society 04/2013; · 4.90 Impact Factor
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Tigran Yu. Magakian,
Elena H. Nikogossian,
Colin Aspin,
Tae-Soo Pyo,
Tigran Khanzadyan,
Tigran Movsessian, Michael D. Smith,
Sharon Mitchison,
Chris J. Davis,
Tracy L. Beck,
and Gerald H. Moriarty-Schieven
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ABSTRACT: We study the population of Herbig-Haro (HH) flows and jets in an area of Cygnus OB7 designated the Braid Nebula star formation region. This complex forms part of the L 1003 dark cloud, and hosts two FU Orionis (FUor)-like objects as well as several other active young stars. To trace outflow activity and to relate both known and newly discovered flows to young star hosts we intercompare new, deep, narrowband Hα and [S II] optical images taken on the Subaru 8 m Telescope on Mauna Kea, Hawaii. Our images show that there is considerable outflow and jet activity in this region suggesting the presence of an extensive young star population. We confirm that both of the FUor-like objects drive extensive HH flows and document further members of the flows in both objects. The L 1003 star formation complex is a highly kinematically active region with young stars in several different stages of evolution. We trace collimated outflows from numerous young stars although the origin of some HH objects remains elusive.
The Astronomical Journal 02/2010; 139(3):969. · 4.03 Impact Factor
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IAU General Assembly; 08/2009
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Colin Aspin,
Tracy L. Beck,
Tae-Soo Pyo,
Chris J. Davis,
G. M. Schieven,
Tigran Khanzadyan,
Tigran Magakian,
Tigran Movsessian,
Elena G. NIkogossian,
Sharon Mitchison, Michael D. Smith
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ABSTRACT: We present 1.4 to 2.5 um integral field spectroscopy of 16 stars in the Braid Nebula star formation region in Cygnus OB7. These data forms one aspect of a large-scale multi-wavelength survey aimed at determining an unbiased estimate of the number, mass distribution, and evolutionary state of the young stars within this one square degree area of the previously poorly studied Lynds 1003 molecular cloud. Our new spectroscopic data, when combined with 2MASS near-IR photometry, provide evidence of membership of many of these objects in the regions pre-main sequence population. We discuss both the characteristics of the young stars found in the region and the level of star forming activity present.
11/2008;
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ABSTRACT: The properties of bipolar outflows depend on the structure in the environment as well as the nature of the jet. To help distinguish between the two, we investigate here the properties pertaining to the ambient medium. We execute axisymmetric hydrodynamic simulations, injecting continuous atomic jets into molecular media with density gradients (protostellar cores) and density discontinuities (thick swept-up sheets). We determine the distribution of outflowing mass with radial velocity (the mass spectrum) to quantify our approach and to compare to observationally determined values. We uncover a sequence from clump entrainment in the flanks to bow shock sweeping as the density profile steepens. We also find that the dense, highly supersonic outflows remain collimated but can become turbulent after passing through a shell. The mass spectra vary substantially in time, especially at radial speeds exceeding 15 km s−1. The mass spectra also vary according to the conditions: both envelope-type density distributions and the passage through dense sheets generate considerably steeper mass spectra than a uniform medium. The simulations suggest that observed outflows penetrate highly non-uniform media.
Monthly Notices of the Royal Astronomical Society 04/2008; 386(4):2091 - 2100. · 4.90 Impact Factor
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ABSTRACT: Powerful outflows are driven from protostars. Since their first discovery in atomic emission lines at optical wavelengths by Herbig and Haro in the 1950s, they have been explored in different parts of the electromagnetic spectrum. In particular, warm, processed and accelerated molecular components have been uncovered in the infrared. This has led to new insights and controversies, as reviewed by Reipurth & Bally (2001).
The outflows are collimated and bipolar, containing distinct regions termed Herbig-Haro (HH) objects. These HH object are the sites of strong internal shock dissipation and points of impact with the interstellar medium. Hence, a determination of the properties of HH objects helps us to constrain the dynamics and physics of both protostellar winds and star-forming environments.
Here we present an investigation of region surrounding the recently discovered (Movsessian et al. 2006) FUOri-type outburst star- Braid which is located in the close proximity of CygnusOB7 complex. In this contribution we present the early results from the 12 degree survey conducted in the near-infrared (2.12 μm) outflow-tracing line of H21-0 S(1).
JENAM 2007 - EAS Symposium 3: Violent Phenomena in Young Stars, Yerevan, Armenia; 08/2007
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ABSTRACT: Molecular outflows and the jets which may drive them can be expected to display signatures associated with rotation if they are the channels through which angular momentum is extracted from material accreting on to protostars. Here, we determine some basic signatures of rapidly rotating flows through three-dimensional numerical simulations of hydrodynamic jets with molecular cooling and chemistry. We find that these rotating jets generate a broad advancing interface which is unstable and develops into a large swarm of small bow features. In comparison to precessing jets, there is no stagnation point along the axis. The greater the rotation rate, the greater the instability. On the other hand, velocity signatures are only significant close to the jet inlet since jet expansion rapidly reduces the rotation speed. We present predictions for atomic, H2 and CO submillimetre images and spectroscopy including velocity channel maps and position–velocity diagrams. We also include simulated images corresponding to Spitzer IRAC band images and CO emission, relevant for APEX and eventual ALMA observations. We conclude that protostellar jets often show signs of slow precession but only a few sources display properties which could indicate jet rotation.
Monthly Notices of the Royal Astronomical Society 06/2007; 378(2):691 - 700. · 4.90 Impact Factor
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ABSTRACT: Jets of gas released from young stars excavate cavities and drive bipolar outflows. The outflow properties may be related to the speed of the jets. To test this, we study the propagation of supersonic overdense jets through axisymmetric hydrodynamic simulations with radiative cooling and chemistry, building on previous studies by injecting molecular and atomic jets with a wide range of speeds, between 50 and 300 km s−1, into both molecular and atomic media. We show that the high collimation of outflows driven by molecular jets holds for all jet speeds. At the higher speeds, we find that the jet Mach number is the critical parameter which determines the shape of the cavity and the cavity is filled with atomic gas. However, at low speeds the jet material is the key factor with atomic jets producing much wider cavities, whereas molecular jets produce narrow cool molecular sheaths. A Mach disc is associated with the leading edge of the atomic simulations, whereas oblique shocks which refocus the jet are found in molecular flows. We also examine the mass spectra (distribution of mass with radial velocity), generally finding quite shallow relationships for all jet speeds (i.e the index is typically 1–2). Steep molecular mass spectra are, however, associated with the atomic-jet–molecular-medium combination. We conclude that the properties of bipolar outflows possess signatures related to the jet speed but are probably more sensitive to other factors.
Monthly Notices of the Royal Astronomical Society 08/2006; 371(3):1448 - 1458. · 4.90 Impact Factor
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ABSTRACT: ABSTRACTA roughly constant temperature over a wide range of densities is maintained in molecular clouds through radiative heating and cooling. An isothermal equation of state is therefore frequently employed in molecular cloud simulations. However, the dynamical processes in molecular clouds include shock waves, expansion waves, cooling induced collapse and baroclinic vorticity, all incompatible with the assumption of a purely isothermal flow. Here, we incorporate an energy equation including all the important heating and cooling rates and a simple chemical network into simulations of 3D, hydrodynamic, decaying turbulence. This allows us to test the accuracy of the isothermal assumption by directly comparing a model run with the modified energy equation to an isothermal model. We compute an extreme case in which the initial turbulence is sufficiently strong to dissociate much of the gas and alter the specific heat ratio. The molecules then reform as the turbulence weakens. We track the true specific heat ratio as well as its effective value. We analyse power spectra, vorticity and shock structures, and discuss scaling laws for decaying turbulence. We derive some limitations to the isothermal approximation for simulations of the interstellar medium using simple projection techniques. Overall, even given the extreme conditions, we find that an isothermal flow provides an adequate physical and observational description of many properties. The main exceptions revealed here concern behaviour directly related to the high-temperature zones behind the shock waves.
Monthly Notices of the Royal Astronomical Society 05/2006; 368(2):943 - 958. · 4.90 Impact Factor
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ABSTRACT: We have performed a 1 square degree 1.2mm dust continuum survey in the rho Oph molecular cloud. 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 5000AU 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. We report a new low-mass Class 0 object and its CO outflow. Comment: accepted for publication in Astronomy and Astrophysics. Full .ps version available at http://www.ifa.hawaii.edu/users/stanke/preprints.html
Astronomy and Astrophysics 11/2005; 447(2):609-622. · 4.59 Impact Factor
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ABSTRACT: We present an optical and near-infrared investigation of a new FUor-like outburst recently discovered in an active star formation region surrounding RNO 127, located in the Cygnus OB7 dark cloud complex [1]. In this region, several new cometary nebulae, Herbig-Haro objects, and outflows/jets were found [1]. The detection of a new near-IR reflection nebula in this region immediately brought our attention to the possibility of its creation by a FUor outburst. This nebula, designated “Braid”, has already been described in detail in [1]. Here, we bring together all available evidence on the nature of the optical and near-IR nebulosity and the underlying young star with the aim of determining whether the associated young star has undergone a FUor-like outburst.
Protostars and Planets V. 10/2005;
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CAHA Colloquium 2005, MPIA, Heidelberg, Germany; 04/2005
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ABSTRACT: The bandpasses for Spitzer images contain numerous molecular hydrogen emission lines. With the additional complication of the non-uniform spectral response, it is necessary to calculate model images in order to analyse observations of molecular outflows. We employ three-dimensional hydrodynamic simulations of a range of dense supersonic molecular jets, including various degrees of velocity pulsation and precession, to demonstrate how the observed structure depends on the band. Features in band 1, which is dominated by emission from vibrational levels, are even more concentrated than in K-band images. In contrast, bands 2–4 are dominated by rotational lines and bow shock wings appear extended. Especially in band 4, broken cavity walls can be detectable. An initial comparison with Spitzer data is made.
Monthly Notices of the Royal Astronomical Society 02/2005; 357(4):1370 - 1376. · 4.90 Impact Factor
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ABSTRACT: We present hydrodynamic simulations of molecular outflows driven by jets with a long period of precession, motivated by observations of arc-like features and S-symmetry in outflows associated with young stars. We simulate images of not only H2 vibrational and CO rotational emission lines, but also of atomic emission. The density cross-section displays a jaw-like cavity, independent of precession rate. In molecular hydrogen, however, we find ordered chains of bow shocks and meandering streamers which contrast with the chaotic structure produced by jets in rapid precession. A feature particularly dominant in atomic emission is a stagnant point in the flow that remains near the inlet and alters shape and brightness as the jet skims by. Under the present conditions, slow jet precession yields a relatively high fraction of mass accelerated to high speeds, as also attested to in simulated CO line profiles. Many outflow structures, characterized by HH 222 (continuous ribbon), HH 240 (asymmetric chains of bow shocks) and RNO 43N (protruding cavities), are probably related to the slow-precession model.
Monthly Notices of the Royal Astronomical Society 01/2005; 357(2):579 - 589. · 4.90 Impact Factor
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ABSTRACT: We search for dense cores and the molecular outflows which accompany stellar birth in the rho Ophiuchi cloud L1688 through two unbiased wide-field surveys. A solution to the problem of how to avoid the dissolution of brown dwarf binaries is suggested: binaries forming in the widely scattered low-mass cores are not susceptible to disruption since the region is dynamically relaxed. We also find weak H_2 outflows which may be driven by proto-brown-dwarfs. The dense cores are detected through continuum emission from associated dust grains at 1.2 mm. Covering over 1 square degree, we detect many previously unknown sources, ranging from extended cores to those harbouring Class II young stars. We analyse the mass and spatial distributions. The core mass function resembles the stellar initial mass function, both within the tightly-packed clumps as well as within the less-crowded surroundings. The cores display a hierarchical spatial distribution with no preferred separation scale length. The orientations of the major axes of cores are consistent with an isotropic distribution whereas the orientations of core pairs possess a preferential direction on all separation scales, consistent with the filamentary cloud appearance. Our near-infrared survey for molecular hydrogen emission covers 35 arcmin × 35 arcmin. We detect several new H_2 flows but the total number of detected outflows is low and is consistent with the paucity of Class 0 and Class 1 sources in the molecular cloud. Most of the candidate driving sources are deeply embedded in dense cores. A very young outflow arises from the newly discovered Class 0 source MMS 126. Flow directions are generally NE-SW, perpendicular to the above preferred direction. The apparent extents of molecular flows are related to either the widths or the separation between cloud filaments.
Memorie della Societa Astronomica Italiana. 01/2005; 76:247.
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ABSTRACT: Here we present results from simulations of turbulence in star forming environments obtained by coupling three-dimensional
hydrodynamical models with appropriate chemical processes. We investigate regimes of decaying high-speed molecular turbulence.
Here we analyse PDFs of density for the volume, mass, molecular mass and the energy distribution over the range of scales.
We compare our results to those previously obtained for isothermal turbulence and suggest possible explanations.
Astrophysics and Space Science 06/2004; 292(1):69-75. · 1.69 Impact Factor
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ABSTRACT: We show that supersonic turbulence accelerates the transition of an atomic cloud into a molecular cloud, quantified here through a demo model and 3D numerical simulations which explicitly include atomic-molecular chemistry. Specific sites where amplified formation may be detectable are suggested.
Astrophysics and Space Science 04/2004; 289:333-336. · 1.69 Impact Factor
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ABSTRACT: The structure of protostellar jets and outflows is determined by both the nature of the driving protostar and the enveloping environment. To deduce protostellar evolution from the outflow evolution, we need to distinguish between these influences. Here, we employ three-dimensional numerical simulations to investigate how outflow properties evolve as the jet direction precesses. We limit this study to wide-angled fast precession of molecular jets through half-angles of 5°, 10° and 20°. We employ a code that includes molecular hydrogen cooling, dissociation and reformation as well as other cooling functions and chemistry appropriate for the high densities assumed. The jet bores out an annulus of increasing radius but constant width, with strong molecular cooling acting to reduce the drag on the impact region. Nevertheless, the expansion decelerates the outflow advance sufficiently that we predict highly precessing molecular jets can reach 1 pc in size between 30 000 and 100 000 yr. Even on the relatively short (500 yr) time-scale of the simulations, the leading edge of the annulus disrupts into numerous bow shocks and some linear shock structures.Images, position–velocity diagrams and channel maps for H2 and CO transitions are analysed. Testable predictions are made for the upcoming generation of high-resolution submillimetre and far-infrared telescopes. The distributions of both mass and CO emission-line flux with radial velocity are predicted and compared to observations. A clear dependence of the slope of the mass–velocity (or luminosity–velocity) distribution on the precession angle is found, which may help us to interpret the variety of reported line profiles.We compute the evolution of radiative emission relative to the mean jet power for these simulations and previous molecular jet simulations in this series. The H2 1–0 S(1) emission is roughly a factor of 0.001 of the mean power in the dense jets and 0.01 in the light jets, consistent with the kinetic energy of the light jets being more efficiently radiated.
Monthly Notices of the Royal Astronomical Society 01/2004; 347(4):1097 - 1112. · 4.90 Impact Factor
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ABSTRACT: The band passes for Spitzer images contain numerous molecular hydrogen emis-sion lines. With the additional complication of the non-uniform spectral response, it is necessary to calculate model images in order to analyse observations of molecular outflows. We employ three dimensional hydrodynamic simulations of a range of dense supersonic molecular jets, including various degrees of velocity pulsation and preces-sion, to demonstrate how the observed structure depends on the band. Features in Band 1, which is dominated by emission from vibrational levels, are even more con-centrated than in K-band images. In contrast, Bands 2–4 are dominated by rotational lines and bow shock wings appear extended and, especially in Band 4, broken cavity walls can be detectable. An initial comparison with Spitzer data is made.
Mon. Not. R. Astron. Soc. 01/2004; 000:1-7.
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Star Formation Workshop at the Armagh Observatory, Armagh Observatory, N. Ireland, UK; 06/2003
