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Post Info TOPIC: IRAS16293-2422
Blobrana


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Posts: 131433
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IRAS 16293-2422B
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Title: ALMA 690 GHz observations of IRAS 16293-2422B: Infall in a highly optically-thick disk
Authors: Luis A. Zapata (CRyA-UNAM), Laurent Loinard (CRyA-UNAM), Luis F. Rodriguez (CRyA-UNAM), Vicente Hernandez-Hernandez (CRyA-UNAM), Satoko Takahashi (ASIAA), Alfonso Trejo (ASIAA), Berengere Parise (MPIfR)

We present sensitive, high angular resolution (~ 0.2 arcsec) submillimetre continuum and line observations of IRAS 16293-2422B made with the Atacama Large Millimetre/Submillimetre Array (ALMA). The 0.45 mm continuum observations reveal a single and very compact source associated with IRAS 16293-2422B. This submillimetre source has a deconvolved angular size of about 400 milli-arcseconds (50 AU), and does not show any inner structure inside of this diameter. The H^{13}CN, HC^{15}N, and CH_{3}OH line emission regions are about twice as large as the continuum emission and reveal a pronounced inner depression or "hole" with a size comparable to that estimated for the submillimetre continuum. We suggest that the presence of this inner depression and the fact that we do not see inner structure (or a flat structure) in the continuum is produced by very optically thick dust located in the innermost parts of IRAS 16293-2422B. All three lines also show pronounced inverse P-Cygni profiles with infall and dispersion velocities larger than those recently reported from observations at lower frequencies, suggesting that we are detecting faster, and more turbulent gas located closer to the central object. Finally, we report a small east-west velocity gradient in IRAS 16293-2422B that suggests that its disk plane is likely located very close to the plane of the sky.

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Blobrana


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Posts: 131433
Date:
IRAS 16293-2422
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Title: ALMA CO J=6-5 observations of IRAS16293-2422: Shocks and entrainment
Authors: L. E. Kristensen, P. D. Klaassen, J. C. Mottram, M. Schmalzl, M. R. Hogerheijde

Observations of higher-excited transitions of abundant molecules such as CO are important for determining where energy in the form of shocks is fed back into the parental envelope of forming stars. The nearby prototypical and protobinary low-mass hot core, IRAS16293-2422 (I16293) is ideal for such a study. The source was targeted with ALMA for science verification purposes in band 9, which includes CO J=6-5 (E_up/k_B ~ 116 K), at an unprecedented spatial resolution (~0.2", 25 AU). I16293 itself is composed of two sources, A and B, with a projected distance of 5". CO J=6-5 emission is detected throughout the region, particularly in small, arcsecond-sized hotspots, where the outflow interacts with the envelope. The observations only recover a fraction of the emission in the line wings when compared to data from single-dish telescopes, with a higher fraction of emission recovered at higher velocities. The very high angular resolution of these new data reveal that a bow shock from source A coincides, in the plane of the sky, with the position of source B. Source B, on the other hand, does not show current outflow activity. In this region, outflow entrainment takes place over large spatial scales, >~ 100 AU, and in small discrete knots. This unique dataset shows that the combination of a high-temperature tracer (e.g., CO J=6-5) and very high angular resolution observations is crucial for interpreting the structure of the warm inner environment of low-mass protostars.

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Blobrana


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RE: IRAS16293-2422
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Title: ALMA and VLA observations of the outflows in IRAS 16293-2422
Authors: Laurent Loinard (CRyA-UNAM, MPIfR), Luis A. Zapata (CRyA-UNAM), Luis F. Rodriguez (CRyA-UNAM), Gerardo Pech (CRyA-UNAM), Claire J. Chandler (NRAO), Crystal L. Brogan (NRAO), David J. Wilner (CfA), Paul T.P. Ho (CfA, ASIAA), Berengere Parise (MPIfR), Lee H. Hartmann (U. Michigan), Zhu Zhaohuan (Princeton), Satoko Takahashi (ASIAA), Alfonso Trejo (ASIAA)

We present ALMA and VLA observations of the molecular and ionised gas at 0.1-0.3 arcsec resolution in the Class 0 protostellar system IRAS 16293-2422. These data clarify the origins of the protostellar outflows from the deeply embedded sources in this complex region. Source A2 is confirmed to be at the origin of the well known large scale north-east--south-west flow. The most recent VLA observations reveal a new ejection from that protostar, demonstrating that it drives an episodic jet. The central compact part of the other known large scale flow in the system, oriented roughly east-west, is well delineated by the CO(6-5) emission imaged with ALMA and is confirmed to be driven from within component A. Finally, a one-sided blueshifted bubble-like outflow structure is detected here for the first time from source B to the north-west of the system. Its very short dynamical timescale (~ 200 yr), low velocity, and moderate collimation support the idea that source B is the youngest object in the system, and possibly one of the youngest protostars known.

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Blobrana


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Posts: 131433
Date:
IRAS 16293-2422
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Title: The First ALMA view of IRAS 16293-2422: Direct detection of infall onto source B and high-resolution kinematics of source A 
Authors: Jaime E. Pineda (1,2), Anaëlle J. Maury (1), Gary A. Fuller (2), Leonardo Testi (1,3), Diego García-Appadoo (4,5), Alison B. Peck (5,6), Eric Villard (5), Stuartt A. Corder (6), Tim A. van Kempen (5,7), Jean L. Turner (8), Kengo Tachihara (5,9), William Dent (5) ((1) European Southern Observatory (ESO), Garching, Germany, (2) UK ARC Node, Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester, UK, (3) INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy, (4) European Southern Observatory, Vitacura, Santiago, Chile, (5) Joint ALMA Observatory, Vitacura, Santiago, Chile, (6) North American ALMA Science Center, National Radio Astronomy Observatory, Charlottesville, VA, USA, (7) Leiden Observatory, Leiden University, Leiden, The Netherlands, (8) Department of Physics and Astronomy, UCLA, Los Angeles, CA, USA, (9) National Astronomical Observatory of Japan, Chile Observatory, Tokyo, Japan) 

Aims: In this paper, we focus on the kinematical properties of a proto-binary to study the infall and rotation of gas towards its two protostellar components.
Methods: We present ALMA Science Verification observations with high-spectral resolution of IRAS 16293-2422 at 220.2 GHz. The wealth of molecular lines in this source and the very high spectral resolution offered by ALMA allow us to study the gas kinematics with unprecedented detail. 
Results: We present the first detection of an inverse P-Cygni profile towards source B in the three brightest lines. The line profiles are fitted with a simple two-layer model to derive an infall rate of 4.5x10^-5 solar masses/yr. This infall detection would rule-out the previously suggested possibility of source B being a T Tauri star. A position velocity diagram for source A shows evidence for rotation with an axis close to the line-of-sight. 

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Blobrana


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RE: IRAS16293-2422
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Title: A study of deuterated water in the low-mass protostar IRAS16293-2422
Authors: Audrey Coutens, Charlotte Vastel, Emmanuel Caux, Cecilia Ceccarelli, Sandrine Bottinelli, Laurent Wiesenfeld, Alexandre Faure, Yohann Scribano, Claudine Kahane

Our aim is to determine precisely the abundance distribution of HDO towards the low-mass protostar IRAS16293-2422 and learn more about the water formation mechanisms by the determination of the HDO/H2O abundance ratio. A spectral survey of the source IRAS16293-2422 has been carried out in the framework of the CHESS Herschel Key program with the HIFI instrument, allowing the detection of numerous HDO lines. Other transitions were previously observed with ground-based telescopes in the framework of TIMASSS. The spherical Monte Carlo radiative transfer code RATRAN has been used to reproduce the observed line profiles of HDO assuming an abundance jump, corresponding to the sublimation of the molecules trapped on the icy grain mantles in the hot corino. To determine the H2O abundance throughout the envelope, a similar study has been applied to the H2-18O observed lines, as the H2O main isotope lines are contaminated by the outflows. We derive an inner HDO abundance of 1.7e-7 and an outer HDO abundance of 8e-11. To reproduce the HDO absorption lines, it is necessary to add an absorbing layer in front of the envelope. It may correspond to a water-rich layer created by the photodesorption of the ices at the edges of the molecular cloud. The HDO/H2O ratio is ~1.4-5.8% in the hot corino whereas it is ~0.2-2.2% in the outer envelope. It is estimated at ~4.8% in the added absorbing layer. Although it is clearly higher than the cosmic D/H abundance, the HDO/H2O ratio remains lower than the D/H ratio derived for other deuterated molecules observed in the same source. The similar ratios derived in the hot corino and in the added absorbing layer suggests that water formed before the gravitational collapse of the protostar, contrary to formaldehyde and methanol which formed later once the CO molecules have depleted on the grains.

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Blobrana


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Title: The solar type protostar IRAS16293-2422: new constraints on the physical structure
Authors: Nicolas Crimier, Cecilia Ceccarelli, Sebastien Maret, Sandrine Bottinelli, Emmanuel Caux, Claudine Kahane, Dariusz C. Lis, Johan Olofsson

Context: The low mass protostar IRAS16293-2422 is a prototype Class 0 source with respect to the studies of the chemical structure during the initial phases of life of Solar type stars. Aims: In order to derive an accurate chemical structure, a precise determination of the source physical structure is required. The scope of the present work is the derivation of the structure of IRAS16293-2422. Methods: We have re-analysed all available continuum data (single dish and interferometric, from millimetre to MIR) to derive accurate density and dust temperature profiles. Using ISO observations of water, we have also reconstructed the gas temperature profile. Results: Our analysis shows that the envelope surrounding IRAS16293-2422 is well described by the Shu "inside-out" collapsing envelope model or a single power-law density profile with index equal to 1.8. In contrast to some previous studies, our analysis does not show evidence of a large (>/- 800 AU in diameter) cavity. Conclusions: Although IRAS16293-2422 is a multiple system composed by two or three objects, our reconstruction will be useful to derive the chemical structure of the large cold envelope surrounding these objects and the warm component, treated here as a single source, from single-dish observations of molecular emission.

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Blobrana


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In the solar system that probably will form around this young star, the innermost planets will orbit in one direction and the outer planets will orbit in the opposite direction.

The scientists studied the star-forming clouds by analysing radio waves emitted at specific, known frequencies by molecules within the clouds. Because the molecules emit radio waves at specific frequencies, shifts in those frequencies caused by motions (called Doppler Shift) can be measured, revealing the direction in which the gas is moving relative to Earth.

The newest VLA observations of the region showed the motion of silicon monoxide (SiO) molecules, which emit radio waves at about 43 GigaHertz (GHz). When the astronomers compared their new VLA measurements of the motion of SiO molecules close to the young star with earlier measurements of other molecules farther away from the protostar, they realized the two were orbiting the star in opposite directions.

Though this is the first time such a phenomenon has been seen in a disk around a young star,

"Similar structures and dynamics commonly occur on small and large scales throughout the Universe. Thus, it is not surprising to find counter-rotation in a protostellar disk since the phenomenon has been previously reported in the disks of galaxies" - Jan M. Hollis, NASA Goddard Space Flight Centre.

Source

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Blobrana


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Astronomers using the National Science Foundation’s Very Large Array radio telescope have discovered that a newborn star has two disks of material rotating in opposite directions.

"This is the first time anyone has seen anything like this, and it means that the process of forming planets from such disks is more complex than we previously expected" - Anthony Remijan, National Radio Astronomy Observatory.

It had been thought that collapsing clouds of gas and dust would rotate in the same direction as the star; and that the planets formed from that disk would rotate in the same direction too.
Though, the phenomenon had already been seen in the disks of galaxies

"The solar system that likely will be formed around this star will include planets orbiting in different directions, unlike our own solar system in which all the planets orbit the Sun in the same direction" - Jan M. Hollis, study co-leader, NASA Goddard Space Flight Centre.

IRAS 16293-2422 is a low-mass star forming region located in the  Ophiuchus cloud complex at a heliocentric distance of 160 pc.


Position2000): RA = 16h32m22s.875, Dec = -24o28'32''.48

The star was discovered within a large, star-forming region where swirling clouds to rotate in different directions. the counter-rotating protostellar accretion disk has enough material to form counter rotating planets...

"We think this system may have gotten material from two clouds instead of one, and the two were rotating in opposite directions" - Anthony Remijan.

The results will be detailed in the April 1 edition of the Astrophysical Journal.

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