Can you imagine a bunch of ghosts surfing in the Orion Nebula? In Ensenada there are a few places where one can always see surfers in their black wetsuits waiting for a wave to catch. Recently, I started to imagine rather more transparent, whitish ghosts riding whispy waves on a glowing reddish ocean of gas and dust illuminated by four bright stars arranged in a Trapezium. Don´t worry, I am not on any weird drugs…it´s just the discovery of 3D Kelvin-Helmholtz instabilities in the Orion Nebula that triggered my imagination … Continue reading
1.3. Today’s new entry:
Galaxy Emission Line Classification Using Three-dimensional Line Ratio Diagrams
Vogt, F.P.A., Dopita, M.A., Kewley, L.J., Sutherland, R.S., Scharwächter, J., Basurah, H.M., Ali, A., Amer, M.A.
Abstract: Two-dimensional (2D) line ratio diagnostic diagrams have become a key tool in understanding the excitation mechanisms of galaxies. The curves used to separate the different regions — H II-like or excited by an active galactic nucleus (AGN) — have been refined over time but the core technique has not evolved significantly. However, the classification of galaxies based on their emission line ratios really is a multi-dimensional problem. Here we exploit recent software developments to explore the potential of three-dimensional (3D) line ratio diagnostic diagrams. We introduce the ZQE diagrams, which are a specific set of 3D diagrams that separate the oxygen abundance and the ionization parameter of H II region-like spectra and also enable us to probe the excitation mechanism of the gas. By examining these new 3D spaces interactively, we define the ZE diagnostics, a new set of 2D diagnostics that can provide the metallicity of objects excited by hot young stars and that cleanly separate H II region-like objects from the different classes of AGNs. We show that these ZE diagnostics are consistent with the key log [N II]/Halpha versus log [O III]/Hbeta diagnostic currently used by the community. They also have the advantage of attaching a probability that a given object belongs to one class or the other. Finally, we discuss briefly why ZQE diagrams can provide a new way to differentiate and study the different classes of AGNs in anticipation of a dedicated follow-up study.
Journal: The Astrophysical Journal, in press
URL of preprint: http://arxiv.org/abs/1406.5186
Comments: Interactive 3D HTML model is here:
Submitted by: Frédéric Vogt
Amateur astronomy has been transformed over the last few decades with the advent of sensitive imaging detectors that are accessible to amateur astronomers of regular financial means. More so, when they put their efforts together, observatories come to being that rival many professional ones. So we often see deep photographs of the sky that are truly amazing in beauty and detail. Of course, even discoveries are made not only of comets and asteroids, but even new nebulae or supernovae are sometimes found visually or with CCD technology.
But where are the amateur theoretical astrophysicists? Continue reading
3D printing is coming … to astrophysics. Also known as additive manufacturing, 3D printing even at home is becoming a serious past-time for tinkerers. Companies that make or use such devices are starting up like mushrooms on an autumn meadow.
“What does that have to do with astrophysics?”, you might ask.
1.2. Today’s new entry:
ALMA data suggest the presence of spiral structure in the inner wind of CW Leonis
L. Decin, A. M.S. Richards, D. Neufeld, W. Steffen, G. Melnick, R. Lombaert
Context: Evolved low-mass stars lose a significant fraction of their mass through stellar winds. While the overall morphology of the stellar wind structure during the asymptotic giant branch (AGB) phase is thought to be roughly spherically symmetric, the morphology changes dramatically during the post-AGB and planetary nebula phase, during which bipolar and multi-polar structures are often observed.
Aims: We aim to study the inner wind structure of the closest well-known AGB star CW Leo. Different diagnostics probing different geometrical scales have implied a non-homogeneous mass-loss process for this star: dust clumps are observed at milli-arcsec scale, a bipolar structure is seen at arcsecond-scale, and multi-concentric shells are detected beyond 1”.
Methods: We present the first ALMA Cycle 0 band 9 data around 650 GHz (450 mum) tracing the inner wind of CW Leo. The full-resolution data have a spatial resolution of 0.̋42 × 0.̋24, allowing us to study the morpho-kinematical structure of CW Leo within ~6”.
Results: We have detected 25 molecular emission lines in four spectral windows. The emission of all but one line is spatially resolved. The dust and molecular lines are centered around the continuum peak position, which is assumed to be dominated by stellar emission. The dust emission has an asymmetric distribution with a central peak flux density of ~2 Jy. The molecular emission lines trace different regions in the wind acceleration region and imply that the wind velocity increases rapidly from about 5 R*, almost reaching the terminal velocity at ~11 R*. The images prove that vibrational lines are excited close to the stellar surface and that SiO is a parent molecule. The channel maps for the brighter lines show a complex structure; specifically, for the 13CO J = 6-5 line, different arcs are detected within the first few arcseconds. The curved structure in the position-velocity (PV) map of the 13CO J = 6-5 line can be explained by a spiral structure in the inner wind of CW Leo, probably induced by a binary companion. From modelling the ALMA data, we deduce that the potential orbital axis for the binary system lies at a position angle of ~10-20° to the north-east and that the spiral structure is seen almost edge-on. We infer an orbital period of 55 yr and a binary separation of 25 au (or ~8.2 R*). We tentatively estimate that the companion is an unevolved low-mass main-sequence star.
Conclusions: A scenario of a binary-induced spiral shell can explain the correlated structure seen in the ALMA PV images of CW Leo. Moreover, this scenario can also explain many other observational signatures seen at different spatial scales and in different wavelength regions, such as the bipolar structure and the almost concentric shells. ALMA data hence for the first time provide the crucial kinematical link between the dust clumps seen at milli-arcsecond scale and the almost concentric arcs seen at arcsecond scale.
Journal: Astronomy & Astrophysics, in press.
URL of preprint: http://adsabs.harvard.edu/abs/2015A%26A…574A…5D
Submitted by: Leen Decin (University of Leuven, Belgium)
Beziér curves on the sun? Excuse me?
Beziér curves are great; they are little wonders of Computer Graphics…or rather Mathematics. One can make very nice smooth structures with them by manipulating just a few points in space. In 3D Computer Graphics they, and some of their relatives, are used all over the place. But in solar physics? Usually I look at scientific papers on the sun only because of the amazing pictures or movies that often accompany them, because the complexity of the physics seems so frightening…increasing my respect to solar research closer and closer to infinity.
However, recently I came accross a paper with the title “A Rapid, Manual Method to Map Coronal-Loop Structures of an Active Region Using Cubic Bézier Curves and Its Applications to Misalignment Angle Analysis“. The paper had my attention: Manual application of Beziér curves on the sun? I needed to know what this was about…