6.5 Today´s new entry:
ALMA high spatial resolution observations of the dense molecular region of NGC 6302
M. Santander-García, V. Bujarrabal, J. Alcolea, A. Castro-Carrizo, C. Sánchez Contreras, G. Quintana-Lacaci, R.L.M. Corradi, and R. Neri
Context. The mechanism behind the shaping of bipolar planetary nebulae is still poorly understood. It is becoming increasingly clear that the main agents must operate at their innermost regions, where a significant equatorial density enhancement should be present and related to the collimation of light and jet launching from the central star preferentially towards the polar directions. Most of the material in this equatorial condensation must be lost during the asymptotic giant branch as stellar wind and later released from the surface of dust grains to the gas phase in molecular form. Accurately tracing the molecule-rich regions of these objects can give valuable insight into the ejection mechanisms themselves. Aims. We investigate the physical conditions, structure and velocity field of the dense molecular region of the planetary nebula NGC 6302 by means of ALMA band 7 interferometric maps. Methods. The high spatial resolution of the 12CO and 13CO J=3−2 ALMA data allows for an analysis of the geometry of the ejecta in unprecedented detail. We built a spatio-kinematical model of the molecular region with the software SHAPE and performed detailed non-LTE calculations of excitation and radiative transfer with the shapemol plug-in. Results. We find that the molecular region consists of a massive ring out of which a system of fragments of lobe walls emerge and enclose the base of the lobes visible in the optical. The general properties of this region are in agreement with previous works, although the much greater spatial resolution of the data allows for a very detailed description. We confirm that the mass of the molecular region is 0.1 M. Additionally, we report a previously undetected component at the nebular equator, an inner, younger ring inclined ∼60◦ with respect to the main ring, showing a characteristic radius of 7.5×1016 cm, a mass of 2.7×10−3 M, and a counterpart in optical images of the nebula. This inner ring has the same kinematical age as the northwest optical lobes, implying it was ejected approximately at the same time, hundreds of years after the ejection of the bulk of the molecular ring-like region. We discuss a sequence of events leading to the formation of the molecular and optical nebulae, and briefly speculate on the origin of this intriguing inner ring
Journal: Astronomy & Astrophysics
URL of preprint: http://arxiv.org/pdf/1609.06455.pdf
Submitted by: Miguel Santander-García
6.4 Today´s new entry:
Modelling the structure and kinematics of the Firework nebula: The nature of the GK Persei nova shell and its jet-like feature
E. Harvey, M.P. Redman, P. Boumis, S. Akras
Abstract: Aims. The shaping mechanisms of old nova remnants are probes for several important and unexplained processes, such as dust formation and the structure of evolved star nebulae. To gain a more complete understanding of the dynamics of the GK Per (1901) remnant, an examination of symmetry of the nova shell is explored, followed by a kinematical analysis of the previously detected jet-like feature in the context of the surrounding fossil planetary nebula.
Methods. Faint-object high-resolution echelle spectroscopic observations and imaging were undertaken covering the knots which comprise the nova shell and the surrounding nebulosity. New imaging from the Aristarchos telescope in Greece and long-slit spectra from the Manchester Echelle Spectrometer instrument at the San Pedro Martir observatory in Mexico were obtained, supplemented ´ with archival observations from several other optical telescopes. Position-velocity arrays are produced of the shell, and also individual knots, and are then used for morpho-kinematic modelling with the shape code. The overall structure of the old knotty nova shell of GK Per and the planetary nebula in which it is embedded is then analysed.
Results. Evidence is found for the interaction of knots with each other and with a wind component, most likely the periodic fast wind emanating from the central binary system. We find that a cylindrical shell with a lower velocity polar structure gives the best model fit to the spectroscopy and imaging. We show in this work that the previously seen jet-like feature is of low velocity.
Conclusions. The individual knots have irregular tail shapes; we propose here that they emanate from episodic winds from ongoing dwarf nova outbursts by the central system. The nova shell is cylindrical, not spherical, and the symmetry axis relates to the inclination of the central binary system. Furthermore, the cylinder axis is aligned with the long axis of the bipolar planetary nebula in which it is embedded. Thus, the central binary system is responsible for the bipolarity of the planetary nebula and the cylindrical nova shell. The gradual planetary nebula ejecta versus sudden nova ejecta is the reason for the different degrees of bipolarity. We propose that the ‘jet’ feature is an illuminated lobe of the fossil planetary nebula that surrounds the nova shell.
Comments: Accepted: 29 August 2016, 14 pages, 14 figures, 5 tables
Journal: Astronomy & Astrophysics
URL of preprint: http://arxiv.org/pdf/1609.01363v1.pdf
Submitted by: Eamonn Harvey
6.3 Today´s new entry:
Finding faint HI structure in and around galaxies: scraping the barrel
Authors: D. Punzo, J.M. van der Hulst, J.B.T.M. Roerdink
Abstract: Soon to be operational HI survey instruments such as APERTIF and ASKAP will produce large datasets. These surveys will provide information about the HI in and around hundreds of galaxies with a typical signal-to-noise ratio of ∼ 10 in the inner regions and ∼ 1 in the outer regions. In addition, such surveys will make it possible to probe faint HI structures, typically located in the vicinity of galaxies, such as extra-planar-gas, tails and filaments. These structures are crucial for understanding galaxy evolution, particularly when they are studied in relation to the local environment. Our aim is to find optimized kernels for the discovery of faint and morphologically complex HI structures. Therefore, using HI data from a variety of galaxies, we explore state-of-the-art filtering algorithms. We show that the intensity-driven gradient filter, due to its adaptive characteristics, is the optimal choice. In fact, this filter requires only minimal tuning of the input parameters to enhance the signal-to-noise ratio of faint components. In addition, it does not degrade the resolution of the high signal-to-noise component of a source. The filtering process must be fast and be embedded in an interactive visualization tool in order to support fast inspection of a large number of sources. To achieve such interactive exploration, we implemented a multi-core CPU (OpenMP) and a GPU (OpenGL) version of this filter in a 3D visualization environment (𝚂𝚕𝚒𝚌𝚎𝚛𝙰𝚜𝚝𝚛𝚘).
Comments: accepted on 13/09/2016, 17 pages, 9 figures, 4 tables
Journal: Astronomy and Computing
URL of preprint: http://arxiv.org/abs/1609.03782
Submitted by: Davide Punzo