Entity

Time filter

Source Type

Puerto Vallarta, Mexico

Lagos P.,University of Porto | Telles E.,Observatorio Nacional | Nigoche-Netro A.,Institute Astronomia y Meteorologia | Carrasco E.R.,Gemini Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2012

Using GMOS-IFU spectroscopic observations of the compact Hii/blue compact dwarf galaxies Tol 0104-388 and Tol 2146-391, we study the spatial distribution of emission lines, equivalent width EW(Hβ), extinction c(Hβ), ionization ratios ([Oiii] λ5007/Hβ, [Sii] λλ6717,6731/Hα and [Nii] λ6584/Hα), kinematics and the chemical pattern (O/H, N/H and N/O) of the warm interstellar medium in these galaxies. We also investigate a possible dependence of these properties on the I(Heii λ4686)/I(Hβ) ratio and find no significant correlation between these variables. In fact, the oxygen abundances appear to be uniform in the regions where the Heii λ4686 emission line was measured. It can be interpreted in the sense that these correlations are related to global properties of the galaxies and not with small patches of the interstellar medium. Although a possible weak N/H gradient is observed in Tol 2146-391, the available data suggest that the metals from previous star formation events are well mixed and homogeneously distributed through the optical extent of these galaxies. The spatial constancy of the N/O ratio might be attributed to efficient transport and mixing of metals by starburst-driven supershells, powered by a plethora of unresolved star cluster in the inner part of the galaxies. This scenario agrees with the idea that most of the observed Heii λ4686 emission line is produced by radiative shocks, although other sources such as Wolf Rayet stars, high mass X-ray Binaries and O stars cannot be excluded. © 2012 The Authors Monthly Notices of the Royal Astronomical Society. © 2012 RAS. Source


Ramos-Larios G.,Institute Astronomia y Meteorologia | Guerrero M.A.,Institute Astrofisica Of Andalucia | Vazquez R.,National Autonomous University of Mexico | Phillips J.P.,Institute Astronomia y Meteorologia
Monthly Notices of the Royal Astronomical Society | Year: 2012

NGC6369 is a double-shell planetary nebula consisting of a bright annular inner shell with faint bipolar extensions and a filamentary envelope. We have used ground- and space-based narrow-band optical and near-infrared (near-IR) images, broad-band mid-IR images, optical long-slit echelle spectra and mid-IR spectra to investigate its physical structure. These observations indicate that the inner shell of NGC6369 can be described as a barrel-like structure shape with polar bubble-like protrusions, and reveal evidence for H 2 and strong polycyclic aromatic hydrocarbons emission from a photodissociative region (PDR) with molecular inclusions located outside the bright inner shell. High-resolution Hubble Space Telescope narrow-band images reveal an intricate excitation structure of the inner shell and a system of 'cometary' knots. The knotty appearance of the envelope, the lack of kinematical evidence for shell expansion and the apparent presence of emission from ionized material outside the PDR make us suggest that the envelope of NGC6369 is not a real shell, but a flattened structure at its equatorial regions. We report the discovery of irregular knots and blobs of diffuse emission in low-excitation and molecular line emission that are located up to 80arcsec from the central star, well outside the main nebular shells. We also show that the filaments associated to the polar protrusions have spatial extents consistent with post-shock cooling regimes, and likely represent regions of interaction of these structures with surrounding material. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS. Source


Phillips J.P.,Institute Astronomia y Meteorologia | Ramos-Larios G.,Institute Astronomia y Meteorologia | Guerrero M.A.,Institute Astrofisica Of Andalucia
Monthly Notices of the Royal Astronomical Society | Year: 2011

Although the planetary nebula NGC6781 appears to possess an elliptical morphology, its kinematic and emission characteristics are in many ways unusual, and it is possible that it may represent a bipolar source oriented close to the line of sight. We shall present deep imaging of this nebula in [Oiii]λ5007, Hα and [Nii]λ6584, and using broad-band (F555W and F814W) filters centred at λ8269 and λ5252. These were taken with the 2.56-m Nordic Optical Telescope and Hubble Space Telescope. This is combined with mid-infrared (MIR) imaging and spectroscopy acquired with the Spitzer Space Telescope (Spitzer), and near-infrared spectroscopy deriving from the Infrared Space Observatory. These reveal details of the complex [Nii] structure associated with extended shell emission, perhaps associated with highly inclined bipolar lobes. We also note the presence of narrow absorbing filaments and clumps projected against the surface of the envelope, components which may be responsible for much of the molecular emission. We point out that such clumps may be responsible for complex source structure in the MIR, and give rise to asymmetries in emission along the major axis of the source. Although most of the MIR H2v= 0-0 emission is clearly concentrated in the bright interior shell, we shall also find evidence for extended emission to the north and south, and determine rotational excitation temperatures of order ~980K. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source


Phillips J.P.,Institute Astronomia y Meteorologia | Cuesta L.C.,CSIC - National Institute of Aerospace Technology | Ramos-Larios G.,Institute Astronomia y Meteorologia
Monthly Notices of the Royal Astronomical Society | Year: 2010

NGC 7009 is a fascinating example of a high-excitation, elliptical planetary nebula (PN) containing circumnebular rings, and FLIERs and jets along the major axis. We present visual spectroscopy along multiple position angles through the nucleus, taken with the Observatorio Astronomico Nacional (Mexico); mid-infrared (MIR) spectroscopy and imaging acquired using the Infrared Space Observatory (ISO) and Spitzer Space Telescope (SST), and narrow-band imaging obtained using the Hubble Space Telescope (HST). The data show that the mid-infrared (MIR) continuum is dominated by a broad ≈100 K continuum, and a strong excess attributable to crystalline silicate emission. The primary peaks in this excess are similar to those observed in Forsterite and clino- and ortho-enstatite. The MIR images, by contrast, appear to be dominated by ionic transitions, with the 8.991 μm transition of [Ar iii] being important in the 8.0-μm band. The morphology and size of the envelope are found to vary with wavelength, with the largest dimensions occurring at 8.0 μm - a trend which is also reflected in an increase in the 8.0 μm/4.5 μm and 5.8 μm/4.5 μm ratios with distance from the nucleus. The visual spectroscopy permits us to map density and temperature throughout the shell, and confirm that the lowest values of ne are located close to the ansae, where densities appear to be of the order of 900-2600 cm-3. We provide mean line intensities for 116 transitions in six regions of the shell, and use mapping to confirm a systematic increase in excitation in the outer portions of the envelope. We finally use the ground-based spectroscopy, and ratioing of HST images to investigate the presence of shocks in the ansae and interior envelope. It is concluded that line ratios in the ansae may be partially consistent with shock excitation, although these features are primarily dominated by photoionization. We also note evidence for shock excitation at the limits of the interior elliptical shell, and for multiple bow-shock structures centred upon the ansae. The orientations of the easterly bow-shocks may have varied over time, indicating precession of the collimating engine at a rate of deg yr-1, whilst the outward splaying of the westerly 'jet' appears consistent with shock refraction modelling. We finally note that HST observations of the halo rings show them to have widths of the order of ~1-3 arcsec, and steep changes in surface brightness consistent with local shock activity. © 2010 The Authors. Journal compilation © 2010 RAS. Source


Ramos-Larios G.,Institute Astronomia y Meteorologia | Phillips J.P.,Institute Astronomia y Meteorologia | Cuesta L.C.,CSIC - National Institute of Aerospace Technology
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present the imaging and spectroscopy of NGC40 acquired using the Spitzer Space Telescope and the Infrared Space Observatory. These are used to investigate the nature of emission from the central nebular shell, from the nebular halo and from the associated circumnebular rings. It is pointed out that a variety of mechanisms may contribute to the mid-infrared (MIR) fluxes, and there is evidence for a cool dust continuum, strong ionic transitions and appreciable emission by polycyclic aromatic hydrocarbons (PAHs). Prior observations at shorter wavelengths also indicate the presence of warmer grains and the possible contribution of H2 transitions. Two of these components (warm dust with TGR∼ 500-620K and PAH emission bands) appear capable, in combination, of explaining the infrared colours of the rings and halo, although the flux ratios are also consistent with shock-excited H2v= 0-0 emission. It is noted that whilst the surface brightness of the rings is greater in the longer wave (5.8- and 8.0-μm) photometric channels, their fractional fluxes (when compared to the halo) are greater at 3.6 and 4.5μm, a trend which is similar to those observed in other planetary nebulae. It is also apparent that the relative intensities of the rings are greater than is observed for the Hα+[Nii] transitions. It is suggested that an apparent jet-like structure to the north-east of the halo represents one of the many emission spokes that permeate the shell and which are observed for the first time in these MIR results. The spokes are likely to be caused by the percolation of UV photons through a clumpy interior shell, whilst the jet-like feature is enhanced due to locally elevated electron densities, a result of interaction between NGC40 and the interstellar medium. It is finally noted that the presence of the PAH, 21- and 30-μm spectral features testifies to appreciable C/O ratios within the main nebular shell. Such a result is consistent with abundance determinations using collisionally excited lines, but not with those determined using optical recombination lines. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS. Source

Discover hidden collaborations