Institute Astronomia y Meteorologia

Mexico

Institute Astronomia y Meteorologia

Mexico
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Marquez-Lugo R.A.,Institute Astronomia y Meteorologia | Ramos-Larios G.,Institute Astronomia y Meteorologia | Guerrero M.A.,Institute Astrofisica Of Andalucia | Vazquez R.,National Autonomous University of Mexico
Monthly Notices of the Royal Astronomical Society | Year: 2013

Mid-infrared (IR) observations of planetary nebulae (PNe) have revealed diffuse emission associated with their main nebular shells and outer envelopes or haloes. The interpretation of this emission is uncertain because the broad-band mid-IR images may include contributions of different components. In particular, the Spitzer Infrared Array Camera 8 μm images, that best reveal these nebular features, can include contributions not only of H2 lines, but also those of ionic species, polycyclic aromatic hydrocarbon features and thermal dust continuum emission. To investigate the nature of the emission detected in mid-IR observations of a sample of 10 PNe, we have obtained narrow-band near-IR H2 λ2.122 μm and optical [N II] λ6584Å images. The comparison between these images confirms that a significant fraction of the emission detected in the IRAC 8 μm images can be attributed to molecular hydrogen, thus confirming the utility of thesemid-IR images to investigate the molecular component of PNe. We have also detected H2 emission from PNe whose physical structure cannot be described as bipolar, but rather as ellipsoidal or barrel like. These detections suggest that, asmore sensitive observations of PNe in the H2 λ2.122 line are acquired, the detection of H2 emission is not exclusive of bipolar PNe, although objects with this morphology are still the brightest H2 emitters. Finally, we remark that the bright H2 emission from the equatorial ring of a bipolar PN does not arise from a photodissociation region shielded from the ultraviolet stellar radiation by the ring itself, but from dense knots and clumps embedded within the ionized material of the ring. © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


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.


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.


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.


Phillips J.P.,Institute Astronomia y Meteorologia | Ramos-Larios G.,Institute Astronomia y Meteorologia
Monthly Notices of the Royal Astronomical Society | Year: 2010

We have investigated the mid-infrared (MIR) and visual structures of seven bipolar planetary nebulae (BPNe), using imaging and spectroscopy acquired using the Spitzer Space Telescope (SST), and the Observatorio Astronomico Nacional in Mexico. The results show that the sources are more extended towards longer MIR wavelengths, as well as having higher levels of surface brightness in the 5.8- and 8.0-μm bands. It is also noted that the 5.8 μm/4.5 μm and 8.0 μm/4.5 μm flux ratios increase with increasing distance from the nuclei of the sources. All of these latter trends may be attributable to emission by polycyclic aromatic hydrocarbons (PAHs) and/or warm dust continua within circumnebular photodissociation regions (PDRs). A corresponding decrease in the flux ratios 8.0 μm/5.8 μm may, by contrast, arise due to changes in the properties of the PAH emitting grains. We note evidence for 8.0 μm ring-like structures in the envelope of NGC 2346, located in a region beyond the minor axis limits of the ionized envelope. An analysis of the inner two rings shows that whilst they have higher surface brightnesses at longer MIR wavelengths, they are relatively stronger (compared to underlying emission) at 3.6 and 4.5 μm. There is also evidence for point-reflection symmetry along the major axis of the outflow. Finally, the fall-off in surface brightness along the nebular minor axis suggests that progenitor mass-loss rates were more-or-less constant. NGC 6905 shows evidence for a centrally located and unresolved MIR emission excess. We show that whilst flux ratios are inconsistent with stellar and ionized gas components of emission, the emission can be explained in terms of shock-excited H2, or grain continuum and PAH emission bands. We provide the deepest image so far published of the outer visual structure of NGC 6445, and compare these results with Spitzer imaging at 8.0 μm. The distributions are quite distinct, and may indicate collimation of the outer ionized emission by a cylindrical PDR. We finally note that the MIR colours of the lobes and nuclei of the sources are radically different. It is also shown that 3.6-μm emission in BPNe differs from that for the generality of planetary nebulae. We discuss various mechanisms which may contribute to these differences of colour. © 2010 The Authors. Journal compilation © 2010 RAS.


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.


Marquez-Lugo R.A.,Institute Astronomia y Meteorologia | Phillips J.P.,Institute Astronomia y Meteorologia
Monthly Notices of the Royal Astronomical Society | Year: 2010

We provide mid-infrared (MIR) imaging, photometry and profiles for the Galactic supernova remnants (SNRs) G001.0-00.1, G355.9-02.5, G355.6-00.0 and W28 based upon data deriving for the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). All of the sources show evidence for interaction with the interstellar medium (ISM), leading to curved frontal structures and apparent voids in the ISM. An analysis of the spectral energy distributions (SEDs) of Class I young stellar objects (YSOs) within the north-westerly interaction region of W28, and of the density of stars within the borders of the SNR, suggests that many of them may have been triggered by the SN event. 2D radiative transfer modelling permits us to constrain the physical parameters of the sources. It is also noted that the location of Class I YSOs about the perimeter of G001.0-00.1, and close to frontal arcs associated with SNR G355.9-02.5, suggests that star formation may have been triggered by these SNRs as well. Finally, it is found that the MIR colours of the frontal structures appear consistent with shock excitation of the v= 0 → 0 transitions of H2, although it is conceivable that emission by polycyclic aromatic hydrocarbons (PAHs) may also play a role. Where the latter mechanism is relevant, it is possible that emission derives from the shattering of larger grains in frontal regions, leading to increased volume densities of PAH carrying grains. © 2010 The Authors. Journal compilation © 2010 RAS.


Ramos-Larios G.,Institute Astronomia y Meteorologia | Phillips J.P.,Institute Astronomia y Meteorologia
Monthly Notices of the Royal Astronomical Society | Year: 2012

We investigate the structure of the planetary nebula NGC 2371 using [Oiii] λ5007 imaging taken with the Jacobus Kapteyn 1.0 m telescope, and [Nii] λ6584, [Oiii] λ5007 and Hα results acquired with the Hubble Space Telescope. These are supplemented with archival mid-infrared (MIR) observations taken with the Spitzer Space Telescope. We note the presence of off-axis low-ionization spokes along a position angle of 65°, and associated collars of enhanced [Oiii] emission. The spokes appear to consist of dense condensations having low-excitation tails, possibly arising due to ultraviolet shadowing and/or ram-pressure stripping of material. Line ratios imply that most of the emission arises through photoionization, and is unlikely to derive from post-shock cooling regions. An analysis of these features in the MIR suggests that they may also be associated with high levels of emission from polycyclic aromatic hydrocarbons (PAHs), together with various permitted and forbidden line transitions. Such high levels of PAH emission, where they are confirmed, may develop as a result of preferentially enhanced far-ultraviolet pumping of the molecules, or shattering of larger grains within local shocks. Although H 2 emission may also contribute to these trends, it is argued that shock-excited transitions would lead to markedly differing results. We finally note that thin filaments and ridges of [Oiii] emission may indicate the presence of shock activity at the limits of the interior envelope, as well as at various positions within the shell itself. We also note that radially increasing fluxes at 3.6, 5.8 and 8.0 μm, relative to the emission at 4.5 μm, may arise due to enhanced PAH emission in external photodissociative regions. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


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.


Phillips J.P.,Institute Astronomia y Meteorologia | Marquez-Lugo R.A.,Institute Astronomia y Meteorologia
Monthly Notices of the Royal Astronomical Society | Year: 2011

We have obtained 24 μm imaging, profiles and fluxes for 224 planetary nebulae (PNe) lying within the limits of the Galactic survey undertaken with the Multiband Imaging Photometer for Spitzer (MIPSGAL). It is noted that most of the PNe having extended 24 μm emission also possess circular morphologies, suggesting that the emission derives from cool grains located within the Asymptotic Giant Branch (AGB) mass-loss regimes. Certain of these haloes are found to have a surface brightness fall-off which may be consistent with secularly invariant mass loss within the PNe progenitors. By contrast, the 8.0 μm envelopes are detected out to smaller distances from the nuclei, and have a steeper rate of surface brightness fall-off; a phenomenon which may arise from changes in the excitation of polycyclic aromatic hydrocarbons (PAHs) within external photo-dissociation regimes (PDRs). Our 24 μm fluxes are compared to those in previously published studies, and this appears to indicate that many of the prior fluxes have been underestimated; a disparity may imply that previous aperture sizes were too small. We have also combined our 24 μm fluxes with measures at shorter mid-infrared (MIR) wavelengths, taken with the Infrared Array Camera (IRAC). These are used to investigate the positioning of PNe within the IRAC-MIPSGAL colour planes. The [8.0]-[24] and [5.8]-[24] colours are found to be large, and extend over the respective ranges 3.4-8.7 mag, and 5.4-10.3 mag; indices which are only explainable where a broad range of mechanisms contribute to the fluxes, including PAH bands, cool dust continua and a variety of ionic transitions. These and other components also affect the morphologies of the sources, and lead to wavelength-dependent changes in the widths of the profiles. © 2010 The Authors. Journal compilation © 2010 RAS.

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