José Alberto López

Universidad Nacional Autónoma de México, Ciudad de México, Mexico City, Mexico

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Publications (19)

  • Margarita Pereyra · José Alberto López · Michael G. Richer
    [Show abstract] [Hide abstract] ABSTRACT: We analyze the internal kinematics of 26 Planetary Nebulae (PNe) with low metallicity that appear to derive from progenitor stars of the lowest masses, including the halo PN population. Based upon spatially-resolved, long-slit, echelle spectroscopy drawn from the San Pedro M\'artir Kinematic Catalogue of PNe (L\'opez et al. 2012), we characterize the kinematics of these PNe measuring their global expansion velocities based upon the largest sample used to date for this purpose. We find kinematics that follow the trends observed and predicted in other studies, but also find that most of the PNe studied here tend to have expansion velocities less than 20 km/s in all of the emission lines considered. The low expansion velocities that we observe in this sample of low metallicity planetary nebulae with low mass progenitors are most likely a consequence of a weak central star wind driving the kinematics of the nebular shell. This study complements previous results (Pereyra et al. 2013, and references therein) that link the expansion velocities of the PN shells with the characteristics of the central star.
    Article · Jan 2016 · The Astronomical Journal
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    [Show abstract] [Hide abstract] ABSTRACT: We present the first detailed spatio-kinematical analysis and modelling of the planetary nebula Abell 65, which is known to host a post-common envelope, binary, central star system. As such, this object is of great interest in studying the link between nebular morphology and central star binarity. [O iii]5007 Å and Hα+[N ii]6584 Å longslit spectra and imagery of Abell 65 were obtained with the Manchester Échelle Spectrometer on the 2.1-m telescope at the San Pedro Martír Observatory (MES-SPM). Further [O iii]5007 Å longslit spectra were obtained with the Ultraviolet and Visual Échelle Spectrograph on the Very Large Telescope (VLT-UVES). These data were used to develop a spatio-kinematical model for the [O iii]5007 Å emission from Abell 65. A ‘best-fitting’ model was found by comparing synthetic spectra and images rendered from the model to the data. The model comprises an outer shell and an inner shell, with kinematical ages of 15000 ± 5000 yr kpc−1 and 8000 ± 3000 yr kpc−1, respectively. Both shells have peanut-shaped bipolar structures with symmetry axes at inclinations of (55 ± 10)° (to the line of sight) for the outer shell and (68 ± 10)° for the inner shell. The near alignment between the nebular shells and the binary orbital inclination [of (68 ± 2)°] is strongly indicative that the binary is responsible for shaping the nebula. Abell 65 is one of a growing number of planetary nebulae (seven to date, including Abell 65 itself) for which observations and modelling support the shaping influence of a central binary.
    Full-text Article · Jun 2013 · Monthly Notices of the Royal Astronomical Society
  • Margarita Pereyra · Michael G. Richer · José Alberto López
    [Show abstract] [Hide abstract] ABSTRACT: We have selected a group of 100 evolved planetary nebulae (PNe) and study their kinematics based upon spatially-resolved, long-slit, echelle spectroscopy. The data have been drawn from the San Pedro M\'artir Kinematic Catalogue of PNe (L\'opez et al. 2012). The aim is to characterize in detail the global kinematics of PNe at advanced stages of evolution with the largest sample of homogenous data used to date for this purpose. The results reveal two groups that share kinematics, morphology, and photo-ionization characteristics of the nebular shell and central star luminosities at the different late stages under study.The typical flow velocities we measure are usually larger than seen in earlier evolutionary stages, with the largest velocities occurring in objects with very weak or absent [N II] \lambda 6584 line emission, by all indications the least evolved objects in our sample. The most evolved objects expand more slowly. This apparent deceleration during the final stage of PNe evolution is predicted by hydrodynamical models, but other explanations are also possible. These results provide a template for comparison with the predictions of theoretical models.
    Article · May 2013 · The Astrophysical Journal
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    David M. Clark · Jose Alberto López · Wolfgang Steffen · Michael G. Richer
    [Show abstract] [Hide abstract] ABSTRACT: We present an extensive, long-slit, high-resolution coverage of the complex planetary nebula (PN), NGC 7026. We acquired ten spectra using the Manchester Echelle Spectrometer at San Pedro Martir Observatory in Baja California, Mexico, and each shows exquisite detail, revealing the intricate structure of this object. Incorporating these spectra into the 3-dimensional visualization and kinematic program, SHAPE, and using HST images of NGC 7026, we have produced a detailed structural and kinematic model of this PN. NGC 7026 exhibits remarkable symmetry consisting of three lobe-pairs and four sets of knots, all symmetrical about the nucleus and displaying a conical outflow. Comparing the 3-D structure of this nebula to recent, XMM-Newton X-ray observations, we investigate the extended X-ray emission in relation to the nebular structure. We find that the X-ray emission, while confined to the closed, northern lobes of this PN, shows an abrupt termination in the middle of the SE lobe, which our long slit data shows to be open. This is where the shocked, fast wind seems to be escaping the interior of the nebula and the X-ray emission rapidly cools in this region.
    Full-text Article · Oct 2012 · The Astronomical Journal
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    [Show abstract] [Hide abstract] ABSTRACT: We study the line widths in the [O III]λ5007 and Hα lines for two groups of planetary nebulae in the Milky Way bulge based upon spectroscopy obtained at the Observatorio Astronómico Nacional in the Sierra San Pedro Mártir (OAN-SPM) using the Manchester Echelle Spectrograph. The first sample includes objects early in their evolution, having high Hβ luminosities, but [O III]λ5007/Hβ < 3. The second sample comprises objects late in their evolution, with He II λ4686/Hβ>0.5. These planetary nebulae represent evolutionary phases preceding and following those of the objects studied by Richer et al. in 2008. Our sample of planetary nebulae with weak [O III]λ5007 has a line width distribution similar to that of the expansion velocities of the envelopes of asymptotic giant branch stars and shifted to systematically lower values as compared to the less evolved objects studied by Richer et al. The sample with strong He II λ4686 has a line width distribution indistinguishable from that of the more evolved objects from Richer et al., but a distribution in angular size that is systematically larger and so they are clearly more evolved. These data and those of Richer et al. form a homogeneous sample from a single Galactic population of planetary nebulae, from the earliest evolutionary stages until the cessation of nuclear burning in the central star. They confirm the long-standing predictions of hydrodynamical models of planetary nebulae, where the kinematics of the nebular shell are driven by the evolution of the central star.
    Full-text Article · May 2010 · The Astrophysical Journal
  • Guillermo García-Segura · José Alberto López · and José Franco
    [Show abstract] [Hide abstract] ABSTRACT: The Hubble Space Telescope (HST) has revealed the existence of multiple, regularly spaced, and faint concentric shells around some planetary nebulae. Here we present two- (and a half) dimensional magnetohydrodynamic numerical simulations of the effects of a solar-like magnetic cycle, with periodic polarity inversions, in the slow wind of an asymptotic giant branch (AGB) star. The stellar wind is modeled with a steady mass-loss at constant velocity. This simple version of a solar-like cycle, without mass-loss variations, is able to reproduce many properties of the observed concentric rings. The shells are formed by pressure oscillations, which drive compressions in the magnetized wind. These pressure oscillations are due to periodic variations in the field intensity. The periodicity of the shells, then, is simply a half of the magnetic cycle since each shell is formed when the magnetic pressure goes to zero during the polarity inversion. As a consequence of the steady mass-loss rate, the density of the shells scales as r-2, and their surface brightness has a steeper drop-off, as observed in the shells of NGC 6543, the best documented case of these HST rings. Deviations from sphericity can be generated by changing the strength of the magnetic field. For sufficiently strong fields, a series of symmetric and equidistant blobs are formed at the polar axis, resembling the ones observed in He 2-90. These blobs are originated by magnetic collimation within the expanding AGB wind.
    Article · Dec 2008 · The Astrophysical Journal
  • Guillermo García-Segura · José Alberto López · and José Franco
    [Show abstract] [Hide abstract] ABSTRACT: This paper explores the effects of post-asymptotic giant branch (AGB) winds driven solely by magnetic pressure from the stellar surface. It is found that winds can reach high speeds under this assumption and lead to the formation of highly collimated proto-planetary nebulae. Bipolar knotty jets with periodic features and constant velocity are well reproduced by the models. Several wind models with terminal velocities from a few tens of km s-1 up to 103 km s-1 are calculated, yielding outflows with linear momenta in the range 1036-1040 g cm s-1, and kinetic energies in the range 1042-1047 ergs. These results are in accord with recent observations of proto-planetary nebulae that have pointed out serious energy and momentum deficits if radiation pressure is considered as the only driver for these outflows. Our models strengthen the notion that the large mass loss rates of post-AGB stars, together with the short transition times from the late AGB to the planetary nebula stage, could be directly linked with the generation of strong magnetic fields during this transition stage.
    Article · Dec 2008 · The Astrophysical Journal
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    Michael G. Richer · José Alberto López · Margarita Pereyra · [...] · and Sol-Haret Báez
    [Show abstract] [Hide abstract] ABSTRACT: We present a systematic study of line widths in the [O III] λ5007 and Hα lines for a sample of 86 planetary nebulae in the Milky Way bulge based on spectroscopy obtained at the Observatorio Astronómico Nacional in the Sierra San Pedro Mártir (OAN-SPM) using the Manchester Echelle Spectrograph. The planetary nebulae were selected with the intention of simulating samples of bright extragalactic planetary nebulae. We separate the planetary nebulae into two samples containing cooler and hotter central stars, defined by the absence or presence, respectively, of the He II λ6560 line in the Hα spectra. This division separates samples of younger and more evolved planetary nebulae. The sample of planetary nebulae with hotter central stars has systematically larger line widths, larger radii, lower electron densities, and lower Hβ luminosities. The distributions of these parameters in the two samples all differ at significance levels exceeding 99%. These differences are all in agreement with the expectations from hydrodynamical models, but for the first time confirmed for a homogeneous and statistically significant sample of Galactic planetary nebulae. We interpret these differences as evidence for the acceleration of the nebular shells during the early evolution of these intrinsically bright planetary nebulae. As is the case for planetary nebulae in the Magellanic Clouds, the acceleration of the nebular shells appears to be the direct result of the evolution of the central stars.
    Full-text Article · Dec 2008 · The Astrophysical Journal
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    Wolfgang Steffen · José Alberto López
    [Show abstract] [Hide abstract] ABSTRACT: We present a powerful new tool to disentangle the 3-D geometry and kinematic structure of gaseous nebulae. The method consists of combining commercially available digital animation software to simulate the 3-D structure and expansion pattern of the nebula with a dedicated, purpose built rendering software and graphical user interface that produce the final images and long slit spectra which are compared to the real data.
    Full-text Article · Apr 2006 · Proceedings of the International Astronomical Union
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    Jose Alberto Lopez · Wolfgang Steffen
    [Show abstract] [Hide abstract] ABSTRACT: Presentamos una nueva herramienta poderosa para analizar y desenredar la geometría 3-D y la estructura cinemática de nebulosas gaseosas. El método consiste en combinar software comercial para animación digital para simular la estructura 3-D y el modo de expansión de la nebulosa junto con un software de representación gráfica de imagenes y perfiles de línea diseñado especialmente para este propósito. Las im´agenes resultantes se comparan directamente con datos reales. Presentamos resultados para las complejas nebulosas planetarias NGC 6369 y Abell 30 basados en espectros de rendija larga obtenidos en el observatorio de San Pedro Mártir.
    Full-text Article · Jan 2006 · Revista mexicana de astronomía y astrofísica
  • José Alberto López · Wolfgang Steffen
    [Show abstract] [Hide abstract] ABSTRACT: Presentamos una nueva herramienta para desenredar la geometr a 3-D y la estructura cinem atica de nebulosas gaseosas. El m etodo consiste en combinar software comercial para animaci on digital para simular la estructura 3-D y el modo de expansi on de la nebulosa junto con un software de representaci on gr a ca de imagenes y per les de l nea dise~nado especialmente para el prop osito.
    Article · Jan 2006 · Revista mexicana de astronomía y astrofísica
  • Michael G. Richer · José Alberto López
    [Show abstract] [Hide abstract] ABSTRACT: Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies
    Article · Nov 2005
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    José Alberto López · Hortensia Riesgo · Wolfgang Steffen
    [Show abstract] [Hide abstract] ABSTRACT: We present a powerful new tool to disentangle the 3-D geometry and kinematic structure of gaseous nebulae. The method consists of combining commercially available digital animation software to simulate the 3-D structure and expansion pattern of the nebula with a dedicated, purpose built rendering software that produces the final images and long slit spectra which are compared to the real data. In this contribution we show results for the complex planetary nebula NGC369 based on long slit spectra obtained at the San Pedro Mártir observatory.
    Full-text Article · Jan 2005 · Revista mexicana de astronomía y astrofísica
  • José Alberto López
    [Show abstract] [Hide abstract] ABSTRACT: It is expected that GTC will start observation in 2006. This contribution examines the impact that participating as partners with the Gran Telescopio Canario (GTC) has had so far on the Institute of Astronomy of the UNAM (IAUNAM).
    Article · Jan 2005 · Revista mexicana de astronomía y astrofísica
  • José Franco · Guillermo García Segura · José Alberto López
    [Show abstract] [Hide abstract] ABSTRACT: Este articulo propone soluciones para el origen de los vientos de estrellas del tipo post-AGB, su aceleración hasta alta velocidad, y la subsecuente formación de nebulosas proto-planetarias altamente colimadas. Se calculan varios modelos de vientos con velocidades terminales desde algunas decenas de km s-1 hasta de 103 km s-1, los cuales producen nebulosas proto-planetarias con momentos lineales en el rango 1036 -1040 g cm s-1 y energías cinéticas en el rango 1042-1047 erg. Estos resultados concuerdan con las observaciones disponibles de nebulosas proto- planetarias. En el esquema simple que se plantea, la presión magnética en la superficie estelar es la única causa de los vientos. En este estudio no se tienen en cuenta otros tipos de fuerzas, excepto la gravedad. La conclusión del estudio es que, tanto las tasas de perdida de masa de las estrellas del tipo post-AGBs como los tiempos de transición entre las fases tardías de estrellas tipo AGB y estrellas centrales de nebulosas planetarias pueden estar directamente ligadas a la producción de campo magnético en los núcleos estelares. Como ejemplo, se predicen tasas de perdida de masa tan altas como 8 x 10-5 M๏ yr-1, y tiempos de transición tan cortos como 5,000 años.
    Article · Jan 2002 · Revista mexicana de astronomía y astrofísica
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    Yolanda Gómez · José Alberto López · Luis F. Rodríguez
    [Show abstract] [Hide abstract] ABSTRACT: We present Very Large Array (VLA) continuum observations of the core of KjPn 8 made with arc second angular resolution and taken at three epochs over a period of 2.8 years. The radio appearance of the planetary nebula seems to have experienced changes, tentatively attributed to variable illumination coming from the nucleus. We also present VLA observations of atomic hydrogen toward this source, made with an angular resolution of about 40 arc sec. We detect associated emission that suggests the presence of a mass of atomic hydrogen of order 0.07 solar masses in the envelope.
    Full-text Article · Jan 2002 · Revista mexicana de astronomía y astrofísica
  • Guillermo Garcia-Segura · Jose Alberto Lopez · Jose Franco
    [Show abstract] [Hide abstract] ABSTRACT: The Hubble Space Telescope has revealed the existence of multiple, regularly spaced, and faint concentric shells around some planetary nebulae. Here we present 2(1/2)D magnetohydrodinamic numerical simulations of the effects of a solar-like magnetic cycle, with periodic polarity inversions, in the slow wind of an AGB star. The stellar wind is modeled with a steady mass-loss at constant velocity. This simple version of a solar-like cycle, without mass-loss variations, is able to reproduce many properties of the observed concentric rings. The shells are formed by pressure oscillations, which drive compressions in the magnetized wind. These pressure oscillations are due to periodic variations in the field intensity. The periodicity of the shells, then, is simply a half of the magnetic cycle since each shell is formed when the magnetic pressure goes to zero during the polarity inversion. As a consequence of the steady mass-loss rate, the density of the shells scales as $r^{-2}$, and their surface brightness has a steeper drop-off, as observed in the shells of NGC 6543, the best documented case of these HST rings. Deviations from sphericity can be generated by changing the strength of the magnetic field. For sufficiently strong fields, a series of symmetric and equisdistant blobs are formed at the polar axis, resembling the ones observed in He 2-90. These blobs are originated by magnetic collimation within the expanding AGB wind.
    Article · May 2001
  • Wolfgang Steffen · Jose Alberto Lopez · Andrew Lim
    [Show abstract] [Hide abstract] ABSTRACT: We present an alternative model for the formation of fast low-ionization emission regions (FLIERs) in planetary nebulae that is able to account for many of their attendant characteristics and circumvent the problems on the collimation/formation mechanisms found in previous studies. In this model, the section of the stellar wind flowing along the symmetry axis carries less mechanical momentum than at higher latitudes, and temporarily develops a concave or inverted shock geometry. The shocked ambient material is thus refracted towards the symmetry axis, instead of away from it, and accumulates in the concave section. The reverse is true for the outflowing stellar wind, which in the reverse shock is refracted away from the axis. It surrounds the stagnation region of the bow-shock and confines the trapped ambient gas. The latter has time to cool and is then compressed into a dense "stagnation knot" or "stagnation jet". In the presence of a variable stellar wind these features may eventually overrun the expanding nebular shell and appear as detached FLIERs. We present representative two and three-dimensional hydrodynamic simulations of the formation and early evolution of stagnation knots and jets and compare their dynamical properties with those of FLIERs in planetary nebulae. Subject Headings: hydrodynamics - ISM: jets and outflows - ISM: kinematics and dynamics - planetary nebulae: FLIERs and stagnation knots Comment: accepted for publication in The Astrophysical Journal
    Article · Apr 2001 · The Astrophysical Journal
  • Wolfgang Steffen · Jose Alberto Lopez
    [Show abstract] [Hide abstract] ABSTRACT: We propose a new model for the formation of fast, low-ionization emission regions (FLIERs) in planetary nebulae that is able to account for many of their attendant characteristics and circumvent the problems on the collimation/formation mechanisms found in previous studies. In this model, FLIERs are formed in the stagnation zone of partially collimated stellar winds with reduced momentum flow along the axis. A concave bow-shock structure is formed due to the lack of momentum flow along the axis of a midly bipolar stellar wind. The stagnation knots are formed when the shocked environment medium accumulates at the apex of the outer shell and is compressed to a dense knot in the {\em concave} section of the bow-shock. We present two-dimensional hydrodynamic simulations of the formation of a stagnation knot and compare the resultant dynamical properties with those of FLIERs in planetary nebulae.
    Article · Sep 1999