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## X-ray studies of supernova remnants: A different view of supernova explosions

Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.79%
The unprecedented spatial and spectral resolutions of Chandra have revolutionized our view of the X-ray emission from supernova remnants. The excellent datasets accumulated on young, ejecta-dominated objects like Cas A or Tycho present a unique opportunity to study at the same time the chemical and physical structure of the explosion debris and the characteristics of the circumstellar medium sculpted by the progenitor before the explosion. Supernova remnants can thus put strong constraints on fundamental aspects of both supernova explosion physics and stellar evolution scenarios for supernova progenitors. This view of the supernova phenomenon is completely independent of, and complementary to, the study of distant extragalactic supernovae at optical wavelengths. The calibration of these two techniques has recently become possible thanks to the detection and spectroscopic follow-up of supernova light echoes. In this paper, I review the most relevant results on supernova remnants obtained during the first decade of Chandra and the impact that these results have had on open issues in supernova research.

## Gamma-ray production in supernova remnants

Gaisser, T.; Protheroe, R.; Stanev, T.
Fonte: IOP Publishing Publicador: IOP Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
66.66%
The bulk of cosmic rays of up to about 100 TeV are thought to be accelerated by the first-order Fermi mechanism at supernova shocks, producing a power-law spectrum. Both electrons and protons should be accelerated, but their ratio on acceleration is not well known. Recently, the EGRET instrument on the Compton Gamma Ray Observatory has observed supernova remnants IC 443 and γ Cygni at GeV energies. On the assumption that the observed γ-rays are produced by accelerated particles in the remnants (rather than, for example, from a central compact object), we model the contributions from pion production, bremsstrahlung, and inverse Compton scattering on the cosmic microwave, diffuse galactic, and locally produced radiation fields. In the case of the same spectral index for both electrons and nuclei and a cutoff at 80 TeV, we find that a spectral index of accelerated particles that is close to 2.4 and a ratio of electrons to protons in the range 0.2-0.3 give a good fit to the observed spectra. For lower cutoff energies, flatter spectra are possible. We also investigate the case in which the electron spectrum is steeper than that of nuclei. We discuss the implications of our results for observations at air shower energies, and for the propagation of cosmic rays.; T. K. Gaisser...

## The cold, the dense and the energetic : cosmic ray bombardment of molecular cores near supernova remnants.

Maxted, Nigel Ivan
Relevância na Pesquisa
56.76%
One of the oldest unsolved mysteries in astrophysics is the origin of cosmic rays, particles that travel at speeds close to the speed of light. A plausible theory to explain the acceleration of these particles is shock-acceleration in the expanding shells of supernova remnants (SNRs) within our galaxy. In this thesis, the interstellar medium towards supernova remnants that display indicators of particle acceleration, ie., gamma-ray emission, are investigated. More specifically, results from mm-wavelength molecular gas surveys towards two gamma-ray emitting SNRs, RXJ1713.7−3946 and CTB37A are presented. Chapter 1 summarises astrophysics at high energies, including what cosmic rays are, how they may be accelerated, their connection to gamma-ray emission and how gamma-ray astronomy is performed from the ground. On the opposite (low-energy) side of the energy spectrum, Chapter 2 describes some of the theory of single dish radio astronomy, which allows us to probe molecular environments. By tuning the receiver to home-in on particular molecular species, different interstellar environoments can be targeted. Some specific molecular species are outlined in Chapter 3, before utilising these species in following chapters. The bulk of chapters 4 and 5 are composed of published articles presenting interstellar gas observations and investigation. Chapter 4 is an in-depth analysis of the molecular environment towards the supernova remnant RXJ1713.7−3946 (in 3 articles) using several independent molecular gas tracers...

## Efectos de ondas de choque en el medio interestelar; Effects of shock waves on the interstellar medium

Petriella, Alberto
Tipo: info:eu-repo/semantics/doctoralThesis; tesis doctoral; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Relevância na Pesquisa
46.82%
En esta Tesis, se estudian desde el punto de vista observacional algunos de los efectos que producen sobre el medio interestelar las ondas de choque asociadas con estrellas de gran masa en diferentes etapas de su vida. Se investiga la interacción de regiones HII, burbujas interestelares y remanentes de supernova con el entorno y se analiza la actividad de formación estelar en sus alrededores con el objetivo de establecer si son agentes disparadores del nacimiento de estrellas nuevas. A partir del estudio de la distribución del gas molecular alrededor de los remanentes de supernova G20.0-0.2 y G24.7+0.6, se encuentran nubes moleculares posiblemente afectadas por los frentes de choque y que presentan actividad de formación estelar. El estudio del medio interestelar alrededor de tres regiones HII (un complejo de regiones HII cercano al remanente de supernova G18.8+0.3, y las regiones HII N65 y G35.673-0.847) muestra la presencia de cáscaras de gas molecular barridas por sus frentes de choque y sobre las cuales se están formando estrellas. Por último, se halla evidencia de la interacción entre los vientos estelares de las estrellas LBV G24.73+0.69 y G26.47+0.02 en distintas etapas de su evolución y el gas molecular circundante. Esta investigación fue realizada analizando observaciones dedicadas de varias transiciones moleculares obtenidas con el Atacama Submillimeter Telescope Experiment (ASTE) y a través del procesamiento de observaciones de archivo no publicadas obtenidas con el telescopio espacial de rayos X Chandra y con el interferómetro en ondas de radio VLA. Estas observaciones se complementaron con datos de relevamientos públicos en las bandas de radio...

## Inverse Compton Emission from Galactic Supernova Remnants: Effect of the Interstellar Radiation Field

Porter, Troy A.; Moskalenko, Igor V.; Strong, Andrew W.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.8%
The evidence for particle acceleration in supernova shells comes from electrons whose synchrotron emission is observed in radio and X-rays. Recent observations by the HESS instrument reveal that supernova remnants also emit TeV gamma-rays; long awaited experimental evidence that supernova remnants can accelerate cosmic rays up to the knee'' energies. Still, uncertainty exists whether these gamma-rays are produced by electrons via inverse Compton scattering or by protons via neutral pion decay. The multi-wavelength spectra of supernova remnants can be fitted with both mechanisms, although a preference is often given to neutral pion decay due to the spectral shape at very high energies. A recent study of the interstellar radiation field indicates that its energy density, especially in the inner Galaxy, is higher than previously thought. In this paper we evaluate the effect of the interstellar radiation field on the inverse Compton emission of electrons accelerated in a supernova remnant located at different distances from the Galactic Centre. We show that contribution of optical and infra-red photons to the inverse Compton emission may exceed the contribution of cosmic microwave background and in some cases broaden the resulted gamma-ray spectrum. Additionally...

## Circumstellar Nebulae in Young Supernova Remnants

Chu, Y. -H.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.8%
Supernovae descendent from massive stars explode in media that have been modified by their progenitors' mass loss and UV radiation. The supernova ejecta will first interact with the circumstellar material shed by the progenitors at late evolutionary stages, and then interact with the interstellar material. Circumstellar nebulae in supernova remnants can be diagnosed by their small expansion velocities and high [N II]/H$\alpha$ ratios. The presence of circumstellar nebulae appears ubiquitous among known young supernova remnants. These nebulae can be compared to those around evolved massive stars to assess the nature of their supernova progenitors. Three types of archeological artifacts of supernova progenitors have been observed in supernovae and/or young supernova remnants: (1) deathbed ejecta, (2) circumstellar nebulae, and (3) interstellar bubbles. Examples of these three types are given.; Comment: 9 pages, 5 figures, proceedings of the 11th October Astrophysics conference in Maryland, "Young Supernova Remnants", eds. Holt and Hwang

## A Spitzer Space Telescope Infrared Survey of Supernova Remnants in the Inner Galaxy

Reach, William T.; Rho, Jeonghee; Tappe, Achim; Pannuti, Thomas G.; Brogan, Crystal L.; Churchwell, Edward B.; Meade, Marilyn R.; Babler, Brian; Indebetouw, Remy; Whitney, Barbara A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.79%
Using Infrared Array Camera (IRAC) images at 3.6, 4.5, 5.8, and 8 microns from the GLIMPSE Legacy science program on the Spitzer Space Telescope, we searched for infrared counterparts to the 95 known supernova remnants that are located within galactic longitudes 65>|l|>10 degrees and latitudes |b|<1 degree. Eighteen infrared counterparts were detected. Many other supernova remnants could have significant infrared emission but are in portions of the Milky Way too confused to allow separation from bright HII regions and pervasive mid-infrared emission from atomic and molecular clouds along the line of sight. Infrared emission from supernova remnants originates from synchrotron emission, shock-heated dust, atomic fine-structure lines, and molecular lines. The detected remnants are G11.2-0.3, Kes 69, G22.7-0.2, 3C 391, W 44, 3C 396, 3C 397, W 49B, G54.4-0.3, Kes 17, Kes 20A, RCW 103, G344.7-0.1, G346.6-0.2, CTB 37A, G348.5-0.0, and G349.7+0.2. The infrared colors suggest emission from molecular lines (9 remnants), fine-structure lines (3), and PAH (4), or a combination; some remnants feature multiple colors in different regions. None of the remnants are dominated by synchrotron radiation at mid-infrared wavelengths. The IRAC-detected sample emphasizes remnants interacting with relatively dense gas...

## Progenitors of Recombining Supernova Remnants

Moriya, Takashi J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.9%
Usual supernova remnants have either ionizing plasma or plasma in collisional ionization equilibrium, i.e., the ionization temperature is lower than or equal to the electron temperature. However, the existence of recombining supernova remnants, i.e., supernova remnants with the ionization temperature higher than the electron temperature, is recently confirmed. One suggested way to have recombining plasma in a supernova remnant is to have a dense circumstellar medium at the time of the supernova explosion. If the circumstellar medium is dense enough, collisional ionization equilibrium can be established in the early stage of the evolution of the supernova remnant and subsequent adiabatic cooling which occurs after the shock wave gets out of the dense circumstellar medium makes the electron temperature lower than the ionization temperature. We study the circumstellar medium around several supernova progenitors and show which supernova progenitors can have a circumstellar medium which is dense enough to establish collisional ionization equilibrium soon after the explosion. We find that the circumstellar medium around red supergiants (especially massive ones) and the circumstellar medium which is dense enough to make Type IIn supernovae can establish collisional ionization equilibrium soon after the explosion and can evolve to recombining supernova remnants. Wolf-Rayet stars and white dwarfs have possibility to be recombining supernova remnants but the fraction is expected to be very small. As the occurrence rate of the explosions of red supergiants is much higher than that of Type IIn supernovae...

## Theoretical study of ionization profiles of molecular clouds near supernova remnants: Tracing the hadronic origin of GeV gamma radiation

Schuppan, Florian; Röken, Christian; Tjus, Julia Becker
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.77%
Context: Since a few years, signatures of supernova remnants associated with molecular clouds have been detected in gamma rays. Whether these gamma rays are generated by cosmic ray electrons or by cosmic ray protons is usually not known. The detection of hadronic ionization signatures in spatial coincidence with gamma ray signatures can help to unambiguously identify supernova remnants as sources of cosmic ray protons. Methods: In order to calculate hadronic signatures from cosmic ray-induced ionization for an examination of the origin of the observed gamma rays, the transport equation for cosmic ray protons propagating in a molecular cloud, including the relevant momentum loss processes, is solved analytically and the proton flux at any position in the cloud is determined. Results: Since the solution of the transport equation is obtained for arbitrary source functions, it can be used for a variety of supernova remnants. The corresponding theoretical ionization rate, as a function of the penetration depth, is derived and compared to photoinduced ionization profiles in a case study with four supernova remnants associated with molecular clouds. Three of the remnants show a clear dominance of the hadronically induced ionization rate...

## Acceleration of cosmic rays and gamma-ray emission from supernova remnants in the Galaxy

Cristofari, P.; Gabici, S.; Casanova, S.; Terrier, R.; Parizot, E.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.89%
Galactic cosmic rays are believed to be accelerated at supernova remnant shocks. Though very popular and robust, this conjecture still needs a conclusive proof. The strongest support to this idea is probably the fact that supernova remnants are observed in gamma-rays, which are indeed expected as the result of the hadronic interactions between the cosmic rays accelerated at the shock and the ambient gas. However, also leptonic processes can, in most cases, explain the observed gamma-ray emission. This implies that the detections in gamma rays do not necessarily mean that supernova remnants accelerate cosmic ray protons. To overcome this degeneracy, the multi-wavelength emission (from radio to gamma rays) from individual supernova remnants has been studied and in a few cases it has been possible to ascribe the gamma-ray emission to one of the two processes (hadronic or leptonic). Here we adopt a different approach and, instead of a case-by-case study we aim for a population study and we compute the number of supernova remnants which are expected to be seen in TeV gamma rays above a given flux under the assumption that these objects indeed are the sources of cosmic rays. The predictions found here match well with current observational results...

## Limits on the Number of Galactic Young Supernova Remnants Emitting in the Decay Lines of 44Ti

Dufour, François; Kaspi, Victoria M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.8%
We revise the assumptions of the parameters involved in predicting the number of supernova remnants detectable in the nuclear lines of the decay chain of 44Ti. Specifically, we consider the distribution of the supernova progenitors, the supernova rate in the Galaxy, the ratios of supernova types, the Galactic production of 44Ti, and the 44Ti yield from supernovae of different types, to derive credible bounds on the expected number of detectable remnants. We find that, within 1 sigma uncertainty, the Galaxy should contain an average of 5.1+2.4-2.0 remnants detectable to a survey with a 44Ti decay line flux limit of 10E-5 photons/cm2/s, with a probability of detecting a single remnant of (2.7+10.0-2.4)%, and an expected number of detections between 2 and 9 remnants, making the single detection of Cas A unlikely but consistent with our models. Our results show that the probability of detecting the brightest 44Ti flux source at the high absolute Galactic longitude of Cas A or above is ~10%. Using the detected flux of Cas A, we attempt to constrain the Galactic supernova rate and Galactic production of 44Ti, but find the detection to be only weakly informative. We conclude that even future surveys having 200 times more sensitivity than state-of-the art surveys can be guaranteed to detect only a few new remnants...

## X-Ray Studies of Supernova Remnants: A Different View of Supernova Explosions

Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.79%
The unprecedented spatial and spectral resolutions of Chandra have revolutionized our view of the X-ray emission from supernova remnants. The excellent data sets accumulated on young, ejecta dominated objects like Cas A or Tycho present a unique opportunity to study at the same time the chemical and physical structure of the explosion debris and the characteristics of the circumstellar medium sculpted by the progenitor before the explosion. Supernova remnants can thus put strong constraints on fundamental aspects of both supernova explosion physics and stellar evolution scenarios for supernova progenitors. This view of the supernova phenomenon is completely independent of, and complementary to, the study of distant extragalactic supernovae at optical wavelengths. The calibration of these two techniques has recently become possible thanks to the detection and spectroscopic follow-up of supernova light echoes. In this paper, I will review the most relevant results on supernova remnants obtained during the first decade of Chandra, and the impact that these results have had on open issues in supernova research.; Comment: 6 pages, 7 figures, invited review to be published in Proceedings of the National Academy of Sciences (part of the special 'First decade of Chandra' issue)

## OH Masers and Supernova Remnants

Wardle, Mark; McDonnell, Korinne
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.82%
OH(1720 MHz) masers are created by the interaction of supernova remnants with molecular clouds. These masers are pumped by collisions in warm, shocked molecular gas with OH column densities in the range 10^{16}--10^{17} cm^{-2}. Excitation calculations suggest that inversion of the 6049 MHz OH line may occur at the higher column densities that have been inferred from main-line absorption studies of supernova remnants with the Green Bank Telescope. OH(6049 MHz) masers have therefore been proposed as a complementary indicator of remnant-cloud interaction. This motivated searches for 6049 MHz maser emission from supernova remnants using the Parkes 63 m and Effelsberg 100 m telescopes, and the Australia Telescope Compact Array. A total of forty-one remnants have been examined by one or more of these surveys, but without success. To check the accuracy of the OH column densities inferred from the single-dish observations we modelled OH absorption at 1667 MHz observed with the Very Large Array towards three supernova remnants, IC 443, W44 and 3C 391. The results are mixed -- the OH column is revised upwards in IC443, downwards in 3C391, and is somewhat reduced in W44. We conclude that OH columns exceeding 10^{17} cm^{-2} are indeed present in some supernova remnants and so the lack of any detections is not explained by low OH column density. We discuss the possibility that non-local line overlap is responsible for suppressing the inversion of the 6049 MHz line.; Comment: 8pages...

## Excited-state OH Masers and Supernova Remnants

Pihlström, Ylva M.; Fish, Vincent L.; Sjouwerman, Loránt O.; Zschaechner, Laura K.; Lockett, Philip B.; Elitzur, Moshe
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.8%
The collisionally pumped, ground-state 1720 MHz maser line of OH is widely recognized as a tracer for shocked regions and observed in star forming regions and supernova remnants. Whereas some lines of excited states of OH have been detected and studied in star forming regions, the subject of excited-state OH in supernova remnants -- where high collision rates are to be expected -- is only recently being addressed. Modeling of collisional excitation of OH demonstrates that 1720, 4765 and 6049 MHz masers can occur under similar conditions in regions of shocked gas. In particular, the 6049 and 4765 MHz masers become more significant at increased OH column densities where the 1720 MHz masers begin to be quenched. In supernova remnants, the detection of excited-state OH line maser emission could therefore serve as a probe of regions of higher column densities. Using the Very Large Array, we searched for excited-state OH in the 4.7, 7.8, 8.2 and 23.8 GHz lines in four well studied supernova remnants with strong 1720 MHz maser emission (SgrAEast, W28, W44 and IC443). No detections were made, at typical detection limits of around 10 mJy/beam. The search for the 6 GHz lines were done using Effelsberg since the VLA receivers did not cover those frequencies...

## Asymmetric supernova remnants generated by Galactic, massive runaway stars

Meyer, D. M. -A.; Langer, N.; Mackey, J.; Velazquez, P. F.; Gusdorf, A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.8%
After the death of a runaway massive star, its supernova shock wave interacts with the bow shocks produced by its defunct progenitor, and may lose energy, momentum, and its spherical symmetry before expanding into the local interstellar medium (ISM). We investigate whether the initial mass and space velocity of these progenitors can be associated with asymmetric supernova remnants. We run hydrodynamical models of supernovae exploding in the pre-shaped medium of moving Galactic core-collapse progenitors. We find that bow shocks that accumulate more than about 1.5 Mo generate asymmetric remnants. The shock wave first collides with these bow shocks 160-750 yr after the supernova, and the collision lasts until 830-4900 yr. The shock wave is then located 1.35-5 pc from the center of the explosion, and it expands freely into the ISM, whereas in the opposite direction it is channelled into the region of undisturbed wind material. This applies to an initially 20 Mo progenitor moving with velocity 20 km/s and to our initially 40 Mo progenitor. These remnants generate mixing of ISM gas, stellar wind and supernova ejecta that is particularly important upstream from the center of the explosion. Their lightcurves are dominated by emission from optically-thin cooling and by X-ray emission of the shocked ISM gas. We find that these remnants are likely to be observed in the [OIII] lambda 5007 spectral line emission or in the soft energy-band of X-rays. Finally...

## Shocks and Particle Acceleration in Supernova Remnants: Observational Features

Vink, Jacco
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.84%
The last ten years a number of observational advances have substantially increased our knowledge of shock phenomena in supernova remnants. This progress has mainly been made possible by the recent improvements in X-ray and Gamma-ray instrumentation. It has become clear that some shell-type supernova remnants, e.g. SN 1006, have X-ray emission dominated by synchrotron radiation, proving that electrons are accelerated up to 100 TeV. This is still an order of magnitude below 3E15 eV, at which energy the ion cosmic ray spectrum at earth shows a spectral break. So one of the major goals is to prove that supernova remnants are capable of accelerating ions at least up that energy. Here I review the evidence that ions and electrons are accelerated up to energies ~100 TeV in supernova remnants, and, in addition, the recent progress that has been made in understanding the physics of collisionless shock fronts and the magnetic fields inside supernova remnants.; Comment: 13 pages, 7 figures. Invited review to appear in "High Energy Studies of Supernova Remnants and Neutron Stars" (COSPAR 2002), Eds. W. Hermsen, W. Becker, Advances in Space Research, in press

## Supernova remnants: the X-ray perspective

Vink, Jacco
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.9%
Supernova remnants are beautiful astronomical objects that are also of high scientific interest, because they provide insights into supernova explosion mechanisms, and because they are the likely sources of Galactic cosmic rays. X-ray observations are an important means to study these objects.And in particular the advances made in X-ray imaging spectroscopy over the last two decades has greatly increased our knowledge about supernova remnants. It has made it possible to map the products of fresh nucleosynthesis, and resulted in the identification of regions near shock fronts that emit X-ray synchrotron radiation. In this text all the relevant aspects of X-ray emission from supernova remnants are reviewed and put into the context of supernova explosion properties and the physics and evolution of supernova remnants. The first half of this review has a more tutorial style and discusses the basics of supernova remnant physics and thermal and non-thermal X-ray emission. The second half offers a review of the recent advances.The topics addressed there are core collapse and thermonuclear supernova remnants, SN 1987A, mature supernova remnants, mixed-morphology remnants, including a discussion of the recent finding of overionization in some of them...

## The Radio Lifetime of Supernova Remnants and the Distribution of Pulsar Velocities at Birth

Frail, D. A.; Goss, W. M.; Whiteoak, J. B. Z.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.86%
We have made VLA images of the fields around three young pulsars which have resulted in the discovery of two new supernova remnants and confirmation of a third. We argue that, in at least two cases and perhaps the third, the pulsars are physically associated with these supernova remnants. A review of all known young pulsars shows that the majority are associated with supernova remnants. We show that the typical density of the interstellar medium into which the supernova remnants are evolving has a density of 0.2 cm$^{-3}$ instead of the low value of 0.01 cm$^{-3}$ which had been calculated from other studies, and results in a considerably longer radio lifetime for supernova remnants. Both the morphology of the supernova remnants and the location of the pulsars imply that most of these young pulsars are born with large transverse velocities ($\sim$500 km s$^{-1}$). This high velocity mean in the distribution of pulsar velocities appears to be a general property of the pulsar population at birth, not seen in proper motion studies, due to selection effects. We explore the implications of this result as it relates to the origin of these velocities and the galactic distribution of pulsars. High velocity pulsars can escape their supernova remnant in a very short timescale...

## Constraints on the distribution of supernova remnants with Galactocentric radius

Green, D. A.
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Article; published version
EN
Relevância na Pesquisa
66.6%
This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stv1885; Supernova remnants (SNRs) in the Galaxy are an important source of energy injection into the interstellar medium, and also of cosmic rays. Currently there are 294 known SNRs in the Galaxy, and their distribution with Galactocentric radius is of interest for various studies. Here I discuss some of the statistics of Galactic SNRs, including the observational selection effects that apply, and difficulties in obtaining distances for individual remnants from the ???D? relation. Comparison of the observed Galactic longitude distribution of a sample of bright Galactic SNRs ? which are not strongly affected by selection effects ? with those expected from models is used to constrain the Galactic distribution of SNRs. The best-fitting power-law/exponential model is more concentrated towards the Galactic Centre than the widely used distribution obtained by Case & Bhattacharya.

## On the Magnetic Field Evolution in shell-like Supernova Remnants

Vukotic,B; Arbutina,B; Uroevic,D
Fonte: Instituto de Astronomía, UNAM Publicador: Instituto de Astronomía, UNAM
Tipo: Artigo de Revista Científica Formato: text/html