H. Andernach

Universidad de Guanajuato, Ciudad Guanajuato, Guanajuato, Mexico

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Publications (131)212.74 Total impact

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    ABSTRACT: We present results of a search for giant radio galaxies (GRGs) with a projected largest linear size in excess of 1 Mpc. We designed a computational algorithm to identify contiguous emission regions, large and elongated enough to serve as GRG candidates, and applied it to the entire 1.4-GHz NRAO VLA Sky survey (NVSS). In a subsequent visual inspection of 1000 such regions we discovered 15 new GRGs, as well as many other candidate GRGs, some of them previously reported, for which no redshift was known. Our follow-up spectroscopy of 25 of the brighter hosts using two 2.1-m telescopes in Mexico, and four fainter hosts with the 10.4-m Gran Telescopio Canarias (GTC), yielded another 24 GRGs. We also obtained higher-resolution radio images with the Karl G. Jansky Very Large Array for GRG candidates with inconclusive radio structures in NVSS.
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    ABSTRACT: We determined accurate positions for 3000 of the "faint blue stars" in the PHL (Palomar-Haro-Luyten) and Ton/TonS catalogues. These were published from 1957 to 1962, and, aimed at finding new white dwarfs, provide approximate positions for about 10750 blue stellar objects. Some of these "stars" had become known as quasars, a type of objects unheard-of before 1963. We derived subarcsec positions from a comparison of published finding charts with images from the first-epoch Digitized Sky Survey. Numerous objects are now well known, but unfortunately neither their PHL or Ton numbers, nor their discoverers, are recognized in current databases. A comparison with modern radio, IR, UV and X-ray surveys leads us to suggest that the fraction of extragalactic objects in the PHL and Ton catalogues is at least 15 per cent. However, because we failed to locate the original PHL plates or finding charts, it may be impossible to correctly identify the remaining 7726 PHL objects.
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    ABSTRACT: Using a new color-color diagnostic diagram in the mid infrared built from WISE data, the MIRDD, we compare narrow emission-line galaxies (NELGs) that exhibit different activity types (star-forming galaxies, SFGs, and AGNs, i.e.,LINERs, Sy2s and TOs), with broad-line AGNs (QSOs and Sy1s) and BL Lac objects at low redshift ($z \le 0.25$). We show that the BL Lac objects occupy in the MIRDD the same region as the LINERs, whereas the QSOs and Sy1s occupy an intermediate region, between the LINERs and the Sy2s.In the MIRDD these galaxies trace a sequence that can be reproduced by a power law, $F_\nu = \nu^{\alpha}$, where the spectral index, $\alpha$, varies from 0 to $-2$, which is similar to what is observed in the optical-ultraviolet part of the spectra of AGNs with different luminosities. For the NELGs, we perform a stellar population synthesis analysis, demonstrating that the ${\rm W}2-{\rm W}3$ color is tightly correlated with the level of star formation in their host galaxies. A comparison of their MIR colors with the colors yielded by energy distributions (SEDs) of galaxies with different activity types, shows that the SED of the LINERs is similar to the SEDs of the QSOs and Sy1s, consistent with AGN galaxies with mild star formation, whereas the SEDs of the Sy2s and TOs are consistent with AGN galaxies with strong star formation components. For the BL Lac objects, we can only fit a SED that has no star formation component, consistent with AGNs in elliptical-type galaxies. From their similarities in MIR colors and SEDs, we infer that, in the nearby universe, the level of star formation activity most probably increases in the host galaxies of emission-line galaxies with different activity types along the sequence BL Lac$\rightarrow$LINER$\rightarrow$QSO/Sy1$\rightarrow$Sy2$\rightarrow$TO$\rightarrow$SFG.
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    ABSTRACT: We present two new catalogues of superclusters of galaxies out to a redshit of z = 0.15, based on the Abell/ACO cluster redshift compilation maintained by one of us (HA). The first of these catalogues, the all-sky Main SuperCluster Catalogue (MSCC), is based on only the rich (A-) Abell clusters, and the second one, the Southern SuperCluster Catalogue (SSCC), covers declinations delta < -17 deg and includes the supplementary Abell S-clusters. A tunable Friends-of-Friends (FoF) algorithm was used to account for the cluster density decreasing with redshift and for different selection functions in distinct areas of the sky. We present the full list of Abell clusters used, together with their redshifts and supercluster memberships and including the isolated clusters. The SSCC contains about twice the number of superclusters than MSCC for delta < -17 deg, which we found to be due to: (1) new superclusters formed by A-clusters in their cores and surrounded by S-clusters (50%), (2) new superclusters formed by S-clusters only (40%), (3) redistribution of member clusters by fragmentation of rich (multiplicity m > 15) superclusters (8%), and (4) new superclusters formed by the connection of A-clusters through bridges of S-clusters (2%). Power-law fits to the cumulative supercluster multiplicity function yield slopes of alpha = -2.0 and alpha = -1.9 for MSCC and SSCC respectively. This power-law behavior is in agreement with the findings for other observational samples of superclusters, but not with that of catalogues based on cosmological simulations.
    Monthly Notices of the Royal Astronomical Society 09/2014; 445(4). DOI:10.1093/mnras/stu1961 · 5.23 Impact Factor
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    ABSTRACT: There is anecdotical evidence of galaxies with different morphologies having different dominant emission-line activity types (Heckman, 1980; Ho, Filippenko & Sargent, 1997; Sabater et al., 2012). We present here statistical evidence of the relation between these two characteristics of galaxies for a large sample of 800,685 galaxies from the SDSS-DR7. Using known relations between the broad-band colours and a concentration index of their brightness profile of subsamples of these galaxies and their morphology classified by eye, we inferred the morphological type of all the 800,685 galaxies. Also, using a standard diagnostic diagram based on emission-line ratios, we classified our large sample of galaxies according to their dominant activity type. We used the STARLIGHT code to measure the emission-line flux of all the lines seen in the spectra of the entire sample of galaxies. For our analysis, we only considered 216,510 galaxies with redshifts 0.03–0.30 and with the lines relevant to the diagnostic diagram with S/N > 3. Using the R suite of statistical analysis, we then compared the distribution of the inferred morphologies of galaxies of different dominant activity types, showing that the difference in the median morphological type between the samples of different activity types is significant. We also tested the significance of the difference in the mean morphological type between all the activity-type samples using an ANOVA model with a modified Tukey test that takes into account heteroscedasticity and the unequal sample sizes. We show this test in the form of simultaneous confidence intervals for all pairwise comparisons of the mean morphological types of the samples. Using this test, scarcely applied in astronomy, we conclude that there are statistically significant differences in the inferred morphologies of galaxies of different dominant activity types.
    IAU Symposium 306: Statistical Challenges in 21st Century Cosmology, Lisbon, Portugal; 05/2014
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    ABSTRACT: Using data from the Wide-field Infrared Survey Explorer (WISE) we show that the mid infrared (MIR) colors of low-luminosity AGNs (LLAGNs) are significanlty different from those of post-asymptotic giant branch stars (PAGBs). This is due to a difference in spectral energy distribution (SEDs), the LLAGNs showing a flat component due to an AGN. Consistent with this interpretation we show that in a MIR color-color diagram the LINERs and the Seyfert~2s follow a power law with specific colors that allow to distinguish them from each other, and from star forming galaxies, according to their present level of star formation. Based on this result we present a new diagnostic diagram in the MIR that confirms the classification obtained in the optical using standard diagnostic diagrams, clearly identifying LINERs and LLAGNs as genuine AGNs.
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    ABSTRACT: Using a sample of 229618 narrow emission-line galaxies, we have determined the normal star formation histories (SFHs) for galaxies with different activity types: star forming galaxies (SFGs), transition type objects (TOs), Seyfert 2s (Sy2s) and LINERs. We find that the variation of the SFH with the activity type is explained by the mass of the galaxies and the importance of their bulge: the LINERs reside in massive early-type galaxies, the Sy2s and TOs are hosted by intermediate mass galaxies with intermediate morphological types, and the SFGs are found in lower mass late-type spirals. Except for the Sy2s, the more massive galaxies formed the bulk of their stars more rapidly than the less massive ones. The Sy2s formed their stars more slowly and show presently an excess in star formation. We have also found that the maximum in star formation rate in the past increases with the virial mass within the aperture (VMA), the VMA increasing from the SFGs to the TOs, to the Sy2s, culminating in the LINERs. This correlation suggests that the bulges and the supermassive black holes at the center of galaxies grow in parallel, in good agreement with the M(BH)-sigma relation.
    Revista mexicana de astronomía y astrofísica 08/2013; · 1.07 Impact Factor
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    Hrant M. Tovmassian, Heinz Andernach
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    ABSTRACT: In order to study the mechanism of formation of cD galaxies we search for possible dependencies between the K-band luminosity of cDs and the parameters of their host clusters which we select to have a dominant cD galaxy, corresponding to a cluster morphology of Bautz-Morgan (BM) type I. As a comparison sample we use cD galaxies in clusters where they are not dominant, which we define here as non-BMI (NBMI) type clusters. We find that for 71 BMI clusters the absolute K-band luminosity of cDs depends on the cluster richness, but less strongly on the cluster velocity dispersion. Meanwhile, for 35 NBMI clusters the correlation between cD luminosity and cluster richness is weaker, and is absent between cD luminosity and velocity dispersion. In addition, we find that the luminosity of the cD galaxy hosted in BMI clusters tends to increase with the cD's peculiar velocity with respect to the cluster mean velocity. In contrast, for NBMI clusters the cD luminosity decreases with increasing peculiar velocity. Also, the X-ray luminosity of BMI clusters depends on the cluster velocity dispersion, while in NBMI clusters such a correlation is absent. These findings favour the cannibalism scenario for the formation of cD galaxies. We suggest that cDs in clusters of BMI type were formed and evolved preferentially in one and the same cluster. In contrast, cDs in NBMI type clusters were either originally formed in clusters that later merged with groups or clusters to form the current cluster, or are now in the process of merging.
    Monthly Notices of the Royal Astronomical Society 12/2012; 427(3). DOI:10.1111/j.1365-2966.2012.22044.x · 5.23 Impact Factor
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    ABSTRACT: A sample of 229618 narrow emission-line galaxies is used to establish two new unambiguous type of evidence for supermassive black holes at the center of their nuclei: 1) the Seyfert 2 galaxies and LINERs follow the same characteristic power law relating the luminosity of ionized flux with that of the continuum; 2) both show the highest concentration of mass at their center, independent of the morphology of the galaxy, consistent with higher binding energies. The Full Width at Half Maximum is shown to be related with the mass concentration, suggesting that the kinetic energy of the gas in AGNs has a gravitational origin. Within the standard accretion model, the Transition-type Objects, Seyfert 2 galaxies and LINERs represent AGNs forming supermassive black holes on different mass-scales, or they could be related through an evolutionary process, the LINERs representing the end product of this evolution.
    Revista mexicana de astronomía y astrofísica 08/2012; · 1.07 Impact Factor
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    ABSTRACT: We present the first attempts to build a user-friendly interface for the Virtual Observatory of the University of Guanajuato. The data tables will be accessible to the public through PHP scripts and SQL database managers, such as MySQL and PostgreSQL, all administrated through phpMyAdmin and pgMyAdmin. Although it is not made public yet, this interface will be the basis upon which the final front end for our VO will be built. Furthermore, we present a preliminary version of a web front end to the publicly available stellar population synthesis code STARLIGHT (starlight.ufsc.br) which will be made available with our VO. This front end aims to provide an easy and flexible access to the code itself, letting users fit their own observed spectra with their preferred combination of physical and technical parameters, rather than making available only the results of fitting a specific sample of spectra with predefined parameters.
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    ABSTRACT: We compare the Spectral Energy Distribution (SED) of radio-loud and radio-quiet AGNs in three different samples observed with SDSS: radio-loud AGNs (RLAGNs), Low Luminosity AGNs (LLAGNs) and AGNs in isolated galaxies (IG-AGNs). All these galaxies have similar optical spectral characteristics. The median SED of the RLAGNs is consistent with the characteristic SED of quasars, while that of the LLAGNs and IG-AGNs are consistent with the SED of LINERs, with a lower luminosity in the IG-AGNs than in the LLAGNs. We infer the masses of the black holes (BHs) from the bulge masses. These increase from the IG-AGNs to the LLAGNs and are highest for the RLAGNs. All these AGNs show accretion rates near or slightly below 10% of the Eddington limit, the differences in luminosity being solely due to different BH masses. Our results suggests there are two types of AGNs, radio quiet and radio loud, differing only by the mass of their bulges or BHs.
    Proceedings of the International Astronomical Union 01/2012; DOI:10.1017/S174392131200909X
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    The Astronomical Journal 09/2011; 142(4):142. DOI:10.1088/0004-6256/142/4/142 · 4.05 Impact Factor
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    ABSTRACT: We discuss the nature and origin of the nuclear activity observed in a sample of 292 SDSS narrow-emission-line galaxies, considered to have formed and evolved in isolation. All these galaxies are spiral like and show some kind of nuclear activity. The fraction of Narrow Line AGNs (NLAGNs) and Transition type Objects (TOs; a NLAGN with circumnuclear star formation) is relatively high, amounting to 64% of the galaxies. There is a definite trend for the NLAGNs to appear in early-type spirals, while the star forming galaxies and TOs are found in later-type spirals. We verify that the probability for a galaxy to show an AGN characteristic increases with the bulge mass of the galaxy (Torres-Papaqui et al. 2011), and find evidence that this trend is really a by-product of the morphology, suggesting that the AGN phenomenon is intimately connected with the formation process of the galaxies. Consistent with this interpretation, we establish a strong connection between the astration rate -- the efficiency with which the gas is transformed into stars - the AGN phenomenon, and the gravitational binding energy of the galaxies: the higher the binding energy, the higher the astration rate and the higher the probability to find an AGN. The NLAGNs in our sample are consistent with scaled-down or powered-down versions of quasars and Broad Line AGNs. (2 data files).
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    ABSTRACT: We discuss the nature and origin of the nuclear activity observed in a sample of 292 SDSS narrow-emission-line galaxies, considered to have formed and evolved in isolation. All these galaxies are spiral like and show some kind of nuclear activity. The fraction of Narrow Line AGNs (NLAGNs) and Transition type Objects (TOs; a NLAGN with circumnuclear star formation) is relatively high, amounting to 64% of the galaxies. There is a definite trend for the NLAGNs to appear in early-type spirals, while the star forming galaxies and TOs are found in later-type spirals. We verify that the probability for a galaxy to show an AGN characteristic increases with the bulge mass of the galaxy (Torre-Papaqui et al. 2011), and find evidence that this trend is really a by-product of the morphology, suggesting that the AGN phenomenon is intimately connected with the formation process of the galaxies. Consistent with this interpretation, we establish a strong connection between the astration rate--the efficiency with which the gas is transformed into stars--the AGN phenomenon, and the gravitational binding energy of the galaxies: the higher the binding energy, the higher the astration rate and the higher the probability to find an AGN. The NLAGNs in our sample are consistent with scaled-down or powered-down versions of quasars and Broad Line AGNs.
    Revista mexicana de astronomía y astrofísica 08/2011; 47. · 1.07 Impact Factor
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    ABSTRACT: EMU is a wide-field radio continuum survey planned for the new Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The primary goal of EMU is to make a deep (rms ~ 10 microJy/beam) radio continuum survey of the entire Southern Sky at 1.3 GHz, extending as far North as +30 degrees declination, with a resolution of 10 arcsec. EMU is expected to detect and catalogue about 70 million galaxies, including typical star-forming galaxies up to z~1, powerful starbursts to even greater redshifts, and AGNs to the edge of the visible Universe. It will undoubtedly discover new classes of object. This paper defines the science goals and parameters of the survey, and describes the development of techniques necessary to maximise the science return from EMU.
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    ABSTRACT: We have selected a sample of 292 SDSS Narrow-Emission-Line galaxies known to have formed and evolved in relative isolation to study the nature and origin of the AGN phenomenon. The galaxies in our sample have line fluxes with S/N>3 and were separated using a standard diagnostic diagram into Star Forming Galaxies (SFGs; 36.0%), Transition type Objects (TOs; 28.4%) and Narrow-Line AGNs (NLAGNs; 35.6%). Having found a strong correlation between the bulge mass and the NLAGN phenomenon, we have applied the same relation as for the Broad-Line AGNs to estimate their black hole (BH) masses. The BH in the NLAGNs are 2 to 3 orders lower in mass than the BHs found in BLAGNs, but are comparable to those observed in Narrow-Line Seyfert~1, although none of our objects can be classified as such. To determine the metallicities, [O/H], of the NLAGNs we calibrated the standard diagnostic diagram [OIII]/Hb vs. [NII]/Ha using similar relation as for the SFGs, which reproduce the values obtained with CLOUDY simulations developed for Bennert et al. [3]. For some individual objects we compared our line ratios with other CLOUDY similations by different authors. This suggests we achieve a typical uncertainty of 0.2 dex on [O/H], increasing to 0.3-0.5 in the Seyfert~2 (S2). This calibration suggests the metallicities of the NLAGNs are subsolar, varying between 1 and 0.3 $Z_\odot$. We find two statistically significant positive correlations: for [O/H] with the BH mass and for [O/H] with the luminosity at 5100\AA, $\lambda L(5100$\AA$)$. No correlation is found between [O/H] and the accretion rate, L_bol/L_Edd. However, comparisons with the BLAGNs suggest the NLAGNs extend the metallicity-accretion rate relationship [24] to the low metallicity regime. Although the NLS1 have similar BH masses as the NLAGNs they show higher accretion rates, which is consistent with their higher metallicities.
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    ABSTRACT: By cross-correlating large samples of galaxy clusters with publicly available radio source catalogs, we construct the volume-averaged radio luminosity function (RLF) in clusters of galaxies, and investigate its dependence on cluster redshift and mass. In addition, we determine the correlation between the cluster mass and the radio luminosity of the brightest source within 50 kpc from the cluster center. We use two cluster samples: the optically selected maxBCG cluster catalog and a composite sample of X-ray selected clusters. The radio data come from the VLA NVSS and FIRST surveys. We use scaling relations to estimate cluster masses and radii to get robust estimates of cluster volumes. We determine the projected radial distribution of sources, for which we find no dependence on luminosity or cluster mass. Background and foreground sources are statistically accounted for, and we account for confusion of radio sources by adaptively degrading the resolution of the radio source surveys. We determine the redshift evolution of the RLF under the assumption that its overall shape does not change with redshift. Our results are consistent with a pure luminosity evolution of the RLF in the range 0.1 < z < 0.3 from the optical cluster sample. The X-ray sample extends to higher redshift and yields results also consistent with a pure luminosity evolution. We find no direct evidence of a dependence of the RLF on cluster mass from the present data, although the data are consistent with the most luminous sources only being found in high-mass systems.
    Astronomy and Astrophysics 03/2011; 529. DOI:10.1051/0004-6361/201016150 · 4.48 Impact Factor
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    ABSTRACT: We present new radial velocities for 307 galaxies (bJ
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    ABSTRACT: We apply a stellar population synthesis code to the spectra of a large sample of SDSS galaxies to classify these according to their activity (using emission-line diagnostic diagrams), environment (using catalogues of isolated and cluster galaxies), and using parameters that correlate with their morphology. Comment: 1 page, 1 figure; to appear in Proceedings of the XIII Latin American Regional IAU Meeting, Morelia, Mexico, 8-12 Nov. 2010
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    ABSTRACT: We present relations between X-ray luminosity and velocity dispersion (L-sigma), X-ray luminosity and gas mass (L-Mgas), and cluster radius and velocity dispersion (r500-sigma) for 62 galaxy clusters in the HIFLUGCS, an X-ray flux-limited sample minimizing bias toward any cluster morphology. Our analysis in total is based on ~1.3Ms of clean X-ray XMM-Newton data and 13439 cluster member galaxies with redshifts. Cool cores are among the major contributors to the scatter in the L-sigma relation. When the cool-core-corrected X-ray luminosity is used the intrinsic scatter decreases to 0.27 dex. Even after the X-ray luminosity is corrected for the cool core, the scatter caused by the presence of cool cores dominates for the low-mass systems. The scatter caused by the non-cool-core clusters does not strongly depend on the mass range, and becomes dominant in the high-mass regime. The observed L-sigma relation agrees with the self-similar prediction, matches that of a simulated sample with AGN feedback disregarding six clusters with <45 cluster members with spectroscopic redshifts, and shows a common trend of increasing scatter toward the low-mass end, i.e., systems with sigma<500km/s. A comparison of observations with simulations indicates an AGN-feedback-driven impact in the low-mass regime. The best fits to the $L-M_{\rm gas}$ relations for the disturbed clusters and undisturbed clusters in the observational sample closely match those of the simulated samples with and without AGN feedback, respectively. This suggests that one main cause of the scatter is AGN activity providing feedback in different phases, e.g., during a feedback cycle. The slope and scatter in the observed r500-sigma relation is similar to that of the simulated sample with AGN feedback except for a small offset but still within the scatter. Comment: 45 pages, 28 figures, A&A proof-version, high-resolution figures in Appendix F can be found in the electronic version on the A&A web
    Astronomy and Astrophysics 11/2010; 526. DOI:10.1051/0004-6361/201015830 · 4.48 Impact Factor

Publication Stats

999 Citations
212.74 Total Impact Points

Institutions

  • 1998–2013
    • Universidad de Guanajuato
      • Departamento de Astronomía
      Ciudad Guanajuato, Guanajuato, Mexico
    • Conalep Guanajuato
      Ciudad Guanajuato, Guanajuato, Mexico
  • 2012
    • Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE)
      Cholula de Riva dabia, Puebla, Mexico
  • 2008–2010
    • University of Bonn
      • Argelander-Institute of Astronomy
      Bonn, North Rhine-Westphalia, Germany
  • 2004
    • University of Virginia
      • Department of Astronomy
      Charlottesville, Virginia, United States
    • National Observatory of Athens
      Athínai, Attica, Greece
  • 1999–2001
    • University of Bologna
      • Department of Physics and Astronomy DIFA
      Bolonia, Emilia-Romagna, Italy
  • 1996–1997
    • INSA
      Альтамира, Tamaulipas, Mexico
  • 1995–1997
    • Tartu Observatory
      Dorpat, Tartu, Estonia
  • 1992
    • Universidade Federal de Santa Maria
      Santa Maria da Boca do Monte, Rio Grande do Sul, Brazil
    • Instituto de Astrofísica de Canarias
      San Cristóbal de La Laguna, Canary Islands, Spain
  • 1982–1990
    • Max Planck Institute for Radio Astronomy
      Bonn, North Rhine-Westphalia, Germany
  • 1984
    • National Research Council
      Roma, Latium, Italy
  • 1979–1980
    • Ruhr-Universität Bochum
      Bochum, North Rhine-Westphalia, Germany