explanation      blue bibcodes open ADS page with paths to full text
Author name code: voegler
ADS astronomy entries on 2022-09-14
author:"Voegler, Alexander" 

---------------------------------------------------------
Title: AWOB: A Collaborative Workbench for Astronomers
Authors: Kim, J. W.; Lemson, G.; Bulatovic, N.; Makarenko, V.; Vogler,
   A.; Voges, W.; Yao, Y.; Kiefl, R.; Koychev, S.
2015ASPC..495..491K    Altcode: 2015adass..24..491K
  We present the Astronomers Workbench (AWOB<SUP>1</SUP>), a web-based
  collaboration and publication platform for a scientific project of any
  size, developed in collaboration between the Max-Planck institutes
  of Astrophysics (MPA) and Extra-terrestrial Physics (MPE) and the
  Max-Planck Digital Library (MPDL). AWOB facilitates the collaboration
  between geographically distributed astronomers working on a common
  project throughout its whole scientific life cycle. AWOB does so by
  making it very easy for scientists to set up and manage a collaborative
  workspace for individual projects, where data can be uploaded and
  shared. It supports inviting project collaborators, provides wikis,
  automated mailing lists, calendars and event notification and has a
  built in chat facility. It allows the definition and tracking of tasks
  within projects and supports easy creation of e-publications for the
  dissemination of data and images and other resources that cannot be
  added to submitted papers. AWOB extends the project concept to larger
  scale consortia, within which it is possible to manage working groups
  and sub-projects. The existing AWOB instance has so far been limited
  to Max-Planck members and their collaborators, but will be opened to
  the whole astronomical community. AWOB is an open-source project and
  its source code is available upon request. We intend to extend AWOB's
  functionality also to other disciplines, and would greatly appreciate
  contributions from the community.

---------------------------------------------------------
Title: Decay of a simulated mixed-polarity magnetic field in the
    solar surface layers
Authors: Cameron, R.; Vögler, A.; Schüssler, M.
2011A&A...533A..86C    Altcode: 2011arXiv1108.1155C
  Magnetic flux is continuously being removed and replenished on the
  solar surface. To understand the removal process we carried out 3D
  radiative MHD simulations of the evolution of patches of photospheric
  magnetic field with equal amounts of positive and negative flux. We
  find that the flux is removed at a rate corresponding to an effective
  turbulent diffusivity, η<SUB>eff</SUB>, of 100-340 km<SUP>2</SUP>
  s<SUP>-1</SUP>, depending on the boundary conditions. For average
  unsigned flux densities above about 70 Gauss, the percentage of surface
  magnetic energy coming from different field strengths is almost
  invariant. The overall process is then one where magnetic elements
  are advected by the horizontal granular motions and occasionally come
  into contact with opposite-polarity elements. These reconnect above
  the photosphere on a comparatively short time scale after which the
  U loops produced rapidly escape through the upper surface while the
  downward retraction of inverse-U loops is significantly slower, because
  of the higher inertia and lower plasma beta in the deeper layers.

---------------------------------------------------------
Title: Fast horizontal flows in a quiet sun MHD simulation and their
    spectroscopic signatures
Authors: Vitas, N.; Fischer, C. E.; Vögler, A.; Keller, C. U.
2011A&A...532A.110V    Altcode:
  Numerical simulations of solar surface convection have predicted
  the existence of supersonic horizontal flows in the photospheric
  granulation. Recently, the detection of such flows in data from the
  Hinode satellite was reported. We study supersonic granular flows in
  detail to understand their signatures in spectral lines and to test
  the observational detection method used to identify these flows in
  the Hinode observations. We perform time-dependent 3D radiative MHD
  numerical simulations and synthesize the Fe i 6302 Å spectral lines at
  the resolution of the Hinode data for different viewing angles covering
  the center-limb variation. There is very large variation in the detailed
  shape of the emergent line profiles depending on the viewing angle and
  the particular flow properties and orientation. At the full simulation
  resolution the supersonic flows can even produce distinct satellite
  lines. After smearing to the Hinode resolution sufficient signature
  of supersonic motion remains. Our analysis shows that the detection
  method used to analyze the Hinode data is indeed applicable. However,
  the detection is very sensitive to ad hoc parameter choices and can
  also misidentify supersonic flows.

---------------------------------------------------------
Title: Intensity contrast from MHD simulations and HINODE observations
Authors: Afram, N.; Unruh, Y. C.; Solanki, S. K.; Schüssler, M.;
   Lagg, A.; Vögler, A.
2011A&A...526A.120A    Altcode: 2010arXiv1011.6102A
  Context. Changes in the solar surface area, which is covered by
  small-scale magnetic elements, are thought to cause long-term changes
  in the solar spectral irradiance, which are important for determining
  the impact on Earth's climate. <BR /> Aims: To study the effect of
  small-scale magnetic elements on the total and spectral irradiance,
  we derive their contrasts from 3-D MHD simulations of the solar
  atmosphere. These calculations are necessary because measurements of
  small-scale flux tube contrasts are confined to a few wavelengths and
  affected by scattered light and instrument defocus, even for space
  observations. <BR /> Methods: To test the contrast calculations,
  we compare rms contrasts from simulations with those obtained with
  the broad-band filter imager mounted on the Solar Optical Telescope
  (SOT) onboard the Hinode satellite and also analyse centre-to-limb
  variations (CLV). The 3-D MHD simulations include the interaction
  between convection and magnetic flux tubes. They are performed by
  assuming non-grey radiative transfer and using the MURaM code. The
  simulations have an average vertical magnetic field of 0 G, 50 G, and
  200 G. Emergent intensities are calculated with the spectral synthesis
  code ATLAS9 and are convolved with a theoretical point-spread function
  to account for the properties of the observations' optical system. <BR
  /> Results: We find reasonable agreement between simulated and observed
  intensity distributions in the visible continuum bands. Agreement is
  poorer for the CN and G-bands. The analysis of the simulations uncovers
  a potentially more realistic centre-to-limb behaviour than calculations
  based on 1-D model atmospheres. <BR /> Conclusions: We conclude that
  starting from 3-D MHD simulations represents a powerful approach
  to obtaining intensity contrasts for a wide wavelength coverage and
  different positions across on the solar disk. This also paves the way
  for future calculations of facular and network contrast as a function
  of magnetic fluxes.

---------------------------------------------------------
Title: Applicability of Milne-Eddington inversions to high spatial
    resolution observations of the quiet Sun
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Vögler, A.; Del
   Toro Iniesta, J. C.
2010A&A...518A...2O    Altcode: 2010arXiv1005.5012O
  Context. The physical conditions of the solar photosphere change on
  very small spatial scales both horizontally and vertically. Such a
  complexity may pose a serious obstacle to the accurate determination
  of solar magnetic fields. <BR /> Aims: We examine the applicability of
  Milne-Eddington (ME) inversions to high spatial resolution observations
  of the quiet Sun. Our aim is to understand the connection between
  the ME inferences and the actual stratifications of the atmospheric
  parameters. <BR /> Methods: We use magnetoconvection simulations of
  the solar surface to synthesize asymmetric Stokes profiles such as
  those observed in the quiet Sun. We then invert the profiles with the
  ME approximation. We perform an empirical analysis of the heights of
  formation of ME measurements and analyze the uncertainties brought
  about by the ME approximation. We also investigate the quality of the
  fits and their relationship with the model stratifications. <BR />
  Results: The atmospheric parameters derived from ME inversions of
  high-spatial resolution profiles are reasonably accurate and can be
  used for statistical analyses of solar magnetic fields, even if the
  fit is not always good. We also show that the ME inferences cannot be
  assigned to a specific atmospheric layer: different parameters sample
  different ranges of optical depths, and even the same parameter
  may trace different layers depending on the physical conditions
  of the atmosphere. Despite this variability, ME inversions tend
  to probe deeper layers in granules than in intergranular lanes. <P
  />Figure 10 and appendix are only available in electronic form at <A
  href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Solar Surface Magnetism and Irradiance on Time Scales from
    Days to the 11-Year Cycle
Authors: Domingo, V.; Ermolli, I.; Fox, P.; Fröhlich, C.; Haberreiter,
   M.; Krivova, N.; Kopp, G.; Schmutz, W.; Solanki, S. K.; Spruit, H. C.;
   Unruh, Y.; Vögler, A.
2009SSRv..145..337D    Altcode:
  The uninterrupted measurement of the total solar irradiance during the
  last three solar cycles and an increasing amount of solar spectral
  irradiance measurements as well as solar imaging observations
  (magnetograms and photometric data) have stimulated the development
  of models attributing irradiance variations to solar surface
  magnetism. Here we review the current status of solar irradiance
  measurements and modelling efforts based on solar photospheric
  magnetic fields. Thereby we restrict ourselves to the study of solar
  variations from days to the solar cycle. Phenomenological models
  of the solar atmosphere in combination with imaging observations of
  solar electromagnetic radiation and measurements of the photospheric
  magnetic field have reached high enough quality to show that a large
  fraction (at least, about 80%) of the solar irradiance variability
  can be explained by the radiative effects of the magnetic activity
  present in the photosphere. Also, significant progress has been made
  with magnetohydrodynamic simulations of convection that allow us to
  relate the radiance of the photospheric magnetic structures to the
  observations.

---------------------------------------------------------
Title: On the origin of microturbulence in hot stars
Authors: Cantiello, M.; Langer, N.; Brott, I.; de Koter, A.; Shore,
   S. N.; Vink, J. S.; Voegler, A.; Yoon, S. -C.
2009CoAst.158...61C    Altcode: 2008arXiv0810.2546C
  We present results from the first extensive study of convection zones
  in the envelopes of hot massive stars, which are caused by opacity
  peaks associated with iron and helium ionization. These convective
  regions can be located very close to the stellar surface. The region
  in the Hertzsprung-Russel diagram in which we predict the convection
  zones and the strength of this convection is in good agreement with
  the occurrence and strength of microturbulence in massive stars. We
  further argue that convection close to the surface may trigger clumping
  at the base of the stellar wind of hot massive stars.

---------------------------------------------------------
Title: Sub-surface convection zones in hot massive stars and their
    observable consequences
Authors: Cantiello, M.; Langer, N.; Brott, I.; de Koter, A.; Shore,
   S. N.; Vink, J. S.; Voegler, A.; Lennon, D. J.; Yoon, S. -C.
2009A&A...499..279C    Altcode: 2009arXiv0903.2049C
  Context: We study the convection zones in the outer envelope of hot
  massive stars which are caused by opacity peaks associated with iron
  and helium ionization. <BR />Aims: We determine the occurrence and
  properties of these convection zones as function of the stellar
  parameters. We then confront our results with observations of OB
  stars. <BR />Methods: A stellar evolution code is used to compute
  a grid of massive star models at different metallicities. In these
  models, the mixing length theory is used to characterize the envelope
  convection zones. <BR />Results: We find the iron convection zone (FeCZ)
  to be more prominent for lower surface gravity, higher luminosity and
  higher initial metallicity. It is absent for luminosities below about
  10<SUP>3.2</SUP> {L}_⊙, 10<SUP>3.9</SUP> {L}_⊙, and 10<SUP>4.2</SUP>
  {L}_⊙ for the Galaxy, LMC and SMC, respectively. We map the strength
  of the FeCZ on the Hertzsprung-Russell diagram for three metallicities,
  and compare this with the occurrence of observational phenomena
  in O stars: microturbulence, non-radial pulsations, wind clumping,
  and line profile variability. <BR />Conclusions: The confirmation of
  all three trends for the FeCZ as function of stellar parameters by
  empirical microturbulent velocities argues for a physical connection
  between sub-photospheric convective motions and small scale stochastic
  velocities in the photosphere of O- and B-type stars. We further suggest
  that clumping in the inner parts of the winds of OB stars could be
  caused by the same mechanism, and that magnetic fields produced in the
  FeCZ could appear at the surface of OB stars as diagnosed by discrete
  absorption components in ultraviolet absorption lines. <P />Tables A.1
  and A.2 are only available in electronic form via http://www.aanda.org

---------------------------------------------------------
Title: Explanation of the activity sensitivity of Mn I 5394.7 Å
Authors: Vitas, N.; Viticchiè, B.; Rutten, R. J.; Vögler, A.
2009A&A...499..301V    Altcode: 2008arXiv0811.3555V
  There is a long-standing debate why the Mn i 5394.7 Å line in the
  solar irradiance spectrum brightens more at higher activity than
  other photospheric lines. The claim that this is caused by spectral
  interlocking to chromospheric emission in the Mg ii h &amp; k lines
  is disputed. In this paper we settle this issue, using classical
  one-dimensional modeling for demonstration and modern three-dimensional
  MHD simulation for verification and analysis. The unusual sensitivity
  of the Mn i 5394.7 Å line to solar activity is due to its excessive
  hyperfine structure. This overrides the thermal and granular Doppler
  smearing through which the other, narrower, photospheric lines lose
  such sensitivity. We take the nearby Fe i 5395.2 Å line as example
  of the latter, and analyze the formation of both lines in detail to
  demonstrate and explain the granular Doppler brightening which affects
  all narrow photospheric lines. Neither the chromosphere nor Mg ii h
  &amp; k emission play a role, nor is it correct to describe the activity
  sensitivity of Mn i 5394.7 Å in terms of plage models with outward
  increasing temperature contrast. The Mn i 5394.7 Å line represents a
  proxy diagnostic of strong-field magnetic concentrations in the deep
  solar photosphere comparable to the G band and the blue wing of Hα,
  but not a better one than these. The Mn i lines are more promising as
  diagnostics of weak fields in high-resolution Stokes polarimetry.

---------------------------------------------------------
Title: Towards Long-Term Solar Irradiance Modelling: Network Contrasts
    from Magneto-Convection Simulations
Authors: Unruh, Y. C.; Solanki, S. K.; Schüssler, M.; Vögler, A.;
   Garcia-Alvarez, D.
2009AIPC.1094..768U    Altcode: 2009csss...15..768U
  Solar irradiance changes on a wide range of time scales and is a key
  driver of the Earth's climate where secular variability in particular is
  relevant. This is, however, not well understood and our knowledge relies
  on reconstructions based on sunspot numbers and similar proxies. <P
  />The prime candidate to produce secular variability is a change
  in the surface coverage of small-scale magnetic elements. Direct
  observational determination of the flux emitted by these magnetic
  elements is difficult, especially as information covering a large
  spectral range is needed. Here we present a theoretical approach
  to this problem using intensity calculations from 3-D simulations
  of solar magneto-convection and compare these with the intensity
  calculations used in the successful semi-empirical S ATIRE models at
  disk centre. Eventually, such a comparison should lead to the removal
  of the last free parameter from S ATIRE-based irradiance reconstruction.

---------------------------------------------------------
Title: The intensity contrast of solar granulation: comparing Hinode
    SP results with MHD simulations
Authors: Danilovic, S.; Gandorfer, A.; Lagg, A.; Schüssler, M.;
   Solanki, S. K.; Vögler, A.; Katsukawa, Y.; Tsuneta, S.
2008A&A...484L..17D    Altcode: 2008arXiv0804.4230D
  Context: The contrast of granulation is an important quantity
  characterizing solar surface convection. <BR />Aims: We compare the
  intensity contrast at 630 nm, observed using the Spectro-Polarimeter
  (SP) aboard the Hinode satellite, with the 3D radiative MHD simulations
  of Vögler &amp; Schüssler (2007, A&amp;A, 465, L43). <BR />Methods:
  A synthetic image from the simulation is degraded using a theoretical
  point-spread function of the optical system, and by considering other
  important effects. <BR />Results: The telescope aperture and the
  obscuration by the secondary mirror and its attachment spider, reduce
  the simulated contrast from 14.4% to 8.5%. A slight effective defocus
  of the instrument brings the simulated contrast down to 7.5%, close to
  the observed value of 7.0%. <BR />Conclusions: A proper consideration
  of the effects of the optical system and a slight defocus, lead to
  sufficient degradation of the synthetic image from the MHD simulation,
  such that the contrast reaches almost the observed value. The remaining
  small discrepancy can be ascribed to straylight and slight imperfections
  of the instrument, which are difficult to model. Hence, Hinode SP data
  are consistent with a granulation contrast which is predicted by 3D
  radiation MHD simulations.

---------------------------------------------------------
Title: Strong horizontal photospheric magnetic field in a surface
    dynamo simulation
Authors: Schüssler, M.; Vögler, A.
2008A&A...481L...5S    Altcode: 2008arXiv0801.1250S
  Context: Observations with the Hinode spectro-polarimeter have
  revealed strong horizontal internetwork magnetic fields in the quiet
  solar photosphere. <BR />Aims: We aim to interpret the observations
  with results from numerical simulations. <BR />Methods: Radiative MHD
  simulations of dynamo action by near-surface convection are analyzed
  with respect to the relation between vertical and horizontal magnetic
  field components. <BR />Results: The dynamo-generated fields show
  a clear dominance of the horizontal field in the height range where
  the spectral lines used for the Hinode observations are formed. The
  ratio between the averaged horizontal and vertical field components is
  consistent with the values derived from the observations. This behavior
  results from the intermittent nature of the dynamo field with polarity
  mixing on small scales in the surface layers. <BR />Conclusions:
  Our results provide further evidence that local near-surface dynamo
  action contributes significantly to the solar internetwork fields.

---------------------------------------------------------
Title: Radiative magnetohydrodynamic simulations of solar pores
Authors: Cameron, R.; Schüssler, M.; Vögler, A.; Zakharov, V.
2007A&A...474..261C    Altcode:
  Context: Solar pores represent a class of magnetic structures
  intermediate between small-scale magnetic flux concentrations in
  intergranular lanes and fully developed sunspots with penumbrae. <BR
  />Aims: We study the structure, energetics, and internal dynamics
  of pore-like magnetic structures by means of exploratory numerical
  simulations. <BR />Methods: The MURaM code has been used to carry
  out several 3D radiative MHD simulations for pores of various sizes
  and with different boundary conditions. <BR />Results: The general
  properties of the simulated pores (morphology, continuum intensity,
  magnetic field geometry, surrounding flow pattern, mean height
  profiles of temperature, pressure, and density) are consistent with
  observational results. No indications for the formation of penumbral
  structure are found. The simulated pores decay by gradually shedding
  magnetic flux into the surrounding pattern of intergranular downflows
  (“turbulent erosion”). When viewed under an angle (corresponding
  to observations outside solar disc center), granules behind the pore
  appear brightened. <BR />Conclusions: Radiative MHD simulations capture
  many observed properties of solar pores.

---------------------------------------------------------
Title: Stokes diagnostics of simulated solar magneto-convection
Authors: Shelyag, S.; Schüssler, M.; Solanki, S. K.; Vögler, A.
2007A&A...469..731S    Altcode: 2007astro.ph..3490S
  We present results of synthetic spectro-polarimetric diagnostics of
  radiative MHD simulations of solar surface convection with magnetic
  fields. Stokes profiles of Zeeman-sensitive lines of neutral iron in
  the visible and infrared spectral ranges emerging from the simulated
  atmosphere have been calculated in order to study their relation to the
  relevant physical quantities and compare with observational results. We
  have analyzed the dependence of the Stokes-I line strength and width as
  well as of the Stokes-V signal and asymmetries on the magnetic field
  strength. Furthermore, we have evaluated the correspondence between
  the actual velocities in the simulation with values determined from
  the Stokes-I (Doppler shift of the centre of gravity) and Stokes-V
  profiles (zero-crossing shift). We confirm that the line weakening in
  strong magnetic fields results from a higher temperature (at equal
  optical depth) in the magnetic flux concentrations. We also confirm
  that considerable Stokes-V asymmetries originate in the peripheral
  parts of strong magnetic flux concentrations, where the line of sight
  cuts through the magnetopause of the expanding flux concentration into
  the surrounding convective donwflow.

---------------------------------------------------------
Title: Photospheric magnetoconvection
Authors: Cameron, Robert; Vögler, Alexander; Schüssler, Manfred
2007IAUS..239..475C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A solar surface dynamo
Authors: Vögler, A.; Schüssler, M.
2007A&A...465L..43V    Altcode: 2007astro.ph..2681V
  Context: Observations indicate that the "quiet" solar photosphere
  outside active regions contains considerable amounts of magnetic energy
  and magnetic flux, with mixed polarity on small scales. The origin of
  this flux is unclear. <BR />Aims: We test whether local dynamo action
  of the near-surface convection (granulation) can generate a significant
  contribution to the observed magnetic flux. <BR />Methods: We have
  carried out MHD simulations of solar surface convection, including the
  effects of strong stratification, compressibility, partial ionization,
  radiative transfer, as well as an open lower boundary. <BR />Results:
  Exponential growth of a weak magnetic seed field (with vanishing net
  flux through the computational box) is found in a simulation run with a
  magnetic Reynolds number of about 2600. The magnetic energy approaches
  saturation at a level of a few percent of the total kinetic energy of
  the convective motions. Near the visible solar surface, the (unsigned)
  magnetic flux density reaches at least a value of about 25 G. <BR
  />Conclusions: .A realistic flow topology of stratified, compressible,
  non-helical surface convection without enforced recirculation is
  capable of turbulent local dynamo action near the solar surface.

---------------------------------------------------------
Title: S imulations Of Science Data Of The Solo-VIM Instrument
Authors: Yelles, L.; Hirzberger, J.; Lagg, A.; Woch, J.; Solanki,
   S. K.; Vögler, A.
2007ESASP.641E..34Y    Altcode:
  The SolO-VIM instrument will be a two-dimensional full-Stokes
  spectro-polarimeter which will provide diffraction-limited
  vector-magnetograms, Dopplergrams, and continuum images of the solar
  photosphere. The instrument's performance depends on various parameters
  such as aperture diameter, filter characteristics, spectral- line
  sampling, and orbital position. Here we compute Stokes profiles in
  realistic 3D MHD simulations. These synthetic data are then degraded to
  match the output ex- pected from the VIM instrument, and subsequently
  inverted using a Milne-Eddington atmosphere. We present parameter
  studies in order to set up minimum require- ments on limitations of
  VIM's capabilities.

---------------------------------------------------------
Title: Magnetoconvection in a Sunspot Umbra
Authors: Schüssler, M.; Vögler, A.
2006ApJ...641L..73S    Altcode: 2006astro.ph..3078S
  Results from a realistic simulation of three-dimensional radiative
  magnetoconvection in a strong background magnetic field corresponding
  to the conditions in sunspot umbrae are shown. The convective energy
  transport is dominated by narrow upflow plumes with adjacent downflows,
  which become almost field-free near the surface layers. The strong
  external magnetic field forces the plumes to assume a cusplike shape
  in their top parts, where the upflowing plasma loses its buoyancy. The
  resulting bright features in intensity images correspond well (in terms
  of brightness, size, and lifetime) to the observed umbral dots in the
  central parts of sunspot umbrae. Most of the simulated umbral dots
  have a horizontally elongated form with a central dark lane. Above
  the cusp, most plumes show narrow upflow jets, which are driven
  by the pressure of the piled-up plasma below. The large velocities
  and low field strengths in the plumes are effectively screened from
  spectroscopic observation because the surfaces of equal optical depth
  are locally elevated, so that spectral lines are largely formed above
  the cusp. Our simulations demonstrate that nearly field-free upflow
  plumes and umbral dots are a natural result of convection in a strong,
  initially monolithic magnetic field.

---------------------------------------------------------
Title: Simulations of Solar Pores
Authors: Cameron, R.; Vögler, A.; Schüssler, M.; Zakharov, V.
2005ESASP.600E..11C    Altcode: 2005ESPM...11...11C; 2005dysu.confE..11C
  No abstract at ADS

---------------------------------------------------------
Title: Stokes diagnostics of simulations of magnetoconvection of
    mixed-polarity quiet-Sun regions
Authors: Khomenko, E. V.; Shelyag, S.; Solanki, S. K.; Vögler, A.
2005A&A...442.1059K    Altcode:
  Realistic solar magneto-convection simulations including the
  photospheric layers are used to study the polarization of the Fe i
  Zeeman-sensitive spectral lines at 6301.5, 6302.5, 15 648 and 15 652
  Å. The Stokes spectra are synthesized in a series of snapshots with
  a mixed-polarity magnetic field whose average unsigned strength varies
  from &lt; B &gt; = 10 to 140 G. The effects of spatial resolution and
  of the amount of magnetic flux in the simulation box on the profiles
  shapes, amplitudes and shifts are discussed. The synthetic spectra show
  many properties in common with those observed in quiet solar regions. In
  particular, the simulations reproduce the width and depth of spatially
  averaged Stokes I profiles, the basic classes of the Stokes V profiles
  and their amplitude and area asymmetries, as well as the abundance of
  the irregular-shaped Stokes V profiles. It is demonstrated that the
  amplitudes of the 1.56 μm lines observed in the inter-network are
  consistent with a "true" average unsigned magnetic field strength of
  20 G. We show that observations using these and visible lines, carried
  out under different seeing conditions (e.g., simultaneous observations
  at different telescopes), may result in different asymmetries and
  even opposite polarities of the profiles in the two spectral regions
  observed at the same spatial point.

---------------------------------------------------------
Title: Dissecting the spiral galaxy M 83: mid-infrared emission and
    comparison with other tracers of star formation
Authors: Vogler, A.; Madden, S. C.; Beck, R.; Lundgren, A. A.; Sauvage,
   M.; Vigroux, L.; Ehle, M.
2005A&A...441..491V    Altcode: 2005astro.ph..8027V
  We present a detailed mid-infrared study of the nearby, face-on
  spiral galaxy M 83 based on ISOCAM data. M 83 is a unique case study,
  since a wide variety of MIR broad-band filters as well as spectra,
  covering the wavelength range of 4 to 18 μm, were observed and are
  presented here. Emission maxima trace the nuclear and bulge area,
  star-formation regions at the end of the bar, as well as the inner
  spiral arms. The fainter outer spiral arms and interarm regions
  are also evident in the MIR map. Spectral imaging of the central 3
  arcmin × 3 arcmin (4 kpc× 4 kpc) field allows us to investigate five
  regions of different environments. The various MIR components (very
  small grains, polycyclic aromatic hydrocarbon (PAH) molecules, ionic
  lines) are analyzed for different regions throughout the galaxy. In
  the total λ4 μm to 18 μm wavelength range, the PAHs dominate the
  luminosity, contributing between 60% in the nuclear and bulge regions
  and 90% in the less active, interarm regions. Throughout the galaxy,
  the underlying continuum emission from the small grains is always a
  smaller contribution in the total MIR wavelength regime, peaking in
  the nuclear and bulge components. The implications of using broad-band
  filters only to characterize the mid-infrared emission of galaxies,
  a commonly used ISOCAM observation mode, are discussed. We present
  the first quantitative analysis of new Hα and λ6 cm VLA+Effelsberg
  radio continuum maps of M 83. The distribution of the MIR emission
  is compared with that of the CO, HI, R band, Hα and λ6 cm radio. A
  striking correlation is found between the intensities in the two
  mid-infrared filter bands and the λ6 cm radio continuum. To explain
  the tight mid-infrared-radio correlation we propose the anchoring of
  magnetic field lines in the photoionized shells of gas clouds.

---------------------------------------------------------
Title: Magnetic flux in the internetwork quiet Sun
Authors: Khomenko, E. V.; Martínez González, M. J.; Collados, M.;
   Vögler, A.; Solanki, S. K.; Ruiz Cobo, B.; Beck, C.
2005A&A...436L..27K    Altcode:
  We report a direct comparison of the amplitudes of Stokes spectra of the
  Fe i 630 nm and 1.56 μm lines produced by realistic MHD simulations
  with simultaneous observations in the same spectral regions. The
  Stokes spectra were synthesized in snapshots with a mixed polarity
  magnetic field having a spatially averaged strength, &lt; B &gt;,
  between 10 and 30 G. The distribution of Stokes V amplitudes depends
  sensitively on &lt; B &gt;. A quiet inter-network region was observed
  at the German VTT simultaneously with TIP (1.56 μm) and POLIS (630
  nm). We find that the Stokes V amplitudes of both infrared and visible
  observations are best reproduced by the simulation snapshot with &lt;
  B &gt; = 20 G. In observations with 1 resolution, up to 2/3 of the
  magnetic flux can remain undetected.

---------------------------------------------------------
Title: Simulations of magneto-convection in the solar photosphere.
    Equations, methods, and results of the MURaM code
Authors: Vögler, A.; Shelyag, S.; Schüssler, M.; Cattaneo, F.;
   Emonet, T.; Linde, T.
2005A&A...429..335V    Altcode:
  We have developed a 3D magnetohydrodynamics simulation code for
  applications in the solar convection zone and photosphere. The code
  includes a non-local and non-grey radiative transfer module and takes
  into account the effects of partial ionization. Its parallel design
  is based on domain decomposition, which makes it suited for use on
  parallel computers with distributed memory architecture. We give a
  description of the equations and numerical methods and present the
  results of the simulation of a solar plage region. Starting with
  a uniform vertical field of 200 G, the processes of flux expulsion
  and convective field amplification lead to a dichotomy of strong,
  mainly vertical fields embedded in the granular downflow network and
  weak, randomly oriented fields filling the hot granular upflows. The
  strong fields form a magnetic network with thin, sheet-like structures
  extending along downflow lanes and micropores with diameters of up to
  1000 km which form occasionally at vertices where several downflow
  lanes merge. At the visible surface around optical depth unity,
  the strong field concentrations are in pressure balance with their
  weakly magnetized surroundings and reach field strengths of up to 2
  kG, strongly exceeding the values corresponding to equipartition with
  the kinetic energy density of the convective motions. As a result of
  the channelling of radiation, small flux concentrations stand out as
  bright features, while the larger micropores appear dark in brightness
  maps owing to the suppression of the convective energy transport. The
  overall shape of the magnetic network changes slowly on a timescale
  much larger than the convective turnover time, while the magnetic flux
  is constantly redistributed within the network leading to continuous
  formation and dissolution of flux concentrations. <P />Appendices A-D
  are only available in electronic form at http://www.edpsciences.org

---------------------------------------------------------
Title: On the effect of photospheric magnetic fields on solar surface
    brightness . Results of radiative MHD simulations
Authors: Vögler, A.
2005MmSAI..76..842V    Altcode:
  Magnetic features in the solar surface layers are assumed to be a
  main cause for solar irradiance variations on timescales of the
  solar cycle and shorter. Realistic radiative MHD simulations of
  photospheric magneto-convection allow us to study the interaction
  between magnetic features, convective flows and radiation in detail
  and help to understand the physical mechanisms underlying irradiance
  variations, whilst at the same time allowing direct comparison with
  observations. We report on a series of local-box MHD simulations
  covering magneto-convection in the photosphere from quiet Sun to strong
  plage conditions. We find that for average magnetic field strengths
  corresponding to plage or facular regions, the total emergent radiation
  flux is increased by 2 - 3 % relative to quiet Sun conditions,
  mainly as a result of increased radiative losses along inclined
  rays from the hot walls of faculae. For stronger average fields,
  the radiative energy output drops below quiet Sun levels, partly
  due to a darker appearance of magnetic features near disk center,
  partly due to reduced granule brightness. The simulations underline
  that the modification of convective and radiative energy transport
  in the photosphere due to surface magnetism is a viable mechanism for
  solar irradiance variations. The center-to-limb variation of bolometric
  intensity and facular contrast show good agreement with observations,
  suggesting that realistic radiative MHD simulations can be useful for
  refined models of solar irradiance variations.

---------------------------------------------------------
Title: The Decay of a Simulated Pore
Authors: Cameron, R.; Vögler, A.; Shelyag, S.; Schüssler, M.
2004ASPC..325...57C    Altcode:
  Using MURaM -- Max-Planck Institut für Aeronomie University of
  Chicago Radiative Magnetohydrodynamics -- an MHD code which includes
  radiative transfer and partial ionization, we have studied the decay
  phase of a solar pore. The simulations are sufficiently realistic
  in their treatment of the photosphere to allow a direct comparison
  with observations, both current and those of upcoming missions such
  as SolarB. As well as discussing the structure and decay of pores,
  we show the formation of shallow, field aligned, convective rolls
  which are an important feature of our solutions.

---------------------------------------------------------
Title: G-band spectral synthesis and diagnostics of simulated solar
    magneto-convection
Authors: Shelyag, S.; Schüssler, M.; Solanki, S. K.; Berdyugina,
   S. V.; Vögler, A.
2004A&A...427..335S    Altcode:
  Realistic simulations of radiative magneto-convection in the solar
  (sub)photosphere are used for a spectral synthesis of Fraunhofer's G
  band, which is dominated by spectral lines from the CH molecule. It
  is found that the spatial pattern of integrated G-band brightness
  closely matches the spatial structure of magnetic flux concentrations
  in the convective downflow regions. The brightness contrast is mainly
  caused by the weakening of CH lines due to the reduced CH abundance
  and the resulting shift of the optical depth scale in the hot and
  tenuous magnetic flux concentrations. Various properties of the
  synthetic brightness images agree well with G-band observations. These
  results lends credit to the observational usage of G-band bright
  features as proxies for magnetic flux concentrations in the solar
  photosphere. However, the converse is only correct in a limited sense:
  only a fraction of the magnetic flux concentrations turn out to be
  bright in the G band.

---------------------------------------------------------
Title: Effects of non-grey radiative transfer on 3D simulations  of
    solar magneto-convection
Authors: Vögler, A.
2004A&A...421..755V    Altcode:
  We compare 3D simulations of photospheric magneto-convection which
  include a multigroup modelling of the non-grey radiative transfer with
  simulations based on a grey radiative transfer using the Rosseland mean
  opacity. While the simulation properties in the solar surface layers
  around τ<SUB>Ross</SUB>=1 are very similar both cases, pronounced
  differences occur both in the temperature structure of magnetic field
  concentrations in the upper photosphere and in the appearance of strong
  magnetic fields in brightness maps. The results show that a non-grey
  treatment of the radiative transfer is mandatory if magneto-convective
  simulations are to be compared with observational results by calculating
  synthetic spectra of temperature-sensitive lines originating in the
  middle and upper photosphere.

---------------------------------------------------------
Title: Approximations for non-grey radiative transfer in numerical
    simulations of the solar photosphere
Authors: Vögler, A.; Bruls, J. H. M. J.; Schüssler, M.
2004A&A...421..741V    Altcode:
  Realistic simulations of solar (magneto-)convection require an
  accurate treatment of the non-grey character of the radiative energy
  transport. Owing to the large number of spectral lines in the solar
  atmosphere, statistical representations of the line opacities have to
  be used in order to keep the problem numerically tractable. We consider
  two statistical approaches, the opacity distribution function (ODF)
  concept and the multigroup (or opacity binning) method and provide a
  quantitative assessment of the errors that arise from the application
  of these methods in the context of 2D/3D simulations. In a first step,
  the ODF- and multigroup methods are applied to a 1D model-atmosphere
  and the resulting radiative heating rates are compared. A number of
  4-6 frequency bins is found to warrant a satisfactory modeling of the
  radiative energy exchange. Further tests in 2D model-atmospheres show
  the applicability of the multigroup method in realistic situations
  and underline the importance of a non-grey treatment. Furthermore, we
  address the question of an appropriate opacity average in multigroup
  calculations and discuss the significance of velocity gradients for
  the radiative heating rates.

---------------------------------------------------------
Title: On the Origin of Solar Faculae
Authors: Keller, C. U.; Schüssler, M.; Vögler, A.; Zakharov, V.
2004ApJ...607L..59K    Altcode:
  Solar faculae appear as bright small features close to the solar
  limb. Recent high-resolution images show these brightenings in
  unprecedented detail. Our analysis of numerical MHD simulations
  reproduces the observed small-scale features. The simulations reveal
  that faculae originate from a thin layer within granules just below
  largely transparent magnetic flux concentrations. This is basically
  the “bright wall” model of Spruit. The dark, narrow lanes often
  associated with faculae occur at the opposite side of the magnetic flux
  concentration and are due to an extended layer with lower-than-average
  temperature.

---------------------------------------------------------
Title: Stokes diagnostics of magneto-convection. Profile shapes
    and asymmetries
Authors: Khomenko, E. V.; Shelyag, S.; Solanki, S. K.; Vögler, A.;
   Schüssler, M.
2004IAUS..223..635K    Altcode: 2005IAUS..223..635K
  We discuss the polarization signals produced in recent realistic 3D
  simulations of solar magnetoconvection. The Stokes profiles of the
  Fe I 6301.5, 6302.5, 15648 and 15652 mathrm{Å} Zeeman-sensitive
  spectral lines are synthesised and smeared to simulate the image
  degradation caused by the Earth's atmosphere and finite telescope
  resolution. A Principal Component Analysis approach is applied to
  classify the profiles. We find that the classes of Stokes V profiles
  as well as their amplitude and area asymmetries are very close to the
  observations in the network and inter-network regions.

---------------------------------------------------------
Title: Stokes Diagnostics of Magnetoconvection. Profile shapes
    and asymmetries.
Authors: Khomenko, E. V.; Shelyag, S.; Solanki, S. K.; Vogler, A.;
   Schussler, M.
2004cosp...35.2131K    Altcode: 2004cosp.meet.2131K
  Stokes profiles observed in the quiet Sun have a broad range of
  asymmetries and show a variety of shapes. These asymmetries are the
  result of the velocity and magnetic field gradients both in horizontal
  and vertical directions. We use the most recent realistic 3D simulations
  of magnetoconvection at the solar surface to synthesize Stokes profiles
  of some photospheric lines and to compare them with observations. Such
  comparison provides an important constrains on the MHD models allowing
  to conclude about their realism and, thus, to understand the nature of
  solar magnetoconvection. The following Zeeman-sensitive spectral lines
  are considered: Fe I 6301.5, 6302.5, 15648 and 15652 Å. These lines are
  extensively used in observations. The computed Stokes profiles of these
  lines were spatially smeared to simulate the effects of a telescope and
  atmospheric seeing. A Principal Component Analysis approach is applied
  to classify the profiles. The effects of spatial resolution and the
  amount of the magnetic flux in the MHD model on the profile shapes are
  discussed. The profiles of different classes are clustered together and
  form patches on the surface. The size of these patches decreases with
  increasing spatial resolution. The distributions of the amplitude and
  area asymmetries of Stokes V profiles are very close to the observations
  in network and inter-network regions. Some 15% of the profiles smeared
  with a 0.”5 seeing have irregular shape with 3 or more lobes. Finally,
  we show that simultaneous observations of the same area of the solar
  disc using infrared Fe I 15648, 15652 Å and the visible Fe I 6301.5,
  6302.5 Å lines done under different seeing conditions (for example
  in the case of simultaneous observations at different telescopes)
  may result in different asymmetries and even different polarities
  of the profiles in two spectral regions observed at the same spatial
  point. This work was partially supported by INTAS grant 00-00084.

---------------------------------------------------------
Title: Simulating Radiative Magneto-convection in the Solar
    Photosphere (With 11 Figures)
Authors: Vögler, Alexander
2004RvMA...17...69V    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Structure and dynamics of photospheric magnetic fields
Authors: Vögler, A.
2004cosp...35.4067V    Altcode: 2004cosp.meet.4067V
  The interaction of convective flows and magnetic fields in the
  solar photosphere and in the uppermost layers of the convection
  zone is crucial for many phenomena of solar activity. Realistic
  magnetohydrodynamic simulations including an accurate treatment of
  radiative processes provide insight into the three-dimensional structure
  of magnetic field configurations in the photosphere and allow for a
  direct comparison with observations. In this talk we present recent
  results of 3D MHD simulations of quiet Sun and plage regions. We
  discuss morphology, time evolution and statistical properties of
  magnetic field concentrations. The questions addressed include the
  origin of the continuum contrast of plage faculae near the limb and
  the decay of magnetic flux in mixed polarity regions.

---------------------------------------------------------
Title: Why Solar Magnetic Flux Concentrations Are Bright in Molecular
    Bands
Authors: Schüssler, M.; Shelyag, S.; Berdyugina, S.; Vögler, A.;
   Solanki, S. K.
2003ApJ...597L.173S    Altcode:
  Using realistic ab initio simulations of radiative magnetoconvection,
  we show that the bright structures in images taken in the “G band,”
  a spectral band dominated by lines of the CH molecule, precisely
  outline small-scale concentrations of strong magnetic fields on the
  visible solar surface. The brightening is caused by a depletion of CH
  molecules in the hot and tenuous magnetic structures, thus confirming
  the model of radiatively heated magnetic flux concentrations. These
  results provide a firm basis for observational studies of the evolution
  and dynamics of the small-scale solar magnetic field derived through
  “proxy magnetometry” with G-band images.

---------------------------------------------------------
Title: On the fractal dimension of small-scale magnetic structures
    in the Sun
Authors: Janßen, K.; Vögler, A.; Kneer, F.
2003A&A...409.1127J    Altcode:
  We compare, by means of fractal analyses, the shapes of observed
  small-scale magnetic structures on the Sun with those of magnetic
  features resulting from numerical simulations of magnetoconvection. The
  observations were obtained with the “Göttingen” Fabry-Perot
  spectrometer at the Vacuum Tower Telescope at the Observatorio del Teide
  on Tenerife. Magnetograms with 0\farcs4-0\farcs5 spatial resolution were
  obtained from two-dimensional Stokes V polarimetry in the Fe I 6302.5 Å
  line and by image reconstruction with speckle methods. The simulations
  of magnetoconvection was performed with the MURAM code. It solves the
  time-dependent MHD equations for a compressible, partly ionized plasma
  including radiative transfer in LTE. To determine the fractal dimensions
  the perimeter-area relation is used. We discuss the influence of seeing
  and noise in the fractal dimension D of the observed magnetograms. A
  dependence of D on the distance from disk center could not be found. The
  observations give D=1.21+/-0.05 for a pixel size corresponding to
  0\farcs105, while for the numerical simulations D=1.38+/-0.07 for a
  pixel size of 20.83 km. If we use a yardstick adapted to the spatial
  resolution the observations give the dimension D=1.41+/-0.05 in close
  agreement with the simulations. This agreement is remarkable since
  the pixel sizes and spatial resolutions of the simulations and of the
  observations differ by a factor of 15. The finding supports the view
  of self-similarity of solar magnetic structures over a large range of
  scales. In addition, it demonstrates the realism of the simulations
  and suggests that all important physical processes are included. We
  discuss our results in comparison with other investigations.

---------------------------------------------------------
Title: Hausdorff-Dimension of Magnetic Structures
Authors: Janssen, Katja; Vögler, Alexander; Kneer, Franz
2003ANS...324...30J    Altcode: 2003ANS...324..D06J
  No abstract at ADS

---------------------------------------------------------
Title: RX J004717.4-251811: The first eclipsing X-ray binary outside
    the Local Group
Authors: Pietsch, W.; Haberl, F.; Vogler, A.
2003A&A...402..457P    Altcode: 2003astro.ph..2546P
  The X-ray source <ASTROBJ>RX J004717.4-251811</ASTROBJ> in the nearby
  starburst galaxy <ASTROBJ>NGC 253</ASTROBJ> was found to undergo
  changes from a low to a high state twice, during an XMM-Newton EPIC
  observation in December 2000 and also during a Chandra observation
  one year earlier. These transitions are interpreted as egresses
  from eclipses of a compact object in a high mass X-ray binary system
  (HMXB). The phase of eclipse egress during the Chandra observation is
  given by barycenter corrected MJD 51539.276+/- 0.006 and the binary
  period determined to p=(352.870+/-0.012)d/n by the time difference
  between the two egresses and number n of periods in-between. Allowed
  periods may be further constrained by additional XMM-Newton,
  Chandra, ROSAT, and Einstein observations resulting in only seven
  acceptable periods with 1.47024 d and 3.20793 d most promising. No
  significant regular pulsations of the source in the range 0.3-1000
  s were found. Fluctuations on time scales of 1000 s were observed
  together with extended intervals of low intensity. The energy spectrum
  during the bright state can best be described by an absorbed flat
  power law (N<SUB>H</SUB>,= 1.9×10<SUP>21</SUP>cm<SUP>-2</SUP>, Gamma
  =1.7). In the bright state the source luminosity is 4x 10<SUP>38</SUP>
  (0.5-5 keV), just compatible with the Eddington luminosity of a 1.4
  M<SUB>sun</SUB> neutron star. A possible optical identification is
  suggested. <ASTROBJ>RX J004717.4-251811</ASTROBJ> parameters are
  compared to other eclipsing X-ray binaries (XRBs). <P />This work is
  based on observations obtained with XMM-Newton, an ESA Science Mission
  with instruments and contributions directly funded by ESA Member States
  and the USA (NASA).

---------------------------------------------------------
Title: Three-dimensional simulations of magneto-convection in the
    solar photosphere
Authors: Vögler, Alexander
2003PhDT........61V    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Studying magneto-convection by numerical simulation
Authors: Vögler, A.; Schüssler, M.
2003AN....324..399V    Altcode:
  Following a brief overview of the two main approaches to investigate
  the interaction between magnetic fields and convective flows near the
  solar surface layers by numerical simulation, namely idealized model
  problems and `realistic' large-eddy simulations, we present first
  results obtained with a newly developed MHD code. The first example
  concerns the realistic simulation of the magnetic field dynamics in a
  solar plage region while the second example demonstrates small-scale
  dynamo action in idealized compressible convection.

---------------------------------------------------------
Title: Simulation of Solar Magnetoconvection
Authors: Vögler, A.; Shelyag, S.; Schüssler, M.; Cattaneo, F.;
   Emonet, T.; Linde, T.
2003IAUS..210..157V    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Detection of supernova remnant and black hole candidates in
    M83 with ROSAT
Authors: Immler, S.; Ehle, M.; Pietsch, W.; Vogler, A.
2001AIPC..599..670I    Altcode: 2001xase.conf..670I
  Within the D<SUB>25</SUB> ellipse of M83, 21 X-ray sources are detected
  with the ROSAT HRI. A variable super-Eddington (3.8×10<SUP>39</SUP> erg
  s<SUP>-1</SUP>) X-ray source is found to coincide with a faint, extended
  optical counterpart. Based on the multiwavelength characteristics,
  the source most likely represents a massive (~30 M<SUB>solar</SUB>)
  accreting black hole binary, located in a compact HII region or
  in a globular cluster in M83. We also detect two luminous (3.7 and
  6.7×10<SUP>38</SUP> erg s<SUP>-1</SUP>) previously unknown supernova
  remnant candidates, located in extended Hα emission complexes and
  coinciding with compact 6 cm and 20 cm radio sources. .

---------------------------------------------------------
Title: The Mid-Infrared Properties of Spiral Galaxies
Authors: Sauvage, M.; Roussel, H.; Vigroux, L.; Bosma, A.; Madden,
   S. C.; Vogler, A.; Reynaud, D.; Gallais, P.
2001ESASP.460..151S    Altcode: 2001phso.conf..151S
  We present the results of our study of 69 nearby spiral galaxies
  observed in the Mid-Infrared (MIR) at 6.75 and 15 microns with ISOCAM,
  the camera on-board ISO. We use these images to investigate the
  spatial distribution of the infrared emission as well as the relation
  between the infrared colors and the star formation activity in normal
  galaxies. We show that at ISOCAM's resolution, the nuclear regions
  of spiral galaxies are the only one where star formation is able to
  produce a significant color enhancement. In the disks of spiral galaxy,
  we evidence a strong correlation between the MIR brightness and the star
  formation rate, identical at both MIR wavelengths. We then use ISOCAM
  capacity to disentangle nuclear from disk emission to comment on the
  relation between star formation and FIR emission in normal galaxies,
  and present the implication this work will have in the FIRST era.

---------------------------------------------------------
Title: Generation of bisymmetric magnetic fields in galaxies with
    tidal interaction
Authors: Vögler, A.; Schmitt, D.
2001A&A...374...36V    Altcode:
  Tidal interactions between neighbouring galaxies are expected to
  induce significant nonaxisymmetric velocities in their disks. It
  has been suggested that these velocities play an important role in
  the generation of bisymmetric magnetic fields observed in interacting
  galaxies. We investigate the effect of a nonaxisymmetric radial outflow
  on a three-dimensional linear mean field dynamo. We find that the
  usually dominant axisymmetric quadrupole is effectively damped by the
  outflow. For sufficiently high velocities a bisymmetric magnetic mode
  is then preferentially excited. The resulting field has a spiral-arm
  structure extending well into the differentially rotating outskirts of
  the disk. The influence of velocity-induced mode-coupling effects on
  bisymmetric field generation is found to be negligible. While being
  highly idealized, the model seems to give reasonable representations
  of the large scale fields of the interacting galaxies M 81 and M 51.

---------------------------------------------------------
Title: Bipolar hypershell models of the extended hot interstellar
    medium in spiral galaxies
Authors: Sofue, Y.; Vogler, A.
2001A&A...370...53S    Altcode: 2001astro.ph..1525S
  We simulated the million degree interstellar medium and its soft
  X-ray images in the disk and halo of spiral galaxies using the bipolar
  hypershell (BHS) model. In this model dumbbell- or hourglass-shaped
  expanding shells of several kpc radii are produced by a sudden
  energy release in the central region. We then applied our model to a
  mini-sample of starburst galaxies seen under different inclinations,
  namely the nearly edge-on galaxies NGC 253, NGC 3079 and M 82, the
  highly inclined galaxies NGC 4258 and NGC 1808 as well as the nearly
  face-on galaxy M 83. For all galaxies, our results reproduce the
  X-ray characteristics observed in the 0.1-2.4 keV ROSAT energy band:
  the bipolar hypershell morphology, the spectral energy distribution
  of the diffuse disk and halo emission as well as absorption gaps in
  the diffuse X-ray emission caused by a shadowing of soft X-rays due
  to cold intervening gas in the disks of the galaxies. In general,
  the required total energy for the starburst is estimated to be of
  the order of 10<SUP>55</SUP> ergs, corresponding to the overall
  kinetic energy generated in ~ 10<SUP>4</SUP> type-II supernova
  explosions. The expansion velocity of the shells is estimated to be ~
  200 km s<SUP>-1</SUP>, which is necessary to heat the gas to ~ 0.2 keV
  (2.3 million K), and the age to be of the order of 3 10<SUP>7</SUP>
  years. In the case of the very nearby, nearly edge-on galaxy NGC 253
  all characteristics of the BHS model can be studied with high spatial
  resolution. Using the property that the shell morphology is sensitive
  to the ambient density distribution, we propose using soft X-ray data
  to probe the gas distributions in the disk, halo and intergalactic
  space in general. The application of our model to images at higher
  spatial and spectral resolution, as provided by Chandra and XMM, will
  help us to further disentangle the ISM density distributions and will
  lead to a better understanding of the disk halo interface.

---------------------------------------------------------
Title: Deep XMM-Newton survey of M33
Authors: Pietsch, W.; Haberl, F.; Ehle, M.; Trinchieri, G.; Vogler, A.
2000HEAD....5.2104P    Altcode: 2000BAAS...32.1212P
  In a re-analysis of all ROSAT PSPC and HRI observations on M33 we
  obtained a catalogue of 184 discrete X-ray sources within 50' of the
  nucleus of the galaxy. Based on timing analysis and hardness ratio
  arguments we characterized them as likely supersoft X-ray sources, X-ray
  binaries, or supernova remnants in M33, or as foreground or background
  objects. In addition, we mapped the diffuse X-ray emission in M33 mainly
  concentrated in the inner few arcminutes and the southern disturbed
  inner disk. We will compare this preparatory work with XMM results
  from 5 first epoch observations (10 ksec each taken in August 2000)
  of a deep survey of M33 (150 ksec in total). The survey will allow us
  to characterize the sources using spectra and time variability to built
  up a unprecedented census of X-ray sources in M33 down to a luminosity
  limit of ~ 10<SUP>35</SUP> erg/s. Of specific interest are the active
  source in the nuclear area (a low luminosity AGN or black hole X-ray
  binary) with Lx ~ 10<SUP>39</SUP> erg/s and the diffuse emission in
  the inner disk.

---------------------------------------------------------
Title: X-ray observations of the starburst galaxy NGC 253 ---
    II. Extended emission from hot gas in the nuclear area, disk, and halo
Authors: Pietsch, W.; Vogler, A.; Klein, U.; Zinnecker, H.
2000A&A...360...24P    Altcode: 2000astro.ph..5335P
  Spatial and spectral analysis of deep ROSAT HRI and PSPC observations
  of the near edge-on starburst galaxy NGC 253 reveal diffuse soft
  X-ray emission, which contributes 80% to its total X-ray luminosity
  (L<SUB>X</SUB> = 5 10<SUP>39</SUP> erg s<SUP>-1</SUP>, corrected for
  foreground absorption). The nuclear area, disk, and halo contribution
  to the luminosity is about equal. The starburst nucleus itself is
  highly absorbed and not visible in the ROSAT band. The emission from
  the nuclear area stems from a heavily absorbed source with an extent
  of 250 pc (FWHM) about 100 pc above the nucleus along the SE minor
  axis ("nuclear source", X34), and the "X-ray plume". The nuclear
  source is best described as having a thermal bremsstrahlung spectrum
  with a temperature of T = 1.2 keV (N<SUB>H</SUB> = 3 10<SUP>21</SUP>
  cm<SUP>-2</SUP>) and L<SUB>X</SUB><SUP>exgal</SUP> = 3 10<SUP>38</SUP>
  erg s<SUP>-1</SUP> (corrected for Galactic foreground absorption). The
  spectrum of the hollow-cone shaped plume (opening angle of 32̂
  and extent of ~ 700 pc along the SE minor axis) is best modeled by a
  composite of a thermal bremsstrahlung (N<SUB>H</SUB> = 3 10<SUP>20</SUP>
  cm<SUP>-2</SUP>, T = 1.2 keV, L<SUB>X</SUB><SUP>exgal</SUP> = 4.6
  10<SUP>38</SUP> erg s<SUP>-1</SUP>) and a thin thermal plasma (Galactic
  foreground absorption, T = 0.33 keV, L<SUB>X</SUB><SUP>exgal</SUP> =
  4 10<SUP>38</SUP> erg s<SUP>-1</SUP>). The diffuse nuclear emission
  components trace interactions between the galactic super-wind emitted
  by the starburst nucleus, and the dense interstellar medium of the
  disk. Diffuse emission from the disk is heavily absorbed and follows the
  spiral structure. It can be described by a thin thermal plasma spectrum
  (T = 0.7 keV, intrinsic luminosity L<SUB>X</SUB><SUP>intr</SUP> = 1.2
  10<SUP>39</SUP> erg s<SUP>-1</SUP>), and most likely reflects a mixture
  of sources (X-ray binaries, supernova remnants, and emission from H
  II regions) and the hot interstellar medium. The surface brightness
  profile reveals a bright inner and a fainter outer component along the
  major axis with extents of ∓3.4 kpc and ∓7.5 kpc. We analysed the
  total halo emission separated into two geometrical areas; the "corona"
  (scale height ~ 1 kpc) and the "outer halo". The coronal emission
  (T = 0.2 keV, L<SUB>X</SUB><SUP>intr</SUP> = 7.8 10<SUP>38</SUP> erg
  s<SUP>-1</SUP>) is only detected from the near side of the disk (in the
  SE), emission from the back (in the NW) is shadowed by the intervening
  interstellar medium unambiguously determining the orientation of NGC
  253 in space. In the NW we see the near edge of the disk is seen,
  but the far component of the halo, and vice versa in the SE. The
  emission in the outer halo can be traced to projected distances from
  the disk of 9 kpc, and shows a horn-like structure. Luminosities are
  higher (10 and 5 10<SUP>38</SUP> erg s<SUP>-1</SUP>, respectively)
  and spectra harder in the NW halo than in the SE. The emission in the
  corona and outer halo is most likely caused by a strong galactic wind
  emanating from the starburst nucleus. As an additional contribution
  to the coronal emission floating on the disk like a spectacle-glass,
  we propose hot gas fueled from galactic fountains originating within
  the boiling star-forming disk. A two temperature thermal plasma model
  with temperatures of 0.13 and 0.62 keV or a thin thermal plasma model
  with temperature of 0.15 keV and Gaussian components above ~0.7 keV
  and Galactic foreground absorption are needed to arrive at acceptable
  fits for the NW halo. This may be explained by starburst-driven
  super-winds or by effects of a non- equilibrium cooling function in
  a plasma expanding in fountains or winds. We compare our results to
  observations at other wavelengths and from other galaxies.

---------------------------------------------------------
Title: The soft X-ray emission components of NGC 4258 decomposed by
    deep ROSAT observations
Authors: Vogler, A.; Pietsch, W.
1999A&A...352...64V    Altcode:
  Spatial, spectral, and timing analysis of deep ROSAT HRI and PSPC
  observations of the active spiral galaxy NGC 4258 are reported. The
  diffuse emission of NGC 4258 has a 0.1-2.4 keV luminosity of L_x ~ 2x
  10<SUP>40</SUP> erg s<SUP>-1</SUP> (corrected for Galactic foreground
  absorption) and fills ~ 40% of the D<SUB>25</SUB> diameter. One
  half of the HRI count rate of this region is caused by a ridge of
  high surface brightness emission following the anomalous spiral
  arms of the galaxy. PSPC spectra of the diffuse emission suggest the
  superposition of two thermal emission components. A 0.2 keV component
  can be attributed to gas in the outer disk and eastern halo hemisphere,
  a second component of higher absorption and temperature (0.5 keV) most
  probably traces hot gas along the anomalous spiral arms. The point
  source catalogue of NGC 4258 contains 15 source candidates within the
  optical extent of the galaxy. At the position of the nucleus, the HRI
  results allow for a point-like source on top of diffuse emission, and,
  if indeed present, the luminosity of such a source is estimated to
  (9+/-4)x 10<SUP>37</SUP> erg s<SUP>-1</SUP>. Excluding the nuclear
  region and two sources which were flagged as extended, the sources
  have luminosities between 7 x 10<SUP>37</SUP> erg s<SUP>-1</SUP> and 9
  x 10<SUP>38</SUP> erg s<SUP>-1</SUP>, accounting for an integrated L_x
  of 2 x 10<SUP>39</SUP> erg s<SUP>-1</SUP>. A deficiency of the 0.1-0.4
  keV band emission in the outer disk of NGC 4258 is detected and can be
  explained by a shadowing of the diffuse soft band background, which
  originates from sources behind the disk of NGC 4258 and is absorbed
  by cold gas in the outer disk. A lower limit of 4.4x 10<SUP>-4</SUP>
  cts s<SUP>-1</SUP> arcmin<SUP>-2</SUP> for the diffuse 0.1-0.4 keV
  background is estimated. The new results are compared to previous
  ROSAT and ASCA observations of NGC 4258 as well as to results from
  other wavelengths and to other spiral galaxies.

---------------------------------------------------------
Title: ROSAT high-resolution X-ray observations of M 83: detection
    of supernova remnant and black hole candidates
Authors: Immler, S.; Vogler, A.; Ehle, M.; Pietsch, W.
1999A&A...352..415I    Altcode:
  High-resolution X-ray observations of the face-on galaxy M 83
  with the HRI onboard ROSAT are presented. The analysis aimed at
  studying the X-ray point source population inside the galaxy and
  disentangling the X-ray emission components (i.e. point sources,
  extended emission from hot gas in the bulge, disk and halo). Within
  the D<SUB>25</SUB> ellipse of M 83, 21 X-ray sources are detected with
  (0.1-2.4 keV band) fluxes ranging from 1.4 to 115 x 10<SUP>-14</SUP>
  erg cm<SUP>-2</SUP> s<SUP>-1</SUP>, corresponding to luminosities of
  (1.3-106) x 10<SUP>38</SUP> erg s<SUP>-1</SUP> for an assumed distance
  of 8.9 Mpc. The sources account for half (2.0 x 10<SUP>40</SUP> erg
  s<SUP>-1</SUP>) of the total X-ray luminosity of the galaxy (4.1 x
  10<SUP>40</SUP> erg s<SUP>-1</SUP>). Using the high spatial resolution
  of the HRI instrument and applying a new technique to search for
  variable sources in the extended bulge region leads to the detection
  of four variable X-ray sources within the bulge (&lt;1 kpc radius
  from the nucleus). The amount of truly diffuse emission from hot gas
  represents ls45 % of the total bulge luminosity (1.0 x 10<SUP>40</SUP>
  erg s<SUP>-1</SUP>). A variable (factor gs2 ), super-Eddington (3.8 x
  10<SUP>39</SUP> erg s<SUP>-1</SUP>) X-ray source is found to coincide
  with a faint, extended optical counterpart. Based on the spectral
  indices optical-to-X-ray alpha_OX =1 and radio-to-optical alpha_RO
  &lt;0, the source is unlikely to be a background galaxy, AGN or quasar
  and most likely represents a massive ( ~ 30M_sun) accreting black
  hole binary, located in a compact HII region or in a globular cluster
  in M 83. We also detect two luminous (3.7 and 6.7 x 10<SUP>38</SUP>
  erg s<SUP>-1</SUP>), previously unknown supernova remnant candidates,
  located in extended Hα emission complexes and coinciding with compact 6
  cm and 20 cm radio sources. Bright extended X-ray emission is discerned
  in the south-western spiral arm from point sources and from the overall
  diffuse emission with the HRI. Spectral analysis of the PSPC data gives
  evidence for the detection of gas flowing into the halo of the galaxy
  (soft 0.26 keV component, absorbed by the Galactic foreground only), and
  hot gas (0.95 keV) with additional intrinsic absorption, that is heated
  by the star-forming activity in the south-western spiral arm of M 83.

---------------------------------------------------------
Title: Million degree interstellar medium in spiral galaxies
Authors: Vogler, A.; Pietsch, W.
1999pcim.conf...50V    Altcode:
  We searched for hot (million degree) interstellar medium in the disks
  and halos of ten spiral galaxies observed with ROSAT. The galaxy sample
  contains starburst, active and normal galaxies. Diffuse X-ray emission
  from million degree gas was detected in the disks and/or halos of seven
  galaxies. With the exception of NGC 4565, all seven galaxies show
  enhanced star formation or obey active galactic nuclei. The results
  are discussed within the framework of models describing the formation
  of hot interstellar medium in the disk and its outflow into the halo.

---------------------------------------------------------
Title: X-ray observations of the starburst galaxy NGC 253. I. Point
    sources in the bulge, disk and halo
Authors: Vogler, A.; Pietsch, W.
1999A&A...342..101V    Altcode: 1998astro.ph.11071V
  We report the results of a deep spatial, spectral, and timing analysis
  of ROSAT HRI and PSPC observations of the edge-on starburst galaxy NGC
  253. In this first paper, point-like X-ray sources detected within the
  galaxy and in the field are discussed. The sources are characterized
  by their X-ray properties (including comparisons with results from the
  Einstein and ASCA satellites), by correlations with other wavelength
  and some optical spectroscopic follow up observations. In total, 73
  X-ray sources have been collected in the NGC 253 field, 32 of which are
  associated with the disk of the galaxy. Though 27 of these disk sources
  are detected with the HRI (some being resolvable with the PSPC), the
  remaining 5 PSPC-only detected sources are likely not to be real point
  sources, being instead due to fluctuations within the X-ray structure
  of the disk. The source close to the center of the galaxy is extended
  (L_x ~ 1x 10(39) erg s(-1) in the ROSAT 0.1-2.4 keV band), and is most
  likely associated with the nuclear starburst activity. The remaining
  sources have luminosities ranging from 7x 10(36) erg s(-1) to 3.0x
  10(38) erg s(-1) , yielding an integrated point source luminosity of
  1x 10(39) erg s(-1) . The brightest point-like source is located ~
  20” south of the nucleus, at the border of a plume of diffuse X-ray
  emission. Its high X-ray luminosity, time variability and hard spectrum
  make it a good candidate for a black hole X-ray binary. Including
  four Einstein detections of X-ray transients the number of point-like
  X-ray sources in NGC 253 increases to 30 sources, 13 of which are time
  variable. These time variable sources are all brighter than 5x 10(37)
  erg s(-1) and most likely represent X-ray binaries radiating close to
  or at the Eddington limit. Besides the nuclear source there is only
  one source above this luminosity that shows no time variability and
  therefore may represent a young supernova or extremely bright supernova
  remnant, or an unresolved cluster of several X-ray sources. The point
  source population of NGC 253 is compared to that of other galaxies,
  and it is shown that the luminosity distribution matches ROSAT results
  obtained for M 31 and M 33. The halo of NGC 253 is filled with diffuse,
  filamentary X-ray emission. Seven sources are located (or projected)
  in this diffuse emission region. Time variability arguments, together
  with optical identifications, are put forward to explain 4 sources
  as background objects, the other 3 sources likely being spurious
  detections caused by local enhancements in the diffuse emission of the
  halo of NGC 253. The diffuse X-ray emission components of NGC 253 will
  be discussed in a separate paper. The sources detected in the field
  outside the disk of NGC 253 cover a flux range from (9 - 300)x 10(-15)
  erg s(-1) cm in the 0.1-2.4 keV band. None of the sources in the field
  correlate with published lists of globular cluster candidates. Optical
  counterparts are proposed for 27 of them, and a few also correlate
  with radio sources. While two sources are identified as foreground
  stars, the remaining ones are mostly background active galactic
  nuclei. Based partially on observations performed at the European
  Southern Observatory, La Silla, Chile