Scientific work and research interests

(Klaus-Peter Schroeder)

  Most of the past 25 years of my scientific career have been devoted to both observational and theoretical stellar astrophysics, especially to interesting problems in connection with highly evolved giant stars (including the distant fate of Earth when the Sun will have become a giant, the astronomical "doomsday" scenario), the final giant phases of stellar evoluton, the related heavy mass-loss and its impact on the chemical evolution of galaxies, and last but not least stellar magnetic activity.
  My future research plans are mainly focusing on these two topics:

  Solar and stellar activity: global dynamo, local dynamo, and....?
  Solar sunspot and other magnetic activity comes in approx. 11 year cycles, and we believe to understand the cyclic interplay between differential rotation, longitudinal stretching of fluxtubes, convection, decay of magnetic fields, twisting by coriolis forces, lateral transport by slow meridianl currents, building-up a new polar field - a process which we call a (global) dynamo. Indeed, some solar-type stars show the same cyclic behaviour as we know from the monitoring of their chromospheric Ca II K line emisison undertaken by O.C. Wilson and his group's legendary Mt.Wilson project from the 1960ies to the 1990ies. From that work, we also know that stellar activity dies down with stellar age.
  But: Most solar-type stars are active in an irregular way. Which conditions are necessary to drive a solar-type dynamo? And how can we describe und understand the other form(s) of stellar activity? Why do many evolved giant stars show activity again? Was it re-activated as a byproduct of stellar evolution? And is it the same dynamo as of solar activity?? - Many, many questions which we want to solve by systematic observation of well-selected and well-characterised samples of stars and giants, using "el TIGRE", formerly the Hamburg Robotic Telescope now working in LaLuz/Guanajuato and its high resolution spectrograph.
  Geophysic and climatologic effects of solar activity or of the long-term absence of it
  Solar and geomagnetic storms, following solar eruptions directed to Earth, and their dangerous impact on satellite and telecomunication technology, sometimes even on large electric power grids (induced high voltage!), are well known phenomena. We need to keep an eye on the Sun to protect our vulnerable technology! Surprisingly, the most dangerous events seem to occur in times of very moderate activity, when solar plasma can travel to us unhindered.
  Less well-known is the fact that once in a while, solar activity cycles become very weak and can even be subdued so much that sunspots mostly disappear for decades (e.g., the famous Maunder Minimum, ca. 1645-1715). While the solar irradiation itself does not change much in such periods, the far-UV radiation of the Sun then is indeed strongly reduced from what we experienced in the 1970ies to 1990ies. Over the last decade, evidence has mounted that the Sun falls again into a low-activity phase. Via (reduced) photoionization of Ozone- and Oxygen, the stratospheric temperature stratification is affected, which in turn has a statistical impact on the strength of the North Atlantic Ozcillation ("Jetstream") and the strength of northern winters. Hence, the solar far-UV flux has become an interesting external forcing factor for refined climate models!
  Here we work with "el TIGRE" to help understand the currently lower UV-fluxes, monitoring the solar chromospheric activity via sunlight reflected by the moon (observing the Sun as a star, i.e. without spatial resolution). In collaboration with climate modellers, these findings will be fed into the latest climate models and the impact on the local climate of northamerica, mexico and europe will be studied very soon.

  Past research work, some of which continues today:
  How well can we 'calibrate' stellar evolutionary tracks and lifetimes? - Critical empirical quantification of post-MS stellar evolution, using wide binaries with giant primaries and characteristic star counts in the solar neighbourhood HR diagram.
  How far does stellar activity (of single stars) and coronal plasma "survive" into late stellar evolution, what are the related changes of chromospheric structure, and in which way does it depend on stellar mass and evolution?
  What exactly happens in the final 10^5 yrs on the AGB? - Consistent computations of intermediate mass, tip-AGB evolution in the presence of heavy mass-losses, derived from state-of-the-art hydrodynamic models of dust-driven ("super-") winds.
  What are the galactic gas and dust (re-)injection rates of the stellar component for a given chemistry, IMF and SFR-history? - A quantitative contribution to galaxy evolution by using synthetic HRD's and detailed mass-loss models.
  Galactic archeology: what can we learn from counting (old) stars?
  Galactic astrophysics will make a quantum leap once the far-reaching astrometric and photometric data of the DIVA and GAIA missions become available. I prepare for a robust, quantitative interpretation by means of comparing synthetic stellar samples with the observed records (i.e., counts of stars and giants in complete, volume-limited samples, discriminating for age and z-value), presently still coming from the Hipparcos Catalogue. This approach yields the IMF (initial mass function) and SFR (star formation rate) history of the galactic disk stellar component, as well as structure, dynamics and evolution of the galactic disk.

  Fig.: Total mass lost by a giant star on the RGB (front), on the AGB (middle), and during its final 30,000 years (superwind, back), as a function of the initial stellar mass.

  Observational experience
  In the past 20 years, I have gained hands-on experience in all standard ground-based observing techniques and their data processing, as well as with space-born missions, including (repeatedly):
  High resolution spectroscopy with CoudeŽ spectrograph and CCD-camera at ESO (CAT), Calar Alto (2.2 m) and Lick (CAT, echelle).
  Space-born observations, as a frequent PI, with IUE (low and high resolution UV spectra) and ROSAT (deep PSPC X-ray exposures).
  Direct CCD imaging, including deep UBV photometry, at the ESO 1.5 m and other telescopes.
  Conventional UBV photometry at the Calar Alto 1.2 m, the Lick 0.6 m, and many other telescopes.
  Conventional wide-field Schmidt photography (on hypersensitised plates) for survey purposes, with and without objective prism at the Calar Alto Schmidt.
  I also take part, as a Co.I., in projects based on HST (GHRS) and SOHO (SUMER) observations. In the more recent years I have temporarily reduced my observing activities to invest more time into valuable theoretical "tools" - i.e., stellar evolution and mass-loss models - which now supply a strong background and motivation for my future observing plans.

  Other experience - i.e., lecturing, science-management, technical
  From 1986 to 1992, as an assistant professor at the University of Hamburg, I gave a variety of astrophysical lectures. I continued lecturing at the Technical Universities of Braunschweig and, presently, Berlin. I received the German university-lecturing qualification 'Habilitation' in 1993 at the University of Hamburg. Altogether, I have a university-lecturing experience of more than 10 years.
  From 1986 to 1992, I was also heavily involved in science management for the spectroscopy group at Hamburg Observatory, including internal organisation of team work, soft-money dependent projects, observing campaigns and the supervision of various PhD projects. Presently, I supervise graduate students and PhD work at the Technical University of Berlin.
  In 1993/94, as a senior research associate at the optical department of the 'Physikalisch-Technische Bundesanstalt' in Braunschweig (Germany), I worked for an EEC project on microscopic measurements with nm-accuracy and studied the diffraction effects at edges of a pronounced profile. Beside some work with near-field diffraction models, I particularly gained valuable experience in contemporary optical and opto-electronic technology.
  My time at the University of Sussex (Jan. 2000 to Sept. 2005) and my two years (1994 to 1996) at the Institute of Astronomy (Cambridge, UK), plus many research visits to Cambridge (including 6 months in 1992 as a visiting scolar of St. John's College) were not only very valuable for me scientifically - I also treasure my time in the UK as an important social and cultural life experience. Now, I'm working at the University of Guanajuato, Departamento de Astronomia and again enjoy a different but very friendly culture!