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
"el TIGRE", formerly the Hamburg Robotic Telescope now working in
LaLuz/Guanajuato and its high
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
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.
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
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
Other experience - i.e., lecturing, science-management,
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
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
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!