Dr Alexander S Ströer

Astrophysics Science Division
NASA/GSFC
Code 663, -
Greenbelt, MD 20771

tel: 301-286-3430
fax:
e-mail: Alexander.Stroeer @ nasa.gov

Present Position

Postdoctoral Research Associate, CRESST, University of Maryland College Park, NASA Goddard Space Flight Center

Brief Bio

2009 - 03 - open: Postdoctoral Research Associate, CRESST, University of Maryland, NASA Goddard Space Flight Center

2007-08 - 2009 - 03: Faculty Research Associate, CRESST, University of Maryland, NASA Goddard Space Flight Center

Educational Background

2006-09 – 2007-07 Predoctoral visiting scholar
Northwestern University Evanston, Illinois, USA

2004-09 – 2007 PhD student, research degree, Physics and astronomy
University of Birmingham, England, United Kingdom
School of Physics and Astronomy
PhD thesis: Gravitational waves: data analysis with LISA, astrophysics of sources

2000-10 – 2004-08 Study of Physics (general)
Friedrich Alexander University Erlangen-Nuremberg, Germany
Graduation: Aug 2004; Diplom Physiker univ. (Dipl.Phys.univ)
Final Grade: 1.00 (graduated with distinction)
(grades ranging from 1.00 to 5.00; 1.00 = best)
Subjects/Grades itemized:
Compulsory optional subject: Astro-, nuclear and particle physics 1.00
Compulsory subject I: Theoretical physics 1.00
Compulsory subject II: Experimental physics 1.00
Minor subject: Geophysics 1.00
Diploma thesis: 1.00
Title: Faint hot stars from the ESO SPY survey: sdO stars

2003-02 – 2003-05 Study of Physics (general), Sokrates / Erasmus exchange student
University of Joensuu, Joensuu, North Carelia, Finland

1999-10 – 2000-07 Study of Physics (general)
Technical University of Munich, Germany

Research Interests

I am interested in the evolution of double white dwarf and subdwarf systems in
our galaxy. In particular the question about the evolutionary link towards a
subdwarf system is in the center of this interest. To research these links I used
and analyzed optical Echelle spectra from the ESO UVES SPY survey of subdwarf
systems in order to find key parameters for the stellar atmosphere. I codeveloped
a complete reduction pipeline for the raw data and conducted
reductions of over 2000+ spectra within SPY. In order to analyze the spectra in
detail I developed a new grid of stellar atmosphere models in Non-local thermal
equilibrium to a precision and density unachieved up to this date, involving data
and absorption lines of hydrogen and helium. High resolution not only enabled a
precise analysis of subdwarf data within my hydrogen/helium model grid, but
further a quantitative analysis of metal lines of carbon, nitrogen and oxygen. I
concluded that metal enrichment plays a fundamental role in the evolution
towards a subdwarf star, in particular in the formation of the observed diversity
of subdwarf subclasses.

I am further interested in gravitational wave emissions from double white dwarf
systems and massive to super-massive black holes within binary systems. I
conduct research for the planned LISA gravitational wave observatory and for
the LIGO/VIRGO ground based gravitational wave detectors. For LISA I
investigate, how well we may be able to measure gravitational wave emissions in
theory (towards the lower limit of uncertainties to parameter estimations). I
tested several scenarios, including AM CVn system emissions and emissions from
verification binaries, electromagnetically well known compact object binaries.
Here I highlighted, that LISA will not be able to achieve complete scientific
information extraction without the use of additional data from e.g. GAIA. I
further investigate data analysis strategies in Bayesian frameworks and develop
automatic reversible jump markov chain monte carlo approaches, data analysis
in case of unknown number of signals, kinds of signals and noise level. I was able
to successfully demonstrate automatic data analysis runs on Mock data in a
variety of cases, including massive black hole binaries, overlapping double white
dwarfs and extreme mass ratio inspirals. For LIGO I co-develop a data analysis
strategy designed for spinning black holes and supervise the implementation of
data analysis algorithms within Bayes frameworks. Here we investigate the most
likely form of signal for a first real detection of gravitational waves, and
contribute to the data analysis effort of the LIGO collaboration with our
automatic approaches and templates for spinning black holes.

Besides Bayesian inference I meanwhile concentrate on signal detection with alternative data analysis methods. Bayesian inference is most powerful to extract astrophysical information about a signal already detected, my current research thus concentrates on methods to detect a signal in a data set with highest efficiency, and further to provide initial information to Bayesian inference. The method of choice is found in the Hilbert Huang transform since it is able to display non-linear signals undistorted or approximated just *as recorded* in the data set, and offers theoretically unlimited resolution in the time-frequency plane, a major tool in signal characterization (now try that with a Fourier method :) ).

Besides my professional research, my interests also touch theoretical physics
and cosmology. I enjoy exploring theories about gravitation and time as for
example quantum loop theories or the M-theory. I further enjoy geophysical
research as applied to planetology.

Current Projects

Most recently I turned my attention to data analysis methods for gravitational wave burst signals as seen by the Laser Interferometer Gravitational Wave Observatory (LIGO). Here in particular detection and signal characterization with the Hilbert-Huang transform (HHT) are performed. As gravitational wave theory is highly non-linear, and as current data analysis routines mostly concentrate on linear approximations to a non-linear problem, the biggest advantage of the
HHT is its capability to capture non-linear features undistorted. It does not impose any transformation to recorded data nor alterations, it just displays the feature *as-is*, thus non-linear. Further by not imposing any base or transformation we can achieve in theory unlimited resolution in the time-frequency plane, a major tool for signal characterization. I develop a pipeline for Burst signal searches with the HHT, and further introduced the HHT explicily for high definition characterization of features as found by other pipelines within the LIGO Burst group.

Selected Publications

1. Full Books (Published, edited, authored, or co-authored).

2. Chapters in books (Published, edited, authored, or co-authored).

3. Refereed articles in archival journals.

Stroeer, A. et al., "Methods for detection and characterization of signals in noisy data with
the Hilbert-Huang Transform", ArXiv e-prints, March 2009. (link)

Stroeer, A. and Camp, J., "Ninja data analysis with a detection pipeline based on the Hilbert-Huang Transform", ArXiv e-prints, Jan 2009. (link)

Aylott, B. et al., "Testing gravitational-wave searches with numerical relativity waveforms: Results from the first Numerical INJection Analysis (NINJA) project", ArXiv e-prints, Jan 2009. [Provided by the SAO/NASA Astrophysics Data System] (link)

Babak, S., Baker, J. G., Benacquista, M. J., Cornish, N. J., Crowder, J., Cutler, C., Larson, S. L., Littenberg, T. B., Porter, E. K., Vallisneri, M., Vecchio, A., data challenge task force, t. M. L., Auger, G., Barack, L., Baut, A., Bloomer, E., Brown, D. A., Christensen, N., Clark, J., Fairhurst, S., Gair, J. R., Halloin, H., Hendry, M., Jimenez, A., Krolak, A., Mandel, I., Messenger, C., Meyer, R., Mohanty, S., Nayak, R., Petiteau, A., Pitkin, M., Plagnol, E., Prix, R., Robinson, E. L., Roever, C., Savov, P., Stroeer, A., Toher, J., Veitch, J., Vinet, J., Wen, L., Whelan, J. T., Woan, G. and Challenge-2 participants, t., "Report on the second Mock LISA data challenge", Classical and Quantum Gravity, Volume 25, 11, pp. 114037-+, Jun 2008. [Provided by the SAO/NASA Astrophysics Data System] (link)

Stroeer, A., Veitch, J., Rover, C., Bloomer, E., Clark, J., Christensen, N., Hendry, M., Messenger, C., Meyer, R., Pitkin, M., Toher, J., Umstatter, R., Vecchio, A. and Woan, G., "Inference on white dwarf binary systems using the first round Mock LISA Data Challenges data sets", Classical and Quantum Gravity, Volume 24, pp. 541-+, Oct 2007. [Provided by the SAO/NASA Astrophysics Data System] (link)

Arnaud, K. A., Auger, G., Babak, S., Baker, J. G., Benacquista, M. J., Bloomer, E., Brown, D. A., Camp, J. B., Cannizzo, J. K., Christensen, N., Clark, J., Cornish, N. J., Crowder, J., Cutler, C., Finn, L. S., Halloin, H., Hayama, K., Hendry, M., Jeannin, O., Krolak, A., Larson, S. L., Mandel, I., Messenger, C., Meyer, R., Mohanty, S., Nayak, R., Numata, K., Petiteau, A., Pitkin, M., Plagnol, E., Porter, E. K., Prix, R., Roever, C., Stroeer, A., Thirumalainambi, R., Thompson, D. E., Toher, J., Umstaetter, R., Vallisneri, M., Vecchio, A., Veitch, J., Vinet, J.-Y., Whelan, J. T. and Woan, G. , "Report on the first round of the Mock LISA Data Challenges", Classical and Quantum Gravity, Volume 24, pp. 529-+, Oct 2007. [Provided by the SAO/NASA Astrophysics Data System] (link)

van der Sluys, M. V., Rover, C., Stroeer, A., Raymond, V., Mandel, I., Christensen, N., Kalogera, V., Meyer, R. and Vecchio, A., "Gravitational-Wave Astronomy with Inspiral Signals of Spinning Compact-Object Binaries", Astrophysical Journal, Letters, Volume 688, pp. L61-L64, Dec 2008. [Provided by the SAO/NASA Astrophysics Data System] (link)

Rover, C., Stroeer, A., Bloomer, E., Christensen, N., Clark, J., Hendry, M., Messenger, C., Meyer, R., Pitkin, M., Toher, J., Umstatter, R., Vecchio, A., Veitch, J. and Woan, G., "Inference on inspiral signals using LISA MLDC data", Classical and Quantum Gravity, Volume 24, pp. 521-+, Oct 2007. [Provided by the SAO/NASA Astrophysics Data System] (link)

Stroeer, A., Heber, U., Lisker, T., Napiwotzki, R., Dreizler, S., Christlieb, N. and Reimers, D., "Hot subdwarfs from the ESO supernova Ia progenitor survey. II. Atmospheric parameters of subdwarf O stars", Astronomy and Astrophysics, Volume 462, pp. 269-280, Jan 2007. [Provided by the SAO/NASA Astrophysics Data System] (link)

Van der Sluys, M., Stroeer, A., Vecchio, A. and Kalogera, V., "Bayesian Inference and Observations of Massive Black-hole Binaries with LISA", Bulletin of the American Astronomical Society, Bulletin of the American Astronomical Society, Volume 38, pp. 992-+, Dec 2006. [Provided by the SAO/NASA Astrophysics Data System] (link)

Stroeer, A., Gair, J. and Vecchio, A., "Automatic Bayesian inference for LISA data analysis strategies", in Merkovitz, S. M. and Livas, J. C., Eds., Laser Interferometer Space Antenna: 6th International LISA Symposium, American Institute of Physics Conference Series, Volume 873, pp. 444-451, Nov 2006. [Provided by the SAO/NASA Astrophysics Data System] (link)

Wickham, E. D. L., Stroeer, A. and Vecchio, A., "A Markov chain Monte Carlo approach to the study of massive black hole binary systems with LISA", Classical and Quantum Gravity, Volume 23, pp. 819-+, Oct 2006. [Provided by the SAO/NASA Astrophysics Data System] (link)

Stroeer, A. and Vecchio, A., "The LISA verification binaries", Classical and Quantum Gravity, Volume 23, pp. 809-+, Oct 2006. [Provided by the SAO/NASA Astrophysics Data System] (link)

Stroeer, A., Vecchio, A. and Nelemans, G., "LISA Astronomy of Double White Dwarf Binary Systems", Astrophysical Journal, Letters, Volume 633, pp. L33-L36, Nov 2005. [Provided by the SAO/NASA Astrophysics Data System] (link)

4. Articles in conference proceedings.

Heber, U., Hirsch, H., Stroer, A., O'Toole, S., Haas, S. and Dreizler, S., "Subluminous O Stars", Baltic Astronomy, Volume 15, pp. 91-98, 2006. [Provided by the SAO/NASA Astrophysics Data System] (link)

Stroer, A., Heber, U., Lisker, T., Napiwotzki, R. and Dreizler, S., "Subluminous O Stars from the ESO Supernova Progenitor Survey - Observation versus Theory", in Koester, D. and Moehler, S., Eds., 14th European Workshop on White Dwarfs, Astronomical Society of the Pacific Conference Series, Volume 334, pp. 309-+, Jul 2005. [Provided by the SAO/NASA Astrophysics Data System] (link)

Publications at the ADS website.