Welcome to the Homepage of Ton Raassen

First spectrum by LETG on board CHANDRA from Capella

Astronomical Institute "Anton Pannekoek"

University of Amsterdam

Faculty of Science, Mathematics and Computer Science

Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

SRON Netherlands Institute for Space Research

Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands


Research programs

Since the beginning of 1999 I work at SRON and the Astronomical Institute "Anton Pannekoek" of the University of Amsterdam. My work is related to the observation of the two X-ray observatories CHANDRA and XMM. Although it is still spectroscopy it is different from the calculations of the low stages of ionizations as I have done in the last years at the atomic physics theory group. The scientific goal is the analyses of X-ray spectra produced by the X-ray satellite CHANDRA, launched by NASA July 23 1999 and the European X-ray Satellite XMM-Newton, launched in Kourou December 10 1999. Both Satellites are equipped with spectrometers. CHANDRA contains a High Energy Transmission Grating (HETG) and a Low Energy Transmission Grating Spectrometer (LETGS). LETGS covers the spectral range from 2.5 keV to 0.07 keV ( 2 - 175 Angstrom). The HETGS covers the range up to 25 Angstrom, but with higher resolution.
XMM-Newton contains two Reflection Grating Spectrometers (RGS) and a CCD-spectrometer (EPIC-MOS). Using XMM-Newton spectrometry and imaging can be done the same time.

Spectrum of ATMic by RGS on board XMM-Newton

Our specific scientific goal is the interpretation of spectra of stellar coronae. The steep rise of the coronal temperature is still a puzzling problem. Over the last two years we analysed the spectra of the coronae of Capella, Procyon, Alpha Centauri and AT Mic. The spectra were investigated using a multi-temperature model of the SPEX code in combination with the MEKAL database, both developed at SRON. A variety of temperatures were obtained; from about 1.5 MK for Alpha Centauri, via 6 Mk for Capella upto even 30 MK for AT Mic. More recently we have analysed hot star spectra, obtained with CHANDRA and XMM. It concerns instabilities in the hot stellar wind, that are responsible for the emitted X-Rays. The targets observed by CHANDRA, as well as the short and long time observation schedules, can be found at chandra.harvard.edu

Spectrum of Procyon (black) obtained by LETGS, modeled by means of SPEX (red)

Recent publications

-A.C Brinkman, C.J.T. Gunsing, J.S. Kaastra, R.L.J. van der Meer, et al.
First light measurements of Capella with the low-energy transmission grating spectrometer aboard the CHANDRA X-ray observatory
ApJ 530, L111-L114(2000)

-H. Nilsson, C.M. Sikstroem, Z.S. Li, H. Lundberg, A.J.J. Raassen, S. Johansson, D.S. Leckrone, S. Svanberg
The FERRUM project: new experimental and theoretical f-values for 4p-4d transitions in Fe II applied to HST spectra of chi Lupi
A&A 362,410-418 (2000)

-M. Audard, E. Behar, M. Güdel, A.J.J. Raassen et al.
The XMM-Newton view of stellar coronae: High-resolution X-ray spectroscopy of Capella
A&A 365, L329-L335 (2001)

-J.-U. Ness, R. Mewe, J. H. M. M, Schmitt, A.J.J. Raassen, et al.
Helium-like triplet density diagnostics. Applications to CHANDRA-LETGS X-ray observations of Capella and Procyon
A&A 367, 282-296 (2001)

-R. Mewe, A. J. J. Raassen, J. J. Drake, J. S. Kaastra, et al.
CHANDRA-LETGS X-ray observations of Capella. Temperature, density and abundance diagnostics
A&A 368, 888-900 (2001)

-D. Porquet, R. Mewe, J. Dubau, A.J.J. Raassen, and J.S. Kaastra
Line ratios for helium-like ions: Applications to collision-dominated plasmas
A&A 376, 1113-1122 (2001)

-J. S. Kaastra, K. C. Steenbrugge, A. J. J. Raassen, et al.
X-ray spectroscopy of NGC 5548
A&A 386, 427-445 (2002)

-A. J. J. Raassen, R. Mewe, M. Audard, et al.
High-resolution X-ray spectroscopy of Procyon by Chandra and XMM-Newton
A&A 389,228-238 (2002)

-J.-U. Ness, J. H. M. M. Schmitt, V. Burwitz, R. Mewe, A. J. J. Raassen, et al.
Coronal density diagnostics with Helium-like triplets: CHANDRA-LETGS observations of Algol, Capella, Procyon, epsilon Eri, alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR 1099
A&A 394, 911-926 (2002)

-A.J.J. Raassen
The X-ray Spectrum of Tau Sco, High Resolution X-ray Spectroscopy with XMM-Newton and Chandra
Proceedings of the international workshop held at the Mullard Space Science Laboratory of University College London, Holmbury St Mary, Dorking, Surrey, UK, October 24 - 25, 2002, Ed. Branduardi-Raymont, G., published electronically at
www.mssl.ucl.ac.uk/~gbr/rgs_workshop/proceedings, p.E32, (2002)

-R. Mewe, A. J. J. Raassen, J. P. Cassinelli, K.A. van der Hucht, N.A. Miller, M. Guedel
High-resolution X-ray spectroscopy of tau Scorpii (B0.2V) with XMM-Newton
A&A 398,203-211 (2003)

-M. Audard, M. Guedel, A. Sres, A.J.J. Raassen, R. Mewe
A study of coronal abundances in RS CVn binaries
A&A 398,1137-1149 (2003)

-A. J. J. Raassen, J.-U. Ness, R. Mewe, et al.
Chandra-LETGS X-ray observation of alpha Centauri: A nearby (G2V + K1V) binary system
A&A 400,671-678 (2003)

-A. J. J. Raassen, K. A. van der Hucht, R. Mewe, et al.
XMM-Newton high-resolution X-ray spectroscopy of the Wolf-Rayet object WR 25 in the Carina OB1 association
A&A 402,653-666 (2003)

-A. J. J. Raassen, Mewe, M. Audard, and M. Guedel
The X-ray spectra of the flaring and quiescent states of AT Microscopii observed by XMM-Newton
A&A 411,509-515 (2003)

-E.J.M. van den Besselaar, A.J.J. Raassen, R. Mewe, R.L.J. van der Meer, M. Guedel, M. Audard
AD Leonis: Flares observed by XMM-Newton and Chandra
A&A 411,587-593 (2003)

-H. Schild, M. Guedel, R. Mewe, W. Schmutz, A. J. J. Raassen, et al.
Wind clumping and the wind-wind collision zone in the Wolf-Rayet binary gamma2 Velorum observations at high and low state. XMM-Newton observations at high and low state
A&A 422,177-191 (2004)

-J. S. Kaastra, A. J. J. Raassen, R. Mewe, et al.
X-ray/UV campaign on the Mrk 279 outflow: Density diagnostics in Active Galactic Nuclei using O V K-shell absorption lines
A&A 428,57-66 (2004)

-U. Mitra-Kraev, L. K. Harra, M. Guedel, M. Audard, G. Branduardi-Raymont, H. R. Kay, R. Mewe, A.J.J. Raassen, L. van Driel-Gesztelyi
Relationship between X-ray and ultraviolet emission of flares from dMe stars observed by XMM-Newton
A&A 431,679-686 (2005)

-A. J. J. Raassen, J. P. Cassinelli, N.A. Miller, R. Mewe, E. Tepedelenlioglu
XMM-Newton observations of beta Centauri (B1 III): The temperature structure in the hot plasma and the photosphere-wind connection
A&A 437,599-609 (2005)

-A. M. T. Pollock, A. J. J. Raassen
A New Paradigm for X-rays from Hot Stars
Proceedings of "Massive Stars and High-Energy Emission in OB Associations", a workshop of the JENAM 2005, "Distant Worlds", held in Liège (Belgium), July 4 - 7, 2005, Eds. G. Rauw, Y. Nazé, R. Blomme, and E. Gosset, p. 35 - 38

-T. Raassen
Variability in the X-ray Spectrum of the Stable Calibration Source Capella
High Resolution X-ray Spectroscopy: towards XEUS and Con-X, Proceedings of the international workshop held at the Mullard Space Science Laboratory of University College London, Holmbury St Mary, Dorking, Surrey, UK, March 27 - 28, 2006, Ed. Branduardi-Raymont, G., published electronically., pE32-36 (2006)

-A. J. J. Raassen, J.S.Kaastra
X-ray variability of Capella
A&A 461,679-683 (2007)

-A. J. J. Raassen, U. Mitra-Kraev, M. Güdel
The X-ray spectra of the flaring and quiescent states of YZ CMi observed by XMM-Newton
MNRAS 379,1075-1082 (2007)

-A. J. J. Raassen, K.A. van der Hucht, N.A. Miller, J.P. Cassinelli
XMM-Newton observations of zeta Orionis (O9.7 Ib): a collisional ionization equilibrium model
A&A 478,513-520 (2008)

-A. J. J. Raassen
The X-ray spectrum of the classical TTauri star TW Hydrae observed by LETGS aboard Chandra
A&A 505,755-762 (2009)

-J. de plaa, I.Zhuravleva, N. Werner, J.S. Kaastra, E. Churazov, R.K. Smith, A. J. J. Raassen, Y.G. Grange
Estimating turbulent velocities in the elliptical galaxies NGC 5044 and NGC 5813
A&A 539,34 (2012)

-P.M. Vreeswijk, C. Ledoux, A.J.J. Raassen, etal.
Time-dependent excitation and ionization modelling of absorption-line variability due to GRB 080310
A&A 549,22 (2013)

-A. J. J. Raassen, A.M.T. Pollock
The X-ray spectrum of delta Orionis observed by LETGS aboard Chandra
A&A 550, 55 (2013)

-T.W. Gorczyca, M.A. Bautista, M.F. Hasoglu, J. García, E. Gatuzz, J.S.Kaastra, T.R. Kallman, S.T. Manson, C. Mendoza, A.J.J. Raassen, C.P. de Vries, O. Zatsarinny
A Comprehensive X-Ray Absorption Model for Atomic Oxygen
ApJ 779, 78 (2013)

Ton Raassen

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Max Planck Institut fur Extraterrestrische Physik