Rudolf Duemmler

High-Resolution Spectroscopy of FU Orionis Stars

High-resolution spectroscopy was obtained of the FUors FU Ori and V1057 Cyg between 1995 and 2002 with the SOFIN spectrograph at NOT and with HIRES at Keck I. During these years FU Ori remained about 1 mag. (in B) below its 1938–39 maximum brightness, but V1057 Cyg (B ≈ 10.5 at peak in 1970–71) faded from about 13.5 to 14.9 and then recovered slightly. Their photospheric spectra resemble that of a rotationally broadened, slightly veiled supergiant of about type G0 Ib, with veq sin i = 70 km s −1 for FU Ori, and 55 km s −1 for V1057 Cyg. As V1057 Cyg faded, P Cyg structure in Hα and the IR Ca II lines strengthened, and a complex shortwarddisplaced shell spectrum of low-excitation lines of the neutral metals (including Li I and Rb I) increased in strength, disappeared in 1999, and reappeared in 2001. Several SOFIN runs extended over a number of successive nights so that a search for rapid and cyclic changes in the spectra was possible. These spectra show rapid night-to-night changes in the wind structure of FU Ori at Hα, including clear evidence of sporadic infall. The equivalent width of the P Cyg absorption varied cyclically with a period of 14.8 days, with phase stability maintained over 3 seasons. This is believed to be the rotation period of FU Ori. The internal structure of its photospheric lines also varies cyclically, but with a period of 3.54 days. A similar variation may be present in V1057 Cyg, but the data are much noisier and that result uncertain. As V1057 Cyg has faded and the continuum level fallen, the emission lines of a pre-existing low-excitation chromosphere have emerged. Therefore we believe that the ‘line doubling’ in V1057 Cyg is produced by these central emission cores in the absorption lines, not by orbital motion in an inclined Keplerian disk. No dependence of veq sin i on wavelength or excitation potential was detected in either FU Ori or V1057 Cyg, again contrary to expectation for a self-luminous accretion disk. It was found also that certain critical lines in the near infrared are not accounted for by synthetic disk spectra. It is concluded that a rapidly rotating star near the edge of stability, as proposed by Larson (1980), can better account for these observations. The possibility is also considered that FUor eruptions are not a property of ordinary T Tauri stars, but may be confined to a special sub-species of rapidly rotating pre-main sequence stars having powerful quasi-permanent winds. Subject headings: stars: evolution — stars: Pre-Main-Sequence — stars: individual (FU Ori, V1057 Cyg)

The Optical/IR Counterpart of the 1998 July 3 Gamma-Ray Burst and Its Evolution

We imaged the X-ray error box of GRB 980703, beginning 22.5 hr after the γ-ray event, in both the optical R and near-infrared H bands. A fading optical/IR object was detected within the X-ray error box, coincident with the variable radio source reported by Frail et al. in 1998, who also detected the optical transient independently of us. Further imagery revealed the gamma-ray burst (GRB) host galaxy, with R = 22.49±0.04 and H=20.5 ± 0.25, the brightest so far detected. When excluding its contribution to the total flux, both the R- and H-band light curves are well fit by a power-law decay with index α1.4. Our data suggest an intrinsic column density in the host galaxy of ~3.5 × 1021 cm-2, which indicates the existence of a dense and gas-rich medium in which the GRB occurred, thus supporting the hypernova model scenarios.

The Muenster Redshift Project. III. Observational Constraints on the Deceleration Parameter

The redshift-volume test for determining the deceleration parameter q0 is applied to 89,125 galaxies with redshifts z ? 0.2 (redshift errors ?z = 0.031) and magnitudes 14.0 ? rF ? 18.0 mag, obtained within the Muenster Redshift Project (MRSP). With samples of this size, cosmic curvature effects can be measured even at intermediate redshifts. Comparatively small z-values and red photometric magnitudes assure that biased object selection and galaxy evolution do not affect the measurements in uncontrolled ways. In the first step of our analysis, the redshift-volume test assumes a minimum model of passive galaxy evolution. For the cosmological constant ? = 0 and for the evolutionary models of Rocca-Volmerange & Guiderdoni, the total sample yields the deceleration parameter q0 = 0.10 with the 95% confidence limit, q0 < 0.75. In a second step, we evaluate?within the errors of the first step?whether our q0-value is over- or underestimated, using those observed evolutionary trends that appear to be nearly q0 independent. The trends indicate that our result q0 = 0.10 can be regarded as an upper limit. Effects of incompleteness, errors in the (K + E)-corrections due to extreme galaxy mixtures, as well as different models of population synthesis, large-scale clustering, galactic reddening, and gravitational lensing, are discussed. We conclude that the combination of MRSP redshift data, observed evolutionary trends in the galaxy luminosity functions, and passive galaxy aging suggests an open universe.

The Muenster Redshift Project

The Muenster Redshift Project is based on microdensitometer scans of pairs of direct and objective prism Schmidt plates, used for the determination of positions, magnitudes, morphological types, and low-dispersion redshifts of galaxies and quasars. From these data structural features and parameters which characterize the present universe are derived. The 0.9 million redshifts, reduced so far, permit us to take a first step towards very large-scale analysis.

Problems and solutions in observational cosmology

Large numbers of data permit a statistical approach to topics in observational cosmology. The derivations of cosmological and structural parameters from deeper and wider samples promise more general solutions, but pose new problems of analysis. Examples are given for the statistical derivation of the quantities Ho, q o , Ωo and A, of structural properties of clusters of galaxies, and of the evolution of clustering.

The cosmological constant — historical annotations

A brief history of the cosmological constant is given. Introduced and later discussed away by Einstein, recognized for its potential of defining cosmic time and tracing the history of the universe by Friedmann, the cosmological constant was first identified with negative vacuum density by Lemaitre. His interpretation was much later revived by Gliner whose work, together with the concept of a variable cosmological “constant” discussed by Linde on the basis of unified field theories, and the work of numerous other authors laid the foundations for the role the cosmological constant was to assume later: that of the very essence of inflationary theories of the universe. The unanswered problems which appear in this context remind us that a general quantum field theory is still lacking, but also that its solution lies with the understanding of vaccum energy, i.e. of Λ.