Time filter

Source Type

Heidelberg, Germany

For similarly named astronomy institutes, see: Institute of Astronomy.The Max-Planck-Institut für Astronomie is a research institute of the Max Planck Society. It is located in Heidelberg, Baden-Württemberg, Germany near the top of the Koenigstuhl, adjacent to the historic Landessternwarte Heidelberg-Königstuhl astronomical observatory.The institute was founded in 1967. Its founding directors were H. Elsässer, and G. Munch, who was followed by S. V. W. Beckwith. The current directors are Hans-Walter Rix and Thomas Henning. G. H. Herbig, Karl-Heinz B\"ohm, Immo Appenzeller, Willy Benz, and Rafael Rebolo have been external scientific members. Wikipedia.

Bailer-Jones C.A.L.,Max Planck Institute for Astronomy
Astronomy and Astrophysics | Year: 2012

I introduce a general, Bayesian method for modelling univariate time series data assumed to be drawn from a continuous, stochastic process. The method accommodates arbitrary temporal sampling, and takes into account measurement uncertainties for arbitrary error models (not just Gaussian) on both the time and signal variables. Any model for the deterministic component of the variation of the signal with time is supported, as is any model of the stochastic component on the signal and time variables. Models illustrated here are constant and sinusoidal models for the signal mean combined with a Gaussian stochastic component, as well as a purely stochastic model, the Ornstein-Uhlenbeck process. The posterior probability distribution over model parameters is determined via Monte Carlo sampling. Models are compared using the "cross-validation likelihood", in which the posterior-averaged likelihood for different partitions of the data are combined. In principle this is more robust to changes in the prior than is the evidence (the prior-averaged likelihood). The method is demonstrated by applying it to the light curves of 11 ultra cool dwarf stars, claimed by a previous study to show statistically significant variability. This is reassessed here by calculating the cross-validation likelihood for various time series models, including a null hypothesis of no variability beyond the error bars. 10 of 11 light curves are confirmed as being significantly variable, and one of these seems to be periodic, with two plausible periods identified. Another object is best described by the Ornstein-Uhlenbeck process, a conclusion which is obviously limited to the set of models actually tested. ©2012 ESO.

Dutton A.A.,Max Planck Institute for Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2012

Most of the baryons in the Universe are not in the form of stars and cold gas in galaxies. Galactic outflows driven by supernovae/stellar winds are the leading mechanisms for explaining this fact. The scaling relation between galaxy mass and outer rotation velocity (also known as the baryonic Tully-Fisher relation, BTF) has recently been used as evidence against this viewpoint. We use a Λ cold dark matter (ΛCDM)-based semi-analytic disc galaxy formation model to investigate these claims. In our model, galaxies with less efficient star formation and higher gas fractions are more efficient at ejecting gas from galaxies. This somewhat counter intuitive result is due to the (observational) fact that galaxies with less efficient star formation and higher gas fractions tend to live in dark matter haloes with lower circular velocities, from which less energy is required to escape the potential well. In our model the intrinsic scatter in the BTF is ≃0.15dex, and mostly reflects scatter in dark halo concentration. The scatter is largely independent of galaxy structure because of the large radius within which galaxy rotation velocities are measured. The observed scatter, equal to ≃0.24dex, is dominated by measurement errors. The best estimate for the intrinsic scatter is that it is less than 0.15dex, and thus our ΛCDM-based model (which does not include all possible sources of scatter) is only just consistent with this. Future observations of the BTF scatter could be made with a more stringent measurement of the intrinsic scatter, and thus provide a strong constraint to galaxy formation models. In our model, gas-rich galaxies, at fixed virial velocity (V vir), with lower stellar masses have lower baryonic masses. This is consistent with the expectation that galaxies with lower stellar masses have had less energy available to drive an outflow. However, when the outer rotation velocity (V flat) is used the correlation has the opposite sign, with a slope in agreement with observations. This is due to the fact there is scatter in the relation between V flat and V vir. In summary, contrary to some previous claims, we show that basic features of the BTF are consistent with a ΛCDM-based model in which the low efficiency of galaxy formation is determined by galactic outflows. © 2012 The Author Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Bailer-Jones C.A.L.,Max Planck Institute for Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2011

Giant impacts by comets and asteroids have probably had an important influence on terrestrial biological evolution. We know of around 180 high-velocity impact craters on the Earth with ages up to 2400Myr and diameters up to 300km. Some studies have identified a periodicity in their age distribution, with periods ranging from 13 to 50Myr. It has further been claimed that such periods may be causally linked to a periodic motion of the Solar system through the Galactic plane. However, many of these studies suffer from methodological problems, for example misinterpretation of p-values, overestimation of significance in the periodogram or a failure to consider plausible alternative models. Here I develop a Bayesian method for this problem in which impacts are treated as a stochastic phenomenon. Models for the time variation of the impact probability are defined and the evidence for them in the geological record is compared using Bayes factors. This probabilistic approach obviates the need for ad hoc statistics, and also makes explicit use of the age uncertainties. I find strong evidence for a monotonic decrease in the recorded impact rate going back in time over the past 250Myr for craters larger than 5km. The same is found for the past 150Myr when craters with upper age limits are included. This is consistent with a crater preservation/discovery bias modulating an otherwise constant impact rate. The set of craters larger than 35km (so less affected by erosion and infilling) and younger than 400Myr is best explained by a constant impact probability model. A periodic variation in the cratering rate is strongly disfavoured in all data sets. There is also no evidence for a periodicity superimposed on a constant rate or trend, although this more complex signal would be harder to distinguish. © 2011 The Author Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Bailer-Jones C.A.L.,Max Planck Institute for Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2010

I introduce an algorithm for estimating parameters from multidimensional data based on forward modelling. It performs an iterative local search to effectively achieve a non-linear interpolation of a template grid. In contrast to many machine-learning approaches, it avoids fitting an inverse model and the problems associated with this. The algorithm makes explicit use of the sensitivities of the data to the parameters, with the goal of better treating parameters which only have a weak impact on the data. The forward modelling approach provides uncertainty (full covariance) estimates in the predicted parameters as well as a goodness-of-fit for observations, thus providing a simple means of identifying outliers. I demonstrate the algorithm, ILIUM, with the estimation of stellar astrophysical parameters (APs) from simulations of the low-resolution spectrophotometry to be obtained by Gaia. The AP accuracy is competitive with that obtained by a support vector machine. For zero extinction stars covering a wide range of metallicity, surface gravity and temperature, ILIUM can estimate Teff to an accuracy of 0.3 per cent at G = 15 and to 4 per cent for (lower signal-to-noise ratio) spectra at G = 20, the Gaia limiting magnitude (mean absolute errors are quoted). [Fe/H] and log g can be estimated to accuracies of 0.1-0.4 dex for stars with G ≤ 18.5, depending on the magnitude and what priors we can place on the APs. If extinction varies a priori over a wide range (0-10 mag) - which will be the case with Gaia because it is an all-sky survey - then log g and [Fe/H] can still be estimated to 0.3 and 0.5 dex, respectively, at G = 15, but much poorer at G = 18.5. T eff and AV can be estimated quite accurately (3-4 per cent and 0.1-0.2 mag, respectively, at G = 15), but there is a strong and ubiquitous degeneracy in these parameters which limits our ability to estimate either accurately at faint magnitudes. Using the forward model, we can map these degeneracies (in advance) and thus provide a complete probability distribution over solutions. Additional information from the Gaia parallaxes, other surveys or suitable priors should help reduce these degeneracies. © 2010 The Authors. Journal compilation © 2010 RAS.

Henning T.,Max Planck Institute for Astronomy
Annual Review of Astronomy and Astrophysics | Year: 2010

Silicate dust particles are an important player in the cosmic life cycle of matter. They have been detected in a wide variety of environments, ranging from nearby protoplanetary disks to distant quasars.This review summarizes the fundamental properties of silicates relevant to astronomical observations and processes. It provides a review of our knowledge about cosmic silicates, mostly based on results from IR spectroscopy. © 2010 by Annual Reviews.

Discover hidden collaborations