Dr. Hans Moritz Guenther

Hans Guenther's work consists of two parts: First, he maintains and develops the MARX code. MARX is a Monte-Carlo code capable of tracing X-rays from the Chandra mirrors through the gratings and onto the detectors. It is used for instrument calibration and helps in the interpretation of observations. MARX is written in C.

Second,Guenther works on young, low-mass stars. Stars form in clouds of gas and dust, which contract under their own gravity. Initially, the proto-stars are hidden behind this envelope, but in later phases most of the mass concentrates in a circum-stellar disk. In this phase stars of spectral type M-F are called classical T Tauri stars (CTTS), and their more massive brethren, the A and B type progenitors are HerbigAeBe stars (HAeBe).

Most of Guenther's work is based on spectroscopy of these young stars observed with space telescopes like Chandra, XMM-Newton and Hubble.

In CTTS the disk does not reach down to the central star, but mass accrets onto the star in magnetically controlled funnels. Guenther developed a model for the X-ray emission from the accretion shock. This model can explain many of the observed features for CTTS, but recent data is no longer compatible with the simple 1D approach. He uses multi-wavelengths monitoring campaigns (currently I am working on data from TW Hya taken in the UV, the optical and X-rays nearly simultaneously).

CTTS and HAeBe stars can drive powerful outflows. In close collaboration with C. Schneider, Dr. Guenther performs Chandra and HST observations of these jets. In these programs we target well-known jets (DG Tau, HD 163293, HH 2), so that we can follow their time evolution.

Looking at the X-ray absorbing column density NH and the optical reddening AV we can constrain the composition of the circumstellar material, because X-rays are sensitive to the gas, while reddening is caused by dust. However, different dust properties also influence the observed AV value, which complicates the analysis. Additionally, I use spectroscopy obtained with VLT/X-Shooter to probe the circumstellar material.