H. Kroker

DEVELOPMENT OF A DUST MANTLE ON THE SURFACE OF AN INSOLATED ICE-DUST MIXTURE : RESULTS FROM THE KOSI-9 EXPERIMENT

Astronomical observations indicate that formation and destruction of dust mantles on cometary nuclei may be the cause for erratic and systematic variations of cometary activity, i.e. emission of dust. A laboratory experiment (KOSI-9) has been performed to study the evolution of a dust mantle on top of a sublimating ice-dust mixture in vacuum. A sample consisting of water ice with a 10% (by weight) admixture of olivine grains has been insolated in three periods at variable intensities from 200 to 1900 W/m2. Both increasing surface temperature of the sample and decreasing gas and particle emissions indicated the formation of a dust mantle during the first period. During the second insolation period after the gas flux had reached a critical value of a few 1021 water molecules m−2 s−1, avalanches of mantle material occurred on the inclined sample surface, broke up the mantle locally, and opened up a fresh icy surface. Enhanced ice and dust particle emission resumed for some time from these spots. A large number of the emitted dust particles were of a fluffy aggregate structure, i.e., they had large cross section to mass ratios compared to compact particles. During the third period the critical gas flux was not reached and no enhanced dust and ice emission was observed. A dry dust mantle of a few millimeters thickness developed during the course of the experiment. Consequences of these findings for cometary scenarios are discussed.

Near-Infrared Integral Field Spectroscopy of Markarian 231

The ultraluminous infrared Seyfert 1 galaxy Mrk 231 has been spectrally imaged in the K band with the new three-dimensional MPE integral field spectrometer. The combined images of the H2 emission lines show, for the first time in an ultraluminous infrared galaxy, the presence of an extended circumnuclear structure of hot molecular gas. The H2 emitting region has a size of ~2.4 kpc and a hot molecular gas mass M ~2 × 104 M☉. The H2 emission-line ratios indicate that the gas is most likely thermally excited. If as in NGC 7469 star formation is associated with the H2 emission, the starburst would have a far-IR luminosity LFIR ~ 1 × 1012 L☉. This value represents an upper limit, since a fraction of the hot molecular gas may be excited by the radiation field emerging from the nucleus. The K-band three-dimensional data cube also shows for the first time the presence of extended narrow Paα emission blueshifted by ~1400 km s-1 with respect to the systemic velocity, and located ~0.6 kpc northwest of the nucleus. The detection of CO absorption bands with a spatial distribution peaking on the K-band continuum provides evidence for a central stellar concentration. The low CO spectroscopic index indicates, however, dilution by hot dust emission or by a nonthermal active galactic nucleus. The Paα/Hα ratio confirms previous extinction measurements based on Balmer line ratios, i.e., visual extinction of AV ~ 2.0-6.6 mag. The quasar-type nucleus of Mrk 231 should then be transparent at 2 μm and also in hard X-rays. A weak nuclear He I λ2.058 μm (He I/Paα = 0.032) is detected, and no detection of [Si VI] λ1.962 μm is made, placing an upper limit of 4 × 10-18 Wm-2 for the coronal gas emission. The ionizing source could either be a far-UV and X-ray quiet quasar or else a nuclear starburst with an upper mass limit ≥60 M☉.

ROGUE - the Rapid Off-axis GUider Experiment

Near infrared imaging spectroscopy at spatial resolutions of 0.5 arc seconds will fundamentally change our understanding of active galactic nuclei. This long desired capability has been achieved for the first time by the latest generation of MPE instruments, ROGUE and 3D. ROGUE, the rapid off-axis guider experiment, is a low order adaptive optics system performing tip-tilt correction in the near infrared using natural guide stars. Three-dimensional is the MPE near infrared imaging spectrometer capable of simultaneous imaging and spectroscopy of the entire H and K atmospheric windows. ROGUE is capable of tip-tilt correction at 40 Hz in a 4 arc-minute diameter isokinetic patch using natural guide stars as faint as 18th magnitude. We discuss the design of the instrument, present the first astronomical results, and outline future efforts to incorporate variable image scales.

IR observations of KOSI samples

Abstract The thermal images received during the experiments KOSI 9, KOSI 10, KOSI 10A and KOSI 11 by a scanning infrared camera sensitive in the wavelength region 3–5 μm are discussed. The common features and the differences of the thermal behaviour of the samples during the different experiments are analysed. The results are compared with the data delivered by a nonimaging radiometer working in the wavelength region 8–14 μm. The main points of the discussion are the phenomena caused by the inhomogeneous character of the thermal surface processes. The observed distributions of the temperature on the surfaces of the samples were not static and are, therefore, not correlated with peculiarities of the sample preparation. This fact illustrates the complicated character of the thermal processes on the surface of an insolated ice-dust mixture.

3D: a new generation imaging spectrometer

MPE has developed 3D, a new type of a highly sensitive near- infrared integral field spectrometer. It has been designed to multiplex spectral as well as spatial information thus obtaining a full data cube in a single integration. At a spectral resolution between 1000 and 2000 and a field of view of 16 by 16 pixels, optimized for subarcsecond spatial resolution imaging spectroscopy, it has a much higher efficiency compared to conventional techniques. Outfitting one of the VLTs with a near-IR 3D type instrument will provide a powerful tool for diffraction-limited integral field spectroscopic research, in particular on faint high-z galaxies in the early universe. The basic design, recent upgrades as well as plans for a possible VLT-3D instrument are presented.

The nuclear stellar cluster in NGC 1068

We present new near-infrared integral field spectroscopy and adaptive optics imaging of the nucleus of NGC 1068. Using the stellar CO absorption features in the H and K bands, we have identified a moderately extincted stellar cluster centered on the nuclear position and of intrinsic size ~50 pc. We show that this nuclear star cluster is probably 5–13 × 108 years in age and contributes at least 10% of the total nuclear luminosity of ~1 × 1011 L⊙.

3D: A new tool for probing the stars and ISM in AGN

Abstract 3D, the new MPE NIR imaging spectrometer, provides us with a unique opportunity to probe in detail the structure of the stars, ionized gas, and hot molecular gas in the very centers of AGN. The instrument delivers data cubes with 16×160.5″ pixels which are 256 spectral channels deep. Thus, in a single observation we are able to obtain data on the entire K-Band over an 8″ × 8″ field of view, with a spectral resolution of R = λ Δλ = 1000 . In this paper we detail the working principles behind the instrument, and show first results from observations of the inner regions of the Seyfert 1 galaxy NGC7469 made at the Calar Alto observatory.

Near-IR Imaging Spectroscopy of CD Galaxy NGC1275

H and K band imaging spectroscopy of the central 12″ (4.2 kpc ) of NGC1275 using the Max-Planck-Institut fur extraterrestrische Physik imaging spectrometer “3D” maps the gas density and temperature in the core and separates the contribution of Seyfert emission to the core light.

Observational Evidence for a Compact Dark Mass at the Galactic Center

We present improved recent results from near-infrared high spatial resolution speckle observations with the MPE SHARP 1 camera at the NTT as well as imaging spectroscopic observations with the MPE 3D spectrometer at the ESO-MPIA 2.2m telescope, both at La Silla, Chile. The new K-band speckle maps reach K magnitudes of about 16 and resolve the previously found object at the position of the radio source Sgr A*(R) into a small cluster of compact sources. With one exception, their polarizations are similar to other sources in its vicinity and thus are probably caused by anisotropic foreground dust extinction in the Galactic plane. The Sgr A*(IR) complex does not exhibit any significant flux density variations at 2.2μm on time scales of minutes or years. We therefore interpret Sgr A*(IR) as a small local clustering of luminous stars (M K ≈-3) near/at the position of the compact radio source. The radial velocity dispersion of 35 early and late type stars with distances of 1 to 12″ from Sgr A* is 153±18 km/s. The new results favour the existence of a central dark mass of the order of ≈3×l06M⊙ (density ≥ 108.5 M⊙ pc-3, M/L≥10 L⊙/M⊙) within 0.14 pc of the dynamic center.

The nature of nuclear starbursts: M82

We have obtained new K-band observations of the nuclear regions of the starburst galaxy M82, with a spatial resolution of 1.5″ and a spectral resolution of 300 km/s. Maps of the Brγ and H2 1 - 0 S(1) line emission and of the CO index are presented, as well as spectra of the nucleus and two bright Brγ sources.