S. Kimeswenger

Molecfit: A general tool for telluric absorption correction I. Method and application to ESO instruments ?;??

Context. The interaction of the light from astronomical objects with the constituents of the Earth’s atmosphere leads to the formation of telluric absorption lines in ground-based collected spectra. Correcting for these lines, mostly a ecting the red and infrared region of the spectrum, usually relies on observations of specific stars obtained close in time and airmass to the science targets, therefore using precious observing time. Aims. We present molecfit, a tool to correct for telluric absorption lines based on synthetic modelling of the Earth’s atmospheric transmission. Molecfit is versatile and can be used with data obtained with various ground-based telescopes and instruments. Methods. Molecfit combines a publicly available radiative transfer code, a molecular line database, atmospheric profiles, and various kernels to model the instrument line spread function. The atmospheric profiles are created by merging a standard atmospheric profile representative of a given observatory’s climate, of local meteorological data, and of dynamically retrieved altitude profiles for temperature, pressure, and humidity. We discuss the various ingredients of the method, its applicability, and its limitations. We also show examples of telluric line correction on spectra obtained with a suite of ESO Very Large Telescope (VLT) instruments. Results. Compared to previous similar tools, molecfit takes the best results for temperature, pressure, and humidity in the atmosphere above the observatory into account. As a result, the standard deviation of the residuals after correction of unsaturated telluric lines is frequently better than 2% of the continuum. Conclusions. Molecfit is able to accurately model and correct for telluric lines over a broad range of wavelengths and spectral resolutions. The accuracy reached is comparable to or better than the typical accuracy achieved using a telluric standard star observation. The availability of such a general tool for telluric absorption correction may improve future observational and analysing strategies, as well as empower users of archival data.

The formation of a massive protostar through the disk accretion of gas.

The formation of low-mass stars like our Sun can be explained by the gravitational collapse of a molecular cloud fragment into a protostellar core and the subsequent accretion of gas and dust from the surrounding interstellar medium. Theoretical considerations suggest that the radiation pressure from the protostar on the in-falling material may prevent the formation of stars above ten solar masses through this mechanism, although some calculations have claimed that stars up to 40 solar masses can in principle be formed via accretion through a disk. Given this uncertainty and the fact that most massive stars are born in dense clusters, it was suggested that high-mass stars are the result of the runaway merging of intermediate-mass stars. Here we report observations that clearly show a massive star being born from a large rotating accretion disk. The protostar has already assembled about 20 solar masses, and the accretion process is still going on. The gas reservoir of the circumstellar disk contains at least 100 solar masses of additional gas, providing sufficient fuel for substantial further growth of the forming star.

DENIS: A DEEP NEAR-INFRARED SURVEY OF THE SOUTHERN SKY

The DENIS project is the first attempt to carry out a complete digitized survey of the southern sky in the range 1–2.5µm. The main objectives of the programme and the main specifications of the camera and of the data processing stream are briefly outlined

An atmospheric radiation model for Cerro Paranal - I. The optical spectral range

Aims. The Earth’s atmosphere affects ground-based astronomical observations. Scattering , absorption, and radiation processes deteriorate the signal-to-noise ratio of the data received. For scheduling astronomical observations it is, therefore, im portant to accurately estimate the wavelength-dependent effect of the Earth’s atmosphere on the observed flux. Methods. In order to increase the accuracy of the exposure time calcul ator of the European Southern Observatory’s (ESO) Very Larg e Telescope (VLT) at Cerro Paranal, an atmospheric model was developed as part of the Austrian ESO In-Kind contribution. It includes all relevant components, such as scattered moonlight, scat tered starlight, zodiacal light, atmospheric thermal radi ation and absorption, and non-thermal airglow emission. This paper focuses on atmospheric scattering processes that mostly affect the blue ( 0.55� m) wavelength regime. While the former is mainly investigated by means of radiative transfe r models, the intensity and variability of the latter is stud ied with a sample of 1186 VLT FORS 1 spectra. Results. For a set of parameters such as the object altitude angle, Moon-object angular distance, ecliptic latitude, bimonthly p eriod, and solar radio flux, our model predicts atmospheric radiati on and transmission at a requested resolution. A comparison of our model with the FORS 1 spectra and photometric data for the night-sky brightness from the literature, suggest a model accuracy o f about 20%. This is a significant improvement with respect to existing pr edictive atmospheric models for astronomical exposure time calculators.

Molecfit: A general tool for telluric absorption correction. . II. Quantitative evaluation on ESO-VLT/X-Shooterspectra

Context. Absorption by molecules in the Earth’s atmosphere strongly affects ground-based astronomical observations. The resulting absorption line strength and shape depend on the highly variable physical state of the atmosphere, i.e. pressure, temperature, and mixing ratio of the different molecules involved. Usually, supplementary observations of so-called telluric standard stars (TSS) are needed to correct for this effect, which is expensive in terms of telescope time. We have developed the software package molecfit to provide synthetic transmission spectra based on parameters obtained by fitting narrow ranges of the observed spectra of scientific objects. These spectra are calculated by means of the radiative transfer code LBLRTM and an atmospheric model. In this way, the telluric absorption correction for suitable objects can be performed without any additional calibration observations of TSS. Aims. We evaluate the quality of the telluric absorption correction using molecfit with a set of archival ESO-VLT/X-Shooter visible and near-infrared spectra. Methods. Thanks to the wavelength coverage from the U to the K band, X-Shooter is well suited to investigate the quality of the telluric absorption correction with respect to the observing conditions, the instrumental set-up, input parameters of the code, the signal-to-noise of the input spectrum, and the atmospheric profiles. These investigations are based on two figures of merit, Ioff and Ires, that describe the systematic offsets and the remaining small-scale residuals of the corrections. We also compare the quality of the telluric absorption correction achieved with molecfit to the classical method based on a telluric standard star. Results. The evaluation of the telluric correction with molecfit shows a convincing removal of atmospheric absorption features. The comparison with the classical method reveals that molecfit performs better because it is not prone to the bad continuum reconstruction, noise, and intrinsic spectral features introduced by the telluric standard star. Conclusions. Fitted synthetic transmission spectra are an excellent alternative to the correction based on telluric standard stars. Moreover, molecfit offers wide flexibility for adaption to various instruments and observing sites.

Metal Enrichment Processes in the Intra-Cluster Medium

Institut fu¨r Astronomie, Universit¨at Wien, Tu¨rkenschanzstr. 17, 1180 Vienna, AustriaReceived / AcceptedAbstract. We present numerical simulations of galaxy clusters which include interaction processes between thegalaxies and the intra-cluster gas. The considered interaction processes are galactic winds and ram-pressurestripping, which both transfer metal-enriched interstellar medium into the intra-cluster gas and hence increase itsmetallicity. We investigate the efficiency and time evolution of the interaction processes by simulated metallicitymaps, which are directly comparable to those obtained from X-ray observations. We find that ram-pressurestripping is more efficient than quiet (i.e. non-starburst driven) galactic winds in the redshift interval between 1and 0. The expelled metals are not mixed immediately with the intra-cluster gas, but inhomogeneities are visiblein the metallicity maps. Even stripes of higher metallicity that a single galaxy has left behind can be seen. Thespatial distribution of the metals transported by ram-pressure stripping and by galactic winds are very differentfor massive clusters: the former process yields a centrally concentrated metal distribution while the latter resultsin an extended metal distribution.Key words. Galaxies:clusters:general – Galaxies:abundances – Galaxies:interactions – Galaxies:ISM – X-ray:galaxies:clusters

An advanced scattered moonlight model for Cerro Paranal

The largest natural source of light at night is the Moon, and it is the major contributor to the astronomical sky background. Being able to accurately predict the sky background, including scattered moonlight is important for scheduling astronomical observations. We have developed an improved scattered moonlight model, in which the components are computed with a better physical understanding as opposed to the simple empirical fit in the frequently used photometric model of Krisciunas & Schaefer (1991, PASP, 103, 1033). Our spectroscopic model can better trace the spectral trends of scattered moonlight for any position of the Moon and target observation. This is the first scattered moonlight model that we know of which is this physical and versatile. We have incorporated an observed solar spectrum, accurate lunar albedo fit, and elaborate scattering and absorption calculations that include scattering off of molecules and aerosols. It was designed for Cerro Paranal, but can be modified for any location with known atmospheric properties. Throughout the optical range, the uncertainty is less than 20%. This advanced scattered moonlight model can predict the amount of scattered moonlight for any given geometry of the Moon and target, and lunar phase for the entire optical spectrum.

The peculiar variable V838 Mon

V838 Mon underwent, after a first nova-like outburst in January and a usual decline, a second outburst after one month, and a third weak one again a month later. Moreover, a very small increase of the temperature at the beginning of April gives us a hint about a physical process with a period of one month. We obtained a BV R IC time-sequence and modelled the photometric behaviour of the object. This leads us to the conclusion that the interstellar foreground extinction has to be 0.6 mag E(B − V ) 0.8 mag and that the quasi-photosphere had persistently unusually low temperatures for nova-like systems. The photometry was used to follow the dramatic changes of the expansion. While the appearing 10-µm excess can be well described by the heating of material ejected during this event, the IRAS emission near the location of the progenitor originates most likely from dust, which were formed during the previous evolution of the object. Assuming that the light echoes are coming from circumstellar material, the distance is 640 to 680 pc ‐ smaller than the 790 pc given in Munari et al. (2002). In our opinion V838 Mon and V4332 Sgr are manifestations of a new class of eruptive variables. We do not count M31RV to be in this class.

Simulations of galactic winds and starbursts in galaxy clusters

School of Mathematics, University of Edinburgh, Edinburgh EH9 3JZ, Scotland, UK-/-Abstract. We present an investigation of the metal enrichmentof the intra-cluster medium (ICM) bygalactic windsand merger-driven starbursts. We use combined N-body/hydrodynamic simulations with a semi-numerical galaxyformation model. The mass loss by galactic winds is obtained by calculating transonic solutions of steady stateoutflows, driven by thermal, cosmic ray and MHD wave pressure. The inhomogeneities in the metal distributioncaused by these processes are an ideal tool to reveal the dynamical state of a galaxy cluster. We present surfacebrightness, X-ray emission weighted temperature and metal maps of our model clusters as they would be observedby X-ray telescopes like XMM-Newton. We show that X-ray weighted metal maps distinguish between pre- orpost-merger galaxy clusters by comparing the metallicity distribution with the galaxy-density distribution: pre-mergers have a metallicity gap between the subclusters, post-mergers a high metallicity between subclusters. Weapply our approach to two observed galaxy clusters, Abell 3528 and Abell 3921, to show whether they are pre-or post-merging systems. The survival time of the inhomogeneities in the metallicity distribution found in oursimulations is up to several Gyr. We show that galactic winds and merger-driven starbursts enrich the ICM veryefficiently after z=1 in the central (∼ 3 Mpc radius) region of a galaxy cluster.Key words. Galaxies: clusters: general - Galaxies: abundances - Galaxies: interactions - Galaxies: ISM - X-ray:galaxies: clusters

Planetary nebula or symbiotic Mira? Near infrared colours mark the difference

Nebulae around symbiotic Miras look very much like genuine planetary nebulae, although they are formed in a slightly different way. We present near infrared photometry of known and suspected symbiotic nebulae obtained with the Deep Near Infrared Southern Sky Survey (DENIS). We demonstrate that the near infrared colours are an excellent tool to distinguish symbiotic from genuine planetary nebulae. In particular we find that the bipolar planetary nebulae M 2-9 and Mz 3 are in fact symbiotic Miras. Further observations on prototype symbiotic Miras prove that the proposed classification scheme works generally.