Hans Ulrich Kaufl

Sulphur and zinc abundances in Galactic halo stars revisited

Aims. Based on a new set of sulphur abundances in very metal-poor stars and an improved analysis of previous data, we aim at resolving current discrepancies on the trend of S/Fe vs. Fe/H and thereby gain better insight into the nucleosynthesis of sulphur. The trends of Zn/Fe and S/Zn will also be studied. Methods. High resolution VLT/UVES spectra of 40 main-sequence stars with −3.3 < [Fe/H] < −1.0 are used to derive S abundances from the weak λ8694. 6S i line and the stronger λλ9212.9, 9237. 5p air of Si lines. For one star, the S abundance is also derived from the S i triplet at 1.046 µm recently observed with the VLT infrared echelle spectrograph CRIRES. Fe and Zn abundances are derived from lines in the blue part of the UVES spectra, and effective temperatures are obtained from the profile of the Hβ line. Results. Comparison of sulphur abundances from the weak and strong S i lines provides important constraints on non-LTE effects. The high sulphur abundances reported by others for some metal-poor stars are not confirmed; instead, when taking non-LTE corrections into account, the Galactic halo stars distribute around a plateau at [S/Fe] ∼ +0.2 dex with a scatter of 0.07 dex only. [Zn/Fe] is close to zero for metallicities in the range −2.0 < [Fe/H] < −1.0 but increases to a level of [Zn/Fe] ∼ +0. 1t o+0.2 dex in the range −2.7 < [Fe/H] < −2.0. At still lower metallicities [Zn/Fe] rises steeply to a value of [Zn/Fe] ∼ +0. 5d ex at [Fe/H] = −3.2. Conclusions. The trend of S/Fe vs. Fe/H corresponds to the trends of Mg/Fe, Si/Fe, and Ca/Fe and indicates that sulphur in Galactic halo stars has been made by α-capture processes in massive SNe. The observed scatter in S/Fe is much smaller than predicted from current stochastic models of the chemical evolution of the early Galaxy, suggesting that either the models or the calculated yields of massive SNe should be revised. We also examine the behaviour of S/Zn and find that departures from the solar ratio are significantly reduced at all metallicities if non-LTE corrections to the abundances of these two elements are adopted. This effect, if confirmed, would reduce the usefulness of the S/Zn ratio as a diagnostic of past star-formation activity, but would bring closer together the values measured in damped Lyman-alpha systems and in Galactic stars.

Spectrally Resolved Pure Rotational Lines of Water in Protoplanetary Disks

We present ground-based high-resolution N-band spectra (Δv = 15 km s^(−1)) of pure rotational lines of water vapor in two protoplanetary disks surrounding the pre-main-sequence stars AS 205N and RNO 90, selected based on detections of rotational water lines by the Spitzer InfraRed Spectrograph. Using VISIR on the Very Large Telescope, we spectrally resolve individual lines and show that they have widths of 30–60 km s^(−1), consistent with an origin in Keplerian disks at radii of ~ 1AU. The water lines have similar widths to those of the CO at 4.67 μm, indicating that the mid-infrared water lines trace similar radii. The rotational temperatures of the water are 540 and 600 K in the two disks, respectively. However, the line ratios show evidence of non-LTE excitation, with low-excitation line fluxes being overpredicted by two-dimensional disk LTE models. Due to the limited number of observed lines and the non-LTE line ratios, an accurate measure of the water ortho/para (O/P) ratio is not available, but a best estimate for AS 205N is O/P = 4.5±1.0, apparently ruling out a low-temperature origin of the water. The spectra demonstrate that high-resolution spectroscopy of rotational water lines is feasible from the ground, and further that ground-based high-resolution spectroscopy is likely to significantly improve our understanding of the inner disk chemistry revealed by recent Spitzer observations.

Technetium and the third dredge up in AGB stars. I. Field stars

Context. We searched for Technetium (Tc) in a sample of bright oxygenrich asymptotic giant branch (AGB) stars located in the oute r galactic bulge. Tc is an unstable element synthesised via the s-proce ss in deep layers of AGB stars, thus it is a reliable indicator of both recent s-process activity and third dredge-up. Aims. We aim to test theoretical predictions on the luminosity lim it for the onset of third dredge-up. Methods. Using high resolution optical spectra obtained with the UVE S spectrograph at ESO’s VLT we search for resonance lines of n eutral Tc in the blue spectral region of our sample stars. These meas ur ments allow us to improve the procedure of classification of stars with respect to their Tc content by using flux ratios. Synthetic spectra ba sed on MARCS atmospheric models are presented and compared t o the observed spectra around three lines of Tc. Bolometric magnitudes are c lculated based on near infrared photometry of the objects . Results. Among the sample of 27 long period bulge variables four were f ound to definitely contain Tc in their atmospheres. Conclusions. The luminosity of the Tc rich stars is in agreement with predi ctions from AGB evolutionary models on the minimum luminosi ty at the time when third dredge-up sets in. However, AGB evolut i nary models and a bulge consisting of a single old populati on cannot be brought into agreement. This probably means that a younger p opulation is present in the bulge, as suggested by various au thors, which contains the Tc-rich stars here identified.

INFRARED OBSERVATIONS OF DUST EMISSION FROM COMET HALE-BOPP

We present infrared imaging and photometry of the bright, giant comet C/1995 O1 (Hale-Bopp). The comet was observed in an extended infrared and optical observing campaign in 1996–1997. The infrared morphology of the comet was observed to change from the 6 to 8 jet “porcupine” structure in 1996 to the “pinwheel” structure seen in 1997; this has implications for the position of the rotational angular momentum vector. Long term light curves taken at 11.3 μm indicate a dust production rate that varies with heliocentric distance as ∶ r−1.4. Short term light curves taken at perihelion indicate a rotational periodicity of 11.3 hours and a projected dust outflow speed of ∶ 0.4 km s−1. The spectral energy distribution of the dust on October 31, 1996 is well modeled by a mixture of 70% silicaceous and 30% carbonaceous non-porous grains, with a small particle dominated size distribution like that seen for comet P/Halley (McDonnell et al., 1991), an overall dust production rate of 2 × 105 kg s−1, a dust-to-gas ratio of ∶5, and an albedo of 39%.

METIS : the mid-infrared E-ELT imager and spectrograph

METIS will be among the first generation of scientific instruments on the E-ELT. Focusing on highest angular resolution and high spectral resolution, METIS will provide diffraction limited imaging and coronagraphy from 3-14μm over an 20x20° field of view, as well as integral field spectroscopy at R ~ 100,000 from 2.9-5.3μm. In addition, METIS provides medium-resolution (R ~ 5000) long slit spectroscopy, and polarimetric measurements at N band. While the baseline concept has already been discussed at previous conferences, this paper focuses on the significant developments over the past two years in several areas: The science case has been updated to account for recent progress in the main science areas circum-stellar disks and the formation of planets, exoplanet detection and characterization, Solar system formation, massive stars and clusters, and star formation in external galaxies. We discuss the developments in the adaptive optics (AO) concept for METIS, the telescope interface, and the instrument modelling. Last but not least we provide an overview of our technology development programs, which ranges from coronagraphic masks, immersed gratings, and cryogenic beam chopper to novel approaches to mirror polishing, background calibration and cryo-cooling. These developments have further enhanced the design and technology readiness of METIS to reliably serve as an early discovery machine on the E-ELT.

GROUND-BASED INFRARED DETECTIONS OF CO IN THE CENTAUR-COMET 29P/SCHWASSMANN-WACHMANN 1 AT 6.26 AU FROM THE SUN

We observed Comet 29P/Schwassmann-Wachmann 1 (hereafter, 29P) in 2012 February and May with CRIRES/VLT and NIRSPEC/Keck-II, when the comet was at 6.26 AU from the Sun and about 5.50 AU from Earth. With CRIRES, we detected five CO emission lines on several nights in each epoch, confirming the ubiquitous content and release of carbon monoxide from the nucleus. This is the first simultaneous detection of multiple lines from any (neutral) gaseous species in comet 29P at infrared wavelengths. It is also the first extraction of a rotational temperature based on the intensities of simultaneously measured spectral lines in 29P, and the retrieved rotational temperature is the lowest obtained in our infrared survey to date. We present the retrieved production rates (~3 × 10^(28) molecules s^(–1)) and remarkably low (~5 K) rotational temperatures for CO, and compare them with results from previous observations at radio wavelengths. Along with CO, we pursued detections of other volatiles, namely H_2O, C_2H_6, C_2H_2, CH_4, HCN, NH_3, and CH_3OH. Although they were not detected, we present sensitive upper limits. These results establish a new record for detections by infrared spectroscopy of parent volatiles in comets at large heliocentric distances. Until now considered to be a somewhat impossible task with IR ground-based facilities, these discoveries demonstrate new opportunities for targeting volatile species in distant comets.

A sky-noise measurement and its implication for ground-based infrared astronomy in the 10μm atmospheric window

A spectral analysis of the fluctuations of the infrared sky radiance at λ ≈ 10μm was made at the ESO-site of La Silla in Northern Chile. The data are compared to literature. The consequences of the results on infrared observing for future large telescopes are discussed: our data suggest that in order to achieve background noise limited performance in the 10μm atmospheric window chopping with frequencies of ≈8 Hz and amplitudes of ≈10 arcsec is mandatory.

Spectral-type dependent rotational braking and strong magnetic flux in three components of the late-M multiple system LHS 1070

We show individual high-resolution spectra of components A, B, and C of the nearby late-M type multiple system LHS 1070. Component A is a mid-M star, and B and C are known to have masses at the threshold to brown dwarfs. From our spectra we measure rotation velocities and the mean magnetic field for all three components individually. We find magnetic flux on the order of several kilo-Gauss in all components. The rotation velocities of the two late-M objects B and C are similar (v sini = 16 km s −1 ), the earlier A component is spinning only at about half that rate. This suggest that net rotational braking at late-M spectral type is weakening, and that the lack of slowly rotating late-M and L dwarfs is real. Furthermore, we found that magnetic flux in the B component is about twice as strong as in component C at a similar rotation rate. This indicates that rotational braking is not proportional to magnetic field strength in fully convective objects and that a different field topology is the reason for the weak braking in low-mass objects.

METIS: System engineering and optical design of the mid-infrared E-ELT instrument

METIS is a mid-infrared instrument proposed for the European Extremely Large Telescope (E-ELT). It is designed to provide imaging and spectroscopic capabilities in the 3μm to 14μm region up to a spectral resolution of 100.000. Here the technical concept of METIS is described which has been developed based on an elaborated science case which is presented elsewhere in this conference. There are five main opto-mechanical modules all integrated into a common cryostat: The fore-optics is re-imaging the telescope focal plane into the cryostat, including a chopper, an optical de-rotator and an un-dispersed pupil stop. The imager module provides diffraction limited direct imaging, low-resolution grism spectroscopy, polarimetry and coronagraphy. The high resolution IFU spectrograph offers a spectral resolution of 100.000 for L- and M-band and optional 50.000 for the N-band. In addition to the WFS integrated into the E-ELT, there is a METIS internal on-axis WFS operating at visual wavelengths. Finally, a cold (and an external warm) calibration unit is providing all kinds of spatial and spectral calibrations capabilities. METIS is planned to be used at one of the direct Nasmyth foci available at the E-ELT. This recently finished Phase-A study carried out within the framework of the ESO sponsored E-ELT instrumentation studies has been performed by an international consortium with institutes from Germany, Netherlands, France, United Kingdom and Belgium.

Studies for the first generation of instruments for the European ELT

The European Southern Observatory (ESO) is conducting a phase B study of a European Extremely Large Telescope (E-ELT). The baseline concept foresees a 42m primary, 5 mirror adaptive telescope with two of the mirrors giving the possibility of very fast correction of the atmospheric turbulence. In parallel to the telescope study, ESO is coordinating 8 studies of instruments and 2 of post-focus Adaptive Optics systems, carried out in collaboration with Institutes in the member states. Scope of the studies, to be completed by 1Q 2010, is to demonstrate that the high priority scientific goals of the E-ELT project can be achieved with feasible and affordable instruments. The main observing modes being considered are: NIR wide field imaging and spectroscopy to the diffraction limit or with partial correction of the atmospheric seeing; high spectral resolution, high stability visible spectroscopy; high contrast, diffraction limited imaging and spectroscopy; DL mid-infrared imaging and spectroscopy. The status of the 8 current studies is presented.