C. Leinert

Max Planck Institute for Astronomy, Heidelburg, Baden-Württemberg, Germany

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Publications (168)234.26 Total impact

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    ABSTRACT: We aim to characterize the distribution and composition of circumstellar material around young massive stars, and to investigate exactly which physical structures in these objects are probed by long-baseline mid-infrared interferometric observations. We used the two-telescope interferometric instrument MIDI of the Very Large Telescope Interferometer of the European Southern Observatory to observe a sample of 24 intermediate- and high-mass young stellar objects in the N band (8-13 micron). We had successful fringe detections for 20 objects, and present spectrally-resolved correlated fluxes and visibility levels for projected baselines of up to 128 m. We fit the visibilities with geometric models to derive the sizes of the emitting regions, as well as the orientation and elongation of the circumstellar material. Fourteen objects in the sample show the 10 micron silicate feature in absorption in the total and correlated flux spectra. For 13 of these objects, we were able to fit the correlated flux spectra with a simple absorption model, allowing us to constrain the composition and absorptive properties of the circumstellar material. Nearly all of the massive young stellar objects observed show significant deviations from spherical symmetry at mid-infrared wavelengths. In general, the mid-infrared emission can trace both disks and outflows, and in many cases it may be difficult to disentangle these components on the basis of interferometric data alone, because of the sparse spatial frequency coverage normally provided by current long-baseline interferometers. For the majority of the objects in this sample, the absorption occurs on spatial scales larger than those probed by MIDI. Finally, the physical extent of the mid-infrared emission around these sources is correlated with the total luminosity, albeit with significant scatter.
    Astronomy and Astrophysics 08/2013; · 5.08 Impact Factor
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    ABSTRACT: We provide the complete set of reduced, spectrally-resolved MIDI visibilities and differential phases for the 20 objects observed as part of the survey presented in the above publication. These interferometric data are provided in FITS format, and, more specifically, conform to the OIFITS standard (see Pauls et al., 2005PASP..117.1255P). Additionally, besides the standard OIFITS columns, the OI_VIS tables in each of the FITS files contain the columns 'CFLUX' and 'CFLUXERR', which contain the calibrated correlated flux and its estimated uncertainty (measured in Jy). (2 data files).
    VizieR Online Data Catalog. 08/2013;
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    ABSTRACT: Low-mass young stellar objects (YSOs) show variability not just at optical and near-infrared wavelengths, but also in the mid-infrared. The amplitude and time-scale of the brightness variations depend on the underlying physical mechanisms (e.g., dust processing, grain growth) and the structure of the circumstellar material. Variability studies can therefore provide us information on the structure and evolution of circumstellar material and can help to understand the initial conditions for planet formation. We studied the structure of the circumstellar material at a several AU scale around two low-mass YSOs, V1647 Ori and DG Tau. For both objects, we obtained multi-epoch mid-infrared interferometric observations with MIDI (Leinert et al. 2003), the mid-infrared instrument on the Very Large Telescope Interferometer (ESO/VLTI).
    07/2013;
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    ABSTRACT: Unlike in previous studies, we have performed a {chi}2-minimi comparing well calibrated optical and infrared spectra with recent cool star synthetic spectra leading to the determination of the physical stellar parameters Teff, radius, and logg for each of the three components of LHS 1070. (5 data files).
    VizieR Online Data Catalog. 08/2012;
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    ABSTRACT: The atlas presents medium-resolution mid-infrared spectra of low- and intermediate mass pre-main sequence objects obtained by the ISOPHOT-S spectrophotometer of the Infrared Space Observatory (ISO) and the Infrared Spectrograph (IRS) of the Spitzer Space Telescope. (2 data files).
    VizieR Online Data Catalog. 07/2012;
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    ABSTRACT: LHS1070 is a nearby multiple systems of low mass stars. It is an important source of information for probing the low mass end of the main sequence, down to the hydrogen-burning limit. The primary of the system consist of a mid-M dwarf and two components are late-M to L dwarf, at the star-brown dwarf transition. It makes it even more valuable to understand the formation of dust in cool stellar atmospheres.This work aims to determine the fundamental parameters of LHS1070 and to test recent model atmospheres.We compared the well calibrated data in the optical and infra-red with synthetic spectra computed from recent cool stars atmosphere models. We derived the physical parameters T_{eff}, radius and log g for three components of LHS1070. The models which include the formation and settle of dust are able to reproduce and describe the main features of the visible to IR spectra of the components.
    12/2011;
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    ABSTRACT: The Extragalactic Background Light (EBL) at UV, optical and NIR wavelengths consists of the integrated light of all unresolved galaxies along the line of sight plus any contributions by intergalactic matter including hypothetical decaying relic particles. The measurement of the EBL has turned out to be a tedious problem. This is because of the foreground components of the night sky brightness, much larger than the EBL itself: the Zodiacal Light (ZL), Integrated Starlight (ISL), Diffuse Galactic Light (DGL) and, for ground-based observations, the Airglow (AGL) and the tropospheric scattered light. We have been developing a method for the EBL measurement which utilises the screening effect of a dark nebula on the EBL. A differential measurement in the direction of a high-latitude dark nebula and its surrounding area provides a signal that is due to two components only, i.e. the EBL and the diffusely scattered ISL from the cloud. We present a progress report of this method where we are now utilising intermediate resolution spectroscopy with ESO's VLT telescope. We detect and remove the scattered ISL component by using its characteristic Fraunhofer line spectral signature. In contrast to the ISL, in the EBL spectrum all spectral lines are washed out. We present a high quality spectrum representing the difference between an opaque position within our target cloud and several clear OFF positions around the cloud. We derive a preliminary EBL value at 400 nm and an upper limit to the EBL at 520 nm. These values are in the same range as the EBL lower limits derived from galaxy counts.
    Proceedings of the International Astronomical Union 11/2011;
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    ABSTRACT: Information about the inner structure of young stellar objects is crucial for understanding how the central forming stars gain their mass. However, especially for observations of (usually further away) high-mass young stellar objects, conventional imaging has limitations in spatial resolution. By means of mid-infrared interferometry, we can peek deeply into the strongly extinguished central 100 AU of such objects. Here, we report on new data we obtained within our programme using MIDI at the VLTI. Shown are preliminary results on the known outflow sources AFGL 2136 IRS 1 and Mon R2 IRS 3A. In particular, we describe how quantities like differential phases give additional geometrical structure information. We demonstrate how the combined interpretation of single-telescope and interferometric data at different wavelength regimes can lead to a more complete picture of the nature of such MYSOs.
    11/2011;
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    ABSTRACT: Mid-infrared (8-13 microns) interferometric data of W Hya were obtained with MIDI/VLTI between April 2007 and September 2009, covering nearly three pulsation cycles. The spectrally dispersed visibility data of all 75 observations were analyzed by fitting a circular fully limb-darkened disk (FDD) model to all data and individual pulsation phases. Asymmetries were studied with an elliptical FDD. Modeling results in an apparent angular FDD diameter of W Hya of about (80 +/- 1.2) mas (7.8 AU) between 8 and 10 microns, which corresponds to an about 1.9 times larger diameter than the photospheric one. The diameter gradually increases up to (105 +/- 1.2) mas (10.3 AU) at 12 microns. In contrast, the FDD relative flux fraction decreases from (0.85 +/- 0.02) to (0.77 +/- 0.02), reflecting the increased flux contribution from a fully resolved surrounding silicate dust shell. The asymmetric character of the extended structure could be confirmed. An elliptical FDD yields a position angle of (11 +/- 20) deg and an axis ratio of (0.87 +/- 0.07). A weak pulsation dependency is revealed with a diameter increase of (5.4 +/- 1.8) mas between visual minimum and maximum, while detected cycle-to-cycle variations are smaller. W Hya's diameter shows a behavior that is very similar to the Mira stars RR Sco and S Ori and can be described by an analogous model. The constant diameter part results from a partially resolved stellar disk, including a close molecular layer of H2O, while the increase beyond 10 microns can most likely be attributed to the contribution of a spatially resolved nearby Al2O3 dust shell.
    Astronomy and Astrophysics 04/2011; 530. · 5.08 Impact Factor
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    ABSTRACT: The file contains the calibrated visibilities of all 75 used observations listed in the observation log (table1) as function of wavelength (8-12micron). Data are ordered by time (same as in table1). (2 data files).
    VizieR Online Data Catalog. 04/2011;
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    ABSTRACT: Performed in November 2007 as a part of the MIDI Guaranteed Time Observation exoplanet program, the observation of the hot Jupiter-like exoplanet Gliese 86b constituted the first attempt of exoplanet detection with the VLTI instrument MIDI. It is also a technical achievement as the first VLTI observation using AMBER and MIDI simultaneously. Fringes were obtained for both instruments with the aim to correct the phase in N-band from the dispersion using the fringes in K-band. In N-band, the parent star has an estimated magnitude of 3.8, and a flux ratio planet/star of about 10-3 is expected. After simulating the effect of the data reduction process of MIDI (EWS), it appears that the theoretical interferometric phase spectrum is a curved-like function with an amplitude (that we call arrow) of about 0.05°. According to the phase spectra of the calibrator HD9362, taken during the first night of observation, we estimate that a precision on the curvature measurement of about 0.33° is currently reached. Consequently, we are at least at a factor 6 from a possible detection. The AMBER data, obtained in parallel, were too noisy to be used to extrapolate and remove the corresponding dispersion in N band at the required level of precision.
    Proc SPIE 01/2010;
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    ABSTRACT: The cosmic infrared background (CIRB) consists mainly of the integrated light of distant galaxies. In the far-infrared the current estimates of its surface brightness are based on the measurements of the COBE satellite. Independent confirmation of these results is still needed from other instruments. In this paper we derive estimates of the far-infrared CIRB using measurements made with the ISOPHOT instrument aboard the ISO satellite. The results are used to seek further confirmation of the CIRB levels that have been derived by various groups using the COBE data. We study three regions of very low cirrus emission. The surface brightness observed with the ISOPHOT instrument at 90, 150, and 180 um is correlated with hydrogen 21 cm line data from the Effelsberg radio telescope. Extrapolation to zero hydrogen column density gives an estimate for the sum of extragalactic signal plus zodiacal light. The zodiacal light is subtracted using ISOPHOT data at shorter wavelengths. Thus, the resulting estimate of the far-infrared CIRB is based on ISO measurements alone. In the range 150 to 180 um, we obtain a CIRB value of 1.08+-0.32+-0.30 MJy/sr quoting statistical and systematic errors separately. In the 90 um band, we obtain a 2-sigma upper limit of 2.3 MJy/sr. The estimates derived from ISOPHOT far-infrared maps are consistent with the earlier COBE results.
    Astronomy and Astrophysics 05/2009; · 5.08 Impact Factor
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    ABSTRACT: Aims. We present high spatial resolution observations in the mid-infrared of the dusty core of the binary system HR 4049. Methods. We used the mid-infrared interferometer MIDI/VLTI with 40 m projected baselines. These observations provided two spectrally dispersed visibility curves at a spatial resolution of ~10 mas. Acquisition images and spectra are in addition obtained with a single telescope spatial resolution of ~250 mas.Results. The MIDI spectra show features due to emission lines (7.9, 8.6 and 11.3 micron) attributed to PAHs. The comparison between ISO and MIDI spectra and dispersed visibility curves allows us to investigate the budget of continuum and PAH emission from distant regions to the inner regions of the compact dusty structure. The flux balance between these different PAH features is different to the one seen in the large beam ISO spectrum, suggesting different contributions at varying locations from the central star for the different PAH species. These features are over-resolved (i.e. their correlated flux is close to zero), placing the bulk of their line forming region at least at 50-70 mas from the central star. The continuum extension is estimated to range between 23 and 27 mas using a Gaussian model, and is very close to the $K$-band sizes measured with VINCI/VLTI, implying that the emitting regions of the near and mid-IR are similar. The visibilities from the two different baselines do not allow us to constrain the shape of the continuum emitting region but noticeable differences between them suggest that the $N$ band dusty environment is flattened in a direction that coincides with the one suggested by previous polarimetric observations.
    Astronomy and Astrophysics 01/2009; · 5.08 Impact Factor
  • Conference Paper: Matisse
    Science with the VLT in the ELT Era; 01/2009
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    ABSTRACT: We report on recent observations of the pre-main sequence star FU Orionis with VLTI/MIDI. FU Ori was observed at the end of 2004 with three different baselines and a maximum resolution of 24 mas, corresponding to approximately 11 AU at a distance of 460 pc. The object was resolved with all three baselines and visibility curves and spectra from 8 micron to 13 micron were obtained. In addition, the recently discovered companion FU Ori S was visible in the acquisition images from which 8 micron photometry could be derived. The observations will be compared to current models describing the FU Ori system.
    Richichi, A.; Delplancke, F.; Paresce, F.; Chelli, A.: The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation Instrumentation, Springer, 243-247 (2008). 01/2008;
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    ABSTRACT: In a recent VLTI experiment we partially resolved the dust enshrouded star IRS 3 in the central light year of our galaxy. This observation is the first step in investigating both IRS 3 in particular and the stellar population of the Galactic Center in general with the VLTI at highest angular resolution. Here some of the scientific issues that can be addressed by a complete MIDI dataset on IRS 3 in the mid infrared are outlined. A bright compact source like IRS 3 is also technically essential for future VLTI phase-reference experiments at 10 mum in order to investigate other nearby sources, e.g. the Sgr A* black hole. For this purpose it is important to know the strength and compactness of IRS 3 on the longest baselines.
    Richichi, A.; Delplancke, F.; Paresce, F.; Chelli, A.: The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation Instrumentation, Springer, 307-312 (2008). 01/2008;
  • T. M. Herbst, C. D. Koresko, Christoph Leinert
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    ABSTRACT: We describe the technique of spatially resolved spectroscopy of close binary stars and present K band spectra of the Haro 6-10 and UY Aur infrared companion (IRC) systems. The IRC’s are characterized by very low infrared colour temperature and high luminosity. Our observations address the debate between those who suggest that the IRC’s are at an earlier evolutionary stage than their primary stars, and those who believe that these objects are relatively normal pre-main-sequence stars with substantial local extinction and accreting matter. In both Haro 6-10 and UY Aur, we detect 2 μm molecular hydrogen emission confined to the infrared companions. The line ratios are consistent with shock heating, strengthening the view that the IRC’s are experiencing ongoing accretion. In the case of UY Aur, non-spherical geometry, such as accretion onto a circumstellar disk, can explain the presence of molecular hydrogen emission, low effective temperature, and high luminosity while allowing moderate extinction to the photosphere at near infrared wavelengths.
    01/2007: pages 58-71;
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    ABSTRACT: We present new, near-infrared, adaptive optics observations of the enigmatic pre-main-sequence object T Tauri, using broadband filter imagery, long-slit spectroscopy, and Fabry-Perot imaging spectra. The broadband filter images spatially resolve the three stellar components of T Tau in the H, Ks, and L' photometric bands. We clearly detect T Tau Sb in the J band, and place upper limits on the J brightness of the infrared companion, T Tau Sa. The K-band spectrum of the T Tau S binary also resolves both components, and confirms strong Brgamma emission in both stars and photospheric features in Sb. We also report 2.058 mum helium recombination radiation associated with T Tau Sb. The Fabry-Perot channel map centered on the v=1-0 S(1) line of molecular hydrogen shows a number of spatially extended structures, including a loop of emission north of the stars that is also visible in continuum frames taken at +/-900 km s-1 from the line center. The continuum-subtracted H2 image displays bow shock structures associated with the southeast-northwest and east-west outflows. The east-west jet system also shows bright, oblique shocks lining the flow channel. The part of the long-slit spectrum that overlaps this channel wall displays H2 line ratios consistent with shock heating. This region also corresponds to the brightest knot of UV fluorescent emission reported by Saucedo and coworkers. The Fabry-Perot images unambiguously identify T Tau S binary as the source of the east-west outflow, although we cannot yet determine which of the two components produces the jet.
    The Astronomical Journal 01/2007; · 4.97 Impact Factor
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    ABSTRACT: We report on observations of circumstellar disks around young stars that have been obtained with the MIDI instrument, which is mounted on the VLT Interferometer and operates in the 10 micrometer atmospheric window. The maximum spatial resolution of 5 milli-arcsec corresponds to sub-AU scales at the distance to nearby star formation regions. Thus, we can study the disks on the spatial scales at which important processes occur, such as accretion, dust processing, and planet formation. The main results obtained so far can be summarized as follows: 1. The measured interferometric visibilities are in good qualitative agreement with those predicted by models of circumstellar disks. In particular, a predicted correlation between the strength of the far-infrared excess and the spatial structure of the disk is confirmed by direct measurements; 2. In several objects strong evidence for deviations from circular symmetry is present, indicating that an inclined disk is indeed the dominant component seen in the mid-infrared; 3. The dust properties are not uniform over the disk, but are instead a strong function of distance to the central star. The dust in the innermost disk regions is observed to be more ``processed'' than the dust further out, both in Herbig Ae star disks and in those around T-Tauri stars. Comment: 19 pages, 12 figures, invited talk at SPIE conference "Astronomical telescopes and instrumentation", Orlando, may 2006
    Proc SPIE 07/2006;
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    ABSTRACT: We review recent advances in our understanding of the innermost regions of the circumstellar environment around young stars, made possible by the technique of long baseline interferometry at infrared wavelengths. Near-infrared observations directly probe the location of the hottest dust. The characteristic sizes found are much larger than previously thought, and strongly correlate with the luminosity of the central young stars. This relation has motivated in part a new class of models of the inner disk structure. The first mid-infrared observations have probed disk emission over a larger range of scales, and spectrally resolved interferometry has for the first time revealed mineralogy gradients in the disk. These new measurements provide crucial information on the structure and physical properties of young circumstellar disks, as initial conditions for planet formation.
    04/2006;

Publication Stats

539 Citations
234.26 Total Impact Points

Institutions

  • 1970–2011
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 2000–2007
    • European Southern Observatory
      Arching, Bavaria, Germany
  • 1998
    • Hungarian Academy of Sciences
      Budapeŝto, Budapest, Hungary