Stefan Hippler

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

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Publications (157)147.43 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Orbital monitoring of M-type binaries is essential for constraining their fundamental properties. This is particularly useful in young systems, where the extended pre-main sequence evolution can allow for precise isochronal dating. Here, we present the continued astrometric monitoring of the more than 200 binaries of the AstraLux Large Multiplicity Survey, building both on our previous work, archival data, and new astrometric data spanning the range of 2010-2012. The sample is very young overall -- all included stars have known X-ray emission, and a significant fraction (18%) of them have recently also been identified as members of young moving groups in the Solar neighborhood. We identify ~30 targets that both have indications of being young and for which an orbit either has been closed or appears possible to close in a reasonable timeframe (a few years to a few decades). One of these cases, GJ 4326, is however identified as probably being substantially older than has been implied from its apparent moving group membership, based on astrometric and isochronal arguments. With further astrometric monitoring, these targets will provide a set of empirical isochrones, against which theoretical isochrones can be calibrated, and which can be used to evaluate the precise ages of nearby young moving groups.
    The Astrophysical Journal Supplement Series 09/2014; 214(2). · 16.24 Impact Factor
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    ABSTRACT: The distribution of multiplicity among low-mass stars is a key issue to understanding the formation of stars and brown dwarfs, and recent surveys have yielded large enough samples of nearby low-mass stars to study this issue statistically to good accuracy. Previously, we have presented a multiplicity study of ~700 early/mid M-type stars observed with the AstraLux high-resolution Lucky Imaging cameras. Here, we extend the study of multiplicity in M-type stars through studying 286 nearby mid/late M-type stars, bridging the gap between our previous study and multiplicity studies of brown dwarfs. Most of the targets have been observed more than once, allowing us to assess common proper motion to confirm companionship. We detect 68 confirmed or probable companions in 66 systems, of which 41 were previously undiscovered. Detections are made down to the resolution limit of ~100 mas of the instrument. The raw multiplicity in the AstraLux sensitivity range is 17.9%, leading to a total multiplicity fraction of 21%-27% depending on the mass ratio distribution, which is consistent with being flat down to mass ratios of ~0.4, but cannot be stringently constrained below this value. The semi-major axis distribution is well represented by a log-normal function with μa = 0.78 and σa = 0.47, which is narrower and peaked at smaller separations than for a Sun-like sample. This is consistent with a steady decrease in average semi-major axis from the highest-mass binary stars to the brown dwarf binaries.
    The Astrophysical Journal 06/2014; 789(2):102. · 6.73 Impact Factor
  • PengQian Yang, Stefan Hippler, JianQiang Zhu
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    ABSTRACT: The adaptive optics system for the second-generation Very Large Telescope-interferometer (VLTI) instrument GRAVITY consists of a novel cryogenic near-infrared wavefront sensor to be installed at each of the four unit telescopes of the Very Large Telescope (VLT). Feeding the GRAVITY wavefront sensor with light in the 1.4–2.4 μm band, while suppressing laser light originating from the GRAVITY metrology system requires custom-built optical componets. In this paper, we present the development of a quantitative near-infraredpoint diffraction interferometric characterization technique, which allows measuring the transmitted wavefront error of the silicon entrance windows of the wavefront sensor cryostat. The technique can be readily applied to quantitative phase measurements in the near-infrared regime. Moreover, by employing a slightly off-axis optical setup, the proposed method can optimize the required spatial resolution and enable real time measurement capabilities. The feasibility of the proposed setup is demonstrated, followed by a theoretical analysis and experimental results. Our experimental results show that the phase error repeatability in the nanometer regime can be achieved.
    Science China: Physics, Mechanics and Astronomy 04/2014; 57(4). · 1.17 Impact Factor
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    ABSTRACT: The adaptive optics system for the second-generation VLT-interferometer (VLTI) instrument GRAVITY consists of a novel cryogenic near-infrared wavefront sensor to be installed at each of the four unit telescopes of the Very Large Telescope (VLT). Feeding the GRAVITY wavefront sensor with light in the 1.4 to 2.4 micrometer band, while suppressing laser light originating from the GRAVITY metrology system, custom-built optical components are required. In this paper, we present the development of a quantitative near-infrared point diffraction interferometric characterization technique, which allows measuring the transmitted wavefront error of the silicon entrance windows of the wavefront sensor cryostat. The technique can be readily applied to quantitative phase measurements in the near-infrared regime. Moreover, by employing a slightly off-axis optical setup, the proposed method can optimize the required spatial resolution and enable real time measurement capabilities. The feasibility of the proposed setup is demonstrated, followed by theoretical analysis and experimental results. Our experimental results show that the phase error repeatability in the nanometer regime can be achieved.
    Optics Express 04/2013; 21(7):9069-80. · 3.55 Impact Factor
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    ABSTRACT: Large flat mirrors can be characterized using a standard interferometer coupled with stitching the subaperture measurement data. Such systems can measure the global full map of the optical surface by minimizing the inconsistency of data in the adjacent regions. We present a stitching technique that makes use of a commercial phase-shifting Twyman- Green interferometer in combination with an iterative optimized stitching algorithm. The proposed method has been applied to determine the surface errors of planar mirrors with an accuracy of a few nanometers. Moreover, the effect of reference wavefront error is explored. The feasibility and the performance of the proposed system are also demonstrated, along with a detailed error analysis and experimental results.
    Proc SPIE 10/2012;
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    ABSTRACT: Observed properties of stars and planets in binary/multiple star systems provide clues to planet formation and evolution. We extended our survey for visual stellar companions to the hosts of transiting exoplanets by 21 stars, using the Lucky Imaging technique with the two AstraLux instruments: AstraLux Norte at the Calar Alto 2.2-m telescope, and AstraLux Sur at the ESO 3.5-m New Technology Telescope at La Silla. We present observations of two previously unknown binary candidate companions, to the transiting planet host stars HAT-P-8 and WASP-12, and derive photometric and astrometric properties of the companion candidates. The common proper motions of the previously discovered candidate companions with the exoplanet host stars TrES-4 and WASP-2 are confirmed from follow-up observations. A Bayesian statistical analysis of 31 transiting exoplanet host stars observed with AstraLux suggests that the companion star fraction of planet hosts is not significantly different from that of solar-type field stars, but that the binary separation is on average larger for planet host stars.
    Monthly Notices of the Royal Astronomical Society 09/2012; 428(1). · 5.52 Impact Factor
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    ABSTRACT: The 'Mid-infrared ELT Imager and Spectrograph' (METIS) will be the third instrument on the European Extremely Large Telescope (E-ELT). METIS will provide diffraction limited imaging in the atmospheric L/M and N-band from 3 to 14 μm over an 18˝×18˝ field of view, as well as high contrast coronagraphy, medium-resolution (R <= 5000) long slit spectroscopy, and polarimetry. In addition, an integral field spectrograph will provide a spectral resolution of R ~ 100,000 at L/M band. Focusing on highest angular resolution and high spectral resolution, METIS will deliver unique science, in particular in the areas of exo-planets, proto-planetary-disks and high-redshift galaxies, which are illustrated in this paper. The reduction of the E-ELT aperture size had little impact on the METIS science case. With the recent positive developments in the area of detectors, the METIS instrument concept has reached a high level of technology readiness. For some key components (cryogenic chopping mirror, immersed grating, sorption cooler and cryogenic derotator) a development and test program has been launched successfully.
    Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 09/2012
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    ABSTRACT: GRAVITY is a second generation instrument for the VLT Interferometer, designed to enhance the near-infrared astrometric and spectro-imaging capabilities of VLTI. Combining beams from four telescopes, GRAVITY will provide an astrometric precision of order 10 micro-arcseconds, imaging resolution of 4 milli-arcseconds, and low and medium resolution spectro-interferometry, pushing its performance far beyond current infrared interfero- metric capabilities. To maximise the performance of GRAVITY, adaptive optics correction will be implemented at each of the VLT Unit Telescopes to correct for the effects of atmospheric turbulence. To achieve this, the GRAVITY project includes a development programme for four new wavefront sensors (WFS) and NIR-optimized real time control system. These devices will enable closed-loop adaptive correction at the four Unit Telescopes in the range 1.4-2.4 {\mu}m. This is crucially important for an efficient adaptive optics implementation in regions where optically bright references sources are scarce, such as the Galactic Centre. We present here the design of the GRAVITY wavefront sensors and give an overview of the expected adaptive optics performance under typical observing conditions. Benefiting from newly developed SELEX/ESO SAPHIRA electron avalanche photodiode (eAPD) detectors providing fast readout with low noise in the near-infrared, the AO systems are expected to achieve residual wavefront errors of \leq400 nm at an operating frequency of 500 Hz.
    Proc SPIE 07/2012;
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    ABSTRACT: METIS, the Mid-infrared E-ELT Imager and Spectrometer is foreseen to be the third instrument on the European Extremely Large Telescope (E-ELT) and the only instrument to provide high sensitivity mid-IR imaging and spectroscopy to the E-ELT. In order to reach the maximum resolution and sensitivity, an adaptive optics system is required. Since the operational wavelength of METIS is the longest of all E-ELT instruments and the field is relatively small, the complexity of the AO system is significantly reduced, both in required speed as well as order of the AO system. Adaptive Optics has been demonstrated to deliver consistently high performance for the current generation of 6-10 meter class telescopes at mid-infrared wavelengths, and similar performance is expected for METIS on the E-ELT. But in order to provide a reliable system on the E-ELT, several effects which have a minor impact on 6-8 meter class telescopes will need to be investigated for their impact on METIS AO. These effects include refractivity, atmospheric composition variations, but also the operation in a complex operational environment given by both METIS as well as the E-ELT. In this paper we describe the scientific requirements on the METIS AO system, the specific issues related to Adaptive Optics in the mid-IR and expected performance of the METIS AO system on the E-ELT.
    Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 07/2012
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    ABSTRACT: The GRAVITY instrument’s adaptive optics system consists of a novel cryogenic near-infrared wavefront sensor to be installed at each of the four unit telescopes of the VLT. Feeding the GRAVITY wavefront sensor with light in the 1.4 - 2.4 micrometer band, while suppressing laser light originating from the GRAVITY metrology system, custom-built optical components are required. Here we report on optical and near-infrared testing of the silicon entrance windows of the wavefront sensor cryostat and other reflective optics used in the warm feeding optics.
    Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 07/2012
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    ABSTRACT: We present the results of an extensive high-resolution imaging survey of M-dwarf multiplicity using the Lucky Imaging technique. The survey made use of the AstraLux Norte camera at the Calar Alto 2.2m telescope and the AstraLux Sur camera at the ESO New Technology Telescope in order to cover nearly the full sky. In total, 761 stars were observed (701 M-type and 60 late K-type), among which 182 new and 37 previously known companions were detected in 205 systems. Most of the targets have been observed during two or more epochs, and could be confirmed as physical companions through common proper motion, often with orbital motion being confirmed in addition. After accounting for various bias effects, we find a total M-dwarf multiplicity fraction of 27+/-3% within the AstraLux detection range of 0.08-6" (semi-major axes of ~3-227 AU at a median distance of 30 pc). We examine various statistical multiplicity properties within the sample, such as the trend of multiplicity fraction with stellar mass and the semi-major axis distribution. The results indicate that M-dwarfs are largely consistent with constituting an intermediate step in a continuous distribution from higher-mass stars down to brown dwarfs. Along with other observational results in the literature, this provides further indications that stars and brown dwarfs may share a common formation mechanism, rather than being distinct populations.
    The Astrophysical Journal 05/2012; 754(1). · 6.73 Impact Factor
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    ABSTRACT: Binary/multiple properties provide clues to the formation of stars. In the AstraLux binary survey, we use the Lucky Imaging technique to search for companions to a large sample of young, nearby M dwarfs. We present results from observations of the first sub-sample, consisting of 124 M dwarfs in the southern sky.
    Proceedings of the International Astronomical Union 04/2012; 7(S282):460-461.
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    ABSTRACT: The GRAVITY instrument is a beam-combining interferometer for the four telescopes of the VLT, and relies upon four near-infrared (1.4-2.4 micron) Shack-Hartmann style wave-front sensors to determine the atmospheric distortion due to atmospheric turbulence. The GRAVITY AO system will then drive the VLT's MACAO deformable mirrors to correct the wavefront, permiting 10 micro-arcsecond astrometry. We present the current design and status of the wave front sensor system, as well as future plans for integration and test.
    01/2012;
  • R. Stuik, S. Hippler, A. Stolte, B. Brandl
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    ABSTRACT: The Mid-infrared E-ELT Imager and Spectrometer (METIS) will bring unprecedented resolution and sensitivity for the mid-infrared to the European Extremely Large Telescope (E-ELT). An adaptive optics system is required to get the most out of METIS both for achieving the resolution as well as the sensitivity and to be competitive and complementary to space missions. Due to the longer wavelength, the complexity of the AO system is significantly reduced, both in required speed as well as order of the AO system, as compared to other E-ELT instruments operating at visible and near-IR wavelengths, but for METIS on the E-ELT, the complexity is still comparable to the high-order AO systems currently coming on-line on the 8-10 meter class telescopes. Adaptive Optics has been demonstrated to deliver consistently Strehl Ratios exceeding 95% on 6-8 meter class telescopes at 10 microns, and similar performance is expected for METIS on the E-ELT. But to provide a reliable system on the E-ELT, several effects which have a minor impact on 6-8 meter class telescopes will need to be investigated for their impact on METIS AO. Refractivity effects and atmospheric composition variations have the potential of significantly decreasing the performance of METIS AO, while operation in a complex operational environment given by both METIS as well as the E-ELT will make the actual implementation of METIS AO non-trivial. In this paper we describe the scientific requirements on the METIS AO system, the trade-off of possible solutions to reach the requirements and expected performance of the METIS AO system on the E-ELT.
    09/2011;
  • Pengqian Yang, Jia Xu, Jianqiang Zhu, Stefan Hippler
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    ABSTRACT: When testing the optical surface errors with an interferometer, it is always important to determine the residual errors in the interferometer optics. The calibration of reference optic for proper accuracy is very important issue if the precise phase measurement results are to be obtained using interferometer. A simple ball calibration method is discussed and the sufficient number of measurements for the ball averaging calibration is determined. Further we analysis some errors, which limit the performance of the calibration method by using a combination of both ray optics and wave optics approach.
    Proc SPIE 05/2011;
  • The Galactic Center: a Window to the Nuclear Environment of Disk Galaxies; 05/2011
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    ABSTRACT: GRAVITY is the second generation Very Large Telescope Interferometer instrument for precision narrow-angle astrometry and interferometric imaging. With its fibre-fed integrated optics, wavefront sensors, fringe tracker, beam stabilisation and a novel metrology concept, GRAVITY will push the sensitivity and accuracy of astrometry and interferometric imaging far beyond what is offered today. Providing precision astrometry of order 10 microarcseconds, and imaging with 4-milliarcsecond resolution, GRAVITY will revolutionise dynamical measurements of celestial objects: it will probe physics close to the event horizon of the Galactic Centre black hole; unambiguously detect and measure the masses of black holes in massive star clusters throughout the Milky Way; uncover the details of mass accretion and jets in young stellar objects and active galactic nuclei; and probe the motion of binary stars, exoplanets and young stellar discs. The instrument capabilities of GRAVITY are outlined and the science opportunities that will open up are summarised.
    The Messenger. 03/2011; 143:16-24.
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    ABSTRACT: The Mid-Infrared ELT Imager and Spectrograph (METIS) will be the mid-infrared instrument for the European Extremely Large Telescope (E-ELT). It will provide diffraction limited imaging, high and low-resolution spectroscopy and phase mask coronography. Our science case for this instrument aims at direct detections of exoplanets and the study of their physical and chemical properties. We plan to observe a sample of M-dwarfs in the solar neighbourhood. In case of a direct detection of an exoplanet, we will conduct spectroscopic follow up observations with the low-resolution spectrograph provided by METIS.
    Coudé du Foresto, Vincent ; Gelino, Dawn M.; Ribas, Ignasi: Pathways Towards Habitable Planets, ASP, 534-538 (2010). 10/2010;
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    ABSTRACT: The 2nd generation Very Large Telescope Interferometer instrument GRAVITY aims at achieving micro-arcsecond accuracy astrometry. In a study of the GRAVITY science cases we investigate the astrometric detection of exoplanets around very low mass stars and closure phase variations during transits . This includes sample selection of M-dwarfs to be surveyed and simulations to identify the "best" survey strategy. With GRAVITY astrometric capability of 10 microarcsec, we expect to detect planets with 4 earth masses in 5 years survey.
    10/2010;
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    ABSTRACT: Astrometric planet searches with the GRAVITY VLTI instrument will be able to detect planets in the range from a few Earth-masses to Neptune-masses around nearby low-mass stars. High-resolution Lucky Imaging with AstraLux has provided a sample of nearby M dwarf binaries which defines a potential target list for astrometric planet detection with GRAVITY. We present the GRAVITY planet detection limits for one of the M dwarf binaries detected in the AstraLux survey.
    Coudé du Foresto, Vincent; Gelino, Dawn M. ; Ribas, Ignasi: Pathways Towards Habitable Planets, ASP, 405-406 (2010). 10/2010;

Publication Stats

493 Citations
147.43 Total Impact Points

Institutions

  • 1993–2014
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 1999
    • University of Massachusetts Amherst
      • Department of Electrical and Computer Engineering
      Amherst Center, MA, United States