Stefan Hippler

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

Are you Stefan Hippler?

Claim your profile

Publications (89)72.34 Total impact

  • Source
    [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). DOI:10.1088/0067-0049/214/2/17 · 14.14 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. DOI:10.1088/0004-637X/789/2/102 · 6.28 Impact Factor
  • PengQian Yang · Stefan Hippler · JianQiang Zhu
    [Show abstract] [Hide abstract]
    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). DOI:10.1007/s11433-013-5264-5 · 0.86 Impact Factor
  • [Show abstract] [Hide abstract]
    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. DOI:10.1364/OE.21.009069 · 3.49 Impact Factor
  • Chinese Journal of Lasers 01/2013; 40(5):0508001. DOI:10.3788/CJL201340.0508001
  • [Show abstract] [Hide abstract]
    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.
    Proceedings of SPIE - The International Society for Optical Engineering 10/2012; DOI:10.1117/12.974568 · 0.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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). DOI:10.1093/mnras/sts019 · 5.23 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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.
    Proceedings of SPIE - The International Society for Optical Engineering 07/2012; DOI:10.1117/12.926558 · 0.20 Impact Factor
  • [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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). DOI:10.1088/0004-637X/754/1/44 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. DOI:10.1017/S1743921311028080
  • Pengqian Yang · Jia Xu · Jianqiang Zhu · Stefan Hippler
    [Show abstract] [Hide abstract]
    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.
    Proceedings of SPIE - The International Society for Optical Engineering 05/2011; DOI:10.1117/12.889458 · 0.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Proceedings of SPIE - The International Society for Optical Engineering 07/2010; DOI:10.1117/12.856242 · 0.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Context. Sun-like stars are promising candidates to host exoplanets and are often included in exoplanet surveys by radial velocity (RV) and direct imaging. In this paper we report on the detection of a stellar companion to the nearby solar-analogue star HD 104304, which previously was considered to host a planetary mass or brown dwarf companion. Aims: We searched for close stellar and substellar companions around extrasolar planet host stars with high angular resolution imaging to characterize planet formation environments. Methods: The detection of the stellar companion was achieved by high angular resolution measurements, using the ``Lucky Imaging'' technique at the ESO NTT 3.5 m with the AstraLux Sur instrument. We combined the results with VLT/NACO archive data, where the companion could also be detected. The results were compared to precise RV measurements of HD 104304, obtained at the Lick and Keck observatories from 2001-2010. Results: We confirmed common proper motion of the binary system. A spectral type of M4V of the companion and a mass of 0.21 M_&sun; was derived. Due to comparison of the data with RV measurements of the unconfirmed planet candidate listed in the Extrasolar Planets Encyclopaedia, we suggest that the discovered companion is the origin of the RV trend and that the inclination of the orbit of i&ap;35°explains the relatively small RV signal. Based on observations made with ESO Telescopes at the La Silla and Paranal Observatory under programme IDs 083.C-0145 and 084.C-0812, and on data obtained from the ESO Science Archive Facility.
    Astronomy and Astrophysics 06/2010; 516. DOI:10.1051/0004-6361/201014740 · 4.48 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Adaptive Optics at mid-IR wavelengths has long been seen as either not necessary or easy. The impact of atmospheric turbulence on the performance of 8-10 meter class telescopes in the mid-IR is relatively small compared to other performance issues like sky background and telescope emission. Using a relatively low order AO system, Strehl Ratios of larger than 95% have been reported on 6-8 meter class telescopes. Going to 30-42 meter class telescopes changes this picture dramatically. High Strehl Ratios require what is currently considered a high-order AO system. Furthermore, even with a moderate AO system, first order simulations show that the performance of such a system drops significantly when not taking into account refractivity effects and atmospheric composition variations. Reaching Strehl Ratios of over 90% at L, M and N band will require special considerations and will impact the system design and control scheme of AO systems for mid-IR on ELTs. In this paper we present an overview of the effects that impact the performance of an AO system at mid-IR wavelengths on an ELT and simulations on the performance and we will present a first order system concept of such an AO system for METIS, the mid-IR instrument for the E-ELT. Comment: 5 pages, 7 figures; Proceedings of the AO4ELT Conference, Paris, France (22-26 June 2009)
    Proceedings of the International Astronomical Union 09/2009; DOI:10.1017/S1743921310010549
  • [Show abstract] [Hide abstract]
    ABSTRACT: Lucky Imaging is an observational technique that aims to achieve nearly-diffraction-limited image quality from the ground on 2-4-metre-class telescopes. While diffraction-limited observations from the ground are usually accomplished with the help of adaptive optics in the near-infrared spectral range at almost all 8-10-metre-class telescopes, Lucky Imaging aims for a similar imaging performance at shorter wavelengths, in particular from 0.7-1.1 microns. AstraLux Sur, a visitor instrument for the NTT, built at the Max-Planck-Institute for Astronomy, is described and some early results are presented.
    09/2009;
  • [Show abstract] [Hide abstract]
    ABSTRACT: METIS (the Mid‐infrared E‐ELT Imager and Spectrograph) is a 3‐ to 14‐micron multimode instrument for the 42‐meter European Extremely Large Telescope (E‐ELT). The instrument modes currently under study include direct and coronagraphic imaging, long‐slit spectroscopy, integral field spectroscopy and polarimetry. METIS will be interfaced with the E‐ELT adaptive optics system, and incorporate its own on‐axis natural guide star wavefront sensor, and thus achieve Strehl ratios above 90% in N band. In this paper we will describe two of the main science goals of this instrument: direct imaging of exoplanets as well as the characterization of protoplanetary disks. Because of the superior angular resolution and high contrast, METIS at the E‐ELT will be able to image exoplanets at considerably closer orbits than its cooperative competitor the Mid‐infrared Instrument (MIRI) on the James Webb Space Telescope (JWST).
    08/2009; 1158(1):333-336. DOI:10.1063/1.3215881
  • [Show abstract] [Hide abstract]
    ABSTRACT: Blending of a target star with background stars or binary companions causes several problems in transit surveys. Aside from potentially yielding false positive detections (through eclipses unrelated to the target under study), the mere presence of such blends introduces a bias in the measured baseline brightness, which leads to an under-estimation of the radius of a transiting companion. Follow-up of transiting planet candidates with state-of-the-art high-resolution methods providing diffraction-limited images from the ground can strongly mitigate this problem. We present initial results from a survey with the AstraLux Lucky Imaging camera to search for close neighbours to known exoplanet hosts. So far, three companions have been detected to transit hosts, only one of which was a previously known binary (WASP-2).
    02/2009; DOI:10.1063/1.3099140
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: AstraLux is the Lucky Imaging camera for the Calar Alto 2.2-m telescope and the 3.5-m NTT at La Silla. It allows nearly diffraction limited imaging in the SDSS i' and z' bands of objects as faint as i'=15.5mag with minimum technical effort. One of the ongoing AstraLux observing programs is a binarity survey among late-type stars with spectral types K7 to M8, covering more than 1000 targets on the northern and southern hemisphere. The survey is designed to refine binarity statistics and especially the dependency of binarity fraction on spectral type. The choice of the SDSS i' and z' filters allows to obtain spectral type and mass estimates for resolved binaries. With an observing efficiency of typically 6 targets per hour we expect to complete the survey in mid-2009. Selected targets will be followed up astrometrically and photometrically, contributing to the calibration of the mass-luminosity relation at the red end of the main sequence and at visible wavelengths. Comment: 4 pages, 3 figures. To appear in proceedings of Cool Stars 15 conference, St. Andrews, 2008
    09/2008; DOI:10.1063/1.3099272

Publication Stats

465 Citations
72.34 Total Impact Points

Institutions

  • 1997–2014
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 2012
    • Shanghai Institute of Optics and Fine Mechanics, CAS
      Shanghai, Shanghai Shi, China
  • 2004
    • University of Massachusetts Amherst
      Amherst Center, Massachusetts, United States