69 research outputs found

    Metallicity determination of M dwarfs - High-resolution IR spectroscopy

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    Context. Several new techniques to determine the metallicity of M dwarfs with better precision have been developed over the last decades. However, most of these studies were based on empirical methods. In order to enable detailed abundance analysis, standard methods established for warmer solar-like stars, i.e. model-dependent methods using fitting of synthetic spectra, still need to be used. Aims. In this work we continue the reliability confirmation and development of metallicity determinations of M dwarfs using high- resolution infrared spectra. The reliability was confirmed though analysis of M dwarfs in four binary systems with FGK dwarf companions and by comparison with previous optical studies of the FGK dwarfs. Methods. The metallicity determination was based on spectra taken in the J band (1.1-1.4 {\mu}m) with the CRIRES spectrograph. In this part of the infrared, the density of stellar molecular lines is limited, reducing the amount of blends with atomic lines enabling an accurate continuum placement. Lines of several atomic species were used to determine the stellar metallicity. Results. All binaries show excellent agreement between the derived metallicity of the M dwarf and its binary companion. Our results are also in good agreement with values found in the literature. Furthermore, we propose an alternative way to determine the effective temperature of M dwarfs of spectral types later than M2 through synthetic spectral fitting of the FeH lines in our observed spectra. Conclusions. We have confirmed that a reliable metallicity determination of M dwarfs can be achieved using high-resolution infrared spectroscopy. We also note that metallicites obtained with photometric metallicity calibrations available for M dwarfs only partly agree with the results we obtain from high-resolution spectroscopy.Comment: 18 page

    Search for extrasolar planets with high-precision relative astrometry

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    We present our search program for substellar companions using high-precision relative astronomy. Due to its orbital motion around the star, an unseen substellar companion would produce a periodic "wobble" of the host star, which is the astrometric signal of the unseen companion. By measuring the separation between the components of stellar double and triple systems, we want to measure this astrometric signal of a possible unseen companion indirectly as a relative and periodic change of these separations. Using a new observation mode (the "cube-mode") where the frames were directly saved in cubes with nearly no loss of time during the readout, an adaptive optics system to correct for atmospheric noise and an infrared narrow band filter in the near infrared to suppress differential chromatic refraction (DCR) effects we achive for our first target (the double star HD 19994) a relative precision for the separation measurements of about 100...150 micro-arsecond per epoch. To reach a precision in the micro-arcsec-regime, we use a statistical approach. We take several thousand frames per target and epoche and after a verification of a Gaussian distribution the measurement precision can be calculated as the standard deviation of our measurements divided by the square root of the number of Gaussian distributed measurements. Our first observed target is the stellar binary HD 19994 A & B, where the A component has a known radial velocity planet candidate.Comment: 4 pages, IAUS 249 conferenc

    Activity and rotation of low mass stars in young open clusters

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    We present first results from a multi-object spectroscopy campaign in IC2602, the Hyades, the Pleiades, and the Coma cluster using VLT/FLAMES. We analysed the data for radial velocity, rotational velocity, and H-alpha activity. Here, we highlight three aspects of this study in the context of rotational braking and the rotation-activity relationship among low mass stars. Finally we discuss the cluster membership of sources in IC2602.Comment: To appear in the proceedings of Cool Stars XV Conference, 4 page

    Integral field spectroscopy of the GQ Lup companion

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    Nur wenige sehr junge und extrem massearme substellare Objekte sind zur Zeit bekannt. Ihr Entstehungsmechanismus ist nur unzureichend verstanden und umstritten. Gängige Entwicklungsmodelle vereinfachen die Anfangsbedingungen für diese Objekte zu stark und ihre Vorhersagen im Altersbereich unter einigen Millionen Jahren sind recht spekulativ. Die Spektren dieser jungen und massearmen Objekte sind nur schwer zu modellieren. Niedrige Temperaturen und Obenflächenschwerkräfte führen zu komplexen chemischen Reaktionen und zu Staubbildung in ihren Atmosphären, Prozesse deren adäquate theoretische Beschreibung durch synthetische Spektren eine große Herausforderung darstellt. Hinzu kommt, dass nur extrem wenige Ankerpunkte im Bereich niedriger Massen und niedrigen Alters bekannt sind. Solche Ankerpunkte, Objekte deren Massen und Radien durch direkte Messungen bestimmt werden, sind jedoch dringend notwendig um die theoretischen Modelle zu eichen und ihre Gültigkeit zu überprüfen.Only few ultra low mass substellar objects are currently observed in their earliest stages of formation. Their exact formation process is only poorly understood and a matter of debate. Evolutionary models oversimplify the initial conditions and are highly speculative for objects up to a few Myr of age. The spectral properties of such objects are hard to model. At extremely low temperatures and low surface gravities complex molecular chemistry and dust formation challenges theoreticians to compute synthetic spectra of high reliability. The extreme scarcity of anchor points - objects whose mass and radius can be measured directly - enhances the difficulties in properly describing and classifying such objects
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