53 research outputs found

    Metallicity determination of M dwarfs - Expanded parameter range in metallicity and effective temperature

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    Context. Reliable metallicity values for M dwarfs are important for studies of the chemical evolution and advancement of planet formation theory in low-mass environments. Historically the determination of stellar parameters of low-mass stars has been challenging due to the low surface temperature, causing several molecules to form in the photospheric layers. In our work we use the fact that infrared high-resolution spectrographs have opened up a new window for investigating M dwarfs. Aims. Metallicity determination using high-resolution spectra is more accurate than the use of low-resolution spectra, but rather time-consuming. In this paper we expand our sample analyzed with this precise method both in metallicity and effective temperature in order to build up a calibration sample for a future revised empirical calibration. Methods. Because of the relatively few molecular lines in the J-band, continuum rectification is possible for high-resolution spectra, allowing the stellar parameters to be determined with greater accuracy than using optical spectra. The metallicity was determined using synthetic spectral fitting of several atomic species. Results. We have analyzed sixteen targets, with a range of effective temperature from 3350-4550 K. The resulting metallicities lie between -0.5 < [M/H] < +0.4. A few targets have previously been analyzed using low-resolution spectra, and we find a rather good agreement with our values. A comparison with available photometric calibrations shows varying agreement, and the spread within all empirical calibrations is large. Conclusions. Including the targets from our previous paper, we have analyzed 28 M dwarfs using high-resolution infrared spectra. The targets spread approximately one dex in metallicity and 1400 K in effective temperature. For individual M dwarfs we achieve uncertainties of 0.05 dex and 100 K on average.Comment: 13 page

    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

    Gaia FGK Benchmark Stars and their reference parameters

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    In this article we summarise on-going work on the so-called Gaia FGK Benchmark Stars. This work consists of the determination of their atmospheric parameters and of the construction of a high-resolution spectral library. The definition of such a set of reference stars has become crucial in the current era of large spectroscopic surveys. Only with homogeneous and well documented stellar parameters can one exploit these surveys consistently and understand the structure and history of the Milky Way and therefore other of galaxies in the Universe.Comment: to appear in ASI Conference Series, 2014, Vol. 10 for the Workshop of Spectral Libraries held in Lyon, Oct. 201

    Interface Control Document for Gaia observed spectral libraries

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    disponible à http://www.obs.u-bordeaux1.fr/m2a/soubiran/dpac_doc.html2009, GAIA-C8-SP-UAO-UH-00

    Spectroscopic Binaries Among λ Bootis-type Stars

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    The small group of λ Bootis stars comprises late B to early F-type stars, with moderate to extreme (up to a factor 100) surface under-abundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O, and S). The main mechanisms responsible for this phenomenon are atmospheric diffusion, meridional mixing, and accretion of material from their surroundings. Especially spectroscopic binary (SB) systems with λ Bootis-type components are very important to investigate the evolutionary status and accretion process in more details. Because also δ Scuti type pulsation was found for several members, it gives the opportunity to use the tools of astroseismology for further investigations. We present the results of our long term efforts of detailed abundance analysis, orbital parameter estimation and photometric time series analysis for five well investigated SB systems

    Observation and modelling of dusty, low gravity L, and M dwarfs

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    Observational facilities allow now the detection of optical and IR spectra of young M- and L-dwarfs. This enables empirical comparisons with old M- and L- dwarfs, and detailed studies in comparison with synthetic spectra. While classical stellar atmosphere physics seems perfectly appropriate for old M-dwarfs, more physical and chemical processes, cloud formation in particular, needs to be modelled in the substellar regime to allow a detailed spectral interpretation. Not much is known so far about the details of the inset of cloud formation at the spectral transition region between M and L dwarfs. Furthermore there is observational evidence for diversity in the dust properties of objects having the same spectral type. Do we understand these differences? The question is also how young M- and L-dwarfs need to be classified, which stellar parameter do they have and whether degenerations in the stellar parameter space due to the changing atmosphere physics are present, like in the L-T transition region. The Splinter was driven by these questions which we will use to encourage interactions between observation and theory. Given the recent advances, both in observations and spectral modelling, an intensive discussion between observers and theoreticians will create new synergies in our field.Comment: Cool Stars XV splinter session summary, to appear in proceedings of Cool Stars XV Conference, 8 page

    Gaia FGK Benchmark Stars: fundamental Teff and log g of the third version

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    Context. Large spectroscopic surveys devoted to the study of the Milky Way, including Gaia, use automated pipelines to massively determine the atmospheric parameters of millions of stars. The Gaia FGK Benchmark Stars are reference stars with Teff and log g derived through fundamental relations, independently of spectroscopy, to be used as anchors for the parameter scale. The first and second versions of the sample have been extensively used for that purpose, and more generally to help constrain stellar models. Aims. We provide the third version of the Gaia FGK Benchmark Stars, an extended set intended to improve the calibration of spectroscopic surveys, and their interconnection. Methods. We have compiled about 200 candidates which have precise measurements of angular diameters and parallaxes. We determined their bolometric fluxes by fitting their spectral energy distribution. Masses were determined using two sets of stellar evolution models. In a companion paper we describe the determination of metallicities and detailed abundances. Results. We provide a new set of 192 Gaia FGK Benchmark Stars with their fundamental Teff and logg, and with uncertainties lower than 2% for most stars. Compared to the previous versions, the homogeneity and accuracy of the fundamental parameters are significantly improved thanks to the high quality of the Gaia data reflecting on distances and bolometric fluxes.Comment: accepted in A&

    Very accurate cryogenic mechanisms for CRIRES+

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    After 5 years of operation on the VLT, a large upgrade of CRIRES (the ESO Cryogenic InfraRed Echelle Spectrograph) was decided mainly in order to increase the efficiency. Using a cross dispersion design allows better wavelength coverage per exposure. This means a complete re-design of the cryogenic pre-optic which were including a predispersion stage with a large prism as dispersive element. The new design requires a move of the entrance slit and associated decker toward the first intermediate focal plane right behind the window. Implement 2 functions with high positioning accuracy in a pre-defined and limited space was a real challenge. The design and the test results recorded in the ESO Cryogenic Test Facility are reported in this paper. The second critical function is the grating wheel which positions the 6 cross disperser gratings into the beam. The paper describes the design of the mechanism which includes a detente system in order to guaranty the 5 arc sec positioning reproducibility requested. The design includes also feedback system, based on switches, in order to ensure that the right grating is in position before starting a long exposure. The paper reports on the tests carried out at cryogenic temperature at the sub-system level. It also includes early performances recorded in the instrument along the first phases of the system test
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