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Ground-based observations of Kepler asteroseismic targets

Ground-based observations of Kepler asteroseismic targets. Joanna Molenda-Żakowicz Instytut Astronomiczny Uniwersytetu Wrocławskiego POLAND. Kepler asteroseismic targets. what are these objects? pulsating, preferably solar-type stars that will be observed by the Kepler space telescope

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Ground-based observations of Kepler asteroseismic targets

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  1. Ground-based observationsof Kepler asteroseismic targets Joanna Molenda-Żakowicz Instytut Astronomiczny Uniwersytetu Wrocławskiego POLAND

  2. Kepler asteroseismic targets • what are these objects? • pulsating, preferably solar-type stars that will be observed by the Kepler space telescope • for what reason? • to study stellar interiors via asteroseismic methods • what this study will result in? • precise radius and mass of the stars can yield precise parameters of their planetary systems providing that the dedicated asteroseismic models of the stars are computed

  3. Ground-based observations • of which objects? • stars that are candidates for Kepler asteroseismic targets • for what reason? • to determine their atmospheric parameters: Teff, logg, and [Fe/H], and to measure their radial velocity, vr ,and projected rotational velocity, v sin i • what this study will result in? • it will allow to compute dedicated asteroseismic and evolutionary models of Kepler asteroseismic targets

  4. Observing sites

  5. Harvard-Smithsonian Center for Astrophysics, USA • Oak Ridge Observatory, Harvard Massachusetts: 1.5-m Wyeth reflector • Fred Lawrence Whipple Observatory, Mount Hopkins, Arizona: 1.5-m Tillinghast reflector • Multiple Mirror Telescope (before it was converted to the monolithic 6.5-m mirror)

  6. Nordic Optical Telescope • Location: Canary Islands, Spain • Altitude: 2,382 m.a.s.l. • Targets: • the faintest candidtes for Kepler asteroseismic targets • stars from open clusters • Photo: Michael J.D. Linden-Vørnle and Bob Tubbs

  7. Nordic Optical Telescope • 2.5-m telescope • FIES instrument • a cross-dispersed high-resolution echelle spectrograph • maximum spectral resolution: R = 65 000 • the spectral range: 370-740 nm • Photo: Michael J.D. Linden-Vørnle and Bob Tubbs

  8. Wrocław University Observatory • Location: Astrophysical Observatory of the University of Wrocław, Białków, Poland • Targets: open clusters • In the figures: the dome and the 60 cm Cassegrain telescope in Białków

  9. Czech Academy of Sciences Observatory • Location: Ondrejov (Czech Republic) • Altitude: 500 m.a.s.l. • 2-m telescope used for high-dispersion coude spectroscopy • Targets: selected binaries from the list of candidates for Kepler asteroseismic targets • Photo: Josef Havelka and Aleš Kolář

  10. Slovak Academy of Sciences Observatory • Location: Tatranska Lomnica (Slovak Republic) • In the figures: the dome and the 60-cm Cassegrain telescope in Tatranska Lomnica

  11. Catania Astrophysical Observatory • Location: Fracastoro Mountain Station, Mt. Etna. Italy • elevation 1,735 m a.s.l • > 200 clear nights per year • occasional breaks in observations due to the activity of Etna

  12. Catania Astrophysical Observatory Instruments

  13. Telescope • Optical configuration: Cassegrain • Main mirror: 91-cm, paraboloid • Secondary mirror: 24-cm • Mount type: German (see the next figure)

  14. Photometer • Single channel photometer • Filters: • Johnson system: U B V • Strömgren system: u b v y Ha (narrow and wide) • Comet narrow band IHW system • In the figure: the photometer and additional equipment in the Catania astrophysical laboratory.

  15. Spectrograph • Fiber-optics Reosc Echelle Spectrograph of Catania Observatory, FRESCO • Gratings • echellette (cross-disperser), reflection grating of 160x106 mm with 300 l/mm • blazed at 4.3 deg • maximum efficiency 80% at the blaze wavelength 5000 A

  16. Spectrograph • Dispersion • varies from 3.5 A/mm at Hg • to 6.8 A/mm at Ha (R=21,000) • The spectral range covered in one exposure is about 2500 A in 19 orders

  17. Spectrograph • Performances • radial velocity measurements precision Dv < 0.3 km/s rms • S/N at Ha 100 with Texp = 10 s for V=6 mag star • limiting magnitude V=11 with S/N =30 and Texp = 1 h • Calibration lamps • halogen flat field lamp at about 2,600oC • Thorium-Argon hollow cathode lamp

  18. Methodology of observations

  19. Calibration images - Bias • measured at the beginning and the end of each night (typically six measurements in total) • the mean is subtracted from flat fields, calibration lamps and stellar spectra

  20. Calibration images - Flat Field • measured at the beginning and the end of each night (typically six measurements in total) • needed for correction for the shape of the blaze function

  21. Calibration images - Flat Field • each spectrum (calibration lamps and stellar spectra) is divided, order by order, by the fit to the mean flat field • in the figure - the second order of the fit to the mean flat field

  22. Calibration images - Thorium-Argon Lamp • measured 2-3 times per night • needed to placethe stellar spectra on the Angstrom scale

  23. Calibration images - Thorium-Argon Lamp • in the figure: emission lines in the spectrum of Thorium-Argon lamp • the emission lines have to be identified in each order

  24. Stars:b Oph (K2III) • radial velocity standard • needed for measuring radial velocity of program stars • observed each night

  25. b Oph (K2III)

  26. Targets of observations

  27. Targets • standard stars • radial velocity standards, e.g,. b Ophiuchi • stars with well-known spectral types needed for MK classification • fast rotating stars, e.g., Altair needed for the removal of telluric lines • program stars • all the candidates for Kepler asteroseismic targets • at least two spectra per star

  28. Primary asteroseismic targets • 15 stars which fall onto active pixels of Kepler CCDs • V = 9-11 mag • have precise Hipparcos parallax so that their luminosity can be computed from it

  29. Secondary asteroseismic targets • 44 stars which fall onto active pixels of Kepler CCDs • V = 9-11 mag • the Hipparcos parallax are not precise so that the star's luminosity can not be computed from it

  30. Brightest asteroseismic targets • 34 stars which fall onto active pixels of Kepler CCDs • V = 8-9 mag • have precise Hipparcos parallax – star's distance and luminosity can be computed

  31. NGC 6811 • the candidates for Kepler asteroseismic targets are plotted with green symbols • stars are labeled with WEBDA numbers or with running numbers • red rectangles show the fields observed in Tatranska Lomnica

  32. NGC 6866 • the candidates for Kepler asteroseismic targets are plotted with green symbols • stars are labeled with WEBDA numbers or with running numbers • red rectangles show the fields observed in Tatranska Lomnica

  33. Results

  34. Radial velocity measurements • The method: the cross-correlation; the template - b Oph • The tool: iraf software

  35. HIP 94734 – SB1 • discovered in the ground-based data to be a single-lined spectroscopic binary (see Molenda-Żakowicz et al. 2007 AcA 57, 301)

  36. SB2 stars • show double peak in the cross-correlation function (here: an SB2 star HIP 94335)

  37. SB2 stars – HIP 94335 • radial velocity of the primary (red) and secondary (blue) component of the SB2 Algol-type system HIP 94335

  38. Measurements of v sin i • measured with the use of a grid of Kurucz model spectra • and with the Full Width Half Maximum method • in the figure: determination of of v sin i of both components of HIP 94335

  39. Determination of atmospheric parameters • measured by comparison with the grid of spectra of reference stars (see Frasca et al. 2003 A&A 405, 149, Frasca et al. 2006 A&A 454, 301) • the method allows simultaneous and fast determination of logTeff, log g and [Fe/H] even for stars which spectra have low signal-to-noise ratio or limited resolution • requires a dense grid of template spectra of stars with precisely determined atmospheric parameters • in the figure: the reference stars in the logTeff – log g – [Fe/H] space

  40. How this method works • the spectrum of the program star is compared with all template spectra • the best-fitting five template spectra are selected • adopted are weighted means of Teff, log g and [Fe/H] of the five templates that have spectra most similar to the spectrum of the program star

  41. log Teff – log g diagram for Kepler primary asteroseismic targets

  42. Evolutionary and asteroseismic models – HIP 94734 • model computed with the use of Monte Carlo Markov Chains. On the right: marginal distributions of model parameters: age and mass. (Bazot et al. in preparation) • mass = 1.114±0.023 M • age = 7.070 ±0.79 Gyr • large separation of solar-like oscillations,Dn= 106.5 ± 3.8 Hz

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