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 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

Ground-based observations of which objects?  stars that are candidates for Kepler asteroseismic targets for what reason?  to determine their atmospheric parameters: T eff, logg, and [Fe/H], and to measure their radial velocity, v r,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

Observing sites

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)

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

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

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

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

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

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

Catania Astrophysical Observatory Instruments

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

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

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

Spectrograph Dispersion  varies from 3.5 A/mm at H g  to 6.8 A/mm at H a (R=21,000) The spectral range covered in one exposure is about 2500 A in 19 orders

Spectrograph Performances  radial velocity measurements precision  v < 0.3 km/s rms  S/N at H  100 with T exp = 10 s for V=6 mag star  limiting magnitude V=11 with S/N =30 and T exp = 1 h Calibration lamps  halogen flat field lamp at about 2,600 o C  Thorium-Argon hollow cathode lamp

Methodology of observations

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

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

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

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

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

Stars:  Oph (K2III) radial velocity standard needed for measuring radial velocity of program stars observed each night

 Oph (K2III)

Targets of observations

Targets standard stars  radial velocity standards, e.g,.  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

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

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

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

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

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

Results

Radial velocity measurements The method: the cross-correlation; the template -  Oph The tool: iraf software

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

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

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

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

Determination of atmospheric parameters measured by comparison with the grid of spectra of reference stars ( see Frasca et al A&A 405, 149, Frasca et al A&A 454, 301 ) the method allows simultaneous and fast determination of logT eff, 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 logT eff – log g – [Fe/H] space

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 T eff, log g and [Fe/H] of the five templates that have spectra most similar to the spectrum of the program star

log T eff – log g diagram for Kepler primary asteroseismic targets

Evolutionary and asteroseismic models – HIP 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 = ±0.79 Gyr large separation of solar-like oscillations,  = ± 3.8  Hz