ground-based observations of kepler asteroseismic targets
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
Ground-based observationsof Kepler asteroseismic targets
Joanna Molenda-Żakowicz
Instytut Astronomiczny Uniwersytetu WrocławskiegoPOLAND
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: Teff
, 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 = 65 000
the spectral range: 370-740 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
to 6.8 A/mm at H (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 Texp
= 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 2,600oC
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 94734 – SB1
discovered in the ground-based data to be a single-lined spectroscopic binary (see Molenda-Żakowicz et al. 2007 AcA 57, 301)
SB2 stars
show double peak in the cross-correlation function (here: an SB2 star HIP 94335)
SB2 stars – HIP 94335
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. 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
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
log Teff – log g diagram for Kepler primary asteroseismic targets
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, = 106.5 ± 3.8 Hz