Kinematical properties
and spatial distribution of red giants
from the Penn State - Toruń Planet Search
P. Zieliński1, A. Niedzielski1, M. Adamów1, G. Nowak1, A. Wolszczan2,3
1
Toruń Centre for Astronomy, Nicolaus Copernicus University, Gagarina 11, 87-100 Toruń, Poland
2
Department for Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802
3
Center for Exoplanets and Habitable Worlds, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802
Abstract
Searches for planets around stars of various masses and evolutionary stages are essential for understanding the planet formation mechanisms
and temporal evolution of planetary systems. Both these ingredients are crucial for a more general project which is search for life in our Galaxy.
The main goal of the Penn State - Toruń Centre for Astronomy Planet Search (PTPS) is the discovery and analysis for planetary systems
around stars more massive than the Sun. To this end we perform an extensive radial velocity search for planets around about 1000 stars (giants,
subgiants and dwarfs) with the Hobby-Eberly Telescope (HET). In parallel to the planet search we conduct a deep and detailed study of our
sample stars. Only well studied sample, containing both stars with planets and single ones, observed and studied in an uniform way, may be
exploited in search for relation between various properties of planets and their stars. An example of such a problem that can be addressed with
a well defined sample in the (lack of) well known planet-metallicity relation for giants (Pasquini et al. 2007, Zieliński et al. 2010). Its nature is
still unclear and to explain it the scenarios concerning galactic star migration are involved (Haywood 2009). Before we will be able to discuss
this issue in detail we present here characteristic of our sample of 332 red clump giants. We summarize here results of a complete spectroscopic
analysis yielding atmospheric parameters together with radial velocities, masses and ages of the stars (Zieliński et al. 2011). We also present and
discuss a detailed kinematical description of our clump giants and their distribution in the Solar neighborhood.
Fundamental stellar parameters
Radial velocities
The Penn State - Toruń Planet Search (PTPS) is devoted to detection
and characterization of planetary systems around stars more evolutionary evolved than the Sun (Niedzielski & Wolszczan 2008). Recently,
the study of a sample of 332 PTPS red giants was completed based
on high-resolution spectra (R = 60 000) which were collected by the
Hobby-Eberly Telescope (HET, Ramsey et al. 1998). In Fig. 1 the
results of our spectroscopic analysis are shown (Zieliński et al. 2011).
Thanks to high-resolution spectra collected for all sample stars by using HET, we were able to measure precise stellar radial velocities (RVs)
with applying a cross-correlation analysis. To construct the crosscorrelation functions (CCFs) we correlated normalized stellar spectra
with numerical mask consisting of 1 and 0 value points. The non-zero
points correspond to the positions of 300 non-blended, isolated stellar
absorption lines at zero velocity. The final RVs were measured by fitting the Gaussian function to the CCF for the whole spectrum. The
mean standard error obtained in this way is σRVCCF = 0.041 kms−1.
120
(a)
(b)
100
150
60
N
40
Galactic space velocities
100
50
20
Sirius branch
0
4800
5600
Teff [K]
6400
1.0
2.0
3.0
log g
4.0
5.0
100
(c)
80
60
N
N
100
200
0
(d)
150
Based on adopted Solar motion relative to the local standard of rest
(LSR) of (10.0, 5.2, 7.2) kms−1 (Nordström et al. 2004) we derived
2 +V2 +
absolute space velocity relative to LSR as |v|LSR = (ULSR
LSR
2 )1/2 for our sample of giants. The results are dispalyed in Fig. 4
WLSR
where the correlations between space velocity relative to LSR, age
and metallicity are considered. Though reasonable trends that older
and metal-deficient stars are moving with higher speed are not unambiguous, this very preliminary result is promising. Therefore, further
investigation of stellar spatial distribution is needed in order to better
constrain basic stellar parameters and evolutionary status of PTPS
giants.
midddle branch
V [km/s]
0
4000
50
Summary
|v|LSR [km/s]
N
80
tainty on (U , V , W ) velocities have to be done before we determine
the membership of the selected stars to the appropriate groups and/or
allocate to them occupied area in the Galaxy.
40
100
50
0
−50
50
150
8.5
9.0
20
Pleiades branch
0
0.50
0.5
1.5
2.5
M/Msun
3.5
ζHerculis branch
−100
Figure 1: The distribution of fundamental parameters of 332 PTPS
stars obtained from our spectroscopic analysis. The following histograms present stellar Teff (a), log g (b), [Fe/H] (c) and M/M (d).
−100
0
50
100
100
9.0
9.5
10.0
[Fe/H]
log Age
M/Msun
3
2
1
8.5
9.0
9.5
10.0
log Age
Figure 2: The correlations between [Fe/H] (top panel) and M/M
(bottom panel) vs. log Age obtained in spectroscopic study of PTPS
subsample of 332 stars. The uncertainties in [Fe/H] and M/M are
presented.
50
−1.0
−0.5
0.0
0.5
Figure 4: The correlations between log Age (top panel) and [Fe/H]
(bottom panel) vs. |v|LSR obtained from stellar space motions of PTPS
subsample of 332 stars. Only the uncertainties in [Fe/H] are presented.
50
0
Acknowledgments
−50
−100
−50
0
50
100
0.0
−1.0
100
[Fe/H]
U [km/s]
−0.5
150
0
−100
0.5
−50
200
U [km/s]
W [km/s]
The atmospheric parameters (Teff , log g and [Fe/H]) were determined
from the study of iron lines with the assumption of excitation and ionization equilibria. Stellar luminosities, masses and ages were obtained
from the evolutionary models fitting by comparing the position of sample stars on the H-R diagram with theoretical evolutionary trakcs (Girardi et al. 2000, Salasnich et al. 2000). The ages of our stars correspond
to final luminosities and masses values but they are uncertain. In Fig. 2
we present stellar mass and metallicity as a function of age. For many
stars from considered sample only bottom age limit is presented confirming in this way the complex nature of red giant clump region and
the difficulties in age determination of single field objects. However,
the study of such correlations as, e.g., the age-metallicity relation is
essential in order to recognize the nature of these candidate exoplanet
host stars.
8.5
10.0
log Age
|v|LSR [km/s]
0
−1.00 −0.50 0.00
[Fe/H]
9.5
Figure 3: Space velocities (U , V , W ) of studied PTPS stars defined
as right-handed Galactic system. U is directed towards Galactic centre, V in Galactic rotation and W towards the north Galactic pole.
Background stars were taken from Nordström et al. (2004). The stellar
kinematic groups are presented following by Skuljan et al. 1999.
Space velocity components (U , V , W ) have been computed for studied
here PTPS stars following by Johnson & Soderblom (1987) formulas.
We used for that stellar parallaxes and proper motions (Hipparcos and
Tycho catalogues) and RVs previously determined by us. In the case of
the lack of parallaxes the distances were calculated spectrophotometricaly. Since our RVs are of excellent accuracy, the dominant source
of uncertainty in space motions is the distance (with its mean 40 %
precision). Fig. 3 demonstrates heliocentric (U , V , W ) of 332 red giants with the comparison of background stars (∼ 16 000) taken from
Nordström et al. (2004) survey of the Solar neighbourhood.
The stars presented here are distributed according to the well-known
location of classic moving groups. Nevertheless, detailed analysis of
these structures as well as study of the influence of distance uncer-
We acknowledge the financial support from the Polish Ministry of Science and Higher Education through grants N N203 510938 and N N203
386237. AW acknowledges support from NASA grant NNX09AB36G.
The Hobby-Eberly Telescope (HET) is a joint project of the University
of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-AugustUniversität Göttingen. The HET is named in honor of its principal
benefactors, William P. Hobby and Robert E. Eberly. The Center for
Exoplanets and Habitable Worlds is supported by the Pennsylvania
State University, the Eberly College of Science, and the Pennsylvania
Space Grant Consortium.
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