J/A+A/511/A54 Magnetic cycles and radial-velocity for 8 stars (Santos+, 2010)
Do stellar magnetic cycles influence the measurement of precise radial
velocities?
Santos N.C., Gomes da Silva J., Lovis C., Melo C.
<Astron. Astrophys. 511, A54 (2010)>
=2010A&A...511A..54S 2010A&A...511A..54S
ADC_Keywords: Stars, G-type ; Radial velocities
Keywords: planetary systems - stars: fundamental parameters -
techniques: spectroscopic - techniques: radial velocities -
stars: activity - starspots
Abstract:
The ever increasing level of precision achieved by present and future
radial velocity instruments is opening the way to the discovery of
very low mass, long period planets (e.g. solar-system analogs). These
systems will be detectable as low amplitude signals in radial-velocity
(RV). However, an important obstacle to their detection may be the
existence of stellar magnetic cycles with similar timescales. Here we
present the results of a long term program to measure simultaneously
radial-velocities and stellar activity indicators (CaII, Hα, HeI)
for a sample of stars with known activity cycles. Our results suggest
that all these stellar activity indexes can be used to trace the
stellar magnetic cycle in solar-type stars. Further to this, we find
clear indications that different parameters of the HARPS
cross-correlation function (BIS, FWHM, and Contrast) are also
sensitive to activity level variations. Finally, we show that though
in a few cases slight correlations or anti-correlations between
radial-velocity and the activity level of the star exist, their origin
is still not clear. We can however conclude that for our targets
(early-K dwarfs) we do not find evidence for radial-velocity
variations induced by variations of the stellar magnetic cycle with
amplitudes significantly above 1m/s.
Description:
Tables contain the data used to produce figures 2, 3, and 8.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 59 8 List of target stars
table5.dat 37 241 CaII S activity level as a function of time
table6.dat 39 275 Hα activity level as a function of time
table7.dat 39 275 HeI D3 activity level as a function of time
table8.dat 125 35 Yearly averages of CaII-S, RV, BIS, FWHM,
and Contrast
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- --- [HD]
3- 8 I6 --- HD Star HD number
9 A1 --- m_HD Multiplicity index on HD
11- 14 F4.2 mag Vmag V magnitude
16- 20 F5.3 mag B-V B-V colour index
22- 28 A7 --- SpType MK spectral type
30- 31 I2 d Prot Rotational period (1)
33- 42 A10 "YYYY/MM/DD" ObsF First observation date
44- 53 A10 "YYYY/MM/DD" ObsL Last observation date
55- 56 I2 --- N Number of nights each star was observed
58- 59 I2 --- <S/N> Average signal-to-noise ratio of individual
spectra in HARPS order 6
(near λ=4000Å)
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Note (1): From Baliunas et al., 1996ApJ...457L..99B 1996ApJ...457L..99B.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- --- [HD]
3- 8 I6 --- HD Star HD number
10- 23 F14.6 d BJD Barycentric Julian date
25- 30 F6.4 --- SMW CaII activity level in MW scale (SMW scale,
see Baliunas et al. 1995ApJ...438..269B 1995ApJ...438..269B)
32- 37 F6.4 --- e_SMW Statistical error in SMW
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- --- [HD]
3- 8 I6 --- HD Star HD number
10- 23 F14.6 d BJD Barycentric Julian date
25- 31 F7.5 --- Halpha Hα activity level
33- 39 F7.5 --- e_Halpha Statistical error in Hα
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- --- [HD]
3- 8 I6 --- HD Star HD number
10- 23 F14.6 d BJD Barycentric Julian date
25- 31 F7.5 --- HeI HeI activity level
33- 39 F7.5 --- e_HeI Statistical error in HeI
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- --- [HD]
3- 8 I6 --- HD Star HD number
10- 13 I4 yr Year Year of the measurements
15- 28 F14.6 d BJD1 ?=- Average Barycentric Julian Date for
SMW values
30- 43 F14.6 d BJD2 Average Barycentric Julian Date for RV, FWHM,
BIS, and Contrast values
45- 51 F7.5 --- ?=- Average activity level in MW scale
53- 59 F7.5 --- e_ ?=- rms uncertainty on
61- 68 F8.4 km/s Average radial velocity
70- 75 F6.4 km/s e_ rms uncertainty on
77- 84 F8.5 km/s Average Bisector Inverse Slope (BIS) value (1)
86- 92 F7.5 km/s e_ rms uncertainty on
94-101 F8.5 % <Cont> Average Cross-Correlation Function's Contrast
value (1)
103-109 F7.5 % e_<Cont> rms uncertainty on <Contrast>
111-117 F7.5 km/s Average FWHM value (1)
119-125 F7.5 km/s e_ rms uncertainty on
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Note (1): Parameters of the HARPS cross-correlation function.
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Acknowledgements:
Nuno Santos, nuno(at)astro.up.pt
(End) Patricia Vannier [CDS] 28-Dec-2009