J/A+A/541/A9 M dwarfs activity and radial velocity (Gomes da Silva+, 2012)
Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program.
II. Activity and radial velocity.
Gomes da Silva, J., Santos, N. C., Bonfils, X., Delfosse, X., Forveille, T.,
Udry, S., Dumusque, X., Lovis, C.
<Astron. Astrophys. 541, A9 (2012)>
=2012A&A...541A...9G 2012A&A...541A...9G
ADC_Keywords: Stars, M-type ; Radial velocities
Keywords: planets and satellites: detection - stars: activity -
stars: late-type - techniques: radial velocities -
techniques: spectroscopic
Abstract:
Due to their low mass and luminosity, M dwarfs are ideal targets if
one hopes to find low-mass planets similar to Earth by using the
radial velocity (RV) method. However, stellar magnetic cycles could
add noise or even mimic the RV signal of a long-period companion.
Following our previous work that studied the correlation between
activity cycles and long-term RV variations for K dwarfs we now expand
that research to the lower-end of the main sequence. Our objective is
to detect any correlations between long-term activity variations and
the observed RV of a sample of M dwarfs. We used a sample of 27
M-dwarfs with a median observational timespan of 5.9 years. The
cross-correlation function (CCF) with its parameters RV, bisector
inverse slope (BIS), full-width-at-half- maximum (FWHM) and contrast
have been computed from the HARPS spectrum. The activity index have
been derived using the Na I D doublet. These parameters were compared
with the activity level of the stars to search for correlations. We
detected RV variations up to ∼5m/s that we can attribute to activity
cycle effects. However, only 36% of the stars with long-term activity
variability appear to have their RV affected by magnetic cycles, on
the typical timescale of ∼6 years. Therefore, we suggest a careful
analysis of activity data when searching for extrasolar planets using
long-timespan RV data.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 50 27 List of studied stars
table1.dat 119 168 Averages of RV, FWHM, contrast, BIS and NaI
activity index
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Simbad name
10- 11 I2 h RAh Simbad Hour of Right Ascension (J2000.0)
13- 14 I2 min RAm Simbad Minute of Right Ascension (J2000.0)
16- 19 F4.1 s RAs Simbad Second of Right Ascension (J2000.0)
21 A1 --- DE- Simbad Sign of the Declination (J2000.0)
22- 23 I2 deg DEd Simbad Degree of Declination (J2000.0)
25- 26 I2 arcmin DEm Simbad Arcminute of Declination (J2000.0)
28- 29 I2 arcsec DEs Simbad Arcsecond of Declination (J2000.0)
32- 37 F6.3 mag Bmag Simbad B band magnitude
39- 44 F6.3 mag Vmag Simbad V band magnitude
46- 50 A5 --- SpType Simbad MK spectral type
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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- 8 A8 --- Name Target identification
10- 21 F12.6 d Average Barycentric Modified Julian Date
23- 24 I2 --- N Number of measurements in the bin
26- 36 F11.6 km/s Average radial velocity
38- 45 F8.6 km/s e_ rms uncertainty on
47- 54 F8.6 km/s Average Full-Width-at-Half-Maximum (FWHM) (1)
56- 63 F8.6 km/s e_ rms uncertainty on
65- 73 F9.6 km/s Average contrast (1)
75- 82 F8.6 km/s e_ rms uncertainty on
84- 92 F9.6 km/s Average Bissector Inverse Slope (BIS) (1)
94-101 F8.6 km/s e_ rms uncertainty on
103-110 F8.6 --- <NaI> Average NaI activity index
112-119 F8.6 --- e_<NaI> rms uncertainty on <NaI>
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Note (1): Parameters of the HARPS cross-correlation function.
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Acknowledgements:
Joao Gomes da SIlva, joao.silva(at)astro.up.pt
References:
Gomes da Silva et al., Paper I, 2011A&A...534A..30G 2011A&A...534A..30G
(End) Patricia Vannier [CDS] 19-Mar-2012