J/A+A/593/A117 GJ 3998 RVs, S and Halpha indexes (Affer+, 2016)
HADES RV program with HARPS-N at the TNG.
GJ 3998: An early M-dwarf hosting a system of super-Earths.
Affer L., Micela G., Damasso M., Perger M., Ribas I., Suarez Mascareno A.,
Gonzalez Hernandez J.I., Rebolo R., Poretti E., Maldonado J., Leto G.,
Pagano I., Scandariato G., Zanmar Sanchez R., Sozzetti A., Bonomo A.S.,
Malavolta L., Morales J.C., Rosich A., Bignamini A., Gratton R.,
Velasco S., Cenadelli D., Claudi R., Cosentino R., Desidera S.,
Giacobbe P., Herrero E., Lafarga M., Lanza A.F., Molinari E., Piotto G.
<Astron. Astrophys. 593, A117 (2016)>
=2016A&A...593A.117A 2016A&A...593A.117A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Stars, M-type ; Planets ;
Spectroscopy ; Radial velocities
Keywords: techniques: radial velocities - techniques: photometric -
methods: data analysis - stars: individual: GJ3998 -
instrumentation: spectrographs - planets and satellites: detection
Abstract:
M dwarfs are considered ideal targets for Doppler radial velocity
searches. Nonetheless, the statistics of frequency of low-mass planets
hosted by low mass stars remains poorly constrained. Our M-dwarf
radial velocity monitoring with HARPS-N can provide a major
contribution to the widening of the current statistics through the
in-depth analysis of accurate radial velocity observations in a narrow
range of spectral sub-types (79 stars, between dM0 to dM3).
Spectral accuracy will enable us to reach the precision needed to
detect small planets with a few earth masses. Our survey will bring a
contribute to the surveys devoted to the search for planets around
M-dwarfs, mainly focused on the M-dwarf population of the northern
hemisphere, for which we will provide an estimate of the planet
occurence.
We present here a long duration radial velocity monitoring of the M1
dwarf star GJ 3998 with HARPS-N to identify periodic signals in the
data. Almost simultaneous photometric observations were carried out
within the APACHE and EXORAP programs to characterize the stellar
activity and to distinguish from the periodic signals those due to
activity and to the presence of planetary companions.
The radial velocities have a dispersion in excess of their internal
errors due to at least four superimposed signals, with periods of
30.7, 13.7, 42.5 and 2.65-days. The analysis of spectral indices based
on Ca II H & K and Hα lines demonstrates that the periods of
30.7 and 42.5-days are due to chromospheric inhomogeneities modulated
by stellar rotation and differential rotation. The shorter periods of
13.74±0.02d and 2.6498±0.0008d are well explained with the
presence of two planets, with minimum masses of 6.26±0.79MEarth
and 2.47±0.27MEarth and distances of 0.089AU and 0.029AU from the
host, respectively.
Description:
In this table we report the observing log for the GJ3998 spectra and
the radial velocities, S, and Hα indexes.
The star GJ3998 has been monitored from BJD=2456439.6 (26 May 2013)
to BJD=2457307.8 (12 October 2015).
We obtained a total of 136 data points spanning 869-days. The spectra
were obtained at high resolution (R=115000) with the optical echelle
spectrograph HARPS-N with exposure times of 15 minutes and an average
signal-to-noise ratio (S/N) of 45 at 5500Å. Of the 136 epochs, 76
were obtained within the GAPS time and 60 within the Spanish time.
Observations were gathered without the simultaneous Th-Ar calibration,
which is commonly used to correct for instrumental drifts during the
night. The M-type stars of the HADES program were observed by the
Italian team in conjunction with other GAPS targets, which used the
Th-Ar simultaneous calibration, therefore we estimated the drift data
between the two fibers (star and reference calibration) for each night
from these observations and evaluated the interpolated drift for
GJ3998 (0.7m/s).
Data reduction and spectral extraction were performed using the Data
Reduction Software (DRS, Lovis & Pepe, 2007A&A...468.1115L 2007A&A...468.1115L, Cat.
J/A+A/468/1115). RVs were measured by means of a weighted
cross-correlation function (CCF) with the M2 binary mask provided with
the DRS. The RVs were also measured by matching the spectra with a
high S/N template obtained by coadding the spectra of the target, as
implemented in the TERRA pipeline (Anglada-Escude & Butler,
2012ApJS..200...15A 2012ApJS..200...15A, Cat. J/ApJS/200/15), which provides a better RV
accuracy when applied to M dwarfs.
We list the observation dates (barycentric Julian date or BJD), the
signal-to-noise ratios (S/Ns), the radial velocities (RVs) from the
DRS and TERRA pipelines (indicated with a T) and the Hα and S
indexes, calculated both by the TERRA pipeline and by an independent
method described in the text. The RV errors reported are the formal
ones and do not include the jitter term. The S index and Hα
errors are calculated as described in the text and do not take into
account the photon noise. The S index and Hα errors derived from
the TERRA pipeline are due to photon noise through error propagation.
Objects:
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RA (2000) DE Designation(s)
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17 16 00.64 +11 03 27.6 GJ 3998 = BD+11 3149
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 102 136 Observing log, RVs, S and Halpha indexes of GJ3998
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 10 F10.5 d BJD Barycentric Julian date (BJD-2456000)
12- 15 F4.1 --- S/N Signal to noise ratio
17- 23 F7.3 m/s RVT Radial velocities with TERRA (1)
25- 29 F5.3 m/s e_RVT Error of RVs with TERRA (1)
31- 40 F10.3 m/s RVD Radial velocities with DRS (2)
42- 46 F5.3 m/s e_RVD Error of RVs with DRS (2)
48- 53 F6.4 --- SindT S index with TERRA (1)
55- 60 F6.4 --- e_SindT Error of S index with TERRA (1)
62- 67 F6.4 --- HalphaT Halpha index with TERRA (1)
69- 74 F6.4 --- e_HalphaT Error of Halpha index with TERRA (1)
76- 81 F6.4 --- Sind S index with our method (3)
83- 88 F6.4 --- e_Sind Error of S index with our method
90- 95 F6.4 --- Halpha Halpha index with our method (3)
97-102 F6.4 --- e_Halpha Error of Halpha index with our method
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Note (1): TERRA pipeline (Anglada-Escude & Butler, 2012ApJS..200...15A 2012ApJS..200...15A).
Average radial velocity has been subtracted from all the radial velocities.
Note (2): Data Reduction Software (DRS v3.7, Lovis & Pepe, 2007A&A...468.1115L 2007A&A...468.1115L).
Absolute radial velocities.
Note (3): see paper for details.
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Acknowledgements:
Laura Affer, affer(at)astropa.inaf.it
(End) Patricia Vannier [CDS] 26-Aug-2016