J/ApJ/801/79 10yr of GJ176 radial velocities & VR photometry (Robertson+, 2015)
Stellar activity and its implications for exoplanet detection on GJ 176.
Robertson P., Endl M., Henry G.W., Cochran W.D., MacQueen P.J.,
Williamson M.H.
<Astrophys. J., 801, 79 (2015)>
=2015ApJ...801...79R 2015ApJ...801...79R
ADC_Keywords: Photometry, VRI ; Radial velocities ; Stars, M-type
Keywords: stars: activity; stars: individual: GJ 176;
stars: late-type; techniques: photometric;
techniques: radial velocities; techniques: spectroscopic
Abstract:
We present an in-depth analysis of stellar activity and its effects on
radial velocity (RV) for the M2 dwarf GJ 176 based on spectra taken
over 10yr from the High Resolution Spectrograph on the Hobby-Eberly
Telescope. These data are supplemented with spectra from previous
observations with the HIRES and HARPS spectrographs, and V- and R-band
photometry taken over six years at the Dyer and Fairborn
observatories. Previous studies of GJ 176 revealed a super-Earth
exoplanet in an 8.8-day orbit. However, the velocities of this star
are also known to be contaminated by activity, particularly at the
39-day stellar rotation period. We have examined the magnetic activity
of GJ 176 using the sodium I D lines, which have been shown to be a
sensitive activity tracer in cool stars. In addition to rotational
modulation, we see evidence of a long-term trend in our Na I D index,
which may be part of a long-period activity cycle. The sodium index is
well correlated with our RVs, and we show that this activity trend
drives a corresponding slope in RV. Interestingly, the rotation signal
remains in phase in photometry, but not in the spectral activity
indicators. We interpret this phenomenon as the result of one or more
large spot complexes or active regions which dominate the photometric
variability, while the spectral indices are driven by the overall
magnetic activity across the stellar surface. In light of these
results, we discuss the potential for correcting activity signals in
the RVs of M dwarfs.
Description:
We have carried out a dedicated M dwarf RV survey using the High
Resolution Spectrograph (HRS) on the Hobby-Eberly Telescope (HET).
Full details on the survey and its results, including the observing
strategy and target properties can be found in Endl et al.
(2003AJ....126.3099E 2003AJ....126.3099E, 2006ApJ...649..436E 2006ApJ...649..436E) and Robertson et al. (2013,
J/ApJ/764/3). We have obtained 98 RVs for GJ 176 over 10yr, which we
list in Table 2.
GJ 176 has also been observed intensively by the HARPS and HIRES
spectrographs.
Prompted by the presence of significant stellar activity in its RVs,
we have monitored GJ 176 for photometric variability with the
Tennessee State University (TSU) automated Celestron C-14 telescope,
through Cousins R and Johnson V filters, between 2007 and 2013 (see
tables 3 and 4).
Objects:
-------------------------------------------------
RA (ICRS) DE Designation(s)
-------------------------------------------------
04 42 55.77 +18 57 29.4 GJ 176 = HD 285968
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 89 99 Radial velocities and spectral activity indices
for our HET/HRS spectra of GJ 176
table3.dat 26 480 Differential R-band photometry of GJ 176
table4.dat 26 604 Differential V-band photometry of GJ 176
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See also:
J/MNRAS/443/2561 : Trumpeting M dwarfs with CONCH-SHELL (Gaidos+, 2014)
J/AJ/147/20 : Spectroscopy of 447 nearby M dwarfs (Newton+, 2014)
J/MNRAS/431/2063 : UV/X-ray activity of M dwarfs within 10pc (Stelzer+, 2013)
J/ApJ/767/95 : Improved parameters of smallest KIC stars (Dressing+, 2013)
J/ApJ/764/3 : Hα indices in M low-mass stars (Robertson+, 2013)
J/AJ/145/102 : Spectroscopy of M dwarfs in the northern sky (Lepine+, 2013)
J/A+A/549/A109 : HARPS XXXI. The M-dwarf sample (Bonfils+, 2013)
J/A+A/546/A61 : Radial velocities for XHIP catalogue (de Bruijne+, 2012)
J/A+A/541/A9 : M dwarfs activity & radial velocity (Gomes da Silva+, 2012)
J/A+A/535/A55 : 4 stars with long-period planets (Dumusque+, 2011)
J/MNRAS/403/1949 : UBV(RcIc)JHK photometry of HIP nearby stars (Koen+, 2010)
J/A+A/505/859 : M dwarfs radial velocities (Zechmeister+, 2009)
J/A+A/493/645 : Gl 176 radial velocities (Forveille+, 2009)
J/A+A/469/309 : Late-type stars chromospheric activity (Cincunegui+, 2007)
J/ApJS/141/503 : Radial Velocities for 889 late-type stars (Nidever+, 2002)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 13 F13.8 d BJD Barycentric Julian Date; minus 2450000
15- 20 F6.2 m/s RVel [-26/21] Radial velocity (1)
22- 25 F4.2 m/s e_RVel [4/10] Uncertainty in RVel
27- 33 F7.5 --- ID1 [0.1/0.15] The ID index in 1Å window (2)
35- 41 F7.5 --- e_ID1 [0.002/0.004] Uncertainty in ID1
43- 49 F7.5 --- ID0.5 [0.08/0.13] The ID index in 0.5Å window (2)
51- 57 F7.5 --- e_ID0.5 [0.001/0.003] Uncertainty in ID0.5
59- 65 F7.5 --- IHa [0.06/0.08] The IHα index
67- 73 F7.5 --- e_IHa [0.0009/0.0016] Uncertainty in IHa
75- 81 F7.5 --- ICaI [0.02/0.03] The I_Ca I_ index for the CaI
line at λ=6572.795Å
83- 89 F7.5 --- e_ICaI [0.0006/0.0009] Uncertainty in ICaI
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Note (1): The secular acceleration has not been subtracted from the velocity.
Note (2): We define our sodium index, ID, according to the definition of
Diaz et al. (2007MNRAS.378.1007D 2007MNRAS.378.1007D). Specifically, we take the ratio
of the fluxes inside windows centered on each of the NaID lines
(λD1=5895.92Å, λD2=5889.95Å), divided by the
flux in the nearby pseudocontinuum. See section 3.2.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 9 F9.4 d BJD Barycentric Julian Date; minus 2450000
11- 18 F8.5 mag dRmag [-2.5/-2.4] Differential R band magnitude (G1)
20- 26 F7.5 mag e_dRmag [0.0002/0.004] Uncertainty in dRmag
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 9 F9.4 d BJD Barycentric Julian Date; minus 2450000
11- 18 F8.5 mag dVmag [-2.1/-1.9] Differential V band magnitude (G1)
20- 26 F7.5 mag e_dVmag [0.0001/0.009] Uncertainty in dVmag
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Global notes:
Note (G1): Magnitudes are reported relative to the mean of five constant stars
in the same CCD field (see Section 3.3).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 16-Jul-2015