J/AJ/155/126 Radial velocities & photometry of the K dwarf HD26965 (Diaz+, 2018)
The test case of HD 26965: difficulties disentangling weak Doppler signals from
stellar activity.
Diaz M.R., Jenkins J.S., Tuomi M., Butler R.P., Soto M.G., Teske J.K.,
Feng F., Shectman S.A., Arriagada P., Crane J.D., Thompson I.B., Vogt S.S.
<Astron. J., 155, 126 (2018)>
=2018AJ....155..126D 2018AJ....155..126D (SIMBAD/NED BibCode)
ADC_Keywords: Stars, dwarfs ; Stars, K-type ; Spectroscopy ; Radial velocities ;
Photometry, UBV ; Exoplanets
Keywords: methods: statistical - stars: activity -
stars: individual (HD 26965) - techniques: radial velocities -
techniques: spectroscopic
Abstract:
We report the discovery of a radial velocity signal that can be
interpreted as a planetary-mass candidate orbiting the K dwarf HD 26965,
with an orbital period of 42.364±0.015 days, or alternatively,
as the presence of residual, uncorrected rotational activity in the
data. Observations include data from HIRES, PFS, CHIRON, and HARPS,
where 1111 measurements were made over 16 years. Our best solution for
HD 26965 b is consistent with a super-Earth that has a minimum mass
of 6.92±0.79 M⊕ orbiting at a distance of 0.215±0.008 au
from its host star. We have analyzed the correlation between spectral
activity indicators and the radial velocities from each instrument,
showing moderate correlations that we include in our model. From this
analysis, we recover a ∼38-day signal, which matches some literature
values of the stellar rotation period. However, from independent
Mt. Wilson HK data for this star, we find evidence for a significant
42-day signal after subtraction of longer period magnetic cycles,
casting doubt on the planetary hypothesis for this period. Although
our statistical model strongly suggests that the 42-day signal is
Doppler in origin, we conclude that the residual effects of stellar
rotation are difficult to fully model and remove from this data set,
highlighting the difficulties to disentangle small planetary signals
and photospheric noise, particularly when the orbital periods are
close to the rotation period of the star. This study serves as an
excellent test case for future works that aim to detect small planets
orbiting "Sun-like" stars using radial velocity measurements.
Description:
Here, we present data from a 16-year precision radial velocity monitoring
campaign, using multiple high-resolution optical spectrographs, of the
nearby (∼5 pc) K0.5 star HD 26965. High-precision Doppler measurements
of HD 26965 were carried out using four different spectrographs: The
High Resolution Echelle Spectrograph (HIRES) installed on the 10 m
Keck Telescope in Hawaii, the Carnegie Planet Finder Spectrograph (PFS)
mounted on the 6.5 m Magellan II (Clay) telescope at Las Campanas
Observatory, CHIRON mounted on the 1.5 m telescope from the Small to
Moderate Aperture Research Telescopes (SMARTS) consortium in Cerro Tololo
Interamerican Observatory, and the High Accuracy Radial velocity Planet
Searcher (HARPS) installed on the 3.6 m ESO telescope at La Silla
Observatory.
To complement the analysis, we gathered photometric data available
from the ASAS Catalog (Pojmanski 1997AcA....47..467P 1997AcA....47..467P) to investigate
if any periodic signal could be seen in light curves, particularly the
rotational period of the star
Objects:
----------------------------------------------------------------
RA (ICRS) DE Designation(s) (Period)
----------------------------------------------------------------
04 15 16.32 -07 39 10.3 HD 26965 = * omi02 Eri (P=42.364)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table7.dat 39 229 Keck/HIRES radial velocities of HD 26965
table8.dat 39 68 Magellan/PFS radial velocities of HD 26965
table9.dat 39 258 SMARTS/CHIRON radial velocities of HD 26965
table10.dat 82 483 HARPS OLD radial velocities of HD 26965
table11.dat 82 82 HARPS NEW radial velocities of HD 26965
table12.dat 111 568 ASAS photometry of HD 26965
table13.dat 25 1029 Mount Wilson HK project measurements of HD 26965
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See also:
III/159 : Ca II H and K Measurements Made at MWO (Duncan+ 1991)
J/A+A/552/A27 : Stellar activity and kinematics of FGK stars (Murgas+, 2013)
J/A+A/596/A116 : Radial velocities of K-M dwarfs (Sperauskas+, 2016)
J/AJ/153/208 : LCES HIRES/Keck radial velocity Exoplanet Survey
(Butler+, 2017)
Byte-by-byte Description of file: table7.dat table8.dat table9.dat
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Bytes Format Units Label Explanations
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1- 13 F13.5 d BJD Barycentric Julian Date of observation
15- 23 F9.5 m/s RV [-17.44736/10.51759] Radial velocity
25- 31 F7.5 m/s e_RV [0.7834/3.16266] Uncertainty in RV
33- 39 F7.5 --- S [0.03494/0.23519]? Mt. Wilson S-index
(Duncan et al. 1991, Cat. III/159; not in
Table 9)
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Byte-by-byte Description of file: table10.dat table11.dat
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Bytes Format Units Label Explanations
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1- 24 F24.16 d BJD Barycentric Julian Date of observation
26- 36 F11.4 m/s RV [-42210.1297/-42161.0701] Radial velocity
38- 43 F6.4 m/s e_RV [0.1083/2.1074] Uncertainty in RV
45- 51 F7.4 m/s BIS [0.102/23.7698] BIS activity indicator
53- 61 F9.4 m/s FWHM [5558.6231/5973.4585] Line full width at half
maximum
63- 68 F6.4 --- S [0.1459/0.5817] Mt. Wilson S-index (Duncan et al.
1991, Cat. III/159)
70- 75 F6.4 --- Halpha [0.1116/0.2982] Hα activity indicator
77- 82 F6.4 --- HeI [0.4313/0.5097] He I activity indicator
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Byte-by-byte Description of file: table12.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Field ASAS field name
14- 26 A13 --- ASAS ASAS designation (HHMMSS+DDMM.m)
28- 37 F10.5 d HJD [1868.68244/5168.67433] Heliocentric Julian Date
of observation (HJD-2450000)
39- 44 F6.3 mag Vmag-4 [4.423/5.826]?=29.999 ASAS V band magnitude
in Aperture 4
46- 51 F6.3 mag Vmag-0 [3.671/6.603]?=29.999 ASAS V band magnitude
in Aperture 0
53- 58 F6.3 mag Vmag-1 [3.861/6.129]?=29.999 ASAS V band magnitude
in Aperture 1
60- 65 F6.3 mag Vmag-2 [4.13/5.903]?=29.999 ASAS V band magnitude
in Aperture 2
67- 72 F6.3 mag Vmag-3 [4.31/5.837]?=29.999 ASAS V band magnitude
in Aperture 3
74- 78 F5.3 mag e_Vmag-4 [0.024/0.15] Uncertainty in Vmag-4 (1)
80- 84 F5.3 mag e_Vmag-0 [0.028/0.121] Uncertainty in Vmag-0 (1)
86- 90 F5.3 mag e_Vmag-1 [0.028/0.105] Uncertainty in Vmag-1 (1)
92- 96 F5.3 mag e_Vmag-2 [0.022/0.106] Uncertainty in Vmag-2 (1)
98-102 F5.3 mag e_Vmag-3 [0.024/0.124] Uncertainty in Vmag-3 (1)
104 A1 --- Grade Photometry grade (2)
106-111 I6 --- Frame [97/334933] Frame number
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Note (1): Frame errors describe average photometric quality of the frame for
each aperture.
Note (2): Photometry grade as follows:
A = Best data, no 29.999 (not measured) indication;
B = Mean data, no 29.999 (not measured) indication;
C = A and B with 29.999 (not measured) indication;
D = Worst data, probably useless.
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Byte-by-byte Description of file: table13.dat
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Bytes Format Units Label Explanations
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1- 6 F6.4 --- S [0.1609/0.2469] Mt. Wilson S-index (Duncan et al.
1991, Cat. III/159)
8- 17 F10.5 d JD [-523.2/5771.64648] Julian Date of observation
(JD-2444000)
19- 25 F7.1 --- W [1428.2/34054.6] Weight
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 07-Nov-2018