J/AJ/152/204 HARPS-N radial velocities of HD 179070 (Lopez-Morales+, 2016)
Kepler-21b: a rocky planet around a V = 8.25 magnitude star.
Lopez-morales M., Haywood R.D., Coughlin J.L., Zeng L., Buchhave L.A.,
Giles H.A.C., Affer L., Bonomo A.S., Charbonneau D., Collier Cameron A.,
Consentino R., Dressing C.D., Dumusque X., Figueira P., Fiorenzano A.F.M.,
Harutyunyan A., Johnson J.A., Latham D.W., Lopez E.D., Lovis C.,
Malavolta L., Mayor M., Micela G., Molinari E., Mortier A., Motalebi F.,
Nascimbeni V., Pepe F., Phillips D.F., Piotto G., Pollacco D., Queloz D.,
Rice K., Sasselov D., Segransan D., Sozzetti A., Udry S., Vanderburg A.,
Watson C.
<Astron. J., 152, 204-204 (2016)>
=2016AJ....152..204L 2016AJ....152..204L (SIMBAD/NED BibCode)
ADC_Keywords: Planets ; Stars, double and multiple ; Radial velocities
Keywords: planets and satellites: formation -
planets and satellites: individual: Kepler-21b -
stars: individual: HD 179070 - techniques: photometric -
techniques: radial velocities - techniques: spectroscopic
Abstract:
HD 179070, aka Kepler-21, is a V=8.25 F6IV star and the brightest
exoplanet host discovered by Kepler. An early detailed analysis by
Howell et al. of the first 13 months (Q0-Q5) of Kepler light curves
revealed transits of a planetary companion, Kepler-21b, with a radius
of about 1.60±0.04R⊕ and an orbital period of about
2.7857days. However, they could not determine the mass of the planet
from the initial radial velocity (RV) observations with Keck-HIRES,
and were only able to impose a 2σ upper limit of 10M⊕.
Here, we present results from the analysis of 82 new RV observations
of this system obtained with HARPS-N, together with the existing 14
HIRES data points. We detect the Doppler signal of Kepler-21b with a
RV semiamplitude K=2.00±0.65ms-1, which corresponds to a planetary
mass of 5.1±1.7M⊕. We also measure an improved radius for
the planet of 1.639 +0.019/-0.015R⊕, in agreement with the
radius reported by Howell et al. We conclude that Kepler-21b, with a
density of 6.4±2.1gcm-3, belongs to the population of small,
≲6M⊕ planets with iron and magnesium silicate interiors,
which have lost the majority of their envelope volatiles via stellar
winds or gravitational escape. The RV analysis presented in this paper
serves as an example of the type of analysis that will be necessary to
confirm the masses of TESS small planet candidates.
Description:
We collected a total of 82 (RV) observations of Kepler-21 with the
HARPS-N spectrograph installed on the 3.6m Telescopio Nazionale
Galileo (TNG) at the Observatorio del Roque de los Muchachos in La
Palma, Spain. HARPS-N is an updated version of HARPS at the ESO 3.6m.
We observed Kepler-21 between 2014 April and 2015 June as part of the
HARPS-N Collaboration's Guaranteed Time Observations (GTO) program,
following a standard observing approach of one or two observations per
night, separated by 2-3hr, on nights assigned to the GTO program.
Kepler-21 is a bright target with V=8.25 (Kp=8.2), so we obtained
spectra with signal-to-noise ratios (S/N) in the range S/N=45-308
(average S/N=167), at 550nm in 10-30 minute exposures, depending on
the seeing and sky transparency. A summary of the observations is
provided in Table4.
Objects:
--------------------------------------------------------------
RA (ICRS) DE Designation(s) (Period)
--------------------------------------------------------------
19 09 26.84 +38 42 50.5 Kepler-21 = HD 179070 (P=2.78574)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 53 82 HARPS-N radial velocity data
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
J/AJ/152/160 : HARPS-N radial velocities of KOI-70 (Buchhave+, 2016)
J/MNRAS/452/2127 : Parameters of Kepler stars (Silva Aguirre+, 2015)
J/ApJ/800/135 : HARPS-N radial velocities of KOI-69 (Dressing+, 2015)
J/A+A/584/A72 : A transiting rocky planet at 6.5pc from Sun (Motalebi+ 2015)
J/A+A/575/L15 : TrES-4b RV and Ic curves (Sozzetti+, 2015)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 12 F12.6 d BJD Barycentric Julian Date (UTC; BJD-2400000)
14- 22 F9.2 m/s RV [-19182.1/-19160.1] Radial velocity
24- 27 F4.2 m/s e_RV [0.88/6] The 1σ uncertainty in RV
29- 33 F5.2 m/s BS [36/58.1] Bisector span
35- 41 F7.4 [-] logR'HK [-5.1/-4.9] Measured log R'HK activity index
43- 48 F6.4 [-] e_logR'HK [0.0019/0.033] 1σ uncertainty in logR'HK
50- 53 I4 s Exp [600/1800] Exposure time (texp)
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 31-Jan-2017