J/A+A/699/A260 Radial velocity measurements of 42 Draconis (Hatzes+, 2025)
No planet around the K giant star 42 Draconi.
Hatzes A.P., Perdelwitz V., Karjalainen K., Koehler J., Hartmann M.
<Astron. Astrophys. 699, A260 (2025)>
=2025A&A...699A.260H 2025A&A...699A.260H (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Radial velocities ; Optical
Keywords: stars: oscillations - planetary systems - stars: individual: 42 Dra -
stars: variables: general
Abstract:
Published radial velocity measurements of the K giant star 42 Dra
taken over a three year time span reveal variations consistent with
a 3.9MJup mass companion in a 479-d orbit.
This exoplanet can be confirmed if these variations are long-lived and
coherent. Continued monitoring may also reveal additional companions.
We have acquired additional radial velocity measurements of 42 Dra so
that the data now span fifteen years. Standard periodogram analyses
were used to investigate the stability of the planet radial velocity
signal. We also investigated variations in the spectral line shapes
using the bisector velocity span as well as infrared photometry from
the COBE mission.
The recent radial velocity measurements do not follow the published
planet orbit. An orbital solution using the 2004-2011 data yields a
period and eccentricity consistent with the published values, but the
radial velocity amplitude has decreased by a factor of four from the
earlier measurements. Including some additional radial velocity
measurements taken between 2014 and 2018 reveal a second period at
530-d. The beating of this period with the one at 479-d may account
for the observed amplitude variations. The planet hypothesis is
conclusively ruled out by COBE/DIRBE 1.25um photometry that shows
variations with the planet orbital period as well as a 170-d period.
The radial velocity of 42 Dra shows significant amplitude variations
which along with the COBE/DIRBE photometry firmly established that
there is no giant planet around this star. The presence of
multi-periodic variations suggests that these we are seeing stellar
oscillations in this star, most likely oscillatory convection modes.
These oscillations may account for some of the long period radial
velocity variations attributed to planets around K giant stars which
may skew the statistics of planet occurrence around intermediate mass
stars. Long- term monitoring with excellent sampling is required to
exclude amplitude variations in the long-periods found in radial
velocity of K giant stars.
Description:
We present the results of long term monitoring of the radial velocity
variations of the the K giant star 42 Draconis that span 2004-2011.
These refute the presence of the giant planet reported in the
literature.
All data were taken with the Tautenburg Coude Echelle Spectrograph of
the 2-m Alfred Jensch Telescope. These span 2008 to 2011 and 2014 to
2018. Radial velocity measurements were made using an iodine gas
absorption cell to provide the wavelength calibration. Short cadence
observations spanning five days.
Objects:
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RA (2000) DE Designation(s)
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8 25 59.14 +65 33 48.5 42 Dra =HR 6945
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 31 104 Radial velocities 2008 to 2011
table3.dat 31 17 Radial velocities 2014 to 2018
table6.dat 31 130 Short-term radial velocities 2014 to 2018
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See also:
J/A+A/499/935 : RV curves of 42 Dra and HD 139357 (Dollinger+, 2009)
Byte-by-byte Description of file: table2.dat table3.dat table6.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 d JD Julian date
14- 21 F8.2 m/s RV Radial velocity
27- 31 F5.2 m/s e_RV rms uncertainty on RV
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Acknowledgements:
Artie P. Hatzes, artie(at)tls-tautenburg.de
(End) Artie Hatzes [TLS, Germany], Patricia Vannier [CDS] 27-Jun-2025