J/A+A/689/A91 NGC 4349 127 RV and activity indices (Spaeth+, 2024)
Non-radial oscillations mimicking a brown dwarf orbiting the cluster giant
NGC 4349 No. 127.
Spaeth D., Reffert S., Hunt E.L., Kaminski A., Quirrenbach A.
<Astron. Astrophys., 689, A91 (2024)>
=2024A&A...689A..91S 2024A&A...689A..91S (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Exoplanets ; Radial velocities ; Optical ;
Spectroscopy
Keywords: techniques: radial velocities - planets and satellites: detection -
stars: evolution - stars: oscillations -
stars: individual: NGC 4349 No. 127
Abstract:
Several evolved stars have been found to exhibit long-period radial
velocity variations that cannot be explained by planetary or brown
dwarf companions. Non-radial oscillations caused by oscillatory
convective modes have been put forth as an alternative explanation,
but no modeling attempt has yet been undertaken.
We provide a model of a non-radial oscillation, aiming to explain the
observed variations of the cluster giant NGC 4349 No. 127. The star
was previously reported to host a brown dwarf companion, but whose
existence was later refuted in the literature.
We reanalyzed 58 archival HARPS spectra of the intermediate-mass giant
NGC 4349 No. 127. We reduced the spectra using the SERVAL and RACCOON
pipelines, acquiring additional activity indicators. We searched for
periodicity in the indicators and correlations between the indicators
and radial velocities. We further present a simulation code able to
produce synthetic HARPS spectra, incorporating the effect of
non-radial oscillations, and compare the simulated results to the
observed variations. We discuss the possibility that non-radial
oscillations cause the observed variations.
We find a positive correlation between chromatic index and radial
velocity, along with closed-loop Lissajous-like correlations between
radial velocity and each of the spectral line shape indicators (full
width at half maximum, and contrast of the cross-correlation function
and differential line width). Simulations of a low-amplitude,
retrograde, dipole (l=1, m=1), non-radial oscillation can reproduce
the observed behavior and explain the observables. Photometric
variations below the detection threshold of the available ASAS-3
photometry are predicted. The oscillation and stellar parameters are
largely in agreement with the prediction of oscillatory convective
modes.
The periodic variations of the radial velocities and activity
indicators, along with the respective phase shifts, measured for the
intermediate-mass cluster giant NGC 4349 No. 127, can be explained by
a non-radial oscillation.
Description:
Table 1 includes 46 RVs from the HARPS spectrograph and its associated
activity indices taken before the HARPS fiber change in 2015. The
data were processed using the SERVAL and RACCOON pipelines. All
measurements were retrieved from the ESO Science Archive Facility.
Table 2 includes 12 RVs from the HARPS spectrograph and its associated
activity indices taken after the HARPS fiber change in 2015. The data
were processed using the SERVAL pipeline. All measurements were
retrieved from the ESO Science Archive Facility.
Objects:
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RA (2000) DE Designation(s)
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12 24 35.47 -61 49 11.8 NGC 4349 127 = TIC 450417907
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
pre2015.dat 111 46 HARPS Doppler measurements and associated activity
indices of NGC 4349 No. 127, acquired prior to
the 2015 HARPS fiber change and analyzed using
the SERVAL and RACCOON pipelines
post2015.dat 27 12 HARPS Doppler measurements and associated activity
indices of NGC 4349 No. 127, acquired after the
2015 HARPS fiber change and analyzed using the
SERVAL pipeline
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Byte-by-byte Description of file: pre2015.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD Barycentric Julian Date
16- 21 F6.1 m/s RV Radial Velocity processed with SERVAL
23- 25 F3.1 m/s e_RV Uncertainty in radial velocity processed
with SERVAL
27- 34 F8.1 m/s RV-R Radial Velocity processed with RACCOON
36- 39 F4.1 m/s e_RV-R Uncertainty in radial velocity processed
with SERVAL
41- 45 F5.1 m/s CRX Chromatic index processed with SERVAL
(in m/s/Np units)
47- 50 F4.1 m/s e_CRX Uncertainty in chromatic index processed
with SERVAL (in m/s/Np units)
52- 56 F5.1 1000m2/s2 dLW Differential linewidth processed
with SERVAL
58- 60 F3.1 1000m2/s2 e_dLW Uncertainty in differential linewidth
processed with SERVAL
62- 67 F6.4 --- Halpha Halpha line index measurement processed
with SERVAL
69- 74 F6.4 --- e_Halpha Uncertainty in Halpha line index
measurement processed with SERVAL
76- 80 F5.3 km/s FWHM Full width at half maximum of
cross-correlation function processed
with RACCOON
82- 86 F5.3 km/s e_FWHM Uncertainty in full width at half maximum
of cross-correlation function processed
with RACCOON
88- 93 F6.3 % Contrast Contrast of cross-correlation function
processed with RACCOON
95- 99 F5.3 % e_Contrast Uncertainty in contrast of
cross-correlation function processed
with RACCOON
101-105 F5.3 km/s BIS Bisector inverse slop processed
with RACCOON
107-111 F5.3 km/s e_BIS Uncertainty in Bisector inverse slop
processed with RACCOON
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Byte-by-byte Description of file: post2015.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 F14.6 d BJD Barycentric Julian date
16- 21 F6.1 m/s RV Radial velocity processed with SERVAL
23- 27 F5.1 m/s e_RV Uncertainty in radial velocity processed
with SERVAL
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History:
From Dane Spaeth, dane.spaeth(at)lsw.uni-heidelberg.de
Acknowledgements:
Based on data obtained from the ESO Science Archive Facility with DOI:
https://doi.eso.org/10.18727/archive/33.
(End) Patricia Vannier [CDS] 08-Jan-2025