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astro-ph.EP · Earth and Planetary Astrophysicsastro-ph.IM · Instrumentation and Methods for Astrophysics

Circular models fit 74 HARPS observations of GJ 3187 better at 72.44 days than at one fifth of a year

We test whether annual terms explain two reported velocity signals in GJ 3187, also called HD 17970. We use 74 public HARPS spectra from 2003 to 2017, with SERVAL and DRS velocities from HARPS-RVBank v2. The two reductions use the same spectra. Each main model has separate offsets before and after the fibre change, circular terms, and fixed added noise of 1 m/s. With an annual term in both models, the 72.44294-day term gives a lower chi-square than the exact 73.05127-day fifth annual harmonic by 40.86 in SERVAL and 46.35 in DRS. The short amplitudes are 2.05 and 2.00 m/s. When one observing season is omitted at a time, the prediction error is 1.08 versus 1.68 m/s in SERVAL and 1.32 versus 1.86 m/s in DRS. Tested activity controls and fixed noise models retain the short signal. The reported 374-day signal is less distinct from annual variation. Eccentric models with a free long period or an exact annual period give similar BIC scores. Noiseless injections show that an annual control can remove much of a real signal at these sampling times. The period selection used the full record, and the tests do not cover all stellar or instrument effects. These results support further observations of the short signal. They do not confirm a planet. The package includes source rows, provenance, code, figures, and fit results.

GJ 3187 · HD 17970 · HARPS · radial velocity · annual harmonic · planet candidate · model comparison · reproducible research

Admitted 1 citing publication

References

8
  1. usesA blind Keplerian search of 743 HARPS-RVBank v2 stars with 30 or more nights recovers 248 of 465 known planets and finds 57 signals (FAP < 0.1 %) with no known match that pass activity tests sci:sha256:17e2629023ac1bcbb507eb643afc93a73a34d8a9d1ba2357cc22bd7bc4f108cb

    This search supplied the target, the two periods, and the reference time series. We test specific annual alternatives and prediction stability for this target.

  2. usesdoi:10.1051/0004-6361/202348263

    HARPS-RVBank v2 supplies the 74 velocities, uncertainties, activity indices, and source rows. We use the CDS table corrected on 20 April 2026.

  3. doi:10.1088/0004-637X/808/2/171

    This study identifies a source of annual velocity errors in HARPS. It motivates the annual controls.

  4. doi:10.1051/0004-6361/201833272

    This study tests improved HARPS wavelength calibration and annual errors.

  5. doi:10.1093/mnras/stae137

    This study includes HD 17970 in its activity sample and gives its mean activity level. It does not give a confirmed rotation period for this star.

  6. doi:10.1051/0004-6361/202244595

    This study shows that the H alpha band width changes activity correlations. Its HD 17970 results limit the interpretation of a single activity index.

  7. usesdoi:10.18727/archive/33

    The ESO HARPS radial velocity catalogue query returns the same 74 exposures. It supplies no independent spectra for this test.

  8. doi:10.1093/mnras/staf1405

    Appendices B and C use HD 17970 as a quiet HARPS comparison star. They show instrument changes in line profiles and list 74 line width measurements.

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