TW Hydrae: evidence of stellar spots instead of a Hot Jupiter

By N. Huelamo, P. Figueira, X. Bonfils, Nuno C. Santos, F. Pepe, M. Gillon, R. Azevedo, Travis S. Barman, M. Fernández, E. D. Folco and 5 more. 2008

178 citations recorded by the source corpus.

Context. TW Hya is a classical T Tauri star that shows significant radial-velocity variations in the optical regime. These variations have been attributed to a 10 MJup planet orbiting the star at 0.04 AU. Aims. The aim of this letter is to confirm the presence of the giant planet around TW Hya by (i) testing whether the observed RV variations can be caused by stellar spots and (ii) analyzing new optical and infrared data to detect the signal of the planet companion. Methods. We fitted the RV variations of TW Hya using a cool spot model. In addition, we obtained new high-resolution optical & infrared spectra, together with optical photometry of TW Hya and compared them with previous data. Results. Our model shows that a cold spot covering 7% of the stellar surface and located at a latitude of 54 ◦ can reproduce the reported RV variations. The model also predicts a bisector semi-amplitude variation <10 m s −1 , which is less than the errors of the RV measurements discussed in Setiawan et al. (2008, Nature, 451, 38). The analysis of our new optical RV data, with typical errors of 10 m s −1 , shows a larger RV amplitude that varies depending on the correlation mask used. A slight correlation between the RV variation and the bisector is also observed although not at a very significant level. The infrared H-band RV curve is almost flat, showing a small variation (<35 m s −1 ) that is not consistent with the published optical orbit. All these results support the spot scenario rather than the presence of a hot Jupiter. Finally, the photometric data shows a 20% (peak to peak) variability, which is much larger than the 4% variation expected for the modeled cool spot. The fact that the optical data are correlated with the surface of the cross-correlation function points towards hot spots as being responsible for the photometric variability. Conclusions. We conclude that the best explanation for the RV signal observed in TW Hya is the presence of a cool stellar spot and not an orbiting hot Jupiter.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/a01c6f840fb11fd7972d958613f68f617be107ce

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In Astronomy and Astrophysics

1. Nuno C. Santos
2. J. Southworth
3. S. Udry
4. M. Mayor
5. D. Charbonneau
6. C. Lovis
7. F. Bouchy
8. F. Pepe

Citations in the corpus

• Star and Protoplanetary Disk Properties in Orion's Suburbs (2009, background): “…the brightness variations that are inherent to the spot model were not detected in 2008 by Rucinski et al. (2008) while the radial velocity variations first seen by Setiawan et al. (2008) remain present (Setiawan et al. in prep), seriously challenging the spot model of Huélamo et al. (2008).”
• State of the Field: Extreme Precision Radial Velocities (2016, unknown): “Huélamo et al. (2008) showed that the radial velocity variations using optical spectroscopy of a star in the TW Hydra association disappeared when observed with CRIRES using near infrared wavelengths.”
• Planetary detection limits taking into account stellar noise - I. Observational strategies to reduce stellar oscillation and granulation effects (2010, background): “As the star rotates, a spot, or a plage, moves across the stellardisk and produces an apparent Doppler shift (Saar & Donahue 1997; Queloz et al. 2001; Huélamo et al. 2008; Lagrange et al. 2010).”
• Disentangling between stellar activity and planetary signals (2010, background): “These inhomogeneities across the stellar surface can induce RV shifts due to changes in the spectral line shape that may add confusions with the Doppler reflex-motion due to a planetary companion (e.g. Queloz et al. 2001; Desidera et al. 2004; Huélamo et al. 2008).”
• Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program I. Comparison of activity indices (2011, unknown): “C-0488(E) duced by extra-solar planets (Queloz et al. 2001; Bonfils et al. 2007; Huélamo et al. 2008).”
• THE NIRSPEC ULTRACOOL DWARF RADIAL VELOCITY SURVEY (2010, methodology): “…(2008a), Prato et al. (2008), and Zapatero Osorio et al. (2009), and a Doppler precision in the range 5–20 m s−1 has been demonstrated on short timescales using the CRIRES instrument on the Very Large Telescope (VLT) by Huélamo et al. (2008), Seifahrt & Käufl (2008), and Figueira et al. (2010b).”
• SOAP 2.0: A TOOL TO ESTIMATE THE PHOTOMETRIC AND RADIAL VELOCITY VARIATIONS INDUCED BY STELLAR SPOTS AND PLAGES (2014, background): “…2003; Dravins 1982), and activity signals (Robertson et al. 2014; Jeffers et al. 2013; Meunier & Lagrange 2013; Lovis et al. 2011; Dumusque et al. 2011a; Boisse et al. 2011, 2009; Saar 2009; Huélamo et al. 2008; Desort et al. 2007; Queloz et al. 2001; Santos et al. 2000; Saar & Donahue 1997).”
• WASP-19b: THE SHORTEST PERIOD TRANSITING EXOPLANET YET DISCOVERED (2010, background): “Starspots can cause periodic low-amplitude RV variations (e.g., Huélamo et al. 2008; Desort et al. 2007) but not photometric transits as well; thus, a single star blended with a fainter stellar eclipsing binary (EB) is the preferred false positive scenario for transiting planets.”