Exoplanets or Dynamic Atmospheres? The Radial Velocity and Line Shape Variations of 51 Pegasi and tau Bootis

The stars 51 Pegasi and tau Bootis show radial velocity variations that have been interpreted as resulting from companions with roughly Jovian mass and orbital periods of a few days. Gray and Gray & Hatzes reported that the radial velocity signal of 51 Peg is synchronous with variations in the shape of the line lambda 6253 Fe I; thus, they argue that the velocity signal arises not from a companion of planetary mass but from dynamic processes in the atmosphere of the star, possibly nonradial pulsations. Here we seek confirming evidence for line shape or strength variations in both 51 Peg and tau Boo, using R = 50,000 observations taken with the Advanced Fiber Optic Echelle. Because of our relatively low spectral resolution, we compare our observations with Gray's line bisector data by fitting observed line profiles to an expansion in terms of orthogonal (Hermite) functions. To obtain an accurate comparison, we model the emergent line profiles from rotating and pulsating stars, taking the instrumental point-spread function into account. We describe this modeling process in detail. We find no evidence for line profile or strength variations at the radial velocity period in either 51 Peg or in tau Boo. For 51 Peg, our upper limit for line shape variations with 4.23 day periodicity is small enough to exclude with 10 sigma confidence the bisector curvature signal reported by Gray & Hatzes; the bisector span and relative line depth signals reported by Gray are also not seen, but in this case with marginal (2 sigma ) confidence. We cannot, however, exclude pulsations as the source of 51 Peg's radial velocity variation because our models imply that line shape variations associated with pulsations should be much smaller than those computed by Gray & Hatzes; these smaller signals are below the detection limits both for Gray & Hatzes's data and for our own. tau Boo's large radial velocity amplitude and v sin i make it easier to test for pulsations in this star. Again we find no evidence for periodic line shape changes, at a level that rules out pulsations as the source of the radial velocity variability. We conclude that the planet hypothesis remains the most likely explanation for the existing data.

51 Pegasi - a planet-bearing Maunder minimum candidate

We observed 51 Peg, the first detected planet-bearing star, in a 55 ks XMM-Newton pointing and in 5 ks pointings each with Chandra HRC-I and ACIS-S. The star has a very low count rate in the XMM observation, but is clearly visible in the Chandra images due to the detectors' different sensitivity at low X-ray energies. This allows a temperature estimate for 51 Peg's corona of T⪉ 1 MK; the detected ACIS-S photons can be plausibly explained by emission lines of a very cool plasma near 200 eV. The constantly low X-ray surface flux and the flat-activity profile seen in optical Ca II data suggest that 51 Peg is a Maunder minimum star; an activity enhancement due to a Hot Jupiter, as proposed by recent studies, seems to be absent. The star's X-ray fluxes in different instruments are consistent with the exception of the HRC Imager, which might have a larger effective area below 200 eV than given in the calibration.

Compte rendu: Johann Wolfgang Unger (2013), The Discursive Construction of the Scots Language : Education, Politics and Everyday Life, Amsterdam, John Benjamins, coll. « Discourse Approaches to Politics, Society and Culture, 51 », 178 p. [ISBN : 978-9-027-20642-8]

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Unesp Ciência, 2014, ano 5, número 51

Revista elaborada pela Assessoria de Comunicação e Imprensa da Reitoria da UNESP

M. Tullius Cicero, Academica priora (1-13), De natura Deorum (13-46v), De fato (46v-50v), Epistolae ad familiares I-VIII, 8, 6 (51-91v). - Dares Phrygius, De excidio Troiae historia (92-97v).

Ce ms. forme un recueil de deux groupes de textes différents (Cicéron, ff. 1-91v et Darès, ff. 92-97v), mais contemporains et homogènes. Chacun possède son propre système de signatures.

Archives parlementaires de 1787 à 1860 ; 34-51. Assemblée nationale législative. Série 1 / Tome 47 / impr. par ordre du Sénat et de la Chambre des députés ; sous la dir. de M. J. Mavidal,... et de M. E. Laurent,... ; avec la collab. de MM. E. Tonnier et C. Pionnier

Collection : Les archives de la Révolution française ; 3.1

Archives parlementaires de 1787 à 1860 ; 34-51. Assemblée nationale législative. Série 1 / Tome 50 et annexes / impr. par ordre du Sénat et de la Chambre des députés ; sous la dir. de M. J. Mavidal,... et de M. E. Laurent,... ; avec la collab. de MM. E. Tonnier et C. Pionnier

Collection : Les archives de la Révolution française ; 3.1

Archives parlementaires de 1787 à 1860 ; 34-51. Assemblée nationale législative. Série 1 / Tome 44 / impr. par ordre du Sénat et de la Chambre des députés ; sous la dir. de M. J. Mavidal,... et de M. E. Laurent,... ; avec la collab. de MM. E. Tonnier et C. Pionnier

Collection : Les archives de la Révolution française ; 3.1

Archives parlementaires de 1787 à 1860 ; 34-51. Assemblée nationale législative. Série 1 / Tome 34 / impr. par ordre du Sénat et de la Chambre des députés ; sous la dir. de M. J. Mavidal,... et de M. E. Laurent,... ; avec la collab. de MM. E. Tonnier et C. Pionnier

Collection : Les archives de la Révolution française ; 3.1

Archives parlementaires de 1787 à 1860 ; 34-51. Assemblée nationale législative. Série 1 / Tome 36 / impr. par ordre du Sénat et de la Chambre des députés ; sous la dir. de M. J. Mavidal,... et de M. E. Laurent,... ; avec la collab. de MM. E. Tonnier et C. Pionnier

Collection : Les archives de la Révolution française ; 3.1

Archives parlementaires de 1787 à 1860 ; 34-51. Assemblée nationale législative. Série 1 / Tome 39 / impr. par ordre du Sénat et de la Chambre des députés ; sous la dir. de M. J. Mavidal,... et de M. E. Laurent,... ; avec la collab. de MM. E. Tonnier et C. Pionnier

Collection : Les archives de la Révolution française ; 3.1