Long-term spectroscopic and precise radial velocity monitoring of Arcturus
Notice bibliographique
Résumé
This dissertation presents an analysis of data obtained from long-term spectroscopic monitoring of the bright, nearby K giant star Arcturus (a Bootis, K1.5 III, HR 5340, HD 124897), conducted using the University of Western Ontario’s Elginfield Observatory. Over 1300 high-resolution spectra ( ) 5 l/Dl ≈ 10 were recorded in the 6250 A spectral region during the 1984– 2006 observing seasons, with 311 simultaneous, precise radial velocity measurements (j ∼ 25 m s ) obtained during the 2002–2006 observing seasons. Temperature variations were measured using the well-established line-depth ratio V i l6251.83 to Fe i l6252.56. Velocity spans were obtained from the line bisector of the Fe i l6252.56 line. Precise radial velocities were measured using the telluric absorption technique outlined by Gray & Brown (2006, PASP, 118, 399). Spectroscopic observations and precise radial velocity measurements reveal variability in Arcturus from hours to years. From velocity span observations, three distinct periods of variability are observed: (1) a semiregular 5 1 yr period interpreted as evidence for a long-term stellar magnetic cycle, (2) a 2.0 0.2 yr modulation identified as the rotation period (see also Gray & Brown 2006, PASP, 118, 1112), and (3) a semicoherent 200 5 day period interpreted as one-fourth of the rotation period, indicating the presence of four magnetically active longitudes on the surface of Arcturus. One of these four active longitudes is postulated to dominate the other three, inducing the observed 2 yr rotational modulation in the velocity span measurements. Line-depth ratio measurements indicate no evidence for variations in temperature in excess of 10 K over the observed magnetic cycle, rotation period, and short-term variability of Arcturus. Precise radial velocity measurements exhibit a long-term period of 222 3 days, with an amplitude of 150 20 m s . This long-term period and the corresponding amplitude are consistent with the radial velocity observations of Hatzes & Cochrane (1993, ApJ, 413, 339). The 222 day period is coherent over the 14 yr time span between the Hatzes & Cochrane (1993, ApJ, 413, 339) data and the observations of this work, and does not correlate with observed line bisector or line-depth ratio variations, suggesting that this observed period is not associated with stellar variability. Hatzes & Cochrane (1993, ApJ, 413, 339) suggested that the observed long-term radial velocity period was due either to rotational modulation or a low-mass companion, but were unable to differentiate between the two explanations, due to a lack of ancillary spectroscopic data. A detection of a low-mass companion is postulated by this work. Assuming a mass of 1 M, for Arcturus, a best-fit Keplerian orbit to the 222 day period is found to have approximately zero eccentricity, a projected semimajor axis ( ) of 0.72 AU, and a companion a sin i mass ( ) of ≥4.4 MJ. M sin i 2 Precise radial velocity observations also demonstrate a scatter (j) of ∼145 m s 1 superimposed on the observed 222 day period, resulting from short-term variability on the timescale of individual nights to days. This short-term variability has been interpreted as being the result of solar-type p-mode oscillations by previous studies, such as Hatzes & Cochrane (1994, ApJ, 422, 366), Merline (1995, Ph.D. thesis, Univ. Arizona), and Retter et al. (2003, ApJ, 591, L151). Observed scatter during individual nights ranges from ∼50 to 180 m s , while the scatter over consecutive nights ranges from ∼70 to 160 m s . These observations are consistent with previous studies of the short-term radial velocity variability of Arcturus. Ultimately, this scatter of ∼145 m s 1 limits the accuracy of studies of the long-term radial velocity variability of Arcturus. Evidence for eruptive events is also suggested from the observed radial velocities.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».