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Dynamical Masses of the Primary Be Star and Secondary sdB Star in the Single-lined Binary κ Dra (B6 IIIe)
Gies, Douglas R.; Wang, Luqian; Klement, Robert +16 more
Because many classical Be stars may owe their nature to mass and angular-momentum transfer in a close binary, the present masses, temperatures, and radii of their components are of high interest for comparison to stellar evolution models. Object κ Dra is a 61.5 day single-lined binary with a B6 IIIe primary. With the CHARA Array instruments MIRC/M…
The Role of Disk Tearing and Precession in the Observed Variability of Pleione
Carciofi, A. C.; Tycner, C.; Jones, C. E. +2 more
We acquired Hα spectroscopic observations from 2005 to 2019 showing Pleione has transitioned from a Be phase to a Be-shell phase during this period. Using the radiative transfer code HDUST, we created a grid of ~100,000 disk models for Pleione. We successfully reproduced the observed transition with a disk model that varies in inclination while ma…
X-Rays in Cepheids: Identifying Low-mass Companions of Intermediate-mass Stars
Drake, Jeremy J.; Evans, Nancy Remage; Breuval, Louise +12 more
X-ray observations have been made of a sample of 20 classical Cepheids, including two new observations (Polaris and l Car) reported here. The occurrence of X-ray flux around the pulsation cycle is discussed. Three Cepheids are detected (δ Cep, β Dor, and Polaris). X-rays have also been detected from the low-mass F, G, and K companions of four Ceph…
Spectroscopic Line Modeling of the Fastest Rotating O-type Stars
Gies, Douglas R.; Shepard, Katherine; Kaper, Lex +1 more
We present a spectroscopic analysis of the most rapidly rotating stars currently known, VFTS 102 ( ${v}_{e}\sin i=649\pm 52$ km s-1; O9: Vnnne+) and VFTS 285 ( ${v}_{e}\sin i=610\pm 41$ km s-1; O7.5: Vnnn), both members of the 30 Dor complex in the Large Magellanic Cloud. This study is based on high-resolution ultraviolet spe…
The Ultraviolet C II Lines as a Diagnostic of κ-distributed Electrons in Planetary Nebulae
Zhang, Yong; Yao, Zheng-Wei
Non-Maxwellian κ electron energy distributions (EEDs) have been proposed in recent years to resolve the so-called "electron temperature and abundance discrepancy problem" in the study of planetary nebulae (PNs). Thus the need to develop diagnostic tools to determine from observations the EED of PNs is raised. Arising from high-energy levels, the u…
The Wind Temperature and Mass-loss Rate of Arcturus (K1.5 III)
Ayres, Thomas R.; Harper, Graham M.; O'Gorman, Eamon
In this paper we aim to constrain the wind temperature, outflow and turbulent velocities, ionization state, and mass-loss rate of the single red giant Arcturus (α Boo K1.5 III) using high spectral resolution Hubble Space Telescope Space Telescope Imaging Spectrograph profiles of Si III 1206.5 Å , O I 1304 Å and 1306 Å, C II 1334 Å and 1335 Å, and …
Modeling the Photometric Variability of Alpha2 CVn with a Dynamical Magnetosphere
Pfeffer, Cameron M.; McSwain, M. Virginia
Alpha2 Canum Venaticorum (α 2 CVn) is a strongly magnetic star with peculiar chemical signatures and periodic variability that have been long attributed to the diffusion of magnetic elements through the photosphere, leading to chemical spots across the stellar surface. However, recent studies of other magnetic hot stars are c…