<i>KEPLER</i>
                    RAPIDLY ROTATING GIANT STARS

Costa, Alessandro; Martins, B. L. Canto; Bravo, J. P.; Paz-Chinchón, F.; Chagas, Maria Liduína das; Leão, I. C.; Oliveira, G. Pereira de; Silva, R. Rodrigues da; Roque, S.; Oliveira, L. L. A. de; Silva, D. Freire da; Medeiros, J. R. De

doi:10.1088/2041-8205/807/2/l21

Cited by 47 publications

(17 citation statements)

References 36 publications

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“…For example, Costa et al (2015) analyzing the Kepler light curves of 1916 giant stars classified as such on the basis of asteroseismic studies (Pinsonneault et al 2014;Tayar et al 2015) conclude that 1.2% of their sample matches rapidly rotating (vsini = 10-30 km/sec) G and K giant stars.…”

Section: Discussionmentioning

confidence: 99%

RAPIDLY ROTATING, X-RAY BRIGHT STARS IN THEKEPLERFIELD

Howell

Mason

Boyd

et al. 2016

ApJ

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Section: Discussionmentioning

confidence: 99%

RAPIDLY ROTATING, X-RAY BRIGHT STARS IN THEKEPLERFIELD

Howell

Mason

Boyd

et al. 2016

ApJ

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“…Nevertheless, measuring the rotation rate of RG stars is of prime importance to understand the evolution of stellar rotation after the MS. For this reason, much effort has lately been devoted to measure their rotation rates from their radiative cores (e.g., Beck et al 2012;Mosser et al 2012a;Deheuvels et al 2015;Gehan et al 2018) to their surfaces (e.g., Carlberg et al 2011;Costa et al 2015;Deheuvels et al 2015;Tayar et al 2015;Ceillier et al 2017).…”

Section: Introductionmentioning

confidence: 99%

“…From high-resolution (HR) spectroscopic measurements of projected rotational velocities v sin i by Carlberg et al (2011), about 2% of RGs are rapid rotators, using a threshold of v sin i = 10 km s −1 as is commonly adopted in the literature (e.g., Drake et al 2002;Massarotti et al 2008;Costa et al 2015;Tayar et al 2015). Although the details of stellar dynamo theory are not yet fully understood, the empirical correlation between magnetic activity and rotation (e.g., Noyes et al 1984) lends support to the expectation that the fraction of stars with detected rotational modulation should be similar to those with rapid rotation (see also Ceillier et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Active red giants: Close binaries versus single rapid rotators

Gaulme

Jackiewicz

Spada

et al. 2020

A&A

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Oscillating red-giant stars have provided a wealth of asteroseismic information regarding their interiors and evolutionary states, which enables detailed studies of the Milky Way. The objective of this work is to determine what fraction of red-giant stars shows photometric rotational modulation, and understand its origin. One of the underlying questions is the role of close binarity in this population, which relies on the fact that red giants in short-period binary systems (less than 150 days or so) have been observed to display strong rotational modulation. We selected a sample of about 4500 relatively bright red giants observed by Kepler, and show that about 370 of them (∼8%) display rotational modulation. Almost all have oscillation amplitudes below the median of the sample, while 30 of them are not oscillating at all. Of the 85 of these red giants with rotational modulation chosen for follow-up radial-velocity observation and analysis, 34 show clear evidence of spectroscopic binarity. Surprisingly, 26 of the 30 nonoscillators are in this group of binaries. On the contrary, about 85% of the active red giants with detectable oscillations are not part of close binaries. With the help of the stellar masses and evolutionary states computed from the oscillation properties, we shed light on the origin of their activity. It appears that low-mass red-giant branch stars tend to be magnetically inactive, while intermediate-mass ones tend to be highly active. The opposite trends are true for helium-core burning (red clump) stars, whereby the lower-mass clump stars are comparatively more active and the higher-mass ones are less active. In other words, we find that low-mass red-giant branch stars gain angular momentum as they evolve to clump stars, while higher-mass ones lose angular momentum. The trend observed with low-mass stars leads to possible scenarios of planet engulfment or other merging events during the shell-burning phase. Regarding intermediate-mass stars, the rotation periods that we measured are long with respect to theoretical expectations reported in the literature, which reinforces the existence of an unidentified sink of angular momentum after the main sequence. This article establishes strong links between rotational modulation, tidal interactions, (surface) magnetic fields, and oscillation suppression. There is a wealth of physics to be studied in these targets that is not available in the Sun.

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“…V501 Aur may be related to a group of rapidly rotating giant stars recently identified in the photometry from the Kepler mission (Costa et al 2015). Among them, we note that KIC 10293335 has properties somewhat similar to those of V501 Aur: Prot = 55.96 days (from a Fourier analysis), T eff = 4363 K, log g = 2.45, R = 21.29 R⊙, and v sin i = 12.7 km s −1 .…”

Section: Discussion and Final Remarksmentioning

confidence: 62%

On the nature of the candidate T-Tauri star V501 Aurigae★

Vaňko

Torres

Hambálek

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We report new multi-colour photometry and high-resolution spectroscopic observations of the long-period variable V501 Aur, previously considered to be a weak-lined T-Tauri star belonging to the Taurus-Auriga star-forming region. The spectroscopic observations reveal that V501 Aur is a single-lined spectroscopic binary system with a 68.8-day orbital period, a slightly eccentric orbit (e ∼ 0.03), and a systemic velocity discrepant from the mean of Taurus-Auriga. The photometry shows quasiperiodic variations on a different, ∼55-day timescale that we attribute to rotational modulation by spots. No eclipses are seen. The visible object is a rapidly rotating (v sin i ≈ 25 km s −1 ) early K star, which along with the rotation period implies it must be large (R > 26.3 R ⊙ ), as suggested also by spectroscopic estimates indicating a low surface gravity. The parallax from the Gaia mission and other independent estimates imply a distance much greater than the Taurus-Auriga region, consistent with the giant interpretation. Taken together, this evidence together with a re-evaluation of the Li I λ6707 and Hα lines shows that V501 Aur is not a T-Tauri star, but is instead a field binary with a giant primary far behind the Taurus-Auriga star-forming region. The large mass function from the spectroscopic orbit and a comparison with stellar evolution models suggest the secondary may be an early-type main-sequence star.

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KEPLER RAPIDLY ROTATING GIANT STARS

Cited by 47 publications

References 36 publications

RAPIDLY ROTATING, X-RAY BRIGHT STARS IN THEKEPLERFIELD

RAPIDLY ROTATING, X-RAY BRIGHT STARS IN THEKEPLERFIELD

Active red giants: Close binaries versus single rapid rotators

On the nature of the candidate T-Tauri star V501 Aurigae★

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