The Rotation of Arcturus and Active Longitudes on Giant Stars

Gray, David F.; Brown, Kevin I. T.

doi:10.1086/507077

Cited by 30 publications

(28 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The lines in red giants are broadened by stellar rotation and macroturbulent motions by a comparable amount. These two phenomena imprint a distinct, yet subtle, signature in the shape of the line profile that is best revealed through Fourier transforms applied to very high spectral resolution and S/N data (e.g., Gray & Brown 2006). In most cases, it is difficult with our observations to clearly disentangle the contribution of these two processes.…”

Section: Line Broadening Parametersmentioning

confidence: 91%

Atmospheric parameters and chemical properties of red giants in the CoRoT asteroseismology fields

Morel

Miglio

Lagarde

et al. 2014

A&A

View full text Add to dashboard Cite

A precise characterisation of the red giants in the seismology fields of the CoRoT satellite is a prerequisite for further in-depth seismic modelling. High-resolution FEROS and HARPS spectra were obtained as part of the ground-based follow-up campaigns for 19 targets holding great asteroseismic potential. These data are used to accurately estimate their fundamental parameters and the abundances of 16 chemical species in a self-consistent manner. Some powerful probes of mixing are investigated (the Li and CNO abundances, as well as the carbon isotopic ratio in a few cases). The information provided by the spectroscopic and seismic data is combined to provide more accurate physical parameters and abundances. The stars in our sample follow the general abundance trends as a function of the metallicity observed in stars of the Galactic disk. After an allowance is made for the chemical evolution of the interstellar medium, the observational signature of internal mixing phenomena is revealed through the detection at the stellar surface of the products of the CN cycle. A contamination by NeNa-cycled material in the most massive stars is also discussed. With the asteroseismic constraints, these data will pave the way for a detailed theoretical investigation of the physical processes responsible for the transport of chemical elements in evolved, low-and intermediate-mass stars.

show abstract

Section: Line Broadening Parametersmentioning

confidence: 91%

Atmospheric parameters and chemical properties of red giants in the CoRoT asteroseismology fields

Morel

Miglio

Lagarde

et al. 2014

A&A

View full text Add to dashboard Cite

show abstract

“…We obtained the synthetic spectrum with the same procedure used for the computation of the Bluered grid, at a resolving power R = 500 000. The normalized spectrum, which we obtained by dividing the emitted flux by the continuum value, has been broadened in the same way as the Sun to account for rotational and macroturbulence velocities of 1.5 km s −1 and 5.2 km s −1 (Gray & Brown 2006), respectively, and convolved with a Gaussian kernel to match the resolving power of the observation.…”

Section: Arcturus and The Molecular Contribution In Cool Starsmentioning

confidence: 99%

Probing Atlas model atmospheres at high spectral resolution

Bertone

Buzzoni²,

Chávez

et al. 2008

A&A

View full text Add to dashboard Cite

Aims. The fast improvement of spectroscopic observations makes mandatory a strong effort on the theoretical side to better reproduce the spectral energy distribution (SED) of stars at high spectral resolution. In this regard, relying on the Kurucz Atlas/Synthe original codes we computed the Bluered library, consisting of 832 synthetic SED of stars, that cover a large parameter space at very high spectral resolution (R = 500 000) along the 3500−7000 Å wavelength range. Methods. Bluered synthetic spectra have been used to assess in finer detail the intrinsic reliability and the performance limits of the Atlas theoretical framework. The continuum-normalized spectra of the Sun, Arcturus, and Vega, plus a selected list of 45 bright stars with high-quality SEDs from the Prugniel & Soubiran Elodie catalog, form our sample designed to probe the global properties of synthetic spectra across the entire range of H-R parameters.Results. Atlas models display a better fitting performance with increasing stellar temperature. High-resolution spectra of Vega, the Sun, and Arcturus have been reproduced at R = 100 000, respectively, within a 0.7%, 4.5%, and 8.8% relative scatter in residual flux. In all the three cases, the residual flux distribution shows a significant asymmetry (skewness parameter γ = −2.21, −0.98, −0.67, respectively), which neatly confirms an overall "excess" of theoretical line blanketing. For the Sun, this apparent discrepancy is alleviated, but not recovered, by a systematic decrease (−40%) of the line oscillator strengths, log(g f ), especially referring to iron transitions. Definitely, a straight "astrophysical" determination of log(g f ) for each individual atomic transition has to be devised to overcome the problem. By neglecting overblanketing effects in theoretical models when fitting high-resolution continuum-normalized spectra of real stars, we lead to a systematically warmer effective temperature (between +80 and +300 K for the solar fit) and a slightly poorer metal content.

show abstract

“…The long-term study of Ca ii H&K lines as classical activity indicators by Brown et al (2008) reveals a range of variability periods between the years 1984 and 2007, exhibiting an apparent magnetic cycle with an estimated duration of < ∼ 14 yr. Owing to the known correlation of magnetic activity with surface temperature observed for the Sun (Gray & Livingston 1997) and other late-type MS stars (Gray et al 1996b,a, and references therein), periodic temperature changes of ≈20 K inferred from line-depth ratio variations support this theory. Assuming a rotational period of 730 d (Peterson et al 1993), or about 2 yr (Gray & Brown 2006), with v sin i = 1.5 ± 0.3 km s −1 , the seasonal variability (200−250 days) can be attributed to four active longitudes. Observed periods in H&K line bisectors can be explained by differential rotation and the latitudinal migration of active regions.…”

Section: Introductionmentioning

confidence: 99%

First detection of a weak magnetic field on the giant Arcturus: remnants of a solar dynamo?

Sennhauser

Berdyugina

2011

A&A

View full text Add to dashboard Cite

Context. Arcturus is the second closest K giant and among the brightest stars in the sky. It has not been found to have a magnetic field, even though Ca ii H&K lines as activity indicators imply that Arcturus is magnetically active. Aims. We measure the mean longitudinal magnetic field strengths and interpret them in terms of an intraseasonal activity modulation. Methods. We apply our new Zeeman component decomposition (ZCD) technique to three single sets of Stokes I and V spectra to measure the longitudinal component of the magnetic field responsible for tiny Zeeman signatures detected in spectral line profiles. Results. For two of the spectra, we report the detection of the Zeeman signature of a weak longitudinal magnetic field of 0.65 ± 0.26 G and 0.43 ± 0.16 G. The third measurement is less significant, but all the measurements closely reproduce a rotationally modulated activity cycle with four active longitudes. Conclusions. For the first time, a magnetic field on Arcturus is directly detected. This field can be attributed to a diminishing solartype αΩ-dynamo acting in the deepening convection zone of Arcturus. We demonstrate that our new method ZCD lowers the detection limit of very weak magnetic fields from spectropolarimetric measurements.

show abstract

The Rotation of Arcturus and Active Longitudes on Giant Stars

Cited by 30 publications

References 42 publications

Atmospheric parameters and chemical properties of red giants in the CoRoT asteroseismology fields

Atmospheric parameters and chemical properties of red giants in the CoRoT asteroseismology fields

Probing Atlas model atmospheres at high spectral resolution

First detection of a weak magnetic field on the giant Arcturus: remnants of a solar dynamo?

Contact Info

Product

Resources

About