Observations of spectral line asymmetries and convective velocities in F, G, and K stars

Gray, David F.

doi:10.1086/159818

Cited by 159 publications

(142 citation statements)

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“…The 0.55 scale factor implies that the granulation velocities in αSer are slightly more than half as large as the solar values. Although this is consistent with the general drop in macroturbulence with declining effective temperature (Gray 1984(Gray , 1988Gray & Nagar 1985;Gray & Toner 1986), a value of 0.55 is one of the lowest yet measured (Gray & Pugh 2012, Papers 1 and 2). It is small compared to 0.80 for βGem and 1.10 for εCyg, but is not inconsistent with the run of values in Figure 7 of Gray & Pugh (2012).…”

Section: The Third Signature Of Granulation-convective Blueshiftssupporting

confidence: 81%

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Rotation and Granulation of the K2 Giant Α Ser

Gray

2016

ApJ

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The red giant α Ser was observed over 10 seasons, 2001-2010, at the Elginfield Observatory with the highresolution coudé spectrograph. Season-mean radial velocities appear to show a small secular rise ∼11±3 m s −1 yr −1 . The absolute spectroscopic radial velocity with convective blueshifts taken into account is 2730 m s −1 . Ten line-depth ratios were investigated and show that the starʼs temperature is constant with any secular variation below 1.3±1.0 K over the 11 years of observation. Fourier analysis of the line broadening yields vsini = 2.0±0.3 km s −1 and a radial-tangential macroturbulence dispersion ζ RT =4.50±0.10 km s −1 . The third-granulation-signature plot shows that the granulation velocities of αSer are only 0.55±0.10 as large as the Sunʼs. The line bisector of Fe I λ6253 has the usual "C" shape and when mapped onto the third-signature plot results in a flux deficit that is slightly broader than seen in other measured K giants. The deficit fractional area of 12.3±1.5% suggests a temperature difference between granules and lanes of 105 K as seen averaged over the stellar disk.

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Section: The Third Signature Of Granulation-convective Blueshiftssupporting

confidence: 81%

“…Modeling is done by integrating the Doppler-shift distributions of rotation and radial-tangential macroturbulence over the stellar disk (Gray 1988(Gray , 2005b. Limb darkening is calculated using the model photosphere from which the thermal profiles were computed.…”

Section: Rotation and Macroturbulencementioning

confidence: 99%

Rotation and Granulation of the K2 Giant Α Ser

Gray

2016

ApJ

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“…To derive the bisector, we first interpolate the CCF profile using a cubic spline interpolation; we then compute the set of midpoints of horizontal line segments extending across the profile (Gray 1982). To assess temporal evolution of the line profile, we calculate the velocity span (as introduced, e.g., by Gray 1982;Queloz et al 2001) v s , given by v t − v b , where v t and v b are respectively the average velocity at the top and bottom parts of the bisector 3 .…”

Section: Computing Rvs and Activity Proxiesmentioning

confidence: 99%

“…To assess temporal evolution of the line profile, we calculate the velocity span (as introduced, e.g., by Gray 1982;Queloz et al 2001) v s , given by v t − v b , where v t and v b are respectively the average velocity at the top and bottom parts of the bisector 3 . For RV variations caused by stellar activity, we commonly observe an anti-correlation between v s and v r (see, e.g., Queloz et al 2001).…”

Section: Computing Rvs and Activity Proxiesmentioning

confidence: 99%

Modelling the RV jitter of early-M dwarfs using tomographic imaging

Hébrard

Donati

Delfosse

et al. 2016

Mon. Not. R. Astron. Soc.

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In this paper we show how tomographic imaging (Zeeman Doppler Imaging, ZDI) can be used to characterize stellar activity and magnetic field topologies, ultimately allowing to filter out the radial velocity (RV) activity jitter of M-dwarf moderate rotators. This work is based on spectropolarimetric observations of a sample of five weakly-active early M-dwarfs (GJ 205, GJ 358, GJ 410, GJ479, GJ 846) with HARPS-Pol and NARVAL. These stars have v sin i and RV jitters in the range 1-2 km s −1 and 2.7-10.0 m s −1 rms respectively.Using a modified version of ZDI applied to sets of phase-resolved Least-Squares-Deconvolved (LSD) profiles of unpolarized spectral lines, we are able to characterize the distribution of active regions at the stellar surfaces. We find that darks spots cover less than 2% of the total surface of the stars of our sample. Our technique is efficient at modeling the rotationally modulated component of the activity jitter, and succeeds at decreasing the amplitude of this component by typical factors of 2-3 and up to 6 in optimal cases. From the rotationally modulated time-series of circularly polarized spectra and with ZDI, we also reconstruct the large-scale magnetic field topology. These fields suggest that bi-stability of dynamo processes observed in active M dwarfs may also be at work for moderately active M dwarfs. Comparing spot distributions with field topologies suggest that dark spots causing activity jitter concentrate at the magnetic pole and/or equator, to be confirmed with future data on a larger sample.

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“…Gray 1982Gray , 1983Gray & Hatzes 1997) or of the cross-correlation function (e.g. Queloz et al 2001).…”

Section: Introductionmentioning

confidence: 99%

Line-depth-ratio temperatures for the close binary ν Octantis: new evidence supporting the conjectured circumstellar retrograde planet

Ramm¹

2015

Monthly Notices of the Royal Astronomical Society

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We explore the possibly that either starspots or pulsations are the cause of a periodic radialvelocity signal (P ∼ 400 days) from the K-giant binary ν Octantis (P ∼ 1050 days, e ∼ 0.25), alternatively conjectured to have a retrograde planet. Our study is based on temperatures derived from 22 line-depth ratios (LDRs) for ν Oct and twenty calibration stars. Empirical evidence and stability modelling provide unexpected support for the planet since other standard explanations (starspots, pulsations and additional stellar masses) each have credibility problems. However, the proposed system presents formidable challenges to planet-formation and stability theories: it has by far the smallest stellar separation of any claimed planet-harbouring binary (a bin ∼ 2.6 AU) and an equally unbelievable separation ratio (a pl /a bin ∼ 0.5), hence the necessity that the circumstellar orbit be retrograde.The LDR analysis of 215 ν Oct spectra acquired between 2001-2007, from which the RV perturbation was first revealed, have no significant periodicity at any frequency. The LDRs recover the original 21 stellar temperatures with an average accuracy of 45 ± 25 K. The 215 ν Oct temperatures have a standard deviation of only 4.2 K. Assuming the host primary is not pulsating, the temperatures converted to magnitude differences strikingly mimic the very stable photometric Hipparcos observations 15 years previously, implying the long-term stability of the star and demonstrating a novel use of LDRs as a photometric gauge. Our results provide substantial new evidence that conventional starspots and pulsations are unlikely causes of the RV perturbation. The controversial system deserves continued attention, including with higher resolving-power spectra for bisector and LDR analyses.

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Observations of spectral line asymmetries and convective velocities in F, G, and K stars

Cited by 159 publications

References 0 publications

Rotation and Granulation of the K2 Giant Α Ser

Rotation and Granulation of the K2 Giant Α Ser

Modelling the RV jitter of early-M dwarfs using tomographic imaging

Line-depth-ratio temperatures for the close binary ν Octantis: new evidence supporting the conjectured circumstellar retrograde planet

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