Velocity fields in stellar photospheres

Gray, David F.

doi:10.1017/cbo9781316036570.020

Cited by 82 publications

(114 citation statements)

References 34 publications

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“…If the inclination is decreased from 90 to 60 , the range of the secondary mass is 0.95-1.27 M . Thus, from Table B1 of Gray (1992), the secondary is likely a late-F or G dwarf. Such a spectral type is consistent with the lack of detection of its lines in our red wavelength spectra.…”

Section: Hd 37824mentioning

confidence: 99%

Chromospherically Active Stars. XXIV. The Giant, Single-lined Binaries HD 37824, HD 181809, and HD 217188

Fekel

Henry

2005

Astron J

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We have obtained spectroscopy and photometry of three chromospherically active, single-lined spectroscopic binaries, HD 37824 (V1149 Ori), HD 181809 (V4138 Sgr), and HD 217188 (AZ Psc). HD 37824 has a circular orbit with a period of 53.57 days. Its primary is a K0 III star, while the secondary is likely a G or K dwarf. HD 181809 has an orbit with a period of 13.04667 days and a low eccentricity of 0.040. The primary has a spectral type of K0 III-IV, and its secondary is probably an M dwarf. The orbit of HD 217188 has a period of 47.1209 days and a moderately high eccentricity of 0.470. The spectral type of the primary is K0 III, while the secondary is likely an M dwarf. All three systems are estimated to have near solar iron abundances. Photometric observations spanning 15-16 years for all three stars yield mean photometric periods of 53.12, 59.85, and 90.89 days for HD 37824, HD 181809, and HD 217188, respectively. Thus, HD 37824 is rotating synchronously with the orbital period, while HD 181809 and HD 217188 are both rotating considerably slower than synchronously. All three stars show longterm variations in mean brightness and photometric amplitude, but no correlations are observed between the seasonal mean brightness, photometric amplitude, and seasonal photometric period in any of the stars. No clear evidence for long-term periodic variations in any of these parameters is present. The circular orbit of HD 37824 and the synchronous rotation of its K giant argue that the star is in the core helium-burning phase of its evolution. The giant components of HD 181809 and HD 217188 are asynchronous rotators, and both systems have eccentric orbits. Thus, those two stars are likely first-ascent giants.

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Section: Hd 37824mentioning

confidence: 99%

Chromospherically Active Stars. XXIV. The Giant, Single-lined Binaries HD 37824, HD 181809, and HD 217188

Fekel

Henry

2005

Astron J

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“…For instance, one of the unknown parameters in fitting FeH lines is the constant of van der Waals broadening γ Waals . It was shown in Shulyak et al (2010) that, in order to fit FeH lines in GJ 1002 with a given T eff = 3100 K and υ sin i = 2.5 km s −1 , the value of γ Waals must be increased by an enhancement factor of f (γ Waals ) = 3.5 compared to a classical value given in Gray (1992). Different combinations of atmospheric parameters, such as iron abundance, γ Waals , and υ sin i, could provide the same accurate fit to the observed spectra: a change in one of these parameter could be compensated for (to a certain extent) by an opposite change in the others.…”

Section: Testing Molecular and Atomic Diagnosticsmentioning

confidence: 99%

Exploring the magnetic field complexity in M dwarfs at the boundary to full convection

Shulyak

Reiners

Seemann

et al. 2014

A&A

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Context. Magnetic fields play a pivotal role in the formation and evolution of low-mass stars, but the dynamo mechanisms generating these fields are poorly understood. Measuring cool star magnetism is a complicated task because of the complexity of cool star spectra and the subtle signatures of magnetic fields. Aims. Based on detailed spectral synthesis, we carry out quantitative measurements of the strength and complexity of surface magnetic fields in the four well-known M dwarfs GJ 388, GJ 729, GJ 285, and GJ 406 that populate the mass regime around the boundary between partially and fully convective stars. Very high-resolution (R = 100 000), high signal-to-noise (up to 400), near-infrared Stokes I spectra were obtained with CRIRES at ESO's Very Large Telescope covering regions of the FeH Wing-Ford transitions at 1 μm and Na i lines at 2.2 μm.Methods. A modified version of the Molecular Zeeman Library (MZL) was used to compute Landé g-factors for FeH lines. We determined the distribution of magnetic fields by magnetic spectral synthesis performed with the Synmast code. We tested two different magnetic geometries to probe the influence of field orientation effects. Results. Our analysis confirms that FeH lines are excellent indicators of surface magnetic fields in low-mass stars of type M, particularly in comparison to profiles of Na i lines that are heavily affected by water lines and that suffer problems with continuum normalization. The field distributions in all four stars are characterized by three distinct groups of field components, and the data are consistent neither with a smooth distribution of different field strengths nor with one average field strength covering the full star. We find evidence of a subtle difference in the field distribution of GJ 285 compared to the other three targets. GJ 285 also has the highest average field of 3.5 kG and the strongest maximum field component of 7-7.5 kG. The maximum local field strengths in our sample seem to be correlated with rotation rate. While the average field strength is saturated, the maximum local field strengths in our sample show no evidence of saturation. Conclusions. We find no difference between the field distributions of partially and fully convective stars. The one star with evidence of field distribution different from the other three is the most active star (i.e. with X-ray luminosity and mean surface magnetic field) rotating relatively fast. A possible explanation is that rotation determines the distribution of surface magnetic fields, and that local field strengths grow with rotation even in stars in which the average field is already saturated.

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“…Specifically, v sin i is related to the FWHM of the Gaussian that better describes the peak of the cross-correlation function by a calibration function. In order to derive the calibration function, we first cross-correlated each template spectrum with itself artificially broadened at different velocities using the rotational profile of Gray (1992); then, we fitted the relation between the values of FWHM and the rotational velocities with a third order polynomial.…”

Section: Rotational Velocitiesmentioning

confidence: 99%

FLAMES spectroscopy of low-mass stars in the young clusters σ Ori and λ Ori

Sacco

Franciosini²,

Randich

et al. 2008

A&A

181

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Aims. We performed a detailed membership selection and studied the accretion properties of low-mass stars in the two apparently very similar young (1-10 Myr) clusters σ Ori and λ Ori. Methods. We observed 98 and 49 low-mass (0.2-1.0 M ) stars in σ Ori and λ Ori respectively, using the multi-object optical spectrograph FLAMES at the VLT, with the high-resolution (R ∼ 17 000) HR15N grating (6470-6790 Å). We used radial velocities, Li and Hα to establish cluster membership and Hα and other optical emission lines to analyze the accretion properties of members. Results. We identified 65 and 45 members of the σ Ori and λ Ori clusters, respectively, and discovered 16 new candidate binary systems. We also measured rotational broadening for 20 stars and estimated the mass accretion rates in 25 stars of the σ Ori cluster, finding values between 10 −11 and 10 −7.7 M yr −1 and in 4 stars of the λ Ori cluster, finding values between 10 −11 and 10 −10.1 M yr −1 . Comparing our results with the infrared photometry obtained by the Spitzer satellite, we find that the fraction of stars with disks and the fraction of active disks is larger in the σ Ori cluster (52 ± 9% and 78 ± 16%) than in λ Ori (28 ± 8% and 40 ± 20%). Conclusions. The different disk and accretion properties of the two clusters could be due either to the effect of the high-mass stars and the supernova explosion in the λ Ori cluster or to different ages of the cluster populations. Further observations are required to draw a definitive conclusion.

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Velocity fields in stellar photospheres

Cited by 82 publications

References 34 publications

Chromospherically Active Stars. XXIV. The Giant, Single-lined Binaries HD 37824, HD 181809, and HD 217188

Chromospherically Active Stars. XXIV. The Giant, Single-lined Binaries HD 37824, HD 181809, and HD 217188

Exploring the magnetic field complexity in M dwarfs at the boundary to full convection

FLAMES spectroscopy of low-mass stars in the young clusters σ Ori and λ Ori

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