scispace - formally typeset
Search or ask a question
Journal ArticleDOI

Rotation, convection, and magnetic activity in lower main-sequence stars

TL;DR: In this paper, the mean level of Ca n H and K emission (averaged over 15 years) is correlated with rotation period, as expected, but there is a further dependence of the emission on spectral type.
Abstract: Rotation periods are reported for 14 main-sequence stars, bringing the total number of such stars with well-determined rotation periods to 41. It is found that the mean level of their Ca n H and K emission (averaged over 15 years) is correlated with rotation period, as expected. However, there is a further dependence of the emission on spectral type. When expressed as the ratio of chromospheric flux to total bolometric flux, the emission is well correlated with the parameter Pohs/Tc, where Pohs is the observed rotation period and tc(B—V) is a theoretically-derived convective overturn time, calculated assuming a mixing length to scale height ratio a ~ 2. This finding is consonant with general predictions of dynamo theory, if the relation between chromospheric emission and dynamo-generated magnetic fields is essentially independent of rotation rate and spectral type for the stars considered. The dependence of mean chromospheric emission on rotation and spectral type is essentially the same for stars above and below the Vaughan-Preston “gap,” thus casting doubt on explanations of the gap in terms of a discontinuity in dynamo characteristics. Subject headings: Ca n emission — convection — stai
Citations
More filters
Journal ArticleDOI
23 Nov 1995-Nature
TL;DR: The presence of a Jupiter-mass companion to the star 51 Pegasi is inferred from observations of periodic variations in the star's radial velocity as discussed by the authors, which would be well inside the orbit of Mercury in our Solar System.
Abstract: The presence of a Jupiter-mass companion to the star 51 Pegasi is inferred from observations of periodic variations in the star's radial velocity. The companion lies only about eight million kilometres from the star, which would be well inside the orbit of Mercury in our Solar System. This object might be a gas-giant planet that has migrated to this location through orbital evolution, or from the radiative stripping of a brown dwarf.

3,957 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented a catalog of stellar properties for 1040 nearby F, G, and K stars that have been observed by the Keck, Lick, and AAT planet search programs.
Abstract: We present a uniform catalog of stellar properties for 1040 nearby F, G, and K stars that have been observed by the Keck, Lick, and AAT planet search programs. Fitting observed echelle spectra with synthetic spectra yielded effective temperature, surface gravity, metallicity, projected rotational velocity, and abundances of the elements Na, Si, Ti, Fe, and Ni, for every star in the catalog. Combining V-band photometry and Hipparcos parallaxes with a bolometric correction based on the spectroscopic results yielded stellar luminosity, radius, and mass. Interpolating Yonsei-Yale isochrones to the luminosity, effective temperature, metallicity, and α-element enhancement of each star yielded a theoretical mass, radius, gravity, and age range for most stars in the catalog. Automated tools provide uniform results and make analysis of such a large sample practical. Our analysis method differs from traditional abundance analyses in that we fit the observed spectrum directly, rather than trying to match equivalent widths, and we determine effective temperature and surface gravity from the spectrum itself, rather than adopting values based on measured photometry or parallax. As part of our analysis, we determined a new relationship between macroturbulence and effective temperature on the main sequence. Detailed error analysis revealed small systematic offsets with respect to the Sun and spurious abundance trends as a function of effective temperature that would be inobvious in smaller samples. We attempted to remove these errors by applying empirical corrections, achieving a precision per spectrum of 44 K in effective temperature, 0.03 dex in metallicity, 0.06 dex in the logarithm of gravity, and 0.5 km s-1 in projected rotational velocity. Comparisons with previous studies show only small discrepancies. Our spectroscopically determined masses have a median fractional precision of 15%, but they are systematically 10% higher than masses obtained by interpolating isochrones. Our spectroscopic radii have a median fractional precision of 3%. Our ages from isochrones have a precision that varies dramatically with location in the Hertzsprung-Russell diagram. We plan to extend the catalog by applying our automated analysis technique to other large stellar samples.

1,571 citations


Cites background from "Rotation, convection, and magnetic ..."

  • ...If correct, the v sin i distributions would imply that most stars in our sample have equatorial velocities of at least 3 km s 1, which is inconsistent with measured rotation periods for inactive field stars (Noyes et al. 1984)....

    [...]

Journal ArticleDOI
TL;DR: In this article, the authors derived an improved activity-age calibration for F7-K2 dwarfs (0:5 mag < B -V < 0.9 mag).
Abstract: While the strong anticorrelation between chromospheric activity and age has led to the common use of the Ca II H and K emission index (R'_(HK) = L_(HK)/L_(bol)) as an empirical age estimator for solar-type dwarfs, existing activity-age relations produce implausible ages at both high and low activity levels.We have compiled R'_(HK) HK data from the literature for young stellar clusters, richly populating for the first time the young end of the activity-age relation. Combining the cluster activity data with modern cluster age estimates and analyzing the color dependence of the chromospheric activity age index,we derive an improved activity-age calibration for F7-K2 dwarfs (0:5 mag < B - V < 0.9 mag). We also present a more fundamentally motivated activity-age calibration that relies on conversion of R'_(HK) values through the Rossby number to rotation periods and then makes use of improved gyrochronology relations. We demonstrate that our new activity-age calibration has typical age precision of ~0.2 dex for normal solar-type dwarfs aged between the Hyades and the Sun (~0.6-4.5 Gyr). Inferring ages through activity-rotation-age relations accounts for some color-dependent effects and systematically improves the age estimates (albeit only slightly). We demonstrate that coronal activity as measured through the fractional X-ray luminosity (R_X = L_X/L_(bol)) has nearly the same age- and rotation inferring capability as chromospheric activity measured through R'_(HK). As a first application of our calibrations, we provide new activity-derived age estimates for a volume-limited sample of the 108 solar-type field dwarfs within 16 pc.

1,325 citations


Cites background or methods from "Rotation, convection, and magnetic ..."

  • ...…(20) Stauffer et al. (1989), (21) Soderblom et al. (1993), (22) Stauffer & Hartmann (1987), (23) Duncan et al. (1991), converted to to logR′ HK following Noyes et al. (1984), (24) Taylor (2006), (25) Paulson et al. (2002), (26) Upgren et al. (1985), (27) Reid (1992), (28) Weis & Upgren (1982),…...

    [...]

  • ...We refer the reader to papers by Noyes et al. (1984); Baliunas et al. (1996, 1995); Henry et al. (1996); Wright et al. (2004, and references therein) for in-depth discussion of how to measure SMW and R′HK, as well as the history of studies using this index....

    [...]

  • ...Chro- mospheric activity is generated through the stellar magnetic dynamo, the strength of which 1http://feps.as.arizona.edu appears to scale with rotation velocity (Kraft 1967; Noyes et al. 1984; Montesinos et al. 2001)....

    [...]

  • ...The S-values from Duncan et al. (1991) were converted to R′HK following Noyes et al. (1984) using B−V colors from Perryman & ESA (1997)....

    [...]

  • ...By “solar-type”, we mean ∼F7-K2 or 0.5 < (B − V )0 < 0.9 mag, which is approximately the color range over which the Noyes et al. (1984) relation for the photospheric contribution to the S-index is applicable, as well as the color range blanketed by recent activity surveys....

    [...]

Journal ArticleDOI
TL;DR: Doppler measurements from Keck exhibit a sinusoidal periodicity in the velocities of the G0 dwarf HD 209458, having a semiamplitude of 81 m s-1 and a period of 3.5239 days, which is indicative of a "51 Peg-like" planet with a minimum mass (Msini) of 0.62 MJup and a semimajor axis of0.046 AU.
Abstract: Doppler measurements from Keck exhibit a sinusoidal periodicity in the velocities of the G0 dwarf HD 209458, having a semiamplitude of 81 m s 21 and a period of 3.5239 days, which is indicative of a “51 Peg‐like” planet with a minimum mass ( ) of 0.62 MJup and a semimajor axis of 0.046 AU. Follow-up photometry reveals M sin i a drop of 0.017 mag at the predicted time (within the errors) of transit by the companion based on the velocities. This is the first extrasolar planet observed to transit its star. The radius of the planet derived from the magnitude of the dimming is 1.42 RJup, which is consistent with models of irradiated Jupiter-mass planets. The transit implies that , leading to a true mass of 0.62 MJup for the planet. The resulting mean density of 0.27 g cm 23 sin i 1 0.993 implies that the companion is a gas giant. Subject headings: planetary systems — stars: individual (HD 209458)

940 citations


Cites methods from "Rotation, convection, and magnetic ..."

  • ...The value measured from our H′RHK and K lines is 24.93 as calibrated by Noyes et al. (1984)....

    [...]

Journal ArticleDOI
TL;DR: In this article, the G0 V star HD 166435 has been observed by the ber-fed spectrograph ELODIE as one of the targets in the large extra-solar planet survey that is conducting at the Observatory of Haute-Provence.
Abstract: The G0 V star HD 166435 has been observed by the ber-fed spectrograph ELODIE as one of the targets in the large extra-solar planet survey that we are conducting at the Observatory of Haute-Provence. We detected coherent, low-amplitude, radial-velocity variations with a period of 3.7987 days, suggesting a possible close-in planetary companion. Subsequently, we initiated a series of high-precision photometric observations to search for possible planetary transits and an additional series of Ca II H and K observations to measure the level of surface magnetic activity and to look for possible rotational modulation. Surprisingly, we found the star to be photometrically variable and magnetically active. A detailed study of the phase stability of the radial-velocity signal revealed that the radial-velocity variability remains coherent only for durations of about 30 days. Analysis of the time variation of the spectroscopic line proles using line bisectors revealed a correlation between radial velocity and line-bisector orientation. All of these observations, along with a one-quarter cycle phase shift between the photometric and the radial-velocity variations, are well explained by the presence of dark photospheric spots on HD 166435. We conclude that the radial-velocity variations are not due to gravitational interaction with an orbiting planet but, instead, originate from line-prole changes stemming from star spots on the surface of the star. The quasi-coherence of the radial-velocity signal over more than two years, which allowed a fair t with a binary model, makes the stability of this star unusual among other active stars. It suggests a stable magnetic eld orientation where spots are always generated at about the same location on the surface of the star.

906 citations

References
More filters
Book
01 Jan 1978

2,987 citations


"Rotation, convection, and magnetic ..." refers background or methods in this paper

  • ...Finally, the period of the star HD 39587 is taken from the work of Stimets and Giles (1980), who extracted it from the long-term survey data of Wilson (1978)....

    [...]

  • ...Such information may be obtainable from photometric and spectrophotometric (HK) rotational modulation light curves. Turning to the detailed dependence of tc on J3— V, we note that the empirical function tc (B—V) closely matches the theoretical convective overturn time for a ~ 2 (Fig. 5). As mentioned above, the scatter in plots of log (R'hk} versus P/t is slightly greater for a = 3 than for a = 2, and very much greater for a = 1. To the extent that the various assumptions made in the analysis are valid, this would suggest that a ~ 2 is a better description of convective envelopes of lower main sequence stars than a ~ 1 or (with somewhat less confidence) a ~ 3. A ratio of mixing length to scale height a ~ 2 implies a deeper convection zone than for the case a ~ 1 ; for the Sun, for example, the models of Gilman (1980) yield convection...

    [...]

  • ...This would cause R'Hk to decrease correspondingly if it bears the same relation to period implied by Figure 8 for both fast and slow rotators, and therefore a gap would result in the distribution of chromospheric emission level. Hypothesis 3 is intriguing, but there is at present no independent evidence supporting such a period of rapid spindown. Soderblom (1983) concludes that the v sin i values...

    [...]

  • ...Also, Hartmann et al (1984) have considered the statistical significance of the gap as outlined in the Vaughan and Preston (1980) neighborhood survey and find that it is not high, which favors hypothesis 1....

    [...]

  • ...—The mean chromospheric H-K flux ratio as obtained from the mean Wilson (1978) survey data plotted in Fig....

    [...]