Red Giants in old Open Clusters

Cannon, R. D.

doi:10.1093/mnras/150.1.111

Cited by 131 publications

(72 citation statements)

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“…However, in choosing a young age based on this activity indicator, they ignored the much greater estimate of >7.4 Gyr which they derived from the kinematic properties of the system. Age constraints are also available if one considers the larger moving group of which ε Indi A is the eponymous member, and for which Cannon (1970) quoted an age of 5 Gyr derived from the observed (B − V) colour of an apparent red giant clump. However with only 15 members (Eggen 1958), it is not clear that there would be enough objects at the end of their main-sequence lives to fit this reliably.…”

Section: Age Of the ε Indi Systemmentioning

confidence: 99%

“…However with only 15 members (Eggen 1958), it is not clear that there would be enough objects at the end of their main-sequence lives to fit this reliably. Furthermore, the moving group members given in Eggen (1958) were presumably used in Cannon (1970), although no details of the members used are given. This membership list was later revised by Eggen (1971) which excluded five stars from the original list of members.…”

Section: Age Of the ε Indi Systemmentioning

confidence: 99%

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$\mathsf{\varepsilon}$ Indi Ba, Bb: a detailed study of the nearest known brown dwarfs

King¹,

McCaughrean

Homeier

et al. 2010

A&A

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The discovery of ε Indi Ba, Bb, a binary brown dwarf system very close to the Sun, makes possible a concerted campaign to characterise the physical parameters of two T dwarfs. Recent observations suggest substellar atmospheric and evolutionary models may be inconsistent with observations, but there have been few conclusive tests to date. We therefore aim to characterise these benchmark brown dwarfs to place constraints on such models. We have obtained high angular resolution optical, near-infrared, and thermal-infrared imaging and medium-resolution (up to R ∼ 5000) spectroscopy of ε Indi Ba, Bb with the ESO VLT and present VRIzJHKL M broad-band photometry and 0.63−5.1 μm spectroscopy of the individual components. The photometry and spectroscopy of the two partially blended sources were extracted with a custom algorithm. Furthermore, we use deep AO-imaging to place upper limits on the (model-dependent) mass of any further system members. We derive luminosities of log L/L = −4.699 ± 0.017 and −5.232 ± 0.020 for ε Indi Ba, Bb, respectively, and using the dynamical system mass and COND03 evolutionary models predict a system age of 3.7−4.3 Gyr, in excess of previous estimates and recent predictions from observations of these brown dwarfs. Moreover, the effective temperatures of 1352−1385 K and 976−1011 K predicted from the COND03 evolutionary models, for ε Indi Ba and Bb respectively, are in disagreement with those derived from the comparison of our data with the BT-Settl atmospheric models where we find effective temperatures of 1300−1340 K and 880−940 K, for ε Indi Ba and Bb respectively, with surface gravities of log g = 5.25 and 5.50. Finally, we show that spectroscopically determined effective temperatures and surface gravities for ultra-cool dwarfs can lead to underestimated masses even where precise luminosity constraints are available.

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Section: Age Of the ε Indi Systemmentioning

confidence: 99%

Section: Age Of the ε Indi Systemmentioning

confidence: 99%

$\mathsf{\varepsilon}$ Indi Ba, Bb: a detailed study of the nearest known brown dwarfs

King¹,

McCaughrean

Homeier

et al. 2010

A&A

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“…It was identified by Cannon (1970) and Faulkner & Cannon (1973) as the location of steady-core helium burning. That finding was elaborated in detail by Girardi (1999).…”

Section: Introductionmentioning

confidence: 99%

The Penn State-Toruń Centre for Astronomy Planet Search stars

Zieliński

Niedzielski

Wolszczan

et al. 2012

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Aims. We present basic atmospheric parameters (T eff , log g, v t , and [Fe/H]) as well as luminosities, masses, radii, and absolute radial velocities for 348 stars, presumably giants, from the ∼1000 star sample observed within the Penn State-Toruń Centre for Astronomy Planet Search with the High Resolution Spectrograph of the 9.2 m Hobby-Eberly Telescope. The stellar parameters (luminosities, masses, radii) are key to properly interpreting newly discovered low-mass companions, while a systematic study of the complete sample will create a basis for future statistical considerations concerning the appearance of low-mass companions around evolved low-and intermediate-mass stars. Methods. The atmospheric parameters were derived using a strictly spectroscopic method based on the LTE analysis of equivalent widths of Fe I and Fe II lines. With existing photometric data and the Hipparcos parallaxes, we estimated stellar masses and ages via evolutionary tracks fitting. The stellar radii were calculated from either estimated masses and the spectroscopic log g or from the spectroscopic T eff and estimated luminosities. The absolute radial velocities were obtained by cross-correlating spectra with a numerical template. Results. We completed the spectroscopic analysis for 332 stars, 327 of which were found to be giants. A simplified analysis was applied to the remaining 16 stars, which had incomplete data. The results show that our sample is composed of stars with effective temperatures ranging from 4055 K to 6239 K, with log g between 1.39 and 4.78 (5 dwarfs were identified). The estimated luminosities are between log L/L = −1.0 and 3 and lead to masses ranging from 0.6 to 3.4 M . Only 63 stars with masses larger than 2 M were found. The radii of our stars range from 0.6 to 52 R with the vast majority between 9−11 R . The stars in our sample are generally less metal-abundant than the Sun with median [Fe/H] = −0.15. The estimated uncertainties in the atmospheric parameters were found to be comparable to those reached in other studies. However, due to lack of precise parallaxes, the stellar luminosities and, in turn, the masses are far less precise, within 0.2 M in best cases and 0.3 M on average.

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“…Since the pioneering work of Cannon (1970) and Faulkner & Cannon (1973), the clump on the red giant branch of open clusters has been recognized as having been formed by stars in the stage of central helium burning. These authors interpreted the near constancy of the clump absolute magnitude as the result of He ignition in an electron-degenerate core.…”

Section: Introductionmentioning

confidence: 99%

A spectroscopic survey of faint, high-Galactic-latitude red clump stars

Valentini

Munari

2010

A&A

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Context. Their high intrinsic brightness and small dispersion in absolute magnitude make red clump (RC) stars a prime tracer of Galactic structure and kinematics. Aims. We aim to derive accurate, multi-epoch radial velocities and atmospheric parameters (T eff , log g, [M/H], V rot sin i) of a large sample of carefully selected RC stars, fainter than those present in other spectroscopic surveys and located over a great circle at high Galactic latitudes. Methods. We acquired data of the program stars of high signal-to-noise ratio (S/N) and high resolution with the Asiago Echelle spectrograph. Radial velocities were obtained by applying cross-correlation and atmospheric parameters via χ 2 fit to a synthetic spectral library. Extensive tests were carried out by re-observing with the same instrument a large number of standard stars taken from a variety of sources in the literature. During these tests, we found that the absolute Tycho V T magnitude of local red clump stars is not dependent on metallicity Results. A total of 277 red clump stars (101 of them with a second epoch observation) of the extended solar neighborhood and 55 calibration stars were observed and included in an output catalog that contains (in addition to relevant support astrometric and photometric data taken from literature) the main output of our survey: accurate multi-epoch radial velocities (σ(RV) ≤ 0.4 km s −1 ), accurate atmospheric parameters (σ(T eff ) = 68 K, σ(log g) = 0.11 dex, σ([M/H]) = 0.10 dex, σ(V rot sin i) = 1.1 km s −1 ), distances, and space velocities (U, V, W).

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Red Giants in old Open Clusters

Cited by 131 publications

References 0 publications

$\mathsf{\varepsilon}$ Indi Ba, Bb: a detailed study of the nearest known brown dwarfs

$\mathsf{\varepsilon}$ Indi Ba, Bb: a detailed study of the nearest known brown dwarfs

The Penn State-Toruń Centre for Astronomy Planet Search stars

A spectroscopic survey of faint, high-Galactic-latitude red clump stars

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