Chromospherically young, kinematically old stars

Rocha-Pinto, Helio J.; Castilho, Bruno V.; Maciel, W. J.

doi:10.1051/0004-6361:20011815

Cited by 34 publications

(35 citation statements)

References 51 publications

(86 reference statements)

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“…The observed dispersion depends critically on the samples considered, and from the results by Evardsson et al (1993) and Feltzing et al (2001), a relatively large dispersion of about 0.3 dex was estimated for the [Fe/H] ratio. Our own results indicate that the actual dispersion may be considerably lower, about 0.2 dex (Rocha-Pinto et al 2000, provided some important corrections are made, concerning the cosmic scatter, incompleteness of the samples and a careful analysis of stars that present contradictory age indicators, as discussed in detail by Rocha-Pinto et al (2002). This value agrees very well with our estimate of the formal uncertainty, as discussed above.…”

Section: 1c Uncertainty Analysissupporting

confidence: 87%

Age distribution of the central stars of galactic disk planetary nebulae

Maciel

Costa

Idiart

2010

A&A

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Context. Determination of the ages of central stars of planetary nebulae (CSPN) is a complex problem, and there is presently no single method that can be generally applied. We have developed several methods of estimating the ages of CSPN, based on both the observed nebular properties and some properties of the stars themselves. Aims. Our aim is to estimate the ages and the age distribution of CSPN and to compare the derived results with mass and age determinations of CSPN and white dwarfs based on empirical determinations of these quantities. Methods. We considered a sample of planetary nebulae in the galactic disk, most of which (∼69%) are located in the solar neighbourhood, within 3 kpc from the Sun. We discuss several methods of deriving the age distribution of CSPN, namely; (i) the use of an age-metallicity relation that also depends on the galactocentric distance; (ii) the use of an age-metallicity relation obtained for the galactic disk; and (iii) the determination of ages from the central star masses obtained from the observed nitrogen abundances. Results. We estimated the age distribution of CSPN with average uncertainties of 1-2 Gyr, and compared our results with the expected distribution based both on the observed mass distribution of white dwarfs and on the age distribution derived from available mass distributions of CSPN. Based on our derived age distributions, we conclude that most CSPN in the galactic disk have ages under 6 Gyr, and that the age distribution is peaked around 2-4 Gyr.

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Section: 1c Uncertainty Analysissupporting

confidence: 87%

Age distribution of the central stars of galactic disk planetary nebulae

Maciel

Costa

Idiart

2010

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“…In this case, radial velocity variations caused by what is now a white dwarf companion are also expected. Although these properties may be found individually in normal stars, their presence alone is not an indication of the blue straggler status; when they all occur together, however, it is a strong sign in favor of this scenario (Rocha-Pinto et al 2002).…”

Section: Introductionmentioning

confidence: 93%

HIP 10725: The first solar twin/analogue field blue straggler

Schirbel

Meléndez

Karakas

et al. 2015

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Context. Blue stragglers are easy to identify in globular clusters, but are much harder to identify in the field. Here we present the serendipitous discovery of one field blue straggler, HIP 10725, that closely matches the Sun in mass and age, but with a metallicity slightly lower than solar. Aims. We characterise the solar twin/analogue HIP 10725 to assess whether this star is a blue straggler. Methods. We employed spectra with high resolution (R ∼ 10 5 ) and high signal-to-noise ratio (330) obtained with UVES at the VLT to perform a differential abundance analysis of the solar analogue HIP 10725. Radial velocities obtained by other instruments were also used to check for binarity. We also studied its chromospheric activity, age, and rotational velocity. Results. HIP 10725 is severely depleted in beryllium ([Be/H] ≤ −1.2 dex) for its stellar parameters and age. The abundances relative to solar of the elements with Z ≤ 30 show a correlation with condensation temperature, and the neutron capture elements produced by the s-process are greatly enhanced, while the r-process elements seem normal. We found its projected rotational velocity (v sin i = 3.3 ± 0.1 km s −1 ) to be significantly higher than solar and incompatible with its isochrone-derived age. Radial velocity monitoring shows that the star has a binary companion. Conclusions. Based on the high s-process element enhancements and low beryllium abundance, we suggest that HIP 10725 has been polluted by mass transfer from an AGB star that probably had an initial mass of about 2 M . The radial velocity variations suggest the presence of an unseen binary companion, probably the remnant of a former AGB star. Isochrones predict a solar-age star, but this disagrees with the high projected rotational velocity and high chromospheric activity. We conclude that HIP 10725 is a field blue straggler, rejuvenated by the mass-transfer process of its former AGB companion.

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“…Finally, Rocha-Pinto et al (2002) classifies ε Indi A as a "chromospherically young, kinematically old" star based on the disagreement between the age from activity indicators and the observed space velocities. They find a chromospheric age of 0.39 Gyr, but note that ε Indi A has no obvious Li i absorption line and so argue that it is an older star than activity suggests.…”

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

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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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Chromospherically young, kinematically old stars

Cited by 34 publications

References 51 publications

Age distribution of the central stars of galactic disk planetary nebulae

Age distribution of the central stars of galactic disk planetary nebulae

HIP 10725: The first solar twin/analogue field blue straggler

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

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