Three Li-rich K Giants: IRAS 12327-6523, 13539-4153, and 17596-3952

Reddy, Bacham E.; Lambert, David L.

doi:10.1086/430190

Cited by 50 publications

(47 citation statements)

References 23 publications

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“…All five stars have lithium abundances higher than 1.5 dex, and are, therefore, to be considered as Li-rich. Three of them present abundances exceeding 2.2 dex and one, namely #313132, belongs to the group of the rare super Li-rich giants (see, e.g., Balachandran et al 2000;Domínguez et al 2004;Reddy & Lambert 2005;Monaco & Bonifacio 2008;Kumar & Reddy 2009). …”

Section: Discussionmentioning

confidence: 99%

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Lithium-rich giants in the Galactic thick disk

Monaco

Villanova

Bidin

et al. 2011

A&A

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Context. Lithium is a fragile element, which is easily destroyed in the stellar interior. The existence of lithium-rich giants still represents a challenge for stellar evolution models. Aims. We have collected a large database of high-resolution stellar spectra of 824 candidate thick-disk giants having 2 MASS photometry and proper motions measured by the Southern Proper-Motion Program (SPM). In order to investigate the nature of Li-rich giants, we searched this database for giants presenting a strong Li I resonance line. Methods. We performed a chemical abundance analysis on the selected stars with the MOOG code along with proper ATLAS-9 model atmospheres. The iron content and atmospheric parameters were fixed by using the equivalent width of a sample of Fe lines. We also derive abundances for C, N, and O and measure or derive lower limits on the 12 C/ 13 C isotopic ratios, which is a sensible diagnostic of the stars evolutionary status. Results. We detected five stars with a lithium abundance higher than 1.5, i.e. Li-rich according to the current definition. One of them (SPM-313132) has A(Li) > 3.3 and, because of this, belongs to the group of the rare super Li-rich giants. Its kinematics makes it a likely thin-disk member and its atmospheric parameters are compatible with it being a 4 M star either on the red giant branch (RGB) or the early asymptotic giant branch. This object is the first super Li-rich giant detected at this phase. The other four are likely low-mass thick-disk stars evolved past the RGB luminosity bump, as determined from their metallicities and atmospheric parameters. The most evolved of them lies close to the RGB-tip. It has A(Li) > 2.7 and a low 12 C/ 13 C isotopic ratio, close to the cool bottom processing predictions.

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Section: Discussionmentioning

confidence: 99%

“…This latter can cause blue-shifted asymmetric H α profiles or the presence of additional blue-shifted absorption lines in the Na doublet (Na D) lines Drake et al 2002;Reddy & Lambert 2005) in the stellar spectra. Figures 6 and 7 present a sample of the spectra obtained for the target stars in the H α and Na D lines regions.…”

Section: Discussionmentioning

confidence: 99%

Lithium-rich giants in the Galactic thick disk

Monaco

Villanova

Bidin

et al. 2011

A&A

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“…In this study, stars in binaries appear to exhibit 0.25 dex less surface lithium than A&A 551, A2 (2013) singles, as one would expect if the depletion mechanism is rotation dependent. On the other hand, there is a small group of single K-giants which show rapid rotation and also larger than expected Li abundances (e.g., Reddy & Lambert 2005;Drake et al 2002;Fekel & Balachandran 1993, and references therein). Charbonnel & Balachandran (2000) concluded that relatively high Li abundance is not abnormal for a low-mass star on the red-giant branch (RGB).…”

Section: Introductionmentioning

confidence: 98%

Doppler imaging of stellar surface structure

Kővári¹,

Korhonen²,

Strassmeier³

et al. 2013

A&A

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Aims. We present the first Doppler imaging study of the two rapidly rotating, single K-giants DP CVn and DI Psc in order to study the surface spot configuration and to pinpoint their stellar evolutionary status. Methods. Optical spectroscopy and photometry were used to determine the fundamental astrophysical properties. Doppler imaging was applied to recover the surface temperature distribution for both stars, while photometric light-curve inversions were carried out for studying the long-term changes of the surface activity of DP CVn. Surface differential rotation of DP CVn was estimated from cross-correlating the available subsequent Doppler reconstructions separated by roughly one rotation period. Results. Both stars appear to have higher than normal lithium abundance, LTE log n of 2.28 (DP CVn) and 2.20 (DI Psc), and are supposed to be located at the end of the first Li dredge-up on the RGB. Photometric observations reveal rotational modulation with a period of 14.010 d (DP CVn) and 18.066 d (DI Psc). Doppler reconstructions from the available mapping lines well agree in the revealed spot patterns, recovering rather low latitude spots for both stars with temperature contrasts of ΔT ≈ 600−800 K below the unspotted photospheric background. Spots at higher latitudes are also found but either with less contrast (DP CVn) or with smaller extent (DI Psc). A preliminary antisolar-type differential rotation with α = −0.035 is found for DP CVn from cross-correlating the subsequent Doppler images. Long-term photometric analysis supports the existence of active longitudes, as well as the differential rotation.

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“…Li-rich giants are already rare, just around 1% (Brown et al 1989), but the number of super-meteoritic Li-rich giants comes down to less than a dozen stars (e.g., de la Reza et al 1997;Balachandran et al 2000;Drake et al 2002;Reddy & Lambert 2005;Kumar & Reddy 2009;Kumar et al 2011, and further references therein).…”

Section: Introductionmentioning

confidence: 99%

Evidence for enhanced mixing on the super-meteoritic Li-rich red giant HD 233517

Strassmeier

Carroll

Weber

et al. 2015

A&A

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Context. HD 233517 is among the most Li-rich stars in the sky. It is a rapidly rotating, single K giant thought to be on its first ascent on the red giant branch. The star has also the highest known infrared excess among any of the known first-ascent giants. Aims. We revisit the physical parameters of the system and aim to map its surface temperature distribution. Methods. New time-series photometry and high-resolution spectroscopy were obtained with our robotic facilities STELLA and Amadeus Automatic Photoelectric Telescope (APT) in 2007-2011. Inverse line-profile modelling is performed on a total of 167 échelle spectra and six Doppler images are presented.Results. Light and radial-velocity variations suggest a stellar rotation period of 47.6 ± 0.3 d. The atmospheric parameters agree with previous studies and verify a super-meteoritic log 7 Li abundance of 4.29 ± 0.10 with undetected 6 Li, while the metals are generally deficient by -0.4 dex with respect to the Sun. We determine a lower than normal isotopic carbon ratio of 12 C/ 13 C = 9 +4 −2 . Our Doppler images indicate warm and cool spots with an average temperature contrast of just ±65 K with respect to the effective temperature.Doppler maps from Li i 670.78 reveal practically identical surface morphology, with a higher average contrast of ±160 K and errors that are five times larger. Reconstructions with simultaneously 1617 and 3007 spectral lines showed both a signal degradation with respect to our 56-line final image. An error analysis indicates an average temperature error per surface pixel of just ±4 K. Conclusions. HD 233517 appears to be an old (≈10-Gyr) single 0.95-M giant currently undergoing mild mass loss in the form of a wind. The cool and warm photospheric features are interpreted to be merely locations of suppressed and enhanced convection, respectively, probably intermingled by a yet undetected weak magnetic field. The low carbon-isotope ratio is indicative of extra mixing rather than of an engulfing event. We tentatively conclude that HD 233517 operates an enhanced non-axisymmetric mixing process that leads to an inhomogeneous super-granulation pattern on the surface in form of large cool and warm features.

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Three Li-rich K Giants: IRAS 12327-6523, 13539-4153, and 17596-3952

Cited by 50 publications

References 23 publications

Lithium-rich giants in the Galactic thick disk

Lithium-rich giants in the Galactic thick disk

Doppler imaging of stellar surface structure

Evidence for enhanced mixing on the super-meteoritic Li-rich red giant HD 233517

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