2001A&A...374.1017P


C.D.S. - SIMBAD4 rel 1.7 - 2021.03.07CET03:57:42

2001A&A...374.1017P - Astronomy and Astrophysics, volume 374, 1017-1029 (2001/8-2)

Lithium in the intermediate age cluster NGC 3680: Following. Li evolution along the C-M diagram.

PASQUINI L., RANDICH S. and PALLAVICINI R.

Abstract (from CDS):

We present an analysis of high resolution spectroscopic observations (R∼30000, S/N=60-150) of 24 members of the intermediate age (∼1.5Gyr) open cluster NGC 3680, covering all regions of the cluster colour-magnitude (C-M) diagram where cluster members are known to exist. These observations represent in many aspects challenges to our understanding of stellar interior and mixing. Four main sequence G stars have, within the errors, the same Li abundance, 0.3dex lower than similar stars in the ∼1Gyr younger Hyades but comparable with those observed in the coeval cluster IC 4651. The cluster shows a clear Li-dip located around the turn-off; two stars on the upper part of the turn-off are out of the dip and reach solar system meteoritic Li abundances. Just above the turn-off, in a very small range of magnitudes (∼0.2 in V), a factor of ∼5 Li depletion occurs. This sudden decrease explains puzzling results recently obtained on field subgiants but it is not at all reproduced by standard (e.g. no rotation, no diffusion) models, whereas it is in somewhat better agreement with the predictions of recent models which include rotational mixing and atomic diffusion. Out of the six cluster giants, one is probably a binary; of the remaining five single cluster members, three have a Li abundance logn(Li)∼1.1 while two have Li abundances from a factor 6 to more than a factor 30 lower than the other three. The star with no detected Li is the coolest and most luminous object in the sample and is most likely an AGB star; the other has instead a similar magnitude and effective temperature as the three more Li rich giants. The reasons for this difference in Li abundance among otherwise similar stars can be ascribed either to differential depletion during main-sequence or post-main sequence evolution, possibly induced by rotation, or to differences in the evolutionary status of these evolved stars. By comparing our results with those found for clusters of similar age and for field stars, we find that none of the possible scenarios gives a fully satisfactory explanation if the present population of NGC 3680 giants reflect the expected ratio of clump vs. first-ascent RGB stars. If the more abundant Li-rich giants in NGC 3680 are indeed clump giants, their relatively high Li content requires that Li is produced, or brought to the surface, between the tip of the RGB and the clump, which is not consistent with observations of the similar age cluster NGC 752, where the more abundant, presumably clump giants have low Li abundances. Finally, we have used our spectra to determine the metallicity of the cluster giants, finding [Fe/H]=-0.17±0.12. This value is in very good agreement with that derived from spectral indexes analysis, but substantially lower than the value inferred from Stroemgren photometry.

Abstract Copyright:

Journal keyword(s): stars: abundances - stars: evolution - open clusters: individual: NGC 3680

CDS comments: Table 1. In column 1 : running number is Cl* NGC 3680 AHTC, E is NGC 3680. In ref list 1996A&AS.118.407N instead of 1996A&AS.98.477N.

Simbad objects: 34

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Number of rows : 34

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 NGC 752 OpC 01 57 41 +37 47.1           ~ 551 0
2 * gam Tau ** 04 19 47.6038491 +15 37 39.515422 5.46 4.64 3.65 4.83   G9.5IIIabCN0.5 520 0
3 Cl Melotte 25 OpC 04 26 54.00 +15 52 00.0           ~ 2743 0
4 * tet01 Tau SB* 04 28 34.4960341 +15 57 43.849432 5.510 4.780 3.840 5.48   G9IIIFe-0.5 474 0
5 NGC 2682 OpC 08 51 18 +11 48.0           ~ 2088 0
6 Cl* NGC 3680 KGP 936 * 11 24 48.4544505332 -43 12 17.118980762   13.123 12.700     ~ 10 0
7 NGC 3680 70 * 11 25 03.4758510149 -43 17 26.301529094   15.220 14.651     ~ 20 0
8 NGC 3680 4 * 11 25 06.3253245448 -43 15 49.348665772   13.45 12.95     ~ 12 0
9 Cl* NGC 3680 KGP 1133 * 11 25 11.6994252846 -43 06 30.956503893   14.573 14.006     ~ 10 0
10 CD-42 6963 * 11 25 16.1744259582 -43 14 24.077225710   11.93 10.78     ~ 34 0
11 NGC 3680 15 * 11 25 18.2481365068 -43 11 49.655050623   13.05 12.54     ~ 16 0
12 NGC 3680 23 * 11 25 32.3253448361 -43 15 10.741842965   14.70 14.06     ~ 14 0
13 NGC 3680 10 * 11 25 32.9773799649 -43 16 50.132639083   13.35 12.91     ~ 17 0
14 NGC 3680 24 * 11 25 34.3431632440 -43 15 21.453638390   14.48 13.92     ~ 16 0
15 Cl* NGC 3680 BFK 125 * 11 25 34.5329324709 -43 15 10.470979188   14.118 13.685     ~ 13 0
16 NGC 3680 38 * 11 25 35.8306403819 -43 11 21.116962126   13.00 12.47     ~ 18 0
17 NGC 3680 25 * 11 25 35.8587071570 -43 15 14.893054279     13.68     ~ 14 0
18 Cl* NGC 3680 BFK 116 * 11 25 36.96 -43 14 21.4   13.29 12.77     ~ 10 0
19 NGC 3680 OpC 11 25 38 -43 14.6   8.40 7.6     ~ 293 0
20 CD-42 6977 * 11 25 38.0643755759 -43 16 06.376798739   12.1 10.8     ~ 36 0
21 NGC 3680 35 * 11 25 38.1499561891 -43 13 27.165693589   13.67 13.17     ~ 18 0
22 CD-42 6976 * 11 25 38.6652318702 -43 13 58.788375927   11.56 10.69     G0V 28 0
23 NGC 3680 36 * 11 25 38.81 -43 12 54.1   14.00 13.44     ~ 11 0
24 NGC 3680 37 * 11 25 41.1598832427 -43 12 09.103015295   13.59 13.13     ~ 14 0
25 NGC 3680 30 * 11 25 41.2060330836 -43 14 32.515460924   14.17 13.63     ~ 13 0
26 NGC 3680 31 * 11 25 41.9525965732 -43 14 03.459689443   13.68 13.22     ~ 12 0
27 NGC 3680 32 * 11 25 47.27 -43 14 11.0   13.44 12.95     ~ 11 0
28 CD-42 6981 * 11 25 48.5315004431 -43 09 52.527192273   12.043 10.886 10.08 9.829 ~ 44 0
29 CD-42 6983 * 11 25 49.9064942749 -43 12 15.701561979   11.3 10.02     K0III 33 0
30 NGC 3680 43 * 11 25 55.0228688836 -43 10 05.028734599   12.95 12.50     ~ 17 0
31 NGC 3680 60 * 11 26 20.7065618739 -43 13 07.466176954   14.99 14.36     ~ 25 0
32 NGC 3680 53 * 11 26 36.4328101278 -43 15 13.915780288   11.8 10.7     K1IV 26 0
33 IC 4651 OpC 17 24 49 -49 56.0           ~ 316 0
34 NGC 7789 OpC 23 57 24 +56 42.5   7.68 6.7     ~ 462 0

    Equat.    Gal    SGal    Ecl

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2021.03.07-03:57:42

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