J/A+A/475/539 BV photometry and Li abundances in NGC3960 (Prisinzano+, 2007)
Lithium abundances in the old open cluster NGC 3960 from VLT/FLAMES
observations.
Prisinzano L., Randich S.
<Astron. Astrophys. 475, 539 (2007)>
=2007A&A...475..539P 2007A&A...475..539P
ADC_Keywords: Clusters, open ; Photometry, UBV ; Abundances
Keywords: stars: abundances - stars: evolution -
Galaxy: open clusters and associations: individual: NGC 3960
Abstract:
Old open clusters are very useful targets to investigate mechanisms
responsible for lithium (Li) depletion during the main sequence.
Comparison of the Li abundances in clusters of different age allows us
to understand the efficiency of the Li destruction process. To
determine the membership and Li abundance in a sample of candidate
members of the open cluster NGC 3960 (age ∼1Gyr), aiming to fill the
gap between 0.6 and 2Gyr in the empirical description of the behavior
of the average Li abundance as a function of the stellar age. We use
VLT/FLAMES Giraffe spectra to determine the radial velocities and thus
the membership of a sample of 113 photometrically selected candidate
cluster members. From the analysis of the Li line we derive Li
abundances for both cluster members and non-members. 39 stars have
radial velocities consistent with membership, with an expected
fraction of contaminating field stars of about 20%. Li is detected in
29 of the radial velocity members; we consider these stars as cluster
members, while we make the reasonable assumption that the remaining 10
radial velocity members without Li are among the contaminating stars.
Li abundances of the stars hotter than about 6000K are similar to
those of stars in the Hyades, while they are slightly smaller for
cooler stars. This confirms that NGC 3960 is older than the Hyades.
The average Li abundance of stars cooler than about 6000K indicates
that the Li Pop. I plateau might start at ∼1Gyr, rather than 2Gyr,
which is the upper limit previously derived in the literature. We also
find that the fraction of field stars with high Li abundance (>1.5) is
about one third of the whole sample, which is in agreement with
previous estimates. The fraction of contaminating field stars is
consistent with that previously derived by us from photometry.
Description:
The observations were carried out in Service Mode during February,
March and April 2004.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 135 113 Stellar parameters for the NGC 3960 stars
observed with GIRAFFE
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See also:
J/A+A/417/945 : BVI & JHK photometry of NGC 3960 (Prisinzano+, 2004)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- P04 Identification number of Prisinzano et al.,
Cat. J/A+A/417/945,
Cl* NGC 3960 PMS NNNNNN in Simbad (1)
8- 16 A9 --- Name Giraffe identification name, OC21-MNNN
18- 20 I3 --- Nsp Spectrum number
22- 33 F12.8 deg RAdeg Right ascension in decimal degrees (J2000)
35- 46 F12.8 deg DEdeg Declination in decimal degrees (J2000)
48- 53 F6.3 mag Vmag V magnitude
55- 59 F5.3 mag e_Vmag rms uncertainty on Vmag
61- 66 F6.3 mag Bmag B magnitude
68- 72 F5.3 mag e_Bmag rms uncertainty on Bmag
74- 79 F6.3 mag V0mag V magnitude corrected for differential
reddening
81- 86 F6.3 mag B0mag B magnitude corrected for differential
reddening
88- 93 F6.2 km/s RV Radial velocity
95- 99 F5.2 km/s e_RV rms uncertainty on RV
101 I1 --- Mmb [0/2] Membership flag based on RV:
0=non-member, 1=member, 2=binary
103-106 I4 K Teff Effective temperature computed for the
(B-V)0 colour index, corrected for
differential reddening
108-110 I3 K e_Teff rms uncertainty on Teff
112 A1 --- l_EW(Li) Limit flag on EW(Li)
113-115 I3 0.1pm EW(Li) ? Li equivalent width (in mÅ)
117-118 I2 0.1pm e_EW(Li) ? rms uncertainty on EW(Li)
120 A1 --- l_A(Li)LTE Limit flag on A(Li)LTE
121-124 F4.2 [-] A(Li)LTE ? LTE Li abundance (H=12, LTE model)
126 A1 --- l_A(Li)NLTE Limit flag on A(Li)NLTE
127-130 F4.2 [-] A(Li)NLTE ? NLTE Li abundance (H=12, non-LTE model)
132-135 F4.2 [-] e_A(Li)NLTE ? rms uncertainty on A(Li)NLTE
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Note (1): Numbers as in the second version of the table (13-Nov-2007)
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 13-Nov-2007