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J/A+A/322/460       NGC 3680 photometry and radial velocities (Nordstrom+ 1997)

Critical tests of stellar evolution in open clusters. II. Membership, duplicity, and stellar and dynamical evolution in NGC 3680 Nordstrom B., Andersen J., Andersen M.I. <Astron. Astrophys. 322, 460 (1997)> =1997A&A...322..460N
ADC_Keywords: Clusters, open ; Photometry ; Radial velocities Keywords: Stars: evolution; fundamental parameters; HR diagram; kinematics; luminosity function; mass function - Open clusters and associations: NGC 3680 Abstract: Based on new, accurate photometry, radial velocities, and proper motions for the intermediate-age open cluster NGC 3680, we identify individual single and binary cluster members and field stars in the colour-magnitude diagram (CMD). This basic step turns out to be crucial for a proper understanding of the cluster CMD: ∼60% of the stars are found to be field stars, and over 50% of the cluster stars are binaries. No bona fide cluster star is found more than 1.5mag below the turnoff, and cluster stars below 1.4M are only found in binary systems. The total present mass of NGC 3680 is ∼100M, excluding any as yet unseen stellar remnants, and its half-mass radius is 3.3' (1.2pc). Comparison with plausible IMFs indicates that only ∼3% of the original stars and ≲10% of the mass now survive, ∼30% of the initial mass being in the form of massive stars that have now completed their evolution, and ∼60% in low-mass stars which may now be located in a distant cluster halo or perhaps have been lost entirely. The single main-sequence cluster members form an extremely tight sequence in the CMD, with E(b-y)=0.034 and [Fe/H]=+0.11. A direct fit to the Hyades main sequence yields (m-M)0=10.5±0.2 for NGC 3680. Isochrones from several stellar models have been fit to the cluster sequence. When based on consistent uvby colour transformations and the above cluster parameters, these fits are very stable and show that standard models are not acceptable for stars with the turnoff mass of NGC 3680. Overshooting models perform much better, but further refinement of the overshooting formalism seems to be needed. The age derived for NGC 3680 is 1.45±0.3Gyr. The limiting factor in a precise comparison of theory and observations is now the transformation from theoretical to observed parameters, particularly (broad-band) colours. Objects: ---------------------------------------------------------- RA (2000) DE Designation(s) ---------------------------------------------------------- 11 25.7 -43 15 NGC 3680 ---------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 59 120 Summary data for 120 stars in the field of NGC 3680
See also: J/A+AS/118/407 : CCD photometry & velocities of NGC 3680 stars, Paper I (Nordstroem+ 1996) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 5 A5 --- Id Identification number (see paper) 7- 12 F6.3 mag Vmag ? V magnitude 14- 18 F5.3 mag b-y ? b-y colour index 19 A1 --- n_b-y [M] M for missing entry 22- 26 F5.3 mag B-V ? B-V colour index 27 A1 --- n_B-V [M] M for missing entry 28- 33 F6.2 km/s RV ? Mean radial velocity 34 A1 --- n_RV [M] M for missing entry 36- 40 F5.2 km/s e_RV ? Mean error of mean radial velocity 41 A1 --- neRV [M] M for missing entry 43- 46 F4.1 --- pRV ? Radial velocity membership probability (%) 47 A1 --- n_pRV [M] M for missing entry 49- 50 I2 --- pPM ? Proper motion membership probability (%) 51 A1 --- n_pPM [M] M for missing entry 53- 56 A4 --- Note1 Remarks on binary stars 57- 59 A3 --- Note2 Remarks on final membership assignment
Acknowledgements: Birgitta Nordstrom
(End) Patricia Bauer [CDS] 09-Jun-1997
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