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 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:
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RA (2000) DE Designation(s)
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11 25.7 -43 15 NGC 3680
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 59 120 Summary data for 120 stars in the field of NGC 3680
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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
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Bytes Format Units Label Explanations
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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
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Acknowledgements:
Birgitta Nordstrom
(End) Patricia Bauer [CDS] 09-Jun-1997