J/A+A/566/A39 UBVI photometry of Melotte 66 (Carraro+, 2014)
Updated properties of the old open cluster Melotte 66:
searching for multiple stellar populations.
Carraro G., de Silva G., Monaco L., Milone A., Mateluna R.
<Astron. Astrophys. 566, A39 (2014)>
=2014A&A...566A..39C 2014A&A...566A..39C
ADC_Keywords: Clusters, open ; Photometry, CCD ; Photometry, UBVRI
Keywords: stars: abundances - open clusters and associations: general -
Galaxy: disk
Abstract:
Multiple generations of stars are routinely encountered in globular
clusters, but no convincing evidence has been found in Galactic open
clusters up to date.
In this paper we use new photometric and spectroscopic data to search
for multiple stellar population signatures in the old, massive open
cluster, Melotte 66. The cluster is know to have a red giant branch
wide in color, which could be an indication of metallicity spread.
Also the main sequence is wider than what expected from photometric
errors only. This evidence might be associated either with
differential reddening or with binaries. Both hypothesis have,
however, to be evaluated in detail before recurring to the presence of
multiple stellar populations.
New, high-quality, CCD UBVI photometry have been acquired to this aim,
together with high-resolution spectroscopy of seven clump stars,
complemented with literature data, thus doubling the number of clump
stars member of the cluster for which high-resolution spectroscopy is
available. All this new material is carefully analyzed in search for
any manifestation, either spectroscopic or photometric, of multiple
populations among the cluster stars. Our photometric study confirms
that the width of the main sequence close to the turn off point is
entirely accounted for by binary stars and differential reddening,
with no need to advocate more sofisticated scenarios, like metallicity
spread or multiple main sequences. By constructing synthetic
color-magnitude diagrams, we infer that the binary fraction has to be
as large as 30%, and their mass ratio in the range 0.6-1.0. As a
by-product of our simulations, we provide new estimates of the cluster
fundamental parameters. We measure a reddening E(B-V)=0.15±0.02,
and confirm the presence of a marginal differential reddening. The
distance to the cluster is 4.7+0.2-0.1kpc, and the age is
3.4±0.3Gyr, somewhat younger and better constrained than previous
estimates.
Our detailed abundance analysis reveals that, overall, Melotte 66
looks like a typical object of the old thin disk population, with no
significant spread in any of the chemical species we could measure.
Finally, we perform a photometric study of the blue straggler star
population, and argue that their number in Melotte 66 has been
significantly over-estimated in the past. The analysis of their
spatial distribution supports the scenario they are most probably
primordial binaries.
Description:
Photometric data in UBVI for stars in the field of the open cluster
Melotte 66. The observations were made at Las Campanas Observatory
on the nights between 2011-01-01 and 2011-01-07.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 80 3474 Melotte 66 UBVI photometry and astrometry
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See also:
J/A+A/283/911 : Abundances in NGC 2243 and Mel 66 (Gratton+, 1994)
J/PASP/106/486 : Mel 66 CCD photometry (Anthony-Twarog+, 1994)
J/A+A/488/943 : Abundances of giants in four Galactic clusters (Sestito+ 2008)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- ID [1/3474] Sequential number
6- 16 F11.7 deg RAdeg [[111.42/111.81] Right ascension (J2000.0)
18- 28 F11.7 deg DEdeg [-47.86/-47.46] Declination (J2000.0)
30- 35 F6.3 mag Vmag [9.7/24.3] Johnson V magnitude
37- 41 F5.3 mag e_Vmag Error in V magnitude
43- 48 F6.3 mag B-V Johnson (B-V) color
50- 54 F5.3 mag e_B-V Error in (B-V)
56- 61 F6.3 mag U-B Johnson (U-B) color
63- 67 F5.3 mag e_U-B Error in (B-V)
69- 74 F6.3 mag V-I Johnson-Cousins (V-I) color
76- 80 F5.3 mag e_V-I Error in (V-I)
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Acknowledgements:
Giovanni Carraro, gcarraro(at)eso.org
History;
* 22-Apr-2014: Original version
* 14-Jul-2016: Columns contain V-band magnitde and colors;
documentation fixed.
(End) Patricia Vannier [CDS] 22-Apr-2014