J/AJ/157/49 Stroemgren photometry in the field of NGC 1978 (Piatti+, 2019)
Search for a metallicity spread in the multiple population Large Magellanic
Cloud cluster NGC 1978.
Piatti A.E., Bailin J.
<Astron. J., 157, 49-49 (2019)>
=2019AJ....157...49P 2019AJ....157...49P (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Clusters, globular ; Stars, giant ;
Photometry, uvby
Keywords: galaxies: individual: LMC - galaxies: star clusters: general
Abstract:
We report on the spread of [Fe/H] values in the massive Large Magellanic
Cloud cluster NGC 1978, recently confirmed to harbor multiple populations
of nearly the same age. We used accurate Stroemgren photometry of carefully
selected cluster red giant branch stars along with a high-dispersion
spectroscopy-based calibration of the metallicity-sensitive index m1.
Once we accounted for the photometry quality, assessed from extensive
artificial star tests to trace the photometric uncertainties as a function
of the position of the cluster's center as well as the stellar brightness,
and those from the metallicity calibration, we found that NGC 1978 exhibits
a small metallicity spread of 0.035 dex (±0.019-0.023), depending on
whether stars with individual σ[Fe/H]=<0.15 dex or those located
in the cluster's outer areas are considered. Such a spread in [Fe/H]
is consistent with a cluster formation model with self-enrichment, if
mass loss higher than 90% due to stellar evolutionary and galactic tidal
effects is assumed. Nevertheless, scenarios in which the apparent [Fe/H]
variation reflects CN abundance anomalies or less extreme mass-loss models
with environmentally dependent self-enrichment should not be ruled out.
Description:
We downloaded publicly available Stroemgren vby images from the National
Optical Astronomy Observatory (NOAO) Science Data Management (SDM) Archives
(http//www.noao.edu/sdm/archives.php). They were obtained, along with
suitable calibration and standard field images, as part of an observational
program aiming at studying the chemical evolution of the LMC from clusters
and field stars (program ID: SO2008B-0917, PI: Pietrzynski). The images
were obtained on the night of 2008 January 18 with the SOAR Optical Imager
(SOI) mounted on the 4.1 m Southern Astrophysical Research (SOAR) telescope
(FOV=5.25'x5.25', scale=0.154"/px), and are of excellent quality
(typical FWHM∼0.6"). They consist of one exposure of 350, 140, and 90 s
in the v, b, and y filters, respectively. We obtained instrumental vby
magnitudes of stars located in the field of NGC 1978 using the stand-alone
versions of DAOPHOT, ALLSTAR, DAOMATCH, and DAOMASTER routine packages
(Stetson et al. 1990ASPC....8..289S 1990ASPC....8..289S). The magnitudes were derived from
point-spread function (PSF) fits performed using previously generated
spatially quadratically varying PSFs.
Objects:
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RA (ICRS) DE Designation(s)
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05 23 34.6 -69 45 22 Large Magellanic Cloud = NAME LMC
05 28 45.33 -66 14 12.0 NGC 1978 = ESO 85-90
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 69 1194 Stroemgren photometry of stars in the field
of NGC 1978
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See also:
J/AJ/136/375 : Chemical composition of LMC red giants (Mucciarelli+, 2008)
J/AJ/142/48 : LMC star clusters structural parameters (Werchan+, 2011)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Star [1/1194] Star number
6- 14 F9.6 deg RAdeg Right Ascension in decimal degrees (J2000)
16- 25 F10.6 deg DEdeg Declination in decimal degrees (J2000)
27- 31 F5.1 arcsec r [2.8/169] Distance to the cluster center
33- 38 F6.3 mag Vmag [14.952/22.146] Stroemgren V band magnitude
40- 44 F5.3 mag e_Vmag [0.002/0.299] Uncertainty in Vmag
46- 50 F5.3 mag b-y [0.103/1.9] Stroemgren b-y color index
52- 56 F5.3 mag e_b-y [0.003/0.327] Uncertainty in b-y
58- 63 F6.3 mag m1 [-0.5/1.137] Stroemgren metallicity-sensitive
index m1
65- 69 F5.3 mag e_m1 [0.006/0.611] Uncertainty in m1
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Acknowledgements:
Andres Eduardo Piatti, andres(at)oac.unc.edu.ar
(End) Tiphaine Pouvreau [CDS] 15-Jul-2019