J/ApJ/906/133 HST UV/optical photometry in NGC 1978 (Li+, 2021)
Multiple Stellar Populations at Less-evolved Stages; Detection of Chemical
Variations among Main-sequence Dwarfs in NGC 1978.
Li C., Tang B., Milone A.P., de Grijs R., Hong J., Yang Y., Wang Y.
<Astrophys. J., 906, 133 (2021)>
=2021ApJ...906..133L 2021ApJ...906..133L
ADC_Keywords: Clusters, globular; Photometry, ultraviolet; Optical;
Stars, dwarfs; Photometry, HST
Keywords: Stellar populations ; Star clusters ; Large Magellanic Cloud ;
Hertzsprung-Russell diagram ; G dwarf stars ; M dwarf stars
Abstract:
Multiple stellar populations (MPs) with different chemical
compositions are not exclusive features of old globular clusters
(older than 10Gyr). Indeed, recent studies reveal that younger
clusters (∼2-6Gyr-old) in the Magellanic Clouds also exhibit
star-to-star chemical variations among evolved stars. However, whether
MPs are present among less-evolved dwarfs of these intermediate-age
clusters is still unclear. In this work, we search for chemical
variations among GK-type dwarfs in the ∼2Gyr old cluster NGC1978,
which is the youngest cluster with MPs. We exploit deep ultraviolet
and visual observations from the Hubble Space Telescope to constrain
the nitrogen (N) and oxygen (O) variations among main-sequence (MS)
stars. To do this, we compare appropriate photometric diagrams that
are sensitive to N and O with synthetic diagrams of simple stellar
populations and MPs. We conclude that the G- and K-type MS stars in
NGC 1978 host MPs. Our statistical analysis shows that the fraction of
N-rich stars ranges from ∼40% to ∼80%, depending on the detailed
distributions of N and O.
Description:
Our data sets are derived from two observational programs observed
through the HST's Ultraviolet and Visible Channel (CENTER aperture) of
the Wide Field Camera 3 (UVIS-CENTER/WFC3); they are programs with an
ID of General Observer (GO)-14069 and GO-15630 (PI: N.Bastian).
Objects:
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RA (2000) DE Designation(s)
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05 28 45.33 -66 14 12.0 NGC1978 = NGC 1978
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig2.dat 63 25071 CF275W,F343N,F438W vs. F814W diagram of NGC 1978
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See also:
J/MNRAS/403/996 : Clusters and associations in SMC and LMC (Bonatto+, 2010)
J/MNRAS/430/676 : Massive clusters in the LMC (Baumgardt+, 2013)
J/A+A/607/A135 : NGC104, 6121 & 6809 AGB & RGB stars Na abund. (Wang+, 2017)
Byte-by-byte Description of file: fig2.dat
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Bytes Format Units Label Explanations
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1- 8 F8.5 deg RAdeg [82.1/82.3] Right Ascension, decimal degree (J2000)
10- 18 F9.5 deg DEdeg [-66.3/-66.2] Declination, decimal degree (J2000)
20- 27 F8.5 mag F275W [16.2/35.7] F275W UVIS-CENTER/WFC3 Vega mag (1)
29- 36 F8.5 mag F343N [16.3/31.2] F343N UVIS-CENTER/WFC3 Vega mag (1)
38- 45 F8.5 mag F438W [17.1/27.8] F438W UVIS-CENTER/WFC3 Vega mag (1)
47- 54 F8.5 mag F814W [15.9/25.1] F814W UVIS-CENTER/WFC3 Vega mag (1)
56- 63 F8.5 mag DColo [-0.13/0.29] Color variation correction (2)
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Note (1): Center apperture
Note (2): Section 2 and Milone+, 2012A&A...540A..16M 2012A&A...540A..16M
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 19-May-2022