J/MNRAS/498/4472 Leveraging HST with MUSE I - NGC 1978 (Saracino+, 2020)
Leveraging HST with MUSE.
I. Sodium abundance variations within the 2-Gyr-old cluster NGC 1978.
Saracino S., Kamann S., Usher C., Bastian N., Martocchia S., Lardo C.,
Latour M., Cabrera-Ziri I., Dreizler S., Giesers B., Husser T.-O.,
Kacharov N., Salaris M.
<Mon. Not. R. Astron. Soc., 498, 4472-4480 (2020)>
=2020MNRAS.498.4472S 2020MNRAS.498.4472S (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Clusters, globular ; Magellanic Clouds ; Colors ;
Abundances, [Fe/H] ; Radial velocities ; Photometry, HST ;
Spectra, optical
Keywords: techniques: photometric - techniques: spectroscopic -
galaxies: star clusters: individual: NGC 1978
Abstract:
Nearly all of the well-studied ancient globular clusters (GCs), in the
Milky Way and in nearby galaxies, show star-to-star variations in
specific elements (e.g. He, C, N, O, Na, and Al), known as 'multiple
populations' (MPs). However, MPs are not restricted to ancient
clusters, with massive clusters down to ∼2Gyr showing signs of
chemical variations. This suggests that young and old clusters share
the same formation mechanism but most of the work to date on younger
clusters has focused on N variations. Initial studies even suggested
that younger clusters may not host spreads in other elements beyond N
(e.g. Na), calling into question whether these abundance variations
share the same origin as in the older GCs. In this work, we combine
Hubble Space Telescope (HST) photometry with Very Large Telescope
(VLT)/Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy of a large
sample of red giant branch (RGB) stars (338) in the Large Magellanic
Cloud cluster NGC 1978, the youngest globular to date with reported
MPs in the form of N spreads. By combining the spectra of individual
RGB stars into N-normal and N-enhanced samples, based on the
'chromosome map' derived from HST, we search for mean abundance
variations. Based on the NaD line, we find a Na difference of
Δ[Na/Fe]=0.07±0.01 between the populations. While this
difference is smaller than typically found in ancient GCs (which may
suggest a correlation with age), this result further confirms that the
MP phenomenon is the same, regardless of cluster age and host galaxy.
As such, these young clusters offer some of the strictest tests for
theories on the origin of MPs.
Description:
This work is based on two HST proposals (GO-14069 and GO-15630, PI: N.
Bastian) composed of near-UV and optical images obtained through the
Wide Field Camera 3 (WFC3) UVIS channel as part of our LMC/SMC survey
of star clusters. In particular, observations in the wide filters
F275W, F336W, F438W, and F814W and in the narrow filter F343N are
available for NGC 1978.
The photometric analysis of the data has been performed using DAOPHOT
IV (Stetson 1987PASP...99..191S 1987PASP...99..191S), and the cross-correlation software
CATAXCORR (Montegriffo et al. 1995MNRAS.276..739M 1995MNRAS.276..739M). The procedure
adopted is standard and has been extensively described in previous
papers of our group (see Martocchia et al. 2018MNRAS.473.2688M 2018MNRAS.473.2688M;
Saracino et al. 2020MNRAS.493.6060S 2020MNRAS.493.6060S as examples).
MUSE observations of NGC 1978 were obtained during two nights, 2019
November 29 and 2019 December 26, in the course of program 0104.D-0257
(PI: Kamann). Each night four 660-s exposures were observed. In
between individual exposures, derotator offsets of 90° were
applied. The seeing during the observations (as measured on the
reduced data) was typically 0.8arcsec.
Objects:
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RA (ICRS) DE Designation(s)
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05 28 45.32 -66 14 12.0 NGC 1978 = ESO 85-90 = KMHK 944
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 134 175 Photometric and spectroscopic information of
the RGB MUSE targets used for the analysis of
NGC 1978
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID [1/175] Internal object identifier
5- 14 F10.7 deg RAdeg Right ascension (J2000)
16- 26 F11.7 deg DEdeg Declination (J2000)
28- 49 F22.19 mag colour F275W-F814W colour
51- 71 F21.18 mag pscolour ΔF275W,F343N,F438W pseudo-colour
73- 83 F11.8 [-] [Fe/H] Fe/H abundance ratio
85- 94 F10.8 [-] e_[Fe/H] Error on [Fe/H]
96- 107 F12.8 km/s RV Radial velocity
109- 118 F10.8 km/s e_RV Error on RV
120- 130 F11.8 --- S/N Signal to noise ratio
132 I1 --- Nexp Number of individual exposures
134 I1 --- Pop Population (P1 or P2) (1)
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Note (1): Population as follows:
1 = The first population is characterized by stars with solar-scaled N
abundance, and is located in the bottom right-hand part of the
chromosome map (see Figure 3)
2 = The second population is populated by N enhanced stars and occupies the
top left-hand region of the chromosome map (see Figure 3)
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History:
From electronic version of the journal
References:
Martocchia et al., Paper II 2020MNRAS.499.1200M 2020MNRAS.499.1200M
(End) Ana Fiallos [CDS] 07-Aug-2023