J/MNRAS/542/2768 NGC 1866 and NGC 1856 spectra (Kamann+, 2025)
Tracing stellar rotation in young massive LMC clusters.
Kamann S., Bastian N., Niederhofer F., Bellini A., Cabrera-Ziri I.,
Dreizler S., Goettgens F., Kozhurina-Platais V., Libralato M., Martens S.,
Saracino S.
<Mon. Not. R. Astron. Soc. 542, 2768 (2025)>
=2025MNRAS.542.2768K 2025MNRAS.542.2768K (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Associations, stellar ; Spectroscopy ;
Optical ; Radial velocities ; Rotational velocities
Keywords: techniques: imaging spectroscopy - stars: rotation -
galaxies: star clusters: individual: NGC 1856, NGC 1866
Abstract:
We present a detailed analysis of stellar rotation along the main
sequences of NGC 1866 and NGC 1856, two young (∼200-300Myr) massive
clusters in the Large Magellanic Cloud, using MUSE integral field
spectroscopy. Differences in stellar rotation have been proposed as an
explanation for the extended main sequence turn-offs and split main
sequences in these clusters. In agreement with this idea, we find
strong links between the photometric colours of the cluster stars and
their projected rotation velocities, Vsini. While stars blueward of
the split main sequences are characterized by a range of relatively
low spins, those with redder colours are fast rotators. Following a
statistical correction for inclination, we measure mean equatorial
velocities for the red main-sequence stars in both clusters of
Veq=300km/s, corresponding to 70-80% of the critical values predicted
for such stars by current stellar models. We discuss these findings in
the context of the different scenarios proposed to explain the stellar
rotation distributions of young massive clusters. We further
investigate whether the high rotation rates provide a natural
explanation for the high fractions of Be stars we observe in both
clusters, peaking at ≥50% at the turn-off. We argue that if ∼85% of
the critical rotation rate is high enough to trigger the formation of
a decretion disk, most upper main sequence stars in the clusters are
expected to become Be stars before leaving the main sequence.
Description:
We publish the individual stellar spectra extracted from the MUSE data cubes
as 1D FITS-images. Each FITS header contains basic information and quality
parameters about the spectrum at hand as HIERARCH keywords:
* HIERARCH STAR ID - Unique identifier of the star for which the spectrum was
extracted. Note that this is different from the ID in
the Niederhofer et al. (2024A&A...689A.162N 2024A&A...689A.162N,
Cat. J/A+A/689/A162) photometry
* HIERARCH STAR RA - Right ascension of the star.
* HIERARCH STAR DEC - Declination of the star.
* HIERARCH STAR MAG - Magnitude used as input for spectrum extraction.
* HIERARCH SPECTRUM SNRATIO - Estimated average signal-to-noise per spectral
pixel
* HIERARCH SPECTRUM MULTISTAR - Flag indicating if several stars contribute
flux
* HIERARCH SPECTRUM MAG F606W - F606W magnitude recovered from the extracted
spectrum
* HIERARCH SPECTRUM MAG F814W - F814W magnitude recovered from the extracted
spectrum
* HIERARCH SPECTRUM HALPHA EW - Equivalent width of the H-alpha line in
Angstrom
* HIERARCH SPECTRUM HALPHA EW ERR - Uncertainty of the H-alpha
equivalent width measurement
* HIERARCH SPECTRUM HBETA EW - Equivalent width of the H-beta line in
Angstrom
* HIERARCH SPECTRUM HBETA EW ERR - Uncertainty of the H-beta equivalent width
measurement
* HIERARCH SPECTRUM MAG ACCURACY - A quality control parameter ranging from 0
(bad) to 1 (good), derived by comparing
the recovered magnitude with the input
magnitude
For each cluster, we also publish a table containing the results of
the spectral analysis using Spexxy.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
ngc1856.dat 283 4406 Spectral analysis results for NGC 1856
ngc1866.dat 283 2531 Spectral analysis results for NGC 1866
spngc1856/* . 4406 NGC 1856 individual fits spectra
spngc1866/* . 2531 NGC 1866 individual fits spectra
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See also:
J/A+A/689/A162 : Astro-photometry of 23 LMC clusters (Niederhofer+, 2024)
J/A+A/618/A25 : Model stellar spectra for B to early-M (Allende Prieto+, 2018)
https://gitlab.gwdg.de/skamann/pampelmuse : PampelMuse spectrum extraction
software
https://github.com/thusser/spexxy : Spexxy spectral analysis software
Byte-by-byte Description of file: ngc1856.dat ngc1866.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 23 A23 --- FileName Name of FITS spectrum (1)
25- 44 F20.15 km/s Vel ?=0 Heliocentric line-of-sight velocity
(STAR.V)
46- 68 E23.17 km/s e_Vel ?=999 Nominal uncertainty of Vel measurement
(STAR.V.ERR)
70- 90 E21.16 km/s vsini ?=999 Projected stellar rotation velocity
(STAR.VSINI)
92-114 E23.17 km/s e_vsini ?=999 Nominal uncertainty of vsini
measurement (STAR.VSINI.ERR)
116-118 F3.1 --- epsilon [0.8] Constant linear limb-darkening
parameter adopted during spectral fit
(STAR.EPSILON)
120-138 F19.16 --- [Fe/H] Scaled-solar metallicity, either derived via
isochrone comparison or spectral fit
(STAR.FEH)
140-159 F20.17 --- e_[Fe/H] ? Nominal uncertainty for [Fe/H] when
derived via spectral fit (STAR.FEH.ERR)
161-163 F3.1 --- logVDOP [0] Constant microturbulence adopted during
spectral fit (STAR.LOG10VDOP)
165-183 F19.13 K Teff Effective temperature (STAR.TEFF)
185-207 E23.19 K e_Teff ? Nominal uncertainty of Teff measurement
(STAR.TEFF.ERR)
209-226 F18.16 [cm/s2] logg Surface gravity, either derived via
isochrone comparison or spectral fit
(STAR.LOGG)
228-230 F3.1 [cm/s2] e_logg [0] Nominal uncertainty for logg when
derived via spectral fit (STAR.LOGG.ERR)
232-236 A5 --- Success [False True] Flag indicating a formally
successful spexxy fit (Success)
238-258 F21.16 --- rchi2 Reduced chi square of spexxy fit (RedChi2)
260-265 A6 --- origin Type of spectral fit, depending on output of
isochrone comparison and emission-line
analysis (origin) (2)
267-271 A5 --- Be [False True] Flag indicating if star is
considered a Be star (be)
273-277 A5 --- shell [False True] Flag indicating if star is
considered a shell star (shell)
279-283 I5 --- N24Id [1906/80619]?=-1 ID of stari, within the
cluster, in Niederhofer et al.
(2024A&A...689A.162N 2024A&A...689A.162N, Cat. J/A+A/689/A162)
where available (Niederhofer.ID)
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Note (1): Spectra in subdirectory spngc1856 for ngc1856, spngc1866 for ngc1866.
Note (2): See Sec. 2.5 of paper for details
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Acknowledgements:
Sebastian Kamann, s.kamann(at)ljmu.ac.uk
(End) Patricia Vannier [CDS] 25-Aug-2025