---
DOAJ_listed: '1'
OA_place: publisher
OA_type: diamond
PlanS_conform: '1'
_id: '21450'
abstract:
- lang: eng
text: Stellar wind mass loss of massive stars is often assumed to depend on their
metallicity Z. Therefore, evolutionary models predict that massive stars in lower-Z
environments are able to retain more of their hydrogen-rich layers and evolve
into brighter cool supergiants (cool SGs; Teff < 7 kK). Surprisingly, in galaxies
in the metallicity range 0.2 ≲ Z/Z⊙ ≲ 1.5, previous studies have not found a metallicity
dependence on the upper luminosity limit Lmax of cool SGs. Here, we add four galaxies
to the sample studied for this purpose with data from the Hubble Space Telescope
and the James Webb Space Telescope (JWST). Observations of the extremely metal-poor
dwarf galaxy I Zw 18 from JWST allow us to extend the studied metallicity range
down to Z/Z⊙ ≈ 1/40. For cool SGs in all studied galaxies, including I Zw 18,
we find a constant value of Lmax ≈ 105.6 L⊙, similar to literature results for
0.2 ≲ Z/Z⊙ ≲ 1.5. In I Zw 18 and the other studied galaxies, the presence of Wolf-Rayet
stars has been previously inferred. Although we cannot rule out that some of them
become intermediate-temperature objects, this paints a picture in which evolved
stars with L > 105.6 L⊙ burn helium as hot, helium-rich stars down to extremely
low metallicity. We argue that metallicity-independent late-phase mass loss would
be the most likely mechanism responsible for this. Regardless of the exact stripping
mechanism (winds or, for example, binary interaction), for the Early Universe
our results imply a limitation on black hole masses and a contribution of stars
born with M ≳ 30 M⊙ to its surprisingly strong nitrogen enrichment. We propose
a scenario in which single stars at low metallicity emit sufficiently hard ionizing
radiation to produce He II and C IV lines. In this scenario, late-phase metallicity-independent
mass loss produces hot, helium-rich stars. Due to the well-understood metallicity
dependence on the radiation-driven winds of hot stars, a window of opportunity
would open below 0.2 Z⊙, where self-stripped helium-rich stars can exist without
dense Wolf-Rayet winds that absorb hard ionizing radiation.
acknowledgement: "We thank our anonymous referee for carefully reading the manuscript
and providing a constructive report with helpful feedback. This work is based in
part on observations made with the NASA/ESA/CSA James Webb Space Telescope. The
data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope
Science Institute, which is operated by the Association of Universities for Research
in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations
are associated with program #1233. The specific observations analyzed can be accessed
via DOI: 10.17909/3c1d-6182. Moreover, this research is based in part on observations
made with the NASA/ESA Hubble Space Telescope obtained from the\r\nSpace Telescope
Science Institute, which is operated by the Association of Universities for Research
in Astronomy, Inc., under NASA contract NAS 5–26555. These observations are associated
with programs #13664, GO-10915, and DD-11307. This research was supported in part
by grant NSF PHY-2309135 to the Kavli Institute for Theoretical Physics (KITP).
LRP acknowledges support by grants PID2019-105552RB-C41 and PID2022-137779OB-C41
funded\r\nby MCIN/AEI/10.13039/501100011033 by “ERDF A way of making Europe”. LRP
acknowledges support from grant PID2022-140483NB-C22 funded by MCIN/AEI/10.13039/501100011033."
article_number: A116
article_processing_charge: No
article_type: original
arxiv: 1
author:
- first_name: Abel
full_name: Schootemeijer, Abel
last_name: Schootemeijer
- first_name: Ylva Louise Linsdotter
full_name: Götberg, Ylva Louise Linsdotter
id: d0648d0c-0f64-11ee-a2e0-dd0faa2e4f7d
last_name: Götberg
orcid: 0000-0002-6960-6911
- first_name: Norbert
full_name: Langer, Norbert
last_name: Langer
- first_name: Giacomo
full_name: Bortolini, Giacomo
last_name: Bortolini
- first_name: Alec S.
full_name: Hirschauer, Alec S.
last_name: Hirschauer
- first_name: Lee
full_name: Patrick, Lee
last_name: Patrick
citation:
ama: Schootemeijer A, Götberg YLL, Langer N, Bortolini G, Hirschauer AS, Patrick
L. A constant upper luminosity limit of cool supergiant stars down to the extremely
low metallicity of I Zw 18. Astronomy & Astrophysics. 2026;707. doi:10.1051/0004-6361/202557675
apa: Schootemeijer, A., Götberg, Y. L. L., Langer, N., Bortolini, G., Hirschauer,
A. S., & Patrick, L. (2026). A constant upper luminosity limit of cool supergiant
stars down to the extremely low metallicity of I Zw 18. Astronomy & Astrophysics.
EDP Sciences. https://doi.org/10.1051/0004-6361/202557675
chicago: Schootemeijer, Abel, Ylva Louise Linsdotter Götberg, Norbert Langer, Giacomo
Bortolini, Alec S. Hirschauer, and Lee Patrick. “A Constant Upper Luminosity Limit
of Cool Supergiant Stars down to the Extremely Low Metallicity of I Zw 18.” Astronomy
& Astrophysics. EDP Sciences, 2026. https://doi.org/10.1051/0004-6361/202557675.
ieee: A. Schootemeijer, Y. L. L. Götberg, N. Langer, G. Bortolini, A. S. Hirschauer,
and L. Patrick, “A constant upper luminosity limit of cool supergiant stars down
to the extremely low metallicity of I Zw 18,” Astronomy & Astrophysics,
vol. 707. EDP Sciences, 2026.
ista: Schootemeijer A, Götberg YLL, Langer N, Bortolini G, Hirschauer AS, Patrick
L. 2026. A constant upper luminosity limit of cool supergiant stars down to the
extremely low metallicity of I Zw 18. Astronomy & Astrophysics. 707, A116.
mla: Schootemeijer, Abel, et al. “A Constant Upper Luminosity Limit of Cool Supergiant
Stars down to the Extremely Low Metallicity of I Zw 18.” Astronomy & Astrophysics,
vol. 707, A116, EDP Sciences, 2026, doi:10.1051/0004-6361/202557675.
short: A. Schootemeijer, Y.L.L. Götberg, N. Langer, G. Bortolini, A.S. Hirschauer,
L. Patrick, Astronomy & Astrophysics 707 (2026).
date_created: 2026-03-15T23:01:35Z
date_published: 2026-03-01T00:00:00Z
date_updated: 2026-03-16T09:07:55Z
day: '01'
ddc:
- '520'
department:
- _id: YlGo
doi: 10.1051/0004-6361/202557675
external_id:
arxiv:
- '2510.12594'
file:
- access_level: open_access
checksum: 02a0cd932340207c96fdd3059490ad29
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creator: dernst
date_created: 2026-03-16T09:05:06Z
date_updated: 2026-03-16T09:05:06Z
file_id: '21455'
file_name: 2026_AstronomyAstrophysics_Schootemeijer.pdf
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intvolume: ' 707'
language:
- iso: eng
month: '03'
oa: 1
oa_version: Published Version
publication: Astronomy & Astrophysics
publication_identifier:
eissn:
- 1432-0746
issn:
- 0004-6361
publication_status: published
publisher: EDP Sciences
quality_controlled: '1'
scopus_import: '1'
status: public
title: A constant upper luminosity limit of cool supergiant stars down to the extremely
low metallicity of I Zw 18
tmp:
image: /images/cc_by.png
legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
short: CC BY (4.0)
type: journal_article
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
volume: 707
year: '2026'
...