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Paper   IPM / Astronomy / 18467
School of Astronomy
  Title:   Discovery of SiC and Iron Dust around AGB Stars in the Very Metal-poor Sextans a Dwarf Galaxy with JWST: Implications for Dust Production at High Redshift
  Author(s): 
1.  M. L. Boyer
2.  G. C. Sloan
3.  A. Nanni
4.  E. Tarantino
5.  I. McDonald
6.  S. Goldman
7.  J.A. .D.L Blommaert
8.  F. Dell'Agli
9.  M. Di Criscienzo
10.  D.A. Garcia-Hernandez
11.  R. D. Gehrz
12.  M.A.T. Groenewegen
13.  A. Javadi
14.  O. C. Jones
15.  F. Kemper
16.  M. Marengo
17.  K. B. W. McQuinn
18.  J. M.. Oliveira
19.  G. Pastorelli
20.  J. Roman-Duval
21.  R. Sahai
22.  E. D. Skillman
23.  S. Srinivasan
24.  J.TH. van Loon
25.  D. R. Weisz
26.  P. A. Whitelock
  Status:   Published
  Journal: Astrophysical Journal
  No.:  1
  Vol.:  991
  Year:  2025
  Pages:   12
  Supported by:  IPM
  Abstract:

Low-resolution infrared spectroscopy from JWST confirms the presence of SiC and likely metallic iron dust around asymptotic giant branch (AGB) stars in the Sextans A dwarf galaxy, which has a metallicity  1%–7% Z . While metal-poor carbon-rich AGB stars are known to produce copious amounts of amorphous carbon dust owing to the dredge up of newly synthesized carbon, this is the first time that Si- and Fe-bearing dust has been detected at this extreme metallicity. Of the six AGB stars observed, one is an intermediate-mass ( 1.2 4 M ) carbon star showing SiC dust, and another is an oxygen-rich M-type star with mass  4 5 M that is likely undergoing hot bottom burning. The infrared excess of the M-type star is strong, but featureless. We tested multiple dust species, and found that it is best fit with metallic iron dust. Assuming its dust-production rate stays constant over the final 2–3 × 104 yr of its evolution, this star will produce  0.9 3.7 times the iron dust mass predicted by models, with the range depending on the adopted stellar mass. The implications for dust production in high-redshift galaxies are potentially significant, especially regarding the assumed dust species used in dust evolution models and the timescale of AGB dust formation. Stars on the upper end of the AGB mass range can begin producing dust as early as 30 50 Myr after they form, and they may therefore rival dust production by supernovae at high redshift.



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