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arxiv: 2604.20478 · v1 · submitted 2026-04-22 · 🌌 astro-ph.SR · astro-ph.GA

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Mid-infrared JWST spectra of carbon stars in the Large Magellanic Cloud

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Pith reviewed 2026-05-09 22:42 UTC · model grok-4.3

classification 🌌 astro-ph.SR astro-ph.GA
keywords carbon starsmid-infrared spectraJWSTLarge Magellanic Cloudmolecular absorptionC3SiC dustpulsation
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The pith

C3 molecule produces strong absorption at 5.2 microns in carbon stars of the Large Magellanic Cloud

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

Mid-infrared spectra from the James Webb Space Telescope provide higher resolution views of carbon stars in the Large Magellanic Cloud than earlier observations. These data identify the C3 molecule as the source of a prominent absorption band at 5.2 microns. The spectra also detect CS in less dusty stars and possibly HCN. Most changes from previous Spitzer observations align with stellar pulsation cycles, except for the loss of one dust feature. A dip at 10 microns and the broad band from C2H2 at 14 microns suggest that some weak silicon carbide dust signals reported before may actually be molecular.

Core claim

High-resolution mid-infrared spectra reveal that the C3 molecule is responsible for a strong absorption band centered at 5.2 um in carbon stars. CS appears in stars with less dust, and HCN may be present as well. Spectral changes between Spitzer and JWST epochs are mostly attributable to the pulsation cycle. A dip at about 10 um, possibly from an unknown carrier or variable molecular emission, together with the C2H2 band at 14 um, indicates that some prior detections of weak SiC dust emission could be spurious.

What carries the argument

Comparison of JWST Medium Resolution Spectrometer spectra with prior Spitzer Infrared Spectrograph data to isolate molecular absorption bands such as C3 and evaluate dust features like SiC.

If this is right

  • More accurate modeling of molecular chemistry in carbon-rich stellar envelopes.
  • Reassessment of dust composition in carbon stars based on clearer separation of molecular and dust contributions.
  • Improved understanding of how pulsation affects observed spectra in these variable stars.
  • Potential revision of dust production rates derived from earlier mid-IR observations.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • This work could lead to better predictions of infrared spectra for carbon stars in other low-metallicity environments.
  • Distinguishing the 10 um feature might require phase-resolved observations across the pulsation cycle.
  • The findings highlight the value of JWST for resolving ambiguities in Spitzer data for evolved stars.

Load-bearing premise

The 10-micron dip is not produced by any known molecular or dust feature already included in the analysis, and the observed changes between observation epochs are driven mainly by stellar pulsation rather than other forms of variability.

What would settle it

Laboratory spectra or atmospheric models that reproduce the exact shape of the 10 um dip using only known molecules and dust species would show that the dip does not undermine previous SiC detections.

Figures

Figures reproduced from arXiv: 2604.20478 by A. A. Zijlstra, B. Aringer, E. J. Montiel, E. Lagadec, G. C. Sloan, I. McDonald, J. Cami, Kathleen E. Kraemer, K. Eriksson, K. Justtanont, M. Matsuura, Paola Marigo, R. Sahai, S. Hoefner.

Figure 1
Figure 1. Figure 1: The sample of nine MRS targets (open circles) in color-color space defined by the four IRAC filters, plotted with data from the OGLE-III sample of carbon-rich long￾period variables in the LMC (Soszy´nski et al. 2009) and the carbon stars observed by the IRS on Spitzer (Sloan et al. 2016). Three of the targets sample the SRV sequence (ma￾genta), and the other six cover the Mira sequence (purple and brown). … view at source ↗
Figure 2
Figure 2. Figure 2: The stars in our sample compared to evolution￾ary tracks by Vassiliadis & Wood (1993) and the period￾luminosity relation for carbon stars (Whitelock et al. 2009). Appendix B describes how the luminosities were calculated [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: MRS spectra of the three SRVs, compared to the spectra from the IRS. The spectra from the MRS are plotted as produced by the pipeline and also after regridding them to the lower-resolution wavelength grid of the IRS. ∼11.5 µm using the Manchester Method, which esti￾mates the continuum by fitting a line segment to either side of the spectral features. Sloan et al. (2016) de￾scribe this method and its histor… view at source ↗
Figure 6
Figure 6. Figure 6: The equivalent width of the 7.5 µm acetylene absorption band as a function of the [6.4]−[9.3] color. The nine stars in the present sample are plotted as small light￾blue diamonds, as observed by the IRS, and large light-blue diamonds, as observed by the MRS. WBP 29 has moved dra￾matically from top left to bottom left, due to its disappearing acetylene band. Section 5.1 discusses the temporal changes at 7.5… view at source ↗
Figure 5
Figure 5. Figure 5: MRS spectra of the three reddest Mira variables, compared to the spectra from the IRS. As in [PITH_FULL_IMAGE:figures/full_fig_p007_5.png] view at source ↗
Figure 7
Figure 7. Figure 7: The strength of the SiC dust emission feature ver￾sus the [6.4]−[9.3] color, with IRS and MRS results plotted as in [PITH_FULL_IMAGE:figures/full_fig_p007_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: The absorption in the synthetic spectra based on hydrostatic models at two temperatures and five C/O ratios. The models have been regridded to the MRS wavelength grid and then smoothed with a 29 pixel boxcar. The 2800 K models show that the spectra are never even close to a real continuum in the mid-infrared [PITH_FULL_IMAGE:figures/full_fig_p009_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Observed spectra of the SRVs compared to ab￾sorption in the synthetic spectra from 4.4 to 8.5 µm at low spectral resolution. The MRS spectra and synthetic spec￾tra have been smoothed with a 29 pixel boxcar. The verti￾cal dotted line at 4.9 µm marks the blue edge of the MRS data. Top: observed MRS data. Middle: full absorption of all molecules and atoms considered in the models at Teff = 3100 K. Bottom: abs… view at source ↗
Figure 11
Figure 11. Figure 11: compares the 8.1–8.6 µm spectra of the three SRVs with CS from the synthetic spectrum from a 3100 K model with C/O = 2.0. Including CS reduces the residuals in all three spectra, and the improvement is particularly clear in KDM 1691 and WBP 17. The other possible contributors—C2H2 and HCN—have dif￾ferent spectral signatures in this wavelength interval, as can be seen in the spectra in Appendix C. The spec… view at source ↗
Figure 12
Figure 12. Figure 12: The synthetic spectrum of a hydrodynamic model of a carbon star, computed without dust opacities and scaled to the spectrum of WBP 29. The synthetic spectrum has been downsampled to the MRS wavelength grid and res￾olution, and the observed spectrum has been smoothed with a 15 pixel boxcar. The model is representative and not fitted specifically to WBP 29. It is for a 1 M⊙ star with Teff = 3000 K and L = 7… view at source ↗
Figure 13
Figure 13. Figure 13: Light curves for the three SRVs in the sample, plotted versus MJD (left) and phased (right). IRAC data color-corrected to the WISE filters are plotted as squares. The fitted sine functions are plotted in light blue for W1 and orange for W2. In the left-hand panels, the vertical dashed lines give the epochs of the IRS and MRS observations. All three panels have the same vertical range, 0.75 mag [PITH_FULL… view at source ↗
Figure 14
Figure 14. Figure 14: Light curves for the three bluest Miras in the sample. The figure key is the same as [PITH_FULL_IMAGE:figures/full_fig_p018_14.png] view at source ↗
Figure 16
Figure 16. Figure 16: Residuals after subtracting the fitted sinusoids from the observed light curves, with diamonds for WISE observations and squares for color-corrected IRAC data. The IRAC data after the color corrections in [PITH_FULL_IMAGE:figures/full_fig_p019_16.png] view at source ↗
Figure 17
Figure 17. Figure 17: shows the resulting SEDs for all nine sources, along with the spectra from the MRS and IRS [PITH_FULL_IMAGE:figures/full_fig_p021_17.png] view at source ↗
Figure 18
Figure 18. Figure 18: The flattened spectra at 4.9–5.2 µm for the nine carbon stars in the sample (in color) and the best-fitting combination of molecular spectra for each (black). The C3 spectrum at the top is from the synthetic spectrum based on an effective temperature of 3100 K. The CO spectrum at the bottom is for 2800 K. Both are for a C/O ratio of 2.0. The observed spectra are shifted to correct for the radial velocitie… view at source ↗
Figure 20
Figure 20. Figure 20: The flattened spectra at 7.0–7.5 µm, with the observed spectra in color and the fitted molecular spectra in black. The HCN and CS at the top are from the synthetic spectra with Teff = 3100 K, and the C2H2 at the bottom is from the 2800 K spectrum. Both have a C/O ratio of 2.0. The observed spectra are corrected for the radial velocities in [PITH_FULL_IMAGE:figures/full_fig_p025_20.png] view at source ↗
Figure 23
Figure 23. Figure 23 [PITH_FULL_IMAGE:figures/full_fig_p026_23.png] view at source ↗
Figure 24
Figure 24. Figure 24: As [PITH_FULL_IMAGE:figures/full_fig_p027_24.png] view at source ↗
Figure 26
Figure 26. Figure 26: Light curves from the AAVSO in gray with the epochs of the SWS observations plotted in color. The mag￾nitudes at the SWS epochs are estimated from AAVSO ob￾servations with ±20 days. In the panels for R Scl and V Cyg, the second and third spectra were obtained the same day, so the green plotting symbol completely covers the blue. Fig￾ure 27 plots the spectra in the same colors. In the published paper, this… view at source ↗
read the original abstract

Mid-infrared spectra from the Medium Resolution Spectrometer on the James Webb Space Telescope have revealed the molecular chemistry of carbon stars in the Large Magellanic Cloud with better resolution and sensitivity than previously possible. Our sample spans a range of dust-production rates and includes three relatively dust-free semiregular variables and six dustier Mira variables. All were observed 15-20 yr earlier with the Infrared Spectrograph on the Spitzer Space Telescope at lower spectral resolution. The new spectra show that the C3 molecule is responsible for a strong absorption band centered at 5.2 um. CS is clearly present in some of the sample, especially the stars with less dust. HCN also appears to be present. Some of the spectra have changed significantly between the Spitzer epoch and the MRS observations in 2023 and 2024, and in most cases these changes can be attributed to the stellar pulsation cycle. One exception is the disappearance of a dust emission feature at ~18 um in one of the Miras. The new spectra reveal a dip centered at ~10 um, which could arise either from an unknown carrier or from variable molecular emission to the red and blue. The presence of this spectral structure on the short-wavelength side of the SiC dust emission feature at ~11.3 um along with the broad C2H2 band centered at 14 um raise the possibility that some previously reported detections of weak SiC dust emission in other carbon stars may not be real.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The work rests on standard infrared molecular spectroscopy databases and prior Spitzer observations; no new free parameters, invented entities, or ad-hoc axioms are introduced.

axioms (1)
  • standard math Laboratory and theoretical wavelengths for C3, CS, HCN, C2H2, and SiC are accurate enough for identification in stellar spectra
    Invoked when assigning the 5.2 um band to C3 and discussing the 10 um and 14 um features.

pith-pipeline@v0.9.0 · 5636 in / 1303 out tokens · 27159 ms · 2026-05-09T22:42:07.578841+00:00 · methodology

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Works this paper leans on

102 extracted references · 4 canonical work pages

  1. [1]

    J., Tielens, A

    Allamandola, L. J., Tielens, A. G. G. M., & Barker, J. R. 1989, ApJS, 71, 733

  2. [2]

    1998, A&A, 340, 222

    Aoki, W., Tsuji, T., & Ohnaka, K. 1998, A&A, 340, 222

  3. [3]

    1999, A&A, 350, 945

    Aoki, W., Tsuji, T., & Ohnaka, K. 1999, A&A, 350, 945

  4. [4]

    2016, MNRAS, 457, 3611

    Aringer, B., Girardi, L., Nowotny, W., et al. 2016, MNRAS, 457, 3611

  5. [5]

    2019, MNRAS, 487, 2133

    Aringer, B., Marigo, P., Nowotny, W., et al. 2019, MNRAS, 487, 2133

  6. [6]

    J., Strange, J

    Barber, R. J., Strange, J. K., Hill, C., et al. 2014, MNRAS, 437, 1828

  7. [7]

    C., et al

    Bernard-Salas, J., Peeters, E., Sloan, G. C., et al. 2009, ApJ, 699, 1541

  8. [8]

    2019, A&A, 623, L119

    Bladh, S., Eriksson, K., Marigo, P., et al. 2019, A&A, 623, L119

  9. [9]

    M., Blanco, V

    Blanco, B. M., Blanco, V. M., & McCarthy, M. F. 1978, Nature, 271, 638

  10. [10]

    M., McCarthy, M

    Blanco, V. M., McCarthy, M. F., & Blanco, B. M. 1980, ApJ, 242, 938

  11. [11]

    L., Sloan, G

    Boyer, M. L., Sloan, G. C., Nanni, A., et al. 2025, ApJ, 991, 24

  12. [12]

    L., Srinivasan, S., Riebel, D., et al

    Boyer, M. L., Srinivasan, S., Riebel, D., et al. 2012, ApJ, 748, 40

  13. [13]

    E., & Tielens, A

    Chiar, J. E., & Tielens, A. G. G. M. 2006, ApJ, 637, 774

  14. [14]

    2006, A&A, 456, 1001

    Cherchneff, I. 2006, A&A, 456, 1001

  15. [15]

    Choudhury, S., Subramaniam, A., & Cole, A. A. 2016, MNRAS, 455, 1855

  16. [16]

    L, Tennyson, J., & Yurchenko, S

    Chubb, K. L, Tennyson, J., & Yurchenko, S. N. 2020, MNRAS, 493, 1531

  17. [17]

    L., Clementini, G., Girardi, L., et al

    Cioni, M.-R. L., Clementini, G., Girardi, L., et al. 2011, A&A, 527, 116

  18. [18]

    L., & Habing, H

    Cioni, M.-R. L., & Habing, H. J. 2003, A&A, 402, 133

  19. [19]

    L., Loup, C., Habing, H

    Cioni, M.-R. L., Loup, C., Habing, H. J., et al. A&AS, 114, 235 de Graauw, T., Haser, L. N., Beintema, D. A., et al. 1996, A&A, 315, L49

  20. [20]

    Dwek, E., Galliano, F., & Jones, A. P. 2007, ApJ, 662, 927

  21. [21]

    2023, A&A, 673, 21

    Eriksson, K., H¨ ofner, S., & Aringer, B. 2023, A&A, 673, 21

  22. [22]

    G., Hora, J

    Fazio, G. G., Hora, J. L., Allen, L. E., et al. 2004, ApJS, 154, 10

  23. [23]

    J., Hawley, S

    Fraser, O. J., Hawley, S. L, & Cook, K. H. 2008, AJ, 136, 1242

  24. [24]

    J., Hawley, S

    Fraser, O. J., Hawley, S. L, Cook, K. H., & Keller, S. C. 2005, AJ, 129, 768

  25. [25]

    Frenklach, M., & Feigelson, E. D. 1989, ApJ, 341, 372 Gaia Collaboration, Prusti, T., de Bruijne J. H. H., et al 2016, A&A, 595, 1 Gaia Collaboration, Brown, A. G. A., Vallenari, A., et al. 2021, A&A, 649, 1 Gaia Collaboration, Vallenari, A., Brown, A. G. A., et al. 2023, A&A, 674, 1

  26. [26]

    P., Mather, J

    Gardner, J. P., Mather, J. C., Abbot, R., et al. 2023, PASP, 135, 68001

  27. [27]

    G., & Hron, J

    Gautschy-Loidl, R., H¨ ofner, S., Jorgensen, U. G., & Hron, J. 2004, A&A, 422, 289

  28. [28]

    Groenewegen, M. A. T. 2004, A&A, 425, 595

  29. [29]

    Groenewegen, M. A. T. 2022, A&A, 659, 145

  30. [30]

    Groenewegen, M. A. T., Nanni, A., Cioni, M.-R. L., et al. 2020, A&A, 636, 48

  31. [31]

    Petersen, E. A. 2009, A&A, 506, 1277

  32. [32]

    Groenewegen, M. A. T., & Sloan, G. C. 2018, A&A, 609, 114

  33. [33]

    Groenewegen, M. A. T., Wood, P. R., & Sloan, G. C. 2007, MNRAS, 376, 313

  34. [34]

    Habing, H. J. 1996, A&A Rv, 7, 97

  35. [35]

    J., Larner, F

    Harris, G. J., Larner, F. C., Tennyson, J., et al. 2008, MNRAS, 390, 143

  36. [36]

    M., Morrison, J

    Helton, J. M., Morrison, J. E., Hainline, K. N., et al. 2026, ApJL, submitted (arXiv 2512.19695)

  37. [37]

    2004, ApJS, 155, 651 H¨ ofner, S., Bladh, S., Aringer, B., & Ahuja, R

    Herwig, F. 2004, ApJS, 155, 651 H¨ ofner, S., Bladh, S., Aringer, B., & Ahuja, R. 2016, A&A, 594, 108 H¨ ofner, S. & Olofsson, H. 2018, A&A Rv, 26, 1

  38. [38]

    R., Roellig, T

    Houck, J. R., Roellig, T. L., & van Cleve, J., et al. 2004, ApJS, 154, 18

  39. [39]

    1983, ARA&A, 21, 271

    Iben, I., & Renzini, A. 1983, ARA&A, 21, 271

  40. [40]

    2004, MNRAS, 353, 705

    Ita, Y., Tanab´ e, T., Matsunaga, N., et al. 2004, MNRAS, 353, 705

  41. [41]

    2021, ApJ, 919, 99

    Iwanek, P., Soszy´ nski, I., & Koz lowski, S. 2021, ApJ, 919, 99

  42. [42]

    2007, PASJ, 59, 615

    Kato, D., Nagashima, C., Nagayama, T., et al. 2007, PASJ, 59, 615

  43. [43]

    E., Clavel, J., et al

    Kessler, M., Anderegg, M. E., Clavel, J., et al. 1996, A&A, 315, L27

  44. [44]

    G., Leech, K., et al

    Kessler, M., M¨ uller, T. G., Leech, K., et al. 2003, The ISO

  45. [45]

    Kim, D.-W., Protopapas, P., Bailer-Jones, C. A. L., et al. 2014, A&A, 566, 43

  46. [46]

    Kloppenborg, B. K. 2025, Observations from the AAVSO International Database (https://www.aavso.org)

  47. [47]

    E., Sloan, G

    Kraemer, K. E., Sloan, G. C., Keller, L. D., et al. 2019, ApJ, 887, 82

  48. [48]

    L., Babusiaux, C., & Cos, N

    Lallement, R., Vergely, J. L., Babusiaux, C., & Cos, N. L. J. 2022, A&A, 661, 147

  49. [49]

    R., Argyriou , I., Gordon , K

    Law, D. R., Argyriou, I., Gordon, K. D., et al. 2024, AJ, in press (arXiv 2409.15435) 30Sloan et al

  50. [50]

    2003, The ISO

    Leech, K., Kester, D., Shipman, R., et al. 2003, The ISO

  51. [51]

    Leisenring, J., Kemper, F., & Sloan, G. C. 2008, ApJ, 681, 1557

  52. [52]

    E., Rothman, L

    Li, G., Gordon, I. E., Rothman, L. S., et al. 2015, ApJS, 216, 15

  53. [53]

    2016, A&A, 589, 130

    Liljegren, S., H¨ ofner, S., Nowotny, W., & Eriksson, K. 2016, A&A, 589, 130

  54. [54]

    1997, Ap&SS, 251, 243

    Loidl, R., Hron J., H¨ oFner, S., et al. 1997, Ap&SS, 251, 243

  55. [55]

    E., Polyansky, L., Tennyson, J., et al

    Lynas-Gray, A. E., Polyansky, L., Tennyson, J., et al. 2024, MNRAS, 535, 1439

  56. [56]

    M., et al

    Mainzer, A., Bauer, J., Cutri, R. M., et al. 2014, ApJ, 792, 30

  57. [57]

    2004, Nature, 431, 533

    Maiolino, R., Schneider, R., Oliva, E., et al. 2004, Nature, 431, 533

  58. [58]

    G., & Rogers, C

    Martin, P. G., & Rogers, C. 1987, ApJ, 322, 374

  59. [59]

    J., Zijlstra, A

    Matsuura, M., Barlow, M. J., Zijlstra, A. A. et al. 2009, MNRAS, 396, 918

  60. [60]

    R., Sloan, G

    Matsuura, M., Wood, P. R., Sloan, G. C., et al. 2006, MNRAS, 371, 415

  61. [61]

    M., & Owen, P

    Matsuura, M., Woods, P. M., & Owen, P. J. 2013, MNRAS, 429, 2527

  62. [62]

    2008, A&A, 484, L5

    Mattsson, L., Wahlin, R., H¨ ofner, S., et al. 2008, A&A, 484, L5

  63. [63]

    2010, A&A, 509, 14

    Mattsson, L., Wahlin, R., & H¨ ofner, S. 2010, A&A, 509, 14

  64. [64]

    2025, MNRAS, 541, 516

    McDonald, I., Srinivasan, S., Scicluna, P., et al. 2025, MNRAS, 541, 516

  65. [65]

    2019, MNRAS, 484, 4678

    McDonald, I., & Trabuchhi, M. 2019, MNRAS, 484, 4678

  66. [66]

    A., Cox, N

    McDonald, I., Zijlstra, A. A., Cox, N. L. J., et al. 2024, RASTI, 3, 89

  67. [67]

    D., Indebetouw, R., et al

    Meixner, M., Gordon, K. D., Indebetouw, R., et al. 2006, AJ, 132, 2268

  68. [68]

    P., Oesch, P

    Naidu, R. P., Oesch, P. A., Brammer, G., et al. 2026, OJAp, in press (arXiv 2505.11263)

  69. [69]

    A., Wolf, C., Bessell, M

    Onken, C. A., Wolf, C., Bessell, M. S., et al. 2024, PASA, 41, 61

  70. [70]

    2022, AJ, 163, 192

    Ou, J.-Y., & Ngeow, C.-C. 2022, AJ, 163, 192

  71. [71]

    1996, The VizieR database of astronomical catalogues, CDS, Centre de Donn ˜A©es astronomiques de Strasbourg, doi: 10.26093/CDS/VIZIER

    Ochsenbein, F., et al. 2000, “The VizieR database of astronomical catalogues,” DOI: 10.26093/cds/vizier

  72. [72]

    J., Yurchenko, S

    Paulose, G., Barton, E. J., Yurchenko, S. N., & Tennyson, J. 2015, MNRAS, 454, 1931

  73. [73]

    E., & Geisler, D

    Piatti, A. E., & Geisler, D. 2013, AJ, 145, 17 Pietrzy´ nski, G., Graczyk, D., Gallenne , A., et al. 2019, Nature, 567, 200

  74. [74]

    M., Salyk, C., Banzatti, A., et al

    Pontoppidan, K. M., Salyk, C., Banzatti, A., et al. 2024, ApJ, 963, 158

  75. [75]

    1981, A&A, 94, 175

    Renzini, A., & Voli, M. 1981, A&A, 94, 175

  76. [76]

    L., Srinivasan, S., et al

    Riebel, D., Boyer, M. L., Srinivasan, S., et al. 2015, ApJ, 807, 1

  77. [77]

    H., & Lebofsky, M

    Rieke, G. H., & Lebofsky, M. H. 1985, ApJ, 288, 618

  78. [78]

    Salpeter, E. E. 1952, ApJ, 115, 326

  79. [79]

    N., Kazarovets, E

    Samus, N. N., Kazarovets, E. V., Durlevich, O. V., et al. 2017, ARep, 61, 1

  80. [80]

    Sanford, R. F. 1944, ApJ, 99, 145

Showing first 80 references.