REVIEW 3 major objections 1 minor 52 references
Origin of $\alpha$-rich young stars: clues from C, N and O
T0 review · 3 major / 1 minor · reviewed 2026-05-25 · grok-4.3
Pith's one-line read Some chemically old stars that appear young are merger products
desk verdict This paper measures CNO abundances in 51 Kepler red giants and splits the alpha-rich young stars into likely post-dredge-up binary products versus possible genuine young or main-sequence merger cases based on N/C ratios. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The N/C surface number density ratio, which separates observed abundances into those matching single-star first-dredge-up trends and those indicating binary mass transfer or merger at different evolutionary stages.
What would settle it
Detailed binary evolution calculations showing that post-dredge-up mass transfer cannot reproduce the low N/C ratios seen in the high-mass group, or independent mass measurements that differ from the asteroseismic values for those same stars.
Extended reading notes
Core claim
The alpha-rich young stars divide based on their N/C surface number density ratios: those with low N/C are interpreted as products of mergers or mass transfer during or after first dredge up because the dredge-up features are the same as for low-mass stars, while the alpha-rich young stars with high N/C follow the expected trend of N/C for their mass and could be either genuine young stars or the results of mergers on the main sequence.
Load-bearing premise
Asteroseismic masses accurately reflect true stellar masses and observed N/C ratios can be compared directly to single-star evolution trends without extra binary modeling or measurement offsets.
Editorial extensions
If this is right
- High-mass alpha-rich stars include both genuine young objects and binary interaction products.
- The unexplained high alpha-to-iron ratios apply only to the high N/C subset.
- CNO abundances combined with asteroseismic masses can identify likely post-dredge-up merger products among red giants.
- The timing of mass transfer or merger determines whether dredge-up signatures are reset to low-mass patterns or retained at high-mass levels.
Reading between the lines
- Binary population synthesis models could be checked by predicting the fraction of stars expected in each N/C group.
- Galactic archaeology age estimates that treat all alpha-rich stars as old may need adjustment for the merger subset.
- Spectroscopic surveys could search for stars with intermediate N/C values to map the transition between the two populations.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript analyzes C, N, and O abundances derived independently from APOGEE spectra for a sample of 51 red-giant stars with asteroseismic masses from Kepler light curves. It reports a wide range of N/C surface ratios and interprets high-mass stars with low N/C as merger or mass-transfer products during or after first dredge-up (matching low-mass single-star dredge-up features), while α-rich young stars with high N/C follow the expected single-star N/C trend for their mass and may be either genuine young stars or main-sequence merger products.
Significance. If the central interpretation holds, the work supplies a binary-evolution channel that could reconcile the apparent youth (from asteroseismic masses) of chemically old α-rich stars, offering a concrete mechanism to explain a long-standing puzzle in Galactic stellar populations.
major comments (3)
- [Abstract] Abstract: the statement that abundances were derived independently and that trends were examined supplies no quantitative results, error bars, sample statistics, or model comparisons, preventing verification of support for the merger interpretation.
- [Asteroseismic masses and N/C analysis] The interpretation that high-mass low-N/C stars are post-dredge-up merger products (and high-N/C α-rich stars are either genuine young or main-sequence mergers) rests on asteroseismic masses accurately distinguishing the ~1.5–2 M⊙ first-dredge-up boundary, yet the manuscript reports no propagation of scaling-relation systematics such as solar reference values or surface-effect corrections.
- [Discussion of merger scenarios] No quantitative binary evolution grids or coupled modeling of mass-transfer effects on both stellar mass and surface CNO abundances are presented to test whether such episodes reproduce the observed N/C split at the reported masses.
minor comments (1)
- [Abstract] The abstract could specify the exact number of stars falling into each N/C category and the mass range spanned by the sample.
Simulated Author's Rebuttal
We thank the referee for their constructive comments on our manuscript. We address each major comment below and indicate where revisions will be made.
read point-by-point responses
-
Referee: [Abstract] Abstract: the statement that abundances were derived independently and that trends were examined supplies no quantitative results, error bars, sample statistics, or model comparisons, preventing verification of support for the merger interpretation.
Authors: We agree the abstract is concise and would benefit from additional quantitative context. In the revised manuscript we will expand the abstract to report the sample size, the observed range in N/C, the fraction of stars showing the low-N/C high-mass signature, and a brief statement of the comparison to single-star expectations. revision: yes
-
Referee: [Asteroseismic masses and N/C analysis] The interpretation that high-mass low-N/C stars are post-dredge-up merger products (and high-N/C α-rich stars are either genuine young or main-sequence mergers) rests on asteroseismic masses accurately distinguishing the ~1.5–2 M⊙ first-dredge-up boundary, yet the manuscript reports no propagation of scaling-relation systematics such as solar reference values or surface-effect corrections.
Authors: The masses are obtained from the standard asteroseismic scaling relations applied to Kepler data, which have been extensively validated. Typical uncertainties are 0.1–0.2 M⊙, sufficient to separate the regimes around the first-dredge-up boundary. We will add a paragraph discussing the possible impact of solar reference values and surface-effect corrections on the mass scale and on the robustness of the N/C split. revision: partial
-
Referee: [Discussion of merger scenarios] No quantitative binary evolution grids or coupled modeling of mass-transfer effects on both stellar mass and surface CNO abundances are presented to test whether such episodes reproduce the observed N/C split at the reported masses.
Authors: The manuscript is an observational study that identifies an empirical N/C dichotomy and proposes a binary channel as a plausible explanation. We do not present new binary-evolution calculations because that lies outside the scope of the present work; the interpretation rests on the mismatch between the observed N/C values and single-star predictions at the measured masses. We will expand the discussion to cite existing binary population-synthesis results that demonstrate mass transfer and mergers can alter both mass and surface abundances in the relevant regime. revision: no
Circularity Check
No circularity: interpretation rests on external trends and independent data
full rationale
The paper's central claim is an interpretive classification of α-rich stars as merger products or genuine young stars, based on comparing observed N/C ratios (derived independently from APOGEE spectra) against expected single-star evolutionary trends at asteroseismic masses. No equations, fitted parameters, predictions, or ansatzes are presented that reduce to the inputs by construction. The analysis draws on external benchmarks (prior literature trends for N/C vs. mass) rather than self-citations, self-definitions, or internal fits, rendering the derivation self-contained.
Assumptions & free parameters
assumptions (1)
- domain assumption N/C surface ratios after first dredge-up follow a predictable trend with stellar mass for single stars
Cite this review
Pith. "Pith review of Origin of $\alpha$-rich young stars: clues from C, N and O." pith.science (2026). https://pith.science/paper/VO4BL37U
@misc{pith2026190610830,
author = {Pith},
title = {Pith review of: Origin of $\alpha$-rich young stars: clues from C, N and O},
year = {2026},
howpublished = {\url{https://pith.science/paper/VO4BL37U}},
note = {Machine review of arXiv:1906.10830}
}
abstract
A small set of chemically old stars that appear young by their independently derived masses has been detected. These are so-called $\alpha$-rich young stars. For a sample of 51 red-giant stars, for which spectra are available from SDSS/APOGEE and masses are available from asteroseismic measures based on \textit{Kepler} lightcurves, we derive the C, N and O abundances through an independent analysis. These stars span a wide range of N/C surface number density ratios. We interpret the high-mass stars with low N/C as being products of mergers or mass transfer during or after first dredge up, because the dredge-up features are the same as for low-mass stars. The $\alpha$-rich young stars with high N/C follow the expected trend of N/C for their mass, and could be either genuine young stars (leaving their high [$\alpha$/Fe] unexplained) or the results of mergers on the main sequence.
Figures
Figures from the paper (1 more)
Reference graph
Works this paper leans on
-
[1]
" write newline "" before.all 'output.state := FUNCTION fin.entry write newline FUNCTION new.block output.state before.all = 'skip after.block 'output.state := if FUNCTION new.sentence output.state after.block = 'skip output.state before.all = 'skip after.sentence 'output.state := if if FUNCTION not #0 #1 if FUNCTION and 'skip pop #0 if FUNCTION or pop #1...
-
[2]
Aller L. H., Greenstein J. L., 1960, @doi [ ] 10.1086/190054 , http://adsabs.harvard.edu/abs/1960ApJS....5..139A 5, 139
-
[3]
Alvarez R., Plez B., 1998, , http://adsabs.harvard.edu/abs/1998A
work page 1998
-
[4]
Anders F., et al., 2017, @doi [ ] 10.1051/0004-6361/201629363 , http://adsabs.harvard.edu/abs/2017A
-
[5]
Asplund M., Grevesse N., Jacques Sauval A., 2006, @doi [Nuclear Physics A] 10.1016/j.nuclphysa.2005.06.010 , http://adsabs.harvard.edu/abs/2006NuPhA.777....1A 777, 1
-
[6]
Bensby T., Feltzing S., Lundstr \"o m I., 2003, @doi [ ] 10.1051/0004-6361:20031213 , http://adsabs.harvard.edu/abs/2003A
-
[7]
Blanton M. R., Bershady M. A., Abolfathi B., Albareti F. D., Allende Prieto C., et al. 2017, @doi [ ] 10.3847/1538-3881/aa7567 , http://adsabs.harvard.edu/abs/2017AJ....154...28B 154, 28
-
[8]
Brooke J. S. A., Bernath P. F., Western C. M., Sneden C., Af s ar M., Li G., Gordon I. E., 2016, @doi [ ] 10.1016/j.jqsrt.2015.07.021 , http://adsabs.harvard.edu/abs/2016JQSRT.168..142B 168, 142
Show all 52 references
-
[9]
L., 2003, in Piskunov N., Weiss W
Castelli F., Kurucz R. L., 2003, in Piskunov N., Weiss W. W., Gray D. F., eds, IAU Symposium Vol. 210, Modelling of Stellar Atmospheres. p. A20
2003
-
[10]
L., 2004, arXiv Astrophysics e-prints, http://adsabs.harvard.edu/abs/2004astro.ph..5087C
Castelli F., Kurucz R. L., 2004, arXiv Astrophysics e-prints, http://adsabs.harvard.edu/abs/2004astro.ph..5087C
2004
-
[11]
W., Aller L
Chamberlain J. W., Aller L. H., 1951, @doi [ ] 10.1086/145451 , http://adsabs.harvard.edu/abs/1951ApJ...114...52C 114, 52
1951 doi
-
[12]
S., Miglio A., Montalb \'a n J., et al
Chiappini C., Anders F., Rodrigues T. S., Miglio A., Montalb \'a n J., et al. 2015, @doi [ ] 10.1051/0004-6361/201525865 , http://adsabs.harvard.edu/abs/2015A
2015 doi
-
[13]
Delgado Mena E., et al., 2019, arXiv e-prints, http://adsabs.harvard.edu/abs/2019arXiv190202127D
2019
-
[14]
L., Nissen P
Edvardsson B., Andersen J., Gustafsson B., Lambert D. L., Nissen P. E., Tomkin J., 1993, , http://adsabs.harvard.edu/abs/1993A
1993
-
[15]
K., et al., 2018, @doi [ ] 10.1093/mnras/sty779 , http://adsabs.harvard.edu/abs/2018MNRAS.477.2326F 477, 2326
Feuillet D. K., et al., 2018, @doi [ ] 10.1093/mnras/sty779 , http://adsabs.harvard.edu/abs/2018MNRAS.477.2326F 477, 2326
2018 doi
-
[16]
Fuhrmann K., 1998, , http://adsabs.harvard.edu/abs/1998A
1998
-
[17]
E., et al., 2016, @doi [ ] 10.3847/0004-6256/151/6/144 , http://adsabs.harvard.edu/abs/2016AJ....151..144G 151, 144
Garc \' a P \'e rez A. E., et al., 2016, @doi [ ] 10.3847/0004-6256/151/6/144 , http://adsabs.harvard.edu/abs/2016AJ....151..144G 151, 144
2016 doi
-
[18]
E., Siegmund W
Gunn J. E., Siegmund W. A., Mannery E. J., Owen R. E., Hull C. L., et al. 2006, @doi [ ] 10.1086/500975 , http://adsabs.harvard.edu/abs/2006AJ....131.2332G 131, 2332
2006 doi
-
[19]
G., Nordlund ., Plez B., 2008, @doi [ ] 10.1051/0004-6361:200809724 , http://adsabs.harvard.edu/abs/2008A
Gustafsson B., Edvardsson B., Eriksson K., J rgensen U. G., Nordlund ., Plez B., 2008, @doi [ ] 10.1051/0004-6361:200809724 , http://adsabs.harvard.edu/abs/2008A
2008 doi
-
[20]
Hawkins K., Masseron T., Jofr \'e P., Gilmore G., Elsworth Y., Hekker S., 2016, @doi [ ] 10.1051/0004-6361/201628812 , http://adsabs.harvard.edu/abs/2016A
2016 doi
-
[21]
A., Shetrone M., Johnson J
Holtzman J. A., Shetrone M., Johnson J. A., et al. 2015, @doi [ ] 10.1088/0004-6256/150/5/148 , http://adsabs.harvard.edu/abs/2015AJ....150..148H 150, 148
2015 doi
-
[22]
A., et al., 2018, @doi [ ] 10.3847/1538-3881/aad4f9 , http://adsabs.harvard.edu/abs/2018AJ....156..125H 156, 125
Holtzman J. A., et al., 2018, @doi [ ] 10.3847/1538-3881/aad4f9 , http://adsabs.harvard.edu/abs/2018AJ....156..125H 156, 125
2018 doi
-
[23]
New York: Van Nostrand Reinhold Company
Huber K., Herzberg G., 1979, Volume IV: Constants of Diatomic Molecules . New York: Van Nostrand Reinhold Company
1979
-
[24]
G., Preece H., Jofre P., Halabi G
Izzard R. G., Preece H., Jofre P., Halabi G. M., Masseron T., Tout C. A., 2018, @doi [ ] 10.1093/mnras/stx2355 , http://adsabs.harvard.edu/abs/2018MNRAS.473.2984I 473, 2984
2018 doi
-
[25]
Jofr \'e P., et al., 2016, @doi [ ] 10.1051/0004-6361/201629356 , http://adsabs.harvard.edu/abs/2016A
2016 doi
-
[26]
I., Lattanzio J
Karakas A. I., Lattanzio J. C., 2014, @doi [ ] 10.1017/pasa.2014.21 , http://adsabs.harvard.edu/abs/2014PASA...31...30K 31, e030
2014 doi
-
[27]
Technical Report 91-001, July 1991
Livingston W., Wallace L., 1991, An atlas of the solar spectrum in the infrared from 1850 to 9000 cm-1 (1.1 to 5.4 m), N.S.O. Technical Report 91-001, July 1991. . Tucson: National Solar Observatory, National Optical Astronomy Observatory
1991
-
[28]
E., Heiter U., 2007, @doi [ ] 10.1086/513194 , http://adsabs.harvard.edu/abs/2007AJ....133.2464L 133, 2464
Luck R. E., Heiter U., 2007, @doi [ ] 10.1086/513194 , http://adsabs.harvard.edu/abs/2007AJ....133.2464L 133, 2464
2007 doi
-
[29]
R., et al., 2017, @doi [ ] 10.3847/1538-3881/aa784d , https://ui.adsabs.harvard.edu/abs/2017AJ....154...94M 154, 94
Majewski S. R., et al., 2017, @doi [ ] 10.3847/1538-3881/aa784d , https://ui.adsabs.harvard.edu/abs/2017AJ....154...94M 154, 94
2017 doi
-
[30]
2015, @doi [ ] 10.1093/mnras/stv1071 , http://adsabs.harvard.edu/abs/2015MNRAS.451.2230M 451, 2230
Martig M., Rix H.-W., Silva Aguirre V., Hekker S., et al. 2015, @doi [ ] 10.1093/mnras/stv1071 , http://adsabs.harvard.edu/abs/2015MNRAS.451.2230M 451, 2230
2015 doi
-
[31]
Martig M., et al., 2016, @doi [ ] 10.1093/mnras/stv2830 , http://adsabs.harvard.edu/abs/2016MNRAS.456.3655M 456, 3655
2016 doi
-
[32]
N., 2018, @doi [ ] 10.3847/1538-4357/aac019 , http://adsabs.harvard.edu/abs/2018ApJ...860...49M 860, 49
Matsuno T., Yong D., Aoki W., Ishigaki M. N., 2018, @doi [ ] 10.3847/1538-4357/aac019 , http://adsabs.harvard.edu/abs/2018ApJ...860...49M 860, 49
2018 doi
-
[33]
Mel \'e ndez J., Barbuy B., 1999, @doi [ ] 10.1086/313261 , http://cdsads.u-strasbg.fr/abs/1999ApJS..124..527M 124, 527
1999 doi
-
[34]
M \'e sz \'a ros S., et al., 2012, @doi [ ] 10.1088/0004-6256/144/4/120 , http://adsabs.harvard.edu/abs/2012AJ....144..120M 144, 120
2012 doi
-
[35]
K., 1964, @doi [ ] 10.1364/AO.3.001337 , http://adsabs.harvard.edu/abs/1964ApOpt...3.1337P 3, 1337
Pierce A. K., 1964, @doi [ ] 10.1364/AO.3.001337 , http://adsabs.harvard.edu/abs/1964ApOpt...3.1337P 3, 1337
1964 doi
-
[36]
H., Elsworth Y., Epstein C., Hekker S., M \'e sz \'a ros S., Chaplin W
Pinsonneault M. H., Elsworth Y., Epstein C., Hekker S., M \'e sz \'a ros S., Chaplin W. J., Johnson J. A., et al. 2014, @doi [ ] 10.1088/0067-0049/215/2/19 , http://adsabs.harvard.edu/abs/2014ApJS..215...19P 215, 19
2014 doi
-
[37]
H., Elsworth Y
Pinsonneault M. H., Elsworth Y. P., Tayar J., Serenelli A., et al. 2018, preprint, http://adsabs.harvard.edu/abs/2018arXiv180409983P ( @eprint arXiv 1804.09983 )
2018 arXiv
-
[38]
Plez B., 2012, Turbospectrum: Code for spectral synthesis , Astrophysics Source Code Library ( @eprint ascl 1205.004 )
2012
-
[39]
Reddy A. B. S., Lambert D. L., 2015, @doi [ ] 10.1093/mnras/stv1876 , http://adsabs.harvard.edu/abs/2015MNRAS.454.1976R 454, 1976
2015 doi
-
[40]
M., Cassisi S., 2015, @doi [ ] 10.1051/0004-6361/201526951 , http://adsabs.harvard.edu/abs/2015A
Salaris M., Pietrinferni A., Piersimoni A. M., Cassisi S., 2015, @doi [ ] 10.1051/0004-6361/201526951 , http://adsabs.harvard.edu/abs/2015A
2015 doi
-
[41]
2018, @doi [ ] 10.1093/mnras/sty150 , http://adsabs.harvard.edu/abs/2018MNRAS.475.5487S 475, 5487
Silva Aguirre V., Bojsen-Hansen M., Slumstrup D., Casagrande L., et al. 2018, @doi [ ] 10.1093/mnras/sty150 , http://adsabs.harvard.edu/abs/2018MNRAS.475.5487S 475, 5487
2018 doi
-
[42]
V., Cunha K., Shetrone M
Smith V. V., Cunha K., Shetrone M. D., Meszaros S., et al. 2013, @doi [ ] 10.1088/0004-637X/765/1/16 , http://adsabs.harvard.edu/abs/2013ApJ...765...16S 765, 16
2013 doi
-
[43]
A., 1973, PhD thesis, THE UNIVERSITY OF TEXAS AT AUSTIN
Sneden C. A., 1973, PhD thesis, THE UNIVERSITY OF TEXAS AT AUSTIN
1973
-
[44]
S., Brooke J
Sneden C., Lucatello S., Ram R. S., Brooke J. S. A., Bernath P., 2014, @doi [ ] 10.1088/0067-0049/214/2/26 , http://adsabs.harvard.edu/abs/2014ApJS..214...26S 214, 26
2014 doi
-
[45]
Talbot J. R. J., Arnett D. W., 1974, @doi [ ] 10.1086/152918 , http://adsabs.harvard.edu/abs/1974ApJ...190..605T 190, 605
1974 doi
-
[46]
Tayar J., et al., 2015, @doi [ ] 10.1088/0004-637X/807/1/82 , http://adsabs.harvard.edu/abs/2015ApJ...807...82T 807, 82
2015 doi
-
[47]
M., 1979, @doi [ ] 10.1086/157039 , http://adsabs.harvard.edu/abs/1979ApJ...229.1046T 229, 1046
Tinsley B. M., 1979, @doi [ ] 10.1086/157039 , http://adsabs.harvard.edu/abs/1979ApJ...229.1046T 229, 1046
1979 doi
-
[48]
A., Richard O., Michaud G., Richer J., 2002, @doi [ ] 10.1086/339895 , http://adsabs.harvard.edu/abs/2002ApJ...571..487V 571, 487
VandenBerg D. A., Richard O., Michaud G., Richer J., 2002, @doi [ ] 10.1086/339895 , http://adsabs.harvard.edu/abs/2002ApJ...571..487V 571, 487
2002 doi
-
[49]
Wallerstein G., 1962, @doi [ ] 10.1086/190067 , http://adsabs.harvard.edu/abs/1962ApJS....6..407W 6, 407
1962 doi
-
[50]
C., et al., 2019, arXiv e-prints: 1902.00928, http://adsabs.harvard.edu/abs/2019arXiv190200928W
Wilson J. C., et al., 2019, arXiv e-prints: 1902.00928, http://adsabs.harvard.edu/abs/2019arXiv190200928W
2019 arXiv
-
[51]
Yong D., et al., 2016, @doi [ ] 10.1093/mnras/stw676 , http://adsabs.harvard.edu/abs/2016MNRAS.459..487Y 459, 487
2016 doi
-
[52]
Zamora O., et al., 2015, @doi [ ] 10.1088/0004-6256/149/6/181 , http://adsabs.harvard.edu/abs/2015AJ....149..181Z 149, 181
2015 doi
Reviewed May 25, 2026 · model on record in the stance chip above.
Discussion (0). Sign in to comment.