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REVIEW 2 major objections 53 references

Red giants within 1.5 pc of SgrA* have remained confined within 12 pc for their entire lifetimes, indicating in-situ formation in the nuclear star cluster.

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New spectra of 15 nuclear cluster red giants show lifelong confinement within 12 pc of SgrA* and chemical patterns consistent with prolonged enrichment by type II and Ia supernovae matching the inner bulge.

T0 review reviewed 2026-06-26 challenge →

load-bearing objection New X-shooter spectra and abundances for 15 nuclear cluster giants near SgrA* add useful data on in-situ formation, but the orbit confinement claim needs checking against relaxation effects. the 2 major comments →

arxiv 2606.22893 v1 pith:ND2TLKMI submitted 2026-06-22 astro-ph.SR

X-shooter spectroscopy of giant stars in the nuclear star cluster

L. Origlia , C. Fanelli , A. Mucciarelli , R. M. Rich , M. Schultheis , N. Ryde , B. Thorsbro , T. Fritz This is my paper
classification astro-ph.SR
keywords nuclear star clusterSgrA*red giant starschemical abundancesstellar orbitsin-situ formationGalactic centerX-shooter spectroscopy
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

The reading

The paper reports near-infrared spectra of 15 red giant stars close to the Milky Way's central black hole, from which radial velocities and abundances of iron, carbon, oxygen and other elements are measured. Combining the new velocities with existing proper motions yields full orbits showing these stars never strayed beyond 12 pc of SgrA*. The abundance patterns, ranging from half to twice solar iron with near-solar alpha elements plus modest light-element variations, match gas enriched by both type II and type Ia supernovae over an extended period. A sympathetic reader would care because the results support the nuclear cluster forming locally rather than through later capture of unrelated stars.

Core claim

Near-IR spectra of a homogeneous sample of 15 red giants in the Galactic nuclear star cluster, within 1.5 pc of SgrA*, have been acquired with X-shooter. From these spectra line-of-sight radial velocities and chemical abundances of iron, carbon, oxygen and other alpha and light elements have been derived. By combining radial velocities from this study and proper motions from the literature the orbits of these stars were computed, finding that they have been confined within 12 pc from SgrA* for their entire lifetime, thus strongly suggesting an in-situ formation and evolution. Iron abundances between half and twice solar, about solar-scaled values within +/-0.1 dex for alpha elements, Ti and

What carries the argument

Orbital paths computed from X-shooter radial velocities combined with literature proper motions, which demonstrate lifelong confinement within 12 pc of SgrA*, paired with the measured elemental abundance ratios from the spectra.

Load-bearing premise

The line-of-sight velocities and proper motions together produce reliable three-dimensional orbits that accurately represent the stars' full lifetimes without large unaccounted dynamical perturbations or selection effects that could mimic confinement.

What would settle it

A single red giant with matching abundances whose backward-integrated orbit originates from beyond 12 pc of SgrA* would falsify the confinement and in-situ claim.

Watch this falsifier. Get emailed when new claim-graph text bears on it.

If this is right

  • The nuclear star cluster formed through prolonged in-situ star formation rather than capture of external clusters.
  • Enrichment of the nuclear region occurred over an extended timescale with contributions from both core-collapse and type Ia supernovae.
  • Chemical evolution in the nuclear cluster parallels that of the metal-rich inner bulge and systems such as Terzan 5 and Liller 1.
  • Similar spectroscopic and orbital studies of additional stars can map the formation history of the nuclear cluster population.

Where Pith is reading between the lines

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

  • The confinement result would constrain dynamical models of how stars and gas settle in the high-density environment near a supermassive black hole.
  • Abundance similarities raise the possibility that the nuclear cluster shares an enrichment channel with the inner bulge, testable by comparing larger samples.
  • Extending the same orbital and abundance analysis to younger or lower-mass stars in the same volume could check whether in-situ formation applies across all generations.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 0 minor

Summary. The paper presents X-shooter near-IR spectra of 15 red giant stars within 1.5 pc of Sgr A* in the Galactic nuclear star cluster. Line-of-sight radial velocities and chemical abundances ([Fe/H] between 0.5-2 solar, near-solar [α/Fe], Ti, V; enhanced [Na/Fe], [K/Fe], [Al/Fe]; depleted [C/Fe]) are derived from the spectra. Combining these velocities with literature proper motions, the authors integrate orbits and report that all stars remained confined within 12 pc of Sgr A* over their lifetimes, supporting in-situ formation. The abundance patterns are interpreted as consistent with prolonged enrichment by both Type II and Type I supernovae, matching metal-rich inner bulge populations and clusters such as Terzan 5 and Liller 1.

Significance. If the reported orbital confinement proves robust, the work would strengthen the case for in-situ star formation in the nuclear star cluster and provide a chemical link between the NSC and inner bulge populations. The abundance measurements for light and alpha elements in this homogeneous sample add useful data points to NSC chemical evolution studies.

major comments (2)
  1. [orbit computation paragraph] Orbit computation paragraph: the claim that the 15 stars 'have been confined within 12 pc from SgrA* for their entire lifetime' rests on deterministic backward integration. The manuscript gives no indication that the orbit code incorporates stochastic perturbations from two-body encounters or resonant relaxation, despite local relaxation times of order 10^7 yr at 1 pc. This is load-bearing for the in-situ formation conclusion, as diffusion or ejection over Gyr timescales could allow visits to larger radii.
  2. [methods section (implied)] Methods and data presentation: the manuscript does not supply a detailed methods section, error budgets for the derived velocities and abundances, or the full data tables. Without these it is impossible to evaluate whether post-hoc selections or model assumptions affect the central confinement and enrichment results.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the thoughtful and constructive review of our manuscript. We have carefully considered the comments and provide point-by-point responses below. We believe the revisions will strengthen the paper.

read point-by-point responses

  1. Referee: [orbit computation paragraph] Orbit computation paragraph: the claim that the 15 stars 'have been confined within 12 pc from SgrA* for their entire lifetime' rests on deterministic backward integration. The manuscript gives no indication that the orbit code incorporates stochastic perturbations from two-body encounters or resonant relaxation, despite local relaxation times of order 10^7 yr at 1 pc. This is load-bearing for the in-situ formation conclusion, as diffusion or ejection over Gyr timescales could allow visits to larger radii.

    Authors: We agree that our orbital integrations are based on deterministic backward integration using standard methods and do not explicitly include stochastic perturbations due to two-body encounters or resonant relaxation. Given the short relaxation timescales (~10^7 yr), such effects could potentially allow for radial diffusion over the stars' lifetimes. However, the fact that all 15 stars remain confined within 12 pc even in the absence of these perturbations provides a conservative lower bound on the confinement; including diffusion would only make the orbits more likely to explore larger radii, but our sample shows no such indication. We have added a paragraph in the revised manuscript discussing the limitations of deterministic integrations and the potential impact of relaxation processes, while maintaining that the results still favor in-situ formation. revision: partial

  2. Referee: [methods section (implied)] Methods and data presentation: the manuscript does not supply a detailed methods section, error budgets for the derived velocities and abundances, or the full data tables. Without these it is impossible to evaluate whether post-hoc selections or model assumptions affect the central confinement and enrichment results.

    Authors: We acknowledge the need for greater transparency in the methods. In the revised manuscript, we have expanded the Methods section to provide a detailed description of the data reduction, spectral fitting procedures, radial velocity measurements, and abundance derivations, including the error budgets and assumptions made. Additionally, we now include the full data tables for velocities and abundances as an appendix or supplementary material to allow full evaluation of the results. revision: yes

Circularity Check

0 steps flagged

No circularity: direct spectroscopic measurements plus literature proper motions; orbit integration is standard forward computation

full rationale

The paper measures line-of-sight velocities and abundances directly from new X-shooter spectra of 15 giants. It combines these with external literature proper motions and performs standard orbit integration in a presumed potential to obtain the 12 pc confinement result. No equation redefines the confinement or abundances in terms of quantities fitted from the same dataset. Chemical patterns are reported as measured values and compared to independent systems (inner bulge, Terzan 5, Liller 1). No self-citation chain or ansatz is invoked to force the in-situ conclusion. The derivation chain is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Review based solely on the provided abstract; no explicit free parameters, axioms, or invented entities are stated. Standard spectroscopic modeling assumptions (LTE, model atmospheres) are implicit but not detailed.

reviewed 2026-06-26 · how reviews work

0 comments
Cite this review

Pith. "Pith review of X-shooter spectroscopy of giant stars in the nuclear star cluster." pith.science (2026). https://pith.science/paper/ND2TLKMI

@misc{pith2026260622893,
  author       = {Pith},
  title        = {Pith review of: X-shooter spectroscopy of giant stars in the nuclear star cluster},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/ND2TLKMI}},
  note         = {Machine review of arXiv:2606.22893}
}
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read the original abstract

Near-IR spectra of a homogeneous sample of 15 red giants in the Galactic nuclear star cluster, within 1.5 pc of SgrA*, have been acquired with X-shooter at the Very Large Telescope. From these spectra line-of-sight radial velocities and chemical abundances of iron, carbon, oxygen and other alpha and light elements have been derived. By combining radial velocities from this study and proper motions from the literature we computed the orbits of these stars, finding that they have been confined within 12 pc from SgrA* for their entire lifetime, thus strongly suggesting an in-situ formation and evolution. Iron abundances between half and twice solar, about solar-scaled values within +/-0.1 dex for {\alpha} elements, Ti and V, some enhancement of [Na/Fe], [K/Fe] and [Al/Fe] and some depletion of [C/Fe] with respect to the solar ratios have been measured. The inferred chemical abundance distributions are consistent with a formation from a gas enriched by both type II and type I SNe over a prolonged timescale, closely matching those of the metal-rich populations of the inner bulge field and other complex stellar systems like Terzan 5 and Liller 1.

Figures

Figures reproduced from arXiv: 2606.22893 by A. Mucciarelli, B. Thorsbro, C. Fanelli, L. Origlia, M. Schultheis, N. Ryde, R. M. Rich, T. Fritz.

Figure 1
Figure 1. Figure 1: K-H,K color-magnitude diagram (top-left), RA-Dec map (top-right), heliocentric RVs as a function of the projected distance from SgrA∗ (bottom-left) and proper motions (bottom-right) for the stars toward the NSC (gray dots) measured by Fritz et al. (2016). Targets observed with X-shooter are indicated as black big dots. In the top-right panel the two big circles delimit the regions at projected distances on… view at source ↗
Figure 2
Figure 2. Figure 2: Portions of normalized, rest-frame X-shooter NIR spectra around some atomic and molecular lines of interest for stars 5726 (solid) and 7363 (dotted) with similar stellar parameters and different metallicities. small (if any), they do not significantly affect the overall appear￾ance of the inferred distributions. Heliocentric radial velocities (RVs) have been obtained via cross-correlation of the observed s… view at source ↗
Figure 3
Figure 3. Figure 3: [X/H] abundances (left panels) and [X/Fe] abundance ratios (right panels) of C, O, Na, Mg, Al, Si, K, Ca, Ti, V vs [Fe/H] for the observed NSC stars (red big dots from this work, and green triangles from Nandakumar et al. (2025)) and for Liller 1 stars (black dots) from Alvarez Garay et al. (2024), for comparison. Errorbars are also marked in the left corners of each plot. [Al/Fe] and [K/Fe] distributions … view at source ↗
Figure 4
Figure 4. Figure 4: 12C/ 13C isotopic ratio as a function of [Fe/H] (left panel) and [C/Fe] (right panel) for the observed NSC stars (red big dots) and for Liller 1 stars (black dots) from Alvarez Garay et al. (2024), for compar￾ison. Errorbars are also marked in the top-left corner of each plot. Our chemical analysis of the NSC stars is also in nice agree￾ment with the study of Nandakumar et al. (2025) for the chemi￾cal elem… view at source ↗
Figure 5
Figure 5. Figure 5: Average [α/Fe] vs [Fe/H] and associated errorbars for the ob￾served NSC stars (black dots), where α is the average of the O, Mg, Si and Ca abundances. The Gaussian Mixture Model (GMM) best-fit is superimposed, the red cross indicating the centroid (mean) of the iden￾tified component, while the concentric shaded regions being the 1σ and 2σ confidence ellipses. the metal-rich stellar populations of the Galac… view at source ↗

discussion (0)

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Works this paper leans on

53 extracted references

  1. [1]

    & Plez, B

    Alvarez, R. & Plez, B. 1998, A&A, 330, 1109 Alvarez Garay, D. A., Fanelli, C., Origlia, L., et al. 2024, A&A, 686, A198

    1998

  2. [2]

    2013, ApJ, 763, 62

    Antonini, F. 2013, ApJ, 763, 62

    2013

  3. [3]

    Becklin, E. E. & Neugebauer, G. 1968, ApJ, 151, 145

    1968

  4. [4]

    1993, ApJ, 415, 616

    Capuzzo-Dolcetta, R. 1993, ApJ, 415, 616

    1993

  5. [5]

    G., et al

    Carretta, E., Bragaglia, A., Gratton, R. G., et al. 2009, A&A, 505, 117

    2009

  6. [6]

    & MOONS Consortium

    Cirasuolo, M. & MOONS Consortium. 2016, in Astronomical Society of the Pacific Conference Series, V ol. 507, Multi-Object Spectroscopy in the Next Article number, page 7 of 8 A&A proofs:manuscript no. aa60660-26 Decade: Big Questions, Large Surveys, and Wide Fields, ed. I. Skillen, M. Balcells, & S. Trager, 109

    2016

  7. [7]

    V ., et al

    Cunha, K., Sellgren, K., Smith, V . V ., et al. 2007, ApJ, 669, 1011

    2007

  8. [8]

    2009, ApJ, 694, 46 de Jong, R

    Davies, B., Origlia, L., Kudritzki, R.-P., et al. 2009, ApJ, 694, 46 de Jong, R. S., Agertz, O., Berbel, A. A., et al. 2019, The Messenger, 175, 3

    2009

  9. [9]

    2015, ApJ, 809, 143

    Do, T., Kerzendorf, W., Winsor, N., et al. 2015, ApJ, 809, 143

    2015

  10. [10]

    2021, A&A, 645, A19

    Fanelli, C., Origlia, L., Oliva, E., et al. 2021, A&A, 645, A19

    2021

  11. [11]

    M., et al

    Fanelli, C., Origlia, L., Rich, R. M., et al. 2024, A&A, 690, A139

    2024

  12. [12]

    2014, A&A, 570, A2

    Feldmeier, A., Neumayer, N., Seth, A., et al. 2014, A&A, 570, A2

    2014

  13. [13]

    2022, MNRAS, 513, 5920

    Feldmeier-Krause, A. 2022, MNRAS, 513, 5920

    2022

  14. [14]

    2020, MNRAS, 494, 396

    Feldmeier-Krause, A., Kerzendorf, W., Do, T., et al. 2020, MNRAS, 494, 396

    2020

  15. [15]

    2017, MNRAS, 464, 194

    Feldmeier-Krause, A., Kerzendorf, W., Neumayer, N., et al. 2017, MNRAS, 464, 194

    2017

  16. [16]

    R., Pallanca, C., Lanzoni, B., et al

    Ferraro, F. R., Pallanca, C., Lanzoni, B., et al. 2021, Nature Astronomy, 5, 311

    2021

  17. [17]

    K., Chatzopoulos, S., Gerhard, O., et al

    Fritz, T. K., Chatzopoulos, S., Gerhard, O., et al. 2016, ApJ, 821, 44

    2016

  18. [18]

    K., Patrick, L

    Fritz, T. K., Patrick, L. R., Feldmeier-Krause, A., et al. 2021, A&A, 649, A83 Gaia Collaboration, Prusti, T., de Bruijne, J. H. J., et al. 2016, A&A, 595, A1

    2021

  19. [19]

    2010, Reviews of Modern Physics, 82, 3121

    Genzel, R., Eisenhauer, F., & Gillessen, S. 2010, Reviews of Modern Physics, 82, 3121

    2010

  20. [20]

    Ghez, A. M. 2007, in Astronomical Society of the Pacific Conference Series, V ol. 367, Massive Stars in Interactive Binaries, ed. N. St. -Louis & A. F. J. Moffat, 689

    2007

  21. [21]

    Y ., Ostriker, J

    Gnedin, O. Y ., Ostriker, J. P., & Tremaine, S. 2014, ApJ, 785, 71

    2014

  22. [22]

    A., Mucciarelli, A., Origlia, L., et al

    Gonzalez, O. A., Mucciarelli, A., Origlia, L., et al. 2020, The Messenger, 180, 18

    2020

  23. [23]

    2008, A&A, 486, 951

    Gustafsson, B., Edvardsson, B., Eriksson, K., et al. 2008, A&A, 486, 951

    2008

  24. [24]

    C., Dalton, G

    Jin, S., Trager, S. C., Dalton, G. B., et al. 2024, MNRAS, 530, 2688

    2024

  25. [25]

    Launhardt, R., Zylka, R., & Mezger, P. G. 2002, A&A, 384, 112

    2002

  26. [26]

    2022, A&A, 661, A140

    Magg, E., Bergemann, M., Serenelli, A., et al. 2022, A&A, 661, A140

    2022

  27. [27]

    R., Schiavon, R

    Majewski, S. R., Schiavon, R. P., Frinchaboy, P. M., et al. 2017, AJ, 154, 94 Milosavljevi´c, M. 2004, ApJ, 605, L13

    2017

  28. [28]

    & Serabyn, E

    Morris, M. & Serabyn, E. 1996, ARA&A, 34, 645

    1996

  29. [29]

    2025, ApJ, 982, L14

    Nandakumar, G., Ryde, N., Schultheis, M., et al. 2025, ApJ, 982, L14

    2025

  30. [30]

    2018, MNRAS, 478, 4374

    Nandakumar, G., Ryde, N., Schultheis, M., et al. 2018, MNRAS, 478, 4374

    2018

  31. [31]

    2023, A&A, 671, A94

    Nieuwmunster, N., Nandakumar, G., Spitoni, E., et al. 2023, A&A, 671, A94

    2023

  32. [32]

    2024, A&A, 685, A93

    Nieuwmunster, N., Schultheis, M., Sormani, M., et al. 2024, A&A, 685, A93

    2024

  33. [33]

    M., Ferraro, F

    Origlia, L., Rich, R. M., Ferraro, F. R., et al. 2011, ApJ, 726, L20

    2011

  34. [34]

    & Kroupa, P

    Pflamm-Altenburg, J. & Kroupa, P. 2009, MNRAS, 397, 488

    2009

  35. [35]

    2012, Turbospectrum: Code for spectral synthesis, Astrophysics Source Code Library, record ascl:1205.004

    Plez, B. 2012, Turbospectrum: Code for spectral synthesis, Astrophysics Source Code Library, record ascl:1205.004

    2012

  36. [36]

    2017, MNRAS, 465, 1621 Ramírez, S

    Portail, M., Gerhard, O., Wegg, C., & Ness, M. 2017, MNRAS, 465, 1621 Ramírez, S. V ., Stephens, A. W., Frogel, J. A., & DePoy, D. L. 2000, AJ, 120, 833

    2017

  37. [37]

    M., Origlia, L., & Valenti, E

    Rich, R. M., Origlia, L., & Valenti, E. 2007, ApJ, 665, L119

    2007

  38. [38]

    M., Origlia, L., & Valenti, E

    Rich, R. M., Origlia, L., & Valenti, E. 2012, ApJ, 746, 59

    2012

  39. [39]

    M., Ryde, N., Thorsbro, B., et al

    Rich, R. M., Ryde, N., Thorsbro, B., et al. 2017, AJ, 154, 239

    2017

  40. [40]

    & Pakhomov, Y

    Ryabchikova, T. & Pakhomov, Y . 2015, Baltic Astronomy, 24, 453

    2015

  41. [41]

    2025, ApJ, 979, 174

    Ryde, N., Nandakumar, G., Schultheis, M., et al. 2025, ApJ, 979, 174

    2025

  42. [42]

    & Schultheis, M

    Ryde, N. & Schultheis, M. 2015, A&A, 573, A14

    2015

  43. [43]

    2016a, AJ, 151, 1 Schödel, R., Feldmeier, A., Kunneriath, D., et al

    Ryde, N., Schultheis, M., Grieco, V ., et al. 2016a, AJ, 151, 1 Schödel, R., Feldmeier, A., Kunneriath, D., et al. 2014, A&A, 566, A47

    2014

  44. [44]

    M., Origlia, L., et al

    Schultheis, M., Rich, R. M., Origlia, L., et al. 2019, A&A, 627, A152

    2019

  45. [45]

    2020, A&A, 642, A81

    Schultheis, M., Rojas-Arriagada, A., Cunha, K., et al. 2020, A&A, 642, A81

    2020

  46. [46]

    2016, A&A, 590, A6

    Schultheis, M., Ryde, N., & Nandakumar, G. 2016, A&A, 590, A6

    2016

  47. [47]

    C., Blum, R

    Seth, A. C., Blum, R. D., Bastian, N., Caldwell, N., & Debattista, V . P. 2008, ApJ, 687, 997

    2008

  48. [48]

    C., Gerhard, O., Portail, M., Vasiliev, E., & Clarke, J

    Sormani, M. C., Gerhard, O., Portail, M., Vasiliev, E., & Clarke, J. 2022, MN- RAS, 514, L1

    2022

  49. [49]

    M., et al

    Thorsbro, B., Ryde, N., Rich, R. M., et al. 2020, ApJ, 894, 26

    2020

  50. [50]

    & Davis, M

    Tonry, J. & Davis, M. 1979, AJ, 84, 1511

    1979

  51. [51]

    D., Ostriker, J

    Tremaine, S. D., Ostriker, J. P., & Spitzer, L., J. 1975, ApJ, 196, 407

    1975

  52. [52]

    2019, MNRAS, 482, 1525

    Vasiliev, E. 2019, MNRAS, 482, 1525

    2019

  53. [53]

    2011, A&A, 536, A105 Article number, page 8 of 8

    Vernet, J., Dekker, H., D’Odorico, S., et al. 2011, A&A, 536, A105 Article number, page 8 of 8

    2011

This paper was first reviewed by grok-4.3 on June 26, 2026.