Pith. sign in

REVIEW 4 major objections 4 minor 9 references

Trumpler's Radial Velocities of Stars in Galactic Star Clusters

T0 review · 4 major / 4 minor · reviewed 2026-08-15 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗ Review JSON

Pith's one-line read Trumpler's 1924–1947 radial velocities of 671 stars in Galactic open clusters are accurate to 2–7 km/s and share the zero-point and scale of modern radial-velocity standards.

desk verdict A valuable digitization of Trumpler's radial velocities, but the headline accuracy claim for all 671 stars is only weakly validated. read the letter →

arxiv 2505.16584 v1 pith:U4C6PHIK submitted 2025-05-14 astro-ph.SR astro-ph.GAphysics.hist-ph

Geoffrey W. Marcy , Dylan M. Lynn This is my paper · ORCID
classification astro-ph.SRastro-ph.GAphysics.hist-ph
keywords radialvelocitiesopenclustersTrumplercataloghistoricalastronomyIAUvelocitystandardsspectroscopicbinariescentury-longbaselinestellarkinematics
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

Robert Trumpler measured Doppler shifts of stars near Galactic open clusters from 1924 to 1947 with a photographic refractor, but the results were locked in a paper-only catalog. This paper argues those old velocities are surprisingly sound: they share the zero-point and scale of today's radial-velocity standard system, with errors of about 2 km/s for bright stars and up to 6–7 km/s for fainter ones. The evidence comes from new high-resolution spectra of four bright stars and from 450 stars with modern velocities. If correct, the catalog becomes a nearly century-long baseline for finding long-period binary companions, cluster accelerations, and perturbations from passing massive objects.

What carries the argument

The load-bearing object is the 671-star catalog itself: each entry carries Trumpler's averaged velocity, his 'probable error', the Julian dates of the first and last observation, and a modern star identification. The accuracy argument runs through a calibration chain: Trumpler removed systematic spectral-type-dependent offsets by comparing bright stars against the General Catalogue of Stellar Radial Velocities, and this paper checks the endpoint of that chain against current standard-system velocities. The century-long time baseline between the 1924–1947 observations and the present is what makes the catalog scientifically valuable.

What would settle it

Take a sample of roughly 25–30 catalog stars fainter than 11th magnitude, measure their radial velocities today with a high-resolution spectrograph, and compare with Trumpler's values; if the RMS difference exceeds about 7 km/s or grows systematically with magnitude, the claim of uniform 2–7 km/s accuracy for the whole catalog is false.

Watch

Extended reading notes

Core claim

Trumpler's published velocities for 671 stars are on the same velocity scale as modern standards, with no significant zero-point offset. New Doppler measurements of four sixth-magnitude FGK giants and supergiants differ from Trumpler's values by a mean of −0.48 km/s with a scatter of 1.89 km/s, and 450 catalog stars compared with modern velocities scatter with a standard deviation of 6 km/s. The paper concludes that Trumpler's errors range from 2 km/s for stars brighter than 8th magnitude to about 6–7 km/s for stars as faint as 13th magnitude, with part of the 6 km/s scatter attributable to binaries and inhomogeneous comparison data. It also supplies secure modern identifications, B-band photometry, and an online copy of the original 392-page catalog including all 3,782 individual velocities with Julian dates.

Load-bearing premise

The stated 2–7 km/s accuracy for the whole catalog assumes that four bright stars observed with a modern spectrograph and the 450 stars with archival modern velocities fairly represent all 671 entries, including the fainter 9th–13th magnitude stars and Be, emission-line, and double-lined stars.

Editorial extensions

If this is right

  • Stars in the catalog can be re-observed today; any velocity change over roughly 80–100 years reveals a companion, a cluster acceleration, or a passing perturber.
  • Cluster membership can be tested with a second epoch: a star that kept the cluster's mean velocity for a century is far more likely to be a true member.
  • The Julian dates in the catalog allow period constraints for long-period binaries, since a changing velocity between two old epochs can be combined with modern measurements.
  • The scanned 392-page original makes all individual measurements, not just averages, available for orbital fits and outlier checks.
  • If the faint-end accuracy holds, the catalog provides an early snapshot of cluster kinematics that can be compared directly with modern surveys.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • Because Trumpler's zero-point was transferred through the mid-century General Catalogue, any systematic error in that intermediate catalog is inherited; comparing faint catalog stars with an independent modern survey would test whether the calibration chain held.
  • The catalog could be cross-matched with modern astrometric and spectroscopic surveys to place a 1930s velocity epoch alongside current kinematics, turning open clusters into four-dimensional dynamical laboratories.
  • A targeted re-measurement of 20–30 of the faintest catalog stars would either confirm the stated 6–7 km/s errors or force a brightness-dependent error model.
Share X Bluesky LinkedIn Reddit HN

Signed reviews

No signed human review yet.

Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

4 major / 4 minor

Summary. The paper digitizes and assesses Robert Trumpler's 1924–1947 Lick Observatory radial velocities of 671 stars near 73 Galactic open clusters, as compiled by Weaver (1966). It provides modern identifications, B-band photometry, notes, and a link to a scanned PDF of the original 392-page volume containing 3,782 individual velocities with Julian dates. The central claim is that Trumpler's velocities share the zero-point and scale of modern IAU radial velocity standards, with errors of 2–7 km/s depending on brightness. This claim rests on two comparisons: four FGK giants/supergiants observed with Keck-HIRES (mean difference -0.48 km/s, standard deviation 1.89 km/s) and 450 stars with SIMBAD radial velocities (standard deviation 6 km/s around the one-to-one line). The paper also notes that Trumpler had applied spectral-type-dependent corrections to force his raw velocities onto the zero-point of the General Catalogue of Stellar Radial Velocities (GCRV).

Significance. If the accuracy claim is supported, the catalog is genuinely valuable: it provides a near-century baseline for detecting long-period binaries, cluster-internal accelerations, and perturbations from passing objects, and it makes previously inaccessible historical measurements publicly available. The authors' careful cross-identification of 671 stars and their inclusion of the full individual-epoch velocities are substantial contributions. The paper is also transparent about the historical GCRV calibration and about the small size of the independent Keck sample. However, the validation currently in the manuscript is not sufficient to establish the stated 2–7 km/s accuracy for the full catalog, especially for faint stars and for the many B, Be, emission-line, and binary stars listed in the Notes.

major comments (4)
  1. [§5, Table 1, Fig. 2] The accuracy claim for all 671 stars (Abstract; §6) is not supported by the presented checks. The Keck comparison comprises only four roughly 6th-magnitude FGK giants/supergiants, and one of them (HD 162587, note 349) is flagged as a close double observed as one star, with a 3.1 km/s residual. No magnitude-binned or spectral-type-binned residual analysis is shown, even though Section 6 states a gradient from 2 km/s brighter than 8th magnitude to 6 km/s at 13th magnitude and the Notes show that the catalog deliberately includes B, Be, emission-line, and double-lined stars. The 450-star SIMBAD comparison in Figure 2 is presented only as an unbinned scatter. I request a binned residual analysis and, ideally, independent modern velocities (for example from Gaia RVS or additional Keck observations) for the faint end and for the spectrally peculiar stars before the full-catalog accuracy range is claimed.
  2. [§5, Fig. 2] The 6 km/s standard deviation around the one-to-one line cannot by itself be read as Trumpler's error of 2–6 km/s; it is the quadrature sum of Trumpler's errors, SIMBAD measurement errors, and real velocity variation from binaries. The text acknowledges this in words but then reaches the strong conclusion that Trumpler's velocities have 'errors of 2 to 6 km/s.' I ask for a decomposition, for example by using stars with multiple modern epochs or by excluding known binaries and variables, so that the fraction of the 6 km/s scatter attributable to Trumpler is actually quantified rather than asserted.
  3. [§5] The zero-point agreement is partly inherited by construction: Trumpler deliberately corrected his raw velocities to the General Catalogue of Stellar Radial Velocities (Wilson 1953), and the GCRV is an ancestor of the modern IAU radial-velocity standard system and of many SIMBAD values. The paper is transparent about this correction, but the concluding sentence of Section 5, 'Trumpler's listed radial velocities are consistent with the zero-point and the scale of the IAU radial velocity standard stars,' is therefore not an independent validation. The only fully independent check is the four-star Keck set. Please state this limitation explicitly and either base the headline claim on the independent subset or add more independent measurements.
  4. [§5, Keck comparison] The Keck-HIRES validation is missing essential observational details that matter when the sample is only four stars: dates of the Keck observations, signal-to-noise ratios, number of spectral orders or lines used, and individual residuals and uncertainties for each of the four stars. Because the entire independent validation rests on these four measurements, these details should be reported so the reader can judge whether, for example, the flagged close double HD 162587 should be excluded or downweighted.
minor comments (4)
  1. [Abstract, §5, §6] The stated accuracy range is inconsistent: the Abstract says 2 to 7 km/s, while Sections 5 and 6 say 2 to 6 km/s. Please unify the quoted range.
  2. [Table 1] Several Julian-date entries appear to be missing a leading digit: for example '2297.066' for a Pleiades star is presumably 22975.066, '2954.847' for a NGC 6709 star is presumably 29544.847, and '20174.784' for a NGC 6231 star is presumably 30174.784. Please correct these before publication.
  3. [§5] There are typographical errors in the text, including a stray comma in 'within 1 km s−1, .' and 'uncertainaties' in the Figure 2 caption; 'newly injested' in Section 5 should be 'newly ingested'; and 'T rumpler' has a stray space.
  4. [§6] The online PDF is hosted on Dropbox; for long-term accessibility I recommend depositing the scanned volume and the machine-readable table in a permanent archive such as Zenodo or the CDS and providing a DOI.

Circularity Check

1 steps flagged · score 4.0 of 10

Zero-point agreement is partly built in via Trumpler's GCRV calibration; a small independent Keck check limits the circularity.

  1. self definitional [Section 5 (The Uncertainties of the Radial Velocities), including Figure 2 caption; echoed in Section 6]
    "He computed the average difference in radial velocity, for a given spectral type and luminosity class, and applied them to all of his raw measurements to yield final radial velocities that had the systematic difference removed between his velocities and those of the Catalogue. In that way, he ensured that his radial velocities had the same zero-point and scale as those in that General Catalogue. ... We also compared Trumpler's measured radial velocities to those listed in the SIMBAD database. ..."

    Trumpler's published velocities are not raw: they are constructed by subtracting spectral-type- and luminosity-class-dependent mean offsets from the GCRV (Wilson 1953). The paper then uses a 450-star SIMBAD comparison as evidence of zero-point and scale agreement. SIMBAD aggregates GCRV entries, and many Table 1 notes explicitly give 'Radial velocity from GCSRV/Wilson', so for those entries Trumpler-minus-SIMBAD is zero by construction, not by independent measurement. The claimed consistency with the IAU zero-point therefore inherits Trumpler's GCRV calibration. Only the four Keck-HIRES FGK giants/supergiants are a genuinely independent check, and they cover only bright, narrow-lined stars, not the full 671-star, 2-13 mag, B/Be/SB2 sample.

full rationale

The paper is transparent about Trumpler's historical calibration to the General Catalogue of Stellar Radial Velocities, and it adds a small independent Keck-HIRES check of four bright stars. Those four stars give a mean offset of -0.48 km/s with a 1.89 km/s scatter, which is real external evidence for the bright-star zero-point and scale. However, the SIMBAD comparison used to extend the claim to the full catalog is partly circular because SIMBAD contains GCRV velocities, the same catalog to which Trumpler's final velocities were adjusted. The paper also repeats Trumpler's GCRV-based 2-6 km/s error estimate as its own conclusion, without magnitude-binned independent validation at the faint end. These issues make the central accuracy claim partially inherited rather than fully derived, but the Keck data and the documented historical measurement procedure keep the work from being wholly circular.

Assumptions & free parameters 0 free parameters · 5 assumptions · 0 invented entities

The central claim rests on the representativeness of the comparison samples and on inherited GCRV calibration; no new physical entities or fitted constants are introduced.

assumptions (5)
  • domain assumption Trumpler's spectral-type/luminosity-class zero-point corrections to GCRV are valid for all catalog stars.
    Section 5 says Trumpler applied average differences from GCRV to all raw measurements; the paper's accuracy claim inherits this calibration for stars outside that comparison.
  • domain assumption The four Keck targets represent the full brightness range of the catalog.
    Section 5 uses four approximately 6th magnitude FGK giants/supergiants to set the bright-star uncertainty; fainter stars are not independently tested.
  • domain assumption SIMBAD radial velocities are accurate enough to serve as a comparison baseline.
    Figure 2 and Section 5 use SIMBAD values as the reference; SIMBAD is heterogeneous and itself contains old velocities.
  • domain assumption The star identifications from Aladin and SKY-MAP are correct.
    Section 2 describes manual cross-matching; a misidentification would corrupt the comparison.
  • domain assumption The scanned PDF is a faithful reproduction of Weaver (1966).
    Section 6 states the PDF is the full catalog, but the scan is provided via a provisional Dropbox link.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Trumpler's Radial Velocities of Stars in Galactic Star Clusters." pith.science (2026). https://pith.science/paper/U4C6PHIK

@misc{pith2026250516584,
  author       = {Pith},
  title        = {Pith review of: Trumpler's Radial Velocities of Stars in Galactic Star Clusters},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/U4C6PHIK}},
  note         = {Machine review of arXiv:2505.16584}
}
read the original abstract

We assess the accuracy of radial velocities of 671 stars located near Galactic clusters, measured by Robert Trumpler between 1924 and 1947 using the Lick Observatory 36 inch refractor equipped with prism spectrometers. We find that Trumpler's velocities share the same zero-point and scale as modern IAU radial velocity standards. Their accuracy ranges from 2 to 7 km/s. We also provide star identifications, B-band photometry, and notes for many stars. We provide a link to an online PDF that contains all 3,782 of Trumpler's individual stellar radial velocities and associated Julian dates. Trumpler's velocities provide a century-long baseline for detecting long-period stellar companions, gravitational perturbations from passing massive objects, and accelerations due to cluster and Galactic dynamics.

Figures

Figures reproduced from arXiv: 2505.16584 by the authors.

Figure 1
Figure 1. A representative page from the three-volume notebook of radial velocity measurements by Trumpler, assembled by Weaver (1966). The first column gives Trumpler’s internal number for the star within its cluster, marked on a separate photograph. The 2nd and 3rd columns provide the displacement in x and y, in arcseconds, relative to the center of the open cluster, NGC 2264. The next two columns give Trumpler’s measured ”… view at source ↗
Figure 2
Figure 2. Radial velocities from Trumpler vs. radial velocities listed in SIMBAD, for those stars having measurements from both. Trumpler obtained all velocity measurements between 1924 to 1947 while the quoted radial velocities in SIMBAD are more recent. The diagonal blue line represents the locus at which both velocities are the same. The clustering around the diagonal line indicates that Trumpler’s radial velocities have t… view at source ↗

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

9 extracted references · 5 canonical work pages

  1. [1]

    , " * write output.state after.block = add.period write newline

    ENTRY address archivePrefix author booktitle chapter doi edition editor eprint howpublished institution journal key month number organization pages publisher school series title misctitle type volume year version url label extra.label sort.label short.list INTEGERS output.state before.all mid.sentence after.sentence after.block FUNCTION init.state.consts ...

  2. [2]

    write newline

    " write newline "" before.all 'output.state := FUNCTION format.url url empty "" new.block "" url * "" * if FUNCTION format.eprint eprint empty "" archivePrefix empty "" archivePrefix "arXiv" = new.block " " eprint * " " * new.block " " eprint * " " * if if if FUNCTION format.doi doi empty "" " " doi * " " * if FUNCTION format.pid doi empty eprint empty ur...

  3. [3]

    ? 3 ! 1 AQa

    thebibliography [1] 20pt to REFERENCES 6pt =0pt -12pt 10pt plus 3pt =0pt =0pt =1pt plus 1pt =0pt =0pt -12pt =13pt plus 1pt =20pt =13pt plus 1pt \@M =10000 =-1.0em =0pt =0pt 0pt =0pt =1.0em @enumiv\@empty 10000 10000 `\.\@m \@noitemerr \@latex@warning Empty `thebibliography' environment \@ifnextchar \@reference \@latexerr Missing key on reference command E...

    2021

  4. [4]

    A., et al

    Chubak , C., Marcy , G., Fischer , D. A., et al. 2012, arXiv e-prints, arXiv:1207.6212, 10.48550/arXiv.1207.6212

    arXiv doi:10.48550/arxiv.1207.6212 2012

  5. [5]

    Gill , D., & Kapteyn , J. C. 1896, Annals of the Cape Observatory, 3, 1

    work page

  6. [6]

    P., Latham , D

    Stefanik , R. P., Latham , D. W., & Torres , G. 1999, in Astronomical Society of the Pacific Conference Series, Vol. 185, IAU Colloq. 170: Precise Stellar Radial Velocities, ed. J. B. Hearnshaw & C. D. Scarfe , 354

    work page 1999

  7. [7]

    Weaver , H. F. 1966, Publications of the Lick Observatory, XXI, 1

    work page 1966

  8. [8]

    Weaver , H. F. 1967, in IAU Symposium, Vol. 30, Determination of Radial Velocities and their Applications, ed. A. H. Batten & J. F. Heard , 153

    work page 1967

Show all 9 references
  1. [9]

    Wilson , R. E. 1953, General Catalogue of Stellar Radial Velocities,"GCSRV",Mount Wilson and Palomar Observatories, Carnegie Institution of Washington D.C.,Caltech

    1953

Pith tools

Reviewed August 15, 2026 · model on record in the stance chip above.