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arxiv: 1906.09500 · v1 · pith:PLLVFB4Ynew · submitted 2019-06-22 · 🌌 astro-ph.GA · astro-ph.SR

Solving the distance discrepancy for the open cluster NGC 2453. The planetary nebula NGC 2452 is not a cluster member

D. Gonz\'alez-D\'iaz , C. Moni Bidin , E. Silva-Villa , G. Carraro , D. Majaess , A. Moitinho , Orquera-Rojas , C. A. L. Morales Mar\'in
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E. Morales-Campa\~na
This is my paper

Pith reviewed 2026-05-25 17:54 UTC · model grok-4.3

classification 🌌 astro-ph.GA astro-ph.SR
keywords open clusterplanetary nebulaNGC 2453NGC 2452radial velocityGaia DR2isochrone fittingcluster membership
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The pith

Radial velocity and Gaia distance data show the planetary nebula NGC 2452 is a foreground object unrelated to the open cluster NGC 2453.

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

The paper measures radial velocities for 11 candidate stars in NGC 2453 and for the planetary nebula NGC 2452, then combines those velocities with Gaia DR2 data to derive the cluster distance. Deep UBVRI photometry is used to fit isochrones to the most probable members and obtain an independent distance and age. The resulting cluster distance of 4.7 kpc and velocity of 78 km/s conflict with the nebula's velocity of 62 km/s, indicating the nebula lies in the foreground. This resolves prior disagreements in the literature and establishes that the nebula is not physically associated with the cluster.

Core claim

The open cluster NGC 2453 lies at 4.7 ± 0.2 kpc with a radial velocity of 78 ± 3 km s^{-1} and an age of 40-50 Myr, while the planetary nebula NGC 2452 has a radial velocity of 62 ± 2 km s^{-1} and is therefore a foreground object in the same line of sight rather than a cluster member.

What carries the argument

Radial velocity measurements of 11 potential members combined with Gaia DR2 parallaxes and UBVRI photometry for isochrone fitting to determine cluster parameters and test membership.

If this is right

  • The cluster parameters can be used without contamination from the unrelated nebula.
  • Membership lists for NGC 2453 should exclude NGC 2452.
  • The previously reported distance discrepancy between the cluster and nebula is resolved in favor of non-membership.
  • Isochrone-derived age of 40-50 Myr is now tied to a firmly measured distance.

Where Pith is reading between the lines

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

  • The same velocity-plus-Gaia approach could test other claimed planetary-nebula memberships in open clusters.
  • Some fraction of previously accepted cluster planetary nebulae may turn out to be line-of-sight coincidences once Gaia data are applied.
  • Updated cluster catalogs should flag NGC 2453 as having no associated planetary nebula.

Load-bearing premise

The 11 selected stars are true cluster members whose radial velocities accurately reflect the cluster's overall motion without major contamination or error.

What would settle it

A precise distance measurement for NGC 2452 that equals 4.7 kpc would falsify the conclusion that the nebula is not a member.

Figures

Figures reproduced from arXiv: 1906.09500 by A. Moitinho, C. A. L. Morales Mar\'in, C. Moni Bidin, D. Gonz\'alez-D\'iaz, D. Majaess, E. Morales-Campa\~na, E. Silva-Villa, G. Carraro, Orquera-Rojas.

Figure 1
Figure 1. Figure 1: Examples of reduced spectra. The wavelength intervals used in RV measurements are shown as horizontal lines. The spectra are labeled as T and A for ‘target’ and ‘additional stars’, respectively. The spectra have been shifted vertically to avoid overlap. 2.2. Photometric data Our study is based on the optical UBVRI photometric catalog presented by Moitinho (2001). The data were acquired in January 1998 at t… view at source ↗
Figure 2
Figure 2. Figure 2: Reduced spectrum of the PN NCG 2452. The flux was normal￾ized to the height of the Hβ line. Teff=22000 K, log g = 4.5, except for MSP 211 and NGC 2453 16, which required a cooler model (6000 and 10000 K, respectively), and the red giant TYC 6548-790-1, for which the correlation height was maximized at Teff = 4000 K and log g = 2.5. Moni Bidin et al. (2011) and Morse et al. (1991) showed that the exact choi… view at source ↗
Figure 4
Figure 4. Figure 4: Proper motion of stars within 20 .5 of the NGC 2453 center (gray points), from the Gaia DR2 catalog. The open red circles and black squares show the position of the target and additional stars, respectively. The triangle indicates the MF54 star. of these measurements, and is reported in [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: CMDs and TCDs of NGC 2453. Left panels: The V-(B − V) CMD. Dashed and solid lines depict isochrones of 40 Myr and 50 Myr, respectively, shifted in magnitude for a distance of 4.7 kpc. Right panels: (U − B)-(B − V) TCDs. Black and red lines depict intrinsic and reddened isochrones, respectively, and the arrow shows the reddening direction. Bottom panels: Zoomed region of the upper panels around the MLM star… view at source ↗
Figure 6
Figure 6. Figure 6: Radial density profile constructed for NGC 2453 using proper motions from Gaia DR2. The radial distance of NGC 2452 is indicated with an arrow. The full line shows the field level as the average of all the points with r > 110 . the inclusion of one or both of these two stars during the isochrone fitting procedure can change the cluster age from 15 to 40 Myr. In [PITH_FULL_IMAGE:figures/full_fig_p007_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Distance–RV plot in the direction of Puppis. The solid curve shows our theoretical model based on Galactic rotation, with the dashed curves used to indicate the 1σ propagation errors. Gray circles are clas￾sical Galactic Cepheids from Mel’nik et al. (2015) in the third quad￾rant with Galatic latitudes −2° < b < 2°, while triangles are bright stars with available RVs from Gaia DR2 with 242.5° < l < 243.5° a… view at source ↗
read the original abstract

The open cluster (OC) NGC 2453 is of particular importance since it has been considered to host the planetary nebula (PN) NGC 2452, however their distances and radial velocities are strongly contested. In order to obtain a complete picture of the fundamental parameters of the OC NGC 2453, 11 potential members were studied. The results allowed us to resolve the PN NGC 2452 membership debate. Radial velocities for the 11 stars in NGC 2453 and the PN were measured and matched with Gaia data release 2 (DR2) to estimate the cluster distance. In addition, we used deep multi-band UBVRI photometry to get fundamental parameters of the cluster via isochrone fitting on the most likely cluster members, reducing inaccuracies due to field stars.The distance of the OC NGC 2453 (4.7 $\pm$ 0.2 kpc) was obtained with an independent method solving the discrepancy reported in the literature. This result is in good agreement with an isochrone fitting of 40-50 Myr. On the other hand, the radial velocity of NGC 2453 ($78 \pm 3$ km s$^{-1}$) disagrees with the velocity of NGC2452 ($62 \pm 2$ km s$^{-1}$). Our results show that the PN is a foreground object in the line of sight. Due to the discrepancies found in the parameters studied, we conclude that the PN NGC 2452 is not a member of the OC NGC 2453.

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.

Referee Report

2 major / 1 minor

Summary. The manuscript claims that new radial velocity measurements for 11 potential members of open cluster NGC 2453 and for PN NGC 2452, combined with Gaia DR2 astrometry and UBVRI photometry for isochrone fitting, yield a cluster distance of 4.7 ± 0.2 kpc and systemic RV of 78 ± 3 km s^{-1}. The PN RV of 62 ± 2 km s^{-1} differs significantly, leading to the conclusion that NGC 2452 is a foreground object and not a cluster member, thereby resolving prior distance and membership discrepancies.

Significance. If the 11-star sample is shown to be uncontaminated, the work would provide an independent Gaia-based distance and RV benchmark that settles a contested association in the literature. The combination of spectroscopy, astrometry, and photometry follows standard practice for cluster parameter determination and could serve as a template for similar PN-OC membership tests.

major comments (2)
  1. [Sample selection / observations] The description of the stellar sample (abstract and § on observations) provides no explicit membership criteria such as Gaia DR2 proper-motion clipping, parallax consistency thresholds, or probability cuts. Because the cluster RV mean of 78 ± 3 km s^{-1} is derived solely from these 11 stars and is the decisive datum separating the PN, lack of documented selection directly undermines in the 16 km s^{-1} offset.
  2. [Isochrone fitting / results] The isochrone fit is performed on 'most likely cluster members' drawn from the same 11-star set used for the RV mean. No quantitative test (e.g., jackknife or contamination simulation) is reported to show how field interlopers would shift either the RV or the fitted distance/age, even though the non-membership claim rests on both quantities being reliable.
minor comments (1)
  1. [Abstract / distance determination] The abstract states the distance was 'obtained with an independent method' but does not clarify whether the Gaia DR2 value is a simple parallax inversion or involves a more involved Bayesian or photometric correction; this should be stated explicitly in the methods.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments, which highlight areas where our methods can be clarified. We address each major comment below and will revise the manuscript to improve transparency.

read point-by-point responses

  1. Referee: [Sample selection / observations] The description of the stellar sample (abstract and § on observations) provides no explicit membership criteria such as Gaia DR2 proper-motion clipping, parallax consistency thresholds, or probability cuts. Because the cluster RV mean of 78 ± 3 km s^{-1} is derived solely from these 11 stars and is the decisive datum separating the PN, lack of documented selection directly undermines in the 16 km s^{-1} offset.

    Authors: We agree that explicit membership criteria were not detailed in the abstract or observations section. The 11 stars were identified as potential members using a combination of positional coincidence, Gaia DR2 proper motions and parallaxes consistent with the cluster, and photometric placement on the expected main sequence. We will revise the observations section to document the specific selection steps and thresholds applied. revision: yes

  2. Referee: [Isochrone fitting / results] The isochrone fit is performed on 'most likely cluster members' drawn from the same 11-star set used for the RV mean. No quantitative test (e.g., jackknife or contamination simulation) is reported to show how field interlopers would shift either the RV or the fitted distance/age, even though the non-membership claim rests on both quantities being reliable.

    Authors: The referee is correct that no quantitative robustness test against contamination is reported. The conclusions rely on the internal consistency between the RV offset, the Gaia-based distance, and the independent isochrone age. We will add a short discussion of possible field-star effects and, if feasible with the existing data, a simple contamination estimate in the revised version. revision: yes

Circularity Check

0 steps flagged

No significant circularity; results from new RV measurements, Gaia DR2 parallaxes, and photometry.

full rationale

The derivation uses direct new spectroscopic radial velocities for the 11 stars and PN, Gaia DR2 data for distance, and independent UBVRI photometry for isochrone fitting. The non-membership conclusion follows from the observed RV offset and distance consistency with the isochrone age. No self-definitional relations, fitted inputs renamed as predictions, or load-bearing self-citations appear in the abstract or described chain. The selection of 'potential members' and 'most likely cluster members' relies on external data sources rather than reducing to prior outputs of the same analysis.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The claim rests on standard domain assumptions in astronomy regarding data reliability and model applicability, with one fitted distance parameter derived from observations.

free parameters (1)
  • cluster distance = 4.7 kpc
    Obtained via matching RV and Gaia DR2, but the precise fitting procedure and any adjustments are not specified in the abstract.
axioms (2)
  • domain assumption Gaia DR2 parallaxes provide reliable distance estimates for stars in this cluster
    Used to estimate cluster distance from the 11 stars.
  • domain assumption Isochrone models accurately represent the stellar population for age determination
    Used for fundamental parameters via isochrone fitting.

pith-pipeline@v0.9.0 · 5874 in / 1463 out tokens · 57995 ms · 2026-05-25T17:54:27.896348+00:00 · methodology

discussion (0)

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Reference graph

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