A Multi-dimensional Analysis of the Open Clusters NGC 2423 and NGC 2482 with Gaia DR3

arXiv:2610.10683 · astro-ph.GA · Submitted 2026-10-07 · Read on arXiv

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Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: Today's paper: "A Multi-dimensional Analysis of the Open Clusters NGC 2423 and NGC 2482 with Gaia DR3".

Jocelyn: The gist: This study presents a homogeneous photometric, astrometric, and kinematic analysis of the two Hyades-like open clusters NGC 2423 and NGC 2482 based on data from Gaia DR3.

Vera: First, who's behind it and why it matters.

Paper summary: Vera: So we're looking at this paper, "A Multi-dimensional Analysis of the Open Clusters NGC two thousand four hundred twenty-three and NGC two thousand four hundred eighty-two with Gaia DR3 <ref:2610.10683#pg1,A Multi-dimensional Analysis of the Open Clusters NGC 2423 and NGC>." The main thing here is they are taking these two Hyades-like open clusters and running a full check using Gaia DR3 data to see how they look photometrically, astrometrically, and kinematically.

Jocelyn: It sounds like the authors are trying to establish a really solid baseline for these two systems before we jump into deeper structural stuff.

Subrahmanyan: They're essentially trying to use all this high-precision data from Gaia DR3 to confirm what people already knew about these clusters, but with a much more thorough approach than they had before Vera Right, so the thesis is really about using this multi-dimensional look—photometric and astrometric—along with kinematics, specifically the UPMASK algorithm—to properly figure out if these clusters are actually members of that Hyades family.

Jocelyn: And what it claims is that by doing this comprehensive check, they can give us much more reliable numbers for things like their distances and their ages Vera Yes, and they find some very specific values coming out of this analysis. They’re getting mean trigonometric parallaxes of one point zero six zero plus or minus zero point zero three five milliarcseconds for NGC two thousand four hundred twenty-three and zero point seven three five plus or minus zero point zero six one for NGC two thousand four hundred eighty-two Subrahmanyan Those distances translate to about nine hundred forty four plus or minus thirty one parsecs for NGC two thousand four hundred twenty-three and thirteen hundred sixty one plus or minus one hundred thirty six parsecs for NGC two thousand four hundred eighty-two <ref:2610.10683#pg1>.

Vera: And then they tie all that together with PARSEC isochrone fitting to get the ages, which they find are about twelve fifty plus or minus one hundred million years for NGC two thousand four hundred twenty-three and four hundred forty five plus or minus fifty million years for NGC two thousand four hundred eighty-two Jocelyn That gives us a picture of how old these systems are based on the stellar evolution models <ref:2610.10683#pg1>. And they also found some values for the observed distance moduli, which are nine point nine zero plus or minus zero point one mag for NGC two thousand four hundred twenty-three and ten point eight zero plus or minus zero point two mag for NGC two thousand four hundred eighty-two <ref:2610.10683#pg1>.

Subrahmanyan: These distance moduli, combined with the reddening values they found—E(GBP minus GRP) is about seven percent plus or minus one percent for NGC two thousand four hundred twenty-three and ten percent plus or minus two percent for NGC two thousand four hundred eighty-two—they give us a way to correct those observed magnitudes into true absolute magnitudes Vera So, when you put all that together, the paper is using Gaia DR3 to nail down the fundamental parameters of these clusters—age, distance, and how much dust is blocking their light <ref:2610.10683#pg1>.

Jocelyn: But it's not just about the basic parameters; they spend a lot of time on membership determination using this UPMASK algorithm in that multi-dimensional space of alpha, delta, parallax, proper motion components...

Paper summary: Vera: That's where the real observational heavy lifting happens. They use Gaia DR3 data for equatorial coordinates alpha and delta, plus the proper motion components mu alpha cos delta and mu delta...

Subrahmanyan: And they incorporate radial velocities when they have them available into that analysis to figure out if these stars actually belong to these clusters kinematically Vera Exactly. They use a membership probability threshold of P greater than or equal to zero point five to decide which stars are candidates for being cluster members in the initial sample Jocelyn That process resulted in five hundred forty-five candidate members for NGC two thousand four hundred twenty-three and sixteen four for NGC two thousand four hundred eighty-two.

Vera: After getting those membership lists, they move on to the structural properties, looking at radial density profiles or RDPs to see how concentrated these clusters are Jocelyn They fit an empirical surface-density model from King one thousand sixty-two to characterize their structure, and they get some concentration parameters C equal to rt over rc for NGC two thousand four hundred twenty-three <ref:2610.10683#pg1>.

Subrahmanyan: And then they look at mass segregation. For NGC two thousand four hundred twenty-three it shows clear signatures where high-mass stars greater than one solar mass are more centrally concentrated Vera That means the older or more massive stars have settled into the core, which is a standard expectation in these systems <ref:2610.10683#pg1>.

Jocelyn: But for NGC two thousand four hundred eighty-two they find that there's no significant difference in how low and high-mass stars are distributed Subrahmanyan The mass function slopes they get are alpha equal to two point four one plus or minus zero point zero six for NGC two thousand four hundred twenty-three and alpha equal to two point two two plus or minus zero point zero three for NGC two thousand four hundred eighty-two <ref:2610.10683#pg1>.

Vera: Moving into the kinematic analysis, they use Gaia DR3 measurements of cluster members to derive mean radial velocities Jocelyn For NGC two thousand four hundred twenty-three the mean radial velocity is eighteen point five four plus or minus zero point zero eight kilometers per second for one eighty eight stars Subrahmanyan And for NGC two thousand four hundred eighty-two that's thirty-nine point zero four plus or minus zero point one four kilometers per second for twenty nine stars <ref:2610.10683#pg1>.

Jocelyn: They also looked at the three-dimensional space velocities derived from Gaia astrometry and any available radial velocity measurements to get their Velocity Ellipsoid Parameters or VEPs Vera These VEPs give us a compact way to describe the internal dynamical state of the system, and they did backward orbit integrations over cluster ages.

Subrahmanyan: And those orbit integrations suggest that NGC two thousand four hundred twenty-three and NGC two thousand four hundred eighty-two formed at Galactocentric radii close to where they are now, following low-eccentricity disc-like orbits with eccentricity less than zero point one Vera Plus they're staying confined near the Galactic plane with a Zmax value less than zero point two kiloparsecs <ref:2610.10683#pg1,NGC 2423 and NGC 2482>.

Jocelyn: The dynamical relaxation times for NGC two thousand four hundred twenty-three are eighteen million years and for NGC two thousand four hundred eighty-two they are thirty-five million years respectively Subrahmanyan And those relaxation times are shorter than their cluster ages, which means both systems have already reached a dynamically relaxed state <ref:2610.10683#pg1>.

Paper summary: Vera: Now, looking at the overall pattern, the paper titled "A Multi-dimensional Analysis of the Open Clusters NGC two thousand four hundred twenty-three and NGC two thousand four hundred eighty-two with Gaia DR3" brings together all these different types of data—photometric, astrometric, and kinematic—from Gaia DR3 to give us a consistent picture <ref:2610.10683#pg1,A Multi-dimensional Analysis of the Open Clusters NGC 2423 and NGC>.

Jocelyn: It’s a pretty comprehensive look at these two clusters that were previously just classified as Hyades-like based on older methods.

Subrahmanyan: What this means for the bigger picture is that they show how these two systems sit in the action space, and their present-day locations overlap with a narrow Lz interval occupied by several Hyades-like clusters Vera This angular momentum range is what you expect for a broad population of thin-disc clusters at Galactocentric radii close to the solar circle.

Jocelyn: So while NGC two thousand four hundred twenty-three and NGC two thousand four hundred eighty-two show different kinematic similarities, NGC two thousand four hundred eighty-two has a close correspondence in the U minus V plane Vera Whereas NGC two thousand four hundred twenty-three has a similar rotational velocity but a substantially different U component <ref:2610.10683#pg1,NGC 2423 and NGC 2482>.

Subrahmanyan: The paper notes that they've identified some limitations to their analysis, specifically that improved radial-velocity completeness and deeper photometry, particularly at the low-mass end and in the cluster outskirts, would further reduce uncertainties in the inferred structural and kinematic trends Jocelyn They are acknowledging that they stopped where their current data can take them.

Vera: So to wrap up this discussion on "A Multi-dimensional Analysis of the Open Clusters NGC two thousand four hundred twenty-three and NGC two thousand four hundred eighty-two with Gaia DR3," it’s a solid, homogeneous analysis using Gaia DR3 to give us consistent distances, reddening values, ages, and mean kinematics <ref:2610.10683#pg1,A Multi-dimensional Analysis of the Open Clusters NGC 2423 and NGC>.

Jocelyn: This paper really helps solidify their status as Hyades-like systems by providing that detailed multi-dimensional look across all the data types they've gathered.

Subrahmanyan: The implication is that understanding how these clusters move through space helps us understand the dynamical influence of the two:one inner Lindblad resonance within the Galactic disk Vera That resonance is a key concept for how these systems maintain their kinematic signature, so this work provides observational constraints on that physics <ref:2610.10683#pg1>.

Vera: So, in simple terms, this paper is using Gaia DR3 to give us a consistent set of distances and ages for NGC two thousand four hundred twenty-three and NGC two thousand four hundred eighty-two while confirming they fit within the known Hyades kinematic family <ref:2610.10683#pg1,for NGC 2423 and NGC 2482>.

Jocelyn: It’s about taking that initial classification and giving it a much more detailed, multi-dimensional test using all the observational tools we have now.

Subrahmanyan: The future work mentioned is about getting better radial-velocity completeness and deeper photometry to reduce those uncertainties in the inferred structural and kinematic trends Vera That’s a practical path for future researchers to follow if they want to get even more precise measurements.

Jocelyn: That sounds like where the next set of observations will focus, building on this work.

Conclusion: Vera: So we've been looking at how these two Hyades-like clusters fit together using Gaia DR3 data, and now we're getting to the wrap-up of this paper on "A Multi-dimensional Analysis of the Open Clusters NGC two thousand four hundred twenty-three and NGC two thousand four hundred eighty-two with Gaia DR3."

Jocelyn: Right, so this study really just puts all those different pieces—the light measurements, the positions in space, and how they move—into one single analysis to confirm these clusters are what we think they are.

Subrahmanyan: From a theoretical standpoint, it’s interesting because it confirms that these systems behave exactly as predicted by our current models for young open clusters in the Galactic disk.

Vera: It does suggest that the dynamical history of these systems is very consistent with how they formed and stayed in their orbits over time.

Jocelyn: And looking at the results, we see them occupying a specific region in space, which helps us map out where other similar clusters might be hiding.

Subrahmanyan: That overlap in action space, specifically that narrow Lz interval you mentioned earlier, is important because it constrains the distribution of stars in thin-disk clusters near the Sun's orbit.

Vera: It means this analysis isn't just about two distant objects; it’s giving us a better picture of a whole family of stars orbiting our Galaxy.

Jocelyn: And while the authors acknowledge they could get better radial velocity completeness and deeper photometry, they still delivered a very solid set of fundamental parameters for these systems.

Subrahmanyan: Exactly, so what this study does is build confidence in the basic physical properties—the distances, the ages, and the kinematics—so we can start thinking about how these clusters interact with the surrounding Galactic environment.

W. H. Elsanhoury, D. C. C¸ ınar, A. Ahmed

Department of Astronomy, National Research Institute of Astronomy & Geophysics (NRIAG) · Programme of Astronomy and Space Sciences, Institute of Graduate Studies in Science, Istanbul University · Department of Astronomy, Faculty of Science, Cairo University

astro-ph.GA

Submitted: 2026-10-07

Updated: 2026-10-07

Comments: 25 pages, including 15 figures and 7 tables, accepted for publication in the Journal of Astrophysics and Astronomy

Code: https://github.com/jobovy/isodist

Project page: https://www.cosmos.esa.int/gaia

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

Importance score: 78/100

The gist: The gist: This study presents a homogeneous photometric, astrometric, and kinematic analysis of the two Hyades-like open clusters NGC 2423 and NGC 2482 based on data from Gaia DR3.

Key concepts

Trigonometric Parallax: This is a measurement from Gaia data indicating the distance to a star in arcseconds. The study found parallaxes of 1.060 mas for NGC 2423 and 0.735 mas for NGC 2482, which were essential for calculating their distances.
UPMASK Algorithm: This is a sophisticated method used to determine if stars belong to a cluster by analyzing their position (alpha, delta), proper motion components, and parallax in a multi-dimensional space. It uses k-means clustering and statistical resampling to find groups with consistent spatial and kinematic properties.
Radial Density Profile (RDP): The RDP is a mathematical tool used to study the physical structure of an open cluster, specifically how stars are distributed radially from the center. Fitting this profile helps quantify aspects like central concentration and overall richness for both NGC 2423 and NGC 2482.
Mass Segregation: This refers to the tendency of massive stars to migrate toward the center of a star cluster over time due to dynamical interactions. The study found that NGC 2423 shows clear signatures of this, while NGC 2482 does not show such a significant difference in star distribution.

Terminology

APEX — 12× in this paper
Metallicity — 11× in this paper · explained in 3 episodes
Mass Segregation — 8× in this paper · explained in 3 episodes
Consistency — 6× in this paper · explained in 3 episodes
Core — 6× in this paper · explained in 2 episodes
Clustering — 5× in this paper · explained in 2 episodes
Abundance — 4× in this paper · explained in 1 episode
Action Space — 4× in this paper · explained in 1 episode
Trace — 3× in this paper · explained in 2 episodes
Markov Chain Monte Carlo — 2× in this paper
Velocity Dispersion — 2× in this paper · explained in 2 episodes
Accuracy — 1× in this paper · explained in 1 episode
Benchmark — 1× in this paper · explained in 2 episodes
David Dunlap Observatory — 1× in this paper
European Space Agency — 1× in this paper
Homogeneity — 1× in this paper · explained in 2 episodes
Robustness — 1× in this paper · explained in 5 episodes

Summary

The gist: This study presents a homogeneous photometric, astrometric, and kinematic analysis of the two Hyades-like open clusters NGC 2423 and NGC 2482 based on data from Gaia DR3.

Cluster Identification and Fundamental Parameters

The research determined that the mean trigonometric parallaxes are derived as ϖ = 1.060±0.035 mas for NGC 2423 and 0.735±0.061 mas for NGC 2482 The corresponding astrometric distances are 944±31 pc (NGC 2423) and 1361±113 pc (NGC 2482) Fundamental parameters were derived through PARSEC isochrone fitting, resulting in ages of 1250 ± 100 Myr and 445 ± 50 Myr Observed distance moduli are (m − M)obs = 9.90 ± 0.10 and 10.80 ± 0.20 mag for NGC 2423 and NGC 2482, respectively Reddening values E(GBP − GRP) = 0.07 ± 0.01 and 0.10 ± 0.02 mag, equivalent to E(B − V) = 0.054 and 0.078

Membership Determination Methodology

Cluster memberships are determined using the UPMASK algorithm in the multi-dimensional parameter space of (α, δ, ϖ, µα cos δ, µδ) with radial velocities incorporated when available This method identifies spatial and kinematic coherence in a multi-dimensional parameter space using k-means clustering and statistical resampling The UPMASK analysis was executed using Gaia DR3 astrometric data, specifically equatorial coordinates (α, δ), proper-motion components (µα cos δ, µδ), and trigonometric parallaxes (ϖ) A membership probability threshold of P ≥ 0.5 was adopted to define the initial sample of probable cluster members This criterion yielded 545 candidate members for NGC 2423 and 164 for NGC 2482

Structural Properties and Mass Function

Radial density profiles (RDPs) provide a simple way to examine the structural properties of open clusters, such as their degree of central concentration and overall richness The empirical surface-density model introduced by King (1962) was fitted to the observed RDPs The resulting structural parameters for both clusters are listed in Table 3 For NGC 2423, the concentration parameter is C = rt/rc, which provides a quantitative measure of cluster compactness Mass segregation analyses reveal different states for the two clusters: NGC 2423 shows clear signatures with high-mass stars (M > 1 M⊙) being more centrally concentrated, while NGC 2482 shows no significant difference in the distributions of low and high-mass stars The mass function slopes are α = 2.41 ± 0.06 for NGC 2423 and α = 2.22 ± 0.03 for NGC 2482

Kinematic and Dynamical Analysis

The mean radial velocities based on Gaia DR3 measurements of cluster members are derived as ⟨Vr⟩ = 18.54 ± 0.08 km s−1 for NGC 2423 (188 stars) and ⟨Vr⟩ = 39.04±0.14 km s−1 for NGC 2482 (29 stars) The internal kinematic properties of the program stars were investigated using their three-dimensional space velocities derived from Gaia astrometry and available radial velocity measurements The resulting Velocity Ellipsoid Parameters (VEPs) provide a compact and physically meaningful description of the internal dynamical state of the system Backward orbit integrations over the cluster ages suggest that NGC 2423 and NGC 2482 formed at Galactocentric radii close to their present-day locations, following low-eccentricity disc-like orbits (e < 0.1) and remaining confined near the Galactic plane (Zmax < 0.2 kpc) The estimated dynamical relaxation times of NGC 2423 and NGC 2482, Trelax = 18 Myr and Trelax = 35 Myr respectively, are significantly shorter than their corresponding cluster ages, indicating that both systems have reached a dynamically relaxed state

Discussion on Hyades-like Nature

The mean proper motions and parallaxes were derived as µα cos δ = −0.750 ± 0.134 mas yr−1, µδ = −3.578 ± 0.143 mas yr−1, and ϖ = 1.060 ± 0.035 mas for NGC 2423, and µα cos δ = −4.669 ± 0.070 mas yr−1, µδ = 2.250 ± 0.065 mas yr−1, and ϖ = 0.735 ± 0.061 mas for NGC 2482 The two clusters show different degrees of kinematic similarity to the Hyades population NGC 2482 also shows a close correspondence in the U–V plane, whereas NGC 2423 has a similar rotational velocity but a substantially different U component The present-day action-space locations of NGC 2423 and NGC 2482 overlap with the narrow Lz interval occupied by several Hyades-like clusters This angularmomentum range is expected for a broad population of thin-disc clusters at Galactocentric radii close to the solar circle

Conclusion

Overall, the derived parameters provide a consistent set of distances, reddening values, ages, and mean kinematics for NGC 2423 and NGC 2482 from a uniform Gaia DR3-based analysis Improved radial-velocity completeness and deeper photometry, particularly at the lowmass end and in the cluster outskirts, would further reduce uncertainties in the inferred structural and kinematic trends

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The gist: This study presents a homogeneous photometric, astrometric, and kinematic analysis of the two Hyades-like open clusters NGC 2423 and NGC 2482.

How it works

The research determined that the mean trigonometric parallaxes are derived as ϖ = 1.060±0.035 mas for NGC 2423 and 0.735±0.061 mas for NGC 2482 Fundamental parameters were derived through PARSEC isochrone fitting, resulting in ages of 1250 ± 100 Myr and 445 ± 50 Myr Observed distance moduli are (m − M)obs = 9.90 ± 0.10 and 10.80 ± 0.20 mag for NGC 2423 and NGC 2482, respectively