Undergrad How accurate is the distance to M4 and its stars according to different sources?

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SUMMARY

The distance to Messier 4 (M4) varies significantly across different sources, with estimates ranging from 7200 light-years (2200 parsecs) to 12400 light-years (3800 parsecs). The discrepancies arise from the inclusion of objects like PSR B1620−26, which some sources classify as a member of M4 while others do not. Gaia's precision in measuring radial distances and peculiar motions of stars in M4 is questioned, particularly regarding its ability to accurately assess the orbits of stars in the cluster's outskirts. The discussion highlights the need for clarity on the methodologies used in these distance measurements.

PREREQUISITES
  • Understanding of Gaia space observatory data and its measurement capabilities
  • Familiarity with globular cluster dynamics and stellar orbits
  • Knowledge of astronomical distance measurement techniques
  • Awareness of the significance of PSR B1620−26 in relation to M4
NEXT STEPS
  • Research Gaia's distance measurement techniques and accuracy
  • Explore the dynamics of globular clusters and their stellar populations
  • Investigate the implications of PSR B1620−26's classification on distance estimates
  • Learn about the methods used to determine stellar orbits in dense clusters
USEFUL FOR

Astronomers, astrophysicists, and students studying stellar dynamics and distance measurement in globular clusters will benefit from this discussion.

snorkack
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How far is M4? I have seen contradictory numbers for M4 and stars in it.
How precise is Gaia in measuring the radial distances to various stars in M4? Their radial position relative to each other? Their peculiar motions?
What kinds of orbits do stars in the outskirts of M4 follow? High eccentricity orbits that bring them to cluster interior on each periapse, or low eccentricity orbits that stay on the outskirts of cluster all along?
Does Gaia have the precision to measure peculiar accelerations of stars in globular clusters?
 
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snorkack said:
I have seen contradictory numbers for M4 and stars in it.
Where?
 
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malawi_glenn said:
Where?
This:
https://en.wikipedia.org/wiki/Messier_4
offers 7200 ly, (2200 pc) with reference to
https://ui.adsabs.harvard.edu/abs/1985A&A...143...8C
But it also claims PSR B1620−26 as a member (rather than a background object), reference to https://esahubble.org/images/potw1236a/
This:
https://en.wikipedia.org/wiki/PSR_B1620−26
claims the distance to PSR B1620−26 as 3800 pc (12 400 ly), source:
http://exoplanet.eu/catalog/psr_b1620-26_(ab)_b/
This:
https://www.eso.org/public/images/m4/
quotes 5500 ly
5500 ly and 12400 ly is a gross difference. Does Gaia have any comment?
 

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