Astronomical and Imaging Data

Useful Informations

Palomar 15 is a faint and remote globular cluster located in the outer halo of the Milky Way Galaxy. It’s one of the 15 globular clusters that make up the sparse and often difficult-to-observe “Palomar” collection.

Discovery and Appearance

• Discovery: Palomar 15 was discovered by Fritz Zwicky in 1959 during a search for faint dwarf galaxies using the 48-inch Schmidt telescope at Palomar Observatory. He initially mistook it for a faint dwarf galaxy due to its appearance.
• Faintness: It is one of the most difficult of the Palomar globular clusters to observe visually due to its faintness (V≈14.00 mag).
• Structure: It has been noted for potentially having an unusually large core radius, which makes it dynamically interesting. Its large tidal radius suggests it hasn’t passed particularly close to the Galactic Center.

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Location and Motion

• Constellation: It is located in the constellation Ophiuchus (The Serpent Bearer).
• Distance from Earth: It is currently estimated to be approximately 147,000 light-years ( ≈ 45.1 kpc) away from the Sun.
• Galactic Location: It resides in the outer halo of the Milky Way, at a significant distance from the Galactic Center ( ≈ 125,200 light-years or 38.4 kpc).
• Radial Velocity: It has a positive radial velocity of approximately +68.9 ± 1.1 km/s, meaning it is moving away from the Sun.

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Chemical Composition

• Metallicity: Palomar 15 is considered metal-poor, with an iron abundance ratio ([Fe/H]) of around −2.07, which is typical for old globular clusters in the outer halo.
• Alpha-Elements: Its chemical composition, including its enhancement in magnesium ([Mg/Fe]) and chemical similarity to other outer halo clusters (like NGC 7492), suggests it is typical of the Milky Way’s outer halo globular cluster system. There’s also some indication of multiple stellar populations based on sodium and aluminum abundances in a few stars.

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