HD 177365
A B9 V visual binary in Telescopium with a 16th-magnitude companion.
HD 177365 is a visual binary system located in the southern constellation Telescopium. The primary star has an apparent magnitude of 6.27, which is just bright enough to be seen with the naked eye under ideal conditions. Based on Gaia DR3 parallax data, the system lies about 373 light-years away and is moving away from Earth with a heliocentric radial velocity. Its brightness is reduced by 0.2 magnitudes due to interstellar dust, and its absolute magnitude is +0.16.
The binary nature was first identified in a 1996 survey by the United States Naval Observatory. A 2006 Hipparcos study of proper motions classified the primary as a probable astrometric binary, with an 89.6% probability. The companion, HD 177365 B, is a 16th-magnitude star located 101.3 arcseconds away at a position angle of 218°, as measured in 2015.
The visible star is classified as B9 V, a B-type main-sequence star fusing hydrogen in its core. It has 3.05 times the Sun's mass and 3.33 times its radius, radiating 119 times the Sun's luminosity from its photosphere. Its effective temperature is given, and it is slightly metal-poor, with an iron abundance 78% of the Sun's ([Fe/H] = −0.11). The system is estimated to be 226 million years old.
- Apparent magnitude
- 6.27
- Distance
- 373 light-years
- Absolute magnitude
- +0.16
- Stellar classification (primary)
- B9 V
- Mass (primary)
- 3.05 M☉
- Radius (primary)
- 3.33 R☉
- Luminosity (primary)
- 119 L☉
Lore & Background
The binarity of HD 177365 was first noticed in a 1996 United States Naval Observatory survey. The system consists of a B9 V primary star and a 16th-magnitude companion located 101.3 arcseconds away along a position angle of 218° as of 2015. A Hipparcos proper motion survey published in 2006 catalogued the primary as a probable astrometric binary with an 89.6% chance, indicating that the companion may be gravitationally bound.
The primary star has 3.05 times the mass of the Sun and 3.33 times its radius, radiating 119 times the solar luminosity from its photosphere. It is slightly metal deficient, with an iron abundance 78% that of the Sun ([Fe/H] = −0.11), and is estimated to be 226 million years old. The system is receding with a heliocentric radial velocity, and its brightness is diminished by two-tenths of a magnitude due to interstellar extinction.
Reader's Guide
HD 177365 serves as an example of a wide visual binary system where the primary is a relatively young, hot B-type star. The system's discovery in a 1996 survey highlights the ongoing efforts to identify and characterize binary stars, particularly those with faint companions that require careful astrometric measurement. The probable astrometric binary classification from the 2006 Hipparcos survey underscores the challenges in confirming physical association for wide pairs, as the 89.6% probability leaves room for uncertainty. The primary's B9 V classification and measured parameters—mass, radius, luminosity, and age—provide a useful data point for stellar evolution models of intermediate-mass stars. Its slight metal deficiency and the presence of interstellar extinction add context to the star's observed properties. The system's location in the southern constellation Telescopium and its near-naked-eye magnitude make it accessible for amateur astronomers with modest equipment, though the 16th-magnitude companion requires larger telescopes to detect.
Did You Know?
- HD 177365 is located in the southern constellation Telescopium.
- The system's brightness is diminished by 0.2 magnitudes due to interstellar extinction.
More in Binary and Multiple Stars, Part 4 1-24
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