BD+29 5007
K5V star with a disputed Argus association companion.
BD+29 5007 is a K-type star in the constellation Pegasus, about 77 light-years from Earth. It has a widely separated companion, first noted in 2016. The pair might belong to the Argus association, a group of stars roughly 45 million years old, but that membership remains uncertain.
The star itself has a mass of 0.671±0.021 times the Sun’s, a radius of 0.703±0.021 times the Sun’s, and a surface temperature of 4327±144 Kelvin. Its spectral type is K5V.
Its companion is designated 2MASS J23512200+3010540 (shortened to 2MASS J2351+3010). This object was discovered in 2010 and first flagged as a possible young, low-mass body in 2014 by the BANYAN II survey, which classified it as an L5.5 dwarf with red near-infrared colors. If it is indeed a member of the Argus association, its mass would be 9–11 Jupiter masses. However, the BANYAN VII survey in 2015 reclassified 2MASS J2351+3010 as a field object—meaning it is not tied to any known star cluster or moving group. This conclusion is supported by measurements of its surface gravity, which match those of a field object. If it is a field object, its mass would exceed 13 Jupiter masses, placing it above the planetary-mass threshold.
In 2016, the object was identified as a possible companion to BD+29 5007. In 2024, it was again proposed as an Argus member, with a mass of 11.9+0.4−0.2 Jupiter masses. The same study calculated a 1.71% probability that the pairing is a false positive. The companion lies 935 arcseconds from the star, which at this distance corresponds to about 22,100 astronomical units. That separation is larger than the 12,000 AU projected separation of Gliese 900 b—currently the planetary-mass object with the longest known orbit—and is comparable to wide brown dwarfs like UCAC4 328-061594.
- Spectral type
- K5V
- Mass
- 0.671±0.021 M☉
- Radius
- 0.703±0.021 R☉
- Temperature
- 4327±144 K
- Distance
- 77 light-years
- Constellation
- Pegasus
Lore & Background
BD+29 5007 is a K5V star with a mass of 0.671±0.021 M☉, a radius of 0.703±0.021 R☉, and a temperature of 4327±144 Kelvin. It lies 77 light-years away in Pegasus. Its companion, 2MASS J23512200+3010540 (short: 2MASS J2351+3010), was discovered in 2010 and first identified as a possibly young low-mass object in 2014 by the BANYAN II survey, which classified it as an L5.5 dwarf with red near-infrared colors. If it is a member of the Argus association, it should have a mass of 9–11 MJ according to those authors. However, the BANYAN VII survey in 2015 revised its status to a field object, not a member of any stellar cluster or association, supported by its measured surface gravity consistent with a field object. This would imply the companion is too massive to have a planetary mass (i.e., larger than 13 MJ). In 2016 it was identified as a possible companion to BD+29 5007. In 2024 it was again identified as an Argus member with a mass of 11.9+0.4−0.2 MJ, with the same authors calculating a 1.71% probability of being a false-positive match. The companion is separated by 935 arcseconds, translating to 22,100 astronomical units at this distance, larger than the 12,000 AU projected separation of Gliese 900 b and similar to brown dwarfs such as UCAC4 328-061594.
Reader's Guide
BD+29 5007 is significant primarily for its wide-separation companion, which highlights the ongoing uncertainty in classifying low-mass objects at extreme orbital distances. The companion's disputed membership in the Argus association—alternately classified as a young low-mass object or a field object—illustrates the challenges in determining the nature of such widely separated companions. If the companion is indeed a member of Argus, its mass of 9–11 MJ (or 11.9+0.4−0.2 MJ per the 2024 study) places it near the planetary-mass boundary, while if it is a field object, its mass exceeds 13 MJ, making it a brown dwarf. The system's separation of 22,100 AU exceeds that of Gliese 900 b, currently the planetary-mass object with the longest known orbit, and is comparable to other wide brown dwarfs. The 1.71% false-positive probability from the 2024 study underscores the statistical caution required. This system thus serves as a case study in the difficulties of confirming wide binary systems and their association with moving groups.
Did You Know?
- BD+29 5007 is a K5V star located 77 light-years away in Pegasus.
- The companion's separation of 935 arcseconds corresponds to 22,100 AU, larger than the 12,000 AU orbit of Gliese 900 b.
- The 2024 study calculated a 1.71% probability that the system is a false-positive match.
Frequently Asked Questions
What is BD+29 5007?
BD+29 5007 is a K5V main-sequence star located in the constellation Pegasus, roughly 77 light-years from Earth. It is notable for hosting a widely separated companion star, making it a binary system.
What are the physical properties of BD+29 5007?
The primary star has a mass of about 0.67 solar masses, a radius of roughly 0.70 solar radii, and a surface temperature near 4,327 K. These values place it firmly in the late-K dwarf category.
What is the companion to BD+29 5007?
The secondary object is catalogued as 2MASS J23512200+3010540 (often shortened to 2MASS J2351+3010) and was first detected in 2010. It was initially flagged as a K5V star and later confirmed as a widely separated companion to BD+29 5007 in 2016.
Is BD+29 5007 a member of the Argus association?
Some researchers have suggested the pair may be associated with the Argus group of young stars, which are approximately 45 million years old. However, that membership has not been firmly established and remains a point of debate in the literature.
How far away is BD+29 5007 and where can I see it?
The system sits about 77 light-years from Earth in the constellation Pegasus. Because of its moderate distance and K-type brightness, it is a target for amateur astrophotographers and small-telescope observers in the northern sky.
More in Binary and Multiple Stars, Part 3 1-24
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