9 Aurigae
A multiple star system and early Gamma Doradus variable.
9 Aurigae is a multiple star system in the constellation Auriga, visible to the naked eye at an apparent magnitude of about 5. It is notable as a well-studied Gamma Doradus variable and was one of the first stars to be classified as such, varying in luminosity due to non-radial pulsations.
- Apparent magnitude
- 4.93 to 5.03
- Variability period
- 1.25804 days
- Distance (hipparcos)
- about 86 light-years (26 parsecs)
- Distance (gaia dr3)
- 88 light-years
- Variable star designation
- V398 Aurigae
- Spectral type (component a)
- F-type main-sequence star
- Orbital period (component a binary)
- 391.7 days
Lore & Background
Kevin Krisciunas and Edward Francis Guinan discovered that 9 Aurigae is a variable star in 1990. It was given the variable star designation V398 Aurigae in 1995. The star's apparent magnitude varies from 4.93 to 5.03 over a period of 1.25804 days, caused by non-radial pulsations characteristic of Gamma Doradus variables.
The system is a multiple star system. The naked-eye component A is a single-lined spectroscopic binary; only the signature of an F-type main-sequence star is visible in the spectrum, but periodic Doppler shifts of absorption lines reveal a hidden companion in a 391.7-day orbit. Four other companions are listed in multiple star catalogs. The closest is a 12th-magnitude red dwarf. Component C, 90 arcseconds away, is a 9th-magnitude star of spectral class K5Ve, which may also be a spectroscopic binary. Component D is a proposed 14th-magnitude red giant, though Gaia astrometry places it at a similar distance and proper motion. Component E is a distant, unrelated star.
Reader's Guide
9 Aurigae holds significance as one of the first stars classified as a Gamma Doradus variable, a type that varies in luminosity due to non-radial pulsations. Its discovery by Krisciunas and Guinan in 1990 and subsequent designation as V398 Aurigae in 1995 marked it as an early benchmark for studying such pulsations. The system's complexity as a multiple star system adds to its interest: component A is a spectroscopic binary with an unseen companion in a 391.7-day orbit, while four other companions are cataloged, including a possible spectroscopic binary (component C) and a proposed red giant (component D) whose distance and proper motion align with the system. The star's visibility to the naked eye in many suburban skies makes it accessible for amateur and professional observation alike. Its well-studied nature, with parallax estimates from Hipparcos and Gaia Data Release 3 providing distances around 86–88 light-years, underscores its role in understanding stellar pulsation and multiple-star dynamics.
Did You Know?
- Component A is a single-lined spectroscopic binary with a 391.7-day orbit.
- The system has five listed companions, including a possible spectroscopic binary and a proposed red giant.
Frequently Asked Questions
What is 9 Aurigae?
It is a multiple star system located in the constellation Auriga that can be spotted with the unaided eye at roughly magnitude 5. Its official variable-star designation is V398 Aurigae.
What type of variable star is 9 Aurigae?
It is a Gamma Doradus variable, a class of stars whose brightness changes because of non-radial surface pulsations rather than uniform expansion and contraction. It was among the very first stars ever identified and classified in this category.
How does 9 Aurigae's brightness change and over what timescale?
Its apparent magnitude oscillates between about 4.93 and 5.03 over a period of roughly 1.258 days. The driving mechanism is non-radial pulsation of the stellar surface, which is the hallmark of Gamma Doradus-type variability.
How far away is 9 Aurigae from Earth?
Hipparcos measurements place it at approximately 86 light-years (26 parsecs), while the more recent Gaia DR3 solution gives a distance of about 88 light-years. Either way it is a relatively nearby stellar system.
What is the spectral type of 9 Aurigae's primary component?
Component A is classified as an F-type main-sequence star, meaning it is a hot, blue-white dwarf that fuses hydrogen in its core. The system as a whole is a multiple star, with additional companions orbiting the primary.
More in Variable Stars, Part 5 1-24
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