HD 3346
A red giant binary and ultra-small-amplitude pulsating variable star.
HD 3346, also designated V428 Andromedae, is a binary star located in the northern constellation Andromeda. With an apparent visual magnitude of 5.14, it appears faint but can be seen without a telescope under good conditions. Its distance, derived from an annual parallax shift of 4.72 milliarcseconds, is roughly 690 light-years (210 parsecs). Interstellar dust reduces its brightness by 0.16 magnitude, and the system is moving toward Earth at a heliocentric radial velocity of −33 km/s.
The system is a single-lined spectroscopic binary. Its orbital period is 576 days, with an eccentricity of 0.3. For the primary star, the product of the semimajor axis and the sine of the unknown orbital inclination (a sin i) is 5.1 ± 0.6 Gm (0.0341 ± 0.0040 AU), giving a minimum value for the actual semimajor axis. The visible component is a red giant, classified as K6 IIIa, and serves as a standard star for that spectral type. Prior to this designation, no standard existed for K6 giants, and HD 3346 had been classified between K5 III and M0 III. In 1996, larger-than-expected radial velocity variations led to proposals of two orbiting companions: one known since 1985 with a period of about 650 days and a minimum mass of roughly 60 Jupiter masses, and a second with a period of 14–40 days and a minimum mass of about 10 Jupiter masses. The existence of this second, possibly planetary, companion was never confirmed.
HD 3346 was listed as a suspected variable star (NSV 15135) in 1982, and its variability was confirmed in 2000. It received the variable star designation V428 Andromedae in 2003. It is a short-period semi-regular variable of type SRS, also described as an ultra-small-amplitude pulsating red giant, with an amplitude of just 0.065 magnitudes. The main pulsation period is 11.5 days, with additional periods of 11, 15, and 22 days detected.
- Apparent visual magnitude
- 5.14
- Distance
- about 690 light-years (210 parsecs)
- Parallax
- 4.72 mas
- Extinction
- 0.16 magnitude
- Heliocentric radial velocity
- -33 km/s
- Orbital period
- 576 days
- Eccentricity
- 0.3
- A sin i
- 5.1 ± 0.6 Gm (0.0341 ± 0.0040 AU)
- Spectral type
- K6 IIIa
- Variability type
- SRS (short-period semi-regular)
Lore & Background
HD 3346 was listed as a suspected variable star (NSV 15135) in 1982 in Pavel Nikolaevich Kholopov's catalog of suspected variable stars. Its variability was confirmed by Gregory W. Henry et al. in the year 2000, and it received its variable star designation, V428 Andromedae, in 2003. The visible component is a red giant star and has been defined as a standard star for the stellar classification of K6 IIIa; prior to that there had been no spectral standard for K6 giants, and HD 3346 had been classified between K5 III and M0 III.
The system is a single-lined spectroscopic binary with an orbital period of 576 days and an eccentricity of 0.3. The a sin i value for the primary is 5.1 ± 0.6 Gm (0.0341 ± 0.0040 AU), providing a minimum value for the actual semimajor axis. In 1996 it was announced that the variations in radial velocity of this star were larger than expected, leading to proposals of two orbiting companions: one known since 1985 with a period of about 650 days and a minimum mass of about 60 MJ, and a second with a period of about 14-40 days and a minimum mass of about 10 MJ. The existence of this second, possibly planetary companion was never confirmed.
Reader's Guide
HD 3346 (V428 Andromedae) holds significance as a standard star for the K6 IIIa spectral class, filling a gap in the classification system for K-type giants. Its variability, confirmed in 2000, is of the short-period semi-regular type (SRS) with an extremely small amplitude of only 0.065 magnitudes, making it an ultra-small-amplitude pulsating red giant. The main pulsation period is 11.5 days, with additional periods of 11, 15, and 22 days detected. The system's legacy also includes the unresolved question of a possible planetary-mass companion: a second, unconfirmed object with a period of about 14-40 days and a minimum mass of about 10 MJ was proposed in 1996 to explain radial velocity variations, but its existence was never confirmed. The binary nature of the system, with a 576-day orbital period and a red giant primary, adds to its astrophysical interest as a spectroscopic binary with a known minimum semimajor axis.
Did You Know?
- HD 3346 is also designated V428 Andromedae and is a short-period semi-regular variable star of type SRS.
- It serves as a spectral standard for the K6 IIIa class, filling a previous gap in stellar classification.
- The system has an unconfirmed second companion proposed in 1996 with a minimum mass of about 10 MJ and a period of 14-40 days.
- Its main pulsation period is 11.5 days, with an amplitude of only 0.065 magnitudes.
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