HD 6226
A Be star cycling between B and Be states with a 2.615-day rotation period.
HD 6226, also known as V442 And, is a variable star in the northern constellation of Andromeda. With an apparent visual magnitude of about 6.8, it is too faint to be readily visible to the naked eye. Based on a parallax shift of 0.8153 mas, it lies approximately 4,000 light years away. It is notable as a Be star that cycles between B and Be states, exhibiting emission lines from a circumstellar disk, and as a slowly pulsating B-type star with a pronounced equatorial bulge.
- Constellation
- Andromeda
- Apparent visual magnitude
- about 6.8
- Distance
- approximately 4,000 light years
- Parallax
- 0.8153 mas
- Spectral classification
- B2.5IIIe
- Projected rotational velocity
- 70 km/s
- Rotation period
- 2.61507 d
Lore & Background
Early spectral studies classified HD 6226 as B2IV-V or B3III, indicating a normal B-type star. Photometric observations between 1982 and 1990 suggested variability, with occasional brightenings hinting at a Be star nature. Follow-up observations confirmed a correlation between brightness and emission-line strength, establishing it as a Be star similar to Omega Canis Majoris. Over years, it was found to cycle between a B and Be state. Its relatively low projected rotational velocity of 70 km/s suggests a nearly pole-on viewing angle. The helium and metallic absorption lines show a strict periodicity of 2.61507 days, likely its rotation period, but this is not seen in the H-alpha line. Periods of stronger emission lines occur on a roughly 630-day cycle. On August 14, 2017, the H-alpha line showed a significant intensity increase, followed by drastic changes on subsequent nights.
Reader's Guide
HD 6226 is significant as a slowly pulsating B-type star with photometric periods of 1.39 and 1.41 days, whose coupling may explain the quasi-periodic behavior of its intermittent outbursts. Its H-alpha emission varies with periods of 212 and 87 days. The stellar classification B2.5IIIe is based on similarity to π2 Cygni. The star has a pronounced equatorial bulge, with a ratio of equatorial to polar radius of 1.27, and its pole is inclined at about 13.4° to the line of sight. It is a runaway star located well outside the galactic plane, though its radial velocity indicates it is returning. It may have been spun up via accretion before being ejected from its original system, in which case its estimated age of 51 Myr likely dates from the completion of mass transfer. These characteristics make it a valuable object for studying Be star evolution, disk dynamics, and stellar ejection mechanisms.
Did You Know?
- HD 6226 has a rotation period of 2.61507 days inferred from helium and metallic absorption lines.
- Its H-alpha line showed a significant intensity increase on August 14, 2017, followed by drastic changes.
- The star has a pronounced equatorial bulge with a radius ratio of 1.27.
Frequently Asked Questions
What is HD 6226?
HD 6226, catalogued as V442 And, is a B2.5IIIe-type variable star located in the northern constellation of Andromeda. It is classified as a Be star that alternates between B and Be spectral states while hosting a circumstellar disk that produces emission lines.
Can I see HD 6226 with the naked eye?
No—its apparent visual magnitude sits around 6.8, placing it just beyond comfortable naked-eye visibility under typical observing conditions. A small telescope or a good pair of binoculars would be needed to pick it out among the fainter stars of Andromeda.
How far is HD 6226 from Earth?
Using a measured parallax of 0.8153 milliarcseconds, astronomers place the star at roughly 4,000 light years away. That makes it a comparatively nearby B-type star in galactic terms.
What is unusual about HD 6226's rotation?
The star completes one spin every 2.615 days with a projected rotational velocity of about 70 km/s, fast enough to produce a pronounced equatorial bulge. That rapid spin flings material into the circumstellar disk responsible for its Be-star emission signature.
Why do variable-star fans track HD 6226?
Its cycling between B and Be states means the emission-line signature from the disk waxes and wanes, giving observers a shifting spectral fingerprint to monitor over time. Paired with its slow pulsation, it offers a compact case study in how rotation, disk physics, and pulsation interact in a B-type star.
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