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Eta Aurigae - B3V (also called Haedus II or Mahasim)
For a B3V type star like Eta Aurigae (also called Haedus II or Mahasim), we enter the category of "heavyweights" of the Milky Way. The suffix "V" indicates that it is on the main sequence, burning its hydrogen steadily, but with an intensity far exceeding that of our Sun.
Here's what your spectrum and astrophysics tell us about this specimen:
1. A "blue" temperature
With a surface temperature of approximately 17,000 K, it is nearly three times hotter than the Sun. This extreme heat explains why:
• Your continuum, after instrumental correction, climbs so sharply towards the blue/UV.
• Neutral helium (He I) is so abundant because it takes a great deal of energy to excite this atom.
2. Measurements and Energy
Eta Aurigae is not a giant in size, but it is dense and massive:
• Mass: Approximately 5 to 6 times that of the Sun.
• Luminosity: It shines about 450 to 500 times brighter than our star. If the Earth orbited it, we would be instantly vaporized.
• Short Lifespan: Unlike the Sun, which will live for 10 billion years, a B3V star consumes its fuel so quickly that it will only remain on the main sequence for a few hundred million years before becoming a red giant, then a massive white dwarf (or a supernova if it were slightly more massive).
3. The Spectral Signature
• Balmer lines: These are narrower than those of an A-type star (like Vega). This is an indicator of its high temperature: the hydrogen is beginning to become too ionized to absorb efficiently.
• Rotation: B-type stars often rotate very rapidly. If your spectral lines appear somewhat "broadened" or "U-shaped" rather than "V-shaped," this is the signature of the Doppler effect due to its rotation (Eta Aurigae rotates at approximately 80 km/s).
4. Its Role in the Galaxy
B3V-type stars are often born in open clusters or associations (like the Orion Association). They are the "beacons" that trace the spiral arms of galaxies because they are young and bright.
The interesting detail: Eta Aurigae is suspected of being a 53 Persei-type variable star, exhibiting slight pulsations in brightness. Precise measurements of chromium and iron could theoretically reveal very slight variations over long periods if monitored over time!
A very interesting 2020 study (using the BRITE and TESS satellites) confirmed that it is not simply a stable star.
It is a Slowly Pulsating B-type star (SPB).
• It has a main pulsation period of 1.29 days.
• These pulsations are caused by internal gravity waves (g-modes) that very slightly alter its brightness and the shape of its spectral lines.
Validated Physical Data
Here are the "official" figures you can use in the legend:
• Effective temperature (Teff): Approximately 17,200 K to 18,600 K depending on the model.
• Rotation speed (v sin i): Approximately 95 km/s. It rotates quickly, which broadens its spectral lines due to the Doppler effect.
• Mass: ~5.4 to 5.6 times that of the Sun.
• Age: It is very young, approximately 39 to 41 million years old (the Sun is 4.5 billion years old).
References:
VSX-AAVSO: https://vsx.aavso.org/index.php?view=detail.top&oid=40446
BRITE photometry and STELLA spectroscopy of bright stars in Auriga: Rotation, pulsation, orbits, and eclipses:
https://ui.adsabs.harvard.edu/abs/2020A%26A...644A.104S/abstract
JBD 2026