<p>If present, an a (or b or ab) do not refer to spectral peculiarities but are part of the luminosity class definition explained further up on the page.</p>
<blockquote>
<p>Occasionally, letters a and b are applied to luminosity
classes other than supergiants; for example, a giant star
slightly less luminous than typical may be given a
luminosity class of IIIb, while a luminosity class IIIa
indicates a star slightly brighter than a typical giant.[27]</p>
</blockquote>

CC BY-SA 4.0
2020-12-01T03:16:13.230Z
2020-12-01T03:16:13.230Z
planetmaker
<p>Looking at the chart for spectral type peculiarities (<a href="https://en.wikipedia.org/wiki/Stellar_classification#Spectral_peculiarities" rel="nofollow noreferrer">here</a>), I noticed that the letter <strong>a</strong> was missing from the chart. This seems to be an error, as the star Vega has spectral type A0Va, with the <strong>a</strong> definitely being a peculiarity. What does the <strong>a</strong> in spectral types mean, and is this actually a spectral peculiarity?</p>

<star><spectra><spectral-type>
What does the "a" at the end of a spectral type mean?
WarpPrime
# What does the "a" at the end of a spectral type mean?

(Asked by: username_0 on 2020-12-01)

Looking at the chart for spectral type peculiarities ([here](https://en.wikipedia.org/wiki/Stellar_classification#Spectral_peculiarities)), I noticed that the letter **a** was missing from the chart. This seems to be an error, as the star Vega has spectral type A0Va, with the **a** definitely being a peculiarity. What does the **a** in spectral types mean, and is this actually a spectral peculiarity?

**Tags:** star, spectra, spectral-type


---

## 1 answers

### Answer by username_1 on 2020-12-01. Score: 3 | Accepted answer

If present, an a (or b or ab) do not refer to spectral peculiarities but are part of the luminosity class definition explained further up on the page.

> Occasionally, letters a and b are applied to luminosity
> classes other than supergiants; for example, a giant star
> slightly less luminous than typical may be given a
> luminosity class of IIIb, while a luminosity class IIIa
> indicates a star slightly brighter than a typical giant.[27]


---

