<p>I ran across this paper's title <a href="https://academic.oup.com/mnras/article-abstract/499/2/2493/5910523?redirectedFrom=fulltext" rel="nofollow noreferrer">η Carinae: high angular resolution continuum, H30α and He30α ALMA images</a> (<a href="https://arxiv.org/abs/2009.10829" rel="nofollow noreferrer">arXiv</a>) and see that the body of the paper also mentions &quot;H40α, H30α and H29α&quot;.</p>
<p>What notation is this, in which contexts is it used, and what exactly to the numbers and greek letters denote? (I'm assuming that H and He are elements).</p>

<observational-astronomy><radio-astronomy><terminology><astrochemistry>
What exactly are "H30α and He30α images"? (ALMA)
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# What exactly are "H30α and He30α images"? (ALMA)

(Asked by: username_0 on 2020-10-28)

I ran across this paper's title [η Carinae: high angular resolution continuum, H30α and He30α ALMA images](https://academic.oup.com/mnras/article-abstract/499/2/2493/5910523?redirectedFrom=fulltext) ([arXiv](https://arxiv.org/abs/2009.10829)) and see that the body of the paper also mentions "H40α, H30α and H29α".

What notation is this, in which contexts is it used, and what exactly to the numbers and greek letters denote? (I'm assuming that H and He are elements).

**Tags:** observational-astronomy, radio-astronomy, terminology, astrochemistry


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