<p>From <a href="https://academic.oup.com/mnras/article/348/4/1282/973630" rel="nofollow noreferrer">Vega stars types, observations studies</a>, include star HD 23362 (Table I.) with a distance 1004 light years</p>

CC BY-SA 4.0
2019-07-24T16:18:29.617Z
When I recommended you [write it up as an answer](https://astronomy.stackexchange.com/questions/32606/how-far-have-individual-stars-been-seen-by-radio-telescopes/32773#comment60541_32606) I was thinking of a proper answer post. This is what we call a "link-only" answer, without the link there is no answer. Can you add some information here explaining more about the observation, and what was the source of the radio emission? *Is it the star, or a dust cloud around it?* I had to read through the paper myself to find HD23362 in Table 1, each reader shouldn't have to do the same. Thanks!
uhoh
CC BY-SA 4.0
2019-07-24T16:21:50.443Z
As far as Vega is concerned, there are two radio observations listed in your link. [1](https://iopscience.iop.org/article/10.1086/340691) and [2](https://iopscience.iop.org/article/10.1086/324226). These are helpful because they show the actual radio images of Vega, so a screen shot or two might make the answer more interesting as well.
uhoh
CC BY-SA 4.0
2019-07-24T15:51:22.490Z
2019-07-24T16:14:27.227Z
2019-07-24T16:14:27.227Z
Adrian R
<blockquote>
  <p>How far have individual stars been seen by radio telescopes?</p>
</blockquote>

<p>The disks of stars <em>have been imaged</em> by radio telescopes at least out to 700 light-years!</p>

<p>From <a href="https://www.star-facts.com/betelgeuse/" rel="nofollow noreferrer">https://www.star-facts.com/betelgeuse/</a></p>

<p><a href="https://i.sstatic.net/eTleS.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/eTleSm.jpg" alt="ALMA image of Betelgeuse"></a> click for full size</p>

<p><strong>note:</strong> The link says that the bright spot is "a convective hot spot on the photosphere". To read further about the size of convection cells on other stars see <a href="https://astronomy.stackexchange.com/a/34917/7982">this answer</a>.</p>

<blockquote>
  <p>This image, made with the Atacama Large Millimeter/submillimeter Array (ALMA), shows the red supergiant Betelgeuse — one of the largest stars known. In the millimeter continuum the star is around 1400 times larger than our Sun. The overlaid annotation shows how large the star is compared to the Solar System. Betelgeuse would engulf all four terrestrial planets — Mercury, Venus, Earth and Mars — and even the gas giant Jupiter. Only Saturn would be beyond its surface. Credit: ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella</p>
</blockquote>

CC BY-SA 4.0
2020-01-23T04:53:12.067Z
2020-02-01T22:05:56.793Z
2020-02-01T22:05:56.793Z
uhoh
<p>Some types of red giant stars are susceptible to intense water and silicon oxide <a href="https://en.wikipedia.org/wiki/Astrophysical_maser#Stellar_atmospheres" rel="nofollow noreferrer">MASER</a> activity in their outer envelopes. This results in intense radio emission. Examples of such maser activity have been observed in the Small Magellanic Cloud,at a distance of <span class="math-container">$\sim 60$</span> kpc  (e.g. <a href="https://arxiv.org/abs/1210.0983" rel="nofollow noreferrer">van Loon 2013</a>).</p>

<p><a href="https://i.sstatic.net/b84x0.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/b84x0m.png" alt="IRAS 05298−6957 water maser van Loon 2013"></a> Click for full size.</p>

<p>IRAS 05298−6957 (<a href="https://arxiv.org/abs/1210.0983" rel="nofollow noreferrer">van Loon 2013</a>): Note the logarithmic wavelength axis; the water maser peak lies at about 18 cm / 1670 MHz. </p>

CC BY-SA 4.0
2019-07-25T21:01:03.227Z
Thanks, this is just what I was looking for.
uhoh
CC BY-SA 4.0
2019-07-26T12:06:48.227Z
Wow. I guess this means we have no actual proof that other Galaxies are made of stars!
SurpriseDog
CC BY-SA 4.0
2019-07-28T14:56:58.410Z
@Benjamin Other stars can be observed in other galaxies, just not at radio wavelengths.
ProfRob
CC BY-SA 4.0
2019-07-28T15:01:19.657Z
@RobJeffries I was under the impression that Radio Telescopes had the highest resolution due to interferometry working for them. That's why the telescope that imaged the black hole in another galaxy (the EHT) was as radio interferometry telescope.
SurpriseDog
CC BY-SA 4.0
2019-07-29T09:13:05.060Z
Stars are much less luminous at radio wavelengths. Cepheid variables were identified in other galaxies in 1908. https://en.wikipedia.org/wiki/Henrietta_Swan_Leavitt
ProfRob
CC BY-SA 4.0
2019-07-25T15:44:59.097Z
2019-07-25T21:06:28.503Z
2019-07-25T21:06:28.503Z
ProfRob
<p>Writing <a href="https://astronomy.stackexchange.com/a/32605/7982">this answer</a> got me thinking.</p>

<p>As far as I understand it, <em>stars themselves</em> radiate most of their energy at optical wavelengths (near-IR through near-UV).</p>

<p>Various types of stellar objects may flare in various ways when in-falling matter from an accretion disk or companion is heated in magnetic fields or undergoes transient nucleosynthesis, <strong>but I'm excluding these types of processes</strong> and asking only about radiation from the stellar object itself, in steady-state.</p>

<p><strong>Question:</strong> How far have individual stars been seen by radio telescopes?</p>

CC BY-SA 4.0
2019-07-13T01:03:24.147Z
["The Sun, the nearest star to Earth, is known to emit radio waves, though it is virtually the only regular star that has been detected in the radio spectrum"](https://en.wikipedia.org/wiki/Radio_star#Normal_stellar_objects).
Keith McClary
CC BY-SA 4.0
2019-07-13T01:06:26.353Z
@KeithMcClary hmm... "virtually only" hmm...
uhoh
CC BY-SA 4.0
2019-07-13T01:17:53.753Z
Also, "regular" and "steady-state". Wiki's source says "few 'adult' stars emit enough radio energy to be detected".
Keith McClary
CC BY-SA 4.0
2019-07-23T18:08:42.693Z
I remember that Vega star has radio telescopes studies, and is so far that
Adrian R
CC BY-SA 4.0
2019-07-23T22:32:59.043Z
@AdrianR yep! millimetre wavlengths can be used to look for dust around stars, so a radio image of the star itself may be present in the data as well even if it's not the primary target. I found this so far: [Submillimetre observations and modelling of Vega-type stars](https://academic.oup.com/mnras/article/348/4/1282/973630) Please feel free to write it up as an answer.
uhoh
CC BY-SA 4.0
2019-07-23T22:35:09.560Z
**update:** See https://books.google.com/books?id=I0b1CAAAQBAJ&pg=PA536&lpg=PA536&dq=radio+observations+of+vega&source=bl&ots=yxmc_XPK8T&sig=ACfU3U0sgy6n0TCX9GMK9UO9Z31m0az3sw&hl=en&sa=X&ved=2ahUKEwiWxPy5i8zjAhU6yIsBHflgCD04ChDoATAQegQICRAB#v=onepage&q=radio%20observations%20of%20vega&f=false for several more stars, but in each case it's not the star itself, but something external to it that is discussed.
uhoh
CC BY-SA 4.0
2019-07-24T04:29:58.333Z
The mechanisms for radio emission from the Sun are discussed [here](https://www.radio2space.com/the-radio-sun/) and [here (paywalled)](https://www.sciencedirect.com/science/article/pii/S0273117705004643). Is this what you mean by "radiation from the stellar object itself, in steady-state"?
Keith McClary
CC BY-SA 4.0
2019-07-26T00:07:41.487Z
[P.3 here](http://www.atnf.csiro.au/research/masermeeting/web_papers/503_RHumphreys.pdf) seems to say that the masing occurs thousands of AU from the star. Is that "from the stellar object itself" ?
Keith McClary
CC BY-SA 4.0
2019-07-26T00:17:19.393Z
@KeithMcClary your point is well taken. I did explicitly rule out "in-falling matter from an accretion disk or companion" but I wonder if the OH in the circumstellar cloud is 1) formed from atoms in the stellar wind itself, or 2) was always around the star and participated in the formation process but never made it inside, or 3) is strictly interstellar or "bystander material" and therefore not part of the star in any way. I just don't know. I'm not an astronomer, but if either 1) or 2) applied I'd call it "good enough" as an answer.
uhoh
CC BY-SA 4.0
2019-07-26T00:23:05.707Z
@KeithMcClary Still, radiation from the photosphere or from electrons trapped within magnetic field lines might be an ideal answer. What do you think? https://arxiv.org/abs/0803.3823 is cited in [van Loon 2013](https://arxiv.org/abs/1210.0983), which is cited in [this answer](https://arxiv.org/abs/0803.3823), it may have some relevance. I suppose I could ask if this cloud of dust and gas "is part of" the star as a separate question if it needs more room for discussion.
uhoh
CC BY-SA 4.0
2019-07-26T18:13:29.670Z
Another approach is to look at which [Emission Mechanisms](https://web.njit.edu/~gary/728/Lecture2.html) can happen on "the stellar object itself".
Keith McClary
<radio-astronomy>
How far have individual stars been seen by radio telescopes?
uhoh
# How far have individual stars been seen by radio telescopes?

(Asked by: username_0 on 2019-07-11)

Writing [this answer](https://astronomy.stackexchange.com/a/32605/7982) got me thinking.

As far as I understand it, *stars themselves* radiate most of their energy at optical wavelengths (near-IR through near-UV).

Various types of stellar objects may flare in various ways when in-falling matter from an accretion disk or companion is heated in magnetic fields or undergoes transient nucleosynthesis, **but I'm excluding these types of processes** and asking only about radiation from the stellar object itself, in steady-state.

**Question:** How far have individual stars been seen by radio telescopes?

**Tags:** radio-astronomy
> **Comments:**
> **username_1**: ["The Sun, the nearest star to Earth, is known to emit radio waves, though it is virtually the only regular star that has been detected in the radio spectrum"](https://en.wikipedia.org/wiki/Radio_star#Normal_stellar_objects).  
> **username_0**: @KeithMcClary hmm... "virtually only" hmm...  
> **username_1**: Also, "regular" and "steady-state". Wiki's source says "few 'adult' stars emit enough radio energy to be detected".  
> **username_2**: I remember that Vega star has radio telescopes studies, and is so far that  
> **username_0**: @AdrianR yep! millimetre wavlengths can be used to look for dust around stars, so a radio image of the star itself may be present in the data as well even if it's not the primary target. I found this so far: [Submillimetre observations and modelling of Vega-type stars](https://academic.oup.com/mnras/article/348/4/1282/973630) Please feel free to write it up as an answer.  
> **username_0**: **update:** See https://books.google.com/books?id=I0b1CAAAQBAJ&pg=PA536&lpg=PA536&dq=radio+observations+of+vega&source=bl&ots=yxmc_XPK8T&sig=ACfU3U0sgy6n0TCX9GMK9UO9Z31m0az3sw&hl=en&sa=X&ved=2ahUKEwiWxPy5i8zjAhU6yIsBHflgCD04ChDoATAQegQICRAB#v=onepage&q=radio%20observations%20of%20vega&f=false for several more stars, but in each case it's not the star itself, but something external to it that is discussed.  
> **username_1**: The mechanisms for radio emission from the Sun are discussed [here](https://www.radio2space.com/the-radio-sun/) and [here (paywalled)](https://www.sciencedirect.com/science/article/pii/S0273117705004643). Is this what you mean by "radiation from the stellar object itself, in steady-state"?  
> **username_1**: [P.3 here](http://www.atnf.csiro.au/research/masermeeting/web_papers/503_RHumphreys.pdf) seems to say that the masing occurs thousands of AU from the star. Is that "from the stellar object itself" ?  
> **username_0**: @KeithMcClary your point is well taken. I did explicitly rule out "in-falling matter from an accretion disk or companion" but I wonder if the OH in the circumstellar cloud is 1) formed from atoms in the stellar wind itself, or 2) was always around the star and participated in the formation process but never made it inside, or 3) is strictly interstellar or "bystander material" and therefore not part of the star in any way. I just don't know. I'm not an astronomer, but if either 1) or 2) applied I'd call it "good enough" as an answer.  
> **username_0**: @KeithMcClary Still, radiation from the photosphere or from electrons trapped within magnetic field lines might be an ideal answer. What do you think? https://arxiv.org/abs/0803.3823 is cited in [van Loon 2013](https://arxiv.org/abs/1210.0983), which is cited in [this answer](https://arxiv.org/abs/0803.3823), it may have some relevance. I suppose I could ask if this cloud of dust and gas "is part of" the star as a separate question if it needs more room for discussion.  
> **username_1**: Another approach is to look at which [Emission Mechanisms](https://web.njit.edu/~gary/728/Lecture2.html) can happen on "the stellar object itself".  

---

## 3 answers

### Answer by username_3 on 2019-07-25. Score: 6 | Accepted answer

Some types of red giant stars are susceptible to intense water and silicon oxide [MASER](https://en.wikipedia.org/wiki/Astrophysical_maser#Stellar_atmospheres) activity in their outer envelopes. This results in intense radio emission. Examples of such maser activity have been observed in the Small Magellanic Cloud,at a distance of $\sim 60$ kpc (e.g. [van Loon 2013](https://arxiv.org/abs/1210.0983)).

[![IRAS 05298−6957 water maser van Loon 2013](https://i.sstatic.net/b84x0m.png)](https://i.sstatic.net/b84x0.png) Click for full size.

IRAS 05298−6957 ([van Loon 2013](https://arxiv.org/abs/1210.0983)): Note the logarithmic wavelength axis; the water maser peak lies at about 18 cm / 1670 MHz.

> **Comments:**
> **username_0**: Thanks, this is just what I was looking for.  
> **username_4**: Wow. I guess this means we have no actual proof that other Galaxies are made of stars!  
> **username_3**: @Benjamin Other stars can be observed in other galaxies, just not at radio wavelengths.  
> **username_4**: @RobJeffries I was under the impression that Radio Telescopes had the highest resolution due to interferometry working for them. That's why the telescope that imaged the black hole in another galaxy (the EHT) was as radio interferometry telescope.  
> **username_3**: Stars are much less luminous at radio wavelengths. Cepheid variables were identified in other galaxies in 1908. https://en.wikipedia.org/wiki/Henrietta_Swan_Leavitt  

---

### Answer by username_2 on 2019-07-24. Score: 1

From [Vega stars types, observations studies](https://academic.oup.com/mnras/article/348/4/1282/973630), include star HD 23362 (Table I.) with a distance 1004 light years

> **Comments:**
> **username_0**: When I recommended you [write it up as an answer](https://astronomy.stackexchange.com/questions/32606/how-far-have-individual-stars-been-seen-by-radio-telescopes/32773#comment60541_32606) I was thinking of a proper answer post. This is what we call a "link-only" answer, without the link there is no answer. Can you add some information here explaining more about the observation, and what was the source of the radio emission? *Is it the star, or a dust cloud around it?* I had to read through the paper myself to find HD23362 in Table 1, each reader shouldn't have to do the same. Thanks!  
> **username_0**: As far as Vega is concerned, there are two radio observations listed in your link. [1](https://iopscience.iop.org/article/10.1086/340691) and [2](https://iopscience.iop.org/article/10.1086/324226). These are helpful because they show the actual radio images of Vega, so a screen shot or two might make the answer more interesting as well.  

---

### Answer by username_0 on 2020-01-23. Score: 0

> How far have individual stars been seen by radio telescopes?

The disks of stars *have been imaged* by radio telescopes at least out to 700 light-years!

From <https://www.star-facts.com/betelgeuse/>

[![ALMA image of Betelgeuse](https://i.sstatic.net/eTleSm.jpg)](https://i.sstatic.net/eTleS.jpg) click for full size

**note:** The link says that the bright spot is "a convective hot spot on the photosphere". To read further about the size of convection cells on other stars see [this answer](https://astronomy.stackexchange.com/a/34917/7982).

> This image, made with the Atacama Large Millimeter/submillimeter Array (ALMA), shows the red supergiant Betelgeuse — one of the largest stars known. In the millimeter continuum the star is around 1400 times larger than our Sun. The overlaid annotation shows how large the star is compared to the Solar System. Betelgeuse would engulf all four terrestrial planets — Mercury, Venus, Earth and Mars — and even the gas giant Jupiter. Only Saturn would be beyond its surface. Credit: ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella


---

