Class M stars

nexium · Feb 14, 2008

I understand red dwarf stars flare. Is that the same thing as a CME = coronal mass ejection? Do 99% of the red dwarfs produce strong and frequent flares, or just a few of them? I'm trying to estimate the hazard to a planet a million miles above the photosphere of a very low mass red dwarf. Are most red dwarves variable stars? Neil

venator_3000 · Feb 14, 2008

First, consider the sun. Solar flares are quite sudden explosions (for lack of a better word) over a given small region on the sun. When this occurs a hot plasma will get shot up from the surface. A plasma is a high temperature ionized gas. You have likely heard that flares occur on an 11 year max/min cycle. A CME is when a skin (I’ll call it a skin, an expert could truly define it) of plasma peels off of the surface of the Sun. A CME will move faster than the solar wind and can drive shock waves into space ahead of it. When a CME hits the Earth we get geomagnetic storms, aurorae, and on occasion damage to electronics. CMEs are sometimes seen with flares, but this may or may not be the case. CMEs are not caused by flares, however. In the case of red dwarfs there is a particular class called UV Ceti variables. The stars will suddenly brighten across the spectrum, both in terms of visible light as well as X-Ray, UV, and radio, as well as IR. Pretty much the whole spectrum! These red dwarf flares are closer to solar flares than CMEs, as far as anyone knows. Not all red dwarfs are variable. Regarding the planet around a dwarf star, I would think the habitable zone would be close-in but also rather cool. This closeness might also lock the hypothetical planet so one side faced the star all the time. I have read some fiction where such world’s have a habitable band where life can exist. Although if you had a very strong atmospheric hadley cell (or even an ocean equivalent to a hadley cell) you might be able to circulate some warmth. I would imagine such a world being like the arctic, maybe. The star Gleese (spelling?) is a red dwarf with a “terrestroid” world. You can imagine beings living on this world and focusing their astronomy on their parent star. The star would be quite dim, but also quite large in the sky, compared to our sun, and they would be able to track and detail starspots. Sometimes starspots might indicate flares. Perh <div class="Discussion_UserSignature"> </div>

alokmohan · Feb 15, 2008

These dwarf stars are most numerous.So we should study it.

3488 · Feb 15, 2008

Very true alokmohan. The Red Dwarfs are a most fascinating type of star. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

3488 · Feb 15, 2008

Also not all Red Dwarfs flare. The younger ones like Proxima Centauri & Wolf 259 do. The older Red Dwarfs like Kapteyn's Star do not flare. Kapteyn's Star orbits the galactic centre in a very highly inclined orbit & at 13 light years is the closest known Halo Star to our solar system. Arcturus / Alpha Bootis is the best known Halo Star as being the fourth brightest star visible from Earth & is a red giant some 40 times wider & 140 times brighter than the Sun. HO Librae / Gliese 581, which had the spotlight last year, being the centre of an entire solar system is also an ancient, quiet red dwarf, somewhat older than the Sun. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

alokmohan · Feb 16, 2008

Andrew you are so thorogh.

3488 · Feb 16, 2008

Hi alokmohan, I am glad to be of service. <img src="/images/icons/laugh.gif" /> This is a most fascinating subject. Red Dwarfs encompass ALL age groups of stars, the only type to do so, due to their low mass, hence exceptionally lengthy life spans. The fact is that we now know that many are centres of planetary systems, by default, these stars may also have some of the oldest planets in the entire universe, not just the galaxy. Some white dwarfs, brown dwarfs, neutron stars & black holes may also have exceptionally ancient planetary systems. Also this looks quite interesting, the Red Dwarf: OGLE-05-390L. Also NASA article of planetary systems around Red Dwarfs. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

alokmohan · Feb 17, 2008

Brown dwarfs fascinate me.

nexium · Feb 20, 2008

The links are interesting, but suggest more questions. I had not seen the term sub dwarf. Would this author call our sun a yellow sub dwarf? I'm puzzled by the (absoute?) luminosity graph which shows the peak output of 1.1 units, at about 3480 units. Does this mean at this wave length this M stare is brighter than our sun? If the wave lenght is nanometers, then it is far infrared? If the wavelength is angstrom units then it is near ultraviolet. He did say it is more bluish than mainsequence red sub dwarfs. Does that mean this star is not main sequence = not fusing hydrogen or mearly that it has low metalisity? Neil

3488 · Feb 20, 2008

Hi Neil. Kapteyn's Star is vastly older than our Sun, perhaps 12 GY old? Very low metallicity. Yes our Sun is a Yellow Sub Dwarf. I have heard of this term before, but has not generally been used for quite a while, usually Yellow Main Sequence. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

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