Cepheids and their 'cocoons'

telfrow · Feb 28, 2006

Using ESO's Very Large Telescope Interferometer (VLTI) at Cerro Paranal, Chile, and the CHARA Interferometer at Mount Wilson, California, a team of French and North American astronomers has discovered envelopes around three Cepheids, including the Pole star. This is the first time that matter is found surrounding members of this important class of rare and very luminous stars whose luminosity varies in a very regular way. Cepheids play a crucial role in cosmology, being one of the first "steps" on the cosmic distance ladder. The southern Cepheid L Carinae was observed with the VINCI and MIDI instrument at the VLTI, while Polaris (the Pole Star) and Delta Cephei (the prototype of its class) were scrutinised with FLUOR on CHARA, located on the other side of the equator. FLUOR is the prototype instrument of VINCI. Both were built by the Paris Observatory (France). For most stars, the observations made with the interferometers follow very tightly the theoretical stellar models. However, for these three stars, a tiny deviation was detected, revealing the presence of an envelope. "The fact that such deviations were found for all three stars, which however have very different properties, seems to imply that envelopes surrounding Cepheids are a widespread phenomenon", said Pierre Kervella, one of the lead authors. The envelopes were found to be 2 to 3 times as large as the star itself. Although such stars are rather large - about fifty to several hundreds of solar radii - they are so far away that they can't be resolved by single telescopes. Indeed, even the largest Cepheids in the sky subtend an angle of only 0.003 arc second. To observe this is similar to viewing a two-storey house on the Moon. Link <div class="Discussion_UserSignature"> Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild. - Tennyson </div>

jatslo · Mar 1, 2006

telfrow's Cut & Paste job: "... a widespread phenomenon ..." Am I in the right forum? *Phenomena*, are we talking about *Phenomena*?

Saiph · Mar 1, 2006

? Do you have a problem with telfrow bringing articles he finds interesting to our attention? <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

jatslo · Mar 1, 2006

Saiph · Mar 1, 2006

and what would that be? <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

jatslo · Mar 1, 2006

It's phenomena, for one; and he never says anything, he just posts. Might as well talk to my hand.

Saiph · Mar 1, 2006

well, it isn't phenomena, as it deals with observations of astrophysical objects (cepheid stars). And he does say things sometimes. Other times he just posts them cause he thinks people could find them interesting. He's hoping to seed a conversation. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

jatslo · Mar 1, 2006

Well, it is *phenomena*; it says so in the article.

Saiph · Mar 1, 2006

The phenomena forum is for threads more inline with strange theories and bermuda triangle sightings, not current astronomy observations. You're being nitpicky about the word used for the forum title. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

jatslo · Mar 1, 2006

Cocoon phenomenons seem pretty, well, *Phenomena* to me, and it seems that I am unbiased in my opinion too.

Saiph · Mar 1, 2006

Cepheid variable stars are highly...well, variable. They pulsate a lot, and it isn't unexpected to find that they've shed some material, and that we'd find some stars with the material still around. It's probably similar to how planetary nebulae are formed. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

jatslo · Mar 1, 2006

Saiph: "... probably ..." *probably* suggests to me that this is a hypothesis, so where can I find {alpha}, or {CI}, which is always given?

Saiph · Mar 1, 2006

<blockquote>In reply to:<hr /> so where can I find {alpha}, or {CI}<hr /></blockquote> eh? That's my guess as to the cause. This is new data, they haven't seen this before. It'll be awhile before there's any information as to the possible cause of the envelopes. A couple years probably. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

jatslo · Mar 1, 2006

Oh, okay, so its not quite scientific yet. Is it astronomy then, and if so, why?

Saiph · Mar 1, 2006

It is scientific, but it's more in line with the empirical observation and categorization, than an experiment, theory, or model. Now, it's astronomy because it's using astronomical instruments and techniques to look at something not on earth. It's using telescopes, interferometry, and spectroscopy, three classic astronomy tools, to look at Cepheid stars. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

jatslo · Mar 1, 2006

Saiph: "... astronomical instruments and techniques to look at something not on earth. It's using telescopes, interferometry, and spectroscopy, three classic astronomy tools, to look at Cepheid stars ..." Astronomy is a branch of science dedicated to the study of everything in the universe that lies above Earth's atmosphere. Science a method of reaming about the world by applying the principles of the scientific method, which includes making empirical observations, proposing hypotheses to explain those observations, and testing those hypotheses in valid and reliable ways; science also refers to the organized body of knowledge that results from scientific study. Empirical observations explain *Phenomena*; therefore, this observed phenomenon is *Phonomena*, and is no different than the Face. There is no hypothesis to explain this *Phenomena*. I would compromise, if you moved this thread to Astronomy, and/or administration changed one Astronomy forum to Empirical Astronomy. I think this would clear up some confusion, in this regard.

Saiph · Mar 1, 2006

"Astronomy is a branch of science dedicated to the study of everything in the universe that lies above Earth's atmosphere." Agreed. "Science a method of reaming about the world by applying the principles of the scientific method, which includes making empirical observations, proposing hypotheses to explain those observations, and testing those hypotheses in valid and reliable ways; science also refers to the organized body of knowledge that results from scientific study." Agreed. "Empirical observations explain *Phenomena*; therefore, this observed phenomenon is *Phonomena*, and is no different than the Face. There is no hypothesis to explain this *Phenomena*." Disagree. Empirical observations sample phenomena, they do nothing to explain it. It's just data, size, color, shape, etc. The pictures of "the face" are also empirical data. No problem. If somebody just posted the picture and discussed it a bit, no problem. However, when arguements arise as to it's artificiality, we start edging into the phenomena forum's area (Which covers unexplained, or unexplainable things like aliens, etc). Also, I just threw out a hypothesis to explain the data, as I'm sure the researchers have as well. "I would compromise, if you moved this thread to Astronomy, and/or administration changed one Astronomy forum to Empirical Astronomy. I think this would clear up some confusion, in this regard." All well and good except: I can't move it myself, and there's no need to. The forum titles are guidelines, not strict definitions of the content. This article discusses an object in space, and some of the science behind it (what cepheids are, the techniques used, the results obtained). And this is the Space Science and Astronomy Forum...so it's already right where you asked for it to be. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

jatslo · Mar 1, 2006

For example, there are two astronomy forums, in which one could be empirical, and the other could involve real hypothecations. Since this already is Space Science & Astronomy, then it makes more since to change the other Astronomy forum. However, there is a problem with terrestrial empirical observations, because they would not fall under empirical astronomy. I will bring Ph. D. Carlotto in here when I have more time, or his paper, that is, and see what happens ... Anyway, it's just a thought ... Do what you want. bye

jatslo · Mar 1, 2006

Also, treating the symptom, which I suspect you are, will not solve the problem.

Saiph · Mar 1, 2006

AtA is generally, in my experience, used to field questions people have. What do I look for in a telescope? Whats RA and DEC? Why does the moon have phases? Etc... I think it's a good idea to have a forum where it's just questions and their answers, as straightforwards as they can get. If people wish to discuss the science behind the answer, they come over to this forum. as for treating the symptom...care to elaborate? <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

jatslo · Mar 1, 2006

It is natural to resist change; we all do. Just look at the big picture, and you will do just fine. I have to get some sleep. write you later.

telfrow · Mar 1, 2006

That's the question I had about the report, Saiph. The link between pulsing and ejection of materials hasn't been clearly established, but would appear to be the cause of the halo or cocoon. And, as you point out, the mechanism involved might be similar to the formation of planetary nebula. So what causes the formation of a halo instead of a planetary nebula? Is it the fact that a pulse, which apparently ejects material every two or three days, never allows the nebula to form? <div class="Discussion_UserSignature"> Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild. - Tennyson </div>

Cepheids and their 'cocoons'

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