What are these "periods"?

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What are these "periods"?

Postby vivian maxine on June 5th, 2016, 7:31 pm 

Can someone please explain what is meant by "period" in the following? The chapter is describing the search for exoplanets. A data chart starts with:

Year first exoplanet discovered: 1992 (PSR 1257+12B)
Number of exoplanets known: 760 (and counting)
Smallest: 0.0022 Earth Mass (PSR 1257+12B)
Largest: 9,852 Earth Masses (CD-35 2722B)

Then, after a dotted line break, it has:

Shortest period: 2.2 Hours (PSR 1719-14B)
Longest period: 1,999 years (OPH 11B)

The periods, of course are time measurements but I don't understand what they are measuring in relation to the exoplanets. Thank you for explanation.
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Re: What are these "periods"?

Postby curiosity on June 5th, 2016, 7:50 pm 

Its how long the exoplanet takes to complete an orbit of its parent star.

Regards,
Graham.
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Re: What are these "periods"?

Postby vivian maxine on June 5th, 2016, 7:56 pm 

curiosity » June 5th, 2016, 6:50 pm wrote:Its how long the exoplanet takes to complete an orbit of its parent star.

Regards,
Graham.


Bless you and thank you. That had occurred to me but both numbers seemed so extreme, especially the 2.2 hours.

That will do it, then. Have a good evening. Viv
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Re: What are these "periods"?

Postby curiosity on June 5th, 2016, 8:14 pm 

I must admit that I was unaware of any exoplanet confirmed to be orbiting its star that quickly, I believe the fastest orbit I had previously heard of was around the five hour mark. It must be damned close to its star, to be able to complete a circuit within that time. "Definitely not within the Goldilocks zone."
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Re: What are these "periods"?

Postby Watson on June 5th, 2016, 9:43 pm 

Just for context, the ISS is orbiting earth at about an hour and a half. To have something exoplanet size out there would have to have a much larger orbital path and thus be moving at a considerably faster rate to maintain a 2.2 hour period. Imagine the moon rising on the horizon and setting opposite in about 6 minutes.

Any chance they referred to a rotational period?
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Re: What are these "periods"?

Postby Eclogite on June 6th, 2016, 2:03 am 

Watson » Mon Jun 06, 2016 1:43 am wrote:Any chance they referred to a rotational period?
I am not aware that any technique that could detect rotation rate is anywhere near the sophistication, precision, or even deployment that would make that possible.
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Re: What are these "periods"?

Postby vivian maxine on June 6th, 2016, 8:43 am 

Watson and Ecoglite, to both of you. Rotation on axis might be it. Explanation:

For some reason, the author did not discuss and explain that "period" in the exoplanets chapter but he did explain the same sort of thing in the chapter on pulsars.

Period of first pulsar: 1.33 seconds
Longest Period pulsar: 8.51 seconds (PSR J2134-3933)

Then, in his explanations, he writes about the pulsars: "Their periods of rotation vary from somewhat less than ten seconds down to a few milliseconds.

All right. I know there is quite a difference between pulsars and exoplanets but it does let us ask if the exoplanets data could be spin. I don't know what a 2.2 hour spin would do to sleep patterns but maybe life would be quite different there. That is, assuming there is life. Maybe such a fast spin would eliminate that possibility?
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Re: What are these "periods"?

Postby Eclogite on June 6th, 2016, 3:19 pm 

Hello Vivian, first a plea. When you are quoting information from sources please provide details of those sources. This can greatly assist in giving a meaningful answer.

So, the period given in your chapter is the orbital period. I confirmed this by consulting The Extrasolar Planets Encyclopaedia and accessing the All Catalogs listing.

There, when you search for PSR 1719-14B you will find its Period (defined in the table as Orbital Period) is 0.090706293 days. That, to one decimal place, is 2.2 hours as reported in your chapter. It no longer holds the record for the shortest orbital period. This is now held by j1433_b with a period of 1.3 hours.

Note that whatever publication you are consulting is now quite outdated. They report 760 exoplanets, while the total today is reported as 3,425 in 2,563 planetary systems.


In regard to pulsars we are able to determine their rotation rate from the interval between the times at which the electromagnetic beam from the star sweeps across the Earth. Their rotation rate is high because angular momentum must be conserved as they collapse from a normal star to an incredibly dense (and small) neutron star. It's the same physics as a spinning ice skater speeding up by drawing her arms in close to her body.

There is a high probability that any planet that close to its star would be tidally locked, as the moon is with respect to the Earth. Though some other resonance might be possible, as is the case with Mercury. I think, though, the consensus leans towards tidal locking.

I am confident that any intelligent life that evolved on a planet with a 2.2 hour day would suspect that life would find it difficult to handle a planet that took ten times as long to rotate. We define normal as what we are accustomed to. The universe may take a different view.

Now Here Is the Neat Stuff!

I stated that I was not aware that any technique that could detect rotation rate is anywhere near the sophistication, precision, or even deployment that would make it possible to determine the rotation of an exoplanet. Mea culpa.

Brogi, M. et al "Rotation and winds of exoplanet HD 189733 b measured with high-dispersion transmission spectroscopy" The Astrophysical Journal, Volume 817, Issue 2 2016

Abstract:

Giant exoplanets orbiting very close to their parent star (hot Jupiters) are subject to tidal forces expected to synchronize their rotational and orbital periods on short timescales (tidal locking). However, spin rotation has never been measured directly for hot Jupiters. Furthermore, their atmospheres can show equatorial super-rotation via strong eastward jet streams, and/or high-altitude winds flowing from the day- to the night-side hemisphere. Planet rotation and atmospheric circulation broaden and distort the planet spectral lines to an extent that is detectable with measurements at high spectral resolution. We observed a transit of the hot Jupiter HD 189733 b around 2.3 μm and at a spectral resolution of R˜105 with CRIRES at the ESO Very Large Telescope. After correcting for the stellar absorption lines and their distortion during transit (the Rossiter-McLaughlin effect), we detect the absorption of carbon monoxide and water vapor in the planet transmission spectrum by cross-correlating with model spectra. The signal is maximized (7.6σ) for a planet rotational velocity of ({3.4}-2.1+1.3) km s-1, corresponding to a rotational period of ({1.7}-0.4+2.9) days. This is consistent with the planet orbital period of 2.2 days, and therefore with tidal locking. We find that the rotation of HD 189733 b is longer than 1 day (3σ). The data only marginally (1.5σ) prefer models with rotation versus models without rotation. We measure a small day- to night-side wind speed of (-{1.7}-1.2+1.1) km s-1. Compared to the recent detection of sodium blueshifted by (8+/- 2) km s-1, this likely implies a strong vertical wind shear between the pressures probed by near-infrared and optical transmission spectroscopy.

Now that's impressive. We have the technology!
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Re: What are these "periods"?

Postby vivian maxine on June 6th, 2016, 3:43 pm 

Talk about mea culpa, I thought I did give the reference. Maybe that was in another thread. So: National Geographic's "Space Atlas" by James Trefil, a physicist and Robinson professor of Physics at George Mason University, Fairfax, VA. How is that? He offers science courses for the non-science major. He also writes texts at a level of comprehension for the non-scientist.

The book was copyrighted in 2012. My copy was printed in 2014 by Barnes & Noble. I do not know if that second printing would have had any updating but, yes, as fast as science moves today, it would be behind in his "and counting" comments.

Thank you for all the explanations. I shall settle down to that. It looks like a great education in itself.
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Re: What are these "periods"?

Postby vivian maxine on June 7th, 2016, 5:35 am 

Eclogite, will you please tell me what this symbol is? 2.3 μm How do you read it?

Thank you.
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Re: What are these "periods"?

Postby Eclogite on June 7th, 2016, 5:38 am 

Thank you Vivian. Off the top of my head I suspect the data would be from 2011 and the Barnes and Noble reprint did not contain any update. (The Kepler results produced a huge surge in numbers of confirmed exoplanets.)

I don't have a copy of NG's Space Atlas, but I do have a 2005 edition of the National Geographic Encyclopedia of Space, which notes "By March 2004, a database maintained by the Paris Observatory listed 120 confirmed extrasolar planets orbiting main sequence stars, 2 pulsar-type planetary systems and another 20 "unconfirmed, controversial, or retracted planets"". Lots of growth!



There is so much good stuff out there on exoplanets you could spend a lifetime studying it. Here is a selection of links:

I've already given this one, but it is the mother lode: http://exoplanet.eu/

In particular there is an excellent listing of papers, books and websites by which to educate yourself further on the subject. http://exoplanet.eu/tutorials/

wikipedia has a wealth of articles on telescopes used for the detection of exoplanets:

Kepler
Automated Planet Finder
Gaia
CHEOPS
PLATO



I just saw your query - μm is a micrometre, one millionth of a metre. I think this is the same as a micron. (Just checked - it is.)
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Re: What are these "periods"?

Postby vivian maxine on June 7th, 2016, 6:22 am 

Thank you, Ecoglite. You are so right about how much there is to learn, not just about exoplanets but about the whole of astronomy. Last night I was reading more of "Space Atlas" and almost forgot to go to sleep. Black holes - one of my favorite topics - Prof. Trefil doesn't begin to answer my questions about those; Worm holes - I'm sure there is a simpler way if dark matter doesn't stop us; the edge of the universe and beyond; so much more.

It is a great subject to study if you do not like heights. You bring the topic to you instead of taking flight to it. :-)
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