Comments on: Oops, TW Hydrae b Isn't a Planet; Just a Sunspot

By: Yael Dragwyla

Yael Dragwyla — Sun, 14 Sep 2008 02:23:54 +0000

Kevin –
Starspots have been detected on at least one other star. See, e.g., APOD: 2003 November 2, "A Giant Starspot on HD 12545" (http://antwrp.gsfc.nasa.gov/apod/ap031102.html).

By: El Sofista - ExopapelÃ³n: TW Hydrae b no es un planeta sino una mancha solar

El Sofista - ExopapelÃ³n: TW Hydrae b no es un planeta sino una mancha solar — Fri, 12 Sep 2008 21:29:46 +0000

Uno tiene que amar verdaderamente a la ciencia, porque siempre hay alguien revisando su trabajo. A comienzos de este aÃ±o se anunciÃ³ el descubrimiento de un nuevo exoplaneta: TW Hydrae b, un enorme planeta casi diez veces mÃ¡s grande que JÃºpiter [...] Fuente: Nancy Atkinson para Universe Today.

By: TK

TK — Thu, 11 Sep 2008 23:10:48 +0000

Kevin F.–Sunspots (or should that be starspots?) have previously been detected on Betelgeuse. I thought I heard that somewhere, and Wikipedia confirms it.

Science–self-correcting by definition!

By: LLDIAZ

LLDIAZ — Thu, 11 Sep 2008 16:25:23 +0000

Revisiting is all scientists ever do, if not there own then someone elses work but just revisiting.

By: geokstr

geokstr — Thu, 11 Sep 2008 12:22:31 +0000

This makes a lot more sense.

I was always a little bit leery of giant exoplanets (and even binary stars) so close to their star that they whipped around it in a couple days. Some, IIRC, have been discovered that supposedly orbit in only few hours, which really strains credulity.

Makes me wonder how many more of the more far-out theories of astronomy need to be re-visited like this, with Occam's Razor firmly in hand.

By: Astrofiend

Astrofiend — Thu, 11 Sep 2008 00:03:20 +0000

7% of the stellar surface – That is one enormous sunspot!

By: Thomas

Thomas — Wed, 10 Sep 2008 23:49:53 +0000

@Kevin F

Star spots have been observed on many stars. BY Draconis variables are stars that are variable due to heavy sunspot activity, for example. In rare occasions, a transiting planet covers up a star spot, causing a brief rise in the apparent brightness of the system–very noticeable in the star's light curve.

By: Jon Hanford

Jon Hanford — Wed, 10 Sep 2008 22:27:38 +0000

Another way to find extrasolar planets may also include direct imaging. I refer to the planetary candidate orbiting the K7V star 1RXS J160929.1-210524, posted at arXiv:0809.1424. Spectroscopy & direct imaging suggest an 8 Jupiter mass object( type L4 ) orbiting this young low-mass star in the upper Scorpius association. Spectra suggest a temp of ~1800 K , but this might be expected of a young(hot) planetary-mass object. I'm familiar with earlier claims of planetary mass objects (which have mostly been inconclusive or just in error). These authors caution that further observations are needed to determine if this object is actually orbiting this star (or may possibly be a free-floating planet) but the evidence they present seems pretty interesting. I'd be interested to see what subsequent observations of this candidate planet may reveal.

By: Kevin F.

Kevin F. — Wed, 10 Sep 2008 21:56:13 +0000

Does this make it the first sunspot detected on another star?

By: Nancy Atkinson

Nancy Atkinson — Wed, 10 Sep 2008 19:40:29 +0000

Talk about someone checking your work! Mass is correct. I pulled "size" from Planet Quest's Twittter feed, which might not be technically accurate. I'm sticking with "sun-sized", however because that's relative.

Thanks guys,
Nancy

By: Aodhhan

Aodhhan — Wed, 10 Sep 2008 18:45:38 +0000

Vagueofxxxxxxx…
Ahh…Kudos, mass should have been transposed. Bad me for not looking at the reference first, and for not paying close enough attention to the question misreading what the REAL question is.

Studies really aren't done by just watching the "gravitational pull" as you put it. You might initially find it this way, but you don't study that 'per se'. After all…what if there is more than one planet pulling on the star?

Common method is using spectral and doppler to plot positions of the star and subject for a period of time; then these figures are put together to come up with a radial velocity curve (where velocity is on one axis, and time is on the other). From this you can come up with quite a few things… such as orbital periods, orbital amplitude, semi major axis and probable mass. I won't bore you with the trigonometry behind it… Actually the data is pushed into computer models and they do the RV comps!

In short.. it's done by both watching the star and probable subject movment and spreading out the light from the star. So both you and John are correct.

By: edu

edu — Wed, 10 Sep 2008 18:39:10 +0000

peer review baby

By: John

John — Wed, 10 Sep 2008 16:45:56 +0000

Not all exosolar planets are detected by gravitational pull, some are detected by occultation of the star, as long as the planet passes in front of the star along the line of sight from observers on Earth.

For this case, it is more likely that it was the occultation that was detected, since the outcome ultimately was a large sunspot, which would not have caused a gravitational pull.

By: Vagueofgodalming

Vagueofgodalming — Wed, 10 Sep 2008 16:29:14 +0000

Aodhhan, the links provided by Nancy make it clear that mass is what's being talked about. We don't know what the dimensions of these planets are, because they've been detected by their gravitational pull.

One of the best things about UT is that they always provide the link to the source so that if you have a question like that, you can look it up.

By: Aodhhan

Aodhhan — Wed, 10 Sep 2008 15:58:40 +0000

Typically when dealing with "Size" in this context they are referring to actual spherical (area) displacement in space, as opposed to "mass" which more closely relates to weight and density.
Which one you use is dependent on what information you have and what you are trying to convey.
In this article, "size" appears to be the correct means of measurement. Also, most people relate to 'size' much better than the mass of an object since what you see is what you get. With mass, this isn't the case; you can have something small in size yet be very massive (like a black hole) or something large in size and not very massive (like Saturn).

By: sps

sps — Wed, 10 Sep 2008 15:53:26 +0000

I hope that this double check will help scientist to be more… spot on.

By: Jorge

Jorge — Wed, 10 Sep 2008 14:43:07 +0000

Nancy, wouldn't it be more correct to talk about "mass" instead of "size"? Or are you really speaking about diameters here?

By: Nelson (from the Simpsons)

Nelson (from the Simpsons) — Wed, 10 Sep 2008 14:41:05 +0000

Ha Ha!