Is ultraviolet astronomy uninteresting?

Ask questions, find resources, browse the virtual shelves.
User avatar
Ann
4725 Å
Posts: 11411
Joined: Sat May 29, 2010 5:33 am

Is ultraviolet astronomy uninteresting?

Post by Ann » Mon Jul 19, 2010 6:51 pm

split from http://asterisk.apod.com/vie ... 25#p127488

As for what the WISE image of the Pleiades tells us about the nebulosity around this cluster, compare it with Rogelio Bernal Andreo's image of the Pleiades and the California Nebula. I personally feel that I learn a lot more about the nebulosity around the Pleiades from Andreo's image than I do from the WISE image:
Here is a link to a larger size of Andreo's image:

http://deepskycolors.com/pics/astro/200 ... 1499WF.jpg

All right. I, too, realize that the WISE image contains temperature information that is lacking in Andreo's image. And I, too, realize that it is always a good thing to have a lot of information about an object. And I, too, realize that other people like other things than I do, and that many people may find the WISE image of the Pleiades beautiful.

I really appreciate infrared images in some circumstances. When it comes to objects that are shrouded by dust, or objects whose light has been redshifted clear out of the visual part of the spectrum, then infrared astronony becomes crucially important. For example, infrared astronomy beats visual astronomy hands down when it comes to detecting star formation, and during future planet hunts, infrared astronomy will likely do so much better than visual astronomy.

I don't disapprove of infrared astronomy, absolutely not. But I still find the WISE image of the Pleiades unimpressive and very, very short on new information.

Ann
Last edited by Ann on Mon Jul 19, 2010 6:59 pm, edited 2 times in total.
Color Commentator

User avatar
owlice
Guardian of the Codes
Posts: 8386
Joined: Wed Aug 04, 2004 4:18 pm
Location: Washington, DC

Re: JPL: WISE Mission Image Releases

Post by owlice » Mon Jul 19, 2010 6:58 pm

Ann wrote:I personally feel that I learn a lot more about the nebulosity around the Pleiades from Andreo's image than I do from the WISE image:
You can't see all the nebulosity in Andreo's image, regardless of how pretty what does appear is. Not all of it shows up!
A closed mouth gathers no foot.

User avatar
Chris Peterson
Abominable Snowman
Posts: 16007
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: JPL: WISE Mission Image Releases

Post by Chris Peterson » Mon Jul 19, 2010 7:17 pm

Ann wrote:As for what the WISE image of the Pleiades tells us about the nebulosity around this cluster, compare it with Rogelio Bernal Andreo's image of the Pleiades and the California Nebula. I personally feel that I learn a lot more about the nebulosity around the Pleiades from Andreo's image than I do from the WISE image...
You may feel that way, but it isn't accurate. The simple fact that the images made in different wavelengths show completely different kinds of structure should be a clue that neither image is providing the entire picture. How you can decide which might or might not be providing more information escapes me.
All right. I, too, realize that the WISE image contains temperature information that is lacking in Andreo's image.
Not at all. Both images reveal temperature information- the IR image simply provides data for lower temperature material. But the primary information in the image has nothing at all to do with temperature, but with the structure of the gas and dust that the stars of the Pleiades are moving through. This simply can't be obtained in such detail with visible light, because most of the nebula is invisible in those wavelengths.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
Ann
4725 Å
Posts: 11411
Joined: Sat May 29, 2010 5:33 am

JPL: WISE Mission Image Releases

Post by Ann » Tue Jul 20, 2010 5:54 am

I said:
All right. I, too, realize that the WISE image contains temperature information that is lacking in Andreo's image.
Chris replied:
Not at all. Both images reveal temperature information- the IR image simply provides data for lower temperature material.
Exactly. So the WISE image contains temperature information that is lacking in Andreo's image, just as Andreo's image contains temperature information that is lacking in the WISE image.

Chris also said:
The simple fact that the images made in different wavelengths show completely different kinds of structure should be a clue that neither image is providing the entire picture. How you can decide which might or might not be providing more information escapes me.
Infrared images are almost never highly resolved. The WISE image of the Pleiades is a lot more blurry than almost any good amateur image of the Pleiades in visible light.

Visible images are often like high-resolution images, while infrared images are almost always like low-resolution images. They just don't provide as much detail. Which would you rather have, a detailed map that shows you every little street and back alley in an unknown city or a map that only shows you the busiest thoroughfares and main streets? Sometimes the infrared images are the only ones we can have of an object, and then they are extremely valuable. But as I said before, I just don't think that an image of the nebulosity around the Pleiades - which contains no star formation and no thick dense pockets of dust - is all that revealing.

I'm not saying that it is wrong to make an infrared image of the nebulosity of the Pleiades. I'm not saying that it reveals no new information at all, just that it doesn't reveal a lot of new information.

And this, of course, is another good argument for why the WISE image of the Pleiades should exist:
This image shows the famous Pleiades cluster of stars as seen through the eyes of WISE, or NASA's Wide-field Infrared Survey Explorer. The mosaic contains a few hundred image frames -- just a fraction of the more than one million WISE has captured so far as it completes its first survey of the entire sky in infrared light.
Imaging the entire sky in infrared light is most definitely a worthy scientific goal. Then it goes without saying that the Pleiades must be photographed too, along with the rest of the sky.

I guess my main objection is not so much that the Pleiades got their infrared portrait taken per se. Rather, I am unhappy with the current extreme concentration on infrared astronomy. Almost all major telescopes that are being planned or being completed today are going to focus on infrared astronomy. The Hubble successor, for example, the James Webb telescope, will not be able to see as far into the short wavelengths as Hubble has been able to.

And that is really my main objection - the lack of interest in short-wavelength astronomy, particularly in ultraviolet astronomy. In my opinion, astronomers today don't know enough about ultraviolet astronomy in the moderately nearby universe. Instead they are building huge telescopes that are going to see the ultraviolet light from distant galaxies as this UV light is redhifted into the infrared. How are astronomers going to be able to understand the redshifted ultraviolet light of distant galaxies, when they take so little interest in the ultraviolet light of nearby galaxies and other objects?

Speaking about ultraviolet astronomy and the Pleaides. Is there an ultraviolet image of the Pleiades? If so, could anybody provide a link to such an image?

Ann
Color Commentator

User avatar
owlice
Guardian of the Codes
Posts: 8386
Joined: Wed Aug 04, 2004 4:18 pm
Location: Washington, DC

Re: JPL: WISE Mission Image Releases

Post by owlice » Tue Jul 20, 2010 7:39 am

Ann wrote:Which would you rather have, a detailed map that shows you every little street and back alley in an unknown city or a map that only shows you the busiest thoroughfares and main streets?
Visible light doesn't show you "every little street and back alley." It can't -- it's blind to everything except visible light.
Ann wrote:Speaking about ultraviolet astronomy and the Pleaides. Is there an ultraviolet image of the Pleiades? If so, could anybody provide a link to such an image?
http://coolcosmos.ipac.caltech.edu/cosm ... m/m45.html
A closed mouth gathers no foot.

User avatar
Ann
4725 Å
Posts: 11411
Joined: Sat May 29, 2010 5:33 am

Re: JPL: WISE Mission Image Releases

Post by Ann » Tue Jul 20, 2010 9:19 am

owlice wrote:
Ann wrote:Which would you rather have, a detailed map that shows you every little street and back alley in an unknown city or a map that only shows you the busiest thoroughfares and main streets?
Visible light doesn't show you "every little street and back alley." It can't -- it's blind to everything except visible light.
I do realize that, Owlice. It's just that visible light seems to reveal much smaller structures than infrared ones, then.

Thank you very much for the link to the ultraviolet image of the Pleiades! But I must say that the image was very disappointing and appallingly resovled. I got the impression that the image is from 1997. Is that true? Has there been no new ultraviolet images made of the Pleiades since then?

Ann
Color Commentator

User avatar
Ann
4725 Å
Posts: 11411
Joined: Sat May 29, 2010 5:33 am

Is ultraviolet astronomy uninteresting?

Post by Ann » Tue Jul 20, 2010 9:56 am

In a thread on another forum, there was an infrared image of the Pleiades. I complained about that image, partly because I thought it looked confusing and non-beautiful, but mostly because of the very strong focus on infrared astronomy these days, so that everything should be imaged in the infrared. It's not as if the Pleaides has not been imaged in the infrared before. This Spitzer Space Telescope infrared image of the Pleiades is from 2007:

Image

There is a pink version of the Spitzer Pleiades image, too:

Image

Exactly why we need a pink version of an already existing yellow-green infrared image of the Pleiades I don't quite get... is it because the Pleiades needs to be pretty in pink, perhaps?

I asked for an ultraviolet image of the Pleiades, and Owlice graciously provided one. But the image is pretty awful-looking and apparently thirteen years old, from 1997:

http://www.jhu.edu/news_info/news/home9 ... eiad1.html

These days you hear news about gamma ray astronomy, X-ray astronomy, visible light astronomy, infrared astronomy (lots and lots of it!) and radio astronomy. Where is the ultraviolet astronomy? Is it not interesting?

When I complained about the infrared image of the Pleiades, I got chastized by some people who thought I was uninterested in science and knowledge. So I have to wonder if these same people are going to tell me that I'm asking for uninteresting knowledge when I'm asking for ultraviolet astronomy. Is ultraviolet the one part of the spectrum that can't provide us with any useful knowledge?

Ann
Color Commentator

User avatar
owlice
Guardian of the Codes
Posts: 8386
Joined: Wed Aug 04, 2004 4:18 pm
Location: Washington, DC

Re: JPL: WISE Mission Image Releases

Post by owlice » Tue Jul 20, 2010 11:06 am

Ann wrote:I got the impression that the image is from 1997. Is that true? Has there been no new ultraviolet images made of the Pleiades since then?
I have no idea; try googling "ultraviolet pleiades" and see what you get.
A closed mouth gathers no foot.

User avatar
owlice
Guardian of the Codes
Posts: 8386
Joined: Wed Aug 04, 2004 4:18 pm
Location: Washington, DC

Re: Is ultraviolet astronomy uninteresting?

Post by owlice » Tue Jul 20, 2010 11:24 am

Ann,

You said nothing in your initial objection to the WISE image about any emphasis on infrared imaging, but complained instead that the image was not blue and was "uninteresting." Something was in there about "the point" of the infrared image of the Pleiades, too, an objection that seemed a little odd in light of the responsible instrument's mission (which is the subject of that entire thread).

__________________
ETA: In fact, here's your entire initial objection to the WISE image:
Ann wrote:Unsurprisingly, I strongly dislike the WISE image of the Pleiades because it takes one of the loveliest and truly bluest naked-eye objects in the sky and turns it into something messy-looking and non-blue.

Phil Plait said:
One of my favorite things in astronomy is seeing a familiar object in an unfamiliar way. It reminds me that there’s still plenty to learn about the Universe.
And I guess the WISE team took that infrared image of the Pleiades in order to learn something about that cluster. So what, then, did they learn? Clearly the Merope nebula is differently colored (cooler?) than the rest of the nebula, which is perhaps no great surprise since the Merope Nebula is the thickest, densest part of the Pleiades nebulosity.

I think an image of this seems to be rather pointless. I can certainly understand astronomers who use infrared astronomy to find brown dwarfs in the Pleiades, but I don't get why people would simply want to color the lovely blue reflection nebula non-blue and make the sparkling bright blue stars look faint - I don't understand the point of it.

Ann
_______________________________

The discussion to which you referred above started with this post on the Observation Deck: http://asterisk.apod.com/vie ... 25#p127480

Owlice
A closed mouth gathers no foot.

User avatar
Chris Peterson
Abominable Snowman
Posts: 16007
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: JPL: WISE Mission Image Releases

Post by Chris Peterson » Tue Jul 20, 2010 2:05 pm

Ann wrote:Infrared images are almost never highly resolved. The WISE image of the Pleiades is a lot more blurry than almost any good amateur image of the Pleiades in visible light.
Not really. Many IR instruments have operated at lower resolutions than visible light images. This is a consequence of the longer wavelength: in order to be diffraction limited, you need a larger aperture with IR, and that is a problem with space-based telescopes. But the WISE camera has a FWHM of 6 arcseconds (and the sensor array oversamples this). Good ground-based narrow field images have FWHM values of around 2 arcseconds, and wide field images are usually much higher. The resolution of the WISE image is quite a bit higher than that of the Andreo image posted for comparison, and similar to images by Gendler and others.
But as I said before, I just don't think that an image of the nebulosity around the Pleiades - which contains no star formation and no thick dense pockets of dust - is all that revealing.
I think you are underestimating the value of seeing regions that were previously unknown. I predict that this data will be used to improve models of dust behavior in the galaxy.
I guess my main objection is not so much that the Pleiades got their infrared portrait taken per se. Rather, I am unhappy with the current extreme concentration on infrared astronomy. Almost all major telescopes that are being planned or being completed today are going to focus on infrared astronomy. The Hubble successor, for example, the James Webb telescope, will not be able to see as far into the short wavelengths as Hubble has been able to.
There have been, and currently still are, more space-based UV telescopes than there are IR telescopes. IR has been largely neglected, which is why the Webb telescope is intended for this wavelength band. We generally know less about the IR sky than the UV sky, and IR has the added advantage that we can see through much of the dust that blocks our views in many directions. I am not sure where you got the idea that UV astronomy has somehow been neglected in favor of IR. It simply isn't true.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
Chris Peterson
Abominable Snowman
Posts: 16007
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: Is ultraviolet astronomy uninteresting?

Post by Chris Peterson » Tue Jul 20, 2010 2:43 pm

Ann wrote:Exactly why we need a pink version of an already existing yellow-green infrared image of the Pleiades I don't quite get... is it because the Pleiades needs to be pretty in pink, perhaps?
You posted two completely different images, showing different things. The yellow-green image was made with data from three bands, 4.5um, 8um, and 24um, mapped to blue, green, and red respectively. The pink image was made with data from four bands, 3.6um, 4.5um, 5.8um, and 8um, mapped to blue, green, yellow, and red respectively (a complex color transform). The images clearly show different structure- all the more so if you are an IR astronomer with skill at interpreting this kind of data.

The choice of colors used for mapping can be arbitrary, it can be convention, or it can be based on what makes particular structures most visible.
These days you hear news about gamma ray astronomy, X-ray astronomy, visible light astronomy, infrared astronomy (lots and lots of it!) and radio astronomy. Where is the ultraviolet astronomy?
There is news all the time about UV astronomy. GALEX, HST, and Swift all regularly return UV images. UV images are also obtained from sounding rockets and balloons. As a rule, UV instruments are narrower field, so you may find the images less aesthetic than others, although that has no bearing on their scientific value. UV emission is associated with high energy processes, so UV imagery is commonly used for compact objects like stars. An object like the Pleiades is generally less interesting in the UV, since little information is provided that can't be obtained easier with visible light. The shorter wavelength is useful for enhancing knowledge about the size of dust particles, but that's about it. This is quite different from the case for IR, where vast regions of dust and gas can be seen in detail that isn't possible at all with shorter wavelengths.

I suspect that you simply don't care for the appearance of most UV images. But there is plenty of imagery out there, and new material is made available all the time.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
mexhunter
Science Officer
Posts: 467
Joined: Tue Apr 27, 2010 1:41 pm
AKA: César Cantú
Location: Monterrey, Mexico.

Re: Is ultraviolet astronomy uninteresting?

Post by mexhunter » Tue Jul 20, 2010 3:12 pm

Hi Ann:
If this is infrared,

Image

sure that is infragreen,

Image

or I'm colorblind. :mrgreen:

Seriously, I found photos of different spectra involved in the study of the Pleiades.
In X Ray:
Image
In ultraviolet, as already noted Owlice:
Image
In Visible:
Image
In Visible Color (Classic)
Image
In Near-Infrared:
Image
In Mid-Infrared:
Image
In Far-Infrared:
Image
In Radio:
Image

Those are the pictures, and sure that to the astronomers, these photons are a trail of scientific knowledge, although I still seem the picture of Radio, a very bad picture of some sad peppercorns. :mrgreen:

http://coolcosmos.ipac.caltech.edu/index.html

Very interesting Chris's analysis.

Greetings
Cesar
I come to learn and to have fun.

User avatar
Ann
4725 Å
Posts: 11411
Joined: Sat May 29, 2010 5:33 am

Re: Is ultraviolet astronomy uninteresting?

Post by Ann » Tue Jul 20, 2010 6:23 pm

Chris said:
There is news all the time about UV astronomy. GALEX, HST, and Swift all regularly return UV images
Chris, thanks for pointing out that the Swift telescope does ultraviolet astronomy on top of it X-ray and gamma ray mission. I had somehow missed its UV work, and I enjoyed exploring the Swift homepage. However, while very valuable, I get the impression that Swift's ultraviolet work is somewhat limited. Much of what could be found on Swift's homepage was artists' impressions rather than actual images made by Swift. Many of the real images that were shown were ultraviolet images of supernovae. This is supremely interesting, but again, somewhat limited. Personally I think that ultraviolet images of galaxies are the most interesting, but the Swift gallery has few such images to offer. The best I could find was an ultraviolet portrait of Andromeda. A sample of galaxies was presented with too little information for me to understand what I was being shown - the galaxies were not identified, and the key term, "BAT Luminosity", was not explained. So all in all, I really did learn new things from the Swift homepage, but I must say that Swift does not seem to be anything even remotely like a cornucopia of ultraviolet images.

As for HST, it is indeed true that it can do ultraviolet astronomy, which I personally appreciate very much indeed. I think, however, that Hubble is limited to doing near ultraviolet astronomy, as far ultraviolet astronomy is beyond it.

Also, as for HST, there are no more plans to repair it, so when it stops working we will no longer get any UV images from it. And Hubble's replacement, the James Webb Telescope, will not be able to do ultraviolet astronomy at all.

As for GALEX, I myself have very much enjoyed the images it has produced. I have particularly liked its gallery of galaxy images, but GALEX has imaged all kinds of targets and has done some great science, in my opinion. Now, however, its far ultraviolet detector has broken down, and it is limited to working with its near ultraviolet detector. It is down to the same capacity as the HST, in other words, and can no longer complement that telescope. When GALEX breaks down completely, I don't think it is going to be replaced, or at least I have heard nothing to that effect.

So I still think that ultraviolet astronomy is not getting nearly as much attention as it deserves. For example, is there anything at all like an all sky ultraviolet survey in the process?

Ann
Color Commentator

User avatar
Chris Peterson
Abominable Snowman
Posts: 16007
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: Is ultraviolet astronomy uninteresting?

Post by Chris Peterson » Tue Jul 20, 2010 6:54 pm

Ann wrote:Chris, thanks for pointing out that the Swift telescope does ultraviolet astronomy on top of it X-ray and gamma ray mission. I had somehow missed its UV work, and I enjoyed exploring the Swift homepage. However, while very valuable, I get the impression that Swift's ultraviolet work is somewhat limited.
Swift is not intended for routine UV imaging, but is utilized for targets of opportunity. Thus, things like supernovas are imaged, since these are the sorts of things where UV data is particularly useful.
As for HST, it is indeed true that it can do ultraviolet astronomy, which I personally appreciate very much indeed. I think, however, that Hubble is limited to doing near ultraviolet astronomy, as far ultraviolet astronomy is beyond it.
The HST can image to 200nm, and supplement that with spectroscopic data to 115nm.
So I still think that ultraviolet astronomy is not getting nearly as much attention as it deserves. For example, is there anything at all like an all sky ultraviolet survey in the process?
Both UV and extreme UV sky surveys have been conducted in the past. Since UV sources are generally points, the purpose of such surveys has been to identify singular sources, which could then be studied with narrow field instruments. It is unclear that there is much need for additional UV surveys, given that existing surveys are of high quality, and that UV sources generally have optical counterparts. All in all, UV astronomy is not very dependent on imaging instruments, but relies much more on spectrometry. This is quite different from IR astronomy, and is part of the reason you see less emphasis now on UV imaging telescopes.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18184
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: Is ultraviolet astronomy uninteresting?

Post by neufer » Tue Jul 20, 2010 7:30 pm

Ann wrote:
So I still think that ultraviolet astronomy is not getting nearly as much attention as it deserves.
51 APODS with SOHO's Extreme ultraviolet Imaging Telescope (EIT):
So when do we get to see the sun in infrared :?: :(
Chris Peterson wrote:
All in all, UV astronomy is not very dependent on imaging instruments, but relies much more on spectrometry. This is quite different from IR astronomy, and is part of the reason you see less emphasis now on UV imaging telescopes.
http://en.wikipedia.org/wiki/Extreme_ultraviolet_Imaging_Telescope wrote:
<<The Extreme ultraviolet Imaging Telescope (EIT) is an instrument on the SOHO spacecraft used to obtain high-resolution images of the solar corona in the ultraviolet range. The EIT instrument is sensitive to light of four different wavelengths: 17.1, 19.5, 28.4, and 30.4 nm, corresponding to light produced by highly ionized iron (XI)/(X), (XII), (XV), and helium (II), respectively. Te EIT wavelengths are of great interest to solar physicists because they are emitted by the very hot solar corona but not by the relatively cooler photosphere of the Sun; this reveals structures in the corona that would otherwise be obscured by the brightness of the Sun itself. EIT was originally conceived as a viewfinder instrument to help select observing targets for the other instruments on board SOHO, but EIT is credited with a good fraction of the original science to come from SOHO, including the first observations of traveling wave phenomena in the corona, characterization of coronal mass ejection onset, and determination of the structure of coronal holes. It currently (2006) produces an Fe XII (19.5 nm wavelength) image of the Sun about four times an hour, around the clock; these are immediately uplinked as time-lapse movies to the SOHO web site for immediate viewing by anyone who is interested. The images are used for long-duration studies of the Sun, for detailed structural analyses of solar features, and for real-time space weather prediction by the NOAA Space Weather Prediction Center.

EIT was a difficult sell to the scientific funding agencies, as it was not clear in the early 1990s that simple imaging of the corona would be scientifically useful (most of the other instruments on board SOHO are spectrographs of various kinds). The EIT PI, Jean-Pierre Delaboudiniere, was forced to scrounge funding and resources from several locations to construct and launch the instrument. Focus adjustment is achieved by thermal expansion: the internal survival heaters (found in most spaceborne instruments) are used to achieve microscopic changes in the size of the telescope structure and hence the mirror spacing. EIT was originally allocated only about 1 kbit/s of data -- about the same speed as a 110 baud teletype -- but after its utility became clear much more telemetry bandwidth was allocated to it.>>
Art Neuendorffer

User avatar
bystander
Apathetic Retiree
Posts: 20700
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

Re: Is ultraviolet astronomy uninteresting?

Post by bystander » Tue Jul 20, 2010 8:17 pm

Here is an interesting composite of the Pleiades:
ultraviolet (blue), optical (green), and far-infrared (red).
Credit: Steven Gibson

User avatar
Ann
4725 Å
Posts: 11411
Joined: Sat May 29, 2010 5:33 am

Re: Is ultraviolet astronomy uninteresting?

Post by Ann » Tue Jul 20, 2010 10:07 pm

Cesar, thank you for all your Pleiades pictures. They are all interesting.

Art, thanks for your UV solar pictures. I agree that great science can be done with these images. Unfortunately they don't do much for me. If I were an astronomer, I wouldn't do solar astronomy, even though I get a kick out of the fact that the Sun is white and not yellow and that is is in the top 5% echelon of stellar brightness in our galaxy.

Bystander, thank you for your Pleiades picture. I really like it. I would still love a very good UV image of the Pleiades, mostly so I could see if the relative UV brightness of the individual Seven Sisters is the same as their relative brightness in visual light. I'm not sure if your image reveals that.

Chris, you said:
Both UV and extreme UV sky surveys have been conducted in the past. Since UV sources are generally points, the purpose of such surveys has been to identify singular sources, which could then be studied with narrow field instruments. It is unclear that there is much need for additional UV surveys, given that existing surveys are of high quality, and that UV sources generally have optical counterparts.
Well, science and I may well need different things, but I know that I would like to see a lot more ultraviolet surveys. In particular I would like to see a truly ambitious galaxy survey in the ultraviolet. GALEX did one that I absolutely loved:

http://www.galex.caltech.edu/media/glx2 ... img01.html

GALEX imaged many galaxies indeed, but not enough of them. There are so many others whose ultraviolet portraits I would like to see and then compare them with the visible appearance of the same galaxies. To me, it is the galaxy surveys that are most interesting about UV astronomy, although I agree, of course, that UV images of supernovae and gamma ray bursts are incredibly important, too.

Ann
Color Commentator

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18184
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Brown Dwarfs and the Seven Snow Whites

Post by neufer » Tue Jul 20, 2010 10:41 pm

http://en.wikipedia.org/wiki/Pleiades_%28star_cluster%29 wrote: <<The Pleiades (Messier object 45) is an open star cluster containing middle-aged hot B-type stars located in the constellation of Taurus. The cluster core radius is about 8 light years and tidal radius is about 43 light years. The cluster contains over 1,000 statistically confirmed members, although this figure excludes unresolved binary stars. It is dominated by young, hot blue stars, up to 14 of which can be seen with the naked eye depending on local observing conditions. The total mass contained in the cluster is estimated to be about 800 solar masses.

The cluster contains many brown dwarfs, which are objects with less than about 8% of the Sun's mass, not heavy enough for nuclear fusion reactions to start in their cores and become proper stars. They may constitute up to 25% of the total population of the cluster, although they contribute less than 2% of the total mass. Astronomers have made great efforts to find and analyse brown dwarfs in the Pleiades and other young clusters, because they are still relatively bright and observable, while brown dwarfs in older clusters have faded and are much more difficult to study.>>
http://www.universetoday.com/2010/07/17/astronomy-without-a-telescope-brown-dwarfs-are-magnetic-too/#more-68213 wrote:
Astronomy Without A Telescope – Brown Dwarfs Are Magnetic Too
Written by Steve Nerlich July 17th, 2010
<<I feel a certain empathy for brown dwarfs. The first confirmed finding of one was only fifteen years ago and they remain frequently overlooked in most significant astronomical surveys. I mean OK, they can only (stifles laughter) burn deuterium but that's something, isn't it?

It has been suggested that a clever way of finding more brown dwarfs is in the radio spectrum. A brown dwarf with a strong magnetic field and a modicum of stellar wind should produce an electron cyclotron maser. Roughly speaking (something you can always depend on from this writer), electrons caught in a magnetic field are spun energetically in a tight circle, stimulating the emission of microwaves in a particular plane from the star's polar regions. So you get a maser, essentially the microwave version of a laser, that would be visible on Earth – if we are in line of sight of it.

While the maser effect can probably be weakly generated by isolated brown dwarfs, it's more likely we will detect one in binary association with a less mass-challenged star that is capable of generating a more vigorous stellar wind to interact with the brown dwarf's magnetic field.

This maser effect is also proposed to offer a clever way of finding exoplanets. An exoplanet could easily outshine its host star in the radio spectrum if its magnetic field is powerful enough.

So far, searches for confirmed radio emissions from brown dwarfs or orbiting bodies around other stars have been unsuccessful, but this may become achievable in the near future with the steadily growing resolution of the European LOw Frequency ARray (LOFAR), which will be the best such instrument around until the Square Kilometer Array (SKA) is built – which won't be seeing first light before at least 2017.

But even if we can't see brown dwarfs and exoplanets in radio yet, we can start developing profiles of likely candidates. Christensen and others have derived a magnetic scaling relationship for small scale celestial objects, which delivers predictions that fit well with observations of solar system planets and low mass main sequence stars in the K and M spectral classes (remembering the spectral class mantra Old Backyard Astronomers Feel Good Knowing Mnemonics).

Using the Christensen model, it's thought that brown dwarfs of about 70 Jupiter masses may have magnetic fields in the order of several kilo-Gauss in their first hundred million years of life, as they burn deuterium and spin fast. However, as they age, their magnetic field is likely to weaken as deuterium burning and spin rate declines.

Brown dwarfs with declining deuterium burning (due to age or smaller starting mass) may have magnetic fields similar to giant exoplanets, anywhere from 100 Gauss up to 1 kilo-Gauss. Mind you, that's just for young exoplanets – the magnetic fields of exoplanets also evolve over time, such that their magnetic field strength may decrease by a factor of ten over 10 billion years.

In any case, Reiners and Christensen estimate that radio light from known exoplanets within 65 light years will emit at wavelengths that can make it through Earth's ionosphere – so with the right ground-based equipment (i.e. a completed LOFAR or a SKA) we should be able to start spotting brown dwarfs and exoplanets aplenty.>>
Art Neuendorffer

User avatar
Ann
4725 Å
Posts: 11411
Joined: Sat May 29, 2010 5:33 am

Re: Is ultraviolet astronomy uninteresting?

Post by Ann » Wed Jul 21, 2010 6:31 am

You mean, Brown Dwarfs and the Seven Sky Blues?

Image

Image

Seven Blues!

Image

Ann
Color Commentator