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FIRE Fingerprints Cold Brown Dwarfs

bdwarf — Wed, 20 Apr 2011 15:02:15 +0000

In this WISE false-color image, a cold brown dwarf appears green

The Folded Port Infrared Echellette (FIRE) spectrograph, commissioned in March 2010, is contributing to the discovery of some of the coldest and least luminous brown dwarfs found to date. In a paper accepted for publication to the Astrophysical Journal, we report the discovery of five late-type T dwarfs from the WISE survey identified by FIRE.

The Wide-field Infrared Survey Explorer, or WISE, has recently imaged the entire sky at mid-infrared wavelengths, between 3 and 22 µm, beyond what our eyes can discern. Yet it is at these wavelengths that cold brown dwarfs emit the majority of their light. With specially-selected filters, WISE can both detect and discriminate the coldest brown dwarfs, by measuring the absorption caused by methane present in their atmospheres. When an object of the right color shows up, it is a good candidate to be a very cold brown dwarf.

Near-infrared FIRE spectra of five cold brown dwarfs discovered by WISE. The spectral types are listed on the right, while the labels indicate what gases are creating the absorption features seen in these spectra.

Confirming these candidates requires spectroscopy, however, and this is a challenge when one is trying to detect very cold, very faint brown dwarfs. Fortunately, FIRE was designed to be highly sensitive in its low-resolution prism mode, and we have used this mode to identify and characterize five new, very late-type T dwarfs (these are the class of brown dwarfs that harbor methane in their atmospheres). The discoveries have temperatures between 600 K and 900 K, or 620 F to 1160 F. While this seems hot from a human perspective, these brown dwarfs are up to 10 times cooler than the Sun, and only twice as warm as the Earth’s atmosphere (on a warm summer day).

This result will be published in in the Astrophysical Journal. The lead authors is Adam J. Burgasser (UCSD).

BROWN STAR

Tap Vann — Wed, 23 Mar 2011 21:50:21 +0000

Astronomers have detected a failed star – a brown dwarf!!

This newly discovered brown dwarf is identified as CFBDSIR 1458+10B, and is the dimmer member of the binary brown dwarf system, which is located only 75 light-years from Earth.

Brown dwarfs lack enough mass for gravity to trigger the nuclear reactions that make stars shine, but they’re more massive than what’s typically considered to be a planet.

The system was detected from observations made by the Very Large Telescope at the European Southern Observatory’s Paranal Observatory in Chile. The telescope’s powerful spectrograph was used to study the object’s infrared spectrum and measure its temperature, which was found to be extraordinarily cold by brown dwarf standards.

In fact, CFBDSIR 1458+10 is the coolest brown dwarf binary system found to date, astronomers said.

“We were very excited to see that this object had such a low temperature, but we couldn’t have guessed that it would turn out to be a double system and have an even more interesting, even colder component,” said Philippe Delorme of the French National Center for Scientific Research and the Joseph Fourier University in Grenoble, France.

Delorme is the co-author of a paper on the brown dwarf finding that will appear in an upcoming issue of the Astrophysical Journal.

The dimmer of the two failed stars has been found to have a temperature of approximately 212 degrees Fahrenheit (100 degrees Celsius), which is the boiling point of water and not much different from the temperature inside a sauna.

Our sun, in comparison, averages a temperature of about 10,000 degrees Fahrenheit (5,500 degrees Celsius), researchers have said.

“At such temperatures we expect the brown dwarf to have properties that are different from previously known brown dwarfs and much closer to those of giant exoplanets – it could even have water clouds in its atmosphere,” said Michael Liu of the University of Hawaii’s Institute for Astronomy, who is the lead author of the study. “In fact, once we start taking images of gas-giant planets around sun-like stars in the near future, I expect that many of them will look like CFBDSIR 1458+10B.”

The hunt for cool objects in the cosmos is an active field of astronomy. NASA’s Spitzer Space Telescope recently identified two other very faint objects as other possible contenders for the coldest known brown dwarfs, but the temperatures of these stars have not been measured as precisely.

The brown dwarfs seen by the Spitzer Space Telescope have temperatures that range from 350 to 620 degrees Fahrenheit. Future observations will better determine how the objects found by Spitzer compare to CFBDSIR 1458+10B.

Liu and his colleagues are planning to observe this newly detected brown dwarf again to better determine its properties, and to begin mapping the binary’s orbit, which, after about a decade of observation, should allow astronomers to determine the system’s mass.

A brown dwarf star that contradicts the perception of all stars being hot has been discovered by U.S. astronomers. This brown dwarf star is not hot, but rather about room temperature, they say.

Like normal stars, brown dwarfs form from collapsing gas clouds, but they don’t become massive enough to sustain nuclear reactions, so they briefly shine red from the heat of formation then fade.

Still, before discovering this latest star, the coolest known brown dwarfs were determined to be hot enough to roast any astronauts who might approach too close, NewScientist.com reported Monday.

Pennsylvania State University astronomers used NASA’s infrared Spitzer Space Telescope to detect the glow of this brown dwarf just 63 light years from Earth with a temperature of only 86 degrees Fahrenheit.

The object, orbiting a white dwarf star, has seven times the mass of Jupiter, a figure that would normally classify it as a planet.

Planets, however, form in discs of gas and dust around stars, researchers say, and this object — dubbed WD 0806-661 B –lies too far from its star to be deemed a planet if it formed where it now is.

While hotter than Jupiter, which is at minus 236 degrees F., it is much cooler than the next coolest known brown dwarf star, measured at 212 degrees F.

This means that WD 0806-661 B will act as a “missing link” to reveal how temperature affects the atmosphere and features of objects that are roughly the size of Jupiter, the astronomers said.

Nibiru Tyche, Planet X Brown Dwarf:

Blurring the Boundaries

davidnm2009 — Tue, 22 Mar 2011 13:44:25 +0000

Aaah, 2006. The year of the great Pluto debacle! I have to admit to having been left unsatisfied by the IAU’s resolution on whether or not Pluto can be said to constitute a ‘planet’. In the end they designated it a ‘dwarf planet’, a designation that smells faintly of the sort of confused fudges beloved of politicians. Science is supposed to supply clarity, and precision on definitions is important.

Except sometimes, one has to be careful with definitions. They can cause more trouble than they solve.

The basic problem here, I think, is more to do with human beings than it is to do with what’s going on in the sky. The human animal is a categorical one – we like to drop objects and phenomena into neat, tidy boxes. It’s probably a side-effect of the sort of pattern-recognition that enabled our ancestors to spot predators lurking in the bushes, and tell them apart from the prey they were stalking. All very useful, from an evolutionary point of view, but not a behaviour that always maps so well onto an untidy, messy universe.

In particular, I’m thinking about this in a brown dwarfs context.

Pluto has some of the characteristics of a planet and some of the characteristics of a more conventional Kuiper Belt object. In an analogous manner, brown dwarfs can have some of the characteristics of giant planets and also some of the characteristics of stars. But they also have a whole set of properties all of their own.

The textbook, lying-to-children description of a brown dwarf goes something like this: an object with a mass range between 13 Jupiter masses to 7.5% of a solar mass. That way it’s just big enough for deuterium fusion to occur for a time, but not big enough for stable, sustained hydrogen fusion to happen.

So far, this is all nice and tidy and neat. And better yet, there’s even a very limited subset of objects for which this description is actually true! (Wonders will never cease…) This subset, in case you’re wondering, is for brown dwarfs with solar metallicity[1].

However, there is a ticking time-bomb lurking in the neat, neurotically-tidy definition: metallicity. You see, metallicity has a huge impact on stellar structure. Change the balance of elements inside a star and you can alter its opacity (its ‘transparency’ to light), you can alter the distribution of pressures inside it and in extremis, you can even alter the process of fusion itself. (The CNO cycle, for instance, uses carbon, nitrogen and oxygen as catalysts for the fusion of hydrogen – take the catalysts away, and no CNO cycle[2].)

Now, people have wondered if all this has implications for the fusion cutoffs. And it turns out, yes it does. Quite dramatic ones, in fact. In the limiting case of zero metallicity (no heavy elements of any kind), the hydrogen-burning threshold creeps up to 1/10th of a solar mass. For supersolar metallicities, however, the hydrogen burning limit can fall to as low as 4% of a solar mass.

So, a zero metallicity brown dwarf could weigh in at just a shade under 0.1 Suns – heavier than many solar-metallicity stars! – whereas a supersolar-metallicity star may weigh in at just more than 4% of a solar mass, meaning that an actual star would be lighter than many brown dwarfs.

Feeling confused? It’s only to be expected. This is the sort of muddle that happens when human ideas about tidiness and category-neatness collide with a complex and messy universe.

Also, a similar variance can happen for the deuterium burning limit as well. Change the metallicity and you can move that up and down as well. So we swiftly arrive at a situation where some things of the same mass are stars and some things are brown dwarfs. But there’s worse – you see, depending on how you look at it, some of the brown dwarfs could also actually be planets.

Unlike planets or stars, brown dwarfs are supported by something called electron degeneracy pressure. This is a consequence of quantum mechanics, and its origins are probably beyond our discussion here[3]. Electron degeneracy starts to put in an appearance at about 4 Jupiter masses – which means you have some nominal ‘planets’ whose internal behaviour is much more like brown dwarfs!

And then there’s the good old spectrum issue. To make the point, here’s Jupiter in the near-infrared, overplotted with a late-type, ‘cold’ T dwarf:

They’re hardly identical, and Jupiter’s shorter wavelengths are dominated by reflected Sunlight – but you can see that there is some similarity. Even now, 4.5 billion years after its formation, Jupiter still radiates more heat than it receives from the Sun. So in this spectroscopic sense, one of our familiar, local planets is behaving like a brown dwarf!

To summarise, if there’s one thing I want you to take away from this post, it’s to treat nice, tidy theoretical definitions with a degree of healthy skepticism. It’s not necessarily that they’re wrong, as such, but rather that any theoretical model is of necessity simpler than the object it describes. Inevitably there will be gaps and errors, and some types of object will blur the boundaries. This is life, and this is why the Universe is worth studying – it’s full of these fascinating little odd pockets!

_________________
[1] Although I’m sure we’ve covered it before, a terminology note for new readers: a star’s metallicity is the proportion of its mass that isn’t composed of hydrogen or helium. The reason for this distinction is that H and most of the He come down to us from the Big Bang, but everything else was made inside stars and novae. (Very technically, the Big Bang also made some lithium, but lithium is pretty rare, so for most purposes we can ignore it.)
[2] See here for more on the CNO cycle.
[3] In detail, it’s due to the Pauli exclusion principle. Inside a brown dwarf, the pressures are far too high for conventional Coulomb pressure – electron shell on electron shell repulsion – to hold matter up against its own weight. But there is no thermal pressure – heat from fusion – to counter the weight, so the core collapses until the electrons are ‘squeezed’ away from their atoms. Adding an electron to this volume requires raising the other electrons’ energy levels to ‘make room’, and there’s only so much room to be had. Beyond this point, the electron-degenerate gas effectively starts ‘pushing’ back out and excludes new material from being added.

Room Temperature Brown Dwarf Discovered

bdwarf — Sun, 20 Mar 2011 13:48:52 +0000

The newly discovered 300 K brown dwarf GJ 3483B, seen in the mid-infrared by Spitzer (left) but invisible in the near-infrared (right).

In collaboration with Penn State colleagues Kevin Luhman and John Bochanski, we have uncovered a remarkably cold brown dwarf whose atmosphere appears to be a mere 300 K. This is the equivalent of a warm day at the beach, not what one expects from the surface of a star. In fact, the properties of this brown dwarf are so unusual that it may actually be a room temperature superplanet on an incredibly long orbit around a dead star.

The source, GJ 3483B, is a co-moving companion to the nearby white dwarf GJ 3483 (aka WD 0806-661), a DQ4 at a distance of 19.2 pc (62.6 lightyears). It was detected by the Spitzer Space Telescope in the mid-infrared 4.5 µm band in 2004 and again in 2009, and the motion of the brown dwarf agrees exactly with that of the white dwarf, validating its physical association. Because we know the distance to the white dwarf, we are able to measure the absolute brightness of GJ 3483B in the mid-infrared. It turns out to be about 2.5 magnitudes, or a factor of 10 times, fainter than the coldest brown dwarf known at the time, UGPS 0722-05. Moreover, it has been undetectable in several other photometric bands to strict limits, reaffirming its very dim nature. Using the mid-infrared brightness, the age of the white dwarf (about 1.5 billion years – a third of the age of our Sun) and brown dwarf evolutionary models, we find an estimated atmospheric temperature of 300 K – the same as the Earth – and a mass about 7 times that of Jupiter.

Absolute near-infrared brightnesses of known brown dwarfs versus color. The previous record holder, UGPS 0722-05, is shown in green; the recently discovered cool binary, CFBDSIR 1458+10AB, is indicated in red. The best limit for GJ 3483B (downward arrows) is roughly 10 times fainter.

The temperature, mass and association of GJ 3483B with another star makes it seem very planet-like in appearance. However, it has an incredibly wide orbit – about 2500 Astronomical Units (1 AU is equal to the Earth-Sun distance) – implying an orbit period of at least 150,000 years. Is this a planet that has been pushed into a wide orbit after its host star, originally twice the mass of the Sun, shed 70% of its mass at the end of its stellar lifetime? Or is this simply a double star system, with one star happening to have a very low, planetary-like mass?

The low temperature inferred for GJ 3483B is itself remarkable, as the only equivalent-temperature atmosphere we know of is that of Earth. It is so cold that ice clouds are expected to be present in its upper atmosphere – an ice star! However, GJ 3483B would not itself be “habitable” – its hydrogen- and helium-rich atmosphere would be poisonous to life as we know it.

GJ 3483B is probably not the only one of its kind. Similarly cool brown dwarfs – referred to as “Y dwarfs” – are being found as companions to other brown dwarfs, and as isolated objects by NASA’s WISE mission. Yet GJ 3483B remains the coldest brown dwarf found so far, and studying its dim atmosphere will require the next generation of large ground-based and space-based telescopes.

This result was published in in the Astrophysical Journal Letters. The authors are Kevin Luhman (Penn State), Adam J. Burgasser (UCSD), and John Bochanski (Penn State). Also see the Science News & Analysis article describing the discovery and this article from Sol Station.

The scientists are puzzled with two sun phenomena By eye

theboldcorsicanflame — Sun, 06 Mar 2011 23:22:33 +0000

READ FULL ARTICLE ON

http://thewatchers.adorraeli.com/2011/03/06/the-scientists-are-puzzled-with-two-sun-phenomena/

EXCERPT
Over 80% of all solar systems have multiple suns, so is it possible that we live in a binary solar system with two suns as well? Recent discoveries point to the existence of an old brown dwarf. Our solar system is surrounded by a vast collection of icy bodies called the Oort Cloud. If our Sun were part of a binary system in which two gravitationally-bound stars orbit a common center of mass, this interaction could disturb the Oort Cloud on a periodic basis, sending comets whizzing towards us. The Oort Cloud is thought to extend about 1 light year from the Sun. The closest known star to the Sun is Proxima Centauri, located 4.2 light years away

Binary star systems are common in the galaxy. It is estimated that one-third of the stars in the Milky Way are either binary or part of a multiple-star system. Red dwarfs are also common – in fact, astronomers say they are the most common type of star in the galaxy. Brown dwarfs are also thought to be common, but there are only a few hundred known at this time because they are so difficult to see. Red and brown dwarfs are smaller and cooler than our Sun, and do not shine brightly. If red dwarfs can be compared to the red embers of a dying fire, then brown dwarfs would be the smoldering ash. Because they are so dim, it is plausible that the Sun could have a secret companion even though we’ve searched the sky for many years with a variety of instruments.

TO BE CONTINUED ON

http://thewatchers.adorraeli.com/2011/03/06/the-scientists-are-puzzled-with-two-sun-phenomena/

READ OTHER ARTICLE ON

http://www.khaleejtimes.com/DisplayArticleNew.asp?col=&section=international&xfile=data/international/2011/January/international_January842.xml

The Earth could soon have a second sun, at least for a week or two. The cosmic phenomenon will happen when sun explodes into a supernova in the night sky.

And, according to a report, the most stunning light show in the planet’s history could happen as soon as this year.

Earth will undoubtedly have a front row seat when the dying red super-giant star Betelgeuse finally blows itself into oblivion, the Daily Mail quoting the Australian website news.com.au. reports.

The explosion will be so bright that even though the star in the Orion constellation is 640 light years away, it will still turn night into day and appear like there are two suns in the sky for a few weeks. The only real debate is over exactly when it will happen.

In stellar terms, Betelgeuse is predicted to crash and burn in the near future. But that doesn’t necessarily mean you have to rush out and buy sunglasses.

Brad Carter, Senior Lecturer of Physics at the University of Southern Queensland in Australia, claimed that the galactic blast could happen before 2012 or any time over the next million years.

”This old star is running out of fuel in its centre,” Carter told news.com.au.

”This fuel keeps Betelgeuse shining and supported. When this fuel runs out, the star will literally collapse in upon itself and it will do so very quickly.

Will the REAL Nibiru Planet X Please Stand Up?

CKH888 — Mon, 28 Feb 2011 08:10:41 +0000

Comparative sizes of known gas giant planets to our sun

Copyright 2011-3011 By Photonic Portal, All Rights Reserved.

Amateur astr0nomers and news junkies are buzzing over the newest announcements by astronomers and scientists that a possible colossal new undiscovered planet may exist hidden in the Oort Cloud which rings our solar system. There are now so many new and confusing news reports on comets, dark stars, brown dwarfs, red dwarfs, gas giants and other astronomical bodies that it tests credulity. Below are just a few of hundreds of citizen journalist reports floating around Youtube on what is being discovered, announced, suppressed, edited, altered, deleted, et al. There’s no doubt something is out there, and someone somewhere does not want humanity to know very much about what it is.

Photonic Portal 2.28.2011

Tags: Planet X, Nemesis, Wormwood, Oort cloud, Cornell University, astronomy, the search for planet x, eris, tyche, new gas giant planet discovered,amateur astronomy

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Will the REAL Nibiru Planet X Please Stand Up?

CKH888 — Mon, 28 Feb 2011 08:10:41 +0000
Comparative sizes of known gas giant planets to our sun Copyright 2011-3011 By Photonic Portal, All

Surfaced At Last

davidnm2009 — Wed, 26 Jan 2011 13:30:48 +0000

It’s been a long time in the making, but my paper has finally seen the light of day:

Blue not brown: UKIDSS T dwarfs with suppressed K-band flux (Murray et al 2011)

I got the acceptance e-mail from MNRAS yesterday, so it was time to get a copy onto arxiv. It’s a good feeling, finally having all of that sorted!

Discovery of a "wide" M dwarf-L dwarf binary

bdwarf — Sun, 12 Dec 2010 21:38:17 +0000

Vanderbilt University graduate student Saurav Dhital and collaborators report the discovery an unusually wide low-mass star plus brown dwarf binary. The dim pair of dwarfs, separated by over 100 AU, presents a new challenge to theories describing the formation of very low mass stars and brown dwarfs.

The system, named 2MASS J01303563-4445411, was discovered serendipitously with the SpeX imager/spectrometer, mounted on the 3m NASA Infrared Telescope Facility. The primary of the system, an M9 dwarf, was originally targeted in early December 2009 as part of an ongoing near-infrared spectroscopic survey to populate the SpeX Prism Spectral Libraries survey. However, an image of the field revealed a faint companion about 3.3″ (0.0009 degrees) to the east. A few weeks later, U. Hawaii graduate student Dagny Looper obtained a spectrum of the companion and found it to be consistent with that of an L6 dwarf. The estimated distances of the two stars were in agreement with each other, and a statistical technique developed by Mr. Dhital as part of his PhD thesis research (Sloan Low-mass Wide Pairs of Kinematically Equivalent Systems, or SLoWPoKES) indicate that they are likely to be a physically bound pair.

Near-infrared spectra of the 2MASS J01303563-4445411 primary (top) and secondary (bottom), taken with SpeX

However, the system, which probably consists of a very low mass, hydrogen-fusing star and a non-fusing brown dwarf, are not bound particularly strongly. With a projected separation of 130 AU, the gravitational force between them is about the same as that between the Sun and Uranus, and one orbit takes roughly 4000 years to complete (monitoring this orbit is not an ideal project for a PhD thesis). Such weakly-bound systems were believed to be ripped apart by encounters with other stars, as most low-mass binary orbits are found to be 10 times smaller, with the exception of a handful of very young binaries which may not have had time to be disrupted. 2MASS J01303563-4445411, on the other hand, appears to be a relatively old system. Developing theories describing the formation of low-mass stars and brown dwarfs must therefore account for the creation of such wide, fragile pairs.

This result was published in in the Astronomical Journal. The authors are Saurav Dhital (Vanderbilt University), Adam J. Burgasser (UCSD), Dagny L. Looper (U. Hawaii) and Keivan G. Stassun (Vanderbilt University).

Clouds on a Young Planet: First Science Results with FIRE

bdwarf — Mon, 15 Nov 2010 16:42:51 +0000

A UKIDSS false color image of the Ross 458 system, composed of a pair of M dwarfs (bright star in upper left corner) and the planetary-mass brown dwarf Ross 458C (circled in lower right corner).

To study the atmospheres of young planets outside our Solar System, we need not look far. The first brown dwarf science with the newly-commissioned FIRE spectrograph has revealed the presence of rock clouds in the atmosphere of a planetary-mass companion to the nearby Ross 458 system. The presence of these clouds, and the planetary nature of the source, defy prior expectations.

The source in question is Ross 458C, a brown dwarf candidate identified in the UKIDSS survey in early 2010 by two independent studies led by Drs. Rolf-Dieter Scholz and Betrand Goldman. This source, also known as ULAS J130041.72+122114.7, is located 1.7′ (0.028 degrees) southeast of the Ross 458 system, a pair of magnetically active M dwarfs only 11.2 pc (36.5 light-years) from the Sun. The colors and faintness of Ross 458C, and that fact that it co-moves with the Ross 458 system, led both studies to conclude that it was potentially a very cool and very low-mass brown dwarf companion. However, neither study had the necessary spectral data to probe its atmosphere.

Enter the Folded-port Infrared Echellette, or FIRE, spectrograph, which was commissioned on the Magellan 6.5m Baade telescope in late February 2010 (see this prior blog post ). One of the first targets we aimed FIRE at was Ross 458C, in order to determine the nature of this interesting faint object. The resulting spectrum revealed strong bands of water and methane gas, typical of low-temperature brown dwarfs of the T spectral class. We classified Ross 458C as a T8 dwarf, found its luminosity to be 400,000 times fainter than the Sun, and estimated its surface temperature to be a mere 650 °K (710 °F) – about the temperature of a pizza oven. The rapid rotation and strong magnetic activity of Ross 458A indicates that the system is relatively young – a mere 150-800 million years old – which would give Ross 458C a mass of only 6-11 times that of Jupiter based on evolutionary models. This is similar to the masses of the planets found orbiting the HR 8799 system.

FIRE spectrum of Ross 458C (black line) compared to best-fit atmosphere models with (blue line) and without (red line) clouds. The cloudy model provides a better fit, evidence that clouds are present in the atmosphere of this source.

Analysis of the FIRE spectrum of Ross 458C revealed another surprise – its atmosphere appears to be covered in clouds. Comparing the spectrum to models created by Drs. Mark Marley and Didier Saumon, we found that the best fits could be made only when the absorption effects of clouds were included in the models. The presence of these clouds – which are made of rocks and metal rather than water – was unexpected, as it is has long been assumed that such clouds are sunk deep below the atmospheres of T-type brown dwarfs. However, the young age of Ross 458C may allow these clouds to reside at higher layers in the atmosphere and form larger particles, in both cases making them easier to detect.

Ross 458C not only challenges our understanding of clouds in brown dwarf atmospheres, it challenges our very definition of what a brown dwarf is. As a non-fusing object in orbit around a pair of stars, and with a mass below the limit of even deuterium fusion (about 13 Jupiter masses), it satisfies all of the requirements for a “planet” as laid out by the International Astronomical Union in 2006 and in an article published by Drs. Gibor Basri and Mike Brown, also in 2006. Yet this is certainly a very unusual planet, since it has an orbit that is roughly 1000 AU in radius and is at least 6 times more massive and hotter than Jupiter. As in many scientific endeavors, the more we learn, the more we find our assumptions and expectations might be wrong!

This result was published in in the Astrophysical Journal, and presented at the 16th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun and the 217th American Astronomical Society Meeting. Authors include Adam J. Burgasser (UCSD), Robert A. Simcoe (MIT), John J. Bochanski (MIT), Didier Saumon (LANL), Eric E. Mamajek (U. Rochester), Michael C. Cushing (NASA/JPL), Mark S. Marley (NASA/Ames), Craig McMurtry (U. Rochester), Judith L. Pipher (U. Rochester) and William J. Forrest (U. Rochester)

Thinking Visually

davidnm2009 — Mon, 25 Oct 2010 12:48:42 +0000

As I’ve said before, one of the great things about astronomy is that you can see stuff.

Aside from the sometimes-raised suggestion that Jupiter could be considered a brown dwarf, I don’t expect to ever actually ‘see’ one of these objects. And it does make you wonder what they would actually look like.

The closest I’ve got to seeing a brown dwarf is the readout screens in some telescope control rooms. However, it’s arguable whether that should count, as all of the images in question were taken in the near-infrared. (For an idea what they look like, this gives some indication.) It’s kind of strange, in a way – I work on these things every day, and yet I haven’t ever actually ‘seen’ one as such. Maybe for some hot, young M-type brown dwarfs, and perhaps also some Ls, it might be possible to glimpse them optically in a telescope, but for T dwarfs it’s quite hopeless. (I seem to recall that the visual magnitude of Epsilon Indi Bb was estimated at +23 or fainter, and the human eyeball gives up at around +6. Just a slight gap there…)

Just to hammer home the point about the faintness in the optical, here’s a spectrum of Epsilon Indi Ba, one the closest currently-known T-dwarfs:

Fig. 1 Spectrum of Epsilon Indi Ba, from King et al. (2010). The spectrum is set to 1 at its maximum point. (Click for a larger version.)

See the two coloured, dotted lines? They mark out the approximate range of the human visual spectrum. Look down between those lines. See that tiny little bump near the bottom of the plot? That’s the bit of the T dwarf’s light that we could actually see, using only our eyeballs. As you can clearly see, it’s nothing next to the infrared emission. And this is for a relatively-hot T dwarf – cooler objects will have even less optical emission.

Anyway, all of this leaves the close-in appearance of these objects a matter of some speculation.

Kirkpatrick and Hurt have proposed that T-dwarfs would actually look sort-of magenta. Sodium and potassium absorb heavily in the green part of the spectrum, and there’s very little light to start with at the blue end. Of course, my immediate thought is to wonder if that would actually make them look genuinely red instead of magenta, as more red-orange light is left (and also, there’s more light being emitted in the red anyway)?

This leads to another thought for me. Supposing a T dwarf is metal-poor, i.e. comparatively-deficient in elements heavier than helium. Presumably this also means that it’s deficient in sodium and potassium as well. So if we take the Kirkpatrick and Hurt argument, would that also make them ‘greener’? (I’m not sure quite what effect adding more green to magenta is going to have on colour … it’s kind of hard to pciture!) Or would they look more bluish?

But it’s interesting to think that composition might strongly-affect the visual colours.

Of course, there’s also the issue of weather, which I’ve been thinking about recently. But that’s a whole different kettle of fish…

An Unsuspecting Pair

bdwarf — Wed, 18 Aug 2010 03:29:39 +0000

Two for the price of one

Spitzer Science Center colleague Christopher Gelino and I report the identification of low-mass binary system that refuses to show itself. The source, 2MASS J20261584–2943124, is an L dwarf which until now had seemed to be a perfectly unassuming source. However, low-resolution, near-infrared spectroscopy we obtained with the IRTF SpeX spectrograph revealed a peculiar absorption feature that is commonly seen in very low-mass “spectral binaries”, blends of stars with different spectral types. Our analysis indicates that this source is an L dwarf plus T dwarf pair, with a relative brightness of roughly 4 magnitudes (or 40 times fainter) in the near-infrared. We were unable to resolve the putative pair with the Keck Observatory laser guide star adaptive optics system, which rules a binary wider than 9 Astronomical Units (about the distance between the Sun and Saturn). Next step: look for Doppler shifts in the spectrum that would indicate the gravitational influence of the unseen companion and allow us to measure its mass.

This research was published in the Astronomical Journal. Authors include Christopher R. Gelino (Spitzer Science Center) and Adam J. Burgasser (UCSD).

July 2010

A Blue Brown Dwarf

bdwarf — Tue, 01 Jun 2010 01:34:52 +0000

Not all brown dwarfs are brown

We report observations of an unusually blue brown dwarf, a nearby object that may be among the coldest and oldest brown dwarfs known. The source, ULAS J141623.94+134836.3, was originally discovered in the UKIDSS survey independently by R. Scholz and B. Burningham et al., and early results indicated its surface could be as cool as 500 K. It could even be the first Y dwarf. Our near-infrared spectrum, obtained with the IRTF SpeX spectrograph, instead shows it to be somewhat warmer (650 K), as well as old, massive and depleted in “metals” (any element other than hydrogen and helium). ULAS J1416+1348 is also a companion to the unusually blue L dwarf SDSS J141624.08+134826.7 discovered earlier this year by several groups. This nearby brown dwarf pair has generated a lot of interest among astronomers, with five publications in six months.

This result was published in in the Astronomical Journal; it was also an IRTF science highlight.

June 2010

FIRE on the Sky: Report from FIRE's Commissioning Run

bdwarf — Fri, 30 Apr 2010 11:15:25 +0000

Early this month, we had our first commissioning run of the Folded Port Infrared Echellette, or FIRE, a near-infrared spectrograph designed for the Magellan Telescopes. After a two-week installation period in late February/early March led by the instrument PI Rob Simcoe, FIRE team members John Bochanski and Matt Smith from MIT and Craig McMurtry from U. Rochester, and Magellan engineers (I missed all the action, teaching 250 students Physics 1), FIRE was ready to view the sky for a week-long commissioning run starting March 28th.

Early results have been spectacular. A few of the image frames from the first week are shown below. The high quantum efficiency and low readnoise of the Teledyne Hawaii 2RG detectors, and the excellent image quality of the Baade Telescope, has resulted in higher sensitivity than originally planned. In the echelle mode, Rob has estimated roughly 20-25% efficiency, including telescope and slit losses, and a nearly-flat zero point of 16-17 AB magnitudes (1 count/sec/pixel) across the 0.85-2.4 micron range. In plain language, this means we can observe very faint sources – such as a the coldest brown dwarfs and highest redshift quasars – with the echelle mode’s moderate resolution (λ/Δλ ≈ 6000). The prism-dispersed mode has also proven very sensitive, and we’ve been able to follow-up several J ≈ 19-20 cold brown dwarf candidates from WISE with relative ease. Look for first science results in the literature soon!

An A0 V "telluric standard" observed with FIRE's echelle mode. The 21 orders span a wavelength range of 0.85 to 2.4 micron from bottom to top. This image is a pairwise subtraction of two 10 s exposures, hence the postive and negative traces.

An unprocessed, 600-second exposure of the late T-type brown dwarf 2MASS 1217-0311 (J = 16) in FIRE's echelle mode. The star's light appears as occasional horizontal streaks in the various orders; the short vertical streaks are emission lines from OH in the Earth's atmosphere. The bright region at top is thermal emission (mostly from Magellan's "warm" mirrors) in the 2-2.5 micron region.

A high-redshift (z=6), J = 20 quasar observed with FIRE's echelle mode. FIRE is sufficiently sensitive to pick up continuum light from this ancient source, enabling studies of the gas along its line of sight. This is a pairwise subtraction of 2 900-second exposures.

Prism-dispersed mode of FIRE of the J = 16.7 T dwarf Ross 458C. This mode gives a lower resolution of 250, but high throughput. This image is a pairwise subtraction of two 150-second exposures, and the wavelengths go from 0.8 micon at the bottom to 2.5 micron at the top.

Acquisition image from FIRE's slit-viewing camera, which has a Mauna Kea J-band filter. The target (left of center) is in the slit, so appears to be split in half. This is a pairwise subtraction of two 5-second exposures.

Fully processed spectra of three cold brown dwarfs, obtained with FIRE's prism-dispersed mode, ranging from J=17 to 18. These data will be published in Burgasser et al. (2010, in preparation)

Star set to collide with solar system

3citynewswire — Wed, 17 Mar 2010 10:18:09 +0000

Scientific American – Have a good look at this star. For astronomers have discovered that it is on course to collide with the outskirts of our solar system with potentially catastrophic consequences.

New calculations show that the orange dwarf, called Gliese 710, will crash through the Oort Cloud that surrounds the Sun. The disruption to this shell of many billions of icy fragments would launch a shower of comets into the inner solar system, threatening the planets with devastating impacts.

Some believe it could lead to a repeat of the Late Heavy Bombardment that left the Moon covered with craters around 4 billion years ago. The good news is that the star is not expected to arrive for a million or more years.

The threat from Gliese 710, a star with about half the mass of the sun 63 light-years away in the constellation of the Serpent, is rated as 86 per cent likely. That is nearly as good as a certainty.

It comes after a European space telescope called Hipparcos measured precise positions and motions for 1000,000 stars in our cosmic neighbourhood. This allowed astronomers to work out accurately which might come close to the sun as they travel around the galaxy.

Russian astronomer Dr Vadim Bobylev, of the Pulkovo Astronomical Observatory in St Petersburg examined new data from 2007. He identified nine stars that have had or will have particularly close encounters by coming within 3 light-years of us.

But he was startled to find that Gliese 710, which can be seen in small telescopes, has our solar system clearly in its sights. He says it is racing towards us at 30,000mph and on course to crash through the Oort Cloud, which lies around a light-year away, within the next million and a half years.

It could even come within a zone of asteroid-like bodies around Pluto called the Kuiper Belt, though the chances of this are put at only one in a thousand. But some astronomers are suggesting that Gliese 710 might be circled by its own Oort Cloud, which could produce a double shower of hazardous comets.

Dr Bobylev’s scientific paper, Searching for Stars Closely Encountering with the Solar System, was submitted to professional journal Astronomy Letters last week. He says: “Our statistical simulations showed that the star has not only a high probability of penetrating into the Oort Cloud, but also a non-zero probability of penetrating into the region where the influence on Kuiper Belt objects is significant.”

The new alert comes days after a NASA astrobiology site reported that an invisible brown dwarf star nicknamed Nemesis may be circling the sun and causing mass extinctions of life on Earth every 26 million years. There are hopes that if Nemesis exists, it will be detected by NASA’s heat-sensitive Wide-Field Infrared Survey Explorer satellite, WISE, which is currently scanning the sky for brown dwarfs.

Orange dwarf called Gliese 710

Cosmic Neighborhood Watch, Keeping Us Safe From Extinction Events

Killian Bundy — Tue, 15 Dec 2009 03:33:13 +0000

NASA Launches Comet-Hunting Space Camera

NASA on Monday successfully launched a space telescope designed to create a highly detailed map of the heavens and spot comets and asteroids that could pose a threat to life on Earth.

NASA’s Wide-field Infrared Survey Explorer, or WISE, lifted off from California’s Vandenberg Air Force Base atop a Delta II rocket at 6:09 a.m. PST.

“”WISE thundered overhead, lighting up the pre-dawn skies,” said William Irace, mission project manager at NASA’s Jet Propulsion Laboratory, in Pasadena, Calif.

“All systems are looking good, and we are on our way to seeing the entire infrared sky better than ever before,” said Irace.

WISE will use an infrared camera to map the cosmos. The mission calls for the unmanned spacecraft to cover the entire sky one-and-a-half times, until its frozen coolant runs out. NASA hopes it will capture everything from near-Earth asteroids to distant galaxies teeming with stars.

“The last time we mapped the whole sky at these particular infrared wavelengths was 26 years ago,” noted UCLA’s Edward Wright, who is principal mission manager.

“Infrared technology has come a long way since then. The old all-sky infrared pictures were like impressionist paintings—now we’ll have images that look like actual photographs,” said Wright.

WISE is designed to provide information about the size, composition, and texture of near-Earth objects such as comets and asteroids.

“We can help protect our Earth by learning more about the diversity of potentially hazardous asteroids and comets,” said Amy Mainzer, deputy project scientist for the mission at JPL.

WISE will also attempt to document the cycle of life in the Universe, as it will capture faraway images of star-hatching galaxies and ravenous, planet-eating black holes.

See also:
WISE Spacecraft Seeks Near Earth Objects, New Stars Using Infrared Wavelengths
NASA launches new mapping spacecraft
Utah-made telescope blasts into space
Infrared Space Telescope Launched From California
NASA launches spacecraft that will map stars, galaxies, asteroids
NASA Craft To Photograph Entire Universe
Nasa sky survey probe blasts off
NASA’s Wide-field Infrared Survey Explorer launched
NASA’s WISE (Wide-Field Infrared Survey Explorer) telescope launched
NASA – Wide-Field Infrared Survey Explorer
Wide-field Infrared Survey Explorer
Delta II Overview
Delta II

/WISE is not only good science, but a good idea for protecting the Earth, well done NASA and JPL

Interview with Professor B!

astrofacts — Wed, 08 Jul 2009 08:24:16 +0000

Professor B!

Charae’ interviews Professor Adam Burgasser – that’s right, Professor B! – about his research and how he first got into astronomy and science. Adam is a Professor of Physics at the Massachusetts Institute of Technology and University of California, San Diego, and studies the lowest mass stars and brown dwarfs in his research. He lives part time in Maui, part time in Boston, part time in Southern California, but spends most of his time travelling (no duh!) all over the world for his research.

Listen here [18:57m]:
Download: astrofacts_090707_interview-adamburgasser.mp3

Original air date 7 July 2009.

Brown Dwarfs: "Over-Achieving Jupiters" not "Failed Stars"

Ian O'Neill — Tue, 21 Apr 2009 10:40:34 +0000

Why is the term “failed star” synonymous with brown dwarfs? On the one hand, brown dwarfs lack the mass to sustain nuclear fusion in their cores. On the other hand, who said brown dwarfs were trying to be stars? Who ever said that becoming a star was the pinnacle of stellar living? Perhaps brown dwarfs are perfectly happy the way they are. In a world of equality and political correctness, brown dwarfs could be viewed as “over-achieving Jupiters”, or gas supergiants…

Brown dwarfs are often considered to be the bridge between planets and stars, they are too massive to be considered to be a planet (as they have convective interiors with no layered differentiation of chemicals with depth), and yet they are too small to be a star (they cannot fuse hydrogen in their cores, although some brown dwarf classes may fuse lithium and deuterium). That said, brown dwarfs do occupy the lower right-hand corner of the Hertzsprung-Russell diagram, so they are still classified in stellar terms. Although “brown dwarf star” is probably a little too generous.

Brown dwarfs are also technically not “brown”, they are a kind of dirty orange (with a hexadecimal colour of #EB4B25) as astronomers don’t recognize brown as a colour.

So “brown” dwarfs aren’t really brown and they are suffering an identity crisis between being a star and a planet. In fact, before brown dwarfs became brown dwarfs, there were suggestions to call these strange planetary/stellar bodies substars or planetars (can you sense the confusion?).

Compared with our Sun, brown dwarfs are pretty small (0.01-0.08 Solar masses) but compared with a gas giant such as Jupiter, they are huge (13-80 Jupiter masses). However, brown dwarfs don’t expand much larger than the radius of Jupiter (making it hard to distinguish between a brown dwarf and a gas giant exoplanet).

Therefore, why don’t we be a little more “glass half-full” when describing brown dwarfs. Although brown dwarfs undoubtedly have star-like qualities, they have strong planet-like qualities too. So in the traditional superlative descriptions of some astronomical objects (i.e. supermassive black hole), why not emphasise the brown dwarf’s strong planetary points. Rather than “brown dwarf”, what about “gas supergiant” and rather than “failed star”, why not “over-achieving Jupiter”?

Just a thought.

Special thanks to Adam Zuckerman for the entertaining conversation we had when discussing the pros and cons of Are Brown Dwarfs More Common Than We Thought?

Are Brown Dwarfs More Common Than We Thought?

Ian O'Neill — Mon, 20 Apr 2009 09:49:11 +0000

In 2007, a very rare event was observed from Earth by several observers. An object passed in front of a star located near the centre of the Milky Way, magnifying its light. Gravitational lensing is not uncommon in itself (the phenomenon was predicted by Einstein in 1915), but if we consider what facilitated this rare “microlensing” event, things become rather interesting.

Gravitational microlensing is very useful transient event for astronomers who want to study objects that do not emit a lot of light. These objects could be distant exoplanets, red dwarf stars, neutron stars or black holes. As one of these objects drift in front of a distant star, the gravitational field of the object will deflect the path of the star light, focusing it and momentarily increasing the star’s brightness. From this increased brightness caused by the focusing effect of the massive body (the lens), some measure of the object’s mass, velocity and distance can be derived. However, such events are rare, especially when the microlensing event is caused by a brown dwarf, otherwise known as a ‘failed star’.

Andrew Gould of Ohio State University in Columbus and colleagues have published a paper detailing the observation of a 2007 transient star brightening event (OGLE-2007-BLG-224) caused by a small brown dwarf lens.

“By several measures OGLE-2007-BLG-224 was the most extreme microlensing event (EME) ever observed,” says Gould in the publication released earlier this month, “having a substantially higher magnification, shorter-duration peak, and faster angular speed across the sky than any previous well-observed event.”

Gould et al. derived the brown dwarf’s mass, velocity and distance from Earth. The brown dwarf is approximately 0.056 solar masses, ~525 parsecs away (1700 light years) and it was measured to be travelling at a transverse velocity of over 110 km/s. All this information is available by analysing the increased brightness of focused starlight from a distant star.

Although this was an amazing observation in itself, it does pose an interesting problem for our understanding of the evolution of our galaxy. From our understanding of stellar development, there should be comparatively few brown dwarfs out there. The probability of detecting a distant failed star (a brown dwarf lacks sufficient mass to initiate hydrogen fusion in its core, hence the almost derogatory ‘failed star’ label) through the gravitational microlensing event is vanishingly small. In fact, astronomers are surprised the observation even happened. “In this light, we note that two other sets of investigators have concluded that they must have been ‘lucky’ unless old-population brown-dwarfs are more common than generally assumed,” the paper concludes.

Serendipitous astronomical observations are not unheard of, but there is a very strong possibility that we saw OGLE-2007-BLG-224 bacause old brown dwarfs are actually a lot more common than we previously believed. Perhaps some tweaking of stellar models is in order…

Source: “The Extreme Microlensing Event OGLE-2007-BLG-224: Terrestrial Parallax Observation of a Thick-Disk Brown Dwarf,” Gould et al., 2009. arXiv:0904.0249v1 [astro-ph.GA]
Via: New Scientist

Robot Astronomy Talk Show

bdwarf — Thu, 12 Mar 2009 17:39:33 +0000

The folks at IRrelevant Astronomy have put together a new episode of their Robot Astronomy Talk Show that features yours truly (in fact, both good and evil versions of yours truly) It is based on our recent find of a very dim pair of brown dwarfs. If you haven’t checked out the various CG-driven videos put together by Michelle Thaller, Doris Doau, Linda Hermans-Killam, Robert Hurt and Jim Keller for the Cool Cosmos website then please do so. The site is chock full of great educational resources focused in infrared astronomy, including tutorials, games, images & videos, and classroom preparation resources. And the material is all very informative, engaging, creative and frankly laugh-out-loud funny. A model for 21st century science outreach and education.

This episode and others can also be seen on YouTube and Funny or Die.

"Dim Brown Dwarfs" Press Release

bdwarf — Wed, 10 Dec 2008 19:06:00 +0000

NASA has just posted a press release on one of my recent results involving the very cold brown dwarf 2MASS J0939-2448. Based on observations from the Spitzer Space Telescope and ground-based astrometry, we find this source to be one of the coldest brown dwarfs known (600+/-35 K) and, because of its overluminosity, an (as-yet) unresolved double. The paper appears in today’s edition of Astrophysical Journal Letters.

Links:

NASA Press release: http://www.jpl.nasa.gov/news/news.cfm?release=2008-232

Original paper in Astrophysical Journal Letters: http://www.journals.uchicago.edu/doi/abs/10.1086/595747

PDF version of result: http://web.mit.edu/~ajb/www/papers/2008ApJ_689_L53.pdf

Andy Lloyd - Electron bombardment points to Dark Star?

andylloyd — Sun, 23 Nov 2008 20:51:49 +0000
A NASA array of balloons high up in the Antarctica’s stratosphere has picked an anomalous bomb

Stellar Racism: Black Holes and Brown Dwarfs

Laz — Thu, 10 Jul 2008 16:43:39 +0000

Recently, a Dallas county commissioner Kenneth Mayfield (melanin expression: low) used the term “black hole” to describe a bureaucracy in the county, to which another commissioner, John Wiley Price (melanin expression: higher), objected and corrected his esteemed colleague by saying that the bureaucracy was a “white hole”.

The presiding judge, Thomas Jones (melanin expression: higher) demanded an apology from Mayfield for his “racially insensitive analogy”. You can read the story here, Dallas County officials spar over ‘black hole’ comment

Now, most people know what a black hole is. One may form when a large star explodes and provided there’s enough mass, voila ! (correct me as deemed necessary).

It’s an astronomical term with no racial undertones, it appears that Mr. Wiley and Mr. Jones are not guilty of PC policing but of ignorance. I’m not sure which is worse, I’ll leave that to the peanut gallery.

For my part, I’m Mexican and vertically-challenged so can I roll with Wiley and Jones’ outrage when I hear the astronomical term, brown dwarf?

Now that I think about it, brown dwarf is pretty offensive. I’m suing astronomy, the corpses of Galileo, Kepler, Brahe, Copernicus, and Gene Roddenberry. Why stop there? We’ll go after NASA, JPL, the European Space Agency, Jill Tarter (the hegemonic and oppressive xenophobe who coined the phrase) and George Lucas (maybe I can recover the money I’ve spent on his Star Wars brand through the years).

Where’s Jackie Chiles when you need him?

Cool star leaves girlfriend cold

andyxl — Wed, 30 May 2007 19:58:13 +0000
A great result has come out of UKIDSS, the IR survey of which I am overall PI, led by Steve Warren a