Posted on by Jon Voisey

Arp’s Phantom Jet

Arp 192 from his publication (left) compared to SDSS image (right). Prominent jet in upper right is present in Arp's image is missing from modern images.
Arp 192 from his publication (left) compared to SDSS image (right). Prominent jet in upper right is present in Arp's image is missing from modern images.

[/caption]

During the “Great Debate” of 1920 astronomers Herber Curtis and Harlow Shapley had a famous debate on the nature of “spiral nebulae”. Curtis argued they were “island universes” or what we would today call a galaxy. Shapley was of the opinion that they were spiral structures within our own galaxy. One of the evidences Shapley put forth was that another astronomer, Adriaan vanMaanen, had reported detecting rotation of these objects over a period of years leading to an overall rotation rate of ~105 years. If these spiral nebulae were truly as far (and thus, as large) as Curtis suggested this would mean they would be rotating well beyond the speed of light at their outer edges.

It was later determined vanMaanen’s rotation was a case of wishful thinking when Hubble eventually determined the true distance to the Andromeda galaxy. From then on, it was well established that galaxies are so large, their motions will not be observed in human lifetimes. Aside from local flare ups of supernovae and other such events, galaxies should be relatively static. Yet in just over 40 years, a distinct, large-scale feature in the galaxy NGC 3303 seems to have disappeared entirely.

In 1964, Halton Arp observed NGC 3303. This oddly shaped spiral galaxy he reported as having a jet protruding from the northwest side. It made it into his famous 1966 compilation of photographs entitled, “The Atlas of Peculiar Galaxies” as Arp object 192. A 2006 publication by Jeff Kanipe and Dennis Webb (The Arp Atlas of Peculiar Galaxies: A Chronicle and Observer’s Guide) listed this jet as a “challenge” for astronomers to capture.

In 2009, an advanced amateur named Rick Johnson attempted a long exposure of NGC 3303. When his image was finished, it was notably lacking the jet. The news of this eventually reached Kanipe and Webb and they suspected that the exposure was simply not long enough to have captured this object. To be sure, they consulted images of the galaxy from the Sloan Digital Sky Survey. The jet was missing from these images as well. A major feature on a galaxy had vanished in 45 years and no one had noticed until 2009.

The only plausible explanation was that the jet Arp detected didn’t really exist. It was possible it was a photographic defect in the glass plate on which the image was taken. Another possibility was that the imaged structure did exist, it just wasn’t what Arp suspected.

When Charles Messier attempted to look for comets, he kept a list of 109 objects that were not comets so he wouldn’t be confused by them. To tell true comets apart from the other fuzzy objects he observed, he observed them over a period of nights. If they moved with respect to background stars, they must be relatively nearby. If not, they were likely very distant. Was Arp’s jet the opposite; A nearby object that had simply moved out of the field of view since his original image?

Kanipe contacted the Minor Planet Center to determine if any of the known asteroids or minor planets had been in the vicinity when the image was taken. It turned out that a minor planet, TU240, discovered on 6 October 2002 by the Near Earth Asteroid Telescope on Haleakala, Maui, Hawaii, was very near to NGC 3303 when Arp imaged it confirming it was a strong candidate for Arp’s disappearing jet.

This isn’t the first time an object has been pre-discovered and its true nature simply missed when it was imaged. There is evidence that the planet Neptune was observed at least three different times (including by Galileo) before its nature was understood. But for this TU240,  this is expected to be the earliest prediscovery photograph. As a result, TU240 was given a new designation just after Thanksgiving 2009. It is now listed as 84447 Jeffkanipe.

(Read this story as told by Rick Johnson at the BAUT Forums.)

Posted on by Jon Voisey

New Studies on the Vela Star Forming Region

A false-color infrared image of the star forming complex in Vela. Two new studies have measured for the first time the dust emission at very long infrared wavelengths, and found a set of young stars that are accreting material and flaring. Credit: NASA and the Spitzer Space Telescope
A false-color infrared image of the star forming complex in Vela. Two new studies have measured for the first time the dust emission at very long infrared wavelengths, and found a set of young stars that are accreting material and flaring. Credit: NASA and the Spitzer Space Telescope

[/caption]

This week at the AAS meeting scientists revealed two new studies on a star forming region in Vela. The first used the Balloon-borned Large Aperture Submillimeter Telescope (BLAST, a proptotype detector for the one on the new Herschel Space Telescope) to classify the young stars and begin mapping the warm dust in the region. The second searched the nebula for flaring young stars. Both studies are to appear in an upcoming publication of the Astrophysical Journal.

Although star formation has been well modeled and understood theoretically, observational astronomy is often made more difficult due to the fact that it occurs shrouded in dusty nebulae. Visible light absorbed by the nebula and reemitted as lower energy infrared light. Most of the wavelengths in this region cannot permeate Earth’s atmosphere.

In order to study regions like this, astronomers are forced to use balloon based and space observatories. Astronomers Massimo Marengo, Giovanni Fazio, and Howard Smith, together with an international team of scientists used BLAST to study just such a star forming region in Vela. The first of their studies searched the nebula for newly formed stars. To do this, they searched for behaviors shown to be indicative of star formation, “such as proto-stellar jets and molecular outflows.” Additionally, to truly classify as a proto-star, the object was required to show up at more than one wavelength. In searching for these candidates, they confirmed 13 cores originally reported by a previous team, but discounted one because it did not have the proper spectral characteristics (although they may still later collapse to form stars).

By analyzing the mass of the forming regions, the team was also able to show that the Core Mass Function (CMF, a function that describes the frequencies of proto-star cores of various masses) is very similar to the Initial Mass Function (IMF, which is the same thing but for already formed stars). Although this is unsurprising, it is a necessary observation to confirm our understanding of how stars form and to show that stars do indeed come from such nebulae.

Another unsurprising confirmation of stellar formation models is that forming cores in the nebula are notably warmer when they’ve reached the density sufficient to create fusion in the core and have an embedded protostar. These results, “can thus provide guidelines
for understanding the physical conditions where the transition between pre- and proto-stellar cores takes place.”

The second of their studies analyzed known young stars to search for large flares thought to be caused by material being accreted onto the young star. The region was imaged once and then a second time six months later. Over this period, 47 of some 170,000 observed stars had increases in brightness consistent with what was expected for flaring. Closer inspection of these stars 19 had the further characteristics (mass, age, environment) expected of such flares. Eight showed evidence of being extremely young (on the order of a hundred thousand years or less) and were still enshrouded in gravitationally bound disks of dust.

Although this cannot confirm the prediction of such youthful flares being due to infalling material (as opposed to magnetic fields or interactions with a companion) it does show that BLAST and its successor, Herschel, will be a powerful tool for further study.

Posted on by Nancy Atkinson

Get Ready for “Largest Meeting in Astronomy History”

Here comes the 215th meeting of the American Astronomical Society, held during January 3-7, 2010 in Washington, DC. With over 2,500 registrants, the AAS has billed this as “the largest meeting in astronomy history.” The AAS 215 will undoubtedly produce some amazing new astronomical announcements, press releases and briefings, and we at Universe Today will work hard to bring you all the news. So get ready for a ridiculous amount of coverage. And if you’re into exoplanets, word has it there will be lots of exoplanet news this week. Stay tuned!

Plus, you can watch public events and press conferences from Astronomy Cast Live’s UStream channels at these web addresses:
Public Events
Press Conferences
Random Roving Reporting

Posted on by Jon Voisey

Do Eruptions of P Cygni Point to a Companion?

The other day, I wrote an article on Luminous Blue Variables (LBVs) which made reference to P Cygni as a well established LBV to which a group made comparisons. While P Cygni is a good example of an LBV, it has many interesting characteristics in its own right. Prior to August 8, 1600, the star was not known to exist, when suddenly, it appeared, flaring to 3rd magnitude. Over the next hundred years it continued to undergo outbursts, fading and brightening.

New research by Amit Kashi of the Israel Institute of Technology suggests this series of flares may be due to the presence of a second star in orbit around P Cygni.Many other Luminous Blue Variables, such as Eta Carinae, are suspected to be binary systems. However, the overwhelming brightness of LBV stars makes it difficult to directly detect stars that would otherwise be considered bright. Kashi takes this further and suggests “all major LBV eruptions are triggered by stellar companions”. In this scenario, as a smaller companion in the system came on its closest approach (periastron) the outer layers of the LBV, which are already unstable and loosely bound due to the size of the star, are pulled off due to tidal forces. The gravitational energy as it merges with the companion is turned into thermal energy and this increases the overall brightness until it is fully absorbed. The cause of such a mass transfer would decrease the orbital size of the companion and result in the next outburst being sooner than if the orbit were constant. Kashi suggests “[t]his process repeats until the instability in the LBV stops. From that point on the orbital period remains approximately stable, changing only very slightly due to mass loss from the LBV, and tidal interaction.”

To test his hypothesis, Kashi modeled a system with a LBV star of similar mass to that estimated for P Cygni and put a 3 solar mass star in a highly eccentric orbit around it. With these simple starting parameters, Kashi showed that it was possible to produce a situation in which the onset of eruptions was similar to the periastron approach. However, there were some uncertainties due to a lack of records during the time period which puts the true beginning of the eruptions in question. Furthermore, Kashi retested his model for a 6 solar mass companion and showed the similarity between periastrons and eruptions was still a good fit making the model robust.

Image from Kashi (2009) showing model orbit superimposed on historical light curve data
Image from Kashi (2009) showing model orbit superimposed on historical light curve data

However, this still leaves many variables for the models unconstrained and able to be fiddled with to make the model fit (Insert joke about being able to fit a curve to a cow with enough degrees of freedom here). Unfortunately, Kashi notes that further testing may be difficult. As earlier mentioned, direct detection of a companion would be hampered by the brightness of the LBV. Even detecting a companion spectroscopically would be difficult if not impossible. The reason is that the wind from P Cygni causes the absorption lines in its spectra to be broadened. For Kashi’s model system, the doppler shift from the companion is not large enough to shift the lines more than they are already broadened which would make detecting the change in radial velocity a challenge. He notes, “the probability of detecting radial velocity due to orbital motion in spectral lines is small for most of the orbit, but might be possible every 7 years, if the inclination angle is large enough. I therefore predict that a continuous 7 year long observation of pronounced lines may reveal a small doppler shift variation, close to the periastron passage.”

Posted on by Jon Voisey

MN112 – A New Luminous Blue Variable Found From Its Nebula?

Eta Carinae. One of the most massive stars known. Image credit: Hubble
Eta Carinae. One of the most massive stars known. Image credit: Hubble

[/caption]

Luminous Blue Variables (LBVs) are a rare class of extremely massive stars that teeter on the very edge of being stable. The most famous of this class of stars is the well studied Eta Carinae. Like many other LBVs, Eta Carinae is shrouded in a nebula of its own making. The instability of the star causes it to throw off large amounts of mass even during its brief main sequence lifetime. What makes these stars so unstable is an open question which has been difficult to answer do the the paucity of known LBVs. Given that the initial mass function predicts that such massive stars should be rare, this is not surprising, but identifying these stars is often made even more difficult due to the reddening caused by their nebulae.

However, an international team working from Russia and South Africa proposes that the nebula itself may be able to help identify potential candidates of LBVs. To test out their hypothesis, they scanned the Spitzer image archives for nebulae with features similar to those of known LBVs. The feature that distinguished potential LBV nebulae from other nebulae was emission only in the 24 ?m images (likely due to the fact that nebulae do not operate as model blackbodies at such wavelengths, but instead emit most strongly at specific wavelengths due to fluorescence).

In their review of potential nebulae, they identified a one known as MN112. To further explore the possibility, the team took high resolution spectra of the central star. They determined the central star had strong similarities to the known LBV P Cygni. Most notably, the candidate LBV showed very strong emission lines for hydrogen and He I right next to absorption lines for the same elements. This is caused by high pressure regions, either in the atmosphere of the star, or as the faster wind from the star interacts with a slower moving nebula around it. The high pressure region becomes more dense and gives emission lines. Since it moves outwards, it is slightly blueshifted and thus, does not appear directly on top of the absorption line caused by the relatively less dense atmosphere. This time of feature is known as a P Cygni profile.

Another identifying feature of Luminous Blue Variables is that they are variable (Surprise!) up to as much as 1-2 magnitudes. The team had records of the star from photographic plates dating back as far as 1965 as well as more recent CCD measurements and found that the star had not been seen to vary significantly from an apparent blue magnitude (mB) of 17. However, in the infrared region, they determined (using their own photometric observations) that the star had brightened by 0.4 magnitudes over the past 19 years. Although this falls short of the expected variability for a LBV, they suggest “it is quite possible that a significant fraction of LBVs (if not all of them) goes through the long quiescent periods (lasting centuries or more; e.g. Lamers 1986) so that the fast variability (on time
scales from years to decades) observed in the vast majority of classical LBVs could be merely due to the selection effect.”

The authors state their intention to continue observation of this candidate LBV “in the hope that the ”duck” will ”quack” in the foreseeable future.”

Posted on by Jon Voisey

Galactic Building Blocks

The current view of galactic formation is that galaxies form from a “bottom-up” method. In this picture, small dwarf galaxies, full of metal poor stars, were attracted by dark matter halos in the early universe which merged into larger galaxies. Many of those metal poor stars can still be seen today in the halo of the galaxy, but it was thought that the building blocks from which the galaxies were constructed were long gone or had evolved on their own and would no longer resemble the primordial building blocks.

However, earlier this year, an extremely metal poor star with only 0.00025% of the iron in the Sun was discovered in the Sculptor dwarf galaxy. If confirmed, this would show a strong link to further support the notion that metal poor dwarf galaxies were related to the metal poor stars that still populate our halo. Confirming this was the subject of a recent paper.

For their study, the authors analyzed the newly discovered star (S1020549) with a high resolution spectrograph. From this, they confirmed that the star had very little iron present (an element generally used as an indicator of overall heavy element abundance since its absorption lines feature prominently in the spectra and are easily detectable). The extremely low ratio of iron to hydrogen makes it currently the most metal poor star known in a dwarf galaxy (the overall record holder for metal deficiency is HE 1327–2327).

The study determined an overall [Fe/H] abundance of -3.8 (see how this abundance is defined here) which is very similar to the [Fe/H] abundance of archetypical halo stars of about -4.0. Furthermore, many of the other elemental abundances that were uncovered with the detailed spectroscopy (especially those of Mg, Ca, Sc, Ti, and Cr) also fit the general abundance level of stars found in our halo.

This isn’t a conclusive tie between the two and more such stars will need to be uncovered to reinforce the similarities, but since S1020549 was discovered with “a relatively modest survey” this may suggest “that future observational searches should discover more such objects in Sculptor and other dwarf galaxies.”

Posted on by Jon Voisey

New Observations of TrES-2b May Reveal New Exoplanet

An artist's impression of a transiting exoplanet. Credit: ESA C Carreau

[/caption]

For those know their solar system history, the discovery of Neptune is an especially exciting story. Before it was detected observationally, its gravitational effects on another planet (Uranus) were discovered. From this, astronomers were able to predict the position of the yet unobserved planet and in 1846 they discovered the predicted planet observationally from Berlin Observatory. (For a more complete retelling of the story, see my summary/review of the book The Neptune File). This discovery prompted searches for other planets from orbital discrepancies attributed to gravitational perturbations on Mercury. However, none were ever found and it was eventually that Mercury’s orbital irregularities were due to relativistic effects.

However, this technique of inferring planets from orbital oddities of a planet may have been used for the first time outside our solar system.

The exoplanet known as TrES-2b is one of the exceptional cases of known exoplanets for which the plane of the orbit lies almost directly in our line of sight. This circumstance means that the planet will appear to cross the disk of the star as it orbits. Although we cannot resolve that disk, it shows up as a characteristic dip in the brightness which can reveal additional information about the system such as “very accurate determinations of the radii of star and planet (relative to the semi-major axis) and the inclination of the orbital plane of the planet”. This additional information allows for excellent determinations of the orbital parameters in order to predict future transits.

A team of German astronomers observed the TrES-2 system in 2006 and 2008 in order to build their understanding of the orbit of the planet. However, when they continued in observation in 2009 they found significant changes in the inclination of the orbit and the period of the orbit. Although planetary migration could change these parameters, it is not expected that such an event could occur on such a short time scale. Additionally, a oddly shaped host star would explain the change, but the degree to which the star would have to be squished at the equator would be impossibly high given the slow rotation rate known for TrES-2.

Instead, the authors suggest “the existence of a third body in the form of an additional planet would provide a very natural explanation”. Although this explanation is anything but conclusive, it does pose an easily testable scenario. If the plane of the orbit of the system is very nearly along the line of sight, this provides the most ideal situation for attempting to detect planets using the radial-velocity of the parent star. The authors even go so far as to suggest a range of periods for a potential planet to have the observed effects. They state, “a planet of one Jovian mass with periods between 50 – 100 days would suffice to cause the observed inclination changes”.

Furthermore, the authors note that several similar systems are known to exist with a close in planet and a second massive planet in a longer orbit. “[I]n the system HIP 14810 there is a close-in planet with a 6.6 day period and a somewhat lighter planet with a period of 147 days, in the HD 160691 system the close-in planet has a period of 9.6 days and two outer planets with Jupiter masses are known with periods of 310 and 643 days.”

Posted on by Jon Voisey

Can the Recurrent Novae RS Oph Become Type Ia Supernovae?

A new kind of supernova. Credit: Tony Piro

[/caption]

The classical scenario for creating Type Ia supernovae is a white dwarf star accreting mass from a nearby star entering the red giant phase. The growing red giant fills its Roche lobe and matter falls onto the white dwarf, pushing it over the Chandrasekhar limit causing a supernova. However, this assumes that the white dwarf is already right at the tipping point. In many cases, the white dwarf is well below the Chandrasekhar limit and matter piles up on the surface. It then ignites as a smaller nova blowing off most (if not all) of the material it worked so hard to collect.

A new paper by a group of European astronomers considers how this cycle will affect the overall accumulation of mass on the white dwarfs which undergo recurrent novae. In a previous, more simplistic 1D study (Yaron et al. 2005) simulations revealed that a net mass gain is possible if the white dwarf accumulates an average of 10-8 times the mass of the Sun each year. However, at this rate, the study suggested that most of the mass would be lost again in the resulting novae, and even a minuscule gain of 0.05 solar masses would take on the order of millions of years. If this was the case, then building up the required mass to explode as a Type Ia supernova would be out of reach for many white dwarfs since, if it took too much longer, the companion’s red giant phase would end and the dwarf would be out of material to gobble.

For their new study, the European team simulated the case of RS Ophiuchi (RS Oph) in a 3D situation. The simulation did not only take into consideration the mass loss from the giant onto the dwarf, but also included the evolution of the orbits (which would also influence the accretion rates) and varied rates for the velocity of the matter being lost from the giant. Unsurprisingly, the team found that for slower mass loss rates from the giant, the dwarf was able to accumulate more. “The accretion rates change from
around 10%  [of the mass of the red giant] in the slow case to roughly 2% in the fast case.”

What was not immediately obvious is that the loss of angular momentum as the giant shed its layers resulted in a decrease in the separation of the stars. In turn, this meant the giant and dwarf grew closer together and the accretion rate increased further. Overall they determined the current accretion rate for RS Oph was already higher than the 10-8 solar masses per year necessary for a net gain and due to the decreasing orbital distance, it would only improve. Since RS Oph’s mass is precipitously close to the 1.4 solar mass Chandrasekhar limit, they suggest, “RS Oph is a good candidate for a progenitor of an SN Ia.”

Posted on by Nancy Atkinson

The Invasion of “Teapots From Space!”

With a combination of alien invasion and British invasion, a new video series provides an amusing way to learn about different aspects of astronomy and space. “Teapots from Space” was created by UK astronomers Edward Gomez, Jon Yardley and Olivia Gomez, and these vodcasts convey lots of science in a short and entertaining package.

“The aim of the series to make astronomy a bit more light hearted but still give a good representation of the science,” said Edward Gomez, from Cardiff University. “I took a lot of inspiration from Douglas Adams when I wrote the episodes, and so the Teapots are like a cross between a sci-fi B-movie and Douglas Adams’ ‘Hitchhikers Guide to the Galaxy.'”

The Teapots come to learn about Earth and the humans that inhabit it. They abduct human scientists who explain all the questions the Teapots have about astronomy, technology and space. But before sending them back to Earth, the scientists’ minds are wiped so they don’t remember the abduction. Sometimes, disembodied robot astronomers provide the answers. Don’t worry, though: no astronomers were harmed in the making of these “potcasts.”

“There are lots of vodcasts available in the world of science but I wanted to make some which were fun and accessible but did not turn down the volume on the science,” Gomez said. “The idea of the Teapots from Space came into being as a vehicle for telling different scientific stories. Nothing is taken too seriously, but the science is all correct.”

Currently there are four episodes available, and another should be released soon. The first episode is about space junk while #2 is about the Herschel and Planck spacecraft; episode 3 is about how to spot (and abduct) astronomers, and the newest episode is about supernovae.

So, settle in on a comfy chair for some afternoon tea and tasty biscuits to watch Teapots From Space.

Posted on by Jon Voisey

New Results from the CDMS II Experiment

It’s no secret that astronomers claim that most of our universe is made of dark matter that cannot be readily detected. From Fritz Zwicky’s observations of the Coma clusters in the 1920’s which suggested that additional mass would be necessary to hold the cluster together, to the flat rotation curves of galaxies, to lensing in such places as the Bullet Cluster, all signs point to matter that neither emits nor absorbs any form of light we can detect. One possible solution was that this missing matter was ordinary, but cold matter floating around the universe. This form was called Massive astrophysical compact halo objects, or MACHOs, but studies to look for these came up relatively empty. The other option was that this dark matter was not so garden variety. It posed the idea of hypothetical particles which were very massive, but would only rarely interact. These particles were nicknamed WIMPs (for weakly interacting massive particles). But if these particles were so weakly interacting, detecting them would be a challenge.

An ambitious project, known as the Cryogenic Dark Matter Search, has been attempting to detect one of these particles since 2003. Today, they made a major announcement.

The experiment is located a half-mile underground in the Soudan mine in northern Minnesota. The detector is kept here to shield it from cosmic rays. The detectors are made from germanium and silicon which, if struck by a potential WIMP, will become ionized and resonate. The combination of these two features allow for the team to gain some insight as to what sort of particle it was that triggered the event. To further weed out false detections, the detectors are all cooled to just above absolute zero which prevents most of the “noise” caused by the random jittering of atoms thanks to their temperature.

Although the detector had not previously found signs for any dark matter they have provided understanding of the background levels to the degree that the team felt confident that they would be able to begin distinguishing true events. Despite this, false positives from neutron collisions have required the team to “throw out roughly 2/3 of the data that might contain WIMPs, because these data would contain too many background events.”

The most recent review of the data covered the 2007-2008 set. After carefully cleaning the data of as many false events and as much background noise as possible the team discovered that two detection events remained. The significance of these two detections was the result of today’s conference.

Although the presence of these two detections from 8/5 and 10/27 2007, could not be ruled out as genuine dark matter detections, the presence of only two detections was not statistically significant enough to be able to truly stand out from the background noise. As the summary of results from the team described it, “Typically there must be less than one chance in a thousand of the signal being due to background. In this case, a signal of about 5 events would have met those criteria.” As such, there is only a 1:4 probability that this was a true case of a detection of WIMPs.

Astronomer turned writer, Phil Plait put it slightly more succinctly in a tweet; “The CDMS dark matter talk indicates two signals, but they are not statistically strong enough to say “here be dark matter”. Damn.”

For more information:

Collaboration’s Website

Liveblogging of Conference by Cosmic Variance