Aug 11

WISE mission discovers coolest class of stars

Source: NASA News

Artist's conception of a "Y dwarf".
Image credits: NASA/JPL-Caltech

Scientists using data from NASA's Wide-field Infrared Survey Explorer (WISE) have discovered the coldest class of star-like bodies, with temperatures as cool as the human body.

Astronomers hunted these dark orbs, termed Y dwarfs, for more than a decade without success. When viewed with a visible-light telescope, they are nearly impossible to see. WISE's infrared vision allowed the telescope to finally spot the faint glow of six Y dwarfs relatively close to our sun, within a distance of about 40 light-years. (read more)

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Jun 11

Star formation at very low density: Is there a limit?

Source: Universe Today/John Voisey

The general picture of star formation envisions stars emerging in clusters, having condensed from cores of gas under self gravity after having passed a critical density threshold. Perhaps the cloud was pushed over the threshold by the shockwave of a supernova or the tidal twisting of a nearby object. How it happens isn’t important since the methods are likely to be many and diverse. What is important is understanding what that threshold is so we may know when it is reached. It is generally referred to as the Jeans mass and observations have generally been well in line with densities predicted by this formulation. However, over the past several years, astronomers have discovered some objects amongst a a new class that form in regions and densities not readily explained by the Jeans mass criterion.

A new class of objects has been established that are now being called Very Low Luminosity Objects or VeLLOs. Among these, L1148-IRS has been an oddity. While still low in overall light output, this object was relatively bright in the infrared when compared to other VeLLOs. Studies of the object and its surrounding gas suggested that the object was forming in an unusually empty region, one in which the usual scenario doesn’t seem to fit. A new paper by the original discoverers of this object, suggest that there may be some peculiarities that may be related to this puzzle. (read more)

Original paper:

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Jun 11

Astronomers observe carbon-atmosphere white dwarf stars with the Hubble Space Telescope

Source: CRAQ

A team of researchers composed of astrophysicists from Québec, and led by Patrick Dufour, postdoctoral research at the Université de Montréal (UdeM) and member of the CRAQ, analyzed data recently obtained from the Hubble Space Telescope with its new instrument, the Cosmic Origin Spectrograph (COS). The work of the researchers (from the UdeM, the University of Colorado, and the Space Telescope Institute in Baltimore), confirmed the luminosity variations of three stars already observed with ground telescopes. They also discovered a new member of the pulsating white dwarf subgroup, for the first time with observations from space. (read more)

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May 11

NASA'S Spitzer Sees Crystal "Rain" In Outer Clouds Of Infant Star

Source: NASA-Spitzer

Image credit: NASA/JPL-Caltech/University of Toledo


Tiny crystals of a green mineral called olivine are falling down like rain on a burgeoning star, according to observations from NASA's Spitzer Space Telescope.

This is the first time such crystals have been observed in the dusty clouds of gas that collapse around forming stars. Astronomers are still debating how the crystals got there, but the most likely culprits are jets of gas blasting away from the embryonic star.(read more)

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May 11

Hubble finds rare 'Blue Straggler' starsin Milky Way's hub

Source: NASA News

Blue straggler stars in the Milky Way bulge.
Credit: NASA, ESA, W. Clarkson (Indiana University and UCLA), and K. Sahu (STScl)

NASA's Hubble Space Telescope has found a rare class of oddball stars called blue stragglers in the hub of our Milky Way, the first detected within our galaxy's bulge.

Blue stragglers are so named because they seemingly lag behind in the aging process, appearing younger than the population from which  they formed. While they have been detected in many distant star clusters, and among nearby stars, they never have been seen inside the core  of our galaxy.

It is not clear how blue stragglers form. A common theory is that they emerge from binary pairs. As the more massive star evolves and expands, the smaller star gains material from its companion. This stirs up hydrogen fuel and causes the growing star to undergo nuclear fusion at a faster rate. It burns hotter and bluer, like a massive young star.

The findings support the idea that the Milky Way's central bulge stopped making stars billions of years ago. It now is home to aging sun-like stars and cooler red dwarfs. Giant blue stars that once lived there have long since exploded as supernovae. The results have been accepted for publication in an upcoming issue of The Astrophysical Journal. Lead author Will Clarkson of Indiana University in Bloomington, will discuss them today at the American Astronomical Society meeting in Boston. (read more)

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May 11

VLT finds a brilliant but solitary Superstar

Source: ESO Science Release eso1117

Star-forming region around the Tarantula Nebula in the Large Magellanic Cloud.
Image credit: ESO/M.-R. Cioni/VISTA Magellanic Cloud survey.
ESO's Acknowledgment: Cambridge Astronomical Survey Unit

An extraordinarily bright isolated star has been found in a nearby galaxy — the star is three million times brighter than the Sun. All previous similar “superstars” were found in star clusters, but this brilliant beacon shines in solitary splendour. The origin of this star is mysterious: did it form in isolation or was it ejected from a cluster? Either option challenges astronomers’ understanding of star formation.(read more)

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Apr 11

NASA Kepler Reaching into the Stars

Source: Kepler Mission

Artist's rendering comparing the size and color of the stars in the triple-eclipsing system HD 181068.
Image credit: NASA/KASC

We are entering a golden era for "stellar physics" – a term coined to describe research about the formation, evolution, interior and the atmospheres of stars. Thanks to a partnership forged among stellar astrophysics, scientists and NASA’s Kepler Mission, a goldmine of data is now available to support the world's efforts to detect planets in the habitable zone around other stars.(read more)

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Mar 11

A Very Cool Pair of Brown Dwarfs

Source: ESO Science Release 1110

Artist’s impression shows the pair of brown dwarfs named CFBDSIR 1458+10.
Image credits: ESO/L.Calçada.

Observations with the European Southern Observatory’s Very Large Telescope, along with two other telescopes, have shown that there is a new candidate for the coldest known star: a brown dwarf in a double system with about the same temperature as a freshly made cup of tea — hot in human terms, but extraordinarily cold for the surface of a star. This object is cool enough to begin crossing the blurred line dividing small cold stars from big hot planets.(read more)

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Nov 10

A new model from Very Low Mass Stars to Brown Dwarfs

Source: arXiv

Since the discovery of brown dwarfs in 1994, and the discovery of dust cloud formation in the latest Very Low Mass Stars (VLMs) and Brown Dwarfs (BDs) in 1996, the most important challenge in modeling their atmospheres as become the understanding of cloud formation and advective mixing.

Many cloud models have been constructed to address this problem in brown dwarfs over the past decade, but none treated the mixing properties of the atmosphere, and the resulting diffusion mechanism realistically enough to reproduce the properties of the spectral transition from M through L and T spectral types without changing cloud parameters. One of the most important challenge in modeling the atmospheres and spectral properties of VLMs and brown dwarfs is the formation of dust clouds and its associated greenhouse effects making the infrared colors of late M and early L dwarfs extremely red compared to colors of low mass stars. The cloud composition, according to equilibrium chemistry, is going from zirconium oxide (ZrO2 ), to refractory ceramics (perovskite and corundum; CaTiO3 , Al2O3 ), to silicates (forsterite; Mg2SiO4 ), to salts (CsCl, RbCl, NaCl), and finally to ices (H2O, NH3 , NH4 SH).

An international team leaded by France Allard, co-authored by Homeier and Freytag has now proposed a 2D a new model atmosphere grid, named BT-Settl, computed using an updated version of the atmosphere code Phoenix and compared it to the AMES-Cond/Dusty models, on several parameters and found that the model is quite god on covering the whole range of VLMs and brown dwarfs and beyond: 1000,000 K < T eff < 400 K; -0.5 < logg <5.5; and +0.5 < [M/H] < -4.0, including various values of the alpha element enhancement. (read full article)

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Nov 10

Pulsating Star Mystery Solved

Source: ESO Science Release eso1046

Artist’s impression of the remarkable double star OGLE-LMC-CEP0227.
Image credit: ESO/L. Calçada

By discovering the first double star where a pulsating Cepheid variable and another star pass in front of one another, an international team of astronomers has solved a decades-old mystery. The rare alignment of the orbits of the two stars in the double star system has allowed a measurement of the Cepheid mass with unprecedented accuracy. Up to now astronomers had two incompatible theoretical predictions of Cepheid masses. The new result shows that the prediction from stellar pulsation theory is spot on, while the prediction from stellar evolution theory is at odds with the new observations. (read more)

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Oct 10

NASA's Kepler Spacecraft Takes Pulse of Distant Stars

Credit: NASA

Credit: KASC Scientific Webpage

An international cadre of scientists that used data from NASA's Kepler spacecraft announced Tuesday the detection of stellar oscillations, or "starquakes,” that yield new insights about the size, age and evolution of stars.(read more)

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May 10

Unique Eclipsing Binary Star System Discovered

Source: Space Daily

Artist conception of the unique binary star NLTT 11748.
Credit: Steve Howell/Pete Marenfeld/NOAO

Santa Barbara CA (SPX) May 19, 2010 Astrophysicists at UC Santa Barbara are the first scientists to identify two white dwarf stars in an eclipsing binary system, allowing for the first direct radius measurement of a rare white dwarf composed of pure helium.

The results will be published in the Astrophysical Journal Letters. These observations are the first to confirm a theory about a certain type of white dwarf star. (read more)

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Feb 10

No Place to Hide: Missing Primitive Stars Outside Milky Way Uncovered

Source:ESO Science Release eso1007

The Fornax dwarf galaxy. Credit: ESO.

After years of successful concealment, the most primitive stars outside our Milky Way galaxy have finally been unmasked. New observations using ESO’s Very Large Telescope have been used to solve an important astrophysical puzzle concerning the oldest stars in our galactic neighbourhood — which is crucial for our understanding of the earliest stars in the Universe. (read more)

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Jan 10

UI astronomers capture first-of-kind image at distant star

Source: University of Iowa

Image: Composite image of a large radio coronal loop superimposed on an artist's conception of Algol, a binary star system. Credit: William Peterson.

Two University of Iowa researchers have made the first direct radio image of a coronal loop at a star, other than the sun, thereby providing scientists with information that may lead to a better understanding of how such phenomena as space weather affect the Earth. (read more)

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Jan 10


Source: arXiv

Comparison of an LBV and the Sun. Credit: University of Florida/Meghan Kennedy.

P Cygni is a good example of an LBV, it has many interesting characteristics in its own right. It was discovered on August 8th, 1600, when it suddenly appeared, flaring up to 3rd magnitude. Over the next hundred years it continued to fade and brighten up what allowed it to be considered as variable. Flares have also been associated to the variability of the star when it brightens.

It now seems possible that the flares may be due to the presence of a second star in orbit around P Cygni. (read more)

Related links:
Universe Today

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Jan 10

MN112: a new Galactic candidate Luminous Blue Variable

Source: Universe Today

Eta Carinae
. Credit: NASA/HST

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. (read more)

Original Scientific Article:

arXiv.org - Gvaramadze,V.V., Kniazev,A.Y., Fabrika, S., Sholukhova,O., L. N. Berdnikov,L.N., Cherepashchuk,A.M., Zharova,A.V. (2009). MN112: a new Galactic candidate Luminous Blue Variable, MNRAS (submitted).

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Dec 09

ESO Science Release 48/09 - Brightness Variations of Sun-like Stars: The Mystery Deepens

Source: ESO

Artists impression of stellar evolution. Credit ESA

An extensive study made with ESO’s Very Large Telescope deepens a long-standing mystery in the study of stars similar to the Sun. Unusual year-long variations in the brightness of about one third of all Sun-like stars during the latter stages of their lives still remain unexplained. Over the past few decades, astronomers have offered many possible explanations, but the new, painstaking observations contradict them all and only deepen the mystery. The search for a suitable interpretation is on.

The release and an image are available on:

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