Stellar News Feed Archive
|Hubble, bubble, some toil but no trouble||Wednesday, April 27, 2016 - 08:50||
The Bubble Nebula really is a bubble. It is being blown into this shape by the bright star known as SAO20575, which sits just to the left of centre in this image. This is a giant star of 10–20 times the mass of the Sun.
The star is pumping out a fearsome torrent of ultraviolet radiation, causing the surrounding gases to glow like a fluorescent light. But it is not this ultraviolet radiation that is blowing the bubble. Instead, it is being created by SAO20575’s stellar wind.
A stellar wind is a high-speed flow of particles streaming away from the star. As they collide with the gas atoms and molecules in the surrounding cloud they push them away, creating this luminous bubble.
|Is T CrB About to Blow its Top?||Thursday, April 21, 2016 - 08:43||
It's one of only about 10 stars in the entire sky classified as a recurrent nova, with two recorded outbursts to its name. Normally, the star slumbers at 10th magnitude, but on May 12, 1866, it hit the roof, reaching magnitude +2.0 and outshining every star in Corona Borealis before quickly fading back to obscurity. Eighty years later, on February 9, 1946, it sprang back to life, topping out at magnitude +3.0.
Many variable star observers include it in their nightly runs because it's easy to find 1° south-southeast of Epsilon (ε) in Corona Borealis and only requires a 3-inch telescope. Not to mention the huge payoff should you happen catch the star during one of its rare explosions.
|Pulsation-Driven Winds in Giant Stars||Friday, April 8, 2016 - 20:44||
The mechanism that drives the winds of giant stars is poorly determined. Astronomers think there are three possibilities: radiative, in which the pressure of the light pushes out the grains, magnetically driven, in which the stellar magnetic field plays a role in powering the flow, and pulsation driven, in which a periodic build-up of radiative energy in the stellar interior is suddenly released. Over the years scientific opinion has varied among these alternatives, depending on each particular stellar example. CfA astronomer Chris Johnson and his colleagues explored the problem of wind-driving mechanism in giant stars by measuring the motion of the outflowing CO gas around one the nearest and brightest giant stars, EU Del, which is only about 380 light-years away and shines with 1600 solar-luminosities. Its radius, if the star were placed at the position of the Sun, would extend past the orbit of Venus. EU Del is known to be a semi-regular variable star which pulses every sixty days or so (but with some secondary periods as well), and infrared observations suggest it has a circumstellar dust shell.
Read the pre-print paper at arXiv: http://arxiv.org/pdf/1512.04695v1.pdf
|Caught For The First Time: The Early Flash Of An Exploding Star||Tuesday, March 22, 2016 - 10:00||
The brilliant flash of an exploding star’s shockwave—what astronomers call the “shock breakout”—has been captured for the first time in the optical wavelength or visible light by NASA's planet-hunter, the Kepler space telescope.
An international science team led by Peter Garnavich, an astrophysics professor at the University of Notre Dame in Indiana, analyzed light captured by Kepler every 30 minutes over a three-year period from 500 distant galaxies, searching some 50 trillion stars. They were hunting for signs of massive stellar death explosions known as supernovae.
In 2011, two of these massive stars, called red supergiants, exploded while in Kepler’s view. The first behemoth, KSN 2011a, is nearly 300 times the size of our sun and a mere 700 million light years from Earth. The second, KSN 2011d, is roughly 500 times the size of our sun and around 1.2 billion light years away.
Read the full story at NASA Ames News
|Hubble unveils monster stars||Thursday, March 17, 2016 - 11:14||
Astronomers using the unique ultraviolet capabilities of the NASA/ESA Hubble Space Telescope have identified nine monster stars with masses over 100 times the mass of the Sun in the star cluster R136. This makes it the largest sample of very massive stars identified to date. The results, which will be published in the Monthly Notices of the Royal Astronomical Society, raise many new questions about the formation of massive stars.
As well as finding dozens of stars exceeding 50 solar masses, this new study was able to reveal a total number of nine very massive stars in the cluster, all more than 100 times more massive as the Sun. However, the current record holder R136a1 does keep its place as the most massive star known in the Universe, at over 250 solar masses. The detected stars are not only extremely massive, but also extremely bright. Together these nine stars outshine the Sun by a factor of 30 million.
Read the full story at Hubble Space Telescope News
|The Kepler and Hale observations of V523 Lyr||Monday, March 7, 2016 - 12:24||
We present new observations of the cataclysmic variable V523 Lyr, a member of the open cluster NGC 6791. The Kepler Space telescope obtained photometric observations of this source and we examine the nearly 3 year long light curve. The observations show numerous small amplitude outbursts recurring on average every 33 days, intermittent quasi-periodic oscillations, and a significant fully coherent period of ~3.8 hr which we identify as the orbital period of the binary. Contemporaneous optical spectroscopy of V523 Lyr reveals a faint blue source with broad Balmer absorption lines containing narrow emission cores. H
Authors: E. Mason, S.B. Howell
|Subaru-HiCIAO Spots Young Stars Surreptitiously Gluttonizing Their Birth Clouds||Tuesday, March 1, 2016 - 10:51||
(Excerpt from press release) A few stars are known to be associated with a sudden and violent "feeding" frenzy from inside their stellar nursery. When they gluttonize on the surrounding material, their visible light increases very suddenly and dramatically, by a factor of about a hundred. These sudden flareups in brightness are called "FU Orionis outbursts" because they were first discovered toward the star FU Orionis.
Not many stars are found to be associated with such outbursts — only a dozen out of thousands. However, astronomers speculate that all baby stars may experience such outbursts as part of their growth. The reason we only see FU Ori outbursts toward a few newborn stars is simply because they are relatively quiet most of the time.
Read the pre-print paper on ArXiv
Authors: Hauyu Baobab Liu, Michihiro Takami, Tomoyuki Kudo, Jun Hashimoto, Ruobing Dong, Eduard I. Vorobyov, Tae-Soo Pyo, Misato Fukagawa, Motohide Tamura, Thomas Henning, Michael M. Dunham, Jennifer Karr, Nobuhiko Kusakabe, Toru Tsuribe
|Variability in young very low mass stars: Two surprises from spectrophotometric monitoring||Friday, February 26, 2016 - 09:20||
We present simultaneous photometric and spectroscopic observations of seven young and highly variable M dwarfs in star forming regions in Orion, conducted in 4 observing nights with FORS2 at ESO/VLT. All seven targets show significant photometric variability in the I-band, with amplitudes between 0.1-0.8 mag, The spectra, however, remain remarkably constant, with spectral type changes less than 0.5 subtypes. Thus, the brightness changes are not caused by veiling that 'fills in' absorption features. Three objects in the
Authors: I. Bozhinova, A. Scholz, J. Eislöffel
|The 2015 super-active state of recurrent nova T CrB and the long term evolution after the 1946 outburst||Thursday, February 25, 2016 - 08:33||
The recurrent nova T CrB has entered in 2015 a phase of unprecedented high activity. To trace something equivalent, it is necessary to go back to 1938, before the last nova eruption in 1946. The 2015 super-active state is characterized by: a large increase in the mean brightness (Delta B =0.72 mag over the uderlying secular trend), vanishing of the orbital modulation from the B-band lightcurve, and appearance of strong and high ionization emission lines, on top of a nebular continuum that overwhelms at optical wavelengths the absoption spectrum of the M giant. Among the emission lines, HeII 4686 attains a flux in excess of Hgamma, the full set of OIII and NIII lines involved in the Bowen fluorescence mechanism are strong and varying in intensity in phase with HeII 4686, and OIV and [NeV] are present. A large increase in the radiation output from the hot source is reponsible for a large expansion in the ionized fraction of the M giant wind. The wind is completely ionized in the direction to the observer. A high electron density is supported by the weakness of forbidden lines and by the large amplitude and short time scale of the reprocessing by the nebular material of the highly variable photo-ionization input from the hot source. During the super-active state the nebula is varying to and from ionization-bounded and density-bounded conditions, and the augmented irradiation of the cool giant has changed the spectral type of its side facing the hot source from M3III to M2III, i.e. an increase of ~80 K in effective temperature.
Authors: U. Munari, S. Dallaporta, G. Cherini
|Longest-lasting stellar eclipse discovered||Thursday, February 18, 2016 - 10:25||
Imagine living on a world where, every 69 years, the sun disappears in a near-total eclipse that lasts for three and a half years.
That is just what happens in an unnamed binary star system nearly 10,000 light years from Earth. The newly discovered system, known only by its astronomical catalog number TYC 2505-672-1, sets a new record for both the longest duration stellar eclipse and the longest period between eclipses in a binary system.
Discovery of the system’s extraordinary properties was made by a team of astronomers from Vanderbilt and Harvard with the assistance of colleagues at Lehigh, Ohio State and Pennsylvania State universities, Las Cumbres Observatory Global Telescope Network and the American Association of Variable Star Observers and is described in a paper accepted for publication in the Astronomical Journal.
|Astronomers Observe a Mystery Star Pretending to be a Supernova||Wednesday, February 17, 2016 - 10:54||
"Most supernovae are visible for a short time and then -- over a matter of weeks -- fade from view," said Breanna Binder, a University of Washington. After a star explodes as a supernova, it usually leaves behind either a black hole or what's called a neutron star -- the collapsed, high-density core of the former star. Neither should be visible to Earth after a few weeks. But this supernova -- SN 2010da -- still was.
"SN 2010da is what we call a 'supernova impostor' -- something initially thought to be a supernova based on a bright emission of light, but later to be shown as a massive star that for some reason is showing this enormous flare of activity," said Binder.
Many supernova impostors appear to be massive stars in a binary system -- two stars in orbit of one another. Stellar astrophysicists think that the impostor's occasional flare-ups might be due to perturbations from its neighbor.
For SN 2010da, the story appeared to be over until September 2010 -- four months after it was confirmed as an impostor -- when Binder pointed NASA's Chandra X-ray Observatory toward NGC300 and found something unexpected.
Read the full story at The Daily Galaxy
|Observation of Gravitational Waves from a Binary Black Hole Merger||Saturday, February 13, 2016 - 12:30||
On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of
|On the 2015 outburst of the EXor variable star V1118 Ori||Friday, February 5, 2016 - 12:44||
After a long-lasting period of quiescence of about a decade, the source V1118 Ori, one of the most representative members of the EXor variables, is now outbursting. Since the initial increase of the near-infrared flux of about 1 mag (JHK bands) registered on 2015 September 22, the source brightness has remained fairly stable. We estimate DeltaV about 3 mag with respect to the quiescence phase. An optical/near-IR low-resolution spectrum has been obtained with the Large Binocular Telescope instruments MODS and LUCI2, and compared with a spectrum of similar spectral resolution and sensitivity level taken during quiescence. Together with the enhancement of the continuum, the outburst spectrum presents a definitely higher number of emission lines, in particular HI recombination lines of the Balmer, Paschen, and Brackett series, along with bright permitted lines of several species, forbidden atomic lines, and CO ro-vibrational lines. Both mass accretion and mass loss rates have significantly increased (by to about an order of magnitude, mass accretion rate = 1.2-4.8 10^-8 M_sun/yr, mass loss rate = 0.8-2 10^-9 M_sun/yr) with respect to the quiescence phase. If compared with previous outbursts, the present one appears less energetic. Alternatively, it could already be in the fading phase (with the maximum brightness level reached when the source was not visible), or, viceversa, still in the rising phase.
Authors: T.Giannini, D.Lorenzetti, S.Antoniucci, A. A.Arkharov, V.M.Larionov, A.Di Paola, S.Bisogni, A.Marchetti
|A new insight into the V1184 Tau variability||Friday, February 5, 2016 - 12:36||
V1184 Tau is a young variable for long time monitored at optical wavelengths. Its variability has been ascribed to a sudden and repetitive increase of the circumstellar extinction (UXor-type variable), but the physical origin of such variation, although hypothesized, has not been fully supported on observational basis. To get a new insight into the variability of V1184 Tau, we present new photometric and spectroscopic observations taken in the period 2008-2015. During these years the source has reached the same high brightness level that had before the remarkable fading of about 5 mag undergone in 2004. The optical spectrum is the first obtained when the continuum is at its maximum level. The observations are interpreted in the framework of extinction driven variability. We analyze light curves, optical and near-infrared colors, SED and optical spectrum. The emerging picture indicates that the source fading is due to an extinction increase of DeltaA_V about 5 mag, associated with a strong infrared excess, attributable to a thermal component at T=1000 K. From the flux of H(alpha) we derive a mass accretion rate between 10^-11 -5 10^-10 M_sun yr^-1 s, consistent with that of classical T Tauri stars of similar mass. The source SED was fitted for both the high and low level of brightness. A scenario consistent with the known stellar properties (such as spectral type, mass and radius) is obtained only if the distance to the source is of few hundreds of parsecs, in contrast with the commonly assumed value of 1.5 kpc. Our analysis partially supports that presented by Grinin (2009), according to which the circumstellar disk undergoes a periodical puffing, whose observational effects are both to shield the central star and to evidence a disk wind activity. However, since the mass accretion rate remains almost constant with time, the source is likely not subject to accretion bursts.
Authors: T. Giannini, D. Lorenzetti, A. Harutyunyan, G. Li Causi, S. Antoniucci, A. A. Arkharov, V. M. Larionov, F. Strafella
|Old Stars’ Fossil Fields||Friday, January 22, 2016 - 10:03||
Stars create magnetic fields through convection, the swirling, Ferris-wheel-like motion of hot, ionized gas (or boiling water, for that matter). Where convection happens in a star depends on how massive the star is: low-mass stars, including the Sun, have convective outer envelopes around a non-convective core, but stars a little bulkier — up to a couple Suns’ worth — do have convective cores.
Recently, Jim Fuller (Caltech) and colleagues found that strong core magnetic fields could explain the oddly weak, on-and-off brightening behavior of a sample of red giant stars. These stars are low- to middle-mass and have stopped fusing hydrogen in their centers, so they don’t have convective hearts. They also often have a mismatched, variable glow, with one hemisphere brightening as the other fades. What was strange about the sample the team looked at was that this group didn’t vary as much in brightness as it should have.
Read the full story at Sky & Telescope
Read the letter by Stello, Dennis et al. “A prevalence of dynamo-generated magnetic fields in the cores of intermediate-mass stars.” Nature. January 21, 2016.
|Record-Shattering Cosmic Blast Could Help Crack the Case of Extreme Supernova Explosions||Friday, January 15, 2016 - 10:52||
Records are made to be broken, as the expression goes, but rarely are records left so thoroughly in the dust. Stunned astronomers have witnessed a cosmic explosion about 200 times more powerful than a typical supernova—events which already rank amongst the mightiest outbursts in the universe—and more than twice as luminous as the previous record-holding supernova.
The record-breaking blast is thought to be an outstanding example of a "superluminous supernova," a recently discovered, supremely rare variety of explosion unleashed by certain stars when they die. Scientists are frankly at a loss, though, regarding what sorts of stars and stellar scenarios might be responsible for these extreme supernovae.
|One Thousand New Dwarf Novae from the OGLE Survey||Wednesday, January 13, 2016 - 13:01||
We present one of the largest collections of dwarf novae (DNe) containing 1091 objects that have been discovered in the long-term photometric data from the Optical Gravitational Lensing Experiment (OGLE) survey. They were found in the OGLE fields toward the Galactic bulge and the Magellanic Clouds. We analyze basic photometric properties of all systems and tentatively find a population of DNe from the Galactic bulge. We identify several dozen of WZ Sge-type DN candidates, including two with superhump periods longer than 0.09 d. Other interesting objects include SU UMa-type stars with "early" precursor outbursts or a Z Cam-type star showing outbursts during standstills. We also provide a list of DNe which will be observed during the K2 Campaign 9 microlensing experiment in 2016. Finally, we present the new OGLE-IV real-time data analysis system: CVOM, which has been designed to provide continuous real time photometric monitoring of selected CVs.
Authors: P. Mroz, A. Udalski, R. Poleski, P. Pietrukowicz, M.K. Szymanski, I. Soszynski, L. Wyrzykowski, K. Ulaczyk, S. Kozlowski, J. Skowron
|Multi-Mode and Non-Standard Classical Cepheids in the Magellanic System||Tuesday, January 12, 2016 - 10:44||
We present a sample of the most interesting classical Cepheids selected from the OGLE collection of classical Cepheids in the Magellanic System. The main selection criterion for this sample was the presence of non-standard, unique pulsational properties.
Authors: I. Soszynski, A. Udalski, M. K. Szymanski, R. Poleski, P. Pietrukowicz, S. Kozlowski, P. Mroz, L. Wyrzykowski, D. Skowron, J. Skowron, G. Pietrzynski, K. Ulaczyk, M. Pawlak
|A newly discovered stellar type: dusty post-red giant branch stars in the Magellanic Clouds||Monday, January 11, 2016 - 13:13||
Context: We present a newly discovered class of low-luminosity, dusty, evolved objects in the Magellanic Clouds. These objects have dust excesses, stellar parameters, and spectral energy distributions similar to those of dusty post-asymptotic giant branch (post-AGB) stars. However, they have lower luminosities and hence lower masses. We suggest that they have evolved off the red giant branch (RGB) instead of the AGB as a result of binary interaction. Aims: In this study we aim to place these objects in an evolutionary context and establish an evolutionary connection between RGB binaries (such as the sequence E variables) and our new sample of objects. Methods: We compared the theoretically predicted birthrates of the progeny of RGB binaries to the observational birthrates of the new sample of objects. Results: We find that there is order-of-magnitude agreement between the observed and predicted birthrates of post-RGB stars. The sources of uncertainty in the birthrates are discussed; the most important sources are probably the observational incompleteness factor and the post-RGB evolution rates. We also note that mergers are relatively common low on the RGB and that stars low on the RGB with mid-IR excesses may recently have undergone a merger. Conclusions: Our sample of dusty post-RGB stars most likely provides the first observational evidence for a newly discovered phase in binary evolution: post-RGB binaries with circumstellar dust.
Authors: D. Kamath, P. R. Wood, H. Van Winckel, J.D. Nie
|Twisted Magnetic Fields Give New Insights on Star Formation||Monday, December 21, 2015 - 16:40||
Using new images that show unprecedented detail, scientists have found that material rotating around a very young protostar probably has dragged in and twisted magnetic fields from the larger area surrounding the star. The discovery, made with the National Science Foundation's Karl G. Jansky Very Large Array (VLA) radio telescope, has important implications for how dusty disks -- the raw material for planet formation -- grow around young stars.
|CK Vul: a smorgasbord of hydrocarbons rules out a 1670 nova (and much else besides)||Wednesday, December 9, 2015 - 12:13||
Abstract: We present observations of CK Vul obtained with the Spitzer Space Telescope. The infrared spectrum reveals a warm dust continuum with nebular, molecular hydrogen and HCN lines superimposed, together with the "Unidentified Infrared" (UIR) features. The nebular lines are consistent with emission by a low density gas. We conclude that the Spitzer data, combined with other information, are incompatible with CK Vul being a classical nova remnant in "hibernation" after the event of 1670, a "Very Late Thermal Pulse", a "Luminous Red Variable" such as V838 Mon, or a "Diffusion-induced nova". The true nature of CK Vul remains a mystery.
Authors: A. Evans (Astrophysics Group, Keele University), R. D. Gehrz, C. E. Woodward (University of Minnesota), P. J. Sarre (University of Nottingham), J. Th. van Loon (Keele University), L. A. Helton (SOFIA/USRA), S. Starrfield (Arizona State University), S. P. S. Eyres (University of Central Lancashire)
|Student discovers stellar chamaeleon had astronomers fooled for years||Friday, December 4, 2015 - 12:20||
A graduate student has discovered that astronomers have for years been mistakenly interpreting the dust in the environment CW Leo, of the brightest infrared star in the Northern sky. Images released today show none of the previously identified bright spots in fact contain the famous star, which is now believed to be buried in its own dust 450 light years from earth.
CW Leo is one of the most extensively studied evolved stars, believed to be on the cusp of planetary nebula formation – the process ending the red giant’s life is potentially already under way.
Also see the press release from the RAS
Download the research paper from the MNRAS
|The variable V381 Lac and its possible connection with the R CrB phenomenon||Thursday, December 3, 2015 - 17:30||
We have performed new medium resolution spectroscopy, optical and near infrared photometry to monitor the variability of the AGB carbon star V 381 Lac. Our observations revealed rapid and deep changes in the spectrum and extreme variability in the optical and near infrared bands. Most notably we observed the change of NaI D lines from deep absorption to emission, and the progressive growing of the [N II] doublet 6548-6584 A emission, strongly related to the simultaneous photometric fading. V381 Lac occupies regions of 2MASS and WISE colour-colour diagrams typical of stars with dust formation in the envelope. The general framework emerging from the observations of V381 Lac is that of a cool AGB carbon star undergoing episodes of high mass ejection and severe occultation of the stellar photosphere reminiscent of those characterising the RCB phenomenon.
Comparing the Spectral Energy Distribution obtained with the theoretical model for AGB evolution with dust in the circumstellar envelope, we can identify V381 Lac as the descendant of a star of initial mass ~2M_sun, in the final AGB phases, evolved into a carbon star by repeated Third Dredge Up episodes. According to our model the star is moderately obscured (tau_10 ~0.22) by dust, mainly formed by amorphous carbon (~80%) and SiC (~20%), with dust grain dimensions around ~0.2 micron and 0.08 micron respectively.
Authors: Corinne Rossi, Flavia Dell'Agli, Andrea Di Paola, Kamo S. Gigoyan, Roberto Nesci
|Missing link between turbulence in collapsing star, hypernovae and gamma-ray bursts||Monday, November 30, 2015 - 13:01||
A supercomputer simulation of a mere 10 milliseconds in the collapse of a massive star into a neutron star proves that these catastrophic events, often called hypernovae, can generate the enormous magnetic fields needed to explode the star and fire off bursts of gamma rays visible halfway across the universe.
The results of the simulation, published online Nov. 30 in advance of publication in the journal Nature, demonstrate that as a rotating star collapses, the star and its attached magnetic field spin faster and faster, forming a dynamo that revs the magnetic field to a million billion times the magnetic field of Earth.
A field this strong is sufficient to focus and accelerate gas along the rotation axis of the star, creating two jets that ultimately can produce oppositely directed blasts of highly energetic gamma rays.
|Aging Star’s Weight Loss Secret Revealed||Wednesday, November 25, 2015 - 11:34||
The star VY Canis Majoris is a red hypergiant, one of the largest known stars in the Milky Way. It is 30–40 times the mass of the Sun and 300 000 times more luminous. In its current state, the star would encompass the orbit of Jupiter, having expanded tremendously as it enters the final stages of its life.
New observations of the star using the SPHERE instrument on the VLT have clearly revealed how the brilliant light of VY Canis Majoris lights up the clouds of material surrounding it and have allowed the properties of the component dust grains to be determined better than ever before.
In this very close-up view from SPHERE the star itself is hidden behind an obscuring disc. The crosses are artefacts due to features in the instrument.
Read the full press release from ESO