Recent Postings from Special Topics

A strong ultraviolet pulse from a newborn type Ia supernova

Type Ia supernovae1 are destructive explosions of carbon-oxygen white dwarfs2, 3. Although they are used empirically to measure cosmological distances4, 5, 6, the nature of their progenitors remains mysterious3. One of the leading progenitor models, called the single degenerate channel, hypothesizes that a white dwarf accretes matter from a companion star and the resulting increase in its central pressure and temperature ignites thermonuclear explosion3, 7, 8. Here we report observations with the Swift Space Telescope of strong but declining ultraviolet emission from a type Ia supernova within four days of its explosion. This emission is consistent with theoretical expectations of collision between material ejected by the supernova and a companion star9, and therefore provides evidence that some type Ia supernovae arise from the single degenerate channel.

 

http://www.nature.com/nature/journal/v521/n7552/full/nature14440.html

44Ti gamma-ray emission lines from SN1987A reveal an asymmetric explosion

In core-collapse supernovae, titanium-44 (44Ti) is produced in the innermost ejecta, in the layer of material directly on top of the newly formed compact object. As such, it provides a direct probe of the supernova engine. Observations of supernova 1987A (SN1987A) have resolved the 67.87- and 78.32–kilo–electron volt emission lines from decay of 44Ti produced in the supernova explosion. These lines are narrow and redshifted with a Doppler velocity of ~700 kilometers per second, direct evidence of large-scale asymmetry in the explosion.

http://www.sciencemag.org/content/348/6235/670.full

Detection of water vapour around dwarf planet (1) Ceres

We report the detection of water vapour on (1) Ceres, the first unambiguous discovery of water on an object in the asteroid main belt. Most of the water vapour stems from localized regions at low latitude, possibly from surface features known from adaptive optics observations. We suggest either cometary-type sublimation from the near surface or cryovolcanism as the origin of the waver vapour [1].

https://www.cfa.harvard.edu/news/latest

http://arxiv.org/abs/1402.6336

MESSENGER Recap

http://science.nasa.gov/science-news/science-at-nasa/2015/30apr_messenger/

Glory on Venus cloud tops and the unknown UV absorber

doi:10.1016/j.icarus.2014.01.030

We report on the implications of the observations of the glory phenomenon made recently by Venus Express orbiter. Glory is an optical phenomenon that poses stringent constraints on the cloud properties. These observations thus enable us to constrain two properties of the particles at the cloud tops (about 70 km altitude) which are responsible for a large fraction of the solar energy absorbed by Venus. Firstly we obtain a very accurate estimate of the cloud particles size to be 1.2 μm with a very narrow size distribution. We also find that for the two observations presented here the clouds are homogenous, as far as cloud particles sizes are concerned, on scale of at least 1200 km. This is in contrast to previous estimates that were either local, from entry probes data, or averaged over space and time from polarization data. Secondly we find that the refractive index for the data discussed here is higher than that of sulfuric acid previously proposed for the clouds composition (Hansen, J.E., Hovenier, J.W. [1974]. J. Atmos. Sci. 31, 1137–1160; Ragent, B. et al. [1985]. Adv. Space Res. 5, 85–115). Assuming that the species contributing to the increase of the refractive index is the same as the unknown UV absorber, we are able to constrain the list of candidates. We investigated several possibilities and argue that either small ferric chloride (FeCl3) cores inside sulfuric acid particles or elemental sulfur coating their surface are good explanations of the observation. Both ferric chloride and elemental sulfur have been suggested in the past as candidates for the as yet unknown UV absorber (Krasnopolsky, V.A. [2006]. Planet. Space Sci. 54, 1352–1359; Mills, F.P. et al. [2007]. In: Esposito, L.W., Stofan, E.R., Cravens, T.E. (Eds.), Exploring Venus as a Terrestrial Planet, vol. 176. AGU Monogr. Ser., Washington, DC, pp. 73–100).

Isolated compact elliptical galaxies: Stellar systems that ran away

Igor Chilingarian, Ivan Zolotukhin

Abstract: Compact elliptical galaxies form a rare class of stellar system (~30 presently known) characterized by high stellar densities and small sizes and often harboring metal-rich stars. They were thought to form through tidal stripping of massive progenitors, until two isolated objects were discovered where massive galaxies performing the stripping could not be identified. By mining astronomical survey data, we have now found 195 compact elliptical galaxies in all types of environment. They all share similar dynamical and stellar population properties. Dynamical analysis for nonisolated galaxies demonstrates the feasibility of their ejection from host clusters and groups by three-body encounters, which is in agreement with numerical simulations. Hence, isolated compact elliptical and isolated quiescent dwarf galaxies are tidally stripped systems that ran away from their hosts.

http://www.sciencemag.org/content/348/6233/418.abstract

Planet heating prevents inward migration of planetary cores

http://www.nature.com/nature/journal/v520/n7545/full/nature14277.html

http://www.nature.com/nature/journal/v520/n7545/full/520040a.html?WT.ec_id=NATURE-20150402

Pablo Benı´tez-Llambay1, Fre´de´ric Masset2, Gloria Koenigsberger2 & Judit Szula´gyi3

Planetary systems are born in the disks of gas, dust and rocky fragments that surround newly formed stars. Solid content assembles into ever-larger rocky fragments that eventually become planetary embryos. These then continue their growth by accreting leftover material in the disk. Concurrently, tidal effects in the disk cause a radial drift in the embryo orbits, a process known as migration1–4. Fast inward migration is predicted by theory for embryos smaller than three to fiveEarthmasses5–7. With only inwardmigration, these embryos can only rarely become giant planets located at Earth’s distance fromthe Sunand beyond8,9, incontrastwith observations10. Here we report that asymmetries in the temperature rise associated with accreting infalling material11,12 produce a force (which gives rise to an effect thatwe call ‘heating torque’) that counteracts inward migration.This provides a channel for the formation of giant planets 8 and also explains the strong planet–metallicity correlation found between the incidence of giant planets and the heavy-element abundance  of the host stars13,14.

Stochastic electron acceleration during spontaneous turbulent reconnection in a strong shock wave

  1. Y. Matsumoto1,*T. Amano2T. N. Kato3M. Hoshino2

Explosive phenomena such as supernova remnant shocks and solar flares have demonstrated evidence for the production of relativistic particles. Interest has therefore been renewed in collisionless shock waves and magnetic reconnection as a means to achieve such energies. Although ions can be energized during such phenomena, the relativistic energy of the electrons remains a puzzle for theory. We present supercomputer simulations showing that efficient electron energization can occur during turbulent magnetic reconnection arising from a strong collisionless shock. Upstream electrons undergo first-order Fermi acceleration by colliding with reconnection jets and magnetic islands, giving rise to a nonthermal relativistic population downstream. These results shed new light on magnetic reconnection as an agent of energy dissipation and particle acceleration in strong shock waves.

http://www.sciencemag.org.ezp-prod1.hul.harvard.edu/content/347/6225/974.full

Saturn’s fast spin determined from its gravitational field and oblateness

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14278.html

The alignment of Saturn’s magnetic pole with its rotation axis precludes the use of magnetic field measurements to determine its rotation period1. The period was previously determined from radio measurements by the Voyager spacecraft to be 10 h 39 min 22.4 s (ref. 2). When the Cassini spacecraft measured a period of 10 h 47 min 6 s, which was additionally found to change between sequential measurements345, it became clear that the radio period could not be used to determine the bulk planetary rotation period. Estimates based upon Saturn’s measured wind fields have increased the uncertainty even more, giving numbers smaller than the Voyager rotation period, and at present Saturn’s rotation period is thought to be between 10 h 32 min and 10 h 47 min, which is unsatisfactory for such a fundamental property. Here we report a period of 10 h 32 min 45 s ± 46 s, based upon an optimization approach using Saturn’s measured gravitational field and limits on the observed shape and possible internal density profiles. Moreover, even when solely using the constraints from its gravitational field, the rotation period can be inferred with a precision of several minutes. To validate our method, we applied the same procedure to Jupiter and correctly recovered its well-known rotation period.

Eyelashes divert airflow to protect the eye

http://rsif.royalsocietypublishing.org/content/12/105/20141294

[quant-ph] Entanglement Enabled Intensity Interferometry

http://arxiv.org/abs/1502.02477

Intensity interferometry (Hanbury Brown – Twiss effect) is an interesting and useful concept that is usually presented as a manifestation of the quantum statistics of indistinguishable particles. Here, by exploiting possibilities for project and entanglement, we substantially widen the scope of its central idea, removing the requirement of indistinguishability. We thereby potentially gain access to a host of new observables, including subtle polarization correlations and entanglement itself. Our considerations also shed light on the physical significance of superselection.

Jupiter’s decisive role in the inner Solar System’s early evolution

http://www.pnas.org/content/early/2015/03/18/1423252112.abstract

Konstantin Batygin & Greg Laughlin

The statistics of extrasolar planetary systems indicate that the default mode of planet formation generates planets with orbital periods shorter than 100 days and masses substantially exceeding that of the Earth. When viewed in this context, the Solar System is unusual. Here, we present simulations which show that a popular formation scenario for Jupiter and Saturn, in which Jupiter migrates inward from a > 5 astronomical units (AU) to a ≈ 1.5 AU before reversing direction, can explain the low overall mass of the Solar System’s terrestrial planets, as well as the absence of planets with a < 0.4 AU. Jupiter’s inward migration entrained s ≳ 10−100 km planetesimals into low-order mean motion resonances, shepherding and exciting their orbits. The resulting collisional cascade generated a planetesimal disk that, evolving under gas drag, would have driven any preexisting short-period planets into the Sun. In this scenario, the Solar System’s terrestrial planets formed from gas-starved mass-depleted debris that remained after the primary period of dynamical evolution.

Dear Colleague: Status of NSF Response to NWNH Decadal Survey

Dear Colleague:
In August 2010, the National Research Council (NRC) released the most recent in its series of decadal surveys in Astronomy and Astrophysics, entitled “New Worlds, New Horizons in Astronomy and Astrophysics. [...] The budget for AST has remained stagnant, rather than increasing at the rate of 4 percent per year in purchasing power (plus inflation) assumed in NWNH. The Fiscal Year (FY) 2015 budget estimate for AST is USD 244.16 million, compared to an actual value of USD 246.53 million in FY 2010. Thus it has not been feasible to implement positive responses to all NWNH recommendations. [...] This letter is an update to the science community on the status of the AST response to NWNH.

Dear Colleague Letter: Status of NSF MPS/AST Response to Recommendations of New Worlds, New Horizons Decadal Survey

Membrane alternatives in worlds without oxygen: Creation of an azotosome

http://advances.sciencemag.org/content/1/1/e1400067

An ultraluminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30

An ultraluminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30
Xue-Bing Wu, Feige Wang, Xiaohui Fan, Weimin Yi, Wenwen Zuo, Fuyan Bian, Linhua Jiang, Ian D. McGreer, Ran Wang, Jinyi Yang, Qian Yang, David Thompson & Yuri Beletsky

Nature 518, 512–515 (26 February 2015)
doi:10.1038/nature14241

Editor’s summary:
Cosmic redshifts of between 6 and 7 represent a time when the intergalactic medium was in transition from a neutral state to being completely ionized. Here Xue-Bing Wu et al. report the discovery of an ultraluminous quasar at redshift z = 6.30 that has optical and near-infrared luminosity several times greater than previously known quasars at redshifts beyond 6. Based on near-infrared spectral data, the authors estimate a mass of approximately twelve-billion solar-masses for the associated black hole, consistent with the thirteen-billion solar masses derived by assuming an Eddington-limited accretion rate, where the force of radiation acting outwards and the gravitational force acting inwards are in balance. As the most luminous quasar known to date at z = 6, this object will be a useful resource for the study of galaxy formation around massive black holes at the end of the epoch of cosmic reionization.

A higher-than-predicted measurement of iron opacity at solar interior temperatures

Nearly a century ago it was recognized1 that radiation absorption by stellar matter controls the internal temperature profiles within stars. Laboratory opacity measurements, however, have never been performed at stellar interior conditions, introducing uncertainties in stellar models2345. A particular problem arose23678 when refined photosphere spectral analysis910 led to reductions of 30–50 per cent in the inferred amounts of carbon, nitrogen and oxygen in the Sun. Standard solar models11 using the revised element abundances disagree with helioseismic observations that determine the internal solar structure using acoustic oscillations. This could be resolved if the true mean opacity for the solar interior matter were roughly 15 per cent higher than predicted23678, because increased opacity compensates for the decreased element abundances. Iron accounts for a quarter of the total opacity212 at the solar radiation/convection zone boundary. Here we report measurements of wavelength-resolved iron opacity at electron temperatures of 1.9–2.3 million kelvin and electron densities of (0.7–4.0) × 1022 per cubic centimetre, conditions very similar to those in the solar region that affects the discrepancy the most: the radiation/convection zone boundary. The measured wavelength-dependent opacity is 30–400 per cent higher than predicted. This represents roughly half the change in the mean opacity needed to resolve the solar discrepancy, even though iron is only one of many elements that contribute to opacity.

http://www.nature.com/nature/journal/v517/n7532/full/nature14048.html

 

2014 Update of the Discoveries of Nuclides

M. Thoennessen

The 2014 update of the discovery of nuclide project is presented. Only six new nuclides were observed for the first time in 2014 while the assignments of seventeen other nuclides were revised. In addition, for another fourteen nuclides the laboratories where they were discovered were reassigned.

http://arxiv.org/abs/1501.06761

Systematic inequality and hierarchy in faculty hiring networks

The faculty job market plays a fundamental role in shaping research priorities, educational outcomes, and career trajectories among scientists and institutions. However, a quantitative understanding of faculty hiring as a system is lacking. Using a simple technique to extract the institutional prestige ranking that best explains an observed faculty hiring network—who hires whose graduates as faculty—we present and analyze comprehensive placement data on nearly 19,000 regular faculty in three disparate disciplines. Across disciplines, we find that faculty hiring follows a common and steeply hierarchical structure that reflects profound social inequality. Furthermore, doctoral prestige alone better predicts ultimate placement than a U.S. News & World Report rank, women generally place worse than men, and increased institutional prestige leads to increased faculty production, better faculty placement, and a more influential position within the discipline. These results advance our ability to quantify the influence of prestige in academia and shed new light on the academic system.

URL:

http://advances.sciencemag.org/content/1/1/e1400005

The formation of a quadruple star system with wide separation

“The formation of a quadruple star system with wide separation”, published in Nature, Feb 12th:

http://www.nature.com/nature/journal/v518/n7538/full/nature14166.html

Detection of galaxy assembly bias

http://arxiv.org/pdf/1305.0350v2.pdf

The double-degenerate, super-Chandrasekhar nucleus of the planetary nebula Henize 2–428

http://www.eso.org/public/archives/releases/sciencepapers/eso1505/eso1505a.pdf

 

“The planetary nebula (PN) stage is the ultimate fate of stars with mass 1 to 8 solar masses (M⊙). The origin of their complex morphologies is poorly understood1 , although several mechanisms involving binary interaction have been proposed 2,3 . In close binary systems, the orbital separation is short enough for the primary star to overfill its Roche lobe as it expands during the Asymptotic Giant Branch (AGB) phase. The excess material ends up forming a common-envelope (CE) surrounding both stars. Drag forces would then result in the envelope being ejected into a bipolar PN whose equator is coincident with the orbital plane of the system. Systems in which both stars have ejected their envelopes and evolve towards the white dwarf (WD) stage are called double-degenerates. Here we report the case of Henize 2-428, the first double-degenerate binary which has, without any ambiguity, a total mass above the Chandrasekhar limit. According to its short orbital period (4.2 hours) and total mass (∼1.8 M⊙), the system should merge in 700 million years, triggering a Type Ia supernova (SN Ia) event. This finding supports the double-degenerate, super-Chandrasekhar evolutionary channel for the formation of SNe Ia4 .”

Planck 2015 Results

http://www.cosmos.esa.int/web/planck/publications#Planck2015

A Joint Analysis of BICEP2/Keck Array and Planck Data

http://new.bicepkeck.org/BKP_paper_20150130.pdf

We report the results of a joint analysis of data from BICEP2/Keck Array and Planck. BICEP2 and Keck Array have observed the same approximately 400 deg2 patch of sky centered on RA 0h, Dec. −57.5°. The combined maps reach a depth of 57 nK deg in Stokes Q and U in a band centered at 150 GHz. Planck has observed the full sky in polarization at seven frequencies from 30 to 353 GHz, but much less deeply in any given region (1.2 µK deg in Q and U at 143 GHz). We detect 150×353 cross-correlation in B-modes at high significance. We fit the single- and cross frequency power spectra at frequencies above 150 GHz to a lensed-ΛCDM model that includes dust and a possible contribution from inflationary gravitational waves (as parameterized by the tensor-to-scalar ratio r). We probe various model variations and extensions, including adding a synchrotron component in combination with lower frequency data, and find that these make little difference to the r constraint. Finally we present an alternative analysis which is similar to a map-based cleaning of the dust contribution, and show that this gives similar constraints. The final result is expressed as a likelihood curve for r, and yields an upper limit r0.05 < 0.12 at 95% confidence. Marginalizing over dust and r, lensing B-modes are detected at 7.0 σ significance.

 

Website:

http://new.bicepkeck.org/bkp_2015_release.html

Press releases:

http://www.nsf.gov/news/news_summ.jsp?cntn_id=134013

http://www.esa.int/Our_Activities/Space_Science/Planck/Planck_gravitational_waves_remain_elusive

BICEP2+Planck Press release

http://public.planck.fr/resultats/253-la-reponse-de-bicep2-keck-planck

Bottom line:

No evidence for primordial gravitational waves:

Planck/WMAP
(mars 2013)
BICEP2
(février 2014)
Planck
(décembre 2014)
BICEP2/KECK/Planck
(janvier 2015)
r < 0.11 r = 0.16-0.20 r < 0.11 r < 0.13

Wind-driven circulation in Titan's seas

http://onlinelibrary.wiley.com/doi/10.1002/2014JE004751/abstract

A higher-than-predicted measurement of iron opacity at solar interior temperatures

http://www.nature.com/nature/journal/v517/n7532/full/nature14048.html

“A higher-than-predicted measurement of iron opacity at solar interior temperatures” by Bailey et al.

Nearly a century ago it was recognized1 that radiation absorption by stellar matter controls the internal temperature profiles within stars. Laboratory opacity measurements, however, have never been performed at stellar interior conditions, introducing uncertainties in stellar models2, 3, 4, 5. A particular problem arose2, 3, 6, 7, 8 when refined photosphere spectral analysis9, 10 led to reductions of 30–50 per cent in the inferred amounts of carbon, nitrogen and oxygen in the Sun. Standard solar models11 using the revised element abundances disagree with helioseismic observations that determine the internal solar structure using acoustic oscillations. This could be resolved if the true mean opacity for the solar interior matter were roughly 15 per cent higher than predicted2, 3, 6, 7, 8, because increased opacity compensates for the decreased element abundances. Iron accounts for a quarter of the total opacity2, 12 at the solar radiation/convection zone boundary. Here we report measurements of wavelength-resolved iron opacity at electron temperatures of 1.9–2.3 million kelvin and electron densities of (0.7–4.0) × 1022 per cubic centimetre, conditions very similar to those in the solar region that affects the discrepancy the most: the radiation/convection zone boundary. The measured wavelength-dependent opacity is 30–400 per cent higher than predicted. This represents roughly half the change in the mean opacity needed to resolve the solar discrepancy, even though iron is only one of many elements that contribute to opacity.

Planck 2014 results

http://www.cosmos.esa.int/documents/387566/387653/Ferrara_Dec1_16h30_Efstathiou_Cosmology.pdf

Planck Press Release Dec 1 2014 (in French, en francais)

Planck press release (now with polarization!) includes two more technical pages (both in French):

Dark Matter and (if I read the bottom panel correctly) no B-Modes and lensing B-modes

http://public.planck.fr/resultats/251-resultats-planck-2014-planck-eclaire-la-matiere-noire-combien-quoi-ou-

and Neutrinos (looks like N_eff ~ 3):

http://public.planck.fr/resultats/250-resultats-planck-2014-ce-que-planck-dit-des-neutrinos

Solar nebula magnetic fields recorded in the Semarkona meteorite

PDF, Supplementary PDF

 

Magnetic fields are proposed to have played a critical role in some of the most enigmatic processes of planetary formation by mediating the rapid accretion of disk material onto the central star and the formation of the first solids. However, there have been no experimental constraints on the intensity of these fields. Here we show that dusty olivine-bearing chondrules from the Semarkona meteorite were magnetized in a nebular field of 54 ± 21 μT. This intensity supports chondrule formation by nebular shocks or planetesimal collisions rather than by electric currents, the x-wind, or other mechanisms near the sun. This implies that background magnetic fields in the terrestrial planet-forming region were likely 5-54 μT, which is sufficient to account for measured rates of mass and angular momentum transport in protoplanetary disks.

http://www.sciencemag.org/content/early/2014/11/12/science.1258022

Unusual Activity in the Atmosphere of Uranus in 2014

Announced at DPS. No paper posted yet. UCB Press release: http://newscenter.berkeley.edu/2014/11/12/amateur-professional-astronomers-alike-thrilled-by-extreme-storms-on-uranus/

 

Abstract:

Uranus continues to evolve as it progresses through the post-equinoctial season. Images taken on 5 and 6 August 2014 at the 10-m Keck 2 telescope show significant atmospheric activity in the planet’s northern (currently sun-facing) hemisphere. Although Keck’s adaptive optics system was underperforming (resulting in artifacts and some blurring), many discrete features were visible on the planet at H (1.6 microns) and K’ (2.2 microns). Many of these features reached altitudes above the 1-bar level, as evidenced by their detection at K’. One feature breaks the record as the brightest ever detected or Uranus at K’, producing 30% of the total light reflected by the planet in that filter, compared to 12% for the previous record in 2005 (Sromovsky et al., Icarus 192, 558-575, 2007). The 2014 feature’s morphology was similar at both K’ and H, suggestive of an underlying vortex (e.g., Hammel et al., Icarus 201, 257-271, 2009). However, the feature’s brightest region in K’ is not particularly bright in H; i.e, although it is relatively high in altitude, it does not have a high optical depth. The total light fraction at H is only 2-3%, compared to the 4-5% found for the 2005 feature. Thus, its visible-wavelength contrast may be low; this could explain why there have been no amateur follow-up detections as of this writing. The new images also reveal development of a long-expected north polar haze as well as polar cloud features. Interestingly, some discrete polar features were visible through the polar haze. This may indicate that the northern polar haze is not yet at an optical depth comparable to that of the fully-formed southern polar haze seen in pre-equinoctial years. Acknowledgements: the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among Caltech, University of California and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation. The authors acknowledge the significant cultural role of Mauna Kea’s summit, and extend thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests.

Punga Mare Waves

Cassini/VIMS observes rough surfaces on Titan’s Punga Mare in specular reflection

http://www.planetary-science.com/content/pdf/s13535-014-0003-4.pdf

The Science of the Movie "Interstellar"

There’s been quite a bit of chatter on the internet regarding the validity of some of the science presented in the movie. It’s not often that this little corner of astrophysics gets such a public presentation, so I figured it might be interesting for astrophysics institutions to discuss the movie for a few minutes around the water cooler.

Birth of Planets Revealed in Astonishing Detail in ALMA's 'Best Image Ever'

[NRAO Press Release]

Astronomers have captured the best image ever of planet formation around an infant star as part of the testing and verification process for the Atacama Large Millimeter/submillimeter Array’s (ALMA) new high-resolution capabilities.

This revolutionary new image reveals in astonishing detail the planet-forming disk surrounding HL Tau, a Sun-like star located approximately 450 light-years from Earth in the constellation Taurus.

ALMA uncovered never-before-seen features in this system, including multiple concentric rings separated by clearly defined gaps. These structures suggest that planet formation is already well underway around this remarkably young star… [abridged]

 

https://public.nrao.edu/news/pressreleases/planet-formation-alma

 

See also Phil Plait’s blog post: http://www.slate.com/blogs/bad_astronomy/2014/11/06/hl_tau_new_observations_of_a_young_planetary_system.html

Pulsations as a driver for LBV variability

Pulsations as a driver for LBV variability
Lovekin, C. C. ; Guzik, J. A.
Monthly Notices of the Royal Astronomical Society, Volume 445, Issue 2, p.1766-1773
Published in Dec 2014

Among the most spectacular variable stars are the luminous blue variables (LBVs), which can show three types of variability. The LBV phase of evolution is poorly understood, and the driving mechanisms for the variability are not known. The most common type of variability, the S Dor instability, occurs on time-scales of tens of years. During an S Dor outburst, the visual magnitude of the star increases, while the bolometric magnitude stays approximately constant. In this work, we investigate pulsation as a possible trigger for the S Dor-type outbursts. We calculate the pulsations of envelope models using a non-linear hydrodynamic code including a time-dependent convection treatment. We initialize the pulsation in the hydrodynamic model based on linear non-adiabatic calculations. Pulsation properties for a full grid of models from 20 to 85 M were calculated, and in this paper, we focus on the few models that show either long-period pulsations or outburst-like behaviour, with photospheric radial velocities reaching 70-80 km s-1. At the present time, our models cannot follow mass-loss, so once the outburst event begins, our simulations are terminated. Our results show that pulsations alone are not able to drive enough surface expansion to eject the outer layers. However, the outbursts and long-period pulsations discussed here produce large variations in effective temperature and luminosity, which are expected to produce large variations in the radiatively driven mass-loss rates.

An ultraluminous X-ray source powered by an accreting neutron star

http://www.nature.com/nature/journal/v514/n7521/full/nature13791.html

The majority of ultraluminous X-ray sources are point sources that are spatially offset from the nuclei of nearby galaxies and whose X-ray luminosities exceed the theoretical maximum for spherical infall (the Eddington limit) onto stellar-mass black holes12. Their X-ray luminosities in the 0.5–10 kiloelectronvolt energy band range from 1039 to 1041 ergs per second3. Because higher masses imply less extreme ratios of the luminosity to the isotropic Eddington limit, theoretical models have focused on black hole rather than neutron star systems12. The most challenging sources to explain are those at the luminous end of the range (more than 1040 ergs per second), which require black hole masses of 50–100 times the solar value or significant departures from the standard thin disk accretion that powers bright Galactic X-ray binaries, or both. Here we report broadband X-ray observations of the nuclear region of the galaxy M82 that reveal pulsations with an average period of 1.37 seconds and a 2.5-day sinusoidal modulation. The pulsations result from the rotation of a magnetized neutron star, and the modulation arises from its binary orbit. The pulsed flux alone corresponds to an X-ray luminosity in the 3–30 kiloelectronvolt range of 4.9 × 1039 ergs per second. The pulsating source is spatially coincident with a variable source4 that can reach an X-ray luminosity in the 0.3–10 kiloelectronvolt range of 1.8 × 1040 ergs per second1. This association implies a luminosity of about 100 times the Eddington limit for a 1.4-solar-mass object, or more than ten times brighter than any known accreting pulsar. This implies that neutron stars may not be rare in the ultraluminous X-ray population, and it challenges physical models for the accretion of matter onto magnetized compact objects.

Data Smashing

Data Smashing

Ishanu Chattopadhyay, Hod Lipson
ArXiv: 1401.0742

Investigation of the underlying physics or biology from empirical data requires a quantifiable notion of similarity – when do two observed data sets indicate nearly identical generating processes, and when they do not. The discriminating characteristics to look for in data is often determined by heuristics designed by experts, e.g., distinct shapes of “folded” lightcurves may be used as “features” to classify variable stars, while determination of pathological brain states might require a Fourier analysis of brainwave activity. Finding good features is non-trivial. Here, we propose a universal solution to this problem: [...] In our examples, the data smashing principle, without access to any domain knowledge, meets or exceeds the performance of specialized algorithms tuned by domain experts.

Water vapor absorption in the clear atmosphere of a Neptune-sized exoplanet

http://www.nature.com/nature/journal/v513/n7519/full/nature13785.html

J. Fraine, D. Deming, B. Benneke, H. Knutson, A. Jordan, N. Espinoza, N. Madhusudhan, A. Wilkins & K. Todorov

Transmission spectroscopy has so far detected atomic and molecular absorption in Jupiter-sized exoplanets, but intense efforts to measure molecular absorption in the atmospheres of smaller (Neptune-sized) planets during transits have revealed only featureless spectra1, 2, 3, 4. From this it was concluded that the majority of small, warm planets evolve to sustain atmospheres with high mean molecular weights (little hydrogen), opaque clouds or scattering hazes, reducing our ability to observe the composition of these atmospheres1, 2, 3, 4, 5. Here we report observations of the transmission spectrum of the exoplanet HAT-P-11b (which has a radius about four times that of Earth) from the optical wavelength range to the infrared. We detected water vapour absorption at a wavelength of 1.4 micrometres. The amplitude of the water absorption (approximately 250 parts per million) indicates that the planetary atmosphere is predominantly clear down to an altitude corresponding to about 1 millibar, and sufficiently rich in hydrogen to have a large scale height (over which the atmospheric pressure varies by a factor of e). The spectrum is indicative of a planetary atmosphere in which the abundance of heavy elements is no greater than about 700 times the solar value. This is in good agreement with the core-accretion theory of planet formation, in which a gas giant planet acquires its atmosphere by accreting hydrogen-rich gas directly from the protoplanetary nebula onto a large rocky or icy core6.

Use “Dead Weight” on Mars Spacecraft to Advance Science and Technology

NASA is looking for creative yet practical ideas to find a dual purpose for Balance mass (“dead weight”) that is jettisoned from Mars landers like the Mars Science Laboratory (MSL) to balance the spacecraft during entry and landing. Payloads replacing Balance mass should perform some type of scientific or technological function adding to our knowledge base while closely matching the volume and weight characteristics of the original Balance mass. Ideas are welcomed from all disciplines. This Challenge requires only a written proposal.

Cash awards up to $1 million.

AMS-02 Press Release on CR Electrons and Positrons

CERN press release including updated positron fraction results

http://press.web.cern.ch/sites/press.web.cern.ch/files/ams_new_results_-_18.09.2014.pdf

High Statistics Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–500 GeV with the Alpha Magnetic Spectrometer on the International Space Station

Phys. Rev. Lett. 113, 121101 – Published 18 September 2014
L. Accardo et al. (AMS Collaboration)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.121101

Electron and Positron Fluxes in Primary Cosmic Rays Measured with the Alpha Magnetic Spectrometer on the International Space Station

Phys. Rev. Lett. 113, 121102 – Published 18 September 2014
M. Aguilar et al. (AMS Collaboration)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.121102

Neutrinos from the primary proton–proton fusion process in the Sun

http://www.nature.com/nature/journal/v512/n7515/full/nature13702.html

Borexino Collaboration

In the core of the Sun, energy is released through sequences of nuclear reactions that convert hydrogen into helium. The primary reaction is thought to be the fusion of two protons with the emission of a low-energy neutrino. These so-called pp neutrinos constitute nearly the entirety of the solar neutrino flux, vastly outnumbering those emitted in the reactions that follow. Although solar neutrinos from secondary processes have been observed, proving the nuclear origin of the Sun’s energy and contributing to the discovery of neutrino oscillations, those from proton–proton fusion have hitherto eluded direct detection. Here we report spectral observations of pp neutrinos, demonstrating that about 99 per cent of the power of the Sun, 3.84 × 1033 ergs per second, is generated by the proton–proton fusion process.

Online networks and subjective well-being

http://arxiv.org/abs/1408.3550

A chemical signature of first-generation very massive stars

http://www.sciencemag.org/content/345/6199/912.full

by W. Aoki, N. Tominaga, T. C. Beers, S. Honda, Y. S. Lee

Numerical simulations of structure formation in the early universe predict the formation of some fraction of stars with several hundred solar masses. No clear evidence of supernovae from such very massive stars has, however, yet been found in the chemical compositions of Milky Way stars. We report on an analysis of a very metal-poor star SDSS J001820.5–093939.2, which possesses elemental-abundance ratios that differ significantly from any previously known star. This star exhibits low [α-element Fe] ratios and large contrasts between the abundances of odd and even element pairs, such as scandium/titanium and cobalt/nickel. Such features have been predicted by nucleosynthesis models for supernovae of stars more than 140 times as massive as the Sun, suggesting that the mass distribution of first-generation stars might extend to 100 solar masses or larger.

 

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