Small Star Research Articles

Connected size Ramsey number for matchings vs. small stars or cycles

The notation $$F\rightarrow (G,H)$$ means that if the edges of F are colored red and blue, then the red subgraph contains a copy of G or the blue subgraph contains a copy of H. The connected size Ramsey number $$\hat{r}_c(G,H)$$ of graphs G and H is the minimum size of a connected graph F satisfying $$F\rightarrow (G,H)$$ . For $$m \ge 2,$$ the graph consisting of m independent edges is called a matching and is denoted by $$mK_2$$ . In 1981, Erdos and Faudree determined the size Ramsey numbers for the pair $$(mK_2, K_{1,t})$$ . They showed that the disconnected graph $$mK_{1,t} \rightarrow (mK_2,K_{1,t})$$ for $$ t,m \ge 1$$ . In this paper, we will determine the connected size Ramsey number $$\hat{r}_c(nK_2, K_{1,3})$$ for $$n\ge 2$$ and $$\hat{r}_c(3K_2, C_4)$$ . We also derive an upper bound of the connected size Ramsey number $$\hat{r}_c(nK_2, C_4),$$ for $$n\ge 4$$ .

The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta

Abstract We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational-wave (GW) source, the binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 and 9.5 days post-merger, using the Southern Astrophysical Research and Magellan telescopes; the UV spectrum was obtained with the Hubble Space Telescope at 5.5 days. Our data reveal a rapidly fading blue component ( T ≈ 5500 K at 1.5 days) that quickly reddens; spectra later than ≳ 4.5 days peak beyond the optical regime. The spectra are mostly featureless, although we identify a possible weak emission line at ∼7900 Å at t ≲ 4.5 days. The colors, rapid evolution, and featureless spectrum are consistent with a “blue” kilonova from polar ejecta comprised mainly of light r-process nuclei with atomic mass number A ≲ 140 . This indicates a sightline within θ obs ≲ 45 ° of the orbital axis. Comparison to models suggests ∼0.03 M ⊙ of blue ejecta, with a velocity of ∼ 0.3 c . The required lanthanide fraction is ∼ 10 − 4 , but this drops to < 10 − 5 in the outermost ejecta. The large velocities point to a dynamical origin, rather than a disk wind, for this blue component, suggesting that both binary constituents are neutron stars (as opposed to a binary consisting of a neutron star and a black hole). For dynamical ejecta, the high mass favors a small neutron star radius of ≲ 12 km. This mass also supports the idea that neutron star mergers are a major contributor to r-process nucleosynthesis.

Three Statistically Validated K2 Transiting Warm Jupiter Exoplanets Confirmed as Low-mass Stars

Abstract We have identified three K2 transiting star–planet systems, K2-51 (EPIC 202900527), K2-67 (EPIC 206155547), and K2-76 (EPIC 206432863), as stellar binaries with low-mass stellar secondaries. The three systems were statistically validated as transiting planets, and through measuring their orbits by radial velocity (RV) monitoring we have derived the companion masses to be (EPIC 202900527 B), (EPIC 206155547 B), and 0.0942 ± 0.0019 (EPIC 206432863 B). Therefore, they are not planets but small stars, part of the small sample of low-mass stars with measured radius and mass. The three systems are at an orbital period range of 12–24 days, and the secondaries have a radius within 0.9–1.9 , not inconsistent with the properties of warm Jupiter planets. These systems illustrate some of the existing challenges in the statistical validation approach. We point out a few possible origins for the initial misclassification of these objects, including poor characterization of the host star, the difficulty in detecting a secondary eclipse in systems on an eccentric orbit, and the difficulty in distinguishing between the smallest stars and gas giant planets as the two populations have indistinguishable radius distributions. Our work emphasizes the need for obtaining medium-precision RV measurements to distinguish between companions that are small stars, brown dwarfs, and gas giant planets.

Beating bands in substellar atmospheres

Brown Dwarfs Brown dwarfs are objects with masses that are between those of large planets and small stars. They share many features with gas giant planets, particularly conditions in their atmospheres. Apai et al. analyzed how the infrared brightness of three brown dwarfs changes over time. Several perplexing features can be explained if bands of clouds rotating within their atmospheres generate beat patterns. Such bands are seen in optical images of Jupiter but best match infrared images of Neptune. The results shed light on the atmospheric physics of brown dwarfs and gas giant planets around the Sun and other stars. Science , this issue p. [683][1] [1]: /lookup/doi/10.1126/science.aam9848

IRTF/TEXES observations of the H ii regions H1 and H2 in the Galactic Centre

Abstract We present new [Ne ii] (12.8 μm) IRTF/TEXES observations of the Galactic Center H ii regions H1 and H2, which are at a projected distance of ∼11 pc from the centre of the Galaxy. The new observations allow us to map the radial velocity distributions of ionized gas. The high spectroscopic resolution (∼4 km s−1) helps us to disentangle different velocity components and enables us to resolve previous ambiguity regarding the nature of these sources. The spatial distributions of the intensity and radial velocity of the [Ne ii] line are mapped. In H1, the intensity distributions of the Paschen-α (1.87 μm) and [Ne ii] lines are significantly different, which suggests a strong variation of extinction across the H ii region of AK ∼ 0.56. The radial velocity distributions across these H ii regions are consistent with the predictions of a bow-shock model for H1 and the pressure-driven model for H2. Furthermore, we find a concentration of bright stars in H2. These stars have similar H − Ks colours and can be explained as part of a 2-Myr-old stellar cluster. H2 also falls on the orbit of the molecular clouds, suggested to be around Sgr A*. Our new results confirm what we had previously suggested: The O supergiant P114 in H1 is a runaway star, moving towards us through the −30 to 0 km s−1 molecular cloud, whereas the O If star P35 in H2 formed in situ, and may mark the position of a so-far unknown small star cluster formed within the central 30 pc of the Galaxy.

Why do we find ourselves around a yellow star instead of a red star?

AbstractM-dwarf stars are more abundant than G-dwarf stars, so our position as observers on a planet orbiting a G-dwarf raises questions about the suitability of other stellar types for supporting life. If we consider ourselves as typical, in the anthropic sense that our environment is probably a typical one for conscious observers, then we are led to the conclusion that planets orbiting in the habitable zone of G-dwarf stars should be the best place for conscious life to develop. But such a conclusion neglects the possibility that K-dwarfs or M-dwarfs could provide more numerous sites for life to develop, both now and in the future. In this paper we analyse this problem through Bayesian inference to demonstrate that our occurrence around a G-dwarf might be a slight statistical anomaly, but only the sort of chance event that we expect to occur regularly. Even if M-dwarfs provide more numerous habitable planets today and in the future, we still expect mid G- to early K-dwarfs stars to be the most likely place for observers like ourselves. This suggests that observers with similar cognitive capabilities as us are most likely to be found at the present time and place, rather than in the future or around much smaller stars.

Outbursts of the intermediate-mass black hole HLX-1: a wind-instability scenario

We model the intermediate-mass black hole HLX-1, using the Hubble Space Telescope, XMM-Newton and Swift. We quantify the relative contributions of a bluer component, function of X-ray irradiation, and a redder component, constant and likely coming from an old stellar population. We estimate a black hole mass of about (2^{+2}_{-1}) x 10^4 M_{sun}, a spin parameter a/M ~ 0.9 for moderately face-on view, and a peak outburst luminosity of about 0.3 times the Eddington luminosity. We discuss the discrepancy between the characteristic sizes inferred from the short X-ray timescale (R ~ a few 10^{11} cm) and from the optical emitter (R sqrt[cos theta] ~ 2.2 x 10^{13} cm). One possibility is that the optical emitter is a circumbinary disk; however, we disfavour this scenario because it would require a very small donor star. A more plausible scenario is that the disk is large but only the inner annuli are involved in the X-ray outburst. We propose that the recurrent outbursts are caused by an accretion-rate oscillation driven by wind instability in the inner disk. We argue that the system has a long-term-average accretion rate of a few percent Eddington, just below the upper limit of the low/hard state; a wind-driven oscillation can trigger transitions to the high/soft state, with a recurrence period of ~1 year (much longer than the binary period, which we estimate as ~10 days). The oscillation that dominated the system in the last decade is now damped such that the accretion rate no longer reaches the level required to trigger a transition. Finally, we highlight similarities between disk winds in HLX-1 and in the Galactic black hole V404 Cyg.

The WAGGS project – I. The WiFeS Atlas of Galactic Globular cluster Spectra

We present the WiFeS Atlas of Galactic Globular cluster Spectra, a library of integrated spectra of Milky Way and Local Group globular clusters. We used the WiFeS integral field spectrograph on the Australian National University 2.3 m telescope to observe the central regions of 64 Milky Way globular clusters and 22 globular clusters hosted by the Milky Way's low mass satellite galaxies. The spectra have wider wavelength coverage (3300 {\AA} to 9050 {\AA}) and higher spectral resolution (R = 6800) than existing spectral libraries of Milky Way globular clusters. By including Large and Small Magellanic Cloud star clusters, we extend the coverage of parameter space of existing libraries towards young and intermediate ages. While testing stellar population synthesis models and analysis techniques is the main aim of this library, the observations may also further our understanding of the stellar populations of Local Group globular clusters and make possible the direct comparison of extragalactic globular cluster integrated light observations with well understood globular clusters in the Milky Way. The integrated spectra are publicly available via the project website.

Star Masses and Star-Planet Distances for Earth-like Habitability.

This paper presents statistical estimates for the location and duration of habitable zones (HZs) around stars of different mass. The approach is based upon the assumption that Earth's location, and the Sun's mass, should not be highly atypical of inhabited planets. The results support climate-model-based estimates for the location of the Sun's HZ except models giving a present-day outer-edge beyond 1.64 AU. The statistical approach also demonstrates that there is a habitability issue for stars smaller than 0.65 solar masses since, otherwise, Earth would be an extremely atypical inhabited world. It is difficult to remove this anomaly using the assumption that poor habitability of planets orbiting low-mass stars results from unfavorable radiation regimes either before, or after, their stars enter the main sequence. However, the anomaly is well explained if poor habitability results from tidal locking of planets in the HZs of small stars. The expected host-star mass for planets with intelligent life then has a 95% confidence range of 0.78 M⊙ < M < 1.04 M⊙, and the range for planets with at least simple life is 0.57 M⊙ < M < 1.64 M⊙. Key Words: Habitability—Habitable zone—Anthropic—Red dwarfs—Initial mass function. Astrobiology 17, 61–77.

From America and Other Poems

from America and Other Poems Ayukawa Nobuo (bio) Translated by Leza Lowitz (bio) and Shogo Oketani (bio) lonely double Somewhere in the distance,the evening sun has been extinguished—more darkness than I can bear.It weighs down my armslike your body. Turn off the light, you said.I try to cover your mouth with my hand,but its blackness scares me.Your body, more than I can hold,weighs down my chest. It's the midnight of the world.Under the moonlight that streams in from the window,you close your eyes tightly, pretending to be dead.In sleep, where I'm not with you,you murmur a secret: I'm alone, I'm alone…where I amble about a roomwearing a single slipper… (Is my heart that generous?) Turn on the light, you said.But I just sit quietly,a vast loneliness before me.If only I were the morning star,if only I had the clear eyes of a martyr. Just as I don't believe in you, you don't,even try to believe in me.We just happen to look at each other's pale faces [End Page 69] wearing innocent smilesthat have been theresince long before we were born. (1950) a story about heaven He stood with hunched shouldersunder the freezing November night sky.On an empty platformwhere only a few human forms were visibleone pale girl said to another:I heard there used to be a place somewhere,a radiant place called heaven. One small star shonein the frozen November night sky.Like this girl, he had somewheredark and cold to return to. I heard that there used to be a beautiful garden…The girl's memory seemed to stopbut continued on again as if passingthrough a small town.The neon signs were extinguishedfrom the freezing November night sky.The thin knife blade of a cold windblew, cutting the city's rough skin. At twelve-ten, the eyes of the clock's handsstared into the heart's darkness—There's the stiff face of a woman whowaits for him, staring into cold soup,there's the stiff bed made of cheap wood. I heard a man called God used to live there.No one knows what happened next…Her words broke off completely.Two girls, afraid of unseen happiness,held the shadows of their wings togetherunder the frozen November night sky.The tracks echo where the last train passes through,reverberating forever in that far-off country.(1953) [End Page 70] soldiers of god It's easier to revive a dead soldierthan to encounterthe Resurrection of Christin a gold-rimmed book.Countless soldiers died any number of timesand came back to life any number of times. (As long as sacred words and mysterious rewards never to be given continue to exist…) Soldiers who die any number of times,and come back to life any number of timeswill line up for a few centurieson continents and oceansas they always have. (Rewards never given are an infinite essence.) One night, in May 1944,I was with a soldier as he died.He lay in a wooden bunk,enduring a high fever,clinging to life. Memory's pale fire engulfed him,as he wept endlessly for his mother, sister, and lover.The border between us couldn't be crossed.I could see death crouching intentlybehind the dimness of an ever-lit lamp. Cursing the war, he left this world.In a room on a hospital ship,crossing the East China Sea at night,he left forever,refusing any reward from God. (Oh, humanity! This beautiful soldier will never come back to life!) [End Page 71] Somewhere in a far-off country,his noble death is shut insidea gold-rimmed book.On it are laid the quiet voice of prayerand a kind woman's hands (1953) dreaming of the mountain These mountains of my homelandare the beginning and end of nature—they are the only place I can return.My father was born in a mountain village,my mother was...

A star passing close to the solar system.

Stellar Astrometry![Figure][1] Many new comets could be produced by the passage of the small star Gliese 710 through the Oort Cloud. PHOTO: WILLIAM ATTARD MCCARTHY/ALAMY STOCK PHOTO The Gaia astrometry satellite has greatly improved measurements of the position and motion of nearby stars. Berski and Dybczynski searched the Gaia data for the star that will pass closest to the Sun. They found that Gliese 710, a small faint star, will pass within 13,000 ± 6,000 astronomical units (one astronomical unit is roughly the distance from Earth to the Sun). That will be well within the Oort Cloud, a collection of small bodies on the outskirts of our solar system. Some of those bodies will be knocked inward, generating large numbers of new comets. Earth is safe for now, though; the encounter will happen in 1.3 million years. Astron. Astrophys. 595 , L10 (2016). [1]: pending:yes

THE TRIPLE SYSTEM ZETA AQUARII*

ABSTRACT Zeta Aquarii is a bright and nearby (28 pc) triple star with a 26-year astrometric subsystem. Almost one-half of the outer 540-year visual orbit has been covered in 238 years of its observations. Both inner and outer orbits are revised here taking into account recent direct resolution of the inner pair Aa,Ab. The inner orbit has a high eccentricity of 0.87 and is inclined to the outer orbit by 140° ± 10°, suggesting that Kozai–Lidov cycles take place. The masses of the stars Aa, B, and Ab are 1.4, 1.4, and 0.6 solar. The age of the system is about 3 Gyr, and the two main components have just left the main sequence. Hypothetically, this system could have formed by a dynamical capture of the small star Ab in the twin binary Aa,B.

Astronomy: Small stars host water worlds.

Astronomy: Small stars host water worlds.

Constraints on CEMP-no progenitors from nuclear astrophysics

The CEMP-no stars are long-lived small mass stars presenting a very low iron content and overabundances of carbon with no sign or only very weak signs for the presence of s- or r-elements. Although the origin of that abundance pattern is still a matter of debate, it was very likely inherited from a previous massive star, that we shall call here the source star. We rely on a recent classification of CEMP-no stars arguing that some of them are made of a material processed by hydrogen burning that was enriched in products of helium burning during the nuclear life of the source star. We examine the possibility of forming CEMP-no stars with this material. We study the nucleosynthesis of the CNO cycle and the Ne-Na Mg-Al chains in a hydrogen burning single zone while injecting the helium burning products $^{12}$C, $^{16}$O, $^{22}$Ne and $^{26}$Mg. We investigate the impact of changing the density and temperature, as well as the injection rate. The nuclear reaction rates involving the creation and destruction of $^{27}$Al are also examined. $^{14}$N, $^{23}$Na, $^{24}$Mg and $^{27}$Al are formed when injecting $^{12}$C, $^{16}$O, $^{22}$Ne and $^{26}$Mg in the hydrogen burning zone. The $^{12}$C/$^{13}$C ratio is constant under various conditions in the hydrogen burning zone. The predicted [Al/Fe] ratio varies up to $\sim 2$ dex depending on the prescription used for the reaction rates involving $^{27}$Al. The experiments we carried out support the view that some CEMP-no stars are made of a material processed by hydrogen burning, coming from a massive star experiencing mild-to-strong rotational mixing. During its burning, this material was likely enriched in helium burning products. No material coming from the carbon-oxygen rich core of the source star should be added to form the daughter star, otherwise the $^{12}$C/$^{13}$C ratio would be largely above the observed range of values.

A New Approach for Small Satellite Gyroscope and Star Tracker Fusion

This paper discusses the use of hybridization of measurements from different sensors (namely the gyroscope and star tracker) in order to estimate the attitude of a satellite. In this study, an adaptive fuzzy logic algorithm is developed in order to add robustness to the existing extended Kalman-filtering method of sensor fusion. Models of the sensor are developed and a simulation is programmed in Matlab in order to examine the effectiveness of the new algorithm. Results from the simulations show that the fuzzy logic algorithm allows for better pointing accuracy during the period of Star tracker unavailability. This method used the EKF filter effectively and optimally when the system parameters and noises are known. However in practice some of these parameters are uncertain, leading to the ineffectiveness when applied to system with high accuracy requirements or complex system. In order to overcome this constraint, fuzzy algorithm can be used to evaluate the reliability of the each component then estimate the appropriate tuning parameters. This approach will facilitate small satellite attitude fault-tolerance estimator.

Large star swallowing smaller star demonstrates Darwin instability

Large star swallowing smaller star demonstrates Darwin instability

Nearby small star has three planets in its habitable region

Nearby small star has three planets in its habitable region

TWO SMALL TEMPERATE PLANETS TRANSITING NEARBY M DWARFS IN K2 CAMPAIGNS 0 AND 1* † ‡

ABSTRACT The prime Kepler mission revealed that small planets (&lt;4 R &oplus; ?> ) are common, especially around low-mass M dwarfs. K2, the repurposed Kepler mission, continues this exploration of small planets around small stars. Here we combine K2 photometry with spectroscopy, adaptive optics imaging, and archival survey images to analyze two small planets orbiting the nearby field-age M dwarfs, K2-26 (EPIC 202083828) and K2-9. K2-26 is an M 1.0 &PlusMinus; 0.5 ?> dwarf at 93 ± 7 pc from K2 Campaign 0. We validate its planet with a day period of 14.5665 and estimate a radius of 2.67 &minus; 0.42 &plus; 0.46 R &oplus; ?> . K2-9 is an M 2.5 &PlusMinus; 0.5 ?> dwarf at 110 ± 12 pc from K2 Campaign 1. K2-9b was first identified by Montet et al.; here we present spectra and adaptive optics imaging of the host star and independently validate and characterize the planet. Our analyses indicate K2-9b is a 2.25 &minus; 0.96 &plus; 0.53 R &oplus; ?> planet with a 18.4498 day period. K2-26b exhibits a transit duration that is too long to be consistent with a circular orbit given its measured stellar radius. Thus, the long transits are likely due to the photoeccentric effect and our transit fits hint at an eccentric orbit. Both planets receive low incident flux from their host stars and have estimated equilibrium temperatures &lt;500 K. K2-9b may receive approximately Earth-like insolation. However, its host star exhibits strong GALEX UV emission which could affect any atmosphere it harbors. K2-26b and K2-9b are representatives of a poorly studied class of small planets with cool temperatures that have radii intermediate to Earth and Neptune. Future study of these systems can provide key insight into trends in bulk composition and atmospheric properties at the transition from silicate dominated to volatile rich bodies.

Relativistic simulations of eccentric binary neutron star mergers: One-arm spiral instability and effects of neutron star spin

We perform general-relativistic hydrodynamical simulations of dynamical capture binary neutron star mergers, emphasizing the role played by the neutron star spin. Dynamical capture mergers may take place in globular clusters, as well as other dense stellar systems, where most neutron stars have large spins. We find significant variability in the merger outcome as a function of initial neutron star spin. For cases where the spin is aligned with the orbital angular momentum, the additional centrifugal support in the remnant hypermassive neutron star can prevent the prompt collapse to a black hole, while for antialigned cases the decreased total angular momentum can facilitate the collapse to a black hole. We show that even moderate spins can significantly increase the amount of ejected material, including the amount unbound with velocities greater than half the speed of light, leading to brighter electromagnetic signatures associated with kilonovae and interaction of the ejecta with the interstellar medium. Furthermore, we find that the initial neutron star spin can strongly affect the already rich phenomenology in the postmerger gravitational wave signatures that arise from the oscillation modes of the hypermassive neutron star. In several of our simulations, the resulting hypermassive neutron star develops the one-arm ($m=1$) spiral instability, the most pronounced cases being those with small but non-negligible neutron star spins. For long-lived hypermassive neutron stars, the presence of this instability leads to improved prospects for detecting these events through gravitational waves, and thus may give information about the neutron star equation of state.

I love shiny things!

Shining silver stars Ask parents to take their children outside on a starry night and talk about what they see. Follow, by showing photographic images of stars from the internet, before providing children with dark blue paper and white or silver paint, for them to create their own ‘Shiny, starry night’. When the paint is dry provide children with small silver sticky stars to place onto their paintings.