Modelling the Surface Distribution of Magnetic Activity on Sun-Like Stars

NASA Astrophysics Data System (ADS)

Isik, Emre

2018-04-01

With the advent of high-precision space-borne stellar photometry and prospects for direct imaging, it is timely and essential to improve our understanding of stellar magnetic activity in rotational time scales. We present models for 'younger suns' with rotation and flux emergence rates between 1 and 16 times the solar rate. The models provide latitudinal distributions and tilt angles of bipolar magnetic regions, using flux tube rise simulations. Using these emergence patterns, we model the subsequent surface flux transport, to predict surface distributions of star-spots. Based on these models, we present preliminary results from our further modelling of the observed azimuthal magnetic fields, which strengthen for more rapidly rotating Sun-like stars.

Limits on radial differential rotation in Sun-like stars from parametric fits to oscillation power spectra

NASA Astrophysics Data System (ADS)

Nielsen, M. B.; Schunker, H.; Gizon, L.; Schou, J.; Ball, W. H.

2017-06-01

Context. Rotational shear in Sun-like stars is thought to be an important ingredient in models of stellar dynamos. Thanks to helioseismology, rotation in the Sun is characterized well, but the interior rotation profiles of other Sun-like stars are not so well constrained. Until recently, measurements of rotation in Sun-like stars have focused on the mean rotation, but little progress has been made on measuring or even placing limits on differential rotation. Aims: Using asteroseismic measurements of rotation we aim to constrain the radial shear in five Sun-like stars observed by the NASA Kepler mission: KIC 004914923, KIC 005184732, KIC 006116048, KIC 006933899, and KIC 010963065. Methods: We used stellar structure models for these five stars from previous works. These models provide the mass density, mode eigenfunctions, and the convection zone depth, which we used to compute the sensitivity kernels for the rotational frequency splitting of the modes. We used these kernels as weights in a parametric model of the stellar rotation profile of each star, where we allowed different rotation rates for the radiative interior and the convective envelope. This parametric model was incorporated into a fit to the oscillation power spectrum of each of the five Kepler stars. This fit included a prior on the rotation of the envelope, estimated from the rotation of surface magnetic activity measured from the photometric variability. Results: The asteroseismic measurements without the application of priors are unable to place meaningful limits on the radial shear. Using a prior on the envelope rotation enables us to constrain the interior rotation rate and thus the radial shear. In the five cases that we studied, the interior rotation rate does not differ from the envelope by more than approximately ± 30%. Uncertainties in the rotational splittings are too large to unambiguously determine the sign of the radial shear.

Astronomers Image Lowest-mass Exoplanet Around a Sun-like Star

NASA Image and Video Library

2017-12-08

Caption: Glowing a dark magenta, the newly discovered exoplanet GJ 504b weighs in with about four times Jupiter's mass, making it the lowest-mass planet ever directly imaged around a star like the sun. Credit: NASA/Goddard/S. Wiessinger Using infrared data from the Subaru Telescope in Hawaii, an international team of astronomers has imaged a giant planet around the bright star GJ 504. Several times the mass of Jupiter and similar in size, the new world, dubbed GJ 504b, is the lowest-mass planet ever detected around a star like the sun using direct imaging techniques. "If we could travel to this giant planet, we would see a world still glowing from the heat of its formation with a color reminiscent of a dark cherry blossom, a dull magenta," said Michael McElwain, a member of the discovery team at NASA's Goddard Space Flight Center in Greenbelt, Md. "Our near-infrared camera reveals that its color is much more blue than other imaged planets, which may indicate that its atmosphere has fewer clouds." Read more: 1.usa.gov/15Ba6fI NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Soaking up the Rays of a Sun-like Star Artist Concept

NASA Image and Video Library

2015-07-23

This artist's concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun. The habitable zone is a region around a star where temperatures are right for water -- an essential ingredient for life as we know it -- to pool on the surface. Scientists do not know if Kepler-452b can support life or not. What is known about the planet is that it is about 60 percent larger than Earth, placing it in a class of planets dubbed "super-Earths." While its mass and composition are not yet determined, previous research suggests that planets the size of Kepler-452b have a better than even chance of being rocky. Kepler-452b orbits its star every 385 days. The planet's star is about 1,400 light-years away in the constellation Cygnus. It is a G2-type star like our sun, with nearly the same temperature and mass. This star is 6 billion years old, 1.5 billion years older than our sun. As stars age, they grow in size and give out more energy, warming up their planets over time. Scientists and artists considered these facts when creating this illustration. If the planet Kepler-452b does in fact have liquid on its surface and has grown warmer due to the older age of its star, it could possibly be experiencing a runaway greenhouse effect, where oceans would begin to evaporate and contribute to increased cloud cover. This, plus other factors such as the planet's large size, was factored into the hypothetical scenario depicted in this illustration. http://photojournal.jpl.nasa.gov/catalog/PIA19824

VUV Spectroscopy of the Sun as a Star

NASA Astrophysics Data System (ADS)

Kankelborg, Charles; Philip, Judge; Winebarger, Amy R.; Kobayashi, Ken; Smart, Roy

2017-08-01

We describe a new sounding rocket mission to obtain the first high resolution, high quality VUV (100-200 nm) spectrum of the Sun-as-a-star. Our immediate science goal is to understand better the processes of chromospheric and coronal heating. HST data exist for a dozen or so Sun-like stars of a quality already beyond our ability to construct a comparable sun-as-a-star UV spectrum. The solar spectrum we obtain will enable us to understand the nature of magnetic energy dissipation as a Sun-like star evolves, and the dependence of magnetic activity on stellar mass and metallicity. This poster presents the instrument design, scientific prospects, and broader impacts of the proposed mission.

Convective penetration in a young sun

NASA Astrophysics Data System (ADS)

Pratt, Jane; Baraffe, Isabelle; Goffrey, Tom; MUSIC developers group

2018-01-01

To interpret the high-quality data produced from recent space-missions it is necessary to study convection under realistic stellar conditions. We describe the multi-dimensional, time implicit, fully compressible, hydrodynamic, implicit large eddy simulation code MUSIC. We use MUSIC to study convection during an early stage in the evolution of our sun where the convection zone covers approximately half of the solar radius. This model of the young sun possesses a realistic stratification in density, temperature, and luminosity. We approach convection in a stellar context using extreme value theory and derive a new model for convective penetration, targeted for one-dimensional stellar evolution calculations. This model provides a scenario that can explain the observed lithium abundance in the sun and in solar-like stars at a range of ages.

Analysis of the Herschel DEBRIS Sun-like star sample

NASA Astrophysics Data System (ADS)

Sibthorpe, B.; Kennedy, G. M.; Wyatt, M. C.; Lestrade, J.-F.; Greaves, J. S.; Matthews, B. C.; Duchêne, G.

2018-04-01

This paper presents a study of circumstellar debris around Sun-like stars using data from the Herschel DEBRIS Key Programme. DEBRIS is an unbiased survey comprising the nearest ˜90 stars of each spectral type A-M. Analysis of the 275 F-K stars shows that excess emission from a debris disc was detected around 47 stars, giving a detection rate of 17.1^{+2.6}_{-2.3} per cent, with lower rates for later spectral types. For each target a blackbody spectrum was fitted to the dust emission to determine its fractional luminosity and temperature. The derived underlying distribution of fractional luminosity versus blackbody radius in the population showed that most detected discs are concentrated at f ˜ 10-5 and at temperatures corresponding to blackbody radii 7-40 au, which scales to ˜40 au for realistic dust properties (similar to the current Kuiper belt). Two outlying populations are also evident; five stars have exceptionally bright emission ( f > 5 × 10-5), and one has unusually hot dust <4 au. The excess emission distributions at all wavelengths were fitted with a steady-state evolution model, showing that these are compatible with all stars being born with a narrow belt that then undergoes collisional grinding. However, the model cannot explain the hot dust systems - likely originating in transient events - and bright emission systems - arising potentially from atypically massive discs or recent stirring. The emission from the present-day Kuiper belt is predicted to be close to the median of the population, suggesting that half of stars have either depleted their Kuiper belts (similar to the Solar system) or had a lower planetesimal formation efficiency.

OBSERVATIONS OF INTENSITY FLUCTUATIONS ATTRIBUTED TO GRANULATION AND FACULAE ON SUN-LIKE STARS FROM THE KEPLER MISSION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karoff, C.; Campante, T. L.; Ballot, J.

2013-04-10

Sun-like stars show intensity fluctuations on a number of timescales due to various physical phenomena on their surfaces. These phenomena can convincingly be studied in the frequency spectra of these stars-while the strongest signatures usually originate from spots, granulation, and p-mode oscillations, it has also been suggested that the frequency spectrum of the Sun contains a signature of faculae. We have analyzed three stars observed for 13 months in short cadence (58.84 s sampling) by the Kepler mission. The frequency spectra of all three stars, as for the Sun, contain signatures that we can attribute to granulation, faculae, and p-modemore » oscillations. The temporal variability of the signatures attributed to granulation, faculae, and p-mode oscillations was analyzed and the analysis indicates a periodic variability in the granulation and faculae signatures-comparable to what is seen in the Sun.« less

Could Ultracool Dwarfs Have Sun-Like Activity?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-11-01

Solar-like stars exhibit magnetic cycles; our Sun, for instance, displays an 11-year period in its activity, manifesting as cyclic changes in radiation levels, the number of sunspots and flares, and ejection of solar material. Over the span of two activity cycles, the Suns magnetic field flips polarity and then returns to its original state.An artists illustration comparing the Sun to TRAPPIST-1, an ultracool dwarf star known to host several planets. [ESO]But what about the magnetic behavior of objects near the cooler end of the stellar main sequence do they exhibit similar activity cycles?Effects of a Convecting InteriorDwarf stars have made headlines in recent years due to their potential to harbor exoplanets. Because these cooler stars have lower flux levels compared to the Sun, their habitable zones lie much closer to the stars. The magnetic behavior of these stars is therefore important to understand: could ultracool dwarfs exhibit solar-like activity cycles that would affect planets with close orbits?The differences in internal structure between different mass stars. Ultracool dwarfs have fully convective interiors. [www.sun.org]Theres a major difference between ultracool dwarfs (stars of spectral type higher than M7 and brown dwarfs) and Sun-like stars: their internal structures. Sun-like stars have a convective envelope that surrounds a radiative core. The interiors of cool, low-mass objects, on the other hand, are fully convective.Based on theoretical studies of how magnetism is generated in stars, its thought that the fully convective interiors of ultracool dwarfs cant support large-scale magnetic field formation. This should prevent these stars from exhibiting activity cycles like the Sun. But recent radio observations of dwarf stars have led scientist Matthew Route (ITaP Research Computing, Purdue University) to question these models.A Reversing Field?During observations of the brown dwarf star J1047+21 in 20102011, radio flares were detected with

The faint young Sun paradox: an observational test of an alternative solar model

NASA Technical Reports Server (NTRS)

Gaidos, E. J.; Gudel, M.; Blake, G. A.

2000-01-01

We report the results of deep observations at radio (3.6 cm) wavelengths of the nearby solar-type star pi 01 Ursa Majoris with the Very Large Array (VLA) intended to test an alternative theory of solar luminosity evolution. The standard model predicts a solar luminosity only 75% of the present value and surface temperatures below freezing on Earth and Mars at 4 Ga, seemingly in conflict with geologic evidence for liquid water on these planets. An alternative model invokes a compensatory mass loss through a declining solar wind that results in a more consistent early luminosity. The free-free emission from an enhanced wind around nearby young Sun-like stars should be detectable at microwave frequencies. Our observations of pi 01 UMa, a 300 million year-old solar-mass star, place an upper limit on the mass loss rate of 4-5 x 10(-11) M(solar) yr-1. Total mass loss from such a star over 4 Gyr would be less than 6%. If this star is indeed an analog of the early Sun, it casts doubt on the alternative model as a solution to the faint young Sun paradox, particularly for Mars.

Young Star HD 141569

NASA Image and Video Library

2017-01-30

This image shows the dusty disk of planetary material surrounding the young star HD 141569, located 380 light-years away from Earth. It was taken using the vortex coronagraph on the W.M. Keck Observatory. The vortex suppressed light from the star in the center, revealing light from the innermost ring of planetary material around the star (blue). The disk around the star, made of olivine particles, extends from 23 to 70 astronomical units from the star. By comparison, Uranus is over 19 astronomical units from our sun, and Neptune about 30 astronomical units. One astronomical unit is the distance between Earth and our sun. http://photojournal.jpl.nasa.gov/catalog/PIA21090

About 30% of Sun-like Stars Have Kepler-like Planetary Systems: A Study of Their Intrinsic Architecture

NASA Astrophysics Data System (ADS)

Zhu, Wei; Petrovich, Cristobal; Wu, Yanqin; Dong, Subo; Xie, Jiwei

2018-06-01

We constrain the intrinsic architecture of Kepler planetary systems by modeling the observed multiplicities of the transiting planets (tranets) and their transit timing variations (TTVs). We robustly determine that the fraction of Sun-like stars with Kepler-like planets, η Kepler, is 30 ± 3%. Here, Kepler-like planets are planets that have radii R p ≳ R ⊕ and orbital periods P < 400 days. Our result thus significantly revises previous claims that more than 50% of Sun-like stars have such planets. Combined with the average number of Kepler planets per star (∼0.9), we obtain that on average each planetary system has 3.0 ± 0.3 planets within 400 days. We also find that the dispersion in orbital inclinations of planets within a given planetary system, σ i,k , is a steep function of its number of planets, k. This can be parameterized as {σ }i,k\\propto {k}α and we find that ‑4 < α < ‑2 at the 2σ level. Such a distribution well describes the observed multiplicities of both transits and TTVs with no excess of single-tranet systems. Therefore we do not find evidence supporting the so-called “Kepler dichotomy.” Together with a previous study on orbital eccentricities, we now have a consistent picture: the fewer planets in a system, the hotter it is dynamically. We discuss briefly possible scenarios that lead to such a trend. Despite our solar system not belonging to the Kepler club, it is interesting to notice that the solar system also has three planets within 400 days and that the inclination dispersion is similar to Kepler systems of the same multiplicity.

Young Stars with SALT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riedel, Adric R.; Alam, Munazza K.; Rice, Emily L.

We present a spectroscopic and kinematic analysis of 79 nearby M dwarfs in 77 systems. All of these dwarfs are low-proper-motion southern hemisphere objects and were identified in a nearby star survey with a demonstrated sensitivity to young stars. Using low-resolution optical spectroscopy from the Red Side Spectrograph on the South African Large Telescope, we have determined radial velocities, H-alpha, lithium 6708 Å, and potassium 7699 Å equivalent widths linked to age and activity, and spectral types for all of our targets. Combined with astrometric information from literature sources, we identify 44 young stars. Eighteen are previously known members ofmore » moving groups within 100 pc of the Sun. Twelve are new members, including one member of the TW Hydra moving group, one member of the 32 Orionis moving group, 9 members of Tucana-Horologium, one member of Argus, and two new members of AB Doradus. We also find 14 young star systems that are not members of any known groups. The remaining 33 star systems do not appear to be young. This appears to be evidence of a new population of nearby young stars not related to the known nearby young moving groups.« less

Occurrence and core-envelope structure of 1-4× Earth-size planets around Sun-like stars.

PubMed

Marcy, Geoffrey W; Weiss, Lauren M; Petigura, Erik A; Isaacson, Howard; Howard, Andrew W; Buchhave, Lars A

2014-09-02

Small planets, 1-4× the size of Earth, are extremely common around Sun-like stars, and surprisingly so, as they are missing in our solar system. Recent detections have yielded enough information about this class of exoplanets to begin characterizing their occurrence rates, orbits, masses, densities, and internal structures. The Kepler mission finds the smallest planets to be most common, as 26% of Sun-like stars have small, 1-2 R⊕ planets with orbital periods under 100 d, and 11% have 1-2 R⊕ planets that receive 1-4× the incident stellar flux that warms our Earth. These Earth-size planets are sprinkled uniformly with orbital distance (logarithmically) out to 0.4 the Earth-Sun distance, and probably beyond. Mass measurements for 33 transiting planets of 1-4 R⊕ show that the smallest of them, R < 1.5 R⊕, have the density expected for rocky planets. Their densities increase with increasing radius, likely caused by gravitational compression. Including solar system planets yields a relation: ρ = 2:32 + 3:19 R=R ⊕ [g cm(-3)]. Larger planets, in the radius range 1.5-4.0 R⊕, have densities that decline with increasing radius, revealing increasing amounts of low-density material (H and He or ices) in an envelope surrounding a rocky core, befitting the appellation ''mini-Neptunes.'' The gas giant planets occur preferentially around stars that are rich in heavy elements, while rocky planets occur around stars having a range of heavy element abundances. Defining habitable zones remains difficult, without benefit of either detections of life elsewhere or an understanding of life's biochemical origins.

Richest Planetary System Discovered - Up to seven planets orbiting a Sun-like star

NASA Astrophysics Data System (ADS)

2010-08-01

Astronomers using ESO's world-leading HARPS instrument have discovered a planetary system containing at least five planets, orbiting the Sun-like star HD 10180. The researchers also have tantalising evidence that two other planets may be present, one of which would have the lowest mass ever found. This would make the system similar to our Solar System in terms of the number of planets (seven as compared to the Solar System's eight planets). Furthermore, the team also found evidence that the distances of the planets from their star follow a regular pattern, as also seen in our Solar System. "We have found what is most likely the system with the most planets yet discovered," says Christophe Lovis, lead author of the paper reporting the result. "This remarkable discovery also highlights the fact that we are now entering a new era in exoplanet research: the study of complex planetary systems and not just of individual planets. Studies of planetary motions in the new system reveal complex gravitational interactions between the planets and give us insights into the long-term evolution of the system." The team of astronomers used the HARPS spectrograph, attached to ESO's 3.6-metre telescope at La Silla, Chile, for a six-year-long study of the Sun-like star HD 10180, located 127 light-years away in the southern constellation of Hydrus (the Male Water Snake). HARPS is an instrument with unrivalled measurement stability and great precision and is the world's most successful exoplanet hunter. Thanks to the 190 individual HARPS measurements, the astronomers detected the tiny back and forth motions of the star caused by the complex gravitational attractions from five or more planets. The five strongest signals correspond to planets with Neptune-like masses - between 13 and 25 Earth masses [1] - which orbit the star with periods ranging from about 6 to 600 days. These planets are located between 0.06 and 1.4 times the Earth-Sun distance from their central star. "We also have

A SUPER-EARTH-SIZED PLANET ORBITING IN OR NEAR THE HABITABLE ZONE AROUND A SUN-LIKE STAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barclay, Thomas; Burke, Christopher J.; Howell, Steve B.

We present the discovery of a super-Earth-sized planet in or near the habitable zone of a Sun-like star. The host is Kepler-69, a 13.7 mag G4V-type star. We detect two periodic sets of transit signals in the 3-year flux time series of Kepler-69, obtained with the Kepler spacecraft. Using the very high precision Kepler photometry, and follow-up observations, our confidence that these signals represent planetary transits is >99.3%. The inner planet, Kepler-69b, has a radius of 2.24{sup +0.44}{sub -0.29} R{sub Circled-Plus} and orbits the host star every 13.7 days. The outer planet, Kepler-69c, is a super-Earth-sized object with a radiusmore » of 1.7{sup +0.34}{sub -0.23} R{sub Circled-Plus} and an orbital period of 242.5 days. Assuming an Earth-like Bond albedo, Kepler-69c has an equilibrium temperature of 299 {+-} 19 K, which places the planet close to the habitable zone around the host star. This is the smallest planet found by Kepler to be orbiting in or near the habitable zone of a Sun-like star and represents an important step on the path to finding the first true Earth analog.« less

Brightness Variations of Sun-like Stars: The Mystery Deepens - Astronomers facing Socratic "ignorance"

NASA Astrophysics Data System (ADS)

2009-12-01

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. "Astronomers are left in the dark, and for once, we do not enjoy it," says Christine Nicholls from Mount Stromlo Observatory, Australia, lead author of a paper reporting the study. "We have obtained the most comprehensive set of observations to date for this class of Sun-like stars, and they clearly show that all the possible explanations for their unusual behaviour just fail." The mystery investigated by the team dates back to the 1930s and affects about a third of Sun-like stars in our Milky Way and other galaxies. All stars with masses similar to our Sun become, towards the end of their lives, red, cool and extremely large, just before retiring as white dwarfs. Also known as red giants, these elderly stars exhibit very strong periodic variations in their luminosity over timescales up to a couple of years. "Such variations are thought to be caused by what we call 'stellar pulsations'," says Nicholls. "Roughly speaking, the giant star swells and shrinks, becoming brighter and dimmer in a regular pattern. However, one third of these stars show an unexplained additional periodic variation, on even longer timescales - up to five years." In order to find out the origin of this secondary feature, the astronomers monitored 58 stars in our galactic neighbour, the Large Magellanic Cloud, over two and a half years. They acquired spectra using the high resolution FLAMES/GIRAFFE spectrograph on ESO's Very Large Telescope and combined them with images from other telescopes [1

Modelling the magnetic activity and filtering radial velocity curves of young Suns : the weak-line T Tauri star LkCa 4

NASA Astrophysics Data System (ADS)

Donati, J.-F.; Hébrard, E.; Hussain, G.; Moutou, C.; Grankin, K.; Boisse, I.; Morin, J.; Gregory, S. G.; Vidotto, A. A.; Bouvier, J.; Alencar, S. H. P.; Delfosse, X.; Doyon, R.; Takami, M.; Jardine, M. M.; Fares, R.; Cameron, A. C.; Ménard, F.; Dougados, C.; Herczeg, G.; Matysse Collaboration

2014-11-01

We report results of a spectropolarimetric and photometric monitoring of the weak-line T Tauri star LkCa 4 within the Magnetic Topologies of Young Stars and the Survival of close-in giant Exoplanets (MaTYSSE) programme, involving ESPaDOnS at the Canada-France-Hawaii Telescope. Despite an age of only 2 Myr and a similarity with prototypical classical T Tauri stars, LkCa 4 shows no evidence for accretion and probes an interesting transition stage for star and planet formation. Large profile distortions and Zeeman signatures are detected in the unpolarized and circularly polarized lines of LkCa 4 using Least-Squares Deconvolution (LSD), indicating the presence of brightness inhomogeneities and magnetic fields at the surface of LkCa 4. Using tomographic imaging, we reconstruct brightness and magnetic maps of LkCa 4 from sets of unpolarized and circularly polarized LSD profiles. The large-scale field is strong and mainly axisymmetric, featuring a ≃2 kG poloidal component and a ≃1 kG toroidal component encircling the star at equatorial latitudes - the latter making LkCa 4 markedly different from classical T Tauri stars of similar mass and age. The brightness map includes a dark spot overlapping the magnetic pole and a bright region at mid-latitudes - providing a good match to the contemporaneous photometry. We also find that differential rotation at the surface of LkCa 4 is small, typically ≃5.5 times weaker than that of the Sun, and compatible with solid-body rotation. Using our tomographic modelling, we are able to filter out the activity jitter in the radial velocity curve of LkCa 4 (of full amplitude 4.3 km s-1) down to an rms precision of 0.055 km s-1. Looking for hot Jupiters around young Sun-like stars thus appears feasible, even though we find no evidence for such planets around LkCa 4.

Our Sun Came Late to the Milky Way’s Star-Birth Party

NASA Image and Video Library

2015-04-09

Caption: Artist's view of night sky from a hypothetical planet within a young Milky Way-like galaxy 10 billion years ago, the sky are ablaze with star birth. Pink clouds of gas harbor newborn stars, and bluish-white, young star clusters litter the landscape. Image Credit: NASA/ESA/Z. Levay (STScI) More info: In one of the most comprehensive multi-observatory galaxy surveys yet, astronomers find that galaxies like our Milky Way underwent a stellar “baby boom,” churning out stars at a prodigious rate, about 30 times faster than today. Our sun, however, is a late “boomer.” The Milky Way’s star-birthing frenzy peaked 10 billion years ago, but our sun was late for the party, not forming until roughly 5 billion years ago. By that time the star formation rate in our galaxy had plunged to a trickle. Missing the party, however, may not have been so bad. The sun’s late appearance may actually have fostered the growth of our solar system’s planets. Elements heavier than hydrogen and helium were more abundant later in the star-forming boom as more massive stars ended their lives early and enriched the galaxy with material that served as the building blocks of planets and even life on Earth. Astronomers don’t have baby pictures of our Milky Way’s formative years to trace the history of stellar growth so they studied galaxies similar in mass to our Milky Way, found in deep surveys of the universe. The farther into the universe astronomers look, the further back in time they are seeing, because starlight from long ago is just arriving at Earth now. From those surveys, stretching back in time more than 10 billion years, researchers assembled an album of images containing nearly 2,000 snapshots of Milky Way-like galaxies. The new census provides the most complete picture yet of how galaxies like the Milky Way grew over the past 10 billion years into today’s majestic spiral galaxies. The multi-wavelength study spans ultraviolet to far-infrared light, combining

ASTRO-ENTOMOLOGY? ANT-LIKE SPACE STRUCTURE PREVIEWS DEATH OF OUR SUN

NASA Technical Reports Server (NTRS)

2002-01-01

From ground-based telescopes, the so-called 'ant nebula' (Menzel 3, or Mz 3) resembles the head and thorax of a garden-variety ant. This dramatic NASA/ESA Hubble Space Telescope image, showing 10 times more detail, reveals the 'ant's' body as a pair of fiery lobes protruding from a dying, Sun-like star. The Hubble images directly challenge old ideas about the last stages in the lives of stars. By observing Sun-like stars as they approach their deaths, the Hubble Heritage image of Mz 3 -- along with pictures of other planetary nebulae -- shows that our Sun's fate probably will be more interesting, complex, and striking than astronomers imagined just a few years ago. Though approaching the violence of an explosion, the ejection of gas from the dying star at the center of Mz 3 has intriguing symmetrical patterns unlike the chaotic patterns expected from an ordinary explosion. Scientists using Hubble would like to understand how a spherical star can produce such prominent, non-spherical symmetries in the gas that it ejects. One possibility is that the central star of Mz 3 has a closely orbiting companion that exerts strong gravitational tidal forces, which shape the outflowing gas. For this to work, the orbiting companion star would have to be close to the dying star, about the distance of the Earth from the Sun. At that distance the orbiting companion star wouldn't be far outside the hugely bloated hulk of the dying star. It's even possible that the dying star has consumed its companion, which now orbits inside of it, much like the duck in the wolf's belly in the story 'Peter and the Wolf.' (See http://oposite.stsci.edu/pubinfo/qt/ssudec.mov for an animation that shows how this might work.) A second possibility is that, as the dying star spins, its strong magnetic fields are wound up into complex shapes like spaghetti in an eggbeater. Charged winds moving at speeds up to 1000 kilometers per second from the star, much like those in our sun's solar wind but millions of

Occurrence and core-envelope structure of 1–4× Earth-size planets around Sun-like stars

PubMed Central

Marcy, Geoffrey W.; Weiss, Lauren M.; Petigura, Erik A.; Isaacson, Howard; Howard, Andrew W.; Buchhave, Lars A.

2014-01-01

Small planets, 1–4× the size of Earth, are extremely common around Sun-like stars, and surprisingly so, as they are missing in our solar system. Recent detections have yielded enough information about this class of exoplanets to begin characterizing their occurrence rates, orbits, masses, densities, and internal structures. The Kepler mission finds the smallest planets to be most common, as 26% of Sun-like stars have small, 1–2 R⊕ planets with orbital periods under 100 d, and 11% have 1–2 R⊕ planets that receive 1–4× the incident stellar flux that warms our Earth. These Earth-size planets are sprinkled uniformly with orbital distance (logarithmically) out to 0.4 the Earth–Sun distance, and probably beyond. Mass measurements for 33 transiting planets of 1–4 R⊕ show that the smallest of them, R < 1.5 R⊕, have the density expected for rocky planets. Their densities increase with increasing radius, likely caused by gravitational compression. Including solar system planets yields a relation: ρ=2.32+3.19R/R⊕ [g cm−3]. Larger planets, in the radius range 1.5–4.0 R⊕, have densities that decline with increasing radius, revealing increasing amounts of low-density material (H and He or ices) in an envelope surrounding a rocky core, befitting the appellation ‘‘mini-Neptunes.’’ The gas giant planets occur preferentially around stars that are rich in heavy elements, while rocky planets occur around stars having a range of heavy element abundances. Defining habitable zones remains difficult, without benefit of either detections of life elsewhere or an understanding of life’s biochemical origins. PMID:24912169

The transiting dust clumps in the evolved disc of the Sun-like UXor RZ Psc

PubMed Central

Kenworthy, Matthew A.; Pepper, Joshua; Rodriguez, Joseph E.; Siverd, Robert J.; Stassun, Keivan G.; Wyatt, Mark C.

2017-01-01

RZ Psc is a young Sun-like star, long associated with the UXor class of variable stars, which is partially or wholly dimmed by dust clumps several times each year. The system has a bright and variable infrared excess, which has been interpreted as evidence that the dimming events are the passage of asteroidal fragments in front of the host star. Here, we present a decade of optical photometry of RZ Psc and take a critical look at the asteroid belt interpretation. We show that the distribution of light curve gradients is non-uniform for deep events, which we interpret as possible evidence for an asteroidal fragment-like clump structure. However, the clumps are very likely seen above a high optical depth midplane, so the disc’s bulk clumpiness is not revealed. While circumstantial evidence suggests an asteroid belt is more plausible than a gas-rich transition disc, the evolutionary status remains uncertain. We suggest that the rarity of Sun-like stars showing disc-related variability may arise because (i) any accretion streams are transparent and/or (ii) turbulence above the inner rim is normally shadowed by a flared outer disc. PMID:28280566

The transiting dust clumps in the evolved disc of the Sun-like UXor RZ Psc

NASA Astrophysics Data System (ADS)

Kennedy, Grant M.; Kenworthy, Matthew A.; Pepper, Joshua; Rodriguez, Joseph E.; Siverd, Robert J.; Stassun, Keivan G.; Wyatt, Mark C.

2017-01-01

RZ Psc is a young Sun-like star, long associated with the UXor class of variable stars, which is partially or wholly dimmed by dust clumps several times each year. The system has a bright and variable infrared excess, which has been interpreted as evidence that the dimming events are the passage of asteroidal fragments in front of the host star. Here, we present a decade of optical photometry of RZ Psc and take a critical look at the asteroid belt interpretation. We show that the distribution of light curve gradients is non-uniform for deep events, which we interpret as possible evidence for an asteroidal fragment-like clump structure. However, the clumps are very likely seen above a high optical depth midplane, so the disc's bulk clumpiness is not revealed. While circumstantial evidence suggests an asteroid belt is more plausible than a gas-rich transition disc, the evolutionary status remains uncertain. We suggest that the rarity of Sun-like stars showing disc-related variability may arise because (i) any accretion streams are transparent and/or (ii) turbulence above the inner rim is normally shadowed by a flared outer disc.

The transiting dust clumps in the evolved disc of the Sun-like UXor RZ Psc.

PubMed

Kennedy, Grant M; Kenworthy, Matthew A; Pepper, Joshua; Rodriguez, Joseph E; Siverd, Robert J; Stassun, Keivan G; Wyatt, Mark C

2017-01-01

RZ Psc is a young Sun-like star, long associated with the UXor class of variable stars, which is partially or wholly dimmed by dust clumps several times each year. The system has a bright and variable infrared excess, which has been interpreted as evidence that the dimming events are the passage of asteroidal fragments in front of the host star. Here, we present a decade of optical photometry of RZ Psc and take a critical look at the asteroid belt interpretation. We show that the distribution of light curve gradients is non-uniform for deep events, which we interpret as possible evidence for an asteroidal fragment-like clump structure. However, the clumps are very likely seen above a high optical depth midplane, so the disc's bulk clumpiness is not revealed. While circumstantial evidence suggests an asteroid belt is more plausible than a gas-rich transition disc, the evolutionary status remains uncertain. We suggest that the rarity of Sun-like stars showing disc-related variability may arise because (i) any accretion streams are transparent and/or (ii) turbulence above the inner rim is normally shadowed by a flared outer disc.

All In The Family: Chandra Finds Evidence That Massive Stars Are More Like The Sun Than Previously Believed

NASA Astrophysics Data System (ADS)

2000-10-01

NASA's Chandra X-ray Observatory has found evidence that massive stars may be much more like the Sun than previously thought. Astronomers determined that magnetic loop structures, similar to those on the Sun, may exist on the surface of so-called O-type stars, some of the most luminous stars in the universe. "This result is quite surprising," says Wayne Waldron of Emergent Information Technologies, Inc., and co-author of a paper submitted to the Astrophysical Journal Letters. "This bucks conventional wisdom to find that these stars may really resemble our Sun." Zeta Orionis Press Image and Caption Using Chandra's High-Energy Transmission Grating Spectrometer (HETGS) in conjunction with a CCD X-ray camera, astronomers observed the star Zeta Orionis (one of the three belt stars in the constellation of Orion) and found strong X-ray line emission from ions of iron, oxygen, and other elements. The high-resolution X-ray spectrum enabled astronomers to determine that the X-ray emitting gas has a density 1000 times larger than predicted by current models, an amount comparable to the atmospheric density just above the surface of the star. For many years, solar astronomers have derived densities of X-ray producing plasmas on the Sun using emission lines of ions like helium, those with just two bound electrons remaining. Chandra allows this approach to be used for other stars and it has detected X-rays from silicon ions that have been stripped of 12 of their usual complement of 14 electrons. This ion is an especially useful diagnostic of plasma densities in the extremely ultraviolet-bright environment surrounding O-stars. Following the discovery of X-ray emission from O-class stars some 20 years ago, astronomers assumed that the X-rays were created in a hot corona near the star, similar to the Sun's corona. Those models were then abandoned in favor of the currently preferred explanation: the X-ray radiation is created by energetic shocks in the stellar winds (steady streams

ACTIVITY-BRIGHTNESS CORRELATIONS FOR THE SUN AND SUN-LIKE STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Preminger, D. G.; Chapman, G. A.; Cookson, A. M.

2011-10-01

We analyze the effect of solar features on the variability of the solar irradiance in three different spectral ranges. Our study is based on two solar-cycles' worth of full-disk photometric images from the San Fernando Observatory, obtained with red, blue, and Ca II K-line filters. For each image we measure the photometric sum, {Sigma}, which is the relative contribution of solar features to the disk-integrated intensity of the image. The photometric sums in the red and blue continuum, {Sigma}{sub r} and {Sigma}{sub b}, exhibit similar temporal patterns: they are negatively correlated with solar activity, with strong short-term variability, and weakmore » solar-cycle variability. However, the Ca II K-line photometric sum, {Sigma}{sub K}, is positively correlated with solar activity and has strong variations on solar-cycle timescales. We show that we can model the variability of the Sun's bolometric flux as a linear combination of {Sigma}{sub r} and {Sigma}{sub K}. We infer that, over solar-cycle timescales, the variability of the Sun's bolometric irradiance is directly correlated with spectral line variability, but inversely correlated with continuum variability. Our blue and red continuum filters are quite similar to the Stroemgren b and y filters used to measure stellar photometric variability. We conclude that active stars whose visible continuum brightness varies inversely with activity, as measured by the Ca HK index, are displaying a pattern that is similar to that of the Sun, i.e., radiative variability in the visible continuum that is spot-dominated.« less

An Introduction to the Sun and Stars

NASA Astrophysics Data System (ADS)

Green, Simon F.; Jones, Mark H.

2015-02-01

Introduction; 1. Seeing the Sun; 2. The working Sun; 3. Measuring stars; 4. Comparing stars; 5. The formation of stars; 6. The main sequence life of stars; 7. The life of stars beyond the main sequence; 8. The death of stars; 9. The remnants of stars; Conclusion; Answers and comments; Appendices; Glossary; Further reading; Acknowledgements; Figure references; Index.

Improved rotation-activity-age relations in Sun-like stars

NASA Astrophysics Data System (ADS)

Meléndez, Jorge; dos Santos, Leonardo A.; Freitas, Fabrício C.

2017-10-01

The evolution of rotational velocity and magnetic activity with age follows approximately a t -1/2 relation, the famous Skumanich law. Using a large sample of about 80 solar twins with precise ages, we show departures from this law. We found a steep drop in rotational velocity and activity in the first 2-3 Gyr and afterwards there seems to be a shallow decrease. Our inferred rotational periods suggest that the Sun will continue to slow down, validating thus the use of gyrochronology beyond solar age. The Sun displays normal rotational velocity and activity when compared to solar twins of solar age. We also show that stars with exceedingly high stellar activity for their age are spectroscopic binaries that also exhibit enhanced rotational velocities and chemical signatures of mass transfer.

Asteroseismology from multi-month Kepler photometry: the evolved Sun-like stars KIC 10273246 and KIC 10920273

NASA Astrophysics Data System (ADS)

Campante, T. L.; Handberg, R.; Mathur, S.; Appourchaux, T.; Bedding, T. R.; Chaplin, W. J.; García, R. A.; Mosser, B.; Benomar, O.; Bonanno, A.; Corsaro, E.; Fletcher, S. T.; Gaulme, P.; Hekker, S.; Karoff, C.; Régulo, C.; Salabert, D.; Verner, G. A.; White, T. R.; Houdek, G.; Brandão, I. M.; Creevey, O. L.; Doǧan, G.; Bazot, M.; Christensen-Dalsgaard, J.; Cunha, M. S.; Elsworth, Y.; Huber, D.; Kjeldsen, H.; Lundkvist, M.; Molenda-Żakowicz, J.; Monteiro, M. J. P. F. G.; Stello, D.; Clarke, B. D.; Girouard, F. R.; Hall, J. R.

2011-10-01

Context. The evolved main-sequence Sun-like stars KIC 10273246 (F-type) and KIC 10920273 (G-type) were observed with the NASA Kepler satellite for approximately ten months with a duty cycle in excess of 90%. Such continuous and long observations are unprecedented for solar-type stars other than the Sun. Aims: We aimed mainly at extracting estimates of p-mode frequencies - as well as of other individual mode parameters - from the power spectra of the light curves of both stars, thus providing scope for a full seismic characterization. Methods: The light curves were corrected for instrumental effects in a manner independent of the Kepler science pipeline. Estimation of individual mode parameters was based both on the maximization of the likelihood of a model describing the power spectrum and on a classic prewhitening method. Finally, we employed a procedure for selecting frequency lists to be used in stellar modeling. Results: A total of 30 and 21 modes of degree l = 0,1,2 - spanning at least eight radial orders - have been identified for KIC 10273246 and KIC 10920273, respectively. Two avoided crossings (l = 1 ridge) have been identified for KIC 10273246, whereas one avoided crossing plus another likely one have been identified for KIC 10920273. Good agreement is found between observed and predicted mode amplitudes for the F-type star KIC 10273246, based on a revised scaling relation. Estimates are given of the rotational periods, the parameters describing stellar granulation and the global asteroseismic parameters Δν and νmax.

Completing the census of young stars near the Sun with the FunnelWeb spectroscopic survey

NASA Astrophysics Data System (ADS)

Lawson, Warrick; Murphy, Simon; Tinney, Christopher G.; Ireland, Michael; Bessell, Michael S.

2016-06-01

From late 2016, the Australian FunnelWeb survey will obtain medium-resolution (R~2000) spectra covering the full optical range for 2 million of the brightest stars (I<12) in the southern sky. It will do so using an upgraded UK Schmidt Telescope at Siding Spring Observatory, equipped with a revolutionary, parallelizable optical fibre positioner ("Starbugs") and spectrograph. The ability to reconfigure a multi-fibre plate in less than 5 minutes allows FunnelWeb to observe more stars per night than any other competing multi-fibre spectrograph and enables a range of previously inefficient bright star science not attempted since the completion of the HD catalogues in the 1940s. Among its key science aims, FunnelWeb will obtain spectra for thousands of young and adolescent (<1 Gyr) stars near the Sun (<200 pc) across a wide range of spectral types. These spectra will include well-studied youth and activity indicators such as H-alpha, Li I 6708A, Ca II H&K, as well as surface gravity diagnostics (e.g. Na I, K I). In addition, FunnelWeb will obtain stellar parameters (Teff, logg, vsini), abundances (Fe/H, alpha/Fe) and radial velocities to 1-2 km/s for every star in the survey. When combined with high precision parallaxes and proper motions from the Gaia mission expected from 2017, this dataset will provide a near-complete census of adolescent stars in the solar neighbourhood. It will help reveal the typical formation environments of young solar-type stars, how such stars move from their stellar nurseries to their adult lives in the field, and identifying thousands of high-priority targets for follow-up direct imaging (GPI, SPHERE), transit (including TESS) and radial velocity exoplanet studies. In this poster contribution we introduce the FunnelWeb survey, its science goals and input catalogue, as well as provide an update on the status of the fibre positioner and spectrograph commissioning at Siding Spring.

Observing the Sun with NuSTAR

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-07-01

The Nuclear Spectroscopic Telescope Array (NuSTAR) is a space telescope primarily designed to detect high-energy X-rays from faint, distant astrophysical sources. Recently, however, its occasionally been pointing much closer to home, with the goal of solving a few longstanding mysteries about the Sun.Intensity maps from an observation of a quiet-Sun region near the north solar pole and an active region just below the solar limb. The quiet-Sun data will be searched for small flares that could be heating the solar corona, and the high-altitude emission above the limb may provide clues about particle acceleration. [Adapted from Grefenstette et al. 2016]An Unexpected TargetThough we have a small fleet of space telescopes designed to observe the Sun, theres an important gap: until recently, there was no focusing telescope making solar observations in the hard X-ray band (above ~3 keV). Conveniently, there is a tool capable of doing this: NuSTAR.Though NuSTARs primary mission is to observe faint astrophysical X-ray sources, a team of scientists has recently conducted a series of observations in which NuSTAR was temporarily repurposed and turned to focus on the Sun instead.These observations pose an interesting challenge precisely because of NuSTARs extreme sensitivity: pointing at such a nearby, bright source can quickly swamp the detectors. But though the instrument cant be used to observe the bright flares and outbursts from the Sun, its the perfect tool for examining the parts of the Sun weve been unable to explore in hard X-rays before now such as faint flares, or the quiet, inactive solar surface.In a recently published study led by Brian Grefenstette (California Institute of Technology), the team describes the purpose and initial results of NuSTARs first observations of the Sun.Solar MysteriesWhat is NuSTAR hoping to accomplish with its solar observations? There are two main questions that hard X-ray observations may help to answer.How are particles accelerated in

The Solar Twin Planet Search. IV. The Sun as a typical rotator and evidence for a new rotational braking law for Sun-like stars

NASA Astrophysics Data System (ADS)

dos Santos, Leonardo A.; Meléndez, Jorge; do Nascimento, José-Dias; Bedell, Megan; Ramírez, Iván; Bean, Jacob L.; Asplund, Martin; Spina, Lorenzo; Dreizler, Stefan; Alves-Brito, Alan; Casagrande, Luca

2016-08-01

Context. It is still unclear how common the Sun is when compared to other similar stars in regards to some of its physical properties, such as rotation. Considering that gyrochronology relations are widely used today to estimate ages of stars in the main sequence, and that the Sun is used to calibrate it, it is crucial to assess whether these procedures are acceptable. Aims: We analyze the rotational velocities, limited by the unknown rotation axis inclination angle, of an unprecedented large sample of solar twins to study the rotational evolution of Sun-like stars, and assess whether the Sun is a typical rotator. Methods: We used high-resolution (R = 115 000) spectra obtained with the HARPS spectrograph and the 3.6 m telescope at La Silla Observatory. The projected rotational velocities for 81 solar twins were estimated by line profile fitting with synthetic spectra. Macroturbulence velocities were inferred from a prescription that accurately reflects their dependence with effective temperature and luminosity of the stars. Results: Our sample of solar twins include some spectroscopic binaries with enhanced rotational velocities, and we do not find any nonspectroscopic binaries with unusually high rotation velocities. We verified that the Sun does not have a peculiar rotation, but the solar twins exhibit rotational velocities that depart from the Skumanich relation. Conclusions: The Sun is a regular rotator when compared to solar twins with a similar age. Additionally, we obtain a rotational braking law that better describes the stars in our sample (v ∝ t-0.6) in contrast to previous, often-used scalings. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programs 188.C-0265, 183.D-0729, 292.C-5004, 077.C-0364, 072.C-0488, 092.C-0721, 093.C-0409, 183.C-0972, 192.C-0852, 091.C-0936, 089.C-0732, 091.C-0034, 076.C-0155, 185.D-0056, 074.C-0364, 075.C-0332, 089.C-0415, 60.A-9036, 075.C-0202, 192

Young and Waltzing Binary Stars

NASA Astrophysics Data System (ADS)

2001-10-01

stars heat up enough to start nuclear burning. When infant stars in RXJ 0529.4+0041 eventually reach middle-age, their sizes will most likely also be quite similar to that of the Sun. The significance of RXJ 0529.4+0041 Few systems are known for which such precise determinations of the stellar parameters have ever been possible - and this binary system represents the first case where both the components are such young stars . A detailed comparison of the derived stellar parameters with current models for the evolution of young stars shows fairly good agreement for the primary component. However, there are certain discrepancies in the case of the secondary component, showing that the current models for the early stages of lower-mass stars must still be refined. More information Part of the results described in this press release are described in more detail in a scientific article ( "RXJ 0529.4+0041: a low-mass pre-main sequence eclipsing-spectroscopic binary" by E. Covino et al.) that has been published in the European research journal Astronomy & Astrophysics (Vol. 361, p. 49). Notes [1] The team consists of Elvira Covino (Principal Investigator), Juan M. Alcalá , Rosita Paladino (all Osservatorio Astronomico di Capodimonte, Napoli, Italy), Antonio Frasca , Santo Catalano , Ettore Marilli (all Osservatorio Astrofisico di Catania, Italy) and Michael Sterzik (ESO-Chile). [2] One solar mass corresponds to 1.99 10 30 kg, or about 330,000 times the mass of the Earth. The Sun is about 4500 million years old and its total lifetime is of the order of 12-13,000 million years. It is an interesting thought that if the Sun would have been somewhat heavier, its total lifetime might have been too short for living organisms to develop on the Earth. In fact, the biological evolution that ultimately lead to the emergence of human beings apparently lasted about 4 billion years; this corresponds to the total lifetime of a star that is only about 20 % heavier than the Sun. Note also the

Hubble Sees a Young Star Take Center Stage

NASA Image and Video Library

2015-03-06

With its helical appearance resembling a snail’s shell, this reflection nebula seems to spiral out from a luminous central star in this NASA/ESA Hubble Space Telescope image. The star in the center, known as V1331 Cyg and located in the dark cloud LDN 981 — or, more commonly, Lynds 981 — had previously been defined as a T Tauri star. A T Tauri is a young star — or Young Stellar Object — that is starting to contract to become a main sequence star similar to the sun. What makes V1331Cyg special is the fact that we look almost exactly at one of its poles. Usually, the view of a young star is obscured by the dust from the circumstellar disc and the envelope that surround it. However, with V1331Cyg we are actually looking in the exact direction of a jet driven by the star that is clearing the dust and giving us this magnificent view. This view provides an almost undisturbed view of the star and its immediate surroundings allowing astronomers to study it in greater detail and look for features that might suggest the formation of a very low-mass object in the outer circumstellar disk. NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Astronomers Find New Evidence for the Violent Demise of Sun-like Stars

NASA Astrophysics Data System (ADS)

2005-06-01

Two astronomers have used NASA's Chandra X-ray Observatory to discover a shell of superheated gas around a dying star in the Milky Way galaxy. Joel Kastner, professor of imaging science at the Rochester Institute of Technology, and Rodolpho Montez, a graduate student in physics and astronomy at the University of Rochester, will present their results today at the American Astronomical Society meeting in Minneapolis. Their discovery shows how material ejected at two million miles per hour during the final, dying stages of sun-like stars can heat previously ejected gas to the point where it will emit X-rays. The study also offers new insight into how long the ejected gas around dying stars can persist in such a superheated state. According to Kastner, the hot gas shows up in high-resolution Chandra X-ray images of the planetary nebula NGC 40, which is located about 3,000 light years away from Earth in the direction of the constellation Cepheus. Chandra X-ray & NOAO Optical Composite of NGC 40 Chandra X-ray & NOAO Optical Composite of NGC 40 "Planetary nebulae are shells of gas ejected by dying stars," Kastner explains. "They offer astronomers a 'forecast' of what could happen to our own sun about five billion years from now - when it finally exhausts the reservoir of hydrogen gas at its core that presently provides its source of nuclear power." In his research, Montez discovered the X-ray emitting shell in NGC 40 by generating an image that uses only specific energy-selected X-rays - revealing a ring of superheated gas that lies just within the portions of the nebula that appear in optical and infrared images. "This hot bubble of gas vividly demonstrates how, as a planetary nebula forms, the gas ejection process of the central, dying star becomes increasingly energetic," Kastner notes. "Mass ejection during stellar death can result in violent collisions that can heat the ejected gas up to temperatures of more than a million degrees." The detection of X-rays from NGC

A young star takes centre stage

NASA Image and Video Library

2015-03-02

With its helical appearance resembling a snail’s shell, this reflection nebula seems to spiral out from a luminous central star in this new NASA/ESA Hubble Space Telescope image. The star in the centre, known as V1331 Cyg and located in the dark cloud LDN 981 — or, more commonly, Lynds 981 — had previously been defined as a T Tauri star. A T Tauri is a young star — or Young Stellar Object — that is starting to contract to become a main sequence star similar to the Sun. What makes V1331Cyg special is the fact that we look almost exactly at one of its poles. Usually, the view of a young star is obscured by the dust from the circumstellar disc and the envelope that surround it. However, with V1331Cyg we are actually looking in the exact direction of a jet driven by the star that is clearing the dust and giving us this magnificent view. This view provides an almost undisturbed view of the star and its immediate surroundings allowing astronomers to study it in greater detail and look for features that might suggest the formation of a verylow-mass object in the outer circumstellar disc.

Activity and magnetic field structure of the Sun-like planet-hosting star HD 1237

NASA Astrophysics Data System (ADS)

Alvarado-Gómez, J. D.; Hussain, G. A. J.; Grunhut, J.; Fares, R.; Donati, J.-F.; Alecian, E.; Kochukhov, O.; Oksala, M.; Morin, J.; Redfield, S.; Cohen, O.; Drake, J. J.; Jardine, M.; Matt, S.; Petit, P.; Walter, F. M.

2015-10-01

We analyse the magnetic activity characteristics of the planet-hosting Sun-like star, HD 1237, using HARPS spectro-polarimetric time-series data. We find evidence of rotational modulation of the magnetic longitudinal field measurements that is consistent with our ZDI analysis with a period of 7 days. We investigate the effect of customising the LSD mask to the line depths of the observed spectrum and find that it has a minimal effect on the shape of the extracted Stokes V profile but does result in a small increase in the S/N (~7%). We find that using a Milne-Eddington solution to describe the local line profile provides a better fit to the LSD profiles in this slowly rotating star, which also affects the recovered ZDI field distribution. We also introduce a fit-stopping criterion based on the information content (entropy) of the ZDI map solution set. The recovered magnetic field maps show a strong (+90 G) ring-like azimuthal field distribution and a complex radial field dominating at mid latitudes (~45 degrees). Similar magnetic field maps are recovered from data acquired five months apart. Future work will investigate how this surface magnetic field distribution affeccts the coronal magnetic field and extended environment around this planet-hosting star.

No Sun-like dynamo on the active star ζ Andromedae from starspot asymmetry.

PubMed

Roettenbacher, R M; Monnier, J D; Korhonen, H; Aarnio, A N; Baron, F; Che, X; Harmon, R O; Kővári, Zs; Kraus, S; Schaefer, G H; Torres, G; Zhao, M; ten Brummelaar, T A; Sturmann, J; Sturmann, L

2016-05-12

Sunspots are cool areas caused by strong surface magnetic fields that inhibit convection. Moreover, strong magnetic fields can alter the average atmospheric structure, degrading our ability to measure stellar masses and ages. Stars that are more active than the Sun have more and stronger dark spots than does the Sun, including on the rotational pole. Doppler imaging, which has so far produced the most detailed images of surface structures on other stars, cannot always distinguish the hemisphere in which the starspots are located, especially in the equatorial region and if the data quality is not optimal. This leads to problems in investigating the north-south distribution of starspot active latitudes (those latitudes with more starspot activity); this distribution is a crucial constraint of dynamo theory. Polar spots, whose existence is inferred from Doppler tomography, could plausibly be observational artefacts. Here we report imaging of the old, magnetically active star ζ Andromedae using long-baseline infrared interferometry. In our data, a dark polar spot is seen in each of two observation epochs, whereas lower-latitude spot structures in both hemispheres do not persist between observations, revealing global starspot asymmetries. The north-south symmetry of active latitudes observed on the Sun is absent on ζ And, which hosts global spot patterns that cannot be produced by solar-type dynamos.

Long-Term Variability of the Sun in the Context of Solar-Analog Stars

NASA Astrophysics Data System (ADS)

Egeland, Ricky

2017-04-01

The Sun is the best observed object in astrophysics, but despite this distinction the nature of its well-ordered generation of magnetic field in 11-year activity cycles remains a mystery. In this work, we place the solar cycle in a broader context by examining the long-term variability of solar analog stars within 5% of the solar effective temperature, but varied in rotation rate and metallicity. Emission in the Fraunhofer H & K line cores from singly-ionized calcium in the lower chromosphere is due to magnetic heating, and is a proven proxy for magnetic flux on the Sun. We use Ca H & K observations from the Mount Wilson Observatory HK project, the Lowell Observatory Solar Stellar Spectrograph, and other sources to construct composite activity time series of over 100 years in length for the Sun and up to 50 years for 26 nearby solar analogs. Archival Ca H & K observations of reflected sunlight from the Moon using the Mount Wilson instrument allow us to properly calibrate the solar time series to the S-index scale used in stellar studies. We find the mean solar S-index to be 5-9% lower than previously estimated, and the amplitude of activity to be small compared to active stars in our sample. A detailed look at the young solar analog HD 30495, which rotates 2.3 times faster than the Sun, reveals a large amplitude 12-year activity cycle and an intermittent short-period variation of 1.7 years, comparable to the solar variability time scales despite its faster rotation. Finally, time series analyses of the solar analog ensemble and a quantitative analysis of results from the literature indicate that truly Sun-like cyclic variability is rare, and that the amplitude of activity over both long and short timescales is linearly proportional to the mean activity. We conclude that the physical conditions conducive to a quasi-periodic magnetic activity cycle like the Sun's are rare in stars of approximately the solar mass, and that the proper conditions may be restricted to a

The influence of the magnetic topology on the wind braking of sun-like stars.

NASA Astrophysics Data System (ADS)

Réville, V.; Brun, A. S.; Matt, S. P.; Strugarek, A.; Pinto, R.

2014-12-01

Stellar winds are thought to be the main process responsible for the spin down of main-sequence stars. The extraction of angular momentum by a magnetized wind has been studied for decades, leading to several formulations for the resulting torque. However, previous studies generally consider simple dipole or split monopole stellar magnetic topologies. Here we consider in addition to a dipolar stellar magnetic field, both quadrupolar and octupolar configurations, while also varying the rotation rate and the magnetic field strength. 60 simulations made with a 2.5D, cylindrical and axisymmetric set-up and computed with the PLUTO code were used to find torque formulations for each topology. We further succeed to give a unique law that fits the data for every topology by formulating the torque in terms of the amount of open magnetic flux in the wind. We also show that our formulation can be applied to even more realistic magnetic topologies, with examples of the Sun in its minimum and maximum phase as observed at the Wilcox Solar Observatory, and of a young K-star (TYC-0486-4943-1) whose topology has been obtained by Zeeman-Doppler Imaging (ZDI).

Long-Term Variability of the Sun in the Context of Solar-Analog Stars

NASA Astrophysics Data System (ADS)

Egeland, Ricky

2018-06-01

The Sun is the best observed object in astrophysics, but despite this distinction the nature of its well-ordered generation of magnetic field in 11-year activity cycles remains a mystery. In this work, we place the solar cycle in a broader context by examining the long-term variability of solar analog stars within 5% of the solar effective temperature, but varied in rotation rate and metallicity. Emission in the Fraunhofer H & K line cores from singly-ionized calcium in the lower chromosphere is due to magnetic heating, and is a proven proxy for magnetic flux on the Sun. We use Ca H & K observations from the Mount Wilson Observatory HK project, the Lowell Observatory Solar Stellar Spectrograph, and other sources to construct composite activity time series of over 100 years in length for the Sun and up to 50 years for 26 nearby solar analogs. Archival Ca H & K observations of reflected sunlight from the Moon using the Mount Wilson instrument allow us to properly calibrate the solar time series to the S-index scale used in stellar studies. We find the mean solar S-index to be 5–9% lower than previously estimated, and the amplitude of activity to be small compared to active stars in our sample. A detailed look at the young solar analog HD 30495, which rotates 2.3 times faster than the Sun, reveals a large amplitude ~12-year activity cycle and an intermittent short-period variation of 1.7 years, comparable to the solar variability time scales despite its faster rotation. Finally, time series analyses of the solar analog ensemble and a quantitative analysis of results from the literature indicate that truly Sun-like cyclic variability is rare, and that the amplitude of activity over both long and short timescales is linearly proportional to the mean activity. We conclude that the physical conditions conducive to a quasi-periodic magnetic activity cycle like the Sun’s are rare in stars of approximately the solar mass, and that the proper conditions may be restricted

Deuterium and 15N fractionation in N2H+ during the formation of a Sun-like star

NASA Astrophysics Data System (ADS)

De Simone, M.; Fontani, F.; Codella, C.; Ceccarelli, C.; Lefloch, B.; Bachiller, R.; López-Sepulcre, A.; Caux, E.; Vastel, C.; Soldateschi, J.

2018-05-01

Although chemical models predict that the deuterium fractionation in N2H+ is a good evolutionary tracer in the star formation process, the fractionation of nitrogen is still a poorly understood process. Recent models have questioned the similar evolutionary trend expected for the two fractionation mechanisms in N2H+, based on a classical scenario in which ion-neutral reactions occurring in cold gas should have caused an enhancement of the abundance of N2D+, 15NNH+, and N15NH+. In the framework of the ASAI IRAM-30m large program, we have investigated the fractionation of deuterium and 15N in N2H+ in the best known representatives of the different evolutionary stages of the Sun-like star formation process. The goal is to ultimately confirm (or deny) the classical `ion-neutral reactions' scenario that predicts a similar trend for D and 15N fractionation. We do not find any evolutionary trend of the 14N/15N ratio from both the 15NNH+ and N15NH+ isotopologues. Therefore, our findings confirm that, during the formation of a Sun-like star, the core evolution is irrelevant in the fractionation of 15N. The independence of the 14N/15N ratio with time, found also in high-mass star-forming cores, indicates that the enrichment in 15N revealed in comets and protoplanetary discs is unlikely to happen at core scales. Nevertheless, we have firmly confirmed the evolutionary trend expected for the H/D ratio, with the N2H+/N2D+ ratio decreasing before the pre-stellar core phase, and increasing monotonically during the protostellar phase. We have also confirmed clearly that the two fractionation mechanisms are not related.

Frequency dependence of p-mode frequency shifts induced by magnetic activity in Kepler solar-like stars

NASA Astrophysics Data System (ADS)

Salabert, D.; Régulo, C.; Pérez Hernández, F.; García, R. A.

2018-04-01

The variations of the frequencies of the low-degree acoustic oscillations in the Sun induced by magnetic activity show a dependence on radial order. The frequency shifts are observed to increase towards higher-order modes to reach a maximum of about 0.8 μHz over the 11-yr solar cycle. A comparable frequency dependence is also measured in two other main sequence solar-like stars, the F-star HD 49933, and the young 1 Gyr-old solar analog KIC 10644253, although with different amplitudes of the shifts of about 2 μHz and 0.5 μHz, respectively. Our objective here is to extend this analysis to stars with different masses, metallicities, and evolutionary stages. From an initial set of 87 Kepler solar-like oscillating stars with known individual p-mode frequencies, we identify five stars showing frequency shifts that can be considered reliable using selection criteria based on Monte Carlo simulations and on the photospheric magnetic activity proxy Sph. The frequency dependence of the frequency shifts of four of these stars could be measured for the l = 0 and l = 1 modes individually. Given the quality of the data, the results could indicate that a physical source of perturbation different from that in the Sun is dominating in this sample of solar-like stars.

Stable Orbits for Exomoons in Earth’s Cousin (Kepler-452b) Orbiting a Sun-like Star

NASA Astrophysics Data System (ADS)

Davachi, Niyousha; Rosario Franco, Marialis; Garza, Sergio; Musielak, Zdzislaw E.

2017-01-01

Kepler 452b, also nicknamed Earth’s cousin, was discovered orbiting the habitable zone (HZ) of a G2 Star (Jenkins et al. 2015). This exoplanet is considered a super Earth, with a mass of 5 ± 2 Mass of Earth and a radius of 1.11 Radius of Earth; and is arguably the first rocky, habitable exoplanet to orbit a sun-like star. With a period of 385 days, conditions are prompt to be similar to those of Earth, and while Kepler-452b orbits the HZ of its parent star, its habitability could also be affected by the presence of an exomoon. Motivated by the need to understand conditions of habitability and orbital stability of Kepler-45b, we have performed a series of N-body integrations to examine the possibility of the exoplanet hosting an exomoon(s). Our results give a range of physical parameters leading to stable orbits for exomoons around this habitable super Earth.

NuSTAR Stares at the Sun

NASA Image and Video Library

2015-07-08

Flaring, active regions of our sun are highlighted in this image combining observations from several telescopes. High-energy X-rays from NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) are shown in blue; low-energy X-rays from Japan's Hinode spacecraft are green; and extreme ultraviolet light from NASA's Solar Dynamics Observatory (SDO) is yellow and red. All three telescopes captured their solar images around the same time on April 29, 2015. The NuSTAR image is a mosaic made from combining smaller images. The active regions across the sun's surface contain material heated to several millions of degrees. The blue-white areas showing the NuSTAR data pinpoint the most energetic spots. During the observations, microflares went off, which are smaller versions of the larger flares that also erupt from the sun's surface. The microflares rapidly release energy and heat the material in the active regions. NuSTAR typically stares deeper into the cosmos to observe X-rays from supernovas, black holes and other extreme objects. But it can also look safely at the sun and capture images of its high-energy X-rays with more sensitivity than before. Scientists plan to continue to study the sun with NuSTAR to learn more about microflares, as well as hypothesized nanoflares, which are even smaller. In this image, the NuSTAR data shows X-rays with energies between 2 and 6 kiloelectron volts; the Hinode data, which is from the X-ray Telescope instrument, has energies of 0.2 to 2.4 kiloelectron volts; and the Solar Dynamics Observatory data, taken using the Atmospheric Imaging Assembly instrument, shows extreme ultraviolet light with wavelengths of 171 and 193 Angstroms. Note the green Hinode image frame edge does not extend as far as the SDO ultraviolet image, resulting in the green portion of the image being truncated on the right and left sides. http://photojournal.jpl.nasa.gov/catalog/PIA19821

Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-Like Star GJ 504

NASA Technical Reports Server (NTRS)

Kuzuhara, M.; Tamura, M.; Kudo, T.; Janson, M; Kandori, R.; Brandt, T. D.; Thalmann, C.; Spiegel, D.; Biller, B.; Carson, J.;

Young Star Probably Ejected From Triple System

NASA Astrophysics Data System (ADS)

2003-01-01

, moving at about 6 miles per second. Then, between 1995 and 1998, it came within about 200 million miles (about two times the distance between the Sun and the Earth) of its companions. Following that encounter, it changed its path, moving away from its companion at about 12 miles per second, double its previous speed. "We clearly see that this star's orbit has changed dramatically after the encounter with its larger companions," said Luis Rodriguez. "By watching over the next five years or so, we should be able to tell if it will escape completely," he added. "We are very lucky to have been able to observe this event," said Loinard. Though studies with computer simulations long have shown that such close approaches and stellar ejections are likely, the time scales for these events in the real Universe are long -- thousands of years. The chance to study an actual ejection of a star from a multiple system can provide a critical test for the dynamical theories. If a young star is ejected from the system in which it was born, it would be cut off from the supply of gas and dust it needs to gain more mass, and thus its development would be abruptly halted. This process, the astronomers explain, could provide an explanation for the very-low-mass "failed stars" called brown dwarfs. "A brown dwarf could have had its growth stopped by being ejected from its parent system," Loinard said. The VLA observations were made at radio frequencies of 8 and 15 GHz. T Tauri, the "Northern" star in this system, is a famous variable star, discovered in October of 1852 by J.R. Hind, a London astronomer using a 7-inch diameter telescope. At its brightest, it is some 40 times brighter than when at its faintest. It has been studied extensively as a nearby example of a young stellar system. While readily accessible with a small telescope, it is not visible to the naked eye. The observed orbital changes took place in the southern components of the system, displaced from the visible star by about one

The Sun: A Star at the Center of Our Solar System

NASA Technical Reports Server (NTRS)

Adams, Mitzi L.

2016-01-01

There is a star at the center of our solar system! But what is a star? How do stars work? What are the characteristics of our Sun and how are these traits different from other stars? How does the Sun compare to stars such as Betelgeuse and Rigel? "Will the Sun end its life with a bang or a whimper?"

Chemical Soups Around Cool Stars

NASA Technical Reports Server (NTRS)

2009-01-01

This artist's conception shows a young, hypothetical planet around a cool star. A soupy mix of potentially life-forming chemicals can be seen pooling around the base of the jagged rocks. Observations from NASA's Spitzer Space Telescope hint that planets around cool stars the so-called M-dwarfs and brown dwarfs that are widespread throughout our galaxy might possess a different mix of life-forming, or prebiotic, chemicals than our young Earth.

Life on our planet is thought to have arisen out of a pond-scum-like mix of chemicals. Some of these chemicals are thought to have come from a planet-forming disk of gas and dust that swirled around our young sun. Meteorites carrying the chemicals might have crash-landed on Earth.

Astronomers don't know if these same life-generating processes are taking place around stars that are cooler than our sun, but the Spitzer observations show their disk chemistry is different. Spitzer detected a prebiotic molecule, called hydrogen cyanide, in the disks around yellow stars like our sun, but found none around cooler, less massive, reddish stars. Hydrogen cyanide is a carbon-containing, or organic compound. Five hydrogen cyanide molecules can join up to make adenine a chemical element of the DNA molecule found in all living organisms on Earth.

Astrometric Jitter of the Sun as a Star

DTIC Science & Technology

2010-05-01

active, fast-rotating stars. The research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology...as the Sun is not affected by star spot noise, but the prospects for more active stars may be limited to giant planets. Subject headings: open clusters ...nearby dwarfs should be as amenable to exoplanet detection as the Sun. The aim of this paper is to determine the solar astrometric jitter directly

HARPS-N OBSERVES THE SUN AS A STAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dumusque, Xavier; Glenday, Alex; Phillips, David F.

Radial velocity (RV) perturbations induced by stellar surface inhomogeneities including spots, plages and granules currently limit the detection of Earth-twins using Doppler spectroscopy. Such stellar noise is poorly understood for stars other than the Sun because their surface is unresolved. In particular, the effects of stellar surface inhomogeneities on observed stellar radial velocities are extremely difficult to characterize, and thus developing optimal correction techniques to extract true stellar radial velocities is extremely challenging. In this paper, we present preliminary results of a solar telescope built to feed full-disk sunlight into the HARPS-N spectrograph, which is in turn calibrated with anmore » astro-comb. This setup enables long-term observation of the Sun as a star with state-of-the-art sensitivity to RV changes. Over seven days of observing in 2014, we show an average 50 cm s{sup −1} RV rms over a few hours of observation. After correcting observed radial velocities for spot and plage perturbations using full-disk photometry of the Sun, we lower by a factor of two the weekly RV rms to 60 cm s{sup −1}. The solar telescope is now entering routine operation, and will observe the Sun every clear day for several hours. We will use these radial velocities combined with data from solar satellites to improve our understanding of stellar noise and develop optimal correction methods. If successful, these new methods should enable the detection of Venus over the next two to three years, thus demonstrating the possibility of detecting Earth-twins around other solar-like stars using the RV technique.« less

Mass Ejection from Old and Young Stars and the Sun

NASA Astrophysics Data System (ADS)

Jatenco-Pereira, V.; Opher, R.

1990-11-01

RESUMEN. Para poder explicar: 1) la enorme cantidad de perdida de masa y la baja velocidad asint5tica de las estrellas gigantes de o, y 2) los flujos de masa observados en protoestrellas, se sugiere un modelo para Ia perdida de masa, en donde se usa un flujo de ondas de Alfvencomo un mecanismo de aceleraci6n para los vientos de estrellas de tipo y vientos en protoestrellas. Se estudian los mecanismos de disipaci5n de las ondas de Alfven: los amortiguamientos no lineal, de superficie reso- nante y turbulento. En nuestro modelo se usa una divergente A(r) = A(R0) (r/r0)5 (donde A(r) es el area a una distancia radial r, y (A(r)/r2)max/(A(ro)/r02 - 10). Tambien se sugiere un modelo para una de hoyo coronal en el Sol. Se muestra que para satisfacer los datos observacionales en el Sol, tomando en cuenta la deposici6n del momento de las ondas de Alfven sobre el viento, se necesita: (a) una divergencia lenta en un hoyo coronal hasta una altura de 0.01 - 0.1 R seguido de (b) una divergencia rap ida de hasta una altura aproximada de 1 R . ABSTRACT: In order to explain (1) a large mass-loss rate and a small asymptotic flow speed of late-type giant stars and (2) the observed protostellar mass outflows, we suggest a model for mass loss, where we use a flux of Alfven waves as a mechanism of acceleration for late-type giant star winds and protostellar winds. We study the Alfven wave dissipation mechanisms: nonlinear damping, resonant surface damping, and turbulent damping. In our model we use a diverging geometry A(r) = A(r0) (r I r )S (where A(r) is the cross sectional area of the geometry at a radial distance r, and(A(r) I r2)max/(A(r0)/r02) = 10). We also suggest a model for a coronal hole geometry in the sun. We show that in order to satisfy the observational data of the sun, taking into account Alfven wave momentum deposition in the wind, we need: (a) a slow divergence in a coronal hole up t6 a height of 0.01 - 0.1 followed by (b) a rapid divergence up to a height of

The Young Solar Analogs Project

NASA Astrophysics Data System (ADS)

Lambert, Ryan; Gray, Richard, , Dr.

2014-03-01

The ultimate goal of the Young Solar Analogs Project is to give insight into the conditions in the early solar system when life was first forming on the earth and to assess the challenges the young, active sun presented to that early life. To achieve this, we have been monitoring since 2007 the stellar activity of 31 young solar-type stars with ages between 0.3 and 1.5 Gyrs. Many of these stars exhibit star spot cycles like the sun, but in a few cases we are seeing evidence for a previously unknown type of star spot cycle. Some vary chaotically. We have detected the presence of differential rotation in several stars. We have also detected a number of powerful flares both photometrically and spectroscopically. Optical irradiance changes in these stars can be as high as 10% in a single year; such solar variability would have led to catastropic climate change on the early earth. We would like to thank NSF for their generous donations to this project.

Global helioseismology (WP4.1): From the Sun to the stars & solar analogs

NASA Astrophysics Data System (ADS)

García, Rafael A.

2017-10-01

Sun-as-a star observations put our star as a reference for stellar observations. Here, I review the activities in which the SPACEINN global seismology team (Working Package WP4.1) has worked during the past 3 years. In particular, we will explain the new deliverables available on the SPACEINN seismic+ portal. Moreover, special attention will be given to surface dynamics (rotation and magnetic fields). After characterizing the rotation and the magnetic properties of around 300 solar-like stars and defining proper metrics for that, we use their seismic properties to characterize 18 solar analogues for which we study their surface magnetic and seismic properties. This allows us to put the Sun into context compared to its siblings.

NTT Observations Indicate that Brown Dwarfs Form Like Stars

NASA Astrophysics Data System (ADS)

2001-06-01

Dusty Disks Detected around Very Young Substellar Objects in the Orion Nebula Summary An international team of astronomers [2] is announcing today the discovery of dusty disks surrounding numerous very faint objects that are believed to be recently formed Brown Dwarfs in the Orion Nebula [3]. This finding is based on detailed observations with SOFI, a specialised infrared-sensitive instrument at the ESO 3.5-m New Technology Telescope at the La Silla Observatory. It is of special interest because it sheds light on the origin and nature of substellar objects, known as "Brown Dwarfs" . In particular, these results suggest that Brown Dwarfs share a common origin with stars and that Brown Dwarfs are more similar in nature to stars than to planets and, like stars, have the potential to form with accompanying systems of planets. Moreover, the presence of dusty protoplanetary disks around the faintest objects in the Orion Nebula cluster confirms both the membership of these faint stars in the cluster and their nature as bona-fide substellar objects, making this the largest population of Brown Dwarf objects yet known . These important results are being reported today to the American Astronomical Society Meeting in Pasadena (California, USA). PR Photo 22a/01 : Infrared picture of the Orion Nebula (NTT + SOFI). PR Photo 22b/01 : "Finding Chart" for Very Young Brown Dwarfs in the Orion Nebula. PR Photo 22c/01 : Animated GIF presentation of PR Photos 22a+b/01. Faint substellar objects in the Milky Way Over the past 5 years, several groups of astronomers have identified a type of very faint, substellar objects within our Milky Way galaxy. These gaseous objects have very low masses and will never shine like normal stars because they cannot achieve central temperatures high enough for sustained thermal nuclear reactions to occur in their cores. Such objects weigh less than about 7% of our Sun and have been variously called "Brown Dwarfs" , "Failed Stars" or "Super Planets

Young Stars in Orion May Solve Mystery of Our Solar System

NASA Astrophysics Data System (ADS)

2001-09-01

Scientists may have to give the Sun a little more credit. Exotic isotopes present in the early Solar System--which scientists have long-assumed were sprinkled there by a powerful, nearby star explosion--may have instead been forged locally by our Sun during the colossal solar-flare tantrums of its baby years. The isotopes--special forms of atomic nuclei, such as aluminum-26, calcium-41, and beryllium-10--can form in the X-ray solar flares of young stars in the Orion Nebula, which behave just like our Sun would have at such an early age. The finding, based on observations by the Chandra X-ray Observatory, has broad implications for the formation of our own Solar System. Eric Feigelson, professor of astronomy and astrophysics at Penn State, led a team of scientists on this Chandra observation and presents these results in Washington, D.C., today at a conference entitled "Two Years of Science with Chandra". "The Chandra study of Orion gives us the first chance to study the flaring properties of stars resembling the Sun when our solar system was forming," said Feigelson. "We found a much higher rate of flares than expected, sufficient to explain the production of many unusual isotopes locked away in ancient meteorites. If the young stars in Orion can do it, then our Sun should have been able to do it too." Scientists who study how our Solar System formed from a collapsed cloud of dust and gas have been hard pressed to explain the presence of these extremely unusual chemical isotopes. The isotopes are short-lived and had to have been formed no earlier than the creation of the Solar System, some five billion years ago. Yet these elements cannot be produced by a star as massive as our Sun under normal circumstances. (Other elements, such as silver and gold, were created long before the creation of the solar system.) The perplexing presence of these isotopic anomalies, found in ancient meteoroids orbiting the Earth, led to the theory that a supernova explosion occurred

Activity of the Baby Sun

NASA Astrophysics Data System (ADS)

Katsova, M. M.; Livshits, M. A.; Mishenina, T. V.; Nizamov, B. A.

2017-05-01

An analysis of the X-ray radiation of G-stars shows that the youngest fast rotating stars are characterized by saturation of activity, but part of stars demonstrate the solar-type activity, starting from rotational periods of 1.4 days. This type of activity, the level of which is determined by the rate of axial rotation, includes the formation of spots, flares and etc; first, activity is irregular, and only then there are conditions for the formation of cycles. The Kepler data show that stars of the same spectral type demonstrate two activity levels. This bimodality of different distributions of stars, change in a character of cycles and a level of Жiзнь i Bceлeннaya flare activity are evidences for an evolution of activity versus the age. By the nature of activity, we call conditionally G-dwarfs with rotation periods from 1 day to 5-6 days by the term "the Baby Sun" (the maximal number of these stars has Prot = 3 d), and we refer G-stars with Prot from 10 to 18 days to "the Young Suns". Ages of the main amount of the Baby Sun are around 200-600 Myr and the Young Sun are of about 1-2 Gyr. The Baby Suns are characterized by enhanced lithium content. We estimate the quasi-stationary X-ray and farultraviolet radiation of the outer atmosphere of the Baby Sun. From the GALEX data we obtain the FUV flux in the range 1350-1750 A for this kind of stars at the distance of 1 AU is 12.8 ± 4.2 erg/(cm^2 c), that exceeds the FUV-flux of the contemporary Sun by more than 6 times. The Kepler data demonstrate that the superflares happen more often namely on the Baby Suns. Our estimate is that superflares of the total energies 10^35 erg occur on the Baby Sun of about one per year.

From the sun to the Galactic Center: dust, stars and black hole(s)

NASA Astrophysics Data System (ADS)

Fritz, Tobias

2013-07-01

collision of stars in a dense young st! ar cluster. Such a cluster could sink to the GC by dynamical friction. There it would consist of few bright stars like IRS13E. Firstly, I analyze the SEDs of the objects in IRS13E. The SEDs of most objects can be explained by pure dust emission. Thus, most objects in IRS13E are pure dust clumps and only three young stars. This reduces the significance of the 'cluster' IRS13E compared to the stellar background. Secondly, I obtain acceleration limits for these three stars. The non-detection of accelerations makes an IMBH an unlikely scenario in IRS13E. However, since its three stars form a comoving association, which is unlikely to form by chance, the nature of IRS13E is not yet settled. In the third study (Chapter 4) I measure and analyze the extinction curve toward the GC. The extinction is a contaminant for GC observations and therefore it is necessary to know the extinction toward the GC to determine the luminosity properties of its stars. I obtain the extinction curve by measuring the flux of the HII region in the GC in several infrared HII lines and in the unextincted radio continuum. I compare these ratios with the ratios expected from recombination physics and obtain extinctions at 22 different lines between 1 and 19 micron. For the K-band I derive A_Ks=2.62+/-0.11. The extinction curve follows a power law with a steep slope of -2.11+/-0.06 shortward of 2.8 micron. At longer wavelengths the extinction is grayer and there are absorption features from ices. The extinction curve is a tool to constrain the properties of cosmic dust between the sun and the GC. The extinction curve cannot be explained by dust grains consisting of carbonaceous and silicate grains only. In addition composite particles, which also contain ices are necessary to fit the extinction curve. In the final part of this thesis (Chapter 5) I look at the properties of most of the stars in the GC. These are the old stars that form the nuclear cluster of the Milky

Silicate Crystal Formation in the Disk of an Erupting Star Artist Concept

NASA Image and Video Library

2009-05-13

This artist's concept illustrates how silicate crystals like those found in comets can be created by an outburst from a growing star. The image shows a young sun-like star encircled by its planet-forming disk of gas and dust. The silicate that makes up most of the dust would have begun as non-crystallized, amorphous particles. Streams of material are seen spiraling from the disk onto the star increasing its mass and causing the star to brighten and heat up dramatically. The outburst causes temperatures to rise in the star's surrounding disk. The animation (figure 1) zooms into the disk to show close-ups of silicate particles. When the disk warms from the star's outburst, the amorphous particles of silicate melt. As they cool off, they transform into forsterite (figure 2), a type of silicate crystal often found in comets in our solar system. In April 2008, NASA's Spitzer Space Telescope detected evidence of this process taking place on the disk of a young sun-like star called EX Lupi. http://photojournal.jpl.nasa.gov/catalog/PIA12008

PLANETARY CONSTRUCTION ZONES IN OCCULTATION: DISCOVERY OF AN EXTRASOLAR RING SYSTEM TRANSITING A YOUNG SUN-LIKE STAR AND FUTURE PROSPECTS FOR DETECTING ECLIPSES BY CIRCUMSECONDARY AND CIRCUMPLANETARY DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mamajek, Eric E.; Quillen, Alice C.; Pecaut, Mark J.

2012-03-15

The large relative sizes of circumstellar and circumplanetary disks imply that they might be seen in eclipse in stellar light curves. We estimate that a survey of {approx}10{sup 4} young ({approx}10 million year old) post-accretion pre-main-sequence stars monitored for {approx}10 years should yield at least a few deep eclipses from circumplanetary disks and disks surrounding low-mass companion stars. We present photometric and spectroscopic data for a pre-main-sequence K5 star (1SWASP J140747.93-394542.6 = ASAS J140748-3945.7), a newly discovered {approx}0.9 M{sub Sun} member of the {approx}16 Myr old Upper Centaurus-Lupus subgroup of Sco-Cen at a kinematic distance of 128 {+-} 13 pc.more » This star exhibited a remarkably long, deep, and complex eclipse event centered on 2007 April 29 (as discovered in Super Wide Angle Search for Planets (SuperWASP) photometry, and with portions of the dimming confirmed by All Sky Automated Survey (ASAS) data). At least five multi-day dimming events of >0.5 mag are identified, with a >3.3 mag deep eclipse bracketed by two pairs of {approx}1 mag eclipses symmetrically occurring {+-}12 days and {+-}26 days before and after. Hence, significant dimming of the star was taking place on and off over at least a {approx}54 day period in 2007, and a strong >1 mag dimming event occurring over a {approx}12 day span. We place a firm lower limit on the period of 850 days (i.e., the orbital radius of the eclipser must be >1.7 AU and orbital velocity must be <22 km s{sup -1}). The shape of the light curve is similar to the lopsided eclipses of the Be star EE Cep. We suspect that this new star is being eclipsed by a low-mass object orbited by a dense inner disk, further girded by at least three dusty rings of optical depths near unity. Between these rings are at least two annuli of near-zero optical depth (i.e., gaps), possibly cleared out by planets or moons, depending on the nature of the secondary. For possible periods in the range 2

Personalised electronic messages to improve sun protection in young adults.

PubMed

Mair, Sarah; Soyer, H Peter; Youl, Philippa; Hurst, Cameron; Marshall, Alison; Janda, Monika

2012-07-01

We studied the acceptability and feasibility of delivering sun protection messages via electronic media such as short message services (SMS) to people aged 18-40 years. An online survey was conducted using a pre-established panel of volunteers. We compared the characteristics of those who indicated that they would like to be alerted to the UV index, with those who would not, using bivariate logistic regression. Characteristics found to be associated with a desire to receive such advice were entered into a multivariate logistic regression analysis. The median age of the 141 participants was 34 years. Overall, 80% of participants agreed that they would like to receive some form of sun protection advice. Of these, 20% preferred to receive it via SMS and 42% via email. Willingness to receive electronic messages about the UV index was associated with being unsure about whether a suntanned person would look healthy and greater use of sun protection in the past. Careful attention to message framing and timing of message delivery, and focus on the short-term effects of sun exposure such as sunburn and skin ageing should increase the acceptability of such messages to young people. Sun protection messages delivered to young adults via electronic media appear to be feasible and acceptable.

Formation of new stellar populations from gas accreted by massive young star clusters.

PubMed

Li, Chengyuan; de Grijs, Richard; Deng, Licai; Geller, Aaron M; Xin, Yu; Hu, Yi; Faucher-Giguère, Claude-André

2016-01-28

Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old 'globular' clusters--those with ages greater than ten billion years and masses several hundred thousand times that of the Sun--often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies' gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.

NEW YOUNG STAR CANDIDATES IN CG4 AND Sa101

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rebull, L. M.; Laine, S.; Laher, R.

2011-07-15

The CG4 and Sa101 regions together cover a region of {approx}0.5 deg{sup 2} in the vicinity of a 'cometary globule' that is part of the Gum Nebula. There are seven previously identified young stars in this region; we have searched for new young stars using mid- and far-infrared data (3.6-70 {mu}m) from the Spitzer Space Telescope, combined with ground-based optical data and near-infrared data from the Two Micron All Sky Survey. We find infrared excesses in all six of the previously identified young stars in our maps and identify 16 more candidate young stars based on apparent infrared excesses. Mostmore » (73%) of the new young stars are Class II objects. There is a tighter grouping of young stars and young star candidates in the Sa101 region, in contrast to the CG4 region, where there are fewer young stars and young star candidates, and they are more dispersed. Few likely young objects are found in the 'fingers' of the dust being disturbed by the ionization front from the heart of the Gum Nebula.« less

Solar-like stars as seen by CoRoT

NASA Astrophysics Data System (ADS)

Garcia, R. A.; Appourchaux, T.; Baglin, A.; Auvergne, M.; Barban, C.; Baudin, F.; Michel, E.; Mosser, B.; Samadi, R.; Data Analysis Team D. A. T

2008-12-01

For more than a year, photometric high-quality data have been achieved from the CoRoT (COnvection ROtation and Planetary Transits; Baglin et al. 2006, Michel et al. 2008) min- isatellite developed by the French space agency (CNES) in collaboration with the Science Program of ESA, Austria, Belgium, Brazil Germany and Spain. The power spectrum of 4 dif- ferent solar-like stars (stars having sub-surface convective zones showing an acoustic (p) mode spectrum) has been obtained with unprecedented quality allowing the precise study of their seismic properties. These solar-like stars are F stars with masses in the range 1.0 to 1.4 M⊙ and are significantly hotter than the Sun.

Differential rotation in main-sequence solar-like stars: Qualitative inference from asteroseismic data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lund, Mikkel N.; Christensen-Dalsgaard, Jørgen; Miesch, Mark S., E-mail: mikkelnl@phys.au.dk

2014-08-01

Understanding differential rotation of Sun-like stars is of great importance for insight into the angular momentum transport in these stars. One means of gaining such information is that of asteroseismology. By a forward modeling approach we analyze in a qualitative manner the impact of different differential rotation profiles on the splittings of p-mode oscillation frequencies. The optimum modes for inference on differential rotation are identified along with the best value of the stellar inclination angle. We find that in general it is not likely that asteroseismology can be used to make an unambiguous distinction between a rotation profile such asmore » a conical Sun-like profile and a cylindrical profile. In addition, it seems unlikely that asteroseismology of Sun-like stars will result in inferences on the radial profile of the differential rotation, such as can be done for red giants. At best, one could possibly obtain the sign of the radial differential rotation gradient. Measurements of the extent of the latitudinal differential from frequency splitting are, however, more promising. One very interesting aspect that could likely be tested from frequency splittings is whether the differential rotation is solar-like or anti-solar-like in nature, in the sense that a solar-like profile has an equator rotating faster than the poles.« less

Disks and Outflows Around Young Stars

NASA Astrophysics Data System (ADS)

Beckwith, Steven; Staude, Jakob; Quetz, Axel; Natta, Antonella

The subject of the book, the ubiquitous circumstellar disks around very young stars and the corresponding jets of outflowing matter, has recently become one of the hottest areas in astrophysics. The disks are thought to be precursors to planetary systems, and the outflows are thought to be a necessary phase in the formation of a young star, helping the star to get rid of angular momentum and energy as it makes its way onto the main sequence. The possible connections to planetary systems and stellar astrophysics makes these topics especially broad, appealing to generalists and specialists alike. The CD not only contains papers that could not be printed in the book but allows the authors to include a fair amount of data, often displayed as color images. The CD-ROM contains all the contributions printed in the corresponding book (Lecture Notes in Physics Vol. 465) and, in addition, those presented exclusively in digital form. Each contribution consists of a file in portable document format (PDF). The electronic version allows full-text searching within each file using Adobe's Acrobat Reader providing instructions for installation on Unix (Sun), PC and Macintosh computers, respectively. All contributions can be printed out; the color diagrams and color frames, which are printed in black and white in the book, can be viewed in color on screen.

Constraints on Variability of Brightness and Surface Magnetism on Time Scales of Decades to Centuries in the Sun and Sun-Like Stars: A Source of Potential Terrestrial Climate Variability

NASA Technical Reports Server (NTRS)

Baliunas, Sallie L.; Sharber, James (Technical Monitor)

2001-01-01

These four points summarize our work to date. (1) Conciliation of solar and stellar photometric variability. Previous research by us and colleagues suggested that the Sun might at present be showing unusually low photometric variability compared to other sun-like stars. Those early results would question the suitability of the technique of using sun-like stars as proxies for solar irradiance change on time scales of decades to centuries. However, our results indicate the contrary: the Sun's observed short-term (seasonal) and longterm (year-to-year) brightness variations closely agree with observed brightness variations in stars of similar mass and age. (2) We have demonstrated an inverse correlation between the global temperature of the terrestrial lower troposphere, inferred from the NASA Microwave Sounding Unit (MSU) radiometers, and the total area of the Sun covered by coronal holes from January 1979 to present (up to May 2000). Variable fluxes of either solar charged particles or cosmic rays, or both, may influence the terrestrial tropospheric temperature. The geographical pattern of the correlation is consistent with our interpretation of an extra-terrestrial charged particle forcing. (3) Possible climate mechanism amplifying the impact of solar ultraviolet irradiance variations. The key points of our proposed climate hypersensitivity mechanism are: (a) The Sun is more variable in the UV (ultraviolet) than in the visible. However, the increased UV irradiance is mainly absorbed in the lower stratosphere/upper troposphere rather than at the surface. (b) Absorption in the stratosphere raises the temperature moderately around the vicinity of the tropopause, and tends to stabilize the atmosphere against vertical convective/diffusive transport, thus decreasing the flux of heat and moisture carried upward from surface. (c) The decrease in the upward convection of heat and moisture tends to raise the surface temperature because a drier upper atmosphere becomes less

NuSTAR Observations of X-Ray Flares from Young Stellar Objects

NASA Astrophysics Data System (ADS)

Vievering, Juliana; Glesener, Lindsay; Grefenstette, Brian; Smith, David

2018-01-01

Young stellar objects (YSOs), which tend to flare more frequently and at higher temperatures than what is typically observed on Sun-like stars, are excellent targets for studying the physical processes behind large flaring events. In the hard x-ray regime, radiation can penetrate through dense circumstellar material, and it is possible to measure thermal emission from hot plasma and to search for nonthermal emission from accelerated particles, which are key components for understanding the nature of energy release in these flares. Additionally, high-energy x-ray emission can ionize material in the disk, which may have implications for planet formation. To investigate hard x-ray emission from YSOs, three 50ks observations of a star-forming region called rho Ophiuchi have been taken with the Nuclear Spectroscopic Telescope Array (NuSTAR). Through use of direct focusing optics, NuSTAR provides unprecedented sensitivity in the hard x-ray regime, making these YSO observations the first of their kind. Multiple stellar flares have been identified in the data set; here we present the current spectral and timing analyses of the brightest of the these events, exploring the way energy is released as well as the effects of these large flares on the surrounding environment.

Exploring Young People's Beliefs and Images about Sun Safety

ERIC Educational Resources Information Center

White, K. M.; Robinson, N. G.; Young, R. McD.; Anderson, P. J.; Hyde, M. K.; Greenbank, S.; Keane, J.; Rolfe, T.; Vardon, P.; Baskerville, D.

2008-01-01

To understand young people's low levels of sun protection behaviour, 145 young people (aged 12 to 20 years) were recruited from Queensland, to participate in a one-hour focus group where they discussed issues related to sun protection and images of tanned and non-tanned people. Responses were content analysed to identify common sun protection…

Hubble Finds an Hourglass Nebula around a Dying Star

NASA Image and Video Library

1996-01-16

This Hubble telescope snapshot of MyCn18, a young planetary nebula, reveals that the object has an hourglass shape with an intricate pattern of etchings in its walls. A planetary nebula is the glowing relic of a dying, Sun-like star.

Stellar Content and Star Formation in Young Clusters Influenced by Massive Stars

NASA Astrophysics Data System (ADS)

Jose, J.

2014-09-01

Star Formation (SF) in extreme environment is always challenging and can be significantly different from that in quiet environments. This study presents the comprehensive multi-wavelength (optical, NIR, MIR and radio) observational analysis of three Galactic starforming regions associated with H II regions/young clusters and located at > 2 kpc, which are found to be evolving under the influence of massive stars within their vicinity. The candidate massive stars, young stellar objects, their mass, age, age spread, the form of K-band Luminosity Function (KLF), Initial Mass Function (IMF) and a possible formation history of each region are studied. The major results on Sh2-252, an extended H II region that appears to be undergoing multiple episodes of SF, are highlighted. Our analysis shows that all the regions are undergoing complex SF activity and the new generation of stars in each region seem to be an outcome of the influence by the presence of massive stars within them. SF process in these regions are likely to be multi-fold and the results suggest that multiple modes of triggering mechanism and hierarchial modes of SF are a common phenomena within young clusters.

The First X-shooter Observations of Jets from Young Stars

NASA Astrophysics Data System (ADS)

Bacciotti, F.; Whelan, E. T.; Alcalá, J. M.; Nisini, B.; Podio, L.; Randich, S.; Stelzer, B.; Cupani, G.

2011-08-01

We present the first pilot study of jets from young stars conducted with X-shooter, on the ESO/Very Large Telescope. As it offers simultaneous, high-quality spectra in the range 300-2500 nm, X-shooter is uniquely important for spectral diagnostics in jet studies. We chose to probe the accretion/ejection mechanisms at low stellar masses examining two targets with well-resolved continuous jets lying on the plane of the sky: ESO-HA 574 in Chameleon I and Par-Lup3-4 in Lupus III. The mass of the latter is close to the sub-stellar boundary (M sstarf = 0.13 M sun). A large number of emission lines probing regions of different excitation are identified, position-velocity diagrams are presented, and mass outflow/accretion rates are estimated. Comparison between the two objects is striking. ESO-HA 574 is a weakly accreting star for which we estimate a mass accretion rate of log (\\dot{M}_{acc}) = -10.8 +/- 0.5 (in M sun yr-1), yet it drives a powerful jet with \\dot{M}_{out} ~ 1.5-2.7 × 10-9 M sun yr-1. These values can be reconciled with a magneto-centrifugal jet acceleration mechanism assuming that the presence of the edge-on disk severely depresses the luminosity of the accretion tracers. In comparison, Par-Lup3-4, with stronger mass accretion (log (\\dot{M}_{acc}) = -9.1 +/- 0.4 M sun yr-1), drives a low-excitation jet with about \\dot{M}_{out} ~ 3.2 × 10-10 M sun yr-1 in both lobes. Despite the low stellar mass, \\dot{M}_{out}/\\dot{M}_{acc} for Par-Lup3-4 is at the upper limit of the range usually measured for young objects, but still compatible with a steady magneto-centrifugal wind scenario if all uncertainties are considered. Based on Observations collected with X-shooter at the Very Large Telescope on Cerro Paranal (Chile), operated by the European Southern Observatory (ESO). Program ID: 085.C-0238(A).

DETECTABILITY OF EARTH-LIKE PLANETS IN CIRCUMSTELLAR HABITABLE ZONES OF BINARY STAR SYSTEMS WITH SUN-LIKE COMPONENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eggl, Siegfried; Pilat-Lohinger, Elke; Haghighipour, Nader, E-mail: siegfried.eggl@univie.ac.at

2013-02-20

Given the considerable percentage of stars that are members of binaries or stellar multiples in the solar neighborhood, it is expected that many of these binaries host planets, possibly even habitable ones. The discovery of a terrestrial planet in the {alpha} Centauri system supports this notion. Due to the potentially strong gravitational interaction that an Earth-like planet may experience in such systems, classical approaches to determining habitable zones (HZ), especially in close S-type binary systems, can be rather inaccurate. Recent progress in this field, however, allows us to identify regions around the star permitting permanent habitability. While the discovery ofmore » {alpha} Cen Bb has shown that terrestrial planets can be detected in solar-type binary stars using current observational facilities, it remains to be shown whether this is also the case for Earth analogs in HZs. We provide analytical expressions for the maximum and rms values of radial velocity and astrometric signals, as well as transit probabilities of terrestrial planets in such systems, showing that the dynamical interaction of the second star with the planet may indeed facilitate the planets' detection. As an example, we discuss the detectability of additional Earth-like planets in the averaged, extended, and permanent HZs around both stars of the {alpha} Centauri system.« less

Identifying Young, Nearby Stars

NASA Technical Reports Server (NTRS)

Webb, Rich; Song, Inseok; Zuckerman, Ben; Bessell, Mike

2001-01-01

Young stars have certain characteristics, e.g., high atmospheric abundance of lithium and chromospheric activity, fast rotation, distinctive space motion and strong X-ray flux compared to that of older main sequence stars. We have selected a list of candidate young (<100Myr) and nearby (<60pc) stars based on their space motion and/or strong X-ray flux. To determine space motion of a star, one needs to know its coordinates (RA, DEC), proper motion, distance, and radial velocity. The Hipparcos and Tycho catalogues provide all this information except radial velocities. We anticipate eventually searching approx. 1000 nearby stars for signs of extreme youth. Future studies of the young stars so identified will help clarify the formation of planetary systems for times between 10 and 100 million years. Certainly, the final output of this study will be a very useful resource, especially for adaptive optics and space based searches for Jupiter-mass planets and dusty proto-planetary disks. We have begun spectroscopic observations in January, 2001 with the 2.3 m telescope at Siding Spring Observatory (SSO) in New South Wales, Australia. These spectra will be used to determine radial velocities and other youth indicators such as Li 6708A absorption strength and Hydrogen Balmer line intensity. Additional observations of southern hemisphere stars from SSO are scheduled in April and northern hemisphere observations will take place in May and July at the Lick Observatory of the University of California. AT SSO, to date, we have observed about 100 stars with a high resolution spectrometer (echelle) and about 50 stars with a medium spectral resolution spectrometer (the "DBS"). About 20% of these stars turn out to be young stars. Among these, two especially noteworthy stars appear to be the closest T-Tauri stars ever identified. Interestingly, these stars share the same space motions as that of a very famous star with a dusty circumstellar disk--beta Pictoris. This new finding better

Unveiling hidden properties of young star clusters: differential reddening, star-formation spread, and binary fraction

NASA Astrophysics Data System (ADS)

Bonatto, C.; Lima, E. F.; Bica, E.

2012-04-01

Context. Usually, important parameters of young, low-mass star clusters are very difficult to obtain by means of photometry, especially when differential reddening and/or binaries occur in large amounts. Aims: We present a semi-analytical approach (ASAmin) that, when applied to the Hess diagram of a young star cluster, is able to retrieve the values of mass, age, star-formation spread, distance modulus, foreground and differential reddening, and binary fraction. Methods: The global optimisation method known as adaptive simulated annealing (ASA) is used to minimise the residuals between the observed and simulated Hess diagrams of a star cluster. The simulations are realistic and take the most relevant parameters of young clusters into account. Important features of the simulations are a normal (Gaussian) differential reddening distribution, a time-decreasing star-formation rate, the unresolved binaries, and the smearing effect produced by photometric uncertainties on Hess diagrams. Free parameters are cluster mass, age, distance modulus, star-formation spread, foreground and differential reddening, and binary fraction. Results: Tests with model clusters built with parameters spanning a broad range of values show that ASAmin retrieves the input values with a high precision for cluster mass, distance modulus, and foreground reddening, but they are somewhat lower for the remaining parameters. Given the statistical nature of the simulations, several runs should be performed to obtain significant convergence patterns. Specifically, we find that the retrieved (absolute minimum) parameters converge to mean values with a low dispersion as the Hess residuals decrease. When applied to actual young clusters, the retrieved parameters follow convergence patterns similar to the models. We show how the stochasticity associated with the early phases may affect the results, especially in low-mass clusters. This effect can be minimised by averaging out several twin clusters in the

MagAO Imaging of Long-period Objects (MILO). II. A Puzzling White Dwarf around the Sun-like Star HD 11112

NASA Astrophysics Data System (ADS)

Rodigas, Timothy J.; Bergeron, P.; Simon, Amélie; Arriagada, Pamela; Faherty, Jacqueline K.; Anglada-Escudé, Guillem; Mamajek, Eric E.; Weinberger, Alycia; Butler, R. Paul; Males, Jared R.; Morzinski, Katie; Close, Laird M.; Hinz, Philip M.; Bailey, Jeremy; Carter, Brad; Jenkins, James S.; Jones, Hugh; O'Toole, Simon; Tinney, C. G.; Wittenmyer, Rob; Debes, John

2016-11-01

HD 11112 is an old, Sun-like star that has a long-term radial velocity (RV) trend indicative of a massive companion on a wide orbit. Here we present direct images of the source responsible for the trend using the Magellan Adaptive Optics system. We detect the object (HD 11112B) at a separation of 2.″2 (100 au) at multiple wavelengths spanning 0.6-4 μm and show that it is most likely a gravitationally bound cool white dwarf. Modeling its spectral energy distribution suggests that its mass is 0.9-1.1 M ⊙, which corresponds to very high eccentricity, near edge-on orbits from a Markov chain Monte Carlo analysis of the RV and imaging data together. The total age of the white dwarf is >2σ, which is discrepant with that of the primary star under most assumptions. The problem can be resolved if the white dwarf progenitor was initially a double white dwarf binary that then merged into the observed high-mass white dwarf. HD 11112B is a unique and intriguing benchmark object that can be used to calibrate atmospheric and evolutionary models of cool white dwarfs and should thus continue to be monitored by RV and direct imaging over the coming years.

Neptune as a Mirror for the Sun

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-01-01

How would the Kepler mission see a star like the Sun? We now know the answer to this question due to a creative approach: a new study has used the Kepler K2 mission to detect signals from the Sun reflected off of the surface of Neptune.Asteroseismology uses different oscillation modes of a star to probe its internal structure and properties. [Tosaka]Information in OscillationsKeplers most glamorous work is in discovering new planets around other stars. To successfully do this, however, the spacecraft is also quietly doing a lot of very useful work in the background, characterizing the many stars in our vicinity that planets might be found around.One of the ways Kepler gets information about these stars is from oscillations of the stars intensities. In asteroseismology, we look at oscillatory modes that are caused by convection-driven pressure changes on the inside of the star. All stars with near-surface convection oscillate like this including the Sun and by measuring the oscillations in intensity of these stars, we can make inferences about the stars properties.A Planetary MirrorWe do this by first understanding our Suns oscillations especially well (made easier by the fact that its nearby!). Then we use asteroseimic scaling relations determined empirically that relate characteristics like mass and radius of other stars to those of the Sun, based on the relation between the stars oscillation properties to the Suns.The trouble is, those oscillation properties are difficult to measure, and different instruments often measure different values. For this reason, wed like to measure the Suns oscillations with the same instrument we use to measure other stars oscillations: Kepler.Top panel: Kepler K2 49-day light curve of Neptune. Bottom panel: power density spectrum as a function of frequency (grey). Neptunes rotation frequencies and harmonics appear toward the left side (blue); the excess power due to the solar modes is visible toward the bottom right. The green curve

SunBlock '99: Young Scientists Investigate the Sun

NASA Astrophysics Data System (ADS)

Walsh, R. W.; Pike, C. D.; Mason, H.; Young, P.; Ireland, J.; Galsgaard, K.

1999-10-01

SunBlock `99 is a Web-based Public Understanding of Science and educational project which seeks to present the very latest solar research as seen through the eyes of young British scientists. These ``solar guides'' discuss not only their scientific interests, but also their extra-curricular activities and the reasons they chose scientific careers; in other words the human face of scientific research. The SunBlock '99 pages gather a range of solar images and movies from current solar space observatories and discuss the underlying physics and its relationship to the school curriculum. The instructional level is pitched at UK secondary school children (aged 13-16 years). It is intended that the material should not only provide a visually appealing introduction to the study of the Sun, but that it should help bridge the often wide gap between classroom science lessons and the research scientist `out in the field'. SunBlock '99 is managed by a team from the Rutherford Appleton Laboratory and the Universities of St Andrews and Cambridge, together with educational consultants. The production has, in part, been sponsored by PPARC and the Millennium Mathematics Project. Web site addresss: http://www.sunblock99.org.uk

Hypervelocity stars from young stellar clusters in the Galactic Centre

NASA Astrophysics Data System (ADS)

Fragione, G.; Capuzzo-Dolcetta, R.; Kroupa, P.

2017-05-01

The enormous velocities of the so-called hypervelocity stars (HVSs) derive, likely, from close interactions with massive black holes, binary stars encounters or supernova explosions. In this paper, we investigate the origin of HVSs as consequence of the close interaction between the Milky Way central massive black hole and a passing-by young stellar cluster. We found that both single and binary HVSs may be generated in a burst-like event, as the cluster passes near the orbital pericentre. High-velocity stars will move close to the initial cluster orbital plane and in the direction of the cluster orbital motion at the pericentre. The binary fraction of these HVS jets depends on the primordial binary fraction in the young cluster. The level of initial mass segregation determines the value of the average mass of the ejected stars. Some binary stars will merge, continuing their travel across and out of the Galaxy as blue stragglers.

Activity Cycles in Stars

NASA Technical Reports Server (NTRS)

Hathaway, David H.

2009-01-01

Starspots and stellar activity can be detected in other stars using high precision photometric and spectrometric measurements. These observations have provided some surprises (starspots at the poles - sunspots are rarely seen poleward of 40 degrees) but more importantly they reveal behaviors that constrain our models of solar-stellar magnetic dynamos. The observations reveal variations in cycle characteristics that depend upon the stellar structure, convection zone dynamics, and rotation rate. In general, the more rapidly rotating stars are more active. However, for stars like the Sun, some are found to be inactive while nearly identical stars are found to be very active indicating that periods like the Sun's Maunder Minimum (an inactive period from 1645 to 1715) are characteristic of Sun-like stars.

The first focused hard X-ray images of the sun with NuSTAR

DOE PAGES

Grefenstette, Brian W.; Glesener, Lindsay; Krucker, Sam; ...

2016-07-18

Here, we present results from the the first campaign of dedicated solar observations undertaken by the Nuclear Spectroscopic Telescope ARray (NuSTAR) hard X-ray (HXR) telescope. Designed as an astrophysics mission, NuSTAR nonetheless has the capability of directly imaging the Sun at HXR energies (>3 keV) with an increase in sensitivity of at least two magnitude compared to current non-focusing telescopes. In this paper we describe the scientific areas where NuSTAR will make major improvements on existing solar measurements. We report on the techniques used to observe the Sun with NuSTAR, their limitations and complications, and the procedures developed to optimizemore » solar data quality derived from our experience with the initial solar observations. These first observations are briefly described, including the measurement of the Fe K-shell lines in a decaying X-class flare, HXR emission from high in the solar corona, and full-disk HXR images of the Sun.« less

The first focused hard X-ray images of the sun with NuSTAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grefenstette, Brian W.; Glesener, Lindsay; Krucker, Sam

Here, we present results from the the first campaign of dedicated solar observations undertaken by the Nuclear Spectroscopic Telescope ARray (NuSTAR) hard X-ray (HXR) telescope. Designed as an astrophysics mission, NuSTAR nonetheless has the capability of directly imaging the Sun at HXR energies (>3 keV) with an increase in sensitivity of at least two magnitude compared to current non-focusing telescopes. In this paper we describe the scientific areas where NuSTAR will make major improvements on existing solar measurements. We report on the techniques used to observe the Sun with NuSTAR, their limitations and complications, and the procedures developed to optimizemore » solar data quality derived from our experience with the initial solar observations. These first observations are briefly described, including the measurement of the Fe K-shell lines in a decaying X-class flare, HXR emission from high in the solar corona, and full-disk HXR images of the Sun.« less

THE FIRST FOCUSED HARD X-RAY IMAGES OF THE SUN WITH NuSTAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grefenstette, Brian W.; Madsen, Kristin K.; Forster, Karl

We present results from the the first campaign of dedicated solar observations undertaken by the Nuclear Spectroscopic Telescope ARray ( NuSTAR ) hard X-ray (HXR) telescope. Designed as an astrophysics mission, NuSTAR nonetheless has the capability of directly imaging the Sun at HXR energies (>3 keV) with an increase in sensitivity of at least two magnitude compared to current non-focusing telescopes. In this paper we describe the scientific areas where NuSTAR will make major improvements on existing solar measurements. We report on the techniques used to observe the Sun with NuSTAR , their limitations and complications, and the procedures developedmore » to optimize solar data quality derived from our experience with the initial solar observations. These first observations are briefly described, including the measurement of the Fe K-shell lines in a decaying X-class flare, HXR emission from high in the solar corona, and full-disk HXR images of the Sun.« less

The First Focused Hard X-Ray Images of the Sun with NuSTAR

NASA Technical Reports Server (NTRS)

Grefenstette, Brian W.; Glesener, Lindsay; Kruckner, Sam; Hudson, Hugh; Hannah, Iain G.; Smith, David M.; Vogel, Julia K.; White, Stephen M.; Madsen, Kristin K.; Marsh, Andrew J.;

First NuSTAR Limits on Quiet Sun Hard X-Ray Transient Events

NASA Astrophysics Data System (ADS)

Marsh, Andrew J.; Smith, David M.; Glesener, Lindsay; Hannah, Iain G.; Grefenstette, Brian W.; Caspi, Amir; Krucker, Säm; Hudson, Hugh S.; Madsen, Kristin K.; White, Stephen M.; Kuhar, Matej; Wright, Paul J.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Hailey, Charles J.; Harrison, Fiona A.; Stern, Daniel; Zhang, William W.

2017-11-01

We present the first results of a search for transient hard X-ray (HXR) emission in the quiet solar corona with the Nuclear Spectroscopic Telescope Array (NuSTAR) satellite. While NuSTAR was designed as an astrophysics mission, it can observe the Sun above 2 keV with unprecedented sensitivity due to its pioneering use of focusing optics. NuSTAR first observed quiet-Sun regions on 2014 November 1, although out-of-view active regions contributed a notable amount of background in the form of single-bounce (unfocused) X-rays. We conducted a search for quiet-Sun transient brightenings on timescales of 100 s and set upper limits on emission in two energy bands. We set 2.5-4 keV limits on brightenings with timescales of 100 s, expressed as the temperature T and emission measure EM of a thermal plasma. We also set 10-20 keV limits on brightenings with timescales of 30, 60, and 100 s, expressed as model-independent photon fluxes. The limits in both bands are well below previous HXR microflare detections, though not low enough to detect events of equivalent T and EM as quiet-Sun brightenings seen in soft X-ray observations. We expect future observations during solar minimum to increase the NuSTAR sensitivity by over two orders of magnitude due to higher instrument livetime and reduced solar background.

Young Star Clusters: Keys to Understanding Massive Stars

NASA Astrophysics Data System (ADS)

Davies, B.

2012-12-01

Young, coeval clusters of stars provide the perfect laboratory in which to test our understanding of how massive stars evolve. Early optical observations limited us to a handful of low-mass clusters within 1kpc. However, thanks to the recent progress in infrared astronomy, the Milky Way's population of young massive star clusters is now beginning to be revealed. Here, I will review the recent progress made in this field, what it has told us about the evolution of massive stars to supernova and beyond, the prospects for this field, and some issues that should be taken into account when interpreting the results.

Is the Young Star RZ Piscium Consuming Its Own (Planetary) Offspring?

NASA Astrophysics Data System (ADS)

Punzi, K. M.; Kastner, J. H.; Melis, C.; Zuckerman, B.; Pilachowski, C.; Gingerich, L.; Knapp, T.

2018-01-01

The erratically variable star RZ Piscium (RZ Psc) displays extreme optical dropout events and strikingly large excess infrared emission. To ascertain the evolutionary status of this intriguing star, we obtained observations of RZ Psc with the European Space Agency’s X-ray Multi-Mirror Mission (XMM-Newton), as well as high-resolution optical spectroscopy with the Hamilton Echelle on the Lick Shane 3 m telescope and with HIRES on the Keck I 10 m telescope. The optical spectroscopy data demonstrate that RZ Psc is a pre-main sequence star with an effective temperature of 5600 ± 75 K and log g of 4.35 ± 0.10. The ratio of X-ray to bolometric luminosity, {log}{L}X/{L}{bol}, lies in the range ‑3.7 to ‑3.2, consistent with ratios typical of young, solar-mass stars, thereby providing strong support for the young star status of RZ Psc. The Li absorption line strength of RZ Psc suggests an age in the range 30–50 Myr, which in turn implies that RZ Psc lies at a distance of ∼170 pc. Adopting this estimated distance, we find the Galactic space velocity of RZ Psc to be similar to the space velocities of stars in young moving groups near the Sun. Optical spectral features indicative of activity and/or circumstellar material are present in our spectra over multiple epochs, which provide evidence for the presence of a significant mass of circumstellar gas associated with RZ Psc. We suggest that the destruction of one or more massive orbiting bodies has recently occurred within 1 au of the star, and we are viewing the aftermath of such an event along the plane of the orbiting debris.

THE GALACTIC CENTER CLOUD G2-A YOUNG LOW-MASS STAR WITH A STELLAR WIND

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scoville, N.; Burkert, A.

2013-05-10

We explore the possibility that the G2 gas cloud falling in toward SgrA* is the mass-loss envelope of a young T Tauri star. As the star plunges to smaller radius at 1000-6000 km s{sup -1}, a strong bow shock forms where the stellar wind is impacted by the hot X-ray emitting gas in the vicinity of SgrA*. For a stellar mass-loss rate of 4 Multiplication-Sign 10{sup -8} M{sub Sun} yr{sup -1} and wind velocity 100 km s{sup -1}, the bow shock will have an emission measure (EM = n {sup 2} vol) at a distance {approx}10{sup 16} cm, similar tomore » that inferred from the IR emission lines. The ionization of the dense bow shock gas is potentially provided by collisional ionization at the shock front and cooling radiation (X-ray and UV) from the post shock gas. The former would predict a constant line flux as a function of distance from SgrA*, while the latter will have increasing emission at lesser distances. In this model, the star and its mass-loss wind should survive pericenter passage since the wind is likely launched at 0.2 AU and this is much less than the Roche radius at pericenter ({approx}3 AU for a stellar mass of 2 M{sub Sun }). In this model, the emission cloud will probably survive pericenter passage, discriminating this scenario from others.« less

Hubble Movies Provide Unprecedented View of Supersonic Jets from Young Stars

NASA Image and Video Library

2017-12-08

AUGUST 31, 2011: A team of scientists has collected enough high-resolution Hubble Space Telescope images over a 14-year period to stitch together time-lapse movies of powerful jets ejected from three young stars. The jets, a byproduct of gas accretion around newly forming stars, shoot off at supersonic speeds in opposite directions through space. These phenomena are providing clues about the final stages of a star’s birth, offering a peek at how our Sun came into existence 4.5 billion years ago. Hubble’s unprecedented sharpness allows astronomers to see changes in the jets over just a few years’ time. Most astronomical processes change over timescales that are much longer than a human lifetime. To read more go to: www.nasa.gov/mission_pages/hubble/science/supersonic-jets... Object Name: HH 2 Image Type: Astronomical Credit: NASA, ESA, and P. Hartigan (Rice University)..NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Hubble Movies Provide Unprecedented View of Supersonic Jets from Young Stars

NASA Image and Video Library

2017-12-08

AUGUST 31, 2011: A team of scientists has collected enough high-resolution Hubble Space Telescope images over a 14-year period to stitch together time-lapse movies of powerful jets ejected from three young stars. The jets, a byproduct of gas accretion around newly forming stars, shoot off at supersonic speeds in opposite directions through space. These phenomena are providing clues about the final stages of a star’s birth, offering a peek at how our Sun came into existence 4.5 billion years ago. Hubble’s unprecedented sharpness allows astronomers to see changes in the jets over just a few years’ time. Most astronomical processes change over timescales that are much longer than a human lifetime. To read more go to: www.nasa.gov/mission_pages/hubble/science/supersonic-jets... Object Name: HH 47 Image Type: Astronomical Credit: NASA, ESA, and P. Hartigan (Rice University)..NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

MagAO IMAGING OF LONG-PERIOD OBJECTS (MILO). II. A PUZZLING WHITE DWARF AROUND THE SUN-LIKE STAR HD 11112

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodigas, Timothy J.; Arriagada, Pamela; Faherty, Jacqueline K.

HD 11112 is an old, Sun-like star that has a long-term radial velocity (RV) trend indicative of a massive companion on a wide orbit. Here we present direct images of the source responsible for the trend using the Magellan Adaptive Optics system. We detect the object (HD 11112B) at a separation of 2.″2 (100 au) at multiple wavelengths spanning 0.6–4 μ m and show that it is most likely a gravitationally bound cool white dwarf. Modeling its spectral energy distribution suggests that its mass is 0.9–1.1 M {sub ⊙}, which corresponds to very high eccentricity, near edge-on orbits from amore » Markov chain Monte Carlo analysis of the RV and imaging data together. The total age of the white dwarf is >2 σ , which is discrepant with that of the primary star under most assumptions. The problem can be resolved if the white dwarf progenitor was initially a double white dwarf binary that then merged into the observed high-mass white dwarf. HD 11112B is a unique and intriguing benchmark object that can be used to calibrate atmospheric and evolutionary models of cool white dwarfs and should thus continue to be monitored by RV and direct imaging over the coming years.« less

A slightly more massive young Sun as an explanation for warm temperatures on early Mars.

PubMed

Whitmire, D P; Doyle, L R; Reynolds, R T; Matese, J J

1995-03-25

The valley network channels on the heavily cratered ancient surface of Mars suggest the presence of liquid water approximately 3.8 Gyr ago. However, the implied warm climate is difficult to explain in the context of the standard solar model, even allowing for the maximum CO2 greenhouse heating. In this paper we investigate the astronomical and planetary implications of a nonstandard solar model in which the zero-age, main-sequence Sun had a mass of 1.05 +/- 0.02 M solar. The excess mass was subsequently lost in a solar wind during the first 1.2(-0.2, +0.4) Gyr of the Sun's main sequence phase. The implied mass-loss rate of 4(+3, -2) x 10(-11) M solar yr-1, or about 10(3)x that of the current Sun, may be detectable in several nearby young solar type stars.

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

PubMed

Waltham, David

2017-01-01

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.

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

PubMed Central

2017-01-01

Abstract 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. PMID:28103107

HOT WHITE DWARF SHINES IN YOUNG STAR CLUSTER

NASA Technical Reports Server (NTRS)

2002-01-01

A dazzling 'jewel-box' collection of over 20,000 stars can be seen in crystal clarity in this NASA Hubble Space Telescope image, taken with the Wide Field and Planetary Camera 2. The young (40 million year old) cluster, called NGC 1818, is 164,000 light-years away in the Large Magellanic Cloud (LMC), a satellite galaxy of our Milky Way. The LMC, a site of vigorous current star formation, is an ideal nearby laboratory for studying stellar evolution. In the cluster, astronomers have found a young white dwarf star, which has only very recently formed following the burnout of a red giant. Based on this observation astronomers conclude that the red giant progenitor star was 7.6 times the mass of our Sun. Previously, astronomers have estimated that stars anywhere from 6 to 10 solar masses would not just quietly fade away as white dwarfs but abruptly self-destruct in torrential explosions. Hubble can easily resolve the star in the crowded cluster, and detect its intense blue-white glow from a sizzling surface temperature of 50,000 degrees Fahrenheit. IMAGE DATA Date taken: December 1995 Wavelength: natural color reconstruction from three filters (I,B,U) Field of view: 100 light-years, 2.2 arc minutes TARGET DATA Name: NGC 1818 Distance: 164,000 light-years Constellation: Dorado Age: 40 million years Class: Rich star cluster Apparent magnitude: 9.7 Apparent diameter: 7 arc minutes Credit: Rebecca Elson and Richard Sword, Cambridge UK, and NASA (Original WFPC2 image courtesy J. Westphal, Caltech) Image files are available electronically via the World Wide Web at: http://oposite.stsci.edu/pubinfo/1998/16 and via links in http://oposite.stsci.edu/pubinfo/latest.html or http://oposite.stsci.edu/pubinfo/pictures.html. GIF and JPEG images are available via anonymous ftp to oposite.stsci.edu in /pubinfo/GIF/9816.GIF and /pubinfo/JPEG/9816.jpg.

VLBA Scientists Study Birth of Sunlike Stars

NASA Astrophysics Data System (ADS)

1999-06-01

Three teams of scientists have used the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope to learn tantalizing new details about how Sun-like stars are formed. Young stars, still growing by drawing in nearby gas, also spew some of that material back into their surroundings, like impatient infants that eat too quickly. The VLBA observations are giving astronomers new insights on both processes -- the accretion of material by the new stars and the outflows of material from them. "For the first time, we're actually seeing what happens right down next to the star in these young systems," said Mark Claussen, of the National Radio Astronomy Observatory (NRAO) in Socorro, NM. Claussen and other researchers announced their findings at the American Astronomical Society's meeting in Chicago. Material attracted by a young star's gravitational pull forms a flat, orbiting disk, called an accretion disk, in which the material circles closer and closer to the star until finally drawn into it. At the same time, material is ejected in "jets" speeding from the poles of the accretion disk. "The VLBA is showing us the first images of the region close to the star where the material in these jets is accelerated and formed into the `beams' of the jet," Claussen said. "We don't understand the details of these processes well," Claussen said. "These VLBA research projects are beginning to help unravel the mysteries of how stars like the Sun form." The teams are observing clumps of water vapor that naturally amplify radio emissions to see details smaller than the orbit of Mercury in young stellar systems as well as track gas motions. The clumps of gas are called masers, and amplify radio emission in much the same way that a laser amplifies light emission. "These images are just fantastic," said Al Wootten of NRAO in Charlottesville, VA. The maser clumps or "spots," emitting radio waves at a specific wavelength, can be tracked as they move over time. In addition

The sun's spectra: coding the light and sounds. application to other stars

NASA Astrophysics Data System (ADS)

Rozelot, J.-P.

2011-04-01

The Sun is our nearest star. Its thorough study permits to extend results to other stars for which one does not think at once to encounter features first discovered on the Sun: spots, differential rotation, oblateness, radial surface displacements, etc. The Sun is thus an irreplaceable laboratory, as much as physical conditions prevailing there are often hardly reproducible on Earth. In this chapter, we do not intend to give an exhaustive survey of what we know about our Sun. We want only to give an original lighting on topical questions related to the subject of this book, based on stellar spectroscopy, and we will focus on what we call the solar code. What can we learn from the solar spectrum? More generally, what are we learning from solar oscillations and from the activity cycle? This chapter is divided into three parts, bearing in mind that results obtained on the Sun are transferable to other stars. In a first part, we will show that the electromagnetic light code permits to access to different atmospheric solar layers. In a second part, we will show that the sound code is a fantastic tool for investigating the internal structure and the dynamics of the Sun. Thus tackled, the Sun is "peeled" as an onion, each successive shells giving an indication on the physical conditions acting in the studied layer, starting from the external atmosphere, crossing the free surface, to progressively go deeper inside, down to the core. In the third part, we will emphasize the "shape" concept, as departures to sphericity are essential in such an approach. This also allows us to study some global astrophysical properties, such as the angular momentum, the gravitational moments and the effect of distortion induced on the visible surface. We will conclude by extending such ideas to other stars, and especially by mentioning new results obtained on the oblateness of Altair and Achernar, including gravity darkening and geometrical distortion. We intentionally replaced this whole

Capture of the Sun's Oort cloud from stars in its birth cluster.

PubMed

Levison, Harold F; Duncan, Martin J; Brasser, Ramon; Kaufmann, David E

2010-07-09

Oort cloud comets are currently believed to have formed in the Sun's protoplanetary disk and to have been ejected to large heliocentric orbits by the giant planets. Detailed models of this process fail to reproduce all of the available observational constraints, however. In particular, the Oort cloud appears to be substantially more populous than the models predict. Here we present numerical simulations that show that the Sun captured comets from other stars while it was in its birth cluster. Our results imply that a substantial fraction of the Oort cloud comets, perhaps exceeding 90%, are from the protoplanetary disks of other stars.

Astronomers Gain Important Insight on How Massive Stars Form

NASA Astrophysics Data System (ADS)

2006-09-01

Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope have discovered key evidence that may help them figure out how very massive stars can form. Young Star Graphic Artist's Conception of Young Star Showing Motions Detected in G24 A1: (1) Infall toward torus, (2) Rotation and (3) outflow. CREDIT: Bill Saxton, NRAO/AUI/NSF Click on image for larger graphic file (JPEG, 129K) "We think we know how stars like the Sun are formed, but there are major problems in determining how a star 10 times more massive than the Sun can accumulate that much mass. The new observations with the VLA have provided important clues to resolving that mystery," said Maria Teresa Beltran, of the University of Barcelona in Spain. Beltran and other astronomers from Italy and Hawaii studied a young, massive star called G24 A1 about 25,000 light-years from Earth. This object is about 20 times more massive than the Sun. The scientists reported their findings in the September 28 issue of the journal Nature. Stars form when giant interstellar clouds of gas and dust collapse gravitationally, compacting the material into what becomes the star. While astronomers believe they understand this process reasonably well for smaller stars, the theoretical framework ran into a hitch with larger stars. "When a star gets up to about eight times the mass of the Sun, it pours out enough light and other radiation to stop the further infall of material," Beltran explained. "We know there are many stars bigger than that, so the question is, how do they get that much mass?" One idea is that infalling matter forms a disk whirling around the star. With most of the radiation escaping without hitting the disk, material can continue to fall into the star from the disk. According to this model, some material will be flung outward along the rotation axis of the disk into powerful outflows. "If this model is correct, there should be material falling inward, rushing outward and rotating

STAR FORMATION AND YOUNG POPULATION OF THE H II COMPLEX Sh2-294

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samal, M. R.; Pandey, A. K.; Chauhan, N.

The Sh2-294 H II region ionized by a single B0V star features several infrared excess sources, a photodissociation region, and also a group of reddened stars at its border. The star formation scenario in this region seems to be quite complex. In this paper, we present follow-up results of Sh2-294 H II region at 3.6, 4.5, 5.8, and 8.0 {mu}m observed with the Spitzer Space Telescope Infrared Array Camera (IRAC), coupled with H{sub 2} (2.12 {mu}m) observation, to characterize the young population of the region and to understand its star formation history. We identified 36 young stellar object (YSO, Classmore » I, Class II, and Class I/II) candidates using IRAC color-color diagrams. It is found that Class I sources are preferentially located at the outskirts of the H II region and associated with enhanced H{sub 2} emission; none of them are located near the central cluster. Combining the optical to mid-infrared (MIR) photometry of the YSO candidates and using the spectral energy distribution fitting models, we constrained stellar parameters and the evolutionary status of 33 YSO candidates. Most of them are interpreted by the model as low-mass (<4 M{sub Sun }) YSOs; however, we also detected a massive YSO ({approx}9 M{sub Sun }) of Class I nature, embedded in a cloud of visual extinction of {approx}24 mag. Present analysis suggests that the Class I sources are indeed a younger population of the region relative to Class II sources (age {approx} 4.5 Multiplication-Sign 10{sup 6} yr). We suggest that the majority of the Class I sources, including the massive YSOs, are second-generation stars of the region whose formation is possibly induced by the expansion of the H II region powered by a {approx}4 Multiplication-Sign 10{sup 6} yr B0 main-sequence star.« less

Anatomy of a flaring proto-planetary disk around a young intermediate-mass star.

PubMed

Lagage, Pierre-Olivier; Doucet, Coralie; Pantin, Eric; Habart, Emilie; Duchêne, Gaspard; Ménard, François; Pinte, Christophe; Charnoz, Sébastien; Pel, Jan-Willem

2006-10-27

Although planets are being discovered around stars more massive than the Sun, information about the proto-planetary disks where such planets have built up is sparse. We have imaged mid-infrared emission from polycyclic aromatic hydrocarbons at the surface of the disk surrounding the young intermediate-mass star HD 97048 and characterized the disk. The disk is in an early stage of evolution, as indicated by its large content of dust and its hydrostatic flared geometry, indicative of the presence of a large amount of gas that is well mixed with dust and gravitationally stable. The disk is a precursor of debris disks found around more-evolved A stars such as beta-Pictoris and provides the rare opportunity to witness the conditions prevailing before (or during) planet formation.

Kepler-22b: A 2.4 EARTH-RADIUS PLANET IN THE HABITABLE ZONE OF A SUN-LIKE STAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borucki, William J.; Koch, David G.; Bryson, Stephen T.

A search of the time-series photometry from NASA's Kepler spacecraft reveals a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626 with a period of 290 days. The characteristics of the host star are well constrained by high-resolution spectroscopy combined with an asteroseismic analysis of the Kepler photometry, leading to an estimated mass and radius of 0.970 {+-} 0.060 M{sub Sun} and 0.979 {+-} 0.020 R{sub Sun }. The depth of 492 {+-} 10 ppm for the three observed transits yields a radius of 2.38 {+-} 0.13 Re for the planet. The system passes a battery of testsmore » for false positives, including reconnaissance spectroscopy, high-resolution imaging, and centroid motion. A full BLENDER analysis provides further validation of the planet interpretation by showing that contamination of the target by an eclipsing system would rarely mimic the observed shape of the transits. The final validation of the planet is provided by 16 radial velocities (RVs) obtained with the High Resolution Echelle Spectrometer on Keck I over a one-year span. Although the velocities do not lead to a reliable orbit and mass determination, they are able to constrain the mass to a 3{sigma} upper limit of 124 M{sub Circled-Plus }, safely in the regime of planetary masses, thus earning the designation Kepler-22b. The radiative equilibrium temperature is 262 K for a planet in Kepler-22b's orbit. Although there is no evidence that Kepler-22b is a rocky planet, it is the first confirmed planet with a measured radius to orbit in the habitable zone of any star other than the Sun.« less

Hubble Movies Provide Unprecedented View of Supersonic Jets from Young Stars

NASA Image and Video Library

2017-12-08

AUGUST 31, 2011: A team of scientists has collected enough high-resolution Hubble Space Telescope images over a 14-year period to stitch together time-lapse movies of powerful jets ejected from three young stars. The jets, a byproduct of gas accretion around newly forming stars, shoot off at supersonic speeds in opposite directions through space. These phenomena are providing clues about the final stages of a star’s birth, offering a peek at how our Sun came into existence 4.5 billion years ago. Hubble’s unprecedented sharpness allows astronomers to see changes in the jets over just a few years’ time. Most astronomical processes change over timescales that are much longer than a human lifetime. To read more go to: www.nasa.gov/mission_pages/hubble/science/supersonic-jets... Object Name: HH 34 Bow Shock Image Type: Astronomical Credit: NASA, ESA, and P. Hartigan (Rice University)..NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

The SEEDS High-Contrast Imaging Survey: Exoplanet and Brown Dwarf Survey for Nearby Young Stars Dated with Gyrochronology and Activity Age Indicators

NASA Astrophysics Data System (ADS)

Kuzuhara, Masayuki; Tamura, Motohide; Helminiak, Kris; Mede, Kyle; Brandt, Timothy; Janson, Markus; Kandori, Ryo; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Hashimoto, Jun

2015-12-01

The SEEDS campaign has successfully discovered and characterized exoplanets, brown dwarfs, and circumstellar disks since it began in 2009, via the direct imaging technique. The survey has targeted nearby young stars, as well as stars associated to star-forming regions, the Pleiades open cluster, moving groups, and debris disks. We selected the nearby young stars that have been dated with age indicators based on stellar rotation periods (i.e., gyrochronology) and chromoshperic/coronal activities. Of these, nearly 40 were observed, with ages mainly between 100 and 1000 Myr and distances less than 40 pc. Our observations typically attain the contrast of ~6 x 10-6 at 1'' and better than ~1 x 10-6 beyond 2'', enabling us to detect a planetary-mass companion even around such old stars. Indeed, the SEEDS team reported the discovery that the nearby Sun-like star GJ 504 hosts a Jovian companion GJ 504b, which has a mass of 3-8.5 Jupiter masses that is inferred according to the hot-start cooling models and our estimated system age of 100-510 Myr. The remaining observations out of the selected ~40 stars have resulted in no detection of additional planets or brown dwarf companions. Meanwhile, we have newly imaged a low-mass stellar companion orbiting the G-type star HIP 10321, for which the presence of companion was previously announced via radial velocity technique. The astrometry and radial velocity measurements are simultaneously analyzed to determine the orbit, providing constraints on the dynamical mass of both objects and stellar evolution models. Here we summarize our direct imaging observations for the nearby young stars dated with gyrochrolorogy and activity age indicators. Furthermore, we report the analysis for the HIP 10321 system with the imaged low-mass companion.

Accretion Models for Young Neutron Stars

NASA Astrophysics Data System (ADS)

Alpar, M. A.

2003-07-01

Interaction with possible fallback material, along with the magnetic fields and rotation rates at birth should determine the fates and categories of young neutron stars. This paper addresses some issues related to pure or hybrid accretion models for explaining the properties of young neutron stars.

Exoplanets Clue to Sun's Curious Chemistry

NASA Astrophysics Data System (ADS)

2009-11-01

A ground-breaking census of 500 stars, 70 of which are known to host planets, has successfully linked the long-standing "lithium mystery" observed in the Sun to the presence of planetary systems. Using ESO's successful HARPS spectrograph, a team of astronomers has found that Sun-like stars that host planets have destroyed their lithium much more efficiently than "planet-free" stars. This finding does not only shed light on the lack of lithium in our star, but also provides astronomers with a very efficient way of finding stars with planetary systems. "For almost 10 years we have tried to find out what distinguishes stars with planetary systems from their barren cousins," says Garik Israelian, lead author of a paper appearing this week in the journal Nature. "We have now found that the amount of lithium in Sun-like stars depends on whether or not they have planets." Low levels of this chemical element have been noticed for decades in the Sun, as compared to other solar-like stars, and astronomers have been unable to explain the anomaly. The discovery of a trend among planet-bearing stars provides a natural explanation to this long-standing mystery. "The explanation of this 60 year-long puzzle is for us rather simple," adds Israelian. "The Sun lacks lithium because it has planets." This conclusion is based on the analysis of 500 stars, including 70 planet-hosting stars. Most of these stars were monitored for several years with ESO's High Accuracy Radial Velocity Planet Searcher. This spectrograph, better known as HARPS, is attached to ESO's 3.6-metre telescope and is the world's foremost exoplanet hunter. "This is the best possible sample available to date to understand what makes planet-bearing stars unique," says co-author Michel Mayor. The astronomers looked in particular at Sun-like stars, almost a quarter of the whole sample. They found that the majority of stars hosting planets possess less than 1% of the amount of lithium shown by most of the other stars

The Faint Young Sun Paradox

NASA Astrophysics Data System (ADS)

Khramova, E. G.

2017-05-01

According to astrophysical models, the luminosity of the young Sun had to be by 30% lower than it is today, while according to paleoclimatic data, the Earth surface temperature in Archaea even somewhat exceeded the present-day values. The article analyzes some existing explanations of this discordance, draws attention to a number of unaccounted factors, and suggests a new hypothesis for solving the paradox.

Ultra-Stable Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (5STAR)

NASA Technical Reports Server (NTRS)

Dunagan, Stephen E.; Johnson, Roy R.; Redemann, Jens; Holben, Brent N.; Schmidt, Beat; Flynn, Connor Joseph; Fahey, Lauren; LeBlanc, Samuel; Liss, Jordan; Kacenelenbogen, Meloe S.;

HD 129333: The Sun in its infancy

NASA Technical Reports Server (NTRS)

Dorren, J. David; Guinan, Edward F.

1994-01-01

HD 129333 is a remarkable young, nearby solar-type G star which offers a unique opportunity of studying the properties of the Sun at a time very shortly after in arrived on the main sequence. Its space motion suggest that it is a member of the Pleiades moving group, with an age of approximately 70 Myr; its lithium abundance is consistent with this. HD 129333 has the highest level of Ca II emission of any G star which is not a member of a close binary. Our observations in 1983 showed it to have low-amplitude (5%) light variations implying a rotation period of about 2.7 days, or about 10 times faster than the Sun. Modeling of the photometric variations on the assumption that they are due to starspots yields a spot temperature about 500 K cooler than the photosphere, and a coverage of about 6% of the stellar surface area. ROSAT observations in 1990 revealed the star to be an X-ray source, with an X-ray luminosity in the 0.2 to 2.4 keV range about 300 times that of the Sun. We have used International Ultraviolet Explorer (IUE) observations in conjuction with ground-based photometry to examine the magnetic activity of this star. The IUE emission-line fluxes reveal a level of chromospheric activity 3 to 20 times greater than the Sun's. The transition-region activity is 20 to 100 times that of the Sun. The activity level of HD 129333 is consistent with the Skumanich law relating activity to age, and with the rotation-activity relation, although it may be near saturation level. This star can yield valuable information about the magnetic dynamo of the young Sun, as well as about stellar dynamos in general. The 1988 IUE observations covered four phases of its rotational cycle. A phase dependence of the Mg II h and k emission flux suggests a close association of chromospheric plages with starspot regions at that time. Systematic variations in the mean brightness of HD 129333 between 1983 and 1993, and in the UV emission fluxes, indicate the presence of an activity cycle of an

Massive stars: flare activity due to infalls of comet-like bodies

NASA Astrophysics Data System (ADS)

Ibadov, Subhon; Ibodov, Firuz S.

2015-01-01

Passages of comet-like bodies through the atmosphere/chromosphere of massive stars at velocities more than 600 km/s will be accompanied, due to aerodynamic effects as crushing and flattening, by impulse generation of hot plasma within a relatively very thin layer near the stellar surface/photosphere as well as ``blast'' shock wave, i.e., impact-generated photospheric stellar/solar flares. Observational manifestations of such high-temperature phenomena will be eruption of the explosive layer's hot plasma, on materials of the star and ``exploding'' comet nuclei, into the circumstellar environment and variable anomalies in chemical abundances of metal atoms/ions like Fe, Si etc. Interferometric and spectroscopic observations/monitoring of young massive stars with dense protoplanetary discs are of interest for massive stars physics/evolution, including identification of mechanisms for massive stars variability.

UV SURFACE ENVIRONMENT OF EARTH-LIKE PLANETS ORBITING FGKM STARS THROUGH GEOLOGICAL EVOLUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rugheimer, S.; Sasselov, D.; Segura, A.

2015-06-10

The UV environment of a host star affects the photochemistry in the atmosphere, and ultimately the surface UV environment for terrestrial planets and therefore the conditions for the origin and evolution of life. We model the surface UV radiation environment for Earth-sized planets orbiting FGKM stars in the circumstellar Habitable Zone for Earth through its geological evolution. We explore four different types of atmospheres corresponding to an early-Earth atmosphere at 3.9 Gyr ago and three atmospheres covering the rise of oxygen to present-day levels at 2.0 Gyr ago, 0.8 Gyr ago, and modern Earth. In addition to calculating the UVmore » flux on the surface of the planet, we model the biologically effective irradiance, using DNA damage as a proxy for biological damage. We find that a pre-biotic Earth (3.9 Gyr ago) orbiting an F0V star receives 6 times the biologically effective radiation as around the early Sun and 3520 times the modern Earth–Sun levels. A pre-biotic Earth orbiting GJ 581 (M3.5 V) receives 300 times less biologically effective radiation, about 2 times modern Earth–Sun levels. The UV fluxes calculated here provide a grid of model UV environments during the evolution of an Earth-like planet orbiting a range of stars. These models can be used as inputs into photo-biological experiments and for pre-biotic chemistry and early life evolution experiments.« less

Dynamos of the Sun, Stars, and Planets - Preface

NASA Astrophysics Data System (ADS)

Stix, M.

2005-04-01

The conference ``Dynamos of the Sun, Stars, and Planets'' was organized by the Kiepenheuer-Institut für Sonnenphysik Freiburg, and was held at the University of Freiburg from 4th to 6th October 2004. About 50 participants attended the conference, with 8 review lectures, 20 contributed talks, and 6 posters. With only few exceptions, these contributions appear in the present issue of Astronomische Nachrichten. This preface summarizes the discussion of the closing session.

YoungStar in Wisconsin: Analysis of Data as of July 2014. YoungStar Progress Report #5

ERIC Educational Resources Information Center

Wisconsin Council on Children and Families, 2014

2014-01-01

YoungStar is a program of the Department of Children and Families (DCF) designed to improve the quality of child care for Wisconsin children. YoungStar is designed to: (1) evaluate and rate the quality of care given by child care providers; (2) help parents choose the best child care for their kids; (3) support providers with tools and training to…

Optical High-resolution Spectroscopy of 14 Young α-rich Stars

NASA Astrophysics Data System (ADS)

Matsuno, Tadafumi; Yong, David; Aoki, Wako; Ishigaki, Miho N.

2018-06-01

We report chemical abundances of 14 young α-rich stars including neutron-capture elements based on high-quality optical spectra from HIRES/Keck I and differential line-by-line analysis. From a comparison of the abundance patterns of young α-rich stars to those of nearby bright red giants with a similar metallicity range (‑0.7 < [Fe/H] < ‑0.2), we confirm their high α-element abundances reported by previous studies based on near-infrared spectroscopy. We reveal for the first time low abundances of s-process elements and high abundances of r-process elements. All the abundances are consistent with those seen in the typical α-rich population of the Galactic disk, and no abundance anomalies are found except for Li-enhancement in one object previously reported and mild enhancement of Na in two stars. In particular, the lack of s-process enhancement excludes the hypothesis that mass transfer from asymptotic giant branch stars plays an important role in the formation of young α-rich stars. The high frequency of radial velocity variation (more than 50%) is also confirmed. We argue that mass transfer from low-mass red giants is the likely dominant formation mechanism for young α-rich stars. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

ultra-Stable Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (5STAR)

NASA Astrophysics Data System (ADS)

Dunagan, S. E.; Johnson, R. R.; Redemann, J.; Holben, B. N.; Schmid, B.; Flynn, C. J.; Fahey, L.; LeBlanc, S. E.; Liss, J.; Kacenelenbogen, M. S.; Segal-Rosenhaimer, M.; Shinozuka, Y.; Dahlgren, R. P.; Pistone, K.; Karol, Y.

2017-12-01

The Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) combines airborne sun tracking and sky scanning with diffraction spectroscopy to improve knowledge of atmospheric constituents and their links to air pollution and climate. Direct beam hyperspectral measurement of optical depth improves retrievals of gas constituents and determination of aerosol properties. Sky scanning enhances retrievals of aerosol type and size distribution. Hyperspectral cloud-transmitted radiance measurements enable the retrieval of cloud properties from below clouds. These measurements tighten the closure between satellite and ground-based measurements. 4STAR incorporates a modular sun-tracking/ sky-scanning optical head with optical fiber signal transmission to rack mounted spectrometers, permitting miniaturization of the external optical tracking head, and future detector evolution. 4STAR has supported a broad range of flight experiments since it was first flown in 2010. This experience provides the basis for a series of improvements directed toward reducing measurement uncertainty and calibration complexity, and expanding future measurement capabilities, to be incorporated into a new 5STAR instrument. A 9-channel photodiode radiometer with AERONET-matched bandpass filters will be incorporated to improve calibration stability. A wide dynamic range tracking camera will provide a high precision solar position tracking signal as well as an image of sky conditions around the solar axis. An ultrasonic window cleaning system design will be tested. A UV spectrometer tailored for formaldehyde and SO2 gas retrievals will be added to the spectrometer enclosure. Finally, expansion capability for a 4 channel polarized radiometer to measure the Stokes polarization vector of sky light will be incorporated. This paper presents initial progress on this next-generation 5STAR instrument. Keywords: atmosphere; climate; pollution; radiometry; technology; hyperspectral; fiber optic

A Multiplicity Census of Young Stars in Chamaeleon I

NASA Astrophysics Data System (ADS)

Lafrenière, David; Jayawardhana, Ray; Brandeker, Alexis; Ahmic, Mirza; van Kerkwijk, Marten H.

2008-08-01

We present the results of a multiplicity survey of 126 stars spanning ~0.1-3 M⊙ in the ~2 Myr old Chamaeleon I star-forming region, based on adaptive optics imaging with the ESO Very Large Telescope. Our observations have revealed 30 binaries and six triples, of which 19 and four, respectively, are new discoveries. The overall multiplicity fraction we find for Cha I (~30%) is similar to those reported for other dispersed young associations, but significantly higher than seen in denser clusters and the field, for comparable samples. Both the frequency and the maximum separation of Cha I binaries decline with decreasing mass, while the mass ratios approach unity; conversely, tighter pairs are more likely to be equal mass. We confirm that brown dwarf companions to stars are rare, even at young ages at wide separations. Based on follow-up spectroscopy of two low-mass substellar companion candidates, we conclude that both are likely background stars. The overall multiplicity fraction in Cha I is in rough agreement with numerical simulations of cloud collapse and fragmentation, but its observed mass dependence is less steep than predicted. The paucity of higher order multiples, in particular, provides a stringent constraint on the simulations, and seems to indicate a low level of turbulence in the prestellar cores in Cha I.

Can Superflares Occur on the Sun? A View from Dynamo Theory

NASA Astrophysics Data System (ADS)

Katsova, M. M.; Kitchatinov, L. L.; Livshits, M. A.; Moss, D. L.; Sokoloff, D. D.; Usoskin, I. G.

2018-01-01

Recent data from the Kepler mission has revealed the occurrence of superflares in Sun-like stars which exceed by far any observed solar flares in released energy. Radionuclide data do not provide evidence for occurrence of superflares on the Sun over the past eleven millennia. Stellar data for a subgroup of superflaring Kepler stars are analysed in an attempt to find possible progenitors of their abnormal magnetic activity. A natural idea is that the dynamo mechanism in superflaring stars differs in some respect from that in the Sun. We search for a difference in the dynamo-related parameters between superflaring stars and the Sun to suggest a dynamo mechanism as close as possible to the conventional solar/stellar dynamo but capable of providing much higher magnetic energy. Dynamo based on joint action of differential rotation and mirror asymmetric motions can in principle result in excitation of two types of magnetic fields. First of all, it is well-known in solar physics dynamo waves. The point is that another magnetic configuration with initial growth and further stabilisation can also be excited. For comparable conditions, magnetic field of second configuration is much stronger than that of the first one just because dynamo does not spend its energy for periodic magnetic field inversions but uses it for magnetic field growth. We analysed available data from the Kepler mission concerning the superflaring stars in order to find tracers of anomalous magnetic activity. As suggested in a recent paper [1], we find that anti-solar differential rotation or anti-solar sign of the mirror-asymmetry of stellar convection can provide the desired strong magnetic field in dynamo models. We confirm this concept by numerical models of stellar dynamos with corresponding governing parameters. We conclude that the proposed mechanism can plausibly explain the superflaring events at least for some cool stars, including binaries, subgiants and, possibly, low-mass stars and young

Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) Instrument Improvements

NASA Technical Reports Server (NTRS)

Dunagan, Stephen E.; Redemann, Jens; Chang, Cecilia; Dahlgren, Robert; Fahey, Lauren; Flynn, Connor; Johnson, Roy; Kacenelenbogen, Meloe; Leblanc, Samuel; Liss, Jordan;

A hot Jupiter orbiting a 2-million-year-old solar-mass T Tauri star.

PubMed

Donati, J F; Moutou, C; Malo, L; Baruteau, C; Yu, L; Hébrard, E; Hussain, G; Alencar, S; Ménard, F; Bouvier, J; Petit, P; Takami, M; Doyon, R; Collier Cameron, A

2016-06-30

Hot Jupiters are giant Jupiter-like exoplanets that orbit their host stars 100 times more closely than Jupiter orbits the Sun. These planets presumably form in the outer part of the primordial disk from which both the central star and surrounding planets are born, then migrate inwards and yet avoid falling into their host star. It is, however, unclear whether this occurs early in the lives of hot Jupiters, when they are still embedded within protoplanetary disks, or later, once multiple planets are formed and interact. Although numerous hot Jupiters have been detected around mature Sun-like stars, their existence has not yet been firmly demonstrated for young stars, whose magnetic activity is so intense that it overshadows the radial velocity signal that close-in giant planets can induce. Here we report that the radial velocities of the young star V830 Tau exhibit a sine wave of period 4.93 days and semi-amplitude 75 metres per second, detected with a false-alarm probability of less than 0.03 per cent, after filtering out the magnetic activity plaguing the spectra. We find that this signal is unrelated to the 2.741-day rotation period of V830 Tau and we attribute it to the presence of a planet of mass 0.77 times that of Jupiter, orbiting at a distance of 0.057 astronomical units from the host star. Our result demonstrates that hot Jupiters can migrate inwards in less than two million years, probably as a result of planet–disk interactions.

Massive Young Star and its Cradle

NASA Image and Video Library

2010-07-14

This star-forming region, captured by NASA Spitzer Space Telescope, is dominated by the bright, young star IRAS 13481-6124; it is the first massive baby star for which astronomers could obtain a detailed look at the dusty disk closely encircling it.

Cool Stars May Have Different Prebiotic Chemical Mix

NASA Technical Reports Server (NTRS)

2009-01-01

NASA's Spitzer Space Telescope detected a prebiotic, or potentially life-forming, molecule called hydrogen cyanide (HCN) in the planet-forming disks around yellow stars like our sun, but not in the disks around cooler, reddish stars.

The observations are plotted in this graph, called a spectrum, in which light from the gas in the disks around the stars has been split up into its basic components, or wavelengths. Data from stars like our sun are yellow, and data from cool stars are orange. Light wavelengths are shown on the X-axis, and the relative brightness of disk emission is shown on the Y-axis. The signature of a baseline molecule, called acetylene (C₂H₂), was seen for both types of stars, but hydrogen cyanide was seen only around stars like our sun.

Hydrogen cyanide is an organic, nitrogen-containing molecule. Five hydrogen cyanide molecules can link up to form adenine, one of the four chemical bases of DNA.

The relevance of the IUE results on young stars for Earth's paleoatmosphere

NASA Technical Reports Server (NTRS)

Canuto, V. M.; Levine, J. S.; Augustsson, T. R.; Imhoff, C. L.; Giampap, M. S.

1982-01-01

Using the latest IUE results for seven T Tauri stars, which are believed to represent the young Sun and a detailed photochemical chemical model of the paleoatmosphere, the vertical distribution of Oxygen and Ozone in the early atmosphere was calculated. The calculations indicate that the surface Oxygen mixing ratio is as much as six orders of magnitude larger than previously estimated, but appears low enough for the formation of amino acids via the Urey-Miller type of experiments. It is believed that the quantification of the oxygen level in the Earth's paleoatmosphere presented can reconcile the demands of both biological and geological considerations.

Our Sun V: A Bright Young Sun Consistent with Helioseismology and Warm Temperatures on Ancient Earth and Mars

NASA Technical Reports Server (NTRS)

Sackmann, I.-Juliana; Boothroyd, Arnold I.

2001-01-01

The relatively warm temperatures required on early Earth and Mars have been difficult to account for with warming from greenhouse gases. A slightly more massive young Sun would be brighter than predicted by the standard solar model, simultaneously resolving this problem for both Earth and Mars. We computed high-precision solar models with seven initial masses, from Mi = 1.01 to 1.07 solar mass - the latter being the maximum permitted if the early Earth is not to lose its water via a moist greenhouse effect. The relatively modest early mass loss that is required remains consistent with observational limits on mass loss from young stars and with estimates of the past solar wind obtained from lunar rocks. We considered three types of mass loss rates: (1) a reasonable choice of a simple exponential decline, (2) an extreme step-function case that gives the maximum effect consistent with observations, and (3) the radical case of a linear decline which is inconsistent with the solar wind mass loss estimates from lunar rocks. Our computations demonstrated that mass loss leaves a fingerprint oil the Sun's internal structure large enough to be detectable with helioseismic observations. All of our mass-losing solar models were consistent with the helioseismic observations; in fact, our preferred mass-losing cases were in marginally better agreement with the helioseismology than the standard solar model was, although this difference was smaller than the effects of other uncertainties in the input physics and in the solar composition. Mass loss has only a relatively minor effect on the predicted lithium depletion; the major portion of the solar lithium depletion must still be due to rotational mixing. Thus the modest mass loss cases considered here cannot be ruled out by observed lithium depletions. For the three mass loss types considered, the preferred initial masses were 1.07 solar mass for the exponential case and 1.04 solar mass for the step-function and linear cases; all

YoungStar: We're Turning Five! Five Year Analysis as of July 2015. YoungStar Progress Report 6

ERIC Educational Resources Information Center

Wisconsin Council on Children and Families, 2015

2015-01-01

This report is the sixth in a series of Wisconsin Council on Children & Families (WCCF) reports tracking the progress of Wisconsin's YoungStar program, a quality rating and improvement system (QRIS) launched in 2010 to improve the quality of Wisconsin child care programs. YoungStar focuses on children of low-income working families receiving…

Evidence for the distribution of angular velocity inside the sun and stars

NASA Technical Reports Server (NTRS)

1972-01-01

A round table discussion of problems of solar and stellar spindown and theory is presented. Observational evidence of the angular momentum of the solar wind is included, emphasizing the distribution of angular velocity inside the sun and stars.

The Age Related Properties of Solar Type Stars

NASA Technical Reports Server (NTRS)

Soderblom, David

1999-01-01

The studies of lithium in solar-type stars in clusters of a wide range of ages has provided critical information on a tracer of convective processes, especially among very young stars. Our most recent work has been on a pre-main sequence cluster (NGC 2264) that took place after this grant expired, but was founded on it. The spread seen in Li in Zero-Age Main Sequence clusters like the Pleiades is huge and possibly related to rotation. No clear spread in seen in NGC 2264, so it does not have its origins in the conditions of formation but is instead a result of processes occurring during PMS evolution. Our observations of M67 were particularly interesting because this cluster is the same age as the Sun, i.e.,very old. Clear evidence was seen for a spread in Li there too, indicating that the spread seen in very young stars perpetuates itself into old age.

Design and Characterization of the 4STAR Sun-Sky Spectrometer with Results from 4- Way Intercomparison of 4STAR, AATS-14, Prede, and Cimel Photometers at Mauna Loa Observatory.

NASA Astrophysics Data System (ADS)

Flynn, C. J.; Dunagan, S. E.; Johnson, R. R.; Schmid, B.; Shinozuka, Y.; Ramachandran, S.; Livingston, J. M.; Russell, P. B.; Redemann, J.; Tran, A. K.; Holben, B. N.

2008-12-01

Uncertainties in radiative forcing of climate are still dominated by uncertainties in forcing by aerosols. Aerosols impact the radiation balance in three primary ways: the direct effect through scattering and absorption of radiation, the indirect effect by acting as cloud condensation nuclei affecting cloud optical depth and longevity, and the semi-direct effect affecting cloud formation and longevity through heating and thermodynamics. An active collaboration between the Pacific Northwest National Laboratory (PNNL), National Aeronautics and Space Administration (NASA) Ames Research Center (ARC), and NASA Goddard Space Flight Center (GSFC) is advancing new instrument concepts with application to reducing these aerosol uncertainties. The concept of 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) combines airborne sun tracking capabilities of the Ames Airborne Tracking Sun Photometer (AATS-14) and Aeronet-like sky scanning capability with state-of-the-art monolithic spectrometry. The overall science goal for the new instruments is to improve knowledge of atmospheric constituents and their links to climate. The high-resolution spectral capability will improve retrievals of gas constituents (e.g., H2O, O3, and NO2) and thereby improve determination of aerosol properties as residual components of the total optical depth. The sky scanning capability will enable retrievals of aerosol type (via complex refractive index and shape) and aerosol size distribution extending to larger sizes than attainable by direct-beam sun photometry alone. Additional technical goals are to reduce instrument size, weight, and power requirements while increasing autonomy and component modularity to permit operation on a wide range of aircraft including unmanned aerial vehicles (UAVs). To investigate techniques to accomplish these goals, we developed a ground-based prototype, 4STAR-Ground. The 4STAR-Ground operating performance has been characterized in many tests

An X-ray outburst from the rapidly accreting young star that illuminates McNeil's nebula.

PubMed

Kastner, J H; Richmond, M; Grosso, N; Weintraub, D A; Simon, T; Frank, A; Hamaguchi, K; Ozawa, H; Henden, A

2004-07-22

Young, low-mass stars are luminous X-ray sources whose powerful X-ray flares may exert a profound influence over the process of planet formation. The origin of the X-ray emission is uncertain. Although many (or perhaps most) recently formed, low-mass stars emit X-rays as a consequence of solar-like coronal activity, it has also been suggested that X-ray emission may be a direct result of mass accretion onto the forming star. Here we report X-ray imaging spectroscopy observations which reveal a factor approximately 50 increase in the X-ray flux from a young star that is at present undergoing a spectacular optical/infrared outburst (this star illuminates McNeil's nebula). The outburst seems to be due to the sudden onset of a phase of rapid accretion. The coincidence of a surge in X-ray brightness with the optical/infrared eruption demonstrates that strongly enhanced high-energy emission from young stars can occur as a consequence of high accretion rates. We suggest that such accretion-enhanced X-ray emission from erupting young stars may be short-lived, because intense star-disk magnetospheric interactions are quenched rapidly by the subsequent flood of new material onto the star.

The evolution of angular momentum among zero-age main-sequence solar-type stars

NASA Technical Reports Server (NTRS)

Soderblom, David R.; Stauffer, John R.; Macgregor, Keith B.; Jones, Burton F.

1993-01-01

We consider a survey of rotation among F, G, and K dwarfs of the Pleiades in the context of other young clusters (Alpha Persei and the Hyades) and pre-main-sequence (PMS) stars (in Taurus-Auriga and Orion) in order to examine how the angular momentum of a star like the sun evolves during its early life on the main sequence. The rotation of PMS stars can be evolved into distributions like those seen in the young clusters if there is only modest, rotation-independent angular momentum loss prior to the ZAMS. Even then, the ultrafast rotators (UFRs, or ZAMS G and K dwarfs with v sin i equal to or greater than 30 km/s) must owe their extra angular momentum to their conditions of formation and to different angular momentum loss rates above a threshold velocity, for it is unlikely that these stars had angular momentum added as they neared the ZAMS, nor can a spread in ages within a cluster account for the range of rotation seen. Only a fraction of solar-type stars are thus capable of becoming UFRs, and it is not a phase that all stars experience. Simple scaling relations (like the Skumanich relation) applied to the observed surface rotation rates of young solar-type stars cannot reproduce the way in which the Pleiades evolve into the Hyades. We argue that invoking internal differential rotation in these ZAMS stars can explain several aspects of the observations and thus can provide a consistent picture of ZAMS angular momentum evolution.

RUNAWAY MASSIVE STARS FROM R136: VFTS 682 IS VERY LIKELY A 'SLOW RUNAWAY'

DOE Office of Scientific and Technical Information (OSTI.GOV)

Banerjee, Sambaran; Kroupa, Pavel; Oh, Seungkyung, E-mail: sambaran@astro.uni-bonn.de, E-mail: pavel@astro.uni-bonn.de, E-mail: skoh@astro.uni-bonn.de

2012-02-10

We conduct a theoretical study on the ejection of runaway massive stars from R136-the central massive, starburst cluster in the 30 Doradus complex of the Large Magellanic Cloud. Specifically, we investigate the possibility of the very massive star (VMS) VFTS 682 being a runaway member of R136. Recent observations of the above VMS, by virtue of its isolated location and its moderate peculiar motion, have raised the fundamental question of whether isolated massive star formation is indeed possible. We perform the first realistic N-body computations of fully mass-segregated R136-type star clusters in which all the massive stars are in primordialmore » binary systems. These calculations confirm that the dynamical ejection of a VMS from an R136-like cluster, with kinematic properties similar to those of VFTS 682, is common. Hence, the conjecture of isolated massive star formation is unnecessary to account for this VMS. Our results are also quite consistent with the ejection of 30 Dor 016, another suspected runaway VMS from R136. We further note that during the clusters' evolution, mergers of massive binaries produce a few single stars per cluster with masses significantly exceeding the canonical upper limit of 150 M{sub Sun }. The observations of such single super-canonical stars in R136, therefore, do not imply an initial mass function with an upper limit greatly exceeding the accepted canonical 150 M{sub Sun} limit, as has been suggested recently, and they are consistent with the canonical upper limit.« less

From Stars to Super-Planets: The Low-Mass IMF in the Young Cluster IC348

NASA Technical Reports Server (NTRS)

Najita, Joan R.; Tiede, Glenn P.; Carr, John S.

2000-01-01

We investigate the low-mass population of the young cluster IC348 down to the deuterium-burning limit, a fiducial boundary between brown dwarf and planetary mass objects, using a new and innovative method for the spectral classification of late-type objects. Using photometric indices, constructed from HST/NICMOS narrow-band imaging, that measure the strength of the 1.9 micron water band, we determine the spectral type and reddening for every M-type star in the field, thereby separating cluster members from the interloper population. Due to the efficiency of our spectral classification technique, our study is complete from approximately 0.7 solar mass to 0.015 solar mass. The mass function derived for the cluster in this interval, dN/d log M alpha M(sup 0.5), is similar to that obtained for the Pleiades, but appears significantly more abundant in brown dwarfs than the mass function for companions to nearby sun-like stars. This provides compelling observational evidence for different formation and evolutionary histories for substellar objects formed in isolation vs. as companions. Because our determination of the IMF is complete to very low masses, we can place interesting constraints on the role of physical processes such as fragmentation in the star and planet formation process and the fraction of dark matter in the Galactic halo that resides in substellar objects.

Nebula-based Primordial Atmospheres of Planets Around Solar-Like Stars Revised

NASA Astrophysics Data System (ADS)

Scherf, Manuel; Lammer, H.; Leitzinger, M.; Odert, P.; Güdel, M.; Hanslmeier, A.

2012-05-01

At the beginning of a planetary system, in the stage of the stellar nebula and the growing-phase of the planets, planetesimals and Earth-like proto-planets accumulate a remarkable amount of gas, mainly consisting of hydrogen and helium. The mass of such a primordial atmosphere was first estimated for the proto-Earth by Hayashi et al. (1979), with up to 1026 g accumulated within 106 years. Furthermore it is commonly expected that these primordial atmospheres will be completely dissipated due to irradiation of the stellar EUV-flux during the first 108 years. Recent observations of young solar-like stars indicate that the efficiency and effect of the EUV-flux after the nebula disappeared, was highly overestimated by previous studies. We show that parts of these dense hydrogen/helium-gas envelopes may sustain this early active stage of a young star. Implications on the habitability are also discussed.

An orbit fit to likely Hermus Stream stars

NASA Astrophysics Data System (ADS)

Martin, Charles; Amy, Paul M.; Newberg, Heidi Jo; Shelton, Siddhartha; Carlin, Jeffrey L.; Beers, Timothy C.; Denissenkov, Pavel; Willett, Benjamin A.

2018-06-01

We selected blue horizontal branch (BHB) stars within the expected distance range and sky position of the Hermus Stream from Data Release 10 of the Sloan Digital Sky Survey. We identify a moving group of 19 BHB stars that are concentrated within two degrees of the Hermus Stream, between 10 and 14 kpc from the Sun. The concentration in velocity is inconsistent with a Gaussian distribution with 98 per cent confidence (2.33 sigma). The stars in the moving group have line-of-sight velocities of vgsr ˜ 50 km s-1, a velocity dispersion of σv ≲ 11 km s-1, a line-of-sight depth of ˜1 kpc, and a metallicity of [Fe/H] = -2.1 ± 0.4. The best-fitting orbit has a perigalacticon of ˜4 kpc, apogalacticon of ˜17 kpc, orbital period of ˜247 Myr, eccentricity e = 0.62, and inclination i ˜ 75° from b = 90°. The BHB stars in the stream are estimated to be 12 Gyr old. An N-body simulation of a mass-follows-light ultrafaint dwarf galaxy with mass 106 M⊙ and radius 40 pc is consistent with the observed properties. The properties of the identified moving group of 19 BHB stars are close enough to those of the Hermus Stream (which is traced predominantly in turnoff stars) that we find it likely that they are associated. If that is the case, then our orbit fit would imply that there is no relationship between the Hermus and Phoenix streams, as previously proposed.

A Star Close Encounter

NASA Image and Video Library

2006-10-03

The potential planet-forming disk (or "protoplanetary disk") of a sun-like star is being violently ripped away by the powerful winds of a nearby hot O-type star in this image from NASA's Spitzer Space Telescope. At up to 100 times the mass of sun-like stars, O stars are the most massive and energetic stars in the universe. The O star can be seen to the right of the image, as the large orange spot with the white center. To the left, the comet-like structure is actually a neighboring solar system that is being destroyed by the O star's powerful winds and intense ultraviolet light. In a process called "photoevaporation," immense output from the O star heats up the nearby protoplanetary disk so much that gas and dust boil off, and the disk can no longer hold together. Photon (or light) blasts from the O star then strip the potential planet-forming disk off its neighbor star by blowing away evaporated material. This effect is illustrated in the smaller system's comet-like structure. The system is located about 2,450 light-years away in the star-forming cloud IC 1396. The image was taken with Spitzer's multiband imaging photometer instrument at 24 microns. The picture is a pseudo-color stretch representing intensity. Yellow and white represent hot areas, whereas purple and blue represent relatively cooler, fainter regions.

Search for OB stars running away from young star clusters. II. The NGC 6357 star-forming region

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.; Kniazev, A. Y.; Kroupa, P.; Oh, S.

2011-11-01

Dynamical few-body encounters in the dense cores of young massive star clusters are responsible for the loss of a significant fraction of their massive stellar content. Some of the escaping (runaway) stars move through the ambient medium supersonically and can be revealed via detection of their bow shocks (visible in the infrared, optical or radio). In this paper, which is the second of a series of papers devoted to the search for OB stars running away from young ( ≲ several Myr) Galactic clusters and OB associations, we present the results of the search for bow shocks around the star-forming region NGC 6357. Using the archival data of the Midcourse Space Experiment (MSX) satellite and the Spitzer Space Telescope, and the preliminary data release of the Wide-Field Infrared Survey Explorer (WISE), we discovered seven bow shocks, whose geometry is consistent with the possibility that they are generated by stars expelled from the young (~1-2 Myr) star clusters, Pismis 24 and AH03 J1725-34.4, associated with NGC 6357. Two of the seven bow shocks are driven by the already known OB stars, HD 319881 and [N78] 34. Follow-up spectroscopy of three other bow-shock-producing stars showed that they are massive (O-type) stars as well, while the 2MASS photometry of the remaining two stars suggests that they could be B0 V stars, provided that both are located at the same distance as NGC 6357. Detection of numerous massive stars ejected from the very young clusters is consistent with the theoretical expectation that star clusters can effectively lose massive stars at the very beginning of their dynamical evolution (long before the second mechanism for production of runaway stars, based on a supernova explosion in a massive tight binary system, begins to operate) and lends strong support to the idea that probably all field OB stars have been dynamically ejected from their birth clusters. A by-product of our search for bow shocks around NGC 6357 is the detection of three circular

Effectiveness of a Multicomponent Sun Protection Program for Young Children

PubMed Central

Ho, Byron K.; Reidy, Katie; Huerta, Imelda; Dilley, Kimberley; Crawford, Susan; Hultgren, Brittney A.; Mallett, Kimberly A.; Turrisi, Rob; Robinson, June K.

2017-01-01

Importance Emphasizing sun protection behaviors among young children may minimize sun damage and foster lifelong sun protection behaviors that will reduce the likelihood of developing skin cancer, especially melanoma. Objective To determine whether a multicomponent sun protection program delivered in pediatric clinics during the summer could increase summertime sun protection among young children. Design, Setting, and Participants Randomized controlled clinical trial with 4-week follow-up that included 300 parents or relatives (hereafter simply referred to as caregivers [mean age, 36.0 years]) who brought the child (2-6 years of age) in their care to an Advocate Medical Group clinic during the period from May 15 to August 14, 2015. Of the 300 caregiver-child pairs, 153 (51.0%) were randomly assigned to receive a read-along book, swim shirt, and weekly text-message reminders related to sun protection behaviors (intervention group) and 147 (49.0%) were randomly assigned to receive the information usually provided at a well-child visit (control group). Data analysis was performed from August 20 to 30, 2015. Intervention Multicomponent sun protection program composed of a read-along book, swim shirt, and weekly text-message reminders related to sun protection behaviors. Main Outcomes and Measures Outcomes were caregiver-reported use of sun protection by the child (seeking shade and wearing sun-protective clothing and sunscreen) using a 5-point Likert scale, duration of outdoor activities, and number of children who had sunburn or skin irritation. The biologic measurement of the skin pigment of a child's arm was performed with a spectrophotometer at baseline and 4 weeks later. Results Of the 300 caregiver-child pairs, the 153 children in the intervention group had significantly higher scores related to sun protection behaviors on both sunny (mean [SE], 15.748 [0.267] for the intervention group; mean [SE], 14.780 [0.282] for the control group; mean difference, 0.968) and

Sun, the Earth, and Near-Earth Space: A Guide to the Sun-Earth System

NASA Technical Reports Server (NTRS)

Eddy, John A.

2010-01-01

In a world of warmth and light and living things we soon forget that we are surrounded by a vast universe that is cold and dark and deadly dangerous, just beyond our door. On a starry night, when we look out into the darkness that lies around us, the view can be misleading in yet another way: for the brightness and sheer number of stars, and their chance groupings into familiar constellations, make them seem much nearer to each other, and to us, that in truth they are. And every one of them--each twinkling, like a diamond in the sky--is a white-hot sun, much like our own. The nearest stars in our own galaxy--the Milky Way-- are more than a million times further away from us than our star, the Sun. We could make a telephone call to the Moon and expect to wait but a few seconds between pieces of a conversation, or but a few hours in calling any planet in our solar system.

Water Loss from Young Planets

NASA Astrophysics Data System (ADS)

Tian, Feng; Güdel, Manuel; Johnstone, Colin P.; Lammer, Helmut; Luger, Rodrigo; Odert, Petra

2018-04-01

Good progress has been made in the past few years to better understand the XUV evolution trend of Sun-like stars, the capture and dissipation of hydrogen dominant envelopes of planetary embryos and protoplanets, and water loss from young planets around M dwarfs. This chapter reviews these recent developments. Observations of exoplanets and theoretical works in the near future will significantly advance our understanding of one of the fundamental physical processes shaping the evolution of solar system terrestrial planets.

Lithium Depletion in Solar-like Stars: Effect of Overshooting Based on Realistic Multi-dimensional Simulations

NASA Astrophysics Data System (ADS)

Baraffe, I.; Pratt, J.; Goffrey, T.; Constantino, T.; Folini, D.; Popov, M. V.; Walder, R.; Viallet, M.

2017-08-01

We study lithium depletion in low-mass and solar-like stars as a function of time, using a new diffusion coefficient describing extra-mixing taking place at the bottom of a convective envelope. This new form is motivated by multi-dimensional fully compressible, time-implicit hydrodynamic simulations performed with the MUSIC code. Intermittent convective mixing at the convective boundary in a star can be modeled using extreme value theory, a statistical analysis frequently used for finance, meteorology, and environmental science. In this Letter, we implement this statistical diffusion coefficient in a one-dimensional stellar evolution code, using parameters calibrated from multi-dimensional hydrodynamic simulations of a young low-mass star. We propose a new scenario that can explain observations of the surface abundance of lithium in the Sun and in clusters covering a wide range of ages, from ˜50 Myr to ˜4 Gyr. Because it relies on our physical model of convective penetration, this scenario has a limited number of assumptions. It can explain the observed trend between rotation and depletion, based on a single additional assumption, namely, that rotation affects the mixing efficiency at the convective boundary. We suggest the existence of a threshold in stellar rotation rate above which rotation strongly prevents the vertical penetration of plumes and below which rotation has small effects. In addition to providing a possible explanation for the long-standing problem of lithium depletion in pre-main-sequence and main-sequence stars, the strength of our scenario is that its basic assumptions can be tested by future hydrodynamic simulations.

Description of the Sun as a Star: General Physical Characteristics

NASA Technical Reports Server (NTRS)

Kucera, Theresa; Crannell, Carol Jo

2000-01-01

Numerical parameters characterizing the size and energy output of the sun are presented. These values are the standard yardstick by which other stars are measured. The large number of significant digits tabulated here serve mainly to illustrate the precision to which these parameters are known. Also listed are parameters characterizing the earth's orbit around the sun and the intensity of the sun's radiation at the mean orbital distance. The appearance of the sun depends critically on how it is observed. Each type of radiation observed carries specific information about the physical processes at work on the sun. Special types of instruments reveal aspects otherwise invisible. Coronagraphs reveal the dimmer outer regions of the sun's atmosphere otherwise visible only during total solar eclipses. Spectroscopy can reveal motions, magnetic field strengths, temperatures and densities. In situ measurements have revealed the characteristics of the solar wind and extended our knowledge of the solar magnetic field both near the earth and beyond the orbits of the planets. As an example, the sun's disk observed almost simultaneously in six different wavelengths of light is shown. In visible light we can see the white disk of the sun with the dark spots known as sunspots. By analyzing the spectral lines produced by the sun we can measure the strength of the sun's magnetic field at its surface, producing a magnetogram. This magnetogram reveals that the sunspots are regions of intense magnetic field. Further images of the sun reveal that the sunspot regions are just the bases of systems of hot loops which emit radio-waves, ultraviolet light and X-rays. The sun imaged in a spectral line of hydrogen known as "H alpha" is shown. In this line we also see the long dark "filaments". These filaments form in long channels between areas of opposing magnetic field. Such channels can be seen in the ultraviolet image. Data concerning the sun are obtained with many different kinds of

Search for OB stars running away from young star clusters. I. NGC 6611

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.; Bomans, D. J.

2008-11-01

N-body simulations have shown that the dynamical decay of the young (~1 Myr) Orion Nebula cluster could be responsible for the loss of at least half of its initial content of OB stars. This result suggests that other young stellar systems could also lose a significant fraction of their massive stars at the very beginning of their evolution. To confirm this expectation, we used the Mid-Infrared Galactic Plane Survey (completed by the Midcourse Space Experiment satellite) to search for bow shocks around a number of young (⪉several Myr) clusters and OB associations. We discovered dozens of bow shocks generated by OB stars running away from these stellar systems, supporting the idea of significant dynamical loss of OB stars. In this paper, we report the discovery of three bow shocks produced by O-type stars ejected from the open cluster NGC 6611 (M16). One of the bow shocks is associated with the O9.5Iab star HD165319, which was suggested to be one of “the best examples for isolated Galactic high-mass star formation” (de Wit et al. 2005, A&A, 437, 247). Possible implications of our results for the origin of field OB stars are discussed.

Observational evidence for enhanced magnetic activity of superflare stars.

PubMed

Karoff, Christoffer; Knudsen, Mads Faurschou; De Cat, Peter; Bonanno, Alfio; Fogtmann-Schulz, Alexandra; Fu, Jianning; Frasca, Antonio; Inceoglu, Fadil; Olsen, Jesper; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Shi, Jianrong; Zhang, Wei

2016-03-24

Superflares are large explosive events on stellar surfaces one to six orders-of-magnitude larger than the largest flares observed on the Sun throughout the space age. Due to the huge amount of energy released in these superflares, it has been speculated if the underlying mechanism is the same as for solar flares, which are caused by magnetic reconnection in the solar corona. Here, we analyse observations made with the LAMOST telescope of 5,648 solar-like stars, including 48 superflare stars. These observations show that superflare stars are generally characterized by larger chromospheric emissions than other stars, including the Sun. However, superflare stars with activity levels lower than, or comparable to, the Sun do exist, suggesting that solar flares and superflares most likely share the same origin. The very large ensemble of solar-like stars included in this study enables detailed and robust estimates of the relation between chromospheric activity and the occurrence of superflares.

Observational evidence for enhanced magnetic activity of superflare stars

PubMed Central

Karoff, Christoffer; Knudsen, Mads Faurschou; De Cat, Peter; Bonanno, Alfio; Fogtmann-Schulz, Alexandra; Fu, Jianning; Frasca, Antonio; Inceoglu, Fadil; Olsen, Jesper; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Shi, Jianrong; Zhang, Wei

2016-01-01

Superflares are large explosive events on stellar surfaces one to six orders-of-magnitude larger than the largest flares observed on the Sun throughout the space age. Due to the huge amount of energy released in these superflares, it has been speculated if the underlying mechanism is the same as for solar flares, which are caused by magnetic reconnection in the solar corona. Here, we analyse observations made with the LAMOST telescope of 5,648 solar-like stars, including 48 superflare stars. These observations show that superflare stars are generally characterized by larger chromospheric emissions than other stars, including the Sun. However, superflare stars with activity levels lower than, or comparable to, the Sun do exist, suggesting that solar flares and superflares most likely share the same origin. The very large ensemble of solar-like stars included in this study enables detailed and robust estimates of the relation between chromospheric activity and the occurrence of superflares. PMID:27009381

John Ellard Gore: "Giant Suns and Miniature Stars"

NASA Astrophysics Data System (ADS)

Holberg, Jay B.

2007-12-01

The Irish amateur astronomer John Ellard Gore (1845-1910) was a founding member of the British Astronomical Association and a prolific author of popular astronomy between 1880 and 1910. He is perhaps best remembered for his books `The Visible Universe’ (1893), an English language translation of Camille Flammarion's `Popular Astronomy’ (1894) and his contributions to Agnes Clerk's `Astronomy’ (1898). I consider a little known investigation that Gore undertook into the question of stellar `sizes’ using binary stars. This led him to the realization of the existence of "Giant Suns” as well as "Miniature Stars” the latter included the sun. Gore also considered the existence of hyper-dense compact objects, now known as white dwarfs. Unfortunately Gore rejected the reality of the latter stellar types. Gore based his conclusions on a formula developed by fellow Irish astronomer W.H.S. Monck, who was reaching similar conclusions about Giant stars through the study of stellar motions.

Chaotic Star Birth

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] [figure removed for brevity, see original site] Click on the image for Poster VersionClick on the image for IRAS 4B Inset

Located 1,000 light years from Earth in the constellation Perseus, a reflection nebula called NGC 1333 epitomizes the beautiful chaos of a dense group of stars being born. Most of the visible light from the young stars in this region is obscured by the dense, dusty cloud in which they formed. With NASA's Spitzer Space Telescope, scientists can detect the infrared light from these objects. This allows a look through the dust to gain a more detailed understanding of how stars like our sun begin their lives.

The young stars in NGC 1333 do not form a single cluster, but are split between two sub-groups. One group is to the north near the nebula shown as red in the image. The other group is south, where the features shown in yellow and green abound in the densest part of the natal gas cloud. With the sharp infrared eyes of Spitzer, scientists can detect and characterize the warm and dusty disks of material that surround forming stars. By looking for differences in the disk properties between the two subgroups, they hope to find hints of the star and planet formation history of this region.

The knotty yellow-green features located in the lower portion of the image are glowing shock fronts where jets of material, spewed from extremely young embryonic stars, are plowing into the cold, dense gas nearby. The sheer number of separate jets that appear in this region is unprecedented. This leads scientists to believe that by stirring up the cold gas, the jets may contribute to the eventual dispersal of the gas cloud, preventing more stars from forming in NGC 1333.

In contrast, the upper portion of the image is dominated by the infrared light from warm dust, shown as red.

Understanding Space Weather: The Sun as a Variable Star

NASA Technical Reports Server (NTRS)

Strong, Keith; Saba, Julia; Kucera, Therese

2011-01-01

The Sun is a complex system of systems and until recently, less than half of its surface was observable at any given time and then only from afar. New observational techniques and modeling capabilities are giving us a fresh perspective of the solar interior and how our Sun works as a variable star. This revolution in solar observations and modeling provides us with the exciting prospect of being able to use a vastly increased stream of solar data taken simultaneously from several different vantage points to produce more reliable and prompt space weather forecasts. Solar variations that cause identifiable space weather effects do not happen only on solar-cycle timescales from decades to centuries; there are also many shorter-term events that have their own unique space weather effects and a different set of challenges to understand and predict, such as flares, coronal mass ejections, and solar wind variations

Understanding Space Weather: The Sun as a Variable Star

NASA Technical Reports Server (NTRS)

Strong, Keith; Saba, Julia; Kucera, Therese

2012-01-01

The Sun is a complex system of systems and until recently, less than half of its surface was observable at any given time and then only from afar. New observational techniques and modeling capabilities are giving us a fresh perspective of the solar interior and how our Sun works as a variable star. This revolution in solar observations and modeling provides us with the exciting prospect of being able to use a vastly increased stream of solar data taken simultaneously from several different vantage points to produce more reliable and prompt space weather forecasts. Solar variations that cause identifiable space weather effects do not happen only on solar-cycle timescales from decades to centuries; there are also many shorter-term events that have their own unique space weather effects and a different set of challenges to understand and predict, such as flares, coronal mass ejections, and solar wind variations.

Candidate Nearby, Young Stars in Gaia's First Data Release

NASA Astrophysics Data System (ADS)

Chalifour, Matthieu; Kastner, Joel H.; Binks, Alex; Rodriguez, David; Punzi, Kristina; Zuckerman, Ben; Sacco, Germano

2018-01-01

The nearest examples of young stars are essential subjects for the study of planet and star formation. The recent data release from Gaia, which contains accurate parallax distances for ~2.5 million stars, allows age determinations via isochronal analysis for thousands of stars within ~100 pc. We have selected nearly 400 candidates nearby, young, late-type stars in the approximate mass range 0.5-1.0 Msun from the Tycho Gaia Astrometric Solution catalog on the basis of (a) D < 100 pc, (b) Galex UV detection, and (c) isochronal age <~ 80 Myr. Approximately 10% of these candidates lie within 50 pc of Earth and, hence, may represent excellent targets for direct-imaging searches for young, self-luminous planets. We discuss our ongoing efforts to assess the accuracy of these stars' isochronal ages via various diagnostic tools, including galactic kinematics, UV excess, relative X-ray luminosity, andoptical spectroscopic indicators of youth.

Brown Dwarfs and Giant Planets Around Young Stars

NASA Astrophysics Data System (ADS)

Mahmud, Naved; Crockett, C.; Johns-Krull, C.; Prato, L.; Hartigan, P.; Jaffe, D.; Beichman, C.

2011-01-01

How dry is the brown dwarf (BD) desert at young ages? Previous radial velocity (RV) surveys have revealed that the frequency of BDs as close companions to solar-age stars in the field is extraordinarily low compared to the frequency of close planetary and stellar companions. Is this a formation or an evolutionary effect? Do close-in BDs form at lower rates, or are they destroyed by migration via interactions with a massive circumstellar disk, followed by assimilation into the parent star? To answer these questions, we are conducting an RV survey of 130 T Tauri stars in Taurus-Auriga (a few Myr old) and a dozen stars in the Pleiades (100 Myr old) to search for stellar reflex motions resulting from close substellar companions. Our goal is to measure the frequency of BDs at young ages. Detecting a higher frequency of BDs in young systems relative to the field will provide evidence for the migration theory as well as set limits on the migration timescale. Two additional goals are (1) to investigate the effect of star spots in young stars on RV observations, and (2) to detect the youngest-known giant exoplanet. We present results from the first few years of this survey. Strikingly, after completing observations of a third of our sample, we have yet to detect a single BD. Thus we can set limits on the dryness of the BD desert at young ages and shed light on the mysterious early lives of these objects.

THE FORMATION AND EVOLUTION OF YOUNG LOW-MASS STARS WITHIN HALOS WITH HIGH CONCENTRATION OF DARK MATTER PARTICLES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casanellas, Jordi; Lopes, IlIDio, E-mail: jordicasanellas@ist.utl.p, E-mail: ilidio.lopes@ist.utl.p

2009-11-01

The formation and evolution of low-mass stars within dense halos of dark matter (DM) leads to evolution scenarios quite different from the classical stellar evolution. As a result of our detailed numerical work, we describe these new scenarios for a range of DM densities on the host halo, for a range of scattering cross sections of the DM particles considered, and for stellar masses from 0.7 to 3 M {sub sun}. For the first time, we also computed the evolution of young low-mass stars in their Hayashi track in the pre-main-sequence phase and found that, for high DM densities, thesemore » stars stop their gravitational collapse before reaching the main sequence, in agreement with similar studies on first stars. Such stars remain indefinitely in an equilibrium state with lower effective temperatures (|DELTAT{sub eff}|>10{sup 3} K for a star of one solar mass), the annihilation of captured DM particles in their core being the only source of energy. In the case of lower DM densities, these protostars continue their collapse and progress through the main-sequence burning hydrogen at a lower rate. A star of 1 M{sub sun} will spend a time period greater than the current age of the universe consuming all the hydrogen in its core if it evolves in a halo with DM density rho{sub c}hi = 10{sup 9} GeV cm{sup -3}. We also show the strong dependence of the effective temperature and luminosity of these stars on the characteristics of the DM particles and how this can be used as an alternative method for DM research.« less

Mass loss from solar-type stars

NASA Technical Reports Server (NTRS)

Hartmann, L.

1985-01-01

The present picture of mass loss from solar-type (low-mass) stars is described, with special emphasis on winds from pre-main-sequence stars. Attention is given to winds from T Tauri stars and to angular momentum loss. Prospects are good for further advances in our understanding of the powerful mass loss observed from young stars; ultraviolet spectra obtainable with the Space Telescope should provide better estimates of mass loss rates and a clearer picture of physical conditions in the envelopes of these stars. To understand the mass ejection from old, slowly rotating main-sequence stars, we will have to study the sun.

Hyperfast pulsars as the remnants of massive stars ejected from young star clusters

NASA Astrophysics Data System (ADS)

Gvaramadze, Vasilii V.; Gualandris, Alessia; Portegies Zwart, Simon

2008-04-01

Recent proper motion and parallax measurements for the pulsar PSR B1508+55 indicate a transverse velocity of ~1100kms-1, which exceeds earlier measurements for any neutron star. The spin-down characteristics of PSR B1508+55 are typical for a non-recycled pulsar, which implies that the velocity of the pulsar cannot have originated from the second supernova disruption of a massive binary system. The high velocity of PSR B1508+55 can be accounted for by assuming that it received a kick at birth or that the neutron star was accelerated after its formation in the supernova explosion. We propose an explanation for the origin of hyperfast neutron stars based on the hypothesis that they could be the remnants of a symmetric supernova explosion of a high-velocity massive star which attained its peculiar velocity (similar to that of the pulsar) in the course of a strong dynamical three- or four-body encounter in the core of dense young star cluster. To check this hypothesis, we investigated three dynamical processes involving close encounters between: (i) two hard massive binaries, (ii) a hard binary and an intermediate-mass black hole (IMBH) and (iii) a single stars and a hard binary IMBH. We find that main-sequence O-type stars cannot be ejected from young massive star clusters with peculiar velocities high enough to explain the origin of hyperfast neutron stars, but lower mass main-sequence stars or the stripped helium cores of massive stars could be accelerated to hypervelocities. Our explanation for the origin of hyperfast pulsars requires a very dense stellar environment of the order of 106- 107starspc-3. Although such high densities may exist during the core collapse of young massive star clusters, we caution that they have never been observed.

A Blind Search for Magnetospheric Emissions from Planetary Companions to Nearby Solar-type Stars

NASA Astrophysics Data System (ADS)

Lazio, T. Joseph W.; Carmichael, S.; Clark, J.; Elkins, E.; Gudmundsen, P.; Mott, Z.; Szwajkowski, M.; Hennig, L. A.

2010-01-01

This paper reports a blind search for planetary magnetospheric emissions from planets around nearby stars. Young stars are likely to have much stronger stellar winds than the Sun, and because planetary magnetospheric emissions are powered by stellar winds, stronger stellar winds may enhance the radio luminosity of any orbiting planets. Using various stellar catalogs, we selected nearby stars (< 30 pc) with relatively young age estimates (< 3 Gyr), finding between 100 and several hundred stars. We stacked images from the 74-MHz (4-m wavelength) VLA Low-frequency Sky Survey, obtaining 3\\sigma limits on planetary emission of between 10 and 33 mJy. These flux density limits correspond to average planetary luminosities less than 5--10 x 1023erg/s. Using models for the scaling of stellar wind velocity, density, and magnetic field with stellar age, we estimate scaling factors for the strength of stellar winds, relative to the Sun, in our samples. The typical kinetic (magnetic) energy carried by the stellar winds in our samples is 15--50 (5--10) times larger than that of the solar wind. If we assume that every star is orbited by a Jupiter-like planet with a luminosity larger than that of the Jovian decametric radiation by the above factors, our limits on planetary luminosities from the stacking analysis are likely to be a factor of 300 above what would be required to detect the planets in a statistical sense. Similar statistical analyses with observations by future instruments, such as the Low Frequency Array (LOFAR) and the Long Wavelength Array (LWA), offer the promise of improvements by factors of 10--100. Basic research in radio astronomy at NRL is supported by 6.1 Base funding. The LUNAR consortium, is funded by the NASA Lunar Science Institute (Cooperative Agreement NNA09DB30A) to investigate concepts for astrophysical observatories on the Moon.

Zodiacal Exoplanets in Time: Searching for Young Stars in K2

NASA Astrophysics Data System (ADS)

Morris, Nathan Ryan; Mann, Andrew; Rizzuto, Aaron

2018-01-01

Observations of planetary systems around young stars provide insight into the early stages of planetary system formation. Nearby young open clusters such as the Hyades, Pleiades, and Praesepe provide important benchmarks for the properties of stellar systems in general. These clusters are all known to be less than 1 Gyr old, making them ideal targets for a survey of young planetary systems. Few transiting planets have been detected around clusters stars, however, so this alone is too small of a sample. K2, the revived Kepler mission, has provided a vast number of light curves for young stars in clusters and elsewhere in the K2 field. This provides us with the opportunity to extend the sample of young systems to field stars while calibrating with cluster stars. We compute rotational periods from starspot patterns for ~36,000 K2 targets and use gyrochronological relationships derived from cluster stars to determine their ages. From there, we have begun searching for planets around young stars outside the clusters with the ultimate goal of shedding light on how planets and planetary systems evolve in their early, most formative years.

Spectrometers for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) Upgrade to Full Sun-Sky-Cloud-Trace Gas Spectrometry Capability for Airborne Science

NASA Astrophysics Data System (ADS)

Dunagan, S. E.; Flynn, C. J.; Johnson, R. R.; Kacenelenbogen, M. S.; Knobelspiesse, K. D.; LeBlanc, S. E.; Livingston, J. M.; Redemann, J.; Russell, P. B.; Schmid, B.; Segal-Rosenhaimer, M.; Shinozuka, Y.

2014-12-01

The Spectrometers for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) instrument has been developed at NASA Ames in collaboration with Pacific Northwest National Laboratory (PNNL) and NASA Goddard, supported substantially since 2009 by NASA's Radiation Science Program and Earth Science Technology Office. It combines grating spectrometers with fiber optic links to a tracking, scanning head to enable sun tracking, sky scanning, and zenith viewing. 4STAR builds on the long and productive heritage of the NASA Ames Airborne Tracking Sunphotometers (AATS-6 and -14), which have yielded more than 100 peer-reviewed publications and extensive archived data sets in many NASA Airborne Science campaigns from 1986 to the present. The baseline 4STAR instrument has provided extensive data supporting the TCAP (Two Column Aerosol Project, July 2012 & Feb. 2013), SEAC4RS (Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys, 2013), and ARISE (Arctic Radiation - IceBridge Sea and Ice Experiment, 2014), field campaigns.This poster presents plans and progress for an upgrade to the 4STAR instrument to achieve full science capability, including (1) direct-beam sun tracking measurements to derive aerosol optical depth spectra, (2) sky radiance measurements to retrieve aerosol absorption and type (via complex refractive index and mode-resolved size distribution), (3) cloud properties via zenith radiance, and (4) trace gas spectrometry. Technical progress in context with the governing physics is reported on several upgrades directed at improved light collection and usage, particularly as related to spectrally and radiometrically stable propagation through the collection light path. In addition, improvements to field calibration and verification, and flight operability and reliability are addressed.

Search for Wide Planetary-Mass Companions in Young Star-Forming Regions with UKIDSS and Pan-STARRS

NASA Astrophysics Data System (ADS)

Aller, Kimberly M.; Kraus, A. L.; Liu, M. C.; Bowler, B. P.

2013-01-01

Over the past decade, planetary-mass (<15 MJup) companions have been discovered in very wide orbits (>100 AU) around young stars. It is unclear whether these objects formed like planets or like stars. If these are planets, then modifications to core accretion or disk instability models are needed to allow formation at such wide orbits, or planet scattering must be an important mechanism. On the other hand, if these objects formed like stars, we need to understand the frequency of these extremely low mass ratio binary companions which challenge brown dwarf formation models. Regardless of their origins, these wide companions are easier to observe than close-in planets and can be used as benchmarks to understand the properties of young planets. We have combined optical and NIR photometry from UKIDSS and Pan-STARRS-1 to search the young star-forming region of Upper Scorpius and Taurus for new planetary-mass objects, going ≈3 mag deeper than previous work with 2MASS. We identified several candidates with very wide separations (≈400-4000 AU) from known members using a combination of color selection and spectral energy distribution (SED) fitting to templates of known low-mass stars and brown dwarfs. Furthermore, we have obtained followup NIR spectra of several Upper Scorpius candidates to spectroscopically identify three new wide very low-mass companions (≈15-25 MJup spectral type of M8-L0).

Observations of the sun, an ultraviolet variable star

NASA Technical Reports Server (NTRS)

Heath, D. F.

1972-01-01

The uncertainty as to whether or not the sun is a variable star in that region of the ultraviolet which is absorbed in the mesosphere and stratosphere led to an experiment with acronym MUSE, Monitor of Ultraviolet Solar Energy. The experiment was first flown on an Aerobee rocket in August 1966 and subsequently on Nimbus 3 and 4 in April 1969 and April 1970 respectively. The basic philosophy behind the design of the experiment was to provide an instrument which would not require a solar pointing mechanism and at the same time would be capable of high radiometric accuracy for long periods in space.

Revisiting the Tale of Hercules: How Stars Orbiting the Lagrange Points Visit the Sun

NASA Astrophysics Data System (ADS)

Pérez-Villegas, Angeles; Portail, Matthieu; Wegg, Christopher; Gerhard, Ortwin

2017-05-01

We propose a novel explanation for the Hercules stream consistent with recent measurements of the extent and pattern speed of the Galactic bar. We have adapted a made-to-measure dynamical model tailored for the Milky Way to investigate the kinematics of the solar neighborhood (SNd). The model matches the 3D density of the red clump giant stars (RCGs) in the bulge and bar as well as stellar kinematics in the inner Galaxy, with a pattern speed of 39 km s-1 kpc-1. Cross-matching this model with the Gaia DR1 TGAS data combined with RAVE and LAMOST radial velocities, we find that the model naturally predicts a bimodality in the U-V-velocity distribution for nearby stars which is in good agreement with the Hercules stream. In the model, the Hercules stream is made of stars orbiting the Lagrange points of the bar which move outward from the bar’s corotation radius to visit the SNd. While the model is not yet a quantitative fit of the velocity distribution, the new picture naturally predicts that the Hercules stream is more prominent inward from the Sun and nearly absent only a few 100 pc outward of the Sun, and plausibly explains that Hercules is prominent in old and metal-rich stars.

An unbiased X-ray sampling of stars within 25 parsecs of the Sun

NASA Technical Reports Server (NTRS)

Johnson, H. M.

1985-01-01

A search of all of the Einstein Observatory IPC and HRI fields for untargeted stars in the Woolley, et al., Catalogue of the nearby stars is reported. Optical data and IPC coordinates, flux density F sub x, and luminosity L sub x, or upper limits, are tabulated for 126 single or blended systems, and HRI results for a few of them. IPC luminosity functions are derived for the systems, for 193 individual stars in the systems (with L sub x shared equally among blended components), and for 63 individual M dwarfs. These stars have relatively large X-ray flux densities that are free of interstellar extinction, because they are nearby, but they are otherwise unbiased with respect to the X-ray properties that are found in a defined small space around the Sun.

Upgrade of the NASA 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) to its Full Science Capability of Sun-Sky-Cloud-Trace Gas Spectrometry in Airborne Science Deployments

NASA Technical Reports Server (NTRS)

Johnson, Roy R.; Russell, P.; Dunagan, S.; Redemann, J.; Shinozuka, Y.; Segal-Rosenheimer, M.; LeBlanc, S.; Flynn, C.; Schmid, B.; Livingston, J.

2014-01-01

The objectives of this task in the AITT (Airborne Instrument Technology Transition) Program are to (1) upgrade the NASA 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) instrument to its full science capability of measuring (a) direct-beam sun transmission to derive aerosol optical depth spectra, (b) sky radiance vs scattering angle to retrieve aerosol absorption and type (via complex refractive index spectra, shape, and mode-resolved size distribution), (c) zenith radiance for cloud properties, and (d) hyperspectral signals for trace gas retrievals, and (2) demonstrate its suitability for deployment in challenging NASA airborne multiinstrument campaigns. 4STAR combines airborne sun tracking, sky scanning, and zenith pointing with diffraction spectroscopy to improve knowledge of atmospheric constituents and their links to air pollution, radiant energy budgets (hence climate), and remote measurements of Earth's surfaces. Direct beam hyperspectral measurement of optical depth improves retrievals of gas constituents and determination of aerosol properties. Sky scanning enhances retrievals of aerosol type and size distribution. 4STAR measurements are intended to tighten the closure between satellite and ground-based measurements. 4STAR incorporates a modular sun-tracking/sky-scanning optical head with fiber optic signal transmission to rack mounted spectrometers, permitting miniaturization of the external optical head, and future detector evolution. 4STAR test flights, as well as science flights in the 2012-13 TCAP (Two-Column Aerosol Project) and 2013 SEAC4RS (Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys) have demonstrated that the following are essential for 4STAR to achieve its full science potential: (1) Calibration stability for both direct-beam irradiance and sky radiance, (2) Improved light collection and usage, and (3) Improved flight operability and reliability. A particular challenge

Long-term radial-velocity variations of the Sun as a star: The HARPS view

NASA Astrophysics Data System (ADS)

Lanza, A. F.; Molaro, P.; Monaco, L.; Haywood, R. D.

2016-03-01

Context. Stellar radial velocities play a fundamental role in the discovery of extrasolar planets and the measurement of their physical parameters as well as in the study of stellar physical properties. Aims: We investigate the impact of the solar activity on the radial velocity of the Sun using the HARPS spectrograph to obtain measurements that can be directly compared with those acquired in the extrasolar planet search programmes. Methods: We used the Moon, the Galilean satellites, and several asteroids as reflectors to measure the radial velocity of the Sun as a star and correlated this velocity with disc-integrated chromospheric and magnetic indexes of solar activity that are similar to stellar activity indexes. We discuss in detail the systematic effects that affect our measurements and the methods to account for them. Results: We find that the radial velocity of the Sun as a star is positively correlated with the level of its chromospheric activity at ~95 percent significance level. The amplitude of the long-term variation measured in the 2006-2014 period is 4.98 ± 1.44 m/s, which is in good agreement with model predictions. The standard deviation of the residuals obtained by subtracting a linear best fit is 2.82 m/s and is due to the rotation of the reflecting bodies and the intrinsic variability of the Sun on timescales shorter than the activity cycle. A correlation with a lower significance is detected between the radial velocity and the mean absolute value of the line-of-sight photospheric magnetic field flux density. Conclusions: Our results confirm similar correlations found in other late-type main-sequence stars and provide support to the predictions of radial velocity variations induced by stellar activity based on current models.

Optical Polarization of 1000 Stars Within 50-PARSECS from the Sun

NASA Astrophysics Data System (ADS)

Leroy, J. L.

1993-11-01

We have prepared a catalogue of optical polarization measurements for 1000 stars closer than 50 parsecs from the Sun. The distances, which are presently those given in the Sky Catalogue 2000.0, 2nd edition (Hirshfeld et al. 1991) are provisional: they will be replaced later by the much safer parallaxes which will result from the Hipparcos mission. The polarization data have been compiled, for 60% in various catalogues with due care to their accuracy for 40% they are new, unpublished, measurements obtained at Pic du Midi Observatory. We expect that this new data base will allow a better understanding of the interstellar medium around the Sun; the analysis, similar to the beautiful work by Tinbergen (1982), is to be found in a companion paper.

Sun behaviour in Canadian children: results of the 2006 National Sun Survey.

PubMed

Pichora, Erin C; Marrett, Loraine D

2010-01-01

Childhood sun exposure is a particularly important determinant of skin cancer, yet little data are available for children. This paper describes sun behaviour among Canadian children for the summer of 2006. As part of the Second National Sun Survey (NSS2), 1,437 parents reported on the time spent in the sun, and the frequency of sun protection behaviours and sunburning for one of their children aged 1 to 12 years. Analysis was carried out using complex survey procedures in SAS and STATA. The majority of children (94%) spend at least 30 minutes in the sun on a typical summer day; however, regular sun protection is only commonly reported for young children (1 to 5 years) and involves covering their heads and wearing sunscreen (85%). The frequency of other protective behaviours is much lower, and sun protection decreases with age. Older children are also twice as likely to spend extended time in the sun and to get a sunburn. Among older children, boys are more likely to cover their heads and girls are more likely to wear sunscreen. Regular sun protection among Canadian children is low, given their sun exposure. Heavy reliance on sunscreen is consistent with previous reports and indicates that other measures, such as seeking shade and wearing protective clothing, need to be promoted. Riskier sun behaviour among older children may reflect decreased parental control, as well as changing attitudes and peer pressure, and highlights the importance of adult role models and targeted interventions for this age group.

Sounds of a Star

NASA Astrophysics Data System (ADS)

2001-06-01

Acoustic Oscillations in Solar-Twin "Alpha Cen A" Observed from La Silla by Swiss Team Summary Sound waves running through a star can help astronomers reveal its inner properties. This particular branch of modern astrophysics is known as "asteroseismology" . In the case of our Sun, the brightest star in the sky, such waves have been observed since some time, and have greatly improved our knowledge about what is going on inside. However, because they are much fainter, it has turned out to be very difficult to detect similar waves in other stars. Nevertheless, tiny oscillations in a solar-twin star have now been unambiguously detected by Swiss astronomers François Bouchy and Fabien Carrier from the Geneva Observatory, using the CORALIE spectrometer on the Swiss 1.2-m Leonard Euler telescope at the ESO La Silla Observatory. This telescope is mostly used for discovering exoplanets (see ESO PR 07/01 ). The star Alpha Centauri A is the nearest star visible to the naked eye, at a distance of a little more than 4 light-years. The new measurements show that it pulsates with a 7-minute cycle, very similar to what is observed in the Sun . Asteroseismology for Sun-like stars is likely to become an important probe of stellar theory in the near future. The state-of-the-art HARPS spectrograph , to be mounted on the ESO 3.6-m telescope at La Silla, will be able to search for oscillations in stars that are 100 times fainter than those for which such demanding observations are possible with CORALIE. PR Photo 23a/01 : Oscillations in a solar-like star (schematic picture). PR Photo 23b/01 : Acoustic spectrum of Alpha Centauri A , as observed with CORALIE. Asteroseismology: listening to the stars ESO PR Photo 23a/01 ESO PR Photo 23a/01 [Preview - JPEG: 357 x 400 pix - 96k] [Normal - JPEG: 713 x 800 pix - 256k] [HiRes - JPEG: 2673 x 3000 pix - 2.1Mb Caption : PR Photo 23a/01 is a graphical representation of resonating acoustic waves in the interior of a solar-like star. Red and blue

Young stars of low mass in the Gum nebula

NASA Technical Reports Server (NTRS)

Graham, J. A.; Heyer, Mark H.

1989-01-01

Observations are presented for four recently formed stars in the vicinity of the Gum nebula which are heavily obscured by surrounding dust and are associated with small reflection nebulae. HH46 is the only currently active star of the sample, and it is found to have a spectral type in the range of late G-early K, with superimposed emission lines of H-alpha, Ca II, Fe I, Fe II, and weak He I at near zero velocities. It is suggested that the observed scenario of low-mass stars in an older massive star environment may be analogous to the circumstances surrounding the birth of the sun.

Aerospace for the Very Young.

ERIC Educational Resources Information Center

2003

This packet includes games and activities concerning aerospace education for the very young. It is designed to develop and strengthen basic concepts and skills in a non-threatening atmosphere of fun. Activities include: (1) "The Sun, Our Nearest Star"; (2) "Twinkle, Twinkle, Little Star, How I Wonder Where You Are"; (3) "Shadows"; (4) "The Earth…

α Centauri A in the far infrared. First measurement of the temperature minimum of a star other than the Sun

NASA Astrophysics Data System (ADS)

Liseau, R.; Montesinos, B.; Olofsson, G.; Bryden, G.; Marshall, J. P.; Ardila, D.; Bayo Aran, A.; Danchi, W. C.; del Burgo, C.; Eiroa, C.; Ertel, S.; Fridlund, M. C. W.; Krivov, A. V.; Pilbratt, G. L.; Roberge, A.; Thébault, P.; Wiegert, J.; White, G. J.

2013-01-01

Context. Chromospheres and coronae are common phenomena on solar-type stars. Understanding the energy transfer to these heated atmospheric layers requires direct access to the relevant empirical data. Study of these structures has, by and large, been limited to the Sun thus far. Aims: The region of the temperature reversal can be directly observed only in the far infrared and submillimetre spectral regime. We aim at determining the characteristics of the atmosphere in the region of the temperature minimum of the solar sister star α Cen A. As a bonus this will also provide a detailed mapping of the spectral energy distribution, i.e. knowledge that is crucial when searching for faint, Kuiper belt-like dust emission around other stars. Methods: For the nearby binary system α Cen, stellar parameters are known with high accuracy from measurements. For the basic model parameters Teff, log g and [Fe/H], we interpolate stellar model atmospheres in the grid of Gaia/PHOENIX and compute the corresponding model for the G2 V star α Cen A. Comparison with photometric measurements shows excellent agreement between observed photospheric data in the optical and infrared. For longer wavelengths, the modelled spectral energy distribution is compared to Spitzer-MIPS, Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry. A specifically tailored Uppsala model based on the MARCS code and extending further in wavelength is used to gauge the emission characteristics of α Cen A in the far infared. Results: Similar to the Sun, the far infrared (FIR) emission of α Cen A originates in the minimum temperature region above the stellar photosphere in the visible. However, in comparison with the solar case, the FIR photosphere of α Cen A appears marginally cooler, Tmin ~ T160 μm = 3920 ± 375 K. Beyond the minimum near 160 μm, the brightness temperatures increase, and this radiation very likely originates in warmer regions of the chromosphere of α Cen A. Conclusions: To the best of

Watching the Sun to Improve Exoplanet Detection

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-12-01

Looking for stars that wobble is one of the key ways by which we detect exoplanets: the gravitational pull of planets cause tiny variations in stars radial velocities. But our ability to detect Earth twins is currently limited by our ability to distinguish between radial-velocity variations caused by exoplanets, and those caused by noise from the star itself. A team of scientists has recently proposed that the key to solving this problem may be to examine our own star.Precision Amid NoiseThe radial-velocity technique works well for detecting large planets on close orbits, but detecting an Earth twin requires being able to detect star motion on the order of 10 cm/s! This precision is hard to reach, because activity on the stellar surface i.e., sunspots, plages (bright spots), or granulation can also cause variations in the measured radial velocity for the star, obscuring the signature of a planet.Because the stars were examining arent resolved, we cant track the activity on their surfaces so how can we better understand the imprint that stellar activity has on radial-velocity measurements? A team of scientists has come up with a clever approach: examine the Sun as though it were a distant star.Wealth of InformationThe team, led by Xavier Dumusque (Branco-Weiss Fellow at the Harvard-Smithsonian Center for Astrophysics) and David F. Phillips (Harvard-Smithsonian Center for Astrophysics), has begun a project to observe the Sun with a ground-based solar telescope. The telescope observes the full disk of the Sun and feeds the data into the HARPS-N spectrograph in Spain, a spectrograph normally used for radial-velocity measurements of other stars in the hunt for exoplanets.But the team has access to other data about the Sun, too: information from satellites like the Solar Dynamics Observatory and SORCE about the solar activity and total irradiance during the time when the spectra were taken. Dumusque and collaborators have combined all of this information, during a week

NEW BROWN DWARF COMPANIONS TO YOUNG STARS IN SCORPIUS-CENTAURUS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Janson, Markus; Jayawardhana, Ray; Bonavita, Mariangela

2012-10-10

We present the discoveries of three faint companions to young stars in the Scorpius-Centaurus region, imaged with the NICI instrument on Gemini South. We have confirmed all three companions through common proper motion tests. Follow-up spectroscopy has confirmed two of them, HIP 65423 B and HIP 65517 B, to be brown dwarfs, while the third, HIP 72099 B, is more likely a very low mass star just above the hydrogen burning limit. The detection of wide companions in the mass range of {approx}40-100 M{sub jup} complements previous work in the same region, reporting detections of similarly wide companions with lowermore » masses, in the range of {approx}10-30 M{sub jup}. Such low masses near the deuterium burning limit have raised the question of whether those objects formed like planets or stars. The existence of intermediate objects as reported here could represent a bridge between lower-mass companions and stellar companions, but in any case demonstrate that mass alone may not provide a clear-cut distinction for the formation of low-mass companions to stars.« less

Angular Momentum Evolution in Young Low Mass Stars

NASA Astrophysics Data System (ADS)

Pinzón, G.; de La Reza, R.

2006-06-01

During the last decades, the study of rotation in young low mass stars has been one of the more active areas in the field of stellar evolution. Many theoretical efforts have been made to understand the angular momentum evolution and our picture now, reveals the main role of the stellar magnetic field in all pre-main sequence stage (Ghosh & Lamb 1979, ApJ, 234, 296; Cameron & Campbell 1993, A&A, 274, 309; Cameron & Campbell 1995, A&A, 298, 133; Kúker, Henning, & Rúdiger 2003, ApJ, 589, 397; Matt & Pudritz 2005, MNRAS, 356, 167). The mean rotation of most of the cool low mass stars remains roughly constant during the T Tauri stage. This can be explained by the disc locking scenario. This paradigm suggest that star start out as CTTS with periods of 4-14 days, perhaps locked to their disc, and that this disc is eventually lost mainly by accretion. At the current time, it is not clear that this is true for all low mass stars. Some authors have questioned its validity for stars less massive than 0.5 solar masses. Although the reality may eventually turn out to be considerably more complex, a simple consideration of the effects of and limits on disc locking of young low mass stars seems necessary.We have investigated the exchange of angular momentum between a low mass star and an accretion disc during the Hayashi Track (Pinzón, Kúker, & de la Reza 2005, in preparation) and also along the first 100Myr of stellar evolution. The model incorporates changes in the star's moment of inertia, magnetic field strength (Elstner & Rúdiger 2000, A&A, 358, 612), angular momentum loss by a magnetic wind and an exponential decrease of the accretion rate. The lifetime of the accretion disc is a free parameter in our model. The resulting rotation rates are in agreement with observed vsin and photometric periods for young stars belonging to co-moving groups and open young clusters.

Astronomy: A small star with an Earth-like planet

NASA Astrophysics Data System (ADS)

Deming, Drake

2015-11-01

A rocky planet close in size to Earth has been discovered in the cosmic vicinity of our Sun. The small size and proximity of the associated star bode well for studies of the planet's atmosphere. See Letter p.204

X-RAY BINARIES AND STAR CLUSTERS IN THE ANTENNAE: OPTICAL CLUSTER COUNTERPARTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rangelov, Blagoy; Chandar, Rupali; Prestwich, Andrea

2012-10-20

We compare the locations of 82 X-ray binaries (XRBs) detected in the merging Antennae galaxies by Zezas et al., based on observations taken with the Chandra X-Ray Observatory, with a catalog of optically selected star clusters presented by Whitmore et al., based on observations taken with the Hubble Space Telescope. Within the 2{sigma} positional uncertainty of Almost-Equal-To 0.''8, we find 22 XRBs are coincident with star clusters, where only two to three chance coincidences are expected. The ages of the clusters were estimated by comparing their UBVI, H{alpha} colors with predictions from stellar evolutionary models. We find that 14 ofmore » the 22 coincident XRBs (64%) are hosted by star clusters with ages of Almost-Equal-To 6 Myr or less. All of the very young host clusters are fairly massive and have M {approx}> 3 Multiplication-Sign 10{sup 4} M {sub Sun }, with many having masses M Almost-Equal-To 10{sup 5} M {sub Sun }. Five of the XRBs are hosted by young clusters with ages {tau} Almost-Equal-To 10-100 Myr, while three are hosted by intermediate-age clusters with {tau} Almost-Equal-To 100-300 Myr. Based on the results from recent N-body simulations, which suggest that black holes are far more likely to be retained within their parent clusters than neutron stars, we suggest that our sample consists primarily of black hole binaries with different ages.« less

Unbound Young Stellar Systems: Star Formation on the Loose

NASA Astrophysics Data System (ADS)

Gouliermis, Dimitrios A.

2018-07-01

Unbound young stellar systems, the loose ensembles of physically related young bright stars, trace the typical regions of recent star formation in galaxies. Their morphologies vary from small few pc-size associations of newly formed stars to enormous few kpc-size complexes composed of stars few 100 Myr old. These stellar conglomerations are located within the disks and along the spiral arms and rings of star-forming disk galaxies, and they are the active star-forming centers of dwarf and starburst galaxies. Being associated with star-forming regions of various sizes, these stellar structures trace the regions where stars form at various length- and timescales, from compact clusters to whole galactic disks. Stellar associations, the prototypical unbound young systems, and their larger counterparts, stellar aggregates, and stellar complexes, have been the focus of several studies for quite a few decades, with special interest on their demographics, classification, and structural morphology. The compiled surveys of these loose young stellar systems demonstrate that the clear distinction of these systems into well-defined classes is not as straightforward as for stellar clusters, due to their low densities, asymmetric shapes and variety in structural parameters. These surveys also illustrate that unbound stellar structures follow a clear hierarchical pattern in the clustering of their stars across various scales. Stellar associations are characterized by significant sub-structure with bound stellar clusters being their most compact parts, while associations themselves are the brighter denser parts of larger stellar aggregates and stellar complexes, which are members of larger super-structures up to the scale of a whole star-forming galaxy. This structural pattern, which is usually characterized as self-similar or fractal, appears to be identical to that of star-forming giant molecular clouds and interstellar gas, driven mainly by turbulence cascade. In this short

The Sun is a plasma diffuser that sorts atoms by mass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manuel, O., E-mail: omatumr@yahoo.com; Kamat, S. A.; Mozina, M.

2006-11-15

The Sun is a plasma diffuser that selectively moves light elements like H and He and the lighter isotopes of each element to its surface. The Sun formed on the collapsed core of a supernova (SN) and is composed mostly of elements made near the SN core (Fe, O, Ni, Si, and S), like the rocky planets and ordinary meteorites. Neutron emission from the central neutron star triggers a series of reactions that generate solar luminosity, solar neutrinos, solar mass fractionation, and an outpouring of hydrogen in the solar wind. Mass fractionation seems to have operated in the parent starmore » and likely occurs in other stars as well.« less

Searching for Young Stars in Cepheus C

NASA Astrophysics Data System (ADS)

Evans, Sam; Rebull, Luisa; Rutherford, Thomas; Stalnaker, Olivia; Taylor, John; Efsits, Gabriel; Harl, Linda; Keil, Shayna; Learman, Duncan; Leonard, Liam; Russell, Aaron

2018-01-01

We used archival Herschel Space Observatory data to search for young stellar objects (YSOs) in the Cepheus C region of the molecular cloud Cepheus OB3. Previous work by Gutermuth et al. (2009) identified 114 YSO candidates in this region based on Spitzer/IRAC data. Work by Orr et al. (2016) refined a list of approximately 300 young star candidates to 245 likely YSOs. Our initial search focused on longer infrared wavelength data – Herschel (70, 160, 250, 350, 500 μm) archival data and SCUBA (450, 850 μm) data from the literature (DiFrancesco et al. 2008). Through image inspection and catalog matching, we assembled a list of 54 candidate YSOs detected at wavelengths longer than 22 μm. For each source, we constructed a spectral energy distribution (SED) by aggregating available shorter wavelength data from the literature and assembling photometry from released PACS catalogs, preliminary SPIRE catalogs, and our own photometric measurements. We also created color-color and color-magnitude diagrams to see how these sources compared to each other, other populations of YSOs, and objects in extragalactic regions. Each source was then classified based on its SED shape and its locations on color-color and color-magnitude diagrams. From the initial list of 54 candidates, we suspect all are likely YSOs, some of which are very embedded; ~40% are likely SED Class I or 0. Approximately 20% of the 54 sources have not been previously identified. By beginning the investigation of YSOs in this region, we are adding to the body of YSO knowledge which can be used to understand the process of star formation. This research was made possible through the NASA/IPAC Teacher Archive Research Program (NITARP) and was funded by NASA Astrophysics Data Program.

Studies of Disks Around the Sun and Other Stars

NASA Technical Reports Server (NTRS)

Stern, S. Alan (Principal Investigator)

1996-01-01

We are conducting research designed to enhance our understanding of the evolution and detectability of comet clouds and disks. This area holds promise for also improving our understanding of outer solar system formation, the bombardment history of the planets, the transport of volatiles and organics from the outer solar system to the inner planets, and to the ultimate fate of comet clouds around the Sun and other stars. According to 'standard' theory, both the Kuiper Disk and the Oort Cloud are (at least in part) natural products of the planetary accumulation stage of solar system formation. One expects such assemblages to be a common attribute of other solar systems. Therefore, searches for comet disks and clouds orbiting other stars offer a new method for inferring the presence of planetary systems. This two-element program consists modeling collisions in the Kuiper Disk and the dust disks around other stars. The modeling effort focuses on moving from our simple, first-generation, Kuiper disk collision rate model, to a time-dependent, second-generation model that incorporates physical collisions, velocity evolution, dynamical erosion, and various dust transport mechanisms. This second generation model will be used to study the evolution of surface mass density and the object-size spectrum in the disk. The observational effort focuses on obtaining submm/mm-wave flux density measurements of 25-30 IR excess stars in order to better constrain the masses, spatial extents and structure of their dust ensembles.

Age-Defying Star

NASA Image and Video Library

2016-08-29

An age-defying star called IRAS 19312+1950 exhibits features characteristic of a very young star and a very old star. The object stands out as extremely bright inside a large, chemically rich cloud of material, as shown in this image from NASA's Spitzer Space Telescope. IRAS 19312+1950 is the bright red star in the center of this image. A NASA-led team of scientists thinks the star -- which is about 10 times as massive as our sun and emits about 20,000 times as much energy -- is a newly forming protostar. That was a big surprise, because the region had not been known as a stellar nursery before. But the presence of a nearby interstellar bubble, which indicates the presence of a recently formed massive star, also supports this idea. http://photojournal.jpl.nasa.gov/catalog/PIA20914

RCW 108: Massive Young Stars Trigger Stellar Birth

NASA Technical Reports Server (NTRS)

2008-01-01

RCW 108 is a region where stars are actively forming within the Milky Way galaxy about 4,000 light years from Earth. This is a complicated region that contains young star clusters, including one that is deeply embedded in a cloud of molecular hydrogen. By using data from different telescopes, astronomers determined that star birth in this region is being triggered by the effect of nearby, massive young stars.

This image is a composite of X-ray data from NASA's Chandra X-ray Observatory (blue) and infrared emission detected by NASA's Spitzer Space Telescope (red and orange). More than 400 X-ray sources were identified in Chandra's observations of RCW 108. About 90 percent of these X-ray sources are thought to be part of the cluster and not stars that lie in the field-of-view either behind or in front of it. Many of the stars in RCW 108 are experiencing the violent flaring seen in other young star-forming regions such as the Orion nebula. Gas and dust blocks much of the X-rays from the juvenile stars located in the center of the image, explaining the relative dearth of Chandra sources in this part of the image.

The Spitzer data show the location of the embedded star cluster, which appears as the bright knot of red and orange just to the left of the center of the image. Some stars from a larger cluster, known as NGC 6193, are also visible on the left side of the image. Astronomers think that the dense clouds within RCW 108 are in the process of being destroyed by intense radiation emanating from hot and massive stars in NGC 6193.

Taken together, the Chandra and Spitzer data indicate that there are more massive star candidates than expected in several areas of this image. This suggests that pockets within RCW 108 underwent localized episodes of star formation. Scientists predict that this type of star formation is triggered by the effects of radiation from bright, massive stars such as those in NGC 6193. This radiation may cause the interior of gas

Star Shows It Has The Right Stuff

NASA Astrophysics Data System (ADS)

2004-01-01

Astronomers have used an observation by NASA's Chandra X-ray Observatory to make the best case yet that a star can be engulfed by its companion star and survive. This discovery will help astronomers better understand how closely coupled stars, and perhaps even stars and planets, evolve when one of the stars expands enormously in its red giant phase. The binary star system known as V471 Tauri comprises a white dwarf star (the primary) in a close orbit -- one thirtieth of the distance between Mercury and the Sun -- with a normal Sun-like star (the secondary). Chandra's data showed that the hot upper atmosphere of the secondary star has a deficit of carbon atoms relative to nitrogen atoms. "This deficit of carbon atoms is the first clear observational evidence that the normal star was engulfed by its companion in the past," according to Jeremy Drake of the Smithsonian Astrophysical Observatory in Cambridge, MA, who coauthored an article on V471 in The Astrophysical Journal Letters with Marek Sarna of the N. Copernicus Astronomical Center in Poland. The white dwarf star was once a star several times as massive as the Sun. Nuclear fusion reactions in the core of such a star convert carbon into nitrogen over a period of about a billion years. When the fuel in the core of the star is exhausted, the core collapses, triggering more energetic nuclear reactions that cause the star to expand and transform into a red giant before eventually collapsing to become a white dwarf. The carbon-poor material in the core of the red giant is mixed with outer part of the star, so its atmosphere shows a deficit of carbon, as compared with Sun-like stars. The X-ray spectra of a red giant star (top panel) and a Sun-like star (bottom panel) show the large difference in the peaks due to carbon atoms in the two stars. Theoretical calculations indicate that a red giant in a binary system can completely envelop its companion star and dramatically affect its evolution. During this common envelope

Observational diagnostics of accretion on young stars and brown dwarfs

NASA Astrophysics Data System (ADS)

Stelzer, Beate; Argiroffi, Costanza

I present a summary of recent observational constraints on the accretion properties of young stars and brown dwarfs with focus on the high-energy emission. In their T Tauri phase young stars assemble a few percent of their mass by accretion from a disk. Various observational signatures of disks around pre-main sequence stars and the ensuing accretion process are found in the IR and optical regime: e.g. excess emission above the stellar photosphere, strong and broad emission lines, optical veiling. At high energies evidence for accretion is less obvious, and the X-ray emission from stars has historically been ascribed to magnetically confined coronal plasmas. While being true for the bulk of the emission, new insight obtained from XMM-Newton and Chandra observations has unveiled contributions from accretion and outflow processes to the X-ray emission from young stars. Their smaller siblings, the brown dwarfs, have been shown to undergo a T Tauri phase on the basis of optical/IR observations of disks and measurements of accretion rates. Most re-cently, first evidence was found for X-rays produced by accretion in a young brown dwarf, complementing the suspected analogy between stars and substellar objects.

Young stars of low mass in the Gum nebula

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graham, J.A.; Heyer, M.H.

1989-06-01

Observations are presented for four recently formed stars in the vicinity of the Gum nebula which are heavily obscured by surrounding dust and are associated with small reflection nebulae. HH46 is the only currently active star of the sample, and it is found to have a spectral type in the range of late G-early K, with superimposed emission lines of H-alpha, Ca II, Fe I, Fe II, and weak He I at near zero velocities. It is suggested that the observed scenario of low-mass stars in an older massive star environment may be analogous to the circumstances surrounding the birthmore » of the sun. 53 refs.« less

Baby Stars in Orion Solve Solar System Mystery

NASA Technical Reports Server (NTRS)

Wanjek, Christopher

2003-01-01

What do X-rays, meteoroids, infant stars in the Orion Nebula, and our solar system have in common? Perhaps much more than anyone thought. Eric Feigelson of Penn State University stumbled onto a connection one day while his thoughts were far from the solar system, turned toward the vibrant neighborhood of young stars, hot gas, and caliginous dust of the Orion Nebula. This nebula, 1500 light-years away, is visible to the naked eye in the constellation Orion, a gem to behold with a good pair of binoculars or a telescope under dark skies. In Orion, Feigelson inadvertently found a possible solution to a long-standing mystery about our own solar system: the presence of exotic isotopes locked away in meteoroids. Scientists have assumed that these short-lived isotopes - special forms of atomic nuclei, such as aluminum-26 and calcium-41 - were transported here by a nearby supernova. Only tenuous evidence for such an explosion exists, but what else could have made the isotopes? The isotopes are about as old as the solar system, and the Sun couldn t possibly have been powerful enough to create them. Well, maybe we need to give the Sun a little more credit. Feigelson found that very young, midsized stars in the Orion Nebula - in the same stellar class as our Sun except they are only a million years old - produce powerful flares visible in X-rays. His team spotted these X-ray flares with the Chandra X-Ray Observatory. These baby-tantrum flares are indeed energetic enough to forge heavy isotopes, Feigelson says. If the infant stars in Orion can do it now, then our Sun could have done the same when the solar system was forming about 4.5 billion years ago, when the Sun itself was only a few million years old.

Pleiades-like Stars in the Hipparcos Catalog

NASA Astrophysics Data System (ADS)

Stauffer, John R.; An, Deokkeun

2010-08-01

The tension between the Hipparcos parallax of the Pleiades and other independent distance estimates continues even after the new reduction of the Hipparcos astrometric data. A short Pleiades distance from the Hipparcos parallax predicts that a number of young field stars in the solar neighborhood should be sub-luminous at a given photospheric abundance (i.e. they should have the "Pleiades disease"). We propose to obtain spectroscopic abundances for a subset of stars in the Hipparcos catalog, which occupy the same region as the Pleiades in the color-magnitude diagram, and to directly test this hypothesis. Failure to find any such sub-luminous, young solar metallicity stars would strongly contradict the Hipparcos Pleiades distance. This is a continuation of a program approved for 2010A (observations scheduled for May 2010), to cover the other half of the northern sky.

Magnetic activity and radial velocity filtering of young Suns: the weak-line T-Tauri stars Par 1379 and Par 2244

NASA Astrophysics Data System (ADS)

Hill, C. A.; Carmona, A.; Donati, J.-F.; Hussain, G. A. J.; Gregory, S. G.; Alencar, S. H. P.; Bouvier, J.; The Matysse Collaboration

2017-12-01

We report the results of our spectropolarimetric monitoring of the weak-line T-Tauri stars (wTTSs) Par 1379 and Par 2244, within the MaTYSSE (Magnetic Topologies of Young Stars and the Survival of close-in giant Exoplanets) programme. Both stars are of a similar mass (1.6 and 1.8 M⊙) and age (1.8 and 1.1 Myr), with Par 1379 hosting an evolved low-mass dusty circumstellar disc, and with Par 2244 showing evidence of a young debris disc. We detect profile distortions and Zeeman signatures in the unpolarized and circularly polarized lines for each star, and have modelled their rotational modulation using tomographic imaging, yielding brightness and magnetic maps. We find that Par 1379 harbours a weak (250 G), mostly poloidal field tilted 65° from the rotation axis. In contrast, Par 2244 hosts a stronger field (860 G) split 3:2 between poloidal and toroidal components, with most of the energy in higher order modes, and with the poloidal component tilted 45° from the rotation axis. Compared to the lower mass wTTSs, V819 Tau and V830 Tau, Par 2244 has a similar field strength, but is much more complex, whereas the much less complex field of Par 1379 is also much weaker than any other mapped wTTS. We find moderate surface differential rotation of 1.4× and 1.8× smaller than Solar, for Par 1379 and Par 2244, respectively. Using our tomographic maps to predict the activity-related radial velocity (RV) jitter, and filter it from the RV curves, we find RV residuals with dispersions of 0.017 and 0.086 km s-1 for Par 1379 and Par 2244, respectively. We find no evidence for close-in giant planets around either star, with 3σ upper limits of 0.56 and 3.54 MJup (at an orbital distance of 0.1 au).

X-ray Flares from Young Stars and the Sun: Bridging the Gap with Chandra+NuSTAR

NASA Astrophysics Data System (ADS)

Canizares, Claude

2017-09-01

It is widely accepted that the coronae of pre-MS stars constitute scaled-up versions of the solar corona. However, the potential hard (>10 keV) non-thermal emission components of pre-MS flares, and the link between such emission and the softer thermal emission accessible to Chandra and XMM, remain unstudied. We propose joint HETG and NuStar observations of V773 Tau, one of the brightest and most energetically flaring pre-MS X-ray sources. By elucidating the connection between hard, non-thermal X-ray emission and softer, thermal emission, these observations will provide an essential test of models invoking scaled-up solar magnetic activity to explain X-ray emission from pre-MS stars.

The Structure of the Young Star Cluster NGC 6231. II. Structure, Formation, and Fate

NASA Astrophysics Data System (ADS)

Kuhn, Michael A.; Getman, Konstantin V.; Feigelson, Eric D.; Sills, Alison; Gromadzki, Mariusz; Medina, Nicolás; Borissova, Jordanka; Kurtev, Radostin

2017-12-01

The young cluster NGC 6231 (stellar ages ˜2-7 Myr) is observed shortly after star formation activity has ceased. Using the catalog of 2148 probable cluster members obtained from Chandra, VVV, and optical surveys (Paper I), we examine the cluster’s spatial structure and dynamical state. The spatial distribution of stars is remarkably well fit by an isothermal sphere with moderate elongation, while other commonly used models like Plummer spheres, multivariate normal distributions, or power-law models are poor fits. The cluster has a core radius of 1.2 ± 0.1 pc and a central density of ˜200 stars pc-3. The distribution of stars is mildly mass segregated. However, there is no radial stratification of the stars by age. Although most of the stars belong to a single cluster, a small subcluster of stars is found superimposed on the main cluster, and there are clumpy non-isotropic distributions of stars outside ˜4 core radii. When the size, mass, and age of NGC 6231 are compared to other young star clusters and subclusters in nearby active star-forming regions, it lies at the high-mass end of the distribution but along the same trend line. This could result from similar formation processes, possibly hierarchical cluster assembly. We argue that NGC 6231 has expanded from its initial size but that it remains gravitationally bound.

IDENTIFYING NEARBY, YOUNG, LATE-TYPE STARS BY MEANS OF THEIR CIRCUMSTELLAR DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schneider, Adam; Song, Inseok; Melis, Carl

2012-10-01

It has recently been shown that a significant fraction of late-type members of nearby, very young associations (age {approx}<10 Myr) display excess emission at mid-IR wavelengths indicative of dusty circumstellar disks. We demonstrate that the detection of mid-IR excess emission can be utilized to identify new nearby, young, late-type stars including two definite new members ('TWA 33' and 'TWA 34') of the TW Hydrae Association (TWA). Both new TWA members display mid-IR excess emission in the Wide-field Infrared Survey Explorer catalog and they show proper motion and youthful spectroscopic characteristics-namely, H{alpha} emission, strong lithium absorption, and low surface gravity featuresmore » consistent with known TWA members. We also detect mid-IR excess-the first unambiguous evidence of a dusty circumstellar disk-around a previously identified UV-bright, young, accreting star (2M1337) that is a likely member of the Lower-Centaurus Crux region of the Scorpius-Centaurus Complex.« less

Structural parameters of young star clusters: fractal analysis

NASA Astrophysics Data System (ADS)

Hetem, A.

2017-07-01

A unified view of star formation in the Universe demand detailed and in-depth studies of young star clusters. This work is related to our previous study of fractal statistics estimated for a sample of young stellar clusters (Gregorio-Hetem et al. 2015, MNRAS 448, 2504). The structural properties can lead to significant conclusions about the early stages of cluster formation: 1) virial conditions can be used to distinguish warm collapsed; 2) bound or unbound behaviour can lead to conclusions about expansion; and 3) fractal statistics are correlated to the dynamical evolution and age. The technique of error bars estimation most used in the literature is to adopt inferential methods (like bootstrap) to estimate deviation and variance, which are valid only for an artificially generated cluster. In this paper, we expanded the number of studied clusters, in order to enhance the investigation of the cluster properties and dynamic evolution. The structural parameters were compared with fractal statistics and reveal that the clusters radial density profile show a tendency of the mean separation of the stars increase with the average surface density. The sample can be divided into two groups showing different dynamic behaviour, but they have the same dynamic evolution, since the entire sample was revealed as being expanding objects, for which the substructures do not seem to have been completely erased. These results are in agreement with the simulations adopting low surface densities and supervirial conditions.

Studies of Young, Star-forming Circumstellar Disks

NASA Astrophysics Data System (ADS)

Bae, Jaehan

2017-08-01

Disks of gas and dust around forming stars - circumstellar disks - last only a few million years. This is a very small fraction of the entire lifetime of Sun-like stars, several billion years. Nevertheless, by the time circumstellar disks dissipate stars complete building up their masses, giant planets finish accreting gas, and terrestrial bodies are nearly fully grown and ready for their final assembly to become planets. Understanding the evolution of circumstellar disks are thus crucial in many contexts. Using numerical simulations as the primary tool, my thesis has focused on the studies of various physical processes that can occur throughout the lifetime of circumstellar disks, from their formation to dispersal. Chapters 2, 3, and 4 emphasize the importance of early evolution, during which time a forming star-disk system obtains mass from its natal cloud: the infall phase. In Chapter 2 and 3, I have modeled episodic outbursts of accretion in protostellar systems resulting from disk instabilities - gravitational instability and magnetorotational instability. I showed that outbursts occur preferentially during the infall phase, because the mass addition provides more favorable conditions for gravitational instability to initiate the outburst cycle, and that forming stars build up a significant fraction of their masses through repeated short-lived, episodic outbursts. The infall phase can also be important for the formation of planets. Recent ALMA observations revealed sets of bright and dark rings in circumstellar disks of young, forming stars, potentially indicating early formation of planets. In Chapter 4, I showed that infall streams can create radial pressure bumps near the outer edge of the mass landing on the disk, from which vortices can form, collecting solid particles very efficiently to make initial seeds of planets. The next three chapters highlight the role of planets in setting the observational appearance and the evolution of circumstellar disks

Diffuse γ-ray emission in the vicinity of young star cluster Westerlund 2

NASA Astrophysics Data System (ADS)

Yang, Rui-zhi; de Oña Wilhelmi, Emma; Aharonian, Felix

2018-04-01

We report the results of our analysis of the publicly available data obtained by the Large Area Telescope (LAT) on board the Fermi satellite towards the direction of the young massive star cluster Westerlund 2. We found significant extended γ-ray emission in the vicinity of Westerlund 2 with a hard power-law energy spectrum extending from 1 to 250 GeV with a photon index of 2.0 ± 0.1. We argue that amongst several alternatives, the luminous stars in Westerlund 2 are likely sites of acceleration of particles responsible for the diffuse γ-ray emission of the surrounding interstellar medium. In particular, the young star cluster Westerlund 2 can provide sufficient non-thermal energy to account for the γ-ray emission. In this scenario, since the γ-ray production region is significantly larger than the area occupied by the star cluster, we conclude that the γ-ray production is caused by hadronic interactions of accelerated protons and nuclei with the ambient gas. In that case, the total energy budget in relativistic particles is estimated of the order of 1050 erg.

Ancient Black Hole Speeds Through Sun's Galactic Neighborhood, Devouring Companion Star

NASA Astrophysics Data System (ADS)

2001-09-01

1118+480 orbits the Galaxy's center in a path similar to those of the globular clusters, moving at 145 kilometers per second (90 miles per second) relative to the Earth. How did it get into such an orbit? "There are two possibilities: either it formed in the Galaxy's plane and was somehow kicked out of the plane or it formed in a globular cluster and was kicked out of the cluster," said Vivek Dhawan, an astronomer at the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico. A massive star ends its life by exploding as a supernova, leaving either a neutron star or a black hole as a remnant. Some neutron stars show rapid motion, thought to result from a sideways "kick" during the supernova explosion. "This black hole has much more mass -- about seven times the mass of our Sun -- than any neutron star," said Dhawan. "To accelerate it to its present speed would require a kick from the supernova that we consider improbable," Dhawan added. "We think it's more likely that it was gravitationally ejected from the globular cluster," Dhawan said. Simulations of the gravitational interactions in globular clusters have shown that the black holes resulting from the collapse of the most massive stars should eventually be ejected from the cluster. "The star that preceded this black hole probably formed in a globular cluster even before our Galaxy's disk was formed," Mirabel said. "What we're doing here is the astronomical equivalent of archaeology, seeing traces of the intense burst of star formation that took place during an early stage of our Galaxy's development." The black hole has consumed so much of its companion star that the inner layers of the smaller star -- only about one-third the mass of the Sun -- now are exposed. The scientists believe the black hole captured the companion before being ejected from the globular cluster, as if it were grabbing a snack for the road. The Very Long Baseline Array "Because this microquasar happened to be relatively close to the

Multiplicity Among Young Brown Dwarfs and Very Low Mass Stars

NASA Astrophysics Data System (ADS)

Ahmic, Mirza; Jayawardhana, R.; Brandeker, A.; Scholz, A.; van Kerkwijk, M. H.; Delgado-Donate, E.; Froebrich, D.

2007-05-01

Characterizing multiplicity in the very low mass (VLM) domain is a topic of much current interest and fundamental importance. Here we report on a near-infrared adaptive optics imaging survey of 28 young brown dwarfs and VLM stars, 26 of which are in the Chamaeleon I star-forming region, using the ESO Very Large Telescope. Our findings in Cha I -- the low multiplicity frequency of 8%, the preference for equal mass pairs, and the lack of wide binaries -- are strikingly similar to what has previously been reported for VLM objects in the field and in open clusters. Thus, we argue that there is no significant evolution of multiplicity with age among brown dwarfs and VLM stars between a few Myr to several Gyr. Instead, the observations to date suggest that VLM objects are either less likely to be born in wide multiple systems than solar mass stars or such systems are disrupted very early (within the first couple of Myr). Our results also imply that systems like 2MASSW J1207334-393254 and Oph 162225-240515, with planetary mass companions at wide separations, are rare. This research was supported by an NSERC grant, University of Toronto research funds and the Ontario Graduate Scholarship.

Zodiacal Exoplanets in Time: Searching for Young Stars in K2

NASA Astrophysics Data System (ADS)

Morris, Nathan; Mann, Andrew W.

2017-06-01

Nearby young, open clusters such as the Hyades, Pleiades, and Praesepe provide an important reference point for the properties of stellar systems in general. In each cluster, all stars are of the same known age. As such, observations of planetary systems around these stars can be used to gain insight into the early stages of planetary system formation. K2, the revived Kepler mission, has provided a vast number of light curves for young stars in the and elsewhere in the K2 field. We aim to compute rotational periods from sunspot patterns for all K2 target stars and use gyrochronometric relationships derived from cluster stars to determine their ages. From there, we will search for planets around young stars outside the clusters with the ultimate goal of shedding light on how planets and planetary systems evolve with time.

Weighing the Smallest Stars

NASA Astrophysics Data System (ADS)

2005-01-01

VLT Finds Young, Very Low Mass Objects Are Twice As Heavy As Predicted Summary Thanks to the powerful new high-contrast camera installed at the Very Large Telescope, photos have been obtained of a low-mass companion very close to a star. This has allowed astronomers to measure directly the mass of a young, very low mass object for the first time. The object, more than 100 times fainter than its host star, is still 93 times as massive as Jupiter. And it appears to be almost twice as heavy as theory predicts it to be. This discovery therefore suggests that, due to errors in the models, astronomers may have overestimated the number of young "brown dwarfs" and "free floating" extrasolar planets. PR Photo 03/05: Near-infrared image of AB Doradus A and its companion (NACO SDI/VLT) A winning combination A star can be characterised by many parameters. But one is of uttermost importance: its mass. It is the mass of a star that will decide its fate. It is thus no surprise that astronomers are keen to obtain a precise measure of this parameter. This is however not an easy task, especially for the least massive ones, those at the border between stars and brown dwarf objects. Brown dwarfs, or "failed stars", are objects which are up to 75 times more massive than Jupiter, too small for major nuclear fusion processes to have ignited in its interior. To determine the mass of a star, astronomers generally look at the motion of stars in a binary system. And then apply the same method that allows determining the mass of the Earth, knowing the distance of the Moon and the time it takes for its satellite to complete one full orbit (the so-called "Kepler's Third Law"). In the same way, they have also measured the mass of the Sun by knowing the Earth-Sun distance and the time - one year - it takes our planet to make a tour around the Sun. The problem with low-mass objects is that they are very faint and will often be hidden in the glare of the brighter star they orbit, also when viewed

Chromospherically Active Stars in the RAVE Survey. II. Young Dwarfs in the Solar Neighborhood

NASA Astrophysics Data System (ADS)

Žerjal, M.; Zwitter, T.; Matijevič, G.; Grebel, E. K.; Kordopatis, G.; Munari, U.; Seabroke, G.; Steinmetz, M.; Wojno, J.; Bienaymé, O.; Bland-Hawthorn, J.; Conrad, C.; Freeman, K. C.; Gibson, B. K.; Gilmore, G.; Kunder, A.; Navarro, J.; Parker, Q. A.; Reid, W.; Siviero, A.; Watson, F. G.; Wyse, R. F. G.

2017-01-01

A large sample of over 38,000 chromospherically active candidate solar-like stars and cooler dwarfs from the RAVE survey is addressed in this paper. An improved activity identification with respect to the previous study was introduced to build a catalog of field stars in the solar neighborhood with an excess emission flux in the calcium infrared triplet wavelength region. The central result of this work is the calibration of the age-activity relation for main-sequence dwarfs in a range from a few 10 {Myr} up to a few Gyr. It enabled an order of magnitude age estimation of the entire active sample. Almost 15,000 stars are shown to be younger than 1 {Gyr} and ˜2000 younger than 100 {Myr}. The young age of the most active stars is confirmed by their position off the main sequence in the J - K versus {N}{UV}-V diagram showing strong ultraviolet excess, mid-infrared excess in the J - K versus {W}1-{W}2 diagram, and very cool temperatures (J-K> 0.7). They overlap with the reference pre-main-sequence RAVE stars often displaying X-ray emission. The activity level increasing with the color reveals their different nature from the solar-like stars and probably represents an underlying dynamo-generating magnetic fields in cool stars. Of the RAVE objects from DR5, 50% are found in the TGAS catalog and supplemented with accurate parallaxes and proper motions by Gaia. This makes the database of a large number of young stars in a combination with RAVE’s radial velocities directly useful as a tracer of the very recent large-scale star formation history in the solar neighborhood. The data are available online in the Vizier database.

The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Grasha, K.; Calzetti, D.; Adamo, A.; Kim, H.; Elmegreen, B. G.; Gouliermis, D. A.; Dale, D. A.; Fumagalli, M.; Grebel, E. K.; Johnson, K. E.; Kahre, L.; Kennicutt, R. C.; Messa, M.; Pellerin, A.; Ryon, J. E.; Smith, L. J.; Shabani, F.; Thilker, D.; Ubeda, L.

2017-05-01

We present a study of the hierarchical clustering of the young stellar clusters in six local (3-15 Mpc) star-forming galaxies using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). We identified 3685 likely clusters and associations, each visually classified by their morphology, and we use the angular two-point correlation function to study the clustering of these stellar systems. We find that the spatial distribution of the young clusters and associations are clustered with respect to each other, forming large, unbound hierarchical star-forming complexes that are in general very young. The strength of the clustering decreases with increasing age of the star clusters and stellar associations, becoming more homogeneously distributed after ˜40-60 Myr and on scales larger than a few hundred parsecs. In all galaxies, the associations exhibit a global behavior that is distinct and more strongly correlated from compact clusters. Thus, populations of clusters are more evolved than associations in terms of their spatial distribution, traveling significantly from their birth site within a few tens of Myr, whereas associations show evidence of disruption occurring very quickly after their formation. The clustering of the stellar systems resembles that of a turbulent interstellar medium that drives the star formation process, correlating the components in unbound star-forming complexes in a hierarchical manner, dispersing shortly after formation, suggestive of a single, continuous mode of star formation across all galaxies.

Sun Protection Preferences and Behaviors among Young Adult Males during Maximum Ultraviolet Radiation Exposure Activities

PubMed Central

Wickenheiser, Marilyn; Baker, Mary Kate; Gaber, Rikki; Blatt, Hanz; Robinson, June K.

2013-01-01

This study explores sun protection attitudes, preferences, and behaviors among young adult males participating in an open-field activity with extreme ultraviolet radiation exposure. Male drum corps members (n = 137) responded to survey questions regarding their behavior and willingness to engage in sun protection and barriers to sunscreen usage. A subset of members (n = 31) participated in cognitive interviews exploring various sunscreen products and intervention techniques. Participants were knowledgeable about health risks and protection benefits regarding sun exposure. Generally, males had positive attitudes and normative beliefs about using sunscreen. A barrier to sunscreen re-application was lack of adequate time to reapply sunscreen during the open field activity. Males preferred a towelette application method, but were unfamiliar with its efficacy and proper use. Thus, they were more likely to use the more familiar sunscreen spray. To increase sun protection behaviors and lower skin cancer risk for males participating in open-field activities, breaks must be allotted every 2 h and have sufficient time to allow sunscreen application. Future development and research into delivery systems that rapidly and evenly apply sunscreen may help lower exposure in this population. PMID:23912201

Family of the Sun-and-Stars Time-Determining Instruments (Ilseong-jeongsi-ui) Invented During the Joseon Dynasty

NASA Astrophysics Data System (ADS)

Lee, Yong Sam; Kim, Sang Hyuk; Mihn, Byeong-Hee

2016-09-01

We analyze the design and specifications of the Sun-and-Stars Time-Determining group of instruments (Ilseong-jeongsi-ui, 日星定時儀) made during the Joseon dynasty. According to the records of the Sejong Sillok (Veritable Records of King Sejong), Sun-and-Stars Time-Determining Instruments measure the solar time of day and the sidereal time of night through three rings and an alidade. One such instrument, the Simplified Time-Determining Instrument (So-jeongsi-ui, 小定時儀), is made without the essential component for alignment with the celestial north pole. Among this group of instruments, only two bronze Hundred-Interval-Ring Sundials (Baekgak-hwan-Ilgu, 百刻環日晷) currently exist. A comparison of the functions of these two relics with two Time-Determining Instruments suggests that the Hundred-Interval-Ring Sundial is a Simplified Sundial (So-ilyeong, 小日影), as recorded in the Sejong Sillok and the Seongjong Sillok (Veritable Records of King Seongjong). Furthermore, the Simplified Sundial is a model derived from the Simplified Time-Determining Instrument. During the King Sejong reign, the Sun-and-Stars Time-Determining Instruments were used in military camps of the kingdom’s frontiers, in royal ancestral rituals, and in royal astronomical observatories.

A debris disk around an isolated young neutron star.

PubMed

Wang, Zhongxiang; Chakrabarty, Deepto; Kaplan, David L

2006-04-06

Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk. Such 'fallback' is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar. The disk does not power the pulsar's X-ray emission but is passively illuminated by these X-rays. The estimated mass of the disk is of the order of 10 Earth masses, and its lifetime (> or = 10(6) years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars.

HERSCHEL FINDS EVIDENCE FOR STELLAR WIND PARTICLES IN A PROTOSTELLAR ENVELOPE: IS THIS WHAT HAPPENED TO THE YOUNG SUN?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ceccarelli, C.; López-Sepulcre, A.; Dominik, C.

2014-07-20

There is evidence that the young Sun emitted a high flux of energetic (≥10 MeV) particles. The collisions of these particles with the material at the inner edge of the Protosolar Nebula disk induced spallation reactions that formed short-lived radionuclei, like {sup 10}Be, whose trace is now visible in some meteorites. However, it is poorly known exactly when this happened, and whether and how it affected the solar system. Here, we present indirect evidence for an ejection of energetic particles in the young protostar, OMC-2 FIR 4, similar to that experienced by the young solar system. In this case, the energeticmore » particles collide with the material in the protostellar envelope, enhancing the abundance of two molecular ions, HCO{sup +} and N{sub 2}H{sup +}, whose presence is detected via Herschel observations. The flux of energetic particles at a distance of 1 AU from the emitting source, estimated from the measured abundance ratio of HCO{sup +} and N{sub 2}H{sup +}, can easily account for the irradiation required by meteoritic observations. These new observations demonstrate that the ejection of ≥10 MeV particles is a phenomenon occurring very early in the life of a protostar, before the disappearance of the envelope from which the future star accretes. The whole envelope is affected by the event, which sets constraints on the magnetic field geometry in the source and opens up the possibility that the spallation reactions are not limited to the inner edge of the Protosolar Nebula disk.« less

The HOSTS Survey—Exozodiacal Dust Measurements for 30 Stars

NASA Astrophysics Data System (ADS)

Ertel, S.; Defrère, D.; Hinz, P.; Mennesson, B.; Kennedy, G. M.; Danchi, W. C.; Gelino, C.; Hill, J. M.; Hoffmann, W. F.; Rieke, G.; Shannon, A.; Spalding, E.; Stone, J. M.; Vaz, A.; Weinberger, A. J.; Willems, P.; Absil, O.; Arbo, P.; Bailey, V. P.; Beichman, C.; Bryden, G.; Downey, E. C.; Durney, O.; Esposito, S.; Gaspar, A.; Grenz, P.; Haniff, C. A.; Leisenring, J. M.; Marion, L.; McMahon, T. J.; Millan-Gabet, R.; Montoya, M.; Morzinski, K. M.; Pinna, E.; Power, J.; Puglisi, A.; Roberge, A.; Serabyn, E.; Skemer, A. J.; Stapelfeldt, K.; Su, K. Y. L.; Vaitheeswaran, V.; Wyatt, M. C.

2018-05-01

The Hunt for Observable Signatures of Terrestrial Systems survey searches for dust near the habitable zones (HZs) around nearby, bright main-sequence stars. We use nulling interferometry in the N band to suppress the bright stellar light and to probe for low levels of HZ dust around the 30 stars observed so far. Our overall detection rate is 18%, including four new detections, among which are the first three around Sun-like stars and the first two around stars without any previously known circumstellar dust. The inferred occurrence rates are comparable for early-type and Sun-like stars, but decrease from {60}-21+16% for stars with previously detected cold dust to {8}-3+10% for stars without such excess, confirming earlier results at higher sensitivity. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal excess luminosity function, we put upper limits on the median HZ dust level of 13 zodis (95% confidence) for a sample of stars without cold dust and of 26 zodis when focusing on Sun-like stars without cold dust. However, our data suggest that a more complex luminosity function may be more appropriate. For stars without detectable Large Binocular Telescope Interferometer (LBTI) excess, our upper limits are almost reduced by a factor of two, demonstrating the strength of LBTI target vetting for future exo-Earth imaging missions. Our statistics are limited so far, and extending the survey is critical to informing the design of future exo-Earth imaging surveys.

SWIRLING GALAXY PARENTS GENERATIONS OF STARS IN ITS CENTER

NASA Technical Reports Server (NTRS)

2002-01-01

The NASA/ESA Hubble Space Telescope has snapped a view of several star generations in the central region of the Whirlpool Galaxy (M51), a spiral region 23 million light-years from Earth in the constellation Canes Venatici (the Hunting Dogs). The galaxy's massive center, the bright ball of light in the center of the photograph, is about 80 light-years across and has a brightness of about 100 million suns. Astronomers estimate that it is about 400 million years old and has a mass 40 million times larger than our Sun. The concentration of stars is about 5,000 times higher than in our solar neighborhood, the Milky Way Galaxy. We would see a continuously bright sky if we lived near the bright center. The dark 'y' across the center is a sign of dust absorption. The bright dot in the middle of the 'y' has a brightness of about one million suns, but a size of less than five light-years. Its power and its tiny size suggest that we have located the elusive central black hole that produces powerful radio jets. Surrounding the center is a much older stellar population that covers a region of about 1,500 light-years in diameter and is at least 8 billion years old, and may be as old as the Universe itself, about 13 billion years. Further away, there is a 'necklace' of very young star-forming regions, clusters of infant stars, younger than 10 million years, which are about 700 light-years away from the center. Normally, young stars are found thousands of light-years away. Astronomers believe that stars in the central region were formed when a dwarf companion galaxy - which is not in the photograph - passed close to it, about 400 million years ago, stirring up dust and material for new star birth. The close encounter has been felt for a long time and is believed to be responsible also for the unusually high star formation activity in the bright necklace of young stars. The color image was assembled from four exposures taken Jan. 15, 1995 with Wide Field Planetary Camera-2 in blue

A Survey of Ca II H and K Chromospheric Emission in Southern Solar-Type Stars

NASA Astrophysics Data System (ADS)

Henry, Todd J.; Soderblom, David R.; Donahue, Robert A.; Baliunas, Sallie L.

1996-01-01

More than 800 southern stars within 50 pc have been observed for chromospheric emission in the cores of the Ca II H and K lines. Most of the sample targets were chosen to be G dwarfs on the basis of colors and spectral types. The bimodal distribution in stellar activity first noted in a sample of northern stars by Vaughan and Preston in 1980 is confirmed, and the percentage of active stars, about 30%, is remarkably consistent between the northern and southern surveys. This is especially compelling given that we have used an entirely different instrumental setup and stellar sample than used in the previous study. Comparisons to the Sun, a relatively inactive star, show that most nearby solar-type stars have a similar activity level, and presumably a similar age. We identify two additional subsamples of stars -- a very active group, and a very inactive group. The very active group may be made up of young stars near the Sun, accounting for only a few percent of the sample, and appears to be less than ~0.1 Gyr old. Included in this high-activity tail of the distribution, however, is a subset of very close binaries of the RS CVn or W UMa types. The remaining members of this population may be undetected close binaries or very young single stars. The very inactive group of stars, contributting ~5%--10% to the total sample, may be those caught in a Maunder Minimum type phase. If the observations of the survey stars are considered to be a sequence of snapshots of the Sun during its life, we might expect that the Sun will spend about 10% of the remainder of its main sequence life in a Maunder Minimum phase.

Circumstellar disks of the most vigorously accreting young stars.

PubMed

Liu, Hauyu Baobab; Takami, Michihiro; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M; Karr, Jennifer L; Kusakabe, Nobuhiko; Tsuribe, Toru

2016-02-01

Stars may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. Our high-resolution near-infrared imaging has verified the presence of the key associated features, large-scale arms and arcs surrounding four young stellar objects undergoing luminous outbursts. Our hydrodynamics simulations and radiative transfer models show that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The effect of those tempestuous episodes of disk evolution on star and planet formation remains to be understood.

StarPals International Young Astronomers' Network Collaborative Projects for IYA

NASA Astrophysics Data System (ADS)

Kingan, Jessi

2008-09-01

StarPals is a nascent non-profit organization with the goal of providing opportunities for international collaboration between students of all ages within space science research. We believe that by encouraging an interest in the cosmos, the one thing that is truly Universal, from a young age, students will not only further their knowledge of and interest in science but will learn valuable teamwork and life skills. The goal is to foster respect, understanding and appreciation of cultural diversity among all StarPals participants, whether students, teachers, or mentors. StarPals aims to inspire students by providing opportunities in which, more than simply visualizing themselves as research scientists, they can actually become one. The technologies of robotic telescopes, videoconferencing, and online classrooms are expanding the possibilities like never before. In honor of IYA2009, StarPals would like to encourage 400 schools to participate on a global scale in astronomy/cosmology research on various concurrent projects. We will offer in-person or online workshops and training sessions to teach the teachers. We will be seeking publication in scientific journals for some student research. For our current project, the Double Stars Challenge, students use the robotic telescopes to take a series of four images of one of 30 double stars from a list furnished by the US Naval Observatory and then use MPO Canopus software to take distance and position angle measurements. StarPals provides students with hands-on training, telescope time, and software to complete the imaging and measuring. A paper will be drafted from our research data and submitted to the Journal of Double Star Observations. The kids who participate in this project may potentially be the youngest contributors to an article in a vetted scientific journal. Kids rapidly adapt and improve their computer skills operating these telescopes and discover for themselves that science is COOL!

Stars at the Tip of Peculiar Elephant Trunk-Like Clouds in IC 1848E: A Possible Third Mechanism of Triggered Star Formation

NASA Astrophysics Data System (ADS)

Chauhan, Neelam; Ogura, Katsuo; Pandey, Anil K.; Samal, Manash R.; Bhatt, Bhuwan C.

2011-08-01

The H II region IC 1848 harbors a lot of intricate elephant trunk-like structures that look morphologically different from usual bright-rimmed clouds (BRCs). Of particular interest is a concentration of thin and long elephant trunk-like structures in the southeastern part of IC 1848E. Some of them have an apparently associated star or two stars at their very tip. We conducted VIc photometry of several of these stars. Their positions on the V/(V - Ic) color-magnitude diagram as well as the physical parameters obtained by SED fittings indicate that they are low-mass pre-main-sequence stars having ages of mostly one Myr, or less. This strongly suggests that they formed from elongated, elephant trunk-like clouds. We presume that such elephant trunk-like structures are genetically different from BRCs, on the basis of the differences in morphology, size distributions, and the ages of the associated young stars. We suspect that those clouds have been caused by hydrodynamical instability of the ionization/shock front of the expanding H II region. Similar structures often show up in recent numerical simulations of the evolution of H II regions. We further hypothesize that this mechanism makes a third mode of triggered star formation associated with H II regions, in addition to the two known mechanisms, i.e., collect-and-collapse of the shell accumulated around an expanding H II region and radiation-driven implosion of BRCs originated from pre-existing cloud clumps.

Investigation of Preservice Science Teachers' Comprehension of the Star, Sun, Comet and Constellation Concepts

ERIC Educational Resources Information Center

Cevik, Ebru Ezberci; Kurnaz, Mehmet Altan

2017-01-01

The purpose of this study is to reveal preservice science teachers' perceptions related to the sun, star, comet and constellation concepts. The research was carried out by 56 preservice science teachers (4th grade) at Kastamonu University taking astronomy course in 2014-2015 academic year. For data collection open-ended questions that required…

The Search for Young Planetary Systems And the Evolution of Young Stars

NASA Technical Reports Server (NTRS)

Beichman, Charles A.; Boden, Andrew; Ghez, Andrea; Hartman, Lee W.; Hillenbrand, Lynn; Lunine, Jonathan I.; Simon, Michael J.; Stauffer, John R.; Velusamy, Thangasamy

2004-01-01

The Space Interferometer Mission (SIM) will provide a census of planetary systems by con- ducting a broad survey of 2,000 stars that will be sensitive to the presence of planets with masses as small as approx. 15 Earth masses (1 Uranus mass) and a deep survey of approx. 250 of the nearest, stars with a mass limit of approx.3 Earth masses. The broad survey will include stars spanning a wide range of ages, spectral types, metallicity, and other important parameters. Within this larger context, the Young Stars and Planets Key Project will study approx. 200 stars with ages from 1 Myr to 100 Myr to understand the formation and dynamical evolution of gas giant planets. The SIM Young Stars and Planets Project will investigate both the frequency of giant planet formation and the early dynamical history of planetary systems. We will gain insight into how common the basic architecture of our solar system is compared with recently discovered systems with close-in giant planets by examining 200 of the nearest (less than 150 pc) and youngest (1-100 Myr) solar-type stars for planets. The sensitivity of the survey for stars located 140 pc away is shown in the planet mass-separation plane. We expect to find anywhere from 10 (assuming that only the presently known fraction of stars. 5-7%, has planets) to 200 (all young stars have planets) planetary systems. W-e have set our sensitivity threshold to ensure the detection of Jupiter-mass planets in the critical orbital range of 1 to 5 AU. These observations, when combined with the results of planetary searches of mature stars, will allow us to test theories of planetary formation and early solar system evolution. By searching for planets around pre-main sequence stars carefully selected to span an age range from 1 to 100 Myr, we will learn a t what epoch and with what frequency giant planets are found at the water-ice snowline where they are expected to form. This will provide insight into the physical mechanisms by which planets form

Magnetic field-related heating instabilities in the surface layers of the sun and stars

NASA Technical Reports Server (NTRS)

Ferrari, A.; Rosner, R.; Vaiana, G. S.

1982-01-01

The stability of a magnetized low-density plasma to current-driven filamentation instabilities is investigated and the results are applied to the surface layers of stars. Unlike previous studies, the initial (i.e., precoronal) state of the stellar surface atmosphere is taken to be a low-density, optically thin magnetized plasma in radiative equilibrium. The linear analysis shows that the surface layers of main-sequence stars (including the sun) which are threaded by magnetic fields are unstable; the instabilities considered lead to structuring perpendicular to the ambient magnetic fields. These results suggest that relatively modest surface motions, in conjunction with the presence of magnetic fields, suffice to account for the presence of inhomogeneous chromospheric and coronal plasma overlying a star's surface.

'My child did not like using sun protection': practices and perceptions of child sun protection among rural black African mothers.

PubMed

Kunene, Zamantimande; Albers, Patricia N; Lucas, Robyn M; Banwell, Cathy; Mathee, Angela; Wright, Caradee Y

2017-08-25

Photodamage is partially mitigated by darker skin pigmentation, but immune suppression, photoaging and cataracts occur among individuals with all skin types. To assess practices and acceptability to Black African mothers of sun protection equipment for their children living in a rural area, participants were recruited at the time of their child's 18-month vaccinations. Mothers completed a baseline questionnaire on usual sun behaviours and sun protection practices. They were then provided with sun protection equipment and advice. A follow-up questionnaire was administered two weeks later. Mothers reported that during the week prior to the baseline questionnaire, children spent on average less than 1 hour of time outdoors (most often spent in the shade). Most mothers (97%) liked the sun protection equipment. However, many (78 of 86) reported that their child did not like any of the sun protection equipment and two-thirds stated that the sun protection equipment was not easy to use. Among Black Africans in rural northern South Africa, we found a mismatch between parental preferences and child acceptance for using sun protection when outdoors. A better understanding of the health risks of incidental excess sun exposure and potential benefits of sun protection is required among Black Africans.

Stars Just Got Bigger - A 300 Solar Mass Star Uncovered

NASA Astrophysics Data System (ADS)

2010-07-01

Using a combination of instruments on ESO's Very Large Telescope, astronomers have discovered the most massive stars to date, one weighing at birth more than 300 times the mass of the Sun, or twice as much as the currently accepted limit of 150 solar masses. The existence of these monsters - millions of times more luminous than the Sun, losing weight through very powerful winds - may provide an answer to the question "how massive can stars be?" A team of astronomers led by Paul Crowther, Professor of Astrophysics at the University of Sheffield, has used ESO's Very Large Telescope (VLT), as well as archival data from the NASA/ESA Hubble Space Telescope, to study two young clusters of stars, NGC 3603 and RMC 136a in detail. NGC 3603 is a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust, located 22 000 light-years away from the Sun (eso1005). RMC 136a (more often known as R136) is another cluster of young, massive and hot stars, which is located inside the Tarantula Nebula, in one of our neighbouring galaxies, the Large Magellanic Cloud, 165 000 light-years away (eso0613). The team found several stars with surface temperatures over 40 000 degrees, more than seven times hotter than our Sun, and a few tens of times larger and several million times brighter. Comparisons with models imply that several of these stars were born with masses in excess of 150 solar masses. The star R136a1, found in the R136 cluster, is the most massive star ever found, with a current mass of about 265 solar masses and with a birthweight of as much as 320 times that of the Sun. In NGC 3603, the astronomers could also directly measure the masses of two stars that belong to a double star system [1], as a validation of the models used. The stars A1, B and C in this cluster have estimated masses at birth above or close to 150 solar masses. Very massive stars produce very powerful outflows. "Unlike humans, these stars are born heavy and lose weight as

HUBBLE SEES DISKS AROUND YOUNG STARS

NASA Technical Reports Server (NTRS)

2002-01-01

[Top left]: This Wide Field and Planetary Camera 2 (WFPC2) image shows Herbig-Haro 30 (HH 30), the prototype of a young star surrounded by a thin, dark disk and emitting powerful gaseous jets. The disk extends 40 billion miles from left to right in the image, dividing the nebula in two. The central star is hidden from direct view, but its light reflects off the upper and lower surfaces of the disk to produce the pair of reddish nebulae. The gas jets are shown in green. Credit: Chris Burrows (STScI), the WFPC2 Science Team and NASA [Top right]: DG Tauri B appears very similar to HH 30, with jets and a central dark lane with reflected starlight at its edges. In this WFPC2 image, the dust lane is much thicker than seen in HH 30, indicating that dusty material is still in the process of falling onto the hidden star and disk. The bright jet extends a distance of 90 billion miles away from the system. Credit: Chris Burrows (STScI), the WFPC2 Science Team and NASA [Lower left]: Haro 6-5B is a nearly edge-on disk surrounded by a complex mixture of wispy clouds of dust and gas. In this WFPC2 image, the central star is partially hidden by the disk, but can be pinpointed by the stubby jet (shown in green), which it emits. The dark disk extends 32 billion miles across at a 90-degree angle to the jet. Credit: John Krist (STScI), the WFPC2 Science Team and NASA [Lower right]: HK Tauri is the first example of a young binary star system with an edge-on disk around one member of the pair. The thin, dark disk is illuminated by the light of its hidden central star. The absence of jets indicates that the star is not actively accreting material from this disk. The disk diameter is 20 billion miles. The brighter primary star appears at top of the image. Credit: Karl Stapelfeldt (JPL) and colleagues, and NASA

Time-dependent Models of Magnetospheric Accretion onto Young Stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robinson, C. E.; Espaillat, C. C.; Owen, J. E.

Accretion onto Classical T Tauri stars is thought to take place through the action of magnetospheric processes, with gas in the inner disk being channeled onto the star’s surface by the stellar magnetic field lines. Young stars are known to accrete material in a time-variable manner, and the source of this variability remains an open problem, particularly on the shortest (∼day) timescales. Using one-dimensional time-dependent numerical simulations that follow the field line geometry, we find that for plausibly realistic young stars, steady-state transonic accretion occurs naturally in the absence of any other source of variability. However, we show that ifmore » the density in the inner disk varies smoothly in time with ∼day-long timescales (e.g., due to turbulence), this complication can lead to the development of shocks in the accretion column. These shocks propagate along the accretion column and ultimately hit the star, leading to rapid, large amplitude changes in the accretion rate. We argue that when these shocks hit the star, the observed time dependence will be a rapid increase in accretion luminosity, followed by a slower decline, and could be an explanation for some of the short-period variability observed in accreting young stars. Our one-dimensional approach bridges previous analytic work to more complicated multi-dimensional simulations and observations.« less

Multiplicity among Young Brown Dwarfs and Very Low Mass Stars

NASA Astrophysics Data System (ADS)

Ahmic, Mirza; Jayawardhana, Ray; Brandeker, Alexis; Scholz, Alexander; van Kerkwijk, Marten H.; Delgado-Donate, Eduardo; Froebrich, Dirk

2007-12-01

We report on a near-infrared adaptive optics imaging survey of 31 young brown dwarfs and very low mass (VLM) stars, 28 of which are in the Chamaeleon I star-forming region, using the ESO Very Large Telescope. We resolve the suspected 0.16'' (~26 AU) binary Cha Hα 2 and present two new binaries, Hn 13 and CHXR 15, with separations of 0.13'' (~20 AU) and 0.30'' (~50 AU), respectively; the latter is one of the widest VLM systems known. We find a binary frequency of 11+9-6%, thus confirming the trend for a lower binary frequency with decreasing mass. By combining our work with previous surveys, we arrive at the largest sample of young VLM objects (72) with high angular resolution imaging to date. Its multiplicity fraction is in statistical agreement with that for VLM objects in the field. Furthermore, we note that many field stellar binaries with lower binding energies and/or wider cross sections have survived dynamical evolution and that statistical models suggest tidal disruption by passing stars is unlikely to affect the binary properties of our systems. Thus, we argue that there is no significant evolution of multiplicity with age among brown dwarfs and VLM stars in OB and T associations between a few megayears to several gigayears. Instead, the observations so far suggest that VLM objects are either less likely to be born in fragile multiple systems than solar-mass stars or such systems are disrupted very early. We dedicate this paper to the memory of our coauthor, Eduardo Delgado-Donate, who died in a hiking accident in Tenerife earlier this year.

A STAR-FORMING RING AROUND κ Ori 250 pc FROM THE SUN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pillitteri, I.; Wolk, S. J.; Megeath, S. T., E-mail: ipillitt@cfa.harvard.edu

2016-04-01

X-rays are a powerful probe of activity in early stages of star formation. They allow us to identify young stars even after they have lost the IR signatures of circumstellar disks and provide constraints on their distance. Here, we report on XMM-Newton observations that detect 121 young stellar objects (YSOs) in two fields between L1641 S and κ Ori. These observations extend the Survey of Orion A with XMM and Spitzer (SOXS). The YSOs are contained in a ring of gas and dust apparent at millimeter wavelengths, and in far-IR and near-IR surveys. The X-ray luminosity function of the YSOs detectedmore » in the two fields indicates a distance of 250–280 pc, much closer than the Orion A cloud and similar to distance estimates of κ Ori. We propose that the ring is a 5–8 pc diameter shell that has been swept up by κ Ori. This ring contains several groups of stars detected by Spitzer and WISE including one surrounding the Herbig Ae/Be stars V1818 Ori. In this interpretation, the κ Ori ring is one of several shells swept up by massive stars within the Orion Eridanus Superbubble and is unrelated to the southern portion of Orion A/L1641 S.« less

The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grasha, K.; Calzetti, D.; Adamo, A.

We present a study of the hierarchical clustering of the young stellar clusters in six local (3–15 Mpc) star-forming galaxies using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). We identified 3685 likely clusters and associations, each visually classified by their morphology, and we use the angular two-point correlation function to study the clustering of these stellar systems. We find that the spatial distribution of the young clusters and associations are clustered with respect to each other, forming large, unbound hierarchical star-forming complexes that are in general very young. Themore » strength of the clustering decreases with increasing age of the star clusters and stellar associations, becoming more homogeneously distributed after ∼40–60 Myr and on scales larger than a few hundred parsecs. In all galaxies, the associations exhibit a global behavior that is distinct and more strongly correlated from compact clusters. Thus, populations of clusters are more evolved than associations in terms of their spatial distribution, traveling significantly from their birth site within a few tens of Myr, whereas associations show evidence of disruption occurring very quickly after their formation. The clustering of the stellar systems resembles that of a turbulent interstellar medium that drives the star formation process, correlating the components in unbound star-forming complexes in a hierarchical manner, dispersing shortly after formation, suggestive of a single, continuous mode of star formation across all galaxies.« less

Long-term Photometric Variability in Kepler Full-frame Images: Magnetic Cycles of Sun–like Stars

NASA Astrophysics Data System (ADS)

Montet, Benjamin T.; Tovar, Guadalupe; Foreman-Mackey, Daniel

2017-12-01

Photometry from the Kepler mission is optimized to detect small, short-duration signals like planet transits at the expense of long-term trends. This long-term variability can be recovered in photometry from the full-frame images (FFIs), a set of calibration data collected approximately monthly during the Kepler mission. Here we present f3, an open-source package to perform photometry on the Kepler FFIs in order to detect changes in the brightness of stars in the Kepler field of view over long time baselines. We apply this package to a sample of 4000 Sun–like stars with measured rotation periods. We find that ≈10% of these targets have long-term variability in their observed flux. For the majority of targets, we find that the luminosity variations are either correlated or anticorrelated with the short-term variability due to starspots on the stellar surface. We find a transition between anticorrelated (starspot-dominated) variability and correlated (facula-dominated) variability between rotation periods of 15 and 25 days, suggesting the transition between the two modes is complete for stars at the age of the Sun. We also identify a sample of stars with apparently complete cycles, as well as a collection of short-period binaries with extreme photometric variation over the Kepler mission.

The origin of interstellar asteroidal objects like 1I/2017 U1 'Oumuamua

NASA Astrophysics Data System (ADS)

Zwart, S. Portegies; Torres, S.; Pelupessy, I.; Bédorf, J.; Cai, Maxwell X.

2018-05-01

We study the origin of the interstellar object 1I/2017 U1 'Oumuamua by juxtaposing estimates based on the observations with simulations. We speculate that objects like 'Oumuamua are formed in the debris disc as left over from the star and planet formation process, and subsequently liberated. The liberation process is mediated either by interaction with other stars in the parental star-cluster, by resonant interactions within the planetesimal disc or by the relatively sudden mass loss when the host star becomes a compact object. Integrating 'Oumuamua backward in time in the Galactic potential together with stars from the Gaia-TGAS catalogue we find that about 1.3 Myr ago 'Oumuamua passed the nearby star HIP 17288 within a mean distance of 1.3 pc. By comparing nearby observed L-dwarfs with simulations of the Galaxy we conclude that the kinematics of 'Oumuamua is consistent with relatively young objects of 1.1-1.7 Gyr. We just met 'Oumuamua by chance, and with a derived mean Galactic density of ˜3 × 105 similarly sized objects within 100 au from the Sun or ˜1014 per cubic parsec we expect about 2 to 12 such visitors per year within 1 au from the Sun.

Cool Stars May Have Different Prebiotic Chemical Mix

NASA Image and Video Library

2009-04-07

NASA Spitzer Space Telescope detected a prebiotic, or potentially life-forming, molecule called hydrogen cyanide HCN in the planet-forming disks around yellow stars like our sun, but not in the disks around cooler, reddish stars.

Young and Exotic Stellar Zoo

NASA Astrophysics Data System (ADS)

2005-03-01

- Westerlund 1 must be very young. The astronomers determine an age somewhere between 3.5 and 5 million years. So, Westerlund 1 is clearly a "newborn" cluster in our Galaxy! The Most Massive Cluster ESO PR Photo 09b/05 ESO PR Photo 09b/05 Properties of Young Massive Clusters [Preview - JPEG: 400 x 511 pix - 20k] [Normal - JPEG: 800 x 1021 pix - 122k] Caption: ESO PR Photo 09b/05 shows the properties of young massive clusters in our Galaxy and in the Large Magellanic Clouds, as well as of Super Star Clusters in star-forming galaxies. The diagram shows the mass and radius of these clusters and also the position of Westerlund 1 (indicated Wd 1). Westerlund 1 is incredibly rich in monster stars - just as one example, it contains as many Yellow Hypergiants as were hitherto known in the entire Milky Way! "If the Sun were located at the heart of Westerlund 1, the sky would be full of stars, many of them brighter than the full Moon", comments Ignacio Negueruela of the Universidad de Alicante in Spain and member of the team. The large quantity of very massive stars implies that Westerlund 1 must contain a huge number of stars. "In our Galaxy, explains Simon Clark of the University College London (UK) and one of the authors of this study, "there are more than 100 solar-like stars for every star weighing 10 times as much as the Sun. The fact that we see hundreds of massive stars in Westerlund 1 means that it probably contains close to half a million stars, but most of these are not bright enough to peer through the obscuring cloud of gas and dust". This is ten times more than any other known young clusterin the Milky Way. Westerlund 1 is presumably much more massive than the dense clusters of heavy stars present in the central region of our Galaxy, like the Arches and Quintuplet clusters. Further deep infrared observations will be required to confirm this. This super star cluster now provides astronomers with a unique perspective towards one of the most extreme environments in the

Circumstellar disks of the most vigorously accreting young stars

PubMed Central

Liu, Hauyu Baobab; Takami, Michihiro; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I.; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M.; Karr, Jennifer L.; Kusakabe, Nobuhiko; Tsuribe, Toru

2016-01-01

Stars may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. Our high-resolution near-infrared imaging has verified the presence of the key associated features, large-scale arms and arcs surrounding four young stellar objects undergoing luminous outbursts. Our hydrodynamics simulations and radiative transfer models show that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The effect of those tempestuous episodes of disk evolution on star and planet formation remains to be understood. PMID:26989772

The Correlation Dimension of Young Stars in Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Odekon, Mary Crone

2006-11-01

We present the correlation dimension of resolved young stars in four actively star-forming dwarf galaxies that are sufficiently resolved and transparent to be modeled as projections of three-dimensional point distributions. We use data from the Hubble Space Telescope archive; photometry for one of the galaxies, UGCA 292, is presented here for the first time. We find that there are statistically distinguishable differences in the nature of stellar clustering among the sample galaxies. The young stars of VII Zw 403, the brightest galaxy in the sample, have the highest value for the correlation dimension and the most dramatic decrease with logarithmic scale, falling from 1.68+/-0.14 to 0.10+/-0.05 over less than a factor of 10 in r. This decrease is consistent with the edge effect produced by a projected Poisson distribution within a 2:2:1 ellipsoid. The young stars in UGC 4483, the faintest galaxy in the sample, exhibit very different behavior, with a constant value of about 0.5 over this same range in r, extending nearly to the edge of the distribution. This behavior may indicate either a scale-free distribution with an unusually low correlation dimension or a two-component (not scale-free) combination of cluster and field stars.

KOI-3278: a self-lensing binary star system.

PubMed

Kruse, Ethan; Agol, Eric

2014-04-18

Over 40% of Sun-like stars are bound in binary or multistar systems. Stellar remnants in edge-on binary systems can gravitationally magnify their companions, as predicted 40 years ago. By using data from the Kepler spacecraft, we report the detection of such a "self-lensing" system, in which a 5-hour pulse of 0.1% amplitude occurs every orbital period. The white dwarf stellar remnant and its Sun-like companion orbit one another every 88.18 days, a long period for a white dwarf-eclipsing binary. By modeling the pulse as gravitational magnification (microlensing) along with Kepler's laws and stellar models, we constrain the mass of the white dwarf to be ~63% of the mass of our Sun. Further study of this system, and any others discovered like it, will help to constrain the physics of white dwarfs and binary star evolution.

Young star clusters in nearby molecular clouds

NASA Astrophysics Data System (ADS)

Getman, K. V.; Kuhn, M. A.; Feigelson, E. D.; Broos, P. S.; Bate, M. R.; Garmire, G. P.

2018-06-01

The SFiNCs (Star Formation in Nearby Clouds) project is an X-ray/infrared study of the young stellar populations in 22 star-forming regions with distances ≲ 1 kpc designed to extend our earlier MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray) survey of more distant clusters. Our central goal is to give empirical constraints on cluster formation mechanisms. Using parametric mixture models applied homogeneously to the catalogue of SFiNCs young stars, we identify 52 SFiNCs clusters and 19 unclustered stellar structures. The procedure gives cluster properties including location, population, morphology, association with molecular clouds, absorption, age (AgeJX), and infrared spectral energy distribution (SED) slope. Absorption, SED slope, and AgeJX are age indicators. SFiNCs clusters are examined individually, and collectively with MYStIX clusters, to give the following results. (1) SFiNCs is dominated by smaller, younger, and more heavily obscured clusters than MYStIX. (2) SFiNCs cloud-associated clusters have the high ellipticities aligned with their host molecular filaments indicating morphology inherited from their parental clouds. (3) The effect of cluster expansion is evident from the radius-age, radius-absorption, and radius-SED correlations. Core radii increase dramatically from ˜0.08 to ˜0.9 pc over the age range 1-3.5 Myr. Inferred gas removal time-scales are longer than 1 Myr. (4) Rich, spatially distributed stellar populations are present in SFiNCs clouds representing early generations of star formation. An appendix compares the performance of the mixture models and non-parametric minimum spanning tree to identify clusters. This work is a foundation for future SFiNCs/MYStIX studies including disc longevity, age gradients, and dynamical modelling.

Evidence for changes in the angular velocity of the surface regions of the sun and stars

NASA Technical Reports Server (NTRS)

1972-01-01

A round table discussion of problems of solar and stellar spindown and theory is presented. Observational evidence of the angular momentum of the solar wind is included, emphasizing changes in the angular velocity of the surface regions of the sun and stars.

Modelling the Dust Around Vega-Like Stars

NASA Technical Reports Server (NTRS)

Sylvester, Roger J.; Skinner, C. J.; Barlow, M. J.

1996-01-01

Models are presented of four Vega-like stars: main-sequence stars with infrared emission from circumstellar dust. The dusty environments of the four stars are rather diverse, as shown by their spectral energy distributions. Good fits to the observations were obtained for all four stars.

A M2FS Spectroscopic Study of Low-mass Young Stars in Orion OB1

NASA Astrophysics Data System (ADS)

Kaleida, Catherine C.; Briceno, Cesar; Calvet, Nuria; Mateo, Mario L.; Hernandez, Jesus

2015-01-01

Surveys of pre-main sequence stars in the ~4-10 Myr range provide a window into the decline of the accretion phase of stars and the formation of planets. Nearby star clusters and stellar associations allow for the study of these young stellar populations all the way down to the lowest mass members. One of the best examples of nearby 4-10 Myr old stellar populations is the Orion OB1 association. The CIDA Variability Survey of Orion OB1 (CVSO - Briceño et al. 2001) has used the variability properties of low-mass pre-main-sequence (PMS) stars to identify hundreds of K and M-type stellar members of the Orion OB1 association, a number of them displaying IR-excess emission and thought to be representative of more evolved disk-bearing young stars. Characterizing these young, low-mass objects using spectroscopy is integral to understanding the accretion phase in young stars. We present preliminary results of a spectroscopic survey of candidate and confirmed Orion OB1 low-mass members taken during November 2014 and February 2014 using the Michigan/Magellan Fiber Spectrograph (M2FS), a PI instrument on the Magellan Clay Telescope (PI: M. Matteo). Target fields located in the off-cloud regions of Orion were identified in the CVSO, and observed using the low and high-resolution modes of M2FS. Both low and high-resolution spectra are needed in order to confirm membership and derive masses, ages, kinematics and accretion properties. Initial analysis of these spectra reveal many new K and M-type members of the Orion OB1 association in these low extinction, off-cloud areas. These are the more evolved siblings of the youngest stars still embedded in the molecular clouds, like those in the Orion Nebula Cluster. With membership and spectroscopic indicators of accretion we are building the most comprehensive stellar census of this association, enabling us to derive a robust estimate of the fraction of young stars still accreting at a various ages, a key constraint for the end of

Observational aspects of Herbig Ae/Be stars and of candidate young A/B stars

NASA Astrophysics Data System (ADS)

de Winter, Dolf

1996-06-01

The thesis consists of several studies on candidate young stars of which most material is published or in press and which can be divided into three parts roughly. Part A is about Herbig Ae/Be stars. A complete review of the observational properties of HAeBes is given in Chapter A1 together with a renewed up-to-date catalogue of HAeBes and HAeBe candidates. As an example of the selection of HAeBes from candidate stars, the observational properties of three candidates is discussed in Chapter A2. They are in particular interesting as they are relatively bright with respect to other HAeBes candidates. An advantage of bright HAeBes is that high resolution spectroscopy can be obtained. For two well know HAeBe objects with a favourable oriented disk, UX and BF Ori, a high resolution spectroscopy monitoring programme is presented in Chapters A3 and A4. First results presented indicate that the disk material of UX Ori is accreting in the form of comet-like bodies. Such pioneering results are also found for BF Ori but more details of the cometaries are given. As discussed in Chapter A1, the IR-excess is one of the fundamental discriminators for the selection of HAeBe candidates. A good understanding of the origin of the IR-excess of HAeBe candidates is necessary to study the disk material that ultimately could produce (proto-)planetary systems. Chapter A5 discusses the amount of IR-excess of HAeBe candidates and ideas about the probable origin. In Part B objects are discussed which were originally selected as HAeBe candidates, but for which a more detailed analysis of the observational characteristics show that they are probably more evolved. This group contains very interesting objects as is shown in Chapters B1, B2 and B3, in which the discovery of a new galactic Luminous Blue Variable (LBV) is reported, WRA 751. A well known B[e] star is HD 45677. The B[e]-group was collected to consist of evolved objects with masses less than those of LBVs and comparable with B[e] stars

Hubble View: Wolf-Rayet Stars, Intense and Short-Lived

NASA Image and Video Library

2017-12-08

This NASA/European Space Agency (ESA) Hubble Space Telescope picture shows a galaxy named SBS 1415+437 (also called SDSS CGB 12067.1), located about 45 million light-years from Earth. SBS 1415+437 is a Wolf-Rayet galaxy, a type of star-bursting galaxy with an unusually high number of extremely hot and massive stars known as Wolf-Rayet stars. These stars can be around 20 times as massive as the sun, but seem to be on a mission to shed surplus mass as quickly as possible — they blast substantial winds of particles out into space, causing them to dwindle at a rapid rate. A typical star of this type can lose a mass equal to that of our sun in just 100,000 years! These massive stars are also incredibly hot, with surface temperatures some 10 to 40 times that of the sun, and very luminous, glowing at tens of thousands to several million times the brightness of the sun. Many of the brightest and most massive stars in the Milky Way are Wolf-Rayet stars. Because these stars are so intense they do not last very long, burning up their fuel and blasting their bulk out into the cosmos on very short timescale — only a few hundred thousand years. Because of this it is unusual to find more than a few of these stars per galaxy — except in Wolf-Rayet galaxies, like the one in this image. Credit: ESA/Hubble & NASA NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram Credit: NOAA/NASA GOES Project

High molecular gas fractions in normal massive star-forming galaxies in the young Universe.

PubMed

Tacconi, L J; Genzel, R; Neri, R; Cox, P; Cooper, M C; Shapiro, K; Bolatto, A; Bouché, N; Bournaud, F; Burkert, A; Combes, F; Comerford, J; Davis, M; Schreiber, N M Förster; Garcia-Burillo, S; Gracia-Carpio, J; Lutz, D; Naab, T; Omont, A; Shapley, A; Sternberg, A; Weiner, B

2010-02-11

Stars form from cold molecular interstellar gas. As this is relatively rare in the local Universe, galaxies like the Milky Way form only a few new stars per year. Typical massive galaxies in the distant Universe formed stars an order of magnitude more rapidly. Unless star formation was significantly more efficient, this difference suggests that young galaxies were much more molecular-gas rich. Molecular gas observations in the distant Universe have so far largely been restricted to very luminous, rare objects, including mergers and quasars, and accordingly we do not yet have a clear idea about the gas content of more normal (albeit massive) galaxies. Here we report the results of a survey of molecular gas in samples of typical massive-star-forming galaxies at mean redshifts of about 1.2 and 2.3, when the Universe was respectively 40% and 24% of its current age. Our measurements reveal that distant star forming galaxies were indeed gas rich, and that the star formation efficiency is not strongly dependent on cosmic epoch. The average fraction of cold gas relative to total galaxy baryonic mass at z = 2.3 and z = 1.2 is respectively about 44% and 34%, three to ten times higher than in today's massive spiral galaxies. The slow decrease between z approximately 2 and z approximately 1 probably requires a mechanism of semi-continuous replenishment of fresh gas to the young galaxies.

Fastest Rotating Star Found in Neighboring Galaxy

NASA Image and Video Library

2017-12-08

NASA image release December 5, 2011 This is an artist's concept of the fastest rotating star found to date. The massive, bright young star, called VFTS 102, rotates at a million miles per hour, or 100 times faster than our Sun does. Centrifugal forces from this dizzying spin rate have flattened the star into an oblate shape and spun off a disk of hot plasma, seen edge on in this view from a hypothetical planet. The star may have "spun up" by accreting material from a binary companion star. The rapidly evolving companion later exploded as a supernova. The whirling star lies 160,000 light-years away in the Large Magellanic Cloud, a satellite galaxy of our Milky Way. The team will use NASA's Hubble Space Telescope to make precise measurements of the star's proper motion across space. To read more go to: hubblesite.org/newscenter/archive/releases/2011/39/full/ Image Type: Artwork Credit: NASA, ESA, and G. Bacon (STScI) NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

On the signatures of flare-induced global waves in the Sun: GOLF and VIRGO observations

NASA Astrophysics Data System (ADS)

Kumar, Brajesh; Mathur, Savita; García, Rafael A.; Jiménez, Antonio

2017-11-01

Recently, several efforts have been made to identify the seismic signatures of flares and magnetic activity in the Sun and Sun-like stars. In this work, we have analysed the disc-integrated velocity and intensity observations of the Sun obtained from the Global Oscillations at Low Frequencies (GOLF) and Variability of solar IRradiance and Gravity Oscillations/Sun photometers (VIRGO/SPM) instruments, respectively, on board the Solar and Heliospheric Observatory space mission covering several successive flare events, for the period from 2011 February 11 to 2011 February 17, of which 2011 February 11 remained a relatively quiet day and served as a `null test' for the investigation. Application of the spectral analysis to these disc-integrated Sun-as-a-star velocity and intensity signals indicates that there is enhanced power of the global modes of oscillations in the Sun during the flares, as compared to the quiet day. The GOLF instrument obtains velocity observations using the Na I D lines which are formed in the upper solar photosphere, while the intensity data used in our analysis are obtained by VIRGO/SPM instrument at 862 nm, which is formed within the solar photosphere. Despite the fact that the two instruments sample different layers of the solar atmosphere using two different parameters (velocity versus intensity), we have found that both these observations show the signatures of flare-induced global waves in the Sun. These results could suffice in identifying the asteroseismic signatures of stellar flares and magnetic activity in the Sun-like stars.

X-ray Emission from Pre-Main-Sequence Stars - Testing the Solar Analogy

NASA Technical Reports Server (NTRS)

Skinner, Stephen L.

2000-01-01

This LTSA award funded my research on the origin of stellar X-ray emission and the validity of the solar-stellar analogy. This research broadly addresses the relevance of our current understanding of solar X-ray physics to the interpretation of X-ray emission from stars in general. During the past five years the emphasis has been on space-based X-ray observations of very young stars in star-forming regions (T Tauri stars and protostars), cool solar-like G stars, and evolved high-mass Wolf-Rayet (WR) stars. These observations were carried out primarily with the ASCA and ROSAT space-based observatories (and most recently with Chandra), supplemented by ground-based observations. This research has focused on the identification of physical processes that are responsible for the high levels of X-ray emission seen in pre-main-sequence (PMS) stars, active cool stars, and WR stars. A related issue is how the X-ray emission of such stars changes over time, both on short timescales of days to years and on evolutionary timescales of millions of years. In the case of the Sun it is known that magnetic fields play a key role in the production of X-rays by confining the coronal plasma in loop-like structures where it is heated to temperatures of several million K. The extent to which the magnetically-confined corona interpretation can be applied to other X-ray emitting stars is the key issue that drives the research summarized here.

Planetary Protection: X-ray Super-Flares Aid Formation of "Solar Systems"

NASA Astrophysics Data System (ADS)

2005-05-01

New results from NASA's Chandra X-ray Observatory imply that X-ray super-flares torched the young Solar System. Such flares likely affected the planet-forming disk around the early Sun, and may have enhanced the survival chances of Earth. By focusing on the Orion Nebula almost continuously for 13 days, a team of scientists used Chandra to obtain the deepest X-ray observation ever taken of this or any star cluster. The Orion Nebula is the nearest rich stellar nursery, located just 1,500 light years away. These data provide an unparalleled view of 1400 young stars, 30 of which are prototypes of the early Sun. The scientists discovered that these young suns erupt in enormous flares that dwarf - in energy, size, and frequency -- anything seen from the Sun today. Illustration of Large Flares Illustration of Large Flares "We don't have a time machine to see how the young Sun behaved, but the next best thing is to observe Sun-like stars in Orion," said Scott Wolk of Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "We are getting a unique look at stars between one and 10 million years old - a time when planets form." A key result is that the more violent stars produce flares that are a hundred times as energetic as the more docile ones. This difference may specifically affect the fate of planets that are relatively small and rocky, like the Earth. "Big X-ray flares could lead to planetary systems like ours where Earth is a safe distance from the Sun," said Eric Feigelson of Penn State University in University Park, and principal investigator for the international Chandra Orion Ultradeep Project. "Stars with smaller flares, on the other hand, might end up with Earth-like planets plummeting into the star." Animation of X-ray Flares from a Young Sun Animation of X-ray Flares from a "Young Sun" According to recent theoretical work, X-ray flares can create turbulence when they strike planet-forming disks, and this affects the position of rocky planets as they

Nearby stars of the Galactic disk and halo. III.

NASA Astrophysics Data System (ADS)

Fuhrmann, K.

2004-01-01

High-resolution spectroscopic observations of about 150 nearby stars or star systems are presented and discussed. The study of these and another 100 objects of the previous papers of this series implies that the Galaxy became reality 13 or 14 Gyr ago with the implementation of a massive, rotationally-supported population of thick-disk stars. The very high star formation rate in that phase gave rise to a rapid metal enrichment and an expulsion of gas in supernovae-driven Galactic winds, but was followed by a star formation gap for no less than three billion years at the Sun's galactocentric distance. In a second phase, then, the thin disk - our ``familiar Milky Way'' - came on stage. Nowadays it traces the bright side of the Galaxy, but it is also embedded in a huge coffin of dead thick-disk stars that account for a large amount of baryonic dark matter. As opposed to this, cold-dark-matter-dominated cosmologies that suggest a more gradual hierarchical buildup through mergers of minor structures, though popular, are a poor description for the Milky Way Galaxy - and by inference many other spirals as well - if, as the sample implies, the fossil records of its long-lived stars do not stick to this paradigm. Apart from this general picture that emerges with reference to the entire sample stars, a good deal of the present work is however also concerned with detailed discussions of many individual objects. Among the most interesting we mention the blue straggler or merger candidates HD 165401 and HD 137763/HD 137778, the likely accretion of a giant planet or brown dwarf on 59 Vir in its recent history, and HD 63433 that proves to be a young solar analog at \\tau˜200 Myr. Likewise, the secondary to HR 4867, formerly suspected non-single from the Hipparcos astrometry, is directly detectable in the high-resolution spectroscopic tracings, whereas the visual binary \\chi Cet is instead at least triple, and presumably even quadruple. With respect to the nearby young stars a

The Stars behind the Curtain

NASA Astrophysics Data System (ADS)

2010-02-01

ESO is releasing a magnificent VLT image of the giant stellar nursery surrounding NGC 3603, in which stars are continuously being born. Embedded in this scenic nebula is one of the most luminous and most compact clusters of young, massive stars in our Milky Way, which therefore serves as an excellent "local" analogue of very active star-forming regions in other galaxies. The cluster also hosts the most massive star to be "weighed" so far. NGC 3603 is a starburst region: a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust. Located 22 000 light-years away from the Sun, it is the closest region of this kind known in our galaxy, providing astronomers with a local test bed for studying intense star formation processes, very common in other galaxies, but hard to observe in detail because of their great distance from us. The nebula owes its shape to the intense light and winds coming from the young, massive stars which lift the curtains of gas and clouds revealing a multitude of glowing suns. The central cluster of stars inside NGC 3603 harbours thousands of stars of all sorts (eso9946): the majority have masses similar to or less than that of our Sun, but most spectacular are several of the very massive stars that are close to the end of their lives. Several blue supergiant stars crowd into a volume of less than a cubic light-year, along with three so-called Wolf-Rayet stars - extremely bright and massive stars that are ejecting vast amounts of material before finishing off in glorious explosions known as supernovae. Using another recent set of observations performed with the SINFONI instrument on ESO's Very Large Telescope (VLT), astronomers have confirmed that one of these stars is about 120 times more massive than our Sun, standing out as the most massive star known so far in the Milky Way [1]. The clouds of NGC 3603 provide us with a family picture of stars in different stages of their life, with gaseous structures that are

3D Simulations of Convection: From the Sun Toward Evolved Stars

NASA Astrophysics Data System (ADS)

Höfner, Susanne

2018-04-01

Basic physical considerations and detailed numerical simulations predict a dramatic increase in the sizes of convection cells during late phases of stellar evolution. The recent progress in high-angular-resolution techniques has made it possible to observe surface structures on several nearby giants and supergiants for a wide range of wavelengths. Such observations provide much-needed checkpoints for convection theory, in addition to the detailed comparisons of models and observations for the sun. In this talk I will give an overview of current 3D convection models for different types of stars and discuss related observable phenomena.

Ozone concentrations and ultraviolet fluxes on Earth-like planets around other stars.

PubMed

Segura, Antígona; Krelove, Kara; Kasting, James F; Sommerlatt, Darrell; Meadows, Victoria; Crisp, David; Cohen, Martin; Mlawer, Eli

2003-01-01

Coupled radiative-convective/photochemical modeling was performed for Earth-like planets orbiting different types of stars (the Sun as a G2V, an F2V, and a K2V star). O(2) concentrations between 1 and 10(-5) times the present atmospheric level (PAL) were simulated. The results were used to calculate visible/near-IR and thermal-IR spectra, along with surface UV fluxes and relative dose rates for erythema and DNA damage. For the spectral resolution and sensitivity currently planned for the first generation of terrestrial planet detection and characterization missions, we find that O(2) should be observable remotely in the visible for atmospheres containing at least 10(-2) PAL of O(2). O(3) should be visible in the thermal-IR for atmospheres containing at least 10(-3) PAL of O(2). CH(4) is not expected to be observable in 1 PAL O(2) atmospheres like that of modern Earth, but it might be observable at thermal-IR wavelengths in "mid-Proterozoic-type" atmospheres containing approximately 10(-1) PAL of O(2). Thus, the simultaneous detection of both O(3) and CH(4) - considered to be a reliable indication of life - is within the realm of possibility. High-O(2) planets orbiting K2V and F2V stars are both better protected from surface UV radiation than is modern Earth. For the F2V case the high intrinsic UV luminosity of the star is more than offset by the much thicker ozone layer. At O(2) levels below approximately 10(-2) PAL, planets around all three types of stars are subject to high surface UV fluxes, with the F2V planet exhibiting the most biologically dangerous radiation environment. Thus, while advanced life is theoretically possible on high-O(2) planets around F stars, it is not obvious that it would evolve as it did on Earth.

Young Star May Be Belching Spheres of Gas, Astronomers Say

NASA Astrophysics Data System (ADS)

2001-05-01

A young star more than 2,000 light-years away in the constellation Cepheus may be belching out spheres of gas, say astronomers who observed it with the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope. Not only is the star ejecting spheres of gas, the researchers say, but it also may be ejecting them repeatedly, phenomena not predicted by current theories of how young stars shed matter. Cepheus A star-forming region with blowups of detail In order to remain stable while accumulating matter, young stars have to throw off some of the infalling material to avoid "spinning up" so fast they would break apart, according to current theories. Infalling matter forms a thin spinning disk around the core of the new star, and material is ejected in twin "jets" perpendicular to the plane of the disk. "Twin jets have been seen emerging from many young stars, so we are quite surprised to see evidence that this object may be ejecting not jets, but spheres of gas," said Paul T.P. Ho, an astronomer at the Harvard-Smithsonian Center for Astrophysics. The research is reported in the May 17 edition of the scientific journal Nature. The astronomers observed a complex star-forming region in Cepheus and found an arc of water molecules that act like giant celestial amplifiers to boost the strength of radio signals at a frequency of 22 GHz. Such radio-wave amplifiers, called masers, show up as bright spots readily observed with radio telescopes. "With the great ability of the VLBA to show fine detail, we could track the motions of these maser spots over a period of weeks, and saw that this arc of water molecules is expanding at nearly 20,000 miles per hour," said Ho. "This was possible because we could detect detail equivalent to seeing Lincoln's nose on a penny in Los Angeles from the distance of New York," Ho added. "These observations pushed the tremendous capabilities of the VLBA and of modern computing power to their limits. This is an extremely complex

A Look into the Hellish Cradles of Suns and Solar Systems

NASA Astrophysics Data System (ADS)

2009-09-01

New images released today by ESO delve into the heart of a cosmic cloud, called RCW 38, crowded with budding stars and planetary systems. There, young stars bombard fledgling suns and planets with powerful winds and blazing light, helped in their task by short-lived, massive stars that explode as supernovae. In some cases, this onslaught cooks away the matter that may eventually form new solar systems. Scientists think that our own Solar System emerged from such an environment. The dense star cluster RCW 38 glistens about 5500 light years away in the direction of the constellation Vela (the Sails). Like the Orion Nebula Cluster, RCW 38 is an "embedded cluster", in that the nascent cloud of dust and gas still envelops its stars. Astronomers have determined that most stars, including the low mass, reddish ones that outnumber all others in the Universe, originate in these matter-rich locations. Accordingly, embedded clusters provide scientists with a living laboratory in which to explore the mechanisms of star and planetary formation. "By looking at star clusters like RCW 38, we can learn a great deal about the origins of our Solar System and others, as well as those stars and planets that have yet to come", says Kim DeRose, first author of the new study that appears in the Astronomical Journal. DeRose did her work on RCW 38 as an undergraduate student at the Harvard-Smithsonian Center for Astrophysics, USA. Using the NACO adaptive optics instrument on ESO's Very Large Telescope [1], astronomers have obtained the sharpest image yet of RCW 38. They focused on a small area in the centre of the cluster that surrounds the massive star IRS2, which glows in the searing, white-blue range, the hottest surface colour and temperatures possible for stars. These dramatic observations revealed that IRS2 is actually not one, but two stars - a binary system consisting of twin scorching stars, separated by about 500 times the Earth-Sun distance. In the NACO image, the astronomers

Dynamics during outburst. VLTI observations of the young eruptive star V1647 Orionis during its 2003-2006 outburst

NASA Astrophysics Data System (ADS)

Mosoni, L.; Sipos, N.; Ábrahám, P.; Moór, A.; Kóspál, Á.; Henning, Th.; Juhász, A.; Kun, M.; Leinert, Ch.; Quanz, S. P.; Ratzka, Th.; Schegerer, A. A.; van Boekel, R.; Wolf, S.

2013-04-01

Context. It is hypothesized that low-mass young stellar objects undergo eruptive phases during their early evolution. These eruptions are thought to be caused by highly increased mass accretion from the disk onto the star, and therefore play an important role in the early evolution of Sun-like stars, of their circumstellar disks (structure, dust composition), and in the formation of their planetary systems. The outburst of V1647 Ori between 2003 and 2006 offered a rare opportunity to investigate such an accretion event. Aims: By means of our interferometry observing campaign during this outburst, supplemented by other observations, we investigate the temporal evolution of the inner circumstellar structure of V1647 Ori, the region where Earth-like planets could be born. We also study the role of the changing extinction in the brightening of the object and separate it from the accretional brightening. Methods: We observed V1647 Ori with MIDI on the VLTI at two epochs in this outburst. First, during the slowly fading plateau phase (2005 March) and second, just before the rapid fading of the object (2005 September), which ended the outburst. We used the radiative transfer code MC3D to fit the interferometry data and the spectral energy distributions from five different epochs at different stages of the outburst. The comparison of these models allowed us to trace structural changes in the system on AU-scales. We also considered qualitative alternatives for the interpretation of our data. Results: We found that the disk and the envelope are similar to those of non-eruptive young stars and that the accretion rate varied during the outburst. We also found evidence for the increase of the inner radii of the circumstellar disk and envelope at the beginning of the outburst. Furthermore, the change of the interferometric visibilities indicates structural changes in the circumstellar material. We test a few scenarios to interpret these data. We also speculate that the changes

Hubble Sweeps a Messy Star Factory

NASA Image and Video Library

2017-12-08

This sprinkle of cosmic glitter is a blue compact dwarf galaxy known as Markarian 209. Galaxies of this type are blue-hued, compact in size, gas-rich, and low in heavy elements. They are often used by astronomers to study star formation, as their conditions are similar to those thought to exist in the early Universe. Markarian 209 in particular has been studied extensively. It is filled with diffuse gas and peppered with star-forming regions towards its core. This image captures it undergoing a particularly dramatic burst of star formation, visible as the lighter blue cloudy region towards the top right of the galaxy. This clump is filled with very young and hot newborn stars. This galaxy was initially thought to be a young galaxy undergoing its very first episode of star formation, but later research showed that Markarian 209 is actually very old, with an almost continuous history of forming new stars. It is thought to have never had a dormant period — a period during which no stars were formed — lasting longer than 100 million years. The dominant population of stars in Markarian 209 is still quite young, in stellar terms, with ages of under 3 million years. For comparison, the sun is some 4.6 billion years old, and is roughly halfway through its expected lifespan. The observations used to make this image were taken using Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys, and span the ultraviolet, visible, and infrared parts of the spectrum. A scattering of other bright galaxies can be seen across the frame, including the bright golden oval that could, due to a trick of perspective, be mistaken as part of Markarian 209 but is in fact a background galaxy. Credit: ESA/Hubble & NASA Acknowledgement: Nick Rose NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments

Orion in a New Light - VISTA exposes high-speed antics of young stars

NASA Astrophysics Data System (ADS)

2010-02-01

The Orion Nebula reveals many of its hidden secrets in a dramatic image taken by ESO's new VISTA survey telescope. The telescope's huge field of view can show the full splendour of the whole nebula and VISTA's infrared vision also allows it to peer deeply into dusty regions that are normally hidden and expose the curious behaviour of the very active young stars buried there. VISTA - the Visible and Infrared Survey Telescope for Astronomy - is the latest addition to ESO's Paranal Observatory (eso0949). It is the largest survey telescope in the world and is dedicated to mapping the sky at infrared wavelengths. The large (4.1-metre) mirror, wide field of view and very sensitive detectors make VISTA a unique instrument. This dramatic new image of the Orion Nebula illustrates VISTA's remarkable powers. The Orion Nebula [1] is a vast stellar nursery lying about 1350 light-years from Earth. Although the nebula is spectacular when seen through an ordinary telescope, what can be seen using visible light is only a small part of a cloud of gas in which stars are forming. Most of the action is deeply embedded in dust clouds and to see what is really happening astronomers need to use telescopes with detectors sensitive to the longer wavelength radiation that can penetrate the dust. VISTA has imaged the Orion Nebula at wavelengths about twice as long as can be detected by the human eye. As in the many visible light pictures of this object, the new wide field VISTA image shows the familiar bat-like form of the nebula in the centre of the picture as well as the fascinating surrounding area. At the very heart of this region lie the four bright stars forming the Trapezium, a group of very hot young stars pumping out fierce ultraviolet radiation that is clearing the surrounding region and making the gas glow. However, observing in the infrared allows VISTA to reveal many other young stars in this central region that cannot be seen in visible light. Looking to the region above the

Radio and infrared properties of young stars

NASA Technical Reports Server (NTRS)

Panagia, Nino

1987-01-01

Observing young stars, or more appropriately, pre-main-sequence (PMS) stars, in the infrared and at radio frequencies has the advantage over optical observation in that the heavy extinction associated with a star forming region is only a minor problem, so that the whole region can be studied thoroughly. Therefore, it means being able to: (1) search for stars and do statistical studies on the rate of star formation; (2) determine their luminosity, hence, to study luminosity functions and initial mass functions down to low masses; and (3) to study their spectra and, thus, to determine the prevailing conditions at and near the surface of a newly born star and its relations with the surrounding environment. The third point is of principal interest. The report limits itself to a consideration of the observations concerning the processes of outflows from, and accretion onto, PMS stars and the theory necessary to interpret them. Section 2 discusses the radiative processes relevant in stellar outflows. The main observational results are presented in Section 3. A discussion of the statistical properties of stellar winds from PMS stars are given in Section 4.

Another Possibility for Boyajian's Star

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-07-01

The unusual light curve of the star KIC 8462852, also known as Tabbys star or Boyajians star, has puzzled us since its discovery last year. A new study now explores whether the stars missing flux is due to internal blockage rather than something outside of the star.Mysterious DipsMost explanations for the flux dips of Boyajians star rely on external factors, like this illustrated swarm of comets. [NASA/JPL-Caltech]Boyajians star shows unusual episodes of dimming in its light curve by as much as 20%, each lasting a few to tens of days and separated by periods of typically hundreds of days. In addition, archival observations show that it has gradually faded by roughly 15% over the span of the last hundred years. What could be causing both the sporadic flux dips and the long-term fading of this odd star?Explanations thus far have varied from mundane to extreme. Alien megastructures, pieces of smashed planets or comets orbiting the star, and intervening interstellar medium have all been proposed as possible explanations but these require some object external to the star. A new study by researcher Peter Foukal proposes an alternative: what if the source of the flux obstruction is the star itself?Analogy to the SunDecades ago, researchers discovered that our own stars total flux isnt as constant as we thought. When magnetic dark spots on the Suns surface block the heat transport, the Suns luminosity dips slightly. The diverted heat is redistributed in the Suns interior, becoming stored as a very small global heating and expansion of the convective envelope. When the blocking starspot is removed, the Sun appears slightly brighter than it did originally. Its luminosity then gradually relaxes, decaying back to its original value.Model of a stars flux after a 1,000-km starspot is inserted at time t = 0 and removed at time t = ts at a depth of 10,000 km in the convective zone. The stars luminosity dips, then becomes brighter than originally, and then gradually decays. [Foukal

A rocky planet transiting a nearby low-mass star.

PubMed

Berta-Thompson, Zachory K; Irwin, Jonathan; Charbonneau, David; Newton, Elisabeth R; Dittmann, Jason A; Astudillo-Defru, Nicola; Bonfils, Xavier; Gillon, Michaël; Jehin, Emmanuël; Stark, Antony A; Stalder, Brian; Bouchy, Francois; Delfosse, Xavier; Forveille, Thierry; Lovis, Christophe; Mayor, Michel; Neves, Vasco; Pepe, Francesco; Santos, Nuno C; Udry, Stéphane; Wünsche, Anaël

2015-11-12

M-dwarf stars--hydrogen-burning stars that are smaller than 60 per cent of the size of the Sun--are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star. The nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. Here we report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away. Our Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the Earth and precisely measured densities. Receiving 19 times more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. Because the host star is nearby and only 21 per cent the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.

Hierarchical Star Formation in Turbulent Media: Evidence from Young Star Clusters

NASA Astrophysics Data System (ADS)

Grasha, K.; Elmegreen, B. G.; Calzetti, D.; Adamo, A.; Aloisi, A.; Bright, S. N.; Cook, D. O.; Dale, D. A.; Fumagalli, M.; Gallagher, J. S., III; Gouliermis, D. A.; Grebel, E. K.; Kahre, L.; Kim, H.; Krumholz, M. R.; Lee, J. C.; Messa, M.; Ryon, J. E.; Ubeda, L.

2017-06-01

We present an analysis of the positions and ages of young star clusters in eight local galaxies to investigate the connection between the age difference and separation of cluster pairs. We find that star clusters do not form uniformly but instead are distributed so that the age difference increases with the cluster pair separation to the 0.25-0.6 power, and that the maximum size over which star formation is physically correlated ranges from ˜200 pc to ˜1 kpc. The observed trends between age difference and separation suggest that cluster formation is hierarchical both in space and time: clusters that are close to each other are more similar in age than clusters born further apart. The temporal correlations between stellar aggregates have slopes that are consistent with predictions of turbulence acting as the primary driver of star formation. The velocity associated with the maximum size is proportional to the galaxy’s shear, suggesting that the galactic environment influences the maximum size of the star-forming structures.

Hierarchical Star Formation in Turbulent Media: Evidence from Young Star Clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grasha, K.; Calzetti, D.; Elmegreen, B. G.

We present an analysis of the positions and ages of young star clusters in eight local galaxies to investigate the connection between the age difference and separation of cluster pairs. We find that star clusters do not form uniformly but instead are distributed so that the age difference increases with the cluster pair separation to the 0.25–0.6 power, and that the maximum size over which star formation is physically correlated ranges from ∼200 pc to ∼1 kpc. The observed trends between age difference and separation suggest that cluster formation is hierarchical both in space and time: clusters that are closemore » to each other are more similar in age than clusters born further apart. The temporal correlations between stellar aggregates have slopes that are consistent with predictions of turbulence acting as the primary driver of star formation. The velocity associated with the maximum size is proportional to the galaxy’s shear, suggesting that the galactic environment influences the maximum size of the star-forming structures.« less

The same frequency of planets inside and outside open clusters of stars.

PubMed

Meibom, Søren; Torres, Guillermo; Fressin, Francois; Latham, David W; Rowe, Jason F; Ciardi, David R; Bryson, Steven T; Rogers, Leslie A; Henze, Christopher E; Janes, Kenneth; Barnes, Sydney A; Marcy, Geoffrey W; Isaacson, Howard; Fischer, Debra A; Howell, Steve B; Horch, Elliott P; Jenkins, Jon M; Schuler, Simon C; Crepp, Justin

2013-07-04

Most stars and their planets form in open clusters. Over 95 per cent of such clusters have stellar densities too low (less than a hundred stars per cubic parsec) to withstand internal and external dynamical stresses and fall apart within a few hundred million years. Older open clusters have survived by virtue of being richer and denser in stars (1,000 to 10,000 per cubic parsec) when they formed. Such clusters represent a stellar environment very different from the birthplace of the Sun and other planet-hosting field stars. So far more than 800 planets have been found around Sun-like stars in the field. The field planets are usually the size of Neptune or smaller. In contrast, only four planets have been found orbiting stars in open clusters, all with masses similar to or greater than that of Jupiter. Here we report observations of the transits of two Sun-like stars by planets smaller than Neptune in the billion-year-old open cluster NGC6811. This demonstrates that small planets can form and survive in a dense cluster environment, and implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars in the Galaxy.

The Beta Pictoris Phenomenon in Young Stars With Accreting Gas

NASA Technical Reports Server (NTRS)

Grady, Carol A.

1999-01-01

Program Hae2BPIC resulted in usable ISO spectra of three young, Herbig Ae stars: HR 5999 (A7e, t=0.6 Myr), SV Cep (al-2e, t=1-3 Myr), and MW Vul (Al-2e, t=1-3 Myr). While too small a sample to pursue our original goal of surveying the silicate emission in these young, protoplanetary disk systems, comparison of these data with ground-based IR spectra, and published ISO observations of other HAe stars (especially the posters at PPIV) reveals the following: The known binary stars in the sample show signatures of partially crystal line silicate features by t=0.6 Myr, at an epoch when ostensibly single Herbig Ae stars have substantially stronger silicate emission dominated by amorphous grains. The known binary stars also show deficits in the optically thick continuum flux relative to coeval single stars. Comparison of ISO spectra indicates that the flux deficit seen in WD 163296 over 10-100 microns relative to AB Aur reflects a real deficit of material interior to 300.

Evolution of massive stars in very young clusters and associations

NASA Technical Reports Server (NTRS)

Stothers, R. B.

1985-01-01

Statistics concerning the stellar content of young galactic clusters and associations which show well defined main sequence turnups have been analyzed in order to derive information about stellar evolution in high-mass galaxies. The analytical approach is semiempirical and uses natural spectroscopic groups of stars on the H-R diagram together with the stars' apparent magnitudes. The new approach does not depend on absolute luminosities and requires only the most basic elements of stellar evolution theory. The following conclusions are offered on the basis of the statistical analysis: (1) O-tupe main-sequence stars evolve to a spectral type of B1 during core hydrogen burning; (2) most O-type blue stragglers are newly formed massive stars burning core hydrogen; (3) supergiants lying redward of the main-sequence turnup are burning core helium; and most Wolf-Rayet stars are burning core helium and originally had masses greater than 30-40 solar mass. The statistics of the natural spectroscopic stars in young galactic clusters and associations are given in a table.

Using behavioral economics to promote healthy behavior toward sun exposure in adolescents and young adults.

PubMed

García-Romero, Maria T; Geller, Alan C; Kawachi, Ichiro

2015-12-01

Skin cancer represents an important public health problem, and it is associated with ultraviolet radiation exposure, particularly at early ages. Unhealthy sun exposure and intentional tanning continue to be the trend among young people. Multiple interventions to raise awareness of the risks of sun exposure have been implemented, without necessarily translating into decreased unhealthy behaviors or skin cancer incidence rates. Behavioral economics adds a set of concepts and tools to potentially boost the efficacy of existing approaches to decrease unhealthy sun exposure. This paper reviews public health interventions that have been based in behavioral economics concepts and their results, and provides examples of new and creative ways physicians and health professionals can actively apply insights from behavioral economics to counsel teenagers and young adults about skin cancer prevention. Copyright © 2015 Elsevier Inc. All rights reserved.

Properties of an Earth-like planet orbiting a Sun-like star: Earth observed by the EPOXI mission.

PubMed

Livengood, Timothy A; Deming, L Drake; A'hearn, Michael F; Charbonneau, David; Hewagama, Tilak; Lisse, Carey M; McFadden, Lucy A; Meadows, Victoria S; Robinson, Tyler D; Seager, Sara; Wellnitz, Dennis D

2011-11-01

NASA's EPOXI mission observed the disc-integrated Earth and Moon to test techniques for reconnoitering extrasolar terrestrial planets, using the Deep Impact flyby spacecraft to observe Earth at the beginning and end of Northern Hemisphere spring, 2008, from a range of ∼1/6 to 1/3 AU. These observations furnish high-precision and high-cadence empirical photometry and spectroscopy of Earth, suitable as "ground truth" for numerically simulating realistic observational scenarios for an Earth-like exoplanet with finite signal-to-noise ratio. Earth was observed at near-equatorial sub-spacecraft latitude on 18-19 March, 28-29 May, and 4-5 June (UT), in the range of 372-4540 nm wavelength with low visible resolving power (λ/Δλ=5-13) and moderate IR resolving power (λ/Δλ=215-730). Spectrophotometry in seven filters yields light curves at ∼372-948 nm filter-averaged wavelength, modulated by Earth's rotation with peak-to-peak amplitude of ≤20%. The spatially resolved Sun glint is a minor contributor to disc-integrated reflectance. Spectroscopy at 1100-4540 nm reveals gaseous water and carbon dioxide, with minor features of molecular oxygen, methane, and nitrous oxide. One-day changes in global cloud cover resulted in differences between the light curve beginning and end of ≤5%. The light curve of a lunar transit of Earth on 29 May is color-dependent due to the Moon's red spectrum partially occulting Earth's relatively blue spectrum. The "vegetation red edge" spectral contrast observed between two long-wavelength visible/near-IR bands is ambiguous, not clearly distinguishing between the verdant Earth diluted by cloud cover versus the desolate mineral regolith of the Moon. Spectrophotometry in at least one other comparison band at short wavelength is required to distinguish between Earth-like and Moon-like surfaces in reconnaissance observations. However, measurements at 850 nm alone, the high-reflectance side of the red edge, could be sufficient to

Observation of Young Stars at the University Observatory Jena

NASA Astrophysics Data System (ADS)

Berndt, A.; Errmann, R.; Maciejewski, G.; Raetz, St.; Marka, C.; Ginski, Ch.; Mugrauer, M.; Schmidt, T. O. B.; Neuhäuser, R.; Seeliger, M.; Moualla, M.; Pribulla, T.; Hohle, M. M.; Tetzlaff, N.; Adam, Ch.; Eisenbeiss, T.; YETI Team

2011-12-01

We report on observation and determination of rotational and orbital periods of young stars and eclipsing binaries in the young open cluster Trumpler 37. Observations were carried out with the "Schmidt-Teleskop-Kamera" (STK) at University Observatory Jena in 2009 and 2010.

Gemini Spectroscopic Survey of Young Intermediate-Mass Star-Forming Regions

NASA Astrophysics Data System (ADS)

Lundquist, Michael; Kobulnicky, Henry

2018-01-01

The majority of stars form in embedded clusters. Current research into star formation has focused on either high-mass star-forming regions or low-mass star-forming regions. We present the results from a Gemini spectroscopic survey of young intermediate-mass star-forming regions. These are star forming regions selected to produce stars up to but not exceeding 8 solar masses. We obtained spectra of these regions with GNIRS on Gemini North and Flamingos-2 on Gemini South. We also combine this with near-infrared imaging from 2MASS, UKIDSS, and VVV to study the stellar content.

A MAGELLAN MIKE AND SPITZER MIPS STUDY OF 1.5-1.0 M{sub sun} STARS IN SCORPIUS-CENTAURUS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Christine H.; Bitner, Martin A.; Mamajek, Eric E.

2011-09-10

We obtained Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) 24 {mu}m and 70 {mu}m observations of 182 nearby, Hipparcos F- and G-type common proper motion single and binary systems in the nearest OB association, Scorpius-Centaurus. We also obtained Magellan/MIKE R {approx} 50,000 visual spectra at 3500-10500 A for 181 candidate ScoCen stars in single and binary systems. Combining our MIPS observations with those of other ScoCen stars in the literature, we estimate 24 {mu}m F+G-type disk fractions of 9/27 (33% {+-} 11%), 21/67 (31% {+-} 7%), and 25/71 (35% {+-} 7%) for Upper Scorpius ({approx}10 Myr), Upper Centaurusmore » Lupus ({approx}15 Myr), and Lower Centaurus Crux ({approx}17 Myr), respectively. We confirm previous IRAS and MIPS excess detections and present new discoveries of 41 protoplanetary and debris disk systems, with fractional infrared luminosities ranging from L{sub IR}/L{sub *} = 10{sup -5} to 10{sup -2} and grain temperatures ranging from T{sub gr} = 40-300 K. We searched for an increase in 24 {mu}m excess at an age of 15-20 Myr, consistent with the onset of debris production predicted by coagulation N-body simulations of outer planetary systems. We found such an increase around 1.5 M{sub sun} stars but discovered a decrease in the 24 {mu}m excess around 1.0 M{sub sun} stars. We additionally discovered that the 24 {mu}m excess around 1.0 M{sub sun} stars is larger than predicted by self-stirred models. Finally, we found a weak anti-correlation between fractional infrared luminosity (L{sub IR}/L{sub *}) and chromospheric activity (R'{sub HK}), that may be the result of differences in stellar properties, such as mass, luminosity, and/or winds.« less

MINERVA-Red: A Census of Planets Orbiting the Nearest Low-mass Stars to the Sun

NASA Astrophysics Data System (ADS)

Blake, Cullen; Johnson, John; Plavchan, Peter; Sliski, David; Wittenmyer, Robert A.; Eastman, Jason D.; Barnes, Stuart

2015-01-01

Recent results from Kepler and ground-based exoplanet surveys suggest that low-mass stars host numerous small planets. Since low-mass stars are intrinsically faint at optical wavelengths, obtaining the Doppler precision necessary to detect these companions remains a challenge for existing instruments. We describe MINERVA-Red, a project to use a dedicated, robotic, near-infrared optimized 0.7 meter telescope and a specialized Doppler spectrometer to carry out an intensive, multi-year campaign designed to reveal the planetary systems orbiting some of the closest stars to the Sun. The MINERVA-Red cross-dispersed echelle spectrograph is optimized for the 'deep red', between 800 nm and 900 nm, where these stars are relatively bright. The instrument is very compact and designed for the ultimate in Doppler precision by using single-mode fiber input. We describe the spectrometer and the status of the MINERVA-Red project, which is expected to begin routine operations at Whipple Observatory on Mt Hopkins, Arizona, in 2015.

To protect or not to protect: examining reasons for sun protection among young women at risk for skin cancer.

PubMed

Auerbach, M V; Heckman, C J; Darlow, S

2018-03-27

We aimed to further the understanding of the low rates of sun protection in young women at risk for skin cancer. Six-hundred-sixty-one daily diary entries were received via text message over 14 days from 56 young women at moderate to high risk of developing skin cancer. Women reported whether or not they used sun protection and also listed what their reasons were for using protection or not using sun protection each day. Multi-level modeling was used to examine the influence of study variables when predicting daily sun protection or lack of protection. The number of days in which sun protection was reported was positively associated with "habit" and "prevention" as reasons for protection and negatively associated with "not-needed" and "unprepared" as reasons for non-protection. Self-reported sun protection increased over the 14-day study period. Results of this study suggest the potential value of interventions aimed at motives for sun-protection behaviors.

Lithium abundance in a sample of solar-like stars

NASA Astrophysics Data System (ADS)

López-Valdivia, R.; Hernández-Águila, J. B.; Bertone, E.; Chávez, M.; Cruz-Saenz de Miera, F.; Amazo-Gómez, E. M.

2015-08-01

We report on the determination of the lithium abundance [A(Li)] of 52 solar-like stars. For 41 objects the A(Li) here presented corresponds to the first measurement. We have measured the equivalent widths of the 6708 Å lithium feature in high-resolution spectroscopic images (R ˜ 80 000), obtained at the Observatorio Astrofísico Guillermo Haro (Sonora, Mexico), as part of the first scientific observations of the revitalized Lunar and Planetary Laboratory (LPL) Echelle Spectrograph, now known as the Cananea High-resolution Spectrograph (CanHiS). Lithium abundances were derived with the Fortran code MOOG, using as fundamental input a set of atmospheric parameters recently obtained by our group. With the help of an additional small sample with previous A(Li) determinations, we demonstrate that our lithium abundances are in agreement, to within uncertainties, with other works. Two target objects stand out from the rest of the sample. The star BD+47 3218 (Teff = 6050 ± 52 K, A(Li) = 1.86 ± 0.07 dex) lies inside the so-called lithium desert in the A(Li)-Teff plane. The other object, BD+28 4515, has an A(Li) = 3.05 ± 0.07 dex, which is the highest of our sample and compatible with the expected abundances of relatively young stars.

The Quest for Quality: How YoungStar Is Affecting Child Care in Milwaukee County

ERIC Educational Resources Information Center

Mueller, Betsy; Peterangelo, Joe; Henken, Rob

2016-01-01

The State of Wisconsin's YoungStar system was created by the Legislature and Governor in 2010 to "drive quality improvement in child care throughout the state." YoungStar uses a five-star system to rate child care providers based on several measures of quality, including staff education levels, learning environment, business methods, and…

Synthesis and Characterization of Stimuli-Responsive Star-Like Polypept(o)ides: Introducing Biodegradable PeptoStars.

PubMed

Holm, Regina; Weber, Benjamin; Heller, Philipp; Klinker, Kristina; Westmeier, Dana; Docter, Dominic; Stauber, Roland H; Barz, Matthias

2017-06-01

Star-like polymers are one of the smallest systems in the class of core crosslinked polymeric nanoparticles. This article reports on a versatile, straightforward synthesis of three-arm star-like polypept(o)ide (polysarcosine-block-polylysine) polymers, which are designed to be either stable or degradable at elevated levels of glutathione. Polypept(o)ides are a recently introduced class of polymers combining the stealth-like properties of the polypeptoid polysarcosine with the functionality of polypeptides, thus enabling the synthesis of materials completely based on endogenous amino acids. The star-like homo and block copolymers are synthesized by living nucleophilic ring opening polymerization of the corresponding N-carboxyanhydrides (NCAs) yielding polymeric stars with precise control over the degree of polymerization (X n = 25, 50, 100), Poisson-like molecular weight distributions, and low dispersities (Đ = 1.06-1.15). Star-like polypept(o)ides display a hydrodynamic radius of 5 nm (μ 2 < 0.05) as determined by dynamic light scattering (DLS). While star-like polysarcosines and polypept(o)ides based on disulfide containing initiators are stable in solution, degradation occurs at 100 × 10 -3 m glutathione concentration. The disulfide cleavage yields the respective polymeric arms, which possess Poisson-like molecular weight distributions and low dispersities (Đ = 1.05-1.12). Initial cellular uptake and toxicity studies reveal that PeptoStars are well tolerated by HeLa, HEK 293, and DC 2.4 cells. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Suppression of sun interference in the star sensor baffling stray light by total internal reflection

NASA Astrophysics Data System (ADS)

Kawano, Hiroyuki; Shimoji, Haruhiko; Yoshikawa, Shoji; Miyatake, Katsumasa; Hama, Kazumori; Nakamura, Shuji

2005-09-01

We have developed a star sensor as an experimental device onboard the SERVIS-1 satellite launched in October 2003. The in-orbit data have verified its fundamental performance. One of the advantages of our star sensor is that the baffle has a small length of 120 mm instead of 182 mm in the conventional two-stage baffle design. The key concepts for light shielding are total internal reflection phenomena inside a nearly half sphere (NHS) lens and scattering light control by gloss black paint. However, undesirable background noise by the sun outside of the field of view (FOV) was observed in the corner of the FOV in the orbital experiment. Ray trace simulations revealed that slight scattering light on the specular baffle wall entered the NHS lens and reached the corner of the image sensor through the multi-reflection path inside the lens. It was found that the stray light path can be shielded effectively if the diameter of the aperture under the NHS lens was reduced. We redesigned the baffle and evaluated the light shielding ability with our sun interference test facility on the ground, and confirmed that the stray light was reduced below the acceptable level. As a result, the light shielding technique which we have proposed was proved to be effective for a small-size baffle. The redesigned star sensor is planned to be installed as a main attitude sensor for the SERVIS-2 satellite scheduled to be launched in February 2008.

Living with a Star: New Opportunities in Sun-Climate Research

NASA Technical Reports Server (NTRS)

2003-01-01

Living With a Star is a NASA initiative employing the combination of dedicated spacecraft with targeted research and modeling efforts to improve what we know of solar effects of all kinds on the Earth and its surrounding space environment, with particular emphasis on those that have significant practical impacts on life and society. The highest priority among these concerns is the subject of this report: the potential effects of solar variability on regional and global climate, including the extent to which solar variability has contributed to the well-documented warming of the Earth in the last 100 years. Understanding how the climate system reacts to external forcing from the Sun will also greatly improve our knowledge of how climate will respond to other climate drivers, including those of anthropogenic origin. A parallel element of the LWS program addresses solar effects on space weather : the impulsive emissions of charged particles, short-wave electromagnetic radiation and magnetic disturbances in the upper atmosphere and near-Earth environment that also affect life and society. These include a wide variety of solar impacts on aeronautics, astronautics, electric power transmission, and national defense. Specific examples are (1) the impacts of potentially- damaging high energy radiation and atomic particles of solar origin on satellites and satellite operations, spacecraft electronics systems and components, electronic communications, electric power distribution grids, navigational and GPS systems, and high altitude aircraft; and (2) the threat of sporadic, high-energy solar radiation to astronauts and high altitude aircraft passengers and crews. Elements of the LWS program include an array of dedicated spacecraft in near- Earth and near-Sun orbits that will closely study and observe both the Sun itself and the impacts of its variations on the Earth's radiation belts and magnetosphere, the upper atmosphere, and ionosphere. These spacecraft, positioned to

What and Whence 1I/`Oumuamua: A Contact Binary from the Debris of a Young Planetary System?

NASA Astrophysics Data System (ADS)

Gaidos, E.

2018-04-01

The first confirmed interstellar interloper in our Solar System, 1I/`Oumuamua, is likely to be a minor body ejected from another star, but its brief flyby and faintness made it difficult to study. Two remarkable properties are its large (up to 2.5 mag) rotational variability and its motion relative to the Sun before encounter. The former suggests an extremely elongated shape (aspect ratio ≥10) and the latter an origin from the protoplanetary disk of a young star in a nearby association. Against expectations, it is also not comet-like. 1I/`Oumuamua's variability can also be explained if it is a contact binary composed of near-equilibrium ellipsoidal components and heterogeneous surfaces, i.e. brighter, dust-mantled inner-facing hemispheres and darker, dust-free outer-facing poles. Such shapes are a plausible outcome of radiation, tides and collisions in systems where planets are clearing planetesimal disks. The probability that 1I/'Oumuamua has the same motion as a young (≲ 100 Myr) stellar association by coincidence is <1%. If it is young, its detection vs. more numerous, older counterparts could be explained as a selection effect due to darkening of surfaces by Galactic cosmic rays and loss of dust. 1I/`Oumuamua's apparent lack of ices can be explained if ejected rocky planetesimals are characteristically smaller and thus far more numerous than their icy counterparts: the Solar System may currently host several such objects captured by the combined gravity of Jupiter and the Sun.

Molecular Gas in Disks around Young Stars with ALMA

NASA Astrophysics Data System (ADS)

Hughes, A. Meredith; Factor, Samuel; Lieman-Sifry, Jesse; Flaherty, Kevin; Daley, Cail; Mann, Rita; Roberge, Aki; Di Francesco, James; Williams, Jonathan; Ricci, Luca; Matthews, Brenda; Bally, John; Johnstone, Doug; Kospal, Agnes; Moor, Attila; Kamp, Inga; Wilner, David; Andrews, Sean; Kastner, Joel H.; Abraham, Peter

2018-01-01

Molecular gas is a critical component of the planet formation process. In this poster, we present two analyses of the molecular gas component of circumstellar disks at extremes (young, old) of the pre-main sequence phase.(1) We characterize the molecular gas content of the disk around d216-0939, a pre-main sequence star in the Orion Nebula Cluster, using ALMA observations of CO(3-2), HCO+(4-3), and HCN(4-3) observed at 0.5" resolution. We model the density and temperature structure of the disk, returning abundances generally consistent with chemical modeling of protoplanetary disks, and obtain a dynamical mass measurement of the central star of 2.2+/-0.4 M_sun, which is inconsistent with the previously determined spectral type of K5. We also report the detection of a spatially unresolved high-velocity blue-shifted excess emission feature with a measurable position offset from the central star, consistent with an object in Keplerian orbit at 60+/-20 au. The feature is due to a local temperature and/or density enhancement consistent with either a hydrodynamic vortex or the expected signature of the envelope of a forming protoplanet within the disk, providing evidence that planet formation is ongoing within this massive and relatively isolated Orion proplyd. This work is published in Factor et al. (2017). (2) We present ~0.4" resolution images of CO(3-2) and associated continuum emission from the gas-bearing debris disk around the nearby A star 49 Ceti, observed with ALMA. We analyze the ALMA visibilities in tandem with the broadband spectral energy distribution to measure the radial surface density profiles of dust and gas emission from the system. The radial extent of the gas disk (~220 au) is smaller than that of the dust disk (~300 au), consistent with recent observations of other gas-bearing debris disks. While there are so far only three broad debris disks with well characterized radial dust profiles at millimeter wavelengths, 49 Ceti’s disk shows a markedly

Terrestrial Planet Formation in Binary Star Systems

NASA Technical Reports Server (NTRS)

Lissauer, J. J.; Quintana, E. V.; Adams, F. C.; Chambers, J. E.

2006-01-01

Most stars reside in binary/multiple star systems; however, previous models of planet formation have studied growth of bodies orbiting an isolated single star. Disk material has been observed around one or both components of various young close binary star systems. If planets form at the right places within such disks, they can remain dynamically stable for very long times. We have simulated the late stages of growth of terrestrial planets in both circumbinary disks around 'close' binary star systems with stellar separations ($a_B$) in the range 0.05 AU $\\le a_B \\le$ 0.4 AU and binary eccentricities in the range $0 \\le e \\le 0.8$ and circumstellar disks around individual stars with binary separations of tens of AU. The initial disk of planetary embryos is the same as that used for simulating the late stages of terrestrial planet growth within our Solar System and around individual stars in the Alpha Centauri system (Quintana et al. 2002, A.J., 576, 982); giant planets analogous to Jupiter and Saturn are included if their orbits are stable. The planetary systems formed around close binaries with stellar apastron distances less than or equal to 0.2 AU with small stellar eccentricities are very similar to those formed in the Sun-Jupiter-Saturn, whereas planetary systems formed around binaries with larger maximum separations tend to be sparser, with fewer planets, especially interior to 1 AU. Likewise, when the binary periastron exceeds 10 AU, terrestrial planets can form over essentially the entire range of orbits allowed for single stars with Jupiter-like planets, although fewer terrestrial planets tend to form within high eccentricity binary systems. As the binary periastron decreases, the radial extent of the terrestrial planet systems is reduced accordingly. When the periastron is 5 AU, the formation of Earth-like planets near 1 AU is compromised.

Studies of Disks Around the Sun and Other Stars

NASA Technical Reports Server (NTRS)

Stern, S. Alan

1997-01-01

This is a NASA Origins of Solar Systems research program, and this NASA Headquarters grant has now been transferred to a new grant at NASA GSFC (NAG5-4082). Thus the need for this 'Final Report' on a project that is not, in fact, complete. We are conducting research designed to enhance our understanding of the evolution and detectability of comet clouds and disks. This area holds promise for also improving our understanding of outer solar system formation, the bombardment history of the planets, the transport of volatiles and organics from the outer solar system to the inner planets, and to the ultimate fate of comet clouds around the Sun and other stars. According to "standard" theory, both the Kuiper Belt and the Oort Cloud are (at least in part) natural products of the planetary accumulation stage of solar system formation. One expects such assemblages to be a common attribute of other solar systems. Our program consists of modeling collisions in the Kuiper Belt and the dust disks around other stars. The modeling effort focuses on moving from our simple, first-generation, Kuiper Belt collision rate model, to a time-dependent, second-generation model that incorporates physical collisions, velocity evolution, dynamical erosion, and various dust transport mechanisms. This second generation model is to be used to study the evolution of surface mass density and the object-size spectrum in the disk.

Anomalous Eclipses of the Young Star RW Aur A

NASA Astrophysics Data System (ADS)

Lamzin, S.; Cheryasov, D.; Chuntonov, G.; Dodin, A.; Grankin, K.; Malanchev, K.; Nadzhip, A.; Safonov, B.; Shakhovskoy, D.; Shenavrin, V.; Tatarnikov, A.; Vozyakova, O.

2017-06-01

Results of UBVRIJHKLM photometry, VRI polarimetry and optical spectroscopy of a young star RW Aur A obtained during 2010-11 and 2014-16 dimming events are presented. During the second dimming the star decreased its brightness to ΔV >4.5 mag, polarization of its light in I-band was up to 30 %, and color-magnitude diagramm was similar to that of UX Ori type stars. We conclude that the reason of both dimmings is an eclipses of the star by dust screen, but the size of the screen is much larger than in the case of UXORs.

Circus Family of Stars (Artist's Concept)

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] Quick Time Movie for PIA03521 Circus Family of Stars

This artist's animation shows the clockwork-like orbits of a triple-star system called HD 188753, which was discovered to harbor a gas giant, or 'hot Jupiter,' planet. The planet zips around the system's main star (yellow, center) every 3.3 days, while the main star is circled every 25.7 years by a dancing duo of stars (yellow and orange, outer orbit). The star pair is locked in a 156-day orbit.

This eccentric star family is a cramped bunch; the distance between the main star and the outer pair of stars is about the same as that between the Sun and Saturn. Though multiple-star systems like this one are common in the universe, astronomers were surprised to find a planet living in such tight quarters.

One reason for the surprise has to do with theories of hot Jupiter formation. Astronomers believe that these planets begin life at the outer fringes of their stars, in thick dusty disks called protoplanetary disks, before migrating inward. The discovery of a world under three suns throws this theory into question. As seen in this animation, there is not much room at this system's outer edges for a hot Jupiter to grow.

The discovery was made using the Keck I telescope atop Mauna Kea mountain in Hawaii. The triple-star system is located 149 light-years away in the constellation Cygnus.

The sizes and orbital periods in the animation are not shown to scale. The relative motions are shown with respect to the main star.

Cannibals in the thick disk: the young α-rich stars as evolved blue stragglers

NASA Astrophysics Data System (ADS)

Jofré, P.; Jorissen, A.; Van Eck, S.; Izzard, R. G.; Masseron, T.; Hawkins, K.; Gilmore, G.; Paladini, C.; Escorza, A.; Blanco-Cuaresma, S.; Manick, R.

2016-10-01

Spectro-seismic measurements of red giants enabled the recent discovery of stars in the thick disk that are more massive than 1.4 M⊙. While it has been claimed that most of these stars are younger than the rest of the typical thick disk stars, we show evidence that they might be products of mass transfer in binary evolution, notably evolved blue stragglers. We took new measurements of the radial velocities in a sample of 26 stars from APOKASC, including 13 "young" stars and 13 "old" stars with similar stellar parameters but with masses below 1.2 M⊙ and found that more of the young starsappear to be in binary systems with respect to the old stars.Furthermore, we show that the young stars do not follow the expected trend of [C/H] ratios versus mass for individual stars. However, with a population synthesis of low-mass stars including binary evolution and mass transfer, we can reproduce the observed [C/N] ratios versus mass. Our study shows how asteroseismology of solar-type red giants provides us with a unique opportunity to study the evolution of field blue stragglers after they have left the main-sequence.

Spectrophotometry of VIIZW421 and IIZW67 - s0 Galaxies Dominated by Young Stars

NASA Astrophysics Data System (ADS)

Sparke, L. S.; Kormendy, J.; Spinrad, H.

1980-02-01

We investigate the stellar content of two SO galaxies whose spectra show deep Balmer absorption lines but little emission. Continuum colors and the Faber-Burstein (Mg)0 index show that the blue light is dominated by young stars. In VII Zw 421 there is a radial population gradient; the nucleus has relatively more young stars than the lens. An approximate spectral synthesis confirms the need for young (rather than metal-poor) stars to produce sufficiently strong Balmer lines. In VII Zw 421 the best synthesis implies that 45Th of the nuclear light at 5000 Å comes from stars close to A1 V in type. In the lens, the young-star contribution is smaller by a factor of 2-3. Also, in the nucleus only, the observed Na D lines are much stronger than in our model. This suggests a connection with the young component and supports Faber and Burstein's conclusion that abnormally strong Na D absorption is sometimes interstellar. Thus VII Zw 421 and II Zw 67 are similar to NGC 5102, the nearest SO galaxy dominated by young stars. The present SO's provide important constraints on any interpretation of the young component. At - 19.9 and -21.5 absolute B mag (H0 = 50 km s-1 1 Mpc-1), they are unusually luminous for their early-type spectra. They are also unusually compact, which may provide them with gravitational potential wells deep enough to retain gas despite processes which remove gas from other early-type galaxies.

YOUNG STARS IN AN OLD BULGE: A NATURAL OUTCOME OF INTERNAL EVOLUTION IN THE MILKY WAY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ness, M.; Debattista, Victor P.; Cole, D. R.

2014-06-01

The center of our disk galaxy, the Milky Way, is dominated by a boxy/peanut-shaped bulge. Numerous studies of the bulge based on stellar photometry have concluded that the bulge stars are exclusively old. The perceived lack of young stars in the bulge strongly constrains its likely formation scenarios, providing evidence that the bulge is a unique population that formed early and separately from the disk. However, recent studies of individual bulge stars using the microlensing technique have reported that they span a range of ages, emphasizing that the bulge may not be a monolithic structure. In this Letter we demonstratemore » that the presence of young stars that are located predominantly nearer to the plane is expected for a bulge that has formed from the disk via dynamical instabilities. Using an N-body+ smoothed particle hydrodynamics simulation of a disk galaxy forming out of gas cooling inside a dark matter halo and forming stars, we find a qualitative agreement between our model and the observations of younger metal-rich stars in the bulge. We are also able to partially resolve the apparent contradiction in the literature between results that argue for a purely old bulge population and those that show a population comprised of a range in ages; the key is where to look.« less

YoungStar in Wisconsin: An Initial Progress Report as of July 2011

ERIC Educational Resources Information Center

Edie, Dave

2011-01-01

YoungStar is a program of the Department of Children and Families (DCF) created to improve the quality of child care for Wisconsin children. YoungStar is designed to: (1) Evaluate and rate the quality of care given by child care providers; (2) Help parents choose the best child care for their kids; (3) Support providers with tools and training to…

PHOENIX IR Spectra of CO in the Sun and the Stars

NASA Astrophysics Data System (ADS)

Ayres, T. R.; Valenti, J. A.; Hinkle, K. H.; Johns-Krull, C. M.; Wiedemann, G. R.

1998-05-01

We report high-resolution (R ~ 5*E(4) ) spectra of the 2143 cm(-1) (4.7 mu m) interval---containing lines from the fundamental (Delta v =1) bands of carbon monoxide---in the Sun and other late-type stars, obtained with the PHOENIX cryogenic infrared spectrometer. The solar work was conducted at the McMath-Pierce telescope during the period 21--26 April 1997, while the stellar observations were obtained on the night of 6 December 1997 at the Kitt Peak 2.1-m. Comparisons of spatially-averaged spectra from the long-slit observations of the Sun with very high-resolution Fourier transform spectrometer scans permitted an evalution of the PHOENIX instrumental profile (affected by flexing of the grating owing to unequal thermal coefficients of the epoxy replica and the silicon substrate). The profile information subsequently was applied in comparisons of the stellar data sets with CO spectra synthesized using a variety of prototype thermal structure models. On the stellar side, we concentrated on bright K-type giants whose broad CO profiles are fully resolved at PHOENIX resolution. Our intent was to test the degree of thermal heterogeneity in the outer layers of the red giant atmospheres; analogous to the ``thermal bifurcation'' effects deduced in the solar context (namely, the dichotomy between classical hot chromosphere and the controversial cool ``COmosphere''). Our spectral analyses provide a preview of the power of PHOENIX for high-resolution infrared spectroscopy of stars; to be realized in the coming months when the original grating is replaced with an improved version. [-2mm] The observations were obtained at the National Optical Astronomy Observatories, which is operated by AURA, Inc., under a cooperative agreement with the National Science Foundation. This work was supported by NSF grant AST-9618505.

A YOUNG ECLIPSING BINARY AND ITS LUMINOUS NEIGHBORS IN THE EMBEDDED STAR CLUSTER Sh 2-252E

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lester, Kathryn V.; Gies, Douglas R.; Guo, Zhao, E-mail: lester@chara.gsu.edu, E-mail: gies@chara.gsu.edu, E-mail: guo@chara.gsu.edu

We present a photometric and light curve analysis of an eccentric eclipsing binary in the K2 Campaign 0 field, which resides in Sh 2-252E, a young star cluster embedded in an H ii region. We describe a spectroscopic investigation of the three brightest stars in the crowded aperture to identify which is the binary system. We find that none of these stars are components of the eclipsing binary system, which must be one of the fainter nearby stars. These bright cluster members all have remarkable spectra: Sh 2-252a (EPIC 202062176) is a B0.5 V star with razor sharp absorption lines, Sh 2-252b is amore » Herbig A0 star with disk-like emission lines, and Sh 2-252c is a pre-main-sequence star with very red color.« less

Dust and gas around young stars

NASA Astrophysics Data System (ADS)

Chen, Christine Hsiao-Ching

To understand how asteroids, planets, and comets form in circumstellar disks of gas and dust, we have carried out a high resolution mid-infrared imaging study and a high resolution ultra violet spectroscopic study of the dust and gas around nearby pre-main sequence Herbig Ae stars and dusty main sequence stars. We have used the Keck I telescope to image at 11.7 μm and 17.9 μm the dust emission around ζ Lep, a main sequence A-type star with an infrared excess, 21.5 pc from the Sun. The excess is at most marginally resolved at 17.9 μm. The dust distance from the star is probably ≤6 AU, although some dust may extend to 9 AU. The mass of observed dust is ˜10 22 g. Since the lifetime of dust particles is about 104 yr because of the Poynting- Robertson effect, we robustly estimate at least 4 × 1026 g must reside in parent bodies which may be asteroids if the system is in a steady state and has an age of ˜300 Myr. This mass is approximately 200 times that contained within the main asteroid belt in our solar system. We have obtained FUSE spectra of σ Her, a nearby binary system, with a main sequence primary, that has a Vega-like infrared excess. We observe absorption in the excited fine structure lines C II* at 1037 Å, N II* at 1085 Å, and N II** at 1086 Å that are blueshifted by as much as ˜30 km/sec with respect to the star. Since these features are considerably narrower than the stellar lines and broader than interstellar features, the C II and N II are circumstellar. Since σ Her has a high luminosity, we suggest that there is a radiatively driven wind, arising from the circumstellar matter, rather than accretion as occurs around β Pic. Assuming that the gas is liberated by collisions between parent bodies at 20 AU, the approximate distance at which blackbody grains are in radiative equilibrium with the star and at which 3-body orbits become unstable, we infer dM/dt ˜6 × 10-12 M⊙ yr-1. This wind depletes the minimum mass of parent bodies in less than

Exotic World Blisters Under the Sun

NASA Technical Reports Server (NTRS)

2006-01-01

This artist's concept shows a Jupiter-like planet soaking up the scorching rays of its nearby 'sun.' NASA's Spitzer Space Telescope used its heat-seeking infrared eyes to figure out that a gas-giant planet like the one depicted here is two-faced, with one side perpetually in the cold dark, and the other forever blistering under the heat of its star. The illustration portrays how the planet would appear to infrared eyes, showing temperature variations across its surface.

The planet, called Upsilon Andromedae b, was first discovered in 1996 around the star Upsilon Andromedae, located 40 light-years away in the constellation Andromeda. This star also has two other planets orbiting farther out.

Upsilon Andromedae b is what's known as a 'hot-Jupiter' planet, because it is made of gas like our Jovian giant, and it is hot, due to its tight, 4.6-day-long jaunt around its star. The toasty planet orbits at one-sixth the distance of Mercury from our own sun. It travels in a plane that is seen neither edge- nor face-on from our solar system, but somewhere in between. Scientists do not know how fast Upsilon Andromedae b is spinning on its axis, but they believe that it is tidally locked to its star, just as our locked moon forever hides its 'dark side' from Earth's view.

Spitzer observed Upsilon Andromedae b at five points during the planet's trip around its star. The planet's light levels went up or down, as detected by Spitzer, depending on whether the planet's sunlit or dark side was pointed toward Earth. These data indicate that the temperature difference between the two hemispheres of the planet is about 1,400 degrees Celsius (2,550 degrees Fahrenheit).

According to astronomers, this means that the side of the planet that faces the star is always as hot as lava, while the other side could potentially be as cold as ice. Specifically, the hot side of the planet ranges from about 1,400 to 1,650 degrees Celsius (2,550 to 3,000 degrees Fahrenheit), and

Young Galaxy Surrounded by Material Needed to Make Stars, VLA Reveals

NASA Astrophysics Data System (ADS)

2001-01-01

Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope have discovered a massive reservoir of cold gas from which a primeval galaxy formed its first stars. Looking more than 12 billion years into the past, the scientists found that the young galaxy experiencing a "burst" of star formation was surrounded by enough cold molecular gas to make 100 billion suns. Optical and Radio Images of APM 08279+5255 at About the Same Scale "This is the first time anyone has seen the massive reservoir of cold gas required for these incredible 'starbursts' to produce a galaxy," said Chris Carilli, an astronomer at the NSF's National Radio Astronomy Observatory (NRAO) in Socorro, NM. "There is much more gas here than we anticipated," Carilli added. The research team was led by Padeli Papadoupoulos of Leiden Observatory in the Netherlands and also included Rob Ivison of University College London and Geraint Lewis of the Anglo-Australian Observatory in Australia. The scientists reported their findings in the January 4 edition of the journal Nature. The astronomers found the gas when studying a quasar called APM 08279+5255, discovered in 1998. Observations with optical and infrared telescopes revealed that the quasar, a young galaxy with a voracious black hole at its center, was forming new stars rapidly in a starburst. At a distance of more than 12 billion light-years, the quasar is seen as it was more than 12 billion years ago, just a billion or so years after the Big Bang. "This thing is at the edge of the dark ages," before the first stars in the universe were born, said Carilli. The year after its discovery, APM 08279+5255 was found to have warm carbon monoxide (CO) gas near its center, heated by the energy released as the galaxy's black hole devours material. The VLA observations revealed cold CO gas much more widely distributed than its warmer counterpart. Based on observations of closer objects, the astronomers presume the CO gas is accompanied

Accreting Planets in the Habitable Zones of M-Stars Are Too Hot to Retain Liquid Water

NASA Astrophysics Data System (ADS)

Ramirez, R. M.; Kopparapu, R. K.; Kasting, J. F.

2014-12-01

Previous studies1,2 have shown that young accreting planets in the habitable zones (HZ) of pre-main sequence M-stars face major dynamical hurdles in both the retention and acquisition of volatiles. High collision rates with other bodies, short planetary formation timescales, and inefficient radial mixing are among the major problems encountered. However, another equally-important concern is the high temperatures predicted within the circumstellar disk, greatly hindering volatile delivery. We use a 1-D radiative-convective climate model to demonstrate that the fluxes received by accreting planets orbiting late K-M stars exceed the runaway greenhouse threshold. Given that M-stars are disproportionately brighter in their pre main-sequence lifetimes as compared to Sun-like stars (i.e. G-class insolation), planets orbiting M-stars are especially susceptible to the runaway, with intensity and duration increasing for cooler M-stars. Thus, accreting planetesimals in the HZs of M-stars could be too hot to maintain liquid water on their surfaces. In contrast, accreting planets located at Earth's distance (or farther) from a pre-main sequence solar analogue (i.e. G2 spectral class) receive stellar fluxes well below that of the runaway point. Our results suggest that future missions and surveys can improve their prospects of finding alien life by targeting HZ planets orbiting Sun-like stars. Moreover, our findings support recent claims that Venus may have lost its water during accretion3. REFERENCES1. Lissauer, Jack J. "Planets formed in habitable zones of M dwarf stars probably are deficient in volatiles." The Astrophysical Journal Letters 660.2 (2007): L149. 2. Raymond, Sean N., John Scalo, and Victoria S. Meadows. "A decreased probability of habitable planet formation around low-mass stars." The Astrophysical Journal 669.1 (2007): 606. 3. Hamano, Keiko, Yutaka Abe, and Hidenori Genda. "Emergence of two types of terrestrial planet on solidification of magma ocean." Nature

THE BRIGHTEST YOUNG STAR CLUSTERS IN NGC 5253

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calzetti, D.; Johnson, K. E.; Adamo, A.

2015-10-01

The nearby dwarf starburst galaxy NGC 5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the “radio nebula”). To investigate the role of these clusters in the starburst energetics, we combine new and archival Hubble Space Telescope images of NGC 5253 with wavelength coverage from 1500 Å to 1.9 μm in 13 filters. These include Hα, Pβ, and Pα, and the imaging from the Hubble Treasury Program LEGUS (Legacy Extragalactic UV Survey). The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses,more » and extinctions of the nine optically brightest clusters (M{sub V} < −8.8) and the two young radio nebula clusters. The clusters have ages ∼1–15 Myr and masses ∼1 × 10{sup 4}–2.5 × 10{sup 5} M{sub ⊙}. The clusters’ spatial location and ages indicate that star formation has become more concentrated toward the radio nebula over the last ∼15 Myr. The most massive cluster is in the radio nebula; with a mass ∼2.5 × 10{sup 5} M{sub ⊙} and an age ∼1 Myr, it is 2–4 times less massive and younger than previously estimated. It is within a dust cloud with A{sub V} ∼ 50 mag, and shows a clear near-IR excess, likely from hot dust. The second radio nebula cluster is also ∼1 Myr old, confirming the extreme youth of the starburst region. These two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars.« less

The Brightest Young Star Clusters in NGC 5253.

NASA Astrophysics Data System (ADS)

Calzetti, D.; Johnson, K. E.; Adamo, A.; Gallagher, J. S., III; Andrews, J. E.; Smith, L. J.; Clayton, G. C.; Lee, J. C.; Sabbi, E.; Ubeda, L.; Kim, H.; Ryon, J. E.; Thilker, D.; Bright, S. N.; Zackrisson, E.; Kennicutt, R. C.; de Mink, S. E.; Whitmore, B. C.; Aloisi, A.; Chandar, R.; Cignoni, M.; Cook, D.; Dale, D. A.; Elmegreen, B. G.; Elmegreen, D. M.; Evans, A. S.; Fumagalli, M.; Gouliermis, D. A.; Grasha, K.; Grebel, E. K.; Krumholz, M. R.; Walterbos, R.; Wofford, A.; Brown, T. M.; Christian, C.; Dobbs, C.; Herrero, A.; Kahre, L.; Messa, M.; Nair, P.; Nota, A.; Östlin, G.; Pellerin, A.; Sacchi, E.; Schaerer, D.; Tosi, M.

2015-10-01

The nearby dwarf starburst galaxy NGC 5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the “radio nebula”). To investigate the role of these clusters in the starburst energetics, we combine new and archival Hubble Space Telescope images of NGC 5253 with wavelength coverage from 1500 Å to 1.9 μm in 13 filters. These include Hα, Pβ, and Pα, and the imaging from the Hubble Treasury Program LEGUS (Legacy Extragalactic UV Survey). The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses, and extinctions of the nine optically brightest clusters (MV < -8.8) and the two young radio nebula clusters. The clusters have ages ˜1-15 Myr and masses ˜1 × 104-2.5 × 105 M⊙. The clusters’ spatial location and ages indicate that star formation has become more concentrated toward the radio nebula over the last ˜15 Myr. The most massive cluster is in the radio nebula; with a mass ˜2.5 × 105 M⊙ and an age ˜1 Myr, it is 2-4 times less massive and younger than previously estimated. It is within a dust cloud with AV ˜ 50 mag, and shows a clear near-IR excess, likely from hot dust. The second radio nebula cluster is also ˜1 Myr old, confirming the extreme youth of the starburst region. These two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars. Based on observations obtained with the NASA/ESA Hubble Space Telescope, at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Chandra Detection of an Evolved Population of Young Stars in Serpens South

NASA Astrophysics Data System (ADS)

Winston, E.; Wolk, S. J.; Gutermuth, R.; Bourke, T. L.

2018-06-01

We present a Chandra study of the deeply embedded Serpens South star-forming region, examining cluster structure and disk properties at the earliest stages. In total, 152 X-ray sources are detected. Combined with Spitzer and 2MASS photometry, 66 X-ray sources are reliably matched to an IR counterpart. We identify 21 class I, 6 flat spectrum, 16 class II, and 18 class III young stars; 5 were unclassified. Eighteen sources were variable in X-rays, 8 exhibiting flare-like emission and one source being periodic. The cluster’s X-ray luminosity distance was estimated: the best match was to the nearer distance of 260 pc for the front of the Aquila Rift complex. The ratio of N H to A K is found to be ∼0.68 × 1022, similar to that measured in other young low-mass regions, but lower than that measured in the interstellar medium and high-mass clusters (∼(1.6–2) × 1022). We find that the spatial distribution closely follows that of the dense filament from which the stars have formed, with the class II population still strongly associated with the filament. There are four subclusters in the field, with three forming knots in the filament, and a fourth to the west, which may not be associated but may be contributing to the distributed class III population. A high percentage of diskless class IIIs (upper limit 30% of classified X-ray sources) in such a young cluster could indicate that processing of disks is influenced by the cluster environment and is not solely dependent on timescale.

Weighing Ultra-Cool Stars

NASA Astrophysics Data System (ADS)

2004-05-01

Large Ground-Based Telescopes and Hubble Team-Up to Perform First Direct Brown Dwarf Mass Measurement [1] Summary Using ESO's Very Large Telescope at Paranal and a suite of ground- and space-based telescopes in a four-year long study, an international team of astronomers has measured for the first time the mass of an ultra-cool star and its companion brown dwarf. The two stars form a binary system and orbit each other in about 10 years. The team obtained high-resolution near-infrared images; on the ground, they defeated the blurring effect of the terrestrial atmosphere by means of adaptive optics techniques. By precisely determining the orbit projected on the sky, the astronomers were able to measure the total mass of the stars. Additional data and comparison with stellar models then yield the mass of each of the components. The heavier of the two stars has a mass around 8.5% of the mass of the Sun and its brown dwarf companion is even lighter, only 6% of the solar mass. Both objects are relatively young with an age of about 500-1,000 million years. These observations represent a decisive step towards the still missing calibration of stellar evolution models for very-low mass stars. PR Photo 19a/04: Orbit of the ultra-cool stars in 2MASSW J0746425+2000321. PR Photo 19b/04: Animated Gif of the orbital motion. Telephone number star Even though astronomers have found several hundreds of very low mass stars and brown dwarfs, the fundamental properties of these extreme objects, such as masses and surface temperatures, are still not well known. Within the cosmic zoo, these ultra-cool stars represent a class of "intermediate" objects between giant planets - like Jupiter - and "normal" stars less massive than our Sun, and to understand them well is therefore crucial to the field of stellar astrophysics. The problem with these ultra-cool stars is that contrary to normal stars that burn hydrogen in their central core, no unique relation exists between the luminosity of the

Interacting Coronae of Two T Tauri Stars: First Observational Evidence for Solar-Like Helmet Streamers

DTIC Science & Technology

2008-01-01

for the first time in stars other than the Sun. The complete extent of each helmet streamer above the stellar surface is about 24 R∗ which implies...is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and...Heliospheric Observatory (SOHO) satellite (Schwenn 2006; Suess & Nerney 2004; Vourlidas 2006). Following the analogy with the Sun, Massi & collaborators

Variability of Young Stars: the Importance of Keeping an Eye on Children

NASA Astrophysics Data System (ADS)

Herbst, W.

2013-06-01

(Abstract only) I will review the state of our understanding of young stars with an emphasis on how and why they vary in brightness. The main causes of the variations will be reviewed, including the rotation of spotted weak-lined T Tauri stars, accretion onto classical T Tauri stars, the eruptive behavior of FUors, and the enigmatic variations of the UXors. The important role that amateurs have and will continue to play in these studies is highlighted. I will also discuss the latest results on two unusual young binaries, BM Orionis in the Trapezium asterism and KH 15D in NGC 2264.

Jets from Young Stars in Cygnus-X

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-03-01

How do you spot very young, newly formed stars? One giveaway is the presence of jets and outflows that interact with the stars environments. In a new study, scientists have now discovered an unprecedented number of these outflows in a nearby star-forming region of our galaxy.Young Stars Hard at WorkCO map of the Cygnus-X region of the galactic plane, with the grid showing the UWISH2 coverage and the black triangles showing the positions of the detected outflows. [Makin Froebrich 2018]The birth and evolution of young stars is a dynamic, energetic process. As new stars form, material falls inward from the accretion disks surrounding young stellar objects, or YSOs. This material can power collimated streams of gas and dust that flow out along the stars rotation axes, plowing through the surrounding material. Where the outflows collide with the outside environment, shocks form that can be spotted in near-infrared hydrogen emission.Though weve learned a lot about these outflows, there remain a number of open questions. What factors govern their properties, such as their lengths, luminosities, and orientations? What is the origin of the emission features we see within the jets, known as knots? What roles do the driving sources and the environments play in the behavior and appearance of the jets?A selection of previously unknown outflows discovered as a result of this survey. Click for a closer look. [Makin Froebrich 2018]To answer these questions, we need to build a large, unbiased statistical sample of YSOs from across the galactic plane. Now, a large infrared survey known as the UKIRT Widefield Infrared Survey for H2 (UWISH2) is working toward that goal.Jackpot in Cygnus-XIn a recent publication, Sally Makin and Dirk Froebrich (University of Kent, UK), present results from UWISH2s latest release: a survey segment targeting a 42-square-degree region in the galactic plane known as the Cygnus-X star-forming region.The teams search for shock-excited emission in Cygnus

The graviton luminosity of the sun and other stars

NASA Technical Reports Server (NTRS)

Gould, R. J.

1985-01-01

Graviton production in electron-electron (e-e) and electron-ion (e-z) scattering is evaluated in the Born approximation. The calculation is compared with that for photon production, that is, Coulomb quadrupole bremsstrahlung, and a number of results are taken over from that problem. Application is made to the sun, and it is found that for the solar plasma the main contribution to the graviton luminosity comes from the central core at r/R approximately 0.1. The total luminosity (Lg) in gravitons is about 7.9 x 10 to the 14th ergs/s, close to an earlier estimate by Weinberg (1965, 1972); about 33 percent of the total results from e-e collisions with the rest from e-z collisions (mainly e-p and e-alpha). Approximate corrections to Born formulas are evaluated, and this Lg includes the associated (approximately + or - 10 percent, respectively) modification. The quantum-mechanical aspects of the solar Lg problem are discussed, and it is shown why a previous classical calculation overestimated Lg by about an order of magnitude. Production of gravitons in binary collisions in other types of stars is discussed briefly. It is found that Lg varies very little along the main sequence. White dwarfs have a typical graviton luminosity LWD approximately 10 to the 19th ergs/s, while neutron stars have LNS approximately 10 to the 25th ergs/s; these estimates are very rough.

Optimal Target Stars in the Search for Life

NASA Astrophysics Data System (ADS)

Lingam, Manasvi; Loeb, Abraham

2018-04-01

The selection of optimal targets in the search for life represents a highly important strategic issue. In this Letter, we evaluate the benefits of searching for life around a potentially habitable planet orbiting a star of arbitrary mass relative to a similar planet around a Sun-like star. If recent physical arguments implying that the habitability of planets orbiting low-mass stars is selectively suppressed are correct, we find that planets around solar-type stars may represent the optimal targets.

MAGNETIC ACTIVITY CYCLES IN THE EXOPLANET HOST STAR {epsilon} ERIDANI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Metcalfe, T. S.; Mathur, S.; Buccino, A. P.

2013-02-01

The active K2 dwarf {epsilon} Eri has been extensively characterized both as a young solar analog and more recently as an exoplanet host star. As one of the nearest and brightest stars in the sky, it provides an unparalleled opportunity to constrain stellar dynamo theory beyond the Sun. We confirm and document the 3-year magnetic activity cycle in {epsilon} Eri originally reported by Hatzes and coworkers, and we examine the archival data from previous observations spanning 45 years. The data show coexisting 3-year and 13-year periods leading into a broad activity minimum that resembles a Maunder minimum-like state, followed bymore » the resurgence of a coherent 3-year cycle. The nearly continuous activity record suggests the simultaneous operation of two stellar dynamos with cycle periods of 2.95 {+-} 0.03 years and 12.7 {+-} 0.3 years, which, by analogy with the solar case, suggests a revised identification of the dynamo mechanisms that are responsible for the so-called 'active' and 'inactive' sequences as proposed by Boehm-Vitense. Finally, based on the observed properties of {epsilon} Eri, we argue that the rotational history of the Sun is what makes it an outlier in the context of magnetic cycles observed in other stars (as also suggested by its Li depletion), and that a Jovian-mass companion cannot be the universal explanation for the solar peculiarities.« less

Results from a Tailored SMS and Behavior-Tracking Pilot Study on Sun-Safe Behaviors in Young Women

ERIC Educational Resources Information Center

Darlow, Susan; Heckman, Carolyn

2017-01-01

Background: The elevated rates of ultraviolet radiation (UVR) exposure and low rates of sun protection in young adult women indicate a need for age- and gender-appropriate interventions that address these behaviors. Aims: To examine the effects of daily behavior tracking and individually tailored text messages on sun protection and UVR exposure…

Photometric properties of stars clusters with young or mixed age stellar populations

NASA Astrophysics Data System (ADS)

Mollá, M.; García-Vargas, M. L.; Martín-Manjón, M. L.

2013-05-01

The main goal of this work is to present and discuss the synthetic photometrical properties of stellar clusters resulting from the PopStar code. Colors in Johnson and SDSS systems, Hα and Hβ luminosities and equivalent widths, and ionizing region size, have been computed for a wide range of metallicities Z = 0.0001, 0.0004, 0.004,0.008,0.02 and 0.05, and ages, from 0.1 Myr to 20 Gyr in Mollá, Garc{í}a-Vargas, & Bressan (2009, MNRAS, 398, 451). Emission lines are shown in Mart{í}n-Manj{ó}n et al. (2010, MNRAS, 403, 2012). Now we calculate colors with the emission lines contribution to the broad band color, so colors include stellar and nebular components, plus the emission lines following the evolution of the cluster and the region geometry in a consistent way. We compare the Single Stellar Populations contaminated and uncontaminated colors (in both Johnson and SDSS systems) and show the importance of emission lines contribution when photometry is used as a tool to characterize stellar populations. With these models we may determine the physical properties of young ionizing clusters when only photometrical observations are available and these correspond to the isolated star forming regions, subtracted the contribution of the underlying population In most cases, however, the ionizing population is usually embedded in a large and complex system, and the observed photometrical properties are the result of the combination of both the young star-forming burst and the host-underlying older population. The second objective of our work is therefore to provide a grid of models for nearby galaxies able to interpret mixed regions where the separation of young and old population is not possible or reliable enough. We obtain a set of PopStar Spectral Energy Distributions (available at PopStar site and also in VO) and derived colors for mixed populations where an underlying host population is combined in different mass ratios with a recent, metal-rich ionizing burst. These

A Multi-Fiber Spectroscopic Search for Low-mass Young Stars in Orion OB1

NASA Astrophysics Data System (ADS)

Loerincs, Jacqueline; Briceno, Cesar; Calvet, Nuria; Mateo, Mario L.; Hernandez, Jesus

2017-01-01

We present here results of a low resolution spectroscopic followup of candidate low-mass pre-main sequence stars in the Orion OB1 association. Our targets were selected from the CIDA Variability Survey of Orion (CVSO), and we used the Michigan/Magellan Fiber Spectrograph (M2FS) on the Magellan Clay 6.5m telescope to obtain spectra of 500 candidate T Tauri stars distributed in seven 0.5 deg diameter fields, adding to a total area of ~5.5 deg2. We identify young stars by looking at the distinctive Hα 6563 Å emission and Lithium Li I 6707 Å absorption features characteristic of young low mass pre-main sequence stars. Furthermore, by measuring the strength of their Hα emission lines, confirmed T Tauri stars can be classified as either Classical T Tauris (CTTS) or Weak-line T Tauris (WTTS), which give indication of whether the star is actively accreting material from a gas and dust disk surrounding the star, which may be the precursor of a planetary system. We confirm a total of 90 T Tauri stars, of which 50% are newly identified young members of Orion; out of the 49 new detections,15 are accreting CTTS, and of these all but one are found in the OB1b sub-region. This result is in line with our previous findings that this region is much younger than the more extended Orion OB1a sub-association. The M2FS results add to our growing census of young stars in Orion, that is allowing us to characterize in a systematic and consistent way the distribution of stellar ages across the entire complex, in order to building a complete picture of star formation in this, one of nearest most active sites of star birth.

Search for kinematic siblings of the sun based on data from the XHIP catalog

NASA Astrophysics Data System (ADS)

Bobylev, V. V.; Bajkova, A. T.

2014-06-01

From the XHIP catalogue, we have selected 1872 F-G-K stars with relative parallax measurement errors <20% and absolute values of their space velocities relative to the Sun <15 km s-1. For all these stars, we have constructed their Galactic orbits for 4.5 Gyr into the past using an axisymmetric Galactic potential model with allowance made for the perturbations from the spiral density wave. Parameters of the encounter with the solar orbit have been calculated for each orbit. We have detected three new stars whose Galactic orbits were close to the solar one during a long time interval in the past. These stars are HIP 43852, HIP 104047, and HIP 112158. The spectroscopic binary HIP 112158 is poorly suited for the role of a kinematic sibling of the Sun by its age and spectroscopic characteristics. For the single star HIP 43852 and the multiple system HIP 104047, this role is quite possible. We have also confirmed the status of our previously found candidates for close encounters, HIP 47399 and HIP 87382. The star HIP 87382 with a chemical composition very close to the solar one is currently the most likely candidate, because it persistently shows close encounters with the Sun on time scales of more than 3 Gyr when using various Galactic potential models both without and with allowance made for the influence of the spiral density wave.

Sun Shines in High-Energy X-rays

NASA Image and Video Library

2014-12-22

X-rays stream off the sun in this first picture of the sun, overlaid on a picture taken by NASA Solar Dynamics Observatory SDO, taken by NASA NuSTAR. The field of view covers the west limb of the sun.

A Glimpse of the Young Milky Way

NASA Astrophysics Data System (ADS)

2002-10-01

VLT UVES Observes Most Metal-Deficient Star Known [1] Summary A faint star in the southern Milky Way, designated HE 0107-5240 , has been found to consist virtually only of hydrogen and helium . It has the lowest abundance of heavier elements ever observed , only 1/200,000 of that of the Sun - 20 times less than the previous record-holding star. This is the result of a major ongoing research project by an international team of astronomers [2]. It is based on a decade-long survey of the southern sky, with detailed follow-up observations by means of the powerful UV-Visual Echelle Spectrograph (UVES) on the 8.2-m VLT KUEYEN telescope at the ESO Paranal Observatory in Chile. This significant discovery now opens a new window towards the early times when the Milky Way galaxy was young, possibly still in the stage of formation. It proves that, contrary to most current theories, comparatively light stars like HE 0107-5240 (with 80% of the mass of the Sun) may form in environments (nearly) devoid of heavier elements. Since some years, astronomers have been desperately searching for stars of the very first stellar generation in the Milky Way, consisting only of hydrogen and helium from the Big Bang. None have been detected so far and doubts have arisen that they exist at all. The present discovery provides new hope that it will ultimately be possible to find such stellar relics from the young Universe and thereby to study "unpolluted" Big Bang material. PR Photo 25a/02 : The sky region around the very metal-deficient star HE 0107-5240 . PR Photo 25b/02 : Comparison of UVES spectra of stars with different metal abundances. Stellar generations in the Milky Way galaxy The Milky Way galaxy in which we live formed from a gigantic cloud of gas, when the Universe was still young, soon after the initial Big Bang. At the beginning, this gas was presumably composed almost exclusively of hydrogen and helium atoms produced during the Big Bang. However, once the first stars formed by

What and whence 1I/`Oumuamua: a contact binary from the debris of a young planetary system?

NASA Astrophysics Data System (ADS)

Gaidos, E.

2018-07-01

The first confirmed interstellar interloper in our Solar system, 1I/`Oumuamua, is likely to be a minor body ejected from another star, but its brief flyby and faintness made it difficult to study. Two remarkable properties are its large (up to 2.5 mag) rotational variability and its motion relative to the Sun before encounter. The former suggests an extremely elongated shape (aspect ratio ≥ 10) and the latter an origin from the protoplanetary disc of a young star in a nearby association. Against expectations, it is also not comet-like. 1I/`Oumuamua's variability can also be explained if it is a contact binary composed of near-equilibrium ellipsoidal components and heterogeneous surfaces, i.e. brighter, dust-mantled inner-facing hemispheres and darker, dust-free outer-facing poles. Such shapes are a plausible outcome of radiation, tides, and collisions in systems where planets are clearing planetesimal discs. The probability that 1I/`Oumuamua has the same motion as a young (≲100 Myr) stellar association by coincidence is <1 per cent. If it is young, its detection versus more numerous, older counterparts could be explained as a selection effect due to darkening of surfaces by Galactic cosmic rays and loss of dust. 1I/`Oumuamua's apparent lack of ices can be explained if ejected rocky planetesimals are characteristically smaller and thus far more numerous than their icy counterparts: the Solar system may currently host several such objects captured by the combined gravity of Jupiter and the Sun.

YoungStar in Milwaukee County: An Initial Progress Report as of July 2011

ERIC Educational Resources Information Center

Edie, Dave

2011-01-01

YoungStar is a program of the Department of Children and Families (DCF) created to improve the quality of child care for Wisconsin children. YoungStar is designed to: (1) Evaluate and rate the quality of care given by child care providers; (2) Help parents choose the best child care for their kids; (3) Support providers with tools and training to…

Chemical Impact of Solar Energetic Particle Event From The Young Sun: Implications for the Origin of Prebiotic Chemistry and the Fain Young Sun Paradox

NASA Astrophysics Data System (ADS)

Airapetian, V.; Gronoff, G.; Hébrard, E.; Danchi, W.

2015-12-01

Understanding how the simple molecules present on the early Earth and possibly Mars may have set a path for complex biological molecules, the building blocks of life, represents one of greatest unsolved questions. Here we present a new model of the rise of the abiotic nitrogen fixation and associated pre-biotic chemistry in the early Earth and Mars atmosphere mediated by solar eruptive events. Our physical models of interaction of magnetic clouds ejected from the young Sun with magnetospheres of the early Earth show significant perturbations of geomagnetic fields that produce extended polar caps. These polar caps provide pathways for energetic particles associated with magnetic clouds to penetrate into the nitrogen-rich weakly reducing atmosphere and initiate the reactive chemistry by breaking molecular nitrogen, carbon dioxide, methane and producing hydrogen cyanide, the essential compound for life. The model also shows that contrary to the current models of warming of early Earth and Mars, major atmospheric constituents, CO2 and CH4 will be destroyed due to collisional dissociation with energetic particles. Instead, efficient formation of the potent greenhouse gas, nitrous oxide, as a by-product of these processes is expected. This mechanism can consistently explain the Faint Young Sun's paradox for the early atmospheres of Earth and Mars. Our new model provides insight into how life may have initiated on Earth and Mars and how to search for the spectral signatures on planets "pregnant" with the potential for life.

Which of Kepler's Stars Flare?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-12-01

The habitability of distant exoplanets is dependent upon many factors one of which is the activity of their host stars. To learn about which stars are most likely to flare, a recent study examines tens of thousands of stellar flares observed by Kepler.Need for a Broader SampleArtists rendering of a flaring dwarf star. [NASAs Goddard Space Flight Center/S. Wiessinger]Most of our understanding of what causes a star to flare is based on observations of the only star near enough to examine in detail the Sun. But in learning from a sample size of one, a challenge arises: we must determine which conclusions are unique to the Sun (or Sun-like stars), and which apply to other stellar types as well.Based on observations and modeling, astronomers think that stellar flares result from the reconnection of magnetic field lines in a stars outer atmosphere, the corona. The magnetic activity is thought to be driven by a dynamo caused by motions in the stars convective zone.HR diagram of the Kepler stars, with flaring main-sequence (yellow), giant (red) and A-star (green) stars in the authors sample indicated. [Van Doorsselaere et al. 2017]To test whether these ideas are true generally, we need to understand what types of stars exhibit flares, and what stellar properties correlate with flaring activity. A team of scientists led by Tom Van Doorsselaere (KU Leuven, Belgium) has now used an enormous sample of flares observed by Kepler to explore these statistics.Intriguing TrendsVan Doorsselaere and collaborators used a new automated flare detection and characterization algorithm to search through the raw light curves from Quarter 15 of the Kepler mission, building a sample of 16,850 flares on 6,662 stars. They then used these to study the dependence of the flare occurrence rate, duration, energy, and amplitude on the stellar spectral type and rotation period.This large statistical study led the authors to several interesting conclusions, including:Flare star incidence rate as a a

Pre-main-sequence stars in the young cluster IC 2391

NASA Technical Reports Server (NTRS)

Stauffer, John; Hartmann, Lee W.; Jones, Burton F.; Mcnamara, Brian R.

1989-01-01

Seven or eight new, late-type members of the poor open cluster IC 2391 are identified, and membership is confirmed for two other stars. The new members fall approximately along a 3 x 10 to the 7th yr isochrone, which is the age estimated for the cluster on the basis of it super main-seqence turnoff. Echelle spectra were obtained for the most probable cluster members. Most show H-alpha in emission and a strong Li 6707 A absorption line, and a few are rapid rotators. The Li abundances for cluster stars cooler than the sun are considerably less than the primordial Li abundance, providing the first direct evidence for substantial premain-sequence Li burning. The rotational velocities show a range from about 15 to 150 km/s, with a distribution of rotational velocities not significantly different from that observed for low-mass stars in the Pleiades.

Sgr A* envelope explosion and the young stars in the centre of the Milky Way

NASA Astrophysics Data System (ADS)

Nayakshin, Sergei; Zubovas, Kastytis

2018-05-01

Sgr A* is the super massive black hole residing in the centre of the Milky Way. There is plenty of observational evidence that a massive gas cloud fell into the central parsec of the Milky Way ˜6 million years ago, triggering formation of a disc of young stars and activating Sgr A* . In addition to the disc, there is an unexplained population of young stars on randomly oriented orbits. Here we hypothesize that these young stars were formed by fragmentation of a massive quasi-spherical gas shell driven out from Sgr A* potential well by an energetic outflow. To account for the properties of the observed stars, the shell must be more massive than 105 Solar masses, be launched from inside ˜0.01 pc, and the feedback outflow has to be highly super-Eddington albeit for a brief period of time, producing kinetic energy of at least 1055 erg. The young stars in the central parsec of the Galaxy may be a unique example of stars formed from atomic rather than molecular hydrogen, and forged by extreme pressure of black hole outflows.

New Low-Mass Members of Nearby Young Moving Groups

NASA Astrophysics Data System (ADS)

Schlieder, Joshua; Simon, Michal; Rice, Emily; Lepine, Sebastien

2012-08-01

We are now ready to expand our program to identify new low-mass members of nearby young moving groups (NYMGs) to stars of mass ≤0.3 M_⊙. This is important to: (1) complete the census of low-mass stars near the Sun, (2) provide high priority targets for disk and exoplanet studies by direct imaging, and (3) provide a well- characterized sample of nearby, young stars for detailed study of their physical and kinematic properties. Our proven technique starts with a proper motion selection algorithm, proceeds to vet the sample for indicators of youth, and requires as its last step the measurement of candidate member radial velocities (RVs). So far, we have measured more than 100 candidate RVs using CSHELL on the NASA-IRTF and PHOENIX on Gemini-South, yielding more than 50 likely new moving group members. Here we propose to continue our RV follow-up of candidate NYMG members using PHOENIX on the KPNO 4m. We aim to measure RVs and determine spectral types of 23 faint (V≥15, H≥9), late-type (≥M4) candidates of the (beta) Pic (10 Myrs), AB Dor (70 Myrs), Tuc/Hor (30 Myrs), and TW Hydrae (8 Myrs) moving groups.

Determining the Frequency and Structure of Mass Flows Around Herbig Ae/Be Stars

NASA Astrophysics Data System (ADS)

Johns-Krull, Christopher

One of the key scientific goals being pursued by NASA, as outlined in its Strategic Plan, is to understand how individual stars form and how those processes that affect star formation also impact the formation of planetary systems. Ultimately, we wish to know how the Earth formed and how life arose on our planet. This knowledge will lead to an understanding of whether there are other life bearing planets in our galaxy and throughout the Universe. In pursuit of this knowledge, we must consider the process of star and planetary system formation for stars of all masses so that we can test and refine our theories related to the origin of life on our planet. It is now well established that planets form in disks of gas and dust that surround newly formed stars. Key factors that determine the structure and lifetime of these disks, thereby determining the likelihood of planet formation, include how rapidly the disk material accretes onto the central star or is expelled in powerful outflows of material that are routinely observed from young stars. It is the goal of this project to study the prevalence of outflows and accretion signature in a class of young stars known as Herbig Ae/Be stars. These stars are higher mass than stars like the Sun; however, they possess unique qualities that allows us to use the study of their accretion and outflow characteristics to test our understanding of these phenomena on solar like stars. This project will combine archival International Ultraviolet Explorer (IUE) satellite data and archival Far-Ultraviolet Spectroscopic Explorer (FUSE) satellite data with spectra at other wavelengths to robustly study the incidence of accretion and outflow signatures around Herbig Ae/Be stars. The IUE and FUSE data are also sensitive to the temperature of these flows and will allow us to understand their overall structure much more completely. This overall project will comprise the PhD thesis research of a graduate student at Rice University. The budget

A Gravitational, Mathematical Model for the Energy, Emitted Power and Longevity of the Sun and Stars that does not use E=mc^2

NASA Astrophysics Data System (ADS)

Morse Kingsley, James

2017-08-01

A gravitational mathematical model for the energy, radiated power and lifetime of the sun and stars is derived that does not use E=mc^2. The speed of solar flares, 200 to 1000km/sec is used to derive the surface temperature of the sun as 1.4(10^6)degrees K. Optical radiation results as gamma rays leave the sun's surface and traverse and lose energy to the ~10^6km of the sun's corona. The corona is a result of solar flares with a speed component of 424km/sec parallel to the sun's surface placing their atoms into gravitational orbit about the sun. The temperature, density, and pressure of the sun are derived as a function of r, i.e. the distance from the center of the sun. The complete article is chapter 11 of my text that can be found on my website www.jmkingsleyiii.info

Spectra of Earth-like Planets through Geological Evolution around FGKM Stars

NASA Astrophysics Data System (ADS)

Rugheimer, S.; Kaltenegger, L.

2018-02-01

Future observations of terrestrial exoplanet atmospheres will occur for planets at different stages of geological evolution. We expect to observe a wide variety of atmospheres and planets with alternative evolutionary paths, with some planets resembling Earth at different epochs. For an Earth-like atmospheric time trajectory, we simulate planets from the prebiotic to the current atmosphere based on geological data. We use a stellar grid F0V to M8V ({T}{eff}=7000–2400 K) to model four geological epochs of Earth's history corresponding to a prebiotic world (3.9 Ga), the rise of oxygen at 2.0 Ga and at 0.8 Ga, and the modern Earth. We show the VIS–IR spectral features, with a focus on biosignatures through geological time for this grid of Sun-like host stars and the effect of clouds on their spectra. We find that the observability of biosignature gases reduces with increasing cloud cover and increases with planetary age. The observability of the visible O2 feature for lower concentrations will partly depend on clouds, which, while slightly reducing the feature, increase the overall reflectivity, and thus the detectable flux of a planet. The depth of the IR ozone feature contributes substantially to the opacity at lower oxygen concentrations, especially for the high near-UV stellar environments around F stars. Our results are a grid of model spectra for atmospheres representative of Earth's geological history to inform future observations and instrument design and are available online at http://carlsaganinstitute.org/data/.

Magnetically Sleepy Stars: An X-ray Survey of Candidate Stars in Extended Magnetic Minima

NASA Astrophysics Data System (ADS)

Saar, Steven

2010-09-01

The Sun occasionally slips into periods of extended magnetic quiescence where the normal magnetic cycle largely ceases (e.g., the Maunder minimum). Understanding these episodes is important for understanding non-linear magnetic dynamos and the Earth's radiation budget. We have developed a new method for determining which stars may be in the stellar analog of these magnetic minima. We propose to study five such stars with Chandra ACIS-S. Combined with archival spectra of more stars, we can 1) explore (by proxy) properties of the solar corona in a Maunder-like minimum, 2) determine what stellar properties affect this state, and 3) investigate the coronal product of the residual turbulent dynamo in a solar mass star.

Dynamical evolution of stars and gas of young embedded stellar sub-clusters

NASA Astrophysics Data System (ADS)

Sills, Alison; Rieder, Steven; Scora, Jennifer; McCloskey, Jessica; Jaffa, Sarah

2018-06-01

We present simulations of the dynamical evolution of young embedded star clusters. Our initial conditions are directly derived from X-ray, infrared, and radio observations of local systems, and our models evolve both gas and stars simultaneously. Our regions begin with both clustered and extended distributions of stars, and a gas distribution that can include a filamentary structure in addition to gas surrounding the stellar sub-clusters. We find that the regions become spherical, monolithic, and smooth quite quickly, and that the dynamical evolution is dominated by the gravitational interactions between the stars. In the absence of stellar feedback, the gas moves gently out of the centre of our regions but does not have a significant impact on the motions of the stars at the earliest stages of cluster formation. Our models at later times are consistent with observations of similar regions in the local neighbourhood. We conclude that the evolution of young protostar clusters is relatively insensitive to reasonable choices of initial conditions. Models with more realism, such as an initial population of binary and multiple stars and ongoing star formation, are the next step needed to confirm these findings.

Star cluster formation in cosmological simulations. I. Properties of young clusters

DOE PAGES

Li, Hui; Gnedin, Oleg Y.; Gnedin, Nickolay Y.; ...

2017-01-03

We present a new implementation of star formation in cosmological simulations by considering star clusters as a unit of star formation. Cluster particles grow in mass over several million years at the rate determined by local gas properties, with high time resolution. The particle growth is terminated by its own energy and momentum feedback on the interstellar medium. We test this implementation for Milky Way-sized galaxies at high redshift by comparing the properties of model clusters with observations of young star clusters. We find that the cluster initial mass function is best described by a Schechter function rather than a single power law. In agreement with observations, at low masses the logarithmic slope ismore » $$\\alpha \\approx 1.8\\mbox{–}2$$, while the cutoff at high mass scales with the star formation rate (SFR). A related trend is a positive correlation between the surface density of the SFR and fraction of stars contained in massive clusters. Both trends indicate that the formation of massive star clusters is preferred during bursts of star formation. These bursts are often associated with major-merger events. We also find that the median timescale for cluster formation ranges from 0.5 to 4 Myr and decreases systematically with increasing star formation efficiency. Local variations in the gas density and cluster accretion rate naturally lead to the scatter of the overall formation efficiency by an order of magnitude, even when the instantaneous efficiency is kept constant. As a result, comparison of the formation timescale with the observed age spread of young star clusters provides an additional important constraint on the modeling of star formation and feedback schemes.« less

Star cluster formation in cosmological simulations. I. Properties of young clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Hui; Gnedin, Oleg Y.; Gnedin, Nickolay Y.

We present a new implementation of star formation in cosmological simulations by considering star clusters as a unit of star formation. Cluster particles grow in mass over several million years at the rate determined by local gas properties, with high time resolution. The particle growth is terminated by its own energy and momentum feedback on the interstellar medium. We test this implementation for Milky Way-sized galaxies at high redshift by comparing the properties of model clusters with observations of young star clusters. We find that the cluster initial mass function is best described by a Schechter function rather than a single power law. In agreement with observations, at low masses the logarithmic slope ismore » $$\\alpha \\approx 1.8\\mbox{–}2$$, while the cutoff at high mass scales with the star formation rate (SFR). A related trend is a positive correlation between the surface density of the SFR and fraction of stars contained in massive clusters. Both trends indicate that the formation of massive star clusters is preferred during bursts of star formation. These bursts are often associated with major-merger events. We also find that the median timescale for cluster formation ranges from 0.5 to 4 Myr and decreases systematically with increasing star formation efficiency. Local variations in the gas density and cluster accretion rate naturally lead to the scatter of the overall formation efficiency by an order of magnitude, even when the instantaneous efficiency is kept constant. As a result, comparison of the formation timescale with the observed age spread of young star clusters provides an additional important constraint on the modeling of star formation and feedback schemes.« less

Star Cluster Formation in Cosmological Simulations. I. Properties of Young Clusters

NASA Astrophysics Data System (ADS)

Li, Hui; Gnedin, Oleg Y.; Gnedin, Nickolay Y.; Meng, Xi; Semenov, Vadim A.; Kravtsov, Andrey V.

2017-01-01

We present a new implementation of star formation in cosmological simulations by considering star clusters as a unit of star formation. Cluster particles grow in mass over several million years at the rate determined by local gas properties, with high time resolution. The particle growth is terminated by its own energy and momentum feedback on the interstellar medium. We test this implementation for Milky Way-sized galaxies at high redshift by comparing the properties of model clusters with observations of young star clusters. We find that the cluster initial mass function is best described by a Schechter function rather than a single power law. In agreement with observations, at low masses the logarithmic slope is α ≈ 1.8{--}2, while the cutoff at high mass scales with the star formation rate (SFR). A related trend is a positive correlation between the surface density of the SFR and fraction of stars contained in massive clusters. Both trends indicate that the formation of massive star clusters is preferred during bursts of star formation. These bursts are often associated with major-merger events. We also find that the median timescale for cluster formation ranges from 0.5 to 4 Myr and decreases systematically with increasing star formation efficiency. Local variations in the gas density and cluster accretion rate naturally lead to the scatter of the overall formation efficiency by an order of magnitude, even when the instantaneous efficiency is kept constant. Comparison of the formation timescale with the observed age spread of young star clusters provides an additional important constraint on the modeling of star formation and feedback schemes.

High Resolution Spectroscopy of Vega-like Stars: Abundances and Circumstellar Gas

NASA Technical Reports Server (NTRS)

Dunkin, S. K.; Barlow, M. J.; Ryan, Sean G.

1996-01-01

Vega-like stars are main-sequence stars exhibiting excess infrared emission. In an effort to improve the information available on this class of star, 13 stars have been analyzed which have been classed as Vega-like, or have an infra-red excess attributable to dust in their circumstellar environment. In a separate paper stellar properties such as effective temperature and log g have been derived and in this poster we highlight the results of the photospheric abundance analysis also carried out during this work. King recently drew attention to the possible link between Vega-like stars and the photospheric metal-depleted class of A-stars, the Lambda Bootis stars. Since Vega-like stars are thought to have disks of dust, it might be expected that accretion of depleted gas onto the surface of these stars may cause this same phenomenon. In the 6 stars studied for depletions, none showed the extreme underabundance patterns observed in Lambda Bootis stars. However, depletions of silicon and magnesium were found in two of the sample, suggesting that these elements are in silicate dust grains in the circumstellar environment of these stars. Absorption lines attributed to circumstellar gas have been positively identified in three stars in our sample. Individual cases show evidence either of high-velocity outflowing gas, variability in the circumstellar lines observed, or evidence of circumstellar gas in excited lines of Fe II. No previous identification of circumstellar material has been made for two of the stars in question.

Finding High Quality Young Star Candidates in Ceph C using X-ray, Optical, and IR data

NASA Astrophysics Data System (ADS)

Orr, Laura; Rebull, Luisa M.; Johnson, Milton; Miller, Alexandra; Aragon Orozco, Anthony; Bakhaj, Benjamin; Bakshian, Jacquelyn; Chiffelle, Elizabeth; DeLint, Arie; Gerber, Stefan; Mader, Jared; Marengo, Amelia; McAdams, Jesse; Montufar, Cassandra; Orr, Quinton; San Emeterio, Lis; Stern, Eliyah; Weisserman, Drew

2017-01-01

We looked for new candidate young stars within the star forming region of Ceph OB3, more specifically in a region of this molecular cloud called Ceph C. While this region lies in the galactic plane and is included in several large surveys, Ceph C has not been well studied in the past and few young stellar objects (YSOs) have been identified there. The YSOVAR team (Rebull et al. 2014) has time-series monitoring data of this region, and in order to understand the diversity of the light curves, it is crucial to understand which objects in the field of view are likely YSOs, and which are foreground/background objects. The goal of our study is to identify candidate YSO sources as well as support the greater understanding of the variety, evolution, and variability of young stars. Our search for young stars includes data in X-ray, optical, and IR. Data points used are from Chandra, SDSS, IPHAS, 2MASS, Spitzer IRAC and MIPS, and WISE, giving us data over many orders of magnitude, 0.001 to 25 microns (0.36 to 25 microns without the X-rays). The catalogs were merged across all available wavelengths. Each source was inspected in all available images to insure good matches and quality of data across wavelengths and to eliminate poor candidates, those with contamination or confusion, and non-YSO objects. Spectral energy distributions (SEDs) for each candidate YSO were constructed and compared to images for greater assessment and reliable YSO identification. Color-color and color-magnitude diagrams have been created for the sources in this region and are used in conjunction with images, SEDs, X-ray, IR excess, and variability properties to identify candidate YSOs. Support provided for this work by the NASA/IPAC Teacher Archive Research Program (NITARP), which receives funding from the NASA ADP program.

Workshop on Physics of Accretion Disks Around Compact and Young Stars

NASA Technical Reports Server (NTRS)

Liang, E (Editor); Stepinski, T. F. (Editor)

1995-01-01

The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was to bring together workers on accretion disks in the western Gulf region (Texas and Louisiana). Part 2 presents the workshop program, a list of poster presentations, and a list of workshop participants. Accretion disks are believed to surround many stars. Some of these disks form around compact stars, such as white dwarfs, neutron stars, or black holes that are members of binary systems and reveal themselves as a power source, especially in the x-ray and gamma regions of the spectrum. On the other hand, protostellar disks are believed to be accretion disks associated with young, pre-main-sequence stars and manifest themselves mostly in infrared and radio observations. These disks are considered to be a natural outcome of the star formation process. The focus of this workshop included theory and observations relevant to accretion disks around compact objects and newly forming stars, with the primary purpose of bringing the two communities together for intellectual cross-fertilization. The nature of the workshop was exploratory, to see how much interaction is possible between distinct communities and to better realize the local potential in this subject. A critical workshop activity was identification and documentation of key issues that are of mutual interest to both communities.

Tracing the journey of the Sun and the Solar siblings through the Milky Way

NASA Astrophysics Data System (ADS)

Martínez-Barbosa, Carmen Adriana

2016-04-01

This thesis is focused on studying the motion of the Sun and the Solar siblings through the Galaxy. The Solar siblings are stars that were born with the Sun in the same molecular cloud 4.6 Gyr ago. In the first part of the thesis, we present an efficient method to calculate the evolution of small systems embedded in larger systems. Generalizations of this method are used to calculate the motion of the Sun and the Solar siblings in an analytical potential containing a central bar and spiral arms. By integrating the orbit of the Sun backwards in time, we determine its birth radius and the amount of radial migration experienced by our star. The birth radius of the Sun is used to investigate the evolution and disruption of the Sun's birth cluster. Depending on the Galaxy model parameters, the present-day phase-space distribution of the Solar siblings might be quite different. We used these data to predict the regions in the Galaxy where it will be more likely to search for So! lar siblings in the future. Finally, we compute the stellar encounters experienced by the Sun along its orbit and their role on the stability of the outer Solar System.

Dynamical systems for modeling evolution of the magnetic field of the Sun, stars and planets

NASA Astrophysics Data System (ADS)

Popova, E.

2016-12-01

The magnetic activity of the Sun, stars and planets are connected with a dynamo process based on the combined action of the differential rotation and the alpha-effect. Application of this concept allows us to get different types of solutions which can describe the magnetic activity of celestial bodies. We investigated the dynamo model with the meridional circulation by the low-mode approach. This approach is based on an assumption that the magnetic field can be described by non-linear dynamical systems with a relatively small number of parameters. Such non-linear dynamical systems are based on the equations of dynamo models. With this method dynamical systems have been built for media which contains the meridional flow and thickness of the spherical shell where dynamo process operates. It was shown the possibility of coexistence of quiasi-biennial oscillations, 22-year cycle, and grand minima of magnetic activity which is consistent with the observational data for the solar activity. We obtained different regimes (oscillations, vacillations, dynamo-bursts) depending on a value of the dynamo-number, the meridional circulation, and thickness of the spherical shell. We discuss features of these regimes and compare them with the observed features of the magnetic fields of the Sun, stars and Earth. We built theoretical paleomagnetic time scale and butterfly-diagrams for the helicity and toroidal magnetic field for different regimes.

Planet Imager Discovers Young Kuiper Belt

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-07-01

A debris disk just discovered around a nearby star is the closest thing yet seen to a young version of the Kuiper belt. This disk could be a key to better understanding the interactions between debris disks and planets, as well as how our solar system evolved early on in its lifetime. Hunting for an analog The best way to understand how the Kuiper belt — home to Pluto and thousands of other remnants of early icy planet formation in our solar system — developed would be to witness a similar debris disk in an earlier stage of its life. But before now, none of the disks we've discovered have been similar to our own: the rings are typically too large, the central star too massive, or the stars exist in regions very unlike what we think our Sun's birthplace was like. A collaboration led by Thayne Currie (National Astronomical Observatory of Japan) has changed this using the Gemini Planet Imager (GPI), part of a new generation of extreme adaptive-optics systems. The team discovered a debris disk of roughly the same size as the Kuiper belt orbiting the star HD 115600, located in the nearest OB association. The star is only slightly more massive than our Sun, and it lives in a star-forming region similar to the early Sun's environment. HD 115600 is different in one key way, however: it is only 15 million years old. This means that observing it gives us the perfect opportunity to observe how our solar system might have behaved when it was much younger. A promising future GPI's spatially-resolved spectroscopy, combined with measurements of the reflectivity of the disk, have led the team to suspect that the disk might be composed partly of water ice, just as the Kuiper belt is. The disk also shows evidence of having been sculpted by the motions of giant planets orbiting the central star, in much the same way as the outer planets of our solar system may have shaped the Kuiper belt. The observations of HD 115600 are some of the very first to emerge from GPI and the new

Gufa, a unique cultural ritual--a tale of forbidden sun and a girl

NASA Astrophysics Data System (ADS)

Shrestha, Pritisha

2015-08-01

Gufa, one of the traditional rituals has been performed in Nepal since time immemorial by an especial indigenous Newar people. Gufa, in its literal translation means cave. Just like in the cave where darkness seeps deep within its wall as the sun’s ray cannot penetrate, in the ritual of Gufa, a young girl who just had her first period is hidden in a dark room for twelve consecutive days. The girl, by strict custom and ritual performance stays in the room, protected from the sun’s light. From her female elders, she also receives informal education on family and societal values and norms.Sun, the reason behind our existence, is forbidden for the girl to observe. This very aspect of purely shunning away from the sun has become the crucial aspect for delving into the explanations offered by cultural astronomy. The present paper would argue that astronomy and astronomy education should not only focus on looking into the future, but also should go back to the ancient civilization to comprehend ritual performance our forefathers had learned from gazing the sky.After twelve days, the girl is carefully brought out to an open space where she sees the forbidden sun and symbolically marries the star via ritual. The logic behind the union after a pure restriction is to protect her sensitive young body and to ward off any harm to her reproductive parts from the sun’s harsh rays.From astronomical point, this logic behind protecting the girl from the effects of then deemed harmful rays should be studied. In ancient times, who with which instruments could have possibly fathom the life-giving sun could harness harmful solar rays. Although it looks like a primitive custom of hiding the girl immediately during her first period, there are logical social, cultural and scientific reasons for doing it even today in modern, urban and among the educated Newar households of Nepal and abroad.The paper would expound the importance of traditional ritual performance and its nexus with

Astronomers puzzle over a peculiar age-defying massive star

NASA Image and Video Library

2017-12-08

An age-defying star designated as IRAS 19312+1950 exhibits features characteristic of a very young star and a very old star. The object stands out as extremely bright inside a large, chemically rich cloud of material, as shown in this image from NASA’s Spitzer Space Telescope. A NASA-led team of scientists thinks the star – which is about 10 times as massive as our sun and emits about 20,000 times as much energy – is a newly forming protostar. That was a big surprise because the region had not been known as a stellar nursery before. But the presence of a nearby interstellar bubble, which indicates the presence of a recently formed massive star, also supports this idea. Read more: go.nasa.gov/2bMza9d Image Credit: NASA/JPL-Caltech

ClassLess: A Comprehensive Database of Young Stellar Objects

NASA Astrophysics Data System (ADS)

Hillenbrand, Lynne A.; baliber, nairn

2015-08-01

We have designed and constructed a database intended to house catalog and literature-published measurements of Young Stellar Objects (YSOs) within ~1 kpc of the Sun. ClassLess, so called because it includes YSOs in all stages of evolution, is a relational database in which user interaction is conducted via HTML web browsers, queries are performed in scientific language, and all data are linked to the sources of publication. Each star is associated with a cluster (or clusters), and both spatially resolved and unresolved measurements are stored, allowing proper use of data from multiple star systems. With this fully searchable tool, myriad ground- and space-based instruments and surveys across wavelength regimes can be exploited. In addition to primary measurements, the database self consistently calculates and serves higher level data products such as extinction, luminosity, and mass. As a result, searches for young stars with specific physical characteristics can be completed with just a few mouse clicks. We are in the database population phase now, and are eager to engage with interested experts worldwide on local galactic star formation and young stellar populations.

Young Stars Emerge from Orion Head

NASA Image and Video Library

2007-05-17

This image from NASA's Spitzer Space Telescope shows infant stars "hatching" in the head of the hunter constellation, Orion. Astronomers suspect that shockwaves from a supernova explosion in Orion's head, nearly three million years ago, may have initiated this newfound birth. The region featured in this Spitzer image is called Barnard 30. It is located approximately 1,300 light-years away and sits on the right side of Orion's "head," just north of the massive star Lambda Orionis. Wisps of green in the cloud are organic molecules called polycyclic aromatic hydrocarbons. These molecules are formed anytime carbon-based materials are burned incompletely. On Earth, they can be found in the sooty exhaust from automobile and airplane engines. They also coat the grills where charcoal-broiled meats are cooked. Tints of orange-red in the cloud are dust particles warmed by the newly forming stars. The reddish-pink dots at the top of the cloud are very young stars embedded in a cocoon of cosmic gas and dust. Blue spots throughout the image are background Milky Way along this line of sight. This composite includes data from Spitzer's infrared array camera instrument, and multiband imaging photometer instrument. Light at 4.5 microns is shown as blue, 8.0 microns is green, and 24 microns is red. http://photojournal.jpl.nasa.gov/catalog/PIA09411

Young Stars Emerge from Orion's Head

NASA Technical Reports Server (NTRS)

2007-01-01

This image from NASA's Spitzer Space Telescope shows infant stars 'hatching' in the head of the hunter constellation, Orion. Astronomers suspect that shockwaves from a supernova explosion in Orion's head, nearly three million years ago, may have initiated this newfound birth

The region featured in this Spitzer image is called Barnard 30. It is located approximately 1,300 light-years away and sits on the right side of Orion's 'head,' just north of the massive star Lambda Orionis.

Wisps of green in the cloud are organic molecules called polycyclic aromatic hydrocarbons. These molecules are formed anytime carbon-based materials are burned incompletely. On Earth, they can be found in the sooty exhaust from automobile and airplane engines. They also coat the grills where charcoal-broiled meats are cooked.

Tints of orange-red in the cloud are dust particles warmed by the newly forming stars. The reddish-pink dots at the top of the cloud are very young stars embedded in a cocoon of cosmic gas and dust. Blue spots throughout the image are background Milky Way along this line of sight.

This composite includes data from Spitzer's infrared array camera instrument, and multiband imaging photometer instrument. Light at 4.5 microns is shown as blue, 8.0 microns is green, and 24 microns is red.

PLANETS AROUND LOW-MASS STARS (PALMS). V. AGE-DATING LOW-MASS COMPANIONS TO MEMBERS AND INTERLOPERS OF YOUNG MOVING GROUPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowler, Brendan P.; Montet, Benjamin T.; Riddle, Reed

2015-06-10

We present optical and near-infrared adaptive optics (AO) imaging and spectroscopy of 13 ultracool (>M6) companions to late-type stars (K7–M4.5), most of which have recently been identified as candidate members of nearby young moving groups (YMGs; 8–120 Myr) in the literature. Three of these are new companions identified in our AO imaging survey, and two others are confirmed to be comoving with their host stars for the first time. The inferred masses of the companions (∼10–100 M{sub Jup}) are highly sensitive to the ages of the primary stars; therefore we critically examine the kinematic and spectroscopic properties of each systemmore » to distinguish bona fide YMG members from old field interlopers. The new M7 substellar companion 2MASS J02155892–0929121 C (40–60 M{sub Jup}) shows clear spectroscopic signs of low gravity and, hence, youth. The primary, possibly a member of the ∼40 Myr Tuc-Hor moving group, is visually resolved into three components, making it a young low-mass quadruple system in a compact (≲100 AU) configuration. In addition, Li i λ6708 absorption in the intermediate-gravity M7.5 companion 2MASS J15594729+4403595 B provides unambiguous evidence that it is young (≲200 Myr) and resides below the hydrogen-burning limit. Three new close-separation (<1″) companions (2MASS J06475229–2523304 B, PYC J11519+0731 B, and GJ 4378 Ab) orbit stars previously reported as candidate YMG members, but instead are likely old (≳1 Gyr) tidally locked spectroscopic binaries without convincing kinematic associations with any known moving group. The high rate of false positives in the form of old active stars with YMG-like kinematics underscores the importance of radial velocity and parallax measurements to validate candidate young stars identified via proper motion and activity selection alone. Finally, we spectroscopically confirm the cool temperature and substellar nature of HD 23514 B, a recently discovered M8 benchmark brown dwarf orbiting

Planets Around Low-mass Stars (PALMS). V. Age-dating Low-mass Companions to Members and Interlopers of Young Moving Groups

NASA Astrophysics Data System (ADS)

Bowler, Brendan P.; Shkolnik, Evgenya L.; Liu, Michael C.; Schlieder, Joshua E.; Mann, Andrew W.; Dupuy, Trent J.; Hinkley, Sasha; Crepp, Justin R.; Johnson, John Asher; Howard, Andrew W.; Flagg, Laura; Weinberger, Alycia J.; Aller, Kimberly M.; Allers, Katelyn N.; Best, William M. J.; Kotson, Michael C.; Montet, Benjamin T.; Herczeg, Gregory J.; Baranec, Christoph; Riddle, Reed; Law, Nicholas M.; Nielsen, Eric L.; Wahhaj, Zahed; Biller, Beth A.; Hayward, Thomas L.

2015-06-01

We present optical and near-infrared adaptive optics (AO) imaging and spectroscopy of 13 ultracool (>M6) companions to late-type stars (K7-M4.5), most of which have recently been identified as candidate members of nearby young moving groups (YMGs; 8-120 Myr) in the literature. Three of these are new companions identified in our AO imaging survey, and two others are confirmed to be comoving with their host stars for the first time. The inferred masses of the companions (˜10-100 MJup) are highly sensitive to the ages of the primary stars; therefore we critically examine the kinematic and spectroscopic properties of each system to distinguish bona fide YMG members from old field interlopers. The new M7 substellar companion 2MASS J02155892-0929121 C (40-60 MJup) shows clear spectroscopic signs of low gravity and, hence, youth. The primary, possibly a member of the ˜40 Myr Tuc-Hor moving group, is visually resolved into three components, making it a young low-mass quadruple system in a compact (≲100 AU) configuration. In addition, Li i λ6708 absorption in the intermediate-gravity M7.5 companion 2MASS J15594729+4403595 B provides unambiguous evidence that it is young (≲200 Myr) and resides below the hydrogen-burning limit. Three new close-separation (<1″) companions (2MASS J06475229-2523304 B, PYC J11519+0731 B, and GJ 4378 Ab) orbit stars previously reported as candidate YMG members, but instead are likely old (≳1 Gyr) tidally locked spectroscopic binaries without convincing kinematic associations with any known moving group. The high rate of false positives in the form of old active stars with YMG-like kinematics underscores the importance of radial velocity and parallax measurements to validate candidate young stars identified via proper motion and activity selection alone. Finally, we spectroscopically confirm the cool temperature and substellar nature of HD 23514 B, a recently discovered M8 benchmark brown dwarf orbiting the dustiest-known member of the

A multiwavelength study of young stars in the Elephant Trunk

NASA Astrophysics Data System (ADS)

López Martí, B.; Bayo, A.; Morales Calderón, M.; Barrado, D.

2013-05-01

We present the results of a multiwavelength study of young stars in IC 1396A, ``the Elephant Trunk Nebula''. Our targets are selected combining optical, near-infrared and mid-infrared photometry. Near-infrared and optical spectroscopy are used to confirm their youth and to derive spectral types for these objects, showing that they are early to mid-M stars, and that our sample includes some of the lowest-mass objects reported so far in the region. The photometric and spectroscopic information is used to construct the spectral energy distributions and to study the properties of the stars (mass, age, accretion, disks, spatial location). The implications for the triggered star formation picture are discussed.

Ultrabass Sounds of the Giant Star xi Hya

NASA Astrophysics Data System (ADS)

2002-05-01

First Observations of Solar-type Oscillations in a Star Very Different from the Sun Summary About 30 years ago, astronomers realised that the Sun resonates like a giant musical instrument with well-defined periods (frequencies). It forms a sort of large, spherical organ pipe. The energy that excites these sound waves comes from the turbulent region just below the Sun's visible surface. Observations of the solar sound waves (known as " helioseismology ") have resulted in enormous progress in the exploration of the interior of the Sun, otherwise hidden from view. As is the case on Earth, seismic techniques can be applied and the detailed interpretation of the observed oscillation periods has provided quite accurate information about the structure and motions inside the Sun, our central star. It has now also become possible to apply this technique to some solar-type stars. The first observations concerned the northern star eta Bootis (cf. ESO PR 16/94 ). Last year, extensive and much more accurate observations with the 1.2-m Swiss telescope at the ESO La Silla Observatory proved that Alpha Centauri , a solar "twin", behaves very much like the Sun (cf. ESO PR 15/01 ), and that some of the periods are quite similar to those in the Sun. These new observational data were of a superb quality, and that study marked a true break-through in the new research field of " asteroseismology " (seismology of the stars) for solar-type stars. But what about other types of stars, for instance those that are much larger than the Sun? Based on an extremely intensive observing project with the same telescope, an international group of astronomers [1] has found that the giant star xi Hya ("xi" is the small greek letter [2]; "Hya" is an abbreviation of "Hydrae") behaves like a giant sub-ultra-bass instrument . This star is located in the constellation Hydra (the Water-Monster) at a distance of 130 light-years, it has a radius about 10 times that of the Sun and its luminosity is about 60

Comet ISON Streaks Toward the Sun

NASA Image and Video Library

2013-11-22

Date: 19 Nov 2013 Comet ISON shows off its tail in this three-minute exposure taken on 19 Nov. 2013 at 6:10 a.m. EST, using a 14-inch telescope located at the Marshall Space Flight Center. The comet is just nine days away from its close encounter with the sun; hopefully it will survive to put on a nice show during the first week of December. The star images are trailed because the telescope is tracking on the comet, which is now exhibiting obvious motion with respect to the background stars over a period of minutes. At the time of this image, Comet ISON was some 44 million miles from the sun -- and 80 million miles from Earth -- moving at a speed of 136,700 miles per hour. Credit: NASA/MSFC/Aaron Kingery -------- More details on Comet ISON: Comet ISON began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- 28 Nov 2013 -- skimming just 730,000 miles above the sun's surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Comet ISON is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide -- some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. NASA has been using a vast fleet of spacecraft, instruments, and space- and Earth-based telescope, in order to learn more about this time capsule from when the solar system first formed. The journey along the way

On the feasibility of studying the exospheres of Earth-like exoplanets by Lyman- α monitoring. Detectability constraints for nearby M stars

NASA Astrophysics Data System (ADS)

Castro, Ana I. Gómez de; Beitia-Antero, Leire; Ustamujic, Sabina

2018-04-01

Observations of the Earth's exosphere have unveiled an extended envelope of hydrogen reaching further than 10 Earth radii composed of atoms orbiting around the Earth. This large envelope increases significantly the opacity of the Earth to Lyman α (Ly α) photons coming from the Sun, to the point of making feasible the detection of the Earth's transit signature from 1.35 pc if pointing with an 8 meter primary mirror space telescope through a clean line of sight ( N H < 1017 cm- 2), as we show. In this work, we evaluate the potential detectability of Earth analogs orbiting around nearby M-type stars by monitoring the variability of the Ly α flux variability. We show that, in spite of the interstellar, heliospheric and astrospheric absorption, the transit signature in M5 V type stars would be detectable with a dedicated Ly α flux monitor implemented in a 4-8 m class space telescope. Such monitoring programs would enable measuring the robustness of planetary atmospheres under heavy space weather conditions like those produced by M-type stars. A 2-m class telescope, such as the World Space Observatory, would suffice to detect an Earth-like planet orbiting around Proxima Centauri, if there was such a planet or nearby M5 type stars.

Detailed photometric analysis of young star groups in the galaxy NGC 300

NASA Astrophysics Data System (ADS)

Rodríguez, M. J.; Baume, G.; Feinstein, C.

2016-10-01

Aims: The purpose of this work is to understand the global characteristics of the stellar populations in NGC 300. In particular, we focused our attention on searching young star groups and study their hierarchical organization. The proximity and orientation of this Sculptor Group galaxy make it an ideal candidate for this study. Methods: The research was conducted using archival point spread function (PSF) fitting photometry measured from images in multiple bands obtained with the Advanced Camera for Surveys of the Hubble Space Telescope (ACS/HST). Using the path linkage criterion (PLC), we cataloged young star groups and analyzed them from the observation of individual stars in the galaxy NGC 300. We also built stellar density maps from the bluest stars and applied the SExtractor code to identify overdensities. This method provided an additional tool for the detection of young stellar structures. By plotting isocontours over the density maps and comparing the two methods, we could infer and delineate the hierarchical structure of the blue population in the galaxy. For each region of a detected young star group, we estimated the size and derived the radial surface density profiles for stellar populations of different color (blue and red). A statistical decontamination of field stars was performed for each region. In this way it was possible to build the color-magnitude diagrams (CMD) and compare them with theoretical evolutionary models. We also constrained the present-day mass function (PDMF) per group by estimating a value for its slope. Results: The blue population distribution in NGC 300 clearly follows the spiral arms of the galaxy, showing a hierarchical behavior in which the larger and loosely distributed structures split into more compact and denser ones over several density levels. We created a catalog of 1147 young star groups in six fields of the galaxy NGC 300, in which we present their fundamental characteristics. The mean and the mode radius values

Detection of X-ray emission from the young low-mass star Rossiter 137B

NASA Technical Reports Server (NTRS)

Vilhu, O.; Linsky, J. L.

1987-01-01

Rst 137B, a close M-dwarf companion to the active K-star HD 36705, has been detected in a High Resolution Image in the Einstein Observatory Archive. The X-ray surface fluxes (0.2-4 keV) from both stars are close to the empirical saturation level, F(x)/F(bol) of about 0.001, defined by rapid rotators and very young stars. This supports the earlier results of the youthfulness of the system. This young couple is an excellent subject for studies of dependence of early evolution on stellar mass. Rst 137B is one of the latest spectral types and thus lowest-mass premain-sequence stars yet detected as an X-ray source.

Intermediate-mass Elements in Young Supernova Remnants Reveal Neutron Star Kicks by Asymmetric Explosions

NASA Astrophysics Data System (ADS)

Katsuda, Satoru; Morii, Mikio; Janka, Hans-Thomas; Wongwathanarat, Annop; Nakamura, Ko; Kotake, Kei; Mori, Koji; Müller, Ewald; Takiwaki, Tomoya; Tanaka, Masaomi; Tominaga, Nozomu; Tsunemi, Hiroshi

2018-03-01

The birth properties of neutron stars (NSs) yield important information about the still-debated physical processes that trigger the explosion as well as on intrinsic neutron-star physics. These properties include the high space velocities of young neutron stars with average values of several 100 km s‑1, with an underlying “kick” mechanism that is not fully clarified. There are two competing possibilities that could accelerate NSs during their birth: anisotropic ejection of either stellar debris or neutrinos. Here we present new evidence from X-ray measurements that chemical elements between silicon and calcium in six young gaseous supernova remnants are preferentially expelled opposite to the direction of neutron star motion. There is no correlation between the kick velocities and magnetic field strengths of these neutron stars. Our results support a hydrodynamic origin of neutron-star kicks connected to asymmetric explosive mass ejection, and they conflict with neutron-star acceleration scenarios that invoke anisotropic neutrino emission caused by particle and nuclear physics in combination with very strong neutron-star magnetic fields.

Young Stars at Home in Ancient Cluster

NASA Image and Video Library

2017-12-08

NASA image release February 8, 2012 Looking like a hoard of gems fit for an emperor's collection, this deep sky object called NGC 6752 is in fact far more worthy of admiration. It is a globular cluster, and at over 10 billion years old is one the most ancient collections of stars known. It has been blazing for well over twice as long as our solar system has existed. NGC 6752 contains a high number of "blue straggler'' stars, some of which are visible in this image. These stars display characteristics of stars younger than their neighbors, despite models suggesting that most of the stars within globular clusters should have formed at approximately the same time. Their origin is therefore something of a mystery. Studies of NGC 6752 may shed light on this situation. It appears that a very high number -- up to 38 percent -- of the stars within its core region are binary systems. Collisions between stars in this turbulent area could produce the blue stragglers that are so prevalent. Lying 13,000 light-years distant, NGC 6752 is far beyond our reach, yet the clarity of Hubble's images brings it tantalizingly close. Credit: ESA/Hubble & NASA NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Spectral Characteristics of Young Stars Associated with the Sh2-296 Nebula

NASA Astrophysics Data System (ADS)

Fernandes, Beatriz; Gregorio-Hetem, Jane

Aiming to contribute to the understanding of star formation and evolution in the Canis Major (CMa R1) Molecular Clouds Complex, we analyze the spectral characteristics of a population of young stars associated with the arc-shaped nebula Sh2-296. Our XMM/Newton observations detected 109 X-ray sources in the region and optical spectroscopy was performed with Gemini telescope for 85 optical counterparts. We identified and characterized 51 objects that present features typically found in young objects, such as Hα emission and strong absorption on the Li I line.

The quest for the Sun's siblings: an exploratory search in the Hipparcos Catalogue

NASA Astrophysics Data System (ADS)

Brown, Anthony G. A.; Portegies Zwart, Simon F.; Bean, Jennifer

2010-09-01

We describe the results of a search for the remnants of the Sun's birth cluster among stars in the Hipparcos Catalogue. This search is based on the predicted phase-space distribution of the Sun's siblings from simple simulations of the orbits of the cluster stars in a smooth Galactic potential. For stars within 100 pc, the simulations show that it is interesting to examine those that have small space motions relative to the Sun. From amongst the candidate siblings thus selected, there are six stars with ages consistent with that of the Sun. Considering their radial velocities and abundances only one potential candidate, HIP21158, remains, but essentially the result of the search is negative. This is consistent with predictions by Portegies Zwart on the number of siblings near the Sun. We discuss the steps that should be taken in anticipation of the data from the Gaia mission in order to conduct fruitful searches for the Sun's siblings in the future.

The Quest For The Sun's Siblings: An Exploratory Search In The Hipparcos Catalogue

NASA Astrophysics Data System (ADS)

Bean, Jennifer; Brown, A.; Portegies Zwart, S.

2011-01-01

We describe the results of a search for the remnants of the Sun's birth cluster among stars in the Hipparcos Catalogue. This search is based on the predicted phase-space distribution of the Sun's siblings from simple simulations of the orbits of the cluster stars in a smooth Galactic potential. For stars within 100 pc, the simulations show that it is interesting to examine those that have small space motions relative to the Sun. From amongst the candidate siblings thus selected, there are six stars with ages consistent with that of the Sun. Considering their radial velocities and abundances only one potential candidate, HIP21158, remains, but essentially the result of the search is negative. This is consistent with predictions by Portegies Zwart on the number of siblings near the Sun. We discuss the steps that should be taken in anticipation of the data from the Gaia mission in order to conduct fruitful searches for the Sun's siblings in the future.

DD 13 - A very young and heavily reddened early O star in the Large Magellanic Cloud

NASA Technical Reports Server (NTRS)

Conti, Peter S.; Fitzpatrick, Edward L.

1991-01-01

This paper investigates the Large Magellanic Cloud star DD 13, which is likely the major ionizing source of the nebula N159A. New optical spectroscopy and new estimates of the broadband photometric properties of DD 13 are obtained. A spectral type of O3-O6 V, E(B-V) = 0.64, and M(V) = -6.93 is found. The spectral type cannot be more precisely defined due to contamination of the spectral data by nebular emission, obliterating the important He I classification lines. These results, plus a published estimate of the Lyman continuum photon injection rate into N159A, suggest that DD 13 actually consists of about 2-4 young, early O stars still enshrouded by their natal dust cloud. The star DD 13 may be a younger example of the type of tight cluster represented by the LMC 'star' Sk-66 deg 41, recently revealed to be composed of six or more components.

Chandra Finds X-ray Star Bonanza in the Orion Nebula

NASA Astrophysics Data System (ADS)

2000-01-01

NASA's Chandra X-ray Observatory has resolved nearly a thousand faint X-ray-emitting stars in a single observation of young stars in the Orion Nebula. The discovery--the richest field of X-ray sources ever obtained in the history of X-ray astronomy--will be presented on Friday, January 14, at the 195th national meeting of the American Astronomical Society in Atlanta, Georgia. The Orion region is a dense congregation of about 2,000 very young stars formed during the past few million years. The discovery of such a wealth of X-ray stars in the closest massive star-forming region to Earth (only 1,500 light years away) is expected to have a profound impact on our understanding of star formation and evolution. "We've detected X-rays from so many fantastic objects, such as very young massive stars and stars so small that they may evolve into brown dwarfs," said Gordon Garmire, Evan Pugh Professor at Penn State University, University Park. "Chandra's superb angular resolution has resolved this dense cluster of stars with arcsecond accuracy and unsurpassed sensitivity." Garmire leads the team using Chandra's ACIS detector, the Advanced CCD Imaging Spectrometer, conceived and developed for NASA by Penn State University and the Massachusetts Institute of Technology. The brilliant Orion region has awed humankind for millennia. The most massive and brightest of these nascent stars are in the Orion Trapezium, which illuminates the Orion Nebula, also known as Messier 42. The Trapezium and its luminous gas can be seen with the unaided eye in the winter sky in the "sword" of the Orion constellation. Young stars, such as those found in Orion, are known to be much brighter in X-rays than middle-aged stars such as the Sun. The elevated X-ray emission is thought to arise from violent flares in strong magnetic fields near the surfaces of young stars. The Sun itself was probably thousands of times brighter in X-rays during its first few million years. Although the enhanced magnetic

Hokupa'a-Gemini Discovery of Two Ultracool Companions to the Young Star HD 130948

NASA Astrophysics Data System (ADS)

Potter, D.; Martín, E. L.; Cushing, M. C.; Baudoz, P.; Brandner, W.; Guyon, O.; Neuhäuser, R.

2002-03-01

We report the discovery of two faint ultracool companions to the nearby (d~17.9 pc) young G2 V star HD 130948 (HR 5534, HIP 72567) using the Hokupa'a adaptive optics (AO) instrument mounted on the Gemini North 8 m telescope. Both objects have the same common proper motion as the primary star as seen over a 7 month baseline and have near-IR photometric colors that are consistent with an early L classification. Near-IR spectra taken with the NIRSPEC AO instrument on the Keck II telescope reveal K I lines, FeH, and H2O band heads. Based on these spectra, we determine that both objects have a spectral type of dL2 with an uncertainty of two spectral subclasses. The position of the new companions on the H-R diagram in comparison with theoretical models is consistent with the young age of the primary star (<0.8 Gyr) estimated on the basis of X-ray activity, lithium abundance, and fast rotation. HD 130948B and C likely constitute a pair of young contracting brown dwarfs with an orbital period of about 10 yr and will yield dynamical masses for L dwarfs in the near future. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (US), the Particle Physics and Astronomy Research Council (UK), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil), and CONICET (Argentina).

The Growing-up of a Star

NASA Astrophysics Data System (ADS)

2008-01-01

Using ESO's Very Large Telescope Interferometer, astronomers have probed the inner parts of the disc of material surrounding a young stellar object, witnessing how it gains its mass before becoming an adult. ESO PR Photo 03/08 ESO PR Photo 03a/08 The disc around MWC 147 (Artist's Impression) The astronomers had a close look at the object known as MWC 147, lying about 2,600 light years away towards the constellation of Monoceros ('the Unicorn'). MWC 147 belongs to the family of Herbig Ae/Be objects. These have a few times the mass of our Sun and are still forming, increasing in mass by swallowing material present in a surrounding disc. MWC 147 is less than half a million years old. If one associated the middle-aged, 4.6 billion year old Sun with a person in his early forties, MWC 147 would be a 1-day-old baby [1]. The morphology of the inner environment of these young stars is however a matter of debate and knowledge of it is important to better understand how stars and their cortège of planets form. The astronomers Stefan Kraus, Thomas Preibisch, and Keiichi Ohnaka have used the four 8.2-m Unit Telescopes of ESO's Very Large Telescope to this purpose, combining the light from two or three telescopes with the MIDI and AMBER instruments. "With our VLTI/MIDI and VLTI/AMBER observations of MWC147, we combine, for the first time, near- and mid-infrared interferometric observations of a Herbig Ae/Be star, providing a measurement of the disc size over a wide wavelength range [2]," said Stefan Kraus, lead-author of the paper reporting the results. "Different wavelength regimes trace different temperatures, allowing us to probe the disc's geometry on the smaller scale, but also to constrain how the temperature changes with the distance from the star." The near-infrared observations probe hot material with temperatures of up to a few thousand degrees in the innermost disc regions, while the mid-infrared observations trace cooler dust further out in the disc. The

Chandra Observatory Uncovers Hot Stars In The Making

NASA Astrophysics Data System (ADS)

2000-11-01

hot massive stars, several externally illuminated objects are also X-ray emitters. Some of them with temperatures up to 100 Million degrees. The ones that do not show X-ray contours are probably too faint to be detected in these particular Chandra observations. Credit: J. Bally, CASA Colorad It is generally assumed that low-mass stars like our Sun, when they are young, are more than 1,000 times more luminous in X-rays. The X-ray emission here is thought to arise from magnetic activity in connection with stellar rotation. Consequently, high temperatures would be observed in very violent and giant flares. Here temperatures as high as 60 million degrees have been observed in very few cases. The absence of many strong flares in the light curves, as well as temperatures in the Chandra ACIS spectra wich exceed the ones in giant flares, could mean that they are either young protostars (i.e stars in the making), or a special class of more evolved, hot young stars. Schulz concedes that although astronomers have gathered many clues in recent years about the X-ray behavior of very young stellar objects, "we are far from being able to uniquely classify evolutionary stages of their X-ray emission." The five main young and massive Trapezium stars are responsible for the illumination of the entire Orion Nebula. These stars are born with masses 15 to 30 times larger than the mass of our Sun. X-rays in such stars are thought to be produced by shocks that occur when high velocity stellar winds ram into slower dense material. The Chandra spectra show a temperature component of about 5 million to 10 million degrees, which is consistent with this model. However, four of these five stars also show additional components between 30 million and 60 million degrees. "The fact that some of these massive stars show such a hot component and some not, and that a hot component seems to be more common than previously assumed, is an important new aspect in the spectral behavior of these stars," said

The Embedded Ring-like Feature and Star Formation Activities in G35.673-00.847

NASA Astrophysics Data System (ADS)

Dewangan, L. K.; Devaraj, R.; Ojha, D. K.

2018-02-01

We present a multiwavelength study to probe the star formation (SF) process in the molecular cloud linked with the G35.673-00.847 site (hereafter MCG35.6), which is traced in a velocity range of 53–62 km s‑1. Multiwavelength images reveal a semi-ring-like feature (associated with ionized gas emission) and an embedded face-on ring-like feature (without the NVSS 1.4 GHz radio emission, where 1σ ∼ 0.45 mJy beam‑1) in MCG35.6. The semi-ring-like feature is originated by the ionizing feedback from a star with spectral type B0.5V–B0V. The central region of the ring-like feature does not contain detectable ionized gas emission, indicating that the ring-like feature is unlikely to be produced by the ionizing feedback from a massive star. Several embedded Herschel clumps and young stellar objects (YSOs) are identified in MCG35.6, tracing the ongoing SF activities within the cloud. The polarization information from the Planck and GPIPS data trace the plane-of-sky magnetic field, which is oriented parallel to the major axis of the ring-like feature. At least five clumps (having M clump ∼ 740–1420 M ⊙) seem to be distributed in an almost regularly spaced manner along the ring-like feature and contain noticeable YSOs. Based on the analysis of the polarization and molecular line data, three subregions containing the clumps are found to be magnetically supercritical in the ring-like feature. Altogether, the existence of the ring-like feature and the SF activities on its edges can be explained by the magnetic field mediated process as simulated by Li & Nakamura.