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Sample records for circumstellar habitable zones

  1. Circumstellar habitable zones for deep terrestrial biospheres

    NASA Astrophysics Data System (ADS)

    McMahon, Sean; O'Malley-James, Jack; Parnell, John

    2013-09-01

    The habitable zone (HZ) is conventionally the thin shell of space around a star within which liquid water is thermally stable on the surface of an Earth-like planet (Kasting et al., 1993). However, life on Earth is not restricted to the surface and includes a “deep biosphere” reaching several km in depth. Similarly, subsurface liquid water maintained by internal planetary heat could potentially support life well outside conventional HZs. We introduce a new term,subsurface-habitability zone (SSHZ) to denote the range of distances from a star within which rocky planets are habitable at any depth below their surfaces up to a stipulated maximum, and show how SSHZs can be estimated from a model relating temperature, depth and orbital distance. We present results for Earth-like, Mars-like and selected extrasolar terrestrial planets, and conclude that SSHZs are several times wider and include many more planets than conventional surface-based habitable zones.

  2. Circumstellar Habitable Zones in Tight Binary Star Systems

    NASA Astrophysics Data System (ADS)

    Pilat-Lohinger, Elke; Funk, Barbara; Eggl, Siegfried

    2013-07-01

    The fact that up to 70% of all stellar systems in our Galaxy may not be single-stellar but multi-stellar systems and the growing number of detected planets in binary star systems require methods for a quick assessment of possible habitability of a terrestrial planet in binary star systems. Concerning planetary motion in a binary star system we distinguish between S-type or circumstellar motion -- where the planet orbits one of the two stars -- and P-type or circumbinary motion -- where the planet orbits both stars. This study is restricted to S-type motion. First we applied the method of Eggl et al. (2012) and calculated the habitable zone(HZ) of a K-M binary star, where the combined gravitational and radiative influence plays an important role. Then we added a giant planet and analysed the perturbations of the giant planet and the secondary star, where mean motion resonances and secular resonances can be observed. Finally, we studied the tight binary star system HD41004 AB (a K-M binary) which habors a giant planet. We determined the conditions of this system to host a habitable planet.

  3. Circumstellar habitable zones of binary-star systems in the solar neighbourhood

    NASA Astrophysics Data System (ADS)

    Eggl, S.; Pilat-Lohinger, E.; Funk, B.; Georgakarakos, N.; Haghighipour, N.

    2013-02-01

    Binary and multiple systems constitute more than half of the total stellar population in the solar neighbourhood. Their frequent occurrence as well as the fact that more than 70 planets have already been discovered in such configurations - most notably the telluric companion of α Cen B - make them interesting targets in the search for habitable worlds. Recent studies have shown that despite the variations in gravitational and radiative environment, there are indeed circumstellar regions where planets can stay within habitable insolation limits on secular dynamical time-scales. In this paper, we provide habitable zones for 19 near S-type binary systems from the Hipparcos and Washington Double Star catalogue (WDS) catalogues with semimajor axes between 1 and 100 au. Hereby, we accounted for the combined dynamical and radiative influence of the second star on the Earth-like planet. Out of the 19 systems presented, 17 offer dynamically stable habitable zones around at least one component. The 17 potentially habitable systems contain 5 F, 3 G, 7 K and 16 M class stars. As their proximity to the Solar system (d < 31 pc) makes the selected binary stars exquisite targets for observational campaigns, we offer estimates on radial velocity, astrometric and transit signatures produced by habitable Earth-like planets in eccentric circumstellar orbits.

  4. Habitable zones in the universe.

    PubMed

    Gonzalez, Guillermo

    2005-12-01

    Habitability varies dramatically with location and time in the universe. This was recognized centuries ago, but it was only in the last few decades that astronomers began to systematize the study of habitability. The introduction of the concept of the habitable zone was key to progress in this area. The habitable zone concept was first applied to the space around a star, now called the Circumstellar Habitable Zone. Recently, other, vastly broader, habitable zones have been proposed. We review the historical development of the concept of habitable zones and the present state of the research. We also suggest ways to make progress on each of the habitable zones and to unify them into a single concept encompassing the entire universe. PMID:16254692

  5. Detectability of Earth-like Planets in Circumstellar Habitable Zones of Binary Star Systems with Sun-like Components

    NASA Astrophysics Data System (ADS)

    Eggl, Siegfried; Haghighipour, Nader; Pilat-Lohinger, Elke

    2013-02-01

    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 α 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 of α 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 α Centauri system.

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

    SciTech Connect

    Eggl, Siegfried; Pilat-Lohinger, Elke; Haghighipour, Nader

    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 of {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.

  7. The habitable zone and extreme planetary orbits.

    PubMed

    Kane, Stephen R; Gelino, Dawn M

    2012-10-01

    The habitable zone for a given star describes the range of circumstellar distances from the star within which a planet could have liquid water on its surface, which depends upon the stellar properties. Here we describe the development of the habitable zone concept, its application to our own solar system, and its subsequent application to exoplanetary systems. We further apply this to planets in extreme eccentric orbits and show how they may still retain life-bearing properties depending upon the percentage of the total orbit which is spent within the habitable zone. Key Words: Extrasolar planets-Habitable zone-Astrobiology. PMID:23035897

  8. The Habitable Zone Gallery

    NASA Astrophysics Data System (ADS)

    Gelino, Dawn M.; Kane, S. R.

    2012-01-01

    The Habitable Zone Gallery (www.hzgallery.org) is a new service to the exoplanet community which provides Habitable Zone (HZ) information for each of the exoplanetary systems with known planetary orbital parameters. The service includes a sortable table with information on the percentage of orbital phase spent within the HZ, planetary effective temperatures, and other basic planetary properties. In addition to the table, we also plot the period and eccentricity of the planets with respect to their time spent in the HZ. We provide a gallery of known systems which plot the orbits and the location of the HZ with respect to those orbits. Here we announce an upgrade to the service which includes improved planetary models, orbital movies, and various other features.

  9. The Habitable Zone Gallery

    NASA Astrophysics Data System (ADS)

    Kane, Stephen R.; Gelino, Dawn M.

    2012-04-01

    The Habitable Zone Gallery is a new service to the exoplanet community that provides habitable-zone (HZ) information for each of the exoplanetary systems with known planetary orbital parameters. The service includes a sortable table with information on the percentage of orbital phase spent within the HZ, planetary effective temperatures, and other basic planetary properties. In addition to the table, we also plot the period and eccentricity of the planets with respect to their time spent in the HZ. The service includes a gallery of known systems that plot the orbits and the location of the HZ with respect to those orbits. Also provided are animations that aid in orbit visualization and provide the changing effective temperature for those planets in eccentric orbits. Here, we describe the science motivation, the underlying calculations, and the structure of the World Wide Web site.

  10. Habitable zones and UV habitable zones around host stars

    NASA Astrophysics Data System (ADS)

    Guo, Jianpo; Zhang, Fenghui; Zhang, Xianfei; Han, Zhanwen

    2010-01-01

    Ultraviolet radiation is a double-edged sword to life. If it is too strong, the terrestrial biological systems will be damaged. And if it is too weak, the synthesis of many biochemical compounds cannot go along. We try to obtain the continuous ultraviolet habitable zones, and compare the ultraviolet habitable zones with the habitable zones of host stars. Using the boundary ultraviolet radiation of ultraviolet habitable zone, we calculate the ultraviolet habitable zones of host stars with masses from 0.08 to 4.00 M ⊙. For the host stars with effective temperatures lower than 4,600 K, the ultraviolet habitable zones are closer than the habitable zones. For the host stars with effective temperatures higher than 7,137 K, the ultraviolet habitable zones are farther than the habitable zones. For a hot subdwarf as a host star, the distance of the ultraviolet habitable zone is about ten times more than that of the habitable zone, which is not suitable for the existence of life.

  11. Habitable zones with stable orbits for planets around binary systems

    NASA Astrophysics Data System (ADS)

    Jaime, Luisa G.; Aguilar, Luis; Pichardo, Barbara

    2014-09-01

    A general formulation to compute habitable zones around binary stars is presented. A habitable zone in this context must satisfy two separate conditions: a radiative one and one of dynamical stability. For the case of single stars, the usual concept of circumstellar habitable zone is based on the radiative condition only, as the dynamical stability condition is taken for granted (assuming minimal perturbation from other planets). For the radiative condition, we extend the simple formulation of the circumstellar habitable zone for single stars, to the case of eccentric stellar binary systems, where two sources of luminosity at different orbital phases contribute to the irradiance of their planetary circumstellar and circumbinary regions. Our approach considers binaries with eccentric orbits and guarantees that orbits in the computed habitable zone remain within it at all orbital phases. For the dynamical stability condition, we use the approach of invariant loops developed by Pichardo et al. to find regions of stable, non-intersecting orbits, which is a robust method to find stable regions in binary stars, as it is based in the existence of integrals of motion. We apply the combined criteria to calculate habitable zones for 64 binary stars in the solar neighbourhood with known orbital parameters, including some with discovered planets. Formulae and interpolating tables are provided, so the reader can compute the boundaries of the habitable zones for an arbitrary binary system, using the stellar flux limits they prefer. Together with the formulae provided for stable zones, these allow the computation of both regions of stability and habitability around any binary stellar system. We found 56 per cent of the cases we consider can satisfy both restrictions, this is a very important constriction to binary systems. Nevertheless, we conclude that these systems where a dynamical and radiative safe zone exists, must be considered strong candidates in the search for habitable planets.

  12. The galactic habitable zone in elliptical galaxies

    NASA Astrophysics Data System (ADS)

    Suthar, Falguni; McKay, Christopher P.

    2012-07-01

    The concept of a Galactic Habitable Zone (GHZ) was introduced for the Milky Way galaxy a decade ago as an extension of the earlier concept of the Circumstellar Habitable Zone. In this work, we consider the extension of the concept of a GHZ to other types of galaxies by considering two elliptical galaxies as examples, M87 and M32. We argue that the defining feature of the GHZ is the probability of planet formation which has been assumed to depend on the metallicity. We have compared the metallicity distribution of nearby stars with the metallicity of stars with planets to document the correlation between metallicity and planet formation and to provide a comparison to other galaxies. Metallicity distribution, based on the [Fe/H] ratio to solar, of nearby stars peaks at [Fe/H]~-0.2 dex, whereas the metallicity distribution of extrasolar planet host stars peaks at [Fe/H]~+0.4 dex. We compare the metallicity distribution of extrasolar planet host stars with the metallicity distribution of the outer star clusters of M87 and M32. The metallicity distribution of stars in the outer regions of M87 peaks at [Fe/H]~-0.2 dex and extends to [Fe/H]~+0.4 dex, which seems favourable for planet formation. The metallicity distribution of stars in the outer regions of M32 peaks at [Fe/H]~-0.2 dex and extends to a much lower [Fe/H]. Both elliptical galaxies met the criteria of a GHZ. In general, many galaxies should support habitable zones.

  13. Concepts of the Habitable Zone

    NASA Astrophysics Data System (ADS)

    Kaltenegger, L.

    2012-04-01

    The HZ around a single star has been calculated by several authors. Two concepts are commonly used throughout the literature for cloud free (see Kasting et al.1993, Underwood et al.2003) and cloudy atmospheres (Selsis et al.2007) which have been derived from the same model originally proposed by Kasting et al.(1993). The main differences among studies of the HZ are the imposed climatic constraints such as a CO2/H2O/N2 atmosphere with varying CO2/H2O/N2 concentrations (e.g., Earth's), or model atmospheres with high H2 concentrations (Gaidos&Pierrehumbert 2010) or limited water supply (Abe et al.2011). We discuss the implication of these constraints on the Habitable Zone and its resulting limits as well as detectable spectral features in a planet's rocky atmosphere that could be used to test our concept of the Habitable Zone.

  14. Exomoon Conditions in Circumbinary Habitability Zones

    NASA Astrophysics Data System (ADS)

    Mason, Paul A.; Zuluaga, J. I.; Clark, J.; Cuartas-Restrepo, P.

    2014-01-01

    Limits on the potential habitability of exomoons orbiting massive planets within circumbinary habitable zones are examined. Exomoons orbiting planets in the habitable zones of single stars and those orbiting circumbinary planets are subject to the, sometimes intense, tidal heating of the planet. So, exomoon orbits need to be sufficiently large and circular to avoid loss of water like Io. However, moons may be lost if their orbits are too large. We show that, in some cases, massive circumbinary planets have larger Hill radii than similar mass planets in single star habitable zones. The range of semimajor axes, beyond the habitable edge for moons is several times larger in some binaries as compared to single stars and is verified by numerical orbit experiments. We discuss implications of this result in the context of the binary habitability mechanism.

  15. Habitable Zones Around Low-Mass Stars

    NASA Astrophysics Data System (ADS)

    Kopparapu, Ravi Kumar; Kasting, J. F.; Ramirez, R.

    2011-09-01

    Classically, the circumstellar habitable zone (HZ) is defined as the region inside which a terrestrial mass planet, with adequate supplies of carbon, water, and internal heat, can sustain liquid water on its surface (Kasting et al. 1993). A conservative estimate for the width of the HZ in our Solar system is 0.93-1.48 AU, assuming that the inner edge is limited by water loss and the outer edge is determined by the maximum greenhouse limit for a dense CO2 atmosphere. These numbers are revisions of ones published by Kasting et al. (1993), based on new climate modeling results. Kasting et al. obtained HZ boundaries for stars with effective temperatures between 3700 K and 7200 K--limits that do not include main-sequence M-dwarfs. In this study we use an updated 1-D radiative-convective, cloud-free climate model to estimate the width of the HZ around these low mass stars. Significant improvements in our climate model include: (1) updated collision-induced absorption coefficients for CO2 (critical for dense CO2 atmospheres at the outer edge) and (2) a revised Rayleigh scattering coefficient for H2O (important for water loss at the inner edge). Assuming Earth-like planets with CO2/H2O/N2 atmospheres, the width of the HZ is 0.24-0.44 AU around an early M star (Teff = 3600 K) and 0.05-0.09 AU for a late M star (Teff = 2800 K). As our model does not include the radiative effects of clouds, the actual HZ boundaries may extend further in both directions than our conservative estimates. Nonetheless, current ground-based surveys (e.g., the MEARTH project) and future space-based characterization missions (e.g., JWST/TPF) may be able to use these HZ boundaries to help guide their efforts to find habitable planets around main-sequence stars. (We acknowledge funding from NASA Astrobiology Institute's Virtual Planetary Laboratory, supported by NASA under cooperative agreement NNH05ZDA001C.)

  16. Oscillations in the habitable zone around α Centauri B

    NASA Astrophysics Data System (ADS)

    Forgan, Duncan

    2012-05-01

    The α Cen AB system is an attractive one for radial velocity observations to detect potential exoplanets. The high metallicity of both α Cen A and B suggests that they could have possessed circumstellar discs capable of forming planets. As the closest star system to the Sun, with well over a century of accurate astrometric measurements (and α Cen B exhibiting low chromospheric activity), high-precision surveys of α Cen B's potential exoplanetary system are possible with relatively cheap instrumentation. Authors studying habitability in this system typically adopt habitable zones (HZs) based on global radiative balance models that neglect the radiative perturbations of α Cen A. We investigate the habitability of planets around α Cen B using one-dimensional latitudinal energy balance models (LEBMs), which fully incorporate the presence of α Cen A as a means of astronomically forcing terrestrial planet climates. We find that the extent of the HZ is relatively unchanged by the presence of α Cen A, but there are variations in fractional habitability for planets orbiting at the boundaries of the zone due to α Cen A, even in the case of zero eccentricity. Temperature oscillations of a few K can be observed at all planetary orbits, the strength of which varies with the planet's ocean fraction and obliquity.

  17. Habitable zone lifetimes of exoplanets around main sequence stars.

    PubMed

    Rushby, Andrew J; Claire, Mark W; Osborn, Hugh; Watson, Andrew J

    2013-09-01

    The potential habitability of newly discovered exoplanets is initially assessed by determining whether their orbits fall within the circumstellar habitable zone of their star. However, the habitable zone (HZ) is not static in time or space, and its boundaries migrate outward at a rate proportional to the increase in luminosity of a star undergoing stellar evolution, possibly including or excluding planets over the course of the star's main sequence lifetime. We describe the time that a planet spends within the HZ as its "habitable zone lifetime." The HZ lifetime of a planet has strong astrobiological implications and is especially important when considering the evolution of complex life, which is likely to require a longer residence time within the HZ. Here, we present results from a simple model built to investigate the evolution of the "classic" HZ over time, while also providing estimates for the evolution of stellar luminosity over time in order to develop a "hybrid" HZ model. These models return estimates for the HZ lifetimes of Earth and 7 confirmed HZ exoplanets and 27 unconfirmed Kepler candidates. The HZ lifetime for Earth ranges between 6.29 and 7.79×10⁹ years (Gyr). The 7 exoplanets fall in a range between ∼1 and 54.72 Gyr, while the 27 Kepler candidate planets' HZ lifetimes range between 0.43 and 18.8 Gyr. Our results show that exoplanet HD 85512b is no longer within the HZ, assuming it has an Earth analog atmosphere. The HZ lifetime should be considered in future models of planetary habitability as setting an upper limit on the lifetime of any potential exoplanetary biosphere, and also for identifying planets of high astrobiological potential for continued observational or modeling campaigns. PMID:24047111

  18. Using a generalized version of the Titius-Bode relation to extrapolate the patterns seen in Kepler multi-exoplanet systems, and estimate the average number of planets in circumstellar habitable zones

    NASA Astrophysics Data System (ADS)

    Lineweaver, Charles H.

    2015-08-01

    The Titius-Bode (TB) relation’s successful prediction of the period of Uranus was the main motivation that led to the search for another planet between Mars and Jupiter. This search led to the discovery of the asteroid Ceres and the rest of the asteroid belt. The TB relation can also provide useful hints about the periods of as-yet-undetected planets around other stars. In Bovaird & Lineweaver (2013) [1], we used a generalized TB relation to analyze 68 multi-planet systems with four or more detected exoplanets. We found that the majority of exoplanet systems in our sample adhered to the TB relation to a greater extent than the Solar System does. Thus, the TB relation can make useful predictions about the existence of as-yet-undetected planets in Kepler multi-planet systems. These predictions are one way to correct for the main obstacle preventing us from estimating the number of Earth-like planets in the universe. That obstacle is the incomplete sampling of planets of Earth-mass and smaller [2-5]. In [6], we use a generalized Titius-Bode relation to predict the periods of 228 additional planets in 151 of these Kepler multiples. These Titius-Bode-based predictions suggest that there are, on average, 2±1 planets in the habitable zone of each star. We also estimate the inclination of the invariable plane for each system and prioritize our planet predictions by their geometric probability to transit. We highlight a short list of 77 predicted planets in 40 systems with a high geometric probability to transit, resulting in an expected detection rate of ~15 per cent, ~3 times higher than the detection rate of our previous Titius-Bode-based predictions.References: [1] Bovaird, T. & Lineweaver, C.H (2013) MNRAS, 435, 1126-1138. [2] Dong S. & Zhu Z. (2013) ApJ, 778, 53 [3] Fressin F. et al. (2013) ApJ, 766, 81 [4] Petigura E. A. et al. (2013) PNAS, 110, 19273 [5] Silburt A. et al. (2014), ApJ (arXiv:1406.6048v2) [6] Bovaird, T., Lineweaver, C.H. & Jacobsen, S.K. (2015, in press) MNRAS, arXiv:14126230v3.

  19. Geophysical Limitations on the Habitable Zone

    NASA Astrophysics Data System (ADS)

    Noack, L.; Van Hoolst, T.

    2015-10-01

    Planets are typically classified as potentially life-bearing planets (i.e. habitable planets) if they are rocky planets and if a liquid (e.g. water) could exist at the surface. The latter depends on several factors, like for example the amount of available solar energy, greenhouse effects in the atmosphere and an efficient CO2-cycle. However, the definition of the habitable zone should be updated to include possible geophy-sical constraints, that could potentially influence the CO2-cycle. Planets like Mars without plate tectonics and no or only limited volcanic events can only be considered to be habitable at the inner boundary of the habitable zone, since the greenhouse effect needed to ensure liquid surface water farther away from the sun is strongly reduced. We investigate how these geophysical processes depend on the mass and interior structure of terrestrial planets. We find that plate tectonics, if it occurs, always leads to sufficient volcanic outgassing and therefore greenhouse effect needed for the outer boundary of the habitable zone (several tens of bar CO2). One-plate planets, however, may suffer strong volcanic limitations if their mass and/or iron content exceeds a critical value, reducing their possible surface habitability.

  20. Habitable zone limits for dry planets.

    PubMed

    Abe, Yutaka; Abe-Ouchi, Ayako; Sleep, Norman H; Zahnle, Kevin J

    2011-06-01

    Most discussion of habitable planets has focused on Earth-like planets with globally abundant liquid water. For an "aqua planet" like Earth, the surface freezes if far from its sun, and the water vapor greenhouse effect runs away if too close. Here we show that "land planets" (desert worlds with limited surface water) have wider habitable zones than aqua planets. For planets at the inner edge of the habitable zone, a land planet has two advantages over an aqua planet: (i) the tropics can emit longwave radiation at rates above the traditional runaway limit because the air is unsaturated and (ii) the dry air creates a dry stratosphere that limits hydrogen escape. At the outer limits of the habitable zone, the land planet better resists global freezing because there is less water for clouds, snow, and ice. Here we describe a series of numerical experiments using a simple three-dimensional global climate model for Earth-sized planets. Other things (CO(2), rotation rate, surface pressure) unchanged, we found that liquid water remains stable at the poles of a low-obliquity land planet until net insolation exceeds 415 W/m(2) (170% that of modern Earth), compared to 330 W/m(2) (135%) for the aqua planet. At the outer limits, we found that a low-obliquity land planet freezes at 77%, while the aqua planet freezes at 90%. High-obliquity land and aqua planets freeze at 58% and 72%, respectively, with the poles offering the last refuge. We show that it is possible that, as the Sun brightens, an aqua planet like Earth can lose most of its hydrogen and become a land planet without first passing through a sterilizing runaway greenhouse. It is possible that Venus was a habitable land planet as recently as 1 billion years ago. PMID:21707386

  1. Flux of icy asteroids towards the habitable zone in binary stars

    NASA Astrophysics Data System (ADS)

    Pilat-Lohinger, Elke; Bancelin, David; Bazso, Akos; Eggl, Siegfried

    2015-08-01

    From studies of habitability in our solar system we can conclude that a fraction of the water on Earth was transported via asteroids and comets to our planet. Assuming that other planetary systems would need similar water-bringing-scenarios we studied the efficiency of the water transport in binary star systems where we considered S-type planetary motion. We will show a detailed analysis of the dynamcial perturbations in the disk for different binary-planet configurations and analyse the efficiency of water transport via icy asteroids into the circumstellar habitable zone.

  2. Habitable zones around main sequence stars

    NASA Technical Reports Server (NTRS)

    Kasting, James F.; Whitmire, Daniel P.; Reynolds, Ray T.

    1993-01-01

    A mechanism for stabilizing climate on the earth and other earthlike planets is described, and the physical processes that define the inner and outer boundaries of the habitable zone (HZ) around the sun and main sequence stars are discussed. Physical constraints on the HZ obtained from Venus and Mars are taken into account. A 1D climate model is used to estimate the width of the HZ and the continuously habitable zone around the sun, and the analysis is extended to other main sequence stars. Whether other stars have planets and where such planets might be located with respect to the HZ is addressed. The implications of the findings for NASA's SETI project are considered.

  3. Dynamical influence of the secondary star on planets in the circumprimary habitable zone

    NASA Astrophysics Data System (ADS)

    Pilat-Lohinger, Elke; Bazso, Akos; Funk, Barbara; Lammer, Helmut; Eggl, Siegfried

    2015-08-01

    From studies of circumstellar planetary motion in tight binary star systems like gamma Cephei or HD41004AB we know that secular perturbations can appear which could also influence planets moving in the circumprimary habitable zone. This depends certainly on the system architecture. To locate the area where the secular resonance causes high eccentricity motion or orbital escapes we use a semi-analytical approach which can easily be applied to circumstellar planetary systems where the giant planet orbits the primary star at larger distances than the habitable zone.In this presentation we will use the system HD41004AB - where we study the area around HD41004A inside the orbit of the detected gas giant -- to explain our method and compare the results to former numerical simulations of this region. The comparison of both studies showed a good agreement so that an application to all known tight binary star systems (up to 100 au separation of the two stars) was carried out. In case the secular resonance is located in the habitable zone we analyse the effect on the planetary motion in detail and discuss possible consequences taking into account former habitability studies of the Earth when moving in an eccentric orbit.

  4. A Population-based Habitable Zone Perspective

    NASA Astrophysics Data System (ADS)

    Zsom, Andras

    2015-11-01

    What can we tell about exoplanet habitability if currently only the stellar properties, planet radius, and the incoming stellar flux are known? A planet is in the habitable zone (HZ) if it harbors liquid water on its surface. The HZ is traditionally conceived as a sharp region around stars because it is calculated for one planet with specific properties. Such an approach is limiting because the planet’s atmospheric and geophysical properties, which influence the presence of liquid water on the surface, are currently unknown but expected to be diverse. A statistical HZ description is outlined that does not favor one planet type. Instead, the stellar and planet properties are treated as random variables, and a continuous range of planet scenarios is considered. Various probability density functions are assigned to each random variable, and a combination of Monte Carlo sampling and climate modeling is used to generate synthetic exoplanet populations with known surface climates. Then, the properties of the subpopulation bearing liquid water is analyzed. Given our current observational knowledge, the HZ takes the form of a weakly constrained but smooth probability function. The HZ has an inner edge, but a clear outer edge is not seen. Currently only optimistic upper limits can be derived for the potentially observable HZ occurrence rate. Finally, we illustrate through an example how future data on exoplanet atmospheres will help to narrow down the probability that an exoplanet harbors liquid water, and we identify the greatest observational challenge in the way of finding a habitable exoplanet.

  5. Galactic Habitable Zone and Astrobiological Complexity

    NASA Astrophysics Data System (ADS)

    Vukotic, B.

    2012-12-01

    This is a short thesis description and for the sake of brevity most things are left out. For more details, those interested are further directed to the thesis related papers in this article reference list. Thesis itself is available at the University of Belgrade library "Svetozar Markovic" (Serbian version only). In this thesis we study the astrobiological history of the Galactic habitable zone through the means of numerical modeling. First group of simulations are unidimensional (time-axis) toy models examine the influence of global regulation mechanisms (gamma-ray bursts and supernovae) on temporal evolution of Galactic astrobiological complexity. It is shown that under the assumption of global regulation classical anti SETI arguments can be undermined. Second group of simulations are more complex bidimensional probabilistic cellular automata models of the Galactic thin disk. They confirm the findings of the toy models and give some insights into the spatial clustering of astrobiological complexity. As a new emerging multidisciplinary science the basic concepts of astrobiology are poorly understood and although all the simulations present here do not include some basic physics (such as Galactic kinematics and dynamics), the input parameters are somewhat arbitrary and could use a future refinement (such as the boundaries of the Galactic habitable zone). This is the cause for low weight and high uncertainty in the output results of the simulations. However, the probabilistic cellular automata has shown as a highly adaptable modeling platform that can simulate various class of astrobiological models with great ease.

  6. Habitable zones around main sequence stars.

    PubMed

    Kasting, J F; Whitmire, D P; Reynolds, R T

    1993-01-01

    A one-dimensional climate model is used to estimate the width of the habitable zone (HZ) around our Sun and around other main sequence stars. Our basic premise is that we are dealing with Earth-like planets with CO2/H2O/N2 atmospheres and that habitability requires the presence of liquid water on the planet's surface. The inner edge of the HZ is determined in our model by loss of water via photolysis and hydrogen escape. The outer edge of the HZ is determined by the formation of CO2 clouds, which cool a planet's surface by increasing its albedo and by lowering the convective lapse rate. Conservative estimates for these distances in our own Solar System are 0.95 and 1.37 AU, respectively; the actual width of the present HZ could be much greater. Between these two limits, climate stability is ensured by a feedback mechanism in which atmospheric CO2 concentrations vary inversely with planetary surface temperature. The width of the HZ is slightly greater for planets that are larger than Earth and for planets which have higher N2 partial pressures. The HZ evolves outward in time because the Sun increases in luminosity as it ages. A conservative estimate for the width of the 4.6-Gyr continuously habitable zone (CHZ) is 0.95 to 1.15 AU. Stars later than F0 have main sequence lifetimes exceeding 2 Gyr and, so, are also potential candidates for harboring habitable planets. The HZ around an F star is larger and occurs farther out than for our Sun; the HZ around K and M stars is smaller and occurs farther in. Nevertheless, the widths of all of these HZs are approximately the same if distance is expressed on a logarithmic scale. A log distance scale is probably the appropriate scale for this problem because the planets in our own Solar System are spaced logarithmically and because the distance at which another star would be expected to form planets should be related to the star's mass. The width of the CHZ around other stars depends on the time that a planet is required to remain habitable and on whether a planet that is initially frozen can be thawed by modest increases in stellar luminosity. For a specified period of habitability, CHZs around K and M stars are wider (in log distance) than for our Sun because these stars evolve more slowly. Planets orbiting late K stars and M stars may not be habitable, however, b ecause they can become trapped in synchronous rotation as a consequence of tidal damping. F stars have narrower (log distance) CHZ's than our Sun because they evolve more rapidly. Our results suggest that mid-to-early K stars should be considered along with G stars as optimal candidates in the search for extraterrestrial life. PMID:11536936

  7. A population-based Habitable Zone perspective

    NASA Astrophysics Data System (ADS)

    Zsom, Andras

    2015-08-01

    What can we tell about exoplanet habitability if currently only the stellar properties, planet radius, and the incoming stellar flux are known? The Habitable Zone (HZ) is the region around stars where planets can harbor liquid water on their surfaces. The HZ is traditionally conceived as a sharp region around the star because it is calculated for one planet with specific properties e.g., Earth-like or desert planets , or rocky planets with H2 atmospheres. Such planet-specific approach is limiting because the planets’ atmospheric and geophysical properties, which influence the surface climate and the presence of liquid water, are currently unknown but expected to be diverse.A statistical HZ description is outlined which does not select one specific planet type. Instead the atmospheric and surface properties of exoplanets are treated as random variables and a continuous range of planet scenarios are considered. Various probability density functions are assigned to each observationally unconstrained random variable, and a combination of Monte Carlo sampling and climate modeling is used to generate synthetic exoplanet populations with known surface climates. Then, the properties of the liquid water bearing subpopulation is analyzed.Given our current observational knowledge of small exoplanets, the HZ takes the form of a weakly-constrained but smooth probability function. The model shows that the HZ has an inner edge: it is unlikely that planets receiving two-three times more stellar radiation than Earth can harbor liquid water. But a clear outer edge is not seen: a planet that receives a fraction of Earth's stellar radiation (1-10%) can be habitable, if the greenhouse effect of the atmosphere is strong enough. The main benefit of the population-based approach is that it will be refined over time as new data on exoplanets and their atmospheres become available.

  8. A population-based Habitable Zone perspective

    NASA Astrophysics Data System (ADS)

    Zsom, Andras

    2015-08-01

    What can we tell about exoplanet habitability if currently only the stellar properties, planet radius, and the incoming stellar flux are known? The Habitable Zone (HZ) is the region around stars where planets can harbor liquid water on their surfaces. The HZ is traditionally conceived as a sharp region around the star because it is calculated for one planet with specific properties e.g., Earth-like or desert planets , or rocky planets with H2 atmospheres. Such planet-specific approach is limiting because the planets atmospheric and geophysical properties, which influence the surface climate and the presence of liquid water, are currently unknown but expected to be diverse.A statistical HZ description is outlined which does not select one specific planet type. Instead the atmospheric and surface properties of exoplanets are treated as random variables and a continuous range of planet scenarios are considered. Various probability density functions are assigned to each observationally unconstrained random variable, and a combination of Monte Carlo sampling and climate modeling is used to generate synthetic exoplanet populations with known surface climates. Then, the properties of the liquid water bearing subpopulation is analyzed.Given our current observational knowledge of small exoplanets, the HZ takes the form of a weakly-constrained but smooth probability function. The model shows that the HZ has an inner edge: it is unlikely that planets receiving two-three times more stellar radiation than Earth can harbor liquid water. But a clear outer edge is not seen: a planet that receives a fraction of Earth's stellar radiation (1-10%) can be habitable, if the greenhouse effect of the atmosphere is strong enough. The main benefit of the population-based approach is that it will be refined over time as new data on exoplanets and their atmospheres become available.

  9. HYDROGEN GREENHOUSE PLANETS BEYOND THE HABITABLE ZONE

    SciTech Connect

    Pierrehumbert, Raymond; Gaidos, Eric E-mail: gaidos@hawaii.edu

    2011-06-10

    We show that collision-induced absorption allows molecular hydrogen to act as an incondensible greenhouse gas and that bars or tens of bars of primordial H{sub 2}-He mixtures can maintain surface temperatures above the freezing point of water well beyond the 'classical' habitable zone defined for CO{sub 2} greenhouse atmospheres. Using a one-dimensional radiative-convective model, we find that 40 bars of pure H{sub 2} on a three Earth-mass planet can maintain a surface temperature of 280 K out to 1.5 AU from an early-type M dwarf star and 10 AU from a G-type star. Neglecting the effects of clouds and of gaseous absorbers besides H{sub 2}, the flux at the surface would be sufficient for photosynthesis by cyanobacteria (in the G star case) or anoxygenic phototrophs (in the M star case). We argue that primordial atmospheres of one to several hundred bars of H{sub 2}-He are possible and use a model of hydrogen escape to show that such atmospheres are likely to persist further than 1.5 AU from M stars, and 2 AU from G stars, assuming these planets have protecting magnetic fields. We predict that the microlensing planet OGLE-05-390Lb could have retained an H{sub 2}-He atmosphere and be habitable at {approx}2.6 AU from its host M star.

  10. Habitable zone dependence on stellar parameter uncertainties

    SciTech Connect

    Kane, Stephen R.

    2014-02-20

    An important property of exoplanetary systems is the extent of the Habitable Zone (HZ), defined as that region where water can exist in a liquid state on the surface of a planet with sufficient atmospheric pressure. Both ground- and space-based observations have revealed a plethora of confirmed exoplanets and exoplanetary candidates, most notably from the Kepler mission using the transit detection technique. Many of these detected planets lie within the predicted HZ of their host star. However, as is the case with the derived properties of the planets themselves, the HZ boundaries depend on how well we understand the host star. Here we quantify the uncertainties of HZ boundaries on the parameter uncertainties of the host star. We examine the distribution of stellar parameter uncertainties from confirmed exoplanet hosts and Kepler candidate hosts and translate these into HZ boundary uncertainties. We apply this to several known systems with an HZ planet to determine the uncertainty in their HZ status.

  11. Tectonics and the photosynthetic habitable zone (Invited)

    NASA Astrophysics Data System (ADS)

    Sleep, N. H.

    2009-12-01

    The traditional habitable zone lies between an inner stellar radius where the surface of the planet becomes too hot for liquid water carbon-based life and on outer radius, where the surface freezes. It is effectively the zone where photosynthesis is feasible. The concept extends to putative life on objects with liquid methane at the surface, like Titan. As a practical matter, photosynthesis leaves detectable biosignatures in the geological record; black shale on the Earth indicates that sulfide and probably FeO based photosynthesis existed by 3.8 Ga. The hard crustal rocks and the mantle sequester numerous photosynthetic biosignatures. Photosynthesis can produce detectable free oxygen with ozone in the atmosphere of extrasolar planets. In contrast, there is no outer limit for subsurface life in large silicate objects. Pre-photosynthetic niches are dependable but meager and not very detectable at great antiquity or great distance, with global productivity less than 1e-3 of the photosynthetic ones. Photosynthetic organisms have bountiful energy that modifies their surface environment and even tectonics. For example, metamorphic rocks formed at the expense of thick black shale are highly radioactive and hence self-fluxing. Active tectonics with volcanism and metamorphism prevents volatiles from being sequestered in the subsurface as on Mars. A heat-pipe object, like a larger Io, differs from the Earth in that the volatiles return to the deep interior distributed within massive volcanic deposits rather than concentrated in the shallow oceanic crust. One the Earth, the return of water to the surface by arc volcanoes controls its mantle abundance at the transition between behaving as a trace element and behaving as a major element that affects melting. The ocean accumulates the water that the mantle and crust do not take. The Earth has the “right” amount of water that erosion/deposition and tectonics both tend to maintain near sea level surfaces. The mantle contains carbon (dioxide) that platform carbonates and the deep continental lithosphere do not take. Weathering and formation of carbonates in the oceanic crust dynamically buffers atmospheric CO2 at habitable levels. N2 is an indirect greenhouse gas in that the total pressure increases the effect of CO2. Photosynthetic life affects the nitrogen cycle as NH4+ replaces K+ in subducted black shale. N2 hence correlates with Ar-40 in volcanic gases. The net effect is that atmospheric pressure and hence the greenhouse effect decrease with time. Continents are in part the result of biological weathering. Their presence allows life to directly affect continental albedo as with “Daisy World” and to indirectly affect albedo as high global temperatures lead to reflective deserts.

  12. The First Atmospheric Characterization of a Habitable-Zone Exoplanet

    NASA Astrophysics Data System (ADS)

    Stevenson, Kevin; Bean, Jacob; Charbonneau, David; Desert, Jean-Michel; Fortney, Jonathan; Irwin, Jonathan; Kreidberg, Laura; Line, Michael; Montet, Ben; Morley, Caroline

    2015-10-01

    Exoplanet surveys have recently revealed nearby planets orbiting within stellar habitable zones. This highly-anticipated breakthrough brings us one step closer in our quest to identify cosmic biosignatures, the indicators of extrasolar life. To achieve our goal, we must first study the atmospheres of these temperate worlds to measure their compositions and determine the prevalence of obscuring clouds. Using observations from the K2 mission, Co-I Montet recently announced the discovery of a 2.2 Earth-radii planet within the habitable zone of its relatively bright, nearby M dwarf parent star, K2-18. This temperate world is currently the best habitable-zone target for atmospheric characterization. Congruent with currently planned HST observations, we propose a Spitzer program to measure the transmission spectrum of the first habitable-zone exoplanet. Both telescopes are essential to revealing K2-18b's chemical composition. In a cloud-free, hydrogen-dominated atmosphere, the precision achieved by these measurements will be sufficient to detect methane, ammonia, and water vapor, which are the dominant C, N, and O bearing species at these temperatures. In turn, elemental abundance constraints from a primordial atmosphere can tell us about the composition of a protoplanetary disk in which Earth-like planets could have formed. Conversely, if the atmosphere contains thick clouds then the multi-wavelength observations from K2, HST, and Spitzer will constrain the clouds' properties. Because temperature plays a key role in the formation of clouds, their detection within the atmosphere of this habitable-zone exoplanet would be an important signpost that serves as a guide to future investigations of smaller, rocky exoplanets. As K2 continues discovering more habitable-zone planets, it is imperative that we perform spectral reconnaissance with Spitzer to determine their physical characteristics and begin understanding the prevalence of potentially-obscuring clouds prior to the launch of JWST.

  13. Stabilizing Cloud Feedback Dramatically Expands the Habitable Zone of Tidally Locked Planets

    NASA Astrophysics Data System (ADS)

    Yang, Jun; Cowan, Nicolas B.; Abbot, Dorian S.

    2013-07-01

    The habitable zone (HZ) is the circumstellar region where a planet can sustain surface liquid water. Searching for terrestrial planets in the HZ of nearby stars is the stated goal of ongoing and planned extrasolar planet surveys. Previous estimates of the inner edge of the HZ were based on one-dimensional radiative-convective models. The most serious limitation of these models is the inability to predict cloud behavior. Here we use global climate models with sophisticated cloud schemes to show that due to a stabilizing cloud feedback, tidally locked planets can be habitable at twice the stellar flux found by previous studies. This dramatically expands the HZ and roughly doubles the frequency of habitable planets orbiting red dwarf stars. At high stellar flux, strong convection produces thick water clouds near the substellar location that greatly increase the planetary albedo and reduce surface temperatures. Higher insolation produces stronger substellar convection and therefore higher albedo, making this phenomenon a stabilizing climate feedback. Substellar clouds also effectively block outgoing radiation from the surface, reducing or even completely reversing the thermal emission contrast between dayside and nightside. The presence of substellar water clouds and the resulting clement surface conditions will therefore be detectable with the James Webb Space Telescope.

  14. STABILIZING CLOUD FEEDBACK DRAMATICALLY EXPANDS THE HABITABLE ZONE OF TIDALLY LOCKED PLANETS

    SciTech Connect

    Yang Jun; Abbot, Dorian S.; Cowan, Nicolas B.

    2013-07-10

    The habitable zone (HZ) is the circumstellar region where a planet can sustain surface liquid water. Searching for terrestrial planets in the HZ of nearby stars is the stated goal of ongoing and planned extrasolar planet surveys. Previous estimates of the inner edge of the HZ were based on one-dimensional radiative-convective models. The most serious limitation of these models is the inability to predict cloud behavior. Here we use global climate models with sophisticated cloud schemes to show that due to a stabilizing cloud feedback, tidally locked planets can be habitable at twice the stellar flux found by previous studies. This dramatically expands the HZ and roughly doubles the frequency of habitable planets orbiting red dwarf stars. At high stellar flux, strong convection produces thick water clouds near the substellar location that greatly increase the planetary albedo and reduce surface temperatures. Higher insolation produces stronger substellar convection and therefore higher albedo, making this phenomenon a stabilizing climate feedback. Substellar clouds also effectively block outgoing radiation from the surface, reducing or even completely reversing the thermal emission contrast between dayside and nightside. The presence of substellar water clouds and the resulting clement surface conditions will therefore be detectable with the James Webb Space Telescope.

  15. What Can the Habitable Zone Gallery Do For You?

    NASA Astrophysics Data System (ADS)

    Gelino, Dawn M.; Kane, Stephen

    2015-12-01

    The Habitable Zone Gallery (www.hzgallery.org) came online in August 2011 as a service to the exoplanet community that provides Habitable Zone (HZ) information for each of the exoplanetary systems with known planetary orbital parameters. The service includes a sortable table, a plot with the period and eccentricity of each of the planets with respect to their time spent in the HZ, a gallery of known systems which plot the orbits and the location of the HZ with respect to those orbits, and orbital movies. Recently, we have added new features including: implementation of both conservative and optimistic HZs, more user-friendly table and movies, movies for circumbinary planets, and a count of planets whose orbits lie entirely within the system's HZ. Here we discuss various educational and scientific applications of the site such as target selection, exploring planets with eccentric or circumbinary orbits, and investigating habitability.

  16. Dynamical effects on the habitable zone for Earth-like exomoons

    NASA Astrophysics Data System (ADS)

    Forgan, Duncan; Kipping, David

    2013-07-01

    With the detection of extrasolar moons (exomoons) on the horizon, it is important to consider their potential for habitability. If we consider the circumstellar habitable zone (HZ, often described in terms of planet semi-major axis and orbital eccentricity), we can ask, `How does the HZ for an Earth-like exomoon differ from the HZ for an Earth-like exoplanet?' For the first time, we use 1D latitudinal energy balance modelling to address this question. The model places an Earth-like exomoon in an orbit around a Jupiter mass planet, which in turn orbits a Sun-like star. The exomoon's surface is decomposed into latitudinal strips, and the temperature of each strip is evolved under the action of stellar insolation, atmospheric cooling, heat diffusion, eclipses of the star by the planet and tidal heating. We use this model to carry out two separate investigations. In the first investigation, four test cases are run to investigate in detail the dependence of the exomoon climate on the orbital direction, orbital inclination and the frequency of the stellar eclipse by the host planet. We find that lunar orbits which are retrograde to the planetary orbit exhibit greater climate variations than prograde orbits, with global mean temperatures around 0.1 K higher due to the geometry of eclipses. If eclipses become frequent relative to the atmospheric thermal inertia time-scale, climate oscillations become extremely small. In the second investigation, we carry out an extensive parameter study, running the model many times to study the habitability of the exomoon in the four-dimensional space composed of the planet semi-major axis and eccentricity, and the moon semi-major axis and eccentricity. We find that for zero moon eccentricity, frequent eclipses allow the moon to remain habitable in regions of high planet eccentricity, but tidal heating severely constrains habitability in the limit of high moon eccentricity, making the HZ a sensitive function of the moon semi-major axis.

  17. Comparable Habitable Zones of Stars - Duration: 25 seconds.

    NASA Video Gallery

    The habitable zone is the distance from a star where one can have liquid water on the surface of a planet. If a planet is too close to its parent star, it will be too hot and water would have evapo...

  18. CANDIDATE PLANETS IN THE HABITABLE ZONES OF KEPLER STARS

    SciTech Connect

    Gaidos, Eric

    2013-06-20

    A key goal of the Kepler mission is the discovery of Earth-size transiting planets in ''habitable zones'' where stellar irradiance maintains a temperate climate on an Earth-like planet. Robust estimates of planet radius and irradiance require accurate stellar parameters, but most Kepler systems are faint, making spectroscopy difficult and prioritization of targets desirable. The parameters of 2035 host stars were estimated by Bayesian analysis and the probabilities p{sub HZ} that 2738 candidate or confirmed planets orbit in the habitable zone were calculated. Dartmouth Stellar Evolution Program models were compared to photometry from the Kepler Input Catalog, priors for stellar mass, age, metallicity and distance, and planet transit duration. The analysis yielded probability density functions for calculating confidence intervals of planet radius and stellar irradiance, as well as p{sub HZ}. Sixty-two planets have p{sub HZ} > 0.5 and a most probable stellar irradiance within habitable zone limits. Fourteen of these have radii less than twice the Earth; the objects most resembling Earth in terms of radius and irradiance are KOIs 2626.01 and 3010.01, which orbit late K/M-type dwarf stars. The fraction of Kepler dwarf stars with Earth-size planets in the habitable zone ({eta}{sub Circled-Plus }) is 0.46, with a 95% confidence interval of 0.31-0.64. Parallaxes from the Gaia mission will reduce uncertainties by more than a factor of five and permit definitive assignments of transiting planets to the habitable zones of Kepler stars.

  19. Europa, tidally heated oceans, and habitable zones around giant planets.

    PubMed

    Reynolds, R T; McKay, C P; Kasting, J F

    1987-01-01

    Tidal dissipation in the satellites of a giant planet may provide sufficient heating to maintain an environment favorable to life on the satellite surface or just below a thin ice layer. In our own solar system, Europa, one of the Galilean satellites of Jupiter, could have a liquid ocean which may occasionally receive sunlight through cracks in the overlying ice shell. In such case, sufficient solar energy could reach liquid water that organisms similar to those found under Antarctic ice could grow. In other solar systems, larger satellites with more significant heat flow could represent environments that are stable over an order of Aeons and in which life could perhaps evolve. We define a zone around a giant planet in which such satellites could exist as a tidally-heated habitable zone. This zone can be compared to the habitable zone which results from heating due to the radiation of a central star. In our solar system, this radiatively-heated habitable zone contains the Earth. PMID:11538217

  20. The Habitable Zones of Pre-main-sequence Stars

    NASA Astrophysics Data System (ADS)

    Ramirez, Ramses M.; Kaltenegger, Lisa

    2014-12-01

    We calculate the pre-main-sequence habitable zone (HZ) for stars of spectral classes F-M. The spatial distribution of liquid water and its change during the pre-main-sequence phase of protoplanetary systems is important for understanding how planets become habitable. Such worlds are interesting targets for future missions because the coolest stars could provide habitable conditions for up to 2.5 billion years post-accretion. Moreover, for a given star type, planetary systems are more easily resolved because of higher pre-main-sequence stellar luminosities, resulting in larger planet-star separation for cool stars than is the case for the traditional main-sequence (MS) HZ. We use one-dimensional radiative-convective climate and stellar evolutionary models to calculate pre-main-sequence HZ distances for F1-M8 stellar types. We also show that accreting planets that are later located in the traditional MS HZ orbiting stars cooler than a K5 (including the full range of M stars) receive stellar fluxes that exceed the runaway greenhouse threshold, and thus may lose substantial amounts of water initially delivered to them. We predict that M-star planets need to initially accrete more water than Earth did, or, alternatively, have additional water delivered later during the long pre-MS phase to remain habitable. Our findings are also consistent with recent claims that Venus lost its water during accretion.

  1. THE HABITABLE ZONES OF PRE-MAIN-SEQUENCE STARS

    SciTech Connect

    Ramirez, Ramses M.; Kaltenegger, Lisa

    2014-12-20

    We calculate the pre-main-sequence habitable zone (HZ) for stars of spectral classes F-M. The spatial distribution of liquid water and its change during the pre-main-sequence phase of protoplanetary systems is important for understanding how planets become habitable. Such worlds are interesting targets for future missions because the coolest stars could provide habitable conditions for up to 2.5 billion years post-accretion. Moreover, for a given star type, planetary systems are more easily resolved because of higher pre-main-sequence stellar luminosities, resulting in larger planet-star separation for cool stars than is the case for the traditional main-sequence (MS) HZ. We use one-dimensional radiative-convective climate and stellar evolutionary models to calculate pre-main-sequence HZ distances for F1-M8 stellar types. We also show that accreting planets that are later located in the traditional MS HZ orbiting stars cooler than a K5 (including the full range of M stars) receive stellar fluxes that exceed the runaway greenhouse threshold, and thus may lose substantial amounts of water initially delivered to them. We predict that M-star planets need to initially accrete more water than Earth did, or, alternatively, have additional water delivered later during the long pre-MS phase to remain habitable. Our findings are also consistent with recent claims that Venus lost its water during accretion.

  2. Planetary Obliquity Evolution in the 47 Uma Habitable Zone

    NASA Astrophysics Data System (ADS)

    Erikson, A.; Skoglöv, E.

    2003-04-01

    In two studies by Laskar and Robuterl (1993) and Laskar et al. (1993) the obliquity evolution of the major planets of the Solar System was investigated. It was found that the terrestrial planets have a high probability of encountering chaotic regimes and thereby initiating large variations in their obliquities. Such variations are expected to have had profound implications for the long-term atmosphere and surface conditions of the planets. The recent discovery of an extra solar planetary system (47 Uma), with a habitable zone that could potentially harbor small terrestrial planets (e.g. Jones and Sleep, 2002 and Thébault et al. 2002), have raised questions about the conditions for habitability in such a system (e.g. Franck et al. 2001 and Cuntz et al. 2003). In that context the effects of the obliquity evolution might be of importance and has been numerically simulated for hypothetical planets located in the habitable zone of 47 Uma. The results found will be presented and discussed in detail. Cuntz et al. 2003. Icarus in press. - Franck et al. 2001. Naturwissenschaften 88, 416. - Jones and Sleep 2002. A&A 393, 1015. - Laskar and Robuterl 1993. Nature 361, 608. - Laskar et al. 1993. Nature 361, 615. - Thébault et al. 2002. A&A 384, 594.

  3. Probing the Compositions of Two Habitable Zone Super-Earths

    NASA Astrophysics Data System (ADS)

    Benneke, Bjorn; Knutson, Heather; Crossfield, Ian; Deck, Katherine; Greene, Tom; Rogers, Leslie; Vanderburg, Andrew; Barman, Travis; Morley, Caroline; Lothringer, Josh; Werner, Michael; Beichman, Charles

    2015-10-01

    The recent discovery of two super-Earths orbiting in the habitable zones of nearby M stars have provided us with an unprecedented new opportunity to characterize the properties of small and potentially habitable planets outside of the solar system. Here, we propose to probe their atmospheric compositions, search for escaping hydrogen, and obtain the first bulk mass and densities estimate of a habitable zone super-Earth. The proposed observations will complement our approved HST WFC3 observations of K2-18b (15-orbits, GO13665, PI Benneke) as well as the approved HST STIS/MAMA observations of K2-18b by PI Ehrenreich. These observations will determine whether or not these two planets have primarily rocky or volatile-rich compositions, and in the volatile-rich case would enable the first studies of atmospheric chemistry in this regime. Mass loss also plays a critical role in the evolution of hydrogen-rich atmospheres on small planets, and our obsevations will provide the first constraints on the stability of these atmospheres.

  4. Determination of the habitable zone through planetary atmospheric absorption analysis

    NASA Astrophysics Data System (ADS)

    Poffo, D. A.; Caranti, G. M.; Comes, R. A.

    2014-03-01

    The so-called Habitable Zone (HZ) is a region around a star where a planet without atmosphere and considered as a black body, is subjected to a radiative flux appropriate to maintain liquid water on its surface. The location of this region is closely related to the physical properties of the star and in particular with its luminosity. It is important to note that being a planet within the HZ region is a necessary condition but may not be a sufficient one to be habitable. The concept of Planetary Habitability means that not only orbital conditions must be satisfied, but also that the planet itself must be able to develop and maintain a biosphere (Porto de Mello et al. 2006). This paper aims to determine the planetary HZ for a planet with similar conditions than the Earth, i.e. having an atmosphere, using a simple model based on the interactions between the star radiation and the radiation emitted by the planet with the atmosphere. The absorption spectrum for the proposed atmospheric chemical composition is calculated as a function of temperature by means of the HITRAN database. Another important factor taken into account in this model is cloud cover. Clouds act as "traps" to the long wave radiation emitted by the surface of the planet, resulting in an additional warming contributing to the greenhouse effect, but at the same time, reflect solar radiation back into space (albedo), producing surface cooling (Porto de Mello 2010). Taken these effects into account on a global level, we find a relationship between the orbital location of the planet and the average surface temperature that allows us to extend the habitable limits proposed by Kasting et al (1993).

  5. Stellar Activity Mimics a Habitable-zone Planet around Kapteyn's Star

    NASA Astrophysics Data System (ADS)

    Robertson, Paul; Roy, Arpita; Mahadevan, Suvrath

    2015-06-01

    Kapteyn’s star is an old M subdwarf believed to be a member of the Galactic halo population of stars. A recent study has claimed the existence of two super-Earth planets around the star based on radial velocity (RV) observations. The innermost of these candidate planets—Kapteyn b (P = 48 days)—resides within the circumstellar habitable zone (HZ). Given recent progress in understanding the impact of stellar activity in detecting planetary signals, we have analyzed the observed HARPS data for signatures of stellar activity. We find that while Kapteyn’s star is photometrically very stable, a suite of spectral activity indices reveal a large-amplitude rotation signal, and we determine the stellar rotation period to be 143 days. The spectral activity tracers are strongly correlated with the purported RV signal of “planet b,” and the 48-day period is an integer fraction (1/3) of the stellar rotation period. We conclude that Kapteyn b is not a planet in the HZ, but an artifact of stellar activity.

  6. Toward the minimum inner edge distance of the habitable zone

    SciTech Connect

    Zsom, Andras; Seager, Sara; De Wit, Julien; Stamenković, Vlada

    2013-12-01

    We explore the minimum distance from a host star where an exoplanet could potentially be habitable in order not to discard close-in rocky exoplanets for follow-up observations. We find that the inner edge of the Habitable Zone for hot desert worlds can be as close as 0.38 AU around a solar-like star, if the greenhouse effect is reduced (∼1% relative humidity) and the surface albedo is increased. We consider a wide range of atmospheric and planetary parameters such as the mixing ratios of greenhouse gases (water vapor and CO{sub 2}), surface albedo, pressure, and gravity. Intermediate surface pressure (∼1-10 bars) is necessary to limit water loss and to simultaneously sustain an active water cycle. We additionally find that the water loss timescale is influenced by the atmospheric CO{sub 2} level, because it indirectly influences the stratospheric water mixing ratio. If the CO{sub 2} mixing ratio of dry planets at the inner edge is smaller than 10{sup –4}, the water loss timescale is ∼1 billion years, which is considered here too short for life to evolve. We also show that the expected transmission spectra of hot desert worlds are similar to an Earth-like planet. Therefore, an instrument designed to identify biosignature gases in an Earth-like atmosphere can also identify similarly abundant gases in the atmospheres of dry planets. Our inner edge limit is closer to the host star than previous estimates. As a consequence, the occurrence rate of potentially habitable planets is larger than previously thought.

  7. Accounting planetary habitability using non standard conditions. Impact on the definition of Habitable Zone

    NASA Astrophysics Data System (ADS)

    Simoncini, E.; Delgado-Bonal, A.; Martin-Torres, F. J.

    2012-12-01

    Although during the 1960s, atmospheric disequilibrium has been proposed as a sign of habitability of Earth and, in general, of a planet [1, 2], no calculation has been done until now. In order to provide a first evaluation of Earth's atmospheric disequilibrium, we have developed a new formulation to account for the thermodynamic conditions of a wide range of planetary atmospheres, from terrestrial planets to icy satellites, to hot exoplanets. Using this new formulation, we estimate the departure of different planetary atmospheres from their equilibrium conditions, computing the dissipation of free energy due to all chemical processes [3]. In particular, we focus on the effect of our proposed changes on O2/CO2 chemistry (comparing Io satellite atmosphere and Earth Mesosphere), N2 (Venus, Earth and Titan) and H2O stability on terrestrial planets and exoplanets. Our results have an impact in the definition of Habitable Zone by considering appropriate physical-chemical conditions of planetary atmospheres. References [1] J. E. Lovelock, A physical basis for life detection experiments. Nature, 207, 568-570 (1965). [2] J. E. Lovelock, Thermodynamics and the recognition of alien biospheres. Proc. R. Soc. Lond., B. 189, 167 - 181 (1975). [3] Simoncini E., Delgado-Bonal A., Martin-Torres F.J., Accounting thermodynamic conditions in chemical models of planetary atmospheres. Submitted to Astrophysical Journal.

  8. Habitable Zones of Post-Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Ramirez, Ramses M.; Kaltenegger, Lisa

    2016-05-01

    Once a star leaves the main sequence and becomes a red giant, its Habitable Zone (HZ) moves outward, promoting detectable habitable conditions at larger orbital distances. We use a one-dimensional radiative-convective climate and stellar evolutionary models to calculate post-MS HZ distances for a grid of stars from 3700 to 10,000 K (∼M1 to A5 stellar types) for different stellar metallicities. The post-MS HZ limits are comparable to the distances of known directly imaged planets. We model the stellar as well as planetary atmospheric mass loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases for super-Moons to super-Earths. A planet can stay between 200 million years up to 9 Gyr in the post-MS HZ for our hottest and coldest grid stars, respectively, assuming solar metallicity. These numbers increase for increased stellar metallicity. Total atmospheric erosion only occurs for planets in close-in orbits. The post-MS HZ orbital distances are within detection capabilities of direct imaging techniques.

  9. The first Earth-sized habitable zone exoplanets

    NASA Astrophysics Data System (ADS)

    Barclay, T.; Quintana, E.

    2014-03-01

    The goal of the Kepler mission is the discovery of Earth-sized planets orbiting within the habitable zone (HZ) of their host star. Most HZ planets found to date are gas giants, but a few such as Kepler-62f are potentially rocky despite being larger than Earth. Here we report on the progress being made to identify transiting planets in Kepler data that are truly Earth-sized and unambiguously terrestrial in nature. We consider the structure of the identified systems and deduce likely formation scenarios. We consider whether water delivery to these planets is probable or even possible. The discovery of the first Earth-like planets will be a milestone on the road toward the finding life outside our solar system.

  10. ABIOTIC OXYGEN-DOMINATED ATMOSPHERES ON TERRESTRIAL HABITABLE ZONE PLANETS

    SciTech Connect

    Wordsworth, Robin; Pierrehumbert, Raymond

    2014-04-20

    Detection of life on other planets requires identification of biosignatures, i.e., observable planetary properties that robustly indicate the presence of a biosphere. One of the most widely accepted biosignatures for an Earth-like planet is an atmosphere where oxygen is a major constituent. Here we show that lifeless habitable zone terrestrial planets around any star type may develop oxygen-dominated atmospheres as a result of water photolysis, because the cold trap mechanism that protects H{sub 2}O on Earth is ineffective when the atmospheric inventory of non-condensing gases (e.g., N{sub 2}, Ar) is low. Hence the spectral features of O{sub 2} and O{sub 3} alone cannot be regarded as robust signs of extraterrestrial life.

  11. ON THE HABITABLE ZONES OF CIRCUMBINARY PLANETARY SYSTEMS

    SciTech Connect

    Kane, Stephen R.; Hinkel, Natalie R.

    2013-01-01

    The effect of the stellar flux on exoplanetary systems is becoming an increasingly important property as more planets are discovered in the habitable zone (HZ). The Kepler mission has recently uncovered circumbinary planets with relatively complex HZs due to the combined flux from the binary host stars. Here, we derive HZ boundaries for circumbinary systems and show their dependence on the stellar masses, separation, and time while accounting for binary orbital motion and the orbit of the planet. We include stability regimes for planetary orbits in binary systems with respect to the HZ. These methods are applied to several of the known circumbinary planetary systems such as Kepler-16, 34, 35, and 47. We also quantitatively show the circumstances under which single-star approximations break down for HZ calculations.

  12. The Catalog of Earth-Like Exoplanet Survey Targets (CELESTA): A Database of Habitable Zones Around Nearby Stars

    NASA Astrophysics Data System (ADS)

    Chandler, Colin Orion; McDonald, Iain; Kane, Stephen R.

    2016-03-01

    Locating planets in circumstellar habitable zones (HZs) is a priority for many exoplanet surveys. Space-based and ground-based surveys alike require robust toolsets to aid in target selection and mission planning. We present the Catalog of Earth-Like Exoplanet Survey Targets (CELESTA), a database of HZs around 37,000 nearby stars. We calculated stellar parameters, including effective temperatures, masses, and radii, and we quantified the orbital distances and periods corresponding to the circumstellar HZs. We gauged the accuracy of our predictions by contrasting CELESTA’s computed parameters to observational data. We ascertain a potential return on investment by computing the number of HZs probed for a given survey duration. A versatile framework for extending the functionality of CELESTA into the future enables ongoing comparisons to new observations, and recalculations when updates to HZ models, stellar temperatures, or parallax data become available. We expect to upgrade and expand CELESTA using data from the Gaia mission as the data become available.

  13. Tidal Constraints on Planetary Habitability

    NASA Astrophysics Data System (ADS)

    Barnes, R.; Jackson, B.; Greenberg, R.; Raymond, S. N.; Heller, R.

    2010-10-01

    We review how tides may impact the habitability of terrestrial-like planets. If such planets form around low-mass stars, then planets in the circumstellar habitable zone will be close enough to their host stars to experience strong tidal forces. We discuss 1) decay of semi-major axis, 2) circularization of eccentric orbits, 3) evolution toward zero obliquity, 4) fixed rotation rates (not necessarily synchronous), and 5) internal heating. We briefly describe these effects using the example of a 0.25 Msun star with a 10 Mearth companion. We suggest that the concept of a habitable zone should be modified to include the effects of tides.

  14. Stabilizing Cloud Feedback Dramatically Expands the Habitable Zone of Tidally Locked Planets

    NASA Astrophysics Data System (ADS)

    Abbot, D. S.; Yang, J.; Cowan, N. B.

    2013-12-01

    The Habitable Zone (HZ) is the circumstellar region where a planet can sustain surface liquid water. Searching for terrestrial planets in the HZ of nearby stars is the stated goal of ongoing and planned extrasolar planet surveys. Previous estimates of the inner edge of the HZ were based on one dimensional radiative-convective models. The most serious limitation of these models is the inability to predict cloud behavior. Here we use global climate models with sophisticated cloud schemes to show that due to a stabilizing cloud feedback, tidally locked planets can be habitable at twice the stellar flux found by previous studies. This dramatically expands the HZ and roughly doubles the frequency of habitable planets orbiting red dwarf stars. At high stellar flux, strong convection produces thick water clouds near the substellar location that greatly increase the planetary albedo and reduce surface temperatures. Higher insolation produces stronger substellar convection and therefore higher albedo, making this phenomenon a stabilizing climate feedback. Substellar clouds also effectively block outgoing radiation from the surface, reducing or even completely reversing the thermal emission contrast between dayside and nightside. The presence of substellar water clouds and the resulting clement surface conditions will therefore be detectable with the James Webb Space Telescope. Climates of tidally locked and non-tidally locked terrestrial planets. (a) global-mean surface temperature (K), (b) stratospheric H2O volume mixing ratio at the substellar point, (c) planetary albedo and (d) global-mean greenhouse effect (K). The upper horizontal axis is the corresponding semimajor axis between an M-star with 2.3% solar luminosity and the planet. 1:1 denotes a tidally locked state, and 2:1 and 6:1 denote 2 or 6 rotations per orbit, respectively. For "no cloud" cases, all clouds are set to zero. The stellar spectrum is for an M-star or a K-star. Results for HD85512b are represented by a pentagram. The gray area denotes the HZ around an M-star with an inner edge of ~1200 W/m2 and an outer edge of ~270 W/m2 (not shown), obtained in a 1D model without clouds (Kopparapu et al., 2013).

  15. Kepler Mission: Detecting Earth-sized Planets in Habitable Zones

    NASA Technical Reports Server (NTRS)

    Kondo, Yoji; Fisher, Richard R. (Technical Monitor)

    2001-01-01

    The Kepler Mission, which is presently in Phase A, is being proposed for launch in 5 years for a 4-year mission to determine the frequency of Earth-sized or larger planets in habitable zones in our galaxy. Kepler will be placed in an Earth-trailing orbit to provide stable physical environments for the sensitive scientific instruments. The satellite is equipped with a photometric system with the precision of 10E-5, which should be sufficient for detecting the transits of Earth-sized or larger planets in front of dwarf stars similar to the Sun. Approximately 100,000 or more sun-like stars brighter than the 14th apparently magnitude will be monitored continuously for 4 years in a preselected region of the sky, which is about 100 square degrees in size. In addition, Kepler will have a participating scientist program that will enable research in intrinsic variable stars, interacting binaries including cataclysmic stars and X-ray binaries, and a large number of solar analogs in our galaxy. Several ten thousand additional stars may be investigated in the guest observer program open to the whole world.

  16. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: NEW ESTIMATES

    SciTech Connect

    Kopparapu, Ravi Kumar; Ramirez, Ramses; Kasting, James F.; Eymet, Vincent; Robinson, Tyler D.; Domagal-Goldman, Shawn; Meadows, Victoria; Mahadevan, Suvrath; Terrien, Ryan C.; Deshpande, Rohit

    2013-03-10

    Identifying terrestrial planets in the habitable zones (HZs) of other stars is one of the primary goals of ongoing radial velocity (RV) and transit exoplanet surveys and proposed future space missions. Most current estimates of the boundaries of the HZ are based on one-dimensional (1D), cloud-free, climate model calculations by Kasting et al. However, this model used band models that were based on older HITRAN and HITEMP line-by-line databases. The inner edge of the HZ in the Kasting et al. model was determined by loss of water, and the outer edge was determined by the maximum greenhouse provided by a CO{sub 2} atmosphere. A conservative estimate for the width of the HZ from this model in our solar system is 0.95-1.67 AU. Here an updated 1D radiative-convective, cloud-free climate model is used to obtain new estimates for HZ widths around F, G, K, and M stars. New H{sub 2}O and CO{sub 2} absorption coefficients, derived from the HITRAN 2008 and HITEMP 2010 line-by-line databases, are important improvements to the climate model. According to the new model, the water-loss (inner HZ) and maximum greenhouse (outer HZ) limits for our solar system are at 0.99 and 1.70 AU, respectively, suggesting that the present Earth lies near the inner edge. Additional calculations are performed for stars with effective temperatures between 2600 and 7200 K, and the results are presented in parametric form, making them easy to apply to actual stars. The new model indicates that, near the inner edge of the HZ, there is no clear distinction between runaway greenhouse and water-loss limits for stars with T{sub eff} {approx}< 5000 K, which has implications for ongoing planet searches around K and M stars. To assess the potential habitability of extrasolar terrestrial planets, we propose using stellar flux incident on a planet rather than equilibrium temperature. This removes the dependence on planetary (Bond) albedo, which varies depending on the host star's spectral type. We suggest that conservative estimates of the HZ (water-loss and maximum greenhouse limits) should be used for current RV surveys and Kepler mission to obtain a lower limit on {eta}{sub Circled-Plus }, so that future flagship missions like TPF-C and Darwin are not undersized. Our model does not include the radiative effects of clouds; thus, the actual HZ boundaries may extend further in both directions than the estimates just given.

  17. Terrestrial, Habitable-zone Exoplanet Frequency from Kepler

    NASA Astrophysics Data System (ADS)

    Traub, Wesley A.

    2012-01-01

    Data from Kepler's first 136 days of operation are analyzed to determine the distribution of exoplanets with respect to radius, period, and host-star spectral type. The analysis is extrapolated to estimate the percentage of terrestrial, habitable-zone (HZ) exoplanets. The Kepler census is assumed to be complete for bright stars (magnitude <14.0) having transiting planets >0.5 Earth radius and periods <42 days. It is also assumed that the size distribution of planets is independent of orbital period and that there are no hidden biases in the data. Six significant statistical results are found: there is a paucity of small planet detections around faint target stars, probably an instrumental effect; the frequency of mid-size planet detections is independent of whether the host star is bright or faint; there are significantly fewer planets detected with periods <3 days, compared to longer periods, almost certainly an astrophysical effect; the frequency of all planets in the population with periods <42 days is 29%, broken down as terrestrials 9%, ice giants 18%, and gas giants 3%; the population has a planet frequency with respect to period which follows a power-law relation dN/dP ~ P β - 1, with β ~= 0.71 ± 0.08; and an extrapolation to longer periods gives the frequency of terrestrial planets in the HZs of FGK stars as η⊕ ~= (34 ± 14)%. Thus about one-third of FGK stars are predicted to have at least one terrestrial, HZ planet.

  18. TERRESTRIAL, HABITABLE-ZONE EXOPLANET FREQUENCY FROM KEPLER

    SciTech Connect

    Traub, Wesley A.

    2012-01-20

    Data from Kepler's first 136 days of operation are analyzed to determine the distribution of exoplanets with respect to radius, period, and host-star spectral type. The analysis is extrapolated to estimate the percentage of terrestrial, habitable-zone (HZ) exoplanets. The Kepler census is assumed to be complete for bright stars (magnitude <14.0) having transiting planets >0.5 Earth radius and periods <42 days. It is also assumed that the size distribution of planets is independent of orbital period and that there are no hidden biases in the data. Six significant statistical results are found: there is a paucity of small planet detections around faint target stars, probably an instrumental effect; the frequency of mid-size planet detections is independent of whether the host star is bright or faint; there are significantly fewer planets detected with periods <3 days, compared to longer periods, almost certainly an astrophysical effect; the frequency of all planets in the population with periods <42 days is 29%, broken down as terrestrials 9%, ice giants 18%, and gas giants 3%; the population has a planet frequency with respect to period which follows a power-law relation dN/dP {approx} P{sup {beta}-1}, with {beta} {approx_equal} 0.71 {+-} 0.08; and an extrapolation to longer periods gives the frequency of terrestrial planets in the HZs of FGK stars as {eta}{sub Circled-Plus} {approx_equal} (34 {+-} 14)%. Thus about one-third of FGK stars are predicted to have at least one terrestrial, HZ planet.

  19. Direct Imaging of Extrasolar Giant Planets in the Habitable Zone

    NASA Astrophysics Data System (ADS)

    Males, J. R.; Close, L. M.; Guyon, O.; Barman, T. S.

    2014-03-01

    Young extrasolar giant planets (EGPs) are initially very luminous as they radiate away gravitational potential energy from formation (Burrows et al., 2001), but they rapidly cool and after a few tens of MYr (depending on mass) are essentially undetectable with typical direct imaging capabilities. Ground-based direct imaging is limited by adaptive optics (AO) performance. As a result of these restrictions direct imaging searches for EGPs have mainly focused on young stars (<~100 MYr) and wide orbital separations (>~10 AU). As AO performance improves we will begin searching for EGPs at much closer separations. Stellar irradiation sets the minimum temperature of a planet atmosphere (depending on albedo), regardless of mass and age. At wide separations this minimum temperature is too low to maintain planet brightness, but closer to the star this minimum temperature is much higher. Furthermore, old EGPs are all roughly the same radius regardless of mass (Fortney et al., 2007). Taken together, these arguments mean that in the habitable zone (HZ) minimum EGP luminosity (proportional to R2T4) is nearly independent of mass and age. We show that this has exciting implications for the thermal-infrared (IR) detectability of EGPs in the HZs of older stars. Similar arguments apply to visible wavelengths as well: in the HZ water clouds significantly increase geometric albedo making EGPs very bright in reflected light. The high performance of second generation adaptive secondary AO systems, employed at the LBT and Magellan, has allowed us to begin searching for EGPs in the HZs of nearby bright stars with current telescopes. The coming generation of giant telescopes will allow us to expand this search to many more stars. Here we present detailed calculations of EGP detectability in the HZ in both the thermal IR and in reflected visible light, describe our observing strategy, and present preliminary results of our search. We also discuss the future of direct imaging in the HZ with giant telescoes.

  20. NASA's Kepler Discovers Its Smallest 'Habitable Zone' Planets to Date - Duration: 2 minutes, 27 seconds.

    NASA Video Gallery

    NASA's Kepler mission has discovered two new planetary systems that include three super-Earth-size planets in the "habitable zone," the range of distance from a star where the surface temperature o...

  1. Astronomers Find First Earth-like Planet in Habitable Zone

    NASA Astrophysics Data System (ADS)

    2007-04-01

    Astronomers have discovered the most Earth-like planet outside our Solar System to date, an exoplanet with a radius only 50% larger than the Earth and capable of having liquid water. Using the ESO 3.6-m telescope, a team of Swiss, French and Portuguese scientists discovered a super-Earth about 5 times the mass of the Earth that orbits a red dwarf, already known to harbour a Neptune-mass planet. The astronomers have also strong evidence for the presence of a third planet with a mass about 8 Earth masses. ESO PR Photo 22a/07 ESO PR Photo 22a/07 The Planetary System Around Gliese 581 This exoplanet - as astronomers call planets around a star other than the Sun - is the smallest ever found up to now [1] and it completes a full orbit in 13 days. It is 14 times closer to its star than the Earth is from the Sun. However, given that its host star, the red dwarf Gliese 581 [2], is smaller and colder than the Sun - and thus less luminous - the planet nevertheless lies in the habitable zone, the region around a star where water could be liquid! The planet's name is Gliese 581 c. "We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid," explains Stéphane Udry, from the Geneva Observatory (Switzerland) and lead-author of the paper reporting the result. "Moreover, its radius should be only 1.5 times the Earth's radius, and models predict that the planet should be either rocky - like our Earth - or fully covered with oceans," he adds. ESO PR Photo 22c/07 ESO PR Photo 22c/07 The star Gliese 581 "Liquid water is critical to life as we know it," avows Xavier Delfosse, a member of the team from Grenoble University (France). "Because of its temperature and relative proximity, this planet will most probably be a very important target of the future space missions dedicated to the search for extra-terrestrial life. On the treasure map of the Universe, one would be tempted to mark this planet with an X." The host star, Gliese 581, is among the 100 closest stars to us, located only 20.5 light-years away in the constellation Libra ("the Scales"). It has a mass of only one third the mass of the Sun. Such red dwarfs are intrinsically at least 50 times fainter than the Sun and are the most common stars in our Galaxy: among the 100 closest stars to the Sun, 80 belong to this class. "Red dwarfs are ideal targets for the search for low-mass planets where water could be liquid. Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun," emphasizes Xavier Bonfils, a co-worker from Lisbon University. Planets lying in this zone are then more easily detected with the radial-velocity method [3], the most successful in detecting exoplanets. ESO PR Photo 22d/07 ESO PR Photo 22d/07 Velocity Variations of Gl 581 Two years ago, the same team of astronomers already found a planet around Gliese 581 (see ESO 30/05). With a mass of 15 Earth-masses, i.e. similar to that of Neptune, it orbits its host star in 5.4 days. At the time, the astronomers had already seen hints of another planet. They therefore obtained a new set of measurements and found the new super-Earth, but also clear indications for another one, an 8 Earth-mass planet completing an orbit in 84 days. The planetary system surrounding Gliese 581 contains thus no fewer than 3 planets of 15 Earth masses or less, and as such is a quite remarkable system. The discovery was made thanks to HARPS (High Accuracy Radial Velocity for Planetary Searcher), perhaps the most precise spectrograph in the world. Located on the ESO 3.6-m telescope at La Silla, Chile, HARPS is able to measure velocities with a precision better than one metre per second (or 3.6 km/h)! HARPS is one of the most successful instruments for detecting exoplanets and holds already several recent records, including the discovery of another 'Trio of Neptunes' (ESO 18/06, see also ESO 22/04). ESO PR Video 22/07 ESO PR Video 22/07 Watch the video! The detected velocity variations are between 2 and 3 metres per second, corresponding to about 9 km/h! That's the speed of a person walking briskly. Such tiny signals could not have been distinguished from 'simple noise' by most of today's available spectrographs. "HARPS is a unique planet hunting machine," says Michel Mayor, from Geneva Observatory, and HARPS Principal Investigator. "Given the incredible precision of HARPS, we have focused our effort on low-mass planets. And we can say without doubt that HARPS has been very successful: out of the 13 known planets with a mass below 20 Earth masses, 11 were discovered with HARPS!" HARPS is also very efficient in finding planetary systems, where tiny signals have to be uncovered. The two systems known to have three low mass planets - HD 69830 and Gl 581 - were discovered by HARPS. "And we are confident that, given the results obtained so far, finding a planet with the mass of the Earth around a red dwarf is within reach," affirms Mayor.

  2. Planetary Atmosphere Stability in the Habitable Zones of M-stars

    NASA Astrophysics Data System (ADS)

    Tian, Feng

    2010-10-01

    The traditional habitable zone depends on conditions suitable for long term stability of liquid water on the surface of planets. It is suggested that the frequent intense stellar CME events could have led to so rapid erosion of planetary atmospheres that generally speaking there is essentially no habitable zones around Earth-mass planets around M-stars. However, fast atmosperic mass loss should put the planetary atmosphere in the hydrodynamic, in which the energy consumption by the outflow could have limited the atmospheric loss and make a CO2-dominant planetary atmosphere stable in the habitable zones of M-stars. In this work we will explore the atmosphere stability of broad range of habitable planets with different mass and atmospheric composition.

  3. Astrophysical, Geochemical, Geophysical and Biological Limits on Planet Habitability

    NASA Astrophysics Data System (ADS)

    Lineweaver, C.

    2014-03-01

    For life forms like us, the most important feature of the Earth is its habitability. Understanding habitability and using that knowledge to locate the nearest habitable planet may be crucial for our survival as a species. Over the past decade, expectations that the universe could be filled with habitable planets have been bolstered by the increasingly large overlap between terrestrial environments known to harbor life and the variety of environments on newly detected rocky exoplanets. The inhabited and uninhabited regions on Earth tell us that temperature and the presence of water are the main constraints that can be used in a habitability classification scheme for rocky planets. Our compilation and review of recent exoplanet detections suggests that the fraction of stars with planets is ~ 100%, and that the fraction with rocky planets may be comparably large. We review extensions to the circumstellar habitable zone including an abiogenesis habitable zone and the galactic habitable zone.

  4. The Habitability of Our Earth and Other Earths: Astrophysical, Geochemical, Geophysical, and Biological Limits on Planet Habitability

    NASA Astrophysics Data System (ADS)

    Lineweaver, Charles H.; Chopra, Aditya

    2012-05-01

    For life-forms like us, the most important feature of Earth is its habitability. Understanding habitability and using that knowledge to locate the nearest habitable planet may be crucial for our survival as a species. During the past decade, expectations that the universe could be filled with habitable planets have been bolstered by the increasingly large overlap between terrestrial environments known to harbor life and the variety of environments on newly detected rocky exoplanets. The inhabited and uninhabited regions on Earth tell us that temperature and the presence of water are the main constraints that can be used in a habitability classification scheme for rocky planets. Our compilation and review of recent exoplanet detections suggests that the fraction of stars with planets is ˜100%, and that the fraction with rocky planets may be comparably large. We review extensions to the circumstellar habitable zone (HZ), including an abiogenesis habitable zone and the galactic habitable zone.

  5. Moon Radius Limits for a Habitable Zone Kepler Transiting Planet Candidate

    NASA Astrophysics Data System (ADS)

    Lewis, K.

    2014-04-01

    In addition to planets being potentially habitable bodies, moons, both inside and beyond the habitable zones of their host star may also be suitable sites for life. One promising method to detect such habitable moons is the through the transit technique, in particular using the high quality, long baseline Kepler dataset. Planets in the habitable zone of Sun-like stars tend to have long orbital periods and thus exhibit few transits within the 3.5 year Kepler mission. In addition, candidate planets are more likely to be confirmed if they are in multiple systems where planetary perturbations may make moon detection through transit timing very challenging. As a result we focus on the direct detection moon technique first described by Sartoretti and Schneider (1999), which involves searching and fitting the extra dip due to a moon in each transit light curve directly. To test this method in the presence of realistic photometric noise, we developed a Kepler light curve simulator that generates noisy light curves corresponding to physically consistent planet-moon systems. Using this program we calculate sets of unique light curve realisations for a Kepler candidate (KOI3681.01) in the habitable zone of a Sun-like star, for a grid of physically realistic moon radii and semi-major axes, and process them using our detection code. This allows us to robustly place constraints on potentially habitable terrestrial moons thus demonstrating the power of this approach.

  6. Hazes at the Inner Edge of the Habitable Zone

    NASA Astrophysics Data System (ADS)

    Domagal-Goldman, S. D.; Robinson, T. D.; Haqq-Misra, J.

    2009-12-01

    The “insolation habitable zone” (IHZ) is the region around a star where the incoming solar radiation, combined with the forcings from the planet’s atmosphere, can keep liquid water stable at the surface of the planet. Historically, studies that consider the forcings from the planet have primarily focused on the greenhouse effect of the planet’s atmosphere. To remain habitable, planets at the inner edge of the IHZ would require small greenhouse effects and planets at the outer edge would require significantly larger ones. These greenhouse forcings would be part of stabilizing feedbacks such as the carbonate-silicate feedback on CO2 or biological feedbacks on CH4. In addition to the greenhouse effect, which interacts with outgoing infrared radiation, a planet’s atmosphere can also control surface temperatures by interacting with incoming UV or visible radiation. Hazes can do this by increasing the reflectivity of the planet via scattering of incoming stellar radiation or by imparting an "anti-greenhouse effect" that absorbs incoming stellar radiation. Either of these effects would decrease the energy reaching the surface and lead to lower surface temperatures. These lower surface temperatures would allow a planet to lie closer to the parent star without losing its oceans, all else being equal. In this presentation, we will consider the effects of global hazes on the inner edge of the IHZ. We will show results from 1-D photochemistry and climate simulations that include forcings from both greenhouse gases and hazes Finally, we will include a discussion on feedback cycles that may be able to stabilize planetary systems at a point where the surface is habitable despite relatively high energy deposition at the top of the atmosphere. These results will have implications for not just planet characterization missions but also for near-term searches for “Earth-like” planets, as some of the planets we will discover that would otherwise be considered too hot for life may indeed be hospitable.

  7. EXPLORING THE HABITABLE ZONE FOR KEPLER PLANETARY CANDIDATES

    SciTech Connect

    Kaltenegger, L.; Sasselov, D.

    2011-08-01

    This Letter outlines a simple approach to evaluate habitability of terrestrial planets by assuming different types of planetary atmospheres and using corresponding model calculations. Our approach can be applied for current and future candidates provided by the Kepler mission and other searches. The resulting uncertainties and changes in the number of planetary candidates in the HZ for the Kepler 2011 February data release are discussed. To first order, the HZ depends on the effective stellar flux distribution in wavelength and time, the planet albedo, and greenhouse gas effects. We provide a simple set of parameters which can be used for evaluating future planet candidates from transit searches.

  8. INDICATION OF INSENSITIVITY OF PLANETARY WEATHERING BEHAVIOR AND HABITABLE ZONE TO SURFACE LAND FRACTION

    SciTech Connect

    Abbot, Dorian S.; Ciesla, Fred J.; Cowan, Nicolas B.

    2012-09-10

    It is likely that unambiguous habitable zone terrestrial planets of unknown water content will soon be discovered. Water content helps determine surface land fraction, which influences planetary weathering behavior. This is important because the silicate-weathering feedback determines the width of the habitable zone in space and time. Here a low-order model of weathering and climate, useful for gaining qualitative understanding, is developed to examine climate evolution for planets of various land-ocean fractions. It is pointed out that, if seafloor weathering does not depend directly on surface temperature, there can be no weathering-climate feedback on a waterworld. This would dramatically narrow the habitable zone of a waterworld. Results from our model indicate that weathering behavior does not depend strongly on land fraction for partially ocean-covered planets. This is powerful because it suggests that previous habitable zone theory is robust to changes in land fraction, as long as there is some land. Finally, a mechanism is proposed for a waterworld to prevent complete water loss during a moist greenhouse through rapid weathering of exposed continents. This process is named a 'waterworld self-arrest', and it implies that waterworlds can go through a moist greenhouse stage and end up as planets like Earth with partial ocean coverage. This work stresses the importance of surface and geologic effects, in addition to the usual incident stellar flux, for habitability.

  9. Indication of Insensitivity of Planetary Weathering Behavior and Habitable Zone to Surface Land Fraction

    NASA Astrophysics Data System (ADS)

    Abbot, Dorian S.; Cowan, Nicolas B.; Ciesla, Fred J.

    2012-09-01

    It is likely that unambiguous habitable zone terrestrial planets of unknown water content will soon be discovered. Water content helps determine surface land fraction, which influences planetary weathering behavior. This is important because the silicate-weathering feedback determines the width of the habitable zone in space and time. Here a low-order model of weathering and climate, useful for gaining qualitative understanding, is developed to examine climate evolution for planets of various land-ocean fractions. It is pointed out that, if seafloor weathering does not depend directly on surface temperature, there can be no weathering-climate feedback on a waterworld. This would dramatically narrow the habitable zone of a waterworld. Results from our model indicate that weathering behavior does not depend strongly on land fraction for partially ocean-covered planets. This is powerful because it suggests that previous habitable zone theory is robust to changes in land fraction, as long as there is some land. Finally, a mechanism is proposed for a waterworld to prevent complete water loss during a moist greenhouse through rapid weathering of exposed continents. This process is named a "waterworld self-arrest," and it implies that waterworlds can go through a moist greenhouse stage and end up as planets like Earth with partial ocean coverage. This work stresses the importance of surface and geologic effects, in addition to the usual incident stellar flux, for habitability.

  10. A Method for Coupling Dynamical and Collisional Evolution of Dust in Circumstellar Disks: The Effect of a Dead Zone

    NASA Astrophysics Data System (ADS)

    Charnoz, Sbastien; Taillifet, Esther

    2012-07-01

    Dust is a major component of protoplanetary and debris disks as it is the main observable signature of planetary formation. However, since dust dynamics are size-dependent (because of gas drag or radiation pressure) any attempt to understand the full dynamical evolution of circumstellar dusty disks that neglect the coupling of collisional evolution with dynamical evolution is thwarted because of the feedback between these two processes. Here, a new hybrid Lagrangian/Eulerian code is presented that overcomes some of these difficulties. The particles representing "dust clouds" are tracked individually in a Lagrangian way. This system is then mapped on an Eulerian spatial grid, inside the cells of which the local collisional evolutions are computed. Finally, the system is remapped back in a collection of discrete Lagrangian particles, keeping their number constant. An application example of dust growth in a turbulent protoplanetary disk at 1 AU is presented. First, the growth of dust is considered in the absence of a dead zone and the vertical distribution of dust is self-consistently computed. It is found that the mass is rapidly dominated by particles about a fraction of a millimeter in size. Then the same case with an embedded dead zone is investigated and it is found that coagulation is much more efficient and produces, in a short timescale, 1-10 cm dust pebbles that dominate the mass. These pebbles may then be accumulated into embryo-sized objects inside large-scale turbulent structures as shown recently.

  11. A METHOD FOR COUPLING DYNAMICAL AND COLLISIONAL EVOLUTION OF DUST IN CIRCUMSTELLAR DISKS: THE EFFECT OF A DEAD ZONE

    SciTech Connect

    Charnoz, Sebastien; Taillifet, Esther

    2012-07-10

    Dust is a major component of protoplanetary and debris disks as it is the main observable signature of planetary formation. However, since dust dynamics are size-dependent (because of gas drag or radiation pressure) any attempt to understand the full dynamical evolution of circumstellar dusty disks that neglect the coupling of collisional evolution with dynamical evolution is thwarted because of the feedback between these two processes. Here, a new hybrid Lagrangian/Eulerian code is presented that overcomes some of these difficulties. The particles representing 'dust clouds' are tracked individually in a Lagrangian way. This system is then mapped on an Eulerian spatial grid, inside the cells of which the local collisional evolutions are computed. Finally, the system is remapped back in a collection of discrete Lagrangian particles, keeping their number constant. An application example of dust growth in a turbulent protoplanetary disk at 1 AU is presented. First, the growth of dust is considered in the absence of a dead zone and the vertical distribution of dust is self-consistently computed. It is found that the mass is rapidly dominated by particles about a fraction of a millimeter in size. Then the same case with an embedded dead zone is investigated and it is found that coagulation is much more efficient and produces, in a short timescale, 1-10 cm dust pebbles that dominate the mass. These pebbles may then be accumulated into embryo-sized objects inside large-scale turbulent structures as shown recently.

  12. 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 497.7451 (2013): 607-610.

  13. Habitable evaporated cores: transforming mini-Neptunes into super-Earths in the habitable zones of M dwarfs.

    PubMed

    Luger, R; Barnes, R; Lopez, E; Fortney, J; Jackson, B; Meadows, V

    2015-01-01

    We show that photoevaporation of small gaseous exoplanets ("mini-Neptunes") in the habitable zones of M dwarfs can remove several Earth masses of hydrogen and helium from these planets and transform them into potentially habitable worlds. We couple X-ray/extreme ultraviolet (XUV)-driven escape, thermal evolution, tidal evolution, and orbital migration to explore the types of systems that may harbor such "habitable evaporated cores" (HECs). We find that HECs are most likely to form from planets with ∼1 M⊕ solid cores with up to about 50% H/He by mass, though whether or not a given mini-Neptune forms a HEC is highly dependent on the early XUV evolution of the host star. As terrestrial planet formation around M dwarfs by accumulation of local material is likely to form planets that are small and dry, evaporation of small migrating mini-Neptunes could be one of the dominant formation mechanisms for volatile-rich Earths around these stars. PMID:25590532

  14. Observations of exoplanets in time-evolving habitable zones of pre-main-sequence M dwarfs

    NASA Astrophysics Data System (ADS)

    Tian, Feng

    2015-09-01

    It is recently proposed that planets in the habitable zones (HZ) of pre-main-sequence (PMS) M dwarfs are good targets for the detection of habitable environments. In this note we show that future ground-based telescopes will be able to observe planets in time-evolving HZ of PMS M dwarfs with duration 10-100 Myrs. Based on X-ray measurements, there are >18 M0-M4 PMS stars within 10 pc, the characterization of potentially habitable exoplanets around which could provide highly valuable information regarding the evolution of habitable environments. There are tens of M dwarfs within 10 pc with X-ray to total luminosity ratios similar to that of the young Sun, the observations of potential planets around which could significantly improve our understanding of the physical states of early Solar System rocky planets.

  15. THERMAL ESCAPE FROM SUPER EARTH ATMOSPHERES IN THE HABITABLE ZONES OF M STARS

    SciTech Connect

    Tian Feng

    2009-09-20

    A fundamental question for exoplanet habitability is the long-term stability of the planet's atmosphere. We numerically solve a one-dimensional multi-component hydrodynamic thermosphere/ionosphere model to examine the thermal and chemical responses of the primary CO{sub 2} atmospheres of heavy super Earths (6-10 Earth masses) in the habitable zones of typical low-mass M stars to the enhanced soft X-ray and ultraviolet (XUV) fluxes associated with the prolonged high-activity levels of M stars. The results show that such atmospheres are stable against thermal escape, even for M stars XUV enhancements as large as 1000 compared to the present Earth. It is possible that the CO{sub 2}-dominant atmospheres of super Earths in the habitable zones of M stars could potentially contain modest amount of free oxygen as a result of more efficient atmosphere escape of carbon than oxygen instead of photosynthesis.

  16. TERRESTRIAL PLANET FORMATION AROUND THE CIRCUMBINARY HABITABLE ZONE: INWARD MIGRATION IN THE PLANETESIMAL SWARM

    SciTech Connect

    Gong Yanxiang; Zhou Jilin; Xie Jiwei E-mail: zhoujl@nju.edu.cn

    2013-01-20

    According to the core accretion theory, circumbinary embryos can form only beyond a critical semimajor axis (CSMA). However, due to the relatively high density of solid materials in the inner disk, a significant amount of small planetesimals must exist in the inner zone when embryos form outside this CSMA. Thus, embryo migration induced by the planetesimal swarm is possible after gas disk depletion. Through numerical simulations, we found that (1) the scattering-driven inward migration of embryos is robust and planets can form in the habitable zone if we adopt a mass distribution of an MMSN-like disk; (2) the total mass of the planetesimals in the inner region and continuous embryo-embryo scattering are two key factors that cause significant embryo migrations; and (3) the scattering-driven migration of embryos is a natural water-delivery mechanism. We propose that planet detections should focus on the close binary with its habitable zone near CSMA.

  17. TRANSIT SURVEYS FOR EARTHS IN THE HABITABLE ZONES OF WHITE DWARFS

    SciTech Connect

    Agol, Eric

    2011-04-20

    To date the search for habitable Earth-like planets has primarily focused on nuclear burning stars. I propose that this search should be expanded to cool white dwarf stars that have expended their nuclear fuel. I define the continuously habitable zone of white dwarfs and show that it extends from {approx}0.005 to 0.02 AU for white dwarfs with masses from 0.4 to 0.9 M{sub sun}, temperatures less than {approx}10{sup 4} K, and habitable durations of at least 3 Gyr. As they are similar in size to Earth, white dwarfs may be deeply eclipsed by terrestrial planets that orbit edge-on, which can easily be detected with ground-based telescopes. If planets can migrate inward or reform near white dwarfs, I show that a global robotic telescope network could carry out a transit survey of nearby white dwarfs placing interesting constraints on the presence of habitable Earths. If planets were detected, I show that the survey would favor detection of planets similar to Earth: similar size, temperature, and rotation period, and host star temperatures similar to the Sun. The Large Synoptic Survey Telescope could place even tighter constraints on the frequency of habitable Earths around white dwarfs. The confirmation and characterization of these planets might be carried out with large ground and space telescopes.

  18. ASTROPHYSICAL PARAMETERS AND HABITABLE ZONE OF THE EXOPLANET HOSTING STAR GJ 581

    SciTech Connect

    Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David R.; Boyajian, Tabetha S.; McAlister, Harold A.; Henry, Todd J.; Jao, Wei-Chun; Riedel, Adric R.; Van Belle, Gerard T.; Lopez-Morales, Mercedes; Subasavage, John P.; Schaefer, Gail; Ten Brummelaar, Theo A.; Sturmann, Laszlo; Sturmann, Judit; Mazingue, Jude; Turner, Nils H.; Farrington, Chris; Goldfinger, P. J.; Ridgway, Stephen

    2011-03-10

    GJ 581 is an M dwarf host of a multiplanet system. We use long-baseline interferometric measurements from the CHARA Array, coupled with trigonometric parallax information, to directly determine its physical radius to be 0.299 {+-} 0.010 R{sub sun}. Literature photometry data are used to perform spectral energy distribution fitting in order to determine GJ 581's effective surface temperature T{sub EFF} = 3498 {+-} 56 K and its luminosity L = 0.01205 {+-} 0.00024 L{sub sun}. From these measurements, we recompute the location and extent of the system's habitable zone and conclude that two of the planets orbiting GJ 581, planets d and g, spend all or part of their orbit within or just on the edge of the habitable zone.

  19. Evolution of the habitable zone of low-mass stars. Detailed stellar models and analytical relationships for different masses and chemical compositions

    NASA Astrophysics Data System (ADS)

    Valle, G.; Dell'Omodarme, M.; Prada Moroni, P. G.; Degl'Innocenti, S.

    2014-07-01

    Context. The habitability of an exoplanet is assessed by determining the times at which its orbit lies in the circumstellar habitable zone (HZ). This zone evolves with time following the stellar luminosity variation, which means that the time spent in the HZ depends on the evolution of the host star. Aims: We study the temporal evolution of the HZ of low-mass stars - only due to stellar evolution - and evaluate the related uncertainties. These uncertainties are then compared with those due to the adoption of different climate models. Methods: We computed stellar evolutionary tracks from the pre-main sequence phase to the helium flash at the red-giant branch tip for stars with masses in the range [0.70-1.10] M⊙, metallicity Z in the range [0.005-0.04], and various initial helium contents. By adopting a reference scenario for the HZ computations, we evaluated several characteristics of the HZ, such as the distance from the host star at which the habitability is longest, the duration of this habitability, the width of the zone for which the habitability lasts one half of the maximum, and the boundaries of the continuously habitable zone (CHZ) for which the habitability lasts at least 4 Gyr. We developed analytical models, accurate to the percent level or lower, which allowed to obtain these characteristics in dependence on the mass and the chemical composition of the host star. Results: The metallicity of the host star plays a relevant role in determining the HZ. The importance of the initial helium content is evaluated here for the first time; it accounts for a variation of the CHZ boundaries as large as 30% and 10% in the inner and outer border. The computed analytical models allow the first systematic study of the variability of the CHZ boundaries that is caused by the uncertainty in the estimated values of mass and metallicity of the host star. An uncertainty range of about 30% in the inner boundary and 15% in the outer one were found. We also verified that these uncertainties are larger than that due to relying on recently revised climatic models, which leads to a CHZ boundary shift within ±5% with respect to those of our reference scenario. We made an on-line tool available that provides both HZ characteristics and interpolated stellar tracks. On-line habitable zone calculator and track interpolator are available at http://astro.df.unipi.it/stellar-models/HZ/. The C code is also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/567/A133

  20. THE HABITABLE ZONE OF EARTH-LIKE PLANETS WITH DIFFERENT LEVELS OF ATMOSPHERIC PRESSURE

    SciTech Connect

    Vladilo, Giovanni; Murante, Giuseppe; Silva, Laura; Provenzale, Antonello; Ferri, Gaia; Ragazzini, Gregorio

    2013-04-10

    As a contribution to the study of the habitability of extrasolar planets, we implemented a one-dimensional energy balance model (EBM), the simplest seasonal model of planetary climate, with new prescriptions for most physical quantities. Here we apply our EBM to investigate the surface habitability of planets with an Earth-like atmospheric composition but different levels of surface pressure. The habitability, defined as the mean fraction of the planet's surface on which liquid water could exist, is estimated from the pressure-dependent liquid water temperature range, taking into account seasonal and latitudinal variations of surface temperature. By running several thousands of EBM simulations we generated a map of the habitable zone (HZ) in the plane of the orbital semi-major axis, a, and surface pressure, p, for planets in circular orbits around a Sun-like star. As pressure increases, the HZ becomes broader, with an increase of 0.25 AU in its radial extent from p = 1/3 to 3 bar. At low pressure, the habitability is low and varies with a; at high pressure, the habitability is high and relatively constant inside the HZ. We interpret these results in terms of the pressure dependence of the greenhouse effect, the efficiency of horizontal heat transport, and the extent of the liquid water temperature range. Within the limits discussed in the paper, the results can be extended to planets in eccentric orbits around non-solar-type stars. The main characteristics of the pressure-dependent HZ are modestly affected by variations of planetary properties, particularly at high pressure.

  1. MOA-2011-BLG-293LB: First microlensing planet possibly in the habitable zone

    SciTech Connect

    Batista, V.; Gould, A.; Yee, J. C.; Gaudi, B. S.; Beaulieu, J.-P.; Bennett, D. P.; Fukui, A.; Sumi, T.; Udalski, A. E-mail: gould@astronomy.ohio-state.edu E-mail: beaulieu@iap.fr E-mail: afukui@oao.nao.ac.jp E-mail: udalski@astrouw.edu.pl

    2014-01-01

    We used Keck adaptive optics observations to identify the first planet discovered by microlensing to lie in or near the habitable zone, i.e., at projected separation r = 1.1 ± 0.1 AU from its M{sub L} = 0.86 ± 0.06 M {sub ☉} host, being the highest microlensing mass definitely identified. The planet has a mass m{sub p} = 4.8 ± 0.3 M {sub Jup}, and could in principle have habitable moons. This is also the first planet to be identified as being in the Galactic bulge with good confidence: D{sub L} = 7.72 ± 0.44 kpc. The planet/host masses and distance were previously not known, but only estimated using Bayesian priors based on a Galactic model. These estimates had suggested that the planet might be a super-Jupiter orbiting an M dwarf, a very rare class of planets. We obtained high-resolution JHK images using Keck adaptive optics to detect the lens and so test this hypothesis. We clearly detect light from a G dwarf at the position of the event, and exclude all interpretations other than that this is the lens with high confidence (95%), using a new astrometric technique. The calibrated magnitude of the planet host star is H{sub L} = 19.16 ± 0.13. We infer the following probabilities for the three possible orbital configurations of the gas giant planet: 53% to be in the habitable zone, 35% to be near the habitable zone, and 12% to be beyond the snow line, depending on the atmospherical conditions and the uncertainties on the semimajor axis.

  2. Atmospheres and Oceans of Rocky Planets In and Beyond the Habitable Zones of M dwarfs

    NASA Astrophysics Data System (ADS)

    Tian, Feng

    2015-12-01

    he evolution of M dwarfs during their pre-main-sequence phase causes rocky planets in and beyond the habitable zones these stars to be in the runaway and moist greenhouse states. This scenario has been studied by three groups of researchers recently (Ramirez and Kaltenegger 2014, Tian and Ida 2015, Luger and Barnes 2015), and their consensus is that massive amount of water could have been lost during this time -- early evolution of M dwarfs could have changed the water contents of rocky planets around them, which could strongly influence the habitability of rocky planets around low mass stars. It has been proposed that dense oxygen dominant atmospheres (up to 2000 bars, Luger and Barnes 2015) because of rapid water loss. Is this true? If so, what's the condition for such atmospheres to exist and can they be maintained? On the other hand, what's the likelihood for sub-Neptunes to shrink into habitable planets under such environment? In general how is the habitability of planets around M dwarfs different from those around Sun-type stars? These are the questions we will attempt to address in this work.

  3. Selections from 2015: Earth-Sized Planet Found in Star's Habitable Zone

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-03-01

    Editors Note:In these last two weeks of 2015, well be looking at a few selections from among the most-downloaded paperspublished in AAS journals this year. The usual posting schedule will resume after the AAS winter meeting.Discovery and Validation of Kepler-452b: a 1.6 R Super Earth Exoplanet in the Habitable Zone of a G2 StarPublished July2015Main takeaway:A phase-folded light curve showing the transit of Kepler-452b. Its transit lasts 10.5 hours, and its period is 385 days. [Jenkins et al. 2015]A team led by Jon Jenkins (NASA Ames Research Center) announced the discovery and confirmation of Kepler-452b, an exoplanet only 60% larger than Earth and located in the habitable zone of its G2 star. This planet orbits its star at a distance of just over 1 AU, taking 385 days to complete an orbit. Kepler-452b also stands a good chance of being rocky, according to estimates.Why its interesting:Kepler-452b is the first near-Earth-sized planet to be found in the habitable zone of a Sun-like star making this the closest analog to the Earth-Sun system found in the Kepler dataset so far.About the history of the system (and the future of ours?):The authors estimate that the system is ~6 billion years old, and that Kepler-452b has been in the habitable zone of its star throughout its lifetime a substantially longer time than Earth has been around and habitable! Kepler-452bs host star, in addition to being 1.5 billion years older than the Sun, is roughly 10% larger. This system might therefore provide a glimpse of what Earths environment may be like in the future, as the Sun slowly expands on its way to becoming a red giant.CitationJon M. Jenkins et al 2015 AJ 150 56. doi:10.1088/0004-6256/150/2/56

  4. Habitable zones exposed: astrosphere collapse frequency as a function of stellar mass.

    PubMed

    Smith, David S; Scalo, John M

    2009-09-01

    Stellar astrospheres--the plasma cocoons carved out of the interstellar medium by stellar winds--are one of several buffers that partially screen planetary atmospheres and surfaces from high-energy radiation. Screening by astrospheres is continually influenced by the passage of stars through the fluctuating density field of the interstellar medium (ISM). The most extreme events occur inside dense interstellar clouds, where the increased pressure may compress an astrosphere to a size smaller than the liquid-water habitable-zone distance. Habitable planets then enjoy no astrospheric buffering from exposure to the full flux of galactic cosmic rays and interstellar dust and gas, a situation we call "descreening" or "astrospheric collapse." Under such conditions the ionization fraction in the atmosphere and contribution to radiation damage of putative coding organisms at the surface would increase significantly, and a series of papers have suggested a variety of global responses to descreening. These possibilities motivate a more careful calculation of the frequency of descreening events. Using a ram-pressure balance model, we compute the size of the astrosphere in the apex direction as a function of parent-star mass and velocity and ambient interstellar density, emphasizing the importance of gravitational focusing of the interstellar flow. The interstellar densities required to descreen planets in the habitable zone of solar- and subsolar-mass stars are found to be about 600(M/M[middle dot in circle])(-2) cm(-3) for the Sun's velocity relative to the local ISM. Such clouds are rare and small, indicating that descreening encounters are rare. We use statistics from two independent catalogues of dense interstellar clouds to derive a dependence of descreening frequency on the parent-star mass that decreases strongly with decreasing stellar mass, due to the weaker gravitational focusing and smaller habitable-zone distances for lower-mass stars. We estimate an uncertain upper limit to the absolute frequency of descreening encounters as 1-10 Gyr(-1) for solar-type stars and 10(2) to 10(9) times smaller for stars between 0.5 and 0.1 M[middle dot in circle]. Habitable-zone planets orbiting late-K to M stars are virtually never exposed to the severe consequences that have been proposed for astrospheric descreening events, but descreening events at a moderate rate may occur for stars with the Sun's mass or larger. PMID:19778278

  5. THERMAL EVOLUTION AND LIFETIME OF INTRINSIC MAGNETIC FIELDS OF SUPER-EARTHS IN HABITABLE ZONES

    SciTech Connect

    Tachinami, C.; Ida, S.; Senshu, H.

    2011-01-10

    We have numerically studied the thermal evolution of different-mass terrestrial planets in habitable zones, focusing on the duration of dynamo activity to generate their intrinsic magnetic fields, which may be one of the key factors in habitability of the planets. In particular, we are concerned with super-Earths, observations of which are rapidly developing. We calculated the evolution of temperature distributions in the planetary interior using Vinet equations of state, the Arrhenius-type formula for mantle viscosity, and the astrophysical mixing-length theory for convective heat transfer modified for mantle convection. After calibrating the model with terrestrial planets in the solar system, we apply it for 0.1-10 M{sub +} rocky planets with a surface temperature of 300 K (in habitable zones) and Earth-like compositions. With the criterion of heat flux at the core-mantle boundary (CMB), the lifetime of the magnetic fields is evaluated from the calculated thermal evolution. We found that the lifetime slowly increases with planetary mass (M{sub p} ), independent of the initial temperature gap at the CMB ({Delta}T{sub CMB}), but beyond the critical value M{sub c,p} ({approx}O(1) M{sub +}) it abruptly declines from the mantle viscosity enhancement due to the pressure effect. We derived M{sub c,p} as a function of {Delta}T{sub CMB} and a rheological parameter (activation volume, V*). Thus, the magnetic field lifetime of super-Earths with M{sub p} >M{sub p,c} sensitively depends on {Delta}T{sub CMB}, which reflects planetary accretion, and V*, which has uncertainty at very high pressure. More advanced high-pressure experiments and first-principle simulation, as well as planetary accretion simulation, are needed to discuss the habitability of super-Earths.

  6. AN ANALYTIC METHOD TO DETERMINE HABITABLE ZONES FOR S-TYPE PLANETARY ORBITS IN BINARY STAR SYSTEMS

    SciTech Connect

    Eggl, Siegfried; Pilat-Lohinger, Elke; Gyergyovits, Markus; Funk, Barbara; Georgakarakos, Nikolaos E-mail: elke.pilat-lohinger@univie.ac.at

    2012-06-10

    With more and more extrasolar planets discovered in and around binary star systems, questions concerning the determination of the classical habitable zone have arisen. Do the radiative and gravitational perturbations of the second star influence the extent of the habitable zone significantly, or is it sufficient to consider the host star only? In this article, we investigate the implications of stellar companions with different spectral types on the insolation a terrestrial planet receives orbiting a Sun-like primary. We present time-independent analytical estimates and compare them to insolation statistics gained via high precision numerical orbit calculations. Results suggest a strong dependence of permanent habitability on the binary's eccentricity, as well as a possible extension of habitable zones toward the secondary in close binary systems.

  7. A New Paradigm for Habitability in Planetary Systems: the Extremophilic Zone

    NASA Astrophysics Data System (ADS)

    Janot-Pacheco, E., Bernardes, L., Lage, C. A. S.

    2014-03-01

    More than a thousand exoplanets have been discovered so far. Planetary surface temperature may strongly depends on its albedo and geodynamic conditions. We have fed exoplanets from the Encyclopedia database with a comprehensive model of Earth's atmosphere and plate tectonics. As CO2 is the main agent responsible for the greenhouse effect, its partial pressure has been taken as a free parameter to estimate the surface temperature of some known planets. We also investigated the possible presence of "exomoons" belonging to giant planets in the Habitable Zone capable of harbour dynamic stability, to retain an atmosphere and to keep geodynamic activity for long time spans. Biological data on earthly micro-organisms classified as "extremophiles" indicate that such kind of microbial species could dwell on the surface of many exoplanets and exomoons. We thus propose an extension of the mainly astronomically defined "Habitable Zone" concept into the more astrobiologically one, the "Extremophililic Zone", that takes into account other parameters allowing survival of more robust life forms. This contribution comes from an ongoing project developed by a French-Brazilian colaboration in Astrophysics and Biophysics to search for living fingerprints in astrobiologically promising exoplanets.

  8. Exploring the Inner Edge of the Habitable Zone with Fully Coupled Oceans

    NASA Technical Reports Server (NTRS)

    Way, M.J; Del Genio, A.D.; Kelley, M.; Aleinov, I.; Clune, T.

    2015-01-01

    The role of rotation in planetary atmospheres plays an important role in regulating atmospheric and oceanic heat flow, cloud formation and precipitation. Using the Goddard Institute for Space Studies (GISS) three dimension General Circulation Model (3D-GCM) we demonstrate how varying rotation rate and increasing the incident solar flux on a planet are related to each other and may allow the inner edge of the habitable zone to be much closer than many previous habitable zone studies have indicated. This is shown in particular for fully coupled ocean runs -- some of the first that have been utilized in this context. Results with a 100m mixed layer depth and our fully coupled ocean runs are compared with those of Yang et al. 2014, which demonstrates consistency across models. However, there are clear differences for rotations rates of 1-16x present earth day lengths between the mixed layer and fully couple ocean models, which points to the necessity of using fully coupled oceans whenever possible. The latter was recently demonstrated quite clearly by Hu & Yang 2014 in their aquaworld study with a fully coupled ocean when compared with similar mixed layer ocean studies and by Cullum et al. 2014. Atmospheric constituent amounts were also varied alongside adjustments to cloud parameterizations (results not shown here). While the latter have an effect on what a planet's global mean temperature is once the oceans reach equilibrium they do not qualitatively change the overall relationship between the globally averaged surface temperature and incident solar flux for rotation rates ranging from 1 to 256 times the present Earth day length. At the same time this study demonstrates that given the lack of knowledge about the atmospheric constituents and clouds on exoplanets there is still a large uncertainty as to where a planet will sit in a given star's habitable zone.

  9. Volatiles in Terrestrial Planets Orbiting Within Habitable Zones of Low-Mass Stars

    NASA Astrophysics Data System (ADS)

    Lissauer, J. J.

    2009-12-01

    Dynamical considerations derived from analytic calculations and numerical experiments imply that Earth-mass planets that accrete in regions that become habitable zones of M dwarf stars form within several million years. Temperatures in these regions during planetary accretion are higher than those encountered by the material that formed the Earth. Collision velocities during and after the prime planetary accretionary epoch are larger than for Earth. These factors suggest that planets orbiting low mass main sequence stars are likely to be either too distant (and thus too cold) for carbon/water based life on their surfaces or have abundances of the volatiles required life that are substantially less than those of Earth.

  10. Exomoon Habitability Constrained by Illumination and Tidal Heating

    PubMed Central

    2013-01-01

    Abstract The detection of moons orbiting extrasolar planets (“exomoons”) has now become feasible. Once they are discovered in the circumstellar habitable zone, questions about their habitability will emerge. Exomoons are likely to be tidally locked to their planet and hence experience days much shorter than their orbital period around the star and have seasons, all of which works in favor of habitability. These satellites can receive more illumination per area than their host planets, as the planet reflects stellar light and emits thermal photons. On the contrary, eclipses can significantly alter local climates on exomoons by reducing stellar illumination. In addition to radiative heating, tidal heating can be very large on exomoons, possibly even large enough for sterilization. We identify combinations of physical and orbital parameters for which radiative and tidal heating are strong enough to trigger a runaway greenhouse. By analogy with the circumstellar habitable zone, these constraints define a circumplanetary “habitable edge.” We apply our model to hypothetical moons around the recently discovered exoplanet Kepler-22b and the giant planet candidate KOI211.01 and describe, for the first time, the orbits of habitable exomoons. If either planet hosted a satellite at a distance greater than 10 planetary radii, then this could indicate the presence of a habitable moon. Key Words: Astrobiology—Extrasolar planets—Habitability—Habitable zone—Tides. Astrobiology 13, 18–46. PMID:23305357

  11. Circumstellar Polarimetry

    NASA Astrophysics Data System (ADS)

    Magalhães, A. M.; Carciofi, A. C.; Seriacopi, D. B.

    2015-10-01

    Starlight polarization provides insight into the physical mechanisms in and around the source as well as its geometry, whether or not the source is resolved. In this talk we will review mechanisms that polarize light in stellar envelopes. The observations and modeling can be used to probe the physics of the circumstellar environment as well as its relation to the ambient interstellar environment.

  12. Extending Galactic Habitable Zone Modeling to Include the Emergence of Intelligent Life.

    PubMed

    Morrison, Ian S; Gowanlock, Michael G

    2015-08-01

    Previous studies of the galactic habitable zone have been concerned with identifying those regions of the Galaxy that may favor the emergence of complex life. A planet is deemed habitable if it meets a set of assumed criteria for supporting the emergence of such complex life. In this work, we extend the assessment of habitability to consider the potential for life to further evolve to the point of intelligence--termed the propensity for the emergence of intelligent life, φI. We assume φI is strongly influenced by the time durations available for evolutionary processes to proceed undisturbed by the sterilizing effects of nearby supernovae. The times between supernova events provide windows of opportunity for the evolution of intelligence. We developed a model that allows us to analyze these window times to generate a metric for φI, and we examine here the spatial and temporal variation of this metric. Even under the assumption that long time durations are required between sterilizations to allow for the emergence of intelligence, our model suggests that the inner Galaxy provides the greatest number of opportunities for intelligence to arise. This is due to the substantially higher number density of habitable planets in this region, which outweighs the effects of a higher supernova rate in the region. Our model also shows that φI is increasing with time. Intelligent life emerged at approximately the present time at Earth's galactocentric radius, but a similar level of evolutionary opportunity was available in the inner Galaxy more than 2 Gyr ago. Our findings suggest that the inner Galaxy should logically be a prime target region for searches for extraterrestrial intelligence and that any civilizations that may have emerged there are potentially much older than our own. PMID:26274865

  13. GJ 832c: A Super-Earth in the Habitable Zone

    NASA Astrophysics Data System (ADS)

    Wittenmyer, Robert A.; Tuomi, Mikko; Butler, R. P.; Jones, H. R. A.; Anglada-Escudé, Guillem; Horner, Jonathan; Tinney, C. G.; Marshall, J. P.; Carter, B. D.; Bailey, J.; Salter, G. S.; O'Toole, S. J.; Wright, D.; Crane, J. D.; Schectman, S. A.; Arriagada, P.; Thompson, I.; Minniti, D.; Jenkins, J. S.; Diaz, M.

    2014-08-01

    We report the detection of GJ 832c, a super-Earth orbiting near the inner edge of the habitable zone of GJ 832, an M dwarf previously known to host a Jupiter analog in a nearly circular 9.4 yr orbit. The combination of precise radial-velocity measurements from three telescopes reveals the presence of a planet with a period of 35.68 ± 0.03 days and minimum mass (m sin i) of 5.4 ± 1.0 Earth masses. GJ 832c moves on a low-eccentricity orbit (e = 0.18 ± 0.13) toward the inner edge of the habitable zone. However, given the large mass of the planet, it seems likely that it would possess a massive atmosphere, which may well render the planet inhospitable. Indeed, it is perhaps more likely that GJ 832c is a "super-Venus," featuring significant greenhouse forcing. With an outer giant planet and an interior, potentially rocky planet, the GJ 832 planetary system can be thought of as a miniature version of our own solar system. This paper includes data gathered with the 6.5 m Magellan Telescopes located at the Las Campanas Observatory, Chile.

  14. Gj 832c: A super-Earth in the habitable zone

    SciTech Connect

    Wittenmyer, Robert A.; Horner, Jonathan; Tinney, C. G.; Marshall, J. P.; Bailey, J.; Salter, G. S.; Wright, D.; Tuomi, Mikko; Jones, H. R. A.; Butler, R. P.; Arriagada, P.; Anglada-Escudé, Guillem; Carter, B. D.; O'Toole, S. J.; Crane, J. D.; Schectman, S. A.; Thompson, I.; Minniti, D.; Jenkins, J. S.; Diaz, M.

    2014-08-20

    We report the detection of GJ 832c, a super-Earth orbiting near the inner edge of the habitable zone of GJ 832, an M dwarf previously known to host a Jupiter analog in a nearly circular 9.4 yr orbit. The combination of precise radial-velocity measurements from three telescopes reveals the presence of a planet with a period of 35.68 ± 0.03 days and minimum mass (m sin i) of 5.4 ± 1.0 Earth masses. GJ 832c moves on a low-eccentricity orbit (e = 0.18 ± 0.13) toward the inner edge of the habitable zone. However, given the large mass of the planet, it seems likely that it would possess a massive atmosphere, which may well render the planet inhospitable. Indeed, it is perhaps more likely that GJ 832c is a 'super-Venus', featuring significant greenhouse forcing. With an outer giant planet and an interior, potentially rocky planet, the GJ 832 planetary system can be thought of as a miniature version of our own solar system.

  15. The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way

    NASA Astrophysics Data System (ADS)

    Lineweaver, Charles

    2007-05-01

    Prerequisites for complex life are not uniformly distributed in our Galaxy. These prerequisites include: Enough heavy elements to form terrestrial planets, sufficient time for biological evolution and an environment free of life-extinguishing supernovae. We have modelled the evolution of the Milky Way to trace the distribution in space and time of these prerequisites. We identify the Galactic Habitable Zone (GHZ) as an annular region between 7 and 9 kiloparsecs from the galactic centre that widens with time and is composed of stars that formed between 8 and 4 billion years ago. This zone of habitability is small in the sense that it encompasses less than 10% of the stars ever formed in the Milky Way. We obtain an age distribution for the stars in the GHZ and thus an age distribution for the complex life that may inhabit our Galaxy. We find that 3/4 of the stars in the GHZ are older than the Earth and that their mean age is 1 Gyr older than the Earth. I will discuss ways in which the luminosity and spectrum of electromagnetic radiation can affect the molecular evolution that we believe led to biogenesis.

  16. Extending Galactic Habitable Zone Modelling to Include the Emergence of Intelligent Life

    NASA Astrophysics Data System (ADS)

    Morrison, I. S.; Gowanlock, M. G.

    2014-03-01

    Previous studies of the Galactic Habitable Zone (GHZ) have been concerned with identifying those regions of the Galaxy that may favour the emergence of "complex life" - typically defined to be land-based life. A planet is deemed "habitable" if it meets a set of assumed criteria for supporting the emergence of such complex life. The notion of the GHZ, and the premise that sufficient chemical evolution is required for planet formation, was quantified by Gonzalez et al. (2001). This work was later broadened to include dangers to the formation and habitability of terrestrial planets by Lineweaver et al. (2004) and then studied using a Monte Carlo simulation on the resolution of individual stars in the previous work of Gowanlock et al. (2011). The model developed in the latter work considers the stellar number density distribution and formation history of the Galaxy, planet formation mechanisms and the hazards to planetary biospheres as a result of supernova sterilization events that take place in the vicinity of the planets. Based on timescales taken from the origin and evolution of complex life on Earth, the model suggests large numbers of potentially habitable planets exist in our Galaxy, with the greatest concentration likely being towards the inner Galaxy. In this work we extend the assessment of habitability to consider the potential for life to further evolve on habitable planets to the point of intelligence - which we term the propensity for the emergence of intelligent life. We assume the propensity is strongly influenced by the time durations available for evolutionary processes to proceed undisturbed by the "resetting" effect of nearby supernovae. The model of Gowanlock et al. (2011) is used to produce a representative population of habitable planets by matching major observable properties of the Milky Way. Account is taken of the birth and death dates of each habitable planet and the timing of supernova events in each planet's vicinity. The times between supernovae provide opportunities for the development of intelligent life. We analyse these times to generate propensity metrics and examine the spatial and temporal variation of these metrics. We find that, even if long time durations are assumed to be required between sterilizations to allow for the emergence of intelligent life, the inner Galaxy provides the greatest number of opportunities, despite the high supernova rate in the region. Our approach avoids placing absolute probabilities on the emergence of complex or intelligent life, which can only be speculated upon given our current sample size of one. However, the approach allows meaningful conclusions to be drawn concerning the relative propensity for intelligent life developing in different regions and epochs of the Galaxy. In particular, it is intended that the results can be interpreted by the SETI community to provide guidance as to the regions of the Galaxy likely to present the best "percentage play" for new search programs.

  17. 55 CANCRI: STELLAR ASTROPHYSICAL PARAMETERS, A PLANET IN THE HABITABLE ZONE, AND IMPLICATIONS FOR THE RADIUS OF A TRANSITING SUPER-EARTH

    SciTech Connect

    Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David R.; Tabetha, S. Boyajian; McAlister, Harold A.; White, Russel; Ten Brummelaar, Theo A.; Schaefer, Gail; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H.; Farrington, Chris; Goldfinger, P. J.; Van Belle, Gerard T.; Raymond, Sean N.; Lopez-Morales, Mercedes; Ridgway, Stephen T.

    2011-10-10

    The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. The study presented here yields directly determined values for 55 Cnc's stellar astrophysical parameters based on improved interferometry: R = 0.943 {+-} 0.010 R{sub sun}, T{sub EFF} = 5196 {+-} 24 K. We use isochrone fitting to determine 55 Cnc's age to be 10.2 {+-} 2.5 Gyr, implying a stellar mass of 0.905 {+-} 0.015 M{sub sun}. Our analysis of the location and extent of the system's habitable zone (HZ; 0.67-1.32 AU) shows that planet f, with period {approx}260 days and Msin i = 0.155 M{sub Jupiter}, spends the majority of the duration of its elliptical orbit in the circumstellar HZ. Though planet f is too massive to harbor liquid water on any planetary surface, we elaborate on the potential of alternative low-mass objects in planet f's vicinity: a large moon and a low-mass planet on a dynamically stable orbit within the HZ. Finally, our direct value for 55 Cancri's stellar radius allows for a model-independent calculation of the physical diameter of the transiting super-Earth 55 Cnc e ({approx}2.05 {+-} 0.15 R{sub +}), which, depending on the planetary mass assumed, implies a bulk density of 0.76 {rho}{sub +} or 1.07 {rho}{sub +}.

  18. 55 Cancri: Stellar Astrophysical Parameters, a Planet in the Habitable Zone, and Implications for the Radius of a Transiting Super-Earth

    NASA Astrophysics Data System (ADS)

    von Braun, Kaspar; Boyajian, Tabetha S.; ten Brummelaar, Theo A.; Kane, Stephen R.; van Belle, Gerard T.; Ciardi, David R.; Raymond, Sean N.; López-Morales, Mercedes; McAlister, Harold A.; Schaefer, Gail; Ridgway, Stephen T.; Sturmann, Laszlo; Sturmann, Judit; White, Russel; Turner, Nils H.; Farrington, Chris; Goldfinger, P. J.

    2011-10-01

    The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. The study presented here yields directly determined values for 55 Cnc's stellar astrophysical parameters based on improved interferometry: R = 0.943 ± 0.010 R sun, T EFF = 5196 ± 24 K. We use isochrone fitting to determine 55 Cnc's age to be 10.2 ± 2.5 Gyr, implying a stellar mass of 0.905 ± 0.015 M sun. Our analysis of the location and extent of the system's habitable zone (HZ; 0.67-1.32 AU) shows that planet f, with period ~260 days and Msin i = 0.155 M Jupiter, spends the majority of the duration of its elliptical orbit in the circumstellar HZ. Though planet f is too massive to harbor liquid water on any planetary surface, we elaborate on the potential of alternative low-mass objects in planet f's vicinity: a large moon and a low-mass planet on a dynamically stable orbit within the HZ. Finally, our direct value for 55 Cancri's stellar radius allows for a model-independent calculation of the physical diameter of the transiting super-Earth 55 Cnc e (~2.05 ± 0.15 R ⊕), which, depending on the planetary mass assumed, implies a bulk density of 0.76 ρ⊕ or 1.07 ρ⊕.

  19. Exomoon habitability constrained by illumination and tidal heating.

    PubMed

    Heller, René; Barnes, Rory

    2013-01-01

    The detection of moons orbiting extrasolar planets ("exomoons") has now become feasible. Once they are discovered in the circumstellar habitable zone, questions about their habitability will emerge. Exomoons are likely to be tidally locked to their planet and hence experience days much shorter than their orbital period around the star and have seasons, all of which works in favor of habitability. These satellites can receive more illumination per area than their host planets, as the planet reflects stellar light and emits thermal photons. On the contrary, eclipses can significantly alter local climates on exomoons by reducing stellar illumination. In addition to radiative heating, tidal heating can be very large on exomoons, possibly even large enough for sterilization. We identify combinations of physical and orbital parameters for which radiative and tidal heating are strong enough to trigger a runaway greenhouse. By analogy with the circumstellar habitable zone, these constraints define a circumplanetary "habitable edge." We apply our model to hypothetical moons around the recently discovered exoplanet Kepler-22b and the giant planet candidate KOI211.01 and describe, for the first time, the orbits of habitable exomoons. If either planet hosted a satellite at a distance greater than 10 planetary radii, then this could indicate the presence of a habitable moon. PMID:23305357

  20. The Properties of Exomoons Around the Habitable Zone Planets, Kepler 22b and HD160691b

    NASA Astrophysics Data System (ADS)

    Bokorney, Jake; Fuse, Christopher R.

    2016-01-01

    As part of a larger study to understand the formation, evolution, and stability of exoplanet satellites, we have examined the Kepler 22 and HD160691 systems. Habitable zone planets (Kopparapu et al. 2013) are found in each system, with Kepler 22b at 0.85 AU and HD160691b at 1.5 AU. While these planets may be habitable, systems of satellites also hold the potential of supporting life. A series of N-body simulations were performed to examine the most stable configuration of moons orbiting each planet. A moonlet disk was designed to span 10 - 80% of the planet's Hill sphere (Ksting et al. 1993). The 100 bodies (mdisk/mplanet = 2 × 10-4) within the disk were randomly placed around each planet. Simulations were run for 500 kyrs, with the star, planets, and moonlets allowed to gravitationally evolve. The Kepler 22b system was able to retain three to four moons in 96% of the simulations, while the HD160691b systems had a stable pair of moons in 73% of the simulations. The remaining simulations produced systems with moons on highly eccentric orbits.

  1. The ultraviolet radiation environment in the habitable zones around low-mass exoplanet host stars

    NASA Astrophysics Data System (ADS)

    France, Kevin; Linsky, Jeffrey L.; Parke Loyd, R. O.

    2014-11-01

    The EUV (200-911 Å), FUV (912-1750 Å), and NUV (1750-3200 Å) spectral energy distribution of exoplanet host stars has a profound influence on the atmospheres of Earth-like planets in the habitable zone. The stellar EUV radiation drives atmospheric heating, while the FUV (in particular, Ly α) and NUV radiation fields regulate the atmospheric chemistry: the dissociation of H2O and CO2, the production of O2 and O3, and may determine the ultimate habitability of these worlds. Despite the importance of this information for atmospheric modeling of exoplanetary systems, the EUV/FUV/NUV radiation fields of cool (K and M dwarf) exoplanet host stars are almost completely unconstrained by observation or theory. We present observational results from a Hubble Space Telescope survey of M dwarf exoplanet host stars, highlighting the importance of realistic UV radiation fields for the formation of potential biomarker molecules, O2 and O3. We conclude by describing preliminary results on the characterization of the UV time variability of these sources.

  2. Gliese 581d is the First Discovered Terrestrial-mass Exoplanet in the Habitable Zone

    NASA Astrophysics Data System (ADS)

    Wordsworth, Robin D.; Forget, François; Selsis, Franck; Millour, Ehouarn; Charnay, Benjamin; Madeleine, Jean-Baptiste

    2011-06-01

    It has been suggested that the recently discovered exoplanet GJ581d might be able to support liquid water due to its relatively low mass and orbital distance. However, GJ581d receives 35% less stellar energy than Mars and is probably locked in tidal resonance, with extremely low insolation at the poles and possibly a permanent night side. Under such conditions, it is unknown whether any habitable climate on the planet would be able to withstand global glaciation and/or atmospheric collapse. Here we present three-dimensional climate simulations which demonstrate that GJ581d will have a stable atmosphere and surface liquid water for a wide range of plausible cases, making it the first confirmed super-Earth (exoplanet of 2-10 Earth masses) in the habitable zone. We find that atmospheres with over 10 bar CO2 and varying amounts of background gas (e.g., N2) yield global mean temperatures above 0°C for both land and ocean-covered surfaces. Based on the emitted IR radiation calculated by the model, we propose observational tests that will allow these cases to be distinguished from other possible scenarios in the future.

  3. Looking for Transits of Jupiter-Size Planets Orbiting Stars in Habitable Zones

    NASA Astrophysics Data System (ADS)

    García-Melendo, E.; Ribas, I.

    2010-10-01

    Owing to detection bias, most of the nearly 400 discovered planets thus far are Jupiter-mass bodies. According to the extreme Venus and Mars criteria for the limits of the habitable zone (HZ) around stars with detected exoplanets (Selsis et al. 2007), a few of these Jupiter-size worlds orbit completely inside their parent star’s HZ. These planets have orbital semi-major axes between 1 and 4 AU and orbital periods around one year or longer. The discovery of a transiting “warm” Jupiter will provide valuable information on its atmosphere, as well as offer the possibility of detecting Earth and super-Earth type satellites (potentially habitable) by using a variety of techniques such as ultra-high precision photometry or long-term transit timings. An evaluation of the transit probability will depend on a careful study of available and new photometric and spectroscopic data to characterize the host stars and to determine improved ephemeris of the planet-star conjunction time. Transit events, with a duration between seven and ten hours, and photometric depths in excess of 1%, might be easily detected from two or three independent ground-based telescopes as shown recently during the discovery of the optical transit of HD80606b.

  4. STABILITY ANALYSIS OF SINGLE-PLANET SYSTEMS AND THEIR HABITABLE ZONES

    SciTech Connect

    Kopparapu, Ravi Kumar; Barnes, Rory

    2010-06-20

    We study the dynamical stability of planetary systems consisting of one hypothetical terrestrial-mass planet (1 or 10 M{sub +}) and one massive planet (10 M{sub +}-10 M{sub jup}). We consider masses and orbits that cover the range of observed planetary system architectures (including non-zero initial eccentricities), determine the stability limit through N-body simulations, and compare it to the analytic Hill stability boundary. We show that for given masses and orbits of a two-planet system, a single parameter, which can be calculated analytically, describes the Lagrange stability boundary (no ejections or exchanges) but diverges significantly from the Hill stability boundary. However, we do find that the actual boundary is fractal, and therefore we also identify a second parameter which demarcates the transition from stable to unstable evolution. We show the portions of the habitable zones (HZs) of {rho} CrB, HD 164922, GJ 674, and HD 7924 that can support a terrestrial planet. These analyses clarify the stability boundaries in exoplanetary systems and demonstrate that, for most exoplanetary systems, numerical simulations of the stability of potentially habitable planets are only necessary over a narrow region of the parameter space. Finally, we also identify and provide a catalog of known systems that can host terrestrial planets in their HZs.

  5. GLIESE 581D IS THE FIRST DISCOVERED TERRESTRIAL-MASS EXOPLANET IN THE HABITABLE ZONE

    SciTech Connect

    Wordsworth, Robin D.; Forget, Francois; Millour, Ehouarn; Charnay, Benjamin; Madeleine, Jean-Baptiste; Selsis, Franck

    2011-06-01

    It has been suggested that the recently discovered exoplanet GJ581d might be able to support liquid water due to its relatively low mass and orbital distance. However, GJ581d receives 35% less stellar energy than Mars and is probably locked in tidal resonance, with extremely low insolation at the poles and possibly a permanent night side. Under such conditions, it is unknown whether any habitable climate on the planet would be able to withstand global glaciation and/or atmospheric collapse. Here we present three-dimensional climate simulations which demonstrate that GJ581d will have a stable atmosphere and surface liquid water for a wide range of plausible cases, making it the first confirmed super-Earth (exoplanet of 2-10 Earth masses) in the habitable zone. We find that atmospheres with over 10 bar CO{sub 2} and varying amounts of background gas (e.g., N{sub 2}) yield global mean temperatures above 0{sup 0}C for both land and ocean-covered surfaces. Based on the emitted IR radiation calculated by the model, we propose observational tests that will allow these cases to be distinguished from other possible scenarios in the future.

  6. An Earth-sized planet in the habitable zone of a cool star.

    PubMed

    Quintana, Elisa V; Barclay, Thomas; Raymond, Sean N; Rowe, Jason F; Bolmont, Emeline; Caldwell, Douglas A; Howell, Steve B; Kane, Stephen R; Huber, Daniel; Crepp, Justin R; Lissauer, Jack J; Ciardi, David R; Coughlin, Jeffrey L; Everett, Mark E; Henze, Christopher E; Horch, Elliott; Isaacson, Howard; Ford, Eric B; Adams, Fred C; Still, Martin; Hunter, Roger C; Quarles, Billy; Selsis, Franck

    2014-04-18

    The quest for Earth-like planets is a major focus of current exoplanet research. Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surfaces. We present the detection of Kepler-186f, a 1.11 ± 0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47 ± 0.05 solar-radius star. The intensity and spectrum of the star's radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form. PMID:24744370

  7. The galactic habitable zone and the age distribution of complex life in the Milky Way.

    PubMed

    Lineweaver, Charles H; Fenner, Yeshe; Gibson, Brad K

    2004-01-01

    We modeled the evolution of the Milky Way Galaxy to trace the distribution in space and time of four prerequisites for complex life: the presence of a host star, enough heavy elements to form terrestrial planets, sufficient time for biological evolution, and an environment free of life-extinguishing supernovae. We identified the Galactic habitable zone (GHZ) as an annular region between 7 and 9 kiloparsecs from the Galactic center that widens with time and is composed of stars that formed between 8 and 4 billion years ago. This GHZ yields an age distribution for the complex life that may inhabit our Galaxy. We found that 75% of the stars in the GHZ are older than the Sun. PMID:14704421

  8. Radiative Convective Transfer Calculations for Effective Stellar Fluxes of Habitable and Life Supporting Zones

    NASA Astrophysics Data System (ADS)

    Ludwig, Wolfgang; Eggl, Siegfried; Neubauer, David; Leitner, Johannes; Firneis, Maria; Hitzenberger, Regina

    2014-05-01

    Recent fields of interest in exoplanetary research include studies of potentially habitable planets orbiting stars outside of our Solar System. Habitable Zones (HZs) are currently defined by calculating the inner and the outer limits of the mean distance between exoplanets and their central stars based on effective solar fluxes that allow for maintaining liquid water on the planet's surface. Kasting et al. (1993), Selsis et al. (2007), and recently Kopparapu et al. (2013) provided stellar flux limits for such scenarios. We compute effective solar fluxes for Earth-like planets using Earth-like and other atmospheric scenarios including atmospheres with high level and low level clouds. Furthermore we provide habitability limits for solvents other than water, i.e. limits for the so called Life Supporting Zone, introduced by Leitner et al. (2010). The Life Supporting Zone (LSZ) encompasses many habitable zones based on a variety of liquid solvents. Solvents like ammonia and sulfuric acid have been identified for instance by Leitner et al (2012) as possibly life supporting. Assuming planets on circular orbits, the extent of the individual HZ is then calculated via the following equation, d(i,o) = [L/Lsun*1/S(i,o)]**0.5 au, where L is the star's luminosity, and d(i,o) and S(i,o) are the distances to the central star for the inner and the outer edge and effective insolation for inner and the outer edge of the HZ, respectively. After generating S(i,o) values for a selection of solvents, we provide the means to determine LSZ boundaries for main sequence stars. Effective flux calculations are done using a one dimensional radiative convective model (Neubauer et al. 2011) based on a modified version of the open source radiative transfer software Streamer (Key and Schweiger, 1998). Modifications include convective adjustments, additional gases for absorption and the use of an offline cloud model, which allow us to observe the influence of clouds on effective stellar fluxes. Kasting, J.F., Whitmire, D.P., & Reynolds, R.T. 1993, Icar, 101, 108 Key JR, Schweiger AJ (1998) Geosci 24:443-451. Kopparapu, R.J., et al. 2013 ApJ 765, 131 Leitner, J. J., Schwarz, R., Firneis, M. G., Hitzenberger, R., and Neubauer, D., Astrobiology Science Conference 2010, 26-29 April 2010, League City, USA, 2010 Leitner, J.J., Schulze-Makuch, D., Firneis, M.G., Hitzenberger, R., Neubauer, D., 2012 Paleontology Journal 46 (9), 1091 Neubauer, D., Vrtala, A., Leitner, J.J., Firneis, M.G., Hitzenberger, R., 2011 Origins of Life and Evolution of Biospheres, 41, 545-552 Selsis, F., Kasting, J.F., Levrard, B., et al. 2007b, A&A, 476, 137

  9. Warm Planets Around Cool Stars: Searches for Habitable Zone Planets Around Late M Dwarfs

    NASA Astrophysics Data System (ADS)

    Ramsey, L.; Wolszczan, A.; Bongiorno, S.; Redman, S.; Engel, L.; Barnes, J.; Jones, H. R. A.

    The low mass of M stars, less than 0.5 solar masses, combined with close in orbits yield radial velocity amplitudes for planets in the habitable zone around these stars that are well within current limits of 1-2 m/s achieved with visible-light instruments. These same instruments become significantly challenged when looking at M5 dwarfs and cooler. However, if one takes advantage of the fact that M-stars emit most of their energy in the near-infrared (NIR), hundreds of targets become accessible to 8-meter class telescopes with instruments such as the Precision Radial Velocity Spectrometer (PRVS) for Gemini. We present some preliminary laboratory results that demonstrate the viability and challenges of PRV work in the NIR.

  10. CALCULATING THE HABITABLE ZONE OF BINARY STAR SYSTEMS. II. P-TYPE BINARIES

    SciTech Connect

    Haghighipour, Nader; Kaltenegger, Lisa

    2013-11-10

    We have developed a comprehensive methodology for calculating the circumbinary habitable zone (HZ) in planet-hosting P-type binary star systems. We present a general formalism for determining the contribution of each star of the binary to the total flux received at the top of the atmosphere of an Earth-like planet and use the Sun's HZ to calculate the inner and outer boundaries of the HZ around a binary star system. We apply our calculations to the Kepler's currently known circumbinary planetary systems and show the combined stellar flux that determines the boundaries of their HZs. We also show that the HZ in P-type systems is dynamic and, depending on the luminosity of the binary stars, their spectral types, and the binary eccentricity, its boundaries vary as the stars of the binary undergo their orbital motion. We present the details of our calculations and discuss the implications of the results.

  11. Space telescope design to directly image the habitable zone of Alpha Centauri

    NASA Astrophysics Data System (ADS)

    Bendek, Eduardo A.; Belikov, Ruslan; Lozi, Julien; Thomas, Sandrine; Males, Jared; Weston, Sasha; McElwain, Michael

    2015-09-01

    The scientific interest in directly imaging and identifying Earth-like planets within the Habitable Zone (HZ) around nearby stars is driving the design of specialized direct imaging missions such as ACESAT, EXO-C, EXO-S and AFTA-C. The inner edge of Alpha Cen A and B Habitable Zone is found at exceptionally large angular separations of 0.7" and 0.4" respectively. This enables direct imaging of the system with a 0.3m class telescope. Contrast ratios on the order of 1010 are needed to image Earth-brightness planets. Low-resolution (5-band) spectra of all planets may allow establishing the presence and amount of an atmosphere. This star system configuration is optimal for a specialized small, and stable space telescope that can achieve high-contrast but has limited resolution. This paper describes an innovative instrument design and a mission concept based on a full Silicon Carbide off-axis telescope, which has a Phase Induced Amplitude Apodization coronagraph embedded in the telescope. This architecture maximizes stability and throughput. A Multi-Star Wave Front algorithm is implemented to drive a deformable mirror controlling simultaneously diffracted light from the on-axis and binary companion star. The instrument has a Focal Plane Occulter to reject starlight into a highprecision pointing control camera. Finally we utilize a Orbital Differential Imaging (ODI) post-processing method that takes advantage of a highly stable environment (Earth-trailing orbit) and a continuous sequence of images spanning 2 years, to reduce the final noise floor in post processing to ~2e-11 levels, enabling high confidence and at least 90% completeness detections of Earth-like planets.

  12. Can there be additional rocky planets in the Habitable Zone of tight binary stars with a known gas giant?

    NASA Astrophysics Data System (ADS)

    Funk, B.; Pilat-Lohinger, E.; Eggl, S.

    2015-04-01

    Locating planets in Habitable Zones (HZs) around other stars is a growing field in contemporary astronomy. Since a large percentage of all G-M stars in the solar neighbourhood are expected to be part of binary or multiple stellar systems, investigations of whether habitable planets are likely to be discovered in such environments are of prime interest to the scientific community. As current exoplanet statistics predicts that the chances are higher to find new worlds in systems that are already known to have planets, we examine four known extrasolar planetary systems in tight binaries in order to determine their capacity to host additional habitable terrestrial planets. Those systems are Gliese 86, γ Cephei, HD 41004 and HD 196885. In the case of γ Cephei, our results suggest that only the M dwarf companion could host additional potentially habitable worlds. Neither could we identify stable, potentially habitable regions around HD 196885 A. HD 196885 B can be considered a slightly more promising target in the search for Earth-twins. Gliese 86 A turned out to be a very good candidate, assuming that the system's history has not been excessively violent. For HD 41004, we have identified admissible stable orbits for habitable planets, but those strongly depend on the parameters of the system. A more detailed investigation shows that for some initial conditions stable planetary motion is possible in the HZ of HD 41004 A. In spite of the massive companion HD 41004 Bb, we found that HD 41004 B, too, could host additional habitable worlds.

  13. BinHab: A Numerical Tool for the Calculation of S/P-Type Habitable Zones in Binary Systems

    NASA Astrophysics Data System (ADS)

    Cuntz, M.; Bruntz, R.

    2015-01-01

    The aim of this contribution is to introduce the numerical tool BinHab, a publicly accessible code, available at The University of Texas at Arlington, that allows the calculation of S-type and P-type habitable zones of general binary systems.

  14. WISE DETECTIONS OF DUST IN THE HABITABLE ZONES OF PLANET-BEARING STARS

    SciTech Connect

    Morales, Farisa Y.; Bryden, G.; Werner, M. W.; Padgett, D. L.; Furlan, E.

    2012-09-20

    We use data from the Wide-field Infrared Survey Explorer (WISE) all-sky release to explore the incidence of warm dust in the habitable zones around exoplanet-host stars. Dust emission at 12 and/or 22 {mu}m (T{sub dust} {approx} 300 and/or {approx}150 K) traces events in the terrestrial planet zones; its existence implies replenishment by evaporation of comets or collisions of asteroids, possibly stirred by larger planets. Of the 591 planetary systems (728 extrasolar planets) in the Exoplanet Encyclopaedia as of 2012 January 31, 350 are robustly detected by WISE at {>=}5{sigma} level. We perform detailed photosphere subtraction using tools developed for Spitzer data and visually inspect all the WISE images to confirm bona fide point sources. We find nine planet-bearing stars show dust excess emission at 12 and/or 22 {mu}m at {>=}3{sigma} level around young, main-sequence, or evolved giant stars. Overall, our results yield an excess incidence of {approx}2.6% for stars of all evolutionary stages, but {approx}1% for planetary debris disks around main-sequence stars. Besides recovering previously known warm systems, we identify one new excess candidate around the young star UScoCTIO 108.

  15. WISE Detections of Dust in the Habitable Zones of Planet-bearing Stars

    NASA Astrophysics Data System (ADS)

    Morales, Farisa Y.; Padgett, D. L.; Bryden, G.; Werner, M. W.; Furlan, E.

    2012-09-01

    We use data from the Wide-field Infrared Survey Explorer (WISE) all-sky release to explore the incidence of warm dust in the habitable zones around exoplanet-host stars. Dust emission at 12 and/or 22 μm (T dust ~ 300 and/or ~150 K) traces events in the terrestrial planet zones; its existence implies replenishment by evaporation of comets or collisions of asteroids, possibly stirred by larger planets. Of the 591 planetary systems (728 extrasolar planets) in the Exoplanet Encyclopaedia as of 2012 January 31, 350 are robustly detected by WISE at >=5σ level. We perform detailed photosphere subtraction using tools developed for Spitzer data and visually inspect all the WISE images to confirm bona fide point sources. We find nine planet-bearing stars show dust excess emission at 12 and/or 22 μm at >=3σ level around young, main-sequence, or evolved giant stars. Overall, our results yield an excess incidence of ~2.6% for stars of all evolutionary stages, but ~1% for planetary debris disks around main-sequence stars. Besides recovering previously known warm systems, we identify one new excess candidate around the young star UScoCTIO 108.

  16. WISE Detections of Dust in the Habitable Zones of Planet-Bearing Stars

    NASA Technical Reports Server (NTRS)

    Morales, Farisa Y.; Padgett, Deborah L.; Bryden, Geoffrey; Werner, M. W.; Furlan, E.

    2012-01-01

    We use data from the Wide-field Infrared Survey Explorer (WISE) all-sky release to explore the incidence of warm dust in the habitable zones around exoplanet-host stars. Dust emission at 12 and/or 22 microns (T(sub dust) approx.300 and/or approx.150 K) traces events in the terrestrial planet zones; its existence implies replenishment by evaporation of comets or collisions of asteroids, possibly stirred by larger planets. Of the 591 planetary systems (728 extrasolar planets) in the Exoplanet Encyclopedia as of 2012 January 31, 350 are robustly detected by WISE at > or = 5(sigma) level. We perform detailed photosphere subtraction using tools developed for Spitzer data and visually inspect all the WISE images to confirm bona fide point sources. We find nine planet-bearing stars show dust excess emission at 12 and/or 22 microns at > or = 3(sigma) level around young, main-sequence, or evolved giant stars. Overall, our results yield an excess incidence of approx.2.6% for stars of all evolutionary stages, but approx.1% for planetary debris disks around main-sequence stars. Besides recovering previously known warm systems, we identify one new excess candidate around the young star UScoCTIO 108.

  17. Exo-oceanography, climate, and habitability of tidal-locking exoplanets in the habitable zone of M dwarfs

    NASA Astrophysics Data System (ADS)

    Hu, Yongyun

    2015-08-01

    The distinctive nature of tidal-locking exoplanets is the very uneven heating by stellar radiation between the dayside and nightside. Thus, the permanent nightside can be extremely cold. It had been worried about that atmosphere and water could be condensed on the nightside of habitable exoplanets around M dwarfs. Previous studies have demonstrated that atmospheric circulations are able to transport sufficient heat to warm the nightside and prevent atmosphere collapse there. However, it remains a question of how ocean heat transports and sea-ice feedbacks play important roles in determining climates and habitability of such kind of exoplanets and whether water could be completely frozen on the nightside. Here, we apply a coupled atmospheric and oceanic general circulation model and a three-dimensional ice-sheet model to this problem. It is found that oceanic zonal heat transport plays important roles in determining climate states of habitable aqua-exoplanets orbiting M-type stars. For sufficiently high greenhouse gas levels, the nightside can be completely ice free due to ocean heat transport. Futhermore, we show that for an ocean planet surface winds drive sea ice toward the dayside and the ocean carries heat toward the nightside, both of which keep the nightside sea ice thin. Our results show that the thickness of nightside sea ice is only about 10 m or less. Thus, nightside water trapping on a water-world should not be significant. We also test whether a large ice sheet could grow on a nightside super-continent using an ice sheet model driven by the climate model output. We find that for weak precipitation generated by the climate model the ice-sheet thickness is strongly dependent on the geothermal heat flux, and could reach 1-2 km if the geothermal heat is similar to Earth's or lower. These suggest that complete nightside water trapping would not happen if exoplanets have fairly deep and extensive oceans.

  18. Constraining the Radiation and Plasma Environment of the Kepler Circumbinary Habitable-zone Planets

    NASA Astrophysics Data System (ADS)

    Zuluaga, Jorge I.; Mason, Paul A.; Cuartas-Restrepo, Pablo A.

    2016-02-01

    The discovery of many planets using the Kepler telescope includes 10 planets orbiting eight binary stars. Three binaries, Kepler-16, Kepler-47, and Kepler-453, have at least one planet in the circumbinary habitable zone (BHZ). We constrain the level of high-energy radiation and the plasma environment in the BHZ of these systems. With this aim, BHZ limits in these Kepler binaries are calculated as a function of time, and the habitability lifetimes are estimated for hypothetical terrestrial planets and/or moons within the BHZ. With the time-dependent BHZ limits established, a self-consistent model is developed describing the evolution of stellar activity and radiation properties as proxies for stellar aggression toward planetary atmospheres. Modeling binary stellar rotation evolution, including the effect of tidal interaction between stars in binaries, is key to establishing the environment around these systems. We find that Kepler-16 and its binary analogs provide a plasma environment favorable for the survival of atmospheres of putative Mars-sized planets and exomoons. Tides have modified the rotation of the stars in Kepler-47, making its radiation environment less harsh in comparison to the solar system. This is a good example of the mechanism first proposed by Mason et al. Kepler-453 has an environment similar to that of the solar system with slightly better than Earth radiation conditions at the inner edge of the BHZ. These results can be reproduced and even reparameterized as stellar evolution and binary tidal models progress, using our online tool http://bhmcalc.net.

  19. Photoevaporation of Earth and Super-Earth Atmospheres in the Habitable Zones of M Dwarfs

    NASA Astrophysics Data System (ADS)

    Mohanty, Subhanjoy

    2015-08-01

    Kepler data show that multiple terrestrial-sized planets (i.e., Earths / super-Earths), packed in very close to the central star, are the norm in exoplanetary systems around low-mass stars. Around M dwarfs, a significant fraction of these planets reside within the Habitable Zone (HZ). This has kindled intense excitement about the possibility of finding habitable planets around these cool red stars. However, M dwarfs also remain extremely magnetically active for much longer than solar-type stars: e.g., an M3 dwarf evinces saturated levels of coronal and chromospheric activity over Gyr timescales, compared to ~100 Myr for solar-mass stars. Thus, basal levels of coronal/chromospheric X-ray/EUV emission from M dwarfs, integrated over their saturated activity lifetimes, may severely photoevaporate the atmospheres of terrestrial planets in M dwarf HZs; this would only be exacerbated by flares (which are correspondingly more intense in active M dwarfs). Here we present detailed hydrodynamic calculations of such photoevaporation for planets spanning a range of Earth/super-Earth sizes, residing in the HZ of M dwarfs of various spectral sub-types, over Gyr evolutionary timescales. Our calculations include the effects of: (1) simultaneous X-ray and EUV heating, using state-of-the-art stellar XUV SED models; (2) the change in the stellar XUV SED over evolutionary timescales; (3) realistic radiative losses (which can both dominate and vary in time); (4) thermal evolution of the planetary core; and (5) a range of initial planetary entropies (i.e.,`hot' or `cold' start) and core compositions. The analysis yields the location and extent of the HZ as a function of planetary mass, core composition, initial conditions and M sub-type. We will focus on H/He dominated (i.e., solar abundance) atmospheres; however, we will also discuss qualtitative trends for CO2 / H2O dominated atmospheres, which we are beginning to explore by coupling a detailed photochemical code with our hydrodynamic simulations. The predictions of these studies can be tested in the near future by missions such as JWST, and will also guide their search for habitable planets.

  20. The EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE)

    NASA Astrophysics Data System (ADS)

    Guyon, Olivier; Schneider, Glenn; Belikov, Ruslan; Tenerelli, Domenick J.

    2012-09-01

    We present an overview of the EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE), selected by NASA for technology development and maturation. EXCEDE will study the formation, evolution and architectures of exoplanetary systems, and characterize circumstellar environments into stellar habitable zones. EXCEDE provides contrast-limited scattered-light detection sensitivities ~ 1000x greater than HST or JWST coronagraphs at a much smaller effective inner working angle (IWA), thus enabling the exploration and characterization of exoplanetary circumstellar disks in currently inaccessible domains. EXCEDE will utilize a laboratory demonstrated high-performance Phase Induced Amplitude Apodized Coronagraph (PIAA-C) integrated with a 70 cm diameter unobscured aperture visible light telescope. The EXCEDE PIAA-C will deliver star-to-disk augmented image contrasts of < 10E-8 and a 1.2 λ/D IWA or 0.14” with a wavefront control system utilizing a 2000-element MEMS DM and fast steering mirror. EXCEDE will provide 0.12” spatial resolution at 0.4 μm with dust detection sensitivity to levels of a few tens of zodis with two-band imaging polarimetry. EXCEDE is a science-driven technology pathfinder that will advance our understanding of the formation and evolution of exoplanetary systems, placing our solar system in broader astrophysical context, and will demonstrate the high contrast technologies required for larger-scale follow-on and multi-wavelength investigations on the road to finding and characterizing exo-Earths in the years ahead.

  1. ‘Ground Truth’ Insights on Space Weather Effects at Habitable Zone Terrestrial Planets

    NASA Astrophysics Data System (ADS)

    Luhmann, Janet G.; Lillis, Robert; Lee, Christina; hara, Takuya; Halekas, Jasper; Morgan, David; Gurnett, Donald; Brain, David; McEnulty, Tess; Fang, Xiaohua; Jakosky, Bruce; Mahaffy, Paul; Eparvier, Frank; Futaana, Yoshifumi; Holmstrom, Matts; Edberg, Niklas; Opgenoorth, Hermann; Leblanc, Francois; Opitz, Andrea; Espley, Jared; Ma, Yingjuan; Russell, Christopher T.; Zhang, Tielong; Withers, Paul; Odstrcil, Dusan

    2015-08-01

    In investigations of the role of atmosphere escape to space in habitable zone terrestrial planet evolution, solar activity and its related interplanetary consequences have been suggested as possibly key to increasing rates to historically significant levels. While at least the present day impacts at planets with magnetospheres is relatively well-understood because of extensive observations at Earth, that at our neighboring weakly magnetized planets remains a matter of wide speculation. We describe the various components of solar activity-produced space weather events and what we look for in observations at Venus and Mars. Effects may include enhanced upper atmosphere heating and ionization from increased solar EUV, X-ray, and precipitating particle fluxes, reduced dayside ionopause/magnetopause altitudes from increased solar wind pressure, greater roles of planetary/interplanetary magnetic field reconnection at Mars in enabling escape, enhanced planetary ion acceleration and pickup, and related atmosphere sputtering. We summarize to what extent these have been identified and characterized in observations so far ranging from Pioneer Venus Orbiter and Venus Express to Mars Express and the MAVEN mission.

  2. Transit and radial velocity survey efficiency comparison for a habitable zone Earth

    SciTech Connect

    Burke, Christopher J.

    2014-09-01

    Transit and radial velocity searches are two techniques for identifying nearby extrasolar planets to Earth that transit bright stars. Identifying a robust sample of these exoplanets around bright stars for detailed atmospheric characterization is a major observational undertaking. In this study we describe a framework that answers the question of whether a transit or radial velocity survey is more efficient at finding transiting exoplanets given the same amount of observing time. Within the framework we show that a transit survey's window function can be approximated using the hypergeometric probability distribution. We estimate the observing time required for a transit survey to find a transiting Earth-sized exoplanet in the habitable zone (HZ) with an emphasis on late-type stars. We also estimate the radial velocity precision necessary to detect the equivalent HZ Earth-mass exoplanet that also transits when using an equal amount of observing time as the transit survey. We find that a radial velocity survey with σ{sub rv} ∼ 0.6 m s{sup –1} precision has comparable efficiency in terms of observing time to a transit survey with the requisite photometric precision σ{sub phot} ∼ 300 ppm to find a transiting Earth-sized exoplanet in the HZ of late M dwarfs. For super-Earths, a σ{sub rv} ∼ 2.0 m s{sup –1} precision radial velocity survey has comparable efficiency to a transit survey with σ{sub phot} ∼ 2300 ppm.

  3. Validation of Twelve Small Kepler Transiting Planets in the Habitable Zone

    NASA Astrophysics Data System (ADS)

    Caldwell, Douglas A.; Torres, Guillermo; Kipping, David M.; Ballard, Sarah; Batalha, Natalie; Borucki, William J.; Bryson, Steve; Ciardi, David R.; Crepp, Justin R.; Everett, Mark; Fressin, Francois; Henze, Christopher; Horch, Elliott; Howard, Andrew; Howell, Steve B.; Isaacson, Howard T.; Jenkins, Jon Michael; Kolbl, Rea; Marcy, Geoffrey W.; McCauliff, Sean D.; Muirhead, Philip Steven; Newton, Elizabeth; Petigura, Erik; Twicken, Joseph D.; Quintana, Elisa V.; Barclay, Thomas

    2015-01-01

    We report on the work to validate twelve candidate-transiting planets from Kepler with orbital periods ranging from 34 to 207 days initially identified in the pipeline search of three years of Kepler data from quarters 1 to 12. The candidates were selected based on pipeline Data Validation models indicating that they are small and potentially in the habitable zone (HZ) of their parent stars. As their expected Doppler signals are too small for a direct measure of their masses, we verify their planetary nature by validating them statistically using the BLENDER technique. BLENDER simulates large numbers of false-positive scenarios and compares the resulting light curves with the Kepler photometry, taking into account additional information from the analysis of Kepler flux centroids and new follow-up observations, including high-resolution optical and NIR spectroscopy, adaptive optics imaging, and speckle imaging. For eleven of the candidates we show that the likelihood they are true planets is far greater than that of a false positive, to a 99.73% confidence level. For the twelfth candidate, the planet confidence level is about 99.2%. Using improved stellar parameters for the host stars, we derive planetary radii ranging from 1.12 to 2.73 R⊕. All twelve objects are confirmed to be in the HZ, and nine are small enough to be rocky. Excluding three of the candidates that have been previously validated by others, our study doubles the number of known potentially rocky planets in the HZ.

  4. RESEARCH PAPER: The dynamical architecture and habitable zones of the quintuplet planetary system 55 Cancri

    NASA Astrophysics Data System (ADS)

    Ji, Jiang-Hui; Kinoshita, Hiroshi; Liu, Lin; Li, Guang-Yu

    2009-06-01

    We perform numerical simulations to study the secular orbital evolution and dynamical structure of the quintuplet planetary system 55 Cancri with the self-consistent orbital solutions by Fischer and coworkers. In the simulations, we show that this system can be stable for at least 108 yr. In addition, we extensively investigate the planetary configuration of four outer companions with one terrestrial planet in the wide region of 0.790 AU <= a <= 5.900 AU to examine the existence of potential asteroid structure and Habitable Zones (HZs). We show that there are unstable regions for orbits about 4:1, 3:1 and 5:2 mean motion resonances (MMRs) of the outermost planet in the system, and several stable orbits can remain at 3:2 and 1:1 MMRs, which resembles the asteroid belt in the solar system. From a dynamical viewpoint, proper HZ candidates for the existence of more potential terrestrial planets reside in the wide area between 1.0 AU and 2.3 AU with relatively low eccentricities.

  5. CALCULATING THE HABITABLE ZONE OF BINARY STAR SYSTEMS. I. S-TYPE BINARIES

    SciTech Connect

    Kaltenegger, Lisa; Haghighipour, Nader

    2013-11-10

    We have developed a comprehensive methodology for calculating the boundaries of the habitable zone (HZ) of planet-hosting S-type binary star systems. Our approach is general and takes into account the contribution of both stars to the location and extent of the binary HZ with different stellar spectral types. We have studied how the binary eccentricity and stellar energy distribution affect the extent of the HZ. Results indicate that in binaries where the combination of mass-ratio and orbital eccentricity allows planet formation around a star of the system to proceed successfully, the effect of a less luminous secondary on the location of the primary's HZ is generally negligible. However, when the secondary is more luminous, it can influence the extent of the HZ. We present the details of the derivations of our methodology and discuss its application to the binary HZ around the primary and secondary main-sequence stars of an FF, MM, and FM binary, as well as two known planet-hosting binaries α Cen AB and HD 196886.

  6. Calculating the habitable zones of multiple star systems with a new interactive Web site

    SciTech Connect

    Müller, Tobias W. A.; Haghighipour, Nader

    2014-02-10

    We have developed a comprehensive methodology and an interactive Web site for calculating the habitable zone (HZ) of multiple star systems. Using the concept of spectral weight factor, as introduced in our previous studies of the calculations of HZ in and around binary star systems, we calculate the contribution of each star (based on its spectral energy distribution) to the total flux received at the top of the atmosphere of an Earth-like planet, and use the models of the HZ of the Sun to determine the boundaries of the HZ in multiple star systems. Our interactive Web site for carrying out these calculations is publicly available at http://astro.twam.info/hz. We discuss the details of our methodology and present its application to some of the multiple star systems detected by the Kepler space telescope. We also present the instructions for using our interactive Web site, and demonstrate its capabilities by calculating the HZ for two interesting analytical solutions of the three-body problem.

  7. Habitable Zone Planets: PLATO, and the search for Earth 2.0

    NASA Astrophysics Data System (ADS)

    Brown, D. J. A.

    2015-10-01

    The PLATO mission, part of ESA's Cosmic Vision program, will launch in 2024 and will revolutionize the field of transiting exoplanets. By observing a large sample of bright stars, PLATO will discover thousands of terrestrial planets, including hundreds in the habitable zones of their host stars. The brightness of PLATO targets allows full characterization of both the planets and their host stars, including asteroseismic analysis to precisely determine masses, radii, and ages. Moreover, PLATO host stars will be bright enough to allow atmospheric spectroscopy. Confirmation and characterization of PLATO planets will require a coordinated, ground-based follow-up program to both eliminate false-positives, and derive planetary masses. I will present an introduction to PLATO, discussing the scientific motivation behind the mission, its aims and goals, and the significant contribution that PLATO will make to the search for a second Earth. I will also talk about the requirements and formulation of the follow-up program, showing that the demands are not as onerous as might be feared.

  8. DIRECT IMAGING IN THE HABITABLE ZONE AND THE PROBLEM OF ORBITAL MOTION

    SciTech Connect

    Males, Jared R.; Skemer, Andrew J.; Close, Laird M.

    2013-07-01

    High contrast imaging searches for exoplanets have been conducted on 2.4-10 m telescopes, typically at H band (1.6 {mu}m) and used exposure times of {approx}1 hr to search for planets with semi-major axes of {approx}> 10 AU. We are beginning to plan for surveys using extreme-AO systems on the next generation of 30 m class telescopes, where we hope to begin probing the habitable zones (HZs) of nearby stars. Here we highlight a heretofore ignorable problem in direct imaging: planets orbit their stars. Under the parameters of current surveys, orbital motion is negligible over the duration of a typical observation. However, this motion is not negligible when using large diameter telescopes to observe at relatively close stellar distances (1-10 pc), over the long exposure times (10-20 hr) necessary for direct detection of older planets in the HZ. We show that this motion will limit our achievable signal-to-noise ratio and degrade observational completeness. Even on current 8 m class telescopes, orbital motion will need to be accounted for in an attempt to detect HZ planets around the nearest Sun-like stars {alpha} Cen A and B, a binary system now known to harbor at least one planet. Here we derive some basic tools for analyzing this problem, and ultimately show that the prospects are good for de-orbiting a series of shorter exposures to correct for orbital motion.

  9. Asteroid flux and water transport towards circumprimary habitable zones in binary star systems

    NASA Astrophysics Data System (ADS)

    Bancelin, D.; Pilat-Lohinger, E.; Eggl, S.; Lammer, H.; Johnston, C.; Maindl, T. I.; Dvorak, R.

    2015-10-01

    Dynamical simulations show that the outcome of planetary formation process can lead to various planetary architectures (i.e. location, size, mass and water content) when the star system is single or double. In the late phase of planetary formation, when embryosized objects dominate the inner region of the system, asteroids are also present and can provide additional material for objects inside the habitable zone (HZ). In this study, we make a comparison of several binary star systems' characteristics and their efficiency to move icy asteroids from beyond the snow-line into orbits crossing the HZ. In our results, we highlight the key role of secular and mean motion resonances, causing an efficient flux of asteroids to the HZ on a short timescale. This in turn leads to asteroids bearing a non negligeable amount of water towards the HZ and available for any planets or embryos moving in this area. We also discuss how mass loss mechanisms can alter the water content on asteroids' surface.

  10. Estimates of dynamic parameters and boundaries of habitable zones of selected stars of the Pulkovo program

    NASA Astrophysics Data System (ADS)

    Shakht, N. A.; Romanenko, L. G.; Gorshanov, D. L.; Vasilkova, O. O.

    2016-01-01

    A list of selected binary stars is presented that have been observed for several decades using a 26-inch refractor at the Pulkovo Observatory. These stars are at a distance from 3.5 to 25 pc from the Sun. They belong to spectral classes F, G, K, and M. Their masses range from 0.3 to 1.5 solar masses. We have analyzed them as possible parent stars for exoplanets taking into account the physical characteristics of these stars. In view of dynamic parameters and orbital elements that we have obtained by Pulkovo observations, ephemerides of positions for the coming years are calculated. The boundaries of the habitable zones around these stars are calculated. The astrometric signal that depends on the gravitational influence of hypothetical planets is estimated. Space telescopes for astrometric observations with microsecond accuracy can be used to detect Earth-like planets near the closest stars of this program. This paper presents an overview of astrometric programs of searches for exoplanets.

  11. Exoplanet dynamics. Asynchronous rotation of Earth-mass planets in the habitable zone of lower-mass stars.

    PubMed

    Leconte, Jérémy; Wu, Hanbo; Menou, Kristen; Murray, Norman

    2015-02-01

    Planets in the habitable zone of lower-mass stars are often assumed to be in a state of tidally synchronized rotation, which would considerably affect their putative habitability. Although thermal tides cause Venus to rotate retrogradely, simple scaling arguments tend to attribute this peculiarity to the massive Venusian atmosphere. Using a global climate model, we show that even a relatively thin atmosphere can drive terrestrial planets' rotation away from synchronicity. We derive a more realistic atmospheric tide model that predicts four asynchronous equilibrium spin states, two being stable, when the amplitude of the thermal tide exceeds a threshold that is met for habitable Earth-like planets with a 1-bar atmosphere around stars more massive than ~0.5 to 0.7 solar mass. Thus, many recently discovered terrestrial planets could exhibit asynchronous spin-orbit rotation, even with a thin atmosphere. PMID:25592420

  12. Delayed Gratification Habitable Zones: When Deep Outer Solar System Regions Become Balmy During Post-Main Sequence Stellar Evolution

    NASA Astrophysics Data System (ADS)

    Stern, S. Alan

    2003-06-01

    Like all low- and moderate-mass stars, the Sun will burn as a red giant during its later evolution, generating of solar luminosities for some tens of millions of years. During this post-main sequence phase, the habitable (i.e., liquid water) thermal zone of our Solar System will lie in the region where Triton, Pluto-Charon, and Kuiper Belt objects orbit. Compared with the 1 AU habitable zone where Earth resides, this "delayed gratification habitable zone" (DGHZ) will enjoy a far less biologically hazardous environment - with lower harmful radiation levels from the Sun, and a far less destructive collisional environment. Objects like Triton, Pluto-Charon, and Kuiper Belt objects, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Kuiper Belt, with >105 objects >=50 km in radius and more than three times the combined surface area of the four terrestrial planets, provides numerous sites for possible evolution once the Sun's DGHZ reaches it. The Sun's DGHZ might be thought to only be of academic interest owing to its great separation from us in time. However, ~109 Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our Solar System (and as inferred in numerous main sequence stellar disk systems), then DGHZs may form a niche type of habitable zone that is likely to be numerically common in the Galaxy.

  13. Delayed gratification habitable zones: when deep outer solar system regions become balmy during post-main sequence stellar evolution.

    PubMed

    Stern, S Alan

    2003-01-01

    Like all low- and moderate-mass stars, the Sun will burn as a red giant during its later evolution, generating of solar luminosities for some tens of millions of years. During this post-main sequence phase, the habitable (i.e., liquid water) thermal zone of our Solar System will lie in the region where Triton, Pluto-Charon, and Kuiper Belt objects orbit. Compared with the 1 AU habitable zone where Earth resides, this "delayed gratification habitable zone" (DGHZ) will enjoy a far less biologically hazardous environment - with lower harmful radiation levels from the Sun, and a far less destructive collisional environment. Objects like Triton, Pluto-Charon, and Kuiper Belt objects, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Kuiper Belt, with >10(5) objects > or =50 km in radius and more than three times the combined surface area of the four terrestrial planets, provides numerous sites for possible evolution once the Sun's DGHZ reaches it. The Sun's DGHZ might be thought to only be of academic interest owing to its great separation from us in time. However, approximately 10(9) Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our Solar System (and as inferred in numerous main sequence stellar disk systems), then DGHZs may form a niche type of habitable zone that is likely to be numerically common in the Galaxy. PMID:14577880

  14. Exoplanet detection. Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581.

    PubMed

    Robertson, Paul; Mahadevan, Suvrath; Endl, Michael; Roy, Arpita

    2014-07-25

    The M dwarf star Gliese 581 is believed to host four planets, including one (GJ 581d) near the habitable zone that could possibly support liquid water on its surface if it is a rocky planet. The detection of another habitable-zone planet--GJ 581g--is disputed, as its significance depends on the eccentricity assumed for d. Analyzing stellar activity using the Hα line, we measure a stellar rotation period of 130 ± 2 days and a correlation for Hα modulation with radial velocity. Correcting for activity greatly diminishes the signal of GJ 581d (to 1.5 standard deviations) while significantly boosting the signals of the other known super-Earth planets. GJ 581d does not exist, but is an artifact of stellar activity which, when incompletely corrected, causes the false detection of planet g. PMID:24993348

  15. THE HUNT FOR EXOMOONS WITH KEPLER (HEK). III. THE FIRST SEARCH FOR AN EXOMOON AROUND A HABITABLE-ZONE PLANET

    SciTech Connect

    Kipping, D. M.; Forgan, D.; Hartman, J.; Bakos, G. Á.; Nesvorný, D.; Schmitt, A.; Buchhave, L.

    2013-11-10

    Kepler-22b is the first transiting planet to have been detected in the habitable zone of its host star. At 2.4 R{sub ⊕}, Kepler-22b is too large to be considered an Earth analog, but should the planet host a moon large enough to maintain an atmosphere, then the Kepler-22 system may yet possess a telluric world. Aside from being within the habitable zone, the target is attractive due to the availability of previously measured precise radial velocities and low intrinsic photometric noise, which has also enabled asteroseismology studies of the star. For these reasons, Kepler-22b was selected as a target-of-opportunity by the 'Hunt for Exomoons with Kepler' (HEK) project. In this work, we conduct a photodynamical search for an exomoon around Kepler-22b leveraging the transits, radial velocities, and asteroseismology plus several new tools developed by the HEK project to improve exomoon searches. We find no evidence for an exomoon around the planet and exclude moons of mass M{sub S} > 0.5 M{sub ⊕} to 95% confidence. By signal injection and blind retrieval, we demonstrate that an Earth-like moon is easily detected for this planet even when the time-correlated noise of the data set is taken into account. We provide updated parameters for the planet Kepler-22b, including a revised mass of M{sub P} < 53 M{sub ⊕} to 95% confidence and an eccentricity of 0.13{sub -0.13}{sup +0.36} by exploiting Single-body Asterodensity Profiling. Finally, we show that Kepler-22b has a >95% probability of being within the empirical habitable zone but a <5% probability of being within the conservative habitable zone.

  16. Detection of a Proto-planetary Clump in the Habitable Zone of GM Cephei

    NASA Astrophysics Data System (ADS)

    Chen, W. P.; Hu, S. C.-L.

    2014-04-01

    GM Cephei is an active T Tauri star in the young open cluster Trumpler 37, showing abrupt UX Orionis type of photometric variability. Its light curves exhibit frequent, sporadic brightening events, each of <0.5 mag and lasting for days, which must have been originated from unsteady circumstellar accretion. In addition, the star undergoes a brightness drop up to ~1 mag lasting for about a month, during which the star became bluer when fainter. Moreover, the brightness drops seem to have a recurrence timescale of about 300 days. It is proposed that the brightness drop arises from obscuration of the central star by an orbiting dust concentration, exemplifying disk inhomogeneity in transition between grain coagulation and planetesimal formation in a young circumstellar disk. GM Cep was found to show a few percent polarization in the optical wavelengths, and an enhanced level of polarization during the occultation phase.

  17. WATER-PLANETS IN THE HABITABLE ZONE: ATMOSPHERIC CHEMISTRY, OBSERVABLE FEATURES, AND THE CASE OF KEPLER-62e AND -62f

    SciTech Connect

    Kaltenegger, L.; Sasselov, D.; Rugheimer, S.

    2013-10-01

    Planets composed of large quantities of water that reside in the habitable zone are expected to have distinct geophysics and geochemistry of their surfaces and atmospheres. We explore these properties motivated by two key questions: whether such planets could provide habitable conditions and whether they exhibit discernable spectral features that distinguish a water-planet from a rocky Earth-like planet. We show that the recently discovered planets Kepler-62e and -62f are the first viable candidates for habitable zone water-planets. We use these planets as test cases for discussing those differences in detail. We generate atmospheric spectral models and find that potentially habitable water-planets show a distinctive spectral fingerprint in transit depending on their position in the habitable zone.

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

    SciTech Connect

    Barclay, Thomas; Burke, Christopher J.; Howell, Steve B.; Rowe, Jason F.; Huber, Daniel; Jenkins, Jon M.; Quintana, Elisa V.; Still, Martin; Twicken, Joseph D.; Bryson, Stephen T.; Borucki, William J.; Caldwell, Douglas A.; Clarke, Bruce D.; Christiansen, Jessie L; Coughlin, Jeffrey L.; Ciardi, David; Fischer, Debra A.; and others

    2013-05-10

    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 radius 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.

  19. Cosmic ray impact on extrasolar earth-like planets in close-in habitable zones.

    PubMed

    Griessmeier, J-M; Stadelmann, A; Motschmann, U; Belisheva, N K; Lammer, H; Biernat, H K

    2005-10-01

    Because of their different origins, cosmic rays can be subdivided into galactic cosmic rays and solar/stellar cosmic rays. The flux of cosmic rays to planetary surfaces is mainly determined by two planetary parameters: the atmospheric density and the strength of the internal magnetic moment. If a planet exhibits an extended magnetosphere, its surface will be protected from high-energy cosmic ray particles. We show that close-in extrasolar planets in the habitable zone of M stars are synchronously rotating with their host star because of the tidal interaction. For gravitationally locked planets the rotation period is equal to the orbital period, which is much longer than the rotation period expected for planets not subject to tidal locking. This results in a relatively small magnetic moment. We found that an Earth-like extrasolar planet, tidally locked in an orbit of 0.2 AU around an M star of 0.5 solar masses, has a rotation rate of 2% of that of the Earth. This results in a magnetic moment of less than 15% of the Earth's current magnetic moment. Therefore, close-in extrasolar planets seem not to be protected by extended Earth-like magnetospheres, and cosmic rays can reach almost the whole surface area of the upper atmosphere. Primary cosmic ray particles that interact with the atmosphere generate secondary energetic particles, a so-called cosmic ray shower. Some of the secondary particles can reach the surface of terrestrial planets when the surface pressure of the atmosphere is on the order of 1 bar or less. We propose that, depending on atmospheric pressure, biological systems on the surface of Earth-like extrasolar planets at close-in orbital distances can be strongly influenced by secondary cosmic rays. PMID:16225432

  20. Observations of interstellar formamide: availability of a prebiotic precursor in the galactic habitable zone.

    PubMed

    Adande, Gilles R; Woolf, Neville J; Ziurys, Lucy M

    2013-05-01

    We conducted a study on interstellar formamide, NH2CHO, toward star-forming regions of dense molecular clouds, using the telescopes of the Arizona Radio Observatory (ARO). The Kitt Peak 12 m antenna and the Submillimeter Telescope (SMT) were used to measure multiple rotational transitions of this molecule between 100 and 250 GHz. Four new sources of formamide were found [W51M, M17 SW, G34.3, and DR21(OH)], and complementary data were obtained toward Orion-KL, W3(OH), and NGC 7538. From these observations, column densities for formamide were determined to be in the range of 1.1×10(12) to 9.1×10(13) cm(-2), with rotational temperatures of 70-177 K. The molecule is thus present in warm gas, with abundances relative to H2 of 1×10(-11) to 1×10(-10). It appears to be a common constituent of star-forming regions that foster planetary systems within the galactic habitable zone, with abundances comparable to that found in comet Hale-Bopp. Formamide's presence in comets and molecular clouds suggests that the compound could have been brought to Earth by exogenous delivery, perhaps with an infall flux as high as ~0.1 mol/km(2)/yr or 0.18 mmol/m(2) in a single impact. Formamide has recently been proposed as a single-carbon, prebiotic source of nucleobases and nucleic acids. This study suggests that a sufficient amount of NH2CHO could have been available for such chemistry. PMID:23654214

  1. Observations of Interstellar Formamide: Availability of a Prebiotic Precursor in the Galactic Habitable Zone

    PubMed Central

    Adande, Gilles R.; Woolf, Neville J.

    2013-01-01

    Abstract We conducted a study on interstellar formamide, NH2CHO, toward star-forming regions of dense molecular clouds, using the telescopes of the Arizona Radio Observatory (ARO). The Kitt Peak 12 m antenna and the Submillimeter Telescope (SMT) were used to measure multiple rotational transitions of this molecule between 100 and 250 GHz. Four new sources of formamide were found [W51M, M17 SW, G34.3, and DR21(OH)], and complementary data were obtained toward Orion-KL, W3(OH), and NGC 7538. From these observations, column densities for formamide were determined to be in the range of 1.1×1012 to 9.1×1013 cm−2, with rotational temperatures of 70–177 K. The molecule is thus present in warm gas, with abundances relative to H2 of 1×10−11 to 1×10−10. It appears to be a common constituent of star-forming regions that foster planetary systems within the galactic habitable zone, with abundances comparable to that found in comet Hale-Bopp. Formamide's presence in comets and molecular clouds suggests that the compound could have been brought to Earth by exogenous delivery, perhaps with an infall flux as high as ∼0.1 mol/km2/yr or 0.18 mmol/m2 in a single impact. Formamide has recently been proposed as a single-carbon, prebiotic source of nucleobases and nucleic acids. This study suggests that a sufficient amount of NH2CHO could have been available for such chemistry. Key Words: Formamide—Astrobiology—Radioastronomy—ISM—Comets—Meteorites. Astrobiology 13, 439–453. PMID:23654214

  2. Validation of 12 Small Kepler Transiting Planets in the Habitable Zone

    NASA Astrophysics Data System (ADS)

    Torres, Guillermo; Kipping, David M.; Fressin, Francois; Caldwell, Douglas A.; Twicken, Joseph D.; Ballard, Sarah; Batalha, Natalie M.; Bryson, Stephen T.; Ciardi, David R.; Henze, Christopher E.; Howell, Steve B.; Isaacson, Howard T.; Jenkins, Jon M.; Muirhead, Philip S.; Newton, Elisabeth R.; Petigura, Erik A.; Barclay, Thomas; Borucki, William J.; Crepp, Justin R.; Everett, Mark E.; Horch, Elliott P.; Howard, Andrew W.; Kolbl, Rea; Marcy, Geoffrey W.; McCauliff, Sean; Quintana, Elisa V.

    2015-02-01

    We present an investigation of 12 candidate transiting planets from Kepler with orbital periods ranging from 34 to 207 days, selected from initial indications that they are small and potentially in the habitable zone (HZ) of their parent stars. Few of these objects are known. The expected Doppler signals are too small to confirm them by demonstrating that their masses are in the planetary regime. Here we verify their planetary nature by validating them statistically using the BLENDER technique, which simulates large numbers of false positives and compares the resulting light curves with the Kepler photometry. This analysis was supplemented with new follow-up observations (high-resolution optical and near-infrared spectroscopy, adaptive optics imaging, and speckle interferometry), as well as an analysis of the flux centroids. For 11 of them (KOI-0571.05, 1422.04, 1422.05, 2529.02, 3255.01, 3284.01, 4005.01, 4087.01, 4622.01, 4742.01, and 4745.01) we show that the likelihood they are true planets is far greater than that of a false positive, to a confidence level of 99.73% (3σ) or higher. For KOI-4427.01 the confidence level is about 99.2% (2.6σ). With our accurate characterization of the GKM host stars, the derived planetary radii range from 1.1 to 2.7 R ⊕. All 12 objects are confirmed to be in the HZ, and nine are small enough to be rocky. Excluding three of them that have been previously validated by others, our study doubles the number of known rocky planets in the HZ. KOI-3284.01 (Kepler-438b) and KOI-4742.01 (Kepler-442b) are the planets most similar to the Earth discovered to date when considering their size and incident flux jointly.

  3. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: DEPENDENCE ON PLANETARY MASS

    SciTech Connect

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kasting, James F.; SchottelKotte, James; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-06-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1 M {sub ⊕} and 5 M {sub ⊕}. Assuming H{sub 2}O-(inner HZ) and CO{sub 2}-(outer HZ) dominated atmospheres, and scaling the background N{sub 2} atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (∼10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H{sub 2}O column depth. For larger planets, the H{sub 2}O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. Hence the inner edge moves inward (∼7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  4. Asteroid flux towards circumprimary habitable zones in binary star systems. I. Statistical overview

    NASA Astrophysics Data System (ADS)

    Bancelin, D.; Pilat-Lohinger, E.; Eggl, S.; Maindl, T. I.; Schäfer, C.; Speith, R.; Dvorak, R.

    2015-09-01

    Context. So far, more than 130 extrasolar planets have been found in multiple stellar systems. Dynamical simulations show that the outcome of the planetary formation process can lead to different planetary architecture (i.e. location, size, mass, and water content) when the star system is single or double. Aims: In the late phase of planetary formation, when embryo-sized objects dominate the inner region of the system, asteroids are also present and can provide additional material for objects inside the habitable zone (HZ). In this study, we make a comparison of several binary star systems and how efficient they are at moving icy asteroids from beyond the snow line into orbits crossing the HZ. Methods: We modelled a belt of 10 000 asteroids (remnants from the late phase of the planetary formation process) beyond the snow line. The planetesimals are placed randomly around the primary star and move under the gravitational influence of the two stars and a gas giant. As the planetesimals do not interact with each other, we divided the belt into 100 subrings which were integrated separately. In this statistical study, several double star configurations with a G-type star as primary are investigated. Results: Our results show that small bodies also participate in bearing a non-negligible amount of water to the HZ. The proximity of a companion moving on an eccentric orbit increases the flux of asteroids to the HZ, which could result in a more efficient water transport on a short timescale, causing a heavy bombardment. In contrast to asteroids moving under the gravitational perturbations of one G-type star and a gas giant, we show that the presence of a companion star not only favours a faster depletion of our disk of planetesimals, but can also bring 4-5 times more water into the whole HZ.

  5. Kepler Mission: A Mission to Find Earth-size Planets in the Habitable Zone

    NASA Technical Reports Server (NTRS)

    Borucki, W. J.

    2003-01-01

    The Kepler Mission is a Discovery-class mission designed to continuously monitor the brightness of 100,000 solar-like stars to detect the transits of Earth-size and larger planets. It is a wide field of view photometer Schmidt-type telescope with an array of 42 CCDs. It has a 0.95 m aperture and 1.4 m primary and is designed to attain a photometric precision of 2 parts in 10(exp 5) for 12th magnitude solar-like stars for a 6 hr transit duration. It will continuously observe 100,000 main-sequence stars from 9th to 14th magnitude in the Cygnus constellation for a period of four years with a cadence of 4/hour. An additional 250 stars can be monitored at a cadence of l/minute to do astro-seismology of stars brighter than 11.5 mv. The photometer is scheduled to be launched into heliocentric orbit in 2007. When combined with ground-based spectrometric observations of these stars, the positions of the planets relative to the habitable zone can be found. The spectra of the stars are also used to determine the relationships between the characteristics of terrestrial planets and the characteristics of the stars they orbit. In particular, the association of planet size and occurrence frequency with stellar mass and metallicity will be investigated. Based on the results of the current Doppler-velocity discoveries, over a thousand giant planets will also be found. Information on the albedos and densities of those giants showing transits will be obtained. At the end of the four year mission, hundreds of Earth-size planets should be discovered in and near the HZ of their stars if such planets are common. A null result would imply that terrestrial planets in the HZ are very rare and that life might also be quite rare.

  6. Bistability of the climate around the habitable zone: a thermodynamic investigation

    NASA Astrophysics Data System (ADS)

    Pascale, S.; Boschi, R.; Lucarini, V.

    2012-12-01

    The goal of this paper is to explore the potential multistability of the cli- mate of a planet around the habitable zone. We apply our methodology to the Earth system, but our investigation has more general relevance. A thor- ough investigation of the thermodynamics of the climate system is performed for very diverse conditions of energy input and infrared atmosphere opacity. Using PlaSim, an Earth-like general circulation model, the solar constant S is modulated between 1160 and 1510 Wm-2 and the CO2 concentration, [CO2], from 90 to 2880 ppm. It is observed that in such a parameter range the climate is bistable, i.e. there are two coexisting attractors, one char- acterised by warm, moist climates (W) and one by completely frozen sea surface (Snowball Earth, SB). Linear relationships are found for the two transition lines (W→SB and SB →W) in (S,[CO2]) between S and the log- arithm of [CO2]. The dynamical and thermodynamical properties - energy fluxes, Lorenz energy cycle, Carnot efficiency, material entropy production - of the W and SB states are very different: W states are dominated by the hydrological cycle and latent heat is prominent in the material entropy production; the SB states are eminently dry climates where heat transport is realized through sensible heat fluxes and entropy mostly generated by dis- sipation of kinetic energy. We also show that the Carnot efficiency regularly increases towards each transition between W and SB, with a large decrease in each transition. Finally, we propose well-defined empirical functions al- lowing for expressing the global non-equilibrium thermodynamical properties of the system in terms of either the mean surface temperature or the mean planetary emission temperature. This paves the way for the possibility of proposing efficient parametrisations of complex non-equilibrium properties and of practically deducing fundamental properties of a planetary system from a relatively simple observable.

  7. A simple evolutional model of Habitable Zone around host stars with various mass and low metallicity

    NASA Astrophysics Data System (ADS)

    Oishi, Midori; Kamaya, Hideyuki

    2016-02-01

    Habitable Zone (HZ) is defined as a life existence area, where water at the surface of the terrestrial planet is in liquid phase. This is caused by the balance of flux from the host star and effective radiative cooling with greenhouse effect of the planet. However, the flux varies according to evolutional phase of the host star. So, a simple but newest HZ model considering stellar mass range from 0.08 to 4.00 M⊙ has been proposed. It studies both at zero-age main sequence (ZAMS) and terminal-age main sequence (TMS) phases to examine persistence of HZ. By the way, it discusses the case of the metallicity like the Sun. Actually, it is interesting to study a HZ model considering host stars with low metallicity. So, we examine the effect of metallicity, following the precedent simple model. In our analysis, metallicity affects little for HZ orbital range at ZAMS, while it affects clearly in case of TMS. Since the inner and outer HZ boundaries at TMS are shifted outward especially in the mass range from 1.5 to 2.0 M⊙, we find persistent HZ is allowed above about 1.8 M⊙. The age of the universe is 13.8 Gyr, which is comparable to main sequence life time of about 0.8 M⊙ for the low metallicity case. Then, the effect of metallicity to estimate HZ of low metallicity host stars is important for the mass range from 0.8 to 1.8 M⊙.

  8. Habitable Zones Around Main-Sequence Stars: Dependence on Planetary Mass

    NASA Technical Reports Server (NTRS)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kotte, James Schottel; Kasting, James F.; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-01-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1M and 5M. Assuming H2O-(inner HZ) and CO2-(outer HZ) dominated atmospheres, and scaling the background N2 atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (approx.10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H2O column depth. For larger planets, the H2O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing long-wave radiation. Hence the inner edge moves inward (approx.7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  9. Extreme water loss and abiotic O2 buildup on planets throughout the habitable zones of M dwarfs.

    PubMed

    Luger, R; Barnes, R

    2015-02-01

    We show that terrestrial planets in the habitable zones of M dwarfs older than ∼1 Gyr could have been in runaway greenhouses for several hundred million years following their formation due to the star's extended pre-main sequence phase, provided they form with abundant surface water. Such prolonged runaway greenhouses can lead to planetary evolution divergent from that of Earth. During this early runaway phase, photolysis of water vapor and hydrogen/oxygen escape to space can lead to the loss of several Earth oceans of water from planets throughout the habitable zone, regardless of whether the escape is energy-limited or diffusion-limited. We find that the amount of water lost scales with the planet mass, since the diffusion-limited hydrogen escape flux is proportional to the planet surface gravity. In addition to undergoing potential desiccation, planets with inefficient oxygen sinks at the surface may build up hundreds to thousands of bar of abiotically produced O2, resulting in potential false positives for life. The amount of O2 that builds up also scales with the planet mass; we find that O2 builds up at a constant rate that is controlled by diffusion: ∼5 bar/Myr on Earth-mass planets and up to ∼25 bar/Myr on super-Earths. As a result, some recently discovered super-Earths in the habitable zone such as GJ 667Cc could have built up as many as 2000 bar of O2 due to the loss of up to 10 Earth oceans of water. The fate of a given planet strongly depends on the extreme ultraviolet flux, the duration of the runaway regime, the initial water content, and the rate at which oxygen is absorbed by the surface. In general, we find that the initial phase of high luminosity may compromise the habitability of many terrestrial planets orbiting low-mass stars. PMID:25629240

  10. Toward detection of terrestrial planets in the habitable zone of our closest neighbor: proxima Centauri

    NASA Astrophysics Data System (ADS)

    Endl, M.; Kürster, M.

    2008-09-01

    Context: The precision of radial velocity (RV) measurements to detect indirectly planetary companions of nearby stars has improved to enable the discovery of extrasolar planets in the Neptune and Super-Earth mass range. Detections of extremely low mass planets, even as small as 1 Earth mass or below, in short-period orbits now appears conceivable in ongoing RV planet searches. Discoveries of these Earth-like planets by means of ground-based RV programs will help to determine the parameter η⊕, the frequency of potentially habitable planets around other stars. Aims: In search of low-mass planetary companions we monitored Proxima Centauri (M5V) as part of our M dwarf program. In the absence of a significant detection, we use these data to demonstrate the general capability of the RV method in finding terrestrial planets. For late M dwarfs the classic liquid surface water habitable zone (HZ) is located close to the star, in which circumstances the RV method is most effective. We want to demonstrate that late M dwarfs are ideal targets for the search of terrestrial planets with the RV technique. Methods: Using the iodine cell technique we obtained differential RV measurements of Proxima Cen over a time span of 7 years with the UVES spectrograph at the ESO VLT. We determine upper limits to the masses of companions in circular orbits by means of numerical simulations. Results: The RV data of Proxima Cen have a total rms scatter of 3.1~m s-1 and a period search does not reveal any significant signals. In contrast to our earlier results for Barnard's star, the RV results for the active M dwarf Proxima Cen are only weakly correlated with Hα line index measurements. As a result of our companion limit calculations, we find that we successfully recover all test signals with RV amplitudes corresponding to planets with m sin i ≥ 2-3 M_⊕ residing inside the HZ of Proxima Cen with a statistical significance of >99%. Over the same period range, we can recover 50% of the test planets with masses of m sin i ≥ 1.5-2.5~M_⊕. Based on our simulations, we exclude the presence of any planet in a circular orbit with m sin i ≥ 1~M_Neptune at separations of a ≤ 1 AU. Based on observations collected at the European Southern Observatory, Paranal, Chile, programmes 65.L-0428, 66.C-0446, 267.C-5700, 68.C-0415, 69.C-0722, 70.C-0044, 71.C-0498, 072.C-0495, 173.C-0606 and 078.C-0829. Table 1 is only available in electronic form at http://www.aanda.org

  11. Planet formation bursts at the borders of the dead zone in 2D numerical simulations of circumstellar disks

    NASA Astrophysics Data System (ADS)

    Lyra, W.; Johansen, A.; Zsom, A.; Klahr, H.; Piskunov, N.

    2009-04-01

    Context: As accretion in protoplanetary disks is enabled by turbulent viscosity, the border between active and inactive (dead) zones constitutes a location where there is an abrupt change in the accretion flow. The gas accumulation that ensues triggers the Rossby wave instability, which in turn saturates into anticyclonic vortices. It has been suggested that the trapping of solids within them leads to a burst of planet formation on very short timescales. Aims: We study in the formation and evolution of the vortices in greater detail, focusing on the implications for the dynamics of embedded solid particles and planet formation. Methods: We performed two-dimensional global simulations of the dynamics of gas and solids in a non-magnetized thin protoplanetary disk with the Pencil code. We used multiple particle species of radius 1, 10, 30, and 100 cm. We computed the particles' gravitational interaction by a particle-mesh method, translating the particles' number density into surface density and computing the corresponding self-gravitational potential via fast Fourier transforms. The dead zone is modeled as a region of low viscosity. Adiabatic and locally isothermal equations of state are used. Results: The Rossby wave instability is triggered under a variety of conditions, thus making vortex formation a robust process. Inside the vortices, fast accumulation of solids occurs and the particles collapse into objects of planetary mass on timescales as short as five orbits. Because the drag force is size-dependent, aerodynamical sorting ensues within the vortical motion, and the first bound structures formed are composed primarily of similarly-sized particles. In addition to erosion due to ram pressure, we identify gas tides from the massive vortices as a disrupting agent of formed protoplanetary embryos. We find evidence that the backreaction of the drag force from the particles onto the gas modifies the evolution of the Rossby wave instability, with vortices being launched only at later times if this term is excluded from the momentum equation. Even though the gas is not initially gravitationally unstable, the vortices can grow to Q ? 1 in locally isothermal runs, which halts the inverse cascade of energy towards smaller wavenumbers. As a result, vortices in models without self-gravity tend to rapidly merge towards a m = 2 or m =1 mode, while models with self-gravity retain dominant higher order modes (m = 4 or m = 3) for longer times. Non-selfgravitating disks thus show fewer and stronger vortices. We also estimate the collisional velocity history of the particles that compose the most massive embryo by the end of the simulation, finding that the vast majority of them never experienced a collision with another particle at speeds faster than 1 m s-1. This result lends further support to previous studies showing that vortices provide a favorable environment for planet formation.

  12. Bistability of the climate around the habitable zone: A thermodynamic investigation

    NASA Astrophysics Data System (ADS)

    Boschi, Robert; Lucarini, Valerio; Pascale, Salvatore

    2013-11-01

    The goal of this paper is to explore the potential multistability of the climate for a planet around the habitable zone. We apply our methodology to the Earth system, but our investigation has more general relevance. A thorough investigation of the thermodynamics of the climate system is performed for very diverse conditions of energy input and infrared atmosphere opacity. Using PlaSim, an Earth-like general circulation model, the solar constant S∗ is modulated between 1160 and 1510 W m-2 and the CO2 concentration, [CO2], between 90 and 2880 ppm. It is observed that in such a parameter range the climate is bistable, i.e. there are two coexisting attractors, one characterised by warm, moist climates (W) and one by completely frozen sea surface (Snowball Earth, SB). The tipping points of both the transitions (W → SB and SB →W) are located along straight lines in the (S∗, log[CO2]) space. The dynamical and thermodynamical properties - energy fluxes, Lorenz energy cycle, Carnot efficiency, material entropy production - of the W and SB states are very different: W states are dominated by the hydrological cycle and latent heat is prominent in the material entropy production; the SB states are eminently dry climates where heat transport is realised through sensible heat fluxes and entropy mostly generated by dissipation of kinetic energy. We also show that the Carnot efficiency regularly increases towards each transition between W and SB, with a large discontinuous decrease at the point of each transition. Finally, we propose well-defined empirical functions allowing for expressing the global non-equilibrium thermodynamical properties of the system in terms of either the mean surface temperature or the mean planetary emission temperature. While the specific results presented in this paper depend on some characteristics of the Earth system (e.g. rotation rate, position of the continents), this paves the way for the possibility of proposing efficient parameterisations of complex non-equilibrium properties and of practically deducing fundamental properties of a planetary system from a relatively simple observable. As a preliminary result, we obtain that when reducing the rotation rate of the planet by a factor of two, the multistability properties, the quantitative estimators of the thermodynamics of the system, and the approximate parameterisations in terms of the surface of emission temperature are only weakly affected.

  13. EFFECT OF METALLICITY ON THE EVOLUTION OF THE HABITABLE ZONE FROM THE PRE-MAIN SEQUENCE TO THE ASYMPTOTIC GIANT BRANCH AND THE SEARCH FOR LIFE

    SciTech Connect

    Danchi, William C.; Lopez, Bruno E-mail: bruno.lopez@oca.eu

    2013-05-20

    During the course of stellar evolution, the location and width of the habitable zone changes as the luminosity and radius of the star evolves. The duration of habitability for a planet located at a given distance from a star is greatly affected by the characteristics of the host star. A quantification of these effects can be used observationally in the search for life around nearby stars. The longer the duration of habitability, the more likely it is that life has evolved. The preparation of observational techniques aimed at detecting life would benefit from the scientific requirements deduced from the evolution of the habitable zone. We present a study of the evolution of the habitable zone around stars of 1.0, 1.5, and 2.0 M{sub Sun} for metallicities ranging from Z = 0.0001 to Z = 0.070. We also consider the evolution of the habitable zone from the pre-main sequence until the asymptotic giant branch is reached. We find that metallicity strongly affects the duration of the habitable zone for a planet as well as the distance from the host star where the duration is maximized. For a 1.0 M{sub Sun} star with near solar metallicity, Z = 0.017, the duration of the habitable zone is >10 Gyr at distances 1.2-2.0 AU from the star, whereas the duration is >20 Gyr for high-metallicity stars (Z = 0.070) at distances of 0.7-1.8 AU, and {approx}4 Gyr at distances of 1.8-3.3 AU for low-metallicity stars (Z = 0.0001). Corresponding results have been obtained for stars of 1.5 and 2.0 solar masses.

  14. Effect of Metallicity on the Evolution of the Habitable Zone from the Pre-main Sequence to the Asymptotic Giant Branch and the Search for Life

    NASA Astrophysics Data System (ADS)

    Danchi, William C.; Lopez, Bruno

    2013-05-01

    During the course of stellar evolution, the location and width of the habitable zone changes as the luminosity and radius of the star evolves. The duration of habitability for a planet located at a given distance from a star is greatly affected by the characteristics of the host star. A quantification of these effects can be used observationally in the search for life around nearby stars. The longer the duration of habitability, the more likely it is that life has evolved. The preparation of observational techniques aimed at detecting life would benefit from the scientific requirements deduced from the evolution of the habitable zone. We present a study of the evolution of the habitable zone around stars of 1.0, 1.5, and 2.0 M ⊙ for metallicities ranging from Z = 0.0001 to Z = 0.070. We also consider the evolution of the habitable zone from the pre-main sequence until the asymptotic giant branch is reached. We find that metallicity strongly affects the duration of the habitable zone for a planet as well as the distance from the host star where the duration is maximized. For a 1.0 M ⊙ star with near solar metallicity, Z = 0.017, the duration of the habitable zone is >10 Gyr at distances 1.2-2.0 AU from the star, whereas the duration is >20 Gyr for high-metallicity stars (Z = 0.070) at distances of 0.7-1.8 AU, and ~4 Gyr at distances of 1.8-3.3 AU for low-metallicity stars (Z = 0.0001). Corresponding results have been obtained for stars of 1.5 and 2.0 solar masses.

  15. Extreme Water Loss and Abiotic O2 Buildup on Planets Throughout the Habitable Zones of M Dwarfs

    PubMed Central

    Barnes, R.

    2015-01-01

    Abstract We show that terrestrial planets in the habitable zones of M dwarfs older than ∼1 Gyr could have been in runaway greenhouses for several hundred million years following their formation due to the star's extended pre-main sequence phase, provided they form with abundant surface water. Such prolonged runaway greenhouses can lead to planetary evolution divergent from that of Earth. During this early runaway phase, photolysis of water vapor and hydrogen/oxygen escape to space can lead to the loss of several Earth oceans of water from planets throughout the habitable zone, regardless of whether the escape is energy-limited or diffusion-limited. We find that the amount of water lost scales with the planet mass, since the diffusion-limited hydrogen escape flux is proportional to the planet surface gravity. In addition to undergoing potential desiccation, planets with inefficient oxygen sinks at the surface may build up hundreds to thousands of bar of abiotically produced O2, resulting in potential false positives for life. The amount of O2 that builds up also scales with the planet mass; we find that O2 builds up at a constant rate that is controlled by diffusion: ∼5 bar/Myr on Earth-mass planets and up to ∼25 bar/Myr on super-Earths. As a result, some recently discovered super-Earths in the habitable zone such as GJ 667Cc could have built up as many as 2000 bar of O2 due to the loss of up to 10 Earth oceans of water. The fate of a given planet strongly depends on the extreme ultraviolet flux, the duration of the runaway regime, the initial water content, and the rate at which oxygen is absorbed by the surface. In general, we find that the initial phase of high luminosity may compromise the habitability of many terrestrial planets orbiting low-mass stars. Key Words: Astrobiology—Biosignatures—Extrasolar terrestrial planets—Habitability—Planetary atmospheres. Astrobiology 15, 119–143. PMID:25629240

  16. Direct Detection of Nearby Habitable Zone Planets Using Slicer Based Integral Field Spectrographs and EPICS on the E-ELT

    NASA Astrophysics Data System (ADS)

    Salter, Graeme S.; Thatte, Niranjan A.; Tecza, Matthias; Clarke, Fraser; Kasper, Markus E.

    2014-04-01

    Early design studies for the future Exo-Planet Imaging Camera and Specrotgraph (EPICS) on the European Extremely Large Telescope (E-ELT) show the ability to probe the region of super-Earths in the habitable zone of stars within 5pc (including Gilese 581d). However, these planets will be lost to us if the correct choice of integral field spectrograph (IFS) technology is not selected for such an instrument the ability to fit and remove the speckle noise that remains is crucial to reaching these contrasts. We conclusively demonstrate, though the use of an experimental setup producing an artificial speckle, that slicer based IFSs and post-processing using spectral deconvolution can achieve speckle rejection factors exceeding 103. Contrary to popular belief, we do not find any evidence that this choice of IFS technology limits the achievable contrast. Coupled with extreme adaptive optics and high performance coronographs, a slicer based integral field spectrograph could achieve contrasts exceeding 109, enabling these super-Earths to be detected in the habitable zone of nearby stars, making it an attractive option for the next generation of instruments being designed for the direct detection of extra solar planets.

  17. Reflected Light from Giant Planets in Habitable Zones: Tapping into the Power of the Cross-Correlation Function

    NASA Astrophysics Data System (ADS)

    Martins, J. H. C.; Santos, N. C.; Figueira, P.; Melo, C.

    2016-03-01

    The direct detection of reflected light from exoplanets is an excellent probe for the characterization of their atmospheres. The greatest challenge for this task is the low planet-to-star flux ratio, which even in the most favourable case is of the order of 10-4 in the optical. This ratio decreases even more for planets in their host's habitable zone, typically lower than 10-7. To reach the signal-to-noise level required for such detections, we propose to unleash the power of the Cross Correlation Function in combination with the collecting power of next generation observing facilities. The technique we propose has already yielded positive results by detecting the reflected spectral signature of 51 Pegasi b (see Martins et al. 2015). In this work, we attempted to infer the number of hours required for the detection of several planets in their host's habitable zone using the aforementioned technique from theoretical EELT observations. Our results show that for 5 of the selected planets it should be possible to directly recover their reflected spectral signature.

  18. "Grandeur in this view of life": N-body simulation models of the Galactic habitable zone

    NASA Astrophysics Data System (ADS)

    Vukotić, B.; Steinhauser, D.; Martinez-Aviles, G.; Ćirković, M. M.; Micic, M.; Schindler, S.

    2016-04-01

    We present an isolated Milky Way-like simulation in GADGET2 N-body SPH code. The Galactic disk star formation rate (SFR) surface densities and stellar mass indicative of Solar neighbourhood are used as thresholds to model the distribution of stellar mass in life friendly environments. SFR and stellar component density are calculated averaging the GADGET2 particle properties on a 2D grid mapped on the Galactic plane. The peak values for possibly habitable stellar mass surface density move from 10 to 15 kpc cylindrical galactocentric distance in 10 Gyr simulated time span. At 10 Gyr the simulation results imply the following. Stellar particles which have spent almost all of their life time in habitable friendly conditions reside typically at ˜16 kpc from Galactic centre and are ˜3 Gyr old. Stellar particles that have spent ≥90% of their 4 - 5 Gyr long life time in habitable friendly conditions, are also predominantly found in the outskirts of the Galactic disk. Less then 1% of these particles can be found at a typical Solar system galactocentric distance of 8 - 10 kpc. Our results imply that the evolution of an isolated spiral galaxy is likely to result in galactic civilizations emerging at the outskirts of the galactic disk around stellar hosts younger than the Sun.

  19. The EXoplanetary Circumstellar Disk Environments and Disk Explorer

    NASA Astrophysics Data System (ADS)

    Schneider, Glenn; Guyon, O.; Science Mission, EXCEDE; Technology Team

    2012-01-01

    We present an overview of the EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE), selected by NASA for technology development and maturation. EXCEDE will study the formation, evolution and architectures of exoplanetary systems, and characterize circumstellar environments into stellar habitable zones. EXCEDE provides contrast-limited scattered-light detection sensitivities 1000x greater than HST or JWST coronagraphs at a much smaller effective inner working angle (IWA), thus enabling the exploration and characterization of exoplanetary CS disks in currently inaccessible domains. EXCEDE will utilize a laboratory demonstrated high-performance Phase Induced Amplitude Apodized Coronagraph (PIAA-C) integrated with a 70 cm diameter unobscured aperture visible light telescope. The EXCEDE PIAA-C will deliver star-to-disk augmented image contrasts of < 10E-8 and a 1.2 lambda/D IWA of 0.14” with a wavefront control system utilizing a 64x64 element MEMS DM and fast steering mirror. EXCEDE will provide 144 mas spatial resolution at 0.4 microns with dust detection sensitivity to levels of a few tens of zodis with two-band imaging polarimetry. EXCEDE is a science-driven technology pathfinder that will advance our understanding of the formation and evolution of exoplanetary systems, placing our solar system in broader astrophysical context, and will demonstrate the high contrast technologies required for larger-scale follow-on and multi-wavelength investigations on the road to finding and characterizing exo-Earths in the years ahead.

  20. STRONG DEPENDENCE OF THE INNER EDGE OF THE HABITABLE ZONE ON PLANETARY ROTATION RATE

    SciTech Connect

    Yang, Jun; Abbot, Dorian S.; Boué, Gwenaël; Fabrycky, Daniel C.

    2014-05-20

    Planetary rotation rate is a key parameter in determining atmospheric circulation and hence the spatial pattern of clouds. Since clouds can exert a dominant control on planetary radiation balance, rotation rate could be critical for determining the mean planetary climate. Here we investigate this idea using a three-dimensional general circulation model with a sophisticated cloud scheme. We find that slowly rotating planets (like Venus) can maintain an Earth-like climate at nearly twice the stellar flux as rapidly rotating planets (like Earth). This suggests that many exoplanets previously believed to be too hot may actually be habitable, depending on their rotation rate. The explanation for this behavior is that slowly rotating planets have a weak Coriolis force and long daytime illumination, which promotes strong convergence and convection in the substellar region. This produces a large area of optically thick clouds, which greatly increases the planetary albedo. In contrast, on rapidly rotating planets a much narrower belt of clouds form in the deep tropics, leading to a relatively low albedo. A particularly striking example of the importance of rotation rate suggested by our simulations is that a planet with modern Earth's atmosphere, in Venus' orbit, and with modern Venus' (slow) rotation rate would be habitable. This would imply that if Venus went through a runaway greenhouse, it had a higher rotation rate at that time.

  1. Diagnosing Circumstellar Debris Disks

    NASA Astrophysics Data System (ADS)

    Hahn, Joseph M.

    2010-08-01

    A numerical model of a circumstellar debris disk is developed and applied to observations of the circumstellar dust orbiting β Pictoris. The model accounts for the rates at which dust is produced by collisions among unseen planetesimals, and the rate at which dust grains are destroyed due to collisions. The model also accounts for the effects of radiation pressure, which is the dominant perturbation on the disk's smaller but abundant dust grains. Solving the resulting system of rate equations then provides the dust abundances versus grain size and dust abundances over time. Those solutions also provide the dust grains' collisional lifetime versus grain size, and the debris disk's optical depth and surface brightness versus distance from the star. Comparison to observations then yields estimates of the unseen planetesimal disk's radius, and the rate at which the disk sheds mass due to planetesimal grinding. The model can also be used to measure or else constrain the dust grain's physical and optical properties, such as the dust grains' strength, their light-scattering asymmetry parameter, and the grains' efficiency of light scattering Qs . The model is then applied to optical observations of the edge-on dust disk orbiting β Pictoris, and good agreement is achieved when the unseen planetesimal disk is broad, with 75 <~ r <~ 150 AU. If it is assumed that the dust grains are bright like Saturn's icy rings (Qs = 0.7), then the cross section of dust in the disk is Ad ~= 2 × 1020 km2 and its mass is Md ~= 11 lunar masses. In this case, the planetesimal disk's dust-production rate is quite heavy, \\dot{M}_d˜ 9 M ⊕ Myr-1, implying that there is or was a substantial amount of planetesimal mass there, at least 110 Earth masses. If the dust grains are darker than assumed, then the planetesimal disk's mass-loss rate and its total mass are heavier. In fact, the apparent dearth of any major planets in this region, plus the planetesimal disk's heavy mass-loss rate, suggests that the 75 <~ r < 150 AU zone at β Pic might be a region of planetesimal destruction, rather than a site of ongoing planet formation.

  2. DIAGNOSING CIRCUMSTELLAR DEBRIS DISKS

    SciTech Connect

    Hahn, Joseph M.

    2010-08-20

    A numerical model of a circumstellar debris disk is developed and applied to observations of the circumstellar dust orbiting {beta} Pictoris. The model accounts for the rates at which dust is produced by collisions among unseen planetesimals, and the rate at which dust grains are destroyed due to collisions. The model also accounts for the effects of radiation pressure, which is the dominant perturbation on the disk's smaller but abundant dust grains. Solving the resulting system of rate equations then provides the dust abundances versus grain size and dust abundances over time. Those solutions also provide the dust grains' collisional lifetime versus grain size, and the debris disk's optical depth and surface brightness versus distance from the star. Comparison to observations then yields estimates of the unseen planetesimal disk's radius, and the rate at which the disk sheds mass due to planetesimal grinding. The model can also be used to measure or else constrain the dust grain's physical and optical properties, such as the dust grains' strength, their light-scattering asymmetry parameter, and the grains' efficiency of light scattering Q{sub s}. The model is then applied to optical observations of the edge-on dust disk orbiting {beta} Pictoris, and good agreement is achieved when the unseen planetesimal disk is broad, with 75 {approx}< r {approx}< 150 AU. If it is assumed that the dust grains are bright like Saturn's icy rings (Q{sub s} = 0.7), then the cross section of dust in the disk is A{sub d} {approx_equal} 2 x 10{sup 20} km{sup 2} and its mass is M{sub d} {approx_equal} 11 lunar masses. In this case, the planetesimal disk's dust-production rate is quite heavy, M-dot {sub d{approx}}9 M {sub +} Myr{sup -1}, implying that there is or was a substantial amount of planetesimal mass there, at least 110 Earth masses. If the dust grains are darker than assumed, then the planetesimal disk's mass-loss rate and its total mass are heavier. In fact, the apparent dearth of any major planets in this region, plus the planetesimal disk's heavy mass-loss rate, suggests that the 75 {approx}< r < 150 AU zone at {beta} Pic might be a region of planetesimal destruction, rather than a site of ongoing planet formation.

  3. A study of the stable regions in the planetary system HD 74156 - Can it host earthlike planets in habitable zones?

    NASA Astrophysics Data System (ADS)

    Dvorak, R.; Pilat-Lohinger, E.; Funk, B.; Freistetter, F.

    2003-10-01

    Using numerical methods we thoroughly investigate dynamical stability in the region between the two planets found in HD 74156. The two planets with semimajor axes 0.28 AU and 3.82 AU move on quite eccentric orbits (e=0.649 and 0.354). There is a region between 0.7 and 1.4 AU which may host additional planets which we checked via numerical integrations for different dynamical models. Besides the orbital evolution of several thousands of massless planets in a three-dimensional restricted 4-body problem (host star, two planets + massless bodies) we also have undertaken test computations of the orbital evolution of fictitious planets with masses of 0.1, 0.3 and 1 MJUP in the region between HD 74156b and HD 74156c. For direct numerical integrations up to 107 years we used the Lie-integrator, a method with adaptive step-size. We also computed the Fast Lyapunov Indicators to detect chaotic motion in this region. We emphasize the important rle of the inner resonances (with the outer planet) and outer resonances (with the inner planet) with test bodies located inside the resonances. In these two ``resonance'' regions almost no orbits survive. The region between the 1:5 outer resonance (0.8 AU) and the 5:1 inner resonance (1.3 AU), just in the right position for habitability, is also not very likely to host planets. Our results do not strictly ``forbid'' planets to move in the habitable zone, but their existence is unlikely.

  4. The effect of planets beyond the ice line on the accretion of volatiles by habitable-zone rocky planets

    SciTech Connect

    Quintana, Elisa V.; Lissauer, Jack J.

    2014-05-01

    Models of planet formation have shown that giant planets have a large impact on the number, masses, and orbits of terrestrial planets that form. In addition, they play an important role in delivering volatiles from material that formed exterior to the snow line (the region in the disk beyond which water ice can condense) to the inner region of the disk where terrestrial planets can maintain liquid water on their surfaces. We present simulations of the late stages of terrestrial planet formation from a disk of protoplanets around a solar-type star and we include a massive planet (from 1 M {sub ⊕} to 1 M {sub J}) in Jupiter's orbit at ∼5.2 AU in all but one set of simulations. Two initial disk models are examined with the same mass distribution and total initial water content, but with different distributions of water content. We compare the accretion rates and final water mass fraction of the planets that form. Remarkably, all of the planets that formed in our simulations without giant planets were water-rich, showing that giant planet companions are not required to deliver volatiles to terrestrial planets in the habitable zone. In contrast, an outer planet at least several times the mass of Earth may be needed to clear distant regions of debris truncating the epoch of frequent large impacts. Observations of exoplanets from radial velocity surveys suggest that outer Jupiter-like planets may be scarce, therefore, the results presented here suggest that there may be more habitable planets residing in our galaxy than previously thought.

  5. Atmospheric expansion in runaway greenhouse atmospheres: the inner edge of the habitable zone depends on planet mass

    NASA Astrophysics Data System (ADS)

    Goldblatt, C.; Zahnle, K. J.

    2014-12-01

    As a wet planet becomes hot, evaporation of the ocean provides a thick steam atmosphere. As the atmosphere thickens, the level at which optical depth is unity (whence radiative emission and absorption dominantly occur) rises into the atmosphere, first for thermal wavelengths and later for solar wavelengths. Consequently, two radiation limits emerge. First, an asymptotic limit on the thermal radiation, as the level at which thermal emission occurs tends towards a fixed temperature, decoupled from surface temperature. Next, a limit the albedo of the planet, as all incoming sunlight is either reflected or absorbed in the atmosphere and almost none reaches the surface. A runaway greenhouse occurs when the product of co-albedo and area-averaged incoming sunlight exceeds the thermal radiation limit. Earth today is perilously close to this [1].Returning to the first sentence, we generate a thick atmosphere: the height of optical depth of unity becomes a non-trivial fraction of the planetary radius. Hence the area of the absorbing and emitting surfaces increase. Thermal emission wins slightly, as this occurs higher, increasing thermal emission in all cases. The underlying tendency is for a larger thermal limit for heavier planets due to pressure effects, making these appear more resistant to a runaway. However, atmospheric expansion affects light planets more, making these seem much more resilient. The least resilient planet would be between Mars-size and Venus-size (Figure 1). It would be foolish to regard small planets as habitable. As the atmospheres become large, so does the problem of atmospheric escape. Theoretical considerations show hydrodynamic escape to happen disastrously for a Europa-size planet. The observation is that Mars is too feeble to hold on to any hefty atmosphere, even far from the Sun as it is, is probably relevant too. The take home points for habitable zone nerds are: (1) planet size matters (2) for small planets, atmospheric escape from a "moist greenhouse" state, with habitable surface temperatures, is the mortal wound. [1] Goldblatt, C., Robinson, T.D., Zahnle, K.J. & Crisp, D., Low simulated radiation limit for runaway greenhouse climates, Nat. Geosci, 6, 661-667, doi:10.1038/NGEO1892

  6. Occurrence and food habits of the round goby in the profundal zone of southwestern Lake Ontario

    USGS Publications Warehouse

    Walsh, M.G.; Dittman, D.E.; O'Gorman, R.

    2007-01-01

    Little is known about the ecology of round goby (Neogobius melanostomus), an invasive benthic fish, in the profundal zone of the Great Lakes. In April 2002-2005 we caught increasing numbers of round gobies with a bottom trawl in the 45-150 m depth range of southwestern Lake Ontario. In 2005, we examined gut contents of 30 round gobies from each of three depths, 55, 95, and 130 m, and qualitatively compared gut contents with density of benthic invertebrates determined by Ponar grabs. Round goby guts contained mostly Dreissena spp. and opposum shrimp, Mysis relicta (Mysis); the frequency of occurrence of dreissenids in guts decreased with depth, whereas the frequency of occurrence of Mysis in guts increased with depth. Abundance of these invertebrates in the environment followed the same pattern, although dreissenids of optimum edible size (3-12 mm) were still abundant (1,373/m2) at 130 m, where round gobies primarily consumed Mysis, suggesting that round gobies may switch from dreissenids to more profitable prey when it is available. Other food items were ostracods and fish, with ostracods generally eaten by smaller round gobies and fish eaten by larger round gobies. Occurrence and increasing abundance of round gobies in the profundal zone and predation on Mysis by round goby could have far-reaching consequences for the Lake Ontario fish community.

  7. A Campaign for the Detection of Earth-Mass Planets in the Habitable Zone of Alpha Centauri

    NASA Astrophysics Data System (ADS)

    Wittenmyer, Robert A.; Endl, Michael; Bergmann, Christoph; Hearnshaw, John; Barnes, Stuart I.; Wright, Duncan

    2014-04-01

    We review the possible formation and orbital stability of Earth-mass or super Earth-mass planets around either of the stars Alpha Centauri A or B and describe a program at Mt John University Observatory using the Doppler method that aims to detect such planets. From New Zealand, we are able to observe the Alpha Centauri system year-round. This is critical in order to acquire data of sufficient quantity and phase coverage to detect the orbit of a terrestrial-mass planet in the habitable zone. Our observations are being made at high resolution (R = 70,000) and high signal-to-noise with the Hercules vacuum echelle spectrograph attached to the 1-m McLellan telescope by a 25-m long optical fibre and using an iodine cell. We discuss the velocity precision and instrumental stability required for success and outline the progress of the observations so far. At present we are collecting about 10,000 observations of each star, A and B, per year with a typical precision of 2.5 m/s per observation.

  8. The Habitable-zone Planet Finder (HPF): Achieving high precision radial velocities and mitigating stellar activity noise

    NASA Astrophysics Data System (ADS)

    Mahadevan, Suvrath; Ramsey, Lawrence W.; Terrien, Ryan; Robertson, Paul; Marchwinski, Robert C.; Hearty, Fred; Levi, Eric; Kári Stefánsson, Gudmundur; Bender, Chad F.; Halverson, Samuel; Roy, Arpita; Nelson, Matt; Schwab, Christian

    2015-01-01

    HPF is a stabilized, fiber-fed, near infrared (NIR) spectrograph currently being built at Penn State for the 10m Hobby-Eberly Telescope (HET). HPF will be capable of discovering low mass planets in the Habitable Zones of mid-late M dwarfs via radial velocity (RV). We discuss the development of critical sub-systems like our high-stability temperature control system, vacuum cryostat, and implementation of new wavelength calibration techniques. The design of the HET enables queue-scheduled operation, but its variable pupil requires attention to both near- and far-field fiber scrambling, which we accomplish with double scramblers and octagonal fibers.HPF will provide partial bandwith coverage of the information-rich z, Y and J NIR bands at a spectral resolving power of R˜50,000. While stellar activity induced RV noise is lower in the NIR than at visible wavelengths, we have carefully included NIR activity indicators in our spectral bandpass to help discriminate stellar activity from real planet signals, as has been recently demonstrated for Gliese 581 and Gliese 667C systems.

  9. Delayed Gratification Habitable Zones (DG-HZs): When Deep Outer Solar System Regions Become Balmy During Post-Main Sequence Stellar Evolution

    NASA Astrophysics Data System (ADS)

    Stern, S. A.

    2002-09-01

    Late in the Sun's evolution it, like all low and moderate mass stars, it will burn as a red giant, generating 1000s of solar luminosities for a few tens of millions of years. A dozen years ago this stage of stellar evolution was predicted to create observable sublimation signatures in systems where Kuiper Belts (KBs) are extant (Stern et al. 1990, Nature, 345, 305); recently, the SWAS spacecraft detected such systems (Melnick et al. 2001, 412, 160). During the red giant phase, the habitable zone of our solar system will lie in the region where Triton, Pluto-Charon, and KBOs orbit. Compared to the 1 AU habitable zone where Earth resided early in the solar system's history, this "delayed gratification habitable zone (DG-HZ)" will enjoy a far less biologically hazardous environment-- with far lower harmful UV radiation levels from the Sun, and a far quieter collisional environment. Objects like Triton, Pluto-Charon, and KBOs, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Sun's DG-HZ may only be of academic interest owing to its great separation from us in time. However, several 108 approximately solar-type Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our solar system (and as inferred in numerous main sequence stellar disk systems), then DG-HZs form a kind of niche habitable zone that is likely to be numerically common in the galaxy. I will show the calculated temporal evolution of DG-HZs around various stellar types using modern stellar evolution luminosity tracks, and then discuss various aspects of DG-HZs, including the effects of stellar pulsations and mass loss winds. This work was supported by NASA's Origins of Solar Systems Program.

  10. Circumstellar Dust Created by Terrestrial Planet Formation in HD 113766

    NASA Astrophysics Data System (ADS)

    Lisse, C. M.; Chen, C. H.; Wyatt, M. C.; Morlok, A.

    2008-02-01

    We present an analysis of the gas-poor circumstellar material in the HD 113766 binary system (F3/F5, 10-16 Myr), recently observed by the Spitzer Space Telescope. For our study we have used the IR mineralogical model derived from observations of the Deep Impact experiment. We find the dust dominated by warm, fine (~1 μm) particles, abundant in Mg-rich olivine, crystalline pyroxenes, amorphous silicates, Fe-rich sulfides, amorphous carbon, and colder water ice. The warm dust material mix is akin to an inner main-belt asteroid of S-type composition. The ~440 K effective temperature of the warm dust implies that the bulk of the observed material is in a narrow belt ~1.8 AU from the 4.4 L☉ central source, in the terrestrial planet-forming region and habitable zone of the system (equivalent to 0.9 AU in the solar system). The icy dust lies in two belts, located at 4-9 and 30-80 AU. The lower bound of warm dust mass in 0.1-20 μm, dn/da ~ a‑3.5 particles is very large, at least 3 × 1020 kg, equivalent to a 320 km radius asteroid of 2.5 g cm‑3 density. Assuming 10 m particles are the largest present, the lower bound of warm dust mass is at least 0.5 MMars. Neither primordial nor mature, the dust around HD 113766A originates from catastrophic disruption of terrestrial planet embryo(s) and subsequent grinding of the fragments or from collisions in a young, extremely dense asteroid belt undergoing planetary aggregation. The persistence of the strong IR excess over the last two decades argues for a mechanism to provide replenishment of the circumstellar material on yearly timescales.

  11. Discovery and Validation of Kepler-452b: A 1.6 R⨁ Super Earth Exoplanet in the Habitable Zone of a G2 Star

    NASA Astrophysics Data System (ADS)

    Jenkins, Jon M.; Twicken, Joseph D.; Batalha, Natalie M.; Caldwell, Douglas A.; Cochran, William D.; Endl, Michael; Latham, David W.; Esquerdo, Gilbert A.; Seader, Shawn; Bieryla, Allyson; Petigura, Erik; Ciardi, David R.; Marcy, Geoffrey W.; Isaacson, Howard; Huber, Daniel; Rowe, Jason F.; Torres, Guillermo; Bryson, Stephen T.; Buchhave, Lars; Ramirez, Ivan; Wolfgang, Angie; Li, Jie; Campbell, Jennifer R.; Tenenbaum, Peter; Sanderfer, Dwight; Henze, Christopher E.; Catanzarite, Joseph H.; Gilliland, Ronald L.; Borucki, William J.

    2015-08-01

    We report on the discovery and validation of Kepler-452b, a transiting planet identified by a search through the 4 years of data collected by NASA’s Kepler Mission. This possibly rocky {1.63}-0.20+0.23 {R}\\oplus planet orbits its G2 host star every {384.843}-0.012+0.007 days, the longest orbital period for a small ({R}{{P}}\\lt 2 {R}\\oplus ) transiting exoplanet to date. The likelihood that this planet has a rocky composition lies between 49% and 62%. The star has an effective temperature of 5757 ± 85 K and a {log}g of 4.32 ± 0.09. At a mean orbital separation of {1.046}-0.015+0.019 AU, this small planet is well within the optimistic habitable zone of its star (recent Venus/early Mars), experiencing only 10% more flux than Earth receives from the Sun today, and slightly outside the conservative habitable zone (runaway greenhouse/maximum greenhouse). The star is slightly larger and older than the Sun, with a present radius of {1.11}-0.09+0.15 {R}⊙ and an estimated age of ˜6 Gyr. Thus, Kepler-452b has likely always been in the habitable zone and should remain there for another ˜3 Gyr.

  12. Determining the Inner Edge of the Habitable Zone Around M and late K-Stars Using 3-D Climate Models

    NASA Astrophysics Data System (ADS)

    Kopparapu, Ravi; Wolf, Eric T.; Haqq-Misra, Jacob; Jun, Yang; Kasting, James; Mahadevan, Suvrath; Terrien, Ryan

    2015-12-01

    We present preliminary results for the inner edge of the habitable zone (HZ) around M and late K-stars, calculated from state of the art 3-D global climate models, the NCAR Community Atmosphere Model and Flexible Modeling System (FMS) developed by the Geophysical Fluid Dynamics. Both 1-D and 3-D models show that, for a water-rich planet, as the surface temperature increases due to increased stellar radiation, water vapor becomes a significant fraction of the atmosphere. M- and late K-stars have their peak flux in the near-infrared, where water is a strong absorber. Our models have been updated with a new radiation scheme and with H2O absorption coefficients derived from the most recent line-by-line databases (HITRAN2012 and HITEMP2010). These updates will most likely result in moving the inner edge of the HZ around M and late-K stars further away from the star than previous estimates. The initial targets for survey missions such as K2 and the Transiting Exoplanet Survey Satellite (TESS) will likely be planets near the inner edge of the HZ due to the increased signal-to-noise ratio that results from their proximity to their host star. The James Webb Space Telescope (JWST) may be capable of probing the atmospheric composition of terrestrial planets around a nearby M-dwarf. Thus, determining the most accurate inner edge of the HZ around M-dwarf stars is crucial for selecting target candidates for atmospheric characterization and to identify potential biomarkers.

  13. The Inner Edge of the Habitable Zone for Synchronously Rotating Planets around Low-mass Stars Using General Circulation Models

    NASA Astrophysics Data System (ADS)

    Kopparapu, Ravi kumar; Wolf, Eric T.; Haqq-Misra, Jacob; Yang, Jun; Kasting, James F.; Meadows, Victoria; Terrien, Ryan; Mahadevan, Suvrath

    2016-03-01

    Terrestrial planets at the inner edge of the habitable zone (HZ) of late-K and M-dwarf stars are expected to be in synchronous rotation, as a consequence of strong tidal interactions with their host stars. Previous global climate model (GCM) studies have shown that, for slowly rotating planets, strong convection at the substellar point can create optically thick water clouds, increasing the planetary albedo, and thus stabilizing the climate against a thermal runaway. However these studies did not use self-consistent orbital/rotational periods for synchronously rotating planets placed at different distances from the host star. Here we provide new estimates of the inner edge of the HZ for synchronously rotating terrestrial planets around late-K and M-dwarf stars using a 3D Earth-analog GCM with self-consistent relationships between stellar metallicity, stellar effective temperature, and the planetary orbital/rotational period. We find that both atmospheric dynamics and the efficacy of the substellar cloud deck are sensitive to the precise rotation rate of the planet. Around mid-to-late M-dwarf stars with low metallicity, planetary rotation rates at the inner edge of the HZ become faster, and the inner edge of the HZ is farther away from the host stars than in previous GCM studies. For an Earth-sized planet, the dynamical regime of the substellar clouds begins to transition as the rotation rate approaches ∼10 days. These faster rotation rates produce stronger zonal winds that encircle the planet and smear the substellar clouds around it, lowering the planetary albedo, and causing the onset of the water-vapor greenhouse climatic instability to occur at up to ∼25% lower incident stellar fluxes than found in previous GCM studies. For mid-to-late M-dwarf stars with high metallicity and for mid-K to early-M stars, we agree with previous studies.

  14. A REVISED ESTIMATE OF THE OCCURRENCE RATE OF TERRESTRIAL PLANETS IN THE HABITABLE ZONES AROUND KEPLER M-DWARFS

    SciTech Connect

    Kopparapu, Ravi Kumar

    2013-04-10

    Because of their large numbers, low-mass stars may be the most abundant planet hosts in our Galaxy. Furthermore, terrestrial planets in the habitable zones (HZs) around M-dwarfs can potentially be characterized in the near future and hence may be the first such planets to be studied. Recently, Dressing and Charbonneau used Kepler data and calculated the frequency of terrestrial planets in the HZ of cool stars to be 0.15{sup +0.13}{sub -0.06} per star for Earth-size planets (0.5-1.4 R{sub Circled-Plus }). However, this estimate was derived using the Kasting et al. HZ limits, which were not valid for stars with effective temperatures lower than 3700 K. Here we update their result using new HZ limits from Kopparapu et al. for stars with effective temperatures between 2600 K and 7200 K, which includes the cool M stars in the Kepler target list. The new HZ boundaries increase the number of planet candidates in the HZ. Assuming Earth-size planets as 0.5-1.4 R{sub Circled-Plus }, when we reanalyze their results, we obtain a terrestrial planet frequency of 0.48{sup +0.12}{sub -0.24} and 0.53{sup +0.08}{sub -0.17} planets per M-dwarf star for conservative and optimistic limits of the HZ boundaries, respectively. Assuming Earth-size planets as 0.5-2 R{sub Circled-Plus }, the frequency increases to 0.51{sup +0.10}{sub -0.20} per star for the conservative estimate and to 0.61{sup +0.07}{sub -0.15} per star for the optimistic estimate. Within uncertainties, our optimistic estimates are in agreement with a similar optimistic estimate from the radial velocity survey of M-dwarfs (0.41{sup +0.54}{sub -0.13}). So, the potential for finding Earth-like planets around M stars may be higher than previously reported.

  15. PLANET HUNTERS. V. A CONFIRMED JUPITER-SIZE PLANET IN THE HABITABLE ZONE AND 42 PLANET CANDIDATES FROM THE KEPLER ARCHIVE DATA

    SciTech Connect

    Wang, Ji; Fischer, Debra A.; Boyajian, Tabetha S.; Schmitt, Joseph R.; Giguere, Matthew J.; Brewer, John M.; Barclay, Thomas; Schwamb, Megan E.; Lintott, Chris; Simpson, Robert; Jek, Kian J.; Hoekstra, Abe J.; Jacobs, Thomas Lee; LaCourse, Daryll; Schwengeler, Hans Martin; Smith, Arfon M.; Parrish, Michael; Lynn, Stuart; Schawinski, Kevin; and others

    2013-10-10

    We report the latest Planet Hunter results, including PH2 b, a Jupiter-size (R{sub PL} = 10.12 ± 0.56 R{sub ⊕}) planet orbiting in the habitable zone of a solar-type star. PH2 b was elevated from candidate status when a series of false-positive tests yielded a 99.9% confidence level that transit events detected around the star KIC 12735740 had a planetary origin. Planet Hunter volunteers have also discovered 42 new planet candidates in the Kepler public archive data, of which 33 have at least 3 transits recorded. Most of these transit candidates have orbital periods longer than 100 days and 20 are potentially located in the habitable zones of their host stars. Nine candidates were detected with only two transit events and the prospective periods are longer than 400 days. The photometric models suggest that these objects have radii that range between those of Neptune and Jupiter. These detections nearly double the number of gas-giant planet candidates orbiting at habitable-zone distances. We conducted spectroscopic observations for nine of the brighter targets to improve the stellar parameters and we obtained adaptive optics imaging for four of the stars to search for blended background or foreground stars that could confuse our photometric modeling. We present an iterative analysis method to derive the stellar and planet properties and uncertainties by combining the available spectroscopic parameters, stellar evolution models, and transiting light curve parameters, weighted by the measurement errors. Planet Hunters is a citizen science project that crowd sources the assessment of NASA Kepler light curves. The discovery of these 43 planet candidates demonstrates the success of citizen scientists at identifying planet candidates, even in longer period orbits with only two or three transit events.

  16. The structure of circumstellar shells

    NASA Technical Reports Server (NTRS)

    Fix, John D.

    1993-01-01

    This document provides a report on research activities carried out with the support of NASA grant NAG 5-1174, the Structure of Circumstellar Shells, funded under the Astrophysics Data Program. The research carried out with the support of this grant is a study of the properties of circumstellar dust shells for which spectra are available through IRAS low resolution spectrometry (LRS). This research consisted of the development and application of models of axisymmetric circumstellar shells and a preliminary survey of the applicability of neural nets for analysis of the IRAS LRS spectra of circumstellar dust shells.

  17. Host's stars and habitability

    NASA Astrophysics Data System (ADS)

    Gallet, F.; Charbonnel, C.; Amard, L.

    2015-12-01

    With about 2000 exoplanets discovered within a large range of different configurations of distance from the star, size, mass, and atmospheric conditions, the concept of habitability cannot rely only on the stellar effective temperature anymore. In addition to the natural evolution of habitability with the intrinsic stellar parameters, tidal, magnetic, and atmospheric interactions are believed to have strong impact on the relative position of the planets inside the so-called habitable zone. Moreover, the notion of habitability itself strongly depends on the definition we give to the term ``habitable''. The aim of this talk is to provide a global and up-to-date overview of the work done during the last few years about the description and the modelling of the habitability, and to present the physical processes currently includes in this description.

  18. Formation, habitability, and detection of extrasolar moons.

    PubMed

    Heller, René; Williams, Darren; Kipping, David; Limbach, Mary Anne; Turner, Edwin; Greenberg, Richard; Sasaki, Takanori; Bolmont, Emeline; Grasset, Olivier; Lewis, Karen; Barnes, Rory; Zuluaga, Jorge I

    2014-09-01

    The diversity and quantity of moons in the Solar System suggest a manifold population of natural satellites exist around extrasolar planets. Of peculiar interest from an astrobiological perspective, the number of sizable moons in the stellar habitable zones may outnumber planets in these circumstellar regions. With technological and theoretical methods now allowing for the detection of sub-Earth-sized extrasolar planets, the first detection of an extrasolar moon appears feasible. In this review, we summarize formation channels of massive exomoons that are potentially detectable with current or near-future instruments. We discuss the orbital effects that govern exomoon evolution, we present a framework to characterize an exomoon's stellar plus planetary illumination as well as its tidal heating, and we address the techniques that have been proposed to search for exomoons. Most notably, we show that natural satellites in the range of 0.1-0.5 Earth mass (i) are potentially habitable, (ii) can form within the circumplanetary debris and gas disk or via capture from a binary, and (iii) are detectable with current technology. PMID:25147963

  19. Formation, Habitability, and Detection of Extrasolar Moons

    NASA Astrophysics Data System (ADS)

    Heller, René; Williams, Darren; Kipping, David; Limbach, Mary Anne; Turner, Edwin; Greenberg, Richard; Sasaki, Takanori; Bolmont, Émeline; Grasset, Olivier; Lewis, Karen; Barnes, Rory; Zuluaga, Jorge I.

    2014-09-01

    The diversity and quantity of moons in the Solar System suggest a manifold population of natural satellites exist around extrasolar planets. Of peculiar interest from an astrobiological perspective, the number of sizable moons in the stellar habitable zones may outnumber planets in these circumstellar regions. With technological and theoretical methods now allowing for the detection of sub-Earth-sized extrasolar planets, the first detection of an extrasolar moon appears feasible. In this review, we summarize formation channels of massive exomoons that are potentially detectable with current or near-future instruments. We discuss the orbital effects that govern exomoon evolution, we present a framework to characterize an exomoon's stellar plus planetary illumination as well as its tidal heating, and we address the techniques that have been proposed to search for exomoons. Most notably, we show that natural satellites in the range of 0.1-0.5 Earth mass (i) are potentially habitable, (ii) can form within the circumplanetary debris and gas disk or via capture from a binary, and (iii) are detectable with current technology.

  20. Formation, Habitability, and Detection of Extrasolar Moons

    PubMed Central

    Williams, Darren; Kipping, David; Limbach, Mary Anne; Turner, Edwin; Greenberg, Richard; Sasaki, Takanori; Bolmont, Émeline; Grasset, Olivier; Lewis, Karen; Barnes, Rory; Zuluaga, Jorge I.

    2014-01-01

    Abstract The diversity and quantity of moons in the Solar System suggest a manifold population of natural satellites exist around extrasolar planets. Of peculiar interest from an astrobiological perspective, the number of sizable moons in the stellar habitable zones may outnumber planets in these circumstellar regions. With technological and theoretical methods now allowing for the detection of sub-Earth-sized extrasolar planets, the first detection of an extrasolar moon appears feasible. In this review, we summarize formation channels of massive exomoons that are potentially detectable with current or near-future instruments. We discuss the orbital effects that govern exomoon evolution, we present a framework to characterize an exomoon's stellar plus planetary illumination as well as its tidal heating, and we address the techniques that have been proposed to search for exomoons. Most notably, we show that natural satellites in the range of 0.1–0.5 Earth mass (i) are potentially habitable, (ii) can form within the circumplanetary debris and gas disk or via capture from a binary, and (iii) are detectable with current technology. Key Words: Astrobiology—Extrasolar planets—Habitability—Planetary science—Tides. Astrobiology 14, 798–835. PMID:25147963

  1. The Habitable Zone Planet Finder: A Proposed High Resolution Nir Spectrograph For The Het To Discover Low Mass Exoplanets Around M Stars

    NASA Astrophysics Data System (ADS)

    Mahadevan, Suvrath; Ramsey, L.; Wolszczan, A.; Wright, J.; Endl, M.; Redman, S.

    2010-01-01

    The Habitable Zone Planet Finder (HZPF) is a proposed instrument for the 9m Hobby Eberly telescope that will be capable of discovering low mass planets around M dwarfs. HZPF will be fiber-fed, provide a spectral resolution R 50,000 and cover the wavelength range 0.9-1.65mm, the Y, J and H near infrared (NIR) bands where most of the flux is emitted by late type M stars, and where most of the radial velocity information is concentrated. Enclosed in a vacuum tank with active temperature control, fiber scrambling and mechanical agitation, HZPF is designed to achieve a radial velocity precision < 3m/s, with a desire to achieve 1m/s for the brightest targets. This instrument will enable a study of the properties of low mass planets around M dwarfs; discover planets in the habitable zones around these stars, and serve as an essential radial velocity confirmation tool for astrometric and transit detections around late M dwarfs. Radial velocity observation the NIR will also enable a search for close in planets around young active stars, complementing the search space enabled by upcoming high-contrast imaging instruments. Tests with our laboratory prototype have already demonstrated the ability to recover radial velocities in the NIR at 7-10 m/s precision from integrated sunlight. We will discuss lessons learned about calibration and NIR array performance from our tests and how they impact the design of the HZPF.

  2. THE LICK-CARNEGIE EXOPLANET SURVEY: A 3.1 M{sub +} PLANET IN THE HABITABLE ZONE OF THE NEARBY M3V STAR GLIESE 581

    SciTech Connect

    Vogt, Steven S.; Rivera, E. J.; Haghighipour, N.; Henry, Gregory W.; Williamson, Michael H.

    2010-11-01

    We present 11 years of HIRES precision radial velocities (RVs) of the nearby M3V star Gliese 581, combining our data set of 122 precision RVs with an existing published 4.3-year set of 119 HARPS precision RVs. The velocity set now indicates six companions in Keplerian motion around this star. Differential photometry indicates a likely stellar rotation period of {approx}94 days and reveals no significant periodic variability at any of the Keplerian periods, supporting planetary orbital motion as the cause of all the RV variations. The combined data set strongly confirms the 5.37-day, 12.9-day, 3.15-day, and 67-day planets previously announced by Bonfils et al., Udry et al., and Mayor et al.. The observations also indicate a fifth planet in the system, GJ 581f, a minimum-mass 7.0 M{sub +} planet orbiting in a 0.758 AU orbit of period 433 days, and a sixth planet, GJ 581g, a minimum-mass 3.1 M{sub +} planet orbiting at 0.146 AU with a period of 36.6 days. The estimated equilibrium temperature of GJ 581g is 228 K, placing it squarely in the middle of the habitable zone of the star and offering a very compelling case for a potentially habitable planet around a very nearby star. That a system harboring a potentially habitable planet has been found this nearby, and this soon in the relatively early history of precision RV surveys, indicates that {eta}{sub +}, the fraction of stars with potentially habitable planets, is likely to be substantial. This detection, coupled with statistics of the incompleteness of present-day precision RV surveys for volume-limited samples of stars in the immediate solar neighborhood, suggests that {eta}{sub +} could well be on the order of a few tens of percent. If the local stellar neighborhood is a representative sample of the galaxy as a whole, our Milky Way could be teeming with potentially habitable planets.

  3. Coronal mass ejection (CME) activity of low mass M stars as an important factor for the habitability of terrestrial exoplanets. I. CME impact on expected magnetospheres of Earth-like exoplanets in close-in habitable zones.

    PubMed

    Khodachenko, Maxim L; Ribas, Ignasi; Lammer, Helmut; Griessmeier, Jean-Mathias; Leitner, Martin; Selsis, Franck; Eiroa, Carlos; Hanslmeier, Arnold; Biernat, Helfried K; Farrugia, Charles J; Rucker, Helmut O

    2007-02-01

    Low mass M- and K-type stars are much more numerous in the solar neighborhood than solar-like G-type stars. Therefore, some of them may appear as interesting candidates for the target star lists of terrestrial exoplanet (i.e., planets with mass, radius, and internal parameters identical to Earth) search programs like Darwin (ESA) or the Terrestrial Planet Finder Coronagraph/Inferometer (NASA). The higher level of stellar activity of low mass M stars, as compared to solar-like G stars, as well as the closer orbital distances of their habitable zones (HZs), means that terrestrial-type exoplanets within HZs of these stars are more influenced by stellar activity than one would expect for a planet in an HZ of a solar-like star. Here we examine the influences of stellar coronal mass ejection (CME) activity on planetary environments and the role CMEs may play in the definition of habitability criterion for the terrestrial type exoplanets near M stars. We pay attention to the fact that exoplanets within HZs that are in close proximity to low mass M stars may become tidally locked, which, in turn, can result in relatively weak intrinsic planetary magnetic moments. Taking into account existing observational data and models that involve the Sun and related hypothetical parameters of extrasolar CMEs (density, velocity, size, and occurrence rate), we show that Earth-like exoplanets within close-in HZs should experience a continuous CME exposure over long periods of time. This fact, together with small magnetic moments of tidally locked exoplanets, may result in little or no magnetospheric protection of planetary atmospheres from a dense flow of CME plasma. Magnetospheric standoff distances of weakly magnetized Earth-like exoplanets at orbital distances

  4. Suppression of the water ice and snow albedo feedback on planets orbiting red dwarf stars and the subsequent widening of the habitable zone.

    PubMed

    Joshi, Manoj M; Haberle, Robert M

    2012-01-01

    M stars comprise 80% of main sequence stars, so their planetary systems provide the best chance for finding habitable planets, that is, those with surface liquid water. We have modeled the broadband albedo or reflectivity of water ice and snow for simulated planetary surfaces orbiting two observed red dwarf stars (or M stars), using spectrally resolved data of Earth's cryosphere. The gradual reduction of the albedos of snow and ice at wavelengths greater than 1 μm, combined with M stars emitting a significant fraction of their radiation at these same longer wavelengths, means that the albedos of ice and snow on planets orbiting M stars are much lower than their values on Earth. Our results imply that the ice/snow albedo climate feedback is significantly weaker for planets orbiting M stars than for planets orbiting G-type stars such as the Sun. In addition, planets with significant ice and snow cover will have significantly higher surface temperatures for a given stellar flux if the spectral variation of cryospheric albedo is considered, which in turn implies that the outer edge of the habitable zone around M stars may be 10-30% farther away from the parent star than previously thought. PMID:22181553

  5. The Habitable Zone Planet Finder Project: A Proposed High Resolution NIR Spectrograph for the Hobby Eberly Telescope (HET) to Discover Low Mass Exoplanets around M Stars

    NASA Astrophysics Data System (ADS)

    Mahadevan, S.; Ramsey, L.; Redman, S.; Zonak, S.; Wright, J.; Wolszczan, A.; Endl, M.; Zhao, B.

    2010-10-01

    Radial velocity precision in the NIR is now approaching the level necessary to detect exoplanets around mid-late M stars that are very faint in the optical and emit most of their flux in the NIR. The Penn State Pathfinder prototype instrument has already demonstrated 7-10 ms-1 precision on sunlight, and similar precision has been reported at the Pathways conference using CRIRES and an ammonia gas-cell. We discuss the science goals that motivate a stable cross-dispersed, high-resolution NIR spectrograph on a large telescope, as well as the path leading from the Pathfinder prototype to one such possible instrument—the fiber-fed Habitable Zone Planet Finder (HZPF) on the Hobby Eberly Telescope (HET). We also discuss wavelength calibration issues specific to the NIR, and our ongoing exploration with Pathfinder to mitigate these issues.

  6. The habitable zone planet finder: a proposed high-resolution NIR spectrograph for the Hobby Eberly Telescope to discover low-mass exoplanets around M dwarfs

    NASA Astrophysics Data System (ADS)

    Mahadevan, Suvrath; Ramsey, Larry; Wright, Jason; Endl, Michael; Redman, Stephen; Bender, Chad; Roy, Arpita; Zonak, Stephanie; Troupe, Nathaniel; Engel, Leland; Sigurdsson, Steinn; Wolszczan, Alex; Zhao, Bo

    2010-07-01

    The Habitable Zone Planet Finder (HZPF) is a proposed instrument for the 10m class Hobby Eberly telescope that will be capable of discovering low mass planets around M dwarfs. HZPF will be fiber-fed, provide a spectral resolution R~ 50,000 and cover the wavelength range 0.9-1.65μm, the Y, J and H NIR bands where most of the flux is emitted by midlate type M stars, and where most of the radial velocity information is concentrated. Enclosed in a chilled vacuum vessel with active temperature control, fiber scrambling and mechanical agitation, HZPF is designed to achieve a radial velocity precision < 3m/s, with a desire to obtain <1m/s for the brightest targets. This instrument will enable a study of the properties of low mass planets around M dwarfs; discover planets in the habitable zones around these stars, as well serve as an essential radial velocity confirmation tool for astrometric and transit detections around late M dwarfs. Radial velocity observation in the near-infrared (NIR) will also enable a search for close in planets around young active stars, complementing the search space enabled by upcoming high-contrast imaging instruments like GPI, SPHERE and PALM3K. Tests with a prototype Pathfinder instrument have already demonstrated the ability to recover radial velocities at 7-10 m/s precision from integrated sunlight and ~15-20 m/s precision on stellar observations at the HET. These tests have also demonstrated the ability to work in the NIR Y and J bands with an un-cooled instrument. We will also discuss lessons learned about calibration and performance from our tests and how they impact the overall design of the HZPF.

  7. Confirmation of Circumstellar Phosphine

    NASA Astrophysics Data System (ADS)

    Agúndez, M.; Cernicharo, J.; Decin, L.; Encrenaz, P.; Teyssier, D.

    2014-08-01

    Phosphine (PH3) was tentatively identified a few years ago in the carbon star envelopes IRC +10216 and CRL 2688 from observations of an emission line at 266.9 GHz attributable to the J = 1-0 rotational transition. We report the detection of the J = 2-1 rotational transition of PH3 in IRC +10216 using the HIFI instrument on board Herschel, which definitively confirms the identification of PH3. Radiative transfer calculations indicate that infrared pumping in excited vibrational states plays an important role in the excitation of PH3 in the envelope of IRC +10216, and that the observed lines are consistent with phosphine being formed anywhere between the star and 100 R * from the star, with an abundance of 10-8 relative to H2. The detection of PH3 challenges chemical models, none of which offer a satisfactory formation scenario. Although PH3 holds just 2% of the total available phosphorus in IRC +10216, it is, together with HCP, one of the major gas phase carriers of phosphorus in the inner circumstellar layers, suggesting that it could also be an important phosphorus species in other astronomical environments. This is the first unambiguous detection of PH3 outside the solar system, and is a further step toward a better understanding of the chemistry of phosphorus in space.

  8. CONFIRMATION OF CIRCUMSTELLAR PHOSPHINE

    SciTech Connect

    Agúndez, M.; Cernicharo, J.; Encrenaz, P.; Teyssier, D.

    2014-08-01

    Phosphine (PH{sub 3}) was tentatively identified a few years ago in the carbon star envelopes IRC +10216 and CRL 2688 from observations of an emission line at 266.9 GHz attributable to the J = 1-0 rotational transition. We report the detection of the J = 2-1 rotational transition of PH{sub 3} in IRC +10216 using the HIFI instrument on board Herschel, which definitively confirms the identification of PH{sub 3}. Radiative transfer calculations indicate that infrared pumping in excited vibrational states plays an important role in the excitation of PH{sub 3} in the envelope of IRC +10216, and that the observed lines are consistent with phosphine being formed anywhere between the star and 100 R {sub *} from the star, with an abundance of 10{sup –8} relative to H{sub 2}. The detection of PH{sub 3} challenges chemical models, none of which offer a satisfactory formation scenario. Although PH{sub 3} holds just 2% of the total available phosphorus in IRC +10216, it is, together with HCP, one of the major gas phase carriers of phosphorus in the inner circumstellar layers, suggesting that it could also be an important phosphorus species in other astronomical environments. This is the first unambiguous detection of PH{sub 3} outside the solar system, and is a further step toward a better understanding of the chemistry of phosphorus in space.

  9. A Joint Approach to the Study of S-Type and P-Type Habitable Zones in Binary Systems: New Results in the View of 3-D Planetary Climate Models

    NASA Astrophysics Data System (ADS)

    Cuntz, Manfred

    2015-01-01

    In two previous papers, given by Cuntz (2014a,b) [ApJ 780, A14 (19 pages); arXiv:1409.3796], a comprehensive approach has been provided for the study of S-type and P-type habitable zones in stellar binary systems, P-type orbits occur when the planet orbits both binary components, whereas in case of S-type orbits, the planet orbits only one of the binary components with the second component considered a perturbator. The selected approach considers a variety of aspects, including (1) the consideration of a joint constraint including orbital stability and a habitable region for a possible system planet through the stellar radiative energy fluxes; (2) the treatment of conservative (CHZ), general (GHZ) and extended zones of habitability (EHZ) [see Paper I for definitions] for the systems as previously defined for the Solar System; (3) the provision of a combined formalism for the assessment of both S-type and P-type habitability; in particular, mathematical criteria are devised for which kind of system S-type and P-type habitability is realized; and (4) the applications of the theoretical approach to systems with the stars in different kinds of orbits, including elliptical orbits (the most expected case). Particularly, an algebraic formalism for the assessment of both S-type and P-type habitability is given based on a higher-order polynomial expression. Thus, an a prior specification for the presence or absence of S-type or P-type radiative habitable zones is - from a mathematical point of view - neither necessary nor possible, as those are determined by the adopted formalism. Previously, numerous applications of the method have been given encompassing theoretical star-panet systems and and observations. Most recently, this method has been upgraded to include recent studies of 3-D planetary climate models. Originally, this type of work affects the extent and position of habitable zones around single stars; however, it has also profound consequence for the habitable regions in binary systems (both S-type and P-type), the topic of the intended presentation.

  10. Habit formation

    PubMed Central

    Smith, Kyle S.; Graybiel, Ann M.

    2016-01-01

    Habits, both good ones and bad ones, are pervasive in animal behavior. Important frameworks have been developed to understand habits through psychological and neurobiological studies. This work has given us a rich understanding of brain networks that promote habits, and has also helped us to understand what constitutes a habitual behavior as opposed to a behavior that is more flexible and prospective. Mounting evidence from studies using neural recording methods suggests that habit formation is not a simple process. We review this evidence and take the position that habits could be sculpted from multiple dissociable changes in neural activity. These changes occur across multiple brain regions and even within single brain regions. This strategy of classifying components of a habit based on different brain signals provides a potentially useful new way to conceive of disorders that involve overly fixed behaviors as arising from different potential dysfunctions within the brain's habit network. PMID:27069378

  11. EXOPLANET CHARACTERIZATION BY PROXY: A TRANSITING 2.15 R{sub Circled-Plus} PLANET NEAR THE HABITABLE ZONE OF THE LATE K DWARF KEPLER-61

    SciTech Connect

    Ballard, Sarah; Charbonneau, David; Fressin, Francois; Torres, Guillermo; Irwin, Jonathan; Newton, Elisabeth; Desert, Jean-Michel; Crepp, Justin R.; Shporer, Avi; Mann, Andrew W.; Ciardi, David R.; Horch, Elliott P.; Everett, Mark E.

    2013-08-20

    We present the validation and characterization of Kepler-61b: a 2.15 R{sub Circled-Plus} planet orbiting near the inner edge of the habitable zone of a low-mass star. Our characterization of the host star Kepler-61 is based upon a comparison with a set of spectroscopically similar stars with directly measured radii and temperatures. We apply a stellar prior drawn from the weighted mean of these properties, in tandem with the Kepler photometry, to infer a planetary radius for Kepler-61b of 2.15 {+-} 0.13 R{sub Circled-Plus} and an equilibrium temperature of 273 {+-} 13 K (given its period of 59.87756 {+-} 0.00020 days and assuming a planetary albedo of 0.3). The technique of leveraging the physical properties of nearby ''proxy'' stars allows for an independent check on stellar characterization via the traditional measurements with stellar spectra and evolutionary models. In this case, such a check had implications for the putative habitability of Kepler-61b: the planet is 10% warmer and larger than inferred from K-band spectral characterization. From the Kepler photometry, we estimate a stellar rotation period of 36 days, which implies a stellar age of >1 Gyr. We summarize the evidence for the planetary nature of the Kepler-61 transit signal, which we conclude is 30,000 times more likely to be due to a planet than a blend scenario. Finally, we discuss possible compositions for Kepler-61b with a comparison to theoretical models as well as to known exoplanets with similar radii and dynamically measured masses.

  12. The effects of circumstellar gas on terrestrial planet formation: Theory and observation

    NASA Astrophysics Data System (ADS)

    Mandell, Avram M.

    Our understanding of the evolution of circumstellar material from dust and gas to fully-formed planets has taken dramatic steps forward in the last decade, driven by rapid improvements in our ability to study gas- and dust-rich disks around young stars and the discovery of more than 200 extra-solar planetary systems around other stars. In addition, our ability to model the formation of both terrestrial and giant planets has improved significantly due to new computing techniques and the continued exponential increase in computing power. In this dissertation I expand on existing theories of terrestrial planet formation to include systems similar to those currently being detected around nearby stars, and I develop new observational techniques to probe the chemistry of gas-rich circumstellar disks where such planetary systems may be forming. One of the most significant characteristics of observed extrasolar planetary systems is the presence of giant planets located much closer to their parent star than was thought to be possible. The presence of "Hot Jupiters", Jovian-mass planets with very short orbital periods detected around nearby main sequence stars, has been proposed to be primarily due to the inward migration of planets formed in orbits initially much further from the parent star. Close-in giant planets are thought to have formed in the cold outer regions of planetary systems and migrated inward, passing through the orbital parameter space occupied by the terrestrial planets in our own Solar System; the migration of these planets would have profound effects on the evolution of inner terrestrial planets in these systems. I first explore this scenario with numerical simulations showing that a significant fraction of terrestrial planets could survive the migration process; damping forces could then eventually re-circularize the orbits at distances relatively close to their original positions. Calculations suggest that the final orbits of a significant fraction of the remaining planets would be located in the Habitable Zone, suggesting that planetary systems with close-in giant planets are viable targets for searches for Earth-like habitable planets around other stars. I then present more realistic dynamical simulations of the effects of a migrating giant planet on a disk of protoplanetary material embedded in a gaseous disk, and the subsequent post-scattering evolution of the planetary system. I numerically investigate the dynamics of several types of post-migration planetary systems over 200 million years: a model with a single migrating giant planet, a model with one migrating and one nonmigrating giant planet, and a model excluding the effects of the gas disk. Material that is shepherded in front of the migrating giant planet by moving mean motion resonances accretes into "hot Earths", but survival of these bodies is strongly dependent on dynamical damping. Furthermore, a significant amount of material scattered outward by the giant planet survives in highly excited orbits; the orbits of these scattered bodies are then damped by gas drag and dynamical friction over the remaining accretion time. In all simulations Earth-mass planets accrete on approximately 100 Myr timescales, often with orbits in the Habitable Zone. These planets range in mass and water content, with both quantities increasing with the presence of a gas disk and decreasing with the presence of an outer giant planet. I use scaling arguments and previous results to derive a simple recipe that constrains which giant planet systems are able to form and harbor Earth-like planets in the Habitable Zone, demonstrating that roughly one third of the known planetary systems are potentially habitable. Finally, I present results from a search for new molecular tracers of warm gas in circumstellar disks using the NIRSPEC instrument on the Keck II telescope. I have detected emission from multiple ro-vibrational transitions in the v = 1--0 band of hydroxyl (OH) located in the inner circumstellar regions of two Herbig Ae stars, AB Aurigae and MWC 758. I analyze the temperature of the emitting gas by constructing rotational diagrams, showing that the temperature of the gas in both systems is approximately 700K. I calculate a secure abundance of emitting OH molecules in the upper vibrational state, and discuss the ramifications of various excitation processes on the extrapolation to the total number of OH molecules. I also calculate an inner radius for the emitting gas, showing that the derived Rin is equivalent to that found by near-IR imaging. I compare these results to models of circumstellar disk chemistry as well as observations of other chemical diagnostics, and discuss further improvements to excitation models that are necessary to fully understand the formation and thermal conditions of the detected OH gas.

  13. Exomoon habitability and tidal evolution in low-mass star systems

    NASA Astrophysics Data System (ADS)

    Zollinger, Rhett R.

    Current technology and theoretical methods are allowing for the detection of sub-Earth sized extrasolar planets. In addition, the detection of massive moons orbiting extrasolar planets ("exomoons'') has become feasible and searches are currently underway. Several extrasolar planets have now been discovered in the habitable zone (HZ) of their parent star. This naturally leads to questions about the habitability of moons around planets in the HZ. Red dwarf stars present interesting targets for habitable planet detection. Compared to the Sun, red dwarfs are smaller, fainter, lower mass, and much more numerous. Due to their low luminosities, the HZ is much closer to the star than for Sun-like stars. For a planet-moon binary in the HZ, the close proximity of the star presents dynamical restrictions on the stability of the moon, forcing it to orbit close to the planet to remain gravitationally bound. Under these conditions the effects of tidal heating, distortion torques, and stellar perturbations become important considerations to the habitability of an exomoon. Utilizing an evolution model that considers both dynamical and tidal interactions, I performed a computational investigation into long-term evolution of exomoon systems. My study focused on satellite systems in the HZ of red dwarf stars and the dependence of exomoon habitability on the mass of the central star. Results show that dwarf stars with masses less than about 0.2 solar masses cannot host habitable exomoons within the stellar HZ due to extreme tidal heating in the moon. These results suggest that a host planet could be located outside the stellar HZ to where higher tidal heating rates could act to promote habitability for an otherwise uninhabitable moon. Perturbations from a central star may continue to have deleterious effects in the HZ up to about 0.5 solar masses, depending on the host planet's mass and its location in the HZ. In cases with lower intensity tidal heating, stellar perturbations may have a positive influence on exomoon habitability by promoting long-term heating rates above a minimum for habitable terrestrial environments. In addition to heating concerns, torques due to tidal and spin distortion can lead to the relatively rapid inward spiraling of a moon. The effects of torque and stability constraints also make it unlikely that long-term resonances between two massive moons will develop in the HZs around red dwarf stars. My study showed that moons in the circumstellar HZ are not necessarily habitable by definition. In addition, the HZ for an exomoon may extend beyond the HZ for an exoplanet. Therefore, an extended model is required when considering exomoon habitability in comparison to exoplanet habitability.

  14. Prediction of Detectability of Potentially Habitable Extrasolar Planets Using a Monte Carlo Simulation

    NASA Astrophysics Data System (ADS)

    Blight, Wilfred J.

    The transit technique is an extrasolar planet detection method that measures very small changes in the brightness of a star caused by a planet that passes in front of its host star. Planet mass, radius, semimajor axis and orbital eccentricity along with the stellar mass and distance have a large impact on transit detectability. To accurately determine the impact of each of these properties and the number of transits that might be observed within and without of the circumstellar habitable zone (HZ), we have built a model with a representative distribution of each property. We ran two simulations, each with a billion stars, each star with a planet, and distributed both stars and planets using distributions created from empirical data. In the first simulation we examined the theoretical outcome, without consideration of technical limits. We found that only 0.76% of stars had transiting planets and that M-type stars had the highest number of HZ transits per star. In the second simulation we limited the stellar apparent magnitudes and photometric precision to values the Kepler telescope will use. 12.13% of the stars fit within the Kepler's apparent magnitude range of 9-15. Overall, A-type stars have the highest number of transits per star, but M-type stars have the highest fraction of habitable planets per star. If all stars had a solar system like our own, we predict that Kepler would be able to detect solar-system-like planets in the habitable zone around K-type, G-type and F-type stars, with Venus-like planets representing 62% of the HZ transits and Earth-like planets representing 38%. Keywords: Astrobiology, Planetary Transits, Habitable Zone, Habitable Planets.

  15. Circumstellar Dust Created by Terrestrial Planet Formation Processes Around HD 113766A

    NASA Astrophysics Data System (ADS)

    Lisse, Carey M.; Chen, C. H.; Wyatt, M. C.; Morlok, A.

    2007-10-01

    We present an analysis of the circumstellar disk material in the HD 113766 binary system (F3/F5, 16 Myr), recently observed by the Spitzer Space Telescope. For our study we have used the infrared mineralogical model derived from observations of the Deep Impact experiment. We find the dust dominated by warm, fine ( 1 um) particles, abundant in Mg-rich olivine, crystalline pyroxenes, amorphous silicates, Fe-rich sulfides, amorphous carbon, and water ice. The material mix is akin to an inner main belt asteroid of S- or V-type composition, and is dissimilar to the organic- and water-rich comet systems 9P/Tempel 1, C/Hale-Bopp 1995 O1, or the comet-dominated YSO HD 100546. The 440 K effective temperature of the warm dust implies that the bulk of the observed material is at 1.8 AU from the 4.4 Lsolar central source, in the terrestrial planet-forming region and habitable zone of the system (equivalent to 0.9 AU in the solar system). The icy dust lies in 2 belts, at 9 AU and at 60-80 AU. The amount of mass responsible for the warm dust emission in dn/da a-3.5 particles is very large, 3 x 1023 kg, or 0.5 MMars. The persistence of the strong IR excess over the last two decades argues for a mechanism to provide replenishment of the circumstellar material on yearly timescales. The disk around HD 113766A appears to arise from collisions in a young, extremely dense asteroid belt, or from catastrophic disruption of terrestrial planet embryo(s) and subsequent grinding of the fragments.

  16. Age aspects of habitability

    NASA Astrophysics Data System (ADS)

    Safonova, M.; Murthy, J.; Shchekinov, Yu. A.

    2016-04-01

    A `habitable zone' of a star is defined as a range of orbits within which a rocky planet can support liquid water on its surface. The most intriguing question driving the search for habitable planets is whether they host life. But is the age of the planet important for its habitability? If we define habitability as the ability of a planet to beget life, then probably it is not. After all, life on Earth has developed within only ~800 Myr after its formation - the carbon isotope change detected in the oldest rocks indicates the existence of already active life at least 3.8 Gyr ago. If, however, we define habitability as our ability to detect life on the surface of exoplanets, then age becomes a crucial parameter. Only after life had evolved sufficiently complex to change its environment on a planetary scale, can we detect it remotely through its imprint on the atmosphere - the so-called biosignatures, out of which the photosynthetic oxygen is the most prominent indicator of developed (complex) life as we know it. Thus, photosynthesis is a powerful biogenic engine that is known to have changed our planet's global atmospheric properties. The importance of planetary age for the detectability of life as we know it follows from the fact that this primary process, photosynthesis, is endothermic with an activation energy higher than temperatures in habitable zones, and is sensitive to the particular thermal conditions of the planet. Therefore, the onset of photosynthesis on planets in habitable zones may take much longer time than the planetary age. The knowledge of the age of a planet is necessary for developing a strategy to search for exoplanets carrying complex (developed) life - many confirmed potentially habitable planets are too young (orbiting Population I stars) and may not have had enough time to develop and/or sustain detectable life. In the last decade, many planets orbiting old (9-13 Gyr) metal-poor Population II stars have been discovered. Such planets had had enough time to develop necessary chains of chemical reactions and may carry detectable life if located in a habitable zone. These old planets should be primary targets in search for the extraterrestrial life.

  17. Habitability in Binary Systems: The Role of UV Reduction and Magnetic Protection

    NASA Astrophysics Data System (ADS)

    Clark, Joni; Mason, P. A.; Zuluaga, J. I.; Cuartas, P. A.; Bustamonte, S.

    2013-06-01

    The number of planets found in binary systems is growing rapidly and the discovery of many more planets in binary systems appears inevitable. We use the newly refined and more restrictive, single star habitable zone (HZ) models of Kopparapu et al. (2013) and include planetary magnetic protection calculations in order to investigate binary star habitability. Here we present results on circumstellar or S-type planets, which are planets orbiting a single star member of a binary. P-type planets, on the other hand, orbit the center of mass of the binary. Stable planetary orbits exist in HZs for both types of binaries as long as the semi-major axis of the planet is either greater than (P-type) or less than (S-type) a few times the semi-major axis of the binary. We define two types of S-type binaries for this investigation. The SA-type is a circumstellar planet orbiting the binary’s primary star. In this case, the limits of habitability are dominated by the primary being only slightly affected by the presence of the lower mass companion. Thus, the SA-type planets have habitability characteristics, including magnetic protection, similar to single stars of the same type. The SB-type is a circumstellar planet orbiting the secondary star in a wide binary. An SB-type planet needs to orbit slightly outside the secondary’s single star HZ and remain within the primary’s single star HZ at all times. We explore the parameter space for which this is possible. We have found that planets lying in the combined HZ of SB binaries can be magnetically protected against the effects of stellar winds from both primary and secondary stars in a limited number of cases. We conclude that habitable conditions exist for a subset of SA-type, and a smaller subset of SB-type binaries. However, circumbinary planets (P-types) provide the most intriguing possibilities for the existence of complex life due to the effect of synchronization of binaries with periods in the 20-30 day range which allows for planets with significant magnetic protection.

  18. THE LICK-CARNEGIE EXOPLANET SURVEY: A SATURN-MASS PLANET IN THE HABITABLE ZONE OF THE NEARBY M4V STAR HIP 57050

    SciTech Connect

    Haghighipour, Nader; Vogt, Steven S.; Rivera, Eugenio J.; Laughlin, Greg; Meschiari, Stefano; Henry, Gregory W.

    2010-05-20

    Precision radial velocities (RV) from Keck/HIRES reveal a Saturn-mass planet orbiting the nearby M4V star HIP 57050. The planet has a minimum mass of Msin i {approx} 0.3 M{sub J}, an orbital period of 41.4 days, and an orbital eccentricity of 0.31. V-band photometry reveals a clear stellar rotation signature of the host star with a period of 98 days, well separated from the period of the RV variations and reinforcing a Keplerian origin for the observed velocity variations. The orbital period of this planet corresponds to an orbit in the habitable zone of HIP 57050, with an expected planetary temperature of {approx}230 K. The star has a metallicity of [Fe/H] = 0.32 {+-} 0.06 dex, of order twice solar and among the highest metallicity stars in the immediate solar neighborhood. This newly discovered planet provides further support that the well-known planet-metallicity correlation for F, G, and K stars also extends down into the M-dwarf regime. The a priori geometric probability for transits of this planet is only about 1%. However, the expected eclipse depth is {approx}7%, considerably larger than that yet observed for any transiting planet. Though long on the odds, such a transit is worth pursuing as it would allow for high quality studies of the atmosphere via transmission spectroscopy with Hubble Space Telescope. At the expected planetary effective temperature, the atmosphere may contain water clouds.

  19. Conditions for oceans on Earth-like planets orbiting within the habitable zone: importance of volcanic CO{sub 2} degassing

    SciTech Connect

    Kadoya, S.; Tajika, E. E-mail: tajika@astrobio.k.u-tokyo.ac.jp

    2014-08-01

    Earth-like planets in the habitable zone (HZ) have been considered to have warm climates and liquid water on their surfaces if the carbonate-silicate geochemical cycle is working as on Earth. However, it is known that even the present Earth may be globally ice-covered when the rate of CO{sub 2} degassing via volcanism becomes low. Here we discuss the climates of Earth-like planets in which the carbonate-silicate geochemical cycle is working, with focusing particularly on insolation and the CO{sub 2} degassing rate. The climate of Earth-like planets within the HZ can be classified into three climate modes (hot, warm, and snowball climate modes). We found that the conditions for the existence of liquid water should be largely restricted even when the planet is orbiting within the HZ and the carbonate-silicate geochemical cycle is working. We show that these conditions should depend strongly on the rate of CO{sub 2} degassing via volcanism. It is, therefore, suggested that thermal evolution of the planetary interiors will be a controlling factor for Earth-like planets to have liquid water on their surface.

  20. Kepler-62: a five-planet system with planets of 1.4 and 1.6 Earth radii in the habitable zone.

    PubMed

    Borucki, William J; Agol, Eric; Fressin, Francois; Kaltenegger, Lisa; Rowe, Jason; Isaacson, Howard; Fischer, Debra; Batalha, Natalie; Lissauer, Jack J; Marcy, Geoffrey W; Fabrycky, Daniel; Désert, Jean-Michel; Bryson, Stephen T; Barclay, Thomas; Bastien, Fabienne; Boss, Alan; Brugamyer, Erik; Buchhave, Lars A; Burke, Chris; Caldwell, Douglas A; Carter, Josh; Charbonneau, David; Crepp, Justin R; Christensen-Dalsgaard, Jørgen; Christiansen, Jessie L; Ciardi, David; Cochran, William D; DeVore, Edna; Doyle, Laurance; Dupree, Andrea K; Endl, Michael; Everett, Mark E; Ford, Eric B; Fortney, Jonathan; Gautier, Thomas N; Geary, John C; Gould, Alan; Haas, Michael; Henze, Christopher; Howard, Andrew W; Howell, Steve B; Huber, Daniel; Jenkins, Jon M; Kjeldsen, Hans; Kolbl, Rea; Kolodziejczak, Jeffery; Latham, David W; Lee, Brian L; Lopez, Eric; Mullally, Fergal; Orosz, Jerome A; Prsa, Andrej; Quintana, Elisa V; Sanchis-Ojeda, Roberto; Sasselov, Dimitar; Seader, Shawn; Shporer, Avi; Steffen, Jason H; Still, Martin; Tenenbaum, Peter; Thompson, Susan E; Torres, Guillermo; Twicken, Joseph D; Welsh, William F; Winn, Joshua N

    2013-05-01

    We present the detection of five planets--Kepler-62b, c, d, e, and f--of size 1.31, 0.54, 1.95, 1.61 and 1.41 Earth radii (R⊕), orbiting a K2V star at periods of 5.7, 12.4, 18.2, 122.4, and 267.3 days, respectively. The outermost planets, Kepler-62e and -62f, are super-Earth-size (1.25 R⊕ < planet radius ≤ 2.0 R⊕) planets in the habitable zone of their host star, respectively receiving 1.2 ± 0.2 times and 0.41 ± 0.05 times the solar flux at Earth's orbit. Theoretical models of Kepler-62e and -62f for a stellar age of ~7 billion years suggest that both planets could be solid, either with a rocky composition or composed of mostly solid water in their bulk. PMID:23599262

  1. Exoplanets, extremophiles and habitability

    NASA Astrophysics Data System (ADS)

    Janot Pacheco, E.; Bernardes, L.

    2012-09-01

    Estimates of the average surface temperature and CO2 partial atmospheric pressure of already discovered exoplanets supposed to be in their Habitable Zone of their stars were surveyed from the Exoplanet Encyclopedia database. Moreover, since planetary surface temperature strongly depends on its albedo and geodynamic conditions, we have been feeding exoplanetary data into a comprehensive model of Earth's atmosphere to get better estimations. We also investigated the possible presence of "exomoons" belonging to giant planets capable of harbour dynamic stability and to retain atmospheric layers and keep geodynamic activity for long time spans. Collected information on biological data of micro-organisms classified as "extremophiles" indicate that such kind of microbial species could dwell in many of them. We thus propose an extension of the more astronomically defined "Habitable Zone" concept into the more astrobiologically "Extremophile Zone", taking into account other refined parameters allowing survival of more robust life forms.

  2. Where to Look for Habitability

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-03-01

    One of the main goals of exoplanet surveys like the Kepler mission is to find potentially habitable planets orbiting other stars. Finding planets in a stars habitable zone, however, is easier when we know in advance where to look! A recent study has provided us with a starting point.Defining the ZoneA habitable zone is defined as the range of distances from a star where liquid water could exist on an orbiting planet, given a dense enough planetary atmosphere. The habitable zone can be calculated from the stars parameters, and the inner and outer edges of a habitable zone are set considering hypothetical planetary atmospheres of different composition.Knowing the parameters of the habitable zones around nearby stars is important for current and future exoplanet surveys, as this information allows them to identify stars with habitable zones that can be probed, given the surveys sensitivity. To provide this target selection tool, a team of scientists led by Colin Chandler (San Francisco State University) has created a catalog of the habitable zones of roughly 37,000 nearby, main-sequence stars.Distribution of habitable-zone widths found in CELESTA, for conservative and optimistic measurements. [Chandler et al. 2016]Selecting for Sun-Like StarsThe Catalog of Earth-Like Exoplanet Survey Targets, or CELESTA, was built starting with the Revised Hipparcos Catalog, a high-precision catalog of photometry and parallax measurements (which provides the stars distance) for 117,955 bright, nearby stars. Chandler and collaborators combined these measurements with stellar models to determine parameters such as effective temperature, radius, and mass of the stars.The authors exclude giant stars and cool dwarfs, choosing to focus on main-sequence stars within the temperature range 26007200K, more similar to the Sun. They test their derived stellar parameters by comparing to observational data from the Exoplanet Data Explorer (EDE), where available, and confirm that their photometrically derived stellar parameters agree well with the parameters in EDE, typically measured spectroscopically.Providing Survey TargetsPlot showing the number of stellar habitable zones that can be probed by a survey, based on how long the stars are observed in the surveys. Surveys listed as reference points are TESS at 27 days, K2 at 75 days, PLATO at 180 days, HARPS at 6 years, and AAPS at 15 years. [Chandler et al. 2016]The final CELESTA catalog details the habitable zones of 37,354 bright, main-sequence stars. The stars habitable-zone widths are generally under 5 AU, with the majority falling between 1 and 1.5 AU. The authors also provide an estimate of how many of these habitable zones current surveys (like Kepler) and upcoming surveys (like the Transiting Exoplanet Survey Satellite, or TESS) will be able to probe, based on the duration of the surveys typical campaigns.Though a planets potential for habitability relies on additional factors besides the location of its orbit, cataloging the locations of stellar habitable zones for nearby, observable stars is an important start. CELESTA is an excellent reference for this, and it will provide a living resource that the authors plan to continue to update with additional stars, as well as with improved-accuracy stellar measurements, expected from upcoming astrometric missions.CitationColin Orion Chandler et al 2016 AJ 151 59. doi:10.3847/0004-6256/151/3/59

  3. Habitable Trinity

    NASA Astrophysics Data System (ADS)

    Dohm, J. M.; Maruyama, S.

    2013-12-01

    We propose a new concept of a habitable environment in the search for life beyond Earth that goes beyond the follow-the-water paradigm, newly named Habitable Trinity. Habitable Trinity is the coexistence of an atmosphere (consisting largely of C and N), an ocean (H and O), and a landmass (supplier of nutrients). It is the minimum requirement for the beginning of life to satisfy (1) formation of membrane, (2) metabolism, and (3) self-replication as we know it. A habitable planet, which has largely been defined as having an adequate climate, a sufficient atmosphere, and the presence of liquid water on its surface, is insufficient to meet the requirements to bear life. Also, material circulation driven by the Sun must be maintained with Habitable Trinity to continue the supply of elements necessary to sustain organic radical reactions that is the basis of life. The Sun is the major engine that links the three components primarily through hydrological cycling, including weathering, erosion, and transport of nutrient-enriched landmass materials to the ocean via far-reaching river systems. Habitable Trinity can be applied to other planets and moons to discuss the presence of extraterrestrial life. Mars is considered to be the best target to test the hypothesis of whether life exists elsewhere in our solar system, as it records an ancient Habitable Trinity (i.e., lakes and oceans which interacted with a landmass (cratered southern highlands) and an atmosphere). Other terrestrial planets, as well as satellites of the gaseous giants such as Europa and Titan, have little chance to harbor life as we know it because they lack Habitable Trinity. Going beyond 'the-follow-the-water-approach', the Habitable-Trinity concept provides an index in the quest for life-containing planetary bodies beyond our solar system as the reconnaissance systems become increasingly autonomous and at higher resolution, affording greater perspective during this golden age of international and interdisciplinary exploration and discovery.

  4. CHARACTERIZING HABITABLE EXOMOONS

    SciTech Connect

    Kaltenegger, L.

    2010-04-01

    We discuss the possibility of screening the atmosphere of exomoons for habitability. We concentrate on Earth-like satellites of extrasolar giant planets (EGPs) that orbit in the Habitable Zone (HZ) of their host stars. The detectability of exomoons for EGPs in the HZ has recently been shown to be feasible with the Kepler Mission or equivalent photometry using transit duration observations. Transmission spectroscopy of exomoons is a unique potential tool to screen them for habitability in the near future, especially around low mass stars. Using the Earth itself as a proxy we show the potential and limits of spectroscopy to detect biomarkers on an Earth-like exomoon and discuss effects of tidal locking for such potential habitats.

  5. Al-26 and circumstellar envelopes

    NASA Technical Reports Server (NTRS)

    Glassgold, A. E.

    1995-01-01

    The effects of the radioactive decay of Al-26 on the circumstellar envelopes of asymptotic giant branch stars are analyzed. The gamma-rays emitted by the product nucleus Mg-26 escape most envelopes, but the beta-decay positrons are stopped and can ionize and heat the gas. The ionization may produce observable effects in C-rich circumstellar envelopes, particularly if the photospheric Al-26 abundance is as large as inferred from measurements of live Al-26 in the primitive solar nebula or the observations of interstellar 1.8 MeV gamma-rays. For the nearby carbon star IRC +10216, the measured abundance of the molecular ion HCO(+) provides an upper limit of about 4 x 10(exp -3) for the photospheric Al-26/Al-27 ratio, consistent with presolar SiC grains with about the same C-12/C-13 ratio.

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

    SciTech Connect

    Borucki, William J.; Koch, David G.; Bryson, Stephen T.; Howell, Steve B.; Lissauer, Jack J.; Batalha, Natalie; Rowe, Jason; Caldwell, Douglas A.; DeVore, Edna; Jenkins, Jon M.; Fressin, Francois; Torres, Guillermo; Geary, John C.; Latham, David W.; Christensen-Dalsgaard, Jorgen; Cochran, William D.; Gautier, Thomas N.; Gilliland, Ronald; Gould, Alan; Marcy, Geoffrey W.; and others

    2012-02-01

    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 tests 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.

  7. Remote life-detection criteria, habitable zone boundaries, and the frequency of Earth-like planets around M and late K stars

    PubMed Central

    Kasting, James F.; Kopparapu, Ravikumar; Ramirez, Ramses M.; Harman, Chester E.

    2014-01-01

    The habitable zone (HZ) around a star is typically defined as the region where a rocky planet can maintain liquid water on its surface. That definition is appropriate, because this allows for the possibility that carbon-based, photosynthetic life exists on the planet in sufficient abundance to modify the planet’s atmosphere in a way that might be remotely detected. Exactly what conditions are needed, however, to maintain liquid water remains a topic for debate. In the past, modelers have restricted themselves to water-rich planets with CO2 and H2O as the only important greenhouse gases. More recently, some researchers have suggested broadening the definition to include arid, “Dune” planets on the inner edge and planets with captured H2 atmospheres on the outer edge, thereby greatly increasing the HZ width. Such planets could exist, but we demonstrate that an inner edge limit of 0.59 AU or less is physically unrealistic. We further argue that conservative HZ definitions should be used for designing future space-based telescopes, but that optimistic definitions may be useful in interpreting the data from such missions. In terms of effective solar flux, Seff, the recently recalculated HZ boundaries are: recent Venus—1.78; runaway greenhouse—1.04; moist greenhouse—1.01; maximum greenhouse—0.35; and early Mars—0.32. Based on a combination of different HZ definitions, the frequency of potentially Earth-like planets around late K and M stars observed by Kepler is in the range of 0.4–0.5. PMID:24277805

  8. Remote life-detection criteria, habitable zone boundaries, and the frequency of Earth-like planets around M and late K stars.

    PubMed

    Kasting, James F; Kopparapu, Ravikumar; Ramirez, Ramses M; Harman, Chester E

    2014-09-01

    The habitable zone (HZ) around a star is typically defined as the region where a rocky planet can maintain liquid water on its surface. That definition is appropriate, because this allows for the possibility that carbon-based, photosynthetic life exists on the planet in sufficient abundance to modify the planet's atmosphere in a way that might be remotely detected. Exactly what conditions are needed, however, to maintain liquid water remains a topic for debate. In the past, modelers have restricted themselves to water-rich planets with CO2 and H2O as the only important greenhouse gases. More recently, some researchers have suggested broadening the definition to include arid, "Dune" planets on the inner edge and planets with captured H2 atmospheres on the outer edge, thereby greatly increasing the HZ width. Such planets could exist, but we demonstrate that an inner edge limit of 0.59 AU or less is physically unrealistic. We further argue that conservative HZ definitions should be used for designing future space-based telescopes, but that optimistic definitions may be useful in interpreting the data from such missions. In terms of effective solar flux, S(eff), the recently recalculated HZ boundaries are: recent Venus--1.78; runaway greenhouse--1.04; moist greenhouse--1.01; maximum greenhouse--0.35; and early Mars--0.32. Based on a combination of different HZ definitions, the frequency of potentially Earth-like planets around late K and M stars observed by Kepler is in the range of 0.4-0.5. PMID:24277805

  9. The M dwarf planet search programme at the ESO VLT + UVES. A search for terrestrial planets in the habitable zone of M dwarfs

    NASA Astrophysics Data System (ADS)

    Zechmeister, M.; Kürster, M.; Endl, M.

    2009-10-01

    We present radial velocity (RV) measurements of our sample of 40 M dwarfs from our planet search programme with VLT+UVES begun in 2000. Although with our RV precision down to 2-2.5 m/s and timebase line of up to 7 years, we are capable of finding planets of a few Earth masses in the close-in habitable zones of M dwarfs, there is no detection of a planetary companion. To demonstrate this we present mass detection limits allowing us to exclude Jupiter-mass planets up to 1 AU for most of our sample stars. We identified 6 M dwarfs that host a brown dwarf or low-mass stellar companion. With the exception of these, all other sample stars show low RV variability with an rms <20 m/s. Some high proper motion stars exhibit a linear RV trend consistent with their secular acceleration. Furthermore, we examine our data sets for a possible correlation between RVs and stellar activity as seen in variations of the Hα line strength. For Barnard's star we found a significant anticorrelation, but most of the sample stars do not show such a correlation. Based on observations collected at the European Southern Observatory, Paranal Chile, ESO programmes 65.L-0428, 66.C-0446, 267.C-5700, 68.C-0415, 69.C-0722, 70.C-0044, 71.C-0498, 072.C-0495, 173.C-0606, 078.C-0829. Radial velocity data are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/505/859

  10. A PLANETARY SYSTEM AROUND THE NEARBY M DWARF GJ 667C WITH AT LEAST ONE SUPER-EARTH IN ITS HABITABLE ZONE

    SciTech Connect

    Anglada-Escude, Guillem; Butler, R. Paul; Arriagada, Pamela; Minniti, Dante; Vogt, Steven S.; Rivera, Eugenio J.; Haghighipour, Nader; Carter, Brad D.; Tinney, C. G.; Wittenmyer, Robert A.; Bailey, Jeremy A.; O'Toole, Simon J.; Jones, Hugh R. A.; Jenkins, James S.

    2012-05-20

    We re-analyze 4 years of HARPS spectra of the nearby M1.5 dwarf GJ 667C available through the European Southern Observatory public archive. The new radial velocity (RV) measurements were obtained using a new data analysis technique that derives the Doppler measurement and other instrumental effects using a least-squares approach. Combining these new 143 measurements with 41 additional RVs from the Magellan/Planet Finder Spectrograph and Keck/High Resolution Echelle Spectrometer spectrometers reveals three additional signals beyond the previously reported 7.2 day candidate, with periods of 28 days, 75 days, and a secular trend consistent with the presence of a gas giant (period {approx}10 years). The 28 day signal implies a planet candidate with a minimum mass of 4.5 M{sub Circled-Plus} orbiting well within the canonical definition of the star's liquid water habitable zone (HZ), that is, the region around the star at which an Earth-like planet could sustain liquid water on its surface. Still, the ultimate water supporting capability of this candidate depends on properties that are unknown such as its albedo, atmospheric composition, and interior dynamics. The 75 day signal is less certain, being significantly affected by aliasing interactions among a potential 91 day signal, and the likely rotation period of the star at 105 days detected in two activity indices. GJ 667C is the common proper motion companion to the GJ 667AB binary, which is metal-poor compared to the Sun. The presence of a super-Earth in the HZ of a metal-poor M dwarf in a triple star system supports the evidence that such worlds should be ubiquitous in the Galaxy.

  11. Exoplanets in the Habitable Zone

    NASA Astrophysics Data System (ADS)

    Borucki, W. J.; Kaltenegger, L.; Doyle, L.

    2012-12-01

    Nearly 3000 planetary candidates have been found with an enormous range of sizes, densities, semi-major axes, and types of stellar hosts. In particular, exoplanets near the size of Earth's moon to those larger than Jupiter have been found orbiting stars much cooler and smaller than the Sun as well to stars hotter and often larger than the Sun. Orbital periods range from 0.84 days to over 1000 days and orbital distances range from 0.01 AU to many AU. In addition to the photometric determination of the sizes of planets, masses can be determined for those planets with large masses and/or short orbital-periods from radial velocity and transit timing measurements. By combining these results, densities of these planets are calculated. The results are indicative of planetary compositions that range from mostly gas, to water planets, and to iron-rich rocky planets. Surprisingly wide ranges of densities have been found for closely-packed planets orbiting the same star. This result implies that contrary to what is observed in our Solar System, the composition (whether rocky, water-rich, or gas) cannot be deduced from its semi-major axis or insolation. For planets with an atmosphere, the surface temperature will be higher than equilibrium temperature Teq and will depend on the amount and spectral characteristics of the insolation as well as atmospheric properties such as mass, composition, and albedo. Unfortunately, the latter are unknown and there are substantial uncertainties in the former because the stellar size is often poorly known. Variations of insolation can be very large for planets orbiting binary stars as well as for those planets with high eccentricity. Thus the associated climatic conditions vary over a very wide range. Because it is much more difficult to find small planets in the HZ compared to finding large planets in short period orbits, only a few dozen planetary candidates and confirmed planets have been discovered in the HZ. Therefore the estimate of the distributions of planetary characteristics and climatic conditions in the HZ benefits from the knowledge of the wider distributions. A summary of the known characteristics of exoplanets, especially small planets and those in the HZ will be presented.

  12. Exoplanet Habitability: Effects of Planetesimal Carbon Chemistry

    NASA Astrophysics Data System (ADS)

    Johnson, Torrence; Mousis, Olivier; Lunine, Jonathan; Madhusudhan, Nikku

    2014-05-01

    We explore the effects of reported differences in C/O values for exoplanet host stars on the composition of planetesimals formed beyond the snow line in these systems. Since the value of C/O in a planet forming nebula has a strong effect on amount of oxygen available for water ice in an oxidizing nebula, exoplanet systems for host stars with C/O greater than the solar value may have planetesimals with very little or no water ice. We have estimated the composition of volatile and refractory material in extrasolar planetesimals using a set of stars with a wide range of measured C/O abundances (Johnson et al. ApJ. 757(2), 192, 2012). The volatile ice content of planetesimals in these systems varies significantly with C/O, controlled primarily by the availability of O for H2O ice condensation. Systems with C/O less than the solar value (C/O = 0.55) should have very water ice rich planetesimals, while water ice mass fraction decreases rapidly with increasing C/O until only ices of CO and CO2 are left in significant proportions. If a significant fraction of C is in the form of refractory CHON particles, C and O are removed from the gas phase and the condensates for super-solar C/O values will be water-poor mixtures of silicates and metal, carbon, and carbon-bearing volatile ices, depending on temperature. For very carbon-rich systems, oxidizing conditions cannot be sustained beyond about C/O=1, due to the oxygen sequestered in solid silicates, oxides and CHON, for refractory C fractions within the Pollack et al. range of 0.4 - 0.7 (ApJ. 421, 615, 1994). These results have implications for assessing the habitability of exoplanets since they constrain the amount of water available beyond the snow line for dynamical delivery to inner planets, depending on the host star's C/O in the circumstellar nebula. Thus one the key chemical ingredients for habitability may be in short supply in carbon-rich, oxygen-poor systems even if planets exist in the 'habitable zone'. TVJ acknowledges government support at JPL/Caltech, under a contract with NASA. NM acknowledges support from Yale University. JIL was supported by the JWST Project through NASA. O.M. acknowledges support from CNES.

  13. Abundant Circumstellar Silica Dust and SiO Gas Created by a Giant Hypervelocity Collision in the 12 Myr HD172555 System

    NASA Astrophysics Data System (ADS)

    Lisse, Carey M.; Chen, C. H.; Wyatt, M. C.; Morlok, A.; Song, I.; Bryden, G.; Sheehan, P.

    2009-09-01

    We have used the IRS Spectrograph onboard the Spitzer Space Telescope to study the warm dust orbiting around the 29 pc distant β Pic analogue star HD172555. The dust mineralogy is very peculiar, composed primarily of highly refractory, non-equilibrium materials, with 3/4 of the Si atoms in silica (SiO2) species. Tektite and obsidian lab thermal emission spectra (non-equilibrium glassy silicas found in impact and magmatic systems) are required to fit the data. The best-fit model size distribution for the observed fine dust is dn/da = a-3.95±0.10. This steep a size distribution argues for a fresh source of material within the last 0.1 Myr. The location of the dust with respect to the star is at 5.8 ± 0.6 AU, within the terrestrial planet formation region but at the outer edge of any possible terrestrial habitability zone. The mass of fine dust is 4 x 1019 - 2 x 1020 kg, equivalent to a 150 - 200 km radius asteroid. Significant emission features centered at 4 and 8 µm due to fluorescing SiO gas are also found. Roughly 1022 kg of SiO gas, formed by vaporizing silicate rock, is also present in the system, and a separate population of very large, cool grains, massing 1021 - 1022 kg and equivalent to the largest sized asteroid currently found in the Solar System's main asteroid belt, dominates the solid circumstellar material by mass. The makeup of the observed dust and gas, and the noted lack of a dense circumstellar gas disk, strong primary x-ray activity, or an extended disk of β meteroids argues that the source of the observed circumstellar materials is a giant hypervelocity (> 10 km sec-1) impact between large rocky planetesimals, similar to the ones which formed the Moon and which stripped the surface crustal material off of Mercury's surface.

  14. Abundant Circumstellar Silica Dust and SiO Gas Created by a Giant Hypervelocity Collision in the 12 Myr HD172555 System

    NASA Astrophysics Data System (ADS)

    Lisse, Carey M.; Chen, C. H.; Wyatt, M. C.; Morlok, A.; Song, I.; Bryden, G.; Sheehan, P.

    2010-01-01

    We have used the InfraRed Spectrograph on the Spitzer Space Telescope to study the fine dust orbiting around the 29 pc distant β Pic analogue star HD172555. The dust mineralogy is is very peculiar, composed primarily of highly refractory, non-equilibrium materials, with 3/4 of the Si atoms in silica (SiO2) species. Tektite and obsidian lab thermal emission spectra (non-equilibrium glassy silicas found in impact and magmatic systems) are required to fit the data. The best-fit model size distribution for the observed fine dust is dn/da = a-3.95±0.10. This steep a size distribution argues for a fresh source of material within the last 0.1 Myr. The location of the dust with respect to the star is at 5.8 ± 0.6 AU, within the terrestrial planet formation region but at the outer edge of any possible terrestrial habitability zone. The mass of fine dust is 4 x 1019 - 2 x 1020 kg, equivalent to a 150 - 200 km radius asteroid. Significant emission features centered at 4 and 8 µm due to fluorescing SiO gas are also found. Roughly 1022 kg of SiO gas, formed by vaporizing silicate rock, is also present in-system, and a separate population of very large, cool grains, massing 1021 - 1022 kg and equivalent to the largest sized asteroid currently found in the Solar System's main asteroid belt, dominates the solid circumstellar material by mass. The makeup of the observed dust and gas, and the noted lack of a dense circumstellar gas disk, strong primary x-ray activity, or an extended disk of β meteroids argues that the source of the observed circumstellar materials is a giant hypervelocity (> 10 km sec-1) impact between large rocky planetesimals, similar to the ones which formed the Moon and which stripped the surface crustal material off of Mercury's surface.

  15. Habitable-zone super-Earth candidate in a six-planet system around the K2.5V star HD 40307

    NASA Astrophysics Data System (ADS)

    Tuomi, M.; Anglada-Escudé, G.; Gerlach, E.; Jones, H. R. A.; Reiners, A.; Rivera, E. J.; Vogt, S. S.; Butler, R. P.

    2013-01-01

    Context. The K2.5 dwarf HD 40307 has been reported to host three super-Earths. The system lacks massive planets and is therefore a potential candidate for having additional low-mass planetary companions. Aims: We re-derive Doppler measurements from public HARPS spectra of HD 40307 to confirm the significance of the reported signals using independent data analysis methods. We also investigate these measurements for additional low-amplitude signals. Methods: We used Bayesian analysis of our radial velocities to estimate the probability densities of different model parameters. We also estimated the relative probabilities of models with differing numbers of Keplerian signals and verified their significance using periodogram analyses. We investigated the relation of the detected signals with the chromospheric emission of the star. As previously reported for other objects, we found that radial velocity signals correlated with the S-index are strongly wavelength dependent. Results: We identify two additional clear signals with periods of 34 and 51 days, both corresponding to planet candidates with minimum masses a few times that of the Earth. An additional sixth candidate is initially found at a period of 320 days. However, this signal correlates strongly with the chromospheric emission from the star and is also strongly wavelength dependent. When analysing the red half of the spectra only, the five putative planetary signals are recovered together with a very significant periodicity at about 200 days. This signal has a similar amplitude as the other new signals reported in the current work and corresponds to a planet candidate with Msini ~ 7 M⊕ (HD 40307 g). Conclusions: We show that Doppler measurements can be filtered for activity-induced signals if enough photons and a sufficient wavelength interval are available. If the signal corresponding to HD 40307 g is a genuine Doppler signal of planetary origin, this candidate planet might be capable of supporting liquid water on its surface according to the current definition of the liquid water habitable zone around a star and is not likely to suffer from tidal locking. Also, at an angular separation of ~46 mas, HD 40307 g would be a primary target for a future space-based direct-imaging mission. Appendix A is available in electronic form at http://www.aanda.org

  16. Barnard's Star as a Proxy for Old Disk dM Stars: Magnetic Activity, Light Variations, XUV Irradiances, and Planetary Habitable Zones

    NASA Astrophysics Data System (ADS)

    Riedel, A. R.; Guinan, E. F.; DeWarf, L. E.; Engle, S. G.; McCook, G. P.

    2005-05-01

    Barnard's Star (GJ 699) is a nearby, high velocity (UVW = -148,+0,+16 km/s), Thick Disk / Intermediate-age Pop II dM4 star. Although old (7-12 Gyr), Barnard's Star appears to be magnetically active, having coronal X-ray emission as well as moderately strong chromospheric UV emissions. Barnard's star holds the speed record for having the largest proper motion of any star yet known (10.4"/yr). At a distance of only 1.82 pc (5.9 lt yrs), it is the nearest star to us after the α Cen system. Recent measures of Barnard's Star results in a luminosity of L = 3.46 ± 0.17 × 10-3 L⊙, R = 0.20 ± 0.008 R⊙, and Teff = 3134 ± 102 K (Dawson & De Robertis 2004, AJ, 127, 2909). Because of its proximity and age, we have selected Barnard's Star for more intensive study, and to serve as a proxy for the numerous old-population dM stars in our Galaxy. These stars may be targets of future planet search missions such as SIM, Kepler, and TPF/Darwin in the next several years. For exobiology, dM stars make interesting targets because the habitable zones (HZ) around dM stars are close to the host star (HZ ˜ 0.05-0.40 AU), making the hypothetical HZ planet more strongly influenced by stellar flares, winds, and plasma ejection events that are frequent in dM stars. We are conducting intensive photoelectric UBVRI and TiO (719nm) photometry of Barnard's Star using the Four College Automatic Photoelectric Telescope in Arizona. This photometry is being conducted to determine starspot coverage and the rotation period. We have also determined X-ray to UV irradiances that will characterize dM stars of similar ages. These measures will be useful in the future if large numbers of older dM stars are found to harbor planets. We will discuss the results of this study, which is a component of a larger program aimed at improving (and testing) our understanding of magnetic-related phenomena in dM stars. This research is supported by NASA and NSF/RUI grants.

  17. Planetary Habitability

    NASA Technical Reports Server (NTRS)

    Kasting, James F.

    1997-01-01

    This grant was entitled 'Planetary Habitability' and the work performed under it related to elucidating the conditions that lead to habitable, i.e. Earth-like, planets. Below are listed publications for the past two and a half years that came out of this work. The main thrusts of the research involved: (1) showing under what conditions atmospheric O2 and O3 can be considered as evidence for life on a planet's surface; (2) determining whether CH4 may have played a role in warming early Mars; (3) studying the effect of varying UV levels on Earth-like planets around different types of stars to see whether this would pose a threat to habitability; and (4) studying the effect of chaotic obliquity variations on planetary climates and determining whether planets that experienced such variations might still be habitable. Several of these topics involve ongoing research that has been carried out under a new grant number, but which continues to be funded by NASA's Exobiology program.

  18. Mapping the Region in the Nearest Star System to Search for Habitable Planets

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Quarles, B.

    2015-01-01

    Circumstellar planets within the alpha Centauri AB star system have been suggested through formation models and recent observations, and ACESat (Belikov et al. AAS Meeting #225, #311.01, 2015) is a proposed space mission designed to directly image Earth-sized planets in the habitable zones of both of these stars. The alpha Centauri system is billions of years old, so planets are only expected to be found in regions where their orbits are long-lived. We evaluate the extent of the regions within the alpha Centauri AB star system where small planets are able to orbit for billion-year timescales and we map the positions in the sky plane where planets on stable orbits about either stellar component may appear. We confirm the qualitative results of Wiegert & Holman (Astron. J. 113, 1445, 1997) regarding the approximate size of the regions of stable orbits, which are larger for retrograde orbits relative to the binary than for prograde orbits. Additionally, we find that mean motion resonances with the binary orbit leave an imprint on the limits of orbital stability, and the effects of the Lidov-Kozai mechanism are also readily apparent. Overall, orbits in the habitable zones near the plane of the binary are stable, whereas high-inclination orbits are short-lived.

  19. Your Child's Habits

    MedlinePlus

    ... for Your Child All About Food Allergies Your Child's Habits KidsHealth > For Parents > Your Child's Habits Print ... Mom or Dad. previous continue Coping With Your Child's Habit The good news is that most habits ...

  20. Circumstellar Dust in Symbiotic Novae

    NASA Astrophysics Data System (ADS)

    Jurkic, T.; Kotnik-Karuza, D.

    2015-12-01

    We present a model of inner dust regions around the cool Mira component of the two symbiotic novae, RR Tel and HM Sge, based on the near-IR photometry, ISO spectra and mid-IR interferometry. The dust properties were determined using the DUSTY code. A compact circumstellar silicate dust shell with inner dust shell temperatures between 900 K and 1300 K and of moderate optical depth can explain all the observations. RR Tel shows the presence of an equatorially enhanced dust density during minimum obscuration. Obscuration events are explained by an increase in optical depth caused by the newly condensed dust. The mass loss rates are significantly higher than in intermediate-period single Miras but in agreement with longer-period O-rich AGB stars.

  1. Dynamics and Habitability in Binary Star Systems

    NASA Astrophysics Data System (ADS)

    Eggl, Siegfried; Georgakarakos, Nikolaos; Pilat-Lohinger, Elke

    2014-07-01

    Determining planetary habitability is a complex matter, as the interplay between a planet's physical and atmospheric properties with stellar insolation has to be studied in a self consistent manner. Standardized atmospheric models for Earth-like planets exist and are commonly accepted as a reference for estimates of Habitable Zones. In order to define Habitable Zone boundaries, circular orbital configurations around main sequence stars are generally assumed. In gravitationally interacting multibody systems, such as double stars, however, planetary orbits are forcibly becoming non circular with time. Especially in binary star systems even relatively small changes in a planet's orbit can have a large impact on habitability. Hence, we argue that a minimum model for calculating Habitable Zones in binary star systems has to include dynamical interactions.

  2. Atmospheric escape, redox evolution, and planetary habitability

    NASA Astrophysics Data System (ADS)

    Catling, D. C.; Zahnle, K. J.

    2011-12-01

    Through the greenhouse effect, the presence and composition of an atmosphere is critical for defining a (conventional) circumstellar habitable zone in terms of planetary surface temperatures suitable for liquid water. Lack of knowledge of planetary atmospheres is likely to frustrate attempts to say with any certainty whether detected terrestrial-sized exoplanets may or may not be habitable. Perhaps an underappreciated role in such considerations is the evolutionary effect of atmospheric escape for determining atmospheric composition or whether an atmosphere exists in the first place. Whether atmospheres exist at all on planets is demonstrably connected to the effect of integrated atmospheric escape. When we observe our own Solar System and transiting exoplanets, the existence of an atmosphere is clearly delineated by a relative vulnerability to thermal escape and impact erosion. The prevalence of thermal escape as a key evolutionary determinant for the presence of planetary atmosphere is shown by a relationship between the relative solar (or stellar) heating and the escape velocity. Those bodies with too much stellar heating and too smaller escape velocity end up devoid of atmospheres. Impact erosion is evident in the relationship between impact velocity and escape velocity. Escape due to impacts is particularly important for understanding the large differences in the atmospheres of giant planet moons, such as Ganymede versus Titan. It is also significant for Mars-sized planets. The oxidation state of atmospheres is important for some theories of the origin of life (where an early reducing atmosphere is helpful for organic synthesis) and the evolution of advanced life (where free molecular oxygen is the best source of high energy metabolism). Surfaces on some relatively small planets and moons are observed to have evolved to an oxidized state, which theory and observation can explain through atmospheric escape. There are several examples in the Solar System where a net escape of hydrogen relative to heavier oxygen is the generally accepted explanation for the present oxidation state: Venus and Mars amongst the planets, and Ganymede, Europa, and Rhea amongst bodies with extremely tenuous atmospheres. We also argue that hydrogen escape was the key factor for oxidizing the Earth and facilitating the increase of photosynthetically-produced oxygen in the Proterozoic atmosphere. Our view about the primacy of hydrogen escape with regard to the Earth's atmospheric oxygenation is perhaps less widely accepted. However, it was inevitable that hydrogen escaped from Earth's early anoxic atmosphere at a significant rate. The result was a very big integrated oxidation consistent with what is observed in the Earth's crust in addition to some export to the mantle. In conclusion, a better understanding of atmospheric escape processes appears critical for understanding the suitability of planets for harboring life from simple to advanced forms.

  3. EXoplanetary Circumstellar Environments and Disk Explorer technology demonstration: Experimental results in air and vacuum

    NASA Astrophysics Data System (ADS)

    Lozi, J.; Belikov, R.; Bendek, E.; Davis, P. K.; Duncan, A.; Greene, T. P.; Guyon, O.; Hix, T.; Irwin, W.; Kendrick, R.; Lynch, D.; Mihara, R.; PIuzhnik, E.; Schneider, G.; Smith, E.; Thomas, S.; Witteborn, F. C.

    2014-03-01

    Coronagraph technology is advancing and promises to enable space telescopes capable of directly detecting and spatially resolving low surface brightness circumstellar debris disks as well as imaging giant planets as close as in the habitable zones of their host stars. One proposed mission capable of doing this is called EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer), which in 2011 was selected by NASA's Explorer program for technology development A (Category Ill). EXCEDE is a 0.7 m space telescope concept designed to achieve raw contrasts of 1e-6 at an inner working angle of 1.2 l/D and 1e-7 at 2 l/D and beyond. In addition to doing fundamental science on debris disks, EXCEDE will also serve as a technological and scientific precursor for an exo-Earth imaging mission. EXCEDE uses a Starlight Suppression System (SSS) based on the PIAA coronagraph, enabling aggressive performance. In this presentation, we report on our continuing progress of developing the SSS for EXCEDE, and in particular the achievement of the first major milestone in our technology development program (1e-6 median raw contrast between a 1.2 l/D inner working angle and 2 l/D, simultaneously with 1e-7 median raw contrast between 2 l/D and 4 l/D, in monochromatic light and in a controlled and repeatable fashion). In addition, we will describe the upgrades to our system, such as (a) the Low Order Wavefront Sensor (LOWFS) which enabled achieving deep contrasts at aggressive inner working angles; (b) efficient model-based wavefront control algorithms; (c) a reconfiguration of our DM to be upstream of the coronagraph and the addition of the "inverse PIAA" system that enables better outer working angles. Finally, we report on preliminary demonstrations in a vacuum chamber. Even though this technology development is primarily targeted towards EXCEDE, it is also germane to any exoplanet direct imaging spacebased telescopes because of the many challenges common to different coronagraph architectures and mission requirements.

  4. Exoplanet habitability.

    PubMed

    Seager, Sara

    2013-05-01

    The search for exoplanets includes the promise to eventually find and identify habitable worlds. The thousands of known exoplanets and planet candidates are extremely diverse in terms of their masses or sizes, orbits, and host star type. The diversity extends to new kinds of planets, which are very common yet have no solar system counterparts. Even with the requirement that a planet's surface temperature must be compatible with liquid water (because all life on Earth requires liquid water), a new emerging view is that planets very different from Earth may have the right conditions for life. The broadened possibilities will increase the future chances of discovering an inhabited world. PMID:23641111

  5. Exoplanet habitability.

    TOXLINE Toxicology Bibliographic Information

    Seager S

    2013-05-03

    The search for exoplanets includes the promise to eventually find and identify habitable worlds. The thousands of known exoplanets and planet candidates are extremely diverse in terms of their masses or sizes, orbits, and host star type. The diversity extends to new kinds of planets, which are very common yet have no solar system counterparts. Even with the requirement that a planet's surface temperature must be compatible with liquid water (because all life on Earth requires liquid water), a new emerging view is that planets very different from Earth may have the right conditions for life. The broadened possibilities will increase the future chances of discovering an inhabited world.

  6. Teaching Your Child Healthy Hair Care Habits

    MedlinePlus

    ... zone Video library Find a dermatologist Teaching your child healthy hair care habits Many common hair care ... Damaged hair looks and feels unhealthy. Teaching your child how to shampoo Healthy hair care begins with ...

  7. Circumstellar dust in symbiotic novae

    NASA Astrophysics Data System (ADS)

    Jurkic, Tomislav; Kotnik-Karuza, Dubravka

    2015-08-01

    Physical properties of the circumstellar dust and associated physical mechanisms play an important role in understanding evolution of symbiotic binaries. We present a model of inner dust regions around the cool Mira component of the two symbiotic novae, RR Tel and HM Sge, based on the long-term near-IR photometry, infrared ISO spectra and mid-IR interferometry. Pulsation properties and long-term variabilities were found from the near-IR light curves. The dust properties were determined using the DUSTY code which solves the radiative transfer. No changes in pulsational parameters were found, but a long-term variations with periods of 20-25 years have been detected which cannot be attributed to orbital motion.Circumstellar silicate dust shell with inner dust shell temperatures between 900 K and 1300 K and of moderate optical depth can explain all the observations. RR Tel showed the presence of an optically thin CS dust envelope and an optically thick dust region outside the line of sight, which was further supported by the detailed modelling using the 2D LELUYA code. Obscuration events in RR Tel were explained by an increase in optical depth caused by the newly condensed dust leading to the formation of a compact dust shell. HM Sge showed permanent obscuration and a presence of a compact dust shell with a variable optical depth. Scattering of the near-IR colours can be understood by a change in sublimation temperature caused by the Mira variability. Presence of large dust grains (up to 4 µm) suggests an increased grain growth in conditions of increased mass loss. The mass loss rates of up to 17·10-6 MSun/yr were significantly higher than in intermediate-period single Miras and in agreement with longer-period O-rich AGB stars.Despite the nova outburst, HM Sge remained enshrouded in dust with no significant dust destruction. The existence of unperturbed dust shell suggests a small influence of the hot component and strong dust shielding from the UV flux. By the use of the CLOUDY code, we have showed that a high-density gas region can effectively stop most of the UV flux from the white dwarf and provide the observed dust shielding.

  8. Polarimetric microlensing of circumstellar discs

    NASA Astrophysics Data System (ADS)

    Sajadian, Sedighe; Rahvar, Sohrab

    2015-12-01

    We study the benefits of polarimetry observations of microlensing events to detect and characterize circumstellar discs around the microlensed stars located at the Galactic bulge. These discs which are unresolvable from their host stars make a net polarization effect due to their projected elliptical shapes. Gravitational microlensing can magnify these signals and make them be resolved. The main aim of this work is to determine what extra information about these discs can be extracted from polarimetry observations of microlensing events in addition to those given by photometry ones. Hot discs which are closer to their host stars are more likely to be detected by microlensing, owing to more contributions in the total flux. By considering this kind of discs, we show that although the polarimetric efficiency for detecting discs is similar to the photometric observation, but polarimetry observations can help to constraint the disc geometrical parameters e.g. the disc inner radius and the lens trajectory with respect to the disc semimajor axis. On the other hand, the time-scale of polarimetric curves of these microlensing events generally increases while their photometric time-scale does not change. By performing a Monte Carlo simulation, we show that almost four optically thin discs around the Galactic bulge sources are detected (or even characterized) through photometry (or polarimetry) observations of high-magnification microlensing events during 10-yr monitoring of 150 million objects.

  9. Comparative Habitability of Transiting Exoplanets

    NASA Astrophysics Data System (ADS)

    Barnes, Rory; Meadows, Victoria S.; Evans, Nicole

    2015-12-01

    Exoplanet habitability is traditionally assessed by comparing a planet’s semimajor axis to the location of its host star’s “habitable zone,” the shell around a star for which Earth-like planets can possess liquid surface water. The Kepler space telescope has discovered numerous planet candidates near the habitable zone, and many more are expected from missions such as K2, TESS, and PLATO. These candidates often require significant follow-up observations for validation, so prioritizing planets for habitability from transit data has become an important aspect of the search for life in the universe. We propose a method to compare transiting planets for their potential to support life based on transit data, stellar properties and previously reported limits on planetary emitted flux. For a planet in radiative equilibrium, the emitted flux increases with eccentricity, but decreases with albedo. As these parameters are often unconstrained, there is an “eccentricity-albedo degeneracy” for the habitability of transiting exoplanets. Our method mitigates this degeneracy, includes a penalty for large-radius planets, uses terrestrial mass-radius relationships, and, when available, constraints on eccentricity to compute a number we call the “habitability index for transiting exoplanets” that represents the relative probability that an exoplanet could support liquid surface water. We calculate it for Kepler objects of interest and find that planets that receive between 60% and 90% of the Earth’s incident radiation, assuming circular orbits, are most likely to be habitable. Finally, we make predictions for the upcoming TESS and James Webb Space Telescope missions.

  10. Host Star Evolution for Planet Habitability

    NASA Astrophysics Data System (ADS)

    Gallet, Florian; Charbonnel, Corinne; Amard, Louis

    2016-04-01

    With about 2000 exoplanets discovered within a large range of different configurations of distance from the star, size, mass, and atmospheric conditions, the concept of habitability cannot rely only on the stellar effective temperature anymore. In addition to the natural evolution of habitability with the intrinsic stellar parameters, tidal, magnetic, and atmospheric interactions are believed to have strong impact on the relative position of the planets inside the so-called habitable zone. Moreover, the notion of habitability itself strongly depends on the definition we give to the term "habitable". The aim of this contribution is to provide a global and up-to-date overview of the work done during the last few years about the description and the modelling of the habitability, and to present the physical processes currently includes in this description.

  11. Small carbon chains in circumstellar envelopes

    NASA Astrophysics Data System (ADS)

    Hargreaves, R. J.; Hinkle, K.; Bernath, P. F.

    2014-11-01

    Observations of carbon-rich circumstellar envelopes were made using the Phoenix spectrograph on the Gemini South telescope to determine the abundance of small carbon chain molecules. Vibration-rotation lines of the ν3 antisymmetric stretch of C3 near 2040 cm-1 (4.902 μm) have been used to determine the column density for four carbon-rich circumstellar envelopes: CRL 865, CRL 1922, CRL 2023 and IRC +10216. We additionally calculate the column density of C5 for IRC +10216, and provide an upper limit for five more objects. An upper limit estimate for the C7 column density is also provided for IRC+10216. A comparison of these column densities suggests a revision to current circumstellar chemical models may be needed.

  12. The circumstellar disks of Beta Pictoris analogs

    NASA Technical Reports Server (NTRS)

    Grady, Carol A.; Bruhweiler, Frederick C.; Cheng, Kwang-Ping; Chiu, Weihsueh A.; Kondo, Yoji

    1991-01-01

    A survey using data from the International Ultraviolet Explorer (IUE) of previously known B and A shell stars with IRAS detections has resulted in the identification of three stars, HD 93563, Sigma Her, and 51 Oph, which have spectral signatures of infalling circumstellar plasma similar to Beta Pic. Two of these systems have infrared flux distributions indicating the presence of circumstellar dust disks, while the other, HD 93563, has an infrared excess consistent with free-free emission from the plasma envelope. With the identification of three such systems, it is clear that infalling circumstellar plasma is more common than previously anticipated among late-type B shell stars. The absence of dust in one system, HD 93563, suggests that infalling plasma in these stars, and possibly also in Beta Pic itself, may not be due to either erosion of a dust disk or to high cometary bombardment rates, but may instead be linked to stellar activity.

  13. HABEBEE: habitability of eyeball-exo-Earths.

    PubMed

    Angerhausen, Daniel; Sapers, Haley; Citron, Robert; Bergantini, Alexandre; Lutz, Stefanie; Queiroz, Luciano Lopes; da Rosa Alexandre, Marcelo; Araujo, Ana Carolina Vieira

    2013-03-01

    Extrasolar Earth and super-Earth planets orbiting within the habitable zone of M dwarf host stars may play a significant role in the discovery of habitable environments beyond Earth. Spectroscopic characterization of these exoplanets with respect to habitability requires the determination of habitability parameters with respect to remote sensing. The habitable zone of dwarf stars is located in close proximity to the host star, such that exoplanets orbiting within this zone will likely be tidally locked. On terrestrial planets with an icy shell, this may produce a liquid water ocean at the substellar point, one particular "Eyeball Earth" state. In this research proposal, HABEBEE: exploring the HABitability of Eyeball-Exo-Earths, we define the parameters necessary to achieve a stable icy Eyeball Earth capable of supporting life. Astronomical and geochemical research will define parameters needed to simulate potentially habitable environments on an icy Eyeball Earth planet. Biological requirements will be based on detailed studies of microbial communities within Earth analog environments. Using the interdisciplinary results of both the physical and biological teams, we will set up a simulation chamber to expose a cold- and UV-tolerant microbial community to the theoretically derived Eyeball Earth climate states, simulating the composition, atmosphere, physical parameters, and stellar irradiation. Combining the results of both studies will enable us to derive observable parameters as well as target decision guidance and feasibility analysis for upcoming astronomical platforms. PMID:23510083

  14. Circumbinary habitability niches

    NASA Astrophysics Data System (ADS)

    Mason, Paul A.; Zuluaga, Jorge I.; Cuartas-Restrepo, Pablo A.; Clark, Joni M.

    2015-07-01

    Binaries could provide the best niches for life in the Galaxy. Although counterintuitive, this assertion follows directly from stellar tidal interaction theory and the evolution of lower mass stars. There is strong evidence that chromospheric activity of rapidly rotating young stars may be high enough to cause mass loss from atmospheres of potentially habitable planets. The removal of atmospheric water is most critical. Tidal breaking in binaries could help reduce magnetic dynamo action and thereby chromospheric activity in favour of life. We call this the Binary Habitability Mechanism (BHM) that we suggest allows for water retention at levels comparable to or better than the Earth. We discuss novel advantages that life may exploit, in these cases, and suggest that life may even thrive on some circumbinary planets. We find that while many binaries do not benefit from BHM, high-quality niches do exist for various combinations of stars between 0.55 and 1.0 solar masses. For a given pair of stellar masses, BHM operates only for certain combinations of period and eccentricity. Binaries having a solar-type primary seem to be quite well-suited niches having wide and distant habitable zones with plentiful water and sufficient light for photosynthetic life. We speculate that, as a direct result of BHM, conditions may be suitable for life on several planets and possibly even moons of giant planets orbiting some binaries. Lower mass combinations, while more restrictive in parameter space, provide niches lasting many billions of years and are rich suppliers of photosynthetic photons. We provide a publicly available web-site (http://bit.ly/BHM-calculator or http://bit.ly/BHM-calculator-mirror), which calculates the BHM effects presented in this paper.

  15. Effects of Exoplanet Planetesimal Carbon Chemistry on Habitability

    NASA Astrophysics Data System (ADS)

    Johnson, T. V.; Mousis, O.; Lunine, J. I.; Madhusudhan, N.

    2013-12-01

    We explore the effects of reported differences in C/O values for exoplanet host stars on the composition of planetesimals formed beyond the snow line in these systems. Since the value of C/O in a planet forming nebula has a strong effect on amount of oxygen available for water ice in an oxidizing nebula, exoplanet systems for host stars with C/O greater than the solar value may have planetesimals with very little or no water ice. We have estimated the composition of volatile and refractory material in extrasolar planetesimals using a set of stars with a wide range of measured C/O abundances (Johnson et al. ApJ. 757(2), 192, 2012). The volatile ice content of planetesimals in these systems varies significantly with C/O, controlled primarily by the availability of O for H2O ice condensation. Systems with C/O less than the solar value (C/O = 0.55) should have very water ice rich planetesimals, while water ice mass fraction decreases rapidly with increasing C/O until only ices of CO and CO2 are left in significant proportions. If a significant fraction of C is in the form of refractory CHON particles, C and O are removed from the gas phase and the condensates for super-solar C/O values will be water-poor mixtures of silicates and metal, carbon, and carbon-bearing volatile ices, depending on temperature. For very carbon-rich systems, oxidizing conditions cannot be sustained beyond about C/O=1, due to the oxygen sequestered in solid silicates, oxides and CHON, for refractory C fractions within the Pollack et al. range of 0.4 - 0.7 (ApJ. 421, 615, 1994). These results have implications for assessing the habitability of exoplanets since they constrain the amount of water available beyond the snow line for dynamical delivery to inner planets, depending on the host star's C/O in the circumstellar nebula. Thus one the key chemical ingredients for habitability may be in short supply in carbon-rich, oxygen-poor systems even if planets exist in the ';habitable zone'. TVJ acknowledges government support at JPL/Caltech, under a contract with NASA. NM acknowledges support from Yale University. JIL was supported by the JWST Project through NASA. O.M. acknowledges support from CNES.Planetesimal compositions for several stellar systems with a fraction, Csolid, of C in solid CHON particles

  16. The Possibility of Multiple Habitable Worlds Orbiting Binary Stars

    NASA Astrophysics Data System (ADS)

    Mason, P. A.

    2014-03-01

    Are there planetary systems for which there is life on multiple worlds? Where are these fruitful planetary systems and how do we detect them? In order to address these questions; conditions which enable life and those that prevent or destroy it must be considered. Many constraints are specific to planetary systems, independent of the number of worlds in habitable zones. For instance, life on rocky planets or moons likely requires the right abundance of volatiles and radiogenic elements for prolonged geologic activity. Catastrophic sterilization events such as nearby supernovae and gamma-ray bursts affect entire planetary systems not just specific worlds. Giant planets may either enhance or disrupt the development of complex life within a given system. It might be rare for planetary systems to possess qualities that promote life and lucky enough to avoid cataclysm. However, multiple habitable planets may provide enhanced chances for advanced life to develop. The best predictor of life on one habitable zone planet might be the presence of life on its neighbor as panspermia may occur in planetary systems with several habitable worlds. Circumbinary habitability may go hand in hand with habitability of multiple worlds. The circumstances in which the Binary Habitability Mechanism (BHM) operates are reviewed. In some cases, the early synchronization of the primary's rotation with the binary period results in a reduction of XUV flux and stellar winds. Main sequence binaries with periods in the 10-50 days provide excellent habitable environments, within which multiple worlds may thrive. Planets and moons in these habitable zones need less magnetic protection than their single star counterparts. Exomoons orbiting a Neptune-like planet, within a BHM protected habitable zone, are expected to be habitable over a wide range of semimajor axes due to a larger planetary Hill radius. A result confirmed by numerical orbital calculations. Binaries containing a solar type star with a lower mass companion provide enhanced habitable zones as well as improved photosynthetic flux for habitable zone worlds.

  17. Flares and habitability

    NASA Astrophysics Data System (ADS)

    Abrevaya, Ximena C.; Cortón, Eduardo; Mauas, Pablo J. D.

    2012-07-01

    At present, dwarf M stars are being considered as potential hosts for habitable planets. However, an important fraction of these stars are flare stars, which among other kind of radiation, emit large amounts of UV radiation during flares, and it is unknown how this events can affect life, since biological systems are particularly vulnerable to UV. In this work we evaluate a well known dMe star, EV Lacertae (GJ 873) as a potential host for the emergence and evolution of life, focusing on the effects of the UV emission associated with flare activity. Since UV-C is particularly harmful for living organisms, we studied the effect of UV-C radiation on halophile archaea cultures. The halophile archaea or haloarchaea are extremophile microorganisms, which inhabit in hypersaline environments and which show several mechanisms to cope with UV radiation since they are naturally exposed to intense solar UV radiation on Earth. To select the irradiance to be tested, we considered a moderate flare on this star. We obtained the mean value for the UV-C irradiance integrating the IUE spectrum in the impulsive phase, and considering a hypothetical planet in the center of the liquid water habitability zone. To select the irradiation times we took the most frequent duration of flares on this star which is from 9 to 27 minutes. Our results show that even after considerable UV damage, the haloarchaeal cells survive at the tested doses, showing that this kind of life could survive in a relatively hostile UV environment.

  18. Isothermal Circumstellar Dust Shell Model for Teaching

    ERIC Educational Resources Information Center

    Robinson, G.; Towers, I. N.; Jovanoski, Z.

    2009-01-01

    We introduce a model of radiative transfer in circumstellar dust shells. By assuming that the shell is both isothermal and its thickness is small compared to its radius, the model is simple enough for students to grasp and yet still provides a quantitative description of the relevant physical features. The isothermal model can be used in a…

  19. Response of Atmospheric Biomarkers to NOx-Induced Photochemistry Generated by Stellar Cosmic Rays for Earth-like Planets in the Habitable Zone of M Dwarf Stars

    PubMed Central

    Grießmeier, Jean-Mathias; von Paris, Philip; Patzer, A. Beate C.; Lammer, Helmut; Stracke, Barbara; Gebauer, Stefanie; Schreier, Franz; Rauer, Heike

    2012-01-01

    Abstract Understanding whether M dwarf stars may host habitable planets with Earth-like atmospheres and biospheres is a major goal in exoplanet research. If such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. Such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. Here, we consider stellar activity of M dwarfs ranging from quiet up to strong flaring conditions and investigate one particular effect upon biomarkers, namely, the ability of secondary electrons caused by stellar cosmic rays to break up atmospheric molecular nitrogen (N2), which leads to production of nitrogen oxides (NOx) in the planetary atmosphere, hence affecting biomarkers such as ozone (O3). We apply a stationary model, that is, without a time dependence; hence we are calculating the limiting case where the atmospheric chemistry response time of the biomarkers is assumed to be slow and remains constant compared with rapid forcing by the impinging stellar flares. This point should be further explored in future work with time-dependent models. We estimate the NOx production using an air shower approach and evaluate the implications using a climate-chemical model of the planetary atmosphere. O3 formation proceeds via the reaction O+O2+M→O3+M. At high NOx abundances, the O atoms arise mainly from NO2 photolysis, whereas on Earth this occurs via the photolysis of molecular oxygen (O2). For the flaring case, O3 is mainly destroyed via direct titration, NO+O3→NO2+O2, and not via the familiar catalytic cycle photochemistry, which occurs on Earth. For scenarios with low O3, Rayleigh scattering by the main atmospheric gases (O2, N2, and CO2) became more important for shielding the planetary surface from UV radiation. A major result of this work is that the biomarker O3 survived all the stellar-activity scenarios considered except for the strong case, whereas the biomarker nitrous oxide (N2O) could survive in the planetary atmosphere under all conditions of stellar activity considered here, which clearly has important implications for missions that aim to detect spectroscopic biomarkers. Key Words: M dwarf—Atmosphere—Earth-like—Biomarkers—Stellar cosmic rays. Astrobiology 12, 1109–1122. PMID:23215581

  20. Response of atmospheric biomarkers to NO(x)-induced photochemistry generated by stellar cosmic rays for earth-like planets in the habitable zone of M dwarf stars.

    PubMed

    Grenfell, John Lee; Grießmeier, Jean-Mathias; von Paris, Philip; Patzer, A Beate C; Lammer, Helmut; Stracke, Barbara; Gebauer, Stefanie; Schreier, Franz; Rauer, Heike

    2012-12-01

    Understanding whether M dwarf stars may host habitable planets with Earth-like atmospheres and biospheres is a major goal in exoplanet research. If such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. Such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. Here, we consider stellar activity of M dwarfs ranging from quiet up to strong flaring conditions and investigate one particular effect upon biomarkers, namely, the ability of secondary electrons caused by stellar cosmic rays to break up atmospheric molecular nitrogen (N(2)), which leads to production of nitrogen oxides (NO(x)) in the planetary atmosphere, hence affecting biomarkers such as ozone (O(3)). We apply a stationary model, that is, without a time dependence; hence we are calculating the limiting case where the atmospheric chemistry response time of the biomarkers is assumed to be slow and remains constant compared with rapid forcing by the impinging stellar flares. This point should be further explored in future work with time-dependent models. We estimate the NO(x) production using an air shower approach and evaluate the implications using a climate-chemical model of the planetary atmosphere. O(3) formation proceeds via the reaction O+O(2)+M→O(3)+M. At high NO(x) abundances, the O atoms arise mainly from NO(2) photolysis, whereas on Earth this occurs via the photolysis of molecular oxygen (O(2)). For the flaring case, O(3) is mainly destroyed via direct titration, NO+O(3)→NO(2)+O(2), and not via the familiar catalytic cycle photochemistry, which occurs on Earth. For scenarios with low O(3), Rayleigh scattering by the main atmospheric gases (O(2), N(2), and CO(2)) became more important for shielding the planetary surface from UV radiation. A major result of this work is that the biomarker O(3) survived all the stellar-activity scenarios considered except for the strong case, whereas the biomarker nitrous oxide (N(2)O) could survive in the planetary atmosphere under all conditions of stellar activity considered here, which clearly has important implications for missions that aim to detect spectroscopic biomarkers. PMID:23215581

  1. ABUNDANT CIRCUMSTELLAR SILICA DUST AND SiO GAS CREATED BY A GIANT HYPERVELOCITY COLLISION IN THE {approx}12 MYR HD172555 SYSTEM

    SciTech Connect

    Lisse, C. M.; Chen, C. H.; Wyatt, M. C.; Morlok, A.; Song, I.; Bryden, G.; Sheehan, P. E-mail: cchen@stsci.edu E-mail: A.Morlok@open.ac.uk E-mail: Geoffrey.Bryden@jpl.nasa.gov

    2009-08-20

    The fine dust detected by infrared (IR) emission around the nearby {beta} Pic analog star HD172555 is very peculiar. The dust mineralogy is composed primarily of highly refractory, nonequilibrium materials, with approximately three quarters of the Si atoms in silica (SiO{sub 2}) species. Tektite and obsidian lab thermal emission spectra (nonequilibrium glassy silicas found in impact and magmatic systems) are required to fit the data. The best-fit model size distribution for the observed fine dust is dn/da = a {sup -3.95{+-}}{sup 0.10}. While IR photometry of the system has stayed stable since the 1983 IRAS mission, this steep a size distribution, with abundant micron-sized particles, argues for a fresh source of material within the last 0.1 Myr. The location of the dust with respect to the star is at 5.8 {+-} 0.6 AU (equivalent to 1.9 {+-} 0.2 AU from the Sun), within the terrestrial planet formation region but at the outer edge of any possible terrestrial habitability zone. The mass of fine dust is 4 x 10{sup 19}-2 x 10{sup 20} kg, equivalent to a 150-200 km radius asteroid. Significant emission features centered at 4 and 8 {mu}m due to fluorescing SiO gas are also found. Roughly 10{sup 22} kg of SiO gas, formed by vaporizing silicate rock, is also present in the system, and a separate population of very large, cool grains, massing 10{sup 21}-10{sup 22} kg and equivalent to the largest sized asteroid currently found in the solar system's main asteroid belt, dominates the solid circumstellar material by mass. The makeup of the observed dust and gas, and the noted lack of a dense circumstellar gas disk, strong stellar X-ray activity, and an extended disk of {beta} meteoroids argues that the source of the observed circumstellar materials is a giant hypervelocity (>10 km s{sup -1}) impact between large rocky planetesimals, similar to the ones which formed the Moon and which stripped the surface crustal material off of Mercury's surface.

  2. Abundant Circumstellar Silica Dust and SiO Gas Created by a Giant Hypervelocity Collision in the ~12 Myr HD172555 System

    NASA Astrophysics Data System (ADS)

    Lisse, C. M.; Chen, C. H.; Wyatt, M. C.; Morlok, A.; Song, I.; Bryden, G.; Sheehan, P.

    2009-08-01

    The fine dust detected by infrared (IR) emission around the nearby β Pic analog star HD172555 is very peculiar. The dust mineralogy is composed primarily of highly refractory, nonequilibrium materials, with approximately three quarters of the Si atoms in silica (SiO2) species. Tektite and obsidian lab thermal emission spectra (nonequilibrium glassy silicas found in impact and magmatic systems) are required to fit the data. The best-fit model size distribution for the observed fine dust is dn/da = a -3.95±0.10. While IR photometry of the system has stayed stable since the 1983 IRAS mission, this steep a size distribution, with abundant micron-sized particles, argues for a fresh source of material within the last 0.1 Myr. The location of the dust with respect to the star is at 5.8 ± 0.6 AU (equivalent to 1.9 ± 0.2 AU from the Sun), within the terrestrial planet formation region but at the outer edge of any possible terrestrial habitability zone. The mass of fine dust is 4 × 1019-2 × 1020 kg, equivalent to a 150-200 km radius asteroid. Significant emission features centered at 4 and 8 μm due to fluorescing SiO gas are also found. Roughly 1022 kg of SiO gas, formed by vaporizing silicate rock, is also present in the system, and a separate population of very large, cool grains, massing 1021-1022 kg and equivalent to the largest sized asteroid currently found in the solar system's main asteroid belt, dominates the solid circumstellar material by mass. The makeup of the observed dust and gas, and the noted lack of a dense circumstellar gas disk, strong stellar X-ray activity, and an extended disk of β meteoroids argues that the source of the observed circumstellar materials is a giant hypervelocity (>10 km s-1) impact between large rocky planetesimals, similar to the ones which formed the Moon and which stripped the surface crustal material off of Mercury's surface.

  3. Technology Demonstration Milestone #1 for the EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE) I. Laboratory/Experimental Results

    NASA Astrophysics Data System (ADS)

    Belikov, Ruslan; Bendek, E.; Davis, P.; Duncan, A.; Greene, T. P.; Guyon, O.; Hix, T.; Irwin, W.; Kendrick, R.; Lozi, J.; Lynch, D.; Mihara, R.; Pluzhnik, E.; Schneider, G.; Smith, E.; Thomas, S.; Witteborn, F. C.

    2014-01-01

    Coronagraph technology is advancing and promises to enable space telescopes capable of directly detecting and spatially resolving low surface brightness circumstellar debris disks as well as imaging giant planets as close as in the habitable zones of their host stars. One proposed mission capable of doing this is called EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer), which in 2011 was selected by NASA's Explorer program for technology development (Category III). EXCEDE is a 0.7m space telescope concept designed to achieve raw contrasts of 1e6 at an inner working angle of 1.2 l/D and 1e7 at 2 l/D and beyond. In addition to doing fundamental science on debris disks, EXCEDE will also serve as a technological and scientific precursor for an exo-Earth imaging mission. EXCEDE uses a Starlight Suppression System (SSS) based on the PIAA coronagraph, enabling aggressive performance. In this presentation, we report on our continuing progress of developing the SSS for EXCEDE, and in particular the achievement of the first major milestone in our technology development program (1e6 median raw contrast between a 1.2 l/D inner working angle and 2 l/D, simultaneously with 1e7 median raw contrast between 2 l/D and 4 l/D, in monochromatic light and in a controlled and repeatable fashion - see companion paper by Schneider et al. for science drivers). In addition, we will describe the upgrades to our system, such as (a) the Low Order Wavefront Sensor (LOWFS) which enabled achieving deep contrasts at aggressive inner working angles; (b) efficient model-based wavefront control algorithms; (c) a reconfiguration of our DM to be upstream of the coronagraph and the addition of the “inverse PIAA” system that enables better outer working angles. Finally, we report on preliminary demonstrations in a vacuum chamber. Even though this technology development is primarily targeted towards EXCEDE, it is also germane to any exoplanet direct imaging space-based telescopes because of the many challenges common to different coronagraph architectures and mission requirements. This work was supported in part by the NASA Explorer program and Ames Research Center, University of Arizona, and Lockheed Martin SSC.

  4. Living with an Old Red Dwarf: X-ray-UV Emissions of Kapteyn’s Star - Effects of X-UV radiation on Habitable Zone Planets hosted by old Red Dwarf Stars

    NASA Astrophysics Data System (ADS)

    Guinan, Edward F.; Durbin, Allyn J.; Engle, Scott G.

    2015-01-01

    Red dwarfs (dM) stars make up over 75% of the local stellar population and a significant fraction (~40-50%) are older than the Sun. Because of the high frequency of red dwarfs and their longevity (> 50 Gyr), there is a greater possibility of more advanced life in red dwarf-exoplanet systems. MEarths, UVES, SDSS-III, and the upcoming TESS mission are some surveys that are targeting red dwarfs in the search for hosted potentially habitalble planets. As part of Villanova's 'Living with a Red Dwarf' program, we have obtained HST-COS Ultraviolet spectra (1150-3000A) and Chandra X-ray observations of Kapteyn's star (GJ 191; M1 V, V = 8.85 mag , d = 12.76 +/- 0.05 ly). Kapyteyn's Star is important for the study of old red dwarfs because it is the nearest (Pop II) halo star with a radial velocity of +245.2 km/s and an estimated age of 11.2 +/-0.9 Gyrs. Recently Kapteyn's Star was found to host two super-Earth mass planets - one of these is orbiting inside the star's Habitable Zone (Anglada-Escude' 2014: MNRAS 443, L89). In our program, Kapteyn's star is the oldest red dwarf and as such serves as an anchor for our age, rotation, and activity relations. The spectra obtained from HST/COS provide one of the cleanest measurements of the important HI Lyman-alpha 1215.6 A emission flux for red dwarfs. This is due to the large Doppler shift from the high radial velocity, separating the stellar Ly-alpha emission from by the Ly-alpha ISM and local geo-coronal sources. These observations further provide calibrations at the old age/low rotation/low activity extremes for our relations. As the nearest and brightest old red dwarf star, Kapteyn's Star also provides insights into its magnetic properties to investigae coronal x-ray and UV emission for the large population of old, slowly rotating red dwarf stars. Kapteyn's star also serves as a proxy for the numerous metal-poor old disk - Pop II M dwarfs by providing information about X-UV emissions. This information is crucial for determining X-ray-UV irradiances for habitable zone planets hosted by these old numerous, cool low luminosity stars.We gratefully acknowledge the support from NSF/RUI Grant AST-1009903, NASA/Chandra Grants GO2-13020X, and HST-GO-13020

  5. Energy Balance Models of planetary climate as a tool for investigating the habitability of terrestrial planets and its evolution

    NASA Astrophysics Data System (ADS)

    Ferri, G.; Murante, G.; Provenzale, A.; Silva, L.; Vladilo, G.

    2012-04-01

    The study of the habitability and potential for life formation of terrestrial planets requires a considerable work of modelization owing to the limited amount of experimental constraints typical of this type of research. As an example, the paucity of experimental Archean data severely limits the study of the habitability of the primitive Earth at the epoch of the origin of life. In the case of exoplanets the amount of experimental information available is quite limited and the need for modelization strong. Here we focus on the modelization of the surface planetary temperature, a key thermodynamical quantity used to define the habitability. Energy Balance Models (EBM) of planetary climate provide a simple way to calculate the temperature-latitude profile of terrestrial planets with a small amount of computing resources. Thanks to this fact EBMs offer an excellent tool to exploring a wide range of parameter space and therefore testing the effects of variations of physical/chemical quantities unconstrained by experimental data. In particular, one can easily probe possible scenarios of habitability at different stages of planetary evolution. We have recently implemented one-dimensional EBMs featuring the possibility of probing variations of astronomical and geophysical parameters, such as stellar luminosity, orbital semi-major axis and eccentricity, obliquity of the planetary axis, planet rotational velocity, land/ocean surface fractions and thermal capacities, and latitudinal heat diffusion. After testing our models against results obtained in previous work (Williams & Kasting 1997, Icarus, 129, 254; Spiegel et al. 2008, ApJ, 681, 1609), we introduced a novel parametrization of the diffusion coefficient as a function of the stellar zenith distance. Our models have been validated using the mean temperature-latitude profiles of the present Earth and its seasonal variations; the global albedo has been used as an additional constraint. In this work we present specific examples of application of our EBMs to studies of habitability of terrestrial planets. In the first part we focus on the primitive Earth, taking into account the effects of the higher speed of Earth rotation and reduced solar luminosity at the epoch of life formation. In the second part we provide examples of habitability studies of planetary systems discovered in surveys of exoplanets. These examples allow us to critically discuss the concept of circumstellar habitable zone.

  6. Psychology of Habit.

    PubMed

    Wood, Wendy; Rünger, Dennis

    2016-01-01

    As the proverbial creatures of habit, people tend to repeat the same behaviors in recurring contexts. This review characterizes habits in terms of their cognitive, motivational, and neurobiological properties. In so doing, we identify three ways that habits interface with deliberate goal pursuit: First, habits form as people pursue goals by repeating the same responses in a given context. Second, as outlined in computational models, habits and deliberate goal pursuit guide actions synergistically, although habits are the efficient, default mode of response. Third, people tend to infer from the frequency of habit performance that the behavior must have been intended. We conclude by applying insights from habit research to understand stress and addiction as well as the design of effective interventions to change health and consumer behaviors. PMID:26361052

  7. Healthy Sleep Habits

    MedlinePlus

    ... Sleep Apnea Testing CPAP Healthy Sleep Habits Healthy Sleep Habits Your behaviors can have a major impact ... team at an AASM accredited sleep center. Quick Sleep Tips Follow these tips to establish healthy sleep ...

  8. Tides and the evolution of planetary habitability.

    PubMed

    Barnes, Rory; Raymond, Sean N; Jackson, Brian; Greenberg, Richard

    2008-06-01

    Tides raised on a planet by the gravity of its host star can reduce the planet's orbital semi-major axis and eccentricity. This effect is only relevant for planets orbiting very close to their host stars. The habitable zones of low-mass stars are also close in, and tides can alter the orbits of planets in these locations. We calculate the tidal evolution of hypothetical terrestrial planets around low-mass stars and show that tides can evolve planets past the inner edge of the habitable zone, sometimes in less than 1 billion years. This migration requires large eccentricities (>0.5) and low-mass stars ( less or similar to 0.35 M(circle)). Such migration may have important implications for the evolution of the atmosphere, internal heating, and the Gaia hypothesis. Similarly, a planet that is detected interior to the habitable zone could have been habitable in the past. We consider the past habitability of the recently discovered, approximately 5 M(circle) planet, Gliese 581 c. We find that it could have been habitable for reasonable choices of orbital and physical properties as recently as 2 Gyr ago. However, when constraints derived from the additional companions are included, most parameter choices that indicate past habitability require the two inner planets of the system to have crossed their mutual 3:1 mean motion resonance. As this crossing would likely have resulted in resonance capture, which is not observed, we conclude that Gl 581 c was probably never habitable. PMID:18598142

  9. OT1_nbillot_1: HYSOVAR: Circumstellar Disks Variability around Young Stellar Objects in the Orion Nebula Cluster with Herschel/PACS

    NASA Astrophysics Data System (ADS)

    Billot, N.

    2010-07-01

    The variability of Young Stellar Objects (YSOs) have been demonstrated over half a century ago from optical observations. More recent time series photometry of YSOs in the thermal infrared have shown their great potential to probe the structure of inner circumstellar disks (r << 1 AU), in particular the presence of warps and `clouds' in the disks which may owe their existence to the gravitational torques from close-in planets. For instance the YSOVAR program used the Spitzer IRAC instrument to monitor over 1400~YSOs and establish that 70% of them show significant variability in the mid-IR. Today the Herschel/PACS spectral coverage, sensitivity and stability offer a unique opportunity to access the wavelength regime sensitive to the dust thermal emission from the terrestrial habitable zone through the ice-line where gas giants are expected to form. We propose the HYSOVAR program, an expansion of YSOVAR with the Herschel/PACS Photometer, to monitor the flux variations of 100+ Class I YSOs in Orion over weeks-to-years time scales. This small (9.9 hours) exploratory program would greatly increase the statistics and sensitivity of previous studies in the far-IR, and it would help us identify the physical processes responsible for the observed infrared variability by placing strong constraints on existing models of star and planet formation.

  10. High contrast imaging polarimetry of circumstellar environments

    NASA Astrophysics Data System (ADS)

    Canovas Cabrera, H.

    2011-09-01

    The work presented in this thesis is based on the analysis of the results produced by ExPo, the Extreme Polarimeter. ExPo is an imaging polarimeter that has been designed and built by the group of prof. Christoph Keller, at Utrecht University. The purpose of this instrument is to use polarimetry to detect and characterize the circumstellar environments around different types of stars. In this work I focus on the polarized features that are produced by scattering by dust grains. Depending on the properties of the particles producing the scattering (size, shape...) and the scattering angle (forward, backward scattering), the light becomes polarized in higher or lower degree. The main problem when studying circumstellar environments is the high contrast ratios that are faced. For example, a young star is typically four orders of magnitude (10000 times) brighter than its protoplanetary disk. On the other hand, the light emitted by the star is largely unpolarized, while the light that is scattered (by the protoplanetary disk in this example) is polarized. Therefore, polarimetry offers a very elegant way to remove most of the starlight, allowing the detection of only the polarized photons. Furthermore, and as explained before, by studying the polarization of the light that we measure we can learn more about the properties of the circumstellar environments (dust composition, geometry, etc.). ExPo has produced a wealth of data, combining observations of very different targets such as protoplanetary disks, post-AGB stars, comets and planets of our Solar System (Venus and Saturn).

  11. Technology Demonstration Milestone #1 for the EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE) II. Science Drivers and Implications

    NASA Astrophysics Data System (ADS)

    Schneider, Glenn; Belikov, R.; Guyon, O.; Lozi, J.; Eduardo, B.; Davis, P.; Greene, T. P.; Lynch, D.; Eugene, P.; Sandrine, T.; Witteborn, F.; Duncan, A.; Kendrick, R.; Hix, T.; Mihara, R.; Smith, E.; Irwin, W.; Debes, J. H.; Carson, J.; Hines, D. C.; Grady, C. A.; Perrin, M. D.; Silverstone, M. D.; Wisniewski, J. P.; Hinz, P.; Moro-Martin, A.; Henning, T.; Tamura, M.; Jang-Condell, H.; Weinberger, A. J.; Woodgate, B. E.; Goto, M.; Serabyn, G.; Rodigas, T.; Kuchner, M. J.; Stark, C. C.; EXCEDE Project Technology Development Team; HST GO 12228 Team

    2014-01-01

    The EXoplanetary Circumstellar (CS) Environments and Disk Explorer (EXCEDE) is an EX class Explorer mission proposed to study the formation, evolution, architectures, and diversity of exoplanetary systems by characterizing suspected planet-hosting CS environments into and beyond host-star habitable zones using a small (0.7 m diameter) off-axis telescope. EXCEDE was selected by NASA (as a Class III Explorer program) for technology demonstration and maturation to advance key elements of its proposed starlight suppression system (SSS) combining the use of a Phase Induced Amplitude Apodized coronagraph, MEMS Deformable Mirror, closed-loop Low-Order Wavefront Sensing and Control, and mid-spatial frequency wavefront error correction and control using the science camera for electric field conjugation and speckle suppression for image contrast enhancement. To meet the science goals of the EXCEDE mission, the SSS must simultaneously, repeatably, and stably, deliver disk-to-starlight raw image contrast per resel of 1E-6 from 1.2 to 2 lambda/D, and 1E-7 from 2 to ~ 20 lambda/D in optical light, which has now been laboratory demonstrated for monochromatic light in an in-air environment (see paper I. by Belikov et al.) This level of performance when extended to 10% - 20% broadband light (technology demonstration milestone #2 to be pursued over the next year) will enable the EXCEDE mission. Here we discuss the applicability of these performance metrics to studying the current "here be dragons" regions of light-scattering CS debris disks, including those now well-observed as revealed at larger stellocentric angular distances with the Hubble Space Telescope Imaging Spectrograph's coronagraph with multiple-roll PSF-template subtracted coronagraphy as imaged in HST GO program 12228 in the context of the EXCEDE science mission goals. This investigation is funded in part by NASA grant NNX12AH39G, and STScI grant GO-12228.

  12. Circumstellar material around young stars in Orion

    NASA Technical Reports Server (NTRS)

    Odell, C. R.

    1994-01-01

    The star cluster associated with the Orion nebula is one of the richest known. Lying at the nearside of the Orion Molecular cloud and at a distance of about 500 pc from us, it contains many premain-sequence stars with ages of about 300,000 yr. The nebula itself is a blister type, representing a wall of material ionized by the hottest star in the Trapezium group (member C). Although this is not the closest star formation region, it is probably the easiest place to detect circumstellar, possibly proto-planetary, material around these solar mass stars. This is because the same process of photoionization that creates the nebula also photoionizes these circumstellar clouds, thus rendering them easily visible. Moreover, their dust component is made visible by extinction of light from the background nebula. Young stars with circumstellar material were found in Orion on the second set of HST images and were called proplyds, indicating their special nature as circumstellar clouds caused to be luminous by being in or near a gaseous nebula. The brightest objects in the field had previously been seen in the optical and radio, and although their true nature had been hypothesized it was the HST images that made it clear what they are. The forms vary from cometlike when near the Trapezium to elliptical when further away, with the largest being 1000 AU and the bright portions of the smallest, which are found closest to the Trapezium, being about 100 AU in diameter. We now have a second set of HST observations made immediately after the refurbishment mission that provides even greater detail and reveals even more of these objects. About half of all the low-luminosity stars are proplyds. The poster paper describes quantitative tests about their fundamental structure and addresses the question of whether the circumstellar material is a disk or shell. One object (HST 16) is seen only in silhouette against the nebula and is easily resolved into an elliptical form of optical depth monotonically increasing toward the central star.

  13. Choosing Stars to Search for Habitable Planets

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    M-dwarf stars are excellent targets for planet searches because the signal of an orbiting planet is relatively larger (and therefore easier to detect!) around small, dim M dwarfs, compared to Sun-like stars. But are there better or worse stars to target within this category when searching for habitable, Earth-like planets?Confusing the SignalRadial velocity campaigns search for planets by looking for signatures in a stars spectra that indicate the star is wobbling due to the gravitational pull of an orbiting planet. Unfortunately, stellar activity can mimic the signal of an orbiting planet in a stars spectrum something that is particularly problematic for M dwarfs, which can remain magnetically active for billions of years. To successfully detect planets that orbit in their stars habitable zones, we have to account for this problem.In a recent study led by Elisabeth Newton (Harvard-Smithsonian Center for Astrophysics), the authors use literature measurements to examine the rotation periods for main-sequence, M-type stars. They focus on three factors that are important for detecting and characterizing habitable planets around M dwarfs:Whether the habitable-zone orbital periods coincide with the stellar rotationFalse planet detections caused by stellar activity often appear as a planet with an orbital period thats a multiple of the stellar rotation period. If a stars rotation period coincides with the range of orbital periods corresponding to its habitable zone, its therefore possible to obtain false detections of habitable planets.How long stellar activity and rapid rotation last in the starAll stars become less magnetically active and rotate more slowly as they age, but the rate of this decay depends on their mass: lower-mass stars stay magnetically active for longer and take longer to spin down.Whether detailed atmospheric characterization will be possibleIts ideal to be able to follow up on potentially habitable exoplanets, and search for biosignatures such as oxygen in the planetary atmosphere. This type of detection will only be feasible for low-mass dwarfs, however, due to the relative size of the star and the planet.An Ideal RangeStellar rotation period as a function of stellar mass. The blue shaded region shows the habitable zone as a function of stellar mass. For M dwarfs between ~0.25 and ~0.5 solar mass, the habitable-zone period overlaps with the stellar rotation period. [Newton et al. 2016]Newton and collaborators find that stars in the mass range of 0.25 to 0.5 solar mass (stellar class M1V-M4V) are non-ideal targets, because their stellar rotation periods (or a multiple thereof) coincide with the orbital periods of their habitable zones. In addition, atmospheric characterization will only be feasible in the near future for stars with mass less than ~0.25 solar mass.On the other hand, dwarfs with mass less than ~0.1 solar masses (stellar classes later than M6V) will retain their stellar activity and faster rotation rates throughout most of their lifetimes, making them non-ideal targets as well.When searching for habitable exoplanets, the best targets are therefore the mid M dwarfs in the mass range of 0.1 to 0.25 solar mass (stellar class M4V-M6V). Building a sample focused on these stars will reduce the likelihood that planets found in the stars habitable zones are false detections. This will hopefully produce a catalog of potentially habitable exoplanets that we can eventually follow up with atmospheric observations.CitationElisabeth R. Newton et al 2016 ApJ 821 L19. doi:10.3847/2041-8205/821/1/L19

  14. Geophysical and atmospheric evolution of habitable planets.

    PubMed

    Lammer, Helmut; Selsis, Frank; Chassefière, Eric; Breuer, Doris; Griessmeier, Jean-Mathias; Kulikov, Yuri N; Erkaev, Nikolai V; Khodachenko, Maxim L; Biernat, Helfried K; Leblanc, Francois; Kallio, Esa; Lundin, Richard; Westall, Frances; Bauer, Siegfried J; Beichman, Charles; Danchi, William; Eiroa, Carlos; Fridlund, Malcolm; Gröller, Hannes; Hanslmeier, Arnold; Hausleitner, Walter; Henning, Thomas; Herbst, Tom; Kaltenegger, Lisa; Léger, Alain; Leitzinger, Martin; Lichtenegger, Herbert I M; Liseau, René; Lunine, Jonathan; Motschmann, Uwe; Odert, Petra; Paresce, Francesco; Parnell, John; Penny, Alan; Quirrenbach, Andreas; Rauer, Heike; Röttgering, Huub; Schneider, Jean; Spohn, Tilman; Stadelmann, Anja; Stangl, Günter; Stam, Daphne; Tinetti, Giovanna; White, Glenn J

    2010-01-01

    The evolution of Earth-like habitable planets is a complex process that depends on the geodynamical and geophysical environments. In particular, it is necessary that plate tectonics remain active over billions of years. These geophysically active environments are strongly coupled to a planet's host star parameters, such as mass, luminosity and activity, orbit location of the habitable zone, and the planet's initial water inventory. Depending on the host star's radiation and particle flux evolution, the composition in the thermosphere, and the availability of an active magnetic dynamo, the atmospheres of Earth-like planets within their habitable zones are differently affected due to thermal and nonthermal escape processes. For some planets, strong atmospheric escape could even effect the stability of the atmosphere. PMID:20307182

  15. FUSE Observations of the ? Pic Circumstellar Environment

    NASA Astrophysics Data System (ADS)

    Lecavelier des Etangs, A.; Vidal-Madjar, A.; Ferlet, R.; Roberge, A.; Feldman, P. D.; Deleuil, M.; Bouret, J.-C.; Andr, M.; Blair, W. P.; Moos, H. W.; FUSE Science Team

    2000-12-01

    We present the first far UV spectrum of Beta Pictoris obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). Although the stellar continuum drops below detectability for wavelengths shorter than 1100 , the Ciii line at 977 and the Ovi doublet at 1032 and 1037 are clearly detected in emission. These emissions are believed to have a stellar origin. Because we did not detect H2 absorption in our spectrum, the coincidence of Ovi and H2 transitions allows us to set a very low upper limit on the H2 column density toward ? Pic. This is surprising, as Beta Pic has one of the largest circumstellar disks seen around a main-sequence star. From the comparison with HST observations, we obtain a CO/H2 ratio above the typical interstellar value of 10-4; this seems to confirm the circumstellar origin of the observed CO. Species observed in the ? Pic circumstellar gas at the stellar radial velocity, like Feii and Caii, feel strong radiation pressure from the star and should be ejected from the system. Lagrange et al. (1998) suggested that these species could be slowed down by a thick, colliding torus of massive gas; our non-detection of H2 toward Beta Pic leaves this dynamical problem unresolved. This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support to U.S. participants has been provided by NASA contract NAS5-32985.

  16. The role of intrinsic magnetic fields in planetary evolution and habitability: the planetary protection aspect

    NASA Astrophysics Data System (ADS)

    Khodachenko, Maxim L.; Lammer, H.; Lichtenegger, H. I. M.; Grießmeier, J.-M.; Holmström, M.; Ekenbäck, A.

    2009-04-01

    The widely used definition of a habitable zone (HZ) for planets as a circumstellar area, where the star's luminosity is sufficiently intense to maintain liquid water at the surface of a planet, is shown to be too simplified. The role of a host star's activity and the intrinsic magnetic field of a planet with respect to their influence on mass loss processes of close-in gas giants and a definition of a HZ for the terrestrial-type exoplanets are discussed. The stellar X-ray/EUV radiation and the stellar wind result in ionization, heating, chemical modification, and slow erosion of the planetary upper atmospheres throughout their lifetime. The closer the planet is to the star, the more efficient are these processes, and therefore, the more important becomes the magnetic protection of a planet as a potential habitat. Different ways for planetary magnetic dipole moment estimation, based on existing magnetic dynamo scaling laws as well as on the recent measurements of hot atomic hydrogen clouds around close-in ‘Hot Jupiters’ are considered, and the predictions of these estimations are compared to each other.

  17. Habitability: A Review.

    PubMed

    Cockell, C S; Bush, T; Bryce, C; Direito, S; Fox-Powell, M; Harrison, J P; Lammer, H; Landenmark, H; Martin-Torres, J; Nicholson, N; Noack, L; O'Malley-James, J; Payler, S J; Rushby, A; Samuels, T; Schwendner, P; Wadsworth, J; Zorzano, M P

    2016-01-01

    Habitability is a widely used word in the geoscience, planetary science, and astrobiology literature, but what does it mean? In this review on habitability, we define it as the ability of an environment to support the activity of at least one known organism. We adopt a binary definition of "habitability" and a "habitable environment." An environment either can or cannot sustain a given organism. However, environments such as entire planets might be capable of supporting more or less species diversity or biomass compared with that of Earth. A clarity in understanding habitability can be obtained by defining instantaneous habitability as the conditions at any given time in a given environment required to sustain the activity of at least one known organism, and continuous planetary habitability as the capacity of a planetary body to sustain habitable conditions on some areas of its surface or within its interior over geological timescales. We also distinguish between surface liquid water worlds (such as Earth) that can sustain liquid water on their surfaces and interior liquid water worlds, such as icy moons and terrestrial-type rocky planets with liquid water only in their interiors. This distinction is important since, while the former can potentially sustain habitable conditions for oxygenic photosynthesis that leads to the rise of atmospheric oxygen and potentially complex multicellularity and intelligence over geological timescales, the latter are unlikely to. Habitable environments do not need to contain life. Although the decoupling of habitability and the presence of life may be rare on Earth, it may be important for understanding the habitability of other planetary bodies. PMID:26741054

  18. Observations of circumstellar circular polarization in four more infrared stars.

    NASA Technical Reports Server (NTRS)

    Angel, J. R. P.; Martin, P. G.

    1973-01-01

    Circular polarization at 0.84 micron has been discovered for four stars with characteristics similar to VY CMa and NML Cyg. This polarization is attributed to multiple scattering in an asymmetric circumstellar dust cloud. Some common properties of the class of stars expected to show circumstellar circular polarization are discussed.

  19. Habitability: from stars to cells

    NASA Astrophysics Data System (ADS)

    Javaux, Emmanuelle J.; Dehant, Véronique

    2010-07-01

    To determine where to search for life in our solar system or in other extrasolar systems, the concept of habitability has been developed, based on the only sample we have of a biological planet—the Earth. Habitability can be defined as the set of the necessary conditions for an active life to exist, even if it does not exist. In astronomy, a habitable zone (HZ) is the zone defined around a sun/star, where the temperature conditions allow liquid water to exist on its surface. This habitability concept can be considered from different scientific perspectives and on different spatial and time scales. Characterizing habitability at these various scales requires interdisciplinary research. In this article, we have chosen to develop the geophysical, geological, and biological aspects and to insist on the need to integrate them, with a particular focus on our neighboring planets, Mars and Venus. Important geodynamic processes may affect the habitability conditions of a planet. The dynamic processes, e.g., internal dynamo, magnetic field, atmosphere, plate tectonics, mantle convection, volcanism, thermo-tectonic evolution, meteorite impacts, and erosion, modify the planetary surface, the possibility to have liquid water, the thermal state, the energy budget, and the availability of nutrients. They thus play a role in the persistence of life on a planet. Earth had a liquid water ocean and some continental crust in the Hadean between 4.4 and 4.0 Ga (Ga: billions years ago), and may have been habitable very early on. The origin of life is not understood yet; but the oldest putative traces of life are early Archean (~3.5 Ga). Studies of early Earth habitats documented in the rock record hosting fossil life traces provide information about possible habitats suitable for life beyond Earth. The extreme values of environmental conditions in which life thrives today can also be used to characterize the “envelope” of the existence of life and the range of potential extraterrestrial habitats. The requirement of nutrients by life for biosynthesis of cellular constituents and for growth, reproduction, transport, and motility may suggest that a dynamic and rocky planet with hydrothermal activity and formation of relief, liquid water alteration, erosion, and runoff is required to replenish nutrients and to sustain life (as we know it). The concept of habitability is very Earth-centric, as we have only one biological planet to study. However, life elsewhere would most probably be based on organic chemistry and leave traces of its past or recent presence and metabolism by modifying microscopically or macroscopically the physico-chemical characteristics of its environment. The extent to which these modifications occur will determine our ability to detect them in astrobiological exploration. Looking at major steps in the evolution of life may help determining the probability of detecting life (as we know it) beyond Earth and the technology needed to detect its traces, be they morphological, chemical, isotopic, or spectral.

  20. A 'dry' condensation origin for circumstellar carbonates.

    PubMed

    Toppani, Alice; Robert, François; Libourel, Guy; de Donato, Philippe; Barres, Odile; d'Hendecourt, Louis; Ghanbaja, Jaafar

    2005-10-20

    The signature of carbonate minerals has long been suspected in the mid-infrared spectra of various astrophysical environments such as protostars. Abiogenic carbonates are considered as indicators of aqueous mineral alteration in the presence of CO2-rich liquid water. The recent claimed detection of calcite associated with amorphous silicates in two planetary nebulae and protostars devoid of planetary bodies questions the relevance of this indicator; but in the absence of an alternative mode of formation under circumstellar conditions, this detection remains controversial. The main dust component observed in circumstellar envelopes is amorphous silicates, which are thought to have formed by non-equilibrium condensation. Here we report experiments demonstrating that carbonates can be formed with amorphous silicates during the non-equilibrium condensation of a silicate gas in a H2O-CO2-rich vapour. We propose that the observed astrophysical carbonates have condensed in H2O(g)-CO2(g)-rich, high-temperature and high-density regions such as evolved stellar winds, or those induced by grain sputtering upon shocks in protostellar outflows. PMID:16237436

  1. Models for circumstellar nebulae around red and blue supergiants

    NASA Astrophysics Data System (ADS)

    Chita, S. M.

    2011-10-01

    In this thesis, we model the circumstellar medium of stars with initial masses of 8, 12, 18 and 20 solar masses, over their entire life from the main sequence until their supernova explosion. During the post-main-sequence stages, stars can evolve through several blue and red supergiant stages depending on their initial mass, composition and rotation rate. The models considered in the second Chapter have long-lasting RSG stages starting after the MS. In this phase, they develop shells of RSG wind material at the location where the free streaming RSG wind is stalled by the thermal pressure of the hot MS bubble, close to the central star. The RSG shells develop violent Rayleigh-Taylor instabilities. Once these start to grow non-linear, the RSG shell becomes highly structured as clumps form, and shell material mixes with material in the hot bubble. Later, the stars evolve to the BSG stage, during which the RSG shells are completely destroyed. These models return to the RSG stage, and build new RSG shells, which are more massive than those formed earlier. RSG shells are essential for our understanding of bipolar emission nebulae around BSGs. In the third Chapter are shown the results of the wind-wind interaction model of single star with 12 solar masses. On a time scale of a few 10000 yr, a BSG hour-glas shaped nebula expands into the sphere defined by the RSG shell. The faster polar parts of the hour glass hit the inner edge of the RSG shell first. The collision creates a pair of hot and dense polar caps. As time passes, the collision zone moves to lower latitudes of the RSG shell and becomes more confined in latitude. At the same time, the interaction of the BSG wind with the equatorial disk defines a second, ring shaped collision zone in the equatorial plane. These structures are reminiscent of the observed nebulae around the blue supergiant Sher 25. In the Chapter 3 we present calculations that predict the properties of the circumstellar medium for rapidly rotating and slowly rotating blue supergiants. In their post-main-sequence phases, the stars with 10 and 12 solar masses undergo a blue-loop following a first red supergiant stage. Before they explode as supernovae, the stars go back for a second time to the red supergiant stage. In case of a rapidly rotating central star, the collision of an hour-glass shaped shell with a stationary red supergiant shell forms a highly structured rotationally symmetric nebula. In contrast: if the star rotates slowly, a spherical nebula may form. The last Chapter shows preliminary results of possible ways for the formation of the outer rings observed around SN 1987A nebula through wind-wind interaction. At the end of the main sequence stage, our star model goes through a first blue supergiant post-main sequence stage becoming later a red supergiant. Before exploding as a supernova, the progenitor enters a second blue supergiant phase. During this phase the star reaches critical rotation. Due to the non-spherical wind of the first BSG phase, a shell of wind material is broken into two parts, with a high density ring-shaped intersection at mid-latitudes, which has some similarity to the outer circumstellar rings of SN 1987A.

  2. On the Habitability of Aquaplanets

    NASA Astrophysics Data System (ADS)

    Cardenas, Rolando; Perez, Noel; Martinez-Frias, Jesus; Martin, Osmel

    2014-08-01

    An Aquatic Habitability Index is proposed, based on Quantitative Habitability Theory, and considering a very general model for life. It is a primary habitability index, measuring habitability for phytoplankton in the first place. The index is applied to some case studies, such as the habitability changes in Earth due to environmental perturbations caused by asteroid impacts.

  3. Dynamical habitability of planetary systems.

    PubMed

    Dvorak, Rudolf; Pilat-Lohinger, Elke; Bois, Eric; Schwarz, Richard; Funk, Barbara; Beichman, Charles; Danchi, William; Eiroa, Carlos; Fridlund, Malcolm; Henning, Thomas; Herbst, Tom; Kaltenegger, Lisa; Lammer, Helmut; Léger, Alain; Liseau, René; Lunine, Jonathan; Paresce, Francesco; Penny, Alan; Quirrenbach, Andreas; Röttgering, Huub; Selsis, Frank; Schneider, Jean; Stam, Daphne; Tinetti, Giovanna; White, Glenn J

    2010-01-01

    The problem of the stability of planetary systems, a question that concerns only multiplanetary systems that host at least two planets, is discussed. The problem of mean motion resonances is addressed prior to discussion of the dynamical structure of the more than 350 known planets. The difference with regard to our own Solar System with eight planets on low eccentricity is evident in that 60% of the known extrasolar planets have orbits with eccentricity e > 0.2. We theoretically highlight the studies concerning possible terrestrial planets in systems with a Jupiter-like planet. We emphasize that an orbit of a particular nature only will keep a planet within the habitable zone around a host star with respect to the semimajor axis and its eccentricity. In addition, some results are given for individual systems (e.g., Gl777A) with regard to the stability of orbits within habitable zones. We also review what is known about the orbits of planets in double-star systems around only one component (e.g., gamma Cephei) and around both stars (e.g., eclipsing binaries). PMID:20307181

  4. TIDAL LIMITS TO PLANETARY HABITABILITY

    SciTech Connect

    Barnes, Rory; Jackson, Brian; Greenberg, Richard; Raymond, Sean N.

    2009-07-20

    The habitable zones (HZs) of main-sequence stars have traditionally been defined as the range of orbits that intercept the appropriate amount of stellar flux to permit surface water on a planet. Terrestrial exoplanets discovered to orbit M stars in these zones, which are close-in due to decreased stellar luminosity, may also undergo significant tidal heating. Tidal heating may span a wide range for terrestrial exoplanets and may significantly affect conditions near the surface. For example, if heating rates on an exoplanet are near or greater than that on Io (where tides drive volcanism that resurfaces the planet at least every 1 Myr) and produce similar surface conditions, then the development of life seems unlikely. On the other hand, if the tidal heating rate is less than the minimum to initiate plate tectonics, then CO{sub 2} may not be recycled through subduction, leading to a runaway greenhouse that sterilizes the planet. These two cases represent potential boundaries to habitability and are presented along with the range of the traditional HZ for main-sequence, low-mass stars. We propose a revised HZ that incorporates both stellar insolation and tidal heating. We apply these criteria to GJ 581 d and find that it is in the traditional HZ, but its tidal heating alone may be insufficient for plate tectonics.

  5. Healthy habits for weight loss

    MedlinePlus

    ... loss, turn healthy eating into a habit. These healthy eating habits can help you lose weight and keep it off. ... The family kitchen can trigger unhealthy eating habits if your shelves ... vegetables in the refrigerator. When you feel hungry, you' ...

  6. The EELT's View of Circumstellar Environments

    NASA Astrophysics Data System (ADS)

    Chauvin, Gael

    2013-12-01

    Considering the fantastic perspective offered by the upcoming generation of instruments of the EELT, a new observing domain will be opened for the exploration of the circumstellar environment. After placing the E-ELT in the context of current and future instrumentation and space missions, I will first briefly summarize the main properties and expected performances of the six currently known E-ELT instruments. I will then highlight the most interesting science cases from the disk-star interactions processes, the proto-planetary and debris disk characterization, the detection and characterization of exoplanets and their atmosphere to the rich environment of evolved stars. I will particularly insist on the unique observing constraints that will be obtained with the E-ELT.

  7. Chemistry and evolution of gaseous circumstellar disks

    NASA Technical Reports Server (NTRS)

    Prinn, Ronald G.

    1993-01-01

    An investigation of the chemical and physical processes which determine the composition and evolution of gas-rich circumstellar disks is reported. Strong mixing in a thermoclinic environment like an accretion disk leads to thermochemical disequilibration due to 'kinetic inhibition' induced by chemical time constants becoming longer than outward mixing time constants. In this case, species thermodynamically stable at high temperatures but not at low temperatures dominate at all temperatures in the disk. Nonaxisymmetric accretion of material at hypersonic speeds is a major forcing mechanism for mixing in the disk and can produce eddy speeds of 1 percent of the sound speed. The implications kinetic inhibition in the carbon, nitrogen, and anhydrous/hydrous silicate families has for the compositions of the terrestrial planets, giant planets, ice-rich satellites, Pluto, comets, meteorites, and asteroids are discussed.

  8. Spectroscopic Survey of Circumstellar Disks in Orion

    NASA Astrophysics Data System (ADS)

    Contreras, Maria; Hernandez, Jesus; Olguin, Lorenzo; Briceno, Cesar

    2013-07-01

    As a second stage of a project focused on characterizing candidate stars bearing a circumstellar disk in Orion, we present a spectroscopic follow-up of a set of about 170 bright stars. The present set of stars was selected by their optical (UBVRI) and infrared behavior in different color-color and color-magnitude diagrams. Observations were carried out at the Observatorio Astronomico Nacional located at the Sierra San Pedro Martir in B.C., Mexico and at the Observatorio Guillermo Haro in Cananea, Sonora, Mexico. Low-resolution spectra were obtained for all candidates in the sample. Using the SPTCLASS code, we have obtained spectral types and equivalent widths of the Li I 6707 and Halpha lines for each one of the stars. This project is a cornerstone of a large scale survey aimed to obtain stellar parameters in a homogeneous way using spectroscopic data. This work was partially supported by UNAM-PAPIIT grant IN-109311.

  9. HL Tauri and its circumstellar disk

    NASA Technical Reports Server (NTRS)

    Cohen, M.

    1983-01-01

    New far infrared observations of HL Tau which support the identification of an edge-on disk surrounding the star are presented. A bolometric luminosity for the star of 7.2 solar luminosities and a ratio of infrared to optical luminosity of 630 are indicated. A circumstellar A(V) of about 7.0 mag is produced, consistent with the silicate optical depth to the star. Data on HL Tau's effective temperature and radius and its position on the HR diagram suggest that the star has recently completed its accretion phase and is only 100,000 yr old. The column masses of ice and silicates are combined with the disk dimensions to build a simple model of the disk for comparison with the primitive solar nebula. Estimates of the far-infrared emitting mass provide independent probes of the mass in larger grains around HL Tau.

  10. The circumstellar environment of UX ORI

    NASA Astrophysics Data System (ADS)

    Natta, A.; Prusti, T.; Neri, R.; Thi, W. F.; Grinin, V. P.; Mannings, V.

    1999-10-01

    This paper presents new observations of UX Ori obtained with the millimeter interferometer of Plateau de Bure and with ISO. UX Ori is the prototype of a group of pre-main-sequence, intermediate-mass stars, often indicated as precursors of beta Pic. The interferometry observations at 1.2 and 2.6 mm show that UX Ori has a circumstellar disk, with outer radius ~ less 100 AU. We determine the spectral index between these two wavelengths to be 2.1+/-0.2, consistent with the disk being optically thick at mm wavelengths. Alternatively, the disk solid matter can be in the form of ``pebbles" (radius ~ 10 cm). In both cases most of the disk mass must be in gas form, and small grains must be present, at least in the disk atmosphere. In both cases also, the disk must be rather massive ( ~ great 0.1 M_sun). The existence of a circumstellar disk supports the model of the UXOR phenomenon in terms of a star+disk system. Self-consistent models of almost edge-on disks account well for the observed emission at all wavelengths longer than about 8mu m, if we include the emission of the optically thin, superheated layers that enshroud the disk. These rather simple disk models fail to account for the strong emission observed in the near-IR (i.e., between ~ 2 and 7 mu m), and we suggest a number of possible explanations. Based in part on observations obtained with ISO. ISO is an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

  11. A Review of Habit Reversal with Childhood Habit Disorders.

    ERIC Educational Resources Information Center

    Woods, Douglas W.; Miltenberger, Raymond G.

    1996-01-01

    This paper first reviews four classes of habit disorders in children: motor and vocal tics, nervous habits, stuttering, and Tourette's disorder. It then describes the habit reversal procedure and reviews the literature on its use and variations to treat each of the four classes of habit disorders. Emphasis is on simplified versions of the original…

  12. Habitability design for spacecraft

    NASA Technical Reports Server (NTRS)

    Franklin, G. C.

    1978-01-01

    Habitability is understood to mean those spacecraft design elements that involve a degree of comfort, quality or necessities to support man in space. These elements are environment, architecture, mobility, clothing, housekeeping, food and drink, personal hygiene, off-duty activities, each of which plays a substantial part in the success of a mission. Habitability design for past space flights is discussed relative to the Mercury, Gemini, Apollo, and Skylab spacecraft, with special emphasis on an examination of the Shuttle Orbiter cabin design from a habitability standpoint. Future projects must consider the duration and mission objectives to meet their habitability requirements. Larger ward rooms, improved sleeping quarters and more complete hygiene facilities must be provided for future prolonged space flights

  13. Habitability: CAMELOT 4

    NASA Technical Reports Server (NTRS)

    Alequin, W.; Barragan, A.; Carro, M.; Garcia, F.; Gonzalez, I.; Mercado, J. A.; Negron, N.; Lopez, D.; Rivera, L. A.; Rivera, M.

    1990-01-01

    During 1988 to 1989 the NASA/USRA Advanced Design Program sponsored research and design efforts aimed at developing habitability criteria and at defining a habitability concept as a useful tool in understanding and evaluating dwellings for prolonged stays in extraterrestrial space. The Circulating Auto sufficient Mars-Earth Luxurious Orbital Transport (CAMELOT) was studied as a case in which the students would try to enhance the quality of life of the inhabitants by applying architectural design methodology. The study proposed 14 habitability criteria considered necessary to fulfill the defined habitability concept, which is that state of equilibrium that results from the interaction between components of the Individual Architecture Mission Complex, which allows a person to sustain physiological homeostatis, adequate performance, and acceptable social relationships. Architecture, design development, refinements and revisions to improve the quality of life, new insights on artificial gravity, form and constitution problems, and the final design concept are covered.

  14. Damaging oral habits.

    PubMed

    Kamdar, Rajesh J; Al-Shahrani, Ibrahim

    2015-04-01

    Oral habits, if persist beyond certain developmental age, can pose great harm to the developing teeth, occlusion, and surrounding oral tissues. In the formative years, almost all children engage in some non-nutritive sucking habits. Clinicians, by proper differential diagnosis and thorough understanding of natural growth and developmental processes, should take a decision for intervening. This article describes case series reports of thumb sucking, finger sucking, and tongue thrusting habits, which have been successfully treated by both removable and fixed orthodontic appliances. The cases shown are ranging from the age group of 9-19 years presenting combination of both mixed and permanent dentition development. All cases show satisfactory correction of habits and stable results. PMID:25954079

  15. Habitability study shuttle orbiter

    NASA Technical Reports Server (NTRS)

    1973-01-01

    Habitability design concepts for the Shuttle Orbiter Program are provided for MSC. A variety of creative solutions for the stated tasks are presented. Sketches, mock-ups, mechanicals and models are included for establishing a foundation for future development.

  16. Damaging Oral Habits

    PubMed Central

    Kamdar, Rajesh J; Al-Shahrani, Ibrahim

    2015-01-01

    Oral habits, if persist beyond certain developmental age, can pose great harm to the developing teeth, occlusion, and surrounding oral tissues. In the formative years, almost all children engage in some non-nutritive sucking habits. Clinicians, by proper differential diagnosis and thorough understanding of natural growth and developmental processes, should take a decision for intervening. This article describes case series reports of thumb sucking, finger sucking, and tongue thrusting habits, which have been successfully treated by both removable and fixed orthodontic appliances. The cases shown are ranging from the age group of 9-19 years presenting combination of both mixed and permanent dentition development. All cases show satisfactory correction of habits and stable results. PMID:25954079

  17. WHERE TO FIND HABITABLE ''EARTHS'' IN CIRCUMBINARY SYSTEMS

    SciTech Connect

    Liu Huigen; Zhang Hui; Zhou Jilin

    2013-04-20

    Six P-type planets have been found thus far around five binary systems, i.e., Kepler-16b, 34b, 35b, 38b, and 47b and c, which are all Neptune- or Jupiter-like planets. The stability of planets and the habitable zones are influenced by the gravitational and radiative perturbations of binary companions. In this Letter, we check the stability of an additional habitable Earth-mass planet in each system. Based on our simulations in 10 Myr, a habitable ''Earth'' is hardly stable in Kepler-16, while a stable ''Earth'' in Kepler-47 close to the boundaries of the habitable zone is possible. In contrast, Kepler-34, 35, and 38 seem to have high probabilities of being able to tolerante a stable ''Earth'' in their habitable zones. The affects of transit time variations are quite small due to the small mass of an undetected ''Earth,'' except that of Kepler-16b. With a time precision of 10{sup -3} day ({approx}88 s), an ''Earth'' in the corotational resonance with Kepler-16b can be detected in three years, while habitable ''Earths'' in the Kepler-34 and 38 systems can be detected in 10 yr. Habitable ''Earths'' in Kepler-35 and 47 are not likely to be detected in 10 yr under this precision.

  18. The Role of Tides in Planetary Habitability

    NASA Astrophysics Data System (ADS)

    Barnes, Rory; Heller, R.; Jackson, B.; Leconte, J.; Greenberg, R.; Mullins, K.; Raymond, S. N.

    2011-01-01

    Terrestrial planets in the classic "habitable zone" (Kasting et al. 1993) of stars may be influenced by tides. Tidal evolution is poorly constrained and multiple acceptable models exist which, although qualitatively similar, predict different rates of evolution. Using different models, we examine how tides may modify several key properties of planets in the habitable zone: semi-major axis, eccentricity, obliquity and rotation rate. Tides can lock the rotation rate and erode the obliquity (to 0 or 180 degrees) in 103-1010 years, depending on the stellar mass and eccentricity. Some tidal models even predict significant obliquity evolution for planets in the habitable zones of solar-mass stars. This evolution dissipates energy in the planet's interior (at the expense of the orbit) and leads to "tidal heating." In extreme cases of high eccentricity and very low mass stars, the heating may initiate a runaway greenhouse, and/or total evaporation of potential surface water, eliminating any hope of habitability. After the spin properties have equilibrated, the planet is said to be "tidally locked" and further evolution primarily changes the orbital angular momentum. For exoplanets, tides tend to reduce eccentricities and semi-major axes, and can also change the rotation period, eventually reaching synchroneity with the orbit when both eccentricity and obliquity reach zero. Orbital circularization requires millions to trillions of years, depending on the planet's initial conditions and the tidal model assumed. Tidal heating also occurs during circularization and planets may pass through a "super-Io" phase prior to reaching internal heating rates similar to the modern day Earth. Tides clearly have the potential to impact habitability and may lead to planets with evolutionary paths markedly different from the Earth. These issues are presented and discussed for the simple case of one planet orbiting one star.

  19. The Habitability of the Milky Way Galaxy

    NASA Astrophysics Data System (ADS)

    Gowanlock, M.

    2014-04-01

    The Galactic Habitable Zone is defined as the region(s) of the Galaxy that may support complex life. Studies of the habitability of the Milky Way are becoming increasingly important with the growing number of extrasolar planet detections, and the multitude of conditions that life is found to thrive on the Earth. Through the evolution of the Galaxy, the distribution of stars and the planets that they host vary throughout space and time. Combining the information of the frequency of extrasolar planets, and the prospects for life in a range of environments within our evolving galaxy, we are able to make initial estimates of the habitability of the Milky Way. Some of the prerequisites for complex life include having enough metallicity, or building blocks for planet formation, enough time for biological evolution and low exposure to transient radiation events, such as supernovae. Our previous work suggests that the inner disk of the Milky Way may contain the greatest number density of habitable planets at the present day at a galactocentric distance of R>2.5 kpc, despite the higher supernovae rate in the region in comparison to the Sun's location at 8 kpc. I will discuss our previous work, and present an overview of dangers to habitable planets beyond supernovae in different galactic environments.

  20. Climate and Habitability of Kepler 452b

    NASA Astrophysics Data System (ADS)

    Hu, Yongyun; Wang, Yuwei; Liu, Yonggang

    2015-12-01

    The discovery of Kepler 452b marks a milestone of searching for habitable exoplanets. While simple estimation indicates that Kepler 452b is located in the habitable zone of a Sun-like star, the climate state and habitability of Kepler 452b require detailed studies. Using a three-dimensional fully coupled atmosphere-ocean climate model and assuming an aqua-planet, we perform simulations to demonstrate climate states of Kepler 452b for different greenhouse effects and ice-albedo feedbacks. Our simulations show that sea ice can only invade from poles to about 45 degree in latitude for extremely low levels of CO2 (5 ppmv), and that surface temperature near the equator remains as high as 300 K. For high level of CO2 (0.2 bars), the exoplanet becomes ice free, and tropical surface temperature reaches about 335 K. The results suggest that Kepler 452b is very close to the inner edge of the habitable zone, and that its climate state can readily reach the runaway greenhouse limit as greenhouse concentration is higher.

  1. Habitable Planets with High Obliquities

    NASA Astrophysics Data System (ADS)

    Williams, D. M.; Kasting, J. F.

    1996-03-01

    The obliquities of the terrestrial planets have been shown to vary chaotically and by large amounts in times less than 10 Myr, thus inviting the possibility for Earth to occasionally reach high obliquity where it might experience climatic conditions unfavorable for life. Although Earth escapes this fate by having its rotation axis stabilized by the Moon, many extrasolar Earth-like planets without large satellites should be subjected to periods of high obliquity. The number of worlds supporting life outside the Solar System, then, may be far fewer than has been suggested if high obliquities render moon-less Earths uninhabitable. Climates at high obliquity are particularly harsh on middle and high latitude continents that warm and cool rapidly in response to large insolation swings. These areas exhibit a wide range of temperatures over a seasonal cycle, with extremes reaching well above or below 273 Kelvin, making them seasonally unsuitable for water-dependent life. We demonstrate here that Earth-like planets will have their temperature extremes mitigated at high obliquity if they possess dense CO2 atmospheres, as is likely for many planets situated in the outer habitable zone (HZ) of a Sun-like star. The climate stabilizing mechanism governing atmospheric CO2 on Earth-like planets is carbonate-silicate weathering. Planets with atmospheres rich in CO2 demonstrate small latitudinal temperature gradients and seasonal temperature cycles, and thus remain habitable at high obliquities.

  2. Kepler Mission: A Search for Habitable Planets

    NASA Technical Reports Server (NTRS)

    Koch, David; Fonda, Mark (Technical Monitor)

    2002-01-01

    The Kepler Mission was selected by NASA as one of the next two Discovery Missions. The mission design is based on the search for Earth-size planets in the habitable zone of solar-like stars, but does not preclude the discovery of larger or smaller planets in other orbits of non-solar-like stars. An overview of the mission, the scientific goals and the anticipated results will be presented.

  3. Circumstellar disks around binary stars in Taurus

    SciTech Connect

    Akeson, R. L.

    2014-03-20

    We have conducted a survey of 17 wide (>100 AU) young binary systems in Taurus with the Atacama Large Millimeter Array (ALMA) at two wavelengths. The observations were designed to measure the masses of circumstellar disks in these systems as an aid to understanding the role of multiplicity in star and planet formation. The ALMA observations had sufficient resolution to localize emission within the binary system. Disk emission was detected around all primaries and 10 secondaries, with disk masses as low as 10{sup 4} M {sub ?}. We compare the properties of our sample to the population of known disks in Taurus and find that the disks from this binary sample match the scaling between stellar mass and millimeter flux of F{sub mm}?M{sub ?}{sup 1.5--2.0} to within the scatter found in previous studies. We also compare the properties of the primaries to those of the secondaries and find that the secondary/primary stellar and disk mass ratios are not correlated; in three systems, the circumsecondary disk is more massive than the circumprimary disk, counter to some theoretical predictions.

  4. An MCMC Circumstellar Disks Modeling Tool

    NASA Astrophysics Data System (ADS)

    Wolff, Schuyler; Perrin, Marshall D.; Mazoyer, Johan; Choquet, Elodie; Soummer, Remi; Ren, Bin; Pueyo, Laurent; Debes, John H.; Duchene, Gaspard; Pinte, Christophe; Menard, Francois

    2016-01-01

    We present an enhanced software framework for the Monte Carlo Markov Chain modeling of circumstellar disk observations, including spectral energy distributions and multi wavelength images from a variety of instruments (e.g. GPI, NICI, HST, WFIRST). The goal is to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in the derived properties. This modular code is designed to work with a collection of existing modeling tools, ranging from simple scripts to define the geometry for optically thin debris disks, to full radiative transfer modeling of complex grain structures in protoplanetary disks (using the MCFOST radiative transfer modeling code). The MCMC chain relies on direct chi squared comparison of model images/spectra to observations. We will include a discussion of how best to weight different observations in the modeling of a single disk and how to incorporate forward modeling from PCA PSF subtraction techniques. The code is open source, python, and available from github. Results for several disks at various evolutionary stages will be discussed.

  5. CIRCUMSTELLAR SHELL FORMATION IN SYMBIOTIC RECURRENT NOVAE

    SciTech Connect

    Moore, Kevin; Bildsten, Lars

    2012-12-20

    We present models of spherically symmetric recurrent nova shells interacting with circumstellar material (CSM) in a symbiotic system composed of a red giant (RG) expelling a wind and a white dwarf accreting from this material. Recurrent nova eruptions periodically eject material at high velocities ({approx}> 10{sup 3} km s{sup -1}) into the RG wind profile, creating a decelerating shock wave as CSM is swept up. High CSM densities cause the shocked wind and ejecta to have very short cooling times of days to weeks. Thus, the late-time evolution of the shell is determined by momentum conservation instead of energy conservation. We compute and show evolutionary tracks of shell deceleration, as well as post-shock structure. After sweeping up all the RG wind, the shell coasts at a velocity {approx}100 km s{sup -1}, depending on system parameters. These velocities are similar to those measured in blueshifted CSM from the symbiotic nova RS Oph, as well as a few Type Ia supernovae that show evidence of CSM, such as 2006X, 2007le, and PTF 11kx. Supernovae occurring in such systems may not show CSM interaction until the inner nova shell gets hit by the supernova ejecta, days to months after the explosion.

  6. Circumstellar Shell Formation in Symbiotic Recurrent Novae

    NASA Astrophysics Data System (ADS)

    Moore, Kevin; Bildsten, Lars

    2012-12-01

    We present models of spherically symmetric recurrent nova shells interacting with circumstellar material (CSM) in a symbiotic system composed of a red giant (RG) expelling a wind and a white dwarf accreting from this material. Recurrent nova eruptions periodically eject material at high velocities (gsim 103 km s-1) into the RG wind profile, creating a decelerating shock wave as CSM is swept up. High CSM densities cause the shocked wind and ejecta to have very short cooling times of days to weeks. Thus, the late-time evolution of the shell is determined by momentum conservation instead of energy conservation. We compute and show evolutionary tracks of shell deceleration, as well as post-shock structure. After sweeping up all the RG wind, the shell coasts at a velocity ~100 km s-1, depending on system parameters. These velocities are similar to those measured in blueshifted CSM from the symbiotic nova RS Oph, as well as a few Type Ia supernovae that show evidence of CSM, such as 2006X, 2007le, and PTF 11kx. Supernovae occurring in such systems may not show CSM interaction until the inner nova shell gets hit by the supernova ejecta, days to months after the explosion.

  7. A database of circumstellar OH masers

    NASA Astrophysics Data System (ADS)

    Engels, D.; Bunzel, F.

    2015-10-01

    We present a new database of circumstellar OH masers at 1612, 1665, and 1667 MHz in the Milky Way galaxy. The database (version 2.4) contains 13 655 observations and 2341 different stars detected in at least one transition. Detections at 1612 MHz are considered to be complete until the end of 2014 as long as they were published in refereed papers. Detections of the main lines (1665 and 1667 MHz) and non-detections in all transitions are included only if published after 1983. The database contains flux densities and velocities of the two strongest maser peaks, the expansion velocity of the shell, and the radial velocity of the star. Links are provided for about 100 stars (<5% of all stars with OH masers) to interferometric observations and monitoring programs of the maser emission published since their beginnings in the 1970s. Access to the database is possible over the Web (http://www.hs.uni-hamburg.de/maserdb), allowing cone searches for individual sources and lists of sources. A general search is possible in selected regions of the sky and by defining ranges of flux densities and/or velocities. Alternative ways to access the data are via the German Virtual Observatory and the CDS. The data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/582/A68

  8. Organics in the interstellar/circumstellar medium

    NASA Astrophysics Data System (ADS)

    Dartois, Emmanuel; Alata, Ivan; Bardin, Nomie; Beroff, Karine; Brunetto, Rosario; Chabot, Marin; Cruz-Diaz, Gustavo A.; Delauche, Lucie; Dumas, Paul; Duprat, Jean; Engrand, Cecile; Gavilan, Lisseth; Jallat, Aurlie; Jamme, Frdric; Muoz Caro, Guillermo M.; Pino, Thomas; Quirico, Eric; Rmusat, Laurent; Sandt, Christophe; Mostefaoui, Smail

    2015-08-01

    The interstellar medium is a physico-chemical laboratory where extreme conditions are encountered and its environmental parameters (e.g. density, reactant nature, radiations, temperature, time scales) define both the structure and the composition of matter.Whereas astrochemists must rely on remote observations to monitor and analyze the physico-chemical composition of interstellar organic solids,planetologists and cosmochemists can infer spectroscopically in the laboratory the actual structure and composition of collected extraterrestrial material.The interstellar/circumstellar observations give essentially access to the molecular functionality of these solids, rarely their elemental composition and the isotopic fractionation can almost only be inferred in the gas phase. Astrochemistery can provide additional information from the study of analogs produced in the laboratory, placed in simulated space environments.In this presentation, I will briefly summarize some observations in the diffuse interstellar medium (DISM) and molecular clouds (MC), setting constraints on both the composition of organic solids and the large molecules belonging to the cycle of matter in the Galaxy and briefly discuss the relations and differences between materials found in the Solar System and the interstellar dust.

  9. Application of the Titius-Bode Rule to the 55 Cancri System: Tentative Prediction of a Possibly Habitable Planet

    NASA Astrophysics Data System (ADS)

    Cuntz, Manfred

    2012-08-01

    Following the notion that the Titius-Bode rule (TBR) may also be applicable to some extrasolar planetary systems, although this number could be relatively small, it is applied to 55 Cancri, which is a G-type main-sequence star currently known to host five planets. Following a concise computational process, we tentatively identified four new hypothetical planetary positions, given as 0.081, 0.41, 1.51, and 2.95 AU from the star. The likelihood that these positions are occupied by real existing planets is significantly enhanced for the positions of 1.51 and 2.95 AU in view of previous simulations on planet formation and planetary orbital stability. For example, Raymond, Barnes, and Gorelick (2008, ApJ, 689, 478) argued that additional planets would be possible between 55 Cnc f and 55 Cnc d, which would include planets situated at 1.51 and 2.95 AU. If two additional planets are assumed to exist between 55 Cnc f and 55 Cnc d, the deduced domains of stability would be given as 1.3-1.6 and 2.2-3.3 AU. The possible planet near 1.5 AU appears to be located at the outskirts of the stellar habitable zone, which is, however, notably affected by the stellar parameters as well as the adopted model of circumstellar habitability. We also computed the distance of the next possible outer planet in the 55 Cnc system, which, if existing, is predicted to be located between 10.9 and 12.2 AU, which is consistent with orbital stability constraints. The inherent statistical significance of the TBR was evaluated following a method by Lynch (2003, MNRAS, 341, 1174). Yet it is up to future planetary search missions to verify or falsify the applicability of the TBR to the 55 Cnc system, and to obtain information on additional planets, if existing.

  10. Effects of Extreme Obliquity Variations on the Habitability of Exoplanets

    PubMed Central

    Barnes, R.; Domagal-Goldman, S.; Breiner, J.; Quinn, T.R.; Meadows, V.S.

    2014-01-01

    Abstract We explore the impact of obliquity variations on planetary habitability in hypothetical systems with high mutual inclination. We show that large-amplitude, high-frequency obliquity oscillations on Earth-like exoplanets can suppress the ice-albedo feedback, increasing the outer edge of the habitable zone. We restricted our exploration to hypothetical systems consisting of a solar-mass star, an Earth-mass planet at 1 AU, and 1 or 2 larger planets. We verified that these systems are stable for 108 years with N-body simulations and calculated the obliquity variations induced by the orbital evolution of the Earth-mass planet and a torque from the host star. We ran a simplified energy balance model on the terrestrial planet to assess surface temperature and ice coverage on the planet's surface, and we calculated differences in the outer edge of the habitable zone for planets with rapid obliquity variations. For each hypothetical system, we calculated the outer edge of habitability for two conditions: (1) the full evolution of the planetary spin and orbit and (2) the eccentricity and obliquity fixed at their average values. We recovered previous results that higher values of fixed obliquity and eccentricity expand the habitable zone, but we also found that obliquity oscillations further expand habitable orbits in all cases. Terrestrial planets near the outer edge of the habitable zone may be more likely to support life in systems that induce rapid obliquity oscillations as opposed to fixed-spin planets. Such planets may be the easiest to directly characterize with space-borne telescopes. Key Words: Exoplanets—Habitable zone—Energy balance models. Astrobiology 14, 277–291. PMID:24611714

  11. Possible Habitability of Ocean Worlds

    NASA Astrophysics Data System (ADS)

    Noack, Lena; Höning, Dennis; Bredehöft, Jan H.; Lammer, Helmut

    2014-05-01

    In the last decade, the number of detected exoplanets has increased to over thousand confirmed planets and more as yet unconfirmed planet candidates. The scientific community mainly concentrates on terrestrial planets (up to 10 Earth masses) in the habitable zone, which describes the distance from the host star where liquid water can exist at the surface (Kasting et al., 1993). Another target group of interest are ocean worlds, where a terrestrial-like body (i.e. with an iron core and a silicate mantle) is covered by a thick water-ice layer - similar to the icy moons of our solar system but with several Earth masses (e.g. Grasset et al., 2009). When an exoplanet is detected and confirmed as a planet, typically the radius and the mass of it are known, leading to the mean density of the planet that gives hints to possible interior structures. A planet with a large relative iron core and a thick ocean on top of the silicate mantle for example would have the same average planet density as a planet with a more Earth-like appearance (where the main contributor to the mass is the silicate mantle). In this study we investigate how the radius and mass of a planet depend on the amount of water, silicates and iron present (after Wagner et al., 2011) the occurence of high-pressure-ice in the water-ice layer (note: we only consider surface temperatures at which liquid water exists at the surface) if the ocean layer influences the initiation of plate tectonics We assume that ocean worlds with a liquid ocean layer (and without the occurence of high-pressure ice anywhere in the water layer) and plate tectonics (especially the occurence of subduction zones, hydrothermal vents and continental formation) may be called habitable (Class III/IV habitats after Lammer et al., 2009). References: Kasting, J.F., Whitmire, D.P., and Reynolds, R.T. (1993). Habitable Zones around Main Sequence Stars. Icarus 101, 108-128. Grasset, O., Schneider, J., and Sotin, C. (2009). A study of the accuracy of mass-radius relationships for silicate-rich and ice-rich planets up to 100 Earth masses. The Astrophysical Journal 693, 722-733. Wagner, F.W., Sohl, F., Hussmann, H., Grott, M., and Rauer, H. (2011). Interior structure models of solid exoplanets using material laws in the infinite pressure limit. Icarus 214, 366-376. Lammer, H., Bredehöft, J.H., Coustenis, A., Khodachenko, M.L., Kaltenegger, L., Grasset, O., Prieur, D., Raulin, F., Ehrenfreund, P., Yamauchi, M., Wahlund, J.-E., Grießmeier, J.-M., Stangl, G., Cockell, C.S., Kulikov, Yu.N., Grenfell, J.L., and Rauer, H. (2009). What makes a planet habitable? Astron Astrophys Rev 17, 181-249.

  12. MAGNETIC SHIELDING OF EXOMOONS BEYOND THE CIRCUMPLANETARY HABITABLE EDGE

    SciTech Connect

    Heller, René; Zuluaga, Jorge I. E-mail: jzuluaga@fisica.udea.edu.co

    2013-10-20

    With most planets and planetary candidates detected in the stellar habitable zone (HZ) being super-Earths and gas giants rather than Earth-like planets, we naturally wonder if their moons could be habitable. The first detection of such an exomoon has now become feasible, and due to observational biases it will be at least twice as massive as Mars. However, formation models predict that moons can hardly be as massive as Earth. Hence, a giant planet's magnetosphere could be the only possibility for such a moon to be shielded from cosmic and stellar high-energy radiation. Yet, the planetary radiation belt could also have detrimental effects on exomoon habitability. Here we synthesize models for the evolution of the magnetic environment of giant planets with thresholds from the runaway greenhouse (RG) effect to assess the habitability of exomoons. For modest eccentricities, we find that satellites around Neptune-sized planets in the center of the HZ around K dwarf stars will either be in an RG state and not be habitable, or they will be in wide orbits where they will not be affected by the planetary magnetosphere. Saturn-like planets have stronger fields, and Jupiter-like planets could coat close-in habitable moons soon after formation. Moons at distances between about 5 and 20 planetary radii from a giant planet can be habitable from an illumination and tidal heating point of view, but still the planetary magnetosphere would critically influence their habitability.

  13. Volatile Gasses in the Beta Pictoris Circumstellar Disk

    NASA Astrophysics Data System (ADS)

    Roberge, Aki

    2005-10-01

    We present the first detection of the important volatile species CII, CIII, and most importantly, OI, in the Beta Pic circumstellar disk. These species are seen in absorption against broad chromospheric emission lines in stellar spectra obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). They are present in the stable circumstellar gas component; additional redshifted components arising from star-grazing planetesimals are seen in the CII absorption lines. Combined with a previous measurement of CI gas (Roberge et al. 2000), the CII and CIII measurements complete the total inventory of stable atomic carbon gas in the disk. OI is the only atomic oxygen species observed to date. The only other oxygen-bearing species observed is CO, dissociation of which accounts for less than 2% of the total carbon gas (Roberge et al. 2000). Previous observations of the Beta Pic circumstellar gas were primarily of metallic species like FeII and SiII. These new measurements permit a much more complete inventory of the Beta Pic circumstellar gas, which, like the dust, is produced by the destruction of planetary bodies. We present a new compilation of the observed bulk gas abundance and composition. The bulk composition is compared to the composition of various astronomical objects (e.g. Sun, comets, meteorites). The inferred gas density is compared to recent theoretical constraints on the circumstellar gas abundance from analysis of the gas dynamics (Brandeker et al. 2004) and the dust dynamics (Thebault & Augereau 2005).

  14. L1551 IRS5 - Circumbinary Envelope to Circumstellar Disks

    NASA Astrophysics Data System (ADS)

    Lim, Jeremy; Takakuwa, Shigehisa; Choi, Minho

    L1551 IRS5 is a binary protostellar system comprising two low-mass stars. Its dusty surroundings consists of a large-scale circumbinary envelope a possible circumbinary disk and circumstellar disks around the individual binary components. Here we present an ongoing study to image the dust emission of the protobinary system at 7 mm in multiple confgurations of the VLA. Our objectives are to study the detailed structure of the individual circumstellar disks at the highest angular resolution currently possible at any wavelength search for the predicted annular gap between the individual circumstellar disks and the circumbinary disk as well as the predicted matter streams that bridge this gap to feed the circumstellar disks and better delineate the structure and radial intensity (density) profile of the circumbinary disk and envelope. In this poster we present observations of the circumstellar disks at an angular resolution of ~20 mas (~3 AU) with VLA in A-array and the Pie Town antenna.. We also present observations of the circumbinary dust at an angular resolution of 0.7 asec (~100 AU) with the VLA in C-array

  15. Europa: Processes and Habitability

    NASA Astrophysics Data System (ADS)

    Pappalardo, R. T.

    Europa may be a habitable world. Evidence points strongly to a subsurface ocean beneath an ice shell about 20 km thick. Europa's surface geology as viewed by Galileo imaging suggests a thin brittle lithosphere above a warm ice layer that is at least in part convecting, in turn situated above a liquid water ocean. This configuration is consistent with thermal and geochemical modeling, and with Galileo magnetometer results. Dynamical modeling and visible crater density suggests a surface age of ˜60 million years, implying that Europa is probably still geologically active today. Large shallow craters and multi-ringed structures imply impact into low-viscosity (warm) subsurface material. The satellite's bright plains are crossed by narrow troughs and double ridges (paired ridges separated by a medial trough); a morphological sequence exists from isolated troughs to double ridges to wider and more complex ridge morphologies. Troughs are inferred as widened fractures formed though tensile and shear failure in response to global stressing of the ice shell above liquid water. Several models exist to explain ridges, but the most promising is one in which localized shear heating triggers upwelling of warm ice along fracture zones. Ruddy diffuse ruddy ridge may have formed through thermal alteration and/or partial melting of briny ice. Wider pull-apart bands represent complete separation and spreading of the icy lithosphere, in a manner broadly analogous to terrestrial sea-floor spreading. Europa's global lineament pattern implies that nonsynchronous rotation and orbital flexing ("diurnal" stressing) have worked together to deform the surface. Diurnal stressing can explain Europa's enigmatic cycloid ridge and fracture patterns, and may drive rapid strike-slip faulting along ridges. Because significant tidal amplitude is necessary to produce significant diurnal stressing, this argues strongly for a subsurface liquid layer. Extremely slow nonsynchronous rotation of the ice shell may drive shear failure in equatorial regions, and may have opened the satellite's pull-apart bands. Mottled terrain consists of pits, domes, dark spots, patches of smooth plains, and regions of chaos terrain. Chaos is characterized by fragmented blocks of the preexisting surface in a hummocky matrix. Mottled terrain landforms suggest vertical deformation and disruption of the surface and localized partial melting. Their formation has been interpreted as due to diapiric upwelling-the expression of solid-state convection of warm subsurface ice-predicted within a tidally strained ice shell tens of kilometers thick above liquid water. Warm ice diapirs can circulate material between Europa's ocean and shallow levels within the ice shell, and can trigger local partial melting of briny ice, potentially creating near-surface biological niches. Europa's astonishing geology and its biological potential makes the satellite a high priority for future orbital and landed exploration.

  16. Stability of habitable exomoons of circumbinary planets

    NASA Astrophysics Data System (ADS)

    Satyal, Suman; Haghighipour, Nader; Quarles, Billy

    2015-12-01

    Among the currently known Kepler circumbinary planets, three, namely Kepler-453b, Kepler-16b, and Kepler-47c are in the binary habitable zone (HZ). Given the large sizes of these planets, it is unlikely that they would be habitable. However, similar to the giant planets in our solar system, these planets may have large moons, which orbit their host planets while in the HZ. These exomoons, if exist, present viable candidates for habitability. As a condition for habitability, the planet-moon system has to maintain its orbital stability for long time. Usually, the empirical formula by Holeman & Wiegert (1999) is used as a measure of orbital stability in circumbinary systems. However, this formula was obtained by assuming planets to be test particles and therefore does not include possible perturbation of the planet on the binary. In this work, we present results of more realistic calculations of stability of circumbinary planets where the interactions between planets and their central binaries are taken into account. We map the region of stability, which in this case will be specific to each system, and determine the range of the orbital parameters of the moons for which their orbits will be long-term stable.

  17. Photochemistry and molecular ions in carbon-rich circumstellar envelopes

    NASA Technical Reports Server (NTRS)

    Glassgold, A. E.; Mamon, G. A.; Omont, A.; Lucas, R.

    1987-01-01

    An earlier theory of ionization of C-rich circumstellar envelopes based on the photochemical model is extended to include the temperature dependence of ion-molecule reactions with polar molecules, particularly HCN, and line self-shielding of CO dissociating radiation. The results are applied to the abundances of HCO(+) and HNC in C-rich circumstellar envelopes. With standard parameters for IRC + 10216, the model is found to be consistent with the new upper limit to the antenna temperature of the J = 1-0 line of HCO(+) obtained with the IRAM 30-m telescope. The photochemical model provides a natural explanation of the relatively large ratio of HCN to HNC observed for C-rich circumstellar envelopes, and good agreement is obtained for the H(C-13)N/HNC antenna temperature ratio measured for IRC + 10216.

  18. First Circumstellar Disk around a Massive Star

    NASA Astrophysics Data System (ADS)

    1998-06-01

    Observations with an infrared-sensitive instrument at the ESO 3.6-m telescope at La Silla have for the first time shown the presence of a disk around a hot and massive star, known as G339.88-1.26 . Until now, disks have only been found around less massive stars. Planets are formed in such disks. The new discovery may thus have important implications for our understanding of the formation of planetary systems around stars. TIMMI observations Observations at mid-infrared wavelengths were carried out in July 1997 by Bringfried Stecklum (Landessternwarte Thüringen, Tautenburg, Germany) and Hans-Ulrich Käufl (ESO), using the TIMMI instrument at the ESO 3.6-m telescope. Additional measurements were carried out in March 1998. TIMMI ( T hermal I nfrared M ulti M ode I nstrument) is a general-purpose camera spectrometer operating at a wavelength of 10 µm. To reach sufficient sensitivity, the camera must be cooled to approx. -260 o C, i.e. a few degrees above the absolute minimum, by use of liquid Helium. Astronomical objects whose temperatures are between -120 o C and 300 o C radiate most of their energy at this wavelength. In addition, dust and haze that are absolutely impenetrable for light visible to the human eye, are often found to be nearly transparent at this wavelength. This is why fire-fighters now use similar equipment to look through smoke. G339.88-1.26: A very special object ESO PR Photo 22a/98 ESO PR Photo 22a/98 [JPEG, 800k] This image is a true-color composite of near-infrared observations of the sky region around the radio source G339.88-1.26 with the ESO/MPI 2.2-m telescope at La Silla. In this image, the visible colors red, green and blue have been used to represent the infrared filters J, H and K (at 1.25, 1.63 and 2.2 µm wavelength, respectively). No object is visible at the position of the radio source, even at these near-infrared wavelengths. A dark band of absorbing dust is clearly visible, exactly at the position of the object (indicated by an arrow). Earlier observations with radio telescopes of the object G339.88-1.26 , deeply embedded in an interstellar nebula, had been interpreted in terms of the possible existence of a circumstellar disk around a high-mass star. It was concluded that the star responsible for heating the surrounding gas must be very hot and also that it must be intrinsically very bright. The star, most likely of spectral type O9, would have a luminosity 10,000 times higher than that of the Sun and a mass of about 20 times that of the Sun. From the measured velocity, the likely distance of this object is about 10,000 light-years. The object is associated with several "spots" of very strong radio emission from methanol molecules (methanol masers). Interestingly, they form a chain in the sky and the measured velocities of the individual spots are indicative for orbital motion in a rotating disk around the central star. The circumstellar disk ESO PR Photo 22/98 ESO PR Photo 22b/98 [JPEG, 640k] The TIMMI 10 µm image of the inclined dust disk around a hot O9 star at the G339.88-1.26 radio source. The diameter of the disk is of the order of 5 arcsec, i.e. at the most probable distance to the object (10,000 lightyears) it is 20,000 times larger than the diameter of the Earth's orbit around the Sun. The new TIMMI observations of G339.88-1.26 showed an elliptical object with strong infrared radiation. The peak of this radiation (as seen in the sky) coincides with the peak of the radio emission. Furthermore, the apparent orientation of the disk is well aligned with that of the methanol maser "spots". There is little doubt that this object is indeed the infrared image of a circumstellar disk, viewed at an angle. As far as known, this is the first direct image of a disk around a very massive star. At a wavelength of 10 µm, however, the central star that is responsible for heating the dust disc, cannot be seen in spite of its rather high luminosity. This is because it radiates mostly in the ultra-violet part of the spectrum. Moreover, the dust disk in which the hot star is embedded, absorbs the stellar ultraviolet light extremely efficiently, thereby re-emitting this energy in the infrared. And any stellar light that escapes the dust shroud is in any case completely blocked by intervening interstellar material in the nebula. Implications of the discovery The formation of disks of dust and gas around young stars is now considered to be a normal feature of star formation. This is well established for stars of about the size and mass of our Sun. However, until now there has been no direct evidence of such disks being also formed around young massive stars. In view of the extremely high luminosity of such massive stars, any surrounding disks are subject to a fierce attack by the enormous flux of light to which they are exposed. Hence the existence of such disks around massive and luminous stars has been questioned by astronomers interested in the physical process of star formation. The discovery of the disk around G339.88-1.26 now settles the question whether such disks can indeed be formed and are stable over periods long enough that they can be observed. Supplementary measurements to investigate the molecules and dust around G339.88-1.26 have been performed with the SEST submillimeter telescope at La Silla in March 1998. Near-infrared images have also been taken at the NTT and at the 2.2-m telescope. The team responsible for this project also includes Thomas Henning and Markus Feldt (Astrophysikalisches Institut & Universitäts-Sternwarte, Jena, Germany), Andreas Eckart (Max-Planck-Institut für extraterrestrische Physik, Garching, Germany) and Lars-Åke Nyman (ESO). Further information is available at URL: http://www.tls-tautenburg.de/research/g339.html. This Press Release is accompanied by ESO PR Photo 22a/98 and ESO PR Photo 22b/98 . They may be reproduced, if credit is given to the European Southern Observatory. How to obtain ESO Press Information ESO Press Information is made available on the World-Wide Web (URL: http://www.eso.org ). ESO Press Photos may be reproduced, if credit is given to the European Southern Observatory.

  19. The Water Vapor Abundance in Circumstellar Envelopes

    NASA Astrophysics Data System (ADS)

    González-Alfonso, Eduardo; Cernicharo, José

    1999-11-01

    The maser emission of the para-H2O 313-->220 line at 183 GHz in O-rich evolved stars has been modeled to account for the empirical characteristics of this line reported by González-Alfonso et al. Likewise, efforts have been made to derive water vapor abundance in these sources. The Sobolev or large velocity gradient (LVG) method has been employed to study the intensity of this line as a function of source properties and physical conditions (i.e., mass-loss rate, p-H2O abundance, velocity field, kinetic temperature profile, stellar luminosity, and the set of collisional rates adopted in the calculations). It has been found that the intensity of the 313-->220 line is sensitive to the mass-loss rate, the p-H2O abundance, and the terminal velocity of the envelope, but it is rather insensitive to the rest of the parameters in stars with high mass-loss rates (Ṁ>10-6 Msolar yr-1). The models reproduce the main spectral characteristics of the emission at 183 GHz in the latter sources. A global fit to the data proves that the observational luminosities can be explained by assuming an H2O abundance relative to H2 [x(H2O)] of 1-2×10-4. Detailed fitting to the line profile in five selected objects yields a similar value for x(H2O). The validity of the LVG approach has been verified by modeling the maser emission at 183 GHz through a nonlocal radiative transfer code. The model calculations with both methods lead to similar results. The pumping of the first bending mode of water vapor through absorption of photons emitted by the dust and the star has been also simulated. This effect is found to be important in the pumping of the H2O rotational levels. Hence, in order to recover LVG results, the water abundance must be increased by a factor of ~2 for stars with high mass-loss rates. Consequently, x(H2O) has been estimated to be 3×10-4 within a factor ~=2. With this value for x(H2O), the expected near- and far-infrared spectra of the circumstellar envelopes of O-rich stars for several mass-loss rates have also been computed. Hence, it is possible to predict that, in some stars, the ro-vibrational lines of the 6 μm water vapor band with wavelengths longer that 6.3 μm--the P-branch--can be observed in emission, rather than in absorption.

  20. Laboratory Studies Of Circumstellar Carbonaceous Grain Formation

    NASA Astrophysics Data System (ADS)

    Contreras, Cesar; Sciamma-O'Brien, Ella; Salama, Farid

    2014-06-01

    The study of the formation processes of dust is essential to understand the budget of extraterrestrial organic molecules. Although dust with all its components plays an important role in the evolution of interstellar (IS) chemistry and in the formation of organic molecules, little is known on the formation processes of carbonaceous dust. We report the progress that was recently achieved in this domain using NASA Ames’ COSmIC facility (Contreras & Salama 2013, ApJS, 208, 6). PAHs are important chemical building blocks of IS dust. They are detected in IDPs and in meteoritic samples. Additionally, observational, laboratory, and theoretical studies have shown that PAHs are an important, ubiquitous component of the ISM. The formation of PAHs from smaller molecules has not been extensively studied. Therefore, we have performed laboratory experiments to study the dynamic processes of carbon grain formation, starting from the smallest hydrocarbon molecules into the formation of larger PAH and further into nanograins. Studies of IS dust analogs formed from a variety of PAH and hydrocarbon precursors as well as species that include the atoms O, N, and S, have recently been performed in our laboratory using the COSmIC facility to provide conditions that simulate IS and circumstellar environments. The species formed in the COSmiC chamber through a pulsed discharge nozzle plasma source are detected and characterized with a cavity ringdown spectrometer coupled to a time-of-flight mass spectrometer, thus providing both spectroscopic and ion mass information in-situ. Analysis of solid soot particles was also conducted using scanning electron microscopy at the UCSC/NASA Ames’ MACS facility. The SEM analysis of the deposition of soot from methane and acetylene precursors seeded in argon plasmas provide examples on the types of nanoparticles and micrograins that are produced in these gas mixtures under our experimental conditions. From these measurements, we derive information on the size and the structure of IS dust grain particles, the growth and the destruction processes of IS dust and the resulting budget of extraterrestrial organic molecules. Acknowledgements: This work is supported by NASA SMD (APRA; Carbon in the Galaxy).

  1. Studying Young Circumstellar Disks with ALMA

    NASA Astrophysics Data System (ADS)

    Ménard, F. C.

    2005-12-01

    Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material for stellar build-up, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve the mystery of the formation of our Solar System. This article focuses on observational studies of circumstellar disks associated with pre-main sequence solar-like stars and presents a few selected problems where ALMA will contribute in finding answers. At optical and near-infrared wavelengths, the direct measurement of disk parameters poses an obvious challenge: at the distance of typical star forming regions (e.g. ˜140 pc for Taurus), a planetary system like ours (with a diameter of ≃ 50 AU out to Pluto, but excluding the Kuiper belt) subtends only 0.35 arcsec. Moreover, its surface brightness is low in comparison to the bright central star. Hence, high angular resolution and high contrast imaging techniques are required if one hopes to resolve and measure such protoplanetary disks. Fortunately, potent imaging instruments have been available for about 10 years now. They cover a large part of the electromagnetic spectrum, from the UV/optical with HST, the near-infrared with ground-based adaptive optics systems to the millimeter range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of disks surrounding low-mass stars has made a gigantic leap forward in the last decade. However, the angular resolution of current millimeter interferometers will remain significantly poorer than the resolution that is available at shorter wavelengths (˜ 0.1 arcsec) until ALMA provides the necessary long baselines. At that time, astronomers will have access to data of comparable resolution over a very large wavelength range, with unprecedented sensitivity. As a direct consequence, our understanding of the disk structure and evolution should improve just as much. In the following pages I will attempt to give an overview of the structural and physical parameters of protoplanetary disks that can be estimated today from direct observations.

  2. Adult Reading Habits and Patterns.

    ERIC Educational Resources Information Center

    Scales, Alice M.; Rhee, Ock

    2001-01-01

    Examines the reading habits and patterns of White and Asian American adults. Hypothesizes that when grouped by demographic variables, participants' responses about their reading habits and patterns would not differ. Concludes that gender, race, and education were predictors for participants' reading habits; education and race were predictors for…

  3. Habitable planets with high obliquities.

    PubMed

    Williams, D M; Kasting, J F

    1997-01-01

    Earth's obliquity would vary chaotically from 0 degrees to 85 degrees were it not for the presence of the Moon (J. Laskar, F. Joutel, and P. Robutel, 1993, Nature 361, 615-617). The Moon itself is thought to be an accident of accretion, formed by a glancing blow from a Mars-sized planetesimal. Hence, planets with similar moons and stable obliquities may be extremely rare. This has lead Laskar and colleagues to suggest that the number of Earth-like planets with high obliquities and temperate, life-supporting climates may be small. To test this proposition, we have used an energy-balance climate model to simulate Earth's climate at obliquities up to 90 degrees. We show that Earth's climate would become regionally severe in such circumstances, with large seasonal cycles and accompanying temperature extremes on middle- and high-latitude continents which might be damaging to many forms of life. The response of other, hypothetical, Earth-like planets to large obliquity fluctuations depends on their land-sea distribution and on their position within the habitable zone (HZ) around their star. Planets with several modest-sized continents or equatorial supercontinents are more climatically stable than those with polar supercontinents. Planets farther out in the HZ are less affected by high obliquities because their atmospheres should accumulate CO2 in response to the carbonate-silicate cycle. Dense, CO2-rich atmospheres transport heat very effectively and therefore limit the magnitude of both seasonal cycles and latitudinal temperature gradients. We conclude that a significant fraction of extrasolar Earth-like planets may still be habitable, even if they are subject to large obliquity fluctuations. PMID:11541242

  4. Habitable planets with high obliquities

    NASA Technical Reports Server (NTRS)

    Williams, D. M.; Kasting, J. F.

    1997-01-01

    Earth's obliquity would vary chaotically from 0 degrees to 85 degrees were it not for the presence of the Moon (J. Laskar, F. Joutel, and P. Robutel, 1993, Nature 361, 615-617). The Moon itself is thought to be an accident of accretion, formed by a glancing blow from a Mars-sized planetesimal. Hence, planets with similar moons and stable obliquities may be extremely rare. This has lead Laskar and colleagues to suggest that the number of Earth-like planets with high obliquities and temperate, life-supporting climates may be small. To test this proposition, we have used an energy-balance climate model to simulate Earth's climate at obliquities up to 90 degrees. We show that Earth's climate would become regionally severe in such circumstances, with large seasonal cycles and accompanying temperature extremes on middle- and high-latitude continents which might be damaging to many forms of life. The response of other, hypothetical, Earth-like planets to large obliquity fluctuations depends on their land-sea distribution and on their position within the habitable zone (HZ) around their star. Planets with several modest-sized continents or equatorial supercontinents are more climatically stable than those with polar supercontinents. Planets farther out in the HZ are less affected by high obliquities because their atmospheres should accumulate CO2 in response to the carbonate-silicate cycle. Dense, CO2-rich atmospheres transport heat very effectively and therefore limit the magnitude of both seasonal cycles and latitudinal temperature gradients. We conclude that a significant fraction of extrasolar Earth-like planets may still be habitable, even if they are subject to large obliquity fluctuations.

  5. Effects of extreme obliquity variations on the habitability of exoplanets.

    PubMed

    Armstrong, J C; Barnes, R; Domagal-Goldman, S; Breiner, J; Quinn, T R; Meadows, V S

    2014-04-01

    We explore the impact of obliquity variations on planetary habitability in hypothetical systems with high mutual inclination. We show that large-amplitude, high-frequency obliquity oscillations on Earth-like exoplanets can suppress the ice-albedo feedback, increasing the outer edge of the habitable zone. We restricted our exploration to hypothetical systems consisting of a solar-mass star, an Earth-mass planet at 1 AU, and 1 or 2 larger planets. We verified that these systems are stable for 10(8) years with N-body simulations and calculated the obliquity variations induced by the orbital evolution of the Earth-mass planet and a torque from the host star. We ran a simplified energy balance model on the terrestrial planet to assess surface temperature and ice coverage on the planet's surface, and we calculated differences in the outer edge of the habitable zone for planets with rapid obliquity variations. For each hypothetical system, we calculated the outer edge of habitability for two conditions: (1) the full evolution of the planetary spin and orbit and (2) the eccentricity and obliquity fixed at their average values. We recovered previous results that higher values of fixed obliquity and eccentricity expand the habitable zone, but we also found that obliquity oscillations further expand habitable orbits in all cases. Terrestrial planets near the outer edge of the habitable zone may be more likely to support life in systems that induce rapid obliquity oscillations as opposed to fixed-spin planets. Such planets may be the easiest to directly characterize with space-borne telescopes. PMID:24611714

  6. Effects of Extreme Obliquity Variations on the Habitability of Exoplanets

    NASA Technical Reports Server (NTRS)

    Armstrong, J. C.; Barnes, R.; Domagal-Goldman, S.; Breiner, J.; Quinn, T. R.; Meadows, V. S.

    2014-01-01

    We explore the impact of obliquity variations on planetary habitability in hypothetical systems with high mutual inclination. We show that large-amplitude, high-frequency obliquity oscillations on Earth-like exoplanets can suppress the ice-albedo feedback, increasing the outer edge of the habitable zone. We restricted our exploration to hypothetical systems consisting of a solar-mass star, an Earth-mass planet at 1 AU, and 1 or 2 larger planets. We verified that these systems are stable for 108 years with N-body simulations and calculated the obliquity variations induced by the orbital evolution of the Earth-mass planet and a torque from the host star. We ran a simplified energy balance model on the terrestrial planet to assess surface temperature and ice coverage on the planet's surface, and we calculated differences in the outer edge of the habitable zone for planets with rapid obliquity variations. For each hypothetical system, we calculated the outer edge of habitability for two conditions: (1) the full evolution of the planetary spin and orbit and (2) the eccentricity and obliquity fixed at their average values. We recovered previous results that higher values of fixed obliquity and eccentricity expand the habitable zone, but we also found that obliquity oscillations further expand habitable orbits in all cases. Terrestrial planets near the outer edge of the habitable zone may be more likely to support life in systems that induce rapid obliquity oscillations as opposed to fixed-spin planets. Such planets may be the easiest to directly characterize with space-borne telescopes.

  7. Habitable Niches In Single and Binary Star Systems

    NASA Astrophysics Data System (ADS)

    Clark, Joni; Mason, P. A.

    2013-01-01

    We investigate habitable niches, defined as locations with optimum conditions for complex life to exist. The recent discovery of planets in several binaries motivates this study to examine favorable habitability circumstances in both single and binary star systems. Stellar evolution calculations are used to model time dependent stellar luminosity, UV flux, photo-synthetic flux and atmospheric water photolysis. Tidal interactions such as synchronization timescales, heat generation, and forcing frequency are also investigated. An Earth-analogue planet in the habitable zone of a 0.8 solar mass star is well suited for complex life. Several high quality niches are available to planets in habitable zones of binaries. For example, orbiting a pair of twin stars each 0.75 solar masses with a binary period of ten days will provide ample photo-synthetic radiation without an overdose of UV radiation, and tidal effects mimicking the Earth-Moon. A solar like star with a close red dwarf companion, like the recently discovered Kepler 47, provides a high quality niche because both stars are relatively long lived and the habitable zone has abundant photo-synthetic light while avoiding harmful UV light. A similar niche exists with a sun like star, which in turn is orbited by a distant red dwarf, providing a roughly annual enhanced red photo-synthetic flux. Also, moons orbiting Jupiter mass planets may exist within habitable zones of both single and binary stars. Such moons might be synchronized to the planet rather than the star. Due to the abundance of binary systems and the presence of high quality niches; binaries may harbor a significant fraction of inhabited planets within the universe. The present study allows for selection of the best habitability follow up targets for large telescopes.

  8. HABITABILITY OF EXOMOONS AT THE HILL OR TIDAL LOCKING RADIUS

    SciTech Connect

    Hinkel, Natalie R.; Kane, Stephen R.

    2013-09-01

    Moons orbiting extrasolar planets are the next class of object to be observed and characterized for possible habitability. Like the host-planets to their host-star, exomoons have a limiting radius at which they may be gravitationally bound, or the Hill radius. In addition, they also have a distance at which they will become tidally locked and therefore in synchronous rotation with the planet. We have examined the flux phase profile of a simulated, hypothetical moon orbiting at a distant radius around the confirmed exoplanets {mu} Ara b, HD 28185 b, BD +14 4559 b, and HD 73534 b. The irradiated flux on a moon at its furthest, stable distance from the planet achieves its largest flux gradient, which places a limit on the flux ranges expected for subsequent (observed) moons closer in orbit to the planet. We have also analyzed the effect of planetary eccentricity on the flux on the moon, examining planets that traverse the habitable zone either fully or partially during their orbit. Looking solely at the stellar contributions, we find that moons around planets that are totally within the habitable zone experience thermal equilibrium temperatures above the runaway greenhouse limit, requiring a small heat redistribution efficiency. In contrast, exomoons orbiting planets that only spend a fraction of their time within the habitable zone require a heat redistribution efficiency near 100% in order to achieve temperatures suitable for habitability. This means that a planet does not need to spend its entire orbit within the habitable zone in order for the exomoon to be habitable. Because the applied systems comprise giant planets around bright stars, we believe that the transit detection method is most likely to yield an exomoon discovery.

  9. Young stellar objects and their circumstellar dust - An overview

    NASA Technical Reports Server (NTRS)

    Rydgren, A. E.; Cohen, M.

    1985-01-01

    The basic observational classes of young stellar objects are briefly reviewed and some of the theoretical and observational problems in premain sequence stellar evolution are discussed. The evidence which indicates that the infrared excesses in recently formed stars are primarily due to thermal emission from circumstellar dust is summarized. Various indirect lines of evidence on the spatial distribution of the circumstellar dust are examined, and it is concluded that the concentration of the dust in a large disk structure is the most viable model at this time.

  10. Circumstellar Disks and Planet Formation with ALMA: Early Data

    NASA Astrophysics Data System (ADS)

    Hughes, A. Meredith

    2012-01-01

    As ALMA enters its early science phase, it is poised to address central questions about circumstellar disks and the properties of the planets they produce. The unprecedented spatial resolution and sensitivity available during Cycles 0 and 1 will allow users to characterize the structure, dynamics, and chemistry of circumstellar disks across their evolutionary spectrum. ALMA provides unique insight into the earliest stages of dust coagulation, the enigmatic dispersal process of primordial gas and dust, and the interaction between disks and the young planets they produce. I will discuss how ALMA observations in early science and beyond will address open questions in the field, highlighting initial results and showcasing data hot off the telescope.

  11. The origin and evolution of dust in interstellar and circumstellar environments

    NASA Technical Reports Server (NTRS)

    Whittet, Douglas C. B.; Leung, Chun M.

    1993-01-01

    This status report covers the period from the commencement of the research program on 1 Jul. 1992 through 30 Apr. 1993. Progress is reported for research in the following areas: (1) grain formation in circumstellar envelopes; (2) photochemistry in circumstellar envelopes; (3) modeling ice features in circumstellar envelopes; (4) episodic dust formation in circumstellar envelopes; (5) grain evolution in the diffuse interstellar medium; and (6) grain evolution in dense molecular clouds.

  12. Trajectories of martian habitability.

    PubMed

    Cockell, Charles S

    2014-02-01

    Beginning from two plausible starting points-an uninhabited or inhabited Mars-this paper discusses the possible trajectories of martian habitability over time. On an uninhabited Mars, the trajectories follow paths determined by the abundance of uninhabitable environments and uninhabited habitats. On an inhabited Mars, the addition of a third environment type, inhabited habitats, results in other trajectories, including ones where the planet remains inhabited today or others where planetary-scale life extinction occurs. By identifying different trajectories of habitability, corresponding hypotheses can be described that allow for the various trajectories to be disentangled and ultimately a determination of which trajectory Mars has taken and the changing relative abundance of its constituent environments. PMID:24506485

  13. Trajectories of Martian Habitability

    PubMed Central

    2014-01-01

    Abstract Beginning from two plausible starting points—an uninhabited or inhabited Mars—this paper discusses the possible trajectories of martian habitability over time. On an uninhabited Mars, the trajectories follow paths determined by the abundance of uninhabitable environments and uninhabited habitats. On an inhabited Mars, the addition of a third environment type, inhabited habitats, results in other trajectories, including ones where the planet remains inhabited today or others where planetary-scale life extinction occurs. By identifying different trajectories of habitability, corresponding hypotheses can be described that allow for the various trajectories to be disentangled and ultimately a determination of which trajectory Mars has taken and the changing relative abundance of its constituent environments. Key Words: Mars—Habitability—Liquid water—Planetary science. Astrobiology 14, 182–203. PMID:24506485

  14. Sleep habits and diabetes.

    PubMed

    Larcher, S; Benhamou, P-Y; Pépin, J-L; Borel, A-L

    2015-09-01

    Sleep duration has been constantly decreasing over the past 50 years. Short sleep duration, sleep quality and, recently, long sleep duration have all been linked to poor health outcomes, increasing the risk of developing metabolic diseases and cardiovascular events. Beyond the duration of sleep, the timing of sleep may also have consequences. Having a tendency to go early to bed (early chronotype) compared with the habit of going to bed later (late chronotype) can interfere considerably with social schedules (school, work). Eventually, a misalignment arises in sleep timing between work days and free days that has been described as 'social jet lag'. The present review looks at how different sleep habits can interfere with diabetes, excluding sleep breathing disorders, and successively looks at the effects of sleep duration, chronotype and social jet lag on the risk of developing diabetes as well as on the metabolic control of both type 1 and type 2 diabetes. Finally, this review addresses the current state of knowledge of physiological mechanisms that could be linking sleep habits and metabolic health. PMID:25623152

  15. Effective Physics Study Habits

    NASA Astrophysics Data System (ADS)

    Zettili, Nouredine

    2011-04-01

    We discuss the methods of efficient study habits and how they can be used by students to help them improve learning physics. In particular, we deal with ideas pertaining to the most effective techniques needed to help students improve their physics study skills. These ideas were developed as part of Project IMPACTSEED (IMproving Physics And Chemistry Teaching in SEcondary Education), an outreach grant funded by the Alabama Commission on Higher Education. This project is motivated by a major pressing local need: A large number of high school physics teachers teach out of field. In the presentation, focus on topics such as the skills of how to develop long term memory, how to improve concentration power, how to take class notes, how to prepare for and take exams, how to study scientific subjects such as physics. We argue that the student who conscientiously uses the methods of efficient study habits will be able to achieve higher results than the student who does not; moreover, a student equipped with the proper study skills will spend much less time to learn a subject than a student who has no good study habits. The underlying issue here is not the quantity of time allocated to the study efforts by the student, but the efficiency and quality of actions. This work is supported by the Alabama Commission on Higher Education as part of IMPACTSEED grant.

  16. HABITABLE CLIMATES: THE INFLUENCE OF ECCENTRICITY

    SciTech Connect

    Dressing, Courtney D.; Spiegel, David S.; Scharf, Caleb A.; Menou, Kristen; Raymond, Sean N. E-mail: dsp@astro.princeton.ed E-mail: caleb@astro.columbia.ed

    2010-10-01

    In the outer regions of the habitable zone, the risk of transitioning into a globally frozen 'snowball' state poses a threat to the habitability of planets with the capacity to host water-based life. Here, we use a one-dimensional energy balance climate model (EBM) to examine how obliquity, spin rate, orbital eccentricity, and the fraction of the surface covered by ocean might influence the onset of such a snowball state. For an exoplanet, these parameters may be strikingly different from the values observed for Earth. Since, for a constant semimajor axis, the annual mean stellar irradiation scales with (1 - e {sup 2}){sup -1/2}, one might expect the greatest habitable semimajor axis (for fixed atmospheric composition) to scale as (1 - e {sup 2}){sup -1/4}. We find that this standard simple ansatz provides a reasonable lower bound on the outer boundary of the habitable zone, but the influence of both obliquity and ocean fraction can be profound in the context of planets on eccentric orbits. For planets with eccentricity 0.5, for instance, our EBM suggests that the greatest habitable semimajor axis can vary by more than 0.8 AU (78%) depending on obliquity, with higher obliquity worlds generally more stable against snowball transitions. One might also expect that the long winter at an eccentric planet's apoastron would render it more susceptible to global freezing. Our models suggest that this is not a significant risk for Earth-like planets around Sun-like stars, as considered here, since such planets are buffered by the thermal inertia provided by oceans covering at least 10% of their surface. Since planets on eccentric orbits spend much of their year particularly far from the star, such worlds might turnout to be especially good targets for direct observations with missions such as TPF-Darwin. Nevertheless, the extreme temperature variations achieved on highly eccentric exo-Earths raise questions about the adaptability of life to marginally or transiently habitable conditions.

  17. Supernova spectra below strong circumstellar interaction

    NASA Astrophysics Data System (ADS)

    Leloudas, G.; Hsiao, E. Y.; Johansson, J.; Maeda, K.; Moriya, T. J.; Nordin, J.; Petrushevska, T.; Silverman, J. M.; Sollerman, J.; Stritzinger, M. D.; Taddia, F.; Xu, D.

    2015-02-01

    We construct spectra of supernovae (SNe) interacting strongly with a circumstellar medium (CSM) by adding SN templates, a black-body continuum, and an emission-line spectrum. In a Monte Carlo simulation we vary a large number of parameters, such as the SN type, brightness and phase, the strength of the CSM interaction, the extinction, and the signal to noise ratio (S/N) of the observed spectrum. We generate more than 800 spectra, distribute them to ten different human classifiers, and study how the different simulation parameters affect the appearance of the spectra and their classification. The SNe IIn showing some structure over the continuum were characterized as "SNe IInS" to allow for a better quantification. We demonstrate that the flux ratio of the underlying SN to the continuum fV is the single most important parameter determining whether a spectrum can be classified correctly. Other parameters, such as extinction, S/N, and the width and strength of the emission lines, do not play a significant role. Thermonuclear SNe get progressively classified as Ia-CSM, IInS, and IIn as fV decreases. The transition between Ia-CSM and IInS occurs at fV ~ 0.2-0.3. It is therefore possible to determine that SNe Ia-CSM are found at the (un-extincted) magnitude range -19.5 >M> -21.6, in very good agreement with observations, and that the faintest SN IIn that can hide a SN Ia has M = -20.1. The literature sample of SNe Ia-CSM shows an association with 91T-like SNe Ia. Our experiment does not support that this association can be attributed to a luminosity bias (91T-like being brighter than normal events). We therefore conclude that this association has real physical origins and we propose that 91T-like explosions result from single degenerate progenitors that are responsible for the CSM. Despite the spectroscopic similarities between SNe Ibc and SNe Ia, the number of misclassifications between these types was very small in our simulation and mostly at low S/N. Combined with the SN luminosity function needed to reproduce the observed SN Ia-CSM luminosities, it is unlikely that SNe Ibc constitute an important contaminant within this sample. We show how Type II spectra transition to IIn and how the Hα profiles vary with fV. SNe IIn fainter than M = -17.2 are unable to mask SNe IIP brighter than M = -15. A more advanced simulation, including radiative transfer, shows that our simplified model is a good first order approximation. The spectra obtained are in good agreement with real data.

  18. Habitable planets around the Sun and other stars

    NASA Astrophysics Data System (ADS)

    Kasting, James F.

    This chapter gives an overview about planetary habitability, which is based on the assumption that a habitable planet is one that supports liquid water on at least part of its surface. The factors that have kept Earth habitable throughout most of its life are reviewed, as well as those that made present-day Mars and Venus uninhabitable. These serve also as indicators for the expected width of the habitable zone around solar-like stars. The last two sections cover the causes for low abiotic O2 abundances expected in Earth's early atmosphere, and the (biological) origin of the current high concentrations of O2 and O3. Implications for the detectability of biological activity on extrasolar planets are discussed.

  19. On the Classification of Infrared Spectra from Circumstellar Dust Shells

    NASA Technical Reports Server (NTRS)

    Sloan, G. C.; Little-Marenin, I. R.; Price, S. D.

    1996-01-01

    We present results from an ongoing effort to classify the infrared spectra produced by circumstellar dust shells. Earlier efforts concentrated on oxygen-rich dust shells from sources associated with the asymptotic giant branch (AGB). Here, we describe the expansion of our classification to include S stars, supergiants, and carbon stars.

  20. Chemical evolution of circumstellar matter around young stellar objects

    NASA Technical Reports Server (NTRS)

    van Dishoeck, E. F.; Blake, G. A.

    1995-01-01

    Recent observational studies of the chemical composition of circumstellar matter around both high- and low-mass young stellar objects are reviewed. The molecular abundances are found to be a strong function of evolutionary state, but not of system mass or luminosity. The data are discussed with reference to recent theoretical models.

  1. Habitability and Life - an Overview

    NASA Astrophysics Data System (ADS)

    Bredehöft, J. H.

    2008-09-01

    Abstract The search for habitable planets has seen a significant boost, since much effort was invested into development of newer and more powerful techniques of detecting such planetary bodies. This search is fuelled by the interest that is sparked by its help in answering the bigger question of the origin of life on Earth and its abundance in the universe. Traditionally a planetary body has been deemed habitable when it provides conditions under which water is liquid. This led to the formulation of a habitable zone across stars, in which liquid water can exist. [1] Liquid water remains to this day the single most important feature in the search for life. There have been various suggestions of life being present in waterless environments like liquid hydrocarbons or even liquid ammonia, but how exactly a living system under such conditions might work, no one can satisfactorily explain. [2] A very important point in this context that is not often raised is that while water might be a favourable medium in which to live and certainly a major constituent of all living organism we know of, water alone is not alive and it will not spontaneously evolve into life. It would thus seem that apart from the presence of liquid water there a number of other, minor, necessary ingredients to life that determine whether a planet is habitable (meaning capable of sustaining life) or whether it is also capable of providing the starting grounds for the evolution of living systems. These other ingredients are determined by the minimum requirements of life itself. They include the molecular components of the most primitive encasing of an organism, the most primitive molecules needed for something like a metabolism and the most primitive way of storing information. [3] In addition to these molecular components, life must be able to utilise a source of energy to drive chemical reactions. Observations of various extremophiles on Earth utilising all kinds disequilibria suggest that these can be very diverse. The exact nature of these other ingredients, their possible presence and history of formation and their impact for the formation and evolution of life will be discussed for several different types of habitats all across the regime in which liquid water can be found, such as very dry and cold bodies like Mars, hot bodies like Venus, bodies covered completely in water or bodies with subsurface oceans. References [1] Kasting J.F., Whitmire D.P., Reynolds R.T., (1993) Icarus 101(1), 108-128 [2] Benner S.A., Ricardo A., Carrigan M.A. (2004) Curr Opin Chem Biol 8(6), 672-689 [3] Ruiz-Mirazo K., Peretó J., Moreno A., (2004) OLEB 34(3), 323-346 EPSC Abstracts, Vol. 3, EPSC2008-A-00039, 2008 European Planetary Science Congress, Author(s) 2008

  2. The infrared spectrum of M8 E - Evidence for circumstellar CO

    NASA Technical Reports Server (NTRS)

    Larson, H. P.; Fink, U.; Hofmann, R.

    1986-01-01

    High-resolution spectroscopic observations of the compact infrared source M8 E are reported in the region from 3 to 5 microns. Very prominent CO absorption lines are observed in the v = 1-0 band at 4.7 microns. The velocity width and rotational temperature suggest that this CO absorption occurs in a highly excited region. The high background continuum flux level and the prominent appearance of the CO features suggest that the CO line-forming region must be in front of the dust emission region. A blister model for M8 E, which places most of the dust continuum emission behind the source, satisfies this requirement. According to this picture, the observed circumstellar CO spectrum shows a high rotational temperature and a large velocity dispersion because of the combined effects of the strong stellar wind and possible shock heating near the dust zone as the wind encounters the ambient molecular cloud.

  3. POST-CAPTURE EVOLUTION OF POTENTIALLY HABITABLE EXOMOONS

    SciTech Connect

    Porter, Simon B.; Grundy, William M.

    2011-07-20

    The satellites of extrasolar planets (exomoons) have been recently proposed as astrobiological targets. Since giant planets in the habitable zone are thought to have migrated there, it is possible that they may have captured a former terrestrial planet or planetesimal. We therefore attempt to model the dynamical evolution of a terrestrial planet captured into orbit around a giant planet in the habitable zone of a star. We find that approximately half of loose elliptical orbits result in stable circular orbits over timescales of less than a few million years. We also find that those orbits are mostly at low inclination, but have no prograde/retrograde preference. In addition, we calculate the transit timing and duration variations for the resulting systems, and find that potentially habitable Earth-mass exomoons should be detectable.

  4. Computer codes for evaluation of control room habitability (HABIT)

    SciTech Connect

    Stage, S.A.

    1996-06-01

    This report describes the Computer Codes for Evaluation of Control Room Habitability (HABIT). HABIT is a package of computer codes designed to be used for the evaluation of control room habitability in the event of an accidental release of toxic chemicals or radioactive materials. Given information about the design of a nuclear power plant, a scenario for the release of toxic chemicals or radionuclides, and information about the air flows and protection systems of the control room, HABIT can be used to estimate the chemical exposure or radiological dose to control room personnel. HABIT is an integrated package of several programs that previously needed to be run separately and required considerable user intervention. This report discusses the theoretical basis and physical assumptions made by each of the modules in HABIT and gives detailed information about the data entry windows. Sample runs are given for each of the modules. A brief section of programming notes is included. A set of computer disks will accompany this report if the report is ordered from the Energy Science and Technology Software Center. The disks contain the files needed to run HABIT on a personal computer running DOS. Source codes for the various HABIT routines are on the disks. Also included are input and output files for three demonstration runs.

  5. Delivery of Volatiles to Habitable Planets in Extrasolar Planetary Systems

    NASA Technical Reports Server (NTRS)

    Chambers, John E.; Kress, Monika E.; Bell, K. Robbins; Cash, Michele; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    The Earth can support life because: (1) its orbit lies in the Sun's habitable zone', and (2) it contains enough volatile material (e.g. water and organics) for life to flourish. However, it seems likely that the Earth was drier when it formed because it accreted in a part of the Sun's protoplanetary nebula that was too hot for volatiles to condense. If this is correct, water and organics must have been delivered to the habitable zone, after dissipation of the solar nebula, from a 'wet zone' in the asteroid belt or the outer solar system, where the nebula was cool enough for volatiles to condense. Material from the wet zone would have been delivered to the Earth by Jupiter and Saturn. Gravitational perturbations from these giant planets made much of the wet zone unstable, scattering volatile-rich planetesimals and protoplanets across the Solar System. Some of these objects ultimately collided with the inner Planets which themselves lie in a stable part of the Solar System. Giant planets are now being discovered orbiting other sunlike stars. To date, these planets have orbits and masses very different from Jupiter and Saturn, such that few if any of these systems is likely to have terrestrial planets in the star's habitable zone. However, new discoveries are anticipated due to improved detector sensitivity and the increase in the timespan of observations. Here we present numerical experiments examining the range of giant-planet characteristics that: (1) allow stable terrestrial Planets to exist in a star's habitable zone, and (2) make a large part of the star's wet zone weakly unstable, thus delivering volatiles to the terrestrial planets over an extended period of time after the dissipation of the solar nebula.

  6. On the probability of habitable planets

    NASA Astrophysics Data System (ADS)

    Forget, François

    2013-07-01

    In the past 15 years, astronomers have revealed that a significant fraction of the stars should harbour planets and that it is likely that terrestrial planets are abundant in our galaxy. Among these planets, how many are habitable, i.e. suitable for life and its evolution? These questions have been discussed for years and we are slowly making progress. Liquid water remains the key criterion for habitability. It can exist in the interior of a variety of planetary bodies, but it is usually assumed that liquid water at the surface interacting with rocks and light is necessary for emergence of a life able to modify its environment and evolve. The first key issue is thus to understand the climatic conditions allowing surface liquid water assuming a suitable atmosphere. These have been studied with global mean one-dimensional (1D) models which have defined the `classical habitable zone', the range of orbital distances within which worlds can maintain liquid water on their surfaces (Kasting et al. 1993). A new generation of 3D climate models based on universal equations and tested on bodies in the solar system are now available to explore with accuracy climate regimes that could locally allow liquid water. The second key issue is now to better understand the processes which control the composition and the evolution of the atmospheres of exoplanets, and in particular the geophysical feedbacks that seem to be necessary to maintain a continuously habitable climate. From that point of view, it is not impossible that the Earth's case may be special and uncommon.

  7. Which Galaxies Are the Most Habitable?

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-09-01

    Habitable zones are a hot topic in exoplanet studies: where, around a given star, could a planet exist that supports life? But if you scale this up, you get a much less common question: which type of galaxy is most likely to host complex life in the universe? A team of researchers from the UK believes it has the answer.Criteria for HabitabilityLed by Pratika Dayal of the University of Durham, the authors of this study set out to estimate the habitability of a large population of galaxies. The first step in this process is to determine what elements contribute to a galaxys habitability. The authors note three primary factors:Total number of starsMore stars means more planets!Metallicity of the starsPlanets are more likely to form in stellar vicinities with higher metallicities, since planet formation requires elements heavier than iron.Likelihood of Type II supernovae nearbyPlanets that are located out of range of supernovae have a higher probability of being habitable, since a major dose of cosmic radiation is likely to cause mass extinctions or delay evolution of complex life. Galaxies supernova rates can be estimated from their star formation rates (the two are connected via the initial mass function).Hospitable Cosmic GiantsLower panel: the number of Earth-like habitable planets (given by the color bar, which shows the log ratio relative to the Milky Way) increases in galaxies with larger stellar mass and lower star formation rates. Upper panel: the larger stellar-mass galaxies tend to be elliptical (blue line) rather than spiral (red line). Click for larger view. [Dayal et al. 2015]Interestingly, these three conditions have previously been shown to be linked via something termed the fundamental metallicity relation, which relates the total stellar masses, metallicities, and star formation rates of galaxies. By using this relation, the authors were able to create predictions for the number of habitable planets in more than 100,000 galaxies in the local universe (cataloged by the Sloan Digital Sky Survey).Based on these predictions, the authors find that the galaxies likely to host the largest number of habitable planets are those that have a mass greater than twice that of the Milky Way and star formation rates less than a tenth of that of the Milky Way.These galaxies tend to be giant elliptical galaxies, rather than compact spirals like our own galaxy. The authors calculate that the most hospitable galaxies can host up to 10,000 times as many Earth-like planets and 1,000,000 times as many gas-giants (which might have habitable moons) as the Milky Way!CitationPratika Dayal et al.2015 ApJ 810 L2 doi:10.1088/2041-8205/810/1/L2

  8. Trace Element Condensation in Circumstellar Envelopes of Carbon Stars

    NASA Astrophysics Data System (ADS)

    Lodders, K.; Fegley, B., Jr.

    1992-07-01

    It is now well established that meteorites contain reduced presolar grains, such as graphite and silicon carbide (SiC), which are probably formed by condensation of dust in the circumstellar envelopes of carbon-rich AGB stars. Here we model condensation in envelopes of carbon stars, with an emphasis on trace elements. Since absolute elemental abundances in stellar atmospheres are generally not known, we assume solar abundances (Anders and Grevesse 1989), except for carbon. A C/O ratio of 2, consistent with the mean and median values of 2.1 and 1.8 respectively, for 61 carbon stars (Gow 1977) was used. The C/O ratio was increased by adding carbon because astrophysicists believe that carbon produced in helium-burning zones may be mixed to the surfaces of C stars (e.g. Lucy 1976). We used physical parameters for the circumstellar shell of the high mass-loss rate, prototypical carbon star IRC +10216 (e.g. Keady et al. 1988, Dominik et al. 1990) and theoretical considerations by Salpeter (1974a,b) to construct a P-T-model of the envelope (see Fig. 1). Thermodynamic equilibrium condensation calculations for a reduced gas include ~600 gaseous and solid compounds of the elements H, C, N, O, S, P, F, Cl, Fe, Mg, Al, Ti, Si, Ca, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and REE. Refractory oxides, sulfides, nitrides, and carbides were considered as condensates. The calculations were done from T = 800 to 2500 K, and P= 10^-5 to 10^-13 bars. The effects of nucleation on condensation temperatures were calculated using the nucleation model discussed by Salpeter (1974a,b) and Cameron and Fegley (1982). The temperature drop required for condensation depends on (P,T, density) in the expanding envelope and also on the abundance, density, and surface energy (Es) of the nucleating compound. The range of E(sub)s values for NaCl-type carbides are about 800-1700 erg/cm^2 (Livey & Murray 1956); however, these data are generally poorly known. Another important variable is the sticking coefficient (s), taken = 10^-3 here. Results of the equilibrium condensation calculations as a function of pressure at C/O = 2 are shown in Table 1 and Fig. 1. The initial major element condensates are graphite, TiC, SiC, Fe3C, AlN, and CaS (Table 1). The data for C(sub)GR TiC, and SiC are also shown in Fig. 1, together with the P-T profile for the carbon star IRC +10216. Also included are the condensation temperatures if nucleation constraints are applied (dotted lines). Neglecting nucleation effects, C(sub)Gr, TiC, and SiC would be present within 2-3 stellar radii from the photosphere (r/R = 1). With nucleation constraints, TiC and SiC form at lower T at a distance of about 5 stellar radii. The T-drop required for graphite condensation is only about 100 K lower than the equilibrium condensation temperatures at higher P. Therefore, graphite grains would be stable at r/R >1.5. We note that at r = 3-5 R there is observational evidence for SiC, graphite and amorphous carbon in the envelope of the C star IRC +10216 (e.g. Keady et al. 1988, Ridgway and Keady 1988). Of the nitrides, AlN is the only which forms initially. Because of its structural similarity to SiC and TiC one could expect formation of AlN solid solutions with NaCl-type carbides. Most trace elements initially form carbides. The most refractory carbides are TaC, WC, NbC, ZrC, and HfC, condensing about 100-250 K higher than TiC. E(sub)s data are available for TaC and ZrC. Nucleation constraints show that only ZrC would form prior to TiC. Other trace element carbides (Mo(sub)2C, MoC, VC(sub)0.88, YC(sub)2, Cr(sub)3C(sub)2) condense as pure compounds below the equilibrium condensation temperatures of C(sub)Gr, TiC, and SiC. However, they may condense in solid solution in TiC or SiC or in both if allowed by their crystal structures. In any case, nitrides are not initial condensates for these trace elements. However, because the carbides and nitrides can form solid solutions, one could expect carbide-nitride solutions. References: Anders E. and Grevesse N. (1989) Geochim. Cosmochim. Acta 53, 197-214. Cameron A.G.W. and M.B. Fegley (1982) Icarus 52, 1-13. Dominik C., Gail H.P., Sedlmayr E., and Winters J.M. (1990) Astron. Astrophys. 240, 365-375. Gow C.E. (1977) Pub. Astron. Soc. Pac. 89, 510-518. Keady J.J., Hall D.N.B. and Ridgway S. T. (1988) Ap. J. 326, 832-842. Livey D.T. and Murray P. (1956) J. Am. Cer. Soc. 39, 363-372. Lucy L. B. (1976) Ap. J. 205, 482-491. Ridgway S. T. and Keady J. J. (1988) Ap. J. 326, 843-858. Salpeter E. E. (1974a) Ap. J. 193, 579-584. Salpeter E. E (1974b) Ap.J. 193, 585-592. Figure 1, which in the hard copy appears here, shows condensation temperatures of graphite, TiC, and SiC at various pressures. Solid lines: equilibrium condensation; dotted lines: nucleation constraints considered. The P-T profile of the carbon star IRC +10216 and the radial pressure variation from the photosphere are also indicated.

  9. Dust mineralogy in the circumstellar envelope of SVS13

    NASA Astrophysics Data System (ADS)

    Fujiyoshi, T.; Wright, C.; Moore, T.

    It is of great interest to study the mineralogy of circumstellar dust around young stars as it represents the original constituents of planetesimals, hence of the rocky planets like our own Earth. To this end, we have obtained an N-band (8-13 µm) spectrum of a pre-main-sequence star SVS13, using the facility mid-infrared imaging spectrometer COMICS on the Japanese 8.2-m Subaru Telescope atop the summit of Mauna Kea, Hawaii. We have fitted various emissivities/absorption coefficients of dust species to the spectrum to examine dust mineralogy in the circumstellar envelope of this remarkable young star. In this presentation, we outline the modelling and highlight some of our findings.

  10. Revising Circumstellar Disk Evolution -- How Binaries Change the Picture

    NASA Astrophysics Data System (ADS)

    Daemgen, Sebastian; Petr-Gotzens, Monika; Meyer, Elliot

    2015-01-01

    We combine new and previously published high-angular resolution near-infrared spectroscopic and photometric observations to measure the presence of accretion and hot circumstellar dust around the individual components of visual multiple stars and confirmed singles with separations between ˜20 and 800 AU in the Orion Nebula Cluster, Chamaeleon I, and Taurus star-forming regions. The data provide evidence for an accelerated disk dispersal in binaries -- in particular of the less massive stellar component -- at a mass accretion rate identical to that of single stars. Our findings have stringent implications on circumstellar disk parameters, which have been traditionally inferred from observations of ``binary-contaminated'' samples. For example, we find an increased single star accretor fraction, i.e., evidence for a longer single star disk lifetime, compared to previous surveys.

  11. CIRCUMSTELLAR ABSORPTION IN DOUBLE DETONATION TYPE Ia SUPERNOVAE

    SciTech Connect

    Shen, Ken J.; Guillochon, James; Foley, Ryan J.

    2013-06-20

    Upon formation, degenerate He core white dwarfs are surrounded by a radiative H-rich layer primarily supported by ideal gas pressure. In this Letter, we examine the effect of this H-rich layer on mass transfer in He+C/O double white dwarf binaries that will eventually merge and possibly yield a Type Ia supernova (SN Ia) in the double detonation scenario. Because its thermal profile and equation of state differ from the underlying He core, the H-rich layer is transferred stably onto the C/O white dwarf prior to the He core's tidal disruption. We find that this material is ejected from the binary system and sweeps up the surrounding interstellar medium hundreds to thousands of years before the SN Ia. The close match between the resulting circumstellar medium profiles and values inferred from recent observations of circumstellar absorption in SNe Ia gives further credence to the resurgent double detonation scenario.

  12. Circumstellar interaction in type Ibn supernovae and SN 2006jc

    NASA Astrophysics Data System (ADS)

    Chugai, N. N.

    2009-12-01

    I analyse peculiar properties of light curve and continua of enigmatic Ibn supernovae, including SN 2006jc, and argue in favour of the early strong circumstellar interaction. This interaction explains the high luminosity and fast flux rise of SN 1999cq, while the cool dense shell (CDS) formed in shocked ejecta can explain the smooth early continuum of SN 2000er and unusual blue continuum of SN 2006jc. The dust is shown to condense in the CDS at about day 50. Monte Carlo modelling of the HeI 7065 Å line profile affected by the dust occultation supports a picture, in which the dust resides in the fragmented CDS, whereas HeI lines originate from circumstellar clouds shocked and fragmented in the forward shock wave.

  13. Detection of circumstellar material in a normal type Ia supernova.

    PubMed

    Patat, F; Chandra, P; Chevalier, R; Justham, S; Podsiadlowski, Ph; Wolf, C; Gal-Yam, A; Pasquini, L; Crawford, I A; Mazzali, P A; Pauldrach, A W A; Nomoto, K; Benetti, S; Cappellaro, E; Elias-Rosa, N; Hillebrandt, W; Leonard, D C; Pastorello, A; Renzini, A; Sabbadin, F; Simon, J D; Turatto, M

    2007-08-17

    Type Ia supernovae are important cosmological distance indicators. Each of these bright supernovae supposedly results from the thermonuclear explosion of a white dwarf star that, after accreting material from a companion star, exceeds some mass limit, but the true nature of the progenitor star system remains controversial. Here we report the spectroscopic detection of circumstellar material in a normal type Ia supernova explosion. The expansion velocities, densities, and dimensions of the circumstellar envelope indicate that this material was ejected from the progenitor system. In particular, the relatively low expansion velocities suggest that the white dwarf was accreting material from a companion star that was in the red-giant phase at the time of the explosion. PMID:17626848

  14. Circumstellar Absorption in Double Detonation Type Ia Supernovae

    NASA Astrophysics Data System (ADS)

    Shen, Ken J.; Guillochon, James; Foley, Ryan J.

    2013-06-01

    Upon formation, degenerate He core white dwarfs are surrounded by a radiative H-rich layer primarily supported by ideal gas pressure. In this Letter, we examine the effect of this H-rich layer on mass transfer in He+C/O double white dwarf binaries that will eventually merge and possibly yield a Type Ia supernova (SN Ia) in the double detonation scenario. Because its thermal profile and equation of state differ from the underlying He core, the H-rich layer is transferred stably onto the C/O white dwarf prior to the He core's tidal disruption. We find that this material is ejected from the binary system and sweeps up the surrounding interstellar medium hundreds to thousands of years before the SN Ia. The close match between the resulting circumstellar medium profiles and values inferred from recent observations of circumstellar absorption in SNe Ia gives further credence to the resurgent double detonation scenario.

  15. Circumstellar grains and the intrinsic polarization of starlight

    NASA Technical Reports Server (NTRS)

    Forrest, W. J.; Gillett, F. C.; Stein, W. A.

    1975-01-01

    Twenty-five long-period variable stars exhibiting intrinsic variable polarization have been monitored over the range 3.5-11 microns for several cycles. No conclusive evidence for gross changes in amount of circumstellar grains has been found. Thus circumstellar infrared emission is attributed to the total abundance of grains surrounding the star, which does not change by a large amount with time, while intrinsic polarization is attributed to more localized scattering and absorption effects. Spectrophotometry with resolution of about 0.015 over the 8-14 microns wavelength range of several stars with different chemical compositions indicates excess emission characteristic of 3 types of grains: (1) 'blackbody' grains, (2) silicate grains, and (3) silicon carbide grains.

  16. External Shaping of Circumstellar Envelopes of Evolved Stars

    NASA Astrophysics Data System (ADS)

    Cox, N. L. J.

    2015-08-01

    The circumstellar envelopes of asymptotic giant branch (AGB) stars and red supergiants (RSGs) are complex chemical and physical environments, and the specifics of their mass-loss history are important for both stellar and galactic evolution. One key aspect in this is to understand how the circumstellar medium of these stars can be shaped and affected by both internal and external mechanisms. These influences can skew our view on the (dust) chemistry and mass-loss history of these stars, and hence their role in the chemical enrichment of galaxies. This contribution focuses on the external mechanism related to the interaction between the slow dusty stellar wind and the local ambient medium. I will discuss what recent observations and hydrodynamical simulations have revealed and how these can help us learn more about AGB stars and RSGs, as well as the interstellar medium (ISM).

  17. The chemistry of molecular anions in circumstellar sources

    SciTech Connect

    Agúndez, Marcelino; Cernicharo, José; Guélin, Michel

    2015-01-22

    The detection of negatively charged molecules in the interstellar and circumstellar medium in the past four years has been one of the most impacting surprises in the area of molecular astrophysics. It has motivated the interest of astronomers, physicists, and chemists on the study of the spectroscopy, chemical kinetics, and prevalence of molecular anions in the different astronomical regions. Up to six different molecular anions have been discovered in space to date, the last one being the small ion CN{sup −}, which has been observed in the envelope of the carbon star IRC +10216 and which contrary to the other larger anions is not formed by electron attachment to CN, but through reactions of large carbon anions with nitrogen atoms. Here we briefly review the current status of our knowledge of the chemistry of molecular anions in space, with particular emphasis on the circumstellar source IRC +10216, which to date is the astronomical source harboring the largest variety of anions.

  18. X-raying Circumstellar Material around Young Stars

    NASA Astrophysics Data System (ADS)

    Schneider, P. C.; Günther, H. M.

    2016-01-01

    Young stars are surrounded by copious amounts of circumstellar material. Its composition, in particular its gas-to-dust ratio, is an important parameter. However, measuring this ratio is challenging, because gas mass estimates are often model dependent. X-ray absorption is sensitive to the gas along the line-of-sight while optical/near-IR extinction depends on the dust. Therefore, the absorber's gas-to-dust ratio is directly given by the ratio between X-ray and optical/near-IR extinction. We present three systems where we used X-ray and optical/near-IR data to constrain the gas-to-dust ratio of circumstellar material; from a dust rich debris disk to gaseous protoplanetary disks.

  19. HABITABLE PLANETS ECLIPSING BROWN DWARFS: STRATEGIES FOR DETECTION AND CHARACTERIZATION

    SciTech Connect

    Belu, Adrian R.; Selsis, Franck; Raymond, Sean N.; Bolmont, Emeline; Palle, Enric; Street, Rachel; Sahu, D. K.; Anupama, G. C.; Von Braun, Kaspar; Figueira, Pedro; Ribas, Ignasi

    2013-05-10

    Given the very close proximity of their habitable zones, brown dwarfs (BDs) represent high-value targets in the search for nearby transiting habitable planets that may be suitable for follow-up occultation spectroscopy. In this paper, we develop search strategies to find habitable planets transiting BDs depending on their maximum habitable orbital period (P{sub HZ{sub out}}). Habitable planets with P{sub HZ{sub out}} shorter than the useful duration of a night (e.g., 8-10 hr) can be screened with 100% completeness from a single location and in a single night (near-IR). More luminous BDs require continuous monitoring for longer duration, e.g., from space or from a longitude-distributed network (one test scheduling achieved three telescopes, 13.5 contiguous hours). Using a simulated survey of the 21 closest known BDs (within 7 pc) we find that the probability of detecting at least one transiting habitable planet is between 4.5{sup +5.6}{sub -1.4}% and 56{sup +31}{sub -13}%, depending on our assumptions. We calculate that BDs within 5-10 pc are characterizable for potential biosignatures with a 6.5 m space telescope using {approx}1% of a five-year mission's lifetime spread over a contiguous segment only one-fifth to one-tenth of this duration.

  20. Thermodynamics and Planetary Habitability

    NASA Astrophysics Data System (ADS)

    Kleidon, A.

    2007-08-01

    The relevance of thermodynamics as the driving force for life has long been recognized, for instance by Boltzmann (1886), Lotka (1922) and Schrödinger (1944). Thermodynamics has also been used to characterize planetary habitability. The Earth's atmosphere in a state far from thermodynamic equilibrium, as reflected by its high oxygen content, has been used as an indication for a habitable planet as this state is maintained by the biosphere (Lovelock, 1965). Yet the question remains regarding the fundamental causes that make planet Earth so habitable, or, in other words, what the driving principles are that make the emergence of life an inevitable feature of Earth system functioning. As an extension to these thermodynamic views, I argue here that the myriad of different biogeochemical processes that we call life act to maximize the planetary rate of entropy production. The possibility to do so exists on Earth because its planetary albedo, and therefore the amount of absorbed sunlight and planetary entropy production, is not a fixed planetary property, but emerges from the dynamics of the climate system and the global biogeochemical cycles that shape the composition of the atmosphere. A dominant effect on the planetary albedo is surface temperature: low temperatures result in more highly reflective snow and sea-ice cover, while high temperatures result in an atmosphere with high moisture contents, low temperature gradients, and likely higher reflective cloud cover. Hence, a minimum planetary albedo should exist for a certain, optimum surface temperature at which the absorption of sunlight and the associated rate of entropy production is maximized. Surface temperature, in turn, can be regulated towards the optimum through the intensity of carbon cycling as it directly impacts the strength of the atmospheric greenhouse effect. Hence, a carbon-cycling biosphere can be seen as the biogeochemical implementation to maximize planetary entropy production. This thermodynamic perspective views life as an intrinsic planetary property that is the inevitable consequence of non-equilibrium thermodynamic systems to maximize their rates of entropy production to the extent possible (Kleidon 2004). Planetary habitability can then be related to the flexibility of the planetary boundary conditions, that is, the extent to which these can be altered by internal dynamics. In this presentation, I describe this view in more detail and will outline methods by which this view can be tested quantitatively with numerical simulation models of the Earth system. References Boltzmann, L.: Der zweite Hauptsatz der mechanischen Wärmetheorie. Almanach der kaiserlichen Akademie der Wissenschaften, 36:225-259, 1886. Kleidon, A.: Beyond Gaia: Thermodynamics of life and Earth system functioning. Clim. Ch., 66:271-319, 2004. Lotka, A. J.: Natural Selection as a Physical Principle. Proc. Natl. Acad. Sci. U.S.A., 8:151-154, 1922. Lovelock, J.˘aE.: A Physical Basis for Life Detection Experiments. Nature, 207:568- 570, 1965. Schrödinger, E.: What is Life? The physical aspect of the living cell. Cambridge University Press, Cambridge, UK, 1944.

  1. Developing Mathematical Habits of Mind

    ERIC Educational Resources Information Center

    Mark, June; Cuoco, Al; Goldenberg, E. Paul; Sword, Sarah

    2010-01-01

    "Mathematical habits of mind" include reasoning by continuity, looking at extreme cases, performing thought experiments, and using abstraction that mathematicians use in their work. Current recommendations emphasize the critical nature of developing these habits of mind: "Once this kind of thinking is established, students can apply it in the…

  2. How Common are Habitable Planets?

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; DeVincenzi, Donald (Technical Monitor)

    2000-01-01

    The Earth is teeming with life, which, occupies a diverse array of environments; other bodies in our Solar System offer fewer, if any, niches which are habitable by life as we know it. Nonetheless, astronomical studies suggest that a large number of habitable planets-are likely to be present within our Galaxy.

  3. Observations of Circumstellar Thermochemical Equilibrium: The Case of Phosphorus

    NASA Technical Reports Server (NTRS)

    Milam, Stefanie N.; Charnley, Steven B.

    2011-01-01

    We will present observations of phosphorus-bearing species in circumstellar envelopes, including carbon- and oxygen-rich shells 1. New models of thermochemical equilibrium chemistry have been developed to interpret, and constrained by these data. These calculations will also be presented and compared to the numerous P-bearing species already observed in evolved stars. Predictions for other viable species will be made for observations with Herschel and ALMA.

  4. The theoretical polarization of pure scattering axisymmetric circumstellar envelopes

    NASA Technical Reports Server (NTRS)

    Fox, G. K.

    1994-01-01

    The Sobolev approach to the scattering of starlight through a pure scattering circumstellar envelope is developed. The theoretical polarization due to electron scattering in Be star envelopes is calculated for two geometries (an equatorially enhanced envelope and a spheroidal envelope). Only the disk-type envelope is found to yield a maximum polarization consistent with the observed range for Be stars. A lower limit, analytical approximation to the theoretical polarization from a pure scattering envelope is obtained.

  5. The Diverse Reflectance Spectra of Young Circumstellar Disks

    NASA Astrophysics Data System (ADS)

    Debes, John H.; Weinberger, A. J.; Schneider, G.

    2007-12-01

    With images of several circumstellar disks at multiple wavelengths, crude measures of dust scattering efficiency can be constructed. We present the latest HST observations of several well-known disks spanning 0.5-2.22 μm. The disks show a wide diversity in spectral shape and thus composition, from very red disks that hint at the presence of organic materials to grey disks that suggest the presence of water ice or silicates.

  6. Magnetic Field and Early Evolution of Circumstellar Disks

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Yusuke

    2016-03-01

    The magnetic field plays a central role in the formation and evolution of circumstellar disks. The magnetic field connects the rapidly rotating central region with the outer envelope and extracts angular momentum from the central region during gravitational collapse of the cloud core. This process is known as magnetic braking. Both analytical and multidimensional simulations have shown that disk formation is strongly suppressed by magnetic braking in moderately magnetised cloud cores in the ideal magnetohydrodynamic limit. On the other hand, recent observations have provided growing evidence of a relatively large disk several tens of astronomical units in size existing in some Class 0 young stellar objects. This introduces a serious discrepancy between the theoretical study and observations. Various physical mechanisms have been proposed to solve the problem of catastrophic magnetic braking, such as misalignment between the magnetic field and the rotation axis, turbulence, and non-ideal effect. In this paper, we review the mechanism of magnetic braking, its effect on disk formation and early evolution, and the mechanisms that resolve the magnetic braking problem. In particular, we emphasise the importance of non-ideal effects. The combination of magnetic diffusion and thermal evolution during gravitational collapse provides a robust formation process for the circumstellar disk at the very early phase of protostar formation. The rotation induced by the Hall effect can supply a sufficient amount of angular momentum for typical circumstellar disks around T Tauri stars. By examining the combination of the suggested mechanisms, we conclude that the circumstellar disks commonly form in the very early phase of protostar formation.

  7. NASA plans relevant to the study of circumstellar matter

    NASA Astrophysics Data System (ADS)

    Stencel, Robert E.

    The Astrophysics program of the National Aeronautics and Space Administration of the United States emphasizes use of vehicles to obtain above-the-atmosphere observational advantages, including expanded electromagnetic frequency access, enhanced sensitivity resulting from reduced or eliminated atmospheric absorption of light and image smearing. Space technology provides a superior means for astrophysical inquiry, particularly in the case of circumstellar material. Much of the flight program is undergoing intensive review following the Space Shuttle disaster of January 1986.

  8. Additional constraints on circumstellar disks in the Trapezium Cluster

    NASA Technical Reports Server (NTRS)

    Stauffer, John R.; Prosser, Charles F.; Hartmann, Lee; Mccaughrean, Mark J.

    1994-01-01

    We discuss the new constraints on the population of compact ionized sources in the Trapezium Cluster thought to arise from the ionization by the central OB stars of circumstellar disks around low-mass pre-main sequence stars. We present new Hubble Space Telescope (HST) Planetary Camera observations of two of these candidate disk sources, resolving extended nebulosity around them. One source shows a small-scale (greater than or approximately = 100 AU) bow-shock structure, previously seen on larger scales by O'Dell et al. We show that the circumstellar disk model is the most likely one for the majority of sources, although is remains plausible that some of the larger objects could be equilibrium globules. We combine the most complete censuses of compact radio sources and stars in the core region to derive the fraction of the stellar population that may be associated with a circumstellar disk. Our estimate of 25%-75% is comparable to that found for pre-main sequence (PMS) stars in the Taurus-Auriga dark clouds, indicating that the dense cluster environment of the Trapezium has not drastically reduced the frequency of disks seen around PMS stars.

  9. Additional constraints on circumstellar disks in the Trapezium Cluster

    NASA Technical Reports Server (NTRS)

    Stauffer, John R.; Prosser, Charles F.; Hartmann, Lee; Mccaughrean, Mark J.

    1994-01-01

    We discuss new constraints on the population of compact ionized sources in the Trapezium Cluster thought to arise from the ionization by the central OB stars of circumstellar disks around low-mass pre-main sequence stars. We present new HST Planetary Camera observations of two of these candidate disk sources, resolving extended nebulosity around them. One source shows a small-scale (greater than 100 AU) bow-shock structure, previously seen on larger scales by O'Dell et al. We show that the circumstellar disk model is the most likely one for the majority of sources, although it remains plausible that some of the larger objects could be equilibrium globules. We combine the most complete censuses of compact radio sources and stars in the core region to derive the fraction of the stellar population that may be associated with a circumstellar disk. Our estimate of 25-75 percent is comparable to that found for PMS stars in the Taurus-Auriga dark clouds, indicating that the dense cluster environment of the Trapezium has not drastically reduced the frequency of disks seen around pre-main sequence stars.

  10. C/O: Effects on Habitability of Stellar Exoplanet Systems

    NASA Astrophysics Data System (ADS)

    Johnson, Torrence V.; Sevin Peckmezci, Gül; Mousis, Olivier; Lunine, Jonathan I.; Madhusudhan, Nikku

    2015-11-01

    We assess how differences in the composition of exoplanet host stars might affect the availability of water in their systems, particularly the role of carbon and oxygen abundances. Water, one of the key chemical ingredients for habitability, may be in short supply in carbon-rich, oxygen-poor systems even if planets exist in the ‘habitable zone’. For the solar system, C/O = 0.55 is particularly important in determining the refractory (silicate and metal) to volatile ice ratio expected in material condensed beyond the snow line (Gaidos E. J. Icarus 145, 637, 2000; Wong M. H. et al. in Oxygen in the Solar System, G.J. MacPherson, Ed., 2008). Our analysis of published compositions for a set of exoplanet host stars (Johnson T. V. et al. ApJ. 757(2), 192, 2012) showed that the amount of condensed water ice in those systems might range from as much as 50% by mass for sub-solar C/O = 0.35 to less than a few percent for super-solar C/O = 0.7. A recent analysis using similar techniques (Pekmezci G. S., Dottorato di Ricerca in Astronomia, Università Degli Studi di Roma “Tor Vergata”, 2014) of a much larger stellar composition data set for 974 FGK stars (Petigura E. and Marcy G. Journal of Astrophysics 735, 2011), allows us to assess the possible range of water ice abundance in the circumstellar accretion disks of these ‘solar-type’ stars (of which 72 were known to have one or more planets as of 2011). Stellar C/O in a subset (457 stars) of this stellar database with reported C, O, Ni, and Fe abundances ranges from 0.3 to 1.4. The resulting computed water ice fractions and refractory (silicate + metal) fractions range from ~0 to 0.6 and 0.3 to 0.9 respectively. These results have implications for assessing the habitability of exoplanets since they constrain the amount of water available beyond the snow line for dynamical delivery to inner planets, depending on the host stars’ C/O in the circumstellar nebula. TVJ acknowledges government support at JPL/Caltech, under a contract with NASA. JIL was supported by the JWST Project through NASA. O.M. acknowledges support from CNES.

  11. Chemistry and distribution of daughter species in the circumstellar envelopes of O-rich AGB stars

    NASA Astrophysics Data System (ADS)

    Li, Xiaohu; Millar, Tom J.; Heays, Alan N.; Walsh, Catherine; van Dishoeck, Ewine F.; Cherchneff, Isabelle

    2016-03-01

    Context. Thanks to the advent of Herschel and ALMA, new high-quality observations of molecules present in the circumstellar envelopes of asymptotic giant branch (AGB) stars are being reported that reveal large differences from the existing chemical models. New molecular data and more comprehensive models of the chemistry in circumstellar envelopes are now available. Aims: The aims are to determine and study the important formation and destruction pathways in the envelopes of O-rich AGB stars and to provide more reliable predictions of abundances, column densities, and radial distributions for potentially detectable species with physical conditions applicable to the envelope surrounding IK Tau. Methods: We use a large gas-phase chemical model of an AGB envelope including the effects of CO and N2 self-shielding in a spherical geometry and a newly compiled list of inner-circumstellar envelope parent species derived from detailed modeling and observations. We trace the dominant chemistry in the expanding envelope and investigate the chemistry as a probe for the physics of the AGB phase by studying variations of abundances with mass-loss rates and expansion velocities. Results: We find a pattern of daughter molecules forming from the photodissociation products of parent species with contributions from ion-neutral abstraction and dissociative recombination. The chemistry in the outer zones differs from that in traditional PDRs in that photoionization of daughter species plays a significant role. With the proper treatment of self-shielding, the N → N2 and C+→ CO transitions are shifted outward by factors of 7 and 2, respectively, compared with earlier models. An upper limit on the abundance of CH4 as a parent species of (≲2.5 × 10-6 with respect to H2) is found for IK Tau, and several potentially observable molecules with relatively simple chemical links to other parent species are determined. The assumed stellar mass-loss rate, in particular, has an impact on the calculated abundances of cations and the peak-abundance radius of both cations and neutrals: as the mass-loss rate increases, the peak abundance of cations generally decreases and the peak-abundance radius of all species moves outwards. The effects of varying the envelope expansion velocity and cosmic-ray ionization rate are not as significant. Conclusions:

  12. Infrared interferometry and spectroscopy of circumstellar envelopes

    NASA Astrophysics Data System (ADS)

    Monnier, John David

    This thesis reports on two experiments designed to reveal fundamentally new information about the inner dust and gas envelopes around mass-losing stars. The mid-infrared Infrared Spatial Interferometer was outfitted with an RF filterbank to allow interferometric observations of molecular absorption features (NH3 and SiH4) with very high spectral resolution ( / ~ 105). These new data permitted the molecular stratification around carbon star IRC +10216 and red supergiant VY CMa to be investigated. For IRC +10216, it was determined that both ammonia and silane form in the dusty outflow significantly beyond both the dust formation and gas acceleration zones ( >~ 20 R* ). More specifically, ammonia was found to form before silane in a region of decaying gas turbulence, while the silane is produced in a region of relatively smooth gas flow much further from the star ( >~ 80 R* ). The depletion of SiS on grains soon after dust formation may fuel silane-producing reactions on the grain surfaces. For VY CMa, a combination of interferometric and spectral observations suggest that NH3 is forming near the termination of the gas acceleration phase in a region of high gas turbulence (~40 R* ). The second half of the thesis describes a novel aperture masking experiment which converted the Keck-I 10-m primary mirror into a separate-element interferometric array. High signal-to-noise images were reconstructed of bright near-infrared sources at the diffraction limit (~ 0.050'' at 2 m m) using VLBI techniques. The inner dust shells of IRC +10216 and VY CMa are shown to be highly clumpy and inhomogeneous, a finding inconsistent with current (simple) models of mass-loss. For IRC +10216, spatial resolution on the scale of the star itself was attained, and proper motion of dust clumps within 10 R* was detected, revealing the dynamics of the outflow directly. Unexpectedly, carbon-rich dust shells around some late- type Wolf-Rayet stars were resolved into highly- collimated, spinning ``pinwheel'' nebulae, formed from the interacting winds of embedded short- period (~1 yr) binaries. Precise orbital parameters and wind velocities are determined from the multi-epoch spiral morphology; important implications on binary and stellar evolution are discussed.

  13. An Investigation of Circumbinary Planet Orbital Stability and Habitability to Identify Potential Planetary Systems with Several Habitable Planets

    NASA Astrophysics Data System (ADS)

    Mason, Paul A.; Zuluaga, Jorge; Cuartas, Pablo A.

    2015-08-01

    The census of planets orbiting the center of mass of binary stars is rapidly growing. The question of stability for circumbinary planets has been the focus of much recent research. We review this work and present results of new simulations, from which we find criteria for the long term stability of exoplanets orbiting binaries. We are especially concerned with the potential stability of planets in habitable zones surrounding binaries. For this purpose, we merge a long-term orbital stability study with an analysis of the rotational evolution of the stellar components. The stellar evolution and rotational study enables estimates of stellar activity, and the effects on the magnetospheres and atmospheres of planets over the course of history for a potentially habitable circumbinary planet. We find that the long-term orbital stability of circumbinary habitable zone depends sensitively on the initial orbit of the binary and on the masses of the stars. We find that stellar twins (binary mass ratio ~ 1) and binaries with circular orbits provide the most stable solutions. However, if the binary orbit evolves too rapidly, planets may be lost due to changes in resonance locations. A subset of binaries are identified possessing both stable orbital solutions for multiple planets in the habitable zone and reduced stellar aggression due to tidal torqueing of the stellar rotation.

  14. Habitability Of Europa's Crust

    NASA Astrophysics Data System (ADS)

    Greenberg, R.; Tufts, B. R.; Geissler, P.; Hoppa, G.

    Physical characterization of Europa's crust shows it to be rich in potentially habitable niches, with several timescales for change that would allow stability for organisms to prosper and still require and drive evolution and adaptation. Studies of tectonics on Europa indicate that tidal stress causes much of the surface cracking, that cracks pen- etrate through to liquid water (so the ice must be thin), and that cracks continue to be worked by tidal stress. Thus a global ocean is (or was until recently) well linked to the surface. Daily tidal flow (period~days) transports substances up and down through the active cracks, mixing surface oxidants and fuels (cometary material) with the oceanic reservoir of endogenic and exogenic substances. Organisms moving with the flow or anchored to the walls could exploit the disequilibrium chemistry, and those within a few meters of the surface could photosynthesize. Cracks remain active for at least ~10,000 yr, but deactivate as nonsynchronous rotation moves them to different stress regimes in less than a million yr. Thus, to survive, organisms squeezed into the ocean must migrate to new cracks, and those frozen in place must hibernate. Most sites remelt and would release captive organisms within about a million yr based on the prevalence of chaotic terrain, which covers nearly half of Europa. Linkage of the ocean to the surface also could help sustain life in the ocean by delivering oxidants and fuels. Suboceanic volcanism (if any) could provide additional sites and support for life, but is not necessary. Recent results support this model. We further constrain the non-synchronous rotation rate, demonstrate the plausibility of episodic melt-through, show that characteristics of pits and uplift features do not imply thick ice, and demonstrate polar wander, i.e. that the ice crust is detached from the solid interior and has slipped as a unit relative to the spin axis. Thus Europa's biosphere (habitable if not inhabited) likely extends from within the ocean up to the surface, with important implications for exploration strategies: Life or its products may be relatively easy to reach, but Europa may be highly susceptible to biological contamination.

  15. Assessing Habitability: Lessons from the Phoenix Mission

    NASA Technical Reports Server (NTRS)

    Stoker, Carol R.

    2013-01-01

    The Phoenix mission's key objective was to search for a habitable zone. The Phoenix lander carried a robotic arm with digging scoop to collect soil and icy material for analysis with an instrument payload that included volatile mineral and organic analysis(3) and soil ionic chemistry analysis (4). Results from Phoenix along with theoretical modeling and other previous mission results were used to evaluate the habitability of the landing site by considering four factors that characterize the environments ability to support life as we know it: the presence of liquid water, the presence of an energy source to support metabolism, the presence of nutrients containing the fundamental building blocks of life, and the absence of environmental conditions that are toxic to or preclude life. Phoenix observational evidence for the presence of liquid water (past or present) includes clean segregated ice, chemical etching of soil grains, calcite minerals in the soil and variable concentrations of soluble salts5. The maximum surface temperature measured was 260K so unfrozen water can form only in adsorbed films or saline brines but warmer climates occur cyclically on geologically short time scales due to variations in orbital parameters. During high obliquity periods, temperatures allowing metabolism extend nearly a meter into the subsurface. Phoenix discovered 1%w/w perchlorate salt in the soil, a chemical energy source utilized by a wide range of microbes. Nutrient sources including C, H, N, O, P and S compounds are supplied by known atmospheric sources or global dust. Environmental conditions are within growth tolerance for terrestrial microbes. Summer daytime temperatures are sufficient for metabolic activity, the pH is 7.8 and is well buffered and the projected water activity of a wet soil will allow growth. In summary, martian permafrost in the north polar region is a viable location for modern life. Stoker et al. presented a formalism for comparing the habitability of various regions visited to date on Mars that involved computing a habitability probability, defined as the product of probabilities for the presence of liquid water (P(sub lw)), energy (P(sub e)), nutrients (P(sub ch)), and a benign environment (P(sub b)). Using this formalism, they argued that the Phoenix site was the most habitable of any site visited to date by landed missions and warranted a follow up mission to search for modern evidence of life. This paper will review that conclusion in view of more recent information from the Mars Exploration Rovers and Mars Science Lander missions.

  16. Endolithic microniches support habitability

    NASA Astrophysics Data System (ADS)

    Gómez, F.; Rodríguez, N.; Rodríguez-Manfredi, J. A.; Fernández-Sampedro, M.; Amils, R.

    2013-09-01

    Particular micro-niches on extreme environments give us some clues about the habitability potential under protected environments with important connotations from an astrobiological point of view [1]. The salts precipitation patters in extreme environments can contribute to biomineralization processes which could be of special interest for organics but also life preservation on environmental harsh conditions. These "oasys" for organics and/or life forms are of special as trobiological interest and should attract our attention in other planets and we should be looking for it during rover exploration missions. Endolithic micro niches in Rio Tinto salts precipitates determine controlled scenarios where phototrops develop under controlled conditions. Rio Tinto, 100 km river located at South West of Spain, is being taken as a well reported Mars analog due to the similarities in the mineralogy of the system which that reported by MER Opportunity Rover missions which landed in Meridiani Planum where sedimentary deposits have been identified in different craters [2]. Interesting multi layered salty deposits were identified in Rio Tinto source area where endolithic micro niches were settled [3]. Green layers appear included in brown stratified salt precipitates. The crust deposit was between 5 mm and 1 cm width. The layered structure is deposited over rocks or over man made structures as dam or mining tunnels walls but always in places with specific environmental characteristics. It appears in not direct Sun light exposed places (shadow side of walls) with thermal and pH stability.

  17. Using infrared observations of circumstellar dust around evolved stars to test dust formation hypotheses

    NASA Astrophysics Data System (ADS)

    Guha Niyogi, Suklima

    Asymptotic Giant Branch (AGB) stars are evolved, low to intermediate mass (0.8--8 M⊙ ) stars. These stars lose a significant fraction of their mass through stellar pulsation. As a result, they are surrounded by gaseous, dusty circumstellar envelopes. They are major contributors of material to the interstellar medium (ISM), new stars, planets and also produce the majority of the dust complement of galaxies. Consequently, understanding the dust around AGB stars is critical to our understanding of the contribution of dust to many aspects of astrophysics. This thesis aims to study how the mineralogy and morphology of circumstellar dust varies with the pulsation cycle of the star and how the variation in spectral dust features (temporally and spatially) can be explained by different competing dust formation hypotheses. In the circumstellar envelopes of oxygen-rich (O-rich) AGB stars, all carbon (C) atoms from the gas are locked into carbon-monoxide (CO), leaving a surplus of oxygen (O) atoms to dominate the chemistry and form silicate dust particles (among other dust species). Consequently, AGB stars are divided into two main categories: oxygen-rich (O-rich) and carbon-rich (C-rich). In this thesis I consider only O-rich AGB stars where silicate dust is expected to dominate. The silicate dust may be present in either crystalline or amorphous form, where the crystalline silicates exhibit sharp and narrow spectral features throughout the infrared (IR) spectral region, while the amorphous silicates show two broad spectral features at 10 and 18 mum. Circumstellar dust should vary both temporally as these stars pulsate; and spatially as dust flows away from the star and physical conditions change. My research on the temporal variation of the spectral dust features with pulsation cycle for single, O-rich Mira variable, T Cep, suggests that its spectral features cannot be explained in terms of the "classic" dust formation hypothesis. Instead, it suggests that the dust is crystalline in nature and iron-rich silicates, neither of which is expected around low mass-loss rate O-rich AGB stars. This scenario may be consistent with the so-called "chaotic solids" hypothesis. My research on spatial variation of spectral dust features investigates seven O-rich AGB stars for which I have acquired spatially resolved spectra using Gemini/MICHELLE spectrometer. In most cases, the observational data show that the spectral features vary significantly but without any spatial trend. These scenarios may also be consistent with the "chaotic solids" hypothesis. These results also suggest that the turbulent dynamics, pulsation shocks in the dust-forming zones around O-rich AGB stars lead to inhomogeneous dust formation, producing fine scale structure in the density of the dust envelope. In this O-rich environment, there are many potential minerals can be formed but their stability is very sensitive to the precise local conditions. In this thesis, I have also explored different parameter space of the IR laboratory spectra of crystalline olivine minerals. The spectral feature parameters (peak, width and amplitude) can be strongly affected by composition, temperature and grain shape and that can create degeneracy, such that a given spectral feature can have more than one explanation. In order to disentangle these effects, I have developed a database, which will allow to study the IR spectral features of crystalline olivine as a combined function of composition and temperature. For future work, I propose tools for mapping and breaking this degeneracy, which will help us in order to have a better understanding on astromineralogy around O-rich AGB stars. This thesis provides a significant contribution to our understanding of dust formation process around O-rich AGB stars, which is considered to be a complicated process and not well understood.

  18. Rotational Synchronization May Enhance Habitability for Circumbinary Planets: Kepler Binary Case Studies

    NASA Astrophysics Data System (ADS)

    Mason, Paul A.; Zuluaga, Jorge I.; Clark, Joni M.; Cuartas-Restrepo, Pablo A.

    2013-09-01

    We report a mechanism capable of reducing (or increasing) stellar activity in binary stars, thereby potentially enhancing (or destroying) circumbinary habitability. In single stars, stellar aggression toward planetary atmospheres causes mass-loss, which is especially detrimental for late-type stars, because habitable zones are very close and activity is long lasting. In binaries, tidal rotational breaking reduces magnetic activity, thus reducing harmful levels of X-ray and ultraviolet (XUV) radiation and stellar mass-loss that are able to erode planetary atmospheres. We study this mechanism for all confirmed circumbinary (p-type) planets. We find that main sequence twins provide minimal flux variation and in some cases improved environments if the stars rotationally synchronize within the first Gyr. Solar-like twins, like Kepler 34 and Kepler 35, provide low habitable zone XUV fluxes and stellar wind pressures. These wide, moist, habitable zones may potentially support multiple habitable planets. Solar-type stars with lower mass companions, like Kepler 47, allow for protected planets over a wide range of secondary masses and binary periods. Kepler 38 and related binaries are marginal cases. Kepler 64 and analogs have dramatically reduced stellar aggression due to synchronization of the primary, but are limited by the short lifetime. Kepler 16 appears to be inhospitable to planets due to extreme XUV flux. These results have important implications for estimates of the number of stellar systems containing habitable planets in the Galaxy and allow for the selection of binaries suitable for follow-up searches for habitable planets.

  19. ROTATIONAL SYNCHRONIZATION MAY ENHANCE HABITABILITY FOR CIRCUMBINARY PLANETS: KEPLER BINARY CASE STUDIES

    SciTech Connect

    Mason, Paul A.; Zuluaga, Jorge I.; Cuartas-Restrepo, Pablo A.; Clark, Joni M.

    2013-09-10

    We report a mechanism capable of reducing (or increasing) stellar activity in binary stars, thereby potentially enhancing (or destroying) circumbinary habitability. In single stars, stellar aggression toward planetary atmospheres causes mass-loss, which is especially detrimental for late-type stars, because habitable zones are very close and activity is long lasting. In binaries, tidal rotational breaking reduces magnetic activity, thus reducing harmful levels of X-ray and ultraviolet (XUV) radiation and stellar mass-loss that are able to erode planetary atmospheres. We study this mechanism for all confirmed circumbinary (p-type) planets. We find that main sequence twins provide minimal flux variation and in some cases improved environments if the stars rotationally synchronize within the first Gyr. Solar-like twins, like Kepler 34 and Kepler 35, provide low habitable zone XUV fluxes and stellar wind pressures. These wide, moist, habitable zones may potentially support multiple habitable planets. Solar-type stars with lower mass companions, like Kepler 47, allow for protected planets over a wide range of secondary masses and binary periods. Kepler 38 and related binaries are marginal cases. Kepler 64 and analogs have dramatically reduced stellar aggression due to synchronization of the primary, but are limited by the short lifetime. Kepler 16 appears to be inhospitable to planets due to extreme XUV flux. These results have important implications for estimates of the number of stellar systems containing habitable planets in the Galaxy and allow for the selection of binaries suitable for follow-up searches for habitable planets.

  20. Galactic Habitable Orbits

    NASA Astrophysics Data System (ADS)

    Rahimi, A.; Mao, S.; Kawata, D.

    2014-03-01

    The fossil record shows that the Earth has experienced several mass extinctions over the past 500 million years1, and it has been suggested that there is a periodicity in extinction events on timescales of tens1 and/or hundreds of millions of years. Various hypotheses have been proposed to explain the cause of the mass extinctions, including the suggestion that the Earth's ozone layer may have been destroyed by intense radiation from a nearby supernovae2- 3, exposing the Earth's surface to damaging UV radiation. Recent observations of cores taken from the ocean floor revealed atoms of a very rare isotope of iron (60Fe) believed to have arrived on Earth around 2 million years ago as fallout from a nearby supernovae4. Astronomical evidence for that past supernovae was recently found in the debris of a young cluster of massive stars5, by tracing its past orbit, putting it at the right place at the right time to explain the mild extinction event. Here we report new high-resolution (both in space and time) N-body chemodynamical simulations (carried out with our novel code GCD+6) of the evolution of a model Milky Way Galaxy, tracing the orbit of èsun-like' stars over a 500 million year period, checking the proximity to supernovae throughout the history of the orbit and comparing the times when this occurs with past mass extinctions on Earth. We additionally explain the important effects of the spiral arm pattern, radial migration of stars and Galactic chemistry on habitability.

  1. Managing away bad habits.

    PubMed

    Waldroop, J; Butler, T

    2000-01-01

    We've all worked with highly competent people who are held back by a seemingly fatal personality flaw. One person takes on too much work; another sees the downside in every proposed change; a third pushes people out of the way. At best, people with these "bad habits" create their own glass ceilings, which limit their success and their contributions to the company. At worst, they destroy their own careers. Although the psychological flaws of such individuals run deep, their managers are not helpless. In this article, James Waldroop and Timothy Butler--both psychologists--examine the root causes of these flaws and suggest concrete tactics they have used to help people recognize and correct the following six behavior patterns: The hero, who always pushes himself--and subordinates--too hard to do too much for too long. The meritocrat, who believes that the best ideas can and will be determined objectively and ignores the politics inherent in most situations. The bulldozer, who runs roughshod over others in a quest for power. The pessimist, who always worries about what could go wrong. The rebel, who automatically fights against authority and convention. And the home run hitter, who tries to do too much too soon--he swings for the fences before he's learned to hit singles. Helping people break through their self-created glass ceilings is the ultimate win-win scenario: both the individual and the organization are rewarded. Using the tactics introduced in this article, managers can help their brilliantly flawed performers become spectacular achievers. PMID:11143157

  2. ISOPHOT Observations of the Circumstellar Environment of Young Stars

    NASA Astrophysics Data System (ADS)

    brahm, P.; Leinert, Ch.; Lemke, D.; Burkert, A.; Henning, T. H.

    The young pre-main sequence T Tau and Herbig Ae/Be stars are associated with circumstellar dust, whose thermal emission can be observed at infrared wavelengths. We report on 3.6-200 micron photometric observations performed with ISOPHOT, the photometer on-board the Infrared Space Observatory. Seven Herbig Ae/Be stars were observed at mid- and far-infrared wavelengths. At ??25?m the emission mainly arises from a compact circumstellar region, and the observed spectral energy distributions follow the power-law relationship F???-n with n typically around 1. The peak of the SEDs (in F?) is at 60-100?m, corresponding to temperatures of around 50 K. At longer wavelengths the observed emission is spatially extended, and at ?>100?m the emission observed by ISOPHOT is never dominated by the Herbig Ae/Be stars. The most likely sources of the far-infrared radiation are arcminute size dust cores located in the vicinity of the stars, and probably related to the star forming process. We also analysed ISOPHOT observations of 16 binary T Tau stars. For the 7 brightest objects the broad-band photometry was supplemented by 2.5-11.7?m spectrophotometry obtained by the PHT-S subinstrument. In most cases strong silicate emission at 10?m was detected with some indications for the presence of crystalline silicate. The comparison of the derived SEDs with those of single T Tau stars will help to understand how the presence of companions could affect the evolution of the circumstellar disks.

  3. Cepheids at high angular resolution: circumstellar envelope and pulsation

    NASA Astrophysics Data System (ADS)

    Gallenne, Alexandre

    2011-12-01

    In 2005, interferometric observations with VLTI/VINCI and CHARA/FLUOR revealed the existence of a circumstellar envelope (CSE) around some Cepheids. This surrounding material is particularly interesting for two reasons: it could have an impact on the distance estimates and could be linked to a past or on-going mass loss. The use of Baade-Wesselink methods for independent distance determinations could be significantly biased by the presence of these envelopes. Although their observations are difficult because of the high contrast between the photosphere of the star and the CSE, several observation techniques have the potential to improve our knowledge about their physical properties. In this thesis, I discuss in particular high angular resolution techniques that I applied to the study of several bright Galactic Cepheids. First, I used adaptive optic observations with NACO of the Cepheid RS Puppis, in order to deduce the flux ratio between the CSE and the photosphere of the star. In addition, I could carry out a statistical study of the speckle noise and inspect a possible asymmetry. Secondly, I analysed VISIR data to study the spectral energy distribution of a sample of Cepheids. These diffraction-limited images enabled me to carry out an accurate photometry in the N band and to detect an IR excess linked to the presence of a circumstellar component. On the other hand, applying a Fourier analysis I showed that some components are resolved. I then explored the K' band with the recombination instrument FLUOR for some bright Cepheids. Thanks to new set of data of Y Oph, I improved the study of its circumstellar envelope, using a ring-like model for the CSE. For two other Cepheids, U Vul and S Sge, I applied the interferometric Baade-Wesselink method in order to estimate their distance.

  4. Evidence for dust grain growth in young circumstellar disks.

    PubMed

    Throop, H B; Bally, J; Esposito, L W; McCaughrean, M J

    2001-06-01

    Hundreds of circumstellar disks in the Orion nebula are being rapidly destroyed by the intense ultraviolet radiation produced by nearby bright stars. These young, million-year-old disks may not survive long enough to form planetary systems. Nevertheless, the first stage of planet formation-the growth of dust grains into larger particles-may have begun in these systems. Observational evidence for these large particles in Orion's disks is presented. A model of grain evolution in externally irradiated protoplanetary disks is developed and predicts rapid particle size evolution and sharp outer disk boundaries. We discuss implications for the formation rates of planetary systems. PMID:11326083

  5. AMBER/VLTI Snapshot Survey on Circumstellar Environments

    NASA Astrophysics Data System (ADS)

    Rivinius, Th.; de Wit, W. J.; Demers, Z.; Quirrenbach, A.

    2015-01-01

    OHANA is an interferometric snapshot survey of the gaseous circumstellar environments of hot stars, carried out by the VLTI group at the Paranal observatory. It aims to characterize the mass-loss dynamics (winds/disks) at unexplored spatial scales for many stars. The survey employs the unique combination of AMBER's high spectral resolution with the unmatched spatial resolution provided by the VLTI. Because of the spatially unresolved central OBA-type star, with roughly neutral colour terms, their gaseous environments are among the easiest objects to be observed with AMBER, yet the extent and kinematics of the line emission regions are of high astrophysical interest.

  6. On the Inner Circumstellar Envelopes of R Coronae Borealis Stars

    NASA Astrophysics Data System (ADS)

    Leão, I. C.; Bright, S. N.; Chesneau, O.

    2015-12-01

    We present different analyses of Very Large Telescope Interferometer (VLTI) data to interpret the inner circumstellar envelope (CSE) morphology of R Coronae Borealis (RCB) stars. Three objects were considered: RY Sgr, V CrA, and V854 Cen. Chi-squared maps of different geometrical models allow to identify a reasonable description of these CSEs, which can be further studied in radiative transfer codes. Overall, the inner CSE morphology of these RCB stars are consistent with a central star surrounded by a dusty shell with at least a bright clump (or a dust cluster).

  7. Photochemistry and molecular ions in oxygen-rich circumstellar envelopes

    NASA Technical Reports Server (NTRS)

    Mamon, G. A.; Glassgold, A. E.; Omont, A.

    1987-01-01

    A theory for the ionization of the circumstellar envelopes around O-rich red giants is developed from the photochemical model. The main source of ionization is photoionization of H2O, OH, and C by the interstellar UV radiation field, supplemented by cosmic-ray ionization of hydrogen. Significant amounts of H3O(+) and HCO(+) are produced, with peak abundances of about 10 to the -7th at intermediate distances from the star. Although H3O(+) may be difficult to detect with current instrumentation, HCO(+) is probably detectable in nearby O-rich envelopes with large millimeter-wave telescopes.

  8. Detection of circumstellar gas associated with GG Tauri

    NASA Technical Reports Server (NTRS)

    Skrutskie, M. F.; Snell, R. L.; Strom, K. M.; Strom, S. E.; Edwards, S.; Fukui, Y.; Mizuno, A.; Hayashi, M.; Ohashi, N.

    1993-01-01

    Double-peaked (C-12)O (1-0) emission centered on the young T Tauri star GG Tau possesses a line profile which may be modeled on the assumption that CO emission arises in an extended circumstellar disk. While bounds on the observed gas mass can be estimated on this basis, it is suggested that a large amount of mass could lie within a small and optically thick region, escaping detection due to beam-dilution effects. In addition, CO may no longer accurately trace the gas mass due to its dissociation, or freezing into grains, or due to the locking-up of carbon into more complex molecules.

  9. Direct UV observations of the circumstellar envelope of alpha Orionis

    NASA Technical Reports Server (NTRS)

    Stencel, R. E.; Carpenter, K. G.; Pesce, J. E.; Skinner, S.; Brown, A.; Judge, P.

    1988-01-01

    Observations were made in the IUE LWP camera, low dispersion mode, with alpha Ori being offset various distances from the center of the Long Wavelength Large Aperture along its major axis. Signal was acquired at all offset positions and is comprised of unequal components of background/dark counts, telescope-scattered light, and scattered light emanating from the extended circumstellar shell. The star is known from optical and infrared observations to possess an extended, arc-minute sized, shell of cool material. Attempts to observe this shell with the IUE are described, although the deconvolution of the stellar signal from the telescope scattered light requires further calibration effort.

  10. Habitability of the Phoenix landing site

    NASA Astrophysics Data System (ADS)

    Stoker, Carol R.; Zent, Aaron; Catling, David C.; Douglas, Susanne; Marshall, John R.; Archer, Douglas; Clark, Benton; Kounaves, Samuel P.; Lemmon, Mark T.; Quinn, Richard; Renno, Nilton; Smith, Peter H.; Young, Suzanne M. M.

    2010-06-01

    The Phoenix mission's key objective was to search for a habitable zone. Mission results are used to evaluate habitability where Phoenix landed. A habitability probability (HI) is defined as the product of probabilities for the presence of liquid water (Plw), energy (Pe), nutrients (Pch), and a benign environment (Pb). Observational evidence for the presence of liquid water (past or present) includes clean ice at a polygon boundary, chemical etching of soil grains, and carbonate minerals. The presence of surface and near subsurface ice, along with thermodynamic conditions that support melting, suggest that liquid water is theoretically possible. Presently, unfrozen water can form only in adsorbed films or saline brines but more clement conditions recur periodically due to variations in orbital parameters. Energy to drive metabolism is available from sunlight, when semitransparent soil grains provide shielding from UV radiation and chemical energy from the redox couple of perchlorate and reduced iron. Nutrient sources including C, H, N, O, P, and S compounds are supplied by known atmospheric sources or global dust. Environmental conditions are within growth tolerance for terrestrial microbes. Surface soil temperatures currently reach 260 K and are periodically much higher, the pH is 7.8 and is well buffered, and the water activity is high enough to allow growth when sufficient water is available. Computation of HI for the sites visited by landers yields Phoenix, 0.47; Meridiani, 0.23; Gusev, 0.22; Pathfinder, 0.05; Viking 1, 0.01; Viking 2, 0.07. HI for the Phoenix site is the largest of any site explored, but dissimilar measurements limit the comparisons' confidence.

  11. Constraints on planetary habitability from interior modelling

    NASA Astrophysics Data System (ADS)

    Noack, Lena; Godolt, Mareike; von Paris, Philip; Plesa, Ana-Catalina; Stracke, Barbara; Breuer, Doris; Rauer, Heike

    2013-04-01

    The most interesting planetary bodies outside the Solar System regarding the search for life are potentially rocky extrasolar planets. Some of them may feature surface conditions that allow for liquid water, which is the elementary prerequisite for life as we know it. The amount of greenhouse gases, like e.g. carbon dioxide (CO2), plays an important role for the determination of the surface temperature, hence the habitability of an extrasolar planet. The amount of greenhouse gases is strongly influenced by their outgassing from the interior. In this study, we investigate under which conditions the planetary interior structure and dynamics allow for the build-up of planetary atmospheres which may lead to habitable surface conditions. We investigate the evolution of a secondary atmosphere for Earth-sized planets with different interior structures (i.e. iron-silicate mixing ratios) by applying a two-dimensional model of interior dynamics [1], which allows for the calculation of the production of partial melt [2]. From this, we estimate the amount of CO2 outgassing for Earth-sized planets with different core and mantle radii after adapting the total CO2 outgassing in 4.5 Gyr for a Venus reference simulation to the present-day atmosphere of Venus. We furthermore investigate the possible influence of plate tectonics on outgassing and the likelihood of plate tectonics depending on the interior structure of the planet. We find that the size of the iron core has a large impact on the production of partial melt, hence on the possible outgassing of CO2, which is due to the pressure-dependence of the melting temperature of silicate rocks: for planets with a large core the planetary mass is larger than for a planet with a small iron core, leading to larger melting temperatures in the upper mantle. Therefore only little outgassing from the interior can be expected. However, for the determination of the outer edge of the habitable zone it is typically assumed that enough greenhouse gas CO2 is available in the atmosphere to lead to liquid water at the surface - independent of the interior of the planet [3]. Our results on the other hand suggest that the outer boundary of the habitable zone may be constrained by the production of partial melt in the interior for planets with a large iron core and a thin silicate mantle. However, if plate tectonics initiates, several tens of bars of CO2 can be outgassed in a short time also for planets with a large iron core. In this case the outer boundary of the habitable zone would not be limited by outgassing as is the case for stagnant-lid planets. It is, however, questionable if planets with a very thin mantle are able to initiate plate tectonics. References [1] Hüttig, C. and Stemmer, K. (2008), PEPI, 171(1-4):137-146. [2] Plesa, A.-C. and Spohn, T. (2012), Transactions of the HLRS 2011, Springer, 551-565. [3] Kasting, J., Whitmire, D.P. and Reynolds, R.T. (1993), Icarus, 101:108-128.

  12. Rotating Stars Can Help Planets Become Habitable

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-12-01

    What characteristics must a terrestrial planet exhibit to have the potential to host life? Orbiting within the habitable zone of its host star is certainly a good start, but theres another important aspect: the planet has to have the right atmosphere. A recent study has determined how host stars can help their planets to lose initial, enormous gaseous envelopes and become more Earth-like.Collecting An EnvelopeWhen a terrestrial planet forms inside a gaseous protoplanetary disk, it can accumulate a significant envelope of hydrogen gas causing the planet to bear more similarity to a mini-Neptune than to Earth. Before the planet can become habitable, it must shed this enormous, primordial hydrogen envelope, so that an appropriate secondary atmosphere can form.So what determines whether a planet can get rid of its protoatmosphere? The dominant process for shedding a hydrogen atmosphere is thermal mass loss: as the planets upper atmosphere is heated by X-ray and extreme-ultraviolet (XUV) radiation from the host star, the envelope evaporates.A Critical DependenceIn a recent study led by Colin Johnstone (University of Vienna), a team of scientists has developed models of this evaporation process for hydrogen planetary atmospheres. In particular, Johnstone and collaborators examine how the host stars initial rotation rate which strongly impacts the stars level of XUV activity affects the degree to which the planets hydrogen atmosphere is evaporated, and the rate at which the evaporation occurs.The authors findings can be illustrated with the example of an Earth-mass planet located in the habitable zone of a solar-mass star. In this case, the authors find four interesting regimes (shown in the plot to the right):Evolution of the hydrogen protoatmosphere of an Earth-mass planet in the habitable zone of a solar-mass star. The four lettered cases describe different initial atmospheric masses. The three curves for each case describe the stellar rotation rate: slow (red), average (green), or fast (blue). [Johnstone et al. 2015]Case A(Initial atmospheric mass of 10-4 Earth masses)Entire atmosphere evaporates quickly, regardless of the rotation speed of the host star.Case B(Initial atmospheric mass of 10-3 Earth masses)Entire atmosphere evaporates, but the timescale is much shorter if the stellar host is fast-rotating as opposed to slow-rotating.Case C(Initial atmospheric mass of 10-2 Earth masses)If the stellar host is fast-rotating, entire atmosphere evaporates on a short timescale. If the host is slow-rotating, very little of the atmosphere evaporates.Case D(Initial atmospheric mass of 10-1 Earth masses)Very little of the atmosphere evaporates, regardless of the rotation speed of the host star.These results demonstrate that the initial rotation rate of a host star not only determines whether a planet will lose its protoatmosphere, but also how long this process will take. Thus, the evolution of host stars rotation rates is an important component in our understanding of how planets might evolve to become habitable.CitationC. P. Johnstone et al 2015 ApJ 815 L12. doi:10.1088/2041-8205/815/1/L12

  13. Detecting Habitable Planets via Astrometry in Current Planetary Systems

    NASA Astrophysics Data System (ADS)

    Liu, Hui-Gen

    2015-08-01

    We explore the potential of astrometry method in finding habitable planets orbiting nearby solar-like stars. We consider different types of planet systems with an undiscovered habitable Earth-like exoplanets in them. We simulate their astrometry signals and use our code to fit the masses and orbits of the habitable planets. When comparing our fitting results with the real ones, we find the threshold of different noise levels and the detection potential in different planet systems. We find astrometry is nearly suitable for all kinds of planet systems we discover today. Only in the case when the other planets in the systems have very short periods(less than 3 days) or long period about 30 years, the fitting errors of the giant planets lead to large fitting errors of the habitbale Earth-like planets. After adding noise in the astrometry data, the fitting of the orbital elemants, such as the eccentricity and inclination, becomes difficult. Under the presicion of 0.3 uas, we suggest 10 earth mass is the boundary of good-fitting, compared to 100 earth mass under the precision of 10 uas. At last, we simulate the discovered planet systems in 50 pc, assuming that 10 earth mass is in the habitable zone at about 1 AU, we use the fitting results of their masses, semi-major axes, eccentricities and inclinations to give a rank to suggest the possibility of discovering habitable exoplanets in these systems.

  14. Children's Work Habits and Reading Performance.

    ERIC Educational Resources Information Center

    Schroeder, Tom S.

    Two types of problems are found in the reading performance of children with poor work habits: a child may have mastered skills but performs inadequately in tasks due to poor work habits, and a child may never have mastered skills because of such habits. Work habit behavior is the student's tendency to apply himself or herself to learning tasks by…

  15. A Habitability Test of the Exoplanetary System K2-3

    NASA Astrophysics Data System (ADS)

    Diaz-Perez, Ryan; Kipping, David M.; Johnson, John A.

    2016-01-01

    The question of habitability is one of the most interesting questions in exoplanetary science. By studying the orbital properties of a planet, like it's eccentricity and habitable zone inner edge distance we can answer this question. Here we answer the habitability question for the planets in the exoplanetary system K2-3 discovered by the Kepler 2 spacecraft. The system is compose of three planets with radii 1.61-2.17 Rearth, and with orbital periods of 10-45 days. The most outer planet in this system known as K2-3d is particularly interesting due to its proximity towards the habitable zone. The eccentricities of the planets in K2-3 were calculated using a method known as stellar density profiling, and from these eccentricities the range of the semi-major axis were determined. The planet K2-3d was calculated to have a semi-major axis of 0.18 AU, which puts it outside the habitable zone where inner edge of the habitable zone is 0.27 AU from its host star. This project was supported by the The Harvard Banneker Institute.

  16. Habitable moons around extrasolar giant planets

    NASA Technical Reports Server (NTRS)

    Williams, D. M.; Kasting, J. F.; Wade, R. A.

    1997-01-01

    Possible planetary objects have now been discovered orbiting nine different main-sequence stars. These companion objects (some of which might actually be brown dwarfs) all have a mass at least half that of Jupiter, and are therefore unlikely to be hospitable to Earth-like life: jovian planets and brown dwarfs support neither a solid nor a liquid surface near which organisms might dwell. Here we argue that rocky moons orbiting these companions could be habitable if the planet-moon system orbits the parent star within the so-called 'habitable zone', where life-supporting liquid water could be present. The companions to the stars 16 Cygni B and 47 Ursae Majoris might satisfy this criterion. Such a moon would, however, need to be large enough (>0.12 Earth masses) to retain a substantial and long-lived atmosphere, and would also need to possess a strong magnetic field in order to prevent its atmosphere from being sputtered away by the constant bombardment of energetic ions from the planet's magnetosphere.

  17. Can habitable planets form in clustered environments?

    NASA Astrophysics Data System (ADS)

    de Juan Ovelar, M.; Kruijssen, J. M. D.; Bressert, E.; Testi, L.; Bastian, N.; Cánovas, H.

    2012-10-01

    We present observational evidence of environmental effects on the formation and evolution of planetary systems. We combine catalogues of resolved protoplanetary discs (PPDs) and young stellar objects in the solar neighbourhood to analyse the PPD size distribution as a function of ambient stellar density. By running Kolmogorov-Smirnov tests between the PPD radii at different densities, we find empirical evidence, at the >97% confidence level, for a change in the PPD radius distribution at ambient stellar densities Σ ≳ 103.5 pc-2. This coincides with a simple theoretical estimate for the truncation of PPDs or planetary systems by dynamical encounters. If this agreement is causal, the ongoing disruption of PPDs and planetary systems limits the possible existence of planets in the habitable zone, with shorter lifetimes at higher host stellar masses and ambient densities. Therefore, habitable planets are not likely to be present in long-lived stellar clusters, and may have been ejected altogether to form a population of unbound, free-floating planets. We conclude that, while highly suggestive, our results should be verified through other methods. Our simple model shows that truncations should lead to a measurable depletion of the PPD mass function that can be detected with ALMA observations of the densest nearby and young clusters. Appendices are available in electronic form at http://www.aanda.org

  18. On the inclination and habitability of the HD 10180 system

    SciTech Connect

    Kane, Stephen R.; Gelino, Dawn M.

    2014-09-10

    There are numerous multi-planet systems that have now been detected via a variety of techniques. These systems exhibit a range of both planetary properties and orbital configurations. For those systems without detected planetary transits, a significant unknown factor is the orbital inclination. This produces an uncertainty in the mass of the planets and their related properties, such as atmospheric scale height. Here we investigate the HD 10180 system, which was discovered using the radial velocity technique. We provide a new orbital solution for the system which allows for eccentric orbits for all planets. We show how the inclination of the system affects the mass/radius properties of the planets and how the detection of phase signatures may resolve the inclination ambiguity. We finally evaluate the Habitable Zone properties of the system and show that the g planet spends 100% of an eccentric orbit within the Habitable Zone.

  19. Are young supernova remnants interacting with circumstellar gas

    SciTech Connect

    Chevalier, R.A.

    1982-08-15

    The young remnants of galactic Type I supernovae (SN 1006, SN 1572, and SN 1604) appear to be interacting with moderately dense gas (n/sub O/> or =0.1 cm/sup -3/). If the gas in the ambient interstellar medium, the observations suggest that gas of this density is fairly pervasive. If the gas is circumstellar, there are important implications for the progenitors of Type I supernovae. A plausible density distribution for circumstellar gas is rhoinfinityr/sup -2/. The expansion of a supernova into such a medium is examined and is compared with expansion into a uniform medium. The two cases can be distinguished on the basis of their density profiles and their rates of expansion. Currently available data factor the hypothesis of expansion in a uniform medium for all three Type I remnants; the evidence is the strongest for SN 1572 and the weakest for SN 1604. Further X-ray and radio observations of the galactic remnants and of extragalactic Type I supernovae should serve to test this hypothesis.

  20. On the gas temperature in circumstellar disks around A stars

    NASA Astrophysics Data System (ADS)

    Kamp, I.; van Zadelhoff, G.-J.

    2001-07-01

    In circumstellar disks or shells it is often assumed that gas and dust temperatures are equal where the latter is determined by radiative equilibrium. This paper deals with the question whether this assumption is applicable for tenuous circumstellar disks around young A stars. In this paper the thin hydrostatic equilibrium models described by Kamp & Bertoldi (\\cite{Kamp}) are combined with a detailed heating/cooling balance for the gas. The most important heating and cooling processes are heating through infrared pumping, heating due to the drift velocity of dust grains, and fine structure and molecular line cooling. Throughout the whole disk gas and dust are not efficiently coupled by collisions and hence their temperatures are quite different. Most of the gas in the disk models considered here stays well below 300 K. In the temperature range below 300 K the gas chemistry is not much affected by Tgas and therefore the simplifying approximation Tgas = Tdust can be used for calculating the chemical structure of the disk. Nevertheless the gas temperature is important for the quantitative interpretation of observations, like fine structure and molecular lines.

  1. Probing Pre-Supernova Mass Loss With Circumstellar Dust Shells

    NASA Astrophysics Data System (ADS)

    Fox, Ori; Filippenko, Alex; Skrutskie, Mike; van Dyk, Schuyler; Kelly, Pat

    2014-12-01

    Late-time (>100 day) mid-infrared (mid-IR) observations of supernovae (SNe) offer a valuable probe of the progenitor system's mass-loss. Already, this technique has been demonstrated with the Type IIn subclass, which often have large, dusty, pre-existing shells formed in pre-SN eruptions. While other SN subclasses are thought of having relatively low density circumstellar environments, a growing number of objects in other subclasses now show evidence for significant pre-SN mass loss and similar mid-IR characteristics. Long after the SN radioactive tail fades, warm dust can stay bright at mid-IR wavelengths due to alternative heating mechanisms, such as shocks. Here we propose a SNAPSHOT survey of a well-studied and high-profile SN sample, extending over a range of subclasses, including both recent and historical events with evidence of a dense CSM and/or dust. This program will (a) discover new SNe with warm dust and (b) monitor the evolution of warm dust in previously detected SNe. Harnessing the success of our previous Spitzer programs, these observations will expand upon that work by probing the similarities in and differences between the subclasses' circumstellar environments, pre-SN mass-loss, and ultimately, the progenitors themselves.

  2. Circumstellar Dust in the Remnant of Kepler's Type Ia Supernova

    NASA Astrophysics Data System (ADS)

    Williams, Brian J.; Blair, W. P.; Borkowski, K. J.; Ghavamian, P.; Long, K. S.; Reynolds, S. P.; Sankrit, R.

    2012-01-01

    Kepler's Supernova Remnant, the remains of the supernova of 1604, is widely believed to be the result of a Type Ia supernova, and shows IR, optical, and X-ray evidence for an interaction of the blast wave with a dense circumstellar medium (CSM). We present low-resolution 7.5-38 μm IR spectra of selected regions within the remnant, obtained with the Spitzer Space Telescope. Spectra of those regions where the blast wave is encountering circumstellar material show strong features at 10 and 18 μm. These spectral features are most consistent with various silicate particles, likely formed in the stellar outflow from the progenitor system during the AGB stage of evolution. While it is possible that some features may arise from freshly formed ejecta dust, morphological evidence suggests that it is more likely that they originate from dust in the CSM. We isolate the dust grain absorption efficiencies for several regions in Kepler and compare them to laboratory data for dust particles of various compositions. The hottest dust in the remnant originates in the regions of dense, radiatively shocked clumps of gas, identified in optical images. Models of collisionally heated dust show that such shocks are capable of heating grains to temperatures of > 150 K. We confirm the finding that Kepler's SNR is still interacting with CSM in at least part of the remnant after 400 years. The significant quantities of silicate dust are consistent with a relatively massive progenitor.

  3. THE PROGENITOR OF SN 2011ja: CLUES FROM CIRCUMSTELLAR INTERACTION

    SciTech Connect

    Chakraborti, Sayan; Ray, Alak; Yadav, Naveen; Smith, Randall; Ryder, Stuart; Sutaria, Firoza; Dwarkadas, Vikram V.; Chandra, Poonam; Pooley, David; Roy, Rupak

    2013-09-01

    Massive stars, possibly red supergiants, which retain extended hydrogen envelopes until core collapse, produce Type II plateau (IIP) supernovae. The ejecta from these explosions shocks the circumstellar matter originating from the mass loss of the progenitor during the final phases of its life. This interaction accelerates particles to relativistic energies which then lose energy via synchrotron radiation in the shock-amplified magnetic fields and inverse Compton scattering against optical photons from the supernova. These processes produce different signatures in the radio and X-ray parts of the electromagnetic spectrum. Observed together, they allow us to break the degeneracy between shock acceleration and magnetic field amplification. In this work, we use X-rays observations from the Chandra and radio observations from the Australia Telescope Compact Array to study the relative importance of processes which accelerate particles and those which amplify magnetic fields in producing the non-thermal radiation from SN 2011ja. We use radio observations to constrain the explosion date. Multiple Chandra observations allow us to probe the history of variable mass loss from the progenitor. The ejecta expands into a low-density bubble followed by interaction with a higher density wind from a red supergiant consistent with M{sub ZAMS} {approx}> 12 M{sub Sun }. Our results suggest that a fraction of Type IIP supernovae may interact with circumstellar media set up by non-steady winds.

  4. An energetic stellar outburst accompanied by circumstellar light echoes.

    PubMed

    Bond, Howard E; Henden, Arne; Levay, Zoltan G; Panagia, Nino; Sparks, William B; Starrfield, Sumner; Wagner, R Mark; Corradi, R L M; Munari, U

    2003-03-27

    Some classes of stars, including novae and supernovae, undergo explosive outbursts that eject stellar material into space. In 2002, the previously unknown variable star V838 Monocerotis brightened suddenly by a factor of approximately 10(4). Unlike a supernova or nova, it did not explosively eject its outer layers; rather, it simply expanded to become a cool supergiant with a moderate-velocity stellar wind. Superluminal light echoes were discovered as light from the outburst propagated into the surrounding, pre-existing circumstellar dust. Here we report high-resolution imaging and polarimetry of those light echoes, which allow us to set direct geometric distance limits to the object. At a distance of >6 kpc, V838 Mon at its maximum brightness was temporarily the brightest star in the Milky Way. The presence of the circumstellar dust implies that previous eruptions have occurred, and spectra show it to be a binary system. When combined with the high luminosity and unusual outburst behaviour, these characteristics indicate that V838 Mon represents a hitherto unknown type of stellar outburst, for which we have no completely satisfactory physical explanation. PMID:12660776

  5. Far-Infrared Water Line Emissions from Circumstellar Outflows

    NASA Technical Reports Server (NTRS)

    Chen, Wesley; Neufeld, David A.

    1995-01-01

    We have modeled the far-infrared water line emission expected from circumstellar outflows from oxygen-rich late-type stars, as a function of the mass-loss rate and the terminal outflow velocity. For each mass-loss rate and terminal outflow velocity considered, we computed self-consistently the gas density, temperature, outflow velocity, and water abundance as a function of distance from the star. We then used an escape probability method to solve for the equilibrium level populations of 80 rotational states of water and thereby obtained predictions for the luminosity of a large number of far-infrared rotational transitions of water. In common with previous models, our model predicts that water will be copiously produced in the warm circumstellar gas and that water rotational emission will dominate the radiative cooling. However, our use of a realistic radiative cooling function for water leads to a lower gas temperature than that predicted in previous models. Our predictions for the far-infrared water line luminosities are consequently significantly smaller than those obtained in previous studies. Observations to be carried out by the Infrared Space Observatory will provide a crucial test of the models presented here.

  6. The Progenitor of SN 2011ja: Clues from Circumstellar Interaction

    NASA Astrophysics Data System (ADS)

    Chakraborti, Sayan; Ray, Alak; Smith, Randall; Ryder, Stuart; Yadav, Naveen; Sutaria, Firoza; Dwarkadas, Vikram V.; Chandra, Poonam; Pooley, David; Roy, Rupak

    2013-09-01

    Massive stars, possibly red supergiants, which retain extended hydrogen envelopes until core collapse, produce Type II plateau (IIP) supernovae. The ejecta from these explosions shocks the circumstellar matter originating from the mass loss of the progenitor during the final phases of its life. This interaction accelerates particles to relativistic energies which then lose energy via synchrotron radiation in the shock-amplified magnetic fields and inverse Compton scattering against optical photons from the supernova. These processes produce different signatures in the radio and X-ray parts of the electromagnetic spectrum. Observed together, they allow us to break the degeneracy between shock acceleration and magnetic field amplification. In this work, we use X-rays observations from the Chandra and radio observations from the Australia Telescope Compact Array to study the relative importance of processes which accelerate particles and those which amplify magnetic fields in producing the non-thermal radiation from SN 2011ja. We use radio observations to constrain the explosion date. Multiple Chandra observations allow us to probe the history of variable mass loss from the progenitor. The ejecta expands into a low-density bubble followed by interaction with a higher density wind from a red supergiant consistent with M ZAMS >~ 12 M ?. Our results suggest that a fraction of Type IIP supernovae may interact with circumstellar media set up by non-steady winds.

  7. Extreme Carbon Overabundance in the 49 Ceti Circumstellar Gas

    NASA Astrophysics Data System (ADS)

    Roberge, Aki; Welsh, Barry; Kamp, Inga; Weinberger, Alycia J.; Grady, Carol A.

    2015-01-01

    We present analysis of C and O absorption in high-resolution HST-STIS FUV spectra of the nearby A1V star 49 Ceti. This disk system is one of the few showing the dust properties of a debris disk, but harboring relatively abundant molecular gas more characteristic of a low-mass protoplanetary disk. Since the disk is nearly edge-on, the line-of-sight to the central star passes through the disk, permitting sensitive probes of the circumstellar gas with absorption spectroscopy.Our FUV spectra show many narrow circumstellar gas lines arising from several atomic species, including neutral carbon (a gas not seen in the local ISM) and neutral oxygen. We present an estimate of the total carbon column density in the line-of-sight gas and limits on the oxygen column density. Comparing the carbon abundance to a previous measurement of the line-of-sight iron abundance, we see that the carbon is extremely overabundant relative to the solar abundance. A similar overabundance is seen in the Beta Pic disk gas, where the carbon brakes other gases from being rapidly blown out by radiation pressure. The carbon in the 49 Cet gas may play a similar role.

  8. Carbon stars with oxygen-rich circumstellar material

    NASA Technical Reports Server (NTRS)

    Jura, Michael; Hawkins, I.

    1991-01-01

    The IUE satellite was used to search for companions to two carbon-rich stars with oxygen-rich circumstellar envelopes, EU And and V778 Cyg. Depending upon the amount of interstellar extinction and distances (probably between 1 and 2 kpc from the Sun) to these two stars, upper limits were placed between approx. 1.5 and 6 solar mass to the mass of any main sequence companions. For the 'near' distance of 1 kpc, it seems unlikely that there are white dwarf companions because the detection would be expected of ultraviolet emission from accretion of red giant wind material onto the white dwarf. A new model is proposed to explain the oxygen-rich envelopes. If these stars have a high nitrogen abundance, the carbon that is in excess of the oxygen may be carried in the circumstellar envelopes in HCN rather than C2H2 which is a likely key seed molecule for the formation of carbon grains. Consequently, carbon particles may not form; instead, oxygen-rich silicate dust may nucleate from the SiO present in the outflow.

  9. Attenuation of supersoft X-ray sources by circumstellar material

    NASA Astrophysics Data System (ADS)

    Nielsen, M. T. B.; Gilfanov, M.

    2015-11-01

    Recent studies have suggested the possibility of significantly obscuring supersoft X-ray sources in relatively modest amounts of local matter lost from the binaries themselves. If correct, then this would have explained the paucity of observed supersoft X-ray sources and would have significance for the search for single-degenerate Type Ia supernova progenitors. We point out that earlier studies of circumbinary obscuration ignored photoionizations of the gas by the emission from the supersoft X-ray source. We revisit the problem using a full, self-consistent calculation of the ionization state of the circumbinary material photoionized by the radiation of the central source. Our results show that the circumstellar mass-loss rates required for obscuration of supersoft X-ray sources is about an order of magnitude larger than those reported in earlier studies, for comparable model parameters. While this does not entirely rule out the possibility of circumstellar material obscuring supersoft X-ray sources, it makes it unlikely that this effect alone can account for the majority of the missing supersoft X-ray sources. We discuss the observational appearance of hypothetical obscured nuclear-burning white dwarfs and show that they have signatures making them distinct from photoionized nebulae around supersoft X-ray sources imbedded in the low-density interstellar medium.

  10. Archival legacy investigations of circumstellar environments: overview and first results

    NASA Astrophysics Data System (ADS)

    Choquet, Élodie; Pueyo, Laurent; Hagan, J. Brendan; Gofas-Salas, Elena; Rajan, Abhijith; Chen, Christine; Perrin, Marshall D.; Debes, John; Golimowski, David; Hines, Dean C.; N'Diaye, Mamadou; Schneider, Glenn; Mawet, Dimitri; Marois, Christian; Soummer, Rémi

    2014-08-01

    We are currently conducting a comprehensive and consistent re-processing of archival HST-NICMOS coronagraphic surveys using advanced PSF subtraction methods, entitled the Archival Legacy Investigations of Circumstellar Environments program (ALICE, HST/AR 12652). This virtual campaign of about 400 targets has already produced numerous new detections of previously unidentified point sources and circumstellar structures. We present five newly spatially resolved debris disks revealed in scattered light by our analysis of the archival data. These images provide new views of material around young solar-type stars at ages corresponding to the period of terrestrial planet formation in our solar system. We have also detected several new candidate substellar companions, for which there are ongoing followup campaigns (HST/WFC3 and VLT/SINFONI in ADI mode). Since the methods developed as part of ALICE are directly applicable to future missions (JWST, AFTA coronagraph) we emphasize the importance of devising optimal PSF subtraction methods for upcoming coronagraphic imaging missions. We describe efforts in defining direct imaging high-level science products (HLSP) standards that can be applicable to other coronagraphic campaigns, including ground-based (e.g., Gemini Planet Imager), and future space instruments (e.g., JWST). ALICE will deliver a first release of HLSPs to the community through the MAST archive at STScI in 2014.

  11. Probing Pre-Supernova Mass Loss With Circumstellar Dust Shells

    NASA Astrophysics Data System (ADS)

    Fox, Ori; Filippenko, Alex; Skrutskie, Mike; van Dyk, Schuyler; Kelly, Pat

    2013-10-01

    Late-time (>100 day) mid-infrared (mid-IR) observations of supernovae (SNe) offer a valuable probe of the progenitor mass-loss. Already, this technique has been exemplified with the Type IIn subclass, which often have large, dusty, pre-existing shells formed in pre-SN eruptions. While other SN subclasses are generally thought of having relatively low density circumstellar environments, a growing number of objects in other subclasses now show evidence for significant pre-SN mass loss and similar mid-IR characteristics. Long after the SN radioactive tail disappears, warm dust can stay bright at mid-IR wavelengths due to alternative heating mechanisms, such as shocks. The success of Spitzer archival studies has already been highlighted by the work of several members of this team. Here we propose a SNAPSHOT survey of a well-studied and high-profile SN sample, extending over a range of subclasses, and including both recent and historical events with evidence of a dense CSM and/or dust. This program will (a) discover new SNe with warm dust and (b) monitor the evolution of warm dust in previously detected SNe. Expanding upon our previous mid-IR work on SNe IIn, these observations will probe the similarities in and differences between the subclasses' circumstellar environments, pre-SN mass-loss, and ultimately, the progenitors themselves.

  12. A circumstellar molecular gas structure associated with the massive young star Cepheus A-HW 2

    NASA Technical Reports Server (NTRS)

    Torrelles, Jose M.; Rodriguez, Luis F.; Canto, Jorge; Ho, Paul T. P.

    1993-01-01

    We report the detection via VLA-D observations of ammonia of a circumstellar high-density molecular gas structure toward the massive young star related to the object Cepheus A-HW 2, a firm candidate for the powering source of the high-velocity molecular outflow in the region. We suggest that the circumstellar molecular gas structure could be related to the circumstellar disk previously suggested from infrared, H2O, and OH maser observations. We consider as a plausible scenario that the double radio continuum source of HW 2 could represent the ionized inner part of the circumstellar disk, in the same way as proposed to explain the double radio source in L1551. The observed motions in the circumstellar molecular gas can be produced by bound motions (e.g., infall or rotation) around a central mass of about 10-20 solar masses (B0.5 V star or earlier).

  13. Mapping α Centauri AB for Possible Habitable Planets

    NASA Astrophysics Data System (ADS)

    Quarles, Billy L.; Lissauer, Jack J.

    2016-06-01

    The alpha Centauri AB star system, our closest stellar neighbors, has been studied for many decades and ACESat (Belikov et al. AAS Meeting #225, #311.01, 2015) is a proposed space mission designed to directly image Earth-sized planets in the habitable zones of both of these stars. The alpha Centauri system is older than our Sun, so any resident planets are expected to occupy long-lived orbits. We evaluate the extent of these trajectories where planets are able to orbit for billion-year timescales. The distribution of long-lived orbits is mapped to the sky plane to indicate regions where planets may appear relative to each stellar component. Our results confirm qualitatively those of Wiegert & Holman (Astron. J. 113, 1445, 1997) regarding the approximate size of the regions of stable orbits, which are larger for retrograde orbits relative to the binary than for prograde orbits. Moreover, we find that orbits beyond each star’s habitable zone are affected by a dynamical imprint from the binary orbit due to mean motion resonances and the Lidov-Kozai Mechanism. Stable planets can exist near the plane of the binary orbit within each stellar habitable zone, whereas highly inclined orbits are typically short-lived. These results are of special interest as they can guide the search process of our stellar neighbors in future missions.

  14. Exotic Earths: forming habitable worlds with giant planet migration.

    PubMed

    Raymond, Sean N; Mandell, Avi M; Sigurdsson, Steinn

    2006-09-01

    Close-in giant planets (e.g., "hot Jupiters") are thought to form far from their host stars and migrate inward, through the terrestrial planet zone, via torques with a massive gaseous disk. Here we simulate terrestrial planet growth during and after giant planet migration. Several-Earth-mass planets also form interior to the migrating jovian planet, analogous to recently discovered "hot Earths." Very-water-rich, Earth-mass planets form from surviving material outside the giant planet's orbit, often in the habitable zone and with low orbital eccentricities. More than a third of the known systems of giant planets may harbor Earth-like planets. PMID:16960000

  15. Pioneering Concepts of Planetary Habitability

    NASA Astrophysics Data System (ADS)

    Raulin Cerceau, Florence

    Famous astronomers such as Richard A. Proctor (1837-1888), Jules Janssen (1824-1907), and Camille Flammarion (1842-1925) studied the concept of planetary habitability a century before this concept was updated in the context of the recent discoveries of exoplanets and the development of planetary exploration in the solar system. They independently studied the conditions required for other planets to be inhabited, and these considerations led them to specify the term "habitability." Naturally, the planet Mars was at the heart of the discussion. Our neighboring planet, regarded as a sister planet of Earth, looked like a remarkable abode for life. During the second part of the nineteenth century, the possibility of Martian intelligent life was intensively debated, and hopes were still ardent to identify a kind of vegetation specific to the red planet. In such a context, the question of Mars' habitability seemed to be very valuable, especially when studying hypothetical Martian vegetation. At the dawn of the Space Age, German-born physician and pioneer of space medicine Hubertus Strughold (1898-1987) proposed in the book The Green and Red Planet: A Physiological Study of the Possibility of Life on Mars (1954) to examine the planets of the solar system through a "planetary ecology." This innovative notion, which led to a fresh view of the concept of habitability, was supposed to designate a new field involving biology: "the science of planets as an environment for life" (Strughold 1954). This notion was very close to the concept of habitability earlier designated by our nineteenth-century pioneers. Strughold also coined the term "ecosphere" to name the region surrounding a star where conditions allowed life-bearing planets to exist. We highlight in this chapter the historical aspects of the emergence of the (modern) concept of habitability. We will consider the different formulations proposed by the pioneers, and we will see in what way it can be similar to our contemporary notion of planetary habitability. This study also shows the convergence of the methodological aspects used to examine the concept of habitability, mainly based on analogy.

  16. The kinematics of circumstellar disks around T Tauri stars

    NASA Astrophysics Data System (ADS)

    Koerner, David William

    1995-09-01

    Aperture synthesis images of molecular gas around the T Tauri stars, GM Aurigae, RY Tauri, DL Tauri, DO Tauri, and AS 209 are interpreted with the aid of a kinematic model of a circumstellar disk. Maps of the relatively old T Tauri star, GM Aur, in the CO-13(2 yields 1) line at 4 sec resolution reveal compact gas associated with the stellar position and at the core of a larger rotating gaseous disk, 950 x 530 AU in extent. The mean velocity gradient across the disk, which is oriented along PA approx. 50 deg, is consistent with rotation about an axis at PA = 140 deg. The structure observed in CO-13 aperture synthesis maps agrees well with synthetic maps of the gas emission generated from a model. For a disk that is inclined 30 deg from face on, in Keplerian rotation, a 0.80 solar mass central mass (star + disk), a systemic velocity, V(HEL), of 15.38 km s-l, and a mass, 0.1 solar mass is derived. Aperture synthesis images of CO(2 yields 1) emission at approx. 2-3 sec resolution from RY Tau, DL Tau, DO Tau, and AS 209 also show resolved and elongated gaseous emission. For RY Tau, the deconvolved, half-maximum radius along the direction of elongation, PA approx 48 deg, is 110 AU. Corresponding radii and orientations for the other sources are: DL Tau -250 AU at PA approx 84 deg, DO Tau -350 AU at PA approx 160 deg, and AS 209-290 AU at PA approx 138 deg. RY Tau, DL Tau, and AS 209 show velocity gradients parallel to the elongation, suggesting that the circumstellar material is rotating. RY Tau and AS 209 also exhibit double-peaked spectra characteristic of a rotating disk. Line emission from DO Tau is dominated by high-velocity blue-shifted gas which complicates the interpretation. Nevertheless, there is in each case sufficient evidence to speculate that the circumstellar emission may arise from a protoplanetary disk similar to that from which our solar system formed.

  17. The Mineralogy of Circumstellar Silicates Preserved in Cometary Dust

    NASA Technical Reports Server (NTRS)

    Keller, L. P.; Messenger, S.

    2010-01-01

    Interplanetary dust particles (IDPs) contain a record of the building blocks of the solar system including presolar grains, molecular cloud material, and materials formed in the early solar nebula. Cometary IDPs have remained relatively unaltered since their accretion because of the lack of parent body thermal and aqueous alteration. We are using coordinated transmission electron microscope (TEM) and ion microprobe studies to establish the origins of the various components within cometary IDPs. Of particular interest is the nature and abundance of presolar silicates in these particles because astronomical observations suggest that crystalline and amorphous silicates are the dominant grain types produced in young main sequence stars and evolved O-rich stars. Five circumstellar grains have been identified including three amorphous silicate grains and two polycrystalline aggregates. All of these grains are between 0.2 and 0.5 micrometers in size. The isotopic compositions of all five presolar silicate grains fall within the range of presolar oxides and silicates, having large (17)O-enrichments and normal (18)O/(16)O ratios (Group 1 grains from AGB and RG stars). The amorphous silicates are chemically heterogeneous and contain nanophase FeNi metal and FeS grains in a Mg-silicate matrix. Two of the amorphous silicate grains are aggregates with subgrains showing variable Mg/Si ratios in chemical maps. The polycrystalline grains show annealed textures (equilibrium grains boundaries, uniform Mg/Fe ratios), and consist of 50-100 nm enstatite and pyrrhotite grains with lesser forsterite. One of the polycrystalline aggregates contains a subgrain of diopside. The polycrystalline aggregates form by subsolidus annealing of amorphous precursors. The bulk compositions of the five grains span a wide range in Mg/Si ratios from 0.4 to 1.2 (avg. 0.86). The average Fe/Si (0.40) and S/Si (0.21) ratios show a much narrower range of values and are approximately 50% of their solar abundances. The latter observation may indicate a decoupling of the silicate and sulfide components in grains that condense in stellar outflows. The amorphous silicate grains described here were not extensively affected by irradiation, sputtering, or thermal processing and may represent relatively pristine circumstellar grains. They are strong candidates for the "dirty silicates" in astronomical observations of circumstellar dust shells. The polycrystalline grains were originally amorphous silicate grains that were likely annealed in the early solar nebula but the processing was not sufficient to erase their anomalous oxygen isotopic compositions.

  18. SN 2007od: A TYPE IIP SUPERNOVA WITH CIRCUMSTELLAR INTERACTION

    SciTech Connect

    Andrews, J. E.; Gallagher, J. S.; Clayton, Geoffrey C.; Chatelain, J. P.; Clem, J. E-mail: jgallagher@phys.lsu.ed E-mail: jchate6@tigers.lsu.ed

    2010-05-20

    SN 2007od exhibits characteristics that have rarely been seen in a Type IIP supernova (SN). Optical V-band photometry reveals a very steep brightness decline between the plateau and nebular phases of {approx}4.5 mag, likely due to SN 2007od containing a low mass of {sup 56}Ni. The optical spectra show an evolution from normal Type IIP with broad H{alpha} emission, to a complex, four-component H{alpha} emission profile exhibiting asymmetries caused by dust extinction after day 232. This is similar to the spectral evolution of the Type IIn SN 1998S, although no early-time narrow ({approx}200 km s{sup -1}) H{alpha} component was present in SN 2007od. In both SNe, the intermediate-width H{alpha} emission components are thought to arise in the interaction between the ejecta and its circumstellar medium (CSM). SN 2007od also shows a mid-infrared excess due to new dust. The evolution of the H{alpha} profile and the presence of the mid-IR excess provide strong evidence that SN 2007od formed new dust before day 232. Late-time observations reveal a flattening of the visible light curve. This flattening is a strong indication of the presence of a light echo, which likely accounts for much of the broad, underlying H{alpha} component seen at late times. We believe that the multi-peaked H{alpha} emission is consistent with the interaction of the ejecta with a circumstellar ring or torus (for the inner components at {+-}1500 km s{sup -1}) and a single blob or cloud of circumstellar material out of the plane of the CSM ring (for the outer component at -5000 km s{sup -1}). The most probable location for the formation of new dust is in the cool dense shell created by the interaction between the expanding ejecta and its CSM. Monte Carlo radiative transfer modeling of the dust emission from SN 2007od implies that up to {approx}4 x 10{sup -4} M{sub sun} of new dust has formed. This is similar to the amounts of dust formed in other core-collapse supernovae such as SNe 1999em, 2004et, and 2006jc.

  19. The Circumstellar Disk of HD 141569 Imaged with NICMOS.

    PubMed

    Weinberger; Becklin; Schneider; Smith; Lowrance; Silverstone; Zuckerman; Terrile

    1999-11-01

    Coronagraphic imaging with the Near-Infrared Camera and Multiobject Spectrometer on the Hubble Space Telescope reveals a large, approximately 400 AU (4&arcsec;) radius, circumstellar disk around the Herbig Ae/Be star HD 141569. A reflected light image at 1.1 µm shows the disk oriented at a position angle of 356&j0;+/-5&j0; and inclined to our line of sight by 51&j0;+/-3&j0;; the intrinsic scattering function of the dust in the disk makes the side inclined toward us, the eastern side, brighter. The disk flux density peaks 185 AU (1&farcs;85) from the star and falls off to both larger and smaller radii. A region of depleted material, or a gap, in the disk is centered 250 AU from the star. The dynamical effect of one or more planets may be necessary to explain this morphology. PMID:10511512

  20. The photochemistry of carbon-rich circumstellar shells

    NASA Technical Reports Server (NTRS)

    Huggins, P. J.; Glassgold, A. E.

    1982-01-01

    The effect of ambient ultraviolet photons on the chemical structure of carbon-rich, circumstellar envelopes is investigated with a simple formulation of the time-dependent, photochemical rate equations valid for optically thick shells. Molecules injected into the shielded inner envelope are broken down when they reach the outer regions where ambient ultraviolet photons can penetrate. A quantitative description of the abundance variations is obtained for the case of uniform expansion by detailed consideration of the shielding of the radiation by the dust and molecules of the envelope. Representative results are presented to illustrate the role of shielding in defining the extent of molecular envelopes, the formation of C I and C II shells by photodestruction of carbon-bearing molecules, and the development of layered chemical structures from the photobreakup of polyatomic molecules. Photochemistry makes the outer parts of thick, carbon-rich envelopes into complex regions containing radicals, ions, and atoms which are of considerable observational and theoretical interest.

  1. The photosphere and circumstellar environment of the Be star Achernar

    NASA Astrophysics Data System (ADS)

    Faes, Daniel M.; Domiciano de Souza, Armando; Carciofi, Alex C.; Bendjoya, Philippe

    2015-01-01

    Achernar is a key target to investigate high stellar rotation and the Be phenonemon. It is also the hottest star for which detailed photospheric information is available. Here we report our results to determine the photospheric parameters of Achernar and evaluate how the emission of a Viscous Decretion Disk (VDD) around it would be observable. The analysis is based on interferometric data (PIONIER and AMBER at ESO-VLTI), complemented by spectroscopy and polarimetry for the circumstellar emission. For the first time fundamental parameters of a Be photosphere were determined. The presence of a residual disk at the quiescent phase and some characteristics of the new formed disk (2013 activity) are also discussed. This is rare opportunity to precisely determine the stellar brightness distribution and evaluate the evolution of a just formed Be disk.

  2. Circumstellar debris and pollution at white dwarf stars

    NASA Astrophysics Data System (ADS)

    Farihi, J.

    2016-04-01

    Circumstellar disks of planetary debris are now known or suspected to closely orbit hundreds of white dwarf stars. To date, both data and theory support disks that are entirely contained within the preceding giant stellar radii, and hence must have been produced during the white dwarf phase. This picture is strengthened by the signature of material falling onto the pristine stellar surfaces; disks are always detected together with atmospheric heavy elements. The physical link between this debris and the white dwarf host abundances enables unique insight into the bulk chemistry of extrasolar planetary systems via their remnants. This review summarizes the body of evidence supporting dynamically active planetary systems at a large fraction of all white dwarfs, the remnants of first generation, main-sequence planetary systems, and hence provide insight into initial conditions as well as long-term dynamics and evolution.

  3. Molecular ions in the circumstellar envelope of IRC + 10216

    NASA Technical Reports Server (NTRS)

    Glassgold, A. E.; Lucas, R.; Omont, A.

    1986-01-01

    Assuming a steady and spherically symmetric mass loss, the spatial distribution of the ionization in a C-rich circumstellar envelope (CSE) is calculated, and it is shown that molecular ions dominate the ionization and chemistry of a large part of the CSE. Cosmic ray ionization of molecular hydrogen yields H3(+), and the photoionization of acetylene and neutral carbon yields C2H2(+) and C(+). In the system, the primary ions generate a series of heavier molecular ions by reactions with neutral molecules before being destroyed by dissociative recombination. The most promising candidate for mm-wavelength detection is found to be HCO(+), and IRC + 10216 antenna temperatures are calculated for different telescope sizes. Photoproduced C2H2(+), the most abundant intermediate distance CSE ion, may be responsible for the synthesis of various heavy hydrocarbon molecules at levels observed in IRC + 10216.

  4. PAH formation in carbon-rich circumstellar envelopes

    NASA Technical Reports Server (NTRS)

    Feigelson, Eric D.; Frenklach, Michael

    1989-01-01

    While there is growing observational evidence that some fraction of interstellar carbon is in polycyclic aromatic hydrocarbons (PAH's), the mechanisms by which these molecules might be formed have not been extensively studied. A detailed investigation of PAH production in the outflowing molecular envelopes of carbon-rich red giant star is presented. The gasphase kinetics of a chemical reaction mechanism developed to study soot production in hydrocarbon flames is modified to apply in circumstellar environments. It was found that astrophysically significant quantities of PAH's can be formed in carbon star envelopes provided the gas is sufficiently dense and resides for a long time in the temperature range of 900 to 1100 k. The precise yield of PAH's is very sensitive to astronomical parameters of the envelope (e.g., mass loss rate, outflow velocity, and acetylene abundance) and certain poorly determined chemical reaction rates.

  5. The circumstellar environments of intermediate mass main sequence stars

    NASA Technical Reports Server (NTRS)

    Grady, Carol A.

    1993-01-01

    Analysis of archival Infrared Astronomy Satellite (IRAS) and International Ultraviolet Explorer (IUE) data resulted in identification of accreting gas toward a 2.8 Myr post-Herbig Be star in the R CrA star formation region, and identification of accreting gas toward HD 93563, previously identified as a classical Be star. Accreting gas was also detected toward two B(e) stars of previously controversial evolutionary state, resulting in identification of these systems as pre-Main Sequence Herbig Be stars viewed edge-on to their circumstellar disks. In parallel with this effort, accreting gas was detected toward the Herbig Ae star HR 5999, resulting in development of identification criteria for edge-on PMS proto-planetary disk systems. The work on individual stars is described.

  6. Archival Legacy Investigation of Circumstellar Environments (ALICE). Survey results

    NASA Astrophysics Data System (ADS)

    Soummer, Remi; Choquet, Elodie; Pueyo, Laurent; Brendan Hagan, J.; Gofas-Salas, Elena; Rajan, Abhijith; Chen, Christine; Perrin, Marshall D.; Debes, John H.; Golimowski, David A.; Hines, Dean C.; N'Diaye, Mamadou; Schneider, Glenn; Mawet, Dimitri; Marois, Christian

    2016-01-01

    We report on the status of the ALICE project (Archival Legacy Investigation of Circumstellar Environments. HST/AR-12652), which consists in a consistent reanalysis of the entire HST-NICMOS coronagraphic archive with advanced post-processing techniques. Over the last two years, we have developed a sophisticated pipeline able to handle the data of the 400 stars of the archive. We present the results of the overall reduction campaign and discuss the first statistical analysis of the candidate detections. As we will deliver high-level science products to the STScI MAST archive, we are defining a new standard format for high-contrast science products, which will be compatible with every new high-contrast imaging instrument and used by the JWST coronagraphs. We present here an update and overview of the specifications of this standard.

  7. Beta Pic-like Circumstellar Gas Disk Around 2 And

    NASA Technical Reports Server (NTRS)

    Cheng, Patricia

    2003-01-01

    This grant was awarded to support the data analysis and publication of results from our project entitled P Pic-like Circumstellar Gas Disk Around 2 And . We proposed to obtain FUSE observations of 2 And and study the characteristics and origin of its circumstellar gas. We observed 2 Andromedae with FUSE on 3-4 July 2001 in 11 exposures with a total exposure time of 21,289 seconds through the LWRS aperture. Our data were calibrated with Version 1.8.7 of the CALFUSE pipeline processing software. We corrected the wavelength scale for the heliocentric velocity error in this version of the CALFUSE software. The relative accuracy of the calibrated wavelength scale is +/- 9 km/s . We produced a co-added spectrum in the LiF 1B and LiF 2A channels (covering the 1100 to 1180 A region) by cross-correlating the 11 individual exposures and doing an exposure-time weighted average flux. The final co-added spectra have a signal-to-noise ratio in the stellar continuum near 1150 A of about 20. To obtain an absolute wavelength calibration, we cross-correlated our observed spectra with a model spectrum to obtain the best fit for the photospheric C I lines. Because the photospheric lines are very broad, this yields an absolute accuracy for the wavelength scale of approx.+/- 15 km/s. We then rebinned 5 original pixels to yield the optimal sampling of .033 A for each new pixel, because the calibrated spectra oversample the spectral resolution for FUSE+LWRS (R = 20,000 +/- 2,000).

  8. Bimodality of Circumstellar Disk Evolution Induced by the Hall Current

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Y.; Iwasaki, K.; Okuzumi, S.; Machida, M. N.; Inutsuka, S.

    2015-09-01

    The formation process of circumstellar disks is still controversial because of the interplay of complex physical processes that occurs during the gravitational collapse of prestellar cores. In this study, we investigate the effect of the Hall current term on the formation of the circumstellar disk using three-dimensional simulations. In our simulations, all non-ideal effects, as well as the radiation transfer, are considered. The size of the disk is significantly affected by a simple difference in the inherent properties of the prestellar core, namely whether the rotation vector and the magnetic field are parallel or anti-parallel. In the former case, only a very small disk (\\lt 1 {AU}) is formed. On the other hand, in the latter case, a massive and large (\\gt 20 {AU}) disk is formed in the early phase of protostar formation. Since the parallel and anti-parallel properties do not readily change, we expect that the parallel and anti-parallel properties are also important in the subsequent disk evolution and the difference between the two cases is maintained or enhanced. This result suggests that the disk size distribution of the Class 0 young stellar objects is bimodal. Thus, the disk evolution can be categorized into two cases and we may call the parallel and anti-parallel systems Ortho-disk and Para-disk, respectively. We also show that the anti-rotating envelopes against the disk rotation appear with a size of ≳ 200 {AU}. We predict that the anti-rotating envelope will be found in the future observations.

  9. TIDALLY INDUCED BROWN DWARF AND PLANET FORMATION IN CIRCUMSTELLAR DISKS

    SciTech Connect

    Thies, Ingo; Kroupa, Pavel; Goodwin, Simon P.; Stamatellos, Dimitrios; Whitworth, Anthony P.

    2010-07-01

    Most stars are born in clusters and the resulting gravitational interactions between cluster members may significantly affect the evolution of circumstellar disks and therefore the formation of planets and brown dwarfs (BDs). Recent findings suggest that tidal perturbations of typical circumstellar disks due to close encounters may inhibit rather than trigger disk fragmentation and so would seem to rule out planet formation by external tidal stimuli. However, the disk models in these calculations were restricted to disk radii of 40 AU and disk masses below 0.1 M{sub sun}. Here, we show that even modest encounters can trigger fragmentation around 100 AU in the sorts of massive ({approx}0.5 M{sub sun}), extended ({>=}100 AU) disks that are observed around young stars. Tidal perturbation alone can do this; no disk-disk collision is required. We also show that very low mass binary systems can form through the interaction of objects in the disk. In our computations, otherwise non-fragmenting massive disks, once perturbed, fragment into several objects between about 0.01 and 0.1 M{sub sun}, i.e., over the whole BD mass range. Typically, these orbit on highly eccentric orbits or are even ejected. While probably not suitable for the formation of Jupiter- or Neptune-type planets, our scenario provides a possible formation mechanism for BDs and very massive planets which, interestingly, leads to a mass distribution consistent with the canonical substellar initial mass function. As a minor outcome, a possible explanation for the origin of misaligned extrasolar planetary systems is discussed.

  10. Circumstellar disks revealed by H/K flux variation gradients

    NASA Astrophysics Data System (ADS)

    Pozo Nuñez, F.; Haas, M.; Chini, R.; Ramolla, M.; Westhues, C.; Hodapp, K.-W.

    2015-06-01

    The variability of young stellar objects (YSO) changes their brightness and color preventing a proper classification in traditional color-color and color magnitude diagrams. We have explored the feasibility of the flux variation gradient (FVG) method for YSOs, using H and K band monitoring data of the star forming region RCW 38 obtained at the University Observatory Bochum in Chile. Simultaneous multi-epoch flux measurements follow a linear relation FH = α + β·FK for almost all YSOs with large variability amplitude. The slope β gives the mean HK color temperature Tvar of the varying component. Because Tvar is hotter than the dust sublimation temperature, we have tentatively assigned it to stellar variations. If the gradient does not meet the origin of the flux-flux diagram, an additional non- or less-varying component may be required. If the variability amplitude is larger at the shorter wavelength, e.g. α< 0, this component is cooler than the star (e.g. a circumstellar disk); vice versa, if α> 0, the component is hotter like a scattering halo or even a companion star. We here present examples of two YSOs, where the HK FVG implies the presence of a circumstellar disk; this finding is consistent with additional data at J and L. One YSO shows a clear K-band excess in the JHK color-color diagram, while the significance of a K-excess in the other YSO depends on the measurement epoch. Disentangling the contributions of star and disk it turns out that the two YSOs have huge variability amplitudes (~3-5 mag). The HK FVG analysis is a powerful complementary tool to analyze the varying components of YSOs and worth further exploration of monitoring data at other wavelengths.

  11. Stellar orbit evolution in close circumstellar disc encounters

    NASA Astrophysics Data System (ADS)

    Muñoz, D. J.; Kratter, K.; Vogelsberger, M.; Hernquist, L.; Springel, V.

    2015-01-01

    The formation and early evolution of circumstellar discs often occurs within dense, newborn stellar clusters. For the first time, we apply the moving-mesh code AREPO, to circumstellar discs in 3D, focusing on disc-disc interactions that result from stellar flybys. Although a small fraction of stars are expected to undergo close approaches, the outcomes of the most violent encounters might leave an imprint on the discs and host stars that will influence both their orbits and their ability to form planets. We first construct well-behaved 3D models of self-gravitating discs, and then create a suite of numerical experiments of parabolic encounters, exploring the effects of pericentre separation rp, disc orientation and disc-star mass ratio (Md/M*) on the orbital evolution of the host stars. Close encounters (2rp ≲ disc radius) can truncate discs on very short time-scales. If discs are massive, close encounters facilitate enough orbital angular momentum extraction to induce stellar capture. We find that for realistic primordial disc masses Md ≲ 0.1M*, non-colliding encounters induce minor orbital changes, which is consistent with analytic calculations of encounters in the linear regime. The same disc masses produce entirely different results for grazing/colliding encounters. In the latter case, rapidly cooling discs lose orbital energy by radiating away the energy excess of the shock-heated gas, thus causing capture of the host stars into a bound orbit. In rare cases, a tight binary with a circumbinary disc forms as a result of this encounter.

  12. Practicing Good Habits, Grade 2.

    ERIC Educational Resources Information Center

    Nguyen Van Quan; And Others

    This illustrated primer, designed for second grade students in Vietnam, consists of stories depicting rural family life in Vietnam. The book is divided into the following six chapters: (1) Practicing Good Habits (health, play, helpfulness); (2) Duties at Home (grandparents, father and mother, servants, the extended family; (3) Duties in School…

  13. 7 Habits of Developmental Coaches

    ERIC Educational Resources Information Center

    Darden, Gibson; Shimon, Jane

    2004-01-01

    In this article, the authors describe how coaches can apply principles of athlete growth and development to the learning and performance of motor skills. They present 7 habits that lead to well-rounded athletes who experience increased enjoyment, self-motivation, skill improvement, and ultimately more success on the playing field. (Contains 1…

  14. The circumstellar environments of dusty main sequence stars

    NASA Astrophysics Data System (ADS)

    Gebrim, Antonio S. Hales

    Our current understanding of the formation of planetary systems is strongly linked to astronomical observations of gas and dust around young stars. This thesis is dedicated to studying the physical conditions acting in the circumstellar environments of pre-main sequence and early main sequence dusty stars. These early stellar ages correspond to the timescales over which planets are thought to be formed. The first part of this work is dedicated to a search for dusty early A-type stars in the northern galactic plane. Data from the IPHAS Ha survey is first used to select a sample of galactic A-type stars. This sample is then correlated with data from the Spitzer Space Telescope in order to search for 8 microns and 24 microns excesses associated with warm dust orbiting the stars. The improved photometric sensitivities of these new galactic surveys allow the list of known galactic 'Vega-like' sources to be extended to unexplored optical magnitude ranges (13.5 < r < 18.5 mags). Only 1.1% of a sample of 3062 A-type stars with available optical to mid-infrared spectral energy distributions showed detectable excesses at 8 microns. Searching over 1860 stars observed at 24 microns yielded similar statistical results (1.2%). Only 10 stars have both 8 and 24 micron excesses. These results support the idea that warm dust located relatively close to the stars is rare in main sequence systems. Follow-up observations of this new sample of dust-excess stars will provide better insights into the properties of the systems. Resolved images are crucial for understanding the dynamics and evolution of proto-planetary disks. Observing the detailed disk structure requires high-contrast, high-spatial resolution imaging very close to the bright central star. As a consequence, only a handful of these systems have yet been resolved. The second part of this work shows how near-infrared Polarimetric Imaging on the 3.8 meter United Kingdom Infrared Telescope can be used to obtain reflected-light images of dust-disks around dust excess stars. This technique allows one to automatically suppress the unpolarised light from the central star, increasing the dynamic range for detecting polarised light scattered by the dust present in circumstellar discs. The detections of extended disks around the classical T Tauri star TW Hya and the Herbig Ac star HD 169142 are reported, as well as the strong but spatially unresolved polarization signals measured toward two other Herbig Ae stars. Monte Carlo scattering simulations are used to fit the J-, H- and K-band polarization images of the disk around TW Hya, providing new constraints on the geometry of TW Hya's disk. The third part of this thesis is dedicated to studying the gas content and dynamics around dust-excess stars. The evolution of circumstellar gas is thought to be strongly linked to the formation of gaseous giant planets similar to Jupiter, Saturn and most currently known extra-solar planets. However, the timescales over which circumstellar gas discs dissipate remains poorly constrained, mainly due to the observational difficulties associated with detecting small amounts of circumstellar gas. An analysis of high-resolution (R 50 000) optical spectroscopic data of a sample of 'Vega-like' candidates from the catalogue of Mannings & Barlow (1998) is presented. Analysis of the stellar spectra allows one to search for narrow absorption features due to circumstellar gas and possible Falling Evaporating Bodies, similar to the ones seen in the (3 Pictoris system. None of the stars from this sample show emission line activity in either Ha, Ca II or Na I, indicating that accretion of material onto the stars has ceased and suggesting they are true main sequence Vega-like stars. Four stars were found to exhibit narrow absorption features near the cores of the photospheric Ca II and Na I D lines, with HD 110058 being the strongest candidate to host a (3 Pictoris-like gas disk. If confirmed, HD 110058 would represent the Vega-like star with the lowest Lir/L* value (3.7 x 10"4) around which a CS gas disk has been detected.

  15. The Quest for Cradles of Life: Using the Fundamental Metallicity Relation to Hunt for the Most Habitable Type of Galaxy

    NASA Astrophysics Data System (ADS)

    Dayal, Pratika; Cockell, Charles; Rice, Ken; Mazumdar, Anupam

    2015-09-01

    The field of astrobiology has made huge strides in understanding the habitable zones around stars (stellar habitable zones) where life can begin, sustain its existence and evolve into complex forms. A few studies have extended this idea by modeling galactic-scale habitable zones (galactic habitable zones) for our Milky Way (MW) and specific elliptical galaxies. However, estimating the habitability for galaxies spanning a wide range of physical properties has so far remained an outstanding issue. Here, we present a “cosmobiological” framework that allows us to sift through the entire galaxy population in the local universe and answer the question, “Which type of galaxy is most likely to host complex life in the cosmos?” Interestingly, the three key astrophysical criteria governing habitability (total mass in stars, total metal mass and ongoing star formation rate) are found to be intricately linked through the “fundamental metallicity relation” as shown by Sloan Digital Sky Survey observations of more than a hundred thousand galaxies in the local universe. Using this relation we show that metal-rich, shapeless giant elliptical galaxies at least twice as massive as the MW (with a tenth of its star formation rate) can potentially host ten thousand times as many habitable (Earth-like) planets, making them the most probable “cradles of life” in the universe.

  16. Classifying cultural food habits and meanings.

    PubMed

    Hertzler, A A; Wenkam, N; Standal, B

    1982-05-01

    Old ideas and themes need to be challenged. Fresh approaches are needed in dealing with problems of food habits so that ultimately scientific knowledge of cultural food habits can produce greater success in nutrition education programs. PMID:6176610

  17. Environmental control system for Habitable-zone Planet Finder (HPF)

    NASA Astrophysics Data System (ADS)

    Hearty, Fred; Levi, Eric; Nelson, Matt; Mahadevan, Suvrath; Burton, Adam; Ramsey, Lawrence; Bender, Chad; Terrien, Ryan; Halverson, Samuel; Robertson, Paul; Roy, Arpita; Blank, Basil; Blanchard, Ken; Stefansson, Gudmundur

    2014-07-01

    HPF is an ultra-stable, precision radial velocity near infrared spectrograph with a unique environmental control scheme. The spectrograph will operate at a mid-range temperature of 180K, approximately half way between room temperature and liquid nitrogen temperature; it will be stable to sub -milli-Kelvin(mK) levels over a calibration cycle and a few mK over months to years. HPF's sensor is a 1.7 micron H2RG device by Teledyne. The environmental control boundary is a 9 m2 thermal enclosure that completely surrounds the optical train and produces a near blackbody cavity for all components. A large, pressure - stabilized liquid nitrogen tank provides the heat sink for the system via thermal straps while a multichannel resistive heater control system provides the stabilizing heat source. High efficiency multi-layer insulation blanketing provides the outermost boundary of the thermal enclosure to largely isolate the environmental system from ambient conditions. The cryostat, a stainless steel shell derived from the APOGEE design, surrounds the thermal enclosure and provides a stable, high quality vacuum environment. The full instrument will be housed in a passive 'meat -locker' enclosure to add a degree of additional thermal stability and as well as protect the instrument. Effectiveness of this approach is being empirically demonstrated via long duration scale model testing. The full scale cryostat and environmental control system are being constructed for a 2016 delivery of the instrument to the Hobby-Eberly Telescope. This report describes the configuration of the hardware and the scale-model test results as well as projections for performance of the full system.

  18. O VI gas - Circumstellar or interstellar. [abundance models due to ionization of circumstellar bubbles or supernova shock waves

    NASA Technical Reports Server (NTRS)

    Jenkins, E. B.

    1978-01-01

    Observations in the UV spectra from the Copernicus satellite have revealed absorption lines from five-times ionized oxygen atoms. To explain this abundance, two explanations have been advanced to supplant the traditional model of steady loss from nearby stars. One, ionization from circumstellar bubbles, is said to result from rapidly rotating stars. The other, examined in more detail, suggests a mechanism whereby shock waves from explosive disturbances in nearby supernovae preferentially channel coronal-type O VI regions in the interstellar medium into areas of high temperature (above 100,000 K). An examination of column densities with increasing distribution is proposed to examine the hypotheses, although the results are as yet inconclusive.

  19. 25 CFR 700.67 - Habitation.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 25 Indians 2 2012-04-01 2012-04-01 false Habitation. 700.67 Section 700.67 Indians THE OFFICE OF NAVAJO AND HOPI INDIAN RELOCATION COMMISSION OPERATIONS AND RELOCATION PROCEDURES General Policies and Instructions Definitions § 700.67 Habitation. The term habitation means the dwelling(s) of each...

  20. 25 CFR 700.67 - Habitation.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 25 Indians 2 2010-04-01 2010-04-01 false Habitation. 700.67 Section 700.67 Indians THE OFFICE OF NAVAJO AND HOPI INDIAN RELOCATION COMMISSION OPERATIONS AND RELOCATION PROCEDURES General Policies and Instructions Definitions § 700.67 Habitation. The term habitation means the dwelling(s) of each...

  1. 25 CFR 700.67 - Habitation.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 25 Indians 2 2011-04-01 2011-04-01 false Habitation. 700.67 Section 700.67 Indians THE OFFICE OF NAVAJO AND HOPI INDIAN RELOCATION COMMISSION OPERATIONS AND RELOCATION PROCEDURES General Policies and Instructions Definitions § 700.67 Habitation. The term habitation means the dwelling(s) of each...

  2. Habitability of enceladus: planetary conditions for life.

    PubMed

    Parkinson, Christopher D; Liang, Mao-Chang; Yung, Yuk L; Kirschivnk, Joseph L

    2008-08-01

    The prolific activity and presence of a plume on Saturn's tiny moon Enceladus offers us a unique opportunity to sample the interior composition of an icy satellite, and to look for interesting chemistry and possible signs of life. Based on studies of the potential habitability of Jupiter's moon Europa, icy satellite oceans can be habitable if they are chemically mixed with the overlying ice shell on Myr time scales. We hypothesize that Enceladus' plume, tectonic processes, and possible liquid water ocean may create a complete and sustainable geochemical cycle that may allow it to support life. We discuss evidence for surface/ocean material exchange on Enceladus based on the amounts of silicate dust material present in the Enceladus' plume particles. Microphysical cloud modeling of Enceladus' plume shows that the particles originate from a region of Enceladus' near surface where the temperature exceeds 190 K. This could be consistent with a shear-heating origin of Enceladus' tiger stripes, which would indicate extremely high temperatures ( approximately 250-273 K) in the subsurface shear fault zone, leading to the generation of subsurface liquid water, chemical equilibration between surface and subsurface ices, and crustal recycling on a time scale of 1 to 5 Myr. Alternatively, if the tiger stripes form in a mid-ocean-ridge-type mechanism, a half-spreading rate of 1 m/year is consistent with the observed regional heat flux of 250 mW m(-2) and recycling of south polar terrain crust on a 1 to 5 Myr time scale as well. PMID:18566911

  3. The Stability of Habitable Planetary Environments

    NASA Astrophysics Data System (ADS)

    Williams, Darren Mark

    1998-12-01

    The recent discoveries of extrasolar planets have generated widespread anticipation of detecting a life-supporting environment, such as an Earth-like planet or moon, around a nearby solar-type star. Future observations will enable life on such worlds to be detected remotely through the spectral identification of CH4 and O3 in their atmospheres. This thesis addresses the climatic and dynamic factors affecting whether an Earth-like biosphere might exist around another star and, hence, the likelihood that extraterrestrial life will be discovered in the foreseeable future. To remain habitable for billions of years, a planetary body must be large enough to form and retain an atmosphere. Earth's Moon (~0.01M⊕) does not satisfy this basic criterion. Objects with atmospheres must orbit their stars within the habitable zone (HZ) for liquid water to exist on their surfaces. Otherwise habitable worlds can have their climates destabilized by the slow brightening of their-stars as the age, or by chaotic variability of their orbits and obliquities over time. Earth's 23.5o-obliquity is presently stable, but the spin-stability of extrasolar Earths will depend on the masses and proximity of satellites and neighboring planets. Climates of planets with high obliquities are investigated using an energy-balance climate model. At high obliquity, Earth's climatic zonation is reversed so that the lower latitudes are permanently frozen and the poles are subjected to extraordinary swings in seasonal temperature. Planets within the outer HZs around their stars are less affected by obliquity because they develop dense-CO2 atmospheres as a result of the carbonate-silicate geochemical cycle. Efficient heat transport within such atmospheres reduce latitudinal temperature gradients and limit the amplitudes of seasonal temperature extremes. Geologic evidence for low-latitude glaciation during the Precambrian era suggests that the obliquity of early-Earth may have been much higher than it is today. Earth's obliquity could have been reduced to its present value as a consequence of obliquity-oblateness feedback. In this process, obliquity-driven changes to continental ice volume and oblateness may have caused a secular downward drift in obliquity of ~30o between 600 Ma and 500 Ma. Such an event may account for the present non-zero inclination of the lunar orbit.

  4. Effects of Exoplanet Planetesimal Carbon Chemistry on Habitability

    NASA Astrophysics Data System (ADS)

    Johnson, Torrence V.; Mousis, O.; Lunine, J. I.; Madhusudhan, N.

    2013-10-01

    We explore the effects of reported differences in C/O values for exoplanet host stars on the composition of planetesimals formed beyond the snow line in these systems. Since the value of C/O in a planet forming nebula has a strong effect on amount of oxygen available for water ice in an oxidizing nebula, exoplanet systems for host stars with C/O greater than the solar value may have planetesimals with very little or no water ice. We have estimated the composition of volatile and refractory material in extrasolar planetesimals using a set of stars with a wide range of measured C/O abundances (Johnson et al. ApJ. 757(2), 192, 2012). The volatile ice content of planetesimals in these systems varies significantly with C/O, controlled primarily by the availability of O for H2 O ice condensation. Systems with C/O less than the solar value (C/O = 0.55) should have very water ice rich planetesimals, while water ice mass fraction decreases rapidly with increasing C/O until only ices of CO and CO2 are left in significant proportions. If a significant fraction of C is in the form of refractory CHON particles, C and O are removed from the gas phase and the condensates for super-solar C/O values will be water-poor mixtures of silicates and metal, carbon, and carbon-bearing volatile ices, depending on temperature. For very carbon-rich systems, oxidizing conditions cannot be sustained beyond about C/O=1, due to the oxygen sequestered in solid silicates, oxides and CHON, for refractory C fractions within the Pollack et al. range of 0.4 - 0.7 (ApJ. 421, 615, 1994). These results have implications for assessing the habitability of exoplanets since they constrain the amount of water available beyond the snow line for dynamical delivery to inner planets, depending on the host star’s C/O in the circumstellar nebula. Thus one the key chemical ingredients for habitability may be in short supply in carbon-rich, oxygen-poor systems even if planets exist in the ‘habitable zone’. TVJ acknowledges government support at JPL/Caltech, under a contract with NASA. NM acknowledges support from Yale University. JIL was supported by the JWST Project through NASA. O.M. acknowledges support from CNES.

  5. TW HYA ASSOCIATION MEMBERSHIP AND NEW WISE-DETECTED CIRCUMSTELLAR DISKS

    SciTech Connect

    Schneider, Adam; Song, Inseok; Melis, Carl E-mail: song@physast.uga.edu

    2012-07-20

    We assess the current membership of the nearby, young TW Hydrae association and examine newly proposed members with the Wide-field Infrared Survey Explorer (WISE) to search for infrared excess indicative of circumstellar disks. Newly proposed members TWA 30A, TWA 30B, TWA 31, and TWA 32 all show excess emission at 12 and 22 {mu}m providing clear evidence for substantial dusty circumstellar disks around these low-mass, {approx}8 Myr old stars that were previously shown to likely be accreting circumstellar material. TWA 30B shows large amounts of self-extinction, likely due to an edge-on disk geometry. We also confirm previously reported circumstellar disks with WISE and determine a 22 {mu}m excess fraction of 42{sup +10}{sub -{sub 9}}% based on our results.

  6. Habitability of extrasolar planets and tidal spin evolution.

    PubMed

    Heller, René; Barnes, Rory; Leconte, Jérémy

    2011-12-01

    Stellar radiation has conservatively been used as the key constraint to planetary habitability. We review here the effects of tides, exerted by the host star on the planet, on the evolution of the planetary spin. Tides initially drive the rotation period and the orientation of the rotation axis into an equilibrium state but do not necessarily lead to synchronous rotation. As tides also circularize the orbit, eventually the rotation period does equal the orbital period and one hemisphere will be permanently irradiated by the star. Furthermore, the rotational axis will become perpendicular to the orbit, i.e. the planetary surface will not experience seasonal variations of the insolation. We illustrate here how tides alter the spins of planets in the traditional habitable zone. As an example, we show that, neglecting perturbations due to other companions, the Super-Earth Gl581d performs two rotations per orbit and that any primordial obliquity has been eroded. PMID:22139513

  7. Climate stability of habitable Earth-like planets

    NASA Astrophysics Data System (ADS)

    Menou, Kristen

    2015-11-01

    The carbon-silicate cycle regulates the atmospheric CO2 content of terrestrial planets on geological timescales through a balance between the rates of CO2 volcanic outgassing and planetary intake from rock weathering. It is thought to act as an efficient climatic thermostat on Earth and, by extension, on other habitable planets. If, however, the weathering rate increases with the atmospheric CO2 content, as expected on planets lacking land vascular plants, the carbon-silicate cycle feedback can become severely limited. Here we show that Earth-like planets receiving less sunlight than current Earth may no longer possess a stable warm climate but instead repeatedly cycle between unstable glaciated and deglaciated climatic states. This has implications for the search for life on exoplanets in the habitable zone of nearby stars.

  8. The compulsive habit of cars.

    PubMed

    Yalachkov, Yavor; Naumer, Marcus J; Plyushteva, Anna

    2014-05-01

    The car dependence of people living in contemporary cities is a major concern for policy makers, who often find it difficult to persuade people into more sustainable transport modes. By contrast, recent insights from neuroscience have shown that a broad spectrum of behaviors can become habitual and, thus, resistant to change. Here, we outline the potential of collaboration between neuroscience and human geography aiming at a better understanding of habits that determine everyday commuting routines. PMID:24767180

  9. Study of variable extinction of hot stars with circumstellar dust shells

    NASA Technical Reports Server (NTRS)

    1984-01-01

    Various projects on the topic of hot stars with circumstellar dust are reported. The surface temperature, wind speed, and interstellar reddening were determined for the variable WC7 star HD 193793. Circumstellar carbon monoxide molecules were detected around a hot star. The dust envelope of the star W90 in the young cluster NGC2264 is discussed, and the spectra of low-redshift and X-ray emitting quasars are mentioned.

  10. Circumstellar emission in Be/X-ray binaries of the Magellanic Clouds and the Milky Way

    NASA Astrophysics Data System (ADS)

    Riquelme, M. S.; Torrejn, J. M.; Negueruela, I.

    2012-03-01

    Aims: We study the optical and near-infrared colour excesses produced by circumstellar emission in a sample of Be/X-ray binaries. Our main goals are exploring whether previously published relations, valid for isolated Be stars, are applicable to Be/X-ray binaries and computing the distance to these systems after correcting for the effects of the circumstellar contamination. Methods: Simultaneous UBVRI photometry and spectra in the 3500-7000 spectral range were obtained for 11 optical counterparts to Be/X-ray binaries in the LMC, 5 in the SMC and 12 in the Milky Way. As a measure of the amount of circumstellar emission we used the H? equivalent width corrected for photospheric absorption. Results: We find a linear relationship between the strength of the H? emission line and the component of E(B - V) originating from the circumstellar disk. This relationship is valid for stars with emission lines weaker than EW ? -15 . Beyond this point, the circumstellar contribution to E(B - V) saturates at a value ?0.17 mag. A similar relationship is found for the (V - I) near infrared colour excess, albeit with a steeper slope and saturation level. The circumstellar excess in (B - V) is found to be about five times higher for Be/X-ray binaries than for isolated Be stars with the same equivalent width EW(H?), implying significant differences in the physical properties of their circumstellar envelopes. The distance to Be/X-ray binaries (with non-shell Be star companions) can only be correctly estimated by taking into account the excess emission in the V band produced by free-free and free-bound transitions in the circumstellar envelope. We provide a simple method to determine the distances that includes this effect. Partially based on observations collected at the European Southern Observatory, La Silla, Chile (66.D-0292; 074.D-0529) and the Nordic Optical Telescope.

  11. Widen the belt of habitability!

    PubMed

    Möhlmann, D

    2012-06-01

    Among the key-parameters to characterize habitability are presence or availability of liquid water, an appropriate temperature range, and the time scale of reference. These criteria for habitability are discussed and described from the point of view of water- and ice-physics, and it is shown that liquid water may exist in the sub-surfaces of planetary bodies like Mars, and possibly of inner asteroids and internally heated ice-moons. Water can remain fluid there also at temperatures far below the "canonical" 0 °C. This behaviour is made possible as a consequence of the freezing point depression due to salty solutes in water or "brines", as they can be expected to exist in nature more frequently than pure liquid water. On the other hand, low temperatures cause a slowing down of chemical processes, as can be described by Arrhenius's relation. The resulting smaller reaction rates probably will have the consequence to complicate the detection of low-temperature life processes, if they exist. Furthermore, the adaptation potential of life is to be mentioned in this context as a yet partially unknown process. Resulting recommendations are given to improve the use of criteria to characterize habitable conditions. PMID:22638839

  12. Insensitivity of weathering behavior to planetary land fraction and effect on habitability

    NASA Astrophysics Data System (ADS)

    Abbot, D. S.; Archer, D.; Pierrehumbert, R. T.; Ciesla, F. J.; Bean, J. L.

    2012-04-01

    It is likely that an increasing number of terrestrial planets of unknown water content will soon be discovered in the habitable zone of their stars. Planetary surface land fraction may, however, influence the functioning of the silicate weathering feedback, which buffers planetary surface climate against changes in stellar luminosity over a star's lifetime. It is therefore worthwhile to consider the effect of land fraction on the planetary carbon cycle and weathering behavior in a general sense. Here a low-order model of weathering and climate is developed that includes both continental silicate weathering and seafloor weathering. This model can be used to gain an intuitive sense of the behavior of terrestrial planets with different land fractions in the habitable zone of main-sequence stars as their star's insolation changes with time. It is found that, as long as seafloor weathering is independent of surface temperature, there can be no weathering feedback on a waterworld. This means that the tenure of a waterworld in the habitable zone (before it undergoes a moist greenhouse) is likely to be much shorter than that of a planet with some land fraction. The silicate weathering feedback, however, is effective even at very low land fractions. A planet with a land fraction of 0.01 should remain in the habitable zone nearly as long as a planet with a land fraction of 0.3. Finally, by comparing the timescale for water loss to space to the weathering timescale, it is found that it is possible for a waterworld to draw down atmospheric CO2 quickly enough as a moist greenhouse is in progress to prevent complete loss of all water. This would imply that waterworlds in the habitable zone of main sequence stars can go through a moist greenhouse stage and end up as planets like Earth with only partial ocean coverage and a habitable climate.

  13. Habitability: From solar system planets to Earth-like exoplanets

    NASA Astrophysics Data System (ADS)

    Lammer, H.

    2007-08-01

    For understanding the principles that generated Earth's long-time habitable environment compared with other terrestrial Solar System planets like Venus and Mars and terrestrial exoplanets inside the habitable zones of late-type stars, one has to understand the evolutionary influence of the solar/stellar radiation and particle environment to the atmosphere and surface. Because the spectral type of the star plays a major role in the photochemistry and evolution of planetary atmospheres and their water inventories must be understood within the context of the evolving stellar energy and particle fluxes. An only stable and dense enough atmosphere, which allows water to be liquid over geological time periods and protects the planetary surface from hostile radiation, will allow the evolution of surface life and Earth-like biospheres. Such long-time habitable environments are ideal cases of course, but life may have also originated in other habitats in the young Solar System. Such habitats could have been the environments of early Venus and Mars, subsurface (during formation maybe surface) oceans of icy satellites like in Europa, Titan, Encleadus, in hydrocarbon lakes of Titan, etc. Therefore, studies related to habitability and comparative planetology in the Solar System are essential for precursor studies dedicated to the investigation of habitability of terrestrial exoplanets.With comparative planetology one means the investigation on how different planetary systems and their individual planets - and particularly Earth-like ones - are formed, how they evolve in their radiation and particle interaction with their host stars under different circumstances, how often they give rise to conditions that could in principle be benevolent enough for the origin of life to occur, and even whether life as we know it could have arisen on any world in Earth's neighborhood. The presentation will point out the synergy of these studies and latest theoretical models currently applied for Solar System planets to terrestrial exoplanet atmospheres, which will be characterized by terrestrial planet finding missions like Darwin.

  14. A model of habitability within the Milky Way galaxy.

    PubMed

    Gowanlock, M G; Patton, D R; McConnell, S M

    2011-11-01

    We present a model of the galactic habitable zone (GHZ), described in terms of the spatial and temporal dimensions of the Galaxy that may favor the development of complex life. The Milky Way galaxy was modeled using a computational approach by populating stars and their planetary systems on an individual basis by employing Monte Carlo methods. We began with well-established properties of the disk of the Milky Way, such as the stellar number density distribution, the initial mass function, the star formation history, and the metallicity gradient as a function of radial position and time. We varied some of these properties and created four models to test the sensitivity of our assumptions. To assess habitability on the galactic scale, we modeled supernova rates, planet formation, and the time required for complex life to evolve. Our study has improved on other literature on the GHZ by populating stars on an individual basis and modeling Type II supernova (SNII) and Type Ia supernova (SNIa) sterilizations by selecting their progenitors from within this preexisting stellar population. Furthermore, we considered habitability on tidally locked and non-tidally locked planets separately and studied habitability as a function of height above and below the galactic midplane. In the model that most accurately reproduces the properties of the Galaxy, the results indicate that an individual SNIa is ∼5.6× more lethal than an individual SNII on average. In addition, we predict that ∼1.2% of all stars host a planet that may have been capable of supporting complex life at some point in the history of the Galaxy. Of those stars with a habitable planet, ∼75% of planets are predicted to be in a tidally locked configuration with their host star. The majority of these planets that may support complex life are found toward the inner Galaxy, distributed within, and significantly above and below, the galactic midplane. PMID:22059554

  15. The Effect of Ultraviolet Radiation on Planetary Habitability

    NASA Astrophysics Data System (ADS)

    Kasting, J. F.; Whittet, D. C. B.; Sheldon, W. R.

    1996-03-01

    Climatic constraints on planetary habitability, specifically the requirement of liquid H2O oceans, provide a definition of the habitable zone around main sequence stars with spectral types in the early-F to mid-K range. However, it has not been demonstrated that planets orbiting such stars would have habitable surfaces when biologically-damaging energetic radiation is also considered. The large amounts of ultraviolet (UV) radiation emitted by early-type stars have been suggested to pose a problem for the evolution of life in their vicinity. It has also been suggested that a significant problem is posed by late-type stars which emit proportionally less radiation at the short wavelengths (lambda < 200 nm) required to photolyze O(sub)2, an essential step in ozone (O(sub)3) formation. The presence of O(sub)3 in a planetary atmosphere is the only shield from UV radiation in the wavelength range 220-320 nm which is capable of inflicting serious damage to organisms on Earth, and presumably elsewhere in the Universe; other components of planetary atmospheres absorb negligibly in this UV range. Here we present detailed calculations of the UV spectrum at the surface of a planet with an Earth-like atmosphere and orbiting three types of main sequence stars, F, G and K within the habitable zone, based on climactic constraints. We conclude that neither of the concerns regarding UV radiation expressed previously should be necessarily fatal to the evolution of advanced life: Earth-like planets orbiting F and K stars are shown to receive less harmful UV radiation at their surfaces than is the case for the Earth.

  16. Space Physics of Close-in Exoplanets and its Implications for Planet Habitability

    NASA Astrophysics Data System (ADS)

    Cohen, Ofer

    2015-04-01

    The search for habitable exoplanets is currently focused on planets orbiting M-dwarf stars, due to the close proximity of the habitable zone to the star. However, the traditional habitability definition does not account for the physical space environment near the planets, which can be extreme at close-in orbits, and can lead to erosion of te planetary atmosphere. In order to sustain their atmosphers, M-dwarf planets need to have either an intrinsic magnetic field, or a thick atmosphere. Here we present a set of numerical magnetohydrodynamic simulations of the interaction of an Earth-like magnetized planet and a Venus-like non-magnetized planet with the stellar wind of M-dwarf star. We study space physics aspects of these interactions and their implications for planet habitability

  17. On circumstellar disks: Spitzer identifies two possible evolutionary paths

    NASA Astrophysics Data System (ADS)

    Teixeira, Paula S.; Lada, Charles J.; Marengo, Massimo; Lada, Elizabeth

    Multi-wavelength surveys have vastly improved our understanding of many astrophysical objects, in particular, circumstellar disks. We present our results for the disk population of the young cluster NGC 2264. Our study was based on data obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer on board the Spitzer Space Telescope combined with previously published optical data. We divide the disk population into 3 classes based on their spectral energy distribution shapes: optically thick disks, homologously depleted anemic disks, and radially depleted transition disks. We find that there are two distinct evolutionary paths for disks: a homologous one, where the disk emission decreases uniformly in NIR and mid-infrared wavelengths (anemic disks) and throughout which most sources pass, and a radially differential one where the emission from the inner region of the disk decreases more rapidly than from the outer region (transition disks). Whether a disk evolves in a homologously or radially depleted fashion is still unknown and may depend on the nature of planet formation in the disk.

  18. Polarization of circumstellar bow shocks due to electron scattering

    NASA Astrophysics Data System (ADS)

    Shrestha, Manisha; Hoffman, J. L.; Neilson, H.; Ignace, R.

    2014-01-01

    Circumstellar material (CSM) provides a link between interacting supernovae and their massive progenitor stars. This CSM arises from stellar winds, outflows, or eruptions from a massive star before it explodes and can be detected around stars or supernovae with polarimetric observations. We use a Monte Carlo based radiative transfer code (SLIP) to investigate the polarization created by different models for the CSM surrounding a central source such as supernovae or massive stars. We vary parameters such as the shape, optical depth, temperature, and brightness of the CSM and compare the simulated flux and polarization behavior with observational data. We present results from new simulations that assume a bow shock shape for the CSM. Bow shocks are commonly observed around massive stars; this shape forms when a star moving more quickly than the speed of sound in the local interstellar medium emits a stellar wind that drives a shock wave into the ISM. Since a bow shock projects an aspherical shape onto the sky, light from the central source that scatters in the shock region becomes polarized. We present electron-scattering polarization maps for this geometry and discuss the behavior of observed polarization with viewing angle in the unresolved case.

  19. Rotation and Circumstellar Disks in the Upper Scorpius OB Association

    NASA Astrophysics Data System (ADS)

    Dahm, Scott E.; Slesnick, C. L.

    2011-01-01

    We present projected rotational velocities for 20 early-type (B8-A9) and 53 late-type (F3-M8) members of the 5 Myr old Upper Scorpius OB Association determined using high-resolution optical spectra obtained with HIRES on Keck I and MIKE on the Magellan Clay telescope. The Upper Scorpius sample is composed of primordial and debris disk systems as well as non-excess sources. We combine the derived rotational velocities with Spitzer Space Telescope IRAC 4.5 and 8.0 μm fluxes and MIPS 24.0 μm photometry in order to examine the influence of circumstellar disks upon stellar and substellar rotation. Preliminary results using non-parametric statistical tests suggest that the late-type disk-bearing members of Upper Scorpius rotate more slowly than their non-disk counterparts at a high confidence level. Among the early-type Upper Scorpius members, however, the rotational velocities of the debris-disk and non-disk populations are indistinguishable. We also compare the rotational velocities of the Upper Scorpius sample with those of similar sources in Taurus-Auriga, where stars may not have had sufficient time to undergo disk-braking.

  20. The formation and structure of circumstellar and interstellar dust

    NASA Technical Reports Server (NTRS)

    Kroto, H. W.

    1990-01-01

    The intriguing abundance of long linear carbon chain molecules in some dark clouds and in circumstellar shells is still not well understood. Recent laboratory studies which have probed this problem indicate that when carbon vapor nucleates to form particles, linear chains and hollow cage molecules (fullerenes) also form at more-or-less the same time. The results have consequences for the formation, structures and spectroscopic properties of the molecular and dust components ejected from cool carbon-rich stars. A most interesting result of the experimental observations relates to the probability that a third character in addition to the chains and grains, the C(sub 60) molecule probably in the form of the ion C(sub 60)(sup +) in the less shielded regions, is present and perhaps responsible for some of the ubiquitously observed interstellar spectroscopic features such as the Diffuse Interstellar Features, the 2170A UV Absorption or perhaps some of the Unidentified Infrared Bands. Further study of small carbon particles which form in the gas phase has resulted in the discovery that they have quasi-icosahedral spiral shell structures. The role that such species may play in the interstellar medium as well as that played by C(sub 60) (or C sub 60 sup +) should soon be accessible to verification by a combination of laboratory experiment and astronomical spectroscopy.

  1. Formation of polycyclic aromatic hydrocarbons in circumstellar envelopes

    NASA Technical Reports Server (NTRS)

    Frenklach, Michael; Feigelson, Eric D.

    1989-01-01

    Production of polycyclic aromatic hydrocarbons in carbon-rich circumstellar envelopes was investigated using a kinetic approach. A detailed chemical reaction mechanism of gas-phase PAH formation and growth, containing approximately 100 reactions of 40 species, was numerically solved under the physical conditions expected in cool stellar winds. The chemistry is based on studies of soot production in hydrocarbon pyrolysis and combustion. Several first-ring and second-ring cyclization processes were considered. A linear lumping algorithm was used to describe PAH growth beyond the second aromatic ring. PAH production using this mechanism was examined with respect to a grid of idealized constant velocity stellar winds as well as several published astrophysical models. The basic result is that the onset of PAH production in the interstellar envelopes is predicted to occur within the temperature interval of 1100 to 900 K. The absolute amounts of the PAHs formed, however, are very sensitive to a number of parameters, both chemical and astrophysical, whose values are not accurately known. Astrophysically meaningful quantities of PAHs require particularly dense and slow stellar winds and high initial acetylene abundance. It is suggested that most of the PAHs may be produced in a relatively small fraction of carbon-rich red giants.

  2. The circumstellar envelope of S 106 - IRS 4

    NASA Astrophysics Data System (ADS)

    Felli, M.; Simon, M.; Fischer, J.; Hamann, F.

    1985-04-01

    The authors present new observations that help set the parameters of the ionized circumstellar envelope of S 106-IRS 4. The part of the envelope that is optically thick at 1.35 cm wavelength is smaller than 0arcsec.15 diameter which corresponds to 90 AU at 600 pc distance. The profiles of the Brackett-α and -γ lines are somewhat different with half power widths of 121±10 and 181±15 km s-1, respectively. The He I (21P-21S) line is detected at the S 106 nebula but not at IRS 4. The He I line emission of the nebula indicates that the central star of IRS 4 must have an effective temperature of about 35,000K. Comparison of the wind model scenario presented by Felli et al. (1984) with the present data and the Paschen line and Paschen edge data of McGregor et al. (1984) shows that the model encounters difficulties when observables that require details of the velocity field and of the innermost regions of the flow are considered.

  3. Inner Structure in the TW Hya Circumstellar Disk

    NASA Astrophysics Data System (ADS)

    Akeson, Rachel L.; Millan-Gabet, R.; Ciardi, D.; Boden, A.; Sargent, A.; Monnier, J.; McAlister, H.; ten Brummelaar, T.; Sturmann, J.; Sturmann, L.; Turner, N.

    2011-05-01

    TW Hya is a nearby (50 pc) young stellar object with an estimated age of 10 Myr and signs of active accretion. Previous modeling of the circumstellar disk has shown that the inner disk contains optically thin material, placing this object in the class of "transition disks". We present new near-infrared interferometric observations of the disk material and use these data, as well as previously published, spatially resolved data at 10 microns and 7 mm, to constrain disk models based on a standard flared disk structure. Our model demonstrates that the constraints imposed by the spatially resolved data can be met with a physically plausible disk but this requires a disk containing not only an inner gap in the optically thick disk as previously suggested, but also some optically thick material within this gap. Our model is consistent with the suggestion by previous authors of a planet with an orbital radius of a few AU. This work was conducted at the NASA Exoplanet Science Institute, California Institute of Technology.

  4. Light echo detection of circumstellar disks around flaring stars

    NASA Technical Reports Server (NTRS)

    Gaidos, Eric J.

    1994-01-01

    Light echoes can be used to detect and characterize disks around flaring stars. Such disks are thought to be a hallmark of planet formation but are very difficult to detect by ordinary means. Dwarf emission-line M stars experience flares with luminosities comparable to their quiescent photospheres on time scales of minutes, less than the light travel time across a disk many astronomical units in extent; they are thus ideal candidates for such a search. Bromley (1992) calculated that the detection of Jupiter-sized companions using light echoes requires photometric accuracies better than 1 part in 10(exp 6). However, a disk consisting of grains or small bodies will scatter a much larger fraction of the light than a planet of similar mass. I estimate the light echo amplitutdes from plausible geometries of circumstellar material and present simulation light curves. The light echo amplitudes are typically 1% of the flare and I conclude that such events will be detected best in cases where the flare is eclipsed by the star. An examination of the time scales associated with internal processes in a protoplanetary disks around dM stars indicates that any primordial disks may become undetectable in 10(exp 4) years and will have completely disappeared by 10(exp 8) years, the estimated age of dMe stars in the solar neighborhood. However, searches for light echoes might constrain the amount of material continuing to fall into these young stellar systems in the form of comet-like objects.

  5. Observation of Circumstellar Gas in the Neighborhood of RZ Psc

    NASA Astrophysics Data System (ADS)

    Potravnov, I. S.; Grinin, V. P.; Ilyin, I. V.

    2013-12-01

    The first evidence is found of the existence of circumstellar gas in the nearest surroundings of the UX Ori star RZ Psc. Spectra obtained at the Terskol Observatory, Special Astrophysical Observatory (SAO), and the Nordic Optical Telescope (NOT) reveal a strong variability in the sodium doublet lines that is indicative of a sporadic outflow of matter. Weak variability was also observed in the core of the Hα line. One nontrivial feature of this discovery is that RZ Psc is of spectral class K0 IV. This means that the star has no intrinsic energy resources for creating the observed outflow of matter. There are no emission lines in the star's spectrum which might indicate that matter is falling into the star so that the observed outflow could be related to an accretion process. We suggest, nevertheless, that the ejection of gas is related to residual (slow) accretion and is driven by a propeller mechanism. The latter is possible if the star has a sufficiently high (on the order of 103 G) magnetic field.

  6. Grain growth and dust trapping in circumstellar disks

    NASA Astrophysics Data System (ADS)

    Pinilla, Paola

    2015-08-01

    Circumstellar disks around young stars are known to be the birthplace of planets. Planet formation starts with the coagulation of micron-sized particles to larger dust aggregates. This process, which covers more than forty orders of magnitude in mass, has different physical challenges. One of the oldest mysteries is how planetesimals are formed, in spite of fragmentation collisions and rapid inward drift. Radial drift theory is in disagreement with the observations of millimetre grains in the cold regions of protoplanetary disks. Nevertheless, a disk model that includes dust coagulation, fragmentation, and the presence of long-lived pressure bumps, which moderate the rapid inward migration of particles, leads to a better agreement between observations and theory. Disks with a dust depleted inner cavity, known as transition disks, are excellent candidates to investigate the dust evolution under the existence of a pressure bump. Millimetre observations of transition disks reveal crescent- and ring-shaped emissions that lend credence to the notion than planetesimals may form in localised hotspots or pressure traps. Recent ALMA observations have showed astonishing dust structures in transition disks, which together with data of CO and its isotopologues, have been giving major support for particle trapping induced by embedded planets, which can solve the old paradigm of radial drift.

  7. Rapid disappearance of a warm, dusty circumstellar disk.

    PubMed

    Melis, Carl; Zuckerman, B; Rhee, Joseph H; Song, Inseok; Murphy, Simon J; Bessell, Michael S

    2012-07-01

    Stars form with gaseous and dusty circumstellar envelopes, which rapidly settle into disks that eventually give rise to planetary systems. Understanding the process by which these disks evolve is paramount in developing an accurate theory of planet formation that can account for the variety of planetary systems discovered so far. The formation of Earth-like planets through collisional accumulation of rocky objects within a disk has mainly been explored in theoretical and computational work in which post-collision ejecta evolution typically is ignored, although recent work has considered the fate of such material. Here we report observations of a young, Sun-like star (TYC 8241 2652 1) where infrared flux from post-collisional ejecta has decreased drastically, by a factor of about 30, over a period of less than two years. The star seems to have gone from hosting substantial quantities of dusty ejecta, in a region analogous to where the rocky planets orbit in the Solar System, to retaining at most a meagre amount of cooler dust. Such a phase of rapid ejecta evolution has not been previously predicted or observed, and no currently available physical model satisfactorily explains the observations. PMID:22763553

  8. A WISE survey of circumstellar disks in Taurus

    SciTech Connect

    Esplin, T. L.; Luhman, K. L.; Mamajek, E. E.

    2014-04-01

    We have compiled photometry at 3.4, 4.6, 12, and 22 μm from the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) for all known members of the Taurus complex of dark clouds. Using these data and photometry from the Spitzer Space Telescope, we have identified members with infrared excess emission from circumstellar disks and have estimated the evolutionary stages of the detected disks, which include 31 new full disks and 16 new candidate transitional, evolved, evolved transitional, and debris disks. We have also used the WISE All-Sky Source Catalog to search for new disk-bearing members of Taurus based on their red infrared colors. Through optical and near-infrared spectroscopy, we have confirmed 26 new members with spectral types of M1-M7. The census of disk-bearing stars in Taurus should now be largely complete for spectral types earlier than ∼M8 (M ≳ 0.03 M {sub ☉}).

  9. The Circumstellar Environments of Born-Again Giants

    NASA Astrophysics Data System (ADS)

    Helton, L. Andrew; Evans, Aneurin; Gehrz, Robert D.; Woodward, Charles; Eyres, Stewart

    2015-08-01

    When a solar-mass star reaches the end of its main sequence life, has shed a planetary nebula or become a proto-planetary nebula, and is heading towards the white dwarf phase of its evolution, the star may reignite residual surface helium and be "reborn". It retraces its path on the HR diagram and once again becomes a giant: it undergoes a Very Late Thermal Pulse (VLTP) and becomes a "Born-Again Giant" (BAG). This alternate scenario for the demise of low mass stars may occur in as many as 20% of cases. During this phase the star may become a prolific dust producer such that the star is completely obscured and the only means of monitoring its evolution is by observing the ejected dust.Over the past 10-20 years we have used ground-based, spaceborne and airborne infrared (IR) facilities to monitor the spectral energy distributions of the dust shells of stars that have recently undergone VLTPs. Covering a time period from ~1996 to the present, and with recent SOFIA observations that extend the spectral coverage from 1 - 38 microns, we have been able to determine mass-loss rates from the stars, and the physical state, nature and extent of their circumstellar dust shells.Our observations throw light on a phase of the evolution of low mass stars that is very rare, poorly observed, and little understood. Understanding these phenomena can potentially give us a glimpse of the ultimate fate of the Sun.

  10. ON THE EXCITATION AND FORMATION OF CIRCUMSTELLAR FULLERENES

    SciTech Connect

    Bernard-Salas, J.; Jones, A. P.; Groenewegen, M. A. T.

    2012-09-20

    We compare and analyze the Spitzer mid-infrared spectrum of three fullerene-rich planetary nebulae in the Milky Way and the Magellanic Clouds: Tc1, SMP SMC 16, and SMP LMC 56. The three planetary nebulae share many spectroscopic similarities. The strongest circumstellar emission bands correspond to the infrared active vibrational modes of the fullerene species C{sub 60} and little or no emission is present from polycyclic aromatic hydrocarbons. The strengths of the fullerene bands in the three planetary nebulae are very similar, while the ratios of the [Ne III]15.5 {mu}m/[Ne II]12.8 {mu}m fine structure lines, an indicator of the strength of the radiation field, are markedly different. This raises questions about their excitation mechanism and we compare the fullerene emission to fluorescent and thermal models. In addition, the spectra show other interesting and common features, most notably in the 6-9 {mu}m region, where a broad plateau with substructure dominates the emission. These features have previously been associated with mixtures of aromatic/aliphatic hydrocarbon solids. We hypothesize on the origin of this band, which is likely related to the fullerene formation mechanism, and compare it with modeled hydrogenated amorphous carbon that present emission in this region.

  11. ALIGNMENT OF PROTOSTARS AND CIRCUMSTELLAR DISKS DURING THE EMBEDDED PHASE

    SciTech Connect

    Spalding, Christopher; Batygin, Konstantin; Adams, Fred C. E-mail: kbatygin@gps.caltech.edu

    2014-12-20

    Star formation proceeds via the collapse of a molecular cloud core over multiple dynamical timescales. Turbulence within cores results in a spatially non-uniform angular momentum of the cloud, causing a stochastic variation in the orientation of the disk forming from the collapsing material. In the absence of star-disk angular momentum coupling, such disk-tilting would provide a natural mechanism for the production of primordial spin-orbit misalignments in the resulting planetary systems. However, owing to high accretion rates in the embedded phase of star formation, the inner edge of the circumstellar disk extends down to the stellar surface, resulting in efficient gravitational and accretional angular momentum transfer between the star and the disk. Here, we demonstrate that the resulting gravitational coupling is sufficient to suppress any significant star-disk misalignment, with accretion playing a secondary role. The joint tilting of the star-disk system leads to a stochastic wandering of star-aligned bipolar outflows. Such wandering widens the effective opening angle of stellar outflows, allowing for more efficient clearing of the remainder of the protostar's gaseous envelope. Accordingly, the processes described in this work provide an additional mechanism responsible for sculpting the stellar initial mass function.

  12. The Solar Neighborhood XXIX: The Habitable Real Estate of Our Nearest Stellar Neighbors

    NASA Astrophysics Data System (ADS)

    Cantrell, Justin R.; Henry, Todd J.; White, Russel J.

    2013-10-01

    We use the sample of known stars and brown dwarfs within 5 pc of the Sun, supplemented with AFGK stars within 10 pc, to determine which stellar spectral types provide the most habitable real estate—defined as locations where liquid water could be present on Earth-like planets. Stellar temperatures and radii are determined by fitting model spectra to spatially resolved broadband photometric energy distributions for stars in the sample. Using these values, the locations of the habitable zones are calculated using an empirical formula for planetary surface temperature and assuming the condition of liquid water, called here the empirical habitable zone (EHZ). Systems that have dynamically disruptive companions are considered not habitable. We consider companions to be disruptive if the separation ratio of the companion to the habitable zone is less than 5:1. We use the results of these calculations to derive a simple formula for predicting the location of the EHZ for main sequence stars based on V - K color. We consider EHZ widths as more useful measures of the habitable real estate around stars than areas because multiple planets are not expected to orbit stars at identical stellar distances. This EHZ provides a qualitative guide on where to expect the largest population of planets in the habitable zones of main sequence stars. Because of their large numbers and lower frequency of short-period companions, M stars provide more EHZ real estate than other spectral types, possessing 36.5% of the habitable real estate en masse. K stars are second with 21.5%, while A, F, and G stars offer 18.5%, 6.9%, and 16.6%, respectively. Our calculations show that three M dwarfs within 10 pc harbor planets in their EHZs—GJ 581 may have two planets (d with msin i = 6.1 M ⊕ g with msin i = 3.1 M ⊕), GJ 667 C has one (c with msin i = 4.5 M ⊕), and GJ 876 has two (b with msin i = 1.89 M Jup and c with msin i = 0.56 M Jup). If Earth-like planets are as common around low-mass stars as recent Kepler results suggest, M stars will harbor more Earth-like planets in habitable zones than any other stellar spectral type.

  13. THE SOLAR NEIGHBORHOOD XXIX: THE HABITABLE REAL ESTATE OF OUR NEAREST STELLAR NEIGHBORS

    SciTech Connect

    Cantrell, Justin R.; Henry, Todd J.; White, Russel J. E-mail: thenry@chara.gsu.edu

    2013-10-01

    We use the sample of known stars and brown dwarfs within 5 pc of the Sun, supplemented with AFGK stars within 10 pc, to determine which stellar spectral types provide the most habitable real estate—defined as locations where liquid water could be present on Earth-like planets. Stellar temperatures and radii are determined by fitting model spectra to spatially resolved broadband photometric energy distributions for stars in the sample. Using these values, the locations of the habitable zones are calculated using an empirical formula for planetary surface temperature and assuming the condition of liquid water, called here the empirical habitable zone (EHZ). Systems that have dynamically disruptive companions are considered not habitable. We consider companions to be disruptive if the separation ratio of the companion to the habitable zone is less than 5:1. We use the results of these calculations to derive a simple formula for predicting the location of the EHZ for main sequence stars based on V – K color. We consider EHZ widths as more useful measures of the habitable real estate around stars than areas because multiple planets are not expected to orbit stars at identical stellar distances. This EHZ provides a qualitative guide on where to expect the largest population of planets in the habitable zones of main sequence stars. Because of their large numbers and lower frequency of short-period companions, M stars provide more EHZ real estate than other spectral types, possessing 36.5% of the habitable real estate en masse. K stars are second with 21.5%, while A, F, and G stars offer 18.5%, 6.9%, and 16.6%, respectively. Our calculations show that three M dwarfs within 10 pc harbor planets in their EHZs—GJ 581 may have two planets (d with msin i = 6.1 M {sub ⊕}; g with msin i = 3.1 M {sub ⊕}), GJ 667 C has one (c with msin i = 4.5 M {sub ⊕}), and GJ 876 has two (b with msin i = 1.89 M {sub Jup} and c with msin i = 0.56 M {sub Jup}). If Earth-like planets are as common around low-mass stars as recent Kepler results suggest, M stars will harbor more Earth-like planets in habitable zones than any other stellar spectral type.

  14. Planning to break unwanted habits: habit strength moderates implementation intention effects on behaviour change.

    PubMed

    Webb, Thomas L; Sheeran, Paschal; Luszczynska, Aleksandra

    2009-09-01

    Implementation intention formation promotes effective goal striving and goal attainment. However, little research has investigated whether implementation intentions promote behaviour change when people possess strong antagonistic habits. Experiment 1 developed relatively habitual responses that, after a task switch, had a detrimental impact on task performance. Forming an if-then plan reduced the negative impact of habit on performance. However, the effect of forming implementation intentions was smaller among participants who possessed strong habits as compared to participants who had weaker habits. Experiment 2 provided a field test of the role of habit strength in moderating the relationship between implementation intentions and behaviour in the context of smoking. Implementation intentions reduced smoking among participants with weak or moderate smoking habits, but not among participants with strong smoking habits. In summary, habit strength moderates the effectiveness of if-then plan formation in breaking unwanted habits. PMID:18851764

  15. The Promise for AGB Stars: Physics and Chemistry of the Inner Circumstellar Envelope, and the Mass Loss History

    NASA Astrophysics Data System (ADS)

    Kerschbaum, F.; Olofsson, H.

    2001-07-01

    The Herschel HIFI heterodyne spectrometer and the PACS imaging/spectrometer instruments will provide important information on the physical and chemical conditions in the inner circumstellar envelopes of AGB-stars, e.g., on the rotational lines of the important coolants CO, HCN, and H2O, and on various molecular species that participate in the initial chemistry of the escaping gas. Dynamical studies in the acceleration zone will be possible with HIFI, too. ISO was limited to high mass loss rate and/or very nearby objects and did not allow high resolution heterodyne spectra. Ground-based observatories cannot study most of the crucial far-infrared and sub-mm domains. The solid state features of circumstellar dust particles are mainly found in the near- and mid-infrared ranges, although a crystalline water-ice feature at 62 microns has been seen towards early post-AGB objects, planetary nebulae, Herbig Ae/Be stars, and Herbig-Haro objects. Most ISO observations in these ranges were suffering from too low S/N-ratios. The sensitivity of Herschel is superior, but the short wavelength end of PACS may limit what can be achieved in this area. The temporal variation of the mass loss rate is to a large extent unknown. This applies to all time scales from the pulsation period to the full time scale of the AGB-phase. Extended dust emission observed with PACS, perhaps in combination with Herschel-SPIRE, will provide important results on the long-term mass loss history.

  16. An Optical Study of the Circumstellar Environment Around the Crab Nebula

    NASA Technical Reports Server (NTRS)

    Fesen, Robert A.; Shull, J. Michael; Hurford, Alan P.

    1997-01-01

    Long-slit spectra of two peripheral regions around the Crab Nebula show no H(alpha) emission down to a flux level of 1.5 x 10(exp -7)erg/sq cm s sr (0.63 Rayleigh), corresponding to an emission measure limit of 4.2 cm(sup - 6) pc (3(sigma)) assuming A(sub V)= 1.6(sup m) and T(sub e)=7000 K. This is below the flux levels reported by Murdin & Clark (Nature, 294, 543 (198 1)) for an H(alpha) halo around the Crab. Narrow H(beta) emission as described by Murdin (MNRAS, 269, 89 (1994)) is detected but appears to be Galactic emission unassociated with the remnant. A review of prior searches indicates no convincing observational evidence to support either a high- or low-velocity envelope around the remnant. Spectral scans confirm a well-organized, N-S expansion asymmetry of the filaments with a approx. 500 km/s central velocity constriction as described by MacAlpine et al. (ApJ, 342, 364 (1989)) and Lawrence et (it. (AJ, 109, 2635 (1995)] but questioned by Hester et al. (ApJ, 448, 240 (1995)). The velocity pinching appears to coincide with an cast-west chain of bright [O III] and helium-rich filaments. This expansion asymmetry might be the result of ejecta interaction with a disk of circumstellar matter, but such a model may be inconsistent with H and He filament abundances in the velocity constriction zone. A re-analysis of the remnant's total mass suggests that the filaments contain 4.6 +/- 1.8 M(solar) in ionized and neutral cas, about twice that of earlier estimates. For a 10M(solar) progenitor, this suggests that approx.equals 4M(solar) remains to be detected in an extended halo or wind.

  17. Discovery of a Circumstellar Disk in the Lagoon Nebula

    NASA Astrophysics Data System (ADS)

    1997-04-01

    Circumstellar disks of gas and dust play a crucial role in the formation of stars and planets. Until now, high-resolution images of such disks around young stars within the Orion Nebula obtained with the Hubble Space Telescope (HST) constituted the most direct proof of their existence. Now, another circumstellar disk has been detected around a star in the Lagoon Nebula - also known as Messier 8 (M8) , a giant complex of interstellar gas and dust with many young stars in the southern constellation of Sagittarius and four times more distant than the Orion Nebula. The observations were carried out by an international team of scientists led by Bringfried Stecklum (Thüringer Landessternwarte, Tautenburg, Germany) [1] who used telescopes located at the ESO La Silla observatory and also observations from the HST archive. These new results are paving the road towards exciting research programmes on star formation which will become possible with the ESO Very Large Telescope. The harsh environment of circumstellar disks The existence of circumstellar disks has been inferred from indirect measurements of young stellar objects, such as the spectral energy distribution, the analysis of the profiles of individual spectral lines and measurements of the polarisation of the emitted light [2]. Impressive images of such disks in the Orion Nebula, known as proplyds (PROto-PLanetarY DiskS), have been obtained by the HST during the recent years. They have confirmed the interpretation of previous ground-based emission-line observations and mapping by radio telescopes. Moreover, they demonstrated that those disks which are located close to hot and massive stars are subject to heating caused by the intense radiation from these stars. Subsequently, the disks evaporate releasing neutral gas which streams off. During this process, shock fronts (regions with increased density) with tails of ionised gas result at a certain distance between the disk and the hot star. These objects appear on photos as tear-drop shaped, bright-rimmed areas with the cusps of the ionised regions aligned towards the exciting star. Such a region is also a very compact source of radio emission. Clearly, the harsh environment in which these disks reside does not favour planet formation. These findings were facilitated by the fact that, at a distance of `only' 1500 lightyears (about 450 parsec), the Orion Nebula is the closest site of high-mass star formation. Furthermore, many circumstellar disks around stars in this nebula are seen in silhouette against a bright and uniform background and are therefore comparatively easy to detect. The Lagoon Nebula In principle, similar phenomena should occur in any giant molecular cloud that gives rise to the birth of massive stars. However, the detection of such disks in other clouds would be very difficult, first of all because of their much larger distance. The Lagoon Nebula (M8) is located four times further away than the Orion Nebula and it is also a site of recent high-mass star formation. Its brightest part constitutes a conspicuous region of ionised hydrogen gas (an `HII-region') dubbed `The Hourglass' because of the resemblance. The gas in this area is ionised by the action of the nearby, hot star Herschel 36 (Her 36) . High-resolution radio maps show that the emission from the ionised gas peaks at 2.7 arcsec southeast of Her 36. An early explanation was that this emission is due to an unseen, massive star that is deeply embedded in the gas and dust and which is causing an ultra-compact HII-region (UCHR), catalogued as G5.97-1.17 according to its galactic coordinates. High-resolution images from ESO During a detailed investigation of such ultra-compact HII regions, Bringfried Stecklum and his colleagues found that, unlike ordinary UCHRs, this particular object is visible on optical images obtained with the HST Wide-Field Planetary Camera (HST-WFPC). This means that, contrary to the others, it is not deeply embedded in the nebula - its light reaches us directly without suffering a high degree of absorption. They subsequently obtained a series of high-resolution, near-infrared images using the adaptive optics camera ADONIS at the ESO 3.6-m telescope and the speckle camera SHARP at the 3.5-m New Technology Telescope, both at the La Silla observatory. These observing techniques revealed a star which is slightly offset from the extended optical image of G5.97-1.17 seen on the HST-WFPC frames [3]. This star is found to radiate strongly in the near-infrared spectral region, quite similar to the reddest central stars of the Orion proplyds . This is a clear sign of the presence of circumstellar dust. In addition, the star is intrinsically not as bright as Her 36; it is therefore less massive and exercises less influence on its immediate surroundings. Thus, it cannot be responsible for the observed ionisation of G5.97-1.17. Caption to ESO PR Photo 09/97 [JPEG, 296k] ESO Press Photo 09/97 shows a true-colour, composite mosaic of several ADONIS near-infrared frames, covering a 35 x 26 arcsec area around the newly found star. The colour coding corresponds to the three wavelength regions of the frames used to make the mosaic, i.e. blue represents the J-filter (at 1.2 microns), green the H-filter (1.6 microns) and red the K-filter (2.2 microns). In this image, hot stars appear white and cool ones red. It is obvious that the brightest object in this area, Her 36, is surrounded by a dense cluster of (young) stars. The central star of G5.97-1.17 is indicated with an arrow. New HST images The recent release by the Space Telescope--European Coordinating Facility (ST-ECF) [4] of new HST images taken during a second series of observations of M8 with the new HST-WFPC2 camera allows an unambiguous identification of the physical nature of G5.97-1.17. On these images, G5.97-1.17 is spatially resolved and presents the typical bow shape with the apex of the bow pointing towards Her 36. The infrared star, seen on the ESO images and barely visible on the HST-WFPC2 images taken at far-red optical wavelengths, is indeed situated behind the bright bow which is most conspicuous in the light of the red H-alpha spectral line, emitted by hydrogen atoms. The appearance of this object is thus similar to that of the proplyd sources found in the Orion Nebula. Caption to ESO PR Photo 10/97 [GIF, 296k] This is quite obvious from ESO Press Photo 10/97 which shows a colour composite based on HST-WFPC2 images obtained through narrow-band optical filtres, isolating the light of doubly ionized oxygen atoms ([OIII]; blue) and atomic hydrogen (H-alpha; green) and in a far-red band (red). Two more faint stars are seen in this image while the bright star Her 36 is outside the border of the image (its location is at the lower left, at the intersection of the vertical, saturated CCD column and the 45 o line caused by the light diffracted in the telescope). In contrast to the Orion Nebula, the non-uniform distribution of light-absorbing dust in the foreground makes the detection of the ionised tail difficult. Note that the image is rotated clockwise by 146 o with respect to the astronomical coordinate system. A proplyd in the Lagoon Nebula The detailed description of these results is the subject of a forthcoming research paper [5]. The new understanding of G5.97-1.17, i.e. as harbouring an evaporating circumstellar disk heated by far-ultraviolet radiation from Her 36, is supported by the fact that a sufficient amount of high-energy ultraviolet light is received from that star to account for the radio emission observed from the ionised bow. This object therefore represents the first proplyd-type object detected outside Orion at a much larger distance . The full description of this phenomenon requires detailed knowledge on the physical conditions of the star Her 36 and the object itself. Unfortunately, sofar little is known about the properties of the stellar wind from Her 36, the mass-loss rate from G5.97-1.17 and the velocities of the interacting matter. The astronomer team therefore intends to carry out further adaptive-optics imaging and spectroscopy with the ESO instruments later this year. Great prospects for related research projects The detection of this new object shows that direct proofs for the existence of circumstellar disks in distant star-forming regions are possible with currently available telescopes. It also represents an important step forward for the preparation of scientific programmes devoted to the formation of stars and planets that will soon be carried out with the ESO Very Large Telescope (VLT). The new results demonstrate that the high-resolution images that will be obtained with the future giant telescopes and, especially, with the VLT Interferometer (VLTI) will most likely lead to important breakthroughs in our understanding on the complicated processes of star formation. This will in turn cast new light on how the Sun and the Earth came into existence, more than 4.5 billion years ago. Where to find additional information More details on the investigation of star formation in M8 and the newly discovered proplyd can be found on the World-Wide Web page of the Thüringer Landessternwarte (URL: http://www.tls-tautenburg.de/M8.html Notes: [1] The team consists of Bringfried Stecklum and Steffen Richter (Thüringer Landessternwarte, Tautenburg, Germany), Thomas Henning, Ralf Launhardt and Markus Feldt (Astrophysikalisches Institut und Universitätssternwarte, Friedrich-Schiller-Universität Jena), Thomas L. Hayward (Center for Radiophysics & Space Research, Cornell University, New York, USA), Melvin G. Hoare (Physics & Astronomy Department, Leeds University, UK) and Peter Hofner (National Astronomy & Ionosphere Center, Arecibo, USA). [2] Some years ago, infrared observations with the IRAS spacecraft led to the discovery of a disk around the isolated, nearby southern star Beta Pictoris . [3] This result was published in a paper by Stecklum et al. in 1995 (ApJ 445, L153). [4] The ST-ECF is a joint ESA/ESO group of specialists that is located at the ESO Headquarters in Garching, Germany. [5] Submitted to the Astronomical Journal . How to obtain ESO Press Information ESO Press Information is made available on the World-Wide Web (URL: http://www.eso.org../). ESO Press Photos may be reproduced, if credit is given to the European Southern Observatory.

  18. Human factor design of habitable space facilities

    NASA Technical Reports Server (NTRS)

    Clearwater, Yvonne A.

    1987-01-01

    Current fundamental and applied habitability research conducted as part of the U.S. space program is reviewed with emphasis on methods, findings, and applications of the results to the planning and design of the International Space Station. The discussion covers the following six concurrent directions of habitability research: operational simulation, functional interior decor research, space crew privacy requirements, interior layout and configuration analysis, human spatial habitability model, and analogous environments research.

  19. Multiwavelength interferometric observations and modeling of circumstellar disks

    NASA Astrophysics Data System (ADS)

    Schegerer, A. A.; Ratzka, T.; Schuller, P. A.; Wolf, S.; Mosoni, L.; Leinert, Ch.

    2013-07-01

    Aims: We investigate the structure of the innermost region of three circumstellar disks around pre-main sequence stars HD 142666, AS 205 N, and AS 205 S. We determine the inner radii of the dust disks and, in particular, search for transition objects where dust has been depleted and inner disk gaps have formed at radii of a few tenths of AU up to several AU. Methods: We performed interferometric observations with IOTA, AMBER, and MIDI in the infrared wavelength ranges 1.6-2.5 μm and 8-13 μm with projected baseline lengths between 25 m and 102 m. The data analysis was based on radiative transfer simulations in 3D models of young stellar objects (YSOs) to reproduce the spectral energy distribution and the interferometric visibilities simultaneously. Accretion effects and disk gaps could be considered in the modeling approach. Results from previous studies restricted the parameter space. Results: The objects of this study were spatially resolved in the infrared wavelength range using the interferometers. Based on these observations, a disk gap could be found for the source HD 142666 that classifies it as transition object. There is a disk hole up to a radius of Rin = 0.30 AU and a (dust-free) ring between 0.35 AU and 0.80 AU in the disk of HD 142666. The classification of AS 205 as a system of classical T Tauri stars could be confirmed using the canonical model approach, i.e., there are no hints of disk gaps in our observations. Based on observations made with telescopes of the European Organisation for Astronomical Research in the southern Hemisphere (ESO) at the Paranal Observatory, Chile, under the programs 073.A-9014, 075.C-0014, 075.C-0064, 075.C-0253, 077.C-0750, 079.C-0101, and 079.C-0595.Appendix A is available in electronic form at http://www.aanda.org

  20. Investigations of the Formation of Carbon Grains in Circumstellar Outflows

    NASA Technical Reports Server (NTRS)

    Contreras, Cesar; Salama, Farid

    2013-01-01

    The study of formation and destruction processes of cosmic dust is essential to understand and to quantify the budget of extraterrestrial organic molecules. Although dust with all its components plays an important role in the evolution of interstellar chemistry and in the formation of organic molecules, little is known on the formation and destruction processes of carbonaceous dust. PAHs are important chemical building blocks of interstellar dust. They are detected in interplanetary dust particles and in meteoritic samples. Additionally, observational, laboratory, and theoretical studies have shown that PAHs, in their neutral and ionized forms, are an important, ubiquitous component of the interstellar medium. Also, the formation of PAHs from smaller molecules has not been extensively studied. Therefore, it is imperative that laboratory experiments be conducted to study the dynamic processes of carbon grain formation from PAH precursors. Studies of interstellar dust analogs formed from a variety of PAH and hydrocarbon precursors as well as species that include the atoms O, N, and S, have recently been performed in our laboratory under conditions that simulate interstellar and circumstellar environments. The species formed in the pulsed discharge nozzle (PDN) plasma source are detected and characterized with a high-sensitivity cavity ringdown spectrometer (CRDS) coupled to a Reflectron time-of-flight mass spectrometer (ReTOF-MS), thus providing both spectroscopic and ion mass information in-situ. We report the first set of measurements obtained in these experiments and identify the species present in the experiments and the ions that are formed in the plasma process. From these unique measurements, we derive information on the size and the structure of interstellar dust grain particles, the growth and the destruction processes of interstellar dust and the resulting budget of extraterrestrial organic molecules.

  1. Evidence of circumstellar matter surrounding the Hercules X-1 system

    NASA Technical Reports Server (NTRS)

    Choi, C. S.; Dotani, T.; Nagase, F.; Makino, F.; Deeter, J. E.; Min, K. W.

    1994-01-01

    We analyze data from two eclipse ingresses of Her X-1 observed with Ginga on 1989 April 30 and May 19. These observations occur, respectively, during the MAIN HIGH and SHORT HIGH states in the 35 day modulation of Her X-1 intensity. We find significant residual X-ray flux during eclipse, with a gradual decrease in flux following the occultation of the neutron star by the atmosphere of HZ Her. During the central part of the eclipse the count rate becomes nearly constant, at 0.5 mCrab in the energy range 1.7-36.8 keV. From a spectral analysis of the residual emission during the total eclipse of the central source in the MAIN HIGH state, we determine the energy spectral index, alpha = 0.8, similar to that before eclipse. A remarkable feature of the eclipse spectrum is that it does not show a significant iron line feature in contrast to massive wind-fed pulsars, such as Vela X-1 and Cen X-3. From a timing analysis of the same eclipse data, we show that there are no pulses. These results imply that the emission comes from the scattering of continuum X-rays by material in a region considerably larger than the companion star. An extended accretion disk corona may be responsible for this scattering. However, partial eclipse of an extended accretion disk corona may be responsible for this scattering. However, partial eclipse of an extended accretion disk corona is insufficient to account for the count rates in mid-eclipse, when known parameters of the binary system are used. Based on the present results, we suggest that scattering occurs not only in the accretion disk corona but also in the circumstellar matter surrounding the system of Her X-1/HZ Her.

  2. Evidence of Circumstellar Matter Surrounding the Hercules X-1 System

    NASA Technical Reports Server (NTRS)

    Choi, C. S.; Dotani, T.; Nagase, F.; Makino, F.; Deeter, J. E.; Min, K. W.

    1994-01-01

    We analyze data from two eclipse ingresses of Her X-1 observed with Ginga on 1989 April 30 and May 19. These observations occur, respectively, during the MAIN HIGH and SHORT HIGH states in the 35 day modulation of Her X-1 intensity. We find significant residual X-ray flux during eclipse, with a gradual decrease in flux following the occultation of the neutron star by the atmosphere of HZ Her. During the central part of the eclipse the count rate becomes nearly constant, at 0.5 mcrab in the energy range 1.7-36.8 keV. From a spec- tral analysis of the residual emission during the total eclipse of the central source in the MAIN MGH state, we determine the energy spectral index, alpha = 0.8, similar to that before eclipse. A remarkable feature of the eclipse spectrum is that it does not show a significant iron line feature in contrast to massive wind-fed pulsars, such as Vela X-1 and Cen X-3. From a timing analysis of the same eclipse data, we show that there are no pulses. These results imply that the emission comes from the scattering of continuum X-rays by material in a region considerably larger than the companion star. An extended accretion disk corona may be responsible for this scattering. However, partial eclipse of an extended accretion disk corona is insufficient to account for the count rates in mid-eclipse, when known parameters of the binary system are used. Based on the present results, we suggest that scattering occurs not only in the accretion disk corona but also in the circumstellar matter surrounding the system of Her X-1/HZ Her.

  3. Doppler tomography of the circumstellar disk of π Aquarii

    NASA Astrophysics Data System (ADS)

    Zharikov, S. V.; Miroshnichenko, A. S.; Pollmann, E.; Danford, S.; Bjorkman, K. S.; Morrison, N. D.; Favaro, A.; Guarro Fló, J.; Terry, J. N.; Desnoux, V.; Garrel, T.; Martineau, G.; Buchet, Y.; Ubaud, S.; Mauclaire, B.; Kalbermatten, H.; Buil, C.; Sawicki, C. J.; Blank, T.; Garde, O.

    2013-12-01

    Aims: The work is aimed at studying the circumstellar disk of the bright classical binary Be star π Aqr. Methods: We analysed variations of a double-peaked profile of the Hα emission line in the spectrum of π Aqr that was observed in many phases during ~40 orbital cycles in 2004-2013. We applied the discrete Fourier transform (DFT) method to search for periodicity in the peak intensity ratio (V/R). Doppler tomography was used to study the structure of the disk around the primary. Results: The dominant frequency in the power spectrum of the Hα V/R ratio is 0.011873 day-1, which corresponds to a period of 84.2(2) days and agrees with the earlier determined orbital period of the system, Porb = 84.1 days. The V/R shows a sinusoidal variation that is phase-locked with the orbital period. Doppler maps of all our spectra show a non-uniform structure of the disk around the primary: a ring with the inner and outer radii at Vin ≈ 450 km s-1 and Vout ≈ 200 km s-1, respectively, along with an extended stable region (spot) at Vx ≈ 225 km s-1 and Vy ≈ 100 km s-1. The disk radius of ≈65 R⊙ = 0.33 AU was estimated by assuming Keplerian motion of a particle on a circular orbit at the disk's outer edge. Table 1 and π Aquarii spectra in FITS format are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/560/A30 http://www.astrosurf.com/aras/

  4. The impact of SN 1987A with its circumstellar ring

    NASA Technical Reports Server (NTRS)

    Luo, Ding; Mccray, Richard; Slavin, Johnathan

    1994-01-01

    The envleope of SN 1987A will strike its circumstellar ring in 12 +/- 3 yr after explosion (A.D. 1999+/-3), the exact time depending weakly on the uncertain density of diffuse gas between the supernova and the ring. The impact will drive a radiative shock into the ring with velocity approximatley 200-400 km s(exp -1). The shocked ring will become a bright optical and ultraviolet emsiison-line source. A bright arc will suddenly appear at the near side of the ring and grow into an entire ring about 11 months later. The luminosities of the brightest lines, H-alpha H-alpha, N v lambda lambda 1238, 1242, and O VI lambda lambda 1032, 1038 will rise rapidly to approxminately 10(exp 36)-10(exp 37) ergs s(exp -1) and remain bright for several years after impact. The emission lines from the shocked ring will have FWHM approximatley 300-600 km s(exp -1) and complex profiles that will depend on position and w