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1

Circumstellar habitable zones for deep terrestrial biospheres  

NASA Astrophysics Data System (ADS)

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.

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

2013-09-01

2

Habitable zones in the universe.  

PubMed

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

Gonzalez, Guillermo

2005-12-01

3

The Galactic Habitable Zone  

SciTech Connect

We propose the concept of a 'Galactic Habitable Zone' (GHZ). Similar to the circumstellar habitable zone (CHZ), the GHZ is that region in a spiral galaxy where life can exist. The width of the GHZ is controlled by two factors. The inner (closest to the center of the galaxy) limit is set by threats to complex life: nearby transient sources of ionizing radiation and comet impacts. Such threats tend to increase close to the galactic center. The outer limit is imposed by galactic chemical evolution, specifically the abundance of heavier elements. Observation of stars in the Milky Way galaxy suggests that the outer reaches of a spiral galaxy may be too poor in heavy elements to allow terrestrial complex life to exist.

Gonzalez, Guillermo (Iowa State University)

2002-08-21

4

The habitable zone and extreme planetary orbits.  

PubMed

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

Kane, Stephen R; Gelino, Dawn M

2012-10-04

5

The Habitable Zone  

NSDL National Science Digital Library

This illustration is an approximate representation of the planets in our solar system and their relation to what scientists call The Habitable Zone. The planet distances from the sun are measured in Astronomical Units (AU) and are not to scale.

2008-03-26

6

Habitable Zones in the Universe  

Microsoft Academic Search

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

Guillermo Gonzalez

2005-01-01

7

Habitable zones and UV habitable zones around host stars  

NASA Astrophysics Data System (ADS)

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.

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

2010-01-01

8

Trojans in habitable zones.  

PubMed

With the aid of numerical experiments we examined the dynamical stability of fictitious terrestrial planets in 1:1 mean motion resonance with Jovian-like planets of extrasolar planetary systems. In our stability study of the so-called "Trojan" planets in the habitable zone, we used the restricted three-body problem with different mass ratios of the primary bodies. The application of the three-body problem showed that even massive Trojan planets can be stable in the 1:1 mean motion resonance. From the 117 extrasolar planetary systems only 11 systems were found with one giant planet in the habitable zone. Out of this sample set we chose four planetary systems--HD17051, HD27442, HD28185, and HD108874--for further investigation. To study the orbital behavior of the stable zone in the different systems, we used direct numerical computations (Lie Integration Method) that allowed us to determine the escape times and the maximum eccentricity of the fictitious "Trojan planets." PMID:16225431

Schwarz, Richard; Pilat-Lohinger, Elke; Dvorak, Rudolf; Erdi, Balint; Sándor, Zsolt

2005-10-01

9

Habitable zones and UV habitable zones around host stars  

Microsoft Academic Search

Ultraviolet radiation is a double-edged sword to life. If it is too strong, the terrestrial biological systems will be damaged.\\u000a And if it is too weak, the synthesis of many biochemical compounds cannot go along. We try to obtain the continuous ultraviolet\\u000a habitable zones, and compare the ultraviolet habitable zones with the habitable zones of host stars. Using the boundary

Jianpo Guo; Fenghui Zhang; Xianfei Zhang; Zhanwen Han

2010-01-01

10

Habitable Zone Lifetimes of Exoplanets around Main Sequence Stars.  

PubMed

Abstract 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 7.79×10(9) 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. Key Words: Exoplanet habitability metrics-Continuously habitable zone-Stellar evolution-Planetary habitability. Astrobiology 13, 833-849. PMID:24047111

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

2013-09-01

11

Habitable Zones Around Low-Mass Stars  

NASA Astrophysics Data System (ADS)

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.)

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

2011-09-01

12

Oscillations in the habitable zone around ? Centauri B  

NASA Astrophysics Data System (ADS)

The ? Cen AB system is an attractive one for radial velocity observations to detect potential exoplanets. The high metallicity of both ? 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 ? Cen B exhibiting low chromospheric activity), high-precision surveys of ? 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 ? Cen A. We investigate the habitability of planets around ? Cen B using one-dimensional latitudinal energy balance models (LEBMs), which fully incorporate the presence of ? 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 ? Cen A, but there are variations in fractional habitability for planets orbiting at the boundaries of the zone due to ? 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.

Forgan, Duncan

2012-05-01

13

The galactic habitable zone in barred galaxies  

Microsoft Academic Search

One of the criteria for the concept of a galactic habitable zone (GHZ) is that the pattern speed of the stars in the GHZ should be close to the pattern speed of the spiral arms. Another criteria is that the stars in it should have a high enough metallicity. In a barred galaxy, the GHZ will be more complicated to

M. Sundin

2006-01-01

14

Habitability and Habitable Zone in Multiple Star Systems  

NASA Astrophysics Data System (ADS)

During the course of its successful operation, in addition to detecting more than 3000 planets and planetary candidates, the Kepler space telescope has identified over 2000 binary stars as well as numerous multiple stars systems, especially some with mutual stellar separations of 20 AU and smaller. The discovery of such multi-star systems prompted us to study the possibility of the formation of terrestrial planets in these systems, and explore their habitability. To determine the habitable zone (HZ) in multiple star systems, we have extended our recent methodology for calculating HZ in and around binary stars, to systems with arbitrary numbers of stellar components, and have developed a generalized formalism for calculating the boundaries of the HZ in any planetary system with two or more stars. Our methodology takes into account the stellar energy distribution of each star, which determines the interaction between the radiation received at the location of the planet and the planet’s atmosphere, and accounts for the motion and dynamics of the stellar system and its consequences on the spatial variations of the boundaries of the HZ. In this talk, we present our methodology and discuss its application to several multiple star systems detected by the Kepler. We show how the boundaries of the HZ are determined, and demonstrate their variations as the stars move in their orbits. Combined with the results of the studies of the orbital stability of an Earth-like planet in our multiple star systems, we discuss the habitability of these systems and the prospect of the detection of Earth-like planets in their habitable zones.

Haghighipour, Nader; Mueller, T.

2013-10-01

15

UV habitable zones around M stars  

Microsoft Academic Search

During the last decade there was a change in paradigm, which led to consider that terrestrial-type planets within liquid-water habitable zones (LW-HZ) around M stars can also be suitable places for the emergence and evolution of life. Since many dMe stars emit large amount of UV radiation during flares, in this work we analyze the UV constrains for living systems

Andrea P. Buccino; Guillermo A. Lemarchand; Pablo J. D. Mauas

2007-01-01

16

Ultraviolet radiation constraints around the circumstellar habitable zones  

Microsoft Academic Search

Ultraviolet radiation is known to inhibit photosynthesis, induce DNA destruction and cause damage to a wide variety of proteins and lipids. In particular, UV radiation between 200 and 300 nm becomes energetically very damaging to most of the terrestrial biological systems. On the other hand, UV radiation is usually considered one of the most important energy source on the primitive

Andrea P. Buccino; Guillermo A. Lemarchand; Pablo J. D. Mauas

2006-01-01

17

Radiative habitable zones in martian polar environments.  

PubMed

The biologically damaging solar ultraviolet (UV) radiation (quantified by the DNA-weighted dose) reaches the martian surface in extremely high levels. Searching for potentially habitable UV-protected environments on Mars, we considered the polar ice caps that consist of a seasonally varying CO2 ice cover and a permanent H2O ice layer. It was found that, though the CO2 ice is insufficient by itself to screen the UV radiation, at approximately 1 m depth within the perennial H2O ice the DNA-weighted dose is reduced to terrestrial levels. This depth depends strongly on the optical properties of the H2O ice layers (for instance snow-like layers). The Earth-like DNA-weighted dose and Photosynthetically Active Radiation (PAR) requirements were used to define the upper and lower limits of the northern and southern polar Radiative Habitable Zone (RHZ) for which a temporal and spatial mapping was performed. Based on these studies we conclude that photosynthetic life might be possible within the ice layers of the polar regions. The thickness varies along each martian polar spring and summer between approximately 1.5 and 2.4 m for H2O ice-like layers, and a few centimeters for snow-like covers. These martian Earth-like radiative habitable environments may be primary targets for future martian astrobiological missions. Special attention should be paid to planetary protection, since the polar RHZ may also be subject to terrestrial contamination by probes. PMID:16044598

Córdoba-Jabonero, Carmen; Zorzano, María-Paz; Selsis, Franck; Patel, Manish R; Cockell, Charles S

2005-06-01

18

Galactic Habitable Zone and Astrobiological Complexity  

NASA Astrophysics Data System (ADS)

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.

Vukotic, B.

2012-12-01

19

Habitable zones around main sequence stars.  

PubMed

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

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

1993-01-01

20

Number of Planets with life in the galactic habitable zone deduced by modified Drake Equation  

NASA Astrophysics Data System (ADS)

In this work we estimate the quantity of planets with life in the Galactic Habitable Zone, using a modified version of the Drake's equation: [ N_L =sumlimits_i {N_i^* fpi nei fvi } ] where i is the spectral class, NL is the number of planets with life, N*I is the number of stars in the galactic ecosphere of spectral class i, fpi is the fraction of stars that have planets, nei is the number of planets in the circumstellar ecosphere, and fvi is the fraction of planets in the ecosphere with life.

Peña-Cabrera, G. V. Y.; Durand-Manterola, H. J.

21

Which habitable zones have the most real estate?  

NASA Astrophysics Data System (ADS)

Over the last few years, our concept of a habitable world has become much broader. Besides terrestrial planets in the conventional habitable zone roughly 0.7-1.5 AU from a Sun-like star, we realize that a moon of a Jovian planet in the habitable zone may be habitable, as well as a moon like Europa that is tidally heated. Habitable planets may exist in eccentric orbits and in multiple-star systems. Even tidally-locked planets may have habitable regions near their terminators. All of this provides a potentially rich variety and diversity of habitable planets. But the total number and relative importance of all of these types of planets remains relatively unexplored. Which of these zones have the most real estate? In this paper, we estimate the total habitable surface area of all the potentially habitable worlds in the Galaxy and distribution of this surface area among the various kinds of habitable zones described above. For each type of habitable world, we estimate the mean habitable surface area per body and the mean number of bodies per spectral type and class of star. For each case we attempt to apply relevant numbers from the solar system, and then we add detail from the growing literature on extrasolar planet distributions as a function of radius, mass, metalicity, etc.. Estimates like these may ultimately help us understand probabilistically the origin of life and prioritize our searches for life elsewhere.

Belikov, R.; Kuchner, M.

2009-12-01

22

Additional planets in the habitable zone of Gliese 581?  

Microsoft Academic Search

Context: The 3-planet system that contains two super Earths has recently been verified around the M dwarf Gliese 581. Recent theoretical work into the system's habitable zone (HZ) still raises questions as to the habitability of the known planets; however, the system remains the best candidate for potentially habitable planets. Aims: We address the possible existence of an undetected, lower

R. Zollinger; J. C. Armstrong

2009-01-01

23

Hydrogen Greenhouse Planets Beyond the Habitable Zone  

NASA Astrophysics Data System (ADS)

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 H2-He mixtures can maintain surface temperatures above the freezing point of water well beyond the "classical" habitable zone defined for CO2 greenhouse atmospheres. Using a one-dimensional radiative-convective model, we find that 40 bars of pure H2 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 H2, 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 H2-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 H2-He atmosphere and be habitable at ~2.6 AU from its host M star.

Pierrehumbert, Raymond; Gaidos, Eric

2011-06-01

24

Sensitivity of Transit Searches to Habitable-Zone Planets  

Microsoft Academic Search

Photon-limited transit surveys in the V band are in principle about 20 times more sensitive to planets of fixed size in the habitable zone around M stars than G stars. In the I band the ratio is about 400. The advantages of a closer habitable zone and smaller stars (together with the numerical superiority of M stars) more than compensate

Andrew Gould; Joshua Pepper; D. L. DePoy

2003-01-01

25

Tectonics and the photosynthetic habitable zone (Invited)  

NASA Astrophysics Data System (ADS)

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.

Sleep, N. H.

2009-12-01

26

Hazes at the Inner Edge of the Habitable Zone  

Microsoft Academic Search

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

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

2009-01-01

27

Candidate Planets in the Habitable Zones of Kepler Stars  

NASA Astrophysics Data System (ADS)

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 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 HZ. Sixty-two planets have p 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 (??) 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.

Gaidos, Eric

2013-06-01

28

Planet formation in the habitable zone of alpha Centauri B  

Microsoft Academic Search

Recent studies have shown that alpha Centauri B might be, from an observational point of view, an ideal candidate for the detection of an Earth-like planet in or near its habitable zone (0.5-0.9au). We study here if such habitable planets can form, by numerically investigating the planet-formation stage which is probably the most sensitive to binarity effects: the mutual accretion

P. Thébault; Francesco Marzari; Hans Scholl

2009-01-01

29

Radiative habitable zones in martian polar environments  

Microsoft Academic Search

The biologically damaging solar ultraviolet (UV) radiation (quantified by the DNA-weighted dose) reaches the martian surface in extremely high levels. Searching for potentially habitable UV-protected environments on Mars, we considered the polar ice caps that consist of a seasonally varying CO2 ice cover and a permanent H2O ice layer. It was found that, though the CO2 ice is insufficient by

Carmen Córdoba-Jabonero; María-Paz Zorzano; Franck Selsis; Manish R. Patel; Charles S. Cockell

2005-01-01

30

Habitable Zones Around Stars and the Search for Extraterrestrial Life  

Microsoft Academic Search

The habitable zone, or HZ, is defined as the region around a star in which liquid water can exist on the surface of a planet. Liquid water can exist in subsurface environments on planets or moons outside of the HZ (e.g., Jupiter's moon, Europa), but this possibility is of little significance, as such environments cannot be observed or otherwise investigated.

J. F. Kasting

2001-01-01

31

Stability of inclined orbits of terrestrial planets in habitable zones  

Microsoft Academic Search

In long-term stability studies of terrestrial planets moving in the habitable zone (HZ) of a sun-like star, we distinguish four different configurations: (i) planets moving in binary star systems, (ii) the inner type (where the gas giant moves outside the HZ), (iii) the outer type (where the gas giant is closer to the star, than the HZ) and (iv) the

Barbara Funk; Richard Schwarz; Elke Pilat-Lohinger; Áron Süli; Rudolf Dvorak

2009-01-01

32

Tidal Heating and the Boundaries of the Habitable Zone  

Microsoft Academic Search

With the discovery of planetary systems beyond our own, and the interest in their implications for extraterrestrial life, the notion of a habitable zone emerged, based on a requirement of surface liquid water, under an atmosphere warmed by stellar radiation [1]. Widespread use of that definition has persisted even as it became increasing clear that one of the most likely

R. Greenberg; R. Barnes; B. Jackson

2009-01-01

33

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

PubMed

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

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

1987-01-01

34

Is there a habitable zone around M and late K-type stars?  

NASA Astrophysics Data System (ADS)

The habitable zone (HZ) is the circumstellar region where the greenhouse effect of a planetary atmosphere can provide surface temperatures above the freezing point of water. The inner and outer limits of the HZ depend on the total stellar luminosity (Lbol) and the planet's orbital distance. In the case of M and late K-type stars, the HZ is much closer to the host star than in the case of solar-type G stars because the total stellar luminosity is significantly lower (<10%). Observations show that late K and M-type stars are very active in the EUV-X region and have a ratio LX/Lbol of nearly 10-3 during the first few Gyr of their lifes. LX/Lbol for solar type stars can also be as high for ages below 100~Myr but it decreases rapidly to a value of about 10-5 in less than 1 Gyr. The high X-EUV irradiation heats dramatically the upper layer (exosphere) of the planetary atmospheres, inducing a strong thermal escape that could affect not only H and He, but also the main constituents of the atmosphere (N, C, O). We investigate thermal escape on terrestrial planets around M and late K-type stars in order to estimate the loss rate of gases for various atmospheric compositions and to put constraints on habitability.

Selsis, F.; Lammer, H.; Ribas, I.

2003-04-01

35

Extrasolar Planetary Habitable Zones and the Number of Gaias  

Microsoft Academic Search

We present a general modelling scheme for assessing the suitability for life on any Earth-like extrasolar planet by calculating the habitable zone (HZ) in main-sequence-star planetary systems. Our approach is based on an integrated Earth system analysis that relates the boundaries of the HZ to the limits of C4-photosynthesis processes. Within this model, the evolution of the HZ for any

W. von Bloh; S. Franck; C. Bounama; M. Steffen; D. Schönberner; H.-J. Schellnhuber

2001-01-01

36

Habitable Zones and the Number of Gaia's Sisters  

Microsoft Academic Search

We present a general modeling scheme for assessing the suit- ability for life on any Earth-like extrasolar planet by calculating the habit- able zone (HZ) in main-sequence-star planetary systems. Our approach is based on an integrated Earth system analysis that relates the boundaries of the HZ to the limits of C4-photosynthetic processes. Within this model, the evolution of the HZ

S. Franck; W. von Bloh; C. Bounama; M. Steffen; D. Schönberner; H.-J. Schellnhuber

2002-01-01

37

Generalizing Habitable Zones in Exoplanetary Systems --- The Concept of the Life Supporting Zone  

Microsoft Academic Search

The concept of Life Supporting Zones is introduced in order to enhance the idea of habitable zones. The restriction to water and to a terrestrial biochemistry is given up and exotic solvents in liquid phases on planetary surfaces will be considered.

J. J. Leitner; R. Schwarz; M. G. Firneis; R. Hitzenberger; D. Neubauer

2010-01-01

38

Tidal Heating and the Boundaries of the Habitable Zone  

NASA Astrophysics Data System (ADS)

With the discovery of planetary systems beyond our own, and the interest in their implications for extraterrestrial life, the notion of a habitable zone emerged, based on a requirement of surface liquid water, under an atmosphere warmed by stellar radiation [1]. Widespread use of that definition has persisted even as it became increasing clear that one of the most likely places in our solar system for extraterrestrial life to first be found, Europa, lies outside of that conventional habitable zone [2]. Europa derives its heat from internal tidal dissipation, rather than insolation. And, although there is no atmosphere to maintain liquid water at the surface, a vast global ocean lies below a relatively thin layer of surface ice. We find that transport of radiolytic oxidants and other substances through the permeable ice layer may be adequate to support life, perhaps even an ecology including complex organisms [3]. Clearly the definition of “habitable zone” needs to be expanded to include planetary bodies where tidal heating is significant. Such heating, which requires an adequate orbital eccentricity, may be common and important in extrasolar systems. Eccentricities themselves tend to be damped by tides, which would turn off the heating, but we have demonstrated several ways that tidal heating can be important: (1) As with Europa, interactions with other orbiters can maintain eccentricities [4]; (2) Many planets previously assumed to have damped to circular orbits may still retain some eccentricity [5]; (3) Even among planets now on circular orbits, many underwent tidal heating recently enough that it remains a factor in current geophysics [6]. Tidal heating may make otherwise uninhabitable planets habitable by, for example, creating Europa-like planets, or driving plate tectonics in small, rocky planets [7]. The notion of a habitable zone needs to be modified to account for this broader array of habitable planetary types. References: [1] Kasting, J., et al., Icarus 101, 108, 1993. [2] Greenberg, R., Europa the Ocean Moon, Springer, 2005. [3] Greenberg, R., Astrobiology, submitted 2009. [4] Barnes, R., et al., Astrophys. J. 695, 1006, 2009. [5] Jackson, B., et al., Astrophys. J. 678, 1396, 2008. [6] Jackson, B., et al., Astrophys. J. 681, 1631, 2008. [7] Jackson, B., et al., Mon. Not. Roy. Astron. Soc. 391, 237, 2008.

Greenberg, R.; Barnes, R.; Jackson, B.

2009-12-01

39

Planetary Obliquity Evolution in the 47 Uma Habitable Zone  

NASA Astrophysics Data System (ADS)

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.

Erikson, A.; Skoglöv, E.

2003-04-01

40

Orbital Stability of Terrestrial Planets inside the Habitable Zones of Extrasolar Planetary Systems  

Microsoft Academic Search

We investigate orbital stability of terrestrial planets inside the habitable zones of three stellar systems, i.e., 51 Peg, 47 UMa, and HD 210277, with recently discovered giant planets. These systems have similar habitable zones; however, their giant planets have different masses and significantly different orbital parameters. It is shown that stable orbits of terrestrial planets exist in the entire habitable

M. Noble; Z. E. Musielak; M. Cuntz

2002-01-01

41

Habitable Zones Around Stars and the Search for Extraterrestrial Life  

NASA Astrophysics Data System (ADS)

The habitable zone, or HZ, is defined as the region around a star in which liquid water can exist on the surface of a planet. Liquid water can exist in subsurface environments on planets or moons outside of the HZ (e.g., Jupiter's moon, Europa), but this possibility is of little significance, as such environments cannot be observed or otherwise investigated. The continuously habitable zone, or CHZ, is the region that remains habitable over some finite period of time. The CHZ for any extended time interval is narrower than the HZ because all main sequence stars grow brighter as they age, so that their HZs move outward with time. The conservative estimate for the inner edge of the HZ in our own Solar System has not changed in the last 13 years. It is at 0.95 AU, which is the distance at which Earth's water would be lost, assuming zero cloud feedback on climate. If clouds tend to cool the climate as the solar flux increases, as seems likely, the inner edge of the HZ could be well inside that distance. Venus' orbital distance, 0.72 AU, provides an empirical, 'optimistic' limit for the inner edge of the HZ. The outer edge of the HZ could lie as far out as 2.4 AU if CO2 ice clouds warm a planet's surface, as predicted by some authors (Forget and Pierrehumbert, Science, 1997). However, the warming by CO2 clouds is problematical, as it depends critically on poorly-known factors such as cloud optical depth, cloud height, and fractional cloud cover. Indeed, it is a challenge to figure out how Mars, at 1.52 AU, managed to stay warm enough to allow liquid water to flow on its surface early in its history when the Sun was less bright. Greenhouse warming by CH4 may be at least part of the answer. If so, the outer edge of the HZ depends on a variety of factors that are not easy to predict. The exciting news on the horizon is that it may eventually be possible to observe planets within stellar HZs by way of NASA's Terrestrial Planet Finder (TPF) mission. If it works, TPF will provide either visible or thermal infrared spectra that will allow us to characterize planetary atmospheres and, perhaps, to look for evidence of life. Once this happens, the study of habitable zones and habitable planets will assume much more practical significance.

Kasting, J. F.

2001-12-01

42

THESIS: terrestrial and habitable zone infrared spectroscopy spacecraft  

NASA Astrophysics Data System (ADS)

THESIS is a concept for a medium class mission designed for spectroscopic characterization of extrasolar planets between 2-14 microns. The concept leverages off the recent first-steps made by Spitzer and Hubble in characterizing the atmospheres of alien gas giants. Under favourable circumstances, THESIS is capable of identifying biogenic molecules in habitable-zone planets, thereby determining conditions on worlds where life might exist. By systematically characterizing many worlds, from rocky planets to gas-giants, THESIS would deliver transformational science of profound interest to astronomers and the general public.

Vasisht, G.; Swain, M. R.; Akeson, R. L.; Burrows, A.; Deming, D.; Grillmair, C. J.; Greene, T. P.

2008-08-01

43

Evolution from Ocean Planet to Land Planet by Water Loss; The Inner Edge of Habitable Zone  

Microsoft Academic Search

We discuss the inner edge of Habitable Zone and imaginary planetary evolution from ocean planet to land planet by focus on water loss. When such evolution occur, planets keep habitable. We demonstrate the possibility of the various type of habitable planets.

T. K. Kodama; H. G. Genda; Y. A. Abe; K. Z. Zahnle

2011-01-01

44

Chemical Evolution and the Galactic Habitable Zone of M31  

NASA Astrophysics Data System (ADS)

We have computed the Galactic Habitable Zones (GHZs) of the Andromeda galaxy (M31) based on the probability of terrestrial planet formation, which depends on the metallicity (Z) of the interstellar medium, and the number of stars formed per unit surface area. The GHZ was obtained from a chemical evolution model built to reproduce a metallicity gradient in the galactic disk, [O/H](r)=-0.015 dex kpc^{-1} × r(kpc) + 0.44 dex. If we assume that Earth-like planets form with a probability law that follows the Z distribution shown by stars with detected planets, the most probable GHZ per pc^2 is located between 3 and 7 kpc for planets with ages between 6 and 7 Gyr. However, the highest number of stars with habitable planets is located in a ring between 12 and 14 kpc with a mean age of 7 Gyr. 11% and 6.5% of the all formed stars in M31 may have planets capable of hosting basic and complex life, respectively.

Carigi, L.; García-Rojas, J.; Meneses-Goytia, S.

2013-10-01

45

Extrasolar Planetary Habitable Zones and the Number of Gaias  

NASA Astrophysics Data System (ADS)

We present a general modelling scheme for assessing the suitability for life on any Earth-like extrasolar planet by calculating the habitable zone (HZ) in main-sequence-star planetary systems. Our approach is based on an integrated Earth system analysis that relates the boundaries of the HZ to the limits of C4-photosynthesis processes. Within this model, the evolution of the HZ for any main-sequence-star planetary system can be calculated straightforwardly, and a convenient filter can be constructed that picks the candidates for photosynthesis-based life from all the extrasolar planets discovered by novel observational methods. These results can be used to determine the average number of planets per planetary system that are within the HZ. With the help of a segment of the Drake equation, the number of ``Gaias'' (i.e., extrasolar terrestrial planets with a globally acting biosphere) can be estimated. Our calculation gives about half a million Gaias in the Milky Way.

von Bloh, W.; Franck, S.; Bounama, C.; Steffen, M.; Schönberner, D.; Schellnhuber, H.-J.

46

The Orbits of Terrestrial Planets in the Habitable Zones of Known Extrasolar Planetary Systems  

Microsoft Academic Search

We show that terrestrial planets could survive in variously restricted regions of the habitable zones of 47 Ursae Majoris, ? Eridani, and ? Coronae Borealis, but nowhere in the habitable zones of Gliese 876 and ? Andromedae. The first three systems between them are representative of a large proportion of the 90 or so extrasolar planetary systems discovered by mid-2002,

Barrie W Jones; P. Nick Sleep

47

The Orbits of Terrestrial Planets in the Habitable Zones of Known Extrasolar Planetary Systems  

Microsoft Academic Search

We show that terrestrial planets could survive in variously restricted regions of the habitable zones of 47 Ursae Majoris, Epsilon Eridani, and Rho Coronae Borealis, but nowhere in the habitable zones of Gliese 876 and Upsilon Andromedae. The first three systems between them are representative of a large proportion of the 90 or so extrasolar planetary systems discovered by mid-2002,

B. W. Jones; P. N. Sleep

2003-01-01

48

Habitable Zones around Main-sequence Stars: New Estimates  

NASA Astrophysics Data System (ADS)

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 CO2 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 H2O and CO2 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 eff <~ 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 ??, 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.

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

2013-03-01

49

The Orbits of Terrestrial Planets in the Habitable Zones of Known Extrasolar Planetary Systems  

NASA Astrophysics Data System (ADS)

We show that terrestrial planets could survive in variously restricted regions of the habitable zones of 47 Ursae Majoris, Epsilon Eridani, and Rho Coronae Borealis, but nowhere in the habitable zones of Gliese 876 and Upsilon Andromedae. The first three systems between them are representative of a large proportion of the 90 or so extrasolar planetary systems discovered by mid-2002, and thus there are many known systems worth searching for terrestrial planets in habitable zones. We reach our conclusions by launching putative Earth-mass planets in various orbits and following their fate with a mixed-variable symplectic integrator.

Jones, B. W.; Sleep, P. N.

50

TERRESTRIAL, HABITABLE-ZONE EXOPLANET FREQUENCY FROM KEPLER  

SciTech Connect

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.

Traub, Wesley A., E-mail: wtraub@jpl.nasa.gov [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

2012-01-20

51

Habitable Planet Formation in Binary Star Systems  

Microsoft Academic Search

Assuming current models of terrestrial planet formation in the Solar System, we numerically investigate the conditions under which the secondary star in a binary system will inhibit planet growth in the circumstellar habitable zone. Runaway accretion is assumed to be precluded if the secondary (1) causes the planetesimal orbits to cross within the runaway accretion time scale and (2) if,

Daniel P Whitmire; John J. Matese; Lee Criswell; Seppo Mikkola

1998-01-01

52

The Orbits of Terrestrial Planets in the Habitable Zones of Known Exoplanetary Systems  

Microsoft Academic Search

We show that terrestrial planets could survive in variously restricted\\u000aregions of the habitable zones of 47 Ursae Majoris, Epsilon Eridani, and Rho\\u000aCoronae Borealis, but nowhere in the habitable zones of Gliese 876 and Upsilon\\u000aAndromedae. The first three systems between them are representative of a large\\u000aproportion of the 90 or so extrasolar planetary systems discovered by mid-2002,

Barrie W Jones; P. Nick Sleep

2002-01-01

53

Probability distribution of terrestrial planets in habitable zones around host stars  

Microsoft Academic Search

With more and more exoplanets being detected, it is paid closer attention to whether there are lives outside solar system.\\u000a We try to obtain habitable zones and the probability distribution of terrestrial planets in habitable zones around host stars.\\u000a Using Eggleton’s code, we calculate the evolution of stars with masses less than 4.00 M\\u000a ?. We also use the fitting

Jianpo Guo; Fenghui Zhang; Xuefei Chen; Zhanwen Han

2009-01-01

54

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

NASA Astrophysics Data System (ADS)

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.

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

2012-09-01

55

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

SciTech Connect

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.

Charnoz, Sebastien; Taillifet, Esther, E-mail: charnoz@cea.fr [Laboratoire AIM, Universite Paris Diderot/CEA/CNRS, 91191 Gif-sur-Yvette Cedex (France)

2012-07-10

56

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

NASA Astrophysics Data System (ADS)

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.

Charnoz, Sébastien; Taillifet, Esther

2012-07-01

57

EXPLORING THE HABITABLE ZONE FOR KEPLER PLANETARY CANDIDATES  

SciTech Connect

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.

Kaltenegger, L. [MPIA, Koenigstuhl 17, 69117 Heidelberg (Germany); Sasselov, D., E-mail: lkaltene@cfa.harvard.edu [Harvard Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)

2011-08-01

58

The dynamical structure of the habitable zone in the HD 38529, HD 168443 and HD 169830 systems  

Microsoft Academic Search

The dynamical structure of the habitable zone in the multiple exoplanetary systems HD 38529, HD 168443 and HD 169830 is investigated. By using long-time numerical integration and fast chaos-detection methods, it is shown that the habitable zone of all three systems is mostly chaotic. There is a stable region between the two known planets only in the system HD 38529,

B. Érdi; R. Dvorak; Zs. Sándor; E. Pilat-Lohinger; B. Funk

2004-01-01

59

Validating the First Habitable-Zone Planet Candidates Identified by the NASA Kepler Mission  

Microsoft Academic Search

At the beginning of Cycle 8, the NASA Kepler Mission will have completed two years of science observations, the minimum baseline sufficient to identify candidate transiting exoplanets orbiting within the habitable-zones of Sun-like stars. The principal task that lies ahead is to reject from this sample the false positives (blends of eclipsing binaries that precisely mimic the signal of a

David Charbonneau; Jean-Michel Desert; Francois Fressin; Sarah Ballard; William Borucki; David Latham; Ronald Gilliland; Sara Seager; Heather Knutson; Jonathan Fortney; Timothy Brown; Eric Ford; Drake Deming; Guillermo Torres

2011-01-01

60

Can terrestrial planets exist in the habitable zones of known exoplanetary systems?  

Microsoft Academic Search

The habitable zone (HZ) is defined as the range of distances from a star within which water at the surface of a terrestrial planet would be in the liquid phase. We have investigated whether terrestrial planets could exit in the HZs of known exoplanetary systems long enough for life to have emerged and to have evolved. Four contrasting systems in

Barrie W. Jones; P. Nick Sleep

2001-01-01

61

The stability of the orbits of terrestrial planets in the habitable zones of known exoplanetary systems  

Microsoft Academic Search

We have investigated whether terrestrial planets can exist in orbits in known exoplanetary systems such that life could have emerged on those planets. Four contrasting systems have been examined in which giant planets have been detected. Mixed-variable symplectic numerical integration has been used to investigate the orbits of putative terrestrial planets within the habitable zone of each system (the range

B. W. Jones; P. N. Sleep; J. E. Chambers

2001-01-01

62

Planets Formed in Habitable Zones of M Dwarf Stars Probably Are Deficient in Volatiles  

Microsoft Academic Search

Dynamical considerations, presented herein via analytic scalings and numerical experiments, imply that Earth-mass planets accreting 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 accretionary epoch are larger

Jack J. Lissauer

2007-01-01

63

Earth-like worlds on eccentric orbits: excursions beyond the habitable zone  

Microsoft Academic Search

any of the recently discovered extrasolar giant planets move around their stars on highly eccentric orbits, and some with e => 0.7. Systems with planets within or near the habitable zone (HZ) will possibly harbour life on terrestrial-type moons if the seasonal temperature extremes resulting from the large orbital eccentricities of the planets are not too severe. Here we use

Darren M. Williams; David Pollard

2002-01-01

64

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

Microsoft Academic Search

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

C. L. Cepko; C. P. Austin; X. Yang; M. Alexiades; D. Ezzeddine

65

Habitable zones around low mass stars and the search for extraterrestrial life.  

PubMed

Habitable planets are likely to exist around stars not too different from the Sun if current theories about terrestrial climate evolution are correct. Some of these planets may have evolved life, and some of the inhabited planets may have evolved O2-rich atmospheres. Such atmospheres could be detected spectroscopically on planets around nearby stars using a space-based interferometer to search for the 9.6 micron band of O3. Planets with O2-rich atmospheres that lie within the habitable zone around their parent star are, in all probability, inhabited. PMID:9150578

Kasting, J F

1997-06-01

66

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

SciTech Connect

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.

Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David R. [NASA Exoplanet Science Institute, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Boyajian, Tabetha S.; McAlister, Harold A.; Henry, Todd J.; Jao, Wei-Chun; Riedel, Adric R. [Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106 (United States); Van Belle, Gerard T. [European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching (Germany); Lopez-Morales, Mercedes [Institut de Ciencies de L'Espai (CSIC-IEEC), Campus UAB, Facultat Ciencies, Torre C5 parell 2, 08193 Bellaterra, Barcelona (Spain); Subasavage, John P. [Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile); Schaefer, Gail; Ten Brummelaar, Theo A.; Sturmann, Laszlo; Sturmann, Judit; Mazingue, Jude; Turner, Nils H.; Farrington, Chris; Goldfinger, P. J. [CHARA Array, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Ridgway, Stephen, E-mail: kaspar@caltech.edu [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726-6732 (United States)

2011-03-10

67

The stability of the orbits of terrestrial planets in the habitable zones of known exoplanetary systems  

NASA Astrophysics Data System (ADS)

We have investigated whether terrestrial planets can exist in orbits in known exoplanetary systems such that life could have emerged on those planets. Four contrasting systems have been examined in which giant planets have been detected. Mixed-variable symplectic numerical integration has been used to investigate the orbits of putative terrestrial planets within the habitable zone of each system (the range of distances from the star within which water at the surface of a terrestrial planet would be in the liquid phase). We have shown that Rho CrB and 47 UMa could have terrestrial planets in orbits that remain confined to their habitable zones for biologically significant lengths of time. We have also shown that the Gliese 876 and Ups And systems are very unlikely to have such orbits.

Jones, B. W.; Sleep, P. N.; Chambers, J. E.

2001-01-01

68

Thermal evolution and lifetime of intrinsic magnetic fields of Super Earths in habitable zones  

Microsoft Academic Search

We have numerically studied the thermal evolution of various-mass terrestrial\\u000aplanets in habitable zones, focusing on duration of dynamo activity to generate\\u000atheir intrinsic magnetic fields, which may be one of key factors in\\u000ahabitability on the planets. In particular, we are concerned with super-Earths,\\u000aobservations of which are rapidly developing. We calculated evolution of\\u000atemperature distributions in planetary interior,

Chihiro Tachinami; Hiroki Senshu; Shigeru Ida

2010-01-01

69

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

Microsoft Academic Search

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

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

2008-01-01

70

Number of Planets with life in the galactic habitable zone deduced by modified Drake Equation  

Microsoft Academic Search

In this work we estimate the quantity of planets with life in the Galactic Habitable Zone, using a modified version of the Drake's equation: [ N_L =sumlimits_i {N_i^* fpi nei fvi } ] where i is the spectral class, NL is the number of planets with life, N*I is the number of stars in the galactic ecosphere of spectral class

G. V. Y. Peña-Cabrera; H. J. Durand-Manterola

2004-01-01

71

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

Microsoft Academic Search

We modeled the evolution of the Milky Way to trace the distribution in space\\u000aand time of four prerequisites for complex life: the presence of a host star,\\u000aenough heavy elements to form terrestrial planets, sufficient time for\\u000abiological evolution and an environment free of life-extinguishing supernovae.\\u000aWe identified the Galactic habitable zone (GHZ) as an annular region between 7

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

2004-01-01

72

Finding Earth-size planets in the habitable zone: the Kepler Mission  

Microsoft Academic Search

The Kepler Mission is a space-based mission whose primary goal is to detect Earth-size and smaller planets in the habitable zone of solar-like stars. The mission will monitor more than 100,000 stars for transits with a differential photometric precision of 20 ppm at V=12 for a 6.5 hour transit. It will also provide asteroseismic results on several thousand dwarf stars.

William Borucki; David Koch; Gibor Basri; Natalie Batalha; Timothy Brown; Douglas Caldwell; Jørgen Christensen-Dalsgaard; William Cochran; Edward Dunham; Thomas N. Gautier; John Geary; Ronald Gilliland; Jon Jenkins; Yoji Kondo; David Latham; Jack J. Lissauer; David Monet

2008-01-01

73

KEPLER: Search for Earth-Size Planets in the Habitable Zone  

Microsoft Academic Search

The Kepler Mission is a space-based mission whose primary goal is to determine the frequency of Earth-size and larger planets in the habitable zone of solar-like stars. The mission will monitor more than 100,000 stars for patterns of transits with a differential photometric precision of 20 ppm at V = 12 for a 6.5 hour transit. It will also provide

William Borucki; David Koch; Natalie Batalha; Douglas Caldwell; Jorgen Christensen-Dalsgaard; William D. Cochran; Edward Dunham; Thomas N. Gautier; John Geary; Ronald Gilliland; Jon Jenkins; Hans Kjeldsen; Jack J. Lissauer; Jason Rowe

2009-01-01

74

Microlensing Sensitivity to Earth-Mass Planets in the Habitable Zone  

Microsoft Academic Search

Microlensing is one of the most powerful methods that can detect extrasolar planets, and a future space-based survey with a high monitoring frequency is proposed to detect a large sample of Earth-mass planets. In this paper, we examine the sensitivity of the future microlensing survey to Earth-mass planets located in the habitable zone. For this, we estimate the fraction of

Byeong-Gon Park; Young-Beom Jeon; Chung-Uk Lee; Cheongho Han

2006-01-01

75

A Search For Earth-Sized Planets In Habitable Zones Using Photometry  

Microsoft Academic Search

Several methods have been suggested for the detection of extra-solar planets. In the habitable zone, the radial velocity and astrometric methods are only sensitive to the detection of massive planets (greater than about ten to one-hundred Earth masses). However, the photometric method is sensitive to Earth-sized planets in inner orbits about solar-like stars. The methodology for conducting a photometric space-based

David Koch; William Borucki

1996-01-01

76

Habitable Zones Exposed: Astrosphere Collapse Frequency as a Function of Stellar Mass  

NASA Astrophysics Data System (ADS)

Stellar astrospheres -- the plasma cocoons carved out of the interstellar medium by stellar windsâ -- 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?)-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 102 to 109 times smaller for stars between 0.5 and 0.1 M?. 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.

Smith, David S.; Scalo, John M.

2009-09-01

77

The Instellation Habitable Zone: Liquid Water Stability on a Single Axis  

NASA Astrophysics Data System (ADS)

The habitable zone is the region around a star for which liquid water might be stable at the surface of a planet. This is roughly defined as orbital distances greater than those for which runaway greenhouses are triggered or water loss via H escape becomes rapid, yet less than those for which snowball Earth conditions are unavoidable. Both of these limits are inherently tied to surface temperature of the planet. Exoplanet observers have often defined habitable zones based on estimates of the equilibrium temperature for a planet, using that as a proxy for surface. However, the calculation of equilibrium temperature requires knowledge of the planet's albedo, which is usually not known. Furthermore, translating a planet's equilibrium temperature into a surface temperature requires estimations of greenhouse and anti-greenhouse effects that are also unknown. Venus presents both of these problems: it has a much-higher albedo than the value commonly assumed for Earth-like exoplanets, and yet its surface temperature is hundreds of degrees higher than its equilibrium temperature. Without knowledge of the albedo of a planet or the magnitude of the greenhouse effect, equilibrium temperature is an unknown quantity that provides unreliable estimates of the surface temperature of a planet. For these reasons, atmospheric modelers have incorporated the effects of albedo and of greenhouse effects into definitions of the habitable zone. Historically, these definitions have been based on the luminosity of the host star and the semi-major axis of the planet's orbit. This has served the community well, as planets are treated and analyzed on a case-by-base basis. However, the presence of two criteria for habitability (semi-major axis and stellar luminosity) presents an impediment to plotting planets in 2-dimensional diagrams that also include geophysical parameters such as planetary radius, mass, or density. While such plots were not previously warranted for ~Earth-sized planets because very few were known, the large number of ~Earth-sized planets currently being discovered by exoplanet surveys such as NASA's Kepler mission increase the need for a single metric that represents the possibility for liquid water to be stable at the surface of a planet. In this presentation, we propose the use of installation - the amount of energy reaching the top of a planet's atmosphere - as a metric for habitability that can be calculated strictly from measured properties and that also allows for display of "surface water stability" on the same chart as other geophysical parameters. The habitable zone presented here is primarily derived from information on planets in our solar system, including knowledge of the history of those planets. We compare this new definition of the habitable zone to traditional ones, and apply it to the February 2011 release of data from the Kepler data set and the database of confirmed extrasolar planets.

Domagal-Goldman, S. D.; Virtual Planetary Laboratory

2011-12-01

78

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

NASA Astrophysics Data System (ADS)

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.

Lissauer, J. J.

2009-12-01

79

Astrobiological Effects of Stellar Radiation in Circumstellar Environments  

NASA Astrophysics Data System (ADS)

The centerpiece of all life on Earth is carbon-based biochemistry. Previous scientific research has suggested that biochemistry based on carbon may also play a decisive role in extraterrestrial life forms, i.e., alien life outside of Earth, if existent. In the following, we explore if carbon-based macromolecules (such as DNA) in the environments of stars other than the Sun are able to survive the effects of energetic stellar radiation, such as UV-C in the wavelength band between 200 and 290 nm. We focus on main-sequence stars akin to the Sun, but of hotter (F-type stars) and cooler (K- and M-type stars) surface temperature. Emphasis is placed on investigating the radiative environment in stellar habitable zones (HZs). Stellar habitable zones have an important relevance in astrobiology because they constitute circumstellar regions in which a planet of suitable size can have surface temperatures for water to exist in liquid form.

Cuntz, Manfred; Gurdemir, Levent; Guinan, Edward F.; Kurucz, Robert L.

2006-10-01

80

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

SciTech Connect

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 +}.

Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David R. [NASA Exoplanet Science Institute, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Tabetha, S. Boyajian; McAlister, Harold A.; White, Russel [Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P. O. Box 4106, Atlanta, GA 30302-4106 (United States); Ten Brummelaar, Theo A.; Schaefer, Gail; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H.; Farrington, Chris; Goldfinger, P. J. [The CHARA Array, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Van Belle, Gerard T. [European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching (Germany); Raymond, Sean N. [Universite de Bordeaux, Observatoire Aquitain des Sciences de l'Univers, 2 rue de l'Observatoire, BP 89, F-33271 Floirac Cedex (France); Lopez-Morales, Mercedes [Institut de Ciencies de L'Espai (CSIC-IEEC), Campus UAB, Facultat Ciencies, Torre C5 parell 2, 08193 Bellaterra, Barcelona (Spain); Ridgway, Stephen T., E-mail: kaspar@caltech.edu [National Optical Astronomy Observatory, P. O. Box 26732, Tucson, AZ 85726-6732 (United States)

2011-10-10

81

Exomoon habitability constrained by illumination and tidal heating.  

PubMed

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

Heller, René; Barnes, Rory

2013-01-10

82

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

SciTech Connect

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.

Wordsworth, Robin D.; Forget, Francois; Millour, Ehouarn; Charnay, Benjamin; Madeleine, Jean-Baptiste [Laboratoire de Meteorologie Dynamique, Institut Pierre Simon Laplace, Paris (France); Selsis, Franck [CNRS, UMR 5804, Laboratoire d'Astrophysique de Bordeaux, 2 rue de l'Observatoire, BP 89, F-33271 Floirac Cedex (France)

2011-06-01

83

STABILITY ANALYSIS OF SINGLE-PLANET SYSTEMS AND THEIR HABITABLE ZONES  

SciTech Connect

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.

Kopparapu, Ravi Kumar [Department of Physics, 104 Davey Lab, Pennsylvania State University, University Park, PA 16802-6300 (United States); Barnes, Rory, E-mail: ravi@gravity.psu.ed [Department of Astronomy, University of Washington, Seattle, WA 98195-1580 (United States)

2010-06-20

84

Calculating the Habitable Zone of Binary Star Systems. II. P-type Binaries  

NASA Astrophysics Data System (ADS)

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.

Haghighipour, Nader; Kaltenegger, Lisa

2013-11-01

85

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

PubMed

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

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

2004-01-01

86

Habitable Climates  

NASA Astrophysics Data System (ADS)

According to the standard liquid-water definition, the Earth is only partially habitable. We reconsider planetary habitability in the framework of energy balance models, the simplest seasonal models in physical climatology, to assess the spatial and temporal habitability of Earth-like planets. We quantify the degree of climatic habitability of our models with several metrics of fractional habitability. Previous evaluations of habitable zones may have omitted important climatic conditions by focusing on close solar system analogies. For example, we find that model pseudo-Earths with different rotation rates or different land-ocean fractions have fractional habitabilities that differ significantly from that of the Earth itself. Furthermore, the stability of a planet's climate against albedo-feedback snowball events strongly impacts its habitability. Therefore, issues of climate dynamics may be central in assessing the habitability of discovered terrestrial exoplanets, especially if astronomical forcing conditions are different from the moderate solar system cases.

Spiegel, David S.; Menou, Kristen; Scharf, Caleb A.

2008-07-01

87

Astrometric Detection of Terrestrial Planets in the Habitable Zones of Nearby Stars with SIM PlanetQuest  

Microsoft Academic Search

SIM PlanetQuest is a space-borne Michelson interferometer with a 9 m baseline, currently slated for launch in 2016. One of the principal science goals of the mission is the astrometric detection and orbital characterization of terrestrial planets in the habitable zones of nearby stars. Differential astrometry of the target star against a set of reference stars lying within a degree

Joseph Catanzarite; Michael Shao; Angelle Tanner; Stephen Unwin; Jeffrey Yu

2006-01-01

88

Calculating the Habitable Zone of Binary Star Systems. I. S-type Binaries  

NASA Astrophysics Data System (ADS)

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 ? Cen AB and HD 196886.

Kaltenegger, Lisa; Haghighipour, Nader

2013-11-01

89

Can terrestrial planets exist in the habitable zones of known exoplanetary systems?  

NASA Astrophysics Data System (ADS)

The habitable zone (HZ) is defined as the range of distances from a star within which water at the surface of a terrestrial planet would be in the liquid phase. We have investigated whether terrestrial planets could exit in the HZs of known exoplanetary systems long enough for life to have emerged and to have evolved. Four contrasting systems in which giant planets have been detected have been examined, and HZs have been defined for each system using conservative definitions for the HZ boundaries. Mixed- variable sympletic numerical integration has ben used to investigate the orbits of putative terrestrial planets launched within the HZ of each system. In Rho CrB the HZ is exterior to the giant, and in 47 UMa it is interior. We have shown that in each of these two systems terrestrial planets could have orbits with semimajor axes that remain confined to the HZ for biologically significant lengths of time. We have also shown that the Gliese 876 and Ups And systems are very unlikely to have such orbits.

Jones, Barrie W.; Sleep, P. Nick

2001-08-01

90

Direct Imaging in the Habitable Zone and the Problem of Orbital Motion  

NASA Astrophysics Data System (ADS)

High contrast imaging searches for exoplanets have been conducted on 2.4-10 m telescopes, typically at H band (1.6 ?m) and used exposure times of ~1 hr to search for planets with semi-major axes of >~ 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 ? Cen A&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.

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

2013-07-01

91

Biomarker Response to Cosmic Rays on Planets orbiting in the Habitable Zone of M-Stars  

NASA Astrophysics Data System (ADS)

Our model predicts that biomarkers from planets orbiting in the Habitable Zone (HZ) of M-Dwarf stars with Earthlike atmospheres (hereafter "M-star worlds") may survive strong fluxes from Galactic Cosmic Rays (GCRs). These calculations included the effects of (albeit weakened) magnetospheric shielding. Our result refers to the effect of cosmic rays producing nitrogen oxides, NOx(=NO+NO2) in earthlike atmospheres which perturb the atmospheric chemistry hence remove ozone. Ozone on the M-star world is resilient to GCR-induced NOx because high methane levels favour the ozoneproducing "smog" mechanism, which is catalysed by NOx as discussed by Grenfell et al. (2007) (Astrobiology Special Issue on M-stars). We have also performed an initial estimate of stellar cosmic ray (SCR) fluxes but these are currently upper estimate fluxes, based on our own Sun, assuming a completely unmagnetised planet scaled to 0.2 AU i.e. in the HZ. SCR results imply that up to 98

Grenfell, J. L.; Griessmeier, J.-M.; Hedelt, P.; Patzer, B.; Rauer, H.; Stracke, B.; von Paris, P.

2007-08-01

92

Formaldehyde in the far outer galaxy: constraining the outer boundary of the galactic habitable zone.  

PubMed

We present results from an initial survey of the 2(12)-1(11) transition of formaldehyde (H2CO) at 140.8 GHz in giant molecular clouds in the far outer Galaxy (RG >or= 16 kpc). Formaldehyde is a key prebiotic molecule that likely plays an important role in the development of amino acids. Determining the outermost extent of the H2CO distribution can constrain the outer limit of the Galactic Habitable Zone, the region where conditions for the formation of life are thought to be most favorable. We surveyed 69 molecular clouds in the outer Galaxy, ranging from 12 to 23.5 kpc in galactocentric radius. Formaldehyde emission at 140.8 GHz was detected in 65% of the clouds. The H2CO spectral line was detected in 26 of the clouds with RG > 16 kpc (detection rate of 59%), including 6 clouds with RG > 20 kpc (detection rate of 55%). Formaldehyde is readily found in the far outer Galaxy-even beyond the edge of the old stellar disk. Determining the relatively widespread distribution of H2CO in the far outer Galaxy is a first step in establishing how favorable an environment this vast region of the Galaxy may be toward the formation of life. PMID:18266563

Blair, Samantha K; Magnani, Loris; Brand, Jan; Wouterloot, Jan G A

2008-02-01

93

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

NASA Astrophysics Data System (ADS)

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.

Stern, S. Alan

2003-06-01

94

How Close Are We To Detecting Earth-like Planets in the Habitable Zone Using the Radial Velocity Technique?  

Microsoft Academic Search

Discovering an Earth-like exoplanet in habitable zone is an important milestone for astronomers in search of extra-terrestrial life. While the radial velocity (RV) technique remains one the most powerful tools in detecting and characterizing exo-planetary sys- tems, we calculate the uncertainties in precision RV measurements considering stellar spectral quality factors, RV calibration sources, stellar noise and telluric contamination in different

Ji Wang; Jian Ge

2011-01-01

95

The stability of the orbits of Earth-mass planets in the habitable zone of 47 Ursae Majoris  

Microsoft Academic Search

We have investigated whether Earth-mass planets could survive in the habitable zone (HZ) of the 47 Ursae Majoris system. Mixed-variable symplectic numerical integration has been used to investigate the orbits of putative Earth-mass planets. Whereas the 47 UMa system as previously known, with just one giant planet, could have Earth-mass planets that remain confined to the HZ for a fairly

B. W. Jones; P. N. Sleep

2002-01-01

96

The Hunt for Exomoons with Kepler (HEK). III. The First Search for an Exomoon around a Habitable-zone Planet  

NASA Astrophysics Data System (ADS)

Kepler-22b is the first transiting planet to have been detected in the habitable zone of its host star. At 2.4 R ?, 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 MS > 0.5 M ? 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 MP < 53 M ? to 95% confidence and an eccentricity of 0.13_{-0.13}^{+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. Based on archival data of the Kepler telescope.

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

2013-11-01

97

Volatile-Rich Earth-Mass Planets in the Habitable Zone  

Microsoft Academic Search

A small planet is not necessarily a terrestrial planet. Planets that form\\u000abeyond the snow line with too little mass to seed rapid gas accretion (<~ 10\\u000aEarth masses) should be rich in volatile ices like water and ammonia. Some of\\u000athese planets should migrate inward by interacting with a circumstellar disk or\\u000awith other planets. Such objects can retain

Marc J. Kuchner

2003-01-01

98

Water-planets in the Habitable Zone: Atmospheric Chemistry, Observable Features, and the Case of Kepler-62e and -62f  

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

99

Effect of land fraction on weathering and tenure in the habitable zone of terrestrial planets around main-sequence stars  

NASA Astrophysics Data System (ADS)

According to current models of volatile delivery, the water fraction of terrestrial planets in the habitable zone of main-sequence stars is likely to be highly variable. This will affect the continental land fraction, and consequently the functioning of weathering and the carbon cycle. We construct a low-order analytical model of climate, continental silicate weathering, and seafloor weathering to investigate, in a general sense, the effect of land fraction on the long-term carbon cycle. This model is useful for gaining physical insight, rather than for making specific predictions. Using our model, we reach the following conclusions: (1) The surface temperature increases with decreasing land fraction, with waterworlds 10's of K warmer than planets with 50% continental coverage. (2) There can be no weathering feedback on a waterworld. The tenure of a waterworld in the habitable zone is therefore likely to be much shorter than the tenure of a planet with some continent in the habitable zone. (3) The silicate weathering feedback is effective even at very low land fractions. The rate of change of a planet's surface temperature as the star it orbits evolves on the main sequence is similar if the land fraction is 0.3 or 0.01.

Abbot, D. S.; Ciesla, F. J.; Pierrehumbert, R.; Archer, D. E.

2011-12-01

100

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

PubMed

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

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

2013-05-08

101

The New Worlds Observer: Direct Detection and Study of Exoplanets from the Habitable Zone Outward  

NASA Astrophysics Data System (ADS)

Direct detection and spectroscopic study of the planets around the nearby stars is generally recognized as a prime goal of astronomy. The New Worlds Observer mission concept is being studied as an Astrophysics Strategic Mission Concept Study for this purpose. NWO features two spacecraft: a general purpose 4m telescope that operates from the UV to the Near IR, and a starshade, a flower-shaped occulter about 50m in diameter flying in alignment about 70,000km away. Our study shows this is the most effective way to map nearby planetary systems. Images will show dust and debris down to a fraction of our zodiacal light level. Planets fainter than the Earth can be seen from the Habitable Zone outward, at distances up to 20pc. High throughput and low noise enable immediate follow-up spectroscopy of discovered planets. NWO can discover many more Earth-like planets than all competing approaches including astrometric, interferometric, and internal coronagraphic. Within hours of discovery, a high quality spectrum can determine the true nature of the exoplanet and open the search for biomarkers and life. Over half of the time will be spent with the starshade in transit to the next target. During those times the telescope will be available to for general astrophysics purposes. Operating from the ultraviolet to the near infrared, this will be a true HST follow-on. The study shows all needed technologies already exist. The cost scales primarily with telescope size. The mission is definitely within the financial and technical reach of NASA for the coming decade.

Cash, Webster C.; New Worlds Study Team

2009-01-01

102

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

PubMed

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

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

2005-10-01

103

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

NASA Astrophysics Data System (ADS)

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.

Boschi, Robert; Lucarini, Valerio; Pascale, Salvatore

2013-11-01

104

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)

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.

Danchi, William C.; Lopez, Bruno

2013-05-01

105

HABITABLE ZONES AROUND LOW MASS STARS AND THE SEARCH FOR EXTRATERRESTRIAL LIFE  

Microsoft Academic Search

. Habitable planets are likely to exist around stars not too different from the Sun ifcurrent theories about terrestrial climate evolution are correct. Some of these planets may haveevolved life, and some of the inhabited planets may have evolved O 2 -rich atmospheres. Suchatmospheres could be detected spectroscopically on planets around nearby stars using a spacebasedinterferometer to search for the

James F. Kasting

1997-01-01

106

Planets in habitable zones:. A study of the binary Gamma Cephei  

Microsoft Academic Search

The recently discovered planetary system in the binary gamma Cep was studied concerning its dynamical evolution. We confirm that the orbital parameters found by the observers are in a stable configuration. The primary aim of this study was to find stable planetary orbits in a habitable region in this system, which consists of a double star (a=21.36 AU) and a

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

2003-01-01

107

[Catalytical properties of the liver monoamine oxidases of the commander squid Berryteuthis magister from various habitation zones].  

PubMed

A detailed kinetic analysis is performed of enzymatic reactions of deamination of tyramine, tryptamine, serotonin, benzylamine, beta-phenylethylamine, and histamine under action of liver monoamine oxidase (MAO) of the Commander squid Berryteuthis magister from various habitation zones in the Bering and Japan Seas. There has been revealed a substrate inhibition by high concentrations of all studied substrates, which seems to indicate mutual effect of various MAO forms present in liver of the studied squids. Analysis of kinetic parameters of enzymatic reactions of deamination of six studied substrates and the substrate-inhibitory analysis with use of two derivatives of acridine and deprenyl indicate the enzyme heterogeneity, the presence of at least two MAO forms and the absence of intraspecies differences in MAO of the Commander squids from various habitation zones. The most active was the MAO form responsible for serotonin deamination. There were obtained quantitative difference in substrate specificity and reaction ability with respect to inhibitor of proflavin for the liver MAO of the Commander and Pacific squids. PMID:19764634

Iagodina, O V

108

The Loss of Nitrogen-rich Atmospheres from Earth-like Exoplanets within M-star Habitable Zones  

NASA Astrophysics Data System (ADS)

After the first discovery of massive Earth-like exoplanets around M-type dwarf stars, the search for exoplanets which resemble more an Earth analogue continues. The discoveries of super-Earth planets pose questions on habitability and the possible origin of life on such planets. Future exoplanet space projects designed to characterize the atmospheres of terrestrial exoplanets will also search for atmospheric species which are considered as bio-markers (e.g. O3, H2O, CH4, etc.). By using the Earth with its atmosphere as a proxy and in agreement with the classical habitable zone concept, one should expect that Earth-like exoplanets suitable for life as we know it should have a nitrogen atmosphere and a very low CO2 content. Whether a water bearing terrestrial planet within its habitable zone can evolve into a habitable world similar than the Earth, depends on the capability of its water-inventory and atmosphere to survive the period of high radiation of the young and/or active host star. Depending on their size and mass, lower mass stars remain at high X-ray and EUV (XUV) activity levels for hundreds of Ma's to Ga's. XUV flux values which are 10 or 20 times higher than that of the present Sun can heat the thermosphere and expand the exobase of N2-rich Earth-like exoplanets to altitudes well above their expected magnetopause distances. This results in magnetically non-protected upper atmospheres and high non-thermal escape rates. We studied this plasma induced N+ ion pick up escape and applied a numerical test-particle stellar wind plasma - exosphere interaction model. Our results indicate that Earth-analogue exoplanets with atmosphere compositions similar to that of present Earth will lose their nitrogen inventories if they are exposed over a sufficient period of time to XUV fluxes ? 10 times that of the present Sun. Because most M-type stars are active in XUV radiation we suggest that these planets will undergo a different atmospheric evolution than the Earth so that life as we know it may not evolve on their surfaces.

Lammer, H.; Lichtenegger, H. I. M.; Khodachenko, M. L.; Kulikov, Y. N.; Griessmeier, J.

2011-12-01

109

Planet Hunters Update: Many New Planet Candidates Identified by Citizen Scientists from Kepler Data, Including Several in the Habitable Zone  

NASA Astrophysics Data System (ADS)

Since December, 2010, more than 250,000 public volunteers have searched through more than 19 million Kepler light curves hunting for transiting planets. The Kepler light curves are shown in 30 day sections, and with ~160,000 Kepler target stars, the users have contributed the equivalent of 180 years of work hours. This vetting process has resulted in over 40 new planet candidates and two new confirmed planets, including several not identified through the Kepler pipeline. Many of our candidate planets lie within their host star's habitable zone. We review the recent large release of new PH candidates in Wang et al. (2013), including one confirmed planet, and give preliminary results for our next PH candidate release.

Schmitt, Joseph; Wang, Ji

2013-07-01

110

Stability of terrestrial planets in the habitable zone of Gl 777 A, HD 72659, Gl 614, 47 Uma and HD 4208  

Microsoft Academic Search

We have undertaken a thorough dynamical investigation of five extrasolar planetary systems using extensive numerical experiments. The systems Gl 777 A, HD 72659, Gl 614, 47 Uma and HD 4208 were examined concerning the question of whether they could host terrestrial-like planets in their habitable zones (HZ). First we investigated the mean motion resonances between fictitious terrestrial planets and the

N. Asghari; C. Broeg; L. Carone; R. Casas-Miranda; J. C. Castro Palacio; I. Csillik; R. Dvorak; F. Freistetter; G. Hadjivantsides; H. Hussmann; A. Khramova; M. Khristoforova; I. Khromova; I. Kitiashivilli; S. Kozlowski; T. Laakso; T. Laczkowski; D. Lytvinenko; O. Miloni; R. Morishima; A. Moro-Martin; V. Paksyutov; A. Pal; V. Patidar; B. Pecnik; O. Peles; J. Pyo; T. Quinn; A. Rodriguez; C. Romano; E. Saikia; J. Stadel; M. Thiel; N. Todorovic; D. Veras; E. Vieira Neto; J. Vilagi; W. von Bloh; R. Zechner; E. Zhuchkova

2004-01-01

111

Coronal Mass Ejection (CME) Activity of Low Mass M Stars as An Important Factor for The Habitability of Terrestrial Exoplanets. II. CME-Induced Ion Pick Up of Earth-like Exoplanets in Close-In Habitable Zones  

Microsoft Academic Search

Atmospheric erosion of CO2 -rich Earth-size exoplanets due to coronal mass ejection (CME)-induced ion pick up within close-in habitable zones of active M-type dwarf stars is investigated. Since M stars are active at the X-ray and extreme ultraviolet radiation (XUV) wave-lengths over long periods of time, we have applied a thermal balance model at various XUV flux input values for

Helmut Lammer; Herbert I. M. Lichtenegger; Yuri N. Kulikov; Jean-Mathias Grießmeier; N. Terada; Nikolai V. Erkaev; Helfried K. Biernat; Maxim L. Khodachenko; Ignasi Ribas; Thomas Penz; Franck Selsis

2007-01-01

112

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)

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.

Stern, S. A.

2002-09-01

113

Circumstellar Dust Created by Terrestrial Planet Formation in HD 113766  

NASA Astrophysics Data System (ADS)

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 ?m) 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 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 two belts, located at 4-9 and 30-80 AU. The lower bound of warm dust mass in 0.1-20 ?m, 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.

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

2008-02-01

114

Creating Habitable Zones, at all Scales, from Planets to Mud Micro-Habitats, on Earth and on Mars  

Microsoft Academic Search

\\u000a The factors that create a habitable planet are considered at all scales, from planetary inventories to micro-habitats in soft\\u000a sediments and intangibles such as habitat linkage. The possibility of habitability first comes about during accretion, as\\u000a a product of the processes of impact and volatile inventory history. To create habitability water is essential, not only for\\u000a life but to aid

Euan Nisbet; Kevin Zahnle; M. V. Gerasimov; Jörn Helbert; Ralf Jaumann; Beda A. Hofmann; Karim Benzerara; Frances Westall

115

Creating Habitable Zones, at all Scales, from Planets to Mud Micro-Habitats, on Earth and on Mars  

Microsoft Academic Search

The factors that create a habitable planet are considered at all scales, from planetary inventories to micro-habitats in soft\\u000a sediments and intangibles such as habitat linkage. The possibility of habitability first comes about during accretion, as\\u000a a product of the processes of impact and volatile inventory history. To create habitability water is essential, not only for\\u000a life but to aid

Euan Nisbet; Kevin Zahnle; M. V. Gerasimov; Jörn Helbert; Ralf Jaumann; Beda A. Hofmann; Karim Benzerara; Frances Westall

2007-01-01

116

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

Microsoft Academic Search

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 0.9-1.65mum, the Y, J and H NIR bands where most of the flux is emitted by

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

2010-01-01

117

A dynamically-packed planetary system around GJ 667C with three super-Earths in its habitable zone  

NASA Astrophysics Data System (ADS)

Context. Since low-mass stars have low luminosities, orbits at which liquid water can exist on Earth-sized planets are relatively close-in, which produces Doppler signals that are detectable using state-of-the-art Doppler spectroscopy. Aims: GJ 667C is already known to be orbited by two super-Earth candidates. We have recently applied developed data analysis methods to investigate whether the data supports the presence of additional companions. Methods: We obtain new Doppler measurements from HARPS extracted spectra and combined them with those obtained from the PFS and HIRES spectrographs. We used Bayesian and periodogram-based methods to re-assess the number of candidates and evaluated the confidence of each detection. Among other tests, we validated the planet candidates by analyzing correlations of each Doppler signal with measurements of several activity indices and investigated the possible quasi-periodic nature of signals. Results: Doppler measurements of GJ 667C are described better by six (even seven) Keplerian-like signals: the two known candidates (b and c); three additional few-Earth mass candidates with periods of 92, 62, and 39 days (d, e and f); a cold super-Earth in a 260-day orbit (g) and tantalizing evidence of a ~1 M? object in a close-in orbit of 17 days (h). We explore whether long-term stable orbits are compatible with the data by integrating 8 × 104 solutions derived from the Bayesian samplings. We assess their stability using secular frequency analysis. Conclusions: The system consisting of six planets is compatible with dynamically stable configurations. As for the solar system, the most stable solutions do not contain mean-motion resonances and are described well by analytic Laplace-Lagrange solutions. Preliminary analysis also indicates that masses of the planets cannot be higher than twice the minimum masses obtained from Doppler measurements. The presence of a seventh planet (h) is supported by the fact that it appears squarely centered on the only island of stability left in the six-planet solution. Habitability assessments accounting for the stellar flux, as well as tidal dissipation effects, indicate that three (maybe four) planets are potentially habitable. Doppler and space-based transit surveys indicate that 1) dynamically packed systems of super-Earths are relatively abundant and 2) M-dwarfs have more small planets than earlier-type stars. These two trends together suggest that GJ 667C is one of the first members of an emerging population of M-stars with multiple low-mass planets in their habitable zones. Based on data obtained from the ESO Science Archive Facility under request number ANGLADA36104. Such data had been previously obtained with the HARPS instrument on the ESO 3.6 m telescope under the programs 183.C-0437, 072.C-0488 and 088.C-0662, and with the UVES spectrograph at the Very Large Telescopes under the program 087.D-0069. This study also contains observations obtained at the W.M. Keck Observatory - which is operated jointly by the University of California and the California Institute of Technology - and observations obtained with the Magellan Telescopes, operated by the Carnegie Institution, Harvard University, University of Michigan, University of Arizona, and the Massachusetts Institute of Technology.Time-series (Table C.2) 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/556/A126Appendices except Table C.2 are available in electronic form at http://www.aanda.org

Anglada-Escudé, Guillem; Tuomi, Mikko; Gerlach, Enrico; Barnes, Rory; Heller, René; Jenkins, James S.; Wende, Sebastian; Vogt, Steven S.; Butler, R. Paul; Reiners, Ansgar; Jones, Hugh R. A.

2013-08-01

118

A Revised Estimate of the Occurrence Rate of Terrestrial Planets in the Habitable Zones around Kepler M-dwarfs  

NASA Astrophysics Data System (ADS)

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 & Charbonneau used Kepler data and calculated the frequency of terrestrial planets in the HZ of cool stars to be 0.15^{+0.13}_{-0.06} per star for Earth-size planets (0.5-1.4 R ?). 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 ?, when we reanalyze their results, we obtain a terrestrial planet frequency of 0.48^{+0.12}_{-0.24} and 0.53^{+0.08}_{-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 ?, the frequency increases to 0.51^{+0.10}_{-0.20} per star for the conservative estimate and to 0.61^{+0.07}_{-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^{+0.54}_{-0.13}). So, the potential for finding Earth-like planets around M stars may be higher than previously reported.

Kopparapu, Ravi Kumar

2013-04-01

119

Dynamics and stability of telluric planets within the habitable zone of extrasolar planetary systems. Numerical simulations of test particles within the HD 4208 and HD 70642 systems  

NASA Astrophysics Data System (ADS)

Aims: We study gravitational perturbation effects of observed giant extrasolar planets on hypothetical Earth-like planets in the context of the three-body problem. This paper considers a large parameter survey of different orbital configuration of two extrasolar giant planets (HD 70642b and HD 4208b) and compares their dynamical effect on Earth-mass planetary orbits initially located within the respective habitable terrestrial region. We are interested in determining giant-planet orbit (and mass) parameters that favor the condition to render an Earth-mass planet to remain on a stable and bounded orbit within the continuous habitable zone. Methods: We applied symplectic numerical integration techniques to studying the short and long term time evolution of hypothetical Earth-mass planets that are treated as particles. In addition, we adopt the MEGNO technique to obtain a complete dynamical picture of the terrestrial phase space environment. Both multi-particle and single-particle simulations were performed to follow an Earth-mass planet in the habitable region and its subsequent long term evolution. Results: Our numerical simulations show that giant planets should be on circular orbits to minimize the perturbative effect on terrestrial orbits. The orbit eccentricity (and hence proximity) is the most important orbital parameter of dynamical significance. The most promising candidate for maintaining an Earth-mass planet on a stable and bounded orbit well-confined to the continuous habitable zone is HD 70642b. Even the large planetary mass of HD 70642b renders an Earth-mass planet habitable during the complete lifetime of the host star. The results allow us to extrapolate similar observed systems and points the necessity further constraining the uncertainty range in giant planet orbital eccentricity by future follow-up observations.

Hinse, T. C.; Michelsen, R.; Jørgensen, U. G.; Go?dziewski, K.; Mikkola, S.

2008-09-01

120

Trojans in Habitable Zones  

Microsoft Academic Search

With the aid of numerical experiments we examined the dynamical stability of fictitious terrestrial planets in 1:1 mean motion resonance with Jovian-like planets of extrasolar planetary systems. In our stability study of the so-called \\

Richard Schwarz; Elke Pilat-Lohinger; Rudolf Dvorak; Balint Érdi; Zsolt Sándor

2005-01-01

121

Planet Hunters. V. A Confirmed Jupiter-size Planet in the Habitable Zone and 42 Planet Candidates from the Kepler Archive Data  

NASA Astrophysics Data System (ADS)

We report the latest Planet Hunter results, including PH2 b, a Jupiter-size (R PL = 10.12 ± 0.56 R ?) 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. .

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

2013-10-01

122

The habitable zone of Earth-mass planets around 47 UMa: results for land and water worlds  

Microsoft Academic Search

In a previous paper, we showed that Earth-type habitable planets around 47 UMa are in principle possible if a distinct set of conditions is warranted. These conditions include that the Earth-type planets have successfully formed and are orbitally stable and, in addition, that the 47 UMa star-planet system is relatively young ([less, similar]6 Gyr). We now extend this study by

S. Franck; M. Cuntz; W. von Bloh; C. Bounama

2003-01-01

123

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

SciTech Connect

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.

Vogt, Steven S.; Rivera, E. J. [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Butler, R. Paul [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015-1305 (United States); Haghighipour, N. [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Manoa, Honolulu, HI 96822 (United States); Henry, Gregory W.; Williamson, Michael H. [Tennessee State University, Center of Excellence in Information Systems, 3500 John A. Merritt Blvd., Box 9501, Nashville, TN 37209-1561 (United States)

2010-11-01

124

The Lick-Carnegie Exoplanet Survey: A 3.1 M ? Planet in the Habitable Zone of the Nearby M3V Star Gliese 581  

NASA Astrophysics Data System (ADS)

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 ~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 ? planet orbiting in a 0.758 AU orbit of period 433 days, and a sixth planet, GJ 581g, a minimum-mass 3.1 M ? 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 ??, 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 ?? 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.

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

2010-11-01

125

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

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

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

126

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

PubMed

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 ?m, 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

Joshi, Manoj M; Haberle, Robert M

2011-12-19

127

Kepler-62: A Five-Planet System with Planets of 1.4 and 1.6 Earth Radii in the Habitable Zone  

NASA Astrophysics Data System (ADS)

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.

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

128

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

NASA Astrophysics Data System (ADS)

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.

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

2007-10-01

129

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

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

130

Submillimeter observations of circumstellar dust  

NASA Astrophysics Data System (ADS)

Five late-type stars with circumstellar envelopes were observed with the James Clerk Maxwell Telescope (JCMT) on 1988 February 7-8. The stars IK Tauri, Alpha Orionis, VY Canis Majoris, CW Leonis, and RW Leonis Minoris were observed in the 450, 800, and 1100 micron wavebands. These data were combined with existing measurements at shorter wavelengths for each star. The combined data were fitted to a circumstellar-dust-shell model based on the computer code by Leung (1975). Derived parameters, including mass-loss rates, are presented for the observed stars.

Marshall, Caroline R.; Leahy, Denis A.; Kwok, Sun

1992-06-01

131

Circumstellar disks and planetary formation  

NASA Astrophysics Data System (ADS)

Circumstellar disks are the the cradle of planetary systems. They are found around a large number of intermediate- and low-mass stellar objects in star forming regions and young clusters. Their study can provide important clues about the timescales and physical conditions for planet formation. In this paper, I review some properties of circumstellar disks that come from the analysis of multi-wavelength observational data, and that are important in the context of planet formation. In addition, I also present the first evidences of planetary formation within the so-called transitional disks.

Huélamo, N.

2013-05-01

132

Gravitational Microlensing of Circumstellar Envelopes  

Microsoft Academic Search

We discuss the flux and polarization signals obtained from the microlensing of stars with extended circumstellar envelopes by a single point-mass lens. We find that stars with extended envelopes will show a high level of variable polarisation (up to 10%), even if they are spherically symmetric. Since the stellar envelopes most likely to be lensed are produced by red giant

J. E. Bjorkman; R. Ignace; J. F. L. Simmons

2002-01-01

133

Infrared observations of circumstellar molecules  

NASA Astrophysics Data System (ADS)

A current listing of IR observations of circumstellar molecules is presented. These observations were performed using Fabry-Perot, Fourier transform, and laser heterodyne spectroscopy. The most abundant species were CO, SiO, and HCN, while trace species included NH3, CH4, SiH4, and CS. Among the undetected species were H2, HCl, and CH2.

Betz, Albert

134

Dynamical Habitability of Known Extrasolar Planetary Systems  

Microsoft Academic Search

Habitability is usually defined as the requirement for a terrestrial planet's atmosphere to sustain liquid water. This definition can be complemented by the dynamical requirement that other planets in the system do not gravitationally perturb terrestrial planets outside of their habitable zone, the orbital region allowing the existence of liquid water. We quantify the dynamical habitability of 85 known extrasolar

Kristen Menou; Serge Tabachnik

2003-01-01

135

Coronal mass ejection (CME) activity of low mass M stars as an important factor for the habitability of terrestrial exoplanets. II. CME-induced ion pick up of Earth-like exoplanets in close-in habitable zones.  

PubMed

Atmospheric erosion of CO2-rich Earth-size exoplanets due to coronal mass ejection (CME)-induced ion pick up within close-in habitable zones of active M-type dwarf stars is investigated. Since M stars are active at the X-ray and extreme ultraviolet radiation (XUV) wave-lengths over long periods of time, we have applied a thermal balance model at various XUV flux input values for simulating the thermospheric heating by photodissociation and ionization processes due to exothermic chemical reactions and cooling by the CO2 infrared radiation in the 15 microm band. Our study shows that intense XUV radiation of active M stars results in atmospheric expansion and extended exospheres. Using thermospheric neutral and ion densities calculated for various XUV fluxes, we applied a numerical test particle model for simulation of atmospheric ion pick up loss from an extended exosphere arising from its interaction with expected minimum and maximum CME plasma flows. Our results indicate that the Earth-like exoplanets that have no, or weak, magnetic moments may lose tens to hundreds of bars of atmospheric pressure, or even their whole atmospheres due to the CME-induced O ion pick up at orbital distances

Lammer, Helmut; Lichtenegger, Herbert I M; Kulikov, Yuri N; Griessmeier, Jean-Mathias; Terada, N; Erkaev, Nikolai V; Biernat, Helfried K; Khodachenko, Maxim L; Ribas, Ignasi; Penz, Thomas; Selsis, Franck

2007-02-01

136

Kepler-22b: A 2.4 Earth-radius Planet in the Habitable Zone of a Sun-like Star  

NASA Astrophysics Data System (ADS)

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 ? and 0.979 ± 0.020 R ?. 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? upper limit of 124 M ?, 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.

Borucki, William J.; Koch, David G.; Batalha, Natalie; Bryson, Stephen T.; Rowe, Jason; Fressin, Francois; Torres, Guillermo; Caldwell, Douglas A.; Christensen-Dalsgaard, Jørgen; Cochran, William D.; DeVore, Edna; Gautier, Thomas N.; Geary, John C.; Gilliland, Ronald; Gould, Alan; Howell, Steve B.; Jenkins, Jon M.; Latham, David W.; Lissauer, Jack J.; Marcy, Geoffrey W.; Sasselov, Dimitar; Boss, Alan; Charbonneau, David; Ciardi, David; Kaltenegger, Lisa; Doyle, Laurance; Dupree, Andrea K.; Ford, Eric B.; Fortney, Jonathan; Holman, Matthew J.; Steffen, Jason H.; Mullally, Fergal; Still, Martin; Tarter, Jill; Ballard, Sarah; Buchhave, Lars A.; Carter, Josh; Christiansen, Jessie L.; Demory, Brice-Olivier; Désert, Jean-Michel; Dressing, Courtney; Endl, Michael; Fabrycky, Daniel; Fischer, Debra; Haas, Michael R.; Henze, Christopher; Horch, Elliott; Howard, Andrew W.; Isaacson, Howard; Kjeldsen, Hans; Johnson, John Asher; Klaus, Todd; Kolodziejczak, Jeffery; Barclay, Thomas; Li, Jie; Meibom, Søren; Prsa, Andrej; Quinn, Samuel N.; Quintana, Elisa V.; Robertson, Paul; Sherry, William; Shporer, Avi; Tenenbaum, Peter; Thompson, Susan E.; Twicken, Joseph D.; Van Cleve, Jeffrey; Welsh, William F.; Basu, Sarbani; Chaplin, William; Miglio, Andrea; Kawaler, Steven D.; Arentoft, Torben; Stello, Dennis; Metcalfe, Travis S.; Verner, Graham A.; Karoff, Christoffer; Lundkvist, Mia; Lund, Mikkel N.; Handberg, Rasmus; Elsworth, Yvonne; Hekker, Saskia; Huber, Daniel; Bedding, Timothy R.; Rapin, William

2012-02-01

137

A Planetary System around the nearby M Dwarf GJ 667C with At Least One Super-Earth in Its Habitable Zone  

NASA Astrophysics Data System (ADS)

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 ~10 years). The 28 day signal implies a planet candidate with a minimum mass of 4.5 M ? 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.

Anglada-Escudé, Guillem; Arriagada, Pamela; Vogt, Steven S.; Rivera, Eugenio J.; Butler, R. Paul; Crane, Jeffrey D.; Shectman, Stephen A.; Thompson, Ian B.; Minniti, Dante; 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.

2012-05-01

138

The Influence of Giant Planets Near a Mean Motion Resonance on Earth-like Planets in the Habitable Zone of Sun-like Stars  

NASA Astrophysics Data System (ADS)

We present a numerical study of several two-planet systems based on the motions of Jupiter and Saturn, in which the two giant planets move in low eccentric orbits close to a mean motion resonance. It is more likely to find two planets with similar characteristics in a system than a clone of the Jupiter-Saturn pair of our solar system. Therefore, we vary the distance between the two planets and their mass ratio by changing Saturn's semimajor axis from 8 to 11 AU and increasing its mass by factors of 2-40. The different two-planets were analyzed for the interacting perturbations due to the mean motion resonances of the giant planets. We select several mass ratios for the gas giants, for which we study their influence on test bodies (with negligible mass) moving in the habitable zone (HZ) of a Sun-like star. The orbits are calculated for 2×107 yr. In all cases the HZ is dominated by a significant curved band, indicating higher eccentricity, which corresponds to a secular resonance with Jupiter. Interesting results of this study are finding (1) an increase of Venus's eccentricity for the real Jupiter and Saturn masses and the actual semimajor axis of Saturn; (2) an increase of the eccentricity of a test planet at Earth's position when Saturn's mass was increased by a factor of 3 or more; and (3) if the two giant planets are in 2:1 resonance, we observe a strong influence on the outer region of the HZ.

Pilat-Lohinger, E.; Süli, Á.; Robutel, P.; Freistetter, F.

2008-07-01

139

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

SciTech Connect

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.

Anglada-Escude, Guillem; Butler, R. Paul [Carnegie Institution of Washington, Department of Terrestrial Magnetism, 5241 Broad Branch Rd. NW, Washington, DC 20015 (United States); Arriagada, Pamela; Minniti, Dante [Department of Astronomy, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile); Vogt, Steven S.; Rivera, Eugenio J. [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Crane, Jeffrey D.; Shectman, Stephen A.; Thompson, Ian B. [Carnegie Observatories, 813 Santa Barbara St., Pasadena, CA 91101-1292 (United States); Haghighipour, Nader [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Monoa, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Carter, Brad D. [Faculty of Sciences, University of Southern Queensland, Toowoomba 4350 (Australia); Tinney, C. G.; Wittenmyer, Robert A.; Bailey, Jeremy A. [Department of Astrophysics, School of Physics, University of New South Wales, Sydney 2052 (Australia); O'Toole, Simon J. [Australian Astronomical Observatory, P.O. Box 296, Epping 1710 (Australia); Jones, Hugh R. A. [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Herts, AL10 9AB (United Kingdom); Jenkins, James S., E-mail: anglada@dtm.ciw.edu [Departamento de Astronomia, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago (Chile)

2012-05-20

140

CHARACTERIZING HABITABLE EXOMOONS  

SciTech Connect

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.

Kaltenegger, L. [Harvard University, 60 Garden Street, 02138 MA, Cambridge (United States)], E-mail: lkaltene@cfa.harvard.edu

2010-04-01

141

Tidal Limits to Planetary Habitability  

Microsoft Academic Search

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

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

2009-01-01

142

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

NASA Astrophysics Data System (ADS)

We have used the IRS Spectrograph onboard the Spitzer Space Telescope to study the warm dust orbiting around the 29 pc distant ? 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 ? 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.

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

2009-09-01

143

Spitzer observations of circumstellar disks  

NASA Astrophysics Data System (ADS)

Thanks to its very high sensitivity, the Spitzer Space Telescope is revisiting many of the questions on circumstellar dust disks evolution raised by previous space-based infrared observatories, in particular IRAS and ISO. I review in this paper recent Spitzer results on disks around young stars, including disk dissipation time-scale estimates, the identification of wTTS with disks, and the finding of transition disks. I will then summarize some of the results on %silicate grains dust mineralogy in T Tauri disks obtained as part of the ``Core to Disks'' (c2d) Legacy Project.

Augereau, J.-C.

2006-06-01

144

HI and CO study of circumstellar environments  

Microsoft Academic Search

Circumstellar shells around red giants are built over long periods of time that may reach several 10^6 years. They may therefore extend over large sizes (˜ 1 pc, possibly more) and different complementary tracers are needed to describe their global properties. We have undertaken a programme designed to gauge the properties of matter in the external parts of circumstellar shells

Y. Libert; T. Le Bertre; E. Gérard; J. M. Winters

2008-01-01

145

Atmospheric escape, redox evolution, and planetary habitability  

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

146

Habitable Worlds  

NSDL National Science Digital Library

In this group activity, learners consider environmental conditionsâtemperature, presence of water, atmosphere, sunlight, and chemical compositionâon planets and moons in our solar system to determine the possibilities of life on any of them. Data cards help prompt learners to compare and contrast how living creatures would adapt on various habitable worlds. This activity can be found on pages 39-42 of the activity guide.

Terc

2007-01-01

147

Geophysical and Atmospheric Evolution of Habitable Planets  

Microsoft Academic Search

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

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

2010-01-01

148

Dynamics and stability of telluric planets within the habitable zone of extrasolar planetary systems. Numerical simulations of test particles within the HD 4208 and HD 70642 systems  

Microsoft Academic Search

Aims: We study gravitational perturbation effects of observed giant extrasolar planets on hypothetical Earth-like planets in the context of the three-body problem. This paper considers a large parameter survey of different orbital configuration of two extrasolar giant planets (HD 70642b and HD 4208b) and compares their dynamical effect on Earth-mass planetary orbits initially located within the respective habitable terrestrial region.

T. C. Hinse; R. Michelsen; U. G. Jørgensen; K. Gozdziewski; S. Mikkola

2008-01-01

149

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

Microsoft Academic Search

We present radial velocity (RV) measurements of our sample of 40 M dwarfs\\u000afrom our planet search programme with VLT+UVES begun in 2000. Although with our\\u000aRV precision down to 2 - 2.5 m\\/s and timebase line of up to 7 years, we are\\u000acapable of finding planets of a few Earth masses in the close-in habitable\\u000azones of M

M. Zechmeister; M. Kürster; M. Endl

2009-01-01

150

Martian Habitability  

NASA Astrophysics Data System (ADS)

Due to the reported Mars surface environmental conditions (Klein, 1978) (oxidative stress, high UV radiation levels, etc.) the possibility for life development in the surface of the red planet is very small. The identification of water-ice on the subsurface on Mars by the Thermal Emission Spectrometer onboard of the Mars Odyssey (Kieffer and Titus, 2001) and from the High Energy Neutron Detector (Litvak, et al., 2006) has important astrobiological connotations, because in addition to be a potential source for water, these locations are shielding habitats against the harsh conditions existing on the planet, like UV radiation (Gomez, et al., 2007; Gomez, et al., 2012). Martian habitability potential could change in particular located micro-niches. Salt deliquescence and hard environmental parameters modification could be relevant for life under protected niches. An example could be endolithic niches inside salt deposits used by phototrophs for taking advantage of sheltering particular light wavelengths. Similar acidic salts deposits are located in Río Tinto extreme environment with shelter life forms which are difficult to localize by eye. Techniques for its localization and study during space missions are needed to develop. Extreme environments are good scenarios where to test and train those techniques and where hypothetical Astrobiological space missions could be simulated for increasing possibilities of micro niches identification. Here we will report some experiments of bacteria exposition to Martian surface conditions in Mars Simulation chamber. Bacteria were shelter and exposed included in simulated salty endolithic micro niches. High percentage of bacteria resistance and adaptation to harsh extreme those conditions was reported (Gómez, F. et al., 2010). These results were used to develop and implement a Habitability Index to study Martian habitability during the next MSL mission to Mars landed on August 2012 on the surface of the red planet.

Gómez, F.

2012-09-01

151

The Role of Planetary System Architecture in Planetary Habitability  

Microsoft Academic Search

Traditionally, the habitable zone is defined as the region around a star in which liquid water can be stable on a planetary surface. At first these calculations considered planets on circular orbits [1]. More recent investigations into nonzero orbital eccentricities found that the limits of the habitable zone should reflect the orbit-averaged flux a planet receives [2]. However, those studies

R. Barnes; B. Jackson; S. Raymond; R. Greenberg

2009-01-01

152

The Role of Planetary System Architecture in Planetary Habitability  

Microsoft Academic Search

Traditionally, the habitable zone is defined as the region around a star in which liquid water can be stable on a planetary surface. At first these assessments considered planets on circular orbits. More recent investigations into nonzero orbital eccentricities found that the limits of the habitable zone should reflect the orbit-averaged flux a planet receives. However, all these studies assumed

Rory Barnes; B. Jackson; S. N. Raymond; R. Greenberg

2010-01-01

153

Effects of Exoplanet Planetesimal Carbon Chemistry on Habitability  

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

154

HABEBEE: habitability of eyeball-exo-earths.  

PubMed

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

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

2013-03-19

155

Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite facies zircons: geochronology of the Ivrea Zone (Southern Alps)  

Microsoft Academic Search

Several types of growth morphologies and alteration mechanisms of zircon crystals in the high-grade metamorphic Ivrea Zone\\u000a (IZ) are distinguished and attributed to magmatic, metamorphic and fluid-related events. Anatexis of pelitic metasediments\\u000a in the IZ produced prograde zircon overgrowths on detrital cores in the restites and new crystallization of magmatic zircons\\u000a in the associated leucosomes. The primary morphology and Th-U

Gerhard Vavra; Rolf Schmid; Dieter Gebauer

1999-01-01

156

Pathways towards Habitable Moons  

NASA Astrophysics Data System (ADS)

The search for life outside of the Solar System should not be restricted to exclusively planetary bodies; large moons of extrasolar planets may also be common habitable environments throughout the Galaxy. Extrasolar moons, or exomoons, may be detected through transit timing effects induced onto the host planet as a result of mutual gravitational interaction. In particular, transit timing variations (TTV) and transit duration variations (TDV) are predicted to produce a unique exomoon signature, which is not only easily distinguished from other gravitational perturbations, but also provides both the period and mass of an exomoon. Using these timing effects, photometry greater or equal to that of the Kepler Mission is readily able to detect habitable-zone exomoons down to 0.2 Mearth and could survey up to 25,000 stars for Earth-mass satellites. We discuss future possibilities for spectral retrieval of such bodies and show that transmission spectroscopy with JWST should be able to detect molecular species with ˜30 transit events, in the best cases.

Kipping, D. M.; Fossey, S. J.; Campanella, G.; Schneider, J.; Tinetti, G.

2010-10-01

157

Flares and habitability  

NASA Astrophysics Data System (ADS)

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.

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

2012-07-01

158

Beyond the Principle of Plentitude: A Review of Terrestrial Planet Habitability  

Microsoft Academic Search

We review recent work that directly or indirectly addresses the habitability of terrestrial (rocky) planets like the Earth. Habitability has been traditionally defined in terms of an orbital semimajor axis within a range known as the habitable zone, but it is also well known that the habitability of Earth is due to many other astrophysical, geological, and geochemical factors. We

E. Gaidos; B. Deschenes; L. Dundon; K. Fagan; L. Menviel-Hessler; N. Moskovitz; M. Workman

2005-01-01

159

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

NASA Astrophysics Data System (ADS)

The fine dust detected by infrared (IR) emission around the nearby ? 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 ?m 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 ? 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.

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

2009-08-01

160

Circumstellar Disk Properties in Young Stellar Clusters  

Microsoft Academic Search

We have completed the first extensive program of L band (3.4 mu m) imaging surveys of eight young clusters. Such clusters are likely responsible for producing most of the stars in the Galaxy. The aims of this study were (1) to determine the circumstellar disk fraction in each cluster, (2) investigate the dependence of the disk fraction on cluster age

K. E. Haisch Jr.; E. A. Lada; C. J. Lada

2000-01-01

161

Chemistry and evolution of gaseous circumstellar disks  

Microsoft Academic Search

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

Ronald G. Prinn

1993-01-01

162

Collisional Evolution of a Circumstellar Debris Disk  

Microsoft Academic Search

A simple and fast model for a circumstellar debris disk has been developed. These disks are of considerable interest because they may be sites of ongoing planet formation. Collisions among unseen planetesimals are thought to be the source of these small dust grains, which upon their creation are launched into very wide orbits due to stellar radiation pressure (Strubbe and

Joseph M. Hahn

2010-01-01

163

Design Considerations for a Ground-Based Transit Search for Habitable Planets Orbiting M Dwarfs  

Microsoft Academic Search

By targeting nearby M dwarfs, a transit search using modest equipment is capable of discovering planets as small as 2 R in the habitable zones of late M dwarfs, and even stronger constraints for planets lying closer than the habitable zone. If the true occurrence rate of habitable planets is 10%, the expected yield would be 2.6 planets.

Philip Nutzman; David Charbonneau

2008-01-01

164

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

NASA Astrophysics Data System (ADS)

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.

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

2012-04-01

165

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

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

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

166

Diurnal Habitability of Frozen Worlds  

NASA Astrophysics Data System (ADS)

In this work we discuss effects allowing local habitability of some extraterrestrial planets of low average surface temperatures. We analyze the problem of diurnal and seasonal changes of temperature and biological productivity at different locations on a hypothetical Earth-like planet. We have found, that under some circumstances the temperature may locally rise well above the average value, allowing periods of enhanced biological activity. In this way, bioproductivity can become periodically possible on a planet that has an average temperature clearly below 0°C. Such thermal conditions are encountered on Mars (Smith et al. in Science 306:1750-1753, 2004) generally considered as inhabitable. In reality, an appropriate temperature is not sufficient for habitability. The presence of liquid water at the considered location is also necessary. We discuss how temperature oscillations affect habitability in the framework of a conceptual model. We find that the considered effect of diurnal and seasonal temperature oscillations can extend the outer boundary of the habitable zone up to 2 AU, while global average temperatures are below 0°C for heliocentric distances R h > 1.12 AU (dry atmosphere, low CO2 pressure), or R h > 1.66 AU (humid atmosphere, high CO2 pressure).

von Bloh, W.; Kossacki, K. J.; Franck, S.; Bounama, C.

2010-01-01

167

Tides and the evolution of planetary habitability.  

PubMed

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

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

2008-06-01

168

Herschel Views on Stellar and Circumstellar Evolution  

NASA Astrophysics Data System (ADS)

We review the first results of Herschel on stellar and circumstellar evolution. - For main-sequence stars, PACS and SPIRE measurements of the debris disks surrounding Vega and Beta Pictoris are presented, revealing the disks with unprecedented spatial resolution at the peaks of their spectral energy distribution. - Through imaging and spectroscopic studies, the mass loss mechanisms and histories during the final stages of stellar evolution are investigated. Imaging of the circumstellar environments of AGB stars enables a detailed discussion of the discontinuous nature of the mass loss processes which induce the final evolution. With their moderately high spectral resolution, PACS and SPIRE reveal spectacularly rich molecular diagnostics on the dynamics of and the chemistry in the environments of objects such as CW Leo and VY CMa.

Waelkens, Christoffel

2010-05-01

169

A Search for Potential Habitable Planets in Multiple Planet Systems  

Microsoft Academic Search

Although the detection of habitable terrestrial planets around nearby stars is currently beyond our observational capabilities, carrying out dynamical studies of known extrasolar planetary systems allows us to search for potential candidates. Following from the work of Menou & Tabachnik (2003), we use a symplectic integrator to search for potential stable terrestrial planetary orbits in the habitable zones of known

S. T. Maddison; M. C. Gino; A. Munro; P. Hinds

2004-01-01

170

Habitable Planets In The Planetary System Of HD 69830  

Microsoft Academic Search

We present the results of a study of the dynamical evolution and habitability of HD 69830 planetary system. Being the first multiplanet extrasolar planetary system with three Neptune-sized objects, HD 69830 provides new grounds for testing the possibility of the existence of smaller objects, such as terrestrial planets, particularly in its habitable zone. We numerically integrated the orbits of the

Sarah Rugheimer; N. Haghighipour

2007-01-01

171

Geophysical and atmospheric evolution of habitable planets.  

PubMed

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

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

172

How to Find a Habitable Planet  

Microsoft Academic Search

Over 400 extrasolar planets have now been discovered by ground-based methods, especially the radial velocity (RV) method. Most of these planets are much bigger than Earth, and only a handful of them are rocky planets that could conceivably harbor life. Within the next few years, we may be able to identify Earth-sized planets within the habitable zones around M stars

J. F. Kasting

2010-01-01

173

Tides and the Evolution of Planetary Habitability  

Microsoft Academic Search

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

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

2008-01-01

174

The origin of hot white dwarf circumstellar features  

NASA Astrophysics Data System (ADS)

We have analysed a sample of 23 hot DAs to better understand the source of the circumstellar features reported in previous work. Unambiguous detections of circumstellar material are again made at eight stars. The velocities of the circumstellar material at three of the white dwarfs are coincident with the radial velocities of interstellar medium (ISM) along the sight-line to the stars, suggesting that the objects may be ionizing the ISM in their locality. In three further cases, the circumstellar velocities are close to the ISM velocities, indicating that these objects are ionizing either the ISM or evaporated planetesimals/material in a circumstellar disc. The circumstellar velocity at WD 1614-084 lies far from the ISM velocities, indicating the ionization of either an undetected ISM component or circumstellar material. The material seen at WD 0232+035 can be attributed to the photoionization of material lost from its M dwarf companion. The measured column densities of the circumstellar material lie within the ionized ISM column density ranges predicted to exist in hot DA Strömgren spheres.

Dickinson, N. J.; Barstow, M. A.; Welsh, B. Y.; Burleigh, M.; Farihi, J.; Redfield, S.; Unglaub, K.

2012-06-01

175

Circumstellar Dust Disks around Stars with Known Planetary Companions  

Microsoft Academic Search

We have searched six stars with known radial velocity planetary companions for circumstellar disks. Disks are expected around stars with planetary systems that accreted from regular protoplanetary disks, and remnant disks are expected to be similar to our solar systems Kuiper Belt. To date, we have detected circumstellar disks around three such stars: 55 Cnc, o CrB, and HD 210277.

D. E. Trilling; R. H. Brown; A. S. Rivkin

2000-01-01

176

Multi-wavelength Observations and Modeling of Circumstellar Disks  

SciTech Connect

The enormous progress in the field of circumstellar disk observations during the last two decades has provided a basis for detailed models of these objects and thus constraints for the initial conditions of the planet formation process. A brief summary of the results derived from modeling various observables of circumstellar disks is provided and illustrated by selected exemplary studies.

Wolf, Sebastian [Christian-Alberts University, Institute of Theoretical Physics and Astrophysics, Leibnitzstr. 15, 24118 Kiel (Germany)

2009-08-05

177

Turnout as a Habit  

Microsoft Academic Search

It is conventional to speak of voting as “habitual.” But what does this mean? In psychology, habits are cognitive associations\\u000a between repeated responses and stable features of the performance context. Thus, “turnout habit” is best measured by an index\\u000a of repeated behavior and a consistent performance setting. Once habit associations form, the response can be cued even in\\u000a the absence

John H. Aldrich; Jacob M. Montgomery; Wendy Wood

178

Happy Safety Habits  

NSDL National Science Digital Library

We will be learning about certain safety habits and how knowing and doing these safety habits can make us happy. Introduction: Learning about different types of safety is important, because it keeps us safe and protected from dangers. Throught this webquest you will see waht safety habits you should use to keep yourself and family protected. Task: You will be asked to come up with a real life situation/story where you ...

Andersen, Miss

2009-03-27

179

Hydrogen Greenhouse Planets Beyond the Habitable Zone  

Microsoft Academic Search

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 H2-He mixtures can maintain surface temperatures above the freezing point of water well beyond the \\

Raymond Pierrehumbert; Eric Gaidos

2011-01-01

180

Extrasolar Trojan planets close to habitable zones  

Microsoft Academic Search

We investigate the stability regions of hypothetical terrestrial planets around the Lagrangian equilibrium points L4 and L5 in some specific extrasolar planetary systems. The problem of their stability can be treated in the framework of the restricted three body problem where the host star and a massive Jupiter-like planet are the primary bodies and the terrestrial planet is regarded as

R. Dvorak; E. Pilat-Lohinger; R. Schwarz; F. Freistetter

2004-01-01

181

The Mineralogy of Interstellar and Circumstellar Dust  

NASA Astrophysics Data System (ADS)

The study of dust in space was for a long time hampered by the lack of resolution and wavelength coverage in the infrared. The launch of the Infrared Space Observatory (ISO) changed this dramatically. Its unprecedented wavelength range (2.4 - 200 7m) together with its relatively high spectral resolution (lambda / Delta lambda = 2000-150) made this instrument ideal to study dust in space. Many new dust species have been found, in pa rticular of oxygen-rich species. The quality of the data allows a detailed mineralogy of individual species. The ISO database can be used to carry out an inventory of the occurrence of dust species in various circumstellar and interstellar environments. The picture that emerges is that of a very rich circumstellar dust mineralogy, while the interstellar medium shows only a limited amount of species. We present an overview of this inventory, as well as of the mineralogy of the dust species found. The implications for our understanding of dust processing in different astrophysical environments are also discussed.

Molster, F. J.; Waters, L. B. F. M.

182

A `dry' condensation origin for circumstellar carbonates  

NASA Astrophysics Data System (ADS)

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.

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

2005-10-01

183

On the possibility of earth-type habitable planets around 47 UMa  

Microsoft Academic Search

We investigate whether Earth-type habitable planets can in principle exist in the planetary system of 47 UMa. The system of 47 UMa consists of two Jupiter-size planets beyond the outer edge of the stellar habitable zone, and thus resembles our own Solar System most closely compared to all exosolar planetary systems discovered so far. Our study of habitability deliberately follows

Manfred Cuntz; Werner von Bloh; Christine Bounama; Siegfried Franck

2003-01-01

184

Tidal Limits to Planetary Habitability  

NASA Astrophysics Data System (ADS)

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 CO2 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.

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

2009-07-01

185

Dynamical habitability of planetary systems.  

PubMed

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

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

186

TIDAL LIMITS TO PLANETARY HABITABILITY  

SciTech Connect

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.

Barnes, Rory [Department of Astronomy, University of Washington, Seattle, WA 98195-1580 (United States); Jackson, Brian; Greenberg, Richard [Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States); Raymond, Sean N. [Virtual Planetary Laboratory (United States)

2009-07-20

187

Habitable Planets for Man.  

National Technical Information Service (NTIS)

Habitable Planets for Man examines and estimates the probabilities of finding planets habitable to human beings, where they might be found, and the number there may be in our own galaxy. The author presents in detail the characteristics of a planet that c...

S. H. Dole

2007-01-01

188

The Extraordinary Circumstellar Environment of U Equ  

NASA Astrophysics Data System (ADS)

We have discovered a star with an optical spectrum unlike any ever observed. Deep, narrow absorption lines of non-photospheric TiO, AlO, and VO riddle the optical spectrum, and indicate a rotation temperature of 700 K. This cold gas is well below the grain condensation temperature, and it takes an unusual circumstellar environment to retain Ti and Al in the gaseous phase. AlO and VO are sometimes seen in the photospheres of only the coldest { 3000 K} M stars, but the underlying spectrum of U Equ seems to be that of a warm mid-G star { 4800 to 5000 K}. The IRAS 25/12 micron colors are consistent with optically thin dust, yet the LRS spectrum shows moderate silicate absorption which is normally associated with optically thick material. Based on the IRAS data, we suspect that the star has an edge-on disk, with extended material giving rise to optically thin emission. We recently obtained an infrared spectrum {1 to 2.4 micron} that includes prominent H2O absorption bands and shows the CO 2-0 overtone band without the bandhead structure normally present in spectra of cool stars, indicating that the material is cold. The absence of CH4 in the spectrum further indicates a low, non-photospheric density. Although there are other warm stars with edge-on disks, none has the cold molecular absorption that U Equ displays. Ground based J and K band {7"} images suggest a bipolar symmetry. With NICMOS we will be able to clearly identify the nature of the circumstellar material around this unusual star.

Barnbaum, Cecilia

1997-12-01

189

Habitable Climates: The Influence of Eccentricity  

NASA Astrophysics Data System (ADS)

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 2)-1/2, one might expect the greatest habitable semimajor axis (for fixed atmospheric composition) to scale as (1 - e 2)-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.

Dressing, Courtney D.; Spiegel, David S.; Scharf, Caleb A.; Menou, Kristen; Raymond, Sean N.

2010-10-01

190

Your Child's Habits  

MedlinePLUS

... may be a sign of anxiety , depression , or obsessive-compulsive disorder (OCD) . Nose Picking Nose picking appears to be a ... to obsessive thoughts may be a sign of OCD. However, most habits don't cause any significant ...

191

The origin and formation of the circumstellar disc  

NASA Astrophysics Data System (ADS)

The formation and evolution of the circumstellar disc in the collapsing molecular cloud with and without magnetic field is investigated from the pre-stellar stage resolving both the molecular cloud core and the protostar itself. In the collapsing cloud core, the first (adiabatic) core appears prior to the protostar formation. Reflecting the thermodynamics of the collapsing gas, the first core is much more massive than the protostar. When the molecular cloud has no angular momentum, the first core falls on to the protostar and disappears a few years after the protostar formation. On the other hand, when the molecular cloud has an angular momentum, the first core does not disappear even after the protostar formation, and directly evolves into the circumstellar disc with a Keplerian rotation. There are two paths for the formation of the circumstellar disc. When the initial cloud has a considerably small rotational energy, two nested discs appear just after the protostar formation. During the early main accretion phase, the inner disc increases its size and merges with the outer disc (i.e. first core) to form a single circumstellar disc with a Keplerian rotation. On the other hand, when the molecular cloud has a rotational energy comparable to observations, a single centrifugally supported disc that corresponds to the first core already exists prior to the protostar formation. In such a cloud, the first core density gradually increases, maintaining the Keplerian rotation and forms the protostar inside it. The magnetic field rarely affects the early formation of the circumstellar disc because the magnetic field dissipates in the high-density gas region where the circumstellar disc forms. As a result, in any case, the protostar at its formation is already surrounded by a massive circumstellar disc. The circumstellar disc is about 10-100 times more massive than the protostar in the main accretion phase. Such discs are favourable sites for the formation of binary companions and gas-giant planets.

Machida, Masahiro N.; Matsumoto, Tomoaki

2011-06-01

192

NASA: Habitable Worlds  

NSDL National Science Digital Library

NASA's Habitable Worlds website encourages visitors to "search the solar system for signs of life," by selecting a "World to Explore." This creatively designed website smartly displays our solar system's colorful planets or worlds amidst the dark background of space. In order to gain in-depth information specific to each planet, users simply click on the world of their choosing. Each planet page provides beautiful images and information about habitability, moons, and more.

193

Motivation and study habits  

Microsoft Academic Search

The first part of the article reviews the literature (mainly British) on the relationships between academic performance in higher education and motivation and study habits. The distinction between goal-orientated and intrinsic motivation is used to clarify the meaning of previous studies. Among the investigations of study habits, the dimension of syllabus-boundness\\/syllabus-freedom helps to relate psychiatric work on study difficulties to

N. J. Entwistle; Jennifer Thompson; J. D. Wilson

1974-01-01

194

The Role of Planetary System Architecture in Planetary Habitability  

NASA Astrophysics Data System (ADS)

Traditionally, the habitable zone is defined as the region around a star in which liquid water can be stable on a planetary surface. At first these calculations considered planets on circular orbits [1]. More recent investigations into nonzero orbital eccentricities found that the limits of the habitable zone should reflect the orbit-averaged flux a planet receives [2]. However, those studies assumed the potentially habitable planet is isolated. If additional planets are in the system, gravitational interactions between planets can cause eccentricity oscillations on timescales of 103 - 106 years. Furthermore, the known multi-planet systems (generally consisting of giant planets) appear to undergo large amplitude eccentricity oscillations [3]. If rocky exoplanets also experience such large variations, then the orbit-averaged flux may change significantly, impacting habitability. We show that plausible architectures of rocky planet systems can indeed lead to orbits with large eccentricity cycles. Moreover, some planets could cross either the inner or outer habitable zone boundaries due to these oscillations. We therefore suggest that the shape of actual habitable zones depends critically on the configuration (orbits and masses) of the entire planetary system. [1] Kasting, J.F. et al. 1993, Icarus, 101, 108. [2] Williams, D.M. & Pollard, D. 2002, I. J. AsBio, 2, 1. [3] Barnes, R., & Greenberg, R. 2006, Astrophys. J., 652, L53.

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

2009-12-01

195

The Detectability of Habitable Exomoons with Kepler  

NASA Astrophysics Data System (ADS)

Now that more than 400 exoplanets have been discovered, focus has moved from finding planets to characterise these alien worlds. As well as detecting the atmospheres of these exoplanets, part of the characterisation process undoubtedly involves the search for extrasolar moons. We explore the motivations for undergoing such a search, review some of the proposed detection techniques and introduce a model for the Transit Time Variation (TTV) and Transit Duration Variation (TDV) signals which permits not only the identification of exomoons but also the derivation of some of their characteristics. The detectability of a habitable-zone exomoon around various configurations of exoplanetary systems with the Kepler Mission or photometry of approximately equal quality is investigated. We calculate both the predicted transit timing signal amplitudes and the estimated uncertainty on such measurements in order to calculate the confidence in detecting such bodies across a broad spectrum of orbital arrangements. The effects of photon noise, stellar variability and instrument noise are all accounted for in the analysis. We validate our methodology by simulating synthetic lightcurves and we find that habitable-zone exomoons down to 0.2 Earth masses may be detected and 25,000 stars could be surveyed for habitable-zone exomoons within Kepler`s field-of-view. Finally, we predict how a further characterisation of these bodies can be carried out.

Campanella, Giammarco; Kipping, David; Fossey, Stephen

196

NIR Imaging of the HR4796A Circumstellar Disk  

NASA Astrophysics Data System (ADS)

We report the first near infrared imaging of a circumstellar annular disk around the young (~ 10Myr) star HR4796A. Observations obtained on 15 March and 16 August, 1998, using the HST/NICMOS coronagraph, reveal a ring-like symmetrical structure seen at 1.1 and 1.6 microns peaking in reflected intensity ~70AU (1.1") from the central A0V star. The annulus, with a characteristic width of ~15AU (0.2"), is abruptly truncated at both the inner and outer edges. The interior region of the disk-plane appears to be optically thin, and may be relatively free of scattering material. These observations, which place the major axis of the ring at a PA of ~28 degrees, inclined ~75 degrees, are in good agreement with the nearly contemporaneous (16 March) thermal infrared detection of an inner truncated disk seen in emission as reported by Koerner, et. al (1998, ApJ, 503, L83) and Jayawardhana, et. al. (1998, ApJ, 503, L79). The confinement of material to this relatively narrow zone implies dynamical constraints on the disk particles by one or more yet unseen orbiting bodies. We report these results as part of the NICMOS IDT Environments of Nearby Stars program. This work is supported by NASA grant NAG 5-3042. This paper is based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555.

Smith, B. A.; Schneider, G.; Becklin, E. E.; Koerner, D. W.; Meier, R.; Terrile, R. J.; Hines, D. C.; Lowrance, P. J.; Thompson, R. I.

1998-12-01

197

CIRCUMSTELLAR SHELL FORMATION IN SYMBIOTIC RECURRENT NOVAE  

SciTech Connect

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.

Moore, Kevin; Bildsten, Lars [Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93106 (United States)

2012-12-20

198

Circumstellar Shell Formation in Symbiotic Recurrent Novae  

NASA Astrophysics Data System (ADS)

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.

Moore, Kevin; Bildsten, Lars

2012-12-01

199

The shapes of the circumstellar silicate features  

NASA Astrophysics Data System (ADS)

Around oxygen-rich stars we find that the spectra of most long-period variables (LPV) show an excess infrared emission which is attributed to circumstellar silicate dust grains. These grains produce emission features at about 10 and 18 micrometers due to bending and stretching modes of SiO respectively. It has been known (Forrest, Gillett and Stein 1975) that the spectral energy distribution of the 10 micrometers emission shows variations from star to star. With the availability of many IRAS Low Resolution Spectra (LRS) in the 9-22 micrometers region of M stars, we can now study the 10-micrometers feature to determine its uniformity (or lack thereof). For this analysis we assume that the 8-22 micrometers emission from these stars is produced by a) the stellar photosphere, b) a continuum emission from the dust grains and c) a strongly wavelength dependent dust grain emission term. By representing the first two terms with blackbody energy distributions and subtracting them from the observed spectrum, we are left with a remaining strongly wavelength dependent emission feature which we call the excess silicate or 10 micrometers emission.

Little-Marenin, Irene R.; Price, S. D.

1986-09-01

200

The Circumstellar Environment of Embedded Massive Stars  

NASA Astrophysics Data System (ADS)

Millimeter and submillimeter wavelength images of massive star-forming regions are revealing the morphologies of the natal material and the complexity of circumstellar environments on size scales from parsecs to 100's of AU. Massive stars appear to be gregarious siblings with regions at different evolutionary stages located within parsecs of each other. Often, different evolutionary stages even co-exist within an overall extended core. Current observational goals include the characterization of an early evolutionary sequence for massive stars, determination if the basic accretion process for massive stars is similar to, or different from, that of low-mass stars, and understanding of the significance of triggered or induced modes of massive star formation. Observations are beginning to make significant progress in many of these areas. Works identifying and characterizing the earliest stages of massive stars are producing a list of candidate sources. More detailed studies of dense warm cores and dense hot cores are refining our understanding of the nature of these regions. Chemical studies of these cores are helping to probe the energetics. Continuuing work over the next few years should provide a good templete for massive star formation and an understanding of their role in cluster formation.

Mundy, Lee G.; et al.

201

Circumstellar features in hot DA white dwarfs  

NASA Astrophysics Data System (ADS)

We present a phenomenological study of highly ionized, non-photospheric absorption features in high spectral resolution vacuum ultraviolet spectra of 23 hot DA white dwarfs. Prior to this study, four of the survey objects (Feige 24, REJ 0457-281, G191-B2B and REJ 1614-085) were known to possess these features. We find four new objects with multiple components in one or more of the principal resonance lines: REJ 1738+665, Ton 021, REJ 0558-373 and WD 2218+706. A fifth object, REJ 2156-546, also shows some evidence of multiple components, though further observations are required to confirm the detection. We discuss possible origins for these features including ionization of the local interstellar environment, the presence of material inside the gravitational well of the white dwarf, mass loss in a stellar wind and the existence of material in an ancient planetary nebula around the star. We propose ionization of the local interstellar medium as the origin of these features in G191-B2B and REJ 1738+665, and demonstrate the need for higher-resolution spectroscopy of the sample, to detect multiple interstellar medium velocity components and to identify circumstellar features that may lie close to the photospheric velocity.

Bannister, N. P.; Barstow, M. A.; Holberg, J. B.; Bruhweiler, F. C.

2003-05-01

202

The Warped Circumstellar Disk of HD 100546  

NASA Astrophysics Data System (ADS)

We propose that the two-armed spiral features seen in visible Hubble Space Telescope images of scattered light in HD 100546's circumstellar disk are caused by the illumination of a warped outer disk. A tilt of 6°-15° from the symmetry plane can cause the observed surface brightness variations, providing the disk is very twisted (highly warped) at radii greater than 200 AU where the spiral features are seen. Dust lanes are due in part to shadowing in the equatorial plane from the inner disk within a radius of 100 AU. HD 100546's outer disk, if viewed edge-on, would appear similar to that of Beta Pictoris. A disk initially misaligned with a planetary system becomes warped due to precession induced by planetesimal bodies and planets. However, the twistedness of HD 100546's disk cannot be explained by precession during the lifetime of the system induced by a single Jovian-mass planet within the clearing at ~13 AU. One possible explanation for the corrugated disk is that precession was induced by massive bodies embedded in the disk at larger radius. This would require approximately a Jupiter mass of bodies well outside the central clearing at 13 AU and within the location of the spiral features or at radii approximately between 50 and 200 AU.

Quillen, Alice C.

2006-04-01

203

The Interaction of Supernovae with Their Circumstellar Medium  

NASA Astrophysics Data System (ADS)

The interaction of supernova (SN) ejecta with circumstellar material supplied by the wind of the evolved progenitor star can sometimes provide enough energy to sustain the SN luminosity for several decades. Existing observations of certain Type II SNe strongly favor such an interpretation over other possible late-time energy sources. Some peculiar SNe II have such dense circumstellar winds that interaction with the ejecta substantially alters their observed properties even at early times. The UV spectrum is a powerful diagnostic for probing the conditions in the shocked outer ejecta and circumstellar gas. We propose to observe two old SNe (t = 7- 15 years) which, due to their extensive radio and optical data records, are particularly well suited for an investigation of the interaction between ejecta and circumstellar gas. We will also observe one of the most recent SNe II (SN 1994Y), which shows strong evidence for very early interaction with its circumstellar medium. The fluxes and intensity ratios of UV emission lines measured in FOS spectra will be used to test theoretical models of the interaction. HST observations of these objects will shed light on differences among them and their shocks, as well as on the mass-loss histories of their progenitor stars.

Filippenko, Alex

1995-07-01

204

Magnetic Shielding of Exomoons beyond the Circumplanetary Habitable Edge  

NASA Astrophysics Data System (ADS)

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.

Heller, René; Zuluaga, Jorge I.

2013-10-01

205

Circumstellar Surroundings of Young Stellar Objectse  

NASA Astrophysics Data System (ADS)

The close surroundings of young low mass stars hold a multitude of physical phenomena related to star formation. This thesis presents a set of works on theoretical, experimental, and observational issues connected with these phenomena. After a description of the properties of T Tauri, FU Orionis and Ae/Be Herbig stars, with a particular emphasis on their accretion disks, I study the vertical structure of such disks which results from the radiative transfer and the hydrostatic equilibrium. The energy dissipation comes from both the viscous friction of disk particles accreting onto the star and from the absorption of the stellar radiation. A disk ``chromosphere'' is shown to result from the grazing stellar radiation. In the following I study the possibility of detecting directly the circumstellar features (disk, binarity, planets, jets,...) thanks to the high angular resolution techniques (adaptive optics and interferometry). I then present the prototype of a coronagraph at high spatial resolution that I designed, modelized, built and tested for that kind of observations. Finally I describe the observations of the young stellar system Z Canis Majoris, which I obtained at the diffraction limit of the 3.6 meter ESO telescope in the near infrared. This object is shown to be composed of a binary system in addition to an elongated disk-like structure perpendicular to the known jet and illuminated not by the central source but by the infrared companion. [A copy of this thesis (which is mostly in french) can be obtained in binary mode by ftp. There is a file 'these_malbet.tar' in the directory '/pub/publications/' at the FTP node 'gag.observ-gr.fr (IP 130.190.200.11)'. By doing 'tar -xvf these_malbet.tar', you create a directory 'these_malbet/' where there is a 'readme' which gives all information.

Malbet, Fabien

1992-12-01

206

Polarization analysis of circumstellar dust disks  

NASA Astrophysics Data System (ADS)

Imaging polarimetry is a powerful technique to study circumstellar dusty environments. Detailed analyses of polarization disks allow to quantitatively evaluate the disk geometries and the dust properties. We present near-infrared (NIR) polarimetric images and radiative transfer modeling of the high-mass protostar CRL 2136 and the Herbig Be star R Mon. In CRL 2136, the data show a central star feature (IRS 1), a spot-like high polarization region towards IRS 1 (PK = 32%), and a linear polarization vector alignment along the equatorial direction around IRS 1. In our spherical grain model, the optical depth of the disk is estimated to be 210 in the V-band. With such an intermediate optical depth, the linear vector alignment and the visible central star feature can not be reproduced simultaneously. We interpret that the linear vector alignment detected in our observation is probably due to dichroism by aligned nonspherical grains. In R Mon, our NIR polarimetric data detected a butterfly-shaped polarization disk with an extension of ~4", low polarizations (P<2%), and a centro-symmetric vector alignment. Our radiative transfer models which reproduce these results expect a large disk radius of 3000 AU and large dust up to ~1000.0 µm in the disk. The polarization disk traces the Keplerian rotating gas disk (~1500 AU) comparably well and the modeled disk is much larger than typical low-mass star disks (~100 AU). Furthermore, the dust disk is found to be geometrically thinner than the gas disk (Fuente et al. 2006) and much thicker than typical T Tauri disks. This result suggests a possible ongoing dust settling.

Murakawa, K.

2012-05-01

207

Habits of Spiders  

Microsoft Academic Search

YOUR correspondent, Mr. Frank Rowbotham, in his letter on the ``Habits of Spiders'' (vol. xxvi. p. 386), gives it as his opinion that a spider shakes the web from a desire ``to effect concealment when it feels danger is near.'' I am inclined to think it does so from a feeling of anger. During a long residence in the tropics,

C. W. J

1882-01-01

208

Atmospheric studies of habitability in the Gliese 581 system  

NASA Astrophysics Data System (ADS)

Context. The M-type star Gliese 581 is orbited by at least one terrestrial planet candidate in the habitable zone, i.e. GL 581 d. Orbital simulations have shown that additional planets inside the habitable zone of GL 581 would be dynamically stable. Recently, two other planet candidates have been claimed, one of them in the habitable zone. Aims: In view of the ongoing search for planets around M stars that is expected to result in numerous detections of potentially habitable super-Earths, we take the GL 581 system as an example for investigating such planets. In contrast to previous studies of habitability in the GL 581 system, we use a consistent atmospheric model to assess surface conditions and habitability. Furthermore, we performed detailed atmospheric simulations for a much larger subset of potential planetary and atmospheric scenarios than previously considered. Methods: A 1D radiative-convective atmosphere model was used to calculate temperature and pressure profiles of model atmospheres, which we assumed to be composed of molecular nitrogen, water, and carbon dioxide. In these calculations, key parameters such as surface pressure and CO2 concentration, as well as orbital distance and planetary mass are varied. Results: Results imply that surface temperatures above freezing could be obtained, independent of the atmospheric scenarios considered here, at an orbital distance of 0.117 AU. For an orbital distance of 0.146 AU, CO2 concentrations as low as 10 times the present Earth's value are sufficient to warm the surface above the freezing point of water. At 0.175 AU, only scenarios with CO2 concentrations of 5% and 95% were found to be habitable, so an additional super-Earth planet in the GL 581 system in the previously determined dynamical stability range would be considered a potentially habitable planet.

von Paris, P.; Gebauer, S.; Godolt, M.; Rauer, H.; Stracke, B.

2011-08-01

209

Habitable Niches In Single and Binary Star Systems  

NASA Astrophysics Data System (ADS)

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.

Clark, Joni; Mason, P. A.

2013-01-01

210

What makes a planet habitable?  

NASA Astrophysics Data System (ADS)

This work reviews factors which are important for the evolution of habitable Earth-like planets such as the effects of the host star dependent radiation and particle fluxes on the evolution of atmospheres and initial water inventories. We discuss the geodynamical and geophysical environments which are necessary for planets where plate tectonics remain active over geological time scales and for planets which evolve to one-plate planets. The discoveries of methane-ethane surface lakes on Saturn’s large moon Titan, subsurface water oceans or reservoirs inside the moons of Solar System gas giants such as Europa, Ganymede, Titan and Enceladus and more than 335 exoplanets, indicate that the classical definition of the habitable zone concept neglects more exotic habitats and may fail to be adequate for stars which are different from our Sun. A classification of four habitat types is proposed. Class I habitats represent bodies on which stellar and geophysical conditions allow Earth-analog planets to evolve so that complex multi-cellular life forms may originate. Class II habitats includes bodies on which life may evolve but due to stellar and geophysical conditions that are different from the class I habitats, the planets rather evolve toward Venus- or Mars-type worlds where complex life-forms may not develop. Class III habitats are planetary bodies where subsurface water oceans exist which interact directly with a silicate-rich core, while class IV habitats have liquid water layers between two ice layers, or liquids above ice. Furthermore, we discuss from the present viewpoint how life may have originated on early Earth, the possibilities that life may evolve on such Earth-like bodies and how future space missions may discover manifestations of extraterrestrial life.

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.; Rauer, H.

2009-06-01

211

Signatures of planets in circumstellar debris disks  

NASA Astrophysics Data System (ADS)

Main sequence stars are commonly surrounded by debris disks, composed of cold dust continuously replenished by a reservoir of undetected dust-producing planetesimals. In the outer Solar System, Kuiper Belt (KB) objects produce dust by mutual or interstellar grain collisions. The orbital evolution of KB dust has been numerically modeled. Its equilibrium radial density distribution can be accurately estimated even though there are inherent uncertainties in the prediction of structure, owing to the chaotic dynamics of dust orbital evolution imposed by resonant gravitational perturbations of the planets. The particle size distribution of dust is greatly changed from the distribution at production, as a result of radiation forces and the perturbations of the planets. The contribution of KB dust to the population of interplanetary dust particles collected at Earth may be as low as a few percent. Gravitational scattering by giant planets creates an outflow of large grains. We quantify the characteristics of this large-particle outflow in different planetary architectures, discuss its implications for exo-planetary debris disks, and for the interpretation of in-situ dust detection experiments in space probes traveling in the outer Solar System. These outflows may contribute to the clearing of circumstellar debris in planetary systems, affecting the particle size distribution of their local ISM. In anticipation of future observations of unresolved debris disks with Spitzer , we are interested in studying how the structure carved by planets affects the shape of the disk's spectral energy distribution (SED), and consequently if the SED can be used to infer the presence of planets. We numerically calculate the equilibrium spatial density distributions and SEDs of dust disks originated by an outer belt of planetesimals (35-50 AU) in the presence of different planetary configurations, and for a representative sample of chemical compositions. The dynamical models are needed to estimate the enhancement of particles near the mean motion resonances with the planets, and to determine how many particles drift inside the planet's orbit. Based on the SEDs and predicted Spitzer colors we discuss what types of planetary systems can be distinguishable from one another.

Moro-Martin, Maria Amaya

2004-12-01

212

Studying Young Circumstellar Disks with ALMA  

NASA Astrophysics Data System (ADS)

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.

Ménard, F. C.

2005-12-01

213

Crystalline Silicates in Circumstellar Dust Shells  

NASA Astrophysics Data System (ADS)

The discovery of crystalline silicates outside our own Solar System by the infrared space observatory (ISO) in both young (Waelkens et al. 1996, A&A 315, L245), and evolved stars (Waters et al. 1996, A&A 315, L361) brought new inside in the circumstellar dust formation and evolution. We will present here an extensive overview of the solid state bands found in a sample of 17 stars all with oxygen-rich dust around them. For all stars good ISO-SWS (short wavelength spectrometer 2--45 ? m) spectra were available and for 12 stars also reliable ISO-LWS (long wavelength spectrometer 43--195 ? m) spectra were taken. We could identify about 50 different spectral features, most of them clustered into one of the 7 complexes (which we defined). Most bands could be identified with crystalline silicates and crystalline water ice, however still roughly 20% remains unidentified. An important result was that the presence of strong crystalline silicates bands always correlates with the presence of a disk like structure (N.B. The presence of a disk does not necessary imply a high fraction of crystalline silicates)(Molster et al. 1999, Nature 401, 563). We found that not only the strength but also the shape of the crystalline silicate features is different for sources with and without the presence of a disk. Another surprising result of this research is that the crystalline silicates contain no measurable amount of Fe. The main minerals found, are forsterite (Mg2 SiO4) and enstatite (MgSiO3). We have calculated mean crystalline silicate spectra for both the disk and the non-disk sources. By simple model fitting we derived estimates for the (relative) mass and temperature of the amorphous silicates, forsterite and enstatite. Based on these results we drew the conclusion that the crystalline and amorphous silicate grains are two separate grain populations. This work was part of a PhD-thesis and funded by NWO.

Molster, F. J.; Waters, L. B. F. M.; Tielens, A. G. G. M.

2000-12-01

214

D/H Fractionation in Circumstellar Disks  

NASA Astrophysics Data System (ADS)

In recent years millimeter-wave interferometers have imaged the gas and dust surrounding over a dozen T Tauri and Herbig Ae stars (see Sargent 1996 in Disks and Outflows from Young Stars, pp. 1-23, for review). These studies demonstrate the potential to improve dramatically our understanding of disk physical and chemical structure, providing unique insights that will ultimately enable a more comprehensive understanding of star and planet formation. In particular, through the comparison of disk properties such as (D/H) fractionation with those of comets and Kuiper belt objects the origin of primitive solar system bodies can be investigated. In this study, 1.3 mm transitions of the deuterated species DCN and HDO were detected toward the T Tauri star LkCa 15 using the Owens Valley Radio Observatory Millimeter Array (for previous observations of various molecules toward LkCa 15 see Qi, PhD thesis, 2000). The resulting DCN abundance was compared to that found for HCN and H13CN. The measured intensity ratios of the (DCN/HCN) transitions lead to (D/H) ratios of <0.5, but are clearly influenced by opacity in the HCN 1-0 transition. Observations of the optically thin isotope H13CN, yield an estimated DCN/HCN ratio of ~ 0.01. This value is much larger than the estimated protosolar D/H of ~ 1.6e-5 (Gautier & Morel 1997 A&A 323, L9) and quite close to that observed in dark molecular clouds, 0.01-0.05 (Wooten 1987 Astrochem 120, 311), indicating that the assignment of cometary origin using D/H fractionation is a complicated endeavor. Through the combination of the observations presented here and chemical models of circumstellar material, the temperature dependence of fractionation and enrichment of deuterium through gas-grain surface reactions can be explored. Further, although H2O cannot be observed and thus HDO/H2O was not measured, differences in the morphology of maps of the observed emission from DCN and HDO may shed light on differences in fractionation seen in the material around young stars. This work was supported by the NASA Graduate Student Researchers Program, NGT5-50231, and the National Science Foundation, AST 9981546.

Kessler, J. E.; Qi, C.; Blake, G. A.

2000-12-01

215

Case studies of habitable Trojan planets in the system of HD 23079  

Microsoft Academic Search

We investigate the possibility of habitable Trojan planets in the HD 23079 star-planet system. This system consists of a solar-type star and a Jupiter-type planet, which orbits the star near the outer edge of the stellar habitable zone in an orbit of low eccentricity. We find that in agreement with previous studies Earth-mass habitable Trojan planets are possible in this

J. Eberle; M. Cuntz; B. Quarles; Z. E. Musielak

2011-01-01

216

Bowel Habit in Pregnancy  

Microsoft Academic Search

One thousand healthy postpartum Israeli women were interviewed on their bowel habit before and during pregnancy. In 54.6% there was no change in the bowel frequency during pregnancy, while 34.4% had an increased and 11% a decreased frequency. An incidence of 4.9% of subjects indicated that they had experienced diarrhea of 2–8 weeks duration in the last trimester. When the

N. Levy; E. Lemberg; M. Sharf

1971-01-01

217

Personality and health habits  

Microsoft Academic Search

Four hundred and fifty-five males and 523 females from a community sample participated in a study on the relationship between seven health practices (sleeping; breakfasting; snacking; being at good weight; smoking; alcohol consumption and physical activity) and seven personality factors (Neuroticism; Social Inadequacy; Rigidity; Hostility; Self-sufficiency; Dominance and Self-esteem).It was found that the seven health habits did not constitute a

A. J. J. M. Vingerhoets; M. Croon; A. J. Jeninga; L. J. Menges

1990-01-01

218

Detection of Circumstellar Material in a Normal Type Ia Supernova  

Microsoft Academic Search

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

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

2007-01-01

219

Newly identified main-sequence A stars with circumstellar dust  

Microsoft Academic Search

The IRAS Faint Source Survey data base and the ADDSCAN\\/SCANPI software are used to search for systems with circumstellar dust in two samples: all of the 62 A stars in Woolley's catalog, which lie near the main sequence and are typically within 25 pc of the sun, and all A stars in the Bright Star Catalogue with mV in the

K.-P. Cheng; F. C. Bruhweiler; Y. Kondo; C. A. Grady

1992-01-01

220

Circumstellar Dynamics and Transfer: Laminar Flows and Shocks  

NASA Astrophysics Data System (ADS)

This paper is both a review and a presentation of new models. Observation and modelization of circumstellar envelopes of early type or late type stars are now quickly evolving because of new techniques and facilities for observations, and increased power of computers. More and more complex physical phenomena involved in mass driving can now be modelized, at many different size scales. While most of models were previously based on informations derived from spectrophotometric data only or on measurements concerning objects observed with no spatial resolution, observations at much increased angular resolution can provide constraints on models of these phenomena. Theory and modelization must take this new situation into account. Two approaches are possible and effectively used. On the one hand, dynamical/physical self consistent models can be built; on the other hand, elaborate semi-empirical models including complicated distributions of matter with asymmetries (3D models) can be built and fitted for direct comparison with results of High Angular Resolution Measurements. Adding such constraints to classical constraints leads to a new insight in the physics of circumstellar matter and, through it, of stellar and interstellar evolution. Two examples have been chosen, in which new models are presented and assuming or not spherical symmetry is carefully discussed: •Circumstellar matter around evolved stars •Shock waves propagating in the circumstellar matter around evolved stars.

Lafon, Jean-Pierre J.; Berruyer, Nicole

1995-02-01

221

The Solar Neighborhood: Habitable Real Estate Around Nearby Stars  

NASA Astrophysics Data System (ADS)

We have determined the amount of habitable "real estate" for 38 stars nearer than 5 parsecs. Using photometric spectral energy distributions (SEDs) derived using available and new UBVRIJHK photometry from the RECONS (Research Consortium on Nearby Stars) effort, we estimate the region around each target star in which liquid water may exist on any orbiting planet, i.e. the classical habitable zone. From the SEDs and parallax data from RECONS, we were able to estimate radii and temperatures for these stars using an IDL curve fitting function and GAIA models. These radii and temperatures were then used to estimate habitable area around each star, and the sums for each spectral type were found. Results indicate that spectral type A stars provide the most habitable real estate as a group, followed by the F stars. This research has been supported by NSF grant AST 05-07711, NASA's Space Interferometry Mission, and Georgia State University.

Cantrell, Justin R.; Jao, W.; Henry, T.; Monteiro, H.

2007-12-01

222

Beyond the principle of plentitude: a review of terrestrial planet habitability.  

PubMed

We review recent work that directly or indirectly addresses the habitability of terrestrial (rocky) planets like the Earth. Habitability has been traditionally defined in terms of an orbital semimajor axis within a range known as the habitable zone, but it is also well known that the habitability of Earth is due to many other astrophysical, geological, and geochemical factors. We focus this review on (1) recent refinements to habitable zone calculations; (2) the formation and orbital stability of terrestrial planets; (3) the tempo and mode of geologic activity (e.g., plate tectonics) on terrestrial planets; (4) the delivery of water to terrestrial planets in the habitable zone; and (5) the acquisition and loss of terrestrial planet carbon and nitrogen, elements that constitute important atmospheric gases responsible for habitable conditions on Earth's surface as well as being the building blocks of the biosphere itself. Finally, we consider recent work on evidence for the earliest habitable environments and the appearance of life itself on our planet. Such evidence provides us with an important, if nominal, calibration point for our search for other habitable worlds. PMID:15815163

Gaidos, E; Deschenes, B; Dundon, L; Fagan, K; Menviel-Hessler, L; Moskovitz, N; Workman, M

2005-04-01

223

Effect of Magnetic Braking on Circumstellar Disk Formation in a Strongly Magnetized Cloud  

NASA Astrophysics Data System (ADS)

Using resistive magnetohydrodynamics simulation, we consider circumstellar disk formation in a strongly magnetized cloud. As the initial state, an isolated cloud core embedded in a low-density interstellar medium with a uniform magnetic field was adopted. The cloud evolution was calculated until almost all gas inside the initial cloud fell onto either the circumstellar disk or a protostar, and a part of the gas was ejected into the interstellar medium by the protostellar outflow driven by the circumstellar disk. In the early main accretion phase, the disk size is limited to ˜10 AU because the angular momentum of the circumstellar disk is effectively transferred by both magnetic braking and the protostellar outflow. In the later main accretion phase, however, the circumstellar disk grows rapidly and exceeds ? 100 AU by the end of the main accretion phase. This rapid growth of the circumstellar disk is caused by depletion of the infalling envelope, while magnetic braking is effective when the infalling envelope is more massive than the circumstellar disk. The infalling envelope cannot brake the circumstellar disk when the latter is more massive than the former. In addition, the protostellar outflow weakens and disappears in the later main accretion phase, because the outflow is powered by gas accretion onto the circumstellar disk. Although the circumstellar disk formed in a magnetized cloud is considerably smaller than that in an unmagnetized cloud, a circumstellar disk exceeding 100 AU can form even in a strongly magnetized cloud.

Machida, Masahiro N.; Inutsuka, Shu-Ichiro; Matsumoto, Tomoaki

2011-06-01

224

Habitability and Life - an Overview  

NASA Astrophysics Data System (ADS)

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

Bredehöft, J. H.

2008-09-01

225

POST-CAPTURE EVOLUTION OF POTENTIALLY HABITABLE EXOMOONS  

SciTech Connect

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.

Porter, Simon B.; Grundy, William M., E-mail: porter@lowell.edu [Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff, AZ 86001 (United States)

2011-07-20

226

The detectability of habitable exomoons with Kepler  

NASA Astrophysics Data System (ADS)

In this paper, the detectability of habitable exomoons orbiting around giant planets in M-dwarf systems using transit timing variations (TTVs) and transit duration variations (TDVs) with Kepler-class photometry is investigated. Light curves of systems with various configurations were simulated around M-dwarf hosts of mass 0.5 M? and radius 0.55 R?. Jupiter-like giant planets which offer the best potential for hosting habitable exomoons were considered with rocky super-Earth-mass moons. The detectability is measured by using the phase-correlation between TTV and TDV signals. Since the TDV signal is typically weaker than the TTV signal, confirmation of an exomoon detection will depend on being able to detect a TDV signal. We find that exomoons around planets orbiting within the habitable zone of an M-dwarf host star can produce both detectable TTV and TDV signatures with Kepler-class photometry. While aliasing between the planet period and moon period may hinder exomoon detection, we also find some strong correlation signatures in our simulation (e.g. correlation: >0.7) which would provide convincing exomoon signatures. With the addition of red noise stellar variability, correlations generally weaken. However simulated examples with planet masses less than around 25 M?, moons of mass 8-10 M? and specific values of planet and moon periods still yield detectable correlation in 25-50 per cent of cases. Our simulation indicates that Kepler provides one of the best available opportunities for exomoon detection.

Awiphan, S.; Kerins, E.

2013-07-01

227

On the probability of habitable planets  

NASA Astrophysics Data System (ADS)

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.

Forget, François

2013-07-01

228

Detection of circumstellar material in a normal type Ia supernova.  

PubMed

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

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

2007-07-12

229

Circumstellar Absorption in Double Detonation Type Ia Supernovae  

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

230

CIRCUMSTELLAR SHELLS IN ABSORPTION IN TYPE Ia SUPERNOVAE  

SciTech Connect

Progenitors of Type Ia supernovae (SNe) have been predicted to modify their ambient circumstellar (CSM) and interstellar environments through the action of their powerful winds. While there is X-ray and optical evidence for circumstellar interaction in several remnants of Type Ia SNe, widespread evidence for such interaction in Type Ia SNe themselves has been lacking. We consider prospects for the detection of CSM shells that have been predicted to be common around Type Ia SNe. Such shells are most easily detected in Na I absorption lines. Variable (declining) absorption is expected to occur soon after the explosion, primarily during the SN rise time, for shells located within {approx}1-10 pc of a SN. The distance of the shell from the SN can be determined by measuring the timescale for line variability.

Borkowski, Kazimierz J.; Blondin, John M.; Reynolds, Stephen P. [Physics Department, North Carolina State U., Raleigh, NC 27695-8202 (United States)], E-mail: kborkow@ncsu.edu

2009-07-10

231

Habitable Planets Eclipsing Brown Dwarfs: Strategies for Detection and Characterization  

NASA Astrophysics Data System (ADS)

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 HZ out). Habitable planets with P HZ 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^{+5.6}_{-1.4}% and 56^{+31}_{-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 ~1% of a five-year mission's lifetime spread over a contiguous segment only one-fifth to one-tenth of this duration.

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

2013-05-01

232

Type-Ia supernovae in dense circumstellar gas  

Microsoft Academic Search

We propose a model for the bolometric light curve of a type-Ia supernova (SN Ia) that explodes in a dense circumstellar (CS)\\u000a envelope. Our modeling of the light curves for SN 2002ic and SN 1997cy shows that the densities of the CS envelopes around\\u000a both supernovae at a radius of ?71015 cm are similar, while the characteristic ejection time for

N. N. Chugai; L. R. Yungelson

2004-01-01

233

On the Crystallization of Small Silica Particles in Circumstellar Environments  

Microsoft Academic Search

Infrared Space Observatory (ISO) observations have revealed the presence of crystalline silicate dust in circumstellar environments of some evolved stars (e.g. Waters et al. 1996, A&A 315, L361). Molster et al. (2001, A&A 366, 923), for instance, reported the discovery of a carbon-rich AGB star surrounded by a highly crystalline silicate dust shell as indicated by the high resolution ISO-SWS

M. John; E. Müller; B. Patzer; M. Lüttke; E. Sedlmayr

2001-01-01

234

NASA plans relevant to the study of circumstellar matter  

NASA Astrophysics Data System (ADS)

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.

Stencel, Robert E.

235

Hot circumstellar material resolved around ? Pic with VLTI/PIONIER  

NASA Astrophysics Data System (ADS)

Aims: We aim at resolving the circumstellar environment around ? Pic in the near-infrared in order to study the inner planetary system (<200 mas, i.e., ~4 AU). Methods: Precise interferometric fringe visibility measurements were obtained over seven spectral channels dispersed across the H band with the four-telescope VLTI/PIONIER interferometer. Thorough analysis of interferometric data was performed to measure the stellar angular diameter and to search for circumstellar material. Results: We detected near-infrared circumstellar emission around ? Pic that accounts for 1.37% ± 0.16% of the near-infrared stellar flux and that is located within the field-of-view of PIONIER (i.e., ~200 mas in radius). The flux ratio between this excess and the photosphere emission is shown to be stable over a period of 1 year and to vary only weakly across the H band, suggesting that the source is either very hot (?1500 K) or dominated by the scattering of the stellar flux. In addition, we derive the limb-darkened angular diameter of ? Pic with an unprecedented accuracy (?LD= 0.736 ± 0.019 mas). Conclusions: The presence of a small H-band excess originating in the vicinity of ? Pic is revealed for the first time thanks to the high-precision visibilities enabled by VLTI/PIONIER. This excess emission is likely due to the scattering of stellar light by circumstellar dust and/or the thermal emission from a yet unknown population of hot dust, although hot gas emitting in the continuum cannot be firmly excluded. Based on data collected at the ESO Paranal Observatory under commissioning time and programme 088.C-0266.

Defrère, D.; Lebreton, J.; Le Bouquin, J.-B.; Lagrange, A.-M.; Absil, O.; Augereau, J.-C.; Berger, J.-P.; di Folco, E.; Ertel, S.; Kluska, J.; Montagnier, G.; Millan-Gabet, R.; Traub, W.; Zins, G.

2012-10-01

236

Thermodynamics and Planetary Habitability  

NASA Astrophysics Data System (ADS)

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.

Kleidon, A.

2007-08-01

237

Folklore and food habits.  

PubMed

The folklore surrounding food habits developed from uncertainty and fear in mankind's quest for food. In an attempt to gain control of his destiny, man developed various magical practices which would perhaps assure an abundance of food. The practice and beliefs did not develop haphazardly, but, on examination, reveal a type of "folk logic" explained by Sir James Frazer's concepts of contagious and homeopathic magic. The "logic" was extended to specific practices in preparing foods, eating of foods on special days, the use of food in curing certain diseases, and forbidding foods at certain times. The folk were attempting to coordinate the phenomena of their world according to cause and effect much the same as modern Americans coordinate their world. However, the basic assuptions were different. PMID:1254878

Shifflett, P A

1976-04-01

238

Building Neural Representations of Habits  

Microsoft Academic Search

Memories for habits and skills (òimplicit or procedural memoryó) and memories for facts (òexplicit or episodic memoryó) are built up in different brain systems and are vulnerable to different neurodegenerative disorders in humans. So that the striatum-based mechanisms underlying habit formation could be studied, chronic recordings from ensembles of striatal neurons were made with multiple tetrodes as rats learned a

M. S. Jog; Y. Kubota; C. I. Connolly; V. Hillegaart; A. M. Graybiel

1999-01-01

239

Learning How to Change Habits  

MedlinePLUS

A lot of your diabetes care is up to you. You may have already changed some habits to take better care of yourself. Perhaps you exercise ... goals. Changing Habits: Getting Started Think about your diabetes care. Then fill in your answers. What’s my goal? ______________________ ______________________ ...

240

An Analysis of Metallic High Ion Absorption Line Profiles at DA White Dwarfs with Circumstellar Material  

NASA Astrophysics Data System (ADS)

Some hot DA stars exhibit circumstellar absorption in the metal resonance lines in their spectra. In many cases, these circumstellar features are unresolved from those originating in the photosphere. To better understand the effect this circumstellar blending has on photospheric abundance estimates, we present here an analysis of the unresolved metal high ion absorption features of six hot white dwarfs. In all cases, given the strong circumstellar C IV detections, the photospheric C IV abundances are reduced; conversely the weak circumstellar Si IV leads to modest photospheric abundance revisions. A possible new technique for modeling these line profiles is discussed, that can better reproduce the observations and provide a greater insight into the conditions of the circumstellar medium.

Dickinson, N. J.; Barstow, M. A.; Welsh, B. Y.

2013-01-01

241

Infrared interferometry and spectroscopy of circumstellar envelopes  

NASA Astrophysics Data System (ADS)

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.

Monnier, John David

242

Bowel Habits After Bariatric Surgery  

Microsoft Academic Search

Background  Disordered bowel habits might influence quality of life after bariatric surgery. Different types of bariatric operations—gastric\\u000a banding (AGB), Roux-en-Y gastric bypass (RYGB), or biliopancreatic diversion (BPD)—might alter bowel habits as a consequence\\u000a of the surgical procedure used. Whether change in bowel habits affects quality of life after AGB, RYGB, or BPD differently\\u000a is unknown.\\u000a \\u000a \\u000a \\u000a Methods  The study group contained 290 severely

Natascha Potoczna; Susanne Harfmann; Rudolf Steffen; Ruth Briggs; Norman Bieri; Fritz F. Horber

2008-01-01

243

Habitability of the Phoenix landing site  

NASA Astrophysics Data System (ADS)

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.

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

244

Formation of Small Iron Clusters in Circumstellar Envelopes  

NASA Astrophysics Data System (ADS)

We have investigated the role of small iron clusters as possible seeds for the formation of dust particles in circumstellar envelopes. Using cluster data available in the literature we constructed a simple cluster model in order to calculate the partition function and the Gibbs energy of formation for FeN clusters (N ? 19). Based on these data we have calculated the equilibrium densities of such clusters under different physical conditions. The results are discussed with respect to the problem of the primary dust condensate in M-type stars.

John, M.; Sedlmayr, E.

1997-07-01

245

Constraining the Physical Parameters of the Circumstellar Disk of ? Ophiuchi  

NASA Astrophysics Data System (ADS)

We present a numerical model describing a circularly symmetric gaseous disk around the Be star ? Ophiuchi. The model is constrained by long-baseline interferometric observations that are sensitive to the H? Balmer line emission from the disk. For the first time, our interferometric observations spatially resolve the inner region of the circumstellar disk around ? Oph, and we use these results to place a constraint on the physical extent of the H?-emitting region. We demonstrate how this in turn results in very specific constraints on the parameters that describe the variation of the gas density as a function of radial distance from the central star.

Tycner, C.; Jones, C. E.; Sigut, T. A. A.; Schmitt, H. R.; Benson, J. A.; Hutter, D. J.; Zavala, R. T.

2008-12-01

246

The discrete nature of circumstellar OH maser emission  

SciTech Connect

The Arecibo radio telescope was used to obtain high-resolution, high-SNR 1612-MHz observations of seven circumstellar OH maser sources. Each spectrum displays the double-peaked emission line profile characteristics of an expanding shell. The jaggedness of the spectra, which varies from source to source, is consistent with statistical fluctuations in the number of discrete emitting elements contributing at a given velocity. In particular, it is found that the spectra of WX Psc and OH 53.6-0.2 contain narrow, weak, isolated emission features which may arise from individual emitting elements. 14 refs.

Zell, P.J.; Fix, J.D. (Iowa Univ., Iowa City (USA))

1990-01-01

247

Managing away bad habits.  

PubMed

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

Waldroop, J; Butler, T

248

Gas phase chemical kinetics at high temperature of carbonaceous molecules: application to circumstellar envelopes  

Microsoft Academic Search

Circumstellar shells of evolved stars are a theater of extremely rich physical and chemical processes. More than seventy molecules of varied nature have been identified in the envelopes through their spectral fingerprints in the microwave or far infrared regions. Many of them are carbon chain molecules and radicals and a significant number are unique to the circumstellar medium. However, observational

L. Biennier; A. Gardez; G. Saidani; R. Georges; B. Rowe; K. P. J. Reddy

2011-01-01

249

Can habitable planets form in clustered environments?  

NASA Astrophysics Data System (ADS)

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 ? ? 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

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

2012-10-01

250

A photospheric metal line profile analysis of hot DA white dwarfs with circumstellar material  

NASA Astrophysics Data System (ADS)

Some hot DA white dwarfs have circumstellar high ion absorption features in their spectra, in addition to those originating in the photosphere. In many cases, the line profiles of these absorbing components are unresolved. Given the importance of the atmospheric composition of white dwarfs to studies of stellar evolution, extra-solar planetary systems and the interstellar medium, we examine the effect of including circumstellar line profiles in the abundance estimates of photospheric metals in six DA stars. The photospheric C and Si abundances are reduced in five cases where the circumstellar contamination is strong, though the relative weakness of the circumstellar Si iv absorption introduces minimal contamination, resulting in a small change in abundance. The inability of previous, approximate models to reproduce the photospheric line profiles here demonstrates the need for a technique that accounts for the physical line profiles of both the circumstellar and photospheric lines when modelling these blended absorption features.

Dickinson, N. J.; Barstow, M. A.; Welsh, B. Y.

2013-01-01

251

Habitable Planets in Compact Close-in Planetary Systems  

Microsoft Academic Search

We investigate the dynamical stability of planetary systems in the CoRoT discovery space. The aim was to check whether they are stable within the habitable zone around M main-sequence stars. We place the first fictitious planet at a distance of 0.01 AU from its host-star and fill-up the CoRoT discovery space with planets so that they are tightly packed according

R. Schwarz; E. Pilat-Lohinger; B. Funk; G. Wuchterl

2010-01-01

252

NASA's Kepler Mission: A Search for Habitable Planets  

NASA Astrophysics Data System (ADS)

The Kepler Mission, launched in March of this year, is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earthsize and smaller planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets. Results from this mission will allow us to place our solar system within the continuum of planetary systems in the Galaxy.

Dupree, Andrea

2009-10-01

253

An energetic stellar outburst accompanied by circumstellar light echoes  

NASA Astrophysics Data System (ADS)

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 ~104. 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 >6kpc, 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.

Bond, Howard E.; Henden, Arne; Levay, Zoltan G.; Panagia, Nino; Sparks, William B.; Starrfield, Sumner; Wagner, R. Mark; Corradi, R. L. M.; Munari, U.

2003-03-01

254

The Progenitor of SN 2011ja: Clues from Circumstellar Interaction  

NASA Astrophysics Data System (ADS)

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.

Chakraborti, Sayan; Ray, Alak; Smith, Randall; Ryder, Stuart; Yadav, Naveen; Sutaria, Firoza; Dwarkadas, Vikram V.; Chandra, Poonam; Pooley, David; Roy, Rupak

2013-09-01

255

Methods for the Development of Shipboard Habitability Design Criteria. Bibliography on Habitability with Abstracts.  

National Technical Information Service (NTIS)

The bibliography on habitability was developed as part of a research project on 'Methods for the Development of Shipboard Habitability Design Criteria.' The bibliography attempts to surveys the methodology and results of habitability research with a parti...

S. Hassid C. McArt H. Blasdel

1973-01-01

256

SN 2007od: A TYPE IIP SUPERNOVA WITH CIRCUMSTELLAR INTERACTION  

SciTech Connect

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.

Andrews, J. E.; Gallagher, J. S.; Clayton, Geoffrey C.; Chatelain, J. P.; Clem, J., E-mail: jandrews@phys.lsu.ed, E-mail: jgallagher@phys.lsu.ed, E-mail: gclayton@fenway.phys.lsu.ed, E-mail: jchate6@tigers.lsu.ed, E-mail: jclem@phys.lsu.ed [Department of Physics and Astronomy, Louisiana State University, 202 Nicholson Hall, Baton Rouge, LA 70803 (United States)

2010-05-20

257

Flash Heating of Circumstellar Clouds by Gamma-Ray Bursts.  

PubMed

The blast-wave model for gamma-ray bursts (GRBs) has been called into question by observations of spectra from GRBs that are harder than can be produced through optically thin synchrotron emission. If GRBs originate from the collapse of massive stars, then circumstellar clouds near burst sources will be illuminated by intense gamma radiation, and the electrons in these clouds will be rapidly scattered to energies as large as several hundred keV. Low-energy photons that subsequently pass through the hot plasma will be scattered to higher energies, hardening the intrinsic spectrum. This effect resolves the "line-of-death" objection to the synchrotron shock model. Illuminated clouds near GRBs will form relativistic plasmas containing large numbers of electron-positron pairs that can be detected within approximately 1-2 days of the explosion before expanding and dissipating. Localized regions of pair annihilation radiation in the Galaxy would reveal past GRB explosions. PMID:10813671

Dermer; Böttcher

2000-05-10

258

Ethylene In The Circumstellar Envelope Of IRC+10216  

NASA Astrophysics Data System (ADS)

Mid-infrared lines of ethylene (C2H4) were detected in the 1980's in the circumstellar shell of the dust obscured AGB star IRC+10216 using a novel heterodyne technique. Due to the symmetry of the molecule ethylene does not have a permanent dipole moment and there are no strong microwave rotational transitions. Ethylene is best detected through the ?7 out-of-plane bending mode at 10.5 ?m. To confirm the previous ethylene detections and to settle outstanding questions about the ethylene excitation temperature and radial abundance we re-observed the 10.5 ?m ?7 band. Observations were made with the cryogenic grating spectrograph TEXES and the IRTF. The observed spectra of the 10.4 - 10.8 ?m region reveal a selection of ethylene, ammonia, and silane lines. We report on an analysis of the ethylene spectrum.

Hinkle, Kenneth H.; Wallace, L.; Richter, M. J.

2007-12-01

259

Dense circumstellar nebulae in wide binary central stars  

NASA Astrophysics Data System (ADS)

Detection of close binary central stars with periods of less than a day is now well-tested and routinely possible via photometric monitoring. For wide binary central stars with periods of weeks to years detection techniques are still in their infancy. Radial velocity monitoring programs are yet to be applied to very large samples and the method suffers from large systematic errors as well as intrinsic wind variability. One alternative we are exploring is the detection of dense circumstellar nebulae residing around a wide companion. The archetype of this class is EGB6 as revealed by HST imaging (Bond 2009). Here we present spectroscopic evidence for other EGB6-like central stars and discuss their relationship to symbiotic stars. A probable 12.5-day irradiated binary is also presented to demonstrate the limits of the photometric monitoring technique.

Miszalski, B.; Acker, A.; Parker, Q. A.; Boffin, H. M. J.; Frew, D. J.; Mikolajewska, J.; Moffat, A. F. J.; Napiwotzki, R.

260

TIDALLY INDUCED BROWN DWARF AND PLANET FORMATION IN CIRCUMSTELLAR DISKS  

SciTech Connect

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.

Thies, Ingo; Kroupa, Pavel [Argelander-Institut fuer Astronomie (Sternwarte), Universitaet Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany); Goodwin, Simon P. [Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH (United Kingdom); Stamatellos, Dimitrios; Whitworth, Anthony P. [School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA (United Kingdom)

2010-07-01

261

Generic Habit-Training Program  

Microsoft Academic Search

For years parents and other care providers have been bringing children with autistic characteristics to the toilet, sitting them down hour after hour, only to find that nothing is accomplished. The following outlines one method of habit training, known are the “challenge” method because the parent or care provider picks one optimum time and challenges the child to urinate in

Mike Wilson

1995-01-01

262

Evolution of a habitable planet  

Microsoft Academic Search

Earth has remained habitable, and inhabited, over most of its 4.5-Gyr history despite an appreciable (30%) increase in solar luminosity over time and despite catastrophic events such as asteroid impacts and ``Snowball Earth'' episodes that have threatened biological survival on a global scale. Life has survived partly because of the resilience of the biota and partly because of feedback mechanisms

James Kasting

2006-01-01

263

Metacognition, Study Habits and Attitudes  

ERIC Educational Resources Information Center

|This study is conducted to investigate the relationship between fifth grade students' metacognition levels, and their study habits and attitudes. Participants of the study consist of 221 students, 125 female and 96 male, enrolling to six public primary schools in Turkey. The results revealed that there is a medium positive relationship between…

Ozsoy, Gokhan; Memis, Aysel; Temur, Turan

2009-01-01

264

Habits of the Toad, Ceratophrys  

Microsoft Academic Search

A MISHAP which throws additional light on the voracious habits of the South American toad Ceratophrys deserves to be put on record. Four of these creatures were received here at the end of June and at the same time two small alligators. When they came, only one vivarium was ready for use, and for a week the toads and alligators

C. W. Parsons

1932-01-01

265

Rotation rate evolution in habitable super-Earths  

NASA Astrophysics Data System (ADS)

Abstract (2,250 Maximum Characters): The search for habitable planets in our neighborwood is one of the most exiting challenges for planetary sciences at present. The recent discovery of Earth-like planets inside the habitable zone of their host stars is an incentive to try to understand how the physical conditions for habitability evolve in these kind of objects. Super Earths, already discovered, GJ581d and GJ667Cc, are possibly habitable because they are located in a close-in orbit (0.22 AU and 0.125 AU respectively), arround low mass stars. The gravitational interaction between the planets and its host stars produce tides that modify their orbits and their rotation periods. We consider the evolution of the tidal torque and the rotation rate as dependent of the rheological properties of the planet's mantle. Several experiments are performed to study the rotation evolution, depending on the the parameters of the rheological model as well as initial conditions. The main interest goal of our investigation is to understand the spin-orbit evolution produced by the gravitational tides between the host star and a close planet and the impact of the rotation rate variation in the thermal and magnetic evolution of the planet.

Melita, Mario; Cuartas Restrepo, P.; Zuluaga, J.; Miloni, O.

2013-05-01

266

Space Station Group Activities Habitability Module Study.  

National Technical Information Service (NTIS)

This study explores and analyzes architectural design approaches for the interior of the Space Station Habitability Module (originally defined as Habitability Module 1 in Space Station Reference Configuration Decription, JSC-19989, August 1984). In the Re...

D. Nixon

1986-01-01

267

Exomoon habitability constrained by energy flux and orbital stability  

NASA Astrophysics Data System (ADS)

Context. Detecting massive satellites that orbit extrasolar planets has now become feasible, which led naturally to questions about the habitability of exomoons. In a previous study we presented constraints on the habitability of moons from stellar and planetary illumination as well as from tidal heating. Aims: Here I refine our model by including the effect of eclipses on the orbit-averaged illumination. I then apply an analytic approximation for the Hill stability of a satellite to identify the range of stellar and planetary masses in which moons can be habitable. Moons in low-mass stellar systems must orbit their planet very closely to remain bounded, which puts them at risk of strong tidal heating. Methods: I first describe the effect of eclipses on the stellar illumination of satellites. Then I calculate the orbit-averaged energy flux, which includes illumination from the planet and tidal heating to parametrize exomoon habitability as a function of stellar mass, planetary mass, and planet-moon orbital eccentricity. The habitability limit is defined by a scaling relation at which a moon loses its water by the runaway greenhouse process. As a working hypothesis, orbital stability is assumed if the moon's orbital period is less than 1/9 of the planet's orbital period. Results: Due to eclipses, a satellite in a close orbit can experience a reduction in orbit-averaged stellar flux by up to about 6%. The smaller the semi-major axis and the lower the inclination of the moon's orbit, the stronger the reduction. I find a lower mass limit of ? 0.2 M? for exomoon host stars that allows a moon to receive an orbit-averaged stellar flux comparable to the Earth's, with which it can also avoid the runaway greenhouse effect. Precise estimates depend on the satellite's orbital eccentricity. Deleterious effects on exomoon habitability may occur up to ? 0.5 M? if the satellite's eccentricity is ? 0.05. Conclusions: Although the traditional habitable zone lies close to low-mass stars, which allows for many transits of planet-moon binaries within a given observation cycle, resources should not be spent to trace habitable satellites around them. Gravitational perturbations by the close star, another planet, or another satellite induce eccentricities that likely make any moon uninhabitable. Estimates for individual systems require dynamical simulations that include perturbations among all bodies and tidal heating in the satellite.

Heller, R.

2012-09-01

268

Habitability of enceladus: planetary conditions for life.  

PubMed

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

Parkinson, Christopher D; Liang, Mao-Chang; Yung, Yuk L; Kirschivnk, Joseph L

2008-06-20

269

TW HYA Association Membership and New WISE-detected Circumstellar Disks  

NASA Astrophysics Data System (ADS)

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 ?m providing clear evidence for substantial dusty circumstellar disks around these low-mass, ~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 ?m excess fraction of 42+10 - 9% based on our results.

Schneider, Adam; Melis, Carl; Song, Inseok

2012-07-01

270

Online Consumer Retention: Development of New Habits  

Microsoft Academic Search

Prior research on online behaviour continuance modeled satisfaction and perceived usefulness as the only determinants of continued adoption, overlooking the important role of habit. We therefore extend the previous models to include online shopping habit as a moderator of the relationship between online shopping satisfaction and online repurchase intention. Most prior studies conceptualized habit as experience, providing little evidence on

Mohamed Khalifa; Vanessa Liu

2005-01-01

271

Experiences of habit formation: A qualitative study  

Microsoft Academic Search

Habit formation is an important goal for behaviour change interventions because habitual behaviours are elicited automatically and are therefore likely to be maintained. This study documented experiences of habit development in 10 participants enrolled on a weight loss intervention explicitly based on habit-formation principles. Thematic analysis revealed three themes: Strategies used to support initial engagement in a novel behaviour; development

Phillippa Lally; Jane Wardle; Benjamin Gardner

2011-01-01

272

Recovery Under the Implied Warranty of Habitability  

Microsoft Academic Search

The New York State legislature codified the implied warranty of habitability for residential leases in Real Property Law section 235-b, but failed to specify remedies for breach. This Note examines the development of the implied warranty of habitability as a basis for expanding a landlord's liability for failure to provide habitable premises and discusses problems relating to recovery for breach

Francis S. LAbbate

1982-01-01

273

University Students' Media Habits: A Lithuanian Study.  

ERIC Educational Resources Information Center

|A study replicated a 1994 study, "College Students' Media Habits: A National Study." In the present study, Lithuanian university students' media habits relative to American students' media habits were gauged. A total of 1500 survey questionnaires were distributed to 7 of the 16 Lithuanian universities. Background biographical questions were…

Kamalipour, Yahya R.; And Others

274

Radiation-hydrodynamic Models of the Evolving Circumstellar Medium around Massive Stars  

NASA Astrophysics Data System (ADS)

We present the results of time-dependent, radiation-hydrodynamic models of the evolving circumstellar medium around stars with initial masses of 40 and 60 Msun. Our models show the difference that the assumption of a rotating star can make to the resulting circumstellar medium, which is principally due to the difference in length of the intense mass-loss stages. We model the formation of structure due to instabilities in the cold shell-fast wind interaction region.

Toalá, J. A.; Arthur, S. J.

2010-06-01

275

Circumstellar Disk Systems in the LMC, SMC, and Milky Way Galaxy  

Microsoft Academic Search

Classical Be stars are rapidly rotating near main-sequence B-type stars which have gaseous circumstellar disks. Our understanding of these stars is incomplete, especially as regards two fundamental questions: 1) Is the Be phenomenon an evolutionary effect? and 2) What role does metallicity play in the formation of Be circumstellar disks? Initial attempts to address these questions have used 2-color diagram

J. P. Wisniewski; K. S. Bjorkman; A. M. Magalhães; J. E. Bjorkman; A. C. Carciofi

2005-01-01

276

Discovery of a Circumstellar Disk in the Lagoon Nebula  

NASA Astrophysics Data System (ADS)

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 obtai

1997-04-01

277

Dynamical Stability and Habitability of Extra-Solar Planets  

NASA Astrophysics Data System (ADS)

Observations of about 60 binary star systems hosting exoplanets indicate the necessity of stability studies of planetary motion in such multi-stellar systems. For wide binary systems with separations between hundreds and thousands of AU, the results from single-star systems may be applicable but, in tight double stars systems, we have to take the stellar interactions into account which influences the planetary motion significantly. This review discusses the different types of planetary motion in double stars and the stability of the planets for different binary configurations. An application to the most famous tight binary system (? Cephei) is also shown. Finally, we analyze the habitability from the dynamical point of view in such systems, where we discuss the motion of terrestrial-like planets in the so-called habitable zone.

Pilat-Lohinger, Elke

2012-04-01

278

Insensitivity of weathering behavior to planetary land fraction and effect on habitability  

NASA Astrophysics Data System (ADS)

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.

Abbot, D. S.; Archer, D.; Pierrehumbert, R. T.; Ciesla, F. J.; Bean, J. L.

2012-04-01

279

The Effect of Ultraviolet Radiation on Planetary Habitability  

NASA Astrophysics Data System (ADS)

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.

Kasting, J. F.; Whittet, D. C. B.; Sheldon, W. R.

1996-03-01

280

Reading habits influence aesthetic preference  

Microsoft Academic Search

The aim of the present study was to determine the extent to which aesthetic preference, previously attributed to cerebral dominance, may be determined by reading habits. One hundred and sixty two normal subjects were presented pairs of images, one being the mirror-image of the other, and were asked for their aesthetic preference. Half of the subjects were left-to-right readers (French

Sylvie Chokron; Maria De Agostini

2000-01-01

281

Zoning Study.  

National Technical Information Service (NTIS)

The study analyzes existing zoned properties in the Shreveport Standard Metropolitan Statistical Area to determine if current development justifies the amount of such zoning. It reviews administrative procedures and policies used in carrying out zoning ch...

1968-01-01

282

Herschel/HIFI deepens the circumstellar NH3 enigma  

NASA Astrophysics Data System (ADS)

Context. Circumstellar envelopes (CSEs) of a variety of evolved stars have been found to contain ammonia (NH3) in amounts that exceed predictions from conventional chemical models by many orders of magnitude. Aims: The observations reported here were performed in order to better constrain the NH3 abundance in the CSEs of four, quite diverse, oxygen-rich stars using the NH3 ortho JK = 10-00 ground-state line. Methods: We used the Heterodyne Instrument for the Far Infrared aboard Herschel to observe the NH3 JK = 10-00 transition near 572.5 GHz, simultaneously with the ortho-H2O JKa , Kc = 11,0 - 10,1 transition, toward VY CMa, OH 26.5+0.6, IRC+10420, and IK Tau. We conducted non-LTE radiative transfer modeling with the goal to derive the NH3 abundance in these objects' CSEs. For the last two stars, Very Large Array imaging of NH3 radio-wavelength inversion lines were used to provide further constraints, particularly on the spatial extent of the NH3-emitting regions. Results: We find remarkably strong NH3 emission in all of our objects with the NH3 line intensities rivaling those of the ground state H2O line. The NH3 abundances relative to H2 are very high and range from 2×10-7 to 3×10-6 for the objects we have studied. Conclusions: Our observations confirm and even deepen the circumstellar NH3 enigma. While our radiative transfer modeling does not yield satisfactory fits to the observed line profiles, it does lead to abundance estimates that confirm the very high values found in earlier studies. New ways to tackle this mystery will include further Herschel observations of more NH3 lines and imaging with the Expanded Very Large Array. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendix A (page 5) is only available in electronic form at http://www.aanda.org

Menten, K. M.; Wyrowski, F.; Alcolea, J.; De Beck, E.; Decin, L.; Marston, A. P.; Bujarrabal, V.; Cernicharo, J.; Dominik, C.; Justtanont, K.; de Koter, A.; Melnick, G.; Neufeld, D. A.; Olofsson, H.; Planesas, P.; Schmidt, M.; Schöier, F. L.; Szczerba, R.; Teyssier, D.; Waters, L. B. F. M.; Edwards, K.; Olberg, M.; Phillips, T. G.; Morris, P.; Salez, M.; Caux, E.

2010-10-01

283

Unveiling the circumstellar environment toward a massive young stellar object  

NASA Astrophysics Data System (ADS)

Aims: As a continuation of a previous work, in which we found strong evidence of massive molecular outflows toward a massive star-forming site, we present a new study of this region based on very high angular resolution observations with the aim of discovering the outflow-driven mechanism. Methods: Using near-IR data acquired with Gemini-NIRI at the broad H- and Ks-bands, we studied a region of 22'' × 22'' around the UCHii region G045.47+0.05, a massive-star forming site at a distance of about 8 kpc. To image the source with the highest spatial resolution possible we employed the adaptative optics system ALTAIR, achieving an angular resolution of about 0.15 arcsec. Results: We discovered a cone shaped nebula that has an opening angle of about 90° and extends eastward of the IR source 2MASS J19142564+1109283, which is very likely a massive young stellar object (MYSO). This morphology suggests a cavity that was cleared in the circumstellar material, and its emission may arise from scattered continuum light, warm dust, and probably also from emission lines from shock-excited gas. The nebula, which presents arc-like features, is connected with the IR source through a jet-like structure, which is aligned with the blueshifted CO outflow found in a previous study. The near-IR structure lies ~3'' north of the radio continuum emission, revealing that it is not spatially coincident with the UCHii region. The observed morphology and structure of the near-IR nebula strongly suggest the presence of a precessing jet. We resolved the circumstellar environment (in scale of a thousand AU) of a distant MYSO, indeed one of the farthest currently known. Reduced NIR data (FITS) 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/559/L2

Paron, S.; Fariña, C.; Ortega, M. E.

2013-11-01

284

Habitability potential of icy moons  

NASA Astrophysics Data System (ADS)

The satellites of Jupiter and Saturn have been revealed as extremely astrobiologically interesting bodies presenting promising conditions for habitability and the development and/or maintenance of life. Titan and Enceladus, Saturn's satellites, were found by the Cassini-Huygens mission to possess active organic chemistries with seasonal variations, unique geological features and possibly internal liquid water oceans, among other. Additionally, Jupiter's Europa and Ganymede show indications of harboring liquid water oceans under their icy crusts, which may be in direct contact with a silicate mantle floor and kept warm through time by tidally generated heat. All of these environments satisfy many of the "classical" criteria for habitability (liquid water, energy sources to sustain metabolism and "nutrients" over a period of time long enough to allow the development of life). In order to study the habitability of icy moons around giant planets, we look at the atmosphere-surface-interior connections with their similarities with the Earth as a starting point [1]. The discovery of the water jets on Enceladus, the possibility for cryovolcanic processes on Titan and the hypothetically active mantle of Europa suggest that icy moons around giant planets may well contain subsurface oceans.

Coustenis, A.; Solomonidou, A.; Bampasidis, G.; Hirtzig, M.; Sohl, F.; Hussmann, H.; Kyriakopoulos, K.; Seymour, K.; Bratsolis, E.; Moussas, X.

2012-09-01

285

Widen the belt of habitability!  

PubMed

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

Möhlmann, D

2012-05-26

286

The Solar Neighborhood XXIX: The Habitable Real Estate of Our Nearest Stellar Neighbors  

NASA Astrophysics Data System (ADS)

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.

Cantrell, Justin R.; Henry, Todd J.; White, Russel J.

2013-10-01

287

Plasticity of Feeding Habits of Two Plectroglyphidodon Damselfishes on Coral Reefs in Southern Taiwan: Evidence from Stomach Content and Stable Isotope Analyses  

Microsoft Academic Search

damsel, Plectroglyphidodon dickii Lienard 1983, has increased more markedly than the sympatric congener, P. johnstonianus Fowler and Ball 1924. To study whether the distribution patterns of the 2 Plectroglyphidodon damselfishes were underlain by food availability and feeding habit plasticity, the reef area in the embayment was divided into 2 different zones, zone A dominated by Acropora corals and zone B

Cheng-Tze Ho; Yi-Cheng Fu; Chi-Lu Sun; Shuh-Ji Kao; Rong-Quen Jan

2009-01-01

288

High-Resolution Imaging and Modeling of Circumstellar Debris: Architectures of Planetary Systems  

NASA Astrophysics Data System (ADS)

Circumstellar debris disks consist of dust freshly generated by the attrition and evaporation of primitive asteroids and comets. They are analogs to our Kuiper Belt and therefore inform the the architecture of trans-Neptunian space around other stars. We wish to study the diversity of these planetary systems around stars of different masses. I present high-resolution observations of debris disks, both imaging of their scattered light with adaptive optics coronagraphy, and of thermal emission in the mid-IR. AU Microscopii is a nearby M dwarf with such a disk. Coronagraphic Keck Adaptive Optics images processed with my speckle-suppression algorithm show a blue color, from optical to the near-IR, with a blue color gradient in the disk beyond 35 AU. I discuss a Monte Carlo radiative transfer code to simultaneously model the scattered light colors and SED. I compare a multi-zoned model of the grain size and space distributions to the physical model of Strubbe & Chiang (2006). In this scenario, a ring of parent bodies at 40 AU produces dust which diffuses into an outer extended disk due to stellar wind and radiation pressure. Comparison of the scattered light modeling to measurements of the disk in polarized light indicates the dust grains must be porous. I also present the first mid-IR images of warm dust grains around the Beta Pic analog HD 32297 (A0V). The structure of the thermal emission indicates an optically thin ring of grains at 65 AU. A ring of parent bodies at this location may be responsible for the production of small, warm grains. I also present high-resolution near-IR Keck imaging of the scattered light disk, which is blue in color. Like in AU Mic, the outward diffusion of these small grains from the ring may be responsible for the disk's scattered light color.

Fitzgerald, Michael; Kalas, P.; Graham, J. R.; Duchêne, G.; Pinte, C.

2006-12-01

289

Simulations of the Atmospheres of Synchronously Rotating Terrestrial Planets Orbiting M Dwarfs: Conditions for Atmospheric Collapse and the Implications for Habitability  

Microsoft Academic Search

Planets within the habitable zones of M dwarfs are likely to be synchronous rotators; in other words, one side is permanently illuminated while the other side is in perpetual darkness. We present results of three-dimensional simulations of the atmospheres of such planets, and comment on their possible habitability. Near the ground, a thermally direct longitudinal cell exists, transporting heat from

M. M. Joshi; R. M. Haberle; R. T. Reynolds

1997-01-01

290

On the Chemistry of Circumstellar Disk Around MWC349A  

NASA Astrophysics Data System (ADS)

The evolutionary status of MWC 349A - the unique source of hydrogen maser and laser radiation arising in a massive circumstellar disk - is still a matter of debate. One way to shed light on this issue would be to measure the isotopic composition of the disk. We performed computer simulations of the chemical composition of the disk using the package CLOUDY (Ferland et al. 1998). The best agreement between the calculated hydrogen line strength ratios and those measured by Hamann and Simon (1986) was achieved for a model with a central (black body) star of T ? 20,000 K and a disk with the inner radius 1014 cm, hydrogen density at the inner radius 108 cm-3 and the r-2 drop of density with radius. We present the column densities predicted by CLOUDY for observed (CO) and several not yet observed molecules containing the major isotopes of C, N, O and discuss the prospects of detecting and measuring the radio lines of these molecules and their isotopologues with existing and forthcoming facilities. This project was supported by NSF/REU grant AST-0851892, the Presidential Award for Excellence in Science, Mathematics and Engineering Mentoring, and the Nantucket Maria Mitchell Association.

Lagergren, Kristen; Bans, A.; Strelnitski, V.

2012-01-01

291

High angular resolution millimeter observations of circumstellar disks  

NASA Astrophysics Data System (ADS)

In this lecture, we review the properties of protoplanetary disks as derived from high angular resolution observations at millimeter wavelengths. We discuss how the combination of several different high angular resolution techniques allow us to probe different regions of the disk around young stellar objects and to derive the properties of the dust when combined with sophisticated disk models. The picture that emerges is that the dust in circumstellar disks surrounding pre-main sequence stars is in many cases significantly evolved compared to the dust in molecular clouds and the interstellar medium. It is however still difficult to derive a consistent picture and timeline for dust evolution in disks as the observations are still limited to small samples of objects. We also review the evidence for and properties of disks around high-mass young stellar objects and the implications on their formation mechanisms. The study of massive YSOs is complicated by their short lifetimes and larger average distances. In most cases high angular resolution data at millimeter wavelengths are the only method to probe the structure of disks in these objects. We provide a summary of the characteristics of available high angular resolution millimeter and submillimeter observatories. We also describe the characteristics of the ALMA observatory being constructed in the Chilean Andes. ALMA is going to be the world leading observatory at millimeter wavelengths in the coming decades, the project is now in its main construction phase with early science activities envisaged for 2010 and full science operations for 2012.

Testi, Leonard; Leurini, Silvia

2008-06-01

292

Identity Crisis: True Composition of Circumstellar Dust Questioned  

NASA Astrophysics Data System (ADS)

Cosmic dust plays an important role in many astrophysical environments. A major source of cosmic dust is dying stars. Intermediate mass stars (0.8-8 solar masses) eventually evolve to become Asymptotic Giant Branch (AGB) stars which produce vast quantities of dust. During the AGB phase, the star expands and contracts releasing shells of gas that drift away from the star and eventually cool to condense dust. Using spectral observations from the Infrared Space Observatory (ISO), we have investigated the far-infrared spectral dust features (in the 15-40 micron range) from a broad range of AGB star spectra. Previously, it has been thought that these circumstellar dust shells are dominated by amorphous (glassy) silicates and that crystalline grains are rare. Furthermore, on those rare occasions that crystalline silicates occur, they are expected (and sometimes observed) to be Mg-rich. Using laboratory spectra of crystalline olivines and pyroxenes with a range of Mg/Fe, we show that the majority of the observed astronomical spectra are matched surprisingly well with crystalline silicates, especially with high iron content. This ground-breaking discovery contradicts the previously accepted dust composition. Fe-rich crystalline silicate dust compositions are inconsistent with current dust formation hypothesis and dust condensation sequences, and thus our research calls the current accepted wisdom into question.

Miller, Lucas; Speck, A.; Guha Niyogi, S.

2010-01-01

293

Identity Crisis: True Composition of Circumstellar Dust Questioned  

NASA Astrophysics Data System (ADS)

Cosmic dust plays an important role in many astrophysical environments. A major source of cosmic dust is dying stars. Intermediate mass stars (0.8-8 solar masses) eventually evolve to become Asymptotic Giant Branch (AGB) stars which produce vast quantities of dust. During the AGB phase, the star expands and contracts releasing shells of gas that drift away from the star and eventually cool to condense dust. Using spectral observations from the Infrared Space Observatory (ISO), we have investigated the far-infrared spectral dust features (in the 15-40 micron range) from a large sample of AGB star spectra. Previously, it has been thought that these circumstellar dust shells are dominated by amorphous (glassy) silicates and that crystalline grains are rare. Furthermore, on those rare occasions that crystalline silicates occur, they are expected (and usually observed) to be Mg-rich. Using laboratory spectra of crystalline olivines and pyroxenes with a range of Mg/Fe, we show that the majority of the observed astronomical spectra are matched surprisingly well with crystalline silicates, especially with high iron content. This discovery contradicts the previously accepted dust composition. Fe-rich crystalline silicate dust compositions are inconsistent with current dust formation hypothesis and dust condensation sequences, and thus our research calls the current accepted wisdom into question.

Miller, Lucas; Speck, A.; Guha Niyogi, S.

2011-01-01

294

Numerical models for the circumstellar medium around Betelgeuse  

NASA Astrophysics Data System (ADS)

The nearby red supergiant (RSG) Betelgeuse has a complex circumstellar medium out to at least 0.5 parsecs from its surface, shaped by its mass-loss history within the past ? 0.1 Myr, its environment, and its motion through the interstellar medium (ISM). In principle its mass-loss history can be constrained by comparing hydrodynamic models with observations. Observations and numerical simulations indicate that Betelgeuse has a very young bow shock, hence the star may have only recently become a RSG. To test this possibility we calculated a stellar evolution model for a single star with properties consistent with Betelgeuse. We incorporated the resulting evolving stellar wind into 2D hydrodynamic simulations to model a runaway blue supergiant (BSG) undergoing the transition to a RSG near the end of its life. The collapsing BSG wind bubble induces a bow shock-shaped inner shell which at least superficially resembles Betelgeuse's bow shock, and has a similar mass. Surrounding this is the larger-scale retreating bow shock generated by the now defunct BSG wind's interaction with the ISM. We investigate whether this outer shell could explain the bar feature located (at least in projection) just in front of Betelgeuse's bow shock.

Mackey, J.; Mohamed, S.; Neilson, H. R.; Langer, N.; Meyer, D. M.-A.

2013-05-01

295

Rapid disappearance of a warm, dusty circumstellar disk.  

PubMed

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

Melis, Carl; Zuckerman, B; Rhee, Joseph H; Song, Inseok; Murphy, Simon J; Bessell, Michael S

2012-07-04

296

Confirmation of Kcn in the Circumstellar Envelope of IRC+10216  

NASA Astrophysics Data System (ADS)

Over the past few years, there has been discussion about the presence of KCN in IRC+10216. To settle the issues on this matter, additional observations have been conducted for KCN and a definitive identification has been made. KCN is a T-shaped, closed shell asymmetric top. A total of ten rotational transitions have been searched for in the frequency range of 85-250 GHz using the Arizona Radio Observatory (ARO) 12m telescope on Kitt Peak and the Submillimeter Telescope (SMT) on Mt. Graham. Emission was detected at all transitions observed, with six blended features and four uncontaminated lines. Transitions for both the K_a=0 and K_a=1 levels were detected. Line intensities ranged from 0.6 mK to 2 mK. A few lines observed required integration times of 200 hours or more to achieve the necessary signal-to-noise ratio, demonstrating the stability of ALMA technology. KCN is the fifth metal cyanide/isocyanide identified in circumstellar gas, along with MgNC, MgCN, NaCN, and AlNC. Derived column densities and abundances will be reported and the significance of this detection will be discussed.

Pulliam, R. L.; Ziurys, L. M.; Savage, C.

2010-06-01

297

On circumstellar disks: Spitzer identifies two possible evolutionary paths  

NASA Astrophysics Data System (ADS)

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.

Teixeira, Paula S.; Lada, Charles J.; Marengo, Massimo; Lada, Elizabeth

298

ON THE EXCITATION AND FORMATION OF CIRCUMSTELLAR FULLERENES  

SciTech Connect

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.

Bernard-Salas, J.; Jones, A. P. [Institut d'Astrophysique Spatiale, CNRS/Universite Paris-Sud 11, F-91405 Orsay (France); Cami, J.; Peeters, E.; Micelotta, E. R. [Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 (Canada); Groenewegen, M. A. T., E-mail: jbernard@ias.u-psud.fr [Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussels (Belgium)

2012-09-20

299

The formation of Polycyclic Aromatic Hydrocarbons in evolved circumstellar environments  

NASA Astrophysics Data System (ADS)

The formation of Polycyclic Aromatic Hydrocarbons in the circumstellar outflows of evolved stars is reviewed, with an emphasis on carbon stars on the Asymptotic Giant Branch. Evidence for PAHs present in their winds is provided by meteoritic studies and recent observations of the Unidentified Infrared bands. We detail the chemical processes leading to the closure of the first aromatic ring as well as the growth mechanisms leading to amorphous carbon grains. Existing studies on PAH formation in evolved stellar envelopes are reviewed and new results for the modelling of the inner wind of the archetype carbon star IRC+10216 are presented. Benzene, C6H6, forms close to the star, as well as water, H2O, as a result of non-equilibrium chemistry induced by the periodic passage of shocks. The growth process of aromatic rings may thus resemble that active in sooting flames due to the presence of radicals like hydroxyl, OH. Finally, we discuss possible formation processes for PAHs and aromatic compounds in the hydrogen-rich R CrB star, V854 Cen, and their implication for the carriers of the Red Emission and the Diffuse Interstellar Bands.

Cherchneff, I.

2011-03-01

300

The IRC + 10216 circumstellar envelope. III - Infrared molecular line profiles  

NASA Astrophysics Data System (ADS)

The 10 micron spectrum (780-1240/cm) has been surveyed with a resolution of 0.009/cm. Numerous molecular vibration-rotation transitions were detected in absorption by the circumstellar shell. Analysis of the line profiles by means of spectral synthesis from models revealed radial abundance ratio variations in some species. SiO is approximately uniformly mixed through the inner shell. SiH4 and NH3 are apparently produced in the region 10 to 40 R(*), possibly by formation on grains. CS is very strongly depleted in the region 100-1000 R(*), perhaps onto grains. From nondetection of H2 the current mass-loss rate is constrained to be less than 4 x 10 exp -5 solar mass/yr. Gathering evidence for a recent decline in the mass-loss rate is strengthened by analysis of the low-excitation heterodyne NH3 line observation, which indicates that the mass-loss rate may have been 2-3 x larger 1000 yr ago.

Keady, J. J.; Ridgway, S. T.

1993-03-01

301

RESOLVING THE CIRCUMSTELLAR DISK OF HL TAURI AT MILLIMETER WAVELENGTHS  

SciTech Connect

We present results of high-resolution imaging toward HL Tau by the Combined Array for Research in Millimeter-wave Astronomy. We have obtained {lambda} = 1.3 mm and 2.7 mm dust continua with an angular resolution down to 0.''13. Through simultaneous model fitting to the two wavelength data sets in Bayesian inference using a flared viscous accretion disk model, we estimate the physical properties of HL Tau, such as density distribution, dust opacity spectral index, disk mass, disk size, inclination angle, position angle, and disk thickness. HL Tau has a circumstellar disk mass of 0.13 M{sub sun}, a characteristic radius of 79 AU, an inclination of 40{sup 0}, and a position angle of 136{sup 0}. Although a thin disk model is preferred by our two wavelength data sets, a thick disk model is needed to explain the high mid- and far-infrared emission of the HL Tau spectral energy distribution. This could imply large dust grains settled down on the midplane with fine dust grains mixed with gas. The HL Tau disk is likely gravitationally unstable and can be fragmented between 50 and 100 AU of radius. However, we did not detect dust thermal continuum supporting the protoplanet candidate claimed by a previous study using observations of the Very Large Array at {lambda} = 1.3 cm.

Kwon, Woojin; Looney, Leslie W. [Department of Astronomy, University of Illinois, Urbana, IL 61801 (United States); Mundy, Lee G., E-mail: wkwon@illinois.edu [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)

2011-11-01

302

Size distribution of circumstellar disks in the Trapezium cluster  

NASA Astrophysics Data System (ADS)

In this paper we present results on the size distribution of circumstellar disks in the Trapezium cluster as measured from HST/WFPC2 data. Direct diameter measurements of a sample of 135 bright proplyds and 14 silhouettes disks suggest that there is a single population of disks well characterized by a power-law distribution with an exponent of -1.9 ± 0.3 between disk diameters 100-400 AU. For the stellar mass sampled (from late G to late M stars) we find no obvious correlation between disk diameter and stellar mass. We also find that there is no obvious correlation between disk diameter and the projected distance to the ionizing Trapezium OB stars. We estimate that about 40% of the disks in the Trapezium have radius larger than 50 AU. We suggest that the origin of the Solar system's (Kuiper belt) outer edge is likely to be due to the star formation environment and disk destruction processes (photoevaporation, collisions) present in the stellar cluster on which the Sun was probably formed. Finally, we identified a previously unknown proplyd and named it 266-557, following convention.

Vicente, S. M.; Alves, J.

2005-10-01

303

Planning to break unwanted habits: habit strength moderates implementation intention effects on behaviour change.  

PubMed

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

Webb, Thomas L; Sheeran, Paschal; Luszczynska, Aleksandra

2008-10-11

304

Is There Anything About the Sun that Makes the Habitable Zone of Our Solar System More Habitable than the Habitable Zones Around Other Stars?  

Microsoft Academic Search

We compare the Sun to other stars and find that with respect to the eleven properties that we examined, the Sun is consistent with being a typical, random star with no anomalous feature that would make it more conducive for life.

J. A. Robles; C. H. Lineweaver; D. Grether; C. Flynn; C. A. Egan; M. B. Pracy; J. Holmberg; E. Gardner

2010-01-01

305

Effects of M dwarf magnetic fields on potentially habitable planets  

NASA Astrophysics Data System (ADS)

We investigate the effect of the magnetic fields of M dwarf (dM) stars on potentially habitable Earth-like planets. These fields can reduce the size of planetary magnetospheres to such an extent that a significant fraction of the planet's atmosphere may be exposed to erosion by the stellar wind. We used a sample of 15 active dM stars, for which surface magnetic-field maps were reconstructed, to determine the magnetic pressure at the planet orbit and hence the largest size of its magnetosphere, which would only be decreased by considering the stellar wind. Our method provides a fast means to assess which planets are most affected by the stellar magnetic field, which can be used as a first study to be followed by more sophisticated models. We show that hypothetical Earth-like planets with similar terrestrial magnetisation (~1 G) orbiting at the inner (outer) edge of the habitable zone of these stars would present magnetospheres that extend at most up to 6 (11.7) planetary radii. To be able to sustain an Earth-sized magnetosphere, with the exception of only a few cases, the terrestrial planet would either (1) need to orbit significantly farther out than the traditional limits of the habitable zone; or else, (2) if it were orbiting within the habitable zone, it would require at least a magnetic field ranging from a few G to up to a few thousand G. By assuming a magnetospheric size that is more appropriate for the young-Earth (3.4 Gyr ago), the required planetary magnetic fields are one order of magnitude weaker. However, in this case, the polar-cap area of the planet, which is unprotected from transport of particles to/from interplanetary space, is twice as large. At present, we do not know how small the smallest area of the planetary surface is that could be exposed and would still not affect the potential for formation and development of life in a planet. As the star becomes older and, therefore, its rotation rate and magnetic field reduce, the interplanetary magnetic pressure decreases and the magnetosphere of planets probably expands. Using an empirically derived rotation-activity/magnetism relation, we provide an analytical expression for estimating the shortest stellar rotation period for which an Earth-analogue in the habitable zone could sustain an Earth-sized magnetosphere. We find that the required rotation rate of the early- and mid-dM stars (with periods ?37-202 days) is slower than the solar one, and even slower for the late-dM stars (?63-263 days). Planets orbiting in the habitable zone of dM stars that rotate faster than this have smaller magnetospheric sizes than that of the Earth magnetosphere. Because many late-dM stars are fast rotators, conditions for terrestrial planets to harbour Earth-sized magnetospheres are more easily achieved for planets orbiting slowly rotating early- and mid-dM stars.

Vidotto, A. A.; Jardine, M.; Morin, J.; Donati, J.-F.; Lang, P.; Russell, A. J. B.

2013-09-01

306

7 habits of highly effective.  

PubMed

There is a pressing need for psychiatric nurse authors to write about their professional image as well as issues they face in clinical practice. In this article, two psychiatric nurses describe how using Covey's The 7 Habits of Highly Effective People: Powerful Lessons in Personal Change can serve as a framework for increasing writing productivity. In addition, the Myers-Briggs Type Indicator can increase awareness of and appreciation for the strengths and differences in each author's writing style. Using these tools, writing can become a process of discovery. PMID:20102131

McGuinness, Teena M; McElroy, Ellen

2010-01-01

307

Habitable periglacial landscapes in martian mid-latitudes  

NASA Astrophysics Data System (ADS)

Subsurface permafrost environments on Mars are considered to be zones where extant life could have survived. For the identification of possible habitats it is important to understand periglacial landscape evolution and related subsurface and environmental conditions. Many landforms that are interpreted to be related to ground ice are located in the martian mid-latitudinal belts. This paper summarizes the insights gained from studies of terrestrial analogs to permafrost landforms on Mars. The potential habitability of martian mid-latitude periglacial landscapes is exemplarily deduced for one such landscape, that of Utopia Planitia, by a review and discussion of environmental conditions influencing periglacial landscape evolution. Based on recent calculations of the astronomical forcing of climate changes, specific climate periods are identified within the last 10 Ma when thaw processes and liquid water were probably important for the development of permafrost geomorphology. No periods could be identified within the last 4 Ma which met the suggested threshold criteria for liquid water and habitable conditions. Implications of past and present environmental conditions such as temperature variations, ground-ice conditions, and liquid water activity are discussed with respect to the potential survival of highly-specialized microorganisms known from terrestrial permafrost. We conclude that possible habitable subsurface niches might have been developed in close relation to specific permafrost landform morphology on Mars. These would have probably been dominated by lithoautotrophic microorganisms (i.e. methanogenic archaea).

Ulrich, M.; Wagner, D.; Hauber, E.; de Vera, J.-P.; Schirrmeister, L.

2012-05-01

308

The MEarth Project to Detect Habitable SuperEarth Exoplanets  

NASA Astrophysics Data System (ADS)

By targeting nearby M dwarfs, a transit search using modest equipment is capable of discovering planets as small as 2 Earth radii in the habitable zones of their host stars. The discovery of such planets is important for two reasons: First, their transiting geometries permit direct estimates of the planetary masses and radii, and hence provide fundamental constraints on the physical structure of planets that are primarily rock and ice in composition. Second, by differencing spectra gathered when the planet is in view from those when it is occulted by the star, we can study the atmospheric chemistry of potentially habitable worlds. The MEarth Project will consist of 8 identical, automated 16-inch telescopes in a single enclosure at Mt Hopkins, AZ. Two of these telescopes have been in operation since January 2008. We will describe the target sample, survey design, and the current photometric precision, with the goal of demonstrating the feasibility of the ground-based detection of habitable exoplanets. We acknowledge funding from the David and Lucile Packard Fellowship for Science and Engineering.

Charbonneau, David; Irwin, J.; Nutzman, P.; Falco, E. E.

2008-05-01

309

A statistical analysis of circumstellar material in Type Ia supernovae  

NASA Astrophysics Data System (ADS)

A key tracer of the elusive progenitor systems of Type Ia supernovae (SNe Ia) is the detection of narrow blueshifted time-varying Na I D absorption lines, interpreted as evidence of circumstellar material surrounding the progenitor system. The origin of this material is controversial, but the simplest explanation is that it results from previous mass-loss in a system containing a white dwarf and a non-degenerate companion star. We present new single-epoch intermediate-resolution spectra of 17 low-redshift SNe Ia taken with XShooter on the European Southern Observatory Very Large Telescope. Combining this sample with events from the literature, we confirm an excess (˜20 per cent) of SNe Ia displaying blueshifted narrow Na I D absorption features compared to redshifted Na I D features. The host galaxies of SNe Ia displaying blueshifted absorption profiles are skewed towards later-type galaxies, compared to SNe Ia that show no Na I D absorption and SNe Ia displaying blueshifted narrow Na I D absorption features have broader light curves. The strength of the Na I D absorption is stronger in SNe Ia displaying blueshifted Na I D absorption features than those without blueshifted features, and the strength of the blueshifted Na I D is correlated with the B - V colour of the SN at maximum light. This strongly suggests the absorbing material is local to the SN. In the context of the progenitor systems of SNe Ia, we discuss the significance of these findings and other recent observational evidence on the nature of SN Ia progenitors. We present a summary that suggests that there are at least two distinct populations of normal, cosmologically useful SNe Ia.

Maguire, K.; Sullivan, M.; Patat, F.; Gal-Yam, A.; Hook, I. M.; Dhawan, S.; Howell, D. A.; Mazzali, P.; Nugent, P. E.; Pan, Y.-C.; Podsiadlowski, P.; Simon, J. D.; Sternberg, A.; Valenti, S.; Baltay, C.; Bersier, D.; Blagorodnova, N.; Chen, T.-W.; Ellman, N.; Feindt, U.; Förster, F.; Fraser, M.; González-Gaitán, S.; Graham, M. L.; Gutiérrez, C.; Hachinger, S.; Hadjiyska, E.; Inserra, C.; Knapic, C.; Laher, R. R.; Leloudas, G.; Margheim, S.; McKinnon, R.; Molinaro, M.; Morrell, N.; Ofek, E. O.; Rabinowitz, D.; Rest, A.; Sand, D.; Smareglia, R.; Smartt, S. J.; Taddia, F.; Walker, E. S.; Walton, N. A.; Young, D. R.

2013-09-01

310

A Study of the Circumstellar Material in RY Per  

NASA Astrophysics Data System (ADS)

High dispersion IUE observations are proposed of the Algol binary RY Per (B3-5V + F0III, P=6.86 days) over one cycle in its orbit to investigate the effect of the cross-section and temperature of the primary on the mass transfer and mass loss in the system. This system contains an early B primary (with a weak wind) that presents a large enough cross-section to impede the flow of the gas stream. According to theoretical expectations, the gas stream in this system should be narrow, highly focused, and will strike the primary obliquely instead of feeding an accretion disk. The presence of very weak H-alpha emission in the system supports this suggestion. We will look for evidence of a hot spot at the predicted site of gas stream impact and a high temperature plasma on the trailing side of the binary and between the stars that may be generated from the gas stream collision and/or subsequent splash. Emission lines from highly ionized species have been seen in this system during total eclipse, and this project will reveal the location, geometry, and extent of the high temperature region that produces this emission. The circumstellar material in RY Per will be compared with that in two similar systems (Z Vul and FV Sco) and AU Mon and CX Dra, which also contain early B primaries but have larger separations. Any mass loss at phase 0.5 or elsewhere will be compared with the inferred rate of mass transfer and with that observed in AU Mon and other systems. Finally we study the apparent carbon depletion and nitrogen enhancement, which we have found in other Algols with A-F secondaries.

Peters, Geraldine J.

311

Type Ia Supernovae Strongly Interacting with Their Circumstellar Medium  

NASA Astrophysics Data System (ADS)

Owing to their utility for measurements of cosmic acceleration, Type Ia supernovae (SNe Ia) are perhaps the best-studied class of SNe, yet the progenitor systems of these explosions largely remain a mystery. A rare subclass of SNe Ia shows evidence of strong interaction with their circumstellar medium (CSM), and in particular, a hydrogen-rich CSM; we refer to them as SNe Ia-CSM. In the first systematic search for such systems, we have identified 16 SNe Ia-CSM, and here we present new spectra of 13 of them. Six SNe Ia-CSM have been well studied previously, three were previously known but are analyzed in depth for the first time here, and seven are new discoveries from the Palomar Transient Factory. The spectra of all SNe Ia-CSM are dominated by H? emission (with widths of ~2000 km s-1) and exhibit large H?/H? intensity ratios (perhaps due to collisional excitation of hydrogen via the SN ejecta overtaking slower-moving CSM shells); moreover, they have an almost complete lack of He I emission. They also show possible evidence of dust formation through a decrease in the red wing of H? 75-100 days past maximum brightness, and nearly all SNe Ia-CSM exhibit strong Na I D absorption from the host galaxy. The absolute magnitudes (uncorrected for host-galaxy extinction) of SNe Ia-CSM are found to be -21.3 mag <= MR <= -19 mag, and they also seem to show ultraviolet emission at early times and strong infrared emission at late times (but no detected radio or X-ray emission). Finally, the host galaxies of SNe Ia-CSM are all late-type spirals similar to the Milky Way, or dwarf irregulars like the Large Magellanic Cloud, which implies that these objects come from a relatively young stellar population. This work represents the most detailed analysis of the SN Ia-CSM class to date.

Silverman, Jeffrey M.; Nugent, Peter E.; Gal-Yam, Avishay; Sullivan, Mark; Howell, D. Andrew; Filippenko, Alexei V.; Arcavi, Iair; Ben-Ami, Sagi; Bloom, Joshua S.; Cenko, S. Bradley; Cao, Yi; Chornock, Ryan; Clubb, Kelsey I.; Coil, Alison L.; Foley, Ryan J.; Graham, Melissa L.; Griffith, Christopher V.; Horesh, Assaf; Kasliwal, Mansi M.; Kulkarni, Shrinivas R.; Leonard, Douglas C.; Li, Weidong; Matheson, Thomas; Miller, Adam A.; Modjaz, Maryam; Ofek, Eran O.; Pan, Yen-Chen; Perley, Daniel A.; Poznanski, Dovi; Quimby, Robert M.; Steele, Thea N.; Sternberg, Assaf; Xu, Dong; Yaron, Ofer

2013-07-01

312

Observations of Circumstellar Material Around Evolved Stars with the ISI  

NASA Astrophysics Data System (ADS)

The U.C. Berkeley Infrared Spatial Interferometer (ISI) is a stellar interferometer operating in the 9-12 micron region and has been in operation from 1988 until the present. It utilizes heterodyne detection using CO2 laser local oscillators and currently includes two 1.65 m movable telescopes mounted in semi-trailers and baselines up to about 65 m in length. A third telescope is being integrated with the other two and within the next year will operate as an imaging interferometer providing data with three simultaneous baselines and a closure phase, and baselines up to about 75 m. During the past twelve years the ISI has been used extensively for studies of circumstellar material around evolved stars. Multi-epoch observations of a sample of prototypical sources have elucidated the location and time scales for dust formation around these stars. These time scales can be as short as 10 years for Mira stars and as long as 100 years for supergiants. For stars like Mira itself there is evidence for departure from spherical symmetry and episodes of dust formation and destruction. For some stars motion of dust has been observed -- IK Tau is one example, and NML Cyg is another. The molecules Silane and Ammonia were observed for the extreme carbon star IRC +10216 and the supergiant VY CMa pinpointing their location relative to the inner radius of the dust shell. Somehwat surprisingly, these molecules were found to form many stellar radii away from the inner radius of the dust shell, implying that they form by interactions with the surfaces of dust grains. Last year observations with the longest baselines lead to new precision diameters of o Ceti and ? Orionis, and are continuing on a somewhat larger set of Mira variable and supergiant stars.

Danchi, W.; Townes, C.

2001-05-01

313

A statistical analysis of circumstellar material in Type Ia supernovae  

NASA Astrophysics Data System (ADS)

A key tracer of the elusive progenitor systems of Type Ia supernovae (SNe Ia) is the detection of narrow blueshifted time-varying Na I D absorption lines, interpreted as evidence of circumstellar material surrounding the progenitor system. The origin of this material is controversial, but the simplest explanation is that it results from previous mass-loss in a system containing a white dwarf and a non-degenerate companion star. We present new single-epoch intermediate-resolution spectra of 17 low-redshift SNe Ia taken with XShooter on the European Southern Observatory Very Large Telescope. Combining this sample with events from the literature, we confirm an excess (˜20 per cent) of SNe Ia displaying blueshifted narrow Na I D absorption features compared to redshifted Na I D features. The host galaxies of SNe Ia displaying blueshifted absorption profiles are skewed towards later-type galaxies, compared to SNe Ia that show no Na I D absorption and SNe Ia displaying blueshifted narrow Na I D absorption features have broader light curves. The strength of the Na I D absorption is stronger in SNe Ia displaying blueshifted Na I D absorption features than those without blueshifted features, and the strength of the blueshifted Na I D is correlated with the B - V colour of the SN at maximum light. This strongly suggests the absorbing material is local to the SN. In the context of the progenitor systems of SNe Ia, we discuss the significance of these findings and other recent observational evidence on the nature of SN Ia progenitors. We present a summary that suggests that there are at least two distinct populations of normal, cosmologically useful SNe Ia.

Maguire, K.; Sullivan, M.; Patat, F.; Gal-Yam, A.; Hook, I. M.; Dhawan, S.; Howell, D. A.; Mazzali, P.; Nugent, P. E.; Pan, Y.-C.; Podsiadlowski, P.; Simon, J. D.; Sternberg, A.; Valenti, S.; Baltay, C.; Bersier, D.; Blagorodnova, N.; Chen, T.-W.; Ellman, N.; Feindt, U.; Förster, F.; Fraser, M.; González-Gaitán, S.; Graham, M. L.; Gutiérrez, C.; Hachinger, S.; Hadjiyska, E.; Inserra, C.; Knapic, C.; Laher, R. R.; Leloudas, G.; Margheim, S.; McKinnon, R.; Molinaro, M.; Morrell, N.; Ofek, E. O.; Rabinowitz, D.; Rest, A.; Sand, D.; Smareglia, R.; Smartt, S. J.; Taddia, F.; Walker, E. S.; Walton, N. A.; Young, D. R.

2013-11-01

314

Extreme Habitability: Formation of Habitable Planets in Systems with Close-in Giant Planets and/or Stellar Companions  

NASA Astrophysics Data System (ADS)

With more than 260 extrasolar planetary systems discovered to-date, the search for habitable planets has found new grounds. Unlike our solar system, the stars of many of these planets are hosts to eccentric or close-in giant bodies. Several of these stars are also members of moderately close (<40 AU) binary or multi-star systems. The formation of terrestrial objects in these “extreme” environments is strongly affected by the dynamics of their giant planets and/or their stellar companions. These objects have profound effects on the chemical structure of the disk of planetesimals and the radial mixing of these bodies in the terrestrial regions of their host stars. For many years, it was believed that such effects would be so destructive that binary stars and also systems with close-in giant planets would not be able to form and harbor habitable bodies. Recent simulations have, however, proven otherwise. I will review the results of the simulations of the formation and long-term stability of Earth-like objects in the habitable zones of such “extreme” planetary systems, and discuss the possibility of the formation of terrestrial planets, with significant amounts of water, in systems with hot Jupiters, and also around the primaries of moderately eccentric close binary stars.

Haghighipour, N.

2009-12-01

315

Formation and Detection of Habitable Trojan Planets/Super-Earths  

NASA Astrophysics Data System (ADS)

Since the discovery of the first transiting planet more than a decade ago, the search for Trojan planets has been a particular subject of interest. Despite a great deal of research in exploring the possibility of the detection of these objects, no Trojan planet has yet been found. However, the success of the Kepler space telescope in discovering several multiplanet transiting systems using transit timing variation method, and in identifying more than 1200 planetary candidates points to the great capability of this telescope in detecting Trojan objects. We have carried out an expansive study of the possibility of the detection of Trojan planet using transit timing variation method, and identified ranges of mass and orbital elements of these objects for which the TTV signal of a transiting giant planet due to its Trojan companion would fall within the range of the photometric sensitivity of Kepler. Given our interest in detecting habitable planets, we have focused our study on M stars where the habitable zone is in close distances. To explain the possible formation of such Trojan habitable planets, we have developed a planet formation-migration code and studied the formation of planets in resonances around M stars. While results point to the combination of giant planet migration and resonance capture as a favorable mechanism for the formation of terrestrial-class objects and super-Earths in resonance with short-period giant planets, they do not present this mechanism equally favorable for the formation of Trojan planets or satellites. However, an alternative, that is, the in-situ formation of Trojan planets around a Jovian-type body, and their simultaneous migration with this object seems to be a more promising scenario. We present the results of our study and discuss their implications for the detection of habitable Trojans using Kepler space telescope.

Haghighipour, Nader

2011-09-01

316

A New Look at Habits and the Habit–Goal Interface  

Microsoft Academic Search

The present model outlines the mechanisms underlying habitual control of responding and the ways in which habits interface with goals. Habits emerge from the gradual learning of associations between responses and the features of performance contexts that have historically covaried with them (e.g., physical settings, preceding actions). Once a habit is formed, perception of contexts triggers the associated response without

Wendy Wood; David T. Neal

2007-01-01

317

On the Habitability of Planets in Binary Star Systems  

NASA Astrophysics Data System (ADS)

The discovery of more and more extra-solar planets in and around binary star systems cause questions concerning the determination of the classical habitable zone (HZ). We present calculations of the radiative and gravitational perturbations of two stars on a terrestrial planet moving in the HZ in different binary - planet configurations. Two types of planetary motion will be considered, i.e. S-type motion (or circumprimary motion) where the planet orbits one star only and P-type (or circumbinary motion) where the binary revolves inside the planet's orbit. It was found that the HZ in S-type configurations tend to be gravitationally dominated, the radiative input due to the second star is negligible compared to its dynamical influence causing secular changes in the eccentricity of the planets. This alters the amount of incident radiation significantly. In P-type configurations the radiation estimates can be determined on shorter time-scales. The radiation amplitude depends on the eccentricity of the binary in both configurations. Finally we present time independent analytical estimates about the habitability of a terrestrial planet in the HZ of a binary star system as shown by Eggl et al.(2012). This work was financed by the Austrian Science Fonds (FWF) P22603-N16 and AS11608-N16 and S.Eggl was financed by the University of Vienna (Forschungsstipendium 2012). Ref.: Eggl, S., Pilat-Lohinger, E., Gerogakarakos, N., Gyergyovits, M. and Funk, B., "Habitable Zones in S-Type Binary Star Systems", ApJ, submitted.

Pilat-Lohinger, E.; Eggl, S.; Gyergyovits, M.

2012-04-01

318

The Habitable Planet: Ecology Lab  

NSDL National Science Digital Library

The Annenberg Media project continues to bring interesting and engaging educational materials to teachers and students, and the ball keeps on rolling with this particular feature. The ecology lab feature here is designed to be used in conjunction with "The Habitable Planet" series, which is also available on the site. Teachers and others will note that the site includes an ecology simulator, and visitors can toggle the various settings to learn how the addition or removal of different species will affect their self-designed ecosystem. The simulator is fairly easy to understand, and there's a "HELP" section designed to provide assistance. Additionally, the site also includes a glossary of relevant ecosystem terms, videos, and an online textbook.

319

Habit reversal training for trichotillomania.  

PubMed

Trichotillomania is characterized by the repeated urge to pull out hair, leading to noticeable hair loss, distress, and social or functional impairment. Most of the cases present initially to dermatologists with complaints of loss of hair and is often confused with other dermatological conditions like alopecia areata, tinea capitis, traction alopecia, and loose anagen syndrome. It is a chronic condition and difficult to treat. No formal treatment algorithm is present for trichotillomania and no drug has been found to be universally effective. We present a case report of a 22-year-old single female diagnosed with trichotillomania, with complaints of recurrent hair pulling resulting in noticeable hair loss since the age of 8 years. She was treated with Habit Reversal Training with Stimulus Control over a period of 12 weeks and attained complete remission. The effectiveness of HRT plus for the treatment of Trichotillomania is ascertained. PMID:22628990

Gupta, Sunil; Gargi, Parshotam Dass

2012-01-01

320

Planetary Conditions for Habitability on Enceladus  

Microsoft Academic Search

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

Christopher D. Parkinson; Amy C. Barr; Mao-Chang Liang; Y. L. Yung

2007-01-01

321

Habitability of Enceladus: Planetary Conditions for Life  

Microsoft Academic Search

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

Christopher D. Parkinson; Mao-Chang Liang; Yuk L. Yung; Joseph L. Kirschivnk

2008-01-01

322

Characteristics of Oral-Digital Habits  

Microsoft Academic Search

This chapter will discuss the two predominant forms of oral-digital habits, thumb\\/finger sucking (finger sucking hereafter) and onychophagia (nail biting hereafter) in terms of their demographics, phenomenology, causes, functions, and clinical associations. The two habits are obviously similar topographically. The extent to which this similarity extends to these other topics will be explored, but only briefly. The differential size and

Patrick C. Friman; Michelle R. Byrd; Erin M. Oksol

323

Computer Technology and College Students' Reading Habits  

Microsoft Academic Search

The purposes of this study were to determine if computer technology had an impact on EFL college students' reading habits and if students' online reading habits and their demographic variables, such as gender, age, CJEE scores, employment status, and online hours were related. 124 valid survey questionnaires were collected from college students in a university in southern Taiwan. The results

Li-Bi Shen

2006-01-01

324

Habitable planets around the star Gliese 581?  

Microsoft Academic Search

Context: Thanks to remarkable progress, radial velocity surveys are now able to detect terrestrial planets at habitable distance from low-mass stars. Recently, two planets with minimum masses below 10 M? have been reported in a triple system around the M-type star Gliese 581. These planets are found at orbital distances comparable to the location of the boundaries of the habitable

F. Selsis; J. F. Kasting; B. Levrard; J. Paillet; I. Ribas; X. Delfosse

2007-01-01

325

Dietary Habits in Transition to Parenthood  

Microsoft Academic Search

Trends in dietary patterns in transition to parenthood were inferentially derived from the literature, in the absence or research in this area. It appears from the material reviewed that dietary habits improve nutritionally from childhood to young adulthood hence most pregnant women probably enter pregnancy with acceptable dietary habits. Exceptions to this generalization may be individuals for the lower socioeconomic

Leta P. Aljadir

1988-01-01

326

SETI and SEH (Statistical Equation for Habitables)  

Microsoft Academic Search

The statistics of habitable planets may be based on a set of ten (and possibly more) astrobiological requirements first pointed out by Stephen H. Dole in his book “Habitable planets for man” (1964). In this paper, we first provide the statistical generalization of the original and by now too simplistic Dole equation. In other words, a product of ten positive

Claudio Maccone

2011-01-01

327

Genetic Influences on Adolescent Eating Habits  

ERIC Educational Resources Information Center

|Behavioral genetic research shows that variation in eating habits and food consumption is due to genetic and environmental factors. The current study extends this line of research by examining the genetic contribution to adolescent eating habits. Analysis of sibling pairs drawn from the National Longitudinal Study of Adolescent Health (Add…

Beaver, Kevin M.; Flores, Tori; Boutwell, Brian B.; Gibson, Chris L.

2012-01-01

328

Can Supermarkets Boost Healthy Eating Habits?  

Microsoft Academic Search

Problems related to obesity as a result of changing dietary habits have generated discussions. This study aimed to make connections between institutional theory and presumable strategies that supermarkets may adopt to minimize problems related to poor nutrition. Eating habits, obesity and overweight indexes were analyzed, leading to the following problem: How can supermarkets contribute to fight epidemic obesity and at

Matheus Dill; Vitor Francisco Dalla Corte; Adriano Adelcino Anselmi; Carlos Alberto Oliveira; Maria Isabel Finger

2012-01-01

329

Genetic Influences on Adolescent Eating Habits  

Microsoft Academic Search

Behavioral genetic research shows that variation in eating habits and food consumption is due to genetic and environmental factors. The current study extends this line of research by examining the genetic contribution to adolescent eating habits. Analysis of sibling pairs drawn from the National Longitudinal Study of Adolescent Health (Add Health) revealed significant genetic influences on variance in an unhealthy

Kevin M. Beaver; Tori Flores; Brian B. Boutwell; Chris L. Gibson

2012-01-01

330

Unsuccessful Study Habits in Foreign Language Courses.  

ERIC Educational Resources Information Center

|This study determined which study habits would distinguish successful from unsuccessful foreign language learners. Participants were 219 college students from a variety of disciplinary backgrounds enrolled in either Spanish, French, German, or Japanese classes. The students completed the Study Habits Inventory and the Background Demographic Form.…

Bailey, Phillip D.; Onwuegbuzie, Anthony J.

331

The Leisure Reading Habits of Urban Adolescents  

ERIC Educational Resources Information Center

|Research indicates that there is a strong relationship between leisure reading and school achievement, but the leisure reading habits of urban adolescents have rarely been studied. From their investigation of the leisure reading habits of 584 urban minority middle school students, the authors identify these key findings: (1) More than two-thirds…

Hughes-Hassell, Sandra; Rodge, Pradnya

2007-01-01

332

Habit Lag: When “Automatization” is Dysfunctional  

Microsoft Academic Search

La Fave's habit lag construct, which specifies conditions under which previously automatized motor responses become disruptive of subsequent performance, was tested. Performance under stress was also examined as a possible factor in the occurrence of habit lag. Following a visual discrimination task, 48 women performed motor responses simultaneously: (a) repeating an invariant lever movement and (b) pushing one of two

Roger C. Mannell; James H. Duthie

1975-01-01

333

Asymmetric Circumstellar Matter in Type Ia Supernova Remnants  

NASA Astrophysics Data System (ADS)

The progenitors of Type Ia supernovae (SNe) are not well understood, but are likely to be of diverse origin, including single- and double-degenerate binary systems. Among single-degenerate progenitors, substantial amounts of circumstellar material (CSM) are expelled prior to the SN explosions by asymptotic giant branch (AGB) companions to the accreting white dwarfs. A subsequent collision of SN ejecta with the dense AGB wind has been detected among several distant SNe such as SN 2002ic, SN 2008J, and more recently PTF11kx. Dense CSM ejected by an AGB companion is present in the remnant of Kepler's SN of 1604, a Type Ia event. Observations of distant SNe hint at strongly asymmetric CSM distributions. A recent study of the CSM in Kepler's SNR by Burkey et al. indicates a large (factor of 10) density contrast between the dense, disk-like equatorial outflow and the more tenuous AGB wind above the orbital plane. A significant fraction of mature Type Ia SNRs in the Large Magellanic Cloud (LMC) shows the presence of dense Fe-rich ejecta in their interiors that cannot be explained by standard models of Type Ia explosions in a uniform ambient interstellar medium. We explore the hypothesis that these remnants originated in Type Ia explosions with strongly asymmetric CSM distributions such as found in Kepler's SNR. We present results of 2-D hydrodynamical simulations of the interaction of SN ejecta with asymmetric, disk-like AGB winds throughout the whole adiabatic stage of SNR evolution. Dense, asymmetric, and highly-ionized Fe-rich ejecta are indeed present in the simulated remnants, while the blast wave assumes a spherical shape shortly after passage through the ambient CSM. We also present simulated X-ray images and spectra and compare them with X-ray observations of selected remnants in the LMC. These remnants include DEM L238 and L249, recently observed by Suzaku, whose X-ray emission is strongly dominated by dense Fe-rich ejecta in their interiors. We contrast these remnants to more typical mature Type Ia SNRs such as 0534-69.9 and 0548-70.4 whose Suzaku spectra can be satisfactorily modeled with standard (without any CSM) X-ray models for Type Ia SNRs.

Borkowski, Kazimierz J.; Reynolds, S. P.; Blondin, J. M.

2013-01-01

334

Two Circumstellar Bubbles around Blue Supergiants in the LMC  

NASA Astrophysics Data System (ADS)

During its evolution, a massive star loses mass via stellar winds. A fast stellar wind may sweep up the ambient medium into a shell, appearing as a ``ring nebula" around the central star. While ring nebulae around Wolf-Rayet stars have received considerable attention in recent years, ring nebulae around O and B stars are far less well-explored. This is because very few well-defined rings around OB stars are known; in our Galaxy only two cases are known, the Bubble Nebula and NGC6164-5. Last year we discovered two ring nebulae around blue supergiants, Sk-69 279 (O9f; V=12.8 mag) and Sk-69 271 (B2; V=12.0 mag), in the Large Magellanic Cloud (Weis et al. 1995, RevMexAASC 3, 237). Both nebulae have diameter ~ 19'', corresponding to ~ 5 pc. To investigate the origin of these nebulae, we obtained long-slit H? +[N II] echelle observations with the 4m telescope at the Cerro Tololo Inter-American Observatory. The nebula around Sk-69 279 shows line-split indicating an expansion velocity of 27km s(-1) , while the nebula around Sk-69 271 shows no line-split, suggesting an expansion velocity <15km s(-1) . Assuming that t = 0.5 r/v, the dynamic age of these nebulae are 1x10(5) yr and >2x10(5) yr, respectively. The most tale-telling information comes from the [N II]/H? ratio. Both nebulae show [N II]/H? ratios significantly higher than those of the background H II emission. This behavior is typical for ring nebulae around WR stars or luminous blue variables that contain stellar nucleosynthesis processed material. Therefore, we conclude that the ring nebulae around Sk-69 279 and Sk-69 271 must be ``circumstellar bubbles" containing processed stellar material. These two blue supergiants must have evolved past the red supergiant phase. The chemical composition of these two ring nebulae could place constraints on models of stellar evolution.

Weis, K.; Chu, Y.-H.; Bomans, D. J.

1996-05-01

335

Modeling the circumstellar structure of Water Fountain evolved stars  

NASA Astrophysics Data System (ADS)

"Water Fountain" (WF) sources are late asymptotic giant branch (AGB) and post-AGB stars with high-velocity water maser emission (>50 km/s) that traces the earliest known manifestation of collimated mass ejection in evolved stars. Optical and mid-infrared observations with high angular resolution toward these sources typically reveal a bipolar structure, with a dark equatorial waist that might correspond to a torus. These features are surrounded by an extended and optically thick dusty envelope, whose emission dominates the far infrared wavelength range. However, the presence of either a disk or a torus could be better traced at mm and submm wavelengths where the envelope is optically thin and, therefore, one can probe the innermost regions. There are 14 WF sources identified to date. We report 1.2 mm observations, carried out with the IRAM 30 m telescope, of eight WF sources. We also report 3 mm and 3.3 mm observations, carried out with the Australia Telescope Compact Array (ATCA), of five WF sources. Using these data, together with observations at shorter wavelengths taken from literature, we built the spectral energy distribution (SED) between 0.8 and 3300 ?m of the sources observed at mm wavelengths. We fitted the broad band SEDs with radiative transfer models that include a star, a circumstellar disk or torus, and an expanding shell. The modeling of the sources allows us to estimate physical parameters of the components, such as masses, sizes, dust grain properties, and geometry. Our radiative transfer models indicate that, in order to fit the SED at IR wavelengths a massive envelope (˜2 M_?) is requiered, while to fit the data at longer wavelengths, a very massive disk (>>2 M_?) is needed. Thus the availability of data over a wide wavelength range has allowed us to trace structures that we would be missing otherwise. Considering that post-AGB stars evolve from progenitors of 0.8-8 M_?, our results suggest that progenitors of WFs are relatively massive (> 4 M_?) within that range. This is consistent with WFs being the precursors of bipolar planetary nebulae.

Durán-Rojas, M. C.; Gómez, J. F.; Osorio, M.; Rizzo, J. R.; Anglada, G.; Suárez, O.; Miranda, L. F.; D'Alessio, P.; Calvet, N.; Pérez-Cáceres, F. J.

2013-05-01

336

Impact of angular differential imaging on circumstellar disk images  

NASA Astrophysics Data System (ADS)

Context. Direct imaging of circumstellar disks requires high-contrast and high-resolution techniques. The angular differential imaging (ADI) technique is one of them, initially developed for point-like sources but now increasingly applied to extended objects such as disks. This new field of application raises many questions because the disk images reduced with ADI depend strongly on the amplitude of field rotation and the ADI data reduction strategy. Both of them directly affect the disk observable properties. Aims: Our aim is to characterize the applicability and biases of some ADI data reduction strategies for different disk morphologies. A particular emphasis is placed on parameters mostly used for disks such as their surface brightness distribution, their width if the disk is a ring, and local features such as gaps or asymmetries. We first present a general method for predicting and quantifying those biases. In a second step we illustrate them for some widely used ADI algorithms applied to typical debris disk morphologies: inclined rings with various inner/outer slopes and width. Last, our aim is also to propose improvements of classical ADI to limit the biases on extended objects. Methods: Simulated fake disks seen under various observing conditions were used to reduce ADI data and quantify the resulting biases. These conclusions are complemented by previous results from NaCo L' real-disk images of HR 4796A. Results: As expected, ADI induces flux losses on disks. This makes this technique appropriate only for low- to medium-inclination disks. A theoretical criterion is derived to predict the amount of flux loss for a given disk morphology, and quantitative estimates of the biases are given in some specific configurations. These biases alter the disk observable properties, such as the slopes of the disk surface brightness or the radial/azimuthal extent of the disk. Additionally, this work demonstrates that ADI can very easily create artificial features without involving astrophysical processes. For example, a particularly striking feature appears for a ring when the amplitude of field rotation is too small. The two ring ansae are surrounded by two flux-depleted regions, which makes them appear as bright blobs. This observation does not require any astrophysical process such as dust blown by radiation pressure, as previously proposed in H-band images of HR 4796A. Conclusions: The ADI techniques behave as spatial filtering algorithms and can bias disk observables. Therefore, the filtering process needs to be properly calibrated when deriving disk parameters from processed images. Appendix A is available in electronic form at http://www.aanda.org

Milli, J.; Mouillet, D.; Lagrange, A.-M.; Boccaletti, A.; Mawet, D.; Chauvin, G.; Bonnefoy, M.

2012-09-01

337

Searching for molecular hydrogen mid-infrared emission in the circumstellar environments of Herbig stars.  

NASA Astrophysics Data System (ADS)

We present a review of high-resolution spectroscopic mid-infrared observations of the pure rotational S(1) line of H_2 at 17.035 ?m, as a tracer of warm gas in the surface layers of circumstellar (CS) disks around Herbig Ae/Be stars with the VLT Imager and Spectrometer for the mid-InfraRed (?sir).

Martin-Zaïdi, C.; Augereau, J.-C.; Ménard, F.; van Dishoeck, E. F.; Habart, E.; Lagage, P.-O.; Pantin, E.; Olofsson, J.

2009-11-01

338

The Dual-Axis Circumstellar Environment of the Type IIn Supernova 1997eg  

NASA Astrophysics Data System (ADS)

We present multi-epoch spectral and spectropolarimetric observations of the Type IIn supernova (SN) 1997eg that indicate the presence of a flattened disklike concentration of circumstellar material surrounding aspherical ejecta, with which the disk is misaligned. The polarization across the broad H?, H?, and He I ?5876 lines of SN 1997eg forms closed loops when viewed in the Stokes q-u plane. Such loops occur when the geometrical symmetry of one or both of the Stokes parameters across spectral lines is broken, in this case most likely by occultation of the ejecta by the equatorial circumstellar matter concentration. The polarization of the narrow Balmer lines possesses an intrinsic axis that differs by 12° from that of the elongated ejecta and probably indicates the orientation of the disklike circumstellar material. The existence of two different axes of symmetry in SN 1997eg suggests that neither rotation of the progenitor nor the influence of a companion star can be the sole mechanism creating a preferred axis within the supernova system. Our model supports the emerging hypothesis that the progenitors of some Type IIn supernovae are luminous blue variable stars, whose presupernova mass eruptions form the circumstellar shells that physically characterize the SN IIn subclass. These conclusions, which are independent of interstellar polarization effects, would have been unobservable with only a single epoch of spectropolarimetry.

Hoffman, Jennifer L.; Leonard, Douglas C.; Chornock, Ryan; Filippenko, Alexei V.; Barth, Aaron J.; Matheson, Thomas

2008-12-01

339

Onset of Type 2 Supernova in Circumstellar Envelope Created by the Stellar Wind from Presupernova.  

National Technical Information Service (NTIS)

The influence of extended circumstellar envelopes on photometric properties and dynamics of type 2 supernovae is investigated. The typical stellar wind of late giants and supergiants (with C/sub rho/ less than or equal to 10/sup 13/ g/cm is shown to have ...

E. K. Grasberg D. K. Nadezhin

1986-01-01

340

High-Resolution Imaging and Modeling of Circumstellar Debris: Architectures of Planetary Systems  

Microsoft Academic Search

Circumstellar debris disks consist of dust freshly generated by the attrition and evaporation of primitive asteroids and comets. They are analogs to our Kuiper Belt and therefore inform the the architecture of trans-Neptunian space around other stars. We wish to study the diversity of these planetary systems around stars of different masses. I present high-resolution observations of debris disks, both

Michael Fitzgerald; P. Kalas; J. R. Graham; G. Duchêne; C. Pinte

2006-01-01

341

Dusty Circumstellar Envelopes as Tracers of Evolutive Sequences of Carbon-Rich Stars  

Microsoft Academic Search

During the Asymptotic Giant Branch phase, stars have a massive mass loss which leads to the formation of circumstellar dust envelopes. Therefore, the dust species formed in these media reflect the chemical composition of their photospheres. In the carbon-rich AGB environments, several compounds of dust are expected to be found, such as graphite, amorphous carbon and SiC. These dust species

A. B. de Mello; S. Lorenz-Martins

2006-01-01

342

Photodissociation Region Models of Photoevaporating Circumstellar Disks and Application to the Proplyds in Orion  

Microsoft Academic Search

We have modeled the neutral flows emerging from circumstellar disks or small clumps of size r_0 illuminated by an external source of ultraviolet radiation. The models are applied to the disks (proplyds) in the Orion Nebula, most of which are illuminated by theta^1C Ori. Our models improve upon the simpler models of Johnstone, Hollenbach, & Ballyby including the results of

H. Störzer; D. Hollenbach

1999-01-01

343

A Deep Chandra Observation of Kepler's Supernova Remnant: A Type Ia Event with Circumstellar Interaction  

Microsoft Academic Search

We present initial results of a 750 ks Chandra observation of the remnant of Kepler's supernova of AD 1604. The strength and prominence of iron emission, together with the absence of O-rich ejecta, demonstrate that Kepler resulted from a thermonuclear supernova, even though evidence for circumstellar interaction is also strong. We have analyzed spectra of over 100 small regions, and

Stephen P. Reynolds; Kazimierz J. Borkowski; Una Hwang; John P. Hughes; Carles Badenes; J. M. Laming; J. M. Blondin

2007-01-01

344

Genetic influences on adolescent eating habits.  

PubMed

Behavioral genetic research shows that variation in eating habits and food consumption is due to genetic and environmental factors. The current study extends this line of research by examining the genetic contribution to adolescent eating habits. Analysis of sibling pairs drawn from the National Longitudinal Study of Adolescent Health (Add Health) revealed significant genetic influences on variance in an unhealthy eating habits scale (h(2) = .42), a healthy eating habits scale (h(2) = .51), the number of meals eaten at a fast-food restaurant (h(2) = .33), and the total number of meals eaten per week (h(2) = .26). Most of the remaining variance was due to nonshared environmental factors. Additional analyses conducted separately for males and females revealed a similar pattern of findings. The authors note the limitations of the study and offer suggestions for future research. PMID:21750320

Beaver, Kevin M; Flores, Tori; Boutwell, Brian B; Gibson, Chris L

2011-07-12

345

Habitability Data Handbook. Volume 6. Personal Hygiene.  

National Technical Information Service (NTIS)

The personal hygiene volume was developed to provide handbook data for use by space systems planners, designers, system engineers and habitability system engineers. This handbook provides a technology base which includes recognition of requirements, and p...

1971-01-01

346

Drinking Habits Linked to Partner Violence  

MedlinePLUS

... on this page, please enable JavaScript. Drinking habits linked to partner violence (*this news item will not ... results, published in Addiction, are a reanalysis of data released last year by the same group in ...

347

Endocannabinoid signaling is critical for habit formation  

Microsoft Academic Search

Extended training can induce a shift in behavioral control from goal-directed actions, which are governed by action-outcome contin- gencies and sensitive to change in the expected value of the outcome, to habits which are less dependent on action-outcome relations and insensitive to changes in outcome value. Previous studies in rats have shown that interval schedules of reinforcement favor habit formation

Monica R. F. Hilário; Emily Clouse; Henry H. Yin; Rui M. Costa

2007-01-01

348

Habitability of Enceladus: Planetary Conditions for Life  

Microsoft Academic Search

The prolific activity and presence of a plume on Saturn's tiny moon Enceladus offers us a unique opportunity to sample the\\u000a interior composition of an icy satellite, and to look for interesting chemistry and possible signs of life. Based on studies\\u000a of the potential habitability of Jupiter's moon Europa, icy satellite oceans can be habitable if they are chemically mixed

Christopher D. Parkinson; Mao-Chang Liang; Yuk L. Yung; Joseph L. Kirschivnk

2008-01-01

349

The Nitrogen Constraint on Habitability of Planets around Low Mass M-stars  

NASA Astrophysics Data System (ADS)

The traditional habitable zones around stars are defined based on the stability of liquid water over geological timescales. Being too far away from the stars, the planet would be incapable of maintaining a warm surface and thus no liquid water. Being too close to the star, the planet would experience a 'runaway' greenhouse phase, during which its oceans could be lost quickly, and end up similar to our sister planet, Venus. The definition of tranditional habitable zones does not consider the availability of other elements important for life. All life as we know it needs nitrogen. Our calculations of upper planetary atmospheres show that nitrogen could be lost rapidly from planetary atmospheres with CO2 concentrations lower than certain threshold. This suggests that life on planets around low mass M-stars may be selflimiting, and planets of low mass M-stars are less favorable places to search for life than G- or K-type stars.

Tian, F.

2011-10-01

350

The Nitrogen Constraint on Habitability of Planets of Low Mass M-stars  

NASA Astrophysics Data System (ADS)

The traditional habitable zones around stars are defined based on the stability of liquid water over geological timescales. Being too far away from the stars, the planet would be incapable of maintaining a warm surface and thus no liquid water. Being too close to the star, the planet would experience a 'runaway' greenhouse phase, during which its oceans could be lost quickly, and end up similar to our sister planet, Venus. The definition of tranditional habitable zones does not consider the availability of other elements important for life. All life as we know it needs nitrogen. Our calculations of upper planetary atmospheres show that nitrogen could be lost rapidly from planetary atmospheres with CO2 concentrations lower than certain threshold. This suggests that life on planets around low mass M-stars may be selflimiting, and planets of low mass M-stars are less favorable places to search for life than G- or K-type stars.

Tian, F.

2011-12-01

351

Make the High School Library a "Habit" for Students  

ERIC Educational Resources Information Center

|How long does it take to form a habit? Recent research done at the University College London by Phillippa Lally and colleagues suggest it takes an average of sixty-six days to form a new habit. Other research indicates that rewards make habits easier to form, but it takes repetition to form a habit. A literature review conducted for Pearson…

Bowling, Barbara L.

2012-01-01

352

Cooked Gems Insights into the Hot Origin of Crystalline Silicates in Circumstellar Disks and the Cold Orgin Gems.  

National Technical Information Service (NTIS)

The comparison of interstellar, circumstellar and primitive solar nebula silicates has led to a significant conundrum in the understanding of the nature of solid materials that begin the planet forming processes. Crystalline silicates are found in circums...

D. E. Brownless D. J. Joswiak J. P. Bradley

2005-01-01

353

The MEarth project: searching for transiting habitable super-Earths around nearby M dwarfs  

Microsoft Academic Search

Due to their small radii, M dwarfs are very promising targets to search for transiting super-Earths, with a planet of 2 Earth radii orbiting an M5 dwarf in the habitable zone giving rise to a 0.5% photometric signal, with a period of two weeks. This can be detected from the ground using modest-aperture telescopes by targeting samples of nearby M

Jonathan Irwin; David Charbonneau; Philip Nutzman; Emilio Falco

2009-01-01

354

On the detectability of habitable exomoons with Kepler-class photometry  

Microsoft Academic Search

In this paper we investigate the detectability of a habitable-zone exomoon\\u000aaround various configurations of exoplanetary systems with the Kepler Mission\\u000aor photometry of approximately equal quality. We calculate both the predicted\\u000atransit timing signal amplitudes and the estimated uncertainty on such\\u000ameasurements in order to calculate the confidence in detecting such bodies\\u000aacross a broad spectrum of orbital arrangements.

David M. Kipping; Stephen J. Fossey; Giammarco Campanella

2009-01-01

355

Emergence of a Habitable Planet  

NASA Astrophysics Data System (ADS)

We address the first several hundred million years of Earth's history. The Moon-forming impact left Earth enveloped in a hot silicate atmosphere that cooled and condensed over ˜1,000 yrs. As it cooled the Earth degassed its volatiles into the atmosphere. It took another ˜2 Myrs for the magma ocean to freeze at the surface. The cooling rate was determined by atmospheric thermal blanketing. Tidal heating by the new Moon was a major energy source to the magma ocean. After the mantle solidified geothermal heat became climatologically insignificant, which allowed the steam atmosphere to condense, and left behind a ˜100 bar, ˜500 K CO2 atmosphere. Thereafter cooling was governed by how quickly CO2 was removed from the atmosphere. If subduction were efficient this could have taken as little as 10 million years. In this case the faint young Sun suggests that a lifeless Earth should have been cold and its oceans white with ice. But if carbonate subduction were inefficient the CO2 would have mostly stayed in the atmosphere, which would have kept the surface near ˜500 K for many tens of millions of years. Hydrous minerals are harder to subduct than carbonates and there is a good chance that the Hadean mantle was dry. Hadean heat flow was locally high enough to ensure that any ice cover would have been thin (<5 m) in places. Moreover hundreds or thousands of asteroid impacts would have been big enough to melt the ice triggering brief impact summers. We suggest that plate tectonics as it works now was inadequate to handle typical Hadean heat flows of 0.2-0.5 W/m2. In its place we hypothesize a convecting mantle capped by a ˜100 km deep basaltic mush that was relatively permeable to heat flow. Recycling and distillation of hydrous basalts produced granitic rocks very early, which is consistent with preserved >4 Ga detrital zircons. If carbonates in oceanic crust subducted as quickly as they formed, Earth could have been habitable as early as 10-20 Myrs after the Moon-forming impact.

Zahnle, Kevin; Arndt, Nick; Cockell, Charles; Halliday, Alex; Nisbet, Euan; Selsis, Franck; Sleep, Norman H.

356

Emergence of a Habitable Planet  

NASA Astrophysics Data System (ADS)

We address the first several hundred million years of Earth’s history. The Moon-forming impact left Earth enveloped in a hot silicate atmosphere that cooled and condensed over ˜1,000 yrs. As it cooled the Earth degassed its volatiles into the atmosphere. It took another ˜2 Myrs for the magma ocean to freeze at the surface. The cooling rate was determined by atmospheric thermal blanketing. Tidal heating by the new Moon was a major energy source to the magma ocean. After the mantle solidified geothermal heat became climatologically insignificant, which allowed the steam atmosphere to condense, and left behind a ˜100 bar, ˜500 K CO2 atmosphere. Thereafter cooling was governed by how quickly CO2 was removed from the atmosphere. If subduction were efficient this could have taken as little as 10 million years. In this case the faint young Sun suggests that a lifeless Earth should have been cold and its oceans white with ice. But if carbonate subduction were inefficient the CO2 would have mostly stayed in the atmosphere, which would have kept the surface near ˜500 K for many tens of millions of years. Hydrous minerals are harder to subduct than carbonates and there is a good chance that the Hadean mantle was dry. Hadean heat flow was locally high enough to ensure that any ice cover would have been thin (<5 m) in places. Moreover hundreds or thousands of asteroid impacts would have been big enough to melt the ice triggering brief impact summers. We suggest that plate tectonics as it works now was inadequate to handle typical Hadean heat flows of 0.2-0.5 W/m2. In its place we hypothesize a convecting mantle capped by a ˜100 km deep basaltic mush that was relatively permeable to heat flow. Recycling and distillation of hydrous basalts produced granitic rocks very early, which is consistent with preserved >4 Ga detrital zircons. If carbonates in oceanic crust subducted as quickly as they formed, Earth could have been habitable as early as 10-20 Myrs after the Moon-forming impact.

Zahnle, Kevin; Arndt, Nick; Cockell, Charles; Halliday, Alex; Nisbet, Euan; Selsis, Franck; Sleep, Norman H.

2007-03-01

357

FORMATION PROCESS OF THE CIRCUMSTELLAR DISK: LONG-TERM SIMULATIONS IN THE MAIN ACCRETION PHASE OF STAR FORMATION  

SciTech Connect

The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of {approx}>3 AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk with a size of >3 AU. This means that unmagnetized protoplanetary disk smaller than <3 AU does not exist. Reflecting the thermodynamics of the collapsing gas, at the protostar formation epoch, the first core (or the circumstellar disk) has a mass of {approx}0.005-0.1 M{sub sun}, while the protostar has a mass of {approx}10{sup -3} M{sub sun}. Thus, just after the protostar formation, the circumstellar disk is about 10-100 times more massive than the protostar. In the main accretion phase that lasts for {approx}10{sup 5} yr, the circumstellar disk mass initially tends to dominate the protostellar mass. Such a massive disk is unstable to gravitational instability and tends to show fragmentation. Our calculations indicate that the low-mass companions may form in the circumstellar disk in the main accretion phase. In addition, the mass accretion rate onto the protostar shows a strong time variability that is caused by the torque from the low-mass companions and/or the spiral arms in the circumstellar disk. Such variability provides an important signature for detecting the substellar mass companion in the circumstellar disk around very young protostars.

Machida, Masahiro N. [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Inutsuka, Shu-ichiro [Department of Physics Nagoya University Furo-cho, Chikusa-ku Nagoya, Aichi 464-8602 (Japan); Matsumoto, Tomoaki, E-mail: masahiro.machida@nao.ac.j, E-mail: inutsuka@nagoya-u.j, E-mail: matsu@hosei.ac.j [Faculty of Humanity and Environment, Hosei University, Fujimi, Chiyoda-ku, Tokyo 102-8160 (Japan)

2010-12-01

358

Formation Process of the Circumstellar Disk: Long-term Simulations in the Main Accretion Phase of Star Formation  

NASA Astrophysics Data System (ADS)

The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of gsim3 AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk with a size of >3 AU. This means that unmagnetized protoplanetary disk smaller than <3 AU does not exist. Reflecting the thermodynamics of the collapsing gas, at the protostar formation epoch, the first core (or the circumstellar disk) has a mass of ~0.005-0.1 M sun, while the protostar has a mass of ~10-3 M sun. Thus, just after the protostar formation, the circumstellar disk is about 10-100 times more massive than the protostar. In the main accretion phase that lasts for ~105 yr, the circumstellar disk mass initially tends to dominate the protostellar mass. Such a massive disk is unstable to gravitational instability and tends to show fragmentation. Our calculations indicate that the low-mass companions may form in the circumstellar disk in the main accretion phase. In addition, the mass accretion rate onto the protostar shows a strong time variability that is caused by the torque from the low-mass companions and/or the spiral arms in the circumstellar disk. Such variability provides an important signature for detecting the substellar mass companion in the circumstellar disk around very young protostars.

Machida, Masahiro N.; Inutsuka, Shu-ichiro; Matsumoto, Tomoaki

2010-12-01

359

Microlensing of circumstellar envelopes. III. Line profiles from stellar winds in homologous expansion  

NASA Astrophysics Data System (ADS)

This paper examines line profile evolution due to the linear expansion of circumstellar material obsverved during a microlensing event. This work extends our previous papers on emission line profile evolution from radial and azimuthal flow during point mass lens events and fold caustic crossings. Both "flavours" of microlensing were shown to provide effective diagnostics of bulk motion in circumstellar envelopes. In this work a different genre of flow is studied, namely linear homologous expansion, for both point mass lenses and fold caustic crossings. Linear expansion is of particular relevance to the effects of microlensing on supernovae at cosmological distances. We derive line profiles and equivalent widths for the illustrative cases of pure resonance and pure recombination lines, modelled under the Sobolev approximation. The efficacy of microlensing as a diagnostic probe of the stellar environs is demonstrated and discussed.

Hendry, M. A.; Ignace, R.; Bryce, H. M.

2006-05-01

360

Radiative transfer modeling of three T Tauri stars: selecting candidates for studying circumstellar disk evolution  

NASA Astrophysics Data System (ADS)

We present modeling work on three young stellar objects that are promising targets for future high-resolution observations to investigate circumstellar disk evolution. The currently available data comprise the spectral energy distribution from optical to millimeter wavelengths which allow constraining the structure of the circumstellar disk using self-consistent radiative transfer models. The results suggest that the assumption of well-mixed dust and gas leads to overestimation of flux in the far-infrared. Observational and theoretical arguments suggest that an overall decrease in far-infrared excess can be explained by dust settling towards the midplane. A new disk model is hence employed to take the effect of dust sedimentation into account. The extended model satisfactorily reproduces all existing observations. The three targets studied here therefore deserve follow-up observations to reveal the evolutionary state of their protoplanetary disks.

Liu, Yao; Wang, Hong-Chi; Wolf, Sebastian; Madlener, David

2013-07-01

361

Lycos Zone  

NSDL National Science Digital Library

In the tradition of Yahooligans (reviewed in the March 22, 1996 Scout Report) and other so-called "green spaces," Lycos has created a new online safe haven for young users which is fairly self-contained, with the exception of the advertisements. (In response to criticisms regarding aggressive marketing to children at similar sites, Lycos claims that the ads are clearly marked and will not collect any personal information.) The site is composed of four sections: the Fun and Games Zone, the Homework Zone, the New and Cool Zone, and an area for parents and teachers. The first two sections are fairly deep, with numerous resources and activities aimed at various age levels. Some links in the Homework Zone lead users outside the site, but they are first presented with a gateway page informing them that they are leaving and offering advice on not divulging personal information.

362

Circumstellar Na I and Ca II lines of type Ia supernovae in symbiotic scenario  

Microsoft Academic Search

Formation of circumstellar lines of Na I and Ca II in type Ia supernovae is\\u000astudied for the case, when supernova explodes in a binary system with a red\\u000agiant. The model suggests a spherically-symmetric wind and takes into account\\u000aionization and heating of the wind by X-rays from the shock wave and by\\u000agamma-quanta of ^{56}Ni radioactive decay. For

N. N. Chugai

2008-01-01

363

Circumstellar Na I and Ca II absorption lines of type Ia supernovae in the symbiotic scenario  

Microsoft Academic Search

The formation of circumstellar Na I and Ca II resonance absorption lines in a type Ia supernova is studied in the case where\\u000a the supernova explodes in a binary system with a red giant. The model suggests a spherically symmetric wind and takes into\\u000a account the nonstationary ionization and heating of the wind by X rays from the shock wave

N. N. Chugai

2008-01-01

364

The composition and evolution of circumstellar dust from AGB to post-AGB and PNe phases  

Microsoft Academic Search

Mid-IR spectroscopy has revealed systematic differences in the dust compounds present around AGB, post-AGB objects and PNe. This has been interpreted as evidence for a rapid evolution of circumstellar dust when low mass stars transit from the AGB to the post-AGB and PNe phases. Moreover, few of these dust spectral signatures are present in the ISM, casting some doubt on

Christoffel Waelkens; Leen Decin; Sacha Hony; Xander Tielens; Hans van Winckel; Rens Waters

2004-01-01

365

Small-scale structure of the circumstellar gas of HL Tauri and R Monocerotis  

Microsoft Academic Search

Interferometric observations of CO (J = 1-0) emission in HL Tau and R Mon reveal small-scale concentrations of molecular gas coincident with both stars. The line widths are small, less than 3 km\\/s, and centered close to the stellar velocities, indicating that these condensations are bound to the stars. Lower limits to the circumstellar masses are derived from the CO

S. Beckwith; A. I. Sargent; N. Z. Scoville; C. R. Masson; B. Zuckerman; T. G. Phillips

1986-01-01

366

Constraints on Circumstellar Material around the Type Ia Supernova 2007af  

NASA Astrophysics Data System (ADS)

Patat et al. recently inferred the existence of circumstellar material around a normal Type Ia supernova (SN Ia) for the first time, finding time-variable Na I D absorption lines in the spectrum of SN 2006X. We present high-resolution spectroscopy of the bright SN Ia 2007af at three epochs and search for variability in any of the Na D absorption components. Over the time range from 4 days before to 24 days after maximum light, we find that the host-galaxy Na D lines appear to be of interstellar rather than circumstellar origin and do not vary down to the level of 18 mÅ (column density of 2×1011 cm-2). We limit any circumstellar absorption lines to be weaker than ~10 mÅ (6×1010 cm-2). For the case of material distributed in spherically symmetric shells of radius ~1016 cm surrounding the progenitor system, we place an upper limit on the shell mass of ~(3×10-8)/X Msolar, where X is the Na ionization fraction. We also show that SN 2007af is a photometrically and spectroscopically normal SN Ia. Assuming that the variable Na D lines in SN 2006X came from circumstellar matter, we therefore conclude that either there is a preferred geometry for the detection of variable absorption components in SNe Ia, or SN 2007af and SN 2006X had different types of progenitor systems. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based in part on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

Simon, Joshua D.; Gal-Yam, Avishay; Penprase, Bryan E.; Li, Weidong; Quimby, Robert M.; Silverman, Jeffrey M.; Allende Prieto, Carlos; Wheeler, J. Craig; Filippenko, Alexei V.; Martinez, Irene T.; Beeler, Daniel J.; Patat, Ferdinando

2007-12-01

367

Testing the Circumstellar Disk Hypothesis of Methanol Maser Rings with High Spatial Resolution Infrared Data  

NASA Astrophysics Data System (ADS)

Though it is generally believed that the formation of massive stars is simply a scaled-up version of disk accretion as seen in low-mass stars, concrete and convincing evidence for the existence of these disks around high mass stars remains elusive. One unique property of massive stars in their formative years is the presence of methanol maser emission. Methanol maser emission comes from regions of dense gas near forming massive (proto)stars. The recent discovery of methanol maser emission coming from ring-like distributions projected on the sky in massive star-forming regions has led to the exciting and plausible hypothesis that they may be tracing emission from the dense gas in circumstellar disks around these high mass (proto)stars. These ring-like maser distributions are on average 0.3" in diameter which, at the typical distances to these sources, implies reasonable circumstellar disk radii of about 400AU. I will discuss the distribution of circumstellar gas and dust around such young and massive accreting (proto)stars, and what infrared emission geometries would be expected for different disk orientations. I will then compare the expected infrared geometries (as inferred from the properties of the maser rings under the assumption they are disks) to actual high spatial resolution near-infrared AO images and super-resolved mid-infrared images. With additional help from SED modeling, I will show that the results from these observations contradict the hypothesis that methanol maser rings trace circumstellar disks around massive young stellar sources.

De Buizer, James M.

2013-01-01

368

HI and CO in the circumstellar environment of the oxygen-rich AGB star RX Lep  

Microsoft Academic Search

Circumstellar shells around AGB stars are built over long periods of time\\u000athat may reach several million years. They may therefore be extended over large\\u000asizes (~1 pc, possibly more), and different complementary tracers are needed to\\u000adescribe their global properties. In the present work, we combined 21-cm HI and\\u000aCO rotational line data obtained on an oxygen-rich semi-regular variable,

Y. Libert; T. Le Bertre; E. Gerard; J. M. Winters

2008-01-01

369

Circumstellar Interaction Around Type Ib\\/c Supernovae and the GRB Connection  

Microsoft Academic Search

Radio observations of Type Ib\\/c supernovae suggest that circumstellar\\u000ainteraction takes place with a wide range of wind densities, comparable to that\\u000aseen in Galactic Wolf-Rayet stars. Efficient production of magnetic field in\\u000athe shocked region is needed. The X-ray emission observed from some Type Ib\\/c\\u000asupernovae is higher than would be expected by the thermal or inverse Compton\\u000amechanisms;

R. A. Chevalier

2006-01-01

370

Circumstellar Interaction Around Type Ib\\/c Supernovae and the GRB Connection  

Microsoft Academic Search

Radio observations of Type Ib\\/c supernovae suggest that circumstellar interaction takes place with a wide range of wind densities, comparable to that seen in Galactic Wolf-Rayet stars. Efficient production of magnetic field in the shocked region is needed. The X-ray emission observed from some Type Ib\\/c supernovae is higher than would be expected by the thermal or inverse Compton mechanisms;

R. A. Chevalier

2007-01-01

371

Infrared Spectra and Circumstellar Emission of Late-Type Stars. III. S-Type Stars  

Microsoft Academic Search

Near-infrared photometry was carried out at the J, H, K, and L bands for 73 S-type stars. The statistical characteristics of the infrared spectra and the circumstellar emission of S-type stars were examined using near-infrared photometric data, IRAS photometric data, and the low-resolution spectra obtained by IRAS. The characteristics of the photometric spectra of S-type stars were compared with those

Kunio Noguchi; Jinghao Sun; Gang Wang

1991-01-01

372

On the formation of inorganic clusters in oxygen-rich circumstellar envelopes of AGB stars  

NASA Astrophysics Data System (ADS)

The formation of inorganic clusters, which are of significant importance for the condensation process of `silicates' in the circumstellar outflows of oxygen-rich AGB-stars, is investigated. The particular focus lies on small aluminium-oxygen clusters that are important in many areas of physics. From an astrophysical point of view these systems are intriguing because clusters of aluminium oxides might play an important role in dust formation processes from the gas phase in circumstellar shells of cool late-type oxygen rich stars. This is supported by observed bulk phase aluminium oxides in the spectra of these astrophysical objects and by the analysis of meteorites. Therefore there has been considerable interest in these metal oxide clusters, all of which disclose an amazingly rich structural diversity of strongly bound neutral and charged isomers. For a study of dust condensation processes information about the thermochemical quantities of the involved gas phase species is required. The relevant molecular properties were determined in the small cluster size regime by detailed quantum-mechanical ab initio calculations (Chang et al. (1998)). Several energetically low-lying stationary points of small mixed isolated aluminium-oxygen systems were investigated. Energies, harmonic vibrational modes, and geometric parameters are used to compute thermochemical data for the various species adhering to the JANAF reference system. Based on the information thus obtained, various nucleation scenarios are discussed with respect to the problem of the primary dust condensate in circumstellar envelopes of oxygen-rich AGB-stars.

Patzer, A. B. C.; Chang, Ch.; John, M.; Sedlmayr, E.

373

PERTURBATIONS OF SNe Ia LIGHT CURVES, COLORS, AND SPECTRAL FEATURES BY CIRCUMSTELLAR DUST  

SciTech Connect

It has been suggested that multiple scattering on circumstellar dust could explain the non-standard reddening observed in the line of sight to Type Ia supernovae. In this work, we use Monte Carlo simulations to examine how the scattered light would affect the shape of optical light curves and spectral features. We find that the effects on the light curve widths, apparent time evolution of color excess, and blending of spectral features originating at different photospheric velocities should allow for tests of the circumstellar dust hypothesis on a case by case basis. Our simulations also show that for circumstellar shells with radii r = 10{sup 16}-10{sup 19} cm, the light curve modifications are well described by the empirical {Delta}m{sub 15} parameter and intrinsic color variations of order {sigma}{sub BV} = 0.05-0.1 arise naturally. For large shell radii an excess light curve tail is expected in B-band, as observed in, e.g., SN2006X.

Amanullah, Rahman; Goobar, Ariel [Oskar Klein Center, Physics Department, Stockholm University, AlbaNova University Center, SE 106 192 Stockholm (Sweden)

2011-07-01

374

Very Large Array Observations of Circumstellar Envelopes in the H I 21-cm Line  

NASA Astrophysics Data System (ADS)

The H I 21-cm line is a powerful tool for probing the circumstellar envelopes of asymptotic giant branch (AGB) stars, as it is able to trace envelope kinematics up to 1 pc from the star and thus envelope interactions with the interstellar medium (ISM). We present Very Large Array D-configuration 21-cm line data of the circumstellar envelopes of three AGB stars, X Her, R Peg, and Y UMa. H I emission had previously been detected in single-dish observations of all three stars. The observed envelope morphologies are complex and diverse. X Her's envelope appears to be swept back into a "cometary” tail by motion through the ISM; R Peg displays an arc- or "horseshoe"-like shape; and Y UMa has an "s"-shaped envelope. The detected H I envelopes have extents of 0.1-1 pc and masses of 0.8 x 10-3 to 6 x 10-3 MSun. These new results strengthen earlier indications that circumstellar envelope morphologies can be significantly influenced by their environments, and may have implications for the morphologies displayed by planetary nebulae. This project was supported through an NSF/REU grant at MIT Haystack Observatory.

Johnson, Marshall C.; Matthews, L. D.

2010-01-01

375

Looking for a habitable planet  

NASA Astrophysics Data System (ADS)

Only very favorable combination of many physical parameters may provide the necessary con-ditions for unicellular organisms to evolve into multicellular animals. The main factors of the planet, that is critical for the evolution and existence of life, form a peculiar labyrinth with many impasses. Most important are mass and temperature conditions on the planet. The planet that meets RNA/ DNA life requirements must have: •a mass about 5E27 g; •some zones with a favorable thermal conditions (273-340K); •an atmosphere that is able to absorb an external hard radiation but transparent for photons with 1-3 eV energy; •a sufficient den-sity of a stellar radiation; •presence of other sources of energy, e.g. of oxidation species in the atmosphere; •a moderate gravitation; •open water with big islands or continents; •a moderate rotation period; •a moderate eccentricity of the orbit; •a moderate inclination of equator plane to the orbit plane; •an intensive meteoritic impacts or other cosmic catastrophes that stimulate evolution of the most perfect beings; •one or more massive satellites; •an intensive volcanism and/or plate tectonics.

Ksanfomality, Leonid

376

Smoking habits of men and women.  

PubMed Central

The smoking habits of 1501 cigarette smokers attending 28 general practitioners in five group practices in London were assessed. Prevalence of smoking, daily cigarette consumption, and the use of cigars, untipped cigarettes, and hand-rolled cigarettes were lower in the women. After controlling for consumption the proportions of men and women who smoked every day were similar. Women who smoked 20 or more a day were similar to men in their self-reported inhaling habits and use of low-nicotine cigarettes. The results suggest that women differ from men in those aspects of smoking that are determined predominantly by social factors but that their smoking habits become similar when pharmacological motivation takes over. This apparently occurs when consumption reaches about 20 cigarettes a day, when smoking almost inevitably becomes a regular event and the sex differences disappear.

Russell, M A; Wilson, C; Taylor, C; Baker, C D

1980-01-01

377

Deciphering spectral fingerprints of habitable exoplanets.  

PubMed

We discuss how to read a planet's spectrum to assess its habitability and search for the signatures of a biosphere. After a decade rich in giant exoplanet detections, observation techniques have advanced to a level where we now have the capability to find planets of less than 10 Earth masses (M(Earth)) (so-called "super Earths"), which may be habitable. How can we characterize those planets and assess whether they are habitable? This new field of exoplanet search has shown an extraordinary capacity to combine research in astrophysics, chemistry, biology, and geophysics into a new and exciting interdisciplinary approach to understanding our place in the Universe. The results of a first-generation mission will most likely generate an amazing scope of diverse planets that will set planet formation, evolution, and our planet into an overall context. PMID:20307185

Kaltenegger, Lisa; Selsis, Frank; Fridlund, Malcolm; Lammer, Helmut; Beichman, Charles; Danchi, William; Eiroa, Carlos; Henning, Thomas; Herbst, Tom; Léger, Alain; Liseau, René; Lunine, Jonathan; Paresce, Francesco; Penny, Alan; Quirrenbach, Andreas; Röttgering, Huub; Schneider, Jean; Stam, Daphne; Tinetti, Giovanna; White, Glenn J

378

Franchise Zone  

NSDL National Science Digital Library

Entrepreneur.com's new service, Franchise Zone, claims to be the "Online Franchise Authority." Featured on the site is Franchise Zone's collection of over 900 franchise opportunities, ranging from financial services to pet businesses. Browseable by name of company as well as by company sector, each franchise is described in detail, including its products or services, company background, costs and fees, number of national and international units, and corporate information. The site also offers news and advice for those looking to buy into a franchise including news-making franchises, the Entrepreneur's Guide to Franchising, an expert advice column, and interactive discussions.

379

A reappraisal of the habitability of planets around M dwarf stars.  

PubMed

Stable, hydrogen-burning, M dwarf stars make up about 75% of all stars in the Galaxy. They are extremely long-lived, and because they are much smaller in mass than the Sun (between 0.5 and 0.08 M(Sun)), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially habitable, wet planets that reside within their habitable zones, which are only about one-fifth to 1/50th of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 M(Earth) orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone does not necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity or thermal and nonthermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life. This paper presents the summary conclusions of an interdisciplinary workshop (http://mstars.seti.org) sponsored by the NASA Astrobiology Institute and convened at the SETI Institute. PMID:17407403

Tarter, Jill C; Backus, Peter R; Mancinelli, Rocco L; Aurnou, Jonathan M; Backman, Dana E; Basri, Gibor S; Boss, Alan P; Clarke, Andrew; Deming, Drake; Doyle, Laurance R; Feigelson, Eric D; Freund, Friedmann; Grinspoon, David H; Haberle, Robert M; Hauck, Steven A; Heath, Martin J; Henry, Todd J; Hollingsworth, Jeffery L; Joshi, Manoj M; Kilston, Steven; Liu, Michael C; Meikle, Eric; Reid, I Neill; Rothschild, Lynn J; Scalo, John; Segura, Antigona; Tang, Carol M; Tiedje, James M; Turnbull, Margaret C; Walkowicz, Lucianne M; Weber, Arthur L; Young, Richard E

2007-02-01

380

Newspaper Readership Habits in the Black Community.  

ERIC Educational Resources Information Center

|This is a report of a survey conducted to determine newspaper readership habits of persons living within the circulation of the "Amsterdam News," a black weekly published in New York City. The survey was conducted with the purpose of increasing advertising revenues and assisting the management of the "Amsterdam News" with changes in the…

Gibbons, R. Arnold

381

STS Mission Duration Enhancement Study: (Orbiter Habitability).  

National Technical Information Service (NTIS)

Habitability improvements for early flights that could be implemented with minimum impact were investigated. These included: (1) launching the water dispenser in the on-orbit position instead of in a locker; (2) the sleep pallet concept; and (3) suction c...

A. D. Carlson

1979-01-01

382

Smoking habits in Japanese patients with schizophrenia  

Microsoft Academic Search

Studies from North America and Western Europe have observed a marked increase of smoking in schizophrenia. This preliminary study investigated smoking habits in Japanese patients with schizophrenia (n=137). The prevalence of smokers (34%) was not higher than in the general Japanese population (37%). Variables associated with smoking were also different from those reported in the Western literature. Different cultural backgrounds

Takeyuki Mori; Tsukasa Sasaki; Akira Iwanami; Tsuyoshi Araki; Kaoru Mizuno; Tadafumi Kato; Nobumasa Kato

2003-01-01

383

Habit tic deformity secondary to guitar playing.  

PubMed

A 29-year-old man exhibited linear ridges of the right thumbnail that had been present for ten years. After he stopped playing the guitar for three months, the proximal portion of the abnormality cleared. Nail changes similar to the habit tic deformity may be produced by guitar playing. PMID:19379660

Wu, Jashin J

2009-03-15

384

Space Station Wardroom Habitability and Equipment Study.  

National Technical Information Service (NTIS)

Experimental designs in life-size mock-up form for the wardroom facility for the Space Station Habitability Module are explored and developed. In Phase 1, three preliminary concepts for the wardroom configuration are fabricated and evaluated. In Phase 2, ...

D. Nixon C. Miller R. Fauquet

1989-01-01

385

Pedagogical Practices: Nurturing and Maintaining Democratic Habits  

ERIC Educational Resources Information Center

This case study examined the pedagogical practices of four teachers of one public elementary school whose mission seeks to nurture and maintain democratic habits for participation in a democratic society. Historically, public schools have been charged with the duty of preparing young minds to live within in a democratic society and as such this…

Hubler-Larimore, Lucretia Marie

2011-01-01

386

How many habitable planets in the universe?  

Microsoft Academic Search

An evaluation is made of the role of such greenhouse gases as CO2 in the creation of circumstances habitable to life-forms in planets whose position relative to their star is comparable to that of Venus and Mars to the sun. The possibility of hydrogen depletion is also considered as a major factor in the possibility of approximation to terrestrial circumstances.

Thomas M. Donahue

1990-01-01

387

Habitability of Planets Around Red Dwarf Stars  

Microsoft Academic Search

Recent models indicate that relatively moderate climates could exist on Earth-sized planets in synchronous rotation around red dwarf stars. Investigation of the global water cycle, availability of photosynthetically active radiation in red dwarf sunlight, and the biological implications of stellar flares, which can be frequent for red dwarfs, suggests that higher plant habitability of red dwarf planets may be possible.

Martin J. Heath; Laurance R. Doyle; Manoj M. Joshi; Robert M. Haberle

1999-01-01

388

Reading Habit Promotion in ASEAN Libraries.  

ERIC Educational Resources Information Center

|This paper describes the activities of the Association of Southeast Asian Nations (ASEAN) libraries have undertaken to promote reading by increasing awareness among their people. First, factors limiting reading habits in ASEAN libraries are addressed, including: we are not a reading society, but a chatting society; the management of "3 M's" (man,…

Sangkaeo, Somsong

389

Listening Habits of iPod Users  

ERIC Educational Resources Information Center

Purpose: To estimate real-environment iPod listening levels for listeners in 4 environments to gain insight into whether average listeners receive dosages exceeding occupational noise exposure guidelines as a result of their listening habits. Method: The earbud outputs of iPods were connected directly into the inputs of a digital recorder to make…

Epstein, Michael; Marozeau, Jeremy; Cleveland, Sandra

2010-01-01

390

Dietary habits of Mauritian school adolescents  

Microsoft Academic Search

Purpose – There is a strong need for nutrition education strategies that foster healthy eating from a young age in Mauritius, as the island has one of the highest rates of diet-related diseases such as obesity, diabetes and cardio-vascular diseases in the world. In order to be effective, the strategies should focus on current eating habits of adolescents. However, there

Brinda Oogarah-Pratap

2007-01-01

391

Dietary Habits of Greek Primary School Children  

ERIC Educational Resources Information Center

|The purpose of this study was to assess Greek primary (1st to 6th grade) school children's dietary habits and the factors influencing them. Our results show that children know the value of different foods. The socio-economic status of father has no effect on the attitude of children towards choosing their diet, however, mothers' educational…

Piperakis, S. M.; Papadimitriou, V.; Zafiropoulou, M.; Piperakis, A. S.; Zisis, P.

2007-01-01

392

Scientific Habits of Mind in Virtual Worlds  

ERIC Educational Resources Information Center

|In today's increasingly "flat" world of globalization (Friedman 2005), the need for a scientifically literate citizenry has grown more urgent. Yet, by some measures, we have done a poor job at fostering "scientific habits of mind" in schools. Recent research on informal games-based learning indicates that such technologies and the communities…

Steinkuehler, Constance; Duncan, Sean

2008-01-01

393

Retrieval of atmospheric properties for habitable planets  

NASA Astrophysics Data System (ADS)

An increasing number of potentially habitable terrestrial planets are found. The search for atmospheric signatures of planetary habitability and life might be possible in the future. We want to quantify the accuracy of retrieved atmospheric parameters obtained from infrared emission spectroscopy. We use synthetic observations of hypothetical habitable planets together with chi2 statistics and least-square fits. When adopting the design of currently planned or proposed exoplanet characterization missions, we find that emission spectroscopy could provide weak limits on surface conditions of terrestrial planets. However, these mission designs are unlikely to allow to characterize the composition of the atmosphere of a habitable planet. Upon increasing the signal-to-noise ratios by about a factor of 2-5 compared to current mission designs, the CO2 content could be characterized to within two orders of magnitude. The detection of the O3 biosignature remains marginal. The atmospheric temperature structure could not be constrained. A full atmospheric characterization seems to be beyond the capabilities of currently planned missions when using only emission spectroscopy.

von Paris, Philip; Hedelt, Pascal; Selsis, Franck; Schreier, Franz; Trautmann, Thomas

2013-07-01

394

Listening Habits of iPod Users  

ERIC Educational Resources Information Center

|Purpose: To estimate real-environment iPod listening levels for listeners in 4 environments to gain insight into whether average listeners receive dosages exceeding occupational noise exposure guidelines as a result of their listening habits. Method: The earbud outputs of iPods were connected directly into the inputs of a digital recorder to make…

Epstein, Michael; Marozeau, Jeremy; Cleveland, Sandra

2010-01-01

395

Habitability of planets around red dwarf stars.  

PubMed

Recent models indicate that relatively moderate climates could exist on Earth-sized planets in synchronous rotation around red dwarf stars. Investigation of the global water cycle, availability of photosynthetically active radiation in red dwarf sunlight, and the biological implications of stellar flares, which can be frequent for red dwarfs, suggests that higher plant habitability of red dwarf planets may be possible. PMID:10472629

Heath, M J; Doyle, L R; Joshi, M M; Haberle, R M

1999-08-01

396

A normative study of family media habits  

Microsoft Academic Search

The present study documents family media habits in six areas: electronic and print Media Use, parental Monitoring of children's media, parental Consistency regarding rules for children's media use, parents' reports of observable Media Effects on their children, parents' Knowledge about media and media effects, and how much children participate in Alternative Activities to electronic media. A random national sample of

Douglas A. Gentile; David A. Walsh

2002-01-01

397

Aquatic Environment and Food Habits of Mayflies.  

National Technical Information Service (NTIS)

The food habits and ecology were studied for 31 species of mayfly nymphs from the St. Maries River in Idaho, during 1967 and 1968. Mayfly nymphs were basically herbivores, feeding on variable amounts of detritus, diatoms and filamentous algae; insects wer...

M. A. Brusven B. R. Gilpin

1969-01-01

398

Characterizing rocky Super Earths - Habitable Other Worlds?  

NASA Astrophysics Data System (ADS)

Detecting the first potentially Habitable Planet is just within our reach.. We already found dozens of super-Earths: In this talk we will explore how we can detect habitability remotely. We present calculations for the potential habitability over evolutionary timescales, around very low-mass stars and brown dwarfs, accounting for evolutionary changes in radius/luminosity and tidal-locking. We also present visible/infrared spectral fingerprints of Earth-like planets around these HZs, using coupled 1-D photochemical climate calculations that account for the existence and evolution of chromospheric and coronal activity. While many uncertainties remain (as will be discussed), our calculations attest to the potential for the habitability of, and detection of biosignatures from, rocky Super-Earths. Ground as well as space based telescopes to characterization rocky exoplanets, are already in development phase (ELT, TNT, GMT, James Webb Space Telescope, Darwin, TPF, NWO). We will assess the best observation strategy to search for the signatures of a biosphere on Super-Earths.

Kaltenegger, Lisa

2009-09-01

399

Study habits of teachers college students  

Microsoft Academic Search

The study habits of 127 teachers college students, freshman to senior, are investigated. Analysis of the distribution of study time over the week shows that the most studying is done on Tuesday, the least on Friday. The average daily study time for the group is one hour and fifty-one minutes. Intelligence score is more diagnostic of scholastic success than is

H. M. Bell

1931-01-01

400

Aptitude, anxiety, study habits, and academic achievement  

Microsoft Academic Search

Confirmed the hypothesis that significant differences in academic performance between extreme anxiety groups may be largely due to differences in ability. Both male and female undergraduates were used as samples in 2 studies using analysis of covariance. Student study habits, however, do make a contribution to achievement independent of ability.

Yi-Guang Lin; Wilbert J. McKeachie

1970-01-01

401

Empowering Teachers To Break the Basal Habit.  

ERIC Educational Resources Information Center

Certain events between the late sixties and the eighties were major influences in empowering Australian reading teachers to break the basal habit. During the late sixties a growing number of elementary classroom teachers and principals were showing an interest in classroom practices that focused on children's individual progression. During the…

Martin, Rodney D.

402

Newspaper Readership Habits in the Black Community.  

ERIC Educational Resources Information Center

This is a report of a survey conducted to determine newspaper readership habits of persons living within the circulation of the "Amsterdam News," a black weekly published in New York City. The survey was conducted with the purpose of increasing advertising revenues and assisting the management of the "Amsterdam News" with changes in the…

Gibbons, R. Arnold

403

High Stellar FUV/NUV Ratio and Oxygen Contents in the Atmospheres of Potentially Habitable Planets  

NASA Astrophysics Data System (ADS)

Searching for life around M dwarfs is considered the fast track to find a second Earth. However, recent observations of several planet-hosting M dwarfs show that they all have FUV/NUV flux ratios 1000 times greater than that of the Sun (France et al. 2013). It has been shown that the atmospheric oxygen contents (O2 and O3) of potentially habitable planets in the habitable zone of M dwarf GJ876 be 3 orders of magnitude greater than those of their counterparts around Sun-like stars as a result of decreased photolysis of O3, H2O2, and HO2. Thus detectable levels of atmospheric oxygen, in combination with the existence of H2O and CO2, are not reliable biosignatures on habitable planets or moons around GJ876 (Tian et al. 2013). In this work we will report results of photochemical simulations using the UV spectra of the other observed M dwarfs, including the GJ667C system containing 3 potentially habitable planets. Different hydrological and outgassing activity levels will also be considered.

Tian, Feng; MUSCLE Team

2013-10-01

404

The atmospheric evolution of Venus the habitable planet. (Invited)  

NASA Astrophysics Data System (ADS)

Modern theories of planetary accumulation do not build Venus dry and Earth wet save by unlucky chance. If Venus and Earth were built of the same stuff, Venus’s descent into ruin must have been caused by its proximity to the Sun: too much sunlight brought a runaway greenhouse effect, the oceans and seas evaporated, and the hydrogen in the water was irrevocably lost to space. If the story has a moral, Venus would be the earth that lost its water. A complication to the story is that early Venus occupies an ambiguous position with respect to the runaway greenhouse effect. If Venus began as an ocean planet like Earth, both runaway and non-runaway states are plausible at first. In the 50 Myr before the Sun reached the main sequence, the Sun was both bright and faint, with Venus moving in and out of the conventional habitable zone. Once the Sun reached the main sequence it settled to a luminosity 70% of today’s. At this point the critical albedo triggering the runaway greenhouse on Venus was ~0.32, slightly higher than Earth’s today. This means that Earth’s albedo would put an ocean-covered Venus in the runaway greenhouse state, but only just barely, while an albedo of a slightly cloudier planet would have let Venus’s ancient oceans condenses. Early Venus’s indecisive state makes the recovery of liquid water oceans from giant impacts such as Earth’s moon-forming impact questionable. Another interesting plot twist is that dry planets (desert worlds with limited surface water) are expected to have some immunity with respect to the runaway greenhouse effect, because the limited water can be cold trapped at high latitudes. On a hot dry planet the dearth of tropical water vapor has two effects: it stabilizes the greenhouse effect (the tropics can radiate at rates well above the traditional runaway limit because the tropical atmosphere is not saturated) and it creates a dry stratosphere that severely limits hydrogen escape. Young Venus, if dry, would have been well within the dry-planet habitable zone. Here we consider the possibility that an ocean planet can evolve into a dry but habitable planet as the Sun brightens without first passing through an uninhabitable runaway greenhouse phase. This can happen because hydrogen escape in the diffusion limit depends on the wetness of the stratosphere: a warm planet can have a wet stratosphere and fast hydrogen escape while maintaining liquid water at the surface, provided that the atmosphere is not too thick. This requires in particular that most of the CO2 now in Venus’s atmosphere was sequestered as carbonate rock. If these conditions were all met, it is possible that Venus may have been a habitable planet as recently as 1 billion years ago.

Zahnle, K. J.; Abe, Y.; Abe-Ouchi, A.; Sleep, N. H.

2010-12-01

405

The Habitability and Detection of Earth-like Planets Orbiting Cool White Dwarfs  

NASA Astrophysics Data System (ADS)

Since there are several ways planets can survive the giant phase of the host star, we examine the habitability and detection of planets orbiting white dwarfs. As a white dwarf cools from 6000 K to 4000 K, a planet orbiting at 0.01 AU would remain in the continuous habitable zone (CHZ) for ~8 Gyr. We show that photosynthetic processes can be sustained on such planets. The DNA-weighted UV radiation dose for an Earth-like planet in the CHZ is less than the maxima encountered on Earth, and hence non-magnetic white dwarfs are compatible with the persistence of complex life. Polarization due to a terrestrial planet in the CHZ of a cool white dwarf (CWD) is 102 (104) times larger than it would be in the habitable zone of a typical M-dwarf (Sun-like star). Polarimetry is thus a viable way to detect close-in rocky planets around white dwarfs. Multi-band polarimetry would also allow us to reveal the presence of a planet atmosphere, providing a first characterization. Planets in the CHZ of a 0.6 M ? white dwarf will be distorted by Roche geometry, and a Kepler-11d analog would overfill its Roche lobe. With current facilities a super-Earth-sized atmosphereless planet is detectable with polarimetry around the brightest known CWD. Planned future facilities render smaller planets detectable, in particular by increasing the instrumental sensitivity in the blue.

Fossati, L.; Bagnulo, S.; Haswell, C. A.; Patel, M. R.; Busuttil, R.; Kowalski, P. M.; Shulyak, D. V.; Sterzik, M. F.

2012-09-01

406

THE HABITABILITY AND DETECTION OF EARTH-LIKE PLANETS ORBITING COOL WHITE DWARFS  

SciTech Connect

Since there are several ways planets can survive the giant phase of the host star, we examine the habitability and detection of planets orbiting white dwarfs. As a white dwarf cools from 6000 K to 4000 K, a planet orbiting at 0.01 AU would remain in the continuous habitable zone (CHZ) for {approx}8 Gyr. We show that photosynthetic processes can be sustained on such planets. The DNA-weighted UV radiation dose for an Earth-like planet in the CHZ is less than the maxima encountered on Earth, and hence non-magnetic white dwarfs are compatible with the persistence of complex life. Polarization due to a terrestrial planet in the CHZ of a cool white dwarf (CWD) is 10{sup 2} (10{sup 4}) times larger than it would be in the habitable zone of a typical M-dwarf (Sun-like star). Polarimetry is thus a viable way to detect close-in rocky planets around white dwarfs. Multi-band polarimetry would also allow us to reveal the presence of a planet atmosphere, providing a first characterization. Planets in the CHZ of a 0.6 M{sub Sun} white dwarf will be distorted by Roche geometry, and a Kepler-11d analog would overfill its Roche lobe. With current facilities a super-Earth-sized atmosphereless planet is detectable with polarimetry around the brightest known CWD. Planned future facilities render smaller planets detectable, in particular by increasing the instrumental sensitivity in the blue.

Fossati, L.; Haswell, C. A.; Patel, M. R.; Busuttil, R. [Department of Physical Sciences, Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom); Bagnulo, S. [Armagh Observatory, College Hill, Armagh BT61 9DG (United Kingdom); Kowalski, P. M. [GFZ German Research Centre for Geosciences, Telegrafenberg, D-14473 Potsdam (Germany); Shulyak, D. V. [Institute of Astrophysics, Georg-August-University, Friedrich-Hund-Platz 1, D-37077 Goettingen (Germany); Sterzik, M. F., E-mail: l.fossati@open.ac.uk, E-mail: C.A.Haswell@open.ac.uk, E-mail: M.R.Patel@open.ac.uk, E-mail: r.busuttil@open.ac.uk, E-mail: sba@arm.ac.uk, E-mail: kowalski@gfz-potsdam.de, E-mail: denis.shulyak@gmail.com, E-mail: msterzik@eso.org [European Southern Observatory, Casilla 19001, Santiago 19 (Chile)

2012-09-20

407

Planetary habitability: is Earth commonplace in the Milky Way?  

NASA Astrophysics Data System (ADS)

Is there life beyond planet Earth? This is one of the grand enigmas which humankind tries to solve through scientific research. Recent progress in astronomical measurement techniques has confirmed the existence of a multitude of extra-solar planets. On the other hand, enormous efforts are being made to assess the possibility of life on Mars. All these activities have stimulated several investigations about the habitability of cosmic bodies. The habitable zone (HZ) around a given central star is defined as the region within which an Earth-like planet might enjoy the moderate surface temperatures required for advanced life forms. At present, there are several models determining the HZ. One class of models utilises climate constraints for the existence of liquid water on a planetary surface. Another approach is based on an integrated Earth system analysis that relates the boundaries of the HZ to the limits of photosynthetic processes. Within the latter approach, the evolution of the HZ for our solar system over geological time scales is calculated straightforwardly, and a convenient filter can be constructed that picks the candidates for photosynthesis-based life from all the extra-solar planets discovered by novel observational methods. These results can then be used to determine the average number of planets per planetary system that are within the HZ. With the help of a segment of the Drake equation, the number of "Gaias" (i.e. extra-solar terrestrial planets with a globally acting biosphere) is estimated. This leads to the thoroughly educated guess that there should exist half a million Gaias in the Milky Way.

Franck, S.; Block, A.; Bloh, W.; Bounama, C.; Garrido, I.; Schellnhuber, H.-J.

2001-08-01

408

Planetary habitability: is Earth commonplace in the Milky Way?  

PubMed

Is there life beyond planet Earth? This is one of the grand enigmas which humankind tries to solve through scientific research. Recent progress in astronomical measurement techniques has confirmed the existence of a multitude of extra-solar planets. On the other hand, enormous efforts are being made to assess the possibility of life on Mars. All these activities have stimulated several investigations about the habitability of cosmic bodies. The habitable zone (HZ) around a given central star is defined as the region within which an Earth-like planet might enjoy the moderate surface temperatures required for advanced life forms. At present, there are several models determining the HZ. One class of models utilises climate constraints for the existence of liquid water on a planetary surface. Another approach is based on an integrated Earth system analysis that relates the boundaries of the HZ to the limits of photosynthetic processes. Within the latter approach, the evolution of the HZ for our solar system over geological time scales is calculated straightforwardly, and a convenient filter can be constructed that picks the candidates for photosynthesis-based life from all the extra-solar planets discovered by novel observational methods. These results can then be used to determine the average number of planets per planetary system that are within the HZ. With the help of a segment of the Drake equation, the number of "Gaias" (i.e. extra-solar terrestrial planets with a globally acting biosphere) is estimated. This leads to the thoroughly educated guess that there should exist half a million Gaias in the Milky Way. PMID:11729808

Franck, S; Block, A; von Bloh, W; Bounama, C; Garrido, I; Schellnhuber, H J

2001-10-01

409

Credit and Habit Modification in the USA: 1959-1997  

Microsoft Academic Search

Since Brown (1952), habit formation models of consumption have assumed that memory loss is a univariate process. This paper dispenses with this assumption to consider habit modification in consumption. A model is proposed where household credit depletes the habit stock and motivates consumers towards a more forward-looking behaviour. The Johansen (1988) and Gregory and Hansen (1996) procedures are applied to

G. Messinis

1999-01-01

410

Habit persistence and welfare gains from international asset trade  

Microsoft Academic Search

We introduce habit formation in a model that studies the link between international trade in financial assets, economic growth, and welfare. As with time separable preferences, asset trade increases the mean growth rate, but it also increases growth-volatility. We demonstrate that the welfare gain from asset trade is lower with habit persistence in consumption. This reflects that the habit-forming households

Egil Matsen

2003-01-01

411

Habit Persistence and Welfare Gains from International Asset Trade  

Microsoft Academic Search

We introduce habit formation in a model that studies the link between international trade in financial assets, economic growth, and welfare. As with time separable preferences asset trade increases the mean growth rate, but it also increases growth-volatility. We demonstrate that the welfare gain from asset trade is lower with habit persistence in consumption. This reflects that the habit-forming households

Egil Matsen

2001-01-01

412

The Erasure of Habit: Tracing the pedagogic body  

Microsoft Academic Search

While education involves much more than a set of habits, their formation is integral to learning. Within many Western countries, however, habit formation is no longer considered a pedagogic goal. Students may still acquire certain habits of learning as a function of schooling, but the process whereby teachers utilize a form of instruction designed to encourage the habituation of particular

Megan Watkins

2005-01-01

413

Evaluation of study skills and habits in medical students  

Microsoft Academic Search

Objective: To investigate the study skills and habits of Zanjan Medical students. Methods: in this descriptive cross-sectional study questionnaires were distributed among all the medical students of Zanjan University in spring 2005. A questionnaire containing 24 questions was designed to assess study skills and habits (time management, concentration, reading speed, note taking, study habits and comprehension). The questionnaires were distributed

Abbasali Nourian; Seyed Nouraddin Mousavinasab; Arezo Fehri; Akbar Mohammadzadeh; Jamshid Mohammadi

414

THE APPLICATION OF HABIT REVERSAL IN TREATING TRICHOTILLOMANIA  

Microsoft Academic Search

Habit reversal is a multicomponent approach of behavioral therapy shown to be effective in treating trichotillomania. This article reviews and outlines the application of habit reversal, drawing upon research, training, and clinical experience in treating this disorder. Included are a case illustration and a 10-session treatment outline incorporating all the components of habit reversal.

Patricia A. Kraemer

1999-01-01

415

Teaching Healthy Habits to Young Children: Handwashing, Toileting and Toothbrushing  

ERIC Educational Resources Information Center

|Teaching children habits is a routine part of many early childhood program curricula, with teachers never really stopping to think about what or how teaching is affecting their students. Habits are formed with consistent practice. Habits can be taught to children easily when teachers have some creativity to the actions. In this article, the…

Oshikanlu, Seyi

2006-01-01

416

DEVELOPING PEACH CULTIVARS WITH NOVEL TREE GROWTH HABITS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Peach germplasm is rich in diversity for plant growth habit. Most of the growth habits in peach are the result of single gene changes and can be readily manipulated by breeders. In spite of this fact, there has been relatively little effort to genetically alter peach tree growth habit. The peach ...

417

A hydrodynamical model of the circumstellar bubble created by two massive stars  

NASA Astrophysics Data System (ADS)

Context. Numerical models of the wind-blown bubble of massive stars usually only account for the wind of a single star. However, since massive stars are usually formed in clusters, it would be more realistic to follow the evolution of a bubble created by several stars. Aims: We develop a two-dimensional (2D) model of the circumstellar bubble created by two massive stars, a 40 M? star and a 25 M? star, and follow its evolution. The stars are separated by approximately 16 pc and surrounded by a cold medium with a density of 20 particles per cm3. Methods: We use the MPI-AMRVAC hydrodynamics code to solve the conservation equations of hydrodynamics on a 2D cylindrical grid using time-dependent models for the wind parameters of the two stars. At the end of the stellar evolution (4.5 and 7.0 million years for the 40 and 25 M? stars, respectively), we simulate the supernova explosion of each star. Results: Each star initially creates its own bubble. However, as the bubbles expand they merge, creating a combined, aspherical bubble. The combined bubble evolves over time, influenced by the stellar winds and supernova explosions. Conclusions: The evolution of a wind-blown bubble created by two stars deviates from that of the bubbles around single stars. In particular, once one of the stars has exploded, the bubble is too large for the wind of the remaining star to maintain and the outer shell starts to disintegrate. The lack of thermal pressure inside the bubble also changes the behavior of circumstellar features close to the remaining star. The supernovae are contained inside the bubble, which reflects part of the energy back into the circumstellar medium. Movies are available in electronic form at http://www.aanda.org

van Marle, A. J.; Meliani, Z.; Marcowith, A.

2012-05-01

418

Radially Sampling the Circumstellar Material around Type Ia SN 2012cg with VLA Monitoring  

NASA Astrophysics Data System (ADS)

We report radio monitoring of the nearby Type Ia SN 2012cg (CBET #3111) with the Karl G. Jansky Very Large Array (VLA). Our four epochs were observed approximately once per month, spanning 2012 May 19.1 to 2012 August 25.9. These radio observations were concurrent with our intensive multi-epoch program to obtain high-resolution optical spectroscopy of this SN with Magellan and MMT. Together, deep radio continuum observations and searches for time-variable optical absorption lines can constrain the density and radial distribution of circumstellar material around Type Ia SNe.

Chomiuk, L.; Soderberg, A.; Simon, J.; Foley, R.

2012-10-01

419

The abundance of SiS in circumstellar envelopes around AGB stars  

NASA Astrophysics Data System (ADS)

Aims:Given their photospheric origin and refractive nature, SiS molecules can provide major constraints on the relative roles of dust condensation and non-equilibrium processes in regulating the chemistry in circumstellar envelopes around evolved stars. Methods: New SiS multi-transition (sub-)millimetre line observations of a sample of AGB stars with varying photospheric C/O-ratios and mass-loss rates are presented. A combination of low- and high-energy lines are important in constraining the circumstellar distribution of SiS molecules. A detailed radiative transfer modelling of the observed SiS line emission is performed, including assessment of the effect of thermal dust grains in the excitation analysis. Results: We find that the circumstellar fractional abundance of SiS in these environments has a strong dependence on the photospheric C/O-ratio as expected from chemical models. The carbon stars (C/O > 1) have a mean fractional abundance of 3.1 × 10-6, about one order of magnitude higher than that found for the M-type AGB stars (C/O < 1) where the mean value is 2.7 × 10-7. These numbers are in reasonable agreement with photospheric LTE chemical models. SiS appears to behave similarly to SiO in terms of photodissociation in the outer part of the circumstellar envelope. In contrast to previous results for the related molecule SiO, there is no strong correlation of the fractional abundance with density in the CSE, as would be the case if freeze-out onto dust grains were important. However, possible time-variability of the line emission in the lower J transitions and the sensitivity of the line emission to abundance gradients in the inner part of the CSE may mask a correlation with the density of the wind. There are indications that the SiS fractional abundance could be significantly higher closer to the star which, at least in the case of M-type AGB stars, would require non-equilibrium chemical processes.

Schöier, F. L.; Bast, J.; Olofsson, H.; Lindqvist, M.

2007-10-01

420

The Be binary star Delta Sco: Revised Orbit and Implications for the Circumstellar Disk  

NASA Astrophysics Data System (ADS)

Delta Scorpii is a Be star and the largest member of a binary with a 10.5 year period. We have revised the orbital elements using the Navy Prototype Optical Interferometer (NPOI), published speckle and radial velocity data. The NPOI observations are the first to clearly resolve the system near periastron passage, at a separation of approximately 20 mas. We present this new orbit, and discuss the implications of the orbit on the stability of the circumstellar disk of Delta Sco. These results will be of interest for planning observations during the next periastron passage in 2011.

Zavala, Robert T.; Tycner, C.; Benson, J.; Hutter, D.; Schmitt, H.

2006-06-01

421

Gas phase chemical kinetics at high temperature of carbonaceous molecules: application to circumstellar envelopes  

NASA Astrophysics Data System (ADS)

Circumstellar shells of evolved stars are a theater of extremely rich physical and chemical processes. More than seventy molecules of varied nature have been identified in the envelopes through their spectral fingerprints in the microwave or far infrared regions. Many of them are carbon chain molecules and radicals and a significant number are unique to the circumstellar medium. However, observational data remain scarce and more than half of the detected species have been observed in only one object, the nearby carbon star IRC + 10216. Chemical kinetic models are needed to describe the formation of molecules in evolved circumstellar outflows. Upcoming terrestrial telescopes such as ALMA will increase the spatial resolution by several orders of magnitude and provide a wealth of data. The determination of relevant laboratory kinetics data is critical to keep up with the development of the observations and of the refinement of chemical models. Today, the majority of reactions studied in the laboratory are the ones involved in combustion and concerning light hydrocarbons. Our objective is to provide the scientific community with rate coefficients of reactions between abundant species in these warm environments. Cyanopolyynes from HC_2N to HC_9N have all been detected in carbon rich circumstellar envelopes in up to 10 sources for HC_3N. Neutral-neutral reactions of the CN radical with unsaturated hydrocarbons could be a dominant route in the formation of cyanopolyynes, even at low temperatures. Our approach aims to bridge the temperature gap between resistively heated flow tubes and shock tubes. The present kinetic measurements are obtained using a new reactor combining a high enthalpy source (Moudens et al. 2011) with a flow tube and a pulsed laser photolysis and laser induced fluorescence system to probe the undergoing chemical reactions. The high enthalpy flow tube has been used to measure the rate constant of the reaction of the CN radical with propane, propene, propadiene, 1,3-butadiene, and butyne over a temperature range extending from 300 to 1200 K. The majority of the reactions studied are rapid, with rate constants greater than 10-10 cm^3 molecule-1 s-1.

Biennier, L.; Gardez, A.; Saidani, G.; Georges, R.; Rowe, B.; Reddy, K. P. J.

2011-05-01

422

The Dynamical Role of Radiative Driving in the Sources and Sinks of Circumstellar Matter in Massive Stars  

NASA Astrophysics Data System (ADS)

The high luminosity of massive stars drives strong stellar wind outflows. In magnetic massive stars, the channeling and trapping of wind material can feed a circumstellar magnetosphere, characterized either by transient suspension and dynamical infall in slow rotators, or by long-term centrifugal support in moderately fast rotators. In th